Depositional environments of the Eocene Mirador and Misoa Formations Maracaibo Basin, Venezuela

Abstract

Outcrops and cored sections of the Lower-Middle Eocene Mirador and Misoa formations in and around Lake Maracaibo have been analysed sedimentologically and palacontologically in order to establish depositional environments. Three genetically distinct sandstone units could be recognised: the fluviatile point bar, the deltaic distributary channel-fill and the offshore bar or barrier beach. Each of these units is characterised by a specific vertical grain-size trend and sequence of bedding types. A fluviatile environment is typical for the Mirador Formation, whereas deltaic plain and delta-fringe environments obtained during deposition of the Misoa. The Misoa constitutes overall a transgressive sequence interrupted by several phases of delta-building which become less important upwards. The Mirador and Misoa sediments are thought to form parts of one alluvial deltaic complex of Mississippi size. A deltaic source for the basinal turbidites of the Trujillo Formation, which is the lateral equivalent of the lower part of the Misoa, is likely. The Misoa grades vertically and laterally into the holo-marine shales of the Pauji Formation.