Abstract

Composite halokinetic sequences (CHS) are unconformity-bounded successions of upturned and thinned strata that form due to drape folding of diapir roofs during passive salt rise. Tabular and tapered CHS have narrow (50–200 m) and broad (300–1000 m) zones of folding, respectively. CHS are originally defined as exposed diapirs bounded by shallow-water strata in La Popa Basin, Mexico. This paper tests the concepts of CHS development at the subsurface, deepwater Auger diapir in the northern Gulf of Mexico. We used 3D wide-azimuth seismic data, well and biostratigraphic data, and structural restorations to interpret and analyzed 11 well-imaged Pleistocene CHS that correlate around the diapir. The lower and uppermost flanks are characterized exclusively by tapered CHS, with wide zones of thinning (240–660 m) and broad taper angles (41°–75°). In between are four discrete CHS with mixed tapered and tabular geometries, with the latter displaying narrow zones of thinning (<100m) and negligible taper. Three of the intervals switch geometry around the diapir. The CHS-bounding unconformities typically intersect the salt at cusps and are continuous with bright amplitudes in the minibasins that tie to biostratigraphically defined condensed sections. CHS represent 50–500 kyr time spans and correlate well with fourth-order sea-level cycles. We corroborated many aspects of the published model of CHS development, showed that the formation of CHS due to drape folding was independent of depositional environment and related to fluctuations in sea level and sediment input. The style of CHS is generally determined by the interplay between salt-rise and sediment-accumulation rates, but variable CHS geometries around the diapir within the same interval suggested that the ultimate control is the roof thickness. Our results are critical to understanding and predicting aspects of hydrocarbon traps against salt, including trap geometry, and reservoir distribution.

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