Subsurface Upper Jurassic stratigraphy in the Campeche shelf, Gulf of Mexico

This sedimentary-stratigraphic study of the Upper Jurassic rocks of the Campeche shelf, Gulf of Mexico, uses material from 50 exploratory wells to describe and formally desigate three lithostratigraphic units in the shelf. The Ek-Balam upper Oxfordian Group consists of three members: (1) lumpy peloidal limestones at the base; (2) massive sand, mudstone, and bentonitic shales with organic material in the middle section; and (3) calcareous sandstones with anhydrite at the top. One of the best oil reservoirs in the Campeche shelf, the Ek-Balam Field produces from the sandy member of this group. The Akimpech Formation of Kimmeridgian age consists of four members: (1) bentonitic mudstones, (2) dolomitized limestones, (3) algal shales, and (4) oolitic limestones. The oolitic and dolomitized limestones are reservoir rocks from the Upper Jurassic in the Campeche offshore region; the algal shales and mudstones are possible source rocks. The Tithonian Edzna Formation consists of shales and clayey limestones with abundant organic material; it is the main source rock in this region. The Campeche shelf is an important oil-producing area located offshore in the southeastern Gulf of Mexico. Formal designation of Jurassic lithostratigraphic units will serve as an aid to oil exploration in this region.