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Loading a Complex Salt Isopach: Progradation Across a Salt-Filled Rift System

Abstract

Deposition of salt during crustal extension adds to the complexity of post-deposition salt tectonics in many ways. For example, salt may be thin or absent across intra-rift highs thus impacting mobility and connectivity, influencing deformation styles during subsequent sediment loading. Physical models investigated salt-tectonic processes in sediment-driven remobilization of a complex salt isopach within a segmented rift system. A stretching rubber sheet generated regional extension. Slabs of weak silicone embedded at the base of the pre-rift stratigraphy localized extension to produce a series of soft-linked discrete graben. Model salt filled the deep graben, thinning across linkage zones. Thin salt covered the horst blocks between graben. The salt basin was tilted and loaded by a series of sedimentary wedges. Distal aggradation gradually buttressed the prograding system. Sediment loading and regional dip drove salt seawards. The continuous thin-salt fringe that covered the segmented basin aided salt mobility, resulting in translation and extension of the sedimentary overburden. Large salt walls formed downdip of the toe of the sedimentary wedge as seaward-flowing salt was buttressed against graben edges, much like our previously published models of gravity gliding across basement relief. Continued thickening of these salt-cored uplifts eventually allowed them to collapse under extension. Sedimentary loading of these extending, flat-topped diapirs formed local minibasins that translated seawards until they welded atop subsalt strata, freezing the adjacent diapirs in place. Diapirs were also deformed as they passed through extensional and contractional hinges associated with topographic monoclines developed above the horst and graben topography in subsalt strata. In portions of the basin with subdued base-salt relief, simpler expulsion rollovers dominate as the lack of buttressing allowed more efficient salt expulsion. Despite the inherent oversimplifications in physical models some good first-order similarities are demonstrated between our results and examples from the Abenaki and Eastern Sable Subbasins on the Scotian margin.