Science.gov

Sample records for silurian foreland basin

  1. Sequences, cycles, and basin dynamics in the Silurian of the Appalachian Foreland Basin

    NASA Astrophysics Data System (ADS)

    Brett, Carlton E.; Goodman, William M.; LoDuca, Steven T.

    1990-12-01

    , roughly upward deepening (to slightly shallowing) successions of strata. In turn, sub-sequences are further divisible into widespread minor parasequences and parasequence sets, probably corresponding to 6th- and 5th-order cycles, respectively. The smaller scale units (0.2-5 mthick) commonly display an upward shallowing motif. The nested relationship of these cycles supports the hierarchical model of transgressive-regressive allocycles proposed by Busch and Rollins (1984). Niagaran cycles discussed herein are equivalent to third-, fourth- and fifth-order cycles and are traceable circumbasinally. Depocenters of successive sequences and sub-sequences display a pattern of eastward-westward-eastward basin-axis migration through the Silurian. During early Llandoverian, the Taconic (Queenston) deltaic complex began to subside, and the basin axis, depocenter, and eastern shoreline shifted eastward approximately 200 km over a 6 million year period. As the basin axis migrated eastward, the western basin ramp (forebulge) was repeatedly upwarded and eroded, resulting in the generation of regionally angular unconformities at the bases of sequences II, IV and VI. The pattern of unconformity (greatest to the west) suggests rise of the Algonquin Arch concomitant with eastward basin-axis migration. During the late Llandoverian to early Wenlockian, the Algonquin Arch subsided slightly, concurrently with a reversal in direction of basin-axis migration. During deposition of upper Clinton and Lockport-Vernon strata (sequences V, VI), the basin axis shifted approximately 300 km back to the west. Eastward migration of the basin axis corresponds with a time of tectonic quiescence and probable thrust-load relaxation. The abrupt reversal of migration in the late Llandoverian may be a signal of renewed thrusting in the hinterland at the onset of the Salinic Disturbance.

  2. Paleocurrent analysis of a deformed Devonian foreland basin in the northern Appalachians, Maine, USA

    USGS Publications Warehouse

    Bradley, D.C.; Hanson, L.S.

    2002-01-01

    New paleocurrent data indicate that the widespread Late Silurian and Devonian flysch and molasse succession in Maine was deposited in an ancestral, migrating foreland basin adjacent to an advancing Acadian orogenic belt. The foreland-basin sequence spread across a varied Silurian paleogeography of deep basins and small islands-the vestiges of an intraoceanic arc complex that not long before had collided with the Laurentian passive margin during the Ordovician Taconic Orogeny. We report paleocurrents from 43 sites representing 12 stratigraphic units, the most robust and consistent results coming from three units: Madrid Formation (southwesterly paleoflow), Carrabassett Formation (northerly paleoflow), and Seboomook Group (westerly paleoflow). Deformation and regional metamorphism are sufficiently intense to test the limits of paleocurrent analysis requiring particular care in retrodeformation. ?? 2002 Elsevier Science B.V. All rights reserved.

  3. Flexural bending of the Zagros foreland basin

    NASA Astrophysics Data System (ADS)

    Pirouz, Mortaza; Avouac, Jean-Philippe; Gualandi, Adriano; Hassanzadeh, Jamshid; Sternai, Pietro

    2017-09-01

    We constrain and model the geometry of the Zagros foreland to assess the equivalent elastic thickness of the northern edge of the Arabian plate and the loads that have originated due to the Arabia-Eurasia collision. The Oligo-Miocene Asmari formation, and its equivalents in Iraq and Syria, is used to estimate the post-collisional subsidence as they separate passive margin sediments from the younger foreland deposits. The depth to these formations is obtained by synthesizing a large database of well logs, seismic profiles and structural sections from the Mesopotamian basin and the Persian Gulf. The foreland depth varies along strike of the Zagros wedge between 1 and 6 km. The foreland is deepest beneath the Dezful embayment, in southwest Iran, and becomes shallower towards both ends. We investigate how the geometry of the foreland relates to the range topography loading based on simple flexural models. Deflection of the Arabian plate is modelled using point load distribution and convolution technique. The results show that the foreland depth is well predicted with a flexural model which assumes loading by the basin sedimentary fill, and thickened crust of the Zagros. The model also predicts a Moho depth consistent with Free-Air anomalies over the foreland and Zagros wedge. The equivalent elastic thickness of the flexed Arabian lithosphere is estimated to be ca. 50 km. We conclude that other sources of loading of the lithosphere, either related to the density variations (e.g. due to a possible lithospheric root) or dynamic origin (e.g. due to sublithospheric mantle flow or lithospheric buckling) have a negligible influence on the foreland geometry, Moho depth and topography of the Zagros. We calculate the shortening across the Zagros assuming conservation of crustal mass during deformation, trapping of all the sediments eroded from the range in the foreland, and an initial crustal thickness of 38 km. This calculation implies a minimum of 126 ± 18 km of crustal

  4. Foreland Basin Structures and Remote Sensing

    NASA Technical Reports Server (NTRS)

    Paylor, E. D.

    1985-01-01

    Rocky Mountain foreland basins are somewhat unique in that the basins may exhibit a variety of structural styles. It is generally agreed that shortening has occurred in the foreland basement but the cause is controversial: vertical vs compressional horizontal tectonics. Even when shortening is attributed to compression, the attitude (dip) of the fault plane and whether the horizontal or vertical component of movement is dominant is unconstrained. The controversy is difficult to resolve from surface data alone due to the variety of possible interpretations. Detailed surface mapping and geologic modeling are needed to constrain subsurface interpretations. In many areas of the Wind River and Bighorn basins detailed geologic maps do not exist. State-of-the-art remote sensing data could potentially provide an efficient means of mapping surface geology. State-of-the-art remote sensing systems now provide geometrically correct data at 30 meter pixel size and increased spectral coverage, capable of more detailed geologic analyses. These data can be photographically enlarged to 1:24,000 scale and combined with 7 1/2' uses topographic quads to provide an excellent base map for geologic interpretations.

  5. Silurian K-bentonites of the Dnestr Basin, Podolia, Ukraine

    USGS Publications Warehouse

    Huff, W.D.; Bergstrom, Stig M.; Kolata, Dennis R.

    2000-01-01

    The Dnestr Basin of Podolia, Ukraine, is an epicratonic basin consisting of neritic carbonate and calcareous mudstone facies including a nearly complete Silurian sequence ranging from late Llandovery to late Pridoli in age. The Silurian section has served as a standard for regional and interregional studies as a consequence of its well-documented macro- and microfaunal assemblages. Approximately 24 mid- to Late Silurian K-bentonites are present in this succession, and their lateral persistence has aided in establishing regional correlations. The K-bentonites range from 1 to 40 cm in thickness and occur in the Bagovitsa (late Wenlock), Malinovtsy (Ludlow) and Skala (Pridoli) Formations. Discrimination diagrams based on immobile trace elements together with rare earth element data suggest the K-bentonites had a volcanic origin in a collision margin setting related to subduction. Thickness and stratigraphic distribution considerations are consistent with a source area in the Rheic Ocean.

  6. The collision of South China with NW India to join Gondwanaland in the Cambrian: Provenance constraints from foreland basins

    NASA Astrophysics Data System (ADS)

    Yao, W.; Li, Z.; Li, W.; Li, X.; Yang, J.

    2013-12-01

    emerging North India orogen. As the collision progressed, the Wuyi-Yunkai orogen stared to form on the Cathaysia side of the SCB in the Ordovician, shedding sediments to the Nanhua foreland basin. Our provenance results indicate that foreland basin deposits during the Ordovician-Silurian time were mainly recycled Ediacaran-Cambrian sedimentary rocks eroded off the nearby orogen. The Silurian strata also recorded contributions from late orogenic magmatism, possibly formed during the orogenic collapse.

  7. Tectono-stratigraphic evolution of the northeastern Pyrenean Foreland Basin

    NASA Astrophysics Data System (ADS)

    Christophoul, Frédéric; Ford, Mary; Grool, Arjan; Géraldine, Rougier; Louis, Hemmer

    2016-04-01

    The Aquitaine basin, on the northern flank of the Pyrenees was subject to intense hydrocarbon exploration until the 1990's, generating a huge dataset that has been under-exploited until now. In the framework of the French Pyramid ANR project this dataset was used, together with new field data, to reconstruct the evolution of this retroforeland basin. This study focuses on the eastern retroforeland, from the Corbières to east to the Toulouse Fault to the west. In terms of age, the main depocentres are however contemporary along the whole eastern basin: 1) From Upper Cretaceous to Paleocene (Campanian to Selandian) the early foreland basin, known as the "Flysch Trough", was filled by a succession of turbidites passing upward into fluvial sediments that prograded axially from the east. 2) From Thanetian to Oligocene, a second cycle started with a deepening upward trend until the Ypresian (inner carbonate platform to mixed open marine) and changed to a shallowing upward succession, passing from open marine sediments, coastal clastic deposits and then to coarse fluvial deposits from Upper Ypresian to Oligocene. Progradation was again initially axial from the east. However, a new south to north fluvial drainage developed from the emerging relief of the Pyrenees to the south. In terms of location and structural style of these depocentres, the salt-free eastern basin (from the Corbières in the east to the Toulouse Fault to the west) reveals a distinctive style to the salt-rich western basin. In eastern foreland (Corbières to Aude Valley), syntectonic depocentres migrated north as a series of wedge-top basins between Late Cretaceous and Late Eocene. The thick-skinned syn-sedimentary foreland structures progressively die out westward. In the western part of the study area (Plantaurel to Petites Pyrenees) stacked depocentres of the same age are preserved in the footwall of the North Pyrenean Frontal thrust recording a slower northward migration associated with a northward

  8. Carboniferous clastic-wedge stratigraphy, sedimentology, and foreland basin evolution: Black Warrior basin, Alabama and Mississippi

    SciTech Connect

    Hines, R.A.

    1986-05-01

    Carboniferous clastic-wedge stratigraphy and sedimentology in the Black Warrior basin of Alabama and Mississippi indicate deposition in an evolving foreland basin flanking the Appalachian-Ouachita fold-thrust belt. The strata reflect specific responses to foreland basin subsidence, orogenic activity, sediment supply, and dispersal systems. Definition of the regional stratigraphy of the clastic wedge provides for interpretation of the foreland basin subsidence history by enabling quantitative reconstruction of regional compaction and subsidence profiles. Comparison of the interpreted subsidence history with model profiles of foreland basin subsidence (predicted from loading and flexure of continental lithosphere) allows evaluation of mechanical models in terms of observed clastic-wedge sedimentology and stratigraphy. Mechanical modeling of foreland basin subsidence predicts formation of a flexural bulge that migrates cratonward ahead of the subsiding foreland basin during loading. In the Black Warrior basin, local stratigraphic thins, pinch-outs, and areas of marine-reworked sediments suggest migration of the flexural bulge. Comparison of flexural bulge migration with thermal maturation history allows evaluation of timing of stratigraphic trapping mechanisms with respect to onset of hydrocarbon generation.

  9. Tectonic classification of Cenozoic Iberian foreland basins

    NASA Astrophysics Data System (ADS)

    De Vicente, G.; Cloetingh, S.; Van Wees, J. D.; Cunha, P. P.

    2011-04-01

    The Iberian microcontinent stands out because of its intense Alpine intraplate deformation. This is reflected in a large number of Cenozoic basins of very different sizes. Most of the contacts between topographic highs and basins are thrust or strike-slip faults. All these basins seem to have undergone a common sedimentary evolution, comprising four stages: initiation of sedimentation, intense syn-tectonic infilling, change from endorheic to exorheic drainage, and accelerated erosion related to fluvial incision. This simple evolutionary model shows a migration from East to West, in which basins are still tectonically active at the Atlantic margin of Iberia. This common evolution is also found in a series of geometrical characteristics, such as the ratio r of length of strike-slip fault and length of thrust fault, that are very similar in both types of basin border settings. Thrust-related basins are mainly associated with segmented pop-downs, whereas the main basins have the characteristics of open-ramp basins. Strike-slip related basins are mostly transpressive structures, although small pull-apart basins are usual along the Vilariça and Messejana faults. For basin areas larger than 100-1000 km 2, a constant r value of 0.6 is found (including the Ebro, Duero, Madrid, Lower Tagus and Badajoz basins). Within the Iberian microcontinent, the total amount of Cenozoic contractional deformation was distributed between strike-slip and thrust faults with an r ratio close to 0.6. However, for small basins this parameter seems to depend on the type of fault, range or deformation belt (pure strike-slip, transtension, transpression, and pop-up) independently of its local tectonic development.

  10. Archean foreland basin tectonics in the Witwatersrand, South Africa

    NASA Technical Reports Server (NTRS)

    Burke, K.; Kidd, W. S. F.; Kusky, T. M.

    1986-01-01

    The Witwatersrand Basin of South Africa is the best-known of Archean sedimentary basins and contains some of the largest gold reserves in the world. Sediments in the basin include a lower flysch-type sequence and an upper molassic facies, both of which contain abundant silicic volcanic detritus. The strata are thicker and more proximal on the northwestern side of the basin which is, at least locally, bound by thrust faults. These features indicate that the Witwatersrand strata may have been deposited in a foreland basin and a regional geologic synthesis suggests that this basin developed initially on the cratonward side of an Andean-type arc. Remarkably similar Phanerozoic basins may be found in the southern Andes above zones of shallow subduction. It is suggested that the continental collision between the Kaapvaal and Zimbabwe Cratons at about 2.7 Ga caused further subsidence and deposition in the Witwatersrand Basin. Regional uplift during this later phase of development placed the basin on the cratonward edge of a collision-related plateau, now represented by the Limpopo Province. Similarities are seen between this phase of Witwatersrand Basin evolution and that of active basins north of the Tibetan Plateau. The geologic evidence does not agree with earlier suggestions that the Witwatersrand strata were deposited in a rift or half-graben.

  11. Archean foreland basin tectonics from the Witwatersrand, South Africa

    SciTech Connect

    Burke, K.; Kidd, W.S.F.; Kusky, T.M.

    1985-01-01

    The Witwatersrand Basin of South Africa is the best-known of Archean sedimentary basins and contains some of the largest gold reserves in the world. Sediments in the basin include a lower flysch-type sequence and an upper molassic facies, both of which contain abundant silicic volcanic detritus. The strata are thicker and more proximal on the northwestern side of the basin which is, at least locally, bound by thrust faults. These and other features indicate that the Witwatersrand strata were deposited in a foreland basin. A regional geologic synthesis suggests that his basin developed initially on the cratonward side of an Andean-type arc. Remarkably similar Phanerozoic basins may be found in the southern Andes above zones of shallow subduction. We suggest that the continental collision between the Kaapvaal and Zimbabwe Cratons at about 2.7 Ga caused further subsidence and deposition in the Witwatersrand Basin. Regional uplift during this later phase of development placed the basin on the cratonward edge of a collision-related plateau, now represented by the Limpopo Province. Striking similarities are seen between this phase of Witwatersrand Basin evolution and active basins located north of the Tibetan Plateau. The geologic evidence is not so compatible with earlier suggestions that the Witwatersrand strata were deposited in a rift or half-graben.

  12. Archean foreland basin tectonics in the Witwatersrand, South Africa

    NASA Technical Reports Server (NTRS)

    Burke, K.; Kidd, W. S. F.; Kusky, T. M.

    1986-01-01

    The Witwatersrand Basin of South Africa is the best-known of Archean sedimentary basins and contains some of the largest gold reserves in the world. Sediments in the basin include a lower flysch-type sequence and an upper molassic facies, both of which contain abundant silicic volcanic detritus. The strata are thicker and more proximal on the northwestern side of the basin which is, at least locally, bound by thrust faults. These features indicate that the Witwatersrand strata may have been deposited in a foreland basin and a regional geologic synthesis suggests that this basin developed initially on the cratonward side of an Andean-type arc. Remarkably similar Phanerozoic basins may be found in the southern Andes above zones of shallow subduction. It is suggested that the continental collision between the Kaapvaal and Zimbabwe Cratons at about 2.7 Ga caused further subsidence and deposition in the Witwatersrand Basin. Regional uplift during this later phase of development placed the basin on the cratonward edge of a collision-related plateau, now represented by the Limpopo Province. Similarities are seen between this Phase of Witywatersrand Basin evolution and that of active basins north of the Tibetan Plateau. The geologic evidence does not agree with earlier suggestions that the Witwatersrand strata were deposited in a rift or half-graben.

  13. Archean foreland basin tectonics in the Witwatersrand, South Africa

    SciTech Connect

    Burke, K.; Kidd, W.S.F.; Kusky, T.M.

    1986-06-01

    The Witwatersrand Basin of South Africa is the best-known of Archean sedimentary basins and contains some of the largest gold reserves in the world. Sediments in the basin include a lower flysch-type sequence and an upper molassic facies, both of which contain abundant silicic volcanic detritus. The strata are thicker and more proximal on the northwestern side of the basin which is, at least locally, bound by thrust faults. These features indicate that the Witwatersrand strata may have been deposited in a foreland basin and a regional geologic synthesis suggests that this basin developed initially on the cratonward side of an Andean-type arc. Remarkably similar Phanerozoic basins may be found in the southern Andes above zones of shallow subduction. It is suggested that the continental collision between the Kaapvaal and Zimbabwe Cratons at about 2.7 Ga caused further subsidence and deposition in the Witwatersrand Basin. Regional uplift during this later phase of development placed the basin on the cratonward edge of a collision-related plateau, now represented by the Limpopo Province. Similarities are seen between this Phase of Witywatersrand Basin evolution and that of active basins north of the Tibetan Plateau. The geologic evidence does not agree with earlier suggestions that the Witwatersrand strata were deposited in a rift or half-graben. 64 references.

  14. Properties of Silurian shales from the Barrandian Basin, Czech Republic

    NASA Astrophysics Data System (ADS)

    Weishauptová, Zuzana; Přibyl, Oldřich; Sýkorová, Ivana

    2017-04-01

    Although shale gas-bearing deposits have a markedly lower gas content than coal deposits, great attention has recently been paid to shale gas as a new potential source of fossil energy. Shale gas extraction is considered to be quite economical, despite the lower sorption capacity of shales, which is only about 10% of coal sorption capacities The selection of a suitable locality for extracting shale gas requires the sorption capacity of the shale to be determined. The sorption capacity is determined in the laboratory by measuring the amount of methane absorbed in a shale specimen at a pressure and a temperature corresponding to in situ conditions, using high pressure sorption. According to the principles of reversibility of adsorption/desorption, this amount should be roughly related to the amount of gas released by forced degassing. High pressure methane sorption isotherms were measured on seven representative samples of Silurian shales from the Barrandian Basin, Czech Republic. Excess sorption measurements were performed at a temperature of 45oC and at pressures up to 15 MPa on dry samples, using a manometric method. Experimental methane high-pressure isotherms were fitted to a modified Langmuir equation. The maximum measured excess sorption parameter and the Langmuir sorption capacity parameter were used to study the effect of TOC content, organic maturity, inorganic components and porosity on the methane sorption capacity. The studied shale samples with random reflectance of graptolite 0.56 to 1.76% had a very low TOC content and dominant mineral fractions. Illite was the prevailing clay mineral. The sample porosity ranged from 4.6 to 18.8%. In most samples, the micropore volumes were markedly lower than the meso- and macropore volumes. In the Silurian black shales, the occurrence of fractures parallel with the original sedimentary bending was highly significant. A greater proportion of fragments of carbonaceous particles of graptolites and bitumens in the

  15. Fluid migration and coal-rank development in foreland basins

    SciTech Connect

    Gayer, R.; Rickard, D.; Garven, G.

    1998-08-01

    Mathematical modeling of regional fluid flow in the South Wales foreland basis shows that heat was transferred from internal to peripheral parts of the basin, where very high geothermal gradients and surface heat flow would have developed. In the fluid-discharge areas, temperatures are modeled to have reached 300 C within the coal measures section and would have generated anthracite, while more internal parts of the basin were cooled by descending fluid flow, and temperatures of only 220 C resulted, sufficient to form bituminous coal. The modeled thermal regime appears to match the pattern of coal rank observed in the basin. The regional flow probably continued for 1 to 2 m.y. before erosion diminished the topographic gradient driving brine migration in the late Paleozoic.

  16. Mesozoic-Cenozoic basins of Western China as example of partitioned retro-arc foreland basin system

    SciTech Connect

    Graham, S.A.; Zuchang, X.; Carroll, A.; McKnight, C.

    1988-01-01

    Mesozoic-Cenozoic sedimentary basins of Xinjiang Autonomous Region, western China, occupy a retro-arc foreland position with respect to the southern Eurasian convergent continental margin. Yet these basins differ in many ways from retro-arc foreland basins in other parts of the world. In North America, for instance, the Cretaceous Rocky Mountain foreland basin overlies basement that has been an integral part of cratonal North America since the Precambrian. The region had a long early Paleozoic history as a divergent continental margin and was later modified by relatively modest continental growth through accretionary tectonics. Once established in the Mesozoic, the Rocky Mountain foreland basin was a structurally simple, large, integrated basin, with the exception of the Laramide time-space segment of the foreland system. In contrast, the Mesozoic-Cenozoic foreland basins of Xinjiang are markedly partitioned, reflecting the process and architecture of major tectonic accretion from the Paleozoic through the collision of India in the Tertiary. The stage was set for a partitioned Mesozoic foreland with the Paleozoic suturing of the Siberia and Tarim cratons and intervening terranes. Although the margins of these blocks were deformed and uplifted during collision, their interiors persisted as depocenters into the foreland basin phase during the Mesozoic. The foreland basins of western China apparently represent poorly documented end members in the spectrum of retro-arc foreland basins. The Chinese examples occur in a region characterized by extreme continental growth through tectonic accretion. Reactivation of structural trends inherited from pre-foreland history were key factors in segmentation of the foreland.

  17. Sequential filling of a late paleozoic foreland basin

    USGS Publications Warehouse

    Mars', J. C.; Thomas, W.A.

    1999-01-01

    Through the use of an extensive data base of geophysical well logs, parasequence-scale subdivisions within a late Paleozoic synorogenic clastic wedge resolve cycles of sequential subsidence of a foreland basin, sediment progradation, subsidence of a carbonate shelf edge, diachronously subsiding discrete depositional centers, and basinwide transgression. Although temporal resolution of biostratigraphic markers is less precise in Paleozoic successions than in younger basins, parasequence-scale subdivisions provide more detailed resolution within marker-defined units in Paleozoic strata. As an example, the late Paleozoic Black Warrior basin in the foreland of the Ouachita thrust belt is filled with a synorogenic clastic wedge, the lower part of which intertongues with the fringe of a cratonic carbonate facie??s in the distal part of the basin. The stratal geometry of one tongue of the carbonate facie??s (lower tongue of Bangor Limestone) defines a ramp that grades basinward into a thin black shale. An overlying tongue of the synorogenic clastic wedge (lower tongue of Parkwood Formation) consists of cyclic delta and delta-front deposits, in which parasequences are defined by marine-flooding surfaces above coarsening- and shallow ing-upward successions of mudstone and sandstone. Within the lower Parkwood tongue, two genetic stratigraphie sequences (A and B) are defined by parasequence offlap and downlap patterns and are bounded at the tops by basinwide maximum-flooding surfaces. The distribution of parasequences within sequences A and B indicates two cycles of sequential subsidence (deepening) and progradation, suggesting subsidence during thrust advance and progradation during thrust quiescence. Parasequence stacking in sequences A and B also indicates diachronous differential tectonic subsidence of two discrete depositional centers within the basin. The uppermost sequence (C) includes reworked sandstones and an overlying shallow-marine limestone, a vertical succession

  18. Alluvial plain dynamics in the southern Amazonian foreland basin

    NASA Astrophysics Data System (ADS)

    Lombardo, U.

    2015-10-01

    Alluvial plains are formed with sediments that rivers deposit on the adjacent flood-basin, mainly through crevasse splays and avulsions. These result from a combination of processes, some of which push the river towards the crevasse threshold, while others act as triggers. Based on the floodplain sedimentation patterns of large rivers in the southern Amazonian foreland basin, it has been suggested that alluvial plain sediment accumulation is primarily the result of river crevasse splays triggered by above normal precipitation events due to La Niña. However, more than 90 % of the Amazonian river network is made of small rivers and it is unknown whether small river floodplain sedimentation is influenced by the ENSO cycle as well. Using Landsat images from 1984 to 2014, here I analyse the behaviour of all the twelve tributaries of the Río Mamoré with a catchment in the Andes. I show that these are very active rivers and that the frequency of crevasses is not linked to ENSO activity. I found that most of the sediments eroded from the Andes by the tributaries of the Mamoré are deposited in the alluvial plains, before reaching the parent river. The mid- to late Holocene paleo-channels of these rivers are located tens of kilometres further away from the Andes than the modern crevasses. I conclude that the frequency of crevasses is controlled by intrabasinal processes that act on a year to decade time scale, while the average location of the crevasses is controlled by climatic or neo-tectonic events that act on a millennial scale. Finally, I discuss the implications of river dynamics on rural livelihoods and biodiversity in the Llanos de Moxos, a seasonally flooded savannah covering most of the southern Amazonian foreland basin and the world's largest RAMSAR site.

  19. Alluvial plain dynamics in the southern Amazonian foreland basin

    NASA Astrophysics Data System (ADS)

    Lombardo, Umberto

    2016-05-01

    Alluvial plains are formed with sediments that rivers deposit on the adjacent flood-basin, mainly through crevasse splays and avulsions. These result from a combination of processes, some of which push the river towards the crevasse threshold, while others act as triggers. Based on the floodplain sedimentation patterns of large rivers in the southern Amazonian foreland basin, it has been suggested that alluvial plain sediment accumulation is primarily the result of river crevasse splays and sheet sands triggered by above-normal precipitation events due to La Niña. However, more than 90 % of the Amazonian river network is made of small rivers and it is unknown whether small river floodplain sedimentation is influenced by the ENSO cycle as well. Using Landsat images from 1984 to 2014, here I analyse the behaviour of all 12 tributaries of the Río Mamoré with a catchment in the Andes. I show that these are very active rivers and that the frequency of crevasses is not linked to ENSO activity. The data suggest that most of the sediments eroded from the Andes by the tributaries of the Mamoré are deposited in the alluvial plains, before reaching the parent river. The mid-to-late Holocene paleo-channels of these rivers are located tens of kilometres further away from the Andes than the modern crevasses. I conclude that the frequency of crevasses is controlled by intrabasinal processes that act on a yearly to decadal timescale, while the average location of the crevasses is controlled by climatic or neo-tectonic events that act on a millennial scale. Finally, I discuss the implications of river dynamics on rural livelihoods and biodiversity in the Llanos de Moxos, a seasonally flooded savannah covering most of the southern Amazonian foreland basin and the world's largest RAMSAR site.

  20. Avulsion flow-path selection on rivers in foreland basins

    NASA Astrophysics Data System (ADS)

    Edmonds, D. A.; Hajek, E. A.; Downton, N.; Bryk, A.

    2016-12-01

    River avulsions help distribute sediment across the floodplain, and the frequency and flow path selected by each avulsion determines flooding and sedimentation patterns. However, rivers avulse infrequently, making it difficult to quantify flow-path behavior and test hypotheses posed by experimental and numerical studies. We used Google Earth Engine to create a novel data set of 55 avulsions that occurred from A.D. 1984 to 2014 in the Andean and Himalayan foreland basins. On each avulsion we measure hop length (the displacement of the avulsion across the floodplain orthogonal to the parent channel) and avulsion length (the length of the parent channel reach). Without controlling for external factors, such as climate or geology, we find that both hop length and avulsion length scale with parent channel-belt width. Avulsion channels tend to hop 2.5 channel-belt widths away from their parent channel and avulsion length is 13.4 parent channel-belt widths. We use these data to test between end-member scenarios where flow paths are randomly selected or steered by floodplain topography. Observed avulsions are inconsistent with flow-path predictions derived from a directed random walk model, and a scaling analysis of alluvial ridge size shows that hop lengths are set by alluvial ridge widths. These results suggest that avulsion flow-path selection in the Andean and Himalayan basins is driven by alluvial ridge topography, which promotes evenly spaced (or compensational) channel sand bodies over decadal time scales. These data and results are important for understanding controls on avulsion flow-path selection and how avulsion processes are represented in the stratigraphic record of foreland basins.

  1. Bulge Migration and Pinnacle Reef Development, Devonian Appalachian Foreland Basin.

    PubMed

    Ver Straeten CA; Brett

    2000-05-01

    Detailed stratigraphic analyses of Late Emsian and Early Eifelian (Lower to Middle Devonian) carbonate-dominated strata in the northern Appalachian Basin indicate anomalous, locally varying relative sea level changes and inversions of topography. The distribution of a major basal-bounding unconformity, basinal pinnacle reefs, local absence of parasequences, and eastward migration of shallow marine carbonate lithofacies and related biofacies in the Onondaga Limestone and underlying strata mark the retrograde migration of an elongate, northeast-southwest-trending area of positive relief, bordered on its cratonward side by a similarly migrating basin of intermediate depth. These features are thought to represent the forebulge and back-bulge basin of the Appalachian foreland basin system as it developed during a time of relative quiescence within the Acadian Orogeny. However, the relatively small size of the bulgelike feature (ca. 80-100-km-wide, 20-50-m positive relief), its great distance from the probable deformation front (>400 km), and the lack of a well-developed foredeep immediately adjacent to the bulgelike feature may indicate that it represents a smaller-scale flexural high ("flexural welt") superposed over the cratonward edge of the larger-scale classical forebulge of the basin. Development of shallow-water reefs on the crest of the bulge during sea level lowstand, followed by migration of the bulge and widespread transgression, permitted growth of economically significant pinnacle reefs in the deep basin center. Further subsurface reef exploration should concentrate along the projected position of the bulge during the basal Onondaga lowstand.

  2. Partitioning of the Taconic foreland basin: Middle to Late Ordovician flysch and molasse sub-basins of New York State and Ontario

    SciTech Connect

    Lehmann, D.; Brett, C.E.; Ingram, S.L. . Dept. of Geological Sciences)

    1992-01-01

    Analysis of field and well data suggest that the foreland basin in New York and Ontario is divisible into two sub-basins containing siliciclastic fill which are separated by a moderately narrow, north/south oriented region of relatively thin siliciclastic strata. The eastern sub-basin contains a thick succession of late Middle and early Late Ordovician basinal black shales and turbiditic siltstones and sandstones (flysch). These strata thicken eastward to over 800 m beneath the thrust belt (Taconic allochthon) in the eastern most portion of the sub-basin. The flysch is, at least in part, time-correlative with ramp carbonates present in the western sub-basin. The western sub-basin contains a relatively thin succession of flysch deposits that overlie Upper Ordovician carbonates. The flysch deposits from the western sub-basin correlate with only the stratigraphically highest strata in the eastern sub-basin. In the western sub-basin, flysch deposits are overlain by Upper Ordovician shallow marine to non-marine mudstones and sandstones (molasse). The molasse is unconformably overlain by Lower Silurian strata. Due to the angularity of the unconformity surface, the molasse is stratigraphically most complete towards the western margin of the western sub-basin; thickest deposits in this sub-basin ([gt] 600 m) are not the most stratigraphically complete. The general sedimentary history of the New York portion of the Taconic siliciclastic wedge is bipartite: (1) rapid subsidence in the eastern sub-basin during the late Middle and early Late Ordovician accompanied by flysch-phase filling; (2) rapid subsidence in the western sub-basin during the middle to late Late Ordovician accompanied by molasse-phase filling.

  3. Shelf to basin transition of Silurian-Devonian rocks, Porcupine River area, east-central Alaska

    SciTech Connect

    Colean, D.A.

    1985-04-01

    Exposures of Silurian to lowermost Devonian strata in the Porcupine River region consist of an unnamed carbonate unit and the Road River Formation. Petrographic studies indicate that these rocks display facies representative of five depositional environments: basin, open sea shelf, deep shelf margin, open platform, and restricted shelf. The unnamed carbonate unit, exposed in the Linear Ridge area, is 390 ft (126 m) thick and records a history of restricted shelf to basinal sedimentation. Stratigraphic relations and paleontological studies suggest a Middle to Late Silurian (Ludlovian) age for this unit. The Road River Formation is Late Silurian (Ludlovian) to Early Devonian (Lochkovian) in age and is exposed near the confluence of the Porcupine-Salmontrout Rivers and downstream along the Lower Ramparts. It consists of 30-190 ft (10-61 m) of graptolitic shale with interbeds of siliceous limestone. Petrographic studies of the shales are interpreted to reflect deposition in a basinal setting, whereas the siliceous limestones represent deep shelf-margin debris flows derived from nearby, coeval shallow-water shelf environments. Together, the unnamed carbonate unit and the Road River Formation represent a shelf to basin transition on a carbonate ramp that transcends the Silurian-Devonian boundary. Petrographic examination of these rocks reveals that they are susceptible to a wide range of diagenetic processes, including (1) micritition, (2) neomorphism, (3) syntaxial overgrowths, (4) pressure solution (stylolitization), (5) trapping of dried hydrocarbons, (6) tensional stress (calcite veining), and (7) silicification.

  4. Flexural analysis of two broken foreland basins; Late Cenozoic Bermejo basin and Early Cenozoic Green River basin

    SciTech Connect

    Flemings, P.B.; Jordan, T.E.; Reynolds, S.

    1986-05-01

    Lithospheric flexure that generates basin in a broke foreland setting (e.g., the Laramide foreland of Wyoming) is a three-dimensional system related to shortening along basin-bounding faults. The authors modeled the elastic flexure in three dimensions for two broken foreland basins: the early Cenozoic Green River basin and the analogous late Cenozoic Bermejo basin of Argentina. Each basin is located between a thrust belt and a reverse-fault-bounded basement uplift. Both basins are asymmetric toward the basement uplifts and have a central basement high: the Rock Springs uplift and the Pie de Palo uplift, respectively. The model applies loads generated by crustal thickening to an elastic lithosphere overlying a fluid mantle. Using the loading conditions of the Bermejo basin based on topography, limited drilling, and reflection and earthquake seismology, the model predicts the current Bermejo basin geometry. Similarly, flexure under the loading conditions in the Green River basin, which are constrained by stratigraphy, well logs, and seismic profiling and summed for Late Cretaceous (Lance Formation) through Eocene (Wasatch Formation), successfully models the observed geometry of the pre-Lance surface. Basin depocenters (> 4 km for the Green River basin; > 7 km for the Bermejo basin) and central uplifts are predicted to result from constructive interference of the nonparallel applied loads. Their Bermejo model implies that instantaneous basin geometry is successfully modeled by crustal loading, whereas the Green River basin analysis suggests that basin evolution can be modeled over large time steps (e.g., 20 Ma). This result links instantaneous basin geometry to overall basin evolution and is a first step in predicting stratigraphic development.

  5. A detrital record of continent-continent collision in the Early-Middle Jurassic foreland sequence in the northern Yangtze foreland basin, South China

    NASA Astrophysics Data System (ADS)

    Qian, Tao; Liu, Shaofeng; Wang, Zongxiu; Li, Wangpeng; Chen, Xinlu

    2016-12-01

    The Mesozoic northern Yangtze foreland basin system was formed by continental collision between the North China and South China plates along the Mianlue suture. Synorogenic stratigraphic sequences of Late Triassic to Early-Middle Jurassic age were developed in the northern Yangtze foreland basin. The upper Middle Jurassic Shaximiao Formation consists mainly of thick-bedded terrestrial successions that serve as the main body of the basin-filling sequences, suggesting intense tectonism in the peripheral orogeny of the foreland basin. Laser-ICP-MS U-Pb analysis of 254 detrital zircon grains from sandstone samples and several published Lower-Middle Jurassic samples, detrital compositions, petrofacies, and paleocurrent reconstructions in the northern Yangtze foreland basin indicate that discrete source areas included the Qinling-Dabieshan ranges and the Mianlue suture zone to the north, and the South China plate to the south. The stratigraphic succession and sediment provenance of the foreland basin imply that the early Mianlue oceanic basin, magmatic arc, and nonmarine molasse foreland basin during the period of deposition were modified or buried by the subsequent continent-continent collision between the North China-Qinling-Dabieshan plate and the Yangtze plate during the Jurassic, which followed the oblique amalgamation between these plates during the Middle-Late Triassic.

  6. Late Archaean foreland basin deposits, Belingwe greenstone belt, Zimbabwe

    NASA Astrophysics Data System (ADS)

    Hofmann, A.; Dirks, P. H. G. M.; Jelsma, H. A.

    2001-06-01

    The c. 2.65 Ga old sedimentary Cheshire Formation of the Belingwe greenstone belt (BDB), central Zimbabwe, has been studied in detail for the first time to shed some light on the much debated evolution of this classical belt. The Cheshire Formation rests sharply on a mafic volcanic unit (Zeederbergs Formation) and comprises a basal, eastward-sloping carbonate ramp sequence built of shallowing-upward, metre-scale sedimentary cycles. The cycles strongly resemble Proterozoic and Phanerozoic carbonate cycles and might have formed by small-scale eustatic sea level changes. The top of the carbonate ramp is represented by a karst surface. The carbonates are overlain by and grade laterally to the east into deeper water (sub-wave base) siliciclastic facies. Conglomerate, shale and minor sandstone were deposited by high- to low-density turbidity currents and were derived from the erosion of Zeederbergs-like volcanic rocks from the east. Shortly after deposition, the Cheshire Formation and underlying volcanics were affected by a northwest-directed thrusting event. Thrusting gave rise to the deformation of semi-consolidated sediments and resulted in the juxtaposition of a thrust slice of Zeederbergs basalts onto Cheshire sediments. The stratigraphy, asymmetric facies and sediment thickness distribution, palaeogeographic constraints and evidence for an early horizontal tectonic event suggest that the Cheshire Formation formed in a foreland-type sedimentary basin.

  7. Development of Tectonostratigraphy in Distal Part of Foreland Basin in Southwestern Taiwan

    NASA Astrophysics Data System (ADS)

    Yang, K.-M.; Wu, J.-C.; Cheng, E.-W.; Chen, Y.-R.; Huang, W.-C.; Tsai, C.-C.; Wang, J.-B.; Ting, H.-H.

    2012-04-01

    In a young and on-going mountain building belt such as that in Taiwan, the geological records in the foreland basin and the fold-and-thrust belt are still well preserved. Analysis of stratal sequences, lithofacies and subsidence history of the basin, especially in the distal part and the forebulge, would not only reveal the evolutionary history of the basin itself but also provide the most crucial implications to infer the kinematics of the mountain-building process. Based on the analysis of subsurface well bore and seismic data, this study aims to reconstruct the tectonostratigraphy and the subsidence history in distal part of the foreland basin in southwestern Taiwan. A typical foreland basin in southwestern Taiwan has been formed by loading from the orogenic belt to the east. During the same period the foreland areas has been under the rifting tectonics. The onset of foreland basin development was at 4.4 Ma, younger than that proposed in some previous studies. After that, the distal part of foreland basin encountered two discernible episodic events of rapid subsidence at 4.4 to 4.2 and 2 to 1.8 Ma. The age of the initial rapid subsidence was younger toward the craton. During the first rapid subsidence in the basin area, concurrent uplifting that corresponds to forebulge happened in the distal part of foreland basin and was followed by rapid subsidence and deposition of the ubiquitous strata onlapping toward the craton. In the next rapid subsidence, the forebulge first shifted toward the basin center and caused part of strata to be eroded. Shortly after that, the uplifted area started to subside again and received another unit of ubiquitous strata. Therefore, there are two unconformities, which divide the foreland basin megasequences into three sequences of third-order scale and are characterized by the following features: 1, they gradually merge into one unconformity toward the craton; 2, the time gap of each unconformity increases toward the craton, except

  8. In search of a Silurian Total Petroleum System in the Appalachian Basin of New York, Ohio, Pennsylvania, and West Virginia

    USGS Publications Warehouse

    Ryder, Robert T.; Swezey, Christopher S.; Trippi, Michael H.; Lentz, Erika E.; Avary, K. Lee; Harper, John A.; Kappel, William M.; Rea, Ronald G.

    2007-01-01

    This report provides an evaluation of the source rock potential of Silurian strata in the U.S. portion of the northern Appalachian Basin, using new TOC and RockEval data. The study area consists of all or parts of New York, Ohio, Pennsylvania, and West Virginia. The stratigraphic intervals that were sampled for this study are as follows: 1) the Lower Silurian Cabot Head Shale, Rochester Shale, and Rose Hill Formation; 2) the Lower and Upper Silurian McKenzie Limestone, Lockport Dolomite, and Eramosa Member of the Lockport Group; and 3) the Upper Silurian Wills Creek Formation, Tonoloway Limestone, Salina Group, and Bass Islands Dolomite. These Silurian stratigraphic intervals were chosen because they are cited in previous publications as potential source rocks, they are easily identified and relatively continuous across the basin, and they contain beds of dark gray to black shale and (or) black argillaceous limestone and dolomite.

  9. New discovery and geological significance of Late Silurian-Carboniferous extensional structures in Tarim Basin

    NASA Astrophysics Data System (ADS)

    Li, Yue-Jun; Wen, Lei; Yang, Hai-Jun; Zhang, Guang-Ya; Shi, Jun; Peng, Geng-Xin; Hu, Jian-Feng; Luo, Jun-Cheng; Huang, Zhi-Bin; Chen, Yan-Gui; Zhang, Qiang

    2015-02-01

    Late Silurian-Carboniferous extensional structures have been discovered after careful interpretation of seismic reflection data in western Manjiaer Sag, Central Tarim Basin in central Asia. The extensional structures comprise numerous small normal faults in nearly N-S strike direction. Groups of normal faults in profile show features suggestive of negative flower structures and small horst-graben structures. Based on growth index calculation, these extensional structures formed in the Late Silurian period, continued activity in the Devonian and Carboniferous and then ceased at the end of Carboniferous. The peak-stage of normal fault activity occurred in Late Silurian. Late Silurian-Carboniferous normal faults also developed in the Tazhong and Tabei areas, which implies that Tarim Basin were under regional extensional tectonic setting during that periods. The extensional structure in southern Tarim resulted from the post-orogeny stress relaxation of the Kunlun Early Paleozoic orogenic belt, and those in northern Tarim resulted from the Paleozoic back-arc rifting which led to the opening of South Tianshan ocean.

  10. Basinwide fold evolution and geometric development of cratonic - foreland basin interaction

    SciTech Connect

    Redly, P.; Hajnal, Z. )

    1996-01-01

    Latest results of the Williston Basin Project incorporate a north-south regional seismic line, which is crossing the deepest part of the Williston Basin from Saskatchewan to South Dakota. The integration of this new profile to the two, existing east-west regional seismic sections, gives a quasi-3D image of the basin. The combined seismic data illustrate alternating extensive and compressive phases during basin development, marked by basinwide circular and radial folds. This alternating pattern of basin subsidence is the very nature of crotonic basin evolution. The structural necessity for compressive phases during crotonic basin subsidence, is shown in a regional scale interpretation that has undergone an Earth-curvature correction. The geometrical evolution of the neighboring foreland basin is also interpreted from data that has been corrected with the Earth-curvature function. It shows that basinwide folds sub-parallel and perpendicular to the longitudinal axis of the basin are analogous to the circular and radial folds of the crotonic basins. These folds, in the foreland belt, are less pronounced because larger scale structural elements can overprint them. Where the crotonic and foreland basins overlap, a complex, deformed zone is present, and contains late stage volcanism, in this area. The geometry of the Williston Basin can be modeled by the Sloss-type [open quote]inverted Gaussian function[close quote] that is modified by the periodic westward tilting of the basin and the Earth-curvature function.

  11. Chert horizons as time-stratigraphic markers in Ordovician and Silurian of eastern Great Basin

    SciTech Connect

    Cameron, G.J.

    1986-08-01

    Data from numerous measured sections show that distinct chert horizons occur at or near the same stratigraphic intervals in a number of Ordovician and Silurian dolomite sequences in the eastern Great basin of Nevada and Utah. In many cases a shallow-water origin for the chert is inferred because of silicified shelfal fauna and lack of deeper water indicators. The cherty intervals appear to transgress across environmentally controlled lithologic boundaries. This fact, coupled with the regional extent of the chert, suggests that these intervals can be used as time-stratigraphic marker horizons. This concept is useful in assessing the degree of stratigraphic thinning of Upper Silurian strata along a regional unconformity. Although chert is almost ubiquitously present in certain stratigraphic intervals, the abundance of chert-bearing horizons within an individual section varies. By contouring the abundance of chert-bearing intervals within the Silurian system, a well-defined pattern is documented that increases in abundance to the northeast toward the northwestern corner of Utah. The ratio of chert to dolomite within the intervals increases correspondingly. It is suggested that the chert is the result of silica supersaturation from the settling of wind-blow volcanic ash on the Silurian epicontinental sea. The distribution of the chert was largely a function of paleowind currents from an easterly or northerly active volcanic source area.

  12. Escape tectonics and foreland basin evolution: The Austrian-German Molasse basin

    NASA Astrophysics Data System (ADS)

    Ortner, Hugo

    2016-04-01

    The Alpine peripheral foreland basin formed during Eocene collision of the lower, European plate and the upper, Adriatic plate. Two marine to continental megasequences fill the basin. The transition form deep marine to continental deposits of the first megasequence at the Early - Late Oligocene boundary has been related to a change from predominant horizontal to vertical movements in the core of the orogenic wedge. The second megasequence is, however, poorly understood, and different models have been put forward. I present an alternative explanation for the development of this second megacycle, based on an analysis of the Subalpine Molasse thrust belt east of the Rhine river (Ortner et al., 2015). The main characteristics of the Subalpine Molasse thrust belt are: 1) A frontal anticline/thrust started to develop during deposition of the older, marine portion of the second megasequence. Structures continued to grow throughout deposition of the younger, continental part of the megasequence. Structural growth is documented by growth strata. 2) The thrusts in the Subalpine Molasse evolved in a break-back sequence. 3) The amount of shortening during depositon of the second megasequence reduces from 40-50 km near the Rhine valley to zero in the east in the Salzburg area. The onset of the second megasequence in the foreland north of the Subalpine Molasse thrust belt is characterized by an angular unconformity documenting a tilt of the foreland toward the orogen, and therefore ongoing flexure of the lower plate. East of the eastern end of the Subalpine Molasse thrust belt, the deposits of the second megasequence are in a horizontal position, lower plate flexure had stopped. In the internal part of the Alpine orogenic wedge, shortening, exhumation and E-directed stretching of the Tauern Window as a consequence of escape tectonics was active. Most probably shortening was transferred from the Alpine front into the zone of lateral escape, causing the break-back thrust sequence

  13. Tectonic implications of Paleocene-Eocene Foreland Basin, Lake Maracaibo, Venezuela

    SciTech Connect

    Lugo, J. ); Mann, P. )

    1993-02-01

    A compilation of industry geological and geophysical data indicates that Paleocene-Eocene clastic sedimentation in the Maracaibo basin records the first manifestation of Cenozoic foreland basin tectonics in northern South America. Isopach maps based on industry seismic data and well logs suggest that the Maracaibo foreland basin formed a 100 to 200 km wide elongate trough along the northeastern edge of the present-day Lake Maracaibo. The basin is asymmetric with a deep (7 km) northeastern margin adjacent to an exposed southwest-verging thrust belt mapped by previous workers. Isopach mapping of seven seismic units within the Eocene suggest a nor-northwest to southeast migration of the depocenter from Paleocene to Middle Eocene time at a rate of 0.6 cm/year. A similar style of foreland basin has been previously identified over a distance of 1000 Km from western central Venezuela to Trinidad. Eocene to Pliocene ages of foreland basin sedimentation in these areas suggest time transgressive, oblique collision of the Caribbean plate along the northern margin of South America. Comparison of the age of deformation along both the northern and southern edges of the pro-Caribbean plate yield reasonable estimates for the rate of relative motion of this small plate relative to the larger America plates.

  14. Foreland basin evolution in the central Andes, Bermejo basin, San Juan Province, Argentina

    SciTech Connect

    Jordan, T.E.; Naeser, C.W.; Johnson, N.M.; Johnsson, P.A.; Johnson, A.; Reynolds, J.; Reynolds, S.A.; Fielding, E.J.

    1985-01-01

    The Bermejo foreland basin in evolving east of and being cannibalized by a N-trending thrust belt (Precordillera (PC)), and west of a NNW-trending basement uplift (Sierra de Valle Fertil (VF)). Located above a flat Benioff zone, the Late Cenozoic nonmarine basin is analogous in scale and structure to the Green River-Hoback basin of Wyoming. Preliminary magnetic reversal stratigraphy, fission track dating, provenance studies, and facies analysis constrain its history. The thickest exposed strata (5 to 6 km) are in the easternmost folds of the PC and the subsurface sequence appears to thicken seaward toward the VF. Surface sections in the interior of the PC are thinner. Coeval strata west of the PC, but east of the Frontal Cordillera, are much thinner; they may not have been part of the Bermejo basin. The authors summarize the tectonic history as follows. There was little sediment accumulation in the foreland basin when the main volcanic arc was active (27 to 11 Ma). Thrusting in the central PC had begun by about 8 Ma, when diagnostic clasts appeared in the detritus to the east and subsidence rate was very high. About that time, volcanic activity and rapid sediment accumulation occurred briefly on the western flank of the PC. Subsequently, thrusting migrated eastward, causing coarsening-upward sections in the eastern PC. Deformation reached the eastern PC after 2.3 Ma. The eastern Bermejo basin continues to subside today. The time of uplift of the VF is poorly known, but was apparently younger than 12 Ma and coincident with thrust belt activity.

  15. Geodynamics of the Sivas Basin (Turkey): from a forearc basin to a retroarc foreland basin

    NASA Astrophysics Data System (ADS)

    Legeay, Etienne; Ringenbach, Jean-Claude; Kergaravat, Charlie; Callot, Jean-Paul; Mohn, Geoffroy; Kavak, Kaan

    2016-04-01

    the north-dipping subduction of the Southern Neotethys beneath the Tauride microcontinent. The Late Eocene records a quick shallowing and the deposition of a thick evaporitic level. The Oligo-Miocene succession is characterized by fluvio-lacustrine deposition, and short lived marine transgression from the East, dated as Chattian -Aquitanian. The post-salt evolution can be divided into three areas with different tectonic deformation styles. The western part of the Sivas Basin presents an East-West elongated trend with classical fold-and-thrust belt geometry, local salt remobilization and minor halokinesis. In contrast, the central part near Sivas, exhibits polygonal distribution of evaporates, which reveals two generations of minibasins, separated by the emplacement of a salt canopy during mid-Oligocene time. Toward the East a primary continental sequence and salt canopy conducted to the deposition of thick halokinetic Oligo-Miocene basins. We conclude that the Sivas Basin represents a Paleogene foreland, characterized by a north verging fold-and-thrust belt, induced by retroarc shortening along the northern margin of the Tauride Platform. In contrast, the Oligo-Miocene sequence was deformed by south-verging back-thrust, above a triangular zone and passive roof detachments in evaporites.

  16. Vertical stacking of reservoirs in Silurian carbonates of Appalachian basin

    SciTech Connect

    Smosna, R.; Conrad, J.M.; Maxwell, T.C.

    1988-08-01

    The distribution of modern reefs and oolites is controlled to a large degree by sea-floor topography. Likewise, paleotopographic highs in the Silurian Lockport Dolomite and underlying Keefer Sandstone provided optimum sites for the deposition of boundstone and grainstone reservoir facies. The Keefer Sandstone in western West Virginia was deposited as a series of subtidal sand waves with a relief of a few meters. During initial Lockport sedimentation, the turbulence, water chemistry, and light intensity were most favorable in shallow water over the Keefer sand waves, encouraging growth of coral-stromatoporoid patch reefs. Skeletal banks in the upper Lockport of eastern Kentucky also were established over topographic highs of earlier Lockport mounds. In a similar fashion, the upper Lockport of West Virginia was deposited as oolitic shoals that formed atop exposed mud mounds in the middle member. A slight rise of sea level created the agitated subtidal environment above the now-submerged mud mounds, and oolite bars developed. The reef, skeletal-bank, and oolite facies of the Lockport, and the Keefer Sandstone, are all petroleum reservoirs. Carbonate reservoirs can be identified in the subsurface by thicks on isopach maps, by their clean gamma-ray signature, and by a relatively high log porosity. Based on these criteria, seven potential fairways have been mapped in Kentucky. Because the distribution of buildups was greatly influenced by that of their predecessors, five of the fairways contain vertically stacked reservoir facies. These are particularly attractive because they can be drilled as multistory targets.

  17. Sequence stratigraphy and depositional facies of the Silurian-Devonian interval of the northern Permian basin

    SciTech Connect

    Canter, K.L.; Geesaman, R.C. ); Wheeler, D. )

    1992-04-01

    The Silurian and Devonian intervals of the northern Central Basin platform area of west Texas and southeastern New Mexico include the Fusselman, Wristen, and Thirtyone formations and the Woodford Shale. The carbonate-rich Fusselman, Wristen, and Thirtyone formations record a transition from ramp to platform deposition. Oolite grainstones of the lower Fusselman Formation were deposited in a ramp setting during an Upper Ordovician/Lower Silurian transgression. The overlying crinoid packstones and grainstones represent shoals that developed along a break in slope separating the evolving platform from a southward-dipping starved basin. By the close of Fusselman deposition, the platform was well developed, with shallow peridtidal mudstones and wackestones, and high-energy grainstones deposited as near-parallel facies tracts over the platform area. The platform system became fully developed during the deposition of the Wristen Formation. Porous dolomitic peridtidal and platform margin facies grade downdip into nonporous, limy and argillaceous open-shelf facies. Platform facies are typified by numerous shallowing-upward parasequences that terminated at subaerial exposure surfaces. The rocks of the Lower Devonian Thirtyone Formation were deposited as a wedge that onlaps the exposed Silurian platform margin. This formation contains a porous, chert-rich, lowstand deposit; a transgressive disconformity; and variably porous, grain-rich highstand deposits representing an overall sea level rise. A major unconformity marks the contact between the karsted upper surface of the Thirtyone Formation and the overlying organic-rich, anoxic Woodford Shale.

  18. Tectonic significance of Cenozoic exhumation and foreland basin evolution in the Western Alps

    NASA Astrophysics Data System (ADS)

    Carrapa, Barbara; Di Giulio, Andrea; Mancin, Nicoletta; Stockli, Daniel; Fantoni, Roberto; Hughes, Amanda; Gupta, Sanjeev

    2016-08-01

    The Alps are the archetypical collisional orogenic system on Earth, and yet our understanding of processes controlling topographic growth in the Cenozoic remains incomplete. Whereas ideas and models on the Alps are abundant, data from the foreland basin record able to constrain the timing of erosion and sedimentation, mechanisms of basin accommodation and basin deformation are sparse. We combine seismic stratigraphy, micropaleontology, white mica 40Ar/39Ar, detrital zircon (U-Th)/He and apatite fission track thermochronology to Oligocene-Pliocene samples from the retrowedge foreland basin (Saluzzo Basin in Italy) and to Oligocene-Miocene sedimentary rocks from the prowedge foreland basin (Bârreme Basin in France) of the Western Alps. Our new data show that exhumation in the Oligocene-Miocene was nonuniform across the Western Alps. Topographic growth was underway since the Oligocene and exhumation was concentrated on the proside of the orogenic system. Rapid and episodic early Miocene exhumation of the Western Alps was concentrated instead on the retroside of the orogen and correlates with a major unconformity in the proximal retroforeland basin. A phase of orogenic construction is recorded by exhumation of the proximal proforeland in both the Central and Western Alps at circa 16 Ma. This is associated with high sedimentation rates, and by inference erosion rates, and suggests that an increase in accretionary flux associated with the dynamics of subduction of Europe under Adria controlled orogenic expansion in the Miocene.

  19. Late burial diagenesis of Niagaran (Middle Silurian) pinnacle reefs in Michigan basin

    SciTech Connect

    Cercone, K.R.; Lohmann, K.C. )

    1987-02-01

    Core samples from Middle Silurian pinnacle reefs in northern Michigan exhibit a regionally consistent assemblage of late diagenetic phases including geopetal diagenetic sediment, disseminated pyrite, pyrobitumen, rhombic dolomite cement, and equant calcite spar. High (> 80{degree}C) fluid inclusion homogenization temperatures and inclusions of Silurian-sourced oil in these diagenetic phases indicate that they formed between the Mississippian and Jurassic, when pinnacle reefs resided in the deep subsurface. Fluid inclusion salinities and stable carbon/oxygen isotopic ratios suggest that late diagenetic carbonates did not precipitate from connate fluids but from basinal brines that were conducted to pinnacle reefs by two regional carbonate aquifers. These data confirm that late burial diagenesis can affect carbonate rocks residing in high-salinity, low-permeability fluid environments. 8 figs., 1 tab.

  20. Deformation style and controlling geodynamic processes at the eastern Guadalquivir foreland basin (Southern Spain)

    NASA Astrophysics Data System (ADS)

    Marín-Lechado, C.; Pedrera, A.; Peláez, J. A.; Ruiz-Constán, A.; González-Ramón, A.; Henares, J.

    2017-06-01

    The tectonic structure of the Guadalquivir foreland basin becomes complex eastward evolving from a single depocenter to a compartmented basin. The deformation pattern within the eastern Guadalquivir foreland basin has been characterized by combining seismic reflection profiles, boreholes, and structural field data to output a 3-D model. High-dipping NNE-SSW to NE-SW trending normal and reverse fault arrays deform the Variscan basement of the basin. These faults generally affect Tortonian sediments, which show syntectonic features sealed by the latest Miocene units. Curved and S-shaped fault traces are abundant and caused by the linkage of nearby fault segments during lateral fault propagation. Preexisting faults were reactivated either as normal or reverse faults depending on their position within the foreland. At Tortonian time, reverse faults deformed the basin forebulge, while normal faults predominated within the backbulge. Along-strike variation of the Betic foreland basin geometry is supported by an increasing mechanical coupling of the two plates (Alborán Domain and Variscan basement) toward the eastern part of the cordillera. Thus, subduction would have progressed in the western Betics, while it would have failed in the eastern one. There, the initially subducted Iberian paleomargin (Nevado-Filábride Complex) was incorporated into the upper plate promoting the transmission of collision-related compressional stresses into the foreland since the middle Miocene. Nowadays, compression is still active and produces low-magnitude earthquakes likely linked to NNE-SSW to NE-SW preexiting faults reactivated with reverse oblique-slip kinematics. Seismicity is mostly concentrated around fault tips that are frequently curved in overstepping zones.

  1. Relationship between sediment provenance of foreland basin and kinematics of orogenic belt in southwestern Taiwan

    NASA Astrophysics Data System (ADS)

    Hsu, Kun-An; Yang, Kenn-Ming; Chien, Chih-Wei; Wu, Leh-chyun

    2017-04-01

    The foreland basin in southwestern Taiwan offers an idealistic example for geologists to study the tectonostratigraphy in the foreland basin development from initial to latest stages. The subsidence analysis indicate that the initial stage of foreland basin development had started in the Mid Pliocene, and the basin went through two rapid subsidence events, along with forebulge moving back-and-forth in the E-W direction during the Late Pliocene to the Pleistocene. Thus, the tectonostratigraphic sequences deposited from the Late Pliocene to the later periods would provide crucial evidences for the relationship between foreland basin and its adjacent orogenic belt. Based on the tectonostratigraphic sequences in the late stage (Upper Pliocene to Pleistocene) of foreland basin development in SW Taiwan, this study aims to explore the mode of interaction between the evolution of foreland basin and kinematics of orogenic belt primarily based on petrofacies analysis. The results of petrofacies analysis were interpreted with the tectonostratigraphic and biostratigraphic frameworks of previous studies to infer the regional and local sediment provenances and transportation modes. The the craton had been the sediment source to the west of the study area in the pre-orogenic period. The maturity of these sediments was high due to slow exhumation rates and long transportation distance. In the initial stage of foreland basin development, the forebulge slowly elevated and started to partially or totally obstruct sediment supplies from the craton. Before the period of NN19 when the forebulge steadily moved westward, the forebulge not only became the barrier of the most continental sediment supplies from the west but also shed a minor amount of detritus into the adjacent area. In addition, regional topographic relief, which was due to syn-orogenic normal faulting during the NN11-15, locally changed the composition and transportation modes of the sediments; the exposed basement of the

  2. Fluid inclusion geochemistry of halite from the Silurian A-1 Evaporite, Michigan Basin

    SciTech Connect

    Leibold, A.W.; Walter, L.M.; Huston, T.J.; O'Neil, J.R. . Dept. of Geological Sciences)

    1992-01-01

    Fluids trapped in primary, inclusion-rich halite from the Silurian A-1 Evaporite of the Michigan Basin were analyzed to determine their elemental and isotopic composition and so constrain the fluid chemistry and regional variability of parent brines. The samples were collected from stratigraphically more complete basin center and basin margin cores than hitherto have been available. These include both inclusion-rich whole rock chips and fluids leached with isopropanol from crushed, inclusion-rich halite. Elemental ratios were determined relative to Mg, which is present only in the fluid phase of monomineralic halite samples and acts as a normalizing parameter against which to quantify fluid inclusion chemistry. Stable isotope ratios were determined on fluids collected from inclusion-rich halite by vacuum-thermal decrepitation. Inclusion fluids define a geochemical trend characterized by a Ca:Mg ratio of 1.4 [+-] 0.47, an Sr:Mg ratio of 0.015 [+-] 0.004 and a K:Mg ratio of 0.5 [+-] 0.17. Fluids are also depleted in SO[sub 4]. Importantly, these values are significantly different from any Michigan Basin formation brines and also cannot be derived from evaporation of modern seawater without extensive diagenetic modification. Two explanations of the data are possible. Pervasive syndepositional dolomitization and anhydrite precipitation may have altered Silurian brines of initial modern seawater composition, as has been suggested for similar data. However, consistently high cation ratios in the A-1 Evaporite on a regional scale demand striking uniformity in the timing and location of such reactions. Alternatively, Silurian seawater may have had elevated Ca:Mg, Sr:Mg and possibly K:Mg ratios relative to modern seawater.

  3. Stratigraphical links between Miocene Alpine Foreland basin and Gulf of Lion Passive Margin during lowstands

    NASA Astrophysics Data System (ADS)

    Rubino, Jean-Loup; Gorini, Christian; Leroux, Estelle; Aslanian, Daniel; Rabineau, Marina; Parize, Olivier; Besson, David

    2015-04-01

    Miocene peri-alpine foreland basin is connected toward the south with the Gulf of Lion passive margin and is predominantly filled by marine shallow water molassic deposits ranging from lower Miocene to Pliocene in age. Nine to ten depositional sequences are recorded and partly preserved in this basin and can be traced into the post rift part of the Gulf of Lion. One of the most surprising feature of the stratigraphic infill is the total lack of lowstand deposits within the foreland basin ; All superimposed sequences only includes transgressive and highstand System Tracts separated by erosional sequence boundaries and the development of incised valley networks filled by tidal deposits during transgression; Besson et al. 2005. It means that the entire foreland basin in SE France is exposed during lowstand periods without any preservation of fluvial deposits. By place few forced regression wedges are preserved at the transition between the foreland and the passive margin, close to the present day coastline. To date no real lowstand wedges have never been reported in the offshore of the Gulf of Lion. A reinterpretation of the best old vintage 2D dip seismic profiles along the passive margin validates the idea that the foreland basin is entirely exposed as well as the proximal part of the passive margin; first because some incised valleys can be occasionally picked on the shelf and second mainly because well defined superimposed or juxtaposed prograding lowstand wedges with nicely defined clinoforms onlapping the sequence boundaries can be recognized on the distal part of the shelf from the Burdigalian to the Messinian. Their ages being constrains by the Calmar well calibration. Unfortunately, they can't be continuously mapped all along the shelf break because of the strong erosion related to the Messinian Unconformity and the associated huge sea level fall.So we have to explain why during the lowstands, exceptionally long fluvial valley networks (more than 300km) can

  4. Three depositional states and sedimentary processes of the western Taiwan foreland basin system

    NASA Astrophysics Data System (ADS)

    Lin, Yi-Jung; Wu, Pei-Jen; Yu, Ho-Shing

    2010-05-01

    The western Taiwan foreland basin formed during the Early Pliocene as the flexural response to the loading of Taiwan orogen on the Eurasian plate. What makes Taiwan interesting is the oblique collision, which allows the foreland basin to be seen at different stages in its evolution at the present day. Due to oblique arc-continent collision from north to south, the western Taiwan foreland basin has evolved into three distinct subbasins: an over-filled basin proximal to the Taiwan orogen, mainly distributed in the Western Foothills and Coastal Plain provinces, a filled basin occupying the shallow Taiwan Strait continental shelf west of the Taiwan orogen and an under-filled basin distal to the Taiwan orogen in the deep marine Kaoping Slope offshore southwest Taiwan, respectively. The over-filled depositional phase is dominated by fluvial environments across the structurally controlled piggy-back basins. The filled depositional state in the Taiwan Strait is characterized by shallow marine environments and is filled by Pliocene-Quaternary sediments up to 4,000 m thick derived from the Taiwan orogen with an asymmetrical and wedge-shaped cross section. The under-filled depositional state is characteristic of deep marine environments in the wedge-top basins accompanied by active structures of thrust faults and mud diapers. Sediments derived from the Taiwan orogen have progressively filled the western Taiwan foreland basin across and along the orogen. Sediment dispersal model suggests that orogenic sediments derived from oblique dischronous collisional highlands are transported in two different ways. Transport of fluvial and shallow marine sediments is perpendicular to hill-slope and across-strike in the fluvial and shallow marine environments proximal to the orogen. Fine-grained sediments mainly longitudinally transported into the deep marine environments distal to the orogen. The present sedimentary processes in the over-filled basin on land are dominated by fluvial

  5. Geodynamic models of convergent margin tectonics: transition from rifted margin to overthrust belt and consequences for foreland-basin development

    SciTech Connect

    Stockmal, G.S.; Beaumont, C.; Boutilier, R.

    1986-02-01

    A quantitative geodynamic model for overthrusting of a passive continental margin during attempted continental subduction demonstrates the mechanical and thermal coupling between overthrust loads, the lithosphere, and the associated foreland basin. The model treated the lithosphere as a two-dimensional nonuniform elastic plate whose strength is controlled thermally. The thermal and flexural evolution of a margin is followed from initial rifting and passive-margin development, through overthrusting and foreland-basin deposition, to postdeformational erosion.

  6. Structural controls on fractured coal reservoirs in the southern Appalachian Black Warrior foreland basin

    USGS Publications Warehouse

    Groshong, R.H.; Pashin, J.C.; McIntyre, M.R.

    2009-01-01

    Coal is a nearly impermeable rock type for which the production of fluids requires the presence of open fractures. Basin-wide controls on the fractured coal reservoirs of the Black Warrior foreland basin are demonstrated by the variability of maximum production rates from coalbed methane wells. Reservoir behavior depends on distance from the thrust front. Far from the thrust front, normal faults are barriers to fluid migration and compartmentalize the reservoirs. Close to the thrust front, rates are enhanced along some normal faults, and a new trend is developed. The two trends have the geometry of conjugate strike-slip faults with the same ??1 direction as the Appalachian fold-thrust belt and are inferred to be the result of late pure-shear deformation of the foreland. Face cleat causes significant permeability anisotropy in some shallow coal seams but does not produce a map-scale production trend. ?? 2008 Elsevier Ltd. All rights reserved.

  7. Recycling an uplifted early foreland basin fill: An example from the Jaca basin (Southern Pyrenees, Spain)

    NASA Astrophysics Data System (ADS)

    Roigé, M.; Gómez-Gras, D.; Remacha, E.; Boya, S.; Viaplana-Muzas, M.; Teixell, A.

    2017-10-01

    In the northern Jaca basin (Southern Pyrenees), the replacement of deep-marine by terrestrial environments during the Eocene records a main drainage reorganization in the active Pyrenean pro-wedge, which leads to recycling of earlier foreland basin sediments. The onset of late Eocene-Oligocene terrestrial sedimentation is represented by four main alluvial fans: Santa Orosia, Canciás, Peña Oroel and San Juan de la Peña, which appear diachronously from east to west. These alluvial fans are the youngest preserved sediments deposited in the basin. We provide new data on sediment composition and sources for the late Eocene-Oligocene alluvial fans and precursor deltas of the Jaca basin. Sandstone petrography allows identification of the interplay of axially-fed sediments from the east with transversely-fed sediments from the north. Compositional data for the alluvial fans reflects a dominating proportion of recycled rock fragments derived from the erosion of a lower to middle Eocene flysch depocentre (the Hecho Group), located immediately to the north. In addition, pebble composition allows identification of a source in the North Pyrenean Zone that provided lithologies from the Cretaceous carbonate flysch, Jurassic dolostones and Triassic dolerites. Thus we infer this zone as part of the source area, located in the headwaters, which would have been unroofed from turbidite deposits during the late Eocene-Oligocene. These conclusions provide new insights on the response of drainage networks to uplift and topographic growth of the Pyrenees, where the water divide migrated southwards to its present day location.

  8. Hydrocarbon Accumulation and Distribution Characteristics of the Silurian in the Tazhong Uplift of Tarim Basin

    NASA Astrophysics Data System (ADS)

    LÜ, Xiuxiang; BAI, Zhongkai; ZHAO, Fengyun

    Hydrocarbon accumulation of the Silurian in the Tazhong uplift of Tarim basin is characterized by "two sources and three stages". "Two sources" means that the hydrocarbons are derived from two source rocks of the Cambrian and Middle-Upper Ordovician. "Three stages" means that asphalt and movable oil undergoes three hydrocarbon accumulation stages, i.e., Late Caledonian, Late Hercynian, and Yanshanian-Himalayan. The formation of asphalt resulted from the destruction of the hydrocarbons accumulated and migrated in the early stages. The present movable oil, mostly derived from Middle-Upper Ordovician source rock, resulted from the hydrocarbons accumulated in the late stage. There are three types of reservoirs, i.e., anticline structural, stratigraphic lithological, and lava shield reservoirs in the Tazhong uplift. Hydrocarbon accumulation of the Silurian in the Tazhong uplift is controlled by the three factors. (1) The background of uplift structure. Around the ancient uplift, the compounding of many types makes up the composite hydrocarbon accumulation areas. (2) Effective cover. The show of oil gas including asphalt, heavy crude oil, and normal oil is quite active in the Silurian. Asphalt and heavy crude oil are distributed under the red mudstone member and movable oil is distributed under the gray mudstone member. (3) High quality reservoir bed. Sandstone is distributed widely in the Tazhong area. Reservoir pore space can be divided into three types: a) secondary origin-primary origin pore space; b) primary origin-secondary origin pore space, and c) micropore space. Porosity is 3.3-17.4%, and permeability is (0.1-667.97) × 10 -3 μm 2.

  9. Biostratigraphic utility of organic-walled phytoplankton, Upper Ordovician-Lower Silurian of Appalachian basin

    SciTech Connect

    Colbath, G.K.

    1986-05-01

    Upper Ordovician-Lower Silurian marine mudstones in the Appalachian basin, which have not been subjected to extensive heating or oxidation, contain abundant organic-walled phytoplankton (prasinophycean algal phycomata and acritarchs). In most areas graptolites and conodonts have not been recovered from these rocks, making the phytoplankton particularly important for biostratigraphic correlation. Recent advances have improved the precision with which these microfossils can be used. By tabulating relative abundance data carefully, an abrupt change in the composition of phytoplankton associations can be recognized at the Ordovician-Silurian boundary can be located with greater precision and confidence than is possible using the stratigraphic ranges of individual species. Many supposedly long-ranging species have relatively short stratigraphic ranges, and thus greater utility, as a result of detailed taxonomic studies. Therefore, type and comparative material are important considerations. Also, vesicle wall architecture and dehiscent structures are valuable taxonomic characters. Scanning electron microscopy examination has improved our understanding of small forms (less than 20 ..mu..m in diameter), and has thus increased the number of taxa available for use in biostratigraphy. Further study of samples from vertically extensive stratigraphic sections of established age should help workers refine the biostratigraphy of these microfossils.

  10. Distant effects in bivergent orogenic belts - How retro-wedge erosion triggers resource formation in pro-foreland basins

    NASA Astrophysics Data System (ADS)

    Hoth, Silvan; Kukowski, Nina; Oncken, Onno

    2008-08-01

    Timeseries derived from two-dimensional sandbox simulations involving surface erosion are taken for the first time to be implemented into flexure calculations of foreland basins. Based on our results we highlight that orogenic systems are a four component system, consisting of a pro-foreland basin, a pro-wedge, a retro-wedge, and a retro-foreland basin. These four components are mechanically coupled via the load dependence of tectonic faulting [Mandl, G., 1988. Mechanics of tectonic faulting, 1st Edition. Elsevier, Amsterdam.] and the finite flexural rigidity of lithospheric plates [Beaumont, C., 1981. Foreland basins. Geophys. J. R. Astron. Soc. 5 (2), 291-329.]. We further demonstrate that the impact of pro-wedge erosion is most pronounced within the pro-wedge but also modifies the shape and size of the retro-wedge, which in turn changes the geometry and propagation velocity of the retro-foreland basin and vice versa. This suggests that one out of the four components of an orogenic system cannot be fully understood without recognition of the other three components. Thus, spatial separation between processes or observations does not necessarily imply their physical independence. This conceptual model is applied in a case study to the Pyrenean orogenic wedge and its Ebro and Aquitaine foreland basins. Our analysis suggests that the Pyrenean pro- and retro-wedge are mechanically coupled and that this coupling manifests itself in the migration of depocentres in both foreland basins. We finally explore implications for the formation of Mississippi Valley Type deposits.

  11. Stratigraphic modeling of foreland basins: Interpreting thrust deformation and lithosphere rheology

    SciTech Connect

    Flemings, P.B.; Jordan, T.E. )

    1990-05-01

    The authors incorporate the processes of erosion and deposition in a numerical model to predict the stratal geometries and facies patterns produced during episodic thrusting in a nonmarine foreland basin. The resultant stratigraphic record is characterized by a stairstepped facies package in which each retrogradation of facies (toward the thrust) marks the onset of a thrusting event. The retrogradation of facies coincides with the migration of the forebulge toward the thrust and the generation of an erosional unconformity. In the past, changes in basin wavelength during basin evolution have been interpreted to record viscoelastic relaxation of the lithosphere. This model suggests that changes in basin wavelength are a natural consequence of the interplay between thrust and sediment loading on an elastic lithosphere.

  12. Tectonosedimentary evolution model of an intracontinental flexural (foreland) basin for paleoclimatic research

    NASA Astrophysics Data System (ADS)

    Fang, Xiaomin; Wang, Jiuyi; Zhang, Weilin; Zan, Jinbo; Song, Chunhui; Yan, Maodu; Appel, Erwin; Zhang, Tao; Wu, Fuli; Yang, Yibo; Lu, Yin

    2016-10-01

    Intracontinental flexural (foreland) basin sediments are now frequently used as archives for detailed paleoclimatic and sedimentary environmental reconstruction, fossil and stratigraphic correlation, and tectonic evolution and uplift of basin and orogen. However, sedimentologic characteristics vary considerably in time-space with the evolution of flexural basin, apt to cause misinterpretation of climatic change and stratigraphic correlation. Based on high resolution fossil mammal and magnetostratigraphic constraints and sedimentary facies analysis, here we took the Linxia Basin at the front of the NE Tibetan Plateau as a case to demonstrate and figure out a model how sedimentology and stratigraphy vary temporospatially with the evolution of such flexural basin. The results show that the Linxia Basin is a type intracontinental foreland basin subjected to two phases of flexural deformation exerted by the West Qin Ling (Mts.) and NE Tibetan Plateau to the south. Phase I began latest at the beginning of the Miocene (23.3 Ma), indicated by a balanced fast flexural subsidence and mostly fine sediment infilling giving rise to the early underlying unconformity. It manifests as an obvious sediment wedge with high filling rate, thickening toward mountains and an occurrence of a mountains-parallel big river - shallow lake system along the foredeep, suggesting a less high mountain topography. In the late Phase I, from 13 Ma to 8 Ma, the subsidence and thickening rates began to decrease, accompanied by faults and deformation propagating gradually into the basin, causing gradual basinward migration of the foredeep and its accompanying river-lake system. Since 8 Ma in Phase II, the West Qin Ling and NE Tibetan began to uplift rapidly and thrust/load onto the Linxia Basin, causing strong mountain erosion, thrust-fold belt propagation and basin overfilling. This forced the mountains-parallel river - lake system to turn to the mountains-perpendicular alluvial - braided river system

  13. Detrital zircon geochronology of Cordilleran retroarc foreland basin strata, western North America

    NASA Astrophysics Data System (ADS)

    Laskowski, Andrew K.; DeCelles, Peter G.; Gehrels, George E.

    2013-09-01

    present a compilation of 8717 U-Pb analyses from 95 detrital zircon samples of Jurassic-Eocene North American Cordillera foreland basin strata. Of these samples, 30 are new and previously unpublished. Variation in detrital zircon age spectra between samples records erosion or recycling of basement and cover rocks within the Cordilleran orogenic wedge. Each sample can be classified into one of six major provenance groups, whose age spectra suggest derivation from (1) Mesozoic eolianites of the western United States, (2) Paleozoic passive margin strata of the western United States, (3) Paleozoic passive margin strata of western Canada, (4) the Mogollon Highlands, (5) the Cordilleran magmatic arc, or (6) Yavapai-Mazatzal Province crystalline basement rocks. Referencing these provenance interpretations to their location and stratigraphic deposition age produces a detailed spatial and temporal record of sediment dispersal within the foreland basin system. Late Jurassic provenance is dominated by recycling of Mesozoic eolianites from sources in the Sevier thrust belt. Cretaceous-Eocene provenance is dominated by recycling of the passive margin, with increasing complexity upsection. We interpret that this provenance transition records a basin-wide unroofing sequence. A composite age-probability plot of 1539 young (<250 Ma) detrital zircons reveals at least four age-abundance peaks that we interpret to represent periodic high-flux magmatism in the Cordilleran arc.

  14. Cycles and stacking patterns in carboniferous rocks of the Black Warrior Foreland Basin

    SciTech Connect

    Pashin, J.C.

    1994-12-31

    Stratigraphic data from the Black Warrior Basin provide a robust basis for testing the influence of tectonics and climate on cyclicity in a foreland basin. The basin fill comprises carbonate-bearing Chester-type and coal-bearing Pottsville-type depositional cycles, and the composition, frequency, and stacking patterns of those cycles reflect dynamically interwoven tectonic and climate factors. Deformational loading evidently gave rise to flexural movements that determined cycle stacking patterns by controlling spatial and temporal variation of subsidence rate. Evolving tectonic highlands, moreover, provided shifting sources of terrigenous clastic sediment, thereby affecting stratal geometry. The transition from carbonate- to coal-bearing cycles reflects drift of southeastern North America into the humid equatorial belt. Change of average cycle duration from 1.1. to less than 0.5 m.y. corresponds to Gondwana glaciation, suggesting significant climatic forcing.

