Field Examination of Exposed Evaporite-Related Structures, United States and Mexico: Relations to Subsurface Gulf of Mexico Examples

J. J. Willis, B. E. Lock, D. A. Ruberg, and K. C. Cornell
Energy Institute, University of Louisiana- Lafayette

Considerable exploration attention has been devoted to salt-withdrawal minibasins and sub-salt in the offshore Gulf of Mexico (GOM) province. Investigation is inherently by geophysical and petrophysical means, utilizing sonar, seismic and gravity data, and scattered well logs, with obvious resolution limitations. Outcrop studies in Texas, Utah and Mexico provide an additional dimension, leading to an improved understanding of  GOM examples.

Outcrops along I-10 between Kerrville and Junction, Texas, provide a remarkable suite of evaporite-withdrawal (dissolution) structures, including varying exposure levels of withdrawal synclines, related secondary structures, and the primary weld surface. Utah exposures include diapirs, revealing intense internal deformation, and various stratigraphic-structural interactions. The La Popa basin in Mexico hosts salt-cored anticlines, diapirs, withdrawal synclines, and a previously-recognized secondary weld.

These outcrop analogues provide excellent insight into GOM structures. For example, GOM welds form potentially important hydrocarbon pathways, but coarse seismic resolution, though revealing significant character changes, leaves many questions unanswered. The Junction and La Popa welds exhibit remarkable diversity along their traces, even over relatively short distances. Some segments exhibit enhanced permeability through brecciation, fracturing, or sandsand juxtaposition, whereas shale smearing or remnant salt limits fluid transmission along other portions.

AAPG Search and Discovery Article #90901©2001 GCAGS, Annual Meeting, Shreveport, Louisiana