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Sample records for neoproterozoic volta basin

  1. The Volta Basin Water Allocation System: assessing the impact of small-scale reservoir development on the water resources of the Volta basin, West Africa

    NASA Astrophysics Data System (ADS)

    Leemhuis, C.; Jung, G.; Kasei, R.; Liebe, J.

    2009-08-01

    In the Volta Basin, infrastructure watershed development with respect to the impact of climate conditions is hotly debated due to the lack of adequate tools to model the consequences of such development. There is an ongoing debate on the impact of further development of small and medium scale reservoirs on the water level of Lake Volta, which is essential for hydropower generation at the Akosombo power plant. The GLOWA Volta Project (GVP) has developed a Volta Basin Water Allocation System (VB-WAS), a decision support tool that allows assessing the impact of infrastructure development in the basin on the availability of current and future water resources, given the current or future climate conditions. The simulated historic and future discharge time series of the joint climate-hydrological modeling approach (MM5/WaSiM-ETH) serve as input data for a river basin management model (MIKE BASIN). MIKE BASIN uses a network approach, and allows fast simulations of water allocation and of the consequences of different development scenarios on the available water resources. The impact of the expansion of small and medium scale reservoirs on the stored volume of Lake Volta has been quantified and assessed in comparison with the impact of climate variability on the water resources of the basin.

  2. Productivity of irrigation technologies in the White Volta basin

    NASA Astrophysics Data System (ADS)

    Ofosu, E. A.; van der Zaag, P.; van de Giesen, N. C.; Odai, S. N.

    Parts of the White Volta basin in northern Ghana and southern Burkina Faso have witnessed a spectacular rise of irrigated agriculture since about 2000, largely without government support, and seems to have been triggered by a strong and growing demand for vegetables, notably tomatoes in the urban centres of southern Ghana. It is interesting to note the variety of different irrigation technologies that individual and groups of smallholder farmers adopted, adapted and implemented. Some technologies are well-known, such as those associated with conventional sources of water like small and large reservoirs; others have been rarely described in literature, such as temporal shallow wells and alluvial dugouts. This paper describes and characterises these different irrigation technologies and conducts a comparative analysis of their productivities, in terms of crop yield, water use and financial returns. The study was conducted in three neighbouring and transboundary watersheds (Anayari, Atankwidi and Yarigatanga) located in the Upper East Region of Ghana and southern Burkina Faso. For the study, 90 tomato farmers with different irrigation technologies were surveyed during one crop season (2007/2008). The results show that adequate fertilizer application is the major contributor to irrigation productivity. Technologies characterised by relatively small farm sizes are better managed by the surveyed farmers because they are able to provide adequate water and crop nutrients thus resulting in higher productivity, and high profit margins. Apart from technologies that depend on reservoirs, all other technologies surveyed in the paper are farmer driven and required no government support. This ongoing type of endogenous irrigation development provides a strong backing that the way forward in sub-Saharan Africa is for governments to create policies that facilitate poor farmers becoming irrigation entrepreneurs. Such policies should aim to enhance the reliability of markets (both

  3. Estimation of Streamflow and Fluvial Sediment Loads in the White Volta Basin under Future Climate Change

    NASA Astrophysics Data System (ADS)

    Lumor, M.; Amisigo, B. A.

    2015-12-01

    The White Volta Basin is one of the major sub-catchments of the Volta Basin of West Africa, covers an estimated 106,000 km2 and is shared between Burkina Faso and Ghana. The basin currently faces many challenges such as flooding, drought, high temporal and spatial variation of rainfall, deforestation, land degradation, climate change and high population growth rate. These challenges put pressure on the quantity and quality of the water resources in the basin. Current infrastructure developments in the basin have already impacted on the hydrological cycle, and future development plans potentially pose a threat to the sustainability of the resources if not appropriately managed. Information on runoff and sediment loads is a very important requirement for sustainable management of the water resources in the basin. This study therefore seeks to assess runoff and sediment loads in the White Volta Basin using the Soil Water Assessment Tool (SWAT) and provide understanding of how climate change impacts on future runoff and sediment loads in the basin.The model was calibrated for the period 1991 to 2003 and validated for the period 2004 to 2013.The model was also validated at one gauging station on the main river and another on a tributary. Analysis of the water balance of the basin shows that 4.90% of the simulated mean annual precipitation is converted to surface runoff while 84.37% evapotranspires. The results also show that the White Volta Basin contributes approximately 5.68x106tonnes/yr of sediment load into the Volta Lake. The calibrated model was used to simulate the water balance for the present time slice (1975-2005) as the basis for comparing with the future (2025-2055) water balance in the WhiteVolta Basin. The results show that annual surface runoff and sediment loads could increase by 56% and 70% respectively. A projected reduction by 0.54% in actual evapotranspiration is however estimated for the selected time period in the basin.

  4. Impact of future climate change on streamflow in the White Volta river basin, West Africa

    NASA Astrophysics Data System (ADS)

    Obuobie, E.; Diekkrüger, B.; Liebe, J.

    2009-04-01

    The Soil and Water Assessment Tool (SWAT) model was applied in the White Volta river basin, West Africa, to simulate the streamflow and to estimate the impact of future climate change on the streamflow. The White Volta river basin is one of the three major sub-basins of the Volta river basin, and drains an area of about 106,000 km2 mainly shared by the riparian countries, Burkina Faso and Ghana. The model was calibrated and validated using daily measured streamflow data from the stream gage at Nawuni, for the period 1980-2000. Impact of future climate change on streamflow was estimated by simulating streamflow of two time slices, the present (1990-2000) and future (2030-2039), using the calibrated SWAT model and stochastically generated daily climate series and comparing their mean annual values. The generated future climate series reflected monthly changes in precipitation and temperature forecasted by the meso-scale climate model MM5, which was downscaled from ECHAM4 scenario IS92a. The results show that SWAT is able to accurately reproduce the streamflow in the White Volta Basin. The coefficient of determination and Nash-Sutcliffe model efficiency were found to be, respectively, higher than 0.8 and 0.7, for both the calibration and validation periods. Compared to the present, the future mean annual streamflow and the annual coefficient of variation of the streamflow in the basin are expected to increase by 33% and 52%, respectively, as a result of future climate change.

  5. Prediction of the distribution of Glossina tachinoides (Diptera: Glossinidae) in the Volta basin of northern Ghana.

    PubMed

    Mahama, C I; Koné, A; de la Rocque, S; De Deken, R; Geerts, S

    2005-02-01

    The classification of a Landsat Thematic Mapper satellite image helped demonstrate prevailing habitat types and land use intensity in the Volta basin of the Northern Region of Ghana. A geo-referenced data layer comprising the capture results of a cross-sectional survey of Glossina tachinoides Westwood was over-laid on a data layer of habitat types within 500 m of either bank of the Volta river and its tributaries. An evaluation of the relationship between habitat types and the capture results of G. tachinoides suggested a strong preference of G. tachinoides for woodland, followed by shrubland, grassland and flood plains. The findings were used to classify the suitability of habitat types for G. tachinoides as 'high', 'medium' and 'low' and a prediction map for the distribution of G. tachinoides in the entire river network was produced. The usefulness of this method in estimating the potential distribution of G. tachinoides in an area of increasing agricultural expansion is discussed. PMID:15705216

  6. Reservoir impact assessment in sub-Saharan Africa: The Volta Basin Water Allocation System (VB-WAS)

    NASA Astrophysics Data System (ADS)

    Leemhuis, C.; Jung, G.; Kasei, R.; Liebe, J.

    2009-04-01

    In the Volta River Basin, infrastructure watershed development with respect to the impact of climate conditions is hotly debated due to the lack of adequate tools to model the consequences of such development. The Volta basin drains an area of approx. 400 000 km² of the subhumid to semiarid West-African savannah zone and is shared by six riparian countries. The region is characterized by erratic rainfall patterns, and domestic and agricultural water users in the upper regions of the Basin complete with hydropower generation in the south for increasingly scarce water resources. There is an ongoing debate on the impact of further development of small, medium and large reservoirs on the water level of Lake Volta. The GLOWA Volta Project (GVP) has developed a Volta Basin Water Allocation System (VB-WAS), a decision support tool that allows assessing the impact of infrastructure development in the basin on the availability of current and future water resources, given the current or future climate conditions. The simulated historic and future discharge time series of the coupled climate-hydrological model (MM5/WaSiM) serve as input data for a river basin management model (MIKE BASIN). MIKE BASIN uses a network approach, and allows fast simulations of water allocation and of the consequences of different development scenarios on the available water resources. Furthermore it is possible to up set up climate scenario time series scenarios for an assessment of the consequences of extreme climate conditions. Within a case study analysis the impact of small and medium scale reservoir development on the water resources of the Volta basin has been evaluated under different climatic conditions. For the evaluation of the impact of large reservoir development in particular the impact of Bui dam, which is under construction on the Black Volta River in Ghana, on the water level of Lake Volta has been simulated with the VB-WAS model. The VB-WAS model allows a quantified impact

  7. Groundwater level monitoring and recharge estimation in the White Volta River basin of Ghana

    NASA Astrophysics Data System (ADS)

    Obuobie, Emmanuel; Diekkrueger, Bernd; Agyekum, William; Agodzo, Sampson

    2012-08-01

    Recharge quantification is an important pre-requisite for effectively managing groundwater resources as recharge estimates are needed to determine sustainable yields of groundwater aquifers for rational and sustainable exploitation of the resource. In this study, the water table fluctuation method has been applied in the White Volta River basin of Ghana (approx. 46,000 km2) to estimate seasonal fluctuations in groundwater levels in the basin and subsequently to estimate recharge to the groundwater for the 2006 and 2007 water years. Results show high seasonal and spatial variability in the water level, with a range of 1240-5000 mm in 2006, and 1600-6800 mm in 2007. Seasonal rainfall was found to be the main source of recharge to the aquifers in the basin as water level rise occurred only in the rainfall season. Recharge to groundwater in the White Volta basin was estimated to vary between 2.5% and 16.5% of the mean annual rainfall, with a mean recharge of 7-8%.

  8. Wetland river flow interaction in a sedimentary formation of the white Volta basin, Ghana

    NASA Astrophysics Data System (ADS)

    Nyarko, B. K.; Diekkruger, B.; Van De Giesen, N.; Barry, B.

    2011-12-01

    Groundwater resources in the floodplain wetlands of the White Volta River basin of Ghana is a major source of water for irrigation activities of communities living around and baseflow to sustain the flow of the river. Hydrology of the floodplain wetlands in the basin are complex, characterized by temporally variable storage volumes with erratic contribution to streamflow. For the continual usage of groundwater resources in the floodplains there is a need to study the form of interaction between the main river and floodplain wetlands. The study, adopted the PM-WIN (MODFLOW) model for simulating the interaction between the wetland and stream. Additionally, the lower boundary discharge output from the HYDRUS-1D model is the estimated recharge. This input quantifies the temporal and spatial variations in sub-surfaces discharges in the floodplain wetland. The simulation of the sub-surface hydraulic head of the wetland indicates a systematic variation relative to the White Volta River response to changes in the rainfall pattern. The interaction conditions vary from season to season with March, April, and May showing the least leakage (estimated values of 0.03mm/day, 0.06mm/day, and 0.15 mm/day, respectively) from the river into the floodplain wetland. Notably, the interaction between the wetland and the river as simulated is bidirectional. With most of the flow coming out from the river into the floodplain wetland, this condition persists in the months of August and September.

  9. Coupled surface water and groundwater modeling over the White Volta Basin, Ghana

    NASA Astrophysics Data System (ADS)

    Rittinger, S. T.; Alo, C. A.; Bitew, M. M.; Yidana, S. M.; Alfa, B.

    2012-12-01

    Sustainable livelihood in the semiarid White Volta Basin in Northern Ghana is dependent on the availability and sustainable development and management of water resources for agricultural activities. Currently, almost all agricultural activities are rain-fed and thus depend on the frequency, spatial, and temporal distribution of rainfall. Recent erratic patterns in the temporal and spatial distribution of rainfall in the basin—largely consistent with the effects of a warming climate—have led to dwindling fortunes in the rain-fed agricultural enterprise. On the other hand, surface water bodies in the forms of rivers and streams are ephemeral and therefore do not serve the immediate irrigation needs of the populations especially in the dry seasons. The conjunctive use of surface and groundwater resources to support local irrigation schemes in the basin has been suggested as a possible buffer against the effects of dwindling rainfall on agriculture in the basin and has the potential of raising the standard of living of the communities dwelling there. Conjunctive surface water/groundwater use involves the balanced application of both groundwater and surface water resources for maximal socio-economic benefit whilst ensuring ecological integrity. However, a detailed assessment of the potentials of the aquifers for commercial development has been constrained by the limited or no understanding of the surface water-groundwater interactions in the basin within the context of climate change/evolving patterns of climate variability and human activities. Here, we present preliminary results from simulations of coupled surface water and groundwater availability and flow over the Volta Basin using an integrated hydrological model.

  10. Monthly streamflow prediction in the Volta Basin of West Africa: A SISO NARMAX polynomial modelling

    NASA Astrophysics Data System (ADS)

    Amisigo, B. A.; van de Giesen, N.; Rogers, C.; Andah, W. E. I.; Friesen, J.

    Single-input-single-output (SISO) non-linear system identification techniques were employed to model monthly catchment runoff at selected gauging sites in the Volta Basin of West Africa. NARMAX (Non-linear Autoregressive Moving Average with eXogenous Input) polynomial models were fitted to basin monthly rainfall and gauging station runoff data for each of the selected sites and used to predict monthly runoff at the sites. An error reduction ratio (ERR) algorithm was used to order regressors for various combinations of input, output and noise lags (various model structures) and the significant regressors for each model selected by applying an Akaike Information Criterion (AIC) to independent rainfall-runoff validation series. Model parameters were estimated from the Matlab REGRESS function (an orthogonal least squares method). In each case, the sub-model without noise terms was fitted first followed by a fitting of the noise model. The coefficient of determination ( R-squared), the Nash-Sutcliffe Efficiency criterion (NSE) and the F statistic for the estimation (training) series were used to evaluate the significance of fit of each model to this series while model selection from the range of models fitted for each gauging site was done by examining the NSEs and the AICs of the validation series. Monthly runoff predictions from the selected models were very good, and the polynomial models appeared to have captured a good part of the rainfall-runoff non-linearity. The results indicate that the NARMAX modelling framework is suitable for monthly river runoff prediction in the Volta Basin. The several good models made available by the NARMAX modelling framework could be useful in the selection of model structures that also provide insights into the physical behaviour of the catchment rainfall-runoff system.

  11. Long-Term Water Balance of the Volta River Basin in West Africa

    NASA Astrophysics Data System (ADS)

    van de Giesen, N.; Andreini, M.; Taylor, J.; Steenhuis, T.

    2002-12-01

    The Volta River drains approximately 400,000 km2 of the semi-arid to sub-humid savanna of West Africa. Average rainfall is about 1000 mm per year. The interannual variation is relatively low with a coefficient of variation of 0.07. Most rainfall returns to the atmosphere as evapotranspiration and only 9% becomes available as river runoff. The interannual variation of river flow is much higher than that of rainfall and has a coefficient of variation of 0.57. In this presentation, the coupling between interannual variation in rainfall and runoff is examined. To a large extent, the high variability in river flow can be explained with the relatively small differences in rainfall between years; the watershed strongly amplifies the atmospheric input. The amplifying effect is, however, not constant over space and time. Over all, the basin received less rain than before in the past two decades. Some parts of the basin did indeed produce less runoff but other parts actually produced more runoff, most likely due to changes in landuse. No clear increase or decrease in the interannual variability could be found for different parts of the basin. To examine the interannual variability of water resources availability under future climates, the applicability of General Circulation Models (GCMs) was examined for West Africa. Comparison of historical and GCM rainfall data showed large discrepancies. Different approaches exist to adjust GCM rainfall with the aid of historical rainfall data but for West Africa some problems remained. This presentation concludes with a focus on differences in mid-term (2-10 years) persistence in annual river flow as produced by historical and GCM data.

  12. Intercomparison of Evapotranspiration Over the Savannah Volta Basin in West Africa Using Remote Sensing Data

    PubMed Central

    Opoku-Duah, S.; Donoghue, D.N.M.; Burt, T. P.

    2008-01-01

    This paper compares evapotranspiration estimates from two complementary satellite sensors – NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) and ESA's ENVISAT Advanced Along-Track Scanning Radiometer (AATSR) over the savannah area of the Volta basin in West Africa. This was achieved through solving for evapotranspiration on the basis of the regional energy balance equation, which was computationally-driven by the Surface Energy Balance Algorithm for Land algorithm (SEBAL). The results showed that both sensors are potentially good sources of evapotranspiration estimates over large heterogeneous landscapes. The MODIS sensor measured daily evapotranspiration reasonably well with a strong spatial correlation (R2=0.71) with Landsat ETM+ but underperformed with deviations up to ∼2.0 mm day-1, when compared with local eddy correlation observations and the Penman-Monteith method mainly because of scale mismatch. The AATSR sensor produced much poorer correlations (R2=0.13) with Landsat ETM+ and conventional ET methods also because of differences in atmospheric correction and sensor calibration over land.

  13. Prospects for the control of onchocerciasis in Africa with special reference to the Volta River basin.

    PubMed

    Waddy, B B

    1969-01-01

    Onchocerciasis is found in association with all the main river systems of northern tropical Africa, and there are endemic foci south of the Equator. Heavy and prolonged infection may cause blindness and intense pruritus. The vectors, Simulium damnosum and S. neavei, are also intolerable pests when they swarm. The disease and its vector together cause serious economic loss and are a main cause of the depopulation of river valleys in the savanna lands.The basin of the River Volta, in which the worst endemic area in the world is situated, is considered to be the most favourable area for a study of the problems involved in the large-scale control of onchocerciasis carried by S. damnosum. Mass treatment or prophylaxis are not practicable at present. The clinical condition progresses for many years in the absence of fresh infection, and drugs capable of mass application are needed. However, the first aim is to attack the larval stages of the vector with insecticides. DDT is ideal for this purpose in large, steadily flowing rivers, but a more suitable insecticide and formulation are needed for small, irregularly flowing streams.Research is needed into many aspects of the adult life of S. damnosum, including feeding and resting habits, dry season survival and flight range. One of the main practical problems is prevention of reinfestation of a treated river system. PMID:5307598

  14. Hydroclimatology of the Volta River Basin in West Africa: Trends and variability from 1901 to 2002

    NASA Astrophysics Data System (ADS)

    Oguntunde, Philip G.; Friesen, Jan; van de Giesen, Nick; Savenije, Hubert H. G.

    Long-term historical records of rainfall ( P), runoff ( Q) and other climatic factors were used to investigate hydrological variability and trends in the Volta River Basin over the period 1901-2002. Potential ( Ep) and actual evaporation ( E), rainfall variability index ( δ), Budyko’s aridity index ( IA), evaporation ratio ( CE) and runoff ratio ( CQ) were estimated from the available hydroclimatological records. Mann-Kendall trend analysis and non-parametric Sen’s slope estimates were performed on the respective time series variables to detect monotonic trend direction and magnitude of change over time. Rainfall variability index showed that 1968 was the wettest year ( δ = +1.75) while 1983 was the driest ( δ = -3.03), with the last three decades being drier than any other comparable period in the hydrological history of the Volta. An increase of 0.2 mm/yr 2 ( P < 0.05) was observed in Ep for the 1901-1969 sub-series while an increased of 1.8 mm/yr 2 ( P < 0.01) was recorded since 1970. Rainfall increased at the rate of 0.7 mm/yr 2 or 49 mm/yr between 1901 and 1969, whereas a decrease of 0.2 mm/yr 2 (6 mm/yr) was estimated for 1970-2002 sub-series. Runoff increased significantly at the rate of 0.8 mm/yr (23 mm/yr) since 1970. Runoff before dam construction was higher (87.5 mm/yr) and more varied (CV = 41.5%) than the post-dam period with value of 73.5 mm/yr (CV = 23.9%). A 10% relative decrease in P resulted in a 16% decrease in Q between 1936 and 1998. Since 1970, all the months showed increasing runoff trends with significant slopes ( P < 0.05) in 9 out of the 12 months. Possible causes, such as climate change and land cover change, on the detected changes in hydroclimatology are briefly discussed.

  15. Levels of total mercury in different fish species and sediments from the Upper Volta Basin at Yeji in Ghana.

    PubMed

    Kwaansa-Ansah, E E; Agorku, S E; Nriagu, J O

    2011-04-01

    In this study, total mercury concentrations were determined in sediments and seven different fish species from the Upper Volta Basin area of Yeji in Ghana. Mercury concentrations found ranged from 44.17 to 85.88 ng/g wet weight for Synodontis gambiesis, from 11.25 to 79.73 ng/g wet weight for Synodontis membranaceus, from 13.11 to 38.64 ng/g wet weight for Synodontis ocellifer, from 16.39 to 25.82 ng/g wet weight for Distishodus rotratus, from 40.80 to 90.30 ng/g wet weight for Bagrus docmac, from 10.48 to 61.90 ng/g wet weight for Chrysichthys nigrodigitatus and from 12.33 to 24.18 ng/g wet weight for Gnathoneus senegalensis. These values are below the 500 ng/g guideline recommended by the WHO/FAO, implying that fish from the Upper Volta Basin area of Yeji are safe for human consumption. Good correlation was observed between mercury concentration and fresh weight (R(2) = 0.6067) and total length (R(2) = 0.8754) for Gnathonemus senegalensis. However, poor correlations were observed between mercury concentration and fresh weight and total length for the other six species. Mercury in sediments ranged from 11.87 to 70.25 ng/g dry weights with a mean of 41.60 ng/g dry weight being below the IAEA threshold of 810 ng/g.. These values show that sections of the Upper Volta River remain relatively clean in spite of substantial loadings of mercury into the river's basin from gold mining activities. PMID:21318735

  16. Provenance analysis and tectonic setting of the Neoproterozoic sediments within the Taoudeni Basin, Northern Mauritania

    NASA Astrophysics Data System (ADS)

    Nicoll, Graeme; Straathof, Gijs; Tait, Jenny; Lo, Khalidou; Ousmane, N'diaye; El Moctar Dahmada, Mohamed; Berndt, Jasper; Key, Roger

    2010-05-01

    We have dated over 800 detrital zircon grains from the Neoproterozoic sediments within the Taoudeni Basin of Mauritania on the West African craton. This sequence of sediments preserves a relatively condensed mixed continental and marine succession as well as Neoproterozoic glacial and glacially influenced deposits. The underlying Archaean and Birimian basement of the West African craton is exposed on the Reguibat shield in the north, and on the Leo shield in the south although smaller inliers occur scattered along the Bassaride and Mauritanide belts, as well as in the core of the Anti-Atlas belt. The large West African craton is totally surrounded by Pan-African fold belts. Sedimentation within the Taoudeni basin started around 1000Ma and lasted until the end of the Carboniferous. The basin is 1000-1500 km in diameter and the sedimentary pile is on average 3000 m thick. All dated zircons in the stratigraphically lowest Char and Atar Groups are older than ~1800Ma. These groups show a strong input of 2950 and 2075Ma ages, indicating sourcing from the local underlying granitic and gneissic basement. These basal sediments also include a large input from a rare 2475Ma source. Samples from the upper Assebet El Hassiane Group contain numerous zircons of 2000-900Ma. While the Neoproterozoic Marinoan glaciogenic "Triad" Jbeliat Group and stratigraphically above formations show a large range of 3200-595Ma ages. We have also undertaken a detailed Carbon isotope profile study through the carbonates which cap the Glacial Jbeliat Group. The upper part of the Jbeliat cap carbonate displays a distinct and pronounced rise from -4.3 to +3.8 13C, followed by the final demise of carbonate productivity. This positive trend is consistent with the upper part of the globally extensive Ghaub/Nantuo/Marinoan cap carbonate sequences. This world-wide sequence is characterized by composite negative-to-positive trends up section and so this isotope stratigraphy along with the zircon data helps

  17. Hydrological Evaluation of Satellite-Based Precipitation Products over the Volta and Baro-Akobo Basin

    NASA Astrophysics Data System (ADS)

    Thiemig, Vera; Zambrano, Mauricio; Rojas, Rodrigo; De Roo, Ad

    2013-04-01

    How useful are satellite-based rainfall estimates (SRFE) as forcing data for hydrological applications? Which SRFE should be favoured for hydrological modelling? What could researchers do to increase the performance of SRFE-driven hydrological simulations? To address these three research questions, four SRFE (CMORPH, RFE 2.0, TRMM-3B42 and PERSIANN) and one reanalysis product (ERA-Interim) are evaluated within a hydrological application for the time period 2003-2008, over two river basins (Volta and Baro-Akobo) which hold distinct physiographic, climatologic and hydrologic conditions. The focus was on the assessment of: a) the individual and combined effect of SRFE-specific calibration and bias-correction on the hydrological performance, b) the level of complexity required regarding bias-correction and interpolation to achieve a good hydrological performance, and c) the hydrological performance of SRFE during high- and low-flow conditions. Results show that 1) the hydrological performance is always higher if the model is calibrated to the respective SRFE rather than to interpolated ground observations; 2) for SRFE that are afflicted with bias, a bias-correction step prior to SRFE-specific calibration is essential, while for SRFE with good intrinsic data quality applying a SRFE-specific model calibration is sufficient; 3) the more sophisticated bias-correction method used in this work (histogram equalization) results generally in a superior hydrological performance, while a more sophisticated interpolation method (Kriging with External Drift) seems to be of added value only over mountainous regions; 4) the bias-correction is not over-proportionally important over mountainous catchments, as it solely depends on where the SRFE show high biases (e.g. for PERSIANN and CMORPH over lowland areas); and 5) the hydrological performance during high-flow conditions is superior thus promoting the use of SRFE for applications focusing on the high-end flow spectrum. These results

  18. Hydrological evaluation of satellite-based rainfall estimates over the Volta and Baro-Akobo Basin

    NASA Astrophysics Data System (ADS)

    Thiemig, Vera; Rojas, Rodrigo; Zambrano-Bigiarini, Mauricio; De Roo, Ad

    2013-08-01

    How useful are satellite-based rainfall estimates (SRFE) as forcing data for hydrological applications? Which SRFE should be favoured for hydrological modelling? What could researchers do to increase the performance of SRFE-driven hydrological simulations? To address these three research questions, four SRFE (CMORPH, RFE 2.0, TRMM-3B42 and PERSIANN) and one re-analysis product (ERA-Interim) are evaluated within a hydrological application for the time period 2003-2008, over two river basins (Volta and Baro-Akobo) which hold distinct physiographic, climatologic and hydrologic conditions. The focus was on the assessment of: (a) the individual and combined effect of SRFE-specific calibration and bias correction on the hydrological performance, (b) the level of complexity required regarding bias correction and interpolation to achieve a good hydrological performance, and (c) the hydrological performance of SRFE during high- and low-flow conditions. Results show that (1) the hydrological performance is always higher if the model is calibrated to the respective SRFE rather than to interpolated ground observations; (2) for SRFE that are afflicted with bias, a bias-correction step prior to SRFE-specific calibration is essential, while for SRFE with good intrinsic data quality applying only a SRFE-specific model calibration is sufficient; (3) the more sophisticated bias-correction method used in this work (histogram equalization) results generally in a superior hydrological performance, while a more sophisticated spatial interpolation method (Kriging with External Drift) seems to be of added value only over mountainous regions; (4) the bias correction is not over-proportionally important over mountainous catchments, as it solely depends on where the SRFE show high biases (e.g. for PERSIANN and CMORPH over lowland areas); and (5) the hydrological performance during high-flow conditions is superior thus promoting the use of SRFE for applications focusing on the high-end flow

  19. On the potentials of multiple climate variables in assessing the spatio-temporal characteristics of hydrological droughts over the Volta Basin.

    PubMed

    Ndehedehe, Christopher E; Awange, Joseph L; Corner, Robert J; Kuhn, Michael; Okwuashi, Onuwa

    2016-07-01

    Multiple drought episodes over the Volta basin in recent reports may lead to food insecurity and loss of revenue. However, drought studies over the Volta basin are rather generalised and largely undocumented due to sparse ground observations and unsuitable framework to determine their space-time occurrence. In this study, we examined the utility of standardised indicators (standardised precipitation index (SPI), standardised runoff index (SRI), standardised soil moisture index (SSI), and multivariate standardised drought index (MSDI)) and Gravity Recovery and Climate Experiment (GRACE) derived terrestrial water storage to assess hydrological drought characteristics over the basin. In order to determine the space-time patterns of hydrological drought in the basin, Independent Component Analysis (ICA), a higher order statistical technique was employed. The results show that SPI and SRI exhibit inconsistent behaviour in observed wet years presupposing a non-linear relationship that reflects the slow response of river discharge to precipitation especially after a previous extreme dry period. While the SPI and SSI show a linear relationship with a correlation of 0.63, the correlation between the MSDIs derived from combining precipitation/river discharge and precipitation/soil moisture indicates a significant value of 0.70 and shows an improved skill in hydrological drought monitoring over the Volta basin during the study period. The ICA-derived spatio-temporal hydrological drought patterns show Burkina Faso and the Lake Volta areas as predominantly drought zones. Further, the statistically significant negative correlations of pacific decadal oscillations (0.39 and 0.25) with temporal evolutions of drought in Burkina Faso and Ghana suggest the possible influence of low frequency large scale oscillations in the observed wet and dry regimes over the basin. Finally, our approach in drought assessment over the Volta basin contributes to a broad framework for hydrological

  20. Trends and Projections of Climatic Extremes in the Black Volta Basin, West Africa: Towards Climate Change Adaptation.

    NASA Astrophysics Data System (ADS)

    Aziz, F.

    2015-12-01

    The water resources of the Black Volta Basin in West Africa constitute a major resource for the four countries (Burkina Faso, Ghana, Côte d'Ivoire, Mali) that share it. For Burkina Faso and Ghana, the river is the main natural resource around which the development of the diverse sectors of the two economies is built. Whereas Ghana relies heavily on the river for energy, land-locked Burkina Faso continuously develops the water for agricultural purposes. Such important role of the river makes it an element around which there are potential conflicts: either among riparian countries or within the individual countries themselves. This study documents the changes in temperature and precipitation extremes in the Black Volta Basin region for the past (1981-2010) and makes projections for the mid-late 21st century (2051-2080) under two emission scenarios; RCP 2.6 and RCP 8.5. The Expert Team on Climate Change Detection and Indices (ETCCDI) temperature- and precipitation-based indices are computed with the RClimdex software. Observed daily records and downscaled CORDEX data of precipitation and maximum and minimum temperatures are used for historical and future trend analysis respectively. In general low emission scenarios show increases in the cold extremes. The region shows a consistent pattern of trends in hot extremes for the 1990's. An increasing trend in hot extremes is expected in the future under RCP 8.5 while RCP 2.5 shows reductions in hot extremes. Regardless of the emission scenario, projections show more frequent hot nights in the 21st century. Generally, the region shows variability in trends for future extreme precipitation indices with only a few of the trends being statistically significant (5% level). Results obtained provide a basic and first step to understanding how climatic extremes have been changing in the Volta Basin region and gives an idea of what to expect in the future. Such studies will also help in making informed decisions on water management

  1. Use of isotopes to study floodplain wetland and river flow interaction in the White Volta River basin, Ghana.

    PubMed

    Nyarko, Benjamin Kofi; Kofi Essumang, David; Eghan, Moses J; Reichert, Barbara; van de Giesen, Nick; Vlek, Paul

    2010-03-01

    Floodplain wetlands influence the timing and magnitude of stream responses to rainfall. In managing and sustaining the level of water resource usage in any river catchment as well as when modelling hydrological processes, it is essential that the role of floodplain wetlands in stream flows is recognised and understood. Existing studies on hydrology within the Volta River basin have not adequately represented the variability of wetland hydrological processes and their contribution to the sustenance of river flow. In order to quantify the extent of floodwater storage within riparian wetlands and their contribution to subsequent river discharges, a series of complementary studies were conducted by utilising stable isotopes, physical monitoring of groundwater levels and numerical modelling. The water samples were collected near Pwalugu on the White Volta River and at three wetland sites adjacent to the river using the grab sampling technique. These were analysed for (18)O and (2)H. The analysis provided an estimate of the contribution of pre-event water to overall stream flow. In addition, the variation in the isotopic composition in the river and wetland water samples, respectively, revealed the pattern of flow and exchange of water between the wetlands and the main river system. PMID:20229387

  2. Application of the MIKE SHE hydrological model in exploring sustainable development of water resources for agricultural activities in the White Volta Basin, Ghana

    NASA Astrophysics Data System (ADS)

    Oteng, F. M.; Alo, C. A.; Bitew, M. M.; Yidana, S. M.

    2013-12-01

    Sustainable abstraction of groundwater resources for commercial irrigation in the White Volta Basin (WVB) holds promise for a fledging agricultural industry in the basin. This is because erratic rainfall patterns attending climate change/variability has imposed mixed fortunes in terms of rain-fed agricultural activities currently practiced in the WVB. Addressing the sustainability of groundwater for commercial abstraction will require the integration of surface and subsurface flows and analysis of the impacts of climate change scenarios on the resource, employing a surface-subsurface flow model. Here, we present early results from surface flow simulation over the basin using the physically-based surface-subsurface flow model MIKE SHE.

  3. Neoproterozoic Glacial Strata of the Centralian Superbasin: New Insight From Subsurface Data in the Southern Georgina Basin, Australia

    NASA Astrophysics Data System (ADS)

    Verdel, C.; Willink, R. J.; Gurney, J.

    2014-12-01

    The Georgina Basin portion of the Centralian Suberbasin locally preserves extensive successions of Neoproterozoic sediments, including some of the thickest Cryogenian glacial deposits in the world. Surficial exposure of these units is poor, however, necessitating description and sampling of subsurface stratigraphic records. We have examined drillcore from boreholes in the southern part of the Georgina Basin that penetrate particularly thick accumulations of glaciogenic strata. One of these cores includes, in stratigraphic succession, ~500 meters of laminated diamictite, an overlying 150 meters of coarse-grained sandstone and conglomerate, and an upper 30 meter interval of carbonate that includes conspicuous pink dolostone. C isotope values of the carbonate interval are approximately -1‰ at its base, rise to values around 0‰ within the pink dolostone, then decline to -1 to -2% at the top of the cored interval. While it is currently unclear whether the carbonate is a Neoproterozoic cap or an unconformably overlying Cambrian unit, correlations based on regional seismic and well data suggest that the thick accumulation of diamictite is a well-preserved record of Neoproterozoic glaciation. We have obtained high-resolution visible and shortwave-infrared reflectance spectroscopy data from these cores with a HyLogger instrument. These data permit detailed mineralogical description of the glacial interval at a scale of ~1 cm and comprise a fully digital stratigraphic record.

  4. Entomological aspects of the first five years of the Onchocerciasis Control Programme in the Volta River Basin.

    PubMed

    Walsh, J F; Davies, J B; Le Berre, R

    1979-09-01

    The history and structure of the WHO Onchocerciasis Control Programme in the Volta River Basin are described. An outline of the vector control operations is given, and the techniques and organisation of the entomological evaluation network are described in detail. During the course of the evaluation and related studies undertaken between November 1974 and October 1978 almost 1.2 million S. damnosum females have been taken in over 52,000 man days of catching, and 674,000 flies were dissected. An assessment based on this effort using Annual Biting Rates and Annual Transmission Potentials shows that the transmission of O. volvulus has been reduced to below a defined maximum permissible level over most of the central part of the Programme Area. The difficulties encountered in the remainder, and at certain problem sites are outlined and relevant data given. The benefits to be expected from extending the area further southwards and the possibilities of later reductions in control activity are discussed. PMID:543001

  5. Geophysical evidence for a major palaeochannel within the Obosum Group of the Volta Basin, Northern Region, Ghana

    NASA Astrophysics Data System (ADS)

    Jessell, Mark; Boamah, Kwame; Duodu, John Agyei; Ley-Cooper, Yusen

    2015-12-01

    We have identified a 230 km long palaeochannel cutting through the sediments of the Obosum Group within the Volta Basin, Ghana. The channel is visible in regional airborne magnetic data as a pair of parallel magnetic anomalies which we interpret to be lateral terrace placer deposits of magnetite or maghemite and show both meandering and braided geometries. The palaeochannel is also visible in the airborne radiometric data for part of its length, as well as in airborne electromagnetic data, where it is marked by a zone of low conductivity. The meanders have a wavelength of around 20 km and together with the 2 km spacing between magnetic anomalies, suggest a major palaeo-river system, of as yet unknown age, although based on published detrital zircon ages for the host sediments and geomorphological arguments it is probably between 509 ± 68 and 45 Ma, and is comparable in size to the modern-day Niger River. Given the known occurrences of alluvial gold and diamonds in Ghana, and the general prospectivity of meandering and braided rivers systems, we believe the region has exploration potential for a range of economically valuable minerals, and could also potentially host a shallow aquifer.

  6. Developing a decision support tool for landscape planning and management to minimize land and water degradation in Volta basin

    NASA Astrophysics Data System (ADS)

    Vlek, Lulseged Tamene, Quang Bao Le, Jens Liebe, Paul L. G.

    2009-04-01

    Although many soil/water-landscape studies have been published in the last two decades, progress in developing operational tools for supporting landscape planning to minimize land and water degradation in developing regions is still modest. Some of the existing tools are very data demanding and/or too complicated to be useful to data scarce regions. A research group at the Center for Development Research (ZEF), University of Bonn has developed a LAndscape Management and Planning Tool (LAMPT) to facilitate land management decision making and landscape planning by optimization. Firstly, we used the Revised Universal Soil Loss Equation (RUSLE) and a Distributed Sediment Delivery Model (DSDM) in a GIS environment to estimate the spatial distribution of areas experiencing different levels of soil loss in the White Volta basin. The RUSLE is employed to map the spatial patterns of major sediment source areas based on data calibrated for the study region. As RUSLE only estimates the potential gross erosion of each grid cell, a DSDM is used to estimate the sediment delivery efficiency of each cell using flow distance and velocity along the flow path. The combined models allow a classification of sub-watersheds experiencing different levels of soil loss using a soil tolerance threshold suitable for the study areas (Burkina Faso and Ghana). The result shows that the majority of areas around north-eastern and eastern parts of the White Volta basin (mainly south-eastern Burkina Faso and upper east region of Ghana) are associated with high levels of sediment yield (over 15 t ha-1 yr-1). The main reason could be high population pressure, poor surface cover and relatively high slope of some of the areas in Ghana. On the other hand, the north-western and southern parts of the basin experience low levels of sediment yield (less than 5 t ha-1 yr-1) mainly due to their flat terrain and good surface cover that encourage sediment deposition rather than erosion. We revealed that a GIS

  7. A longitudinal epidemiological survey of bovine trypanosomosis and its vectors in the White Volta river basin of Northern Ghana.

    PubMed

    Mahama, C I; Desquesnes, M; Dia, M L; Losson, B; De Deken, R; Speybroeck, N; Geerts, S

    2005-03-31

    A longitudinal epidemiological survey of bovine trypanosomosis and its vectors was carried out in the Volta river basin of Northern Ghana to determine the relationship between cattle management and the incidence of bovine trypanosomosis. Two groups of sentinel cattle under different systems of management, classified as "fully-sedentary" and "partially-sedentary" (depending on the type of management) were followed over a 1-year period starting from March 2003 onwards. Cattle were screened at intervals of 3 months using the buffy coat technique (BCT). Buffy coat specimen from animals that were positive for the BCT and those that were negative, but with a packed cell volume (PCV) of less than 21% were further tested using the polymerase chain reaction (PCR). Plasma from all animals were tested for antibody using the indirect antibody enzyme-linked immunosorbent assay (ELISA). Trypanosomosis challenge was determined in tandem with the epidemiological survey with watering sites of sentinel cattle being the foci of interest. The parasitological prevalence at the start of the survey was higher in the fully-sedentary group (9%) than in the partially-sedentary group (3%). In subsequent visits, however, the parasitological incidence was consistently higher in the partially-sedentary group than in the fully-sedentary group. The mean seroprevalence (ELISA) of both groups increased from 3% in March to 54% in December. Statistical analysis of the serological results using a random effect logistic regression, showed a significant difference in incidence of bovine trypanosomosis between the two groups. There was also a significant effect of time. The influence of cattle herding on host-vector-parasite interface and its consequence on the incidence of trypanosomosis are discussed. PMID:15740857

  8. Predicting the downstream impact of ensembles of small reservoirs with special reference to the Volta Basin, West Africa

    NASA Astrophysics Data System (ADS)

    van de Giesen, N.; Andreini, M.; Liebe, J.; Steenhuis, T.; Huber-Lee, A.

    2005-12-01

    After a strong reduction in investments in water infrastructure in Sub-Saharan Africa, we now see a revival and increased interest to start water-related projects. The global political willingness to work towards the UN millennium goals are an important driver behind this recent development. Large scale irrigation projects, such as were constructed at tremendous costs in the 1970's and early 1980's, are no longer seen as the way forward. Instead, the construction of a large number of small, village-level irrigation schemes is thought to be a more effective way to improve food production. Such small schemes would fit better in existing and functioning governance structures. An important question now becomes what the cumulative (downstream) impact is of a large number of small irrigation projects, especially when they threaten to deplete transboundary water resources. The Volta Basin in West Africa is a transboundary river catchment, divided over six countries. Of these six countries, upstream Burkina Faso and downstream Ghana are the most important and cover 43% and 42% of the basin, respectively. In Burkina Faso (and also North Ghana), small reservoirs and associated irrigation schemes are already an important means to improve the livelihoods of the rural population. In fact, over two thousand such schemes have already been constructed in Burkina Faso and further construction is to be expected in the light of the UN millennium goals. The cumulative impact of these schemes would affect the Akosombo Reservoir, one of the largest manmade lakes in the world and an important motor behind the economic development in (South) Ghana. This presentation will put forward an analytical framework that allows for the impact assessment of (large) ensembles of small reservoirs. It will be shown that despite their relatively low water use efficiencies, the overall impact remains low compared to the impact of large dams. The tools developed can be used in similar settings elsewhere

  9. Estimation of small reservoir storage capacities in the São Francisco, Limpopo, Bandama and Volta river basins using remotely sensed surface areas

    NASA Astrophysics Data System (ADS)

    Rodrigues, Lineu; Senzanje, Aidan; Cecchi, Philippe; Liebe, Jens

    2010-05-01

    People living in areas with highly variable rainfall, experience droughts and floods and often have insecure livelihoods. Small multi-purpose reservoirs (SR) are a widely used form of infrastructures to provide people in such areas with water during the dry season, e.g. in the basins of São Francisco, Brazil, Limpopo, Zimbabwe, Bandama, Ivory Coast and Volta, Ghana. In these areas, the available natural flow in the streams is sometimes less than the flow required for water supply or irrigation, however water can be stored in times of surplus, for example, from a wet season to a dry season. Efficient water management and sound reservoir planning are hindered by the lack of information about the functioning of these reservoirs. Reservoirs in these regions were constructed in a series of projects funded by different agencies, at different times, with little or no coordination among the implementing partners. Poor record keeping and the lack of appropriate institutional support result in deficiencies of information on the capacity, operation, and maintenance of these structures. Estimating the storage capacity of dams is essential to the responsible management of water diversion. Most of SR in these basins have never been evaluated, possibly because the tools currently used for such measurement are labor-intensive, costly and time-consuming. The objective of this research was to develop methodology to estimate small reservoir capacities as a function of their remotely sensed surface areas in the São Francisco, Limpopo, Bandama and Volta basins, as a way to contribute to improve the water resource management in those catchments. Remote sensing was used to identify, localize and characterize small reservoirs. The surface area of each was calculated from satellite images. A sub-set of reservoirs was selected. For each reservoir in the sub-set, the surface area was estimated from field surveys, and storage capacity was estimated using information on reservoir surface

  10. Lake Volta, Ghana

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This true-color image of Lake Volta in Ghana was acquired March 31, 2002 by the Moderate Resolution Imaging Spectroradiometer (MODIS). Lake Volta is one of the world's largest artificially created lakes. Lake Volta is actually a reservoir formed from the damming of the Volta River, and extends 250 miles north of the Akosombo Dam. The lake covers an area of 8,482 square km. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

  11. Physical and isotopic characteristics in peri-urban landscapes: a case study at the lower Volta River Basin, Ghana

    NASA Astrophysics Data System (ADS)

    Gampson, E. K.; Nartey, V. K.; Golow, A. A.; Akiti, T. T.; Sarfo, M. A.; Salifu, M.; Aidoo, F.; Fuseini, A. R.

    2015-05-01

    The study presents the application of selected multivariate techniques: display methods (principal component analysis) and unsupervised pattern recognition (cluster analysis) in an attempt to discriminate sources of variation of water quality. PCA has allowed the identification of a reduced number of latent factors with a hydrochemical meaning: natural and anthropogenic (domestic and agricultural activities) factors, which also agrees with the R-mode hierarchical cluster analysis (HCA). Q-mode HCA also corroborates the results of the correlation analysis in relation to sampling sites established on hydrochemical parameters, indicating that there are no spatial and temporal characteristics among the sampling sites in the study area. The suitability of river water for irrigation use was assessed in the study area. A plot of the sodium adsorption ratio (SAR) and salinity data on a semilog axis suggests that river water provides good irrigation quality in the area. According to the SAR values plotted in the USSL Staff diagram, 100 % of the river water samples fall in C1-S1 (low salinity-low sodium type) group, which provides good irrigation quality to river water from this area. Also, all the data points showed permeability index values in Class II category which is suitable for irrigation purposes. Recorded magnesium ratio and Kelly's ratio showed that <50 % of the river water samples were suitable for irrigation purposes. Stable isotope data of water (δ18O and δ2H) obtained revealed that stream waters joining the Volta River were depleted and possibly recharged by rain and waters from the Akwapim Mountains (located at the western part of the Volta River) than the isotopically heavy evaporated waters found within the Lower Volta River. These results would therefore be useful for water balance studies in the study area.

  12. Vestiges of an Iapetan rift basin in the New Jersey Highlands: Implfications for the Neoproterozoic Laurentian margin

    USGS Publications Warehouse

    Gates, A.E.; Volkert, R.A.

    2004-01-01

    Thin, discontinuous remnants of Neoproterozoic intracratonic rift-basin deposits of the Chestnut Hill Formation occur in the western New Jersey Highlands. These deposits form an important link between well-documented Iapetan rift-basins in both the northern and southern Appalachians. The close spatial relations of Chestnut Hill rocks to Paleozoic sedimentary rocks open the possibility that additional Iapetan rift-basins could be concealed beneath the rocks of the Valley and Ridge Province to the west indicating a much broader zone of rifting than has been previously proposed. The Chestnut Hill Formation is intermittently exposed along a 100 km-long band that extends northeast from Pennsylvania nearly to New York State. The lower part of the Chestnut Hill Formation is composed of interbedded lithic pebble- to boulder-conglomerate and feldspathic sandstone grading upward into interbedded phyllite, feldspathic and quartz sandstone, local paleosaprolite, quartz-pebble conglomerate, thin limestone lenses, volcanic, and volcaniclasic rocks, abundant bedded ironstone (hematite ore), and ultimately into diamictites that are interpreted as possible tilloids and containing rounded intra and extrabasinal clasts of the other lithologies. Extensive soft-sediment deformation, cross bedding, and clastic dikes are common in all but the lowest and upper facies. Banded hematite layers occur preferentially in fine-grained tuffs and tuffaceous sediments, but hematitization has affected most lithologies. Volcanic rocks consist of altered rhyolitic tuffs and lapilli tuffs that are interbedded with sediments. The Chestnut Hill Formation is interpreted to have been deposited in early alluvial, and later a complex of fluvial, lacustrine and deltaic environments. Provenance studies based upon petrographic and geochemical analysis of clastic rocks indicate that the sediments are predominantly immature and reflect derivation from local uplifted felsic basement sources in a rifted

  13. Pedogenic calcretes within fracture systems and beddings in Neoproterozoic limestones of the Irecê Basin, northeastern Brazil

    NASA Astrophysics Data System (ADS)

    Borges, S. V. F.; Balsamo, F.; Vieira, M. M.; Iacumin, P.; Srivastava, N. K.; Storti, F.; Bezerra, F. H. R.

    2016-07-01

    Calcretes or caliches are continental limestones developed by surficial weathering process that takes place mostly in arid and semi-arid regions. In the Irecê Basin, northeastern Brazil, in addition to the regular occurrence of pedogenic calcretes, a peculiar type of structurally controlled calcretes occurs on Neoproterozoic limestones. These peculiar calcretes developed near the surface and occur (1) between layers, (2) inside fractures and (3) within major thrust faults. Fieldwork on selected outcrops was integrated with petrographic, mineralogic, geochemical, density and mercury intrusion porosity analyses to constrain the environment of formation and their petrophysical properties. The results revealed that this type of calcrete is the product of multiepisodic events of dissolution and precipitation occurring during the wet and dry seasons in the region along fractures and beddings. Based on the petrophysical results, we suggest that these calcretes may have an important role in the migration of fluids through the impermeable host carbonate rock and that they act as a conduit for fluid flow, as revealed by their high porosity (mean value = 26%) and remarkable pore connectivity.

  14. Derivation of S and Pb in phanerozoic intrusion-related metal deposits from neoproterozoic sedimentary pyrite, Great Basin, United States

    USGS Publications Warehouse

    Vikre, P.G.; Poulson, S.R.; Koenig, A.E.

    2011-01-01

    The thick (???8 km), regionally extensive section of Neoproterozoic siliciclastic strata (terrigenous detrital succession, TDS) in the central and eastern Great Basin contains sedimentary pyrite characterized by mostly high d34S values (-11.6 to 40.8%, <70% exceed 10%; 51 analyses) derived from reduction of seawater sulfate, and by markedly radiogenic Pb isotopes ( 207Pb/204Pb <19.2; 15 analyses) acquired from clastic detritus eroded from Precambrian cratonal rocks to the east-southeast. In the overlying Paleozoic section, Pb-Zn-Cu-Ag-Au deposits associated with Jurassic, Cretaceous, and Tertiary granitic intrusions (intrusion-related metal deposits) contain galena and other sulfide minerals with S and Pb isotope compositions similar to those of TDS sedimentary pyrite, consistent with derivation of deposit S and Pb from TDS pyrite. Minor element abundances in TDS pyrite (e.g., Pb, Zn, Cu, Ag, and Au) compared to sedimentary and hydrothermal pyrite elsewhere are not noticeably elevated, implying that enrichment in source minerals is not a precondition for intrusion-related metal deposits. Three mechanisms for transferring components of TDS sedimentary pyrite to intrusion-related metal deposits are qualitatively evaluated. One mechanism involves (1) decomposition of TDS pyrite in thermal aureoles of intruding magmas, and (2) aqueous transport and precipitation in thermal or fluid mixing gradients of isotopically heavy S, radiogenic Pb, and possibly other sedimentary pyrite and detrital mineral components, as sulfide minerals in intrusion-related metal deposits. A second mechanism invokes mixing and S isotope exchange in thermal aureoles of Pb and S exsolved from magma and derived from decomposition of sedimentary pyrite. A third mechanism entails melting of TDS strata or assimilation of TDS strata by crustal or mantle magmas. TDS-derived or assimilated magmas ascend, decompress, and exsolve a mixture of TDS volatiles, including isotopically heavy S and radiogenic Pb

  15. Using a spatio-temporal dynamic state-space model with the EM algorithm to patch gaps in daily riverflow series, with examples from the Volta Basin, West Africa

    NASA Astrophysics Data System (ADS)

    Amisigo, B. A.; van de Giesen, N. C.

    2005-04-01

    A spatio-temporal linear dynamic model has been developed for patching short gaps in daily river runoff series. The model was cast in a state-space form in which the state variable was estimated using the Kalman smoother (RTS smoother). The EM algorithm was used to concurrently estimate both parameter and missing runoff values. Application of the model to daily runoff series in the Volta Basin of West Africa showed that the model was capable of providing good estimates of missing runoff values at a gauging station from the remaining series at the station and at spatially correlated stations in the same sub-basin.

  16. A force-of-infection model for onchocerciasis and its applications in the epidemiological evaluation of the Onchocerciasis Control Programme in the Volta River basin area.

    PubMed

    Remme, J; Ba, O; Dadzie, K Y; Karam, M

    1986-01-01

    A simple force-of-infection model for onchocerciasis has been developed for a study of the age-specific epidemiological trends during a period of vector control in the Onchocerciasis Control Programme in the Volta River basin area (OCP). The most important factors included in the model are the longevity of an infection, the aspect of super-infection, age-specific exposure, and the intensity of transmission during the pre-control period. The aim of the study was to determine the most appropriate statistics for the epidemiological evaluation in the OCP. There was generally good agreement between the epidemiological trends, predicted by the model, and the observed trends in the prevalence and mean load of microfilariae in skin snips taken from a cohort population from 23 villages in an area with 8 years of successful vector control in the OCP. It is concluded that the epidemiological trends during the control period are not uniform but depend on the initial age and the initial endemicity level of the population. The epidemiological indices for cohorts of children, born before the start of control, will not show a decrease during the first 8 years of interruption of transmission. The prevalence is too insensitive to be useful for the evaluation in hyperendemic villages during most of the control period. The most sensitive and meaningful statistic for a comparative analysis and for the assessment of epidemiological changes is the geometric mean microfilarial load in a cohort of adults. This index, which is called the Community Microfilarial Load (CMFL), is now routinely used in the OCP. The new analytical methodology has enabled a much better appreciation of the significant epidemiological impact of 8 years of vector control in the OCP. Several related aspects of the pre- and post-control dynamics of onchocerciasis infection are also discussed and priorities are formulated for further work on applied modelling of onchocerciasis. PMID:3492300

  17. A force-of-infection model for onchocerciasis and its applications in the epidemiological evaluation of the Onchocerciasis Control Programme in the Volta River basin area

    PubMed Central

    Remme, J.; Ba, O.; Dadzie, K. Y.; Karam, M.

    1986-01-01

    A simple force-of-infection model for onchocerciasis has been developed for a study of the age-specific epidemiological trends during a period of vector control in the Onchocerciasis Control Programme in the Volta River basin area (OCP). The most important factors included in the model are the longevity of an infection, the aspect of super-infection, age-specific exposure, and the intensity of transmission during the pre-control period. The aim of the study was to determine the most appropriate statistics for the epidemiological evaluation in the OCP. There was generally good agreement between the epidemiological trends, predicted by the model, and the observed trends in the prevalence and mean load of microfilariae in skin snips taken from a cohort population from 23 villages in an area with 8 years of successful vector control in the OCP. It is concluded that the epidemiological trends during the control period are not uniform but depend on the initial age and the initial endemicity level of the population. The epidemiological indices for cohorts of children, born before the start of control, will not show a decrease during the first 8 years of interruption of transmission. The prevalence is too insensitive to be useful for the evaluation in hyperendemic villages during most of the control period. The most sensitive and meaningful statistic for a comparative analysis and for the assessment of epidemiological changes is the geometric mean microfilarial load in a cohort of adults. This index, which is called the Community Microfilarial Load (CMFL), is now routinely used in the OCP. The new analytical methodology has enabled a much better appreciation of the significant epidemiological impact of 8 years of vector control in the OCP. Several related aspects of the pre- and post-control dynamics of onchocerciasis infection are also discussed and priorities are formulated for further work on applied modelling of onchocerciasis. PMID:3492300

  18. A Remote Sensing-Based Land Surface Phenology Application for Cropland Monitoring in the Volta River Basin of West Africa

    NASA Astrophysics Data System (ADS)

    Abd Salam El Vilaly, Mohamed; El Vilaly, Audra; Badiane, Ousmane

    2015-04-01

    Understanding the complex feedbacks between climate, environmental change, and human activities is essential to the development of sustainable agricultural systems. A key aspect of crop production that shows immediate response to climate change is crop phenology, which defines the shape and progress of the growing season and is an integrator of all environmental factors controlling crop production. This research aims to characterize remote sensing-based land surface phenology of cropped areas and compare them to the actual crop growing seasons recorded by farmers: planting, emergences, flowering, fruiting, and harvest date. We use the 2000-2013 MODIS Terra 16-day record of vegetation index to extract 4 phenometrics (Start and Length of Growing Season, Date of Growing Season Peak, and the Growing Season Cumulative Signal). Most of these metrics are simple time-related phenometrics. A spatiotemporal phenological characterization of cropped/managed lands in the basin already shows distinct response patterns and trajectories along climate gradients. This permits us to monitor cropped lands and their responses to disturbances, such as drought, fire, flooding, and human activities. In turn, interviewing farmers in the basin and consulting their phenological records. This study will allow for robust validation of remote sensing LSP algorithms, and more crucially, will help characterize any remote sensing-based metrics that contrast with the actual biological phenophases of monitored crops. In terms of its larger significance, this study demonstrates the fundamental role that remote sensing plays in global agriculture in informing conservation and management practices.

  19. A comparative analysis of groundwater recharge estimates from three major methods: An analysis of subsurface recharge in the Nabogo sub-catchment of the White Volta Basin, Northern Ghana

    NASA Astrophysics Data System (ADS)

    Fynn, O. F.; Yidana, S. M.; Alo, C. A.; Mensah, F. O.

    2013-12-01

    Groundwater recharge in the Nabogo sub-catchment of the White Volta Basin is assessed using three main methods: the water table fluctuations method, baseflow recession method, and chloride mass balance approach. The objective is to quantify the relative proportions of direct vertical infiltration and percolation of rainwater in the area and subsurface flows in determining the total groundwater recharge in the basin. Groundwater resources development for commercial irrigation activities is an essential aspect of the livelihoods of communities living within the catchments of the Volta Basin. A comprehensive assessment of the recharge component of groundwater budgets in the basin is critical towards determining optimal abstraction rates in order to ensure resource sustainability and ecological integrity. This will form the basis for quantifying abstraction rates that are permissible to support large scale irrigation activities in the basin. The presence and thickness of the clay layer in the unsaturated zone serves to limit vertical infiltration of rainwater, and thus reduce vertical groundwater recharge in the area. In this study, the chloride mass balance technique, supported by the analysis of stable isotope signatures, has been used to estimate the vertical groundwater recharge and its spatial pattern of distribution in the area. The water table fluctuations technique and base flow recession method are then used to estimate total groundwater recharge in the basin. It is then possible to quantify the relative contributions of subsurface flows in the groundwater recharge in the basin. Temporal variations in groundwater recharge in the area are examined from time series of estimates from the baseflow recession technique. The results will assist in assessing the short term impacts of rainfall variability on groundwater budgets in the area.

  20. Integrated water research in the GLOWA Volta Project

    NASA Astrophysics Data System (ADS)

    van de Giesen, N.; Andreini, M.; Berger, T.; Iskandarani, M.; Kunstmann, H.; Park, S.; Vlek, P.

    2003-04-01

    The Volta Basin covers 400,000 km2 of the West African savanna. The river feeds Lake Volta, that provides over 95% of the electricity in Ghana and has the largest surface of any man-made lake in the world. The rural population (per capita income US600/year) increasingly turns to small scale irrigation development to improve the returns on their agricultural activities and reduce dependence on the highly variable rainfall. The irrigation development stands in direct competition with the hydropower generation that drives development in the more urbanized South. The GLOWA Volta Projects seeks to develop a Decision Support System (DSS) for the management of water resources in the basin under changing global and regional conditions. The DSS is built upon a scientific analysis of all factors that affect water supply and demand. To understand all aspects of the hydrological cycle in the Volta Basin one needs to take physical (atmosphere, land, water) as well as social aspects (population, economic development, institutions) into account. The major scientific challenge of the GLOWA Volta Project is the integrated analysis of the bio- physical and socio-economic factors that affect the hydrological cycle in the Volta Basin. The presentation introduces the GLOWA Volta Project, focusing on activities that integrate different disciplines. Specifically, we present three sets of activities: (1) the coupling between meteorology and hydrology, (2) development of a Common Sampling Frame for the collection of socio-economic and bio-physical data, and (3) a water use optimization model that incorporates economy, hydrology, and institutional analysis. Finally, we look at recent initiatives in the basin that link science, stakeholders, and policy makers.

  1. A New age Constraint on Sturtian Glaciation: SHRIMP U-Pb zircon geochronology of Neoproterozoic Altungol Formation in Tarim Basin, NW China

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Li, J.; Li, W.; Wang, H.

    2013-12-01

    Neoproterozoic glaciations with a wide distribution, punctuated the largely ice-free Precambrian world within tropical latitudes, interpreted as evidence record the cold paleoclimate intervals which made a Snowball Earth with the frozen ocean. More recently, Quruqtagh of Northeast Tarim Basin, Northwest China, catches the increasing eyes, not only because of its three or four Neoproterzoic glacial periods in China, but also its tectonic significance for breakup of Rodinia supercontinent. There are many Neoproterozoic glaciation strata exposures in Quruqtagh. The Nanhua System is divided into the Bayisi, Zhaobishan (absent in south aera), Altungol and Tereeken formations. Thick tillites were found in Bayisi, Tereeken and Hankalchough formations, while minor was found in Altungol Formation. After the field investigation of the south Yaerdang Mountain in the South aera, it is suggested that the Altungol Formation in the South aera differs from that the North aera. In the North, it is a set of littoral-neritic clastic facies sediment with few volcanic rocks and marine tillites in the bottom. In South Quruqtagh, it consists of 45m-thick gray-green tillites in the bottom with different size and complex components gravels, volcanic interbed near the top of tillites, overlying strata is cap dolomite of 15m thickness, with abundant drop-stones, the upper is black shales and gray to black thin-interbeded siliceous rock. The reported ages without Altungol glaciation age are all focused on the north Quruqtagh and conversely in South Quruqtagh without reported glaciation age. Based on field investigation of Nanhua System (Cryogenian) in NE Tarim Basin, we offer the first set of Sturtian glaciation age 729.4×6.6Ma, in the form of SHRIMP(sensitive high-resolution ion microprobe) U-Pb zircon age dating of volcanic interbedded near the top of Altungol Formation tillites, South Quruqtagh, which provides a new constraint on the Sturtian glaciation from global perspective. It is a

  2. The Neoproterozoic.

    PubMed

    Butterfield, Nicholas J

    2015-10-01

    The Neoproterozoic era was arguably the most revolutionary in Earth history. Extending from 1000 to 541 million years ago, it stands at the intersection of the two great tracts of evolutionary time: on the one side, some three billion years of pervasively microbial 'Precambrian' life, and on the other the modern 'Phanerozoic' biosphere with its extraordinary diversity of large multicellular organisms. The disturbance doesn't stop here, however: over this same stretch of time the planet itself was in the throes of change. Tectonically, it saw major super-continental reconfigurations, climatically its deepest ever glacial freeze, and geochemically some of the most anomalous perturbations on record. What lies behind this dramatic convergence of biological and geological phenomena, and how exactly did it give rise to the curiously complex world that we now inhabit? PMID:26439347

  3. The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins.

    PubMed

    Sommer, Carlos A; Lima, Evandro F; Nardi, Lauro V S; Liz, Joaquim D; Waichel, Breno L

    2006-09-01

    The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources. PMID:16936944

  4. Modeling the impact of a hydropower reservoir on the habitat of a megaherbivore in the Black Volta Basin in Ghana, West Africa

    NASA Astrophysics Data System (ADS)

    Manful, Desmond

    2010-05-01

    The Black Volta watershed is approximately 134 000 km2 in size at the gauge at Bamboi. It is part of the main 414 000 km2 Volta system. The Volta river was dammed at Akosombo in 1965 resulting in the largest man-made lake in the world, the Volta Lake. The Bui dam is a new 400 MW scheme currently under development on the Black Volta River in the Bui national park in Ghana. The reservoir created by the Bui barrage is expected to impact (through inundation) the habitat of two species of hippos know to exist in the park, the Hippopotamus amphibius and the Choeropsis liberiensis. Computer-based models present a unique opportunity to assess quantitatively the impact of the new reservoir on the habitat of the target species in this case the H. amphibious. Until this undertaking, there were very few studies documenting the habitat of the H. amphibious let alone model it. The work and subsequent presentation will show the development of a habitat model for the Hippopotamus amphibius. The Habitat Information retrieval Program based on Streamflow Analysis, in short HIPStrA, is a one dimensional (1D) in-stream, spatially explicit hybrid construct that combines physico-chemical evidence and expert knowledge to forecast river habitat suitability (Hs) for the Hippopotamus amphibius. The version of the model presented is specifically developed to assess the impact of a reservoir created by a hydroelectric dam on potential dwelling areas in the Bui gorge for hippos. Accordingly, this version of HIPStrA simulates a special reservoir suitability index (Rsi), a metric that captures the "hippo friendliness" of any lake or reservoir. The impact of measured and simulated flood events as well as low flows, representing extreme events is also assessed. Recommendations are made for the operating rules of the reservoir in the post-construction phase of the dam. A great deal of work has been done on the effects of stream flow changes on fish especially salmonids. Very little work however has

  5. Replacement of benthic communities in two Neoproterozoic-Cambrian subtropical-to-temperate rift basins, High Atlas and Anti-Atlas, Morocco

    NASA Astrophysics Data System (ADS)

    Clausen, Sébastien; Álvaro, J. Javier; Zamora, Samuel

    2014-10-01

    The ‘Cambrian explosion’ is often introduced as a major shift in benthic marine communities with a coeval decline of microbial consortia related to the diversification of metazoans and development of bioturbation (‘Agronomic Revolution’). Successive community replacements have been reported along with ecosystem diversification and increase in guild complexity from Neoproterozoic to Cambrian times. This process is recorded worldwide but with regional diachroneities, some of them directly controlled by the geodynamic conditions of sedimentary basins. The southern High Atlas and Anti-Atlas of Morocco record development of two rifts, Tonian (?) - early Cryogenian and latest Ediacarian-Cambrian in age, separated by the onset of the Pan-African Orogeny. This tectonically controlled, regional geodynamic change played a primary control on pattern and timing of benthic ecosystem replacements. Benthic communities include microbial consortia, archaeocyathan-thromboid reefal complexes, chancelloriid-echinoderm-sponge meadows, and deeper offshore echinoderm-dominated communities. Microbial consortia appeared in deeper parts of the Tonian (?) - early Cryogenian fluvio-deltaic progradational rift sequences, lacustrine environments of the Ediacaran Volcanic Atlasic Chain (Ouarzazate Supergroup) and the Ediacaran-Cambrian boundary interval, characterized by the peritidal-dominated Tifnout Member (Adoudou Formation). They persisted and were largely significant until Cambrian Age 3, as previous restricted marine conditions precluded the immigration of shelly metazoans in the relatively shallow epeiric parts of the Cambrian Atlas Rift. Successive Cambrian benthic communities were replaced as a result of distinct hydrodynamic and substrate conditions, which allow identification of biotic (e.g., antagonistic relationships between microbial consortia and echinoderms, and taphonomic feedback patterns in chancelloriid-echinoderm-sponge meadows) and abiotic (e.g., rifting

  6. Tectonostratigraphy and depositional history of the Neoproterozoic volcano-sedimentary sequences in Kid area, southeastern Sinai, Egypt: Implications for intra-arc to foreland basin in the northern Arabian-Nubian Shield

    NASA Astrophysics Data System (ADS)

    Khalaf, E. A.; Obeid, M. A.

    2013-09-01

    This paper presents a stratigraphic and sedimentary study of Neoproterozoic successions of the South Sinai, at the northernmost segment of the Arabian-Nubian Shield (ANS), including the Kid complex. This complex is composed predominantly of thick volcano-sedimentary successions representing different depositional and tectonic environments, followed by four deformational phases including folding and brittle faults (D1-D4). The whole Kid area is divisible from north to south into the lower, middle, and upper rock sequences. The higher metamorphic grade and extensive deformational styles of the lower sequence distinguishes them from the middle and upper sequences. Principal lithofacies in the lower sequence include thrust-imbricated tectonic slice of metasediments and metavolcanics, whereas the middle and upper sequences are made up of clastic sediments, intermediate-felsic lavas, volcaniclastics, and dike swarms. Two distinct Paleo- depositional environments are observed: deep-marine and alluvial fan regime. The former occurred mainly during the lower sequence, whereas the latter developed during the other two sequences. These alternations of depositional conditions in the volcano-sedimentary deposits suggest that the Kid area may have formed under a transitional climate regime fluctuating gradually from warm and dry to warm and humid conditions. Geochemical and petrographical data, in conjunction with field relationships, suggest that the investigated volcano-sedimentary rocks were built from detritus derived from a wide range of sources, ranging from Paleoproterozoic to Neoproterozoic continental crust. Deposition within the ancient Kid basin reflects a complete basin cycle from rifting and passive margin development, to intra-arc and foreland basin development and, finally, basin closure. The early phase of basin evolution is similar to various basins in the Taupo volcanics, whereas the later phases are similar to the Cordilleran-type foreland basin. The

  7. Sensitive high resolution ion microprobe (SHRIMP) detrital zircon geochronology provides new evidence for a hidden neoproterozoic foreland basin to the Grenville Orogen in the eastern Midwest, U.S.A

    USGS Publications Warehouse

    Santos, J.O.S.; Hartmann, L.A.; McNaughton, N.J.; Easton, R. M.; Rea, R.G.; Potter, P.E.

    2002-01-01

    A sensitive high resolution ion microprobe (SHRIMP) was used in combination with backscattered electron (BSE) and cathodoluminescence (CL) images to determine the age of detrital zircons from sandstones in the Neoproterozoic Middle Run Formation of the eastern Midwest, United States. Eleven samples from seven drill cores of the upper part of the Middle Run Formation contain detrital zircons ranging in age from 1030 to 1982 Ma (84 analyses), with six distinctive modes at 1.96, 1.63, 1.47, 1.34, 1.15, and 1.08 Ga. This indicates that most, but not all, of the zircon at the top of the Middle Run Formation was derived from the Grenville Orogen. The youngest concordant detrital zircon yields a maximum age of 1048 ?? 22 Ma for the Middle Run Formation, indicating that the formation is younger than ca. 1026 Ma minus the added extra time needed for later uplift, denudation, thrusting, erosion, and transport to southwestern Ohio. Thus, as judged by proximity, composition, thickness, and geochronology, it is a North American equivalent to other Neoproterozoic Grenvillian-derived basins, such as the Torridon Group of Scotland and the Palmeiral Formation of South America. An alternate possibility, although much less likely in our opinion, is that it could be much younger, any time between 1048 ?? 22 Ma and the deposition of the Middle Cambrian Mount Simon Sandstone at about 510 Ma, and still virtually almost all derived from rocks of the Grenville Orogen.

  8. Detrital zircon U-Pb geochronology and whole-rock Nd-isotope constraints on sediment provenance in the Neoproterozoic Sergipano orogen, Brazil: From early passive margins to late foreland basins

    NASA Astrophysics Data System (ADS)

    Oliveira, E. P.; McNaughton, N. J.; Windley, B. F.; Carvalho, M. J.; Nascimento, R. S.

    2015-11-01

    SHRIMP U-Pb detrital zircon geochronology and depleted-mantle Nd-model ages of clastic rocks were combined to understand the sediment provenance in the Neoproterozoic Sergipano Belt. The Sergipano is the main orogenic belt between the Borborema province and the São Francisco Craton, eastern South America; it is divisible into several lithostratigraphic domains from North to South: Canindé, Poço Redondo-Marancó, Macururé, Vaza Barris, and Estância. Nd model ages (TDM) and detrital zircon U-Pb SHRIMP geochronology indicate that the protoliths of clastic metasedimentary rocks from the Marancó and Macururé domains were mostly derived from eroded late Mesoproterozoic to early Neoproterozoic rocks (1000-900 Ma), whereas detritus of similar rocks from the Canindé domain came from a younger source (ca. 700 Ma and 1000 Ma). Samples from the Vaza Barris domain show the greatest scatter of both TDM and zircon ages amongst all domains, but with important contributions from Proterozoic sources (690-1050 Ma and ca. 2100 Ma) and less from Archaean sources. The Estância domain samples have zircon population peaks at 570 Ma, 600 Ma, and 920-980 Ma, with a few older grains; one diamictite contains only ca. 2150 Ma zircon grains. Our preliminary results support a model in which sediments of the Marancó and Macururé domains were deposited on a continental margin of the ancient Borborema plate before its collision with the São Francisco Craton; the Canindé domain is likely to be an aborted Neoproterozoic rift assemblage within the southern part of the Borborema plate (Pernambuco-Alagoas massif). The basal units of the Vaza Barris and Estância domains have clast sources from the São Francisco Craton and are best interpreted as passive margin sediments. However, the uppermost units of the Estância and Vaza Barris domains come from foreland basins formed during collision of Borborema plate with the São Francisco Craton.

  9. Detrital zircon analysis of Mesoproterozoic and neoproterozoic metasedimentary rocks of northcentral idaho: Implications for development of the Belt-Purcell basin

    USGS Publications Warehouse

    Lewis, R.S.; Vervoort, J.D.; Burmester, R.F.; Oswald, P.J.

    2010-01-01

    The authors analyzed detrital zircon grains from 10 metasedimentary rock samples of the Priest River complex and three other amphibolite-facies metamorphic sequences in north-central Idaho to test the previous assignment of these rocks to the Mesoproterozoic Belt-Purcell Supergroup. Zircon grains from two samples of the Prichard Formation (lower Belt) and one sample of Cambrian quartzite were also analyzed as controls with known depositional ages. U-Pb zircon analysis by laser ablation - inductively coupled plasma - mass spectrometry reveals that 6 of the 10 samples contain multiple age populations between 1900 and 1400 Ma and a scatter of older ages, similar to results reported from the Belt- Purcell Supergroup to the north and east. Results from the Priest River metamorphic complex confirm previous correlations with the Prichard Formation. Samples from the Golden and Elk City sequences have significant numbers of 1500-1380 Ma grains, which indicates that they do not predate the Belt. Rather, they are probably from a relatively young, southwestern part of the Belt Supergroup (Lemhi subbasin). Non-North American (1610-1490 Ma) grains are rare in these rocks. Three samples of quartzite from the Syringa metamorphic sequence northwest of the Idaho batholith contain zircon grains younger than the Belt Supergroup and support a Neoproterozoic age. A single Cambrian sample has abundant 1780 Ma grains and none younger than ~1750 Ma. These results indicate that the likely protoliths of many high-grade metamorphic rocks in northern Idaho were strata of the Belt-Purcell Supergroup or overlying rocks of the Neoproterozoic Windermere Supergroup and not basement rocks.

  10. Sediment-hosted stratabound copper assessment of the Neoproterozoic Roan Group, central African copperbelt, Katanga Basin, Democratic Republic of the Congo and Zambia: Chapter T in Global mineral resource assessment

    USGS Publications Warehouse

    Zientek, Michael L.; Bliss, James D.; Broughton, David W.; Christie, Michael; Denning, Paul D.; Hayes, Timothy S.; Hitzman, Murray W.; Horton, John D.; Frost-Killian, Susan; Jack, Douglas J.; Master, Sharad; Parks, Heather L.; Taylor, Cliff D.; Wilson, Anna B.; Wintzer, Niki E.; Woodhead, Jon

    2014-01-01

    This study estimates the location, quality, and quantity of undiscovered copper in stratabound deposits within the Neoproterozoic Roan Group of the Katanga Basin in the Democratic Republic of the Congo and Zambia. The study area encompasses the Central African Copperbelt, the greatest sediment-hosted copper-cobalt province in the world, containing 152 million metric tons of copper in greater than 80 deposits. This study (1) delineates permissive areas (tracts) where undiscovered sediment-hosted stratabound copper deposits may occur within 2 kilometers of the surface, (2) provides a database of known sediment-hosted stratabound copper deposits and prospects, (3) estimates numbers of undiscovered deposits within these permissive tracts at several levels of confidence, and (4) provides probabilistic estimates of amounts of copper and mineralized rock that could be contained in undiscovered deposits within each tract. The assessment, conducted in January 2010 using a three-part form of mineral resource assessment, indicates that a substantial amount of undiscovered copper resources might occur in sediment-hosted stratabound copper deposits within the Roan Group in the Katanga Basin. Monte Carlo simulation results that combine grade and tonnage models with estimates of undiscovered deposits indicate that the mean estimate of undiscovered copper in the study area is 168 million metric tons, which is slightly greater than the known resources at 152 million metric tons. Furthermore, significant value can be expected from associated metals, particularly cobalt. Tracts in the Democratic Republic of the Congo (DRC) have potential to contain near-surface, undiscovered deposits. Monte Carlo simulation results indicate a mean value of 37 million metric tons of undiscovered copper may be present in significant prospects.

  11. Sustainable Development of Research Capacity in West Africa based on the GLOWA Volta Project

    NASA Astrophysics Data System (ADS)

    Liebe, Jens R.; Rogmann, Antonio; Falk, Ulrike; Amisigo, Barnabas; Nyarko, Kofi; Harmsen, Karl; Vlek, Paul L. G.

    2010-05-01

    The Sustainable Development of Research Capacity (SDRC) in West Africa is an 18 month project, funded by the German Ministry of Education and Research, to strengthen the research capacity, give access to data and models, and to support the establishment of the newly formed Volta Basin Authority. The SDRC project largely builds on the results and models developed in the framework of the GLOWA Volta Project (GVP), a nine-year, interdisciplinary research project (May 2000 - May 2009). The GVP's central objectives were to analyze the physical and socio-economic determinants of the hydrological cycle in the Volta Basin in the face of global change, and to develop scientifically sound decision support resources. Another major achievement of GVP was the extensive capacity building. Of the 81 participating students (57 Ph.D.'s), 44 originated from West Africa, and 85% of the West African graduates returned to their home countries. The SDRC makes use of the wide range of research results and decision support tools developed in the course of the GVP. It is based on three columns: I. knowledge transfer and strengthening of human capacity, which focus on a training on the modeling of the onset of the rainy season, hydrological, economic, and hydro-economic modeling, and training of geospatial database managers; II. strengthening of infrastructural research capacity through the support of a research instrumentation network through the operation and transfer of a weather station network, a network of tele-transmitted stream gauges; and III. the transfer of a publicly accessible online Geoportal for the dissemination of various geospatial data and research results. At the center of the SDRC effort is the strengthening of the Volta Basin Authority, a river basin authority with a transnational mandate, especially through the transfer of the Geoportal, and the associated training and promotion efforts. The Geoportal is an effort to overcome the data scarcity previously observed in

  12. Influence of Neoproterozoic tectonic fabric on the origin of the Potiguar Basin, northeastern Brazil and its links with West Africa based on gravity and magnetic data

    NASA Astrophysics Data System (ADS)

    de Castro, David Lopes; Bezerra, Francisco H. R.; Sousa, Maria O. L.; Fuck, Reinhardt A.

    2012-03-01

    The Potiguar Basin is a ˜6,000 m thick aborted NE-trending rift that was formed during the Cretaceous in the continental margin of northeastern Brazil. Its ˜E-W-trending offshore faults form part of the successful continental margin rift that evolved into the South Atlantic Ocean. The region represents one of the most significant pre-Pangea breakup piercing points between eastern South America and West Africa. We used gravity, aeromagnetic, and geological data to assess the role of reactivated Precambrian shear zones and major terrain boundaries in the development of the Potiguar Basin from the Cretaceous to the Cenozoic. We also looked for possible links between these structures in northeastern Brazil and their continuation in West Africa. Our results indicate that the major fault systems of the Potiguar Basin were superimposed on the Precambrian fabric. Both gravity and magnetic maps show lineaments related to the shear zones and major terrain boundaries in the Precambrian crystalline basement, which also characterize the architecture of the rift. For example, the Carnaubais fault, the master fault of the rift system, represents the reactivation of the Portalegre shear zone, the major tectonic boundary between Precambrian terrains in the crystalline basement. In addition, part of the Moho topography is controlled by these shear zones and developed during the period of main rift extension in the Neocomian. The shear zones bounding the Potiguar rift system continue in West Africa around and underneath the Benue Basin, where fault reactivation also took place.

  13. Alessandro Volta and the politics of pictures.

    PubMed

    Fara, Patricia

    2009-12-01

    An astute diplomat, Alessandro Volta secured the patronage of Napoleon Bonaparte to promote his rise to fame as an electrical expert. Reciprocally, politicians helped their own causes by presenting him as a national as well as a scientific figurehead. PMID:19879000

  14. Volta and Galvani: New Electricity from Old. Experiment No. 22.

    ERIC Educational Resources Information Center

    Devons, Samuel

    Presented is a descriptive account of Alessandro Volta's first notable success in 1775, the invention of a unique method of generating electricity. Luigi Galvani's announcement of his theory of "animal electricity" in 1972 is integrated into this interpretation of Volta's discoveries with electricity. Five experiments are described: (1)…

  15. Early Neoproterozoic Global Change Through the Lens of the Tambien Group, Northern Ethiopia

    NASA Astrophysics Data System (ADS)

    Swanson-Hysell, N.; Maloof, A. C.; Condon, D. J.; Park, Y.; MacLennan, S. A.; Schoene, B.; Tremblay, M. M.; Alene, M.; Anttila, E.; Haileab, B.; Tesema, T.

    2015-12-01

    The early Neoproterozoic is a crucial period in the evolution of life and climate on Earth. Basins that developed during the time contain a record of the diversification of eukaryotic life as well as large-scale changes to the carbon cycle and paleogeography during the period leading up to Cryogenian glaciation. Understanding global change leading up to Cryogenian glaciation is key for interpreting the boundary conditions that resulted in the beginning of dramatic climate and geochemical oscillations during this critical interval. Existing age models for Neoproterozoic nonglacial intervals, such as the time leading up to Cryogenian glaciation, largely have been based on correlation of carbonate δ13C values, but there are few tests of the assumed synchroneity of these records between basins. In contrast to the ash-poor successions typically targeted for Neoproterozoic chemostratigraphy, the Tonian to Cryogenian Tambien Group (Tigray region, Ethiopia) was deposited in an arc-proximal basin where volcanic tuffs suitable for U-Pb geochronology are preserved within the mixed carbonate-siliciclastic sedimentary succession. We use physical and isotopic stratigraphic data sets from Tambien Group sedimentary rocks in concert with high-precision U-Pb dates from intercalated tuffs to establish global synchroneity of large scale carbon isotopic change. These new temporal constraints strengthen the case for interpreting Neoproterozoic carbon isotope variation as a record of large-scale changes to the carbon cycle. Furthermore, these dates strengthen the temporal framework for interpreting paleogeographic change, geochemical cycling, and environmental evolution during the radiation of early eukaryotes.

  16. Nutrition and carbon metabolism of Methanococcus voltae.

    PubMed Central

    Whitman, W B; Ankwanda, E; Wolfe, R S

    1982-01-01

    Methanococcus voltae is a heterotrophic, H2-oxidizing methanogenic bacterium. In complex medium, this bacterium has a doubling time of 1.2 h at its temperature optimum of 38 degrees C. In defined medium, optimal growth is obtained with 0.75 mM isoleucine, 0.75 mM leucine, 2.5 mM acetate, 5 mM NH4Cl, 84 mM MgSO4, 0.4 M NaCl, 1 mM CaCl2, 10 microM Fe2O3, and 0.2 microM NiCl2. In addition, pantothenate, sodium selenate, and cobalt stimulate growth. Optimal growth is obtained between pH 6.0 and 7.0 with either H2 or formate as the electron donor. The volatile fatty acids 2-methylbutyrate and isovalerate can substitute for isoleucine and leucine, respectively. Cellular carbon is derived from acetate (31%), isoleucine (22%), leucine (25%), and carbon dioxide (23%). The amino acids and fatty acids are incorporated almost exclusively into protein. A comparison of the incorporation of U-14C-amino acids and 1-14C-fatty acids indicated that the fatty acids are degraded during incorporation into cell protein. The distribution of carbon from the amino acids suggests that acetyl coenzyme A is not a major intermediate in the degradation of these compounds. Thus, M. voltae may convert isoleucine and leucine to other amino acids by a unique mechanism. The lipid carbon is derived largely from acetate. Thus, the isoprenoid lipids are synthesized de novo from acetate rather than by degradation of leucine. The carbon in the nucleic acids is derived from carbon dioxide (45%), the C-1 of acetate (25%), the C-2 of acetate (22%), and isoleucine and leucine (7%). This labeling pattern is consistent with known biochemical pathways. PMID:6801012

  17. Polyphase Neoproterozoic orogenesis within the east Africa- Antarctica orogenic belt in central and northern Madagascar

    USGS Publications Warehouse

    Key, R.M.; Pitfield, P.E.J.; Thomas, Ronald J.; Goodenough, K.M.; Waele, D.; Schofield, D.I.; Bauer, W.; Horstwood, M.S.A.; Styles, M.T.; Conrad, J.; Encarnacion, J.; Lidke, D.J.; O'connor, E. A.; Potter, C.; Smith, R.A.; Walsh, G.J.; Ralison, A.V.; Randriamananjara, T.; Rafahatelo, J.-M.; Rabarimanana, M.

    2011-01-01

    Our recent geological survey of the basement of central and northern Madagascar allowed us to re-evaluate the evolution of this part of the East Africa-Antarctica Orogen (EAAO). Five crustal domains are recognized, characterized by distinctive lithologies and histories of sedimentation, magmatism, deformation and metamorphism, and separated by tectonic and/or unconformable contacts. Four consist largely of Archaean metamorphic rocks (Antongil, Masora and Antananarivo Cratons, Tsaratanana Complex). The fifth (Bemarivo Belt) comprises Proterozoic meta-igneous rocks. The older rocks were intruded by plutonic suites at c. 1000 Ma, 820-760 Ma, 630-595 Ma and 560-520 Ma. The evolution of the four Archaean domains and their boundaries remains contentious, with two end-member interpretations evaluated: (1) all five crustal domains are separate tectonic elements, juxtaposed along Neoproterozoic sutures and (2) the four Archaean domains are segments of an older Archaean craton, which was sutured against the Bemarivo Belt in the Neoproterozoic. Rodinia fragmented during the early Neoproterozoic with intracratonic rifts that sometimes developed into oceanic basins. Subsequent Mid- Neoproterozoic collision of smaller cratonic blocks was followed by renewed extension and magmatism. The global 'Terminal Pan-African' event (560-490 Ma) finally stitched together the Mid-Neoproterozoic cratons to form Gondwana. ?? The Geological Society of London 2011.

  18. Stable isotopes of oxygen and carbon compositions in the Neoproterozoic of South Gabon (Schisto-Calcaire Subgroup, Nyanga Basin): Are cap carbonates and lithoherms recording a particular destabilization event after the Marinoan glaciation?

