Stratigraphy and geochemistry of rock salt from Maha Sarakham formation in changwat Chaiyaphum, northeastern Thailand

Abstract

Maha Sarakham Formation is one of massive potash deposits in the Khorat Plateau extending from northeastern of Thailand to central of Lao PDR. Maha Sarakham Formation consists of three rock salt members (the lower, middle and upper members) interbedded with claystone. Potash minerals are associated with the thick bed of rock salt in the upper part of lower salt member. Previous studies are still under discussion on whether the origin of rock salt from marine or non-marine (hydrothermal origin and mixed fluids) deposit. The purpose of this study is to analyze the origin of rock salt based on elemental compositions and isotope analysis. In addition, stratigraphic correlations were done in five boreholes (K-201-205) located in Amphoe Bamnetnarong and Chaturat, Changwat Chaiyaphum, Thailand. As stratigraphical correlation results, the rock salt shows a dome structure. The limbs of salt dome are interpreted from lithostratigraphy correlations of K-201, K-202, K-203 and K-205 based on two beds of rock salt and potash zone in the lower salt member. The geochemical analysis of the lower and middle/upper rock salts in borehole K-203, and rare earth elements (REE) of claystone in five boreholes suggests that major and trace elements showing contents according to the formula of minerals and δ11B value (12.26‰ -32.62‰) indicates almost halite influenced seawater. However, the anomaly of carnallite by δ11B value (12.26‰) preferred possible influx of hydrothermal into the Khorat basin. REE of claystone are comparable with the REE in sandstone from the Simao Basin of China, the similar of REE pattern inferred the identical provenances both of clastic sedimentary rocks.