  15. Patterns of conodont extinction selectivity during Ireviken event (Lower Silurian), example from Eastern Baltic basin

    NASA Astrophysics Data System (ADS)

    Spiridonov, A.; Brazauskas, A.

    2012-04-01

    Ireviken event (Early Silurian) is one of the most prominent early paleozoic species turnovers identified by now. Earlier investigations showed that during considered biotic crisis large number of conodont species became extinct. Just twelwe out of sixty globally known species survived (Calner, 2008). A lot of attention concerning Irreviken event have been addressed toward description of timing of species extinctions and environmental factors that probably caused them. Here we suggest another point of view. We analized how conodont species level aggregate and emmergent traits (sensu Jablonski, 2008) influenced their extinction risk. Our analysis was confound to conodont spiecies from South Eastern part of Silurian Baltic Basin (Lithuania). Extinction probability influecing factors were evaluated using generalized linear modeling (GLM) methodology. The species were categorized into two types: those who lived before event and eventualy went extinct reaching it and those (and/or their conjectured descendants) who originated before event and survived it. Analysis of extinction risk revealed some unexpected results. Best predictor of conodont species survivorship during Ireviken event was level of variation of local abundances of individuals of given species (irrespective how we measure it - as standard deviation or coefficient of variation). Second important factor which determined extinction risk was geographic ranges of genuses to which analized species belonged. Higher variace of population size and larger geographical areas occupied by genera to which species belonged - the higher probability of survival during extinction event. Factors such as mean local population size and mean conodont species richness in samples from stratigraphic ranges of analized species are statistically insignificant as descriptors of extinction risk.

  16. Permian evolution of sandstone composition in a complex back-arc extensional to foreland basin: The Bowen Basin, eastern Australia

    SciTech Connect

    Baker, J.C. . Centre for Microscopy and Microanalysis); Fielding, C.R. . Dept. of Earth Sciences); Caritat, P de . Dept. of Geology); Wilkinson, M.M. )

    1993-09-01

    The Bowen Basin is a Permo-Triassic, back-arc extensional to foreland basin that developed landward of an intermittently active continental volcanic arc associated with the eastern Australian convergent plate margin. The basin has a complex, polyphase tectonic history that began with limited back-arc crustal extension during the Early Permian. This created a series of north-trending grabens and half grabens which, in the west, accommodated quartz-rich sediment derived locally from surrounding, uplifted continental basement. In the east, coeval calc-alkaline, volcanolithic-rich, and volcaniclastic sediment was derived from the active volcanic arc. This early extensional episode was followed by a phase of passive thermal subsidence accompanied by episodic compression during the late Early Permian to early Late Permian, with little contemporaneous volcanism. In the west, quartzose sediment was shed from stable, polymictic, continental basement immediately to the west and south of the basin, whereas volcanolithic-rich sediment that entered the eastern side of the basin during this time was presumably derived from the inactive, and possibly partly submerged volcanic arc. During the late Late Permian, flexural loading and increased compression occurred along the eastern margin of the Bowen Basin, and renewed volcanism took place in the arc system to the east. Reactivation of this arc led to westward and southward spread of volcanolithic-rich sediment over the entire basin. Accordingly, areas in the west that were earlier receiving quartzose, craton-derived sediment from the west and south were overwhelmed by volcanolithic-rich, arc-derived sediment from the east and north. This transition from quartz-rich, craton-derived sediments to volcanolithic-rich, arc-derived sediments is consistent with the interpreted back-arc extensional to foreland basin origin for the Bowen Basin.

  17. Evolution of sedimentary architecture in retro-foreland basin: Aquitaine basin example from Paleocene to lower Eocene.

    NASA Astrophysics Data System (ADS)

    Ortega, Carole; Lasseur, Eric; Guillocheau, François; Serrano, Olivier; Malet, David

    2017-04-01

    The Aquitaine basin located in south western Europe, is a Pyrenean retro-foreland basin. Two main phases of compression are recorded in this retro-foreland basin during the Pyrenean orogeny. A first upper Cretaceous phase corresponding to the early stage of the orogeny, and a second one usually related to a Pyrenean paroxysmal phase during the middle Eocene. During Paleocene to lower Eocene deformations are less pronounced, interpreted as a tectonically quiet period. The aim of the study is to better constrain the sedimentary system of the Aquitaine basin during this period of Paleocene-lower Eocene, in order to discuss the evolution of the sedimentary architecture in response of the Pyrenean compression. This work is based on a compilation of a large set of subsurface data (wells logs, seismic lines and cores logs) represented by isopachs and facies map. Three main cycles were identified during this structural quiet period: (1) The Danian cycle, is recorded by the aggradation of carbonate reef-rimmed platform. This platform is characterized by proximal facies (oncoid carbonate and mudstone with thalassinoides) to the north, which leads to distal deposit facies southern (pelagic carbonate with globigerina and slump facies) and present a significant thickness variation linked to the platform-slope-basin morphology. (2) The upper Selandian-Thanetian cycle follows a non-depositional/erosional surface associated with a Selandian hiatus. The base of this cycle marked the transition between the last reef rimmed platform and a carbonate ramp. The transgressive cycle is characterized by proximal lagoon facies to the north that leads southward to distal hemipelagic facies interfingered by turbiditic Lowstand System Tracks (LST). The location of these LST is strongly controlled by inherited Danian topography. The regressive cycle ends with a major regression associated with an erosional surface. This surface is linked with a network of canyons in the north, an important

  18. Controls of erosional denudation in the orogen on foreland basin evolution: The Oligocene central Swiss Molasse Basin as an example

    NASA Astrophysics Data System (ADS)

    Schlunegger, Fritz; Jordan, Teresa E.; Klaper, Eva Maria

    1997-10-01

    A high-resolution three-dimensional reconstruction of the 25-m.y.-old central Swiss Molasse Basin reveals two sedimentary domains separated by a ˜5-km-wide flood-plain. The proximal domain of the basin attained a width of 20 km, and its basement is steeply flexed (6°-7° dip). Petrographic data indicate that it was filled by sediment from the Rigi dispersal system derived from the central Alps of eastern Switzerland and by locally sourced bajadas. In contrast, the distal sedimentary domain, located farther north, was gently dipping (<2°) and was filled by the meandering Lac Léman and Honegg dispersal systems. Chronological data reveal that sedimentation in the northern proximal part of the basin started at ˜27 Ma, when sediment supply to the basin started to increase. Deflection of the foreland plate at ˜25 Ma is successfully simulated by flexural modeling of the thrust load and the sediment load. The model reveals that the Lac Léman and Honegg dispersal systems are located on a buried flexural bulge. Furthermore, it shows that burial and suppression of the flexural bulge at ˜27 Ma as well as an increase of the basin wavelength were controlled by the contemporaneous increase in the sediment supply rate of the Rigi system. The model presented suggests that the tectonic subsidence of the Molasse Basin was mainly controlled by tectonic events in the northern part of the orogen, within ˜70 km distance from the tip of the orogenic wedge. Crustal thickening in this part of the orogen is reflected in the proximal Molasse by sedimentary cycles characterized by an increase in the sediment accumulation rates up section and by the presence of locally sourced bajada fans at the top of each cycle. Although south vergent back thrusting along the Insubric Line ˜150 km south of the foreland basin contributed little to flexure, it resulted in an increase of the sediment supply to the foreland basin. This is reflected in the Molasse by coarsening and thickening upward

  19. Preliminary hydrogeologic framework of the Silurian and Devonian carbonate aquifer system in the Midwestern Basins and Arches Region of Indiana, Ohio, Michigan, and Illinois

    SciTech Connect

    Casey, G.D. )

    1992-01-01

    The aquifer and confining units have been identified; data on the thickness, extent, and structural configuration of these units have been collected; and thickness and structure-contour maps have been generated. Hydrologic information for the confining units and the aquifer also has been compiled. Where present, the confining unit that caps the carbonate aquifer consists of shales of Middle and Upper Devonian age and Lower Mississippian age, however, these units have been eroded from a large part of the study area. The regional carbonate aquifer consists of Silurian and Devonian limestones and dolomites. The rocks that comprise the aquifer in Indiana and northwestern Illinois are grouped into four major stratigraphic units: Brassfield and Sexton Creek Limestones or the Cataract Formation, the Salamonie Dolomite, the Salina Group, and the Detroit River and Traverse Formations or the Muscatatuck Group. In Ohio and southern Michigan the aquifer is grouped into ten stratigraphic units: Brassfield Limestone and Cataract Formation, the Dayton Limestone, the Rochester Shale equivalent, the Lockport Dolomite, the Salina Formation, the Hillsboro Sandstone, the Detroit River Group, the Columbus Limestone, the Delaware Limestone, and the Traverse Formation. The thickness of the carbonate aquifer increases from the contact with the outcropping Ordovician shales in the south-central part of the study area from the contact into the Appalachian Foreland Structural Basin from 0 ft at the contact to more than 700 ft at the eastern boundary of the study area, to more than 1,000 ft beneath Lake Erie and greater than 1,200 ft in southeastern Michigan. At the edge of the Michigan Intercontinental Structural Basin in western Ohio and eastern Indiana, the thickness ranges from 700 to 900 ft. and from 200 ft to 300 ft in south-central Indiana along the northeastern edge of the Illinois Intercontinental Structural Basin.

  20. Sequence stratigraphy and depositional systems of the Lower Silurian Medina Group, northern Appalachian basin

    SciTech Connect

    Castle, J.W. )

    1991-08-01

    Detailed sedimentological analysis of 3500 ft of continuous core from 44 wells in Pennsylvania, Ohio, Ontario, New York, and West Virginia, combined with regional study of geophysical logs, results in new interpretations of sequence stratigraphy and depositional systems in Lower Silurian siliciclastic rocks of the northern Appalachian basin. Above a type-1 sequence boundary at the base of the Medina Group are a lowstand systems tract and a transgressive systems tract that are represented, respectively, by the Whirlpool Sandstone and by the overlying Cabot Head Shale. The thickest sandstones in the Medina Group occur in the Grimsby Sandstone, which is interpreted as a highstand systems tract with basinward-prograding parasequences. Sea level rise after Grimsby parasequence deposition is represented by marine-shelf shale in the uppermost part of the Medina Group. Based on facies successions in the cores, four mappable depositional systems are interpreted for the Grimsby Sandstone and correlative sandstone units; (1) wave-dominated middle shelf, (2) wave- and tide-influenced inner shelf, (3) tide dominated shoreline, and (4) fluvial. The wave-dominated middle-shelf system, which includes very fine-grained shelf-ridge sandstones encased in marine shale, is the most basinward system, occurring from Ontario through parts of eastern Ohio. Shoreward, across the northern Appalachian basin, the influence of tidal processes relative to wave processes generally increased, which may have been related to distance across the shelf, water depth, and shoreline configuration. The shoreline may have been deltaic in some areas and straight in other areas.

  1. Magnetostratigraphic constraints on the development of paired fold-thrust belts/foreland basins in the Argentine Andes

    SciTech Connect

    Reynolds, J.H. ); Damanti, J.F. ); Jordan, T.E. )

    1991-03-01

    Development of a paired fold thrust-thrust belt/foreland basin is correlated to the flattening of the subducting Nazca plate between 28-33{degree}S. Magnetostratigraphic studies in neogene basin-filling continental strata determine local basin subsidence rates and provide relatively precise chronostratigraphic correlation between different depositional environments. The data demonstrate that most existing lithostratigraphic units are diachronous and require new tectonic interpretations. Increases in sediment accumulation rates closely correspond to changes in provenance and indicate that the Frontal Cordillera, on the Chile-Argentina border was a positive topographic province by 18 Ma. The Precordillera evolved from {approx}16 Ma to the present as thrusting migrated from west to east. Published ages from intercalated airfall tuffs constrain some sedimentary sections in the eastern Sierras Pampeanas where the earliest uplift occurred since 10 Ma. The youngest uplifts are on the west side close to continuing thrusting in the Precordillera. Not all fold-thrust belt/foreland basin pairs are associated with flat subduction, suggesting that tectonic controls exceeding the scale of individual plate segments may be important. The hydrocarbon-producing Subandean fold-thrust belt/foreland basin, located in the area of 'steep' subduction that underlies northern Argentina and Bolivia (18-24{degree}S), is also believed to have evolved since middle Miocene time. Recently initiated magnetostratigraphic studies in the Subandean foreland basin will attempt to temporally constrain the Neogene tectonic evolution for comparison with the southern region.

  2. Increasing influence of exotic terranes as sources of shales from the Sevier and Taconic Foreland basins : Evidence from Nd isotopes

    SciTech Connect

    Samson, S.D.; Andersen, C.B. . Dept. of Earth Sciences)

    1994-03-01

    The influence of outboard tectonostratigraphic terranes as a source of sediment to Ordovician foreland basins is unknown. To determine if there were changes in provenance, or changes in the importance of a given source region, the authors have analyzed shales from two foreland basins, the Tactonic Foreland basin of central New York and the Sevier Foreland basin of Tennessee, for their Nd isotopic compositions. Shales from the Taconic basin include those from the lower portion of Utica shale, Corynoides americanus graptolite Zone, and the uppermost portion of the Utica shale, including the Geniculograptus pygmaeus graptolite Zone. Initial [epsilon][sub Nd] values for the oldest Taconic basin shales are [minus]12. Initial [epsilon][sub Nd] values for the younger Taconic basin shales range from [minus]9.7 to [minus]8.4. This increase in [epsilon][sub Nd] may reflect an increased influence of terranes outboard of the Laurentian margin. Samples from the Sevier basin include those from the Blockhouse and Tellico Formations. A sample of the lower Blockhouse Fm. has an initial [epsilon][sub Nd] of [minus]9.4, while mid-formation levels have [epsilon][sub Nd] = [minus]8.8. Initial [epsilon][sub Nd] ranges from [minus]8.0 to [minus]7.2 from Tellico Formation shales. Thus a trend towards increasing [epsilon][sub Nd] with decreasing age is also seen in the Sevier basin. This again suggests the possibility of an increasing influence from nearby terranes. The fact that the [epsilon][sub Nd] values are higher in the Sevier basin than in the Taconic basin indicates that the Sevier shales received detritus with a less evolved isotopic composition. This may reflect fundamentally different sources, such as a more juvenile terrane as an important source of Sevier basin shales.

  3. Formation of the Maturín Foreland Basin, eastern Venezuela: Thrust sheet loading or subduction dynamic topography

    NASA Astrophysics Data System (ADS)

    JáCome, Maria I.; Kusznir, Nick; Audemard, Felipe; Flint, Steve

    2003-10-01

    The Maturín Basin in eastern Venezuela is considered a good example of a peripheral foreland basin. Earthquake and tomographic data indicate that eastern Venezuela is affected by the oblique subduction of the South American Plate underneath the Caribbean Plate. New forward flexural isostatic modeling of eastern Venezuela has been carried out in order to determine whether the Maturín Basin was generated purely by thrust sheet loading from the Serranía and Monagas Foreland Thrust Belts. A sequence of forward models from middle Miocene to Present was generated for 3 profiles across the Serranía del Interior Thrust Belt, the Monagas Foreland Thrust Belt, and the Maturín Foreland Basin. The predictions of these models are constrained using seismic reflection and well data. The flexural isostatic modeling shows that thrust sheet loading associated with the Serranía del Interior and Monagas Foreland thrust belts is insufficient to generate the observed subsidence within the Maturín Basin. Dynamic fluid flow modeling of subduction related dynamic topography of eastern Venezuela has been used to investigate the influence of South American Plate subduction on the generation of the accommodation space observed in the Maturín Basin. Fluid flow modeling of subduction related dynamic topography suggests that the subduction of the South American lithospheric mantle caused downward deflection of the South American crust affecting the Maturín Basin and the Serranía Thrust Belt. This modeling suggests that the Maturín Basin subsidence has two components: 55% related to thrust sheet loading and 45% driven by continental subduction.

  4. Hinterland tectonics and drainage evolution recorded by foreland basin archives: the Neogene Siwaliks of the Himalaya

    NASA Astrophysics Data System (ADS)

    Huyghe, Pascale; van der Beek, Peter; Matthias, Bernet; Catherine, Chauvel; Jean-Louis, Mugnier; Laurent, Husson; François, Chirouze

    2014-05-01

    Provenance analysis and detrital thermochronology of detrital synorogenic sediments, derived from erosion of mountain belts and deposited in surrounding sedimentary basins, are well-established methods to examine the exhumation history of convergent zones, tectonic activity and the associated evolution of the drainage network. We have conducted multidisciplinary studies on magnetostratigraphically dated sections throughout the Neogene Siwalik foreland basin of the Himalayan belt since more than 10 years. Sr, Nd and Hf isotopes are used as provenance indicators, providing information on the nature and size of catchment basins and their evolution through time in response to tectonics. Detrital zircon and apatite thermochronology provides constraints on exhumation rates in the hinterland of the Himalaya and the deformation of the Sub-Himalayan foreland basin. Throughout the Himalaya, detrital zircons from the Siwaliks generally show three age peaks: two static peaks (i.e., displaying constant peak ages through time), and a moving peak. The latter shows a constant lag time of ~4 m.y. corresponding to source-area exhumation rates on the order of 1.8 km/my, while the two static peaks respectively reveal a major 15-20 Ma exhumation event in the belt, the significance of which is still debated, and inheritance of pre-Himalayan ages that indicate recycling of Tethyan sediments. Therefore, our ZFT results suggest that the exhumation dynamics are broadly similar throughout the Himalaya since at least 13 m.y, as also shown by the Bengal Fan detrital sediment record. We relate this switch in tectonic regime to the destabilization of the Himalayan wedge that is rendered overcritical as a response to the transience of dynamic topography caused by the deforming underlying Indian slab. Nonetheless, in detail, the timing of thrusting in the Siwalik domain is delayed by about 1 my eastward as demonstrated by both structural and apatite fission-track data, suggesting overall eastward

  5. Geometry and depositional history of the southern Antler foreland basin, Eleana FM, Nevada Test Site

    SciTech Connect

    Trexler, J.H. Jr.; Cashman, P.H. . Dept. of Geological Sciences)

    1993-04-01

    Analysis of the Mississippian Eleana Formation on the Nevada Test Site allows new insight into the history of filling and three-dimensional shape of the southern end of the Antler foreland basin. Previous work has shown that the Eleana Fm. comprises a relatively thick section of submarine-fan sediments, time equivalent to the deep-marine Chainman Shale and the fluvial to shallow-marine Diamond Peak Fm. in central Nevada. The mudstone section originally described as the upper part of the Eleana Fm. is coeval with, but does not record, submarine-fan deposition, and is not discussed here. The Eleana Fm. occurs in at least two fault slices that juxtapose unlike stratigraphic sections. Lower plate stratigraphy includes multiple channel-complex and fan lobe facies, with dominant paleoflow to the south-southwest, changing upward to southeast. Upper plate strata comprise a single, fining-upward sequence of inner-fan channel conglomerate and sandstone, giving way upward to intra-channel pelagic sediments, with dominant paleoflow to the south and southwest. Submarine fan deposition persisted from latest Devonian until at least latest Mississippian time. The upper plate has apparently been carried eastward over the lower, but accurate restoration of original lateral relationships between fault slices is not yet possible. The upper plate is interpreted as the main, axial submarine-fan, while the lower plate is thought to be a prograding eastern fan-fringe deposit. These strata record the filling of a remnant ocean basin that persisted at the southern end of the orogen after the basin was filled to sea-level in the north. This basin was filled axially by sediments from the north, both recycled early foreland fill and Antler orogenic sediments and volcanics.

  6. Deep-water carbonate slope failure events in a newly discovered Silurian basin, Blue Ridge province, southern Appalachians, Tennessee

    SciTech Connect

    Unrug, R. )

    1991-03-01

    Siliciclastic deep-water turbidites of the Walden Creek Group, Ocoee Supergroup, underlying the foothills of the Great Smoky Mountains, contain olistolith blocks and olistostromal debris-flow breccia beds. Paleozoic fossils discovered recently in the olistoliths indicate Silurian age of the carbonates. The Walden Creek Group is therefore Silurian or younger, not late Proterozoic in age, as believed previously. The carbonate olistoliths and breccias formed by collapse of post-Taconic Silurian carbonate-dominated basin present in the Blue Ridge province of the Southern Appalachians into the younger basin of the Walden Creek Group. Two modes of occurrence of the olistoliths are present: (1) discrete horizons in which olistoliths are sitting spaced ten to hundreds of meters apart underneath a widespread conglomerate bed and (2) accumulations of olistoliths in localized stacked horizons in the vertical sequence of the enclosing siliciclastic rocks. Both modes can be related to failure of active fault scarps. Rocks of the olistolith are lithologically varied and record an older event of slope failure within the Silurian carbonate-dominated basin. Three facies assemblages representing two sedimentary environments are present in the olistoliths. Facies assemblage A includes oolitic limestone, stromatolite, carbonate breccia encrusted by stromatolite, and massive sandy limestone. It represents a high-energy, shallow-water, carbonate platform environment. Facies assemblage B consists of bedded dark limestone, alternating with black shale, and represents sediments of the carbonate platform slope. Facies assemblage C includes carbonate breccias intercalated in the bedded limestones and shales and is interpreted as deposits of the lower slope formed by failure of the carbonate platform margin.

  7. Depositional model, dolomitization, and porosity of Henryhouse Formation (Silurian), Anadarko basin, Oklahoma

    SciTech Connect

    Beardall, G.B.

    1987-08-01

    The Upper Silurian Henryhouse Formation, which is part of the Hunton Group, is a major hydrocarbon reservoir in the Anadarko basin. Three basic lithofacies are present in the Henryhouse, based on sedimentary structures, lithology, fossil content, and fabric relationships. These facies, represented in general by massive lime mudstone with diverse fauna, burrowed dolowackestone/packstone with mainly crinoids, and massive to laminated dolomudstone with fenestral fabrics and sparse fauna, are inferred to represent subtidal, intertidal, and supratidal environments, respectively. These facies comprise a vertical sequence that represents regressive deposition. The Henryhouse consists of several of these sequences. The Henryhouse commonly is partly or completely dolomitized in western Oklahoma. Three stages of dolomitization were documented: (1) penecontemporaneous hypersaline dolomite occurring as brownish, hypidiotopic rhombs concentrated in the supratidal and intertidal facies, (2) mixed marine and freshwater dolomite occurring as white rims around preexisting hypersaline dolomite, and as subhedral, white rhombs in vugs and molds, and (3) deep-burial vug, mold, and fracture-filling saddle dolomite. Production in the Henryhouse is generally from porous zones in dolomite. However, lithofacies reflecting depositional environments in which they were formed are equally important in porosity development.

  8. Mantle-derived helium in foreland basins in Xinjiang, Northwest China

    NASA Astrophysics Data System (ADS)

    Xu, Sheng; Zheng, Guodong; Zheng, Jianjing; Zhou, Shixin; Shi, Pilong

    2017-01-01

    Hydrocarbon-rich natural gases from the Tarim, Junggar, Turpan-Hami and Santanghu basins in Xinjiang, Northwest China have measured 3He/4He ratios from 0.01 to 0.6 times higher than the atmospheric value, indicating 0-7% helium derived from the mantle. The mantle-derived helium is high in foreland basins associated with the Tianshan, Kunlun and Zhayier-Halalate orogenic mountains, but low towards the center of basins. This spatial distribution suggests that the mantle-derived helium originates either from fluids or small scale melts in the upper asthenospheric or lithospheric mantle which have found pathways into the root zones of the major faults defining these mountains, but do not significantly move into the basins themselves. During upward transport to near the surface, the mantle-derived helium is significantly diluted by radiogenic helium produced in the crust. Despite the lack of recent magmatic activity or extensional tectonics within the basins, this pattern shows strong evidence that the major faults play an important role in mantle-derived components degassing from the mantle to the surface.

  9. Structural geology and tectonic significance of foreland thrust belts, Tarim and Junggar basins, northwest China

    SciTech Connect

    McKnight, C.L.; Chu, J.; Corroll, A.R.; Hendrix, M.S.; Wang, X.; Graham, S.A.; Liang, Y.H.; Wang, Z.X.; Xiao, X.

    1989-03-01

    The Kalpin uplift, located on the northwestern margin of the Tarim basin is characterized by a series of thin, southeast-vergent thrust plates modified by strike-slip faults. Each thrust plate repeats a sedimentary sequence consisting of upper Proterozoic through Permian shallow marine to nonmarine carbonates and clastics. Tertiary rocks as young as Neogene are affected by the deformation. The most basinward thrust sheet abuts the Bachu uplift, an older structural feature trending almost perpendicular to the thrusts. Sedimentary rocks as old as late Proterozoic are exposed in the Bachu uplift, which apparently represents a west-vergent Late Silurian to Early Devonian thrust belt. An unconformable Silurian-Devonian contact, the presence of Devonian red beds, and another unconformable contact separating Devonian from Upper Carboniferous strata support the interpretation of a middle Paleozoic deformational event. Another unconformity, at the Carboniferous-Permian boundary, apparently coincides with the time of collision of the Tarim craton with the southern margin of central Asia. The Shihezi fold trend, located in the southern Junggar basin, consists of three lines of surface anticlines trending parallel to the axis of the Urumqi foredeep. A thick sequence of Mesozoic and Cenozoic nonmarine sedimentary rocks accumulated in the growing foredeep. Mesozoic and Paleogene strata are deformed in the southern foldbelt, with Jurassic rocks forming the cores of these thrusted anticlines. The Qigu oil field is located in this southern belt. Deformed Neogene and Quaternary strata are exposed in the thrusted anticlines of the middle and northern foldbelts. The Dushanzi oil field is located in the northern belt. The episodic development of compressional structures in northwestern China documents the accretion of a number of tectonic units to the growing southern margin of central Asia through time.

  10. Evolution of the passive margin of the peripheral foreland basin: an example from the Lower Miocene Carpathian Foredeep (Czech Republic)

    NASA Astrophysics Data System (ADS)

    Francírek, Michal; Nehyba, Slavomír

    2016-02-01

    The Karpatian deposits of the central part of the Carpathian Foredeep in Moravia, which are deeply buried under the Outer Western Carpathians, provide a unique opportunity to reconstruct the former evolutionary stages of this peripheral foreland basin and its paleogeography. A succession of three depositional units characterized by a distinct depositional environment, provenance, and partly also foreland basin depozone, have been identified. The first depositional unit represents a proximal forebulge depozone and consists of lagoon-estuary and barred coastline deposits. The source from the "local" crystalline basement played here an important role. The second depositional unit consists of coastline to shallow marine deposits and is interpreted as a forebulge depozone. Tidalites recognized within this unit represent the only described tide-generated deposits of the Neogene infill of the Carpathian Foredeep basin in Moravia. The source from the basin passive margin (the Bohemian Massif) has been proved. The third depositional unit is formed by offshore deposits and represents a foredeep depozone. The provenance from both passive and active basin margin (Silesian Unit of the Western Carpathian Flysch Zone) has been proved. Thus, both a stepwise migration of the foredeep basin axis and shift of basin depozones outwards/cratonwards were documented, together with forebulge retreat. The shift of the foreland basin depozones more than 50 km cratonward can be assumed. The renewed thrusting along the basin's active margin finally completely changed the basin shape and paleogeography. The upper part of the infill was deformed outside the prograding thrust front of flysch nappes and the flysch rocks together with a strip of Miocene sediments were superposed onto the inner part of the basin. The width and bathymetric gradient of the entire basin was changed/reduced and the deposition continued toward the platform. The basin evolution and changes in its geometry are interpreted

  11. Integration of geologic data by applying sequence stratigraphic methods to foreland basins

    SciTech Connect

    Nunez, F.J.; Tover, G.N.S. )

    1993-02-01

    Much doubt exists about the application of sequence stratigraphy in areas of strong tectonic influence. The purpose of this paper is to demonstrate the wide applicability of sequence stratigraphy as an alternative to classical lithostratigraphy by utilizing this tool to explain deformed geometries of passive margin basins described by Vail et al as they became deformed within the foreland basins. The information that is summarized in the present study is the result of the integration of existing data in an area of the Eastern Venezuela Basin. We combined the biostratigraphic data (abundance and diversity curves of fossils from planktonic and benthonic forminifera to calcareous nannoplancton and palinomorphs) with their depths relation to the electrical log in order to identify condensed sections and sequence boundaries in the manner of Vail and Wornardt. Dipmeter data is incorporated in this study by using stereoplots of structural poles which allows a priori determination of the source and direction of basin fill and reconstruction of the paleogeography. Combining all of these analytical elements one derives a conceptual geological model that is then transferred into the interpretation of the seismic lines.

  12. Compressional salt tectonics in the early stages of the South Pyrenean foreland basin

    NASA Astrophysics Data System (ADS)

    Burrel, Laura; Teixell, Antonio

    2017-04-01

    Salt tectonics in the Pyrenees has been widely documented for the Cretaceous extensional episode, defining the existence of salt walls and minibasins along the northern and southern Pyrenean paleomargins. The original geometry of these salt structures was heavily overprinted by shortening during the Alpine orogeny, but restored models have been documented. Other features explored regarding salt tectonics are the big domic or equidimensional diapirs that evolved during the Late Tertiary and still retain their shape in the southern Pyrenees. In either case, the Triassic Keuper evaporite layer is the source layer for the diapiric structures, which is also traditionally recognized as the main detachment level for the external Pyrenean thrust belts. In this work we focus on the role played by salt during the early stages of Alpine compression, which has been comparatively much less investigated. The Late Cretaceous to Eocene early foreland basin of the Southern Pyrenees shows evidence of salt movement that is often overlooked due to the most evident imprint of thrusts and associated fault-related folds. In this preliminary study we report field examples that shed some light on the interplay between halokinesis and buckling in the low-strain compressional regime during the early stages of the Pyrenean orogeny. Also we discuss how the growing salt structures control the local subsidence and the sediment dispersal patterns within the basin. We describe cases of salt-related geometries in the Eocene basins of the southern Pyrenees in areas as the footwall of the Montsec thrust -the Ager basin-, the External Sierras south of the Jaca basin, and the Pobla de Segur and Senterada intramontane conglomerate deposits on the Boixols and Nogueres thrust sheets. The examples are separate, but they offer a wide range of geometries such as tight synclines, vertical and overturned fold limbs, growth strata, and fault boundaries that can be interpreted as thrust welds. These serve as a

  13. Paleostress pattern and salt tectonics within a developing foreland basin (north-western Subhercynian Basin, northern Germany)

    NASA Astrophysics Data System (ADS)

    Brandes, Christian; Schmidt, Carolin; Tanner, David Colin; Winsemann, Jutta

    2013-11-01

    Analysing the paleostress field in sedimentary basins is important for understanding tectonic processes and the planning of drilling campaigns. The Subhercynian Basin of northern Germany is a perfect natural laboratory to study the paleostress field in a developing foreland basin. The simple layer-cake geometry of the basin-fill is dominated by several piercing and non-piercing salt structures. We derived the paleostress field from the orientation of fracture sets, faults, slickensides and stylolites. On a regional scale, the basin-fill is characterized by a horizontal compressional paleostress vector that is mainly NNE-SSW-oriented, which reflects the Late Cretaceous inversion phase in Central Europe. We show that the local paleostress field is distinctly perturbated due to the salt structures. Along the edge of the salt pillows, the maximum horizontal paleostress vector is deflected by up to 90° from the regional trend. In the case of the Elm salt pillow, it forms a radial pattern. Restoration of balanced cross-sections demonstrates at least 9 % of the shortening of the north-western part of the Subhercynian Basin was achieved by folding. The salt structures in the north-western Subhercynian Basin are the result of varying stress conditions. Initial extension in the Triassic caused first salt movements that prevailed during the Jurassic and Early Cretaceous. Most important is the Late Cretaceous contractional phase that shortened the diapirs and led to the formation of the salt pillows between diapirs due to detachment folding. We derive four main controlling factors for such salt-dominated contractional basins: (1) the wedge-shape basin-fill is the product of the dynamic load at the southern margin of the basin, (2) a basal salt layer fed the diapirs and acted as a detachment horizon during the later shortening, (3) detachment folding was the dominating deformation mechanism during contraction, and (4) the pre-existing diapirs controlled the position of the

  14. Thermal effects of Caledonian foreland basin formation, based on fission track analyses applied on basement rocks in central Sweden

    NASA Astrophysics Data System (ADS)

    Huigen, Yvette; Andriessen, Paul

    Increasing evidence from fission track studies in Sweden indicate that large parts of the Fennoscandian Shield have been affected by a large-scale thermotectonic event in the Palaeozoic. In this study the results of 17 apatite fission track analyses from central Sweden are presented collected along three NW-SE transects trending from the Bothnian Sea to the Caledonides. On the Bothnian coast samples have been collected directly from the Sub-Cambrian Peneplain. The sedimentary cover protecting this surface until recently is responsible for the thermal increase detected through apatite fission track (FT) thermochronology. The apatite FT ages range between 516 ± 46 Ma (±1 σ) on the Bothnian coast around sea level to 191 ± 11 Ma in the Caledonides (∼500-1500 m.a.s.l.). The mean track lengths vary from 11.3 ± 2.2 μm (±1 σ) in the east to 14.2 ± 2.8 μm in the west, indicating a longer stay in the PAZ in the east, versus a continuous cooling pattern in the west. This pattern in combination with other geological constraints indicates that the crystalline basement rocks near the Caledonian deformation front in the west experienced higher temperatures after the formation of the Sub-Cambrian Peneplain followed by denudation, compared with the basement rocks in the east near the Bothnian coast. The apatite FT data near the Caledonian deformation front indicates prevailing temperatures of more than 110 ± 10 °C prior to the Mid Palaeozoic, causing a resetting of the apatite fission track clock. The temperatures were progressively lower away from the deformation front. Apatite fission track analysis of samples collected from the Sub-Cambrian Peneplain along the Bothnian coast indicate maximum temperatures of 90 ± 15 °C during Late Silurian-Early Devonian time. This heating event is argued to be the result of burial beneath a developing foreland basin in front of the Caledonian orogeny. Assuming a geothermal gradient of 20 °C/km, this temperature increase can be

  15. Flexure of lithosphere beneath the Alberta Foreland Basin: Evidence of an eastward stiffening continental lithosphere

    SciTech Connect

    Wu, P. )

    1991-03-01

    The flexure of the Mississippian Unconformity (MU) is used to constrain the stiffness of the lithosphere beneath the Alberta Foreland Basin (AFB). This flexure supports the sedimentological evidence for the absence of a forebulge in the AFB and implies that the peak of the forebulge lies further east of the Alberta Saskatchewan border. It is demonstrated that an eastwards stiffening lithosphere is required in order to fit the flexure of the MU. When flexural stiffness is expressed in terms of effective thickness, it varies from about 38km west of the Rocky Mountains to more than 200km underneath the North American craton. This variation of stiffness indicates that there is a strong lateral temperature and chemical variation underneath. Eastwards stiffening also implies an eastwards thickening of the elastic lithosphere. Such a model is in good agreement with recent petrological and geophysical evidences in the west and underneath the craton.

  16. An unrecognized development of retro-arc foreland basin system in northeast China during late Cretaceous (Campanian-Maastrichtian)

    NASA Astrophysics Data System (ADS)

    Zhang, F. Q., Sr.; Chen, H.; Dilek, Y.; Yang, S.; Meng, Q. A.

    2016-12-01

    Regional variations of stratigraphy, internal structures and infill architecture defined an unrecognized Campanian-Maastrichtian retro-arc foreland basin system in northeast China. In the most proximal part of this foreland basin system, the discrete Upper Cretaceous of the eastern zone suffered multi-stage intense folding-thrusting deformation before early Cenozoic extension. The continuous Cretaceous Songliao Basin of the central zone, almost occupied the main position of the foredeep depozone, where the round accumulating infill system was abruptly changed to westward fluvial-delta drainage system with the synchronous occurrence of an NNE-trending elongate trough since the early Campanian. The NNE-strike Great Xing'an Range acted as the forebulge uplift, missing the Upper Cretaceous. A thin saucer-shaped sag basin developed in the Hailar and Erlian basins during the late Campanian-Maastrichtian represents a back-bulge subsidence. Compressive deformation both in the western and central zones almost formed at the latest Cretaceous and weakened westward. Ancient counterparts of these four depozones can be identified in northeast China suggest that a foreland basin system was coupled with the coastal orogeny under a retro-arc setting during the Campanian-Maatrichtian of late Cretaceous, which is inferred to be the response of tectonic switch from West Pacific-type to Andean-type subduction along northeastern Asia.

  17. Depositional history of Dakota Sandstone, Moxa Arch and vicinity, southwestern Wyoming - implications for early evolution of Cretaceous Foreland Basin

    SciTech Connect

    Ryer, T.A.; McClurg, J.J.; Muller, M.M.

    1987-05-01

    The Dakota Sandstone in the vicinity of the Moxa Arch is divided into upper and lower parts using an unconformity identified on the basis of petrographic evidence and facies relationships. The unconformity is believed to be of subaerial origin and came into being during a pronounced lowering of relative sea level during the late Albian. The lower Dakota consists predominantly of shoreline sandstone and offshore marine shale on the northern part of the Moxa Arch; it consists predominantly of fluvial strata on the southern part of the arch. Meander belts of the lower Dakota trend north-northeastward toward the west-northwest-trending shoreline of the Thermopolis Sea. The upper Dakota consists predominantly of strata deposited in low-energy, restricted marine paleoenvironments that came into being during gradual transgression of the Shell Creek/Mowery Sea. Barrier-island sandstones bodies are elongate toward the northeast, indicating that the shoreline trended in that direction. The reorientation of the shoreline from west-northwest-trending in the lower Dakota to northeast-trending in the upper Dakota is attributed to acceleration in the rate of subsidence in the foreland basin. The Shell Creek Sea advanced down the eastern side of the foreland basin, transgressing over lacustrine deposits that accumulated there during the low-stand of sea level. The Moxa Arch appears to have served as the eastern hinge of the foreland basin during the Dakota; only later, in the Late Cretaceous, did it assume the characteristics of a foreland welt.

  18. Crustal geoelectric structure of the Sikkim Himalaya and adjoining Gangetic foreland basin

    NASA Astrophysics Data System (ADS)

    Pavan Kumar, G.; Manglik, A.; Thiagarajan, S.

    2014-12-01

    We present the results of a broadband magnetotelluric survey along a 200-km-long profile across the Sikkim Himalaya. The data were acquired at average station spacing of 5-6 km and transfer functions of 31 sites in 0.01-1000 s period range have been used for 2-D joint inversion of TE and TM modes. The composite model incorporating the effect of transverse strike reveals several features that correlate with the available seismic and kinematic models of the region. A major result of the present study is that the Main Himalayan Thrust forms the base of several resistive blocks within the wedge and that a ramp structure is present south of the Main Central Thrust Zone (MCTZ). Another significant result is that the crust and mantle lithosphere beneath the MCTZ and the Higher Himalayan Crystallines (HHC) seem to be compositionally/geologically different from the lithosphere south of the MCTZ. A steep crustal-scale fault with the Moho offset of 14 km is inferred to be separating these two blocks. The deep crustal seismicity could be related to this fault whereas shallow seismicity can be linked to the deformation within the wedge. The results also reveal the presence of some more conductors. We relate the conductor within the HHC to the sedimentary rocks of the Tethyan sequence exposed in a window about 40 km west of the profile and north of the South Tibetan Detachment System (STDS). The conductor at 90 km profile location is linked to the Gondwana rocks exposed in the Rangit Window. A 4-6 km thick sedimentary layer overlies the basement in the Gangetic foreland basin. We also delineate a sub-crustal conductor at 50-60 km depth beneath the foreland basin at the southern end of the profile, the cause of which is not apparent and needs to be explored.

  19. A new age model for the early-middle Miocene in the North Alpine Foreland Basin

    NASA Astrophysics Data System (ADS)

    Reichenbacher, Bettina; Krijgsman, Wout; Pippèrr, Martina; Sant, Karin; Kirscher, Uwe

    2016-04-01

    The establishment of high-resolution age models for sedimentary successions is crucial for numerous research questions in the geosciences and related disciplines. Such models provide an absolute chronology that permits precise dating of depositional episodes and related processes such as mountain uplift or climate change. Recently, our work in the Miocene sediments of the North Alpine Foreland Basin (NAFB) has revealed a significantly younger age (16.6 Myr) for sediments that were thought to have been deposited 18 Myr ago. This implies that a fundamentally revised new age model is needed for the entire suite of lower-middle Miocene sedimentary rocks in the NAFB (20 to 15-Myr). Our new data also indicate that previously published reconstructions of early-middle Miocene palaeogeography, sedimentation dynamics, mountain uplift and climate change in the NAFB all require a critical review and revision. Further, the time-span addressed is of special interest, since it encompasses the onset of a global warming phase. However, it appears that a fundamentally revised new age model for the entire suite of lower-middle Miocene sedimentary rocks in the NAFB can only be achieved based on a 500 m deep drilling in the NAFB for which we currently seek collaboration partners to develop a grant application to the International Continental Deep Drilling Program (ICDP). Reference: Reichenbacher, B., W. Krijgsman, Y. Lataster, M. Pippèrr, C. G. C. Van Baak, L. Chang, D. Kälin, J. Jost, G. Doppler, D. Jung, J. Prieto, H. Abdul Aziz, M. Böhme, J. Garnish, U. Kirscher, and V. Bachtadse. 2013. A new magnetostratigraphic framework for the Lower Miocene (Burdigalian/Ottnangian, Karpatian) in the North Alpine Foreland Basin. Swiss Journal of Geosciences 106:309-334.

  20. Cyclicity and stacking patterns in Carboniferous strata of the Black Warrior Foreland Basin

    SciTech Connect

    Pashin, J.C.

    1994-09-01

    Cyclicity in Carboniferous stratigraphic successions has long been attributed to tectonism and climate, but the ways these variables interact to determine the architecture of sedimentary basin fills remain a subject of intense debate. Geophysical well logs and cores from the Black Warrior basin were used to test the effects of tectonism and climate on cyclicity and stacking patterns in a foreland-basin setting. The Black Warrior basin formed in Carboniferous time by diachronous tectonic loading of the Alabama continental promontory along the Appalachian-Ouachita juncture. Climatic changes affecting the basin during this time include drift of southeastern North America from the arid southern tradewind belt toward the humid equatorial belt, as well as the onset of a major Gondwana glaciation just prior to the end of the Chesterian. The fill of the Black Warrior basin comprises carbonate and coal-bearing depositional cycles, and the composition, frequency, and stacking patterns of those cycles reflect dynamically interwoven tectonic and climatic factors. Tectonic loading evidently gave rise to flexural movements that determined cycle stacking patterns by controlling spatial and temporal variation of subsidence rate. Evolving tectonic highlands, moreover, fostered a shift from cratonic to orogenic sources of terrigenous elastic sediment, thereby affecting stratal geometry. Climate, by contrast, regulated the composition and frequency of the cycles. The transition from carbonate-bearing cycles with oxidized, calcic paleosols to coal-bearing cycles with reduced, histic paleosols reflects drift of southeastern North America into the humid equatorial belt. Change of average cycle duration from 1.3 m.y. to less than 0.4 m.y. corresponds with the onset of Gondwana glaciation, suggesting significant climatic forcing of sea level variation.

  1. Upper Ordovician-Lower Silurian shelf sequences of the Eastern Great Basin: Barn Hills and Lakeside Mountains, Utah

    SciTech Connect

    Harris, M.T. . Dept. of Geosciences); Sheehan, P.M. . Dept of Geology)

    1993-04-01

    Detailed stratigraphic sections through Upper Ordovician-Lower Silurian shelf strata of the Eastern Great Basin were measured in two Utah localities, Barn Hills (Confusion Range) and Lakeside Mountains. Six major subfacies occur in these strata: mud-cracked and crinkly laminated subfacies, Laminated mudstone subfacies, cross-bedded grainstone subfacies, cross-laminated packstone subfacies, grainy bioturbated subfacies, muddy bioturbated subfacies, and thalassinoides burrowed subfacies. These occur in 1--10 m thick cycles in three facies: muddy cyclic laminite facies (tidal flats), cross-bedded facies (subtidal shoals), and bioturbated facies (moderate to low-energy shelf). The vertical facies succession, stacking patterns of meter-scale cycles, and exposure surfaces define correlatable sequences. The authors recognize four Upper Ordovician sequences (Mayvillian to Richmondian). An uppermost Ordovician (Hirnantian) sequence is missing in these sections but occurs basinward. Lower Silurian sequences are of early Llandoverian (A), middle Llandoverian (B), early late Llandoverian (C1--C3), late late Llandoverian (C4--C5), latest Llandoverian (C6) to early Wenlock age. In general, Upper Ordovician and latest Llandoverian-Wenlockian facies are muddier than intervening Llandoverian facies. The shift to muddier shelf facies in latest Llandoverian probably corresponds to the development of a rimmed shelf. The sequence framework improves correlation of these strata by combining sedimentologic patterns with the biostratigraphic data. For example, in the Lakesides, the Ordovician-Silurian boundary is shifted 37 m downward from recent suggestions. In addition, the sequence approach highlights intervals for which additional biostratigraphic information is needed.

  2. Post-orogenic evolution of mountain ranges and associated foreland basins: Initial investigation of the central Pyrenees

    NASA Astrophysics Data System (ADS)

    Bernard, Thomas; Sinclair, Hugh; Ford, Mary; Naylor, Mark

    2017-04-01

    Mountain topography, including surrounding foreland basins, results from the long-term competition between tectonic and surface processes linked to climate. Numerous studies on young active mountain ranges such as the Southern Alps, New Zealand and Taiwan, have investigated the interaction between tectonics, climate and erosion on the topographic landscape. However most of the mountain ranges in the world are in various stages of post-orogenic decay, such as the European Alps, Urals, Caledonides, Appalachians and Pyrenees. The landscape evolution of these decaying mountains, which involve relatively inactive tectonics, should appear simple with progressive and relatively uniform erosion resulting in a general lowering of both elevation and topographic relief. However, in a number of examples, post-orogenic systems suggest a complex dynamism and interactions with their associated foreland basins in term of spatio-temporal variations in erosion and sedimentary flux. The complexity and transition to post-orogenesis is a function of multiple processes. Underpinning the transition to a post-orogenic state is the competition between erosion and crustal thickening; the balance of these processes determines the timing and magnitude of isostatic rebound and hence subsidence versus uplift of the foreland basin. It is expected that any change in the parameters controlling the balance of erosion versus crustal thickening will impact the topographic evolution and sediment flux from the mountain range and foreland basin to the surrounding continental margin. This study will focus on the causes and origins of the processes that define post-orogenesis. This will involve analyses of low-temperature thermochronological and topographic data, geodynamical modelling and sedimentological analyses (grainsize distribution). The Pyrenees and its associated northern retro-foreland basin, the Aquitaine basin, will form the natural laboratory for the project as it is one of the best

  3. Fluvial sedimentology of a Mesozoic petrified forest assemblage, Shishu Formation, Junggar foreland basin, Xinjiang, China

    SciTech Connect

    McKnight, C.L.; Gan, O.; Carroll, A.R.; Dilcher, D.; Zhao, M.; Liang, Y.H.; Graham, S.A.

    1988-02-01

    The Upper Jurassic(.) Shishu Formation of the eastern Junggar basin, Xinjiang, northwest China, is a fluvial sand unit containing an important assemblage of well-preserved, silicified tree trunks and rooted stumps. Numerous logs, up to 83 ft (25.5 m) long, occur at several levels within a 33.6-ft (10.3 m) stratigraphic section of fluvial sand, gravel, and mud and several paleosol horizons. The uppermost logbearing layer includes a number of rooted tree stumps in growth position, with diameters of up to 8 ft (2.5 m). The maximum root length observed is 40 ft (12.3 m). The trees have been identified by Chinese paleontologists as Cupressinoxylon. The petrified forest assemblage is preserved on the northeast margin of the Mesozoic Junggar foreland basin, a large continental basin subsiding under thrust loading from the south. Logs found within channel gravel units are oriented with their log axes parallel to the channel axis. Sedimentary structures, including epsilon and trough cross-stratification and imbricated channel gravels, indicate paleocurrent flow generally to the south, toward the basin center. The size of the logs suggests the presence of a major fluvial system. The epsilon cross-sets suggest a channel depth of 26 ft (8 m). The oriented silicified logs and their enclosing clastic sediments provide important information on the depositional systems active on the northeastern margin of the Junggar basin in the Late Jurassic(.) time. Hopefully, further detailed study of the fossil trees, including the spacing of the rooted stumps, will provide new information on the paleoecology of Mesozoic forests and the climatic conditions prevailing in the region at the time of deposition.

  4. Geometric and kinematics of West Segment of South Dabashan Foreland Fold-and-Thrust Belt, Northeast Sichuan Basin, China

    NASA Astrophysics Data System (ADS)

    He, Dengfa

    2017-04-01

    The west segment of South Daba Shan (WSD) foreland thrust belt is an ideal area to disclose the intra-continental tectonic processes. Based on the latest pre-stack depth migration of 3-D seismic data, 2-D seismic profile, well data and geological outcrop, the paper explore the structural geometric and kinematic features of WSD with the application of fault-related folding theories. WSD is characterized by multi-level detachment deformation due to the three predominant sets of weak layers, Lower Triassic Jialingjiang Formation gypsum interval, Silurian mudstone beds and Cambrian shale zone. It is accordingly subdivided vertically into three tectonic systems. The upper one is above the Jialingjiang Formation gypsolith layer and presents a Jura-like fold-and-thrust belt. The middle one takes Silurian shale as the base and Jialingjiang Formation gypsolith interval as the passive roof, in which imbricate thrusts developed. The lower one is bounded to Cambrian and Silurian detachment layers, in which duplex dominated. The Sinian and Proterozoic basements below Cambrian have not been involved in deformation. WSD underwent four periods of tectonic evolution: Late Jurassic -Cretaceous (150-110Ma); Late Cretaceous (110-70Ma); Latest Cretaceous to Paleogene (70-30Ma); Oligocene to Quaternary (30-0 Ma). The deformation propagated southward as an imbricate style, which results in the passive uplifting of overlying structural layer. WSD exhibits a rather low taper tectonic wedge. According to the magnetotelluric and deep seismic profiles, it is inferred that the WSD tectonic processes is mainly controlled by the Yangtze continental block subduction northward under the Qingling Mountains and the pro-wedge multi-level thrusting during late Jurassic to Cretaceous. The Upper Paleozoic carbonates in the middle tectonic deformation system are favorable for gas exploration in thea area.

  5. 3D structural model of the North Alpine Foreland Basin, Bavarian Part

    NASA Astrophysics Data System (ADS)

    Przybycin, Anna M.; Scheck-Wenderoth, Magdalena; Schneider, Michael

    2013-04-01

    The continental collision of Europe and Africa leads to the rise of the European Alps, which gave way to the formation of the North Alpine Foreland Basin, also referred to as the Molasse Basin, since the Tertiary. This typically wedge formed "foredeep" basin is filled with predominantly clastic sediments originating from erosional processes of the Alps which overly a southward dipping Mesozoic and Paleozoic succession. With our project we want to contribute to the understanding of the structure and subsequently of the thermal configuration of the Molasse Basin and its underlying deposits on a basin wide scale. We constructed a 3D structural model of the basin down to the crust-mantle-boundary, beginning with the Bavarian part. Therefore we used an approach of already existing local to midscale 2D and 3D structural models (e.g. Lüschen et al. 2006) as well as surface maps, seismic, well and gravity data. This 3D structural model resolves 5 sedimentary layers of the Mesozoic, including the geothermally utilized carbonate Malm aquifer (e.g. Birner et al. 2011), as well as the combined Paleozoic basement. Assuming isostatic equilibrium of the system a lithosphere-asthenosphere-boundary (LAB) has been calculated and compared to other published LABs of the region. Subsequently the model has been further constrained by 3D gravity modeling. The outcomes show that Cretaceous sediments are restricted to a small region in the central to eastern model area and are mostly overlain by the Tertiary Molasse sediments. The Triassic sediments occur in the northern and western part of the model area and do not continue far under the Molasse basin proper, while the Jurassic can be tracked as far south as beneath the Alps. The evaluation of the gravity indicates that the crystalline crust consists of a lighter upper crust and a denser lower crust. Our final LAB is shallowest under the Triassic subbasin, descending below the Bohemian Massif and the Molasse Basin proper and rising again

  6. Geomorphic assessment of the tectonic activity of Qiulitagh fold-belt, Kuqa foreland basin, Xinjiang, China

    NASA Astrophysics Data System (ADS)

    Saint Carlier, Dimitri; Graveleau, Fabien; Delcaillau, Bernard; Hurtrez, Jean-Emmanuel; Vendeville, Bruno

    2014-05-01

    significantly along-strike, which allows to divide the fold belt into several morphologic structures. These morphologic structures are suspected to be developing under variable uplift rates due to partitioning of deformation. In addition, the observation of very regular landscapes that become more complex along-strike allows investigating relief evolution mechanisms from transient to steady-state. Finally, our morphometric analysis suggests some new insights on the topographic growth of Qiulitagh folds in relation with the growth of sub-surface structures and the accommodation of convergence in Kuqa foreland basin. References : Chen, J., Heermance, R., Burbank, D. W., Scharer, K. M., Miao, J., and Wang, C., 2007, Quantification of growth and lateral propagation of the Kashi anticline, southwest Chinese Tian Shan: Journal of Geophysical Research, v. 112, no. B03S16, p. doi:10.1029/2006JB004345. Hubert-Ferrari, A., Suppe, J., Gonzalez-Mieres, R., and Wang, X., 2007, Mechanisms of active folding of the landscape (southern Tian Shan, China): Journal of Geophysical Research, v. 112, B03S09, doi:10.1029/2006JB004362. Li, S., Wang, X., and Suppe, J., 2012, Compressional salt tectonics and synkinematic strata of the western Kuqa foreland basin, southern Tian Shan, China: Basin Research, v. 23, p. 1-23. Wang, X., Suppe, J., Guan, S., Hubert-Ferrari, A., Gonzalez- Mieres, R., and Jia, C., 2011, Cenozoic structure and tectonic evolution of the Kuqa fold belt, southern Tianshan, China, in McClay, K., Shaw, J. H., and Suppe, J., eds., Thrust-Fault Related folding, Volume 94, American Association of Petroleum Geologists Memoir, p. 1-29.

  7. Coarse Grain Progradation in a Foreland basin: Application of Detrital Zircon Double Dating to Cenozoic Stratigraphy, Eastern Cordillera, Colombia.

    NASA Astrophysics Data System (ADS)

    Odoh, S.; Saylor, J. E.; Higuera-Diaz, C.; Lapen, T. J.; Copeland, P.

    2015-12-01

    Progradation of coarse clastic material into distal foreland basins has been attributed to both 1) enhanced sediment production during rapid tectonic exhumation and 2) sediment reworking during tectonic quiescence. The Floresta and Medina basins in the Eastern Cordillera record deposition of alternating coarse- and fine-grained clastic strata in medial and distal (respectively) Cenozoic foreland basins. The Medina Basin records the continued eastward progradation of the deformation front in the Neogene. We use detrital zircon U-Pb (ZPb) and (U-Th)/He (ZHe) analyses from the Paleogene Floresta Basin and the entire Cenozoic Medina Basin record to evaluate the effects of episodic thrust-belt exhumation and wide-spread deposition of coarse-grained sediments in the adjacent foreland basin. Both ZPb and ZHe systems are applied to individual grains (double dating) to constrain source area and up-section variations in exhumation rates. Changes in exhumation rate or introduction of new sediment sources are recorded as changes in lag time (ZHe age - depositional age). Analysis of 6 samples from the Floresta Basin shows a decrease in lag time during deposition of the coarse-grained middle Eocene Picacho Formation and upper Paleocene Socha Sandstone suggesting that Paleogene deposition of coarse-grained intervals in this medial location corresponds to an increase in exhumation rate. However, initial results from the Medina basin are less clear as there is evidence for Paleocene volcanic input but no clear evidence for thrust-belt related sediment until the Oligocene-early Miocene. We interpret the evidence for different sediment sources for Eocene strata in the axial Eastern Cordillera (Floresta) versus the Eastern foothills (Medina) as indicative of separation of these two regions by an emergent forebulge. Exhumation rate and granularity appear to be inversely correlated in post-Oligocene strata, though confirmation of initial interpretations awaits larger samples sizes

  8. Origin and chemical evolution of formation waters from Silurian-Devonian strata in the Illinois basin, USA

    SciTech Connect

    Stueber, A.M. ); Walter, L.M. )

    1991-01-01

    A suite of formation-water samples from Silurian-Devonian reservoirs in the Illinois basin has been analyzed for major, minor, and trace element concentrations and for H, O, and Sr isotopic compositions in order to interpret origin of salinity and geochemical evolution of brine compositions in this evaporite- and shale-poor cratonic basin. Although chloride concentrations range from 2,000 to 137,000 mg/L, Cl/Br ratios (291 {plus minus} 18) are consistent with those of seawater or seawater evaporated short of halite saturation (Cl/Br = 292). Thus, during Silurian-Devonian time, subaerially evaporated, penesaline brine entered the subsurface where it was chemically modified through brine-rock interactions. Cation/Br ratios and mineralogy of associated strata indicate that Na and K were depleted through interaction with clay minerals, Ca was enriched and Mg depleted by dolomitization, and Sr was enriched as a result of CaCO{sub 3} recrystallization and dolomitization. Brine {sup 87}Sr/{sup 86}Sr ratios range from 0.7092 to 0.7108; when these ratios are plotted versus 1/Sr, a two-component mixing trend is suggested, although Sr concentrations have experienced local diagenetic modification. A {sup 87}Sr-enriched fluid may have accompanied petroleum migration from New Albany shales into adjacent Silurian-Devonian carbonates where it mixed with remnant evaporated seawater. This event probably preceded the influx of meteoric water, as {delta}D and {delta}{sup 18}O are not correlated with Sr isotopic compositions of formation waters.

  9. Tectonic factors controlling initiation and distribution of Silurian reefs in Illinois basin, southwestern Indiana

    SciTech Connect

    Furer, L.C. )

    1989-08-01

    The authors discuss the relative effects of differential compaction and tectonics on the distribution, growth, geometry, and age of Silurian reefs in the Illinois basis. Their working hypothesis is that both differential compaction and tectonics have had a significant effect on the reefs, each at a different time. Examples are given.

  10. Growth of the Zagros Fold-Thrust Belt and Foreland Basin, Northern Iraq, Kurdistan

    NASA Astrophysics Data System (ADS)

    Koshnaw, Renas; Horton, Brian; Stockli, Daniel; Barber, Douglas; Ghalib, Hafidh; Dara, Rebwar

    2016-04-01

    The Zagros orogenic belt in the Middle Eastern segment of the Alpine-Himalayan system is among the youngest seismically active continental collision zones on Earth. However, due to diachronous and incremental collision, the precise ages and kinematics of shortening and deposition remain poorly understood. The Kurdistan region of the Zagros fold-thrust belt and foreland basin contains well-preserved Neogene wedge-top and foredeep deposits that include clastic nonmarine fill of the Upper Fars, Lower Bakhtiari, and Upper Bakhtiari Formations. These deposits record significant information about orogenic growth, fold-thrust dynamics, and advance of the deformation front. Thermochronologic and geochronologic data from thrust sheets and stratigraphic archives combined with local earthquake data provide a unique opportunity to address the linkages between surface and subsurface geologic relationships. This research seeks to constrain the timing and geometry of exhumation and deformation by addressing two key questions: (1) Did the northwestern Zagros fold-thrust belt evolve from initial thin-skinned shortening to later thick-skinned deformation or vice-versa? (2) Did the fold-thrust belt advance steadily under critical/supercritical wedge conditions involving in-sequence thrusting or propagate intermittently under subcritical conditions with out-of-sequence deformation? From north to south, apatite (U-Th)/He ages from the Main Zagros Thrust, the Mountain Front Flexure (MFF), and additional frontal thrusts suggest rapid exhumation by ~10 Ma, ~5 Ma, and ~8 Ma respectively. Field observations and seismic sections indicate progressive tilting and development of growth strata within the Lower Bakhtiari Formation adjacent to the frontal thrusts and within the Upper Bakhtiari Formation near the MFF. In the Kurdistan region of Iraq, a regional balanced cross section constrained by new thermochronometric results, proprietary seismic reflection profiles, and earthquake hypocenters

  11. Neogene transpressional foreland basin development on the north side of the central alaska range, usibelli group and nenana gravel, tanana basin

    USGS Publications Warehouse

    Ridgway, K.D.; Thoms, E.E.; Layer, P.W.; Lesh, M.E.; White, J.M.; Smith, S.V.

    2007-01-01

    Neogene strata of the Tanana basin provide a long-term record of a northwardpropagating, transpressional foreland-basin system related to regional shortening of the central Alaska Range and strike-slip displacement on the Denali fault system. These strata are ???2 km thick and have been deformed and exhumed in thrust faults that form the foothills on the north side of the Alaska Range. The lower part of the sedimentary package, the Usibelli Group, consists of 800 m of mainly Miocene strata that were deposited in fluvial, lacustrine, and peat bog environments of the foredeep depozone of the foreland-basin system. Compositional data from conglomerate and sandstone, as well as recycled Upper Cretaceous palynomorphs, indicate that the Miocene foreland-basin system was supplied increasing amounts of sediment from lithologies currently exposed in thrust sheets located south of the basin. The upper part of the sedimentary package, the Nenana Gravel, consists of 1200 m of mainly Pliocene strata that were deposited in alluvial-fan and braidplain environments in the wedge-top depozone of the foreland-basin system. Compositional data from conglomerate and sandstone, as well as 40Ar/39Ar dating of detrital feldspars in sandstone and from granitic clasts in conglomerate, indicate that lithologies exposed in the central Alaska Range provided most of the detritus to the Pliocene foreland-basin system. 40Ar/39Ar dates from detrital feldspar grains also show that two main suites of plutons contributed sediment to the Nenana Gravel. Detrital feldspars with an average age of 56 Ma are interpreted to have been derived from the McKinley sequence of plutons located south of the Denali fault. Detrital feldspars with an average age of 34 Ma are interpreted to have been derived from plutons located north of the Denali fault. Plutons located south of the Denali fault provided detritus for the lower part of the Nenana Gravel, whereas plutons located north of the Denali fault began to

  12. Geodynamics of continental plate collision during late tertiary foreland basin evolution in the Timor Sea: constraints from foreland sequences, elastic flexure and normal faulting

    NASA Astrophysics Data System (ADS)

    Londoño, John; Lorenzo, Juan M.

    2004-11-01

    Tectonic subsidence of the Australian lithosphere during the Late Tertiary propagates from the southwest to the northeast in the Timor Sea, as a consequence of the oblique collision between the Eurasian and Australian plates. We reconstruct the asynchronous nature of deflection of the Australian plate created during the plate convergence by best-matching the geometry of de-compacted foreland strata against the predictions of simple bending elastic beam models. We infer a maximum subsidence of 3500 m and a maximum width for the basin of ˜470 km. The effective elastic thickness of the Australian lithosphere (˜80 to 100 km) does not change significantly during basin evolution. The low curvature imposed on the plate (˜5.1×10 -8 m -1) during bending is too small to weaken the plate. Yet, abundant but small-slip, normal faulting related to bending implies some degree of inelastic yielding. The polarity of fault propagation supports the oblique nature of the collision. Flexural models indicate that at least 570 km of Australian plate (mostly areas of stretched continental crust) was flexed, primarily by the tectonic loading of the Timor Island and that the total amount of subducted plate was at least 100 km during basin evolution.

  13. A multistorey sandstone complex in the Himalayan Foreland Basin, NW Himalaya, India

    NASA Astrophysics Data System (ADS)

    Kumar, Rohtash; Sangode, Satish J.; Ghosh, Sumit K.

    2004-07-01

    Ten parallel stratigraphic sections (1500-1800 m thick) spread over an area of >400 km 2 in Dehra Dun sub-basin (DSB) of the Himalayan Foreland Belt (HFB) were studied to understand the anatomy of one of the largest (900-1200 m thick) fluviatile Multistorey Sandstone Complexes (MSC) of the world using fluvial geometry, compositional data and magnetic fabrics over a magnetostratigraphically controlled master section. The multistorey sandstone complex, between 10-5 Ma representing the Middle Siwalik sub-Group, comprises of grey, medium- to fine-grained lithic arenites to lithic greywacke and records tectonic and/or climatic episodes. Three main facies associations are recognised: sandstone-mudstone, sandstone, and conglomerate-sandstone that represent fluvial fan deposit. Palaeocurrent data show radial palaeoflow pattern with major palaeodrainage towards the southern quadrant. The magnetic fabric studies suggest three major tectonic pulses. The first pulse at ˜8.7 Ma resulted in the development of major depocenter for the MSC, the second pulse at ˜7.65 Ma enhanced the sedimentation and progradation, while the third pulse at ˜6.5 Ma records overlapping earlier fluvial fan by another coarse grained piedmont alluvial fan. Thrust movement in the northern fold belt, basement lineaments and rate of basin subsidence controlled the lateral and vertical facies distribution and palaeodrainage. The sedimentation pattern of the multistorey complex is characterised by mainly sheet flood deposits of laterally avulsing unconfined braided rivers and resembles to the modern megafan sedimentation in the Ganga Basin to the south.

  14. Fluvial response to foreland basin overfilling; the Late Permian Rangal Coal Measures in the Bowen Basin, Queensland, Australia

    NASA Astrophysics Data System (ADS)

    Fielding, C. R.; Falkner, A. J.; Scott, S. G.

    1993-05-01

    The latest Permian Rangal Coal Measures and equivalents accumulated during a phase of declining volcanism and active thrust loading in the complex retroarc foreland Bowen Basin in eastern Queensland, Australia. The unit was formed in predominantly alluvial environments which covered the entire Bowen Basin and it represents the final phase of coal formation in the basin. Large opencut mine exposures, mainly in the Blackwater area, have allowed the establishment of a facies scheme for the Rangal Coal Measures. Seven facies have been recognised on the basis of lithology, geometrical criteria and palaeocurrent relationships. (1) Sheet-like Sandstone Channel Bodies; (2) Laterally Accreted, Heterolithic Channel Bodies; (3) Levee (Proximal Overbank) Deposits; (4) Minor Crevasse Channel Fill; (5) Floodbasin; (6) Stagnant Lake Floor; and (7) Mire. Together, these constitute an array typical of alluvial, coal-bearing systems. The depositional style of the Rangal Coal Measure channels is unusual, and considered to be related to the periodic oversupply of coarse sediment to the system. Heterolithic channel fills (Facies 2), which comprise alternations of thinly interbedded sandstone/siltstone and sharp-bounded sandstone, formed under conditions of dramatically variable sediment supply. Such channel deposits, while formed dominantly by lateral accretion, were the product of only slightly sinuous streams (less than 1.5). Facies 1 sheet sandstones, however, are interpreted to have formed during times of sand oversupply to the basin, and were the product of low-sinuosity, probably braided streams. The overall character of the Rangals is considered a response to overfilling of the basin by immature, volcanic sediment released by the uplift of thrust sheets in the adjacent orogen.

  15. From foreland rift to forearc basin: Tectono-thermal controls on subsidence and stratigraphic development in the Mesozoic-Recent Salar de Atacama basin, Chilean Andes

    SciTech Connect

    Flint, S. ); Turner, P. ); Hartley, A. ); Jolley, E. )

    1991-03-01

    The Salar de Atacama and westerly adjacent Domeyko basins originated as Permian foreland rifts, containing some 2 km of Triassic synrift red beds. Continued extension and volcanic are establishment resulted in deposition of important Jurassic marine source rocks in the Domeyko basin. Rift basin subsidence was controlled by extension, followed by thermal sagging. Middle Cretaceous contraction (opening of the south Atlantic) inverted the Domeyko back-arc basin as a thrustbelt. To the east, the Salar basin subsequently accommodated 4 km of Late Cretaceous-Palaeocene continental detritus. Accommodation space reflected the interplay between limited flexural loading and thermal effects related to a 150 km eastward jump of the Andean volcanic arc to the margin of the arc-related, foreland-style basin. Late Eocene transpression (high rate of oblique convergence between the Farallon and South American plates) inverted the western basin margin, sourcing a 2 km thick Oligocene intra-arc basin-fill component. Accommodation space was controlled by thermal sagging associated with a further 100 km eastward arc jump. The Salar de Atacama basin thus provides a model for the evolution of complex, mixed origin basins associated with a migrating volcanic arc and varying crustal stress regime. The complex interplay between variable tectonic style and thermal processes in controlling subsidence and resultant stratigraphic development is not yet adequately constrained. However, simple, single stage tectono-sedimentary models commonly used in play definition may not be appropriate in complex, arc-related basin settings.

  16. Comparative effects of tectonism on Silurian carbonate platform evolution

    SciTech Connect

    Soja, C.M. . Geology Dept.)

    1992-01-01

    Detailed comparisons of Silurian carbonates that formed under similar subtropical-tropical conditions in an island arc (Alexander terrane, Alaska), an orogenic belt (Oslo region, Norway), and on a stale craton (Gotland, Sweden) are used to evaluate tectonic controls on carbonate platform sedimentation. Silurian carbonates from Alaska record the evolution of a submarine platform in an island arc affected by late Silurian orogenesis. Silurian limestones that formed on the Baltoscandinavian epicontinental platform experienced Caledonian orogenesis in the Oslo region but accumulated on Gotland several 100 km east of the Caledonide front under quiescent tectonic conditions. This study shows that previous models for carbonate platform development do not predict the disproportionately thick carbonate sequences and characteristics of rocks preserved in the Alaskan island arc. High rates of subsidence and accumulation, steep submarine slopes, tectonic instability, and biogeographic isolation resulted in extraordinarily thick platform and periplatform carbonates, sequential evolution of fringing and barrier reefs, and patterns of faunal turnover that differentiate Silurian arc deposits from coeval carbonates that formed on the craton and in the orogenic belt. On the craton and in the orogenic belt, marine organisms were relatively unaffected by tectonic disturbances, but in the island arc marine biotas experienced regional extinction and faunal turnover. Similarities in the stages in carbonate platform development in the Oslo region and Alaska reflect comparable events involving compression, foreland basin evolution, and subsequent rejuvenation of carbonate depositional sites. Widespread destruction of carbonate environments correlated with orogenic activity and global marine regression eventually produced similar subaerial conditions in the Alexander terrane and across Baltoscandinavia by the late Silurian.

  17. Provenance of late Oligocene to quaternary sediments of the Ecuadorian Amazonian foreland basin as inferred from major and trace element geochemistry and Nd-Sr isotopic composition

    NASA Astrophysics Data System (ADS)

    Roddaz, Martin; Christophoul, Frédéric; Burgos Zambrano, José David; Soula, Jean-Claude; Baby, Patrice

    2012-08-01

    Oligocene to Quaternary deposits from the Oriente Amazonian foreland basin (Ecuador and Peru) were analyzed for major and trace element geochemistry (46 and 32 samples respectively) and Nd-Sr isotopic systematics (n = 10). Chemical Index of Alteration values lower than those of other Amazonian foreland basin sediments and scattering along the AK join in the A-CN-K diagram indicate that the Oriente foreland basin has been continuously fed by poorly to moderately weathered sediments having an overall Andesitic composition since the Oligocene. Chemical ratios such as Cr/Th and Th/Sc as well as Eu anomaly and Nd-Sr isotopic compositions indicate that most of the analyzed sediments contained a greater proportion of volcanic arc rock material than the other Amazonian foreland basin sediments. When compared with the older sediments The Quaternary sediments are characterized by a greater contribution of the volcanic arc source. The composition of the sediments deposited in the Ecuadorian Amazonian foreland basin is mainly controlled by geodynamic processes. We suspect the Late Pliocene-Pleistocene subduction of the Carnegie ridge to be responsible for the back arc volcanism feeding the Amazonian foreland with more basic materials. Input of young Ecuadorian volcanic rocks may explain the difference in Sr and Nd isotopic ratios of suspended sediments between the Solimoes and the Madeira rivers.

  18. Confined deep water system development on the accretionary wedge (Miocene, Kahramanmaraş Foreland Basin, S turkey)

    NASA Astrophysics Data System (ADS)

    Gül, Murat; Cronin, Bryan T.; Gürbüz, Kemal

    2012-09-01

    According to theoretical studies, the foreland basin consists of: accretionary wedge (including wedge top or piggyback basin), foredeep, forebulge and backbulge depozones. All of them are parallel to the orogenic belts of the overlying and underlying plates. The closure of the southern branch of the Neotethys during the Late Cretaceous led to an oblique collision of the Arabian Plate and the Anatolide-Taurides Platform, leading to the development of the Miocene Kahramanmaraş Foreland Basin (KFB). Thus, the promontory shape of the Arabian Plate prevented the development of an accretionary wedge parallel to the orogenic belt. The accretionary wedge of the KFB includes blocks of various sizes and age (mainly Mesozoic limestone) scattered within an Early Tertiary matrix (mass wasting deposits and shallow to deep marine sediments). At the beginning of the Miocene, transtensional tectonism led to the development of half-graben basins on top of the accretionary wedge. These basins (namely; the Tekir and Çukurhisar) also cut the foredeep of the KFB obliquely (in contrast with the theoretical study). This paper focuses on the evolution and fillings of those basins. Initially, claystone and basin margin reef deposits filled the half-graben basins as a consequence of the Lower Miocene sea invasion. Then, long and narrow conglomeratic channels starting from the northern edge of the basins (fan-delta) progressed southwards, passing into sandy lobes, then into claystones. An activation of the boundary faults of the wedge top basin stopped the progression of the Lower-Middle Miocene sediments and led to their deformation. Then, the sedimentation of the KFB shifted towards the basin centre during the Middle Miocene.

  19. Cementation and compaction history of synorogenic foreland basin sedimentary rocks from Huaco, Argentina

    SciTech Connect

    Damanti, J.F.; Jordan, T.E.

    1989-07-01

    The Sierra de Huaco exposes the western flank of the Bermejo foreland basin of central western Argentina. The exposed 5400-m section is well dated (14-2.3 Ma) and consists of synorogenic continental strata. Petrographic data combined with decompaction techniques provide first-order estimates of the absolute age of cementation of the sandstones. This information can be used to interpret petroleum migration paths and reservoir potential. Three diagenetic zones have been recognized, each characterized by a dominant cementing material within a distinct framework texture. These textures reflect varying degrees of compaction and framework-grain replacement prior to cementation. The diagenetic histories of the three zones were genetically linked to thrusting in the adjacent Precordillera, changes in depositional environment, and subsurface fluid flow. The depth at which cementation occurred in each zone is constrained by comparison of observed intergrain volume to predicted volumes (for uncemented sands) at any given burial depth. First-order estimates of the absolute age of cementation in each zone were made possible by comparing these relationships with a curve of accumulation history of the decompacted strata. The lowest zone compacted with little interstitial cement for as long as 11 m.y. after deposition. The middle zone was cemented within 3 m.y. after deposition. The upper zone experienced framework-grain replacement by calcite at very shallow depths within 2 m.y. and experienced little compaction. 14 figures, 1 table.

  20. Geochemistry of Lower Cretaceous strata of northern Priverkhoyansk Foreland Basin (NE SIBERIA): implications for provenance

    NASA Astrophysics Data System (ADS)

    Vasiliev, Dmitry; Ershova, Victoria; Ivensen, Galina; Prokopiev, Andrei

    2014-05-01

    The study area is located in the lower reaches of the Lena R., in between Chekurovka and Chucha Capes. The Lower Cretaceous clastic rocks of the northern part of the Priverkhoyansk foreland basin adjacent to the front of the Verkhoyansk fold-and-thrust belt have been studied. The Lower Cretaceous sections are composed of marine and fluvial terrigenous rocks. Marine deposits are represented by alternating sandstones and siltstones, while continental ones by alternating thick sandstones units (up to 400 m) and shale units with subordinate sandstones beds. The thickness of studied strata varies from 800-1900 m. The whole-rock geochemical analyses were done for 121 samples The geochemical study show: 1) uniform, persistent chemical composition close to that of acid igneous rocks; 2) low TiO2 content; 3) low MgO and FeO* values; 4) prevalence of FeO over Fe2O3 ; 5) high alkalies content with prevailing Na2O; 6) positive correlation between TiO2 and FeO* contents and negative correlation between Na2 O+K2 O and FeO* values. The data point to the same source of sediments both for marine and fluvial deposits with prevailing felsic rocks in provenance area. This research was supported by RFBR grants 14-05-31298, 13-05-00700, 13-05-00943 research grant of Saint Petersburg State University and Grant of President of Russia for Young Scientist MK-2902.2013.5.

  1. Diagenetic Evolution and Reservoir Quality of Sandstones in the North Alpine Foreland Basin: A Microscale Approach.

    PubMed

    Gross, Doris; Grundtner, Marie-Louise; Misch, David; Riedl, Martin; Sachsenhofer, Reinhard F; Scheucher, Lorenz

    2015-10-01

    Siliciclastic reservoir rocks of the North Alpine Foreland Basin were studied focusing on investigations of pore fillings. Conventional oil and gas production requires certain thresholds of porosity and permeability. These parameters are controlled by the size and shape of grains and diagenetic processes like compaction, dissolution, and precipitation of mineral phases. In an attempt to estimate the impact of these factors, conventional microscopy, high resolution scanning electron microscopy, and wavelength dispersive element mapping were applied. Rock types were established accordingly, considering Poro/Perm data. Reservoir properties in shallow marine Cenomanian sandstones are mainly controlled by the degree of diagenetic calcite precipitation, Turonian rocks are characterized by reduced permeability, even for weakly cemented layers, due to higher matrix content as a result of lower depositional energy. Eocene subarkoses tend to be coarse-grained with minor matrix content as a result of their fluvio-deltaic and coastal deposition. Reservoir quality is therefore controlled by diagenetic clay and minor calcite cementation.Although Eocene rocks are often matrix free, occasionally a clay mineral matrix may be present and influence cementation of pores during early diagenesis. Oligo-/Miocene deep marine rocks exhibit excellent quality in cases when early cement is dissolved and not replaced by secondary calcite, mainly bound to the gas-water contact within hydrocarbon reservoirs.

  2. Testing some models of foreland deformation at the Thermopolis anticline, southern Bighorn Basin, Wyoming

    SciTech Connect

    Paylor, E.D.; Lang, H.R.; Conel, J.E.; Adams, S.L. ); Muncy, H.L. )

    1989-01-01

    The Thermopolis anticline is a typical structure in the Rocky Mountain foreland, southern Bighorn Basin, Wyoming. Photogeologic interpretation of Landsat Thematic Mapper data, in combination with the evaluation of topographic, bore hole, seismic reflection, and field data were used to analyze structure and constrain tectonic models. The anticline is near-concentric, asymmetric with a southwest sense of vergence, and plunges to the northwest. The steeply dipping to overturned southwest limb of the fold is cut at the surface by several thrust faults dipping northeast. Approximately 25% of the stratigraphic section on the southwest limb is missing due to faulting. Two east to northeast-striking, basement-controlled compartmental faults segment the anticline into three blocks that apparently deformed simultaneously but probably independently from one another. Slickensides indicate a dominant southwest tectonic transport direction. Additionally, subtle northeast-trending folds are superposed on the dominant northwest structural trend. Structural patterns at Thermopolis anticline can be explained using models that propose a single phase of northeast Laramide compression, combined with shear-zone deformation.

