Testing New Organic Geochemical Evidence for Sea Surface Temperature Changes at the Onset of the Messinian Salinity Crisis

Courtney Turich
Penn State University Department of Geosciences
University Park, PA
cturich@geosc.psu.edu

In Central Sicily, several Tripoli Formation outcrops (6.96-5.93 Ma) provide high-resolution, stratigraphically constrained, and continuous records of the transition from marine to hypersaline conditions leading to the Messinian Salinity Crisis (MSC). Numerous studies have examined microfossil, sedimentological, and stable isotope evidence of environmental changes during this interval, but this is the first study to incorporate organic matter characterization of these outcrops.

Specifically, we are testing a new organic geochemical proxy, the TetraEther indeX (TEX86), to determine sea surface temperatures during the paroxysmal phase of the MSC, where microfossil temperature indicators are absent. The TEX86 proxy is based on the ratio of 4 different tetraether-linked membrane lipids synthesized by planktonic Archaea, and preserved in sediments.

Our initial results reveal that sea surface temperatures may trace eccentricity cycles, with the coolest temperatures occurring just as basin-wide gypsum deposition began. We will test the authenticity of these temperature calculations by examining the effect of diagenesis on the ratio of tetraether lipids in extractable organic matter. We will desulphurize both the bitumen and kerogen, and analyze the products for tetraether lipids. If we find tetraether lipids bound in diagenetic polymers, we will quantify their concentrations and determine if the lipid ratio used in the TEX86 proxy is affected. We anticipate that the organic geochemical record will provide new data and insights into the recognition and interpretation of environment change during the MSC.