Sedimentology of Acid Saline Lakes in Southern Western Australia: Newly Described Processes and Products of an Extreme Environment

Abstract

Naturally acid saline systems with pH values between 1.7 and 4 are common on the Yilgarn Craton of southern Western Australia. A combination of physical and chemical processes here yield a previously undescribed type of modern sedimentary environment. Flooding, evapoconcentration, desiccation, and eolian transport at the surface, as well as influx of acid saline groundwaters, strongly influence these lakes. Halite, gypsum, kaolinite, and iron oxides precipitate from acid hypersaline lake waters. Shallow acid saline groundwaters affect the sediments of the lakes and associated mudflats, sandflats, channels, and dunes by precipitating early diagenetic halite, gypsum, iron oxides, clays, jarosite, and alunite. These modern environments would likely yield a rock record composed mostly of bedded red siliciclastic and reworked gypsum sand, alternating with less common beds of bottom-growth gypsum and halite, with alteration by early diagenetic features diagnostic of acid saline waters. This documentation of sedimentary processes and products of modern acid saline environments is an addition to the comparative sedimentology knowledge base and an expansion of the traditional models for classifying brines. Implications include better interpretations of terrestrial redbeds and lithified martian strata, improved acid remediation methods, new models for the formation and occlusion of pores, and the new setting for finding previously undescribed extremophiles.

Land use change suppresses precipitation

“…Hydrologic reasons such as the variable groundwater table would be a plausible explanation for the different biogeochemical characteristics of the lakes (Benison, 2007).…”

“…We used small, low and slow flying aircraft which allow investigations very close to the surface, yet still able to cover distances of more than 200 km and climbing rapidly above cloud levels. The region is part of the Yilgarn Craton, a flat terrain of more than 1000×1000 km between 265 and 365 m above sea level (Benison, 2007). The agricultural land along the fence extends over ∼300 km W/E and >600 km N/S direction.…”

The paleoclimatic and geochronologic utility of coring red beds and evaporites: a case study from the RKB core (Permian, Kansas, USA)

“…7) yields complete and well-preserved core necessary for assessing high-resolution depositional and early diagenetic conditions. For example, the displacive halite lithology (aka "chaotic halite" in some older literature), composed of red mudstone with randomly oriented large halite crystals, forms syndepositionally in groundwater-saturated saline mudflats adjacent to ephemeral saline lakes in arid climates (Benison and Goldstein 2001;Benison et al 2007;Lowenstein and Hardie 1985). This lithology is the most abundant lithology in the Flowerpot Shale in the RKB core .…”

“…Petrographic documentation of halite and gypsum crystal types and sedimentary features lead to informed interpretations of depositional environments. Because most evaporite depositional environments are sensitive to climate, petrographic observations provide qualitative information about paleoclimate, such as relative aridity (i.e., Benison et al 2007;Lowenstein and Hardie 1985). Secondly, fluid inclusion data from bedded halite yield high-resolution, quantitative records of paleoclimate.…”

Secondary halite deposits in the Iranian salt karst: general description and origin

“…), we found fragments of various more or less solidified fine-grained sediments (mostly mudstones) containing displacive hopper-shaped quartz pseudomorphs after halite, or cubic, often deformed cavities, sometimes filled by hematite or dolomite. Therefore, it is obvious that halite was a common subaerial chemogenic precipitate (c.f., Gornitz & Schreiber, 1987;Benison et al, 2000;Pope & Grotzinger, 2003) pointing to saline depositional environments also in the more distant geological history of the diapirs. Destruction of secondary halite deposits Most commonly, destruction is a direct effect of heavy rains and floods.…”