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Alexandra Isern, National Science Foundation

Sea-Level Magnitudes Recorded by Continental Margin Sequences on the Marion Plateau, Northeast Australia: ODP Leg 194. Alexandra Isern, National Science Foundation Flavio Anselmetti, Federal Institute of Technology, Zurich Switzerland Peter Blum, Ocean Drilling Program

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Alexandra Isern, National Science Foundation

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  1. Sea-Level Magnitudes Recorded by Continental Margin Sequences on the Marion Plateau, Northeast Australia: ODP Leg 194 Alexandra Isern, National Science Foundation Flavio Anselmetti, Federal Institute of Technology, Zurich Switzerland Peter Blum, Ocean Drilling Program and the Leg 194 Shipboard Scientific party

  2. Acknowledgements • Collection of scientific data: • 22 Members of the Leg 194 Shipboard Scientific Party • Seismic Survey: • Australian Geological Survey Organization (AGSO) • Australian Research Council • Mike Sexton • Coring operations and core analysis: • ODP drill crew • ODP technical support personnel

  3. Introduction • The Miocene Climatic Optimum (~14.5-17 Ma), a period of extreme warmth, was followed by global cooling • A series of sea level falls at ~14-12 Ma has been interpreted from the geological record (e.g., Haq et al. 1987, 100-200 m) • ODP Leg 194 embarked on a drilling mission in early 2001 to examine this event and associated processes as documented in the Marion carbonate platforms

  4. ODP Drilling on Marion Plateau • ODP Leg 194 drilled at 8 sites: • Water depths of 304-419 m • Penetrations per hole of 265-675 m • Core recoveries per hole of 11% - 100% • late Oligocene to Pleistocene sediments • Principal results: • Magnitude of l. middle Miocene sea-level fall • Cool subtropical platform growth environment • bryozoans, larger benthic foraminifers, red algea • Ocean current rather than wind control • Records of higher-order sea-level changes in drifts • Fluid flow through the platform • Diagenetic history

  5. Marion Plateau Setting Next Figure

  6. Survey Lines and Site Locations

  7. Original Interpretation

  8. Southern Marion Platform

  9. Northern Marion Platform Margin

  10. Lithostratigraphy at Sea-Level Section

  11. Highstand/Lowstand Platform Superposition

  12. Timing I: Age Model for Site 1193

  13. Timing II: Age Model for Site 1194

  14. Paleo-water Depths

  15. Compensation for Sediment Compaction

  16. Compensation for Sediment Compaction

  17. Potential Effect of Crustal Flexure

  18. Potential Effect of Crustal Flexure

  19. Potential Effect of Crustal Flexure

  20. Conclusions • ODP drilling on the Marion Plateau provided facies, timing, and porosity information necessary to quantify a major late middle Miocene sea level fall. • Preliminary data and their reduction suggest a sea level fall of at least 56-116 m (86±30 m) at ~13±1 Ma. • If differential isostatic response occurred between Sites 1193 and 1194, the magnitude of the sea level fall could have been significantly smaller. • The precision of our sea-level fall estimate depends strongly on the precision of the paleowater depth estimates, which are a few tens of meters under the best circumstances.

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