Science.gov

Sample records for silurian foreland basin

  1. Tectonostratigraphic history of the Ediacaran-Silurian Nanhua foreland basin in South China

    NASA Astrophysics Data System (ADS)

    Yao, Wei-Hua; Li, Zheng-Xiang

    2016-04-01

    This paper presents the tectonostratigraphic evolution of the Ediacaran-Silurian Nanhua Basin in South China and explores the relationship between clastic sedimentation in the basin and evolution of the adjacent Wuyi-Yunkai orogen. Sedimentary facies in the basin comprises, in an ascending order, turbiditic marine, shallow marine, and fluvial-dominated deltaic facies, featuring a lateral migration from southeast to northwest. We interpret the Ediacaran-Silurian Nanhua Basin as a foreland basin with a three-stage evolution history. Stage 1: the Ediacaran-Cambrian stage, recording the start of tectonic subsidence with turbiditic marine siliciclastic deposition, fed by exotic orogens outboard South China; Stage 2: the Ordovician to earliest-Silurian stage, characterized by a migrating depocenter with dominant shallow marine and deltaic siliciclastic deposition, fed by the local and northwestward propagating Wuyi-Yunkai orogen; Stage 3: the Silurian stage, showing the arrival of depocenter in the Yangtze Block during the waning stage of the orogeny with deltaic deposition in the remanent foreland basin. The Wuyi-Yunkai orogen remained the dominant sedimentary source region during Stage 3. Stage 1 was likely related to the collision of the South China Block toward northern India during the assembly of Gondwana, whereas Stages 2 and 3 recorded sedimentation during the northwestward propagation and subsequent orogenic root delamination/collapse of the Wuyi-Yunkai orogen, respectively. The Wuyi-Yunkai orogeny in South China is interpreted to have resulted from the far-field stress of the collision between South China and Indian Gondwana.

  2. Stratigraphic evidence from the Appalachian Basin for continuation of the Taconian orogeny into Early Silurian time

    NASA Astrophysics Data System (ADS)

    Ettensohn, Frank R.; Brett, Carlton E.

    2002-01-01

    Traditional interpretations of the Appalachian Basin during Silurian time suggest a period of tectonic stability between Taconian and Acadian orogenies. However, recent interpretations of evidence from deformation and igneous sources in the northern Appalachians indicate Silurian tectonism centered on and near the St. Lawrence promontory and that this tectonism probably effected sedimentation in parts of the Appalachian Basin during much of Silurian time. Of special interest is the tectonism that extended from latest Ordovician into Early Silurian time and the nature of its relationships with known orogenic events. Although evidence and interpretations from deformation and igneous sources have become increasingly well established, there has been little support from the stratigraphic record. Now, however, criteria based on the implications of flexural models, namely the nature and distribution of unconformities, the presence of flexural stratigraphic sequences, and the distribution in time and space of dark-shale-filled foreland basins, provide stratigraphic evidence from the Appalachian Basin that supports Early Silurian (Medinan; early Llandoverian) tectonism related to Taconian orogeny. In particular, the distribution and local angularity of the Ordovician-Silurian or Cherokee unconformity suggest major tectonic influence and a latest Ordovician to Early Silurian inception for that tectonism. An overlying flexural stratigraphic sequence represented by the Lower Silurian Medina Group and the presence of a dark-shale-filled foreland basin reflected by the Power Glen-lower Cabot Head shales support interpretations of flexural subsidence related to deformational loading. Moreover, the distribution in space and time of the foreland basin containing these shales indicates that the basin is more likely a continuation of the northwestwardly shifting trend of earlier Taconian basins than that of later Salinic basins. Although the kinematic regime may be different from

  3. 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.

  4. 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.

  5. Irregular plate boundary controls on Foreland Basin sedimentation (Miocene, Kahramanmaraş Foreland Basin, SE Turkey)

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    The northern movement of the Arabian Plate led to the development of a compressional regime in the south-eastern part of Turkey after the Late Cretaceous. The collision of the Arabian Plate with the Anatolide-Taurides Platform and subsequent development of the Kahramanmaraş Foreland Basin at the beginning of the Miocene evolved as a result of this movement. An irregular plate geometry or promontory of the Arabian Plate caused partitioning of the plate margin (precollision-collision-postcollision). This irregular plate boundary was delimited by western and northern boundary faults and an interior basin fault. The NW-oriented small wedge top basins on the overlying Anatolide-Taurides Platform obliquely cut through the foredeep basin. The region (across the wedge top basin) on the irregular promontory of the underlying Arabian Plate contains different sedimentation depocentres. Small fining-upward submarine fan deposits (including pebbly channel deposits and coarsening-upward lobe sequences) are located at the centre of the irregular part of the plate (in the Tanır region) and overlie planktic foraminifera-bearing claystones. These submarine fan sediments pass outboard into distal interbedded turbidite claystones and siltstones in a downdip direction (S-SE). The boundary fault intersection of the promontory led to the development of a submarine slope environment with irregular sea-floor topography in the Fırnız area (4-5 km south-east of the Tanır region). The slump deposits, sandy debrites, and fine-grained thin-bedded turbidites filled this region. Structural alignments and seismicity associated with the plate margin were the main controlling factors on the geometry of the depocentre, sediment quantity, sediment input, sedimentary facies, local sea level changes, and post-sedimentary deformation in the Kahramanmaraş Foreland Basin.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  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. 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.

  12. 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.

  13. 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.

  14. 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. PMID:10769160

  15. Development of foreland basins around western Sichuan basin, and implications for mountain building in eastern Tibet

    NASA Astrophysics Data System (ADS)

    Chen, S.; Liu, M.

    2014-12-01

    The Sichuan basin is surrounded by the Tibetan Plateau to the west, and the Michang Shan and Daba Shan mountains to the north and northwest. Foreland basins have been developed along the western and northern margins of the Sichuan basin since Triassic, receiving sediments with significant along-strike variations. These sediment records provide useful insights into the history of mountain building around the Sichuan Basin. We have collected exploration well data from western Sichuan Basin. Using backstripping, we reconstructed the basement deformation history, which reflect sedimentary and tectonic loadings related to mountain building. We used a 3-D numerical modeling technique with multi-grid technique to simulate flexural deformation of the Sichuan Basin lithosphere, and to infer tectonic loading and mountain building along western and northern margins of the Sichuan Basin from the late Triassic to the Cenozoic. Our results suggest that the shortening of the Daba Shan and Michuan Shan orogens mainly occurred during the late Jurassic-Cretaceous. During Cenozoic, the tectonic loading mainly occurred along the southwestern margins of the Sichuan Basin, corresponding to the development of the Longmen Shan mountain belt. The tectonic loading of the northern Longmen Shan on the Sichuan Basin has been markedly reduced since the Cenozoic, evidenced by the lack of Cenozoic foreland basin development. This indicates mechanical decoupling between uplift of the Tibetan Plateau and the Sichuan Basin, consistent with the deep down-cutting of the Longmen Shan fault and predominantly strike-slip motion on the fault. The limited Cenozoic foreland basin development in the southwestern margin of the Sichuan Basin is consistent with localized high-angle thrusting of the southern Longmen Shan mountains. This work was supported by the National Natural Science Foundation of China (grants 41104046).

  16. Rejuvenation of the Kuqa foreland basin, northern flank of the Tarim basin, northwest China

    SciTech Connect

    Lu Huafu; Jia Dong; Cai Dongsheng

    1994-12-01

    The Kuqa depression along the northern flank of the Tarim basin is filled with a thick sequence of Neogene and Quaternary coarse elastic continental sediments. This structural depression is part of a large foreland basin that leads south of the Tianshan - an orogenic belt of intracontinental convergence resulting from the northward propagation of stress following the collision of India with the southern margin of Eurasia. 11 refs., 6 figs., 1 tab.

  17. The fate of giant Silurian paleo-reservoirs in Tarim Basin

    SciTech Connect

    Chen, J.H.; Fu, J.M.; Sheng, G.Y.

    1996-10-01

    Tarim Basin is located in the south part of the Xinjiang Yugur autonomous region of China, between Tianshan and Kunlun mountains. Tarim Basin is the largest petroliferous sedimentary basin in China, with a total area of 560,000 km{sup 2}. Within the past five years` exploration, it was revealed that there occur widely tar sands and heavy oils in the Silurian formation in North and Central uplifts of Tarim basin in a huge volume. Based on the geochemical data including distribution of biological markers, this talk will discuss how these tar sands and heavy oils were formed by destruction and degradation of giant Silurian reservoirs. It will also be pointed that these tar sand bitumen have made important contribution to petroleum accumulation as an unique hydrocarbon source in Tarim basin.

  18. 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.

  19. Paleoceanography of Silurian Seaways in the Midwestern Basins and Arches Region

    NASA Astrophysics Data System (ADS)

    Droste, J. B.; Shaver, R. H.

    1987-04-01

    Prima facie isotopic, salinity, and other geochemical data of the kind normally cited as evidence for a set of stated oceanographic parameters scarcely exist for the mostly highly dolomitized rocks of the Silurian System in the midwestern basins and arches region. This lack requires that Silurian paleoceanographic reconstructions be highly generalized as projections from a recently published integrative stratigraphy and from prior proposals of regional cyclicity in sedimentation, bathymetry, and salinity. We propose that midwestern Silurian sea level fluctuated only in modest amounts from late Early to middle Late Silurian time. Further, bathymetric differentiation among some of the basins and arches was modest. These bathymetric generalities for three selected time slices are representative of a complex history of Silurian cyclicity: mid-Wenlockian time, 50 to more than 75 m in the basins, about 30 m on the intervening platforms, and less than 15 m in parts of major carbonate bank and reef areas; latest Wenlockian, about 100 m in the Illinois Basin, about 20 m to supratidal on the carbonate shelves, and 10 m and, at times, less in the Appalachian and Michigan evaporite basins; and mid-Ludlovian, only a modest 10-15 m deeper than that of latest Wenlockian time. The mid-Ludlovian deepening was sufficient, however, to restore circulation and salinity to normal on the interbasin platforms and to near normal in the evaporite basins. Near the evaporite basins, net current flow was toward and into the basins through belts of increasing evaporation. Such currents became increasingly enriched in Mg ions and effected early dolomitization of Silurian carbonate, including reef sediments. Biotas ranged from normal marine, high-diversity communities, which were most widespread during mid-Wenlockian time, to variably restricted, algae-dominated communities and were even nonexistent in the evaporite basins during latest Wenlockian time. Generally, shallow depth may have been more

  20. 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.

  1. Deep seismic expression of a foreland basin: Taranaki basin, New Zealand

    NASA Astrophysics Data System (ADS)

    Stern, T. A.; Davey, F. J.

    1990-10-01

    A deep seismic-reflection profile shot across the South Taranaki basin, New Zealand, indicates up to 10 km of crustal thickening beneath the Taranaki boundary fault at the eastern margin of the basin. The seismic data also show a broad flexure of the entire crust, the locus of the flexure-producing load appearing to be in the vicinity of the Taranaki boundary fault. Such crustal thickening and flexure suggest a compressional, foreland-basin style of late Cenozoic development rather than the rift-graben origin previously assumed. This change in interpretation for the South Taranaki basin has implications for evaluating the thermal history of the basin and its possibilities for hydrocarbon prospects. The study therefore demonstrates the value of deep seismic exploration of a hydrocarbon-bearing basin in its early stage of exploration.

  2. 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.

  3. 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.

  4. Effects of Flat Slab Subduction on Andean Thrust Kinematics and Foreland Basin Evolution in Western Argentina

    NASA Astrophysics Data System (ADS)

    Horton, B. K.; Fuentes, F.; McKenzie, N. R.; Constenius, K. N.; Alvarado, P. M.

    2014-12-01

    Debate persists over the effects of flat-slab subduction on the kinematics of overriding plate deformation and the evolution of retroarc sedimentary basins. In western Argentina, major spatial and temporal variations in the geometry of the subducting Nazca slab since ~15 Ma provide opportunities to evaluate the late Cenozoic response of the Andean fold-thrust belt and foreland basin to subhorizontal subduction. Preliminary results from several structural and sedimentary transects spanning the frontal thrust belt and foreland basin system between 31°S and 35°S reveal Oligocene-middle Miocene hinterland exhumation during normal-slab subduction followed thereafter by progressive slab shallowing with initial rapid cratonward propagation of ramp-flat thrust structures (prior to basement-involved foreland uplifts) and accompanying wholesale exhumation and recycling of the early Andean foreland basin (rather than regional dynamic subsidence). Detrital zircon U-Pb geochronologic data prove instrumental for revealing shifts in thrust-belt exhumation, defining depositional ages within the foreland basin, and constraining the timing of activity along frontal thrust structures. In both the San Juan (31-32°S) and Malargüe (34-35°S) segments of the fold-thrust belt, geochronological results for volcaniclastic sandstones and syndeformational growth strata are consistent with a major eastward advance in shortening at 12-9 Ma. This episode of rapid thrust propagation precedes the reported timing of Sierras Pampeanas basement-involved foreland uplifts and encompasses modern regions of both normal- and flat-slab subduction, suggesting that processes other than slab dip (such as inherited crustal architecture, critical wedge dynamics, and arc magmatism) are additional regulators of thrust-belt kinematics and foreland basin evolution.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Lithologic mixing in a modern foreland basin: Evidence from Landsat thematic mapper images

    SciTech Connect

    Damanti, J.F. )

    1990-09-01

    Reflectance spectra of synorogenic sediments accumulating in a modern foreland basin indicate that alluvial-fan sediment changes composition as drainage networks expand through tilted strata. The spectral signatures of several sediment mixtures can be used to identify zones of lithologic mixing and to infer erosional unroofing sequences and drainage development in a modern foreland region. A practical graphic analysis of sediment mixing was developed for digital Landsat thematic mapper data. This technique determines the relative proportions of end-member compositions in a binary sediment mixture. Vegetation effects on the spectral response of rock and sediment can also be evaluated.

  13. Comparative hydrocarbon geology of two Mesozoic Circum-Pacific foreland basins as function of sediment provenance: Surat basin, eastern Australia and western Canada basin

    SciTech Connect

    Hawlader, H.M. )

    1990-06-01

    The Surat basin in Queensland and New South Wales, Australia, is a foreland basin formed in response to a magmatic arc during Early Jurassic to mid-Cretaceous time. It has a maximum basin-fill of about 2.5 km of Jurassic and Lower Cretaceous sediments. The first commercial production of oil in Australia came from this basin in the early 1960s. The Western Canada basin is a retro-arc foreland basin with up to 3.5 km of sediments deposited during the Middle Jurassic to Late Cretaceous. The basin was developed on the cratonward side of an arc/cordillera by plate convergence. It is a composite basin with sediments ranging in age from Devonian to Tertiary and is one of the prolific petroliferous basins of the world. The famous Athabasca-Peace River-Lloydminister tar sands alone contain a reserve of about 3 {times} 10{sup 12} barrels of oil, which exceeds three times the recoverable reserves of the world's known oil. The main sediment source was, in both basins, a rising arc/cordillera that shed a cratonward tapering clastic wedge into the flanking foreland basins. Sedimentation, in both cases, was episodic and the patterns of sedimentation in each present striking similarities. During the waxing phase of magmatism/orogeny in the arc/cordillera, the foreland subsided in response to flexural loading of the foreland fold-thrust belt and downward drag by the subducting plate. Continental synorogenic sediments were rapidly emplaced in mainly terrestrial environments into the subsiding foreland. These sediments are lithic-labile in nature and because of their physical and chemical reactivity are prone to be tight and thus of little hydrocarbon reservoir potential. During the waning phase of the arc/orogen the foreland gently rose in response partly to the cessation of drag (decoupling) by the subducting plate and to isostatic rebound (tectonic relaxation).

  14. 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

  15. Substratum transverse faults in Kuqa Foreland Basin, northwest China and their significance in petroleum geology

    NASA Astrophysics Data System (ADS)

    Cai, Jun; Lü, Xiuxiang

    2015-08-01

    The importance of transverse faults in basin evolution and petroleum geology has been often emphasized. However, the transverse faults in the Kuqa Foreland Basin, the most important gas producing area in China, have rarely been studied. Interpreted seismic sections and earthquake focal mechanism solutions, as well as other geological and geophysical data, allow us to identify a few widely-spaced, approximately NS trending, transverse strike-slip faults separating major structural units, and to clarify the geometry and kinematics of these transverse faults hidden below thrust faults. In the Kuqa Foreland Basin, two major structural domains can be distinguished. Transverse faults in the northern Kuqa Foreland Basin are mainly NNE trending sinistral, indicating clockwise-rotation of fault-bounded blocks. In contrast, the predominant NW trending dextral faults in the southern Kuqa Foreland Basin imply counterclockwise-rotation of fault-bounded blocks. We propose a tectonic model in which crustal blocks are bounded by strike-slip faults in a zone of simple shear rotation about vertical axis. The strike-slip faulting and thrust faulting in the Kuqa Foreland Basin suggest that some of the convergence between South Tianshan and Tarim blocks may have been accommodated not only by obvious crustal shortening and thickening along thrust faults, but also by rotation and possible lateral movement of the crust along transverse faults. Controlled by the remote collision of Indian block with Eurasian block since the Miocene, these reactivated substratum faults, which may inherit from Paleozoic deformation, control various elements relevant to gas accumulation in the Kuqa Foreland Basin which should expect to be paid more attention in the future. These elements include maturity of Tertiary and Jurassic source rocks, a difference in the regional cap of Kumugelimu salt beds from east to west, reservoir bed properties, gas migration channels, and traps formation. In addition, the

  16. Dating of the oldest continental sediments from the Himalayan foreland basin.

    PubMed

    Najman, Y; Pringle, M; Godin, L; Oliver, G

    2001-03-01

    A detailed knowledge of Himalayan development is important for our wider understanding of several global processes, ranging from models of plateau uplift to changes in oceanic chemistry and climate. Continental sediments 55 Myr old found in a foreland basin in Pakistan are, by more than 20 Myr, the oldest deposits thought to have been eroded from the Himalayan metamorphic mountain belt. This constraint on when erosion began has influenced models of the timing and diachrony of the India-Eurasia collision, timing and mechanisms of exhumation and uplift, as well as our general understanding of foreland basin dynamics. But the depositional age of these basin sediments was based on biostratigraphy from four intercalated marl units. Here we present dates of 257 detrital grains of white mica from this succession, using the 40Ar-39Ar method, and find that the largest concentration of ages are at 36-40 Myr. These dates are incompatible with the biostratigraphy unless the mineral ages have been reset, a possibility that we reject on the basis of a number of lines of evidence. A more detailed mapping of this formation suggests that the marl units are structurally intercalated with the continental sediments and accordingly that biostratigraphy cannot be used to date the clastic succession. The oldest continental foreland basin sediments containing metamorphic detritus eroded from the Himalaya orogeny therefore seem to be at least 15-20 Myr younger than previously believed, and models based on the older age must be re-evaluated. PMID:11242076

  17. Sedimentary basinal responses to a Late Precambrian Wilson Cycle: the Damara Orogen and Nama Foreland, Namibia

    NASA Astrophysics Data System (ADS)

    Stanistreet, Ian G.; Kukla, Peter A.; Henry, George

    In the Damara Orogen sedimentary basinal responses are important in recording the evolution of the fold belt. Here we integrate sedimentological patterns and tectonics to characterise the basin development of both the pre- to syn-orogenic Damara Sequence and the syn- to post-orogenic Nama Group. The evolution of an entire Late Proterozoic Wilson Cycle involved initial rifting, with the opening of two oceanic arms through convergence to collision and foreland basin development. Rift initiation (stage 1) took place along old tectonic weaknesses and extensional rift basins (stage 2) were filled by continental sediments and alkaline/bimodal volcanics. Two oceanic openings occurred: (i) the Adamastor Ocean (stage 3) produced a break-up unconformity and eastward transgression over the Kalahari and Congo Cratons; and (ii) the Khomas Sea gulf subsequently developed betwen the two cratons (stage 4) and is associated with break-up unconformities, and ultimately the development of mature shleves (stage 5). In the latter opening, we envisage an anticlockwise rotation of the Kalahari Craton with respect to the Congo Craton. During convergence the closing Khomas Sea produced an accretionary prism/arc/retro-arc system (stage 6) and the first deformation phase in the Southern Zone. The Khomas Orogeny records the collision between the Kalahari and Congo Cratons (stage 7) including the obduction of oceanic elements onto the Kalahari Craton foreland, and caused the second and third deformation phases in the Southern Zone and first and second deformation phases in the Central Zone. A peripheral foreland basin and peripheral bulge on the Kalahari Craton resulted, which respectively contained and affected the marine and fluvial Nama Group sedimentation. A complementary hinterland basin accepted Mulden Group sediments on the Congo Craton. Ultimately the collision of the South American continent with the newly reconstituted African foreland (stage 8) caused the Adamastor Orogeny and

  18. 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.

  19. 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.

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

    USGS Publications Warehouse

    Groshong, R.H., Jr.; 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.

  1. 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.

  2. Silurian-Niagaran reef belt around the Michigan basin--a synergistic review

    SciTech Connect

    Aminian, K.; Tek, M.R.; Wilson, J.L.

    1982-09-01

    The Silurian-Niagaran pinnacle reefs occur on a belt which encircles the entire Michigan Basin including areas presently covered by the Great Lakes. The annual production from these reefs in Michigan has reached 30 million barrels of oil and 150 billion cubic feet of natural gas. Two different structural settings existed in the Michigan Basin during the Silurian Period, which resulted in formation of the pinnacle reefs with somewhat different characteristics in different parts of the basin. The pinnacles of the northern trend occur at depths of 4000-7000 feet, are up to 700 feet thick, and average about 100 acres in area. The southern pinnacles occur at depths of 2000-3000 feet, are shorter, about 300 feet thick, and attain larger areas. The pinnacle reefs underwent several diagenetic changes, which resulted in concentration of the majority of the hydrocarbon reserves of the northern trend in pinnacles which occur on a band 3-4 miles wide inside the middle of the trend. There exists a regional partitioning of oil and gas in the northern pinnacle reefs, which can best be explained by Gussow Theory of migration and differential entrapment. Such a reserve concentration or hydrocarbon differentiation has not been observed in the southern trend. A probabilistic model for exploration in a play was found applicable in mature areas of the northern trend and the results were extended to other parts. The results suggest that the effectiveness of exploration, based on seismic surveys, is 8 to 10 times better than random drilling. The reserves of the reef belt are in excess of 7 billion barrels of oil and 15 trillion cubic feet of natural gas in place.

  3. Patagonian Andean evolution from Miocene foreland basin detrital zircon geochronology (Invited)

    NASA Astrophysics Data System (ADS)

    Lo, S.; Fosdick, J. C.

    2009-12-01

    Sedimentary basins record the erosional history of their sediment sources, and in particular, the unroofing evolution of nearby mountain belts. As such, we use the unique U-Pb crystallization age distribution of zircon crystals separated from basin sediments to assess the spatial distribution of mountain belt exhumation. The Magallanes retroarc foreland basin in southernmost Chile and Argentina developed in response to crustal loading of the Patagonian fold-thrust belt during orogenesis. As such, this basin filled with sediment during the active formation of the Patagonian fold-thrust belt. Previous work suggests that the Cretaceous basin fill was derived from the magmatic arc and fold-thrust belt, and that the growth of the thrust belt progressively isolated the basin from detrital input from the magmatic arc. Our project goal is to evaluate the rates and timing of thrust belt growth by comparing the sediment source age and exhumation record in the Paleogene-Neogene basin fill. We separated zircons from paired sandstone and volcanic ash samples collected from the syntectonic Paleogene-Neogene section of the Magallanes Basin in Chile and Argentina, Patagonia (51 30’S). Our analytical strategy involves three steps: 1) refine stratigraphic age of sandstones by U-Pb dating of nearby volcanic ashes, 2) characterize sediment source age by detrital zircon U-Pb dating. These sandstone and ash samples were prepared for zircon U-Pb geochronologic analysis using a variety of mineral separation methods. These included crushing, grinding of bulk samples, Gemini table separation of dense and light grains, and magnetic frantz removal of iron-rich minerals. A heavy liquid, lithium meta-tungstate (LMT) was used to further separate minerals, and finally, samples were handpicked under a binocular microscope. New zircon U-Pb SHRIMP age results from the volcanic ashes indicate the syntectonic sedimentary succession was deposited between ca. 21-18 Ma. These ages refine the existing

  4. 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.

  5. Shoreline position in clastic wedges of marine foreland basins: A modeling study

    SciTech Connect

    Slingerland, R.L.; Furlong, K.P. )

    1990-05-01

    The transgressive-regressive history of an active margin bordering a marine foreland basin is controlled by the relative rates of sediment supply, basin subsidence, and sea level change. The purpose of this research is to better understand the functional relationships among these factors and shoreline position by exploring solutions to a coupled source-basin numerical model. The model consists of a critically tapered, accretionary wedge, and a single-thread river of known discharge and width carrying sediment eroded off the wedge to a basin of specified initial depth, with the elastically deforming lithosphere responding to the tectonic and sedimentary loads. The accretionary wedge, modeled as a steady state critically tapered wedge, provides the initial supracrustal load that creates the basin, the initial slope of the river, and a sediment load the river must carry. The river builds a delta and alluvial plain into a standing body of water of specified surface elevation. The river/transport system is modeled using the equations of unsteady, gradually varied flow, modified Bagnold bed load transport, and conservation of bed material. The lithosphere deforms according to elastic flexure under a distributed supracrustal load. The authors model the evolution of topography and basin bathymetry from initial conditions to steady state when the sediment flux overpassing the foreland basin equals the convergence flux into the wedge at its toe. The results are strongly dependent upon characteristic times for the completing processes. For example, an increase in the convergence rate causes an increase in the height and width of the wedge, increasing both the sediment volume to be carried by the river and magnitude of the load. This load increases basin subsidence, allowing additional accumulation of sediments (and loading) in the basin.

  6. Depositional sequences in a foreland basin (north-western domain of the continental Duero basin, Spain)

    NASA Astrophysics Data System (ADS)

    Herrero, Antonio; Alonso-Gavilán, Gaspar; Colmenero, Juan Ramón

    2010-01-01

    floodplain deposits. The north-western domain of the Duero basin is interpreted to have been formed in response to the tectonic uplifting of the Cantabrian Mountains since Middle-Eocene times. Integration of the data concerning the surface and subsurface geology in this domain reveals that this basin edge behaved as a foreland basin during Cenozoic stages. The foredeep, with a depth of 2800 m, is oriented east-west and has a sediment thickness of up to 3500 m. The forebulge is located in the southwestern zone and represents an area of basement uplifting in which a minimum thickness of materials from the Cenozoic depositional sequences has accumulated.

  7. Latest Miocene to Quaternary deformation in the southern Chaiwopu Basin, northern Chinese Tian Shan foreland

    NASA Astrophysics Data System (ADS)

    Lu, Honghua; Wang, Zhen; Zhang, Tianqi; Zhao, Junxiang; Zheng, Xiangmin; Li, Youli

    2015-12-01

    Basinward propagation of fold and thrust belts is a crucial geological process accommodating Cenozoic crustal shortening within the India-Eurasia collision zone. Anticlinal growth strata in the southern Chaiwopu Basin (a piggyback basin) of the northern Chinese Tian Shan foreland record basinward encroachment of the Tian Shan along the Junggar Frontal Thrust Fault. A new magnetostratigraphic section constrains the onset of syntectonic growth strata at circa 6.4 Ma and suggests synchronous basinward thrusting and propagation of the Tian Shan. The intense alluviation in the southern Chaiwopu Basin ceased at circa 0.55 Ma due to significant anticlinal growth and its resultant river incision. More recent anticlinal growth and deformation during the late Quaternary are revealed by folded river terraces developing across the anticline. The terrace height profile indicates that terrace T1H has been vertically offset about 0.6 m by thrust faulting since its formation at about 7 Ka. The stratigraphic and geomorphic data presented in this work are helpful to understand the initiation of thrust-related folding, as well as aggradation and subsequent incision, in foreland basins of the Tian Shan in relation to the India-Asia collision.

  8. Initiation of the Magallanes foreland basin: Timing of the southernmost Patagonian Andes orogeny revised by detrital zircon provenance analysis

    USGS Publications Warehouse

    Fildani, A.; Cope, T.D.; Graham, S.A.; Wooden, J.L.

    2003-01-01

    New sensitive high-resolution ion microprobe-reverse geometry U-Pb detrital zircon data establish the timing of onset of foreland basin subsidence in the Magallanes basin and the age of the Patagonian Andes in southernmost Chile. Initiation of the Magallanes foreland basin is signaled by the abrupt occurrence of sandstone of the Punta Barrosa Formation, loosely dated as upper Albian-Cenomanian from biofacies assemblages. Detrital zircon analyses demonstrate that the Punta Barrosa Formation is not older than 92 ?? 1 Ma and that the linked Andean belt started forming in the Turonian.

  9. 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.

  10. The sedimentary record of oblique collision, Western Foreland basin of Taiwan

    NASA Astrophysics Data System (ADS)

    Nagel, S.; Castelltort, S.; Lin, A. T.; Mouthereau, F.; Willett, S.; Kaus, B. J.

    2011-12-01

    Taiwan is a young orogen developed due to collision of the Luzon Volcanic Arc (Pacific Sea Plate) with the continental margin of China (Eurasian Plate). The oblique collision is considered to propagate southward as the South China Sea progressively "zippers" shut towards the South. The idea of southward propagation has had important influences on the development of two fundamental concepts of modern earth surface dynamics: steady state orogenic wedges and foreland basin filling-up sequence. However, beyond the initial geometrical models of oblique collision, there are no clear data supporting the southward propagation. One of our main objectives, therefore, is to examine the arc-continent collision in the context of a progressive filling of the foreland basin marked by an early underfilled stage with deep marine facies and ending with a late overfilled stage marked by fluvial sedimentation. We generated a set of paleogeographic maps for the times of 12.5 Ma, 5.5 Ma, 3.0 Ma, 2.0 Ma and 0.50 Ma which allow discussion of the propagation of the collision. These maps document the progressive westward and southward migration of the coastline. We find that the emerged southern tip of the collision has propagated at a rate of 21-57 km/Ma. The relatively slow southward migration with respect to the plate velocity of the Philippine Sea Plate and the substantial along-strike facies variation may reflect a more complex relationship to the initial shape of the (rifted) continental margin than previously envisioned. The results of this study provide important evidence for the space and time evolution of the orogen-related loading of the foreland basin. Project funded by SNF grant #200020-131890

  11. 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.

  12. 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.

  13. Unraveling burial heating and sediment recycling in retroarc foreland basins: Detrital thermochronologic insights from the northern Magallanes Basin, Patagonian Andes

    NASA Astrophysics Data System (ADS)

    Fosdick, J. C.; Grove, M. J.; Graham, S. A.; Hourigan, J. K.; Lovera, O. M.; Romans, B.

    2014-12-01

    Sediment recycling is expected in many tectonic settings, such as foreland basins, where the path followed by grains initially derived from erosion of a basement source region typically involves significant intermediate stages of crustal evolution before the detritus is finally incorporated into tectonically stable basin strata. The shallow-crustal thermal histories experienced by eroded sediment may go undetected by traditional provenance methods but are potentially recoverable by thermochronologic methods. The Patagonian Magallanes retroarc foreland basin affords an excellent case study of sediment burial and recycling within a thrust belt setting. Combined detrital zircon U-Pb geochronology and (U-Th)/He thermochronology data and thermal modeling results confirm delivery of both rapidly cooled, first-cycle volcanogenic sediments from the Patagonian magmatic arc and recycled sediment from deeply buried and exhumed Cretaceous foredeep strata to the Cenozoic Magallanes basin depocenter. Numerical models of temperature-time histories indicate that ca. 54-45 Ma burial of the Maastrichtian Dorotea Formation produced 164-180°C conditions and heating to within the zircon He partial retention zone. Such deep burial is unusual for Andean foreland basins and may have resulted from combined effects of high basal heat flow and high sediment accumulation within a rapidly subsiding foredeep that was floored by basement weakened by previous Late Jurassic rifting. In this interpretation, Cenozoic thrust-related deformation deeply eroded the Dorotea Formation and underlying strata from ~5 km burial depths and may be associated with the development of a regionally extensive Paleogene unconformity. Results from the Cenozoic Río Turbio and Santa Cruz formations confirm that they contain both Cenozoic first-cycle zircon from the Patagonian magmatic arc and highly outgassed recycled zircon. This work suggests that Middle Miocene sediments were most likely derived from recycling of

  14. 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.

  15. Basin center - fractured source rock plays within tectonically segmented foreland (back-arc) basins: Targets for future exploration

    SciTech Connect

    Weimer, R.J.

    1994-09-01

    Production from fractured reservoirs has long been an industry target, but interest in this type play has increased recently because of new concepts and technology, especially horizontal drilling. Early petroleum exploration programs searched for fractured reservoirs from shale, tight sandstones, carbonates, or basement in anticlinal or fault traps, without particular attention to source rocks. Foreland basins are some of the best oil-generating basins in the world because of their rich source rocks. Examples are the Persian Gulf basin, the Alberta basin and Athabasca tar sands, and the eastern Venezuela basin and Orinoco tar sands. Examples of Cretaceous producers are the wrench-faulted La Paz-Mara anticlinal fields, Maracaibo basin, Venezuela; the active Austin Chalk play in an extensional area on the north flank of the Gulf of Mexico continental margin basin; and the Niobrara Chalk and Pierre Shale plays of the central Rocky Mountains, United States. These latter plays are characteristic of a foreland basin fragmented into intermontane basins by the Laramide orogeny. The Florence field, Colorado, discovered in 1862, and the Silo field, Wyoming, discovered in 1980, are used as models for current prospecting and will be described in detail. The technologies applied to fracture-source rock plays are refined surface and subsurface mapping from new log suites, including resistivity mapping; 3D-3C seismic, gravity, and aeromagnetic mapping; borehole path seismic mapping associated with horizontal drilling; fracture mapping with the Formation MicroScanner and other logging tools; measurements while drilling and other drilling and completion techniques; surface geochemistry to locate microseeps; and local and regional lineament discrimination.

  16. Thermicity and fluid flow related to the evolution of the South Pyrenean Foreland Basin (SPFB)

    NASA Astrophysics Data System (ADS)

    Crognier, Nemo; Hoareau, Guilhem; Lacroix, Brice; Aubourg, Charles; Dubois, Michel; Lahfid, Abdeltif; Labaume, Pierre; Suarez-Ruiz, Isabel

    2015-04-01

    The East-West trending South Pyrenean Foreland Basin (SPFB), 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 the western part of the SPFB (Jaca basin, Spain), from the North to the South the basin is subdivided into four parts: the internal Sierras, the turbiditic basin, the molassic basin and the external Sierras. In order to better constrain the fluid flow dynamic and the thermal regime of the basin during its tectonic evolution, we propose to estimate the temperatures and the O and C isotopic signatures of fluids, as well as the maximum temperatures recorded by pre- to syn-tectonic sediments of the Jaca basin. The C and O isotopic composition has been measured on ~100 veins and host sediment samples. The peak temperatures have also been estimated on 80 bulk rocks and calcite/quartz veins using a combination of several techniques, including Raman Spectroscopy of Carbonaceous Material, vitrinite reflectance, fluid inclusion microthermometry and mass-47 clumped isotopes. We show that in most tectonic fractures, primary fluid inclusions are characterized by moderate salinities (~2.5 wt%) compatible with connate or evolved meteoric waters, with increasing meteoric signature in the south of the basin. As suggested by temperature determinations and stable isotopes, involved fluids were generally in thermal and isotopic equilibrium with the host sediments, suggesting a low fluid-rock ratio (i.e., no significant fluid flow). These results support previous speculations of moderate fluid-flow through thrust faults and the hydrological compartmentalization of the Jaca basin during deformation (Lacroix et al., 2014). In addition we demonstrate that measured peak temperatures rapidly decrease southward, from ~240°C±30°C in Cretaceous to Eocene sediments located in the North of the basin close to the axial

  17. 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

  18. Thermochronology of Upper Cretaceous and Paleocene Deposits in the Central Cordilleran Foreland Basin

    NASA Astrophysics Data System (ADS)

    Painter, C. S.; Carrapa, B.; DeCelles, P. G.

    2011-12-01

    Since the mid-1980's the significance of coarse-grained fluvial deposits in distal foreland basins has been hotly debated. In one school of thought such deposits represent the stratigraphic signature of tectogenic topographic rejuvenation in the thrust belt during episodes of thrust propagation. More recently such deposits have been interpreted to indicate thrust belt tectonic quiescence and erosionally driven isostatic rebound. One way to address this issue is to investigate the time span between source exhumation and sedimentation (i.e. lag time); coarse sediment produced and deposited during a period of rapid thrust propagation should exhibit short lag times, whereas coarse sediment produced by post-tectonic isostatic rebound should have longer lag times. We sampled coarse-grained proximal units in the Sevier thrust belt in Utah and their distal equivalents up to 300 km east of the thrust front, and generated detrital apatite fission track (AFT) and zircon (U-Th)/He (ZHe) ages. In the proximal foreland, the Campanian Price River Formation and the Maastrichtian to Paleocene North Horn Formation in the Charleston-Nebo salient of north-central Utah were sampled in order to, (1) identify the thermochronometer that most effectively records the source exhumation and, (2) measure lag times in foreland basin units of the proximal part of the foreland basin. ZHe ages from the Price River and North Horn Formations, as well as their distal equivalents, are discordant, indicating that the system was not fully reset. This suggests that these strata never experienced T> ~180 °C; or, it could be that α-damage has contributed to He retention. AFT ages from these samples appear to be fully reset and show a consistent younging up-section. AFT cooling ages for the upper Campanian Price River Formation are 79.8 ± 6.3 Ma in the lower part of the formation and 74.5 ± 6.4 Ma higher up in the section. The Maastrichtian to Paleocene North Horn Formation, which is separated from the

  19. Tectono-stratigraphic evolution of the Eastern Maturin Foreland basin (Eastern Venezuela)

    SciTech Connect

    Azavache, A.; Flinch, J.; Giffuni, G.; Martinez, R.

    1996-08-01

    The Eastern Venezuelan Basin is a classical foreland basin related to the loading of the Serrania del Interior thrust-sheets. The flexure of the basin started during Upper Oligocene-Lower Miocene time and is evidenced by a major unconformity between the Cretaceous and the Lower Miocene Oficina Formation (Basal Foredeep Unconformity). The sedimentary-filling of the Basin commences with coastal transgressive sandstones of the Oficina Formation (Lower Miocene) that constitute the main reservoir of this petroleum province. The overlying deposits of the basin can be subdivided into: (1) Deep-water stage represented by the upper Oficina shales and the Freites Formation in the south and the Carapita Formation in the north (Middle Miocene). This shale interval constitutes the main seal of the region. This stage is characterized by major onlap and a major flooding surface. (2) Progradational stage characterized by shelf-slope deposits of the Lower-Middle La Pica Formation (Upper Miocene). Siliciclastic shelf wedges consisting of deltaic facies. (3) Aggradational stage fluvial-alluvial delta plain deposits represented by the Upper La Pica, Mesa and Las Piedras Formations (Pliocene-Pleistocene). In the northern part of the basin, southward-vergent thrusting deformed the basement and its thin Cretaceous-Lower Miocene cover. South of the Rio Tigre area compressional structures are combined with normal faults related to flexural extension. The boundary between basement-involved thrusting and flexural extension controls the type of structural traps within the basin.