  3. Subsidence modeling of the Sabah Basin, a foreland basin, Northwest Borneo, Malaysia

    SciTech Connect

    Azim-Ibrahim, N. ); White, N. )

    1994-07-01

    The Sabah Basin is located on the northwestern side of Borneo. It is a piggy back northeast-southwest-trending basin, riding on a north-westward directed imbricate thrust system. The basin contains approximately 10 to 12 km of sediment in the deepest part deposited in two main episodes of basin development; (1) a pre-early middle Miocene phase of generally deep-marine clastic deformation, which was later subjected to compression and (2) a post-early middle Miocene episode of clastic deposition, comprising bathyal to upper coastal plain sediments. Tectonic subsidence of the post-middle Miocene sequence was determined using the 1-D Airy and 2-D flexure backstripping techniques and wells and selected dip profiles, where the effects of compaction and sediment loading were removed. Variation in paleowater depth was also taken into account. The results show an extremely rapid subsidence phase dominating the earlier part of the basin history, with the later part corresponding to passive basin infilling. The boundary between these two phases becomes younger toward the northwest. The rapid subsidence phase is attributed to tectonic loading, possibly as a result of continuing thrusting at the basin margin. The results also imply that sedimentary sequences formed during the earlier phase were tectonically controlled and marked by transgressive events, while those deposited during the later phase bear the imprints of both tectonic and eustasy.

  4. Nature, origin, and production characteristics of the Lower Silurian regional oil and gas accumulation, central Appalachian basin, United States

    USGS Publications Warehouse

    Ryder, R.; Zagorski, W.A.

    2003-01-01

    Low-permeability sandstones of the Lower Silurian regional oil and gas accumulation cover about 45,000 mi2 (117,000 km2) of the Appalachian basin and may contain as much as 30 tcf of recoverable gas resources. Major reservoirs consist of the "Clinton" sandstone and Medina Group sandstones. The stratigraphically equivalent Tuscarora Sandstone increases the area of the Lower Silurian regional accumulation (LSRA) by another 30,000 mi2 (78,000 km2). Approximately 8.7 tcf of gas and 400 million bbl of oil have been produced from the Clinton/Medina reservoirs since 1880. The eastern predominantly gas-bearing part of the LSRA is a basin-center gas accumulation, whereas the western part is a conventional oil and gas accumulation with hybrid features of a basin-center accumulation. The basin-center accumulations have pervasive gas saturation, water near irreducible saturation, and generally low fluid pressures. In contrast, the hybrid-conventional accumulations have less-pervasive oil and gas saturation, higher mobile-water saturation, and both normal and abnormally low fluid pressures. High mobile-water saturation in the hybrid-conventional reservoirs form the updip trap for the basin-center gas creating a broad transition zone, tens of miles wide, that has characteristics of both end-member accumulation types. Although the Tuscarora Sandstone part of the basin-center gas accumulation is pervasively saturated with gas, most of its constituent sandstone beds have low porosity and permeability. Commercial gas fields in the Tuscarora Sandstone are trapped in naturally fractured, faulted anticlines. The origin of the LSRA includes (1) generation of oil and gas from Ordovician black shales, (2) vertical migration through an overlying 1000-ft (305-m)-thick Ordovician shale; (3) abnormally high fluid pressure created by oil-to-gas transformation; (4) updip displacement of mobile pore water by overpressured gas; (5) entrapment of pervasive gas in the basin center; (6) postorogenic

  5. Provenance and sediment-dispersal system in tectonically active rapidly evolving foreland basin, Western Interior

    SciTech Connect

    Khandaker, N.I.; Vondra, C.F.

    1989-03-01

    The Upper Cretaceous Frontier Formation, along the mobile edge of the Western Interior foreland basin, is composed mainly of clastic sediments and was deposited during the initial Late Cretaceous transgressive-regressive phases of the Western Interior seaway across Wyoming. The formation contains many persistent bentonite beds and several sandstone packages in its lower part and a thin, lenticular lithic wacke-polymictic conglomerate association at its upper contact (Torchlight Sandstone Member). Abundant granule to cobble-sized clasts of andesite, granite, chert, and quartzite are set in a poorly sorted sand-to-granule grade volcaniclastic matrix. There is a lithologic continuity of this volcaniclastic unit across the Bighorn Mountains into the Powder River basin. A high-energy distributary complex of sizable areal extent is invoked for the deposition of this linear conglomerate facies. Geochemical investigations of the whole-rock andesite clasts and bentonite allowed more precise definition of character, tectonic setting, and evolutionary stages of sedimentary distributive provinces. Bentonites and andesites are strongly enriched in strontium and barium, but only mildly enriched in heavy rare earth elements and high field-strength elements. These analyzed rocks have trace element characteristics similar in a general way to those of typical orogenic volcanics; they show some significant differences in detail. Composition of volcaniclasts and paleocurrent data indicate a proximal sediment source for the extrabasinal detritus within the Frontier Formation. The possibility of a contribution from a Mesozoic volcanic center in the neighborhood of southwestern Montana is strongly favored. The products of this volcanism constitute an assemblage of deep crustal to mantle( ) derived rocks, and their composition record time-integrated enrichment in light over heavy rare earth elements.

  6. Testing orbital forcing in the Eocene deltaic sequences of the South-Pyrenean Foreland Basins.

    NASA Astrophysics Data System (ADS)

    Garcés, Miguel; López-Blanco, Miguel; Valero, Luis; Beamud, Elisabet; Pueyo-Morer, Emilio; Rodríguez-Pinto, Adriana

    2014-05-01

    Paleoclimate proxy records from marine pelagic sediments show that a link exists between long-period orbital cyclicity and the pattern of high latitude glaciations. Thus, a sound possibility exist that transgressive-regressive third-order sequences from shallow marine environments reflect long-period orbital (glacioeustatic) forcing, as suggested from a variety of shallow marine settings of different ages, from Mesozoic to Paleogene. In this study we aim at testing the role of the 400 kyr eccentricity cycle in the sequential organization of the Late Eocene deltaic sequences of the Belsue-Atares Formation, in the Jaca-Pamplona Basin. The overall record spans from latest Lutetian to early Priabonian and consists of nearly 1000 meters of siliciclastic deltaic to mixed platform sequences of various scales. Very notorious lateral changes in both stratigraphic thickness and sedimentary facies witness the synkinematic character of these sediments, deposited simultaneously to intrabasinal fold growth. A magnetostratigraphy based chronostratigraphic framework is used, first, to determine the age and duration of the sequences and, second, to establish a robust correlation with other deltaic sequences within the south-pyrenean foreland. The long-distance correlation exercise is used to discriminate between local (tectonic) and global (climatic) forcing factors, under the assumption that climate signature is synchronous, while tectonic forcing is prone to yield diachronic units at basin scale. Astronomical tuning with the 400-kyr cycle of the eccentricity solution of the Earth orbit is attempted on the basis of derived magnetostratigraphic age constrains. Our results suggest that transgressive (regressive) trends correlate with maxima (minima) of eccentricity cycle, a phase-relationship which is compatible with a base-level (accommodation) driven forcing.

  7. Crustal thickening or isostatic rebound of orogenic wedge deduced from tectonostratigraphic units in Indosinian foreland basin, Longmen Shan, China

    NASA Astrophysics Data System (ADS)

    Li, Yong; Li, Haibing; Zhou, Rongjun; Su, Dechen; Yan, Liang; Yan, Zhaokun

    2014-04-01

    Longmen Shan is located at the boundary between the Sichuan Basin and Tibetan Plateau, representing the steepest gradient of any edges of the plateau. Three endmember models of uplift process and mechanism have been proposed, including crustal thickening, crustal flow, and crustal isostatic rebound. Here, we use tectonostratigraphic units in the Late Triassic foreland basin to restraint uplift process and mechanism in the Longmen Shan during Indosinian orogeny. The Late Triassic foreland basin developed as a flexural foredeep on the Yangtze passive continental margin during the Indosinian orogeny. The basin fill includes the Maantang Formation, the Xiaotangzi Formation and the Xujiahe Formation, and it is divided into four tectonostratigraphic units with wedge-shaped or tabular cross-sectional geometry by unconformities and flooding surfaces in this paper. The first and third ones are wedge-shaped tectonostratigraphic units and correspond to underfilled condition with basal unconformities or major flooding surfaces, the high rate of subsidence and sediment accumulation, coarsening-upward succession and a dual sediment supply, and them may link to strong active thrust loading events or the rapidly advance rate of the orogenic wedge; the second and fourth ones are tabular tectonostratigraphic units and correspond to overfilled condition with the unconformity, the low rate of subsidence and sediment accumulation, fining-upward succession, a single sediment supply, the mass emergence of conglomerate layers, and they may be related to isostatic rebound and erosion unloading. Two endmember models of uplift process and mechanism in the Longmen Shan during Indosinian cycle have been proposed by coeval Late Triassic sedimentary sequences in the foreland basin here: (1) crustal thickening during the wedge-shaped tectonostratigraphic units, (2) crustal isostatic rebound during the tabular tectonostratigraphic units. This two endmember models proposed in this paper may be

  8. Stratigraphic Framework and Depositional Sequences in the Lower Silurian Regional Oil and Gas Accumulation, Appalachian Basin: From Licking County, Ohio, to Fayette County, West Virginia

    USGS Publications Warehouse

    Ryder, Robert T.

    2006-01-01

    The Lower Silurian regional oil and gas accumulation was named by Ryder and Zagorski (2003) for a 400-mile (mi)-long by 200-mi-wide hydrocarbon accumulation in the central Appalachian basin of the Eastern United States and Ontario, Canada. From the early 1880s to 2000, approximately 300 to 400 million barrels of oil and eight to nine trillion cubic feet of gas have been produced from the Lower Silurian regional oil and gas accumulation (Miller, 1975; McCormac and others, 1996; Harper and others, 1999). Dominant reservoirs in the regional accumulation are the Lower Silurian 'Clinton' and Medina sandstones in Ohio and westernmost West Virginia and coeval rocks in the Lower Silurian Medina Group (Grimsby Sandstone (Formation) and Whirlpool Sandstone) in northwestern Pennsylvania and western New York. A secondary reservoir is the Upper Ordovician(?) and Lower Silurian Tuscarora Sandstone in central Pennsylvania and central West Virginia, a more proximal eastern facies of the 'Clinton' sandstone and Medina Group (Yeakel, 1962; Cotter, 1982, 1983; Castle, 1998). The Lower Silurian regional oil and gas accumulation is subdivided by Ryder and Zagorski (2003) into the following three parts: (1) an easternmost part consisting of local gas-bearing sandstone units in the Tuscarora Sandstone that is included with the basin-center accumulation; (2) an eastern part consisting predominantly of gas-bearing 'Clinton' sandstone-Medina Group sandstones that have many characteristics of a basin-center accumulation (Davis, 1984; Zagorski, 1988, 1991; Law and Spencer, 1993); and (3) a western part consisting of oil- and gas-bearing 'Clinton' sandstone-Medina Group sandstones that is a conventional accumulation with hybrid features of a basin-center accumulation (Zagorski, 1999). With the notable exception of the offshore part of Lake Erie (de Witt, 1993), the supply of oil and (or) gas in the hybrid-conventional part of the regional accumulation continues to decline because of the many

  9. Late Burdigalian sea retreat from the North Alpine Foreland Basin: new magnetostratigraphic age constraints

    NASA Astrophysics Data System (ADS)

    Sant, K.; Kirscher, U.; Reichenbacher, B.; Pippèrr, M.; Jung, D.; Doppler, G.; Krijgsman, W.

    2017-05-01

    Accurate reconstruction of the final sea retreat from the North Alpine Foreland Basin (NAFB) during the Burdigalian (Early Miocene) is hampered by a lack of reliable age constraints. In this high resolution magnetostratigraphic study we try to solve a significant age bias for the onset of the Upper Freshwater Molasse (OSM) deposition in the neighboring S-German and Swiss Molasse Basins. We measured > 550 samples from eleven drill cores covering the transition from marine to brackish to freshwater environments in the S-German Molasse Basin. Based on combined bio-, litho- and magnetostratigraphic constraints, the composite magnetostratigraphic pattern of these cores provides two reasonable age correlation options (model 1 and 2). In model 1, the base of the brackish succession lies within Chron C5Cr ( 16.7-17.2 Ma), and the onset of OSM deposition has an age of 16.5 Ma. Correlation model 2 suggests the transition to brackish conditions to be within C5Dr.1r ( 17.7-17.5 Ma), and yields an age around 16.7 Ma for the shift to the OSM. Most importantly, both models confirm a much younger age for the OSM base in the study area than previously suggested. Our results demonstrate a possible coincidence of the last transgressive phase (Kirchberg Fm) with the Miocene Climatic Optimum (model 1), or with the onset of this global warming event (model 2). In contrast, the final retreat of the sea from the study area is apparently not controlled by climate change. Supplementary material B. Profiles of the eleven studied drill cores including lithologies, all magnetostratigraphic data (inclinations), interpreted polarity pattern (this study and Reichenbacher et al., 2013) and magnetic susceptibility (this study). Legend for graphs on page 1. Samples without a stable direction above 200 °C or 20 mT are depicted as +-signs and plotted at 0° inclination. The interpreted normal (black), reversed (white) and uncertain (grey) polarity zones in the polarity columns are based on at least

  10. Hydraulic testing of low-permeability Silurian and Ordovician strata, Michigan Basin, southwestern Ontario

    NASA Astrophysics Data System (ADS)

    Beauheim, Richard L.; Roberts, Randall M.; Avis, John D.

    2014-02-01

    Straddle-packer hydraulic testing was performed in 31 Silurian intervals and 66 Ordovician intervals in six deep boreholes at the Bruce nuclear site, located near Tiverton, Ontario, as part of site-characterization activities for a proposed deep geologic repository (DGR) for low- and intermediate-level radioactive waste. The straddle-packer assembly incorporated a hydraulic piston to initiate in situ pulse tests within low hydraulic conductivity (<1E-10 m/s) test intervals. Pressure transient data collected during the hydraulic tests were analyzed using the well-test simulator nSIGHTS to estimate the hydraulic properties specified as fitting parameters for the tested intervals, quantify parameter uncertainty, and define parameter correlations. Horizontal hydraulic conductivities of the Silurian test intervals range from approximately 4E-14 to 4E-8 m/s. The average horizontal hydraulic conductivities of the Ordovician intervals range from 2E-16 to 2E-10 m/s. The Lower Member of the Cobourg Formation, the proposed host formation of the DGR between 660 and 688 meters below ground surface, was found to have a horizontal hydraulic conductivity of 4E-15 to 3E-14 m/s. The formation pressures inferred from the hydraulic testing, confirmed by long-term monitoring, show that the Upper Ordovician and Middle Ordovician Trenton Group are significantly underpressured relative to a density-compensated hydrostatic condition and relative to the overlying Silurian strata and underlying Black River Group and Cambrian strata. These underpressures could not persist if hydraulic conductivities were not as low as those measured.

  11. Silurian-Niagaran reef belt of the Michigan basin: an update

    SciTech Connect

    Aninian, K.; Bomar, R.M.

    1984-09-01

    Exploration of Silurian-Niagaran pinnacle reefs is discussed. Recent discoveries have extended the reef belt into new areas in the western and northeastern parts of Michigan's lower peninsula, and the results of exploration in the northeastern part of the reef belt indicate that some reef characteristics in that area are not similar to those of the rest of the belt. This required a more detailed study, based on recent data available from the drilling activity in the area, to update the reserves potential and the reef belt extension into Lake Huron.

  12. (U-Th)/He and U-Pb double dating constraints on the interplay between thrust deformation and basin development, Sevier foreland basin, Utah

    NASA Astrophysics Data System (ADS)

    Pujols, E.; Stockli, D. F.; Horton, B. K.; Steel, R. J.; Constenius, K. N.

    2015-12-01

    The degree of connectivity between thrust-belt deformation and foreland basin evolution has been a matter of debate for decades. This is in part due to the lack of temporal constraints on the relationship between thrust-belt deformation and associated deposition. New high-resolution zircon (U-Th)-(Pb-He) double dating of pre- and syn-tectonic sedimentary strata along the Sevier thrust front and basin provide an unprecedented geochronological framework to temporally and spatially link the Sevier foreland basin stratigraphy to deforming hinterland sources. Results improve constraints on timing and magnitude of deformation, depositional ages, sediment dispersal and sources. In Late Cretaceous proximal deposits of the Indianola Group (IG) and Canyon Range Conglomerates (CRC), detrital zircon U-Pb (zUPb) and (U-Th)/He ages (ZHe) chronicle the sequential unroofing of the Charlestone-Nebo Salient (CNS) and Canyon Range (CR) duplexes. Furthermore, short ZHe depositional lag-times indicate rapid hinterland exhumation (>1km/my) associated with active thrusting during Cenomanian and Coniacian-Santonian times as supported by bedrock ZHe ages in the CNS and CR thrust sheets. Detrital zircon analyses on the Late Cretaceous marine Book Cliffs strata suggest a more complex source-to-sink evolution compared to the time-equivalent IG and CRC proximal strata due to mixing of multi-source detrital zircons, sediment recycling and more prominent volcanic input. Nonetheless, the overall cooling history recorded in the Book Cliffs clearly reflects three hinterland exhumational phases, an early phase derived from the frontal thrusts and two additional phases with more integrated hinterland ZHe signatures. These three short lag-time phases correlate with fast clastic progradational wedges in the Sevier foreland. These results strengthen the role played by hinterland deformation on clastic progradation and elucidate the temporal relationship between thrusting and foreland basin architecture.

  13. Onset of foreland -- Basin subsidence in the Middle Jurassic Utah -- Idaho trough, E Nevada and W Utah

    SciTech Connect

    Bjerrum, C.J.; Dorsey, R.J.; Becker, U. . Dept. of Geology)

    1993-04-01

    Analysis of Middle Jurassic strata and regional unconformities of the central Colorado Plateau indicates that these sediments were deposited in the distal part of a retroarc foreland basin. Middle Jurassic strata are divided into two major unconformity-bounded sequences (of Riggs and Blakey, 1993) for modeling purposes. Numerical flexural modeling has produced deflection profiles that match published regional stratigraphic profiles of the two sequences. The best fits between the flexural models and stratigraphic data were obtained using an infinite plate with a flexural rigidity of 10[sup 24] Nm, a mountain-belt topography similar to the Cretaceous Sevier fold-thrust belt, and a tapered alluvial-fluvial system extending 400 km and 600 km, respectively, eastward from the margin of the inferred thrust load. The match between the model and the data is improved by including a dune-field topography on the edge of the forebulge. The models do not include post-depositional uplift, erosion, and development of regional unconformities in the area of the forebulge. However, the stratigraphic architecture and geometry of unconformities closely resemble facies patterns produced in recent numerical models of sedimentation and erosion in foreland basins controlled by episodic thrusting. The data and model results strongly suggest that the onset of regional flexural subsidence in the early Sevier foreland basin took place at the time of formation of the J-2 (or possibly J-1) unconformity. Initial erosion of the J-2 occurred approximately during early Bajocian time ([approximately]170 Ma), which is close to the time of earliest known regional contraction in SE California and Nevada.

  14. Revised age of proximal deposits in the Zagros foreland basin and implications for Cenozoic evolution of the High Zagros

    NASA Astrophysics Data System (ADS)

    Fakhari, Mohammad D.; Axen, Gary J.; Horton, Brian K.; Hassanzadeh, Jamshid; Amini, Abdolhossein

    2008-04-01

    The regionally extensive, coarse-grained Bakhtiyari Formation represents the youngest synorogenic fill in the Zagros foreland basin of Iran. The Bakhtiyari is present throughout the Zagros fold-thrust belt and consists of conglomerate with subordinate sandstone and marl. The formation is up to 3000 m thick and was deposited in foredeep and wedge-top depocenters flanked by fold-thrust structures. Although the Bakhtiyari concordantly overlies Miocene deposits in foreland regions, an angular unconformity above tilted Paleozoic to Miocene rocks is expressed in the hinterland (High Zagros). The Bakhtiyari Formation has been widely considered to be a regional sheet of Pliocene-Pleistocene conglomerate deposited during and after major late Miocene-Pliocene shortening. It is further believed that rapid fold growth and Bakhtiyari deposition commenced simultaneously across the fold-thrust belt, with limited migration from hinterland (NE) to foreland (SW). Thus, the Bakhtiyari is generally interpreted as an unmistakable time indicator for shortening and surface uplift across the Zagros. However, new structural and stratigraphic data show that the most-proximal Bakhtiyari exposures, in the High Zagros south of Shahr-kord, were deposited during the early Miocene and probably Oligocene. In this locality, a coarse-grained Bakhtiyari succession several hundred meters thick contains gray marl, limestone, and sandstone with diagnostic marine pelecypod, gastropod, coral, and coralline algae fossils. Foraminiferal and palynological species indicate deposition during early Miocene time. However, the lower Miocene marine interval lies in angular unconformity above ~ 150 m of Bakhtiyari conglomerate that, in turn, unconformably caps an Oligocene marine sequence. These relationships attest to syndepositional deformation and suggest that the oldest Bakhtiyari conglomerate could be Oligocene in age. The new age information constrains the timing of initial foreland-basin development and

  15. Sequence stratigraphy, geodynamics, and detrital geothermochronology of Cretaceous foreland basin deposits, western interior U.S.A

    NASA Astrophysics Data System (ADS)

    Painter, Clayton S.

    Three studies on Cordilleran foreland basin deposits in the western U.S.A. constitute this dissertation. These studies differ in scale, time and discipline. The first two studies include basin analysis, flexural modeling and detailed stratigraphic analysis of Upper Cretaceous depocenters and strata in the western U.S.A. The third study consists of detrital zircon U-Pb analysis (DZ U-Pb) and thermochronology, both zircon (U-Th)/He and apatite fission track (AFT), of Upper Jurassic to Upper Cretaceous foreland-basin conglomerates and sandstones. Five electronic supplementary files are a part of this dissertation and are available online; these include 3 raw data files (Appendix_A_raw_isopach_data.txt, Appendix_C_DZ_Data.xls, Appendix_C_U-Pb_apatite.xls), 1 oversized stratigraphic cross section (Appendix_B_figure_5.pdf), and 1 figure containing apatite U-Pb concordia plots (Appendix_C_Concordia.pdf). Appendix A is a combination of detailed isopach maps of the Upper Cretaceous Western Interior, flexural modeling and a comparison to dynamic subsidence models as applied to the region. Using these new isopach maps and modeling, I place the previously recognized but poorly constrained shift from flexural to non-flexural subsidence at 81 Ma. Appendix B is a detailed stratigraphic study of the Upper Cretaceous, (Campanian, ~76 Ma) Sego Sandstone Member of the Mesaverde Group in northwestern Colorado, an area where little research has been done on this formation. Appendix C is a geo-thermochronologic study to measure the lag time of Upper Jurassic to Upper Cretaceous conglomerates and sandstones in the Cordilleran foreland basin. The maximum depositional ages using DZ U-Pb match existing biostratigraphic age controls. AFT is an effective thermochronometer for Lower to Upper Cretaceous foreland stratigraphy and indicates that source material was exhumed from >4--5 km depth in the Cordilleran orogenic belt between 118 and 66 Ma, and zircon (U-Th)/He suggests that it was exhumed

  16. Overview of the potential and identified petroleum source rocks of the Appalachian basin, eastern United States: Chapter G.13 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

    USGS Publications Warehouse

    Coleman, James L.; Ryder, Robert T.; Milici, Robert C.; Brown, Stephen; Ruppert, Leslie F.; Ryder, Robert T.

    2014-01-01

    The Appalachian basin is the oldest and longest producing commercially viable petroleum-producing basin in the United States. Source rocks for reservoirs within the basin are located throughout the entire stratigraphic succession and extend geographically over much of the foreland basin and fold-and-thrust belt that make up the Appalachian basin. Major source rock intervals occur in Ordovician, Devonian, and Pennsylvanian strata with minor source rock intervals present in Cambrian, Silurian, and Mississippian strata.

  17. Stratigraphic and provenancial evidence for recognition of an underfilled foreland basin in central Himalaya: implication for timing of India-Asia initial collision

    NASA Astrophysics Data System (ADS)

    Hu, X.; Wang, J.; Jansa, L.; Wu, F.; Yu, J.

    2009-12-01

    The Himalayan peripheral foreland basin developed when India and Asia collided. Previous studies in the Himalayan foreland were mostly concentrated on Neogene continental clastic sedimentation in sub-Himalaya or Paleogene shallow marine sedimentation along Pakistan, India, and Nepal in Lesser Himalaya. The lack of early stage of underfilled, deep-water facies in the Himalayan foreland basin is intriguing, because classic peripheral foreland basins involves generally a progression from “underfilled” (deep-water flysch facies), to “overfilled” (continental facies) stage. In this study, we present a new model of an early (underfilled) Himalayan foreland basin, through stratigraphic, sedimentologic and provenance analysis of Upper Cretaceous - Lower Paleogene deposits at the Zhepure Mountain, southern Tibet. Four main conclusions were achieved: 1) Detrital zircon U-Pb and Hf isotopic data indicated that sediments of both the Eocene Enba Formation and overlying Zhaguo Formation have mainly sourced from rocks of the Trans-Himalaya, with minor contribution from the Tethyan Himalaya. The first arrival of orogenic detritus occurred around 50.6 Ma (P8, Zhu et al., 2005), when the siliclastic sediments of Enba Formation were deposited. 2) The Paleocene-Early Eocene Zhepure Shan Formation represents establishment of a stable carbonate ramp, which began with deposition of oolitic bars at high-energy shoals, and progressively changed to a typical open marine ramp environment (Willems et al., 1996). This carbonate ramp is interpreted to develop on the northern flank of the peripheral forebulge of the underfilled Himalayan foreland basin, analogous to carbonate build-ups that occupy submarine forebulges in many other collisional foreland regions such as Alps, Papua New Guinea, Pyrenees, and Arabian Gulf. 3) The Zhepure Shanpo Formation (middle Maastrichtian - Lower Danian) and the overlying Jidula Formation (Upper Danian) show an overall shallowing-upward trend from the

  18. Tectonic development of the North Patagonian Andes and their related Miocene foreland basin (41°30‧-43°S)

    NASA Astrophysics Data System (ADS)

    Orts, DaríO. Leandro; Folguera, AndréS.; Encinas, Alfonso; Ramos, Miguel; Tobal, Jonathan; Ramos, VíCtor A.

    2012-06-01

    The Northern Patagonian Andes have been constructed through multiple mechanisms that range from tectonic inversion of extensional structures of Early to Middle Jurassic age in the Main Andes to Oligocene in the Precordilleran region. These have acted during two distinctive orogenic stages, first in late Early Cretaceous and later in Miocene times Late Oligocene extension separates these two contractional periods and is recorded by half-grabens developed in the retroarc region. The last contractional stage coexists with an eastward foreland expansion of the late Miocene arc whose roots are presently exposed as minor granitic stocks and volcanic piles subordinately in the Main Andes, east of the present arc. As a consequence of this orogenic stage a foreland basin has developed, having progressed from 18 Ma in the main North Patagonian Andes, where the mountain front was flooded by a marine transgression corresponding to the base of the Ñirihuau Formation, to 11 Ma in the foreland area. Cannibalization of this foreland basin occurred initially in the hinterland and then progressed to the foreland zone. Blind structures formed a broken foreland at the frontal zone inferred from growth strata geometries. During Pliocene to Quaternary times most of the contractional deformation was dissipated in the orogenic wedge at the time when the arc front retracted to its present position.

  19. Petrophysics of Lower Silurian sandstones and integration with the tectonic-stratigraphic framework, Appalachian basin, United States

    USGS Publications Warehouse

    Castle, J.W.; Byrnes, A.P.

    2005-01-01

    Petrophysical properties were determined for six facies in Lower Silurian sandstones of the Appalachian basin: fluvial, estuarine, upper shoreface, lower shoreface, tidal channel, and tidal flat. Fluvial sandstones have the highest permeability for a given porosity and exhibit a wide range of porosity (2-18%) and permeability (0.002-450 md). With a transition-zone thickness of only 1-6 m (3-20 ft), fluvial sandstones with permeability greater than 5 md have irreducible water saturation (Siw) less than 20%, typical of many gas reservoirs. Upper shoreface sandstones exhibit good reservoir properties with high porosity (10-21%), high permeability (3-250 md), and low S iw (<20%). Lower shoreface sandstones, which are finer grained, have lower porosity (4-12%), lower permeability (0.0007-4 md), thicker transition zones (6-180 m [20-600 ft]), and higher S iw. In the tidal-channel, tidal-flat, and estuarine facies, low porosity (average < 6%), low permeability (average < 0.02 md), and small pore throats result in large transition zones (30-200 m; 100-650 ft) and high water saturations. The most favorable reservoir petrophysical properties and the best estimated production from the Lower Silurian sandstones are associated with fluvial and upper shoreface facies of incised-valley fills, which we interpret to have formed predominantly in areas of structural recesses that evolved from promontories along a collisional margin during the Taconic orogeny. Although the total thickness of the sandstone may not be as great in these areas, reservoir quality is better than in adjacent structural salients, which is attributed to higher energy depositional processes and shallower maximum burial depth in the recesses than in the salients. Copyright ??2005. The American Association of Petroleum Geologists. All rights reserved.

  20. A Geochronological Study of Paleogene -Neogene Foreland Basin Sediments Western Nepal Himalaya: Implication of Provenance Analysis

    NASA Astrophysics Data System (ADS)

    Baral, U.; Lin, D.; Chamlagain, D.

    2015-12-01

    After the collision between the Indian and Asian plates, during early Cenozoic several south propagating thrusts were active and the sediments deposited at the northern tip of the Greater India have been reworked, recycled and metamorphosed, and were subsequently exhumed and transported to the foreland basin. Petrography, detrital zircon (DZ) dating and Lu-Hf isotope analysis, and trace element analysis were conducted from two sections of Nepal Himalaya for the determination of change in provenance, and constrain the possible timing of Indo-Asiacollision. The U-Pb ages of the DZ grains from Upper Cretaceous to Paleocene Amile Formation are older than early Mesoproterozoic with dominant number of grains showing ƐHf (t) value between 0 to +10. The trace element data shows that the sediments are from passive margin with northward paleoflow direction. These finding conclude that the sediments during this time was sourced from northern margin of Indian Plate that elucidate the possibility of the Ind0-Asia collisionsomewhere between late Paleocene to early Eocene (~58-50 Ma).The U-Pb ages from the marine Eocene Bhainskati Formation dominantly clusters between ~1000 and 500 Ma and the ƐHf (t) values ranges from -10 to +10. The trace element result shows that the sediments were from both the passive and active continental margin. The transition of deposition from marine Bhainskati Formation to continental Dumri Formation is marked by 3-4 m thick Oxisol layer with a ~10-15 Mya deposition gap during the Oligocene. The U-Pb ages of detritus from Early to mid-Miocene Dumri Formation have a wide range of detritus ranging from Archean to Mesozoic age with dominant numbers resembling the age of the Tethys Himalaya (TH) and Upper Lesser Himalaya (ULH). The presence of younger grains of Cenozoic age (~80-50 Ma) put the possibility of the Gangdase arc source deposited directly in Dumri Formation or first deposited in the TH and later transported to it. The ƐHf (t) value ranges

  1. Value of coenocorrelation curves in documenting sea level changes in Appalachian basin during Late Silurian and Early Devonian

    SciTech Connect

    Wong, S.

    1986-05-01

    A detailed paleoecological analysis of the Keyser Limestone was conducted at five localities in Virginia and West Virginia, using two multivariate statistical techniques: cluster analysis and detrended correspondence analysis. Through this analysis, the Keyser fauna was divided into communities along a nearshore to offshore environmental gradient, and each community was assigned to a benthic assemblage. Having established the proximity of the various faunal elements to the shoreline, the faunal zones at other localities, as described in the literature, were assigned to the appropriate benthic assemblage. Coenocorrelation curves were then constructed, based on benthic assemblage membership. By correlating the curves between each locality, the history of sea level changes in the Appalachian basin during the Late Silurian to Early Devonian were determined. Through this technique, more localities can be incorporated into detailed basin analysis studies. In this study, using coenocorrelation curves, it was found that the Keyser Limestone records several transgressive pulses. An initial transgressive pulse, affecting Virginia and West Virginia, resulted in the deposition of facies containing benthic assemblages 4 and 5. A second transgressive pulse resulted in the extension of these facies into Pennsylvania and New York. This transgressive pulse was followed by regressive conditions and the expansion of facies containing benthic assemblage 3. Subsequent transgression led to a return of facies containing benthic assemblages 4 and 5. Keyser deposition ended with a major regressive event, as recorded in the deposition of facies containing benthic assemblages 1-3.

  2. Petrology and provenance of the Toro Negro Formation (Neogene) of the Vinchina broken-foreland basin (Central Andes of Argentina)

    NASA Astrophysics Data System (ADS)

    Ciccioli, P. L.; Marenssi, S. A.; Limarino, C. O.

    2014-01-01

    Detrital modes of sandstones and conglomerates of the Toro Negro Formation (Late Miocene-early Pliocene) were used to analyze the evolution of the broken-foreland stage of the Vinchina Basin (28°30‧-29°00‧ S and 68°30‧-68°20‧ W) of NW Argentina. This basin located in the Western Sierras Pampeanas is bounded to the west by the Precordillera and to the east by the Famatina System. Three sandstone petrofacies: plutonic-metamorphic, volcanic and mixed petrofacies and three conglomerate lithic associations: basement, sedimentary and volcanic lithic associations were recognized, allowing to establish three source areas: Western Sierras Pampeanas (Toro Negro and Umango Ranges), Cordillera Frontal and Precordillera.

  3. Stress and strain evolution in foreland basins and its relation to the structural style : insights from the Bighorn Basin (Wyoming, USA)

    NASA Astrophysics Data System (ADS)

    Beaudoin, N.; Leprêtre, R.; Bellahsen, N.; Lacombe, O.; Amrouch, K.; Callot, J.-P.; Emmanuel, L.; Daniel, J.-M.

    2012-04-01

    The Rocky Mountains in western US provide amongst the best examples of thick-skinned tectonics: following the thin-skinned Sevier orogeny, the subsequent compressional reactivation of basement faults gave birth to the so-called Laramide uplifts/arches. The Bighorn basin, located in Wyoming, is therefore a key place to study the stress evolution during the transition from thin- to thick-skinned tectonics in orogenic forelands in terms of structural, microstructural and stress/strain evolution. We report the results of the analyses of fracture populations, inversion of fault-slip data and calcite twin data for stress as well as of calcite twinning paleopiezometry performed in two famous Laramide basement-cored structures located on each side of the basin: the Rattlesnake Mountain Anticline (RMA) and the Sheep Mountain Anticline (SMA). The comparison between the stress evolution in both folds allows to unravel (i) the pattern of both paleostress orientations and magnitudes and their evolution in time and space and (ii) the tectonic history at the basin scale. Structural and microstructural analyses show that both folds share similar kinematics. Most of the fractures are related to three main events: the Sevier thin-skinned contraction, the Laramide thick-skinned contraction, and the Basin and Range extension. During the thin-skinned period, in the innermost part of the foreland, the stress regime evolved from strike-slip to reverse while it remained strike-slip in the outermost part of the basin. Moreover, some fracture sets related to layer-parallel shortening during the early Sevier contraction formed only close to the Sevier deformation front and remained poorly expressed further away. Stress attenuation toward the craton interior is thus clearly shown by the dataset and illustrates the prominent role of the distance to the front of deformation in the way fracture sets developed in orogenic forelands. Alternatively, during the thick-skinned period, the evolution of

  4. The preliminary data on the Aeronian (Silurian) machaerids from Lithuania (Baltic Basin)

    NASA Astrophysics Data System (ADS)

    Radzevičius, S.; Ekleris, A.

    2012-04-01

    Machaerids are stem-Lophotrochozoans, closely related to the Annelids, and known from the Early Ordovician to Middle Permian. Machaerids is a group of worm-like benthic marine, bilaterally symmetrical, armoured invertebrate. Their body is covered by an external scleritome. The scleritome is imbricated of longitudinally arranged series of plates or sclerites. Completely articulated specimens of machaeridians are very rare, yet the systematic position of machaerids is controversial. Machaeridians had been assigned to different groups, such as barnacles, mollusks, echinoderms and annelids. The latter is prevailing, however their exact place within the annelids still remains unresolved. New findings of disarticulated Silurian machaerids have been recorded in western Lithuania, Geniai-1 core. This well has been drilled with exploration purposes regarding the Cambrian oil reservoir; therefore the biggest part of the Silurian core has not been collected. The exceptions are some parts of the Llandovery and Ludlow, which have partially recovered well core, but the identification of the precise stratigraphical position is complicated. Disarticulated sclerites of machaeridians have been found at the 1756.4 m depth, in the argillite, together with some graptolites and brachiopods. Several rhabdosome fragments of Normalograptus scalaris (Hisinger) were found together with the machaenid sclerites as well. N. scalaris has wide biostratigraphical distribution from the Rhudanian to the lower part of Telychian, which comprises the convolutus - triangulates graptolite biozones, corresponding to the 1756.8 - 1756 m depth. Convolutus - triangulates biozones represent Aeronian, and the machaeridian sclerites come from this interval, together with the Jonsea grayi (Davidson) brachiopod shells, which are very common and correspond to the BA 5-6 benthic assemblage, as well as do the graptolites found together. In previous studies, two orders of machaerids have been recognized: the

  5. Lithospheric flexure and composite tectonic loads in the foreland of the Marathon orogenic belt: Permian Basin, west Texas and southern New Mexico

    SciTech Connect

    Yang, Kenn Ming; Dorobek, S. . Dept. of Geology)

    1992-01-01

    Lithospheric flexure caused by loading of orogenic belts is regarded as the main process that produces subsidence in foreland basins. However in some foreland areas, subsidence may be affected by synorogenic foreland uplifts that act as additional loads. The Permian Basin is located in the foreland area of the late Paleozoic Marathon orogenic belt (Mob). The Permian Basin consists of several sub-basins that are separated by several structurally complex uplifts. Uplift of the Central Basin Platform (CBP) and subsidence in adjacent basins were coeval with final stages of deformation in the Marathon orogen. The CBP is oriented at high angles to the Marathon orogen and consists of several blocks arranged in an en echelon pattern. Data suggest that uplift of the CBP was affected by clockwise rotation of crustal blocks between NNW-SSE trending boundary faults. Although both the Delaware Basin (DB) and Val Verde Basin (VVB) are adjacent to the Mob, the synorogenic geometries of these basins are different. The VVB has a typical flexural profile that apparently is due to loading of the Marathon orogen. However, the flexural profile becomes narrower and deeper toward the western end of the VVB where the basin is bordered by the southernmost block of the CBP. In contrast, synorogenic DB profiles have composite wavelengths which show maximum deflection next to the Mob and toward the uplifted blocks of the CBP. This suggests that synorogenic subsidence of the DB was affected by loading of the CBP. In addition, the loading geometry across the uplifted CBP is asymmetric, with greater uplift and basement shortening on the western side of the CBP and less uplift and basement shortening on the eastern side. This may explain greater synorogenic subsidence in the DB than the Midland Basin.

  6. Structural evolution of the Ardmore basin, Oklahoma, U.S.A.: Progressive deformation in the foreland of the Ouachita collision

    NASA Astrophysics Data System (ADS)

    Granath, James W.

    1989-10-01

    Synthesis of oil field studies, seismic reflection data, and surface geology has resulted in a reconstruction of the Pennsylvanian evolution of the structural style of fault systems bordering and within the Ardmore Basin in south central Oklahoma. Faults bounding the margins of the basin were part of a broader left-lateral shear belt that affected southern Oklahoma during the early Pennsylvanian. The mid-Pennsylvanian and later zone of deformation contracted in southern Oklahoma to concentrate on the Washita Valley-Eola Robberson fault systems along the northern edge of the basin, and on the Criner Uplift-Healdton-Stephens County fault systems along the southern and western side of the basin. Deformation on the floor of the basin was amplified, with left-lateral strike-slip faults slicing the basin into a system of rhombohedral blocks. Deformation continued at least into Virgil time (late Pennsylvanian). A two-dimensional displacement field derived for the middle to late Pennsylvanian deformation reveals that a strong component of transpression affected both the basin-bounding faults and, by reason of the geometry of their connections to the west, the Wichita Mountain front as well. Broadly spread left-lateral shear evolved into crustal scale transpression during the Pennsylvanian Period. That progressive contraction of deformation and the change in style correlate with mid-Pennsylvanian approach and passage of the Ouachita collision along the Ouachita embayment (Thomas, 1983) on the southern margin of the North American craton. Inasmuch as the Ardmore Basin was located at the sharp internal corner of the embay ment, the coincidence suggests that the style of evolution records (1) early far-field influence of the approaching Ouachita collision during early Pennsylvanian, (2) passage of the suture during mid-Pennsylvanian, and (3) concentration of foreland deformation at the corner of the embayment as the Arkoma and Fort Worth flexural basins evolved to the south

  7. 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

    Intracontinental subduction of the South China Block below the North China Block in the Late Triassic resulted in formation of the transpressional Sichuan foreland basin on the South China Block. The Upper Triassic Xujiahe Formation was deposited in this basin and consists of an eastward-tapering wedge of predominantly continental siliciclastic sedimentary rocks that are up to 3.5 km thick in the western foredeep depocenter and thin onto the forebulge and into backbulge depocenters. Five facies associations (A-E) make up the Xujiahe Formation and these are interpreted, respectively, as alluvial fan, transverse and longitudinal braided river, meandering river, overbank or shallow lacustrine, and deltaic deposits. This study establishes a sequence stratigraphic framework for the Xujiahe Formation which is subdivided into four sequences (SQ1, 2, 3 and 4). Sequence boundaries are recognized on the basis of facies-tract dislocations and associated fluvial rejuvenation and incision, and systems tracts are identified based on their constituent facies associations and changes in architectural style and sediment body geometries. Typical sequences consist of early to late transgressive systems tract deposits related to a progressive increase in accommodation and represented by Facies Associations A, B and C that grade upwards into Facies Association D. Regionally extensive and vertically stacked coal seams define maximum accommodation and are overlain by early highstand systems tract deposits represented by Facies Associations D, E and C. Late highstand systems tract deposits are rare because of erosion below sequence boundaries. Sequence development in the Xujiahe Formation is attributed to active and quiescent phases of thrust-loading events and is closely related to the tectonic evolution of the basin. The Sichuan Basin experienced three periods of thrust loading and lithospheric flexure (SQ1, lower SQ2 and SQ3), two periods of stress relaxation and basin widening (upper

  8. The Building of a Magnetostratigraphic Framework: Lessons Learned from the Ebro Foreland Basin (Paleogene-Neogene, NE Spain)

    NASA Astrophysics Data System (ADS)

    Garces, M.

    2015-12-01

    The extensive rock outcrops spanning the complete basin fill of the South-Pyrenean foreland make this region best suited for magnetostratigraphic analysis. Over the last decades, a biochronological framework, based fundamentally on fossil benthic foraminifera and vertebrates, is being replaced with a magnetostratigraphy-based chronology. The increasing length of the composite record has allowed magnetostratigraphic correlation to work with decreasing dependence on existing biostratigraphic constraints. This has provided integrated basin studies with a time frame of unprecedented resolution, crucial to unravel the interactions and causal relationships between the diverse forcing mechanisms involved in basin formation and filling. In the ideal progress towards an independent magnetochronological framework, a fundamental issue arises recurrently: To which extent biochronological information should limit the solutions of magnetostratigraphy? The answer to this question is not simple since the chronostratigraphic significance and age accuracy of key bioevents needs to be addressed in a case-by-case basis. In the other hand, the continuity and steadiness of the sedimentary record, which is hardly assessed a priori, reveals crucial for magnetostratigraphic correlation to work. Examples from the Eocene to Miocene of the Ebro Basin illustrate the need for an effort of a basin-scale integration of all (lito-, bio- and magneto-) stratigraphic disciplines.

  9. Thermal evolution, fluid flow, and fracture development related to the structuration of the South Pyrenean Foreland Basin

    NASA Astrophysics Data System (ADS)

    Crognier, N.; Hoareau, G.; Aubourg, C.; Branellec, M.; Dubois, M.; Lahfid, A.; Lacroix, B.; Labaume, P.; Suarez-Ruiz, I.

    2015-12-01

    The E-W trending South Pyrenean Foreland Basin, formed during the upper Cretaceous and the early Miocene due to the collision between Iberian and European plates, is filled by marine to continental deposits affected by a set of successive southvergent thrusts. In order to constrain the links between fracture development, thermal regime, and fluid flow in the basin, we estimated temperatures of formation and C-O isotope signatures of fracture-filling minerals (veins), maximum paleo-temperatures of sediments, and the timing and orientation of major fracture sets. The isotopic composition of 150 veins and sediment samples has been measured. Peak temperatures of 100 bulk rocks and veins have been estimated, using Raman spectroscopy, vitrinite reflectance, fluid inclusion microthermometry and mass-47 clumped isotopes. The orientation of ~5000 joints and veins has been used to link major tectonic events to fracture development. Most primary fluid inclusions show moderate salinities (~2.5 wt%), compatible with connate or evolved meteoric waters. Fluids were generally in thermal and isotopic equilibrium with host sediments, suggesting a low fluid-rock ratio, and thus a limited impact of fractures on fluid-flow. Peak temperatures (T max) decrease southward, from ~240°C in Cretaceous to Eocene sediments close to the axial zone, to ~60°C. In a same location dominant compaction joints were mineralized close to T max, ~40°C higher than tectonic shear veins. All fracture orientations were likely controlled by Pyrenean shortening. Genetic relationships between fracture sets are currently under investigation. Finally, temperatures of 240°C measured in Eocene sediments cannot be explained by balanced cross sections using geothermal gradient expected in foreland basins (20-25°C/km). 1D thermal modeling is being performed to explain this thermal anomaly, which could result from high heat flow following mid-Cretaceous extension, the ingress of hot fluids, or undocumented tectonic

  10. Provenance evolution of Southern Pyrenees foreland basin fill during inversion and early orogenesis using detrital zircon (U-Th)/(He-Pb) double dating

    NASA Astrophysics Data System (ADS)

    Odlum, M.; Thomson, K. D.; Stockli, D. F.; Fildani, A.; Clark, J. D.; Puigdefabregas, C.

    2016-12-01

    New detrital zircon (DZ) U-Pb and (U-Th)/He double dating from exceptionally preserved extensional and contractional basin stratigraphy shows changes in drainage and provenance that elucidate the dynamics among pre-orogenic rift basins, the orogenic hinterland, and foreland basins during tectonic inversion and orogenesis in the Pyrenees. Flysch deposits of the Vallcarga Fm. represent the initiation of foreland basin deposition during the Late Cretaceous in response to tectonic inversion of the hyperextended Iberian-Eurasian margin. DZ U-Pb data from Vallcarga flysch indicate sediment sources derived from recycling of syn-rift sediments. DZ U-Pb data from the Paleocene Tremp Fm. suggest continued recycling of Early Cretaceous-Triassic sediments sourced from the north and east with input from S-SE sources in the Catalan Coastal Ranges and/or Iberian basement blocks. Eocene sandstones from the Ripoll Basin suggest primary sediment sources from the eastern Axial Zone with minor input from the Catalan Coastal Ranges. Ripoll Basin DZ data show a systematic up section decrease in grains derived from the Catalan Coastal Ranges compensated by an increase in grains from the Axial Zone as the orogen started to develop significant topography exhuming and eroding Paleozoic basement rocks. The Pyrenees are ideally suited to use DZ double-dating to study foreland basin evolution and sediment routing during orogenesis. New double-dated DZ data allow for a more detailed understanding of the provenance evolution of the foreland basin fill during tectonic inversion. The earliest foreland basin deposits after the onset of convergence 83 Ma are sourced from both north and eastern recycled syn-rift basin fill and southern sources which persisted for 20 myrs as the highly-attenuated crust thickened. Eocene deposits record the initiation of the basement-involved Axial Zone shortening and progressive orogenic unroofing during convergence. These results demonstrate that recycling of early

  11. Stratigraphic and tectonic studies in the central Aquitaine Basin, northern Pyrenees: Constraints on the subsidence and deformation history of a retro-foreland basin

    NASA Astrophysics Data System (ADS)

    Rougier, Géraldine; Ford, Mary; Christophoul, Frédéric; Bader, Anne-Gaëlle

    2016-03-01

    The central North-Pyrenean retrowedge developed on a thinned lithosphere, rich in Keuper evaporites. The behavior of this retro-foreland system is studied using subsidence analyses and a sequentially restored cross-section (120 km, Saint-Gaudens to Castelsarrasin) constrained by new chrono- and lithostratigraphy, surface and subsurface data. During the Late Cretaceous, a first episode of foreland subsidence (E1) produced a narrow marine depocenter (Comminges Basin, 30 km wide), supplied from the east. A synchronous early deformation involved inversion of basement faults and gentle shortening (4.5 km) of the Mesozoic strata above a Keuper decoupling layer. A tectonically quiet period (Q, Paleocene), characterized by a condensed succession (marine and continental), was followed by a second episode of subsidence (E2), basin migration and gentle thick- and thin-skinned shortening (8 km). Continental sedimentation, supplied by the uplifting orogen, first filled a narrow flexural basin (E2, M-L Eocene), then expanded across the Aquitaine Platform (E3, Oligocene-Miocene).

  12. Depositional and provenance record of the Paleogene transition from foreland to hinterland basin evolution during Andean orogenesis, northern Middle Magdalena Valley Basin, Colombia

    NASA Astrophysics Data System (ADS)

    Moreno, Christopher J.; Horton, Brian K.; Caballero, Victor; Mora, Andrés; Parra, Mauricio; Sierra, Jair

    2011-10-01

    The Central Cordillera and Eastern Cordillera of the northern Andes form the topographic flanks of the north-trending Magdalena Valley Basin. Constraining the growth of these ranges and intervening basin has implications for Andean shortening and the transformation from a foreland to hinterland basin configuration. We present sedimentological, paleocurrent, and sandstone petrographic results from Cenozoic type localities to provide insights into the tectonic history of the northern Middle Magdalena Valley Basin of Colombia. In the Nuevo Mundo Syncline, the mid-Paleocene transition from marine to nonmarine deposystems of the Lisama Formation corresponds with a paleocurrent shift from northward to eastward transport. These changes match detrital geochronological evidence for a contemporaneous shift from cratonic (Amazonian) to orogenic (Andean) provenance, suggesting initial shortening-related uplift of the Central Cordillera and foreland basin generation in the Magdalena Valley by mid-Paleocene time. Subsequent establishment of a meandering fluvial system is recorded in lower-middle Eocene strata of the lower La Paz Formation. Eastward paleocurrents in mid-Paleocene through uppermost Eocene fluvial deposits indicate a continuous influence of western sediment source areas. However, at the upper middle Eocene (˜40 Ma) boundary between the lower and upper La Paz Formation, sandstone compositions show a drastic decrease in lithic content, particularly lithic volcanic fragments. This change is accompanied by a facies shift from mixed channel and overbank facies to thick, amalgamated braided fluvial deposits of possible fluvial megafans, reflecting changes in both the composition and proximity of western sediment sources. We attribute these modifications to the growing influence of exhumed La Cira-Infantas paleohighs in the axial Magdalena Valley, features presently buried beneath upper Eocene-Quaternary basin fill along the western flank of the Nuevo Mundo Syncline. In

  13. Using the stratigraphic record to document tectonic-geomorphologic interactions in a foreland basin setting: outcrop study of the Ainsa Basin, Spain

    NASA Astrophysics Data System (ADS)

    Pyles, D. R.; Moody, J.; Gordon, G.; Hoffman, M.; Moss-Russell, A.; Silalahi, H.; Setiawan, P.; Clark, J.; Bracken, B.; Guzofski, C.

    2013-12-01

    Eocene strata of the Ainsa Basin (Spain) contain clastic and carbonate strata deposited in a relatively small (100 km^2), structurally active piggyback foreland basin. The basin is bounded by the Mediano Anticline to the east and the Boltana Anticline to the west. Clastic strata were sourced by an eastern fluvial-deltaic system whereas carbonate strata were sourced from shallow-water carbonate systems that rimmed the southern and western margins of the basin. Four time-stratigraphic units, which form an upward transect through the basin-fill succession, were studied in detail: Ainsa, Morillo, Guaso, Sobrarbe-Escanilla. The study uses the stratigraphic record to document linkages between progressive uplift of the basin-bounding structures, spatial-temporal changes in the amount and location of subsidence, and temporal changes in the landscape. The Ainsa unit contains submarine channels that entered the basin from the east and exited the basin to the northwest, although some channels locally transfer to lobes near the northwest end of the basin. The Morillo unit contains submarine channels that entered the basin from the east, dispersed onto the basin floor, then converged at the western end of the basin where they continued onto the longitudinally adjacent Jaca Basin. The Guaso unit contains submarine channels that entered the basin from the east and transfer to a ponded distributive submarine fan at the center of the basin. The Escanilla-Sobrarbe unit contains a linked shelf-to-basin system that prograded from south to north and records the final filling of the basin. Four lines of evidence collectively support the basin-fill succession was deposited during structural growth. First, the depocenter, which is interpreted to reflect the position of maximum subsidence during deposition, of the systems systematically shifted westward as the basin filled. Second, the axial part of the clastic sediment systematically shifted southward as the basin filled. Third, the

  14. Provenance of eastern Magallanes foreland basin sediments: Heavy mineral analysis reveals Paleogene tectonic unroofing of the Fuegian Andes hinterland

    NASA Astrophysics Data System (ADS)

    Zahid, Khandaker M.; Barbeau, David L., Jr.

    2010-07-01

    Documenting variations in the composition of foreland basin detrital sediments is a useful tool for reconstructing the kinematic history of associated orogenic systems. Herein we report the results of our SEM-EDS heavy mineral analysis of the Late Cretaceous to early Miocene eastern Magallanes basin of southernmost Argentina. Our data indicate that Campanian to middle Eocene sediments had a mafic/ophiolitic provenance, which we interpret as being derived from the Patagonian-Fuegian magmatic arc and the mafic floor of the preceding Rocas Verdes marginal basin. Upper middle Eocene to lower Miocene heavy minerals, on the other hand, indicate a metamorphic/metasedimentary provenance, which we interpret as being derived from the Cordillera Darwin metamorphic complex. Together, these data indicate an abrupt shift in sediment provenance in middle to late Eocene time, thereby corroborating recent interpretations of the basin's detrital-zircon geochrononology, and providing further support for temporal and possibly genetic relationships between development of the Patagonian orocline, the opening of Drake Passage and the Oi-1 glaciation of Antarctica.

  15. Migration of the carbonate ramp and sponge buildup driven by the orogenic wedge advance in the early stage (Carnian) of the Longmen Shan foreland basin, China

    NASA Astrophysics Data System (ADS)

    Li, Yong; Yan, Zhaokun; Liu, Shugen; Li, Haibing; Cao, Junxing; Su, Dechen; Dong, Shunli; Sun, Wei; Yang, Rongjun; Yan, Liang

    2014-04-01

    The marine Carnian the Maantang Fm. overlies a flexural forebulge unconformity and records the initial establishment, drowning and migration of a carbonate ramp and sponge buildup along the forebulge margin of the Longmen Shan foreland basin. The Maantang Fm. is of wedge-shaped geometry, and is composed of oolitic and bioclastic limestones, siliceous sponge reef and shale in an upward-fining succession. The formation shows the establishment and drowning of a distal margin carbonate ramp and sponge buildup, deepening into offshore marine muds, followed by progradation of marginal marine siliciclastics. The formation also shows the transition from shale cratonward into carbonate rock southeastward. The sponge reefs and shoal were deposited on a carbonate ramp on the distal margin of the early foreland basin. The growth rate of sponge reefs is 0.04 mm/yr, equivalent to the rate of relative sea level rise of 0.01-0.05 mm/yr. The sponge buildup and oolitic shoal are divided into seven zones southeastward on the carbonate ramp along the basal unconformity. Their migration rate of 18 mm/yr from NW to SE coincides with the estimated orogenic wedge advance rate (5-15 mm/yr, Li et al., 2003), a clear indication that the advancing wedge controlled the migration rate of foreland oolitic shoal-siliceous sponge reef. We have inferred that the tectonic load of the Longmen Shan orogenic wedge led to flexural subsidence and rising relative sea level in the foreland basin located at the western margin of the Yangtze Craton, driving the growth and subsequent drowning of the oolitic shoal-sponge buildup in the early stage of the foreland basin. We propose that the drowning and migration processes were the sedimentary response to the orogenic wedge advance toward the Yangtze Craton, and to the rapid closure of the Carnian Songpan-Ganzi remnant ocean basin.

  16. Paleo-environments of Late Pliocene to Early Pleistocene Foreland-Basin Deposits in the Western Foothills of South-Central Taiwan

    NASA Astrophysics Data System (ADS)

    Chiu, Tzu-Hsuan; Tien-Shun Lin, Andrew; Chi, Wen-Rong; Wang, Shih-Wei

    2017-04-01

    Lithofacies and paleo-environmental analyses of the Pliocene-Pleistocene deposits of Taiwan provide a framework to understand the stratigraphic development of foreland basin to the west of the orogenic belt. In this study, we performed lithofacies analyses and biostratigraphic studies on calcareous nannofossils in two areas in south-central Taiwan, the Jhuoshuei River, and the Hushan Reservoir, respectively. The studied lithostratigraphic units are the Chinshui Shale, the Cholan Formation, and the Toukoshan Formation, in an ascending order, with a total stratigraphic thickness more than 3500 m in central Taiwan. Sixteen lithofacies and four lithofacies associations are identified, pertaining to tide-dominated deltaic systems bordering a shallow marine setting in the foreland basin. A few wide-spread layers of thickly-bedded sandstones featuring ball-and-pillow structures are interpreted as resulting from earthquake shaking (i.e., seismites). In addition, the vertical facies change shows a coarsening and shallowing-upward succession, indicating the gradually filling up of the foreland basin by sediment progradation. The progradation is interpreted to result from westward migrating orogenic belt and an increase in sediment supply. The top 2000-m thick foreland succession (i.e., the uppermost part of the Cholan Formation, and the Toukoshan Formation) is dominantly fluvial deposits with occasional intercalations of shoreface sediments, indicating an extremely rapid and balanced rate of basin subsidence and sediment supply for the past 1.5 Ma. Vertebrate fossils of deer and elephants are identified in the upper Cholan Formation deposited in coastal to fluvial settings. Keywords: Pliocene-Pleistocene Epoch, lithofacies, foreland basin, Taiwan

  17. Late Quaternary faulting on the Manas and Hutubi reverse faults in the northern foreland basin of Tian Shan, China

    NASA Astrophysics Data System (ADS)

    Gong, Zhijun; Li, Sheng-Hua; Li, Bo

    2015-08-01

    The Tian Shan Range lies in the actively deforming part of the India-Asia collision zone. In the northern foreland basin of Tian Shan, the strata were intensively deformed by Cenozoic folding and faulting. Slip rate studies along these faults are important for understanding the dynamics of crustal deformation and evaluating the seismic hazards in the region. Two reverse faults (the Manas and Hutubi faults) in the northern foreland basin were investigated. Due to past faulting events along these faults, the terrace treads along the Manas River were ruptured, forming fault scarps several meters in height. Loess deposits were trapped and preserved at the surface ruptures along these scarps. The thickness of the trapped loess is dependent on the size of the ruptures. The minimum and maximum ages of these scarps are constrained by dating the loess preserved at the surface ruptures and the terrace treads, respectively, using the quartz optically stimulated luminescence (OSL) dating technique. Our dating results suggest that the loess trapped at the ruptures was deposited from the early to mid-Holocene at the Hutubi Fault, and from the mid- to late-Holocene at the Manas Fault. The vertical displacements of the faults were evaluated by measuring the topographic profiles across the investigated fault scarps using the differential global position system (DGPS). Our results suggest that, during the late Quaternary in the studied region, the vertical slip rates of the Manas Fault were between ˜ 0.74 mm /yr and ˜ 1.6 mm /yr, while the Hutubi Fault had a much lower vertical slip rate between ˜ 0.34 mm /yr and ˜ 0.40 mm /yr. The tectonic implications of our results are discussed.

  18. U-Pb geochronology and geochemistry of the McCoy Mountains Formation, southeastern California: A Cretaceous retroarc foreland basin

    USGS Publications Warehouse

    Barth, A.P.; Wooden, J.L.; Jacobson, C.E.; Probst, K.

    2004-01-01

    The timing of deposition of fluvial sediments now forming the >7-km-thick McCoy Mountains Formation is one of the key uncertainties in reconstructing the Mesozoic poleogeography of southern California and western Arizona. Ion-microprobe U-Pb geochronologic data for individual zircons from nine sandstones from the McCoy Mountains type section and six associated igneous rocks provide significant new constraints on the tectonic setting and the timing of deposition within the northwest-trending McCoy basin. U-Pb zircon data from a metavolcanic rock of the underlying Dome Rock sequence in the Palen Mountains confirm that the McCoy Mountains Formation was deposited after regional Middle to Late Jurassic arc magmatism. U-Ph zircon data from a Late Cretaceous granodiorite intruding the formation in the Coxcomb Mountains confirm that the formation was deformed and metamorphosed prior to 73.5 ?? 1.3 Ma. Populations of detrital zircons vary systematically with both rock type and stratigraphic height; lithic arkoses predominantly derived from the west have consistently more abundant younger zircons than do litharenite sandstones predominantly derived from the north, and the youngest zircons yield maximum depositional ages that decrease from 116 Ma near the base to 84 Ma near the top of the section. The detrital-zircon data permit a Late Jurassic age for the basal, comparatively quartz-rich sandstone. However, the data further suggest that >90% of the formation was deposited between middle Early and middle Late Cretaceous time. These results are consistent with the hypothesis that most of the McCoy Mountains Formation represents a retroarc foreland basin, deposited behind the active, evolving Cretaceous Cordilleran continental-margin magmatic arc that lay to the west and in the foreland of the actively deforming Cretaceous Maria fold-and-thrust belt.

  19. Using Sequential Kinematic and Thermochronometric Modeling to Temporally and Spatially Link Thrust Belt Exhumation with Basin Development in the Bolivian Fold-Thrust-Belt-Foreland Basin System.

    NASA Astrophysics Data System (ADS)

    Rak, A. J.; McQuarrie, N.

    2014-12-01

    Applying isostasy and erosion to sequentially deformed balanced cross sections links the growth of hinterland structures to the developing foreland basins (FB) adjacent to fold-thrust belts (FTB), adding geologic constraints to modeled exhumation pathways. We sequentially deform the Rio Beni cross section in northern Bolivia (McQuarrie et al., 2008) with kinematic modeling software Move. In our model, topography evolves and basins develop for each model step as deformation, erosion, and isostasy are applied; and are a direct function of the geometry and kinematics of the cross section. The model is constrained by the depth of the foreland and hinterland basins, geology present at the surface, the depth and angle of the decollement, and the shape of the modern observed topography. Topography develops as thrusting occurs and loads the crust, producing a flexural wave and creating accommodation space in adjacent basins. Erosion of material above a newly generated topographic profile unloads the section while basin space is filled. Once the model sufficiently duplicates geologic constraints, a 0.5 km X 0.5 km grid of unique points is deformed with the model and used to determine displacement vectors for each 10 km shortening step. These displacement vectors, in conjunction with a prescribed time interval for each step, determine a velocity field that can be used in a modified version of the advection diffusion modeling software Pecube. Cooling ages predicted using this method are based on deformation rates, geometry, topography, and thermal parameters, and offer insight into possible rates of deformation, erosion, and deposition throughout FTB and FB development. Incorporating erosion, deposition, and isostasy in sequentially deformed balanced cross sections highlights the spatiotemporal aspects of sedimentary wedge propagation, identifies necessary external negative buoyancy affects, and provides additional geologic constraints to modeled exhumation pathways.

  20. Gas accumulations in Oligocene-Miocene reservoirs in the Alpine Foreland Basin (Austria): evidence for gas mixing and gas degradation

    NASA Astrophysics Data System (ADS)

    Pytlak, L.; Gross, D.; Sachsenhofer, R. F.; Bechtel, A.; Linzer, H.-G.

    2017-09-01

    Two petroleum systems are present in the eastern (Austrian) sector of the Alpine Foreland Basin. Whereas oil and thermogenic gas in Mesozoic and Eocene reservoir rocks have been generated beneath the Alps in Lower Oligocene source rocks, relative dry gas in Oligocene-Miocene clastic rocks deposited in the deep marine basin-axial channel system (Puchkirchen Channel) is interpreted as microbial in origin. Detailed investigations of the molecular and isotope composition of 87 gas samples from 86 wells, representing all producing fields with Oligocene and Miocene reservoir rocks, suggest that the presence of pure microbial gas is rare and limited mainly to the northern basin flank (e.g., KK field). All other fields contain varying amounts of thermogenic gas, which has been generated from a source rock with oil-window maturity. A relation with the underlying thermogenic petroleum system is obvious. Upward migration occurred along discrete fault zones (e.g., H field) or through low-permeability caprocks. Local erosion of Lower Oligocene sediments, the principal seal for the thermogenic petroleum system, as well as a high percentage of permeable rocks within the Puchkirchen Channel favored upward migration and mixing of thermogenic and microbial gas. All gas samples in Oligocene-Miocene reservoirs are biodegraded. Biodegradation and the formation of secondary microbial gas resulted in gas drying. Therefore, the gas samples analyzed in this study are relative dry, despite significant contributions of thermogenic hydrocarbons. Biodegradation probably continues at present time. The degree of biodegradation, however, decreases with depth.

  1. Gas accumulations in Oligocene-Miocene reservoirs in the Alpine Foreland Basin (Austria): evidence for gas mixing and gas degradation

    NASA Astrophysics Data System (ADS)

    Pytlak, L.; Gross, D.; Sachsenhofer, R. F.; Bechtel, A.; Linzer, H.-G.

    2016-11-01

    Two petroleum systems are present in the eastern (Austrian) sector of the Alpine Foreland Basin. Whereas oil and thermogenic gas in Mesozoic and Eocene reservoir rocks have been generated beneath the Alps in Lower Oligocene source rocks, relative dry gas in Oligocene-Miocene clastic rocks deposited in the deep marine basin-axial channel system (Puchkirchen Channel) is interpreted as microbial in origin. Detailed investigations of the molecular and isotope composition of 87 gas samples from 86 wells, representing all producing fields with Oligocene and Miocene reservoir rocks, suggest that the presence of pure microbial gas is rare and limited mainly to the northern basin flank (e.g., KK field). All other fields contain varying amounts of thermogenic gas, which has been generated from a source rock with oil-window maturity. A relation with the underlying thermogenic petroleum system is obvious. Upward migration occurred along discrete fault zones (e.g., H field) or through low-permeability caprocks. Local erosion of Lower Oligocene sediments, the principal seal for the thermogenic petroleum system, as well as a high percentage of permeable rocks within the Puchkirchen Channel favored upward migration and mixing of thermogenic and microbial gas. All gas samples in Oligocene-Miocene reservoirs are biodegraded. Biodegradation and the formation of secondary microbial gas resulted in gas drying. Therefore, the gas samples analyzed in this study are relative dry, despite significant contributions of thermogenic hydrocarbons. Biodegradation probably continues at present time. The degree of biodegradation, however, decreases with depth.

  2. Detrital zircon (U-Th)/(He-Pb) double-dating constraints on provenance and foreland basin evolution of the Ainsa Basin, south-central Pyrenees, Spain

    NASA Astrophysics Data System (ADS)

    Thomson, Kelly D.; Stockli, Daniel F.; Clark, Julian D.; Puigdefàbregas, Cai; Fildani, Andrea

    2017-07-01

    South central Pyrenean foreland basin fill preserves the eroded remnants of the early stages of fold-thrust belt evolution and topographic growth. Specifically, the Eocene Hecho Group in the Ainsa Basin contains a succession of turbiditic channels and levees deposited in the transition zone between the fluvial-deltaic and deep marine depozones. Detailed isotopic provenance analyses allow for the reconstruction of sediment sources of the ancient sediment routing systems. This study presents 2332 new detrital zircon (DZ) U-Pb ages and 246 new DZ double-dated (U-Th)/(He-Pb) ages from 19 turbiditic and fluvio-deltatic sandstones in the Ainsa Basin. These data indicate a progressive provenance shift from Cadomian/Caledonian plutonic and metamorphic rocks of the eastern Pyrenees to Variscan plutonic rocks in the central Pyrenees. Minor sediment contributions from sources located to the S and SE of the basin are seen throughout the section. New DZ (U-Th)/He results identify four main cooling events: Pyrenean orogenesis ( 56 Ma), initial basin inversion ( 80 Ma), Cretaceous rifting ( 100 Ma), and pre-Mesozoic cooling ages related to earlier tectonic phases. This study imposes new constraints on the paleogeographic evolution of the Pyrenees and illustrates that high-frequency fluctuations in sediment delivery processes and sediment routing introduce superimposed noise upon the basin-scale long-term provenance evolution during orogenesis.

  3. Reevaluation of the Bedford--Berea sequence on Ohio and adjacent states: New perspectives on sedimentation and tectonics in foreland basins

    SciTech Connect

    Pashin, J.C. ); Ettensohn, F.R. )

    1992-01-01

    The Late Devonian Bedford-Berea (BB) sequence provided an early basis for models of epeiric sedimentation, but controversy regarding its origin has arisen in recent years. This study was designed to resolve this controversy and to identify factors that control depositional architecture in foreland basins on the basis of outcrop and subsurface data. The BB is a siliciclastic succession that was deposited in the Appalachian foreland basin during a relaxational phase of the Acadian orogeny. Among the salient features of the BB are an eastern platform and a western basin. The platform was characterized largely by erosion of Catskill sediment and subsequent deposition of aggradational valley-fill sequences, whereas the basin was characterized mainly by progradational delta and shelf deposits that overlie conformably the distalmost part of the Catskill clastic wedge. BB depositional history and paleogeography is divided into two episodes: (1) basin filling and (2) delta destruction. Basin filling was characterized by regressive fluvial-deltaic systems that eroded the Catskill wedge and supplied prograding deltaic and shelf sediment to the western basin. Delta destruction began after the basin was full with sediment and was dominated by flexural relaxation, which gave rise to unusual facies patterns. Delta-front deposits in the western basin were uplifted and reworked, and a shelf silt blanket prograded back toward the incised valleys on the rapidly subsiding eastern platform where estuaries were forming. Reevaluation of the BB sequence demonstrates that the depositional architecture and paleogeographic history of foreland basins is much more elaborate than is commonly recognized. Tectonism, relict topography, differential compaction, and relative sea-level variation functioned collectively to determine the complex depositional history and paleogeography of the BB sequence.

  4. Exploration for stratigraphic traps in a foreland basin using a sequence stratigraphic simulation: Examples from the Eocene/Oligocene of the Apure-Llanos basin, Venezuela

    SciTech Connect

    Reistroffer, J.; Levine, P.A.; Kendall, C.G. ); Finno, A. )

    1996-01-01

    Foreland basin depositional sequences provide a sensitive record of the interaction between tectonism, eustatic sea level fluctuations, and sedimentation rates. Interplay between these controlling factors creates sedimentary geometries which are unique to this tectonic setting and form excellent stratigraphic hydrocarbon traps. Incised valley fill deposits, [open quote]forced regression[close quote] deposits, and combination structure-stratigraphic traps are the predominant reservoir types. In an effort to extend our understanding of the development of these traps, the sequence stratigraphy of a regional seismic transact through the Apure-Llanos basin was simulated. From the Late Eocene through Oligocene, the Apure-Llanos basin was Characterized by multiple phases of compression and a southeast migrating depocenter. Sands of the Mirador and Carbonera formations, which onlap the Arauca Arch to the southeast, were shed from the Guyana craton and were Cannibalized from sediments along the deformation front to the northwest. These sands comprise the principal reservoirs in the study area. Shales of the Leon Formation, which act as a regional seal, were deposited during rapid flexural subsidence and eustatic sea level rise during the early Oligocene. The Arauca Arch acted as a focal mechanism for east and southeast migrating hydrocarbons. Simulation results predict an important stratigraphic pinchout of the Mirador Formation sands against the Arauca Arch, which correlates with the Arauca Reid in Colombia to the southwest. Also, modeling indicates that minimal Tertiary oil production In the La Victoria Field to the east is due to the lack of an adequate seal. Our results provide a conceptual model which predicts hydrocarbon reservoir and seal relationships in a foreland basin setting with limited data control.

  5. Broken foreland basins in the India-Eurasia collision zone and in the central Andes: tectonic, geomorphic and sedimentologic similarities (Invited)

    NASA Astrophysics Data System (ADS)

    Strecker, M. R.; Bookhagen, B.; Hilley, G. E.; Kirby, E.; Sobel, E. R.

    2010-12-01

    Deformation in broken forelands may be accommodated far into the foreland by reactivation of crustal anisotropies, producing steep, but short-wavelength topography. The discontinuous nature of this deformation and potentially rapid rock uplift rates relative to those within fold-and-thrust belts favors sediment ponding behind active mountain ranges built atop reactivated geologic structures. In the realm of the greater Indo-Eurasian collision zone the Tien Shan of Kyrgyzstan and China or the Qilian Shan comprise such settings, where ongoing shortening excises and uplifts basement blocks and eventually compartmentalizes a formerly contiguous foreland. In the Qilian Shan and ranges of NE Tibet, an early Tertiary foreland was disrupted by diachronous range growth and formation of isolated basins. Reconnection to external base level did not occur until Quaternary time. The Argentine Santa Barbara and Pampean ranges are examples of such environments in a non-collisional orogen. Here, several generations of transient basin fills were deposited and re-excavated in intermontane basins that are near the headwaters of rivers currently draining the broken foreland basin system. Despite differing settings, there similarities between basins in both environments, including: (1) multiple episodes of filling and excavation; (2) steep precipitation gradients; and, (4) highly disparate and diachronous deformation and uplift. Comparison of basin histories from the Andes and Central Asia suggests that these characteristics are the consequence of similar factors. First, deformation is typically localized along inherited crustal zones of weakness and the evolving topographic load above the reactivated faults. The high-angle structures produce large amounts of uplift for a given increment of shortening, facilitating rapid removal of cover sediments and exposing resistant lithologies. Second, transient basin fills typically occur where moisture-laden winds are prevented from reaching the

  6. Origin of middle Silurian Keefer sandstone, east-central Appalachian basin

    SciTech Connect

    Meyer, S.C.; Textoris, D.A.; Dennison, J.M.

    1988-08-01

    The Keefer Sandstone of northeastern West Virginia and western Maryland was deposited in back-barrier, barrier-island, and marine shelf environments along a prograding, storm-dominated, mesotidal coastline of probable low wave energy. Back-barrier sediments were deposited in tidal-flat and lagoonal environments. Barrier-island sediments are dominated by cross-bedded sandstones deposited in deep, laterally migrating tidal inlets. Erosion accompanying the passage of a migrating tidal inlet usually resulted in the removal of underyling shoreface and shelf sands, so that tidal-inlet sandstones commonly lie with a markedly erosive contact on subtidal shales of the underlying Rose Hill Formation. Sand was transported to the shelf from the coastline by downwelling, storm-generated currents. Chamosite ooids formed in gently agitated waters immediately below fair-weather wave base. Outcrops to the east, which preserve back-barrier and barrier-island lithofacies, record a single basinward progradation of the shoreline. However, outcrops farther west, which preserve finer grained sandstone, shale, and limestone shelf lithofacies, document four progradational events in stacked coarsening-upward sequences. Each is typically capped by transgressive sandstones, commonly hematite ooid-bearing, which mark episodes of coastal retreat. Retreat occurred through shoreface and nearshore erosion. Chamosite ooids were transported basinward during coastal retreat and altered to hematite prior to burial. Transgressive shelf sands contain abundant coarse sand eroded from tidal-inlet deposits. Deposition of the Keefer was a response to a decrease in rate of eustatic sea level rise, or a decrease in basin subsidence rate. This was followed by deposition of the transgressive basin facies of the Rochester Shale.

  7. Late Cretaceous-Cenozoic Evolution of the Central Andean Foreland Basin System in the Eastern Cordillera to Subandean Zone, Southern Bolivia

    NASA Astrophysics Data System (ADS)

    Calle, A.; Horton, B. K.; Anderson, R. B.; Long, S. P.

    2015-12-01

    Evaluation of foreland basin deposystems and provenance across southern Bolivia reveals punctuated growth of the central Andean orogenic wedge. New and published sedimentology, provenance data, stratigraphy, subcrop mapping, and apatite (U-Th)/He thermochronometry along two transects (19.5, 21°S) from the easternmost Eastern Cordillera (EC) to the western Subandean Zone (SAZ) shed light on Late Cretaceous-Miocene thrust belt and foreland basin dynamics. Sediment dispersal patterns are constrained by paleocurrents, detrital zircon U-Pb geochronology, sandstone petrography, and conglomerate clast compositions. Spatial and temporal changes in the Andean thrust belt are recorded in asymmetric foreland basin thicknesses, facies distributions, and provenance within the EC (Incapampa and Camargo synclines) and SAZ (El Rosal and Entre Rios synclines). The >4 km uppermost Cretaceous-lower Miocene EC succession and ~2.5 km upper Oligocene-Miocene SAZ clastic successions record a shift from fluvial backbulge to pedogenic forebulge deposition. Braided, meandering, and lacustrine foredeep deposition records the most-rapid subsidence, with a later shift to progradational braided and alluvial fan deposition in the wedge-top zone. Growth strata preserved in EC and SAZ wedge-top deposits suggest unsteady eastward advance of the deformation front. Distal foreland deposits show west-directed paleocurrents with >1 Ga detrital zircon populations. Emerging Andean sources are indicated by east-directed paleocurrents, <0.7 Ga detrital zircon populations, and hinterland clast compositions. Time-transgressive patterns of punctuated exhumation in the EC (>36-25 Ma), Interandean Zone (IAZ, ~22-7 Ma) and SAZ (<6 Ma) can be linked to eastward passage of a flexural forebulge, recorded as a 50-200 m thick condensed zone in EC and SAZ basin fill. Integrated assessment of basin architecture, provenance, and exhumation highlights the potential influence of pre-Cenozoic IAZ heterogeneities on

  8. Reconstruction of fluid (over-)pressure evolution from sub-seismic fractures in folds and foreland basins

    NASA Astrophysics Data System (ADS)

    Beaudoin, Nicolas; Lacombe, Olivier; Bellahsen, Nicolas; Emmanuel, Laurent

    2013-04-01

    at 2 to 3 km depth, and emphasize that the LPS-related stress build-ups during Sevier and Laramide are associated with an increase in fluid overpressure until it reaches the lithostatic pressure. In each fold studied, the evolution of fluid pressure however reflects peculiar periods during which tensile fracture and vein sets developed under a nearly hydrostatic fluid pressure, suggesting a high hydraulic permeability of the sedimentary cover. The hydraulic behavior of these tensile fracture/vein sets which formed during regional foreland flexure and at fold hinges in response to local strata bending is fully supported by independent geochemical studies performed on the cements of the same veins. At the basin scale, the evolution of the fluid overpressure possibly reflects the eastward fluid migration in the Rocky Mountain foreland during the Laramide contractional event. Finally, considering that fluid overpressure was released during folding permits to estimate syn-folding exhumation of strata, the value of which is consistent with independent paleo-barometric reconstruction based on hydrocarbon fluid inclusions and with exhumation-uplift rates derived from apatite fission-track data in neighboring Laramide uplifts. To conclude, in a geological setting where the paleo-hydrological, the microstructural and the structural histories are well-constrained, we are now able to (semi-)quantitatively reconstruct the evolution of fluid (over-) pressure and to integrate this evolution in a consistent tectonic-fluid flow scenario at both fold scale and basin scale, to be compared with outputs of numerical modeling of fluid flow in basins.

