Genetic Model of Mud-Clast Conglomerates in Salt Rocks and Their Significance for Salt Mineralization in Mohei Area, Simao Basin, China: A Case Study of Well L-2

Abstract

The Simao Basin is one of the most important Mesozoic salt basins in China, and the salt rocks generally contain mud-clast conglomerates. The characteristics of mud-clast conglomerates can provide effective information indicating the evolution process of the salt deposits. A combined analysis of trace elements and clay minerals was performed to characterize the genetic model of mud-clast conglomerates in the salt rocks. The results show that the sedimentary materials are felsic rocks from the Upper Crust. Ternary plot diagrams show that the tectonic settings are between the continental margin and the continental island arc. The clay minerals in the samples mainly contain illite and illite–smectite mixed layers. A dry and hot climate prevailed during the deposition of the Mengyejing Formation, and the warm-humid climate that also occurred is interspersed in some periods. Evaporation makes the water bodies shallower, and the concentrated brine starts to precipitate salt under the arid and hot climate conditions. Redox proxies indicate that most of the samples were deposited in relatively oxic conditions. The Sr/Ba ratios (average of 0.5) and paleosalinity (average of ∼35‰) during the depositional period indicate an increase in terrigenous freshwater input and carry of clasts into the evaporation basin. Furthermore, the freshwater supply enhances the hydrodynamics; as a result, the detritus that deposited in the early stage is broken into mud-clast conglomerates and co-deposited with the salt rocks. The results provide a geochemical basis for further study of mud-clast conglomerates in the Simao Basin and supply recommendations for the origin of salt deposits in similar basins around the world.

Element Geochemical Characteristics and Geological Significance of Mudstones from the Middle Jurassic Shaximiao Formation in Sichuan Basin, Southwest China

“…It is widely accepted that the V/(V + Ni) ratio > 0.84, 0.54–0.82, and 0.46–0.6 represent anoxic, hypoxic, and oxygen-enriched sedimentary conditions, respectively ( Figure 10 A). 62 The V/(V + Ni) range of Sha-1 Member is 0.58 to 0.82 (average = 0.71), and the value in Sha-2 Member varies from 0.68 to 0.87 (average = 0.75) ( Table 2 ), indicating a hypoxic environment. The V/Cr value can also be used as a parameter to identify the redox environment.…”

“…According to previous studies, the redox state of the sedimentary environment can be characterized according to the ratios of V/Cr, V/(V + Ni), etc. , The higher the V/(V + Ni) ratio, the lower the degree of oxidation of the water during deposition. It is widely accepted that the V/(V + Ni) ratio > 0.84, 0.54–0.82, and 0.46–0.6 represent anoxic, hypoxic, and oxygen-enriched sedimentary conditions, respectively (Figure A) . The V/(V + Ni) range of Sha-1 Member is 0.58 to 0.82 (average = 0.71), and the value in Sha-2 Member varies from 0.68 to 0.87 (average = 0.75) (Table ), indicating a hypoxic environment.…”

Genesis of Pyrite in Clastic Rocks of Deep Salt-Related Strata in the Simao Basin and Its Implication for Potash Mineralization: A Case Study of the Well MK-3

“…Salt rocks discovered in the basin are mainly found in the Mengyejing Formation of the Lower Cretaceous, with a maximum burial depth above 1251 m. From west to east, salt rocks can be divided into the Jinggu salt-bearing belt, Zhengdong-Mengla salt-bearing belt, and Jiangcheng salt-bearing belt [2,15]. The surrounding rock of salt rock is mainly mud-clast conglomerates, and there is no carbonate rock and sulfate rock of corresponding scale in normal evaporative deposition sequence, and mud-clast conglomerates often appear in salt rock [16,17]. The potash deposit occurs in the Mengyejing area of the Jiangcheng salt-bearing belt in the southeast of the basin, and the ore beds are produced in the upper member of the Mengyejing Formation [18][19][20].…”