Case studies in sedimentation along passive margins; Argo Abyssal Plain, northwest Indian Ocean, and Maiyumerak Mountains, northwest Alaska
University of California, Santa Cruz
365 p., Illus., Maps
Alaska Resources Library & Information Services: QE571 D86 1991; Rasmuson Library: ALASKA QE571 D86 1991a (microfiche); Geophysical Institute Library: THESIS NOT UAF
Case studies of sedimentary sequences formed along passive continental margins in the NW Indian Ocean (ODP Site 765 and DSDP Site 261) and in NW Alaska indicate that similar factors controlled sedimentary patterns in the two areas. The Indian Ocean sediments are of Late Jurassic-Cenozoic age and accumulated in a deep basin floored by new oceanic crust; the Alaskan rocks are Devonian-Mississippian and were deposited on a platform along the continental shelf edge. Sedimentation histories, as delineated by petrologic analysis and regional correlation, show that the configuration of the continental margin, eustatic shifts in sea level, and local tectonic events controlled patterns of sedimentation in both successions. The Argo Abyssal Plain (AAP) formed as a result of Late Jurassic seafloor spreading along the NW Australian margin as Gondwanaland broke apart. AAP sediments of Jurassic age were slowly deposited near the carbonate compensation depth (CCD) and contain winnowed concentrations of inoceramid prisms and nannofossils, manganese nodules, and volcanic detritus. Lower Cretaceous and younger sediments accumulated below the CCD and consist of noncalcareous background claystone intercalated with calcareous pelagic turbidites. Turbidites were derived from relatively deep parts of the continental margin, below the photic zone but above the CCD. Major pulses of calcareous turbidite deposition occurred in the Valanginian, Aptian, and Neogene--all times of eustatic lowstands and depressed CCD levels. Sediment redeposited on the AAP came largely from the Australian outer shelf, continental slope, or rise; most detritus from the continent itself was trapped in epicontinental basins. Middle Devonian-Mississippian carbonate rocks in the Maiyumerak Mountains, NW Alaska, are part of the North Slope-Chukotka continental block; this block underwent rifting in the middle to late Paleozoic, and a passive margin developed. The Maiyumerak succession formed in a range of shallow-water, middle to inner shelf environments on a carbonate platform, the Kelly platform, attached to this rifted margin. Terrigenous material in the Maiyumerak succession probably came from the Endicott delta. The Kelly platform drowned in the Late Mississippian, most likely due to tectonic factors, although short-term eustatic shifts may have also played a role.
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