Halokinetic deformation adjacent to the deepwater Auger diapir, Garden Banks 470, northern Gulf of Mexico: Testing the applicability of an outcrop-based model using subsurface data

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 ([Formula: see text]) 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.

Lateral terminations of salt walls and megaflaps: An example from Gypsum Valley Diapir, Paradox Basin, Colorado, USA

“…In both cases the variations in stratal geometries were explained as being caused, in part by changes in the style and/or amount of shortening along the lengths of the walls. In contrast, Hearon, Rowan, Giles, and Hart () tracked composite halokinetic sequences around the Auger salt stock in the northern Gulf of Mexico, demonstrating that composite halokinetic sequences progressively change in geometry around the margin of the diapir and suggesting this was caused by local variations in diapir‐roof thickness. Despite these studies, very little is known about strike‐parallel changes in structural and stratigraphic architecture at the terminations of salt walls or megaflaps.…”

The Impact of Salt Tectonics on the Thermal Evolution and the Petroleum System of Confined Rift Basins: Insights from Basin Modeling of the Nordkapp Basin, Norwegian Barents Sea

“…Based on the structural restorations, near-diapir structural and stratigraphic traps were present since the end of the Early Triassic (Figures 4 and 11). Megaflaps [5,63] and halokinetic sequences [5,64,65], which formed in response to the active and passive stages of diapirism from the Early Triassic to Cretaceous (Figure 4, IV-VII, and Figure 11), are present at different stratigraphic levels. Potential traps also include Early-Middle Triassic half turtle structures (Figure 4, IV) and suprasalt fault complexes at the basin boundaries ( Figure 4B, I).…”

Four‐dimensional Variability of Composite Halokinetic Sequences

“…Minibasin deformation and associated stratal thickness variations occur at two main scales: (i) minibasin-scale, which is associated with the development of broad folds that span the minibasin width; and (ii) diapir-flank-scale, which is associated with a much narrower zone of drape folding and thinning of diapir roof strata, typically within 1 km of the salt-sediment interface (e.g. Vendeville and Jackson, 1991;Rowan et al, 2003;Giles and Rowan, 2012;Rowan et al, 2014). Syn-kinematic growth strata associated with diapir-flank scale deformation are referred to as halokinetic sequences (HS), which are defined as unconformitybounded packages of thinned and folded strata adjacent to passive diapirs (Giles and Lawton, 2002; Giles and Rowan, 2012;Hearon et al, 2014).…”

“…Vendeville and Jackson, 1991;Rowan et al, 2003;Giles and Rowan, 2012;Rowan et al, 2014). Syn-kinematic growth strata associated with diapir-flank scale deformation are referred to as halokinetic sequences (HS), which are defined as unconformitybounded packages of thinned and folded strata adjacent to passive diapirs (Giles and Lawton, 2002; Giles and Rowan, 2012;Hearon et al, 2014). Deformation of these strata is controlled by drape folding and upturn of ephemeral, thin diapir-roofs and associated flank strata during passive diapirism.…”

“…Rotation and flexure are accommodated by layer-parallel slip, with little to insignificant vertical (i.e. diapir-parallel) shearing or drag fold (Giles and Rowan, 2012;Rowan et al, 2003;Hearon et al, 2014;Jackson and Hudec, 2017). Giles and Rowan (2012) define two end-member styles of halokinetic sequence (HS): i) hooks, characterized by narrow zones of folding (<200 m), high-angle truncations (>70°) beneath bounding unconformities, and abrupt facies transitions towards the salt-sediment interface;…”