  20. 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.

  1. 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.

  2. Biochronological continuity of the Paleogene sediments of the Himalayan Foreland Basin: paleontological and other evidences

    NASA Astrophysics Data System (ADS)

    Bhatia, S. B.; Bhargava, O. N.

    2006-04-01

    The paleontological and field evidences presented in the paper demonstrate a biochronological continuity from the marine Subathu (Late Thanetian to Middle Lutetian) through the Passage Beds (Late Lutetian to Middle Bartonian) to the Dagshai and equivalent formations (Late Bartonian to Rupelian) of the Himalayan Foreland Basin, east of Hazara-Kashmir syntaxis. A similar continuity has also been demonstrated in the Sulaiman Range based on an assignment of Oligocene age to the Bugti vertebrate fauna, hitherto considered to be of Early Miocene age. Thus, the concept of a >10 Ma hiatus in the foreland basin based on 40Ar/ 39Ar dates of single detrital muscovite grains from the supposed basal Dagshai arenite is no longer tenable. While the occurrence of Cr-spinel and K-T boundary nannoplanktons in the Subathu Formation and Passage Beds indicate a westerly-northwesterly provenance, that of the radiolarian chert in the Dagshai and coeval formations indicates a northerly provenance from the Indus Suture Zone, coinciding with the first influx of the Himalayan detritus around 40 Ma.

  3. Strong Coupled and Segmented Nature of the Himalaya and the Adjoining Gangetic Foreland Basin

    NASA Astrophysics Data System (ADS)

    Parkash, B.; Rathor, S.; Pati, P.

    2012-04-01

    Our studies in the Gangetic plains and review of the work on the Himalaya suggest that both theses features are marked by abrupt changes across the Rapti River, flowing N-S in the plains and region N to it, instead of a gradual change from E to W as postulated earlier. The Eastern Nepal Himalaya N to the Middle Gangetic Plains (east of the Rapti River) is characterized by a high rate of convergence, which sustains the highest peaks in the world, including the Mount Everest. These lofty peaks cause significant crustal loading leading to high rate of subsidence in the foreland basin and also shed large sediment load, carried by the rivers to the plains to form megafans (e.g. Kosi and Gandak megafans). In the NW and the W Nepal Himalaya, rates of crustal shortening due to movements along the Himalayan Frontal Trust (HFT) are low, which are able to support lower heights of the Himalayan ranges (< 7000 m). These ranges shed small amounts of sediments, which are carried by streams to the plains. The adjoining foreland basin, the Upper Gangetic plain lying W to the Rapti River, is subsiding at a low rate, all major rivers are incised, and form large uplands. Moderately to strongly developed soils occur on the upland plains. These situations indicate the prevalence of separate steady states between the Upper- and Middle Gangetic plains and adjoining Himalaya.

  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. Minibasins and salt canopy in foreland fold-and-thrust belts: The central Sivas Basin, Turkey

    NASA Astrophysics Data System (ADS)

    Kergaravat, Charlie; Ribes, Charlotte; Legeay, Etienne; Callot, Jean-Paul; Kavak, Kaan Sevki; Ringenbach, Jean-Claude

    2016-06-01

    The Sivas Basin in the Central Anatolian Plateau (Turkey), which formed in the context of a foreland fold-and-thrust belt (FTB), exhibits a typical wall and basin (WAB) province characterized by symmetric minibasins separated by continuous steep-flanked walls and diapirs. Extensive fieldwork including regional and detailed local mapping of the contacts and margins of minibasins, and interpretation of a set of 2-D regional seismic lines, provide evidence for the development of a shallow evaporite level separating two generations of minibasins within the WAB province. Here beds of symmetric exposed minibasins along diapir flank are younger than minibasins observed over autochthonous evaporites. Laterally away from the WAB province, increase in wavelength of the tectonic structures suggests a deepening of the decollement level. We interpret that a shallower evaporite level developed in the form of an evaporite canopy, triggered by significant lateral shortening. The Upper Eocene-Lower Oligocene autochthonous Tuzhisar evaporite level was remobilized by the northward migrating sedimentary load and the tilting of the southern basin margin during propagation of the foreland fold-and-thrust belt. Asymmetric and symmetric primary minibasins were overrun by an allochthonous sheet forming a canopy. A second generation of salt withdrawal minibasins subsided into the allochthonous salt sheet. The polygonal pattern of the WAB province influences the growing fold-and-thrust belt system during the late stage of the secondary minibasins development. The Sivas FTB basin is the result of the interaction between fold-and-thrust belt propagation, evaporite remobilization, and interaction between evaporite flow and sedimentation in the minibasins.

  6. Structure and tectonic history of the foreland basins of southernmost South America

    NASA Astrophysics Data System (ADS)

    Ghiglione, Matías C.; Quinteros, Javier; Yagupsky, Daniel; Bonillo-Martínez, Pedro; Hlebszevtich, Julio; Ramos, Victor A.; Vergani, Gustavo; Figueroa, Daniel; Quesada, Santiago; Zapata, y. Tomás

    2010-03-01

    The common elements and differences of the neighboring Austral (Magallanes), Malvinas and South Malvinas (South Falkland) sedimentary basins are described and analyzed. The tectonic history of these basins involves Triassic to Jurassic crustal stretching, an ensuing Early Cretaceous thermal subsidence in the retroarc, followed by a Late Cretaceous-Paleogene compressional phase, and a Neogene to present-day deactivation of the fold-thrust belt dominated by wrench deformation. A concomitant Late Cretaceous onset of the foreland phase in the three basins and an integrated history during the Late Cretaceous-Cenozoic are proposed. The main lower Paleocene-lower Eocene initial foredeep depocenters were bounding the basement domain and are now deformed into the thin-skinned fold-thrust belts. A few extensional depocenters developed in the Austral and Malvinas basins during late Paleocene-early Eocene times due to a temporary extensional regime resulting from an acceleration in the separation rate between South America and Antarctica preceding the initial opening of the Drake Passage. These extensional depocenters were superimposed to the previous distal foredeep depocenter, postdating the initiation of the foredeep phase and the onset of compressional deformation. Another pervasive set of normal faults of Paleocene to Recent age that can be recognized throughout the basins are interpreted to be a consequence of flexural bending of the lithosphere, in agreement with a previous study from South Malvinas basin. Contractional deformation was replaced by transpressive kinematics during the Oligocene due to a major tectonic plate reorganization. Presently, while the South Malvinas basin is dominated by the transpressive uplift of its active margin with minor sediment supply, the westward basins undergo localized development of pull-apart depocenters and transpressional uplift of previous structures. The effective elastic thickness of the lithosphere for different sections of

  7. 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.

  8. Latest Cretaceous-Paleogene basin development and resultant sedimentation patterns in the thrust belt and broken foreland of central Utah

    SciTech Connect

    Lawton, T.F. ); Franczyk, K.J.; Pitman, J.K. )

    1990-05-01

    Latest Cretaceous tectonism in central and east-central Utah formed several intermontane basins both atop thrust sheets and between the thrust front and basement-involved uplifts in the former foreland basin. The upper Campanian Castlegate Sandstone and its inferred western equivalents were the last strata deposited prior to segmentation of the foreland basin. Thereafter, eastward transport of the thrust allochthon uplifted the most proximal part of the Castlegate depositional wedge. West of the thrust front, small intermontane basins formed on the allochthon. Sediment was transported into these basins from both eastern and western sources. In each basin, facies grade from basin-margin conglomeratic alluvial fan deposits to basin-interior flood-plain and lacustrine deposits within a few kilometers. These intermontane basins existed from latest Campanian through the late Paleocene, and may have been transported a short distance eastward as they formed. East of the thrust front in the latest Campanian and contemporaneous with basin formation on the allochthon, a northward-northeastward-flowing big river system transported sediment into the foreland basin from feldspar-rich source areas southwest of the study area. Subsequently, major movement of the San Rafael uplift in the very late Campanian or early Maastrichtian gave rise to an intermontane basin between the thrust front and the San Rafael uplift. Northwestward-flowing, pebble-bearing braided rivers deposited the oldest sediments in this basin prior to an influx from the south and southwest of sediment that formed a thick Maastrichtian clastic sequence. In contrast to deposition in basins on the allochthon, deposition east of the thrust front in the Paleocene was intermittent and restricted to rapidly shifting centers of basin subsidence.

  9. 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.

  10. Geometry and kinematics of extensional structures in the alpine foreland basin of southeastern France

    NASA Astrophysics Data System (ADS)

    Roure, F.; Brun, J.-P.; Colletta, B.; Van Den Driessche, J.

    1992-05-01

    The basin of southeastern France is developed between the Bresse Graben and the Mediterranean Sea. In this area, the Western European Oligocene rift system is locally superimposed on early Jurassic (Liassic) extensional structures of the Tethyan palaeomargin, and was later involved in Neogene compressive deformation of the Alpine foreland. The aim of this paper is to reconstruct the initial configuration of both thin-skinned and deep-seated Oligocene structures that are now locally inverted, and to separate the effects of Oligocene extension from Liassic extension. Cross-section balancing techniques have been applied to complex multiphase structures whose present geometries are clearly controlled by surface and subsurface geology. The resulting Oligocene configurations are compared with laboratory models and are discussed in terms of the regional extensional history.

  11. 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.

  12. 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.

  13. Oil fields and new plays in the Rioni foreland basin, Republic of Georgia

    SciTech Connect

    Robinson, A.G.; Griffith, E.T. ); Sargeant, J. )

    1996-01-01

    The Rioni Basin in West Georgia is an Oligocene foredeep that evolved into a Miocene to Pliocene foreland basin, north of the Achara-Trialeti thrust belt and south of the Greater Caucasus. It extends to the west into the Black Sea. A large number of exploration wildcats have been drilled onshore since the nineteenth century and have led to the discovery of three fields. Exploration was prompted by seeps and restricted to frontal ramp anticlines mapped at surface. No wells have been drilled offshore. Supsa (discovered 1889) contains 29 MMbbl oil in clastic Sarmatian reservoirs. The field has around 50 wells but less than 0.5 MMbbl have been produced. Shromisubani (discovered 1973) contains oil within Maeotian and Pontian clastic reservoirs, Chaladidi oil within Upper Cretaceous chalk. Despite this long and apparently intensive exploration effort, several factors make the basin an exciting target for field redevelopment and further exploration. The quality of existing seismic is very poor both on-and offshore. Reinterpretation of the structure of the fold and thrust belt has suggested the presence of new targets and plays which may be imaged by modern seismic methods. In addition, due to problems associated with central planning, discovered fields have not been optimally developed or even fully appraised. The application of new technology, geological interpretation and investment promises to delineate substantial remaining reserves even after more than one hundred years of exploration.

  14. Oil fields and new plays in the Rioni foreland basin, Republic of Georgia

    SciTech Connect

    Robinson, A.G.; Griffith, E.T.; Sargeant, J.

    1996-12-31

    The Rioni Basin in West Georgia is an Oligocene foredeep that evolved into a Miocene to Pliocene foreland basin, north of the Achara-Trialeti thrust belt and south of the Greater Caucasus. It extends to the west into the Black Sea. A large number of exploration wildcats have been drilled onshore since the nineteenth century and have led to the discovery of three fields. Exploration was prompted by seeps and restricted to frontal ramp anticlines mapped at surface. No wells have been drilled offshore. Supsa (discovered 1889) contains 29 MMbbl oil in clastic Sarmatian reservoirs. The field has around 50 wells but less than 0.5 MMbbl have been produced. Shromisubani (discovered 1973) contains oil within Maeotian and Pontian clastic reservoirs, Chaladidi oil within Upper Cretaceous chalk. Despite this long and apparently intensive exploration effort, several factors make the basin an exciting target for field redevelopment and further exploration. The quality of existing seismic is very poor both on-and offshore. Reinterpretation of the structure of the fold and thrust belt has suggested the presence of new targets and plays which may be imaged by modern seismic methods. In addition, due to problems associated with central planning, discovered fields have not been optimally developed or even fully appraised. The application of new technology, geological interpretation and investment promises to delineate substantial remaining reserves even after more than one hundred years of exploration.

  15. Link between Neogene and modern sedimentary environments in the Zagros foreland basin

    NASA Astrophysics Data System (ADS)

    Pirouz, Mortaza; Simpson, Guy; Bahroudi, Abbas

    2010-05-01

    The Zagros mountain belt, with a length of 1800 km, is located in the south of Iran and was produced by collision between the Arabian plate and the Iran micro plate some time in the early Tertiary. After collision, the Zagros carbonate-dominated sedimentary basin has been replaced by a largely clastic system. The Neogene Zagros foreland basin comprises four main depositional environments which reflect the progressive southward migration of the deformation front with time. The oldest unit - the Gachsaran formation - is clastic in the northern part of the basin, but is dominated by evaporates in southern part, being deposited in a supratidal Sabkha-type environment. Overlying the Gachsaran is the Mishan formation, which is characterized by the Guri limestone member at the base, overlain by marine green marls. The thickness of the Guri member increases dramatically towards the southeast. The next youngest unit is the Aghajari Formation which consists of well sorted lenticular sandstone bodies in a red silty-mudstone. This formation is interpreted as representing the floodplain of dominantly meandering rivers. Finally, the Bakhtiari formation consists of mainly coarse-grained gravel sheets which are interpreted to represent braided river deposits. Each of these Neogene depositional environments has a modern day equivalent. For example, the braided rivers presently active in the Zagros mountains are modern analogues of the Bakhtiari. In the downstream direction, these braided rivers become meandering systems, which are equivalents of the Aghajari. Eventually, the meandering rivers meet the Persian gulf which is the site of the ‘modern day' Mishan shallow marine marls. Finally, the modern carbonate system on the southern margin of Persian Gulf represents the Guri member paleo-environment, behind which Sabkha-type deposits similar to the Gachsaran are presently being deposited. One important implication of this link between the Neogene foreland basin deposits and the

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. Complex tectonic and tectonostratigraphic evolution of an Alpine foreland basin: The western Duero Basin and the related Tertiary depressions of the NW Iberian Peninsula

    NASA Astrophysics Data System (ADS)

    Martín-González, F.; Heredia, N.

    2011-04-01

    The tectonic and tectonostratigaphic evolution of foreland basins and related Tertiary depressions are the key to investigate deformation history and the uplifting of the continental lithosphere of the Alpine-Pyrenean Orogeny. The northern part of the Duero basin is the foreland basin of the Cantabrian Mountains, which are, in turn, the western part of the Pyrenean Orogen. We have studied the western sharp end of the Duero foreland basin, and its relation to the Tertiary deposits of the NW Iberian Peninsula and the topography evolution. In order to propose a coherent tectonic and tectonosedimentary model that could explain all Tertiary deposits, we have analysed the depositional environment, stratigraphic sequences, paleocurrents and established a correlation of the main outcrops. Besides, a detailed structural mapping of the Alpine structures that limit and affect the main Tertiary outcrops has been carried out. The Tertiary deposits of the NW Iberian Peninsula depressions are affected and fragmented by Alpine structures that limit their extensions and locations. The stratigraphic succession is similar in the NW Tertiary outcrops; they are mainly terrigenous and carbonated continental deposits formed by assemblage of alluvial fans developed at the mountains front, in arid or semiarid conditions. Three formations can be identified in the main depressions: Toral Fm, Santalla Fm and Médulas Fm. The NW Tertiary outcrops were the western deposits of the Duero foreland basin that surrounded the lateral termination of the Pyrenean Orogen. These deposits were fragmented and eroded by the subsequent uplift of the Galaico-Leoneses Mountains and the NE-SW strike-slip faults activity (broken foreland basin). Only the latest stages of some of these outcrops can be considered as intramontane basins as traditionally have been interpreted. The sedimentation started in the northeast (Oviedo-Infiesto) during the Eocene and migrated to the west (As Pontes) during the Late Oligocene

  1. The South Westland Basin: seismic stratigraphy, basin geometry and evolution of a foreland basin within the Southern Alps collision zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Sircombe, Keith N.; Kamp, Peter J. J.

    1998-12-01

    This paper develops further the case for a foreland basin origin of South Westland Basin, located adjacent to the Southern Alps mountain belt. Geohistory analyses show Middle Miocene initiation of subsidence in the basin, with marked increases at 5-6 Ma. Five seismic reflection horizons, including basement, Middle Miocene (top Awarua Limestone), top Miocene, mid-Pliocene (PPB) and mid-Pleistocene (PPA) have been mapped through the grid of seismic data. A series of five back-stripped structure contour maps taken together with five isopach maps show that prior to the Middle Miocene, subsidence and sedimentation occurred mainly along the rifted continental margin of the Challenger Plateau facing the Tasman Sea; subsequently it shifted to a foredeep trending parallel to the Southern Alps and located northwest of them. Through the Late Miocene-Recent this depocentre has progressively widened, and the loci of thickest sediment accumulation have moved northwestward, most prominently during the Late Pliocene and Pleistocene with the progradation of a shelf-slope complex. At the northern end of the basin the shelf-slope break is currently located over the forebulge, which appears not to have migrated significantly, probably because the mountain belt is not advancing significantly northwestwards. Modelling of the lithospheric flexure of the basement surface normal to the trend of the basin establishes values of 3.1 to 9.8×10 20 N m for the flexural rigidity of the Australia Plate. This is at the very low end of rigidities for plates, and 1-2 orders of magnitude less than for the Australia Plate beneath the Taranaki Basin. Maps of tectonic subsidence where the influence of sediment loading is removed also clearly identify the source of the loading as lying within or beneath the mountain belt. The basin fill shows a stratigraphic architecture typical of underfilled ancient peripheral foreland basins. This comprises transgressive (basal unconformity, thin limestone, slope

  2. Implications of Paleogene Foreland Basin Evolution in NW Argentina for Timing of Andean Orogenesis

    NASA Astrophysics Data System (ADS)

    Decelles, P. G.; Carrapa, B.; Horton, B. K.; Starck, D.; Gehrels, G. E.

    2004-12-01

    The timing and paleogeography of early Andean mountain building are topics of ongoing debate. We track development of the early central Andes in Bolivia and NW Argentina by studying widespread Tertiary deposits in the Altiplano-Puna and Eastern Cordillera. These deposits accumulated on top of Late Cretaceous post-rift marginal marine facies and Precambrian-Paleozoic basement. Over a north-south distance of 1000 km, the Paleocene-Oligocene succession consists of three stratigraphic assemblages: (1) Paleocene-Eocene fluvial- lacustrine siltstone and marl, up to ~200 m thick; (2) a 10-100 m thick zone of stacked Eocene paleosols, including stage III-IV Calcisols, Vertisols, and strongly reduced Gleysols; and (3) an upward coarsening, several km-thick sequence of fluvial to alluvial fan deposits. Locally, upper Eocene-Miocene rocks consist of thick (>2 km), proximal alluvial fan deposits containing growth structures. Modal petrographic data indicate derivation from metasedimentary and plutonic source terranes, and paleocurrent data show eastward sediment transport. Detrital zircon U-Pb ages indicate derivation from Paleozoic low-grade metasedimentary and igneous source rocks. Eocene detrital AFT ages from apatite grains that yield early Paleozoic U-Pb crystallization ages require rapid exhumation (0.4 mm/yr to >1mm/yr) of western source areas in neighboring regions such as the Eastern Cordillera and indicate a constructional orogen. Combined with previous structural studies, our data are consistent with a Late Cretaceous-Eocene thrust belt in the Cordillera de Domeyko in northern Chile, flanked to the east by a several hundred km wide foreland basin system. Flexural subsidence dominated the proximal region, and back-bulge and post-rift thermal subsidence may have operated in the distal eastern part of the basin. Approximately 500 km of eastward migration of the foreland basin system produced the vertical succession preserved in the Paleogene of the Puna and Eastern

  3. Implications of Paleogene Foreland Basin Evolution in NW Argentina for Timing of Andean Orogenesis

    NASA Astrophysics Data System (ADS)

    Decelles, P. G.; Carrapa, B.; Horton, B. K.; Starck, D.; Gehrels, G. E.

    2007-12-01

    The timing and paleogeography of early Andean mountain building are topics of ongoing debate. We track development of the early central Andes in Bolivia and NW Argentina by studying widespread Tertiary deposits in the Altiplano-Puna and Eastern Cordillera. These deposits accumulated on top of Late Cretaceous post-rift marginal marine facies and Precambrian-Paleozoic basement. Over a north-south distance of 1000 km, the Paleocene-Oligocene succession consists of three stratigraphic assemblages: (1) Paleocene-Eocene fluvial- lacustrine siltstone and marl, up to ~200 m thick; (2) a 10-100 m thick zone of stacked Eocene paleosols, including stage III-IV Calcisols, Vertisols, and strongly reduced Gleysols; and (3) an upward coarsening, several km-thick sequence of fluvial to alluvial fan deposits. Locally, upper Eocene-Miocene rocks consist of thick (>2 km), proximal alluvial fan deposits containing growth structures. Modal petrographic data indicate derivation from metasedimentary and plutonic source terranes, and paleocurrent data show eastward sediment transport. Detrital zircon U-Pb ages indicate derivation from Paleozoic low-grade metasedimentary and igneous source rocks. Eocene detrital AFT ages from apatite grains that yield early Paleozoic U-Pb crystallization ages require rapid exhumation (0.4 mm/yr to >1mm/yr) of western source areas in neighboring regions such as the Eastern Cordillera and indicate a constructional orogen. Combined with previous structural studies, our data are consistent with a Late Cretaceous-Eocene thrust belt in the Cordillera de Domeyko in northern Chile, flanked to the east by a several hundred km wide foreland basin system. Flexural subsidence dominated the proximal region, and back-bulge and post-rift thermal subsidence may have operated in the distal eastern part of the basin. Approximately 500 km of eastward migration of the foreland basin system produced the vertical succession preserved in the Paleogene of the Puna and Eastern

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. 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

  9. 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.

  10. Subduction, platform subsidence, and foreland thrust loading: The late Tertiary development of Taranaki Basin, New Zealand

    NASA Astrophysics Data System (ADS)

    Holt, W. E.; Stern, T. A.

    1994-10-01

    Borehole, seismic, and gravity data are used to investigate deformation of continental lithosphere at a Miocene collisional zone. Deformation is manifested in the three following principal forms: a long wavelength (>500 km) platform subsidence ascribed to mantle convection; flexural deformation on a scale of 100-200 km due to crustal thrusting at the eastern boundary of the Taranaki Basin; and a ductile thickening, evident on the deep seismic section of Taranaki Basin, that occurs on a scale of ˜10 km. Evidence for flexural deformation principally comes from the deep seismic section that shows a 150-km wavelength bending of the Moho down toward the major zone of thrusting within the Taranaki Fault Zone. Paleowater depths, however, provide evidence for an initial early Miocene regional subsidence that is too long in wavelength to be explained by flexure induced from thrust sheet loading. Instead, we propose that this broad "platform subsidence" was driven by loading from a deep source, probably subduction-induced flow in the mantle. By ˜22-19 Ma, 1-2 km of water existed over most of the area now occupied by South Taranaki Basin. By ˜19-17 Ma the water depth in the zone east of the Taranaki Basin, the Taranaki Fault Zone, had been replaced by rock due to submarine thrusting and crustal thickening. This build up of submarine topography in the Taranaki Fault Zone constitutes part of the load (25±8 MPa) that created and maintains South Taranaki Basin. Gravity data place further constraints on loading at the thrust front and point to an additional intracrustal loading, equivalent to 15±7 MPa over a 50-km-wide zone. This intracrustal load is explained as being due to thick-skinned thrusting bringing denser, lower-crustal rocks nearer to the surface in the thrust zone. The complete load on the Taranaki foreland is therefore in three parts; the submarine-topographic load, the intracrustal load, and the loading of infilling sediments.

  11. Structural development and petroleum potential of the Dagestan foreland thrust belt, Terek-Caspian Basin, Russia

    SciTech Connect

    Sobornov, K. )

    1994-07-01

    The Dagestan foreland thrust belt represents a transition zone between the Terek-Caspian basin and Caucasus. Boreholes and seismic data obtained during the last decade in the course of petroleum exploration reveal considerable differences between the surface and subsurface structures of the area. The new data suggest that the allochthonous assemblage of the belt is formed mainly by stacked north-verging thrust sheets made up mostly of Mesozoic carbonates and sandstones bounded at the top and bottom by conjugate detachment surfaces. The thrust sheets are interpreted to be inserted into the clastic section of the Terek-Caspian foredeep along the base of Oligocene-early Miocene mudstones. The interpreted geometry of the thrust-belt front implies a shortening of about 20-50 km. The blind subsurface thrusts have been active since late Miocene and Holocene. The interpreted structural relationships between Mesozoic-Cenozoic stratigraphic units imply that principal thrusts were formed due to reactivation and inversion of low-angle normal faults, which were active in the Jurassic - early Miocene. Mechanical weakness and low density of the overpressured Oligocene - lower Miocene Maykop Formation aided subsurface thrusting. The new interpretation of the regional structure offers a petroleum exploration play consisting of structural traps within the buried antiformal stacks. Oil- and gas-bearing Upper Cretaceous and Upper Jurassic carbonate rocks involved in thrust sheets are considered primary prospecting targets.

  12. 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. PMID:26365327

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. Cenozoic sedimentary dynamics of the Ouarzazate foreland basin (Central High Atlas Mountains, Morocco)

    NASA Astrophysics Data System (ADS)

    El Harfi, A.; Lang, J.; Salomon, J.; Chellai, E. H.

    2001-06-01

    Cenozoic continental sedimentary deposits of the Southern Atlas named "Imerhane Group" crop out (a) in the Ouarzazate foreland basin between the Precambrian basement of the Anti Atlas and the uplifted limestone dominated High Atlas, and (b) in the Aït Kandoula and Aït Seddrat nappes where Jurassic strata detached from the basement have been thrust southwards over the Ouarzazate Basin. New biostratigraphic and geochronological data constraining the final Eocene marine regression, the characterization of the new "Aït Ouglif Detrital Formation" presumed to be of Oligocene age, and the new stratigraphic division proposed for the Continental Imerhane Group clarify the major tectonogenetic alpidic movements of the Central High Atlas Range. Four continental formations are identified at regional scale. Their emplacement was governed principally by tectonic but also by eustatic controls. The Hadida and Aït Arbi formations (Upper Eocene) record the major Paleogene regression. They are composed of margino-littoral facies (coastal sabkhas and fluviatile systems) and reflect incipient erosion of the underlying strata and renewed fluvial drainage. The Aït Ouglif Formation (presumed Oligocene) had not been characterized before. It frequently overlies all earlier formations with an angular unconformity. It includes siliciclastic alluvial deposits and is composed predominantly of numerous thin fining-upward cycles. The Aït Kandoula Formation (Miocene-Pliocene) is discordant, extensive, and represents a thick coarsening-upward megasequence. It is composed of palustro-lacustrine deposits in a context of alluvial plain with localized sabkhas, giving way to alluvial fans and fluviatile environments. The Upper Conglomeratic Formation (Quaternary) is the trace of a vast conglomeratic pediment, forming an alluvial plain and terraces. The second and third formations correspond to two megasequences engendered by the uplift of the Central High Atlas in two major compressive phases

  20. Reconstruction of Tertiary palaeovalleys in the South Alpine Foreland Basin of France (Eocene-Oligocene of the Castellane arc)

    NASA Astrophysics Data System (ADS)

    Grosjean, Anne-Sabine; Pittet, Bernard; Ferry, Serge; Mahéo, Gweltaz; Gardien, Véronique

    2012-11-01

    The dynamics of depositional environments and the spatial deformation of drainage networks in foreland basins reflect the tectonic and erosional dynamics associated with the development of mountain belts. The spatial and temporal organization of the Eocene-Oligocene (40-25 Ma) sedimentation in the external part of the South Alpine Foreland Basin of France was reconstructed using an integrated cartographic, sedimentological and petrographic analysis of the Tertiary sedimentary successions. The depositional geometries and variations in facies and thickness of the Palaeogene Nummulitic succession, as well as the observed flow directions in various continental and marine sediments, suggest that the Barrême, Blieux and Taulanne synclines were present as palaeovalleys since the Eocene. The sedimentological analysis of the Nummulitic succession allows the identification of three depositional sequences separated by transgressive surfaces that are recognized in the Barrême, Blieux and Taulanne synclines. Correlation of these sequences between the three synclines suggests that these palaeovalleys were connected by a local valley network that recorded the same sea-level fluctuations during the marine Nummulitic sedimentation. The palaeovalley network was structurally controlled by the east-west axes of the Blieux and Taulanne synclines and the north-south axis of the Barrême syncline formed during the "Pyrenean-Provençal" (Late Cretaceous-Middle Eocene) shortening and the first stage of the Alpine history (Middle Eocene) respectively. Later on, the westward "Alpine" compression (since the Early Oligocene) induced local depocenter migration and reversal in flow direction. However, compared to the modern river pattern, the palaeovalley orientation highlights a geometrical stability since their formation (about 40 Ma), suggesting a long-term stability of the early structures in the foreland basin. This constancy can be explained by the location of the study area in a piggy

  1. Modeling of thermo-rheological structure of lithosphere under the foreland basin and mountain belt of Taiwan

    NASA Astrophysics Data System (ADS)

    Zhou, Di; Yu, Ho-Shing; Xu, He-Hua; Shi, Xiao-Bin; Chou, Ying-Wei

    2003-10-01

    The system of Taiwan mountain belt and the West Taiwan foreland basin is a manifestation of the collision between eastern Asian continental margin and the Philippine volcanic arc. It provides an ideal place for the study of the flexure behavior of lithosphere under the mountain-basin system. The paper presents results of thermal and rheological modeling of the system along Profile B, which extends 200 km in a NW-SE direction from the Taiwan Strait across the foreland basin and mountain range to the Longitudinal Valley. Along the profile, the crustal structure is constrained by wide-angle seismic and gravity data as well as P-wave tomography, while the structure of the foreland basin is constrained by multichannel seismic and drilling. Assuming that a steady-state deformation has proceeded in Taiwan since the collision of the Luzon Arc with the SE Eurasian margin at 6.5 Ma, the present-day thermal and rheological structures of the lithosphere are modeled by finite element analysis. The base of lithosphere is assumed to be isothermal, with a temperature of 1300 °C. The interior heat source consists of radiogenic heating, frictional heating on thrust faults and basal decollement, and body heating by internal friction within thrust sheets. In addition to conduction, the heat convection is carried out by the subduction of the Eurasian margin, the exhumation and erosion in the mountain range, and the sedimentation in the foreland basin. Thermal parameters are carefully selected and updated based on available data on surface heat flow, downhole thermal gradient, and thermal conductivity from Taiwan and nearby regions. The mechanical parameters are determined based on regional geology. The resulting thermal model predicts well the elevated surface heat flow in the mountain range and the depressed surface heat flow in the thrust front. A high-temperature core of >500 °C appears in the bottom of thrust sheets and the uppermost upper crust. Sensitivity analysis indicates

  2. 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.

  3. 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.

  4. 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

  5. Initiation and development of normal faults within the German alpine foreland basin: The inconspicuous role of basement structures

    NASA Astrophysics Data System (ADS)

    Hartmann, Hartwig; Tanner, David C.; Schumacher, Sandra

    2016-06-01

    In a large seismic cube within the German Alpine Molasse Basin, we recognize large normal faults with lateral alternating dips that displace the Molasse sediments. They are disconnected but strike parallel to fault lineaments of the underlying carbonate platform. This raises the question how such faults could independently develop. Structural analysis suggests that the faults grew both upward and downward from the middle of the Molasse package, i.e., they newly initiated within the Molasse sediments and were not caused by reactivation of the faults in the carbonate platform and/or crystalline basement. Numerical modeling of the basin proves that temporarily and spatially confined extensional stresses existed within the Molasse sediments but not in the carbonate platform and basement during lithospheric bending. The workflow shown here gives a new and as yet undocumented insight in the tectonic and structural processes within a foreland basin that was affected by buckling and bending in front of the orogen.

  6. 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

  7. 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., Jr.; Ryder, Robert T.; Milici, Robert C.; Brown, Stephen

    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.

  8. 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.

  9. 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

  10. Investigating the kinematics of mountain building in Taiwan from the spatiotemporal evolution of the foreland basin and western foothills

    NASA Astrophysics Data System (ADS)

    Simoes, Martine; Avouac, Jean Philippe

    2006-10-01

    The Taiwanese range has resulted from the collision between the Luzon volcanic arc and the Chinese continental margin, which started about 6.5 Myr ago in the north, and has since propagated southward. The building of the range has been recorded in the spatiotemporal evolution of the foreland basin. We analyze this sedimentary record to place some constraints on the kinematics of crustal deformation. The flexure of the foreland under the load of the growing wedge started with a 1.5 Myr long phase of rapid subsidence and sedimentation, which has migrated southward over the last 3.5 Myr at a rate of 31 +10/-5 mm/yr, reflecting the structural evolution of the range and the growth of the topography during the oblique collision. Isopachs from the Toukoshan (˜0 to 1.1 Ma) and Cholan (˜1.1 to 3.3 Ma) formations, as well as the sedimentation rates retrieved from a well on the Pakuashan anticline, indicate that the foreland basement has been moving toward the center of mass of the orogen by ˜45-50 mm/yr during the development of the basin. From there, we estimate the long-term shortening rate across the range to 39.5-44.5 mm/yr. By considering available data on the thrust faults of the foothills of central Taiwan, we show that most (if not all) the shortening across the range is accommodated by the most frontal structures, with little if any internal shortening within the wedge. The range growth appears therefore to have been essentially sustained by underplating rather than by frontal accretion. In addition, only the upper ˜7 to 9 km of the underthrusted crust participates to the growth of the orogen. This requires that a significant amount of the Chinese passive margin crust is subducted beneath the Philippine Sea plate.

  11. 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

  12. Early-Middle Miocene subtle compressional deformation in the Ebro foreland basin (northern Spain); insights from magnetic fabrics

    NASA Astrophysics Data System (ADS)

    Soto, Ruth; Larrasoaña, Juan C.; Beamud, Elisabet; Garcés, Miguel

    2016-03-01

    The results of anisotropy of magnetic susceptibility analyses of 19 sites carried out on magnetostrigraphically-dated, Lower to Middle Miocene (20.4 to 13.7 Ma) "non-deformed" mudstones from the central part of the Ebro basin reveal the presence of a subtle tectonic overprint lasting at least until the Langhian (Middle Miocene) in the southern Pyrenean foreland. Magnetic ellipsoids show a sedimentary fabric in 42% of sites and a weak and well-defined magnetic lineation in 47% and 11% of sites. The magnetic lineation is roughly oriented around the east-west direction, compatible with a very weak deformation occurring there and related to the north-south compression linked to the convergence between Europe, Iberia and Africa during the Early-Middle Miocene. A slight variation of the magnetic parameters Km, Pj, and T exists through time, probably due to changes in the sedimentary conditions in the basin.

  13. 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

  14. Assessing tectonic and climatic causal mechanisms in foreland-basin stratal architecture: insights from the Alborz Mountains, northern Iran

    NASA Astrophysics Data System (ADS)

    Ballato, Paolo; Strecker, Manfred

    2015-04-01

    The southern foreland basin of the Alborz Mountains of northern Iran is characterized by an approximately 7.3-km-thick sequence of Miocene sedimentary rocks, constituting three basin-wide coarsening-upward units spanning a period of 106 years. We assess available magnetostratigraphy, paleoclimatic reconstructions, stratal architecture, records of depositional environments, and sediment-provenance data to characterize the relationships between tectonically-generated accommodation space (A) and sediment supply (S). Our analysis allows an inversion of the stratigraphy for particular forcing mechanisms, documenting causal relationships, and providing a basis to decipher the relative contributions of tectonics and climate (inferred changes in precipitation) in controlling sediment supply to the foreland basin. Specifically, A/S > 1, typical of each basal unit (17.5-16.0, 13.8-13.1 and 10.3-9.6 Ma), is associated with sharp facies retrogradation and reflects substantial tectonic subsidence. Within these time intervals, arid climatic conditions, changes in sediment provenance, and accelerated exhumation in the orogen suggest that sediment supply was most likely driven by high uplift rates. Conversely, A/S < 1 (13.8 and 13.8-11 Ma, units 1, and 2) reflects facies progradation during a sharp decline in tectonic subsidence caused by localized intra-basinal uplift. During these time intervals, climate continued to be arid and exhumation active, suggesting that sediment supply was again controlled by tectonics. A/S < 1, at 11-10.3 Ma and 9-6-7.6 Ma (and possibly 6.2; top of units 2 and 3), is also associated with two episodes of extensive progradation, but during wetter phases. The first episode appears to have been linked to a pulse in sediment supply driven by an increase in precipitation. The second episode reflects a balance between a climatically-induced increase in sediment supply and a reduction of subsidence through the incorporation of the proximal foreland into the

  15. 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

  16. 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

  17. Remagnetization of lower Silurian black shale and insights into shale gas in the Sichuan Basin, south China

    NASA Astrophysics Data System (ADS)

    Zhang, Yong; Jia, Dong; Yin, Hongwei; Liu, Mancang; Xie, Wuren; Wei, Guoqi; Li, Yongxiang

    2016-02-01

    The organic-rich lower Silurian shale of the Longmaxi Formation in the Sichuan Basin is the most important target for shale-gas exploration in China. Most Paleozoic rocks of the Sichuan Basin have experienced extraordinarily pervasive remagnetizations. To test a hypothesized connection between hydrocarbon generation and remagnetization and contribute to shale-gas exploration in the region, we undertook an integrated magnetic, geochemical, and petrographic study of 160 specimens from the shale. The results suggest that the shale contains a reliable remanent magnetization (Dec = 41.4°, Inc = 40.8°, and α95 = 6.8°). The magnetization predates tilting, and the paleopole plots close to the Late Triassic segment of the south China apparent polar wander path. The rock magnetic data and scanning electron microscope (SEM) observations confirm that framboidal magnetites carry the bulk of the magnetization, which suggest a Late Triassic chemical remanent magnetization in the shale. 87Sr/86Sr and magnetic analyses indicate that the amount of magnetite was unaffected by fluid alterations around the veins but is strongly covariant with the amount of total organic matter. Moreover, SEM observations reveal possible evidence of the replacement of pyrite framboids by magnetite, probably in the presence of organic acids. These analyses, therefore, suggest that the remagnetization was caused by organic maturation rather than orogenic fluids and that the maturation occurred in the Late Triassic. This timing of organic maturation has been validated by independent modeling studies and provides important constraints on the complex thermal history of the Longmaxi Shale as well as contributing to shale-gas exploration efforts.

