Abstract

The stratigraphy adjacent to the El Papalote diapir in the La Popa basin, northeastern Mexico, displays depositional thinning, abrupt lateral facies changes, and intense local deformation near the diapir. The strata comprise a series of halokinetic sequences that provide a means of local correlation of stratal packages in an otherwise complex patchwork of seemingly disparate facies. Halokinetic sequences are relatively conformable successions of growth strata genetically influenced by near-surface or extrusive salt movement and are locally bounded at the top and base by angular unconformities that become disconformable to conformable with increasing distance from the diapir.

Halokinetic sequences differ from traditional depositional sequences in scale and mechanism of formation. Halokinetic sequences at El Papalote diapir could not be traced farther than 1 km from the diapir, whereas depositional sequences are typically basin wide. Halokinetic sequences form as the rate of net vertical diapiric rise varies relative to the local sediment-accumulation rate, whereas depositional sequences form as the accommodation rate varies relative to the regional sediment-accumulation rate. Angular unconformities form when the net diapiric-rise rate exceeds the local sediment-accumulation rate, allowing diapiric inflation at the surface to generate steep, unstable slopes along which subjacent growth strata are either truncated by attendant slope failure or by current or shoreface erosion. In the case of slope failure, the sequence-bounding unconformity is typically overlain by mass-transport deposits derived from gravitational failure of the domed salt body. Increasing the local sediment-accumulation rate relative to the net diapiric-rise rate results in diapir onlap and overlap, which suppress diapiric surface topography and erosion.

Halokinetic sequences are previously unrecognized but probably common features around near-surface or extrusive salt bodies in salt basins found elsewhere in the world. Their understanding may be used to predict the geometry, distribution, and quality of reservoir facies directly adjacent to salt bodies and provide critical data to determine the complex evolution of migrating passive salt bodies.

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