Late Pleistocene stratigraphy and geologic development of Cozumel Island, Quintana Roo, Mexico
Spaw, Richard Hoencke
Wilson, James Lee
Master of Arts
Knowledge of the depositional history of Cozumel Island is important for an understanding of the tectonics of the block-faulted eastern Yucatan and Belize continental margin. Basic information was derived from field reconnaissance and petrographic and mineralogic descriptions of thin sectioned and x-rayed samples. Two older Pleistocene, ten late Pleistocene, and one Holocene shallow-water carbonate facies are differentiated by their geometries and positions, megafauna, sedimentary structures, textures, carbonate grain-types, mineralogies and cements. The two older Pleistocene facies represent patch reef and sandy backreef environments of deposition. The late Pleistocene facies were deposited in windward and leeward coral reef, reef pass, seagrass-stabilized backreef, oolite shoal, storm channel, beach, and dune environments. Beachrock is the only Holocene rock on the island. Previously described 125, + 15, B.P. reef, backreef, and beachnearshore facies on the eastern Yucatan coast are in the same positions as the late Pleistocene facies on Cozumel Island; thus, the late Pleistocene Cozumel facies probably were deposited during the Sangamon Interglacial. A world-wide sea level fluctuation curve compiled from the literature is applied to deposition on Cozumel. Rocks from the island record two periodsof submergence with associated shallow-water carbonate deposition, and two intervening periods of emergence with associated subaerial vadose diagenesis. In reconstructing the depositional history of the island, it is determined that no tectonic activity has occurred since the latter part of the middle Pleistocene.