A Shallow‐Basin Model for ‘Saline Giants’ Based on Isostasy‐Driven Subsidence

Abstract

The common assumption that 'saline giants' must have formed in deep basins and that their thickness reflects initial basin depth ignores the principle of isostasy. Due to the high density of anhydrite and high precipitation rates for evaporite minerals, isostatic compensation is much more important in evaporite than in non-evaporite settings. The main implication is that evaporite precipitation drives subsidence rather than the other way round, and that thick evaporite deposits require an initial basin depth much less than their final thickness. Once initiated, evaporite precipitation and consequent isostatic subsidence is a self-sustaining process that can result in kilometre-scale evaporite stratigraphy. Rapid isostatic compensation is facilitated by thin, fractured crust in extensional basins, which explains the typical occurrence of saline giants in such settings. It is shown that a shallow-basin origin in combination with rapid isostatic compensation can well explain the extreme thickness of saline giants as well as the commonly associated shallow-water sedimentary facies. Although there is no reason to exclude the possibility of a basin-wide dropdown of a few thousand metres as proposed for some saline giants, a desiccated deep basin is certainly not a requirement. An initially shallow basin that rapidly deepens by isostatic adjustment in response to the precipitation of evaporites eliminates the need for deep-basin desiccation, gigantic waterfalls, and repeated opening and closure of a connection to the world ocean, and makes the extreme thickness of saline giants less enigmatic.

Sequence Stratigraphy: Methodology and Nomenclature

“…Thick and relatively rapidly-precipitated evaporites can have a significant loading effect on the crust (Van der Belt and de Boer 2007). This may well lead to increased subsidence of basin margins and basin floors, thereby creating further accommodation for more evaporites (Fig.…”

Influence of Climate and Tectonics on the Crystallization of Carnallite and Related Salts in the Congolese Atlantic Basin during the Lower Cretaceous, Republic of Congo

“…The shallow nature of these facies as well as the great thickness of these salt deposits, sometimes reaching 800 m in certain wells, confirms the subsiding nature of this basin. [2] [13] [17] [18] [19] [20] [21] confirm the subsiding nature of this basin, but the mode of emplacement and its evolution in a geodynamic and sedimentation context has not been addressed by these authors. [22] [23] [24], dismiss this subsiding character of the Congo and Gabon basins, because for them, the sedimentation rate which is 5 mm/year in these basins is much higher than that of rifting which is 1 mm/year and defines a deep basin.…”

Sedimentology and depositional environment of the Late Eocene marine siliciclastic to evaporite transition in the Sivas Basin (Turkey)

“…Moreover, a significant part of the space needed for evaporite accumulation might have been provided during evaporite sedimentation by a fast subsidence rate of the foredeep, which can be as high as 500 m/Ma (Vergés et al, 1998). This flexural subsidence could have been promoted by the loading (i) of the growing southern fold-and-thrust belt, and (ii) of the evaporitic deposition that enabled a rapid isostatic compensation (van den Belt and de Boer, 2007).…”