Transition from storm wave-dominated outer shelf to gullied upper slope: The mid-Pliocene Orinoco shelf margin, South Trinidad

Sedimentology ◽  
2017 ◽  
Vol 64 (6) ◽  
pp. 1511-1539 ◽  
Author(s):  
Yang Peng ◽  
Ronald J. Steel ◽  
Cornel Olariu
Keyword(s):  
Outer Shelf ◽  
Storm Wave ◽  
Shelf Margin ◽  
Upper Slope

scholarly journals Lateral variability of shelf-edge and basin-floor deposits, Santos Basin, offshore Brazil

2020 ◽  
Vol 90 (9) ◽  
pp. 1198-1221
Author(s):  
Michael J. Steventon ◽  
Christopher A-L. Jackson ◽  
David M. Hodgson ◽  
Howard D. Johnson
Keyword(s):  
Mass Movement ◽  
Three Dimensional ◽  
Outer Shelf ◽  
Continental Margins ◽  
Shelf Edge ◽  
Sequence Stratigraphic ◽  
Se Brazil ◽  
Basin Floor ◽  
Shelf Margin ◽  
Upper Slope

ABSTRACT Construction of continental margins is driven by sediment transported across the shelf to the shelf edge, where it is reworked by wave, tide, and fluvial processes in deltas and flanking clastic shorelines. Stalling of continental-margin progradation often results in degradation of the outer shelf to upper slope, with resedimentation to the lower slope and basin floor via a range of sediment gravity flows and mass-movement processes. Typically, our understanding of how these processes contribute to the long-term development of continental margins has been limited to observations from broadly two-dimensional, subsurface and outcrop datasets. Consequently, the three-dimensional variability in process regime and margin evolution is poorly constrained and often underappreciated. We use a large (90 km by 30 km, parallel to depositional strike and dip, respectively) post-stack time-migrated 3D seismic-reflection dataset to investigate along-strike variations in shelf-margin progradation and outer-shelf to upper-slope collapse in the Santos Basin, offshore SE Brazil. Early Paleogene to Eocene progradation of the shelf margin is recorded by spectacularly imaged, SE-dipping clinoforms. Periodic failure of the outer shelf and upper slope formed ca. 30-km-wide (parallel to shelf-margin strike) slump scars, which resulted in a strongly scalloped upper-slope. Margin collapse caused: 1) the emplacement of slope-attached mass-transport complexes (MTCs) (up to ca. 375 m thick, 12+ km long, 20 km wide) on the proximal basin floor, and 2) accommodation creation on the outer shelf to upper slope. This newly formed accommodation was infilled by shelf-edge-delta clinoforms (up to 685 m thick), that nucleated and prograded basinward from the margin-collapse headwall scarp, downlapping onto the underlying slump scar and/or MTCs. Trajectory analysis of the shelf-edge deltas suggests that slope degradation-created accommodation was generated throughout the sea-level cycle, rather than during base-level fall as would be predicted by conventional sequence-stratigraphic models. Our results highlight the significant along-strike variability in depositional style, geometry, and evolution that can occur on this and other continental margins. Coeval strata, separated by only a few kilometers, display strikingly different stratigraphic architectures; this variability, which could be missed in 2D datasets, is not currently captured in conventional 2D sequence stratigraphic models.

Morphology of the Andaman outer shelf and upper slope of the Thai exclusive economic zone

2012 ◽  
Vol 46 ◽  
pp. 78-85 ◽  
Author(s):  
Pachoenchoke Jintasaeranee ◽  
Wilhelm Weinrebe ◽  
Ingo Klaucke ◽  
Anond Snidvongs ◽  
Ernst R. Flueh
Keyword(s):  
Outer Shelf ◽  
Exclusive Economic Zone ◽  
Economic Zone ◽  
Upper Slope

Lithostratigraphy of the Kookfontein Formation (Ecca Group, Karoo Supergroup), South Africa

2017 ◽  
Vol 120 (3) ◽  
pp. 447-458
Author(s):  
H. de V. Wickens ◽  
D.I. Cole
Keyword(s):  
South Africa ◽  
Depositional Environment ◽  
Delta Front ◽  
Southwestern Part ◽  
Fine Grained ◽  
Karoo Basin ◽  
Deformation Features ◽  
Stratigraphic Position ◽  
Shelf Margin ◽  
Upper Slope