  9. Reservoir characteristics of Putnam zone (Silurian Interlake Formation) lithofacies, southwestern Williston basin

    SciTech Connect

    Inden, R. ); Oglesby, C. ); Byrnes, A. ); Cluff, B. )

    1991-06-01

    Reservoirs in the Putnam zone (lower Interlake Formation) in the southwestern part of the Williston basin include oolitic-pellet dolomite grainstone, fossil-pellet grainstone, and a wide spectrum of reef-related, fossil-corral dolomite packstones and coral-stromatoporoid rudstone/boundstones. Each of these potential reservoirs has a unique pore system and, thus a different set of petrophysical properties which define their reservoir characteristics. Oolitic grainstones have a homogeneous intercrystalline-micro-crystalline pore system, whereas the fossil-pellet dolomite grainstone facies consists of separate mesovugs dispersed in well-interconnected intercrystalline porosity. Capillary pressure curves indicate that pore-throat heterogeneity is greater, and entry pressures lower, for reefal lithofacies than for pelletal grainstones. These curves also demonstrate why many of the producing fields tend to have high water cuts. In many oolitic-pellet grainstone units, irreducible water saturations of 10% would not be reached until a hydrocarbon column of 700 ft was reached. High water production characteristics are therefore expected because Red River/Interlake structures attain only 50-100 ft of closure. This, however, does not mean that Putnam is not an economic zone, especially as a secondary objective. Wells in Putnam and Crane fields, for instance, have reserves in excess of 300,000 bbl of oil. The reservoirs here may be dominated by the reef-related facies, which have an extremely high relative permeability to oil.

  10. Evolution of the Neogene Andean foreland basins of the Southern Pampas and Northern Patagonia (34°-41°S), Argentina

    NASA Astrophysics Data System (ADS)

    Folguera, Alicia; Zárate, Marcelo; Tedesco, Ana; Dávila, Federico; Ramos, Victor A.

    2015-12-01

    The Pampas plain (30°-41°S) has historically been considered as a sector that evolved independently from the adjacent Andean ranges. Nevertheless, the study of the Pampas showed that it is reasonable to expect an important influence from the Andes into the extraandean area. The Pampas plain can be divided into two sectors: the northern portion, adjacent to the Pampean Ranges, has been studied by Davila (2005, 2007, 2010). The southern sector (34°-41°S) is the objective of the present work. The study of this area allowed to characterize two separate foreland basins: the Southern Pampa basin and the Northern Patagonian basin. The infill is composed of Late Miocene and Pliocene units, interpreted as distal synorogenic sequences associated with the late Cenozoic Andean uplift at this latitudinal range. These foreland basins have been defined based on facies changes, distinct depositional styles, along with the analysis of sedimentary and isopach maps. The basins geometries are proposed following De Celles and Gilles (1996) taking into account the infill geometry, distribution and grain size. In both cases, these depocenters are located remarkably far away from the Andean tectonics loads. Therefore they cannot be explained with short-wave subsidence patterns. Elastic models explain the tectonic subsidence in the proximal depocenters but fail to replicate the complete distal basins. These characteristics show that dynamic subsidence is controlling the subsidence in the Southern Pampas and Northern Patagonian basins.

  11. Rock magnetic properties and paleoenvironmental implications of an 8-Ma Late Cenozoic terrigenous succession from the northern Tian Shan foreland basin, northwestern China

    NASA Astrophysics Data System (ADS)

    Lu, Honghua; Zhang, Weiguo; Li, Youli; Dong, Chenyin; Zhang, Tianqi; Zhou, Zuyi; Zheng, Xiangmin

    2013-12-01

    In the northern Tian Shan foreland basin, northwestern China, the thick Cenozoic terrigenous succession is crucial for paleoclimate-environmental reconstruction of the Asian interior. Here we present a detailed rock magnetic investigation on 245 samples from the ~ 1200-m-thick Neogene Taxi He section with a magnetostratigraphic age span of ca. 8.0 to 2.0 Ma in the northern Tian Shan foreland basin. Our rock magnetic results indicate that the significant variations in composition, concentration and grain size of magnetic minerals occurred at ca. 6.0, 3.7 and 2.7 Ma. The comparable compositions of rare earth elements (REEs) throughout the Neogene Taxi He section suggest no significant modification of the source materials during the interval between ca. 8.0 and 2.0 Ma, and thus sediment provenance is not regarded as responsible for these observed variations in rock magnetic properties. Our further analyses show that the variations in magnetic properties of the Taxi He section are casually linked mainly with lithofacies transition due to range encroachment into foreland basin as well as climate aridification. Identified enhancement of aridification was chronologically constrained at ca. 6.0 and 2.7 Ma. Such climate events are important archives for reconstructing the Late Cenozoic paleoclimatic history of the Asian interior. Further comparison between different paleoclimate records clearly indicates that magnetic parameters such as S- 100mT are potentially effective proxy indices for paleoclimate-environmental reconstruction in the Tian Shan foreland basins and the nearby areas.

  12. Discriminating Sediment Supply versus Accommodation Controls on Foreland Basin Stratigraphic Architecture in the Book Cliffs, central Utah using Detrital Double Dating

    NASA Astrophysics Data System (ADS)

    Bartschi, N.; Saylor, J. E.; Blum, M. D.

    2014-12-01

    Middle-late Campanian strata of the Book Cliffs record the deposition of three clastic wedges in the foreland basin east of the Sevier fold-thrust belt. Variations in wedge geometries provide an opportunity to evaluate the effects of sediment supply versus accommodation on foreland basin architecture. There is an increase in eastward progradation rate between the L. and M. Castlegate Sandstone, followed by a return to slower progradation rates in the overlying Bluecastle Tongue, and Price River Formation, as well as their lateral equivalents. Rapid progradation may be caused by increased sediment supply, due either to rapid exhumation in the Sevier fold-thrust belt, or changes in the sediment source. Alternatively, reduced accommodation within the foreland basin due to uplift during initial Laramide deformation could produce the same rapid progradation. In this scenario, decreased progradation would be coincident with enhanced foreland basin subsidence and rapid sediment accumulation in the proximal foredeep. We test these hypotheses using thermo- and geochronology to double date individual detrital grains, enabling identification of changes in lag time and sediment provenance. Upsection decreases or increases in lag time correspond to increased or decreased exhumation rates, respectively, or introduction of a new upper crustal sedimentary source. We focus on 21 samples from 7 measured sections along depositional strike and dip. Samples were collected from the upper Blackhawk Formation, L. and M. Castlegate Sandstone, Bluecastle Tongue, Price River Formation, and their lateral equivalents. Initial results indicate major sediment provenance changes associated with the transition between slow and rapid wedge progradation, as well as minor provenance changes within individual wedges. There is also a significantly greater proportion of Cordilleran magmatic arc grains in distal locations than in proximal locations, interpreted as sediment mixing during transport.

  13. Provenance and detrital zircon geochronologic evolution of lower Brookian foreland basin deposits of the western Brooks Range, Alaska, and implications for early Brookian tectonism

    USGS Publications Warehouse

    Moore, Thomas; O'Sullivan, Paul B.; Potter, Christopher J.; Donelick, Raymond A.

    2015-01-01

    The Upper Jurassic and Lower Cretaceous part of the Brookian sequence of northern Alaska consists of syntectonic deposits shed from the north-directed, early Brookian orogenic belt. We employ sandstone petrography, detrital zircon U-Pb age analysis, and zircon fission-track double-dating methods to investigate these deposits in a succession of thin regional thrust sheets in the western Brooks Range and in the adjacent Colville foreland basin to determine sediment provenance, sedimentary dispersal patterns, and to reconstruct the evolution of the Brookian orogen. The oldest and structurally highest deposits are allochthonous Upper Jurassic volcanic arc–derived sandstones that rest on accreted ophiolitic and/or subduction assemblage mafic igneous rocks. These strata contain a nearly unimodal Late Jurassic zircon population and are interpreted to be a fragment of a forearc basin that was emplaced onto the Brooks Range during arc-continent collision. Synorogenic deposits found at structurally lower levels contain decreasing amounts of ophiolite and arc debris, Jurassic zircons, and increasing amounts of continentally derived sedimentary detritus accompanied by broadly distributed late Paleozoic and Triassic (359–200 Ma), early Paleozoic (542–359 Ma), and Paleoproterozoic (2000–1750 Ma) zircon populations. The zircon populations display fission-track evidence of cooling during the Brookian event and evidence of an earlier episode of cooling in the late Paleozoic and Triassic. Surprisingly, there is little evidence for erosion of the continental basement of Arctic Alaska, its Paleozoic sedimentary cover, or its hinterland metamorphic rocks in early foreland basin strata at any structural and/or stratigraphic level in the western Brooks Range. Detritus from exhumation of these sources did not arrive in the foreland basin until the middle or late Albian in the central part of the Colville Basin.These observations indicate that two primary provenance areas provided

  14. 3D Architecture and evolution of the Po Plain-Northern Adriatic Foreland basin during Plio-Pleistocene time

    NASA Astrophysics Data System (ADS)

    Amadori, Chiara; Toscani, Giovanni; Ghielmi, Manlio; Maesano, Francesco Emanuele; D'Ambrogi, Chiara; Lombardi, Stefano; Milanesi, Riccardo; Panara, Yuri; Di Giulio, Andrea

    2017-04-01

    The Pliocene-Pleistocene tectonic and sedimentary evolution of the eastern Po Plain and northern Adriatic Foreland Basin (PPAF) (extended ca. 35,000 km2) was the consequence of severe Northern Apennine compressional activity and climate-driven eustatic changes. According with the 2D seismic interpretation, facies analysis and sequence stratigraphy approach by Ghielmi et al. (2013 and references therein), these tectono-eustatic phases generated six basin-scale unconformities referred as Base Pliocene (PL1), Intra-Zanclean (PL2), Intra-Piacenzian (PL3), Gelasian (PL4), Base Calabrian (PS1) and Late Calabrian (PS2). We present a basin-wide detailed 3D model of the PPAF region, derived from the interpretation of these unconformities in a dense network of seismic lines (ca. 6,000 km) correlated with more than 200 well stratigraphies (courtesy of ENI E&P). The initial 3D time-model has been time-to-depth converted using the 3D velocity model created with Vel-IO 3D, a tool for 3D depth conversions and then validated and integrated with depth domain dataset from bibliography and well log. Resultant isobath and isopach maps are produced to inspect step-by-step the basin paleogeographic evolution; it occurred through alternating stages of simple and fragmented foredeeps. Changes in the basin geometry through time, from the inner sector located in the Emilia-Romagna Apennines to the outermost region (Veneto and northern Adriatic Sea), were marked by repeated phases of outward migration of two large deep depocenters located in front of Emilia arcs on the west, and in front of Ferrara-Romagna thrusts on the east. During late Pliocene-early Pleistocene, the inner side of the Emilia-Romagna arcs evolved into an elongated deep thrust-top basin due to a strong foredeep fragmentation then, an overall tectono-stratigraphic analysis shows also a decreasing trend of tectonic intensity of the Northern Apennine since Pleistocene until present.

  15. Part I: Neoacadian to Alleghanian foreland basin development and provenance in the central appalachian orogen, pine mountain thrust sheet Part II: Structural configuration of a modified Mesozoic to Cenozoic forearc basin system, south-central Alaska

    NASA Astrophysics Data System (ADS)

    Robertson, Peter Benjamin

    Foreland and forearc basins are large sediment repositories that form in response to tectonic loading and lithospheric flexure during orogenesis along convergent plate boundaries. In addition to their numerous valuable natural resources, these systems preserve important geologic information regarding the timing and intensity of deformation, uplift and erosion history, and subsidence history along collisional margins, and, in ancient systems, may provide more macroscopic information regarding climate, plate motion, and eustatic sea level fluctuations. This thesis presents two studies focused in the Paleozoic Appalachian foreland basin system along the eastern United States and in the Mesozoic to Cenozoic Matanuska forearc basin system in south-central Alaska. Strata of the Appalachian foreland basin system preserve the dynamic history of orogenesis and sediment dispersal along the east Laurentian margin, recording multiple episodes of deformation and basin development during Paleozoic time. A well-exposed, >600 m thick measured stratigraphic section of the Pine Mountain thrust sheet at Pound Gap, Kentucky affords one of the most complete exposures of Upper Devonian through Middle Pennsylvanian strata in the basin. These strata provide a window into which the foreland basin's development during two major collisional events known as the Acadian-Neoacadian and the Alleghanian orogenies can be observed. Lithofacies analysis of four major sedimentary successions observed in hanging wall strata record the upward transition from (1) a submarine deltaic fan complex developed on a distal to proximal prodelta in Late Devonian to Middle Mississippian time, to (2) a Middle to Late Mississippian carbonate bank system developed on a slowly subsiding, distal foreland ramp, which was drowned by (3) Late Mississippian renewed clastic influx to a tidally influenced, coastal deltaic complex to fluvial delta plain system unconformably overlain by (4) a fluvial braided river complex

  16. Silurian stratigraphy of Central Iran - an update

    NASA Astrophysics Data System (ADS)

    Hairapetian, Vachik; Pour, Mansoureh Ghobadi; Popov, Leonid E.; Männik, Peep; Miller, C. Giles

    2017-06-01

    The Silurian biostratigraphy, lithostratigraphy, and facies of Central Iran including the Kashmar (Boghu Mountains), Tabas (Derenjal Mountains, Ozbak-Kuh), Anarak (Pol-e Khavand) and Kerman regions is reviewed and updated. The current state of knowledge of the Silurian in the Zagros Basin, Alborz, Kopet-Dagh and Talysh regions, as well as in a few areas scattered across the Sabzevar Zone, and the Sanandaj-Sirjan terranes is also reviewed. Silurian volcanism in various parts of Iran is briefly discussed. The end of the Ordovician coincided with a widespread regression across Iran synchronous with the Hirnantian glaciation, and only in the Zagros Basin is there a continuous Ordovician-Silurian transition represented by graptolitic black shales of the Sarchahan Formation. In the Central-East Iranian Platform marine sedimentation re-commenced in the early to mid Aeronian. By the Sheinwoodian, carbonate platform depositional environments were established along its north-eastern margin. In other parts of Iran (e.g., Kopet-Dagh and the Sabzevar Zone), siliciclastic sedimentation continued probably into the late Silurian. The Silurian conodont and brachiopod biostratigraphy of Central Iran is significantly updated facilitating a precise correlation with the Standard Global Chronostratigraphic Scale, as well as with key Silurian sections in other parts of Iran. The Silurian lithostratigraphy is considerably revised and two new lithostratigraphical units, namely the Boghu and Dahaneh-Kalut formations, are introduced.

  17. New Late Permian tectonic model for South Africa's Karoo Basin: foreland tectonics and climate change before the end-Permian crisis.

    PubMed

    Viglietti, Pia A; Rubidge, Bruce S; Smith, Roger M H

    2017-09-07

    Late Permian Karoo Basin tectonics in South Africa are reflected as two fining-upward megacycles in the Balfour and upper Teekloof formations. Foreland tectonics are used to explain the cyclic nature and distribution of sedimentation, caused by phases of loading and unloading in the southern source areas adjacent to the basin. New data supports this model, and identifies potential climatic effects on the tectonic regime. Diachronous second-order subaerial unconformities (SU) are identified at the base and top of the Balfour Formation. One third-order SU identified coincides with a faunal turnover which could be related to the Permo-Triassic mass extinction (PTME). The SU are traced, for the first time, to the western portion of the basin (upper Teekloof Formation). Their age determinations support the foreland basin model as they coincide with dated paroxysms. A condensed distal (northern) stratigraphic record is additional support for this tectonic regime because orogenic loading and unloading throughout the basin was not equally distributed, nor was it in-phase. This resulted in more frequent non-deposition with increased distance from the tectonically active source. Refining basin dynamics allows us to distinguish between tectonic and climatic effects and how they have influenced ancient ecosystems and sedimentation through time.

  18. Seismic transpressive basement faults and monocline development in a foreland basin (Eastern Guadalquivir, SE Spain)

    NASA Astrophysics Data System (ADS)

    Pedrera, A.; Ruiz-Constán, A.; Marín-Lechado, C.; Galindo-Zaldívar, J.; González, A.; Peláez, J. A.

    2013-12-01

    We examine the late Tortonian to present-day deformation of an active seismic sector of the eastern Iberian foreland basement of the Betic Cordillera, in southern Spain. Transpressive faults affecting Paleozoic basement offset up to Triassic rocks. Late Triassic clays and evaporites constitute a décollement level decoupling the basement rocks and a ~100 m thick cover of Jurassic carbonates. Monoclines trending NE-SW to ENE-WSW deform the Jurassic cover driven by the propagation of high-angle transpressive right-lateral basement faults. They favor the migration of clays and evaporites toward the propagated fault tip, i.e., the core of the anticline, resulting in fluid overpressure, fluid flow, and precipitation of fibrous gypsum parallel to a vertical σ3. The overall geometry of the studied monoclines, as well as the intense deformation within the clays and evaporites, reproduces three-layer discrete element models entailing a weak middle unit sandwiched between strong layers. Late Tortonian syn-folding sediments recorded the initial stages of the fault-propagation folding. Equivalent unexposed transpressive structures and associated monoclines reactivated under the present-day NW-SE convergence are recognized and analyzed in the Sabiote-Torreperogil region, using seismic reflection, gravity, and borehole data. A seismic series of more than 2100 low-magnitude earthquakes was recorded within a very limited area of the basement of this sector from October 2012 to May 2013. Seismic activity within a major NE-SW trending transpressive basement fault plane stimulated rupture along a subsidiary E-W (~N95°E) strike-slip relay fault. The biggest event (mbLg 3.9, MW 3.7) occurred at the junction between them in a transpressive relay sector.

  19. Regional diagenetic variations in Middle Pennsylvanian foreland basin sandstones of the southern Appalachians: Comparison to passive margin Cenozoic sandstones of the Gulf of Mexico

    SciTech Connect

    Milliken, K.L. . Dept. of Geological Science)

    1992-01-01

    Water/rock interactions recorded by authigenic phases in lithic-rich sandstones of the southern Appalachian basin, in the region of the Pine Mountain Overthrust (PMO), began with early post-depositional burial, extended through deeper burial and temperatures > 100 C during the Alleghenian orogeny, and continued through uplift and exposure at the modern weathering surface. Early-formed carbonate in the form of highly localized calcite concretions preserves IGVs greater than 30% and has widely ranging trace element concentrations. Later-formed calcite is characterized by relative low trace element concentrations in sandstones of low IGV. Precipitation of kaolinite cement and grain replacements partially overlapped formation of early carbonate and quartz cement. Dissolution and albitization of detrital feldspars are the primary types of grain alteration observed. Complete loss of the detrital feldspar assemblage is observed only around the eastern end of the PMO where a portion of the feldspar loss is recorded as quartz-replaced grains. Compaction due to ductile behavior of phyllosilicate-rich rock fragments and pressure solution of detrital quartz has reduced IGV to an average of around 11% below the PMO and 6% above the fault. In general, these foreland basin sandstones manifest authigenic phases and sequences of diagenetic events similar to those observed in the passive margin Gulf of Mexico sedimentary basin. The most striking diagenetic differences between the two basins are seen in terms of the comparative amounts of compaction (greater in the foreland basin) and grain alteration (less in the foreland basin) which most likely relate to primary differences in the texture and mineralogy of the sediments.

  20. Permian to Late Triassic evolution of the Longmen Shan Foreland Basin (Western Sichuan): Model results from both the lithospheric extension and flexure

    NASA Astrophysics Data System (ADS)

    He, Lijuan

    2014-10-01

    The lithosphere was extended during the Permian-Middle Triassic in the Yangtze Craton where the Sichuan Basin located, and then bent due to thrusting of the Longmen Shan orogen, leading to formation of the Longmen Shan Foreland Basin (Western Sichuan) during the Late Triassic Indosinian orogeny. The lateral variation of the lithospheric strength resulted by former differential extension would inevitably influence the subsequent evolution of the foreland basin. In order to investigate this, both extensional and flexural models were applied in modeling Permian-Late Triassic basin evolution. A 2D kinematic extensional model was initially developed along a profile crossing the Yangtze Craton to simulate the lithospheric thermal evolution during the Permian-Middle Triassic. Based on the thermal results, the thermal-rheological structure, as well as the effective elastic thickness of the lithosphere (Te), was then determined. Extension model show that the stretching factors decrease gradually from Songpan-Ganzi to the Sichuan Basin, leading to variable thermal-rheological structure and increased Te from west to east. Taking into account of the Te variation, a flexural model was finally constructed to investigate the evolution of the Longmen Shan Foreland Basin during the Late Triassic spanning the time period c. 227-206 Ma. Three episodes were divided according to the corresponding tectonostratigraphic units. By matching the stratigraphic observations, three phase advance distances eastward of the Longmen Shan along the Qingchuan-Maowen Fault turned out to be 18, 22, and 18 km. It implied a slow and similar thrust advance rate of 3.6 (c.227-222 Ma), 2.2 (c.222-212 Ma), and 3 mm/yr (c.212-206 Ma), respectively.

  1. Magnetostratigraphic Record of the Early Evolution of the Southwestern Tian Shan Foreland Basin (Ulugqat Area), Interactions with Pamir Indentation and India-Asia Collision

    NASA Astrophysics Data System (ADS)

    Yang, W.; Wang, S.

    2015-12-01

    The Tian Shan range is an inherited intracontinental structure reactivated by the far-field effects of India-Asia collision. A growing body of thermochronology and magnetostratigraphy datasets shows the range grew through several tectonic pulses since ~25 Ma, however the early Cenozoic history remains poorly constrained. Particularly enigmatic is the time-lag between the Eocene India-Asia collision and the Miocene onset of Tian Shan exhumation. This peculiar period is potentially recorded along the southwestern Tian Shan piedmont. There, recently dated late Eocene marine deposits of the proto-Paratethys epicontinental sea transition to continental foreland basin sediments of unknown age. We provide magnetostratigraphic dating of these continental sediments from the 1700-m-thick Mine section integrated with previously published detrital apatite fission track and U/Pb zircon ages. The most likely correlation to the geomagnetic polarity time scale indicates an age span from 20.8 to 13.3 Ma with a marked accumulation rate increase at 19-18 Ma. This implies the entire Oligocene period is missing between the last marine and first continental sediments, as suggested by previous southwestern Tian Shan results. This differs from the southwestern Tarim basin where Eocene marine deposits are continuously overlain by late Eocene-Oligocene continental sediments. This supports a simple evolution model of the western Tarim basin with Eocene-Oligocene foreland basin activation to the south related to northward thrusting of the Kunlun Shan, followed by early Miocene activation of northern foreland basin related to overthrusting of the south Tian Shan. Our data also support southward propagation of the Tian Shan piedmont from 20-18 Ma that may relate to motion on the Talas Fergana Fault. The coeval activation of a major right-lateral strike-slip system allowing indentation of the Pamir Salient into the Tarim basin, suggest far-field deformation from the India-Asia collision zone

  2. Neogene shortening and exhumation of the Zagros fold-thrust belt and foreland basin in the Kurdistan region of northern Iraq

    NASA Astrophysics Data System (ADS)

    Koshnaw, Renas I.; Horton, Brian K.; Stockli, Daniel F.; Barber, Douglas E.; Tamar-Agha, Mazin Y.; Kendall, Jerome J.

    2017-01-01

    The Zagros fold-thrust belt in the Kurdistan region of Iraq encroached southward toward a rapidly subsiding Neogene foreland basin and was later partitioned by out-of-sequence shortening focused along the Mountain Front Flexure (MFF), as defined by new low-temperature thermochronologic, stratigraphic, and provenance results. Apatite (U-Th)/He ages document rapid deformation advance from the Main Zagros Fault to southern frontal structures (Kirkuk, Shakal, and Qamar thrusts) at 10-8 Ma, followed by potential basement-involved out-of-sequence development of the MFF (Qaradagh anticline) by 5 Ma. Distinct shifts in detrital zircon U-Pb provenance signatures for Neogene foreland basin fill provide evidence for drainage reorganization during fold-thrust belt advance. U-Pb age spectra and petrologic data from the Injana (Upper Fars) Formation indicate derivation from a variety of Eurasian, Pan-African, ophiolitic and Mesozoic-Cenozoic volcanic terranes, whereas the Mukdadiya (Lower Bakhtiari) and Bai-Hasan (Upper Bakhtiari) Formations show nearly exclusive derivation from the Paleogene Walash-Naopurdan volcanic complex near the Iraq-Iran border. Such a sharp cutoff in Eurasian, Pan-African, and ophiolitic sources is likely associated with drainage reorganization and tectonic development of the geomorphic barrier formed by the MFF. As a result of Zagros crustal shortening, thickening and loading, the Neogene foreland basin developed and accommodated an abrupt influx of fluvial clastic sediment that contains growth stratal evidence of synkinematic accumulation. The apparent out-of-sequence pattern of upper crustal shortening in the hinterland to foreland zone of Iraqi Kurdistan suggests that structural inheritance and the effects of synorogenic erosion and accumulation are important factors influencing the irregular and episodic nature of orogenic growth in the Zagros.

  3. Trapping models for the Lower Silurian Medina Sandstone Group - A comparison of trapping styles and exploration methodology for both deep and shallow medina plays in the Appalachian basin

    SciTech Connect

    Zagorski, W.A. )

    1991-08-01

    The Lower Silurian Medina Sandstone Group has been a major oil and gas producer in the Appalachian basin since the late 1800s and remains a primary objective in parts of New York, Ohio, and Pennsylvania. Although classified as a stratigraphic trap, production from the Medina is obtained from a wide variety of trapping conditions ranging from pure stratigraphic to structural stratigraphic in the shallower producing areas of the Medina to deep basin (i.e., Elmworth field, western Canada) trapping in the deeper producing regions of strategies must be employed for optimum prospect development and maximum economic success ratios. Several producing areas of the Medina are presented to compare and contrast these various trapping mechanisms together with suggested exploration models applicable to each trap type.

  4. Tectonic and unroofing history of Neogene Manantiales foreland basin deposits, Cordillera Frontal (32°30'S), San Juan Province, Argentina

    NASA Astrophysics Data System (ADS)

    Pérez, Daniel J.

    2001-12-01

    The Miocene Manantiales foreland basin is located in Cordillera Frontal of San Juan, between 32°30' and 33°S. The unroofing study of the synorogenic Miocene deposits provides information about the structural evolution of Cordón de La Ramada fold-and-thrust belt. These Tertiary deposits are represented by the Chinches Formation and comprise seven members (Tc0-Tc6). They are the result of the uplift of Mesozoic sequences that crop out in La Ramada fold-and-thrust belt of the Cordillera Principal. Quaternary deposits unconformably overlying the Chinches Formation are composed of granitic and rhyolitic blocks, and represent the final uplift of the Cordón del Espinacito and a series of out-of-sequence thrusts. The unroofing studies also provide sufficient information to establish the out-of-sequence timing of the deformation at this latitude. Initial deposition of the Tertiary deposits can be dated at about 20 Ma, or early Miocene. Andesitic lavas dated in 9.2±0.3, 10.7±0.7, and 12.7±0.7 Ma unconformably overlie the structure of La Ramada fold-and-thrust belt. These facts constrain the uplift of the High Andes between 20 and 10 Ma at this latitude. The unconformity between Tertiary and Quaternary deposits suggests final uplift during Pliocene-Pleistocene times.

  5. Tectonic influence on deposition and erosion in a ramp setting: Upper Cretaceous Cardium Formation, Alberta foreland basin

    SciTech Connect

    Hart, B.S.; Plint, A.G. )

    1993-12-01

    This paper presents the results of a combined outcrop and subsurface investigation of the Upper Cretaceous Cardium Formation in northwestern Alberta and adjacent British Columbia, Canada. More than 100 measured core and outcrop sections combined with more than 1,100 well logs were used to examine stratigraphic relationships in an area of over 45,000 km[sup 2]. The Cardium consists of stacked regressive-transgressive cycles deposited during shoreline progradation along the western margin of a foreland basin occupied by the Western Interior seaway. In general, these cycles consist of shoaling upward successions (highstand systems tracts composed of shoreface sandstones and conglomerates and heterolithic offshore deposits) capped by transgressive erosion surfaces. Linear incised lowstand coarse-grained shoreface deposits are present at some stratigraphic levels. A single, thick (locally more than 20 m thick in the study area) nonmarine wedge that overlies shoreface sandstones is interpreted to represent deposition during rising sea level rather than accumulation behind a prograding strandline. Preservation of the incised lowstand shoreface deposits is associated with topographic breaks. In places, trends of isopachs, facies transitions, erosional bevels on transgressive erosion surfaces, synsedimentary faults, and modern production trends can be directly superimposed and closely correspond to basement structural trends. This suggests that basement structures were being remobilized during Cardium deposition, possibly in response to thrusting in the orogenic belt.

  6. Transition from marine deep slope deposits to evaporitic facies of an isolated foreland basin: case study of the Sivas Basin (Turkey)

    NASA Astrophysics Data System (ADS)

    Pichat, Alexandre; Hoareau, Guilhem; Legeay, Etienne; Lopez, Michel; Bonnel, Cédric; Callot, Jean-Paul; Ringenbach, Jean-Claude

    2017-04-01

    The Sivas Basin, located in the central part of the Anatolian Plateau in Turkey, formed after the closure of the northern Neotethys from Paleocene to Pliocene times. It developed over an ophiolitic basement obducted from the north during the Late Cretaceous. During Paleocene to Eocene times, the onset of the Tauride compression led to the development of a foreland basin affected by north-directed thrusts. The associate general deepening of the basin favored the accumulation of a thick marine turbiditic succession in the foredeep area, followed by a fast shallowing of the basin and thick evaporitic sequence deposition during the late Eocene. We present here the detailed sedimentological architecture of this flysch to evaporite transition. In the northern part of the basin, volcanoclastic turbidites gradually evolved into basinal to prodelta deposits regularly fed by siliciclastic material during flood events. Locally (to the NE), thick-channelized sandstones are attributed to the progradation of delta front distributary channels. The basin became increasingly sediment-starved and evolved toward azoic carbonates and shaly facies, interlayered with organic-rich shales before the first evaporitic deposits. In the southern part of the basin, in the central foredeep, the basinal turbidites become increasingly gypsum-rich and record a massive mega-slump enclosing olistoliths of gypsum and of ophiolitic rocks. Such reworked evaporites were fed by the gravitational collapsing of shallow water evaporites that had previously precipitated in silled piggy-back basins along the southern fold-and-thrust-belt of the Sivas Basin. Tectonic activity that led to the dismantlement of such evaporites probably also contributed to the closure of the basin from the marine domain. From the north to the south, subsequent deposits consist in about 70 meters of secondary massive to fine-grained gypsiferous beds interpreted as recording high to low density gypsum turbidites. Such facies were

  7. Migration of the Acadian Orogen and foreland basin across the Northern Appalachians of Maine and adjacent areas

    USGS Publications Warehouse

    Bradley, Dwight Culver; Tucker, Robert D.; Lux, Daniel R.; Harris, Anita G.; McGregor, D. Colin

    2000-01-01

    The timing of Acadian orogenesis in Maine is reassessed, on the basis of a new Silurian-Devonian time scale, new U/Pb and 40Ar/39Ar ages of Acadian plutons, new conodont and palynomorph ages of strata that constrain the age of deformation, and published information. This analysis shows that the Acadian deformation front migrated some 240 km (present distance) from southeast to northwest during a span of about 40 million years from Late Silurian to Middle Devonian time.

  8. Along-strike variability of back-arc basin collapse and the initiation of sedimentation in the Magallanes foreland basin, southernmost Andes (53-54.5°S)

    NASA Astrophysics Data System (ADS)

    McAtamney, Janelle; Klepeis, Keith; Mehrtens, Charlotte; Thomson, Stuart; Betka, Paul; Rojas, Lisandro; Snyder, Shane

    2011-10-01

    The Patagonian Andes record the Cretaceous demise of the quasi-oceanic Rocas Verdes back-arc basin and formation of the Magallanes foreland basin. For >500 km along the strike of the mountains, this tectonic transition is marked by a sandstone-mudstone package that records the beginning of turbiditic sand deposition and fan growth. Sandstone modal analyses and U-Pb detrital zircon spectra show changes in rock composition and provenance across the transition on a basin-wide scale, indicating it has tectonic significance and is related to orogenic uplift and the progressive evolution of the Andean fold-thrust belt. Spatial variations in transition zone characteristics indicate the foreland basin's central and southern sectors were fed by different sources and probably record separate fans. At Bahía Brookes, on Tierra del Fuego, foreland basin sedimentation began at least after 88-89 Ma, and possibly after ˜85 Ma, several million years after it did ˜700 km away at the northern end of the basin. This event coincided with increased arc volcanism and the partial obduction of the basaltic Rocas Verdes basin floor onto continental crust. By 81-80 Ma, conglomerate deposition and increased compositional and provenance complexity, including the abundance of metamorphic lithic fragments, indicate that the obducted basaltic floor first became emergent and was eroding. The results suggest that the beginning of turbidite sedimentation in the Magallanes foreland basin and the progressive incorporation and exhumation of deeply buried rocks in the Andean fold-thrust belt, occurred later in southern Patagonia than in the north by a few million years.

  9. Silurian extension in the Upper Connecticut Valley, United States and the origin of middle Paleozoic basins in the Québec embayment

    USGS Publications Warehouse

    Rankin, D.W.; Coish, R.A.; Tucker, R.D.; Peng, Z.X.; Wilson, S.A.; Rouff, A.A.

    2007-01-01

    Pre-Silurian strata of the Bronson Hill arch (BHA) in the Upper Connecticut Valley, NH-VT are host to the latest Ludlow Comerford Intrusive Suite consisting, east to west, of a mafic dike swarm with sheeted dikes, and an intrusive complex. The rocks are mostly mafic but with compositions ranging from gabbro to leucocratic tonalite. The suite is truncated on the west by the Monroe fault, a late Acadian thrust that carries rocks of the BHA westward over Silurian-Devonian strata of the Connecticut Valley-Gaspe?? trough (CVGT). Dikes intrude folded strata with a pre-intrusion metamorphic fabric (Taconian?) but they experienced Acadian deformation. Twenty fractions of zircon and baddeleyite from three sample sites of gabbrodiorite spanning nearly 40 km yield a weighted 207Pb/206Pb age of 419 ?? 1 Ma. Greenschist-facies dikes, sampled over a strike distance of 35 km, were tholeiitic basalts formed by partial melting of asthenospheric mantle, with little or no influence from mantle or crustal lithosphere. The dike chemistry is similar to mid-ocean ridge, within-plate, and back-arc basin basalts. Parent magmas originated in the asthenosphere and were erupted through severely thinned lithosphere adjacent to the CVGT. Extensive middle Paleozoic basins in the internides of the Appalachian orogen are restricted to the Que??bec embayment of the Laurentian rifted margin, and include the CVGT and the Central Maine trough (CMT), separated from the BHA by a Silurian tectonic hinge. The NE-trending Comerford intrusions parallel the CVGT, CMT, and the tectonic hinge, and indicate NW-SE extension. During post-Taconian convergence, the irregular margins of composite Laurentia and Avalon permitted continued collision in Newfoundland (St. Lawrence promontory) and coeval extension in the Que??bec embayment. Extension may be related to hinge retreat of the northwest directed Brunswick subduction complex and rise of the asthenosphere following slab break-off. An alternative hypothesis is

  10. Tectonics vs. Climate efficiency in triggering detrital input in sedimentary basins: the Po Plain-Venetian-Adriatic Foreland Basin (Northern Italy)

    NASA Astrophysics Data System (ADS)

    Amadori, Chiara; Di Giulio, Andrea; Toscani, Giovanni; Lombardi, Stefano; Milanesi, Riccardo; Panara, Yuri; Fantoni, Roberto

    2017-04-01

    The relative efficiency of tectonics respect to climate in triggering erosion of mountain belts is a classical but still open debate in geosciences. The fact that data both from tectonically active and inactive mountain regions in different latitudes, record a worldwide increase of sediment input to sedimentary basins during the last million years concomitantly with the cooling of global climate and its evolution toward the modern high amplitude oscillating conditions pushed some authors to conclude that Pliocene-Pleistocene climate has been more efficient than tectonics in triggering mountain erosion. Po Plain-Venetian-Adriatic Foreland System, made by the relatively independent Po Plain-Northern Adriatic Basin and Venetian-Friulian Basin, provides an ideal case of study to test this hypothesis and possibly quantify the difference between the efficiency of the two. In fact it is a relatively closed basin (i.e. without significant sediment escape) with a fairly continuous sedimentation (i.e. with a quite continuous sedimentary record) completely surrounded by collisional belts (Alps, Northern Apennines and Dinarides) that experienced only very weak tectonic activity since Calabrian time, i.e. when climate cooling and cyclicity increased the most. We present a quantitative reconstruction of the sediment flow delivered from the surrounding mountain belts to the different part of the basin during Pliocene-Pleistocene time. This flow was obtained through the 3D reconstruction of the Venetian-Friulian and Po Plain Northern Adriatic Basins architecture, performed by means of the seismic-based interpretation and time-to-depth conversion of six chronologically constrained surfaces (seismic and well log data from courtesy of ENI); moreover, a 3D decompaction of the sediment volume bounded by each couple of surfaces has been included in the workflow, in order to avoid compaction-related bias. The obtained results show in both Basins a rapid four-folds increase of the

  11. Cenozoic sedimentation and exhumation of the foreland basin system preserved in the Precordillera thrust belt (31-32°S), southern central Andes, Argentina

    NASA Astrophysics Data System (ADS)

    Levina, Mariya; Horton, Brian K.; Fuentes, Facundo; Stockli, Daniel F.

    2014-09-01

    Andean retroarc compression associated with subduction and shallowing of the oceanic Nazca plate resulted in thin-skinned thrusting that partitioned and uplifted Cenozoic foreland basin fill in the Precordillera of west-central Argentina. Evolution of the central segment of the Precordillera fold-thrust belt is informed by new analyses of clastic nonmarine deposits now preserved in three intermontane regions between major east directed thrust faults. We focus on uppermost Oligocene-Miocene basin fill in the axial to frontal Precordillera at 31-32°S along the Río San Juan (Albarracín and Pachaco sections) and the flank of one of the leading thrust structures (Talacasto section). The three successions record hinterland construction of the Frontal Cordillera, regional arc volcanism, and initial exhumation of Precordillera thrust sheets. Provenance changes recorded by detrital zircon U-Pb age populations suggest that initial shortening in the Frontal Cordillera coincided with an early Miocene shift from eolian to fluvial accumulation in the adjacent foreland basin. Upward coarsening of fluvial deposits and increased proportions of Paleozoic clasts reflect cratonward (eastward) advance of deformation into the Precordillera and resultant structural fragmentation of the foreland basin into isolated intermontane segments. Apatite (U-Th)/He thermochronometry of basin fill constrains to 12-9 Ma the most probable age of uplift-induced exhumation and cooling of Precordillera thrust sheets. This apparent pulse of exhumation is evident in each succession, suggestive of rapid, large-scale exhumation by synchronous thrusting above a single décollement linking major structures of the Precordillera.

  12. The age of the Keystone thrust: laser-fusion 40Ar/39Ar dating of foreland basin deposits, southern Spring Mountains, Nevada

    USGS Publications Warehouse

    Fleck, R.J.; Carr, M.D.

    1990-01-01

    Nonmarine sedimentary and volcaniclastic foreland-basin deposits in the Spring Mountains are cut by the Contact and Keystone thrusts. These synorogenic deposits, informally designated the Lavinia Wash sequence by Carr (1980), previously were assigned a Late Jurassic to Early Cretaceous(?) age. New 40Ar.39Ar laser-fusion and incremental-heating studies of a tuff bed in the Lavinia Wash sequence support a best estimate age of 99.0 ?? 0.4 Ma, indicating that the Lavinia Wash sequence is actually late Early Cretaceous in age and establishing a maximum age for final emplacement of the Contact and Keystone thrust plates consistent with the remainder of the Mesozoic foreland thrust belt. -from Authors

  13. Synergetic study of Silurian-Niagaran pinnacle reef belt around the Michigan Basin for exploration and production of oil and gas. Volumes 1 and 2

    SciTech Connect

    Aminian, K.

    1982-01-01

    The Silurian-Niagaran pinnacle reef occur on a belt which encircles the entire Michigan Basin including areas presently covered by the Great Lakes Huron and Michigan. Two different structural settings existed in the Michigan Basin during the Silurian Period. This resulted in formation of pinnacle reefs with somewhat different characteristics in the northern and southern parts of the basin. The pinnacles of the northern trend occur at depths of 4000 to 7000 ft, are up to 700 ft thick, and average about 100 acres in area. The southern pinnacles occur at depths of 2000 to 3000 ft, are shorter, about 300 ft, and attain larger areas. The majority of the hydrocarbon reserves of the northern trend are concentrated in pinnacles which occur on a band 3 to 4 miles wide inside the middle of the trend. There exists a regional partitioning of oil and gas in the northern pinnacle reefs which can be best explained by Gussaw Theory of migration and differential entrapment. A probabilistic model for exploration in play was found applicable in mature areas of the northern trend. The results were extended to other parts of the northern trend based on similar reef density and size distribution. In the southern trend where the reef density and size distribution is entirely different, the model was tested against limited data and results of future exploration were predicted. The effectiveness of exploration on the reef belt, based on seismic surveys, is 8 to 10 times better than random drilling. The reserves of the reef belt is in excess of 7 bbl of oil and 15 trillion ft/sup 3/ of natural gas originally in place. The oil primary and secondary recovery factors are 20 and 30%, respectively.

  14. Stratigraphic responses to a major tectonic event in a foreland basin: the Ecuadorian Oriente Basin from Eocene to Oligocene times

    NASA Astrophysics Data System (ADS)

    Christophoul, Frédéric; Baby, Patrice; Dávila, Celso

    2002-02-01

    The Eocene to Oligocene sediments of the Ecuadorian Oriente Basin record two kinds of second-order stratigraphic response to the tectonic evolution. Lower Eocene shows evidences of local scale syntectonic deposits. This tectonic activity can be related to right lateral convergent movements inverting pre-cretaceous extensional structures. Upper Eocene and Oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition. This response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations. These data have allowed us to propose a new geodynamic model for the Paleogene evolution of the Oriente Basin.

  15. Geomorphic characterization of hilly relief in the north alpine foreland basin: The Hausruck- and Kobernaußerwald region

    NASA Astrophysics Data System (ADS)

    Baumann, Sebastian; Robl, Jörg; Keil, Melanie; Salcher, Bernhard

    2014-05-01

    The area of the Hausruck and Kobernaußerwald represents the highest relief of the Molasse Basin in Upper Austria. The region is characterized by a dissected landscape with elevation differences of 400 m and peaks reaching up to 800 m. The latest marine influence of this realm is dated to 11 Ma before present and constrains the onset of the inversion of the peripheral alpine foreland basin. Since that time the relief evolution is controlled by surface uplift and fluvial erosion. The Hausruck-Kobernaußerwald region forms a local watershed and is drained by three drainage systems that are tributaries of the Inn River, the Traun River and the Trattnach River. The Danube River represents the base level for all these streams. In contrary to the nearby Eastern Alps the study area shows no evidence for local deformation or glacial overprint. Therefore, the Hausruck- Kobernaußerwald region represents a perfect testing ground to explore the evolution of relief in a setting of regional uplift and relative base level lowering. This is done by characterizing the fluvial and hillslope system and exploring the effect of contrasting lithology and different base levels. We further give constraints on the geomorphological state of equilibrium and provide a discussion about the spatial position of the highest relief within the Molasse Basin in Upper Austria. Therefore, we have performed a series of morphometric analyses on a high resolution LiDAR digital elevation model. This includes longitudinal channel profiles, the best fit concavity index, the steepness and the normalized steepness index, the slope-area relationship, the slope elevation distribution and hypsometric curves of all individual catchments. All longitudinal channel profiles are graded and show a concave form without any natural knickpoints with best fit concavity indices in the range of 0.35 and 0.55. All observed knick points in the channel profiles could be traced back to an anthropogenic impact like bridges or

  16. Determining orogenic exhumation, steady state, and frontal accretion, using the sediment record: an example from the Himalayan foreland basin

    NASA Astrophysics Data System (ADS)

    Najman, Y.; Pringle, M.; Bickle, M.; Garzanti, E.; Ando, S.; Burbank, D.; Brozovic, N.

    2003-04-01

    The sediment archive can provide an invaluable record of a mountain belt's evolution, where information from rocks in the mountain belt itself has been lost by overprinting due to later metamorphism or removed by tectonism or erosion. In this study of the Himalayan foreland basin sediments, we demonstrate the use of Ar-Ar dating of detrital white micas to provide information on the cooling, exhumation and tectonic history of the source region. Calculation of lag times, defined as the difference between the detrital mica Ar-Ar age and its host sediment depositional age, allows: 1) Determination of cooling and exhumation rates in the orogen. Short lag times indicate periods of rapid exhumation. Exhumation rates can be quantified using a simple thermal model that allows for advection modification of the geotherm. 2) An assessment of the orogen's maturity in terms of its progress towards steady-state. Exhumational steady-state is defined as "when ages obtained from a specific thermochronometer in a specified thermal domain are time-invariant" (Willett &Brandon, Geology, 2002). Exhumational steady-state can be identified using the sediment record, represented by periods when lag times remain constant through time. Additionally, temporal variation in detrital mica Ar-Ar ages can be used to track provenance changes in the source region, the result of tectonic exhumation. This technique, combined with additional provenance tools of Sm-Nd whole rock isotopic analyses, petrographic and heavy mineral data, allows us to document a period of frontal accretion in the Himalaya, which can be interpreted in terms of critical wedge theory.

  17. Paleogeography And Diachronous Infill Of An Ancient Deep-Marine Foreland Basin, Upper Cretaceous Cerro Toro Axial Channel, Magallanes Basin, Chile

    NASA Astrophysics Data System (ADS)

    Bernhardt, A.; Jobe, Z. R.; Grove, M.; Lowe, D. R.

    2011-12-01

    The details of how narrow, orogen-parallel ocean basins are filled with sediment by large axial submarine channels is important to understand because these depositional systems commonly form in through-like basins in various tectonic settings. The Magallanes foreland basin is an excellent location to study an orogen-parallel deep-marine system. Conglomerate lenses of the Upper Cretaceous Cerro Toro Formation have been previously interpreted to represent the fill of a single submarine channel (4-8 km wide, > 100 km long) that funneled coarse detritus southward along the basin axis. This interpretation was based on lithologic correlations. New U/Pb dating of zircons from volcanic ashes and sandstones, coupled with strontium isotope stratigraphy, refine the controls on depositional ages and provenance. Results demonstrate that north-south oriented conglomerate lenses are contemporaneous within error limits (~ 84-82 Ma) supporting that they represent parts of an axial channel belt. Channel deposits 20 km west of the axial location are 87-82 Ma in age. These channels are partly contemporaneous with the ones within the axial channel belt, making it likely that they represent feeders to the axial channel system. The northern Cerro Toro Formation spans an Turonian to Campanian interval (~ 90-82 Ma) whereas the formation top, 70 km to the south, is as young as ~ 76 Ma. Kolmogorov-Smirnoff statistical analysis on detrital zircon age distributions shows that the northern uppermost Cerro Toro Formation yields a statistically different age distribution than other samples from the same formation but shows no difference relative to the overlying, much finer-grained Tres Pasos Formation. These results suggest the partly coeval deposition of both formations representing the gradual transition from an out-of-grade to a graded margin system. Integration of previously acquired geochronologic and stratigraphic data with new data show a pronounced southward younging pattern in all four

  18. Large-scale avulsion of the late Quaternary Sutlej river in the NW Indo-Gangetic foreland basin

    NASA Astrophysics Data System (ADS)

    Singh, Ajit; Gupta, Sanjeev; Sinha, Rajiv; Carter, Andrew; Thomsen, Kristina J.; Mark, Darren F.; Buylaert, Jan-Pieter; Mason, Philippa J.; Murray, Andrew S.; Jain, Mayank; Paul, Debajyoti

    2015-04-01

    River avulsions are important processes in the spatial evolution of river systems in tectonically active sedimentary basins as they govern large-scale patterns of sediment routing. However, the pattern and timing of avulsions in large river systems are poorly documented and not well understood. Here we document late Quaternary paleo-river channel changes in the Indo-Gangetic basin of northwest India. Using a combination of satellite remote sensing and detailed sediment coring, we analyse the large-scale planform geometry, and detailed sedimentary and stratigraphic nature of a major fluvial sedimentary deposit in the shallow subsurface. This sediment body records aggradation of multiple fluvial channel fills. Satellite remote sensing analysis indicates the trace of the buried channel complex and demonstrates that it exists in region of the Himalayan foreland where no major rivers are currently present. Thus it records the former drainage pathway of a major river, which has since been diverted. We use optically stimulated luminescence dating techniques to develop an age model for the stratigraphic succession and hence constrain the timing of river channel existence and diversion. Provenance analysis based on U-Pb dating of detrital zircons and detrital mica Ar-Ar ages indicate sediment sources in the Higher Himalayan Crystalline and Lesser Himalayan Crystalline Series indicating that this paleo-river channel system formed a major perennial river derived from the main body of the Himalaya. Specifically we are able to fingerprint bedrock sources in the catchment of the present-day Sutlej river indicating that the paleo-fluvial system represents the former course of the Sutlej river prior to a major nodal avulsion to its present day course. Our results indicate that on geologically relatively short time-scales, we observe dramatic along strike shifts in the location of major Himalayan rivers. Our sediment records when combined with high-resolution dating and

  19. Discriminating Sediment Supply Versus Accommodation Controls on Late Cretaceous Foreland Basin Stratigraphic Architecture in the Book Cliffs, Central Utah Using Double Dating

    NASA Astrophysics Data System (ADS)

    Bartschi, N.; Saylor, J. E.; Lapen, T. J.; Copeland, P.; Blum, M. D.

    2015-12-01

    Middle to late Campanian strata of the Book Cliffs, Utah record the Late Cretaceous deposition of three clastic wedges in the North American Cordilleran foreland basin east of the Sevier thrust belt. Variations in wedge geometries provide an opportunity to evaluate the effects of sediment supply versus accommodation on foreland basin stratal architecture. There is an increase in eastward progradation rate between the Lower and Upper Castlegate Sandstone. However, the progradation rate decreases in the overlying Bluecastle and Price River formations, as well as the laterally equivalent Farrer and Tuscher formations. Rapid progradation during Upper Castlegate deposition may be caused by increased sediment supply from either rapid exhumation of the Sevier thrust belt or changes in the sediment source. Alternatively, reduced accommodation within the proximal foreland basin from uplifts associated with Laramide deformation, or a transition from flexural to dynamic subsidence, could produce the same observed rapid wedge progradation. We identify changes in sediment provenance and source-area exhumation rate using detrital zircon geochronology. Initial detrital zircon U-Pb data reveals a significant up-section and spatial shift in provenance between all wedge boundaries. Quantitative comparisons between new and previously published detrital zircon U-Pb provenance data indicates an overall up-section decrease in thrust-belt-sourced Mesozoic eolianite and North American passive-margin source areas coupled with an increase in southern magmatic arc and Mogollon Highland source. We observe an east-west diachroneity in the arrival of the southern-sourced sediment, but little to no variation from samples along a north-south transect. Initial results suggest the shift in sediment source is not consistent with an increased exhumation rate of the source area, although further work using thermochronology is required to better understand the exhumation rate.

  20. The radioisotopically constrained Viséan onset of turbidites in the Moravian-Silesian part of the Rhenohercynian foreland basin (Central European Variscides)

    NASA Astrophysics Data System (ADS)

    Jirásek, Jakub; Otava, Jiří; Matýsek, Dalibor; Sivek, Martin; Schmitz, Mark D.

    2017-08-01

    The Březina Formation represents the initiation of siliciclastic flysch turbidite sedimentation at the eastern margin of Bohemian Massif or within the Rhenohercynian foreland basin. Its deposition started after drowning of the Devonian carbonate platform during Viséan (Mississippian) times, resulting in a significant interval of black siliceous shale and variegated fossiliferous shale deposition in a starved basin. Near the top of the Březina Formation an acidic volcanoclastic layer (tuff) of rhyolitic composition has been dated with high precision U-Pb zircon chemical abrasion isotope dilution method at 337.73 ± 0.16 Ma. This new radiometric age correlates with the previously inferred stratigraphic age of the locality and the current calibration of the Early Carboniferous geologic time scale. Shales of the Březina Formation pass gradually upwards into the siliciclastics of the Rozstání Formation of the Drahany culm facies. Thus our new age offers one of the few available radioisotopic constraints on the time of onset of siliciclastic flysch turbidites in the Rhenohercynian foreland basin of the European Variscides.

  1. Stratigraphy and structure of the Sevier thrust belt and proximal foreland-basin system in central Utah: A transect from the Sevier Desert to the Wasatch Plateau

    USGS Publications Warehouse

    Lawton, T.F.; Sprinkel, D.A.; Decelles, P.G.; Mitra, G.; Sussman, A.J.; Weiss, M.P.

    1997-01-01

    The Sevier orogenic belt in central Utah comprises four north-northwest trending thrust plates and two structural culminations that record crustal shortening and uplift in late Mesozoic and early Tertiary time. Synorogenic clastic rocks, mostly conglomerate and sandstone, exposed within the thrust belt were deposited in wedge-top and foredeep depozones within the proximal part of the foreland-basin system. The geologic relations preserved between thrust structures and synorogenic deposits demonstrate a foreland-breaking sequence of thrust deformation that was modified by minor out-of-sequence thrust displacement. Structural culminations in the interior part of the thrust belt deformed and uplifted some of the thrust sheets following their emplacement. Strata in the foreland basin indicate that the thrust sheets of central Utah were emplaced between latest Jurassic and Eocene time. The oldest strata of the foredeep depozone (Cedar Mountain Formation) are Neocomian and were derived from the hanging wall of the Canyon Range thrust. The foredeep depozone subsided most rapidly during Albian through Santonian or early Campanian time and accumulated about 2.5 km of conglomeratic strata (Indianola Group). The overlying North Horn Formation accumulated in a wedge-top basin from the Campanian to the Eocene and records propagation of the Gunnison thrust beneath the former foredeep. The Canyon Range Conglomerate of the Canyon Mountains, equivalent to the Indianola Group and the North Horn Formation, was deposited exclusively in a wedge-top setting on the Canyon Range and Pavant thrust sheets. This field trip, a three day, west-to-east traverse of the Sevier orogenic belt in central Utah, visits localities where timing of thrust structures is demonstrated by geometry of cross-cutting relations, growth strata associated with faults and folds, or deformation of foredeep deposits. Stops in the Canyon Mountains emphasize geometry of late structural culminations and relationships of

  2. In search of a Silurian total petroleum system in the Appalachian basin of New York, Ohio, Pennsylvania, and West Virginia: Chapter G.11 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

    USGS Publications Warehouse

    Ryder, Robert T.; Swezey, Christopher S.; Trippi, Michael H.; Lentz, Erika E.; Avary, K. Lee; Harper, John A.; Kappel, William M.; Rea, Ronald G.; Ruppert, Leslie F.; Ryder, Robert T.

    2014-01-01

    Although the TOC analyses in this study indicate that good to very good source rocks are present in the Salina Group and Wills Creek Formation of southwestern Pennsylvania and northern West Virginia, data are insufficient to propose a new Silurian total petroleum system in the Appalachian basin. However, the analytical results of this investigation are encouraging enough to undertake more systematic studies of the source rock potential of the Salina Group, Wills Creek Formation, and perhaps the Tonoloway Formation (Limestone) and McKenzie Limestone (or Member).

  3. Geochronology, Stratigraphy, and Provenance of the Early Fill of the Magallanes-Austral Basin, Southern Patagonia: Diachronous Initiation of a Retroarc Foreland Basin

    NASA Astrophysics Data System (ADS)

    Malkowski, M. A.; Sharman, G.; Graham, S. A.

    2014-12-01

    coarse detritus into the basin may reflect orogen-parallel variations in pre-existing structures and crustal composition from the earlier tectonic history of this region. These results highlight the influence of tectonic inheritance on patterns of foreland basin initiation in Cordilleran-style margins.

  4. Late quaternary deltaic and carbonate sedimentation in the Gulf of Papua foreland basin: Response to sea-level change

    USGS Publications Warehouse

    Harris, P.T.; Pattiaratchi, C.B.; Keene, J.B.; Dalrymple, R.W.; Gardner, J.V.; Baker, E.K.; Cole, A.R.; Mitchell, D.; Gibbs, P.; Schroeder, W.W.

    1996-01-01

    The rivers that drain the wet, mountainous island of New-Guinea discharge about 1.5 billion tonnes/yr of sediments into the adjacent seas, including the foreland basin between New Guinea and Australia. Despite this huge sediment input, there appears to have been only limited deposition in the Gulf of Papua during the (Holocene) postglacial rise in sea level. Seismic and core data indicate that the transgressive systems tract in the Gulf of Papua is thin and patchy. It is confined to regions within and north of an incised, east-west-trending shelf-valley system. Of the possible explanations for the absence of a significant transgressive systems tract, inland storage and along- and off-shelf transport of the sediment are of greatest significance. Reef growth up to the latitude of the east-west-trending incised-valley system in the southern Gulf of Papua is considered to have been facilitated by a northward-flowing coastal boundary current, the Coral Sea Coastal Current. This current now sweeps turbid, brackish waters and terrigenous sediments discharged by the rivers northwards away from the reefs. An observed northward offset in transgressive sediments in relation to the axis of the shelf valleys suggests that such a northward-flowing shelf current operated during the late Pleistocene and early Holocene. The northern limit of the Great Barrier Reef could thus be controlled by the balance between fluvial sediment supply and northward advection of suspended sediment by the Coral Sea Coastal Current. This current may also be important in maintaining a supply of clear water to the eastern Gulf of Papua, thus enabling photosynthesis and the flourishing of calcareous-algae (Halimeda) bioherms or biostromes at depths of up to 100 m over much of the middle and outer shelf, directly offshore of the modern Fly Delta. These carbonate sediments represent the exposed maximum flooding surface and condensed section. Modern highstand delta deposits have begun to prograde over this

  5. Recycling of quartz-poor/lithic-rich foreland-basin sediments in arid climate (Euphrates-Tigris-Karun river system)

    NASA Astrophysics Data System (ADS)

    Garzanti, Eduardo; Juboury, Ali Ismail Al; Zoleikhaei, Yousef; Vermeesch, Pieter; Hamzah Abdulhussein Jotheri, Jaafar; Akkoca, Dicle Bal; Allen, Mark; Andò, Sergio; Limonta, Mara; Padoan, Marta; Resentini, Alberto; Vezzoli, Giovanni

    2016-04-01

    Arabia all along the western side of the foreland basin, and are traced along the Gulf shores as far as the northeastern edge of the Rub' al-Khali sand sea ca. 4000 km from the Euphrates headwaters.

  6. Wide Angle Seismic Imaging of (serpentinite ?) Fault Zones that Pass Through the Moho in a - Foreland Basin Setting

    NASA Astrophysics Data System (ADS)

    Stern, T. A.; Henrys, S. A.; Okaya, D. A.; Dimech, J.; Sato, H.; Iwasaki, T.

    2015-12-01

    We report strong, wide-angle, seismic reflections from the mantle beneath the Taranaki Fault zone, southwest North Island, New Zealand. We attribute these reflections to a serpentinised fault zone that accommodated large amounts (~100km) of shortening during the Miocene. Other manifestations of the collision zone are a fold and thrust belt in the overriding Australian plate, a 3-4 km deep foreland basin and fragments of serpentine outcropping at the surface. The 2011 SAHKE experiment carried out multi-component, active-source seismic surveys along a length of about 300 km. The middle 100 km of the line is on land. Twelve large explosions (500 kg weight) were detonated onshore into an array of ~ 900 vertical component and 300 horizontal component seismographs in the on land section. Deep reflections are evident on both the land and marine seismic data. At 30 s two way travel time (twtt) are ~ 100 km deep reflections that have been interpreted to be due to arise from the base of the subducting Pacific plate*. But at 20 s twtt there are back-dipping reflections that when migrated are located in the mantle wedge of the overriding Australian plate. These reflections are in the depth range of 40-70 km and dip ~45 degrees to the southeast. Coincident S-S reflections are also seen on the horizontal geophones of the land array coming in at ~ 34 s twtt. This timing implies a Vp/Vs ratio = 34/20= 1.7 for the time averaged reflection path. Zoeprittz equation solutions show that if both P-P and S-S arrivals are generated from a common reflector a negative impedance contrast is required. We suggest serpentinite is the most likely cause of the reflectivity. Marine reflection data also show low-frequency reflections around the Moho depths that we also associate with both serpentinite, and recently documented slow-slip events on the subducted plate interface. * Stern T.A. et al (2015). A seismic reflection image for the base of a tectonic plate, Nature, 518, pp. 85-88, doi10

  7. Cobleskill and Akron members of the Rondout formation: late Silurian carbonate shelf sedimentation in the Appalachian Basin, New York

    SciTech Connect

    Belak, R.

    1980-12-01

    The outcrop of the upper Silurian Cobleskill and Akron members of the Rondout formation of New York State extends from Buffalo to E. Schoharie County and is continuous except where the units have been removed by pre-onondaga erosion. Strata included in the Cobleskill, Akron, and Chrysler members of the Rondout formation, underlying Williamsville member of the Bertie formation, and underlying Brayman Shale include several distinct Carbonate facies which have been identified by field characteristics, thin section petrography, insoluble residue analysis, and x-ray diffraction. Subfacies of the Cobleskill include subtidal biomicrites with stromatoporoid biostromes and intertidal fossiliferous micrites, whereas the Akron contains dolomitized analogs of these limestones. The overlying Chrysler is composed of supratidal, laminated, thinly bedded, finely crystalline dolostone. Careful lateral tracing of lithofacies, analysis of vertical lithofacies sequences, and study of key beds within the Cobleskill and Akron have resulted in recognition of the lateral equivalence of these 2 members. 32 references.

  8. Fluid-assisted particulate flow of turbidites at very low temperature: A key to tight folding in a submarine Variscan foreland basin of SW Europe

    NASA Astrophysics Data System (ADS)

    Marques, F. O.; Burg, J.-P.; Lechmann, S. M.; Schmalholz, S. M.

    2010-04-01

    The problem addressed in this article is how sedimentary formations like turbidites in a foreland basin, which include layers with apparently great competence contrast, can be tightly folded in a regular manner under very low temperature and pressure. This raises two major issues: the rheological behavior of the rocks at the time of folding and the role played by fluids. In order to understand very low temperature folding and the structural evolution of a submarine foreland basin, we carried out detailed structural work in turbidites with alternating sandstone and shale, for which estimated peak temperature conditions were top diagenetic to very low grade metamorphism. Folds are tight to isoclinal, with local collapsed hinges, which implies that the incompetent shale was mobile enough to flow away from strongly flattened areas. We did not find evidence for cataclastic flow or crystal plasticity at mesoscopic and microscopic scales. Other structures (mostly boudins, foliations, conjugate brittle faults, and quartz veins) associated with folds denote anisotropic compaction by fluid extraction during regional shortening. This is possible if the folded rocks were unconsolidated, fluid-saturated sediments. The estimated low peak temperature is consistent with the shale being unlithified. Poorly cemented grains are free to slide past one another under shallow burial or high pore pressure conditions. Following this line of thought, we consider independent particulate flow assisted by fluids under very low confining pressure (bean bag analogy) as the rock deformation mechanism active during the described intense folding. Similar deformation is likely occurring (and has occurred) in other submarine accretionary wedges.

  9. Late Cenozoic evolution in the Pamir-Tian Shan convergence: New chronological constraints from the magnetostratigraphic record of the southwestern Tianshan foreland basin (Ulugqat area)

    NASA Astrophysics Data System (ADS)

    Qiao, Qingqing; Huang, Baochun; Biggin, Andrew J.; Piper, John D. A.

    2017-10-01

    The northeastern Pamir-Tian Shan convergence zone is a key region for understanding ongoing intracontinental mountain building. A detailed magnetostratigraphic study combined with color reflectance variations of continental sediments from the 1120 m-thick Sankeshu Section in the south west sector of the Tianshan Foreland Basin of western China yields important insights into the tectonic evolution of this zone. Correlation with the geomagnetic polarity time scale identifies deposition lasting from 16.7 to 2.6 Ma with a marked increase in sedimentation rate at 7 Ma. A further rapid increase occurred after 2.6 Ma with influx of the conglomeratic Xiyu Formation. Observed height-dependent changes of rock magnetic parameters (shape parameter T and AMS ellipsoid parameters) show that these sediments were influenced by weak deformation, with the sediments accumulated before 11 Ma recording a signature of compressive deformation from northward indentation by the Pamir. The succession of sedimentary events in the foreland basin is comparable to previous investigations of magnetostratigraphic and sedimentological analyses, and with thermochronology collectively showing that deformation in the Tian Shan region has been concentrated in Miocene and later times. The regional correlations resulting from these analyses show that sedimentary events correlate with the episodic nature of regional uplift with the latter inducing climatic changes that are in turn recorded in the sediment record.

  10. The India-Asia collision in north Pakistan: Insight from the U-Pb detrital zircon provenance of Cenozoic foreland basin

    NASA Astrophysics Data System (ADS)

    Ding, Lin; Qasim, Muhammad; Jadoon, Ishtiaq A. K.; Khan, Muhammad Asif; Xu, Qiang; Cai, Fulong; Wang, Houqi; Baral, Upendra; Yue, Yahui

    2016-12-01

    The northernmost exposures of sub-Himalayan Cenozoic strata in the Hazara-Kashmir syntaxial region of north Pakistan comprises the Paleocene-Eocene marine strata in the lower part and Oligocene-Miocene nonmarine strata in the upper part. This study provides the detrital zircon U-Pb geochronology of the Cenozoic strata in this area. The strong resemblance of U-Pb age spectra of Paleocene Hangu, Lockhart and Patala formations with those of Himalayan strata indicate an Indian plate provenance. The first appearance of <100 Ma detrital zircon U-Pb ages within the lower most part of the Early Eocene Margalla Hill Limestone indicates a shift from an Indian to Asian provenance. Geologic mapping shows the existence of a disconformity between the lower and upper most part of the Patala Formation, which is interpreted to have been formed by the migration of a flexural forebulge through this region. We consider the upper most part of the Patala Formation to have been deposited within the distal foredeep of the foreland basin. The Indian to Asian provenance shift and the presence of a possible foreland basin forebulge provide strong evidence that India-Asia collision was underway in northern Pakistan at ca. 56-55 Ma.

  11. Silurian and Lower Devonian of southwestern Virginia

    SciTech Connect

    Dennison, J.M.

    1984-12-01

    Thermal maturity of the Silurian and Lower Devonian rocks in Virginia west of New River decreases southwestward. Oil and gas shows are reported. The total thickness of Lower Devonian plus Silurian strata ranges from 52 to 1000 ft (16 to 305 m), with a maximum in Buchanan County. Sandstones were derived from sources southeast of the central Appalachian basin, some from lands southeast of the outcrop belt, and some formed by reworking of sandstones within the outcrop areas. Sandstones change northwestward to shales in the Clinch and Rose Hill Formations. In the Middle Silurian and Helderberg Group, sandstones grade northwestward to limestones. Limestones in the Hancock Formation change westward to dolomite. The Onesquethaw Stage is represented by sandstone, chert, and limestone assigned to the Wildcat Valley and Huntersville Formations. In the Middle Silurian (Keefer or Big Six sandstone) and Early Devonian (Wildcat Valley Sandstone), longshore currents carried sand across the southwest end of the basin toward Kentucky. Several regional unconformities are present. These unconformities are mostly related to sea level changes, but some are probably tectonic in origin. Five unconformities are significant: 1) at base of Silurian, 2) at base of upper Helderberg over much of the area, 3) at base of Oriskany Sandstone, 4) at base of Huntersville Formation, and 5) at base of Upper Devonian black shales in extreme western Virginia, where Chattanooga Shale overlies middle Devonian to Middle Silurian strata.

  12. Isotopic composition of Silurian seawater

    SciTech Connect

    Knauth, L.P.; Kealy, S.; Larimer, S.

    1985-01-01

    Direct isotopic analyses of 21 samples of the Silurian hydrosphere preserved as fluid inclusions in Silurian halite deposits in the Michigan Basin Salina Group yield delta/sup 18/O, deltaD ranging from 0.2 to +5.9 and -26 to -73, respectively. delta/sup 18/O has the same range as observed for modern halite facies evaporite waters and is a few per thousand higher than 100 analyses of fluid inclusions in Permian halite. deltaD is about 20 to 30 per thousand lower than modern and Permian examples. The trajectory of evaporating seawater on a deltaD-delta/sup 18/O diagram initially has a positive slope of 3-6, but hooks strongly downward to negative values, the shape of the hook depending upon humidity. Halite begins to precipitate at delta values similar to those observed for the most /sup 18/O rich fluid inclusions. Subsequent evaporation yields progressively more negative delta values as observed for the fluid inclusions. The fluid inclusion data can be readily explained in terms of evaporating seawater and are consistent with the degree of evaporation deduced from measured bromide profiles. These data are strongly inconsistent with arguments that Silurian seawater was 5.5 per thousand depleted in /sup 18/O. delta/sup 18/O for evaporite waters is systematically related to that of seawater, and does not show a -5.5 per thousand shift in the Silurian, even allowing for variables which affect the isotope evaporation trajectory. The lower deltaD may indicate a component of gypsum dehydration waters or may suggest a D-depleted Silurian hydrosphere.

  13. Detrital zircon microtextures and U-PB geochronology of Upper Jurassic to Paleocene strata in the distal North American Cordillera foreland basin

    NASA Astrophysics Data System (ADS)

    Finzel, E. S.

    2017-07-01

    Detrital zircon surface microtextures, geochronologic U-Pb data, and tectonic subsidence analysis from Upper Jurassic to Paleocene strata in the Black Hills of South Dakota reveal provenance variations in the distal portion of the Cordillera foreland basin in response to tectonic events along the outboard margin of western North America. During Late Jurassic to Early Cretaceous time, nonmarine strata record initially low rates of tectonic subsidence that facilitated widespread recycling of older foreland basin strata in eolian and fluvial systems that dispersed sediment to the northeast, with minimal sediment derived from the thrust belt. By middle Cretaceous time, marine inundation reflects increased subsidence rates coincident with a change to eastern sediment sources. Lowstand Albian fluvial systems in the Black Hills may have been linked to fluvial systems upstream in the midcontinent and downstream in the Bighorn Basin in Wyoming. During latest Cretaceous time, tectonic uplift in the study area reflects dynamic processes related to Laramide low-angle subduction that, relative to other basins to the west, was more influential due to the greater distance from the thrust load. Provenance data from Maastrichtian and lower Paleocene strata indicate a change back to western sources that included the Idaho-Montana batholith and exhumed Belt Supergroup. This study provides a significant contribution to the growing database that is refining the tectonics and continental-scale sediment dispersal patterns in North America during Late Jurassic-early Paleocene time. In addition, it demonstrates the merit of using detrital zircon grain shape and surface microtextures to aid in provenance interpretations.

  14. Cenozoic foreland basin evolution during Andean shortening in the Malargüe region of western Argentina (35°S)

    NASA Astrophysics Data System (ADS)

    Ramirez, S. G.; Horton, B. K.; Fuentes, F.

    2015-12-01

    Cenozoic clastic deposits in western Argentina provide key opportunities to evaluate the timing and duration of Andean deformation and uplift. We studied the Malargüe segment of the Andean foreland basin at 35°S to better understand latest Cretaceous to Pliocene deformation and eastward propagation of Andean retroarc shortening. Our multi-technique approach included logging of a well-exposed ~1500m Paleocene-Miocene stratigraphic succession, paleocurrent measurements, conglomerate clast counts, and detrital zircon U-Pb geochronological analyses of basin fill exposed in the Sosneado region along the Rio Atuel. The Pircala and Coihueco Formations define the lowermost ~180 m of the section and are represented by fine to medium sandstones, siltstones, claystones and marls interpreted as distal fluvial floodplain and localized lacustrine deposits. Pircala paleocurrents show a major reversal from west- to east-directed flow. These finer deposits of the lower succession are separated from the overlying coarser-grained ~800 m thick Agua de la Piedra Formation by a conspicuous unconformity that spans up to roughly 20 Myr. The Agua de la Piedra Formation is composed of upward-coarsening amalgamated beds of massive medium to coarse sandstones and lenticular conglomerates interpreted as a prograding proximal fluvial to alluvial fan system. Conglomerate clast counts show initial dominance by Mesozoic detritus from the pre-Andean Neuquen basin system, with a progressive upsection increase in Cenozoic volcanic detritus from the Andean magmatic arc. Collectively, the paleocurrents, clast compositions, sedimentary facies associations, and emerging U-Pb results suggest a long-term shift, commencing in the Paleocene, from eastern cratonic sources to magmatic-arc and thrust-belt sources during a systematic eastward propagation of deformation, with a pronounced phase of Miocene magmatism and shortening that incorporated the proximal foreland basin into the advancing thrust belt.

  15. Late Miocene to Recent formation of the Aure-Moresby fold-thrust belt and foreland basin as a consequence of Woodlark microplate rotation, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Ott, Bryan; Mann, Paul

    2015-06-01

    The Aure-Moresby fold-thrust belt and Aure-Moresby foreland basin are located in the eastern Gulf of Papua (GOP), Papua New Guinea (PNG), and formed during late Miocene-Recent as the result of large-scale, counterclockwise rotation of the 355,000 km2 Woodlark microplate. To document the structure, stratigraphy, and age of convergent deformation along the poorly studied, western edge of the rotating Woodlark microplate, we integrate results of 2,538 km of previously unpublished 2-D seismic reflection data with onshore geologic and GPS studies from previous workers. The late Miocene Aure-Moresby fold-thrust belt is a 400 km long, northwest-trending fold-belt exposed onshore in Papua New Guinea that plunges to the southeast, where continuous folds and northeast-dipping thrusts can be imaged in the subsurface for more than 250 km. The arcuate trend of the Aure-Moresby fold-thrust belt along the southwestern coast and offshore areas of the Papuan peninsula parallels the shape of the adjacent, offshore Aure-Moresby foreland basin and the strike of the transpressional segment of the left-lateral Owen-Stanley fault zone (OSFZ) passing along the center of the Papuan peninsula. As the OSFZ becomes more transtensional east of 148°E, folds of the Aure-Moresby fold-thrust belt along southern coast of the peninsula become less prominent, and the adjacent Aure-Moresby foreland basin transitions into an undeformed Cenozoic passive margin setting. These observations of convergent an left-lateral deformation along the Aure-Moresby fold-thrust belt are consistent with: (1) counterclockwise rotation of the Woodlark microplate known from regional GPS studies; (2) coeval opening of the Woodlark basin along its southern edge in the late Miocene; and (3) rapid subduction at the New Britain trench along its northern edge. The kinematics of the rotating Woodlark microplate are driven by slab pull forces acting on the actively subducting northern edge of the microplate.

  16. Rock magnetic properties of an 8-Ma terrigenous succession from the northern Tian Shan foreland basin, northwestern China and aridification of the Asian inland

    NASA Astrophysics Data System (ADS)

    Lu, H.; Zhang, W.; Li, Y.; Dong, C.; Zhang, T.; Zhou, Z.; Zheng, X.

    2013-12-01

    The Asian inland is characterized by exceptional topographic relief and widespread deserts and semi-deserts. Its environmental evolution during the late Cenozoic is featured by two processes: (1) growth and uplift of the Tibetan Plateau (including the hinterland to the north) and (2) stepwise development of dry climate. Many previous investigations have attempted to reconstruct the process of plateau uplift or constrain the aridification history. The relative role of the Tibetan Plateau uplift and Cenozoic global cooling in the aridification process of the Asian interior, however, remains an issue of debate. More detailed paleoclimatic/tectonic investigations over a broad area should be beneficial to better answer this question. In the northern Tian Shan foreland basin, northwestern China was deposited thick Cenozoic terrigenous succession, which is crucial for paleoenvironmental reconstruction of the Asian interior. Here we present a detailed rock magnetic investigation on 245 samples from the ~1,200-m-thick Neogene Taxi He section with a magnetostratigraphic age span of ca. 8.0 to 2.0 Ma in the northern Tian Shan foreland basin. Our rock magnetic results indicate that the significant variations in composition, concentration and grain size of magnetic minerals occurred at ca. 6.0, 3.7 and 2.7 Ma. The comparable compositions of rare earth elements (REEs) throughout the Neogene Taxi He section suggest no significant modification of the source materials during the interval between ca. 8.0 and 2.0 Ma, and thus sediment provenance is not regarded as responsible for these observed variations in rock magnetic properties. Our further analyses show that the variations in magnetic property of the Neogene Taxi He deposits are casually linked mainly with lithofacies transition due to range encroachment into foreland basin as well as climate aridification. Identified enhancement of aridification was chronologically constrained at ca. 6.0 and 2.7 Ma based on the variations of

  17. Discriminating Sediment Supply versus Accommodation Controls on Late Cretaceous Foreland Basin Stratigraphic Architecture in the Book Cliffs, Utah using Detrital Zircon Double Dating

    NASA Astrophysics Data System (ADS)

    Bartschi, N.; Saylor, J. E.