  18. Morphotectonics and sedimentation in convergent margin basins: An example from juxtaposed marginal sea basin and foreland basin, Northern South China Sea

    NASA Astrophysics Data System (ADS)

    Yu, Ho-Shing; Huang, Zehn-Yin

    2009-03-01

    arc-continent collision in the southern Taiwan. The slope profile of the passive Chinese margin is characterized by a sigmoidal curvature, representing a typical primary depositional setting of a passive margin. Slope canyons occur mainly on the upper slope and cut the sea floor, resulting in irregular topography and representing effects of erosion. Being under the initial arc-continent condition, the offshore SW Taiwan has experienced the transition from a rifted margin to an overthrust belt and becomes a foreland basin, which is acting as a catch basin for orogenic debris derived from SW Taiwan. Arguments from tectonics and sedimentation suggest that the Koping shelf-slope region is considered to be an immature foreland basin rather than an accretionary wedge. More specifically, the Kaoping shelf-slope can be regarded as a depositional wedge top where exists an overlap area between rapid sedimentation and active deformation of the Kaoping shelf-slope sediments in the external orogenic wedge of southern Taiwan.

  19. 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).

  20. Didi Shiraki piggyback basin in the Georgian part of Kura foreland: implications for timing and development of the thrust wedge (south-east Georgia)

    NASA Astrophysics Data System (ADS)

    Alania, V.; Enukidze, O.

    2009-04-01

    In south-east Georgia, Plio-Pleistocene synorogenic deposits in the Didi Shiraki syncline of north Kura foreland record the transition from foreland-basin to piggyback basin deposition on the hangingwall of the thrust. Unconformity-bounded sedimentary units within the basin thin both southward and northward onto structures generated by thrust faulting. Seismic reflection profiles and Didi Shiraki well show that Up to 750 m of Plio-Pleistocene (Akchagil-Apsheronian) strata accumulated between these structures, which consist of a ramp anticline in the south and a thrust duplex in the north. Thrust systems are represents the Tertiary strata: post-Maikopian basin-fill and Akchagil-Apsheronian growth strata (alluvial-fluvial conglomerates, gravelites and poor cemented sandstones). Sequential balanced models are illustrating the development of Didi Shiraki syncline from the seismic profiles by kink-band migration and fault-bend folding with deposition.

  1. 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.

  2. Heat flow-heat production relationship not found: what drives heat flow variability of the Western Canadian foreland basin?

    NASA Astrophysics Data System (ADS)

    Majorowicz, Jacek A.

    2016-06-01

    Heat flow high -80 ± 10 mW/m2 in the northern western parts of the Western Canadian foreland basin is in large contrast to low heat flow to the south and east (50 ± 7 mW/m2) of the same basin with the same old 2E09 year's Precambrian basement and some 200-km-thick lithosphere. Over-thrusted and flat-laying sedimentary units are heated from below by heat flow from the old craton' crust and low 15 ± 5 mW/m2 mantle contribution. The heat flow vs. radiogenic heat production statistical relationship is not found for this area. To account for this large heat flow contrast and to have 200-km-thick lithosphere, we would need to assume that high heat production layer of the upper crust varies in thickness as much as factor of 2 and/or that the measured heat production at top of Precambrian basement is not representative for deeper rocks. The other explanation proposed before that heat in the basin is redistributed by the regional fluid flow systems driven from high hydraulic head areas close to the foothills of the Rocky Mountains toward low elevation areas to the east and north cannot be explained by observed low Darcy fluid velocities and the geometry of the basin.

  3. 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

  4. 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

  5. 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.

  6. Cenozoic foreland basin system in the central Andes of northwestern Argentina: Implications for Andean geodynamics and modes of deformation

    NASA Astrophysics Data System (ADS)

    Decelles, P. G.; Carrapa, B.; Horton, B. K.; Gehrels, G. E.

    2011-12-01

    Cenozoic strata in the central Andes of northwestern Argentina record the development and migration of a regional foreland basin system analogous to the modern Chaco-Paraná alluvial plain. Paleocene-lower Eocene fluvial and lacustrine deposits are overlain by middle-upper Eocene hypermature paleosols or an erosional disconformity representing 10-15 Myr. This `supersol/disconformity' zone is traceable over a 200,000 km2 area in the Andean thrust belt, and is overlain by 2-6 km of upward coarsening, eastward thinning, upper Eocene through lower Miocene fluvial and eolian deposits. Middle Miocene-Pliocene fluvial, lacustrine, and alluvial fan deposits occupy local depocenters with contractional growth structures. Paleocurrent and petrographic data demonstrate westerly provenance of quartzolithic and feldspatholithic sediments. Detrital zircon ages from Cenozoic sandstones cluster at 470-491, 522-544, 555-994, and 1024-1096 Ma. Proterozoic-Mesozoic clastic and igneous rocks in the Puna and Cordillera Oriental yield similar age clusters, and served as sources of the zircons in the Cenozoic deposits. Arc-derived zircons become prominent in Oligo-Miocene deposits and provide new chronostratigraphic constraints. Sediment accumulation rate increased from ˜20 m/Myr during Paleocene-Eocene time to 200-600 m/Myr during the middle to late Miocene. The new data suggest that a flexural foreland basin formed during Paleocene time and migrated at least 600 km eastward at an unsteady pace dictated by periods of abrupt eastward propagation of the orogenic strain front. Despite differences in deformation style between Bolivia and northwestern Argentina, lithosphere in these two regions flexed similarly in response to eastward encroachment of a comparable orogenic load beginning during late Paleocene time.

  7. Syn- and post-sedimentary controls on clay mineral assemblages in a tectonically active basin, Andean Argentinean foreland

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    In the northern part of the Calchaquí Valley (NW Argentina), Palaeogene Andean foreland sediments are represented by a 1400-metre-thick continental succession (QLC: Quebrada de Los Colorados Formation) consisting of claystones, siltstones, sandstones, and conglomerates representing sedimentation in fluvial-alluvial plains and alluvial fan settings. To understand the main syn- and postsedimentary variables controlling the clay mineral assemblages of this succession, we have studied the fine-grained clastic sediments by X-ray diffraction and electron microscopy, along with a detailed sedimentary facies analysis, for two representative sections. In the northern section, the whole succession was sampled and analysed by XRD, whereas in the second section, a control point 15 km to the south, only the basal levels were analysed. The XRD study revealed a strong contrast in clay mineral assemblages between these two sections as well as with sections in the central Calchaquí Valley studied previously. In the northernmost part of the study area, a complete evolution from smectite at the top to R3 illite/smectite mixed-layers plus authigenic kaolinite at the bottom, through R1-type mixed-layers in between, has been recognized, indicating the attainment of late diagenesis. In contrast, the clay mineral assemblages of equivalent foreland sediments cropping out only 15 km to the south contain abundant smectite and micas, subordinate kaolinite and chlorite, and no I/S mixed-layers to the bottom of the sequence. Early diagenetic conditions were also inferred in a previous study for equivalent sediments of the QLC Formation cropping out to the south, in the central Calchaquí Valley, as smectite occurs in basal strata. Burial depths of approximately 3000 m were estimated for the QLC Formation in the central and northern Calchaquí Valley; in addition, an intermediate to slightly low geothermal gradient can be considered likely for both areas as foreland basins are regarded as

  8. 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.

  9. Exploring for Silurian-Niagaran pinnacle reefs in the southern Michigan basin

    SciTech Connect

    Labo, J.; Cousins, J.; Werner, W.G.; Pan, P.H.

    1981-06-22

    Mobil's exploration program in the southern reef area of the southeast Michigan basin sought to identify (1) the factors indicating where and why the reefs grew, and (2) the prospecting methods most likely to work in unexplored reef areas. Gravity methods gave inconclusive data; the CDP seismic method however, along with static programs, was able to locate reefs in spite of problems such as the presence of a highly variable glacial till. Extensive study of a proven model led to a set of seismic reef criteria that were applied to actual data from the exploration program, modified as each well was drilled, and then applied to the remaining prospects.

  10. Calcium pumping and anhydrite/halite relationships in Silurian A unit of Michigan basin

    SciTech Connect

    Leibold, A.W.; Howell, P.D.

    1989-03-01

    Observed relationships between anhydrite and halite in the A unit of the Michigan basin are not easily explained by classical evaporite depositional models. Within the Northern Reef trend, productive Niagaran pinnacle reefs are surrounded by A unit halite, which commonly exceeds 100 m in total thickness. However, A unit evaporites consist of thick anhydrite deposits on reef flanks and above reefs in the A-1 and A-2, respectively, Stratigraphic data suggest that the anhydrites surrounding reefs are contemporaneous with off-reef halite deposits. This reef-evaporite relationship poses three problems. (1) Why would gypsum precipitate from a halite-saturated brine (2) Why are anhydrites associated with the reefs (3) Why are anhydrites significantly thicker than predicted by evaporation models In a normal marine evaporation sequence (Hardie-Eugster model), gypsum is deposited from a brine until calcium is depleted. Upon further evaporation, the resultant halite-saturated brine would precipitate gypsum only in contact with a calcium source. The authors propose a calcium pumping mechanism whereby calcium-rich water associated with pinnacle reefs is responsible for gypsum precipitation around these reefs contemporaneous with off-reef halite. The additional supply of calcium also explains the anomalous thickness of these anhydrite deposits. Similar anhydrite halos around pinnacle reefs have been observed in the Devonian Elk Point basin.

  11. 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.

  12. 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.

    1996-12-31

    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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Early Cenozoic Shortening and Foreland Basin Sedimentation in the Marañon Fold-thrust Belt, Central Peruvian Andes

    NASA Astrophysics Data System (ADS)

    Jackson, L. J.; Carlotto, V.; Horton, B. K.; Rosell, L. N.

    2015-12-01

    The Marañon fold-thrust belt in the westernmost Andes of Peru has long been considered a robust signature of early Cenozoic shortening in the Andean orogenic belt. However, the structural details and potential records of coeval synorogenic sedimentation remain elusive. We report results from new geologic mapping (1:50,000), cross-section construction, and U-Pb geochronology for the Matucana-Ticlio region at 11-12°S along the Lima-La Oroya highway. Zircon U-Pb age data from volcanic rocks and clastic basin fill provide a maximum depositional age of ~43 Ma for a middle Eocene syndeformational unit that we identify as the Anta Formation, which overlies the Paleocene Casapalca Formation. Sedimentary lithofacies and unconformable relationships within the volcaniclastic Anta Formation reveal mixed fluvial, alluvial-fan, and volcanic depositional conditions during shortening accommodated by a NE-verging thrust/reverse fault and corresponding backthrust (here named the Chonta fault system). Our cross-section reconstruction and geochronological data indicate that the region is a critical, possibly unique, zone of the broader NE-directed Marañon fold-thrust belt where pre-Neogene synorogenic sediments and their associated structures are preserved. We interpret this combined structural and basin system as an Eocene-age (Incaic) frontal thrust belt and corresponding foredeep to wedge-top depozone in central Peru. As one of the better-constrained segments of the Marañon fold-thrust belt, this zone provides insight into potential linkages with elusive early Cenozoic (Incaic) structures and foreland basin fill of the Western Cordillera and Altiplano farther south in the central Andean plateau.

  1. 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

  2. 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.

  3. Miocene biostratigraphy of Northern Monagas, Eastern Venezuela: Biological signals of sea level and Paleoceanographic changes in a foreland basin

    SciTech Connect

    Crespo de Cabrera, S. ); Radford, S. )

    1993-02-01

    Foraminiferal studies in the Carapita and La Pica formations have provided interesting patterns which could be correlated with paleoceanographic changes brought about by relative sea level changes, among other causes. By their effects on physicochemical parameters, relative sea level changes will affect the character, composition and distribution of marine biofacies. Patterns of foraminiferal abundance and diversity and the appearances and extinctions of species have been used to attempt a characterization of system tracts. This is a part of sequence stratigraphy very poorly understood, especially in deep water environments, where abundance peaks occur at several condensed sections within lowstand system tracts in addition to maximum flooding surfaces. The Carapita Formation is of Early to Middle Miocene age, zones N4 to N14 and correspond to the upper part of the TB1 and TB2 second order cycles of the Hag et al. chart. It was deposited predominantly in bathyal paleoenvironments, though neritic conditions have been determined at the base and summit of this formation. It is unconformably overlain by intercalations of sandstones and shales known as La Pica Formation, of Late Miocene age, deposited on environments ranging from inner neritic to continental. This probably correlates with the lower part of the TB3 super cycle. Both formations were deposited in a foreland basin, formed at the beginning of the Neogene by the southeastward thrusting of the Caribbean plate over the South American continent.

  4. 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.

  5. 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

  6. Indian Castle Shale: late synorogenic siliciclastic succession in an evolving Middle to Late Ordovician foreland basin, eastern New York State

    NASA Astrophysics Data System (ADS)

    Baird, Gordon C.; Brett, Carlton E.

    2002-01-01

    The thick, organic-rich, Indian Castle Shale, is a major component of the greater Utica Shale basinal facies succession associated with the Taconian Orogeny. Detailed correlations of numerous Indian Castle sections, presented herein, are based on physical matching of numerous altered ash layers (K-bentonites) coupled with use of submarine discontinuities and other distinctive beds. Several important trends are observed: first, the Dolgeville Formation extends eastward into the eastern Mohawk Valley region (Hoffmans Fault area) lithologically separating an older Utica division (Flat Creek Shale) from Indian Castle Shale proper. Second, Indian Castle Shale strata are observed to overlap the regional top-Dolgeville and post-Trenton disconformity towards the northwest. Third, the lower part, and possibly the upper part, of the Indian Castle succession is differentially thickened in the west-central Mohawk Valley region due to differential subsidence and syntectonic fault activity. Fourth, the lower part of the Indian Castle Shale succession in the central-to-eastern part of the Mohawk Valley region continues to thin slightly with little evidence for major eastward transition of Utica facies into turbiditic Schenectady deposits. Fifth, K-bentonitic beds, many displaying distinctive sedimentological features, are clustered in intervals of apparent Indian Castle stratigraphic condensation. Ashes also display an overall upward decrease in abundance within the Indian Castle Shale succession. These patterns indicate that Indian Castle deposition, influenced by lithospheric flexural processes, localized fault activity and eustatic fluctuations, occurred when the foreland basin was maximally developed. Indian Castle deposition was probably linked to a collisional tectophase of Taconian overthrusting.

  7. 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.

  8. The Late Miocene to recent erosion pattern of the Alpine foreland basin reflects Eurasian slab-unloading beneath the western Alps rather than global climate change

    NASA Astrophysics Data System (ADS)

    Friedrich, Anke; Schlunegger, Fritz; Baran, Ramona

    2014-05-01

    It has been proposed that mountainous erosion increased globally around 5 Ma in response to global climate change, mainly because this increase coincides with a cooling trend indicated by global isotopic data (e.g., Herman et al. 2013). The Alps have played a prominent role in this debate. Published sedimentary budgets for the western and eastern Alps for the past 35 Ma show a substantial increase in the erosion of the Alps at c. 5 Ma (e.g., Kuhlemann, 2000). This temporal coincidence was used to call for a climate driver, mainly because this increase was not accompanied by tectonic convergence across the Alps during this time period. However, several authors emphasized the importance of lithospheric-scale processes beneath the Alps, which could also explain the increase in erosion rates through surface uplift. To provide a new perspective on this debate, we synthesized a spatial gradient map of erosion rates for the Alps and the entire Alpine foreland basin. Our data base consists of published (1) apatite fission-track (AFT) cooling ages for the Alps (e.g., Vernon et al. 2008; Luth and Willingshofer 2008; Wölfler et al. 2012; (2) AFT ages from wells from the Swiss foreland basin (e.g., Cederbom et al. 2011), and (3) stratigraphic data from industry wells in the German and Austrian foreland basin (e.g., Lemcke 1974; Genser et al. 2007). We focus our analysis on the shape and scale of the areas undergoing erosion since 5 Ma. Our synthesis of published denudation rate data for the past 5 Million years reveals that erosion of the Alpine foreland basin is highest in front of the western Alps (between 2 and 0.6 km), and decreases eastward over a distance of 700 km to the Austrian foreland basin (c. 200 m). For the western Alps, the compilation of apatite-fission-track ages yields erosion rates > 0.6 km/Ma, while erosion rates for the eastern foreland basin and the adjacent eastern Alps are < 0.1 km/Ma, except for a small-scale signal in the Tauern window. The results

  9. The Madong Early Paleozoic fold-thrust belt in southern Tarim Basin

    NASA Astrophysics Data System (ADS)

    Li, Yue-Jun; Wen, Lei; Li, Hui-Li; Peng, Geng-Xin; Qiu, Bin; Zheng, Duo-Ming; Luo, Jun-Cheng; Zhang, Qiang; Jia, Tie-Gan

    2016-01-01

    The Madong fold-thrust belt, which strikes NE-SW and thrusts southeastward, locates in the southern Tarim Basin. It is a part of the Kunlun Early Paleozoic foreland fold-thrust belt, and so is the Tangnan fold-thrust belt on the southeast of Madong. The Madong and Tangnan fold-thrust belts developed in Cambrian-Ordovician strata, and the Middle Cambrian gypsum-salt layer serves as the main décollement surface. The Middle Silurian and above strata unconformably overlie Madong while the upper Lower Silurian unconformably overlie Tangnan. On the basis of the facts that: (1) the Upper Ordovician is the youngest strata involved in the fold-thrust deformation, (2) the upper-Lower to Middle Silurian is the oldest strata unconformably overlying the foreland fold-thrust belt (including Madong and Tangnan), and growth strata exist in the upper part of the Upper Ordovician, we infer that the deformation time of the Kunlun Early Paleozoic foreland fold-thrust belt (including Madong and Tangnan) was during the Late Ordovician-Early Silurian. Tangnan is the residual of the major part of the foreland fold-thrust belt. Its northwestward thrust direction represents the main thrust direction of the foreland fold-thrust belt. Madong is the front belt of the foreland fold-thrust belt. It mainly thrusts southeastward and serves as the back-thrust belt of the Kunlun Early Paleozoic foreland fold-thrust belt. It is a triangle zone between Madong and Tangnan. The Madong fold-thrust belt is the best-preserved section of the Kunlun Early Paleozoic collisional orogenic belt, and thus is an important geological record of the Kunlun Early Paleozoic orogeny.

  10. 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.

  11. History of diagenetic fluids in a distant foreland area, Middle and Upper Pennsylvanian, Cherokee basin, Kansas, USA: Fluid inclusion evidence

    NASA Astrophysics Data System (ADS)

    Wojcik, Krzysztof M.; Goldstein, Robert H.; Walton, Anthony W.

    1994-02-01

    Analysis of fluid inclusion data in diagenetic cements from Pennsylvanian limestones and sandstones of the Cherokee basin in southeastern Kansas reveals the succession of diagenetic fluids in a distant foreland of the Arkoma-Ouachita system. This succession includes early low-salinity (0.0-2.4 wt% NaCl eq.) fluids of meteoric affinity (Fluid I) followed by low-temperature Na-Ca-Cl brines (Fluid II with salinities between 8.4 and 24.1 wt% NaCl eq.). Fluids I and II were present in the system during precipitation of early-stage calcite cements at temperatures less than about 50°C. Another Na-Ca-Cl brine (Fluid III with salinity up to 25 wt% NaCl eq.) was present in the system later, at temperatures of maximum burial (at least 80-85°C) and higher. Fluid III is followed by a Na-Cl brine (Fluid IV, with salinities about 19-21 wt% NaCl eq.) characterized by temperatures distinctly higher than maximum burial, up to 150°C. Fluid III and Fluid IV were entrapped during precipitation of late-stage baroque dolomite and Fe-dolomite in Pennsylvanian limestones, and late-stage Fe-dolomite and ankerite in Pennsylvanian sandstones. The record of progression from Fluid III to Fluid IV may have been partially obscured by thermal re-equilibriation of some inclusions during migration of Fluid IV. Fluids with Na-Ca-Cl chemistry (Fluid II and III) were either indigenous subsurface fluids of the Cherokee and Arkoma basins, or might have originated as reflux fluids in a Permian evaporitic basin of Central Kansas. Later Na-Cl brine (Fluid IV) originated in deeper parts of the Arkoma-Ouachita system and might have acquired their salinity by dissolution of hypothetical salts buried beneath the Ouachitas. Temperatures recorded by fluid inclusions in late-diagenetic carbonates are 20-60°C higher than those calculated for the maximum burial of the studied section. This thermal anomaly suggests an advective heat transfer from the Arkoma-Ouachita system onto the shelf of the Cherokee basin

  12. 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.

  13. 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

  14. 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

  15. Petroleum systems along the foldbelt associated to the Maranon-Oriente-Putomayo Foreland Basins

    SciTech Connect

    Marksteiner, R.; Aleman, A.M.

    1996-08-01

    Along strike variations in structural style of the foldbelt associated to the Maranon-Oriente-Putumayo (MOP) Basins and timing of deformation accounts for the major variations in their petroleum systems. Space-time changes in structural style controlled the timing of maturation and generation as well as reservoir and seal quality. Source rock distribution and richness could vary along the foldbelt, however, they are difficult to document. The Foldbelt associated to the Oriente and Putumayo Basins is characterized by thick-skinned style of deformation and contains the only commercial accumulations. A thick sedimentary wedge of the Tena Formation in front of the Napo and Cutucu Uplifts documents Late Cretaceous/Paleocene deformation (Peruvian Phase). AFT data in the Putumayo, Napo and Cutucu Uplifts documents a Middle Eocene Uplift (Incaic Phase) followed by a Late Miocene Pliocene renewal of uplift. The main phase for hydrocarbon generation and migration was from Late Cretaceous to Middle Eocene, therefore, the productive structures must have an older component. Biodegradation and water washing accounts for the destruction of the largest accumulation of heavy oil in the southern plunge of the Napo Uplift. The Peruvian segment includes the salt-related Santiago and Huallaga Foldbelts which are still poorly explored. Although there are strong indications for salt movement and basin inversion since Mesozoic times, the main episode of folding and thrusting was Late Miocene to Pliocene. This is supported by AFT and modern seismic data. Although there are several structures showing Mesozoic thinning against the salt, the major episodes of salt withdrawal took place during the Tertiary. This accounts for significant burial of the reservoir rocks with concomitant reduction of the primary porosity.

  16. Simulation of foreland basin stratisgraphy using a diffusion model of mountain belt uplift and erosion: An example from the central Alps, Switzerland

    NASA Astrophysics Data System (ADS)

    Sinclair, H. D.; Coakley, B. J.; Allen, P. A.; Watts, A. B.

    1991-06-01

    Foreland basin stratigraphy can be considered as the result of three interacting processes: thrust deformation, which builds the tectonic load, sedimentary and erosional processes which redistribute that load, and the flexural response of the lithosphere. The resultant stratigraphy of foreland basins is commonly composed of a small number of shallowing and coarsening upward cycles bounded by regional unconformities. To understand the development of these unconformities, we present a simple model of these three processes, coupling an evolving thrust wedge on a linear elastic plate with erosion and sedimentation defined by the diffusion equation applied to topography. Our model demonstrates the development of regional unconformities without recourse to either eustasy or complex viscoelastic models for the continental lithosphere. The model describes the thrust wedge-foreland basin system in terms of four parameters: (1) the effective elastic thickness of the foreland plate (Te), (2) the sediment transport coefficient (K), (3) the thrust wedge advance rate, (4) the surface slope of the thrust wedge. The model is applied to the Oligocene-Miocene North Alpine Foreland Basin (NAFB) of eastern Switzerland. The stratigraphy of the NAFB can be simplified into two large-scale shallowing upward cycles separated by an unconformity at the base of the Burdigalian (22 Ma). Geological information is taken from the NAFB to estimate suitable values for the parameters listed above. Assuming a linear elastic lithospheric rheology, the Te value is estimated at 10±5 km from decompacted sediment columns. Data to constrain the sequential development of the thrust wedge come from structural geology. The early stages (40-24 Ma) of compression involved a relatively low-angle thrust wedge with an advance rate of approximately 2-4 mm/yr. At about 24 Ma the wedge advance slowed down and thickened by underplating crystalline basement of the foreland plate. The value for the transport

  17. New paleontological and geological data on the Ordovician and Silurian of Bolivia

    NASA Astrophysics Data System (ADS)

    Gagnier, P. Y.; Blieck, A.; Emig, C. C.; Sempere, T.; Vachard, D.; Vanguestaine, M.

    1996-11-01

    The oldest vertebrates of South America are from the thick Anzaldo (=Cuchupunata) Formation in central Bolivia. At the scale of the basin, the Anzaldo is overlain by the San Benito, Tokochi, Cancañiri, Llallagua and Kirusillas/Uncía formations. The Anzaldo was classically dated Caradoc (early Late Ordovician), but recent paleontological data have suggested a Llanvirn age (early Middle Ordovician). The only significant fossil invertebrates recently collected in the Anzaldo, viz., lingulid brachiopods, give an age not older than Late Ordovician. Fossils from the Tokochi suggest a Caradoc age. The microfossils (acritarchs and foraminifers mainly) collected in the Cancañiri and Kirusillas/Uncía formations indicate an Ashgill to Wenlock age (late Late Ordovician to late Early Silurian) for these formations. A Caradoc (or perhaps older) age thus seems more correct for the Anzaldo Formation. These new paleontological data have major implications on our knowledge of the Ordovician-Silurian basins of Bolivia: 1) transition from a Middle Ordovician marine foreland basin to a Late Ordovician-Llandovery glacial-marine to turbidite trough in the Altiplano occurred in the (late?) Caradoc; 2) a major sea-level rise developed around the Llandovery-Wenlock boundary; 3) a fossiliferous limestone member of shallow origin and early Wenlock age is present approximately between Cochabamba and Santa Cruz.

  18. 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.

    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).

  19. 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

  20. 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.

  1. Authigenic chlorites in sandstones as indicators of high-temperature diagenesis, Arkoma Foreland Basin, USA

    SciTech Connect

    Spoetl, C.; Houseknecht, D.W. ); Longstaffe, F.J. . Dept. of Earth Sciences)

    1994-07-01

    Abundant authigenic chamosite associated with higher-than-average porosities is present in a deep gas reservoir (Spiro sandstone) of the Arkoma Basin, east-central Oklahoma. Three types of chlorite can be distinguished petrographically, all of which appear texturally to have formed early: chlorite peloids, diffuse matrix, and grain coatings. X-ray diffraction, scanning electron microscopy, and electron microprobe studies show that most chlorites are composed of two distinct polytypes, Ib ([beta] = 90[degree]) and IIb. A third structure, Ia[prime] polytype, was identified in only one sample. The relative percentage of the high-temperature IIb structure increases gradually with increasing thermal maturity, from [le] 10% at 2.0% R[sub o] up to [le] 40% at 3.5% R[sub o]. IIb chlorite forms rather thick, blocky crystals distinct from the thin, pseudohexagonal plates typical of low-temperature Ib chlorite. Temperature estimates based on data on vitrinite reflectance and fluid inclusions suggest that IIb chlorite formed at burial temperatures [ge] 150--180 C. Higher contents of tetrahedral Al[sup 3+] and slightly higher Fe/[Fe+Mg] ratios in IIb chlorite are consistent with precipitation temperatures higher than those of the Ib structure. A higher-temperature origin for the IIb structure is also consistent with oxygen isotope data.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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, Wei; Dupont-Nivet, Guillaume; Jolivet, Marc; Guo, Zhaojie; Bougeois, Laurie; Bosboom, Roderic; Zhang, Ziya; Zhu, Bei; Heilbronn, Gloria

    2015-03-01

    The Tian Shan range is an inherited intracontinental structure reactivated by the far-field effects of the India-Asia collision. A growing body of thermochronology and magnetostratigraphy datasets shows that the range grew through several tectonic pulses since ~ 25 Ma, however the early Cenozoic history remains poorly constrained. The time-lag between the Eocene India-Asia collision and the Miocene onset of Tian Shan exhumation is particularly enigmatic. This peculiar period is potentially recorded along the southwestern Tian Shan piedmont. There, late Eocene marine deposits of the proto-Paratethys epicontinental sea transition to continental foreland basin sediments of unknown age were recently dated. 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 increase in accumulation rates at 19-18 Ma. This implies that 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 to 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, suggests far-field deformation from the

  8. 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.

  9. 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

  10. The Aquitaine Basin: 60 years of gas exploration and production in the foreland of the Pyrenean fold and thrust belt

    SciTech Connect

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

    1995-08-01

    Over the last 60 years, Exploration in the Aquitaine Basin has led to the discovery of about 13 TCF of gas associated with 100 MMBls of condensate. The first gas discovery was made on the St Marcet surface anticline in 1939. However the major step was accomplished in 1951 by the discovery of the Giant Lacq field (9 TCF of gas), which was followed in 1965 by the discovery of the Meillon Field (2,5 TCF). Production started in 1944 at St Marcel, in 1957 at Lacq and in 1967 at Meillon leading to a cumulative production of 10 TCF of gas as of December 1994. The fields are located in the immediate foreland of the Alpine Pyrenean Thrust Belt. The region shows as a result extreme structural complexity, which is also linked to the polyphased geological evolution of the area. Overprinted on the faulting pattern of the basement (Variscan and Hercynian orgenies), the area is characterized by a general E-W extension during the Jurassic and the Early Cretaceous, followed by a major submeridian compression from the Late Cretaceous to the Oligo-Miocene. In this context the traps for the fields consist in deep (3500 to 4500 m in average) faulted blocks derived from the Early to Mid Mesozoic extension, inverted at various degrees during the Late Cretaceous and Tertiary compressive events. In such a petroleum context, the challenge for the 90`s is to evaluate the remaining potential and to optimize the development of existing fields as well as to discover new fields especially within the unexplored zones along the leading edge of the Pyrenean Fold and Thrust Belt. Recent onshore 3D seismic (over 1500 km2 shot from 1987 to 1993) has proven to be efficient in defining good geometry for the fields and in delineating precisely the fractured zones of the reservoirs. It has as well allowed to develop a comprehensive understanding of the area and therefore a good evaluation of the unexplored zones within this very prolific region.

  11. 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.

  12. 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.

  13. Provenance evolution of the Western foreland basin and its relationship to the exhumation of source rocks during arc-continent collision

    NASA Astrophysics Data System (ADS)

    Nagel, S.; Fellin, M. G.; Castelltort, S.; Willett, S. D.; Mouthereau, F.; Lin, A. T.

    2012-04-01

    Late Miocene to Pleistocene sedimentary rocks in the Western foreland basin of Taiwan record the evolution of an orogenic wedge during oblique arc-continent collision between the Luzon volcanic arc and the Chinese passive margin. Our stratigraphic record reaches back to pre-collisional sediments of the Late Miocene to Pliocene, which were deposited on the Chinese passive margin. A dramatic change is observed in the Pliocene, as the depositional center shifts to a collisional basin developing on the passive margin due to the obliquely colliding Luzon Arc and input of sediment from the approaching accretionary wedge. Synorogenic sedimentation continues into the Pleistocene providing a history of material being eroded from the growing mountains to the east. We apply standard provenance analysis techniques on several stratigraphic profiles along the strike of the orogen to relate the sediments to their source and reconstruct possible distribution pathways to further enhance a paleogeographic reconstruction of the area. Unmetamorphosed mudstones within our sedimentary record contain abundant detrital illite, chlorite and zircons. The Illite Crystallinity Index (IC) and the fission-track dating of detrital zircons provides robust information about the thermal history of source terrains, and we combine these methods to infer the timing of exhumation of metamorphic rocks in the Central Range of Taiwan. The initial input of illite minerals with high crystallinity and of zircons with reset ages (younger than 10 Ma) is recorded in the Yutengping fm. and Chinsui Shale, around 3.5 Ma in the north and around 2.5 Ma in the South, contemporaneously with a deepening and widening of the depositional basin. This is the time of deposition of the mud-dominated Chinshui shale, interpreted as the "underfilled" stage of the foreland basin. This clearly marks accelerated subsidence caused by the approach of the growing orogen. In the south, the illite crystallinity and the frequency of

  14. Source versus depositional controls on sandstone composition in a foreland basin: The El Imperial Formation (Mid Carboniferous-Lower Permian), San Rafael basin, western Argentina

    SciTech Connect

    Espejo, E.S. ); Lopez-Gamundi, O.R. . Frontier Exploration Dept.)

    1994-01-01

    The El Imperial Formation (mid-Carboniferous-Lower Permian) constitutes a progradational sandstone-rich succession deposited in the San Rafael foreland basin of western Argentina. Four facies associations have been identified: a basal glacial marine association, a shallow marine association, a deltaic association, and an uppermost fluvial association. Sand-prone deposits in the deltaic association, a shallow marine association, a deltaic association, and an uppermost fluvial association. Sand-prone deposits in the deltaic association are represented by prodelta and delta-front shales and subordinate fine sandstones (Facies A), deltaic platform, wave-reworked channel mouth-bar sandstones (Facies B), and fluvial-dominated distributary channel sandstones (Facies C). Analysis of framework grains of sandstone samples from Facies B and C shows two distinct mineral assemblages or petrofacies. The quartzose petrofacies is characterized by high contents of quartz and low percentages of feldspar and lithic grains. The quartzolithic petrofacies shows an increase in labile components, in particular lithic fragments, and a concomitant decrease in quartz. The quartzolithic petrofacies shows a source signature. Average detrital modes of sandstones from this petrofacies are similar to those from overlying fluvial sandstones. All wave-reworked, channel mouth-bar sandstones (Facies B) correspond compositionally to the quartzose petrofacies, whereas detrital modes from the distributary-channel sandstones (Facies C) fall into the quartzolithic petrofacies. This correspondence between depositional environment and petrofacies suggests a strong depositional influence on composition (depositional signature). Abrasion (mechanical breakdown) by wave action in shallow marine environments accounts for the quartz-rich nature and paucity of labile grains in the quartzose petrofacies.

  15. 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.

  16. 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

  17. 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

    NASA Astrophysics Data System (ADS)

    Das, Nachiketa; Horita, Juske; Holland, Heinrich 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 4-2, somewhat depleted in Na + and Mg +2, and greatly enriched in Ca +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 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 k +/m Br - ratio and the functions [m Ca +2 + m Mg +2/- m SO 4-2 - m HCO 3-/2m Br -and [if m cl - - m Na +/m Br -] 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 δ34S in Silurian marine anhydrites and with the 87Sr /86Sr ratios of Late Silurian marine carbonates.

  18. 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.

  19. 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

  20. 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

  1. The Bartonian-Priabonian marine record of the Eastern South Pyrenean Foreland Basin (NE Spain): A new calibration of the larger foraminifers and calcareous nannofossil biozonations.

    NASA Astrophysics Data System (ADS)

    Costa, E.; Garcés, M.; López-Blanco, M.; Serra-Kiel, J.; Bernaola, G.; Cabrera, L.; Beamud, E.

    2012-04-01

    The up to 5000-m-thick sedimentary infill of the South Pyrenean Foreland Basin (in NE Spain) records the Cenozoic evolution of the NE Iberian plate. This region is an excellent area where to perform a combined biomagnetostratigraphic study of a Paleogene succession as the present level of erosion of the basin infill and its surrounding mountain ranges is at an optimal stage for studying a continuous and thick stratigraphic record. In this sense, a biochronological framework of the South Pyrenean Foreland Basin has been developed since the early 1950's, which was later combined with magnetostratigraphic studies. This biochronological framework, together with all the available literature on the biostratigraphy and magnetostratigraphy of the Paleocene and Eocene Tethys, were integrated in a general chronostratigraphic framework used to define and calibrate the larger foraminifer biozonation (Shallow Benthic Zones, SBZ). However, in the Gelogical Time Scale 2004 no correlation of the Paleogene SBZ zonation with the geomagnetic polarity time scale was provided. Here we present a combined biostratigraphic (larger foraminifers, calcareous nannofossils) and magnetostratigraphic study of the Middle and Late Eocene marine units of the Igualada area, on the eastern Ebro Basin. The studied sections of Santa Maria de Miralles and La Tossa encompass the complete marine succession of the Santa Maria Group. A total of 224 paleomagnetic sites and 64 biostratigraphic samples were collected along a 1350-m-thick section that ranges from chron C20n to chron C16n (ca. 43-36 Ma). The resulting magnetostratigraphy-based chronology challenges existing chronostratigraphic interpretations of these units and results in a new calibration of the larger foraminifers and calcareous nannofossil biozonations. The traditional division of the Bartonian stage into two complete larger foraminifers zones, SBZ17 and SBZ18, is challenged. Zone SBZ17 embraces most of the Bartonian, while Zone SBZ18 extends

  2. 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

  3. 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

  4. 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

  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. 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

  7. Nd, Sr-isotopic provenance and trace element geochemistry of Amazonian foreland basin fluvial sands, Bolivia and Peru: implications for ensialic Andean orogeny

    NASA Astrophysics Data System (ADS)

    Basu, Asish R.; Sharma, Mukul; DeCelles, Peter G.

    1990-10-01

    Nd and Sr isotopes and the trace element contents, including the rare earths, were determined for fluvial sands of lithic arenite composition from the Madre de Dios foreland basin of Bolivia and Peru. On standard petrologic ternary diagrams, the sands fall in the recycled orogen provenance field and thus are similar to typical ancient foreland basin composition. The average rare earth elemental pattern of the sands is identical to the upper continental crustal average, as estimated from post-Archean composite shales of different continents. Ratios ofTh/U, Co/Th, La/Sc and Th/Sc of the fluvial sands are intermediate between an average magmatic arc and an upper crustal average compositions. The dispersion of some trace elemental patterns in the sands can be attributed to fractionation of dense minerals, including zircon, during the sedimentation process. The variations of Nd isotopes in conjunction with the petrographic parameters of lithic metamorphic (Lm) and volcanic (Lv) fragments allow a two-fold classification of the sands. These two sand types can be interpreted in terms of mixing among three different provenances: one volcanic rock-suite with less negativeɛ Nd(O) parameter than the other volcanic suite, and a third metasedimentary source withɛ Nd(O) value of around -12, which is considered to be similar to the average western Brazilian shield composition. Thus the overall compositions of the sands has been modeled as mechanical mixtures of two components, an Andean magmatic arc and the Brazilian shield-derived metasediments. The model is strongly supported by a plot ofɛ Nd(O) versusɛ Sr(O) of the sands. In this plot, the Type 1 and 2 sands define two coherent hyperbolic trends contiguous with two different portions of the Andean magmatic trend. This relationship has been interpreted to indicate that the observed Andean magmatic trend in anɛ Sr(O)-ɛ Nd(O) diagram is the result of varying degrees of contamination of a "primitive arc-type" magma by the

  8. Combined tectonic-sediment supply-driven cycles in a Lower Carboniferous deep-marine foreland basin, Moravice Formation, Czech Republic

    NASA Astrophysics Data System (ADS)

    Bábek, Ondřej; Mikuláš, Radek; Zapletal, Jan; Lehotský, Tomáš

    The Lower Carboniferous Moravian-Silesian Culm Basin (MSCB) represents the easternmost part of the Rhenohercynian system of collision-related, deep-water foreland basins (Culm facies). The Upper Viséan Moravice Formation (MF) of the MSCB shows a distinct cyclic stratigraphic arrangement. Two major asymmetric megacycles bounded by basal sequence boundary, each about 500 to 900 m thick, have been revealed. The megacycles start with 50- to 250-m-thick, basal segments of erosive channels: overbank successions and slope apron deposits interpreted as lowstand turbidite systems. Up-section they pass into hundred metre-thick, fine-grained, low-efficiency turbidite systems. Palaeocurrent data show two prominent directions, basin axis-parallel, SSW-NNE directions, which are abundant in the whole MF, and basin axis-perpendicular to oblique, W-E to NW-SE directions, which tend to be confined to the basal parts of the megacycles or channel-lobe transition systems in their upper parts. Based on the facies characteristics, palaeocurrent data, sandstone composition data and trace-fossil distribution data, we suggest a combined tectonics-sediment supply-driven model for the MF basin fill. Periods of increased tectonic activity resulted in slope oversteepening probably combined with increased rate of lateral W-E sediment supply into the basin, producing the basal sequence boundary and the subsequent lowstand turbidite systems. During subsequent periods of tectonic quiescence, the system was filled mainly from a distant southern point source, producing the thick, low efficiency turbidite systems. Consistently with the previous models, our own sediment composition data indicate a progressively increasing sediment input from high-grade metamorphic and magmatic sources up-section, most probably related to an uplift in the source area and progressive unroofing of its structurally deeper crustal parts. The first occurrence of the Cruziana-Nereites ichnofacies in sand-rich turbidite

  9. 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.

