AbstractsEarth & Environmental Science

Sedimentology, diagenesis, and dolomitization of the Brac Formation (Lower Oligocene), Cayman Brac, British West Indies

by Breanna C. Uzelman

Institution: University of Alberta
Department: Department of Earth & Atmospheric Sciences
Degree: MS
Year: 2009
Keywords: sedimentology; diagenesis; dolomitization; sucrosic; dolomite; carbonate; Cayman; Brac; Oligocene; stratigraphy; facies; isotopes; geochemistry
Record ID: 1839732
Full text PDF: http://hdl.handle.net/10048/525


The Oligocene Brac Formation is the oldest part of the Bluff Group that is exposed on Cayman Brac. Sediments of the Brac Formation were deposited on a small, open bank in shallow marine waters. Today, the formation is composed of limestone, finely crystalline dolostone, and coarsely crystalline sucrosic dolostone. The Pollard Bay member, defined herein, comprises the sucrosic dolomite that is exposed only on the south coast of Cayman Brac. Changes in sea level and subsequent groundwater chemistry mediated a complex diagenetic evolution that is responsible for the lithological heterogeneity that now characterizes the formation. Field, petrographic, and geochemical analyses indicate that dolomitization was probably mediated by normal to slightly modified seawater. Multiphase dolomite crystals represent different stages of textural and geochemical maturity, and attest to time-transgressive dolomitization processes that evolved in various hydrologic regimes through time.