Cenozoic Cool-water Carbonates of the Great Australian Bight : Reading the Record of Southern Ocean Evolution, Sealevel, Paleoclimate, and Biogenic Production : Revised ODP Proposal - December 1994

Brief description

This proposal advocates the drilling of a transect of holes across the southern continental margin of Australia; the largest cool-water carbonate shelf on Earth today. This latitude-parallel shelf along the northern margin of the Southern Ocean contains fundamental geological and paleoceanographic information of global geodynamic, sedimentological, paleobiological, and paleoclimatological
importance. The major objectives of this proposal are: 1) to ascertain the way in which a large, high- to mid-latitude shelf carbonate platform evolved throughout the past 65 m.y. in response to oceanographic and biotic change; and 2) to extract information contained in the carbonate sediments detailing global sealevel fluctuations, physical and chemical paleo-ocean dynamics, biotic evolution,
hydrology, and diagenesis. Furthermore, because of architectural and compositional similarities with many older Phanerozoic carbonate platforms, the results from the proposed drilling would be of tremendous importance for the actualistic modelling of ancient open platforms and ramps.

Offshore seismic data and limited drillhole information indicate that the margin has been the site of dominantly cool-water carbonate shelf deposition since the Eocene, and show a detailed accretionary history of progradation, erosion, and biogenic mound growth. The subsidence history is relatively simple, resulting in a 1 km-thick Cenozoic section. Onshore exposures provide a basis for predictive
analysis of the offshore sequences identified in seismic sections, and confirm that the sediments are predominantly soft, friable, and abundantly fossiliferous.

A shallow shelf to deep continental rise transect of 12 holes is proposed, located to penetrate inner shelf, outer shelf, upper slope, upper slope terrace, and continental rise settings. The primary drilling objective is a more detailed understanding of global environmental change in high- to mid-latitude settings. Cores from different facies at various depths during a range of geologic periods will yield a detailed anatomy of a Cenozoic cool-water carbonate shelf. The response of this depositional system to inferred sealevel fluctuations will be compared to records from warm-water, rimmed and un-rimmed carbonate platforms in order to test and refine the global sealevel curve, and most importantly to describe the reaction of cool-water carbonate depositional systems to different phases of the sealevel cycle. Biological and chemical paleoenvironmental proxies will be used to decipher a detailed
paleoceanographic record, in order to more precisely describe the timing and paleoceanographic effects of the opening of the Tasman Gateway, and the influence of the Leeuwin Current on paleoproductivity over time. The shelf-to-basin transect will also provide high resolution data on the tempo and pattern of biotic evolution in oceanic and neritic environments.

Secondary objectives are directed towards understanding the hydrology of a carbonate platform adjacent to a vast inland karst with sluggish water circulation; and the nature of early burial diagenesis (lithification and dolomitization) in a cold, seawater-dominated system.

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