Imaging the Pre-Salt Gulf of Mexico: Basin Classification and Comparison With Other World Class Petroleum Basins

Abstract

Abstract

With an extensive history of exploration in the Gulf of Mexico, the pre-salt syn-rift and sag plays of the deepwater remain poorly understood and untested. A basinwide analysis of gravity and magnetic data integrated with long-offset, depth-migrated, regional 2-D seismic data reveals elements of the basin's crustal structure and a complex syn-rift history along Mexico's eastern and Yucatan margins. We compare the pre-salt syn-rift and sag sections in the GoM with seismic examples from similar basins with established petroleum systems along a (1) moderately magma-rich margin (Campos & Santos basins), and (2) a magma-poor margin (Scotian basin). Data acquired offshore Mexico and from NE GoM show that the Outer Marginal Trough along most of the GoM margins lacks significant break up magmatism. However, type-1 seaward dipping reflectors (SDRs, extruded over continental crust) influence half-graben fill and record localized syn-rift magmatism with a presumed age sometime between 200 and ∼165 Ma. The GoM pre-salt sedimentary sequences reach ∼6 km, shared between synrift and sag, both presumed to be mostly terrestrial clastics with potential for lacustrine intervals. These strata are observed as parallel to sub-parallel seismic reflectors that progressively fill grabens and onlap the underlying rifted basement. In most of the GoM, these observations are similar to those observed in the magma-poor Scotian Basin. The more magmatic parts of the GoM appear to be similar to large areas of the Santos and Campos basins, which also have a volcanic component in the pre-salt sections. The magma-influenced areas of NE Yucatan and NW Florida form conjugates in syn-rift reconstructions, suggesting that GoM spreading in this area developed on a previously volcanic rift. For the basins investigated here, the uppermost pre-salt sequences are topped by a well-defined, generally unfaulted, base-salt surface. The transition to salt marks the first known influx of marine water, but there is no apparent incision of the unconformity nor indication of interbedded sag and salt sequences, arguing against the idea of catastrophic or progressive infilling of a subaerial depression well below sea level. The presence of lacustrine source rocks in pre-salt sections of the GoM is currently speculative, but can be hypothesized within localized fluvio-lacustrine-playa closed basin successions, as observed from seismic analogs from other basins.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016