CRUSTAL TYPE, TECTONIC ORIGIN, AND PETROLEUM POTENTIAL OF THE BAHAMAS CARBONATE PLATFORM

I used a compilation of publicly available, free-air and Bouguer-corrected gravity and ship-borne magnetic surveys of the Bahama carbonate platform to determine its underlying crustal type, total sedimentary thickness, plate tectonic history, and petroleum potential. Gravity and magnetic data provide important constraints on the crustal structure of the Bahamas because existing seismic reflection data are unable to penetrate the up-to-7-km-thick carbonate cover of the platform. I created gravity and magnetic models for six 700-1400 km-long, regional dip transects and one 2000-km-long strike transect crossing the Bahamas and the southeastern margin of North America. I generated magnetic models to create a depth-to-basement map that is consistent with a depth-to-basement map that I made independently using gravity data. Both magnetic and gravity maps were combined to create an overall basement depth and structure map for the Bahama platform region. These maps show basement crustal rocks with a density 2.8 g/cm3 and crustal thicknesses about twice as thick as normal oceanic crust. I interpret most of the Bahama basement to have formed as a southeasterly continuation of the volcanic passive margin of the eastern USA that formed during the Triassic (~201 Ma) eruption of the Central Atlantic Magmatic Province now found on Africa, southeastern North America, and northern South America. Locally thick crustal areas with within the Bahamas are interpreted as seamounts with the volcanic passive margin.

I used variations in sedimentary thicknesses derived from the gravity and magnetic-based depth of basement map along with estimated subsidence from sparse wells and heat flow values based on measurements made in the Bahamas region to calculate the thermal maturity of an inferred Late Jurassic source rock deposited in the Bahamas area. Subsidence modeling supports greater tectonic subsidence over the thinner crust of the large igneous crust areas of the Great Bahama bank than for thicker continental crust beneath eastern Florida. Subsidence models predict peak maturation and generation for Upper Jurassic rocks at modern depths greater than 4500 m occurred in the mid Miocene less than 20 million years ago using an average heat flow of 40 mW/m2 measured in the Bahamas area. Assuming limited upward vertical migration of hydrocarbons, deeper wells (7-8 km) would be needed to penetrate to the depth of reservoirs where hydrocarbons are mature.