Authors / CoAuthors
O'Brien, P.E. | Cooper, A.K.
Abstract
ODP drilling in Prydz Bay by Leg 119 (1988) and Leg 188 (2000) investigated Cainozoic paleoenvironments of the continental shelf, slope and rise. Drilling on the shelf reveal a pre-glacial alluvial or delta plain system covering the Prydz Bay basin -- a plain characterized by austral conifer woodland in Late Cretaceous that changed to Nothofagus rainforest scrub by mid to late Eocene time. Evidence of mountain glaciation in late Eocene time is seen in sand grain textures in channel sands. Interbedded clays and sands and an increase in marine dinoflagellates signals a marine transgression of the delta plain. In the late Eocene to early Oligocene, Prydz Bay shifted from being a fluvio-deltaic complex with vegetation to a marine continental shelf environment. The transition is marked by a sequence boundary and marine flooding surface onlapped by glaciomarine muds with dropstones that denote the first appearance of floating ice on the shelf, followed by diamicts that contain shelly fossils. No core exists for early Oligocene to early Miocene times, and seismic data suggest the transition from shallow to normal depth, prograding continental shelf, with submarine canyons on the slope and channel/levees on the rise. Cores from the continental rise provide evidence of a Neogene long-term (m.y.) decrease in sedimentation rates and short-term (Milankovitch periods) cyclicity between principally biogenic and terrigenous sediment supply due possibly to cyclic changes in onshore glaciers and related changes in ocean circulation. Mid Miocene times saw more-rapid slowing of sedimentation rates, a shift to enhanced IRD, and changes in clays and other minerals. These transitions result from enhanced glacial erosion of onshore and shelf source areas and reduced input from glacial meltwater as the ice became progressively colder. The Early Pliocene saw the deposition of overcompacted glacial diamictons on the shelf, and bank/trough morphology produced by formation of an ice stream ice in western Prydz Bay. Debris flows formed a trough mouth fan on the continental slope. Compositional changes in the trough mouth fan suggests peak erosion and therefore possibly peak ice volumes at about 1.1 Ma. Late Pleistocene times (post 780 ka.) saw a reduction in frequency of extreme advances by the main ice drainage system, in response to reduced precipitation accompanying cooling, extreme erosion of the inner shelf and changes in the interaction of the ice sheet response time and the prevailing climate cycle length. These changes probably reflect the overall cooling of the Antarctic from non-glacial, to restricted temperate glaciers to poly thermal ice sheet to the present cold based ice sheet. Superimposed on this overall cooling trend are pulses of warmer conditions, indicated by beds of warmer water nannoplankton and changes diatom assemblages
Product Type
nonGeographicDataset
eCat Id
60447
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Custodian
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
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- External PublicationAbstract
- ( Theme )
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- climate
- ( Theme )
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- continental margins
- ( Theme )
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- geoscience
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- AQ
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2004-01-01T00:00:00
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geoscientificInformation
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