Evolution of Erosional Unconformities in the Cenozoic Succession of the Cayman Islands Open Access
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- Degree grantor
University of Alberta
- Author or creator
- Supervisor and department
Jones, Brian (Earth and Atmospheric Sciences)
- Examining committee member and department
Lowenstein, Tim (Geology, State University of New York)
Harris, Nicholas (Earth and Atmospheric Sciences)
Gingras, Murray (Earth and Atmospheric Sciences)
Keddie, Andrew (Biological Sciences)
Department of Earth and Atmospheric Sciences
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Doctor of Philosophy
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The carbonate succession on Grand Cayman and Cayman Brac, located close to each other in the Caribbean Sea, includes the Bluff Group that is formed of the unconformity-bounded Brac Formation (early Oligocene), Cayman Formation (middle Miocene), and Pedro Castle Formation (early Pliocene), which is overlain by the Ironshore Formation (Pleistocene). The erosional unconformities that now separate these formations developed during the sea-level lowstands.
The karst relief of at least 62 m on the upper surface of the Cayman Formation on Grand Cayman provides the minimum estimate for the Messinian drop of sea level in Caribbean. The rugged interior landscape and peripheral rims on this surface reflect the interplay between the rate of runoff and rainfall. Compared to Grand Cayman, the upper surface of the Cayman Formation on the uplifted central core of Cayman Brac is tilted with up to 120 m of the Cayman Formation lost to erosion, more pronounced peripheral rims, and lower karst relief. Nevertheless, exposures of this formation on the two islands are characterized by phytokarst, sinkholes, photolineaments, and solution-widened joints. Such comparisons indicate that uplift played an important role in the development of this erosional unconformity.
Sinkholes developed in the Cayman Formation on Grand Cayman and Cayman Brac are open, filled with water, or filled with lithified deposits that include rootcrete, and breccias that are formed of dolostone, white limestone and black limestone lithoclasts that are held in white (oncoids or skeletal), yellow, and orange limestone matrices. The rare earth elements (REE) and isotopes of these sinkhole-filling deposits are different from those derived from the bedrock carbonates. Interpretation of these data indicates that the (1) rootcrete, oncoids, and the red and orange limestones are terrestrial in origin, whereas the other sinkhole-filling deposits are of marine origin, (2) red and orange limestones probably formed under more arid condition than the other sinkhole-filling deposits, (3) formation of the black limestone lithoclasts, oncoids, and rootcrete was probably related to biogenic factors, and (4) REE can be used to determine provenance. The sinkhole-filling deposits offer a record of the processes that took place while the erosional unconformities were developing.
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