Eustatic and Tectonic Controls on the Development of the Stratigraphic Architecture of the Cayman Islands, British West Indies

• Author / Creator

  McCormick, Cole

• The Paleogene to Neogene carbonate sedimentary successions that form the cores of each of the Cayman Islands, which are located within 150 km of each other, developed on isolated banks that were surrounded by deep oceanic water. Although each of the Cayman Islands has experienced uniform changes in eustatic sea level, each island is situated atop separate fault blocks that have undergone independent tectonic histories. Cayman Brac for example, was uplifted and tilted between the late Pliocene and ~125 ka, whereas evidence from the stratigraphic framework and 87Sr/86Sr isotope ratios suggests that Grand Cayman has been subsiding since the early Miocene. Accordingly, by comparing the successions on each of the Cayman Islands, the impacts of eustasy can be decoupled from the impacts of tectonism.
  Each of the cores of the Cayman Islands is comprised by the Bluff Group that includes the Brac Formation (Lower Oligocene), Cayman Formation (Middle Miocene), and Pedro Castle Formation (Pliocene). On western and central Grand Cayman, the Brac Formation is at least 69 m thick, the Cayman Formation is 45 m - 129 m thick, and the Pedro Castle Formation is 0 m - 22 m thick. Six facies have been identified in the Brac Formation (assigned to facies associations FA1 and FA2), whereas nine facies have been identified in the Cayman Formation (assigned to facies associations FA3 and FA4). Antecedent topography on the Brac Unconformity, which forms the upper boundary of the Brac Formation and is located from 72 m - 129 m below sea level, restricted bank circulation and influenced the deposition of the sediments that now form FA3 of the Cayman Formation. FA3, which is 12 m - 73 m thick, consists of a deepening-upwards succession of benthic foraminifera and red algae grainstone and rudstone that onlapped and filled paleo-topographic lows on the underlying Brac Unconformity. FA4, which is 26 m - 47 m thick with minimal variability, consists of a shallowing-upwards succession of branching coral, rhodolith, green algae, and bivalve wackestone and floatstone. FA3 has an average porosity of 32.5%, an average maximum horizontal permeability (Kmax) of 2379 mD, and an average vertical permeability (Kvert) of 1586 mD, whereas FA4 has an average porosity of 9.3%, an average Kmax of 1044 mD, and an average Kvert of 44.2 mD.

• Subjects / Keywords

  • Carbonate Sedimentology
  • Diagenesis
  • Sea Level
  • Paleoenvironment
  • Tectonics

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-fwrj-4202

• License

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