224 Paleoclimatology/Paleoceanography

Wednesday, 12 October 2011
8:00 AM - 12:00 PM
Room 200FG

WET CLIMATE IN SOUTHEAST SPAIN DURING THE MESSINIAN SALINITY CRISIS

Paper number: 224-5
Program: Technical Sessions
Time: 9:00 AM – 9:15 AM

Authors

Abstract

The desiccation of the Mediterranean Sea during the Messinian Salinity Crisis (MSC; 5.59 – 5.33 Myr ago) was one of the most dramatic episodes of oceanic change in the Neogene, but our understanding of its impacts on nearby terrestrial systems remains poorly understood. We reconstruct latest Miocene paleoenvironments on the Iberian Peninsula through combined facies and stable isotopic analyses of continental sediments deposited under dominantly endorheic conditions in the intramontane Baza Basin (Betic Cordillera, southeast Spain). Biostratigraphic and paleomagnetic analyses of these sediments constrain their age to between ca. 5.9 and 5.3 Ma, suggesting temporal overlap with the MSC. The lower part of our composite stratigraphic section is dominated by cross-stratified sandstone, siltstone, and carbonate-rich mudstone with root traces, indicating distal alluvial fan and palustrine facies. The upper part of the composite section is dominated by interbedded diatomite and massive calcitic micrite with fossil gastropods, indicating lacustrine facies. We interpret this facies change as an increase in lake level during the terminal Miocene.

The facies transition is accompanied by an upsection decrease in the stable carbon and oxygen isotopic composition (δ13C and δ18O) of pedogenic, palustrine, and lacustrine carbonate. The δ13C decrease is consistent with a transition to wetter conditions (e.g., increased runoff of 13C-depleted terrestrial carbon, decreased water residence time), but our data are insufficient to rule out changes in lake primary productivity and/or decomposition. The δ18O decrease is consistent with decreasing evaporative 18O-enrichment of surface waters under increasingly wet conditions. The δ18O of lacustrine calcite from our composite section is lower than observed and predicted calcite δ18O for modern Iberian closed and low-elevation (< 1000 m) open lakes, suggesting that the latest Miocene Baza Basin was not entirely endorheic and/or a large component of lake water was derived from 18O-depleted high-elevation precipitation. Our working hypothesis explaining these observations is that the MSC caused strong low pressure over the Mediterranean Basin, which resulted in strengthened westerly storm tracks and increased orographic uplift of airmasses over the Betic Cordillera.