Stratigraphy of Intermontane, Lacustrine Delta, Catatumbo River, Lake Maracaibo, Venezuela

Abstract

Lake Maracaibo, Venezuela, including the Catatumbo River delta, is an excellent analog to the ancient, intermontane basins that occupied the North American Rocky Mountains and other major mountain systems. These basins are of considerable interest because of their proved oil and gas potential and because of recent interest in oil shales and coals. The Maracaibo basin has been rapidly subsiding during the Cenozoic, and Catatumbo River has been a significant source of Holocene sediments. Each distributary has a middle-ground bar orifice caused by the similarity between effluent and ambient water densities. The coarse bed load is spread over a relatively wide area and down to the delta front, which is steep (5°) but lacks large-scale subaqueous landslide features. The stratigraphic column of the Catatumbo River delta is a sequence which coarsens upward but differs from many other deltaic sequences in that it lacks slump deposits at its base and overlying tidal deposits. There are relatively few current-oriented sedimentary structures. Grain-flow deposits and, less commonly, turbidites occur at the base of the slope. The proximal to distal sedimentation is characterized by an increasing ratio of mudstone to sandstone. Lenses of transported coal are present from the orifice basinward, and extensive coals occur in the freshwater swamps. It is suggested that the Fort Union Formation, which was deposited in the Paleocene Waltman Lake of the Wind River basin of Wyoming, was formed, in part, by several loci of deltaic sedimentation prograding into the lake from the southwest in a manner analogous to the progradation of the modern Catatumbo River into Lake Maracaibo. The reservoir quality of Waltman Lake deltaic bar-finger sands and other similarly deposited intermontane, lacustrine deltaic sands should be excellent.