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Depositional Sequences (depositional + sequence)

Distribution by Scientific Domains

Earth and Environmental Science	88%

Selected Abstracts

DEPOSITIONAL HISTORY AND SEQUENCE STRATIGRAPHY OF OUTCROPPING TERTIARY CARBONATES IN THE JAHRUM AND ASMARI FORMATIONS, SHIRAZ AREA (SW IRAN)

JOURNAL OF PETROLEUM GEOLOGY, Issue 2 2004
M. Nadjafi
The Oligo-Miocene Asmari Formation is one of the most important petroleum reservoir units in the Zagros Basin of south and SW Iran. It mainly consists of limestones and dolomitic limestones with interbedded shales, together with a few intervals of sandstone and gypsum assigned to the Ahwaz and Kalhur Members, respectively. The Asmari Formation rests on the thin-bedded limestones of the Jahrum Formation (Paleocene-Eocene). In this paper, we report on the lithofacies characteristics of these two formations using data from three measured outcrop sections near Shiraz in SW Iran. From field and petrographic data, we have identified four major lithofacies and twelve subfacies which are interpreted to have been deposited in open-marine, shoal, lagoon and tidal flat settings. We show that the Asmari and Jahrum Formations constitute two separate depositional sequences which are separated by a thin palaeosol, representing a type-one sequence boundary which can be correlated with global curves of relative sea-level. Each depositional sequence is composed of many metre-scale shallowing-upward parasequences. This is the first time that the Asmari and Jahrum Formations have been differentiated in the study area. We hope that this study will lead to a better understanding of the Asmari Formation in the subsurface in other parts of the Zagros Basin. [source]

The Tendaguru Formation (Late Jurassic to Early Cretaceous, southern Tanzania): definition, palaeoenvironments, and sequence stratigraphy

FOSSIL RECORD-MITTEILUNGEN AUS DEM MUSEUM FUER NATURKUNDE, Issue 2 2009
Robert Bussert
Abstract The well-known Late Jurassic to Early Cretaceous Tendaguru Beds of southern Tanzania have yielded fossil plant remains, invertebrates and vertebrates, notably dinosaurs, of exceptional scientific importance. Based on data of the German-Tanzanian Tendaguru Expedition 2000 and previous studies, and in accordance with the international stratigraphic guide, we raise the Tendaguru Beds to formational rank and recognise six members (from bottom to top): Lower Dinosaur Member, Nerinella Member, Middle Dinosaur Member, Indotrigonia africana Member, Upper Dinosaur Member, and Rutitrigonia bornhardti-schwarzi Member. We characterise and discuss each member in detail in terms of derivation of name, definition of a type section, distribution, thickness, lithofacies, boundaries, palaeontology, and age. The age of the whole formation apparently ranges at least from the middle Oxfordian to the Valanginian through Hauterivian or possibly Aptian. The Tendaguru Formation constitutes a cyclic sedimentary succession, consisting of three marginal marine, sandstone-dominated depositional units and three predominantly coastal to tidal plain, fine-grained depositional units with dinosaur remains. It represents four third-order sequences, which are composed of transgressive and highstand systems tracts. Sequence boundaries are represented by transgressive ravinement surfaces and maximum flooding surfaces. In a more simple way, the depositional sequences can be subdivided into transgressive and regressive sequences/systems tracts. Whereas the transgressive systems tracts are mainly represented by shallow marine shoreface, tidal channel and sand bar sandstones, the regressive systems tracts predominantly consist of shallow tidal channel, tidal flat, and marginal lagoonal to supratidal deposits. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Jurassic depositional records and sandstone provenances in Hefei Basin, central China: Implication for Dabie orogenesis

