Molluscan Taphonomy as a Proxy for Recognizing Fossil Seagrass Beds
Seagrass beds, important marine ecosystems both economically and environmentally, have a poor fossil record. As a result, little is known about the geographic distribution of seagrasses over historic and geologic time, or their abundance when unaltered by anthropogenic effects. The purpose of this study is to define a taphonomic signature unique to seagrass beds that can be used as a proxy for identifying the seagrass habitat in the fossil record. In order to develop this proxy, sediment samples from Recent seagrass and non-seagrass environments were collected, and the molluscan bioclasts from these samples were categorically ranked for the following taphonomic characteristics: encrustation, bioerosion, abrasion, dissolution, fragmentation, edge chipping, and edge rounding. Samples of faunal assemblages associated with deposits inferred to be from seagrass beds were collected from the Eocene Moodys Branch Formation (Copenhagen, LA) and an unnamed Pleistocene unit from Bocas del Toro, Panama. The molluscs from these samples were examined for the same characteristics as the Recent molluscs to test if taphonomic characteristics associated with seagrass habitats are preserved in fossil samples.
Taphonomic data were analyzed using both canonical discriminant analysis, and assignment tests. Differences between seagrass and non-seagrass environments are apparent, although these differences may be distorted by localized transport of shells between environments, and by differential response of various taxonomic groups to taphonomic processes. Taphonomic characteristics that best discriminant between seagrass and non-seagrass environments are a combination of edge rounding, abrasion, dissolution, and fragmentation. The assignment tests suggest that these taphonomic characteristics are preserved in the fossil record, making it possible to identify fossil seagrass beds based on their taphonomic signature. However, error rates associated with assignment tests suggest that more sampling of environments is necessary to better define the taphonomic signature of seagrass beds.
Advisor:John Wrenn; Samuel Bentley; Laurie C. Anderson
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:05/31/2005