    NASA Astrophysics Data System (ADS)

    Préat, Alain; Prian, Jean-Pierre; Thiéblemont, Denis; Obame, Rolf Mabicka; Delpomdor, Franck

    2011-06-01

    Geologic evidence of tropical sea level glaciation in the Neoproterozoic remains a matter of debate in the Snowball Earth hypothesis. The Niari Tillite Formation and the cap carbonates record the late Neoproterozoic Marinoan glaciation in South Gabon. These cap carbonates are located at the base of the Schisto-Calcaire Subgroup a predominantly carbonate succession that rests with sharp contact on top of the Niari Tillite. Integrating sedimentological and stable isotope data, a consistent sequence of precipitation events is proposed, with strongly negative δ 13C values pointing to a particular event in the cap carbonates (average δ 13C value = -3.2‰ V-PDB) and in a further newly defined lithohermal unit (average δ 13C value = -4.6‰ V-PDB). Subsequent shallow evaporitive platform carbonates display carbon and oxygen isotopic compositions indicative of relatively unaltered seawater values. Strongly negative δ 18O values in the lithoherms and replacement of aragonite fans by equigranular calcite suggest flushing of meteoric water derived from glacial meltwater.

  19. Flood Basalts and Neoproterozoic Glaciation

    NASA Astrophysics Data System (ADS)

    Halverson, G. P.; Cox, G. M.; Kunzmann, M.; Strauss, J. V.; Macdonald, F. A.

    2014-12-01

    Large igneous provinces (LIPs), which are commonly associated with supercontinental break-up, are the product of the emplacement of >106 km3 of mafic rocks in less than a few million years. LIP magmatism, in particular continental flood basalt (CFB) volcanism, perturbs global climate on shorter time scales through the radiative effects of degassed SO2 and CO2. On longer time scales, CFBs alter climate through the effect of the high weatherabilty of mafic rocks (5-10 times greater than average continental crust) on global silicate weathering. A link between flood basalt weathering, Rodinia break-up, and Neoproterozoic snowball glaciation has been postulated. Here we present a new compilation of Nd isotope data on Neoproterozoic mudstones from Laurentia, Australia, and South China along with a new seawater strontium isotope record from well preserved carbonates that support this hypothesis. These datasets are consistent with an outsized role of basalt weathering on the global silicate weathering budget during the second half of the Tonian period (~850 to 725 Ma). Along with Os isotope data, they also suggest that an additional pulse of basalt weathering at the end of the Tonian may have initiated the Sturtian snowball glaciation. CFBs have relatively high concentrations of phosphorous. Hence, the drawdown in atmospheric CO2 required to trigger the Sturtian snowball Earth was likely accomplished through a combination of increased silicate weathering rates and enhanced biological productivity driven by greater nutrient supply to the oceans. CFBs were also the likely source of the iron in Neoproterozoic iron formation (IF), all significant occurrences of which are restricted to Sturtian-aged glacial successions. Dramatic declines in ɛNd following the Cryogenian snowball glaciations are mirrored by stepwise increases in 87Sr/86Sr, reflecting the scouring of the continents by global ice sheets. This continental resurfacing removed the extensive basalt carapace as well as

  20. Uncovering the Neoproterozoic carbon cycle.

    PubMed

    Johnston, D T; Macdonald, F A; Gill, B C; Hoffman, P F; Schrag, D P

    2012-03-15

    Interpretations of major climatic and biological events in Earth history are, in large part, derived from the stable carbon isotope records of carbonate rocks and sedimentary organic matter. Neoproterozoic carbonate records contain unusual and large negative isotopic anomalies within long periods (10-100 million years) characterized by δ(13)C in carbonate (δ(13)C(carb)) enriched to more than +5 per mil. Classically, δ(13)C(carb) is interpreted as a metric of the relative fraction of carbon buried as organic matter in marine sediments, which can be linked to oxygen accumulation through the stoichiometry of primary production. If a change in the isotopic composition of marine dissolved inorganic carbon is responsible for these excursions, it is expected that records of δ(13)C(carb) and δ(13)C in organic carbon (δ(13)C(org)) will covary, offset by the fractionation imparted by primary production. The documentation of several Neoproterozoic δ(13)C(carb) excursions that are decoupled from δ(13)C(org), however, indicates that other mechanisms may account for these excursions. Here we present δ(13)C data from Mongolia, northwest Canada and Namibia that capture multiple large-amplitude (over 10 per mil) negative carbon isotope anomalies, and use these data in a new quantitative mixing model to examine the behaviour of the Neoproterozoic carbon cycle. We find that carbonate and organic carbon isotope data from Mongolia and Canada are tightly coupled through multiple δ(13)C(carb) excursions, quantitatively ruling out previously suggested alternative explanations, such as diagenesis or the presence and terminal oxidation of a large marine dissolved organic carbon reservoir. Our data from Namibia, which do not record isotopic covariance, can be explained by simple mixing with a detrital flux of organic matter. We thus interpret δ(13)C(carb) anomalies as recording a primary perturbation to the surface carbon cycle. This interpretation requires the revisiting of

  1. Learning to tell Neoproterozoic time

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.

    2000-01-01

    In 1989, the International Commission on Stratigraphy established a Working Group on the Terminal Proterozoic Period. Nine years of intensive, multidisciplinary research by scientists from some two dozen countries have markedly improved the framework for the correlation and calibration of latest Proterozoic events. Three principal phenomena--the Marinoan ice age, Ediacaran animal diversification, and the beginning of the Cambrian Period--specify the limits and character of this interval, but chemostratigraphy and biostratigraphy based on single-celled microfossils (acritarchs), integrated with high-resolution radiometric dates, provide the temporal framework necessary to order and evaluate terminal Proterozoic tectonic, biogeochemical, climatic, and biological events. These data also provide a rational basis for choosing the Global Stratotype Section and Point (GSSP) that will define the beginning of this period. A comparable level of stratigraphic resolution may be achievable for the preceding Cryogenian Period, providing an opportunity to define this interval, as well, in chronostratigraphic terms--perhaps bounded at beginning and end by the onset of Sturtian glaciation and the decay of Marinoan ice sheets, respectively. Limited paleontological, isotopic, and radiometric data additionally suggest a real but more distant prospect of lower Neoproterozoic correlation and stratigraphic subdivision.

  2. Geological evolution of the Neoproterozoic Bemarivo Belt, northern Madagascar

    USGS Publications Warehouse

    Thomas, Ronald J.; De Waele, B.; Schofield, D.I.; Goodenough, K.M.; Horstwood, M.; Tucker, R.; Bauer, W.; Annells, R.; Howard, K. J.; Walsh, G.; Rabarimanana, M.; Rafahatelo, J.-M.; Ralison, A.V.; Randriamananjara, T.

    2009-01-01

    The broadly east-west trending, Late Neoproterozoic Bemarivo Belt in northern Madagascar has been re-surveyed at 1:100 000 scale as part of a large multi-disciplinary World Bank-sponsored project. The work included acquisition of 14 U-Pb zircon dates and whole-rock major and trace element geochemical data of representative rocks. The belt has previously been modelled as a juvenile Neoproterozoic arc and our findings broadly support that model. The integrated datasets indicate that the Bemarivo Belt is separated by a major ductile shear zone into northern and southern "terranes", each with different lithostratigraphy and ages. However, both formed as Neoproterozoic arc/marginal basin assemblages that were translated southwards over the north-south trending domains of "cratonic" Madagascar, during the main collisional phase of the East African Orogeny at ca. 540 Ma. The older, southern terrane consists of a sequence of high-grade paragneisses (Sahantaha Group), which were derived from a Palaeoproterozoic source and formed a marginal sequence to the Archaean cratons to the south. These rocks are intruded by an extensive suite of arc-generated metamorphosed plutonic rocks, known as the Antsirabe Nord Suite. Four samples from this suite yielded U-Pb SHRIMP ages at ca. 750 Ma. The northern terrane consists of three groups of metamorphosed supracrustal rocks, including a possible Archaean sequence (Betsiaka Group: maximum depositional age approximately 2477 Ma) and two volcano-sedimentary sequences (high-grade Milanoa Group: maximum depositional age approximately 750 Ma; low grade Daraina Group: extrusive age = 720-740 Ma). These supracrustal rocks are intruded by another suite of arc-generated metamorphosed plutonic rocks, known as the Manambato Suite, 4 samples of which gave U-Pb SHRIMP ages between 705 and 718 Ma. Whole-rock geochemical data confirm the calc-alkaline, arc-related nature of the plutonic rocks. The volcanic rocks of the Daraina and Milanoa groups also

  3. Neoproterozoic evolution of the basement of the South-American platform

    NASA Astrophysics Data System (ADS)

    de Brito Neves, Benjamim Bley; Fuck, Reinhardt A.

    2013-11-01

    Neoproterozoic geologic and geotectonic processes were of utmost importance in forming and structuring the basement framework of the South-American platform. Two large domains with distinct evolutionary histories are identified with respect to the Neoproterozoic era: the northwest-west (Amazonian craton and surroundings) and the central-southeast (the extra-Amazonian domain). In the first domain, Neoproterozoic events occurred only locally and were of secondary significance, and the geologic events, processes, and structures of the pre-Neoproterozoic (and syn-Brasiliano) cratonic block were much more influential. In the second, the extra-Amazonian domain, the final evolution, structures and forms are assigned to events related to the development of a complex net of Neoproterozoic mobile belts. These in turn resulted in strong reworking of the older pre-Neoproterozoic basement. In this domain, four distinct structural provinces circumscribe or are separated by relatively small pre-Neoproterozoic cratonic nuclei, namely the Pampean, Tocantins, Borborema and Mantiqueira provinces. These extra-Amazonian provinces were formed by a complex framework of orogenic branching systems following a diversified post-Mesoproterozoic paleogeographic scenario. This scenario included many types of basement inliers as well as a diversified organization of accretionary and collisional orogens. The basement inliers date from the Archean to Mesoproterozoic periods and are different in nature. The escape tectonics that operated during the final consolidation stages of the provinces were important to and responsible for the final forms currently observed. These latest events, which occurred from the Late Ediacaran to the Early Ordovician, present serious obstacles to paleogeographic reconstructions. Two groups of orogenic collage systems are identified. The older system from the Tonian (>850 Ma) period is of restricted occurrence and is not fully understood due to strong reworking

  4. Droughts, Irrigation Development, and Hydropower: Different Development Priorities in Ghana and Burkina Faso and Their Effect on Management of the Volta River, West Africa

    NASA Astrophysics Data System (ADS)

    van de Giesen, N.; Andreini, M.; van Edig, A.

    2001-05-01

    The Volta Basin covers 400,000 km2 of the West-African savanna zone. Ghana lies downstream and contains 42% of the basin. Most of the upstream part of the basin lies in Burkina Faso (43% of total), and the remaining 15% lies in Mali, Côte d'Ivoire, Togo, and Benin. Average rainfall is 1000 mm per year of which around 9% or 36 km3 becomes available as runoff in the Volta River. Small variations in rainfall cause relatively large variations in runoff. The Volta Basin is undergoing rapid changes in land use and water resource development, mainly driven by the high population growth of 3% per year. However, different countries pursue economic development in different ways. At independence in 1957, Ghana's leaders saw industrialization as essential to development and electric power from the Volta Dam as central to that industrialization. In 1964, the Volta Dam was built and Ghana's economic growth in the mining, industrial, and service sectors has depended on the dam's hydropower ever since. In contrast, land-locked Burkina Faso has less industrial potential and seeks to develop through its agriculture, both for subsistence and export crops. Given the extremely unreliable rainfall, irrigation development is seen as the only way to increase agricultural production. In general, irrigation in Burkina Faso takes the form of many small scale, village-based schemes of which the downstream impact is difficult to gauge. A minor drought in 1997 and 1998 caused the level of Lake Volta to drop, resulting in widespread power outages. In the ensuing public discussion, hydraulic development in Burkina Faso was seen as one of the potential causes of the lack of water. No firm data were available to substantiate this claim. In fact, over-withdrawals in previous years combined with climate variability were more likely culprits. A recently initiated multi-disciplinary research project will be presented that seeks to provide a scientific basis on which future discussions between the two

  5. Continental flood basalt weathering as a trigger for Neoproterozoic Snowball Earth

    NASA Astrophysics Data System (ADS)

    Cox, Grant M.; Halverson, Galen P.; Stevenson, Ross K.; Vokaty, Michelle; Poirier, André; Kunzmann, Marcus; Li, Zheng-Xiang; Denyszyn, Steven W.; Strauss, Justin V.; Macdonald, Francis A.

    2016-07-01

    Atmospheric CO2 levels and global climate are regulated on geological timescales by the silicate weathering feedback. However, this thermostat has failed multiple times in Earth's history, most spectacularly during the Cryogenian (c. 720-635 Ma) Snowball Earth episodes. The unique middle Neoproterozoic paleogeography of a rifting, low-latitude, supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo. Under these primed conditions, the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation. Weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios (δ13 C) of Neoproterozoic seawater due to their elevated P contents. In order to test these hypotheses, we have compiled new and previously published Neoproterozoic Nd isotope data from mudstones in northern Rodinia (North America, Australia, Svalbard, and South China) and Sr isotope data from carbonate rocks. The Nd isotope data are used to model the mafic detrital input into sedimentary basins in northern Rodinia. The results reveal a dominant contribution from continental flood basalt weathering during the ca. 130 m.y. preceding the onset of Cryogenian glaciation, followed by a precipitous decline afterwards. These data are mirrored by the Sr isotope record, which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early-middle Neoproterozoic ocean, including a pulse of unradiogenic Sr input into the oceans just prior to the onset of Cyrogenian glaciation. Hence, our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average δ13 C of seawater in the Neoproterozoic and to the initiation of the first (Sturtian) Snowball Earth.

  6. Accelerating Neoproterozoic Research through Scientific Drilling

    NASA Astrophysics Data System (ADS)

    Condon, Daniel; Prave, Anthony; Boggiani, Paulo; Fike, David; Halverson, Galen; Kasemann, Simone; Knoll, Andrew; Zhu, Maoyan

    2014-05-01

    The Neoproterozoic Era (1.0 to 0.541 Ga) and earliest Cambrian (541 to ca. 520 Ma) records geologic changes unlike any other in Earth history: supercontinental tectonics of Rodinia followed by its breakup and dispersal into fragments that form the core of today's continents; a rise in oxygen that, perhaps for the first time in Earth history, resulted in the deep oceans becoming oxic; snowball Earth, which envisages a blanketing of global ice cover for millions of years; and, at the zenith of these combined biogeochemical changes, the evolutionary leap from eukaryotes to animals. Such a concentration of hallmark events in the evolution of our planet is unparalleled and many questions regarding Earth System evolution during times of profound climatic and geological changes remain to be answered. Neoproterozoic successions also offer insight into the genesis of a number of natural resources. These include banded-iron formation, organic-rich shale intervals (with demonstrated hydrocarbon source rocks already economically viable in some countries), base and precious metal ore deposits and REE occurrences, as well as industrial minerals and dimension stone. Developing our understanding of the Neoproterozoic Earth-system, combined with regional geology has the potential to impact the viability of these resources. Our understanding of the Neoproterozoic and early Cambrian, though, is overwhelmingly dependent on outcrop-based studies, which suffer from lack of continuity of outcrop and, in many instances, deep weathering profiles. A limited number of research projects study Precambrian strata have demonstrated the potential impact of scientific drilling to augment and complement ongoing outcrop based studies and advancing research. An ICDP and ECORD sponsored workshop, to be held in March 2014, has been convened to discuss the utility of scientific drilling for accelerating research of the Neoproterozoic through early Cambrian (ca. 0.9 to 0.52 Ga) rock record. The aim is to

  7. Transduction-like gene transfer in the methanogen Methanococcus voltae

    NASA Technical Reports Server (NTRS)

    Bertani, G.

    1999-01-01

    Strain PS of Methanococcus voltae (a methanogenic, anaerobic archaebacterium) was shown to generate spontaneously 4.4-kbp chromosomal DNA fragments that are fully protected from DNase and that, upon contact with a cell, transform it genetically. This activity, here called VTA (voltae transfer agent), affects all markers tested: three different auxotrophies (histidine, purine, and cobalamin) and resistance to BES (2-bromoethanesulfonate, an inhibitor of methanogenesis). VTA was most effectively prepared by culture filtration. This process disrupted a fraction of the M. voltae cells (which have only an S-layer covering their cytoplasmic membrane). VTA was rapidly inactivated upon storage. VTA particles were present in cultures at concentrations of approximately two per cell. Gene transfer activity varied from a minimum of 2 x 10(-5) (BES resistance) to a maximum of 10(-3) (histidine independence) per donor cell. Very little VTA was found free in culture supernatants. The phenomenon is functionally similar to generalized transduction, but there is no evidence, for the time being, of intrinsically viral (i.e., containing a complete viral genome) particles. Consideration of VTA DNA size makes the existence of such viral particles unlikely. If they exist, they must be relatively few in number;perhaps they differ from VTA particles in size and other properties and thus escaped detection. Digestion of VTA DNA with the AluI restriction enzyme suggests that it is a random sample of the bacterial DNA, except for a 0.9-kbp sequence which is amplified relative to the rest of the bacterial chromosome. A VTA-sized DNA fraction was demonstrated in a few other isolates of M. voltae.

  8. Transduction-Like Gene Transfer in the Methanogen Methanococcus voltae

    PubMed Central

    Bertani, Giuseppe

    1999-01-01

    Strain PS of Methanococcus voltae (a methanogenic, anaerobic archaebacterium) was shown to generate spontaneously 4.4-kbp chromosomal DNA fragments that are fully protected from DNase and that, upon contact with a cell, transform it genetically. This activity, here called VTA (voltae transfer agent), affects all markers tested: three different auxotrophies (histidine, purine, and cobalamin) and resistance to BES (2-bromoethanesulfonate, an inhibitor of methanogenesis). VTA was most effectively prepared by culture filtration. This process disrupted a fraction of the M. voltae cells (which have only an S-layer covering their cytoplasmic membrane). VTA was rapidly inactivated upon storage. VTA particles were present in cultures at concentrations of approximately two per cell. Gene transfer activity varied from a minimum of 2 × 10−5 (BES resistance) to a maximum of 10−3 (histidine independence) per donor cell. Very little VTA was found free in culture supernatants. The phenomenon is functionally similar to generalized transduction, but there is no evidence, for the time being, of intrinsically viral (i.e., containing a complete viral genome) particles. Consideration of VTA DNA size makes the existence of such viral particles unlikely. If they exist, they must be relatively few in number;perhaps they differ from VTA particles in size and other properties and thus escaped detection. Digestion of VTA DNA with the AluI restriction enzyme suggests that it is a random sample of the bacterial DNA, except for a 0.9-kbp sequence which is amplified relative to the rest of the bacterial chromosome. A VTA-sized DNA fraction was demonstrated in a few other isolates of M. voltae. PMID:10321998

  9. Taphonomic and evolutionary changes across the Mesoproterozoic-Neoproterozoic transition

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.; Sergeev, V. N.

    1995-01-01

    The principal biological distinction between Mesoproterozoic and Neoproterozoic is the abundance and diversity of eukaryotic fossils in the Neoproterozoic rocks, but the two eras also differ in the composition of preserved cyanobacterial assemblages. Evolving eukaryotes provide a partial explanation for observed differences in prokaryotic fossils, but the taphonomic and environmental influences of shifting carbonate depositional pattern are also important.

  10. Two diamictites, two cap carbonates, two δ13C excursions, two rifts: The Neoproterozoic Kingston Peak Formation, Death Valley, California

    NASA Astrophysics Data System (ADS)

    Prave, A. R.

    1999-04-01

    Stratigraphic mapping of the Neoproterozoic glaciogenic Kingston Peak Formation (Death Valley, California) provides evidence for two temporally discrete extensional deformation episodes. These episodes are bracketed by the Sourdough Limestone and Noonday Dolomite, the facies characteristics and δ13C data (ranging between 2.15 and -2.56‰ and -1.88 and -4.86‰, respectively) of which make them equivalent to Sturtian and Varangian age cap carbonates, respectively. This constrains the two extensional episodes along the southwestern margin of Laurentia to ca. 700 Ma and ca. 600 Ma. These observations and data show that the field evidence for mid-Neoproterozoic breakup and the predictions from tectonic subsidence curves for a latest Neoproterozoic breakup are both correct. Thus, Neoproterozoic plate reconstructions must account for two discrete rift episodes separated by 100 m.y. or more. Confining rifting to within the Kingston Peak Formation thereby places the younger Proterozoic rocks of the southwestern Great Basin in the rift to drift tectonic phase.

  11. Sedimentary talc in Neoproterozoic carbonate successions

    NASA Astrophysics Data System (ADS)

    Tosca, N. J.; MacDonald, F. A.; Strauss, J. V.; Johnston, D. T.; Knoll, A. H.

    2010-12-01

    Talc, Mg3Si4O10(OH)2, is normally considered a high temperature mineral and usually forms from hydrothermal alteration or metamorphism of ultramafic rocks. Talc has also been identified in evaporites, but is more scarce in association with carbonate rocks. Here we report the unusual occurrence of early diagenetic talc associated with early Neoproterozoic (~800-700 Ma) carbonate deposited on two separate platform margins. In the Akademikerbreen Group of Svalbard, the talc occurs as nodules that pre-date microspar cements, filling molar tooth structures and primary porosity in stromatolitic carbonates. In the upper Fifteenmile Group of the Ogilvie Mtns, NW Canada, the talc is present as nodules, coated grains, rip-up clasts and massive beds that are several meters thick and can be traced laterally over 150 km. All of the Neoproterozoic talc samples exhibit a high degree of stacking disorder and are essentially turbostratic, with no mixed layering or occurrences with sepiolite. Sedimentary talc requires a specific set of chemical conditions for its precursors and formation, and its occurrence on two margins suggests a link (direct or indirect) to contemporaneous ocean chemistry. At low temperatures, the Mg-silicate system is controlled mainly by kinetic phenomena and constraints on early diagenetic chemistry are difficult to derive based on thermodynamics alone. To address this problem, we designed an experimental program to evaluate the roles of pH, Mg2+ and SiO2(aq) on the formation of Mg-silicates from low-SO4 (~2.8 mmol/kg), Neoproterozoic-like seawater. Our experiments reveal a sharp and reproducible pH boundary (at ~ 8.66), only above which does poorly crystalline Mg-silicate precipitate. Increasing Mg2+ and/or SiO2(aq) alone is insufficient to nucleate the material; the pH control can be explained by Mg-silica complexing activated by the deprotonation of silicic acid above pH ~8.6-8.7. FT-IR, TEM and XRD analyses of the primary precipitate reveal a talc-like 2

  12. Neoproterozoic Glacial Extremes: How Plausible is the

    NASA Astrophysics Data System (ADS)

    Peltier, W. R.

    2004-05-01

    The suggestion that the glaciation events of the Neoproterozoic could have been global in extent, so-called "snowball" glaciations, during which the oceans were entirely covered by sea ice and the continents by massive continental ice sheets, is an idea tha is recurrent in the geological and climate dynamics literature. It is an idea that haa both critics and defenders but concensus concerning it's plausiblity has yet to emerge. Previous work on this problem has led to the suggestion that a more likely scenario than the "hard snowball" is one in which open water continues to persist at the equator, thus enabling biological evolution into the Cambrian to proceed, perhaps stimulated by the transition from the cold conditions of the Neoproterozoic to the warm condition of the Cambrian, thus leading to the Cambrian "explosion of life". We will discuss recent extensions of our previous efforts to model the extreme climate of the Neoproterozoic, using both the University of Toronto Glacial Systems Model and the NCAR Community Climate System Model. With an appropriate choice for the albedo of sea ice, the former model conntinues to deliver hysteresis in the surface temperature vs. CO2 concentration space when solar luminosity is reduced by 6% below modern, and thus continues to suggest the existence of the previously hypothesized "CO2 attractor". We argue here that the system could be locked onto this attractor by the strong "out of equilibrium" effects of the carbon cycle recently discussed by Rothman et al. (PNAS, 2003). The open water solution is confirmed as the preferred mode of the system by the detailed CCSM integrations that we have performed.

  13. Genetic transformation in the methanogen Methanococcus voltae PS

    NASA Technical Reports Server (NTRS)

    Bertani, G.; Baresi, L.

    1987-01-01

    Mutations causing requirements for histidine, purine, and vitamin B12 were obtained in strain PS of Methanococcus voltae (archaebacteria) upon irradiation with UV or gamma rays. The first two mutations were shown to revert at low frequencies and were used to demonstrate the occurrence of transformation with homologous, wild-type DNA. The transformation rates obtained for these presumably chromosomal markers were in the range of 2 to 100 transformants per microgram of DNA. Mutants resistant to 2-bromoethanesulfonate and to 5-methyl-DL-tryptophan were also isolated.

  14. Genetic transformation in the methanogen Methanococcus voltae PS

    SciTech Connect

    Bertani, G.; Baresi, L.

    1987-06-01

    Mutations causing requirements for histidine, purine, and vitamin B/sub 12/ were obtained in strain PS of Methanococcus voltae (archaebacteria) upon irradiation with UV or gamma rays. The first two mutations were shown to revert at low frequencies and were sued to demonstrate the occurrence of transformation with homologous, wild-type DNA. The transformation rates obtained for these presumably chromosomal markers were in the range of 2 to 100 transformants per ..mu..g of DNA. Mutants resistant to 2-bromoethanesulfonate and to 5-methyl-DL-tryptophan were also isolated.

  15. Provenance of Neoproterozoic sedimentary basement of northern Iran, Kahar Formation

    NASA Astrophysics Data System (ADS)

    Etemad-Saeed, Najmeh; Hosseini-Barzi, Mahboubeh; Adabi, Mohammad Hossein; Sadeghi, Abbas; Houshmandzadeh, Abdolrahim

    2015-11-01

    This article presents new data to understand the nature of the hidden crystalline basement of northern Iran and the tectonic setting of Iran during late Neoproterozoic time. The siliciclastic-dominated Kahar Formation represents the oldest known exposures of northern Iran and comprises late Ediacaran (ca. 560-550 Ma) compositionally immature sediments including mudrocks, sandstones, and conglomerates. This work focuses on provenance of three well preserved outcrops of this formation in Alborz Mountains: Kahar Mountain, Sarbandan, and Chalus Road, through petrographic and geochemical methods. Mineralogical Index of Alteration (MIA) and Chemical Index of Alteration (CIA-after correction for K-metasomatism) values combined with A-CN-K relations suggest moderate weathering in the source areas. The polymictic nature of Kahar conglomerates indicates a mixed provenance for them. However, modal analysis of Kahar sandstones (volcanic to plagioclase-rich lithic arkose) and whole rock geochemistry of mudrocks suggest that they are largely first-cycle sediments and that their sources were remarkably late Ediacaran, intermediate-felsic igneous rocks from proximal arc settings. Tectonic setting discrimination diagrams also indicate a convergent plate margin and continental arc related basin for Kahar sediments. This interpretation is supported by the phyllo-tectic to tectic composition and geochemistry of mudrocks. These results reveal the presence of a felsic/intermediate subduction-related basement (∼600-550 Ma) in this region, which provides new constraints on subduction scenario during this time interval in Iran, as a part of the Peri-Gondwanan terranes.

  16. Development of the VOLT-A shuttle experiment

    NASA Technical Reports Server (NTRS)

    Bifano, W. J.; Bozek, J. M.; Ferguson, D. C.

    1985-01-01

    The NASA Lewis Research Center (LeRC) is investigating potential problems associated with the operation of high voltage solar cell arrays in the space plasma environment. At high voltages, interactions between the solar array and the space plasma could result in unacceptable levels of electrical discharge (arcing) and/or parasitic losses (current drains from the array to the plasma). The objective of the Voltage Operating Limit Tests (VOLT-A) Shuttle bay experiment is to characterize space plasma/solar cell panel interactions in low earth orbit. VOLT-A consists of an experiment plate subassembly which contains four solar panels, an electronics subassembly and a Langmuir probe subassembly mounted on an MPESS carrier. During a given 8.25 hour data taking period (5-1/2 continuous orbits), the solar panels, which represent state-of-the-art solar cell technologies, will be sequentially subjected to bias voltages in steps ranging from minus 626 V to plus 313 V. Appropriate measurements will be made at each voltage to characterize arcing and parasitic losses. Corresponding measurements of the plasma environment (plasma density, electron temperature and neutral density) will also be made. Data will be recorded on an on-board tape recorder for subsequent data reduction and analysis.

  17. The Precambrian of Transangaria, Yenisei Ridge (Siberia): Neoproterozoic microcontinent, Grenville-age orogen, or reworked margin of the Siberian craton?

    NASA Astrophysics Data System (ADS)

    Kuzmichev, Alexander B.; Sklyarov, Eugene V.

    2016-01-01

    The Yenisei Ridge was traditionally perceived as an uplifted segment of the western Siberian craton affected by Neoproterozoic collision events. However, the suggestions for Archaean or Palaeoproterozoic ('Siberian') basement in Transangaria have not been confirmed by reliable geochronological data. A new view regards most of the Ridge, namely, its Transangarian segment, to be an exotic Neoproterozoic terrane that collided with Siberia in the late Neoproterozoic. This paper presents new U-Pb SHRIMP zircon ages demonstrating that Archaean rocks (2611 ± 12 Ma) actually exist in this territory. We also provide a review of published U-Pb zircon ages for igneous and metamorphic rocks of Transangaria together with our new age data. This geochronological dataset clarifies the geology of the Yenisei Ridge and leads to new conclusions, as follows. (1) It is likely that Transangaria was originally underlain by an Archaean-Palaeoproterozoic basement, similar to that of the Siberian craton. (2) Geochronological data do not confirm the idea of widespread "Greenvillian age" granitoides in Transangaria. (3) The Neoproterozoic evolution of the Yenisei Ridge segment of the Siberian craton margin includes the following events. (i) Collision of an unidentified terrane with the western margin (in recent coordinates) of the Siberian craton during 900-855 Ma. The colliding terrane is no longer present in the current structure. (ii) Dextral shearing during 830-800 Ma may have been caused by counter-clockwise rotation of the Siberian craton. (iii) Extensional conditions prevailed during 800-700 Ma. The Isakovka oceanic basin formed at this time interval. (iv) Thrusting of the Isakovka island arc and accretionary prism onto the Siberian margin occurred during the late Neoproterozoic (650-630 Ma) and caused high-pressure metamorphism.

  18. Sedimentary talc in Neoproterozoic carbonate successions

    NASA Astrophysics Data System (ADS)

    Tosca, Nicholas J.; Macdonald, Francis A.; Strauss, Justin V.; Johnston, David T.; Knoll, Andrew H.

    2011-06-01

    Mineralogical, petrographic and sedimentological observations document early diagenetic talc in carbonate-dominated successions deposited on two early Neoproterozoic (~ 800-700 million years old) platform margins. In the Akademikerbreen Group, Svalbard, talc occurs as nodules that pre-date microspar cements that fill molar tooth structures and primary porosity in stromatolitic carbonates. In the upper Fifteenmile Group of the Ogilvie Mountains, NW Canada, the talc is present as nodules, coated grains, rip-up clasts and massive beds that are several meters thick. To gain insight into the chemistry required to form early diagenetic talc, we conducted precipitation experiments at 25 °C with low-SO 4 synthetic seawater solutions at varying pH, Mg 2+ and SiO 2(aq). Our experiments reveal a sharp and reproducible pH boundary (at ~ 8.7) only above which does poorly crystalline Mg-silicate precipitate; increasing Mg 2+ and/or SiO 2(aq) alone is insufficient to produce the material. The strong pH control can be explained by Mg-silica complexing activated by the deprotonation of silicic acid above ~ 8.6-8.7. FT-IR, TEM and XRD of the synthetic precipitates reveal a talc-like 2:1 trioctahedral structure with short-range stacking order. Hydrothermal experiments simulating burial diagenesis show that dehydration of the precipitate drives a transition to kerolite (hydrated talc) and eventually to talc. This formation pathway imparts extensive layer stacking disorder to the synthetic talc end-product that is identical to Neoproterozoic occurrences. Early diagenetic talc in Neoproterozoic carbonate platform successions appears to reflect a unique combination of low Al concentrations (and, by inference, low siliciclastic input), near modern marine salinity and Mg 2+, elevated SiO 2(aq), and pH > ~ 8.7. Because the talc occurs in close association with microbially influenced sediments, we suggest that soluble species requirements were most easily met through microbial influences on

  19. Constructing a Neoproterozoic Seawater Strontium Isotope Curve

    NASA Astrophysics Data System (ADS)

    Zhou, Y.; Shields-Zhou, G. A.; Manning, C. J.; Thirlwall, M.; Thurow, J. W.; Zhu, M.; Ling, H.

    2014-12-01

    The strontium isotopic composition of seawater has varied throughout Earth history in response to the balance between Sr isotopic exchange with ocean crust and input of riverine Sr derived from continental weathering. Because of this, seawater 87Sr/86Sr highs are interpreted to reflect erosion events, related to mountain building, while 87Sr/86Sr lows are considered to result from low weathering rates or increased seafloor spreading. Seawater 87Sr/86Sr also responds to changes in the isotopic composition of material undergoing weathering. The largest ever increase in seawater 87Sr/86Sr took place sometime from approximately 900 Ma to 500 Ma, and was associated with a permanent step shift in baseline 87Sr/86Sr composition. The unprecedented size of this increase, its timing and causation remains unconstrained. This study attempts firstly to reconstruct global seawater 87Sr/86Sr trends through this increase, using well-preserved carbonate rock samples from the North China craton, calibrated against additional 87Sr/86Sr and δ13C data from Neoproterozoic samples collected from other sections around the world. Sample preparation techniques for bulk carbonate Sr isotope stratigraphy are being honed during the course of this study. Other stable isotope systems (δ13C and δ18O) and trace elements, including REE have been investigated on the same samples to identify pristine samples for Sr isotope analysis and help in interpretation. The newly obtained data from this study (mainly Huaibei group of Huaibei area), using the excellently preserved early marine calcite cements and some bulk rock samples, confirm that the carbonate strata across the Jiao-Liao-Xu-Huai stratigraphic realm of the North China Craton exhibit the moderately positive δ13C values and low 87Sr/86Sr values that are characteristic of the early Neoproterozoic (Tonian).The results help to recreate the global curve by linking negative excursions in the Shijia (Xuzhou) (Xiao et al., 2014, Precambr. Res., 246

  20. SCANNING VOLTA POTENTIALS MEASUREMENTS OF METALS IN IRRADIATED AIR.

    SciTech Connect

    ISAACS, H.S.; ADZIC, G.; AND ENERGY SCIENCES AND TECHNOLOGY DEPARTMENT; JEFFCOATE, C.S.

    2000-10-22

    A method for direct dc measurement of the Volta potential is presented. High intensity synchrotron x-ray beams were used to locally irradiate the atmosphere adjacent to the metal surface and produce a conducting path between a sample and a reference probe. The direct measurements of potential in the ionized air could be made at probe heights of around 1 mm compared to less than 0.1 mm for the Kelvin probe. The measurements were similar to traditional Kelvin probe measurements, but had a poorer spatial resolution. In contrast to the Kelvin probe methods, the approach described allows observation of the current as a function of impressed voltage. Methods to improve the special resolution of the technique and applications to corrosion under coating will be presented.

  1. Constraining the margins of Neoproterozoic ice masses: depositional signature, palaeoflow and glaciodynamics

    NASA Astrophysics Data System (ADS)

    Busfield, Marie; Le Heron, Daniel

    2016-04-01

    The scale and distribution of Neoproterozoic ice masses remains poorly understood. The classic Snowball Earth hypothesis argues for globally extensive ice sheets, separated by small ocean refugia, yet the positions of palaeo-ice sheet margins and the extent of these open water regions are unknown. Abundant evidence worldwide for multiple cycles of ice advance and recession is suggestive of much more dynamic mass balance changes than previously predicted. Sedimentological analysis enables an understanding of the changing ice margin position to be gained through time, in some cases allowing it to be mapped. Where the maximum extent of ice advance varies within a given study area, predictions can also be made on the morphology of the ice margin, and the underlying controls on this morphology e.g. basin configuration. This can be illustrated using examples from the Neoproterozoic Kingston Peak Formation in the Death Valley region of western USA. Throughout the Sperry Wash, northern Kingston Range and southern Kingston Range study sites the successions show evidence of multiple cycles of ice advance and retreat, but the extent of maximum ice advance is extremely variable, reaching ice-contact conditions at Sperry Wash but only ice-proximal settings in the most distal southern Kingston Range. The overall advance is also much more pronounced at Sperry Wash, from ice-distal to ice-contact settings, as compared to ice-distal to ice-proximal settings in the southern Kingston Range. Therefore, the position of the ice margin can be located at the Sperry Wash study site, where the more pronounced progradation is used to argue for topographically constrained ice, feeding the unconstrained shelf through the northern into the southern Kingston Range. This raises the question as to whether Neoproterozoic ice masses could be defined as topographically constrained ice caps, or larger ice sheets feeding topographically constrained outlet glaciers.

  2. Late Neoproterozoic Paleogeography of the Western Part of Baltica- Constraints From Paleomagnetic and Tectonic Analysis.

    NASA Astrophysics Data System (ADS)

    Nawrocki, J.; Poprawa, P.; Boguckyj, A.

    2003-12-01

    Neoproterozoic break-up of supercontinent Rodinia resulted with development of several individual lithospheric plates, including Baltica. Global configuration of continents after break-up, in particular paleogeographic position of Baltica and its relation to Godwana, are the matter of recent disputes. According to Scandinavian paleomagnetic poles (c.f. Torsvik and Rehnstr”m, 2001) in the late Neoproterozoic and Cambrian time the Baltic plate occupied moderate paleolatitudes of southern hemisphere. Vendian paleomagnetic pole from the White Sea region (Popov et al., 2002) is, however, completely different. It implies moderate northern paleolatitudes of Baltica in the Vendian time and probably equatorial position of this plate in the Early Cambrian (c.f. Nawrocki, 2003). In the present contribution we discuss impact of recent paleomagnetic and tectonic analysis conducted for the western part of Baltica on the above mentioned issue. As a consequence of the break-up process the western and central part of Baltica became a site of intensive basic volcanism (Orsha-Volhyn Zone) and development of sedimentary basins related to rifting. Geochronology of volcanic processes at the western slope of Baltica is poorly controlled, except of its expiring, dated by U/Pb method as 551 Ma (Compston et al., 1995). However its geotectonic setting is geochemically documented as rift-related (Bialowolska et al., 2002). Subsequently during the late-most Neoproterozoic-Middle Ordovician a system of sedimentary basins developed, controlled by post-rift thermal sag mechanism. Regional pattern of their subsidence allows to reconstruct passive continental margin along western margin of Baltica (Peri-Tornquist Zone, corresponding to later Trans-European Suture Zone) (Poprawa et al., 1999). Preliminary paleomagnetic analysis of the Vendian basalts and underlying basaltic tuffs from the Volhynia (NW Ukraine) revealed paleomagnetic directions concordant with the data from the White Sea region

  3. The Guarguaraz Complex and the Neoproterozoic-Cambrian evolution of southwestern Gondwana: Geochemical signatures and geochronological constraints

    NASA Astrophysics Data System (ADS)

    López de Azarevich, Vanina L.; Escayola, Mónica; Azarevich, Miguel B.; Pimentel, Márcio M.; Tassinari, Colombo

    2009-12-01

    The Guarguaraz Complex, in western Argentina, comprises a metasedimentary assemblage, associated with mafic sills and ultramafic bodies intruded by basaltic dikes, which are interpreted as Ordovician dismembered ophiolites. Two kinds of dikes are recognized, a group associated with the metasediments and the other ophiolite-related. Both have N-MORB signatures, with ɛNd between +3.5 and +8.2, indicating a depleted source, and Grenville model ages between 0.99 and 1.62 Ga. A whole-rock Sm-Nd isochron yielded an age of 655 ± 76 Ma for these mafic rocks, which is compatible with cianobacteria and acritarchae recognized in the clastic metasedimentary platform sequences, that indicate a Neoproterozoic (Vendian)-Cambrian age of deposition. The Guarguaraz metasedimentary-ophiolitic complex represents, therefore, a remnant of an oceanic basin developed to the west of the Grenville-aged Cuyania terrane during the Neoproterozoic. The southernmost extension of these metasedimentary sequences in Cordón del Portillo might represent part of this platform and not fragments of the Chilenia terrane. An extensional event related to the fragmentation of Rodinia is represented by the mafic and ultramafic rocks. The Devonian docking of Chilenia emplaced remnants of ocean floor and slices of the Cuyania terrane (Las Yaretas Gneisses) in tectonic contact with the Neoproterozoic metasediments, marking the Devonian western border of Gondwana.

  4. Tectonic evolution of Kazakhstan and Tien Shan in Neoproterozoic and Early-Middle Paleozoic

    NASA Astrophysics Data System (ADS)

    Samygin, S. G.; Kheraskova, T. N.; Kurchavov, A. M.

    2015-05-01

    Geological information on Kazakhstan and the Tien Shan obtained up to the present time has been considered and integrated in order to demonstrate the main features of continental massifs, basins with oceanic crust, island arcs, marginal volcanic-plutonic belts, and transform fault zones differing in type and age. We ascertained the character and probable causes of their evolution and transformations resulting in the origination and development of mosaic structural assembly at margin of the Paleoasian ocean that existed from Neoproterozoic. The main stages of the geodynamic history of Paleozoides in Kazakhstan and Tien Shan are characterized, and a model of the probable course of regional tectonic events has been proposed. This model is illustrated by published paleomagnetic data and a series of paleotectonic reconstructions for time intervals 950-900, 850-800, 750-700, 650-630, 570-550, 530-515, 500-470, 460-440, and 390-380 Ma.

  5. Volta potential phase plate for in-focus phase contrast transmission electron microscopy

    PubMed Central

    Danev, Radostin; Buijsse, Bart; Khoshouei, Maryam; Plitzko, Jürgen M.; Baumeister, Wolfgang

    2014-01-01

    We describe a phase plate for transmission electron microscopy taking advantage of a hitherto-unknown phenomenon, namely a beam-induced Volta potential on the surface of a continuous thin film. The Volta potential is negative, indicating that it is not caused by beam-induced electrostatic charging. The film must be heated to ∼200 °C to prevent contamination and enable the Volta potential effect. The phase shift is created “on the fly” by the central diffraction beam eliminating the need for precise phase plate alignment. Images acquired with the Volta phase plate (VPP) show higher contrast and unlike Zernike phase plate images no fringing artifacts. Following installation into the microscope, the VPP has an initial settling time of about a week after which the phase shift behavior becomes stable. The VPP has a long service life and has been used for more than 6 mo without noticeable degradation in performance. The mechanism underlying the VPP is the same as the one responsible for the degradation over time of the performance of thin-film Zernike phase plates, but in the VPP it is used in a constructive way. The exact physics and/or chemistry behind the process causing the Volta potential are not fully understood, but experimental evidence suggests that radiation-induced surface modification combined with a chemical equilibrium between the surface and residual gases in the vacuum play an important role. PMID:25331897

  6. Newly Discovered Exposures of Neoproterozoic Diamictite within the Samre Fold-Thrust Belt of Northern Ethiopia

    NASA Astrophysics Data System (ADS)

    Park, Y.; Anttila, E.; MacLennan, S. A.; Swanson-Hysell, N.; Maloof, A. C.; Schoene, B.; Haileab, B.

    2015-12-01

    Life and climate evolved dramatically during the early Neoproterozoic - sedimentary rocks from this period record both the diversification of eukaryotic life as well as large scale fluctuations of the carbon cycle and paleogeography during the lead up to Cryogenian glaciation. Understanding global change leading up to this glaciation is critical for interpreting the conditions that initiated dramatic climate and geochemical oscillations. The Tonian-Cryogenian Tambien Group (Tigray region, northern Ethiopia) is a mixed carbonate-siliciclastic sedimentary succession deposited in an arc proximal basin that culminates in the Negash diamictite interpreted to represent the ca. 717-662 Ma Sturtian Glaciation. The presence of intercalated tuffs suitable for high precision U-Pb geochronology makes these sedimentary rocks an ideal target to temporally constrain physical and isotopic stratigraphic data sets of the early Neoproterozoic. The lower Tambien Group has been temporally constrained and used to establish global synchroneity of large scale carbon isotopic change ca. 800 Ma (Swanson-Hysell et al., 2015). We report the discovery of extensive exposures of upper Tambien Group successions southeast of the town of Samre within a newly mapped fold-thrust belt. Stratigraphic study across these exposures opens an opportunity to document environmental change across the basin during the apparently conformable transition from a mixed carbonate-siliciclastic platform into the Negash diamictite of the Sturtian Glaciation. The presence of ashes within the sediments holds the promise of combining high-precision dates with chemostratigraphic data to constrain global change before and during the onset of Snowball Earth glaciation.

  7. Electron cryotomography of vitrified cells with a Volta phase plate.

    PubMed

    Fukuda, Yoshiyuki; Laugks, Ulrike; Lučić, Vladan; Baumeister, Wolfgang; Danev, Radostin

    2015-05-01

    Electron cryotomography provides a means of studying the three dimensional structure of pleomorphic objects, such as organelles or cells, with a resolution of 1-3nm. A limitation in the study of radiation sensitive biological samples is the low signal-to-noise ratio of the tomograms which may obscure fine details. To overcome this limitation, the recently developed Volta phase plate (VPP) was applied in electron cryotomographic studies of a wide range of cellular structures, from magnetotactic bacteria to primary cultured neurons. The results show that the VPP improves contrast significantly and consequently the signal-to-noise ratio of the tomograms, moreover it avoids disturbing fringing artifacts typical for Zernike phase plates. The contrast improvement provided by the VPP was also confirmed in projection images of relatively thick (∼400nm) samples. In order to investigate the respective contributions of the VPP and the energy filter, images acquired with different combinations of the two were compared. Zero-loss energy filtering reduced the background noise in thicker areas of the sample and improved the contrast of features such as poly-β-hydroxybutyrate granules in magnetotactic bacteria, whereas the VPP provided an overall contrast improvement for all sample areas. After 3D reconstruction, tomograms acquired with the combination of a VPP and an energy filter showed structural features in neuronal processes with outstanding clarity. We also show that the VPP can be combined with focused ion beam milling to examine structures embedded deeply inside cells. Thus, we expect that VPP will become a standard element of the electron cryotomography workflow. PMID:25770733

  8. The paleoclimatic significance of deformation structures in Neoproterozoic successions

    NASA Astrophysics Data System (ADS)

    Arnaud, Emmanuelle

    2012-01-01

    This paper reviews the different types of soft sediment deformation structures that can form in glacial and non-glacial settings and explores the potential use of these structures in resolving long standing debates in paleoenvironmental reconstructions of Neoproterozoic glacigenic successions. Soft sediment deformation structures are created when compressional, gravitational or shear stress is applied to unlithified sediments during or shortly after deposition. In subglacial or ice marginal glacial settings, shear and compressional stress imparted by ice moving on top of a deformable substrate or advancing ice buldozing unlithified ice marginal sediments can result in a wide range of folding, faulting and shear structures. In glaciofluvial or stagnant ice marginal setting, gravitational collapse and remobilization of sediments associated with the melting of buried ice can result in normal faulting and broad folding. In glaciolacustrine or glaciomarine settings, compressional, shear and gravitational types of deformation structures can occur as a result of grounding ice or icebergs, rapid sedimentation and reworking downslope associated with high sedimentation rates. In non glacial settings, similar deformation structures can form as a result of slope instability and reworking of sediments downslope, rapid sedimentation, seismic shaking, wave induced shearing or loading. In this context, two case studies are presented to demonstrate the type of paleoenvironmental information that an analysis of deformation structures can provide. In the first case study, analysis of deformation in the Port Askaig Formation (Scotland) reveals a distinctive stratigraphic distribution of deformation structures. The types of deformation observed together with their recurrence over several 100s of meters and their basinal context are used to infer a seismic origin for the deformation, which in turn suggests a significant tectonic control on sedimentation atop a record of ice margin

  9. a Snowball's Chance in Death Valley: Re-Evaluation of the Number and Magnitude of Neoproterozoic Ice Ages

    NASA Astrophysics Data System (ADS)

    Kaufman, A. J.; Corsetti, F. A.; Marenco, P. J.

    2002-05-01

    The Neoproterozoic Ibex Formation, previously considered to represent a basinal facies of platform carbonates in the lower Noonday Dolomite, Great Basin, USA, is shown to rest on the eroded surface of the lower Noonday and older units. At the type section, the basal Ibex Formation consists of polymict conglomerate and laminated mudstone; the upper surface of the mudstone is pierced by large angular clasts of all underlying units, including distinctive lower Noonday tube stromatolites. A thin, finely laminated pink dolostone unit that records negative carbon isotope values caps the Ibex conglomerate. We interpret the erosional unconformity upon which the basal Ibex Formation is deposited to be glacioeustatic in origin, the basal conglomerate-pierced mudstone to be glaciogenic, and the overlying dolostone to be a classic cap carbonate. Above the cap dolostone marine transgression led to the deposition of deeper water ferruginous shale and limestone, which is overlain by dolostone as water depths again shallowed. These post-glacial Ibex carbonates also record negative carbon isotope values similar to upper Noonday lithofacies preserved on the platform. A notable oxidized paleosol occurs at the top of the upper Ibex dolostone immediately below a coarse sandstone correlative with the basal Johnnie Formation. Combined with the record of glacial sediments and cap carbonates from underlying units, in particular the Kingston Peak Formation, the Death Valley succession unambiguously records three discrete Neoproterozoic ice ages in a single continuous section. These new observations provide the lithological and geochemical proof that at least three, and potentially more, ice ages characterized Neoproterozoic time. As each sustained global glaciation represents a critical environmental hurdle, the number and the magnitude of discrete ice ages is an important constraint on the tempo of metazoan evolution.

  10. Volta phase plate cryo-EM of the small protein complex Prx3.

    PubMed

    Khoshouei, Maryam; Radjainia, Mazdak; Phillips, Amy J; Gerrard, Juliet A; Mitra, Alok K; Plitzko, Jürgen M; Baumeister, Wolfgang; Danev, Radostin

    2016-01-01

    Cryo-EM of large, macromolecular assemblies has seen a significant increase in the numbers of high-resolution structures since the arrival of direct electron detectors. However, sub-nanometre resolution cryo-EM structures are rare compared with crystal structure depositions, particularly for relatively small particles (<400 kDa). Here we demonstrate the benefits of Volta phase plates for single-particle analysis by time-efficient cryo-EM structure determination of 257 kDa human peroxiredoxin-3 dodecamers at 4.4 Å resolution. The Volta phase plate improves the applicability of cryo-EM for small molecules and accelerates structure determination. PMID:26817416

  11. Volta phase plate cryo-EM of the small protein complex Prx3

    NASA Astrophysics Data System (ADS)

    Khoshouei, Maryam; Radjainia, Mazdak; Phillips, Amy J.; Gerrard, Juliet A.; Mitra, Alok K.; Plitzko, Jürgen M.; Baumeister, Wolfgang; Danev, Radostin

    2016-01-01

    Cryo-EM of large, macromolecular assemblies has seen a significant increase in the numbers of high-resolution structures since the arrival of direct electron detectors. However, sub-nanometre resolution cryo-EM structures are rare compared with crystal structure depositions, particularly for relatively small particles (<400 kDa). Here we demonstrate the benefits of Volta phase plates for single-particle analysis by time-efficient cryo-EM structure determination of 257 kDa human peroxiredoxin-3 dodecamers at 4.4 Å resolution. The Volta phase plate improves the applicability of cryo-EM for small molecules and accelerates structure determination.

  12. Geochronology of Neoproterozoic Plutons and Sandstones in the Western Jiangnan Orogen: a Reappraisal of Amalgamation between Yangtze and Cathaysia Blocks in South China

    NASA Astrophysics Data System (ADS)

    Ma, X.; Yang, K.

    2015-12-01

    Widespread exposure of Meso-Neoproterozoic strata and abundant Neoproterozoic plutons occur along the Jiangnan orogenic belt, a tectonic suture between the composite Cathaysia and Yangtze Blocks in South China, with remarkable angular unconformities between the Xiajiang Group and the underlying Sibao. LA-ICP-MS U-Pb dating of the basement sedimentary sequences (e.g. Xiajiang Group and Sibao Group) and the relevant granitic pluton (Motianling pluton) provides new information about the pre-Cambrian evolution of the southeastern Yangtze block margin along the western Jiangnan orogen. The depositional age of Sibao Group located in the Southeast Guizhou Province can be constrained at 825-835 Ma by the youngest detrital zircon ages and crystallization age of the intrusive Motianling granitic pluton. The maximum depositional age of the Xiajiang Group is estimated to be ca. 795 Ma. Four main age populations are evident in Sibao Group: 0.83-1.0 Ga, 1.3-1.5 Ga, 1.6-1.8 Ga and 2.2-2.6 Ga. The distinguished age populations in the Xiajiang Group are identical to those in the Sibao Group but lack in ranges of 1.3-1.5 Ga. Local abundant (<0.9 Ga) granitoid outcrops, distant early-Neoproterozoic (0.9-1.0 Ga) components and pre-Neoproterozoic recycled materials from the interior of the Yangtze Block both contribute to the sedimentation of the Neoproterozoic basement sequences. We suggest that a rapid exhumation and uplift occurred after 820 Ma along the southeastern margin of Yangtze Block, and provided abundant detritus to the Neoproterozoic basin between the Yangtze and Cathaysia blocks, after which the assembly process gradually ceased till ca. 800 Ma rather than immediately paused or switched to extension after ca. 820 Ma. Regarding the location of the South China Block in the breakup the Rodinia, it is more reasonable to place Yangtze and Cathaysia Blocks on the western margin rather than the center of Rodinia supercontinent during the late-Neoproterozoic time.

  13. 'Zipper-rift': a tectonic model for Neoproterozoic glaciations during the breakup of Rodinia after 750 Ma

    NASA Astrophysics Data System (ADS)

    Eyles, Nicholas; Januszczak, Nicole

    2004-03-01

    The 'Snowball Earth' model of Hoffman et al. [Science 281 (1998) 1342] has stimulated renewed interest in the causes of glaciation in Earth history and the sedimentary, stratigraphic and geochemical response. The model invokes catastrophic global Neoproterozoic refrigerations when oceans froze, ice sheets covered the tropics and global temperatures plummeted to -50 °C. Each event is argued to be recorded by tillites and have lasted up to 10 million years. Planetary biological activity was arrested only to resume in the aftermath of abrupt and brutal volcanically generated 'greenhouse' deglaciations when global temperatures reached +50 °C. The 'Cambrian explosion' is regarded by some as a consequence of post-Snowball glacioeustatic flooding of continental shelves. We shall show by a systematic review of the model that it is based on many long standing assumptions of the character and origin of the Neoproterozoic glacial record, in particular, 'tillites', that are no longer valid. This paper focusses on the sedimentological and stratigraphic evidence for glaciation in the light of current knowledge of glacial depositional systems. By integrating this analysis with recent understanding of the tectonic setting of Neoproterozoic sedimentary basins, an alternative 'Zipper-rift' hypothesis for Neoproterozoic glaciations is developed. The 'Zipper-rift' model emphasises the strong linkage between the first-order reorganisation of the Earth's surface created by diachronous rifting of the supercontinent Rodinia, the climatic effects of uplifted rift flanks and the resulting sedimentary record deposited in newly formed rift basins. Initial fragmentation of Rodinia commenced after about 750 Ma (when the paleo-Pacific Ocean started to form along the western margin of Laurentia) and culminated sometime after 610 Ma (with the opening of the paleo-Atlantic Ocean on the eastern margin of Laurentia). Breakup is recorded by well-defined 'tectonostratigraphic' successions that were

  14. Commodification of Ghana's Volta River: An Example of Ellul's Autonomy of Technique

    ERIC Educational Resources Information Center

    Agbemabiese, Lawrence; Byrne, John

    2005-01-01

    Jacques Ellul argued that modernity's nearly exclusive reliance on science and technology to design society would threaten human freedom. Of particular concern for Ellul was the prospect of the technical milieu overwhelming culture. The commodification of the Volta River in order to modernize Ghana illustrates the Ellulian dilemma of the autonomy…

  15. Water and carbon fluxes from savanna ecosystems of the Volta River watershed, West Africa

    NASA Astrophysics Data System (ADS)

    Freitag, Heiko; Ferguson, Paul R.; Dubois, Kristal; Hayford, Ebenezer Kofi; von Vordzogbe, Vincent; Veizer, Ján

    2008-03-01

    The fluxes of water and carbon from terrestrial ecosystems are coupled via the process of photosynthesis. Constraining the annual water cycle therefore allows first order estimates of annual photosynthetic carbon flux, providing that the components of evapotranspiration can be separated. In this study, an isotope mass-balance equation is utilized to constrain annual evaporation flux, which in turn, is used to determine the amount of water transferred to the atmosphere by plant transpiration. The Volta River watershed in West Africa is dominated by woodland and savanna ecosystems with a significant proportion of C 4 vegetation. Annually, the Volta watershed receives ˜ 380 km 3 of rainfall, ˜ 50% of which is returned to the atmosphere via transpiration. An annual photosynthetic carbon flux of ˜ 170 × 10 12 g C yr - 1 or ˜ 428 g C m - 2 was estimated to be associated with this water vapor flux. Independent estimates of heterotrophic soil respiration slightly exceeded the NPP estimate from this study, implying that the exchange of carbon between the Volta River watershed and the atmosphere was close to being in balance or that terrestrial ecosystems were a small annual source of CO 2 to the atmosphere. In addition to terrestrial carbon flux, the balance of photosynthesis and respiration in Volta Lake was also examined. The lake was found to evade carbon dioxide to the atmosphere although the magnitude of the flux was much smaller than that of the terrestrial ecosystems.

  16. Global Neoproterozoic (Sturtian) post-glacial sulfide-sulfur isotope anomaly recognised in Namibia

    NASA Astrophysics Data System (ADS)

    Gorjan, Paul; Walter, Malcolm R.; Swart, Roger

    2003-02-01

    The Neoproterozoic Earth experienced at least two, probably global, glaciations. Each glaciation was superceded by deposition of a layer of carbonate ('cap-carbonate') that has a distinctive lithology and depletion in 13C ( δ13C carbonate ˜ -5‰). The ˜700 Ma Sturtian glaciation is followed by deposition of a cap-carbonate and post-glacial succession which contain bacterially produced sulfides extremely enriched in 34S (average δ34S sulfide ˜ +30‰) with maximum values up to +60‰. This level of 34S enrichment in sulfides is unique to the Sturtian post-glacial succession and recognised in Australia, Canada, and China. In the Neoproterozoic of the Nama Basin, Namibia, the Gobabis Member is the basal unit of the Court Formation, which overlies the glacial Blaubeker Formation. δ13C carbonate analyses from the Gobabis Member range from -5.2 to -2.2‰ (average = -3.7‰; n = 10). δ34S sulfide ranges from +16.1 to +61.1‰ (average = +37.6‰; n = 8). These results are consistent with a Sturtian age for the Blaubeker Formation and overlying Gobabis Member, which have previously been interpreted as Sturtian. The sulfur isotopic results are comparable with δ34S sulfide in Sturtian post-glacial units of Australia, Canada and China. This adds to the evidence for correlation of the Blaubeker Formation with Sturtian glaciations on other continents. The cause of such elevated δ34S sulfide is enigmatic. Geochemical evidence suggests the sulfide was not formed from low sulfate waters nor in euxinic conditions, which discounts any known modern analogue. 34S enrichment in sulfides is therefore postulated to be caused by enrichment of 34S in contemporaneous seawater ( δ34S sulfate up to +60‰?). The rise in seawater δ34S sulfate is considered to be the result of intense bacterial sulfate reduction in an anoxic ocean during the Sturtian glaciation.

  17. Microanalyzes of remarkable microfossils of the Late Mesoproterozoic-Early Neoproterozoic

    NASA Astrophysics Data System (ADS)

    Cornet, Yohan; Beghin, Jérémie; Baludikay, Blaise; François, Camille; Storme, Jean-Yves; Compère, Philippe; Javaux, Emanuelle

    2016-04-01

    The Late Mesoproterozoic-Early Neoproterozoic is an important period to investigate the diversification of early eukaryotes [1]. Following the first appearance of red algae in the Late Mesoproterozoic, other (morphological or molecular) fossils of crown groups are recorded during the Early Neoproterozoic, including green algae, sponges, amoebozoa and possibly fungi. Other microfossils also includes unambiguous eukaryotes, including several distinctive forms for that time period, such as the acritarchs Cerebrosphaera buickii (˜820-720 Ma), Trachyhystrichosphaera aimika and T . botula (1100-720 Ma), and the multicellular eukaryotic problematicum taxon Jacutianema solubila (1100-?720 Ma). To further characterize the taxonomy of these microfossils and to test hypotheses about their possible relationships to crown groups, we combine analyzes of their morphology, wall ultrastructure and microchemistry, using optical microscopy, Scanning and Transmission Electron microscopy (SEM and TEM), as well as Raman and FTIR microspectroscopy respectively. Cerebrosphaera populations from the Svanbergfjellet formation, Spitsbergen, and from the Kanpa Formation, Officer Basin, Australia, include organic vesicles with dark and robust walls ornamented by cerebroid folds [2]. Our study shows the occurrence of complex tri- or bi-layered wall ultrastructures and a highly aromatic composition [3]. The genus Trachyhystrichosphaera includes various species characterized by the presence of a variable number of hollow heteromorphic processes [2]. Preliminary infrared microspectroscopy analyzes performed on two species, T. aimika and T. botula, from the 1.1 Ga Taoudeni Basin, Mauritania, and from the ˜1.1 - 0.8 Ga Mbuji-Mayi Supergroup, RDC, indicate a strong aliphatic and carbonyl composition of the wall biopolymer, with some differences linked to thermal maturity between the two locations. TEM is also performed to characterize the wall ultrastructure of these two species. Various morphotypes

  18. Is the Neoproterozoic oxygen burst a supercontinent legacy?

    NASA Astrophysics Data System (ADS)

    Macouin, Melina; Roques, Damien; Rousse, Sonia; Ganne, Jerome; Denele, Yoann; Trindade, Ricardo

    2015-09-01

    The Neoproterozoic (1000-542 Myr ago) witnessed the dawn of Earth as we know it with modern-style plate tectonics, high levels of O2 in atmosphere and oceans and a thriving fauna. Yet, the processes leading to the fully oxygenation of the external envelopes, its exact timing and its link with the inner workings of the planet remain poorly understood. In some ways, it is a "chicken and egg" question: did the Neoproterozoic Oxygenation Event (NOE) cause life blooming, low-latitudes glaciations and perturbations in geochemical cycles or is it a consequence of these phenomena? Here, we suggest that the NOE may have been triggered by multi-million years oxic volcanic emissions along a protracted period at the end of the Neoproterozoic when continents were assembled in the Rodinia supercontinent. We report a very oxidized magma source at the upper mantle beneath a ring of subducting margins around Rodinia, and detail here the evidence at the margin of the Arabian shield. We investigate the 780 Ma Biotite and Pink granites and associated rocks of the Socotra Island with rock magnetic and petrographic methods. Magnetic susceptibility and isothermal remanent magnetization acquisitions show that, in these granites, both magnetite and hematite are present. Hematite subdivides magnetite grains into small grains. Magnetite and hematite are found to be primary, and formed at the early magmatic evolution of the granite at very high oxygen fugacity. Massive degassing of these oxidized magmas would reduce the sink for oxygen, and consequently contribute to its rise in the atmosphere with a net O2 flux of at least 2.25 x 107 Tmol. Our conceptual model provides a deep Earth link to the NOE and implies the oxygenation burst has occurred earlier than previously envisaged, paving the way for later changes in the outer envelopes of the planet epitomized on the extreme Neoproterozoic glaciations and the appearance of the first animals.

  19. Strontium isotopic variations of Neoproterozoic seawater: Implications for crustal evolution

    SciTech Connect

    Asmerom, Y.; Jacobsen, S.B.; Knoll, A.H.; Butterfield, N.J. ); Swett, K. )

    1991-10-01

    The authors report high precision Sr isotopic data on carbonates from the Neoproterozoic Shaler Group, Victoria Island, Northwest Territories, Canada. Samples with low {sup 87}Rb/{sup 86}Sr ratios (<0.01) were selected for Sr isotopic analysis. {delta}{sup 18}O, Mn, Ca, Mg, and Sr data were used to recognize altered samples. The altered samples are characterized by high Mn/Sr ({ge}2) and variable {delta}{sup 18}O; most are dolomites. The data indicate that between ca. 790-850 Ma the {sup 87}Sr/{sup 86}Sr ratio of seawater varied between 0.70676 and 0.70561. The samples show smooth and systematic variation, with the lowest {sup 87}Sr/{sup 86}Sr value of 0.70561 at ca. 830 Ma. The low {sup 87}Sr/{sup 86}Sr ratio of carbonates from the lower parts of the section is similar to a value reported for one sample from the Adrar of Mauritania ({approx}900 Ma), West African Craton. Isotopic ratios from the upper part of the Shaler section are identical to values from the lower part of the Neoproterozoic Akademikerbreen Group, Spitsbergen. Although a paucity of absolute age determinations hinders attempts at the precise correlation of Neoproterozoic successions, it is possible to draw a broad outline of the Sr isotopic composition of seawater for this period. Data from this study and the literature are used to construct a curve of the {sup 87}Sr/{sup 86}Sr ratio of Neoproterozoic seawater. The Sr isotope composition of seawater reflects primarily the balance between continental Sr input through river input and mantle input via hydrothermal circulation of seawater through mid-ocean ridges. Coupling of Nd and Sr isotopic systems allows the authors to model changes in seafloor spreading rates (or hydrothermal flux) and continental erosion. The Sr hydrothermal flux and the erosion rate (relative to present-day value) are modeled for the period 500-900 Ma.

  20. Neoproterozoic to Early Cambrian clastics sedimentation and stratigraphy in the Central and Southern Appalachians: An overview

    SciTech Connect

    Schwab, F.L. . Dept. of Geology)

    1993-03-01

    A clear understanding of paleogeography, tectonics, and sedimentary framework now exists for Neoproterozoic to Early Cambrian clastics in the Central and Southern Appalachians. It is based on well-constrained data on mineralogy, texture, and sedimentary structures and less precise information on age and regional variations in lithology and thickness. From 900 m.y. ago until 600 m.y. ago, tension along the eastern edge of North America produced a series of NE-SW basins (grabens and aulacogens ). These rift-related basins filled with thick, coarse, arkosic clastics (Mechum River Fm., Mt. Rogers Volc. Gp., Grandfather Mtn. Fm., portions of the Ocoee Series) mimicking the setting that later typified the Triassic of eastern North America. Coeval sequences exposed along the southeastern edge of the Blue Ridge in Va. and N.C. (Fauquier Fm., Lynchburg Gp., Ashe Fm.) define the hinge zone of a developing continental margin. Farther south in Tenn., Ga., and Ala., the picture is less clear. In latest Precambrian and Early Cambrian time, a passive Atlantic-type'' margin existed. This consisted of paired continental shelf and continental slope-rise areas (shallow water deposits of the Chilhowee Gp. and overlying muds and carbonates to the northwest; deep water clastics of the Evington Gp. and Alligator Back Fm. to the southeast). The cohesiveness of this framework argues against these tectonostratigraphic belts being considered terranes.

  1. An emerging picture of Neoproterozoic ocean chemistry: Insights from the Chuar Group, Grand Canyon, USA

    NASA Astrophysics Data System (ADS)

    Johnston, David T.; Poulton, Simon W.; Dehler, Carol; Porter, Susannah; Husson, Jon; Canfield, Donald E.; Knoll, Andrew H.

    2010-02-01

    Detailed iron, sulfur and carbon chemistry through the > 742 million year old Chuar Group reveals a marine basin dominated by anoxic and ferrous iron-rich (ferruginous) bottom waters punctuated, late in the basin's development, by an intrusion of sulfide-rich (euxinic) conditions. The observation that anoxia occurred frequently in even the shallowest of Chuar environments (10s of meters or less) suggests that global atmospheric oxygen levels were significantly lower than today. In contrast, the transition from ferruginous to euxinic subsurface water is interpreted to reflect basinal control—specifically, increased export of organic carbon from surface waters. Low fluxes of organic carbon into subsurface water masses should have been insufficient to deplete oxygen via aerobic respiration, resulting in an oxic oxygen minimum zone (OMZ). Where iron was available, larger organic carbon fluxes should have depleted oxygen and facilitated anaerobic respiration using ferric iron as the oxidant, with iron carbonate as the expected mineralogical signature in basinal shale. Even higher organic fluxes would, in turn, have depleted ferric iron and up-regulated anaerobic respiration by sulfate reduction, reflected in high pyrite abundances. Observations from the Chuar Group are consistent with these hypotheses, and gain further support from pyrite and sulfate sulfur isotope abundances. In general, Chuar data support the hypothesis that ferruginous subsurface waters returned to the oceans, replacing euxinia, well before the Ediacaran emergence of persistently oxygenated conditions, and even predating the Sturtian glaciation. Moreover, our data suggest that the reprise of ferruginous water masses may relate to widespread rifting during the break-up of Rodinia. This environmental transition, in turn, correlates with both microfossil and biomarker evidence for an expanding eukaryotic presence in the oceans, suggesting a physiologically mediated link among tectonics, environmental

  2. Pre-Snowball Earth ecosystems, insights from nitrogen isotopes in the Neoproterozoic Kwagunt Formation of the Chuar Supergroup, Grand Canyon.

    NASA Astrophysics Data System (ADS)

    Junium, C. K.; Arthur, M. A.; Freeman, K. H.

    2008-12-01

    Reconstructing marine ecosystems prior to the Neoproterozoic Snowball Earth episodes is an important constraint to our understanding of these events and to the biogeochemical evolution of the Neoproterozoic. The mixed siliciclastic and carbonate sequence comprising the Chuar Supergroup, Grand Canyon, USA, encompasses the period in Earth history immediately prior to the first of the Snowball Earth episodes 740 million years ago and presents a unique opportunity explore this issue in relatively immature rocks. In the Phanerozoic, there is a consistent relationship between euxinic basins, widespread black shale deposition, and δ15N values below 0‰ that are indicative of nitrogen-fixation supported primary productivity. Fe-speciation data from black shales of the Walcott Member of the Kwagunt Formation, upper Chuar Supergroup suggest that the Chuar water column and the middle Neoproterozoic deep ocean was euxinic. Bulk δ15N values from the Walcott Member range from +1.7 to +4.7‰, which are not directly supportive of nitrogen fixation. Preliminary nitrogen isotope data from organic extracts suggest that organic nitrogen may be more significantly enriched than bulk isotopes suggest. These relatively 15N- enriched values contrast those from Phanerozoic episodes of black shale deposition. The Walcott primary producer community is interpreted to have utilized a nitrogen substrate that had an isotopic composition more like that of nitrate in modern, relatively oxygenated marine systems. On the basis of biomarker data many black shale sequences of the Phanerozoic (e.g. Devonian, Permo-Triassic and Cretaceous) record the presence of an active phototrophic sulfide oxidizer community. In contrast, our best efforts have yet to yield biomarker evidence of photic zone euxinia within the Walcott. We therefore suggest that the sulfidic chemocline during Walcott deposition was consistently below the photic zone. Oxygenic phototrophic primary producers utilized nitrate from the

  3. Stories from Lake Volta: the lived experiences of trafficked children in Ghana.

    PubMed

    Hamenoo, Emma Seyram; Sottie, Cynthia Akorfa

    2015-02-01

    Child trafficking is one of the worst forms of child maltreatment and is often difficult to recognize when it happens intra-country. This paper presents the narratives of children on their experiences as victims of trafficking in fishing communities along the Volta Lake in the Volta region of Ghana. The narratives were co-constructed with the children through child-friendly participatory approaches which involved drawings, writing, and in-depth interviews. The stories reflect the magnitude of maltreatment trafficked children suffer, which ranges from physical to psychological and emotional. The authors recommend commitment by the government to the implementation of the Human Trafficking Act to deter child traffickers. Further studies on the living conditions of rescued children and the need to implement strategies to prevent re-trafficking are suggested. PMID:25015268

  4. Volta phase plate cryo-EM of the small protein complex Prx3

    PubMed Central

    Khoshouei, Maryam; Radjainia, Mazdak; Phillips, Amy J.; Gerrard, Juliet A.; Mitra, Alok K.; Plitzko, Jürgen M.; Baumeister, Wolfgang; Danev, Radostin

    2016-01-01

    Cryo-EM of large, macromolecular assemblies has seen a significant increase in the numbers of high-resolution structures since the arrival of direct electron detectors. However, sub-nanometre resolution cryo-EM structures are rare compared with crystal structure depositions, particularly for relatively small particles (<400 kDa). Here we demonstrate the benefits of Volta phase plates for single-particle analysis by time-efficient cryo-EM structure determination of 257 kDa human peroxiredoxin-3 dodecamers at 4.4 Å resolution. The Volta phase plate improves the applicability of cryo-EM for small molecules and accelerates structure determination. PMID:26817416

  5. A photovoltaic power system in the remote African village of Tangaye, Upper Volta

    NASA Technical Reports Server (NTRS)

    Bifano, W. J.; Ratajczak, A. F.; Martz, J. E.

    1979-01-01

    A photovoltaic (PV) system powering a grain mill and a water pump was installed in the remote West African village of Tangaye, Upper Volta. Village characteristics as well as system design, hardware, installation and operation to date are described. The PV system cost is discussed. A baseline socio-economic study performed and a follow-up study is planned to determine the impact of the system on the villagers.

  6. Isolation and characterization of an archaebacterial viruslike particle from Methanococcus voltae A3

    SciTech Connect

    Wood, A.G.; Konisky, J. ); Whitman, W.B. )

    1989-01-01

    Small amounts of 23-kilobase covalently closed circular DNA molecule were isolated from unwashed cells of Methanococcus voltae A3. Further investigation indicated the presence of greater quantities of the circular DNA in the culture supernatant, complexed with protein in a manner rendering the DNA resistant to DNase. Electron-microscopic examination of supernatant material revealed the presence of particles which morphologically resemble virus. Phenol extraction of viruslike particle preparations resulted in the recovery of DNase-sensitive open-circular DNA molecules. As many as 30 viruslike particles per cell were recovered from some cultures. Hybridization data clearly indicated the presence of a chromosomally integrated copy of the viruslike particle DNA. Although M. voltae PS was not observed to produce viruslike particles, DNA homologous to the viruslike particle DNA was detected in its chromosome. A mutant of M. voltae A3 was isolated which produced no particles; its DNA was deleted for 80% of the integrated viruslike particle DNA. Despite any similarities to lysogenic bacteriophages of eubacteria, neither infectivity nor inducibility of the viruslike particles could by demonstrated.

  7. Preliminary schistosomiasis survey in the lower Volta River below Akosombo Dam, Ghana.

    PubMed

    Wen, S T; Chu, K Y

    1984-04-01

    Snail surveys were carried out in Kpong Lake, in southern Ghana, and along the lower Volta River below the lake. Bulinus globosus and Biomphalaria pfeifferi were abundant in the Kpong Lake and B. truncatus and Biom . pfeifferi, especially the latter, were widespread below the lake. Urine surveys among primary school children at eight localities along the lower Volta showed Schistosoma haematobium prevalence rates of 38.8-96.2%. At Bator and Mepe , where records for an earlier survey were available for comparison, the present survey showed more than a doubling in prevalence rate in ten years: at Bator , from 27.1% in 1971-72 to 74.6% in 1981; at Mepe the corresponding figures were 36.4 and 88.0%. In Ghana infection with S. mansoni is less common than with S. haematobium and the known foci of S. mansoni transmission are few and widely scattered. In the present survey the disease is first reported along the lower Volta at Bator , Mepe , Adidome and Tefle , with prevalence rates ranging from 6.7% at Bator to 52.4% at Tefle . This survey has added an important focus of S. mansoni infection to those already known. PMID:6742926

  8. Possible Record of Neoproterozoic Ice Sheet Collapse: The Kapp Lyell Diamictite Sequence of southwest Spitsbergen, Svalbard

    NASA Astrophysics Data System (ADS)

    Bjornerud, M.

    2008-12-01

    The Late Proterozoic Kapp Lyell diamictites of northern Wedel Jarlsberg Land, southwest Spitsbergen, have long been recognized as ancient glacial deposits, but their place within the global stratigraphic framework of 'Snowball Earth' has remained unclear owing to the complexity of superimposed Caledonian deformation and to the inaccessible terrain in which they occur. Newly deglaciated exposures of the rocks now provide a more complete picture of the changing environment in which they were deposited and their place in the global chronostratigraphy. The Kapp Lyell Sequence (KLS) is the higher of two diamictic to conglomeratic Neoproterozoic units in SW Spitsbergen. The lower of these, the Konglomeratfjellet Formation, is not unambiguously glaciogenic, but it is topped by a carbonate sequence with textures similar to 'cap' carbonate units in other Neoproterozoic sequences. These carbonates are succeeded by ca. 2000 m of black phyllite with rare lone stones. The phyllite is overlain with apparent conformity by the 2000-3000 m thick KLS, which actually consists of three distinct types of diamictite, all apparently glaciomarine. The KLS begins with 500- 1000 m of finely laminated diamictite punctuated by pebble- to boulder-sized lone stones, presumably ice- rafted. The cm-scale laminae are defined by layers of sand-to-silt sized particles of detrital dolomite alternating with thin films of graphitic phyllite. Preliminary delta 13C values from this graphitic material are very negative, pointing to a biogenic origin. The extraordinary uniformity of the laminae indicates repetitive, possibly seasonal, depositional cycles, but the density of lone stones increases upsection, recording accelerating delivery of ice-rafted debris to the basin. Carbonate clasts predominate, and many have distinctive textures (cm-sized ooids, digitate stromatolites) that link them with the 'cap' carbonate unit lower in the section. The laminated diamictite interval ends abruptly with the

  9. Ancient Life at the Extremes: Molecular Fossils and Paleoenvironmental Contexts of a Neoproterozoic Hypersaline Setting

    NASA Astrophysics Data System (ADS)

    Schinteie, R.; Brocks, J. J.

    2011-12-01

    We present the first molecular investigation of the biotic composition and biogeochemistry of an evaporitic, hypersaline environment from the Neoproterozoic (~800 Ma). Through detailed analyses of both sedimentary textures and their lipid biomarkers, we provide the oldest evidence of organisms that could exist at extremely saline conditions. Such research is timely, since the discovery of evaporite deposits on Mars highlights the need to understand their capacities as biological archives. Samples for this study were derived from evaporitic sediments of the Neoproterozoic Bitter Springs Formation, Amadeus Basin, central Australia. Due to the broad shallow nature of the basin and a tenuous connection with the ocean, the water was characterized by elevated salinity levels during that time. As a result, thick (100 m to >2000 m) evaporite units were deposited. All samples for this study were derived from drill cores held at Geoscience Australia (Canberra) and at the Northern Territory Geological Survey at Alice Springs. We extracted biomarkers from evaporitic sediments composed of dolomite, anhydrite and/or halite. The dolomite layers commonly assume the shape of microbial mat-like formations that exhibit roll-up structures and tearing. Framboidal pyrite was commonly associated with the dolomite and together with other textural and stable isotopic data provide the oldest putative evidence for biologically-induced dolomite precipitation. Full scan gas chromatography-mass spectrometry (GCMS) of the saturate fractions of these evaporites revealed high ratios of mono-and dimethylalkanes relative to n-alkanes. Such a pattern is typical of Precambrian and Cambrian samples. These molecules, together with elevated relative concentrations of n-C17, provide evidence of a photoautotrophic community - especially cyanobacteria. A further outstanding characteristic of these samples are the presence of several pseudohomologous series of both regular (to C25) and irregular (to C40

  10. A true polar wander model for Neoproterozoic plate motions

    SciTech Connect

    Ripperdan, R.L. )

    1992-01-01

    Recent paleogeographic reconstructions for the interval 750--500 Ma (Neoproterozoic to Late Cambrian) require rapid rates of plate motion and/or rotation around an equatorial Euler pole to accommodate reconstructions for the Early Paleozoic. Motions of this magnitude appear to be very uncommon during the Phanerozoic. A model for plate motions based on the hypothesis that discrete intervals of rapid true polar wander (RTPW) occurred during the Neoproterozoic can account for the paleogeographic changes with minimum amounts of plate motion. The model uses the paleogeographic reconstructions of Hoffman (1991). The following constraints were applied during derivation of the model: (1) relative motions between major continental units were restricted to be combinations of great circle or small circle translations with Euler poles of rotation = spin axis; (2) maximum rates of relative translational plate motion were 0.2 m/yr. Based on these constraints, two separate sets of synthetic plate motion trajectories were determined. The sequence of events in both can be summarized as: (1) A rapid true polar wander event of ca 90[degree] rafting a supercontinent to the spin axis; (2) breakup of the polar supercontinent into two fragments, one with the Congo, West Africa, Amazonia, and Baltica cratons, the other with the Laurentia, East Gondwana, and Kalahari cratons; (3) great circle motion of the blocks towards the equator; (4) small circle motion leading to amalgamation of Gondwana and separation of Laurentia and Baltica. In alternative 1, rifting initiates between East Antarctica and Laurentia and one episode of RTPW is required. Alternative 2 requires two episodes of RTPW; and that rifting occurred first along the eastern margin and later along the western margin of Laurentia. Synthetic plate motion trajectories are compared to existing paleomagnetic and geological data, and implications of the model for paleoclimatic changes during the Neoproterozoic are discussed.

  11. Modelling the carbon cycle though Neoproterozoic Earth system changes

    NASA Astrophysics Data System (ADS)

    Bjerrum, C. J.; Canfield, D. E.

    2011-12-01

    The Neoproterozoic-Cambrian records major changes in geochemical proxies as a result of a profound reorganization of the Earth system. Extensive glaciations and the first oxygenation of the deep ocean with a shift from sulfidic/ferruginous conditions to more oxic conditions was accompanied by the radiation of the first animals. The reorganization was also recorded in enigmatic large-amplitude fluctuations in the isotopic composition of marine carbonate carbon (δ13CIC ), were only some are associated with major known glaciations. The carbon isotope events seem to grow in amplitude through the Neoproterozoic culminating in the Shuram anomaly - the largest in Earth history. The δ13CIC events are also accompanied by changes in the isotope composition of marine organic carbon (δ13COC), where the co-variation of δ13CIC and δ13COC seems to evolve from markedly positive relationship over a subdued δ13COC variation and an almost inverse pattern. There is limited understanding as to why or how the structure of these isotope events evolved over time and how these events may tie to the reorganization of the Earth system. We use our published quantitative model of the Shuram anomaly to explore carbon cycle dynamics during the Neoproterozoic. By changing in pre-event atmosphere-ocean chemistry we explore which factors contribute to the observed patterns of the large Neoproterozoic carbon isotope events. In particular, decreasing atmospheric CO2 and a slight increase of oxygen together with an increasing CO source from rising DOC concentrations results in progressively larger event amplitudes with changing co-variation between δ13CIC and δ13COC , culminating with the structure observed for the Shurum-Wonaka anomaly in the Ediacaran. In our model, the carbon isotope excursions were driven by methane from sediment-hosted clathrate hydrate deposits. Being a powerful greenhouse gas, methane increased temperature and melted icecaps. These combined to produce a negative 18O

  12. Neoproterozoic Glaciations and the Early Evolution of Animals

    NASA Astrophysics Data System (ADS)

    Narbonne, G. M.

    2004-05-01

    The intense climatic changes that characterized the Neoproterozoic world were marked by equally profound evolutionary changes that ultimately led to the Cambrian Explosion. Early and Middle Neoproterozoic oceans contained prokaryotes and diverse eukaryotic lineages, including crown-group red, green, and heterokont algae. The survival of diverse eukaryotic lineages through the Sturtian, Marinoan, and Gaskiers glaciations implies that, although these were among the most extreme glaciations Earth has ever experienced, sea ice was not as thick or pervasive as required by earlier "hard Snowball" models. Most molecular clocks predict the existence of animals well before 600 Ma and a few tantalizing hints have been found, but the oldest definite evidence of animal life are phosphatized eggs and embryos overlying Marinoan glacial deposits in China. The subsequent Late Neoproterozoic is characterized by the global occurrence of the Ediacara biota, an assemblage of cm- to m-scale fossils of soft-bodied organisms that probably represent a mixture of stem groups of modern phyla and "failed experiments" in evolution. The oldest Ediacaran fossils occur in eastern Newfoundland, and postdate the glacial diamictites and cap carbonate of the Gaskiers Formation (580 Ma) by only 5 million years, implying a causal relationship between the end of the Neoproterozoic glaciations and the proliferation of animal life. These fossils include architecturally complex fronds up to two metres long, implying either extremely rapid rates of evolution or a pre-glacial origin of the Ediacara biota. Fossils of the Mistaken Point biota (575-560 Ma) were completely sessile and show a similar fractal architecture that is difficult to relate to any existing life forms. Some of these taxa persisted into the White Sea biota (560-550 Ma), which also contains trace fossils and metameric fossils that confirm the evolution of mobile bilaterians. The youngest Ediacaran fossils (550-543 Ma) exhibit the first

  13. Neoproterozoic Earth System change: Observations of the rock record

    NASA Astrophysics Data System (ADS)

    Prave, A. R.; Fallick, A. E.; Hoffmann, K. H.; Benn, D.

