Testing the Applicability of Halokinetic Sequences in a Deepwater Depositional Setting

Hearon, Thomas E.¹; Rowan, Mark G.; Hart, William H.; and Giles, Katherine A.
¹[email protected]

Halokinetic sequences (HS) are localized (<1 km) unconformity-bound successions of growth strata adjacent to salt diapirs that form as drape folds due to the interplay between salt rise rate (R) and sediment accumulation rate (A). Hook and wedge HS stack vertically to form tabular and tapered composite halokinetic sequences (CHS), respectively. Tabular CHS have a narrow zone of stratal upturn (50-200m), whereas tapered CHS have a broad zone of stratal upturn and thinning (300-1000m). Tabular and tapered CHS form under relatively high and low ratios, respectively, of R and A. CHS boundaries, which form during times of maximum topographic relief, have been tentatively linked to third-order transgressive systems tracts in shelf depositional settings as the concepts of CHS formation are derived from outcrops in shallow water to subaerial depositional environments in La Popa Basin, Mexico and the Flinders Ranges, South Australia. These concepts have yet to be fully applied or tested in a deepwater setting.

To that end, wide-azimuth seismic data, well and biostratigraphic data and structural restorations were utilized to document a vertical succession of ten well-imaged CHS adjacent to the Auger diapir in the deepwater northern Gulf of Mexico. We observe variations in CHS geometry with depth and around the diapir flanks. For example, where the NW (updip) flank is dominated by tapered CHS, the SE flank contains a nearly equal proportion of tabular and tapered CHS. In accordance with the HS model, tabular and tapered CHS stack vertically into four different geometric configurations. Tabular CHS exhibit narrow zones of stratal upturn and thinning (<100m), whereas tapered CHS have wider zones (285-1265m). Rates of sediment accumulation for tabular CHS (2.1-4.6m/kyr) are generally lower than those for tapered CHS (1.5-19m/kyr). CHS depositional intervals also appear to occur on the fourth-order depositional cycle (130kyr to 940kyr), instead of third-order cycles, with CHS boundaries generally corresponding to sequence boundaries, when topographic relief was greatest.

Our findings generally corroborate established halokinetic sequence criteria, showing that some concepts learned from outcrops of diapirs in shelfal to subaerial depositional environments do apply to deepwater settings. The results are critical to understanding and predicting combined structural-stratigraphic trap geometry, reservoir distribution and hydrocarbon containment in diapir-flank settings.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013