ABSTRACT

Regional and detailed structural-stratigraphic studies of the Oligocene in the Burgos Basin (Northeast Mexico) point up the great significance of numerous growth and post-depositional faults. Several unconformities, together with abrupt facies changes, add to the complexity of stratigraphic and structural analysis.

A team approach was used, involving the construction of both regional and detailed electrical log correlation grids. Such correlations were supplemented by petrological, micropaleontological, and seismic studies.

Within a selected Pilot Area, the lower Oligocene (Vicksburg) sediments consist primarily of marine shales interbedded with marine lenticular sandstones. The middle Oligocene (Frio) consists predominantly of non-marine sandstones interbedded with shale which have a maximum overall thickness of 2000 meters.

The upper Oligocene (Anahuac) is a westward-thinning wedge of marine sandstones and shales, with a maximum observed thickness of 1000 meters. Although in the Gulf Coast of Texas, the Anahuac generally is considered to be late Oligocene in age, the lowest portion of this thick wedge of sediments in northeastern Mexico appears to be late middle Oligocene in age. The basal Marginulina zone was deposited under marine transgressive conditions which interfinger with non-marine Frio sediments. It is only the thinnest (upper) portion of this zone that overlies non-marine Frio.

FIGURE 1. Burgos Basin base map, showing oil and gas pools and Pilot Area.

End_Page 136------------------------