New Estimates of the Timing and Magnitude of Early to Middle Miocene Eustasy based on Mixed Carbonate-Siliciclastic Sequences from the Marion Plateau (ODP Leg 194)
Abstract
Eustasy is a key parameter to understand sedimentary sequences on continental margins and to reconstruct continental ice volume in the Cenozoic, but its timing and magnitude remains controversial, especially for the Miocene Epoch. The best record of the magnitude of eustatic changes beyond the Plio-Pleistocene is based on the stacked highstand siliciclastic sequences from the New Jersey margin. However, sample bias and local effects on the sea-level variation cannot be entirely ruled out and the amplitude calculation derived from the New Jersey margin must be verified by independent estimates from other continental margins. The Marion Plateau, offshore northeastern Australia (ODP Leg 194) offers an ideal location to reconstruct the timing and amplitude of Miocene eustasy on a current dominated, mixed siliciclastic-carbonate margin. We analyzed sediment cores from the Marion Plateau to define the mechanisms and timing of sequence formation at this location, and to estimate the amplitude of Miocene eustatic adjustments. We identified sequence boundaries on seismic reflection lines, significantly revised the existing biostratigraphic age models based on calcareous nannofossils and planktic foraminifera, and investigated the sedimentary response to sea-level changes across the Marion Plateau. We subdivided the Miocene sediments into three sequence sets comprising a set of prograding clinoforms, a muddy prograding bryozoan ramp evolving into an aggrading platform, and a lowstand ramp. We recognized eight individual sequences dated at 18.0 Ma, 17.2 Ma, 16.6 Ma, 15.4 Ma, 14.7 Ma, 13.9 Ma, 12.7 Ma, and 12.0 Ma. We demonstrate that sequences on the Marion Plateau are controlled by glacio-eustasy since each sequence boundary is marked by an increase in δ18O, which reflects increased ice volume primarily on Antarctica. Our backstripping estimates suggest that sea-level fell by 9-12 m at 16.6 Ma, 19-28 m at 15.4 Ma, 41-59 m at 14.7 Ma, and 60-87m at 13.9 Ma. Combining backstripping with δ18O estimates yields sea-level fall amplitudes of 25±15 m at 16.6 Ma, 24±5 m at 15.4 Ma, 44±3 m at 15.7 Ma, and 62±3 m at 13.9 Ma. The new independent amplitude estimates are crucial as the Miocene is the geologic period for which the New Jersey margin sea-level record is least constrained.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP13F..08J
- Keywords:
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- 1621 GLOBAL CHANGE / Cryospheric change;
- 1641 GLOBAL CHANGE / Sea level change;
- 3036 MARINE GEOLOGY AND GEOPHYSICS / Ocean drilling;
- 4944 PALEOCEANOGRAPHY / Micropaleontology