# A Review of Evaporite Beds Potential for Storage Caverns: Uncovering New Opportunities
## 2 Evaporites and Bedded Evaporite Deposits
### Depositional Environment of Evaporites  
The depositional environment refers to the conditions in which sedimentary rocks form. The depositional environment influences characteristics such as rock lithology, mineral composition, texture, and sedimentary structures [59]. Evaporite deposits are generally classified as marine, non-marine, or a combination of both, depending on the source of their primary brine [60]. According to [PERSON]'s Bar Theory, the depositional environment for thick evaporites is a lagoon separated from the sea by a barrier. This setting is typically warm, arid, and limited in freshwater influx [54]. Ancient marine evaporites, which are the dominant type, are further divided into two settings: platform evaporites (with beds less than 50 m thick) and basinwide evaporites (with units greater than 50-100 m thick) [61]. [PERSON]'s Desert-Basin Theory describes non-marine environments for thick evaporite deposits [54], with such deposits often forming in saline lakes, such as perennial lakes, ephemeral lakes, playa lakes, plays, salinas, and other similar settings [62]. Other researchers have proposed different classifications for evaporite depositional environments. For instance, three main types of evaporite basins--lagoon basin, salina basin, and saline lake--are identified in [63]. Figure 7 illustrates these three types of evaporite basins. A classification that applies to both marine and non-marine environments was proposed in [64]. The three depositional environments identified are marginal (a mix of shallow subaqueous and subaerial), shallow subaqueous, and deep subaqueous. Figure 8 displays and describes these environments. Figure 7: Three major evaporite basins: (**a**) lagoon basin, (**b**) salina basin, (**c**) saline lake [63]. According to [65], evaporites can form in various settings such as sabkhas, barred basins, and shallow epeiric shelves. This source also links evaporites to black shale and limestone deposits, suggesting deposition in euxinic (low-oxygen) conditions. Most North American evaporites are classified as intra-basin deposits (formed in the center of basins), while others are basin-margin deposits. Intra-basin evaporites are further classified based on sill types as tectonically silled or reef-enclosed, whereas basin-margin evaporites are divided into back-reef and topographically silled basin-margin deposits [66]. A separate study in [67] suggests that modern marine evaporites are deposited in supratidal and coastal salina margins of marine basins, reflecting the hot, arid conditions conducive to their formation. This study also examines the impact of meteoric water on the mineralogy and sediment characteristics of evaporite sequences. Other studies have investigated how microbial activities influence evaporite sediment structures [68; 69; 70]. Although direct precipitation is identified as the main factor driving evaporite accumulation, the depositional environment is complex, with additional factors such as sediment transport, currents, biological activity, groundwater gradients, and underground movements influencing deposition [71]. Several studies focus on evaporite depositional environments in the U.S. and Canada [72; 73; 74; 75; 76; 77; 78; 79]. For instance, bedded halite in the Permian San Andres Formation was deposited in perennial brine-pool conditions, according to [73]. Additionally, ref. [74] defined two cycles in the McNutt Potash Zone of the Permian Salado evaporites: one cycle in a shallow, marginal marine basin and another in a shallow saline lake. Another study on Permian Basin salt deposition proposes a coastal sabkha salt pan environment [72]. Research on Michigan basin salt indicates a deep-water depositional setting, whereas salt in the Appalachian basin is linked to shallow, turbulent water environments [75]. For the Williston Basin, three depositional environments--marine open-circulation, euxinic, and evaporitic--have been identified [77]. The Elk Point Basin in Canada is described by a deep-basin model [80].