  10. Modeling the flexural evolution of the Amiran and Mesopotamian foreland basins of NW Zagros (Iran-Iraq)

    NASA Astrophysics Data System (ADS)

    Saura, Eduard; Garcia-Castellanos, Daniel; Casciello, Emilio; Parravano, Vanessa; Urruela, Aritz; Vergés, Jaume

    2015-03-01

    The evolution of the Amiran and Mesopotamian flexural basins of the Zagros belt is approached by coupled 2-D forward modeling of orogenic wedge formation, lithospheric flexural isostasy, and stream power erosion/transport/sedimentation. Thrust geometries and sequence of emplacement derived from geometric and kinematic models presented here are the inputs to our evolutionary model, constrained by basin geometry, sediment volume, and topography. Modeling results confirm that the Zagros flexural basins evolution is consistent with two stages of deformation: (1) the obduction stage involving the Kermanshah accretionary complex and a basement unit and (2) the collision stage, emplacing the Gaveh Rud and Sanandaj-Sirjan domains in the hinterland and forming a basement duplex in the outer part. Results provide quantitative insights into processes involved in mountain and basin building. The lithospheric equivalent elastic thickness (Te) changed from 20 km during the Amiran stage (~90-50 Ma) to 55 km during the Mesopotamian subsidence stage (last 20 Myr). The Amiran basin results from flexure of the Arabian plate below the load of the Kermanshah cover and basement thrust sheets. During this stage, material eroded in the inner parts was enough to fill the flexural trough. The Mesopotamian basin formed in front of the outermost basement units flexing the Arabian plate. During this latter stage, material eroded from the orogenic wedge was not enough to fill the Mesopotamian basin. An additional longitudinal sediment supply of up to 200 m/Myr is required to fill the flexural basin.

  11. 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.

  12. 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

  13. Apatite fission-track thermochronology of the Appalachian foreland basin from the Virginia Piedmont to eastern Ohio

    SciTech Connect

    Roden, M.K. . Dept. of Earth and Environmental Science); Cerveny, P.F.; Bergman, S.C. . Research and Technical Services)

    1992-01-01

    Apatite fission-track ages have been determined for 29 samples from two transects in the southern Appalachians. The northern transect extends from the VA Piedmont northwest through the Valley and Ridge Province, Cumberland Plateau, and into the Appalachian foreland of southeastern OH. An additional transect was collected from the Pine Mountain thrust in southeastern KY extending northwest to the Cincinnati Arch. Precambrian gneisses and granites from the VA Piedmont yield reset apatite fission-track ages ranging from 103 [+-] 6 to 138 [+-] 11 Ma. Ordovician through Mississippian sedimentary rocks from the Valley and Ridge Province of VA-WV also yield reset apatite fission-track ages ranging from 120 [+-] 8 to 144 [+-] 20 Ma. The cooling histories for the Piedmont and Valley and Ridge rocks of VA and WV thus appear similar, having cooled rapidly between about 103 and 144 Ma. Pennsylvanian samples from the Cumberland Plateau of WV yield rest apatite fission-track ages of 112 [+-] 7 to 169 [+-] 13 MA in the southeast which grade into partially reset (mixed ages) northwest of Charlestown (133 [+-] 13 to 156 [+-] 10 Ma). The Permian Dunkard Formation from the OH-WV border yielded a mixed age of 197 [+-] 13 Ma, suggesting that the Permian has not been subjected to temperatures > 100 C for times greater than 1 Ma, since it was deposited. Mississippian--Pennsylvanian samples from eastern KY yield reset apatite fission-track ages which decrease from the Pine Mt. Thrust (186 [+-] 16 Ma) to Mozelle, KY (136 [+-] 12 Ma), then increase toward the Cincinnati Arch (166 [+-] 18 [minus] 186 [+-] 21 Ma). This is consistent with older apatite fission-track ages (200 Ma) from Ordovician K-bentonites in the vicinity of the Cincinnati Arch.

  14. 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.

  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. 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.

  17. Comparative Tertiary stratigraphy of the Rhine Graben, Bresse Graben and Molasse Basin: correlation of Alpine foreland events

    NASA Astrophysics Data System (ADS)

    Sissingh, W.

    1998-12-01

    Comparative tectonostratigraphic analysis of the Tertiary (Middle Eocene-Pliocene) of the Rhine-Bresse graben system and the western Molasse Basin demonstrates the occurrence of eleven correlative sequences (CRF I-XI). These show a close relationship between intra-basinal tectonics and depositional history. Their punctuated sediment accumulation can be related to phases of extra-Alpine taphrogenesis and Alpine orogenesis, and to coeval eustatic changes in sea-level. Apparent simultaneity in rift and foredeep sequence development, structural deformation and global change in sea-level suggests a common causal control in which the development of the Alps played an important role.

  18. 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

  19. The nonmarine Lower Cretaceous of the North American Western Interior foreland basin: New biostratigraphic results from ostracod correlations and early mammals, and their implications for paleontology and geology of the basin—An overview

    NASA Astrophysics Data System (ADS)

    Sames, Benjamin; Cifelli, Richard L.; Schudack, Michael E.

    2010-08-01

    The timespan represented by the hiatus between nonmarine Upper Jurassic (Early Berriasian?) and unconformably overlying Lower Cretaceous deposits throughout the North American Western Interior foreland basin has been under discussion for the entire 20th century and remains controversial to date. Ongoing research in revision of Early Cretaceous nonmarine ostracods of some respective North American formations leads to a breakthrough concerning the verification of their biostratigraphic utility as well as their subsequent application. These ostracods are not as endemic as hitherto believed and can be used for supraregional and regional correlation, as well as improvement of the age determination of North American units. New results strongly suggest a maximum age of Late Berriasian to Valanginian (˜ 142-138 Ma) for the lower part of the Lakota (Black Hills area, South Dakota) and Cedar Mountain (Utah) formations. A pre-Aptian maximum age for the Lakota Formation is supported by early mammals. These biostratigraphic results affect the correlatable formations as well, and therefore have broad implications on basin-related geologic and paleontologic topics that are overviewed and discussed herein. The central issue hampering an integrated synthesis of the foreland basin is its yet imprecise chronostratigraphic framework and documentation. Temporal relationships between the gologic processes of the basin and their control factors are still insufficiently calibrated or controversial. Detailed ongoing revision of North American Early Cretaceous nonmarine ostracods demonstrates their applicability, utility, and further potential as tool for improvement of the chronostratigraphy of the Western Interior foreland basin at both small and large scales. These ostracods also foster understanding of animal (e.g. early mammals and dinosaurs) and plant (angiosperms) evolution on the North American continent and show promise of providing age determinations for single-sample horizons in

  20. Cenozoic tectonic evolution of the Alto Tunuyán foreland basin above the transition zone between the flat and normal subduction segment (33°30' 34°S), western Argentina

    NASA Astrophysics Data System (ADS)

    Giambiagi, Laura B.; Tunik, Maisa A.; Ghiglione, Matías

    2001-12-01

    The Alto Tunuyán basin is a Neogene foreland basin located between Cordillera Principal and Cordillera Frontal, from 33°30' to 34°00' south latitude. At this latitude, the feature that characterizes the subduction geometry beneath the Andean Cordillera is a transition in the slab dip from nearly horizontal, north of 33°S, to normal dip, south of 34°S. This particular tectonic setting apparently controlled the Neogene tectonic history of the area. The Neogene sedimentary infill of the basin is represented by the Tunuyán Conglomerate and the Palomares, Butaló, and Papal formations. Thrusting and uplift of the Cordillera Principal began during the early Miocene. Deformation and uplift of the volcanic arc, located on the western part of the thrust belt, produced the sediment source for the lower 200 m of the Tunuyán Conglomerate. As deformation migrated progressively eastward during middle Miocene times, it involved the underlying Mesozoic sequences, the erosion of which provided the material accumulated in the rest of the Tunuyán Conglomerate. The Palomares Formation unconformably overlying the former unit reflects the uplift of Cordillera Frontal. Deposition of the Butaló and Papal formations over the partially deformed broken foreland basin reflects accumulation during a period of tectonic quiescence and low rate of erosion in the eastern part of Cordillera Principal and the western part of Cordillera Frontal. The basement uplift of Cordillera Frontal generated a sticking point that prevented the propagation of the thrust belt toward the foreland. Consequently, out-of-sequence thrusts developed in the Cordillera Principal and the basin was partially cannibalized.

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

    USGS Publications Warehouse

    Blake, B.M., Jr.; 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. 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., Jr.; 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

  4. 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

  5. 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

  6. Glacioeustatic cyclicity of a Pennsylvanian carbonate platform in a foreland basin setting: An example from the Bachende Formation of the Cantabrian Zone (NW Spain)

    NASA Astrophysics Data System (ADS)

    Corrochano, Diego; Barba, Pedro; Colmenero, Juan R.

    2012-03-01

    By analysis of outcrop data, sequence stratigraphy was used to interpret the stratal architecture and evolution of a Moscovian (Pennsylvanian) carbonate platform (Bachende Formation) located in the Variscan foreland basin of the Cantabrian Zone (NW Spain). The Bachende Formation represents a delta-top carbonate platform developed in highly subsiding (average subsidence rate of 254 m/My) distal shelf areas of the basin. It reached a thickness of 650 m and covered an area of ~ 170 km2 (after conservative palinspastic restorations). The platform interior succession is mostly composed of low-relief mound-shaped micritic boundstones, alternating with bioclastic mudstones/wackestones, peloidal-foraminiferal packstones/grainstones, calcareous algal bafflestones and skeletal and ooidal grainstones. Landwards (to the W), carbonate platform beds alternate and interfinger with deltaic sandstones and shallow marine shales. The platform interior consists of three sequences (S1, S2 and S3), ranging from 180 to 230 m in thickness and from 1.3 to 0.5 My in age. These sequences are in turn subdivided into several meter-scale (10.6 m average thickness), high-frequency (110 to 15 ky), subtidal transgressive-regressive cycles. These cycles are bounded by subaerial exposure or marine flooding surfaces and are inferred to be laterally continuous across the platform-top. They vary from mixed carbonate-siliciclastic to carbonate-dominated cycles. Cyclicity on the Bachende platform was strongly influenced by glacioeustatic sea level variations and changes in subsidence and sedimentation rates. Subaerial exposure surfaces capping high-frequency cycles are better developed in the sequence 1 (late Kashirian/early Podolskian), when subsidence was relatively low and glacioeustatic sea level fluctuations could have exposed subtidal deposits during base-level falls. On the basis of the conservative estimated duration of each cycle and spectral analysis of cycle thickness, the precessional (~ 20

  7. 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

  8. 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.

  9. 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

  10. 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.

  11. Hydrocarbon accumulations in the Tarim basin, China

    SciTech Connect

    Li Desheng; Liang Digang; Jia Chengzao; Wang Gang

    1996-10-01

    The Tarim basin is the largest and least explored inland basin in China. The areal extent of the basin reaches 560,000 km{sup 2}. The interior of the basin is mostly covered by the Takla Mekan Desert, which is about 330,000 km{sup 2} in areal extent. The basin has become the object of special attention since China set aside first- and third-round onshore bidding blocks in the Tarim basin for foreign oil firms to explore. The Tarim basin is a polyhistory superimposed basin that has experienced seven evolutionary stages: (1) Sinian-Cambrian-Ordovician aulacogen stage, (2) Silurian-Devonian intracratonic depression stage, (3) Carboniferous marginal sea stage, (4) Permian rift basin stage, (5) Triassic-Jurassic foreland basin stage, (6) Cretaceous-Paleogene NeoTethys bay stage, and (7) Neogene-Pleistocene foreland and inland basin stage. Both the basin`s Paleozoic marine platform sequences and the Mesozoic-Cenozoic terrestrial fills are believed to contain substantial volumes of hydrocarbons. After recent years of exploration, nine oil and gas fields have been proven and 23 discoveries have been made in the Tabei, Tazhong, and Southwest areas. Kekeya, Lunnan, Sangtamu, Jiefangqudong, Donghetang, and Tazhong 4 oil fields have been put into production. Output of crude oil was 2.6 million t (metric tons) (52,000 BOPD) in 1995. The production will increase to 5 million t (100,000 BOPD) in 1997. Giant oil and gas traps probably will be discovered in the Tarim basin. The prospect is promising.

  12. Fluid history related to the Alpine compression at the margin of the south-Pyrenean Foreland basin: the El Guix anticline

    NASA Astrophysics Data System (ADS)

    Travé, A.; Calvet, F.; Sans, M.; Vergés, J.; Thirlwall, M.

    2000-05-01

    and its deformed southern foreland basin were compartmentalised hydrologically in time and space. During the early Eocene, when the thrust front affected soft-sediment in the Ainsa basin, the thrust faults were dominated by a medium scale fluid flow. The fluids in the basin were basically formation fluids derived from Eocene marine waters trapped in the underlying Eocene marls, although influences of meteoric waters were also present. During the middle Eocene, coeval with the Gavarnie thrust emplacement, the thrust fault was dominated by a medium scale fluid flow. The fluid was basically a hypersaline Sr-rich brine stored within Triassic redbeds. No evidence of a significant input of either surface or metamorphic fluids during thrusting was found. During the same period, in the crystalline basement of the central Pyrenees the thrust faults were dominated by a large scale fluid flow mainly derived from the underlying silicate rocks as a result of metamorphic devolatilisation reactions. During the Oligocene, the most external part of the fold-and-thrust belt developed on top of a salt detachment horizon. The thrust front affected cemented continental materials of late Eocene-Oligocene age. At this moment, the thrusts were conduits for meteoric fluids arriving from the surface and also for evolved meteoric fluids migrating a short distance upwards after being in contact with the underlying evaporitic beds.

  13. Long-to-short term Milankovitch Forcing in a Foreland Basin: The Los Monegros lake system of the Ebro Basin (late Oligocene-Miocene)

    NASA Astrophysics Data System (ADS)

    Valero, L.; Garces, M.; Cabrera, L.

    2012-12-01

    The Ebro basin is particular among the Mediterranean alpine regions because it underwent an endorheic basin from late Eocene to middle Miocene. The cause for this prolonged internally drained regime was the presence of three bounding active thrust belts: the Pyrenees (North), the Iberian Ranges (Southwest) and the Catalan Coastal Ranges (Southeast). Fluvial and alluvial systems fed a central lacustrine system, dominated by evaporitic formations in the central and western sectors, and shallow lake carbonates towards the East. Repeated expansions and retractions of the lake system in the central basinal sectors have lead to an alternation of shallow-lake carbonates and distal alluvial red mudstone units. Magnetostratigraphy-based age control of the Oligocene-early Miocene basin infill allows to suggest long term Milankovitch forcing, spreading of the lacustrine units being related to the 2,4-Myr eccentricity maxima. A detailed study of the latest Oligocene-Miocene lacustrine units of the Monegros system has been carried out in order to decipher the response of the lacustrine systems to higher frequency orbital forcing, with focus on the 100 and 400-kyr eccentricity cycle. A new magnetostratigraphic age model based in new magnetostratigraphic data has been constructed for these sequences. Facies analysis permitted generating a sedimentary model from which a relative paleobathimetry time series has been produced. The resulting spectral analyses in time domain reveal significant peaks matching with the 400-kyr and 100-kyr eccentricity cycle. Assumed our magnetostratigraphy-based age model, a correlation of phases of lacustrine expansion with periods of eccentricity maxima is derived, which is the same phase relationship suggested for the 2.4-Myr megasequential arrangement. We conclude that climate (orbital) forcing controlled the sequential facies arrangement from high to low frequencies of the lacustrine systems of the eastern Ebro Basin. The accumulation of several

  14. 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.

    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.

  15. Metamorphosis in a Silurian barnacle

    PubMed Central

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

    2005-01-01

    Exceptionally preserved fossils from the Wenlock Series (Silurian) of Herefordshire, UK, provide unique evidence of metamorphosis from free-swimming cyprid larva to attached juvenile in a Palaeozoic barnacle. The larva had large brush-like anterior limbs. The juvenile shows the head transformed into a stalk and the development of the primordial condition of five mineralized plates within the carapace. The discovery of a cyprid larva indicates that crown group cirripedes had evolved by the Silurian. PMID:16243697

  16. 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

  17. Nacimiento uplift and its similarity to foreland uplifts with associated production

    SciTech Connect

    Pinnell, M.L.

    1984-07-01

    The Nacimiento mountain front, east flank of the San Juan basin, is a well-documented foreland uplift. Based on detailed surface geology, its northern flank shows strong similarity to the Laramie Range and Owl Creek Mountain-Casper arch foreland uplifts of Wyoming. Petroleum has been discovered beneath these two uplifts by wells drilled through thrusted Precambrian rocks. Recent exploration for petroleum trapped beneath Rocky Mountain foreland uplifts has provided a wealth of geologic and geophysical data not previously available. These recently published data, both from wells and reflection seismic profiles, show surface geology integrated with subsurface geology. Northern Nacimiento uplift surface geology is so similar to these other well-documented foreland uplifts that subsurface anticlines and/or faulted closures are very probably similar to productive subsurface structures under Wyoming's foreland uplifts. Such structures, if present under Nacimiento foreland uplift, could contain significant quantities of hydrocarbons considering the prolific production from stratigraphic traps in the immediately adjacent San Juan basin.

  18. 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.

  19. Early Palaeozoic foreland thrusting and basin reactivation at the Palaeo-Pacific margin of the southeastern Australian Precambrian Craton: a reappraisal of the structural evolution of the Southern Adelaide Fold-Thrust Belt

    NASA Astrophysics Data System (ADS)

    Flöttmann, Thomas; James, Pat; Rogers, Jamie; Johnson, Tim

    1994-06-01

    Regional and detailed structural mapping, kinematic analysis and balancing and restoration of cross sections has lead to a re-interpretation of the Adelaide Fold Belt in South Australia. In this belt sedimentary rocks of the Late Proterozoic Adelaidean and Early Cambrian Normanville and Kanmantoo sequences were deposited during at least two episodes of subsidence related to major crustal attenuation. Contraction and crustal thickening accompanied by granitoid intrusions are related to the Cambro-Ordovician Delamerian orogeny. During this event both basins were reactivated ("inverted") and the sedimentary rocks are now incorporated in a WNW-verging foreland fold and thrust belt at the margin of the Proterozoic southeast Australian craton. Maximal shortening of the orogen was around 55%. Within the Adelaidean basin, shortening is dominantly accommodated by major mylonitic shear zones and reverse faults. In the Cambrian Kanmantoo basin, several thrusts are demonstrably reactivated growth faults, across which thickness changes of Cambrian sedimentary rocks are revealed by balancing and restoration of cross sections. Owing to the steep easterly dips of these faults, in the western part of the Kanmantoo basin lateral shortening of up to 58% is largely accommodated by intense folding and fold axial-planar flattening strain. Further east, strain magnitudes wane and the overall shortening of around 30% is accommodated by both, discrete thrust zones and regional folds. The basin reactivation along the Australian part of Gondwana's palaeo-Pacific craton margin reflects the rapid transition from passive to active tectonism, which possibly is a consequence of the disintegration of the formerly conjugate margins of Gondwana and Laurentia.

  20. Tectonic and thermal history of the western Serrania del Interior foreland fold and thrust belt and Guarico Basin, north central Venezuela: Implications of new apatite fission track analysis and seismic interpretation

    NASA Astrophysics Data System (ADS)

    Perez de Armas, Jaime Gonzalo

    Structural analysis, interpretation of seismic reflection lines, and apatite fission-track analysis in the Western Serrania del Interior fold and thrust belt and in the Guarico basin of north-central Venezuela indicate that the area underwent Mesozoic and Tertiary-to-Recent deformation. Mesozoic deformation, related to the breakup of Pangea, resulted in the formation of the Espino graben in the southernmost portion of the Guarico basin and in the formation of the Proto-Caribbean lithosphere between the diverging North and South American plates. The northern margin of Venezuela became a northward facing passive margin. Minor normal faults formed in the Guarico basin. The most intense deformation took place in the Neogene when the Leeward Antilles volcanic island arc collided obliquely with South America. The inception of the basal foredeep unconformity in the Late Eocene-Early Oligocene marks the formation of a perisutural basin on top of a buried graben system. It is coeval with minor extension and possible reactivation of Cretaceous normal faults in the Guarico basin. It marks the deepening of the foredeep. Cooling ages derived from apatite fission-tracks suggest that the obduction of the fold and thrust belt in the study area occurred in the Late Oligocene through the Middle Miocene. Field data and seismic interpretations suggest also that contractional deformation began during the Neogene, and specifically during the Miocene. The most surprising results of the detrital apatite fission-track study are the ages acquired in the sedimentary rocks of the easternmost part of the study area in the foreland fold and thrust belt. They indicate an Eocene thermal event. This event may be related to the Eocene NW-SE convergence of the North and South American plates that must have caused the Proto-Caribbean lithosphere to be shortened. This event is not related to the collision of the arc with South America, as the arc was far to the west during the Eocene.

  1. 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

  2. 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

  3. 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

  4. 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.

  5. Paleozoic accretionary orogenesis in the Paleo-Asian Ocean: Insights from detrital zircons from Silurian to Carboniferous strata at the northwestern margin of the Tarim Craton

    NASA Astrophysics Data System (ADS)

    Han, Yigui; Zhao, Guochun; Sun, Min; Eizenhöfer, Paul R.; Hou, Wenzhu; Zhang, Xiaoran; Liu, Dongxing; Wang, Bo; Zhang, Guowei

    2015-02-01

    A detrital zircon U-Pb and Lu-Hf isotopic study was carried out in the Middle Silurian to Late Carboniferous sedimentary strata of the northwestern Tarim Craton in order to understand accretionary processes in the southern part of the Central Asian Orogenic Belt. Detrital zircons from these strata yielded U-Pb ages clustering around 2.8-2.3 Ga, 2.0-1.7 Ga, 1.3-0.9 Ga, 880-600 Ma, and 500-400 Ma, with age populations and Hf isotopic signatures matching those of magmatic rocks in the Tarim Craton and the Central Tianshan Block. Abundant 500-400 Ma detrital zircons most likely reflect deposition in a retroarc foreland basin inboard of an Andean-type magmatic arc to the north, supporting the northern Tarim-Central Tianshan connection during early Paleozoic time. The absence of 380-310 Ma zircon population in the Carboniferous siliciclastic rocks suggests that the Central Tianshan Block may have been separated from the Tarim Craton in the Early Devonian, caused by the interarc/back-arc opening of the South Tianshan Ocean. We propose an accretionary orogenic model switching from advancing to retreating mode during Paleozoic time in the southwestern part of the Paleo-Asian Ocean. This transition most likely occurred coevally with the rifting of Southeast Asian blocks from the northeastern margin of Gondwana.

  6. 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.

  7. High-frequency cyclicity in the latest Messinian Adriatic foreland basin: Insight into palaeoclimate and palaeoenvironments of the Mediterranean Lago-Mare episode

    NASA Astrophysics Data System (ADS)

    Cosentino, D.; Cipollari, P.; Lo Mastro, S.; Giampaolo, C.

    2005-07-01

    Late Messinian Lago-Mare deposits show high-frequency cyclicity in the whole Mediterranean Basin. Both millimeter- and centimeter-scale cyclicities have been observed in several ODP sites as well as in stratigraphic sections from the Mediterranean borderland. We have analyzed a well-exposed late Messinian Lago-Mare section from the Adriatic side of the central Apennines (Italy). At the Fonte dei Pulcini section (SE Majella Mts.), millimeter- and centimeter-scale white-and-dark couplets have been observed in the field. A 50 cm regular-spaced sampling has been performed in the uppermost 53 m of the late Messinian Lago-Mare clays. On the 107 collected samples, geochemical (CaCO 3 content), mineralogical (XRD analyses), and micropalaeontological investigations have been performed. In addition, SEM and microprobe investigations as well as mineralogical and micropalaeontological analyses have been carried out on single lamina from a 34-cm-thick interval of millimeter-scale laminites. Besides the 10 3 cycles/m and 10 2 cycles/m frequencies observed in the field, spectral analyses performed on the CaCO 3 data set indicated other high-frequency cyclicities: 0.47 cycles/m, 0.35 cycles/m, and 0.17 cycles/m. Taking into account the estimated sedimentation rate, these frequencies correspond, respectively, to periodicities of: 1 year, 10 years, 2.1 kyr, 2.8 kyr, and 5.6 kyr. These sub-Milankovitch cyclicities have been related to annual and sunspot solar activity. The millimeter-scale couplets are interpreted as varves sedimented in an ephemeral water environment marginal to a perennial brackish water lagoonal basin. These varved sediments reflect a marked seasonality characterized by the alternation of arid and more humid climatic phases. The presence of high values of smectite (60-80%) in the clay minerals of the analyzed samples could be a consequence of these climatic oscillations from drier to moister conditions. The climatic scenario suggested in this paper for the late

  8. Fluvial system response to abrupt climate change: sedimentary record example of the Paleocene-Eocene Thermal Maximum (PETM) in the South-Pyrenean foreland basin, Spain

    NASA Astrophysics Data System (ADS)

    Chen, Chen; Castelltort, Sebastien; Foreman, Brady; Hassenruck-Gudipati, Hima J.

    2015-04-01

    The "Paleocene-Eocene Thermal Maximum" (PETM), is understood to be an extreme and short-lived (ca.150-220kya) global warming event that occurred 55.8 million years ago and during which global annual temperatures are estimated to have increased by ca. 5-8°C, with respect to sea surface temperatures and ca. 4-5°C, with respect to the deep sea. A remaining outstanding question is: in addition to the global increase in temperature, how was precipitation perturbed during the event, and how did fluvial surface processes respond to the perturbation? In the southern Spanish Pyrenees, the Paleocene succession of the Tremp-Graus Basin is made up of the Talarn (Danian) and Esplugafreda (Thanetian) red bed formations. The Esplugafreda section is composed of approximately 250m of reddish paleosols and contains numerous lenticular bodies of calcareous conglomerates, which are interpreted as braided channels. The Esplugafreda Formation is overlain by the Claret Conglomerate -- an extensive sheet-like unit which ranges in thickness between 1m and 4m of clast-supported calcareous conglomerate and pebbly calcarenites and is interpreted as marking the fluvial response to a dramatic climate change, in the form of the transformation of a braided river and floodplain system into an enormous conglomeratic braided plain (formed over at least 2000km2 conservatively) due to dramatic change in the hydrologic cycle. The conglomerate unit ends abruptly and is overlaid by fine-grained yellowish soils which are mainly made up of silty mudstones with abundant small size carbonate nodules suggesting another shift in the hydrological cycle after the PETM. Here we present paleo-channel geometry and grain size data collected in the southern Pyrenees (Tremp, Aren, and Serraduy sections) that we invert to reconstruct paleoflow conditions during the Paleocene and during the Paleocene-Eocene Thermal Event. We confront paleohydraulic results with sea level, isotope and lithological records in order to

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  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.

    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. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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

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

    PubMed

    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

  4. 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

  5. A Silurian soft-bodied biota

    USGS Publications Warehouse

    Mikulic, Donald G.; Briggs, D.E.G.; Kluessendorf, Joanne

    1985-01-01

    A new Silurian (Llandoverian) biota from Wisconsin with a significant soft-bodied and lightly sclerotized component is dominated by arthropods and worms. The fauna includes the earliest well-preserved xiphosure, a possible marine uniramian, three new arthropods of uncertain affinity, and possibly the first Paleozoic leech. This may be only the second locality to yield a conodont animal. Lack of a normal shelly fauna suggests an unusual environment. The discovery adds significantly to the few such exceptionally preserved faunas known from Lower Paleozoic rocks.

  6. 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

  7. Sperm carriers in Silurian sea scorpions.

    PubMed

    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. PMID:21892606

  8. 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.

  9. 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

  10. 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.

  11. 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).

  12. Silurian geology of the Des Plaines River Valley, northeastern Illinois

    NASA Astrophysics Data System (ADS)

    Mikulic, D. G.; Sargent, M. L.; Norby, R. D.; Kolata, D. R.

    Silurian dolomites are among the most poorly understood rock units in the midwestern United States. These rocks have not attracted as much interest as those in other Paleozoic systems for several reasons. Destruction of primary fabric by dolomitization discourages sedimentological studies, carbonate buildups complicate local correlations. However, the development of large, deep quarries has advanced the understanding of the lithostratigraphy of Silurian rocks, particularly in northeastern Illinois, where the growth of the Chicago area has supported a large stone industry for the last 150 years. This field trip provides a good overview of Chicago-area Silurian geology.

  13. 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.

  14. Distal Limits and Composition of a Late Ordovician (Mohawkian) Biotite-Bearing Volcanic ash, Foreland Carbonate Platform (Verulam Formation), Ottawa Embayment: Helping to Define Magmatic Change in Volcanism Following Later Platform Foundering

    NASA Astrophysics Data System (ADS)

    Al-Delami, M.; Dix, G. R.

    2009-05-01

    burial temperatures of 130oC, in keeping with burial temperature estimates according to conodont alteration indices (CAI = 3) for the host carbonate platform succession. The MgO and FeO % of biotites from these beds plot within the same field as the slightly older Millbrig and Deike bentonites that also represent ash deposition within shallow-water carbonate platform environments from widespread Late Ordovician eruptions that occurred along the foreland basin margin. Collectively, these compositions are higher in FeO and lower in MgO % values compared those associated with a bentonite within the overlying Taconic foreland shale succession of the Ottawa Embayment, and bentonites in Lower Silurian successions of western Europe. This contrast strengthens a previous hypothesis (Sharma et al., 2005) that there was significant change in magmatic composition along the Taconic arc following or coincident with foundering of the foreland carbonate platform.

  15. 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.

  16. 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.

  17. 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.

  18. Late Ordovician to Early Silurian amalgamation of the Dalradian and adjacent Ordovician rocks in the British Isles

    NASA Astrophysics Data System (ADS)

    Bluck, B. J.; Leake, Bernard E.

    1986-11-01

    From detailed radiometric and pressure-temperature estimates of the metamorphic history, uplift, and erosion of the Dalradian rocks of the British Isles, we find that 15 25 km of erosion took place mainly in Ordovician time. None of this vast volume of material is apparently present in the Ordovician sedimentary basins that now flank the Dalradian block. We conclude that the Ordovician basins to the south of the Dalradian block are exotic terranes, and we document their emplacement into their present position during Late Ordovician to Early Silurian time (i.e., Taconic) by using evidence mainly from western Ireland.

  19. 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.

  20. 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

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  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. 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.

  10. 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

  11. Silurian clastic sediments in the North Qilian Shan, NW China: Chemical and isotopic constraints on their forearc provenance with implications for the Paleozoic evolution of the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Yan, Z.; Xiao, W. J.; Windley, B. F.; Wang, Z. Q.; Li, J. L.

    2010-11-01

    The North Qilian Shan is an accretion-collision orogenic belt in the northeastern margin of the Tibetan Plateau that connects the North China plate to the north with the Tethyan orogenic assemblage to the south. Its Early Paleozoic temporal-spatial tectonic evolution has been extensively studied, but the nature and tectonic setting of its Silurian deposition is poorly understood. Our new petrological analysis suggests that the clast composition of fan conglomerates is complex. In the Danbanshan and Zhongdabanshan sections, abundant lenticular conglomerate beds contain mainly subrounded-rounded metamorphic clasts; whereas the Tongziba and Haichaoba sections contain volcanic, chert, limestone, ultramafic and granitoid clasts. However, in the Sunan area, clast types are relatively simple, dominated by basalt and granitoids, and at Tongziba gabbro and basalt clasts are subrounded and angular, indicating two different types of provenance. Ultramafic, limestone and abundant chert clasts in the Haichaoba and Tonghe conglomerates indicate an ophiolitic source, whereas subrounded-rounded quartzite and granitoid gneiss clasts were probably derived from the Central Qilian basement. Geochemical data from the volcanic and granitoid clasts suggest an arc-related source and their zircon U-Pb ages of 515-429 Ma suggest that the arc magmatism did not end in the Mid-Silurian. Sandstone petrology and detrital modes suggest that the Silurian sediments were deposited in a forearc basin. Paleogeographic reconstructions inferred from NNW-NNE paleocurrent data indicate that an island arc was present off the southern margin of the Silurian basin, and that southward subduction of oceanic crust between North China and the Qilian Shan was active or continued in the Silurian.

  12. The effect of drainage reorganization on paleoaltimetry studies: An example from the Paleogene Laramide foreland

    NASA Astrophysics Data System (ADS)

    Davis, Steven J.; Wiegand, Bettina A.; Carroll, Alan R.; Chamberlain, C. Page

    2008-11-01

    Using multiple isotope systems, we examine the complex effects of drainage reorganization in the Laramide Foreland in the context of stable isotope paleoaltimetry. Strontium, oxygen and carbon isotopic data from lacustrine carbonates formed in the southwestern Uinta Basin, Utah between the Late Cretaceous and late Middle Eocene reveal a two stage expansion in the drainage basin of Lake Uinta beginning at ~ 53 Ma culminating in the Mahogany highstand at 48.6 Ma. A marked increase in 87Sr/ 86Sr ratios of samples from the Main Body of the Green River Formation is interpreted as the result of water overflowing the Greater Green River Basin in Wyoming and entering Lake Uinta from the east via the Piceance Creek Basin of northwestern Colorado. This large new source of water caused a rapid expansion of Lake Uinta and was accompanied by a significant and rapid increase in the O isotope record of carbonate samples by ~ 6‰. The periodic overspilling of Lake Gosiute probably became continuous at ~ 49 Ma, when the lake captured low- δ18O water from the Challis and Absaroka Volcanic Fields to the north. However, evaporation in the Greater Green River and Piceance Creek Basins meant that the waters entering Lake Uinta were still enriched in 18O. By ~ 46 Ma, inflows from the Greater Green River Basin ceased, resulting in a lowstand of Lake Uinta and the deposition of bedded evaporites in the Saline Facies of the Green River Formation. We thus show that basin development and lake hydrology in the Laramide foreland were characterized by large-scale changes in Cordilleran drainage patterns, capable of confounding paleoaltimetry studies premised on too few isotopic systems, samples or localities. In the case of the North American Cordillera of the Paleogene, we further demonstrate the likelihood that (1) topographic evolution of distal source areas strongly influenced the isotopic records of intraforeland basins and (2) a pattern of drainage integration between the hinterland and

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. Cenozoic detachment folding in the southern Tianshan foreland, NW China: Shortening distances and rates

    NASA Astrophysics Data System (ADS)

    Tian, Zhonghua; Sun, Jimin; Windley, Brian F.; Zhang, Zhiliang; Gong, Zhijun; Lin, Xu; Xiao, Wenjiao

    2016-03-01

    Intracontinental foreland basins with fold-and-thrust belts on the southern periphery of the Tianshan orogenic belt in China resulted from still-active contractional deformation ultimately cased by the India-Asia collision. To quantify the amounts of shortening distance and the rates of deformation, and to decipher the architectural framework, we mapped the stratigraphy and structure of four anticlines in the Kuqa and Baicheng foreland thrust belts in the central southern Tianshan. In the Baicheng foreland thrust belts, Lower Cretaceous Baxigai and Bashijiqike Formations located in the core of the Kumugeliemu anticline are overlain by the Paleocene to Eocene Kumugeliemu Formation, above which are conformable Oligocene through Pleistocene sediments. A disharmonic transition from parallel to unconformable bedding at the boundary of the Miocene Kangcun and Pliocene Kuqa Formations suggests a change from pre-detachment folded strata to beds deposited on top of a growing anticline. Most of the anticlines have steep limbs (70-90°) and are box to isoclinal folds, suggestive of detachment folding or faulted detachment folding (faults that transect a fold core or limb). Shortening estimates calculated from the cross-sections by the Excess area method indicate that the total shortening for the Kelasu, Kuchetawu, Kezile and Yaken sections are 6.3 km, 6.4 km, 5.8 km and 0.6 km, respectively, and the respective depths of the detachment zones are (2.3 km and 6.9 km), 2.3 km, 2.5 km and 3.4 km. Time estimates derived from a paleomagnetic study indicate that the transition to syn-folding strata occurred at ∼6.5 Ma at the Kuchetawu section along the Kuqa river. In addition, according to our field observations and previous sedimentary rate studies, the initial time of folding of the Yaken anticline was at 0.15-0.21 Ma. Therefore, the average shortening rate that began at ∼6 Ma was ∼2 mm/a for the Kelasu, Kuchetawu and Kezile sections. At 0.15-0.21 Ma, the average shortening

  20. Tectonic evolution and oil and gas of Tarim basin

    NASA Astrophysics Data System (ADS)

    Yuzhu, Kang; Zhihong, Kang

    According to the new results achieved in the past ten years and more, using mobilism and the theory of polycycle by Huang Jiqing (1977, 1984), the formation of the basement of the Tarim basin and its characteristics are summarized. The prototype basins formed since Sinian times are classified into rift basin, continental marginal basin, cratonic basin, foreland basin and others. The Tarim basin is regarded as a huge oil- and gas-bearing basin superposed by prototype basins of different ages. The tectonic characteristics of these basins including tectonic movements, tectonic migrations, faults and trap types are summarized. In addition, structural control over oil and gas and oil-forming features are analysed.

  1. 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

  2. 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.

  3. Palaeontological evidence bearing on global Ordovician-Silurian continental reconstructions

    NASA Astrophysics Data System (ADS)

    Fortey, Richard A.; Cocks, L. Robin M.