    2003-04-01

    Radically nonuniformitarian modes of Earth System behaviour have been hypothesized as hallmarks of Neoproterozoic Earth history. In particular, severe climatic extremes (worldwide glaciations marked by globally frozen oceans to ultra-greenhouses) are envisaged to have occurred at least twice; these inferred harsh climates are invoked as a potential driving mechanism for biospheric evolution. Such hypotheses are intellectually elegant and their vividness grabs public attention, but how strictly do they adhere to the observational facts of the rock record? Here we show examples of Neoproterozoic glacigenic successions that imply severe, but not catastrophic climate change. The first example is the Port Askaig Tillite of Scotland. This unit was deposited in low latitudes (<30^o) and records the older ("Sturtian") glacial episode. Importantly, it contains evidence for freeze-thaw cycles on a number of time scales and, when combined with similar features observed in glacial rocks elsewhere (from both the younger and older glacial episodes), indicates that low-latitude climate does not record a simple unidirectional, long-term refrigeration of Earth. The second example is δ13C datasets associated with the older and younger glacial episodes in Namibia and California, USA. When combined with detailed stratigraphic data, these show: (1) that presumed coeval carbonates that cap the glacigenic successions display a wide range in δ13C values but share similar long-term trends; and (2) carbonates units below the erosive base of the glacigenic rocks record a decline in δ13C (as noted by previous workers) but in several cases a recovery towards heavier values is preserved in the topmost carbonate strata. These data imply that biogeochemically mediated conditions were regionally variable, both before and in the immediate aftermath of Neoproterozoic glaciations. Thus, any attempts to infer or model the nature, magnitude and potential significance of Neoproterozoic climate change

  14. Energy transduction in the methanogen Methanococcus voltae is based on a sodium current.

    PubMed Central

    Dybas, M; Konisky, J

    1992-01-01

    We provide experimental support for the proposal that ATP production in Methanococcus voltae, a methanogenic member of the archaea, is based on an energetic system in which sodium ions, not protons, are the coupling ions. We show that when grown at a pH of 6.0, 7.1, or 8.2, M. voltae cells maintain a membrane potential of approximately -150 mV. The cells maintain a transmembrane pH gradient (pH(in) - pH(out)) of -0.1, -0.2, and -0.2, respectively, values not favorable to the inward movement of protons. The cells maintain a transmembrane sodium concentration gradient (sodium(out)/sodium(in)) of 1.2, 3.4, and 11.6, respectively. While the protonophore 3,3',4',5-tetrachlorosalicylanilide inhibits ATP formation in cells grown at pH 6.5, neither ATP formation nor growth is inhibited in cells grown in medium at pH 8.2. We show that when grown at pH 8.2, cells synthesize ATP in the absence of a favorably oriented proton motive force. Whether grown at pH 6.5 or pH 8.2, M. voltae extrudes Na+ via a primary pump whose activity does not depend on a proton motive force. The addition of protons to the cells leads to a harmaline-sensitive efflux of Na+ and vice versa, indicating the presence of Na+/H+ antiporter activity and, thus, a second mechanism for the translocation of Na+ across the cell membrane. M. voltae contains a membrane component that is immunologically related to the H(+)-translocating ATP synthase of the archaeabacterium Sulfolobus acidocaldarius. Since we demonstrated that ATP production can be driven by an artificially imposed membrane potential only in the presence of sodium ions, we propose that ATP production in M. voltae is mediated by an Na+-translocating ATP synthase whose function is coupled to a sodium motive force that is generated through a primary Na+ pump. Images PMID:1324904

  15. Neoproterozoic to Paleozoic Geological Evolution of Mongolia: Constraints on Modes of "Crustal Growth" in the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Macdonald, F. A.; Bold, U.; Smith, E.; Olin, P. H.; Crowley, J. L.; Schmitz, M. D.

    2012-12-01

    The Central Asian Orogenic Belt (CAOB) is widely considered the largest area of Phanerozoic juvenile crustal growth on Earth. However, the timing and nature of the orogenic events in the core of the CAOB in Mongolia has remained poorly constrained due to a dearth of detailed geological and geochronological studies. To bridge this gap and test models of crustal growth, here we refine the sequencing of geological events by focusing on the formation and destruction of Neoproterozoic and Paleozoic tectonic basins. Mongolia's basins record a complete Neoproterozoic to Cambrian Wilson cycle with rifting of the Mongolian continent at ca. 700 Ma, the development of a Cryogenian to Ediacaran thermally subsiding passive margin, an arc-continent collision at ca. 520 Ma, and a continent-arc-continent collision at ca. 500 Ma. During this collisional orogeny, that is the Cambrian Altaids, crustal growth occurred largely through the obduction of ophiolites. Rifting of the southern margin occurred during the Ordovician Period, with the development of a Silurian passive margin. Oblique northwest-dipping subduction was initiated during the Devonian and resulted in a transpressional accretionary orogen. The CAOB culminated with a continent-arc-continent collision and the accretion of the North China and Tarim Blocks in the latest Permian. The Devonian to early Permian accretionary orogen is associated not only with voluminous plutonism, but also, major translational structures oblique to the margin resulting in the appearance of many accreted terranes. These data are consistent with existing coarse Hf and Nd isotopic data, but also provide a framework for future detailed studies. Although our geological constraints suggest distinct periods of apparent crustal growth through either collisional or accretionary orogenies, net crustal growth after accounting for recycling is equivocal.

  16. Geochemistry of the Neoproterozoic metabasic rocks from the Negele area, southern Ethiopia: Tectonomagmatic implications

    NASA Astrophysics Data System (ADS)

    Yihunie, Tadesse; Adachi, Mamoru; Yamamoto, Koshi

    2006-03-01

    Neoproterozoic metabasic rocks along with metasediments and ultramafic rocks constitute the Kenticha and Bulbul lithotectonic domains in the Negele area. They occur as amphibolite and amphibole schist in the Kenticha, and amphibole schist and metabasalt in the Bulbul domains. These rocks are dominantly basaltic in composition and exhibit low-K tholeiitic characteristics. They are slightly enriched in large ion lithophile (LIL) and light rare earth (LRE) elements and depleted in high field strength (HFS) and heavy rare earth (HRE) elements. They exhibit chemical characteristics similar to back-arc basin and island-arc basalts, but include a few samples with slightly higher Y, Zr and Nb contents. Initial Sr isotopic ratios and ɛNd values for the Kenticha metabasic rocks range from 0.7048 to 0.7051 and from 4.7 to 9.6 whereas for the Bulbul metabasic rocks they range from 0.7032 to 0.7055 and from -0.1 to 5.5, respectively. The trace elements and Sr-Nd isotope compositions of samples from the Kenticha and Bulbul domains suggest similar, but isotopically heterogeneous magma sources. The magma is inferred to have derived from depleted source with a contribution from an enriched mantle source component.

  17. Concordant paleolatitudes for Neoproterozoic ophiolitic rocks of the Trinity Complex, Klamath Mountains, California

    USGS Publications Warehouse

    Mankinen, E.A.; Lindsley-Griffin, N.; Griffin, J.R.

    2002-01-01

    New paleomagnetic results from the eastern Klamath Mountains of northern California show that Neoproterozoic rocks of the Trinity ophiolitic complex and overlying Middle Devonian volcanic rocks are latitudinally concordant with cratonal North America. Combining paleomagnetic data with regional geologic and faunal evidence suggests that the Trinity Complex and related terranes of the eastern Klamath plate were linked in some fashion to the North American craton throughout that time, but that distance between them may have varied considerably. A possible model that is consistent with our paleomagnetic results and the geologic evidence is that the Trinity Complex formed and migrated parallel to paleolatitude in the basin between Laurasia and Australia-East Antarctica as the Rodinian supercontinent began to break up. It then continued to move parallel to paleolatitude at least through Middle Devonian time. Although the eastern Klamath plate served as a nucleus against which more western components of the Klamath Mountains province amalgamated, the Klamath superterrane was not accreted to North America until Early Cretaceous time.

  18. Possible organisms similar to Ediacaran forms from the Bhander Group, Vindhyan Supergroup, Late Neoproterozoic of India

    NASA Astrophysics Data System (ADS)

    De, Chirananda

    2003-01-01

    Fossil Medusoid genera resembling Ediacaria ( Sprigg 1947) and Hiemalora ( Fedonkin 1982) and having distinctive Ediacaran affinity have been discovered in a shale horizon occurring at the base of the Bhander Group, the uppermost unit of the Vindhyan Supergroup of central India. This is the first record of unequivocal occurrence of Ediacara-like fossils in a Proterozoic basin of the Peninsular India. This finding substantially extends the previously known biogeographic range of the Ediacaran elements to Peninsular India and further enhances their biostratigraphpic potential for correlation of the upper Vindhyans with some Ediacaran horizons of Canada, Australia, South Africa and Russian Platforms. With this extension, the representatives of the genus Ediacaria can be regarded as having a global distribution in places now occupying both lower and higher latitudes. The genus Hiemalora, which appeared to be endemic to the Russian block, also has wide biogeographic coverage. These fossils assign an Ediacaran (550-543 Ma) age for the host Lakheri Limestone and suggest that the Lakheri unit was deposited within 6 million years of the Precambrian-Cambrian boundary. They also support and refine the traditional view of the Late Neoproterozoic age for the lower Bhander Group. These fossils provide positive stratigraphic clues for locating the Precambiran-Cambrian boundary strata in the overlying Lakheri-Sirbu segment of the Vindhyan sequence. They also indicate a depositional environment typical of a muddy shallow shelf setting above storm wave-base.

  19. Selenium isotope evidence for progressive oxidation of the Neoproterozoic biosphere

    PubMed Central

    Pogge von Strandmann, Philip A. E.; Stüeken, Eva E.; Elliott, Tim; Poulton, Simon W.; Dehler, Carol M.; Canfield, Don E.; Catling, David C.

    2015-01-01

    Neoproterozoic (1,000–542 Myr ago) Earth experienced profound environmental change, including ‘snowball' glaciations, oxygenation and the appearance of animals. However, an integrated understanding of these events remains elusive, partly because proxies that track subtle oceanic or atmospheric redox trends are lacking. Here we utilize selenium (Se) isotopes as a tracer of Earth redox conditions. We find temporal trends towards lower δ82/76Se values in shales before and after all Neoproterozoic glaciations, which we interpret as incomplete reduction of Se oxyanions. Trends suggest that deep-ocean Se oxyanion concentrations increased because of progressive atmospheric and deep-ocean oxidation. Immediately after the Marinoan glaciation, higher δ82/76Se values superpose the general decline. This may indicate less oxic conditions with lower availability of oxyanions or increased bioproductivity along continental margins that captured heavy seawater δ82/76Se into buried organics. Overall, increased ocean oxidation and atmospheric O2 extended over at least 100 million years, setting the stage for early animal evolution. PMID:26679529

  20. Selenium isotope evidence for progressive oxidation of the Neoproterozoic biosphere.

    PubMed

    Pogge von Strandmann, Philip A E; Stüeken, Eva E; Elliott, Tim; Poulton, Simon W; Dehler, Carol M; Canfield, Don E; Catling, David C

    2015-01-01

    Neoproterozoic (1,000-542 Myr ago) Earth experienced profound environmental change, including 'snowball' glaciations, oxygenation and the appearance of animals. However, an integrated understanding of these events remains elusive, partly because proxies that track subtle oceanic or atmospheric redox trends are lacking. Here we utilize selenium (Se) isotopes as a tracer of Earth redox conditions. We find temporal trends towards lower δ(82/76)Se values in shales before and after all Neoproterozoic glaciations, which we interpret as incomplete reduction of Se oxyanions. Trends suggest that deep-ocean Se oxyanion concentrations increased because of progressive atmospheric and deep-ocean oxidation. Immediately after the Marinoan glaciation, higher δ(82/76)Se values superpose the general decline. This may indicate less oxic conditions with lower availability of oxyanions or increased bioproductivity along continental margins that captured heavy seawater δ(82/76)Se into buried organics. Overall, increased ocean oxidation and atmospheric O2 extended over at least 100 million years, setting the stage for early animal evolution. PMID:26679529

  1. Selenium isotope evidence for progressive oxidation of the Neoproterozoic biosphere

    NASA Astrophysics Data System (ADS)

    Pogge von Strandmann, Philip A. E.; Stüeken, Eva E.; Elliott, Tim; Poulton, Simon W.; Dehler, Carol M.; Canfield, Don E.; Catling, David C.

    2015-12-01

    Neoproterozoic (1,000-542 Myr ago) Earth experienced profound environmental change, including `snowball' glaciations, oxygenation and the appearance of animals. However, an integrated understanding of these events remains elusive, partly because proxies that track subtle oceanic or atmospheric redox trends are lacking. Here we utilize selenium (Se) isotopes as a tracer of Earth redox conditions. We find temporal trends towards lower δ82/76Se values in shales before and after all Neoproterozoic glaciations, which we interpret as incomplete reduction of Se oxyanions. Trends suggest that deep-ocean Se oxyanion concentrations increased because of progressive atmospheric and deep-ocean oxidation. Immediately after the Marinoan glaciation, higher δ82/76Se values superpose the general decline. This may indicate less oxic conditions with lower availability of oxyanions or increased bioproductivity along continental margins that captured heavy seawater δ82/76Se into buried organics. Overall, increased ocean oxidation and atmospheric O2 extended over at least 100 million years, setting the stage for early animal evolution.

  2. Biologically induced initiation of Neoproterozoic snowball-Earth events

    PubMed Central

    Tziperman, Eli; Halevy, Itay; Johnston, David T.; Knoll, Andrew H.; Schrag, Daniel P.

    2011-01-01

    The glaciations of the Neoproterozoic Era (1,000 to 542 MyBP) were preceded by dramatically light C isotopic excursions preserved in preglacial deposits. Standard explanations of these excursions involve remineralization of isotopically light organic matter and imply strong enhancement of atmospheric CO2 greenhouse gas concentration, apparently inconsistent with the glaciations that followed. We examine a scenario in which the isotopic signal, as well as the global glaciation, result from enhanced export of organic matter from the upper ocean into anoxic subsurface waters and sediments. The organic matter undergoes anoxic remineralization at depth via either sulfate- or iron-reducing bacteria. In both cases, this can lead to changes in carbonate alkalinity and dissolved inorganic pool that efficiently lower the atmospheric CO2 concentration, possibly plunging Earth into an ice age. This scenario predicts enhanced deposition of calcium carbonate, the formation of siderite, and an increase in ocean pH, all of which are consistent with recent observations. Late Neoproterozoic diversification of marine eukaryotes may have facilitated the episodic enhancement of export of organic matter from the upper ocean, by causing a greater proportion of organic matter to be partitioned as particulate aggregates that can sink more efficiently, via increased cell size, biomineralization or increased C∶N of eukaryotic phytoplankton. The scenario explains isotopic excursions that are correlated or uncorrelated with snowball initiation, and suggests that increasing atmospheric oxygen concentrations and a progressive oxygenation of the subsurface ocean helped to prevent snowball glaciation on the Phanerozoic Earth. PMID:21825156

  3. The Neoproterozoic oxygenation event: Environmental perturbations and biogeochemical cycling

    NASA Astrophysics Data System (ADS)

    Och, Lawrence M.; Shields-Zhou, Graham A.

    2012-01-01

    The oxygen content of the Earth's surface environment is thought to have increased in two broad steps: the Great Oxygenation Event (GOE) around the Archean-Proterozoic boundary and the Neoproterozoic Oxygenation Event (NOE), during which oxygen possibly accumulated to the levels required to support animal life and ventilate the deep oceans. Although the concept of the GOE is widely accepted, the NOE is less well constrained and its timing and extent remain the subjects of debate. We review available evidence for the NOE against the background of major climatic perturbations, tectonic upheaval related to the break-up of the supercontinent Rodinia and reassembly into Gondwana, and, most importantly, major biological innovations exemplified by the Ediacarian Biota and the Cambrian 'Explosion'. Geochemical lines of evidence for the NOE include perturbations to the biogeochemical cycling of carbon. Generally high δ 13C values are possibly indicative of increased organic carbon burial and the release of oxidative power to the Earth's surface environment after c. 800 Ma. A demonstrably global and primary record of extremely negative δ 13C values after about 580 Ma strongly suggests the oxidation of a large dissolved organic carbon pool (DOC), the culmination of which around c. 550 Ma coincided with an abrupt diversification of Ediacaran macrobiota. Increasing 87Sr/ 86Sr ratios toward the Neoproterozoic-Cambrian transition indicates enhanced continental weathering which may have fuelled higher organic production and burial during the later Neoproterozoic. Evidence for enhanced oxidative recycling is given by the increase in sulfur isotope fractionation between sulfide and sulfate, exceeding the range usually attained by sulfate reduction alone, reflecting an increasing importance of the oxidative part in the sulfur cycle. S/C ratios attained a maximum during the Precambrian-Cambrian transition, further indicating higher sulfate concentrations in the ocean and a

  4. Late Proterozoic-Paleozoic evolution of the Arctic Alaska-Chukotka terrane based on U-Pb igneous and detrital zircon ages: Implications for Neoproterozoic paleogeographic reconstructions

    USGS Publications Warehouse

    Amato, J.M.; Toro, J.; Miller, E.L.; Gehrels, G.E.; Farmer, G.L.; Gottlieb, E.S.; Till, A.B.

    2009-01-01

    similar to those in the peri-Gondwanan Avalonian-Cadomian arc system, the Timanide orogen of Baltica, and other circum-Arctic terranes that were proximal to Arctic Alaska prior to the opening of the Amerasian basin in the Early Cretaceous. Our Neoproterozoic reconstruction places the Arctic Alaska-Chukotka terrane in a position near Baltica, northeast of Laurentia, in an arc system along strike with the Avalonian-Cadomian arc terranes. Previously published faunal data indicate that Seward Peninsula had Siberian and Laurentian links by Early Ordovician time. The geologic links between the Arctic Alaska-Chukotka terrane and eastern Laurentia, Baltica, peri-Gondwanan arc terranes, and Siberia from the Paleoproterozoic to the Paleozoic help to constrain paleogeographic models from the Neoproterozoic history of Rodinia to the Mesozoic opening of the Arctic basin. ?? 2009 Geological Society of America.

  5. The Neoproterozoic and Paleozoic tectonostratigraphic evolution of Southwestern Mongolia and implications for crustal growth in Asia

    NASA Astrophysics Data System (ADS)

    Macdonald, F. A.; Bold, U.; Buchwaldt, R.; Smith, E. F.

    2013-12-01

    Neoproterozoic and Paleozoic strata on the Zavkhan Terrane of southwestern Mongolia contain unique geochemical and paleontological records that have become central to our understanding of this pivital era of Earth history. Here we present sedimentological, stratigraphic, structural, geochemical, and geochronological data that provide context for these records, and for the tectonic evolution of the Central Asian Orogenic Belt (CAOB). The CAOB is commonly cited as the largest region of Phanerozoic crustal growth on Earth, yet the tectonic evolution of this region is poorly constrained. In contrast to previous studies that depicted a back-arc basin setting for deposition of Neoproterozoic strata in Mongolia, we propose that the Zavkhan Terrane is a segment of a ribbon continent, which formed through collapse of an extensive ca. 811-802 Ma continental arc system on the Tarim margin of Rodinia, associated with the subduction of a mid-ocean ridge at around 800 Ma. Extension is recorded by emplacement of mafic dike swarms, normal faulting, growth fault deposition of more than 500m of cobble conglomerates and the eruption of ignimbrites in the Zavkhan Volcanics. As the Zavkhan Terrane detached, an additional succession of coarse siliciclastic strata was deposited in the Khasagtin suite, followed by passive margin sedimentation consisting of limestone and glacial deposits of the Tsagaan Olom Group on an isolated carbonate platform. Detrital zircon in the glacigenic Maikhan Ul Formation constrain its age to younger than 730 Ma. Chemostratigraphy in the overlying Tayshir Formation further suggests that the Maikhan Ul diamictite is correlative with the ca. 717-662 Ma Sturtian glacial epoch. By the time limestone of the overlying Tayshir Formation was deposited, arc volcanism had been inactive for over 100 Myrs. After rifting, the Proterozoic terranes of Mongolia formed an isolated ribbon continent that was mantled with passive margin carbonate platform sedimentation through

  6. Diachronous evolution of volcano-sedimentary basins north of the Congo craton: Insights from U Pb ion microprobe dating of zircons from the Poli, Lom and Yaoundé Groups (Cameroon)

    NASA Astrophysics Data System (ADS)

    Toteu, Sadrack Félix; Penaye, Joseph; Deloule, Etienne; Van Schmus, William Randall; Tchameni, Rigobert

    2006-04-01

    Ion microprobe U-Pb dating of zircons from Neoproterozoic volcano-sedimentary sequences in Cameroon north of the Congo craton is presented. For the Poli basin, the depositional age is constrained between 700-665 Ma; detrital sources comprise ca. 920, 830, 780 and 736 Ma magmatic zircons. In the Lom basin, the depositional age is constrained between 613 and 600 Ma, and detrital sources include Archaean to Palaeoproterozoic, late Mesoproterozoic to early Neoproterozoic (1100-950 Ma), and Neoproterozoic (735, 644 and 613 Ma) zircons. The Yaoundé Group is probably younger than 625 Ma, and detrital sources include Palaeoproterozoic and Neoproterozoic zircons. The depositional age of the Mahan metavolcano-sedimentary sequence is post-820 Ma, and detrital sources include late Mesoproterozoic (1070 Ma) and early Neoproterozoic volcanic rocks (824 Ma). The following conclusions can be made from these data. (1) The three basins evolved during the Pan-African event but are significantly different in age and tectonic setting; the Poli is a pre- to syn-collisional basin developed upon, or in the vicinity of young magmatic arcs; the Lom basin is post-collisional and intracontinental and developed on old crust; the tectono-metamorphic evolution of the Yaoundé Group resulted from rapid tectonic burial and subsequent collision between the Congo craton and the Adamawa-Yade block. (2) Late Mesoproterozoic to early Neoproterozoic inheritance reflects the presence of magmatic event(s) of this age in west-central Africa.

  7. Late Paleoproterozoic-Neoproterozoic multi-rifting events in the North China Craton and their geological significance: A study advance and review

    NASA Astrophysics Data System (ADS)

    Zhai, Mingguo; Hu, Bo; Zhao, Taiping; Peng, Peng; Meng, Qingren

    2015-11-01

    An important Paleoproterozoic mobile belt event took place in the North China Craton (NCC), termed the Hutuo Movement. This event has been interpreted to represent cratonic reworking characterized by rifting-subduction-collision processes. The NCC then evolved into a stable platform or para-platform tectonic setting in Earth's middle age period more than ~ 1.0 Ga. Thick Late Paleoproterozoic-Neoproterozoic sedimentary sequences were extensively deposited on the early metamorphic basement. The major sedimentary basins include the Xiong'er aulacogen system in the south-central NCC, the Yan-Liao aulacogen system in the north-central NCC, the Northern marginal rift system in the northwestern NCC and the Eastern marginal rift system in the eastern NCC. The following four stages of magmatic activity are recognized in the Late Paleoproterozoic to Neoproterozoic interval: (1) ~ 1800 to 1780 Ma Xiong'er igneous province (XIP), (2) ~ 1720 to 1620 Ma anorogenic magmatic association, (3) ~ 1350 to 1320 Ma diabase sill swarms, and (4) ~ 900 Ma mafic dyke swarms. These four magmatic events suggest that the NCC was situated in an intra-plate setting for a long time from ~ 1.8 Ga to ~ 0.7 Ga or even younger, and the magmatic events were associated with multi-stage rifting activities. We document that the NCC was in a long-term extensional tectonic setting during Late Paleoproterozoic-Neoproterozoic era. The main ore deposits in this period are magmatic type iron deposits related to anorthosite-gabbro bodies, REE-Nb-Fe and Pb-Zn-Cu-Fe deposits related to Mesoproterozoic-Neoproterozoic rifts. Orogenic metal deposits are absent. There is no evidence indicating that the Grenville or other orogenic events affected the NCC. The reason for the absence of Grenvillian aged events in the NCC is probably because it was far from the edge of the Nuna supercontinent, if such a supercontinent did exist. There is another possibility that the Earth's middle age represented a particular tectonic

  8. Chemostratigraphy of early Neoproterozoic sedimentary rocks of Yenisei ridge (Siberia, Russia)

    NASA Astrophysics Data System (ADS)

    Vishnevskaya, Irina; Pisareva, Natalia; Kanygina, Nadejda; Proshenkin, Artem

    2014-05-01

    One of the biggest Proterozoic sedimentary basins in Russia is around the Siberian platform. This study about little part of them - Neoproterozoic sedimentary rocks of Yenisei ridge (Southwestern margin of Siberian Platform). Thise geological structure is ancient and very difficult for reaserch. It is a collage of different blocks: volcanic arcks, ophiolite complexes and sedimentary rocks of various ages and degrees of metamorphism. Sedimentary complexes of Siberian platform are outcropping along Angara River and its tributary. Neoproterozoic ones are presented by terrigenous-carbonate rocks of Tungusik and Oslyan groups. Despite the long study history of the area is still controversial question of time of formation of these rocks. As determination of the age of Precambrian sedimentary rocks is very difficult, Sr isotopic chemostratigraphy appears to be the only approach to establish the age of carbonate sequences. All Rb-Sr author's data was investigated by the method of selective dissolution with the preliminary removal of epigenetic carbonate phases. The isotope dilution method with mixed 87Rb + 84Sr spike was used to determine Rb and Sr concentrations in both fractions on the MI 1201AT mass spectrometer. Sr isotope ratios were measured on the Finnigan MAT-262 (BAC CU, Irkutsk, Russia) and Triton Plus (IGG UB RAS, Ekaterinburg, Russia). The C-O isotopic composition in carbon samples was measured on the Finnigan MAT-253 equipment. The main criteria for integrity were correlations of impurity-elements (Mn, Fe, Sr) and stable isotopes (C, O) with each other. The less altered rocks of the Tungusik Group are characterized by 87Sr/86Sr ratio of 0.7055-0.7058, and wide variations in the δ13CPDB values from 0 to +5o [1]. The primary 87Sr/86Sr of Dashka Formation (Oslyan Group) is 0.7057 - 0.7060 and δ13CPDB value varies in interval 3.7-4.3o like in upper part of Tungusik Group. High positive values of δ13CPDB indicate that carbonates had accumulated in warm sea

  9. Relationship between the Neoproterozoic snowball Earth and Cambrian explosion

    NASA Astrophysics Data System (ADS)

    Maruyama, S.; Yoshihara, A.; Isozaki, Y.

    2007-12-01

    Origin of snowball Earth has been debated in terms of greenhouse gas (e.g., Hoffman and Schrag), obliqueness of Earth's rotation axis (Williams, 1975), true polar wander (Evans, 2003), Galactic cosmic ray radiation (Shaviv and Veizer, 2003; Svensmark, 2006), or weakened geomagnetism (Maruyama and Yoshihara, 2003). A major difficulty for the greenhouse gas hypothesis is the on-off switch causing decrease and increase of appropriate amounts of CO2 by plume- and plate tectonics, and also in available amount of CO2 in atmosphere to be consistent with the observations. In contrast, the cosmic ray radiation models due to the star burst peaked at 2.5- 2.1 Ga and 1.4-0.8 Ga can explain on-off switch more easily than the greenhouse gas model. Cosmic ray radiations, however, must be modified by the geomagnetic intensity, fluctuating 150"% to < 10"% of the present-day level through geologic time. Our compilation suggests the idea of extensive glaciation appeared when the intensity decreased below 50% of the present-day value, as typically seen in the Neoproterozoic time. This proposes the idea of extensive cloudiness by increased cosmic rays in the Neoproterozoic to cause the snowball Earth. Time difference between the Neoproterozoic snowball Earth and Cambrian explosion is as large as 250 millions years, and this refuses their direct close-relationship. Role of frequent mass extinctions, i.e., 8 times during 100 m.y. from 585 Ma to 488 Ma, during the Ediacaran and Cambrian, has been proposed (Zhu et al., 2007). This frequency is one order of magnitude higher compared to that in the post-Ordovician time. Yet, the Cambrian explosion cannot be explained by mass extinction which replaced the vacant niches shortly after the mass extinction and never created a new animal with a new body plan. A new model proposed herein is derived from weakened geomagnetism and resultant extensive cosmic radiation to alter gene and genome for a long period over advancement of low magnetic

  10. Tectonics in the Cuddapah fold-thrust belt in the Indian shield, Andhra Pradesh, India and its implication on the crustal amalgamation of India and Rayner craton of Antarctica during Neoproterozoic orogenesis

    NASA Astrophysics Data System (ADS)

    Matin, Abdul

    2014-01-01

    Neoproterozoic orogenesis in East Antarctica and India led to the amalgamation of northern Prince Charles Mountains-Rayner complex of Antarctica with the Krishna Province of India along the present eastern coast of India with the development of ~990-900 Ma old fold-thrust belt. The frontal part of the fold-thrust belt [henceforth called the Cuddapah fold-thrust belt (CFTB)], recognized in the intercratonic, Palaeoproterozoic-Neoproterozoic Cuddapah Basin, includes two frontal thrust sheets carried by the eastern Velikonda and the western Nallamalai thrusts, along with a part of the undeformed foreland, constituting frontal part of a larger fold-thrust belt now fragmented and separated in different continents of Gondwanaland. Therefore, the intercratonic deformation now preserved in the Palaeoproterozoic-Neoproterozoic Cuddapah Basin is related to the collision of the Indian shield to the Antarctic block during the amalgamation of the Rodinia Supercontinent. CFTB is dominated by quasi-plastic deformational structures, representing exhumed deeper level fault-propagation folding related to the Velikonda thrust, while the Nallamalai thrust represents the forelandward thrust of the CFTB dominated by elastico-frictional deformation structures.

  11. Importance of the aquatic weed Ceratophyllum to transmission of Schistosoma haematobium in the Volta Lake, Ghana*

    PubMed Central

    Klumpp, R. K.; Chu, K. Y.

    1980-01-01

    Results of 5 years of sampling for Bulinus rohlfsi in human-water contact sites of villages along the Volta Lake, Ghana, have confirmed that the aquatic macrophyte, Ceratophyllum, is the most important ecological factor for sustaining high levels of cercarial transmission of Schistosoma haematobium. Data available so far indicate that growth of this weed largely determines the size of the snail populations. Increasing density of Ceratophyllum correlates with increasing levels of cercarial transmission potential in the water contact sites and of S. haematobium infection in the village populations. PMID:6975187

  12. The Volta Grande do Xingu: reconstruction of past environments and forecasting of future scenarios of a unique Amazonian fluvial landscape

    NASA Astrophysics Data System (ADS)

    Sawakuchi, A. O.; Hartmann, G. A.; Sawakuchi, H. O.; Pupim, F. N.; Bertassoli, D. J.; Parra, M.; Antinao, J. L.; Sousa, L. M.; Sabaj Pérez, M. H.; Oliveira, P. E.; Santos, R. A.; Savian, J. F.; Grohmann, C. H.; Medeiros, V. B.; McGlue, M. M.; Bicudo, D. C.; Faustino, S. B.

    2015-12-01

    The Xingu River is a large clearwater river in eastern Amazonia and its downstream sector, known as the Volta Grande do Xingu ("Xingu Great Bend"), is a unique fluvial landscape that plays an important role in the biodiversity, biogeochemistry and prehistoric and historic peopling of Amazonia. The sedimentary dynamics of the Xingu River in the Volta Grande and its downstream sector will be shifted in the next few years due to the construction of dams associated with the Belo Monte hydropower project. Impacts on river biodiversity and carbon cycling are anticipated, especially due to likely changes in sedimentation and riverbed characteristics. This research project aims to define the geological and climate factors responsible for the development of the Volta Grande landscape and to track its environmental changes during the Holocene, using the modern system as a reference. In this context, sediment cores, riverbed rock and sediment samples and greenhouse gas (GHG) samples were collected in the Volta Grande do Xingu and adjacent upstream and downstream sectors. The reconstruction of past conditions in the Volta Grande is necessary for forecasting future scenarios and defining biodiversity conservation strategies under the operation of Belo Monte dams. This paper describes the scientific questions of the project and the sampling surveys performed by an international team of Earth scientists and biologists during the dry seasons of 2013 and 2014. Preliminary results are presented and a future workshop is planned to integrate results, present data to the scientific community and discuss possibilities for deeper drilling in the Xingu ria to extend the sedimentary record of the Volta Grande do Xingu.

  13. Evidence of giant sulphur bacteria in Neoproterozoic phosphorites.

    PubMed

    Bailey, Jake V; Joye, Samantha B; Kalanetra, Karen M; Flood, Beverly E; Corsetti, Frank A

    2007-01-11

    In situ phosphatization and reductive cell division have recently been discovered within the vacuolate sulphur-oxidizing bacteria. Here we show that certain Neoproterozoic Doushantuo Formation (about 600 million years bp) microfossils, including structures previously interpreted as the oldest known metazoan eggs and embryos, can be interpreted as giant vacuolate sulphur bacteria. Sulphur bacteria of the genus Thiomargarita have sizes and morphologies similar to those of many Doushantuo microfossils, including symmetrical cell clusters that result from multiple stages of reductive division in three planes. We also propose that Doushantuo phosphorite precipitation was mediated by these bacteria, as shown in modern Thiomargarita-associated phosphogenic sites, thus providing the taphonomic conditions that preserved other fossils known from the Doushantuo Formation. PMID:17183268

  14. Strontium isotopic variations of Neoproterozoic seawater: implications for crustal evolution.

    PubMed

    Asmerom, Y; Jacobsen, S B; Knoll, A H; Butterfield, N J; Swett, K

    1991-01-01

    We report high precision Sr isotopic data on carbonates from the Neoproterozoic Shaler Group, Victoria Island, Northwest Territories, Canada. Lithostratigraphic correlations with the relatively well-dated Mackenzie Mountains Supergroup constrain Shaler deposition to approximately 770-880 Ma, a range corroborated by 723 +/- 3 Ma lavas that disconformably overlie Shaler carbonates and by Late Riphean microfossils within the section. Samples with low 87Rb/86Sr ratios (<0.01) were selected for Sr isotopic analysis. Delta 18O, Mn, Ca, Mg, and Sr data were used to recognize altered samples. The altered samples are characterized by high Mn/Sr (> or = 2) and variable delta 18O; most are dolomites. The data indicate that between ca. 790-850 Ma the 87Sr/86Sr ratio of seawater varied between 0.70676 and 0.70561. The samples show smooth and systematic variation, with the lowest 87Sr/86Sr value of 0.70561 at ca. 830 Ma. The low 87Sr/86Sr ratio of carbonates from the lower parts of our section is similar to a value reported for one sample from the Adrar of Mauritania (approximately 900 Ma), West African Craton. Isotopic ratios from the upper part of the Shaler section are identical to values from the lower part of the Neoproterozoic Akademikerbreen Group, Spitsbergen. Although a paucity of absolute age determinations hinders attempts at the precise correlation of Neoproterozoic successions, it is possible to draw a broad outline of the Sr isotopic composition of seawater for this period. Indeed, the Sr isotope data themselves provide a stratigraphic tool of considerable potential. Data from this study and the literature are used to construct a curve of the 87Sr/86Sr ratio of Neoproterozoic seawater. The new data reported in this study substantially improve the isotopic record of Sr in seawater for the period 790-850 Ma. The Sr isotope composition of seawater reflects primarily the balance between continental Sr input through river input and mantle input via hydrothermal

  15. Neoproterozoic ice ages, boron isotopes, and ocean acidification

    NASA Astrophysics Data System (ADS)

    Kasemann, S. A.; Prave, A. R.; Fallick, A. E.; Hawkesworth, C. J.; Hoffmann, K.

    2010-12-01

    The Neoproterozoic Earth underwent at least two severe glaciations, each extending to low palaeomagnetic latitudes and punctuating warmer climates. In concert with the environmental changes, the rocks display large amplitude fluctuations in their stable isotopic composition. These fluctuations are stratigraphically systematic, occur in many sections worldwide and are interpreted as being globally significant1. Thus, the Neoproterozoic carbonates provide a unique geological and isotopic archive to improve our understanding of major non-anthropogenically influenced changes in Earth System behaviour. The two widespread older and younger Cryogenian glacial deposits (commonly referred to as the Sturtian and Marinoan, respectively) in Namibia are directly overlain by cap carbonates deposited under inferred periods of high atmospheric carbon dioxide concentrations. Oceanic uptake of carbon dioxide decreases ocean pH and here we present a record of Cryogenian inter-glacial ocean pH, based on boron isotopes in marine carbonates. Our data document characteristically different B isotope profiles of the two Cryogenian carbonate transects that are consistent with the presence of two panglacial climate states, but indicate that each had its own distinct environmental conditions. The Marinoan interglacial δ11B profiles are systematic and remarkably consistent, and they vary by up to 11‰. This yields a relative pH variation of up to 1.5 pH units, and implies a pH of 8.5 at the onset of cap carbonate deposition, followed by a decrease in pH to ~7 and then a return to pH ~8 for the upper part of the section. The transient ocean acidification excursion and the alkaline pH condition near the start and termination of the inferred greenhouse state suggests a rapid draw-down of CO2 initiated at the start of the deglaciation and supports inferences of a thick, global sea-ice shield with minimal air-sea gas exchange during glaciation. In contrast, largely constant B isotope values for

  16. Integrated Geochemical-Petrographic Insights on Neoproterozoic Ocean Oxygenation

    NASA Astrophysics Data System (ADS)

    Hood, A.; Planavsky, N.; Wallace, M. W.; Wang, X.; Gueguen, B.

    2015-12-01

    Novel isotope systems have the potential to provide new insights into biogeochemical cycling in Earth's evolving oceans. However, much recent paleo-redox work has been done without extensive consideration of sample preservation or paleoenvironmental setting. Neoproterozoic reef complexes from South Australia provide a perfect setting to test geochemical redox proxies (e.g. uranium isotopes and trace metal chemistry) within a well-defined sedimentological and petrographic context. These reefs developed significant frameworks over ~1km of steep platform relief from the seafloor, and contain a variety of carbonate components including primary dolomite marine cements. Analysis of a variety of components within these reefs reveals significant variation in uranium isotope composition and trace metal chemistry between components, even within a single sample. Marine cements, which precipitated directly from seawater, have much lower contamination element concentrations (e.g. Al, Zr, Th) than depositional micrites, and appear to represent the best archive of ancient ocean conditions. These cements have high levels of Fe, Mn in shallow and deep reef facies (e.g. 2-3wt% Fe), but only Fe-oxide inclusions in peritidal settings. This distribution suggests ferruginous conditions under a surficial chemocline in this Neoproterozoic seawater. Uranium isotopes from pristine marine cements have relatively heavy values compared to modern seawater (median = -0.22 δ238U). These values are essentially unfractionated from riverine inputs, which we interpret as tracking extensive near quantitative low-T reduction of U(VI) to U(IV) by abundant soluble iron in seawater. Depositional components and late stage cements have a much lighter and more variable U isotope compositions (-0.71 to -0.08 δ238U). This work highlights the need for fundamental petrographic constraints on the preservation of depositional geochemical signatures in the future use and development of sedimentary redox proxies.

  17. Techniques for estimating densities of Bulinus truncatus rohlfsi and its horizontal distribution in Volta Lake, Ghana

    PubMed Central

    Chu, K. Y.; Vanderburg, J. A.

    1976-01-01

    Bulinus truncatus rohlfsi is the intermediate host of urinary schistosomiasis, which is highly endemic in the man-made Volta Lake. In 1971, a WHO/UNDP schistosomiasis project was established in the Pawmpawm branch and part of the Afram branch of Volta Lake. Malacological findings of the preliminary phase indicated that the snails were distributed in the littoral zone of the lake, and that this distribution was correlated with the presence of vegetation, especially Ceratophyllum. Transmission nearly always occurred in “water contact sites”, i.e., places where people come into contact with water. A snail-sampling technique with palm-leaf mats was developed and standardized after it had been shown in sensitivity trials to compare favourably with a modified version of the “man—time” sampling method, in which the number of snails collected per man-hour is recorded. It is recommended that both these methods should be used to conduct ecological studies of B. rohlfsi in water contact sites. PMID:1088354

  18. Ecological studies of Bulinus rohlfsi, the intermediate host of Schistosoma haematobium in the Volta Lake

    PubMed Central

    Klumpp, R. K.; Chu, K. Y.

    1977-01-01

    In the present ecological study of cercarial transmission of Schistosoma haematobium in the Volta Lake, Ghana, habitat observations and sampling of Bulinus truncatus rohlfsi were conducted within a 60-km stretch of shoreline. Observations revealed that human water contact sites in each village undergo constant changes in shape and vegetation. Snail sampling surveys in water contact sites were carried out monthly (for 27 months) in 8 villages using newly designed palm-leaf traps, and in 8 additional villages (for 16 months) using a modification of Olivier & Sneidermann's man—time method. Results to date confirm the finding by Chu & Vanderburg that cercarial transmission in the lake takes place almost exclusively within water contact sites. Additional results indicate that even within individual water contact sites this transmission is focal, most infected snails being found very close to the shoreline. Transmission also varies significantly according to shape, vegetation, and geographical location of the water contact sites, and is distinctly seasonal in most villages. These findings lead us to conclude that control of cercarial transmission in the Volta Lake is both attainable and feasible with existing methods. PMID:304396

  19. Cryogenian-Ediacaran Carbon Isotope Stratigraphy of the Amadeus Basin, Central Australia

    NASA Astrophysics Data System (ADS)

    Joubert, R. L.; Verdel, C.; Schultz, I.

    2014-12-01

    Deciphering the nature of extreme Neoproterozoic climatic and biogeochemical perturbations hinges on correlating sedimentary sequences within and across different basins. To improve these correlations within central Australia, we have focused on the abundant and laterally extensive glaciogenic and carbonate deposits of the Amadeus Basin. Here, we present new high-resolution carbonate C isotope profiles from Cryogenian-Ediacaran stratigraphic successions (the Areyonga, Aralka, Olympic, and Julie Formations) that are particularly well exposed in the northeastern part of the basin. The data appear to span a duration of >100 Ma, from the end of the older Cryogenian glaciation to the upper Ediacaran. In addition to major isotopic excursions resembling those described from other Neoproterozoic successions, the Amadeus Basin isotopic profiles display consistent fine-scale patterns and lateral trends that allow us to identify diachronous strata and refine the overall stratigraphic and tectonic architecture of the basin.

  20. Neoproterozoic geodynamic evolution of SW-Gondwana: a southern African perspective

    NASA Astrophysics Data System (ADS)

    Frimmel, H. E.; Basei, M. S.; Gaucher, C.

    2011-04-01

    Our current understanding of the tectonic history of the principal Pan-African orogenic belts in southwestern Africa, reaching from the West Congo Belt in the north to the Lufilian/Zambezi, Kaoko, Damara, Gariep and finally the Saldania Belt in the south, is briefly summarized. On that basis, possible links with tectono-stratigraphic units and major structures on the eastern side of the Río de la Plata Craton are suggested, and a revised geodynamic model for the amalgamation of SW-Gondwana is proposed. The Río de la Plata and Kalahari Cratons are considered to have become juxtaposed already by the end of the Mesoproterozoic. Early Neoproterozoic rifting led to the fragmentation of the northwestern (in today's coordinates) Kalahari Craton and the splitting off of several small cratonic blocks. The largest of these ex-Kalahari cratonic fragments is probably the Angola Block. Smaller fragments include the Luis Alves and Curitiba microplates in eastern Brazil, several basement inliers within the Damara Belt, and an elongate fragment off the western margin, named Arachania. The main suture between the Kalahari and the Congo-São Francisco Cratons is suspected to be hidden beneath younger cover between the West Congo Belt and the Lufilian/Zambezi Belts and probably continues westwards via the Cabo Frío Terrane into the Goiás magmatic arc along the Brasilia Belt. Many of the rift grabens that separated the various former Kalahari cratonic fragments did not evolve into oceanic basins, such as the Northern Nosib Rift in the Damara Belt and the Gariep rift basin. Following latest Cryogenian/early Ediacaran closure of the Brazilides Ocean between the Río de la Plata Craton and the westernmost fragment of the Kalahari Craton, the latter, Arachania, became the locus of a more than 1,000-km-long continental magmatic arc, the Cuchilla Dionisio-Pelotas Arc. A correspondingly long back-arc basin (Marmora Basin) on the eastern flank of that arc is recognized, remnants of which

  1. Micropaleontology and chemostratigraphy of the Neoproterozoic Mbuji-Mayi Supergroup, Democratic Republic of Congo.

    NASA Astrophysics Data System (ADS)

    Baludikay, Blaise; Bekker, Andrey; Baudet, Daniel; Asael, Dan; Storme, Jean-Yves; Javaux, Emmanuelle

    2014-05-01

    The Mbuji-Mayi Supergroup, deposited between 1170 ± 22 Ma and ca. 800 Ma [1], outcrops in the eastern Oriental Kasai Province and western Katanga Province of the Democratic Republic of Congo. It is the youngest Precambrian unit of the Kasai block and was deposited in the SE-NW trending failed-rift Sankuru-Mbuji-Mayi-Lomami-Lovoy basin filled with siliciclastic and carbonate sediments. In the northern part of this basin (Oriental Kasai Province), the Mbuji-Mayi Supergroup rests unconformably upon the Archean Dibaya Granite Complex, but in the southern part (northeastern Katanga Province), it overlies the Mesoproterozoic Kibaran Supergroup. The Supergroup is divided into two groups: the lower, ~ 500-m thick siliciclastics-rich BI Group and the upper, ~ 1000-m thick carbonate-rich BII Group. Our own and previous sedimentological observations [2] indicate facies ranging from subtidal, low-energy stromatolitic environments to overlying intertidal to supratidal evaporitic settings of lagoon and sabkha. In order to characterize the diversity of microfossil assemblages, their paleobiology and paleoecology as well as redox conditions in their depositional setting, we have sampled three drill cores (KAFUKU 15, B13 KANSHI, and S70 LUBI) from the collections of the Royal Museum for Central Africa (RMAC). Our biostratigraphic and chemostratigraphic data also provide further constraints on the age of the Mbuji-Mayi Supergroup. Here we present preliminary data on microfossil diversity from the Kanshi drill core and carbon isotope chemostratigraphy for all three drill cores. The well-preserved and diverse assemblage of acritarchs and filamentous forms includes prokaryotes and eukaryotes, and is similar to other coeval assemblages described worldwide outside of Africa. The presence of the acanthomorph acritarch Trachyhystrichosphaera aimika is significant as it is indicative of the late Meso- to early Neoproterozoic age elsewhere, and is reported for the first time in Central

  2. Analysis of drug resistance in the archaebacterium Methanococcus voltae with respect to potential use in genetic engineering

    SciTech Connect

    Possot, O.; Gernhardt, P.; Klein, A.; Sibold, L.

    1988-03-01

    The sensitivity of the methanogenic archaebacterium Methanococcus voltae to 12 inhibitors was tested in liquid medium. Four compounds appeared to be inhibitors of growth. Their MICs were as follows: pseudomonic acid, 0.1 ..mu..g/ml (0.19 ..mu..M); puromycin, 2 ..mu..g/ml (3.6 ..mu..M); methionine sulfoximine, 30 ..mu..g/ml (170 ..mu..M); and fusidic acid, 100 ..mu..g/ml (170 ..mu..M). On solid medium, the MICs were similar and the frequency of spontaneous resistance was found to be 5 x 10/sup -5/ (methionine sulfoximine), 10/sup -7/ (pseudomonic acid), and <10/sup -7/ (puromycin and fusidic acid). Pseudomonic acid was found to inhibit isoleucyl-tRNA synthetase activity as measured by the in vitro aminoacylation of M. voltae tRAN with L-(U-/sup 14/C) isoleucine. Fusidic acid and puromycin were shown to inhibit poly(U)-dependent polyphenylalanine synthesis in S30 extracts. Acetylpuromycin was inhibitory at much higher concentrations both in vivo and in vitro for M. voltae. Thus, the pac gene of Streptomyces alboniger, which is responsible for acetylation of puromycin and which conferred resistance to puromycin when introduced in eubacterian and eucaryotes, is a potential selective marker in gene transfer experiments with M. voltae. The latter was recently shown to be transformable. The same would be true for the cat gene of Tn9, which enodes resistance to fusidic acid in eubacteria in addition to resistance to chloramphenicol.

  3. Neoproterozoic cap-dolostone deposition in stratified glacial meltwater plume

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Wang, Zhengrong; Raub, Timothy D.; Macdonald, Francis A.; Evans, David A. D.

    2014-10-01

    Neoproterozoic cap carbonates host distinctive geochemical and sedimentological features that reflect prevailing conditions in the aftermath of Snowball Earth. Interpretation of these features has remained contentious, with hypotheses hinging upon timescale and synchronicity of deposition, and whether or not geochemical signatures of cap carbonates represent those of a well-mixed ocean. Here we present new high-resolution Sr and Mg isotope results from basal Ediacaran cap dolostones in South Australia and Mongolia. Least-altered Sr and Mg isotope compositions of carbonates are identified through a novel incremental leaching technique that monitors the purity of a carbonate sample and the effects of diagenesis. These data can be explained by the formation of these cap dolostones involving two chemically distinct solutions, a glacial meltwater plume enriched in radiogenic Sr, and a saline ocean residue with relatively lower 87Sr/86Sr ratios. Model simulations suggest that these water bodies remained dynamically stratified during part of cap-dolostone deposition, most likely lasting for ∼8 thousand years. Our results can potentially reconcile previous conflicts between timescales estimated from physical mixing models and paleomagnetic constraints. Geochemical data from cap carbonates used to interpret the nature of Snowball Earth and its aftermath should be recast in terms of a chemically distinct meltwater plume.

  4. Strontium isotopic variations of Neoproterozoic seawater - Implications for crustal evolution

    NASA Technical Reports Server (NTRS)

    Asmerom, Yemane; Jacobsen, Stein B.; Knoll, Andrew H.; Butterfield, Nicholas J.; Swett, Keene

    1991-01-01

    High-precision Sr isotopic data were obtained on carbonate samples from the Neoproterozoic Shaler Group, Victoria Island (Canada). Results indicate that, between ca. 790 and 850 Ma, the Sr-87/Sr-86 ratio of seawater varied betweeen 0.70676 and 0.70561, with the minimum value at about 830 Ma. A curve of the Sr-87/Sr-86 seawater ratio vs. age showed that the new data substantially improve the existing isotopic record of Sr in seawater for the period 790-850 Ma. The Sr isotopic system data were coupled with data for the Nd isotopic system to model changes in the seafloor spreading rates (hydrothermal flux) and the continental erosion for the period 500-900 Ma. Results indicate that hydrothermal flux reached a maximum value at ca. 830 Ma, while a maximum in erosion rate occurred at ca. 570 Ma. These peaks are considered to be related to the developments in the Pan-African and related orogenic events.

  5. Initial field studies in Upper Volta with dichlorvos residual fumigant as a malaria eradication technique*

    PubMed Central

    Quarterman, K. D.; Lotte, M.; Schoof, H. F.

    1963-01-01

    Laboratory and simulated field tests have shown that dichlorvos, a volatile insecticide, can be prepared in a solid formulation which releases the dichlorvos vapour over a period of several months at a relatively uniform rate high enough to kill adult anopheline mosquitos but low enough to have no effect on man and the higher animals. A field experiment is in progress in Wakara, Upper Volta, to evaluate the residual fumigant technique under practical field conditions. Chemical, biological, toxicological and epidemiological data obtained during the first nine months indicate that the method produced dichlorvos vapours in a concentration effective against mosquitos for 3 to 5 months per treatment, that the occupants of the treated dwellings showed no detectable effects from the insecticidal vapours, and that the malaria rates were reduced by 38%-55% among the population of the treated village as compared with a nearby untreated control village. ImagesFIG. 1FIG. 2 PMID:14056276

  6. Operational performance of the photovoltaic-powered grain mill and water pump at Tangaye, Upper Volta

    NASA Technical Reports Server (NTRS)

    Martz, J. E.; Ratajczak, A. F.; Delombard, R.

    1982-01-01

    The first two years of operation of a stand alone photovoltaic (PV) power system for the village of Tangaye, Upper Volta in West Africa are described. The purpose of the experiment was to demonstrate that PV systems could provide reliable electrical power for multiple use applications in remote areas where local technical expertise is limited. The 1.8 kW (peak) power system supplies 120-V (d.c.) electrical power to operate a grain mill, a water pump, and mill building lights for the village. The system was initially sized to pump a part of the village water requirements from an existing improved well, and to meet a portion of the village grain grinding requirements. The data, observations, experiences, and conclusions developed during the first two years of operation are discussed. Reports of tests of the mills used in the project are included.

  7. Contributions to the knowledge of amphibians and reptiles from Volta Grande do Xingu, northern Brazil.

    PubMed

    Vaz-Silva, W; Oliveira, R M; Gonzaga, A F N; Pinto, K C; Poli, F C; Bilce, T M; Penhacek, M; Wronski, L; Martins, J X; Junqueira, T G; Cesca, L C C; Guimarães, V Y; Pinheiro, R D

    2015-08-01

    The region of Volta Grande do Xingu River, in the state of Pará, presents several kinds of land use ranging from extensive cattle farming to agroforestry, and deforestation. Currently, the Belo Monte Hydroelectric Power Plant affects the region. We present a checklist of amphibians and reptiles of the region and discuss information regarding the spatial distribution of the assemblies based on results of Environmental Programmes conducted in the area. We listed 109 amphibian (Anura, Caudata, and Gymnophiona) and 150 reptile (Squamata, Testudines, and Crocodylia) species. The regional species richness is still considered underestimated, considering the taxonomic uncertainty, complexity and cryptic diversity of various species, as observed in other regions of the Amazon biome. Efforts for scientific collection and studies related to integrative taxonomy are needed to elucidate uncertainties and increase levels of knowledge of the local diversity. PMID:26691094

  8. Mercury accumulation in the clam, Galatea paradoxa (Born 1778) at the Volta estuary, Ghana.

    PubMed

    Obirikorang, K A; Amisah, S; Adjei-Boateng, D; Madkour, H A; Otchere, F A

    2010-11-01

    The concentration of mercury in the tissues of the clam, Galatea paradoxa at in the Volta estuary, Ghana, were analysed over an 18-month period, from March 2008 to August 2009. The concentrations were well below the International Human Consumption Advisory Limit of THg (0.5 μg/g wet weight). The concentrations in the tissues of the different clam size classes were between 6 and 18 times lower than the WHO Safety Reference Standard. Variation in the mean mercury concentration in the different clam size classes was not significant (p > 0.05) for clams from Aveglo but were highly significant (p < 0.0001) for clams from Ada, indicating a possible effect of size on accumulation. G. paradoxa is therefore suitable for human consumption based on the WHO Safety Reference Standards. PMID:20972534

  9. Recognition and characterisation of high-grade ignimbrites from the Neoproterozoic rhyolitic volcanism in southernmost Brazil

    NASA Astrophysics Data System (ADS)

    Sommer, Carlos Augusto; Lima, Evandro Fernandes; Machado, Adriane; Rossetti, Lucas de Magalhães May; Pierosan, Ronaldo

    2013-11-01

    Neoproterozoic magmatism in southern Brazil is associated with translithospheric shear belts and strike-slip basins in a post-collisional setting related to the last stages of the Brasilian-Pan African Orogenic Cycle. It evolved from an association of high-K calc-alkaline, leucocratic-peraluminous and continental tholeiitic magmas, to an association with shoshonitic magmas and, eventually, to an association with magmas of the sodic mildly alkaline series. This magmatism varies from metaluminous to peralkaline and exhibits alkaline sodic affinity. A large volcanism is related to this alkaline sodic magmatism and is named the Acampamento Velho Formation. This unit was coeval with subaerial siliciclastic sedimentation in post-collisional basins preserved in the region. The Acampamento Velho Formation consists of pyroclastic and effusive volcanic deposits, which are mainly silicic, emplaced under subaerial conditions. The best exposures of this volcanism occur on the Ramada and Taquarembó plateaus, located southwest of Rio Grande do Sul in southernmost Brazil. The pyroclastic flow deposits are composed mainly of juvenile fragments such as pumices, shards and crystal fragments. Welding is very effective in these units. High-grade ignimbrites occur at the base and intermediate portions of the deposits and rheoignimbrites are observed at the top. The pre-eruptive temperature calculations, which were obtained at the saturation of zircon, revealed values between 870 °C and 978 °C for Taquarembó Plateau and 850 °C-946 °C for Ramada Plateau. The calculated viscosity values vary from 6.946 to 8.453 log η (Pas) for the rheoignimbrites and 7.818 to 10.588 log η (Pas) for the ignimbrites. Zr contents increase toward the top of the pyroclastic sequence, which indicates an increase in peralkalinity and determines the reduction in viscosity for clasts at the upper portions of the flows. The patterns of the structures of the ignimbrites and rheoignimbrites in the Taquaremb

  10. High frequency peritidal cycles of the upper Araras Group: Implications for disappearance of the neoproterozoic carbonate platform in southern Amazon Craton

    NASA Astrophysics Data System (ADS)

    Rudnitzki, Isaac Daniel; Romero, Guilherme Raffaeli; Hidalgo, Renata; Nogueira, Afonso Cesar Rodrigues

    2016-01-01

    activity in the vicinity of the basin and the rapid uplift of source areas to the west and to the east of the basin preceding the progradation of the siliciclastic fluvial-coastal environments related to the Alto Paraguay sedimentation. This event resulted in erosion of shallow carbonate basins and, potentially, the demise and disintegration of the Neoproterozoic carbonate platforms in southern Amazon Craton.

  11. An exposed slab window margin: the eastern part of the Neoproterozoic Baikal-Muya belt, Russia

    NASA Astrophysics Data System (ADS)

    Fedotova, A.; Khain, E.; Razumovskiy, A.; Anosova, M.; Orlova, A.

    2012-04-01

    substantially completed about 600-620 Ma ago. Cessation of the subduction was probably the first stage of collision process between the Siberian craton and the Baikal-Muya tectonic collage, that resulted in oceanic slab break-off, and emergency of an asthenosphere (slab) window. Indicator complexes of an upper edge of the window we consider to be granulites intruded by adakites veins 591±3 Ma ago. The evolution of the marginal basin of Siberian craton had been terminated at least in one of its segments in the late Neoproterozoic, and shelf-type deposition gave place to accumulation of coarse-grained sediments in the mountain valleys (Kholodnenskaya suite and coeval formations). The tectonic setting in the north of the present-day Australian shelf (Timor Island) can be used as a modern analogue to the reconstucted junction between the Neoproterozoic Siberian marginal (shelf) basin and the adjacent mobile belt. Amelin, Yu.V., Rytsk, E.Yu., Krymskii, R.Sh., Neymark, L.A., and Skublov, S.G., 2000. Vendian age of enderbites from a granulite complex of the Baikal-Muya ophiolite belt, northern Baikal region: U-Pb and Sm-Nd isotope evidence // Transactions (Doklady) of the Russian Acad. of Sciences, Earth Science Section, 371, no. 3, 455-457. Izokh, A.E., Gibsher, A.S., Zhuravlev, D.Z., Balykin, P.A., 1998. Sm-Nd Data on the age of ultramafic-mafic massifs, eastern branch of the Baikal-Muya ophiolite belt // Doklady Akad. Nauk, 360, no. 1, 88-92 (in Russian). Rytsk, E.Yu. Kovach, V.P., Kovalenko, V.I., and Yarmolyuk, V.V. 2007. Structure and Evolution of the Continental Crust in the Baikal Fold Region. Geotectonics. 41, no. 6, p. 440-464. Makrygina, V.A., Konnikov, E.G., Neymark, L.A., Pakhol'chenko, Yu.A., Posokhov, V.F., Sandimirova, G.P., Tomilenko, A.A., Tsygankov, A.A., Vrublevskaya, T.T., 1993. The age of granulite-charnockite complex of Nurundyukan Suite, northern Cisbaikalia (paradox of radiochronology) // Doklady Acad. Nauk., 332, no. 4, 486-490 (in Russian). Shatskii, V

  12. The Santa Terezinha-Campos Verdes emerald district, central Brazil: structural and Sm-Nd data to constrain the tectonic evolution of the Neoproterozoic Brası´lia belt

    NASA Astrophysics Data System (ADS)

    D'el-Rey Silva, Luiz José Homem; Barros Neto, Leonel de Souza

    2002-12-01

    Structural analysis coupled with Sm-Nd isotope data and a detailed description of the geology of the Santa Terezinha-Campos Verdes emerald district (Goiás State, Central Brazil) constrain the evolution of the Neoproterozoic Brası´lia belt. The area is composed of tectonic slices of Archean-Paleoproterozoic gneiss, a Meso-Neoproterozoic metavolcanic sedimentary sequence called the Santa Terezinha sequence, and crustal-derived intrusive rocks such as mylonitic (ortho)gneiss and a syntectonic porphyry granite. It underwent a Neoproterozoic greenschist facies polyphase ductile deformation (D 1-D 3). Structures indicate an event of rotational deformation along a typical frontal ramp dipping gently to the west (i.e. an event of simple shear with top to ESE relative regional movement due to a subhorizontal WNW-ESE compression). A Sm-Nd whole-rock isochron age of 577±77 Ma for the intrusive rocks constrains the timing of at least part of the deformation/metamorphism in the area. Primary and metamorphic planar structures (mainly D 1-D 2) strike SW-NE and dip at low to moderate angles to the NW in the northern part of the area. However, they gradually rotate to SSE in the central SE part, where the Peixe River synclinorium is developed. This synclinorium is also the nest of the D 2 sheath folds that control emerald ore shoots. The Santa Cruz dome is a basement-cored, major elliptic structure in the SW of the area. The Santa Terezinha sequence represents a back-arc basin that received input from the Neoproterozoic Goiás magmatic arc to the west and the São Francisco ancient continental margin to the east. The basal and upper sections of this sequence correlate, respectively, with other passive margin and back-arc sequences of the Brası´lia belt.

  13. Groundwater resource sustainability in the Nabogo Basin of Ghana

    NASA Astrophysics Data System (ADS)

    Lutz, Alexandra; Thomas, James M.; Pohll, Greg; McKay, W. Alan

    2007-10-01

    In order to address groundwater resource sustainability, a conceptual groundwater flow model is developed for a hydrographic basin of northern Ghana. A three-dimensional steady-state model is applied to the Nabogo Basin, a sub-catchment of the White Volta River Basin. Mean annual data are used for input parameters. Parameters include rates of precipitation, recharge, surface water discharge, and groundwater extraction (pumpage). The model indicates that current well pumpage rates are significantly less than annual groundwater recharge to the basin. Model results for several scenarios tested (i.e., increased population, access to potable water for all citizens, and/or decreased rainfall) indicate that extraction rates will still be less than groundwater input to the basin.

  14. Giant submarine landslide grooves in the Neoproterozoic/Lower Cambrian Phe Formation, northwest Himalaya: Mechanisms of formation and palaeogeographic implications

    NASA Astrophysics Data System (ADS)

    Draganits, E.; Schlaf, J.; Grasemann, B.; Argles, T.

    2008-04-01

    Giant groove casts have been found in the upper Proterozoic to Lower Cambrian Phe Formation (Haimanta Group), a siliciclastic sandstone/shale succession in the Tethyan Zone of the Higher Himalaya tectonic unit. The grooves are among the largest linear erosion structures related to submarine mass-movements observed in the geologic record. They are up to 4 m wide, about 0.2 m deep and can be traced for more than 35 m without changing their character. The grooves are straight, subparallel to cross-cutting striations with shallow semi-circular cross-sections and well-defined superimposed minor ridges and grooves. Groove casts exist on the soles of several sandstone beds within a 73 m thick logged section, commonly associated with flute casts. Their characteristics were compared with several other types of ancient and modern submarine linear erosion structures. A sand-rich, non-channelized basin floor depositional environment is inferred from the lithofacies, the combination of sedimentary structures, the lack of coarse-grained pebbly facies, the lateral continuity of beds, and the lack of channel structures. The grooves probably formed by laminar debris flows/concentrated density flows dragging blocks of already lithified sediment across the basin floor. When the bedding is structurally rotated back to horizontal, the groove casts show consistent North-South oriented palaeocurrent trends, with South-directed palaeocurrent directions indicated by flute casts. These palaeocurrent orientations contrast with previous palaeogeographic reconstructions of this area, which propose sediment delivery from the South. We therefore suggest a new "double provenance" model for the spatial relationship of late Proterozoic to Early Cambrian strata of the Himalaya, in which Lesser and Tethyan Himalayan age-equivalent sediment was deposited in a connected basin, where the former received detritus from the South, and the latter from a hitherto unknown source in the North. One possible

  15. Biotic enhancement of weathering, atmospheric oxygen and carbon dioxide in the Neoproterozoic

    NASA Astrophysics Data System (ADS)

    Lenton, Timothy M.; Watson, Andrew J.

    2004-03-01

    It has been suggested that biological colonization of the land surface began in the Neoproterozoic 1000-544 million years ago (Ma). We hypothesize that this colonization involved selective weathering of P from rocks, as well as an amplification of overall weathering rates. We show that two recent models, despite differences in the feedback mechanisms represented, predict that an increase in the weathering flux of P to the ocean would have caused a rise in atmospheric O2 in the Neoproterozoic. This in turn may have provided a necessary condition for the evolution of animals with hard skeletons seen in the 'Cambrian explosion'. Increased weathering of silicate rocks would also have caused a decline in atmospheric CO2, which could have been a causal factor in the Neoproterozoic glaciations.

  16. World Map Showing Surface and Subsurface Distribution, and Lithologic Character of Middle and Late Neoproterozoic Rocks

    USGS Publications Warehouse

    Stewart, John H.

    2007-01-01

    INTRODUCTION The map was prepared to outline the basic information on where Neoproterozoic rocks are present in the World, and of the lithologic character of these rocks. The information provides a better understanding of major Neoproterozoic tectonic subdivisions useful in paleogeographic and plate tectonic reconstructions. The time frame of the map is within the middle and late Neoproterozoic from approximately 870 to 540 Ma and is after widespread Mesoproterozoic Grenville-age collisional events that are considered to have formed the hypothetical supercontinent of Rodinia. Much of the time represented by the map is interpreted to be during the fragmentation of Rodinia. The recognition of Neoproterozoic rocks is commonly difficult because of limited isotopic or paloeontological dating. Thus, some rocks shown on the map could be older or younger than the age indicated. However, at the scale of the map the the problem may be minor. Enough information seems to be available to indicate the general age of the rocks. Many of the successions contain diamictite deposits considered to be glaciogenic and dated as middle or late Neoproterozoic. These deposits thus show a rough correlation of middle and late Neoproterozoic rocks of the world. The map is a Richardson map projection, except for Antarctica which is a polar projection. The map was prepared from about 650 references, shown in the text linked below under 'Sources of Information', used to outline distribution patterns, determine rock types, and provide information on the regional and local geologic framework of the rocks. The focus of the references is on the geologic information needed to prepare the map. Other information, such as plate tectonic reconstructions or paleomagnetic studies is generally not included. The 'Sources of Information' lists references alphabetically for each of 14 regions. In brackets is a code for each area. These codes provide help in locating the specific regions in the references.

  17. Early Neoproterozoic Ocean Chemistry: Fe-S Systematics from the Chuar Group

    NASA Astrophysics Data System (ADS)

    Johnston, D. T.; Poulton, S. W.; Dehler, C. M.; Canfield, D. E.; Knoll, A. H.

    2008-12-01

    Recent work suggests that Fe-rich, Archean-like ocean conditions returned during the Neoproterozoic. This provocative finding raises a number of questions about the triggers for this transition and the geochemical and biological consequences. To better address these questions, we present a high-resolution geochemical record through the early Neoproterozoic Chuar Group. The Chuar Group is composed of more than 1500 meters of gently folded, unmetamorphosed inter-bedded fossiliferous shales and meter scale carbonate- sandstones. Focusing primarily on the shales, Fe-speciation and sulfur isotope data provide the backbone of the study. Fe-speciation data, in particular, allows for the story of Neoproterozoic ocean anoxia to be updated and extended. Interestingly, these data illustrate transitions between Fe-rich and S-rich anoxic conditions, and shed light on how these reversions behave and are initiated. Just as important as the local information gained from the Chuar sediments, these data further elucidate our understanding of the early Neoproterozoic world. Specifically, we gain information about one of the most influential and complex factors in Neoproterozoic geochemistry - the size and speciation of the marine sulfur reservoir. For instance, necessarily low levels of seawater sulfate 1) limit the prominence of sulfate reducing bacteria in remineralization reactions, 2) increase the relative iron efflux from hydrothermal systems, and 3) may have consequences for the marine methane hydrate budget. When paleontological and biomarker records are interpreted in light of these geochemical findings, questions ranging from the abundance and distribution of microfossils, to transitions in dominant primary producers, and potential inhibitors to eukaryotic evolution, are more fully understood. Together, these data contribute to an evolving picture of the Neoproterozoic world.

  18. Estimating duration and intensity of Neoproterozoic snowball glaciations from Ir anomalies.

    PubMed

    Bodiselitsch, Bernd; Koeberl, Christian; Master, Sharad; Reimold, Wolf U

    2005-04-01

    The Neoproterozoic glaciations supposedly ended in a supergreenhouse environment, which led to rapid melting of the ice cover and precipitation of the so-called cap carbonates. If Earth was covered with ice, then extraterrestrial material would have accumulated on and within the ice and precipitated during rapid melting at the end of the glaciation. We found iridium (Ir) anomalies at the base of cap carbonates in three drill cores from the Eastern Congo craton. Our data confirm the presence of extended global Neoproterozoic glaciations and indicate that the duration of the Marinoan glacial episode was at least 3 million, and most likely 12 million, years. PMID:15821088

  19. Gametogenic development and spawning of the freshwater clam, Galatea paradoxa (Born 1778) from the Volta River Estuary, Ghana.

    PubMed

    Adjei-Boateng, D; Wilson, J G

    2013-01-01

    The study focused on the reproductive cycle of Galatea paradoxa (Born 1778), a major species for artisanal fishery in the Volta River estuary, Ghana. Condition indices and histological observation of the gonads revealed that G. paradoxa has a single spawning event between July and October. Gametogenesis started in December progressing steadily to a peak in June-July when spawning began until November when individuals were spent. Condition and gonadal indices showed a clear relationship with the gametogenic stages. PMID:25141603

  20. Geochemical and isotopic composition of Pan-African metabasalts from southwestern Gondwana: Evidence of Cretaceous South Atlantic opening along a Neoproterozoic back-arc

    NASA Astrophysics Data System (ADS)

    Will, Thomas M.; Frimmel, Hartwig E.; Gaucher, Claudio; Bossi, Jorge

    2014-08-01

    A lithogeochemical and Sr-Nd-Pb isotope study of former oceanic crustal rocks from the Cuchilla Dionisio Terrane in the southern Dom Feliciano Belt, Uruguay (La Tuna amphibolites) and metabasites in the Chameis Subterrane of the Marmora Terrane in the Gariep Belt, Namibia/South Africa shows that these rocks are compositionally very similar and probably represent the same unit on opposite sides of the modern South Atlantic. The mafic rocks from both terranes are tholeiitic metabasalts and -andesites and have depleted rare earth element patterns, generally low TiO2 (< 1.5 wt.%), very low Th/Nb ratios and lack negative Nb-Ta anomalies, all features that are typical of ‘normal' mid-ocean ridge basalts (N-MORB) and/or back-arc basin basalts (BABB). In addition, both rock suites have extremely depleted Nd isotope compositions (εNd630 Ma = 6.7-9.4), superchondritic 147Sm/144Nd ratios, and low 206Pb/204Pb and 207Pb/204Pb initial ratios. The 87Sr/86Sr initial ratios of the La Tuna mafic rocks are low, whereas the Chameis metagabbro samples have higher, possibly alteration-related ratios. The geochemical and isotopic signatures are consistent with the formation of both rock suites in the same mature Neoproterozoic back-arc basin (Marmora Basin), supporting conclusions drawn from earlier provenance studies of metasedimentary units from these terranes. Other mafic rocks from the Marmora Terrane are interpreted as ocean island basalts that formed in a within-plate setting. A corollary of the conclusion that the mafic rocks in the Cuchilla Dionisio and Marmora Terranes formed in the same back-arc basin is (1) that the main Pan-African suture between the Río de la Plata Craton and the Kalahari Craton lies to the west of the Dom Feliciano Belt in South America, and (2) that the opening of the modern South Atlantic did not occur along that suture but along the axis of the Neoproterozoic Marmora back-arc basin.

  1. Fe Isotope Composition of Neoproterozoic Post-Glacial "Cap Dolostones"

    NASA Astrophysics Data System (ADS)

    Halverson, G. P.

    2005-12-01

    The largest variations in the Fe isotope composition in the geological record are found in sedimentary rocks, presumably as the result of redox transformations of iron during mineral precipitation, microbial processing, and diagenesis (Johnson et al., Cont. Min. Petrol., 2003). Systematic trends in the variability of the Fe isotope composition of sulfide minerals formed in ancient marine black shales broadly mirror patterns in sulfur isotope data (Δ33S, Δ34S), which are consistent with geological and other geochemical evidence for the progressive oxidation of the earth's surface during the Precambrian (Rouxel et al., Science, 2005). Therefore, the record of the Fe isotope composition of minerals formed in the marine environment appears to be a promising proxy for the redox evolution of the ocean. We have developed a method to extract the marine Fe isotope composition from carbonates in an attempt to establish higher resolution records of changes in marine redox changes than permitted by black shale geochemistry. We have applied this method to the study of ca. 635 Ma iron-rich dolostones, which are found in Neoproterozoic successions worldwide and immediately post-date a purported snowball (Marinoan) glaciation during which time the deep ocean is thought to have become anoxic (Hoffman et al., Science, 1998), allowing its Fe isotopic composition to evolve towards the composition of relatively light (δ57Fe vs. IRMM-14 ~ -0.6‰) hydrothermal iron (Beard et al., Geology, 2003). Fe isotope compositions were measured relative to IRMM-14 in medium-resolution mode on a Neptune MC-ICP-MS with a long-term external (2σ) reproducibility of < 0.04‰/amu. Preliminary data on dolomite samples from Svalbard, northern Namibia and northwest Canada show a range in δ57Fe values from -0.65 to 0.04‰, similar to the range found in siderite and Fe-rich dolomite in ancient BIFs (Johsnon et al., 2003) and to values for the Namibian cap dolostone reported by Leighton et al

  2. Neoproterozoic variations in the C-isotopic composition of seawater: stratigraphic and biogeochemical implications

    NASA Technical Reports Server (NTRS)

    Kaufman, A. J.; Knoll, A. H.

    1995-01-01

    The recent proliferation of stratigraphic studies of delta 13C variation in carbonates and organic C in later Neoproterozoic and basal Cambrian successions (approximately 850-530 Ma) indicates a strong oscillating trend in the C-isotopic composition of surface seawater. Alone, this trend does not adequately characterize discrete intervals in Neoproterozoic time. However, integrated with the vectorial signals provided by fossils and Sr-isotopic variations, C isotope chemostratigraphy facilitates the interbasinal correlation of later Neoproterozoic successions. Results of these studies are evaluated in terms of four stratigraphic intervals: (1) the Precambrian/Cambrian boundary, (2) the post-Varanger terminal Proterozoic, (3) the late Cryogenian, and (4) the early Cryogenian. Where biostratigraphic or radiometric data constrain the age of Neoproterozoic sedimentary sequences, secular variations in C and Sr isotopes can provide a level of stratigraphic resolution exceeding that provided by fossils alone. Isotopic data place strong constraints on the chemical evolution of seawater, linking it to major tectonic and paleoclimatic events. They also provide a biogeochemical framework for the understanding of the initial radiation of macroscopic metazoans, which is associated stratigraphically, and perhaps causally, with a global increase in the burial of organic C and a concomitant rise of atmospheric O2.

  3. Geochronological Constraints on Neoproterozoic Glaciations, the first appearance of Metazoans, and the Cambrian Explosion.

    NASA Astrophysics Data System (ADS)

    Bowring, S.; Condon, D.; Ramezani, J.; Myrow, P.; Landing, E.

    2004-05-01

    Studies of Neoproterozoic climate fluctuations, plate reconstructions, biological evolution and their interrelationships have been hindered by a lack of high-precision geochronological constraints. The correlation and estimates of duration for Neoproterozoic glaciations has relied on physical/chemo-stratigraphy, and thermal subsidence models respectively. New geochronological constraints from Neoproterozoic successions worldwide have sharpened the debate as to the number, synchroneity, and duration of glacial episodes and the relationship, if any, between Metazoan evolution and global glaciation(s). Crucial to the debate are correct interpretation of geochronological data that range from U-Pb zircon studies of intercalated volcanic ash-beds, U-Pb detrital zircon studies, Re-Os from black shales, Rb-Sr from clay-rich rocks, U-Pb and Pb-Pb from carbonates and phosphates, and Lu-Hf from phosphates. Development of a highly resolved Neoproterozoic timescale will require integration and cross-calibration of multiple dating techniques and consideration of what is actually being recorded by each chronometer. A review of available geological and geochronological data indicate that there were at least three and perhaps as many as five periods of Neoproterozoic glacial deposition including rocks from United States (Idaho and Virginia), Newfoundland and the Northwest Territories of Canada, Namibia, and Oman. What must be evaluated is how the paleogeographic distribution of glaciated regions varied with time during the Neoproterozoic. Do Neoproterozoic glacial successions distributed worldwide record a small number of globally synchronous, long-lived glaciations, or numerous diachronous glacial epochs, or a combination of both? At present, the duration of only one glacial deposit, the ca 581 Ma Gaskiers Formation (Newfoundland), is known and it is on the order of 1 Ma, at odds with a long-lived global glaciation predicted by the snowball Earth hypothesis. Other major issues are

  4. Nd isotopes and the provenance of detrital sediments of the Neoproterozoic Brası´lia Belt, central Brazil

    NASA Astrophysics Data System (ADS)

    Pimentel, M. M.; Dardenne, M. A.; Fuck, R. A.; Viana, M. G.; Junges, S. L.; Fischel, D. P.; Seer, H. J.; Dantas, E. L.

    2001-11-01

    .2 Ga, indicating that the original sediments represent products of erosion of the arc itself. Therefore, part of the rock units that have been mapped as Araxá and Ibiá groups can be deeper water equivalents of a passive margin sequence (sediments with Paleoproterozoic model ages). However, another part has been clearly deposited under the influence of an island arc source, most probably in a back-arc basin. The Bambuı´ Group sediments (<0.8 Ga?), at the top of the sequence, also indicate the presence of a young source. TDM model ages vary between ca. 1.4 and 1.9 Ga. However, the distribution pattern of TDM values is more uniform, being intermediate between the Neoproterozoic juvenile source and the Paleoproterozoic continental source area. The Bambuı´ Group is interpreted as a post-inversion sequence, with detrital sediments being mostly derived from erosion of a mountain range in the west, after accretion of the Goiás Magmatic Arc.

  5. The economics of blindness prevention in Upper Volta under the Onchocerciasis Control Program.

    PubMed

    Prescott, N; Prost, A; Le Berre, R

    1984-01-01

    This paper proposes a new approach to the economics of blindness prevention under the Onchocerciasis Control Program in Upper Volta. It differs from previous economic analyses of onchocerciasis control in three important respects. First, it uses empirical data as the basis of an estimate of the epidemiological effectiveness of the intervention. Second, it focuses on the prevention of permanent disability and premature death due to onchocercal blindness as the major health improvement attributable to onchocerciasis control. Third, it emphasizes cost-effectiveness rather than cost-benefit analysis. This limitation is imposed by the difficulty of undertaking a comprehensive assessment of the benefits of onchocerciasis control. In particular, the extent to which control of partial visual impairment and infection without ocular involvement would increase the effective supply of labor, and also the extent to which control would increase the effective supply of land by inducing new settlement in the river valleys, have not been clearly established. The cost-effectiveness approach is limited because it foregoes the opportunity provided by cost-benefit analysis to compare the relative desirability of investing in onchocerciasis control with alternative investments in other sectors. However, it does permit useful judgments to be made about the relative efficiency of allocating scarce resources to onchocerciasis control compared to other possible investments within the health sector. For this purpose, an illustrative comparison is made with estimates of the cost-effectiveness of measles immunization. PMID:6098020

  6. Body condition and gametogenic cycle of Galatea paradoxa (Mollusca: Bivalvia) in the Volta River estuary, Ghana

    NASA Astrophysics Data System (ADS)

    Adjei-Boateng, D.; Wilson, J. G.

    2013-11-01

    The reproductive cycle of Galatea paradoxa which is the basis for an artisanal fishery in the Volta River estuary, Ghana, was studied using condition indices and histological methods from March 2008 to July 2009. The cycle is annual with a single spawning event between June and October. Gametogenesis starts in November progressing steadily to a peak in June-July when spawning begins until October when the animal is spent. The condition indices (shell-free wet weight/total wet weight, ash-free dry weight/shell weight and gonad wet weight/shell weight) showed a clear relationship with the gametogenic stage rising from a minimum at stage (I) start of gametogenesis, to their highest values at stages (IIIA) ripe and (IIIB) start of spawning before declining significantly to stage (IV) spent.It is suggested that condition index may prove a valuable technique in fishery management to recognise the reproductive stages of G. paradoxa as it is less expensive and time consuming than histological techniques in addition to being easier to teach to non-specialists. The data presented in this study provide information on the timing of spawning events for G. paradoxa, which is necessary for developing sustainable management strategies and selection of broodstock for aquaculture.

  7. Report on a preliminary survey by the WHO Bilharziasis Advisory Team in Upper Volta

    PubMed Central

    McMullen, Donald B.; Francotte, Jean

    1962-01-01

    The WHO Bilharziasis Advisory Team made a survey in Upper Volta during May and June 1960. Data available indicate that S. haematobium is widely scattered throughout the country and that about 50% of the population, or more than 1.5 million people, are infected at some time during their lives. The examination of faeces is not a common practice, and it is therefore impossible to estimate the prevalence of S. mansoni and the intestinal helminths. The available evidence indicates, however, that S. mansoni is more prevalent in the country than is generally suspected. The distribution of the known snail habitats and the bilharziasis foci indicate that most of the major watersheds are infested, but that transmission sites may be rather sharply defined. It will be necessary to take this and various seasonal factors into consideration in planning a bilharziasis control programme. An analysis of the various public health problems in the country indicated that a programme of bilharziasis control would not be of practical value unless it was combined with a general attack on filth- and vector-borne diseases, and that it was essential to consider such a programme in conneixon with plans for the development of water and soil resources. PMID:20604120

  8. Siberian Origins of Neoproterozoic to Upper Triassic Rocks of Arctic Alaska

    NASA Astrophysics Data System (ADS)

    Clough, J. G.; Blodgett, R. B.

    2007-12-01

    found in the Canadian Arctic Islands Richly diverse Upper Triassic fauna (halobiid and monotid bivalves, brachiopods) are present in the both the Shublik Formation and Otuk Group. These show closer affinities with NE Siberia rather than to western or northern North America, suggesting close spatial relationships between Siberia and Arctic Alaska at least until Late Triassic time. Sedimentary provenance studies in eastern Brooks Range Precambrian rocks indicate age ranges that are dissimilar to Proterozoic detrital-zircon ages from clastic rocks of the northern Canadian Cordillera and Canadian Arctic Islands where a detrital source within the Grenville orogen is indicated. Paleocurrent directions for the Neoproterozoic Katakturuk Dolomite in the northeast Brooks Range and similar-age units in the adjacent Victoria Island and Amundsen Basin are in approximately 100 degree opposition for a counterclockwise rotational- restored Arctic Alaska. Upper Devonian clastics of northern Alaska are in 180 degree opposition to coeval units in the Canadian Arctic Islands when the Arctic Alaska plate is restored in the rotational model. Therefore, based on paleobiogeography, sediment provenance, stratigraphy and sedimentology, tectonic models for the opening of the Canada Basin must take into account that Triassic and older rocks in Arctic Alaska have Siberian origins or were deposited proximal to Siberia.

  9. Neoproterozoic active continental margin in the southeastern Yangtze Block of South China: Evidence from the ca. 830-810 Ma sedimentary strata

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Zhou, Mei-Fu; Zhao, Jun-Hong; Pandit, Manoj K.; Zheng, Jian-Ping; Liu, Ze-Rui

    2016-08-01

    The Jiangnan Fold Belt in the South China Block has been traditionally assumed to be Mesoproterozoic in age and related to the global Grenville orogeny. Sedimentary successions in the Jiangnan Fold Belt archive direct record of tectonic evolution; however, they have not yet been evaluated properly. The Lushan massif, comprising Kangwanggu and Xingzi groups, is the major basement complex in the Jiangnan Belt. Regional correlation of these two groups is poorly constrained, such as with the Shuangqiaoshan group, and thus their role in the regional tectonic evolution is not clear. Detrital zircon U-Pb ages suggest that the Xingzi and Kangwanggu groups were deposited at 820-810 and ca. 830 Ma, respectively. They are composed of dominantly felsic to intermediate volcanic detritus, as indicated by the relatively high Th/Cr (0.24-0.06) ratios and radiogenic Nd isotopes (εNd(t) values = + 1.5 to - 2.9) of the sedimentary rocks. An overwhelming abundance of Neoproterozoic (ca. 860-810 Ma) angular, detrital zircon grains in both the groups indicates derivation chiefly from locally distributed syn-sedimentary igneous rocks. A predominance of zircons with ages close to the time of deposition implies a convergent plate margin setting for Kangwanggu and Xingzi groups. Geochemical signatures, such as La-Th-Co and Th-Sc-Zr/10 plots for Xingzi and Kangwanggu sedimentary rocks also underline tectonically active settings, consistent with the arc affinity of the associated mafic and felsic volcanic rocks. In contrast to the dominant Neoproterozoic detritus in the Kangwanggu sandstone, argillaceous rocks of the Xingzi group received additional input of pre-Neoproterozoic detritus. Moreover, the Xingzi argillaceous rocks have εNd(t) values (+ 0.9 to - 2.9) slightly lower than those of the Kangwanggu sandstones (+ 1.5 to 0.0), indicating contribution from mature crustal materials exposed during progressive uplift of continental basement during orogenesis. These features suggest the

  10. The evolution of ocular onchocerciasis in the Volta River Basin Area over a period of five years of vector control.

    PubMed

    Dadzie, K Y; Rolland, A; Thylefors, B

    1984-03-01

    The results of an ophthalmological evaluation conducted in seven West African savannah villages before and after 5 years of vector control, were analysed to determine the effect of an interrupted or greatly reduced transmission of Onchocerca volvulus on the evolution of ocular onchocerciasis. Cross-sectional data showed a significant reduction of the prevalence of ocular onchocerciasis in five of the villages, and the rates of irreversible ocular lesions and blindness were generally lower after 5 years of vector control. A longitudinal study of a defined population showed that the ocular status of most patients with ocular onchocerciasis remained stable or improved over the 5 year period, particularly in lightly infected cases. The evolution of ocular onchocerciasis showed a deterioration in a minor proportion, restricted to cases of already existing severe lesions, resulting in blindness. A comparison of ophthalmic data from adjacent areas without vector control, indicates that a five year period of vector control may reduce the risk of developing eye lesions or blindness due to onchocerciasis by 50%. PMID:6608814

  11. Comparing and contrasting observed adaptations in three deltas: the Ganges-Meghna-Brahmaputra, Mahanadi and Volta

    NASA Astrophysics Data System (ADS)

    Nicholls, R. J.; Suckall, N.; Mensah, A.; Mondal, S.; Dey, S.; Hazra, S.

