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Geology and mammalian biostratigraphy of a part of the northern Cady Mountains, Mojave Desert, California

1980; United States Department of the Interior; Linguagem: Inglês

10.3133/ofr80878

2332-4899

Susan T. Miller,

Evolution and Paleontology Studies

Approximately 1250 ft (381 m) of interbedded basalt, tuff, and volcaniclastic sedimentary rock crop out in the northern Cady Mountains, Mojave Desert, California.These rocks are assigned to the Hector Formation of Woodburne, Tedford, Stevens, and Taylor (1974).Sediments in the Hector Formation accumulated in alluvial and lacustrine depositional environments.These environments occurred in a paleogeographic setting that incorporated a basin-plain complex of lakes, ponds, and marshes; a gently-inclined alluvial plain complex; and a distal alluvial-fan complex.Sediments deposited in these environments lapped onto an erosional surface that was developed on an older volcanic and sedimentary terrain.This terrain provided epiclastic volcanic and granitic constituents to the Hector Formation.Intermittent volcanism of basaltic and rhyolitic composition accompanied deposition of the alluvial/lacustrine sediments.The volcanic events are represented by a basalt flow and a rhyolitic ash-flow tuff, and by beds of vitric air-fall tuff that occur intermittently throughout the sequence. Radiometric age determinations and mammalian fossils indicate that the Hector Formation in the northernCady Mountains is early Miocene in age.Three volcanic units have yielded ages of 22.9 + 0.4, 18.6 + 0.2, and 17.9 + 0.3 m.y.b.p.Fossil mammals indicate an age span of early Hemingfordian through late Hemingfordian.The Hector Formation thus spans late Arikareean through at least late Heraingfordian time.Mammalian fossils from the Hector Formation are grouped into two local faunas: (1) the Lower Cady Mountains local fauna, and (2) the Upper Cady Mountains local fauna.The Lower Cady Mountains local fauna contains three taxa: Merychvus (Merychyus) sp., cf.M. (M.) calaminthus, Aletomerycinae, and Merychyinae The Upper Cady Mountains local fauna contains 7 taxa: Proheteromys sulculus, Tomarctus sp.cf.T. hippophagus, Merychippus carrizoensis, cf.Diceratherium sp., cf.Aepycamelus sp., Merycodus sp., and "Miolabis" cf.MM.* " tenuis.The Lower Cady Mountains local fauna is middle Hemingfordian in age.The Upper Cady Mountains local fauna is late Heraingfordian in age.117-'.'/•"/.»"*f'«V,/' *«."",',' >f \ ''*••*..