The paradox of minibasin subsidence into salt: Clues to the evolution of crustal basins

Abstract

Why do salt-fl oored minibasins subside? An almost universal explanation is that salt is forced from beneath the sinking basin by the weight of its sedimentary fi ll. This explanation is valid if the average density of the basin fi ll exceeds that of salt, which in the Gulf of Mexico needs at least 2300 m of siliciclastic fi ll to ensure enough compaction. However, most minibasins start sinking when they are much thinner than this. Some mechanism other than density inversion must explain the early history of these minibasins. Conventional understanding of minibasin subsidence is thus incomplete. Here, we identify fi ve alternatives to density-driven subsidence of minibasins. (1) During diapir shortening, the squeezed diapirs infl ate, leaving the intervening minibasins as bathymetric depressions.(2) In extensional diapir fall, stretching of a diapir causes it to sag, producing a minibasin above its subsiding crest. (3) During decay of salt topography, a dynamic salt bulge subsides as upward fl ow of salt slows, which lowers the salt surface below the regional sediment surface. (4) During sedimentary topographic loading, sediments accumulate as a bathymetric high above salt. (5) Finally, subsalt deformation affecting the base of salt may produce relief at the top of salt. Each mechanism (including density-driven subsidence) produces a different bathymetry, which interacts with sediment transport to produce different facies patterns in each type of minibasin. The particular mechanism for minibasin subsidence depends on the tectonic environment, regional bathymetry, and sedimentation rate. Their spatial variation on a continental margin creates provinces in which a given minibasin style is dominant.An appreciation of subsidence mechanisms should thus improve our understanding of minibasin fi ll patterns and allow genetic comparisons between minibasins.The mechanics of a minibasin sinking into fl uid salt is in many ways analogous to a crustal basin sinking into a fl uid asthenosphere. However, minibasins lack the complex rheologies, thermal histories, and compositional variations that make study of crustal basins so challenging. Minibasins are thus natural analogs and have the potential to elucidate fundamentals of subsidence mechanics.

Stress and pore pressure histories in complex tectonic settings predicted with coupled geomechanical-fluid flow models

“…This ensures that realistic porosities are predicted, essential to a coupled geomechanical/fluid flow analysis. In this case the hardening law of the sediments (which has a first order effect on mechanical compaction) has been calibrated according to a regional compaction trend for Golf of Mexico published in (Hudec et al, 2009). …”

“…The hardening law for clay is defined according to a regional compaction trend in Gulf of Mexico by (Hudec et al, 2009) assuming that sediments were are normally pressured. The hardening law for the sand is defined according to a typical sand normal compaction trend.…”

Reservoir quality of fluvial sandstone reservoirs in salt-walled mini-basins: an example from the Seagull field, Central Graben, North Sea, UK

“…The Late Permian Zechstein salt strongly controlled the Triassic deposition by forming salt withdrawal mini-basins within an overall rift-controlled basinal tectonic setting (Smith et al 1993;Bishop 1996;Matthews et al 2007). The initiation of mini-basin subsidence or creation of salt-walled mini-basins requires the presence of salt with a sufficient thickness to allow halokinesis (Hudec et al 2009), and a mechanism to initiate halokinesis, i.e. extension, compression, differential loading or buoyancy (Banham and Mountney 2013a).…”

“…Such studies have increased our understanding of salt movement, the development of salt-walled mini-basins and on the effects of coeval halokinesis on sedimentary Edited by Jie Hao processes and facies distribution (e.g. Fox 1998;Hudec et al 2009;Banham and Mountney 2013a, b). However, a detailed understanding of the effects of contemporaneous salt movement on diagenesis and reservoir quality is yet to be established.…”

The Effect of A Pre-Deposited Mobile Substrate On Terminal-Fan Evolution and Channel Organization: Tank Experiments

“…Relatively few experimental and theoretical studies have been conducted to understand the interactions between a depositional body of sediment and a pre-existing, deformable, viscous substrate (Hudec et al 2009;Piliouras et al 2014;Kopriva et al 2015). Each of these studies, however, has revealed the significance of specific variables in controlling the morphology and evolving stratigraphy in experimental settings and how these apply to real world basinal settings.…”