    2015-12-01

    In low and middle-income countries, many deltaic communities directly depend on the natural environment for income and well-being. Current environmental concerns that threaten deltaic communities, such as increasing salinity, sedimentation, erosion and subsidence are likely to be exacerbated by climate change and variability, for example sea-level rise, increased storminess and rising temperatures. Such changes, along with other social and environmental stressors, mean that communities must adapt. This paper outlines findings of a systematic review of the peer-reviewed and grey literature that examines observed adaptations in three deltas of differing sizes in various geographical contexts: the Ganges-Meghna-Brahmaputra in India and Bangladesh, the Mahanadi in India, and the Volta in Ghana. It compares and contrasts various elements of observed adaptations, including who is driving the adaptation, the beneficiaries, barriers to participation and evidence for maladaptation. The predominant drivers of adaptation vary from government (at state level in India and national level in Bangladesh) and NGOs (in Ghana). Autonomous adaptations are not widely reported in the literature from any of the deltas. In all three deltas there is a focus on supporting adaptation in farming rather than fishing; despite the fact that fisheries contribute to local food security as well as national economies. Lack of access to financial, natural, physical and human capital are common barriers to adaptation in all three deltas. Additionally the Indian literature in particular highlights the lack of coordination between different government departments, coupled with an excessively top-down (state-driven) approach to adaptation. Maladaptation is most commonly reported in the literature from Bangladesh, for example, loss of employment of inland fishermen in embanked areas. The paper concludes by highlighting some of the implications of these findings for adaptation policy in deltas.

  12. Neoproterozoic-Cambrian stratigraphic framework of the Anti-Atlas and Ouzellagh promontory (High Atlas), Morocco

    NASA Astrophysics Data System (ADS)

    Álvaro, J. Javier; Benziane, Fouad; Thomas, Robert; Walsh, Gregory J.; Yazidi, Abdelaziz

    2014-10-01

    In the last two decades, great progress has been made in the geochronological, chrono- and chemostratigraphic control of the Neoproterozoic and Cambrian from the Anti-Atlas Ranges and the Ouzellagh promontory (High Atlas). As a result, the Neoproterozoic is lithostratigraphically subdivided into: (i) the Lkest-Taghdout Group (broadly interpreted at c. 800-690 Ma) representative of rift-to-passive margin conditions on the northern West African craton; (ii) the Iriri (c. 760-740 Ma), Bou Azzer (c. 762-697 Ma) and Saghro (c. 760?-610 Ma) groups, the overlying Anezi, Bou Salda, Dadès and Tiddiline formations localized in fault-grabens, and the Ouarzazate Supergroup (c. 615-548 Ma), which form a succession of volcanosedimentary complexes recording the onset of the Pan-African orogeny and its aftermath; and (iii) the Taroudant (the Ediacaran-Cambrian boundary lying in the Tifnout Member of the Adoudou Formation), Tata, Feijas Internes and Tabanite groups that have recorded development of the late Ediacaran-Cambrian Atlas Rift. Recent discussions of Moroccan strata to select new global GSSPs by the International Subcommissions on Ediacaran and Cambrian Stratigraphy have raised the stratigraphic interest in this region. A revised and updated stratigraphic framework is proposed here to assist the tasks of both subcommissions and to fuel future discussions focused on different geological aspects of the Neoproterozoic-Cambrian time span.

  13. Neoproterozoic Land Colonisation, Rising Oxygen, Global Cooling and the Cambrian Explosion

    NASA Astrophysics Data System (ADS)

    Lenton, T. M.; Watson, A. J.

    2004-12-01

    The Neoproterozoic (1000-542 Ma BP) was a time of severe glaciations and a major transition from microscopic to macroscopic life forms. We develop the hypothesis that a rise in atmospheric oxygen in the Neoproterozoic was driven by the biological colonization of the land surface. If early forms of photosynthetic land life selectively weathered continental rock in order to extract nutrients, this would have led to an increase in the flux of biologically available phosphorus to the ocean. We show that recent models for coupled biogeochemical cycles, despite differences in the feedback mechanisms represented, predict this would lead to a rise in atmospheric oxygen concentration, consistent with biological and geochemical evidence. Increased weathering of silicate rocks would also have caused a decline in atmospheric carbon dioxide, which could have been a causal factor in the Neoproterozoic glaciations. A rise in oxygen may have provided a necessary condition for the evolution of animals with hard skeletons seen in the Cambrian explosion. Furthermore, an increase in phosphorus supply to the ocean may have driven an increase in the phosphorus content of marine primary producers. This would have represented an increase in food quality for grazing animals, which have a high phosphorus requirement, and may thus have removed a further limitation on their evolutionary radiation.

  14. Biotic enhancement of weathering, atmospheric oxygen and carbon dioxide in the Neoproterozoic

    NASA Astrophysics Data System (ADS)

    Watson, A.; Lenton, T.

    2003-04-01

    The Neoproterozoic (1000-544Ma BP) was a time of severe glaciations and a major transition from microscopic to macroscopic life forms. Here we develop the hypothesis that a rise in atmospheric oxygen in the Neoproterozoic was driven by the biological colonization of the land surface. If early forms of photosynthetic land life selectively weathered continental rock in order to extract nutrients, this would have led to an increase in the flux of biologically available phosphorus to the ocean. We show that recent models for coupled biogeochemical cycles, despite differences in the feedback mechanisms represented, predict this would lead to a rise in atmospheric oxygen concentration, consistent with biological and geochemical evidence. A rise in oxygen may in turn have provided a necessary condition for the evolution of animals with hard skeletons seen in the Cambrian explosion. Increased weathering of silicate rocks would also have caused a decline in atmospheric carbon dioxide, which could have been a causal factor in the Neoproterozoic glaciations.

  15. Molar tooth structures in calcareous nodules, early Neoproterozoic Burovaya Formation, Turukhansk region, Siberia

    NASA Astrophysics Data System (ADS)

    Pope, Michael C.; Bartley, Julie K.; Knoll, Andrew H.; Petrov, Peter Yu.

    2003-05-01

    Molar tooth structures are abundant in large (1-2 m diameter) carbonate nodules within fine-grained, subtidal carbonates of the early Neoproterozoic (lower Upper Riphean) Burovaya Formation along the Sukhaya Tunguska River, Turukhansk Uplift, northwestern Siberia. Although molar tooth structures are regionally abundant in this unit, here they occur only within the nodules. Stable isotopic compositions of molar-tooth-filling dolomicrospar cements and of thinly bedded dolomicrite within and surrounding the nodules are indistinguishable from one another. The carbon isotopic compositions (mean δ13C=+2.8‰ PDB±0.4) reflect mean average oceanic surface water composition during their formation; the light oxygen isotopic compositions (mean δ18O=-6.4‰ PDB±2.2) are generally similar to those of other little-altered Meso- to Neoproterozoic limestones and dolostones. These molar tooth structures have no features that would support a tectonic origin; they more likely formed through bacterial processes. Carbonate cement filling of these voids occurred soon after their formation, but the mechanism responsible for this carbonate precipitation is currently uncertain. Local restriction of molar tooth structures to early diagenetic nodules suggests that penecontemporaneous lithification was required for the formation, or at least preservation, of these widespread Mesoproterozoic to Neoproterozoic features.

  16. Evidence from detrital zircons for recycling of Mesoproterozoic and Neoproterozoic crust recorded in Paleozoic and Mesozoic sandstones of southern Libya

    NASA Astrophysics Data System (ADS)

    Meinhold, Guido; Morton, Andrew C.; Fanning, C. Mark; Frei, Dirk; Howard, James P.; Phillips, Richard J.; Strogen, Dominic; Whitham, Andrew G.

    2011-12-01

    The geodynamic history of the Precambrian basement in central North Africa as well as the age and provenance of its sedimentary cover sequence are still poorly constrained. Here we present first detrital zircon ages (obtained by LA-SF-ICP-MS and SHRIMP) from Paleozoic and Mesozoic sandstones of the eastern Murzuq Basin, southern Libya, which unconformably overlie the Saharan Metacraton. Establishing the age and provenance of these sandstones has important implications for our understanding of the evolution of northern Gondwana during the Paleozoic, especially for reconstructions of paleo-source areas and transport paths. Detrital zircons from the sandstones show mainly early Paleozoic to Neoarchean ages with four main age populations, at 2750-2500 Ma (8%), 2200-1750 Ma (16%), 1060-920 Ma (18%), and 720-530 Ma (39%). About 13% of all concordant grains yield ages of 1600-1000 Ma. In addition, there are 9 zircon grains (0.7% of all concordant grains) with ages of 3600-2800 Ma. The presence of a high number of ca. 1 Ga zircons is enigmatic and their origin is controversial. Besides direct sourcing from ca. 1 Ga igneous rocks in eastern Chad and ca. 1 Ga igneous rocks along the southeastern margins of the Congo and Tanzania cratons, recycling of Neoproterozoic sediments containing ca. 1 Ga zircons is another alternative hypothesis to explain the presence of ca. 1 Ga zircons in the Paleozoic sedimentary sequence of central North Africa. The ubiquitous occurrence of ca. 1 Ga zircons in Paleozoic sediments of southern Libya provides insights into the correlation and paleotectonic arrangement of Gondwana-derived terranes, present, for example, in the eastern Mediterranean and in southwestern Europe. Current paleotectonic models of dextral terrane transport along the northern Gondwana margin during the early Paleozoic may need to be revised.

  17. Origin of Neoproterozoic ophiolitic peridotites in south Eastern Desert, Egypt, constrained from primary mantle mineral chemistry

    NASA Astrophysics Data System (ADS)

    Khedr, Mohamed Zaki; Arai, Shoji

    2013-10-01

    The ophiolitic peridotites in the Wadi Arais area, south Eastern Desert of Egypt, represent a part of Neoproterozoic ophiolites of the Arabian-Nubian Shield (ANS). We found relics of fresh dunites enveloped by serpentinites that show abundances of bastite after orthopyroxene, reflecting harzburgite protoliths. The bulk-rock chemistry confirmed the harzburgites as the main protoliths. The primary mantle minerals such as orthopyroxene, olivine and chromian spinel in Arais serpentinites are still preserved. The orthopyroxene has high Mg# [=Mg/(Mg + Fe2+)], ~0.923 on average. It shows intra-grain chemical homogeneity and contains, on average, 2.28 wt.% A12O3, 0.88 wt.% Cr2O3 and 0.53 wt.% CaO, similar to primary orthopyroxenes in modern forearc peridotites. The olivine in harzburgites has lower Fo (93-94.5) than that in dunites (Fo94.3-Fo95.9). The Arais olivine is similar in NiO (0.47 wt.% on average) and MnO (0.08 wt.% on average) contents to the mantle olivine in primary peridotites. This olivine is high in Fo content, similar to Mg-rich olivines in ANS ophiolitic harzburgites, because of its residual origin. The chromian spinel, found in harzburgites, shows wide ranges of Cr#s [=Cr/(Cr + Al)], 0.46-0.81 and Mg#s, 0.34-0.67. The chromian spinel in dunites shows an intra-grain chemical homogeneity with high Cr#s (0.82-0.86). The chromian spinels in Arais peridotites are low in TiO2, 0.05 wt.% and YFe [= Fe3+/(Cr + Al + Fe3+)], ~0.06 on average. They are similar in chemistry to spinels in forearc peridotites. Their compositions associated with olivine’s Fo suggest that the harzburgites are refractory residues after high-degree partial melting (mainly ~25-30 % partial melting) and dunites are more depleted, similar to highly refractory peridotites recovered from forearcs. This is in accordance with the partial melting (>20 % melt) obtained by the whole-rock Al2O3 composition. The Arais peridotites have been possibly formed in a sub-arc setting (mantle wedge), where

  18. Sedimentary genesis and lithostratigraphy of Neoproterozoic megabreccia from Mufulira, Copperbelt of Zambia

    NASA Astrophysics Data System (ADS)

    Wendorff, Marek

    2005-07-01

    The Lufilian arc is an orogenic belt in central Africa that extends between Zambia and the Democratic Republic of Congo (DRC) and deforms the Neoproterozoic-Lower Palaeozoic metasedimentary succession of the Katanga Supergroup. The arc contains thick bodies of fragmental rocks that include blocks reaching several kilometres in size. Some megablocks contain Cu and Cu-Co-mineralised Katangan strata. These coarse clastic rocks, called the Katangan megabreccias, have traditionally been interpreted in the DRC as tectonic breccias formed during Lufilian orogenesis due to friction underneath Katangan nappes. In mid-90th, several occurrences in Zambia have been interpreted in the same manner. Prominent among them is an occurrence at Mufulira, considered by previous workers as a ≈1000 m thick tectonic friction breccia containing a Cu-Co-mineralised megablock. This paper presents new results pertaining to the lower stratigraphic interval of the Katanga Supergroup at Mufulira and represented by the Roan Group and the succeeding Mwashya Subgroup of the Guba Group. The interval interpreted in the past as tectonic Roan megabreccia appears to be an almost intact sedimentary succession, the lower part of which consists of Roan Group carbonate rocks with siliciclastic intercalations containing several interbeds of matrix-supported conglomerate. A Cu-Co-mineralised interval is not an allochthonous block but a part of the stratigraphic succession underlain and overlain by conglomerate beds, which were considered in the past as tectonic friction breccias. The overlying megabreccia is a syn-rift sedimentary olistostrome succession that rests upon the Roan strata with a subtle local unconformity. The olistostrome succession consists of three complexes typified by matrix-supported debris-flow conglomerates with Roan clasts. Some of the conglomerate beds pass upwards to normally graded turbidite layers and are accompanied by solitary slump beds. The three conglomeratic assemblages are

  19. Epidemiology of human Schistosoma haematobium infection around Volta Lake, Ghana, 1973-75

    PubMed Central

    Scott, D.; Senker, K.; England, E. C.

    1982-01-01

    There was a dramatic rise in the prevalence of urinary schistosomiasis around Volta Lake within a year of its full impoundment in 1968. Research was undertaken to investigate the epidemiology of the disease in preparation for a control programme. The interplay of three factors—age, sex, and ethnic affiliation—largely defined the demographic patterns of the prevalence and the intensity of infection. Both of these increased in young children up to a peak at age 10-14 years, and then declined, the intensity of infection more rapidly than the prevalence. The prevalence and intensity of infection were both greater in males than females (above ages 15-24 years and 5-9 years, respectively), and differences between the two main ethnic groups were related to differences in their lake-related activities. Differences between the patterns of prevalence and intensity of infection are attributed to the greater sensitivity of the latter measurement in indicating changes in the level of transmission. Practical difficulties were encountered in obtaining a precise measurement of incidence, the most important being the considerable degree of population movement. A field cohort study showed a seasonality of transmission, greatest between January and April, during the period of high level of the lake and in the early part of the draw-down. Research on the intermediate snail host (Bulinus truncatus rohlfsi) and lakeside ecology established the focality of transmission at human water-contact sites serving the shore-line communities and, in conjunction with parasitological surveys, its seasonality: variations in ecology that accompanied the annual rise and fall of the lake led to high levels of transmission when the water level was high and lower levels during the draw-down. The geographical distribution of the infection was also affected by differences in ecology, specifically by variations in the distribution and abundance of the aquatic weed Ceratophyllum demersum. A non

  20. Hydrochemical analysis of groundwater using multivariate statistical methods - The Volta region, Ghana

    USGS Publications Warehouse

    Banoeng-Yakubo, B.; Yidana, S.M.; Nti, E.

    2009-01-01

    Q and R-mode multivariate statistical analyses were applied to groundwater chemical data from boreholes and wells in the northern section of the Volta region Ghana. The objective was to determine the processes that affect the hydrochemistry and the variation of these processes in space among the three main geological terrains: the Buem formation, Voltaian System and the Togo series that underlie the area. The analyses revealed three zones in the groundwater flow system: recharge, intermediate and discharge regions. All three zones are clearly different with respect to all the major chemical parameters, with concentrations increasing from the perceived recharge areas through the intermediate regions to the discharge areas. R-mode HCA and factor analysis (using varimax rotation and Kaiser Criterion) were then applied to determine the significant sources of variation in the hydrochemistry. This study finds that groundwater hydrochemistry in the area is controlled by the weathering of silicate and carbonate minerals, as well as the chemistry of infiltrating precipitation. This study finds that the ??D and ??18O data from the area fall along the Global Meteoric Water Line (GMWL). An equation of regression derived for the relationship between ??D and ??18O bears very close semblance to the equation which describes the GMWL. On the basis of this, groundwater in the study area is probably meteoric and fresh. The apparently low salinities and sodicities of the groundwater seem to support this interpretation. The suitability of groundwater for domestic and irrigation purposes is related to its source, which determines its constitution. A plot of the sodium adsorption ratio (SAR) and salinity (EC) data on a semilog axis, suggests that groundwater serves good irrigation quality in the area. Sixty percent (60%), 20% and 20% of the 67 data points used in this study fall within the medium salinity - low sodicity (C2-S1), low salinity -low sodicity (C1-S1) and high salinity - low

  1. Implications for the Neoproterozoic Biological and Climatic History from Dating of the Doushantuo Phosphorites, S. China

    NASA Astrophysics Data System (ADS)

    Barfod, G. H.; Albarede, F.; Knoll, A. H.; Xiao, S.; Frei, R.; Baker, J.

    2002-12-01

    Models such as "Snowball Earth" suggest a link between Neoproterozoic glaciation events and the animal diversifications that preceded the Cambrian explosion. To evaluate such hypotheses, it is critical to resolve the precise chronology of the Neoproterozoic. As of now, ages of many Neoproterozoic sedimentary successions are only weakly constrained by bio- and chemostratigraphical correlation to successions that contain dated ash layers. Furthermore, attempts to radiometrically date sedimentary successions have had limited success. Pb-Pb and Lu-Hf dating of phosphates yield consistent ages close to 600 Ma for the Doushantuo phosphorites, South China. These age constraints are consistent with a depositional age estimate of 580 Ma +/- 20 Ma based on C-isotopic and biostratigraphic correlations (Knoll and Xiao, 1999, Acta Micropalaeontol. 16). The dates are however significantly younger than earlier reported Rb-Sr and Sm-Nd ages (610-700 Ma) for the Doushantuo sediments, which have been ascribed to the influence from detrital clay on the measured isotope compositions. The Lu-Hf and Pb-Pb ages indicate that the exquisitely preserved animal remains found in the Doushantuo Formation predate diverse Ediacaran fossil assemblages and thus represent the earliest animal ancestry assemblage known. The Doushantuo formation lies directly above the Nantuo Tillite deposits, which is generally correlated with the "Marinoan" glaciation - the younger of the two major Neoproterozoic ice ages. Age constraints for "Marinoan" glaciogenic deposits only exist in Newfoundland and Massachusetts, where radiometric dating constrain the glaciation to be younger than 595.5 +/- 2 Ma. Compared to this date, the Pb-Pb age of 599.3 +/- 4.2 Ma for the Doushantuo phosphorites indicates that the Nantuo glaciation predates the glaciation recorded in Eastern North America and therefore support the occurrence of a distinct post-Marinoan glaciation. The combination of Pb-Pb and Lu-Hf dating applied to

  2. Studies on nodules and adult Onchocerca volvulus during a nodulectomy trial in hyperendemic villages in Liberia and Upper Volta. I. Palpable and impalpable onchocercomata.

    PubMed

    Albiez, E J

    1983-03-01

    In hyperendemic onchocerciasis areas of West Africa nodulectomy trials were performed. 163 nodule carriers from four villages in the Liberian rain-forest and 52 nodule carriers from a savanna village in Upper Volta were operated on. During the surveys in the villages in Liberia and Upper Volta, an average of three and five nodules respectively per patient were palpated. Before each operation a further palpation was done and two more nodules per patient from both countries were found. The nodulectomies revealed 75% more nodules in the Liberian patients and 53% more in the patients from Upper Volta than were palpated immediately before. Half of these additional subcutaneous nodules extirpated in Liberians were superficially located, the other half deeper and impalpable through the skin. In the patients from Upper Volta two thirds of the additional nodules were seated in the depth of the subcutis. In both countries an average of three deep subcutaneous nodules per patient were found and this was equivalent to 20% of all extirpated onchocercomata. Most of these deep subcutaneous nodules were at those sites where most of the superficial nodules were located. PMID:6682581

  3. Organic carbon cycling as the keystone of Neoproterozoic climate evolution (Invited)

    NASA Astrophysics Data System (ADS)

    Pierrehumbert, R.

    2009-12-01

    Snowball glaciations are the most charismatic feature of the Neoproterozoic, but the central problem of Neoproterozoic climate evolution is the operation of the carbon cycle, as evidenced in the return of extreme 13C fluctuations after nearly a billion years of quiescence. A key organizing principle for the Neoproterozoic is the existence of a massive hypothetical organic carbon pool in the ocean, which is oxidized by the end of the Neoproterozoic (as laid out by Fike, et al. 2006 ). The carbon cycle couples to climate through its influence on atmospheric greenhouse gas content -- notably CO2 and CH4; accumulation of atmospheric O2 feeds back on this through atmospheric and oceanic chemistry. Evolution of oxygenic photosynthesis unquestionably occurred long before the dawn of the Neoproterozoic, so the Neoproterozoic climate and carbon turmoil is a product of the organic carbon storage dynamics rather than gross biological innovation. In this talk I will discuss how certain key components of the physical and geochemical system operate, though a comprehensive model accounting for all crucial aspects of the geological record is still lacking. Conversion of CO2 to O2 by photosynthesis and carbon burial, converts a greenhouse gas to a non-greenhouse gas,cooling the climate. Conversely, oxidation of an organic carbon pool either through respiration or sulfate reduction, releases CO2 and acts as a warming influence,also leading to a negative carbonate 13C excursion, as probably happened during the Shuram. If the Marinoan excursion has a similar mechanism we face the question of how such an event could initiate a glaciation, whereas the much stronger Shuram excursion did not. (The Gaskiers glaciation came long after the Shuram , and was not a Snowball). I will discuss how the climate response depends on the time scale of the exchange, with emphasis on buffering due to the response of silicate weathering. Insofar as the organic carbon pool existed at all, the key question

  4. Neoproterozoic fragmentation of the Scottish Sector of Laurentia - an ancient analogue for the Iberian and UK/Irish ocean-continent transition zones

    NASA Astrophysics Data System (ADS)

    Leslie, G.; Krabbendam, M.

    2009-04-01

    The Neoproterozoic Dalradian Supergroup of Scotland and Ireland is intensively deformed and metamorphosed by mid-Ordovician arc-accretion (c. 460 Ma) during the Caledonian Orogeny. Emplacement of an extensive suite of Siluro-Devonian Caledonian granitoids further complicates reading the sedimentary record. Nevertheless we can determine a history of stretching and break-up affecting the Neoproterozoic supercontinent of Rodinia and leading to creation of the Iapetus Ocean. Three key intervals of late-Neoproterozoic sediment accumulation are recognised - new geological mapping, isotopic datasets (Sr, O and C, U/Pb zircon, Sm/Nd WR), and sequence stratigraphical approaches are refining constraints on the lithostratigraphical architecture and basin evolution of the Dalradian Supergroup. Thick siliciclastic deposits accumulated (pre-800 Ma?) during an early stretching phase (distributed high angle faulting) that led to crustal thinning (low angle shearing). Three major limestone - pelite - quartzite depositional cycles succeeded these earlier siliciclastic deposits, recording episodic subsidence in an intracratonic but largely marine environment; the second cycle overlaps the late Precambrian (Cryogenian) glaciation and concludes with the distinctive Marinoan tillite succession (c. 635Ma). The last of the three cycles is terminated, in some parts of the Dalradian, by deposition of serpentinitic muds and conglomerates and volcaniclastic sediments; pods and lenses of both massive and serpentinised ultramafic rock also interrupt the sedimentary record at this level (thus possibly indicating mantle exhumation). In other areas, a major part of the ‘type' Dalradian succession is absent and we now recognise a major overstep unconformity at this level. From this level onwards across the Dalradian, rapid foundering of the margin, and the transition from rift- to drift-dominated processes, resulted in an overstepping accumulation of laterally and vertically variable

  5. Coupled Changes in Sulfur and Carbon Isotopes Preceding the Sturtian Glaciation of the Neoproterozoic

    NASA Astrophysics Data System (ADS)

    Gouldey, J.; Hurtgen, M.

    2014-12-01

    The relationship between the carbon and sulfur cycles in the Neoproterozoic has proven to be complex. Unusually high δ13Ccarbonate persists throughout this period, however large negative excursions precede both the Sturtian (~710 Ma) and the Marinoan (635 Ma) glaciations, the mechanisms of which are still debated. Previous data shows that during the interglacial interval, sulfate concentrations were very low and abnormally enriched δ34Spyrite values inversely correlate with shifts in δ13Ccarbonate. However, very little carbonate-associated sulfate (CAS) could be extracted from these sections. To better understand the relationship between the global carbon and sulfur cycles during this tumultuous time, high-resolution coupled records of δ13Ccarbonate and δ34Ssulfate are needed. Here we present paired δ34Ssulfate and δ34Spyrite data from carbonates of the Coates Lake Group (Mackenzie Mountains, Canada), which represent deposition preceding the Sturtian glaciation, to further explore the connection between the Neoproterozoic sulfur and carbon cycles, and to gain insight into the possible mechanisms driving major perturbations in the carbon isotope record. Leading into the glaciation, δ13Ccarbonate increases from -9.5‰ to 8‰ over approximately 200 meters of section, then abruptly drops to ~2‰ over 30 meters. Both sulfate and pyrite isotopes track these changes, indicating that as organic carbon burial is steadily increasing and driving δ13Ccarbonate more positive, pyrite burial is increasing as well. Δ34S decreases as δ13Ccarbonate and δ34S increase, providing further evidence that more organic carbon and pyrite are being buried, leading to a decrease in oceanic sulfate concentrations. Δ34S then increases as δ13Ccarbonate decreases, indicating a positive flux to the sulfate reservoir prior to the Sturtian glaciation. This relationship between carbon and sulfur differs significantly from what is seen during the interglacial interval, and represents

  6. Molecular Fossils for Understanding Biodiversity During the Neoproterozoic-Cambrian Transition in China

    NASA Astrophysics Data System (ADS)

    Pi, Y.; Tuo, J.; McFadden, K.; Xiao, S.; Zhang, C. L.

    2005-12-01

    Neoproterozoic-Cambrian rocks in South China contain an extraordinary fossil record, including exceptionally well preserved animal embryos, acritarchs, and multi-cellular algae. The goal of this study was to evaluate the microbial diversity associated with these remarkably preserved fossil assemblages at the Neoproterozoic-Cambrian transition. Rock samples of 520-632 Ma in age were collected in the Yangtze Gorges area and southern Anhui Province, China. Samples were powdered and extracted for organic biomarkers. The content of bitumen A accounted for 4-16% of the rock material and most of it (49-79%) was asphaltenes. Saturated and aromatic hydrocarbons accounted for 2-6% and 1-3%, respectively. Analysis using GC-MS indicated the predominance of n-alkanes and less abundant isoprenoid alkanes in the saturated fractions. The n-alkanes were characterized by homologues dominated by C15-C17, which is consistent with the result of high thermal-evolution (Brocks et al., 2003. GCA 67:4321-4335). Hopanoids were present in less abundance and ranged from C29 to C32. A smaller amount of heavy-molecular-weight n-alkanes (C23-C39) was also detected, which indicated a source of high plants and must be contamination from younger organic matter. Still, patterns of variation can be detected among these samples. For example, the ratio of pristane to phytane was all greater than 1.0 except for one sample (JLW9.3) from Yangtze Gorges area. The results indicate that sample JLW9.3 might have been deposited in a reducing environment whereas the other samples might have been formed in relatively oxidative environments. The overall results, however, suggest that rock samples from the Neoproterozoic-Cambrian transition in China have gone through significant metamorphism; thus, understanding of microbial communities using molecular biomarkers in such altered rocks needs to be cautiously executed.

  7. Pressure-temperature evolution of Neoproterozoic metamorphism in the Welayati Formation (Kabul Block), Afghanistan

    NASA Astrophysics Data System (ADS)

    Collett, Stephen; Faryad, Shah Wali

    2015-11-01

    The Welayati Formation, consisting of alternating layers of mica-schist and quartzite with lenses of amphibolite, unconformably overlies the Neoarchean Sherdarwaza Formation of the Kabul Block that underwent Paleoproterozoic granulite-facies and Neoproterozoic amphibolite-facies metamorphic events. To analyze metamorphic history of the Welayati Formation and its relations to the underlying Sherdarwaza Formation, petrographic study and pressure-temperature (P-T) pseudosection modeling were applied to staurolite- and kyanite-bearing mica-schists, which crop out to the south of Kabul City. Prograde metamorphism, identified by inclusion trails and chemical zonation in garnet from the micaschists indicates that the rocks underwent burial from around 6.2 kbar at 525 °C to maximum pressure conditions of around 9.5 kbar at temperatures of around 650 °C. Decompression from peak pressures under isothermal or moderate heating conditions are indicated by formation of biotite and plagioclase porphyroblasts which cross-cut and overgrow the dominant foliation. The lack of sillimanite and/or andalusite suggests that cooling and further decompression occurred in the kyanite stability field. The results of this study indicate a single amphibolite-facies metamorphism that based on P-T conditions and age dating correlates well with the Neoproterozoic metamorphism in the underlying Sherdarwaza Formation. The rocks lack any paragenetic evidence for a preceding granulite-facies overprint or subsequent Paleozoic metamorphism. Owing to the position of the Kabul Block, within the India-Eurasia collision zone, partial replacement of the amphibolite-facies minerals in the micaschist could, in addition to retrogression of the Neoproterozoic metamorphism, relate to deformation associated with the Alpine orogeny.

  8. Co-evolution of Eukaryotes and Ocean and Atmosphere Oxygenation in the Neoproterozoic and Paleozoic Eras

    NASA Astrophysics Data System (ADS)

    Lenton, T. M.; Daines, S. J.; Mills, B.; Boyle, R. A.

    2014-12-01

    The nature, timing and cause(s) of the Earth's second oxygenation event are widely debated. It has been argued that there was a single pronounced rise in atmospheric oxygen toward present levels in the Late Neoproterozoic, which in turn triggered the evolution of animals. Here we suggest a more complex co-evolutionary scenario, with fluctuations in ocean and atmosphere oxygenation in the Late Neoproterozoic and Early Paleozoic caused partly by the evolution of animals, followed by a pronounced rise of atmospheric oxygen to present levels later in the Paleozoic caused by the rise of land plants. Current geochemical evidence suggests some parts of the deep oceans became oxygenated during the Ediacaran, but there was subsequent de-oxygenation of the ocean during the Cambrian that may have persisted into the Ordovician. Only later in the Paleozoic is there evidence for widespread oxygenation of the deep ocean, together with charcoal indicating atmospheric oxygen had approached present levels. The limited Neoproterozoic oxygenation of the ocean could be explained by the evolution of filter-feeding sponges removing oxygen demand from the water column and encouraging a shift from cyanobacteria to faster-sinking eukaryotic algae, which transferred oxygen demand to greater depths and into sediments. The resulting oxygenation of shelf bottom waters would have increased phosphorus removal from the ocean thus lowering global productivity and oxygen demand in a positive feedback loop encouraging ocean oxygenation [1]. The subsequent Cambrian de-oxygenation of the ocean could be explained by the evolution of bioturbating animals oxygenating the sediments and thus lowering the C/P burial ratio of organic matter, reducing organic carbon burial and lowering atmospheric oxygen [2]. The later rise of land plants, selectively weathering phosphorus from continental rocks and producing recalcitrant high C/P biomass, increased organic carbon burial and atmospheric oxygen, finally

  9. Late neoproterozoic igneous complexes of the western Baikal-Muya Belt: Formation stages

    NASA Astrophysics Data System (ADS)

    Fedotova, A. A.; Razumovskiy, A. A.; Khain, E. V.; Anosova, M. O.; Orlova, A. V.

    2014-07-01

    The paper presents new geological, geochemical, and isotopic data on igneous rocks from a thoroughly studied area in the western Baikal-Muya Belt, which is a representative segment of the Neoproterozoic framework of the Siberian Craton. Three rock associations are distinguished in the studied area: granulite-enderbite-charnockite and ultramafic-mafic complexes followed by the latest tonalite-plagiogranitegranite series corresponding to adakite in geochemical characteristics. Tonalites and granites intrude the metamorphic and gabbroic rocks of the Tonky Mys Point, as well as Slyudyanka and Kurlinka intrusions. The tonalites yielded a U-Pb zircon age of 595 ± 5 Ma. The geochronological and geological information indicate that no later than a few tens of Ma after granulite formation they were transferred to the upper lithosphere level. The Sm-Nd isotopic data show that juvenile material occurs in rocks of granitoid series (ɛNd(t) = 3.2-7.1). Ophiolites, island-arc series, eclogites, and molasse sequences have been reviewed as indicators of Neoproterozoic geodynamic settings that existed in the Baikal-Muya Belt. The implications of spatially associated granulites and ultramafic-mafic intrusions, as well as granitoids with adakitic geochemical characteristics for paleogeodynamic reconstructions of the western Baikal-Muya Belt, are discussed together with other structural elements of the Central Asian Belt adjoining the Siberian Platform in the south.

  10. Sedimentary and tectonic history of the Holowilena Ironstone, a Neoproterozoic iron formation in South Australia

    NASA Astrophysics Data System (ADS)

    Lechte, Maxwell Alexander; Wallace, Malcolm William

    2015-11-01

    The Holowilena Ironstone is a Neoproterozoic iron formation in South Australia associated with glacial deposits of the Sturtian glaciation. Through a comprehensive field study coupled with optical and scanning electron microscopy, X-ray fluorescence, and X-ray diffraction, a detailed description of the stratigraphy, sedimentology, mineralogy, and structure of the Holowilena Ironstone was obtained. The Holowilena Ironstone comprises ferruginous shales, siltstones, diamictites, and is largely made up of hematite and jasper, early diagenetic replacement minerals of precursor iron oxyhydroxides, and silica. These chemical precipitates are variably influenced by turbidites and debris flows contributing clastic detritus to the depositional system. Structural and stratigraphic evidence suggests deposition within a synsedimentary half-graben. A model for the Holowilena Ironstone is proposed, in which dense oxic fluids expelled during sea ice formation in the Cryogenian pool in the depression of the half-graben, allowing for long-lived mixing with the ferruginous seawater and the deposition of iron oxides. This combination of glacial dynamics, tectonism, and ocean chemistry may explain the return of iron formations in the Neoproterozoic.

  11. Neoproterozoic diamictite-cap carbonate succession and δ13C chemostratigraphy from eastern Sonora, Mexico

    USGS Publications Warehouse

    Corsetti, Frank A.; Stewart, John H.; Hagadorn, James W.

    2007-01-01

    Despite the occurrence of Neoproterozoic strata throughout the southwestern U.S. and Sonora, Mexico, glacial units overlain by enigmatic cap carbonates have not been well-documented south of Death Valley, California. Here, we describe in detail the first glaciogenic diamictite and cap carbonate succession from Mexico, found in the Cerro Las Bolas Group. The diamictite is exposed near Sahuaripa, Sonora, and is overlain by a 5 m thick very finely-laminated dolostone with soft sediment folds. Carbon isotopic chemostratigraphy of the finely-laminated dolostone reveals a negative δ13C anomaly (down to − 3.2‰ PDB) characteristic of cap carbonates worldwide. Carbon isotopic values rise to + 10‰ across ∼ 400 m of section in overlying carbonates of the Mina el Mezquite and Monteso Formations. The pattern recorded here is mostly characteristic of post-Sturtian (ca. ≤ 700 Ma), but pre-Marinoan (ca. ≥ 635 Ma) time. However, the Cerro Las Bolas Group shares ambiguity common to most Neoproterozoic successions: it lacks useful radiometric age constraints and biostratigraphically useful fossils, and its δ13C signature is oscillatory and therefore somewhat equivocal.

  12. A global transition to ferruginous conditions in the early Neoproterozoic oceans

    NASA Astrophysics Data System (ADS)

    Guilbaud, Romain; Poulton, Simon W.; Butterfield, Nicholas J.; Zhu, Maoyan; Shields-Zhou, Graham A.

    2015-06-01

    Eukaryotic life expanded during the Proterozoic eon, 2.5 to 0.542 billion years ago, against a background of fluctuating ocean chemistry. After about 1.8 billion years ago, the global ocean is thought to have been characterized by oxygenated surface waters, with anoxic and sulphidic waters in middle depths along productive continental margins and anoxic and iron-containing (ferruginous) deeper waters. The spatial extent of sulphidic waters probably varied through time, but this surface-to-deep redox structure is suggested to have persisted until the first Neoproterozoic glaciation about 717 million years ago. Here we report an analysis of ocean redox conditions throughout the Proterozoic using new and existing iron speciation and sulphur isotope data from multiple cores and outcrops. We find a global transition from sulphidic to ferruginous mid-depth waters in the earliest Neoproterozoic, coincident with the amalgamation of the supercontinent Rodinia at low latitudes. We suggest that ferruginous conditions were initiated by an increase in the oceanic influx of highly reactive iron relative to sulphate, driven by a change in weathering regime and the uptake of sulphate by extensive continental evaporites on Rodinia. We propose that this transition essentially detoxified ocean margin settings, allowing for expanded opportunities for eukaryote diversification following a prolonged evolutionary stasis before one billion years ago.

  13. The Mafic Lower Crust of Neoproterozoic age beneath Western Arabia: Implications for Understanding African Lower Crust

    NASA Astrophysics Data System (ADS)

    Stern, R. J.; Mooney, W. D.

    2011-12-01

    We review evidence that the lower crust of Arabia - and by implication, that beneath much of Africa was formed at the same time as the upper crust, rather than being a product of Cenozoic magmatic underplating. Arabia is a recent orphan of Africa, separated by opening of the Red Sea ~20 Ma, so our understanding of its lower crust provides insights into that of Africa. Arabian Shield (exposed in W. Arabia) is mostly Neoproterozoic (880-540 Ma) reflecting a 300-million year process of continental crustal growth due to amalgamated juvenile magmatic arcs welded together by granitoid intrusions that make up as much as 50% of the Shield's surface. Seismic refraction studies of SW Arabia (Mooney et al., 1985) reveal two layers, each ~20 km thick, separated by a well-defined Conrad discontinuity. The upper crust has average Vp ~6.3 km/sec whereas the lower crust has average Vp ~7.0 km/sec, corresponding to a granitic upper crust and gabbroic lower crust. Neogene (<30 ma) lava fields in Arabia (harrats) extend over 2500 km, from Yemen to Syria. Many of these lavas contain xenoliths, providing a remarkable glimpse of the lower-crustal and upper-mantle lithosphere beneath W. Arabia. Lower crustal xenoliths brought up in 8 harrats in Saudi Arabia, Jordan, and Syria are mostly 2-pyroxene granulites of igneous (gabbroic, anorthositic, and dioritic) origin. They contain plagioclase, orthopyroxene, and clinopyroxene, and a few contain garnet and rare amphibole and yield mineral-equilibrium temperatures of 700-900°C. Pyroxene-rich and plagioclase-rich suites have mean Al2O3 contents of 13% and 19%, respectively: otherwise the two groups have similar elemental compositions, with ~50% SiO2 and ~1% TiO2, with low K2O (<0.5%) and Na2O (1-3%). Both groups show tholeiitic affinities, unrelated to their alkali basalt hosts. Mean pyroxene-rich and plagioclase-rich suites show distinct mean MgO contents (11% vs. 7%), Mg# (67 vs. 55), and contents of compatible elements Ni (169 vs. 66 ppm

  14. Chemostratigraphy of stable chromium isotopes in cap carbonate sequences - tracing the aftermath of Earth's Neoproterozoic icehouse climates

    NASA Astrophysics Data System (ADS)

    Frei, R.; de Andrade Caxito, F.; Gaucher, C.

    2012-12-01

    The Neoproterozoic Era (1000-542 Ma) was a time of extreme climatic variation as recorded in sedimentary rocks of this age across the globe. Of special interest are often occurring associations of glacial deposits with warm climate carbonate platforms, features which are preferentially explained to have resulted from extreme icehouse-greenhouse fluctuations unprecedented in the Phanerozoic record. Despite local differences in the sedimentation regime (clastic, mixed or carbonate), these events are represented by glacial deposits of diverse nature, overlain by distinctive "cap carbonate" sequences. The chemostratigraphy (particularly of δ13C and 87Sr/86Sr signatures) of carbonate sequences has been invoked as a promising alternative tool for regional and global correlation., and these signatures provide proxies for seawater composition at the time of deposition, and may indirectly signalize climatic fluctuations on land. We studied a cap carbonate profile pertaining to the Bambuí Group (Sete Lagoas Formation; Correntina section; previously studied by Caxito et al., 2012)) in the north central part of the São Franciso basin in Brazil. This section lies atop Archean to Paleoproterozoic gneisses of the São Francisco craton basement. The section begins with two-metre thick massive to finely laminated pink dolostone which grade upward into a reddish to purple limestone rhythmite. δ53Cr values of the cap dolostone are within the range typical of magmatic inventory signatures (δ53Cr = 0.1 +/- 0.1 permil; Schoenberg et al., 2008). Our preliminary few first data from the sequence above the cap dolostones show magmatic values also for samples from within the first 20 metres of laminated limestones, which then tend to increase to δ53Cr values of ~+0.3 permil in the following ca. 100 metres of carbonates. Although our data set at this stage is sparse, we note a trend that δ53Cr values correlate with fluctuations of δ13C and δ18O values (Caxito et al., 2012). These

  15. Syn- and Post-Accretionary Structures in the Neoproterozoic Central Allaqi-Heiani Suture Zone, Southeastern Egypt

    NASA Astrophysics Data System (ADS)

    Abdeen, M. M.; Abdelghaffar, A. A.

    2012-04-01

    The Allaqi-Heiani suture (AHS) is the western part of the main Allaqi-Heiani-Gerf-Onib-Sol Hamed-Yanbu suture and represents one of the Neoproterozoic, arc-arc sutures in the Arabian-Nubian Shield (ANS). It separates the ca. 750 Ma South Eastern Desert terrane in the north from the ca. 830-720 Ma Gabgaba terrane in the south. The AHS is a deformed belt of ophiolitic rocks, syn-tectonic granitoids and metasediments. The central AHS zone is divided into three structural domains. The western domain (Ι) is characterized by NNE low thrusts and SSW-vergent folds. The central domain (ΙΙ) includes upright tight to isoclinal NNW-SSE oriented folds and transpressional faults. The eastern domain (ΙΙΙ) shows NNW-SSE oriented open folds. Structural analysis indicates that the area has a poly-phase deformation history involving at least two events. Event D1 was an N-S to NNE-SSW regional shortening generating the SSW-verging folds and the NNE dipping thrusts. Event D2 was an ENE-WSW shortening producing NNW-SSE oriented folds in the central and eastern parts of the study area and reactivating older thrusts with oblique-slip reverse fault movement. The tectonic evolution of the area involves two episodes of collision: an early collision between the South Eastern Desert terrane and the Gabgaba terrane along the AHS after the consumption of a basin floored by oceanic crust above a north-dipping subduction zone; and a later collision between East- and West-Gondwanas at ca. 750-650 Ma, leading to the closure of the Mozambique Ocean. This collision deformed the AHS along N-S trending shortening zones and produced NW-SE and NE-SW oriented sinistral and dextral transpressional faults, respectively. The early collision episode is related to the terrane accretion during the early Pan-African orogen, while the later phase is related to a late Pan-African or Najd orogen.

  16. The tectonic evolution of the Neoproterozoic Brasília Belt, central Brazil, based on SHRIMP and LA-ICPMS U-Pb sedimentary provenance data: A review

    NASA Astrophysics Data System (ADS)

    Pimentel, Márcio M.; Rodrigues, Joseneusa B.; DellaGiustina, Maria Emilia S.; Junges, Sergio; Matteini, Massimo; Armstrong, Richard

    2011-04-01

    The Brasília Belt is a Neoproterozoic orogenic belt in central Brazil, developed between the Amazon, São Francisco-Congo and Paranapanema cratons. It consists of a thick sedimentary pile, made up of several stratigraphic units, which have been deformed and metamorphosed along the western margin of the São Francisco Craton during the Brasiliano orogenic cycle. In the western part of the belt, a large, juvenile magmatic arc is exposed (the Goiás Magmatic Arc), consisting of calc-alkaline plutonic suites as well as volcano-sedimentary sequences, ranging in age between ca. 860 and 650 Ma. Regional-scale, west-dipping thrusts and reverse faults normally mark the limits between the main stratigraphic units, and clearly indicate tectonic transport towards the east. The age of deposition and tectonic significance of the sedimentary units comprising the Brasília Belt have been a matter of continuous debate over the last three decades. In the present paper, recent provenance data based on LA-ICPMS U-Pb ages of detrital zircon grains from several of these units, are reviewed and their significance for the age of deposition of the original sediments and tectonic evolution of the Brasília Belt are discussed. The Paranoá, Canastra and the Vazante groups, in the central part of the Belt, have detrital zircon grains with ages older than ca. 900 Ma and are interpreted as representative of the passive margin sequence deposited on the western margin of the São Francisco Craton. On the other hand, samples from the Araxá and Ibiá groups have a much younger population of Neoproterozoic zircon grains, as young as 650 Ma, and have been interpreted as syn-orogenic (fore-arc?) deposits. The Bambuí Group, exposed in the easternmost part of the belt and covering large areas of the São Francisco Craton also has young zircon grains and is interpreted, at least in part, as the foreland basin of the Brasília Belt.

  17. GCM Simulations of Neoproterozoic "Snowball Earth" Conditions: Implications for the Environmental Limits on Terrestrial Metazoans and Their Extraterrestrial Analogues

    NASA Technical Reports Server (NTRS)

    Sohl, L. E.; Chandler, M. A.

    2001-01-01

    The Neoproterozoic Snowball Earth intervals provide excellent opportunities to examine the environmental limits on terrestrial metazoans. A series of GCM simulations was run in order to quantify climatic conditions during these intervals. Additional information is contained in the original extended abstract.

  18. Growth and mortality of Cichla spp. (Perciformes, Cichlidae) introduced in Volta Grande Reservoir (Grande River) and in a small artificial lake in Southeastern Brazil.

    PubMed

    Gomiero, L M; Carmassi, A L; Rondineli, G R; Villares Junior, G A; Braga, F M S

    2010-11-01

    The growth and mortality parameters were estimated through the analysis of length frequency distribution for species of Cichla spp. introduced into a lake in Leme (SP), and in Volta Grande reservoir (SP-MG). In Leme, Cichla kelberi presented larger frequency in the inferior classes of lengths, larger instantaneous rate of natural mortality, and smaller number of cohorts than C. kelberi and C. piquiti in Volta Grande. The values of growth performance obtained for the species were similar, corroborating the validity of the estimated growth and mortality parameters. The increase of the growth rate in small and less diverse environments occurs due to predation. The genus Cichla adapts well in locations in which it is introduced, however this adaptation shows itself to be strongly adjusted to each particular location, determining great plasticity and establishment capacity. PMID:21180920

  19. The Neoproterozoic-Cambrian Paraguay Belt, central Brazil: Part I - New structural data and a new approach on the regional implications

    NASA Astrophysics Data System (ADS)

    Silva, Luiz José Homem D'el-Rey; Walde, Detlef Hans-Gerd; Saldanha, Davi Oliveira

    2016-04-01

    Together with the Araguaia and Brasília belts, the Paraguay belt forms in central Brazil, the Tocantins Province that is one of the largest orogens of western Gondwana. The Corumbá area occupies the site where the northern and southern parts of the Paraguay belt form, together with the Chiquitos-Tucavaca aulacogen (stretching E-W in the adjacent Bolivian territory) an R-R-R basin system opened-filled in the ~ 700/650-540 Ma interval within the Amazon-Rio Apa paleo-continent. The sedimentary (volcanic) rocks of the Jacadigo and Corumbá Groups found around the Corumbá city record part of the Neoproterozoic-Cambrian passive margin precursor of the Paraguay belt. Our pioneer structural analysis reveals that these rocks experienced progressive deformation (phases D1-D2-D3) and low-grade metamorphism during the Brasiliano Cycle (540-513 Ma). The crystalline basement was also involved, according to structural data and K-Ar ages in the literature. The paleo-passive margin was thickened during the D1-D2 deformation and was lately shortened (D3) in two orthogonal directions, SE-NW (D3P) and SW-NE (D3T). Developed co-axially and verging to NW, D1-D2-D3P structures record the closure of the basin precursor of the Paraguay belt, whereas D3T structures seem related to the inversion of the aulacogen. Although the tectonic transport to NW, as observed in the Corumbá area, matches the reported transport of Paraguay belt's supracrustal rocks towards the eastern margin of the Rio Apa block and Araguaia belt's rocks towards the Amazon craton, the transport direction is opposite in other parts of the Paraguay belt. Our comprehensive discussion of these facts brings to light profound regional implications.

  20. Multiple rifting and alkaline magmatism in southern India during Paleoproterozoic and Neoproterozoic

    NASA Astrophysics Data System (ADS)

    Renjith, M. L.; Santosh, M.; Satyanarayanan, M.; Rao, D. V. Subba; Tang, Li

    2016-06-01

    The Southern Granulite Terrane (SGT) in India preserves the history of tectonothermal events ranging from Paleoarchean to latest Neoproterozoic-Cambrian. Here we investigate alkaline magmatism possibly associated with rifting events in Paleoproterozoic and Neoproterozoic based on petrological, geochemical and zircon U-Pb and Lu-Hf isotopic studies on the alkaline complexes of Korangani (KGAC) and Kambamettu (KAC) in the Madurai Block of SGT. The mica pyroxenite which represents the first intrusive phase at KGAC crystallized from a mildly alkaline hydrous magma derived from a metasomatized mantle. The younger shoshonitic syenite was emplaced at 2533 ± 16 Ma, carries mafic microgranular enclaves, and shows trace-elements ratios consistent with magma mixing trend, and zircon εHf(t) values display mixed positive and negative values - 2.6 to 3.6 suggesting the mixing of adakite-like felsic crustal melt and non-adakitic mantle derived melt. In KAC, four distinct magmatic intrusions are identified: i) quartz-monzonite (emplaced at 2498 ± 16 Ma), an ultrapotassic adakitic rock derived from a carbonated alkali-rich lower crustal source with negative zircons εHf(t) values in zircon (- 8.0 to - 0.8); Y/Nb (> 1.2) and Th/Ce (0.03-0.8) ratios; lower Ni (< 30 ppm) and Cr (< 14 ppm) contents; ii) phlogopite-rich pyroxenite, crystallized from an alkali-rich basaltic parental magma derived from carbonate metasomatized mantle; iii) mantle derived high Ba-Sr carbonatite (emplaced at 2470 ± 15 Ma); and iv) shoshonitic peralkaline syenite rock (emplaced at 608 ± 6 Ma) with strong adakitic signature, low MgO (< 1 wt.%), Ni (12-5 ppm) and Cr (49-35 ppm) contents and negative zircon εHf(t) values (- 30.3 to - 27.3) and trough of Zr-Hf in spidergrams suggesting a carbonated alkali-rich garnet-bearing crustal source. The geochemical features and petrogenetic considerations of the felsic shoshonitic-ultrapotassic adakite-like rocks (syenite, quartz monzonite), mica-pyroxenites and

  1. Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution

    NASA Astrophysics Data System (ADS)

    Fritz, H.; Abdelsalam, M.; Ali, K. A.; Bingen, B.; Collins, A. S.; Fowler, A. R.; Ghebreab, W.; Hauzenberger, C. A.; Johnson, P. R.; Kusky, T. M.; Macey, P.; Muhongo, S.; Stern, R. J.; Viola, G.

    2013-10-01

    The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world´s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara-Congo-Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ∼850 and 550 Ma. The northern part of the orogen, the Arabian-Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ∼850 and 620 Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite-Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ∼650-620 Ma granulite-facies metamorphism. Completion of the nappe assembly around 620 Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, southern parts of the Congo-Tanzania-Bangweulu Cratons and the Zimbabwe-Kalahari Craton. They closed during the ∼600-500 Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ∼600-550 Ma extension is recorded in the Arabian-Nubian Shield and the Eastern Granulite-Cabo Delgado Nappe Complex. Later ∼550-480 Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings resulted in the evolution of

  2. Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution☆

    PubMed Central

    Fritz, H.; Abdelsalam, M.; Ali, K.A.; Bingen, B.; Collins, A.S.; Fowler, A.R.; Ghebreab, W.; Hauzenberger, C.A.; Johnson, P.R.; Kusky, T.M.; Macey, P.; Muhongo, S.; Stern, R.J.; Viola, G.

    2013-01-01

    The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world́s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara–Congo–Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ∼850 and 550 Ma. The northern part of the orogen, the Arabian–Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ∼850 and 620 Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite–Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ∼650–620 Ma granulite-facies metamorphism. Completion of the nappe assembly around 620 Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, southern parts of the Congo–Tanzania–Bangweulu Cratons and the Zimbabwe–Kalahari Craton. They closed during the ∼600–500 Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ∼600–550 Ma extension is recorded in the Arabian–Nubian Shield and the Eastern Granulite–Cabo Delgado Nappe Complex. Later ∼550–480 Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings

  3. The Neoproterozoic Abu Dahr ophiolite, South Eastern Desert, Egypt: petrological characteristics and tectonomagmatic evolution

    NASA Astrophysics Data System (ADS)

    Gahlan, Hisham A.; Azer, Mokhles K.; Khalil, Ahmed E. S.

    2015-10-01

    The Neoproterozoic Abu Dahr ophiolite, South Eastern Desert, Egypt, is one of the best preserved and least dismembered ophiolite successions in the Arabian-Nubian Shield. It contains a Penrose-type ophiolite sequence from mantle section below mafic crust upward to oceanic sedimentary cover overlying mafic volcanics, although the original magmatic (stratigraphic) contact between the mantle and crustal sections is disrupted by tectonism. The Abu Dahr ophiolite is metamorphosed under greenschist facies conditions, and low-temperature alteration is widespread. Petrography reveals that: (i) the mantle is homogenous, serpentinized, and dominated by harzburgite and less abundant dunite; (ii) the cumulate ultramafics are represented by wehrlite and pyroxenite; and (iii) the crustal section is represented by metagabbros, meta-anorthosites and metabasalts. The Abu Dahr serpentinized peridotites show high Mg# (0.92-0.93), with enrichment of Ni, Cr and Co, and depletion of Al2O3 and CaO, and nearly flat and unfractionated REE chondrite-normalized pattern. Major and trace element characteristics of the Abu Dahr metagabbro and metabasalt (crustal section) indicate a tholeiitic to calc-alkaline affinity. Units of the crustal section have low-Nb and Zr concentrations, low Dy/Yb and relatively elevated La/Yb ratios, high U/Yb and Th/Yb ratios, and LREE enriched chondrite-normalized pattern. All of the Abu Dahr ophiolite units have trace-element signatures characterized by enrichment of LILE over HFSE. Rare and trace element patterns indicate a genetic link between the Abu Dahr mantle, cumulate ultramafics, and crust. Chromian spinel has survived metamorphism and is used as a petrogenetic indicator in the Abu Dahr serpentinized peridotites. The spinel is homogeneous with a limited composition, and shows high-Cr# (>0.6) combined with low-TiO2 character (mostly <0.1 wt.%). The Abu Dahr ophiolite is interpreted as a fragment of depleted oceanic lithosphere that experienced high degrees

  4. Neoproterozoic-Early Paleozoic rifting of the craton margin in eastern Kentucky: Evidence from subsidence analysis

    SciTech Connect

    Goodman, P.T. . Dept. of Geological Sciences); Walker, D. )

    1992-01-01

    Analysis of subsidence along the craton margin in eastern Kentucky indicates a Neoproterozoic to Early through Middle Cambrian rifting event developing on a subsiding passive margin of the Laurentian craton to the Iapetus Ocean. Subsidence associated with rifting is confined to the Rome Trough; an internally broken half-graben within the Laurentian craton; the trough trends sub-parallel to the Appalachian orogenic belt. In cross section the through as an abrupt faulted margin on the carton side and a tapering, gentle extension toward the orogenic belt. The stratigraphic sequence within the Rome Trough and toward the orogen consists of Neoproterozoic or early Cambrian basal sands overlying Grenville basement, and succeeded by silts, shales and discontinuous carbonates of the Rome Fm. that are overlain by shales and carbonates of the Conesauga Fm. Stratigraphic relationships suggest that an out-of-sequence, inboard rift developed along the Laurentian margin adjacent to a drift-phase continental shelf represented by strata of the Blue Ridge and Valley and Ridge. Analysis of the subsidence history of this region reveals trends which support the notion that the subsidence history of this area cannot be accounted for by typical passive-margin development. The subsidence history of the area within the Rome Trough presents a pattern of high thermal subsidence and produces beta values greater than in areas nearer the craton margin. These data indicate that an inboard locus of anomalous crustal extension occurred in the area of the Rome Trough while the remainder of the cratonal margin underwent drift-phase subsidence, and that the timing and magnitude of this event is related to the development of the Iapetan margin.

  5. Formation of Neoproterozoic metamorphic complex during oblique convergence (Eastern Desert, Egypt)

    NASA Astrophysics Data System (ADS)

    Fritz, H.; Wallbrecher, E.; Khudeir, A. A.; Abu el Ela, F.; Dallmeyer, D. R.

    1996-10-01

    Major portions of the Pan-African Orogen in the Eastern Desert of Egypt were formed by island-arc accretion in the Neoproterozoic. These areas are characterized by their lack of major crustal thickening. Metamorphic core complexes occur parallel to the strike of the Eastern Desert Orogen. These domes exhibit polyphase metamorphism and deformation in contrast to the structurally overlying nappes which include ophiolitic melanges and island-arc volcanic rocks. These nappes show northwest directed, orogen-parallel thrusting in the internal parts and west to southwest directed imbrication in the external parts of the orogen. Structures related to exhumation of the metamorphic core complexes partition into different displacement paths localized within a crustal-scale wrench corridor of the Najd fault system. Northwest trending orogen-parallel, sinistral strike-slip faults define the western and eastern margins of the domes. North and south dipping low-angle normal faults developed along the northern and southern margins of the domes and form extensional bridges between them. {40Ar}/{39Ar} ages obtained from syntectonic muscovites within the shear zones gave Neoproterozoic ages of 595.9±0.5 and 588.2±0.3 Ma. The synchronous activity of strike-slip and normal faults suggests a regional east-west shortening which was accomodated by deep-level basal decollement beneath the metamorphic core complexes and a coeval northwest-southeast, orogen-parallel extension. This extension was accompanied by intramontane molasse sedimentation and emplacement of calc-alkaline plutons. Since the rapid exhumation of gneisses in the core complexes cannot be explained by thickening of the crust, the authors favour a model which calls for enhanced heat flow along the Najd fault system which would have enabled the formation of syn-extensional plutonism and triggered the exhumation of the metamorphic core complexes. Lateral buoyancy forces were concentrated within the Najd wrench corridor and

  6. Detrital zircon geochronology of Neoproterozoic to Middle Cambrian miogeoclinal and platformal strata: Northwest Sonora, Mexico

    USGS Publications Warehouse

    Gross, E.L.; Stewart, John H.; Gehreis, G.E.

    2000-01-01

    Eighty-five detrital zircon grains from Mesoproterozoic and/or Neoproterozoic to Middle Cambrian sedimentary strata in northwest Sonora, Mexico, have been analyzed to determine source terranes and provide limiting depositional ages of the units. The zircon suites from the Mesoproterozoic and/or Neoproterozoic El Alamo Formation and El Aguila unit yield ages between 1.06 Ga and 2.67 Ga, with predominant ages of 1.1 to 1.2 Ga. Zircons from the Lower? and Middle Cambrian Bolsa Quartzite show age groups from 525 Ma to 1.63 Ga, with a dominant population of 1.1 to 1.2 Ga grains. Grains older than 1.2 Ga in the samples were most likely derived from basement terranes and ???1.4 Ga granitic bodies of the southwest U.S. and northwest Mexico. It is also possible that the sediments were transported from the south, although source rocks of the appropriate age are not presently exposed south of the study area in northern Mexico. Three possibilities for the dominant 1.1 to 1.2 Ga grains include derivation from: (I) exposures of the Grenville belt in southern North America, (2) local 1.1-1.2 Ga granite bodies, or (3) a southern source, such as the Oaxaca terrane, that was subsequently rifted away. Sampling of additional units in the western U.S. and northern Mexico may help resolve the ambiguity surrounding the source of the 1.1 to 1.2 Ga grains.

  7. Post-collisional subvolcanic rhyolites associated with the Neoproterozoic Pelotas Batholith, southern Brazil

    NASA Astrophysics Data System (ADS)

    Oliveira, Diego Skieresz de; Sommer, Carlos Augusto; Philipp, Ruy Paulo; Lima, Evandro Fernandes de; Basei, Miguel Ângelo Stipp

    2015-11-01

    Neoproterozoic volcanic and subvolcanic rhyolitic systems in southernmost Brazil are correlated with acid magmatism linked to different petrotectonic associations of the Sul-Rio-Grandense Shield. A portion of this volcanism in the Dom Feliciano Belt is associated with the Pelotas Batholith, which resulted from magmatic episodes associated with the Ediacaran post-collisional evolution of southern Brazil. Ana Dias Rhyolite is the main subvolcanic occurrence of this volcanism that took place in the Quitéria region, in the central part of Rio Grande do Sul State. The acid magmatism has been commonly associated with the most differentiated granite suite phases during the final stages of emplacement of the Pelotas Batholith. The Ana Dias Rhyolite is characterized as an intrusive body with rocks that present a porphyritic to seriated texture and a gradational variation to fine-grained equigranular rocks. New zircon U-Pb dating indicates crystallization age of 581.9 ± 1.9 Ma for the Ana Dias Rhyolite. Geochemistry data characterize the rhyolites as belonging to the alkaline series; they present a metaluminous to peraluminous character; elevated SiO2 and alkali concentrations, high FeOt/FeOt + MgO ratios and agpaitic index; and low Al2O3, CaO, and MgO contents. The Zr, Rb, Y, Nb, and Ga concentrations are moderate when compared with the relatively low Ba and Sr contents. These geochemistry characteristics are common in acid magmas with alkaline affinity. The behavior of certain trace elements and REE demonstrate enrichment in more incompatible elements, in addition to the negative anomaly of Ba, the slight enrichment in Ce relative to adjacent elements, as well as the enrichment in K2O and Rb relative to Nb, suggesting magmas derived from mantle sources enriched in incompatible elements with some crustal contamination. The chemical characteristics are similar to those of A-type granites associated with Neoproterozoic post-collision magmatism in the Sul

  8. Glacial trinity: Neoproterozoic Earth history within the British-Irish Caledonides

    NASA Astrophysics Data System (ADS)

    McCay, G. A.; Prave, A. R.; Alsop, G. I.; Fallick, A. E.

    2006-11-01

    Two distinct Neoproterozoic glacial episodes are known for the Dalradian Supergroup in the British-Irish Caledonides, the Port Askaig Formation and the Inishowen Loch na Cille ice-rafted debris (IRD) beds. Here we describe a third, intermediate between those two, the Stralinchy-Reelan formations, composed of diamictite and IRD. Developed directly above these rocks is the Cranford Limestone, which consists of a basal, 1 6-m-thick, tan-gray dolostone overlain by a variably developed, but as much as 340-m-thick, sequence of thin-bedded limestone and dolostone. This unit exhibits a C isotopic trend that begins negative in the basal dolostone, reaches a nadir of -7‰, and then rises to 0‰ 2‰. These characteristics match strikingly those of Marinoan-style cap carbonates. Consequently, we interpret the Port Askaig Formation, the Stralinchy-Reelan units, and the Inishowan Loch na Cille beds as equivalents of the ca. 700 Ma Sturtian, the 635 Ma Marinoan, and the ca. 580 Ma Gaskiers glacials, respectively. Two additional observations are noteworthy. Carbonate rocks below the Port Askaig Formation record a δ13C decline to -6‰ that implies that such downturns may occur in both pre-Sturtian and pre-Marinoan strata. In addition, the Bonahaven Dolomite is not a cap carbonate to the Port Askaig Formation, but exhibits a δ13C rise to 12‰, which we correlate with the inferred global Keele peak. These data further document the utility of Neoproterozoic glacial cap carbonate sequences in global correlations and denote the base of the Cranford Linestone as the Cryogenian-Ediacaran boundary.

  9. A model for Iapetan rifting of Laurentia based on Neoproterozoic dikes and related rocks

    USGS Publications Warehouse

    Burton, William C.; Southworth, Scott

    2010-01-01

    Geologic evidence of the Neoproterozoic rifting of Laurentia during breakup of Rodinia is recorded in basement massifs of the cratonic margin by dike swarms, volcanic and plutonic rocks, and rift-related clastic sedimentary sequences. The spatial and temporal distribution of these geologic features varies both within and between the massifs but preserves evidence concerning the timing and nature of rifting. The most salient features include: (1) a rift-related magmatic event recorded in the French Broad massif and the southern and central Shenandoah massif that is distinctly older than that recorded in the northern Shenandoah massif and northward; (2) felsic volcanic centers at the north ends of both French Broad and Shenandoah massifs accompanied by dike swarms; (3) differences in volume between massifs of cover-sequence volcanic rocks and rift-related clastic rocks; and (4) WNW orientation of the Grenville dike swarm in contrast to the predominately NE orientation of other Neoproterozoic dikes. Previously proposed rifting mechanisms to explain these features include rift-transform and plume–triple-junction systems. The rift-transform system best explains features 1, 2, and 3, listed here, and we propose that it represents the dominant rifting mechanism for most of the Laurentian margin. To explain feature 4, as well as magmatic ages and geochemical trends in the Northern Appalachians, we propose that a plume–triple-junction system evolved into the rift-transform system. A ca. 600 Ma mantle plume centered east of the Sutton Mountains generated the radial dike swarm of the Adirondack massif and the Grenville dike swarm, and a collocated triple junction generated the northern part of the rift-transform system. An eastern branch of this system produced the Long Range dike swarm in Newfoundland, and a subsequent western branch produced the ca. 554 Ma Tibbit Hill volcanics and the ca. 550 Ma rift-related magmatism of Newfoundland.

  10. Health insurance in Ghana: evaluation of policy holders’ perceptions and factors influencing policy renewal in the Volta region

    PubMed Central

    2013-01-01

    Background Health insurance is an important mechanism that succors individuals, states and the nation at large. The purpose of this study was to assess individual’s attitude towards health insurance policy and the factors that influence respondents’ decision to renew their health insurance policy when it expires. Methods This cross sectional study was conducted in the Volta region of Ghana. A total of 300 respondents were randomly sampled and interviewed for the study. Data was collected at the household level and analyzed with STATA software. Descriptive statistics was used to assess the demographic characteristics of the respondents while Logistic regression model was used to assess factors that influence respondents’ decision to take up health insurance policy and renew it. Results The study results indicate that 61.1% of respondents are currently being enrolled in the NHIS, 23.9% had not renewed their insurance after enrollment and 15% had never enrolled. Reasons cited for non-renewal of insurance included poor service quality (58%), lack of money (49%) and taste of other sources of care (23%). The gender, marital status, religion and perception of health status of respondents significantly influenced their decision to enroll and remain in NHIS. Conclusion NHIS has come to stay with clients testifying to its benefits in keeping them strong and healthy. Efforts therefore must be put in by all stakeholders including the community to educate the individuals on the benefits of health insurance to ensure all have optimal access. PMID:23822579

  11. Relationship between gonad maturation and heavy metal accumulation in the clam, Galatea paradoxa (Born 1778) from the Volta estuary, Ghana.

    PubMed

    Adjei-Boateng, D; Obirikorang, K A; Amisah, S; Madkour, H A; Otchere, F A

    2011-12-01

    The relationship between gonadal development and the concentrations of four heavy metals Mn, Zn, Fe and Hg in the tissues of the clam Galatea paradoxa was evaluated at the Volta estuary, Ghana, over an 18-month period. Metal concentrations in the clam tissues were highly variable over the sampling period and seemed to be influenced by the reproductive cycle of the clam. Mn concentrations varied over a wide range from 49 to 867 μg/g and exhibited a significant positive correlation with gonadal development (p = 0.0146, r(2) = 0.3190). Zn and Fe concentrations ranged from 13 to 59 μg/g and 79 to 484 μg/g, respectively and both revealed negative relationships between gonad development and metal accumulation (Zn (p = 0.0554, r(2) = 0.0554) and Fe (p = 0.1040, r(2) = 0.1567)). Hg concentrations ranged from 0.026 to 0.059 μg/g over the sampling period and exhibited a slight positive relationship between gonadal development and metal accumulation (p = 0.0861, r(2) = 0.1730). PMID:21947544

  12. Operational performance of the photovoltaic-powered grain mill and water pump at Tangaye, Burkina Faso (formerly Upper Volta)

    NASA Technical Reports Server (NTRS)

    Martz, J. E.; Roberts, A. F.

    1985-01-01

    A photovoltaic (PV) system powering a grain mill and water pump was installed in the remote African village of Tangaye, Burkina Faso (formerly Upper Volta) under the sponsorship of the U.S. Agency for International Development (AID) and by the National Aeronautics and Space Administration (NASA) Lewis Research Center (LeRC) in early 1979. The presence reports covers the second two years of operation from April 1981 through June 1983. During this time, the grain mill and water pump were operational 96 and 88 percent of the time respectively, and the PV system generated sufficient electricity to enable the grinding of about 111 metric tons of finely ground flow and the pumping of over 5000 cm sq of water from the 10 m deep well. The report includes a description of the current configuration of the system, a review of system performance, a discussion of the socioeconomic impact of the system on the villagers and a summary of results and conclusions covering the entire four-year period.

  13. [Epidemic of yellow fever in the southeastern region of Upper Volta (October-December, 1983). Epidemiological study. Preliminary results].

    PubMed

    Roux, J; Baudon, D; Robert, V; Stanghellini, A; Gazin, P; Lhuillier, M; Saluzzo, J F; Cornet, M; Sarthou, J L; Molez, J F

    1984-01-01

    An epidemic of yellow fever raged during the last three months of 1983 in South East of Upper Volta. It spread on about ten thousand square kilometers, in a bushy savanna area, affecting only populations living in contact with forest galleries, belonging especially to the peul ethnical group. The transmission of the virus was effected by sylvatic vectors, essentially Aedes furcifer. Serological tests showed that about 50 % of the population living in contact with forest galleries was affected, that is to say 15.000 to 17.500 people. The average death rate on the whole area was 4 % (800 to 1.700 deaths); the lethality rate was estimated between 6 and 10 % of affected people. On the whole, 54 strains of yellow fever virus were isolated from human blood samples, and 26 strains from batches of mosquitoes. We called this epidemic "intermediate sylvatic epidemic". The epidemic quickly decreased in the sylvatic area, owing to climatic conditions. A mass campaign of vaccinations prevented it from spreading to near urban centres. On this particular case, the thermostability on field of the vaccine 17D provided by the Institute Pasteur of Dakar was proved to be effective. PMID:6542965

  14. Neoproterozoic Chuar Group (˜800-742 Ma), Grand Canyon: a record of cyclic marine deposition during global cooling and supercontinent rifting

    NASA Astrophysics Data System (ADS)

    Dehler, Carol M.; Elrick, Maya; Karlstrom, Karl E.; Smith, Gary A.; Crossey, Laura J.; Timmons, J. Michael

    2001-06-01

    Chuar Group sediments were deposited in a marine cratonic basin synchronously with marine deposition in other basins of western North America and Australia. The top of the Chuar Group is 742 Ma; thus, this succession offers a potentially important record of global climatic and tectonic changes during the mid-Neoproterozoic — a critical time leading to possible global glaciation during supercontinent rifting. Chuar Group cycles and sequences may record glacioeustatic fluctuations during the climatic transition into the Sturtian Ice Age (˜750-700 Ma), as well as extension related to the dispersal of Rodinia. The mid-Neoproterozoic Chuar Group (1600 m thick) is predominantly composed of mudrock with subordinate meter-scale beds of dolomite and sandstone. Facies analysis leads to the interpretation of a wave- and tidal-influenced marine depositional system. Diagnostic marine features include: (1) marine fossils and high local pyrite content in the mudrock facies; (2) mudcracked mud-draped symmetric ripples and reverse flow indicators in the sandstone facies; (3) facies associations between all facies; and (4) no unequivocal terrestrial deposits. Chuar facies stack into ˜320 dolomite- and sandstone-capped meter-scale cycles (1-20 m thick) and non-cyclic intervals of uniform mudrock facies (20-150 m thick). Nearly all cycles have mudrock bases indicating subtidal water depths. Dolomite-capped cycles shallow to peritidal environments (peritidal cycles), some indicating subaerial exposure of varying degrees (exposure cycles). Sandstone-capped cycles shallow to peritidal environments with no evidence of prolonged exposure (peritidal cycles). Non-cyclic intervals represent the deepest water depths (˜10s of meters). Peritidal cycles and non-cyclic intervals dominate the lower and middle Chuar Group. In the upper Chuar Group, the percentage of exposure cycles increases, as does the thickness of individual cycles and non-cyclic intervals, and the degree of subaerial

  15. Biological Feedbacks as Cause and Demise of Neoproterozoic Icehouse: Astrobiological Prospects for Faster Evolution and Importance of Cold Conditions

    PubMed Central

    Janhunen, Pekka; Kaartokallio, Hermanni; Oksanen, Ilona; Lehto, Kirsi; Lehto, Harry

    2007-01-01

    Several severe glaciations occurred during the Neoproterozoic eon, and especially near its end in the Cryogenian period (630–850 Ma). While the glacial periods themselves were probably related to the continental positions being appropriate for glaciation, the general coldness of the Neoproterozoic and Cryogenian as a whole lacks specific explanation. The Cryogenian was immediately followed by the Ediacaran biota and Cambrian Metazoan, thus understanding the climate-biosphere interactions around the Cryogenian period is central to understanding the development of complex multicellular life in general. Here we present a feedback mechanism between growth of eukaryotic algal phytoplankton and climate which explains how the Earth system gradually entered the Cryogenian icehouse from the warm Mesoproterozoic greenhouse. The more abrupt termination of the Cryogenian is explained by the increase in gaseous carbon release caused by the more complex planktonic and benthic foodwebs and enhanced by a diversification of metazoan zooplankton and benthic animals. The increased ecosystem complexity caused a decrease in organic carbon burial rate, breaking the algal-climatic feedback loop of the earlier Neoproterozoic eon. Prior to the Neoproterozoic eon, eukaryotic evolution took place in a slow timescale regulated by interior cooling of the Earth and solar brightening. Evolution could have proceeded faster had these geophysical processes been faster. Thus, complex life could theoretically also be found around stars that are more massive than the Sun and have main sequence life shorter than 10 Ga. We also suggest that snow and glaciers are, in a statistical sense, important markers for conditions that may possibly promote the development of complex life on extrasolar planets. PMID:17299594

  16. Neoproterozoic Orogeny-Related Magmatic Event in the Northwestern Yangtze Block and Its Implications for the Unification of South China

    NASA Astrophysics Data System (ADS)

    Wafa, B.

    2014-12-01

    Neoproterozoic tectonic history of South China has long been an issue of debate, including its connection with the cycle of Rodinia. The South China block has been traditionally thought to have formed by Neoproterozoic welding between the Yangtze and Cathysian blocks along the Jiangnan Orogen. However, increasing evidence suggests that the Neoproterozoic unification of South China comprises a set of collision events. Here we report a newly recognized syn-collisional intrusive suite at the northwestern Yangtze block. The igneous suite is located at the Wangcang area, NE Sichuan province. It consists of tholeiitic- and alkali mafic rocks, and adakitic to calc-alkali felsic intrusions. They are dated at 8554Ma to 8675 Ma by U-Pb zircon, and show arc-related geochemical affinities with highly variable whole rock ɛNd (up to +7.78) and zircon ɛHf(t) values. The Wangcang suite is featured by high deformation and metamorphism of upper greenschist to amphibolitic facieses, which is contrast to the low grade ~820-750 Ma igneous suites in the same region. It suggests that the northwestern Yangtze block experienced an arc-continental orogenic event occurred during ~860-820 Ma. Our recent work has revealed that the Shennongjia terrain and the Yangtze continental nucleus was welded between ~1100-950Ma. These findings suggest that the unification of South China comprises a set of collision events. This work provides a new clue for our understanding of the connection between the Neoproterozoic evolution of South China and Rodinia cycle. This study was supported by the NSFC (Grants 41173048 and 41373037).

  17. Evaluating key parameters for the initiation of a Neoproterozoic Snowball Earth with a single Earth System Model of intermediate complexity

    NASA Astrophysics Data System (ADS)

    Spiegl, T. C.; Paeth, H.; Frimmel, H. E.

    2015-04-01

    Even after more than two decades of intense research the main drivers for a potential Neoproterozoic Snowball Earth continue to be discussed controversially. In this study we present results from 37 sensitivity experiments that were performed with the Planet Simulator (PlaSim), an Earth System Model of intermediate complexity. In contrast to previous studies, in which only a limited number of potential climate-controlling parameters were assessed with different climate models, we tested our presumed key parameters within one single model. This approach makes it easier to compare the influence of the various parameters on extreme climate change as postulated for the Neoproterozoic Era. Furthermore we compare the results obtained to most recent high complexity state-of-the-art approaches. This comparison helps to estimate, which internal model interactions and physics are crucial for a Snowball Earth simulation and hence should be included into a model that is capable of realistically simulating a Neoproterozoic climate. To this effect we carried out simulations that involved reduced solar irradiation, land-sea distributions, atmospheric CO2 concentrations, relief of the land surface and length of day. In addition, we focus on different land surface albedo values, which were most likely exceptionally low and similar to the Martian albedo, and obliquity changes between 23.5° and 80°. Our findings suggest that changes in land surface albedo are a strong climate driver that can compensate a much lower Neoproterozoic total solar irradiance if it is combined with shifts in obliquity or atmospheric CO2 levels. We also obtained a critical threshold for increased obliquities beyond which a Snowball Earth situation turns into an extreme greenhouse climate with almost absent cryosphere, and furthermore, obliquity values that lead to a tropical ice age with sea ice spreading from the equator to high latitudes.

  18. Biological feedbacks as cause and demise of the Neoproterozoic icehouse: astrobiological prospects for faster evolution and importance of cold conditions.

    PubMed

    Janhunen, Pekka; Kaartokallio, Hermanni; Oksanen, Ilona; Lehto, Kirsi; Lehto, Harry

    2007-01-01

    Several severe glaciations occurred during the Neoproterozoic eon, and especially near its end in the Cryogenian period (630-850 Ma). While the glacial periods themselves were probably related to the continental positions being appropriate for glaciation, the general coldness of the Neoproterozoic and Cryogenian as a whole lacks specific explanation. The Cryogenian was immediately followed by the Ediacaran biota and Cambrian Metazoan, thus understanding the climate-biosphere interactions around the Cryogenian period is central to understanding the development of complex multicellular life in general. Here we present a feedback mechanism between growth of eukaryotic algal phytoplankton and climate which explains how the Earth system gradually entered the Cryogenian icehouse from the warm Mesoproterozoic greenhouse. The more abrupt termination of the Cryogenian is explained by the increase in gaseous carbon release caused by the more complex planktonic and benthic foodwebs and enhanced by a diversification of metazoan zooplankton and benthic animals. The increased ecosystem complexity caused a decrease in organic carbon burial rate, breaking the algal-climatic feedback loop of the earlier Neoproterozoic eon. Prior to the Neoproterozoic eon, eukaryotic evolution took place in a slow timescale regulated by interior cooling of the Earth and solar brightening. Evolution could have proceeded faster had these geophysical processes been faster. Thus, complex life could theoretically also be found around stars that are more massive than the Sun and have main sequence life shorter than 10 Ga. We also suggest that snow and glaciers are, in a statistical sense, important markers for conditions that may possibly promote the development of complex life on extrasolar planets. PMID:17299594

  19. Length-weight relationship of the freshwater clam, Galatea paradoxa (born 1778) from the Volta Estuary, Ghana.

    PubMed

    Obirikorang, K A; Adjei-Boateng, D; Madkour, H A; Amisah, S; Otchere, F A

    2013-02-15

    The length-weight relationship of the threatened freshwater clam, Galatea paradoxa (Born 1778) from the Volta Estuary, Ghana was studied over a two-year period, from March 2008 to February 2010, to aid in the development of stock assessment models for the sustainable management of the remaining clam stock. Data reported in this study were collected at monthly intervals and covered varying depths of the Estuary ranging from 0.5 to about 10 m. Overall, a total of 5276 clams with shell lengths ranging from 3.40 to 89.24 mm and total weight from 0.10 to 154.00 g were sampled during the study period. The length-weight relationships were highly significant (p < 0.0001) for all the months and the b-values ranged from 2.023 (January 2010) to 3.874 (June 2009). The calculated b-values indicated that clams exhibited different growth patterns at different periods but overall, the pooled samples of 5276 individuals exhibited an isometric growth pattern (b = 3.003). The observed monthly growth patterns exhibited by G. paradoxa appeared to be largely influenced by the reproductive cycle of the organism. During the periods leading to spawning, the clams generally exhibited positive allometric growth patterns (weight increasing faster than length) which appeared to be strongly linked to the build-up of proteins and carbohydrates in their tissues. Successive negative allometric growth patterns (length increasing faster relative to weight) were, however, observed from March to June 2008 and from December 2009 to February 2010, which are possibly indicative of the loss in tissue weight that occurs as a direct result of the spawning process. It will thus be suitable to institute a close season to coincide with the spawning period of the clams to avoid the harvesting of clams during the spawning period which will enhance future recruitment of the clam stock. PMID:24171267

  20. Hydrochemical study of water collected at a section of the Lower Volta River (Akuse to Sogakope area), Ghana

    NASA Astrophysics Data System (ADS)

    Gampson, E. K.; Nartey, V. K.; Golow, A. A.; Akiti, T. T.

    2014-06-01

    The present hydrochemical study at the Lower Volta River (Akuse to Sogakope area), Ghana was conducted by determining the physico-chemical parameters (pH, temperature, total dissolved solute, electrical conductivity, total hardness, phosphate (PO4 3-), nitrate (NO3 -), sulfate (SO4 2-), dissolve oxygen (DO), biological oxygen demand, calcium (Ca2+), sodium (Na+), magnesium (Mg2+), total iron (Fe), manganese (Mn), copper (Cu) nickel (Ni), and total chromium (Cr) at 38 sampling sites during the wet and the dry seasons. The physical and ionic parameters were mostly found within the WHO (Guidelines for drinking-water quality, 3rd edn, Geneva 2004) standard for drinking water. The trace metals except Cu at some sites recorded values above the WHO (Guidelines for drinking-water quality, 3rd edn, Geneva 2004) standard for drinking water. This shows that the river water is not entirely fit for drinking. Mean values of physico-chemical parameters were mostly found to be high in the dry season as compared to the wet season. Cluster analysis (CA) and principal component analysis (PCA) were employed to evaluate the water quality and the interrelationship between variables. CA grouped the physico-chemical parameters into three groups (physical/minor ions, major ions and trace elements). Correlation analysis showed that physico-chemical parameters do not vary much in terms of the sampling sites. Thus, based on obtained information, it is possible to design a future, desirable sampling strategy, which could reduce the number of sampling stations and associated costs for effective river water quality management. Results showed that four principal components (industrial effect, domestic factor, natural source and agricultural effect) accounted for 65.59 % of the total variance among the water quality parameters. PCA also identified sampling sites 69R, 63R, 51M, 87L, 35L, 74L and 84L as polluted with metals. Therefore, water quality monitoring and control of release of industrial

  1. Changes in the fish community of the Kpong Headpond, lower Volta River, Ghana after 25 years of impoundment.

    PubMed

    Quarcoopome, Theodore; Amevenku, Francis; Ofori-Danson, Patrick

    2011-12-01

    The Kpong Headpond was the second created on the Volta River after Akosombo Dam, primarily as a source of hydroelectric power generation and potable water supply, and additionally, it has supported some fish production in Ghana since impoundment. The changes in fish community of the Kpong Headpond were studied to provide baseline information for strategies formulation to support the socio-economic development of the reservoir. The study identified changes in the fish community of the reservoir by comparing occurrence, composition, relative abundance and relative importance estimates of fish species, families and trophic groups, from available previous studies in the reservoir. From the collated information all fishes identified in the reservoir were categorised based on occurrence and importance as disappeared, appeared, permanent, declined or important, to show current status. The results indicated that the fish community has experienced a shift in the composition and relative abundance of important species, families and trophic groups in terms of number and weight, while remaining ecologically balanced. Representatives of the families Osteoglossidae, Centropomidae and Characidae have declined while representatives of the families Claroteidae, Cyprinidae and Cichlidae have increased. The aufwuch-detritus and herbivores declined while semi-pelagic omnivores increased resulting in a shift in dominance to benthic and semi pelagic omnivores. The appearance of five species and the disappearance of 25 others indicated a dynamic restructuring of the fish community in the reservoir, as expected. Enforcement of fishing regulations including the use of appropriate gear and fishing methods, fishery access control, promotion of culture-based fisheries and improvement in fisher education are recommended topics for sustainable fisheries in the reservoir. PMID:22208085

  2. Neoproterozoic/Lower Palaeozoic geodynamic evolution of Dronning Maud Land: integrating geology and geophysics

    NASA Astrophysics Data System (ADS)

    Jacobs, Joachim; Andreas, Läufer; Clark, Chris; Kleinhanns, Ilka; Elburg, Marlina; Ruppel, Antonia; Estrada, Solveig; Damaske, Detlef; Jokat, Wilfried; Riedel, Sven; Lucka, Nicole

    2013-04-01

    East Antarctica probably formed by amalgamation of a number of cratons along distinct Ediacaran mobile belts, including the ca. 600-500 Ma East African-Antarctic Orogen (EAAO) that dissects Dronning Maud Land (DML). New field-work during the international expeditions Geodynamic Evolution of East Antarctica (GEA) I + II in the austral summers 2010/11 and 2011/12, and first geochronological results from eastern DML reveal a complex tectonic architecture across the belt. In western DML, the EAAO reworks older Mesoproterozoic crust of the Maud Belt; the westernmost boundary of the mobile belt is characterized by a major dextral transpressional shear zone. In central DML, a major magnetic anomaly, the Forster anomaly, was interpreted as a cryptic suture of the EAAO (Riedel et al. 2012). The area where the Forster anomaly crosses the DML mountains is poorly investigated so far, but appears to coincide with a major strike slip shear zone in the southern Kurze Mts. and the occurrence of major Ediacaran granulite bodies. East of the Forster anomaly, the magnetic anomaly pattern changes significantly and typical Maud type crust is not present any longer. GEA II targeted a range of nunataks between Sør Rondane and central DML that had never been visited previously (from Blåklettane and Bergekongen in the E to Urna and Sørsteinen in the W). These nunataks are dominated by medium- to high-grade metasedimentary and metavolcanic rocks of possibly Neoproterozoic age, including abundant marble and graphite schists. Sør Rondane in eastern DML, is dominated by two distinct blocks separated by the dextral Main Shear Zone. The northwestern block is still part of the eastern EAAO, where new SHRIMP zircon data from metamorphic rims provide ages of ca. 560 Ma. The southeastern block is made up of a TTG terrane, which provides four new SHRIMP zircon dates between 990-980 Ma, interpreted as igneous crystallization ages (oceanic arc). The TTG terrane shows limited tectonic overprint and

  3. The Jormungand Global Climate State and Implications for the Neoproterozoic Snowball Paradox (Invited)

    NASA Astrophysics Data System (ADS)

    Abbot, D. S.; Voigt, A.; Koll, D.; Pierrehumbert, R. T.

