The K/T-boundary carbonate breccia succession at the Cantarell Field, Campeche Bay area: a representative example of the influence of the Chicxulub meteorite-impact event on the formation of extraordinary petroleum reservoirs

Over the last decade, intense petroleum exploration and exploitation activities have been conducted in the Campeche Bay area. Detailed stratigraphic studies in this region based on seismic, well logs, and core data have allowed the documentation of numerous deep-water carbonate breccia deposits throughout the Cretaceous stratigraphic column. However, the uppermost carbonate breccia succession is very distinctive in terms of its sedimentological properties compared to the underlying and older calcareous breccia layers. The unique characteristics of this deposit include: its unusual thickness, stratigraphic position, distribution, and content of impact-metamorphic constituents. At the Cantarell field, this carbonate breccia sedimentary package is a representative example of how the Chuxulub meteorite-impact event influenced the formation of a remarkable carbonate reservoir. This deposit was the most important oil-producing stratigraphic horizon for long time in that field. Nevertheless, this reservoir is still important not only in that field but also in other fields in offshore Campeche. The K/T boundary carbonate breccia succession is a typical fining-upward deposit made up, from base to top, of three units. The 50 to 300-m thick, basal Unit 1 consists of a coarse-grained carbonate breccia. Unit 2 is a 10 to 20 m-thick, fine-grained carbonate breccia. The 25 to 30 m-thick, uppermost Unit 3 is a greenish interval of friable sand, silt and clay-sized constituents with abundant ejecta material. In some wells, a 10 to 20 m-thick, non-oil producing fine-grained calcareous breccia occurs interbedded within Unit 3. The K/T boundary carbonate sedimentary package is underlain and overlain by deep-water shaly calcareous facies of Upper Maastrichtian and Lower Paleocene age, respectively. Studies of cronostratigraphic-equivalent outcrop analogs of this K/T boundary carbonate reservoir carried out by the authors in the Sierra de Chiapas (El Guayal, Tabasco and Bochil, Chiapas) support the stratigraphic architecture documented at the Cantarell Field. Lithoclasts of the calcareous breccias were derived dominantly from platform-interior and platform-margin environments and a few from deep-water settings. Ejecta material includes: shocked quartz, quartz with ballen structure, shocked plagioclase, altered melt rock, and rare fragments of the crystalline basement. Its paleogeographic distribution, stratigraphic position, and abundance of impact-metamorphic constituents in this carbonate breccia deposit are the most striking evidences of a genetic relation to the Chicxulub meteorite-impact event. Hence, this carbonate breccia succession, deposited by gravity-driven processes under deep-water conditions, represents the collapse of the western paleomargin of the Yucatan Peninsula, ballistic transport and tsunami-related current reworking as a consequence of the Chicxulub meteorite-impact incident.