Browsing by Subject "Shelf-edge trajectory"

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Controls on sedimentary processes and 3D stratigraphic architecture of a mid-Miocene to recent, mixed carbonate-siliciclastic continental margin : northwest shelf of Australia
(2011-05) Sanchez, Carla Maria, 1978-; Fulthorpe, Craig Stephen, 1954-; Steel, R. J.; Mohrig, David; Austin, James A.; Kerans, Charles; Janson, Xavier
Determining the relative importance of processes that control the generation and preservation of continental margin stratigraphy is fundamental to deciphering the history of geologic, climatic and oceanographic forcing imprinted on their sedimentary record. The Northern Carnarvon Basin (NCB) of the North West Shelf of Australia has been a site of passive margin sedimentation throughout the Neogene. Cool-water carbonate sedimentation dominated during the early-middle Miocene, quartz-rich siliciclastics prograded over the shelf during the late-middle Miocene, and carbonate sedimentation resumed in the Pliocene. Middle Miocene to Pliocene siliciclastics were deposited as clinoform sets interpreted as delta lobes primarily based on their plan-view morphology and their relief of 40-100 m. Shelf-edge trajectory analysis suggests that part of this stratigraphic succession was built during a long-term, third order, regressive phase, producing shelf-edge deltas, followed by an aggradational episode. These trends appear to correlate with third-order global eustatic cycles. Slope incisions were already conspicuous on the slope before deltas reached the shelf-break. Nevertheless, slope gullies immediately downdip from the shelf-edge deltas are wider and deeper (>1 km wide, ~100 m deep) than coeval incisions that are laterally displaced from the deltaic depocenter (~0.7 km wide, ~25 m deep). This change in gully morphology is likely the result of greater erosion by sediment gravity flows sourced from shelf-edge deltas. Total late-middle to late Miocene margin progradation increased almost three times from 13 km in the southwest to 34 km in the northeast, where shelf-edge deltas were concentrated. Flat-topped carbonate platforms seem to have initiated on subtle antecedent topographic highs resulting from these deltaic lobes. A reduction of siliciclastic supply to the outer paleo-shelf during the Pliocene combined with the onset of a southwestward-flowing, warm-water Leeuwin Current (LC) most likely controlled the initiation of these carbonate platforms. These platforms display marked asymmetry, likely caused by an ancestral LC, which created higher-angle, upcurrent platform margins, and lower-angle, downcurrent clinoforms. The along-strike long-term migration trend of the platforms could be the result of differential subsidence. These platforms constitute the first widespread accumulation of photozoan carbonates in the Northern Carnarvon Basin. They became extinct after the mid-Pleistocene when the LC weakened or became more seasonal.
Deep lacustrine clinoforms : formation, architectures, and deposits
(2016-08-16) Fong-Ngern, Rattanaporn; Steel, R. J.; Olariu, C. (Cornel); Mohrig, David C.; Kim, Wonsuck; Krézsek, Csaba
This dissertation is a study of the occurrence, geometry, stratigraphy and sedimentological characteristics of shelf-margin clinoforms in a deep lake setting. Because of their formation in a hydrologically closed environment, and reduced salinity water, lake clinoforms’ characteristics can differ from their well-studied marine counterparts. An investigation on lake clinoforms can lead to a better understanding of lake depositional processes, particularly those that provide a linkage between the co-genetic shallow-deepwater depositional environments, and consequent sediment dispersals in a deep lake setting. Even though similar processes also operate in a deep-marine setting, their interaction within the reduced salinity water of a lake can build deposits and stratigraphy that differ from marine basin fill. Hence, this study provides a good example of lake clinoforms and their deposits, which can be used for comparison with those of marine environment. For the most part, this study is performed on the western Dacian Basin datasets, which comprise subsurface and outcrop data. The subsurface dataset includes three overlapping 3D seismic volumes that cover 1,700 square-kilometer area and well data. The entire basin fill succession is exposed and allows up to 1000 m thick sedimentological data to be collected. The seismic data analysis suggests that a closed nature and isolation from the effects of eustatic sea-level changes contributed to limited aggradation of the Dacian clinoform topsets and significant sediment partition to the deep-lacustrine environments, which led to rapid foreset progradation and high bottomset aggradation. Integration between the subsurface and outcrop datasets shows that direct sediment transport from the shelf to the basin-floor environments is common and carried through hyperpycnal-flow channels and mass-wasting of the shelf edge. Based on the Dacian Basin clinoforms’ distinctive bottomset geometry, a special attention was given to the base-of-slope as a crucial point to scrutinize basin-floor sedimentation and sediment partitioning between the deepwater slope and basin floor settings. From the Dacian Basin seismic dataset, a base-of-slope trajectory analytical concept is developed and proposed as a complimentary predictive tool to the shelf-edge trajectory concept. The base-of-slope trajectory analysis was also applied to other published clinoform data to test its applicability