Sedimentary Conditions of Evaporites in the Late Jurassic Xiali Formation, Qiangtang Basin: Evidence from Geochemistry Records

Abstract

The Qiangtang Basin (QB), located in the central Tibetan Plateau, is a Jurassic marine basin and one of the most important prospective salt resource belts in China. In recent decades, many outcrops of gypsiferous bed have been found in the Jurassic marine strata in the basin. Salt springs with abnormally high sodium (Na+) contents had been identified in the Late Jurassic Xiali Formation (Fm.) in the basin in the last years. However, to date, no potash or halite deposits have been identified in the QB. Gypsum outcrops and salt springs are very important signs in the investigation of halite and potash deposits. Therefore, the Xiali Fm. is a potentially valuable layer to evaluate for the possible presence of halite and potash deposits in the basin. However, few studies have explored the formation conditions of evaporites in the unit. Here, we present detailed geochemical records from the Yanshiping section related to the study of the formation conditions of evaporites in the Xiali Fm. of the QB. Climate proxies based on the obviously increased anion concentrations of SO42− and Cl− and the significant correlation coefficients of Ca2+‐SO42− (R = 0.985) and Na+‐Cl− (R = 0.8974) reveal that the upper member of the Xiali Fm. (the upper Xiali Fm.) formed under an arid climate and evolved into the sulfate phase or early chloride phase. Provenance proxies based on the obviously increased K+ and Na+ ion concentrations and the significant correlation coefficient of Na+‐Cl− (R = 0.8974) suggest that the upper Xiali Fm. featured optimal provenance conditions for the possible formation of halite deposits. The regression and the semi‐closed tidal flat environment in the upper Xiali Fm. were favorable for the formation of potash and halite deposits. The low Mg2+ /Ca2+ values (mean value = 1.82) and significant Na+‐Cl− correlation coefficient (R = 0.8974) also suggest that the upper Xiali Fm. is the layer most likely to contain potential halite deposits. In addition, the macroscopic correlations of tectonism, provenance, paleoclimate, saliferous strata and sedimentary environment between the QB and the adjoining Amu Darya Basin in Central Asia reveal that the two basins shared similar geologic settings that were favorable for the formation of evaporites during the Late Jurassic. Therefore, the upper Xiali Fm. is a valuable layer to explore for halite deposit and may be potentially valuable in the future exploration for potash deposits in the QB.

Subsidence and exhumation of the Mesozoic Qiangtang Basin: Implications for the growth of the Tibetan plateau

“…of the South Qiangtang; Wang, Tan, Li et al, ). The upper sequences of the Middle Jurassic consist of marine platform limestones, dolomites (Buqu Fm., Ding, Wan, Zhang, & Han, ) and regressional semi‐closed tidal flat sediments (Xiali Fm., Song, Zeng et al, ). The Upper Jurassic unit is represented by intra‐platform littoral‐neritic carbonate rocks and black shales deposited in a closed, deep and static marine environment (Suowa Fm., Wang, Zhang, Cai, & Han, ).…”

Hydrogeochemical Characteristics and Water–Rock Interactions of Coalbed-Produced Water Derived from the Dafosi Biogenic Gas Field in the Southern Margin of Ordos Basin, China

“…Ion contents are also important indicators of the sedimentary environment [48]. The high content of Na + and low ranges of Ca 2+ and Mg 2+ of the water in the central and western parts of the study area show that the underground coalbed was in a closed groundwater environment.…”

Formation Mechanism and Sedimentary Pattern of Abandoned Channels

“…The methods of sandbody isopach mapping, sandbody top contour mapping, geochemistry records and well logging microfacies analysis amalgamation were adopted (Song et al, 2017), and we found that the abandoned channel of the meandering river is laterally associated with the point bar, which is the convex bank boundary at the Fig. 6.…”