Rock types of Trinidad & Tobago

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The islands of Trinidad & Tobago are located within the southeast Caribbean, just off the northeastern corner of South America.  The rocks that make up these two islands differ significantly in type, age, and occurrence and this has led geologists to infer vastly different geological histories despite their close proximity. The rocks of Trinidad share a greater affinity to those found on the South American continent while those of Tobago are unique compared to other surrounding islands of the southeast Caribbean. 

Trinidad comprises a mix of sedimentary, metamorphic and igneous rocks. Sedimentary rocks occur over the southern two-thirds of the island with abundant sandstone, mudstone and limestone deposits. The northern third of the island consist of metamorphic rocks that make up the prominent Northern Range mountain belt. The composition and texture of these rocks were modified from their original depositional character by the application of heat and pressure over a prolonged period of time. Igneous rocks of magmatic origin, are limited to an area of approximately 4 sq km at the north eastern tip of the island. This miniature exposure, formally referred to as the San Souci Formation, is unique among Trinidad’s rocks given its meta-volcanic composition.  

Tobago, in contrast, comprises predominantly igneous and metamorphic rocks. The northeast third of the island comprise metamorphic rocks formally termed the North Coast Schist Group and these are associated with the highest elevations on the island occurring within the Main Ridge area. Adjacent and to the southwest of the metamorphic schists occur a group of volcanic and plutonic rocks appropriately termed the Tobago Volcanic Group. Together, these two groups of rocks record a unique geological history that involved ancient island arcs, crustal movements and intense volcanism. In contrast to Trinidad, sedimentary rocks occupy a limited area along the southwestern end of the island, and coincides with the relatively flat-lying topography of the “Lowlands” area. These sedimentary rocks are mainly silty mudstone and overlying coral reef deposits that have been elevated hundreds of metres from their original site of deposition. As an analogy, if one can picture the famous Buccoo Reef being uplifted from its current position below the pristine waters of Buccoo, to topographic elevations existing in the Signal Hill area, then you are one step closer to understanding the complex geological history of the ancient sedimentary rocks of Tobago.