Unraveling Sources and Climate Conditions Prevailing during the Deposition of Neoproterozoic Evaporites Using Coupled Chemistry and Boron Isotope Compositions (δ11B): The Example of the Salt Range, Punjab, Pakistan

In this study, the ion concentrations (K+, Na+, Ca2+, Mg2+, Cl-, SO42-, Br-, NO3-, and B3+) and boron isotope compositions (delta B-11) of 34 halite and brines samples from the Neoproterozoic Salt Range Formation, Punjab, Pakistan were studied. Relation among B3+ vs. Mg2+, B3+ vs. SO42-, delta B-11 vs. B3+, and delta B-11 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 delta B-11 vs. 1/B plot. Molar ratios of B/Cl vs. delta B-11 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 delta B-11 from the Salt Range Formation vary from +2.1 to +24.4 parts per thousand, compared to +17.3 to +26.1 parts per thousand in the salt pool brines, and suggest that boron isotope compositions are controlled by the delta B-11 of the B sources. The positive relationship between the boron content and the corresponding delta B-11 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 delta B-11 in the present study, demonstrate compatibility with other marine basins of the world, arising the need for further investigations to better characterize the B-11-enriching processes.

Automated summary

This study investigated the ion concentrations and boron isotope compositions of halite and brines samples from the Neoproterozoic Salt Range Formation in Punjab, Pakistan. The results suggest that the elements studied originated from multiple sources, including seawater, B desorption from clays, and meteoric precipitation. Boron isotope compositions were controlled by the delta B-11 of the B sources, indicating higher salinity and drier paleoclimate conditions during the Late Neoproterozoic period. The study highlights the need for further investigations to better understand the enriching processes of B-11 in marine basins.