INVESTIGATING THE ORIGIN OF PLATY LITHOID TUFA FROM THE WILSON CREEK FORMATION, MONO LAKE, CA
Israel Russell (1889, Artemisia Press) first described these exposed tufa deposits at length. He concluded that there were three forms of tufa deposited during the late Pleistocene: lithoid, dendritic, and thinolitic. Lajoie (1968, Berkeley Ph.D. thesis) also recognized these forms in the Mono Basin’s Late Pleistocene Wilson Creek Formation (WCF). He also distinguished a particular variety of the lithoid tufa, which he termed platy lithoid tufa; its origin remains enigmatic.
Our current stratigraphic work in the Mono Basin brings new observations of platy lithoid tufa to the discussion: 1) that the platy lithoid tufa is composed of twin laminae--one, detritus-rich and the other, less detritus-rich; 2) that an upward-growing, domal morphology characterizes their structures. Observations 1) and 2) suggest that these calcareous deposits are stromatolites.
We have investigated these stromatolites in the context of developing a fluctuation record of Mono Lake that spans WCF time. We dated some of these stromatolites using the U-Th system, and found some are as old as 49.21 ± 0.14 kyr. We hope to measure the stable carbon isotopic signature of the carbonates. This will allow aphotic- and photic-zone stromatolites to be distinguished from one another. Our goal is to use the measured ages from photic-zone stromatolites as a near-lake-level constraint. Additionally, we hope our investigations can provide a geologic and geochronologic context for future planetary explorations that target ancient microbialites.