B. C. Schreiber1, R. P. Philp2, S. Benali3 , M L. Helman4, J. A de la Peña5, R. Marfil5, P. Landais6, A. D. Cohen7, and C.G.St.C. Kendall7
1 Department of Geology, Appalachian State University, 195 Rankin science building, Boone NC, 28608, USA. corresponding author: geologo@aol.com
2 School of Geology and Geophysics, University of Oklahoma, 100 East Boyd St., Norman OK, 73019-0628, USA.
3 School of Earth and Environmental Science, Queens College (C.U.N.Y.), 65-30 Kissena Boulevard, Flushing N.Y., 11367, USA.
4 United States Army Corps of Engineers, 26 Federal Plaza, New York N.Y. 10278-0090, USA.
5 Universidad Complutense de Madrid, Facultad de Ciencias Geológicas, Departamento de Petrología y Geoquímica, 28040 Madrid, Spain
6 UMR G2R, Université Henri Poincaré, BP 239, 54506 Vandoeuvre Cédex, France.
7 Department of Geological Sciences, University of South Carolina, Columbia SC, 29208, USA.
Sediments deposited under hypersaline conditions, particularly those laid down in the transition zone between marine carbonates and evaporites, are increasingly recognised as a potential source for oil. Recent environments that lie in waters with elevated salinities are sites of very high biological productivity that can be used as models for evaporite-related sedimentation in the geological record. Of particular importance is the range of elevated salinities well above the range for normal marine biota, in which organic-rich cyanobacterial carbonates form and accumulate in large quantities. Such organic matter collected from a number of modern evaporative settings has been examined in terms of oil potential and for biomarkers characteristic of hypersaline environments. The regions studied include marine-fed salinas (Santa Pola, Spain); marine-fed sabkhas (Abu Dhabi, UAE); and continental ponds and lakes (La Mancha region, Spain). High values of H/C ratio and HI demonstrate the oil source potential of this organic matter. The hydrocarbons generated during artificial maturation of these immature sediments resemble those naturally occurring in ancient petroleum-generating evaporitic systems. Variations in the total extracts, saturate, aromatic, resin, and asphaltene fractions evolve to an oil-like composition. Similarly, the distributions of n-alkanes, hopanoids, and steroids evolve progressively to those typically found in crude oils from evaporitic environments. The most relevant biomarkers, such as gammacerane, 2,6,10-7-(3-methylbutyl)-dodecane, C20–isoprenoid thiophenes or chromans characteristic of hypersalinity as previously described in the literature, are not always originally present in the environments studied, and their distribution can be affected by both maturation and the mineral matrix. Therefore caution should be exercised when using these biomarkers to assess ancient environments of deposition in terms of salinity.