Cold water carbonate deposits of Quaternary Lake Russell, California

For ~150 years, the lakes & Quaternary lacustrine sediments of the Great Basin of western United States have provided investigators with exceptional opportunities to examine past regional climate and hydrology changes. In addition, several of the extant lakes allow researchers to gain critical insight into a number of important sedimentological processes, ranging from carbonate & evaporite mineral formation and diagenesis to turbidity flow mechanisms. The spectacular exposures of shoreline and nearshore lacustrine tufas in the Lahontan Basin, in particular, have long attracted the attention of geochemists, mineralogists and limnogeologists. At Pyramid Lake, the largest remnant of Lake Lahontan, the fabric and crystal morphologies of much of the material making up the impressively large tufa mounds have suggested that at least part of this carbonate was precipitated originally as the mineral ikaite (CaCO3 6H2O) associated with spring discharge sites at near-freezing lake bottom conditions. Similarly, although much less well-studied, late Pleistocene-early Holocene tufa mounds and deposits of the Wilson Creek Formation of Lake Russell, the precursor of Mono Lake in eastern California and not a contiguous part of Lake Lahontan, have also been attributed to cold-water ikaite formation between ~9-12k years ago. Although biological activity and microbial processes have been linked to many lacustrine carbonate mineral formation processes, and modern ikaite deposits elsewhere often host highly diverse biological communities, surprisingly little is known about the specific role of organisms in ikaite formation in Great Basin lakes. Indeed, it is usually tacitly assumed the long, delicate “thinolite” crystals of Lahontan & Russell are the result of displacive inorganic chemical precipitation within the lake sediments. We are investigating the detailed petrography and morphology of the Lake Russell tufas in an effort to compare with those of the older Lake Lahontan deposits and to disentangle the role of organisms from that of abiological groundwater/lake water mixing. These data and interpreted formative processes will help us better understand this strategically important mineral.Angelo State Undergraduate Faculty Mentored Research Progra