Relationships Between Foraminifera and Geomorphology: Holocene, Crooked-Acklins Platform, Southern Bahamas

Although general ecologic controls on the occurrence, growth and shape of foraminifera are well understood, the spatial patterns of foraminiferal distribution across carbonate isolated platforms and their relationship to geomorphic setting are not well constrained. To provide a tool for constraining and predicting spatial variability in ancient analogs, this study tests the hypothesis that foraminiferal populations vary among geomorphic settings by studying Holocene sediment of Crooked-Acklins Platform, southern Bahamas, by foraminiferal population analysis (including the abundance and diversity of foraminiferal genera). To test the hypothesis, this study integrates observations of remote sensing data, bottom type, epifauna, grain sizes, and foraminiferal populations. Results reveal that foraminiferal abundances, diversity and assemblages vary systematically across the isolated carbonate platform. On this platform, twenty-two foraminiferal genera include generalists (genera present across the platform; e.g., Archaias, Peneroples and Quinqueloculina) and specialists (genera that are spatially restricted; e.g. Clavulina, Rosalina and Homotrema). The abundances of these foraminifera, and the diversity and evenness of associations in surficial sediment in, the geomorphic are greater in geomorphic elements near the open ocean (back-reef shelf, southern unrimmed shelf and southern part of the shoal). In contrast, geomorphic elements further from the margin (northern part of the shoal part of the shoal, platform interior and tidal flat) have generally low diversity, evenness and foraminiferal abundance. The distribution patterns and abundances of the 22 distinct genera suggests that not all geomorphic elements are uniquely defined by one foraminiferal assemblage – some geomorphic elements include more than one assemblage, and some assemblages extend across two or more geomorphic elements. Similarly, foraminiferal distribution trends in shallow Holocene sediment cores reveals patterns that the mimics the distribution of the surface sediment, although details appear altered by taphonomic changes from bioturbation and rhizoturbation. The results suggest that coupled sedimentologic and foraminiferal characterization provide the most accurate interpretation. Integrated sedimentologic observations, foraminiferal patterns, and previous studies provide a basis for a conceptual model for controls on foraminiferal distribution. This conceptual model could be applied to ancient systems to understand and predict depositional variability related to distinct geomorphic and depositional settings