ISLAND ARC, Issue 2 2004
Zhong Li
Abstract Detrital composition and major element geochemistry of Jurassic sandstones in the south Hefei Basin, central China, show their provenance to be the Dabie Mountains, whose tectonic attributes are closely related to continent,island arc complexes. It was found that a provenance change, from recycled orogen signatures and mixed orogenic sandstones to arc orogen, occurs from the lower Middle Jurassic to the Upper Jurassic (the Zhougongshan Formation). Dissected magmatic arc sources were gradually exposed in the Dabie Mountains due to intensive exhumation during the Late Jurassic, particularly after the Fenghuangtai depositional phase. Furthermore, it can be infered that the magmatic arc was initially present in both the Early Paleozoic and the Triassic, according to isotopic dating studies in previously published reports. ,13C,,18O tracing between existing marbles of different strata in the Dabie block and marble gravels of the Fenghuangtai Formation in the Hefei Basin indicate that partial lithostratigraphic units for the Jurassic provenances have entirely disappeared from the Dabie block; therefore, it is impossible to reconstruct integral orogenic processes from studies on the remaining Dabie block alone. These findings, together with basin-fill sequences, also suggest that the Hefei Basin was mainly subjected to compressive mechanical regimes rather than extensional regimes in the Jurassic, which resulted in reverse-grading clastic depositional sequences, and is probably related to the northward intracontinental deep subduction of the Yangtze Plate. Regional exhumation properties and a tectonic model of the Late Mesozoic Dabie orogenesis are discussed in this paper. [source]

DEPOSITIONAL HISTORY AND SEQUENCE STRATIGRAPHY OF OUTCROPPING TERTIARY CARBONATES IN THE JAHRUM AND ASMARI FORMATIONS, SHIRAZ AREA (SW IRAN)

ROSS AND BUDE FORMATIONS (CARBONIFEROUS, IRELAND AND ENGLAND): REINTERPRETED AS LAKE-SHELF TURBIDITES

JOURNAL OF PETROLEUM GEOLOGY, Issue 1 2004
R. Higgs
The Ross Formation (Namurian, Ireland) and the near-identical Bude Formation (Westphalian, England), both amply described in the literature, are used by oil companies as deep-sea-fan reservoir analogues. However, the Ross Formation is reinterpreted here, like the Bude Formation in recent publications, to be composed of river-fed turbidites deposited on the wave-influenced northern shelf of a Variscan foreland-basin lake, which also had a southern flysch trough. Key features of these formations are: (i) two classes of thin (, 0.4m) sandstone "event bed" in shale comprising (a) structureless turbidite-like beds, and (b) rippled beds with combined-flow ripples and/or hummocky cross-stratification, neither structure having previously been reported from the Ross Formation; (ii) "trademark" tabular packets (1,10 m) of amalgamated event beds which interfinger laterally with mudstones; (iii) sharp packet bases and tops; (iv) rare sinuous channel fills; and (v) rare thick (1,10m) shale units, each containing a thin (cm-dm) fossiliferous band. The fossil bands are interpreted here as maximum flooding surfaces, reflecting glacioeustatic marine incursions over the lake spill point (sill), forcing the lake to rise and to turn marine or strongly brackish; these bands define Galloway-type depositional sequences 50,100 m thick. During eustatic falls, the lake was forced down to sill level, where it perched and turned fresh (desalination). Intervals containing sandstone packets are attributed to the falling-stage and lowstand systems tracts, each packet representing a higher-order lowstand systems tract. Packets are interpreted as tongue shaped, supplied by river-fed underflows. Packet bases (sharp) represent the storm-wave-graded equilibrium shelf profile, glacioeustatically forced to its lowstand position. On this erosion surface were deposited underflow turbidites produced by floods in the catchment. Occasional catastrophic storms on the lake shaved these turbidites and interfingering fair-weather muds back down to the equilibrium level, leaving behind a subsidence-accommodated increment whose surface was sculpted by storm wind and wave currents, forming hummocks, combined-flow ripples and erosional megaflutes. Whenever a river-fed underflow accompanied one of these storms, the resulting highly erosive combined flow carved a sinuous channel on the wave-sculpted equilibrium surface. Sandstone-shale intervals separating the sandstone packets are interpreted as transgressive- and highstand systems tracts. They contain both turbidites and wave-modified turbidites (rippled beds), deposited on the out-of-equilibrium drowned shelf. A gradual rotation in sole-mark direction with time in both formations is attributed to a reversal of Coriolis deflection as the plate drifted north across the equator, causing underflows (deflected along-shelf geostrophically) to flow first NEwards and then SWwards on an inferred SE-facing shelf. The lack of evidence for emergence in the Ross and Bude Formations, in spite of the great thicknesses (460m and 1,290m, respectively) of these shallow-water deposits, is attributed to regulation of minimum water depth firstly by the lake sill blocking eustatically-forced exposure, and secondly by storm grading, preventing emergence by sedimentation. [source]

