Sea level controls sedimentation and environments in coastal caves and sinkholes

TitleSea level controls sedimentation and environments in coastal caves and sinkholes
Publication TypeJournal Article
Year of Publication2011
Authorsvan Hengstum, PJ, Scott, DB, Groecke, DR, Charette, MA
JournalMarine Geology

Quaternary climate and sea-level research in coastal karst basins (caves, cenotes, sinkholes, blueholes, etc.) generally focuses on analyzing isotopes in speleothems, or associating cave elevations prior sea-level highstands. The sediments in coastal karst basins represent an overlooked source of climate and sea-level information in the coastal zone, but to accurately interpret these sediments first requires an understanding of the forcing mechanisms that emplace them. In this study, we hypothesize that coastal karst basins transition through vadose, littoral, anchialine, and finally into submarine environments during sea-level rise because groundwater and sea level oscillate in near synchrony in the coastal zone, causing each environment to deposit a unique sedimentary facies. To test this hypothesis, the stratigraphy in twelve sediment cores from a Bermudian underwater cave (Green Bay Cave) was investigated and temporally constrained with twenty radiocarbon dates. The results indicate that we recovered the first succession spanning the entire Holocene from an underwater cave (similar to 13 ka to present). The sediments were characterized with X-radiography, fossil remains, bulk organic matter, organic geochemistry (delta(13)C(org), C:N), and grain size analysis. Four distinct facies represent the four depositional environments: (i) vadose facies (>7.7 ka, calcite rafts lithofacies), (ii) littoral facies (7.7 to 7.3 ka: calcite rafts and mud lithofacies), (iii) anchialine facies (7.3 to 1.6 ka: slackwater and diamict lithofacies), and (iv) submarine facies (