2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 218-16
Presentation Time: 12:45 PM


SMITH, Christopher W., Auburn University, 420 N Dean Rd, Apt 13C, Auburn, AL 36830 and LEWIS, Ronald, Department of Geosciences, Auburn University, Beard Eaves Memorial Coliseum, Room 2063, Auburn, AL 36449-5305

Relatively few studies focus on the distribution of encrusting foraminifera – species permanently attached to hard substrates ­– as paleoenvironmental indicators. However, the use of encrusting foraminifera has many potential advantages over the study of free species. They are very sensitive to environmental variables such as ambient light and water energy and are abundant in their preferred habitats. Because encrusting foraminifera are fixed in place, they are more likely to stay in the original habitat; their tests remain in place after death, leaving a post-mortem history.

Field work took place at Cat Island, Bahamas, in May 2014. SCUBA was used to collect cobbles at eight sites representing different environments from the nearshore sites, offshore patch reefs, and relatively deep water at the shelf edge. Foraminifera and other encrusting organisms were examined in 10-cm2quadrats. Foraminifera were identified to genus and species; in addition, morphotype and taphonomic grade were assessed. ImageJ was used to determine the area covered for each encruster category. Data analysis includes ANOVA and cluster analysis. Results are compared to those of a similar study by Tichenor and Lewis on nearby San Salvador island.

Differences between the various sites are readily apparent from both the overall density of encrusting organisms and the relative proportion of the different encrusting foraminiferan species. Nearshore localities are marked by high density, as measured by the number of specimens per quadrat. Most nearshore foraminiferal assemblages are dominated by well-preserved Homotrema rubrum and Nubecularia; the relative dominance of these species varies from site to site. Patch-reef localities have a lower density of encrusting foraminifera and a higher proportion of Planorbulina in relation to Homotrema rubrum. Shelf-edge locations are distinctive because of the low density of encrusting foraminifera and the conspicuous presence of Gypsina plana, which dominates assemblages when measured by surface area. The main results of this study to date are consistent with the findings of the prior research on San Salvador, supporting the use of encrusting foraminifera in paleoenvironmental reconstructions of shallow-water carbonate systems.