Prepared by Matt Unruh
ES 767 Global Tectonics Emporia State University
Located in the western Caribbean Sea to the northwest of Jamaica, the Cayman Islands are a British overseas territory comprised of three islands. Grand Cayman, Cayman Brac, and Little Cayman make up the Caymans, and these islands occupy around 250 square kilometers of land area. The Cayman Islands are outcrops of the Cayman Ridge, a submarine mountain range extending west-southwest from the Sierra Maestra range in southeastern Cuba to the Misteriosa Bank near Belize. This web presentation will examine the geology of the Cayman Islands and the tectonic forces that helped to create this tropical landscape.
The Cayman Islands are the outcrops of the submarine mountain range associated with the Cayman Ridge. The Cayman Ridge has formed over geologic time due to the interaction between the North American and Caribbean tectonic plates. This submarine mountain range stretches from the Sierra Maestra mountain range of Cuba to the Gulf of Honduras and the Misteriosa Bank near Belize. The Cayman Ridge forms the northern margin of the Cayman Trough, which is around 250 kilometers wide and reaches depths in excess of 5,000 meters. The position of the Cayman Islands near the Oriente Transform fault and the mid-Cayman rise of the Cayman Ridge reveals that these three islands are individually uplifted fault blocks that were forced upward due to the frictional forces on the North American/Caribbean tectonic plate margin.
Geologic research of these islands has revealed that the Caymans have a granodiorite base, followed by a cap of basalt. The upper most geologic layer of the Caymans is composed mostly of carbonates, which were formed by living organisms (corals, algae, and shells) and were laid down during sea level changes over the past 30 million years. The deposition of these carbonates and formation of calcareous rock over time follows the same general pattern on all three Cayman Islands. The central part of each of the Caymans is formed of substantial Bluff Group Tertiary limestones and dolostones which were formed around 30 million years ago in the Oligocene-Miocene period. This limestone and dolostone core is surrounded unconformly by the poorly lithified Ironshore Formation limestones, which were deposited at various periods during the Pleistocene. Due to the porous nature of the limestones that are present on the Caymans Islands along with the absence of much relief of any kind, all of the Caymans l ack rivers or streams. This lack sediment runoff due to erosion of topsoil has created extremely clear waters offshore of the Caymans, making the Caymans one of the most popular snorkeling and scuba diving areas in the world.
Located on the northern margin of the Cayman Trough, the Cayman Ridge has formed over geologic time as a result of frictional forces created by the tectonic plate movement of the North American and Caribbean plates. This friction has caused a submarine mountain range to form on the southern margin of the North American plate near the North American/Caribbean tectonic plate margin. Covering over around 1500 km from the Sierra Maestra Mountains of Cuba to the Misteriosa Bank near Belize and the Gulf of Honduras, this submarine range does not have active volcanoes in the vicinity of the Cayman Islands.
Despite the fact that Cayman Ridge does not have any active volcanoes presently, this ridge has experienced volcanic activity in the geologic past. Geologic investigations of the Cayman Ridge have revealed that one of the initial known episodes of explosive volcanism in the Caribbean region occurred during the late Paleocene through the middle Eocene in the form of island arc volcanoes that extended from the Cayman Ridge to the currently-exposed Sierra Maestra range of eastern Cuba. Analysis of seafloor core samples collected offshore of the Sierra Maestra have revealed a substantial lower to middle Eocene volcanic ash and volcaniclastic turbidite succession that can be correlated to the Sierra Maestra arc of Cuba.
The Cayman Trough is a depression area on the seafloor of the Caribbean that extends from the Belize margin to northern Jamaica. At its deepest point, the Cayman Trough is over 7,500 meters deep. The northern boundary of the Caribbean tectonic plate is located along the Cayman Trough. This margin consists of a 100-250 km wide seismogenic zone of generally left-lateral strike-slip deformation which covers over 2000 km along the northern edge of the Caribbean Sea. This left-lateral strike-slip displacement is due to the eastward movement of the Caribbean plate relative to the adjacent North American plate. Geological and geophysical data from the region suggest that the Cayman Trough is underlain by oceanic crust accreted along a short north-south spreading center located between the Oriente and Swan transform faults. Ultrasonic seismic profiles of the Cayman Trough reveal that the steep northern wall of the trench is virtually sediment free.
The top industry for the Cayman Islands is tourism, and the landscape present on these tropical islands presents travelers with many choices for entertainment. Snorkeling in the clear waters offshore or scuba diving in the depths of the Cayman Trough are popular recreational activities, but a geologic formation present on the west shore of Grand Cayman Island has become a popular destination within the last 40 years for people willing the take a trip to Hell. Hell, Grand Cayman Island, is a unique formation which is characterized by jagged, spongy pinnacles of black-covered limestone. This phytokarst formation is produced when attacking filamentous algae interact with the Ironshore Formation limestone present at this location. A post office opened on site in 1962 to meet the requests from tourists who wanted to send post cards home to friends and families from “Hell”.
The Cayman Islands occupy one of the interesting geologic landscapes that Earth has to offer. The interaction between the North American and Caribbean tectonic plates has created an area that draws researchers and tourists from around the world to discover what is hidden both above and below the surfaces of these islands. With the proximity of the Caymans to the Cayman Ridge and the Cayman Trough, researchers will continue come to Grand Cayman, Little Cayman, and Cayman Brac for years to come to collect and analyze geologic data in an attempt to better understand the tectonic and geologic history of Earth.