H.I. Petersen1*, B. Holland2, H.P. Nytoft1, A. Cho3, S. Piasecki4, J. de la Cruz5, J.H. Cornec6

1Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.

2Blue Creek Exploration Ltd., P.O. Box 30, Punta Gorda, Belize.

3Geology and Petroleum Department, Ministry of Natural Resources and the Environment, Market Square, Belmopan, Belize.

4Institute of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen, Denmark.

5Perenco Guatemala Ltd., 5a. Av. 5–55 Zone 14, Europlaza Torre 4, Nivel 14, Guatemala City, Guatemala.

61867 South Marion Street, Denver, CO 80210, USA.

Guatemala is separated by the east-west trending La Libertad arch into the North and South Petén Basins. The arch is the westward continuation of the Maya Mountains fault block of central Belize which divides the Corozal Basin in northern Belize from the Belize Basin to the south. Small-scale oil production takes place in the Corozal Basin and the North and South Petén Basins, and numerous petroleum seeps have been reported in both basins of Belize. This study reviews the stratigraphy and the poorly documented petroleum geology of the Belize-Guatemala area. Samples of crude oil, seepage oil and potential source rocks were collected from both countries and were investigated by organic geochemical analyses and microscopy. The oil samples consisted of non-biodegraded crude oils and slightly to severely biodegraded seepage oils, both of which were generated from source rocks with similar thermal maturities.

Non-biodegraded oils were generated from marine carbonate source rocks and could be divided into three groups:

Group 1 oils come from the North Petén Basin in Guatemala and the NW part of the Corozal Basin of Belize, and have a typical carbonate-sourced geochemical composition. The oils correlate with extracts of organic-rich limestones assigned to the Upper Cretaceous “Xan horizon” in the Xan field in the North Petén Basin. The oils were generated from a single source facies in the North Petén Basin, but were charged from two different sub-basins.

Group 2 oils include crude oils from the South Petén Basin, Guatemala. They have characteristics typical of carbonate-sourced oils, but these are less pronounced than in the Group 1 oils. A mixed marine/lacustrine source facies deposited under strongly reducing conditions in a local kitchen area is inferred.

Group 3 oils include crude oils from the Corozal Basin, Belize. A carbonate but also more “shaly” source rock composition for the oils is inferred. A severely biodegraded seepage oil from Belmopan, the capital of Belize, resembles a nearby crude oil. A local depression in the North Petén Basin may potentially be the kitchen area for these oils, and for the seeps found in the western part of the Corozal Basin.

The seepage oils from the Corozal and Belize Basins are moderately to severely biodegraded and generated from carbonate source rocks. Some of the seepage oils have identical C27–29 sterane distributions to the Group 2 oils, but “biodegradation insensitive” biomarker ratios show that these seepage oils can be divided into separate sub-groups. Severely and slightly biodegraded seepage oils in the Belize Basin were probably almost identical prior to biodegradation.

Lower Cretaceous limestones from the Belize Basin have petroleum generation potential, but the samples are immature. The kitchen for the seepage oils in the Belize Basin remains unknown.

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