    2003-06-01

    The discreteness or otherwise of major Ordovician and Silurian terranes can be recognised by the shallow-water benthic faunas which lived upon them. Their borders are often indicated by the disposition of progressively shallow- to deep-water assemblages at the terrane edge as well as by structural features. Their positions relative to each other in the Early Palaeozoic can be best indicated by a combination of palaeomagnetic and faunal evaluation: the latter is the topic of this paper. Faunal evaluation is now possible quantitatively as well as quantitatively. Global palaeobiogeography is reviewed for the period as deduced from faunal evidence. There was one supercontinent, Gondwana, which stretched from West Gondwana (today's southern Europe and North Africa) at high latitudes to tropical East Gondwana (Australasia and adjacent areas), with intermediate palaeolatitudes in the Middle East and South America. Around Gondwana, especially to its north, were a large number of peri-Gondwanan terranes, particularly Avalonia, Perunica, parts of Turkey and Arabia and Sibumasu. In addition, there were the substantial independent continents of Laurentia, Baltica, Siberia, Annamia, North China and South China. Analysis of the shallow-water benthos, particularly trilobites and brachiopods, provides distinctive signatures for palaeo-position in most cases. Despite a large faunal turnover particularly corresponding with the latest Ordovician glacial event, the progressive evolution of the ecologies of benthic shelly faunas were also much influenced by changing geographies during the 80-Ma period. In the early Ordovician, oceans were at their widest, enabling Baltica and Laurentia to have different signatures from either East or West Gondwana. Siberia in early Ordovician times had faunal contact with Laurentia and East Gondwana, but in the mid-Ordovician, there were more endemics, and by the late Silurian, it was the only continent of substance in the northern hemisphere (hosting

  4. The paradox of vertical σ2 in foreland fold and thrust belts

    NASA Astrophysics Data System (ADS)

    Tavani, Stefano

    2014-05-01

    Occurrence of aesthetically appealing thrust systems and associated large scale anticlines, in both active and fossil foreland fold and thrust belts, is commonly interpreted as an evidence for Andersonian compressional framework. Indeed, these structures would testify for a roughly vertical σ3. Such a correlation between thrusts occurrence and stress field orientation, however, frequently fails to explain denser observations at a smaller scale. The syn-orogenic deformation meso-structures hosted in exposed km-scale thrust-related folds, in fact, frequently and paradoxically witness for a syn-thrusting strike-slip stress configuration, with a near-vertical σ2 and a sub-horizontal σ3. This apparent widespread inconsistency between syn-orogenic meso-structures and stress field orientation is here named "the σ2 paradox". A possible explanation for such a paradox is provided by inherited extensional deformation structures commonly developed prior to thrusting, in the flexural foreland basins located ahead of fold and thrust belts. Thrust nucleation and propagation is facilitated and driven by the positive inversion of the extensional inheritances, and their subsequent linkage. This process eventually leads to the development of large reverse fault zones and can occur both in compressive and strike-slip stress configurations.

  5. 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

  6. Cenozoic thrust emplacement of a Devonian batholith, northeastern Brooks Range: Involvement of crystalline rocks in a foreland fold-and-thrust belt

    SciTech Connect

    Wallace, W.K.; Hanks, C.L. )

    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.

  7. A chrono-tectonostratigraphic framework for the Sydney Basin

    NASA Astrophysics Data System (ADS)

    Mohammad, O. A.; Jones, B. G.; Fergusson, C. L.

    2013-12-01

    The Sydney Basin is a foreland basin forming the southern part of the Bowen-Gunnedah-Sydney Basin system in Eastern Australia. Tectonically the Sydney Basin is regarded as a retro-arc foreland basin that developed through Late Carboniferous to Middle Triassic. Constructing a tectonstratigraphic framework for the basin is difficult due to the complex stratigraphy and poor age control, along with its complex tectonic history. A chrono-tectonostratigraphic framework for the Sydney Basin is presented based on literature synthesis combined with new data analysis. The chrono-tectonostratigraphic framework will provide an up-to-date and easy to follow detailed basin history which can be utilize in the exploration for conventional and unconventional resources in the Sydney Basin.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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.

  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.

    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

  2. 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

  3. 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

  4. Tectonic setting and origin of the Black Warrior basin

    SciTech Connect

    Thomas, W.A.; Whiting, B.M. . Dept. of Geological Sciences)

    1994-03-01

    The Black Warrior basin has a triangular outline that is framed by the Ouachita thrust belt on the southwest, the Appalachian thrust belt on the southeast, and the North American craton on the north. The stratigraphy of the Black Warrior basin includes two distinct parts: a Cambrian-Mississippian passive-margin carbonate-shelf succession, and a Mississippian-Pennsylvanian clastic succession, the lower (Mississippian) part of which grades northeastward into a carbonate-shelf facies. The provenance and dispersal system of the Mississippian-Pennsylvanian clastic deposits have been interpreted in four different ways, each of which has significantly different implications for origin of the basin: (1) Ouachita orogenic source and northeastward prograding; (2) Alabama Appalachian orogenic source and northwestward prograding; (3) Georgia-tennessee Appalachian orogenic source and westward prograding; and (4) cratonic source and southward prograding. Subsidence history determined from calculations of decompacted thickness indicates that (1) the Black Warrior basin is an orogenic foreland basin related primarily to the Ouachita thrust load on the southwest; (2) later emplacement of the Alabama Appalachian thrust belt modified the southeastern side of the Ouachita-related Black Warrior foreland basin; and (3) a separate foreland basin, representing the southern end of the Appalachian foreland basin, formed in response to the Georgia-Tennessee Appalachian thrust load. The previously used criteria do not necessarily support a unique interpretation, but synthesizing these data with subsidence history leads to the conclusion that the Black Warrior basin is a tectonically driven, orogenic foreland basin dominated by Ouachita thrusting and modified by Appalachian thrusting.

  5. 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

  6. New Insights into Arctic Tectonics: Uranium-Lead, (Uranium-Thorium)/Helium, and Hafnium Isotopic Data from the Franklinian Basin, Canadian Arctic Islands

    NASA Astrophysics Data System (ADS)

    Anfinson, Owen Anthony

    More than 2300 detrital zircon uranium-lead (U-Pb) ages, 32 176Hf/177Hf (eHf) isotopic values, 37 apatite helium (AHe) ages, and 72 zircon helium (ZHe) ages represent the first in-depth geochronologic and thermochronologic study of Franklinian Basin strata in the Canadian Arctic and provide new insight on >500 M.y. of geologic history along the northern Laurentian margin (modern orientation). Detrital zircon U-Pb age data demonstrate that the Franklinian Basin succession is composed of strata with three distinctly different provenance signatures. Neoproterozoic and Lower Cambrian formations contain detrital zircon populations consistent with derivation from Archean to Paleoproterozoic gneisses and granites of the west Greenland--northeast Canadian Shield. Lower Silurian to Middle Devonian strata are primarily derived from foreland basin strata of the East Greenland Caledonides (Caledonian orogen). Middle Devonian to Upper Devonian strata also contain detrital zircon populations interpreted as being primarily northerly derived from the continental landmass responsible for the Ellesmerian Orogen (often referred to as Crockerland). U-Pb age data from basal turbidites of the Middle to Upper Devonian clastic succession suggest Crockerland contributed sediment to the northern Laurentian margin by early-Middle Devonian time and that prior to the Ellesmerian Orogeny Crockerland had a comparable geologic history to the northern Baltica Craton. Detrital zircon U-Pb ages in Upper Devonian strata suggest Crockerland became the dominant source by the end of Franklinian Basin sedimentation. Mean eHf values from Paleozoic detrital zircon derived from Crockerland suggest the zircons were primarily formed in either an island arc or continental arc built on accreted oceanic crust setting. ZHe cooling ages from Middle and Upper Devonian strata were not buried deeper than 7 km since deposition and suggest Crockerland was partially exhumed during the Caledonian Orogen. AHe cooling ages

  7. 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.

  8. 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. PMID:22967511

  9. 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.

  10. 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

  11. 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.

  12. Origin of the Upper Ordovician-lower Silurian cherts of the Yangtze block, South China, and their palaeogeographic significance

    NASA Astrophysics Data System (ADS)

    Ran, Bo; Liu, Shugen; Jansa, Luba; Sun, Wei; Yang, Di; Ye, Yuehao; Wang, Shiyu; Luo, Chao; Zhang, Xuan; Zhang, Changjun

    2015-08-01

    Volcanic rocks, black shales, calcareous sandstones and cherts occur in the Wufeng and Longmaxi formations, which cross late Katian through Rhuddanian exposed along the northern and central part of the Yangtze block, South China. The evidence provided by radiolarite occurrences, sedimentological features and immobile elements indicate that the silica in these rocks is sedimentary and not of hydrothermal origin. Precursors of chert were deposited on a continental margin, or in a deeper basin on the shelf, during blooms of radiolarians and times of decreased clastic input. Interbedded volcanic tuffs of rhyolitic to andesitic composition suggest the presence of a continental volcanic arc to the east-southeast. The large regional extent of bentonites documents explosive volcanicity resulting in silica saturation of waters, leading to high bioproductivity and radiolarian blooms. Deepening of the sedimentary environment is most probably the result of orogenesis generated by an accretion of the Cathaysia Block to the Yangtze Block during the Ordovician-Silurian transition. Increasing water depth together with a decrease in clastic input contributed to the development of the radiolarian cherts in the basin.

  13. 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.

  14. Biogeography of late Silurian and devonian rugose corals

    USGS Publications Warehouse

    Oliver, W.A., Jr.

    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.

  15. 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.

  16. Spacing of Rocky Mountain foreland arches and Laramide magmatic activity

    SciTech Connect

    Schmidt, C.J.; Evans, J.P.; Fletcher, R.C.; Spang, J.H.

    1985-01-01

    First-order Late Cretaceous and Paleocene folds in the Rocky Mountain foreland have a spacing (S) ranging from 45 to 300 km. Spacing of folds and major mountain flank thrusts was controlled in part by the depth of the brittle-ductile transition (BDT). Analysis of folding of a brittle layer of thickness H above a ductile substrate suggests S/H approx. = 4-6. Experimental data indicate that the BDT in quartz rich rock occurs at 300/sup 0/ +/- 50/sup 0/C and therefore its depth depends on geothermal gradient. Regions with high Laramide geothermal gradients should have had a shallower depth to the BDT and a shorter spacing of first-order folds than regions with low gradients. A regional compilation for the Montana and Wyoming foreland shows a correlation between the value of S and syntectonic magmatic activity. The mean S value for southwestern Montana, where Late Cretaceous and Paleocene magmatic activity was widespread, is 65 km. This value of S indicates a relatively shallow (11-16 km) depth of the BDT and suggests a relatively high (16-32/sup 0/C/km) Laramide geothermal gradient. The mean S value for the Wyoming foreland, where no syntectonic magmatic activity is indicated, is 150 km. Measurements of S may allow some predictions of depth to rheologically-controlled mid-crustal decoupling zones. They may also indicate areas where the depth to the BDT was not a major control on S. Structures with S < 40 km correspond to inadmissably shallow BDT zones and were probably controlled by other factors such as preexisting fault zones or basement lithology.

  17. Geomorphic characteristics of the Lannemezan megafan: an insight in the Late-Cenozoic evolution of the northern Pyrenean foreland (France)

    NASA Astrophysics Data System (ADS)

    Mouchené, Margaux; van der Beek, Peter; Mouthereau, Frédéric; Carcaillet, Julien

    2014-05-01

    Large alluvial fans, either active or incised, characterize the orogen - foreland-basin transition in nearly all mountain belts worldwide. Understanding the evolution of fossil foreland alluvial fans and the incision history of their elevated paleo-surfaces can provide critical information on their past and present evolution and to distinguish between climatic and tectonic forcing. The most striking morpho-sedimentary feature of the northern Pyrenean foreland (SW France) is the Miocene Lannemezan megafan, but little is known about its evolution: what controlled the development of this fan and how is this related to the orogenic growth? When and why was the fan abandoned and incised? How large was the feature when it was active? We combine a quantitative morphometric analysis with field observations, low-temperature thermochronometry and cosmogenic dating to address these questions. The Lannemezan fan is exceptionally large (104km2), especially when compared to the other fans of the northern Pyrenean foreland and the fan area/catchment area ratio is anomalous. Calculations of the eroded vs. deposited volumes corroborate this unbalanced budget. The Neste River, which most likely used to feed the megafan, now bends 90° eastwards near the apex of the fan, indicating it was captured by the larger Garonne River in Quaternary times. The material forming the fan and the strath terrace system incising the fan, show a rather unusual sedimentological pattern for an alluvial fan setting, characterized by a very fine clay and sand matrix supporting sporadic pebbles and boulders (up to 50 cm in diameter). We show that the terrace slope increases with time and the current rivers exhibit markedly concave long profiles (reference concavity = 0.7), which could indicate late tilting of the fan. New cosmogenic nuclide analysis (10Be,26Al) will be used to date the abandonment of the fan surface and the terrace staircase chronology to provide constraints on incision rates and

  18. 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

  19. 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.

  20. Slab rollback orogeny in the Alps and evolution of the Swiss Molasse basin

    NASA Astrophysics Data System (ADS)

    Schlunegger, Fritz; Kissling, Edi

    2015-10-01

    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.

  1. 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

  2. Slab rollback orogeny in the Alps and evolution of the Swiss Molasse basin.

    PubMed

    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

  3. 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.

  4. 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

  5. Geometry and evolution of the frontal part of the Magallanes foreland thrust and fold belt (Vicuna Area), Tierra del Fuego, southern Chile

    SciTech Connect

    Alvarez-Marron, J.; McClay, K.R. ); Harambour, S.; Rojas, L.; Skarmeta, J. )

    1993-11-01

    The Magallanes foreland thrust and fold belt is a thin-skinned foreland thrust and fold belt of Paleocene to Oligocene age that deforms Upper Jurassic through Tertiary volcanic, volcaniclastic, and siliciclastic strata of the Magallanes basin, southern Andean Cordillera, Chile. This paper is a detailed description and analysis of the geology and structural evolution of the thrust front (Vicuna area of southern Tierra del Fuego). Reflection seismic and well data, together with 1:50,000 scale geological mapping, have been used in the analysis. In the southern part of the Vicuna area, two different thrust systems have been found: an upper imbricate fan that deforms Upper Jurassic and Cretaceous strata, and a younger, lower duplex composed of Cretaceous and probably Upper Jurassic rocks. The imbricate fan is characterized by fault-propagation folding in which listric thrust faults merge downward into a sole thrust that probably is located within the Upper Jurassic stratigraphy. The sole thrust of the upper imbricates forms the roof thrust of the underlying duplex. In the northern part of the Vicuna area, the syntectonic sedimentary wedge of the foredeep consists of Late Cretaceous through Tertiary siliciclastics that have been deformed and uplifted by passive back thrusting at the triangle zone. The structural style in the foreland region shows three main subhorizontal detachment levels located within the sedimentary wedge as a result of the progressive transfer of slip from the thrust belt to the foreland. Minor blind thrusts produce stacked [open quotes]pop up[close quotes] and triangle structures that result in complex geometries in the cores of anticlines. A forward-breaking sequence of thrusting is interpreted. During deformation, the active foredeep wedge migrated at least 10 km northward. Balanced geological cross sections indicate approximately 60% (-30 km) shortening for this part of the Magallanes thrust belt.

  6. Chemostratigraphy of the Silurian Qusaiba Member, Eastern Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Craigie, Neil W.

    2016-01-01

    Given the unavailability of high resolution biostratigraphic data and difficulties in using lithostratigraphy for stratigraphic correlation, it was decided to employ chemostratigraphy to propose a scheme for the Silurian Qusaiba Member encountered in five wells in Eastern Saudi Arabia. Chemostratigraphy may be defined as a reservoir correlation technique involving the utilization of inorganic geochemical data. Although Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) were used to acquire data for 50 elements, the scheme is based on changes in the following 'key' element ratios: Zr/Th, Cr/Ti, Th/Nb, Zr/P, Y/Yb, Zr/Yb and Y/P. Variations in these parameters are largely dependent on changes in source/provenance, reflecting increases or decreases in the abundances of particular detrital heavy minerals. The scheme comprises a hierarchical order of four zones, seven subzones and four divisions. The zones are labelled C1, C2, C3 and C4 is ascending stratigraphic order, with two, three and two subzones identified in C2, C3 and C4 respectively. In addition to this, chemostratigraphic divisions are noted in two of the subzones. The chemostratigraphic scheme is considered robust as chemozones (general term used to describe any zone, subzone or division) are clearly defined in each well using geochemical profiles and binary diagrams plotted for key element ratios. Furthermore, high levels of statistical confidence are associated with the chemozones and most are correlative between three or more wells. The nonexistence of chemozones in particular wells is mainly explained by the sampling strategy employed. For example, the absence of subzone C3-2 (occurring towards the center of zone C3) in wells 4 and 5 is most likely to be explained by the uppermost part of the Qusaiba Member not being sampled. In other instances, particular chemozones may be missing as a result of erosion/non-deposition on a

  7. Biodiversity and endemism of the Silurian vertebrates in the Siberian palaeocraton

    NASA Astrophysics Data System (ADS)

    Žigaitä-, Živilä--

    2010-05-01

    Vertebrate fossil record in the Silurian successions of northwestern Mongolia, Tuva, central and southern parts of the East Siberia between Yenisey and Lena rivers (Siberian platform) comprises large diversity of endemic fish species and genera. All this present day terrirories are infered to have been existed as united Siberian palaeocraton, an independent geological terrane in the Palaeozoic. Comparative isolation of the Siberian palaeocontinent throughout the Palaeozoic also meant that the area was colonised by marine faunas, which are not found elsewhere on Earth (Cocks & Torsvik, 2007). A separate palaeobiogeographical province has been suggested, and can be confirmed by the abundance, content, and distribution of early fish. Majority of vertebrate groups, such as thelodonts and acanthodians, reported from the region (Karatajūtė-Talimaa, 1978; Karatajūtė-Talimaa & Smith, 2003; Žigaitė, in press) are diverse, abundant and restricted to the province, showing palaeobiogeographical unity of the territory. Distinct in their taxonomic content, but less common are chondrichthyans (Žigaitė & Karatajūtė-Talimaa, 2008). Finally, the most peculiar types of early vertebrates as mongolepids, tesakoviaspids, and tesserated galeaspids (Afanasieva & Janvier, 1985; Karatajūtė-Talimaa et al., 1990; Karatajūtė-Talimaa & Smith, 2004; Karatajūtė-Talimaa & Žigaitė, 2005), also specific heterostracans refer the region to strong faunal endemism and favours consideration of the separate palaeobiogeographical province. The biodiversity of vertebrates indicates warm and productive palaeobasins, which most likely have been existed as well connected epeiric seas on the integral Siberian palaeocraton. It might have been a proper place for origin and radiation of at least some early vertebrates in the Silurian (Žigaitė & Blieck, 2006). Nevertheless, recent palaeogeographical studies place Siberia at high northern latitudes, inferring the inherent endemic brachiopod

  8. Positive inversion tectonics in foreland fold-and-thrust belts: A reappraisal of the Umbria-Marche Northern Apennines (Central Italy) by integrating geological and geophysical data

    NASA Astrophysics Data System (ADS)

    Scisciani, Vittorio; Agostini, Simone; Calamita, Fernando; Pace, Paolo; Cilli, Andrea; Giori, Italiano; Paltrinieri, Werter

    2014-12-01

    Unraveling the tectonic style in the outer zones of fold-and-thrust belts is generally puzzling because the basement-cover relationships are often hidden in the subsurface as in the outer Northern Apennines of Italy. This study aims to reconstruct the deep setting of the Northern Apennine foreland thrust belt by integrating surface structural-geological and subsurface seismic reflection profile and well data, corroborated by a gravity-magnetic modeling. A remarkable mountain ridge, the Umbria-Marche Apennine Ridge (UMAR), which corresponds to a prominent area of structural and topographic elevation, characterizes the morphology of the Northern Apennines. This mountain ridge is constituted by Meso-Cenozoic carbonates involved in Neogene compressive structures and is surrounded by wide exposures of foredeep deposits. The basement-cover relationships are poorly constrained and both thin- and thick-skinned tectonic styles have been applied. The interpretation of subsurface data allowed recognizing a thick pre-Jurassic sedimentary sequence filling a late Paleozoic(?)-Triassic symmetric fault-bounded extensional basin, lying directly below the UMAR. This deep-rooted basin underwent positive inversion during the Neogene compression and thrust-fold development. The reconstructed thick-skinned inversion tectonic model is consistent with both the modest amount of shortening and the remarkable structural elevation of the UMAR. The outcomes of this study reveal that prominent mountain ridges occurring in foreland thrust belts are most likely related to the deep-rooted basement-involved positive inversion of pre-existing extensional basins.

  9. 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.

  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. 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. 

  12. Neotectonics and seismic hazard in the northern Alpine foreland (Northern Switzerland and adjacent France and Germany)

    NASA Astrophysics Data System (ADS)

    Schmid, S. M.; Ustaszewski, K.; Deichmann, N.; Müller, W. H.; Slejko, D.

    2003-04-01

    The analysis of the present-day tectonic framework of the northern Alpine foreland is of great importance in terms of (1) the search for host formations for storing high-level and long-lived intermediate and high-level nuclear waste in Northern Switzerland, and, (2) a Probabilistic Seismic Hazard Analysis (PSHA), which re-evaluates the safety of the Swiss Nuclear Power Plant Sites. The recently established close scientific cooperation between pure and applied geosciences led to a growing consensus that deformation linked to Alpine orogeny is still ongoing at present, after having propagated northwards into the Molasse basin and the Jura Mountains in Miocene to Pliocene times. It is not entirely clear yet, how this presently ongoing deformation in the Northern Alpine foreland, associated with convergence rates in the order of 1 mm/a or less, is partitioned between basement (crystalline basement, including Permo-Carboniferous troughs) and the sedimentary cover, the latter being rheologically decoupled along the Triassic evaporites. There is a consensus amongst most authors that classical Jura folding and thrusting was "thin-skinned", i.e. that shortening in the basement was confined to the northern rim of the Alps ("distant push hypothesis"). NW-SE- to N-S directed shortening within the basement migrated northward into Northern Switzerland and adjacent France and Germany since Late Pliocene times, inducing a change from former "thin"- to presently active "thick-skinned" deformation. Its precise extent, however, is uncertain. Knowledge of rate and mode of deformation within the basement is crucial for seismic hazard analysis. The remaining epistemic uncertainty will be built into a Probabilistic Seismic Hazard Analysis. It is hoped that further investigations in the framework of projects EUCOR-URGENT (Upper Rhine Graben: Evolution and Neo-Tectonics) and ENTEC (Environmental Tectonics) will significantly reduce these uncertainties. Knowledge about the seismic source of

  13. 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.

  14. 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.

  15. 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.

  16. Comment on "Comparison of Michigan Basin crude oils" by Vogler et al .

    NASA Astrophysics Data System (ADS)

    Pruitt, J. D.

    1983-06-01

    Data is presented for Michigan Basin oils that indicate, in addition to the three distinct oil types, oils of mixed composition, intermediate between the Silurian and Ordovician types, also exist. These mixed oils which occur in Devonian (Detroit River) reservoirs are identified primarily by their isoprenoid and normal paraffin compositions.

  17. Geologic evolution of Uinta-Piceance basin province, northwestern Colorado and northeastern Utah

    SciTech Connect

    Johnson, S.Y.; Tuttle, M.L.; Bryant, B.H.; Dubiel, R.F.; Fouch, T.D.; Franczyk, K.J.; Grauch, V.J.S.; Grout, M.A.; Johnson, R.C.; Molenaar, C.M.; Nichols, D.J.; Nichols, K.M.; Nuccio, V.F.; Peterson, F.; Pitman, J.K.; Perry, W.J. Jr.; Potter, C.J.; Sawatzky, D.L.; Scott, R.W. Jr.; Verbeek, E.R.; Wanty, R.B. )

    1990-05-01

    The Uinta-Piceance basin province (UPBP) has a complex Phanerozoic history characterized by five distinct phases of basin development (1) The UPBP formed part of a continental platform shelf on the northwestern flank of North America during the early and middle Paleozoic. Cambrian through Mississippian strata consist mainly of carbonate rocks, shale, and quartzite; contain major unconformities; and thicken westward. (2) Pennsylvanian-Permian uplifts of the ancestral Rocky Mountain orogeny segmented this continental platform shelf into the Eagle, Paradox, and Oquirrh basins. Basin-margin tectonics and cyclic eustatic-climatic fluctuations strongly controlled deposition of the clastic, carbonate, and evaporitic fill of these basins. (3) During the early Mesozoic, the UPBP formed part of a slowly subsiding continental platform. Triassic-Jurassic rocks include eolian, alluvial, and lacustrine deposits that thicken and grade westward into marine facies. (4) Paleozoic and early Mesozoic strata in the westernmost part of the UPBP were thrust eastward during the late Mesozoic Sevier orogeny, causing subsidence in the adjacent foreland basin. The history of the UPBP part of this foreland basin is recorded by thick nonmarine deposits within and adjacent to the thrust belt that grade eastward into thinner accumulations of marine rocks. (5) The geometry and style of regional compressional deformation changed markedly with onset of the latest Cretaceous-Paleogene Laramide orogeny. Laramide uplifts segmented the UPBP foreland basin into the Uinta and Piceance intermontane lacustrine basins. The geometry of these lacustrine basins is notably different from that of the late Paleozoic segment basins.

  18. Assessment of potential shale-oil and shale-gas resources in Silurian shales of Jordan, 2014

    USGS Publications Warehouse

    Schenk, Christopher J.; Pitman, Janet K.; Charpentier, Ronald R.; Klett, Timothy R.; Tennyson, Marilyn E.; Mercier, Tracey J.; Nelson, Philip H.; Brownfield, Michael E.; Pawlewicz, Mark J.; Wandrey, Craig J.

    2014-01-01

    Using a geology-based assessment methodology, the U.S. Geological Survey estimated means of 11 million barrels of potential shale-oil and 320 billion cubic feet of shale-gas resources in Silurian shales of Jordan.

  19. Tectonic controls of Mississippi Valley-type lead-zinc mineralization in orogenic forelands

    USGS Publications Warehouse

    Bradley, D.C.; Leach, D.L.

    2003-01-01

    Most of the world's Mississippi Valley-type (MVT) zinc-lead deposits occur in orogenic forelands. We examine tectonic aspects of foreland evolution as part of a broader study of why some forelands are rich in MVT deposits, whereas others are barren. The type of orogenic foreland (collisional versus Andean-type versus inversion-type) is not a first-order control, because each has MVT deposits (e.g., Northern Arkansas, Pine Point, and Cevennes, respectively). In some MVT districts (e.g., Tri-State and Central Tennessee), mineralization took place atop an orogenic forebulge, a low-amplitude (a few hundred meters), long-wavelength (100-200 km) swell formed by vertical loading of the foreland plate. In the foreland of the active Banda Arc collision zone, a discontinuous forebulge reveals some of the physiographic and geologic complexities of the forebulge environment, and the importance of sea level in determining whether or not a forebulge will emerge and thus be subject to erosion. In addition to those on extant forebulges, some MVT deposits occur immediately below unconformities that originated at a forebulge, only to be subsequently carried toward the orogen by the plate-tectonic conveyor (e.g., Daniel's Harbour and East Tennessee). Likewise, some deposits are located along syn-collisional, flexure-induced normal and strike-slip faults in collisional forelands (e.g., Northern Arkansas, Daniel's Harbour, and Tri-State districts). These findings reveal the importance of lithospheric flexure, and suggest a conceptual tectonic model that accounts for an important subset of MVT deposits-those in the forelands of collisional orogens. The MVT deposits occur both in flat-lying and in thrust-faulted strata; in the latter group, mineralization postdated thrusting in some instances (e.g., Picos de Europa) but may have predated thrusting in other cases (e.g., East Tennessee).

  20. Eustatic and tectonic control of sedimentation in the Pennsylvanian strata of the Central Appalachian Basin

    SciTech Connect

    Chesnut, D.R. Jr. . Kentucky Geological Survey)

    1992-01-01

    Analysis of the Breathitt Group of the Central Appalachian Basin reveals three orders of depositional cycles or trends. The Breathitt coarsening-upward trend (20 million years (my)) represents increasing intensity of the Alleghenian Orogeny. The major transgression (MT) cycle (2.5 my) was controlled by an unknown eustatic or tectonic mechanism. The major coal beds and intervening strata make up the coal-clastic cycle (CC cycle) (=Appalachian cyclothem) which has a 0.4 my periodicity. This periodicity supports eustatic control of sedimentation modulated by an orbital periodicity. Extensive coastal peats deposited at lowstand (CC cycle) were preserved as coals, whereas highstand peats were eroded during the subsequent drop in sea level. Autocyclic processes such as delta switching and avulsion occurred within CC cycles. An Early Pennsylvanian unconformity represents uplift and erosion of mid-Carboniferous foreland basin deposits. Alluvial deposits (Breathitt Group) derived from the highlands were transported to the northwest toward the forebulge. During lowstand, the only outlet available to further sediment transport (Lee sandstones) was toward the southwest (Ouachita Trough), along the Black Warrior-Appalachian foreland basins. The Middle Pennsylvanian marks a period of intermittent overfilling of the foreland basin and cresting of the forebulge. Marine transgressions entered through the foreland basins and across saddles in the forebulge. After the Ouachita Trough was destroyed during the late Middle Pennsylvanian, marine transgressions migrated only across saddles in the forebulge. In the Late Pennsylvanian, marine waters entered the basin only across the diminished forebulge north of the Jessamine Dome.

  1. How is Silurian-Early Devonian faulting in the North America continental interior related to orogenic processes at plate boundaries? A working hypothesis from the Canadian North

    NASA Astrophysics Data System (ADS)

    Pinet, Nicolas

    2015-04-01

    The Paleozoic Appalachian/Franklinian orogen that rims the North America continent on its eastern and northern sides is comparable in size with Tethyan orogenic belts. However, the far-field effects in the continental interior of the multiple Ordovician to Carboniferous deformation phases that built the orogen were relatively minor if compared with those associated with the Himalayas and Alps, a characteristics related to the high integrated strength of the North American craton. Despite the generally little deformation of the continental interior, two regional-scale tectonic features preserved evidence of significant Paleozoic tectonism: the fault bounded Hudson Bay Central High (HBCH) and the Boothia uplift/Cornwallis fold belt (BUCF) in the Canadian Arctic. In the Hudson Bay intracratonic basin, the lower part of the sedimentary succession (Upper Ordovician to Lower Devonian) is cut by high-angle faults and overlain by a saucer-shape, essentially underformed sedimentary package (Middle to Upper Devonian). The main structural feature is the NNW-trending HBCH that extends for a minimum length of 500 km with normal faults characterized by throws up to 500 m that were mainly active during the Silurian - Early Devonian period. The >700-km long, N-trending BUCF is nearly perpendicular to the deformation front of the Franklinian mobile belt. In its southern segment (Boothia uplift), its western side is characterized by an east-dipping reverse fault zone that puts Precambrian rocks over Paleozoic strata. In its northern segment (Cornwallis fold belt), the Paleozoic succession is involved in open folds and cuts by steeply dipping reverse faults. Syn-tectonic clastic sediments constrain the age of structures to the latest Silurian-Early Devonian. Comparison of the HBCH and BUCF indicates that they are grossly parallel, partly contemporaneous but with different kinematics. This kinematic variability may be explained if they are genetically linked with different segments of

  2. Bimodal Silurian and Lower Devonian volcanic rock assemblages in the Machias-Eastport area, Maine

    USGS Publications Warehouse

    Gates, Olcott; Moench, R.H.

    1981-01-01

    Exposed in the Machias-Eastport area of southeastern Maine is the thickest (at least 8,000 m), best exposed, best dated, and most nearly complete succession of Silurian and Lower Devonian volcanic strata in the coastal volcanic belt, remnants of which crop out along the coasts of southern New Brunswick, Canada, and southeastern New England in the United States. The volcanics were erupted through the 600-700-million-year-old Avalonian sialic basement. To test the possibility that this volcanic belt was a magmatic arc above a subduction zone prior to presumed Acadian continental collision, samples representing the entire section in the Machias-Eastport area of Maine were chemically analyzed. Three strongly bimodal assemblages of volcanic rocks and associated intrusives are recognized, herein called the Silurian, older Devonian, and younger Devonian assemblages. The Silurian assemblage contains typically nonporphyritic high-alumina tholeiitic basalts, basaltic andesites, and diabase of continental characterand calc-alkalic rhyolites, silicic dacites, and one known dike of andesite. These rocks are associated with fossiliferous, predominantly marine strata of the Quoddy, Dennys, and Edmunds Formations, and the Leighton Formation of the Pembroke Group (the stratigraphic rank of both is revised herein for the Machias-Eastport area), all of Silurian age. The shallow marine Hersey Formation (stratigraphic rank also revised herein) of the Pembroke Group, of latest Silurian age (and possibly earliest Devonian, as suggested by an ostracode fauna), contains no known volcanics; and it evidently was deposited during a volcanic hiatus that immediately preceded emergence of the coastal volcanic belt and the eruption of the older Devonian assemblage. The older Devonian assemblage, in the lagoonal to subaerial Lower Devonian Eastport Formation, contains tholeiitic basalts and basaltic andesites, typically with abundant plagioclase phenocrysts and typically richer in iron and

  3. Palaeomagnetic evidence from the Ordovician and Silurian of northwest Peninsular Malaysia

    NASA Astrophysics Data System (ADS)

    Haile, N. S.

    1980-06-01

    The Ordovician and Silurian Setul Limestone of the Langkawi Islands, northwest Peninsular Malaysia, has a mean magnetic vector of D = 338°, I = 62° after cleaning and correction for tilt. This is equivalent to a palaeolatitude of 43°, and a palaeomagnetic pole at 46°N, 76°E. The Silurian part of the Setul limestone also shows a similar direction. The Ordovician results are equivalent to a palaeolatitude of 43°, N or S. Recent reconstructions, based on palaeontology, place Indochina and China in the northern hemisphere in the Ordovician; if this is correct, a palaeolatitide of 43° for Langkawi would imply that Malaya-Indochina was the most northerly continental fragment at that time.

  4. Lower Silurian stratigraphy and brachiopods of the Chingiz range, eastern Kazakhstan

    NASA Astrophysics Data System (ADS)

    Nikitina, O. I.; Nikitin, I. F.; Olenicheva, M. A.; Palets, L. M.

    2015-05-01

    New data on the stratigraphy and faunal assemblages of the Lower Silurian of the Chingiz region are presented. Owing to the discovery of Ruddanian brachiopods in the basal Alpeis Formation, the position of the Ordovician-Silurian boundary has been revised. The stratigraphic range of the Alpeis Formation has been revised to correspond to the range of the Alpeis Horizon in the stratotype and is limited to the beds with the brachiopod Eospirifer cinghizicus and the beds with the graptolites of the Coronograptus gregarius Zone. Beds with Pentamerus longiseptatus of the Donenzhal Horizon are assigned to the Zhumak Formation. A new Ruddanian brachiopod assemblage (ten species) is recognized in the lower part of the beds with E. cinghizicus.

  5. Thermally Altered Silurian Cyanobacterial Mats: A Key to Earth's Oldest Fossils

    NASA Astrophysics Data System (ADS)

    Kazmierczak, Józef; Kremer, Barbara

    2009-10-01

    Diagenetic changes in thermally altered cyanobacterial mats from early Silurian black radiolarian cherts of southwestern Poland (Bardzkie Montains, Sudetes) have been studied. These early diagenetically silicified mats are composed of variously degraded remains of benthic microbes that resemble some modern chroococcalean and pleurocapsalean cyanobacteria. Two modes of degradational processes have been recognized in the studied mats: (i) early postmortem biodegradation and (ii) late diagenetic thermal or thermobaric degradation. The latter led to partial transformation of the fossilized organic remnants of cyanobacterial sheaths and capsules, which resulted in the formation of objects morphologically distant from the original microbiota but preserved features that allow for their identification as bona fide biogenic structures. Some of these thermally generated Silurian fossils are highly similar to the controversial microfossil-like carbonaceous structures described from the Early Archean Apex Chert of Australia. This similarity opens a promising way for credible recognition of remnants of cyanobacteria and similar microbiota in other thermally metamorphosed Archean sedimentary rocks

  6. Thermally altered Silurian cyanobacterial mats: a key to Earth's oldest fossils.

    PubMed

    Kazmierczak, Józef; Kremer, Barbara

    2009-10-01

    Diagenetic changes in thermally altered cyanobacterial mats from early Silurian black radiolarian cherts of southwestern Poland (Bardzkie Montains, Sudetes) have been studied. These early diagenetically silicified mats are composed of variously degraded remains of benthic microbes that resemble some modern chroococcalean and pleurocapsalean cyanobacteria. Two modes of degradational processes have been recognized in the studied mats: (i) early postmortem biodegradation and (ii) late diagenetic thermal or thermobaric degradation. The latter led to partial transformation of the fossilized organic remnants of cyanobacterial sheaths and capsules, which resulted in the formation of objects morphologically distant from the original microbiota but preserved features that allow for their identification as bona fide biogenic structures. Some of these thermally generated Silurian fossils are highly similar to the controversial microfossil-like carbonaceous structures described from the Early Archean Apex Chert of Australia. This similarity opens a promising way for credible recognition of remnants of cyanobacteria and similar microbiota in other thermally metamorphosed Archean sedimentary rocks. PMID:19845445

  7. Late Ordovician-Early Silurian chitinozoans from north-eastern and western Illinois, USA

    USGS Publications Warehouse

    Butcher, A.; Mikulic, Donald G.; Kluessendorf, Joanne

    2010-01-01

    Samples of uppermost Ordovician and Silurian strata from two cores from north-eastern and western Illinois were processed for chitinozoans. Due to apparent sea-floor oxidation or palaeoenvironmental constraints, very few samples yielded specimens, but those that did allow tentative correlation with established biostratigraphical zonations for the Chitinozoa. Samples from the Wilhelmi Formation of core DH76-21 in north-eastern Illinois yielded Spinachitina fragilis, a typically earliest Silurian taxon. A sample from the Maquoketa Group strata of core Principia #4, western Illinois, yielded a monospecific assemblage of Conochitina elegans, which is suggestive of a late Ordovician age. Higher in this core, a sample from the upper strata of the Bowling Green Dolomite yielded an assemblage indicating a late Rhuddanian to Aeronian age, including Angochitina hansonica, previously only described from strata in Nevada, and one new species, Fungochitina illinoisensis. ?? 2009 Elsevier B.V. All rights reserved.

  8. Ordovician and Silurian Phi Kappa and Trail Creek formations, Pioneer Mountains, central Idaho; stratigraphic and structural revisions, and new data on graptolite faunas

    USGS Publications Warehouse

    Dover, James H.; Berry, William B.N.; Ross, Reuben James, Jr.