    2010-12-01

    We present a previously undescribed global climate state, the Jormungand state, that is nearly ice-covered with a narrow (~10-15 degrees of latitude) strip of open ocean near the equator. This state is sustained by internal dynamics of the hydrological cycle and the cryosphere. There is a new bifurcation in global climate climate associated with the Jormungand state that leads to significant hysteresis. We investigate the Jormungand state in a coupled ocean-atmosphere GCM, in multiple atmospheric GCMs coupled to a mixed layer ocean run in an idealized configuration, and we make a simple modification to the Budyko-Sellers model so that it produces Jormungand states. We suggest that the Jormungand state may be a better model for the Neoproterozoic glaciations (~635 Ma and ~715 Ma) than either the hard Snowball or the Slushball models. A Jormungand state would have a large enough region of open ocean near the equator to explain the micropaleontological and molecular clock evidence that photosynthetic eukaryotes thrived both before and immediately after the Neoproterozoic episodes. Additionally, since there is significant hysteresis associated with the Jormungand state, it can explain the cap carbonate sequences, the oxygen isotopic evidence that suggests high CO2 values, and the various evidence that suggests lifetimes for the glaciations of 1 Myrs or more. Since there is not significant hysteresis associated with the Slushball model, the Slushball model cannot explain these observations. Finally, we note that although the Slushball and Jormungand models share the characteristic of open ocean in the tropics, the Jormungand state is produced by entirely different physics, is entered through a new bifurcation in global climate, and is associated with significant hysteresis. Bifurcation diagram of global climate in the CAM global climate model, run with no continents, a 50 m mixed layer with no ocean heat transport, an eccentricity of zero, and annually and diurnally

  4. Dronning Maud Lands (East Antarctica) significance for Late Mesoproterozoic/Early Neoproterozoic supercontinent reconstructions

    NASA Astrophysics Data System (ADS)

    Jacobs, Joachim; Elburg, Marlina; Laeufer, Andreas; Kleinhanns, Ilka C.; Henjes-Kunst, Friedhelm; Estrada, Solveig; Ruppel, Antonia; Damaske, Detlef; Montero, Pilar; Bea, Fernando

    2015-04-01

    The recent study of a so far white spot on the geological map of Dronning Maud Land (DML) during the international GEA expeditions sheds new light on the significance of major tectono-metamorphic provinces of Dronning Maud Land, East Antarctica. The western part of eastern DML allows the characterization and ground-truthing of a large and mostly ice-covered area, that is geophysically distinct and which was previously interpreted as a potentially older cratonic block south of a Late Neoproterozoic/EarlyPaleozoic mobile belt, which is exposed in the Sør Rondane Mts. (SRM). SHRIMP/SIMS zircon analyses of 20 samples together with new geochemistry indicate that the exposed basement consists of a ca. 1000-900 Ma juvenile terrane that is very similar to the juvenile rocks of the SW-Terrane of the SRM, a characteristic gabbro-trondhjemite-tonalite-granite suite. However, in contrast to the southern part of the SW-Terrane, our study area shows intense crustal reworking at medium to high-grade conditions between ca. 630-520 Ma, associated with significant felsic melt production, including A-type granitoid magmatism. Therefore, the study area, and thereby the aeromagnetically distinct SE DML province does neither represent the foreland of a Late Neoproterozoic/EarlyPaleozoic mobile belt, nor a craton, as has previously been speculated. It more likely represents the westward continuation of Rayner-age crust (1000-900 Ma) that has undergone additional protracted LN/EP overprinting. We interpret the southern part of the only weakly overprinted SW-Terrane as a mega-boudin within a broad, rheologically weaker, NW-SE trending LN/EP mobile belt. Rayner-type crust likely continues further west, where it abuts along the SW-trending Forster Magnetic Anomaly. The latter is interpreted as a suture, which separates typical Grenville-age crust of the Maud Belt to the W from Rayner-age crust to the E. The study area has therefore clearly Indian affinities. Its juvenile character with a

  5. Influence of the fusion of two subunits of the F420-non-reducing hydrogenase of Methanococcus voltae on its biochemical properties.

    PubMed

    Bingemann, R; Pierik, A J; Klein, A

    2000-11-01

    In Methanococcus voltae, one of the two [NiFeSe] hydrogenases is unusual in that the large subunit is split into two subunits, each contributing two ligands to the [NiFe] center that catalyzes the heterolytic cleavage of the dihydrogen molecule. We have engineered a fusion of these two subunits. The resulting new enzyme showed no significant difference in hydrogen uptake activity or in the Ni-C or Ni-L EPR spectra compared to the the wild-type enzyme, but exhibited a tenfold increase in both the Km for hydrogen and the Ki for the competitive inhibitor carbon monoxide. PMID:11131028

  6. Factors in the Effective Utilization of a LANDSAT Related Inventory in West Africa. [resource management in onchocerciasis-free Benin, Upper Volta, and Ghana

    NASA Technical Reports Server (NTRS)

    Hall, L.

    1982-01-01

    A comprehensive LANDSAT related resource inventory was performed in parts of Ghana, Benin, and Upper Volta to determine resource development potential in areas freed of the disease onchocerciasis. The ultimate success of the project lies in the effective use of the data by host country personnel in resource development projects. This requires project follow-through, adequate training of regional counterparts, and integration of the data into an easily used framework. Present levels of support systems and technical expertise in West Africa indicate that an automated system for natural resource data is not currently appropriate. Suggestions for the greater implementation of such inventories are explored.

  7. Geochemistry of the Neoproterozoic Johnnie Formation and Stirling Quartzite, southern Nopah Range, California: Deciphering the roles of climate, tectonics, and sedimentary process in reconstructing the early evolution of a rifted continental margin

    NASA Astrophysics Data System (ADS)

    Schoenborn, William A.

    The Neoproterozoic Stirling Quartzite and Johnnie Formation in the southern Nopah Range, southeastern California, comprise a thick sequence of predominantly siliciclastic sediment that is exposed along the Cordilleran margin. Located above the syn-rift Kingston Peak Formation, they mark the early deposits of passive margin sedimentation during the breakup of the Rodinia supercontinent. Disagreement exists between field-based observations and subsidence modeling as to whether these units represent rift or passive margin deposition. In this study, major-, trace-, and rare earth--element (REE) geochemistry, and U-Pb detrital zircon geochronology are used to determine their provenance, paleoclimatic information, and, consequently their paleotectonic setting. Geochemical and petrologic evidence confirm that Johnnie Formation mudstones and sandstones were the initial siliciclastic deposits laid along the Cordilleran Laurentian margin following the Neoproterozoic break-up of Rodinia. Johnnie Formation sediment has corrected CIA values between 63 and 83, and likely higher, which suggests moderate to intense weathering of the source. Modeling suggests the unweathered source likely possessed a composition of a 90% granodiorite + 10% high-K granite. This mixture balances petrographic observations, major element geochemistry, and the REE: (La/Sm)N = 4.19 +/- 1.26, (Gd/Yb)N = 1.34 +/- 0.38, Eu/Eu* = 0.63 +/- 0.09 and (La/Yb)N = 9.55 +/- 2.27. The hypothesis of a primary tectonic control on sediment composition (i.e. rift-basin deposition) is rejected because Johnnie Formation sediments largely lack lithic fragments that are indicative of derivation from a source area with rugged topography. Feldspars are distributed unevenly in finer grained sediments. Observed fluctuations in feldspar content of sediments from the lower to upper Johnnie Formation are attributed to increased abrasion and hydrodynamic sorting, which differentially segregated feldspars into finer grained

  8. Paleobiology of a Neoproterozoic tidal flat/lagoonal complex: the Draken Conglomerate Formation, Spitsbergen

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.; Swett, K.; Mark, J.

    1991-01-01

    Carbonates and rare shales of the ca 700-800 Ma old Draken Conglomerate Formation, northeastern Spitsbergen, preserve a record of environmental variation within a Neoproterozoic tidal flat/lagoon complex. Forty-two microfossil taxa have been recognized in Draken rocks, and of these, 39 can be characterized in terms of their paleoenvironmental distributions along a gradient from the supratidal zone to permanently submerged lagoons. Supratidal to subtidal trends include: increasing microbenthic diversity, increasing abundance and diversity of included allochthonous (presumably planktonic) elements, decreasing sheath thickness of mat-building organisms (with significant taphonomic consequences), and an increasing sediment/fossil ratio in fossiliferous rocks. Five principal and several minor biofacies can be distinguished. The paleoecological resolution obtainable in the Draken Conglomerate Formation rivals that achieved for most Phanerozoic fossil deposits. It documents the complexity and diversity of Proterozoic coastal ecosystems and indicates that both environment and taphonomy need to be taken into explicit consideration in attempts to understand evolutionary trends in early fossil record. Three species, Coniunctiophycus majorinum, Myxococcoides distola, and M. chlorelloidea, are described as new; Siphonophycus robustum, Siphonophycus septatum, and Gorgonisphaeridium maximum are proposed as new combinations.

  9. Sr isotopic characteristic of neoproterozoic carbonate sediments from the southern Yenisei Ridge

    NASA Astrophysics Data System (ADS)

    Vishnevskaya, I. A.; Kochnev, B. B.; Letnikova, E. F.; Kuznetsov, A. B.; Proshenkin, A. I.

    2012-04-01

    This paper presents the first Sr isotopic data for the Late Precambrian carbonate rocks of the southern Yenisei Ridge. Their geochemical study allowed estimation of the degree of secondary alterations and gave the possibility to reveal rocks with a less disturbed Rb-Sr isotopic system. The Sr isotopic data indicated Neoproterozoic sedimentation of the rocks about 1070-750 Ma ago. Sr and C isotopic data showed that carbonate rocks of the Sukhoi Pit, Tungusik, and Shirokino groups are Late Riphean and could be comparable with sedimentary sequences of three Precambrian key sections of the Northern Eurasia: the subsequent Derevnino, Burovaya, and Shorikha formations from the Turukhansk Uplift, the Lakhanda Group from the Uchur-Maya region, and the Karatav Group from the South Urals. All studied carbonate rocks are older than 750 Ma and, according to the International Stratigraphic Chart, accumulated prior to global glaciations in the Cryogenian. This is evident from sedimentological study indicating the absence of tillite horizons in the studied sections. δ13C values in the sections vary from +0.4 up to +5.3‰, which testifies to the absence of periods of great cold.

  10. Co-evolution of eukaryotes and ocean oxygenation in the Neoproterozoic era

    NASA Astrophysics Data System (ADS)

    Lenton, Timothy M.; Boyle, Richard A.; Poulton, Simon W.; Shields-Zhou, Graham A.; Butterfield, Nicholas J.

    2014-04-01

    The Neoproterozoic era (about 1,000 to 542 million years ago) was a time of turbulent environmental change. Large fluctuations in the carbon cycle were associated with at least two severe -- possible Snowball Earth -- glaciations. There were also massive changes in the redox state of the oceans, culminating in the oxygenation of much of the deep oceans. Amid this environmental change, increasingly complex life forms evolved. The traditional view is that a rise in atmospheric oxygen concentrations led to the oxygenation of the ocean, thus triggering the evolution of animals. We argue instead that the evolution of increasingly complex eukaryotes, including the first animals, could have oxygenated the ocean without requiring an increase in atmospheric oxygen. We propose that large eukaryotic particles sank quickly through the water column and reduced the consumption of oxygen in the surface waters. Combined with the advent of benthic filter feeding, this shifted oxygen demand away from the surface to greater depths and into sediments, allowing oxygen to reach deeper waters. The decline in bottom-water anoxia would hinder the release of phosphorus from sediments, potentially triggering a potent positive feedback: phosphorus removal from the ocean reduced global productivity and ocean-wide oxygen demand, resulting in oxygenation of the deep ocean. That, in turn, would have further reinforced eukaryote evolution, phosphorus removal and ocean oxygenation.

  11. Calcified microbes in Neoproterozoic carbonates: implications for our understanding of the Proterozoic/Cambrian transition

    NASA Technical Reports Server (NTRS)

    Knoll, A. H.; Fairchild, I. J.; Swett, K.

    1993-01-01

    Tidal flat and lagoonal dolostones of the Neoproterozoic Draken Formation, Spitsbergen, exhibit excellent preservation of carbonate fabrics, including heavily calcified microfossils. The crust-forming cyanobacterium Polybessurus is preserved locally by carbonate precipitated on and within sheaths in mildly evaporitic upper intertidal to supratidal environments. In contrast, calcified filaments in columnar stromatolites reflect subtidal precipitation. Filament molds in dolomicrites independently document extremely early lithification. The presence of heavily calcified cyanobacteria in Draken and other Proterozoic carbonates constrains potential explanations for the widespread appearance of calcified microorganisms near the Proterozoic-Cambrian boundary. We propose that the rarity of Proterozoic examples principally reflects the abundance and wide distribution of carbonate crystals precipitated on the sea floor or in the water column. Cyanobacterial sheaths would have competed effectively as sites for carbonate nucleation and growth only where calcitic and/or aragonitic nuclei were absent. In this view, the Proterozoic-Cambrian expansion of calcified microfossils primarily reflects the emergence of skeletons as principal agents of carbonate deposition.

  12. Geology and metallogeny of the Ar Rayn terrane, eastern Arabian shield: Evolution of a Neoproterozoic continental-margin arc during assembly of Gondwana within the East African orogen

    USGS Publications Warehouse

    Doebrich, J.L.; Al-Jehani, A. M.; Siddiqui, A.A.; Hayes, T.S.; Wooden, J.L.; Johnson, P.R.

    2007-01-01

    characteristics of the Ar Rayn terrane are analogous to the Andean continental margin of Chile, with opposite subduction polarity. The Ar Rayn terrane represents a continental margin arc that lay above a west-dipping subduction zone along a continental block represented by the Afif composite terrane. The concentration of epithermal, porphyry Cu and IOCG mineral systems, of central arc affiliation, along the AAF suggests that the AAF is not an ophiolitic suture zone, but originated as a major intra-arc fault that localized magmatism and mineralization. West-directed oblique subduction and ultimate collision with a land mass from the east (East Gondwana?) resulted in major transcurrent displacement along the AAF, bringing the eastern part of the arc terrane to its present exposed position, juxtaposed across the AAF against a back-arc basin assemblage represented by the Abt schist of the Ad Dawadimi terrane. Our findings indicate that arc formation and accretionary processes in the Arabian shield were still ongoing into the latest Neoproterozoic (Ediacaran), to about 620-600 Ma, and lead us to conclude that evolution of the Ar Rayn terrane (arc formation, accretion, syn- to postorogenic plutonism) defines a final stage of assembly of the Gondwana supercontinent along the northeastern margin of the East African orogen. ?? 2007 Elsevier B.V. All rights reserved.

  13. Crustal structure beneath the Paleozoic Parnaíba Basin revealed by airborne gravity and magnetic data, Brazil

    USGS Publications Warehouse

    de Castroa, David L.; Fuck, Reinhardt A.; Phillips, Jeffrey D. Phillips; Vidotti, Roberta M.; Bezerra, Francisco H.R.; Dantas, Elton L.

    2014-01-01

    The Parnaíba Basin is a large Paleozoic syneclise in northeastern Brazil underlain by Precambrian crystalline basement, which comprises a complex lithostructural and tectonic framework formed during the Neoproterozoic–Eopaleozoic Brasiliano–Pan African orogenic collage. A sag basin up to 3.5 km thick and 1000 km long formed after the collage. The lithologic composition, structure, and role in the basin evolution of the underlying basement are the focus of this study. Airborne gravity and magnetic data were modeled to reveal the general crustal structure underneath the Parnaíba Basin. Results indicate that gravity and magnetic signatures delineate the main boundaries and structural trends of three cratonic areas and surrounding Neoproterozoic fold belts in the basement. Triangular-shaped basement inliers are geophysically defined in the central region of this continental-scale Neoproterozoic convergence zone. A 3-D gravity inversion constrained by seismological data reveals that basement inliers exhibit a 36–40.5 km deep crustal root, with borders defined by a high-density and thinner crust. Forward modeling of gravity and magnetic data indicates that lateral boundaries between crustal units are limited by Brasiliano shear zones, representing lithospheric sutures of the Amazonian and São Francisco Cratons, Tocantins Province and Parnaíba Block. In addition, coincident residual gravity, residual magnetic, and pseudo-gravity lows indicate two complex systems of Eopaleozoic rifts related to the initial phase of the sag deposition, which follow basement trends in several directions.

  14. Evidence for a redox stratified Cryogenian marine basin, Datangpo Formation, South China

    NASA Astrophysics Data System (ADS)

    Li, Chao; Love, Gordon D.; Lyons, Timothy W.; Scott, Clinton T.; Feng, Lianjun; Huang, Jing; Chang, Huajin; Zhang, Qirui; Chu, Xuelei

    2012-05-01

    Here, in an effort to explore Cryogenian seawater chemistry, we present chemostratigraphic results for iron, carbon, molybdenum, and sulfur for two outcrop sections for the ca. 663-654 Ma Datangpo Formation deposited between the two major Neoproterozoic glacial episodes (Sturtian and Marinoan) in the Nanhua Basin, South China. Paleogeographic reconstruction suggests that the interglacial Nanhua Basin was an emerging young ocean basin, which opened by rifting from ca. 820-630 Ma. Seawater exchange with the open ocean was restricted; such interglacial conditions may have been a common feature throughout the region and the world in association with widespread rifted margins during global sea-level lowstands. Geochemical profiles generated for the shallow water Yangjiaping and deeper water Minle sections demonstrate broadly consistent stratigraphic variations and generally point to anoxic (mostly euxinic) deep water deposition for the lower black shales but increasing oxygenation for the upper siltstones deposited in shallower water at both sections. Fluctuations in water chemistry recorded in the Datangpo Formation can be explained by a stratified redox model in which water column chemistry was strongly controlled by Fe availability and other nutrient fluxes, low dissolved marine sulfate concentrations, sea level variation, and varying inputs of marine organic carbon delivered via primary production. A compilation of new and published sulfur isotope data for the Datangpo Formation indicates that the extremely 34S-enriched pyrite (up to 69‰) in the basal carbonates and shales was formed mainly in the deep waters of the Nanhua Basin. The most likely explanation is a 34S-enriched deep marine sulfate pool generated, in part, during the Sturtian glaciation by bacterial sulfate reduction in combination with severely suppressed riverine sulfate inputs and restriction of the marginal basin during a dramatic drop in sea level. This study highlights the importance of both

  15. Generation of continental crust in the northern part of the Borborema Province, northeastern Brazil, from Archaean to Neoproterozoic

    NASA Astrophysics Data System (ADS)

    de Souza, Zorano Sérgio; Kalsbeek, Feiko; Deng, Xiao-Dong; Frei, Robert; Kokfelt, Thomas Find; Dantas, Elton Luiz; Li, Jian-Wei; Pimentel, Márcio Martins; Galindo, Antonio Carlos

    2016-07-01

    (TZ). Early Neoproterozoic volcanism at 1091 Ma, and A-type plutonism, from 920 to 775 Ma, mark the intracontinental magmatism in the TZ. In the Seridó Domain, the Late Neoproterozoic registers several events of plutonism, at 600-593, 575-560, 548-533, 528-510, 495-450 Ma. These rocks cover ca. 15% of the area, while Neoproterozoic supracrustal rocks cover ca. 30%. The most important magmatic event is that at 575 Ma, consistent with the peak of widespread transpression and synchronous high temperature metamorphism. The Neoproterozoic rocks are mostly K-enriched alkaline or transitional to calc-alkaline. Inherited Archaean and Palaeoproterozoic zircons and Nd model ages, as well as moderate to strongly negative (-21 to -9) epsilon Nd, and persistent negative anomalies for Ta-Nb, Ti and P indicate significant crustal contributions in their genesis. While a convergent setting (subduction zone) could explain the Archaean and Palaeoproterozoic units, this is not so for the Neoproterozoic rocks which mimic the geochemical and isotopic features of the older sources. In the study area, the peak of juvenile accretion (mantle derived magmas) took place in the Archaean (3.4-2.7 Ga) and Palaeproterozoic (2.4-2.11 Ga), whereas crustal recycling predominated in the Neoproterozoic.

  16. An O-17 record of Neoproterozoic snowball Earth in Kimberley, Western Australia

    NASA Astrophysics Data System (ADS)

    Bao, H.; Chen, Z.; Zhou, C.

    2011-12-01

    Non-mass-dependently 17O-depleted signatures have recently been found in sulfate associated with the aftermath of Marinoan glacial meltdown at ca. 635 million years ago. The anomaly was proposed to be inherited from atmospheric O2 via oxidative weathering of sulfides. An extremely high pCO2 atmosphere could produce such an anomaly. The finding has become one of the strongest lines of evidence supporting a "hard" snowball Earth hypothesis. Further studies linking the Δ17O of barite to sedimentological-geological context in Marinoan South China confirm that the 17O-depleted sulfate was derived from oxidative weathering and the anomalous 17O signal was detectable at sites close to paleo-continental runoffs while diluted and often undetectable in the open oceans. On the other hand, host minerals or rocks for the Marinoan 17O anomalies have been limited to barite (South China and West Africa) and carbonate-associated sulfate (CAS) in limestone lenses within the diamictite (Svalbard). If the 17O depletion is indeed closely related to an extraordinary atmospheric condition associated with the great Marinoan meltdown, the signal should be global in its distribution. Kimberley region of Western Australia was close to a continent in late Neoproterozoic, according to Rodinia reconstruction and regional geology. A confirmation of this anomalous signal in Australia is a critical test to our hypothesis. We report here that the Δ17O of carbonate-associated sulfate reaches as low as -0.68% in the dolostones draping the Neoproterozoic Moonlight-Valley (MLV) diamictite, Texas/Mabel Downs, Kimberley, Western Australia. The magnitude of the 17O depletion gradually decreases (i.e. approaching normal) when going up towards the overlying Ranford sandstone. A positive correlation between the δ34S and the Δ17O exists, as does the case in South China and Svalbard. The CAS in the MLV cap dolostones in the Palm Spring section, however, does not bear distinct 17O depletion. Neither does

  17. Geochronological constraints on terminal Neoproterozoic events and the rise of Metazoan

    NASA Astrophysics Data System (ADS)

    Bowring, S.; Myrow, P.; Landing, E.; Ramezani, J.; Grotzinger, J.

    2003-04-01

    A full understanding of Neoproterozoic history has been plagued by a lack of precise geochronological constraints. In particular the correlation and duration of global or "Snowball" glaciations has relied on physical stratigraphy and chemostratigraphy which has given rise to much debate about the number, magnitude, and duration of glacial deposits. New U-Pb constraints on the age of the Gaskiers Formation glacial deposits in Newfoundland, an age for the oldest Ediacaran fossils in the same area, and the age and significance of the Cambrian/Precambrian boundary in Oman have important implications for global correlation and the timing of the rise of Metazoans. In the central and eastern parts of the Avalon Peninsula, southeastern Newfoundland, the oldest rocks are arc-related tuffs, agglomerates, and flows of the Harbour Main Group (>1.5 km thick) that have published dates from 606-630 Ma. These are overlain by approximately 7.5 km of marine siliciclastic rocks of the Conception Group. Over 2,300 m of deep-water deposits of the Mall Bay and Drook formations are separated by the regionally extensive glacial diamictite of the Gaskiers Formation (up to 300 m-thick). This unit is often described as a Varanger-age glaciomarine deposit and is locally overlain by a thin cap carbonate bed with a highly negative C isotopic signature. Thin (1-15 cm) silicic ash beds are found interlayered with turbidites just below and above the glacial deposits and the glacial deposits locally contain volcanic bombs, pyroclastic debris, and lavas. U-Pb geochronology of zircons separated from ash-beds below, within, and above the glacial deposits indicates that they are ca 580 Ma. This is considerably younger than previous estimates and calls into question many of the global correlations with similar rocks. An ash-bed within the overlying Drook formation is preserved in depositional contact with spectacular surfaces exposing Ediacaran fossils. Zircons separated from it yield an age of 575 Ma

  18. Is high obliquity a still plausible explanation for Neoproterozoic low-latitude glaciations ?

    NASA Astrophysics Data System (ADS)

    Levrard, B.; Laskar, J.

    2003-04-01

    The observations of enigmatic low-latitude glaciogenic sequences during the Sturtian (˜ 750-700 Ma) and the Varanger (˜ 620-570 Ma) glacial intervals of the Neopropterozo& uml;i c era remain the subject of controversial debates concerning possible scenarii. Of the many models that have been proposed to account for theses paradoxical features, the high-obliquity scenario invoked by G.E. Williams (1975) appears to be still largely considered. However, a such scenario requires a dissipative mechanism to bring back the Earth's obliquity from a value higher than 55o to the present value (˜ 23.5o) in less than 200 Ma. Williams (1993) suggested that core-mantle friction could have explained this substantial decrease. However, it was demonstrated by Néron de Surgy and Laskar (1997) and confirmed by Pais et al. (1999) that, not only it requires abnormal values of effective viscosity, but due to the conservation of the angular momentum, it is also largely conflicting with the paleorotation data. D.M Williams et al. (Nature, 1998) recently proposed that ``climate friction" could have produced this decrease in less than 100 Ma between ˜ 600 Ma and 500 Ma. We have revisited in details this mecanism (Levrard and Laskar, submitted to Geo. J. Int., 2002) for the Neoproterozoic glaciations. In response to periodic variations in the obliquity, the redistribution of ice/water mass and the isostatic adjusment to the surface loading affect the dynamical ellipticity of the Earth. Delayed responses in the mass redistribution may introduce a secular term in the obliquity evolution (Bills, 1994; Rubincam, 1995; Ito et al, 1995). We analyze the obliquity-oblateness feedback using non-linear response of ice sheets (Imbrie and Imbrie, 1980) to insolation forcing and layered models with Maxwell visco-elastic rheology. Possible increase in the non-linear response of ice sheets to insolation forcing and latitudinal changes in this forcing strongly limit the contribution of the obliquity

  19. Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoxia; Wang, Tao; Zhang, Chengli

    2013-08-01

    The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U-Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979-711 Ma), Paleozoic (507-400 Ma), and Early (252-185 Ma) and Late (158-100 Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979-911 Ma, weakly deformed I-type granites at 894-815 Ma, and A-type granites at 759-711 Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507-470 Ma, 460-422 Ma and ˜415-400 Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507-470 Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460-422 Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ˜415-400 Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185 Ma, with the cluster in 225-200 Ma. It took place predominantly in the western part of the South Qinling Belt. The 250-240 Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction

  20. Post-collisional potassic granitoids from the southern and northwestern parts of the Late Neoproterozoic East African Orogen: a review

    NASA Astrophysics Data System (ADS)

    Küster, Dirk; Harms, Ulrich

    1998-12-01

    Potassic metaluminous granitoids with enrichments of HFS elements constitute part of widespread post-collisional magmatism related to the Late Neoproterozoic Pan-African orogeny in northeastern Africa (Sudan, Ethiopia, Somalia) and Madagascar. The plutons were emplaced between 580 and 470 Ma and comprise both subsolvus and hypersolvus biotite-granite, biotite-hornblende-granite, quartz-monzonite and quartz-syenite. Pyroxene-bearing granitoids are subordinate. Basic dikes and enclaves of monzodioritic composition are locally associated with the granitoid plutons. Granitoids emplaced in pre-Neoproterozoic crust have Sr i-ratios between 0.7060 and 0.7236 and ɛNd( t) values between -15.8 and -5.6 while those emplaced in, or close to the contact with, juvenile Neoproterozoic crust have lower Sr i-ratios (0.7036-0.7075) and positive ɛNd( t) values (4.6). However, it is unlikely that the potassic granitoids represent products of crustal melting alone. The association with basic magmas derived from subduction-modified enriched mantle sources strongly suggests that the granitoids represent hybrid magmas produced by interaction and mixing of mantle and crust derived melts in the lower crust. The most intense period of this potassic granitoid magmatism occurred between 585 and 540 Ma, largely coeval with HT granulite facies metamorphism in Madagascar and with amphibolite facies retrogression in northeastern Africa (Somalia, Sudan). Granitoid magmatism and high-grade metamorphism are probably both related to post-collisional lithospheric thinning, magmatic underplating and crustal relaxation. However, the emplacement of potassic granites continued until about 470 Ma and implies several magmatic pulses associated with different phases of crustal uplift and cooling. The potassic metaluminous granites are temporally and spatially associated with post-collisional high-K calc-alkaline granites with which they share many petrographical, geochemical and isotopical similarities

  1. Neoproterozoic structural evolution of the NE-trending Ad-Damm Shear Zone, Arabian Shield, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Hamimi, Zakaria; El-Sawy, El-Sawy K.; El-Fakharani, Abdelhamid; Matsah, Mohamed; Shujoon, Abdulrahman; El-Shafei, Mohamed K.

    2014-11-01

    The Ad-Damm Shear Zone (AdSZ) is a major NE- (to NNE-) trending fault zone separating Jiddah and Asir tectonic terranes in the Neoproterozoic Juvenile Arabian Shield (AS). AdSZ is characterized by the development of dextral transcurrent shear-sense indicators and moderately to steeply NW plunging stretching lineations. It is mainly developed under high amphibolite-to greenschist-facies conditions and extends ∼380 km, with an average width ∼2-4 km, from the conspicuous Ruwah Fault Zone in the eastern shield to the Red Sea Coastal plain. It was believed to be one of the conjugate shears of the NW- to NNW-trending sinistral Najd Shear System. This assumption is, based on the noteworthy dextral shear criteria recorded within the 620 Ma mylonitic granite of No'man Complex. A total shear-zone strike length exceeding 117 km is carefully investigated during this study to reconstruct its structural evolution. Shear-sense indicators and other field observations including overprinting relations clearly demonstrate a complicated Neoproterozoic history of AdSZ, involving at least three phases of deformations (D1-D3). Both D1 and D2 phases were of contractional regime. During D1 phase a NW-SE compression led to the formation of NE-oriented low-angle thrusts and tight-overturned folds. D2 is represented by a NE-SW stress oriented that led to the development of an open folding. D3 is expressed by the NE-SW intensive dextral transcurrent brittle-ductile shearing. It is overprinting the early formed fabrics and played a significant role in the creation of AdSZ and the mega-scale related folds. Such deformation history reflects the same Neoproterozoic deformation regime recognized in the NE-trending shear zones in the Arabian-Nubian Shield (ANS).

  2. Neoproterozoic extension in the greater dharwar craton: A reevaluation of the "betsimisaraka suture" in madagascar

    USGS Publications Warehouse

    Tucker, R.D.; Roig, J.-Y.; Delor, C.; Amlin, Y.; Goncalves, P.; Rabarimanana, M.H.; Ralison, A.V.; Belcher, R.W.

    2011-01-01

    The Precambrian shield of Madagascar is reevaluated with recently compiled geological data and new U-Pb sensitive high-resolution ion microprobe (SHRIMP) geochronology. Two Archean domains are recognized: the eastern Antongil-Masora domain and the central Antananarivo domain, the latter with distinctive belts of metamafic gneiss and schist (Tsaratanana Complex). In the eastern domain, the period of early crust formation is extended to the Paleo-Mesoarchean (3.32-3.15 Ga) and a supracrustal sequence (Fenerivo Group), deposited at 3.18 Ga and metamorphosed at 2.55 Ga, is identified. In the central domain, a Neoarchean period of high-grade metamorphism and anatexis that affected both felsic (Betsiboka Suite) and mafic gneisses (Tsaratanana Complex) is documented. We propose, therefore, that the Antananarivo domain was amalgamated within the Greater Dharwar Craton (India + Madagascar) by a Neoarchean accretion event (2.55-2.48 Ga), involving emplacement of juvenile igneous rocks, high-grade metamorphism, and the juxtaposition of disparate belts of mafic gneiss and schist (metagreenstones). The concept of the "Betsimisaraka suture" is dispelled and the zone is redefined as a domain of Neoproterozoic metasedimentary (Manampotsy Group) and metaigneous rocks (Itsindro-Imorona Suite) formed during a period of continental extension and intrusive igneous activity between 840 and 760 Ma. Younger orogenic convergence (560-520 Ma) resulted in east-directed overthrusting throughout south Madagascar and steepening with local inversion of the domain in central Madagascar. Along part of its length, the Manampotsy Group covers the boundary between the eastern and central Archean domains and is overprinted by the Angavo-Ifanadiana high-strain zone that served as a zone of crustal weakness throughout Cretaceous to Recent times.

  3. Late Neoproterozoic Nuqara Dokhan Volcanics, Central Eastern Desert, Egypt: Geochemistery and petrogenesis

    NASA Astrophysics Data System (ADS)

    Hassan, Tharwat; Asran, Asran; Amron, Taha; Natflos, Theo

    2014-05-01

    The Nuqara volcanic is one of the northernmost outcrops of the Arabian-Nubian Shield Dokhan volcanics. The origin and tectonic setting of the late Neoproterozoic Dokhan volcanics (ca. 610-560 Ma) in the Egyptian Eastern Desert is highly debated. The debate concerns the tectonic setting where they formed during transition between convergent to extensional regime or after the East- and the West-Gondwana collision (~600Ma). In order to solve this problem, lavas from Nuqara area were studied geologically and geochemically. Nuqara Dokhan volcanics comprises two main rock suites: (a) an intermediate volcanic suite, consisting of basaltic andesite, andesite and their associated pyroclastics rocks; and (b) a felsic volcanic suite composed of dacite, rhyolite and ignimbrites. The two suites display well-defined major and trace element trends and continuum in composition with wide ranges in SiO2 (52-75.73%), CaO (9.19-0.22%), MgO (5.29-0.05%), Sr (1367-7.4 ppm), Zr (688.5-172.7 ppm), Cr (207-0.4 ppm), and Ni (94.3-0.2 ppm). The Nuqara Dokhan volcanics are characterized by strong enrichment in LILE relative to HFSE and affiliated to the calc-alkaline subducted - related magmatism. Geochemical Modeling displays that the evolution of these rocks was governed by fractional crystallization of plagioclase, amphiboles, pyroxene, magnetite and apatite in the intermediate varieties and plagioclase, amphibole, magnetite, apatite and zircon in the felsic varieties. The obtained mineral chemistry of these volcanics reveals: (a) Plagioclase range in composition from An55 to An40 in basaltic andesite and from An39 to An24 in andesite. (b) Alkali feldspars have sanidine composition. (c) Clinopyroxenes have augite composition. The low Al2O3 contents (1.94-5.588 wt %) indicate that clinopyroxene crystallized at low - pressure conditions. (d) Amphiboles have magnesio- hornblende composition.

  4. The petrogenesis of late Neoproterozoic mafic dyke-like intrusion in south Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Azer, M. K.; Abu El-Ela, F. F.; Ren, M.

    2012-08-01

    New field, petrographical and geochemical studies are presented here for the late Neoproterozoic Rimm intrusion (˜15 km long) exposed in the southern Sinai Peninsula, Egypt in the northernmost Arabian-Nubian Shield (ANS). Field relations indicate that the Rimm intrusion is younger than the surrounding metamorphic rocks and calc-alkaline syn-tectonic granodiorite and it was not affected by regional metamorphism. The anorogenic peralkaline granite of Gebel Serbal crosscuts the Rimm intrusion. The Rimm intrusion is made up of several consanguineous rock types with gradational contacts. It is composed chiefly of pyroxene-hornblende gabbro, hornblende gabbro and minor quartz diorite. The chemical composition of the mafic minerals indicated that the studied rocks derived from calc-alkaline mafic magma. Geochemically, the studied rocks are characterized by enrichment in LILE relative to HFSE and LREE relative to HREE [(Ce/Yb)N = 4.50-6.36]. Quartz diorite display slightly concave HREE pattern and slightly negative Eu-anomaly [(Eu/Eu*)n = 0.91] which may be the result of fractionation of amphibole and plagioclase from the source melt, respectively. The Rimm intrusion evolved from mafic mantle magma into different type rocks by fractional crystallization with minor crustal contamination. The initial magma corresponds to pyroxene-hornblende gabbro and the crystallization of hornblende was caused by slight H2O increase in magma after crystallization of near-liquidus clinopyroxene and Ca-rich plagioclase. Amphiboles geobarometer indicate that the gabbroic rocks of the Rimm intrusion crystallized at pressures between 4.8 and 6.4 Kb, while quartz diorite crystallized at 1.3-2.1 Kb. Crystallization temperatures range between 800 and 926 °C for the gabbros and between 667 and 784 °C for the quartz diorite. The Rimm intrusion represents a post-orogenic phase formed during the crustal thinning and extension of the Arabian-Nubian Shield.

  5. Triple oxygen isotope evidence for elevated CO2 levels after a Neoproterozoic glaciation.

    PubMed

    Bao, Huiming; Lyons, J R; Zhou, Chuanming

    2008-05-22

    Understanding the composition of the atmosphere over geological time is critical to understanding the history of the Earth system, as the atmosphere is closely linked to the lithosphere, hydrosphere and biosphere. Although much of the history of the lithosphere and hydrosphere is contained in rock and mineral records, corresponding information about the atmosphere is scarce and elusive owing to the lack of direct records. Geologists have used sedimentary minerals, fossils and geochemical models to place constraints on the concentrations of carbon dioxide, oxygen or methane in the past. Here we show that the triple oxygen isotope composition of sulphate from ancient evaporites and barites shows variable negative oxygen-17 isotope anomalies over the past 750 million years. We propose that these anomalies track those of atmospheric oxygen and in turn reflect the partial pressure of carbon dioxide (P(CO2)) in the past through a photochemical reaction network linking stratospheric ozone to carbon dioxide and to oxygen. Our results suggest that P(CO2) was much higher in the early Cambrian than in younger eras, agreeing with previous modelling results. We also find that the (17)O isotope anomalies of barites from Marinoan (approximately 635 million years ago) cap carbonates display a distinct negative spike (around -0.70 per thousand), suggesting that by the time barite was precipitating in the immediate aftermath of a Neoproterozoic global glaciation, the P(CO2) was at its highest level in the past 750 million years. Our finding is consistent with the 'snowball Earth' hypothesis and/or a massive methane release after the Marinoan glaciation. PMID:18497821

  6. Tectonic significance of Neoproterozoic magmatism of Nakora area, Malani igneous suite, Western Rajasthan, India

    NASA Astrophysics Data System (ADS)

    Kumar, Naresh; Vallinayagam, G.

    2014-05-01

    Three magmatic phases are distinguished in the Neoproterozoic Nakora Ring Complex (NRC) of Malani Igneous Suite (MIS), namely (a) Extrusive (b) Intrusive and (c) Dyke phase. Magmatism at NRC initiated with minor amount of (basic) basalt flows and followed by the extensive/voluminous acid (rhyolites-trachytes) flows. The ripple marks are observed at the Dadawari area of NRC in tuffaceous rhyolite flow which suggests the aqueous condition of flows deposition. The emplacement of the magma appears to have been controlled by a well defined NE-SW tectonic lineament and cut by radial pattern of dykes. These NE-SW tectonic lineaments are the linear zones of crustal weakness and high heat flow. The spheroidal and rapakivi structures in the Nakora acid volcanics indicate the relationship between genetic link and magma mixing. Basalt-trachyte-rhyolite association suggests that the large amount of heat is supplied to the crust from the magma chamber before the eruption. The field (elliptical/ring structures), mineralogical and geochemical characteristics of Nakora granites attest an alkaline character in their evolution and consistent with within plate tectonic setting. The emplacement of these granites and associated volcanics is controlled by ring structures, a manifestation of plume activity and cauldron subsidence, an evidence of extensional tectonic environment. NRC granites are the product of partial melting of rocks similar to banded gneiss from Kolar Schist Belt of India. The present investigations suggest that the magmatic suites of NRC rocks are derived from a crustal source and the required heat supplied from a mantle plume.

  7. What Can Earth Paleoclimates Reveal About the Resiliency of Habitable States? An Example from the Neoproterozoic Snowball Earth

    NASA Astrophysics Data System (ADS)

    Sohl, L.

    2014-04-01

    The Neoproterozoic "Snowball Earth" glaciations (~750-635 Ma) have been a special focus for outer habitable zone investigations, owing in large part to a captivating and controversial hypothesis suggesting that Earth may have only narrowly escaped a runaway icehouse state on multiple occasions (a.k.a. "the hard snowball"; Hoffman and Schrag 2001). A review of climate simulations exploring snowball inception (Godderis et al. 2011) reveals that a broad range of models (EBMs, EMICs and AGCMs) tend to yield hard snowball solutions, whereas models with greater 3-D dynamic response capabilities (AOGCMs) typically do not, unless some of their climate feedback responses (e.g., wind-driven ocean circulation, cloud forcings) are disabled (Poulsen and Jacobs 2004). This finding raises the likelihood that models incorporating dynamic climate feedbacks are essential to understanding how much flexibility there may be in the definition of a planet's habitable zone boundaries for a given point in its history. In the first of a series of new Snowball Earth simulations, we use the NASA/GISS ModelE2 Global Climate Model - a 3-D coupled atmosphere/ocean model with dynamic sea ice response - to explore the impacts of wind-driven ocean circulation, clouds and deep ocean circulation on the sea ice front when solar luminosity and atmospheric carbon dioxide are reduced to Neoproterozoic levels (solar = 94%, CO2 = 40 ppmv). The simulation includes a realistic Neoproterozoic land mass distribution, which is concentrated at mid- to tropical latitudes. After 300 years, the sea ice front is established near 30 degrees latitude, and after 600 years it remains stable. As with earlier coupled model simulations we conclude that runaway glacial states would have been difficult to achieve during the Neoproterozoic, and would be more likely to have occurred during earlier times in Earth history when solar luminosity was less. Inclusion of dynamic climate feedback capabilities in habitable zone

  8. The Mintom Formation (new): Sedimentology and geochemistry of a Neoproterozoic, Paralic succession in south-east Cameroon

    NASA Astrophysics Data System (ADS)

    Caron, V.; Ekomane, E.; Mahieux, G.; Moussango, P.; Ndjeng, E.

    2010-06-01

    This paper presents a lithologic and stratigraphic description of the Neoproterozoic (ante- or syn- Pan-African orogeny) Mintom Formation (new) of southeastern Cameroon, and provides a new facies and geochemical analysis of the sedimentary succession, formerly referred to as the upper Dja series. The Mintom Formation can be subdivided from base to top into four members that record a general increase in carbonate content. The members (all new) from lower to upper are: Kol Member (diamictite and pelite), Metou Member (dolostone), Momibolé Member (calcareous pelite), and Atog Adjap Member (limestone). Although the lithostratigraphic architecture looks very similar to that of well-documented syn- and post-glacial Neoproterozoic deposits, physical evidence of glacial influence is absent. By contrast with other Central African Neoproterozoic carbonates deposited in ramp settings, the succession does not contain open marine facies. Limestones consist of monotonous subhedral microsparitic calcite mosaics and display occasional microbial laminae. These observations force reevaluation of both previous paleoenvironmental interpretations of the deposits and their comparison with neighboring Ediacaran carbonates. We assume that the graded basal succession from diamictite to laminated pelitic facies is compatible with emplacement of mass flow deposits in toe-of-slope setting during regional uplift. Interpretation of the overlying Métou dolostone is uncertain though sedimentological and geochemical properties point to a likely quiet depositional setting. The upper part of the Formation, including the Momibolé and Atog Adjap Members, is conspicuously laminated, in places rhythmically and ripple-bedded, suggesting shallow subaqueous and calm depositional conditions only interrupted by occasional slumps indicative of a locally steepened bottom topography. Evaporitic fabrics and fenestral pores further indicate shallow water, possibly peritidal, environmental conditions. In spite

  9. Studies on the reinvasion of the Onchocerciasis Control Programme in the Volta River Basin by Simulium damnosum s.I. with emphasis on the south-western areas.

    PubMed

    Garms, R; Walsh, J F; Davies, J B

    1979-09-01

    The aerial larvicidng operation of the Onchocerciasis Control Programme of the World Health Organization which began in February 1975 resulted in a sharp reduction in Simulium damnosum numbers. However, at the onset of the rainy season the fly population increased in certain areas. Detailed surveys both on the ground and by helicopter did not reveal any significant failures of treatments that could account for the fly densities observed, and it was concluded that the flies must originate from sources outside the controlled zone. This reinvasion proved to be an annual occurrence which has been studied in detail between 1975 and 1978 in the south-western parts of the control zone. The methods used included full day catches by vector collectors carried out every day throughout the season, cytotaxonomic determination of larvae, detailed morphological examination of reared and biting adults and treatment of suspected source rivers with insecticide. The results indicate that the invasion takes place in a SW-NE direction across country for distances of 300 km or more along the track of the monsoon winds. It involves mainly the savanna cytospecies S. damnosum s. str. and S. sirbanum. The invading populations are composed of older parous flies, many of which carry infective 3rd stage larvae indistinguishable from those of Onchocerca volvulus. These females tend to bite close to the rivers and do not disperse as far as normal populations with a higher proportion of younger flies. PMID:575581

  10. Biostratigraphic and chemostratigraphic correlation of Neoproterozoic sedimentary successions: upper Tindir Group, northwestern Canada, as a test case

    NASA Technical Reports Server (NTRS)

    Kaufman, A. J.; Knoll, A. H.; Awramik, S. M.

    1992-01-01

    Recent advances in Proterozoic micropaleontology and sedimentary isotope geochemistry suggest that improved interbasinal correlation of Neoproterozoic (1000-540 Ma) successions is possible. Because widely varying interpretations of its age have been suggested and no reliable radiometric dates or paleomagnetic data are available, the upper Tindir Group of northwestern Canada provides an opportunity to test this hypothesis. The age of these strata is of paleontological importance because silicified carbonates near the top of the group contain disc-shaped-scale microfossils that may provide insights into the early evolution of biomineralization. A reinterpretation of upper Tindir microfossil assemblages suggests a late Riphean age. Although diagenesis and contact metamorphism have altered the isotopic compositions of some carbonates, least altered samples indicate that delta 13C of contemporaneous seawater was at least +4.7%, typical of Neoproterozoic, but not Cambrian, carbonates. Strontium isotopic compositions of the least altered samples yield values of approximately 0.7065, which can be uniquely correlated with late Riphean seawater. Together, micropaleontology and the isotopic tracers of C and Sr constrain the upper Tindir carbonates and their unique fossils to be late Riphean, likely between 620 and 780 Ma.

  11. Neoproterozoic-Early Paleozoic tectonic evolution of the western part of the Kyrgyz Ridge (Northern Tian Shan) caledonides

    NASA Astrophysics Data System (ADS)

    Degtyarev, K. E.; Ryazantsev, A. V.; Tretyakov, A. A.; Tolmacheva, T. Yu.; Yakubchuk, A. S.; Kotov, A. B.; Salnikova, E. B.; Kovach, V. P.

    2013-11-01

    The conducted comprehensive study of the western part of Kyrgyz Ridge provided new data on the structure, composition and age of Precambrian and Early Paleozoic stratified and igneous complexes. The main achievements of these studies are: (1) the establishment of a wide age spectrum, embracing the interval from the Neoproterozoic to the end of the Early Ordovician, for the clastic-carbonate units composing the cover of the Northern Tian Shan sialic massif; (2) the reconstruction and dating of Early and Late Cambrian ophiolite complexes formed in suprasubduction settings;(3) the discovery and dating of the Early-Middle Ordovician volcano-sedimentary complex of island-arc affinity; and (4) proof of the wide occurrence of Late Ordovician granitoids, some of which bear Cu-Au-Mo ores. The intricate thrust-and-fold structure of the western part of the Kyrgyz Ridge, formed in several stages from the Middle Cambrian (?) until the end of the Middle Ordovician, was scrutinized; the importance of the Early Ordovician stage was demonstrated. The intrusion of large batholiths in the early Late Ordovician accomplished the caledonide structural evolution. Formation of Neoproterozoic and Early Paleozoic caledonide complexes, which were possibly related to the protracted and entangled evolution of the active continental margin, ceased by the Late Ordovician.

  12. Removing the effects of metamorphism from the Neoproterozoic carbon isotope record: a case study on Islay, western Scotland

    NASA Astrophysics Data System (ADS)

    Skelton, Alasdair

    2016-04-01

    The Port Askaig Formation on Islay, western Scotland is the first discovered tillite (glacial sediment) of Neoproterozoic age. This formation is sandwiched between carbonate rocks which preserve an extreme negative carbon isotope excursion. This so called "Islay anomaly" has been correlated with other such anomalies worldwide and together with the tillites has been cited as evidence of major (worldwide) glaciation events. During subsequent mountain building, this carbonate-tillite- carbonate sequence has been folded, producing a major en-echelon anticlinal fold system. Folding was accompanied by metamorphism at greenschist facies conditions which was, in turn, accompanied by metamorphic fluid flow. Mapping of the δ18O and δ13C values of these carbonate rocks reveals that metamorphic fluids were channelled through the axial region of the anticlinal fold. The metamorphic fluid was found to have a highly negative δ13C value, which was found to be in equilibrium with metamorphosed graphitic mudstones beneath the carbonate-tillite-carbonate sequence. Devolatilisation of these mudstones is therefore a likely source of this metamorphic fluid. Removal of the effects of metamorphic fluid flow on δ13C values recorded by metamorphosed carbonate rocks on Islay allows us to re-evaluate the isotopic evidence used to reconstruct Neoproterozoic climate. We are able to show that extreme negative δ13C values can partly be attributed to metamorphic fluid flow.

  13. Biostratigraphic and chemostratigraphic correlation of Neoproterozoic sedimentary successions: upper Tindir Group, northwestern Canada, as a test case.

    PubMed

    Kaufman, A J; Knoll, A H; Awramik, S M

    1992-02-01

    Recent advances in Proterozoic micropaleontology and sedimentary isotope geochemistry suggest that improved interbasinal correlation of Neoproterozoic (1000-540 Ma) successions is possible. Because widely varying interpretations of its age have been suggested and no reliable radiometric dates or paleomagnetic data are available, the upper Tindir Group of northwestern Canada provides an opportunity to test this hypothesis. The age of these strata is of paleontological importance because silicified carbonates near the top of the group contain disc-shaped-scale microfossils that may provide insights into the early evolution of biomineralization. A reinterpretation of upper Tindir microfossil assemblages suggests a late Riphean age. Although diagenesis and contact metamorphism have altered the isotopic compositions of some carbonates, least altered samples indicate that delta 13C of contemporaneous seawater was at least +4.7%, typical of Neoproterozoic, but not Cambrian, carbonates. Strontium isotopic compositions of the least altered samples yield values of approximately 0.7065, which can be uniquely correlated with late Riphean seawater. Together, micropaleontology and the isotopic tracers of C and Sr constrain the upper Tindir carbonates and their unique fossils to be late Riphean, likely between 620 and 780 Ma. PMID:11537751

  14. Transcriptional regulation of genes encoding the selenium-free [NiFe]-hydrogenases in the archaeon Methanococcus voltae involves positive and negative control elements.

    PubMed Central

    Noll, I; Müller, S; Klein, A

    1999-01-01

    Methanococcus voltae harbors genetic information for two pairs of homologous [NiFe]-hydrogenases. Two of the enzymes contain selenocysteine, while the other two gene groups encode apparent isoenzymes that carry cysteinyl residues in the homologous positions. The genes coding for the selenium-free enzymes, frc and vhc, are expressed only under selenium limitation. They are transcribed out of a common intergenic region. A series of deletions made in the intergenic region localized a common negative regulatory element for the vhc and frc promoters as well as two activator elements that are specific for each of the two transcription units. Repeated sequences, partially overlapping the frc promoter, were also detected. Mutations in these repeated heptanucleotide sequences led to a weak induction of a reporter gene under the control of the frc promoters in the presence of selenium. This result suggests that the heptamer repeats contribute to the negative regulation of the frc transcription unit. PMID:10430564

  15. CYP1A andother biomarker responses to effluents from a textile mill in the Volta River (Ghana) using caged tilapia (Oreochromis niloticus) andsediment-exposed mudfish (Clarias anguillaris).

    PubMed

    Gadagbui, B K; Goksrøyr, A

    1996-01-01

    Abstract The ecotoxicological effects of a textile mill effluent were investigated by caging tilapia (Oreochromis niloticus) in the Volta River, Ghana, andby exposing mudfish (Clarias anguillaris) to sediment collected from the same river. Tilapia were caged for 3 weeks at three locations (0.6, 4, and8 km) downstream from the effluent outlet. Mudfish were exposed in the laboratory for 2 weeks to sediment collected from the vicinity of the effluent outlet and8 km downstream. Upstream reference locations 2 km (tilapia) and10.2 km (mudfish) were included. Liver cytochrome P4501A (CYP1A) monooxygenase activity (measured as activity of 7-ethoxyresorufin O-deethylase, EROD, andCYP1A protein level) andtwo conjugation enzymes, UDP-glucuronosyl transferase (UDP-GT) andglutathione Stransferase (GST), were analysed. A distance-related decrease in EROD activity andCYP1A protein level was observed. EROD activity was 21-fold higher in tilapia caged at the site nearest the effluent outlet and25-fold higher in mudfish exposed to sediment collected from the vicinity of the outlet, compared with the respective reference values. UDP-GT andGST levels increased significantly by 70 and27%, respectively, in tilapia while the respective levels in mudfish were 73 and28%, compared with reference values. The results clearly indicate that the textile mill effluent contains some highly potent inducers of biotransformation enzymes. This first assessment of the biological effects of organic pollutants in the Volta River demonstrates the utility of the CYP1A system as a valuable early warning biomarker of industrial effluents andalso as a biomarker to detect exposure of aquatic resources to environmental chemical contamination in tropical waters. PMID:23888992

  16. Adaptation strategies to climate change and climate variability: a comparative study between seven contrasting river basins.

    NASA Astrophysics Data System (ADS)

    Droogers, P.

    2003-04-01

    Climate change and climate variability is and will have a tremendous impact on hydrology and consequently on food security and environmental protection. From the four major components in climate change and climate variability studies, projection, mitigation, impact and adaptation, has the latter so far received less attention than the other three. An international collaboration of ten institutions is comparing adaptation strategies between contrasting basins ranging from wet to dry and from poor to rich. Basins included are: Mekong, Walawe (Sri Lanka), Rhine, Sacramento, Syr Darya, Volta, and Zayandeh (Iran). Simulation models at basin and field scale have been set up and possible adaptation strategies are explored by these models. Preliminary results indicate that appropriate adaptation strategies are different between these seven contrasting basins. It is also clear that these adaptation strategies should focus on increased variability rather than on the overall change of the mean. The focus was hereby not only on an increase in variation but especially on the number of successive dry and wet years. Results show that the studies on these adaptation strategies could not be performed only at one scale, but that a combination of field scale as well as basin scale analysis is essential.

  17. Geochemical Signatures of Neoproterozoic Granites and Granitoid-gneisses from Angavo Belt, Central Madagascar

    NASA Astrophysics Data System (ADS)

    Raharimahefa, T.

    2015-12-01

    The basement rocks of Madagascar record high-grade metamorphism, magmatism, and contractional and extensional structures that accompanied the collision of the eastern and western Gondwana segments of the supercontinent followed by its collapse. In the eastern central Madagascar, granitoids dominate the landscape and occur in a large area near and within the N-S trending highly strained zone known as the Angavo Shear Zone or Angavo belt. The area is a key in understanding the evolution of basement of Madagascar and the reconstruction of the Gondwana supercontinent. These granitoids range from layered to massive and previously published U-Pb zircon dating yielded three distinctive Neoproterozoic magmatisms at 770 Ma to 820 Ma, ca. 660Ma, and ca 550Ma. However, it was unknown whether these ages represent distinct magmatic pulses or reflect a continuous granitoid emplacement. This work contributes to the knowledge of the Malagasy basement rocks and to explore and discuss the origin and petrotectonic evolution of the granites and granitoid-gneisses from this part of the Madagascar. The rock samples are placed into three groups: group A and B for granitoid-gneisses and a third group for the granite layers. Group A and B are metaluminous and slightly peraluminous, respectively. All rocks have typical subduction zone calc-alkaline signatures. Group A is characterized by enrichment in large ion lithophile elements (LILE) but low U, LREE enrichment, depletion in the high field strength elements (HFSE). In contrast, Group B has REE patterns closely similar to Archean sediments. The granite layers show fractionated REE patterns in which HREE patterns show strong correlation with Zr abundances. Trends in major element variation diagrams and the enrichment of incompatible elements could be explained by simple fractional crystallization, while the overall geochemical signatures reflect either (1) melting of ancient crust or (2) crustal contamination of a more evolved magmas that

  18. Evolution of a Neoproterozoic suture in the Iberian Massif, Central Portugal: New U-Pb ages of igneous and metamorphic events at the contact between the Ossa Morena Zone and Central Iberian Zone

    NASA Astrophysics Data System (ADS)

    Henriques, S. B. A.; Neiva, A. M. R.; Ribeiro, M. L.; Dunning, G. R.; Tajčmanová, L.

    2015-04-01

    A Neoproterozoic suture is exposed at the contact between the Ossa Morena Zone and the Central Iberian Zone, in the Iberian Massif (Central Portugal), the westernmost segment of the European Variscides. Although, the Cadomian magmatic and tectonometamorphic events have been previously documented, their timing is still poorly constrained, particularly in the inner zones of the suture. We used geochronological (ID-TIMS U-Pb) data to establish the sequence of events, isotopic (Rb-Sr, Sm-Nd) data to characterize the magmatic sources and thermodynamic modelling to determine the maximum P-T conditions attained during the Cadomian metamorphism. The first event, in the future Ossa Morena Zone, is the onset of island arc magmatism represented mainly by tholeiites with a MORB signature. Their igneous crystallization age is unknown, but they are older than ca. 539 Ma. This magmatic activity was accompanied by deposition of fine-grained sediments in a Neoproterozoic basin. The second event is the evolution of the Cadomian magmatic arc in different stages. The earliest magmatic stage occurs at ca. 692 Ma, which is the oldest igneous age known in the Ossa Morena Zone. It is followed by the generation of subalkaline and peraluminous protoliths at ca. 569 Ma, with the isotopic signature of old crustal sources. The final phase of the arc magmatism (ca. 548-544 Ma) involved mainly partial melting of continental crust. The range of the main magmatic activity must have been between ca. 569 Ma and ca. 544 Ma as mentioned for other areas in the Ossa Morena Zone. A major metamorphic event, recorded in metamorphic monazite, zircon and titanite at ca. 540 Ma, attained upper amphibolite facies conditions close to the transition to granulite facies (7-8 kbar and 640-660 °C). It represents the continental arc accretion of the Ossa Morena Zone with the Iberian Autochthon passive margin (future Central Iberian Zone). The Early Ordovician rocks (ca. 483-477 Ma) were generated from depleted and

  19. Collapse and Melting in a Confined Orogenic Belt: Preliminary Results From the Neoproterozoic Araçuaí Belt of Eastern Brazil

    NASA Astrophysics Data System (ADS)

    Whittington, A.; Connelly, J.; Pedrosa-Soares, A.; Marshak, S.; Alkmim, F.

    2001-12-01

    The Neoproterozoic Araçuaí belt of eastern Brazil records the closure of a Red Sea-type basin between the São Francisco and Congo cratons of West Gondwana, and is part of the Brasiliano (Pan-African) orogenic system. In its southern part this basin contained oceanic crust, so that closure involved subduction and arc magmatism prior to continental collision. In its northern part, the basin was entirely ensialic. After the cessation of subduction, a period of magmatic quiescence and possible plateau development ended with the collapse of the orogen. Extensional structures are observed across the preserved Brazilian portion of the orogen (the eastern segment of the orogen is now in West Africa). Six distinct syn- to post- kinematic granite suites were emplaced within the orogen, although the temporal relation of the different granite suites to contractional and post-collision extensional tectonism has remained enigmatic. Preliminary U-Pb ages for key granite suites are related to the structural history of the orogen, placing important constraints on the timing and duration of orogenic collapse. The age of the northernmost pluton of the subduction-related (G1) granite suite is consistent with published ages for this suite of 625 to 575 Ma. The G2 suite consists of an "anatectic sea" of variably foliated S-type migmatitic leucosomes, leucogranitic sheets and plutons, commonly associated with locally extensional mesoscopic shear zones. This migmatite-leucogranite association covers >75% of the outcrop over an area of ~20,000 km2. A preliminary U-Pb zircon age of ca. 536 Ma from a well-foliated G2 pluton is significantly younger than published ages from other G2 bodies (590 to 570 Ma). Bodies sampled from the other suites are: an I-type granite showing flow foliation but little or no tectonic fabric (G3I suite), an undeformed S-type leucogranite (G4 suite), and an undeformed I-type granite containing dioritic enclaves (G5 suite). Preliminary U-Pb zircon ages from all

  20. Towards a new understanding of the Neoproterozoic-early palæozoic Lufilian and northern Zambezi belts in Zambia and the Democratic Republic of Congo

    NASA Astrophysics Data System (ADS)

    Porada, Hubertus; Berhorst, Volker

    2000-04-01

    The Lufilian Belt is of geological significance and economic importance due to rich CuCo mineralisation in the Katanga Province of the Democratic Republic of Congo and the Copperbelt of Zambia. Though thorough exploration has yielded much information on the mines districts, the understanding of the belt as a whole appears, to some extent, historically charged and confused. In the first part of this article, basic knowledge and assumptions are reviewed and existing models critically assessed. Results include recognition of standard lithostratigraphies of the Katanga Supergroup comprising the Roan, Mwashia, Lower and Upper Kudelungu Groups in the Copperbelt and Katanga, a lower limit for the onset of deposition at about 880 Ma, and a major orogenetic event involving northeast directed thrusting (Lufilian Orogeny) at 560-550 Ma. The depositional history of the Lufilian Belt was controlled by continental rifting leading to formation of a passive continental margin. Continental rifting related to the dispersal of Rodinia began ca 880 Ma ago and was accompanied by magmatism (Kafue rhyolites: 879 Ma; Nchanga Granite: 877 Ma; Lusaka Granite: 865 Ma). Differential subsidence of the northwestward propagating rift soon allowed invasion by the sea advancing from the southeast, and subsequent development of marine rift-basin and platform domains. The standard stratigraphies for the Roan Group are restricted to the platform domain that bordered the rift-basin on its northeastern side. This domain included the Domes region of the Lufilian Belt and extended southeastwards into the northern Zambezi Belt. The platform was differentiated into a carbonate platform (barrier) represented by the Bancroft Subgroup (previously 'Upper Roan') in Zambia and Kambove Dolomite Formation in Katanga and a lagoon-basin (lower Kitwe Subgroup/Zambia; Dolomitic Shale Formation/Katanga) with mudflats (R.A.T. Subgroup/Katanga) and a siliciclastic margin towards the hinterland. The mineralised

  1. Parana basin

    SciTech Connect

    Zalan, P.V.; Wolff, S.; Conceicao, J.C.J.; Vieira, I.S.; Astolfi, M.A.; Appi, V.T.; Zanotto, O.; Neto, E.V.S.; Cerqueira, J.R.

    1987-05-01

    The Parana basin is a large intracratonic basin in South America, developed entirely on continental crust and filled with sedimentary and volcanic rocks ranging in age from Silurian to Cretaceous. It occupies the southern portion of Brazil (1,100,000 km/sup 2/ or 425,000 mi/sup 2/) and the eastern half of Paraguay (100,000 km/sup 2/ or 39,000 mi/sup 2/); its extension into Argentina and Uruguay is known as the Chaco-Parana basin. Five major depositional sequences (Silurian, Devonian, Permo-Carboniferous, Triassic, Juro-Cretaceous) constitute the stratigraphic framework of the basin. The first four are predominantly siliciclastic in nature, and the fifth contains the most voluminous basaltic lava flows of the planet. Maximum thicknesses are in the order of 6000 m (19,646 ft). The sequences are separated by basin wide unconformities related in the Paleozoic to Andean orogenic events and in the Mesozoic to the continental breakup and sea floor spreading between South America and Africa. The structural framework of the Parana basin consists of a remarkable pattern of criss-crossing linear features (faults, fault zones, arches) clustered into three major groups (N45/sup 0/-65/sup 0/W, N50/sup 0/-70/sup 0/E, E-W). The northwest- and northeast-trending faults are long-lived tectonic elements inherited from the Precambrian basement whose recurrent activity throughout the Phanerozoic strongly influenced sedimentation, facies distribution, and development of structures in the basin. Thermomechanical analyses indicate three main phases of subsidence (Silurian-Devonian, late Carboniferous-Permian, Late Jurassic-Early Cretaceous) and low geothermal gradients until the beginning of the Late Jurassic Permian oil-prone source rocks attained maturation due to extra heat originated from Juro-Cretaceous igneous intrusions. The third phase of subsidence also coincided with strong tectonic reactivation and creation of a third structural trend (east-west).

  2. The Cenozoic history of the Armorican Massif: New insights from the deep CDB1 borehole (Rennes Basin, France)

    NASA Astrophysics Data System (ADS)

    Bauer, Hugues; Bessin, Paul; Saint-Marc, Pierre; Châteauneuf, Jean-Jacques; Bourdillon, Chantal; Wyns, Robert; Guillocheau, François

    2016-05-01

    Borehole CDB1 (675.05 m) crosses the deepest Cenozoic sedimentary basin of the Armorican Massif, the Rennes Basin, to reach the underlying basement at a depth of 404.92 m, made up of the Late Neoproterozoic to Early Cambrian Brioverian Group, weathered down to 520 m depth. The basin's Cenozoic deposits are divided into seven formations, ranging from Early-Middle Bartonian to Late Pliocene in age. Coastal sediments at the very base, along with a thick Priabonian lacustrine episode, imply a major revision of the regional palaeogeography, whilst a very steady and low-energy lacustrine-palustrine environment throughout the Priabonian and Early Rupelian argue for an aggradational system associated with uniform subsidence. Palynological assemblages attest to environmental and climatic changes through the Eocene and Early Oligocene, in accordance with regional and global trends (Eocene-Oligocene Transition).

  3. The 780 Gunbarrel Magmatic Event: U-Pb Documentation of Widespread Mafic Magmatism Along the Neoproterozoic Western of Laurentia

    NASA Astrophysics Data System (ADS)

    Harlan, S. S.; Heaman, L.; Lecheminant, A. N.; Premo, W. R.

    2003-12-01

    Precise U-Pb baddeleyite dating of mafic igneous rocks provide evidence for a widespread and synchronous magmatic event that extended for >2400 km along the western margin of the Neoproterozoic Laurentian craton. The gabbros dated in this study include three mafic sheets that intrude crystalline basement rocks of the Northwest Territories (the Gunbarrel, Calder and Faber Lake gabbros), a mafic sill exposed in the Mackenzie Mountains (Concajou Canyon sill), a mafic dike in the Muskwa Ranges of British Columbia (Muncho Lake diabase), and three northwest-trending mafic dikes in the Tobacco Root (group B dikes) and Beartooth Mountains (Christmas Lake dike) of Montana and Wyoming. U-Pb baddeleyite analyses for eight intrusions from seven localities yield 207Pb/206Pb ages that range from 775 to 782 Ma, with most analyses less than 2% discordant. The 207Pb/206Pb dates from the eight mafic dikes and sheets are statistically indistinguishable and we have combined sixteen individual baddeleyite analyses to yield a composite U-Pb Concordia age of 780.3 +/- 1.4 Ma (95% confidence level). We term this 780 Ma event the Gunbarrel magmatic event based on exposures of the Gunbarrel gabbro found along Gunbarrel Inlet, Great Bear Lake, Northwest Territories. Other mafic rocks that may be part of the gunbarrel event include some of the voluminous mafic sills that intrude the Belt/Purcell Supergroups in the U.S. and Canada and the northwest-trending dike at Mount Moran in the Teton Mountains of Wyoming. Overall, this is the geographically largest mafic event yet identified along the Neoprotoerozoic western margin of Laurentia. The origin of the mafic magmatism of the Gunbarrel event is not clear, but it may be related to mantle plume activity or the upwelling of asthenosphere leading to crustal extension accompanying initial breakup of the supercontinent Rodinia and development of the proto-Pacific Ocean. The mafic magmatism of the Gunbarrel magmatic event at 780 Ma predates the

  4. High-pressure thermal aureoles around two Neoproterozoic synorogenic magmatic epidote-bearing granitoids, Northeastern Brazil

    NASA Astrophysics Data System (ADS)

    Caby, Renaud; Sial, Alcides N.; Ferreira, Valderez P.

    2009-02-01

    Unusual high-pressure inner thermal aureoles are described from the Minador and Angico Torto epidote-bearing tonalitic plutons that emplaced into greenschist-facies metasedimentary rocks of the Neoproterozoic Cachoeirinha-Salgueiro belt, northeastern Brazil. The foliated pelitic hornfelses display the mineral assemblage garnet, kyanite, staurolite, muscovite, biotite, plagioclase ± quartz. Rare fibrolite is only found very close to the contacts. Hornfelses display steep mineral lineations and steeply-dipping foliations concordant with magmatic contacts. Leucocratic veinlets containing quartz, oligoclase, garnet, kyanite, staurolite, rutile and ilmenite suggest that limited melting conditions were reached very close to magmatic contacts ( T ⩾ 650 °C, P around 8 kbar). These high-pressure hornfelses form a few meters thick, rigid envelopes around the two plutons. Contrary to known examples of kyanite-bearing hornfelses that recorded high-temperature decompression, the nearly isobaric cooling down to ca. 450 °C is constrained by 3.20-3.30 Si contents of retrogressive phengites from both inner hornfelses and ductilely-deformed tonalite at the pluton margins. Isograds and bathograds are, therefore, apparently telescoped due to HP/LT shearing, possibly caused by subsequent differential vertical movements affecting these two solidified plutons. The unusual depth of emplacement of these syn-kinematic calc-alkaline plutons is explained by a tentative geodynamic model involving a pre-620 Ma-subduction setting. Resumen Las aureolas internas que rodean dos plutones tonalíticos emplazados dentro de rocas cajas en facies esquistos verdes del Cinturón-plegado Cachoeirinha-Salgueiro al noreste de Brasil, contienen hornfelses pelíticos foliados con granate, kyanita, estaurolita, muscovita, biotita, plagioclasa ± cuarzo. Fibrolita es rara ó es encontrada solamente cerca de las zonas de contacto. Los hornfelses desarrollaron foliaciones concordantes con buzamiento fuerte

  5. Transposition of structures in the Neoproterozoic Kaoko Belt (NW Namibia) and their absolute timing

    NASA Astrophysics Data System (ADS)

    Ulrich, Stanislav; Konopásek, Jiří; Jeřábek, Petr; Tajčmanová, Lucie

    2010-05-01

    The Neoproterozoic Kaoko Belt in Namibia is classical example of lower to middle crust transpressional orogeny developed between attenuated Congo Craton margin and the Coastal Terrane. The transpression has been described as a two phase event of early oblique thrusting followed by sinistral wrench shearing on the same foliation planes rotated into the subvertical orientations (e.g. Goscombe et al., 2003). Konopásek et al. (2005) argued that early fabric is not rotated, but intensely folded and the wrench stage operates on newly developed foliation parallel to axial planes of these folds. Three structural profiles across the Coastal Terrane, the Boundary Igneous Complex and the Orogen Core derived from the Congo Craton have been studied in order to assess mechanism of transpression and evaluate absolute timing of individual deformation events. The oldest known subhorizontal Si fabric occurs in the Coastal Terrane only, and is inherited from a pre-collisional HT-LP event dated at 650-630Ma. The S1 fabric occurs in all tectonic units, it is gently dipping to the W-SW and contains subhorizontal stretching lineation. Temperature as well as intensity of its development decreases westwards from penetrative granulite facies fabric in the Orogen Core to lower amphibolite facies axial plane cleavage in the Coastal Terrane. Associated kinematic criteria as S-C fabric in deformed granitoids of the Boundary Igneous Complex show very oblique, top-to-the-SE-oriented thrusting to sinistral shearing. Superimposed subvertical S2 fabric developed in axial planes of upright isoclinal folds, almost homogeneously reworking S1 fabric in the Orogen Core, whereas in the Boundary Igneous Complex and the Coastal Terrane, the S2 fabric is developed with increasing intensity from south to north. Temperature conditions of S2 development decrease westwards. Stretching lineations developed on S2 planes show the same orientation as those on the S1 planes and kinematic indicators associated with D

  6. A complex microbiota from snowball Earth times: Microfossils from the Neoproterozoic Kingston Peak Formation, Death Valley, USA

    PubMed Central

    Corsetti, Frank A.; Awramik, Stanley M.; Pierce, David

    2003-01-01

    A thin carbonate unit associated with a Sturtian-age (≈750–700 million years ago) glaciogenic diamictite of the Neoproterozoic Kingston Peak Formation, eastern California, contains microfossil evidence of a once-thriving prokaryotic and eukaryotic microbial community (preserved in chert and carbonate). Stratiform stromatolites, oncoids, and rare columnar stromatolites also occur. The microbial fossils, which include putative autotrophic and heterotrophic eukaryotes, are similar to those found in chert in the underlying preglacial units. They indicate that microbial life adapted to shallow-water carbonate environments did not suffer the significant extinction postulated for this phase of low-latitude glaciation and that trophic complexity survived through snowball Earth times. PMID:12682298

  7. Geological Influences on Bedrock Topography and East Antarctic Ice Sheet Dynamics in the Wilkes Subglacial Basin

    NASA Astrophysics Data System (ADS)

    Ferraccioli, F.; Armadillo, E.; Young, D. A.; Blankenship, D. D.; Jordan, T. A.; Balbi, P.; Bozzo, E.; Siegert, M. J.

    2014-12-01

    The Wilkes Subglacial Basin (WSB) extends for 1,400 km from George V Land into the interior of East Antarctica and hosts several major glaciers that drain a large sector of the East Antarctic Ice Sheet (EAIS). This region is of key significance for the long-term stability of the ice sheet in East Antarctica, as it lies well below sea level and its bedrock deepens inland, making it potentially prone to marine ice sheet instability, much like areas of the West Antarctic Ice Sheet (WAIS) that are presently experiencing significant mass loss. We present new enhanced potential field images of the WSB combined with existing radar imaging to study geological controls on bedrock topography and ice flow regimes in this key sector of the ice sheet. These images reveal mayor Precambrian and Paleozoic basement faults that exert tectonic controls both on the margins of the basin and its sub-basins. Several major sub-basins can be recognised: the Eastern Basin, the Central Basins and the Western Basins. Using ICECAP aerogeophysical data we show that these tectonically controlled interior basins connect to newly identified basins underlying the Cook Ice Shelf region. This connection implies that any ocean-induced changes at the margin of the EAIS could potentially propagate rapidly further into the interior. With the aid of simple magnetic and gravity models we show that the WSB does not presently include major post Jurassic sedimentary infill. Its bedrock geology is highly variable and includes Proterozoic basement, Neoproterozoic and Cambrian sediments, intruded by Cambrian arc rocks, and cover rocks formed by Beacon sediments intruded by Jurassic Ferrar sills. Enhanced ice flow in this part of the EAIS occurs therefore in a area of mixed and spatially variable bedrock geology. This contrasts with some regions of the WAIS where more extensive sedimentary basins may represent a geological template for the onset and maintenance of fast glacial flow.

  8. Chemostratigraphy of predominantly siliciclastic Neoproterozoic successions: a case study of the Pocatello Formation and Lower Brigham Group, Idaho, USA

    PubMed

    Smith, L H; Kaufman, A J; Knoll, A H; Link, P K

    1994-05-01

    Isotopic chemostratigraphy has proven successful in the correlation of carbonate-rich Neoproterozoic successions. In successions dominated by siliciclastic rocks, chemostratigraphy can be problematic, but if thin carbonates punctuate siliciclastic strata, useful isotopic data may be obtained. The upper Pocatello Formation and lower Brigham Group of southeastern Idaho provide an opportunity to assess the potential and limitations of isotopic chemostratigraphy in overwhelmingly siliciclastic successions. The 5000 m thick succession consists predominantly of siliciclastic lithologies, with only three intervals that contain thin intercalated carbonates. Its depositional age is only broadly constrained by existing biostratigraphic, sequence stratigraphic and geochronometric data. The lowermost carbonates include a cap dolomite atop diamictites and volcanic rocks of the Pocatello Formation. The delta 13C values of these carbonates are distintly negative (-5 to -3), similar to carbonates that overlie Neoproterozoic glaciogenic rocks worldwide. Stratigraphically higher carbonates record a major positive delta 13C excursion to values as high as +8.8 within the carbonate member of the Caddy Canyon Quartzite. The magnitude of this excusion is consistent with post-Sturtian secular variation recorded elsewhere in the North American Cordillera, Australia, Svalbard, Brazil and Nambia, and exceeds the magnitude of any post-Varanger delta 13C excursion documented to date. In most samples, Sr-isotopic abundances have been altered by diagenesis and greenschist facies metamorphism, but a least-altered value of approximately 0.7076 supports a post-Sturtian and pre-Marinoan/Varanger age for upper Pocatello and lower Brigham rocks that lie above the Pocatello diamictite. Thus, even though available chemostratigraphic data are limited, they corroborate correlations of Pocatello Formation diamictites and overlying units with Sturtian glaciogenic rocks and immediately post

  9. Environmental Change in the Prelude to a Neoproterozoic Ice Age: Sulfur Isotope Evidence from the Shaler Supergroup, Northwest Territories, Canada

    NASA Astrophysics Data System (ADS)

    Kaufman, A. J.; Williams, B. P.; Johnston, D. T.; Farquhar, J.; Knoll, A. H.; Butterfield, N. J.; Rainbird, R.

    2006-05-01

    The >723 Ma Shaler Supergroup on Victoria Island in the Northwest Territories of Canada is unusual for marginal marine Neoproterozoic successions insofar as thickly bedded sulfate evaporites are preserved. This unique sedimentary window for the Neoproterozoic allows us to investigate isotopic changes in the oxidized sulfur reservoir in the run up to a potential ice age, which is evidenced by a strong negative δ13C excursion in Kilian Formation carbonates at the top of the interval. Similar carbon isotope anomalies are recorded in carbonates beneath glacial diamictites of broadly the same age from the Mackenzie Mountains in Canada and in the Otavi Group of northern Namibia. Stratigraphically coincident with the 8‰ drop in 13C abundances in the Kilian Formation is a 15‰ rise in 34S of bedded sulfates, to a maximum of near +30‰. Anti-correlated isotope trends of smaller magnitude are recorded in mixed carbonates and evaporites at the top of the underlying Minto Inlet Formation. Comparison of 33S and 34S abundances of Shaler sulfates with values modeled from the results of culture experiments suggests that both anaerobic sulfate reducers and aerobic sulfur disproportionators populated the shallow open ocean. Notably, the profound 34S enrichment in the Kilian Formation is not coupled with similar enrichments in 33S. This observation is consistent with a system primarily driven by an increase in pyrite burial. Given the presence of shallow marine evaporites it is unlikely that sulfate concentrations were limited at this time. We hypothesize that this flux was enhanced during sea level fall at the onset of an ensuing ice age by the spread of anoxic conditions in deep oceans populated by sulfate reducing bacteria.

  10. Studies on nodules and adult Onchocerca volvulus during a nodulectomy trial in hyperendemic villages in Liberia and Upper Volta. II. Comparison of the macrofilaria population in adult nodule carriers.

    PubMed

    Albiez, E J; Büttner, D W; Schulz-Key, H

    1984-09-01

    In the Liberian rain-forest and the savanna of Upper Volta 189 adult nodule carriers were operated on. From 2231 extirpated nodules 3327 male and 5713 female macrofilariae were isolated. About 98% of the male worms and 88% of the female worms were found alive. The sex ratio of the live male and female worms was 1:1.5 in Liberia and 1:1.6 in Upper Volta. Less than 1% of all live macrofilariae were immature in both countries. 22% of the live male worms in Liberia were regarded as old. The percentage of old male and female worms in Upper Volta and that of the old female worms in Liberia were similar (5-7%). The portion of old worms was independent of the age of the patients in Liberia. Dead worms were found in 66% of the Liberians and in 85% of the Voltaics. The percentage of patients with dead worms increased with the age. About 0.5% of all male and 8% of all female worms were calcified. In Liberia the percentage of calcified worms increased with the age of the patients. In both countries the highest number of live and dead worms were found on the pelvic girdle. On the thorax many more macrofilariae were found in Upper Volta than in Liberia. This may contribute to the severe eye lesions in this savanna area. The presented findings provide some basic information for the planning and performance of trials with macrofilaricidal drugs in hyperendemic areas of West Africa. However, the striking differences between individual worm burdens have to be considered. PMID:6541822

  11. Molybdenum (Mo) and Iron (Fe) Isotope Evidence of Tepla-Barrandian Black Shales Against Widespread Deep Ocean Oxygenation in the Late Neoproterozoic

    NASA Astrophysics Data System (ADS)

    Kurzweil, F.; Pasava, J.; Drost, K.; Wille, M.; Schoenberg, R.

    2014-12-01

    The late Neoproterozoic was a period of major environmental perturbations including tectonic reorganizations, biologic evolution and environmental oxygenation (Neoproterozoic oxygenation event). Authigenic enrichments in redox-sensitive elements such as Mo, V and U in late Neoproterozoic black shales prior to the appearance of the first metazoan fossils indicate that increasing oxygen levels in the atmosphere-hydrosphere system have facilitated the evolution and diversification of multi-cellular life. The isotopic composition of these elements is another tool to trace (possibly global) changes in the oceanic redox state. For example, significantly higher δ98Mo of seawater and black shales are expected, when the sink of isotopically light Mo in oxic deep marine settings increased. Accordingly, modern anoxic sediments in the Black Sea as well as the well oxygenated seawater show high δ98Mo of 2.3 ‰. However, Mesoproterozoic black shales show relatively low δ98Mo values up to 1.4 ‰. To test if the enrichment of redox-sensitive elements and metazoan evolution temporally correlate with an increase in seawater δ98Mo, we present Mo and Fe isotope data of slightly younger late Neoproterozoic black shales of the Tepla-Barrandian, Czech Republic. We observe a perfect correlation of Fe/Al ratios with δ56Fe that is best explained by mixing of detrital derived Fe with δ56Fe of ~0.1 ‰ and hydrothermal sourced Fe with δ56Fe of ~-0.7 ‰. Hydrothermally dominated samples with low δ56Fe are also enriched in heavy metals such as Ni, Cu and Zn as well as hydrothermally derived Mo (with δ98Mo of ~0.6 ‰). Samples with minor hydrothermal influence show authigenic Mo enrichment from seawater with a maximum δ98Mo of 1.2 ‰. This estimate indicates no significant increase in the seawater δ98Mo during the Neoproterozoic and after the evolution of metazoan life. Thus, our Mo isotope dataset provides no evidence for deep ocean oxygenation during the Neoproterozoic

  12. How juvenile is the Arabian Nubian Shield? Evidence from Nd isotopes and pre-Neoproterozoic inherited zircon in the Bi'r Umq suture zone, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Hargrove, U. S.; Stern, R. J.; Kimura, J.-I.; Manton, W. I.; Johnson, P. R.

    2006-12-01

    The Bi'r Umq suture zone (BUSZ) in western Saudi Arabia comprises Neoproterozoic oceanic-arc plutonic, volcanosedimentary, and ophiolitic rocks that record some of the earliest magmatic and tectonic events of the East African Orogen in the Arabian-Nubian Shield (ANS). New Nd isotopic analyses are combined with data on zircon inheritance and published isotopic studies to establish the case that pre-Neoproterozoic crust had a greater influence on the oceanic portion of the ANS than is appreciated. Highly positive initial ɛNd (+ 3.9 to + 8.5) and Nd model ages (560-830 Ma) that approximate crystallization ages (573-813 Ma) of BUSZ igneous rocks are comparable to upper crust in other parts of the ANS considered to be juvenile (mantle-derived) and to some xenoliths from the lower crust and lithospheric mantle. Overall, the data suggest that the 40-km-thick crust beneath much of the Arabian Shield is juvenile and that most of it was extracted from depleted mantle during the interval ˜ 740-830 Ma. Although much of the ANS is isotopically juvenile, some Neoproterozoic igneous rocks in the northern ANS contain zircon inherited from pre-Neoproterozoic sources. Samples from the BUSZ that show inheritance yield slightly lower initial ɛNd than contemporary samples that do not show inheritance, suggesting that some juvenile magmas assimilated older continental material. The age of that material is inferred to be largely early Neoproterozoic and Mesoproterozoic, with minor Paleoproterozoic and Archean components, based on U-Pb ages of inherited zircon and Nd model ages for ANS upper crustal rocks and xenoliths of the lower crust and mantle lithosphere. Inherited zircon may have been assimilated from terrigenous sediment shed from nearby passive margins, and transported fluvially or by glaciers, or by assimilation of cryptic early Neoproterozoic to Archean basement that underlies the "juvenile" core of the ANS. Zircon morphologies are consistent with both sedimentary origins

  13. Detrital zircon geochronology of some neoproterozoic to triassic rocks in interior alaska

    USGS Publications Warehouse

    Bradley, D.C.; McClelland, W.C.; Wooden, J.L.; Till, A.B.; Roeske, S.M.; Miller, M.L.; Karl, S.M.; Abbott, J.G.

    2007-01-01

    We report 777 U-Pb SHRIMP detrital zircon ages from thirteen sandstones and metasandstones in interior Alaska. About sixty grains per sample were analyzed; typically, half to three-fourths of these were concordant within ?? 10%. Farewell terrane. Two quartzites were collected from Ruby quadrangle and a third from Taylor Mountains quadrangle. All three are interpreted to represent a low stratigraphic level in the Nixon Fork platform succession; the samples from Ruby quadrangle are probably late Neoproterozoic, and the sample from Taylor Mountains quadrangle is probably Cambrian in age. The youngest detrital zircon in any of the three is 851 Ma. The two Ruby quadrangle samples area almost identical: one has a major age cluster at 1980-2087 and minor age clusters at 944-974 and 1366-1383 Ma; the other has a major age cluster at 1993-2095 Ma and minor age clusters at 912-946 and 1366-1395 Ma. The Taylor Mountains sample shows one dominant peak at 1914-2057 Ma. Notably absent are zircons in the range 1800-1900 Ma, which are typical of North American sources. The detrital zircon populations are consistent with paleontological evidence for a peri- Siberian position of the Farewell terrane during the early Paleozoic. Mystic subterrane of the Farewell terrane. Three graywackes from flysch of the Mystic subterrane, Talkeetna quadrangle, were sampled with the expectation that all three were Pennsylvanian. Asample from Pingston Creek is Triassic (as revealed by an interbedded ash dated at ca. 223 Ma) and is dominated by age clusters of 341-359 and 1804-1866 Ma, both consistent with a sediment source in the Yukon-Tanana terrane. Minor age clusters at 848-869 and 1992-2018 Ma could have been sourced in the older part of the Farewell terrane. Still other minor age clusters at 432-461, 620-657, 1509-1536, and 1627-1653 Ma are not readily linked to sources that are now nearby. Asample from Surprise Glacier is mid-Mississippian or younger. Adominant age cluster at 1855-1883 and a

  14. Can We Determine Temperatures Associated with Critical Transitions During the Evolution of Metazoan life? Application of 'Clumped' Isotope Thermometry to the Neoproterozoic and Paleozoic

    NASA Astrophysics Data System (ADS)

    Defliese, W.; Gutierrez, M.; Flores, S.; Retallack, G.; Tripati, A.

