The Geology of Jamacia
The island of Jamaica has significant oil and gas potential with play settings akin to those in southern Sumatra and Northwest Java in western Indonesia. The island consists of Cenozoic carbonate sequences overlying a basement composed of Albian to Maastrichtian volcanics and plutonic rocks and is thought to have been formed as an intra-oceanic arc complex which was active throughout most of the Cretaceous. The dominant structural fault systems trend east to west, being related to Tertiary movements along the Cayman Trough, and north-west to south-east due to the accommodation of the left lateral strike slip movement. Expression of the latter can be seen in the prominent Paleogene Wagwater Graben that crosses the island towards its eastern end and is the focus of most of the present day earthquake activity.
Offshore to the south of the island, the Pedro Bank is located in water shallower than 200m and covers an area 200km by some 50km. The dominant fault-trend is southwest to northeast and related to the fracture zones within the South Walton Basin. Two wells have been drilled in this area, both abandoned without shows. The first well, Pedro Bank 1 (TD 1,978m), was drilled in the Pedro Bank Basin by Occidental in 1970 and encountered Eocene dated intrusive volcanics which are believed to be localized. The second well, the 1982 Union Texas-operated Arawak 1 (TD 4,585m), bottomed in Lower Eocene Red Beds after encou8ntering a thick Eocene section.
Onshore source rock studies indicate that numerous gas-prone organic-rich shales and mudstones are present on the island. The Cretaceous sediments are relatively poor in organic content while the Tertiary sediments are generally fair to rich. With respect to oil generation, the Tertiary sediments are generally immature to early mature while Cretaceous sediments are mostly mature. Onshore, oil seeps have been reported and shows have been observed in limestones, although no oil has been produced on test. The central Gulf Coast region Smackover Basin source horizons could have subsequently incorporated into Jamaica from Chortis and/or Yucatan as the island arc that dominates the island’s geology was assembled in the Late Cretaceous. An in-situ continental block could therefore underlie, beneath a southwards directed thrust associated with the transcurrent Cayman Trough, the known geology of Jamaica. This latter possibility is therefore compatible with the proposal that the Caribbean has an in-situ that is non-Pacific origin.