Search

The depositional history of the Bonneville Salt Flats, a perennial saline pan in Utah's Bonneville basin, has poor temporal constraints, and the climatic and geomorphic conditions that led to saline pan formation there are poorly understood. We explore the late Pleistocene to Holocene depositional record of Bonneville Salt Flats cores. Our data challenge the assumption that the saline pan formed from the desiccation of Lake Bonneville, the largest late Pleistocene lake in the Great Basin, which covered this area from 30 to 13 cal ka BP. We test two hypotheses: whether climatic transitions from (1) wet to arid or (2) arid to wet led to saline pan deposition. We describe the depositional record with radiocarbon dating, sedimentological structures, mineralogy, diatom, ostracode, and portable X-ray fluorescence spectrometer measurements. Gypsum and carbonate strontium isotope ratio measurements reflect changes in water sources. Three shallow saline lake to desiccation cycles occurred from >45 and >28 cal ka BP. Deflation removed Lake Bonneville sediments between 13 and 8.3 cal ka BP. Gypsum deposition spanned 8.3 to 5.4 cal ka BP, while the oldest halite interval formed from 5.4 to 3.5 cal ka BP during a wetter period. These findings offer valuable insights for sedimentologists, archaeologists, geomorphologists, and land managers. [ABSTRACT FROM AUTHOR]

Fractured rock aquifers cover much of Earth's surface and are important mountain sites for groundwater recharge but are poorly understood. To investigate groundwater systematics of a fractured‐dominated aquifer in Baja California Sur, Mexico, we examined the spatial patterns of aquifer recharge and connectivity using the geochemistry of springs. We evaluate a range of geochemical data within the context of two endmember hypotheses describing spatial recharge patterns and fracture connectivity. Hypothesis 1 is that the aquifer system is segmented, and springs are fed by local recharge. Hypothesis 2 is that the aquifer system is well connected, with dominant recharge occurring in the higher elevations. The study site is a small <15 km2 catchment. Thirty‐four distinct springs and two wells were identified in the study area, and 24 of these sites were sampled for geochemical analyses along an elevation gradient and canyon transect. These analyses included major ion composition, trace element and strontium isotopes, δ18O and δ2H isotopes, radiocarbon, and tritium. δ18O and δ2H isotopes suggest that the precipitation feeding the groundwater system has at least two distinct sources. Carbon isotopes showed a change along the canyon transect, suggesting that shorter flowpaths feed springs in the top of the transect, and longer flowpaths discharge near the bottom. Geochemical interpretations support a combination of the two proposed hypotheses. Understanding of the connectivity and provenance of these springs is significant as they are the primary source of water for the communities that inhabit this region and may be impacted by changes in recharge and use. Article impact statement: We use isotopic geochemistry to understand groundwater movement through mountainous aquifers in arid landscapes. [ABSTRACT FROM AUTHOR]

The Bonneville Salt Flats form a saline pan in western Utah, USA. This modern saline pan has a unique history of land‐speed racing and potash mining. Multi‐decadal measurements record decreasing evaporite volume and extent, spurring multiple environmental studies. The goal of this work is to describe saline pan evaporite morphologies within the context of environmental measurements. Environmental data include field observations, groundwater and dust trap samples, precipitation, albedo, time‐lapse photography, groundwater level, and temperature measurements of air, groundwater and the shallow evaporite crust. Petrographic data include thick sections, evaporite slabs and sediments, and X‐ray computed tomography of evaporites. Diverse halite morphologies are formed at the surface, vadose and phreatic zones. The presence and preservation of these morphologies are influenced by spatially heterogenous natural and anthropogenic processes, including daily to seasonal changes in brine salinity, mineral saturation states, and water level within and across saline pan stages. In addition to hydrological balances delineated by the saline pan stages of flooding, evapoconcentration and desiccation, changes in vertical brine movement, temperature and surficial sedimentary structures influence evaporite morphologies. These results are transferable to the interpretation of altered evaporites and enhancing saline pan depositional models. [ABSTRACT FROM AUTHOR]

Primary fluid inclusions in bedded halite from the 830-m.y.-old Browne Formation of central Australia contain organic solids and liquids, as documented with transmitted light and ultraviolet--visible (UV-vis) petrography. These objects are consistent in size, shape, and fluorescent response with cells of prokaryotes and eukaryotes and with organic compounds. This discovery shows that microorganisms from saline depositional environments can remain well preserved in halite for hundreds of millions of years and can be detected in situ with optical methods alone. This study has implications for the search for life in both terrestrial and extraterrestrial chemical sedimentary rocks. [ABSTRACT FROM AUTHOR]