T211 The Mono Lake Basin: A Gathering of Disciplines

Tuesday, 11 October 2011
1:30 PM - 5:30 PM
Room M100DE

ORIGIN OF THE REMANENCE RECORDING THE MONO LAKE EXCURSION IN THE MONO BASIN, CA

Paper number: T211-12
Program: Technical Sessions
Time: 4:30 PM – 4:45 PM

Authors

Abstract

In the Mono Basin, CA, fine sand, silt, and volcanic ash deposited in Pleistocene Lake Russell are exposed on the margin of Mono Lake, the remnant of Lake Russell, and on Paoha Island in the lake. The silt records the Mono Lake Excursion (MLE)(Denham and Cox, 1971; Liddicoat and Coe, 1979) and several tens of thousands of years of paleomagnetic secular variation (Denham and Cox, 1971; Liddicoat, 1976; Lund et al., 1988).

The paleomagnetic directions and relative field intensity during the MLE are negative inclination (about -30˚) and westerly declination (about 290˚) during reduced intensity that are followed by steep positive inclination (about 85˚) and easterly declination (about 100˚) during high intensity at eight of 11 localities around Mono Lake. The three exceptions are at wave-cut cliffs on the east side of the lake where the negative inclination and westerly declination are absent (Coe and Liddicoat, 1994). On Paoha Island, the entire excursion is recorded.

X-radiographs of the sediment and lineation measurements show patterns of normal bedding with layers aligned such that the minimum axes are within 5-10˚of normal bedding, with 10 percent foliation and 1 percent lineation (Coe and Liddicoat, 1994).

We explored reasons for the absence of part of the MLE at the wave-cut cliffs beyond the interpretation of Coe and Liddicoat (1994) that paleomagnetic field strength is a controlling factor. The reasons might be the sedimentation rate – it is about 60 percent greater at the wave-cut cliffs than at Wilson Creek and Mill Creek on the western margin of the lake – and the grain size and percentage of Total Inorganic Carbon (TIC) in the silt, acting separately or in combination. At Mill Creek, which is about 15 km from the wave-cut cliffs on the opposite side of the lake, the percentage of the finer-grained (less than 2 microns) non-magnetic sediment fraction is less than at the wave-cut cliffs by a factor of two (2.1 vs 4.2), whereas nearly the opposite occurs for the TIC percentage by weight (14.1 vs 6.0) for the two localities.