Warren,J.K.(2010): Evaporites through time: Tectonic, climatic and eustatic controls in marine and nonmarine deposits. Earth-Science Reviews, 98, 217-268.

『蒸発岩の時代推移:海成および非海成鉱床の構造運動と気候と海水面変動によるコントロール』


Abstract
 Throughout geological time, evaporite sediments form by solar-driven concentration of a surface or nearsurface brine. Large, thick and extensive deposits dominated by rock-salt (mega-halite) or anhydrite (mega-sulfate) deposits tend to be marine evaporites and can be associated with extensive deposits of potash salts (mega-potash). Ancient marine evaporite deposition required particular climatic, eustatic or tectonic juxtapositions that have occurred a number of times in the past and will so again in the future. Ancient marine evaporites typically have poorly developed Quaternary counterparts in scale, thickness, tectonics and hydrology. When mega-evaporite settings were active within appropriate arid climatic and hydrological settings then huge volumes of seawater were drawn into the subsealevel evaporitic depressions. These systems were typical of regions where the evaporation rates of ocean waters were at their maximum, and so were centered on the past latitudinal equivalents of today's horse latitudes. But, like today's nonmarine evaporites, the location of marine Phanerozoic evaporites in zones of appropriate adiabatic aridity and continentality extended well into the equatorial belts.
 Exploited deposits of borate, sodium carbonate (soda-ash) and sodium sulfate (salt-cake) salts, along with evaporitic sediments hosting lithium-rich brines require continental-meteoric not marine-fed hydrologies. Plots of the world's Phanerozoic and Neooproterozoic evaporite deposits, using a GIS base, shows that Quaternary evaporite deposits are poor counterparts to the greater part of the world's Phanerozoic evaporite deposits. They are only directly relevant to same-scale continental hydrologies of the past and, as such, are used in this paper to better understand what is needed to create beds rich in salt-cake, soda-ash, borate and lithium salts. These deposits tend be Neogene and mostly occur in suprasealevel hydrographycally-isolated (endorheic) continental intermontane and desert margin settings that are subject to the pluvial-interpluvial oscillations of Neogene ice-house climates. When compared to ancient marine evaporites, today's marine-fed subsealevel deposits tend to be small sea-edge deposits, their distribution and extent is limited by the current ice-house driven eustasy and a lack of appropriate hydrographycally isolated subsealevel tectonic depressions.
 For the past forty years, Quaternary continental lacustrine deposit models have been applied to the interpretation of ancient marine evaporite basins without recognition of the time-limited nature of this type of comparison. Ancient mega-evaporite deposits (platform and/or basinwide deposits) require conditions of epeiric seaways (greenhouse climate) and/or continent-continent proximity. Basinwide evaporite deposition is facilitated by continent-continent proximity at the plate tectonic scale (Late stage E through stage B in the Wilson cycle). This creates an isostatic response where, in the appropriate arid climate belt, large portions of the collision suture belt or the incipient opening rift can be subsealevel, hydrographycally isolated (a marine evaporite drawdown basin) and yet fed seawater by a combination of ongoing seepage and occasional marine overflow. Basinwide evaporite deposits can be classified by their tectonic setting into: convergent (collision basin), divergent (rift basin; prerift, synrift and postrift) and intracratonic settings. Ancient platform evaporites can be a subset of basinwide deposits, especially in intracratonic sag basins, or part of a widespread epeiric marine platform fill. In the latter case they tend to form mega-sulfate deposits and are associated with hydrographycally isolated marine fed saltern and evaporitic mudflat systems in a greenhouse climatic setting. The lower amplitude 4 and 5th order marine eustatic cycles and the greater magnitude of marine freeboard during greenhouse climatic periods encourages deposition of marine platform mega-sulfates. Platform mega-evaporites in intracratonic settings are typically combinations of halite and sulfate beds.

Keywords: evaporite; deposition; marine; nonmarine; plate tectonics; economic geology; classification』

Contents
1. Introduction
2. Depositional parity across time and space
3. Nonmarine evaporites
 3.1. Nonmarine hydrogeochemistry
 3.2. Climatic framework
4. Nonmarine salts across time and tectonics
 4.1. Borate evaporites
 4.2. Sodium sulfate evaporites (salt-cake)
 4.3. Sodium carbonate (soda-ash)
5. Marine evaporites
 5.1. Marine hydrogeochemistry
 5.2. The now and then of marine climates
6. Marine evaporites across time and tectonics
 6.1. Platform evaporites
 6.2. Basinwide evaporites
 6.3. Tectonic settings for marine-fed basinwide evaporites
 6.4. Potash salts
7. Evaporite brines (lithium and CaCl2)
 7.1. CaCl2 brines and minerals
 7.2. Lithium brines
8. Summary
Appendix A
References


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