184-7 Depositional Mechanisms of Gray Event Layers in Early Holocene Sediments from Mono Lake: Evidence for Early Holocene Storminess?

Session: Lakes of the World Through Space and Time: Archives of Climate, Paleoenvironments, Ecosystems, Geohazards, and Economic Resources (Posters)

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Environmental changes at the Pleistocene-Holocene transition are evident in sedimentary and paleoecological records from the eastern Sierra Nevada, a region of great importance to California’s water resources. Mono Lake is one of the oldest and most-studied lacustrine basins in the eastern Sierra Nevada, yet much remains unknown about its deepwater sedimentary processes. Here we use well-dated sediments from the UWI-MONO15-1C/D composite core and examine gray event layers (n = 41) in Early and Middle Holocene Mono Lake deposits leveraging high-resolution imaging techniques, thin sections, petrography, microfacies analysis, and scanning X-ray fluorescence. The gray event layers consist of normally graded detrital silts and commonly contain ostracode valves and terrestrial organic matter; these are best interpreted as high-concentration turbidites. Interestingly, the gray layers are frequently organized as the uppermost layer of a triplet. The basal layer of the triplet consists of reworked shallow-water carbonates and often shows evidence of minor basal scour, detrital grain lags, and occasionally reverse grading. The middle layer consists of fine silt and clay with dispersed ostracode valves and terrestrial organic matter, which we interpret as low-concentration turbidites. Taking a comprehensive view, the depositional triplet shares characteristics consistent with wave-enhanced sediment gravity flows. These layers may have formed due to storms that both reworked the littoral zone and spurred erosive Wilson Creek Formation-laden runoff that transformed into underflows upon entering the lake (represented by the gray layers). The data also suggest the possibility of Early Holocene summer rainfall in the Mono Basin, perhaps due to an enhanced North American monsoon or teleconnections to other global climate phenomena.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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