Abstract The Permian Kookfontein Formation forms part of the upper Ecca Group in the southwestern part of the main Karoo Basin of South Africa. It occupies a stratigraphic position between the underlying Skoorsteenberg Formation and the overlying Waterford Formation, with its regional extent limited to the cut-off boundaries of the Skoorsteenberg Formation. The Kookfontein Formation has an average thickness of 200 m, coarsens upwards, and predominantly comprises dark grey shale, siltstone and thin- to thick-bedded, fine- to very fine-grained, feldspathic litharenite. Characteristic upward-coarsening and thickening successions and syn-sedimentary deformation features reflect rapid deposition and progradation of a predominantly fluvially-dominated prodelta and delta front slope environment. The upward increase in the abundance of wave–ripple marks further indicates a gradual shallowing of the depositional environment through time. The upper contact with the Waterford Formation is gradational, which indicates a transition from deposition in an unstable upper slope/shelf margin environment to a more stable shelf setting.

scholarly journals Taphonomy and ecology of deep-water Ediacaran organisms from northwestern Canada

1992 ◽  
Vol 6 ◽  
pp. 219-219 ◽  
Author(s):  
Guy M. Narbonne ◽  
Robert W. Dalrymple
Keyword(s):  
Shallow Water ◽  
Deep Water ◽  
Microbial Mats ◽  
Bedding Plane ◽  
Thin Layers ◽  
Sea Bottom ◽  
Windermere Supergroup ◽  
Storm Wave ◽  
Upper Slope

Although most occurrences of Ediacaran fossils are from shallow-shelf deposits, taxonomically-similar assemblages have recently been described from a 2.5 km-thick succession of dark mudstones and turbiditic sandstones in the Windermere Supergroup of the Mackenzie Mountains, northwestern Canada. The paleogeographic position (20-40 km seaward of the shelf edge), abundant evidence of mass flow, and the complete absence of in situ shallow-water features imply that deposition took place on a slope considerably below storm wave-base. Ediacaran fossils were not observed in axial trough deposits (lower parts of the Twitya and Sheepbed formations), but megafossils occur sporadically in lower to middle slope deposits higher in the same formations. Megafossils and trace fossils are present in upper slope settings (Blueflower Formation) at the top of the Ediacaran succession. The megafossil assemblage varies stratigraphically, but in all formations is dominated by discoid forms (e.g. Cyclomedusa, Ediacaria, Nimbia); frondose forms and vendomiids are very rare.Megafossils are preserved mainly as positive features on the soles of thin turbidite beds. Most fossiliferous beds begin with the rippled layer of the turbidite (Tc), but a few begin with the graded (Ta) or parallel-laminated (Tb) layer. Consistent orientation and high relief of individuals, evidence of mutual deformation during growth of adjacent organisms, and other taphonomic features imply that virtually all of the taxa represent benthic polypoid and frond-like organisms (not jellyfish). Slump structures occur commonly in the sandstone fill of fossils, suggesting that many of the organisms were buried alive by the turbidite and later decomposed. Other individuals, even on the same bedding plane, exhibit graded to laminated fill identical to that of the overlying turbidite bed, indicating that the depressions on the sea bottom produced by these individuals were empty at the time of turbidite deposition. Escape structures are absent, suggesting that the Ediacaran organisms were not capable of burrowing up through even thin layers of sand.Ediacaran megafossils are invariably preserved on black, wrinkled surfaces similar to those elsewhere interpreted as microbial mats. Molding of delicate features (including tentacles), preservation of open molds as negative epireliefs, and sedimentological evidence of considerable cohesion of these surfaces relative to the underlying turbiditic muds (Td,e) supports this interpretation, and suggests that microbial mats were as important in the preservation of these deep-water Ediacara faunas as they were in their shallow-water equivalents. The presence of the wrinkled mats and their associated Ediacaran fossils almost exclusively in the pyritic intervals of the succession suggests that both may have lived under exaerobic conditions in this deep-water setting.

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