HOLOCENE SEDIMENTATION PATTERNS AND VOLCANIC HISTORY FROM BINGO EXPEDITION SEDIMENT CORE, MONO LAKE, CALIFORNIA, USA

Mono Lake, California is a closed basin lake sitting at the eastern foot of the Sierra Nevada, and the modern lake closely tracks the Sierran snowpack, mostly precipitation from Pacific storms tracking over northern California. Geomorphic evidence for lake level changes over the last 2,000 years and during the last glacial period have been extensively described, but lake-level changes from the deglacial through middle Holocene are less well-known. We have recovered a 6.25 m-long core from ~3 m of water in the western embayment of Mono Lake, which is shown by initial radiocarbon dates to cover at least the last 10,000 years.

Although no terrestrial material for radiocarbon dating was found in the lowermost 3 m of the core, we interpret the light gray, ostracode-bearing silt at the base as recording late glacial or early deglacial time. Black to dark-gray, fine-grained, finely-bedded silts above a disrupted, sand-bearing interval likely indicate a relatively deep lake persisting into the early Holocene, after the initial dramatic regression from late Pleistocene levels. Although further work is required to definitively identify the Holocene ashes, a radiocarbon age of 9905 ± 215 cal yr BP near the base of the succeeding long sequence of finely-laminated olive-green mud suggests that this is the middle Holocene deep lake of previous cores (Davis, 1999 QR v52, 243-249 and Newton, 1994, SEPM Sp. Pub. 50, pp143-157). The laminated interval grades into coarser and more colorful sediment, rich in carbonate, indicating a relatively shallower and more variable lake after ~5000 years ago. A short interval of olive-green, laminated fine sand/silt just above a radiocarbon date of 3870 ± 360 cal yr BP may record the Dechambeau Ranch highstand of Stine (1990; PPP v. 78 pp333-381) at ~3800 cal yr BP. This grades into a quite coarse reddish creamy unit, followed by a second finer, more massive interval and a short interval of laminated, organic-rich pea-green mud. A 6 cm-thick ash above the second finer interval is interpreted to be the 1200 year Mono Craters ash because of the coarse lapilli layer in the middle, while a 2 cm-thick ash with coarse lapilli at the base, some ~30 cm above the older ash, is likely the 600-year Mono Craters ash. The top of the core is quite coarse, possibly due to the proximity of the coring site to the 1982 A.D. lowstand of 1942 m.