A TAPHONOMIC ASSESSMENT OF THE STRATIFIED LAKE MODEL

A unique field approach was used to assess the fossil preservation potential in lacustrine environments that has long been attributed to chemical stratification in lakes. It is well documented that chemical stratification of a lake can result in the deposition and preservation of fine laminae or varves. It is also suggested that chemical stratification creates an environment responsible for the preservation of fossils. The field approach used to test the preservation potential of the Stratified Lake Model included the collection of sediment samples from several modern lakes in the northeastern United States that exhibit seasonal or long-term chemical stratification. Sediment samples were also collected from a lake in southern California that is not chemically stratified. All the lakes contain resident fish populations. The sediment samples were analyzed for the presence of laminae, fish and other organic remains.

In the lakes that exhibit chemical stratification, laminae are deposited and preserved; however, fish remains are not preserved within the laminated deposits. These results suggest that chemical stratification and the resulting lack of bioturbation activity can be a mechanism for the preservation of fine laminae. However, the absence of fish remains in these deposits suggests that simple chemical stratification may not be the appropriate model for preservation of fish as seen in ancient lake deposits such as those in the Tertiary Greater Green River Basin. Results that further support this suggestion were found in the sediment samples collected from the non-chemically stratified lake. In these samples, both laminae and fish remains were present.

We conclude that preservation of fish and other biota in lacustrine environments must be dependent upon more than a simple chemical stratification of the overlying water column.