Vertebrate Paleontology and Magnetostratigraphy of the Upper Aguja Formation (Late Campanian), Talley Mountain Area, Big Bend National Park, Texas.
Date of Award
Doctor of Philosophy (PhD)
Geology and Geophysics
Judith A. Schiebout
Considerable north-south latitudinal diversification existed among vertebrate faunas along the Western Interior Seaway during the late Campanian; this has caused difficulty correlating isolated faunas, especially southern ones, which contained endemic taxa and often lack non-paleontologic age control. The Talley Mt. local fauna is a late Campanian vertebrate fauna from the upper Aguja Formation, Big Bend National Park, Texas. It is one of the southernmost late Campanian vertebrate faunas, and is one of the few associated with magnetostratigraphy. The fauna is from five channel deposits, spanning 20 meters of section, from the lower portion of the upper shale member of the Aguja Formation. Deposition occurred within a coastal floodplain during the final marine regression from the area. Fossils were recovered by bulk sampling ($\sim$1630 kg) and acid-disaggregating pedogenic nodule-rich, carbonate-cemented, conglomeratic rocks. The fauna contains 35 terrestrial and aquatic taxa, including 8 chondrichthyans, 2 actinopterygians, 3 amphibians, 1 trionychid turtle, 4 squamates (including Chamops and Peneteius sp. nov., new records for the Aguja), 5 crocodylomorphs, 6 dinosaurs, and 6 mammals (Cimolomys sp., Meniscoessus sp., cf. Cimexomys, Paracimexomys sp., Alphadon cf. A. halleyi, and A. cf. A. sahnii). Aquatic taxa decrease in abundance upsection, reflecting the marine regression from the area and the beginning of drier, more seasonable climates. The fauna is taxonomically similar to the nearby Terlingua local fauna, but with significant taphonomic and sampling differences. The 52 meter paleomagnetic polarity sequence contains two reversed polarity zones, and is correlated to the base of Chronozone 32 based on the Tudithian taxa in the fauna and on the ages of underlying and overlying Aguja deposits. On the basis of this correlation and on average sedimentation rates of 29 meters/million years (My), the Talley Mt. local fauna is approximately 73.6 to 74.3 Ma.
Sankey, Julia Tippins, "Vertebrate Paleontology and Magnetostratigraphy of the Upper Aguja Formation (Late Campanian), Talley Mountain Area, Big Bend National Park, Texas." (1998). LSU Historical Dissertations and Theses. 6762.