TEPHRA STRATIGRAPHY AND AMS MACROFOSSIL RADIOCARBON CHRONOLOGY OF HOLOCENE MONO CRATERS ERUPTIONS FROM MULTIPLE SEDIMENT CORES, MONO LAKE BASIN, CALIFORNIA

The Mono-Inyo Craters are a chain of domes, craters, coulees, and flows stretching south from Mono Lake to the northern rim of the Long Valley Caldera, and have been volcanically active from at least 65 ka to as recently as 600 years ago. The tephras provide important time markers for late Pleistocene and Holocene lake and meadow sediments within and east of the Mono Lake basin, but they cannot be distinguished by the elemental chemistry of the volcanic glass. However, recent work showed that analysis of titanomagnetite chemistry can distinguish between the Craters-derived tephras of the late Pleistocene Wilson Creek formation (Marcaida et al. 2014; doi: 10.1016/j.jvolfeores.2013.12.008).

Here we report titanomagnetite chemistry for Holocene and deglacial tephras in sediment cores from Mono Lake, from domes and craters of the volcanic chain, and in sediment cores from Crooked Meadows (37° 49' lat., -118° 50' long., 2680 m elevation), located south of the lake and east of the Craters. A pair of cores recovered from the Meadow are composed of alternating coarse tephra material and organic-rich muds and peats, providing abundant material for identified macrofossil AMS radiocarbon analysis, which indicates that the Meadow has existed since at least 13 ka. Titanomagnetite crystals separated from the sediment core tephra layers and outcrop samples have been analyzed by microprobe. As for previous studies, concentrations of FeO, MgO, and TiO₂ are most diagnostic in separating and matching tephras and vents. Unfortunately, titanomagnetites from the Crooked Meadows cores are frequently too altered to analyze, especially for tephras in the upper parts of the cores. In the lake cores, Holocene tephras are generally distinguishable from the Wilson Creek tephras, all of which are older than ~15 ka. A comprehensive fingerprinting of tephras and vents in the context of core age models will provide important new information on the age and evolution of volcanic activity in the Mono-Inyo Craters chain, as well as providing valuable dating and correlation tools for regional paleoclimate records.