Structural Styles, Architecture, and Evolution on the Bay of Campeche Shelf

Abstract

The shelf and deepwater provinces of the Bay of Campeche, southern Gulf of Mexico, are dominated by long-lived contraction and salt diapirism basinward of the Comalcalcos extensional system. Here we use modern depth-migrated 3D seismic data to examine the complex structural architecture along a strip of the shelf approximately 220 km long and 40 km wide that includes Blocks 2 through 11 and the recent Zama giant oil discovery. The results have implications for trap development, reservoir distribution, and hydrocarbon maturation and migration throughout the area.

Contractional structures include both salt-cored anticlines and thrusted folds. Many are detached only at the Campeche salt level, whereas others also have shallower detachment levels that partly decouple deformation above and below (Eocene shales in the west and a lower Miocene mass-transport complex in the east). The folds and thrusts extend away from or link squeezed diapirs, which range from wide, vertical stocks to vertical or thrusted welds; relatively rare styles include counterregional and pop-up feeders. Salt generally flares upward to form local salt sheets and canopies. The maximum lateral extent of shallow salt typically occurs at the mid-Miocene unconformity, with slightly folded upper Miocene and younger strata burying the diapirs. Fold and thrust trends are highly variable, forming an overall polygonal geometry, although N-S to NE-SW trends dominate to the west, closer to the lateral edge of the salt basin. Contractional structures and diapirs are overprinted by Plio-Pleistocene extensional faults, mostly counterregional, along the proximal portions of the study area.

Quantitative sequential restoration of one profile crossing a squeezed diapir and a decoupled fold illustrates the structural evolution. Deformation began during the Late Jurassic to Cretaceous with the formation of a minor contractional structure, a salt-evacuation depocenter, and a passive diapir. Shortening continued through the Paleogene and into the Miocene, culminating in the middle Miocene with a pulse of more rapid contraction. The diapir grew and was progressively squeezed until it formed a vertical weld; salt flared into minor sheets at the end of the middle Miocene and erosional truncation occurred over the fold crest. Shortening slowed dramatically during the late Miocene and was effectively nonexistent during the Plio-Pleistocene, leading to diapir burial.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018