Browsing by Subject "Carbonate platforms"
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Item 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, XavierDetermining 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.Item Tectonic and sea level controls on the back-stepping early miocene carbonate platforms: Adana Basin, Turkey(2015-12) Gurbuz, Mehmet Ozen; Janson, Xavier; Fisher, William Mr; Catlos, Elizabeth MrsThe Karaisali complex exposes Miocene carbonate platforms that developed on a tectonically controlled, rugged antecedent topography during an ice-house system. The factors affecting platform initiation, architecture, facies distribution, and eventually drowning of those Miocene platforms remain poorly understood because of the stratigraphic and structural complexities of the Adana Basin. In this work, sedimentological and structural analysis supplemented by dating using strontium isotope lead to a better understanding of platform developing in a strongly subsiding basin. Using twenty one measured sections, ultra-high resolution photopans, petrographic, and strontium isotope analysis; an interpreted depositional model and detailed cross section were built. The architecture of the platforms can be divided into two transgressive and two highstand systems tracts separated by a maximum flooding surface. This work shows that the small attached carbonate platforms of the Karaisali Formation colonized a steep-rugged basement topography in a rapidly subsiding basin without any significant syn-sedimentary movement. The combination of rapid subsidence with a subsidence rate of more than 400 m/MA and eustacy drove the carbonate platform to successively nucleate, aggrade with minor progradation, and eventually drown on basement highs. The relative sea level rise resulted in back-stepping of the carbonate platforms towards landwards and development of Early Burdigalian to Late Serravalian reefal carbonates on the paleo-highs of the antecedent topography further in northernwest.