The Chicontepec Formation in eastern central Mexico has long been explored for its oil accumulations and contains several large unconformities, which in the past seem to have been miscorrelated across the Tampico-Misantla Basin. The formation is of current interest because it may help us to understand the mechanisms of delivery of the Wilcox sands in the deep Gulf of Mexico. In the northern part of the Chicontepec play, outcrop data indicate that a major unconformity occurs at about 55 Ma (i.e., the Paleocene/Eocene boundary). Outcrops overlying this unconformity show a ?classic? section about 150 meters thick; mass transport complexes on top of the unconformity are in turn overlain by sheet sandstones, channels, and channel levee complexes. In the central part of the play, there is a major unconformity in the Eocene, between 47 and 53 Ma (probably late early Eocene). In the southern part of the play (in the Agua Fria Field area) the first major erosional unconformity is between 43.6 and 50.4 Ma. In the extreme southern part of the play, in the Presidente Aleman area, the oldest unconformity is at approximately 40 Ma. The unconformities all have been generated in submarine environments. Without the benefit of seismic and high-resolution biostratigraphic data, earlier workers miscorrelated these unconformities and assumed that they were one large unconformity, forming the Chicontepec ?paleocanyon.? All the unconformities are regional events and occur throughout the basin. The 43.6 to 50.4 Ma erosional event (unconformity A) is a correlatable seismic event across a large proportion of the Tampico-Misantla Basin. This event has been cored in at least two wells. In the closest well to the canyon, a 110 meter thick mass transport deposit immediately overlies the unconformity. The mass transport deposit consists of a basal 30-meter pebbly mudstone debrite, overlain by an 80 meter thick slump. Recent interpretation in the Agua Fria, Tajin and Coapechaca (ATC) fields, west of Poza Rica, Veracruz, has allowed more detailed mapping of the erosional unconformities and a better estimate of the volume of material removed at unconformity A. In this area, the feature is up to 6 km wide and, in some places more than 600 meters of consolidated Paleocene and Cretaceous strata have been removed. Production from the ATC fields west of Poza Rica, is from the infill of the ?paleocanyon? (canyon-fill trap) and the pre-erosion strata (canyon truncation trap), and the trapping mechanism is both stratigraphic and diagenetic in nature.
Author(s): Cossey, Stephen P.J.