Geology Of The Cayman Islands

Grand Cayman, Little Cayman, and Cayman Brac are, in reality, the summits of independent fault blocks that rise from the depths of the Caribbean Sea. This book traces the geological evolution of these islands over the last 30 to 35 million years. The balance between deposition of carbonate sediments and karst development of the exposed land was dictated by the interaction between ever-changing sea levels and vertical tectonic movement of the fault blocks. Today, drinking water needed for the ever-increasing populations of the islands is supplied largely by desalinization plants that are located in accord with a detailed knowledge of the bedrock. This book is based on an extensive data base that has been assembled over the last 40 years of field work and laboratory analyses. Noteworthy aspects of this database include: Approximately 60 visits to the islands over last 40 years – sampling and documentation of virtually every accessible outcrop on the islands (including some that no longer exist). Most samples have been fully documented petrographically and geochemically. Data from 120 wells that have been drilled to depths up to 245 m (most less than 125 m). Wells have been cored and/or chip sampled. Full documentation of drilling histories, XRD analyses of samples, extensive geochemical analyses for major and minor elements, stable isotopes, 87Sr/86Sr ratios, and Rare Earth Elements from numerous samples. Mapping and sampling of modern sediments, including sediment cores, from most of the lagoons around Grand Cayman. Extensive thin section petrography, scanning electron microscope, and electron microprobe analyses of the dolostones and limestones that form the bedrock of the islands. Samples and data collected from numerous caves on Grand Cayman and Cayman Brac have been used to track their developmental history. Detailed analyses of phosphates collected from Little Cayman. Detailed analyses of terra rossa collected from each of the islands.

In the course of the last century a considerable amount of scientific work has been carried out in the Cayman Islands. The results of this (outlined in Chapter 1) are widely distributed in unpublished reports, university theses, various scientific publications and books, many of these sources being difficult to find and some now unobtainable. The purpose of this book, therefore, is to bring all this scattered information together and to present a coherent account of the biogeography and ecology of the Islands, as an easily available reference source and as a foundation on which future work can be based.

Investigations were conducted on Grand Cayman, located some 150 miles osuth of Cuba and approximately the same distance northwest of Jamaica. Its variety of both Recent and Pleistocene carbonates provides excellent opportunity for studying a spatially coherent group of carbonate environments which can be examined in a minimum of time and travel. The sedimentary deposits of which Grand Cayman is composed are exclusively carbonates derived from a broad spectrum of environments. These sediments display an extensive array of textures, constituent particles, and diagenetic alterations which are the resultants of combined physical, chemical, and biological processes. Catastrophic events, such as storms and sea level fluctuations, help shape both Recent and Pleistocene sedimentary deposits. A systematic environment by environment evaluation of the major marine habitats is given from the quiet water areas of sounds to the high energy reef crest and across the fore-reef shelf to a maximum depth of about 100m. Emphasis is placed on organic community structure and zonation. Process-form relationships are discussed with regard to each major environmental subdivision. Maps summarize the distribution of major organic communities and bottom types around the entire island to a depth of approximately 20m are presented.