129-62 High-resolution chemical stratigraphy of saline lakes of the Southern High Plains

Abstract:

The saline lakes of the Southern High Plains of Texas and New Mexico are sensitive to regional climate shifts. The shallow, transient state of the lakes today reflects the modern interpluvial climate, while Late Pleistocene records of expanded lake depth and extent reflect corresponding pluvial conditions. Prior studies of basin morphology, palynology, and stratigraphy document the millennial-scale drying of the saline lakes during the Late Pleistocene and Holocene. We present a higher-resolution stratigraphy of sedimentation and evaporite formation to interpret smaller-scale changes and variability in the region's climate over the late Quaternary. 

We collected two sediment cores (both ~4 meters in length) and float samples of carbonate strata (thicknesses range 1–4 cm) from White Lake and Salt Lake, near Muleshoe, TX, and Arch, NM, respectively. We measured downcore geochemistry with an X-ray fluorescence (XRF) analyzer and sub-millimeter-scale geochemical variability in carbonate strata with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).

We report preliminary data from a 129 cm core section of White Lake (389–261 cm depth) and two 2-cm carbonate strata from Salt Lake. Downcore chemical proxies record changes in evaporite formation, lake salinity, and relative detrital content, all of which reflect trends of wetting and drying. In the lowermost 43 cm, these proxies indicate initially wet conditions, followed by drying that culminated in precipitation of an evaporitic carbonate layer, and then increased moisture and lake expansion. The remaining 86 cm reflect prolonged drought conditions. Salt Lake carbonates evidence a monotonically warming and/or drying climate across the 2 cm of precipitation. Both littoral and basinal samples record increasing carbonate growth and salinity in rising Mg/Ca ratios. While the more littoral sample exhibits continuously decreasing detrital content (inferred from falling Si/Ca), the more basinal sample records episodic increases in detrital input, implying that shoreline retreat and rearrangement changed and redirected detrital inputs to the system.

We will report additional XRF bulk chemistry for the remaining 3 m of core from White Lake and a 4 m core from Salt Lake. We will also report additional carbonate EDX geochemistry for float samples from White Lake and for in-place carbonate strata from White Lake and Salt Lake.  

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