New constraints on Miocene sea-level

 

A long-term objective of the carbonate groups is to provide some constrain on the timing and magnitude of eustasy through time (i.e. global sea-level). To date, the best record for eustasy comes from the New Jersey margin, where Ken Miller and co-authors have worked for 20 years. However, deriving a record of global sea-level changes based on a single margin represents some risks, in part because tectonic movement are possible even on a passive margin. Furthermore, the Miocene sequences on the New Jersey margin had been poorly recovered until 2010.

We have worked over the last 4 years at identifying sedimentary sequences on the Marion Plateau of Australia, a carbonate building that grew in subtropical waters during the Miocene and was drilled during ODP Leg 194. We have then quantified the magnitude of eustasy for the Miocene using both sediment backstripping and some oxygen isotope constraints. The Marion Plateau is a passive margin, and carbonates represent the best "dip stick" for sea-level study because highstand deposits are often cemented early and tend to be better preserved during lowstands. Our results, published in the Earth and Planetary Science Letters (Volume 304, Issues 3-4, 15 April 2011, Pages 455-467, doi:10.1016/j.epsl.2011.02.013), suggest a greater magnitude for the cumulative sea-level fall of the Miocene: between 54-69 meters of sea-level change (see figure). This is a critical result, because the Miocene is the period when Antarctic became fully glaciated. Our study suggest that between 60-90% of the East Antarctic ice sheet must have been formed during that critical period. This study was done in collaboration with Garry Karner (ExxonMobil), Mark Leckie (Umass), Emily Browning (Umass), Zenon Mateo (IODP), Chris Lowery (Umass) and Brooke Carson (Chevron). The project was financed by the ACS PRF.