T111 Cenozoic Lakes Across Western North America – from the Varved Beds of the Green River Formation to the Ice-Covered Alpine Lakes of the Sierra Nevada (Posters)

Monday, 23 September 2024
8:00 AM - 5:30 PM
Hall D

A 21,000 YEAR RECORD OF HYDROCLIMATIC VARIABILITY FROM BIG LAKE, CALIFORNIA (NORTHERN CALIFORNIA COAST RANGE)

Paper number: T111-4
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

Our study focuses on Big Lake, located in the Northern Coast Range of California. Big Lake represents a key site for understanding California’s water history due to its position along the north-south California precipitation dipole. BigLRC 19-01, BigLRC19-04, and BigLRC 19-05 were taken along a transect from the lake’s depocenter to nearshore. Discrete organic material was sampled from the cores for radiocarbon dating to create an age model. Core BigLRC19-1 spans 21,000 calendar years before present – an exceptionally long record for a small lake. The following sedimentological analyses were performed at 1 cm contiguous intervals on all three sediment cores: magnetic susceptibility (MagS), grain size (10 size classes), and percent total organic matter (%TOM, loss-on-ignition at 550℃). We used principal component analysis (PCA) on the longest and oldest core – core BigLRC19-1 – to isolate the dominant sedimentary interrelationships. PC 1 explains 50.2 % of the data variability. Positive PC 1 values are associated with MagS, % clay, % very fine, fine silt, and very coarse sand which we infer to represent low energy, deep water conditions with greater runoff from the drainage basin. PC 1 negative values are associated with % TOM, medium and coarse silt, and very fine, fine, medium, and coarse sand. We interpret negative PC 1 values as high energy, shallow water conditions. The late Glacial is characterized as a wetter climate with deeper water conditions. Lake level drops at the end of the Younger Dryas and highly variable until about 8.5 kcal years BP. A comparison of all 3 cores suggests a severe and sustained lowstand between 8.5 and 5.0 kcal years BP. Conditions rebound to a wetter climate after 5.0 kcal years BP, punctuated by a dry Medieval Climatic Anomaly and a wet Little Ice Age, although the timing for the MCA and LIA requires additional age control.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-403493

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