Searles Lake evaporite sequences: Indicators of late Pleistocene/Holocene lake temperatures, brine evolution, and pCO2

Searles Lake, California, was a saline-alkaline lake that deposited >25 non-clastic minerals that record the history of lake chemistry and regional climate. Here, the mineralogy and petrography from the late Pleistocene/Holocene (32−6 ka) portion of a new Searles Lake sediment core, SLAPP-SRLS17, is combined with thermodynamic models to determine the geochemical and paleoclimate conditions required to produce the observed mineral phases, sequences, and abundances. The models reveal that the primary precipitates formed by open system (i.e., fractional crystallization), whereas the early diagenetic salts formed by salinity-driven closed system back-reactions (i.e., equilibrium crystallization). For core SLAPP-SRLS17, the defining evaporite sequence trona → burkeite → halite indicates brine temperatures within a 20−29 °C range, implying thermally insulating lake depths >10 m during salt deposition. Evaporite phases reflect lake water pCO2 consistent with contemporaneous atmospheric values of ∼190−270 ppmv. However, anomalous layers of nahcolite and thenardite indicate pulses of pCO2 > 700−800 ppm, likely due to variable CO2 injection along faults. Core sedimentology indicates that Searles Lake was continuously perennial between 32 ka and 6 ka such that evaporite units reflect periods of net evaporation but never complete desiccation. Model simulations indicate that cycles of partial evaporation and dilution strongly influence long-term brine evolution by amassing certain species, particularly Cl−, that only occur in late-stage soluble salts. A model incorporating long-term brine dynamics corrects previous mass-balance anomalies and shows that the late Pleistocene/Holocene (32−6 ka) salts are partially inherited from the solutes introduced into earlier lakes going back at least 150 ka.

Lithostratigraphy, mineralogy and the boron-bearing brine evolution of DaQaidam Salt Lake in Qaidam Basin since Holocene period, northern Qinghai-Tibet Plateau

Little attention has been paid to the study of sedimentary records from DaQaidam Salt Lake regarding brine evolution and hydro-climate change. Here we report the results of AMS 14C dating and mineralogical investigation on a sediment profile D4 from the south central of perennial saline water-body. The result revealed that pinnoite deposit in the lakebed was formed in early Holocene, the lake underwent three stages of lake-level and brine evolution in Holocene period, which were determined mainly by precipitation-controlled catchment inflow. The mineralogical records also depicted fluctuations in lake level and hydrochemistry on decadal and centennial scales.

Analysis of the Hydrochemical Characteristics and the Evolutionary Stages of Brine in Mahai Salt Lake in the Qaidam Basin

The objective of this study was to contribute to the understanding of the hydrochemical processes and evolution of brine in the Qaidam basin, in order to provide a theoretical basis for the application of brine resources in the region. The hydrochemical characteristics and evolutionary stages of brine in Mahai Salt Lake were investigated using factor analysis on brine chemistry data from 109 sampling points. Our results showed that the centre of the Salt Lake has the highest concentration of total dissolved solids (TDS), and the hydrochemical type of brine is chloride-magnesium. The brine at the centre of the lake is at the later stages of mirabilite precipitation, and the content of K+ is relatively stable. Comparatively, the hydrochemical type of brine in the slope area of the Salt Lake is Cl-Na-Mg, and is at the early stages of brine evolution. It is of guiding significance to further develop and utilize brine resources, especially to evaluate its resource development potential.

Groundwater Chemistry and Overpressure Evidences in Cerro Prieto Geothermal Field

In order to understand the geological and hydrogeological processes influencing the hydrogeochemical behavior of the Cerro Prieto Geothermal Field (CP) aquifer, Mexico, a characterization of the water samples collected from geothermal wells was carried out. Different hydrochemical diagrams were used to evaluate brine evolution of the aquifer. To determine pressure conditions at depth, a calculation was performed using hydrostatic and lithostatic properties from CP, considering geological characteristics of the study area, and theoretical information about some basin environments. Groundwater shows hydrogeochemical and geological evidences of the diagenetic evolution that indicate overpressure conditions. Some physical, chemical, textural, and mineralogical properties reported in the lithological column from CP are explained understanding the evolutionary process of the sedimentary material that composes the aquifer.