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ABSTRACT: The Regional Distribution of Eocene Sediments in Lake Maracaibo, Venezuela

Rodolfo Meyer

The present work is part of a geological study of the Eocene sediments in northern, central, and eastern Lake Maracaibo, with the objectives to establish a coherent sedimentary and structural model and to define exploratory prospects. The Eocene section has accounted for 11.8 billion bbl of the oil produced in the Maracaibo basin.

The study area of approximately 2250 km2 includes siliciclastic sediments of the Trujillo, Misoa, and Pauji formations, 850-4900 m thick, and bounded by major unconformities of Paleocene and Oligocene-Miocene age. The depositional environments are predominantly deltaic and nearshore shallow marine. Fluvial sediments are restricted to the south and southwest of the area, shelf deposits to the north and east. A major middle Eocene regressive sequence of 150-300 m thickness (informal members B6 to C1, Misoa Formation) is preceded and overlain by smaller regressions within large-scale transgressive stacking patterns.

Overall subsidence of the Eocene basin was to the northeast, with listric normal faults striking northwest-southeast, but the distribution of sediments was controlled by north-northeast-striking fault systems of recurring synsedimentary normal displacements and likely strike-slip motions. During the Miocene the basin was inverted with reactivation and reversal of the preexistent growth faults, affecting the final reservoir distribution.

The exploratory prospects are related to (1) the presently poorly defined complex structure along the Pueblo Viejo high, (2) basinward extension of the older regressive sequences (informally C4-C7, Misoa Formation) and associated transgressive sands along the Lama-Icotea trend, and (3) traps at deeper levels within the rollover anticlines of listric growth faults. Detailed sequence analysis and further seismic interpretation will aid in locating and delimiting the reservoirs.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990