Degree Year

2019

Document Type

Thesis - Open Access

Degree Name

Bachelor of Arts

Department

Geology

Advisor(s)

Karla Parsons-Hubbard

Committee Member(s)

Steven F. Wojtal
Dennis K. Hubbard

Keywords

Taphonomy, Taphofacies, Seagrass, Mollusks, Callianassa, St. Croix, Lagoon, Infuanal, Epifaunal, Paleontology, Bioturbation, Environmental change, Smugglers cove

Abstract

Sediments collect in reef lagoons, and the shells within these can record changes in the environment as they accumulate. Smuggler’s Cove (St. Croix, USVI) has been accumulating a sediment package for at least 5,000 years based on radiocarbon ages. Callianassid shrimp severely bioturbate this lagoon’s sediment package by moving shell material into shelly, subsurface lags that have a high chance of becoming fossilized. Shell condition (taphonomy) was compared between surface and lag to see whether the lag is an accurate representation of the living surface fauna. Guild membership, taxon, and mollusk size between surface and lag assemblages were analyzed. It was found that the surface beds were more similar to each other than to lags regardless of habitat, and subsurface beds were also more like one another. The dominance of infaunal guilds and the scarcity of epifaunal guilds in the subsurface suggests that it is difficult for callianassids to bring down surface shells. The decrease in taphonomic alteration in the lower beds suggests that shrimp are not pulling shells down by size alone but rather by life guild, favoring infaunal over epifaunal organisms. Since infaunal organisms are less subject to taphonomic alteration than epifaunal ones and tend to be small, guild membership is driving the overall taphonomic signal and influences the results for species and size. Therefore, infaunal species may be overrepresented in the fossil record in these types of environments. The epifaunal surface shells on the other hand, may persist there until degraded into sand.

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