--> ABSTRACT: Geochemistry and Organic Petrography of Tertiary Coal Cycles in the Maracaibo Basin, Western Venezuela, by Maria Julia Mendez, Wolfgang Scherer; #91020 (1995).

Datapages, Inc.Print this page

Geochemistry and Organic Petrography of Tertiary Coal Cycles in the Maracaibo Basin, Western Venezuela

Maria Julia Mendez, Wolfgang Scherer, S. A. Intevep

The Maracaibo basin has been known since the beginning of this century as a prolific oil province, generating more than 2MM BOPD. Less well known is the fact that it was discovered as a coal basin in 1875, long before oil was found in commercial quantities. During the last 20 years abundant coal reserves have been found and developed in the Guasare, Paso Diablo, Lobatera and Rubio mines. There are two major sedimentary-tectonic cycles that include commercially exploitable coal measures. The rich Paleocene-lower Eocene cycle includes up to 14 measures, some up to 14 m in thickness in the Marcelina Fm., that are developed along strike for more than 250 km in N-S direction on the western flank of the Maracaibo basin. The upper Eocene cycle contains coal measures in the Carbo era Fm, found only in the southern portion of the basin.

A regional sedimentological and geochemical study of 10 stratigraphic sections measured along the western, southern and eastern rim of the Maracaibo basin was undertaken in order to discern the regional pattern of coal deposition represented by several delta systems and by the geometry and facies of the cyclothems. More than 250 rock samples from the major cycles were analyzed using pyrolysis, soxhlet extraction, gas chromatography, biomarker mass spectra, as well as vitrinite reflectance, maceral composition and fluorescence spectra. Associated oil seeps and Paleocene produced crude oil samples were also analyzed.

Results of this study show that significant amounts of paraffin-rich hydrocarbons could have been generated in the western and southern portions of the basin from Marcelina Fm source rocks. The number and thickness of Paleocene coal measures increases towards the northern end of the west flank of the Maracaibo basin.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995