Relation between sediment distribution and halokinetic geometries along salt structures: a review and new insights from field studies

Sediment distribution and stratigraphic traps in salt-controlled minibasins are important targets for the hydrocarbon industry and for gas storage projects (i.e. carbon and green hydrogen). However, predicting sediment dispersal patterns along salt structures remains a significant challenge. Based on a compilation of relevant outcrop analogs of salt-controlled sedimentary successions (Sivas basin, Turkey; Paradox Basin, USA; Bakio Diapir and Cotiella Basin, Spain; La Popa basin, Mexico), the relation between the sediment distribution pattern and diagnostic halokinetic geometries is highlighted in this paper. A new model is proposed with enhanced capacity to predict sediment distribution and the occurrence of stratigraphic traps.

Halokinetic geometries result from horizontal to gently dipping depositional surfaces formed by the differential evacuation/inflation of an underlying salt layer. These geometries exhibit diverse shapes across varying scales. The most extensive halokinetic geometry examined herein is the recently defined Minibasin Tectonostratigraphic Succession (MTS), which comprises sedimentary strata extending over many kilometers and with thicknesses of hundreds to thousands of meters. Such multiple km-scale halokinetic geometries can be clearly imaged using seismic data and can be employed to predict the facies distribution. The key parameters controlling facies distribution patterns are (i) the steepness of the sediment–salt interface during MTS formation; (ii) the type of sedimentary system—marine/continental siliciclastics or marine carbonates. In siliciclastic systems, when paleocurrents are axial with respect to the length of the depocenter or salt structure strike, the reservoir facies tend to concentrate within the depocenter. When plaeocurrents are transversal, the entry/exit points of the minibasins may exhibit better reservoir properties in topographically higher and thinned areas. In contrast, marine carbonates tend to form over salt-topographic highs and may be the source of breccia facies developed on the flanks of the salt structure; (iii) the differential topography during deposition, from the salt-topographic high to the subsiding minibasin.

Layer MTSs comprise strata with constant thickness even as they approach the salt structure. The Layer MTSs formed along a gently dipping salt/sediment interface exhibits minor variations in the facies distribution, than the ones formed along a steeply dipping salt/sediment interface. The latter show minor facies variations in marine/continental clastic systems, while in marine carbonate settings, the reservoir facies tend to be located along the salt structure along with a Composite Halokinetic Sequence (CHS). Generally, a Thickening-wedge MTS, which comprises strata that expand toward the salt structure, exhibits a higher concentration of reservoir facies near the salt structure, while a Thinning-wedge MTS, which comprises strata converging toward the salt structure, exhibits marine and continental clastic reservoirs aligning with the depocenter and marine carbonate reservoirs inversely positioned along the salt structure. However, the reservoir facies distribution within Thinning- and Thickening-wedge MTSs exhibit notable variability depending on the dip of the salt–sediment interface during deposition, which determines the potential occurrence of CHS that impact near-diapir facies distribution.

This paper provides quantification of the facies variations, and discusses the key parameters such as the impact of smallest-scale halokinetic geometries (i.e., HSs and CHSs), and the ratio of the sedimentation rate to the differential subsidence rate.