    2016-12-01

    Middle to late Campanian strata of the Book Cliffs, Utah record the Late Cretaceous deposition of three clastic wedges in the North American Cordilleran foreland basin east of the Sevier thrust-belt. Variations in wedge geometries provide an opportunity to evaluate the effects of sediment supply versus accommodation on foreland basin stratal architecture. There is a significant increase in eastward progradation rate from the Lower to the Upper Castlegate Sandstone. However, the progradation rate decreases in the overlying Bluecastle and Price River formations, as well as the laterally equivalent Farrer and Tuscher formations. Rapid progradation during Upper Castlegate deposition may be caused by increased sediment supply from either rapid exhumation of the Sevier thrust-belt or introduction of a new sediment source. Alternatively, reduced accommodation within the proximal foreland basin from uplifts associated with Laramide deformation, or a transition from flexural to dynamic subsidence, could produce the observed rapid wedge progradation. Changes in sediment provenance and source-area exhumation rate can be identified using a combination of detrital zircon U-Pb geochronology and (U-Th)/He thermochronology. Quantitative comparisons between collected samples and published provenance data indicates an upsection increase in a new sediment source, revealing a significant overall shift in provenance between wedge boundaries. This change in provenance is coupled by an upsection decrease in lag time between the Lower and Upper Castlegate, consistent with an increase in exhumation rate. Conversely, there is no change in lag time between the Upper Castlegate and overlying Price River Formation, suggesting a relatively constant exhumation rate. Near-zero lag times during the Upper Castlegate is consistent with rapid exhumation associated with increased thrusting of the Sevier thrust-belt. Therefore, progradation of the Upper Castlegate can be attributed to an increase in

  18. Characteristics of discrete and basin-centered parts of the Lower Silurian regional oil and gas accumulation, Appalachian basin; preliminary results from a data set of 25 oil and gas fields

    USGS Publications Warehouse

    Ryder, Robert T.

    1998-01-01

    Oil and gas trapped in Lower Silurian 'Clinton' sands and Medina Group sandstone constitute a regional hydrocarbon accumulation that extends 425 mi in length from Ontario, Canada to northeastern Kentucky. The 125-mi width of the accumulation extends from central Ohio eastward to western Pennsylvania and west-central New York. Lenticular and intertonguing reservoirs, a gradual eastward decrease in reservoir porosity and permeability, and poorly segregated gas, oil, and water in the reservoirs make it very difficult to recognize clear-cut geologic- and production-based subdivisions in the accumulation that are relevant to resource assessment. However, subtle variations are recognizable that permit the regional accumulation to be subdivided into three tentative parts: a western gas-bearing part having more or less discrete fields; an eastern gas-bearing part having many characteristics of a basin-centered accumulation; and a central oil- and gas-bearing part with 'hybrid' fields that share characteristics of both discrete and basin-centered accumulation. A data set of 25 oil and gas fields is used in the report to compare selected attributes of the three parts of the regional accumulation. A fourth part of the regional accumulation, not discussed here, is an eastern extension of basin-centered accumulation having local commercial gas in the Tuscarora Sandstone, a proximal facies of the Lower Silurian depositional system. A basin-centered gas accumulation is a regionally extensive and commonly very thick zone of gas saturation that occurs in low-permeability rocks in the central, deeper part of a sedimentary basin. Another commonly used term for this type of accumulation is deep-basin gas accumulation. Basin-centered accumulation is a variety of continuous-type accumulation. The 'Clinton' sands and Medina Group sandstone part of the basin-centered gas accumulation is characterized by: a) reservoir porosity ranging from about 5 to 10 percent; b) reservoir permeability

  19. The lithospheric-scale 3D structural configuration of the North Alpine Foreland Basin constrained by gravity modelling and the calculation of the 3D load distribution

    NASA Astrophysics Data System (ADS)

    Przybycin, Anna M.; Scheck-Wenderoth, Magdalena; Schneider, Michael

    2014-05-01

    The North Alpine Foreland Basin is situated in the northern front of the European Alps and extends over parts of France, Switzerland, Germany and Austria. It formed as a wedge shaped depression since the Tertiary in consequence of the Euro - Adriatic continental collision and the Alpine orogeny. The basin is filled with clastic sediments, the Molasse, originating from erosional processes of the Alps and underlain by Mesozoic sedimentary successions and a Paleozoic crystalline crust. For our study we have focused on the German part of the basin. To investigate the deep structure, the isostatic state and the load distribution of this region we have constructed a 3D structural model of the basin and the Alpine area using available depth and thickness maps, regional scale 3D structural models as well as seismic and well data for the sedimentary part. The crust (from the top Paleozoic down to the Moho (Grad et al. 2008)) has been considered as two-parted with a lighter upper crust and a denser lower crust; the partition has been calculated following the approach of isostatic equilibrium of Pratt (1855). By implementing a seismic Lithosphere-Asthenosphere-Boundary (LAB) (Tesauro 2009) the crustal scale model has been extended to the lithospheric-scale. The layer geometry and the assigned bulk densities of this starting model have been constrained by means of 3D gravity modelling (BGI, 2012). Afterwards the 3D load distribution has been calculated using a 3D finite element method. Our results show that the North Alpine Foreland Basin is not isostatically balanced and that the configuration of the crystalline crust strongly controls the gravity field in this area. Furthermore, our results show that the basin area is influenced by varying lateral load differences down to a depth of more than 150 km what allows a first order statement of the required compensating horizontal stress needed to prevent gravitational collapse of the system. BGI (2012). The International

  20. Chemistry of fluid inclusions in halite from the Salina group of the Michigan basin: Implications for Late Silurian seawater and the origin of sedimentary brines

    SciTech Connect

    Das, N.; Horita, J.; Holland, H.D. )

    1990-02-01

    Fluid was extracted from 18 fluid inclusions in halite of the Late Silurian Salina Group exposed in the Crystal Mine on the outskirts of Detroit, Michigan. Compared with modern seawater evaporated to the same degree, the inclusion fluids are severely depleted in SO{sub 4}{sup {minus}2}, somewhat depleted in Na{sup +} and Mg{sup +2}, and greatly enriched in Ca{sup +2}. The composition of the inclusion fluids can be derived from Silurian seawater with a composition close to that of modern seawater, if it is assumed that the composition of the Silurian seawater was modified by dolomitizing CaCO{sub 3}-rich sediments and by albitizing silicate minerals during its evolution into evaporite brines. Since the evolution of the brines involved a number of chemical reactions, it is impossible to recover the initial concentration of all of the major ions in the parent Silurian seawater from the composition of the inclusion fluids alone. It is likely, however, that the m{sub K+}/m{sub Br-} ratio and the functions in Late Silurian seawater had values close to those of modern seawater. Measurements of the isotopic composition of sulfur and of Sr in anhydrite within and associated with the halite host of the fluid inclusions are consistent with previous measurements of {delta}{sup 34}S in Silurian marine anhydrites and with the {sup 87}Sr/{sup 86}Sr ratios of Late Silurian marine carbonates.

  1. The major-ion composition of Silurian seawater

    USGS Publications Warehouse

    Brennan, S.T.; Lowenstein, T.K.

    2002-01-01

    One-hundred fluid inclusions in Silurian marine halite were analyzed in order to determine the major-ion composition of Silurian seawater. The samples analyzed were from three formations in the Late Silurian Michigan Basin, the A-1, A-2, and B Evaporites of the Salina Group, and one formation in the Early Silurian Canning Basin (Australia), the Mallowa Salt of the Carribuddy Group. The results indicate that the major-ion composition of Silurian seawater was not the same as present-day seawater. The Silurian ocean had lower concentrations of Mg2+, Na+, and SO2-4, and much higher concentrations of Ca2+ relative to the ocean's present-day composition. Furthermore, Silurian seawater had Ca2+ in excess of SO2-4. Evaporation of Silurian seawater of the composition determined in this study produces KC1-type potash minerals that lack the MgSO4-type late stage salts formed during the evaporation of present-day seawater. The relatively low Na+ concentrations in Silurian seawater support the hypothesis that oscillations in the major-ion composition of the oceans are primarily controlled by changes in the flux of mid-ocean ridge brine and riverine inputs and not global or basin-scale, seawater-driven dolomitization. The Mg2+/Ca2+ ratio of Silurian seawater was ~1.4, and the K+/Ca2+ ratio was ~0.3, both of which differ from the present-day counterparts of 5 and 1, respectively. Seawaters with Mg2+/Ca2+ 2 (e.g., modern seawater) facilitate the precipitation of aragonite and high-magnesian calcite. Therefore, the early Paleozoic calcite seas were likely due to the low Mg2+/Ca2+ ratio of seawater, not the pCO2 of the Silurian atmosphere. Copyright ?? 2002 Elsevier Science Ltd.

  2. Kinky vitrinite reflectance well profiles: evidence of paleopore pressure in low-permeability, gas-bearing sequences in Rocky Mountain foreland basins

    USGS Publications Warehouse

    Law, B.E.; Nuccio, V.F.; Barker, C.E.

    1989-01-01

    Vitrinite reflectance (Rm) profiles of wells drilled in abnormally pressured, low-permeability gas-bearing sequences in Rocky Mountain foreland basins are commonly non-linear with two or more nonparallel segments. These kinky profiles are most likely due to perturbations of the thermal gradient caused by contrasting heat transfer processes associated with the development of abnormally high pressures. We interpret the intersection of the shallow and intermediate Rm segments to mark the approximate original boundary between normal-pressured, water-bearing rocks and underlying overpressured gas- and water-bearing rocks. The intersection of the intermediate and deep Rm segments marks the approximate original boundary between overpressured gas- and water-bearing rocks and underlying overpressured gas-bearing rocks. However, because overpressuring is a transient condition that eventually evolves into normal pressuring or underpressuring, these intersections may not coincide with the present top of abnormal pressuring. -from Authors

  3. Epigenetic dolomitization of the Přaídolí formation (Upper Silurian), the Barrandian basin, Czech Republic: implications for burial history of Lower Paleozoic strata

    NASA Astrophysics Data System (ADS)

    Suchý, V.; Rozkošný, I.; Žák, K.; Franců, J.

    1996-06-01

    Stratabound epigenetic dolomite occurs in carbonate facies of the Barrandian basin (Silurian and Devonian), Czech Republic. The most intense dolomitization is developed in bioclastic calcarenites within the transition between micritic limestone and shaledominated Přídolí and Lochkov formations deposited on a carbonate slope. Medium-crystalline (100-400 µm), inclusion-rich, xenotopic matrix dolomite ( δ 18O=-4.64 to -3.40‰ PDB; δ 13C=+1.05 to +1.85‰ PDB) which selectively replaced most of the bioclastic precursor is volumetrically the most important dolomite type. Coarse crystalline saddle dolomite ( δ 18O=-8.04 to -5.14‰ PDB; δ 18C=+0.49 to +1.49 PDB) which precipitated in fractures and vugs within the matrix dolomite represents a later diagenetic dolomitization event. In some vugs, saddle dolomite coprecipitated with petroleum inclusion-rich authigenic quartz crystals and minor sulfides which, in turn, were post-dated by semisolid asphaltic bitumen. The interpretation of the dolomitization remains equivocal. Massive xenotopic dolomite, although generally characteristic of a deeper burial setting, may have been formed by a recrystallization of an earlier, possibly shallow burial dolomite. Deeper burial recrystallization by reactive basinal pore fluids that presumably migrated through the more permeable upper portion of the Přídolí sequence appears as a viable explanation for this dolomitization overprint. Saddle dolomite cement of the matrix dolomite is interpreted as the last dolomitization event that occurred during deep burial at the depth of the oil window zone. The presence of saddle dolomite, the fluid inclusion composition of associated quartz crystals, and vitrinite paleogeothermometry of adjacent sediments imply diagenetic burial temperatures as high as 160°C. Although high geothermal gradients in the past or the involvement of hydrothermally influenced basinal fluids can account for these elevated temperatures, burial heating beneath

  4. Epigenetic dolomitization of the Přídolí formation (Upper Silurian), the Barrandian basin, Czech Republic: implications for burial history of Lower Paleozoic strata

    NASA Astrophysics Data System (ADS)

    Suchý, V.; Rozkošný, I.; Žák, K.; Franců, J.

    Stratabound epigenetic dolomite occurs in carbonate facies of the Barrandian basin (Silurian and Devonian), Czech Republic. The most intense dolomitization is developed in bioclastic calcarenites within the transition between micritic limestone and shale-dominated Přídolí and Lochkov formations deposited on a carbonate slope. Medium-crystalline (100-400μm), inclusion-rich, xenotopic matrix dolomite (δ18O=-4.64 to -3.40ö PDBδ13C=+1.05 to +1.85ö PDB) which selectively replaced most of the bioclastic precursor is volumetrically the most important dolomite type. Coarse crystalline saddle dolomite (δ18O=-8.04 to -5.14ö PDBδ18C=+0.49 to +1.49 PDB) which precipitated in fractures and vugs within the matrix dolomite represents a later diagenetic dolomitization event. In some vugs, saddle dolomite coprecipitated with petroleum inclusion-rich authigenic quartz crystals and minor sulfides which, in turn, were postdated by semisolid asphaltic bitumen. The interpretation of the dolomitization remains equivocal. Massive xenotopic dolomite, although generally characteristic of a deeper burial setting, may have been formed by a recrystallization of an earlier, possibly shallow burial dolomite. Deeper burial recrystallization by reactive basinal pore fluids that presumably migrated through the more permeable upper portion of the Přídolí sequence appears as a viable explanation for this dolomitization overprint. Saddle dolomite cement of the matrix dolomite is interpreted as the last dolomitization event that occurred during deep burial at the depth of the oil window zone. The presence of saddle dolomite, the fluid inclusion composition of associated quartz crystals, and vitrinite paleogeothermometry of adjacent sediments imply diagenetic burial temperatures as high as 160 °C. Although high geothermal gradients in the past or the involvement of hydrothermally influenced basinal fluids can account for these elevated temperatures, burial heating beneath approximately 3

  5. Tectonic controls on deposition of Middle Jurassic strata in a retroarc foreland basin, Utah-Idaho trough, western interior, United States

    NASA Astrophysics Data System (ADS)

    Bjerrum, Christian J.; Dorsey, Rebecca J.

    1995-08-01

    An electronic supplement of this material may be obtained on a diskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN to AGU's FTP account using ANONYMOUS as the username and GUEST as the password. Go to the right directory by typing CD APEND. Type LS to see what files are available. Type GET and the name of the file to get it. Finally, type EXIT to leave the system.) (Paper 95TC01448, Tectonic controls on deposition of Middle Jurassic strata in a retroarc foreland basin, Utah-Idaho trough, western interior, United States, Christian J. Bjerrum and Rebecca J. Dorsey). Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N. W., Washington, DC 20009; $15.00. Payment must accompany order. A thick succession of Jurassic nonmarine and marine sedimentary rocks is exposed in a large area from northern Arizona to eastern Idaho and western Wyoming. These sediments accumulated in the Utah-Idaho trough, a deep elongate cratonal basin whose origin has recently been debated. Detailed stratigraphic analysis, subsidence analysis, and first-order flexural modeling of these deposits (this study) provide new insights into the timing and mechanisms of subsidence in the Utah-Idaho trough. Lower and Middle Jurassic strata are divided into six unconformity-bounded sequences. In contrast to the overall uniform thickness of Lower Jurassic sequences (1 and 2), Middle Jurassic strata (sequences 3 through 6) consist of distinctly westward thickening sedimentary packages in which basal shallow marine deposits onlap eastward onto bounding unconformities. Basal strata of sequences 3 through 6 pass upward into widespread progradational continental deposits that are truncated progressively toward the east (cratonward) by the next unconformity. Decompacted total subsidence curves show that the rate of subsidence in most sections increased sharply at the end of sequence 2 time (J-2 unconformity; ˜170 Ma). This is interpreted to record the onset of Middle Jurassic deposition

  6. Modeling and Inversion of three-dimensional crustal structures beneath the Pyrenees and their foreland basins based upon geological, gravimetric and seismological data

    NASA Astrophysics Data System (ADS)

    Spangenberg, Hannah; Chevrot, Sébastien; Courrioux, Gabriel; Guillen, Antonio

    2017-04-01

    Our goal is to obtain a three-dimensional (3D) model of mass density and seismic velocities beneath the Pyrenees and their foreland basins (Aquitaine and Ebro basins), which accounts for all the geological and geophysical information available for that region. This model covers the whole mountain range going from the Atlantic Ocean to the Mediterranean Sea, and from the Iberian range to the Massif Central. The model is described by different units: the lower, middle, and upper crusts, the accretionary prism, and the consolidated and unconsolidated sediment layers. Furthermore, a sub-continental, serpentinized European mantle is introduced to describe the exhumed mantle bodies which are responsible for the positive Bouguer gravity anomalies in the western Pyrenees. We build a first 3D model using all the geological information: drill-hole surveys, seismic sections, and the geological map. We use the potential field method implemented in Geomodeler to interpolate these geological data. However, these data are too sparse to build a model that explains seismic travel times or gravimetric data, especially the Labourd and the St. Gaudens Bouguer gravity anomalies. In addition, inconsistencies between the different data sets exist. We thus add by trial and error additional data points, comparing modeled and observed Bouguer gravimetric anomalies. The result of this procedure is a 3D geological model that respects the geological data and explains the measured Bouguer gravimetric anomalies. In a second step, we use this model to determine the average density and seismic velocities inside each geological unit assuming uniform layers. To constrain the seismic velocities we use travel time picks extracted from the bulletin of the Pyrenean seismicity released by the Observatoire Midi Pyrenées. In a third step, we use this 3D a priori model in a Monte Carlo inversion to invert jointly gravimetric data and seismic travel times from the bulletin. This probabilistic approach

  7. U-Pb geochronology of modern river sands from the flat-slab segment of the southern central Andes, Argentina, 29-31°S: Implications for Neogene foreland and hinterland basin evolution

    NASA Astrophysics Data System (ADS)

    Capaldi, T.; Horton, B. K.; McKenzie, R.; Stockli, D. F.

    2015-12-01

    This study investigates how Andean river sediments in the flat-slab segment of western Argentina record active mixing of lithologically and geochemically distinct source regions comprising the Principal Cordillera, Frontal Cordillera, Precordillera fold-thrust belt, Sierras Pampeanas basement uplifts, and recycled Neogene basin fill. Detrital zircon U-Pb geochronological results for modern river sands discriminate variations from hinterland source regions, through river tributaries and main trunks of the Bermejo, Jachal, San Juan, and Mendoza rivers, and their respective fluvial megafans within the active foreland basin. Proportions of proximal zircon populations in the hinterland trunk rivers (with extensive Permian-Triassic and Cenozoic igneous exposures) diminish downstream with progressive contributions from the frontal Precordillera fold-thrust belt (dominantly Paleozoic sedimentary rocks) and Pampean basement uplifts. However, this systematic downstream dilution is perturbed in several catchments by significant recycling of older foreland basin fill. The degree of recycling depends on the position and extent of Oligocene-Pliocene exposures within the catchments. To discern the effects of the variable detrital zircon sources, multiple statistical methods are utilized. Quantitative comparisons suggest that variations in detrital zircon age distributions among the modern sands, and with older foreland basin fill and exposed bedrock, are dependent on spatial and temporal variations in exhumation and drainage network evolution within their respective Andean catchments. The present surface area of competing source regions and the configuration of hinterland tributary rivers largely dictate the degree of downstream dilution and/or recycling. This study provides a modern analogue and baseline for reconstructing Neogene shifts in foreland basin provenance, depositional systems, and drainage configurations during a critical transition to flat-slab subduction.

  8. The Areal Extent of Continuous Type Gas Accumulations in Lower Silurian Clinton Sands and Medina Group Sandstones of the Appalachian Basin and the Environments Affected by Their Development

    USGS Publications Warehouse

    Wandrey, C.J.; Ryder, Robert T.; Nuccio, Vito F.; Aggen, Kerry L.

    1997-01-01

    In order to best preserve and manage our energy and natural resources we must understand the relationships between these resources and the impacts of their development. To further this understanding the U.S. Geological Survey is studying unconventional continuous-type and, to a lesser extent, conventional oil and gas accumulations and the environmental impacts associated with their development. Continuous-type gas accumulations are generally characterized by low matrix permeabilities, large areal extents, and no distinct water contacts. This basin scale map shows the overall extent of these accumulations and the general land use types that may be impacted by their development. The Appalachian Basin has the longest history of oil and gas exploration and production in the United States. Since Drake's Titusville discovery well was drilled in 1859, oil and gas has been continuously produced in the basin. While there is still a great deal of oil and gas production, new field discoveries are rare and relatively small. For most of the second half of the 20th century the Appalachian basin has been considered a mature petroleum province because most of the large plays have already been discovered and developed. One exception to this trend is the Lower Silurian Clinton Sands and Medina Group Gas play which is being developed in New York, Pennsylvania, and Ohio. This continuous-type gas play has been expanding since the early 1970's (see inset maps). In the 1980's economic incentives such as large increases in wellhead prices further stimulated continuous-type gas resource development. Continuous-type gas plays can be large in areal extent and in thickness. 'Sweetspots' (areas of greater prodcution) are hard to predict and generally associated with better than average permeabilities, and enhanced by natural fracture systems. With an overall success rate often approaching 90%, drilling most of the play with closely spaced wells is often the best way to maximize gas recovery

  9. Anhydrite cements after dolomitization of shallow marine Silurian carbonates of the Gascoyne Platform, Southern Carnarvon Basin, Western Australia

    NASA Astrophysics Data System (ADS)

    El-Tabakh, Mohamed; Mory, Arthur; Schreiber, B. Charlotte; Yasin, Raza

    2004-02-01

    Carbonates and evaporites in the Dirk Hartog Group were deposited in subtidal, peritidal and shallow-marine evaporitic mudflat environments across the Gascoyne Platform within the Southern Carnarvon Basin, Western Australia. The carbonates are composed of ooids, peloids and minor bioclastic fragments, with early cements. They have been extensively dolomitized and replaced, in part, by late anhydrite sparry cements. Four types of dolomite which range from early to burial types are identified, incorporating re-equilibration or re-crystallization from basin brines. Accordingly, they exhibit distinctive petrographic features and isotopic signatures of carbon and oxygen. Evaporites deposited are present as discrete beds and displacive nodules in carbonate and siliciclastic beds, and show δ34S CDT values and 87Sr/ 86Sr ratios indicative of variable marine and non-marine conditions. Late dissolution of evaporites has produced satin spar gypsum veins in the shallowest section of the platform, whereas blocky and sparry anhydrite cements and void fillings formed deeper within the platform. Dissolution of the evaporites and formation of anhydrite cements post-date dolomitization.

  10. Chronology and tectono-sedimentary evolution of the Upper Pliocene to Quaternary deposits of the lower Guadalquivir foreland basin, SW Spain

    NASA Astrophysics Data System (ADS)

    Salvany, Josep Maria; Larrasoaña, Juan Cruz; Mediavilla, Carlos; Rebollo, Ana

    2011-11-01

    This paper presents new litho, chrono and magnetostratigraphic data from cores of 23 exploratory boreholes drilled in the Abalario and marshlands areas of the lower Guadalquivir basin (the western sector of the Guadalquivir foreland basin, SW of Spain). The lithologic logs of these boreholes identify four main sedimentary formations, namely: Almonte Sand and Gravel, Lebrija Clay and Gravel, Marismas Clay and Abalario Sand, respectively interpreted as proximal-alluvial, distal-alluvial, alluvial-estuarine and aeolian. From radiocarbon and magnetostratigraphic data, these formations were dated as Upper Pliocene to Holocene. In the marshlands area, three main sedimentary sequences are present: an Upper Pliocene to Lower Pleistocene sequence of the Almonte and Lebrija (lower unit) formations, a Pleistocene sequence of the Lebrija (upper unit) and the lower Marismas formations, and a latest Pleistocene to present-day sequence of the upper Marismas Formation. The three sequences began as a rapid alluvial progradation on a previously eroded surface, and a subsequent alluvial retrogradation. In the third sequence, estuarine and marsh sediments accumulated on top of the alluvial sediments. The aeolian sands of the Abalario topographic high developed coeval to alluvial and estuarine sedimentation after the first alluvial progradation, and continuously until the present. Correlation with the surrounding areas show that the sequences are the result of the forebulge uplift of the northern margin of the basin (Sierra Morena) and the adjacent Neogene oldest sediments of their northern fringe, both form the main source area of the study formations. This uplift occurred simultaneous to the flexural subsidence (SSE tilting) of the southern part of the basin, where sedimentary aggradation dominated.

  11. South China connected to north India in Gondwana: sedimentary basin and detrital provenance analyses

    NASA Astrophysics Data System (ADS)

    Yao, W.; Li, Z. X.; Li, W. X.; Li, X. H.; Yang, J. H.

    2015-12-01

    The paleoposition of South China during the Ediacaran-Silurian is important for understanding the assembly of Gondwana. We report here the tectonostratigraphic evolution of the Ediacaran-Silurian Nanhua foreland basin in South China, and discuss South China's connection with Gondwana and potential tectonic triggers for both the Wuyi-Yunkai orogeny in South China and the Bhimphedian orogeny in north India. The Nanhua basin was involved in a three-stage evolution, which are: Stage 1 (the Ediacaran-Cambrian) recording the start of tectonic subsidence with turbiditic marine clastic deposition, fed by exotic orogens outboard South China; Stage 2 (the Ordovician to earliest-Silurian) featured by migrating depocentres with dominant shallow marine to deltaic clastic deposition, fed by the local Wuyi-Yunkai orogen; and Stage 3 (the Silurian) showing the arrival of depocentre in the Yangtze Block during the waning stage of the Wuyi-Yunkai orogeny with deltaic deposition in the remanent foreland basin. Detrital zircon analyses of the Ediacaran-Silurian sandstones across the Nanhua basin reveal a prominent age population of 1100-900 Ma (with a peak age at ~980 Ma) and moderate populations of Archean-Paleozoic ages, grossly matching that of crystalline and sedimentary rocks in northern India. Zircon isotopes of the Stage 1 samples suggest three Precambrian episodes of juvenile crustal growth at 3.0 Ga, 2.5 Ga and 1.0 Ga, and a major crustal reworking at 580-500 Ma for the source areas, which are constraint to be northwestern India and its surrounding orogens. Together with other evidence, we propose that South China likely collided with northwestern India during the Gondwana assembly, generated the Bhimphedian orogeny in north India and formed two foreland basins on both the north India and South China sides. Far-field stress of the collision triggered the Ordovician-Silurian Wuyi-Yunkai orogeny in South China. The Stage 2-3 samples in the Nanhua basin of South China were shed

  12. Application of actualistic models to unravel primary volcanic control on sedimentation (Taveyanne Sandstones, Oligocene Northalpine Foreland Basin)

    NASA Astrophysics Data System (ADS)

    Di Capua, Andrea; Groppelli, Gianluca

    2016-05-01

    This work is focused on the Taveyanne Sandstones (Grés de Taveyanne), an Oligocene volcaniclastic turbidite sequence cropping out in the Northern Alpine Molassa between SE France and Central Switzerland, with the aim to investigate the temporal relationship between volcanic activity and sediment supply. Detailed stratigraphic, sedimentological, and petrographic (XRD analyses on mudstones and point counts on sandstones) studies conducted on three sections (Col de l'Oulette and Flaine in SE France, Taveyanne in SW Switzerland) allow a discrimination of three main facies, among which only one is extremely enriched in volcaniclastic detritus and characterized by features similar to those of disaggregated pyroclastic density current deposits. The other two facies are characterized by variable to no volcanic detritus but supplied by crystalline and sedimentary detritus. Such sediment trends are similar to those of modern, volcanically controlled source-to-sink systems. This allows a reinterpretation of the Taveyanne Sandstones as a syn-volcanic turbidite system, episodically supplied by large amounts of volcanic detritus, which periodically modified the drainage paths. Moreover, the well-known temporal and spatial persistence of such modifications in modern settings leads to conciliate the syn-volcanic supply with the location of the volcanic centers in the internal part of the Alps, without invoking particular climatic and tectonic conditions controlling foreland sedimentation.

  13. Differential exhumation across the eastern Greater Caucasus from low-temperature thermochronology: Implications for plate boundary reorganization and foreland basin deformation

    NASA Astrophysics Data System (ADS)

    Niemi, N. A.; Avdeev, B.

    2010-12-01

    The Greater Caucasus, stretching from the Black Sea to the Caspian Sea, are the highest mountain range in Europe, and form the northern boundary of the Arabia-Eurasia collision zone. The role that the Greater Caucasus plays, and has played, in accommodating strain within this orogen, however, remains elusive. Estimates of the onset of rapid exhumation and deformation of range span a large fraction of the Cenozoic, from Eocene or Oligocene at the western end of the range in Georgia, to late Miocene or early Pliocene in the central Greater Caucasus of Russia, and Pliocene at the eastern end of the range in Azerbaijan. Such controversies have also served to obscure the role of the Greater Caucasus in responding to a major, and widely recognized, plate boundary reorganization at ~5 Ma, characterized by the genesis of many active faults, increased supply of detritus from the Greater Caucasus to its foreland basins, and the onset of deformation of foreland basin sediments. Here we present low-temperature thermochronology data, including apatite (U-Th)/He and fission-track data, from a north-south transect at ~48°E across the eastern Greater Caucasus in Azerbaijan that demonstrates differential exhumation rates and timing across the range. In the northern portion of the range, which is underlain by sedimentary strata of the Scythian Platform, rounded and substantially abraded detrital apatites were recovered from Cretaceous and Jurassic sandstones. Thermal modeling of these data reveal onset of cooling of the northern Greater Caucasus at ~20 Ma at 2-4oC/My and a significant increase in cooling rate at ~5 Ma to rates >10oC/My. Maximum exhumation of northern Caucasus strata is ~4 km. Strata of the northern Greater Caucasus are separated from those of the southern Greater Caucasus by the Zangi thrust, south of which strata of the Vandam Zone are comprised of early Cretaceous volcaniclastic sediments of andesitic composition. Detrital apatites from these strata are pristine

  14. Evidence of a large deep conductive body within the basement of the Guadalquivir foreland Basin (Betic Cordillera, S-Spain) from tipper vector modelling: Tectonic implications

    NASA Astrophysics Data System (ADS)

    González-Castillo, L.; Galindo-Zaldívar, J.; Junge, A.; Martínez-Moreno, F. J.; Löwer, A.; Sanz de Galdeano, C.; Pedrera, A.; López-Garrido, A. C.; Ruiz-Constán, A.; Ruano, P.; Martínez-Martos, M.

    2015-11-01

    The Betic Cordillera is an Alpine belt formed by the interaction of the Eurasian and African plates and the westward motion of the Alboran Domain. Long Period Magnetotelluric observations at 26 sites in its westernmost part provide induction arrows that have been compared with 3D forward models including bathymetry and major geological bodies. The results highlight the presence of a major conductive body (0.05 Ω m) unknown to date and located within the basement of the Guadalquivir foreland basin. Aeromagnetic and field magnetic measurements further support the occurrence of magnetic anomalies related to the top of this anomalous body. This major structure is interpreted as an intermediate or basic igneous rock, with a high proportion of metallic mineralization. Its origin is discussed in the framework of the regional geological setting, possibly produced in the southern Iberian Variscan Massif by a huge concentration of volcanogenic massive sulphide (VMS) in the prolongation of the Iberian Pyrite Belt during Devonian-early Carboniferous times. Another possibility is that the conductive anomaly is due to magmatic intrusions associated with the Mesozoic fragmentation of Southern Iberia and the opening of the Tethys.

  15. Testing microtaphofacies as an analytic tool for integrated facies and sedimentological analysis using Lower Miocene mixed carbonate/siliciclastic sediments from the North Alpine Foreland Basin

    NASA Astrophysics Data System (ADS)

    Nebelsick, James; Bieg, Ulrich

    2010-05-01

    Taphonomic studies have mostly concentrated on the investigation and quantification of isolated macroscopic faunal and floral elements. Carbonate rocks, in contrary to isolated macroscopic objects, have rarely been specifically addressed in terms of taphonomic features, although many aspects of microfacies analyses are directly related to the preservation of constituent biogenic components. There is thus a high potential for analyzing and quantifying taphonomic features in carbonate rocks (microtaphofacies), not the least as an additional tool for facies analysis. Analyzing the role of taphonomy in carbonate environments can be used to determine how different skeletal architectures through time and evolving synecological relationships (bioerosion and encrustation) have influence carbonate environments and their preservation in the rock record. This pilot study analyses the microtaphofacies of Lower Miocene, shallow water, mixed carbonate - siliciclastic environment from the North Alpine Foreland Basin (Molasse Sea) of southern Germany. The sediments range from biogenic bryomol carbonates to pure siliciclastics. This allows environmental interpretation to be made not only with respect to biogenic composition (dominated by bivalves, gastropods, bryozoans and barnacles), but also to siliciclastic grain characteristics and sedimentary features. Facies interpretation is relatively straight forward with a somewhat varied near shore facies distribution characterized dominated by carbonate which grade into higher energy, siliciclastic offshore sediments. Taphonomic features are assessed along this gradient with respect to total component composition as well as by following the trajectories of individual components types. The results are interpreted with respect to biogenic production, fragmentation, abrasion and transport.

  16. A direct comparison of the ages of detrital monazite versus detrital zircon in Appalachian foreland basin sandstones: Searching for the record of Phanerozoic orogenic events

    NASA Astrophysics Data System (ADS)

    Hietpas, Jack; Samson, Scott; Moecher, David

    2011-10-01

    The provenance potential of detrital monazite was investigated by in situ measurement of 232Th- 208Pb dates of grains isolated from six Middle Carboniferous-Permian sandstones from the Appalachian foreland basin. Provenance assessment of these units was previously investigated by measuring U-Pb crystallization ages of detrital zircon (Thomas et al., 2004; Becker et al., 2005, 2006). Approximately 90% of the detrital zircon ages record Mesoproterozoic or older ages, with only 10% recording the three major pulses of tectonism (Taconian, Acadian and Alleghanian) that are the hallmark of the Appalachian Orogen. 232Th- 208Pb ages of detrital monazite, however, strongly record the complex phases of Paleozoic orogenesis. Nearly 65% of the ages record Paleozoic events, while 35% record Neoproterozoic or older ages. In several of the analyzed sandstones, detrital monazite ages record Paleozoic orogenic events that are completely missed by detrital zircon ages, demonstrating that monazite ages more accurately reflect the character of the sediment source rocks. The inferred maximum age of sediment deposition, as determined by the youngest monazite grains, is ~ 550 Ma younger for two of the analyzed sandstones compared to depositional constraints based on the youngest detrital zircon. The different physical properties and petrogenesis of zircon and monazite are interpreted to be factors for the dramatic differences in sediment provenance information provided by each mineral. The results from this study have important implications for determining sediment provenance, constraining maximum age of sediment deposition, and developing robust regional tectonic models.

  17. Late Quaternary tectonic switching of siliciclastic provenance in the strike-slip-dominated foreland of the Western Carpathians; Upper Morava Basin, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Novák, Aleš; Bábek, Ondřej; Kapusta, Jaroslav

    2017-06-01

    younger) differs from the older fluvial deposits representing the other cores. It indicates that a major provenance change occurred between the latest Saalian and the late Weichselian. In the late Weichselian, the Morava River started to recycle loess deposits, which cover large areas of its catchment. Based on OSL dating, it may be assumed that the Morava River turned from degrading (between 92.6 ± 8.03 and 34.53 ± 3.42 ka) to aggrading in style (from 34.53 ± 3.42 ka to the present day) due to coeval tectonic movements in the UMB, which are indirectly indicated by present-day seismicity, geomorphic faults and palaeoseismic evidence. Both the tectonic context and fluvial deposition styles of the Upper Morava Basin show similar features to the Upper Rhine Graben of the Alpine foreland.

  18. The age of volcanic tuffs from the Upper Freshwater Molasse (North Alpine Foreland Basin) and their possible use for tephrostratigraphic correlations across Europe for the Middle Miocene

    NASA Astrophysics Data System (ADS)

    Rocholl, Alexander; Schaltegger, Urs; Gilg, H. Albert; Wijbrans, Jan; Böhme, Madelaine

    2017-07-01

    The Middle Miocene Upper Freshwater Molasse sediments represent the last cycle of clastic sedimentation during the evolution of the North Alpine Foreland Basin. They are characterized by small-scale lateral and temporal facies changes that make intra-basin stratigraphic correlations at regional scale difficult. This study provides new U-Pb zircon ages as well as revised 40Ar/39Ar data of volcanic ash horizons in the Upper Freshwater Molasse sediments from southern Germany and Switzerland. In a first and preliminary attempt, we propose their possible correlation to other European tephra deposits. The U-Pb zircon data of one Swiss (Bischofszell) and seven southern German (Zahling, Hachelstuhl, Laimering, Unterneul, Krumbad, Ponholz) tuff horizons indicate eruption ages between roughly 13.0 and 15.5 Ma. The stratigraphic position of the Unterneul and Laimering tuffs, bracketing the ejecta of the Ries impact (Brockhorizon), suggests that the Ries impact occurred between 14.93 and 15.00 Ma, thus assigning the event to the reversed chron C5Bn1r (15.032-14.870 Ma) which is in accordance with paleomagnetic evidence. We combine our data with published ages of tuff horizons from Italy, Switzerland, Bavaria, Styria, Hungary, and Romania to derive a preliminary tephrochronological scheme for the Middle Miocene in Central Europe in the age window from 13.2 to 15.5 Ma. The scheme is based on the current state of knowledge that the Carpathian-Pannonian volcanic field was the only area in the region producing explosive calc-alkaline felsic volcanism. This preliminary scheme will require verification by more high-quality ages complemented by isotopic, geochemical and paleomagnetic data.

  19. Integrated stratigraphy of the Ammer section, Northern Alpine Foreland Basin, Germany: examining the age and origin of the earliest deposits in the Paratethys

    NASA Astrophysics Data System (ADS)

    van der boon, Annique; Beniest, Anouk; Ciurej, Agnieszka; Gaździcka, Elzbieta; Grothe, Arjen; Sachsenhofer, Reinhard; Langereis, Cor; Krijgsman, Wout

    2017-04-01

    The Northern Alpine Foreland Basin (NAFB) was an arm of the epicontinental Paratethys Sea during the Oligocene. The Oligocene and Miocene deposits in the Paratethys are linked to a long-term phase of episodically oxygen-poor conditions. This led to the deposition of organic-rich shales over millions of years, which nowadays make up the most important part of the source rocks of the Paratethys. At the Eocene-Oligocene transition (EOT), global sea-level dropped by an estimated 70 meters. Both this eustatic sea-level drop and large scale tectonic movements are inferred as mechanisms for restriction of connections to the global ocean and consecutive basin isolation in the Paratethys. Discriminating sea-level effects from tectonic processes requires accurate dating of Oligocene deposits. Here, we use an integrated stratigraphic approach, combining different biostratigraphic techniques with magnetostratigraphy and organic geochemistry, to determine the age of the Tonmergel formation along the Ammer River in southern Germany. The Tonmergel formation is usually interpreted as the equivalent of the Paratethys Lower Oligocene organic-rich shales. The age of deposits (typically mapped as Oligocene) in this region is currently under debate, as some studies suggest they might be late Eocene in age. The absence of marker species for biostratigraphic zones, the scarcity of ash layers and the lack of formally defined boundaries of nannoplankton zones around the Eocene-Oligocene interval (e.g. the NP19-20/NP21 boundary) further obstruct accurate dating. Here we present the results of our magnetostratigraphy, biostratigraphy and organic geochemistry and interpret whether any lithological changes can be linked to climate forcing or tectonic processes. Based on the combined results of our study we provide several options for the age of these earliest Paratethys deposits, and discuss our preferred option.

  20. Gravity sliding in basinal setting, a surficial record of tectonic and geodynamic evolution; examples from the southern W. Alps and their foreland

    NASA Astrophysics Data System (ADS)

    Dumont, T.; Franzi, V.; Matthews, S. J.

    2012-04-01

    The occurrence of large-scale submarine landslides, although commonly observed in the present basins, is only exceptionally mentioned in the Alpine orogen and foreland. The southern part of the Western Alpine arc and the SE basin of France provide examples of such features which could be related with particular geodynamic events, in relation with the motion of the Iberian and Adriatic microplates : - A >50km2 slump scar formed in Aptian times at the northwestern edge of the SE France (so-called Vocontian) basin, giving a low-angle detachment surface which was onlapped by Albian hemipelagic marls (Ferry & Flandrin, 1979). The latter mark the maximum deepening stage of the basin, and the head of the scar is located over a deep-seated fault bounding the platform, which strongly suggest that sliding was caused by differential subsidence due to Middle Cretaceous extension, as a consequence of Iberia-Europe divergence. - Later on, a deep-marine erosion surface developed further down the basin over a >100km2 area (Dévoluy massif; Michard et al., 2010), which had been previously affected by Mid-Cretaceous extension. Typical inversion structures are found beneath the surface, which indicate that NS shortening overprinted the extensional pattern. The removal of up to 400m of Mesozoic sediments was controlled by gravity processes, probably triggered by the deformation of the basin floor following tectonic inversion. The overlying pelagic carbonates indicate that shortening occurred before the Campanian, which is closely comparable with the earliest stages of tectonic inversion in the Pyrenees. - The transition slope between the Paleogene Alpine flexural basin and the NW-ward propagating accretionary prism provides examples of basin floor degradation and of gravity-driven emplacement of large-scale blocks, generally regarded as thrust-sheets in the Alps. These features allow to reconstruct the early stages of the Adria-Europe collision, which strongly differ from the Oligo

  1. Deciphering the mid-Carboniferous eustatic event in the central Appalachian foreland basin, southern West Virginia, USA

    USGS Publications Warehouse

    Blake, B.M.; Beuthin, J.D.

    2008-01-01

    A prominent unconformity, present across shallow shelf areas of the Euramerican paleoequatorial basins, is used to demark the boundary between the Mississippian and Pennsylvanian subsystems. This unconformity, the mid-Carboniferous eustatic event, is generally attributed to a major glacio-eustatic sea-level fall. Although a Mississippian-Pennsylvanian unconformity is recognized throughout most of the Appalachian region, the record of the mid-Carboniferous eustatic event in the structurally deepest part of the basin has been controversial. Based on early reports that suggested the most complete Pennsylvanian section was present in southern West Virginia, various conceptual depositional models postulated continuous sedimentation between the youngest Mississippian Bluestone Formation and the oldest Penn-sylvanian Pocahontas Formation. In contrast, tabular-erosion models envisioned axial drainage systems that evolved in response to changing basin dynamics. These models predicted a Mississippian-Pennsylvanian unconformity. All these models suffered from a lack of biostratigraphic control. The presence of a sub-Pocahontas paleovalley, herein named the Lashmeet paleovalley, has been confirmed in southern West Virginia. The Lashmeet paleovalley was incised over 35 m into Bluestone strata and filled by lithic sands derived from the Appalachian orogen to the northeast and east. The polygenetic Green Valley paleosol complex marks the Bluestone-Pocahontas contact on associated interfluves. Together, these features indicate a substantial period of subaerial exposure and argue strongly in favor of a Mississippian-Pennsylvanian unconformity. Paleontologic data from the Bluestone Formation, including marine invertebrates and conodonts from the marine Bramwell Member and paleofloral data, support a late, but not latest, Arnsbergian age assignment. Marine fossils are not known from the Pocahontas Formation, but macrofloral and palynomorph taxa support a Langsettian age for most of

  2. 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

  3. The evolution of a terrace sequence along the Manas River in the northern foreland basin of Tian Shan, China, as inferred from optical dating

    NASA Astrophysics Data System (ADS)

    Gong, Zhijun; Li, Sheng-Hua; Li, Bo

    2014-05-01

    The Tian Shan range lies in the actively deforming part of the India-Asia collision zone. The uplift rate and deformation pattern of the Tian Shan are important for understanding the dynamics of crustal deformation in the region. The river terraces in northern Tian Shan provide key records of past changes in climate and/or regional tectonics. In this study, a terrace sequence along the Manas River in a tectonically active zone in the northern foreland basin of Tian Shan is investigated. Six river terraces were identified and dated using optically stimulated luminescence (OSL). The results show that the six terraces were abandoned at ~ 0.5 ka, ~ 1.4 ka, ~ 3.1 ka, ~ 4.0 ka, ~ 12.4 ka and ~ 19.9 ka, respectively. Together with high resolution Global Positioning System (GPS) measurements on the terrace treads, the fluvial history of Manas River is reconstructed. From ~ 20 ka to ~ 4.8 ka, the height of the fluvial bed of Manas River decreased at an average rate of 2.2 ± 0.6 mm/yr. From ~ 4.8 ka to the present, the height of the fluvial bed decreased at an average rate of 13.5 ± 0.6 mm/yr, corresponding to intensified incision of Manas River during the late Holocene. This accelerated incision is very likely caused by the tectonic forces rather than climatic influences alone, suggesting that the tectonic uplift activity was significantly intensified since ~ 4.8 ka in the northern piedmont of Tian Shan. Other controlling factors on the incision of Manas River are also discussed.

  4. Detrital zircon U-Pb and (U-Th)/He double-dating of Upper Cretaceous-Cenozoic Zagros foreland basin strata in the Kurdistan Region of northern Iraq

    NASA Astrophysics Data System (ADS)

    Barber, D. E.; Stockli, D. F.; Koshnaw, R. I.; Horton, B. K.; Tamar-Agha, M. Y.; Kendall, J. J.

    2014-12-01

    The NW Zagros orogen is the result of the multistage collisional history associated with Late Cretaceous-Cenozoic convergence of the Arabian and Eurasian continents and final closure of Neotethys. Siliciclastic strata preserved within a ~400 km segment of the NW Zagros fold-thrust belt and foreland basin in the Iraqi Kurdistan Region (IKR) provide a widespread record of exhumation and sedimentation. As a means of assessing NW Zagros foreland basin evolution and chronostratigraphy, we present coupled detrital zircon (DZ) U-Pb and (U-Th)/He geo-thermochronometric data of Upper Cretaceous to Pliocene siliciclastic strata from the Duhok, Erbil, and Suleimaniyah provinces of IKR. LA-ICP-MS U-Pb age analyses reveal that the foreland basin fill in IKR in general was dominantly derived from Pan-African/Arabian-Nubian, Peri-Gondwandan, Eurasian, and Cretaceous volcanic arc terrenes. However, the provenance of these strata varies systematically along strike and through time, with an overall increase in complexity upsection. DZ age distribution of Paleocene-Eocene strata is dominated by a ~95 Ma grain age population, likely sourced from the Late Cretaceous Hassanbag-Bitlis volcanic arc complex along the northern margin of Arabia. In contrast, DZ U-Pb age distributions of Neogene strata show a major contribution derived from various Eurasian (e.g., Iranian, Tauride, Pontide; ~45, 150, 300 Ma) and Pan-African (~550, 950 Ma) sources. The introduction of Eurasian DZ ages at the Paleogene-Neogene transition likely records the onset of Arabian-Eurasian collision. Along strike to the southeast, the DZ U-Pb spectra of Neogene strata show a decreased percentage of Pan-African, Peri-Gondwandan, Tauride, and Ordovician ages, coupled with a dramatic increase in 40-50 Ma DZ ages that correspond to Urumieh-Dokhtar magmatic rocks in Iran. Combined with paleocurrent data, this suggests that Neogene sediments were transported longitudinally southeastward through an unbroken foreland basin

  5. Provenance of eastern Magallanes foreland basin sediments: Mineralogical and geochemical analyses reveal Paleogene tectonic unroofing of the Fuegian Andes

    NASA Astrophysics Data System (ADS)

    Zahid, Khandaker

    Though southern South America and the Antarctic Peninsula were previously connected through a Paleozoic-Mesozoic subduction system on the western margin of Gondwana, this connection was tectonically disrupted in the Cenozoic by forming the Drake Passage in the Scotia Sea. Heavy mineral composition data from the eastern Magallanes basin of southernmost South America indicate that Campanian to middle Eocene sediments had a mafic/ophiolitic provenance which is interpreted as being derived from the Patagonian-Fuegian magmatic arc and the mafic floor of the preceding Rocas Verdes marginal basin. Upper middle Eocene to lower Miocene heavy minerals, on the other hand, indicate a metamorphic/metasedimentary provenance, which suggest being derived from the Cordillera Darwin metamorphic complex. While the rare earth element patterns of all of these samples are typical to those of average post-Archean upper continental crustal types, the younger middle-upper Eocene and lower Oligocene samples contain a higher concentration of the light REEs (LaN/SmN) ratio compared to the older upper Cretaceous to middle Eocene samples suggesting an eastern Andean metamorphic complex provenance for younger sediments. Trace elements plot of stratigraphically older samples exhibit a lower Th/Sc ratio compared to the younger samples suggesting a mafic origin. Nd isotope data show a shift in epsilonNd values from a less negative to a more negative value also during the middle to late Eocene. Together, these data indicate an abrupt shift in sediment provenance in middle to late Eocene time, thereby corroborating recent interpretations of the basin's detrital-zircon geochrononology and thermochronology, and providing further support for temporal and possibly genetic relationships between development of the Patagonian orocline, the opening of Drake Passage and the Oi-1 glaciation of Antarctica. Quantifying the relative abundance of different framework mineral components of sandstone is a common

  6. Using U-Pb Detrital Zircon to Identify Evolution of Sediment Drainage in the South Central Pyrenean Foreland Basin, Spain

    NASA Astrophysics Data System (ADS)

    Clark, J. D.; Stockli, D. F.; McKay, M. P.; Thomson, K.; Puigdefabregas, C.; Castelltort, S.; Dykstra, M.; Fildani, A.

    2014-12-01

    Until the 2011 Mw9.0 Tohoku earthquake, the role of earthquakes as agents of sediment dispersal and deposition at erosional trenches was largely under-appreciated. A series of cruises carried out after the 2011 event has revealed a variety of unsuspected sediment transport mechanisms, such as tsunami-triggered sheet turbidites, suggesting that great earthquakes may in fact be important agents for dispersing sediments across trench slopes. To complement these observational data, we have modeled the pathways of sediments across the trench slope based on bathymetric grids. Our approach assumes that transport direction is controlled by slope azimuth only, and ignores obstacles smaller than 0.6-1 km; these constraints are meant to approximate the behavior of turbidites. Results indicate that (1) most pathways issued from the upper slope terminate near the top of the small frontal wedge, and thus do not reach the trench axis; (2) in turn, sediments transported to the trench axis are likely derived from the small frontal wedge or from the subducting Pacific plate. These results are consistent with the stratigraphy imaged in seismic profiles, which reveals that the slope apron does not extend as far as the frontal wedge, and that the thickness of sediments at the trench axis is similar to that of the incoming Pacific plate. We further applied this modeling technique to the Cascadia, Nankai, Middle-America, and Sumatra trenches. Where well-defined canyons carve the trench slopes, sediments from the upper slope may routinely reach the trench axis (e.g., off Costa Rica and Cascadia). In turn, slope basins that are isolated from the canyons drainage systems must mainly accumulate locally-derived sediments. Therefore, their turbiditic infill may be diagnostic of seismic activity only - and not from storm or flood activity. If correct, this would make isolated slope basins ideal targets for paleoseismological investigation.

  7. The Cretaceous-Paleogene boundary in the shallow northeastern Mexican foreland basins: Evidence for paleoseismic liquefaction, tsunami deposition, and Chicxulub ejecta

    NASA Astrophysics Data System (ADS)

    Schulte, Peter; Smit, Jan; Deutsch, Alex; Friese, Andrea; Beichel, Kilian

    2010-05-01

    Understanding the depositional sequence and composition of impact ejecta is critical for the interpretation of timing and effects of the Chicxulub impact regarding the mass extinction at the Cretaceous-Paleogene (K-Pg) boundary. Preliminary investigations have shown that the shallow La Popa and Parras foreland basins in northeastern Mexico both feature outstanding and continuous 3D exposures of the Chicxulub ejecta-rich, K-Pg boundary event deposit (Lawton et al., 2005). The m-thick sand-siltstone interval directly underlying the ejecta-rich mass flows shows evidence of slumping and liquefaction, locally leading to complete disorganization and disruption of the pre-impact late Cretaceous sedimentary sequence. The subsequent ejecta-rich sequence consists of an up to one m-thick basal carbonate-rich bed that discontinuously fills a valley-like topography. Besides abundant silicic and carbonate ejecta spherules (up to 50%) that are excellently preserved, this bed includes abundant mollusks and gastropod shells, as well as vertebrate bones and teeth. The conglomeratic bed is overlain by a series of alternating fine- to medium grained calcareous sandstones with shell debris and ejecta that were deposited by repeated currents / mass flow events incorporating varying source areas. Hummocky-cross-stratified strata that mark the return to a normal out-shelf depositional regime conformably overly these sandstones. We interpret this sequence as evidence for presumably seismic-induced sediment liquefaction followed by a series of impact-related tsunami deposits. The specific depositional sequence and Fe-Mg-rich ejecta composition as well as the petrography of the sandstones all closely link the K-Pg boundary sequence in the La Popa and Parras basin to the well-known deep-water K-Pg sites in the Gulf of Mexico (e.g. El Mimbral; Smit et al., 1996; Schulte and Kontny, 2005). Lawton, T.F., et al., 2005, Geology, v. 33, p. 81-84. Smit, J. et al., 1996, GSA Special Paper v. 307, p

  8. Biostratigraphy and sedimentology of the Fluviatile Untere Serie (Early and Middle Miocene) in the central part of the North Alpine Foreland Basin: implications for palaeoenvironment and climate

    NASA Astrophysics Data System (ADS)

    Prieto, J.; Böhme, M.; Maurer, H.; Heissig, K.; Abdul Aziz, H.

    2009-10-01

    The Early to Middle Miocene Fluviatile Untere Serie lithostratigraphic unit of the Upper Freshwater Molasse (UFM) in the North Alpine Foreland Basin (NAFB) crops out in a 40 m long section at Untereichen-Altenstadt (central part of the NAFB). This section yields a unique superposition of two vertebrate assemblages belonging to different biostratigraphic units: early part OSM C + D (Karpatian) and OSM E (Early Badenian). Detailed taxonomic analyses reveal different diversity patterns in the two assemblages. Nine small mammal and six ectothermic vertebrate taxa occur in the older level UA 540 m, while 20 small mammal and 23 ectothermic vertebrate taxa are recorded for the younger level UA 565 m. From the latter locality comes a small-sized representative of the biostratigraphically significant Megacricetodon lappi lineage. This evolutionary level has not been documented previously for the eastern part of the NAFB. Bioclimatic analysis combined with lithofacies and architectural element analysis indicates that significant changes in the fluvial sedimentation style, surface-water runoff and tectonics occurred between the Early Karpatian and Early Badenian. A meandering fluvial system (marly unit) is erosively overlain by sandy braided river deposits (sandy unit). Overbank deposits of the marly unit revealed that the older vertebrate fossil assemblage (UA 540 m) is deposited in an animal burrow that was presumably produced by owls. Both reptilian and mammalian taxa are indicative of a relatively open environment and dry, probably semi-arid climate. Conversely, vertebrates from the sandy unit (UA 565 m), which are accumulated in channel fill deposits, suggest closed as well as open habitats with a subtropical humid climate and mean annual rainfall of about 1,000 mm. According to the sequence stratigraphic analysis the marly unit is interpreted as a highstand-system-tract of the TB 2.2 global 3rd order sequence. The new results add support to the hypothesis that the

  9. Possible continuous-type (unconventional) gas accumulation in the Lower Silurian "Clinton" sands, Medina Group and Tuscarora Sandstone in the Appalachian Basin; a progress report of the 1995 project activities

    USGS Publications Warehouse

    Ryder, Robert T.; Aggen, Kerry L.; Hettinger, Robert D.; Law, Ben E.; Miller, John J.; Nuccio, Vito F.; Perry, William J.; Prensky, Stephen E.; Filipo, John J.; Wandrey, Craig J.

    1996-01-01

    INTRODUCTION: In the U.S. Geological Survey's (USGS) 1995 National Assessment of United States oil and gas resources (Gautier and others, 1995), the Appalachian basin was estimated to have, at a mean value, about 61 trillion cubic feet (TCF) of recoverable gas in sandstone and shale reservoirs of Paleozoic age. Approximately one-half of this gas resource is estimated to reside in a regionally extensive, continuous-type gas accumulation whose reservoirs consist of low-permeability sandstone of the Lower Silurian 'Clinton' sands and Medina Group (Gautier and others, 1995; Ryder, 1995). Recognizing the importance of this large regional gas accumulation for future energy considerations, the USGS initiated in January 1995 a multi-year study to evaluate the nature, distribution, and origin of natural gas in the 'Clinton' sands, Medina Group sandstones, and equivalent Tuscarora Sandstone. The project is part of a larger natural gas project, Continuous Gas Accumulations in Sandstones and Carbonates, coordinated in FY1995 by Ben E. Law and Jennie L. Ridgley, USGS, Denver. Approximately 2.6 man years were devoted to the Clinton/Medina project in FY1995. A continuous-type gas accumulation, referred to in the project, is a new term introduced by Schmoker (1995a) to identify those natural gas accumulations whose reservoirs are charged throughout with gas over a large area and whose entrapment does not involve a downdip gas-water contact. Gas in these accumulations is located downdip of the water column and, thus, is the reverse of conventional-type hydrocarbon accumulations. Commonly used industry terms that are more or less synonymous with continuous-type gas accumulations include basin- centered gas accumulation (Rose and others, 1984; Law and Spencer, 1993), tight (low-permeability) gas reservoir (Spencer, 1989; Law and others, 1989; Perry, 1994), and deep basin gas (Masters, 1979, 1984). The realization that undiscovered gas in Lower Silurian sandstone reservoirs of the

  10. Late Mesozoic and Cenozoic thermotectonic evolution of the central Brooks Range and adjacent North Slope foreland basin, Alaska: Including fission track results from the Trans-Alaska Crustal Transect (TACT)

    USGS Publications Warehouse

    O'Sullivan, P. B.; Murphy, J.M.; Blythe, A.E.

    1997-01-01

    Apatite fission track data are used to evaluate the thermal and tectonic history of the central Brooks Range and the North Slope foreland basin in northern Alaska along the northern leg of the Trans-Alaska Crustal Transect (TACT). Fission track analyses of the detrital apatite grains in most sedimentary units resolve the timing of structures and denudation within the Brooks Range, ranging in scale from the entire mountain range to relatively small-scale folds and faults. Interpretation of the results indicates that rocks exposed within the central Brooks Range cooled rapidly from paleotemperatures 110?? to 50??C during discrete episodes at ???100??5 Ma, ???60??4 Ma, and ???24??3 Ma, probably in response to kilometer-scale denudation. North of the mountain front, rocks in the southern half of the foreland basin were exposed to maximum paleotemperatures 110??C in the Late Cretaceous to early Paleocene as a result of burial by Upper Jurassic and Cretaceous sedimentary rocks. Rapid cooling from these elevated paleotemperatures also occurred due to distinct episodes of kilometer-scale denudation at ???60??4 Ma, 46??3 Ma, 35??2 Ma, and ???24??3 Ma. Combined, the apatite analyses indicate that rocks exposed along the TACT line through the central Brooks Range and foreland basin experienced episodic rapid cooling throughout the Late Cretaceous and Cenozoic in response to at least three distinct kilometer-scale denudation events. Future models explaining orogenic events in northern Alaska must consider these new constraints from fission track thermochronology. Copyright 1997 by the American Geophysical Union.

  11. Analogue modeling of 3-D structural segmentation in fold-and-thrust belts: interactions between frictional and viscous provinces in foreland basins

    NASA Astrophysics Data System (ADS)

    Borderie, Sandra; Graveleau, Fabien; Witt, César; Vendeville, Bruno C.

    2016-04-01

    Accretionary wedges are generally segmented both across and along strike because of diverse factors including tectonic and stratigraphic inheritance. In fold-and-thrust belts, along-strike stratigraphic changes in the foreland sequence are classically observed and cause a curvature of the deformation front. Although the parameters controlling this curvature are well documented, the structural interactions and mutual influences between adjacent provinces are much less analyzed. To investigate this question, we deformed analogue models in a compressional box equipped with digital cameras and a topographic measurement apparatus. Models where shortened above a basal frictional detachment (glass microbeads) and segmentation was tested by having a region in which we added an interbedded viscous level (silicone polymer) within the sedimentary cover (dry sand). By changing the number (2 or 3) and the relative width of the purely frictional and viscous provinces, our goal was to characterize geometrically and kinematically the interactions between the viscous and the purely frictional provinces. We used a commercial geomodeller to generate 3-D geometrical models. The results indicate that regardless of the relative width of the purely frictional vs. viscous provinces, the deformation style in the frictional province is not influenced by the presence of the adjacent viscous province. On the contrary, the structural style and the deformation kinematics in the viscous province is significantly impacted by the presence or absence of an adjacent purely frictional province. At first order, the deformation style in the viscous province depends on its width, and three structural styles can be defined along strike. Far from the frictional area, structures are primarily of salt-massif type, and they do not seem to be influenced by the frictional wedge province. Towards the frictional province, deformation changes gradually to a zone of purely forethrusts (foreland verging), and

  12. From Source to Sink: Exhumation of the North America Cordillera Revealed by Multi-dating of Detrital Minerals from Upper Jurassic-Upper Cretaceous Sevier Foreland Basin

    NASA Astrophysics Data System (ADS)

    Painter, C. S.; Carrapa, B.; DeCelles, P. G.; Gehrels, G. E.; Thomson, S. N.

    2013-12-01

    We sampled twenty-two Late Jurassic to Late Cretaceous syn-orogenic conglomerate clasts in proximal units in the Sevier fold-thrust belt and their distal sandstone equivalents up to 300 km east of the thrust front, in Utah, Colorado, Wyoming, and South Dakota. To better constrain depositional ages, these samples were analyzed using detrital zircon U-Pb (DZ U-Pb) geochronology. To identify a thermochronometer that measures source exhumation in the North America Cordillera, both zircon (U-Th)/He and apatite fission track (AFT) thermochronology was utilized, on both the conglomerate cobbles and sandstone (detrital) samples. Eleven samples were analyzed with zircon (U-Th)/He; however, discordant ages in the conglomerate cobble samples suggest that this system was not fully reset and never experienced T> ~180 °C in the source stratigraphy during the Sevier orogeny. Eleven other samples are analyzed using apatite fission track thermochronology (AFT); AFT ages are generally similar or older than depositional ages indicating that the detrital ages record source exhumation signals, and that exhumation depth corresponds to T>~120 °C. In order to test whether or not the youngest cooling AFT age population represents a source exhumation signal or a co-magmatic signal we here performed double dating of the detrital AFT samples using apatite U-Pb thermochronology. Maximum depositional ages using DZ U-Pb match existing age controls on basin stratigraphy. Our study shows that AFT is an effective thermochronometer to detect source exhumation for Cretaceous foreland stratigraphy in the western U.S.A. Lag-times (i.e. the difference between the source exhumation age and depositional age) are ~0 to 5 Myr with relatively steady-state to slightly increasing exhumation rates suggesting orogenic growth at this time. The very short lag times also indicate limited to no storage time between source and sink. The AFT lag time of the Early Cretaceous Kelvin Formation is ~5 Myr and represents

  13. Correlation of aptian-albian carbon isotope excursions in continental strata of the cretaceous Foreland Basin, Eastern Utah, U.S.A.

    USGS Publications Warehouse

    Ludvigson, Greg A.; Joeckel, R.M.; Gonzalez, Luis A.; Gulbranson, E.L.; Rasbury, E.T.; Hunt, G.J.; Kirkland, J.I.; Madsen, S.

    2010-01-01

    Nodular carbonates ("calcretes") in continental foreland-basin strata of the Early Cretaceous Cedar Mountain Formation (CMF) in eastern Utah yield ??13C and ??O records of changes in the exogenic carbon cycle related to oceanic anoxic events (OAEs), and terrestrial paleoclimate. Chemostratigraphic profiles of both forebulge and foredeep sections show two prominent positive ??13C excursions, each with a peak value of -3% VPDB, and having background ??13C values of about -6% VPDB. These excursions correlate with the global early Aptian (Ap7) and late Aptian-early Albian (Apl2-All) carbon isotope excursions. Aptian-Albian positive ??13C excursions in the CMF also correspond to 3-4 per mil increases in carbonate ??18O. These phenomena record local aridification events. The chemostratigraphic profile on the thinner forebulge section of the CMF is calibrated, for the first time, by a radiogenic U-Pb date of 119.4 ?? 2.6 Ma on a carbonate bed, and by detrital zircon U-Pb dates on two bounding sandstone units (maximum depositional ages of 146 Ma and 112 Ma). P??trographie observations and diagenetic analyses of micritic to microsparitic carbonates from nodules indicate palustrine origins and demonstrate that they crystallized in shallow early meteoric phreatic environments. Meteoric calcite lines derived from CMF carbonates have ??18O values ranging between -8.1 to -7.5%o VPDB, supporting an estimate of zonal mean groundwater ??18O of -6% VSMOW for an Aptian-Albian paleolatitude of 34?? N. Furthermore, our two chemostratigraphic profiles exhibit a generally proportionate thinning of correlative strata from the foredeep on to the forebulge, suggesting that there were consistently lower rates of accumulation on the forebulge during the Aptian-Albian. Identification of the global Aptian-Albian ??13C excursions in purely continental strata, as demonstrated in this paper, opens a new avenue of research by identifying specific stratigraphie intervals that record the terrestrial

  14. Integrated analysis for constraining palaeoclimatic and volcanic influences on clay-mineral assemblages in orogenic basins (Palaeogene Andean foreland, Northwestern Argentina)

    NASA Astrophysics Data System (ADS)

    Do Campo, Margarita; del Papa, Cecilia; Nieto, Fernando; Hongn, Fernando; Petrinovic, Ivan

    2010-07-01

    Variations in clay-mineral assemblages in ancient continental deposits are frequently used to reconstruct past climate changes. In active settings, volcanic events can supply highly labile volcaniclastic material, which can easily be transformed into smectite via diagenesis, which can produce a noticeable footprint in clay-mineral assemblages. Southern Central Andean foreland deposits are appropriate case studies to ascertain whether the climatic signal was preserved in the clay assemblages of their fine-grained sediments as tectonic uplift, volcanism, and sedimentation have been interacting since the Cretaceous. We have studied a 1400-m-thick coarsening-upward Palaeogene succession of the Tin Tin basin (northern Calchaquí Valley, Argentina), applying X-ray diffraction (XRD), electron microscopy, and detailed sedimentary facies analysis with the aim of comparing tendencies in the vertical fluctuations of clay minerals with evidence from sedimentological facies. Illite-muscovite plus smectite account for 78% to 100% of the clay minerals in the fine fraction, with kaolinite and chlorite in subordinate amounts. The vertical variation of sedimentary settings from an overbank/lacustrine domain to fluvial braided plains and an aeolian dune field suggests a gradual increase in aridity upsection. However, smectite abundances do not show a gradual decreasing trend compatible with progressively lower hydrolyzing conditions; their relative abundances vary widely throughout the section, depicting pulse-like, abrupt fluctuations. Despite the absence of field evidence for volcanic influence, several indications of volcanic and volcaniclastic material have been found under scanning electron microscopy (SEM) in levels with high smectite abundances from the middle to the top of the succession. They include quartz crystals showing embayments and skeletal forms, with smectite filling the voids, microcrystalline silica, as well as heulandite crystals in close association with

  15. Forward modeling of the southern Apennines foreland

    SciTech Connect

    Endignoux, L.; Moretti, I.; Roure, F.

    1988-08-01

    Thrust belts and foreland areas are characterized by a fluxural depression lying between the subducting lithospheric plate and the topographic surface. This depression is continuously filled with tectonic units (accretionary prism) and synorogenic deposits (foredeep basin). Internal geometry of this wedge evolves continuously through time in response to the progressive migration of the deformation toward the foreland, simultaneous erosion of tectonized units, and redeposition of reworked materials in piggy-back basins and foredeep. We use forward modeling to reconstruct the successive geometries of a geological section across the southern Apennines. Results are discussed in the light of regional constraints, which favor basement-involved structures at depth. Amounts of shortening are calculated using two opposite hypotheses: thin-skinned vs. basement-involved tectonics. Effects of erosion and evolution of piggy-back basins are also taken into account.

  16. Silurian pinnacle reef distribution in Illinois: model for hydrocarbon exploration

    SciTech Connect

    Whitaker, S.T.

    1987-09-01

    Approximately 92 million bbl of oil have been produced in Illinois from buried Silurian pinnacle reefs and from younger strata draped over these reefs. Better understanding of Silurian reef distribution and the use of appropriate exploration methods should lead to the discovery of new reef-associated hydrocarbon reserves. Evidence presented in this study suggest that Silurian pinnacle reef development was not limited to hinge-line trend around a subsiding basin center. Instead, isolated reefs grew through most of Illinois along a broad ramp dipping gently southeastward under a relatively shallow sea that opened to the south during the Silurian. Uplift of the Wabash platform in Indiana enabled concurrent pinnacle reef development along its flanks and formed the Fort Wayne and Terre Haute banks. These reef banks merged with and extended the scattered trends in Illinois. Erosion of Silurian strata prior to the Middle Devonian, particularly along the emerging Sangamon arch, removed or reduced the pinnacle reef structures across much of the central Illinois. These reef remnants are not easily detected by exploration methods commonly used in the basin, yet they can be oil-productive. Applications of geophysical and detailed lithologic surveys can greatly enhance the ability to locate these reefs.

  17. A Silurian sea spider.

    PubMed

    Siveter, Derek J; Sutton, Mark D; Briggs, Derek E G; Siveter, David J

    2004-10-21

    Pycnogonids (sea spiders) are marine arthropods numbering some 1,160 extant species. They are globally distributed in depths of up to 6,000 metres, and locally abundant; however, their typically delicate form and non-biomineralized cuticle has resulted in an extremely sparse fossil record that is not accepted universally. There are two opposing views of their phylogenetic position: either within Chelicerata as sister group to the euchelicerates, or as a sister taxon to all other euarthropods. The Silurian Herefordshire Konservat-Lagerstatte in England (approximately 425 million years (Myr) bp) yields exceptionally preserved three-dimensional fossils that provide unrivalled insights into the palaeobiology of a variety of invertebrates. The fossils are preserved as calcitic void in-fills in carbonate concretions within a volcaniclastic horizon, and are reconstructed digitally. Here we describe a new pycnogonid from this deposit, which is the oldest adult sea spider by approximately 35 Myr and the most completely known fossil species. The large chelate first appendage is consistent with a chelicerate affinity for the pycnogonids. Cladistic analyses place the new species near the base of the pycnogonid crown group, implying that the latter had arisen by the Silurian period.

  18. Composition of natural gas and crude oil produced from 10 wells in the Lower Silurian "Clinton" Sandstone, Trumbull County, Ohio: Chapter G.7 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

    USGS Publications Warehouse

    Burruss, Robert A.; Ryder, Robert T.; Ruppert, Leslie F.; Ryder, Robert T.

    2014-01-01

    Natural gases and associated crude oils in the “Clinton” sandstone, Medina Group sandstones, and equivalent Tuscarora Sandstone in the northern Appalachian basin are part of a regional, continuous-type or basin-centered accumulation. The origin of the hydrocarbon charge to regional continuoustype accumulations is poorly understood. We have analyzed the molecular and stable isotopic composition of gases and oils produced from 10 wells in the “Clinton” sandstone in Trumbull County, Ohio, in an initial attempt to identify the characteristics of the accumulated fluids. The analyses show that the fluids have remarkably uniform compositions that are similar to previously published analyses of oils (Cole and others, 1987) and gases (Laughrey and Baldasarre, 1998) in Early Silurian reservoirs elsewhere in Ohio; however, geochemical parameters in the oils and gases suggest that the fluids have experienced higher levels of thermal stress than the present-day burial conditions of the reservoir rocks. The crude oils have an unusual geochemical characteristic: they do not contain detectable levels of sterane and triterpane biomarkers. The origin of these absences is unknown.

  19. Inner vs. outer wedge-top depozone "sequences" in the Late Miocene (late Tortonian-early Messinian) Sicilian Foreland Basin System; new data from the Terravecchia Formation of NW Sicily

    NASA Astrophysics Data System (ADS)

    Gugliotta, C.

    2012-04-01

    The wedge-top depozone belongs to the innermost portion of a Foreland Basin System (FBS) (DeCelles and Giles, 1996) and includes all sediments, typically coarse-grained proximal facies, that bury the active frontal part of a fold and thrust belt. The Terravecchia Formation (Flores, 1959; Schmidt Di Friedberg, 1962, 1964-1965; Catalano, 1979) is a composite lithostratigraphic unit widespread in Sicily (southern Italy) which has been recently considered (Gugliotta, 2010) as a part of the stratigraphic record of the Late Miocene (late Tortonian to early Messinian) Sicilian wedge-top depozone and represent the main object of this paper. Two end-member wedge-top "sequences" the (i) the inner wedge-top sequence (IWS) and (ii) the outer wedge-top sequence (OWS), respectively, were recognized in the Terravecchia Formation outcropping in different sectors of NW Sicily and here described and compared on the base of both their depositional and deformative pattern. The differences existing between the IWS and OWS clearly reflect the tectono-depositional evolution of sedimentary basins located at different position across the wedge-top depozone. The more coarse grained and IWS was deposited filling narrow and often oversupplied basins located in the inner sectors of the wedge-top depozone. In these basins the sedimentary evolution has been strongly controlled by a syn-sedimentary transpressional tectonics which produced, since the late Tortonian, the development of "local scale" intraformational angular unconformities. Contemporaneously, the more fine-grained OWS was deposited filling relatively wide and mainly shallow-water marine basins, probably open to major marine areas, located in a less external position of the wedge-top depozone. In these external areas during the late Tortonian-early Messinian the transpressional tectonics was active but still confined to the deeper structural layers producing long wavelength deformation and "basin-scale" unconformities. Integrating

  20. Sichuan Basin and beyond: Eastward foreland growth of the Tibetan Plateau from an integration of Late Cretaceous-Cenozoic fission track and (U-Th)/He ages of the eastern Tibetan Plateau, Qinling, and Daba Shan

    NASA Astrophysics Data System (ADS)

    Yang, Zhao; Shen, Chuanbo; Ratschbacher, Lothar; Enkelmann, Eva; Jonckheere, Raymond; Wauschkuhn, Bastian; Dong, Yunpeng

    2017-06-01

    Combining 121 new fission track and (U-Th)/He ages with published thermochronologic data, we investigate the Late Cretaceous-Cenozoic exhumation/cooling history of the eastern Tibetan Plateau, Qinling, Daba Shan, and Sichuan Basin of east central China. The Qinling orogen shows terminal southwestward foreland growth in the northern Daba Shan thrust belt at 100-90 Ma and in the southern Daba Shan fold belt at 85-70 Ma. The eastern margin of Tibetan Plateau experienced major exhumation phases at 70-40 Ma (exhumation rate 0.05-0.08 mm/yr), 25-15 Ma (≤1 mm/yr in the Pengguan Massif; 0.2 mm/yr in the imbricated western Sichuan Basin), and since 11-10 Ma along the Longmen Shan ( 0.80 mm/yr) and the interior of the eastern Tibetan Plateau (Dadu River gorge, Min Shan; 0.50 mm/yr). The Sichuan Basin records two basin-wide denudation phases, likely a result of the reorganization of the upper Yangtze River drainage system. The first phase commenced at 45 Ma and probably ended before the Miocene; >1 km of rocks were eroded from the central and eastern Sichuan Basin. The second phase commenced at 12 Ma and denudated the central Sichuan Basin, Longmen Shan, and southern Daba Shan; more than 2 km of rocks were eroded after the lower Yangtze River had cut through the Three Gorges and captured the Sichuan Basin drainage. In contrast to the East Qinling, which was weakly effected by late Cenozoic exhumation, the West Qinling and Daba Shan have experienced rapid exhumation/cooling since 15-13 Ma, a result of growth of the Tibetan Plateau beyond the Sichuan Basin.

  1. Combined Sm-Nd and Lu-Hf dating of garnets from the Putomayo foreland basin in south-central Colombia and implications

    NASA Astrophysics Data System (ADS)

    Bloch, E. M.; Ibanez-mejia, M.; Ganguly, J.

    2013-12-01

    Garnet-whole rock (Grt-WR) ages of metapelites determined by the Lu-Hf decay system are almost always older than those determined by the Sm-Nd system. Unambiguous interpretation of the observed age differences has been hindered by a lack of adequate information about grain size, diffusion data for Hf in garnet, and in many cases about peak metamorphic conditions and cooling rates, all of which affect the closure temperatures of these decay systems. As part of a broader study on basement rocks from the Andean Putomayo foreland basin in south-central Colombia, we have determined the Lu-Hf and Sm-Nd Grt-WR ages of these rocks using painstakingly handpicked garnets of ~50 μm radius, and obtained ages of 1070 × 5.6 and 1007 × 2.9 Ma, respectively. By modeling the retrograde Fe-Mg zoning in garnet adjacent to biotite according to an asymptotic cooling model (1/T = 1/To + ηt) with the diffusion data from [1], an initial cooling rate of ~2-5 °C/Ma is obtained independently of the geochronological data; peak P-T conditions of ~8 kb, 675 °C are imposed by garnet-orthopyroxene thermobarometry. Using the above data in conjunction with the Nd diffusion data from [2] and Hf diffusion data from our recent study, we obtain closure temperatures for the Lu-Hf and Sm-Nd decay systems in garnet of ~545-565 °C and 415-430 °C, respectively. Results from analytical solutions [3, 4] and a more flexible numerical method are found to be in good agreement with one another. The calculated difference of closure temperatures predicts a difference of ~105-40 Ma between the ages determined by the two decay systems, as compared to the observed age difference of 63 × 6 Ma. The predicted peak metamorphic age derived from the measured and calculated resetting ages of the two decay systems is between ~1030 and 1185 Ma, as compared to the Lu-Hf age of 1070 ×1.9 Ma; we are currently working to obtain U-Pb zircon ages to better constrain this peak metamorphic age. In calculating these results

  2. Power-law Scaling of Fracture Aperture Sizes in Otherwise-Undeformed Foreland Basin Sandstone: An Example From the Cozzette Sandstone, Piceance Basin, Colorado

    NASA Astrophysics Data System (ADS)

    Hooker, J. N.; Gale, J. F.; Laubach, S. E.; Gomez, L. A.; Marrett, R.; Reed, R. M.

    2007-12-01

    Power-law variation of aperture size with cumulative frequency has been documented in vein arrays, but such patterns have not been conclusively demonstrated from open or incompletely mineralized opening-mode fractures (joints) in otherwise-undeformed sedimentary rocks. We used subhorizontal core from the nearly flat- lying Cretaceous Cozzette Sandstone, Piceance Basin, Colorado, to document fracture aperture sizes over five orders of magnitude. We measured microfractures (0.0004-0.1164 mm in aperture) along a 276-mm-long scanline using scanning electron microscope-based cathodoluminescence; we measured macrofractures (0.5- 2.15 mm in aperture) in 35 m of approximately horizontal core cut normal to fracture strike. Microfractures are typically filled with quartz. Macrofractures are mostly open and resemble non-mineralized joints, except for thin veneers of quartz cement lining their walls. Micro- and macrofractures share both a common orientation and the same timing with respect to diagenetic sequence, only differing in size and the degree to which they are filled with quartz cement. Power-law scaling equations were derived by fitting trendlines to aperture vs. cumulative frequency data for the microfractures. These equations successfully predicted the cumulative frequencies of the macrofractures, accurate to within a factor of four in each test and within a factor of two in 75 percent of tests. Our results show that tectonic deformation is not prerequisite for power-law scaling of fractures, but instead suggest that scaling emerges from fracture interaction during propagation.

