Continental Rifted Margins 1. Gwenn Peron-Pinvidic
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Название: Continental Rifted Margins 1

Автор: Gwenn Peron-Pinvidic

Издательство: John Wiley & Sons Limited

Жанр: Физика

Серия:

isbn: 9781119986911

isbn:

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       – General: (Leeder and Gawthorpe 1987; Prosser 1993; Gawthorpe and Leeder 2000; Wilson et al. 2001; Masini et al. 2013; Ribes et al. 2019).

Schematic illustration of the definitions of sedimentary subdivision into pre-, syn- and post-tectonics.

Schematic illustration of summarizing the major structural and stratigraphic characteristics. Schematic illustration of the tectono-sedimentary evolution of a normal fault array.

       1.5.2. Salt

       Section written in collaboration with Mark Rowan.

      In geology, the term “salt” refers to an evaporitic mineral, a rock (halite, also known as rocksalt) and an interbedded sedimentary sequence composed mostly or largely of evaporitic material. Evaporites designate rocks formed by the precipitation of minerals in arid, isolated basins where the loss of water by evaporation exceeds the inflow. There are more than 80 evaporite minerals (Warren 2016), with the most common being halite and anhydrite/gypsum. They are usually interbedded with carbonate and siliciclastic rocks in layered evaporite sequences (LES) that can be up to 5+ km thick.

      Halite, anhydrite and other evaporite minerals are distinguished based on their composition and crystal structure: for example, halite is a sodium-chloride (NaCl) isometric crystal, anhydrite is a sulfate (CaSo4) with orthorhombic crystals, and gypsum is a hydrous variation of anhydrite. The minerals precipitate at different stages during water evaporation, in the reverse order of their solubilities (gypsum/anhydrite precipitates before halite, and bittern salts form in extremely evaporative conditions – see Warren (2016)). Halite is typically the most abundant constituent of LES.

Schematic illustration of evaporite deposition at different stages of rifting.

      Salt has physical characteristics and mechanical properties (Jackson and Hudec 2017) that make it special in rift evolution and thus a critical consideration when interpreting subsurface geometries. First, it has a constant low density (2.160 g/cm3 for pure halite) and is thus incompressible. Other sediments become denser with burial and compaction/cementation, so there will be a density inversion for the deeply buried salt. Much more important, however, is that halite has a low viscosity that allows it to easily flow, compared to surrounding rocks. Where the encasing rocks behave as relatively strong, brittle materials, salt is best viewed as a pressurized fluid that flows in a viscous manner (Vendeville and Jackson 1992). The drivers for salt movement are extension, contraction and differential loading, and the consequent way in which salt deforms is known as salt tectonics, halokinesis or halotectonics.

      In the case of late syn-rift salt, salt tectonics is dominated by post-rift gravitational failure of the salt and its overburden (see Rowan 2020). The primary drivers are the basinward tilt of the margin, caused by the thermal subsidence of oceanic crust, and proximal sediment loading. The deformation is thin-skinned, comprising of linked systems of proximal extension, translation and distal contraction СКАЧАТЬ