Long-Term Sea-Level Variations and Diagenesis Recorded on a Miocene Subtropical Carbonate Platform as Evidenced by Palynological Data, ODP Site 1007, Bahamas

In 1996 Ocean Drilling Program (ODP) Site 1007, Bahamas was drilled in 647.4 meters of water on the toe-of-slope of the Bahamas Platform to complete a transect across the bank and to improve understanding of changing sedimentary environments in periplatform sediments during Neogene sea-level fluctuations. The Miocene sequence recovered at Hole 1007C consist of decimetric to centimetric-scale cyclic alternations of dark and light layers with varying degrees of compaction/cementation. However, in carbonate sedimentary systems the environmental signals are frequently masked by diagenetic overprints. Fortunately, organic-walled microfossils such as dinoflagellate cysts, pollen and acritarchs are chemically unaffected by diagenetic changes, while usefully recording the degree of sediment compaction by distortion of their walls. Thirty-seven samples from the lower part of Hole 1007C are being investigated for their palynological content and total palynomorphs concentration per gram of sediment, in order to understand differential diagenesis and sea-level fluctuations on the toe-of-slope of a passive subtropical carbonate platform.

Dark layers show a set of common features characterized by higher values of insoluble residues and aragonite, a higher level of compaction, and lower degree of cementation compared with the light layers. Moreover, the dark layers consistently contain elevated amounts of dinoflagellate cysts per gram of sediment. Of the samples with high concentrations of dinoflagellate cysts, many come from intervals interpreted either as Low System Tracts (LST) or Transgressive System Tracts (TST). Conversely, the light layers, which have been interpreted as High System Tracts (HST), contain lower concentrations of dinoflagellate cysts.

Examination of sedimentological and palynological data presented in this work, suggests a strong relationship between diagenesis, sedimentary environment, sea-level fluctuations, and the palynological record, highlighting the potential use of organic-walled palynomorphs to assist in the modeling of depositional and diagenetic studies in carbonate rocks.