  3. Ground-water quality in the eastern part of the Silurian-Devonian and upper Carbonate aquifers in the eastern Iowa basins, Iowa and Minnesota, 1996

    USGS Publications Warehouse

    Savoca, Mark E.; Sadorf, Eric M.; Akers, Kymm K.B.

    1999-01-01

    The presence of regional confining units and thick overlying Quaternary-age deposits have an effect on water quality in the Silurian-Devonian and Upper Carbonate aquifers in the study area. Tritium-based ground-water ages were significantly older, and dissolved-solids concentrations were significantly higher in relatively well protected areas (where the aquifers are overlain by a bedrock confining unit or more than 100 feet of Quaternary-age deposits). Ammonia concentrations were significantly higher in relatively well protected areas and in samples from wells that produced older water. Higher ammonia concentrations also were observed in ground water with dissolved-oxygen concentrations of 0.5 milligram per liter or less, allowing for the anaerobic reduction of nitrate to ammonia. Nitrate concentrations were significantly higher in relatively poorly protected areas (where the aquifers are not overlain by a bedrock confining unit or are overlain by less than 100 feet of Quaternaryage deposits) and in samples from wells that produced recently recharged water. Pesticide and metabolite concentrations were significantly higher in samples from wells that produced recently recharged water. Atrazine, metolachlor, and deethylatrazine were not detected in any samples from relatively well protected areas of the aquifers.

  4. Tectonically induced climate and its control on the distribution of depositional systems in a continental foreland basin, Cloverly and Lakota Formations (Lower Cretaceous) of Wyoming, U.S.A.

    NASA Astrophysics Data System (ADS)

    Elliott, William S.; Suttner, Lee J.; Pratt, Lisa M.

    2007-12-01

    Continental sediments of the Cloverly and Lakota Formations (Lower Cretaceous) in Wyoming are subdivided into three depositional systems: perennial to intermittent alluvial, intermittent to ephemeral alluvial, and playa. Chert-bearing sandstones, conglomerates, carbonaceous mudrocks, blocky mudrocks, and skeletal limestones were deposited by perennial to intermittent alluvial systems. Carbonaceous mudrocks contain abundant wood fragments, cuticle and cortical debris, and other vascular plant remains representing deposition in oxbow lakes, abandoned channels, and on floodplains under humid to seasonal conditions. Intraformational conglomerates, sandstones, bioturbated and blocky mudrocks with caliche nodules, and bioturbated limestones characterize deposition in intermittent to ephemeral alluvial systems. Bioturbated limestones are encased in bioturbated mudrocks with abundant pseudo-slickensides. The presence of caliche nodules in some of the blocky to bioturbated mudrocks is consistent with supersaturation and precipitation of calcium carbonate from groundwater under semi-arid conditions. Caliche nodules, pseudo-slickensides, and carbonate-rich floodplain sediments are interpreted to have been deposited by intermittent to ephemeral alluvial systems under seasonal to semi-arid climatic conditions. Laminated mudrocks, siltstones, vuggy carbonates, bedded to nodular evaporites, pebbly mudrocks, and diamictites were deposited in evaporative alkaline lakes or playas. Pebbly mudrocks and diamictites are interpreted to represent deposition from channelized and unchannelized hyperconcentrated flows on a playa, resulting from intense rain events within the basin. The areal abundance and distribution of these depositional systems change systematically across the overfilled portion of the Early Cretaceous Cordilleran foreland basin in Wyoming. The lower part (A-interval) of the Cloverly and Lakota Formations is characterized by deposits of perennial to intermittent rivers

  5. Applications of molecular analysis for the study of early land plant evolution during the upper Silurian - Lower Devonian: borehole M.G.1, Ghadamis Basin, southern Tunisia, North Africa

    NASA Astrophysics Data System (ADS)

    Romero, M. F.; Vecoli, M.; Riboulleau, A.; Versteegh, G.

    2009-04-01

    in the palynofacies of all sampling levels. REFERENCES [1]Spina, A., Vecoli, M., 2008. Palynostratigraphy and miospore biodiversity dynamics across the Silurian-Devonian boundary in North Africa (Ghadamis Basin, southern Tunisia). Geophysical Research Abstracts, Vol. 10, EGU2008-A-09147. [2]Grice, K., Backhouse, J., Alexander, R., Marshall, N., Logan, G., 2005. Correlating terrestrial signatures from biomarker distributions, 13C, and palynology in fluvio-deltaic deposits from NW Australia (Triassic - Jurassic). Organic Geochemistry 36, 1347 - 1358. [3]Ellis, L., Singh, R., Alexander, R., Kagi, R., 1996. Formation of isohexyl alkylaromatic hydrocarbons from aromatization-rearrangement of terpenoids in the sedimentary environment: A new class of biomarker. Geochimica and Cosmochimica Acta. Vol. 60, No. 23. 4747 - 4763. [4]Van Aarssen, B., Alexander, R., Kagi, R., 2000. Higher plant biomarkers reflect palaeovegetation changes during Jurassic times. Geochimica and Cosmochimica Acta. Vol. 64, No. 8. 1417 - 1424. [5]Wen, Z., Ruiyong, W., Radke, M., Qingyu, W., Guoying, S., Zhili, L., 2000. Retene in pyrolysates of algal and bacterial organic matter. Organic Geochemistry 31, 757 - 762.

  6. Late Miocene-Pleistocene evolution of India-Eurasia convergence partitioning between the Bhutan Himalaya and the Shillong Plateau: New evidences from foreland basin deposits along the Dungsam Chu section, eastern Bhutan

    NASA Astrophysics Data System (ADS)

    Coutand, Isabelle; Barrier, Laurie; Govin, Gwladys; Grujic, Djordje; Hoorn, Carina; Dupont-Nivet, Guillaume; Najman, Yani

    2016-12-01

    The Shillong Plateau is a unique basement-cored uplift in the foreland of the eastern Himalaya that accommodates part of the India-Eurasia convergence since the late Miocene. It was uplifted in the late Pliocene to 1600 m, potentially inducing regional climatic perturbations by orographically condensing part of the Indian Summer Monsoon (ISM) precipitations along its southern flank. As such, the eastern Himalaya-Shillong Plateau-ISM is suited to investigate effects of tectonics, climate, and erosion in a mountain range-broken foreland system. This study focuses on a 2200 m thick sedimentary section of the Siwalik Group strategically located in the lee of the Shillong Plateau along the Dungsam Chu at the front of the eastern Bhutan Himalaya. We have performed magnetostratigraphy constrained by vitrinite reflectance and detrital apatite fission track dating, combined with sedimentological and palynological analyses. We show that (1) the section was deposited between 7 and 1 Ma in a marginal marine deltaic transitioning into continental environment after 5 Ma, (2) depositional environments and paleoclimate were humid with no major change during the depositional period indicating that the orographic effect of the Shillong Plateau had an unexpected limited impact on the paleoclimate of the Bhutanese foothills, and (3) the diminution of the flexural subsidence in the basin and/or of the detrital input from the range is attributable to a slowdown of the displacement rates along the Main Boundary Thrust in eastern Bhutan during the latest Miocene-Pleistocene, in response to increasing partitioning of the India-Eurasia convergence into the active faults bounding the Shillong Plateau.

  7. Similarities between Silurian and Cenozoic basalts in rock-magnetic properties and its implication for Silurian paleogeography

    NASA Astrophysics Data System (ADS)

    Schnabl, P.; Pruner, P.; Cajz, V.; Tasaryova, Z.; Cizkova, K.; Kletetschka, G.

    2013-05-01

    We compare two groups of basalts produced in similar conditions of environment, but significantly different in age. The younger ones represent the Ústí Fm. volcanics of the České stredohorí Mts., situated inside the Eger Graben; and the others are developed in Silurian of the Prague Basin (Barrandian). Rocks of both groups were usually produced into the wet environs. Hyaloclastite are commonly observable rocks, documenting the environment in the time of their origin. We suppose similar primary composition of magnetic carriers because both groups represent the same petrologic type. The only difference is in their age - during the time, some secondary changes on magnetic carriers could take place. The set of Cenozoic basalts consists of 292 samples (23 locations) and the Silurian set includes 485 samples (32 locations). For the comparison, we have used magnetomineralogical properties like natural remanent magnetization (NRM; Silurian 1.1±3.8 A/m, Cenozoic 2.0±2.1 A/m) , magnetic susceptibility (MS; Silurian 7.0±16.1 x10-3SI, Cenozoic 24.4±11.5 x10-3SI), unblocking temperature (UT; Silurian 200-580°C, Cenozoic 150-580°C), mean destructive field (MDF; Silurian 4-58 mT, Cenozoic 3-60 mT), Königsberger 's parameter Q (Silurian 3.93, Cenozoic 2.05) and K-parameter (precision parameter coming from Fisher statistics; Silurian7-102, Cenozoic14-643). NRM reflects the quantity of ferromagnetic minerals; MS represents total amount of paramagnetic and ferromagnetic minerals; UT is the temperature of the steepest decrease of demagnetisation curve and it is close to transition between para- and ferromagnetic behaviour; MDF represents stability character of NRM during alternating field demagnetization when 50% of initial value is reached; Q-parameter is the ratio of the remanent magnetization to the induced magnetization (product of susceptibility and the Earth's magnetic field strength - a large Q-value indicates that the magnetic material will tend to maintain

  8. Erosion of the French Alpine foreland controlled by crustal thickening

    NASA Astrophysics Data System (ADS)

    Schwartz, Stéphane; Gautheron, Cécile; Audin, Laurence; Nomade, Jérôme; Dumont, Thierry; Barbarand, Jocelyn; Pinna-Jamme, Rosella; van der Beek, Peter

    2017-04-01

    In alpine-type collision belts, deformation of the foreland may occur as a result of forward propagation of thrusting and is generally associated with thin-skinned deformation mobilizing the sedimentary cover in fold-and-thrust belts. Locally, foreland deformation can involve crustal-scale thrusting and produce large-scale exhumation of crystalline basement resulting in significant relief generation. In this study, we investigate the burial and exhumation history of Tertiary flexural basins located in the western Alpine foreland, at the front of the Digne thrust-sheet (SE France), using low-temperature apatite fission-track (AFT) and (U-Th)/He (AHe) thermochronology. Based on the occurrence of partially to totally reset apatite grain ages, we document 3.3 to 4.0 km burial of these basins remnants between 12-6 Ma, related to thin-skinned thrust-sheet emplacement without major relief generation. The onset of exhumation is dated at 6 Ma and is linked to erosion associated with subsequent relief development. This evolution does not appear controlled by major climate changes (Messinian crisis) or by European slab breakoff. Rather, we propose that the erosional history of the Digne thrust-sheet corresponds to basement involvement in foreland deformation, leading to crustal thickening and the incipient formation of a new external crystalline massif. Our study highlights the control of deep-crustal tectonic processes on foreland relief development and its erosional response at mountain fronts.

  9. Horizontal compression and a mechanical interpretation of Wyoming foreland deformation

    SciTech Connect

    Scheevel, J.R.

    1983-08-01

    If the basement fault-controlled style of deformation in the Wyoming foreland is dominated by elastic response of the upper lithosphere, and the deformation in the foreland is genetically linked to the horizontal compression characteristic of the thin-skinned thrust belt to the west, then concepts of continuum mechanics can be combined with results of experimental rock mechanics to suggest the following. (1) Basement faults initiate at the basement surface, propagate downward at an approximate 35/sup 0/ dip, and die at a depth dependent upon the magnitude of elastic shortening. Displacement on these faults necessarily decreases with depth. The faults are not expected to be appreciably curved in cross section. (2) Foreland structures develop early as fault-cored folds of small amplitude (< 1,500 m, 4,900 ft), with selected ones developing to large amplitudes (up to 13,000 m, 43,000 ft). Regions where the entire lithosphere has not failed (early stage) show only small-scale structures (e.g., Colorado Plateau), whereas regions where the lithosphere has experienced through-going failure will show small intra-basinal structures (early) isolated by more widely spaced large basin-margin structures (late). This biomodal size distribution of structures is present in the Wyoming foreland. In this study, horizontal compression as a sole causal mechanism can be combined with accepted mechanical concepts to produce a plausible model which adequately explains the regional features of Wyoming foreland deformation.

  10. Quantifying retro-foreland evolution in the Eastern Pyrenees.

    NASA Astrophysics Data System (ADS)

    Grool, Arjan R.; Ford, Mary; Huismans, Ritske S.

    2015-04-01

    The northern Pyrenees form the retro-foreland of the Pyrenean orogen. Modelling studies show that retro-forelands have several contrasting characteristics compared to pro-forelands: They tend to show a constant tectonic subsidence during the growth phase of an orogen, and no tectonic subsidence during the steady-state phase. Retro-forelands are also not displaced into the core of the orogen once the steady state phase is achieved. This means they tend to preserve the subsidence history from the growth phase of the orogen, but little or no history from the steady state phase. The northeastern Pyrenees (Carcassonne high) are a good location to test these characteristics against real-world data, because syn-orogenic sediments are preserved and the lack of postrift thermal subsidence and Triassic salt reduce complicating factors. In order to test the model, quantification of the following parameters is needed: Timing, amount and distribution of deformation, subsidence and sedimentation. We use subsurface, field, map and literature data to construct 2 balanced and restored cross sections through the eastern north Pyrenean foreland, stretching from the Montagne Noire in the north, to the Axial Zone in the south. We will link this to published thermochronology data to further constrain the evolution of the retro-foreland and investigate the link with the Axial Zone towards the south. We will quantify subsidence, deformation and sedimentation and link them to exhumation phases in the North Pyrenean Zone (NPZ) and the Axial Zone. The north Pyrenean retro-foreland is divided into two parts: the external foreland basin (Aquitaine basin) to the north and the North Pyrenean Zone to the south, separated by the North Pyrenean Frontal Thrust (NPFT). South of the NPZ lies the Axial Zone, separated from the retro-foreland by the North Pyrenean Fault which is believed to be the suture between Iberia and Europe. The NPFT was the breakaway fault on the European continent during the

  11. The cosmogenic record of mountain erosion transmitted across a foreland basin: Source-to-sink analysis of in situ10Be, 26Al and 21Ne in sediment of the Po river catchment

    NASA Astrophysics Data System (ADS)

    Wittmann, Hella; Malusà, Marco G.; Resentini, Alberto; Garzanti, Eduardo; Niedermann, Samuel

    2016-10-01

    We analyze the source-to-sink variations of in situ10Be, 26Al and 21Ne concentrations in modern sediment of the Po river catchment, from Alpine, Apennine, floodplain, and delta samples, in order to investigate how the cosmogenic record of orogenic erosion is transmitted across a fast-subsiding foreland basin. The in situ10Be concentrations in the analyzed samples range from ∼ 0.8 ×104 at /gQTZ to ∼ 6.5 ×104 at /gQTZ. The 10Be-derived denudation rates range from 0.1 to 1.5 mm/yr in the Alpine source areas and from 0.3 to 0.5 mm/yr in the Apenninic source areas. The highest 10Be-derived denudation rates are found in the western Central Alps (1.5 mm/yr). From these data, we constrain a sediment flux leaving the Alpine and the Apenninic source areas (>27 Mt/yr and ca. 5 Mt/yr, respectively) that is notably higher than the estimates of sediment export provided by gauging (∼10 Mt/yr at the Po delta). We observe a high variability in 10Be concentrations and 10Be-derived denudation rates in the source areas. In the Po Plain, little variability is observed, and at the same time, the area-weighed 10Be concentration of (2.29 ± 1.57) ×104 at /gQTZ (±1 SD of the dataset) from both the Alps and the Apennines is poorly modified (by tributary input) in sediment of the Po Plain ((2.68 ± 0.78 , ± 1 SD) ×104 at /gQTZ). The buffering effect of the Po floodplain largely removes scatter in 10Be signals. We test for several potential perturbations of the cosmogenic nuclide record during source to sink transfer in the Po basin. We find that sediment trapping in deep glacial lakes or behind dams does not significantly change the 10Be-mountain record. For example, similar 10Be concentrations are measured upstream and downstream of the postglacial Lake Maggiore, suggesting that denudation rates prior to lake formation were similar to today's. On the scale of the entire basin, the 10Be concentration of basins with major dams is similar to those without major dams. A potential

  12. Mid-Max field: A piece of the Silurian-Devonian exploration puzzle

    SciTech Connect

    Entzminger, D.J.; Basham, W.L. ); Gonzales, E. )

    1992-04-01

    The Mid-Max field, Andrews County, Texas, provides an example for the exploration and development of subtle stratigraphic targets in the Permian basin. The integration of all available data, including seismic, log, core, and engineering data, is essential in this mature area as the search for hydrocarbons turns toward subtle structural and stratigraphic prospects. The Mid-Max field, on the Central basin platform, is a Silurian reef. Seismic data support the geologic interpreation of Woodford Shale thinning over a Silurian high, a Silurian to Fusselman thick, and the presence of a relatively flat Fusselman reflector beneath the Silurian high. Whole cores and rotary sidewall cores from the field contain stromatoporoids, corals, algal stromatolites, crinoidal grainstones and other reef elements. The reservoir is predominantly dolomite with porosity and permeability being variable and controlled by the presence of lime mud, fracturing, and diagenesis. The 26-29 API gravity sour crude produced at Mid-Max field is atypical of Siluria-Devonian oils, which commonly are sweet crudes of 35 to 45 API gravity. This atypical oil is explained by the mixing of two types of Woodford-sourced oils and biodegradation. Tectonism appears to have played a minor role in the formation of the Mid-Max field, unlike the conventional faulted-anticline prospects in the Silurian-Devonian of the Permian basin. Although modern common-depth-point seismic data and a dry Silurian test exited over the Mid-Max prospect prior to drilling, these illusive traps commonly are misinterpreted or overlooked, which would suggest that there might be similar subtle Silurian prospects elsewhere in the Permian basin.

  13. Characteristics and origin of the relatively high-quality tight reservoir in the Silurian Xiaoheba Formation in the southeastern Sichuan Basin.

    PubMed

    Gong, Xiaoxing; Shi, Zejin; Wang, Yong; Tian, Yaming; Li, Wenjie; Liu, Lei

    2017-01-01

    A mature understanding of the sandstone gas reservoir in the Xiaoheba Formation in the southeastern Sichuan Basin remains lacking. To assess the reservoir characteristics and the origin of the high-quality reservoir in the Xiaoheba Formation, this paper uses systematic field investigations, physical property analysis, thin section identification, scanning electron microscopy and electron microprobe methods. The results indicate that the Xiaoheba sandstone is an ultra-tight and ultra-low permeability reservoir, with an average porosity of 2.97% and an average permeability of 0.56×10-3 μm2. This promising reservoir is mainly distributed in the Lengshuixi and Shuangliuba regions and the latter has a relatively high-quality reservoir with an average porosity of 5.28% and average permeability of 0.53×10-3 μm2. The reservoir space comprises secondary intergranular dissolved pores, moldic pores and fractures. Microfacies, feldspar dissolution and fracture connectivity control the quality of this reservoir. The relatively weak compaction and cementation in the interbedded delta front distal bar and interdistributary bay microfacies indirectly protected the primary intergranular pores and enhanced late-stage dissolution. Late-stage potassium feldspar dissolution was controlled by the early-stage organic acid dissolution intensity and the distance from the hydrocarbon generation center. Early-stage fractures acted as pathways for organic acid migration and were therefore important factors in the formation of the reservoir. Based on these observations, the area to the west of the Shuangliuba and Lengshuixi regions has potential for gas exploration.

  14. Characteristics and origin of the relatively high-quality tight reservoir in the Silurian Xiaoheba Formation in the southeastern Sichuan Basin

    PubMed Central

    Gong, Xiaoxing; Shi, Zejin; Wang, Yong; Tian, Yaming; Li, Wenjie; Liu, Lei

    2017-01-01

    A mature understanding of the sandstone gas reservoir in the Xiaoheba Formation in the southeastern Sichuan Basin remains lacking. To assess the reservoir characteristics and the origin of the high-quality reservoir in the Xiaoheba Formation, this paper uses systematic field investigations, physical property analysis, thin section identification, scanning electron microscopy and electron microprobe methods. The results indicate that the Xiaoheba sandstone is an ultra-tight and ultra-low permeability reservoir, with an average porosity of 2.97% and an average permeability of 0.56×10−3 μm2. This promising reservoir is mainly distributed in the Lengshuixi and Shuangliuba regions and the latter has a relatively high-quality reservoir with an average porosity of 5.28% and average permeability of 0.53×10−3 μm2. The reservoir space comprises secondary intergranular dissolved pores, moldic pores and fractures. Microfacies, feldspar dissolution and fracture connectivity control the quality of this reservoir. The relatively weak compaction and cementation in the interbedded delta front distal bar and interdistributary bay microfacies indirectly protected the primary intergranular pores and enhanced late-stage dissolution. Late-stage potassium feldspar dissolution was controlled by the early-stage organic acid dissolution intensity and the distance from the hydrocarbon generation center. Early-stage fractures acted as pathways for organic acid migration and were therefore important factors in the formation of the reservoir. Based on these observations, the area to the west of the Shuangliuba and Lengshuixi regions has potential for gas exploration. PMID:28686735

  15. Detrital zircon U-Pb age and Hf isotopic composition from foreland sediments of the Assam Basin, NE India: Constraints on sediment provenance and tectonics of the Eastern Himalaya

    NASA Astrophysics Data System (ADS)

    Vadlamani, Ravikant; Wu, Fu-Yuan; Ji, Wei-Qiang

    2015-11-01

    Synorogenic Palaeogene-Neogene sediments of the Assam foreland basin, were derived by erosion of adjacent crustal and orogenic sources following the Greater India-Eurasia collision since ∼55 Ma. To constrain source sediment influx, and its relation to Himalayan tectonics, from pre- to post-collision time, detrital zircon U-Pb geochronology and their Hf isotopic compositions were carried out. The varying detrital zircon spectral patterns analyzed from the Paleogene Jaintia, Barail and Neogene Surma and Tipam Groups, with sediment petrography, track source sediment derived from cratonic India, Gangdese and eastern Transhimalayan batholiths and the eastern Himalaya. These sources are tested against Cenozoic paleopositions proposed for the northeastward motion of the Indian plate. Precollisional cratonic detritus to Middle to Late Eocene Sylhet Formation shifted to Tethyan Himalaya and arc sources of the Gangdese and eastern Transhimalayan batholiths to Late Eocene Kopili and Barail Formations, consistent with the proposed paleoposition proximal to the Indus-Yarlung suture. This Sylhet-Kopili Formation transition, within the Jaintia Group, reflects one of the earliest Himalayan hinterland exhumation stages during the Late Eocene. Major shift in provenance to Higher Himalayan Crystalline and arc detritus is recorded from the Surma Group, constraining Mid Miocene Himalayan tectonic exhumation from the eastern Himalaya. Late Miocene Tipam Group preserves sediment of Higher Himalayan Crystalline detritus, ophiolite and likely Lesser Himalayan rocks.

  16. Geochemical study of calcite veins in the Silurian and Devonian of the Barrandian Basin (Czech Republic): evidence for widespread post-Variscan fluid flow in the central part of the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Suchy, V.; Heijlen, W.; Sykorova, I.; Muchez, Ph; Dobes, P.; Hladikova, J.; Jackova, I.; Safanda, J.; Zeman, A.

    2000-03-01

    Carbonate fracture cements in limestones have been investigated by fluid inclusion and stable isotope analysis to provide insight into fluid evolution and deformation conditions of the Barrandian Basin (Silurian-Devonian) of the Czech Republic. The fractures strike generally north-south and appear to postdate major Variscan deformation. The most common fracture cement is calcite that is locally accompanied by quartz, natural bitumen, dolomite, Mn-oxides and fluorite. Three successive generations of fracture-filling calcite cements are distinguished based on their petrographical and geochemical characteristics. The oldest calcite cements (Stage 1) are moderate to dull brown cathodoluminescent, Fe-rich and exhibit intense cleavage, subgrain development and other features characteristic of tectonic deformation. Less tectonically deformed, variable luminescent Fe-poor calcite corresponds to a paragenetically younger Stage 2 cement. First melting temperatures, Te, of two-phase aqueous inclusions in Stages 1 and 2 calcites are often around -20°C, suggesting that precipitation of the cements occurred from H 2O-NaCl fluids. The melting temperature, Tm, has values between 0 and -5.8°C, corresponding to a low salinity between 0 and 8.9 eq. wt% NaCl. Homogenization temperatures, Th, from calcite cements are interpreted to indicate precipitation at about 70°C or less. No distinction could be made between the calcite of Stages 1 and 2 based on their fluid inclusion characteristics. In some Stage 2 cements, inclusions of highly saline (up to 23 eq. wt% NaCl) brines appear to coexist with low-salinity inclusions. The low salinity fluid possibly contains Na-, K-, Mg- and Ca-chlorides. The high salinity fluid has a H 2O-NaCl-CaCl 2 composition. Blue-to-yellow-green fluorescing hydrocarbon inclusions composed of medium to higher API gravity oils are also identified in some Stages 1 and 2 calcite cements. Stage 1 and 2 calcites have δ18O values between -13.2‰ and -7.2‰ PDB

  17. Source rocks of the Sub-Andean basins

    SciTech Connect

    Raedeke, L.D. )

    1993-02-01

    Seven source rock systems were mapped using a consistent methodology to allow basin comparison from Trinidad to southern Chile. Silurian and Devonian systems, deposited in passive margin and intracratonic settings, have fair-good original oil/gas potential from central and northern Bolivia to southern Peru. Kerogens range from mature in the foreland to overmature in the thrust belt. Permian to Carboniferous deposition in local restricted basins formed organic-rich shales and carbonates with very good original oil/gas potential, principally in northern Bolivia and southern Peru. Late Triassic to early Jurassic marine shales and limestones, deposited in deep, narrow, basins from Ecuador to north-central maturity. Locally, in the Cuyo rift basin of northern Argentina, a Triassic lacustrine unit is a very good, mature oil source. Early Cretaceous to Jurassic marine incursions into the back-arc basins of Chile-Argentina deposited shales and limestones. Although time transgressive (younging to the south), this system is the principal source in southern back-arc basins, with best potential in Neuquen, where three intervals are stacked A late Cretaceous marine transgressive shale is the most important source in northern South America. The unit includes the La Luna and equivalents extending from Trinidad through Venezuela, Colombia, Ecuador, and into northern Peru. Elsewhere in South America upper Cretaceous marine-lacustrine rocks are a possible source in the Altiplano and Northwest basins of Bolivia and Argentina. Middle Miocene to Oligocene source system includes shallow marine, deltaic, and lacustrine sediments from Trinidad to northern Peru.

  18. Fault-related Silurian Clinton sandstone deposition in Ohio

    SciTech Connect

    Coogan, A.H. )

    1988-08-01

    Mapping the thickness of the Silurian Clinton sandstone reservoir and associated shale, sandstone, and carbonate facies in the subsurface of 40 counties in eastern Ohio reveals a general correspondence between major patterns of deposition and the location of faults that strike parallel with or subparallel to the depositional trends. Clinton delta-front sandstones, which occur along a line from Hocking and Perry Counties, through Knox, Holmes, and Wayne Counties northeast to Lake County, Ohio, parallel a line of major change in magnetic intensity in the basement, which is interpreted here to be the juncture between the more stable, less subsiding central Ohio carbonate bank and the more subsiding western edge of the Appalachian basin. The principal Clinton deltaic lobes occur in east-central and northeastern Ohio. The Clinton sandstone interval is thinner and starved of coarse clastic sediment close to the Rome trough, which is located along the southeasternmost Ohio border. Sediment distribution patterns indicate that deltaic deposits of Clinton sandstone were captured in the subsiding Rome trough at the border of southern Ohio during the Early Silurian. Farther north, deltaic sediments spread out across eastern Ohio to reach an elongate depocenter caused by minor subsidence at the central Ohio platform edge. There, deltaic sands intermittently filled the delta-edge trough, and spilled out as thin shelf sands onto the more stable platform, a site of predominantly mixed shale and carbonate deposition during the Early Silurian.

  19. Late Silurian plutons in Yucatan

    NASA Astrophysics Data System (ADS)

    Steiner, M. B.; Walker, J. Douglas

    1996-08-01

    U-Pb measurements of zircons from two composite plutons in the Maya Mountains of the Yucatan Block (Belize) give Late Silurian ages. Zircons from one of the five compositional phases of the Mountain Pine Ridge pluton yield an age of 418±3.6 Ma. A second compositional phase gives a minimum age of 404 Ma, and zircons from a third phase, although plagued with high common Pb, yield ages consistent with the other two. Zircons from one compositional phase of the Hummingbird-Mullins River pluton indicate an age of about 410-420 Ma. These data demonstrate that two of the three Maya Mountains plutons residing among the strata of the Late Pennsylvanian through Permian Santa Rosa Group are older than that sedimentation. Although the third pluton was not dated, both the similarity of sedimentary facies patterns adjacent to it to those adjacent to one of the plutons dated as Late Silurian and a published single Rb-Sr age of 428 ± 41 Ma suggest this third pluton also was emergent during Santa Rosa deposition. Thus the new U/Pb dates and other data suggest that all three Maya Mountains plutons pre-date Late Carboniferous sedimentation and that none intrude the Santa Rosa Group. Although very uniform ages of about 230 Ma amongst all plutons, derived from abundant earlier dating by the K-Ar system, led to the conclusion that intrusion mostly had occurred in the Late Triassic, the U-Pb ages (obtained from the same sites as the K-Ar dates) demonstrate that the K-Ar ages do not derive from a Late Triassic intrusive episode. The K-Ar dates probably are a signature of the rifting associated with Pangean breakup and formation of the Gulf of Mexico. In a reconstructed Pangea, the position of the Maya Mountains Late Silurian plutons suggests that the Late Silurian Acadian-Caledonian orogen of eastern North America extended through the region of the future Gulf of Mexico. Finally, the U-Pb ages of the Maya Mountains plutons are the same as those of a group of shocked zircons found in the

  20. Geochronological and sedimentological evidences of Panyangshan foreland basin for tectonic control on the Late Paleozoic plate marginal orogenic belt along the northern margin of the North China Craton

    NASA Astrophysics Data System (ADS)

    Li, Jialiang; Zhou, Zhiguang; He, Yingfu; Wang, Guosheng; Wu, Chen; Liu, Changfeng; Yao, Guang; Xu, Wentao; Zhao, Xiaoqi; Dai, Pengfei

    2017-08-01

    There is a wide support that the Inner Mongolia Palaeo-uplift on the northern margin of the North China Craton has undergone an uplifting history. However, when and how did the uplift occurred keeps controversial. Extensive field-based structural, metamorphic, geochemical, geochronological and geophysical investigations on the Inner Mongolia Palaeo-uplift, which suggested that the Inner Mongolia Palaeo-uplift was an uplifted region since the Early Precambrian or range from Late Carboniferous-Early Jurassic. The geochemical characteristics of the Late Paleozoic to Early Mesozoic intrusive rocks indicated that the Inner Mongolia Palaeo-uplift was an Andean-type continental margin that is the extensional tectonic setting. To address the spatial and temporal development of the Inner Mongolia Palaeo-uplift, we have carried out provenance analysis of Permian sedimentary rocks which collected from the Panyangshan basin along the northern margin of the North China Craton. The QFL diagram revealed a dissected arc-recycled orogenic tectonic setting. Moreover, the framework grains are abundant with feldspar (36-50%), indicating the short transport distance and unstable tectonic setting. Detrital zircon U-Pb analysis ascertained possible provenance information: the Precambrian basement ( 2490 and 1840 Ma) and continental arc magmatic action ( 279 and 295 Ma) along the northern margin of the North China Craton. The projection in rose diagrams of the mean palaeocurrent direction, revealing the SSW and SSE palaeoflow direction, also shows the provenance of the Panyangshan basin sources mainly from the Inner Mongolia Palaeo-uplift. The andesite overlying the Naobaogou Formation has yielded U-Pb age of 277.3 ± 1.4 Ma. The additional dioritic porphyry dike intruded the Naobaogou and Laowopu Formations, which has an emplacement age of 236 ± 1 Ma. The above data identify that the basin formed ranges from Early Permian to Middle Triassic (277-236 Ma). Accordingly, the Inner Mongolia

  1. Pennsylvanian-Permian Antler foreland of eastern Nevada

    SciTech Connect

    Snyder, W.S. . Dept. of Geosciences); Trexler, J.H. Jr. . Dept. of Geological Sciences)

    1993-04-01

    Models for the Antler foreland generally assume that it was a Mississippian feature dominated by a single, large basin (the Antler foredeep). Recent work indicates that the foreland, as a tectonic region, is longer-lived, and is better described as a series of sub-basins separated by intervening structural highs. Long sections reveal space/time changes in depositional facies and sedimentologic features indicative or suggestive of this repeated tectonism. For example, in the southern Pancake Range, the fluvial-deltaic clastic units of the Late Mississippian-earliest Pennsylvanian Neward Canyon sequence are overlain by 540 m of cyclical Pennsylvanian Ely Limestone. The flooding event that marks the boundary between these units occurs during a long-term 2nd order eustatic low stand and thus reflects the regional tectonism that created the Ely basin'. Further, tectonically driven subsidence seems necessary to sustain deposition of the thick of marginal marine-open shelf Ely Limestone at this locality. Regionally, Early Permian deposition within the Dry Mountain trough was dominated by a complex series of local tectonic controls. Within eastern Nevada, tectonic influences on the stratigraphy continued through at least the Middle Permian, and this tectonism perhaps merged with that of the classic Late Permian-Early Triassic Sonoma orogeny. One consequence of this protracted tectonism was development or reactivation of zones of structural weakness that fragmented the foreland into a series of basins and highs and that accommodated differing geometries and styles of deformation.

  2. Microfabric analysis of the Appalachian basin Williamson and Willowvale shales

    SciTech Connect

    Burkins, D.L.; Woodard, M. . Geology Dept.)

    1993-03-01

    Shale samples from the Williamson and Willovale formations (Upper Llandoverian, Silurian) were studied to determine the relationship of microfabric (particle orientation) to sedimentary environment and processes. The shales were sampled along a traverse from Utica to Rochester, New York in the Appalachian foreland basin. Samples were taken from proximal and distal parts of the basin and analyzed using a scanning electron microscope (SEM) and using thin sections to determine the relationship between microfabric and basin position. Results show samples taken from the proximal part of the basin contain large amounts of silt grains, random orientation of clay flakes, and a high degree of bioturbation. Basinward, the samples become less silty, less bioturbated, and have more preferred orientation of clay flakes. The samples at the basin axis show the highest degree of preferred orientation and contain no silt grains. It can be concluded that the shale fabrics vary basinward and microfabric analysis is useful in determining the relative position of samples within a sedimentary basin.

  3. The development of miocene extensional and short-lived basin in the Andean broken foreland: The Conglomerado Los Patos, Northwestern Argentina

    NASA Astrophysics Data System (ADS)

    del Papa, Cecilia E.; Petrinovic, Ivan A.

    2017-01-01

    The Conglomerado Los Patos is a coarse-grained clastic unit that crops out irregularly in the San Antonio de los Cobres Valley in the Puna, Northwestern Argentina. It covers different units of the Cretaceous-Paleogene Salta Group by means of an angular unconformity and, in turn, is overlaid in angular unconformity by the Viscachayoc Ignimbrite (13 ± 0.3 Ma) or by late Miocene tuffs. Three lithofacies have been identified in the Corte Blanco locality; 1) Bouldery matrix-supported conglomerate (Gmm); 2) Clast-supported conglomerate (Gch) and 3) Imbricated clast-supported conglomerate (Gci). The stratigraphic pattern displays a general fining upward trend. The sedimentary facies association suggests gravitational flow processes and sedimentation in alluvial fan settings, from proximal to medial fan positions, together with a slope decrease upsection. Provenance studies reveal sediments sourced from Precambrian to Ordovician units located to the southwest, except for volcanic clasts in the Gmm facies that shows U/Pb age of 14.5 ± 0.5 Ma. This new age represents the maximum depositional age for the Conglomerado Los Patos, and it documents that deposition took place simultaneously during a period of increased tectonic and volcanic activity in the area. The structural analysis of the San Antonio de los Cobres Valley and the available thermochronological ages, indicate active N-S main thrusts and NW-SE transpressive and locally normal faults during the middle Miocene. In this context, we interpret the Conglomerado Los Patos to represent sedimentation in a small, extensional and short-lived basin associated with the compressional Andean setting.

  4. The sequence stratigraphy of the latest Cretaceous sediments of northern Wyoming: The interplay of tectonic and eustatic controls on foreland basin sedimentation

    SciTech Connect

    Hicks, J.F. . Dept. of Geology); Tauxe, L. )

    1992-01-01

    A west-east chronostratigraphic correlation has been made of the latest Cretaceous sediments of northern Wyoming. Five sections from Jackson Hole to Red Bird have been dated magnetostratigraphically (C34N-C26R) and radiometrically (81-68 Ma), and integrated with the ammonite biostratigraphy of the Niobrara and Pierre Shale. Four major sequence surfaces have been identified in section and the time missing within the unconformities has been measured and traced laterally. These bounding unconformities define six alloformations. The lowest straddles the C34N/C33R chronic boundary and contains the Cody, Telegraph Creek and Eagle Fms. The second ranges from the mid- to upper part of C33N of C32R and contains the Claggett and Judith River/Mesaverde Fms. The third (C32R ) is the Teapot Sandstone Member of the Mesaverde Fm. The fourth extends from the lower to upper part of C32N or to mid-C31R and includes the Bearpaw Shale and Meeteetse Fm. The fifth extends from C31N to C30N or C29N and includes the Harebell and Lance Fms. The base of the uppermost alloformation has been identified within C26R in the uppermost alloformation has been identified within C26R in the lowermost Fort Union. The unconformable surfaces are angular adjacent to the Sevier Thrust Belt but form paraconformities or hiatuses in the marine units to the east. The unconformities are eustatically controlled throughout the Campanian, but become tectonically driven in the Maastrichtian with the onset of rapid foredeep subsidence in Jackson Hole, and forebulge uplift in the Bighorn and Wind River Basin region which correlates exactly to the rapid regression of the Bearpaw Sea from the area in the range of Baculites clinolobatus.

  5. Northeast-southwest structural transect: Rocky Mountain foreland, Wyoming

    SciTech Connect

    Stone, D.S.

    1987-08-01

    A northeast-southwest structural transect has been constructed across the Rocky Mountain foreland in Wyoming, a distance of about 400 mi. The line of transect begins in the northern Black Hills and traverses the northern Powder River basin, the Bighorn Mountains from Buffalo to Bonanza, the Big Horn basin from Worland to Hamilton dome, the Owl Creek Mountains, the northern Wind River basin at Maverick Springs, the Wind River Mountains to Pinedale in the Green River basin, the Moxa Arch at Big Piney and Riley Ridge, and into the thrust belt, ending at the Idaho border. In terms of a vertical and horizontal scale of 1 in. = 2000 ft, the section is about 90 ft long (i.e., the section is approximately 409 mi long). The data base for the transect includes published geologic maps, commercial photogeologic mapping, well data, and modern seismic data through critical parts of the basin areas. The data base provides an excellent found for analyzing structural relationships on both a regional and a local scale. Regional horizontal shortening of the foreland has occurred primarily through basement-involved displacements on basin-boundary megathrusts, which separate the mountain ranges from sedimentary basins, and on the smaller, intrabasin thrusts, which produced the anticlinal traps for Paleozoic oil accumulations.

  6. Lower Silurian `hot shales' in North Africa and Arabia: regional distribution and depositional model

    NASA Astrophysics Data System (ADS)

    Lüning, S.; Craig, J.; Loydell, D. K.; Štorch, P.; Fitches, B.

    2000-03-01

    large palaeohigh at that time. The depositional model presented may help in better understanding the source potential of the basal Silurian shales in less-explored regions of North Africa and Arabia including Morocco, northern Niger and the Kufra Basin in southeast Libya.

  7. Paleogeographic setting of the Late Devonian to Early Mississippian Antler foreland, eastern Nevada and western Utah

    SciTech Connect

    Goebel, K.A. )

    1991-02-01

    Late Devonian through Early Mississippian depositional patterns in eastern Nevada and western Utah reflect transition from passive to collisional margin regimes. The Late Devonian (Frasnian) passive margin sequence (Devils Gate Limestone, Guilmette Limestone) was flexurally warped by thrust loading of the Roberts Mountains allochthon during eastward tectonic emplacement onto the continental margin. The foreland basin received minimal clastic input consisting primarily of bedded chert and hemipelagic claystone (Pine Cone Sequence, Woodruff Formation). Paleocurrent data from the northeast-southwest-trending back-bulge basin (Pilot basin) indicate that clastic detritus was derived from the forebulge to the north-northwest. The southern Pilot basin was the site of relatively shallow water carbonate deposition (West Range Limestone). During the Late Devonian (Famennian) and Early Mississippian (early Kinderhook), northern siliciclastic strata prograded over the southern carbonates, and the axis of the Pilot basin migrated eastward in conjunction with migration of the forebulge, foreland basin, and Antler thrust front. During the Early Mississippian (early Kinderhook), the forebulge migrated rapidly eastward through eastern Nevada and western Utah to produce local erosional surfaces of shoaling-upward sequences. The cratonward edge of the foreland basin was the site basin, west of the carbonate bank, shale and siltstone were deposited and grade westward into hemipelagic clay (Webb Formation). During the Early Mississippian (Osage), carbonate turbidites (Tripon Pass Limestone) derived from eroded highlands to the east in Utah and to the southeast in southern Nevada were deposited in the foreland trough.

  8. New high precision U-Pb ages for the Vinchina Formation: Implications for the stratigraphy of the Bermejo Andean foreland basin (La Rioja province, western Argentina)

    NASA Astrophysics Data System (ADS)

    Ciccioli, P. L.; Limarino, C. O.; Friedman, R.; Marenssi, S. A.

    2014-12-01

    important episode of volcanism recorded in the Cerro Las Tórtolas Formation, located ˜90 km to the west in the Andean Cordillera, but also the upper tuff could be related to the late Miocene Puna volcanism. Comparison of the new ages with previous chronological data suggests coetaneous sedimentation along different depocenters of the Bermejo basin (e.g., Vinchina and Talampaya depocenters in Western Sierras Pampeanas and La Troya depocenter and Huaco-Mogna sections in Precordillera) and strenghten the need for correlation among them. In addition the age of 15.6 ± 0.4 Ma constrains the end of the severe arid conditions recorded in the Sierras Pampeanas and Precordillera region.

  9. Grenville foreland thrust belt hidden beneath the eastern US midcontinent

    SciTech Connect

    Hauser, E.C. )

    1993-01-01

    Grenville foreland thrust structures are observed beneath the eastern US midcontinent on COCORP (Consortium for Continental Reflection Profiling) line OH-1 and a short seismic line in southwest Ohio. These structures represent the first evidence for a significant Grenville foreland thrust belt preserved in eastern North America. On the COCORP lines, the structures include a thrust ramp anticline and an associated asymmetric syncline. The Grenville front tectonic zone appears to truncate these foreland structures, indicating a later, second phase expressed as a deeply penetrating, out-of-sequence thrust zone associated with the main uplift of the Grenville province on the east. A short, shallow seismic line in southwestern Ohio reveals an east-dipping sequence of prominently layered rocks that may lie above a footwall ramp to a deeper Grenville thrust fault. A drill hole into the less reflective top of this dipping sequence encountered unmetamorphosed sedimentary rocks like those increasingly reported from other drill holes in southwestern Ohio and adjacent states. Although possibly part of a late Precambrian (Keweenawan ) rift, these clastic sedimentary rocks may instead preserve evidence of a heretofore unrecognized Grenville foreland basin in eastern North America. Alternatively these Precambrian sedimentary rocks together with an underlying, but yet undrilled, strongly layered sequence may correlate with similarly layered rocks observed on COCORP and industrial seismic lines within the Middle Proterozoic granite-rhyolite province to the west in Indiana and Illinois and indicate that unmetamorphosed sedimentary material is an important constituent of the granite-rhyolite province. 25 refs., 6 figs.

  10. 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.

  11. Evaluation of Silurian-Niagaran reef belt in Northeastern Michigan

    SciTech Connect

    Aminian, K.; Ameri, S.; Bomar, R.M.

    1987-12-01

    Silurian pinnacle reefs have remained the main exploration targets in the Michigan basin over the last decade. Recent discoveries have extended the reef belt into new areas in the western and northeastern parts of Michigan's lower peninsula. Meanwhile, the exploration for these reefs has continued in more developed areas of the belt in northern Michigan, southwestern Ontario, and southern Michigan. The results of exploration activities in northeastern Michigan in Cheboygan, Montmorency, and Presque Isle counties is different from the rest of the northern portion of the belt. A detailed study used the data available from the exploration activities in this area to determine the reef belt characteristics and reserves potential in northeastern Michigan and its extension into Lake Huron. The results indicated some interesting features, including the narrowing of the belt as it approaches Lake Huron. It was concluded that the different depositional environment during the Silurian Age had affected the development of the belt and the hydrocarbon accumulation in the pinnacle reefs in this part of the basin.

  12. Influence of a tectonically active mountain belt on its foreland basin: Evidence from detrital zircon dating of bedrocks and sediments from the eastern Tibetan Plateau and Sichuan Basin, SW China

    NASA Astrophysics Data System (ADS)

    Zhong, Ning; Song, Xiangsuo; Xu, Hongyan; Jiang, Hanchao

    2017-09-01

    The tectonically active eastern Tibetan Plateau (TP) impacts the populous Sichuan Basin in the form of dust and exhumed detrital materials. To better understand a detailed transport process of detrital material from the eastern TP to the Sichuan Basin, eight samples were collected from the upper reaches of the Min River in the eastern TP to the Sichuan Basin, for zircon U-Pb chronological and grain-size analysis. The results are compared with those of previously studies. Zircon grains are comparatively coarse in three bedrock samples, one fluvial sand sample and one dust sample, but are distinctly fine in three lacustrine samples. Intriguingly, the zircon grain-size parameters from the fluvial sand and dust samples are similar to each other. Consistent with previous studies of this area, the analysis of our U-Pb zircon ages indicates five major age populations at 180-350 Ma, 350-550 Ma, 700-1000 Ma, 1600-2000 Ma, and 2200-2600 Ma, which broadly correspond to five known granitoid magmatic events within the Yangtze Block. The Min River links lacustrine sediments from Lixian, fluvial sands from Wenchuan, Leshan, Yibin, and from the Dadu River and the Dayi conglomerate, implying the Dayi conglomerate was transported by fluvial rather than glacial processes. The denuded detrital material, mainly generated by seismic events in the eastern TP, was transported by water flow into the western Sichuan Basin, where two thick sedimentary depocenters developed, and the relatively fine grains were then transported by wind to the northern Sichuan Basin. Thus, the thick sediments in the western Sichuan Basin mainly transported by the Min River probably exerted a major influence on dust deposition in the northern Sichuan Basin. In contrast, the Jialing and Dadu rivers made a minor contribution.

  13. Calcified algae and bryozoans from the Ordovician - Silurian successions of the Spiti Himalaya, India

    NASA Astrophysics Data System (ADS)

    Pandey, Shivani; Parcha, Suraj Kumar

    2015-04-01

    The Tethys Himalaya contains an extensive record of sediments ranging from Precambrian to Cretaceous. These successions are well exposed in Pin, Parahio, Kunzum La and in the Takche sections. The present work is focused on the Ordovician and Silurian succession in the Pin Valley. The Ordovician succession consists of purple coloured quartzite, shale, siltstone, grits, dolarenites etc. Whereas, the Silurian succession comprises of thick sequence of slate, dolomite, calcarenites, olive green shale, limestone and pink dolomite. Both the successions contain a rich assemblage of the microfossils along with other body fossils. These successions show a wide variety of marine calcareous algae, along with corals and bryozoans. The calcified algae and bryozoans reported from the Ordovician - Silurian succession are mostly in carbonate beds. The various genera of bryozoan identified are as Calloporella, Cyphotrypa, Dekayai, Eridotrypa, Insignia, Trematopora, etc. along with them are various forms of calcified algae which were found in association in the same thin sections. The prominent genera of calcified algae are as: Dasyporella, Moniliporella, and Vermiporella. The algal assemblages mainly consist of the order Dasycladales, which predominants in the entire successions. Three genera of Dasycladacean algae were identified, among them genus Moniliporella was reported first time from the Pin section. The presence of bryozoans and calcified green algae in these successions indicates shallow marine to near shore environmental conditions followed by different stages of regression and transgression during this time span. Based on the faunal elements, middle to late Ordovician age can be assigned to Thango Formation and late Ordovician to late Silurian to the Takche Formation.The bryozoan communities identified indicates a correlation with that of southern China, Russia, Siberia, Kazakhstan and Mongolia. The genera Insignia and Tremaptopora which are reported from the Spiti Basin

  14. The petroleum systems of the Aquitaine Foreland

    SciTech Connect

    Biteau, J.J.; Masset, J.M.; Le Vot, M.

    1995-08-01

    The Aquitaine Basin of southwestern France lies in the foreland of the Pyrenean Fold and Thrust Belt. Since the first gas production in 1939, the area has produced as of December 1994, around 290 Gm3 of gas, 13,6 MT of condensates and 12,7 MT of oil. The hydrocarbon charge of the traps, the migration paths and the different types of fluids have been recently studied in detail by Elf. The parameters of the Aquitaine petroleum systems are therefore completely reevaluated. In this framework the hydrocarbon traps are related to inherited structures linked to the Early Cretaceous extension (tilted blocks of Jurassic and Barremian carbonates) and to the associated salt tectonics (such as erosional pinch outs of the Jurassic and Barremian reservoirs). Some of these features have then been locally reversed within the Pyrenean Fold and Thrust Belt and Foreland area. In this complex structural setting, conventionnal 2D seismic data revealed poor quality for a precise field geometry. From 1987 to 1992, over 1500 km2 of 3D seismic were acquired in the area with the purposes of field development and as well as oil and gas exploration. The good subsurface data (3D and 2D reinterpretations) have allowed us to define the distribution, geometries and relationships of the different tectono-sedimentary units as well as of the structures associated to the petroleum traps. This work has greatly enhanced the knowledge of the whole area in helping to define its geodynamic evolution based on the results of hydrocarbon generation models and on several organic geochemical and fluids data.

  15. Neogene foreland tectonics in the southern Appenines

    SciTech Connect

    Roure, F.; Casero, P.; Moretti, I.; Mueller, C.; Sage, L.; Vially, R.

    1988-08-01

    Combined structural and biostratigraphic analyses and seismic interpretation help them to balance cross sections through the southern Apennines from the Adriatic to the Tyrrhenian Sea and to propose an overall model for the evolution of the belt. Three lithostratigraphic units have been distinguished according to their Mesozoic facies and style of deformation: the western platform (upper unit), the Lagonegro-Molise basin, and the eastern platform. Foreland deformation migrated from west to east, and external domains were reached progressively by synorogenic flysch deposits (foredeep) and later incorporated into the thrust sheets. Presently, only the most external part of the eastern platform is still unaffected by thrusting, while internal parts are building the overthrust belt at depth, which is masked on the surface by allochthonous basinal nappes. The evolutive geometry of thrust and piggy-back basins results from the continuous understacking of new material at the bottom of the tectonic prism. The deeper basement is also progressively involved in the deformation, giving rise to large nappe anticlines. Despite the early subsidence and deformation of the western platform and basinal domains in Langhian to Tortonian time, all the deformation of the eastern platform has occurred since Messinian time. These compressive structures are thus contemporaneous with the opening of the Tyrrhenian Sea. To the west, the upper tectonic units of the Apennines are indeed affected by listric normal faulting, with previous thrust planes having been locally reactivated during the distension. Post-Messinian shortening in the sedimentary cover is accompanied by a crustal thickening outlined by the Moho's geometry. The authors interpret it as a result of the subduction of the Apulian continental lithosphere. Recent uplift of the Apennines is indeed directly related to this crustal root.

  16. Composition of natural gas and crude oil produced from 14 wells in the Lower Silurian "Clinton" Sandstone and Medina Group Sandstones, northeastern Ohio and northwestern Pennsylvania: Chapter G.6 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

    USGS Publications Warehouse

    Burruss, Robert A.; Ryder, Robert T.; Ruppert, Leslie F.; Ryder, Robert T.

    2014-01-01

    The geochemical processes that control the distribution of hydrocarbons in the regional accumulation of natural gas and crude oil in reservoirs of Early Silurian age in the central Appalachian basin are not well understood. Gas and oil samples from 14 wells along a down-dip transect through the accumulation in northeastern Ohio and northwestern Pennsylvania were analyzed for molecular and stable isotopic compositions to look for evidence of hydrocarbon source, thermal maturation, migration, and alteration parameters. The correlation of carbon and hydrogen stable isotopic composition of methane with thermal maturation indicates that the deepest gases are more thermally mature than independent estimates of thermal maturity of the reservoir horizon based on the conodont alteration index. This correlation indicates that the natural gas charge in the deepest parts of the regional accumulation sampled in this study originated in deeper parts of the Appalachian basin and migrated into place. Other processes, including mixing and late-stage alteration of hydrocarbons, may also impact the observed compositions of natural gases and crude oils.

  17. Stratigraphy, structure, and zonation of large Silurian reef at Delphi, Indiana

    SciTech Connect

    Archer, A.W.; Bottjer, D.J.; Droste, J.B.; Horowitz, A.S.; Kelly, S.M.; Krisher, D.L.; Shaver, R.H.

    1980-01-01

    A Silurian reef complex at Delphi, Indiana, consists of two subcircular reefs occupying an area of about 4 sq mi (10.6 sq km). The reef is more than 400 ft (62 m) thick, has a volume of about 0.15 cu mi (0.64 cu km), and effected as much as 75 ft (23 m) of compaction-induced drape in the overlying Middle Devonian strata. Stratigraphically, the complex extends upward from Salamonie (Middle Silurian) into Salina rocks (Upper Silurian). Growth of the complex proceeded through alternating periods of lateral expansion and restriction as reflected in the cross-sectional geometry of at least one of the reefs. These growth characteristics probably reflect the conditions that led to cyclic deposition of carbonate and evaporite rocks in the Michigan basin during Middle to Late Silurian time. Present dips along reef flanks locally exceed 35/sup 0/ but structural and stratigraphic analyses suggest that original depositional slopes may have been more gentle, that reef tops were never appreciably more than 200 ft (60 m) above the seafloor (although reef thicknesses of several hundred feet were attained before erosion), and that the central parts of the main reef masses were occupied by relatively rigid and volumetrically litle changing structural cores. Biozones include: two central areas of highest organic-framework buildup characterized by corals and stromatoporoids and flanking zones characterized separately by echinodermal and other debris, pentamerid brachiopods, gastropods, and fine debris and chert. The zonal distribution is similar to that already proposed for the large Silurian reef at Monon, Indiana, and somewhat resembles that proposed for the reef at Thornton, Illinois. These similarities and the fact of zonation in itself help to support the conclusion that the often debated Silurian buildups in the Great Lakes area satisfy all but the most rigid definitions of ecologic (organic-framework) reefs. 8 figures, 1 table.

  18. Silurian sequence stratigraphy in the North American craton, Great Lakes area

    USGS Publications Warehouse

    Shaver, R.H.; ,

    1996-01-01

    A notable circumstance of late Early through Late Silurian sedimentation on the Great Lakes area craton is that at least two and possibly three cycles of third-order duration (if eustatically considered) are recognized in basin and shallow-platform settings alike. Both virtually pure and siliciclastic-rich carbonate rocks exist in parts of platform-situated sections in contrast to siliciclastic-rich to evaporite-dominated basin sections. Knowledge of the reef history, together with evidence of incidental periodic incursions of siliciclastic sediments, permitted understanding of a regional event or sequence stratigraphy more than 15 years ago before conventional biostratigraphic and physical stratigraphic evidence became adequate to corroborate. This midwestern US and Ontario Silurian record has become strategic for testing different schools of thought that champion either tectonism or eustasy to explain cyclical sequences.

  19. A revised 87Sr/86Sr curve for the Silurian: Implications for global ocean chemistry and the Silurian timescale

    USGS Publications Warehouse

    Cramer, Bradley D.; Munnecke, Axel; Schofield, D.I.; Haase, K.M.; Haase-Schramm, A.

    2011-01-01

    Recent recalibration of the Silurian timescale and improved global chronostratigraphic correlation of Silurian strata significantly altered the Silurian 87Sr/86Sr curve and the temporal extent of available data. Whereas previous Silurian 87Sr/86Sr composites showed a generally monotonic increase throughout the Silurian, revisions to the Silurian timescale now require a major increase in the rate of change in 87Sr/86Sr at or near the onset of the Gorstian Age of the Ludlow Epoch. Similarly, improved chronostratigraphic correlations between Silurian outcrops on Anticosti Island, Canada, and Gotland, Sweden, indicate that the middle part of the Telychian Age, which is roughly 10%-15% of the total duration of the Silurian period, is undersampled and underrepresented in Silurian 87Sr/86Sr composites. A revised Silurian 87Sr/86Sr curve based on 241 new and published analyses confirms the significant increase in the rate of change of 87Sr/86Sr toward more radiogenic values near the base of the Ludlow Series. On the basis of these data, we propose that the rapid trend toward more radiogenic 87Sr/86Sr values is indicative of increased weathering of old sialic crust exposed during the Silurian uplift of portions of Baltica, Laurentia, and Avalonia. Importantly, however, the actual rate of change of 87Sr/86Sr will remain equivocal until the durations of Silurian epochs and ages are better constrained. ?? 2011 by The University of Chicago. All rights reserved.

  20. Lack of Young Subsidence in the East Tibetan Foreland: Implications for Crustal Thickening Processes at Depth

    NASA Astrophysics Data System (ADS)

    Royden, L. H.; Burchfiel, B. C.

    2008-12-01

    The Wenchuan earthquake of May 12, 2008 occurred on a west-dipping reverse fault (with a pronounced right-slip component) located along the steep eastern edge of the Tibetan plateau. It has been suggested that thrust faulting here may not be indicative of large-scale shortening and thickening of the upper crust, but may rather be an expression of vertical uplift of the upper crust, with minor shortening. This interpretation is compatible with the lack of young flexural subsidence in the Sichuan foreland provided that the flexurally competent layers of the Sichuan foreland lithosphere are loaded from below, or internally, by thickening crustal domains deep within the mid or lower crust of the eastern plateau, rather than from above, by emplacement of thrust sheets at shallow crustal levels onto the flexurally competent layer of the foreland. This interpretation reconciles gravity anomalies across the plateau margin, the young age of the high topography of eastern Tibet, and the old age of the Sichuan basin with the lack of Cenozoic flexural subsidence in the Sichuan foreland. A similar lack of asymmetric foreland subsidence is also present along the northeastern margin of the Tibetan plateau where it abuts the (southeastern) Tarim Basin, suggesting that a similar mechanism may operate here.

  1. Structural influences on facies distribution in Silurian Medina Group of northwestern New York

    SciTech Connect

    Pearce, M.A.; Seyler, B.J.

    1984-12-01

    The gas-bearing sandstones of the Medina Group in western New York are the basal Whirlpool Sandstone and the Grimsby Sandstone. Toward the west, these are separated by the Cabot Head Shale and the Manitoulin Limestone. Farther east, the Grimsby overlies and interfingers with the Whirlpool. The reservoir is underlain by the Ordovician Queenston Shale and is capped by shales of the Silurian Clinton Group. The depositional sequence of the Medina Group may be summarized as a marine transgression toward the east that yielded the Whirlpool, Cabot Head, and Manitoulin formations, followed by westward progradation of the deltaic Grimsby formation. Aspects of internal stratigraphy noted in subsurface studies may be correlated with anomalies in units much higher in the Silurian section and with disturbances on the Silurian-Devonian unconformity. Repetitive adjustments of large-scale structural features are inferred. These changes mark the transition from the westward-facing depositional front of the Ordovician to development of the isolated basins that dominated the Silurian Period.

  2. Gravity anomalies in Silurian pinnacle reef trend, southwestern Indiana

    SciTech Connect

    Malinconico, L.L. Jr.; Gognat, T.A.; Scher, P.L. )

    1989-08-01

    Structures produced over the top or along the margins of Silurian Pinnacle reefs have proven to be the source of significant oil production in the eastern Illinois basin. The authors have been able to refine gravity methods that can assist in the exploration of such reef targets. A gravity/density model was developed by combining the 1980 work of Dana at the Wilfred pool (Sullivan County, Indiana) with other lithologic and log data in southwestern Indiana. This model includes the density differences between the reef facies and surrounding lithologies as well as density variations that are the result of compaction of the sedimentary sequence above the reef. The density models suggest that positive gravity anomalies with amplitude between 1.5 to 2.5 mgals might occur over the reefs.

  3. Silurian Extrusion Wedge Tectonics in the Central Scandinavian Caledonides

    NASA Astrophysics Data System (ADS)

    Grimmer, J. C.; Glodny, J.; Drüppel, K.; Greiling, R. O.

    2015-12-01

    The Scandian fold-thrust belt of the central Scandinavian Caledonides host the high-grade metamorphic Seve Nappe Complex bounded on top by a normal sense shear zone and at the base by a reverse sense shear zone. Rb-Sr multimineral geochronology in synkinematic assemblages indicates simultaneous movements at the normal-sense roof shear zone and at the reverse-sense floor shear zone between 434 Ma and 429 Ma. Pressure temperature pseudosection calculations provide evidence for eclogite facies metamorphic conditions and nearly isothermal decompression at ~670 ± 50 °C from 17.5 to 14.5 kbar in garnet-kyanite mica schists during reverse-sense shearing, and from 15 to 11 kbar in garnet mica schists during normal-sense shearing. These and other published data and the presence of decompression-related pegmatites dated at 434 Ma and 429 Ma indicate that the Seve nappes form a 1-2 km thin extrusion wedge that extends along strike for at least 150 km. Devonian ductile extensional to transtensional deformation of the more internal parts of the orogen did not affect the early to mid-Silurian extrusion wedge that was preserved in the more external parts of the orogen due to foreland-directed nappe displacements in the order of >400 km. This wedge marks an early stage of exhumation of (ultra-)high-pressure metamorphic rocks and orogenic wedge formation in this part of the Scandinavian Caledonides predating the ≥10 km thick, post-415 Ma exhumation processes of ultrahigh-pressure rocks in southwestern Norway.

  4. Silurian to Early Carboniferous plate tectonic model of Central Europe

    NASA Astrophysics Data System (ADS)

    Golonka, Jan; Barmuta, Jan; Barmuta, Maria

    2014-05-01

    The presented plate tectonic model focuses on Silurian to Early Carboniferous evolution of Central Europe with special attention given to the Sudetes region (north and north-east part of the Bohemian Massif). During our studies, we tested alternative models focused on the position of the Armorican terranes, known as the Armorican Terrane Assembly (ATA) (e.g.: Matte, 2001) and tried to refine the existing reconstructions, which describe Armorica as an individual continent during the Late Silurian and Devonian (e.g. Lewandowski, 2003, Winchester, 2002). Our plate tectonic model depict that these small blocks were scattered along the northern margin of Gondwana, where they formed the "Armorican Spour" as suggested by Kroner and Romer (2013). The seaways were present between blocks. Because of the north dipping subduction zone along the southern margin of the Laurussia continent the back-arc basin and island arc were formed. The narrowing of the Rheic ocean led to the complicated collision of Gondwana and Laurussia. Three main stages of this event can be distinguished: (1) collision of the Armorican Spour with the Laurussian island arc, (2) back-arc basin closure, (3) final Gondwana and Laurussian collision. Those stages correlate well with Variscan Subduction Zone System proposed by Kroner and Romer (2013). Interactive modeling performed in GPlates, shows that the presented model is valid from kinematic and geometrical point of view. Kroner U., Romer R., L., 2013, Two plates - many subduction zones: the Variscan orogeny reconsidered. Gondwana Research, 24: 298-329. Lewandowski M., 2003, Assembly of Pangea: Combined paleomagnetic and paleoclimatic approach, Advances in Geophysics, 46: 199-236 Matte P., 2001, The Variscan collage and orogeny (480 290 Ma) and the tectonic definition of the Armorica microplate: a review. Terra Nova, 13: 122¨C128. Winchester J., A., The Pace TMR Network Team, 2002, Palaeozoic amalgamation of Central Europe: new results from recent

  5. Diagenesis of niagaran (middle silurian) pinnacle reefs, northwest Michigan

    NASA Astrophysics Data System (ADS)

    Cercone, K. R.

    The presence of geothermal gradients 10 to 20 C higher than the current average gradient (25 C/km), and of one kilometer of now eroded overburden in the Michigan Basin during the Paleozoic can be inferred from the high organic maturity of basin strata using the Lopatin method. These data are used to reconstruct the burial history of a single pinnacle reef from northwest Michigan, allowing absolute time constraints to be placed on reef diagenesis. Partial dolomitization occurred during subaerial exposure just after reef growth; regional dolomitization occurred between the late Silurian and the Devonian; and late mineralization by calcite, dolomite and pyrite occurred after Mississippian hydrocarbon emplacement and before the end of the Jurassic. There is no evidence that a well-developed fresh-water lens was ever present in this reef. Regional controls on carbonate diagenesis in this northwest reef trend include: size and hydraulic conductivity of reefs, thickness and lithology of adjacent and overlying evaporites, migration paths of late gypsum-derived and basinal brines, and the timing of anaerobic fermentation in organic-rich carbonates.

  6. Flexural bending of southern Tibet in a retro foreland setting

    PubMed Central

    Wang, Erchie; Kamp, Peter J. J.; Xu, Ganqing; Hodges, Kip V.; Meng, Kai; Chen, Lin; Wang, Gang; Luo, Hui

    2015-01-01

    The highest elevation of the Tibetan Plateau, lying 5,700 m above sea level, occurs within the part of the Lhasa block immediately north of the India-Tibet suture zone (Yarlung Zangbo suture zone, YZSZ), being 700 m higher than the maximum elevation of more northern parts of the plateau. Various mechanisms have been proposed to explain this differentially higher topography and the rock uplift that led to it, invoking crustal compression or extension. Here we present the results of structural investigations along the length of the high elevation belt and suture zone, which rather indicate flexural bending of the southern margin of the Lhasa block (Gangdese magmatic belt) and occurrence of an adjacent foreland basin (Kailas Basin), both elements resulting from supra-crustal loading of the Lhasa block by the Zangbo Complex (Indian plate rocks) via the Great Counter Thrust. Hence we interpret the differential elevation of the southern margin of the plateau as due originally to uplift of a forebulge in a retro foreland setting modified by subsequent processes. Identification of this flexural deformation has implications for early evolution of the India-Tibet continental collision zone, implying an initial (Late Oligocene) symmetrical architecture that subsequently transitioned into the present asymmetrical wedge architecture. PMID:26174578

  7. Paleogeography and evolution of the Ordovician/Silurian (Whiterockian-Llandoverian) continental margin in central Nevada

    SciTech Connect

    Britt, L.W. )

    1991-02-01

    In central Nevada, stratigraphic successions of Whiterockian-Llandoverian lithofacies, transitional with autochthonous platform/shelf carbonates to the east, occur in isolated windows in outer slope to basinal lithotopes of the Roberts Mountains allochthon. Petrologic, chronostratigraphic and lithostratigraphic, and paleontologic comparison of those successions with platform/shelf facies to the east is integral for reconstruction of Ordovician-Silurian platform margin paleogeography and pre-Antler genesis of the western North American continental margin. Numerous facies changes and/or stratigraphic omissions in central Nevada can be related to sea level fluctuation and aggradation/progradation of the carbonate platform to the east, and not to a postulated, offshore geanticline (i.e., the Toiyabe Ridge). Stratigraphic omission of the Eureka Quartzite above Pogonip equivalents in transitional successions of the Toquima Range and the presence of correlative quartzite in outer slope/basinal parautochthonous facies of the Toiyabe Range suggest development of a possible bypass-margin during the Middle Ordovician. Deposition of Late Ordovician platform margin dolostones (Ely Springs Dolostone) and upper ramp limestones (Hanson Creek Formation and Martin Ridge strata) followed Late Ordovician transgression that drowned the margin and reestablished the carbonate factory. Glacioeustatic drawdown of Late Ordovician-earliest Silurian seas due to the Gondwanan glacial fluctuation can be recognized in strata along the platform margin and upper ramp. Rapid, Early Silurian transgression produced dark-gray carbonates and may have induced marginal flexure and regional, massive slope failure in central Nevada, generating stratigraphic hiatuses west of the platform margin.

  8. Depositional response to foreland deformation in the Carboniferous of eastern Kentucky

    SciTech Connect

    Tankard, A.J.

    1986-06-01

    The Appalachian basin is a typical foreland basin that has subsided episodically under the loads of successive thrust sheets. The dynamics of basin subsidence and upwarping of basin-margin arch systems reflects the flex-ural properties of the lithosphere. Quantitative models of the lithosphere depend on assumed rheological properties. This study attempts to test these geodynamic models in a part of the Appalachian basin. Mississippian deposition is correlated with waning Acadian tectonism. Orogenic quiescence coincided with basin overdeepening and uplift of the Cincinnati arch or fore-bulge. Although the foreland basin was mudstone dominated, shoaling along the crest of the basin-margin arch system resulted in reworking and wedges of unconformities. In contrast, the onset of Alleghenian orogenesis during the Pennsylvanian is reflected in a thick wedge of terrigenous clastic sediments. The Pennsylvanian basin fluctuated between underfilled (restricted marine) and overfilled (nonmarine) conditions. Rapid response of the basin to thrust-sheet loading is inferred. These characteristics of Mississippian and Pennsylvanian deposition support a viscoelastic model of the lithosphere.

  9. Search for high-calcium limestone in Silurian reefs of northern Indiana.

    USGS Publications Warehouse

    Ault, C.H.; Carr, D.D.

    1981-01-01

    During Silurian time, the Indiana part of the Wabash Platform was a shallow-water area between the proto-Illinois and proto- Michigan Basins and a site of growth of hundreds, or perhaps thousands, of reefs. Today, most reefs of northern Indiana are dolomite, but some are dolomitic limestone, and a few are limestone of high purity in deposits that can be mined by openpit methods. Four of the five generations of reefs of Silurian age in the Great Lakes area have been recognized in northern Indiana. All known limestone reefs are restricted to an area of six countries in north-central Indiana, although no apparent depositional environment as revealed from study of surrounding inter-reef rocks has been found to account for any restriction. Dolomitization is more likely related to the textures and lithologies of the individual reefs.-from Authors

  10. Chronology and tectonic controls of late tertiary deposition in the southwestern Tian Shan foreland, NW China

    USGS Publications Warehouse

    Heermance, R.V.; Chen, J.; Burbank, D.W.; Wang, C.

    2007-01-01

    Magnetostratigraphy from the Kashi foreland basin along the southern margin of the Tian Shan in Western China defines the chronology of both sedimentation and the structural evolution of this collisional mountain belt. Eleven magnetostratigraphic sections representing ???13 km of basin strata provide a two- and three-dimensional record of continuous deposition since ???18 Ma. The distinctive Xiyu conglomerate makes up the uppermost strata in eight of 11 magnetostratigraphic sections within the foreland and forms a wedge that thins southward. The basal age of the conglomerate varies from 15.5??0.5 Ma at the northernmost part of the foreland, to 8.6??0.1 Ma in the central (medial) part of the foreland and to 1.9??0.2, ???1.04 and 0.7??0.1 Ma along the southern deformation front of the foreland basin. These data indicate the Xiyu conglomerate is highly time-transgressive and has prograded south since just after the initial uplift of the Kashi Basin Thrust (KBT) at 18.9??3.3 Ma. Southward progradation occurred at an average rate of ???3 mm year -1 between 15.5 and 2 Ma, before accelerating to ???10 mm year-1. Abrupt changes in sediment-accumulation rates are observed at 16.3 and 13.5 Ma in the northern part of the foreland and are interpreted to correspond to southward stepping deformation. A subtle decrease in the sedimentation rate above the Keketamu anticline is determined at ???4.0 Ma and was synchronous with an increase in sedimentation rate further south above the Atushi Anticline. Magnetostratigraphy also dates growth strata at <4.0, 1.4??0.1 and 1.4??0.2 Ma on the southern flanks the Keketamu, Atushi and Kashi anticlines, respectively. Together, sedimentation rate changes and growth strata indicate stepped migration of deformation into the Kashi foreland at least at 16.3, 13.5, 4.0 and 1.4 Ma. Progressive reconstruction of a seismically controlled cross-section through the foreland produces total shortening of 13-21 km and migration of the deformation front at

  11. Origin and Spatiotemporal Control of Cuspate Forelands

    NASA Astrophysics Data System (ADS)

    McNinch, J. E.

    2006-12-01

    Cuspate shoreline forms are ubiquitous throughout shorelines of the world and span a wide range in size from sub-meter to 102 kilometers; in grain size from fine to coarse; and in energetic settings from small lakes and lagoons to open ocean beaches with virtually unlimited fetch. Cuspate forelands, with wavelengths ranging from 1-120 km, are found worldwide and are the largest of the rhythmic coastal forms. The origin of cuspate forelands has been debated for well over a century but no theory has emerged that fully explains both the origin and the processes controlling the size and time necessary for development. Despite this uncertainty of spatiotemporal controls, large-scale rhythmic morphology of cuspate forelands strongly suggests that scaling and linkages between physical and sedimentary processes may span many orders of magnitude. The same hydrodynamic forces driving sediment transport at the granular scale, such as wave orbital motion and mean currents, likely play a role in shaping the much larger cuspate shorelines. A survey of passive margin, microtidal shorelines from the US and select locations around the world reveals that cuspate forelands are only found in regions where the predominant wind direction is shore-parallel. Modeling and observations of waves, currents, and sediment accumulation from Cape Lookout, North Carolina indicate that water and sediment are transported well seaward of cuspate foreland promontories by wind-driven and tidal residual currents leading to: 1) the rapid growth of spits and sub-aqueous shoals, 2) elimination of sediment exchange between adjacent littoral cells, and 3) control of the wave diffraction point around the promontories. These results and earlier modeling work related to high-angle waves suggest that wind leads to feedback between waves, currents, and promontory-shoal bathymetry and ultimately defines the size and development time of cuspate forelands. Lastly, a linear relationship between the size of cuspate

  12. Silurian shale origin for light oil, condensate, and gas in Algeria and the Middle East

    SciTech Connect

    Zumberge, J.E. ); Macko, S. ) Engel, M. )

    1996-01-01

    Two of the largest gas fields in the world, Hasi R'Mel, Algeria and North Dome, Qatar, also contain substantial condensate and light oil reserves. Gas to source rock geochemical correlation is difficult due to the paucity of molecular parameters in the former although stable isotope composition is invaluable. However, by correlating source rocks with light oils and condensates associated with gas production using traditional geochemical parameters such as biomarkers and isotopes, a better understanding of the origin of the gas is achieved. Much of the crude oil in the Ghadames/Illizi Basins of Algeria has long been thought to have been generated from Silurian shales. New light oil discoveries in Saudi Arabia have also been shown to originate in basal euxinic Silurian shales. Key sterane and terpane biomarkers as well as the stable carbon isotopic compositions of the C15+ saturate and aromatic hydrocarbon fractions allow for the typing of Silurian-sourced, thermally mature light oils in Algeria and the Middle East. Even though biomarkers are often absent due to advanced thermal maturity, condensates can be correlated to the light oils using (1) carbon isotopes of the residual heavy hydrocarbon fractions, (2) light hydrocarbon distributions (e.g., C7 composition), and (3) compound specific carbon isotopic composition of the light hydrocarbons. The carbon isotopes of the C2-C4 gas components ran then be compared to the associated condensate and light oil isotopic composition.

  13. Silurian shale origin for light oil, condensate, and gas in Algeria and the Middle East

    SciTech Connect

    Zumberge, J.E.; Macko, S. Engel, M.

    1996-12-31

    Two of the largest gas fields in the world, Hasi R`Mel, Algeria and North Dome, Qatar, also contain substantial condensate and light oil reserves. Gas to source rock geochemical correlation is difficult due to the paucity of molecular parameters in the former although stable isotope composition is invaluable. However, by correlating source rocks with light oils and condensates associated with gas production using traditional geochemical parameters such as biomarkers and isotopes, a better understanding of the origin of the gas is achieved. Much of the crude oil in the Ghadames/Illizi Basins of Algeria has long been thought to have been generated from Silurian shales. New light oil discoveries in Saudi Arabia have also been shown to originate in basal euxinic Silurian shales. Key sterane and terpane biomarkers as well as the stable carbon isotopic compositions of the C15+ saturate and aromatic hydrocarbon fractions allow for the typing of Silurian-sourced, thermally mature light oils in Algeria and the Middle East. Even though biomarkers are often absent due to advanced thermal maturity, condensates can be correlated to the light oils using (1) carbon isotopes of the residual heavy hydrocarbon fractions, (2) light hydrocarbon distributions (e.g., C7 composition), and (3) compound specific carbon isotopic composition of the light hydrocarbons. The carbon isotopes of the C2-C4 gas components ran then be compared to the associated condensate and light oil isotopic composition.

  14. 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).

  15. Sperm carriers in Silurian sea scorpions

    NASA Astrophysics Data System (ADS)

    Kamenz, Carsten; Staude, Andreas; Dunlop, Jason A.

    2011-10-01

    Invasion of the land by arachnids required adaptations of numerous organs, such as gills evolving into lungs, as well as mechanisms facilitating sperm transfer in a terrestrial environment. Many modern arachnids use spermatophores for this purpose, i.e. sperm transmitters detached from the body. Exceptionally preserved Silurian (423 Ma) fossils of Eurypterus tetragonophthalmus Fischer, 1839 (Chelicerata: Eurypterida) preserve so-called `horn organs' which we here demonstrate as being equivalent to the spermatophore-producing parts of the genital tract in certain modern arachnids. This clarifies a long-running debate about sexing eurypterids based on the shape of the median abdominal (or genital) appendage. To our knowledge this is also the oldest direct evidence for spermatophore-mediated sperm transfer in the fossil record and suggests that eurypterids had evolved mating techniques using spermatophores as early as the Silurian, a valuable prerequisite for life on land. Spermatophores are absent in sea spiders (Pycnogonida) and horseshoe crabs (Xiphosura); thus the shared presence of sclerotized sperm-transfer devices in eurypterids and arachnids is a novel character, newly elucidated here, which offers explicit support for (Eurypterida + Arachnida). For this clade the name Sclerophorata n. nov. is proposed. Arachnida can be further defined by fusion of the originally paired genital opening.

