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

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

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

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

Marion Plateau Setting

Next Figure

Survey Lines and Site Locations

Original Interpretation

Southern Marion Platform

Northern Marion Platform Margin

W ESite 1194Site 1193

Lithostratigraphy at Sea-Level Section

Highstand/Lowstand Platform Superposition

Timing I: Age Model for Site 1193

Timing II: Age Model for Site 1194

Paleo-water Depths

Compensation for Sediment Compaction

??

Compensation for Sediment Compaction

Potential Effect of Crustal Flexure

Potential Effect of Crustal Flexure

Potential Effect of Crustal Flexure

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.