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Flecker, R.1, S. de Villiers2, R. M. Ellam3
(1) Bristol University, Bristol, United Kingdom
(2) University of Natal, Durban, South Africa
(3) Scottish Universities Environmental Research Centre, East Kilbride, United Kingdom

ABSTRACT: Sr Isotope Constraints on Isolation Events in Marginal Marine Successions: an Example from the Late Miocene Mediterranean and its Implications for Sea Level Change in the Black Sea

Source rock and reservoir sequences deposited in marginal marine systems like the Mediterranean, Black Sea and Caspian are commonly difficult to date and correlate. This is because the application of open-ocean stratigraphic techniques to restricted basin sediments is problematic. For example, the impoverished faunal assemblages and indigenous species typical of marginal marine successions result in substantial biostratigraphic uncertainty. New research demonstrates that Sr isotopes can be used to identify and constrain the timing of ancient isolation events in marginal environments. In addition, the degree of restriction can be quantified using simple Sr isotope models. The construction of local Sr curves for comparative marginal basin successions can significantly improve inter- and intra-basin correlation and provide useful insights into their sea level history.
Marine fossil assemblages suggest that the Mediterranean maintained typical marine salinity (~38 g/l) until just prior to evaporite precipitation in the latest Miocene. However, Sr isotope analysis of pre-evaporite samples shows that northern Mediterranean sub-basins experienced several periods of reduced exchange with the Atlantic when less than 15% of the source water derived from the global ocean. Comparison of the global ocean Sr isotope curve with the isotopic data from the Mediterranean constrains the timing of these restriction events to within +/- 0.5 Ma or better. This provides an event stratigraphy that can be linked to evidence for sea level change in the Black Sea.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.