  16. Silurian pinnacle reefs of the Canadian Arctic

    SciTech Connect

    De Freitas, T.A.; Dixon, O.A. ); Mayr, U. )

    1993-04-01

    Pinnacle reefs are commonly an attractive target for oil exploration because they are usually porous carbonate bodies entombed in impervious, deep-water shales that provide both the source and the seal for hydrocarbons. Silurian pinnacle reefs, the first described in the Canadian Arctic Archipelago, are exposed on Ellesmere and Devon Islands. Two main reef trends occur, one of early middle Llandovery to middle Ludlow age and a second of middle Ludlow to Late Silurian or Early Devonian age. Reefs of both phases contain lime mudstone cores: some are stromatactoid-rich and others consist predominantly of microbialite-rich lime mudstone or microbial boundstone. Facies sequences of both reef phases show evidence of upward-shallowing overall, but, in the older reefs, isochronous capping facies are dominated either by coral-mirian or by stromatoporoid boundstone and floatstone. This difference perhaps reflects variation in wave stress and apparent ability of a few corals,thickly encrusted by or associated with microbial boundstone and skeletal algae, to withstand greater wave energy than a stromatoporoid-coral-rich reef community. These reefs constitute one of the bright prospects of hydrocarbon exploration in rocks of the Franklinian succession. 43 refs., 9 figs.

  17. A Silurian short-great-appendage arthropod

    PubMed Central

    Siveter, Derek J.; Briggs, Derek E. G.; Siveter, David J.; Sutton, Mark D.; Legg, David; Joomun, Sarah

    2014-01-01

    A new arthropod, Enalikter aphson gen. et sp. nov., is described from the Silurian (Wenlock Series) Herefordshire Lagerstätte of the UK. It belongs to the Megacheira (=short-great-appendage group), which is recognized here, for the first time, in strata younger than mid-Cambrian age. Discovery of this new Silurian taxon allows us to identify a Devonian megacheiran representative, Bundenbachiellus giganteus from the Hunsrück Slate of Germany. The phylogenetic position of megacheirans is controversial: they have been interpreted as stem chelicerates, or stem euarthropods, but when Enalikter and Bundenbachiellus are added to the most comprehensive morphological database available, a stem euarthropod position is supported. Enalikter represents the only fully three-dimensionally preserved stem-group euarthropod, it falls in the sister clade to the crown-group euarthropods, and it provides new insights surrounding the origin and early evolution of the euarthropods. Recognition of Enalikter and Bundenbachiellus as megacheirans indicates that this major arthropod group survived for nearly 100 Myr beyond the mid-Cambrian. PMID:24452026

  18. A review of Alpine tectonics in Portugal: Foreland detachment in basement and cover rocks

    NASA Astrophysics Data System (ADS)

    Ribeiro, A.; Kullberg, M. C.; Kullberg, J. C.; Manuppella, G.; Phipps, S.

    1990-12-01

    The Alpine foreland in Portugal was deformed by compressional tectonism during the Miocene. In the NNE-SSW oriented Lusitanian Basin, most folds and thrusts in the Meso-Cenozoic cover are oriented ENE-WSW, parallel to the Alpine front in the Betic Cordillera, and verge towards the north-northwest and south-southeast. The thrusts are connected by lateral ramps: most of these are oriented NNE-SSW to N-S and show sinistral movement, and some are transpressional. The lateral ramps result from reactivation of older extensional faults related to crustal thinning of the continental margin. In the E-W oriented Algarve Basin a simpler basin inversion occurred, with older E-W normal faults reactivated as essentially pure thrusts. In both basins Alpine structures formed above décollements in the Hettangian evaporite-clastic complex. Variscan basement was also deformed by ENE-WSW reverse faults during Miocene time. The similarity in orientation and style of the basement structures to those in the cover suggests that they also occurred by detachment, but their larger scale indicates that the detachment is deep and involves much of the crust. Thus, we interpret the Central Cordillera, in which basement rocks are thrust over Miocene sediments on both sides, as a "pop-up" of crustal scale, elevated above downward-flattening faults that dip towards each other and merge into a single deep detachment. Alpine structures in the Iberian foreland are therefore similar in structural style to those of the Appalachian and Laramide forelands of North America and the Alpine foreland of northwest Europe.

  19. Role of extensional tectonics in the formation of Talladega belt--Blue Ridge successor basins

    SciTech Connect

    Tull, J.F. . Dept. of Geology)

    1993-03-01

    Polydeformed and metamorphosed sequences occurring unconformably above the Cambrian-Ordovician (C-O) miogeoclinal sequence are nested within the Talladega belt (Talladega Group-TG) and Blue Ridge (Mineral Bluff Group-MBG). These successor basin sequences are 2.5--3 km thick and have a possible age range from Ordovician to Devonian, representing the youngest stratigraphic units east of the foreland. They are dominated by turbiditic metaclastic rocks derived from erosion of Grenville basement and its overlying cover of clastic and carbonate rock. Bimodal volcanic rocks occur in the TG, and within-plate mafic extrusive rocks are found in the MBG. The TG consists of a coarsening, thickening, and shallowing upward sequence with a submarine fan-like unit (Lay Dam Formation-LDF) at the base. The LDF contains a thick proximal boulder-bearing olistostromal facies with debris fan lobes stacked vertically and shed from a proximal fault scarp to the SE or S. The vertical stacking of olistostromal deposits, absence of crystalline-cored thrust sheets of this age at the structural top of the basin, and other relationships indicate that the basin did not result from detached deformation to the SE or transcurrent faulting, but rather from extensional faulting. Relationships within the C-O carbonate sequence (Sylacauga Marble Group) unconformably below the TG indicate that the TG basin developed above shallow shelf miogeoclinal rocks inboard of the continental margin hinge line, and thus indicate that Silurian-Devonian extensional structures affected relatively thick Laurentian crust. Similarities in lithofacies and stratigraphic sequence between the TG and MBG indicate that the settling of the MBG may have also been within an extensional basin but basin boundary faults have not yet been identified within the structural block below the pre-MBG unconformity. This basin developed above Laurentian crust previously thinned during late Protozoic rifting.

  20. Foreland normal fault control on northwest Himalayan thrust front development

    NASA Astrophysics Data System (ADS)

    Blisniuk, Peter M.; Sonder, Leslie J.; Lillie, Robert J.

    1998-10-01

    In the Trans-Indus Ranges along the western part of the northwest Himalayan thrust front, unconformities, changes in paleocurrent directions, and locally derived conglomerates in synorogenic foreland basin deposits provide evidence for major local deformation at ≥3.5 Ma. The tectonic history of the Trans-Indus Ranges has previously been described in terms of a single episode of major thrusting at ≤1 Ma, thus our work implies that there were two distinct phases of deformation. In conjunction with published evidence in the Salt Range to the east for two phases of deformation (˜6 to 5 Ma, and ˜2.5 Ma to present), this study demonstrates that these two phases of deformation are regionally significant and probably correlative along the entire present-day NW Himalayan thrust front. Reconstruction of possible source areas for the locally derived conglomerates shows that the earlier deformation is probably related to normal faulting. These results suggest that the tectonic evolution of the area along the present-day thrust front is characterized by (1) latest Miocene to early Pliocene formation of north dipping normal fault zones (total throw ≥ 600 m) within the foreland basin, related to syn-orogenic flexure of the Indian plate, and (2) late Pliocene to early Pleistocene initiation of south directed thrusting along the present-day thrust front, related to outward growth of the NW Himalayan thrust wedge. The location of the present-day thrust front appears to be controlled by north dipping normal faults and monoclines that formed during the earlier deformation and subsequently localized structural ramps during later thrusting.

  1. Silurian magmatism in eastern Senegal and its significance for the Paleozoic evolution of NW-Gondwana

    NASA Astrophysics Data System (ADS)

    Fullgraf, Thomas; Ndiaye, Papa Moussa; Blein, Olivier; Buscail, François; Lahondère, Didier; Le Métour, Joël; Sergeev, Sergey; Tegyey, Monique

    2013-02-01

    Submarine basalt and trachyte of the Nandoumba group occur in eastern Senegal within the Bassarides branch of the Mauritanides orogen. The unit forms part of the parautochthonous domain which is stacked between underlying Neoproterozoic to Paleozoic foreland and overlying Variscan nappes. The crystallisation age of the volcanic to subvolcanic rocks has been determined by U-Pb single zircon SHRIMP method at 428 ± 5.2 Ma whereas zircon xenocryst ages vary from 500 to 2200 Ma. The shape of the xenocryst grains document proximal Neo- and Paleoproterozoic and distal Mesoproterozoic provenance areas for assimilated sediments. This is compatible with the Paleoproterozoic Birimian basement and Neoproterozoic cover rocks nearby whereas an origin from the Amazonian craton could be assumed for distal Mesoproterozoic zircons. Geochemical and Sm-Nd isotope whole rock analysis show that basalts of the Nandoumba group are similar to modern transitional to alkaline volcanic lavas in intraplate settings. Those basalts have a deep mantle source with a great contribution of a recycled mantle component such as EM1 and/or EM2. The basalts resemble in their composition those from the Meguma terrane of Nova Scotia which are of similar age suggesting a common source and therefore connection of Meguma with Gondwana during this period. Review of circum-Atlantic Silurian magmatism indicates ongoing fragmentation of NW-Gondwana that started in Cambro/Ordovician times.

  2. Kinematics of Pre- to Syn-orogenic Normal Faulting in Foreland Area, SW Taiwan

    NASA Astrophysics Data System (ADS)

    Yang, Kenn-Ming; Kuo, Yung-Chien; Wu, Jong-Chang; Chen, Yi-Ju; Wang, Jar-Ben; Ting, Hsin-Hsiu

    2015-04-01

    Taiwan is located at the convergent zone between the Eurasia and Philippine Sea plates, and tectonically characterized by an active orogenic belt. Before arc-continent collision, the foreland area in southwestern Taiwan was a rift basin. The latest rift event started in the Middle to Late Miocene. After the foreland basin development began in the Early Pliocene, normal faulting was still active till the end of the Pliocene or the Early Pleistocene. Today, extensional tectonics is still going on in the most distal part of the foreland basin. The causal relationship of the extensional tectonics to the orogeny is still in debate. In order to understand the relationship between foreland basin and normal faulting, we analyzed the kinematics of normal faults, i.e., the time-spatial variation in the slip rate of normal faulting through the transition from the extensional to foreland basin periods.In this study, normal fault systems were analyzed with seismic interpretation, Allan map, or fault plane analysis, D-L profile and T-Z plot. Normal fault evolutionary history was constructed by the study of normal faults interaction and linkage. Most of normal faults in the study area are characterized by one maximum of slip magnitude in the interior part of a solitude fault plane. The maximum of slip magnitude is not always in the middle part of fault plane but biased to the segment overlapping with the other laterally adjacent fault. However, the summation of D-L plot of two laterally adjacent normal faults indicates maximum of slip magnitude right in the area where two faults are overlapping. Such mode of D-L plot suggests slip transfer from one normal fault to the other. Some D-L plots that show two maxima of slip magnitude may indicate the evolution of linkage between two originally separated faults. Difference between two D-L plots for different formation tops would tell the evolution of fault slip and length. T-Z plots were made on some seismic profiles with well

  3. Gravity survey of marine field: Case study for Silurian reef exploration

    SciTech Connect

    Heigold, P.C.; Whitaker, S.T. )

    1989-08-01

    A gravity survey conducted over and around Marine field in southwestern Illinois has been used as an example to show how measurement of the local gravity field can aid in the search for Silurian reefs in the Illinois basin. Acquisition parameters for gravity surveys over Silurian reefs should be calculated beforehand from simple models of the reef based on estimates of density contrasts, depths, and size. Residual and derivative mapping techniques generally enhance gravity anomalies and enable more accurate portrayals of the structural relief on buried reefs. The second vertical derivative map of the residual Bouguer gravity anomaly surface at Marine field compares very well with the structure of the reef as mapped from subsurface data. This study indicates that similar mapping techniques could be effective on other reefs throughout the Illinois basin. Although gravity mapping methods are potentially powerful exploration tools in themselves, the writers believe that their proper role is as a part of a more comprehensive exploration approach. Gravity surveys can be used effectively as an initial exploration method in reef-prone areas to define smaller, prospect-size areas in which more intensive exploration techniques can subsequently be focused.

  4. Development of sedimentary cycles on the east Sahara craton since Silurian time (northwest Sudan/southwest Egypt)

    SciTech Connect

    Wycisk, P. )

    1988-08-01

    The sedimentary succession of southwest Egypt and northwest Sudan, formerly called the Nubia(n) Sandstone, has been subdivided into a number of formations. The predominantly fluvial sediments which characterize Silurian to Upper Cretaceous strata of this region were repeatedly interrupted by marine transgressions that rapidly progressed toward the south since Ordovician time. Thin, shallow marine sequences of different ages can be traced for more than 1,000 km within the studied area. The development of the sedimentary cycles will be pointed out by surface and subsurface data along a cross section from the southern Dakhla basin in the north to the Misaha trough and Abyad basin in the south.

  5. Upper Jurassic carbonate sediments and reefs in the Carpathian foreland of Poland

    SciTech Connect

    Golenka, J. )

    1993-09-01

    Paleogeographic analyses and plate reconstructions indicate that the Upper Jurassic series of the Carpathian foreland accumulated on the Eurasian shelf of the Tethys Ocean. In the Carpathian foreland of southern Poland, marine Upper Jurassic carbonate series, exceeding 1000 m in thickness, are covered by Tertiary Molasse series or by thrust units of the Outer Carpathians. From a lithostratigraphic point of view, six facies units can be recognized in these Oxfordian to Tithonian carbonates, namely calcareous plankton, calcareous sponge, algal-oolitic, calcareous-marly coquina, dolomitic-calcareous, and upper algal series. During the lower part of the Upper Jurassic, deeper neritic conditions prevailed (calcareous plankton series). These gave way to upward shoaling conditions (calcareous sponge series, deeper basin calcareous-marly series) and a final shallow water environment (algal-oolitic and younger series). Thickness changes of the calcareous-marly series and the diachronous character of the facies boundary between the Oxfordian and Kimmeridgian show that the basin deepened to the south. Barrier reefs and associated fore-reef and back-reef facies occur within the algal-oolitic series. These trend northwest-southeast and reach 30-50 m in thickness. The reefs were mainly built by algae. Algal reefs under the Molasse and Carpathian thrust sheets are potential hydrocarbon exploration targets. The paleogeographic position of the Jurassic of the Carpathian foreland lies within the Tethys realm, which contains a large part of the world's producible oil reserves; this lends encouragement to this play.

  6. Tectonic control of Silurian carbonate-shelf margin morphology and Facies, North Greenland

    SciTech Connect

    Hurst, J.M.; Surlyk, F.

    1984-01-01

    On the basis of profile and topography, three carbonateshelf margin configurations in North Greenland are identified as having been formed during the Silurian. They include escarpment margins which are abrupt and characterized by slope angles of 35/sup 0/ to 40/sup 0/; stepped margins consisting of blocks downstepping into the deep-water basin and with the slope angle inclined from a few up to 40/sup 0/; and ramp margins characterized by gentle slopes and lack of a pronounced break between carbonate shelf and deepwater basin. The carbonate-shelf margins are related to the Navarana Fjord fault and Permin Land flexure. The stepped margin had a similar origin and relation to controlling faults, but later shelf-margin downdropping of blocks may have been contemporaneous with shelf sedimentation.

  7. Integrated provenance analysis of a convergent retroarc foreland system: U-Pb ages, heavy minerals, Nd isotopes, and sandstone compositions of the Middle Magdalena Valley basin, northern Andes, Colombia

    NASA Astrophysics Data System (ADS)

    Nie, Junsheng; Horton, Brian K.; Saylor, Joel E.; Mora, Andrés; Mange, Maria; Garzione, Carmala N.; Basu, Asish; Moreno, Christopher J.; Caballero, Victor; Parra, Mauricio

    2012-01-01

    Sediment provenance analysis remains a powerful method for testing hypotheses on the temporal and spatial evolution of uplifted source regions, but issues such as recycling, nonunique sources, and pre- and post-depositional modifications may complicate interpretation of results from individual provenance techniques. Convergent retroarc systems commonly contain sediment sources that are sufficiently diverse (continental magmatic arc, fold-thrust belt, and stable craton) to enable explicit provenance assessments. In this paper, we combine detrital zircon U-Pb geochronology, heavy mineral identification, Nd isotopic analyses, conventional sandstone petrography, and paleocurrent measurements to reconstruct the clastic provenance history of a long-lived sedimentary basin now exposed in an intermontane zone of the northern Andean hinterland of Colombia. The Middle Magdalena Valley basin, situated between the Central Cordillera and Eastern Cordillera, contains a 5-10 km-thick succession of Upper Cretaceous to Quaternary fill. The integrated techniques show a pronounced change in provenance during the Paleocene transition from the lower to upper Lisama Formation. We interpret this as a shift from an eastern cratonic source to a western Andean source composed of magmatic-arc rocks uplifted during initial shortening of the Central Cordillera. The appearance of detrital chloritoid and a shift to more negative ɛ Nd(t=0) values in middle Eocene strata of the middle La Paz Formation are attributed to shortening-related exhumation of a continental basement block (La Cira-Infantas paleohigh), now buried, along the axis of the Magdalena Valley. The diverse provenance proxies also show distinct changes during middle to late Eocene deposition of the Esmeraldas Formation that likely reflect initial rock uplift and exhumation of the fold-thrust belt defining the Eastern Cordillera. Upsection, detrital zircon U-Pb ages and heavy mineral assemblages for Oligocene and younger clastic

  8. Permian tectonism in Rocky Mountain foreland and its importance in Exploration for Minnelusa and Lyons sandstones

    SciTech Connect

    Moore, W.R.

    1985-05-01

    Permian sandstones are important producers of oil in the Powder River and Denver basins of the Rocky Mountain foreland region. In the Powder River basin, Wolfcampian Minnelusa Sandstone produces oil from structural and stratigraphic traps on both sides of the basin axis, whereas in Denver basin, the Leonardian Lyons Sandstone produces oil mainly from structural traps on the west flank of the basin. Two fields, North Fork-Cellars Ranch in the Powder River basin, and Black Hollow in the Denver basin, are examples of Permian growth of structural features. At North Fork-Cellars Ranch, a period of Permian structural growth and resultant differential sedimentation is documented by structure and isopach maps of the Minnelusa and overlying Goose Egg Formation. Structural growth began at the end of Minnelusa deposition and resulted in deposition of a much thicker Goose Egg section on the west flank of the field. At Black Hollow, mapping indicates structural growth was initiated before deposition of the Lyons Sandstone and continued throughout Leonardian time. In both fields growth abruptly ceased in the Late Permian. Both North Fork-Cellars Ranch and Black Hollow are located on structural highs, or arches, which trend east-west across the Powder River and Denver basins. These arches were present during the pre-Laramide migration of Paleozoic-sourced hydrocarbons into the basins and acted as pathways for migration. Exploration for Permian reservoirs in the two basins should be concentrated on the arches, as the early formed traps were present when migration began.

  9. 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.

  10. Main consistent patterns of Stromatoporoid Development in the Late Ordovician and Silurian in the North Urals Palaeobasin

    NASA Astrophysics Data System (ADS)

    Antropova, E.

    2009-04-01

    In the history of the Earth there have been no basins with similar characteristics. The North Urals palaeobasin had its own unique features. The dominant benthic organisms of basin ecosystem during the Ordovician and Silurian were stromatoporoids, corals, and brachiopods. This fauna is vitally important for the aims of stratigraphy so long as conodonts are extremely rare in sections of the Northern Urals area. The most complete ordering of stromatoporoid complexes has been established and made it possible to estimate rates and measures of extinction at a level of the province. It was also found out that stromatoporoids were organisms responsive to subtle changes of environment and that they accommodated differently to those changing conditions. The evolution of stromatoporoids was accompanied by phylogenetic reorganization and formation of endemic communities in the Late Ordovician and Early Silurian. In the Late Silurian taxonomical diversity of stromatoporoids was mainly controlled by migration processes and cosmopolites with wide palaeogeographic links prevailed in the palaeobasin. Therefore palaeobasin at that time was open to stromatoporoid fauna migration which is confirmed by the occurrence of genera and species that disperse in coeval deposits of many areas, for example, Baltic States, Sweden, Ukraine (Podolia), Western Siberia, Arctic islands of Russia, Mongolia, Canada (islands). The evolution of stromatoporoid communities in the Ordovician-Silurian was intermitted by biotic crises. The analysis of stromatoporoid development helps to define crucial points of ecosystem's reorganizations coinciding with critical geological and biotic events in the history of the North Urals palaeobasin existence, as well as global events during the Ordovician and Silurian (Hirnantian Event, Ireviken Event, Lau Event). The analysis of crises indicates local dependence of stromatoporoid biodiversity on depositional environments. Large local biocenos reorganizations and biotic

  11. Late Early Silurian (Wenlockian) paleoclimate using a general circulation model

    SciTech Connect

    Moore, G.T.; Hayashida, D.N.; Jacobson, S.R. ) Ross, C.A. )

    1992-01-01

    The Silurian Period (439--409 Ma) is synonymous with organic-rich, graptolitic, black shales. The physical conditions that prevailed during the Mid-Silurian drove the paleoclimate and controlled the deposition of this globally ubiquitous, lithotope. The paleoclimate in turn concomitantly created a paleoceanic environment favorable for the generation, deposition, and preservation of phytoplankton. A study of the relationship of the paleogeographic framework on the paleoclimate conditions that forced the deposition of this unique rock type is a problem suitable for study with a general circulation model. For this study the authors chose the Wenlockian Stage (430--424 Ma), the late Early Silurian. The Wenlockian physical world was composed of an oceanic northern hemisphere and a southern hemisphere dominated by the giant continent of Gondwana. The high latitude position of Gondwana placed much of its extensive margin in the mid-latitudes. Laurentia and Baltica occupied a tropical position while Siberia and Kazakh laid to the north. The Silurian fits a paleoatmosphere with an elevated greenhouse effect. Estimated Silurian values of atmospheric CO[sub 2] vary. They chose 1,120 ppm CO[sub 2], a value of 4[times] that of the pre-industrial level. The overall paleoclimate is forced by the diverse paleogeography of the two hemispheres. The northern hemisphere is dominated by strong zonality in all seasons. In contrast, the continental southern hemisphere reactors to the summer heating and winter cooling of Gondwana.

  12. A not-so-big crisis: re-reading Silurian conodont diversity in a sequence-stratigraphic framework

    NASA Astrophysics Data System (ADS)

    Jarochowska, Emilia; Munnecke, Axel

    2016-04-01

    Conodonts are extensively used in Ordovician through Triassic biostratigraphy and fossil-based geochemistry. However, their distribution in rock successions is commonly taken at face value, without taking into account their diverse and poorly understood ecology. Multielement taxonomy, ontogenetic and environmental variability, difficulties in extraction, and relative rarity all contribute to the general lack of quantitative studies on conodont stratigraphic distribution and temporal turnover. With respect to Silurian conodonts, the concept of recurrent conodont extinction events - the so called Ireviken, Mulde and Lau events - has become a standard in the stratigraphic literature. The concept has been proposed based on qualitative observations of local extirpations of open-marine pelagic or nekto-benthic taxa and temporary dominance of shallow-water species in the Silurian succession of the Swedish island of Gotland. These changes coincided with positive carbon isotope excursions, abrupt facies shifts, "blooms" of benthic fauna, and changes in reef communities, which have all been combined into a general view of Silurian bio-geochemical events. This view posits a deterministic, reproducible pattern in Silurian conodont diversity, attributed to recurrent ecological or geochemical conditions. The growing body of sequence-stratigraphic interpretations across these events in Gotland and other sections worldwide indicate that in all cases the Silurian "events" are associated with rapid global regressions. This suggests that faunal changes such as the dominance of shallow-water, low-diversity conodont fauna and the increase of benthic invertebrate diversity and abundance represent predictable consequences of the variation in the completeness of the rock record and preservation potential of different environments. Our studies in Poland and Ukraine indicate that the magnitude of change in the taxonomic composition of conodont assemblages across the middle Silurian global

  13. Foreland crustal structure of the New York recess, northeastern United States

    USGS Publications Warehouse

    Herman, G.C.; Monteverde, D.H.; Schlische, R.W.; Pitcher, D.M.

    1997-01-01

    A new structural model for the northeast part of the Central Appalachian foreland and fold-and-thrust belt is based on detailed field mapping, geophysical data, and balanced cross-section analysis. The model demonstrates that the region contains a multiply deformed, parautochthonous fold-and-thrust system of Paleozoic age. Our interpretations differ from previous ones in which the entire region north of the Newark basin was considered to be allochthonous. The new interpretation requires a substantial decrease in Paleozoic tectonic shortening northeastward from adjacent parts of the Central Appalachian foreland and illustrates the common occurrence of back-thrusting within the region. During early Paleozoic time northern New Jersey consisted of a Taconic orogenic foreland in which cover folds (F1) involved lower Paleozoic carbonate and flysch overlying Middle Proterozoic basement. F1 folds are open and upright in the foreland and more gently inclined to recumbent southeastward toward the trace of the Taconic allochthons. F1 structures were cut and transported by a fold-and-thrust system of the Allegheny orogeny. This thrust system mostly involves synthetic faults originating from a master decollement rooted in Proterozoic basement. Antithetic faults locally modify early synthetic overthrusts and S1 cleavage in lower Paleozoic cover and show out-of-sequence structural development. The synthetic parts of the regional thrust system are bounded in the northwestern foreland by blind antithetic faults interpreted from seismic-reflection data. This antithetic faulting probably represents Paleozoic reactivation of Late Proterozoic basement faults. Tectonic contraction in overlying cover occurred by wedge faulting where synthetic and antithetic components of the foreland fault system overlap. S2 cleavage in the Paleozoic cover stems from Alleghanian shortening and flattening and commonly occurs in the footwall of large overthrust sheets. Paleozoic structures in Proterozoic

  14. Chemostratigraphic and U-Pb geochronologic constraints on carbon cycling across the Silurian-Devonian boundary

    NASA Astrophysics Data System (ADS)

    Husson, Jon M.; Schoene, Blair; Bluher, Sarah; Maloof, Adam C.

    2016-02-01

    The Devonian Period hosts extraordinary changes to Earth's biosphere. Land plants began their rise to prominence, with early vascular vegetation beginning its colonization of near-shore environments in the latest Silurian. Across the Silurian-Devonian (Pridoli-Lochkovian) transition, carbon isotope analyses of bulk marine carbonates (δC13carb) from Laurentian and Baltic successions reveal a positive δC13carb shift. Known as the Klonk Event, values reach + 5.8 ‰, making it one of the largest carbon isotope excursions in the Phanerozoic. Assigning rates and durations to these significant events requires a robust, precise Devonian time scale. Here we present 675 micritic matrix and 357 fossil-specific δC13carb analyses from the lower Devonian Helderberg Group of New York and West Virginia that exhibit the very positive δC13carb values observed in other Silurian-Devonian basins. This chemostratigraphic dataset is coupled with 66 ID-TIMS U-Pb dates on single zircons from six ash falls intercalated within Helderberg sediments, including dates on the stratigraphically lowest Devonian ashes yet developed. In this work, we (a) demonstrate that matrix and fossil-specific δC13carb values track one another closely in the Helderberg Group, (b) estimate the Silurian-Devonian boundary age in New York to be 421.3 ± 1.2 Ma (2σ; including decay constant uncertainties), and (c) calculate the time required to evolve from baseline to peak δC13carb values at the onset of the Klonk event to be 1.00 ± 0.25 Myr. Under these constraints, a steady-state perturbation to the global carbon cycle can explain the observed excursion with modern fluxes, as long as DIC concentration in the Devonian ocean remained below ∼2× the modern value. Therefore, potential drivers, such as enhanced burial of organic carbon, need not rely on anomalously high total fluxes of carbon to explain the Klonk Event.

  15. Seismic expression of Marts field (Silurian reef) in Sullivan County, Indiana

    SciTech Connect

    Renick, H.J. Jr.; Rene, R.M.; Hester, N.C.; Stanonis, F.L. )

    1989-08-01

    The Marts field of Sullivan County, Indiana, is associated with a Silurian reef that is part of the Terre Haute bank on the eastern flank of the Illinois basin. Gas production has come from Pennsylvanian sandstones at Marts field, and oil is presently being produced from limestones of the Devonian Muscatatuck Group. Hydrocarbons were trapped in the Devonian limestones because of structural drape over the reef. A 2.8-km (1.8-mi) north-south 24-CDP reflection seismic profile across the Marts field was obtained by using a hydraulic-assisted weight drop with a source array interval of 16.7 m (55 ft). The data were digitally processed through statics corrections, deconvolution, stack, and migration. These data clearly image drape in Carboniferous and Devonian strata, a characteristic change in reflection pattern at the reef flanks, and diffractions associated with the reef flanks. Near Marts field, one well penetrates Silurian strata, and a synthetic seismogram for this off-reef well is tied to the seismic section. Using well data from Marts and other reefs, mirror-imaged cross-plots of depths to tops of formations vs. depth to top of the Devonian limestone aid in examination of the drape. These plots of transformed cross sections approximate those of vertically stacked right circular cones indicative of the linear relationships between depths to formations.

  16. Late Proterozoic and Silurian alkaline plutons within the southeastern New England Avalon zone

    SciTech Connect

    Hermes, O.D. ); Zartman, R.E. )

    1992-07-01

    Distinct pulses of quartz-bearing, alkaline plutonism and volcanism are known to have occurred in the Avalon zone of southeastern New England during the Late Ordovician, Early Silurian, Devonian, and Carboniferous. Zircon separates from the Franklin and Dartmouth plutons demonstrate that two additional, previously unrecognized periods of alkaline magmatism occurred. The Franklin pluton yields an age of 417 {plus minus} 6 Ma (Late Silurian), whereas the Dartmouth pluton is Late Proterozoic (595 {plus minus} 5 Ma) and markedly older than the other plutons of alkaline affinity. The new ages further emphasize the episodic nature and long-term duration of such alkaline igneous events within the southeastern New England Avalon zone. The Dartmouth pluton may represent a post-collisional alkaline granite emplaced in the Late Proterozoic, almost immediately after a major period of calcalkaline igneous activity that accompanied plate convergence and continental accretion. The abrupt change from orogenic calcalkaline igneous activity to post-collisional alkaline granite, followed by younger episodes of anorogenic emplacement, is remarkably similar to igneous events reported from pan-African mobile belts widespread throughout Africa. In addition, parts of the Dartmouth pluton exhibit features indicative of mixing and commingling of felsic and mafic melts that are associated with coevally formed mylonitic fabrics. Because these fabrics are conformable to those in adjacent gneisses, but discordant with Alleghanian fabrics in the nearby Carboniferous Narragansett basin, they represent some of the best candidates for pre-Alleghanian structures thus far identified in the southeastern New England Avalon zone.

  17. A possible explanation for foreland thrust propagation

    NASA Astrophysics Data System (ADS)

    Panian, John; Pilant, Walter

    1990-06-01

    A common feature of thin-skinned fold and thrust belts is the sequential nature of foreland directed thrust systems. As a rule, younger thrusts develop in the footwalls of older thrusts, the whole sequence propagating towards the foreland in the transport direction. As each new younger thrust develops, the entire sequence is thickened; particularly in the frontal region. The compressive toe region can be likened to an advancing wave; as the mountainous thrust belt advanced the down-surface slope stresses drive thrusts ahead of it much like a surfboard rider. In an attempt to investigate the stresses in the frontal regions of thrustsheets, a numerical method has been devised from the algorithm given by McTigue and Mei [1981]. The algorithm yields a quickly computed approximate solution of the gravity- and tectonic-induced stresses of a two-dimensional homogeneous elastic half-space with an arbitrarily shaped free surface of small slope. A comparison of the numerical method with analytical examples shows excellent agreement. The numerical method was devised because it greatly facilitates the stress calculations and frees one from using the restrictive, simple topographic profiles necessary to obtain an analytical solution. The numerical version of the McTigue and Mei algorithm shows that there is a region of increased maximum resolved shear stress, τ, directly beneath the toe of the overthrust sheet. Utilizing the Mohr-Coulomb failure criterion, predicted fault lines are computed. It is shown that they flatten and become horizontal in some portions of this zone of increased τ. Thrust sheets are known to advance upon weak decollement zones. If there is a coincidence of increased τ, a weak rock layer, and a potential fault line parallel to this weak layer, we have in place all the elements necessary to initiate a new thrusting event. That is, this combination acts as a nucleating center to initiate a new thrusting event. Therefore, thrusts develop in sequence

  18. Silurian Gastropoda from the Alexander terrane, southeast Alaska

    USGS Publications Warehouse

    Rohr, D.M.; Blodgett, R.B.

    2008-01-01

    Gastropods are described from Ludlow-age strata of the Heceta Limestone on Prince of Wales Island, southeast Alaska. They are part of a diverse megabenthic fauna of the Alexander terrane, an accreted terrane of Siberian or Uralian affinities. Heceta Limestone gastropods with Uralian affinities include Kirkospira glacialis, which closely resembles "Pleurotomaria" lindstromi Oehlert of Chernyshev, 1893, Retispira cf. R. volgulica (Chernyshev, 1893), and Medfracaulus turriformis (Chernyshev, 1893). Medfracaulus and similar morphotypes such as Coelocaulus karlae are unknown from rocks that are unquestionably part of the North American continent (Laurentia) during Late Silurian time. Beraunia is previously known only from the Silurian of Bohemia. Pachystrophia has previously been reported only from western North American terranes (Eastern Klamath, York, and Farewell terranes) and Europe. Bathmopterus Kirk, 1928, is resurrected and is only known from the Silurian of southeast Alaska. Newly described taxa include Hecetastoma gehrelsi n. gen. and n. sp. and Baichtalia tongassensis n. gen. and n. sp. ??2008 The Geological Society of America.

  19. The largest Silurian vertebrate and its palaeoecological implications

    PubMed Central

    Choo, Brian; Zhu, Min; Zhao, Wenjin; Jia, Liaotao; Zhu, You'an

    2014-01-01

    An apparent absence of Silurian fishes more than half-a-metre in length has been viewed as evidence that gnathostomes were restricted in size and diversity prior to the Devonian. Here we describe the largest pre-Devonian vertebrate (Megamastax amblyodus gen. et sp. nov.), a predatory marine osteichthyan from the Silurian Kuanti Formation (late Ludlow, ~423 million years ago) of Yunnan, China, with an estimated length of about 1 meter. The unusual dentition of the new form suggests a durophagous diet which, combined with its large size, indicates a considerable degree of trophic specialisation among early osteichthyans. The lack of large Silurian vertebrates has recently been used as constraint in palaeoatmospheric modelling, with purported lower oxygen levels imposing a physiological size limit. Regardless of the exact causal relationship between oxygen availability and evolutionary success, this finding refutes the assumption that pre-Emsian vertebrates were restricted to small body sizes. PMID:24921626

  20. A New Noncalcified Dasycladalean Alga from the Silurian of Wisconsin

    USGS Publications Warehouse

    LoDuca, S.T.; Kluessendorf, Joanne; Mikulic, Donald G.

    2003-01-01

    Noncalcified thalli, consisting of a narrow main axis with numerous branched hairlike laterals in whorls and a subapical array of undivided clavate laterals, from the Silurian (Llandovery) Brandon Bridge Formation of southeastern Wisconsin, constitute the basis for a new genus and species of dasycladalean alga, Heterocladus waukeshaensis. A relationship within the family Triploporellaceae is indicated by the whorled arrangement of the laterals and the absence of gametophores on mature specimens. A compilation of occurrence data suggests that noncalcified dasyclads, as a whole, were more abundant and diverse during the Ordovician and Silurian than at any other time in their history. The heterocladous thallus architecture of this alga adds to a wide range of morphological variation documented among Ordovician and Silurian dasyclads, the sum of which indicates that Dasycladales underwent a significant evolutionary radiation during the early Paleozoic.

  1. Late Silurian trilete spores from northern Jiangsu, China.

    PubMed

    Wang; Li

    2000-08-01

    The Late Silurian is generally considered to a particular significant key period in the study of early land vascular plants. A trilete spore assemblage of the Upper Silurian is described from northern Jiangsu, China. This assemblage comprises 11 genera and 20 species of trilete spores (including laevigate, apiculate, perinotrilite, patinate, rarely distally murornate and equatorially crassitate, and three indeterminate trilete miospores forms). It has similarities to those described from coeval assemblages from around the world (e.g., England and South Wales; Tripolitania, Libya; Cornwallis Island, Canadian Arctic; Northwest Spain). The rare cryptospore, only one specimen (Tetrahedraletes sp.) had been found to be associated with the Chinese trilete spore assemblage. The discovery of the trilete spores from Late Silurian rocks indicates the existence of early land plants, some possibly vascular, at that time in northern Jiangsu, China.

  2. Silurian tectonic history of Penobscot Bay region, Maine

    USGS Publications Warehouse

    Stewart, D.B.; Unger, J.D.; Hutchinson, D.R.

    1995-01-01

    Early Paleozoic amalgamation of composite terranes was contemporaneous at widely separated regions that were later accreted to either ancestral North America or to Gondwana as those two continents approached each other. Peri-Gondwanan terranes formed from Late Cambrian and Early Ordovician rocks were amalgamated in the Late Ordovician and Early Silurian to form the Salinic orogenic belt. Salinic orogenic activity involved extensive thrust faulting and metamorphism, large strike-slip faults, and plutonism. In the Penobscot Bay region, Maine, the peri-Gondwanan St. Croix terrane was thrust northwest in the Silurian(?) upon middle amphibolite facies Ordovician and Early Silurian rocks of the Fredericton trough. The strike-slip faults are interpreted to either remain steep until they reach the sole of the thrust sheet or to become listric within the thrust sheet. -from Authors

  3. What controls the growth and shape of the Himalayan foreland fold-and-thrust belt?

    NASA Astrophysics Data System (ADS)

    Grujic, Djordje; Hirschmiller, John; Mallyon, Deirdre

    2014-05-01

    We provide empirical evidence for the impact of surface processes on the structure and geometry of the present-day foreland fold-and-thrust belt (FTB) of the Himalaya. We have reconstructed and analysed ten balanced cross sections distributed along the entire length of the Himalayan arc. Here, we focus on the Siwalik Group, which represents the deformed part of the foreland basin and consists of synorogenic middle Miocene to Pleistocene sediments that form the youngest and frontal part of the Himalayan orogen. Within the active foreland fold-and-thrust belt of the Himalaya, extension, strain rate, and belt morphology vary systematically from west to east. Strain rates correlate well with west-to east increases in convergence rates according to both long-term plate velocity data and GPS data, suggesting that Pliocene to Holocene shortening is externally imposed and related to plate convergence rates. Conversely, the eastward decrease in belt width corresponds to an eastward increase in rainfall rates and specific stream power. Although mass accretion rates have not been well constrained, we argue that they remain relatively constant along the FTB. We suggest that the morphology of the Himalayan FTB is controlled primarily by erosion, in accordance with the critical taper model. Surface material removal is mainly controlled through rainfall and runoff and can be expressed as specific stream power. Thus, we propose that climatically induced erosion is the principal control on Himalayan foreland fold-and-thrust belt morphology. We test this hypothesis through a series of 1D numerical models. Among the parameters controlling the form of a wedge, lithology, erodibility, and rock mechanical properties are relatively homogeneous throughout the belt. Hence, within the range of observed values in the Himalaya, we investigate the sensitivity of the shape of the Himalayan fold-and-thrust belt to the sole-out depth of the basal décollement, flux of tectonically added material

  4. Oblique slip in Laramide foreland arches

    SciTech Connect

    Erslev, E.A.; Selvig, B.; Molzer, P. . Dept. of Earth Resources)

    1993-03-01

    Don Wise was one of the first structural geologists to recognize the complex, four-dimensional (space and time) nature of basement-involved faulting in the Rocky Mountain foreland. His focus on both small scale kinematic indicators and regional tectonic hypotheses has provided a launching point for many Rocky Mountain geologists. The implications of the anastomosing patterns of Laramide foreland arches on models of regional stress and strain have provoked considerable debate. Hypotheses range from those invoking multiple stages of lateral compression from different directions to single-stage models necessitating a component of strike-slip motion in east-west and north-south arches. These hypotheses were tested using slickenline analysis of minor faulting in structures with different orientations. In Wyoming, structures paralleling the dominant northwest structural trend have slickenlines in the NE-SW vertical plane, consistent with shortening and compression in this direction. The east-west Owl Creek and Casper Mountain structures also have NE-SW trending slickenlines, indicating slip oblique to these arches. In Colorado, minor faults in the north-south margin of the northeastern Front Range also indicate oblique slip, with shortening in the NE-SW quadrant. The actual trend of the slickenlines is more easterly, however, suggesting a change of slip trajectory with latitude, not time, possibly in response to identation by the Colorado Plateau.

  5. Variscan fold belt and its foreland in western Europe from late Carboniferous to Permian time

    SciTech Connect

    Mascle, A.; Benard, F.; Cazes, M.; Le Gall, B.

    1988-08-01

    The Variscan front was emplaced in the Later Carboniferous with a south-to-north or southeast-to-northwest-trending vergence of thrusting. At the same time, folds were formed in the foreland. In England and southern Scotland, such structures were induced by an east-west direction of shortening, followed by a more subdued north-south compressive event. In Stephanian time, isolated basins developed on the Hercynian belt. In the Massif Central Marues Massif, they are closely related to transcurrent faults which developed in response to north-south-trending compressive stresses. The distribution of stresses completely changed in Early Permian time when extension dominated almost everywhere. Three kinds of basins developed at that time: those related to the relaxation of stresses on the Hercynian range, a north-south-trending rift system in the western United Kingdom and the North Sea, and a broad flexural evaporitic basin from eastern England to Poland.

  6. A starfish with three-dimensionally preserved soft parts from the Silurian of England

    PubMed Central

    Sutton, M.D; Briggs, D.E.G; Siveter, David J; Siveter, Derek J; Gladwell, D.J

    2005-01-01

    Palaeozoic asteroids represent a stem-group to the monophyletic post-Palaeozoic Neoasteroidea, but many aspects of their anatomy are poorly known. Using serial grinding and computer reconstruction, we describe fully articulated Silurian (ca 425 Myr) specimens from the Herefordshire Lagerstätte, preserved in three dimensions complete with soft tissues. The material belongs to a species of Bdellacoma, a genus previously assigned to the ophiuroids, but has characters that suggest an asteroid affinity. These include a pyloric system in the gut, and the presence of large bivalved pedicellariae, the latter originally described under the name Bursulella from isolated valves. Ampullae are external and occur within podial basins; the radial canal is also external. Podia are elongate and lack terminal suckers. The peristome is large relative to the mouth. Aspects of the morphology are comparable to that of the extant Paxillosida, supporting phylogenetic schemes that place this order at the base of the asteroid crown group. PMID:16024357

  7. Silurian of central Texas: a first record for the region.

    PubMed

    Barnes, V E; Boucot, A J; Cloud, P E; Miller, R H; Palmer, A R

    1966-11-25

    Silurian outcrops, not previously recorded from central Texas, have been identified from the Llano uplift, where they occur in collapse structures within the Lower Ordovician Honeycut Formation of the Ellenburger Group. The formation is a pinkish-gray granular limestone, contains fossils of probable Wenlock age, and is named the Starcke Limestone.

  8. Subsurface stratigraphy of Medina Group (Lower Silurian), Clinton Group (Lower to Upper Silurian), and Lockport Group (Upper Silurian) of New York

    SciTech Connect

    Kearney, M.W.; Rickard, L.V.

    1984-12-01

    A network of ten regional cross sections across New York reveals the detailed subsurface stratigraphy of the Medina Group (Lower Silurian), Clinton Group (Lower to Upper Silurian), and Lockport Group (Upper Silurian). Both ..gamma..-ray logs and sample logs were used to correlate from outcrop to subcrop and well to well throughout the subsurface of New York. Approximately 250 well logs and 125 sample logs were incorporated into this study. The study indicates that the Median Group can be subdivided into the Whirlpool, Power Glen, and Grimsby Formations. The Clinton Group is subdivided into 16 formations. In the west, the Clinton Group includes the Thorold, Reynales, Irondequoit, and Rochester Formations. In central and eastern New York, this group is subdivided into the Oneida, Bear Creek, Kodak, Sodus, Wolcott, Otsquaqo, Willowvale, Sauquoit, Williamson, Irondequoit, Dawes, and Heidimer Formations. Two formations are recognized in the Lockport Group: the Sconondoa and Ilion Formations. In addition to the stratigraphy, the cross sections also display the regional geometry of this rock sequence, vertical and lateral changes in lithology, and the presence and nature of several unconformities.

  9. Foreland sedimentary record of Andean mountain building during advancing and retreating subduction

    NASA Astrophysics Data System (ADS)

    Horton, Brian K.

    2016-04-01

    As in many ocean-continent (Andean-type) convergent margins, the South American foreland has long-lived (>50-100 Myr) sedimentary records spanning not only protracted crustal shortening, but also periods of neutral to extensional stress conditions. A regional synthesis of Andean basin histories is complemented by new results from the Mesozoic Neuquén basin system and succeeding Cenozoic foreland system of west-central Argentina (34-36°S) showing (1) a Late Cretaceous shift from backarc extension to retroarc contraction and (2) an anomalous mid-Cenozoic (~40-20 Ma) phase of sustained nondeposition. New detrital zircon U-Pb geochronological results from Jurassic through Neogene clastic deposits constrain exhumation of the evolving Andean magmatic arc, retroarc thrust belt, foreland basement uplifts, and distal eastern craton. Abrupt changes in sediment provenance and distal-to-proximal depositional conditions can be reconciled with a complex Mesozoic-Cenozoic history of extension, post-extensional thermal subsidence, punctuated tectonic inversion involving thick- and thin-skinned shortening, alternating phases of erosion and rapid accumulation, and overlapping igneous activity. U-Pb age distributions define the depositional ages of several Cenozoic stratigraphic units and reveal a major late middle Eocene-earliest Miocene (~40-20 Ma) hiatus in the Malargüe foreland basin. This boundary marks an abrupt shift in depositional conditions and sediment sources, from Paleocene-middle Eocene distal fluviolacustrine deposition of sediments from far western volcanic sources (Andean magmatic arc) and subordinate eastern cratonic basement (Permian-Triassic Choiyoi igneous complex) to Miocene-Quaternary proximal fluvial and alluvial-fan deposition of sediments recycled from emerging western sources (Malargüe fold-thrust belt) of Mesozoic basin fill originally derived from basement and magmatic arc sources. Neogene eastward advance of the fold-thrust belt involved thick

  10. Late miocene tidal deposits in the amazonian foreland basin.

    PubMed

    Räsänen, M E; Linna, A M; Santos, J C; Negri, F R

    1995-07-21

    Late Miocene tidal sediments of Acre, Brazilian Amazonia, were deposited in an embayment or interior seaway located in the sub-Andean zone. This late Tertiary embayment system may once have connected the Caribbean with the South Atlantic. The tidal coasts of the embayment-seaway have provided an avenue for the earliest waif (over water) dispersal phases of the great American biotic interchange in the late Miocene. The subsequent change from semimarine to terrestrial environments is of value in assessing the importance of earlier hypotheses on the evolution of the westem Amazonian landscape and gives insight into the formation of several observed biogeographic patterns, especially of aquatic biota.

  11. Late Miocene Tidal Deposits in the Amazonian Foreland Basin

    NASA Astrophysics Data System (ADS)

    Rasanen, Matti E.; Linna, Ari M.; Santos, Jose C. R.; Negri, Francisco R.

    1995-07-01

    Late Miocene tidal sediments of Acre, Brazilian Amazonia, were deposited in an embayment or interior seaway located in the sub-Andean zone. This late Tertiary embayment system may once have connected the Caribbean with the South Atlantic. The tidal coasts of the embayment-seaway have provided an avenue for the earliest waif (over water) dispersal phases of the great American biotic interchange in the late Miocene. The subsequent change from semimarine to terrestrial environments is of value in assessing the importance of earlier hypotheses on the evolution of the western Amazonian landscape and gives insight into the formation of several observed biogeographic patterns, especially of aquatic biota.

  12. Offshore-onshore recent tectonic deformations in the eastern Rif and its foreland (Alhoceima-Nador, Morocco)

    NASA Astrophysics Data System (ADS)

    Ruano, Patricia; Galindo-Zaldívar, Jesús; Comas, Menchu; Chalouan, Ahmed; Azzouz, Omar; Jesús Román-Alpiste, Manuel; Pedrera, Antonio; Sanz de Galdeano, Carlos; López-Garrido, Ángel Carlos; Benmakhlouf, Mohamed; Roldán-García, Francisco Javier; Anahnah, Farida; González-Castillo, Lourdes

    2014-05-01

    The Rif Cordillera is formed by the southwestwards emplacement of the internal zones on the African foreland in the western Alboran Sea. However, the recent deformations are driven also by interaction with the NW-SE convergence of the Eurasian and African plates. The eastern Rif and its foreland constitute a key region to study the variability in structure and stresses related to a lateral boundary of this Alpine Cordillera. The continental crust of the Rif thinned toward Alboran Sea. The onshore and offshore area nearby the coast line, between Al Hoceima and Nador are suitable for recent tectonics studies due to the presence of wide Neogene and Quaternary basins that contribute to record the activity of recent structures. Multichannel seismic reflection data obtained along the coast during the GASALB cruise in November 2011, together with available data, allows to characterize the differences of the Rif and forleland Neogene-Quaternary basins. Offshore results are compared with field observations, that detailed cover several areas. In the Rif Cordillera (Al Hoceima area), recent basins open towards the Alboran Sea are formed by the active roughly N-S oriented faults in this seismogenic area. They are mainly normal in onshore area and becomes strike-slip offshore connecting with sinistral Al-Idrisi fault zone. In contrast, in the foreland represented by the Trois Fourches area, onshore N-S faults are inactive and are developed above a very well exposed folded detachment. Paleostress data in this area support the activity of the exhumed low-angle faults with NE-SW extension and a late radial extension. These new data allows underline the different stresses and age of deformation in the Rif and its foreland and support a westward displacement of deformation along recent time. Then, the most active and hence higher seismic hazard along Moroccan coast, also related to possible tsunamogenic faults, are located offshore Alhoceima area.

  13. BASINS

    EPA Pesticide Factsheets

    Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) is a multipurpose environmental analysis system designed to help regional, state, and local agencies perform watershed- and water quality-based studies.

  14. Stratigraphic sequence analysis of the Antler foreland

    SciTech Connect

    Silberling, N.J.; Nichols, K.M.; Macke, D.L. )

    1993-04-01

    Mid-Upper Devonian to Upper Mississippian strata in western Utah were deposited in the distal Antler foreland. They record lateral and vertical changes in depositional environments that define five successive stratigraphic sequences, each representing a third-order transgressive-regressive cycle. In ascending order, these sequences are informally named the Langenheim (LA) of late Frasnian to mid-Famennian age, the Gutschick (GU) of late Famennian to early Kinderhookian age, the Morris (MO) of late Kinderhookian age; the Sadlick (SA) of Osagean to early Meramecian age, and the Maughan (MA) of mid-Meramecian to Chesterian age. MO is widespread and recognized within carbonate rocks of the Fitchville Formation and Joana Limestone. SA formed in concert with and to the east and south of the Wendover foreland high; the Delle phosphatic event marks maximum marine flooding during SA deposition. The transgressive systems tract of MA includes rhythmic-bedded limestone in the upper part of the Deseret Limestone in west-central Utah and, farther west, the hypoxic limestone and black shale of the Skunk Spring Limestone Bed and part of the overlying Chainman Shale. Traced westward into Nevada, MA first oversteps SA and then MO. Lithostratigraphic correlation of these sequences still farther west into the Eureka thrust belt (ETB) could mean that the youngest strata truncated by the Roberts Mountains thrust belong to the MA and that this thrust is simply part of the post-Mississippian ETB. However, some strata in central Nevada that lithically resemble those of the MA are paleontologically dated as Early Mississippian, the age of sequences overstepped by MA not far to the east. Thus, at least some imbricates of the ETB may contain a sequence stratigraphy which reflects local tectonic control.

  15. Paleogeographic and paleotectonic setting of sedimentary basins in the Sevier thrust belt and hinterland, eastern Great Basin

    SciTech Connect

    Schmitt, J.G. . Dept. of Earth Sciences); Vandervoort, D.S. . Dept. of Geological Sciences); Suydam, J.D. . Dept. of Geology)

    1993-04-01

    The eastern Great Basin contains a sparse record of broadly distributed Cretaceous sedimentary rocks which record: evolution of intermontane basins during development of the Sevier (Sv)contractional orogen and incipient extensional collapse of the elevated Sv hinterland (east-central NV), and complex tectono-sedimentary interactions between frontal thrust belt structures and the western margin of the adjacent foreland basin. Palinspastic restoration of these strata and associated structures to pre-Tertiary extension positions reveals a clearer pictures of Cretaceous basin paleogeography and allows comparison with the Puna/Altiplano plateau and precordillera thrust belt of the Neogene Andean orogen. Two syntectonic stratal assemblages are present in east-central NV. Lower Cretaceous alluvial strata (Newark Canyon Fm) record basin development coeval with emergence of contractional structures in the Sv hinterland. Localized early Cretaceous basins were possibly piggyback immature; periods of open drainage to the to the east and south suggest connection with the nascent Sv foreland basin to the east (Cedar Mountain/Sanpete Fms) prior to major thrust loading in central Utah. Development of hinterland structures is almost recorded by Aptian-Albian foreland basin alluvial deposits in SW Utah (Dakota Fm) and southern Nevada (Willow Tank Fm). Upper Cretaceous to Eocene strata (Sheep Pass Fm) record inception of regionally abundant alluvial-lacustrine basins which developed in response to onset of latest Cretaceous extension and associated collapse of the Sv hinterland. Evolution of the structurally complex western margin of the Sv foreland basin is recorded in Cretaceous through Eocene strata deposited in: piggyback basins which were at times hydrologically connected to the adjacent foreland basins, and thrust-proximal portions of the foreland basin. These proximal areas are characterized by folding and faulting of basin fill and development of intrabasinal unconformities.

  16. Northward collapse of the Variscan orogen in response to multiple detachments: a view from the French internides to the Irish Sea foreland

    NASA Astrophysics Data System (ADS)

    Praeg, D.

    2003-04-01

    The Permo-Carboniferous transition from compression to extension across the Variscan orogen and its northern foreland has been attributed to models driven by plate movements, such as wrench-faulting, that imply regionally synchronous post-orogenic activity. In contrast, models of late-orogenic collapse predict diachronous tectonism, in which outward migrating extension may be compensated by peripheral compression. A review of published data on the ages of extensional and compressional structures along a 1500 km transect from the Variscan internides (Massif Central) to the foreland in the Irish Sea area provides evidence of diachronous tectonism. Three stages of outward collapse are identified: i) late Visean to mid-Westphalian (ca. 330-310 Ma) crustal extension within a relatively narrow (<500 km) central axis, accompanied to the north by deposition within a broad seaway inherited from closure of the Rheic ocean; ii) a dramatic expansion of tectonic activity, beginning with a mid-Westphalian (ca. 310 Ma) phase of compression that extended northward to the foreland, followed by the Stephanian formation of basins (outward younging and thinning), coeval with final nappe emplacement along the northern orogenic front; iii) widespread uplift and erosion of the foreland in the late Stephanian (ca. 300-295 Ma), followed by equally widespread basin formation in the Early Permian. The first two stages are consistent with previous proposals that the collapse of the Variscan orogen was driven by successive detachments from the base of the lithosphere of an orogenic root and of a previously subducted (Rheic) oceanic slab. The third stage is argued to record the detachment of a second Rheic oceanic slab subducted northward beneath the Irish foreland. Multiple detachments of lower lithospheric material are a predictable consequence of ocean closure and continental collision, so that episodic collapse may be a common process in the rise and fall of orogens and the tectonic

  17. Agglutinated foraminifera from the Ludlow (Silurian) of Ireland

    NASA Astrophysics Data System (ADS)

    Kaminski, Michael; Ferretti, Annalisa; Messori, Fabio; Papazzoni, Cesare Andrea; Sevastopulo, George

    2017-04-01

    Agglutinated foraminifera are one of the most primitive groups of foraminifera, possibly already appearing in the Cryogenian but usually rare in lower Paleozoic rocks. Their mean standing diversity slowly increased during Cambrian and Ordovician times, reaching a stable value of about 50 genera in the mid-Silurian which remained fairly constant up to the Triassic. An assemblage of agglutinated foraminifera was unexpectedly found in conodont residue from material collected in the Dingle Peninsula, County Kerry, southwestern Ireland. This material comes from rare calcareous occurrences in volcanoclastics previously known for their rich trilobite and conodont assemblages. The limestones are trilobite-crinoidal silty wackestone to packstone, with local brachiopod concentrations, documenting brachiopod-trilobite-crinoidal dominated communities of shallow and well-ventilated water that might have periodically colonized the bottom intercalating with volcanic events and then successively redeposited in deeper waters. The conodont fauna indicates an early Ludlow (Gorstian-earliest Ludfordian) age (Kaminski et al., 2016). The foraminiferal assemblage has limited potential for stratigraphical correlation as long-range taxa are present, but it represents the first record from the Silurian of Ireland. The assemblage is dominated by tubothalamids (Rectoammodiscus and rare Sansabaina), with less abundant monothalamids (Psammosiphonella and Psammosphaera). The assemblage displays low diversity compared with other assemblages described from the British Isles (Kircher & Brasier, 1989). At the species level, this assemblage is identical to those described previously from the Silurian of North America but with lower diversity. Only Rectoammodiscus diai had apparently a wider geographic distribution, including not only the central USA (Oklahoma and Kansas) but also the Welsh Borderlands and Senegal. The affinities with the assemblages reported at several localities in the central

  18. Off-platform Silurian sequences in the Ambler River quadrangle: A section in Geologic studies in Alaska by the U.S. Geological Survey during 1987

    USGS Publications Warehouse

    Dumoulin, Julie A.; Harris, Anita G.

    1988-01-01

    Lithofacies changes in coeval upper Paleozoic rocks have been used to unravel the tectonic history of northern Alaska (for example, Mayfield and others, 1983). Conodont biostratigraphy and detailed petrologic studies are now revealing facies differences in lower Paleozoic rocks that can also be used to constrain their tectono-sedimentary framework (Dumoulin and Harris, 1987). A basic element of basin analysis is the discrimination of shallow-water shelf and platform sequences from deeper water slope and basinal deposits. This report documents several new localities of deeper water, off-platform Silurian deposits in the Ambler River quadrangle and briefly outlines some of their paleogeographic implications.

  19. Iridium abundances across the ordovician-silurian stratotype.

    PubMed

    Wilde, P; Berry, W B; Quinby-Hunt, M S; Orth, C J; Quintana, L R; Gilmore, J S

    1986-07-18

    Chemostratigraphic analyses in the Ordovician-Silurian boundary stratotype section, bracketing a major extinction event in the graptolitic shale section at Dob's Linn, Scotland, show persistently high iridium concentrations of 0.050 to 0.250 parts per billion. There is no iridiumn concentration spike in the boundary interval or elsewhere in the 13 graptolite zones examined encompassing about 20 million years. Iridium correlated with chromium, both elements showing a gradual decrease with time into the middle part of the Lower Silurian. The chromium-iridium ratio averages about 10(6). Paleogeographic and geologic reconstructions coupled with the occurrence of ophiolites and other deep crustal rocks in the source area suggest that the high iridium and chromium concentrations observed in the shales result from terrestrial erosion of exposed upper mantle ultramafic rocks rather than from a cataclysmic extraterrestrial event.

  20. Imprint of foreland structure on the deformation of a thrust sheet: The Plio-Pleistocene Gela Nappe (southern Sicily, Italy)

    NASA Astrophysics Data System (ADS)

    Ghisetti, Francesca C.; Gorman, Andrew R.; Grasso, Mario; Vezzani, Livio

    2009-08-01

    In Sicily, the progressive imbrication of the Apenninic thrust belt above the Pelagian-African Foreland is traced by the southward migration of marine basins that were progressively shortened during the late Miocene-Pleistocene. The outermost and youngest thrust sheet (Gela Nappe) displays a peculiar shortening, with Messinian to early Pliocene E-W folds refolded in the late Pliocene-early Pleistocene by approximately N-S folds (subparallel to the transport direction of the thrust sheets). This structural interference is documented in south Sicily within localized belts of refolding spaced ˜5-8 km apart. The significance of this fold interference pattern is highlighted by our analysis of the offshore seismic reflection line M23A (CROP Mare Project) that intersects the Gela Nappe along a trace suborthogonal to the thrust transport direction. Migration and depth conversion of the line reveal multiple imbrications and draping of the allochthonous units above structural highs of the foreland, delimited by inherited N-S faults. The largest faults bound mid-late Miocene extensional basins but were reactivated in compression during the late Pliocene-early Pleistocene, causing (1) superposed folding along discordant N-S structural trends, (2) compressional extrusion of the whole wedge of the Gela Nappe, and (3) offset of its sole thrust. The reactivation of faults subparallel to the transport direction accommodates differential flexure of the rigid foreland beneath the Apenninic wedge, and these late stage deformations in the foreland are responsible for the superposition of E-W finite shortening onto N-S shortening.

  1. Correlation of hierarchal Upper Silurian stacking patterns generated by Milankovitch orbital forcing

    SciTech Connect

    Mauriello, D.J.; Ketterer, M.W. . Dept. of Geology)

    1993-03-01

    The Upper Silurian Wills Creek Formation in Pennsylvania and Maryland is entirely divisible into meter-scale allocycles. Stacking patterns of these allocycles reveal a hierarchy consistent with predictions based on the Milankovitch model of orbital forcing. Asymmetrical Sixth-Order cycles (PACs), bounded by surfaces produced by precessional sea-level rises, are divisible into a lower highstand portion and an upper lowstand portion separated by a sharp sea-level fall surface produced by a rapid sea-level drop within the precessional cycle. Sixth-Order cycles may be genetically grouped into Fifth-Order (100 ky.) and subsequently, Fourth-Order (400 ky.) cycles, each of which exhibits a distinct internal symmetry. Fifth-Order cycles, on average three to four meters in thickness, are composed of a basal transgressive portion consisting of two PACs followed by two or three successively regressive PACs. Four Fifth-Order cycles constitute a complete Fourth-Order cycle, in which the second Fifth-Order cycle contains facies representing the deepest or least restricted paleoenvironments. In each case, the fundamental Sixth-Order cycles were generated by the precessional signal modulated by orbital eccentricity variations. Over distances in excess of 100 km, Wills Creek facies change laterally from nearshore marine to fluvial coastal plain. Stacking patterns in these distinct facies are identical, and thus correlative, indicating the basin-wide extent of the stratigraphic events which produced these patterns. These correlations demonstrate that Milankovitch-driven eustatic sea-level fluctuations were occurring during the Late Silurian.

  2. Land animals in the silurian: arachnids and myriapods from shropshire, England.

    PubMed

    Jeram, A J; Selden, P A; Edwards, D

    1990-11-02

    A new assemblage of arthropod cuticles from Upper Silurian rocks in Shropshire, England, includes at least two centipedes and a trigonotarbid arachnid. This unequivocal terrestrial fauna from the Silurian constitutes the earliest direct record of land animals. The presence of predatory arthropods suggests that complex terrestrial ecosystems were in place by the late Silurian (414 x 10(6) years before present) and that the animal invasion of the land occurred earlier than was previously thought.

  3. Subsurface geology of Medina Group (Lower Silurian) and Clinton Group (Lower to Upper Silurian) of New York

    SciTech Connect

    Kearney, M.W.

    1984-12-01

    The depositional environments and geologic history of the Medina Group (Lower Silurian) and the Clinton Group (Lower to Upper Silurian) of New York have been interpreted from a regional subsurface study using approximately 250 ..gamma..-ray logs and 125 sample logs. A sequence of paleogeographic maps illustrate the geologic history and depositional environments associated with this predominantly clastic, rock sequence. Seven principle depositional environments are recognized on the basis of subsurface sedimentary facies. The Silurian clastic rocks were deposited during an overall marine transgression that was interrupted by three major progradational phases. The orogenic episodes represented by these progradational phases steadily decreased in intensity. The sediment influx during the first progradational phase was large enough to produce a deltaic system that extended throughout New York. During the second progradational phase, the sediment influx was small relative to the first event, and subsidence probably increased from loading of the Grimsby sediments. The deltaic system that developed during this time was restricted to east-central New York. The final progradational phase represents an even smaller influx of terrigenous material; only a linear clastic shoreline developed in eastern New York. This phase marks the last major influx of terrigenous clastic sediments until Devonian time.

  4. Upper Homerian (Silurian) high-resolution correlation using cyclostratigraphy: an example from western Lithuania

    NASA Astrophysics Data System (ADS)

    Radzevičius, Sigitas; Tumakovaitė, Brigita; Spiridonov, Andrej

    2017-06-01

    The Gėluva regional stage stratigraphically corresponds to the late Wenlock. This time interval witnessed significant graptolite extinctions and turnovers of conodont faunas, as well as a large positive Mulde carbon isotopic excursion. Thus, the development of a detailed stratigraphy is a necessary step in understanding the complex patterns of regional and global variations in the sediments accumulating during the time interval studied. Therefore, in this contribution we present a cyclostratigraphic analysis of gamma ray (GR) logs from four wells, which are located in the deep water facies belt of the Lithuanian part of the Silurian Baltic Basin of the Gėluva regional stage. The analysis was performed using REDFIT spectral estimation, continuous wavelet transform and signal filtering techniques. As a result two 4th order and five 5th order cycles were distinguished and named in all sections. The correlation of cycles between sections was calibrated with the graptolite biozones. The comparative analysis revealed that intra-basinal cyclostratigraphic correlation could achieve resolution of the order of several tens of thousands of years.

  5. The Ordovician-Silurian tectonic evolution of the northeastern margin of the Tarim block, NW China: Constraints from detrital zircon geochronological records

    NASA Astrophysics Data System (ADS)

    Dong, Shunli; Li, Zhong; Jiang, Lei

    2016-05-01

    The northeastern margin of the Tarim block is a key tectonic-unit for understanding the evolution processes and geodynamic mechanisms of basin-range coupling between the Paleo-Asian tectonic realm to the north and the Tarim block to the south during the Paleozoic period. Four Upper Ordovician-Silurian sandstone samples were collected from the Tabei and Quruqtagh areas for measuring the detrital zircon U-Pb dating and Hf isotopic compositions, with an aim to decipher the provenances and elucidate the tectonic implications. The results show that all the sandstone samples yield evident detrital zircon U-Pb age groups of ca. 1100-720 Ma and ca. 2100-1700 Ma, demonstrating that the Tarim block was once a part of the Rodinia and Columbia supercontinents during the Neoproterozoic and the Paleoproterozoic, respectively. Remarkably, the Upper Ordovician sandstone sample from the Tabei area yields a higher proportion in age group of ca. 1100-900 Ma than that of ca. 860-720 Ma, whilst the Lower Silurian sample yields the opposite result. The former and the latter age groups aforementioned are consistent with the age patterns of the tectono-thermal events in the Central Tianshan microcontinent and the Tarim block, respectively. Combined with valuable igneous rock information, it is indicative that the Central Tianshan microcontinent drifted away from the proto Tarim block (with attachment of the Central Tianshan microcontinent) most likely at the Early Silurian. The Upper Silurian sandstone in the South Quruqtagh area yield massive detrital zircon U-Pb ages with a peak age of ca. 450 Ma, combining the Late Ordovician magmatic rocks reported from the Central Tianshan and northeastern Tarim margin, which suggests that there was a broad magmatic arc along the northeastern proto Tarim margin during the Late Ordovician. The opening of the South Tianshan Ocean began in the Early Silurian and continued in the Late Silurian, leaving a remanent magmatic arc along northeastern Tarim

  6. Stratigraphy of the Silurian outcrop belt on the east side of the Cincinnati Arch in Kentucky, with revisions in the nomenclature

    USGS Publications Warehouse

    McDowell, Robert C.

    1983-01-01

    , is predominantly grayish-green clay shale with a thin (0.5-3 ft) dolomite member (the Waco, or its northern equivalent, the Dayton Dolomite Member, reduced in rank from Dayton Limestone) near the base. North of Bath County, the Lulbegrud Shale and Dayton Dolomite Members are reassigned to the underlying Drowning Creek Formation, the Estill Shale Member is elevated to formational status, and the Alger is dropped. The Bisher Dolomite, which overlies the Estill Shale in the northernmost part of the Silurian belt, ranges from 0 to 300 ft in thickness and is composed of medium-to coarse-grained, gray, fossiliferous dolomite. The Silurian section overlies Upper Ordovician rocks in apparent conformity, although faunal studies suggest a minor hiatus, and is overlain by Middle to Upper Devonian rocks in a regional angular unconformity that truncates the entire Silurian section at the southwest end of the outcrop belt, where it is nearest the axis of the Cincinnati Arch. All of the units recognized in the Silurian appear to thicken eastward, away from the axis of the arch and towards the Appalachian basin. This, with the presence of isolated remnants of the Brassfield near the axis, suggest that formation of the arch was initiated in Early Silurian time by subsidence of its eastern flank.

  7. Cenozoic thrust emplacement of a Devonian batholith, northeastern Brooks Range: Involvement of crystalline rocks in a foreland fold-and-thrust belt

    NASA Astrophysics Data System (ADS)

    Hanks, Catherine L.; Wallace, Wesley K.

    1990-05-01

    Involvement of crystalline rocks in thrusting near the foreland basin of a fold-and-thrust belt is relatively uncommon. In the northeastern Brooks Range, the Devonian Okpilak batholith was thrust northward and structurally elevated above adjacent foreland basin deposits during Cenozoic fold-and-thrust deformation. The batholith may have acted initially as a regional structural buttress, but a drop in the basal detachment surface to greater depth south of the batholith resulted in northward transport of the batholith. Shortening within the batholith was accommodated by (1) the development of discrete thrust slices bounded by ductile shear zones, (2) simple shear and development of penetrative mesoscopic and microscopic fabrics throughout the batholith, or both. The Mississippian Kayak Shale, a regional detachment horizon at the base of the overlying cover sequence, is depositionally thin or absent adjacent to the batholith. Thus, most of the cover sequence remained structurally coupled to the batholith during thrusting and was shortened by the development of penetrative structures.

  8. Using enteric pathogens to assess sources of fecal contamination in the silurian dolomite aquifer: preliminary results

    USDA-ARS?s Scientific Manuscript database

    The fractured Silurian dolomite aquifer is an important, but vulnerable, source of drinking water in northeast Wisconsin. Areas underlain by the Silurian dolomite aquifer are extremely vulnerable to groundwater contamination from various land-use activities, especially the disposal of human wastewat...

  9. Silurian Medina gas revitalizing Pennsylvania's historic Oil Creek

    SciTech Connect

    Pees, S.T.

    1994-10-17

    The Oil Creek Valley of Pennsylvania--in production from shallow wells since 1859 and for many hundreds of years before then by collection pits dug by Native Americans--is seeing the pursuit of an oil field phenomenon known as the deeper pool discovery. A portion of the early North American oil belt is now realizing good gas production from Lower Silurian Medina group sandstones that have thick development on a trend that cuts south-eastward across historic Oil Creek in Venango County. The paper discusses the early drilling activities, deep gas production, the medina stratigraphy, medina reservoirs, and future objectives for the area.

  10. Comparison of Michigan Basin crude oils

    NASA Technical Reports Server (NTRS)

    Vogler, E. A.; Meyers, P. A.; Moore, W. A.

    1981-01-01

    Michigan Basin oils from the Ordovician Trenton, Silurian Niagaran, and Devonian Dundee formations have been geochemically compared by GC, GC-MS, and carbon isotope mass spectrometry. One oil from each formation was selected for detailed analysis which included measurement of individual n-alkane delta 13 C values. The Ordovician and Devonian oils are strikingly similar to one another, yet clearly different from the Silurian oil. This pattern is unexpected because Ordovician and Devonian reservoirs are physically separated by the Silurian strata. From time-temperature considerations, the Devonian oil probably was formed in older strata and has migrated to its present location. Our analyses suggest a common source for the Devonian and Ordovician oils.

  11. Tectonic analysis of a flexed foreland: the Ragusa Platform

    NASA Astrophysics Data System (ADS)

    Barrier, Eric

    1992-05-01

    Detailed field studies of fracture patterns and paleostress reconstructions based on analyses of fault-slip data sets allow the identification of the Late Cenozoic stress pattern evolution of the Ragusa Platform. During the Late Miocene to Early Pleistocene period, a complex extensional pattern developed. It was dominated in almost the entire Hyblean Plateau by NW-SE to NNW-SSE extensions related to the flexure of the foreland under the load of the allochthonous units of the Sicilian Fold and Thrust Belt. These extensional tectonics were characterized by NE-SW to ENE-WSW trending normal faults and grabens. In eastern Hyblea, NE-SW to ENE-WSW extension have prevailed at least since the Late Cretaceous. They are linked to the effects of the Malta Escarpment. In the western Ragusa Platform, a third, minor, WNW-ESE extension associated with sets of NNE-SSW trending normal faults, may be correlated with the development of the Gela basin. In addition, these major extensions induced complex patterns of perpendicular normal fault systems through permutations between the principal stress axes σ2 and σ3. The Pliocene-Pleistocene extensional paleostress field evolution is marked in almost the entire platform by the alternation of two or three main extensional stress patterns (NE-SW to NNW-SSE, WNW-ESE and NE-SW to ENE-WSW extensions), each of them controlled by particular boundary conditions. Three minor compressional paleostress orientations have been identified. They correspond to three minor compressional events dominated by 020°-030°, 070°-080° and 100°-110° compressional directions. These events occurred in within the general Pliocene-Pleistocene extensive context. The 100°-110° event is of Early-Middle Pliocene age. Its large regional distribution suggests that this event may have resulted from interactions between the major blocks constituting the Africa-Eurasian boundary. The relative chronology shows that the 020°-030° compression predates the 070°-080

  12. The origin of oriented lakes in the Andean foreland, Parque Nacional Torres del Paine (Chilean Patagonia)

    NASA Astrophysics Data System (ADS)

    Gonzales, Joseph; Aydin, Atilla

    2008-05-01

    The Parque Nacional Torres Del Paine and surrounding area in the Magallanes foreland basin in Chilean Patagonia is the site for numerous lakes fed by glaciers and rivers in the Andean highlands to the west. The lakes are elongate and have conspicuously systematic orientations. We hypothesize that the origin of the oriented lakes lies in the fault system, composed of a right-lateral strike-slip fault set oriented 58° from north, a left-lateral strike-slip set oriented 87°, and a thrust fault set oriented 167°, that exists within the underlying rocks. To test this hypothesis quantitatively, we determined the shape and orientation of the lakes by fitting each lake with an ellipse of appropriate aspect ratio, and later with multiple ellipses consistent with the composite geometry of some lakes. We then examined the faults in the area in terms of their kinematics, orientation and distribution. The distribution of lake orientations showed three distinct groups which appear to correspond to the three main fault groups. For lakes fitted with multiple ellipses, the difference in means between the right-lateral, left-lateral, and thrust faults and their corresponding groups of lakes are 3.05°, 1.57°, and 5.17°. Using a Kolmogorov-Smirnov (K-S) statistical test to compare the orientations of faults with respect to the lakes suggests that there is not a strongly significant difference between the fault orientations and the corresponding lake groups. These results indicate that the faults have a profound control on the orientation, shape, and distribution of the lakes. We attribute this to faults and their damage zones being weaker and therefore prone to a faster rate of erosion, and to stress perturbations associated with discontinuous faults resulting in localized high density fracturing and surface subsidence. These results have implications for lake and drainage system morphologies in other foreland basins along the Andes and other similar settings.

  13. A new osteichthyan from the late Silurian of Yunnan, China.

    PubMed

    Choo, Brian; Zhu, Min; Qu, Qingming; Yu, Xiaobo; Jia, Liantao; Zhao, Wenjin

    2017-01-01

    Our understanding of early gnathostome evolution has been hampered by a generally scant fossil record beyond the Devonian. Recent discoveries from the late Silurian Xiaoxiang Fauna of Yunnan, China, have yielded significant new information, including the earliest articulated osteichthyan fossils from the Ludlow-aged Kuanti Formation. Here we describe the partial postcranium of a new primitive bony fish from the Kuanti Formation that represents the second known taxon of pre-Devonian osteichthyan revealing articulated remains. The new form, Sparalepis tingi gen. et sp. nov., displays similarities with Guiyu and Psarolepis, including a spine-bearing pectoral girdle and a placoderm-like dermal pelvic girdle, a structure only recently identified in early osteichthyans. The squamation with particularly thick rhombic scales shares an overall morphological similarity to that of Psarolepis. However, the anterior flank scales of Sparalepis possess an unusual interlocking system of ventral bulges embraced by dorsal concavities on the outer surfaces. A phylogenetic analysis resolves Sparalepis within a previously recovered cluster of stem-sarcopterygians including Guiyu, Psarolepis and Achoania. The high diversity of osteichthyans from the Ludlow of Yunnan strongly contrasts with other Silurian vertebrate assemblages, suggesting that the South China block may have been an early center of diversification for early gnathostomes, well before the advent of the Devonian "Age of Fishes".

  14. Silurian gastropoda from southeastern and west-central Alaska

    USGS Publications Warehouse

    Rohr, D.M.; Blodgett, R.B.; Fryda, J.

    2008-01-01

    Additional Silurian (Ludlovian) gastropods are described from the Heceta Formation in the Alexander terrane on Prince of Wales Island, southeastern Alaska. Species include Spinicharybdis krizi n. sp., Spinicharybdis boucoti n. sp., Morania wagneri n. sp., Haplospira craigi n. sp., Australonema sp., Pachystrophia cf. gotlandica (Lindstro??m, 1884), and Medfrazyga gilmulli n. sp. An additional new Silurian species, Morania nixonforkensis n. sp., is described from the Nixon Fork subterrane of the Farewell terrane of west-central Alaska. The spine-bearing Spinicharybdis is placed into a new subfamily Spinicharybdiinae together with Hystricoceras Jahn, 1894. Joint occurrences of genera Beraunia, Coelocaulus, and Morania, as well as members of subfamily Spinicharybdiinae in the gastropod fauna from the Heceta Formation, support its close relationship with gastropod fauna of Bohemia. Additionally, the occurrence of the genus Medfrazyga suggests a faunal link between the Alexander and Farewell terranes of Alaska. Medfrazyga gilmulli n. sp. is the oldest known and the only early Paleozoic member of the family Palaeozygopleuridae. Copyright ?? 2008, The Paleontological Society.