    2015-12-01

    The evolution and development of metazoan life during the Neoproterozoic and Paleozoic was one of the largest and monumental events in Earth history. Conditions surrounding these events are uncertain, as there remain many questions about the types of environment transitions such as the development of multicellular life, evolution of hard shells, and the transitions of life to land took place in. While mass-47 clumped isotope signatures are prone to thermal resetting and diagenesis, it remains the best tool for reconstructing temperatures in uncertain regimes, and can be integrated along with traditional tools such as textural petrography and cathodoluminescence to screen for diagenetic alteration. In this context, we analyze suites of Neoproterozoic and Paleozoic sediments and brachiopods for clumped isotope temperatures, and combine with microscopy and stratigraphic data to infer diagenetic and burial histories of these rocks. Samples judged to be unaltered will be further analyzed for the conditions prevalent during critical transitions during the evolution of metazoan life.

  15. Diachronism in the late Neoproterozoic-Cambrian arc-rift transition of North Gondwana: A comparison of Morocco and the Iberian Ossa-Morena Zone

    NASA Astrophysics Data System (ADS)

    Álvaro, J. Javier; Bellido, Félix; Gasquet, Dominique; Pereira, M. Francisco; Quesada, Cecilio; Sánchez-García, Teresa

    2014-10-01

    In the northwestern border of the West African craton (North Gondwana), a transition from late Neoproterozoic subduction/collision to Cambrian rift processes was recorded in the Anti-Atlas (Morocco) and in the Ossa-Morena Zone (Iberia). Cambrian rifting affected both Pan-African and Cadomian basements in a stepwise and diachronous way. Subsequently, both areas evolved into a syn-rift margin episodically punctuated by uplift and tilting that precluded Furongian sedimentation. A comparison of sedimentary, volcanic and geodynamic evolution is made in the late Neoproterozoic (Pan-African and Cadomian) belts and Cambrian rifts trying to solve the apparent diachronous (SW-NE-trending) propagation of an early Palaeozoic rifting regime that finally led to the opening of the Rheic Ocean.

  16. Infection levels of proteocephalidean cestodes in Cichla piquiti (Osteichthyes: Cichlidae) of the Volta Grande Reservoir, Minas Gerais, Brazil, relative to host body weight and gender.

    PubMed

    Martins, M L; Pereira, J; de Chambrier, A; Mouriño, J L P

    2011-12-01

    We evaluated the relationship between infection by proteocephalid cestodes and the sex and weight classes of tucunaré (Cichla piquiti) captured between August 1999 and June 2001 in the Volta Grande Reservoir, Minas Gerais, Brazil. A total of 96 fish, 75.9 ± 9.3% males and 88.9 ± 6.4% females, were parasitized by Proteocephalus macrophallus and P. microscopicus, with total mean intensities of 76.6 ± 23.9 and 145.2 ± 36.7, respectively, during this period. In the majority of the months analysed, males showed 71.4-100% prevalence of parasitism and females 80-100%. Although there was no significant difference, females showed a higher mean intensity of infection (145.2 ± 36.7) than males (76.6 ± 23.9). Fish weighing 300-800 g showed a higher mean abundance of parasites (P < 0.05) compared with the biggest specimens weighing 801-2750 g. Analysing both males and females together, the greatest mean intensities of infection were found in October and December (P < 0.05) independent of the year, which coincides with the months of highest rainfall. These results show that fish living in reservoirs may be more susceptible to intermediate hosts than those that live in rivers. PMID:21208512

  17. An all sulfur analogue of the smallest subunit of F420-non-reducing hydrogenase from Methanococcus voltae--metal binding and structure.

    PubMed

    Pfeiffer, M; Klein, A; Steinert, P; Schomburg, D

    The 25 amino acid long subunit VhuU of the F420-non-reducing hydrogenase from Methanococcus voltae contains selenocysteine within the consensus sequence of known [NiFe] hydrogenases DP(C or U)CxxCxxH (U = selenocysteine). The sulfur-analogue VhuUc was chemically synthesized, purified and its metal binding capability, the catalytic properties, and structural features were investigated. The polypeptide was able to bind nickel, but did not catalyse the heterolytic activation of H2. 2D-NMR spectroscopy revealed an alpha-helical secondary structure for the 15 N-terminal amino acids in 50% TFE. Nickel only binds to the C-terminus, which contains the conserved amino acid motif. Structures derived from the NMR data are compatible with the participation of both sulfur atoms from the conserved cysteine residues in a metal ion binding. Structures obtained from the data sets for Ni.VhuUc as well as Zn.VhuUc showed no further ligands. The informational value for Ni.VhuUc was low due to paramagnetism. PMID:9084873

  18. Paleoenvironments in Meso-Neoproterozoic carbonates of the Mbuji-Mayi Supergroup (Democratic Republic of Congo) - Microfacies analysis combined with C-O-Sr isotopes, major-trace elements and REE + Y distributions

    NASA Astrophysics Data System (ADS)

    Delpomdor, F.; Blanpied, C.; Virgone, A.; Préat, A.

    2013-12-01

    The Meso- and Neoproterozoic Mbuji-Mayi Supergroup (1155 Ma to ca. 800 Ma) was deposited in the SE-NW trending siliciclastic-carbonate failed-rift in the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. Drillcore- and outcrop-derived microfacies, isotope (C, O and Sr) compositions of carbonates and REE + Y distributions are integrated to unravel the paleoenvironmental and chemical conditions prevailing during deposition and alteration (or contamination) of the Mbuji-Mayi carbonates. The carbonate succession (BIe subgroup and BIIa to BIIe subgroups), composed of 11 microfacies (MF), records the evolution of a marine ramp submitted to evaporation, with basinal and low-energy outer-ramp environments (MF1-MF5), biohermal mid-ramp (MF6) and restricted tide-dominated lagoon inner-ramp (MF7-MF9) settings, overlain by lacustrine (MF10) and sabkha (MF11) environments. The ramp margin is characterized by thick stacks of stromatolitic bioherms. δ13C and δ18O relationships in the Mbuji-Mayi carbonates allow discrimination between meteoric (δ13C: -7.5‰ to +0.0‰, δ18O: -7.0‰ to -1.0‰) and burial lithifications (δ13C: -1.5‰ to +0.0‰, δ18O: -15.1‰ to -7.0‰), that overprinted a primary marine signal (δ13C: -1.5‰ to +2.0‰, δ18O: -3.0‰ to +0.5‰) partially preserved in the subgroups. Unaltered pristine signals are found in the Mbuji-Mayi carbonates with 87Sr/86Sr ratios (0.7065-0.7082) similar to those of the marine-preserved strontium signatures of the early Neoproterozoic oceans. The PAAS-normalized REE + Y distributions indicate that the BIe carbonates were altered by Fe-oxide-rich hydrothermal fluids. BIIb and BIIe carbonates exhibit uniform light REE depleted patterns suggesting inputs of detrital river material whereas a marine seawater, highlighted by the REE + Y distributions is preserved in BIIc and BIId carbonates. The pattern of carbon, oxygen and strontium isotopic variations in the Mbuji-Mayi carbonates reflects deposition and early diagenesis in

  19. Evidence for Mojave-Sonora megashear-Systematic left-lateral offset of Neoproterozoic to Lower Jurassic strata and facies, western United States and northwestern Mexico

    USGS Publications Warehouse

    Stewart, John H.

    2005-01-01

    Major successions as well as individual units of Neoproterozoic to Lower Jurassic strata and facies appear to be systematically offset left laterally from eastern California and western Nevada in the western United States to Sonora, Mexico. This pattern is most evident in units such as the "Johnnie oolite," a 1- to 2-m-thick oolite of the Neoproterozoic Rainstorm Member of the Johnnie Formation in the western United States and of the Clemente Formation in Sonora. The pattern is also evident in the Lower Cambrian Zabriskie Quartzite of the western United States and the correlative Proveedora Quartzite in Sonora. Matching of isopach lines of the Zabriskie Quartzite and Proveedora Quartzite suggests ???700-800 km of left-lateral offset. The offset pattern is also apparent in the distribution of distinctive lithologic types, unconformities, and fossil assemblages in other rocks ranging in age from Neoproterozoic to Early Jurassic. In the western United States, the distribution of facies in Neoproterozoic and Paleozoic strata indicates that the Cordilleran miogeocline trends north-south. A north-south trend is also suggested in Sonora, and if so is compatible with offset of the miogeocline but not with the ideas that the miogeocline wrapped around the continental margin and trends east-west in Sonora. An imperfect stratigraphic match of supposed offset segments along the megashear is apparent. Some units, such as the "Johnnie oolite" and Zabriskie-Proveedora, show almost perfect correspondence, but other units are significantly different. The differences seem to indicate that the indigenous succession of the western United States and offset segments in Mexico were not precisely side by side before offset but were separated by an area-now buried, eroded, or destroyed-that contained strata of intermediate facies. ?? 2005 Geological Society of America.

  20. Neoproterozoic Structural Evolution of the NE-trending 620-540 Ma Ad-Damm Shear Zone, Arabian Shield, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Hamimi, Z.; El-Sawy, E. K.; El-Fakharan, A. S.; Shujoon, A.; Matsah, M.; El-Shafei, M.

    2012-04-01

    Ad-Damm Shear Zone (ASZ) is a NE-trending fault zone separating Jeddah and Asir tectonostratigraphic terranes in the Neoproterozoic juvenile Arabian Shield. ASZ extends ~380 km, with an average width ~2-3 km, from the eye-catching Ruwah Fault Zone in the eastern shield to the Red Sea Coastal plain. It was believed to be one of the conjugate shears of the NW- to NNW- trending sinistral Najd Shear System based on noteworthy dextral shear criteria recorded within the 620 Ma sheared granites of Numan Complex, as well as right-lateral offsets within quartz veins and dikes transected by the shear zone. The present study is an integrated field-based structural analysis and remote sensing. We utilized the ASTER data for lithologic discrimination and automatic structural lineament extraction and analysis of the Neoproterozoic basement lithologies encountered along and within the vicinity of ASZ. Various false color composite images were generated and evaluated for lithological mapping and structural lineaments. The obtained map was analyzed using GIS techniques to interpret the behavior of the existing lineaments and their spatial distribution. Based on the results of the ASTER data, two significant areas; around Bir Ad-Damm and to the south of Wadi Numan, are selected for detailed field investigation. Shear-sense indicators and overprinting relations clearly show a complicated Neoproterozoic history of ASZ, involving at least three deformations: (1) an early attenuated NE-SW sinistral shearing; followed by (2) a SE-directed thrusting phase resulted in the formation SE-verging thrusts and associated thrust-related folds; and (3) late NE-SW intensive dextral transcurrent shearing played a significant role in the creation of mesoscopic shear-zone related folds, particularly in the area near Bir Ad-Damm. Such deformation history demonstrates the same episode of Neoproterozoic deformation exhibited in the NE-trending shear zones in the Arabian-Nubian Shield (ANS).

  1. Petrology and Sm-Nd dating of the Genina Gharbia Alaskan-type complex (Egypt): Insights into deep levels of Neoproterozoic island arcs

    NASA Astrophysics Data System (ADS)

    Helmy, Hassan M.; Abd El-Rahman, Yasser M.; Yoshikawa, Masako; Shibata, Tomoyuki; Arai, Shoji; Tamura, Akihiro; Kagami, Hiroo

    2014-06-01

    The deep levels of Neoproterozoic island arcs are poorly known due to limited accessibility. The Genina Gharbia Alaskan-type complex (south Eastern Desert, Egypt) is the remains of a magma chamber that crystallized at the base (crust-mantle boundary) of a mature Neoproterozoic island arc. The rock assemblage comprises hornblende-bearing harzburgite, lherzolite, pyroxenite, norite and gabbro. All lithologies show cumulus texture with evidence of extensive cumulus mineral-melt interactions. Clinopyroxenes from all lithologies have similar rare earth element (REE) patterns with slight medium-rare earth element (MREE) enrichment. Hornblendes are slightly enriched in MREE and light rare earth elements (LREE). Island arc signatures are indicated by high contents of large ion-lithophile elements and low concentration of high field-strength elements. Positive initial εNd (+ 5.7 to + 7.0) and Nd model ages (963 ± 81 Ma) are consistent with the Genina Gharbia magma being extracted from a depleted mantle source. Modeling of estimated parental magma indicates 10% partial melting of a 90% depleted mantle source with a 10% (MORB + sediments)-derived fluid, commencing in the spinel stability field (< 85 km). Relative to Phanerozoic arcs, the Neoproterozoic arcs were more hydrous, had low oxidation states and probably lasted shorter time to build-up. The hydrous nature of the sub-Arabian-Nubian Shield mantle and the long-life of the arcs are among reasons responsible for the vast crustal growth during the Pan-African Orogeny throughout the Gondwana.

  2. Towering sponges in an Early Cambrian Lagerstätte: Disparity between nonbilaterian and bilaterian epifaunal tierers at the Neoproterozoic-Cambrian transition

    NASA Astrophysics Data System (ADS)

    Yuan, Xunlai; Xiao, Shuhai; Parsley, Ronald L.; Zhou, Chuanming; Chen, Zhe; Hu, Jie

    2002-04-01

    Epifaunal, suspension-feeding bilaterian animals in the Cambrian lived close to the sediment-water interface, and hence their ecological tiering levels were low (<10 cm). Here we report an Early Cambrian (Diandongian or probably Tommotian-Atdabanian) Lagerstätte from the Hetang Formation in Anhui Province, south China. The Hetang biota is characterized by high-tiering (to 50 cm) sponges and small (<0.5 cm) bilaterians (including orthothecid hyoliths and bivalved arthropods). Nonbilaterian suspension feeders (sponges, cnidarians, and archaeocyathids) as high-tiering animals and bilaterian suspension feeders as low-tiering animals also characterize other Neoproterozoic-Cambrian assemblages, such as the Ediacaran, Chengjiang, Burgess Shale, and Sinsk biotas. These data are consistent with medium- to high-tiering levels in Neoproterozoic-Cambrian epifaunal communities, but suggest that nonbilaterians achieved such tiering levels long before bilaterian suspension feeders did so in the Early Ordovician. The disparity between bilaterian and nonbilaterian tierers during the Neoproterozoic-Cambrian transition and the delayed appearance of high-tiering bilaterians demand phylogenetic and ecological explanations. The Cambrian substrate revolution may have triggered a cascade of ecological evolution, including the rise of bilaterian animals in high-tiering levels during the Ordovician radiation of the Paleozoic fauna.

  3. Neoproterozoic diamictite in the Eastern Desert of Egypt and Northern Saudi Arabia: evidence of ~750 Ma glaciation in the Arabian-Nubian Shield?

    NASA Astrophysics Data System (ADS)

    Ali, Kamal A.; Stern, Robert J.; Manton, William I.; Johnson, Peter R.; Mukherjee, Sumit K.

    2010-06-01

    The Neoproterozoic Atud diamictite in Wadi Kareim and Wadi Mobarak in the Eastern Desert of Egypt and the Nuwaybah formation in NW Saudi Arabia consist of poorly sorted, polymictic breccia, with clasts up to 1 m of granitoid, quartz porphyry, quartzite, basalt, greywacke, marble, arkose, and microconglomerate in fine-grained matrix. Stratigraphic relations indicate that the diamictite was deposited in a marine environment. Integrated field investigation, petrographic study and U-Pb SHRIMP zircon ages demonstrate that the Atud and Nuwaybah are correlative. The distribution of zircon ages indicate that ~750 Ma ages are dominant with a significant component of older materials, characterized by minor Mesoproterozoic and more abundant Paleoproterozoic and Neoarchean ages. Some matrix and metasedimentary clast zircons yield ages that are a few 10s of Ma younger than the age of the youngest clast (754 ± 15 Ma), suggesting Atud/Nuwaybah diamictite deposition ~750 Ma or slightly later, broadly consistent with being deposited during the Sturtian glaciation (740-660 Ma). The Paleoproterozoic and Neoarchean clasts have no source within the ensimatic Arabian-Nubian Shield. The distribution of the pre-Neoproterozoic ages are similar to the distribution of the pre-Neoproterozoic ages in Yemen and Saharan Metacraton, suggesting that these clasts have been transported hundreds of kilometers, maybe by ice-rafting. The Atud diamictite may represent important evidence for Cryogenian “Snowball Earth” in the Arabian-Nubian Shield.

  4. Stratigraphic records of paleogeography and global change from two late Proterozoic basins

    NASA Astrophysics Data System (ADS)

    Swanson-Hysell, Nicholas L.

    As sediments and volcanic deposits accumulate on Earth's surface, they record information about Earth's climate, the motion of continents, and the evolution of the biosphere. Through the study of ancient stratigraphic sequences, we can gain a window into our planet's varied, and sometimes tumultuous, past. In this dissertation, I employ a combination of field observations, magnetic data, and chemostratigraphic data in the Keweenawan Mid-continent Rift of North America and the Amadeus Basin of Central Australia to study the paleogeography and paleoclimate during and after the transition between the Mesoproterozoic (1.7 to 1.0 billion-years ago) and Neoproterozoic Eras (1.0 to 0.54 billion-years ago). The supercontinent Rodinia formed at the boundary between the Eras and broke apart throughout the Neoproterozoic. Basins that developed as Rodinia rifted apart record large changes in the biogeochemical cycling of carbon and sulfur, the waxing and waning of low-latitude ice sheets, and the progressive oxygenation of the atmosphere that facilitated the evolution of animals. I report high-resolution paleomagnetic data in stratigraphic context from Mamainse Point, Ontario---the most complete succession in the 1.1 billion-year-old Mid-continent Rift. The results demonstrate that previous suggestions of large non-dipolar geomagnetic field components at the time stemmed from low temporal resolution across geomagnetic reversals during a period of rapid plate motion. This result strengthens the framework for evaluating records of tectonics and climate across the Mesoproterozoic/Neoproterozoic boundary. Rock magnetic experiments on Mamainse Point lavas, paired with electron microscopy, demonstrate that a component of the magnetization in oxidized flows that is antiparallel to the characteristic remanence is a result of martite self-reversal. This component is the best resolved natural example of the experimentally observed self-reversal that accompanies the maghemite to hematite

  5. Anisotropy of thermoremanent magnetisation of Cryogenian glaciogenic and Ediacaran red beds, South Australia: Neoproterozoic apparent or true polar wander?

    NASA Astrophysics Data System (ADS)

    Schmidt, Phillip W.; Williams, George E.

    2013-11-01

    Determining the effects of compaction-related inclination shallowing of remanence directions is crucial for ascertaining the validity of low palaeolatitudes for Neoproterozoic red beds in South Australia that are central to the debate concerning low-latitude Proterozoic glaciation. The inclination correction (or flattening) factor, f, is defined as tan(ID)/tan(IF), where ID and IF are the inclinations of the measured detrital remanence and the ancient inducing field, respectively. The anisotropy can be estimated using anisotropy of magnetic susceptibility and the anisotropy of high-field isothermal remanence (hf-AIR). The elongation-inclination (E-I) method has also been used to infer inclination shallowing. We add the anisotropy of thermoremanent magnetisation (ATR) to these methods. For the late Cryogenian Elatina Formation arenites, which constitute the bulk of the Elatina data set, the inclination correction using f = 0.738 derived from ATR increases the palaeolatitude of the Elatina Formation from 6.5 ± 2.2° to 8.8 ± 3.2°, which confirms that the Elatina glaciation occurred near the palaeoequator. Inclination corrections for the Ediacaran argillaceous Brachina and Wonoka formations, using f = 0.35-0.38 derived from ATR, are significantly greater than for the more arenaceous Elatina Formation, which increases their palaeolatitudes from ~ 12° to ~ 30°. Carbonates from the basal Ediacaran Nuccaleena Formation yielded f = 0.8 from ATR, which represents only a small palaeolatitude correction from 19° to 23°. The anisotropy results imply that the characteristic remanent magnetisations carried by all these units were acquired early as depositional remanent magnetisations, essentially at the time of deposition. The shift of the palaeopoles from argillaceous units indicating significantly higher palaeolatitudes introduces a distinctive loop into the late Cryogenian-Ediacaran-Cambrian pole path for Australia. This loop shows similarities with the North American

  6. Identification of a Sturtian cap carbonate in the Neoproterozoic Sete Lagoas carbonate platform, Bambuí Group, Brazil

    NASA Astrophysics Data System (ADS)

    Vieira, Lucieth Cruz; Trindade, Ricardo I. F.; Nogueira, Afonso C. R.; Ader, Magali

    2007-03-01

    A sedimentological and C-O isotopic study has been carried out in nine sections of the Sete Lagoas Formation at its classical outcropping area, in the southern tip of the São Francisco craton (central Brazil), with the objective of refining its stratigraphic position within the Neoproterozoic. At the study area, the Neoproterozoic Sete Lagoas Formation comprises two shallowing-upward megacycles, corresponding to more than 200 m in thickness. Each cycle is limited by a flooding surface amalgamated with a third-order sequence boundary. The first megacycle presents deep-platform deposits with abundance of crystal fans (aragonite pseudomorphs). These deposits are characterized by negative C-isotope values (-4.5‰). They grade upward to storm-wave and tide-influenced layers with δ13C values around 0‰. In the second megacycle, a new transgression drowned the platform, depositing a thick, mixed sub-storm wave-base succession. This megacycle comprises deposits of lime mudstone-pelite rhythmite, which grade to crystalline limestone rich in organic matter, both with unusually positive δ13C values (up to + 14‰). Regional correlation of Sete Lagoas deposits indicate that they rest atop glaciomarine rocks of the Macaúbas Group and basal strata show seafloor precipitates with negative δ13C values. Therefore, it is possible to characterize the Sete Lagoas carbonate as a cap carbonate sequence. The very high δ13C in the second megacycle together with geochronologic data suggest that this unit correlates better with post-Sturtian sequences. Some differences in the depositional record are observed between Sete Lagoas and the other post-Sturtian units previously described in North America, Australia, and Namibia. Those differences may in part be due to deposition in shallower settings of the Sete Lagoas carbonates, thus preserving a thick record of storm- and wave-influenced sedimentation not found elsewhere. Alternatively, they may also be attributed to diachronic

  7. Beginning the Modern Regime of Subduction Tectonics in Neoproterozoic time: Inferences from Ophiolites of the Arabian-Nubian Shield

    NASA Astrophysics Data System (ADS)

    Stern, R.

    2003-04-01

    It is now clear that the motive force for plate tectonics is provided by the sinking of dense lithosphere in subduction zones. Correspondingly, the modern tectonic regime is more aptly called ``subduction tectonics" than plate tectonics, which only describes the way Earth's thermal boundary layer adjusts to subduction. The absence of subduction tectonics on Mars and Venus implies that special circumstances are required for subduction to occur on a silicate planet. This begs the question: When did Earth's oceanic lithosphere cool sufficiently for subduction to began? This must be inferred from indirect lines of evidence; the focus here is on the temporal distribution of ophiolites. Well-preserved ophiolites with ``supra-subduction zone" (SSZ) affinities are increasingly regarded as forming when subduction initiates as a result of lithospheric collapse (± a nudge to get it started), and the formation of ophiolitic lithosphere in evolving forearcs favors their emplacement and preservation. The question now is what percentage of ophiolites with ``supra-subduction zone" (SSZ) chemical signatures formed in forearcs during subduction initiation events? Most of the large, well-preserved ophiolites (e.g., Oman, Cyprus, California, Newfoundland) may have this origin. If so, the distribution in space and time of such ophiolites can be used to identify ``subduction initiation" events, which are important events in the evolution of plate tectonics. Such events first occurred at the end of the Archean (˜2.5Ga) and again in the Paleoproterozoic (˜1.8 Ga), but ophiolites become uncommon after this. Well-preserved ophiolites become abundant in Neoproterozoic time, at about 800±50 Ma. Ophiolites of this age are common and well-preserved in the Arabian-Nubian Shield (ANS) of Egypt, Sudan, Ethiopia, Eritrea, and Saudi Arabia. ANS ophiolites mostly contain spinels with high Cr#, indicating SSZ affinities. Limited trace element data on pillowed lavas supports this interpretation

  8. Wilson-cycle "kick-off": Constraining the influence of a Large Igneous Province during the Neoproterozoic evolution of the pre-Caledonian margin of Baltica

    NASA Astrophysics Data System (ADS)

    Jørgen Kjøll, Hans; Andersen, Torgeir B.; Tegner, Christian; Corfu, Fernando; Planke, Sverre

    2016-04-01

    The supercontinent Rodinia broke up in the late Neoproterozoic to form the oceans and margins separating paleocontinents such as Baltica, Avalonia and Laurentia, which in turn later collided to form the Caledonian - Appalachian mountain belts. Some of the geological products of the complex evolution from passive-margin- to break-up are presently found in nappe complexes within the Scandinavian Caledonides. As described by P-G. Andreasson and co-workers in several papers from the 1990's, the break-up was associated with emplacement of major dolerite dike-complexes of Ediacaran age (c. 600 Ma), probably constituting a pre-Caledonian Large Igneous Province (pCLIP). The dominantly dolerite-dike swarms intruded a thinned continental crust comprising both crystalline basement and marine sediments deposited in pre- to early syn-rift basins. During peak rifting a sheeted dike complex defining the ocean-continent transition (OCT) evolved. More than 100 Myr later, during early stages of plate convergence, distal parts of the margin and the OCT experienced high to ultra-high pressure metamorphism, before the remnants of the dike swarms and the OCT were finally thrusted onto Baltica as the Seve and Särv Nappe Complexes. This occurred during the Scandian phase of the Caledonian orogeny at c. 425 Ma. Parts of the ancient magma-rich rifted margin are now exposed in the Scandinavian Caledonides. The best-preserved parts provide a remarkable analogue to present day OCTs and adjacent areas that generally only is observable in seismic sections. In order to understand the dynamics of the continental break-up, we will investigate the exposed areas to better constrain the active mechanisms that eventually produced oceanic crust. Also, with an improved understanding of magma-rich segments, a better comprehension may be achieved for magma-poor segments, which in the present study area occur both to the south and north of the pCLIP-segment in central Scandinavia. This presentation reports

  9. Impact of climate change on vegetation dynamics in a West African river basin

    NASA Astrophysics Data System (ADS)

    Sawada, Y.; Koike, T.

    2012-12-01

    Future changes in terrestrial biomass distribution under climate change will have a tremendous impact on water availability and land productivity in arid and semi-arid regions. Assessment of future change of biomass distribution in the regional or the river basin scale is strongly needed. An eco-hydrological model that fully couples a dynamic vegetation model (DVM) with a distributed biosphere hydrological model is applied to multi-model assessment of climate change impact on vegetation dynamics in a West African river basin. In addition, a distributed and auto optimization system of parameters in DVM is developed to make it possible to model a diversity of phonologies of plants by using different parameters in the different model grids. The simple carbon cycle modeling in a distributed hydrological model shows reliable accuracy in simulating the seasonal cycle of vegetation on the river basin scale. Model outputs indicate that generally, an extension of dry season duration and surface air temperature rising caused by climate change may cause a dieback of vegetation in West Africa. However, we get different seasonal and spatial changes of leaf area index and different mechanisms of the degradation when we used different general circulation models' outputs as meteorological forcing of the eco-hydrological model. Therefore, multi-model analysis like this study is important to deliver meaningful information to the society because we can discuss the uncertainties of our prediction by this methodology. This study makes it possible to discuss the impact of future change of terrestrial biomass on climate and water resources in the regional or the river basin scale although we need further sophistications of the system. Performance of the eco-hydrological model (WEB-DHM+DVM) in Volta River Basin, with basin-averaged leaf area index from model (blue solid line) and AVHRR satellite-derived product (red rectangles).

  10. Brasiliano crustal structure and the tectonic setting of the Parnaíba basin of NE Brazil: Results of a deep seismic reflection profile

    NASA Astrophysics Data System (ADS)

    Daly, Michael C.; Andrade, Vander; Barousse, Chuck A.; Costa, Rafaela; McDowell, Kenneth; Piggott, Neil; Poole, Alan J.

    2014-11-01

    A 1430 km, deep crustal, seismic reflection profile of the Parnaíba basin shows an asymmetric, structured western margin and a gently dipping eastern margin. The ~3 km thick, Phanerozoic sedimentary section overlies a pronounced, planar, regional unconformity that crosses three Precambrian blocks with differing seismic facies: the Amazonian/Araguaia block, the Parnaíba block, and the Borborema block. The blocks are separated by steep crustal-scale boundaries across which seismic facies change abruptly. In the west, the ophiolitic metasedimentary rocks of the Araguaia Group overlie the Amazonian craton. Both craton and metasediments terminate eastward against a steep, east dipping fault zone defining the Amazonian/Araguaia block and Parnaíba block boundary. Reactivation of this Neoproterozoic margin in the Late Triassic and Late Jurassic/Early Cretaceous, folded and elevated basement and basin over 2 km. A second crustal boundary defines the eastern margin of the Parnaíba block with the Neoproterozoic Borborema block. This boundary is interpreted as the extension of the Transbrasiliano shear zone. These data demonstrate that the basement of the Parnaíba basin was formed during Brasiliano orogenesis by west directed collision-related thrusting, succeeded by lateral accretion along steep, crustal-scale boundaries. After formation of a post-Brasiliano peneplain, the Parnaíba basin developed seamlessly across three very different crustal blocks and appears to have been significantly larger than its present outline. No extensive underlying rift system is evident suggesting that basement structure had little to do with basin formation, but that episodic reactivation of the boundary zones and basement fabric has controlled the structuring and preservation of the basin.

  11. Late Neoproterozoic magmatism in South Qinling, Central China: Geochemistry, zircon U-Pb-Lu-Hf isotopes and tectonic implications

    NASA Astrophysics Data System (ADS)

    Wang, Ruirui; Xu, Zhiqin; Santosh, M.; Yao, Yuan; Gao, Li'e.; Liu, Chunhua

    2016-06-01

    The Neoproterozoic tectonic evolution of the northern margin of the Yangtze Block in South China remains debated. In this study, we present results from LA-ICP-MS zircon U-Pb geochronology on a suite of intermediate-felsic rocks in South Qinling, Central China which show a mean age of ca. 630 Ma. The zircon εHf(t) values of these rocks mostly range from + 0.44 to + 14.78. Geochemically, the granites and syenite show high total alkali contents, with enrichment in LREE, LILE (Rb, Ba, and K), and HFSE (Th, U, Nb, Ta, Zr, and Hf), and depletion in Sr, P, and Ti, similar to the features of A-type granites. The meta-diorite shows high Na2O, with depletion in Eu, Ti, and LILE (Sr, Rb, Ba, and K), and enrichment in HFSE (Th, U, Nb, Ta, Zr, and Hf). The geochemical features are consistent with formation of the intermediate-felsic suite through fractionation from underplated basaltic magma that originated from sub-continental lithospheric mantle metasomatized by asthenosphere-derived oceanic-island-basalt-like (OIB-like) melts, coupled with minor crustal contamination. We correlate the ca. 630 Ma magmatism with a back-arc rift setting that probably developed in relation to slab tearing during continued slab rollback.

  12. Petrogenesis of the Neoproterozoic West Highland Granitic Gneiss, Scottish Caledonides: Cryptic mantle input to S-type granites?

    NASA Astrophysics Data System (ADS)

    Fowler, M.; Millar, I. L.; Strachan, R. A.; Fallick, A. E.

    2013-05-01

    The Neoproterozoic (c. 870 Ma) West Highland Granitic Gneiss, exposed in the Northern Highlands Terrane of Scotland, has elemental characteristics that are strikingly similar to those of the host Moine metasediments, which are thus consistent with an origin involving major Moine melting. Most of the constituent bodies have compositions significantly removed from minimum melts of pelites, and trace element constraints suggest variable but significant restite entrainment leading to less silicic bulk compositions with enhanced REE, Zr and Y. However, initial Nd and Hf isotope ratios are not coincident with contemporary Moine and imply a significant juvenile contribution. Close association with a regional suite of metabasites prompts consideration of mafic magma input, for which binary mixing models offer qualitative support. Quantitative difficulties with typical Moine metasediments are eased with radiogenic pelites or by partial melting of the mafic component. A possible alternative is currently unexposed Grenvillian felsic crust. Subsequent interaction of the granitic gneisses with meteoric water has significantly perturbed the oxygen and Sr isotope systems, the timing of which is equivocal but probably occurred during Caledonian events. The elemental characteristics of the West Highland Granitic Gneiss show many similarities with Scandinavian (rift-related?) granites of the same age, but since their geochemistry is largely inherited from the protolith it would be unwise to pursue palaeotectonic attribution on this basis. However, the probable incorporation of significant mantle-derived mafic magma of MORB-like affinity is consistent with an extensional setting.

  13. Hypothesized link between Neoproterozoic greening of the land surface and the establishment of an oxygen-rich atmosphere.

    PubMed

    Kump, Lee R

    2014-09-30

    Considerable geological, geochemical, paleontological, and isotopic evidence exists to support the hypothesis that the atmospheric oxygen level rose from an Archean baseline of essentially zero to modern values in two steps roughly 2.3 billion and 0.8-0.6 billion years ago (Ga). The first step in oxygen content, the Great Oxidation Event, was likely a threshold response to diminishing reductant input from Earth's interior. Here I provide an alternative to previous suggestions that the second step was the result of the establishment of the first terrestrial fungal-lichen ecosystems. The consumption of oxygen by aerobes respiring this new source of organic matter in soils would have necessitated an increase in the atmospheric oxygen content to compensate for the reduced delivery of oxygen to the weathering environment below the organic-rich upper soil layer. Support for this hypothesis comes from the observed spread toward more negative carbon isotope compositions in Neoproterozoic (1.0-0.542 Ga) and younger limestones altered under the influence of ground waters, and the positive correlation between the carbon isotope composition and oxygen content of modern ground waters in contact with limestones. Thus, the greening of the planet's land surfaces forced the atmospheric oxygen level to a new, higher equilibrium state. PMID:25225378

  14. Extreme winds and waves in the aftermath of a Neoproterozoic glaciation.

    PubMed

    Allen, Philip A; Hoffman, Paul F

    2005-01-13

    The most severe excursions in the Earth's climatic history are thought to be associated with Proterozoic glaciations. According to the 'Snowball Earth' hypothesis, the Marinoan glaciation, which ended about 635 million years ago, involved global or nearly global ice cover. At the termination of this glacial period, rapid melting of continental ice sheets must have caused a large rise in sea level. Here we show that sediments deposited during this sea level rise contain remarkable structures that we interpret as giant wave ripples. These structures occur at homologous stratigraphic levels in Australia, Brazil, Canada, Namibia and Svalbard. Our hydrodynamic analysis of these structures suggests maximum wave periods of 21 to 30 seconds, significantly longer than those typical for today's oceans. The reconstructed wave conditions could only have been generated under sustained high wind velocities exceeding 20 metres per second in fetch-unlimited ocean basins. We propose that these extraordinary wind and wave conditions were characteristic of the climatic transit, and provide observational targets for atmospheric circulation models. PMID:15650730

  15. On the occurrence of gold mineralization in the Pala Neoproterozoic formations, South-Western Chad

    NASA Astrophysics Data System (ADS)

    Tchameni, Rigobert; Doumnang, Jean Claude; Deudibaye, Marambaye; Branquet, Yannick

    2013-08-01

    The Pala region, in southwestern Chad, belongs to the northern part of the Central African Pan-African Fold Belt. It is made up of greenschist-facies schists and is characterized by bimodal, mainly mafic, magmatism. This schist unit named Goueigoudoum Series is intruded by pre- to post-tectonic plutonic rocks dated between 737 and 570 Ma and dykes of quartz. Gold is mined artisanally from alluvial deposits and primary chalcopyrite-pyrite-bearing quartz veins, brecciated and silicified zones and shear zones. The majority of the mineralized shear zones and some quartz veins generally trend N-S to NNE-SSW or NW-SE and are interpreted as extensional shear fractures related to regional NE-SW-trending sinistral strike-slip shear zones. The geological context of the Pala region clearly indicates hydrothermal fluids formed along active continental margins during collisional orogenesis, and subsequent associated fluid migration typically occurred during strike-slip events. Although the origin of fluids may be varied (magmatic, metamorphic or meteoric fluids, Proterozoic seawater, or sedimentary basin formation waters), the distribution of the mineralizations along the granitoid intrusions suggests that magmatism played a major role in the dynamics of the mineralizing fluids.

  16. Paleobiology of the Mesoproterozoic-Neoproterozoic transition: the Sukhaya Tunguska Formation, Turukhansk Uplift, Siberia

    NASA Technical Reports Server (NTRS)

    Sergeev, V. N.; Knoll, A. H.

    1997-01-01

    Silicified carbonates of the latest Mesoproterozoic Sukhaya Tunguska Formation, northwestern Siberia, contain abundant and diverse permineralized microfossils. Peritidal environments are dominated by microbial mats built by filamentous cyanobacteria comparable to modern species of Lyngbya and Phormidium. In subtidal to lower intertidal settings, mat-dwelling microbenthos and possible coastal microplankton are abundant. In contrast, densely woven mat populations with few associated taxa characterize more restricted parts of tidal flats; the preservation of vertically oriented sheath bundles and primary fenestrae indicates that in these mats carbonate cementation was commonly penecontemporaneous with mat growth. Eoentophysalis mats are limited to restricted environments where microlaminated carbonate precipitates formed on or just beneath the sediment surface. Most microbenthic populations are cyanobacterial, although eukaryotic microfossils may occur among the simple spheroidal cells interpreted as coastal plankton. Protists are more securely represented by large (up to 320 micrometers in diameter) but poorly preserved acritarchs in basinal facies. The Sukhaya Tunguska assemblage contains 27 species in 18 genera. By virtue of their stratigraphic longevity and their close and predictable association with specific paleoenvironmental conditions, including substrates, Proterozoic cyanobacteria support a model of bacterial evolution in which populations adapt rapidly to novel environments and, thereafter, resist competitive replacement. The resulting evolutionary pattern is one of accumulation and stasis rather than the turnover and replacement characteristic of Phanerozoic plants and animals.

  17. The Effect of Improved Water Supply on Diarrhea Prevalence of Children under Five in the Volta Region of Ghana: A Cluster-Randomized Controlled Trial

    PubMed Central

    Cha, Seungman; Kang, Douk; Tuffuor, Benedict; Lee, Gyuhong; Cho, Jungmyung; Chung, Jihye; Kim, Myongjin; Lee, Hoonsang; Lee, Jaeeun; Oh, Chunghyeon

    2015-01-01

    Although a number of studies have been conducted to explore the effect of water quality improvement, the majority of them have focused mainly on point-of-use water treatment, and the studies investigating the effect of improved water supply have been based on observational or inadequately randomized trials. We report the results of a matched cluster randomized trial investigating the effect of improved water supply on diarrheal prevalence of children under five living in rural areas of the Volta Region in Ghana. We compared the diarrheal prevalence of 305 children in 10 communities of intervention with 302 children in 10 matched communities with no intervention (October 2012 to February 2014). A modified Poisson regression was used to estimate the prevalence ratio. An intention-to-treat analysis was undertaken. The crude prevalence ratio of diarrhea in the intervention compared with the control communities was 0.85 (95% CI 0.74–0.97) for Krachi West, 0.96 (0.87–1.05) for Krachi East, and 0.91 (0.83–0.98) for both districts. Sanitation was adjusted for in the model to remove the bias due to residual imbalance since it was not balanced even after randomization. The adjusted prevalence ratio was 0.82 (95% CI 0.71–0.96) for Krachi West, 0.95 (0.86–1.04) for Krachi East, and 0.89 (0.82–0.97) for both districts. This study provides a basis for a better approach to water quality interventions. PMID:26404337

  18. Polyphase deformation history and strain analyses of the post-amalgamation depositional basins in the Arabian-Nubian Shield: Evidence from Fatima, Ablah and Hammamat Basins

    NASA Astrophysics Data System (ADS)

    Hamimi, Zakaria; El-Fakharani, Abdelhamid; Abdeen, Mamdouh M.

    2014-11-01

    Post-amalgamation depositional basins <650 Ma (PADBs), dominated by volcano-sedimentary assemblages, unconformably overlying Neoproterozoic juvenile (mantle-derived) arcs, represent one of the main collage in the Arabian-Nubian Shield (ANS). In this work, three distinguished PADBs; namely Fatima, Ablah and Hammamat PADBs, are the subject matter of detailed field investigations and quantitative strain analysis in an attempt to highlight the polyphase deformation history of these PADBs and to discern whether the ANS's PADBs were deformed at the same time or not. The Fatima PADB is studied in its type locality along the northwestern flank of Wadi Fatima; between Jabal Abu Ghurrah and Jabal Daf, in Jeddah tectonic terrane. The Ablah PADB is examined around Wadi Yiba, further south of its type locality near Jabal Ablah in Al-Aqiq Quadrangle, in Asir tectonic terrane. The Hammamat PADB is investigated in Wadi Umm Gheig, Wadi Allaqi and Wadi Hodein in the Egyptian Eastern Desert tectonic terrane. It is supposed that the Fatima is a basin controlled by dextral transcurrent shearing occurred along the NE-oriented Wadi Fatima Shear Zone and the Ablah is a strike-slip pull-apart basin, and both basins were believed to be deposited during and soon after the Nabitah Orogeny (680-640 Ma) that marked suturing of the Afif terrane with the oceanic ANS terranes to the west. They were affected by at least three Neoproterozoic deformation phases and show geometric and kinematic relationships between folding and thrusting. The Hammamat PADB is a fault-bounded basin affected by a NW-SE- to NNW-SSE-oriented shortening phase just after the deposition of the molasse sediments, proved by NW- to NNW-verging folds and SE- to SSE-dipping thrusts that were refolded and thrusted in the same direction. The shortening phase in the Hammamat was followed by a transpressional wrenching phase related to the Najd Shear System, which resulted in the formation of NW-SE sinistral-slip faults associated

  19. Active deformation of the Congo intracratonic basin and its eastern margin

    NASA Astrophysics Data System (ADS)

    Everaerts, Michel; Delvaux, Damien; Beoka, Ateba

    2015-04-01

    The Congo basin, one of the largest intracontinental sedimentary basin in the world, developed in Central Africa since the early Neoproterozoic during successive tectonically controlled stages. It formed over an heterogeneous basement as highlighted by aeromagnetic data, composed of Archean cores welded by Proterozoic mobile belts. It contains an average of 4 km and locally up to 8 km of Neoproterozoic to Mesozoic sediments. Since late Mesozoic (Cenomanian), it was submitted to intraplate stresses due to the action of ridge-push forces related to the spreading of the South Atlantic. As a result, most part of the basin entered in an erosional stage while only a small part is still accumulating sediments. Active deformation of this vast region (5°N-11°S and 12-27°E) is indicated by a certain level of seismic activity, with about 270 earthquakes instrumentally recorded with magnitudes ranging from 2.2 to 5.5 inside the basin and up to up to 6.3 along its NW (Gabon) and NW (Katanga) margins. The dozen available focal mechanisms indicate that the basin is under ENE-WSW horizontal compression, under a compressional regime in its center and strike-slip regime along its northern and western margins. Low-angle slickensided fault planes are observed in the Samba cored well, constraining the onset of the recent compressional setting in the late Albian, at a time when South America was already separated from Africa and the South Atlantic Ridge was already functioning. Although subtle, recent tectonic deformations (faulting and buckling undulations) can also be inferred from the reflection seismic profiles and the topography and river network. The overall neotectonic picture is inferred as reflecting the development of compressional tectonic instabilities in the basin fill and its margins under the action of intraplate stress field and the control of the basement heterogeneity. This is a contribution to preparation of the Seismotectonic Map of Africa by the working group of

  20. Syn-rift, syn-glacial and syn-orogenic sedimentary mélanges as indicators of tectonic and palaeoclimatic evolution of the Lufilian Belt, Neoproterozoic-Lower Palaeozoic of Central Africa

    NASA Astrophysics Data System (ADS)

    Wendorff, Marek

    2010-05-01

    The Lufilian belt is an important segment of the Neoproterozoic-Lower Palaeozoic orogenic network within southern and central Africa. It deforms a sedimentary suite of the Katanga Supergroup (880-500 Ma). Mélange occurrences, traditionally called the Katangan breccias/megabreccias, are a prominent feature of the belt architecture. Some mélange bodies reach thickness of 2000 m and contain huge blocks of Katangan rocks. They were previously considered as tectonic mélanges ("friction breccias") marking regional decollement zones related to thrusting during the Pan-African orogenesis. However, these fragmental rocks were recently shown to be of sedimentary origin. They form two regionally extensive olistostrome bodies and one glaciogenic unit. The main lines of evidence for the olistostrome genesis are following: (1) lack of pervasive shearing that would point to tectonic fragmentation; (2) textures and structures diagnostic for subaqueous sediment gravity flows ranging from debris flows to turbidites; (3) roundness and provenance of clasts, and lateral facies gradients implying erosion, abrasion and unroofing of the Katangan source rocks elevated in the source areas; (4) lower boundaries of fragmental bodies are not tectonic but stratigraphic; (5) injections of unconsolidated conglomeratic matrix filling open joints in allochthonous blocks embedded in olistostrome lithosomes. The oldest mélange is a disorganised to locally organised syn rift olistostrome complex with olistoliths reaching 5 metres across. The clasts were derived from the uplifted rift margin and redeposition resulted from mass-wasting (rockfalls producing sedimentary breccias), sliding of solitary blocks, and pebbly to cobbly debris flows. The succeeding glaciogenic mélange complex originated during the Grand Conglomerat glaciation (correlative to the Sturtian glacial). It consists of disorganised clast-in-matrix facies that resulted from glacial erosion of the uplifted rift margin and

  1. Provenance of upper Triassic sandstone, southwest Iberia (Alentejo and Algarve basins): tracing variability in the sources

    NASA Astrophysics Data System (ADS)

    Pereira, M. F.; Ribeiro, C.; Gama, C.; Drost, K.; Chichorro, M.; Vilallonga, F.; Hofmann, M.; Linnemann, U.

    2016-01-01

    Laser ablation ICP-MS U-Pb analyses have been conducted on detrital zircon of Upper Triassic sandstone from the Alentejo and Algarve basins in southwest Iberia. The predominance of Neoproterozoic, Devonian, Paleoproterozoic and Carboniferous detrital zircon ages confirms previous studies that indicate the locus of the sediment source of the late Triassic Alentejo Basin in the pre-Mesozoic basement of the South Portuguese and Ossa-Morena zones. Suitable sources for the Upper Triassic Algarve sandstone are the Upper Devonian-Lower Carboniferous of the South Portuguese Zone (Phyllite-Quartzite and Tercenas formations) and the Meguma Terrane (present-day in Nova Scotia). Spatial variations of the sediment sources of both Upper Triassic basins suggest a more complex history of drainage than previously documented involving other source rocks located outside present-day Iberia. The two Triassic basins were isolated from each other with the detrital transport being controlled by two independent drainage systems. This study is important for the reconstruction of the late Triassic paleogeography in a place where, later, the opening of the Central Atlantic Ocean took place separating Europe from North America.

  2. Provenance and chemostratigraphy of the Neoproterozoic West Congolian Group in the Democratic Republic of Congo

    NASA Astrophysics Data System (ADS)

    Frimmel, Hartwig E.; Tack, Luc; Basei, Miguel S.; Nutman, Allen P.; Boven, Ariel

    2006-10-01

    Lithogeochemical, chemostratigraphic, Rb-Sr and Sm-Nd isotope as well as U-Pb single zircon age data from the principal stratigraphic units of the West Congolian Group (West Congo Supergroup) in the West Congo Belt, Democratic Republic of Congo, presented in this reconnaissance study provide new insights into regional stratigraphic correlation and sediment provenance. The oldest unit (Sansikwa Subgroup) is a continental rift basin fill that culminated in a marine glacial diamictite (Lower Mixtite Formation), which is correlated with the global 750-720 Ma Sturtian glaciation. This is followed by a post-glacial, marine carbonate-dominated succession (Haut Shiloango Subgroup), a second diamictite unit (Upper Mixtite Formation) for which a syn-Marinoan (636 Ma) age is favoured, a post-glacial carbonate succession (Schisto-Calcaire Subgroup) and finally molasse sediments that experienced orogenic deformation at c. 566 Ma, as indicated by new 40Ar- 39Ar data. The youngest unit (Inkisi Group) is post-orogenic, derived from the West Congo Belt, and thus not part of the same supersequence. The proposed regional to global correlation of the various units is in line with progressively younger detrital zircon age spectra up-section. Overall, these age spectra indicate a Neoarchaean basement source (Congo Craton) and a Palaeoproterozoic source from the known Kimezian Supergroup to the west of the belt, which corresponds in age with the Eburnean of southern Africa. In addition, we identified a hitherto unknown late Mesoproterozoic source to the west of the belt, the age of which is comparable to the Espinhaço Supergroup of the Araçuai Belt in Brazil.

  3. Neoproterozoic ophiolite and related high-grade rocks of the Baikal-Muya belt, Siberia: Geochronology and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Kröner, A.; Fedotova, A. A.; Khain, E. V.; Razumovskiy, A. A.; Orlova, A. V.; Anosova, M. O.; Perelyaev, V. I.; Nekrasov, G. E.; Liu, D. Y.

    2015-11-01

    We report zircon for from ophiolitic and high-grade rocks of the Neoproterozoic Baikal-Muya belt of Siberia that occupies an arc-shaped area on the southeastern margin of the Siberian craton. It consists of arc-related plutonic, metavolcanic and metasedimentary rocks as well as fragmented ophiolites and high-grade metamorphic assemblages. Magmatic zircons from two plagiogranite dyke samples of the Mamakan ophiolite complex in the Sredne-Mamakan massif of the eastern Baikal-Muya belt yielded similar and concordant SHRIMP mean 206Pb/238U ages of 640.0 ± 4.1 and 650 ± 6 Ma, respectively, that reflect the time of dyke emplacement and from which we suggest an age of ca. 645 Ma as the most likely time of ophiolite formation. Enderbitic gneisses of the North Baikal area, in the western part of the Baikal-Muya belt, contain complex zircon populations that reflect variable recrystallization, Pb-loss and metamorphic overgrowth during granulite-facies metamorphism. LA-ICP-MS dating of these zircons yielded inconclusive results that led us to undertake a detailed study of cathodoluminescence images combined with U-Pb SHRIMP dating. Well-preserved magmatic domains in zircons from enderbite sample 2821 yielded concordant results with a mean 206Pb/238U age of 640 ± 5 Ma, slightly higher but broadly comparable with the data obtained by LA-ICP-MS. The zircon populations of two more enderbitic gneiss samples are more complex, and their LA-ICP-MS data constitute broad swaths along concordia between ca. 840 and 600 Ma, reflecting two end-member isotopic components, namely an igneous crystallization event at ca. 800 Ma and a Pb-loss and recrystallization event at ca. 600 Ma. SHRIMP analyses of magmatic zircon domains of these samples yielded concordant data with identical mean 206Pb/238U ages of 826 ± 7.5 Ma and 826 ± 8 Ma, respectively, whereas low-U metamorphic rims crystallized at 640 ± 7 Ma. Newly crystallized ball-round metamorphic zircons in one sample produced a mean 206Pb

  4. The importance of XRD analysis in provenance and palaeoenvironmental studies of the Piedras de Afilar Formation, Neoproterozoic of Uruguay

    NASA Astrophysics Data System (ADS)

    Pamoukaghlian, K.; Poiré, D. G.; Gaucher, C.; Uriz, N.; Cingolani, C.; Frigeiro, P.

    2009-04-01

    The Piedras de Afilar Formation crops out in the southeast part of Uruguay, forming part of the Tandilia Terrane (sensu Bossi et al. 2005). Pamoukaghlian et al. (2006) and Gaucher et al. (2008) have published δ13C, δ18O and U/Pb SHRIMP results, which indicate a Neoproterozoic age for this formation. The palaeoenvironment has been defined as a shallow marine platform based on the presence of interference ripples, hummocky and mega-hummocky cross-stratification. X-ray diffraction (XRD) analyses help to better constrain the palaeoenvironment: the presence of chlorite/smectite found in black shales, suggest a reducing environment, and abundant illite indicates a cold to temperate climate. Provenance studies have been undertaken that utilise a combination of detailed palaeocurrent measurements, petrographic descriptions, XRD analyses, and geochemical isotopic analyses, including U/Pb SHRIMP determinations. Mineral compositional diagrams for sandstones suggest a stable cratonic provenance. Palaeocurrents are mainly from the NNE, indicating a provenance from the cratonic areas of the Tandilia Terrane. The illite crystal index indicates diagenetic to low-metamorphic conditions for the sequence; this is important to confirm that the identified minerals are authigenic. Clay minerals identified by XRD analysis of sandstones from the siliciclastic member are illite (80 - 90%), kaolinite (5 - 10%), and chlorite (5 - 10%). This is consistent with a provenance from the cratonic areas (quartz-feldspar dominated rock types). Isotopic analyses have been undertaken to provide better constraints on the tectonic setting. U/Pb SHRIMP ages for the youngest zircons are 990 Ma (Gaucher et al. 2008), and the basal granite (Granito de la Paz) is 2056 ± 11 Ma (Hartmann et al. 2001), suggesting a provenance from the Archaean basement for the Piedras de Afilar Formation, like its counterparts in the Rio de la Plata Craton. References Bossi, J., Piñeyro, D., Cingolani, C. (2005). El l

  5. Chemical variations of mineral inclusions in Neoproterozoic high-Cr chromitites from Egypt: Evidence of fluids during chromitite genesis

    NASA Astrophysics Data System (ADS)

    Khedr, Mohamed Zaki; Arai, Shoji

    2016-01-01

    This paper details the mode of occurrence, petrography, and chemistry of mineral inclusions hosted in chromian spinels of the Neoproterozoic chromitites in the Southern Eastern Desert of Egypt. Neoproterozoic podiform chromitites from the Arais, Balamhindit, and Abu Dahr areas, in the Southern Eastern Desert, can be texturally and chemically classified into two main types: primary high-Al (spinel Cr# < 0.67) and high-Cr (spinel Cr# > 0.75) chromitites. The former, being free of primary-mineral inclusions, was crystallized mainly from the MORB-like tholeiitic melt generated during proto-forearc spreading at the initiation of subduction, whereas the latter was formed from boninitic melts resulting from the high-degree melting of the sub-arc depleted mantle in the presence of slab-derived fluids at a mature-arc stage. The primary mineral inclusions, such as Na- and K-phlogopites, pargasite-edenite and olivine with subordinate pyroxenes, millerite, and laurite, were trapped within the chromian spinel during the magmatic precipitation of the chromitites. The Abu Dahr chromitites are free of primary hydrous inclusions; on the other hand, Arais and Balamhindit high-Cr chromitites are enriched in Na- and K-phlogopites, respectively, as a result of a difference in the K/Na ratio of the magma responsible for chromitite crystallization at different mantle depths. This difference in the K/Na ratio can possibly be attributed to fractionation of the upward-migrating hydrous fluids/melts by the crystallization of K- or Na-rich minerals. The Balamhindit complex, where the chromitite showed K-phlogopite inclusions within the chromian spinel, was probably derived from a deeper part of the mantle than the other areas, where the chromitite shows inclusions of Na-rich hydrous phases. Both K- and Na-phlogopites were possibly formed from alkali-rich hydrous fluids/melts trapped within the chromian spinels during the chromitite formation at different mantle depths, where the K/Na ratio

  6. Mid-Neoproterozoic (ca. 830-800 Ma) metamorphic P-T paths link Tarim to the circum-Rodinia subduction-accretion system

    NASA Astrophysics Data System (ADS)

    Ge, Rongfeng; Zhu, Wenbin; Wilde, Simon A.

    2016-06-01

    Long-lived exterior accretionary orogeny shapes tectonothermal evolution of the peripheral building blocks of supercontinents and leads to considerable crustal growth. However, such accretionary orogeny has only been locally recognized for the Rodinia supercontinent. Here a suite of newly discovered mid-Neoproterozoic high-grade metamorphic rocks in the northern Tarim Craton, NW China, are used to test the exterior accretion hypothesis for Rodinia. These rocks occur as dark-colored mafic and calc-silicate boudins in impure marbles and mica schists. Geochemical data suggest a protolith of arc-related basalts metasomatized by Ca-rich fluids. Mineral assemblages, phase diagram modeling, and mineral compositions for a garnet pyroxenite and a garnet clinopyroxene gneiss reveal upper amphibolite to high-pressure granulite facies peak metamorphism (660-700°C, 11-12 kbar) following a counterclockwise P-T path, which is characterized by prograde burial and heating, followed by near-isothermal burial and retrograde exhumation and cooling. This P-T path is interpreted to have recorded crustal thickening of an earlier magmatic arc transformed to a fore arc by subduction erosion and subsequent burial along bent isotherms near the subduction channel. All studied samples record ca. 830-800 Ma metamorphic zircon U-Pb ages, which probably date the early exhumation and cooling according to Ti-in-zircon temperatures, zircon rare earth element patterns, and Hf isotopes. This is the first mid-Neoproterozoic P-T-t path in Tarim, and it provides metamorphic evidence for a mid-Neoproterozoic advancing-type accretionary orogeny, which is coeval with the initial breakup events of Rodinia and thus links Tarim to the circum-Rodinia accretion system, supporting the peripheral subduction model.

  7. Geochemistry of accreted metavolcanic rocks from the Neoproterozoic Gwna Group of Anglesey-Lleyn, NW Wales, U.K.: MORB and OIB in the Iapetus Ocean

    NASA Astrophysics Data System (ADS)

    Saito, Takuya; Uno, Masaoki; Sato, Tomohiko; Fujisaki, Wataru; Haraguchi, Satoru; Li, Yi-bing; Sawaki, Yusuke; Yamamoto, Shinji; Maruyama, Shigenori

    2015-11-01

    The Gwna Group in Anglesey-Lleyn, NW Wales, UK, is a Neoproterozoic accretionary complex that consists of basalt, bedded chert, red claystone, and trench turbidite that have been intercalated in coherent and incoherent mélanges that are considered typical Ocean plate stratigraphy (OPS). The sediments in the OPS can be useful for constraining the geological environment in the Iapetus Ocean. Most basalts in this area have undergone hydrothermal alteration, greenschist facies regional metamorphism, and surface oxidation. This indicates that immobile elements such as Al2O3 and TiO2, Rare Earth Elements (REE) and High Field Strength Elements (HSFE) are appropriate for discriminating the origin of the basalts in the Gwna Group. Most basalts showing light REE-enriched pattern in CI chondrite-normalized spider diagrams in within-plate basalt (WPB) fields, and some have flat patterns in spider diagrams in mid-oceanic ridge basalt (MORB) fields. In view of these relations, we conclude that the former erupted in an oceanic island. Oceanic island basalts (OIB) are common in Phanerozoic accretionary complexes, and this study presents the first evidence of OIB in a Neoproterozoic accretionary complex of the Gwna Group in Anglesey-Llyen and Llyen area. The OIB-like basalts are locally capped by red hematite-rich claystones. This indicates that a fully oxic pelagic condition was present around the oceanic island in the Iapetus Ocean in the Neoproterozoic, which is consistent with the redox condition estimated from contemporaneous shallow marine sediments. On the other hand, the presence of black mudstones on top of MORB-like meta-basalts suggests that deep-sea anoxia conditions were prevalent during the end-Proterozoic.

  8. SHRIMP U-Pb geochronology of Neoproterozoic Windermere Supergroup, central Idaho: Implications for rifting of western Laurentia and synchroneity of Sturtian glacial deposits

    USGS Publications Warehouse

    Lund, K.; Aleinikoff, J.N.; Evans, K.V.; Fanning, C.M.

    2003-01-01

    In central Idaho roof pendants, a northwest-trending belt of metamorphosed strata, correlative with the Windermere Supergroup, links northern and southern segments of the western Laurentia Neoproterozoic rift belt. Nine newly named formations within the Gospel Peaks sequence-A through Gospel Peaks sequence-D record Cryogenian preglacial, rift-glacial, and postglacial events as well as Neoproterozoic III glacial and rift events. The Edwardsburg Formation of Gospel Peaks sequence B includes interfingered bimodal rift-related volcanic and glaciogenic diamictite strata. Zircons from a rhyodacite flow in the lower Edwardsburg Formation and from a rhyolite flow at its top, dated by using the sensitive high-resolution ion microprobe (SHRIMP), yielded a weighted average of 685 ?? 7 Ma and 684 ?? 4 Ma. Reevaluation of geochronology and correlations indicates that Cryogenian rifting may have been (1) protracted between 780 and 685 Ma, (2) diachronous along the Cordillera, and/or (3) stepwise with a Cordilleran-wide event at ca. 685 Ma that initiated the formation of the Cordilleran miogeocline and set its geometry. Reevaluation of the Cryogenian glacial record indicates that (1) two associated ca. 685 Ma glacial intervals in the Edwardsburg Formation correlate with the Rapitan glaciation, (2) the Sturtian snowball Earth event must be reevaluated on the basis of revision of Rapitan glaciation from 750-700 Ma to ca. 685 Ma, and (3) there were older Cryogenian glaciations or Cryogenian glaciations were not globally synchronous. New dates and correlations significantly impact the number and synchroneity of possible snowball Earth events and the paleolatitudes of Cryogenian glaciations. Western Laurentian events at ca. 685 Ma particularily affect Neoproterozoic paleocontinental reconstructions by indicating diachronous and multi step breakup of supercontinent Rodinia.

  9. Zircon (U-Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

    NASA Astrophysics Data System (ADS)

    Powell, Jeremy; Schneider, David; Stockli, Daniel; Fallas, Karen

    2016-03-01

    Sedimentary strata of the Neoproterozoic Mackenzie Mountains Supergroup (MMSG) and Windermere Supergroup (WSG) occupy the cores of anticlines in the Mackenzie Mountains of the Canadian Cordilleran Foreland Belt. Stratigraphic and structural evidence suggest that these rocks have undergone several episodes of burial and unroofing relatively intact. We report single-grain detrital muscovite 40Ar/39Ar and zircon (U-Th)/He (ZHe) data from a suite of samples across the fold-thrust belt and the Neoproterozoic stratigraphic record. The strata have not reached high enough temperatures to reset the muscovite 40Ar/39Ar system, and instead our detrital muscovite data refine Tonian-Cryogenian depositional ages. Single-crystal ZHe dates range from 432 ± 35 to 46 ± 4 Ma, indicating that MMSG and WSG strata have not been heated sufficiently to fully reset the ZHe system. These factors make the Neoproterozoic strata an attractive natural laboratory to test the utility of the zircon radiation damage and annealing model on the quantification of thermal histories from detrital zircon populations that have accumulated radiation damage over long geologic timescales. Thermal modeling reveals that (1) a substantial sedimentary package was deposited following the Devonian and removed during Permo-Triassic cooling, and (2) the Cordilleran deformation front propagated through the study area from the Albian to the Paleocene, with a moderate increase in cooling rates between 75-67 Ma in the southwest and 60-55 Ma at the deformation front. Ultimately, relationships between radiation damage and helium diffusion kinetics in zircon explain substantial ZHe date dispersion and elucidate the temperature-time history of the northern Canadian Cordillera.

  10. U-Pb zircon geochronology and Nd-Hf-O isotopic systematics of the Neoproterozoic Hadb adh Dayheen ring complex, Central Arabian Shield, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Ali, Kamal A.; Jeon, Heejin; Andresen, Arild; Li, Shuang-Qing; Harbi, Hesham M.; Hegner, Ernst

    2014-10-01

    A combined study of single zircon U-Pb dating, Hf-O zircon isotopic analyses and whole-rock Nd isotopic compositions was carried out to infer the magma sources of Neoproterozoic post-collisional A-type granitoids in Saudi Arabia. U-Pb zircon dating of magmatic zircons of two samples from the Hadb adh Dayheen ring complex yielded ages of 625 ± 11 Ma for a hornblende-biotite granite sample, and 613 ± 4 Ma for a monzogranite sample. The granitic rocks show initial εNd values of + 4.1 to + 5.3 and εHf of + 4.5 to + 8.4 that are lower than those of a model depleted mantle (εHf ~+ 14 and εNd ~+ 6.5) and consistent with melting of subduction-related crustal protoliths that were formed during the Neoproterozoic assembly of the Arabian-Nubian Shield (ANS). Crustal-model ages (Hf-tNC) of 0.81 to 1.1 Ga are inconsistent with depleted-mantle Nd model ages of 0.71 to 0.81 Ga and indicate that the post-collisional Hadb adh Dayheen granites were derived mostly from juvenile crust formed in Neoproterozoic time. Single zircons data show a wide range in δ18O values from + 3.2‰ to + 6.4‰, possibly indicating crystallization of zircon from magma derived from magmatic rocks altered by meteoric water in a magma chamber-caldera system.

  11. Superposed folding and associated fracturing influence hypogene karst development in Neoproterozoic carbonates, São Francisco Craton, Brazil

    NASA Astrophysics Data System (ADS)

    Ennes-Silva, Renata A.; Bezerra, Francisco H. R.; Nogueira, Francisco C. C.; Balsamo, Fabrizio; Klimchouk, Alexander; Cazarin, Caroline L.; Auler, Augusto S.

    2016-01-01

    Porosity and permeability along fractured zones in carbonates could be significantly enhanced by ascending fluid flow, resulting in hypogene karst development. This work presents a detailed structural analysis of the longest cave system in South America to investigate the relationship between patterns of karst conduits and regional deformation. Our study area encompasses the Toca da Boa Vista (TBV) and Toca da Barriguda (TBR) caves, which are ca. 107 km and 34 km long, respectively. This cave system occurs in Neoproterozoic carbonates of the Salitre Formation in the northern part of the São Francisco Craton, Brazil. The fold belts that are around and at the craton edges were deformed in a compressive setting during the Brasiliano orogeny between 750 and 540 Ma. Based on the integrated analysis of the folds and brittle deformation in the caves and in outcrops of the surrounding region, we show the following: (1) The caves occur in a tectonic transpressive corridor along a regional thrust belt; (2) major cave passages, at the middle storey of the system, considering both length and frequency, developed laterally along mainly (a) NE-SW to E-W and (b) N to S oriented anticline hinges; (3) conduits were formed by dissolutional enlargement of subvertical joints, which present a high concentration along anticline hinges due to folding of competent grainstone layers; (4) the first folding event F1 was previously documented in the region and corresponds with NW-SE- to N-S-trending compression, whereas the second event F2, documented for the first time in the present study, is related to E-W compression; and (5) both folding events occurred during the Brasiliano orogeny. We conclude that fluid flow and related dissolution pathways have a close relationship with regional deformation events, thus enhancing our ability to predict karst patterns in layered carbonates.

  12. Paleogeographic Evolution of the Late Neoproterozoic and Early Phanerozoic with New Paleomagnetic Constraints from West African Craton

    NASA Astrophysics Data System (ADS)

    Robert, B.; Besse, J.; Blein, O.; Greff-Lefftz, M.; Baudin, T.; Fernando, L.; Meslouh, S.; Belbadaoui, M.

    2015-12-01

    The paleogeographic evolution of the late Neoproterozoic and early Phanerozoic is dominated by the dispersion of Rodinia and the assembly of Gondwana. The timing of these two episodes is still highly debated, partly due to the low number of good quality paleomagnetic data. In order to better constrain the paleogeography for this epoch, we bring new paleomagnetic data on volcanic series from the West African Craton (WAC), which is a key block to understand the evolution of these two supercontinents. We have sampled well dated pyroclastic and lava flows from the groups of Ouarzazate (upper Ediacaran) and Taroudant (lower Cambrian) in the Anti-Atlas (Morocco). 500 samples from 105 sites were thermally demagnetized in laboratory. Our results highlight two major groups of directions, mainly carried by minerals of the titano-hematite family. Magnetite may also contribute sometimes to the magnetization. The first group displays a single polarity direction, with a shallow inclination and a south-east declination. This direction close to the expected direction derived from the Permo-Carboniferous segment of the Gondwana apparent polar wander path (APWP) is due to a remagnetization acquired during the Kiaman reversed polarity superchron (320-262Ma). The second group, observed in the Ouarzazate and Taroudant groups, consists of a dual polarity high inclination direction and may represent the characteristic magnetization. On the basis of geologic and paleomagnetic data from literature, we constructed an APWP for both WAC and Amazonia between 615 and 530Ma, assuming these two blocks were already accreted. We found a paleomagnetic solution in which Laurentia and WAC-Amazonia remained attached from ~615Ma up to the late Ediacaran, Laurentia remaining at low latitude during this period. Around ~550Ma, WAC-Amazonia separated from Laurentia and finally collided with the other Gondwanan blocks during the lower Cambrian, marking the final accretion of Gondwana.

  13. Neoproterozoic Cana Brava chrysotile deposit (Goiás, Brazil): Geology and geochemistry of chrysotile vein formation

    NASA Astrophysics Data System (ADS)

    Biondi, João Carlos

    2014-01-01

    The Cana Brava chrysotile asbestos deposit of Goiás, Brazil, contains approximately 150 Mt of ore with an average of 3.5 wt.% of cross-fiber chrysotile and lies in the differentiated, mafic-ultramafic Neoproterozoic Cana Brava complex. This complex was formed at approximately 0.79 Ga and metamorphosed at 0.77 to 0.76 and 0.63 Ga. The 0.77 to 0.76 Ga metamorphic event was a high-grade one that transformed the mafic and ultramafic rocks into meta-peridotites and meta-pyroxenites. The low-grade 0.63 Ga metamorphism allowed the formation of black, red and brown serpentinite, graphitic, magnesite-rich talc serpentinite, and rodingite, which became folded and foliated. At the end of the 0.63 Ga metamorphism, black serpentinites were oxidized to form red serpentinites, the main type of serpentinite that outcrops today at the Cana Brava mineralized region. Post-metamorphic fluids reactivated the process of serpentinization, thereby generating massive green serpentinite from the red. Green formed on the most fractured zones, and double red and green reaction rims formed on the sides of the veins located outside the green serpentinite zones. This process did not cause significant variation in the volume of the rocks and resulted in a strongly reducing system thanks to the loss of Fe2O3 and iron and the subsequent crystallization of magnetite within veinlets and altered rocks. Low angle shear, developed under brittle conditions, caused hydraulic fracturing and the generation of oversaturated, oxidizing fluids that crystallized the cross-fiber chrysotile inside open fractures. Very densely fractured zones with fractures filled with cross-fiber chrysotile constitute the ore that is mined at present.

  14. Zircon U-Pb and Lu-Hf isotope study of the Neoproterozoic Haizhou Group in the Sulu orogen: Provenance and tectonic implications

    NASA Astrophysics Data System (ADS)

    Zhou, Jian-Bo; Wilde, Simon A.; Liu, Fu-Lai; Han, Jie

    2012-04-01

    The Neoproterozoic Haizhou Group crops out sporadically in the Sulu orogen in east-central China. It is divided into the Jinping and Yuntai formations and consists of quartzite, quartz schist, marble and graphite- and apatite-bearing sequences. Major and trace element data for quartz schist from the two formations indicate that these rocks have a greywacke protolith and have been deposited during strong tectonic activity. LA-ICPMS U-Pb dating of detrital zircon yields ages of 635 to 1074 Ma for three samples from the Jinping Formation and 611 to 943 Ma for two samples from the Yuntai Formation. More than 78% of the detrital zircons from the two formations have U-Pb ages grouped between 700 and 890 Ma, with two clusters peaking at 758 Ma and 828 Ma, respectively. This indicates that their provenance is magmatic rocks of Neoproterozoic age that have a tectonic affinity to the South China Block (SCB). A few older zircon populations with peak U-Pb ages at 943 and 1074 Ma are also present. A younger population shows peaks at 661 and 611 Ma. This suggests that deposition of the Haizhou Group was later than ~ 611 Ma rather than during the Mesoproterozoic as previously thought. Zircon Lu-Hf isotope data collected from the same U-Pb sites show negative ɛHf(t) values of - 22.8 to - 7.4 and Hf model ages of 2341 to 3100 Ma. This indicates that the Neoproterozoic magmatic rocks were derived from reworking of ancient Paleoproterozoic to Archean crust. The results support the contention that the Haizhou Group is similar to the Wulian Group at the northwestern edge of the Sulu orogen, both having a SCB affinity, but that the Penglai Group does not belong to the SCB because of the absence of Neoproterozoic ages. This lends support to the conclusion that the Triassic suture between the North China and South China blocks is located along the Baichihe-Yantai Fault, which lies north of the Wulian Complex and south of the Jiaobei Terrane; thus the Wulian-Yantai Fault is not the suture

  15. The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton, Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana

    NASA Astrophysics Data System (ADS)

    Hofmann, Mandy; Linnemann, Ulf; Hoffmann, Karl-Heinz; Gerdes, Axel; Eckelmann, Katja; Gärtner, Andreas

    2014-07-01

    magmas generated from Mesoproterozoic crustal material show more juvenile ɛHf( t) signatures of +14, +8 to +4 with TDM model ages of 1.05-1.6 Ga. During Neoproterozoic deposition, only old cratonic crust with an inherited continental arc signature was available in the source area clearly demonstrated by Hf isotope composition of detrital zircon and geochemical bulk analysis of sedimentary rocks. The granodiorites of the Palaeoproterozoic basement underlying Namuskluft section are ca. 1.9 Ga old and show ɛHf( t) signatures of -3 to -5.5 with TDM model ages of 2.4-2.7 Ga. These basement rocks demonstrate the extreme uplift and deep erosion of the underlying Kalahari Craton at its western margin before general subsidence during Cryogenian and Ediacaran time. The sedimentary sequence of the two examined sections (Namuskluft and Dreigratberg) proposes the presence of a basin and an increasing subsidence at the SW part of the Kalahari Craton during the Cryogenian. Therefore, we propose the initial formation of an intra-cratonic sag basin during the Lower Cryogenian that evolved later to a rift basin at the cratonic margin due to increasing crustal tension and rifting together with the opening of the Adamastor Ocean. As the zircons of the sedimentary rocks filling this basin show neither rift-related U/Pb ages nor an exotic craton as a possible source area, the only plausible sedimentary transport direction providing the found U/Pb ages would be from the E or the SE, directly from the heart of the Kalahari Craton. Due to subsidence and ongoing sedimentation from E/SE directions, the rift-related magmatic rocks were simply covered by the input of old intra-cratonic material that explains the absence of Neoproterozoic zircon grains in our samples. The geochemical analyses show the erosion of a continental arc and related sedimentary rocks with an overall felsic provenance. The source area was a deeply eroded and incised magmatic arc that evolved on continental crust, without

  16. Seasonal variations in phytoplankton diversity in the Bui dam area of the Black Volta in Ghana during the pre- and post-impoundment periods.

    PubMed

    Alhassan, Elliot Haruna

    2015-03-01

    Phytoplankton constitutes the primary producers of aquatic ecosystems and represents the food chain base that supports the commercial fisheries of most water bodies. Nowadays, there is lack of information on phytoplankton assemblages of most reservoirs in Africa. To contribute with this knowledge, this study was carried out to determine the density and diversity of seasonal variations of phytoplankton species in the Bui dam area of the Black Volta, during the pre- (2011) and post-impoundment (2012) periods. For this, a three-level stratified random sampling approach was adopted for 22 months. Phytoplankton samples were obtained by towing a 0.5m diameter phytoplankton net (35 microm mesh size and 0.25m2 mouth surface area) from a non-motorized canoe through a distance of about 100 m against the current from downstream to upstream of the river. In 2011, 35 species of phytoplankton belonging to four classes, Bacillariophyceae (7.6%), Chlorophyceae (43%), Cyanophyceae (48.6%) and Euglenophyceae (0.8%) were identified. In the 2012 sampling, 18 species belonging to three classes, Bacillariophyceae (2.2%), Chlorophyceae (26.1%) and Cyanophyceae (71.7%) were observed. A total of 17 species of phytoplankton, including Gyrosigma sp., Surirella sp., Carteria sp., Chlosterium sp., Chlorogonium sp., Coelastrum sp., Cosmarium sp., Volvox sp., Chroococcus sp., Coelosphaerium sp., Rivularia sp. and Spirulina sp., were absent during the late post-impoundment period. Mean monthly total phytoplankton abundance decreased from June (7 384 cells/M3) to August (106 cells/m3) in 2011. In 2012 however, mean total phytoplankton decreased from February (1237 cels/m3) to August (4 cells/m3). The results also showed that variations occurred between seasons among some phytoplankton groups. The dry and pre-wet seasons had significantly (p<0.05) higher mean phytoplankton abundance than the wet season during the 22 months of sampling period. The biotic indices of Shannon-Wiener (HI) were

  17. The Jebel Ohier deposit—a newly discovered porphyry copper-gold system in the Neoproterozoic Arabian-Nubian Shield, Red Sea Hills, NE Sudan

    NASA Astrophysics Data System (ADS)

    Bierlein, F. P.; McKeag, S.; Reynolds, N.; Bargmann, C. J.; Bullen, W.; Murphy, F. C.; Al-Athbah, H.; Brauhart, C.; Potma, W.; Meffre, S.; McKnight, S.

    2016-08-01

    Ongoing exploration in the Red Sea Hills of NE Sudan has led to the identification of a large alteration-mineralization system within a relatively undeformed Neoproterozoic intrusive-extrusive succession centered on Jebel Ohier. The style of mineralization, presence of an extensive stockwork vein network within a zoned potassic-propylitic-argillic-advanced argillic-altered system, a mineralization assemblage comprising magnetite-pyrite-chalcopyrite-bornite (±gold, silver and tellurides), and the recurrence of fertile mafic to intermediate magmatism in a developing convergent plate setting all point to a porphyry copper-gold association, analogous to major porphyry Cu-Au-Mo deposits in Phanerozoic supra-subduction settings such as the SW Pacific. Preliminary U-Pb age dating yielded a maximum constraint of c. 730 Ma for the emplacement of the stockwork system into a significantly older ( c. 800 Ma) volcanic edifice. The mineralization formed prior to regional deformation and accretion of the host terrane to a stable continental margin at by c. 700 Ma, thus ensuring preservation of the deposit. The Jebel Ohier deposit is interpreted as a relatively well-preserved, rare example of a Neoproterozoic porphyry Cu-Au system and the first porphyry Cu-Au deposit to be identified in the Arabian-Nubian Shield.

  18. The Jebel Ohier deposit—a newly discovered porphyry copper-gold system in the Neoproterozoic Arabian-Nubian Shield, Red Sea Hills, NE Sudan

    NASA Astrophysics Data System (ADS)

    Bierlein, F. P.; McKeag, S.; Reynolds, N.; Bargmann, C. J.; Bullen, W.; Murphy, F. C.; Al-Athbah, H.; Brauhart, C.; Potma, W.; Meffre, S.; McKnight, S.

    2015-12-01

    Ongoing exploration in the Red Sea Hills of NE Sudan has led to the identification of a large alteration-mineralization system within a relatively undeformed Neoproterozoic intrusive-extrusive succession centered on Jebel Ohier. The style of mineralization, presence of an extensive stockwork vein network within a zoned potassic-propylitic-argillic-advanced argillic-altered system, a mineralization assemblage comprising magnetite-pyrite-chalcopyrite-bornite (±gold, silver and tellurides), and the recurrence of fertile mafic to intermediate magmatism in a developing convergent plate setting all point to a porphyry copper-gold association, analogous to major porphyry Cu-Au-Mo deposits in Phanerozoic supra-subduction settings such as the SW Pacific. Preliminary U-Pb age dating yielded a maximum constraint of c. 730 Ma for the emplacement of the stockwork system into a significantly older (c. 800 Ma) volcanic edifice. The mineralization formed prior to regional deformation and accretion of the host terrane to a stable continental margin at by c. 700 Ma, thus ensuring preservation of the deposit. The Jebel Ohier deposit is interpreted as a relatively well-preserved, rare example of a Neoproterozoic porphyry Cu-Au system and the first porphyry Cu-Au deposit to be identified in the Arabian-Nubian Shield.

  19. Oceanic basins in prehistory of the evolution of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Khain, V. E.; Filatova, N. I.

    2010-06-01

    During geodynamic reconstruction of the Late Mezozoic-Cenozoic evolution of the Arctic Ocean, a problem arises: did this ocean originate as a legacy structure of ancient basins, or did it evolve independently? Solution of this problem requires finding indicators of older oceanic basins within the limits of the Arctic Region. The Arctic Region has structural-material complexes of several ancient oceans, namely, Mesoproterozoic, Late Neoproterozoic, Paleozoic (Caledonian and Hercynian), Middle Paleozoic-Late Jurassic, and those of the Arctic Ocean, including the Late Jurassic-Early Cretaceous Canadian, the Late Cretaceous-Paleocene Podvodnikov-Makarov, and the Cenozoic Eurasian basins. The appearances of all these oceans were determined by a complex of global geodynamical factors, which were principally changed in time, and, as a result of this, location and configuration of newly opened oceans, as well as ones of adjacent continents, which varied from stage to stage. By the end of the Paleozoic, fragments of the crust corresponding to Precambrian and Caledonian oceans were transported during plate-tectonic motions from southern and near equatorial latitudes to moderately high and arctic ones, and, finally, became parts of the Pangea II supercontinent. The Arctic Ocean that appeared after the Pangea II breakup (being a part of the Atlantic Ocean) has no direct either genetic or spatial relation with more ancient oceans.

  20. Evaluation of the Re-Os Geochronometer in Organic-rich Mudrocks as a Method for Constraining the Absolute Ages of Neoproterozoic Glaciogenic Deposits

    NASA Astrophysics Data System (ADS)

    Kendall, B. S.; Creaser, R. A.; Ross, G. M.

    2002-12-01

    Absolute-age constraints on the Neoproterozoic glaciations are generally poor due to a paucity of suitable plutonic and volcanic igneous rocks that are temporally and spatially related to Neoproterozoic glaciogenic deposits and are amenable to radiometric dating methods. In this study, the Re-Os isotope systematics of dark gray, sulfidic slates from the Old Fort Point Formation (OFP) of the Windermere Supergroup (near Jasper, Alberta) were examined to test the ability of the Re-Os geochronometer to provide an absolute age constraint for a Neoproterozoic glaciogenic deposit. The OFP has been interpreted as the deep water expression of post-glacial sea level rise and therefore is comparable stratigraphically to cap carbonates that immediately overlie glaciogenic deposits worldwide. Despite the relatively low Re (6-16 ppb) and Os (0.07-0.14 ppb) concentrations and total organic contents (~ 0.5% TOC) of the slates compared to other organic-rich mudrocks used in previous Re-Os isotope studies, precise well-fitted Re-Os isochrons have been obtained with two different dissolution methods. An age of 620.8 +/- 8.1 Ma (MSWD = 0.9; initial 187Os/188Os = 0.68 +/- 0.06) is obtained using conventional aqua regia dissolution. Using a method designed to selectively dissolve organic matter alone, an age of 609.0 +/- 8.3 Ma (MSWD = 1.5; initial 187Os/188Os = 0.62 +/- 0.05) is obtained. These absolute age results are in accord with existing age constraints (e.g., stratigraphically younger Hamill Group with a U-Pb zircon age of 569 Ma). The well-defined Re-Os systematics of the OFP slates demonstrates for the first time that the Re-Os system is not disturbed in organic-rich sediments during lower greenschist (-chlorite) grade metamorphic conditions. The whole-rock analysis of each individual sample yields consistently higher initial 187Os/188Os isotope ratios than the corresponding organic matter analysis and suggests that a significant radiogenic detrital Os component is present

  1. Petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli-Erguna area of Inner Mongolia, China: Geochronological, geochemical and Hf isotopic evidence

    NASA Astrophysics Data System (ADS)

    Gou, Jun; Sun, De-You; Ren, Yun-Sheng; Liu, Yong-Jiang; Zhang, Shu-Yi; Fu, Chang-Liang; Wang, Tian-Hao; Wu, Peng-Fei; Liu, Xiao-Ming

    2013-05-01

    U-Pb dating and Hf isotopic analyses of zircons from various granitoids, combined with major and trace element analyses, were undertaken to determine the petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli-Erguna area of Inner Mongolia, China. The Neoproterozoic granitoids are mainly biotite monzogranites with zircon U-Pb ages of 894 ± 13 Ma and 880 ± 10 Ma, and they are characterised by enrichment in large ion lithophile elements (LILEs; e.g., Rb, Ba, K) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Ti) and heavy rare earth elements (HREEs). The Late Devonian granitoids are dominantly syenogranites and mylonitised syenogranites with zircon U-Pb ages of 360 ± 4 Ma, and they form a bimodal magmatic association with subordinate gabbroic rocks of the same age. The Late Devonian syenogranites have A-type characteristics including high total alkalis, Zr, Nb, Ce and Y contents, and high FeOt/MgO, Ga/Al and Rb/Sr ratios. The Carboniferous granitoids are mainly tonalites, granodiorites and monzogranites with U-Pb ages varying from 319 to 306 Ma, and they show very strong adakitic characteristics such as high La/Yb and Sr/Y ratios but low Y and Yb contents. The Late Permian granitoids are dominated by monzogranites and syenogranites with zircon U-Pb ages ranging between 257 and 251 Ma. Isotopically, the ɛHf(t) values of the Neoproterozoic granitoids range from +4.3 to +8.3, and the two-stage model ages (TDM2) from 1.2 to 1.5 Ga. The Late Devonian granitoids are less radiogenic [ɛHf(t) from +12.0 to +12.8 and TDM2 from 545 to 598 Ma] than the Carboniferous [ɛHf(t) from +6.8 to +9.5 and TDM2 from 722 to 894 Ma] and Late Permian granitoids [ɛHf(t) from +6.1 to +9.4 and TDM2 in the range of 680-895 Ma]. These data indicate (1) the Neoproterozoic granitoids may have been generated by melting of a juvenile crust extracted from the mantle during the Mesoproterozoic

  2. Newly discovered Cryogenenian Diamicties and Cap-carbonate in the Neoproterozoic successions from the Tarim Craton, NW China

    NASA Astrophysics Data System (ADS)

    Wen, B.; Evans, D. A.; Li, Y.; Wang, Z.

