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

3. Introduction n The Miocene Climatic Optimum (~14.5-17 Ma), a period of extreme warmth, was followed by global cooling n 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) n 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 n ODP Leg 194 drilled at 8 sites: u Water depths of 304-419 m u Penetrations per hole of 265-675 m u Core recoveries per hole of 11% - 100% u late Oligocene to Pleistocene sediments n Principal results: u Magnitude of l. middle Miocene sea-level fall u Cool subtropical platform growth environment F bryozoans, larger benthic foraminifers, red algea u Ocean current rather than wind control u Records of higher-order sea-level changes in drifts u Fluid flow through the platform u 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

17. Potential Effect of Crustal Flexure

20. Conclusions n ODP drilling on the Marion Plateau provided facies, timing, and porosity information necessary to quantify a major late middle Miocene sea level fall. n Preliminary data and their reduction suggest a sea level fall of at least 56-116 m (86±30 m) at ~13±1 Ma. n If differential isostatic response occurred between Sites 1193 and 1194, the magnitude of the sea level fall could have been significantly smaller. n 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.