2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 27
Presentation Time: 9:00 AM-6:00 PM


TICHENOR Jr, Hal R., Department of Geological Sciences, East Carolina University, 101 Graham Building, Greenville, NC 27858 and LEWIS, Ronald D., Department of Geosciences, Auburn University, Auburn, AL 36849-5305, Tichenorh10@ecu.edu

Foraminifera attached permanently to hard substrates have received relatively little research attention in actualistic distribution studies compared to free specimens. However, in many regards, attached (encrusting) species are better as paleoenvironmental indicators. They occur in sediment samples as whole tests attached to sand and pebble grains and as partial tests broken from their substrates. When attached to larger substrates such as coral rubble, they are less likely to be transported and abraded than are free species. Some attached foraminifera are known to be restricted to specific environmental conditions, such as the low-light levels found in cavities and crevices. These qualities have made attached foraminifera useful in paleoenvironmental reconstructions in studies of ancient limestone.

Field work took place at San Salvador, Bahamas, primarily in June 2008 and May 2009. SCUBA was used to collect clasts along shore-to-shelf-edge transects through Telephone Pole Reef in Fernandez Bay and at Rocky Point; through the channel at Cut Cay (North Point); and at numerous spot localities, including two bank-barrier reefs. Clasts were examined in 10-cm2 quadrats: attached specimens were counted and their taphonomic conditions were recorded.

Zonation results primarily from differences in relative abundance of the same taxa in different zones and from differences in average taphonomic states. Near-shore, subtidal assemblages on the west (lee) and north sides of the island are highly abundant, nearly pristine, and dominated by Homotrema and/or Miniacina; on the windward side, Homotrema/Miniacina is less common. Midshelf assemblages vary with locality, although all have fewer Homotrema/Miniacina and more Planorbulina than the near-shore assemblages. Cobbles collected in areas of high sedimentation rates and low reef growth have assemblages that are nearly barren with respect to attached foraminifera. Bank-barrier reef assemblages are similar to those near the shore but show more diversity and a greater abundance of Gypsina plana. Shelf margin assemblages are the most distinct because they are dominated by the large, sheet-like Gypsina plana, with other taxa being sparse and poorly preserved.