PRELIMINARY DETRITAL ZIRCON STUDY OF THE OLIGOCENE TITUS CANYON FORMATION, DEATH VALLEY, SUGGESTS CENTRAL NEVADA SOURCES

The Titus Canyon Fm., mapped and studied by Reynolds (1969), Sayer (1991), Snow and Lux (1999) and Niemi (2002), unconformably overlies Neoproterozoic to Cambrian strata in the upper plate of the Boundary Canyon Fault in the Funeral and Grapevine Mts. Its sources and relation to local faulting are poorly understood. In its type area (Titus Canyon), basal redbeds with angular clasts of underlying lithologies are overlain by fluvial/alluvial sandstones, conglomerates and lacustrine shales and limestone (variegated facies of Reynolds, 1969). Verterbrate fossils are Early Oligocene (Stock and Bode, 1935) and ca. 15 Ma and younger volcanic rocks overlie the clastic sequence. Conglomerates contain a high % of chert clasts that include red radiolarian-bearing chert and black chert with phosphatic concretions, similar to lithologies in the Golconda and Roberts Mountains allochthons (GA and RMA). Cobbles of conglomerate (Antler overlap assemblage?) include chert, quartzite and mafic volcanic clasts with distinctive lithologies like those in the Ordovician Valmy Quartzite. Carbonate clasts increase up-section as do volcanic ash-rich beds, which dominate the upper part of the section.

Two samples near the base of the unit near Monarch Canyon contain mostly Mesozoic detrital zircons, derived from batholithic rocks exposed to the west and north of the area (Triassic, Jurassic and Cretaceous peaks are represented). Two samples higher in the section have similar Mesozoic detrital zircon ages and prominent Cenozoic age peaks. Ages ca. 36 Ma (N=20) and 34-35 Ma (N=30) provide maximum depositional ages in agreement with fossil ages. Further analyses are planned.

The preliminary field and DZ data suggest derivation of the lower part of the Titus Canyon from the north, where zircon from caldera-forming eruptions of appropriate age could mix or be reworked with cobbles derived from the RMA and GA. Studies of basins in the southernmost Sierra by Lechler et al. (2013) describe Paleocene sections deposited near or at sea level so it is reasonable that northerly derived sediment might travel southward from sources in Nevada but the data question the position of the southern edge of the hypothetical Nevadaplano, its inferred extent, and proposed drainage divide.