    1980-01-01

    Recent geologic mapping in the northern Pioneer Mountains combined with the identification of graptolites from 116 new collections indicate that the Ordovician and Silurian Phi Kappa and Trail Creek Formations occur in a series of thrust-bounded slices within a broad zone of imbricate thrust faulting. Though confirming a deformational style first reported in a 1963 study by Michael Churkin, our data suggest that the complexity and regional extent of the thrust zone were not previously recognized. Most previously published sections of the Phi Kappa and Trail Creek Formations were measured across unrecognized thrust faults and therefore include not only structural repetitions of graptolitic Ordovician and Silurian rocks but also other tectonically juxtaposed lithostratigraphic units of diverse ages as well. Because of this discovery, the need to reconsider the stratigraphic validity of these formations and their lithology, nomenclature, structural distribution, facies relations, and graptolite faunas has arisen. The Phi Kappa Formation in most thrust slices has internal stratigraphic continuity despite the intensity of deformation to which it was subjected. As revised herein, the Phi Kappa Formation is restricted to a structurally repeated succession of predominantly black, carbonaceous, graptolitic argillite and shale. Some limy, light-gray-weathering shale occurs in the middle part of the section, and fine-grained locally pebbly quartzite is present at the base. The basal quartzite is here named the Basin Gulch Quartzite Member of the Phi Kappa. The Phi Kappa redefined on a lithologic basis represents the span of Ordovician time from W. B. N. Berry's graptolite zones 2-4 through 15 and also includes approximately 17 m of lithologically identical shale of Early and Middle Silurian age at the top. The lower contact of the formation as revised is tectonic. The Phi Kappa is gradationally overlain by the Trail Creek Formation as restricted herein. Most of the coarser

  9. Scaphopoda from the Alexander Terrane, Southeast Alaska-The first occurrence of Scaphopoda in the Silurian

    USGS Publications Warehouse

    Rohr, D.M.; Blodgett, R.B.; Baichtal, J.

    2006-01-01

    The scaphopods Dentalium hecetaensis n. sp. and Rhytiodentalium cf. kentuckyensis Pojeta et Runnegar, 1979, are described from Ludlow-age strata of the Heceta Limestone on Prince of Wales Island, Southeast Alaska. This is the first occurrence of Silurian scaphopods known to date. They are part of a diverse macrobenthic fauna of the Alexander terrane, an accreted southern Alaskan terrane of Siberian or Uralian affinities. ?? 2006 Nanjing Institute of Geology and Palaeontology, CAS.

  10. The Mississippian Antler foreland and continental margin in southern Nevada: The Eleana Formation reinterpreted

    SciTech Connect

    Cashman, P.H.; Trexler, J.H. Jr. )

    1991-02-01

    Rocks mapped as the Mississippian Eleana Formation at the type locality on the Nevada Test Site appear to comprise two completely different, but coeval, sedimentary units. In the Eleana Range (Western Eleana Formation), the strata are siliciclastic and carbonate turbidites of Mississippian age. From immediately east of the Eleana Range to Syncline Ridge (Eastern Eleana Formation), the strata are Devonian-Mississippian mudstone and quartzite conformably overlying Devonian limestone and underlying Pennsylvanian limestone. Although the contact between the two sedimentary packages is not exposed, small-scale structures document an east-dipping fault contact and reverse motion. Sandstone petrography and stratigraphic considerations support the age data in identifying two separate Mississippian units. Sandstones from the Western Eleana are chert litharenites with significant amount of feldspar and both volcanic and sedimentary lithic grains. These rocks are interpreted to be a submarine fan deposit; southwest-directed paleocurrent indicators suggest that they were deposited in an elongate trough, filled axially from the northeast. The source of the sediments was the antler allochthon and foreland basin. The authors tentatively correlate this section with the Dale Canyon-Chainman-Diamond Peak section near Eureka, Nevada. Sandstones from the Eastern Eleana are quartz arenites with rare chert and detrital heavy minerals. These strata are tentatively interpreted to be a shallow shelf deposit, with sediments derived from the continent to the east. They tentatively correlate this section with the Guilmette-Pilot-Scotty Wash-Chainman section of eastern Nevada. These sedimentary systems are initially separated an unknown distance across the late Paleozoic continental margin.

  11. The foreland deformation in the south-western Basque-Cantabrian Belt (Spain)

    NASA Astrophysics Data System (ADS)

    Quintà, A.; Tavani, S.

    2012-11-01

    In the south-western portion of the Cenozoic Basque-Cantabrian Belt, structural data collected in pre-orogenic Upper Cretaceous limestones were combined with aerial images interpretation in flat-lying areas. Observations about fracture strike, type, orientation and overprinting relationships, both at the macro and mesoscales, allow to constrain the pre-thrusting and pre-folding deformational sequence that affected the area when it was forming part of the foreland basin. WNW-ESE striking extensional structures represent the oldest elements, developed during the very late stages of the Mesozoic rifting associated with the opening of the Bay of Biscay. The onset of convergence is marked by the development of extensional structures striking roughly NNW-SSE and WSW-ENE, which are associated with belt-parallel stretching in the foredeep and outer-arc extension in the peripheral bulge, respectively, and developed in a non fluid assisted environment. These elements are postdated by a pre-folding layer-parallel shortening pattern, which includes WSW-ENE striking pressure solution cleavages and reverse faults (both of them frequently reactivating inherited early-orogenic WSW-ENE striking extensional elements), and right-lateral reactivation of WNW-ESE striking pre-orogenic extensional structures. This stage was followed by a syn- to post-folding E-W oriented belt-parallel compression, WNW-ESE striking left-lateral faults being the most outstanding elements associated with this stage. The presence of such elements in Upper Cretaceous sediments, provides support to the idea that left-lateral shear zones of the area related with a Cenozoic intrabelt lateral extrusion tectonics. Our results indicate, coherently with previously published works in the Pyrenean Orogen, that most of the mesoscale deformation has been acquired before layer's tilting.

  12. Conodont biostratigraphy of the Ordovician-Silurian boundary in the Central Appalachian Valley and Ridge Province

    SciTech Connect

    Philips, P.L. Jr.; Hall, J.C. . Dept. of Earth Sciences)

    1993-03-01

    Conodont biostratigraphy of the Ordovician-Silurian boundary in the Central Appalachian Valley and Ridge Province is based primarily on lithologic criteria. Although the boundary is precisely defined lithologically, virtually nothing is known about the biostratigraphic relationships in this interval due to a historic lack of detailed studies in this region. The present study is based on nearly 50 samples from 7 sections in Tennessee and Virginia, aimed at establishing a conodont-based biostratigraphic framework useful for local and regional correlation of lithostratigraphic units and boundaries. The data at hand show uppermost Ordovician rocks in this region have conodont faunas which are characterized by species of Oulodus, Aphelognathus, Phragmodus, and Plectodina. These faunas represent associations which locally correspond to the Oulodus velicuspis to Aphelognathus divergens Zones. Lowermost Silurian rocks contain faunas dominated by species of Ozarkodina, Distomodus, Pranognathus, and Walliserodus that correspond to the faunas of the Distomodus kentuckyensis Zone. Conodont ages indicate that the uppermost Ordovician rocks in the Central Appalachians range in age from upper Edenian to upper Richmondian and lowermost Silurian rocks range in age from upper Rhuddanian to lower Telychian in age. No conodont faunas which characterize the uppermost Richmondian, Gamachian, or lowermost Rhuddanian have yet been identified. The results of this study are in agreement with those of out previous study of the Southern Appalachian Valley and Ridge Province.

  13. Lower Silurian-Upper Ordovician subsurface glacial outwash deposits, northern Saudi Arabia

    SciTech Connect

    Dobson, P.B. )

    1991-08-01

    Recently acquired seismic data reinterpreted well information in northwest Saudi Arabia extends outcropping Lower Silurian to Upper Ordovician Zarqa/Sarah glacial and periglacial deposits into the subsurface. These deposits range from northeast-trending outwash-filled channels deeply incised into the underlying Ordovician Qasim and the Cambrian-Ordovician Saq Formation in the east. A southwest source for these sediments is implied by this new data. This supports previously interpreted source directions mapped from outcrop. It also correlates with the position of the Arabian plate relative to known Gonwanaland ice caps during the Early Silurian-Late Ordovician. The recognition of glacial outwash sediments in the subsurface provides new insight into the continuity and environments of deposition of the Qasim Formation members in northwest Saudi Arabia. The hydrocarbon-prone Lower Silurian Qusaiba Member of the Qalibah Formation overlies the Zarqa/Sarah Formations. The Qusaiba represents a rapid transgression of the Paleo-Tethys Sea during the final melting of the Gondwanaland ice caps. The seal-source characteristics of the Qusaiba Member, combined with the good porosity and permeability of the underlying outwash deposits, suggest a prospective hydrocarbon exploration play. Gas is produced from this reservoir in the Risha field of eastern Jordan.

  14. Arthrophycus in the Silurian of Alabama (USA) and the problem of compound trace fossils

    USGS Publications Warehouse

    Rindsberg, A.K.; Martin, A.J.

    2003-01-01

    Arthrophycus brongniartii (Harlan, 1832) is common in marginal-marine deposits in the Silurian Red Mountain Formation of Alabama. The ichnospecies, the second to be named in North America, is revived and emended after long disuse. Transitional forms to Rusophycus isp. and other morphologic evidence indicate that the maker of Arthrophycus was an arthropod, perhaps a trinucleine (raphiophorid?) trilobite. Interconnection of Arthrophycus and Nereites biserialis, as well as intergradation of Arthrophycus with Cruziana aff. quadrata, Phycodes flabellum, and Asterosoma ludwigae, indicate that these Red Mountain trace fossils were made by the same species of arthropod. Possible relationships with Arthrophycus alleghaniensis (Harlan, 1831) in the Silurian belt from Ontario to Tennessee are also explored. Ichnofamily Arthrophycidae Schimper, 1879 is emended. The ichnofamily is interpreted as chiefly the work of arthropods. Arthrophycus and other trace fossils from the Silurian of Alabama constitute a test case to build criteria for recognizing the members of complexes of trace fossils. In general, criteria such as interconnection of different forms, intergradation among unconnected forms, similarity of size, similarity of morphologic elements, and co-occurrence should be examined in order to determine the biologic and ethologic interrelationships of trace fossils. ?? 2003 Elsevier Science B.V. All rights reserved.

  15. Tectonic and depositional model of the Arabian and adjoining plates during the Silurian-Devonian

    SciTech Connect

    Husseini, M.I. )

    1991-01-01

    During the Late Ordovician and Early Silurian, the western part of the Arabian Peninsula was covered by polar glaciers that advanced from the south pole in African Gondwana. During this period, nondeposition, erosion, or marginal marine conditions prevailed in eastern and northern Arabia. When the glaciers melted in the Early Silurian, sea level rose sharply and the paleo-Tethys Ocean transgressed the Arabian and adjoining plates depositing a thick, organic-rich shale directly over the glaciogenic and periglacial rocks and related unconformities. The post-glacial sequence coarsens upward reflecting the passage of a coastline prograding northward from African and Arabian Gondwana to northern Arabia. A sea level drop in the Late Silurian placed the study area in a terrestrial environment; however, as sea level recovered in the Early Devonian, a carbonate sequence blanketed most of the area. The transgression, however, was interrupted by regional uplift and local orogenic movements in the Middle and Late Devonian. These movements constitute the onset of Hercynian tectonism, which resulted in erosion of the older sequences, depositional hiatuses, and regional facies changes.

  16. Deep seismic data offer new view of basin

    SciTech Connect

    Stern, T. )

    1990-09-17

    Deep seismic reflection is the application of standard oil industry seismic methods to the study of the whole of the earth's crust. In continental areas the crustal thickness generally varies from about 20 to 50 km. This paper is, a description and interpretation of a deep seismic reflection profile from New Zealand's principal oil-producing basin-the Taranaki basin. The paper demonstrates how deep seismic data have led to an interpretation of the South Taranaki basin in terms of a compressionally driven, foreland basin structure.

  17. Geology and hydrocarbon potential of the Oued Mya basin, Algeria

    SciTech Connect

    Benamrane, O.; Messaoudi, M.; Messelles, H. )

    1993-09-01

    The Oued Mya hydrocarbon system is located in the Sahara basin. It is one of the best producing basins in Algeria, along with the Ghadames and Illizi basins. The stratigraphic section consists of Paleozoic and Mesozoic, and is about 5000 m thick. This intracratonic basin is limited to the north by the Toughourt saddle, and to the west and east it is flanked by regional arches, Allal-Tilghemt and Amguid-Hassi Messaoud, which culminate in the super giant Hassi Messaoud and Hassi R'mel hydrocarbon accumulations, respectively, producing oil from the Cambrian sands and gas from the Trissic sands. The primary source rock in this basin is lower Silurian shale, with an average thickness of 50 m and a total organic carbon of 6% (14% in some cases). Results of maturation modeling indicate that the lower Silurian source is in the oil window. The Ordovician shales are also source rocks, but in a second order. Clastic reservoirs are in the Trissic sequence, which is mainly fluvial deposits with complex alluvial channels, and the main target in the basin. Clastic reservoirs in the lower Devonian section have a good hydrocarbon potential east of the basin through a southwest-northwest orientation. The Late Trissic-Early Jurassic evaporites that overlie the Triassic clastic interval and extend over the entire Oued Mya basin, are considered to be a super-seal evaporite package, which consists predominantly of anhydrite and halite. For paleozoic targets, a large number of potential seals exist within the stratigraphic column. This super seal does not present oil dismigration possibilities. We can infer that a large amount of the oil generated by the Silurian source rock from the beginning of Cretaceous until now still is not discovered and significantly greater volumes could be trapped within structure closures and mixed or stratigraphic traps related to the fluvial Triassic sandstones, marine Devonian sands, and Cambrian-Ordovician reservoirs.

  18. Basins in ARC-continental collisions

    USGS Publications Warehouse

    Draut, Amy E.; Clift, Peter D.

    2012-01-01

    collisional orogenesis ends up in the foreland basin that forms as a result of collision, and may be preserved largely undeformed. Compared to continent-continent collisional foreland basins, arc-continent collisional foreland basins are short-lived and may undergo partial inversion after collision as a new, active continental margin forms outboard of the collision zone and the orogen whose load forms the basin collapses in extension.

  19. Bison basin, central Wyoming - geologic overview

    SciTech Connect

    Pinnell, M.L.

    1984-07-01

    The northeastern part of the Great Divide basin is a separate, unique, and until recently, little-explored subbasin sometimes called the Bison basin. It is bounded by the Wind River Mountains, Sweetwater-Granite Mountain foreland uplift, Lost Soldier-Wertz structure, and a little-studied very positive east-west structural arch approximately coincident with the Sweetwater-Fremont county line. A comprehensive seismic, Landsat, and subsurface geologic examination or, better, dissection of the Bison basin was initiated in 1978. Numerous oil and gas prospects were delineated by this study. Since this small, 12 by 40 mi (19 by 64 km) basin is bordered by known reserves of 260 million bbl of oil and 90 million bcf of gas, these prospects proved to be a popular target of the drill bit. At least one of these prospects appears to be productive; others are currently being drilled. The presence of major east-west wrench faults, a well-documented foreland uplift, until recently undrilled surface and subsurface structures, faults with throw measured in tens of thousands of feet, and an oil seep indicate possible additional hydrocarbon potential in the Bison basin that could exceed presently known reserves. Currently drilling wells and abundant already acquired reflection seismic data are the beginning step in an ongoing exploration program of an interesting, complex, and rewarding small basin with a lot of promise.

  20. Michigan Basin basement implications for future exploration

    SciTech Connect

    Harper, J.D. . Dept. of Earth Sciences)

    1992-01-01

    The Michigan Basin has had a long history of responding to new exploration ideas, technologies, and pursuits. The future still holds opportunity for this Basin. A critical factor in future exploration will be incorporation of the details of basement structure into exploration plays. Facies distributions are strongly influenced by basement structure and diastrophism. In central Michigan successful exploration has focused on structures beneath Devonian oil fields and salts. In southern Michigan Ordovician fracture reservoirs have been the main producers. Between these two areas, outside of the Devonian salt edge, exploration has been minimal to none. This anomaly is unwarranted because structure styles in this middle area are continuous with structure of the central and southern bounding areas. Several potential play concepts can be established for this region. Improved definition of the extensions and continuity of the Silurian reef belt is possible because Silurian shelf margins, and the distributions of pinnacle reefs and basinal evaporite facies coincide with basement structural boundaries. Recognition of sea-level terraces at the top of the Trenton in Indiana and Ohio must be integrated into the depositional models for the Michigan Trenton. Cambro-Ordovician stratigraphy still offers opportunities for alternative correlations which have significant implications for depositional models and hydrocarbon occurrence. Improved seismic resolution, detailed basinal studies, and detailed reservoir characterization analogues will result in definition of new discoveries.

  1. Alongshore momentum balance analysis on a cuspate foreland

    NASA Astrophysics Data System (ADS)

    Kumar, Nirnimesh; Voulgaris, George; List, Jeffrey H.; Warner, John C.

    2013-10-01

    Nearshore measurements of waves and currents off Cape Hatteras, North Carolina, U.S.A, are used to investigate depth-averaged subtidal circulation and alongshore momentum balances in the surf and inner shelf region around a cuspate foreland. Data were collected on both sides of the cape representing shorefaces with contrasting shoreline orientation (north-south vs. northwest-southeast) subjected to the same wind forcing. In the nearshore, the subtidal flow is aligned with the local coastline orientation while at the cape point the flow is along the existing submerged shoal, suggesting that cape associated shoals may act as an extension of the coastline. Alongshore momentum balance analysis incorporating wave-current interaction by including vortex and Stokes-Coriolis forces reveals that in deep waters surface and bottom stress are almost in balance. In shallower waters, the balance is complex as nonlinear advection and vortex force become important. Furthermore, linearized momentum balance analysis suggests that the vortex force can be of the same order as wind and wave forcing. Farther southwest of Cape Hatteras point, wind and wave forcing alone fail to fully explain subtidal flow variability and it is shown that alongshore pressure gradient as a response to the wind forcing can close the momentum balance. Adjacent tide gauge data suggest that the magnitude of pressure gradient depends on the relative orientation of local coastline to the wind vector, and in a depth-averaged sense the pressure gradient generation due to change in coastline orientation even at km length scale is analogous to the effect of alongshore variable winds on a straight coastline.

  2. Late exhumation of the Alpine foreland (Digne nappe, France) constrained by low temperature thermochronology

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    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 displacement of this nappe is dated Late Miocene thanks to continental molasses of the foreland basin, which are folded in its footwall and form the famous Vélodrôme recumbent syncline. The stratigraphic series of the Digne nappe is made of more than 5000 m thick Liassic to Eocene deposits a part of which overthrust the vélodrôme syncline. In order to quantify this overburden and the timing of the subsequent exhumation and erosion of the Valavoire thrust-sheet we performed a low temperature apatite fission tracks (AFT) and (U-Th)/He (AHe) study on the Tertiary molasses sampled at Faucon du Caire and Esclangon area in order to (i) characterize the thermal conditions during burial and exhumation (ii) and to propose a coherent evolution of the European foreland in the front of the Digne nappe. AHe and AFT data obtained on detrital grains present for Faucon du Caire and Esclangon molasses minimum ages ranging of 3-5 Ma. From these data we determine than the Faucon du Caire molasses have been totally reset for He system and whereas the Esclangon molasses have been only partially reset. Using QTQt inverse modeling and He damage codes (Gallagher et al., 2012), the thermal history results implied a burial at 90-100°C for the Esclangon molasses and >120°C for the Faucon du Caire molasses and a similar exhumation starting at 5.5±0.5 Ma. From these results, we conclude that the thermal conditions during burial associated with the Digne nappe thrusting were enough sufficient to reset the detrital apatites in Miocene sediments. This implies several kilometers of tectonic overload. Maximum burial occurred at ~6 Ma ago, which precludes the occurrence of any Messinian incision overlain by the nappe in the Barles half-window as recently proposed (Hippolyte et al., 2011

  3. Slab rollback orogeny in the Alps inferred from the stratigraphic evolution of the Swiss Molasse basin

    NASA Astrophysics Data System (ADS)

    Schlunegger, Fritz; Kissling, Edi

    2016-04-01

    The stratigraphic development of foreland basins have been related to orogenic processes, where continent- continent collision resulted in the construction of topography and the downwarping of the foreland plate. These mechanisms have been used to explain the Oligocene to Miocene evolution of the Molasse basin, situated on the northern side 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. In particular, the use of empirical relationships between the spacing of alluvial megafans, orogen width and morphometric properties of stream channels feeding the fans imply a general trend towards an increasing total fluvial relief until 1,900±1,000 m at ca. 20 Ma, followed by a prolonged period of time during which this variable has remained nearly constant. Accordingly, larger topographic loads cannot be invoked to explain the continuous deflection of the foreland plate. Alternatively, a scenario where horizontal forces cause a downward dragging of the foreland plate would offer a valuable explanation for the decoupling between basin depth and topographic loads. However, such a scenario would be associated with the occurrence of compressional forces within the foreland plate, which is not in agreement with observations in the Molasse Basin, at least for the present, where focal mechanisms of current seismic events imply the occurrence of extensional forces at work. We suggest that rollback orogeny, driven by the gravitational pull of the European slab, provides a mechanism to explain the increasing deflection of the foreland in the absence of larger topographic forcing, and it agrees with the geologic record that the subducting European plate did not

  4. Hinterland-to-foreland structural evolution of the base of the Himalayan metamorphic core, west Nepal

    NASA Astrophysics Data System (ADS)

    Braden, Z.; Godin, L.; Yakymchuk, C.; Kellett, D.; Cottle, J. M.

    2015-12-01

    The base of the Himalayan metamorphic core is a folded reverse-sense shear zone exposed extensively along its transport direction. In west Nepal, along-transport exposures show a transition in structural style from hinterland to foreland, and sampled quartzite and pelite show variations in thermobarometry, quartz crystallographic preferred orientation (CPO), monazite Th-Pb ages and 40Ar/39Ar thermochronology. In the hinterland region, the shear zone yields a deformation temperature gradient from > 700°C at the top of the shear zone down to 400°C at the base. Metamorphic grade also decreases downwards through the shear zone. Muscovite 40Ar/39Ar ages are ca. 6 Ma. In the transition zone separating hinterland and foreland on the north flank of the Karnali klippe, a comparable structural section yields a deformation temperature gradient that similarly decreases down structural level from ~700 to 500°C. Muscovite 40Ar/39Ar dating yield ca. 14-12 Ma cooling ages. In-situ monazite geochronology indicates prograde metamorphism at ca. 43-34 Ma and melt crystallization at ca. 26-18 Ma. In the foreland, deformation is not strictly brittle; CPO analyses on sheared quartzite on the south flank of the Karnali klippe suggest deformation temperatures decreasing from 500 to 400°C downwards through the shear zone. Muscovite from the foreland yields 40Ar/39Ar ages of ca. 17 Ma. Deformation temperatures decrease marginally from hinterland to foreland and structurally downward within the shear zone, and estimates suggest ductile deformation prevails well into the foreland. Hinterland 40Ar/39Ar muscovite ages in west Nepal are anomalously young, and are possibly related to recent exhumation due to the SE-propagating mid-Miocene Gurla Mandhata-Humla system. Alternatively, they could be linked to the activation of a young duplex in the footwall of the Himalayan metamorphic core due to along-strike variation in geometry of the Main Himalayan thrust ramp.

  5. Fluvial sedimentology and basin analyses of the Permian Fairchild and Buckley formations, Beardmore Glacier region, and the Weller Coal Measures, southern Victoria Land, Antarctica

    SciTech Connect

    Isbell, J.L.

    1990-01-01

    The Beardmore Glacier region contains a 1-km-thick Permian fluvial sequence that was deposited in an elongate basin along the margin of the East Antarctica craton. Fluvial architecture, sandstone composition and paleocurrents within the basin record a change from an early Permian cratonic to a late Permian foreland basin. The Lower Permian Fairchild Formation consists entirely of overlapping channel-form sandstone bodies deposited by braided streams. Arkosic sandstone was deposited by SE flowing streams. Fairchild strata record slow subsidence within a broad cratonic basin. The Lower to Upper Permian Buckley Formation consists of an arkosic lower member and a volcaniclastic upper member. Paleocurrents which consist of transverse and longitudinal paleocurrents, suggest a cratonward migration of the basin axis through time. The Buckley Formation was deposited within a braided stream setting and is an important unit because it contains interstratified channel-sandstone sheets, shale and coal, along with evidence of channel-belt avulsions. Sandstone sheets predominate at the base of the formation, while flood-plain deposits thicken and increase in abundance upward. The interaction between fluvial processes and subsidence rates produced this alluvial stratigraphy. The Lower Permian Weller Coal Measures in southern Victoria Land were deposited within a narrow basin located cratonward of the foreland basin. Basin geometry and depositional patterns are similar to those of fault-bounded basins. Although basin formation is not constrained, deposition of the Weller was contemporaneous with the development of the foreland basin. This suggests a relationship between subsidence within the two basins.

  6. Detrital zircon provenance of Silurian-Devonian and Triassic sedimentary rocks of the western Yangtze Block: Constraint for the location of South China in Gondwana supercontinent

    NASA Astrophysics Data System (ADS)

    Chen, Qiong; Sun, Min; Zhao, Guochun

    2016-04-01

    During Paleozoic even to early Mesozoic, South China, along with a series of Asia continental blocks, dispersed from the northern margin of Gondwana, drifting across the Tethys Ocean and accreting to the final assembly of Asia in Triassic, which also accepted sediments sourced from the adjoining segments of east Gondwana and itself successively. However, the exact location of South China within the east Gondwana and other Asia blocks is arguing and confusing. Detrital zircon U-Pb geochronology and Hf isotope data from Paleozoic sedimentary rocks and massive Triassic flysch sequences kept in the western margin of South China (Danba-Longmenshan regions) provide a record of the source from which they were derived, and thus being applied to constraining the distribution of basement block in paleogeographic reconstructions and the tectonic setting of the basin. Two Longmenshan Devonian sediments exhibit dominant Grenvillian ages (0.9-1.1 Ga), with mid-Neoproterozoic (730-850 Ma), Pan-African (500-680 Ma) and Neoarchean (2.4-2.5 Ga) age populations, indicative of a typical Gondwana-derived affinity, which is also recorded by the Danba Silurian sample and other Paleozoic sediments (Devonian-Cambrian) in the resting South China block, including the east Yangtze block and the Cathaysia. However, the similar age patterns are not observed in the Devonian sample of Danba region, which exhibits a different age pattern with only two significant age groups of Pan-African (440-600 Ma) and Neoproterozoic (660-994 Ma) with an apparent lack of older zircon grains (>1.0 Ga). The Triassic sandstone from Songpan-Ganze covering sequences shows a distinguished zircon age distribution with prominant mid-Neoproterozoic (649-843 Ma), mid-Paleoproterozoic (1724-1951 Ma) and subordinated Permian-Triassic (236-298 Ma), Paleozoic (375-530 Ma) ages, mainly derived by melting of old crust with few input of juvenile material. Considering provenance changes along with the temporal and variation in

  7. Pleistocene-Recent Drainage Evolution in the Western Himalayan Foreland Basin

    NASA Astrophysics Data System (ADS)

    Clift, P. D.; Giosan, L.; Macklin, M.; Carter, A.; Tabrez, A. R.

    2011-12-01

    The rivers of the upper Indus flood plains support large populations in an area where rainfall is relatively weak. Nonetheless, the region has been one in which early civilizations flourished and then dispersed, most notably the Indus Valley or Harappan Culture. We investigated potential links between human settlement and drainage evolution by drilling abandoned and filled river channels on the northern edge of the Thar Desert to see how they have evolved. Pb isotope data from single K-feldspar grains from Holocene and Pleistocene sands showed that the channels were sourced from Himalayan rivers before and at 6-8 ka, but that after that time the proportion of high isotopic ratio grains rose, indicating increased contribution from the Thar Desert dunes prior to ~4.5 ka when flow in the Ghaggar-Hakra ceased entirely. U-Pb dating of single zircon sand grains confirms this general pattern. Grain ages <300 Ma are typical of the Thar Desert and become more common around 6-8 ka as the river flux decreased and desert began to encroach. Zircons ages at ~1900 Ma can be linked to a westward flow of the Yamuna River into the Indus but this flow may have finished as early as 49 ka, so that this capture does not affect the Harappan Culture. After this time the Sutlej and Beas River flowed through the region until they were both captured away to the north prior to 6-8 ka. The Harappan centers on the north of the Thar Desert likely dispersed because of unpredictable water supply as the monsoon weakened and because the flow of major rivers had ceased well before 4 ka.

  8. Strata-bound, silver-bearing iron, lead, and zinc sulfide deposits in Silurian and Ordovician rocks of allochthonous terranes, Nevada and northern Mexico

    USGS Publications Warehouse

    Ketner, Keith Brindley

    1983-01-01

    Allochthonous terranes in northern Nevada contain strata-bound sulfide deposits at two horizons in Silurian and Ordovician siliceous sedimentary rocks. The most intensively mineralized horizon and most extensive deposit is at the base of the Silurian. Another less extensive deposit is in the lower Middle Ordovician. Spectrographic analyses of gossan from the basal Silurian horizon indicate anomalously high values of lead and zinc; and in about 40 percent of the samples, silver values are anomalously high. Suhsurface samples contain the primary minerals pyrite, galena, and sphalerite. The basal Silurian deposits are in thick-bedded chert that is overlain by micaceous siltstone. They are underlain by a thick-bedded black chert unit of Late Ordovician age. The basal Silurian gossan has been identified also in southwestern Nevada and in northern Mexico in stratigraphic sequences very similar to that of northern Nevada.

  9. Mesozoic geology of southwestern China: Indosinian foreland overthrusting and subsequent deformation

    NASA Astrophysics Data System (ADS)

    Qiu, Liang; Yan, Dan-Ping; Tang, Shuang-Li; Wang, Qin; Yang, Wen-Xin; Tang, Xiangli; Wang, Jibin

    2016-05-01

    The southwestern part of the South China Block (SCB) records Triassic and subsequent deformations and is a key region that provides evidence of the post-amalgamation tectonic evolution of Southeast Asia. Here, we outline the tectonothermal evolution of early Mesozoic orogenesis in this region using structural analysis and fission track thermochronology. This region is divided into three tectonic units (south to north): the Youjiang Fold-and-Thrust Belt (YFTB), the Qianzhong Massif (QZM), and the Thin-skinned Thrust Belt (TTB) of the southeastern Sichuan Basin, all three of which record three deformation events, here termed D1, D2, and D3. D1 deformation is represented by Triassic top-to-the-north thrusts (F1) and fault-related folds (f1) that are indicative of N-S shortening. The intensity of deformation decreases toward the north. The subsequent D2 and D3 deformations are marked by Cretaceous top-to-the-NW thrusting and fault-propagation folding, and Cenozoic NE-SW trending normal faults (F3), respectively. The temperature-time (t-T) path obtained by apatite fission-track modeling of samples from the YFTB, QZM, and TTB areas provides evidence of uplift and denudation. The D1 deformation at ∼230-210 Ma is characterized by buried thrusts within the relatively stable YFTB and QZM, and an increase in depth of the TTB. This was coeval with the Late Triassic northward migration of uplift and denudation that is evidenced by a Late Triassic stratigraphic gap within the YFTB, a thin layer of coarse-grained continental clastics within the QZM, and a thick layer of clastic rocks within the TTB. The study area records a Triassic thrust system (D1) that progressively migrated northwards and represents a foreland fold-and-thrust belt that formed during the Indochina-SCB collision. This initial deformation was subsequently overprinted by Late Jurassic to Cretaceous NW-SE thrusting (D2) and the development of Cenozoic NW-SE extensional structures (D3).

  10. Reservoir zonation in Silurian-Devonian carbonates of Wells field, Dawson County, Texas

    SciTech Connect

    Mazzullo, L.J. )

    1992-04-01

    Wells field in Dawson County, Texas, has produced over 7.5 million bbl since 1955 from Silurian-Devonian carbonates. Although originally classified as a Devonian field, production there actually is out of the Silurian Wristen and Fusselman formations. Wells field is an extremely complex system of structured and stratigraphic reservoirs not easily characterized by traditional subsurface mapping techniques. Detailed lithologic analyses of well cuttings from 29 wells in and around this field were done to evaluate reservoir zonation and potentials for either new field development wells, or recompletions from existing well bores. These analyses have shown that paleotopographic highs on the Fusselman unconformity across the field created optimum sites for Fusselman dolomite reservoir development, and collateral development of Wristen reservoirs. The Wristen reservoirs are in the form of porous carbonate mounds that grew adjacent to the paleotopographically high areas, or simple compactionally fractured cherty carbonates over these highs. The recognition of Fusselman paleotopography in most wells is implied by thickness and facies changes in the overlying Wristen section. A certain amount of structure and facies-induced reservoir separation has been documented. The results of this study have been used to identify several areas of the field where each of the three reservoirs could be exploited for underdeveloped reserves.

  11. Sedimentology of the Ripogenus Formation, Maine: A Silurian carbonate-siliciclastic depositional system

    SciTech Connect

    Comrie, T.A.; Caldwell, D.W. . Dept. of Geology)

    1993-03-01

    The Ripogenus Formation of north-central Maine is shallow marine unit of probable Wenlockian age characterized by interbeds of sandstone and limestone less than 50 cm. in thickness and separated by sharp, often erosional, contacts. Reefal material with abundant stromatoporoids is exposed in the eastern part of the formation and is overlain locally by Silurian andesite and Siluro-Devonian redbeds. Sediment size and bed thickness decrease to the west, as does the relative amount of carbonate sediment. Common fossils also include stromatolites, brachiopods, gastropods, crinoids, and corals. Large fossils, notably the stromatoporoids and stromatolites, are often found in growth position, but smaller fossils are usually found to have been abraided and transported. The formation was deposited in an area shown by paleogeographic reconstructions to have been located just south of the equator (probably near one or more islands) in the lapetus Ocean prior to its closure. Although sedimentary structures are often not well preserved due to its closure. Although sedimentary structures are often not well preserved due to soft-sedimentary deformation and slight metamorphism, there is some evidence of storm-controlled deposition. Deposition of this unit and other Silurian carbonates found in Maine and the Maritime Provinces are unlike those found throughout N. America in that they are the product of localized deposition in an unstable tectonic environment.

  12. Diagenesis of Upper Carboniferous rocks in the Ouachita foreland shelf in mid-continent USA: an overview of widespread effects of a Variscan-equivalent orogeny

    USGS Publications Warehouse

    Walton, A.W.; Wojcik, K.M.; Goldstein, R.H.; Barker, C.E.

    1995-01-01

    Diagenesis of Upper Carboniferous foreland shelf rocks in southeastern Kansas took place at temperatures as high as 100-150?? C at a depth of less than 2 km. High temperatures are the result of the long distance (hundreds of kilometers) advection of groundwater related to collisional orogeny in the Ouachita tectonic belt to the south. Orogenic activity in the Ouachita area was broadly Late Carboniferous, equivalent to the Variscan activity of Europe. Mississippi Valley-type Pb-Zn deposits and oil and gas fields in the US midcontinent and elsewhere are commonly attributed to regional groundwater flow resulting from such collisional events. This paper describes the diagenesis and thermal effects in sandstone and limestone of Upper Carboniferous siliciclastic and limestone-shale cyclothems, the purported confining layer of a supposed regional aquifer. Diagenesis took place in early, intermediate, and late stages. Many intermediate and late stage events in the sandstones have equivalents in the limestones, suggesting that the causes were regional. The sandstone paragenesis includes siderite cement (early stage), quartz overgrowths (intermediate stage), dissolution of feldspar and carbonates, followed by minor Fe calcite, pore-filling kaolinite and sub-poikilotopic Ca ankerite (late stage). The limestone paragenesis includes calcite cement (early stage); megaquartz, chalcedony, and Fe calcite spar (intermediate stage); and dissolution, Ca-Fe dolomite and kaolinite (late stage). The Rm value of vitrinite shows a regional average of 0.6-0.7%; Rock-Eval TmaX suggests a comparable degree of organic maturity. The Th of aqueous fluid inclusions in late stage Ca-Fe-Mg carbonates ranges from 90 to 160?? and Tmice indicates very saline water (>200000 ppm NaCl equivalent); ??18O suggests that the water is of basinal origin. Local warm spots have higher Rm, Tmax, and Th. The results constrain numerical models of regional fluid migration, which is widely viewed as an artesian flow

  13. Large amplitude carbon isotope excursion during the Late Silurian Lau Event

    NASA Astrophysics Data System (ADS)

    Schoenmaker, N. R.; Reichart, G. J.; Nierop, K. G. J.; Mann, U.; White, T.; Sancay, R. H.

    2010-05-01

    High magnitude excursions in the stable carbon isotope record reveal that the Silurian greenhouse world (443.7-416.0 Ma) represents a period of globally unstable environmental conditions. Fundamental changes in the global carbon cycle were more frequent and had a larger impact during the Silurian compared to any other period of the Phanerozoic [1]. The late Silurian "Lau event" is the largest of four major positive d13Ccarb excursions. The carbon isotope excursion associated with the "Lau event" is recognized globally and reaches values ranging from +6‰ from the Eastern Baltic, +8.5‰ on Gotland, 11‰ from southern Sweden and even up to 12‰ in Australia, Queensland. This makes the "Lau event" the strongest d13C excursion of the entire Phanerozoic, comparable in amplitude to Precambrian events. However, the mechanism underlying the Silurian stable isotope excursions is ill understood. Scenarios proposed include enhanced carbon burial due to anoxic conditions [2] and/or enhanced productivity [3]. Alternative hypotheses range from alternating wet and humid periods influencing global ocean circulation [4], weathering of carbonates [5] to changes in the primary producer community [6]. Evaluating these different scenarios critically relies on establishing the true magnitude of the isotopic excursions and rates of change. Existing stable carbon isotope studies of the Lau event were based on analyses of bulk carbonates or bulk organic matter. Both signal carriers are subject to admixing of organic matter or carbonates from various sources. Moreover, preferential preservation of some organic moieties, e.g. lipids, over other potentially offsets isotopic records, since the carbon isotopic signatures between these moieties substantially differ. A stable organic geochemical composition over the isotope events is thus crucial to ensure capturing the true amplitude of the excursion. Here we therefore investigate, using Curie point pyrolysis GC-MS, the composition of the

  14. Landscape evolution and bedrock incision in the northern Alpine Foreland since the last 2 Ma

    NASA Astrophysics Data System (ADS)

    Claude, Anne; Akçar, Naki; Schlunegger, Fritz; Ivy-Ochs, Susan; Kubik, Peter; Christl, Marcus; Vockenhuber, Christof; Dehnert, Andreas; Kuhlemann, Joachim; Rahn, Meinert; Schlüchter, Christian

    2016-04-01

    The landscape evolution of the Swiss Alpine Foreland since the early Pleistocene is of utmost importance for modelling the long-term safety of deep geological repositories for nuclear waste disposal in the northern Alpine Foreland. The oldest Quaternary sediments in the northern foreland are proximal glaciofluvial sediments lying unconformably on Tertiary Molasse or Mesozoic carbonate bedrock. These deposits form topographically distinct and discontinuous isolated plateaus. Terrace morphostratigraphy has a reversed stratigraphic relationship, i.e. today older sediments are located at higher altitudes and vice versa. In this study, we focus on the landscape evolution and long-term bedrock incision in the Swiss Alpine Foreland. We reconstruct the terrace chronology in the foreland at six key locations at different altitudes ranging from 433 m a.s.l. to 675 m a.s.l. by applying cosmogenic depth-profile and isochron-burial dating techniques. First results from these sites indicate that the gravels at studied sites were accumulated in the foreland between 1 and 2 Ma. Based on this reconstructed chronology, long-term bedrock incision rates between 0.1 and 0.2 mm/a were calculated. Thus, we inferred a landscape at that time that was most likely characterized by smoother hillslopes than at present. During the Mid-Pleistocene Revolution (ca. 0.95 Ma), a re-organization of the drainage systems occurred in the Alpine Foreland with a significant lowering of the base level of stream channels. Existing data suggest slightly increased incision rates after this drainage network re-organisation compared to our results. The reconstruction of the chronology at the remaining sites may allow quantifying a pronounced incision as well as the exact timing of the acceleration in the incision rates. REFERENCES Heuberger, S. & Naef, H. (2014). NAB 12-35: Regionale GIS-Kompilation und -Analyse der Deckenschotter-Vorkommen im nördlichen Alpenvorland. Nagra Arbeitsbericht. Kuhlemann, J. & Rahn

  15. Relationship of Ordovician and Silurian reservoir development to unconformities at Midland farms and Inez fields, Andrews County, Texas

    SciTech Connect

    Mear, C.E.; Becher, J.W.

