Vitrinite Reflectance Data Reveal a Highly Asymmetric Thermal Anomaly near the El Gordo Diapir, La Popa Basin, Mexico

Thirty seven samples of the Lower Potrerillos Mudstone were collected from the El Gordo salt-withdrawal minibasin in La Popa basin, Mexico. All samples are uppermost Cretaceous and were collected from strata that crop out in a roughly circular pattern, which is intersected by the diapir in the northeastern portion of the study area. All samples were collected from the same stratigraphic horizon directly below the end-Cretaceous tsunami-related Delgado Sandstone. Samples were blindly analyzed using vitrinite reflectance and the results reveal consistent changes linked to their proximity to the diapir.

Samples to the southwest, which are furthest from the diapir, range between 0.75-0.85 and are interpreted as being representative of regional values. Vitrinite values increase systematically towards the NW side of the diapir and reach maximum values of 1.44 Ro. Interestingly, values decrease systematically for samples collected SE of the diapir and are as low as 0.5 adjacent to the diapir. Previous structural interpretations based on surface mapping assumed that the diapir is sub-vertical but the data strongly indicate that the diapir is tilted and plunges to the NW. If this interpretation is correct, the data illuminate significant differences in the thermal history in sub-salt and supra-salt areas, which has important implications for source rock maturation and preservation of reservoir quality adjacent to salt features. Future research will assess whether the differences in thermal history also impacted porosity within units that are analogues for reservoirs adjacent to salt.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California