Tectono-sedimentary processes along an active marine/lacustrine half-graben margin: Alkyonides Gulf, E. Gulf of Corinth, Greece

BASIN RESEARCH, Issue 1 2002
M. R. Leeder
ABSTRACT The Alkyonides half-graben is separated from the Gerania Range to the south by active faults whose offshore traces are mapped in detail. The East Alkyonides and Psatha Faults have well-defined, Holocene-active tip zones and cannot be extrapolated from the onshore Skinos Fault into a single continuous surface trace. During the late Quaternary, catchments draining the step-faulted range front have supplied sediment to alluvial fans along a subsiding marine ramp margin in the hangingwall of the Skinos Fault, to shelf ledge fans on the uplifting footwall to the East Alkyonides Fault and to the Alepochori submarine fan in the hangingwall of the latter. During late Pleistocene lowstand times (c. 70,12 ka), sediment was deposited in Lake Corinth as fan deltas on the subsiding Skinos shelf ramp which acted as a sediment trap for the adjacent 360 m deep submarine basin plain. At the same time, the uplifting eastern shelf ledge was exposed, eroded and bypassed in favour of deposition on the Alepochori submarine fan. During Holocene times, the Skinos bajada was first the site of stability and soil formation, and then of substantial deposition before modern marine erosion cut a prominent cliffline. The uplifting eastern shelf ledge has developed substantial Holocene fan lobe depositional sequences as sediment-laden underflows have traversed it via outlet channels. We estimate mean Holocene displacement rates towards the tip of the Psatha Fault in the range 0.7,0.8 mm year,1. Raised Holocene coastal notches indicate that this may be further partitioned into about 0.2 mm year,1 of footwall uplift and hence 0.5,0.6 mm year,1 of hangingwall subsidence. Holocene displacement rates towards the tip of the active East Alkyonides Fault are in the range 0.2,0.3 mm year,1. Any uplift of the West Alkyonides Fault footwall is not keeping pace with subsidence of the Skinos Fault hangingwall, as revealed by lowstand shelf fan deltas which show internal clinoforms indicative of aggradational deposition in response to relative base-level rise due to active hangingwall subsidence along the Skinos Fault. Total subsidence here during the last 58 kyr lowstand interval of Lake Corinth was some 20 m, indicating a reduced net displacement rate compared to estimates of late Holocene (< 2000 bp) activity from onshore palaeoseismology. This discrepancy may be due to the competition between uplift on the West Alkyonides Fault and subsidence on the onshore Skinos Fault, or may reflect unsteady rates of Skinos Fault displacement over tens of thousands of years. [source]

Carbonate sedimentation in a starved pull-apart basin, Middle to Late Devonian, southern Guilin, South China