    2014-12-01

    Neoproterozoic cap carbonates associated with glacial deposits have been the unique lithofacies for establishing regional or interregional correlations and understanding the environmental conditions in the postglacial oceans. Here, we report a newly discovered Cryogenian tillite (in Aksu section), and a diamictite and cap-carbonate couplet (DCC) (in Wushi section) from the northwestern margin of Tarim Craton, NW China. The Aksu tillite is represented by reddish conglomerates, comprising angular to subrounded, poorly sorted clasts with diameters of 5-30 cm. Notably, the glaciogenic features, such as striations on clasts can be observed. The DCC member in Wushi section, sits atop an angular unconformity, and represents the end-Cryogenian strata according to the regional sequence stratigraphy (at the base of the Sugetbrak Fm, redbeds with interbedded 615-Ma mafic magmatism). The upper cap-carbonate of the DCC member consists of a < 2m-thick pink dolomite, which directly and conformably overlies the lower red diamictite. Given the striking similarity in both sedimentological characteristics and stratigraphic positions, the Aksu tillites and the Wushi DCC member may represent the same glaciation, most likely the Marinoan glaciation. To further test the correlation, high-resolution C-O isotopes and representative samples for geochemistry (Strontium isotope and trace element ratios) from the cap-dolomite are measured. As for the Sr isotope analyses, an incremental leaching technique was employed to extract the information about the chemical compositions of post-glacial ocean water. The δ13CPDB results consistently show moderate negative values of ca. -2.5‰. The minimum 87Sr/86Sr ratio from the leachates of each sample defines the contemporaneous seawater value, with the Mg/Ca ratio close to 1 (0.8). The 87Sr/86Sr ratios of all representative samples vary from 0.70680 to 0.70855. All the chemostratigraphic and cap-dolomite characteristics may suggest that our newly

  3. Deep inside a neoproterozoic intra-oceanic arc: growth, differentiation and exhumation of the Amalaoulaou complex (Gourma, Mali)

    NASA Astrophysics Data System (ADS)

    Berger, Julien; Caby, Renaud; Liégeois, Jean-Paul; Mercier, Jean-Claude C.; Demaiffe, Daniel

    2011-10-01

    We show here that the Amalaoulaou complex, in the Pan-African belt of West Africa (Gourma, Mali), corresponds to the lower and middle sections of a Neoproterozoic intra-oceanic arc. This complex records a 90-130-Ma-long evolution of magmatic inputs and differentiation above a subducting oceanic slab. Early c. 793 Ma-old metagabbros crystallised at lower crustal or uppermost mantle depths (25-30 km) and have geochemical characteristic of high-alumina basalts extracted from a depleted mantle source slightly enriched by slab-derived sedimentary components ((La/Sm)N < 1; ɛNd: +5.4-6.2; 87Sr/86Sr: 0.7027-0.7029). In response to crustal thickening, these mafic rocks were recrystallised into garnet-granulites (850-1,000°C; 10-12 kbar) and subject to local dehydration-melting reactions, forming trondhjemititic leucosomes with garnet-clinopyroxene-rutile residues. Slightly after the granulitic event, the arc root was subject to strong HT shearing during partial exhumation (detachment faults/rifting or thrusting), coeval with the emplacement of spinel- and garnet-pyroxenite dykes crystallised from a high-Mg andesitic parental magma. Quartz and hornblende-gabbros (700-660 Ma) with composition typical of hydrous volcanic rocks from mature arcs ((La/Sm)N: 0.9-1.8; ɛNd: +4.6 to +5.2; 87Sr/86Sr: 0.7028-0.7031) were subsequently emplaced at mid-arc crust levels (~15 km). Trace element and isotopic data indicate that magmas tapped a depleted mantle source significantly more enriched in oceanic sedimentary components (0.2%). Exhumation occurred either in two stages (700-660 and 623 Ma) or in one stage (623 Ma) with a final exhumation of the arc root along cold P-T path (550°C, 6-9 kbar; epidote-amphibolite and greenschist facies conditions) during the main Pan-African collision event (620-580 Ma). The composition of magmas forming the Cryogenian Amalaoulaou arc and the processes leading to intra-arc differentiation are strikingly comparable to those observed in the deep section

  4. Mg Isotope variations of Marinoan Cap Carbonates: implications for the chemical evolution of Neoproterozoic Ocean after snowball earth

    NASA Astrophysics Data System (ADS)

    Liu, C.; Macdonald, F. A.; Raub, T.; Wang, Z.; Evans, D. A.

    2012-12-01

    We report Mg isotope profiles of two cap-carbonates: Nuccaleena formation from south Australia (mostly dolostones) and Tsagaan Oloom Formation from southwest Mongolia (including dolostones, aragonite crystal fans, and lime-mudstones). These data provide additional constraints on the chemical evolution of Neoproterozoic Oceans after the Marinoan deglaciation. An incremental leaching technique using ammonium acetate and various concentrations of acetic acid and hydrochloric acid was applied to separate metals in various forms from cap-carbonates (including surface adsorbed phases, calcite, dolomite and clay minerals). The leachates were then passed through chromatographic columns to extract pure Mg and Sr, which were then analyzed for their isotopic compositions by MC-ICP-MS (Neptune) at Yale University. Elemental ratios (Mg/Ca and Sr/Ca) in each leaching steps were also measured. Our results show that small variations of δ26MgDSM3 with leaching steps were observed in most dolostone samples when secondary calcite is absent. In contrast, large Mg isotope variations (up to 1.5 per mil) were shown in the leaching steps of limestone and crystal fans. The primary δ26MgDSM3 value of each sample was chosen from the leachate that has the lowest 87Sr/86Sr ratios. The δ26MgDSM3 value of Nuccaleena dolostone increases from -2.2‰ at the basal part of the section to -1.7‰ in the middle, and then turns back to -2.0‰ on the top, with a positive correlation between 26Mg/24Mg and 87Sr/86Sr ratios, implying that the high δ26MgDSM3 values may be caused by alteration or inherit from continental-derived fluids. In contrast, small δ26MgDSM3 variations in Tsagaan Oloom dolostones were exhibited in different leaching steps or cross the section (~-1.7‰), with high 87Sr/86Sr ratios (~0.7090), resembling cap dolostones from middle part of Nuccaleena dolostone, implying that they are formed in a similar environment. However, the δ26MgDSM3 value of upper lime-mudstones and crystal

  5. Late Neoproterozoic overprinting of the cassiterite and columbite-tantalite bearing pegmatites of the Gatumba area, Rwanda (Central Africa)

    NASA Astrophysics Data System (ADS)

    Dewaele, Stijn; Henjes-Kunst, Friedhelm; Melcher, Frank; Sitnikova, Maria; Burgess, Ray; Gerdes, Axel; Fernandez, Max Alonso; De Clercq, Friso; Muchez, Philippe; Lehmann, Bernd

    2011-08-01

    The Mesoproterozoic Kibara belt in Central Africa has recently been redefined and subdivided into the Karagwe-Ankole belt (KAB) and the Kibara belt (KIB), separated by Palaeoproterozoic (Rusizian) terranes. The KIB and KAB are characterised by the presence of numerous rare metal mineralised (Nb-Ta-Sn) pegmatites and Sn-W mineralised quartz veins that are related to the youngest granite generation, i.e. the G4-granites in Rwanda, which formed at 986 ± 10 Ma. The pegmatites of the Gatumba area (western Rwanda) have historically been mined for their columbite-tantalite and cassiterite mineralisation, but contain also beryl, apatite, spodumene, amblygonite, and rare phosphates. Columbite-tantalite formed during the crystallisation of the pegmatites, followed by intense alkali metasomatism, i.e. widespread growth of albite and white mica. The major part of the cassiterite mineralisation is, however, concentrated in zones associated with intense phyllic alteration. U-Pb ages of columbite-tantalite samples vary between ˜975 Ma and ˜930 Ma. The oldest ages (975 + 8.2/-8.3 Ma and 966 + 8.7/-8.6 Ma) overlap with previous reported Rb-Sr ages of the emplacement of the pegmatites (˜965 Ma) and are interpreted to reflect the crystallisation of the Nb-Ta mineralisation. The youngest ages (951 ± 15 Ma to 936 ± 14 Ma) are apparently related to variable degrees of resetting by (metasomatic) post-crystallisation processes. The resetting could either be due to recrystallisation of early Nb-Ta minerals or due to the disturbance of the U-Pb isotopic signature of the Nb-Ta minerals. The 40Ar- 39Ar spectra of muscovite samples associated with different steps in the paragenesis of the pegmatites show a spread of apparent ages between ˜940 Ma and ˜560 Ma that reflect Late Neoproterozoic tectonothermal events. One plateau age of 592.2 ± 0.8 Ma is interpreted to reflect far-field effects of the East African orogeny on the Karagwe-Ankole Belt.

  6. New aspects of deformed cross-strata in fluvial sandstones: Examples from Neoproterozoic formations in northern Norway

    NASA Astrophysics Data System (ADS)

    Røe, Signe-Line; Hermansen, Marita

    2006-05-01

    Extensive (20-200 m long) exposures of tabular cross-sets in Neoproterozoic fluvial sandstone in Northern Norway demonstrate that deformed cross-strata, in the form of recumbently folded cross-strata with associated massive sand, are localized features passing in both up- and down-current direction into undeformed, concave-upward or sigmoidal cross-strata. The deformation occurs in down-current inclined, tangential wedge-shaped zones beneath reactivation surfaces, and less commonly as flat-topped lenticular zones. The localized nature of the sediment deformation is attributed to local liquefaction below the top of the bed in the case of the flat-topped lenses and at the dune front in the case of the more common tangential wedges. The position of the flat-topped lenses suggests deformation by the shear stress of high-velocity, suspension-laden currents. Although liquefaction of the dune front implies the action of gravity forces, it is argued that the fluvial currents were the main driving force at the instant of bed liquefaction. Post-folding gravitational shearing probably enhanced the deformation within the upper part of the wedges, with their long, flat-lying toeset resulting from redeposition of downslope-moving liquefied sand. The down-current alternation of deformed tangential wedges and undeformed cross-strata suggests that the mechanism that triggered the liquefaction of the dune lee side was related to the fluvial system itself and hence was of autokinetic origin. The tabular cross-sets have previously been interpreted as a product of the dune upper-stage plane-bed flow regime. In this flow context, it can be speculated that the liquefaction and deformation occurred when the flow conditions approached the plane-bed phase, probably inducing a highly differential turbulent pattern and pressure fluctuations sufficient to liquefy the fine/medium sand. The small flat-topped deformation lenses also suggest liquefaction by cyclic loading, whereas the solitary

  7. The lithospheric architecture of a Neoproterozoic collision zone in Southern Africa inferred from deep probing magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Khoza, D. T.; Jones, A. G.; Muller, M. R.; Evans, R. L.; Miensopust, M. P.; Hamilton, M.; Garcia, X. A.; Cole, P.; Ngwisanyi, T.; Hutchins, D.; Fourie, S.; Jelsma, H.; Pettit, W.; Aravanis, T.; Webb, S. J.; Wasborg, J.

    2009-12-01

    Cratonic margins have played a major role in shaping the modern Southern African tectonic landscape, and central to our knowledge is information about the lithospheric-scale structures and geometries using geophysical methods. Understanding the evolution of the younger orogenic belts around Archean cratons using electrical resistivity data is one of the primary objectives of the Southern African Magnetotelluric Experiment (SAMTEX); the largest ever land-based magnetotelluric (MT) project. MT data were acquired along four profiles crossing the enigmatic Rehoboth Terrane, the Neo-Proterozoic Ghanzi-Chobe/Damara belts (collectively termed the Damara Mobile Belt, DMB) and the southern Angola craton. The extended Groom and Bailey distortion decomposition technique was applied to the MT data and analyses show significant depth and along-profile variations in geo-electric strike and dimensionality on all transects crossing these three tectonic units (i.e. Rehoboth Terrane, Angola craton and the DMB). Geo-electric strikes are generally parallel to the north-east trending tectonic fabric, as inferred from the magnetic data, but the significant strike variations with depth are expressions of heterogeneity in lithospheric structure. Electrical resistivity models derived from the data provide the first pseudo three-dimensional tectonic structure of the Damara orogen and adjacent terranes. Regional-scale resistivity models constructed from two-dimensional inversions of the MT data indicate significant variations in lithospheric resistivity structure along and across strike from the younger orogen to the older adjacent cratons. The Damara belt lithosphere, although generally more conductive and significantly thinner than adjacent Angola craton and Rehoboth terrane, exhibits upper resistive upper crustal features tentatively interpreted to be caused by igneous intrusions emplaced during Pan-African magmatic event. Upper crustal listric faults are imaged as conductive features and

  8. Geology of East Egypt greenstone field in Neoproterozoic isoand arc: Reconstruction of Iron formation sedimentary environment.

    NASA Astrophysics Data System (ADS)

    Kiyokawa, S.; Suzuki, T.

    2015-12-01

    Geology of East Egypt greenstone-granit belt which is northern part of Nubia shield was identified neoproterozoic island arc amalgamated sections. There are several iron formation within these greenstone belt. Age data shows this iron formation may be overlaped during 700 Ma Snowball period, how ever, there is no detail report of well preserved ice related evidences. We now started detail field work for identified tectonic reconstruction, original stratigraphy around Iron formation and sedimentary environment during the iron formation sedimentation area. East Egyptian shield was divided three geology, Proterozoic greenstone complex, 700-600 Granitic domes and cover sequence (Hammamet Group). We focus three area to identified sedimentary environment of iron sedimentation. Along the north-south trend of Wadi EL Dabban area are, we named Wadi branch as West site is RW-0 ~ 12, East site is RE-0 ~ 12 from north to south. Northern area is structurally moderate, southern portion is north dipping. Southern portion was intruded by granite and several place contain granitic dikes. Northeast to eastern area are identified younger sedimentary sequence (Hammamat Group) which is unconformablly overlay on the other iron formation bearing greenstone belt. Structurally these area is divided four units. Wadi was divided by right-lateral strike-ship fault. The displacement are more than 3 km. Also north dipping faults are identified.East-West trend fault are divided two units. It is divided NE, SE, NW and NS units.SW unit is most well preserved thick sequence of the Iron formation. SW unit is well preserved iron formation sequence within thick volcaniclastics. This unit mostly north dipping around 40-60 degree. Structural repetition in not well understand. Reconstract stratigraphy in this unit is at least 4000m in thickness. 5 member is identified in this sequence. Several thin iron formations are observed with in pillow lava and volcaniclastic sequence. These very thick

  9. Late Neoproterozoic metamorphic assemblages along the Pan-African Hamisana Shear Zone, southeastern Egypt: Metamorphism, geochemistry and petrogenesis

    NASA Astrophysics Data System (ADS)

    Ali-Bik, Mohamed W.; Sadek, Mohamed F.; Ghabrial, Doris Sadek

    2014-11-01

    A variety of Late Neoproterozoic gneisses and amphibolites are distributed along the N-S trending Hamisana Shear Zone (HSZ), in southeastern Egypt. The HSZ originated after the accretion of the Arabian-Nubian Shield (ANS) and covers an area of about 1500 km2 in southeastern Egypt and northeastern Sudan. The architecture of the northern part of the HSZ is best explained as a tectono-stratigraphic column, in which allochthonous ophiolitic mélange was thrusted onto metamorphosed island-arc assemblages (gneisses and amphibolites). The latter rock units were generally subjected to two successive phases of amphibolite facies metamorphism, followed by a thermal phase and retrograde overprint. The early penetrative, low- to medium-pressure metamorphism (M1) was synchronous with D1-gneissosity and N-S trending lineation, demarcating the high strain HSZ. The mineral assemblages formed during the M1 phase include quartz + andesine + hornblende (I) + biotite (I) in hornblende-biotite gneiss, quartz + andesine + pargasitic hornblende (I) + ferroan pargasitic hornblende (I) + edenitic hornblende (I) in hornblende-schist, quartz + plagioclase + biotite + muscovite in psammopelitic gneiss, and diopside + tremolite + calcite + sphene ± garnet in calc-silicates, being characteristic for amphibolite facies with metamorphic conditions of 600 ± 50 °C and 5-6.5 kbar. The second metamorphic phase (M2) is related to the crystallization of biotite and/or hornblende in S2 foliation demarcating the NE-SW trending dextral shear deformation (D2). The calculated temperature for this M2 phase is about 592 °C. Subsequent thermal events are documented by growth of spinel and scapolite in calc-silicate rocks and of cordierite in psammopelitic gneiss in response to uplift, decomposition and heat provided by the nearby late-formed igneous intrusions. Finally, the rocks reached a temperature of about 530 °C during the cooling retrogressive stage. Based on geological, petrological and geochemical

  10. Reserves in western basins

    SciTech Connect

    Caldwell, R.H.; Cotton, B.W.

    1992-06-01

    This project requires generation of producible tight gas sand reserve estimates for three western basins. The requirement is to perform such reserve estimates using industry accepted practices so that results will have high credibility and acceptance by the oil and gas industry. The ultimate goal of the project is to encourage development of the tight gas formation by industry through reduction of the technical and economic risks of locating, drilling and completing commercial gas wells. The three geological basins selected for study are the Greater Green River Basin, Uinta Basin and Piceance Basin, located in the Colorado, Utah and Wyoming Rocky Mountain region.

  11. Reserves in western basins

    SciTech Connect

    Caldwell, R.H.; Cotton, B.W.

    1992-01-01

    This project requires generation of producible tight gas sand reserve estimates for three western basins. The requirement is to perform such reserve estimates using industry accepted practices so that results will have high credibility and acceptance by the oil and gas industry. The ultimate goal of the project is to encourage development of the tight gas formation by industry through reduction of the technical and economic risks of locating, drilling and completing commercial gas wells. The three geological basins selected for study are the Greater Green River Basin, Uinta Basin and Piceance Basin, located in the Colorado, Utah and Wyoming Rocky Mountain region.

  12. Equilibrium and Disequilibrium of River Basins: Effects on Stream Captures in Serra do Mar and Serra da Mantiqueira, Brazil

    NASA Astrophysics Data System (ADS)

    DA Silva, L. M.

    2015-12-01

    Landscapes are mainly driven by river processes that control the dynamic reorganization of networks. Discovering and identifying whether river basins are in geometric equilibrium or disequilibrium requires an analysis of water divides, channels that shift laterally or expand upstream and river captures. Issues specifically discussed include the variation of drainage area change and erosion rates of the basins. In southeastern Brazil there are two main escarpments with extensive geomorphic surfaces: Serra do Mar and Serra da Mantiqueira Mountains. These landscapes are constituted of Neoproterozoic and early Paleozoic rocks, presenting steep escarpments with low-elevation coastal plains and higher elevation interior plateaus. To identify whether river basins and river profiles are in equilibrium or disequilibrium in Serra do Mar and Serra da Mantiqueira Mountains, we used the proxy (χ), evaluating the effect of drainage area change and erosion rates. We selected basins that drain both sides of these two main escarpments (oceanic and continental sides) and have denudation rates derived from pre-existing cosmogenic isotopes data (Rio de Janeiro, Paraná and Minas Gerais). Despite being an ancient and tectonically stable landscape, part of the coastal plain of Serra do Mar Mountain in Rio de Janeiro and Paraná is in geometric disequilibrium, with water divides moving in the direction of higher χ values. To achieve equilibrium, some basins located in the continental side are retracting and disappearing, losing area to the coastal basins. On the contrary, there are some adjacent sub-basins that are close to equilibrium, without strong contrasts in χ values. The same pattern was observed in Serra da Mantiqueira (Minas Gerais state), with stream captures and river network reorganization in its main rivers. The initial results suggest a strong contrast between erosion rates in the continental and the oceanic portions of the escarpments.

  13. Divergent/passive margin basins

    SciTech Connect

    Edwards, J.D. ); Santogrossi, P.A. )

    1989-01-01

    This book discusses the detailed geology of the four divergent margin basins and establishes a set of analog scenarios which can be used for future petroleum exploration. The divergent margin basins are the Campos basin of Brazil, the Gabon basin, the Niger delta, and the basins of the northwest shelf of Australia. These four petroleum basins present a wide range of stratigraphic sequences and structural styles that represent the diverse evolution of this large and important class of world petroleum basins.

  14. A basin redox transect at the dawn of animal life

    NASA Astrophysics Data System (ADS)

    Sperling, Erik A.; Halverson, Galen P.; Knoll, Andrew H.; Macdonald, Francis A.; Johnston, David T.

    2013-06-01

    Multiple eukaryotic clades make their first appearance in the fossil record between ~810 and 715 Ma. Molecular clock studies suggest that the origin of animal multicellularity may have been part of this broader eukaryotic radiation. Animals require oxygen to fuel their metabolism, and low oxygen levels have been hypothesized to account for the temporal lag between metazoan origins and the Cambrian radiation of large, ecologically diverse animals. Here, paleoredox conditions were investigated in the Fifteenmile Group, Ogilvie Mountains, Yukon, Canada, which hosts an 811 Ma ash horizon and spans the temporal window that captures the inferred origin and early evolution of animals. Iron-based redox proxies, redox-sensitive trace elements, organic carbon percentages and pyrite sulfur isotopes were analyzed in seven stratigraphic sections along two parallel basin transects. These data suggest that for this basin, oxygenated shelf waters overlay generally anoxic deeper waters. The anoxic water column was dominantly ferruginous, but brief periods of euxinia likely occurred. These oscillations coincide with changes in total organic carbon, suggesting euxinia was primarily driven by increased organic carbon loading. Overall, these data are consistent with proposed quantitative constraints on Proterozoic atmospheric oxygen being greater than 1% of modern levels, but less than present levels. Comparing these oxygen levels against the likely oxygen requirements of the earliest animals, both theoretical considerations and the ecology of modern oxygen-deficient settings suggest that the inferred oxygen levels in the mixed layer would not have been prohibitive to the presence of sponges, eumetazoans or bilaterians. Thus the evolution of the earliest animals was probably not limited by the low absolute oxygen levels that may have characterized Neoproterozoic oceans, although these inferred levels would constrain animals to very small sizes and low metabolic rates.

  15. Neoproterozoic diamictite-bearing sedimentary rocks in the northern Yili Block and their constraints on the Precambrian evolution of microcontinents in the Western Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    He, Jingwen; Zhu, Wenbin; Zheng, Bihai; Wu, Hailin; Cui, Xiang; Lu, Yuanzhi

    2015-12-01

    The origin and tectonic setting of Precambrian sequences in the Central Asian Orogenic Belt (CAOB) have been debated due to a lack of high resolution geochronological data. Answering this question is essential for the understanding of the tectonic framework and Precambrian evolution of the blocks within the CAOB. Here we reported LA-ICP-MS detrital zircon U-Pb ages and in-situ Hf isotopic data for Neoproterozoic sedimentary cover in the northern Yili Block, an important component of the CAOB, in order to provide information on possible provenance and regional tectonic evolution. A total of 271 concordant U-Pb zircon ages from Neoproterozoic sedimentary cover in the northern Yili Block define three major age populations of 1900-1400 Ma, 1300-1150 Ma and 700-580 Ma, which are quite different from cratons and microcontinents involved in the CAOB. Although it is not completely consistent with the local basement ages, an autochthonous provenance interpretation is more suitable. Some zircon grains show significant old Hf model ages (TDMC; 3.9-2.4 Ga) and reveal continental crust as old as Paleoarchean probably existed. Continuous Mesoproterozoic zircon age populations exhibit large variations in the εHf(t) ratios, suggesting the long-time involvement of both reworked ancient crust and juvenile material. Similar Mesoproterozoic evolution pattern is identified in many continental terranes involved in the CAOB that surround the Tarim Craton. Based on our analysis and published research, we postulate that the northern Yili Block, together with Chinese Central Tianshan, Kyrgyz North Tianshan and some other microcontinents surrounding the Tarim Craton, once constituted the continental margin of the Tarim Craton in the Mesoproterozoic, formed by long-lived accretionary processes. Most of the late Neoproterozoic zircons exhibit significant positive εHf(t) ratios, suggesting the addition of juvenile crust. It is consistent with the tectonic event related to the East Africa

  16. Mid-Paleozoic arc granitoids in SW Japan with Neoproterozoic xenocrysts from South China: New zircon U-Pb ages by LA-ICP-MS

    NASA Astrophysics Data System (ADS)

    Aoki, Kazumasa; Isozaki, Yukio; Yamamoto, Atsushi; Sakata, Shuhei; Hirata, Takafumi

    2015-01-01

    The Kurosegawa belt in SW Japan preserves fragments of Early-Middle Paleozoic granitoids traditionally called the Mitaki igneous rocks and previously dated ca. 470-435 Ma by several isotope analyses such as Rb-Sr, K-Ar and U-Pb, together with high-grade metamorphic rocks and Silurian strata, in a narrow belt. However, the timing of the oldest arc-related plutonism in Japan is constrained by laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb ages of zircon from Mitaki granitoids in 3 areas in SW Japan; i.e. Kyushu, Shikoku, and Kii Peninsula. Weighted mean U-Pb ages of these zircons are 431.8 ± 3.9 for a granodiorite from the Mt. Mitaki area in Shikoku, 444.1 ± 5.8 Ma for a granodiorite from Kuraoka area in central Kyushu, and 444.5 ± 7.6 Ma for a quartzdiorite from the Nabaenohana area in western Kii peninsula, respectively. These ages confirm that the Mitaki igneous rocks have ca. 445-435 Ma (late Ordovician to mid-Silurian) ages. They are some of the oldest subduction-related plutonic rocks in SW Japan. Particularly noteworthy is a "tonalite" from the Nabaenohana area, which has a unique spectrum of zircon U-Pb ages with distinct 3 clusters; ca. 700-500 Ma (Neoproterozoic-Cambrian), ca. 1350-830 Ma (Meo-Neoproterozoic), and ca. 3230-1560 Ma (Paleoarchean-Mesoproterozoic). Of the 44 dated zircon grains, the youngest (possibly xenocrystic) grains are ca. 500 Ma. Older zircon grains with ages >500 Ma range up to 3230 Ma and are interpreted as inherited xenocrysts in the "tonalite". The Mitaki igneous rocks are interpreted to have been derived by melting of post-500 Ma terrigenous sedimentary rocks that yielded a unique tonalitic S-type granitoid magma. From the presence of abundant 1350-700 Ma (Meso- to Neoproterozoic) zircon grains in the "tonalite" we conclude that during the Early Paleozoic, proto-Japan was located close to the Cathaysian margin of South China.

  17. Arc magmatism in the Delhi Fold Belt: SHRIMP U-Pb zircon ages of granitoids and implications for Neoproterozoic convergent margin tectonics in NW India

    NASA Astrophysics Data System (ADS)

    Dharma Rao, C. V.; Santosh, M.; Kim, Sung Won; Li, Shengrong

    2013-12-01

    The northwestern region of Peninsular India preserves important records of Precambrian plate tectonics and the role of Indian continent within Proterozoic supercontinents. In this study, we report precise SHRIMP zircon U-Pb ages from granitoids from the Sirohi terrane located along the western fringe of the Delhi Fold Belt in Rajasthan, NW India. The data reveal a range of Neoproterozoic ages from plagiogranite of Peshua, foliated granite of Devala, and porphyritic granite of Sai with zircon crystallization from magmas at 1015 ± 4.4 Ma, 966.5 ± 3.5 and 808 ± 3.1 respectively. The plagiogranite shows high SiO2, Na2O and extremely low K2O, Rb, Ba, comparable with typical oceanic plagiogranites. These rocks possess low LREE and HREE concentrations and a relatively flat LREE-HREE slope, a well-developed negative Eu-anomaly and conspicuous Nb and Ti anomalies. Compared to the plagiogranite, the foliated Devala granite shows higher SiO2 and moderate Na2O, together with high K2O and comparatively higher Rb, Ba, Sr and REE, with steep REE profiles and a weak positive Eu anomaly. In contrast to the plagiogranite and foliated granite, the porphrytic Sai granite has comparatively lower SiO2 moderately higher Na2O, extremely high Y, Zr, Nb and elevated REE. The geochemical features of the granitoids [HFSE depletion and LILE enrichment, Nb- and Ta-negative anomalies], and their plots in the fields of Volcanic Arc Granites and those from active continental margins in tectonic discrimination diagrams suggest widespread Neoproterozoic arc magmatism with changing magma chemistry in a protracted subduction realm. Our results offer important insights into a long-lived active continental margin in NW India during early and mid Neoproterozoic, consistent with recent similar observations on Cryogenian magmatic arcs widely distributed along the margins of the East African Orogen, and challenge some of the alternate models which link the magmatism to extensional tectonics associated

  18. Inversion of calcite twin data, paleostress reconstruction and multiphase weak deformation in cratonic interior - Evidence from the Proterozoic Cuddapah basin, India

    NASA Astrophysics Data System (ADS)

    Tripathy, Vikash; Saha, Dilip

    2015-08-01

    Paleostress orientations from mechanically twinned calcite in carbonate rocks and veins in the neighborhood of large faults were investigated to comment on the nature of weak upper crustal stresses affecting sedimentary successions within the Proterozoic Cuddapah basin, India. Application of Turner's P-B-T method and Spang's Numerical dynamic analysis on Cuddapah samples provided paleostress orientations comparable to those derived from fault-slip inversion. Results from the neighborhood of E-W faults cutting through the Paleoproterozoic Papaghni and Chitravati groups and the Neoproterozoic Kurnool Group in the western Cuddapah basin, reveal existence of multiple deformation events - (1) NE-SW σ3 in strike-slip to extensional regime along with an additional event having NW-SE σ3, for lower Cuddapah samples; (2) compressional/transpressional event with ESE-WNW or NNE-SSW σ1 mainly from younger Kurnool samples. Integrating results from calcite twin data inversion, fault-slip analysis and regional geology we propose that late Mesoproterozoic crustal extension led to initial opening of the Kurnool sub-basin, subsequently influenced by weak compressional deformation. The dynamic analysis of calcite twins thus constrains the stress regimes influencing basin initiation in the southern Indian cratonic interior and subsequent basin inversion in relation to craton margin mobile belts and plausible global tectonic events in the Proterozoic.

  19. Paleomagnetic and Geochronologic Investigation of the Dzabkhan Microcontinent during the Neoproterozoic and Implications for the Assembly of Gondwana

    NASA Astrophysics Data System (ADS)

    Yff, J. A.; Levishova, N.; Badarch, G.; Meert, J. G.

    2006-12-01

    A paleomagnetic and geochronologic investigation was undertaken on the Dzabkhan volcanics in the Altay region of southwestern Mongolia. Our goal is to define the paleolocation of the Dzabkhan microcontinent during the Neoproterozoic for the higher purpose of addressing the puzzling nature of pre-Phanerozoic glaciations and the tectonic evolution of the Ural-Mongol belt. A total of 184 samples (24 sites) were analyzed from a bimodal suite of volcanic rocks. Alternating field treatments up to 130 mT removed 90% of the natural remanent magnetization (NRM). Thermal demagnetization was applied up to temperatures of 565°C for the mafic samples and up to 680° C for some of the more felsic samples. Based on a preliminary analysis of the data, we identify 3 components of remanent magnetization in the Dzabkhan complex. Present day overprints unblocked at a temperature range of 100-250°C. Other components unblocked at higher temperature ranges of 530-550°C. The first component yielded a direction (in-situ) of 246.1/ -69.5, (k=86, a95=5). This component had a negative fold test. The second component had a shallower NW direction with in-situ mean 282.9/ -42.9 (k=109, a95=5.8). The sites were from a monocline and the tilt-corrected direction is 319/-75.4. The third component (also monoclinally dipping) yielded and in-situ mean of 306.4/24.7, (k=184, a95=5.7) and tilt corrected values 289.9/-59. All three components are high-temperature/high coercivity but a mean of the three components (either in-situ or tilt- corrected) is poorly grouped. A fold test conducted for components 1 and 3 is negative whereas a fold test for components 2 and 3 is positive above the 95% confidence interval. The overall mean for this tilt-corrected direction is 301.7/-69.1 (k=44.6, a95=6.6). This component is similar to, but statistically distinct from components observed in the overlying Tsagaan Oloom and Bayan Gol formations, but still may represent a remagnetization prior to folding

  20. Neoproterozoic tectonic evolution of the Jebel Saghro and Bou Azzer - El Graara inliers, eastern and central Anti-Atlas, Morocco

    USGS Publications Warehouse

    Walsh, Gregory J.; Aleinikoff, John N.; Harrison, Richard W.; Burton, William C.; Quick, James E.; Benziane, Foudad; Yazidi, Abdelaziz; Saadane, Abderrahim

    2012-01-01

    New mapping, geochemistry, and 17 U–Pb SHRIMP zircon ages from rocks of the Sirwa, Bou Azzer–El Graara, and Jebel Saghro inliers constrain the Neoproterozoic evolution of the eastern Anti-Atlas during Pan-African orogenesis. In the Sirwa inlier, Tonian quartzite from the pre Pan-African passive margin deposits of the Mimount Formation contains detrital zircon derived entirely from the West African Craton (WAC), with most grains yielding Eburnean Paleoproterozoic ages of about 2050 Ma. Cryogenian Pan-African orogenic activity (PA1) from about 760 to 660 Ma included northward-dipping subduction to produce a volcanic arc, followed by ophiolite obduction onto the WAC. In the Bou Azzer–El Graara inlier, calc-alkaline granodiorite and quartz diorite, dated at 650–646 Ma, are syn- to post-tectonic with respect to the second period of Pan-African orogenesis (PA2), arc-continent accretion, and related greenschist facies metamorphism. Slab break-off and lithospheric delimination may have provided the source for the supra-subduction calc-alkaline plutons. At about 646 Ma, quartz diorite intruded the Tiddiline formation placing an upper limit on molassic deposition. Widespread Ediacaran high-K calc-alkaline to shoshonitic plutonism and volcanism during the final stage of Pan-African orogenesis (PA3) occurred in a setting related to either modification of the margin of the WAC or formation of a continental volcanic arc above a short-lived southward-dipping subduction zone. In the Saghro inlier, eight plutonic rocks yield ages ranging from about 588 to 556 Ma. Sampled plutonic rocks previously considered to be Cryogenian yielded Ediacaran ages. Peraluminous rhyolitic volcanic rocks in the lower part of the Ouarzazate Supergroup, including ash-flow tuffs of the Oued Dar’a caldera, yield ages between about 574 and 571 Ma. The Oued Dar’a caldera developed in a pull-apart graben produced by a left-step in a northeast-trending, left-lateral strike-slip fault zone, and

  1. Juxtaposition of Neoproterozoic units along the Baruda - Tulu Dimtu shear-belt in the East African Orogen of western Ethiopia

    USGS Publications Warehouse

    Braathen, A.; Grenne, Tor; Selassie, M.G.; Worku, T.

    2001-01-01

    Amalgamation of East and West Gondwanaland during the Neoproterozoic East African Orogen is recorded by several shear-belts or 'suture zones', some of which are associated with ultramafic and mafic complexes that have been interpreted as ophiolite fragments. The Baruda shear-belt is a major structure of this type that belongs to the N-S trending Barka - Tulu Dimtu zone. The significance of this zone has been studied within a transect in western Ethiopia which covers a variety of metasedimentary and metavolcanic sequences, ultramafic rocks and synkinematic intrusive complexes. All rocks participated in the regional D1 event as reflected in a penetrative steep foliation in supracrustal rocks and marginal parts of the intrusions. Highly strained rocks contain a stretching lineation that plunge to the east. The several-km thick Baruda shear-belt, comprising mylonitic supracrustal and plutonic rocks including mafic-ultramafic mega-lenses, is the most prominent expression of this event. Shear-sense indicators demonstrate top-to-the-west shear. Subsequent D2 deformation is recorded in 2-300 m wide, N-S striking, subvertical shear-zones with subhorizontal stretching lineation relatable to sinistral transcurrent movements. Our data indicate that rock units on either side of the Baruda shear-belt are related, rather than being exotic to each other as implied in suture zone models, since there is no major lithologic or metamorphic difference, geochemical data on metavolcanic rocks and pre-tectonic intrusions suggest a paleotectonic link, and style and extent of deformation is similar across the shear-belt. A tentative model for the transect suggests an arc and back-arc setting which experienced later continental collision and tectonic shortening. The initial setting was that of a shallow marine platform characterised by carbonates and sandstones, which covered extensive areas prior to break-up of a pre-existing supercontinent. Continental convergence is first recorded in high

  2. Derivation of detrital rutile in the Yaoundé region from the Neoproterozoic Pan-African belt in southern Cameroon (Central Africa)

    NASA Astrophysics Data System (ADS)

    Stendal, Henrik; Toteu, Sadrack Félix; Frei, Robert; Penaye, Joseph; Njel, Urbain Olivier; Bassahak, Jean; Nni, Jean; Kankeu, Boniface; Ngako, Vincent; Hell, Joseph Victor

    2006-04-01

    Rutile, as an important component in alluvial or eluvial heavy mineral deposits, is known in southern Cameroon. These deposits are underlain by the Neoproterozoic low- to high-grade Yaoundé Group. Geochemical, thermometric, fluid inclusion and Pb isotopic studies of the rutile from alluvial and eluvial concentrates and from medium-grade micaschist from the nearby Yaoundé region permit the following conclusions: (1) alluvial and eluvial rutile of the Yaoundé region are derived from the degradation of metapelites, metamafic rocks and pegmatites of the nearby Yaoundé Group; (2) rutile in the Yaoundé Group formed during the Pan-African metamorphism, or was inherited as detrital rutile from a ˜900 Ma source. The study also shows that the rutile can be used to trace the history of the Pan-African belt north of the Congo craton.

  3. Geochronology, petrogenesis, and tectonic setting of Neoproterozoic and Late Paleozoic granitoids of the Manzhouli-Ergun area of Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Gou, J.; Sun, D.; Fu, C.; Ren, Y.; Liu, X.

    2012-12-01

    U-Pb dating and Hf isotopic analysis of zircons from various granitoids, combined with major and trace element analysis, was undertaken to determine the petrogenesis and geodynamics of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli-Ergun area of Inner Mongolia, China. Neoproterozoic granitoids are mainly composed of biotite monzogranite with zircon U-Pb ages of 880 ± 10 and 894 ± 13 Ma, and are characterized by enrichment in LILE and LREE relative to HFSE and HREE with negative Nb, Ta, P and Ti anomalies. Late Devonian granitoids are dominantly composed of syenitegranite and mylonitized syenitegranite with zircon U-Pb age of 360 ± 4 Ma, and show a bimodal magmatic association and A-type granitiod geochemical characteristics including high total alkalis, Zr, Nb, Ce and Y contents and high FeOt/MgO, Ga/Al and Rb/Sr ratios. Carboniferous granitoids consist principally of tonalite, granodiorite and monzogranite with U-Pb ages varying from 320 to 306 Ma, and show the strongest adakitic characteristics such as high La/Yb and Sr/Y ratios but low Y and Yb contents. Late Permian granitoids are dominated by granodiorite and monzogranite with zircon U-Pb ages ranging between 257 and 251 Ma and show low Sr and Yb content characteristic of Himalaya-type granitoid. Isotopically, the ɛHf(t) values of Neoproterozoic granitoids range from +2.30 to +4.14 and two-stage model ages (TDM2) vary from 1.5 to 1.6 Ga, Late Devonian granitoids display values less radiogenic [ɛHf(t) from +11.95 to +12.77 and TDM2 from 546 to 599 Ma] in comparison to Carboniferous granitoids [ɛHf(t) from +7.82 to +8.47 and TDM2 from 791 to 832 Ma] and Late Permian granitoids [ɛHf(t) from +6.70 to +7.35 and TDM2 in the range of 813-855 Ma]. These data indicate that Neoproterozoic granitoids may have generated in equilibrium with an amphibolitic (plagioclase + amphibole) residue at depths of 30-40 km and are most likely associated with the accretion of Ergun microcontinent block to the

  4. U-Pb zircon geochronology of the Paleoproterozoic Tagragra de Tata inlier and its Neoproterozoic cover, western Anti-Atlas, Morocco

    USGS Publications Warehouse

    Walsh, G.J.; Aleinikoff, J.N.; Benziane, F.; Yazidi, A.; Armstrong, T.R.

    2002-01-01

    New U-Pb zircon data obtained by sensitive high resolution ion microprobe (SHRIMP) from the Tagragra de Tata inlier in the western Anti-Atlas, Morocco establish Paleoproterozoic ages for the basement schists, granites, and metadolerites, and a Neoproterozoic age for an ignimbrite of the Ouarzazate Series in the cover sequence. The age of interbedded felsic metatuff in the metasedimentary and metavolcanic sequence of the basement schists is 2072 ?? 8 Ma. This date represents: (1) the first reliable age from the metasedimentary and metavolcanic sequence; (2) the oldest reliable age for the basement of the Anti-Atlas; (3) the first date on the timing of deposition of the sediments on the northern edge of the Paleoproterozoic West African craton; (4) a lower age limit on deformation during the Eburnean orogeny; and (5) the first date obtained from the non-granitic Paleoproterozoic basement of Morocco. Ages of 2046 ?? 7 Ma (Targant granite) and 2041 ?? 6 Ma (Oudad granite) support earlier interpretations of a Paleoproterozoic Eburnean igneous event in the Anti-Atlas. The granites post-date the Eburnean D1 deformation event in the Paleoproterozoic schist sequence, and place a ???2046 Ma limit on short-lived Eburnean deformation in the area. Cross-cutting metadolerite is 2040 ?? 6 Ma; this is the first date from a metadolerite in the western Anti-Atlas. All of the dolerites in the area post-date emplacement of the two granites and the new age constrains the onset of late- or post-Eburnean extension. Ignimbrite of the Ouarzazate Series, immediately above the Paleoproterozoic basement is 565 ?? 7 Ma. This Neoproterozoic age agrees with ages of similar volcanic rocks elsewhere from the Ouarzazate Series. The date also agrees with the ages of associated hypabyssal intrusions, and marks the second and final stage of Pan-African orogenic activity in the western Anti-Atlas. ?? 2002 Elsevier Science B.V. All rights reserved.

  5. Mid-Neoproterozoic ridge subduction and magmatic evolution in the northeastern margin of the Indochina block: Evidence from geochronology and geochemistry of calc-alkaline plutons

    NASA Astrophysics Data System (ADS)

    Qi, Xuexiang; Santosh, M.; Zhao, Yuhao; Hu, Zhaocuo; Zhang, Chao; Ji, Fengbao; Wei, Cheng

    2016-04-01

    The mid-Neoproterozoic medium- to high-K calc-alkaline magmatic rocks in the northeastern margin of the Indochina block, SW China, provide important insights into the relationship of the Indochina block with the Gondwana supercontinent. Here we report zircon LA-ICP-MS U-Pb data from the early and late stage plutons which yield weighted mean 206Pb/238U ages of 765 Ma and 732-739 Ma suggesting mid-Neoproterozoic emplacement. The zircon εHf(t) values show a range of - 3.2 to + 2.4 (average + 0.1 ± 0.9) with TDMC of 1510 to 1870 Ma for the early plutons, and - 5.4 to + 5.1 (average + 2.1 to - 3.9) with TDMC of 1366 to 1985 Ma for late plutons. Both groups show similar geochemical characteristics including high Mg#, enrichment of LILE and LREE, slight negative Eu anomalies, and strongly negative Nb, Ta and Ti anomalies, with all the samples falling within the continental/island arc field in tectonic discrimination diagrams. These features suggest that the early and late stage magmas were produced by the mixing of mantle-derived magma and crust-derived magma in different proportion within an active continental margin, in subduction-related continental-arc tectonic setting. The linear zoning and roughly parallel distribution of the two generations of intrusions with a hiatus of 20 Ma might suggest an episode of ridge subduction with asthenosphere upwelling through the slab window that generated the second phase of plutons.

  6. Late Neoproterozoic felsite (602.3 +/- 2 Ma) and associated metadiabase dikes in the Reading Prong, Pennsylvania, and rifting of Laurentia

    USGS Publications Warehouse

    Smith, R.C., II

    2003-01-01

    Felsite dikes in the Rittenhouse Gap iron mine district of the Reading Prong, eastern Pennsylvania, have a close geochemical affinity with the peralkaline Battle Mountain Member of the Robertson River Igneous Suite (RRIS), northern Virginia. These newly recognized Rittenhouse Gap Felsite dikes of the Swabia Creek Igneous Suite (SCIS) of eastern Pennsylvania plot as within-plate, A-type, A1 granites on various discriminant diagrams, but are quite distinct from late Neoproterozoic Catoctin Metarhyolite of Pennsylvania which has lower Ga/Al and Nb, but higher Eu. Newly recognized metadiabase dikes, also found in the Rittenhouse Gap district and proposed as Tunnel Mine Metadiabase of the SCIS, classify as alkali within-plate or continental initial rifting alkali tholeiites. They are quite distinct chemically and mineralogically from Catoctin Metabasalt flows and equivalent metadiabase dikes in Pennsylvania, which have lower Nb. Sr and Nd isotopic data indicate that the Tunnel Mine Metadiabase and Rittenhouse Gap Felsite are of mantle origin, but that the latter also includes a crustal component. The SCIS bimodal volcanics in Pennsylvania suggest a previously unrecognized rift environment in Pennsylvania at 602 Ma, somewhat predating the recognized, latest Neoproterozoic Catoctin event in Pennsylvania. As such, they fill in both temporal and geographic gaps for the rifting of Laurentia in Pennsylvania. It is proposed that the SCIS melt developed from a remnant ember of the northeastward trace of the older Mount Rogers-RRIS hotspot as Laurentia rotated clockwise. However, release and intrusion of the SCIS may have been related to younger Catoctin event crustal thinning that slightly predated the mafic dike phase of the Catoctin as Laurentia later migrated northward over a second hotspot. Eventually, the mafic phase associated with this second hotspot sufficiently attenuated the crust to allow introduction of Catoctin volcanics.

  7. Early Neoproterozoic multiple arc-back-arc system formation during subduction-accretion processes between the Yangtze and Cathaysia blocks: New constraints from the supra-subduction zone NE Jiangxi ophiolite (South China)

    NASA Astrophysics Data System (ADS)

    Wang, Xin-Shui; Gao, Jun; Klemd, Reiner; Jiang, Tuo; Zhai, Qing-Guo; Xiao, Xu-Chang; Liang, Xin-Quan

    2015-11-01

    ophiolite originated from an isotopically homogeneous depleted mantle source. The diversity of MORB- to IAB-like basalts and the presence of Fe-Ti basalts favor a formation of the NE Jiangxi ophiolite during the initial rifting phase of an intra-oceanic back-arc basin between an oceanic arc (Huaiyu Terrane) and the continental margin of the Yangtze Block (Jiuling Terrane) at ca. 990 Ma. Both the present and previous studies imply that multiple arc-back-arc systems formed during long-lasting subduction-accretion processes between the Yangtze and Cathaysia blocks during the early Neoproterozoic.

  8. Origin of cratonic basins

    NASA Astrophysics Data System (ADS)

    Dev. Klein, George; Hsui, Albert T.

    1987-12-01

    Tectonic subsidence curves show that the Illinois, Michigan, and Williston basins formed by initial fault-controlled mechanical subsidence during rifting and by subsequent thermal subsidence. Thermal subsidence began around 525 Ma in the Illinois Basin, 520 460 Ma in the Michigan Basin, and 530 500 Ma in the Williston Basin. In the Illinois Basin, a second subsidence episode (middle Mississippian through Early Permian) was caused by flexural foreland subsidence in response to the Alleghanian-Hercynian orogeny. Resurgent Permian rifting in the Illinois Basin is inferred because of intrusion of well-dated Permian alnoites; such intrusive rocks are normally associated with rifting processes. The process of formation of these cratonic basins remains controversial. Past workers have suggested mantle phase changes at the base of the crust, mechanical subsidence in response to isostatically uncompensated excess mass following igneous intrusions, intrusion of mantle plumes into the crust, or regional thermal metamorphic events as causes of basin initiation. Cratonic basins of North America, Europe, Africa, and South America share common ages of formation (around 550 to 500 Ma), histories of sediment accumulation, temporal volume changes of sediment fills, and common dates of interregional unconformities. Their common date of formation suggests initiation of cratonic basins in response to breakup of a late Precambrian super-continent. This supercontinent acted as a heat lens that caused partial melting of the lower crust and upper mantle followed by emplacement of anorogenic granites during extensional tectonics in response to supercontinent breakup. Intrusion of anorogenic granites and other partially melted intrusive rocks weakened continental lithosphere, thus providing a zone of localized regional stretching and permitting formation of cratonic basins almost simultaneously over sites of intrusion of these anorogenic granites and other partially melted intrusive rocks.

  9. Intra-platform tectono-sedimentary response to geodynamic transition along the margin of the Tarim Basin, NW China

    NASA Astrophysics Data System (ADS)

    Gao, Zhiqian; Fan, Tailiang

    2014-12-01

    The Tarim Basin has experienced three tectonic evolutionary phases from the Cambrian to Ordovician: (1) Regional extension from the late Neoproterozoic to Mid-Early Cambrian, (2) Relatively weak regional compression from the Late Cambrian to Mid-Early Ordovician, and (3) Regional compression during the Late Ordovician. Intra-platform tectonic and sedimentary characteristics indicate a clear linkage to the tectonic evolution of the basin margin during early Paleozoic time. During the Cambrian, small intra-platform rift-related depressions formed during an extensional setting. During the Mid-Early Ordovician, a transition from extension to compression caused formation of the Tazhong and Tabei paleo-uplifts and major unconformities T74 (base of the Late Ordovician). The evolving paleo-geomorphology led to differentiation of sedimentary facies, and numerous intra-platform shoals formed during deposition of the Early Ordovician Yingshan Formation. During the Late Ordovician, regional compression began, which changed the platform margin slopes into four slopes that surrounded the three isolated island uplifts of Tabei, Tazhong, and Tangnan in the Late Ordovician. Simultaneously, the basin margin dynamic conditions also changed the relative sea level and filling pattern of the basin. In the Early and Middle Cambrian, the Tarim Basin mainly developed a progradational ramp-type platform due to relative sea level fall. From the Late Cambrian to Early Ordovician the relative sea level began to rise, resulting in an aggradational-retrograding rimmed margins-type platform. In the Late Ordovician, along with a further rise in relative sea level, the basin mainly developed isolated platform.

  10. Stabilization of large drainage basins over geological time scales: Cenozoic West Africa, hot spot swell growth, and the Niger River

    NASA Astrophysics Data System (ADS)

    Chardon, Dominique; Grimaud, Jean-Louis; Rouby, Delphine; Beauvais, Anicet; Christophoul, Frédéric

    2016-03-01

    Reconstructing the evolving geometry of large river catchments over geological time scales is crucial to constraining yields to sedimentary basins. In the case of Africa, it should further help deciphering the response of large cratonic sediment routing systems to Cenozoic growth of the basin-and-swell topography of the continent. Mapping of dated and regionally correlated lateritic paleolandscape remnants complemented by onshore sedimentological archives allows the reconstruction of two physiographic configurations of West Africa in the Paleogene. Those reconstructions show that the geometry of the drainage is stabilized by the late early Oligocene (29 Ma) and probably by the end of the Eocene (34 Ma), allowing to effectively link the inland morphoclimatic record to offshore sedimentation since that time, particularly in the case of the Niger catchment—delta system. Mid-Eocene paleogeography reveals the antiquity of the Senegambia catchment back to at least 45 Ma and suggests that a marginal upwarp forming a continental divide preexisted early Oligocene connection of the Niger and Volta catchments to the Equatorial Atlantic Ocean. Such a drainage rearrangement was primarily enhanced by the topographic growth of the Hoggar hot spot swell and caused a stratigraphic turnover along the Equatorial margin of West Africa.

  11. Climate change impact on water resources for several river basins: a European, Asian and African case study.

    NASA Astrophysics Data System (ADS)

    Mariotti, L.; Coppola, E.; Gao, X.; Im, E. S.; Giorgi, F.

    2009-04-01

    Changes in temperature and precipitation patterns resulting from changes in climate are expected to impact the spatial and temporal distribution of water resources (IPCC 2007). Because climate change doesn't occur uniformly throughout the globe, climate change is expected to impact each region differently. Few examples are reported where a possible change in water availability could heavily effects the life of peoples: • The Volta River in Africa is responsible for 70% of the electricity production in Ghana. • More than the 80% of the northern Italian GDP (Gross Domestic Product) is connected to the Po River. • The Miyun Reservoir in China is the major water supply for Beijing and already in the last decades Beijing suffered from water storage deficiency. • The Soyang, Chungju, and Daecheong Basins in Korea provide municipal, industrial, and irrigational water to downstream users, as well as control flooding and generate hydropower. The Soyang and Chungju dams supply water to Seoul the largest metropolitan areas in Korea. These River Basins have been reconstructed using the CHYM hydrological model and by coupling CHYM with the regional climate model RegCM3 the possible impact on water resources has been quantified.

  12. The Oquirrh basin revisited

    SciTech Connect

    Erskine, M.C.

    1997-04-01

    The upper Paleozoic succession in the Oquirrh basin in unusually thick, up to 9300 m, and consists mainly of a Pennsylvanian-middle Permian miogeocline of northwestern Utah. Previous workers have suggested a tectonic origin for the Oquirrh basin that is incompatible with the basin location in both time and space. There is no evidence for Pennsylvanian and Lower Permian tectonism in the middle of the miogeocline. Thermal evidence from the Mississippian Mission Canyon shale does no support the implied deep burial of the crustal sag models of basin formation. Stratigraphic and facies evidence indicates a growth fault origin for the basin. Regional isopach maps and facies maps are powerful tools in interpreting depositional environments and in reconstructing fold-and-thrust belts. However, the location of measured sections relative to the location of the growth fault basin. The Charleston-Nebo thrust may have essentially reversed the movement on a growth fault. Thick Oquirrh basin sedimentary rocks may not be required to balance structural sections across this thrust fault. A thin-skinned, extensional growth fault origin for the Oquirrh basin implies that the Cordilleran miogeocline did not participate in the Pennsylvanian north-vergent uplifts of the Ancestral Rocky Mountains.

  13. Characterization of Sao Francisco basin, Brazil: joint inversion of multiple geophysical data

    NASA Astrophysics Data System (ADS)

    Solon, F. F.; Fontes, S. L.

    2013-05-01

    The need to improve the characterization of the near surface and to generate consistent images of multiple geophysical data has led us to adopt a cross-gradient joint inversion methodology. We applied this method to characterize the basement fracture-zones and heterogeneous reservoir rocks underneath thick overburden at São Francisco basin in Brazil. The basin is mainly filled by Neoproterozoic clastic and carbonates rocks of the Bambui group formed in the Upper Proterozoic (Vendian) which makes the São Francisco basin interesting for hydrocarbon prospecting. Exploring the combined use of different geophysical methods will enhance the structural resemblance in the images that each one provides. The strategy explored in this work is to use a two-dimensional structured-coupled joint inversion from Gallardo and Meju (2003) applying to four data sets: land seismic reflection, magnetotelluric (MT), gravity and magnetic data sets along a 100 km profile across a region called Remanso do Fogo. For the joint inversion approach, we need to determine appropriate processing parameters to better estimate the individual contribution from each geophysical data type. A first experiment using three data sets (gravity, magnetic and MT) is shown in fig. 1. The evolution of the joint inversion showed that the solution is controlled by the development of common features in all models. The results of joint inversion using three and four models clearly mapped the compartmentation of the basement in this sector of São Francisco Basin. Also it is possible to identify the units of Bambui group, resulting in a constrained geological interpretation.; Fig. 1: Sections obtained in interaction 6 after joint inversion of gravity, magnetic and MT data.

  14. Cryogenian Interglacial Litho- and C Isotope Chemo-stratigraphy of the Amadeus Basin, Central Australia

    NASA Astrophysics Data System (ADS)

    Verdel, C.; Campbell, M.; Phelps, B.

    2015-12-01

    The Cryogenian stratigraphy of the Amadeus Basin in central Australia consists of the Areyonga, Aralka, and Olympic Formations. Both the Areyonga and Olympic Fms. include glacial deposits overlain by cap carbonates, observations that have prompted correlation of these formations with the global Sturtian and Marinoan glaciations, respectively. In this study we focus on the interglacial stratigraphic unit (Aralka Fm.), which is subdivided into the lower Ringwood Mbr. and the upper Limbla Mbr. C isotope values from carbonates within the Limbla Mbr. are particularly large (up to +10 per mil), suggesting that it correlates with the global "Keele Peak" anomaly. The underlying Ringwood Mbr. (the base of which comprises the Sturtian cap carbonate of the Amadeus Basin) varies from thin or non-existent in the northwestern part of the basin to hundreds of meters thick in eastern parts. C isotope values from Ringwood Mbr. carbonates are roughly -5 per mil at its base and rise rapidly up-section. A mid-interglacial negative C isotope excursion to values of approximately -5 per mil in the Ringwood Mbr. may correlate with the Tayshir anomaly of the Mongolian Neoproterozoic succession. Interglacial carbonates of the Aralka Fm. therefore have C isotope compositions that span at least 15 per mil and include both positive and negative isotopic excursions that seem to be globally correlative. Furthermore, detailed field observations from the Ringwood Mbr. suggest that it can be subdivided into three submembers, each of which is marked by stromatolitic intervals. Shallowing-upward parasequences in the Ringwood Mbr., as well as a major change in lithology from siltstones and microbialites of the Ringwood Mbr. to dominantly coarse-grained, cross-stratified sandstones of the Limbla Mbr., suggest that the interglacial strata of the Amadeus Basin were deposited during a period of significant and repeated changes in relative sealevel.

  15. K Basin safety analysis

    SciTech Connect

    Porten, D.R.; Crowe, R.D.

    1994-12-16

    The purpose of this accident safety analysis is to document in detail, analyses whose results were reported in summary form in the K Basins Safety Analysis Report WHC-SD-SNF-SAR-001. The safety analysis addressed the potential for release of radioactive and non-radioactive hazardous material located in the K Basins and their supporting facilities. The safety analysis covers the hazards associated with normal K Basin fuel storage and handling operations, fuel encapsulation, sludge encapsulation, and canister clean-up and disposal. After a review of the Criticality Safety Evaluation of the K Basin activities, the following postulated events were evaluated: Crane failure and casks dropped into loadout pit; Design basis earthquake; Hypothetical loss of basin water accident analysis; Combustion of uranium fuel following dryout; Crane failure and cask dropped onto floor of transfer area; Spent ion exchange shipment for burial; Hydrogen deflagration in ion exchange modules and filters; Release of Chlorine; Power availability and reliability; and Ashfall.

  16. Continental break-up and collision in the Neoproterozoic and Palaeozoic — A tale of Baltica and Laurentia

    NASA Astrophysics Data System (ADS)

    Torsvik, T. H.; Smethurst, M. A.; Meert, J. G.; Van der Voo, R.; McKerrow, W. S.; Brasier, M. D.; Sturt, B. A.; Walderhaug, H. J.

    1996-06-01

    During the Neoproterozoic and Palaeozoic the two continents of Baltica and Laurentia witnessed the break-up of one supercontinent, Rodinia, and the formation of another, but less long-lived, Pangea. Baltica and Laurentia played central roles in a tectonic menage a trois that included major orogenic events, a redistribution of palaeogeography and a brief involvement of both with Gondwana. Many of these plate re-organisations took place over a short time interval and invite a re-evaluation of earlier geodynamic models which limited the speeds at which large continental plates could move to an arbitrarily low value. Baltica and Laurentia probably shared a common drift history for the time interval 750 - 600 Ma as they rotated clockwise and drifted southward from an equatorial position during the opening of the Proto-Pacific between Laurentia and East Gondwana (initial break-up of Rodinia). On their combined approach toward the south pole, Baltica and Laurentia were glaciated during the Varanger glaciations. Although the two continents drifted toward the south pole during the Late Proterozoic, they began to separate at around 600 Ma (rift to drift) to form the Iapetus Ocean through asymmetric rifting and relative rotations of up to 180°. Initiation of rifting on the Baltic margin is marked by the 650 Ma Egersund tholeiitic dykes (SW Norway) which contain abundant lower crustal zenoliths, and the tholeiitic magma was probably derived from a mantle plume. In latest Precambrian time, the final redistribution of Rodinia is characterised by high plate velocities. In particular, Laurentia began a rapid, up to 20 cm/yr, ascent to equatorial latitudes and essentially stayed in low latitudes throughout most of the Palaeozoic. The high velocities suggest either that Laurentia was pushed off a lower mantle heat anomaly originating from supercontinental mantle insulation or that Laurentia was pulled toward a subduction-generated cold spot in the proto-Pacific. Baltica, except for

  17. Reserves in western basins

    SciTech Connect

    Caldwell, R.H.; Cotton, B.W.

    1995-04-01

    The objective of this project is to investigate the reserves potential of tight gas reservoirs in three Rocky Mountain basins: the Greater Green River (GGRB), Uinta and Piceance basins. The basins contain vast gas resources that have been estimated in the thousands of Tcf hosted in low permeability clastic reservoirs. This study documents the productive characteristics of these tight reservoirs, requantifies gas in place resources, and characterizes the reserves potential of each basin. The purpose of this work is to promote understanding of the resource and to encourage its exploitation by private industry. At this point in time, the GGRB work has been completed and a final report published. Work is well underway in the Uinta and Piceance basins which are being handled concurrently, with reports on these basins being scheduled for the middle of this year. Since the GGRB portion of the project has been completed, this presentation win focus upon that basin. A key conclusion of this study was the subdivision of the resource, based upon economic and technological considerations, into groupings that have distinct properties with regard to potential for future producibility, economics and risk profile.

  18. Abundance of African invader fly, Bactrocera invadens drew, tsuruta and white (diptera: tephritidae) and influence of weather parameters on trap catches in mango in the Volta region of Ghana.

    PubMed

    Adzim, Charles Amankwa; Billah, Maxwell Kelvin; Afreh-Nuamah, Kwame

    2016-01-01

    The seasonal abundance of African Invader fly, Bactrocera invadens and the influence of temperature and rainfall on fly catches was determined in two agro ecological zones; moist semi-deciduous forest area and the coastal grassland area of the Volta Region of Ghana for year of mango production. Traps containing methyl eugenol were used in monitoring the abundance of the Africa invader fly, Bactrocera invadens where data on both temperature and rainfall were collected from Meteorological Services of Ghana in Volta region. A total of 49,322 organisms captured, 45,829 were identified as Bactrocera invadens and 3493 were non-fruit fly. There were significant differences (p < 0.05) in the number of Bactrocera invadens captured between the agro ecological zones with relative fly densities of 5.06 F/T/D in moist semi deciduous forest area and 2.38 F/T/D in the coastal grassland zone. The result shows that climatic factors affected Bactrocera invadens differently in different agro ecological area. There was negative correlation and highly significant (p < 0.001) correlation between fruit flies and temperature whereas there was negative correlation and high significant (p < 0.01) difference between rainfall in the moist semi deciduous forest area. In the coastal grassland area, there was negative correlation and highly significant (p < 0.001) between Bactrocera invadens for both rainfall and temperature. Bactrocera invadens activities peaked differently during the study period due to favourable climatic conditions. The activities of Bactrocera invadens peaked during weeks 7 and 29 in the moist semi deciduous forest area while their activities peaked during weeks 3 and 24 for the coastal grassland areas. Both agro ecological zones recorded the presence of Bactrocera invadens, their number and proportion varied considerably with associated effects of the weather parameters on their abundance. The effect of weather parameters on the abundance of bactrocera invadens

  19. Structural analysis of the Creignish Hills Mylonite Zone, Cape Breton Island, Nova Scotia: implications for Neoproterozoic core complex development along the northern Gondwanan margin?

    NASA Astrophysics Data System (ADS)

    Wessel, Zachary R.; Nance, R. Damian; Keppie, J. Duncan; Murphy, J. Brendan

    2005-04-01

    Late Neoproterozoic ductile shear zones that juxtapose low-grade over high-grade assemblages are characteristic features of parts of the peri-Gondwanan terranes of the Canadian Appalachians. One such ductile shear zone, in the Creignish Hills of Cape Breton Island, Nova Scotia, brings low-grade platformal metasedimentary rocks of the George River Metamorphic Suite into contact with underlying high-grade rocks of the Bras d’Or Gneiss. The low-grade assemblage includes quartzite, marble, schist, and phyllite with interlayered felsic volcanogenic units and mafic flows, whereas the high-grade unit comprises low-pressure, high-temperature gneiss and migmatite, including pelitic paragneiss of likely volcanogenic origin. The ductile shear zone between the two assemblages (Creignish Hills Mylonite Zone) envelopes the high-grade rocks in the form of a WNW-plunging antiform. The structural dome is truncated to the east against Carboniferous strata by high-angle faulting. Kinematic indicators within the mylonite, including asymmetric porphyroclasts, fractured veins, S C fabrics, and folded mylonitic foliation, suggest a broadly top-to-the-southeast (dextral) sense of shear, while the presence of gneissic granitoid sheets that are broadly concordant but locally cross-cut and are folded about the mylonitic foliation, suggest that mylonitization was accompanied by partial melting and syntectonic intrusion. Monazite from the gneiss and zircon from the granitoid sheets have yielded near-identical U Pb ages of ca. 550 Ma. Juxtaposition of low-grade over high-grade assemblages in several peri-Gondwanan basement blocks in central Cape Breton Island suggests that the Creignish Hills Mylonite Zone is part of a series of regional low-angle detachments with a core complex geometry. Similar ductile shear zones with easterly components of shear and low-angle pre-Carboniferous orientations also place low-grade over high-grade rocks in southern New Brunswick and the Cobequid Highlands of

  20. Paleomagnetic results from the Upper Unkar Group and overlying Nankoweap Formation from the Grand Canyon Supergroup (GCSG), Arizona: Implications for Laurentia's Neoproterozoic APWP

    NASA Astrophysics Data System (ADS)

    Weil, A. B.; Geissman, J.; Van der Voo, R.

    2001-12-01

    Paleomagnetic sampling was carried out within the Cardenas basalts and an underlying suite of mafic intrusions from the uppermost Unkar Group (lower GCSG), as well as from the unconformably overlying Nankoweap Fm. The GCSG is one of the thickest and best preserved Neoproterozoic sequences in North America. The lower GCSG was deposited between 1200 Ma (cooling age of the underlying Vishnu schist) and about 1100 Ma (Rb-Sr dates on Cardenas basalts) during a failed rift event. The Nankoweap Fm. is hypothesized to have been deposited during extension subsequent to deposition of the lower GCSG; however, the relationship of the Nankoweap Fm. to the underlying lower GCSG and the overlying upper GCSG is poorly understood. The estimated age of the Nankoweap Fm. is 950 Ma. Sixteen sites were collected from the Cardenas basalts and from a suite of dikes and sills that intrude the Unkar Group. The dikes and sills are considered feeders to the Cardenas basalt, based on geochemical similarities and stratigraphic relationships. After thermal treatment the sixteen sites yield a stable characteristic magnetization direction of D = 286\\deg %, I = +58\\deg % (kappa = 26, alpha95 = 7), corresponding to a paleopole of 181\\deg % E, 33\\deg % N. The remanence in the intrusions is confirmed by a partial contact test on host Dox Formation strata. The samples collected along the margin of the dikes give statistically the same normal-polarity direction as the intrusion; however, samples more than several dike widths from the contact yield mainly unresolvable characteristic remanence directions. Nine sites were collected from the Nankoweap Fm., which unconformably overlies the Cardenas basalts. After thermal treatment the nine sites yield a stable characteristic magnetization direction of D = 257\\deg %, I = -3\\deg % (kappa = 80, alpha95 = 7.5), which corresponds to a paleopole of 165\\deg % E, 11\\deg % S. A fold test of the nine sites reveals a pre-folding magnetization acquisition

  1. 900 Ma Pole from the Bjerkreim-Sokndal Layered Intrusion, Rogaland Igneous Complex, Norway: Where Was Baltica in the Early Neoproterozoic?

    NASA Astrophysics Data System (ADS)

    Brown, L. L.; McEnroe, S. A.

    2014-12-01

    of a contact aureole around the intrusion. Comparison to other early Neoproterozoic paleomagnetic poles from southern Scandinavia confirms the high southern latitude position of Baltica at this time. A paucity of ~900 Ma poles from other ancient cratons precludes a more detailed picture of Rodinia in the early Neoproterozoic.

  2. Minimum age of the Neoproterozoic Seven Hundred Acre Island Formation and the tectonic setting of the Islesboro Formation, Islesboro block, Maine

    USGS Publications Warehouse

    Stewart, D.B.; Tucker, R.D.; Ayuso, R.A.; Lux, D.R.

    2001-01-01

    Two platformal stratigraphic sequences occur on Islesboro, Penobscot Bay, Maine. The older Seven Hundred Acre Island Formation is at least 200 m thick, its base is not exposed, and it makes up fault-bounded blocks of siliceous colour-banded dolomitic marble, muscovite-rich quartzite, coarse-grained splendent muscovite-garnet-staurolite-andalusite schist, and calcareous metapelite, with minor garnet amphibolite and amphibolite. It was initially metamorphosed to lower amphibolite facies and was later to lower greenschist facies. The lower amphibolite facies metamorphism is Neoproterozoic (670 to 650 Ma) as inferred from the 40Ar/39Ar high temperature release spectra of hornblende separates. A U-Pb zircon age of 646.7 ?? 2.7 Ma obtained for a pegmatite that intruded deformed rocks is taken to be the minimum age of the Formation. The platformal Islesboro Formation probably unconformably overlies the Seven Hundred Acre Island Formation. It is primarily turbiditic pelite with many beds of quartzite, impure dolomitic marble, some conglomerate, and a few feldsparrich volcaniclastic beds and is thought to be either Neoproterozoic or Cambrian. It was metamorphosed only to lower greenschist facies, possibly in the same event that retrograded the Seven Hundred Acre Island Formation. Geochemical interpretations of minor and trace element analyses of six amphibolite and four schist samples from the Seven Hundred Acre Island Formation show that the protoliths of the amphibolite samples were intermediate between tholeiitic and within-plate type basaltic flows or dikes that intruded attenuated continental crust, or were eroded from these basalts. Four amphibolite and three schist samples analyzed for Pb isotopes were found to be enriched in radiogenic Pb. The Pb isotopic compositions are similar to those in peri-Gondwanan basement rocks from Atlantic Canada. The peri-Gondwanan Islesboro block was placed against the peri-Gondwanan Middle and Late Cambrian Ellsworth terrane on the

  3. Structural controls on Neoproterozoic mineralization in the South Eastern Desert, Egypt: an integrated field, Landsat TM, and SIR-C/X SAR approach

    NASA Astrophysics Data System (ADS)

    Kusky, Timothy M.; Ramadan, Talaat M.

    2002-07-01

    The Arabian-Nubian Shield represents a complex amalgam of arcs and microcontinents assembled during Neoproterozoic closure of the Mozambique Ocean. The 750-720 Ma Allaqi suture is an arc/arc collision zone, formed when the Gerf terrane in the north overrode the circa 830-720 Ma Gabgaba terrane in the south, prior to closure of the Mozambique Ocean. Neoproterozoic rocks include ophiolitic ultramafic-mafic rocks, metasediments, intermediate metavolcanic rocks, intrusive gabbro-diorite rocks, granodiorites, biotite granites, and leucocratic granites. High-pressure/low-temperature metamorphism has been documented in rocks of the suture zone. Mineral deposits include nickel-copper-platinum and podiform chromite in ultramafic rocks, marble, gold-bearing quartz-veins in D 2 and D 3 shear zones, and radioactive mineralization associated with late leucocratic granitic rocks. Integrated field mapping and remote sensing techniques are used to distinguish and map the relationships between rock units, structures, and alteration zones associated with mineral deposits along the Allaqi suture of Egypt's SE Desert. Landsat TM images processed using a band ratioing technique show different rock types remarkably well, and are able to distinguish between alteration zones associated with ultramafic rocks (listwaenites) and those associated with leucocratic granitic rocks (greisenization, silicification and albitization). Black and white L-band SIR-C/X SAR images outline foliations, faults and folds that control mineralization at several deposits in the area, whereas color composite multiband Chh-Lhh-Lhv SIR-C/X SAR images reveal some elliptical granitic bodies that host radioactive mineralization. E-trending, tight to isoclinal, gently dipping folds, thrust faults and subvertical shear zones related to the Allaqi suture are overprinted by N-oriented structures related to the Wadi Ungate shear zone, formed during collision of east and west Gondwana during closure of the Mozambique Ocean

  4. The evolution of the neoproterozoic São Gabriel juvenile terrane, southern Brazil based on SHRIMP and LA-ICP-MS U-Pb ages and ?18O data on detrital zircon

    NASA Astrophysics Data System (ADS)

    Lena, L. O.; Pimentel, M. M.; Philipp, R. P.; Armstrong, R. A.; Sato, K.

    2013-12-01

    The São Gabriel terrane is a segment of juvenile crust exposed in the western part of the Dom Feliciano Belt in the southern Mantiqueira Province, southern Brazil. In this study, SHRIMP and LA-ICPMS U-Pb geochronological data for 171 detrital zircons of the Cambaizinho Complex are used to investigate the tectonic evolution of this juvenile terrain. Eighty-one grains were later selected for SIMS δ18O analyses. Ages ranged from 840 to 660 Ma, with a strong concentration between ca. 750 and 700 Ma. The age spectrum of the detrital zircon grains from this meta-sedimentary succession suggests that the original sediments were derived from the erosion of the arc, most likely in a short-lived syn-orogentic basin. Th/U ratios and internal structures of the zircon grains reveal that they were mostly eroded from the arc magmatic rocks, without any relevant contribution from their metamorphic counterparts, or from any other older source. The δ18O values varied from 3.2 to 9.6‰, indicating the coeval crystallization of both unaltered, pristine mantle magmas alongside altered mantle magmas, and strongly contaminated continental crustal magmas generated in both continental and oceanic arc setting. Three periods in the progressive evolution of the terrane were recognized: Period I is represented by the installation of an island-arc subduction zone. The data set suggest that this period started at ca. 840 Ma and went on until 750 Ma. In this period δ18O values varied between 3.2 to 5.5 ‰, suggesting the crystallization of normal mantle-derived magmas, and juvenile magmas with assimilation of hydrothermally altered crust. Period II took place between ca. 750-690 Ma, which represents the peak of magmatic activity suggested by the large abundance of detrital zircons in the probability density diagrams. Here, δ18O values ranged from 4.0 to 9.4 ‰. The wide range of δ18O values reveals the coexistence of magmas with continental, mantle, and altered mantle isotopic signatures

  5. K Basin Hazard Analysis

    SciTech Connect

    PECH, S.H.

    2000-08-23

    This report describes the methodology used in conducting the K Basins Hazard Analysis, which provides the foundation for the K Basins Final Safety Analysis Report. This hazard analysis was performed in accordance with guidance provided by DOE-STD-3009-94, Preparation Guide for U. S. Department of Energy Nonreactor Nuclear Facility Safety Analysis Reports and implements the requirements of DOE Order 5480.23, Nuclear Safety Analysis Report.

  6. K Basins Hazard Analysis

    SciTech Connect

    WEBB, R.H.

    1999-12-29

    This report describes the methodology used in conducting the K Basins Hazard Analysis, which provides the foundation for the K Basins Safety Analysis Report (HNF-SD-WM-SAR-062, Rev.4). This hazard analysis was performed in accordance with guidance provided by DOE-STD-3009-94, Preparation Guide for U. S. Department of Energy Nonreactor Nuclear Facility Safety Analysis Reports and implements the requirements of DOE Order 5480.23, Nuclear Safety Analysis Report.

  7. Adolescents and parents’ perceptions of best time for sex and sexual communications from two communities in the Eastern and Volta Regions of Ghana: implications for HIV and AIDS education

    PubMed Central

    2013-01-01

    Background Adolescents and parents’ differ in their perceptions regarding engaging in sexual activity and protecting themselves from pregnancy and sexually transmitted infections (STIs). The views of adolescents and parents from two south-eastern communities in Ghana regarding best time for sex and sexual communications were examined. Methods Focus Group interviews were conducted with parents and adolescents (both In-school and Out-of school) from two communities (Somanya and Adidome) in the Eastern and Volta regions of Ghana with epidemiological differentials in HIV infection. Results Findings showed parents and adolescents agree that the best timing for sexual activity amongst adolescents is determined by socioeconomic viability. In practice however, there were tensions between adolescents and parents crystallized by spoilt generation and physiological drive ideologies. Whilst one community relied on a more communal approach in controlling their children; the other relied on a confrontational approach. Sex-talk is examined as a measure to reduce these tensions, and children in both communities were ambivalent over sexual communication between their parents and themselves. Parents from the two communities however differed in their perceptions. Whilst parents in one community attributed reduced teenage pregnancies to sex education, those in the other community indicated a generalized adolescents’ sexual activeness manifested in the perceived widespread delinquency in the community. Conclusion Parents in both communities reported significant barriers to parents-adolescents sexual communication. Parents in both communities should be educated to discuss the broader issues on sexuality that affects adolescents and their reproductive health needs. PMID:24070548

  8. Metazoan parasites of Mandi-amarelo Pimelodus maculatus and of Jundiá Rhamdia quelen (Osteichthyes: Siluriformes) of Paraíba do Sul River, Volta Redonda, Rio de Janeiro.

    PubMed

    Venancio, Aline Cristine Pinto; de Aguiar, Gesilene Ribeiro; Lopes, Patrícia da Silva; Alves, Dimitri Ramos

    2010-01-01

    Forty-one specimens of mandi-amarelo Pimelodus maculatus Lacépède, 1803 (Siluriformes: Pimelodidae) and 54 specimens of jundiá Rhamdia quelen (Quoy & Gaimard, 1824) (Siluriformes: Heptapteridae) were collected from the Paraíba do Sul River, Volta Redonda, State of Rio de Janeiro, Brazil between November 2007 and October 2008. These fish underwent necropsy so their infracommunities of metazoan parasites could be studied. The same three species of parasites were collected in the two fish species studied. These were one monogenean, one nematode, and one hirudinean. Cucullanus pinnai (Travassos, Artiga, and Pereira, 1928) (Nematoda: Cucullanidae) and Aphanoblastella sp. (Monogenea: Dactylogyridae) were the dominant species with the highest prevalence in P. maculatus and R. quelen. The parasite species of P. maculatus and R. quelen showed an atypical over-dispersed pattern of distribution. No parasite species showed significant correlation between the body total length of the siluriform hosts and their prevalence and abundance. The parasite species richness showed a mean value of 0.87 ± 0.67 (0-2) and 0.57 ± 0.56 (0-2) in P. maculatus and R. quelen, respectively, and no correlation with the body total length. PMID:20943019

  9. Rapid adaptation of phytoplankters to geothermal waters is achieved by single mutations: were extreme environments 'Noah's Arks' for photosynthesizers during the Neoproterozoic 'snowball Earth'?

    PubMed

    Costas, Eduardo; Flores-Moya, Antonio; López-Rodas, Victoria

    2008-01-01

    Geothermal waters often support remarkable communities of microalgae and cyanobacteria apparently living at the extreme limits of their tolerance. Little is known about the mechanisms allowing adaptation of mesophilic phytoplankters to such extreme conditions, but recent studies are challenging many preconceived notions about this. The aim of this study was to analyse mechanisms allowing adaptation of mesophilic microalgae and cyanobacteria to stressful geothermal waters. To distinguish between the pre-selective or post-selective origin of adaptation processes allowing the proliferation of mesophilic phytoplankters in geothermal waters, several Luria-Delbrück fluctuation analysis were performed with the microalga Dictyosphaerium chlorelloides and the cyanobacterium Microcystis aeruginosa, both isolated from nonextreme waters. Geothermal waters from seven places in Italy and five icebound places at Los Andes in Argentina were used as selective agents. Physiological adaptation was achieved in the least toxic waters. In contrast, rapid genetic adaptation was observed in waters ostensibly lethal for the experimental organisms. This adaptation was achieved as consequence of single mutations at one locus. It was hypothesized that a similar mechanism of rapid genetic adaptation could explain the survival of photosynthetic life during the Neoproterozoic 'snowball Earth,' where geothermal refuges such as those studied could have been 'Noah's Arks' for microalgae and cyanobacteria. PMID:18803596

  10. Evidence for a Battle Mountain-Eureka crustal fault zone, north-central Nevada, and its relation to Neoproterozoic-Early Paleozoic continental breakup

    USGS Publications Warehouse

    Grauch, V.J.S.; Rodriguez, B.D.; Bankey, V.; Wooden, J.L.

    2003-01-01

    Combined evidence from gravity, radiogenic isotope, and magnetotelluric (MT) data indicates a crustal fault zone that coincides with the northwest-trending Battle Mountain-Eureka (BME) mineral trend in north-central Nevada, USA. The BME crustal fault zone likely originated during Neoproterozoic-Early Paleozoic rifting of the continent and had a large influence on subsequent tectonic events, such as emplacement of allochthons and episodic deformation, magmatism, and mineralization throughout the Phanerozoic. MT models show the fault zone is about 10 km wide, 130-km long, and extends from 1 to 5 km below the surface to deep crustal levels. Isotope data and gravity models imply the fault zone separates crust of fundamentally different character. Geophysical evidence for such a long-lived structure, likely inherited from continental breakup, defies conventional wisdom that structures this old have been destroyed by Cenozoic extensional processes. Moreover, the coincidence with the alignment of mineral deposits supports the assertion by many economic geologists that these alignments are indicators of buried regional structures.

  11. Geochemical and Sr-Nd-Hf-O-C isotopic constraints on the origin of the Neoproterozoic Qieganbulake ultramafic-carbonatite complex from the Tarim Block, Northwest China

    NASA Astrophysics Data System (ADS)

    Ye, Hai-Min; Li, Xian-Hua; Lan, Zhong-Wu

    2013-12-01

    The Qieganbulake ultramafic-carbonatite complex located within the northeastern margin of the Tarim Block of Northwest China hosts the world's second largest vermiculite deposit. Field observations, radiometric dating results and Sr-Nd-Hf isotopes reveal that the parental magmas of the carbonatite and ultramafic rocks are cogenetic and formed synchronously at ~ 810 Ma. They are characterized by unusually enriched Sr-Nd-Hf isotopic compositions (ISr = 0.70570-0.70762, εNd(t) = - 7.7 to - 12.5, and εHf(t) = - 6.7 to - 12.9), indicating that the parent magmas were derived mainly from a subcontinental mantle source that had been metasomatised by subduction processes. Higher δ13C (- 3.65 to - 4.11‰) values compared to primary magmatic carbonate (- 8 to - 4‰) argue for incorporation of recycled inorganic carbon derived from subducted oceanic crusts. The carbonatites and clinopyroxenties define two distinct differentiation trends, which suggest that liquid immiscibility rather than crystal fractionation controlled the petrogenetic process. Pyroxenities have clearly higher apatite ISr and δ18O values than coexisting carbonatites, indicating involvement of crustal components during their emplacement. The Qieganbulake complex is closely associated in time and space with the mid-Neoproterozoic Rodinia breakup event triggered by mantle plume activities in the Tarim Block. Therefore, the mantle plume likely induced partial malting of, and likely mixed with, the metasomatized subcontinental lithospheric mantle, to form the Qieganbulake ultramafic-carbonatite complex.

  12. 18O/16O and V/Cr ratios in gem tsavorites from the Neoproterozoic Mozambique metamorphic belt: a clue towards their origins?

    NASA Astrophysics Data System (ADS)

    Giuliani, Gaston; Fallick, Anthony E.; Feneyrol, Julien; Ohnenstetter, Daniel; Pardieu, Vincent; Saul, Mark

    2011-10-01

    The combination of oxygen isotope composition with V-Cr-Mn trace element concentrations of V-bearing garnets (tsavorites) originating from the main deposits of the Neoproterozoic Mozambique Metamorphic Belt is reported for the first time. The database enables the identification of the geological and geographical sources of the main productive areas from northern and southern Tanzania, Kenya, and Madagascar. Three consistent sets of δ18O values between 9.5‰ and 11.0‰, 11.6‰ and 14.5‰, and 15.5‰ and 21.1‰ have been recognized for primary deposits hosted in graphitic gneisses related to the Neoproterozic metasedimentary series. The δ18O value of tsavorite is a good tracer of the environment of its formation; the δ18O of the fluid in equilibrium with tsavorite was buffered by the host rock during metamorphism and fluid-rock interaction. This study is a first step in characterizing the geochemistry of gem tsavorite from most of the deposits and occurrences worldwide.

  13. Geochemistry and zircon ages of mafic dikes in the South Qinling, central China: evidence for late Neoproterozoic continental rifting in the northern Yangtze block

    NASA Astrophysics Data System (ADS)

    Zhu, Xiyan; Chen, Fukun; Liu, Bingxiang; Zhang, He; Zhai, Mingguo

    2015-01-01

    Neoproterozoic volcanic-sedimentary sequences of the southern Qinling belt, central China, were intruded by voluminous mafic dikes. secondary ion mass spectrometry zircon U-Pb dating indicates that these dikes were emplaced at 650.8 ± 5.2 Ma, coeval with mafic rocks occurring at the northern margin of the Yangtze block. The dikes are characterized by enrichment of large ion lithophile elements, high Ti contents (up to 3.73 wt%) and Nb/Ta ratios between 14.5 and 19.6, suggesting a mantle source of oceanic island basalt affinity. Initial 87Sr/86Sr ratios show positive correlation with SiO2 contents and negative correlation with Zr/Nb ratios, implying that these rocks were affected by crustal contamination during the magma ascend and emplacement process. The dikes have initial ɛ Nd values of +0.2 to +3.3, low 206Pb/204Pb ratios of 16.96-17.45, and moderate 87Sr/86Sr ratios of 0.7043-0.7076, likely pointing to the involvement of an enriched mantle source. The mafic dikes and coeval mafic volcanic equivalents in the South Qinling and the northern Yangtze are hypothesized to be related with the prolonged breakup of the supercontinent Rodinia, suggesting that continental rifting lasted until ca. 650 Ma.

