SUCCESSIONS IN A BERMUDIAN UNDERWATER CAVE TRACK HOLOCENE SEA-LEVEL RISE: A GLOBAL MODEL FOR COASTAL CAVE ENVIRONMENTS

Walther’s Law of the Correlation of Facies states that continuous sedimentary facies observed laterally in modern space can also be observed as stacked on top of one another in stratigraphic section. This central tenet of sedimentary geology has been applied globally to both terrestrial and marine environments, but a lack of physical evidence has precluded application of the law to coastal caves. Environments in coastal caves are (a) independent of speleogenesis, (b) represent the phreatic to vadose continuum with respect to sea level: vadose, littoral, anchialine, submarine, and (c) are widely investigated by cave ecologists. Currently, all the above cave environments can be identified with respect to sea level in Bermuda. Twelve sediment cores constrained with 19 radiocarbon ages were collected on SCUBA in Green Bay Cave, Bermuda, affording the first stratigraphic record from a phreatic cave spanning the Holocene (13 ka to present). Green Bay Cave is ideally suited to test the hypothesis because an anchialine cave entrance is connected to a submarine cave passage by over 200 m of cave passage. Six lithofacies (calcite raft, calcite raft and mud, slackwater, diamict, carbonate mud, and shell hash) were characterized in the cores using X-radiography, organic matter content (wt. %), δ¹³C_org, C:N, and particle size analysis (interpolated particle size distributions, mean, median, mode, standard deviation). These lithofacies can be correlated through the cave basin stratigraphy, and organized into four depositional environments: Vadose Cave (> 7.6 ka: calcite rafts), Littoral Cave (7.6 - 7.9 ka: calcite rafts and muds), Anchialine Cave (<6 ka: slackwater lithofacies and diamict near the anchialine entrance), and Submarine Cave (<2 ka: carbonate muds and shell hash near the submarine exit). The successions from Green Bay Cave provide strong evidence that Walther’s Law can be applied when interpreting coastal cave sediments because coastal cave sedimentary facies exist both laterally in modern space and in succession as a response to Holocene sea-level rise.