| Measurement of the major, minor, and trace element composition of the rocks from the Lower Triassic Union Wash Formation of east-central California was performed at two localities (Union Wash, CA and Darwin Hills, CA) in order to reconstruct sedimentological and environmental conditions during deposition. Results indicate that concomitant enrichment of Mo and V and positive Cerium anomalies in the Union Wash area suggest deposition under quiet, moderately deep bottom waters that were anoxic and punctuated by periods of euxinia. At Darwin Hills, recurrent negative Cerium anomalies and Cr, FeO, and V enrichment indicate that relatively higher oxygen levels occurred in a shallower, nearshore environment where anoxia was disrupted by lengthy episodes of denitrification and oxygenation.; Productivity is generally low throughout the Union Wash Formation, except for peaks near the base of the middle member at Union Wash and in subunit A of the upper member at Darwin Hills. Higher levels of Cu, Mo, Ni, V, and Zn in the Union Wash area suggest high productivity led to the development of euxinia. Oxygen-depleted conditions existed during deposition of most of the formation and during periods of high and low productivity, suggesting that both regional and global marine processes affected the region.; Lack of abundant fossils, except for pelagic organisms such as ammonoids and conodonts, coupled with the presence of anoxia, low levels of productivity, and CO2 degassing, demonstrate deposition under persistent harsh environmental conditions, and concomitant dampening of the biotic recovery in the study area. |