  14. Neoproterozoic oceanic remnants in eastern Brazil: Further evidence and refutation of an exclusively ensialic evolution for the Araçuaí West Congo orogen

    NASA Astrophysics Data System (ADS)

    Pedrosa-Soares, Antônio Carlos; Vidal, Philippe; Leonardos, Othon Henry; Bley de Brito Neves, Benjamin

    1998-06-01

    The Araçuaí (eastern Brazil) and West Congo (southwestern Africa) belts are counterparts of the same Neoproterozoic orogen located between the São Francisco and Congo cratons. The Macaúbas Group represents a major passive margin sequence and is a key unit for interpreting the evolution of that orogen. The Salinas Formation is the distal rock assemblage of the Macaúbas Group and consists of a deep-sea sand-mud sequence, and a volcanic-sedimentary unit called the Ribeirão da Folha facies. The latter includes metamorphosed volcanic-exhalative sediments associated with ocean-floor basalts (amphibolites). The magmatic protoliths of these amphibolites crystallized at about 816 ± 72 Ma (Sm-Nd whole-rock isochron, ɛNd(t) =+3.8 ± 0.2). Regional metamorphism reached the amphibolite facies at about 630 Ma (Rb-Sr whole-rock isochron), when slabs of ultramafic rocks were tectonically emplaced over the Ribeirão da Folha facies. We consider this volcanic-sedimentary facies and the coeval slabs of ultramafic rocks to be remnants of a branch of the Adamastor-Brazilide ocean. The extensive occurrence of syntectonic to late tectonic calc-alkalic granitoids along the internal domain of the Araçuaí belt implies that a reasonably large amount of ocean crust was consumed, via an east-dipping subduction zone, during formation of the Araçuaí West Congo orogen.

  15. Nam Con Son Basin

    SciTech Connect

    Tin, N.T.; Ty, N.D.; Hung, L.T.

    1994-07-01

    The Nam Con Son basin is the largest oil and gas bearing basin in Vietnam, and has a number of producing fields. The history of studies in the basin can be divided into four periods: Pre-1975, 1976-1980, 1981-1989, and 1990-present. A number of oil companies have carried out geological and geophysical studies and conducted drilling activities in the basin. These include ONGC, Enterprise Oil, BP, Shell, Petro-Canada, IPL, Lasmo, etc. Pre-Tertiary formations comprise quartz diorites, granodiorites, and metamorphic rocks of Mesozoic age. Cenozoic rocks include those of the Cau Formation (Oligocene and older), Dua Formation (lower Miocene), Thong-Mang Cau Formation (middle Miocene), Nam Con Son Formation (upper Miocene) and Bien Dong Formation (Pliocene-Quaternary). The basement is composed of pre-Cenozoic formations. Three fault systems are evident in the basin: north-south fault system, northeast-southwest fault system, and east-west fault system. Four tectonic zones can also be distinguished: western differentiated zone, northern differentiated zone, Dua-Natuna high zone, and eastern trough zone.

  16. SURVEY OF CROSS-BASIN BOAT TRAFFIC, ATCHAFALAYA BASIN, LOUISIANA

    EPA Science Inventory

    For flood control and for the preservation and enhancement of environmental quality of overflow swamp habitats, introduction of sediment from the Atchafalaya Basin Main Channel into backwater areas of the Atchafalaya Basin Floodway should be minimized. This introduction occurs ma...

  17. River basin management

    SciTech Connect

    Newsome, D.H.; Edwards, A.M.C.

    1984-01-01

    The quality of water is of paramount importance in the management of water resources - including marine waters. A quantitative knowledge of water quality and the factors governing it is required to formulate and implement strategies requiring an inter-disciplinary approach. The overall purpose of this conference was to bring together the latest work on water quality aspects of river basin management. These proceedings are structured on the basis of five themes: problems in international river basins; the contribution of river systems to estuarial and marine pollution; the setting of standards; monitoring; and practical water quality management including use of mathematical models. They are followed by papers from the workshop on advances in the application of mathematical modelling to water quality management, which represent some of the current thinking on the problems and concepts of river basin management.

  18. Geology, exploration status of Uruguay's sedimentary basins

    SciTech Connect

    Goso, C.; Santa Ana, H. de )

    1994-02-07

    This article attempts to present the geological characteristics and tectonic and sedimentary evolution of Uruguayan basins and the extent to which they have been explored. Uruguay is on the Atlantic coast of South America. The country covers about 318,000 sq km, including offshore and onshore territories corresponding to more than 65% of the various sedimentary basins. Four basins underlie the country: the Norte basin, the Santa Lucia basin, the offshore Punta del Este basin, and the offshore-onshore Pelotas-Merin basin. The Norte basin is a Paleozoic basin while the others are Mesozoic basins. Each basin has been explored to a different extent, as this paper explains.

  19. Linked sequence stratigraphy and tectonics in the Sichuan continental foreland basin, Upper Triassic Xujiahe Formation, southwest China

    NASA Astrophysics Data System (ADS)

    Li, Yingjiao; Shao, Longyi; Eriksson, Kenneth A.; Tong, Xin; Gao, Caixia; Chen, Zhongshu

    2014-07-01

    SQ 2 and SQ3) and one phase of isostatic rebound (SQ4). Paleogeographic reconstruction of the Sichuan Basin in the Late Triassic indicates that the Longmen Mountains to the west, consisting of metamorphic, sedimentary and pre-Neoproterozoic basement granitoid rocks, was the major source of sediment to the foredeep depocenter. Subordinate sediment sources were the Xuefeng Mountains to the east to backbulge depocenters, and the Micang Mountains to the northwest during the late history of the basin. This study has demonstrated the viability of sequence stratigraphic analysis in continental successions in a foreland basin, and the influence of thrust loading on sequence development.

  20. Trinity river basin, Texas

    USGS Publications Warehouse

    Ulery, Randy L.; Van Metre, Peter C.; Crossfield, Allison S.

    1993-01-01

    In 1991 the Trinity River Basin National Water-Quality Assessment (NAWQA) will include assessments of surface-water and ground-water quality. Initial efforts have focused on identifying water-quality issues in the basin and on the environmental factors underlying those issues. Physical characteristics described include climate, geology, soils, vegetation, physiography, and hydrology. Cultural characteristics discussed include population distribution, land use and land cover, agricultural practices, water use, an reservoir operations. Major water-quality categories are identified and some of the implications of the environmental factors for water quality are presented.

  1. [Impact of the dynamics of human settlement on tsetse and trypanosomosis distribution in the Mouhoun river basin (Burkina Faso)].

    PubMed

    Rouamba, J; Jamonneau, V; Sidibé, I; Solano, P; Courtin, F

    2009-03-01

    In Burkina Faso, the Mouhoun river basin (formerly "Black Volta") constitutes a historical focus of Human (HAT) and Animal (AAT) African Trypanosomoses, both transmitted by tsetse flies. Nowadays, HAT seems to have disappeared from this area, while AAT still causes severe economic losses. In order to explain these different epidemiological situations, we undertook a geographical study based on the analysis of aerial pictures between 1952 and 2007, and field surveys to collect medical, entomological, and veterinary data on trypanosomoses. Our results suggest that in this area, landscapes have been dramatically modified as a consequence of population growth, and in turn have had an impact on the number and distribution of tsetse flies. Combined with the historical medical action on HAT which probably led to the disappearance of T. b. gambiense, this environmental degradation and the development of hydrological structures provide explanations for the local disappearance of HAT, and for the maintenance of AAT. It appears necessary to extrapolate these studies to other areas in order to identify the factors explaining the presence/absence of trypanosomoses in the context of human population growth and climatic changes, in order to help to target priority areas for the control of these diseases. PMID:19353947

  2. Age, composition, and source of continental arc- and syn-collision granites of the Neoproterozoic Sergipano Belt, Southern Borborema Province, Brazil

    NASA Astrophysics Data System (ADS)

    Oliveira, Elson P.; Bueno, Juliana F.; McNaughton, Neal J.; Silva Filho, Adejardo F.; Nascimento, Rosemery S.; Donatti-Filho, José P.

    2015-03-01

    The Sergipano belt is the outcome of collision between the Pernambuco-Alagoas Domain (Massif) and the São Francisco Craton during Neoproterozoic assembly of West Gondwana. Although the understanding of the Sergipano belt evolution has improved significantly, the timing of emplacement, geochemistry and tectonic setting of granitic bodies in the belt is poorly known. We recognized two granite age groups: 630-618 Ma granites in the Canindé, Poço Redondo and Macururé domains, and 590-570 Ma granites in the Macururé metasedimentary domain. U-Pb SHRIMP zircon ages for granites of first age group indicated ages of 631 ± 4 Ma for the Sítios Novos granite, 623 ± 7 Ma for the Poço Redondo granite, 619 ± 3.3 Ma for the Lajedinho monzodiorite, and 618 ± 3 Ma for the Queimada Grande granodiorite. These granitoids are dominantly high-K calc-alkaline, magnesian, metaluminous, mafic enclave-rich (Queimada Grande and Lajedinho), or with abundant inherited zircon grains (Poço Redondo and Sitios Novos). Geochemical and isotope data allow us to propose that Sítios Novos and Poço Redondo granites are product of partial melting of Poço Redondo migmatites. Sr-Nd isotopes of the Queimada Grande granodiorite and Lajedinho monzodiorite suggest that their parental magma may have originated by mixing between a juvenile mafic source and a crustal component that could be the Poço Redondo migmatites or the Macururé metasediments. Other 630-618 Ma granites in the belt are the mafic enclave-rich Coronel João Sá granodiorite and the Camará tonalite in the Macururé sedimentary domain. These granites have similar geochemical and isotopic characteristics as the Lajedinho and Queimada Grande granitoids. We infer for the Camará tonalite and Coronel João Sá granodiorite that their parental magmas have had contributions from mafic lower crust and felsic upper crust, most probably from underthrust São Francisco Craton, or Pernambuco-Alagoas Domain. The younger 590-570 Ma granite

  3. Geochemistry, geochronology, and Sr-Nd isotopes of the Late Neoproterozoic Wadi Kid volcano-sedimentary rocks, Southern Sinai, Egypt: Implications for tectonic setting and crustal evolution

    NASA Astrophysics Data System (ADS)

    Moghazi, Abdel-Kader M.; Ali, Kamal A.; Wilde, Simon A.; Zhou, Qin; Andersen, Tom; Andresen, Arild; Abu El-Enen, Mahrous M.; Stern, Robert J.

    2012-12-01

    The Kid Group is one of the few exposures of Neoproterozoic metavolcano-sedimentary rocks in the basement of southern Sinai in the northernmost Arabian-Nubian Shield. It is divided into the mostly metamorphosed volcaniclastic Melhaq and siliciclastic Um Zariq formations in the north and the mostly volcanic Heib and Tarr formations in the south. The Heib, Tarr, and Melhaq formations reflect an intense episode of igneous activity and immature clastic deposition associated with core-complex formation during Ediacaran time, but Um Zariq metasediments are relicts of an older (Cryogenian) sedimentary sequence. The latter yielded detrital zircons with concordant ages as young as 647 ± 12 Ma, which may indicate that the protolith of Um Zariq schist was deposited after ~ 647 Ma but 19 concordant zircons gave a 206Pb/238U weighted mean age of 813 ± 6 Ma, which may represent the maximum depositional age of this unit. In contrast, a cluster of 11 concordant detrital zircons from the Melhaq Formation yield a weighted mean 206Pb/238U age of 615 ± 6 Ma. Zircons from Heib Formation rhyolite clast define a 206Pb/238U weighted mean age of 609 ± 5 Ma, which is taken to approximate the age of Heib and Tarr formation volcanism. Intrusive syenogranite sample from Wadi Kid yields a 206Pb/238U weighted mean age of 604 ± 5 Ma. These constraints indicate that shallow-dipping mylonites formed between 615 ± 6 Ma and 604 ± 5 Ma. Geochemical data for volcanic samples from the Melhaq and Heib formations and the granites show continuous major and trace element variations corresponding to those expected from fractional crystallization. The rocks are enriched in large ion lithophile and light rare earth elements, with negative Nb anomalies. These reflect magmas generated by melting of subduction-modified lithospheric mantle, an inference that is further supported by ɛNd(t) = + 2.1 to + 5.5. This mantle source obtained its trace element characteristics by interaction with fluids and melts

  4. 'East Basin' Panorama

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Click on the image for 'East Basin' Panorama (QTVR)

    NASA's Mars Exploration Rover Spirit used its panoramic camera to obtain this view of the impact feature called 'East Basin' to the northeast of 'Husband Hill.' The images combined into this mosaic were taken during Spirit's 653rd Martian day, or sol (Nov. 3, 2005), just before Spirit descended eastward onto 'Haskin Ridge.' The view is about 150 degrees wide. It is an approximately true-color rendering generated using the camera's 750-nanometer, 530-nanometer, and 480-nanometer filters.

    Dark features on the far side of the basin, just left of center in this view, are basaltic sand deposits that were emplaced on the lee sides of hills by northwesterly winds. Haskin Ridge is visible along the right margin of the image, capped by a light-toned layer of rock. Spirit investigated the light-toned rock unit after taking this image. The basaltic plains located east of the 'Columbia Hills' can be seen in the distance beyond 'East Basin.' The rim of Thira crater is just visible on the distant horizon some 15 kilometers (9.3 miles) away.

  5. Archaean and Palaeoproterozoic gneisses reworked during a Neoproterozoic (Pan-African) high-grade event in the Mozambique belt of East Africa: Structural relationships and zircon ages from the Kidatu area, central Tanzania

    NASA Astrophysics Data System (ADS)

    Vogt, M.; Kröner, A.; Poller, U.; Sommer, H.; Muhongo, S.; Wingate, M. T. D.

    2006-06-01

    This study presents new zircon ages and Sm-Nd whole-rock isotopic compositions for high-grade gneisses from the Udzungwa Mountain area in the central part of the Mozambique belt, Tanzania. The study area comprises a succession of layered granulite-facies para- and orthogneisses, mostly retrograded to amphibolite-facies. The original intrusive contacts became obscured or severely modified during non-coaxial ductile deformation, and extensive shearing occurred during retrogression. Structures reflecting the early deformational history were mostly obscured when the rocks were transported into the lower crust as documented by severe flattening. Only the fragmented gneisses in the eastern part of the area testify to a brittle regime. Structures in narrow low strain zones that predate the currently observed layering are preserved in rootless isoclinal folds and boudins. Magmatic and detrital zircons from tonalitic to felsic orthogneisses and a metapelite sample were dated using the U-Pb and Pb-Pb evaporation methods and SHRIMP II. Cathodoluminiscence images reveal ubiquitous xenocrystic cores, rimmed by clear, unzoned overgrowth due to high-grade metamorphism. Discordant U-Pb data therefore reflect core-rim relationships, and it was not always possible to obtain precise crystallisation ages. The analyses reveal Neoarchaean, Palaeoproterozoic and Neoproterozoic protolith ages. Nd isotopic systematics yielded strongly negative ɛNd( t) -values and Neoarchaean to Palaeoproterozoic model ages, even for gneisses emplaced in the Neoproterozoic. The trace element distribution suggests upper crustal derivation of the gneisses. Therefore, our study provides evidence that recycling of older crust played a major role during the evolution of the Kidatu area. Neoarchaean rocks are interpreted to represent fragments of the Tanzania craton. Our results, together with those of earlier workers, lead to the conclusion that the central part of the Mozambique belt mainly consists of ancient

  6. Composition, age, and origin of the ~620 Ma Humr Akarim and Humrat Mukbid A-type granites: no evidence for pre-Neoproterozoic basement in the Eastern Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Ali, Kamal A.; Moghazi, Abdel-Kader M.; Maurice, Ayman E.; Omar, Sayed A.; Wang, Qiang; Wilde, Simon A.; Moussa, Ewais M.; Manton, William I.; Stern, Robert J.

    2012-10-01

    The Humr Akarim and Humrat Mukbid plutons, in the central Eastern Desert of Egypt, are late Neoproterozoic post-collisional alkaline A-type granites. Humr Akarim and Humrat Mukbid plutonic rocks consist of subsolvus alkali granites and a subordinate roof facies of albite granite, which hosts greisen and Sn-Mo-mineralized quartz veins; textural and field evidence strongly suggest the presence of late magmatic F-rich fluids. The granites are Si-alkali rich, Mg-Ca-Ti poor with high Rb/Sr (20-123), and low K/Rb (27-65). They are enriched in high field strength elements (e.g., Nb, Ta, Zr, Y, U, Th) and heavy rare earth elements (La n /Yb n = 0.27-0.95) and exhibit significant tetrad effects in REE patterns. These geochemical attributes indicate that granite trace element distribution was controlled by crystal fractionation as well as interaction with fluorine-rich magmatic fluids. U-Pb SHRIMP zircon dating indicates an age of ~630-620 Ma but with abundant evidence that zircons were affected by late corrosive fluids (e.g., discordance, high common Pb). ɛNd at 620 Ma ranges from +3.4 to +6.8 (mean = +5.0) for Humr Akarim granitic rocks and from +4.8 to +7.5 (mean = +5.8) for Humrat Mukbid granitic rocks. Some slightly older zircons (~740 Ma, 703 Ma) may have been inherited from older granites in the region. Our U-Pb zircon data and Nd isotope results indicate a juvenile magma source of Neoproterozoic age like that responsible for forming most other ANS crust and refute previous conclusions that pre-Neoproterozoic continental crust was involved in the generation of the studied granites.

  7. Regional setting and characteristics of the Neoproterozoic Wadi Hamama Zn-Cu-Ag-Au prospect: evidence for an intra-oceanic island arc-hosted volcanogenic hydrothermal system

    NASA Astrophysics Data System (ADS)

    Abd El-Rahman, Yasser; Surour, Adel A.; El-Manawi, Abdel Hamid W.; El-Dougdoug, Abdel-Monem A.; Omar, Sayed

    2015-04-01

    The Wadi Hamama area is a volcanogenic Zn-Cu-Au-Ag prospect. It is hosted by a Neoproterozoic bimodal-mafic sequence, which comprises basalt, dacite and rhyolite along with volcaniclastic rocks. The rocks have a low-K tholeiitic affinity and are enriched in large ion lithophile elements over high field strength elements, which indicated their formation in an intra-oceanic island arc tectonic setting. The area was intruded by a tonalite-trondhjemite body, which has an intra-oceanic island arc affinity and later by diorite, which has a cordilleran-margin geochemical affinity. These rock units were intruded by post-tectonic granite dykes, which have a within-plate geochemical signature. There is a quartz-carbonate horizon extending along the contact between the basalt and the volcaniclastic rocks, mainly banded and lapilli tuffs. This horizon is of exhalative origin and is underlain by a mushroom-shaped alteration zone extending from the horizon down to the massive basalt. The footwall alteration is characterized by a silica-rich core surrounded by a thick chlorite sheath. Both the quartz-carbonate horizon and the footwall-altered rocks enclose historical trenches and pits. Sulfide-rich core samples are enriched in Zn, relative to Cu, and in Ag, which indicates the low-temperature nature of the hydrothermal system. The prospect was affected by supergene processes, which led to the widespread occurrence of secondary copper minerals and gold enrichment relative to the leached base metals, especially Zn. The prospect formed through a limited rifting of an intra-oceanic island arc which resulted in the formation of a small-scale volcanogenic Zn-Cu-Ag-Au prospect.

  8. Redox condition of the late Neoproterozoic pelagic deep ocean: 57Fe Mössbauer analyses of pelagic mudstones in the Ediacaran accretionary complex, Wales, UK

    NASA Astrophysics Data System (ADS)

    Sato, Tomohiko; Sawaki, Yusuke; Asanuma, Hisashi; Fujisaki, Wataru; Okada, Yoshihiro; Maruyama, Shigenori; Isozaki, Yukio; Shozugawa, Katsumi; Matsuo, Motoyuki; Windley, Brian F.

    2015-11-01

    We report geological and geochemical analysis of Neoproterozoic pelagic deep-sea mudstones in an accretionary complex in Lleyn, Wales, UK. Ocean plate stratigraphy at Porth Felen, NW Lleyn, consists of mid-ocean ridge basalt (> 4 m), bedded dolostone (2 m), black mudstone (5 m), hemipelagic siliceous mudstone (1 m,) and turbiditic sandstone (15 m), in ascending order. The absence of terrigenous clastics confirms that the black and siliceous mudstone was deposited in a pelagic deep-sea. Based on the youngest U-Pb age (564 Ma) of detrital zircons separated from overlying sandstone, the deep-sea black mudstone was deposited in the late Ediacaran. The 5 m-thick black mudstone contains the following distinctive lithologies: (i) black mudstone with thin pyritic layers (0.8 m), (ii) alternation of black mudstone and gray/dark gray siliceous mudstone (2.4 m), (iii) thinly-laminated dark gray shale (1 m), and (iv) black mudstone with thin pyritic layers (1 m). 57Fe Mössbauer spectroscopy confirms that these black mudstones contain pyrite without hematite. In contrast, red bedded claystones (no younger than 542 Ma) in the neighboring Braich section contain hematite as their main iron mineral. These deep-sea mudstones in the Lleyn Peninsula record a change of redox condition on the pelagic deep-sea floor during the Ediacaran. The black mudstone at Porth Felen shows that deep-sea anoxia existed in the late Ediacaran. The eventual change from a reducing to an oxidizing deep-sea environment likely occurred in the late Ediacaran (ca. 564-542 Ma).

  9. U-Pb zircon geochronology, petrochemical and Sr-Nd isotopic characteristic of Late Neoproterozoic granitoid of the Bornaward Complex (Bardaskan-NE Iran)

    NASA Astrophysics Data System (ADS)

    Bagherzadeh, R. Monazzami; Karimpour, M. H.; Farmer, G. Lang; Stern, C. R.; Santos, J. F.; Rahimi, B.; Heidarian Shahri, M. R.

    2015-11-01

    The Bornaward Granitoid Complex (BGC) in the Taknar Zone is located in the northeast of Central Iranian Block. The BGC consists of granite, alkaligranite, syenogranite, leucogranite, granophyre, monzogranite, granodiorite, tonalite and diorite that have intruded into the center of Taknar Zone. These intrusive rocks affected by low grade metamorphism. Because of there are no reliable isotope dating data, for the Bornaward Granitoid Complex rocks have been proposed discordant ages (Jurassic, Cretaceous or even younger ages) by many studies. In the present study, new isotopic information based on zircon U-Pb dating has revealed the origin and time of the formation of the BGC. These new results do not confirm previously proposed ages. The results obtained from zircon U-Pb dating of the BGC rocks suggest late-Neoproterozoic (Precambrian) age (540-550 Ma). The Bornaward Granitoid Complex is middle-high metaluminous to lower-middle peraluminous and belongs to tholeiite, calc-alkaline to high-K calc-alkaline rock series with enrichment in LIL (Cs, Rb and Ba, U, K, Zr, Y, Th) and depletion in HIL (Sr and Nb, Ta, Ti) elements. Chondrite-normalized Rare Earth Elements (REE) plots indicate minor enrichment of LREE compared to HREE, and strong negative anomaly of Eu compared to other Rare Earth Elements. Furthermore, initial 87Sr/86Sr and 143Nd/144Nd range from 0.70351 to 0.71689 and 0.511585 to 0.512061, respectively, and initial εNd isotope values for granite, granodiorite and diorite range from -6.73 to 2.52. These all indicate that the BGC has derived from partial melting of distinct basement source regions with very high initial 87Sr/86Sr and undergoing extensive crustal contamination (S-type granite).

  10. Late Neoproterozoic post-collisional mafic magmatism in the Arabian-Nubian Shield: A case study from Wadi El-Mahash gabbroic intrusion in southeast Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Khalil, A. E. S.; Obeid, M. A.; Azer, M. K.

    2015-05-01

    Late Neoproterozoic gabbroic intrusion of Wadi El-Mahash lays in the northwestern sector of the Arabian-Nubian Shield (ANS) which is exposed in the Sinai Peninsula, Egypt. It occurs as small undeformed mafic body intruding metamorphic rocks and truncated by alkali granites. Field relations, mineralogical characteristics and chemical data indicate that Wadi El-Mahash mafic intrusion is unmetamorphosed. The intrusion consists of medium- to coarse-grained gabbroic rocks. The medium-grained one (hornblende gabbro) formed nearly simultaneous with, or slightly later than, the coarse-grained rock (pyroxene-hornblende gabbro). Geochemically, the gabbroic samples are characterized by enrichment in LILE relative to HFSE and LREE relative to HREE [(La/Yb)n = 4.52-6.35]. They show geochemical signature similar to other post-collisional gabbroic intrusions of south Sinai. The subduction-related geochemical characteristic of the gabbroic intrusion of Wadi El-Mahash can be explained by partial melting of a relatively enriched lithospheric mantle source following a previous subduction process in the ANS. The gabbroic rocks crystallized at pressures between 6.2 and 6.5 kbar (∼15-20 km depth) with crystallization temperature ranging from 750 to 970 °C. Lithospheric delamination model is suggested for the mafic magma of Wadi El-Mahash since delamination of lithospheric mantle allowed asthenosphere to rise rapidly causing partial melting and generating gabbroic melts. The produced melts then infiltrated the base of the crust to induce the post-collisional magmatism in south Sinai.

  11. Mineralogy and geochemistry of Neoproterozoic siliceous manganese formations from Ntui-Betamba (Cameroon Pan-African Fold Belt): implications for mineral exploration

    NASA Astrophysics Data System (ADS)

    Timoleon, Ngnotue; Sylvestre, Ganno; Kouankap Nono, Gus Djibril; Paul, Nzenti Jean

    2015-07-01

    The siliceous manganese formations from Ntui-Betamba area have been studied with the aim to constrain their mineralogy, geochemistry, and genesis. Neoproterozoic manganese-bearing rocks at Ntui-Betamba include garnet-galaxite-bearing quartzite and galaxite-bearing quartzite that—besides a characteristic quartz, spessartine-garnet, and galaxite (MnAl2O4) assemblage—comprises also graphite and rutile. Galaxite crystals show chemical zoning from core to rim due to the change in composition from galaxite to cryptomelane. Bulk rock geochemistry reveals that the studied rocks are characterized by high SiO2 content (52.83 wt%). They are enriched in Fe2O3 and Al2O3 and display Mn/Fe ratio of 1.2. MnO concentrations are high in galaxite-bearing quartzite (16 wt%), and moderate (8.03 wt%) in garnet-galaxite-bearing quartzite. The transition trace metal (Co, Cu, and Ni) contents are lower, with Co and Cu markedly depleted relative to Ni, and variable contents of Zn. The REE pattern of garnet-galaxite-bearing quartzite shows Ce-positive anomaly similar to the hydrogenous sediment, but differs from the later with strong Eu-negative anomaly and the lack of weak positive anomaly in Yb, whereas the galaxite-bearing quartzite is characterized by the lack of Ce anomaly and the weak Eu-negative anomaly. Both rocks show HREE content close to that of hydrothermal sediment and exhibit flat HREE trend. The high contents of silica, iron, and aluminum, together with the Co/Zn ratios (~0.3) and the contrasting behavior of REE, suggest that the studied manganese-bearing rocks are of sedimentary origin probably derived from a mixed hydrothermal-hydrogenous source. The high content of Mn-bearing minerals in these rocks represents indicators of concealed or buried mineralization and could be used as exploration guide.

  12. Neoproterozoic uppermost Haut-Shiloango Subgroup (West Congo Supergroup, Democratic Republic of Congo): Misinterpreted stromatolites and implications for sea-level fluctuations before the onset of the Marinoan glaciation

    NASA Astrophysics Data System (ADS)

    Delpomdor, F.; Kant, F.; Préat, A.

    2014-02-01

    The middle Neoproterozoic carbonate-dominated uppermost Haut-Shiloango Subgroup (Sh8h and Sh8i members) in the Lower-Congo Province of the Democratic Republic of Congo is considered as recording pre-glacial shallow-marine sedimentation with stromatolitic reefs overlain by the Upper Diamictite Formation. We investigated these stromatolitic carbonates in order to highlight their biogenicity. Newly defined lithofacies and geochemical analyses (stable isotopes, major, trace and REE+Y elements) are used to provide insights into the origins of the depositional events that occurred immediately before Marinoan global glaciation. These insights should in turn provide constraints on the models developed for this glaciation event.

  13. Rift flank uplift and thermal evolution of an intracratonic rift basin (eastern Canada) determined by combined apatite and zircon (U-Th)/He thermochronology

    NASA Astrophysics Data System (ADS)

    Hardie, Rebecca; Schneider, David; Metcalf, James; Flowers, Rebecca

    2015-04-01

    As a significant portion of the world's oil reserves are retrieved from rift systems, a better understanding of the timing of thermal evolution and burial history of these systems will increase the potential for the discovery of hydrocarbon-bearing rifts. The Ottawa Embayment of the St. Lawrence Platform of eastern Canada is a reactivated intracratonic rift basin related to the opening of the Iapetus Ocean at ca. 620-570 Ma, followed by the formation of the well-developed continental passive margin. Siliciclastic sediments derived from the adjacent uplifted Neoproterozoic Grenville basement provide the basin fill material. Apatite and zircon (U-Th)/He thermochronology allows for low-temperature analysis across the exposed crystalline rift flank into the synrift sedimentary sequence to resolve the unroofing, burial and subsidence history of the region. Samples were collected along a ~250 km NE-SW transect, oblique to the axis of the rift, from Mont-Tremblant, Québec (~900 m) to the central axis of the Paleozoic rift in the Southern Ontario Lowlands (~300 m). Targets included Neoproterozoic metamorphic rocks of the Grenville Province along the rift flank and basinal Cambro-Ordovician Potsdam Group. Samples from the rift flank yield zircon ages from ca. 650 Ma to ca. 560 Ma and apatite ages from ca. 290 Ma to ca. 190 Ma, with a weak positive correlation between age and grain size. Zircon ages demonstrate a strong negative correlation with radiation damage: as eU increases, age decreases. By incorporating (U-Th)/He ages with regional constraints in the thermal modelling program HeFTy, viable temperature time paths for the region can be determined. Through inverse and forward modeling, preliminary rift flank (U-Th)/He ages correspond to post-Grenville cooling with <4 km of post-Carboniferous burial. The data define slow and long episodes of syn- to post-rift cooling with rates between 0.4 and 0.1 °C/Ma. (U-Th)/He dating of samples along the full-length of the transect

  14. Bransfield Basin and Cordilleran Orogenesis

    NASA Astrophysics Data System (ADS)

    Dalziel, I. W.; Austin, J. A.; Barker, D. H.; Christensen, G. L.

    2003-12-01

    Tectonic uplift of the Andean Cordillera was initiated in the mid-Cretaceous with inversion of a composite marginal basin along 7500 km of the continental margin of South America, from Peru to Tierra del Fuego and the North Scotia Ridge. In the southernmost Andes, from 50-56 degrees S, the quasi-oceanic floor of this basin is preserved in the obducted ophiolitic rocks of the Rocas Verdes (Green Rocks) basin. We suggest that the basin beneath Bransfield Strait, 61-64 degrees S, separating the South Shetland Islands from the Antarctic Peninsula, constitutes a modern analog for the Rocas Verdes basin. Marine geophysical studies of Bransfield basin have been undertaken over the past 12 years by the Institute for Geophysics, University of Texas at Austin, under the auspices of the Ocean Sciences Division and United States Antarctic Program, National Science Foundation. These studies have elucidated the structure and evolution of Bransfield basin for comparison with the Rocas Verdes basin, with a view to eventual forward modeling of the evolution of a hypothetical cordilleran orogen by compression and inversion of the basin. These are the processes that can be observed in the tectonic transformation of the Rocas Verdes basin into the southernmost Andean cordillera, as South America moved rapidly westward in an Atlantic-Indian ocean hot-spot reference frame during the mid-Cretaceous. Multi-channel reflection seismic data from the Bransfield basin reveal an asymmetric structural architecture characterized by steeply-dipping normal faults flanking the South Shetlands island arc and gently dipping listric normal faults along the Antarctic Peninsula margin. Normal fault polarity reversals appear to be related to distributed loci of magmatic activity within the basin. This architecture is remarkably similar to that deduced from field structural studies of the Rocas Verdes basin. Notably, the oceanward-dipping, low angle normal faults along the Antarctic Peninsula margin

  15. Newly Discovered Martian Impact Basins

    NASA Technical Reports Server (NTRS)

    Stam, M.

    1985-01-01

    Three previously unrecognized Martian impact basins were discovered through detailed mapping of landforms, structures and terrains near Cassini and Al Qahira basins. Al Qahira A lies on the Martian dichotomy boundary and intersects the older basin, Al Qahira. It has four rings that are expressed by a variety of landforms. Southwestward Al Qahira A is out by a younger Basin, Al Qahira B. Al Qahira B is a highly degraded basin with one identifiable ring. Its ring is expressed by a few massifs, knobs and inward-facing scarps, but is recognized by the distributions of wrinkle ridges and plains units. Cassini A lies southward of the younger Cassini Basin and is intersected by it. It probably has four rings. The importance of detailed mapping of various types of landforms and terrains to the discovery of basins on Mars are demonstrated.

  16. Natural frequency of regular basins

    NASA Astrophysics Data System (ADS)

    Tjandra, Sugih S.; Pudjaprasetya, S. R.

    2014-03-01

    Similar to the vibration of a guitar string or an elastic membrane, water waves in an enclosed basin undergo standing oscillatory waves, also known as seiches. The resonant (eigen) periods of seiches are determined by water depth and geometry of the basin. For regular basins, explicit formulas are available. Resonance occurs when the dominant frequency of external force matches the eigen frequency of the basin. In this paper, we implement the conservative finite volume scheme to 2D shallow water equation to simulate resonance in closed basins. Further, we would like to use this scheme and utilizing energy spectra of the recorded signal to extract resonant periods of arbitrary basins. But here we first test the procedure for getting resonant periods of a square closed basin. The numerical resonant periods that we obtain are comparable with those from analytical formulas.

  17. Mixed carbonate-siliciclastic sedimentation in forebulge grabens: An example from the Ediacaran Bambuí Group, São Francisco Basin, Brazil

    NASA Astrophysics Data System (ADS)

    Reis, Humberto L. S.; Suss, João F.

    2016-06-01

    Mixed carbonate-siliciclastic successions have been described in multiple Phanerozoic sedimentary settings recording the dynamic interplay of tectonics, eustasy, climate, in situ carbonate production, and variations in siliciclastic sediment supply. The Ediacaran Bambuí 1st-order sequence (i.e., Bambuí Group) covers most of the intracratonic São Francisco basin (southeast Brazil) and encompasses thick packages of carbonate and fine- to coarse-grained siliciclastic strata. Recording a marine foreland basin stage that developed in the São Francisco plate during the Neoproterozoic-early Paleozoic West Gondwana assembly, the Ediacaran deposits unconformably overlie Archean-Paleoproterozoic metamorphic assemblages of the Sete Lagoas basement high and fill a series of kilometer-long grabens in the southern São Francisco basin. Seismic data reveal that these troughs developed through the extensional reactivation of ancient basement structures along with the tectonically driven forebulge uplift of the Sete Lagoas high, in the early evolutionary stages of the Bambuí basin cycle. Based on the detailed description of continuous drill cores of a well recently drilled during hydrocarbon exploration campaigns, we recognized two transgressive-regressive 2nd-order sequences preserved within one of the focused grabens: (i) Sequence 1 includes the glaciogenic deposits of the basal Carrancas Formation that grade upward into the carbonate ramp successions of the Sete Lagoas Formation; (ii) Sequence 2 contains the siliciclastic-dominated and deep water to deltaic strata of the Serra de Santa Helena Formation and passes upward into peritidal carbonates of the Lagoa do Jacaré Formation. These sedimentary successions encompass suites of retrogradational, aggradational, and progradational lower-rank cycles and are bounded by erosional surfaces. Regional seismic interpretation, well data, and the available literature indicate that most of these deposits and their correlatives are

  18. Global analysis of intraplate basins

    NASA Astrophysics Data System (ADS)

    Heine, C.; Mueller, D. R.; Dyksterhuis, S.

    2005-12-01

    Broad intraplate sedimentary basins often show a mismatch of lithospheric extension factors compared to those inferred from sediment thickness and subsidence modelling, not conforming to the current understanding of rift basin evolution. Mostly, these basins are underlain by a very heterogeneous and structurally complex basement which has been formed as a product of Phanerozoic continent-continent or terrane/arc-continent collision and is usually referred to as being accretionary. Most likely, the basin-underlying substrate is one of the key factors controlling the style of extension. In order to investigate and model the geodynamic framework and mechanics controlling formation and evolution of these long-term depositional regions, we have been analysing a global set of more than 200 basins using various remotely sensed geophysical data sets and relational geospatial databases. We have compared elevation, crustal and sediment thickness, heatflow, crustal structure, basin ages and -geometries with computed differential beta, anomalous tectonic subsidence, and differential extension factor grids for these basins. The crust/mantle interactions in the basin regions are investigated using plate tectonic reconstructions in a mantle convection framework for the last 160 Ma. Characteristic parameters and patterns derived from this global analysis are then used to generate a classification scheme, to estimate the misfit between models derived from either crustal thinning or sediment thickness, and as input for extension models using particle-in-cell finite element codes. Basins with high differential extension values include the ``classical'' intraplate-basins, like the Michigan Basin in North America, the Zaire Basin in Africa, basins of the Arabian Penisula, and the West Siberian Basin. According to our global analysis so far, these basins show, that with increasing basin age, the amount of crustal extension vs. the extension values estimated from sediment thickness

  19. Buried-euxenic-basin model sets Tarim basin potential

    SciTech Connect

    Hsu, K.J. )

    1994-11-28

    The Tarim basin is the largest of the three large sedimentary basins of Northwest China. The North and Southwest depressions of Tarim are underlain by thick sediments and very thin crust. The maximum sediment thickness is more than 15 km. Of the several oil fields of Tarim, the three major fields were discovered during the last decade, on the north flank of the North depression and on the Central Tarim Uplift. The major targets of Tarim, according to the buried-euxenic-basin model, should be upper Paleozoic and lower Mesozoic reservoirs trapping oil and gas condensates from lower Paleozoic source beds. The paper describes the basin and gives a historical perspective of exploration activities and discoveries. It then explains how this basin can be interpreted by the buried-euxenic-basin model. The buried-euxenic-basin model postulates four stages of geologic evolution: (1) Sinian and early Paleozoic platform sedimentation on relic arcs and deep-marine sedimentation in back-arc basins in Xinjiang; (2) Late Paleozoic foreland-basin sedimentation in north Tarim; (3) Mesozoic and Paleogene continental deposition, subsidence under sedimentary load; and (4) Neogene pull-apart basin, wrench faulting and extension.

  20. Canada Basin revealed

    USGS Publications Warehouse

    Mosher, David C.; Shimeld, John; Hutchinson, Deborah R.; Chian, D; Lebedeva-Ivanova, Nina; Jackson, Ruth

    2012-01-01

    More than 15,000 line-km of new regional seismic reflection and refraction data in the western Arctic Ocean provide insights into the tectonic and sedimentologic history of Canada Basin, permitting development of new geologic understanding in one of Earth's last frontiers. These new data support a rotational opening model for southern Canada Basin. There is a central basement ridge possibly representing an extinct spreading center with oceanic crustal velocities and blocky basement morphology characteristic of spreading centre crust surrounding this ridge. Basement elevation is lower in the south, mostly due to sediment loading subsidence. The sedimentary succession is thickest in the southern Beaufort Sea region, reaching more than 15 km, and generally thins to the north and west. In the north, grabens and half-grabens are indicative of extension. Alpha-Mendeleev Ridge is a large igneous province in northern Amerasia Basin, presumably emplaced synchronously with basin formation. It overprints most of northern Canada Basin structure. The seafloor and sedimentary succession of Canada Basin is remarkably flat-lying in its central region, with little bathymetric change over most of its extent. Reflections that correlate over 100s of kms comprise most of the succession and on-lap bathymetric and basement highs. They are interpreted as representing deposits from unconfined turbidity current flows. Sediment distribution patterns reflect changing source directions during the basin’s history. Initially, probably late Cretaceous to Paleocene synrift sediments sourced from the Alaska and Mackenzie-Beaufort margins. This unit shows a progressive series of onlap unconformities with a younging trend towards Alpha and Northwind ridges, likely a response to contemporaneous subsidence. Sediment source direction appeared to shift to the Canadian Arctic Archipelago margin for the Eocene and Oligocene, likely due to uplift of Arctic islands during the Eurekan Orogeny. The final

  1. Insights from heavy minerals and zircon U-Pb ages into the middle Miocene-Pliocene provenance evolution of the Yinggehai Basin, northwestern South China Sea

    NASA Astrophysics Data System (ADS)

    Jiang, Tao; Cao, Licheng; Xie, Xinong; Wang, Zhenfeng; Li, Xushen; Zhang, Yingzhao; Zhang, Daojun; Sun, Hui

    2015-08-01

    The well-preserved Cenozoic sedimentary record in the Yinggehai Basin, South China Sea, is suitable to explore the tectonic and climatic evolution of SE Asia. Red River, a large-scale fluvial system in this region, was previously regarded as the major sediment source for the basin. Here we combine heavy mineral analysis and detrital zircon U-Pb dating to shed new light on the middle Miocene-Pliocene provenance evolution at a basin scale. The results clearly reveal potential source areas additional to the Red River. Sediments have been delivered to the proximal areas from Hainan Island, as indicated by the high zircon content and the Yanshanian U-Pb ages in the southern segment of the Yingdong Slope. A provenance from Central Vietnam is explicitly discerned in the upper Miocene of the Central Depression, where sediments are characterized by few metamorphic heavy minerals and the U-Pb age pattern peaking at around 250 Ma and 440 Ma. Coeval large-scale relative sea-level fall and rapid exhumation along the Vietnamese margin together may have facilitated this long-distance sediment transport. Provenance of sediments from the Red River seems to change over time. Song Lo River, on the north side of the main stream, probably flowed from the NE and carried Neoproterozoic-early Paleozoic zircons to the Yinggehai Basin during the middle Miocene. Since the late Miocene, rocks along the Red River Fault Zone have become the dominant source. Subsequently, widespread metamorphic minerals in the Central Depression of the Yinggehai Basin, combined with the strong river incision and high offshore sedimentation rates, indicate an increased sediment supply from the Red River in the Pliocene.

  2. Provenance and paleogeography of the Devonian Durazno Group, southern Parana Basin in Uruguay

    NASA Astrophysics Data System (ADS)

    Uriz, N. J.; Cingolani, C. A.; Basei, M. A. S.; Blanco, G.; Abre, P.; Portillo, N. S.; Siccardi, A.

    2016-03-01

    A succession of Devonian cover rocks occurs in outcrop and in the subsurface of central-northern Uruguay where they were deposited in an intracratonic basin. This Durazno Group comprises three distinct stratigraphic units, namely the Cerrezuelo, Cordobés and La Paloma formations. The Durazno Group does not exceed 300 m of average thickness and preserves a transgressive-regressive cycle within a shallow-marine siliciclastic shelf platform, and is characterized by an assemblage of invertebrate fossils of Malvinokaffric affinity especially within the Lower Devonian Cordobés shales. The sedimentary provenance of the Durazno Group was determined using petrography, geochemistry, and morphological studies of detrital zircons as well as their U-Pb ages. Sandstone petrography of Cerrezuelo and La Paloma sequences shows that they have a dominantly quartz-feldspathic composition with a minor contribution of other minerals. Whole-rock geochemical data indicate that alteration was strong in each of the three formations studied; chondritic-normalized REE patterns essentially parallel to PAAS, the presence of a negative Eu-anomaly, and Th/Sc and La/Hf ratios point to an average source composition similar to UCC or slightly more felsic. Within the Cerrezuelo Formation, recycling of older volcano-metasedimentary sources is interpreted from Zr/Sc ratios and high Hf, Zr, and REE concentrations. U-Pb detrital zircon age populations of the Cerrezuelo and La Paloma formations indicate that the principal source terranes are of Neoproterozoic age, but include also minor populations derived from Mesoproterozoic and Archean-Paleoproterozoic rocks. A provenance from the Cuchilla Dionisio-Dom Feliciano, Nico Pérez and Piedra Alta terranes of Uruguay and southern Brazil is likely. This study establishes an intracratonic extensional tectonic setting during Durazno time. Considering provenance age sources, regional paleocurrent distributions and the established orogenic history recorded in SW

  3. Tracking the Archean-Proterozoic suture zone in the northeastern Great Basin, Nevada and Utah

    USGS Publications Warehouse

    Rodriguez, B.D.; Williams, J.M.

    2008-01-01

    It is important to know whether major mining districts in north-central Nevada are underlain by crust of the Archean Wyoming craton, known to contain major orogenic gold deposits or, alternatively, by accreted crust of the Paleoproterozoic Mojave province. Determining the location and orientation of the Archean-Proterozoic suture zone between these provinces is also important because it may influence subsequent patterns of sedimentation, deformation, magmatism, and hydrothermal activity. The suture zone is exposed in northeastern Utah and south-western Wyoming and exhibits a southwest strike. In the Great Basin, the suture zone strike is poorly constrained because it is largely concealed below a Neoproterozoic-Paleozoic miogeocline and Cenozoic basin fill. Two-dimensional resistivity modeling of three regional north-south magnetotelluric sounding profiles in western Utah, north-central Nevada, and northeastern Nevada, and one east-west profile in northeastern Nevada, reveals a deeply penetrating (>10 km depth), broad (tens of kilometers) conductor (1-20 ohm-meters) that may be the Archean-Proterozoic suture zone, which formed during Early Proterozoic rifting of the continent and subsequent Proterozoic accretion. This major crustal conductor changes strike direction from southwest in Utah to northwest in eastern Nevada, where it broadens to ???100 km width that correlates with early Paleozoic rifting of the continent. Our results suggest that the major gold belts may be over-isolated blocks of Archean crust, so Phanerozoic mineral deposits in this region may be produced, at least in part, from recycled Archean gold. Future mineral exploration to the east may yield large gold tonnages. ?? 2008 Geological Society of America.

  4. Mercury's Caloris Basin

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Mercury: Computer Photomosaic of the Caloris Basin

    The largest basin on Mercury (1300 km or 800 miles across) was named Caloris (Greek for 'hot') because it is one of the two areas on the planet that face the Sun at perihelion.

    The Image Processing Lab at NASA's Jet Propulsion Laboratory produced this photomosaic using computer software and techniques developed for use in processing planetary data. The Mariner 10 spacecraft imaged the region during its initial flyby of the planet.

    The Mariner 10 spacecraft was launched in 1974. The spacecraft took images of Venus in February 1974 on the way to three encounters with Mercury in March and September 1974 and March 1975. The spacecraft took more than 7,000 images of Mercury, Venus, the Earth and the Moon during its mission.

    The Mariner 10 Mission was managed by the Jet Propulsion Laboratory for NASA's Office of Space Science in Washington, D.C.

  5. Climate change and land-use change impact on Western African river basins

    NASA Astrophysics Data System (ADS)

    Mariotti, Laura; Coppola, Erika; Giorgi, Filippo

    2010-05-01

    The main resource in western Africa is agriculture and therefore availability and quality of fresh water resources threaten food production in many regions. Quantifying the impact of climate and land-use change in very vulnerable regions like western Africa is therefore of crucial importance for developing appropriate adaptation and mitigation strategies. In this work the International Center for theoretical Physic (ICTP) regional climate model (RegCM3) is used to perform a 120 (1980-2100) years climate change simulation under the A1B scenario using ECHAM5 as boundary condition (BC). To further investigate which it would be the combined effect of the land-use change together with the climate change a 10 years time simulation has been completed using the future projected land-use from IIASA (The International Institute for Applied Systems Analysis). Both simulations have been coupled with a physical based fully distributed hydrological model (CHyM) to asses which it would be the final effect of climate and land-use change on the river discharge. The two rivers used for this analysis are the Niger and Volta basin. The CHyM model has been validated coupling fist the hydrological model with a perfect boundary regional model simulation using ERA-interim as BC and using the runoff observations available along the two river basins. The model is able to reproduce the monthly seasonal cycle in both river basins reasonably well, therefore this allow us to use the same setting for a climate and land-use change simulation. Two hydrological time slice simulations have been performed with and without land-use change included. Results are presented and discussed for the monsoon season (JJA) on a station based, for the same stations used for validation purposed, but also the spatial change in discharge is presented in both cases and compared with the simple precipitation change observed in the region. Although the portion of change in precipitation due to the green house gases

  6. Evaluation of Satellite Based Rainfall Estimation over Major River Basins in Africa

    NASA Astrophysics Data System (ADS)

    Bitew, M. M.; Gebremichael, M.

    2012-12-01

    Accuracy of satellite rainfall estimates are poorly known over Africa because of sparse ground based observations. We examined four widely used high resolution satellite products: the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) which is near-real-time (TMPA 3B42RT), the TMPA method post-real-time research version seven (TMPA 3B42v7), the Climate Prediction Center's morphing technique (CMORPH) and the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN). The main objective of the evaluation was to assess the performance of the satellite based estimates in capturing the overall climatological blueprints of rainfall over Africa at various spatio-temporal scale, and inter-comparison of the estimates across the various climatological regimes in Africa. In the tropical, complex terrain region of East Africa, the results show poor skills of satellite rainfall in capturing elevation dependent rainfall structure; microwave based CMORPH and 3B42RT estimates provide relatively accurate estimate of rainfall in high elevation areas but showed excessive overestimation in low elevation, and merging GTS-based rain gauges with the Satellite-Only products deteriorated the accuracy of rainfall estimation in high elevation areas of the Blue Nile. In this study we present the findings over seven other large and sparsely gauged river basins: Sengal (419,659 km2), Jubba (497,655 km2), Volta (407,093 km2), Ogooue (223,656 km2), Ubangi (613,202 km2) Okavango (721,277 km2) and Kasai (925,172 km2) river basins representing different topography and climate system between 250 N and 250 S. The accuracy of those products is assessed using a ground based GPCC datasets and through inter-comparision among the products between 2003 -2011 at a resolution of 25 km by 25-km and 3 hr data. Based on these datasets we present annual, seasonal and monthly spatial structure of rainfall in terms of depth, rainy days

  7. ADVANCED CHEMISTRY BASINS MODEL

    SciTech Connect

    William Goddard III; Lawrence Cathles III; Mario Blanco; Paul Manhardt; Peter Meulbroek; Yongchun Tang

    2004-05-01

    The advanced Chemistry Basin Model project has been operative for 48 months. During this period, about half the project tasks are on projected schedule. On average the project is somewhat behind schedule (90%). Unanticipated issues are causing model integration to take longer then scheduled, delaying final debugging and manual development. It is anticipated that a short extension will be required to fulfill all contract obligations.

  8. Petroleum basin studies

    SciTech Connect

    Shannon, P.M. ); Naylor, D. )

    1989-01-01

    This book reviews the tectonic setting, basin development and history of exploration of a number of selected petroleum provinces located in a variety of settings in the Middle East, North Sea, Nigeria, the Rocky Mountains, Gabon and China. This book illustrates how ideas and models developed in one area may be applied to other regions. Regional reviews and the reassessment of petroleum provinces are presented.

  9. Albuquerque Basin seismic network

    USGS Publications Warehouse

    Jaksha, Lawrence H.; Locke, Jerry; Thompson, J.B.; Garcia, Alvin

    1977-01-01

    The U.S. Geological Survey has recently completed the installation of a seismic network around the Albuquerque Basin in New Mexico. The network consists of two seismometer arrays, a thirteen-station array monitoring an area of approximately 28,000 km 2 and an eight-element array monitoring the area immediately adjacent to the Albuquerque Seismological Laboratory. This report describes the instrumentation deployed in the network.

  10. Dimension of fractal basin boundaries

    SciTech Connect

    Park, B.S.

    1988-01-01

    In many dynamical systems, multiple attractors coexist for certain parameter ranges. The set of initial conditions that asymptotically approach each attractor is its basin of attraction. These basins can be intertwined on arbitrary small scales. Basin boundary can be either smooth or fractal. Dynamical systems that have fractal basin boundary show final state sensitivity of the initial conditions. A measure of this sensitivity (uncertainty exponent {alpha}) is related to the dimension of the basin boundary d = D - {alpha}, where D is the dimension of the phase space and d is the dimension of the basin boundary. At metamorphosis values of the parameter, there might happen a conversion from smooth to fractal basin boundary (smooth-fractal metamorphosis) or a conversion from fractal to another fractal basin boundary characteristically different from the previous fractal one (fractal-fractal metamorphosis). The dimension changes continuously with the parameter except at the metamorphosis values where the dimension of the basin boundary jumps discontinuously. We chose the Henon map and the forced damped pendulum to investigate this. Scaling of the basin volumes near the metamorphosis values of the parameter is also being studied for the Henon map. Observations are explained analytically by using low dimensional model map.

  11. Advanced Chemistry Basins Model

    SciTech Connect

    William Goddard; Mario Blanco; Lawrence Cathles; Paul Manhardt; Peter Meulbroek; Yongchun Tang

    2002-11-10

    The DOE-funded Advanced Chemistry Basin model project is intended to develop a public domain, user-friendly basin modeling software under PC or low end workstation environment that predicts hydrocarbon generation, expulsion, migration and chemistry. The main features of the software are that it will: (1) afford users the most flexible way to choose or enter kinetic parameters for different maturity indicators; (2) afford users the most flexible way to choose or enter compositional kinetic parameters to predict hydrocarbon composition (e.g., gas/oil ratio (GOR), wax content, API gravity, etc.) at different kerogen maturities; (3) calculate the chemistry, fluxes and physical properties of all hydrocarbon phases (gas, liquid and solid) along the primary and secondary migration pathways of the basin and predict the location and intensity of phase fractionation, mixing, gas washing, etc.; and (4) predict the location and intensity of de-asphaltene processes. The project has be operative for 36 months, and is on schedule for a successful completion at the end of FY 2003.

  12. Great Basin Paleontological Bibliography

    USGS Publications Warehouse

    Blodgett, Robert B.; Zhang, Ning; Hofstra, Albert H.; Morrow, Jared R.

    2007-01-01

    Introduction This work was conceived as a derivative product for 'The Metallogeny of the Great Basin' project of the Mineral Resources Program of the U.S. Geological Survey. In the course of preparing a fossil database for the Great Basin that could be accessed from the Internet, it was determined that a comprehensive paleontological bibliography must first be compiled, something that had not previously been done. This bibliography includes published papers and abstracts as well as unpublished theses and dissertations on fossils and stratigraphy in Nevada and adjoining portions of California and Utah. This bibliography is broken into first-order headings by geologic age, secondary headings by taxonomic group, followed by ancillary topics of interest to both paleontologists and stratigraphers; paleoecology, stratigraphy, sedimentary petrology, paleogeography, tectonics, and petroleum potential. References were derived from usage of Georef, consultation with numerous paleontologists and geologists working in the Great Basin, and literature currently on hand with the authors. As this is a Web-accessible bibliography, we hope to periodically update it with new citations or older references that we have missed during this compilation. Hence, the authors would be grateful to receive notice of any new or old papers that the readers think should be added. As a final note, we gratefully acknowledge the helpful reviews provided by A. Elizabeth J. Crafford (Anchorage, Alaska) and William R. Page (USGS, Denver, Colorado).

  13. Caribbean basin framework, 3: Southern Central America and Colombian basin

    SciTech Connect

    Kolarsky, R.A.; Mann, P. )

    1991-03-01

    The authors recognize three basin-forming periods in southern Central America (Panama, Costa Rica, southern Nicaragua) that they attempt to correlate with events in the Colombian basin (Bowland, 1984): (1) Early-Late Cretaceous island arc formation and growth of the Central American island arc and Late Cretaceous formation of the Colombian basin oceanic plateau. During latest Cretaceous time, pelagic carbonate sediments blanketed the Central American island arc in Panama and Costa Rica and elevated blocks on the Colombian basin oceanic plateau; (2) middle Eocene-middle Miocene island arc uplift and erosion. During this interval, influx of distal terrigenous turbidites in most areas of Panama, Costa Rica, and the Colombian basin marks the uplift and erosion of the Central American island arc. In the Colombian basin, turbidites fill in basement relief and accumulate to thicknesses up to 2 km in the deepest part of the basin. In Costa Rica, sedimentation was concentrated in fore-arc (Terraba) and back-arc (El Limon) basins; (3) late Miocene-Recent accelerated uplift and erosion of segments of the Central American arc. Influx of proximal terrigenous turbidites and alluvial fans in most areas of Panama, Costa Rica, and the Colombian basin marks collision of the Panama arc with the South American continent (late Miocene early Pliocene) and collision of the Cocos Ridge with the Costa Rican arc (late Pleistocene). The Cocos Ridge collision inverted the Terraba and El Limon basins. The Panama arc collision produced northeast-striking left-lateral strike-slip faults and fault-related basins throughout Panama as Panama moved northwest over the Colombian basin.

  14. Understanding Reservoir Quality in the Petroleum System of the Ediacaran-Early Cambrian Ara Group (South Oman Salt Basin):

    NASA Astrophysics Data System (ADS)

    Becker, S.; Reuning, L.; Kukla, P.; Marquez, X.; Farquani, S.; Rawahi, Z.

    2009-04-01

    The Ediacaran-Early Cambrian Ara Group of the South Oman Salt Basin consists of six carbonate to evaporite (rock salt, gypsum) sequences. These Ara Group carbonates are termed A0C to A6C from the bottom towards the top of the basin. Differential loading of locally 5 km thick Cambrian to Ordovician clastics onto the mobile rock salt of the Ara Group caused growth of isolated salt diapirs, which resulted in strong fragmentation and faulting of the carbonate intervals into several isolated so-called ‘stringers'. These carbonate stringers represent a unique intra-salt petroleum system, which has been successfully explored in recent years. Initially the reservoir properties of the carbonate stringers were controlled by their depositional facies. After deposition, the stringers experienced a complex diagenetic history from the shallow to the deep burial realm. Diagenetic processes like anhydrite and halite plugging exerted a negative affect on poroperm properties, whereas e.g. calcite dissolution had a positive affect. Our goal is to detect spatial and temporal distribution patterns of diagenetic phases and their effect on reservoir properties. Mineralogy, rock fabrics, paragenetic relationships and geochemistry of ~ 200 samples from several petroleum wells from the late Neoproterozoic A2C interval were analyzed. For a mineralogical overview the samples were measured by XRD - powder diffraction, whereas the rock fabric was studied by thin section analysis and if required additionally with SEM. This high-resolution dataset was used in combination with external petrophysical observations to defined porosity-permeability trends for different rock-fabric groups according to LUCIA (1995). The spatial distribution of these petrophysical characteristics will be displayed in field-scale distribution maps of the analyzed diagenetic phases. The expected integrated 3D - diagenesis model will enable better predictions of the reservoir qualities in the Ara fields and will

  15. Triple-oxygen and sulfur isotopic evidence for diagenetic overprinting of carbonate-associated sulfate in Neoproterozoic samples from a drill core

    NASA Astrophysics Data System (ADS)

    Peng, Y.; Wang, W.; Pratt, L. M.; Zhou, C.; Bao, H.; Hayles, J. A.

    2014-12-01

    Carbonate-associated sulfate (CAS) is used in many studies to reconstruct the isotopic composition of ancient seawater sulfate and to infer stages in the development of Earth's oxygenated atmosphere. CAS is acid extractable and commonly is referred to as structurally substituted sulfate in carbonate minerals. Several recent studies, however, have raised concerns about sulfate overprinting during early or late diagenesis, including contamination by modern secondary atmospheric sulfate (SAS) and by sulfide oxidation during laboratory processing. To test for overprinting and contamination, we studied the isotopic composition of sulfate in a bedded carbonate succession of the Neoproterozoic Lantian Formation, South China. Materials were obtained from a drilling core (635Ma- 551Ma). Water-leachable sulfate (WLS), acid-leachable sulfate (ALS, i. e. extracted CAS), and chromium-reducible sulfur (CRS) were sequentially extracted out and triple oxygen isotopic compositions of WLS and ALS were analyzed as well as sulfur isotope of WLS, ALS, and CRS. We also analyzed the oxygen isotope of sulfate resulting from pyrite oxidation at a condition similar to the extraction of WLS and ALS in the laboratory and the δ18O value is at ~ -1.4‰ (VSMOW). The slightly negative ∆17O values of all WLS and ALS indicates that the ALS was not contaminated by sulfate of modern SAS. The WLS from the first 24 hours with consistently negative values of δ18O (about -11.0‰) and low δ34S values (about +5‰) suggests that the WLS resulted from sulfide oxidation in water with very negative δ18O values, likely glacial melt-water in the distant past, which had likely soaked the whole stratigraphy of Lantian Formation for a long time. The WLS also comprised a significant fraction of ALS because both δ18O and δ34S of ALS have wide ranges, from -6.9 to +15.8‰, and +12.7 to +31.7‰, respectively. More importantly, there is a strong positive correlation between δ18O and δ34S of ALS. Our

  16. Geodynamic models for the Neoproterozoic Yenisey Ridge orogenic belt (western Siberian Craton continental margin) and evolution of granitoid and alkaline magmatism

    NASA Astrophysics Data System (ADS)

    Vernikovsky, Valery; Vernikovskaya, Antonina

    2010-05-01

    of the forming of accretional orogens in the western margin of the Siberian craton in the Neoproterozoic.

  17. Neoproterozoic A-type granitoids of the central and southern Appalachians: Intraplate magmatism associated with episodic rifting of the Rodinian supercontinent

    USGS Publications Warehouse

    Tollo, R.P.; Aleinikoff, J.N.; Bartholomew, M.J.; Rankin, D.W.

    2004-01-01

    Emplacement of compositionally distinctive granitic plutons accompanied two pulses (765-680 and 620-550Ma) of crustal extension that affected the Rodinian craton at the present location of the central Appalachians during the Neoproterozoic. The dominantly metaluminous plutons display mineralogical and geochemical characteristics of A-type granites including high FeO t/MgO ratios, high abundances of Nb, Zr, Y, Ta, and REE (except Eu), and low concentrations of Sc, Ba, Sr, and Eu. These dike-like, sheet complexes occur throughout the Blue Ridge province of Virginia and North Carolina, and were emplaced at shallow levels in continental crust during active extension, forming locally multiple-intrusive plutons elongated perpendicular to the axis of extension. New U-Pb zircon ages obtained from the Polly Wright Cove (706??4Ma) and Suck Mountain (680??4Ma) plutons indicate that metaluminous magmas continued to be replenished near the end of the first pulse of rifting. The Suck Mountain body is presently the youngest known igneous body associated with earlier rifting. U-Pb zircon ages for the Pound Ridge Granite Gneiss (562??5Ma) and Yonkers Gneiss (563??2Ma) in the Manhattan prong of southeastern New York constitute the first evidence of plutonic felsic activity associated with the later period of rifting in the U.S. Appalachians, and suggest that similar melt-generation processes were operative during both intervals of crustal extension. Fractionation processes involving primary minerals were responsible for much of the compositional variation within individual plutons. Compositions of mapped lithologic units in a subset of plutons studied in detail define overlapping data arrays, indicating that, throughout the province, similar petrologic processes operated locally on magmas that became successively more chemically evolved. Limited variation in source-sensitive Y/Nb and Yb/Ta ratios is consistent with results of melting experiments and indicates that metaluminous

  18. Methanogenesis produces strong 13C-enrichment in stromatolites of Lagoa Salgada, Brazil: A modern analogue for Palaeo-/Neoproterozoic stromatolites?

    NASA Astrophysics Data System (ADS)

    Meister, Patrick; Birgel, Daniel; Lundberg, Rebecca; Horat, Thomas; Bontognali, Tomaso; Bahniuk Rumbelsperger, Anelize; Rezende, Carlos; Vásconcelos, Crisógono; McKenzie, Judith A.

    2015-04-01

    methanogenesis. Radiogenic Sr-isotope compositions support a mixed water scenario with continental ground or surface water as additional source of alkalinity. Evaporative concentration during dry periods increased the carbonate saturation state in the brine inducing spontaneous or perhaps microbially catalysed precipitation of carbonate. Unusually 13C-enriched stomatolitic deposits also appear in the geological record during prolonged periods in the Palaeo- and Neoproterozoic. Thus, Lagoa Salgada represents a possible modern analogue to conditions that may have been widespread in the Proterozoic, at times when low sulphate concentrations in seawater allowed methanogens to prevail over sulphate-reducing bacteria.

  19. Sources of granite magmatism in the Embu Terrane (Ribeira Belt, Brazil): Neoproterozoic crust recycling constrained by elemental and isotope (Sr-Nd-Pb) geochemistry

    NASA Astrophysics Data System (ADS)

    Alves, Adriana; Janasi, Valdecir de Assis; Campos Neto, Mario da Costa

    2016-07-01

    Whole rock elemental and Sr-Nd isotope geochemistry and in situ K-feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810-580 Ma), and is dominated by crust-derived relatively low-T (850-750 °C, zircon saturation) biotite granites to biotite-muscovite granites. Two Cryogenian plutons show the least negative εNdt (-8 to -10) and highest mg# (30-40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI ∼ 1.2) ∼660 Ma Serra do Quebra-Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI = 0.96-1.00) ∼ 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ∼810 Ma. The predominant Ediacaran (595-580 Ma) plutons have a spread of compositions from biotite granites with SiO2 as low as ∼65% (e.g., Itapeti, Mauá, Sabaúna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ∼75% SiO2). εNdT are characteristically negative (-12 to -18), with corresponding Nd TDM indicating sources with Paleoproterozoic mean crustal ages (2.0-2.5 Ga). The Guacuri and Santa Branca muscovite granites have the more negative εNdt, highest 87Sr/86Srt (0.714-0.717) and lowest 208Pb/206Pb and 207Pb/206Pb, consistent with an old metasedimentary source with low time-integrated Rb/Sr. However, a positive Nd-Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Mauá granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The

  20. Petrogenesis and tectonic implications of the Neoproterozoic Datian mafic-ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China

    NASA Astrophysics Data System (ADS)

    Yang, Yi-Jin; Zhu, Wei-Guang; Bai, Zhong-Jie; Zhong, Hong; Ye, Xian-Tao; Fan, Hong-Peng

    2016-03-01

    Mafic-ultramafic dykes are important geological markers that can punctuate the onset of crustal extension during the breakup of a continent and provide valuable information on the mantle source. This study reports secondary ion mass spectroscopy zircon and baddeleyite U-Pb ages, elemental and Nd isotopic data for the Datian mafic-ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China. Two kinds of rocks are confirmed: the picritic rock and the dolerite. Based on petrographic and geochemical features, the dolerite dykes are further subdivided into two groups: Group I mafic and Group II mafic dykes, which emplaced at ~760 Ma (zircon U-Pb) and ~800 Ma (zircon and baddeleyite U-Pb), respectively. All samples from the picritic rocks and the Group I mafic rocks show the features of high-Ti and alkaline basaltic magma in composition as well as "humped" trace element patterns, which are similar to those of typical alkaline basalts associated with continental rifts except for the slightly negative Nb-Ta anomalies. The Group II mafic rocks display the features of low-Ti and tholeiitic magma, moderately enriched in LILE and LREE, and characterized by distinctively negative Nb-Ta anomalies. The primary magmas of the picritic rocks and the Group I mafic rocks were generated from ca 25 % partial melting of an OIB-like, Nd isotopically depleted but incompatible elements relatively enriched mantle source within a garnet stable field. The Group II mafic rocks crystallized from crustal contaminated mafic magmas that were derived from a spinel-bearing sub-continental lithospheric mantle source, because of low ratios of La/Yb, Ti/Y and Sm/Yb. Geochemical features suggest that these groups of mafic-ultramafic dykes were formed in a continental rift setting, but derived from different mantle sources. In combination with other Neoproterozoic igneous rocks in the western margin of Yangtze Block, it is suggested that the Datian mafic-ultramafic dykes in the Panzhihua area

  1. Moho depth and crustal structure of the Siberian Craton and the West Siberian Basin: An appraisal of existing seismic data

    NASA Astrophysics Data System (ADS)

    Cherepanova, Yulia; Artemieva, Irina M.; Thybo, Hans

    2013-04-01

    We present a digital model of the crustal structure of the Archean-Proterozoic Siberian craton and the Paleozoic-Mesozoic West Siberian basin, based on seismic profiles published since 1960 in international and Russian journals, books, theses and reports. Data quality was assessed and quantitatively assigned to each profile based on acquisition and interpretation method and completeness of the model. The database represents major improvement in coverage and resolution with a nominal sample interval of 50 km before interpolation onto a uniform grid. It includes depth to Moho, thickness and average P-wave velocity of five crustal layers (sediments, and upper, middle, lower, and lowermost crust) and Pn velocity. Results are presented in maps and cross-sections, which demonstrate strong crustal heterogeneity. Crustal structure shows weak correlation with tectono-thermal age and strong correlation with tectonic setting. Sedimentary thickness varies from 0-3 km in stable craton to 10-20 km in extended regions. Typical Moho depths are 44-46 km in stable Archean crust, 40-42 km in Proterozoic craton and Neoproterozoic/Paleozoic orogens, 35-38 km in extended cratonic crust, and 38-40 km in the West Siberian basin. Average crustal velocity is ~6.2-6.4 km/s, ranging from <5.8 km/s in deep sedimentary basins to ~6.6 km/s around the up-to 54 km thick Anabar shield crust. The cratonic crust generally consists of three layers and has no high-velocity lowermost crust (Vp~7.4 km/s), which is observed only in magmatic areas. Upper mantle Pn velocities are generally ~8.2 km/s in the craton and West Siberian Basin, lower in Baikalian and Caledonian areas, higher in the Tunguska and Viluy basins, and abnormally high (8.6-8.9 km/s) around kimberlite fields. We provide an extensive summary of the tectonic and geodynamic evolution of the region and discuss the origin of crustal heterogeneity and processes of crustal evolution in Precambrian cratons and major Phanerozoic basins and rift

  2. Great Basin paleontological database

    USGS Publications Warehouse

    Zhang, N.; Blodgett, R.B.; Hofstra, A.H.

    2008-01-01

    The U.S. Geological Survey has constructed a paleontological database for the Great Basin physiographic province that can be served over the World Wide Web for data entry, queries, displays, and retrievals. It is similar to the web-database solution that we constructed for Alaskan paleontological data (www.alaskafossil.org). The first phase of this effort was to compile a paleontological bibliography for Nevada and portions of adjacent states in the Great Basin that has recently been completed. In addition, we are also compiling paleontological reports (Known as E&R reports) of the U.S. Geological Survey, which are another extensive source of l,egacy data for this region. Initial population of the database benefited from a recently published conodont data set and is otherwise focused on Devonian and Mississippian localities because strata of this age host important sedimentary exhalative (sedex) Au, Zn, and barite resources and enormons Carlin-type An deposits. In addition, these strata are the most important petroleum source rocks in the region, and record the transition from extension to contraction associated with the Antler orogeny, the Alamo meteorite impact, and biotic crises associated with global oceanic anoxic events. The finished product will provide an invaluable tool for future geologic mapping, paleontological research, and mineral resource investigations in the Great Basin, making paleontological data acquired over nearly the past 150 yr readily available over the World Wide Web. A description of the structure of the database and the web interface developed for this effort are provided herein. This database is being used ws a model for a National Paleontological Database (which we am currently developing for the U.S. Geological Survey) as well as for other paleontological databases now being developed in other parts of the globe. ?? 2008 Geological Society of America.

  3. Apollo Basin, Moon: Estimation of Impact Conditions

    NASA Astrophysics Data System (ADS)

    Echaurren, J. C.

    2015-07-01

    The Apollo Basin is a, pre-Nectarian, multi-ring basin located within the large South Pole-Aitken Basin (SPA). Multispectral data from both Galileo and Clementine showed that the composition of materials in Apollo is distinct…

  4. Advanced Chemistry Basins Model

    SciTech Connect

    Blanco, Mario; Cathles, Lawrence; Manhardt, Paul; Meulbroek, Peter; Tang, Yongchun

    2003-02-13

    The objective of this project is to: (1) Develop a database of additional and better maturity indicators for paleo-heat flow calibration; (2) Develop maturation models capable of predicting the chemical composition of hydrocarbons produced by a specific kerogen as a function of maturity, heating rate, etc.; assemble a compositional kinetic database of representative kerogens; (3) Develop a 4 phase equation of state-flash model that can define the physical properties (viscosity, density, etc.) of the products of kerogen maturation, and phase transitions that occur along secondary migration pathways; (4) Build a conventional basin model and incorporate new maturity indicators and data bases in a user-friendly way; (5) Develop an algorithm which combines the volume change and viscosities of the compositional maturation model to predict the chemistry of the hydrocarbons that will be expelled from the kerogen to the secondary migration pathways; (6) Develop an algorithm that predicts the flow of hydrocarbons along secondary migration pathways, accounts for mixing of miscible hydrocarbon components along the pathway, and calculates the phase fractionation that will occur as the hydrocarbons move upward down the geothermal and fluid pressure gradients in the basin; and (7) Integrate the above components into a functional model implemented on a PC or low cost workstation.

  5. Atlantic marginal basins of Africa

    SciTech Connect

    Moore, G.T.

    1988-02-01

    The over 10,000-km long Atlantic margin of Africa is divisible into thirty basins or segments of the margin that collectively contain over 18.6 x 10/sup 6/ km/sup 3/ of syn-breakup and post-breakup sediments. Twenty of these basins contain a sufficiently thick volume of sediments to be considered prospects. These basins lie, at least partially, within the 200 m isobath. The distribution of source rocks is broad enough to give potential to each of these basins. The sedimentation patterns, tectonics, and timing of events differ from basin to basin and are related directly to the margin's complex history. Two spreading modes exist: rift and transform. Rifting dates from Late Triassic-Early Jurassic in the northwest to Early Cretaceous south of the Niger Delta. A complex transform fault system separated these two margins. Deep-water communication between the two basins became established in the middle Cretaceous. This Mesozoic-Cenozoic cycle of rifting and seafloor spreading has segmented the margin and where observable, basins tend to be bounded by these segments.

  6. MASSACHUSETTS DRAINAGE SUB-BASINS

    EPA Science Inventory

    MassGIS has produced a statewide digital datalayer of the approximately 2300 sub-basins as defined and used by the USGS Water Resources Division and the Mass Water Resources Commission and as modified by Executive Office of Environmental Affairs (EOEA) agencies. These sub-basins...

  7. Estancia Basin dynamic water budget.

    SciTech Connect

    Thomas, Richard P.

    2004-09-01

    The Estancia Basin lies about 30 miles to the east of Albuquerque, NM. It is a closed basin in terms of surface water and is somewhat isolated in terms of groundwater. Historically, the primary natural outlet for both surface water and groundwater has been evaporation from the salt lakes in the southeastern portion of the basin. There are no significant watercourses that flow into this basin and groundwater recharge is minimal. During the 20th Century, agriculture grew to become the major user of groundwater in the basin. Significant declines in groundwater levels have accompanied this agricultural use. Domestic and municipal use of the basin groundwater is increasing as Albuquerque population continues to spill eastward into the basin, but this use is projected to be less than 1% of agricultural use well into the 21st Century. This Water Budget model keeps track of the water balance within the basin. The model considers the amount of water entering the basin and leaving the basin. Since there is no significant surface water component within this basin, the balance of water in the groundwater aquifer constitutes the primary component of this balance. Inflow is based on assumptions for recharge made by earlier researchers. Outflow from the basin is the summation of the depletion from all basin water uses. The model user can control future water use within the basin via slider bars that set values for population growth, water system per-capita use, agricultural acreage, and the types of agricultural diversion. The user can also adjust recharge and natural discharge within the limits of uncertainty for those parameters. The model runs for 100 years beginning in 1940 and ending in 2040. During the first 55 years model results can be compared to historical data and estimates of groundwater use. The last 45 years are predictive. The model was calibrated to match to New Mexico Office of State Engineer (NMOSE) estimates of aquifer storage during the historical period by

  8. Stratigraphic modeling of sedimentary basins

    SciTech Connect

    Aigner, T. ); Lawrence, D.T. )

    1990-11-01

    A two-dimensional stratigraphic forward model has been successfully applied and calibrated in clastic, carbonate, and mixed clastic/carbonate regimes. Primary input parameters are subsidence, sea level, volume of clastics, and carbonate growth potential. Program output includes sequence geometries, facies distribution lithology distribution, chronostratigraphic plots, burial history plots, thermal and maturity histories, and crossplots. The program may be used to predict reservoir distribution, to constrain interpretations of well and seismic data, to rapidly test exploration scenarios in frontier basins, and to evaluate the fundamental controls on observed basin stratigraphy. Applications to data sets from Main Pass (US Gulf Coast), Offshore Sarawak (Malaysia), Rub'al Khali basin (Oman), Paris basin (France), and Baltimore Canyon (US East Coast) demonstrate that the program can be used to simulate stratigraphy on a basin-wide scale as well as on the scale of individual prospects.

  9. The deep Ionian Basin revisited

    NASA Astrophysics Data System (ADS)

    Tugend, Julie; Chamot-Rooke, Nicolas; Arsenikos, Stavros; Frizon de Lamotte, Dominique; Blanpied, Christian

    2016-04-01

    The deep Eastern Mediterranean Basins (Ionian and Herodotus) are characterized by thick sedimentary sequences overlying an extremely thinned basement evidenced from different geophysical methods. Yet, the nature of the crust (continental or oceanic) and the timing of the extreme crustal and lithosphere thinning in the different sub-basins remain highly controversial, casting doubts on the tectonic setting related to the formation of this segment of the North Gondwana paleo-margin. We focus on the Ionian Basin located at the western termination of the Eastern Mediterranean with the aim of identifying, characterizing and mapping the deepest sedimentary sequences. We present tentative age correlations relying on calibrations and observations from the surrounding margins and basins (Malta shelf and Escarpment, Cyrenaica margin, Sirte Basin, Apulian Platform). Two-ship deep refraction seismic data (Expanding Spread Profiles from the PASIPHAE cruise) combined with reprocessed reflection data (from the ARCHIMEDE survey) enabled us to present a homogeneous seismic stratigraphy across the basin and to investigate the velocity structure of its basement. Based on our results, and on a review of geological and geophysical observations, we suggest an Upper Triassic-Early Dogger age for the formation of the deep Ionian Basin. The nature of the underlying basement remains uncertain, both highly-thinned continental and slow-spreading type oceanic crust being compatible with the available constraints. The narrow size and relatively short-lived evolution of the Ionian Basin lead us to suggest that it is more likely the remnant of an immature oceanic basin than of a stable oceanic domain. Eventually, upscaling these results at the scale of the Eastern Mediterranean Basins highlights the complex interaction observed between two propagating oceans: The Central Atlantic and Neo-Tethys.

  10. RESERVES IN WESTERN BASINS PART IV: WIND RIVER BASIN

    SciTech Connect

    Robert Caldwell

    1998-04-01

    Vast quantities of natural gas are entrapped within various tight formations in the Rocky Mountain area. This report seeks to quantify what proportion of that resource can be considered recoverable under today's technological and economic conditions and discusses factors controlling recovery. The ultimate goal of this project is to encourage development of tight gas reserves by industry through reducing the technical and economic risks of locating, drilling and completing commercial tight gas wells. This report is the fourth in a series and focuses on the Wind River Basin located in west central Wyoming. The first three reports presented analyses of the tight gas reserves and resources in the Greater Green River Basin (Scotia, 1993), Piceance Basin (Scotia, 1995) and the Uinta Basin (Scotia, 1995). Since each report is a stand-alone document, duplication of language will exist where common aspects are discussed. This study, and the previous three, describe basin-centered gas deposits (Masters, 1979) which contain vast quantities of natural gas entrapped in low permeability (tight), overpressured sandstones occupying a central basin location. Such deposits are generally continuous and are not conventionally trapped by a structural or stratigraphic seal. Rather, the tight character of the reservoirs prevents rapid migration of the gas, and where rates of gas generation exceed rates of escape, an overpressured basin-centered gas deposit results (Spencer, 1987). Since the temperature is a primary controlling factor for the onset and rate of gas generation, these deposits exist in the deeper, central parts of a basin where temperatures generally exceed 200 F and drill depths exceed 8,000 feet. The abbreviation OPT (overpressured tight) is used when referring to sandstone reservoirs that comprise the basin-centered gas deposit. Because the gas resources trapped in this setting are so large, they represent an important source of future gas supply, prompting studies to

  11. Mineralogy and geochemistry of the Late Neoproterozoic rare metal granitoids of Gabal El-Ineigi pluton, Northern Arabian-Nubian Shield, Egypt

    NASA Astrophysics Data System (ADS)

    Sami, Mabrouk; Ntaflos, Theodoros; Mohamed, Haroun A.; Farahat, Esam S.; Ahmed, Awaad F.

    2016-04-01

    characterize the late magmatic stage differentiation. On the other hand, the SG are remarkably enriched in Sr and Ba (58-76 and 299-422 ppm, respectively) and show a relatively invariable enrichment in light rare earth elements (LREEs). The extremely high 87Sr/86Sr (1.7491-2.5376) ratios of the AFG is almost related to the disturbance in the Rb-Sr isotope system at the proposed high temperature magma-fluid interaction. On the other hand, the Sr-Nd isotope systematics of the SG are characterized by a high initial 87Sr/86Sr ratios of 0.7087-0.7109 and ɛNd(t) values of +4.7 to +5.8, with depleted mantle model ages (tDM) between 0.82 and 0.98 Ga, implying a juvenile magma source of Neoproterozoic age, typical of other granitoids from the ANS continental crust.

  12. Timing of maturation of a Neoproterozoic oceanic arc during Pan-African Orogeny: the Asmlil complex (Anti-Atlas, South Morocco)

    NASA Astrophysics Data System (ADS)

    Triantafyllou, Antoine; Berger, Julien; Baele, Jean-Marc; Bruguier, Olivier; Diot, Hervé; Ennih, Nasser; Plissart, Gaëlle; Monnier, Christophe; Watlet, Arnaud; Vandycke, Sara

    2016-04-01

    Many intra-oceanic paleo-arcs are exposed in the Pan-African belt surrounding the West African Craton. In the Moroccan Anti-Atlas, remnants of Intra-Oceanic Subduction Zone (IOSZ) are preserved in few erosional windows moulded along the Anti-Atlas Major fault. These complexes highlight a Neoproterozoic paleo-suture made of 760 My back-arc ophiolites thrusted to the south onto a dismembered band of oceanic arc relics. The Asmlil arc complex, located in the southern part of the Bou Azzer inlier, is made of (i) 755 to 745 My- intermediate banded gneiss interpreted as metavolcanic products of a juvenile oceanic arc. This latter has been intruded by (ii) medium-grained hornblende-gabbro and dioritic magmas, in turn intruded by (iii) medium- to coarse grained hornblenditic-granodioritic decametric intrusions under sub-magmatic HT conditions. Hornblende-gabbros are made of garnet + amphibole/cpx relics + epidote + rutile paragenesis. Calculated pseudosections yielded P ~ 11-12 kbar for T ranging between 600 and 720°C for garnet growth. Measured Zr-in-rutile thermometer gave slightly higher temperature ranging between 710-790°C. On the field, garnet-rich leucocratic veinlets suggest that moderate partial melting of the mafic rock or localized dehydration reactions took place under garnet-granulite conditions (>800°C for hydrated chemical system). New geochronological data on garnet-bearing leucogabbros constrain their emplacement at 700 ±7 My (U-Pb zircon with low Th/U < 0.3). Cooling age (< 700°C) of these HP-HT rocks yielded to a younger age of 654 ±7 My (U-Pb method on rutile). Geochemical data of each mafic and ultramafic facies (hornblende gabbro, garnet-bearing facies and hornblendite) show typical arc signature (marked by e.g. Nb-Ta anomaly, (La/Sm)N: 0.8-1.6 ; (Nb/La) < 0.46 ; high Nb/Ba ratio ; 0.4 < K2O < 2.1 wt%). Intrusive granodioritic magmas show depleted HREE trend similar to granitoids in the Kohistan paleo-arc. Melting modeling suggests they are

  13. Zircon dating of Neoproterozoic and Cambrian ophiolites in West Mongolia and implications for the timing of orogenic processes in the central part of the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Jian, Ping; Kröner, Alfred; Jahn, Bor-ming; Windley, Brian F.; Shi, Yuruo; Zhang, Wei; Zhang, Fuqin; Miao, Laicheng; Tomurhuu, Dondov; Liu, Dunyi

    2014-06-01

    , we re-subdivide West Mongolia into: a latest Neoproterozoic-early Cambrian, arc-microcontinent collision zone north of the MML; a Cambrian Gobi Altai ophiolite-microcontinent collision zone and a Cambrian Trans-Altai forearc complex south of the MML. The central CAOB evolved in five phases: subduction initiation and arc formation (ca. 573 to > ca. 540 Ma); arc-microcontinent collision (ca. 535-524 Ma); a continuum of slab delamination, overthrusting, crustal thickening and surface uplift (ca. 519-482 Ma) in Northwest Mongolia; initiation of new subduction zones in South Mongolia (ca. 523-511 Ma); and continuing orogeny with local surface uplift. Overall, the current, documented timing of orogenic development in the central CAOB is largely consistent with a W/SW-Pacific style of evolution in terms of subduction initiation, short timescales of individual orogenies, and episodic subduction-collision during a continuing migration of subduction zones.

  14. Neoproterozoic chromite-bearing high-Mg diorites in the western part of the Jiangnan orogen, southern China: Geochemistry, petrogenesis and tectonic implications

    NASA Astrophysics Data System (ADS)

    Chen, Xin; Wang, Di; Wang, Xiao-Lei; Gao, Jian-Feng; Shu, Xu-Jie; Zhou, Jin-Cheng; Qi, Liang

    2014-07-01

    -stage model for the petrogenesis of the high-Mg diorites: 1) the mantle source was firstly metasomatized by melts from partial melting of subducting terrigenous sediments to form the enriched Nd-Hf isotopic characteristics; and then 2) the mantle-derived high-Mg mafic melts mixed with the crust-derived low-Mg granitic melts to form the high-Mg diorites and medium-Mg granodiorites. The occurrence of high-Mg diorites implies the existence of Neoproterozoic subduction-related metasomatism in the western part of the Jiangnan orogen.

  15. Petrography, geochemistry and U-Pb zircon age of the Matongo carbonatite Massif (Burundi): Implication for the Neoproterozoic geodynamic evolution of Central Africa

    NASA Astrophysics Data System (ADS)

    Midende, Gilbert; Boulvais, Philippe; Tack, Luc; Melcher, Frank; Gerdes, Axel; Dewaele, Stijn; Demaiffe, Daniel; Decrée, Sophie

    2014-12-01

    The Matongo carbonatite intrusion belongs to the Neoproterozoic Upper Ruvubu alkaline plutonic complex (URAPC), that is located in Burundi along the western branch of the East African Rift. Beside the Matongo carbonatite, the URAPC alkaline complex comprises feldspathoidal syenites, diorites, quartz-bearing syenites and granites. Three main facies have been recognized in the Matongo carbonatite: (1) Sövites represent the dominant facies. Two varieties have been recognized. A scarce coarse-grained sövite (sövite I), which is altered and poorly enriched in REE (4 < ΣREE < 8 ppm), is encountered in highly fractured zones. A fine-grained sövite (sövite II), which is made of saccharoidal calcite, commonly associated with apatite, aegirine and amphibole, is abundant in the intrusion. Sövite II is enriched in LREE (442 < ΣREE < 1550 ppm, 49 < LaN/YbN < 175). (2) Fe