Paper No. 3
Presentation Time: 8:30 AM
GEOCHEMICAL EVIDENCE FOR A GLACIOGENIC ORIGIN OF THE CRYOGENIAN WILDROSE DIAMICTITE, UPPER KINGSTON PEAK FORMATION, GOLER WASH, DEATH VALLEY, CALIFORNIA
Synrift sediments of the upper Kingston Peak Formation are widely interpreted to be glaciogenic based on evidence of massive diamictite lithofacies and their stratigraphic associations, faceted/striated clasts, and dropstones. However, diamictite facies may form by debris flows, for example, in tectonically active settings, as well as in glacial environments. Here we present new whole-rock geochemical evidence in support of a glaciogenic interpretation for the Wildrose Diamictite member of the Kingston Peak Formation using samples collected in Goler Wash, Panamint Mountains, Death Valley, California. There the Wildrose sits unconformably on granitic gneiss, and bedrock clasts dominate the lower part of the diamictite. Two samples of fresh basement were analyzed to test the degree to which they were chemically weathered and as a comparative reference for local bedrock composition; seven sedimentary samples include diamictite matrix and clasts, and interbedded argillite. Basement samples have chemical index of alteration (CIA) values ~50, indicating they are unweathered. A clast extracted from the diamictite matrix has a similar CIA value of ~50, and major-, trace-, and rare earth element (REE) abundances nearly identical to unweathered basement, which is consistent with derivation from local bedrock sources. Diamictite matrix has low CIA values (48-55), consistent with very little chemical weathering and similar to other glaciogenic diamictites. Matrix samples possess overall REE characteristics similar to the basement and clasts in the diamictite. Strong variation in Ti and nearly constant Al suggest deposition of the diamictite matrix samples took place in a setting characterized by minimal weathering and moderate sorting. Matrix materials are also enriched in MgO, total FeO, Sc, V, Cr, Co, and Ni relative to basement samples, consistent with preferential accumulation of biotite and ‘mafic’ minerals in the matrix due to physical abrasion and sorting during transport. In association with textural and stratigraphic aspects, the low CIA values for the bedrock and diamictite indicate the Wildrose accumulated in a paleoenvironment characterized by intense physical comminution but minimal chemical weathering, consistent with previous interpretations for a glaciogenic origin.