The Pleistocene Ironshore Formation, Grand Cayman: Diagenetic Response to Sea Level Change

• Author / Creator

  Li, Rong

• The Ironshore Formation, a Pleistocene limestone succession found on Grand Cayman, is formed of six unconformity-bounded units (A to F) that developed in response to transgressive-regressive cycles. Highstands led to deposition whereas lowstands led to diagenetic change in the earlier deposited limestones. Analysis of the diagenetic features in the matrices and corals from each unit shows that the diagenetic styles of individual samples cannot be linked to specific unconformities. Instead, both intrinsic (e.g., skeletal microstructure, porosity and permeability of substrate) and extrinsic (e.g., sea level position, climate, exposure time) factors controlled development of the heterogeneous diagenetic patterns. The fact that the matrices of the limestones have undergone more meteoric diagenetic alteration than the corals can probably be ascribed to the higher permeabilities of the matrices that allowed larger volumes of water to flow through them. Maximum diagenesis took place during the lowstands that followed the deposition of units C and D, which can be attributed to the long-lasting lowstands that were accompanied by a wet climate with high rainfall. Interpretation of the diagenesis displayed in the Ironshore Formation highlights the fact that the diagenetic fabrics in a carbonate succession do not necessarily follow a systematic pattern that can be linked to the transgressive-regressive cycles that governed its formation.
  The laminar and non-laminar calcretes developed on Unit D of the Ironshore Formation on Grand Cayman display various diagenetic features that reflect the interactions between substrate, soil cover, climate, and biological influences that dictated their development. The δ13C values of the laminar calcretes record a change from C3 dominated vegetation that grew in a cool, wet climate to a C3/C4 mixed plant vegetation that grew in a drier, hotter climate. The similarities between Cayman calcareous crusts and those found in Florida suggest that such crusts are related to regional climate conditions and may therefore facilitate regional stratigraphic correlation.

• Subjects / Keywords

  • Calcareous crust
  • Pleistocene
  • Ironshore Formation
  • Grand Cayman
  • Diagenesis

• Graduation date

  Spring 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3NC5SM8W

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.