Different scales of salt–sediment interaction during passive diapirism

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中文题名被动底辟过程中盐-沉积物相互作用的不同尺度
作者Mark G. Rowan; Katherine A. Giles
作者单位Rowan Consulting, Inc., Boulder, Colorado
刊名AAPG BULLETIN
2023
01
摘要
Salt–sediment interaction during passive diapirism typically occurs at two distinct scales that are related to depositional relief from the highs above diapirs to the lows of adjacent depocenters. At the large scale, subsidence into salt generates horizontal to gently dipping depositional surfaces and consequent minibasin tectonostratigraphic successions. These have widths of multiple kilometers and geometries categorized as (1) layer minibasin tectonostratigraphic successions, with strata maintaining their thickness approaching the diapir; (2) thinning-wedge minibasin tectonostratigraphic successions, in which the bounding surfaces converge toward the diapir; and (3) thickening-wedge minibasin tectonostratigraphic successions, where they expand toward the diapir. Internally, wedge minibasin tectonostratigraphic successions comprise smaller-scale stratal wedges that are concordant, discordant, base-discordant, or top-discordant. Minibasin fill may form a single minibasin tectonostratigraphic succession or have one or more switches between different minibasin tectonostratigraphic succession types. At the small scale, drape folding of the roof over the steep diapir edge generates a topographic scarp and resultant diapir-flanking, unconformity-bound halokinetic sequences that are less than 1 km wide. Halokinetic sequences stack into composite halokinetic sequences: hook halokinetic sequences form when the roof is thin and stack into tabular composite halokinetic sequence within 200 m of the diapir; and wedge halokinetic sequences represent thicker roofs and stack into broader, tapered composite halokinetic sequences. Distinguishing between the two scales of salt–sediment interaction is important because they have different implications for exploration and production in three-way traps against diapirs or equivalent welds. Different stacking patterns of minibasin tectonostratigraphic successions impact risk assessment of trap size, reservoir thickness trends, and hydrocarbon charge, whereas composite halokinetic sequences complicate the updip portions of traps and impact both reservoir distribution and seal.

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