Investigations of the Origin of the Magnetic Remanence in Late Pleistocene Lacustrine Sediments in the Mono Basin, CA

Abstract:

In the Mono Basin, CA, fine sand, silt, and volcanic ash deposited in Pleistocene Lake Russell is exposed on the margin of Mono Lake, and on Paoha Island in the lake. The silt records the Mono Lake Excursion (MLE: Denham and Cox, 1971) and several tens of thousands of years of paleomagnetic secular variation (PSV: Denham and Cox, 1971; Liddicoat, 1976; Lund et al., 1988). The sediment is believed to be an accurate recorder of PSV because the MLE has the same signal at widely separated localities in the basin (Denham, 1974; Liddicoat and Coe, 1979; Liddicoat, 1992) with the exception at wave-cut cliffs on the southeast side of the lake (Coe and Liddicoat, 1994). Magnetite, titanomagnetite, and titanomaghemite are present in the sediment (Denham and Cox, 1971; Liddicoat, 1976; Liddicoat and Coe, 1979), which is glacial flour from the adjacent Sierra Nevada (Lajoie, 1968). X-rays of the sediment and lineation measurements show patterns of normal bedding with layers aligned such that the minimum axes are within 5-10 degrees of normal bedding, with 10 percent foliation and 1 percent lineation (Coe and Liddicoat, 1994).

We explore reasons for the difference in part of the PSV record at the wave-cut cliffs beyond the interpretation of Coe and Liddicoat (1994) that paleomagnetic field strength is a controlling factor. Possibilities include the sedimentation rate – at localities on the margin of Mono Lake the rate is about 60 percent less than at the wave-cut cliffs – and lithology of the sediment. At Mill Creek on the northwest side of Mono Lake, the non-magnetic sediment fraction is coarser-grained than at the wave-cut cliffs by a factor of about two, and there is a similar difference in the total inorganic carbon (TIC) percentage by weight for the two localities. (Spokowski et al., 2011) Studies of the sediment at two localities in the basin where the Hilina Pali Excursion (Teanby et al., 2002) might be recorded (Wilson Creek and South Shore Cliffs; Liddicoat and Coe, 2013) and at an extension of the PSV record of Lund et al. (1988) show a similar pattern to the grain size distribution and TIC percentage described above. Additional measurements of the TIC in the sediments from both sides of Mono Lake for the intervals recording the possible HPE and PSV extension of Lund et al. (1988) are in progress and will be presented.