User:Abyssal/Dawson Creek

Aguja Formation
Julia T. Sankey published a description of "multiple, closely associated mixed bone beds from the Aguja Formation". These bone beds date back to the Campanian and were discovered in the Big Bend area of Texas. The fossils in the bonebed originated as "components of channel lags during major flooding events". Sankey reports one of the bone beds producing the most complete known skull of Agujaceratops mariscaslensis. Paleosols associated with the bonebeds allowed her to correlate the bonebeds with the better studied Dawson Creek section to "provide a critical stratigraphic context" both for the A. mariscalensis skull and the bonebeds generally. Overall, the bonebeds represented a "rich assemblage of plants, invertebrates, and other vertebrates" and provide significant information about the local fauna, permitting scientists to compare the Late Cretaceous wildlife of the Big Bend area with the contemporary life of Montana and Alberta fossil sites.

The Tornillo Basin of western Texas bears sedimentary deposits representing shoreline, coastal plains, and alluvial sediments. These outcrops date from the late Campanian through the Paleocene and represent the southernmost formations from the timespan in the United States to preserve vertebrate fossils. Paleosols exposed at Dawson Creek in Big Bend have allowed scientists to construct a detailed framework for understanding the stratigraphy and ancient climate of the area. The Dawson Creek exposures are so informative that scientists have been able to estimate the ancient temperatures and rainfall levels of the area. Additionally, the Dawson Creek exposures record significant data about both middle and late Maastrichtian greenhouse events. In fact, the Dawson Creek strata are the only known series of terrestrial sedimentary deposits in the world to do so. The Tornillo Basin overall provides what Sankey characterizes as an "excellent record of the effects of the Western Interior Seaway's fluctuations on alluvial deposits". From the "lates" Campanian to the Paleocene the distance between the sohreline and the Tornillo Basin deposits varied from 100 to 500 km. The shoreline was less than 100 km away during the deposition of the Rattlesnake Mountain bone beds.

The vertebrate microsites of Rattlesnake Mountain are "hosted" by grey, silty mudstones that are rich in organic matter. These paleosols can be directly correlated to paleosols #42 and #43 of the Dawson Creek site on the basis of shared morphology, color, carbon and oxygen isotope ratios, and carbonate nodules in the ancient soil.

In 1986 Standhardt interpreted an ankylosaur tooth recovered from Dawson Creek as being from Euoplocephalus or a related animal. Sankey, however, noted that this "cf. Euoplocephalus" tooth closely resembled specimens she referred to Edmontonia.

Reference

 * Sankey, J.T. 2010. Faunal composition and significance of high diversity, mixed bonebeds containing Agujaceratops mariscalensis and other dinosaurs, Aguja Formation (upper Cretaceous), Big Bend, Texas; pp. 520–537. In: New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium, M. Ryan, B. Chinnery-Allgeier, and D. Eberth (eds). Indiana University Press (Bloomington).