BASIN RESEARCH, Issue 2 2001
D. Chen
ABSTRACT Geological mapping and sedimentological investigations in the Guilin region, South China, have revealed a spindle- to rhomb-shaped basin filled with Devonian shallow- to deep-water carbonates. This Yangshuo Basin is interpreted as a pull-apart basin created through secondary, synthetic strike-slip faulting induced by major NNE,SSW-trending, sinistral strike-slip fault zones. These fault zones were initially reactivated along intracontinental basement faults in the course of northward migration of the South China continent. The nearly N,S-trending margins of the Yangshuo Basin, approximately coinciding with the strike of regional fault zones, were related to the master strike-slip faults; the NW,SE-trending margins were related to parallel, oblique-slip extensional faults. Nine depositional sequences recognized in Givetian through Frasnian strata can be grouped into three sequence sets (Sequences 1,2, 3,5 and 6,9), reflecting three major phases of basin evolution. During basin nucleation, most basin margins were dominated by stromatoporoid biostromes and bioherms, upon a low-gradient shelf. Only at the steep, fault-controlled, eastern margin were thick stromatoporoid reefs developed. The subsequent progressive offset and pull-apart of the master strike-slip faults during the late Givetian intensified the differential subsidence and produced a spindle-shaped basin. The accelerated subsidence of the basin centre led to sediment starvation, reduced current circulation and increased environmental stress, leading to the extensive development of microbial buildups on platform margins and laminites in the basin centre. Stromatoporoid reefs only survived along the windward, eastern margin for a short time. The architectures of the basin margins varied from aggradation (or slightly backstepping) in windward positions (eastern and northern margins) to moderate progradation in leeward positions. A relay ramp was present in the north-west corner between the northern oblique fault zone and the proximal part of the western master fault. In the latest Givetian (corresponding to the top of Sequence 5), a sudden subsidence of the basin induced by further offset of the strike-slip faults was accompanied by the rapid uplift of surrounding carbonate platforms, causing considerable platform-margin collapse, slope erosion, basin deepening and the demise of the microbialites. Afterwards, stromatoporoid reefs were only locally restored on topographic highs along the windward margin. However, a subsequent, more intense basin subsidence in the early Frasnian (top of Sequence 6), which was accompanied by a further sharp uplift of platforms, caused more profound slope erosion and platform backstepping. Poor circulation and oxygen-depleted waters in the now much deeper basin centre led to the deposition of chert, with silica supplied by hydrothermal fluids through deep-seated faults. Two ,subdeeps' were diagonally arranged in the distal parts of the master faults, and the relay ramp was destroyed. At this time, all basin margins except the western one evolved into erosional types with gullies through which granular platform sediments were transported by gravity flows to the basin. This situation persisted into the latest Frasnian. This case history shows that the carbonate platform architecture and evolution in a pull-apart basin were not only strongly controlled by the tectonic activity, but also influenced by the oceanographic setting (i.e. windward vs. leeward) and environmental factors. [source]

Late Carboniferous-Early Permian Sequence Stratigraphy and Depositional Evolution in the Northeast Ordos Basin, North China

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010
YANG Minghui
Abstract: Sequence stratigraphical analysis was applied to the Upper Carboniferous-Lower Permian sedimentary succession of the northeastern Ordos Basin, north China based on data acquired from ten entire logging curves and eight outcrops. The facies framework of the lithostratigraphical unit, the Taiyuan Formation comprises seven facies in two facies associations, varying from fluvio-delta to shelf-barrier islands. The facies are presented within a chronostratigraphical framework, linked by systems tract, which in turn are limited by flooding surfaces and sequence boundaries. Six third-order depositional sequences are recognised, bounded by six type 2 unconformities. An upwards-shallowing epicontinental sea sedimentary model is created, which consists of a sandstone, coal seam and carbonate succession. [source]

Geophysical evidence for Holocene lake-level change in southern California (Dry Lake)

BOREAS, Issue 1 2010
BROXTON W. BIRD
Bird, B. W., Kirby, M. E., Howat, I. M. & Tulaczyk, S. 2009: Geophysical evidence for Holocene lake-level change in southern California (Dry Lake). Boreas, 10.1111/j.1502-3885.2009.00114.x. ISSN 0300-9483. Ground penetrating radar (GPR) data are used in combination with previously published sediment cores to develop a Holocene history of basin sedimentation in a small, alpine lake in southern California (Dry Lake). The GPR data identify three depositional sequences spanning the past 9000 calendar years before present (cal. yr BP). Sequence I represents the first phase of an early Holocene highstand. A regression between <8320 and >8120 cal. yr BP separates Sequence I from Sequence II, perhaps associated with the 8200 cal. yr BP cold event. Sequence II represents the second phase of the early-to-mid Holocene highstand. Sequence IIIa represents a permanent shift to predominantly low lake stands beginning ,5550 cal. yr BP. This mid-Holocene shift was accompanied by a dramatic decrease in sedimentation rate as well as a contraction of the basin's area of sedimentation. By ,1860 cal. yr BP (Sequence IIIb), the lake was restricted to the modern, central basin. Taken together, the GPR and core data indicate a wet early Holocene followed by a long-term Holocene drying trend. The similarity in ages of the early Holocene highstand across the greater southern California region suggests a common external forcing , perhaps modulation of early Holocene storm activity by insolation. However, regional lake level records are less congruous following the initial early Holocene highstand, which may indicate a change in the spatial domain of climate forcing(s) throughout the Holocene in western North America. [source]