PALEOSOLS FROM ELEUTHERA, THE BAHAMAS: PETROGRAPHIC ANALYSIS

Field reconnaissance of paleosols on Eleuthera, The Bahamas occurred during winter 2015 field season. During this work, 48 samples were collected that consisted of terra rossa paleosols and micritic crusts. Standard petrographic thin sections were created from each sample; however, only terra rossa paleosols were examined for this project. Standard petrographic analysis using a polarizing light microscope coupled with a mechanical stage were conducted to determine texture and composition of these samples.

Paleosols, lithified soils, are a common topographic feature found on carbonate platforms, however, the amount of research conducted on paleosols in The Bahamas has been marginal. Most Eleutheran paleosols appeared to be poorly cemented and highly porous in the field. Thin section analysis revealed that porosity is much lower than expected from field observations (never exceeding 9%) and that the paleosols are fairly well cemented (sometimes with as much as 33% cement).

Based on petrographic texture, two types of paleosols were identified on Eleuthera. Type 1 Paleosols are described as paleosols with greater than or to equal relative percentages of insoluble material compared to the percentages of allochems. Type 2 Paleosols are described as paleosols with significantly more allochems than insoluble material. While the texture of these two paleosol types differ, their formation is the same. As insoluble dust and other material collects on an exposed platform surface, a soil develops. The platform surface is highly karstified, so soil thickness varies with the bedrock surface. Type 1 Paleosols are thought to represent lithified soil material, while Type 2 Paleosols represent infiltration of soil material into the underlying bedrock and/or a paleokarst breccia surface. Outcrops that have Type 2 Paleosols exposed represent paleosol deposits that were eroded prior to lithification or have been eroded since modern exposure. Outcrops with Type 1 Paleosols represent thicker accumulations of relic soil material either through less erosion or thicker accumulations due to topographic lows in the paleosol bedrock surface.