    1986-03-01

    Hydrocarbons are being produced at Midland Farms and Inez fields from Ellenburger dolomites and Fusselman limestones. Reservoirs developed there during Ordovician and Silurian periods of minor folding and faulting, followed by regional uplift and subaerial exposure of the carbonates. Vuggy, cavernous, and solution-enlarged fracture porosity was developed in the Lower Ordovician Ellenburger dolomites prior to deposition of the overlying Middle Ordovician shales of the Simpson Group. Vuggy and cavernous porosity developed in the Lower Silurian Fusselman crinoid-ostracod-pellet packstones and grainstones before deposition of the overlying Silurian Wristen shales. Montoya siliceous limestones of Late Ordovician age were truncated during a period of pre-Silurian erosion, but porosity development is not indicated in Montoya rock cuttings. Only minor amounts of porosity developed in the Lower to Middle Devonian Thirty-one packstones and wackestones as a result of uplift and erosion in the Middle Devonian. Regional compression during the post-Mississippian enhanced doubly plunging anticlines now having up to 91 m (300 ft) of closure at the Ellenburger through Thirty-one formations at Midland Farms and Inez fields. Fractures may have developed in Paleozoic limestones during this period of folding, but reservoir enhancement appears to have resulted only in the Ellenburger dolomites. Representative porosity measurements of the Ellenburger and Fusselman pay zones cannot be made from wireline log calculations, due to the fractured, vuggy, and cavernous nature of the porosity.

  16. Revised correlation of Silurian Provincial Series of North America with global and regional chronostratigraphic units and δ13Ccarb chemostratigraphy

    USGS Publications Warehouse

    Cramer, Bradley D.; Brett, Carlton E.; Melchin, Michael J.; Mannik, Peep; Kleffner, Mark A.; McLaughlin, Patrick I.; Loydell, David K.; Munnecke, Axel; Jeppsson, Lennart; Corradini, Carlo; Brunton, Frank R.; Saltzman, Matthew R.

    2011-01-01

    Recent revisions to the biostratigraphic and chronostratigraphic assignment of strata from the type area of the Niagaran Provincial Series (a regional chronostratigraphic unit) have demonstrated the need to revise the chronostratigraphic correlation of the Silurian System of North America. Recently, the working group to restudy the base of the Wenlock Series has developed an extremely high-resolution global chronostratigraphy for the Telychian and Sheinwoodian stages by integrating graptolite and conodont biostratigraphy with carbonate carbon isotope (??13Ccarb) chemostratigraphy. This improved global chronostratigraphy has required such significant chronostratigraphic revisions to the North American succession that much of the Silurian System in North America is currently in a state of flux and needs further refinement. This report serves as an update of the progress on recalibrating the global chronostratigraphic correlation of North American Provincial Series and Stage boundaries in their type area. The revised North American classification is correlated with global series and stages as well as regional classifications used in the United Kingdom, the East Baltic, Australia, China, the Barrandian, and Altaj. Twenty-four potential stage slices, based primarily on graptolite and conodont zones and correlated to the global series and stages, are illustrated alongside a new composite ??13Ccarb curve for the Silurian. Conodont, graptolite, isotope, New York, Ontario, series, Silurian, stage. ?? 2010 The Authors, Journal compilation ?? 2010 The Lethaia Foundation.

  17. The Silurian to Permian history of a metamorphic core complex in Lofoten, northern Scandinavian Caledonides

    NASA Astrophysics Data System (ADS)

    Steltenpohl, Mark G.; Hames, Willis E.; Andresen, Arild

    2004-02-01

    The Lofoten archipelago exposes Precambrian Baltic basement and Caledonian allochthonous sequences within a 1000 km long chain of gravity and magnetic highs and structural culminations along the extended, British and Norwegian continental shelf. Previous regional geophysical studies indicate that post-Caledonian extension and development of the northern Norwegian shelf occurred during broadly defined Carboniferous-Permian, Cretaceous-Jurassic, and early Tertiary events. Structures related to these events are known to young westward. We report field, structural, and 40Ar/39Ar thermochronologic data from rocks exposed in Lofoten that further define the history and style of post-Caledonian extension. The islands of southwest Lofoten also represent the most outboard exposures of Caledonian basement in northern Norway that presumably formed the middle to deep crustal core of the orogen. Metasedimentary rocks and penetratively deformed basement in Lofoten record high-grade Silurian-Devonian metamorphism and top-to-the-east (hereinafter tops-east) thrusting followed by episodes of Late Devonian to Early Carboniferous, tops-west, ductile extension which progressed into oblique left-slip movements. The structural style and timing of Silurian contraction in this area are remarkably similar to that determined for the more forelandward areas on the mainland, ˜120 km to the east, supporting the inference that distal parts of the Baltic continental margin that were once deeply subducted are presently exposed in Lofoten. The timings of post-Devonian structural events that affected rocks in Lofoten are partially constrained by the ages of unconformities and strata known to be preserved in graben flanking the Lofoten culmination. The radiometric age and structural data presented in this study, in combination with stratigraphic constraints, suggest a westward progression through time of extensional deformation over a protracted interval of Silurian to Permian time. The latest

  18. Hydraulic Testing of Silurian and Ordovician Strata at the Bruce Site

    NASA Astrophysics Data System (ADS)

    Beauheim, R. L.; Avis, J. D.; Chace, D. A.; Roberts, R. M.; Toll, N. J.

    2009-05-01

    Ontario Power Generation is proposing a Deep Geologic Repository (DGR) for the long-term management of its Low and Intermediate Level Radioactive Waste (L&ILW) within a Paleozoic-age sedimentary sequence beneath the Bruce Site near Tiverton, Ontario, Canada. The concept envisions that the DGR would be excavated at a depth of approximately 680 m within the Ordovician Cobourg Formation, a massive, dense, argillaceous limestone. A key attribute of the Bruce site is the extremely low permeabilities associated with the thick Ordovician carbonate and argillaceous bedrock formations that will host and enclose the DGR. Such rock mass permeabilities are thought sufficiently low to contribute toward or govern a diffusion-dominated transport regime. To support this concept, hydraulic testing was performed in 2008 and 2009 in two deep boreholes at the proposed repository site, DGR-3 and DGR-4. The hydraulic testing was performed using a straddle-packer tool with a 30.74-m test interval. Sequential tests were performed over the entire open lengths of the boreholes from the F Unit of the Silurian Salina Formation into the Ordovician Gull River Formation, a distance of approximately 635 m. The tests consisted primarily of pressure-pulse tests, with a few slug tests performed in several of the higher permeability Silurian units. The tests are analyzed using the nSIGHTS code, which allows the entire pressure history a test interval has experienced since it was penetrated by the drill bit to be included in the test simulation. nSIGHTS also allows the model fit to the test data to be optimized over an n-dimensional parameter space to ensure that the final solution represents a true global minimum rather than simply a local minimum. The test results show that the Ordovician-age strata above the Coboconk Formation (70+ m below the Cobourg) have average horizontal hydraulic conductivities of 1E-13 m/s or less. Coboconk and Gull River hydraulic conductivities are as high as 1E-11 m

  19. Petroleum potential of the Reggane Basin, Algeria

    SciTech Connect

    Boudjema, A.; Hamel, M.; Mohamedi, A.; Lounissi, R. )

    1990-05-01

    The intracratonic Reggane basin is located on the Saharan platform, southwest of Algeria. The basin covers an area of approximately 140,000 km{sup 2}, extending between the Eglab shield in the south and the Ougarta ranges in the north. Although exploration started in the early 1950s, only a few wells were drilled in this basin. Gas was discovered with a number of oil shows. The sedimentary fill, mainly Paleozoic shales and sandstones, has a thickness exceeding 5,000 m in the central part of the basin. The reservoirs are Cambrian-Ordovician, Siegenian, Emsian, Tournaisian, and Visean sandstones with prospective petrophysical characteristics. Silurian Upper Devonian and, to a lesser extent Carboniferous shales are the main source rocks. An integrated study was done to assess the hydrocarbon potential of this basin. Tectonic evolution source rocks and reservoirs distribution maturation analyses followed by kinetic modeling, and hydrogeological conditions were studied. Results indicate that gas accumulations could be expected in the central and deeper part of the basin, and oil reservoirs could be discovered on the basin edge.

  20. The last erosional stage of the Molasse Basin and the Alps

    NASA Astrophysics Data System (ADS)

    Schlunegger, Fritz; Mosar, Jon

    2011-07-01

    We present a synoptic overview of the Miocene-present development of the northern Alpine foreland basin (Molasse Basin), with special attention to the pattern of surface erosion and sediment discharge in the Alps. Erosion of the Molasse Basin started at the same time that the rivers originating in the Central Alps were deflected toward the Bresse Graben, which formed part of the European Cenozoic rift system. This change in the drainage direction decreased the distance to the marine base level by approximately 1,000 km, which in turn decreased the average topographic elevation in the Molasse Basin by at least 200 m. Isostatic adjustment to erosional unloading required ca. 1,000 m of erosion to account for this inferred topographic lowering. A further inference is that the resulting increase in the sediment discharge at the Miocene-Pliocene boundary reflects the recycling of Molasse units. We consider that erosion of the Molasse Basin occurred in response to a shift in the drainage direction rather than because of a change in paleoclimate. Climate left an imprint on the Alpine landscape, but presumably not before the beginning of glaciation at the Pliocene-Pleistocene boundary. Similar to the northern Alpine foreland, we do not see a strong climatic fingerprint on the pattern or rates of exhumation of the External Massifs. In particular, the initiation and acceleration of imbrication and antiformal stacking of the foreland crust can be considered solely as a response to the convergence of Adria and Europe, irrespective of erosion rates. However, the recycling of the Molasse deposits since 5 Ma and the associated reduction of the loads in the foreland could have activated basement thrusts beneath the Molasse Basin in order to restore a critical wedge. In conclusion, we see the need for a more careful consideration of both tectonic and climatic forcing on the development of the Alps and the adjacent Molasse Basin.

  1. Petroleum prospectivity in Precambrian and Early Paleozoic basins, Australia

    SciTech Connect

    Goldstein, B.A. )

    1991-03-01

    Proterozoic to Devonian age strata with some potential for petroleum accumulations are known from sedimentary basins covering {approximately}1,870,000 km{sup 2} onshore Australia. Portions of these very old basins have not sustained the deleterious effects of deep burial. Explorers with vision continue to target these very old rocks in the MacArthur/South Nicholson, Amadeus, Canning, Adavale, and Bonaparte basins. Approximately 429,000 km{sup 2} of these basins remain under license for petroleum exploration. The oldest known oil in Australia is reservoired within and sourced from the mid-Proterozoic in the McArthur basin. The Early Ordovician Pacoota Sandstone of the Amadeus basin is the oldest formation commercially exploited for oil and gas in Australia. Significant discoveries awaiting development include Dingo, Pictor, and Gilmore. The Tern gas field trap in the Bonaparte basin is related to a salt diapir; the salt probably being Silurian-Devonian in age. Salt probably of the same age has formed diapirs in the Canning basin, too. Cambrian and Proterozoic salt-bearing strata are likewise the cause and core of some anticlinal and diapiric structures in the Amadeus basin. Minor oil shows have been reported from the Cambrian of the Officer basin. The Warburton, Pedirka, Arrowie, Ord, Wiso, Georgina, and Ngalia basins contain Proterozoic and early Paleozoic sedimentary rocks but are ascribed only limited petroleum prospectivity at this time.

  2. Stable isotopic perturbation at the Ordovician-Silurian transition in NE Poland

    SciTech Connect

    Hoffman, A.; Gruszczynski, M.; Malkowski, K. . Paleobiology Inst.); Satir, M. ); Halas, S. . Physics Inst.)

    1992-01-01

    An interpretation of the time series of stable isotopic proportions of carbon, oxygen, and sulfur in rock samples from subsurface Ordovician-Silurian transition in north-eastern Poland demonstrates a clearcut perturbation that must imply some global scale controlling factors. This perturbation is particularly emphasized by its comparison to the sustained secular Paleozoic trend in isotopic characteristics of the oceanic system. On the other hand, this isotopic perturbation contrasts with unidirectional local changes in geochemical elemental proportions in the same rock samples. The perturbation is most parsimoniously explained as linked to the onset of a major glaciation. Its relationship to the second largest mass extinction in the history of the biosphere still remains to be elucidated.

  3. Silurian sponges and some associated fossils from the Heceta Limestone, Prince of Wales Island, southeastern Alaska

    USGS Publications Warehouse

    Rigby, J.K.; Rohr, D.M.; Blodgett, R.B.; Britt, B.B.

    2008-01-01

    A small faunule of hypercalcified agelasiid demosponges has been recovered from outcrops of the Silurian Heceta Formation on Prince of Wales Island in southeastern Alaska. Included are abundant Girtyocoeliana epiporata (Rigby and Potter, 1986), of the Girtyocoeliidae Finks and Rigby, 2004; fragments of Alaskaspongiella laminosa n. gen. and sp., Polyplacospongia nodosa n. gen. and sp., and Monolaminospongia gigantia n. gen. and sp., of the Auriculospongiidae Termier and Termier, 1977, and Cladospongia alaskensis n. gen. and sp., Virgulaspongia uniforma n. gen. and sp., and Stipespongia laminata n. gen. and sp. of the Preperonidellidae Finks and Rigby, 2004. Also included are a few fossils of uncertain taxonomic placement, including Turbospongia biperforata n. gen. and sp., along with a small, chambered, tubular fragment and several porous tubular stems that may be additional poriferans. Some isolated octactine-based heteractinid spicules were also recovered from the etched residues. Copyright ?? 2008, The Paleontological Society.

  4. A new mid-Silurian aquatic scorpion—one step closer to land?

    PubMed Central

    Waddington, Janet; Rudkin, David M.; Dunlop, Jason A.

    2015-01-01

    One of the oldest known fossil scorpions, a new species from the mid-Silurian Eramosa Formation (430 myr) of Ontario, Canada, exhibits several surprising features. The depositional environment and associated biota indicate a marine habitat; however, the leg morphology of this scorpion, which has a short tarsus in common with all Recent scorpions, suggests that a key adaptation for terrestrial locomotion, the ability to support its weight on a subterminal ‘foot’, appeared remarkably early in the scorpion fossil record. Specimens are preserved intact and undisturbed in a splayed posture typical of moults rather than carcasses. We postulate that these animals were aquatic, but occasionally ventured into extremely shallow water, or onto a transient subaerially exposed surface while moulting, before returning to deeper water. Shed exuviae were preserved in situ by rapid overgrowth of bacterial biofilm. PMID:25589484

  5. A new synziphosurine (Chelicerata: Xiphosura) from the Late Llandovery (Silurian) Waukesha Lagerstatte, Wisconsin, USA

    USGS Publications Warehouse

    Moore, R.A.; Briggs, D.E.G.; Braddy, S.J.; Anderson, L.I.; Mikulic, Donald G.; Kluessendorf, Joanne

    2005-01-01

    A new synziphosurine (Chelicerata:Xiphosura) is described from the Late Llandovery (Silurian) Konservat-Lagerstatte of Waukesha, Wisconsin, USA. Venustulus waukeshaensis n.gen. and sp. is characterized by a semicircular carapace with a slightly procurved posterior margin lacking genal spines and an opisthosoma composed of 10 freely articulating segments, divided into a preabdomen of seven segments with blunt pleurae and a postabdomen of three segments lacking pleurae. The tail spine is short and styliform. This is the earliest known unequivocal synziphosurine, extending their fossil record from the Wenlock to the Llandovery, and only the second species to be described with prosomal appendages; the presence of six pairs (a pair of chelicerae and five pairs of walking legs) contrasts with the seven in the synziphosurine Weinbergina opitzi, but is comparable to the number in modern horseshoe crabs. V. waukeshaensis n. gen. and sp. is not assigned to a family here pending a wider revision, but it bears most resemblance to the Weinberginidae.

  6. Ordovician-Silurian tectonism in northern California:The Callahan event

    NASA Astrophysics Data System (ADS)

    Cotkin, Spencer 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 magmatic 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. A Bohemian-type Silurian (Wenlockian) pelecypod faunule from Arctic Canada.

    USGS Publications Warehouse

    Pojeta, J., Jr.; Norford, B.S.

    1987-01-01

    The pelecypod genera Slava and Rhombopteria are reported for the first time from Canada, where they occur in a limestone concretion within the Cape Phillips Formation, Cornwallis Island, Arctic Archipelago. These genera are characteristic of Silurian rocks in Bohemia, Czechoslovakia. Graptolites from the same concretion indicate the Monograptus ludensis Zone (uppermost Wenlockian); this age is substantiated by associated conodonts, trilobites, vertebrates, and pelecypods but with less precision. It is difficult to explain the occurrence of Slava and Rhombopteria in the middle of Laurentia on the basis of some map reconstructions of the Wenlockian world. The Canadian material of Slava novaterra n. sp. and Rhombopteria cf. R. mira (Barrande) is described. Leptodesma (Leptodesma) sp. A and an indeterminate grammysiid pelecypod from the same concretion are illustrated. Information is provided to show that Newsomella Foerste, from Wenlockian-Ludlovian rocks of Illinois, Wisconsin, and Tennessee, is not a subgenus of Rhombopteria Jackson. -Authors

  8. Origin of Silurian reefs in the Alexander Terrane of southeastern Alaska

    SciTech Connect

    Soja, C.M. )

    1991-04-01

    Lower to Upper Silurian (upper Llandovery-Ludlow) limestones belonging to the Heceta Formation record several episodes of reef growth in the Alexander terrane of southeastern Alaska. As the oldest carbonates of wide-spread distribution in the region, the Heceta limestones represent the earliest development of a shallow-marine platform within the Alexander arc and the oldest foundation for reef evolution. These deposits provide important insights into the dynamic processes, styles, and bathymetry associated with reef growth in tectonically active oceanic islands. Massive stromatoporoids, corals, and red algae are preserved in fragmental rudstones and represent a fringing reef that formed at the seaward edge of the incipient marine shelf. Accessory constituents in this reef include crinoids and the cyanobacterium Girvanella. Small biostromes were constructed by ramose corals and stromatoporoids on oncolitic substrates in backreef or lagoonal environments. These buildups were associated with low-diversity assemblages of brachiopods and with gastropods, amphiporids, calcareous algae and cyanobacteria. Microbial boundstones reflect the widespread encrustation of cyanobacteria and calcified microproblematica on shelly debris as stromatolitic mats that resulted in the development of a stromatactoid-bearing mud mound and a barrier reef complex. Epiphytaceans, other microbes, and aphrosalpingid sponges were the primary frame-builders of the barrier reefs. These buildups attained significant relief at the shelf margin and shed detritus as slumped blocks and debris flows into deep-water sites along the slope. The similarity of these stromatolitic-aphrosalpingid reefs to those from Siluro-Devonian strata of autochthonous southwestern Alaska suggests paleobiogeographic ties of the Alexander terrane to cratonal North America during the Silurian.

  9. Tropical Silurian Paleotemperatures from Clumped Isotope Analysis of Coexisting Dolomite and Calcite

    NASA Astrophysics Data System (ADS)

    Winkelstern, I. Z.; Lohmann, K. C.

    2013-12-01

    In many instances, pervasive diagenetic alteration of original material prevents the use of quantitative climate proxies on Paleozoic or older rocks. As an inherently diagenetic phase, dolomite may provide a more resilient paleotemperature resource. The Δ47 carbonate clumped isotope thermometer has been shown to be an accurate paleothermometer and, in a limited way, has been shown to be applicable to dolomites. The shallow water carbonates of the Pipe Creek Jr. Reef in central Indiana offer an opportunity to test the viability of the technique in ancient dolomite. After formation in the late Silurian, a sea level drop resulted in a diagenetic sequence of meteoric phreatic alteration of marine cement and biotic components, which included precipitation of dolomite cements inter-grown within the meteoric phreatic calcite cement. This was post-dated by a coarse void filling calcite spar formed at burial temperatures of ~100°C (based on fluid inclusion analysis). Preliminary analyses of coexisting dolomite and calcite suggest that near-surface temperatures are preserved in dolomites despite having experienced elevated thermal diagenetic effects.. In contrast, co-existing early-formed calcites exhibit resetting of earth surface temperatures to elevated values. Δ47 measurements in dolomites yield temperatures around 30°C using the Guo et al., (2009) theoretical calibration. This contrasts with analyses of early (original) and late (hydrothermal) calcites, which record temperatures greater than ~80°C using the Δ47-calcite calibration of Dennis and Schrag (2010). These data support the hypothesis that dolomite can be a more resilient paleotemperature proxy relative to calcite in deep-time studies. Temperatures from dolomites compare reasonably with other late Silurian paleoclimate studies, and offer insight into regional-scale paleoclimate.

  10. Silurian trace fossils in carbonate turbidites from the Alexander Arc of southeastern Alaska

    SciTech Connect

    Soja, C.M. )

    1990-05-01

    Early to Late Silurian (Wenlock-Ludlow) body and trace fossils from the Heceta Formation are preserved in the oldest widespread carbonates in the Alexander terrane of southeastern Alaska. They represent the earliest shelly benthos to inhabit a diversity of marine environments and are important indicators of the early stages in benthic community development within this ancient island arc. The trace fossils are significant because they add to a small but growing body of knowledge about ichnofaunas in deep-water Paleozoic carbonates. Proximal to medial carbonate turbidites yield a low-diversity suite of trace fossils that comprises five distinct types of biogenic structures. Bedding planes reveal simple epichnial burrows (Planolites), cross-cutting burrows (Fucusopsis), and tiny cylindrical burrows. These and other casts, including chondrites( )-like burrow clusters, represent the feeding activities (fodinichnia) of preturbidite animals. Hypichnial burrows and rare endichnial traces reflect the activities of postturbidite animals. Broken and offset traces indicate that infaunal biota commenced burrowing before slumping and subsequent soft-sediment deformation. The abundance and density of trace fossils increases offshore in the medial turbidites associated with a decrease in the size and amount of coarse particles and with an increase in mud and preserved organic material. Although diversity levels are similar in the proximal and medial turbidite facies, they are much lower than in Paleozoic siliciclastic turbidites. This may reflect unfavorable environmental conditions for infaunal biota or paleobiogeographic isolation of the Alexander terrane during the Silurian. A greater use of trace fossils in terrane analysis will help to resolve this issue and should provide new data for reconstructing the paleogeography of circum-Pacific terranes.

  11. Late ordovician—early silurian glaciofluvial deposits preserved in palaeovalleys in South Jordan

    NASA Astrophysics Data System (ADS)

    Powell, John H.; Moh'd, Basim Khalil; Masri, Ahmed

    1994-03-01

    Periglacial, fluvial strata of Late Ordovician age, infilling incised palaeovalleys in the lower part of the shallow-marine, siliciclastic Khreim Group (Late Ordovician to Silurian) are described from outcrops in south Jordan. The palaeovalley fill predominantly comprises poorly sorted, medium- to coarse-grained, sub-arkose with subordinate beds of pebble- to cobble-size diamictite. Clasts include subangular rip-up sandstone and sparse shelly fossils derived from the local bedrock, together with exotic, rounded pebbles and cobbles derived from the Cambro-Ordovician sandstones and granitoid Precambrian rocks in the palaeohinterland, situated to the south. The palaeovalley fill is locally characterised by synsedimentary slump folds, micro-faulting and contorted bedding. These are attributed either to gravitational slumping at palaeovalley margins, or collapse due to melting of stagnant supporting ice. At some localities, the sandstones are typically trough cross-bedded, and exhibit upward-fining trends terminating in current ripples, suggesting episodic infill of the palaeovalleys. The few palaeocurrent measurements available from these sedimentary structures indicate a general palaeoflow to the north, coincident with the general orientation of the exposed palaeovalleys. The palaeovalleys may have been formed by glacial and/or fluvial processes; their predominantly sandstone fill is interpreted as fluvial and/or glaciofluvial in origin, and was probably deposited as proximal proglacial outwash at some distance from the ice-sheet which lay to the south, in present-day Saudi Arabia. The Batra Mudstone, which overlies coeval, non-channelised, glaciofluvial sandstones yields an Early Llandovery fauna, thus constraining the upper age of the palaeovalley infilling. By analogy with similar strata in Saudi Arabia, erosion of the palaeovalleys and infilling is likely to have taken place during Ashgill to Early Llandovery times. Erosion of the palaeovalleys and their

  12. The role of strain partitioning on intermontane basin inception and isolation, External Western Gibraltar Arc

    NASA Astrophysics Data System (ADS)

    Jiménez-Bonilla, A.; Expósito, I.; Balanyá, J. C.; Díaz-Azpiroz, M.; Barcos, L.

    2015-12-01

    The intermontane Ronda Basin, currently located in the Western Betics External Zones, started as an embayment of the Betic foreland basin during the Tortonian. We have characterized a post-Serravallian, basin-related deformation event that overprinted the former fold-and-thrust belt. Updated structural and kinematic maps allow us to identify NW-SE basinward-dipping normal faults at the southwestern and northeastern boundaries of the basin and NE-SW shortening structures (large-scale folds and reverse faults) affecting both the outcropping basement and partially the basin infill. In order to test the possible tectonic activity of these structures during the last 5 Ma, exhaustive geomorphologic analyses in the Ronda Basin area have been done. This included the qualitative study of relief and drainage network, together with the characterization of quantitative indices (SLk, Smf, Vf and HI). These results obtained from this analysis are coherent with structural data and suggest that the identified post-Serravallian structures were active up to at least 5 Ma. We also conclude that the Ronda Basin was generated by along strike segmentation of the relief in the Western Betics induced by NE-SW (arc-parallel) stretching accompanied with NW-SE shortening. In the NW basin boundary, the strain was partitioned into ENE-WSW dextral strike-slip faults and NE-SW shortening structures, which gave rise to a Messinian transpressive structural high that disconnected the former Ronda Basin from its parental foreland basin.

  13. The origin and geologic evolution of the East Continent Rift Basin

    SciTech Connect

    Drahovzal, J.A. . Kentucky Geological Survey)

    1992-01-01

    The East Continent Rift Basin (ECRB) is a newly recognized, dominantly sedimentary-volcanic Proterozoic rift basin that apparently represents the southern extension of the Keweenawan Midcontinent Rift. The ECRB extends from central Michigan at least as far south as south-central Kentucky. The inferred age of the rift fill is approximately 1,000 Ma. Evidence supporting a rift origin for the ECRB includes: interbedding of continental flood basalts and felsic volcanics with siliciclastics; sedimentary fill consisting of distal, arid-climate alluvial fan sediments that lack metamorphic lithologies; close proximity and similar lithologic succession to the Keweenawan rift-fill rocks of the Michigan Basin; and inferred marginal block faulting of Granite-Rhyolite Province rocks near the western edge of the ECRB. ECRB evolution is interpreted as follows: (1) formation of Granite-Rhyolite Province rocks (1,500--1,340 Ma); (2) Keweenawan crustal extension and rifting with development of central mafic complexes, emplacement of volcanic rocks, and deposition of siliciclastic fill from eroded marginal Granite-Rhyolite Province tilted fault blocks (ca 1,000 Ma); (3) overthrusting of the Grenville allochthon and associated foreland thrusting and folding of the rift sequence rocks together with deposition of foreland basin sediments (975---890 Ma); (4) Late Proterozoic erosional removal of the foreland basin sediments and interpreted wrench faulting along the Grenville Front (post-975 to pre-570 Ma); and (5) tectonic inversion, with the ECRB area remaining relatively high during major cambrian subsidence in central Kentucky (590--510 Ma).

  14. BASIN STRUCTURE FROM TWO-DIMENSIONAL SEISMIC REFLECTION DATA, CRAZY MOUNTAINS BASIN, MONTANA

    SciTech Connect

    David J. Taylor

    2003-08-01

    Some 140 miles of multichannel seismic reflection data, acquired commercially in the 1970's, were reprocessed by the U.S. Geological Survey in late 2000 and early 2001 to interpret the subsurface geology of the Crazy Mountains Basin, an asymmetric Laramide foreland basin located in south-central Montana. The seismic data indicate that the northwestern basin margin is controlled by a thrust fault that places basement rocks over a thick (22,000 feet) sequence of Paleozoic and Mesozoic sedimentary rocks to the south. From the deep basin trough, Paleozoic through Tertiary rocks slope gently upward to the south and southeast. The northern boundary of the basin, which is not imaged well by the seismic data, appears to be folded over a basement ridge rather than being truncated against a fault plane. Seismic data along the basin margin to the south indicate that several fault controlled basement highs may have been created by thin-skinned tectonics where a series of shallow thrust faults cut Precambrian, Paleozoic, and early Mesozoic rocks, whereas, in contrast, Cretaceous and Tertiary strata are folded. The data are further interpreted to indicate that this fault-bounded asymmetric basin contains several structures that possibly could trap hydrocarbons, provided source rocks, reservoirs, and seals are present. In addition, faults in the deep basin trough may have created enough fracturing to enhance porosity, thus developing ''sweet spots'' for hydrocarbons in basin-centered continuous gas accumulations.

  15. Foreland segmentation along an active convergent margin: New constraints in southeastern Sicily (Italy) from seismic and geodetic observations

    NASA Astrophysics Data System (ADS)

    Musumeci, Carla; Scarfì, Luciano; Palano, Mimmo; Patanè, Domenico

    2014-09-01

    We performed an in-depth analysis of the ongoing tectonics of a large sector of southern Sicily, including the Hyblean Foreland and the front of the Maghrebian Chain, as well as the Ionian Sea offshore, through the integration of seismic and GPS observations collected in the nearly two decades. In particular, a dataset consisting of more than 1100 small-to moderate-magnitude earthquakes (1.0 ≤ ML ≤ 4.6) has been used for local earthquake tomography in order to trace the characteristics of the faulting systems, and for focal mechanisms computation to resolve the current local stress field and to characterise the faulting regime of the investigated area. In addition, GPS measurements, carried out on both episodic and continuous stations, allowed us to infer the main features of the current crustal deformation pattern. Main results evidence that the Hyblean Plateau is subject to a general strike-slip faulting regime, with a maximum horizontal stress axis NW-SE to NNW-SSE oriented, in agreement with the Eurasia-Nubia direction of convergence. The Plateau is separated into two different tectonic crustal blocks by the left-lateral strike-slip Scicli-Ragusa Fault System. The western block moves in agreement with central Sicily while the eastern one accommodates part of the contraction arising from the main Eurasia-Nubia convergence. Furthermore, we provided evidences leading to consider the Hyblean-Maltese Escarpment Fault System as an active boundary characterised by a left-lateral strike-slip motion, separating the eastern block of the Plateau from the Ionian basin. All these evidences lend credit to a crustal segmentation of the southeastern Sicily.

  16. Provenance change of sediment input in the northeastern foreland of Pamir related to collision of the Indian Plate with the Kohistan-Ladakh arc at around 47 Ma

    NASA Astrophysics Data System (ADS)

    Sun, Jimin; Xiao, Wenjiao; Windley, Brian F.; Ji, Weiqiang; Fu, Bihong; Wang, Jiangang; Jin, Chunsheng

    2016-02-01

    The Pamir plateau forms a prominent tectonic salient that marks the western end of the Himalayan orogen containing several terranes that were accreted to Eurasia from the Late Paleozoic to Cenozoic. A detailed knowledge of the tectonic evolution of the Pamir salient during the Cenozoic is important for our understanding of the intracontinental deformation in the western Himalaya. Although the tectonic evolution of the Pamir salient has long been studied, the timing of collision between the Indian Plate and the Kohistan-Ladakh arc is still a matter of debate. We present new U-Pb ages and Hf isotopes of detrital zircons, magnetic fabrics, and stable isotopes from the foreland basin on the northeastern margin of the Pamir that indicate a change in sediment provenance started at about 47 Ma. Sediments in the southwest Tarim Basin were partially derived from the uplifted and eroded Karakoram and Kohistan terranes created by the collision between the Indian Plate and the Kohistan-Ladakh arc at circa 47 Ma, as a result of northward thrusting and propagation of the Indian Plate under Eurasia.

  17. Areal extent, hydrogeologic characteristics, and possible origins of the carbonate rock Newburg Zone (Middle-Upper Silurian) in Ohio

    USGS Publications Warehouse

    Strobel, M.L.; Bugliosi, E.F.

    1991-01-01

    The zone occurs in carbonate rocks of Middle to Late Silurian age across much of Ohio. Known also to well drillers as the "Second Water' in the "Big Lime' carbonate sequence, the Newburg zone is a source of hydrocarbons in northeast Ohio, brines in southeast Ohio, and a widespread source of water over much of west-central Ohio. Close to recharge areas, the quality of the water is comparable to that of the overlying carbonate rocks; thus, the Newburg zone warrants further investigation as a source of water for domestic use. Theories for the porosity and permeabilty of the Newburg zone include: 1) deposition of carbonate or quartz sand along an erosional surface and later lithified to porous and permeable sandstone; 2) dissolution of fossils within Silurian reef complexes; 3) fracture-induced porosity along thrust faults developed during the Alleghenian orogeny; and 4) a combination of these processes. -from Authors

  18. Carbonate clumped isotope constraints on Silurian ocean temperature and seawater δ18O

    NASA Astrophysics Data System (ADS)

    Cummins, Renata C.; Finnegan, Seth; Fike, David A.; Eiler, John M.; Fischer, Woodward W.

    2014-09-01

    Much of what we know about the history of Earth’s climate derives from the chemistry of carbonate minerals in the sedimentary record. The oxygen isotopic compositions (δ18O) of calcitic marine fossils and cements have been widely used as a proxy for past seawater temperatures, but application of this proxy to deep geologic time is complicated by diagenetic alteration and uncertainties in the δ18O of seawater in the past. Carbonate clumped isotope thermometry provides an independent estimate of the temperature of the water from which a calcite phase precipitated, and allows direct calculation of the δ18O of the water. The clumped isotope composition of calcites is also highly sensitive to recrystallization and can help diagnose different modes of diagenetic alteration, enabling evaluation of preservation states and identification of the most pristine materials from within a sample set-critical information for assessing the quality of paleoproxy data generated from carbonates. We measured the clumped isotope composition of a large suite of calcitic fossils (primarily brachiopods and corals), sedimentary grains, and cements from Silurian (ca. 433 Ma) stratigraphic sections on the island of Gotland, Sweden. Substantial variability in clumped isotope temperatures suggests differential preservation with alteration largely tied to rock-buffered diagenesis, complicating the generation of a stratigraphically resolved climate history through these sections. Despite the generally high preservation quality of samples from these sections, micro-scale observations of calcite fabric and trace metal composition using electron backscatter diffraction and electron microprobe analysis suggest that only a subset of relatively pristine samples retain primary clumped isotope signatures. These samples indicate that Silurian tropical oceans were likely warm (33 ± 7 °C) and similar in oxygen isotopic composition to that estimated for a “modern” ice-free world (δ18OVSMOW of -1

  19. Origin of arches in the northwestern Gulf of Mexico basin

    SciTech Connect

    Laubach, S.E.; Jackson, M.L.W. )

    1990-07-01

    The San Marcos and Sabine arches are prominent north- to northwest-trending basement uplifts in the northwestern Gulf of Mexico basin that may be late Mesozoic to Cenozoic foreland or intraplate folds rather than domes over plutons or buoyant basement blocks. These arches are subparallel to and contemporaneous with orogenic episodes in the northwest-trending fold-thrust belt of Mexico. Arch movement was also contemporaneous with rapid convergence between the North American and Pacific plates. Arch development in the gulf as a result of tectonic compression is plausible in view of increasing recognition of wide zones of foreland and intraplate deformation in continents. Current tectonic models of the development of the gulf inaccurately predict gradual, decelerating subsidence when these arches were most active.

  20. The East Carpathians: Indications of phase transitions, lithospheric failure and decoupled evolution of thrust belt and its foreland

    NASA Astrophysics Data System (ADS)

    Artyushkov, E. V.; Baer, M. A.; Mörner, N.-A.

    1996-09-01

    An analysis is presented of the tectonic development of the East Carpathians since the Late Oligocene. The geological and geomorphological data show that five epochs of convergence and nappe emplacement took place with the last one occurring 11-12 m.y. B.P. After these compressional events the nappe surface remained near sea level. The crustal uplift which formed the present mountains began 3 m.y. B.P. and after 99% of the shortening of the Carpathians had been completed. The Pre-Carpathian foreland basin, up to 3-5 km deep, formed on the margin of the East European Platform in the Middle Miocene. Analysis of the evolution of the basin shows that it deepened away from the nappe-stack and most of the subsidence occurred when there was no convergence. This precludes lithospheric flexure due to convergence as a mechanism for basin formation. At 11-12 m.y. B.P. the inner part of the basin, ˜ 50 km wide, was overridden by the Carpathian nappe, up to 12-14 km thick. At that time, a slight crustal uplift took place, rather than subsidence, in the shallow remnant-outer basin part (the present foredeep) which emerged above sea level. An additional 7-8 km of subsidence then occurred in the foredeep of the southeastern Carpathians in the Late Miocene-Early Pleistocene when very little convergence took place. The evolution of the Carpathian foredeep shows that lithospheric flexure of 2-5 km occurred in regions, 20-40 km wide. Similar amounts of flexure and large basement faults exist under the nappe. This style of deformation indicates flexural rigidity of the lithosphere that is several orders of magnitude smaller than in stable cratonic regions. Under a low flexural rigidity, the crust should be close to local isostasy. Then the isostatic response to superposition of a 10-13-km-thick nappe on the platform margin which was near sea level would form high mountains. The crustal surface, however, remained at a low altitude. We interpret this to be the result of contraction of

  1. An integrated model for the tectonic development of the frontal Brooks Range and Colville Basin 250 km west of the Trans-Alaska Crustal Transect

    USGS Publications Warehouse

    Cole, F.; Bird, K.J.; Toro, J.; Roure, F.; O'Sullivan, P. B.; Pawlewicz, M.; Howell, D.G.

