Abstract
In this study, the ion concentrations (K+, Na+, Ca2+, Mg2+, Cl−, SO42−, Br−, NO3−, and B3+) and boron isotope compositions (δ11B) of 34 halite and brines samples from the Neoproterozoic Salt Range Formation, Punjab, Pakistan were studied. Relation among B3+ vs. Mg2+, B3+ vs. SO42−, δ11B vs. B3+, and δ11B vs K+ were observed, they indicated that these elements originate from multiple sources and the end members were identified as seawater, B desorption from clays, and meteoric precipitation. Halite samples of the area under study displayed a Na-HCO3-type to Ca-Cl type sedimentary basin of deposition, on δ11B vs. 1/B plot. Molar ratios of B/Cl vs. δ11B revealed the addition of B in some of the studied samples from desorption of clay minerals. This type of diagenetic desorption of B from clays is the consequence of a stress driven mechanism, generated in the proximity of a decollement zone. Results confirm that the number of B stable isotopes that fractionate between the brine and the halite is low. The halite δ11B from the Salt Range Formation vary from +2.1 to +24.4‰, compared to +17.3 to +26.1‰ in the salt pool brines, and suggest that boron isotope compositions are controlled by the δ11B of the B sources. The positive relationship between the boron content and the corresponding δ11B indicates a higher salinity and drier paleoclimate conditions during the formation process, associated with a high evaporation rate in the Late Neoproterozoic time. Presence of elevated δ11B in the present study, demonstrate compatibility with other marine basins of the world, arising the need for further investigations to better characterize the 11B-enriching processes.
Highlights
Boron (B) is a lithophile light weight trace element, and classified as a semimetal [1,2]
Elemental and B stable isotope (δ11B) compositions of halite and brines from the oldest member of the Salt Range Formation were made with the objectives of: (1) identifying the elements that control the budget of boron; (2) constraining the processes responsible for the incorporation of B from the brines into the halite; (3) understanding the corresponding δ11B isotopes behavior to identify the paleoclimatic conditions and compare the variations in δ11B isotopes and its fractionation between halite and brines in a distinctive sedimentary basin system
This is similar to the trends observed in the Qarhan playa [5,20] but differ from the results from the Mahai and Lenghu salt lake brines in China [24]
Summary
Boron (B) is a lithophile light weight trace element, and classified as a semimetal [1,2]. The coupling of δ11B stable isotopes and of elemental chemistry has been used to trace the origin and define geochemical processes involved in the formation of brines, evaporites and sediments [20]. Elemental and B stable isotope (δ11B) compositions of halite and brines from the oldest member of the Salt Range Formation were made with the objectives of: (1) identifying the elements that control the budget of boron; (2) constraining the processes responsible for the incorporation of B from the brines into the halite; (3) understanding the corresponding δ11B isotopes behavior to identify the paleoclimatic conditions and compare the variations in δ11B isotopes and its fractionation between halite and brines in a distinctive sedimentary basin system
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