Palaeoenvironments and potential of Cretaceous and Paleogene source rocks in Jamaica

Abstract

The island of Jamaica contains several potential Cretaceous and Tertiary source rocks. This study examined over 800 samples from on- and offshore Jamaica and presents the geochemical and palynological evidence for the deposition of these source rocks and quantifies their source potential for hydrocarbon generation. Detailed geochemical evaluation of source rocks, hydrocarbon shows, and newly identified oil seeps reveal the presence of a number of source rocks in Jamaica whilst a revised and updated stratigraphic framework ties in depositional cycles to third-order sequences, giving comprehensive insights into depositional environments. The main potential source rocks in Jamaica are identified within the Cenomanian age Rio Nuevo Formation, Campanian age Sunderland Formation and the Middle Eocene age Litchfield Formation. The upper part of the Rio Nuevo Formation consists of interbedded shallow water limestones and organic-rich shales interpreted to have been deposited during short term oscillations in relative sea-level. Up-section increases in the amounts of land-derived and water-transported fern spores assemblages indicate an increasing proximity to the hinterland. Biomarker analysis highlights the presence of .-carotane and tetra-polyprenoids (TTP) within hydrocarbon shows from the Rio Nuevo shales in the Windsor-1 well, contributing to the interpretation that the Rio Nuevo Shales were deposited in a highly restricted, anoxic, estuarine or lagoonal setting. The presence of a small amount of oleanane from the hydrocarbon shows supports a ‘Middle’ Cretaceous age for the Rio Nuevo Formation source rock. Evidence presented in this study also points to the heterogeneity of the Rio Nuevo Formation between the Windsor-1 and Retrieve-1 wells. An oil seep collected from the Hanover Parish of Jamaica shares geochemical characteristics to an oil show from the Windsor-1 well, interpreted to have been generated locally within the Rio Nuevo Formation. The Middle Eocene, Lutetian, age Litchfield Formation is also interpreted to represent paralic, estuarine sediments. Geochemical analyses indicate the presence of resin-derived biomarkers and oleanane consistent with the input from terrestrial organic matter. This is supported by the high abundances of the pollen Lanagiopollis crassa, observed in outcrop, which is considered to reflect input from significant developments of mangrove-like vegetation along the adjacent coastline. Samples from the Litchfield Formation show good to excellent organic richness and contain oil-prone herbaceous kerogen. The Sunderland Formation source rock is interpreted to be atypical for Jamaica, having been deposited during a period of high relative sea level. The presence of Planolites ichnotaxa and high abundance of globular planktonic foraminifera relative to carinate forms suggest deposition on the middle to outer shelf. The occasionally high abundance of Pediastrum spp. reflects significant freshwater runoff on to the shelf. GC-MS analysis of oil samples from the Sunderland Formation indicates the presence of significant amounts of oleanane, suggesting a Late Cretaceous age. Additionally, a middle Campanian age is confirmed based on nannofossil and palynological evidence. Geochemical analysis from a lateral equivalent of the Sunderland Formation in the Hertford-1 well indicates possible correlations to an oil seep collected from the Trelawny Parish. The discovery of two independent oil seeps from different parts of the island is the first documented occurrence of liquid hydrocarbons from onshore Jamaica. Geochemical analyses of these seeps, compared to hydrocarbon shows from wells and potential source rock samples from outcrop and the subsurface, confirm the presence of an active petroleum system on the island. Evidence of this petroleum system suggests the island may become an attractive region for future oil exploration in the Caribbean.

AAPG Datapages/Search and Discovery Article #90330©2018 AAPG Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins “Integration of the geology of the area from the southern onshore of North America to the northern onshore of South America”, Siguenza, Guadalajara, Spain, July 2-5, 2018