    1997-01-01

    We present a kinematic model for the sequence of deformation and sedimentation in the frontal Brooks Range and adjacent Colville Basin in the Etivluk River region, 250 km west of the Trans-Alaska Crustal Transect (TACT). The model is based on a tectonic subsidence analysis of the foreland basin, combined with structural, stratigraphic, and thermal studies of the northern edge of the Brooks Range thrust belt. We interpret six discrete tectonic events that led to the present-day configuration of the thrust belt in this area: (1) emplacement of ophiolitic allochthons over the distal continental margin rocks in Valanginian time, hundreds of kilometers south of this study, (2) Hauterivian uplift of the Barrow Arch rift margin, affecting the northern part of the Colville Basin, (3) Barremian contraction involving emplacement of distal continental margin and ophiolitic allochthons onto the Endicott Mountains allochthon and creation of a southward dipping flexural basin on the North Slope autochthon, (4) mid-Cretaceous exhumation of imbricated rocks in the Brooks Range during northward propagation of the thrust front into the foreland, (5) minor thrusting in Late Cretaceous-Paleocene in the northern foreland to the northern limit of contractional structures, and (6) regional exhumation of the orogen and the foreland in Paleocene-Eocene time. This sequence of deformation agrees well with a simple model of a forward propagating thrust system. Copyright 1997 by the American Geophysical Union.

  2. The Lower Silurian Osmundsberg K-bentonite. Part I: Stratigraphic position, distribution, and palaeogeographic significance

    USGS Publications Warehouse

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

    1998-01-01

    A large number of Lower Silurian (Llandovery) K-bentonite beds have been recorded from northwestern Europe, particularly in Baltoscandia and the British Isles, but previous attempts to trace single beds regionally have yielded inconclusive results. The present study suggests that based on its unusual thickness, stratigraphic position and trace element geochemistry, one Telychian ash bed, the Osmundsberg K-bentonite, can be recognized at many localities in Estonia, Sweden and Norway and probably also in Scotland and Northern Ireland. This bed, which is up to 115 cm thick, is in the lower-middle turriculatus Zone. The stratigraphic position, thickness variation and geographic distribution of the Osmundsberg K-bentonite are illustrated by means of 12 selected Llandovery successions in Sweden, Estonia, Norway, Denmark, Scotland and Northern Ireland. In Baltoscandia, the Osmundsberg K-bentonite shows a trend of general thickness increase in a western direction suggesting that its source area was located in the northern Iapetus region between Baltica and Laurentia. Because large-magnitude ash falls like the one that produced the Osmundsberg K-bentonite last at most a few weeks, such an ash bed may be used as a unique time-plane for a variety of regional geological and palaeontological studies.

  3. Terminal Ordovician extinction: geochemical analysis of the Ordovician/Silurian boundary, Anticosti Island, Quebec

    SciTech Connect

    Orth, C.J.; Gilmore, J.S.; Quintana, L.R.; Sheehan, P.M.

    1986-05-01

    Elemental abundances (including Ir), carbon and oxygen ratios in carbonates, mineral content, and thin sections have been measured in samples collected across the conodont-defined Ordovician/Silurian (O/S) boundary exposed on Anticosti Island, Quebec. The Ir concentrations ranged from 5 to a maximum at the boundary of 58 parts per trillion (ppt). However, there is no evidence, on the basis of these Ir results, for the association of a large-body-Earth impact with the O/S extinction, because the Ir concentrations, like those of most other trace elements, are simply proportional to the clay (Al) content in the carbonate sequence. The /sup 13/C//sup 12/C and /sup 18/O//sup 16/O ratios decrease abruptly at the boundary, then just as abruptly increase to a long period of higher than preboundary ratios. These patterns are probably related to the salinity in the seaway, which was shallowing up to boundary time and then deepened and developed patch-reefs. Fresh-water input from rivers would have been most influential during the shallow-water conditions. 32 references, 4 figures.

  4. Occurrence and significance of Silurian K-bentonite beds at Arisaig, Nova Scotia, eastern Canada

    USGS Publications Warehouse

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

    1997-01-01

    The most extensive succession of K-bentonite beds known in the Silurian of North America occurs at Arisaig on the northern coast of Nova Scotia. At least 40 ash beds are present in the Llandoverian Ross Brook Formation and at least four in the early Ludlovian McAdam Brook Formation. Most of the beds are thin (<5 cm), but one bed (the Smith Brook K-bentonite bed) in the late Llandoverian crenulata Zone and another (the McAdam Brook K-bentonite bed) in the early Ludlovian nilssoni Zone each reach a thickness of 20 cm. New graptolite collections provide critical information on the biostratigraphic position of the K-bentonite beds in the Ross Brook Formation. Geochemical data show that the Arisaig ash beds represent calc-alkaline magmas from plate margin, subduction-related volcanic vents. Differences in K-bentonite stratigraphie distribution, combined with paleogeographic considerations, suggest that the volcanoes were located much farther to the south in the Iapetus than the source volcanoes of the British - Baltoscandian Llandoverian K-bentonites.

  5. Diversity dynamics of silurian-early carboniferous land plants in South china.

    PubMed

    Xiong, Conghui; Wang, Deming; Wang, Qi; Benton, Michael J; Xue, Jinzhuang; Meng, Meicen; Zhao, Qi; Zhang, Jing

    2013-01-01

    New megafossil and microfossil data indicate four episodes in the diversification of Silurian-Early Carboniferous land plants of South China, a relatively continuous regional record. Plant diversity increased throughout, but the rising curve was punctuated by three major falls. There were peaks of origination in the Ludlow-Pragian, Givetian, late Famennian and Visean and peaks of extinction in the Pragian-Emsian, Givetian and early Tournaisian. Speciation and extinction rates were highest in the Lochkovian-Pragian and became progressively lower in subsequent stages. High correlation coefficients indicate that these events are associated with the availability of land habitat contingent on eustatic variations and increasing numbers of cosmopolitan genera. Meanwhile, proportions of endemic genera declined gradually. Due to less endemism and more migrations, both speciation and species extinction rates reduced. The changes of diversity and the timing of the three extinctions of land plants in South China are similar to those known already from Laurussia. However, the largest events in the Lochkovian-Pragian and subsequent smaller ones have not been seen in the global pattern of plant evolution. These land plant events do not correspond well temporally with those affecting land vertebrates or marine invertebrates. In South China, the diversity curve of land plants is generally opposite to that of marine faunas, showing a strong effect of eustatic variations. The increasing diversity of both land vertebrates and plants was punctuated above the Devonian-Carboniferous boundary, known as Romer's Gap, implying common underlying constraints on macroevolution of land animals and plants. PMID:24073276

  6. A new phyllocarid (Crustacea: Malacostraca) from the Silurian Fossil-Lagerstätte of Herefordshire, UK.

    PubMed Central

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

    2004-01-01

    A new three-dimensionally preserved arthropod, Cinerocaris magnifica, from the Wenlock Series (Silurian) of Herefordshire, UK, is described and assigned to the Phyllocarida (Crustacea). The description and reconstruction are based on specimens that have been serially ground, reconstructed by computer and rendered in three dimensions as coloured virtual models. Cinerocaris magnifica displayed the tagmosis characteristic of phyllocarids, with eight thoracic and seven abdominal somites, terminating in a telson with furca. The remarkable preservation of the appendages makes this the earliest completely known malacostracan crustacean. Two pairs of antennae (the first with two flagella) were followed by a mandible and first maxilla, each with a slender palp-like ramus. The second maxilla consisted of a limb stem with endites and an endopod that tapered distally. There was no exopod. The thoracopods comprised a limb stem with six or seven endites, an arrangement previously known only in entomostracans, and an endopod with about five endites. Flap-like outer rami correspond to an exopod and epipods. The pleopods bore two long slender oar-blade-like rami. Cladistic analysis places C. magnifica as a plesion within the Echinocaridina. It provides critical evidence of the limb morphology of an early malacostracan, which will be important in understanding crustacean evolution. PMID:15058388

  7. Subsidence history in basins of northern Algeria

    NASA Astrophysics Data System (ADS)

    Bracene, Rabah; Patriat, Martin; Ellouz, Nadine; Gaulier, Jean-Michel

    2003-02-01

    The Tellian foreland in Algeria represents a part of the southern Tethyan margin during the Mesozoic. Its tectonic evolution includes a rifting stage during the Triassic and Liassic times characterised by tilted blocks and early diapiric events during the Liassic, a post-rift regime from Middle Jurassic up to the Late Cretaceous and basin inversion during the Tertiary related to the African and European plates convergence. The subsidence modelling supported by surface and subsurface data integration emphasises different subsidence phases. Liassic subsidence phase under Tethyan and Atlantic control related to crustal thinning. Late Jurassic, Cretaceous and Tertiary subsidence phases, where the first one is linked to diapiric events and the second in eastern Algeria to the effects of the rifting event developed more easterly in the Gulf of Gabès and Sirte. The last one is flexural and occurs in foreland basins during the Tertiary. Taking into account the subsidence record of each structural domain, a correlation between tectonic events and the subsidence phases can be established.

  8. The Jura Mountains — an active foreland fold-and-thrust belt?

    NASA Astrophysics Data System (ADS)

    Becker, Arnfried

    2000-06-01

    Recently completed in situ stress measurements using the borehole slotter at 33 new test sites within the Swiss and French Jura Mountains, combined with previously published stress data, allow a detailed description of the contemporary state of stress in this fold-and-thrust belt and the adjacent foreland. Five stress provinces can be recognized, with two different general orientations of maximum horizontal stress SH: (1) the Central and Southwest Provinces with a NNW-SSE to NNE-SSW orientation; (2) the East, Northwest and Southeast Provinces with an E-W to NW-SE orientation. Stress magnitudes are in general higher in the southern than in the northern Jura Mountains. Characteristic of the northern Jura is an E-W-trending zone of low stress magnitudes which can be traced from the Bresse Depression south of Besançon to the eastern end of the Jura northwest of Zurich. Boundaries of stress provinces show poor agreement with boundaries of tectonic units in the Jura. In addition, stress provinces extend beyond the boundaries of the Jura Mountains into their foreland. Furthermore, palaeo-stress orientations show large discrepancies with respect to the contemporary stress orientation. These findings are considered to indicate a termination of Jura thin-skinned foreland tectonics, which probably took place some time between 9 and 4 Ma according to palaeontological and tectonic evidence. It is suggested that a new style of tectonics has commenced in the Jura Mountains, deforming both the basement directly below the Jura fold-and-thrust belt and the cover rocks in a similar mode.

  9. The basins on the Argentine continental margin

    SciTech Connect

    Urien, C.M.

    1996-08-01

    After the stabilization of the central Gondwana Craton, orogenic belts were accreted, as a result of convergence events and an extensive passive margin developed in southwestern Gondwana. Thermal subsidence in Parana, Karoo-Ventania basins and the Late Paleozoic-Early Mesozoic rifts, were modified by the Gondwana breakup and the South Atlantic opening. Early Paleozoic marine transgressions deposited the Table Mountain Group in Ventania. In southwestern Patagonia foreland clastics were deposited. Magmatic arcs and marine units indicate a tectonic trough was formed, alternating with continental sequences, over Late Paleozoic metamorphics and intrusives, resulting from plastered terrains along the Gondwana margin. In Patagonia, Permo-Carboniferous continental and glacio marine clastics infill the basins, while in Ventania, paralic sequences, grade from neritic to continental to the northeast, extending beneath the continental margin. The Triassic-Jurassic rift basins progressed onto regional widespread acid lavas and were infilled by lagoonal organic-rich sequences. Early drift phase built basins transverse to the margin, with fluvio-lacustrine sequences: Salado, Colorado, Valdes-Rawson, San Julian and North Malvinas intracratonic basins, which underwent transtensional faulting. Post-Oxfordian to Neocomian brackish sequences, onlapped the conjugate basins during the margin`s drift, with petroleum systems, as in Austral and Malvinas. In the Valanginian, basic extrusions commenced to form on the continental border, heralding the oceanic phase. Due to thermal subsidence, offlaping sediments prograded onto the remaining half-grabens. Several petroleum systems, proven and hypothetical, are identified in this region.

  10. Miocene sedimentation and subsidence during continent-continent collision, Bengal basin, Bangladesh

    NASA Astrophysics Data System (ADS)

    Uddin, Ashraf; Lundberg, Neil

    2004-02-01

    The Bengal basin, a complex foreland basin south of the eastern Himalayas, exhibits dramatic variability in Neogene sediment thickness that reflects a complicated depositional and tectonic history. This basin originally formed as a trailing margin SE of the Indian continental crust, complicated by convergence with Asia to the north and oblique convergence with Burma to the east. Newly compiled isopach data and previously reported seismic data show evidence of thickening of basin fill toward the south, opposite of the pattern typically seen in foreland basins. This is presumably due to sedimentary loading of voluminous deltaic sediments near the continent-ocean boundary and basinward downfaulting analogous to that in the Gulf of Mexico. Isopach data show that there is considerable vertical relief along the base of the Miocene stratigraphic sequence, probably due to down-to-the-basin faulting caused by focused deltaic sedimentation and associated crustal flexure. In contrast, when viewed in east-west profile, basin shape is more typical of a foreland basin, with strata thickening eastward toward the Indo-Burman ranges, which reflects east-west convergence with Southeast Asia. Comparison of the lateral and vertical extent of the Bhuban and Boka Bil Formations with the Bouguer anomaly map of Bangladesh suggests that considerable subsidence of the Sylhet trough (in the northeastern part of the Bengal basin), which has the lowest gravity value of the region, had not taken place by the end of the Miocene. This post-Miocene subsidence is attributed to tectonic loading from southward thrusting of the Shillong Plateau along the Dauki fault. Relatively uniform Miocene isopachs across the Sylhet trough confirm that this began in the Pliocene, consistent with results of recent research on sediment provenance. In the northwest, in the region south of the Siwalik foreland basin, continental crust has not as yet been loaded, allowing relatively little accommodation space for

  11. Research on the Quaternary fluvial geomorphological surface sequence of the foreland region in southern Longmen Shan, eastern Tibet

    NASA Astrophysics Data System (ADS)

    Jiang, Dawei; Zhang, Shimin; Li, Wei

    2016-09-01

    Research on the complex structure of the Longmen Shan foreland is of great significance for understanding the tectonism of the eastern Tibetan Plateau. Therefore, using field survey of abandoned alluvial fans that developed during the middle Pleistocene and the terraces of the modern Qingyi River, a geomorphological surface sequence for the foreland region was established to study the tectonic surface processes. We know that the deformations of river terraces can serve as foundations for the study of tectonic activity. Because the Qingyi River ran through the foreland region in the south range of Longmen Shan, it is an appropriate research area and was adopted to solve these problems. However, in the humid temperate region, the terraces are strongly eroded and hardly retain continuous morphological surfaces. In addition, no marker horizons are available that can be utilized to restrain the corresponding relationships among terraces at the same level. To solve these problems, high-precision field measurements of the terraces and alluvial fan were made, and a series of long cross sections were acquired to determine the spatial relationships between the geomorphological surfaces; moreover, based on major element tests and grain size analyses, we found that the sediments of the geomorphological surfaces at all levels had favorable corresponding relationships. Using those specific analyses of geomorphological surfaces and sediments, a geomorphological surface sequence was derived for the foreland region. The surface sequence can be employed to study the tectonism of the foreland region over larger spatial and temporal ranges rather than using the limited modern terraces. In addition, after the ages of the geomorphological surfaces at various levels were further tested, the evolution of Qingyi River especially its two migrations since the middle Pleistocene in the foreland was determined.

  12. Paleozoic basins in West Africa and the Mauritanide thrust belt

    NASA Astrophysics Data System (ADS)

    Villeneuve, Michel

    2005-10-01

    The evolution of the Paleozoic basins of West Africa is strongly depending on the structuration of the different belts which are surrounding the West African Craton. We distinguish the "Taoudeni Basin" located in the center of the craton from the basins located on the West African Craton margin (Tindouf, Tamale and several troughs limiting the western side of the Taoudeni Basin). Other basins are located on top of the Pan-African or Hercynian belts (Bové, Kandi, Ouallen in Semmen and Diourbel basins) or on top of the Proterozoic shields (The Ghana basins). Some are evidenced underneath the Mesozoic-Cenozoic coastal basins (Bové and Ghana basins). The sedimentation started with the Marinoan glacial event (620-580 Ma) and ended with the carbonates of the Early Carboniferous. The main tectonic or climatic events that occurred during this period are registered by the sediments. Among them are, the "Série pourprée glaciogenic deposits, the Pan-African II tectonic event (550-500 Ma) which affects the southwestern part of the Taoudeni Basin, the Late Ordovician glaciogenic event, the Early Silurian marine transgression, the Early Devonian marine regression and the Hercynian tectonic event (330-270 Ma) which affects the Paleozoic basins located on the western and northern parts of the West African Craton. The second part of this paper is devoted to a synthetic review of the Mauritanides Belt which is extending from Southern Senegal to the Moroccan High Atlas. This belt includes both old Pan-African belts and Paleozoic sediments (belonging to the western part of the Bové, Taoudeni and Tindouf basins) tectonised and metamorphosed during the Hercynian orogen. The third part points out the close relationships between the Paleozoic basins and the main tectonic event for the main periods of the West African Craton evolution.

  13. Age and geochemistry of Silurian gabbroic rocks in the Tongbai orogen, central China: Implications for the geodynamic evolution of the North Qinling arc-back-arc system

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Wu, Yuan-Bao; Qin, Zheng-Wei; Zhu, Liu-Qin; Liu, Qian; Liu, Xiao-Chi; Gao, Shan; Wijbrans, Jan R.; Zhou, Lian; Gong, Hu-Jun; Yuan, Hong-Lin

    2013-10-01

    The tectonic properties of the Erlangping unit and the subduction polarity of oceanic basins in the North Qinling-Tongbai orogen have been the focus of debate for more than twenty years. The resolution of these controversies hinges on the refined constraints on the location and nature of subduction-related magmatism. In this contribution, we provide a combined study of zircon U-Pb ages, major and trace element geochemistry, and Sr-Nd-Hf isotope compositions of gabbroic rocks from the Erlangping unit in the Tongbai orogen. U-Pb dating of zircons from two gabbroic diorite samples yielded two weighted mean ages of 443 ± 3 and 440 ± 4 Ma. The Erlangping gabbroic rocks are tholeiitic in composition with variable MgO (4.48-8.17%), and low K2O (0.25-1.01%) and TiO2 (0.60-1.79%) contents. They are characterized by enrichment of LILEs, depletion of HFSEs, and highly positive whole-rock ɛNd(t) (3.76-5.68) and zircon ɛHf(t) (12.0-12.1) values. The geochemical features indicate that the Erlangping gabbroic rocks were derived from a depleted lithospheric mantle that had been exposed to metasomatism by slab-derived fluid shortly before their generation. Their occurrence, coupled with coeval granitoids with highly positive ɛNd(t) values, manifest significant crustal growth in the North Qinling-Tongbai orogen during the late Ordovician-Silurian. In addition, the Erlangping gabbroic rocks have low Sr/Y (7.32-26.2) and (La/Yb)N (1.34-4.07) ratios, but high HREEs, Y and Sc contents. This implies that their mantle source had no residual garnet, and thus partial melting of the lithospheric mantle occurred under relatively low-pressure conditions. The generation of the Erlangping gabbroic rocks might result from incipient rifting of the Erlangping back-arc basin induced by the northward subduction of the Paleotethyan Shangdan Ocean. Taking into account the ca. 490 Ma collision between the Erlangping arc and North Qinling microcontinent, we suggested that the evolution of the North

  14. The Lower Silurian Osmundsberg K-bentonite. Part II: Mineralogy, geochemistry, chemostratigraphy and tectonomagmatic significance

    USGS Publications Warehouse

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

    1998-01-01

    The Lower Silurian Osmundsberg K-bentonite is a widespread ash bed that occurs throughout Baltoscandia and parts of northern Europe. This paper describes its characteristics at its type locality in the Province of Dalarna, Sweden. It contains mineralogical and chemical characteristics that permit its regional correlation in sections elsewhere in Sweden as well as Norway, Estonia, Denmark and Great Britain. The < 2 ??m clay fraction of the Osmundsberg bed contains abundant kaolinite in addition to randomly ordered (RO) illite/smectite (I/S). Modelling of the X-ray diffraction tracings showed the I/S consists of 18% illite and 82 % smectite. The high smectite and kaolinite content is indicative of a history with minimal burial temperatures. Analytical data from both pristine melt inclusions in primary quartz grains as well as whole rock samples can be used to constrain both the parental magma composition and the probable tectonic setting of the source volcanoes. The parental ash was dacitic to rhyolitic in composition and originated in a tectonically active collision margin setting. Whole rock chemical fingerprinting of coeval beds elsewhere in Baltoscandia produced a pronounced clustering of these samples in the Osmundsberg field of the discriminant analysis diagram. This, together with well-constrained biostratigraphic and lithostratigraphic data, provides the basis for regional correlation and supports the conclusion that the Osmundsberg K-bentonite is one of the most extensive fallout ash beds in the early Phanerozoic. The source volcano probably lay to the west of Baltica as part of the subduction complex associated with the closure of Iapetus.

  15. Shale gas reservoir characteristics of Ordovician-Silurian formations in the central Yangtze area, China

    NASA Astrophysics Data System (ADS)

    Shan, Chang'an; Zhang, Tingshan; Wei, Yong; Zhang, Zhao

    2016-07-01

    The characteristics of a shale gas reservoir and the potential of a shale gas resource of Ordovician-Silurian age in the north of the central Yangtze area were determined. Core samples from three wells in the study area were subjected to thin-section examination, scanning electron microscopy, nuclear magnetic resonance testing, X-ray diffraction mineral analysis, total organic carbon (TOC) testing, maturity testing, gas-bearing analysis, and gas component and isothermal adsorption experiments. A favorable segment of the gas shale reservoir was found in both the Wufeng Formation and the lower part of the Longmaxi Formation; these formations were formed from the late Katian to early Rhuddanian. The high-quality shale layers in wells J1, J2, and J3 featured thicknesses of 54.88 m, 48.49 m, and 52.00 m, respectively, and mainly comprised carbonaceous and siliceous shales. Clay and brittle minerals showed average contents of 37.5% and 62.5% (48.9% quartz), respectively. The shale exhibited type II1 kerogens with a vitrinite reflectance ranging from 1.94% to 3.51%. TOC contents of 0.22%-6.05% (average, 2.39%) were also observed. The reservoir spaces mainly included micropores and microfractures and were characterized by low porosity and permeability. Well J3 showed generally high gas contents, i.e., 1.12-3.16 m3/t (average 2.15 m3/t), and its gas was primarily methane. The relatively thick black shale reservoir featured high TOC content, high organic material maturity, high brittle mineral content, high gas content, low porosity, and low permeability. Shale gas adsorption was positively correlated with TOC content and organic maturity, weakly positive correlated with quartz content, and weakly negatively correlated with clay content. Therefore, the Wufeng and Longmaxi formations in the north of the central Yangtze area have a good potential for shale gas exploration.

  16. Late Wenlock (middle Silurian) bio-events: Caused by volatile boloid impact/s

    NASA Technical Reports Server (NTRS)

    Berry, W. B. N.; Wilde, P.

    1988-01-01

    Late Wenlockian (late mid-Silurian) life is characterized by three significant changes or bioevents: sudden development of massive carbonate reefs after a long interval of limited reef growth; sudden mass mortality among colonial zooplankton, graptolites; and origination of land plants with vascular tissue (Cooksonia). Both marine bioevents are short in duration and occur essentially simultaneously at the end of the Wenlock without any recorded major climatic change from the general global warm climate. These three disparate biologic events may be linked to sudden environmental change that could have resulted from sudden infusion of a massive amount of ammonia into the tropical ocean. Impact of a boloid or swarm of extraterrestrial bodies containing substantial quantities of a volatile (ammonia) component could provide such an infusion. Major carbonate precipitation (formation), as seen in the reefs as well as, to a more limited extent, in certain brachiopods, would be favored by increased pH resulting from addition of a massive quantity of ammonia into the upper ocean. Because of the buffer capacity of the ocean and dilution effects, the pH would have returned soon to equilibrium. Major proliferation of massive reefs ceased at the same time. Addition of ammonia as fertilizer to terrestrial environments in the tropics would have created optimum environmental conditions for development of land plants with vascular, nutrient-conductive tissue. Fertilization of terrestrial environments thus seemingly preceded development of vascular tissue by a short time interval. Although no direct evidence of impact of a volatile boloid may be found, the bioevent evidence is suggestive that such an impact in the oceans could have taken place. Indeed, in the case of an ammonia boloid, evidence, such as that of the Late Wenlockian bioevents may be the only available data for impact of such a boloid.

  17. Neogene coupling between Kuqa Basin and Southern Tien Shan Orogen, Northwestern China.

    PubMed

    He, Guang-Yu; Chen, Han-Lin

    2004-08-01

    Based on the sedimentary and subsiding features of Kuqa foreland basin, this paper presents the following characteristics of Neogene coupling relationship between Kuqa Basin and Southern Tien Shan Orogen, Northwestern China: (1) The Southern Tien Shan Orogen underwent Neogene uplifting of 4 km in height and the Kuqa Basin underwent Neogene subsidence of 4-6 km in depth accordingly beginning in 25 Ma; (2) The Southern Tien Shan Orogen moved continuously toward the Kuqa Basin, with largest structural shortening rate of greater than 53.7%, and the north boundary of the Kuqa Basin retreated continuously southward accordingly since the Miocene; (3) There are two subsidence centers with high subsiding rates and large subsiding extent, located in the eastern and western Kuqa Basin respectively, with the subsiding maximizing in the deposition period of Kuqa Formation. PMID:15236483

  18. A comparative analysis of pre-Silurian crustal building blocks of the northern and the southern Appalachian orogen

    USGS Publications Warehouse

    Hibbard, J.P.; van Staal, C.R.; Rankin, D.W.

    2007-01-01

    The New York promontory serves as the divide between the northern and southern segments of the Appalachian orogen. Antiquated subdivisions, distinct for each segment, implied that they had lithotectonic histories that were independent of each other. Using new lithotectonic subdivisions we compare first order features of the pre-Silurian orogenic 'building blocks' in order to test the validity of the implication of independent lithotectonic histories for the two segments. Three lithotectonic divisions, termed here the Laurentian, Iapetan, and the peri-Gondwanan realms, characterize the entire orogen. The Laurentian realm, composed of native North American rocks, is remarkably uniform for the length of the orogen. It records the multistage Neoproterozoic-early Paleozoic rift-drift history of the Appalachian passive margin, formation of a Taconic Seaway, and the ultimate demise of both in the Middle Ordovician. The Iapetan realm encompasses mainly oceanic and magmatic arc tracts that once lay within the Iapetus Ocean, between Laurentia and Gondwana. In the northern segment, the realm is divisible on the basis of stratigraphy and faunal provinciality into peri-Laurentian and peri-Gondwanan tracts that were amalgamated in the Late Ordovician. South of New York, stratigraphic and faunal controls decrease markedly; rock associations are not inconsistent with those of the northern Appalachians, although second-order differences exist. Exposed exotic crustal blocks of the peri-Gondwanan realm include Ganderia, Avalonia, and Meguma in the north, and Carolinia in the south. Carolinia most closely resembles Ganderia, both in early evolution and Late Ordovician-Silurian docking to Laurentia. Our comparison indicates that, to a first order, the pre-Silurian Appalachian orogen developed uniformly, starting with complex rifting and a subsequent drift phase to form the Appalachian margin, followed by the consolidation of Iapetan components and ending with accretion of the peri

  19. Eramosa Lagerstätte—Exceptionally preserved soft-bodied biotas with shallow-marine shelly and bioturbating organisms (Silurian, Ontario, Canada)

    NASA Astrophysics Data System (ADS)

    von Bitter, Peter H.; Purnell, Mark A.; Tetreault, Denis K.; Stott, Christopher A.

    2007-10-01

    The middle Silurian Eramosa Lagerstätte of Ontario, Canada, preserves taxonomically and taphonomically diverse biotas including articulated conodont skeletons and heterostracan fish, annelids and arthropods with soft body parts, and a diverse marine flora. Soft tissues are preserved as calcium phosphate and carbon films, the latter possibly stabilized by early diagenetic sulfurization. It is significant that the biotas also include a decalcified, autochthonous shelly marine fauna, and trace fossils. This association of exceptionally preserved and more typical fossils distinguishes the Eramosa from other Silurian shallow-marine Lagerstätten, such as the Waukesha Lagerstätte, and suggests that the Eramosa is not the product of exceptional preservation in an atypical environment, a bias claimed for many post-Cambrian Lagerstätten. The Eramosa Lagerstätte may provide a more reliable, balanced measure of what has been lost from the Silurian fossil record.

  20. The petroleum geology of the sub-Andean basins

    SciTech Connect

    Mathalone, J.M.P.

    1996-08-01

    The sub-Andean trend of basins spans the entire length of South America from Venezuela in the north to Argentina in the south. All the basins produce hydrocarbons with the exception of the Argentinean Bolsones complex and the Peruvian Madro de Dios which is prospective but virtually unexplored. There have been some 119 billion barrels of oil and 190 TCF of gas discovered to date, comprising 93% of the continent`s oil reserves. The basins lie immediately east of the Andes mountain range and are mainly asymmetric Upper Tertiary, westerly dipping foreland basins that overlie a series of earlier Tertiary, Mesozoic and Paleozoic depocentres. All the basins have been compressively deformed as recently as the Upper Miocene, by the eastwards growth of the Andean Cordillera. Giant oil and gas fields sourced from shales of varying age, have been found along the whole trend of basins, with a predominance of gas in the south. The rich marine Upper Cretaceous La Luna and equivalent shales of Venezuela, Colombia and Ecuador have been responsible for generating 86% of the hydrocarbons discovered to date in the sub-Andean basins. Proven sources include Devonian, Carboniferous, Permian and Triassic shales in the central area, comprising Peru, Bolivia and northern Argentina. In southern Argentina, oils have been sourced from Uppermost Jurassic and Lower Cretaceous marine and lacustrine shales. Over 7500 wildcat wells have been drilled in basins along the trend, with a 15% success rate. Many of the basins are very lightly explored, with considerable potential for future discoveries.

  1. Heterogeneity in Mississippi oil reservoirs, Black Warrior basin, Alabama: An overview

    SciTech Connect

    Kugler, R.L.; Pashin, J.C.; Irvin, G.D. )

    1993-09-01

    Four Mississippian sandstone units produce oil in the Black Warrior basin of Alabama: (1) Lewis; (2) Carter; (3) Millerella, and (4) Gilmer. Reservoir geometries differ for each producing interval, reflecting variation in depositional style during the evolution of a foreland basin. Widespread strike-elongate bodies of Lewis sandstone with complex internal geometry were deposited during destruction of the Fort Payne-Tuscumbia carbonate ramp and represent inception of the foreland basin and initial forebulge migration. Synorogenic Carter sandstone is part of the first major deltaic foreland basin fill and accounts for more than 80% of oil production in the basin. Millerella sandstone was deposited as transgressive sand patches during the final stages of delta destruction. Gilmer sandstone occurs as imbricate sandstone lenses deposited in a constructive shoal-water delta and is part of the late relaxational basin fill. Interaction of siliciclastic sediment with ancestral and active carbonate ramps was a primary control on facies architecture and reservoir heterogeneity. Patterns of injection and reservoir fluid production, as well as field- to basin-scale depositional, petrological, petrophysical and geostatistical modeling reveal microscopic to megascopic controls on reservoir heterogeneity and hydrocarbon producibility. At a megascopic scale, isolation or continuity of reservoir bodies is a function of depositional topography and the degree of marine reworking of genetically coherent sandstone bodies. These factors result in amalgamated reservoir bodies or in compartments that may remain uncontacted or unconnected during field development. Within producing fields, segmentation of amalgamated sandstone bodies into individual lenses, grain size variations, depositional barriers, and diagenetic baffles further compartmentalize reservoirs, increase tortuosity of fluid flow, and affect sweep efficiency during improved recovery operations.

  2. The petroleum system of the lower Palaeozoic strata in the central part of the Baltic basin

    NASA Astrophysics Data System (ADS)

    Lazauskiene, Jurga; Zdanaviciute, Onyte

    2013-04-01

    The Baltic Basin is an intra-cratonic sedimentary basin with conspicuous Early Palaeozoic sections. In terms of hydrocarbon prospectively, the it has been perceived as a classical oil basin with several tens of relatively small oil and gas fields occur there over a wide stratigraphic interval, ranging from the crystalline basement through the entire Lower Palaeozoic succession. Until now conventional oil has been predominantly produced in the basin, i.e. only few conventional gas accumulations have been found in the Polish Baltic Sea offshore. Petroleum potential within the basin also is associated with Silurian reefogenic and carbonate build-ups. New organic geochemistry data as well revealed the potential for shale gas/oil in the basin. The analysis of the composition of the organic matter and crude oils from Kaliningrad region (Russia) and Lithuanian revealed genesis and the general trends of the migration of hydrocarbons in the Baltic Basin. The organic matter of the source rocks is of similar composition and represents typical marine type II, showing considerable variations of the maturity thought the basin: ranging from immature in the eastern Lithuania and Kaliningrad region of Russia to oil window to the south-west. In some places the anomalously high maturity of organic matter, indicating the lower part of the wet gas/condensate window have been recorded, most probably being related to the locally increased paleo-temperatures. Oils of the Baltic Basin have low densities (< 31,1 API; 790.5-870.0 kg/m3), and low asphaltene (<2.2%) and sulphur (<0.44%) contents. The saturated hydrocarbon content varies from 35.3 to 77.8%, and the ratio of saturate to aromatic hydrocarbons ranges in 2.1-5.2, indicating long-distance hydrocarbons migration or high thermal maturities. Oils of the Baltic Basin are not biodegraded, despite their early emplacement (e.g. by the Lower Palaeozoic age) and the relatively low present reservoir temperatures. Results of biomarker and

  3. Evaluation of Ordos Basin in China

    SciTech Connect

    Zhou, J.G.

    1996-06-01

    Ordos basin lies in the north-central China, in a compression tectonic regime, with an area of approximately 250,000 km{sup 2}, including several pay zones ranging from Cambrian to Jurassic. It is one of the earliest-formed marine to continental-superimposed basin in China, characterized by Proterozoic basin-marginal rifling and Lower-Paleozoic carbonate platform development followed by western thrusting and foreland depression during Mesozoic. It underwent several tectonic movements and is covered by several structural layers, with many play types developed, primarily thrust and anticlinal plays in the west, and differential compaction (river-channel sand lens) or drape as well as buried hill plays in the basin center and east. Ordos basin is a prolific gas basin with an estimated resource potential of gas 656,091 billion m{sup 3} in the Paleozoic strata and oil 2.0474 billion tons in the Mesozoic strata. In 1986, in the western part of the basin, the well Tian-1 on the Tianchi structure tested gas at a rate of 16 x 10{sup 4} m{sup 3}/d (about 5.6496 MCF per day). By year-end 1991, only 26 wells had been drilled in the Jingbian to Hengshan areas (northeastern part of the basin), but 16 of them flowed commercial gas, ranging from 3.2 x 10{sup 4} m{sup 3}/d to 126 x 10{sup 4} m{sup 3}/d. However, the gas pipe just starts budding. Therefore, there will be a lot of gas yet to find, and the most critical factor for petroleum potential of each local structure or play in this basin is the reservoir development.

  4. Drainage reorganization explains the large-scale fan-shape morphology of the northern Pyrenean landscape: no megafan in the northern Pyrenean foreland

    NASA Astrophysics Data System (ADS)

    Bonnet, Stéphane; Carretier, Sébastien; Christophoul, Frédéric; Regard, Vincent

    2016-04-01

    On the Northern side of the Pyrenees, the morphology of the foreland corresponds to a piedmont which is currently eroded by rivers belonging to the Garonne and Adour drainage basins. A particularity of this network of rivers is to show a regional divergent pattern at the scale of the piedmont, from a source area located at the mountain-piedmont transition, at mid-distance between the Mediterranee and the Atlantic Ocean. The radial drainage network is closely associated with a large-scale fan-shape topography of the whole piedmont (radius > 100 km, height ~500 m). Some recent studies proposed that this regional-scale fan-shape is the consequence of a recent localized differential uplift of the piedmont, or that it resulted primarily from recent deposition in a unique huge alluvial fan, the megafan of Lannemezan. Here, we show that none interpretation is satisfying and we use numerical simulations of surface processes (numerical code CIDRE) to propose an alternative model for explaining this particular landscape of the northern Pyrenean piedmont. We show that it likely results from successive steps of drainage reorganization, primarily linked to the geometry of boundary conditions for erosion. Our simulations successively reproduce most morphological observations and characteristics of the northern Pyrenean landscape. Then, we show that no recent deformation of the piedmont needs to be invoked to explain its morphology and that there is not any megafan on the northern flank of the Pyrenees.

  5. Active fold-thrust belts in the foreland of eastern Tibet, the Longquan and Xiongpu anticlines in Sichuan, China

    NASA Astrophysics Data System (ADS)

    Lee, Jian-Cheng; Chan, Yu-Chang; Lu, Chia-Yu; Chen, Chih-Tung; Chu, Hao-Tsu; Liu, Yuiping; Li, Jianzhong

    2016-04-01

    The 2008 M7.9 Wenchuan earthquake ruptured from the Longmenshan fault system, which is the frontal thrust system in eastern Tibet. Further east toward the foreland area in the Sichuan basin, it sits two anticlinal structures, the Longquan and Xiongpu anticlines, which trends sub-parallel to the Longmenshan range with a distance of about 70-100 km to the mountain front. It is widely considered that these two anticlinal features are attributed to propagation of the eastward extrusion of the eastern Tibetan plateau, similar to the stress system the Wenchuan earthquake. In this study, we carried out field investigations on these two active anticlinal structures in order to characterize the bulk deformation of the anticlines. We also conducted fracture analysis and fault-slip data analysis, in an attempt to characterize the fracture developments of the rock and the paleostress states related to the faulting events associated growth of the anticlines. We thus constructed a series of geological cross sections along these two anticlines. Our results show that the Longquan anticline is characterized by pop up structure with a dominant west-vergent thrust (i.e., backthrust) on the western limb. On the other hand to the