Betts, T., Heness, E.A., Semian, Z.M., Malenda, M.G., Simpson, E.L., and Friehauf, K., 2013, A unique occurrence of adipocere on the lacustrine shoreline, Salton Sea California: Geological Society of America National Meeting, Denver, Colorado (27

A unique occurrence of adipocere on the lacustrine shoreline, Salton Sea California

Betts, T., Heness, E.A., Semian, Z.M., Malenda, M.G., Simpson, E.L., and Friehauf, K., 2013, A unique occurrence of adipocere on the lacustrine shoreline, Salton Sea California: Geological Society of America National Meeting, Denver, Colorado (27–30 October, 2013).

Marlena Rock presenting research at the national Geological
Society of America meeting in Denver, Colorado

The Salton Sea – a hypersaline, closed-system lake in southern California USA – experiences periodic fish kills dominated by the hybrid tilapia (Oreochromis mossambicus). High wind events overturn the stratified water column, initiating algae blooms that consume dissolved oxygen resulting in anoxia. This study examines the unique occurrence of organic “spheres” taphonomically associated with disarticulated tilapia fish hard parts along the lake shoreline. Chemical analyses demonstrate that the composition of the spheres is consistent with tilapia, and that the extent of adipocere formation is significant.
Fieldwork on the Salton Sea bone beach deposits in March 2013 revealed the presence of brown to dark orange, low density (0.7± 0.16 g/cm3) spheres. Historical photographs of the Salton Sea shoreline and 1.5 meter deep trenches indicate the spheres are a recent phenomenon occurring at high water stands.

Infrared spectroscopy (IR) along with gas chromatography (GC) revealed the presence of both triglycerides and free fatty acids. Comparison with IR analysis of synthetic standards composed of various mixtures of olive oil and oleic acid indicates the organic components of the Salton Sea spheres are 46 ± 2% triglycerides and 54 ± 2% salts of free fatty acids. These results are consistent with the formation of adipocere by hydrolysis of triglycerides to free fatty acids. GC analysis indicates the adipocere consists primarily of palmitic, oleic, pentadecanoic, and myristic acids, consistent with an origin from tilapia soft tissue linked to the bone deposits.

Because adipocere formation is linked to degradation by anaerobic bacteria, this new phenomenon at the Salton Sea indicates environmental conditions have at least temporarily and locally developed that favor dominantly anaerobic taphonomic break down of tilapia soft tissues.

Kurt Friehauf - February 2014