Dove Spring Formation
Dove Spring Formation
late to middle Miocene
Predominantly fluvial and lacustrine sediments interbedded with lesser pyroclastic deposits and lava flows occurring in the El Paso Mountains (in southeastern map area) and northwest-adjacent basin (Loomis and Burbank, 1988). Sedimentary deposits are quite varied and consist of arkosic to lithic sandstone, pebble to local boulder conglomerate, clay, mudstone, limestone, chert, and siltstone (Loomis and Burbank, 1988). Coarser clastic sediments are typically polylithic with predominantly plutonic and volcanic clasts. Sandstones are massive to planar bedded and cross bedded. Interbedded volcanics include pyroclastic flow and (some waterlain) pyroclastic fall deposits, tuff breccia, and basaltic lava flows. Upper unit of Ricardo Group defined by Loomis and Burbank (1988), unconformably underlain by lower unit (Cudahy Camp formation; map unit cuv). Composite stratigraphic thickness is 1,560-2,000 m (Loomis and Burbank, 1988). Contains Clarendonian vertebrate fossils (e.g., Cox and Diggles, 1986). Magnetostratigraphy established by Loomis and Burbank (1988) using the Clarendonian fossil ages, 8.4 ± 1.8 and 10.4 ± 1.6 Ma zircon fission-track ages (Cox and Diggles, 1986) and a 11.8 ± 0.9 Ma fission-track age from their study, gives an interpreted total age range of ~13.5 to ~7 Ma.