THE BEJUCO PALEOCANYON (CRETACEOUS‐PALEOCENE) IN THE TAMPICO DISTRICT, MEXICO

The Bejuco area (4,200 sq. km) is in Eastern Mexico, south of the Tampico District. Ammonites, gumma‐neutron logs, and lithologic samples of 65 exploratory wells were studied in order to construct structural maps at several levels within the Neocomian and Upper Jurassic. The purpose of this work was to study the stratigraphy, paleogeography, erosional unconformities, and also the occurrences of hydrocarbons of Late Jurassic‐Neocomian age. In most of the area, the Huasteca series of Middle‐Late Jurassic age lies discordantly on rocks of continental facies. In a few places in the NW, south, SE and centre, the Huasteca overlies intrusive rocks, and in the NW, the Huasteca also overlies metamorphic rocks in a few localities. Marine sedimentation commenced at the beginning of middle Callovian time in the eastern part of the region. Several successive periods of transgression took place: (1) during the early Kimmeridgian (central and western area); (2) the late Tithonian (north); and (3) the late Hauterivian (southern part). An important geological phenomenon is the submarine erosional unconformity which represents the Neocomian‐Eocene time‐interval. The area underlain by this unconformity has a delta shape and extends from the SW to the east. This is the precise area of the Bejuco paleocanyon. The unconformity today lies at a depth of between 1,200 and 2,900 m. The presence of hydrocarbons in either Tithonian or Neocomian rocks is controlled by structural traps, and in some places by combination traps.