  15. A new osteichthyan from the late Silurian of Yunnan, China

    PubMed Central

    Zhu, Min; Qu, Qingming; Yu, Xiaobo; Jia, Liantao; Zhao, Wenjin

    2017-01-01

    Our understanding of early gnathostome evolution has been hampered by a generally scant fossil record beyond the Devonian. Recent discoveries from the late Silurian Xiaoxiang Fauna of Yunnan, China, have yielded significant new information, including the earliest articulated osteichthyan fossils from the Ludlow-aged Kuanti Formation. Here we describe the partial postcranium of a new primitive bony fish from the Kuanti Formation that represents the second known taxon of pre-Devonian osteichthyan revealing articulated remains. The new form, Sparalepis tingi gen. et sp. nov., displays similarities with Guiyu and Psarolepis, including a spine-bearing pectoral girdle and a placoderm-like dermal pelvic girdle, a structure only recently identified in early osteichthyans. The squamation with particularly thick rhombic scales shares an overall morphological similarity to that of Psarolepis. However, the anterior flank scales of Sparalepis possess an unusual interlocking system of ventral bulges embraced by dorsal concavities on the outer surfaces. A phylogenetic analysis resolves Sparalepis within a previously recovered cluster of stem-sarcopterygians including Guiyu, Psarolepis and Achoania. The high diversity of osteichthyans from the Ludlow of Yunnan strongly contrasts with other Silurian vertebrate assemblages, suggesting that the South China block may have been an early center of diversification for early gnathostomes, well before the advent of the Devonian “Age of Fishes”. PMID:28273081

  16. Silurian and Devonian in Vietnam—Stratigraphy and facies

    NASA Astrophysics Data System (ADS)

    Thanh, Tống Duy; Phương, Tạ Hoàng; Janvier, Philippe; Hùng, Nguyễn Hữu; Cúc, Nguyễn Thị Thu; Dương, Nguyễn Thùy

    2013-09-01

    Silurian and Devonian deposits in Viet Nam are present in several zones and regions, including Quang Ninh, East Bac Bo, and West Bac Bo Zones of the Bac Bo Region, the Dien Bien-Nghe An and Binh Tri Thien Zones of the Viet-Lao Region, and the South Trung Bo, and Western Nam Bo Zones of the South Viet Nam Region (Fig. 1). The main lithological features and faunal composition of the Silurian and Devonian Units in all these zones are briefly described. The Silurian consists of deep-water deposits of the upper parts of the Co To and Tan Mai Formations in the Quang Ninh Zone, the upper parts of the Phu Ngu Formation in the East Bac Bo Zone and the upper parts of the Long Dai and Song Ca Formations in the Viet-Lao Region. Shallow water facies Silurian units containing benthic faunas are more widely distributed, including the upper part of the Sinh Vinh and Bo Hieng Formations in the West Bac Bo Zone, the Kien An Formation in the Quang Ninh Zone, and, in the Viet-Lao Region, the Dai Giang Formation and the upper part of the Tay Trang Formation. No Lower and Middle Devonian deposits indicate deep water facies, but they are characterized by different shallow water facies. Continental to near shore, deltaic facies characterize the Lower Devonian Song Cau Group in the East Bac Bo Zone, the Van Canh Formation in the Quang Ninh Zone, and the A Choc Formation in the Binh Tri Thien Zone. Similar facies also occur in the Givetian Do Son Formation of the Quang Ninh Zone, and the Tan Lap Formation in the East Bac Bo Zone, and consist of coarse terrigenous deposits—cross-bedded conglomerates, sandstone, etc. Most Devonian units are characterized by shallow marine shelf facies. Carbonate and terrigenous-carbonate facies dominate, and terrigenous facies occur in the Lower and Middle Devonian sections in some areas only. The deep-water-like facies is characteriztic for some Upper Devonian formations in the Bac Bo (Bang Ca and Toc Tat Formations) and Viet-Lao Regions (Thien Nhan and

  17. Bacterial succession in a glacier foreland of the High Arctic

    PubMed Central

    Schütte, Ursel M.E.; Abdo, Zaid; Bent, Stephen J.; Williams, Christopher J.; Schneider, G. Maria; Solheim, Bjørn; Forney, Larry J.

    2009-01-01

    Succession is defined as changes in biological communities over time. It has been extensively studied in plant communities, but little is known about bacterial succession, in particular in environments such as High Arctic glacier forelands. Bacteria carry out key processes in the development of soil, biogeochemical cycling, and facilitating plant colonization. In this study we sampled two roughly parallel chronosequences in the foreland of Midre Lovén glacier on Svalbard, Norway and tested whether any of several factors were associated with changes in the structure of bacterial communities, including time after glacier retreat, horizontal variation caused by the distance between chronosequences, and vertical variation at two soil depths. The structures of soil bacterial communities at different locations were compared using terminal restriction fragment length polymorphisms (T-RFLP) of 16S rRNA genes, and the data were analyzed by sequential analysis of log-linear statistical models. While no significant differences in community structure were detected between the two chronosequences, statistically significant differences between sampling locations in the surface and mineral soils could be demonstrated even though glacier forelands are patchy and dynamic environments. These findings suggest bacterial succession occurs in High Arctic glacier forelands but may differ in different soil depths. PMID:19587774

  18. Bacterial succession in a glacier foreland of the High Arctic.

    PubMed

    Schütte, Ursel M E; Abdo, Zaid; Bent, Stephen J; Williams, Christopher J; Schneider, G Maria; Solheim, Bjørn; Forney, Larry J

    2009-11-01

    Succession is defined as changes in biological communities over time. It has been extensively studied in plant communities, but little is known about bacterial succession, in particular in environments such as High Arctic glacier forelands. Bacteria carry out key processes in the development of soil, biogeochemical cycling and facilitating plant colonization. In this study we sampled two roughly parallel chronosequences in the foreland of Midre Lovén glacier on Svalbard, Norway and tested whether any of several factors were associated with changes in the structure of bacterial communities, including time after glacier retreat, horizontal variation caused by the distance between chronosequences and vertical variation at two soil depths. The structures of soil bacterial communities at different locations were compared using terminal restriction fragment length polymorphisms of 16S rRNA genes, and the data were analyzed by sequential analysis of log-linear statistical models. Although no significant differences in community structure were detected between the two chronosequences, statistically significant differences between sampling locations in the surface and mineral soils could be demonstrated even though glacier forelands are patchy and dynamic environments. These findings suggest that bacterial succession occurs in High Arctic glacier forelands but may differ in different soil depths.

  19. Geomorphology and Tectonics at the Intersection of Silurian and Death Valleys, Southern California - 2005 Guidebook Pacific Cell Friends of the Pleistocene

    USGS Publications Warehouse

    Miller, David M.; Valin, Zenon C.

    2007-01-01

    This publication describes results from new regional and detailed surficial geologic mapping, combined with geomorphologic, geochronologic, and tectonic studies, in Silurian Valley and Death Valley, California. The studies address a long-standing problem, the tectonic and geomorphic evolution of the intersection between three regional tectonic provinces: the eastern California shear zone, the Basin and Range region of southern Nevada and adjacent California, and the eastern Mojave Desert region. The chapters represent work presented on the 2005 Friends of the Pleistocene field trip and meeting as well as the field trip road log.

  20. Fletcher field: a Silurian patch/barrier-reef complex in southwestern Ontario

    SciTech Connect

    Meadows, J.R.; Churcher, P.L.; Lawson, D.E.; Dusseault, M.B.

    1986-08-01

    The importance of reef growth to Silurian oil and gas production in the Michigan basin is reflected in the large number of studies that have been conducted. Unfortunately, most of these studies have focused on pinnacle reefs, with patch and barrier reefs being virtually ignored, although they represent viable oil and gas exploration targets. Many patch reefs in Ontario also represent targets for enhanced oil recovery projects. Without detailed geologic studies, these projects cannot be readily implemented. A recent sedimentologic study defined the facies distribution of a patch- and barrier-reef complex and its associated producing zones (A-1 carbonate). The Fletcher field, located in southwestern Ontario, was chosen for study. Structures and facies relationships were defined using nine cored holes and geophysical well logs. In addition, detailed studies were made of the clay mineralogy and the controversial Guelph A-1 carbonate contact. Defined facies relationships indicate that the Fletcher patch/barrier reef differs in many respects to pinnacle reefs. The facies are simpler and fewer, consisting of a poorly zoned reef core overlain by a micritized reef-top, lagoonal, and supratidal sequence. The origin of the green shale at the Guelph A-1 contact is interpreted as resulting partly from subaerial exposure and partly from the concentration of insolubles by pressure solution. The clay mineralogy consists of a monomineralic assemblage of illite. The amount and distribution of this assemblage would not significantly affect enhanced oil recovery.

  1. Glacier meltwater flow paths and storage in a geomorphologically complex glacial foreland: The case of the Tapado glacier, dry Andes of Chile (30°S)

    NASA Astrophysics Data System (ADS)

    Pourrier, J.; Jourde, H.; Kinnard, C.; Gascoin, S.; Monnier, S.

    2014-11-01

    The Tapado catchment is located in the upper Elqui river basin (4000-5550 m) in northern Chile. It comprises the Tapado glacial complex, which is an assemblage of the Tapado glacier and the glacial foreland (debris-covered glacier, rock glacier, and moraines). Although the hydrological functioning of this catchment is poorly known, it is assumed to actively supply water to the lower semi-arid areas of the Elqui river basin. To improve our knowledge of the interactions and water transfers between the cryospheric compartment (glacier, debris-covered glacier, and rock glacier) and the hydrological compartment (aquifers, streams), the results of monitoring of meteorological conditions, as well as discharge, conductivity and temperature of streams and springs located in the Tapado catchment were analyzed. The hydrological results are compared to results inferred from a ground penetrating radar (GPR) survey of the underground structure of the glacial foreland. Water production from the Tapado glacier was shown to be highly correlated with daily and monthly weather conditions, particularly solar radiation and temperature. The resulting daily and monthly streamflow cycles were buffered by the glacial foreland, where underground transfers took place through complex flow paths. However, the development of a thermokarst drainage network in a portion of the glacial foreland enabled rapid concentrated water transfers that reduced the buffer effect. The glacial foreland was shown to act as a reservoir, storing water during high melt periods and supplying water to downstream compartments during low melt periods. GPR observations revealed the heterogeneity of the internal structure of the glacial foreland, which is composed of a mixture of ice and rock debris mixture, with variable spatial ice content, including massive ice lenses. This heterogeneity may explain the abovementioned hydrological behaviors. Finally, calculation of a partial hydrological budget confirmed the

  2. El Furrial oil field, Northeastern Venezuela: First giant in foreland fold and thrust belts of Western Hemisphere

    SciTech Connect

    Not Available

    1988-01-01

    The El Furrial giant oil field lies on the northern flank of the prolific Eastern Venezuela basin. Major tectonic elements of the region consist of a fold and thrust belt and a deep foreland basin, whose deformation is a product of right-oblique arc-continent collision. This mountain-front oil province displays parallel bands of thrusts and associated folds that extend over 150 mi and have relay trend patterns. The El Furrial structure is a long, doubly plunging anticline, flanked by imbricated, blind thrusts. Seismic data indicate vertical closure of about 3,000 ft over an area of 17,300 ac. The prospective section, of middle Tertiary to Late Cretaceous age, is mainly clastic, with an oil column of 1,800 ft. The interval of greater hydrocarbon potential is equated with shallow marine platform sandstones. Production tests reach sustained daily flow rates exceeding 9,500 bbl of 28/sup 0/API oil and 9,100 mcf of gas. Analysis of the oil suggests a marine Cretaceous source. Although in an early stage of development, the field is estimated to contain approximately 2 billion bbl of recoverable oil reserves. This places El Furrial in the forefront of the giant oil fields in the foreland fold and thrust belt provinces of the Western Hemisphere, second only to the supergiant accumulations of the Zagros zone in the Persian Gulf. The eastern Venezuela basin probably contains on the order of 2 trillion bbl of oil in place, making it the largest oil-bearing basin in the world. An ultimate recovery of 500 billion bbl is estimated. Therefore, the basin offers significant geologic scope for exploration for other giant fields.

  3. Gravity anomalies, spatial variation of flexural rigidity, and role of inherited crustal structure in the Aquitaine Basin

    NASA Astrophysics Data System (ADS)

    Angrand, Paul; Ford, Mary; Watts, Anthony; Bell, Rebecca E.

    2016-04-01

    The Aquitaine foreland basin developed from Campanian to Miocene by flexure of the upper (European) plate during the Pyrenean orogeny. The foreland basin forms a syn-orogenic sedimentary wedge up to 6 km thick in the south, thinning rapidly north and has a maximum width of 200 km in the west. The flexural basin was superimposed on a lithosphere previously affected by Apto-Albian hyper-extension. What are the effects of an inherited extremely weak and narrow rifted zone on the behavior of a superimposed flexural foreland basin? Coupled with surface and subsurface data, Bouguer gravity anomalies were used to determine the crustal structure of the northern Pyrenean retrowedge and the flexure of the European plate. In the centre, the basin shows a regional Bouguer anomaly pattern typical of foreland basins with the maximum of syn-orogenic deposits corresponding to a low and the forebulge to a high. However, south of the North Pyrenean Frontal Thrust (NPFT) this regional field is overprinted by strong positive Bouguer anomalies, which correspond to high density bodies (mantle or lower crust) transported along the NPFT. Stratigraphy shows that the central basin evolved as a series of narrow, laterally variable depocentres that migrated north. Shortening is accommodated mainly by thick skinned deformation and local reactivation of salt structures. In the east, the Toulouse Fault separates the central and eastern foreland. The eastern foreland shows a broader zone of negative Bouguer values. This foreland is salt-free and stratigraphy records higher subsidence. The easternmost basin is completely overprinted by the opening of the Gulf of Lion. In the west, the foreland does not show a typical regional gravity anomaly pattern due to overprinting by the opening of the Bay of Biscay. Instead, a major gravity high is centered on the northern Landes High, with a second high centered on the Labourd massif south of the NPFT. Neither the Parentis rift basin nor the salt

  4. Paleozoic evolution of active margin basins in the southern Central Andes (northwestern Argentina and northern Chile)

    NASA Astrophysics Data System (ADS)

    Bahlburg, H.; Breitkreuz, C.

    The geodynamic evolution of the Paleozoic continental margin of Gondwana in the region of the southern Central Andes is characterized by the westward progression of orogenic basin formation through time. The Ordovician basin in the northwest Argentinian Cordillera Oriental and Puna originated as an Early Ordovician back-arc basin. The contemporaneous magmatic arc of an east-dipping subduction zone was presumably located in northern Chile. In the back-arc basin, a ca. 3500 meter, fining-up volcaniclastic apron connected to the arc formed during the Arenigian. Increased subsidence in the late Arenigian allowed for the accomodation of large volumes of volcaniclastic turbidites during the Middle Ordovician. Subsidence and sedimentation were caused by the onset of collision between the para-autochthonous Arequipa Massif Terrane (AMT) and the South American margin at the Arenigian-Llanvirnian transition. This led to eastward thrusting of the arc complex over its back-arc basin and, consequently, to its transformation into a marine foreland basin. As a result of thrusting in the west, a flexural bulge formed in the east, leading to uplift and emergence of the Cordillera Oriental shelf during the Guandacol Event at the Arenigian-Llanvirnian transition. The basin fill was folded during the terminal collision of the AMT during the Oclóyic Orogeny (Ashgillian). The folded strata were intruded post-tectonically by the presumably Silurian granitoids of the "Faja Eruptiva de la Puna Oriental." The orogeny led to the formation of the positive area of the Arco Puneño. West of the Arco Puneño, a further marine basin developed during the Early Devonian, the eastern shelf of which occupied the area of the Cordillera Occidental, Depresión Preandina, and Precordillera. The corresponding deep marine turbidite basin was located in the region of the Cordillera de la Costa. Deposition continued until the basin fill was folded in the early Late Carboniferous Toco Orogeny. The basin

  5. Evidences of Silurian dextral transpression in the Scandinavian Caledonides

    NASA Astrophysics Data System (ADS)

    Torgersen, Espen; Viola, Giulio

    2017-04-01

    The Scandinavian Caledonides are classically interpreted as a fold and thrust belt resulting from the collision between Laurentia and Baltica during the Silurian, which involved the up-to-400 km ESE-wards translation of nappes onto the Baltoscandian platform. It has been suggested that the Caledonian fold and thrust belt formed through several distinct orogenic episodes, from early shortening in the Late Ordovician to orogenic collapse in the Devonian. The classic Caledonian, orogen-perpendicular ESE-ward nappe transport is constrained by abundant and consistently oriented stretching lineations across the entire orogen and unambiguous kinematic indicators. However, there is also a large number of NW-SE-trending and roughly orogen-parallel lineations, particularly in the upper ophiolite- and eclogite-bearing nappes, which are more challenging to interpret with the traditional orogeny evolution model. The analysis of the areal extent, spatial distribution and geometrical relationships of the Caledonian nappes in southern and central Norway, however, offers new insights and allows for new constraints on the bulk kinematic framework of the shortening history of the belt. Here we present new, first-order geological observations that demonstrate a two-fold compressional history and associated strain partitioning during Caledonian convergence. More specifically, we propose that Late Ordovician NNW-SSE shortening caused early compression, followed by WNW-ESE Early Silurian shortening, which resulted in strain partitioning along the planar fabrics and discontinuities from the earlier event. In detail, orogen-parallel dextral wrench tectonics caused significant lateral displacement along at least three, orogen-scale NE-SW striking corridors, wherein the nappes appear to be consistently displaced in a dextral fashion. We propose that the Møre-Trøndelag Fault Complex, which accommodated significant sinistral displacements during the later Devonian orogenic collapse

  6. Ordovician-Silurian tectonism in northern California: The Callahan event

    SciTech Connect

    Cotkin, S.J. )

    1992-09-01

    Middle Ordovician to Early Silurian volcanism, plutonism, metamorphism, deformation, and sedimentation in the Yreka and Trinity terranes, eastern Klamath Mountains, northern California, are considered to be related phenomena that occurred in response to an episode of tectonism known as the Callahan event. A diverse array of evidence is used to construct a tectonic model for the Callahan event that involves a subduction zone, a magnetic arc, and a back-arc spreading center, and to show that tectonism likely occurred within the framework of the North American continental margin. Evidence pertaining to subduction polarity is meager, but is consistent with an eastward dip. The Callahan event represents the earliest Phanerozoic convergent-margin tectonic event recognized within the U.S. Cordillera.

  7. Climate warming could increase recruitment success in glacier foreland plants.

    PubMed

    Mondoni, Andrea; Pedrini, Simone; Bernareggi, Giulietta; Rossi, Graziano; Abeli, Thomas; Probert, Robin J; Ghitti, Michele; Bonomi, Costantino; Orsenigo, Simone

    2015-11-01

    Glacier foreland plants are highly threatened by global warming. Regeneration from seeds on deglaciated terrain will be crucial for successful migration and survival of these species, and hence a better understanding of the impacts of climate change on seedling recruitment is urgently needed to predict future plant persistence in these environments. This study presents the first field evidence of the impact of climate change on recruitment success of glacier foreland plants. Seeds of eight foreland species were sown on a foreland site at 2500 m a.s.l., and at a site 400 m lower in altitude to simulate a 2·7 °C increase in mean annual temperature. Soil from the site of origin was used to reproduce the natural germination substrate. Recruitment success, temperature and water potential were monitored for 2 years. The response of seed germination to warming was further investigated in the laboratory. At the glacier foreland site, seedling emergence was low (0 to approx. 40 %) and occurred in summer in all species after seeds had experienced autumn and winter seasons. However, at the warmer site there was a shift from summer to autumn emergence in two species and a significant increase of summer emergence (13-35 % higher) in all species except two. Survival and establishment was possible for 60-75 % of autumn-emerged seedlings and was generally greater under warmer conditions. Early snowmelt in spring caused the main ecological factors enhancing the recruitment success. The results suggest that warming will influence the recruitment of glacier foreland species primarily via the extension of the snow-free period in spring, which increases seedling establishment and results in a greater resistance to summer drought and winter extremes. The changes in recruitment success observed here imply that range shifts or changes in abundance are possible in a future warmer climate, but overall success may be dependent on interactions with shifts in other components of the

  8. Climate warming could increase recruitment success in glacier foreland plants

    PubMed Central

    Mondoni, Andrea; Pedrini, Simone; Bernareggi, Giulietta; Rossi, Graziano; Abeli, Thomas; Probert, Robin J.; Ghitti, Michele; Bonomi, Costantino; Orsenigo, Simone

    2015-01-01

    Background and Aims Glacier foreland plants are highly threatened by global warming. Regeneration from seeds on deglaciated terrain will be crucial for successful migration and survival of these species, and hence a better understanding of the impacts of climate change on seedling recruitment is urgently needed to predict future plant persistence in these environments. This study presents the first field evidence of the impact of climate change on recruitment success of glacier foreland plants. Methods Seeds of eight foreland species were sown on a foreland site at 2500 m a.s.l., and at a site 400 m lower in altitude to simulate a 2·7 °C increase in mean annual temperature. Soil from the site of origin was used to reproduce the natural germination substrate. Recruitment success, temperature and water potential were monitored for 2 years. The response of seed germination to warming was further investigated in the laboratory. Key Results At the glacier foreland site, seedling emergence was low (0 to approx. 40 %) and occurred in summer in all species after seeds had experienced autumn and winter seasons. However, at the warmer site there was a shift from summer to autumn emergence in two species and a significant increase of summer emergence (13–35 % higher) in all species except two. Survival and establishment was possible for 60–75 % of autumn-emerged seedlings and was generally greater under warmer conditions. Early snowmelt in spring caused the main ecological factors enhancing the recruitment success. Conclusions The results suggest that warming will influence the recruitment of glacier foreland species primarily via the extension of the snow-free period in spring, which increases seedling establishment and results in a greater resistance to summer drought and winter extremes. The changes in recruitment success observed here imply that range shifts or changes in abundance are possible in a future warmer climate, but overall success may be dependent

  9. Cyclicity in Silurian island-arc carbonates, Alexander terrane, Alaska

    SciTech Connect

    Kittredge, L.E.; Soja, C.M. . Dept. of Geology)

    1993-03-01

    Silurian carbonates from Alaska (Alexander terrane) record the evolution of a submarine platform during waning volcanism in an island arc. A detailed stratigraphic analysis of a 47 meter-thick sequence revealed the existence of cyclically repeated limestones: coral-stromatoporoid wackestones alternate with oncoid packstones and bioturbated, silty lime mudstones. The coral-stromatoporoid deposits are characterized by a low-diversity assemblage of dendroid corals, massive stromatoporoids, Atrypoidea brachiopods, and rare occurrences of biostromes associated with Solenopora, high-spired gastropods, and crinoids. Oncoids typically are 2-6 mm in diameter and form massive, meter-thick units. Coated grains are symmetrically developed, have a shell or algal nucleus, and are also a minor component of coral-stromatoporoid beds. These lithologic units form seven, shallowing-upwards cycles (parasequences) that range in thickness from 3-9 meters. Coral-stomatoporoid wackestones form the base of each cycle and grade upwards into oncoid packstones with silty, lime mudstones at the top. This succession of lithofacies within each cycle reflects an increase in energy levels from relatively deeper water environments to relatively shallower ones. The lack of abrasion in the corals and stromatoporoids suggests predominantly quiet-water conditions in shallow subtidal areas affected by periodic turbulence. Comparison with correlative sections in Alaska and lack of correspondence with global sea level curves suggest that the primary cause of cyclicity was tectonic perturbations with secondary eustatic effects. Cyclic deposition in peri/subtidal sites was terminated by rapid drowning of the carbonate platform during late Silurian orogenesis.

  10. Hydrocarbon habitat of San Martin and Cashiriari gas/condensate discoveries, southern Ucayali basin of Peru

    SciTech Connect

    Mohler, H.P.

    1989-03-01

    Fifteen trillion ft/sup 3/ of wet gas in place containing some 800 million bbl of associated liquids have been discovered in the San Martin and Cashiriari anticlines, which are located in the Subandean thrusted foldbelt of the Southern Ucayali basin of Peru. Ultimate recoverable volumes are estimated at 10 trillion ft/sup 3/ of gas and 500 million bbl of liquids including condensate (C5+) and LPG (C3/C4). Most of these potentially recoverable reserves are located in the Cashiriari structure (80% of the gas and 70% of the liquids). They were encountered in fair-excellent sandstone reservoirs of Early Permian and Late Cretaceous age and are thought to be derived from Carboniferous coaly shale source rocks. The Paleozoic (pre-Andean) sedimentary megacycle is represented by deeper shallow marine clastics of Ordovician to Early Carboniferous age (5000 m maximum), including Silurian glaciomarine deposits, overlain by up to 1200 m of Permian-Carboniferous platform carbonates and 600-1000( ) m of Lower Permian-lower Upper Permian coastal-continental clastics. The Mesozoic-Tertiary (Andean) megacycle is represented by a Campanian-Maastrichtian transgressive marine clastic/carbonate and overlying regressive clastic sequence (450 m maximum), followed by several thousand meters of Molasse-type continental infill of the Tertiary foredeep, which was created by the crustal loading in the wake of the compressional Andean orogeny (Peru, Inca, and Quechua phases). Late Tertiary folding and thrusting of the sub-Andean belt was superseded by regional Pleistocene uplift, and parts of the foreland continue to subside.

  11. Glacier meltwater flow paths and storage in a geomorphologically complex glacial foreland: the case of the Tapado glacier, dry Andes of Chile (30°S)

    NASA Astrophysics Data System (ADS)

    Pourrier, J.; Jourde, H.; Kinnard, C.; Gascoin, S.; Monnier, S.

    2013-12-01

    In the Dry Andes, high altitude glacierized catchments are important contributor to streamflow and aquifer recharge. In this study we focused on the Tapado catchment, (30°S, 9 km2, elevation range: 4000m - 5550m) located in the upper Elqui river basin in northern Chile. This catchment encompasses the Tapado glacial complex, composed of an assemblage of the Tapado glacier and the glacial foreland (debris-covered glacier, rock glacier and moraines). Here we present the results of intensive hydrometeorological observations conducted over the 2011 glacier melt season (February to April). Weather, discharge and water electrical conductivity were monitored near the glacier snout and at the outlet of the glacial foreland. GPR observations realized on the glacial foreland are used to verify or complete interpretations of underground transfer modalities. The results show that the water production from the Tapado glacier is highly correlated with weather conditions, in particular incoming shortwave radiation and air temperature. Resulting daily and seasonal streamflow variability is buffered by the glacial foreland, where underground transfers occur through complex flow paths. However, the development of a thermokarst drainage network in a part of the glacial foreland, allows fast and concentrated water transfers, which reduces this buffering effect. The glacial foreland is shown to act as a reservoir, storing water during period of strong ice melt and providing water to downstream areas during periods of low melt. The internal structure of the glacial foreland revealed by GPR observations corroborates these analyses. The south-western part is composed by massive ice, covered by rock debris. The north-eastern part is composed by mixed ice and rock debris, presenting spatially variable ice content. Finally, the computation of the catchment water balance shows that the Tapado catchment presents a particularly high specific discharge in summer under a dry hydro

  12. Provenance and depositional setting of Lower Silurian siliciclastic rocks on Hainan Island, South China: Implications for a passive margin environment of South China in Gondwana

    NASA Astrophysics Data System (ADS)

    Zou, Shaohao; Wu, Chuanjun; Xu, Deru; Shan, Qiang; Zhang, Xiaowen; Hollings, Pete; Hou, Maozhou

    2016-06-01

    Diverse models have been proposed for interpreting the early Paleozoic tectonic setting of the Cathaysia Block in South China. However, few of them undertook a comprehensive study of clastic sedimentary rocks in the Cathaysia Block. This study reports the petrography and sedimentary facies, the whole-rock geochemistry and Sm-Nd isotopic data, and the LA-ICP-MS U-Pb ages of detrital zircon from the Lower Silurian meta-siliciclastics on Hainan Island in order to constrain the early Paleozoic tectonic setting. The source rocks for the Lower Silurian meta-siliciclastics have suffered moderate to intense weathering, indicated by the weathering indices, like Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Weathering Index (W index). The Lower Silurian rocks have high Th/Sc (generally between 1.1 and 2.0) and Th/U (generally between 4 and 6) ratios, LREE-enriched REE patterns with negative Eu anomalies (avg. 0.55), and low εNd(t) values (-16.2 to -8.5), suggesting a continental margin basin receiving detritus mostly derived from a recycled-orogen or cratonic provenance. This Early Silurian turbiditic succession with rhythmic flysch and incomplete Bouma sequences also reveals a neritic to abyssal facies, continental shelf to continental slope depositional setting. The geochemical features like the pattern of REEs, the ratios of trace elements (e.g., Th/Sc, Th/Co, La/Sc, Cr/Th, La/Th), and the binary plots and ternary diagrams (e.g., A-CN-K and FMW diagram), demonstrate that the source-areas are dominated by felsic rocks. Together with the two-stage Nd depleted mantle model age (TDM-2) (ca. 2.3 Ga), the detrital zircon U-Pb age populations with peaks mainly at ca. 1635 Ma confirm that the source rocks are dominated by the Paleo- to Mesoproterozoic Baoban Group and ca. 1430 Ma granitoids on Hainan Island. Linked to the early Paleozoic tectonic development of South China, the Lower Silurian siliciclastic rocks on Hainan Island can be interpreted

  13. Low temperature thermochronological constrains on the late exhumation of the Alpine foreland (Digne nappe, France).

    NASA Astrophysics Data System (ADS)

    Schwartz, S.; Gautheron, C.; Audin, L.; Dumont, T.; Nomade, J.; Pinna-Jamme, R.

    2015-12-01

    The frontal part of the southwestern Alpine belt is characterized by important compressional deformation marked by the emplacement of the Digne nappe and the formation of the Valavoire thrust-sheet. The final emplacement of this nappe is dated Late Miocene thanks to Tertiary continental molasses of the foreland basin that are involved in the famous Vélodrôme recumbent syncline and exposed in erosional windows. The stratigraphic series of the Digne nappe is made of ~5000 m thick Liassic to Eocene deposits, which overthrust the vélodrôme syncline. We performed a low temperature apatite fission tracks (AFT) and (U-Th)/He (AHe) study on detrital grains of Tertiary molasses in order to (i) characterize the thermal conditions during burial and exhumation and to (ii) propose a late tectonic evolution in the front of the European Alpine foreland. Tertiary molasses were sampled in two sites of the erosional windows at different elevations. Samples present dispersed AHe and AFT ages due to an incomplete resetting of both thermochronometers, expected for the lowest elevation samples. In detail, AHe ages ranges from 2±0.2 to 60.4±5.4 Ma, whereas central AFT ages range from 11±1 to 67±16 Ma. On both sites, the total and partial reset of the thermochronological data suggests a heating event after the sediment deposition. Using QTQt inverse modeling and He damage codes, we determined the samples thermal history. The results implied a common burial temperature at 110±5°C during ~5Ma and a similar exhumation starting at 6±1 Ma. From these results, we conclude that the thermal conditions during burial associated with the Digne nappe thrusting were sufficient to reset the detrital apatites. Using mean surface temperature of 10°C and typical thermal gradient from 25°C/km, our new data show that the Digne Nappe reached at least 4.5 to 3.6 km-thick on both sites before further erosion. We propose that the late exhumation occurred at ~6 Ma ago, before the Messinian incision

  14. Hydrologic environment of the Silurian salt deposits in parts of Michigan, Ohio, and New York

    USGS Publications Warehouse

    Norris, Stanley E.

    1978-01-01

    The aggregate thickness of evaporites (salt, gypsum, and anhydrite) in the Silurian Salina sequence in Michigan exceeds 1200 feet in areas near the periphery of the Michigan basin, where the salt beds are less than 3000 feet below land surface. In northeast Ohio the aggregate thickness of salt beds is as much as 200 feet in places, and in western New York it is more than 500 feet, where th beds are less than 3000 feet deep. The salt-bearing rocks dip regionally on the order of 50 feet per mile; those in Michigan dip toward the center of the Michigan basin, and those in Ohio and New York, in the Appalachian basin, dip generally southward. The rocks in both basins thicken downdip. Minor folds and faults occur in the salt-bearing rocks in all three states. Some of this defrmation has been attenuated or absorbed bo the salt beds. Occuring near the middle of thick sedimentary sequences, the salt beds are bounded aboe and below by beds containing water having dissolved-solids concentrations several times that seawter. The brines occur commonly in discrete zones of high permeability at specific places in the stratigraphic sequence. In northeast Ohio two prominent brine zones are recognized by the driller, the Devonian Oriskany Sandstone, or 'first water' zone, above the Salina Formation, and the Newburg or 'second water' zone below the Salina. In each aquifer there is a vertical component of hydraulic head, but little brine probably moves through the salt beds because their permeability is extremely low. Also, ther is little evidence of dissolution of the salt in areas distant from the outcrop, suggesting that if brine does move through the salt, movement is at a slow enough rate so that, in combination with the saturated or near-saturated condition of the water, it precludes significant dissolution. Principal brine movement is probably in the permeable zones in the direction of the hydraulic gradient. Two areas in Michigan and one area each in Ohio and New York appear

  15. A Multi-Proxy Analysis of two Loess-Paleosol Sequences in the Northern Harz Foreland

    NASA Astrophysics Data System (ADS)

    Krauss, Lydia; Zens, Joerg; Zeeden, Christian; Schulte, Philipp; Eckmeier, Eileen; Lehmkuhl, Frank

    2016-04-01

    Within the second phase of the "Collaborative Research Centre 806 (CRC806) - Our Way to Europe - Culture-Environment Interaction and Human Mobility in the Late Quaternary" two loess-paleosol sections in the northern Harz foreland are being investigated. The region is part of the Northern European loess belt. The northern edge of the loess distribution is characterized by an interlocking of Weichselian silt and sand sized aeolian sediments. To the south the Northern European loess belt is limited by the central German uplands (Mittelgebirge). Here the continuous loess cover disperses into separated loess basins. In comparison to relatively long, continuous and intensively studied sections, e.g. along the Rhine river, investigations on loess-paleosol sequences in the northern Harz foreland have been sparse so far. In 2006 REINECKE created an overview of Pleistocene landscape developments by investigating terrace sequences and loess sections in this area. Due to improvements of research methods over the last ten years, the two loess-paleosol sequences Hecklingen and Zilly are being reinvestigated. Aiming towards a better understanding of the paleoenvironmental conditions during the Weichselian in an area close to the Scandinavian ice sheet, results from grain size, geochemical (XRF, CNS) and color measurements are combined. The results show an increased input of aeolian material during the last glacial maximum and the last cover loess period, supporting the theory of dryer and colder conditions during this time frame. Further, we can see a stronger short distant input within the recent soil and during the last glacial maximum in both profiles. In Hecklingen this is also observed within the MIS 3 soil material. Since soil material dating to the MIS 3 is present, we can assume that surface processes where less intrusive during the MIS 3 and 2 as in e.g. the Lower Rhine Embayment. REINECKE, V. (2006): Untersuchungen zur mittel- und jungpleistozänen Reliefentwicklung und

  16. Faulting, fracturing, and sealing in foreland thrust belts: Examples from the subalpine chains

    SciTech Connect

    Bowler, S.; Butler, R.W.H.

    1988-08-01

    The hydrocarbon potential of foreland thrust belts arises from source and reservoir rocks juxtaposed by the movement of thrust sheets, promoting maturation by loading and generating structural traps. Deformation in thrust belts can be localized on fault zones or distributed throughout thrust sheets; different deformation mechanisms operate to increase and decrease permeability. Migration and reservoir properties may be enhanced or reduced by faulting and fault-related deformation. These processes are examined in detail using examples from the northwest subalpine chains of France, a fold-and-thrust belt of well-differentiated Mesozoic shales and carbonates. Seeps of bitumen in foreland basin sediments indicate some migration of hydrocarbons along faults linking probable source and reservoir areas. Detailed examination of fault rocks and thrust sheets shows that fracture formation is an important strain mechanism which has the potential to form regions of enhanced permeability in structures such as hanging wall anticlines. However, the fractures observed are in general recemented, forming with crack-seal crystal growth. The faults themselves are complex zones up to tens of meters thick of subparallel anastomosing gouge, fractures, stylolites, and crystalline calcite, indicating synchronous cataclasis and pressure solution. The range of scales of fracturing suggests stick-slip (microseismic) fault activity. Permeability of the fault zones is enhanced during seismic fault slip and is otherwise steadily decreased by pressure solution and calcite deposition. The available migration pathways, and hence the location of potential reservoirs, is controlled by the timing, mechanisms, and extent of fault activity in this common and productive tectonic regime.

  17. Regressive-transgressive cyclothem with facies record of the re-flooding window in the Late Silurian carbonate succession (Podolia, Ukraine)

    NASA Astrophysics Data System (ADS)

    Łuczyński, Piotr; Kozłowski, Wojciech; Skompski, Stanisław

    2015-09-01

    The term "re-flooding window" was recently proposed as a time-interval connected with the transgressive stage of present day peri-reefal development. In the analysis presented here, a fossil record of a re-flooding window has been recognized. Nine Late Silurian carbonate sections exposed on the banks of the Dnister River in Podolia (Ukraine) have been correlated base on bed-by-bed microfacies analysis and spectral gamma ray (SGR) measurements. Correlated were sections representing settings ranging from the inner part of a shallow-water carbonate platform to its slope, through an organic buildup. The reconstructed depositional scenario has been divided into six development stages, with the first three representing a regressive interval and the latter three a transgressive interval of the basin's history. The re-flooding window has been identified at the beginning of a transgressive part of the succession. Surprisingly, it is characterized by an extremely fast growth of a shallow, tide-dominated platform and by deposition of calciturbiditic layers in a more basinal area. The interpreted succession is a small-scale model illustrating the reaction of carbonate depositional sub-environments to sea level changes and determining the facies position of the stromatoporoid buildups within the facies pattern on a Silurian shelf. The use of SGR analyses in shallow water, partly high-energy, carbonate facies, both for correlation purposes and for identifying depositional systems, is a relatively new method, and thus can serve as a reference for other studies of similar facies assortment.

  18. Intraguild predation in pioneer predator communities of alpine glacier forelands

    PubMed Central

    Raso, Lorna; Sint, Daniela; Mayer, Rebecca; Plangg, Simon; Recheis, Thomas; Brunner, Silvia; Kaufmann, Rüdiger; Traugott, Michael

    2014-01-01

    Pioneer communities establishing themselves in the barren terrain in front of glacier forelands consist principally of predator species such as carabid beetles and lycosid spiders. The fact that so many different predators can co-inhabit an area with no apparent primary production was initially explained by allochthonous material deposited in these forelands. However, whether these populations can be sustained on allochthonous material alone is questionable and recent studies point towards this assumption to be flawed. Intraguild predation (IGP) might play an important role in these pioneer predator assemblages, especially in the very early successional stages where other prey is scarce. Here, we investigated IGP between the main predator species and their consumption of Collembola, an important autochthonous alternative prey, within a glacier foreland in the Ötztal (Austrian Alps). Multiplex PCR and stable isotope analysis were used to characterize the trophic niches in an early and late pioneer stage over 2 years. Results showed that intraguild prey was consumed by all invertebrate predators, particularly the larger carabid species. Contrary to our initial hypothesis, the DNA detection frequency of IGP prey was not significantly higher in early than in late pioneer stage, which was corroborated by the stable isotope analysis. Collembola were the most frequently detected prey in all of the predators, and the overall prey DNA detection patterns were consistent between years. Our findings show that IGP appears as a constant in these pioneer predator communities and that it remains unaffected by successional changes. PMID:24383765

  19. Geology and hydrocarbon potential of the Hamada and Murzuq basins in western Libya

    SciTech Connect

    Kirmani, K.U.; Elhaj, F.

    1988-08-01

    The Hamada and Murzuq intracratonic basins of western Libya form a continuation of the Saharan basin which stretches from Algeria eastward into Tunisia and Libya. The tectonics and sedimentology of this region have been greatly influenced by the Caledonian and Hercynian orogenies. Northwest- and northeast-trending faults are characteristic of the broad, shallow basins. The Cambrian-Ordovician sediments are fluvial to shallow marine. The Silurian constitutes a complete sedimentary cycle, ranging from deep marine shales to shallow marine and deltaic sediments. The Devonian occupies a unique position between two major orogenies. The Mesozoic strata are relatively thin. The Triassic consists of well-developed continental sands, whereas the Jurassic and Cretaceous sediments are mainly lagoonal dolomites, evaporites, and shales. Silurian shales are the primary source rock in the area. The quality of the source rock appears to be better in the deeper part of the basin than on its periphery. The Paleozoic has the best hydrocarbon potential. Hydrocarbons have also been encountered in the Triassic and Carboniferous. In the Hamada basin, the best-known field is the El Hamra, with reserves estimated at 155 million bbl from the Devonian. Significant accumulations of oil have been found in the Silurian. Tlacsin and Tigi are two fields with Silurian production. In the Murzuq basin the Cambrian-Ordovician has the best production capability. However, substantial reserves need to be established before developing any field in this basin. Large areas still remain unexplored in western Libya.

  20. Influence of preexisting tectonic trends on geometries of Sevier orogenic belt and its foreland in Utah

    SciTech Connect

    Picha, F.; Gibson, R.I.

    1985-05-01

    The tectonic style of the late Mesozoic Sevier orogenic belt in Utah was greatly affected by preexisting structural trends that date from the late Precambrian rifting and fragmentation of the North American continent. The late Precambrian cratonic margin (Cordilleran hinge line) was marked by a system of prominent faults including the north-south-trending ancestral Wasatch and ancient Ephraim faults and the southwest-northeast-trending Leamington, Scipio, Cove Fort, and Paragonah faults. During the Paleozoic and Mesozoic, renewed activity on these faults affected the geometries of the late Paleozoic Paradox and Oquirrh basins, the boundaries of the Jurassic Arapien Formation, and the sedimentary pattern of the Cretaceous foreland basin. Many of these fault zones were reactivated as tectonic ramps (e.g., the ancient Ephraim fault) and tear faults (e.g., the Leamington fault) during the compressional Sevier tectonism. The Fillmore arch and some other structural highs situated along the edge of the late Precambrian craton caused ramping of the inner Keystone-Pavant-Canyon thrust sheets and telescoping of the frontal thrust sheets. Post-thrust uplift of basement highs led to tectonic denudation and to the development of low-angle, extensional faults, such as the Sevier detachment. Northeast-trending lineaments, such as the Cove Fort and Paragonah lineaments, were reactivated as right-lateral strike-slip faults. They also affected the extent of the Marysvale volcanic field.

  1. Reinterpretation of Halokinetic Features in the Ancestral Rocky Mountains Paradox Salt Basin, Utah and Colorado

    NASA Astrophysics Data System (ADS)

    Thompson, J. A.; Giles, K. A.; Rowan, M. G.; Hearon, T. E., IV

    2016-12-01

    The Paradox Basin in southeastern Utah and southwestern Colorado is a foreland basin formed in response to flexural loading by the Pennsylvanian-aged Uncompaghre uplift during the Ancestral Rocky Mountain orogen. Thick sequences of evaporites (Paradox Formation) were deposited within the foreland basin, which interfinger with clastic sediments in the foredeep and carbonates around the basin margin. Differential loading of the Pennsylvanian-Jurassic sediments onto the evaporites drove synsedimentary halokinesis, creating a series of salt walls and adjacent minibasins within the larger foreland basin. The growing salt walls within the basin influenced patterns of sediment deposition from the Pennsylvanian through the Cretaceous. By integrating previously published mapping with recent field observations, mapping, and subsurface interpretations of well logs and 2D seismic lines, we present interpretations of the timing, geometry, and nature of halokinesis within the Paradox Basin, which record the complex salt tectonic history in the basin. Furthermore, we present recent work on the relationships between the local passive salt history and the formation of syndepositional counter-regional extensional fault systems within the foreland. These results will be integrated into a new regional salt-tectonic and stratigraphic framework of the Paradox Basin, and have broader implications for interpreting sedimentary records in other basins with a mobile substrate.

  2. Episodic sedimentation on a lower Silurian storm-dominated carbonate ramp, Anticosti Island, Quebec, Canada

    SciTech Connect

    Sami, T.; Desrochers, A.

    1989-03-01

    The 130-170-m thick Becscie Formation represents continuous deposition on a shallow, open-marine carbonate ramp across the Ordovician-Silurian boundary. The sequence reflects a generally quiet, shallow marine environment punctuated by episodic, storm-generated, high-energy events. These events deposited individual storm units, or tempestites, which occur as fining-upward sequences ranging from 0.5 to 80 cm thick. A complete ideal storm deposit consists of a sharp erosional base overlain by intraclastic to bioclastic rudstone fining upward into calcarenite and then into finely laminated calcisiltite grading upward into shale. Tempestites exhibit a variety of storm-generated structures which are today exposed on extensive bedding planes. Gutters and gutter casts occur throughout the sequence and show a range of morphologies and fill/substrate combinations. Hummocky cross-stratification is widespread and restricted exclusively to the calcisiltite-rich tempestites. Flat-pebble conglomerates (intraclastic rudstone) occur through most of the sequence and contain clasts of mudstone, packstone, and grainstone, indicating extensive early sea floor lithification. Tempestite sequences display lateral and vertical variations controlled by water depth and distance from shore. Construction of proximality trends permits recognition of lower order sea level changes within the overall regressive sequence. Sea level changes are believed to be eustatic, yet diastrophic-tectonic influences should not be dismissed due to regional tectonic activity. Paleocurrent data suggest sediment transport by predominantly southwest-oriented geostrophic currents. Together with sedimentologic evidence, this supports a combined-flow model for storm sediment transport in the Anticosti basin.

  3. A Silurian armoured aplacophoran and implications for molluscan phylogeny.

    PubMed

    Sutton, Mark D; Briggs, Derek E G; Siveter, David J; Siveter, Derek J; Sigwart, Julia D

    2012-10-04

    The Mollusca is one of the most diverse, important and well-studied invertebrate phyla; however, relationships among major molluscan taxa have long been a subject of controversy. In particular, the position of the shell-less vermiform Aplacophora and its relationship to the better-known Polyplacophora (chitons) have been problematic: Aplacophora has been treated as a paraphyletic or monophyletic group at the base of the Mollusca, proximate to other derived clades such as Cephalopoda, or as sister group to the Polyplacophora, forming the clade Aculifera. Resolution of this debate is required to allow the evolutionary origins of Mollusca to be reconstructed with confidence. Recent fossil finds support the Aculifera hypothesis, demonstrating that the Palaeozoic-era palaeoloricate 'chitons' included taxa combining certain polyplacophoran and aplacophoran characteristics. However, fossils combining an unambiguously aplacophoran-like body with chiton-like valves have remained elusive. Here we describe such a fossil, Kulindroplax perissokomos gen. et sp. nov., from the Herefordshire Lagerstätte (about 425 million years bp), a Silurian deposit preserving a marine biota in unusual three-dimensional detail. The specimen is reconstructed three-dimensionally through physical-optical tomography. Phylogenetic analysis indicates that this and many other palaeoloricate chitons are crown-group aplacophorans.

  4. Silurian horseshoe crab illuminates the evolution of arthropod limbs

    PubMed Central

    Briggs, Derek E. G.; Siveter, Derek J.; Siveter, David J.; Sutton, Mark D.; Garwood, Russell J.; Legg, David

    2012-01-01

    The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates. PMID:22967511

  5. A soft-bodied lophophorate from the Silurian of England

    PubMed Central

    Sutton, M. D.; Briggs, D. E. G.; Siveter, David J.; Siveter, Derek J.

    2011-01-01

    Soft-bodied taxa comprise an important component of the extant lophophorate fauna, but convincing fossils of soft-bodied lophophorates are extremely rare. A small fossil lophophorate, attached to a brachiopod dorsal valve, is described from the Silurian (Wenlock Series) Herefordshire Lagerstätte of England. This unmineralized organism was bilaterally symmetrical and comprised a subconical body attached basally to the host and partially enclosed by a broad ‘hood’; the body bore a small, coiled lophophore. Where the hood attached laterally, there is a series of transverse ridges and furrows. The affinities of this organism probably lie with Brachiopoda; the hood is interpreted as the homologue of a dorsal valve/mantle lobe, and the attachment as the homologue of the ventral valve and/or pedicle. The ridges are arranged in a manner that suggests constructional serial repetition, indicating that they are unlikely to represent mantle canals. Extant brachiopods are not serially structured, but morphological and molecular evidence suggests that their ancestors were. The new organism may belong to the brachiopod stem group, and might also represent a significant element of the Palaeozoic lophophorate fauna. PMID:20685698

  6. Silurian horseshoe crab illuminates the evolution of arthropod limbs

    NASA Astrophysics Data System (ADS)

    Briggs, Derek E. G.; Siveter, Derek J.; Siveter, David J.; Sutton, Mark D.; Garwood, Russell J.; Legg, David

    2012-09-01

    The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.

  7. Silurian horseshoe crab illuminates the evolution of arthropod limbs.

    PubMed

    Briggs, Derek E G; Siveter, Derek J; Siveter, David J; Sutton, Mark D; Garwood, Russell J; Legg, David

    2012-09-25

    The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.

  8. Influence of structural evolution on reservoir development and distribution in the Silurian Fusselman: Vermejo-Moore Hopper field, Loving and Ward Counties, Texas

    SciTech Connect

    Colleary, W.M.; Hulme, J.R. ); Crafton, J.W. Gas Research Institute, Chicago, IL )

    1992-04-01

    The Vermejo-Moore Hooper field lies in the deep Delaware basin adjacent to the Pecos River in Loving and Ward counties, Texas. Discovered in 1973, the field produces dry gas from the Fusselman and Ellenburger formations. The Fusselman reservoir has produced over 400 bcf of gas from depths between 18,500 and 19,200 ft. The field primarily is a structural trap, but the distribution of reserves in the reservoir suggests a strong stratigraphic component. The reservoir is composed of fractured dolomites and cherts of the Silurian Fusselman and overlying Wristen formations. Unconformities and their accompanying diagenetic processes play a major role in the reservoir. The occurrence of pervasive dolomitization and nodular cherts are interpreted to indicate diagenesis associated with subaerial exposure and karsting. Thick sections also may be absent due to erosion over paleostructures, and preserved in flanking positions. Detailed paleostructural interpretation of the Vermejo-Moore Hooper field reveals a history of recurrent movement of the basement and demonstrates the influence of structural growth on the development and distribution of porosity and permeability in the Fusselman reservoir. Early structural growth can influence the distribution of both depositional facies and erosional processes. Paleostructure maps in the Silurian-Devonian indicate that a series of northwest-southeast-trending, low-relief structures existed during the Silurian. Growth of these structures through the Devonian can be documented and the presence of fault-bounded basement blocks can be inferred. The influence of this structural growth on the development of the reservoir is also demonstrated.

  9. The Fusselman Formation (Lower and Middle Silurian) of the Franklin Mountains of west Texas and south-central New Mexico

    SciTech Connect

    LeMone, D.V. )

    1992-04-01

    The Fusselman Formation of the Franklin Mountains is a massive, vuggy, finely to coarsely crystalline, whitish unit with 185 m stratotype in the north-central part of the range where it forms the main ridge. The formation has been subdivided into three members (in ascending order): Chamberino (80 m), Flag Hill (29 m), and Crazy Cat (76 m). The members may be broadly interpreted as a series of three shoaling-upward sequences with minor karsting reported at the contact between the Chamberino and the Flag Hill members. The formation is dolomitic with the exception of a few limestone ('Hi Cal') lenses in the Crazy Cat Member. The formation rests disconformably on the karsted, low-relief surface of the underlying Cutter Formation of the Late Ordovician Montoya Group. The age of the Fusselman has been determined to be Early-Middle Silurian (Alexandrian-Niagaran) in the Franklins. The Fusselman is overlain by the upper Middle Devonian Canutillo Formation. The disconformity between the underlying uppermost Tippecanoe Fusselman and the overlying basal Kaskaskia Canutillo is on the order of 40 m.y. Extensive karsting developed on the top of Crazy Cat Member and its equivalents on the Tobosa basin ramp during this time. This karsted terrain, where overlain by the proper seal and supplied by an adequate source bed, produces within the Permian basin.

  10. Thin and Thick Skinned Foreland Deformation in the Central Andes: A Numerical Simulation Study

    NASA Astrophysics Data System (ADS)

    Babeyko, A. Y.; Sobolev, S. V.

    2004-12-01

    The two main segments of the Central Andean plateau, Altiplano and Puna, demonstrate since the Late Miocene different styles of tectonic shortening. Initially pure shear shortening in the Altiplano plateau switched at 13-9 Ma into the simple shear mode accompanied by formation of one of the world largest thin skinned foreland belt. Further to the south, in the Puna, the pure shear shortening continued until much more recently, gradually transforming into mixed pure and simple shear mode with thick skinned deformation in the foreland (the Santa Barbara System). Through numerical simulation of thermo-mechanical processes we show that different shortening modes - pure and simple shear accompanied by thin or thick skinned tectonics - might be controlled by (i) strength of the foreland uppermost crust and (ii) temperature of the foreland lithosphere. As a numerical tool we use a 2-D parallel thermo-mechanical finite element code LAPEX-2D. The code combines explicit lagrangian finite element FLAC algorithm with particle-in-cell technique. Particles track not only material properties but also full strain and stress tensors minimizing numerical diffusion. We employ Maxwell visco-elastic rheology with temperature- and stress-dependent viscosity, simulating ductile flow, as well as Mohr-Coulomb elasto-plastic rheology, simulating brittle deformation. Both rheological models may experience strain softening. Previous geodynamic models indicated the importance of the lateral temperature variations in the lithosphere on the style of tectonic shortening. However, they failed to reproduce migration of the deformation from the Altiplano plateau into its foreland before the major uplift of the plateau. We show that deformation may easily migrate from the plateau into the foreland by rapidly propagating thin skinned thrust belt as a consequence of dramatic mechanical weakening of the Palaeozoic sediments overlying the cold lithosphere of the Altiplano foreland. The processes in the

  11. Early Oligocene paleosols of the Dagshai Formation, India: A record of the oldest tropical weathering in the Himalayan foreland

    NASA Astrophysics Data System (ADS)

    Srivastava, Pankaj; Patel, Subhra; Singh, Nandita; Jamir, Toshienla; Kumar, Nandan; Aruche, Manini; Patel, Ramesh C.

    2013-08-01

    This study reports paleopedological features of the fossil soils that formed during the earliest phase of continental sedimentation in the Himalayan foreland. The fluvial sequence of the Dagshai Formation (31.6 ± 3.9 Ma to 30.3 ± 3.9 Ma) exposed along the Koshaliya River, NW Himalaya, contains four pedofacies (named Pedofacies A-D) of ferruginous paleosol sequences contained within overbank sediments. The Dagshai Formation unconformably overlies the marine Subathu Formation. Pedofacies A consists of 3-4 well-developed ferruginous paleosols overlain by gray sandstone beds. Pedofacies B-D are marked by a progressive decrease in pedogenesis. These paleosols occur as 0.5 m to 1.5 m thick Bw/Bt/Btk/Bk/Bss horizons that are marked by extensive development of rhizoliths, pedogenic carbonate, and iron-rich clay pedofeatures that correspond to modern Entisols, Inceptisols, Alfisols and Vertisols. Based on early Oligocene paleogeographic position of the northward-drifting Indian Plate, it is inferred that these paleosols were formed at ~ 18°N paleolatitude in the Dagshai sub-basin in the Himalayan foreland. Micromorphology, geochemical analyses, weathering indices, and stable isotope composition of paleosols indicate tropical climate (paleoprecipitation of 947-1256 mm and paleotemperature of ~ 25 °C) with an initial phase of monsoonal conditions during pedogenesis. These paleoclimatic conditions favored C3 paleovegetation immediately after the transition from greenhouse to icehouse conditions.

  12. Slab rollback orogeny in the Alps and evolution of the Swiss Molasse basin

    PubMed Central

    Schlunegger, Fritz; Kissling, Edi

    2015-01-01

    The stratigraphies of foreland basins have been related to orogeny, where continent–continent collision causes the construction of topography and the downwarping of the foreland plate. These mechanisms have been inferred for the Molasse basin, stretching along the northern margin of the European Alps. Continuous flexural bending of the subducting European lithosphere as a consequence of topographic loads alone would imply that the Alpine topography would have increased at least between 30 Ma and ca. 5–10 Ma when the basin accumulated the erosional detritus. This, however, is neither consistent with observations nor with isostatic mass balancing models because paleoaltimetry estimates suggest that the topography has not increased since 20 Ma. Here we show that a rollback mechanism for the European plate is capable of explaining the construction of thick sedimentary successions in the Molasse foreland basin where the extra slab load has maintained the Alpine surface at low, but constant, elevations. PMID:26472498

  13. Intraguild predation in pioneer predator communities of alpine glacier forelands.

    PubMed

    Raso, Lorna; Sint, Daniela; Mayer, Rebecca; Plangg, Simon; Recheis, Thomas; Brunner, Silvia; Kaufmann, Rüdiger; Traugott, Michael

    2014-08-01

    Pioneer communities establishing themselves in the barren terrain in front of glacier forelands consist principally of predator species such as carabid beetles and lycosid spiders. The fact that so many different predators can co-inhabit an area with no apparent primary production was initially explained by allochthonous material deposited in these forelands. However, whether these populations can be sustained on allochthonous material alone is questionable and recent studies point towards this assumption to be flawed. Intraguild predation (IGP) might play an important role in these pioneer predator assemblages, especially in the very early successional stages where other prey is scarce. Here, we investigated IGP between the main predator species and their consumption of Collembola, an important autochthonous alternative prey, within a glacier foreland in the Ötztal (Austrian Alps). Multiplex PCR and stable isotope analysis were used to characterize the trophic niches in an early and late pioneer stage over 2 years. Results showed that intraguild prey was consumed by all invertebrate predators, particularly the larger carabid species. Contrary to our initial hypothesis, the DNA detection frequency of IGP prey was not significantly higher in early than in late pioneer stage, which was corroborated by the stable isotope analysis. Collembola were the most frequently detected prey in all of the predators, and the overall prey DNA detection patterns were consistent between years. Our findings show that IGP appears as a constant in these pioneer predator communities and that it remains unaffected by successional changes. © 2014 The Authors. Molecular Ecology Published by John Wiley & Sons Ltd.

  14. Microbial Succession in Glacial Foreland Soils of the Canadian Subarctic

    NASA Astrophysics Data System (ADS)

    Kazemi, S.; Lanoil, B. D.

    2014-12-01

    The Canadian arctic has experienced increasing temperatures over the past century leading to heightened rate of glacial retreat. Glacial retreat leads to subsequent exposure of foreland soils to atmospheric conditions, thus creating a sequence of change in these ecosystems. Microbes are critical for soil development and nutrient dynamics in glacial systems as they are the primary colonizers of these soils and have been demonstrated to play a role in geochemical weathering and nutrient cycling beneath the glacier. Although viable microbial communities exist beneath glaciers and are known to be important for the glacial ecosystem, the impact of glacial retreat on these communities and development of the resulting foreland ecosystem is not well understood. Here, we investigate how microbial communities respond to changing conditions brought on by glacial retreat and whether a pattern of succession, such as those found in well characterized plant systems, occurs along a soil foreland in these microbial communities. We hypothesis that time since deglaciation is the major determinant of structure and composition of microbial assemblages. To test this, soil samples were collected along two glacier forelands, Trapridge Glacier and Duke River Glacier, located in Kluane National Park, Yukon Territory. Chronosequence dating of satellite images using geographic information system software revealed sampling sites have been ice-free from ~30 years to over 60 years. Soil chemistry analysis of major nutrients revealed no change in chemical parameters along the chronosequence, suggesting that presence of microbes after exposure from subglacial environments does not significantly alter soil characteristics in the timeframe observed. Furthermore, next-generation IonTorrentTM sequencing performed on soil samples revealed over five million sequencing reads, suggesting prominent microbial presence within these soils. Further analysis on sequencing data is needed to establish the

  15. Sedimentary history and biostratigraphy of Late Silurian-Early Devonian of southern Appalachians and southeastern Craton

    SciTech Connect

    Broadhead, T.W.; Capaccioli, D.A.; Neff, N.E.; Reid, S.R.

    1986-05-01

    The Late Silurian and Early Devonian sedimentary record of the southern Appalachians is preserved as a patchwork of shallow marine carbonate and terrigenous clastic rocks. These units commonly are bounded by unconformities, and biostratigraphic resolution has been lacking until recently. In Tennessee, the Sneedville formation (Hancock Dolomite of USGS usage) contains stromatoporoid faunas that correlate it with the Upper Silurian (Pridoli) Rondout (New York) and Tonoloway (central Appalachians) Formations, but recent conodont discoveries suggest a lower age limit in the Ludlow (crispa zone). Sneedville carbonates and clastics represent a broad range of shallow subtidal and peritidal facies that underwent periodic deepening and shoaling. In Georgia, correlative rocks are absent, and the Red Mountain Formation (Lower Silurian, Llandovery) is locally overlain by upper Lower Devonian Armuchee Chert-Frog Mountain Sandstone or by uppermost Devonian Chattanooga Shale. Reevaluation of the Red Mountain-Frog Mountain interval in Alabama showed a brachiopod fauna that correlated to the Keyser Limestone (uppermost Silurian-lowermost Devonian) of the central Appalachians. Cratonward, a relatively complete success of Upper Silurian-Lower Devonian carbonate rocks in west-central Tennessee (Decatur Limestone, Ross Formation) contrasts with the hiatus-bounded sections of the Appalachians. Toward the south, the Decatur intertongues with the lower Ross (eosteinhornensis zone), but to the north, the upper Decatur and Ross are both Devonian (woschmidti zone). The Decatur-Ross interval correlates with the Hunton Group of Oklahoma and is an ecologic analog and part temporal equivalent of parts of the Helderberg Group of New York.

  16. Exploration model for shallow Silurian (Kankakee) carbonate reservoirs in western Illinois

    SciTech Connect

    Crockett, J.E.; Seyler, B.J.; Whitaker, S.

    1987-09-01

    Reservoirs in shallow (600-650 ft deep) basal Silurian Kankakee carbonates at Buckhorn consolidated, Siloam, and Kellerville oil fields in western Illinois have produced nearly 2 million bbl of oil, but were developed essentially by random drilling. A new exploration model that combines lithologic studies and isopach mapping has been developed at the Illinois State Geological Survey. Isopach mapping of Silurian and Devonian rocks between an organic facies in the Mississippian-Devonian New Albany Shale and the top of the Ordovician Maquoketa Shale reveals thickened sequences that coincide with most of the oil fields. These thickened intervals apparently reflect subtle paleovalleys eroded into the Maquoketa shale during the Ordovician-Silurian hiatus. During the initial Silurian marine transgression, these paleovalleys at the base of the Kankakee were filled with carbonates to form the thickened sequences. Differential erosion at the top of the Kankakee does not satisfactorily explain the locally thickened sequences in the Kankakee. Lithologic studies suggest that subsurface fluid flows concentrated along these paleovalleys contributed to subsequent diagenesis of valleyfill carbonates. Diagenetic alteration of these carbonates resulted in development of basal Kankakee reservoirs within the paleovalleys. This concept of Kankakee reservoirs occurring within paleovalleys at the Ordovician-Silurian unconformity is a new exploration model that can aid in the search for similar traps in western Illinois.

  17. Geomorphology and dynamics of a traveling cuspate foreland, Authie estuary, France

    NASA Astrophysics Data System (ADS)

    Hesp, Patrick A.; Ruz, Marie-Hélène; Hequette, Arnaud; Marin, Denis; Miot da Silva, Graziela

    2016-02-01

    Cuspate forelands or salients occur all over the world in lakes, estuaries and on ocean shores, yet there have been few studies conducted on traveling cuspate forelands (or salients), that is, forelands that migrate or travel alongshore. This paper presents a study of a traveling foreland in the Authie estuary, France, termed the Bec du Perroquet. Historical shoreline changes may be traced from the 1200's AD and the region has experienced both marked intertidal-subtidal accretion extending from the south, and massive erosion in the north since this period. An analysis of aerial photographs from 1947 until the present shows that the original Bec foreland was established at the mouth of the Authie estuary, but gradually disappeared by the 1960's and a new foreland developed in the middle of the northern-central portion of the bay. This foreland was composed of a suite of foredune ridges which have been successively eroded on the northern margin and initiated on the southern margin as the foreland traveled or migrated southwards. As the foreland traveled south, from 1947 to 2009 the northern part of the bay retreated more than 350 m, while mid-bay, the coastline retreated ~ 215 m. As the foreland evolves and migrates, incipient foredunes can develop rapidly (e.g. 18 ridges formed in an 11 week period), while at other times the ridges form slowly and may be eroded and disappear. Two or more foredune ridges may blend into a single ridge over time depending on the initial degree of vegetation cover on the ridge and swale set. Aeolian processes in dune swales are much more important in this system than in typical prograding foredune plain systems due to the sometimes marked lack of vegetation colonization in the swales following foredune ridge development, and aeolian deflation of the swales (along with blowout development) is important particularly when they become open conduits to the beach as erosion of the NW foreland proceeds. The ages of each of the surviving ridges

  18. Biogeography of late Silurian and devonian rugose corals

    USGS Publications Warehouse

    Oliver, W.A.

    1977-01-01

    Three marine benthic faunal realms can be recognized in the Early and Middle Devonian. The Eastern Americas Realm consisted of most of the eastern half of North America and South America north of the Amazon. This realm extended in a southwest direction from the Devonian equator to approximately 35??S and was an isolated epicontinental sea during much of its history. The Eastern Americas Realm was bounded on the west by the Transcontinental Arch, on the north by the Canadian Shield and on the east and southeast by a peninsular extension of the Old Red Continent. These barriers were emergent during much, but not all, of Devonian time. Seaways beyond these barriers belonged to the Old World Realm. The Malvinokaffric Realm that was farther south was apparently temperate to arctic in climate and latitudinal position and contained few corals. Rugose corals in the Eastern Americas Realm show increasing generic-level endemism from the Late Silurian through the Early Devonian; during the late Early Devonian, 92% of the rugosan genera are not known anywhere else in the world. Endemism decreased through the Middle Devonian to zero in the early Late Devonian. The Early Devonian increase in endemism paralleled, and was probably related to, the development of the Old Red Continent as a barrier between America and Africa-Europe. The waning of endemism in the Middle Devonian reflects the breaching of the land barriers. This permitted some migration in and out of the realm in early Middle Devonian time but greatest movements were in late Middle Devonian time. Principal migration directions were from western or Arctic North America into the Michigan-Hudson Bay area and from the southern Appalachian area into Africa. ?? 1977.

  19. Time hierarchical analysis of the conodont paleocommunities and environmental change before and during the onset of the lower Silurian Mulde bioevent - A preliminary report

    NASA Astrophysics Data System (ADS)

    Spiridonov, Andrej; Kaminskas, Donatas; Brazauskas, Antanas; Radzevičius, Sigitas

    2017-10-01

    The Silurian period, and the Wenlock epoch in particular, experienced a series of powerful bioevents, among which was the Mulde event (upper Homerian). Here, the results of a study of the mid- to late Wenlock conodont paleocommunities in the shallow platform environments of the Lithuanian part of the Silurian Baltic Basin are presented. The analyses are based on a detailed quantitative description of the abundance and diversity patterns of the conodonts, as well as the geochemical and geophysical environmental proxies in the Ledai-179 core (central Lithuania). A model selection analysis of the conodont rank abundance distributions revealed episodic and progressive change from the complex communities of the early Jaagarahu time (lower Homerian), to the simple and much more even communities of the early Gėluva time (lower part of the upper Homerian). Spectral and cross-spectral analyses of the conodont species' apparent richness, evenness and abundance, as well as the δ13C and natural gamma ray trends, revealed transient episodes of 5th order periodic fluctuations. It is shown that the transitions in the community states and the transient episodes of the oscillations approximately coincided with the onset of the Mulde event (latest Jaagarahu and early Gėluva time).

  20. South American sedimentary basins

    SciTech Connect

    Urien, C.M.

    1984-04-01

    More than 64 sedimentary basins have been identified on the South American continent. According to their regional structural character and tectonic setting, they are classified in 4 super groups. About 20 interior or intracratonic basins occur on South American cratons (Guayanas, Brazilian, and Patagonian). In most cases, their sedimentary fill is Paleozoic or early Mesozoic. Rift or transverse grabens resulting from incipient sea floor spreading extend towards the continental margin. Seventeen basins are located along the Atlantic stable margin, and consist primarily of half grabens with downfaulted seaward blocks. These rifts (or pull-apart basins) were separated as results of the migration of the African and American continental blocks. Therefore the sedimentation is chiefly Cretaceous and Tertiary. On the western edge of South American cratons, almost 20 basins of downwarped blocks extend from Orinoco down to the Malvinas plateau in a relatively uninterrupted chain of retroarc basins, bordered by the Andean orogen. They lie on a flexured Precambrian and Paleozoic basement, and are highly deformed in the west (Subandean belt) due to the action of compressional forces caused by the tectonic influence of the Mesozoic Andean batholith. Westward, the Pacific margin is bordered by 27 foreland and forearc basins, which alternate from north to south on an unstable or quasistable margin, fringed by a trench and slope complex where the ocean crust is subducted beneath the continental plate.

  1. Frontier petroleum basins of Colombia

    SciTech Connect

    Keith, J.F. Jr.; Perez, V.E.

    1989-03-01

    The frontier basins of Colombia with hydrocarbon potential are numerous, have varying geological histories, and are in different stages of exploration development. In this paper, sedimentary or structural basins are classified as frontier petroleum basins if commercial discoveries of hydrocarbons are lacking, if the basin has not attained a high degree of exploration development, or if a new play concept has been perceived or developed for a portion of a mature exploration basin. Using these criteria for classification, the authors discuss the Cauca-Patia Choco-Pacifico, and Lower Magdalena basin complexes; the Cordillera Oriental foreland basin; and the Cesar-Rancheria, Sabana, and Amazonas basins. A comprehensive geological and structural setting of each of these frontier basins will be presented. The depositional and tectonic evolution of the basins will be highlighted, and the play concepts for each will be inventoried, catalogued, and categorized as to whether they are theoretical or established. The discussion of the available plays in each of these basins will include the main play concept elements of reservoirs traps, seals, source rocks, maturation, and timing. When detailed data permit, the reservoir and trap geometry will be presented.

  2. Vitrinite equivalent reflectance of Silurian black shales from the Holy Cross Mountains, Poland

    NASA Astrophysics Data System (ADS)

    Smolarek, Justyna; Marynowski, Leszek; Spunda, Karol; Trela, Wiesław

    2014-12-01

    A number of independent methods have been used to measure the thermal maturity of Silurian rocks from the Holy Cross Mountains in Poland. Black shales are characterized by diverse TOC values varying from 0.24-7.85%. Having calculated vitrinite equivalent reflectance using three different formulas, we propose that the most applicable values for the Silurian rocks are those based on Schmidt et al. (2015) equation. Based on this formula, the values range from % 0.71 VReqvVLR (the vitrinite equivalent reflectance of the vitrinite-like macerals) to % 1.96 VReqvVLR. Alternative, complementary methods including Rock Eval pyrolysis and parameters based on organic compounds (CPI, Pr/n-C17, Ph/n-C18, MPI1, and MDR) from extracts did not prove adequate as universal thermal maturity indicators. We have confirmed previous suggestions that Llandovery shales are the most likely Silurian source rocks for the generation of hydrocarbons in the HCM.

  3. The Jura thrust belt and its foreland: Tectonic history and petroleum plays

    SciTech Connect

    Mascle, A.; Yann, P. )

    1993-09-01

    The Jura thrust belt in eastern France is the accurate leading edge of the alps, which developed in the Neogene as a thin-skinned wedge of imbricate sheets of Mesozoic calcareous and marly platform sediments. The basal decollement generally is hosted in middle and late Triassic evaporites and salt layers. The foreland to the west in the Bresse basin, a complex late Eocene-early Miocene north-south-elongated rift superimposed on the Mesozoic platform and on more locally distributed Stephanian and Permian troughs related to the post-compressional collapse of the Variscan chain. Two main source rock intervals have been recognized so far in the whole area: coal measures and bituminous shales of the Stephanian-Autunian and marine black marls of the Toarcien. Reservoirs and associated seals are distributed more randomly and include sandstones, limestones, and dolostones of the Triassic and Jurassic. Tiny gas fields were exploited at the Jura front in the past but have now been abandoned. Significant oil shows have been encountered recently in Triassic sandstones at the southern edge of the Jura mountains. They have boosted exploratory plays considerably and, as a result, about 50% of the Jura and Bresse area presently is covered by licenses and license applications.

  4. 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.

  5. Stasis and extinction of Silurian (Llandovery-Wenlock) trilobite associations related to oceanic cyclicity

    USGS Publications Warehouse

    Mikulic, Donald G.; Kluessendorf, Joanne

    1999-01-01

    Silurian trilobites of the central United States belong to a series of temporally-successive associations which appeared abruptly, maintained taxonomic stasis for a time, and then disappeared abruptly. Their disappearance resulted from global perturbations of short-term duration and moderate magnitude, which caused substantial taxonomic replacement but no reorganization of major ecosystems. The most significant extinction and replacement in Silurian trilobite associations in the study area occurs near the Llandovery-Wenlock boundary. This turnover in trilobite associations appears to correspond to Jeppsson's Ireviken Event in his model of oceanic and climatic cyclicity. Major sea-level changes earlier in the Llandovery did not have a similar impact on trilobite associations.

  6. 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.

  7. Successive reactivation of older structures under variable heat flow conditions evidenced by K-Ar fault gouge dating in Sierra de Ambato, northern Argentine broken foreland

    NASA Astrophysics Data System (ADS)

    Nóbile, Julieta C.; Collo, Gilda; Dávila, Federico M.; Martina, Federico; Wemmer, Klaus

    2015-12-01

    The Argentine broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains are the result of N-S reverse faults that disrupted a W-E Miocene Andean foreland basin. In the Sierra de Ambato (northern Argentine broken foreland) the reverse faults offset Neogene sedimentary rocks (Aconquija Fm., ˜9 Ma) and affect the basement comprising Paleozoic metamorphic rocks that have been dated at ˜477-470 Ma. In order to establish a chronology of these faults affecting the previous continuous basin we date the formation age of clay minerals associated with fault gouge using the K-Ar dating technique. Clay mineral formation is a fundamental process in the evolution of faults under the brittle regime (<<300 °C). K-Ar ages (9 fractions from 3 samples collected along a transect in the Sierra de Ambato) vary from Late Devonian to Late Triassic (˜360-220 Ma). This age distribution can be explained by a long lasting brittle deformation history with a minimum age of ˜360 Ma and a last clay minerals forming event at ˜220 Ma. Moreover, given the progression of apparent ages decreasing from coarse to fine size fractions (˜360-311 Ma for 2-1 μm grain size fraction, ˜326-286 Ma for 1-0.2 μm and ˜291-219 Ma of <0.2 μm), we modeled discrete deformation events at ˜417 Ma (ending of the Famatinian cycle), ˜317-326 Ma (end of Gondwanic orogeny), and ˜194-279 Ma (Early Permian - Jurassic deformation). According to our data, the Neogene reactivation would not have affected the K-Ar system neither generated a significant clay minerals crystallization in the fault gouge, although an exhumation of more than 2 Km is recorded in this period from stratigraphic data.

  8. Early silurian spore tetrads from new york: earliest new world evidence for vascular plants?

    PubMed

    Gray, J; Boucot, A J

    1971-09-03

    Several taxa of abundant cutinized trilete spores from earliest Silurian shale in New York predate by almost an entire period vascular land plant megafossils. Paleoecological evidence suggests that these spores may represent vascular land or semiaquatic plants but a bryophytic origin cannot be precluded on the basis of spore characters. An algal origin is considered unlikely.

  9. Red iron-ore beds of Silurian age in northeastern Alabama, northwestern Georgia, and eastern Tennessee

    USGS Publications Warehouse

    Whitlow, Jesse W.

    1962-01-01

    Geological studies have determined the lithology and approximate extent of the red iron ores of Silurian age in the Southeast. Detailed investigations have been made by private companies and government agencies. Most of this work has been in the Birmingham, Ala., district, and the remainder of the region has relatively little study in recent years. 

  10. Submarine intrareef pisoliths and the origin of Silurian carbonate clinothems, northcentral Indiana

    SciTech Connect

    Frank, T.D.; Wilkinson, B.H.; Lohmann, K.C. . Dept. of Geological Sciences)

    1992-01-01

    Evaluation of the relative importance of biological versus physical processes during the deposition of midwestern Silurian carbonate buildups has resulted in three generally incompatible scenarios: (1) that bioherms consist largely of autochthonous debris generated and deposited in deep shelf settings; (2) that most carbonate was generated in reefal settings, but styles of accumulation evolved from primarily core accretion to dominantly flank bed progradation with upward growth to shallower depths, and (3) that larger Silurian buildups are neither reefs nor bioherms in that they consist almost entirely of allochthonous biotic debris derived from high-energy wave-swept benches. Vertical tension fractures that crosscut proximal flank beds in the Pipe Creek Junior quarry of northcentral Indiana formed during compaction of underlying interreef muds and are commonly filled with well-sorted pisolitic grainstone. Pisolith cortices are petrologically indistinguishable from marine cement between pisoliths, from marine cement lining tension fractures, and from marine cement in surrounding grainstone. Isotopic signatures and trace element concentrations for these components are identical. In addition, the pisolitic grainstone commonly exhibits lateral grading, with pisolith size increasing toward fracture interiors. These features demonstrate that pisoliths are submarine cave pearls that formed from Silurian seawater within synsedimentary tension cracks during flank bed deposition and progradation. This origin supports an interpretation that present exposure levels at Pipe Creek Junior are generally coincident with the Silurian depositional top of the buildup, as minimum current energies necessary for the formation of large coated grains require high-energy, shallow-water conditions.

  11. Ordovician and Silurian acritarch assemblages from the west Leinster and Slievenamon areas of southeast Ireland.

    PubMed

    Maziane-Serraj, N; Brück, P M.; Higgs, K T.; Vanguestaine, M

    2000-12-01

    The Lower Palaeozoic sequences west of the Leinster Granite and in the Slievenamon Inlier of southeast Ireland have been palynologically re-investigated. Most of the productive samples yielded sufficient identifiable acritarchs for positive stratigraphical age determinations for several of the formations. The samples also include rare cryptospores, scolecodonts and tubular structures. Previous work in the area west of the Leinster Granite proposed an unbroken succession from Early Ordovician Ribband Group turbidites and volcanics passing up conformably to Early Ordovician to Late Silurian Kilcullen Group. The new palynological data clearly show that the Kilcullen Group in this area is entirely Silurian (Llandovery-early Wenlock) in age, also results obtained from the same group at Slievenamon confirm the previously reported Silurian age. Ordovician acritarchs found in the Kilcullen Group of both study areas are reworked and range in age from late Tremadoc to Llanvirn. The new data reveal a major stratigraphic break between the Ribband Group dated as Early and Middle Ordovician and the Silurian Kilcullen Group. This major break extends some hundreds of kms southwest to the Dingle Peninsula and possibly equates with a similar discontinuity in the Isle of Man to the northeast. This break would thus appear to be a major feature within the northwestern Avalonian margin sequence.

  12. Silurian granites of northern Kazakhstan: U-Pb age and tectonic position

    NASA Astrophysics Data Syst