ABSTRACT

Numerous, shallow marine, stacked, coarsening upward bar sequences characterize the Eocene Misoa Formation ("B" sands), on the east coast of Lake Maracaibo. The sandy part of the bars varies from 5 to 15 m in thickness. Four sandstone subfacies and a heterolithic bioturbated unit constitute the bars. The typical coarsening-upward sequence implies upward shoaling with an increase in current and wave energies. As bars grow upward, grain size and sorting increase, along with current velocity. The nature of lithological stacking, i.e., sandy intervals between marine shaly horizons, suggests that bar development is related to transgressive-regressive cycles. Cyclic repetition of smaller, sandy, regressive sequences may be related to periodic stillstands in an otherwise rising sea level. Sand distribution in space and time clearly indicates an eastward deepening of the basin. The coarsening-upward sand sheets show a progressive younging westward toward Lake Maracaibo. During transgression the retrogradational sand sheets were formed. Unlike many of the modern and ancient shelf bars, the Misoa bars are less elongated and more equidimensional in nature. The north-northwest-south-southeast orientation of the bars is parallel to the paleoshoreline of the basin to the west.

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