Taphonomic alteration differences between bivalves and barnacles from two taphofacies

Daley, G.M., H. Schultz, B.W. Matthews, D. Geary 2004
Geological Society of America Abstracts with Program 36(5): 382.

The amount and type of taphonomic alteration of fossil deposits has proven useful in analyzing and reconstructing paleoenvironment. However, taphonomic analyses frequently examine the remains of only one type of organisms (e.g., bivalves, brachiopods, or foraminifera). In this study we examine the amount of taphonomic alteration in both bivalve and barnacle remains collected from two different Florida Pleistocene, shallow subtidal paleoenvironmental settings (Facies E from the Bermont Formation and Facies I from the Fort Thompson Formation).

An examination of fragmentation and abrasion of the shells of the venerid Chione cancellata revealed a greater degree of post-mortem alteration in samples from Facies I. Samples from both facies contained well preserved C. cancellata, but very poorly preserved C. cancellata were only abundant in samples from Facies I. We interpreted the relative abundance of severely worn C. cancellata in Facies I to indicate that the remains either had longer residence time in the taphonomically active zone, or that the local paleoenivironmental conditions were more energetic in Facies I.

The amount of post-mortem alteration of barnacle remains was determined by examining both the amount of disarticulation and the mass of the preserved fragments. Well-preserved, complete barnacle fossils were common in samples from Facies I, which was the facies in which taphonomic alteration of C. cancellata shells was greater. Complete barnacles were uncommon in Facies E, where taphonomic alteration of C. cancellata shells was low. In contrast, the average mass of barnacle fragments found in samples from Facies E was higher than those found in Facies I, perhaps indicating the same pattern of taphonomic alteration found in the analysis of C. cancellata.

These results that indicated a more complex interpretation of paleoenvironmental conditions and taphonomic alteration was required than that yielded by either analysis alone. We will examine several possible interpretations of these results.