Introduction

The U.S. Geological Survey (USGS) assessed the potential for undiscovered, technically recoverable conventional oil and gas resources within the North Cuba area (fig. 1). The assessment is based on an analysis of a composite total petroleum system (TPS) that developed in this area through a multiphase tectonic evolution (Saura and others, 2008; Stanek and others, 2009; Escalona and Yang, 2013; Ramos and Mann, 2023). Triassic–Early Jurassic rifting between the North American plate, the Yucatan block, and the South American plate began the fragmentation of Pangaea and led to rift basins filled with synrift fluvial-alluvial and lacustrine sediments, possibly including lacustrine source rocks. Intermittent access to the ocean as rifting continued during the Middle Jurassic (Bajocian) led to the deposition of as much as 2,000 meters of salt on extended continental crust (Pindell and others, 2021). As rifting waned, organic-rich Oxfordian and Tithonian source rocks were deposited on the Bajocian salt. Seafloor spreading began in the Oxfordian as the Yucatan block rotated counterclockwise, opening the Gulf of America. Spreading formed proto-Caribbean oceanic crust between North America and South America. From the Berriasian to the Albian, thermal subsidence and open marine conditions led to the deposition of basinal organic-rich marl source rocks and extensive, stacked carbonate platforms along the passive margins. Transgression in the Late Cretaceous led to the drowning of the platforms and the deposition of organic-rich Upper Cretaceous (Cenomanian–Turonian) shale source rocks. The major tectonic event in the North Cuba area was the Late Cretaceous–Eocene progressive collision of the Greater Antilles arc with the passive margin of North America as proto-Caribbean oceanic crust subducted southwestward beneath the Caribbean plate. Northeast-directed contraction formed the North Cuba fold and thrust belt and the adjacent foreland basin. The stacked thrust sheets consist largely of synrift, postrift, and passive margin stratigraphic successions of the proto-Caribbean that include the major source rocks and reservoirs (Pszczółkowski and Myczyński, 2010). The foreland basin filled with as much as 5 kilometers of synorogenic and postorogenic clastic sediment.

Total Petroleum System and Assessment Units

The USGS defined a Mesozoic–Cenozoic Composite TPS to encompass oil and gas sourced from several organic-rich shales and marls. Petroleum source rocks in this composite TPS are Upper Jurassic (Oxfordian and Tithonian) marls, Lower Cretaceous marls, Cenomanian–Turonian shales, and possibly Paleogene shales (Jacques and Clegg, 2002; Moretti and others, 2003; Magnier and others, 2004; Zhang and others, 2023). Late Triassic–Early Jurassic synrift lacustrine shales are speculative source rocks. Organic-rich Oxfordian and Tithonian marls are interpreted to be the most substantial in terms of volumes of oil and gas generated, migrated, and potentially trapped (Jacques and Clegg, 2002; Moretti and others, 2003; Zhang and others, 2023). Thrust loading and foreland burial led to thermal maturation of speculative Jurassic and Cretaceous source rocks, whereas Paleogene source rocks in the foreland basin may not be thermally mature for oil generation.

Three conventional assessment units (AUs) were defined within the composite TPS based on the major structural elements in the North Cuba area: the North Cuba Fold and Thrust Belt AU, North Cuba Foreland Basin AU, and North Cuba Platform Margin Carbonate AU (fig. 1). The North Cuba Fold and Thrust Belt AU encompasses the onshore and offshore areas of the Late Cretaceous–Eocene fold and thrust belt. More than 30 oil fields have been discovered mostly in the onshore part of the AU, indicating that a petroleum system is or was active in the North Cuba area. Main reservoirs are fractured fine-grained carbonates within structural traps, but progressive deformation may have breached some seals. The North Cuba Foreland Basin AU outlines the foreland basin adjacent to the fold and thrust belt and has the potential for oil and gas in sandstone reservoirs within synrift–postrift structural and stratigraphic traps. The North Cuba Platform Margin Carbonate AU is defined by oil and gas that may have migrated updip into a spectrum of platform-margin reservoirs such as karst, dolomites, reefs, mounds, and debris-flow breccias mainly in stratigraphic traps, and by similar reservoirs in rift-related structural traps along the Yucatan, Florida, and Bahamas Platforms.

The geologic model for this assessment is for oil and gas generated from several source rocks by Late Cretaceous–Eocene thrust loading and foreland burial to have migrated into carbonate reservoirs along the margins of the Yucatan, Florida, and Bahamas carbonate platforms; possible synrift clastic reservoirs and orogenic and postorogenic sandstone reservoirs in the foreland basin; and fractured carbonate reservoirs within the fold and thrust belt (fig. 2). Oil fields discovered in this composite TPS are within the North Cuba Fold and Thrust Belt AU, but little exploration has occurred in the North Cuba Foreland Basin AU, and none has occurred in the North Cuba Platform Margin Carbonate AU (Ananev and others, 2014). The assessment input data for three conventional AUs are summarized in table 1 and in Schenk (2025).

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered conventional oil and gas resources in three AUs in the North Cuba area (table 2). The estimated mean undiscovered resources are 4,098 million barrels of oil (MMBO), or 4.1 billion barrels of oil, with an F95–F5 range from 900 to 10,701 MMBO; 13,268 billion cubic feet of gas (BCFG), or 13.3 trillion cubic feet of gas, with an F95–F5 range from 2,308 to 39,404 BCFG; and 273 million barrels of natural gas liquids (MMBNGL), with an F95–F5 range from 43 to 854 MMBNGL.

For More Information

Assessment results are also available at the USGS Energy Resources Program website, https://www.usgs.gov/programs/energy-resources-program.

North Cuba Area Assessment Team

Christopher J. Schenk, Tracey J. Mercier, Phuong A. Le, Andrea D. Cicero, Ronald M. Drake II, Sarah E. Gelman, Jane S. Hearon, Benjamin G. Johnson, Jenny H. Lagesse, Heidi M. Leathers-Miller, and Kira K. Timm