Award Date

5-1-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geoscience

First Committee Member

Stephen Rowland

Second Committee Member

Andrew Hanson

Third Committee Member

Fred Bachhuber

Fourth Committee Member

Levent Atici

Fifth Committee Member

Brett Riddle

Number of Pages

118

Abstract

Until 2004 very little paleobiology, let alone paleoecology, had been studied within exposures of the Sevier retro-arc foreland and hinterland, in the state of Nevada. This is due largely to poor and spotty exposure. This study focuses on taphonomic processes within three stratigraphic intervals in the foreland and hinterland of the Sevier retro-arc region, and what these taphonomic indicators reveal about the geography of the hinterland.

First, the Willow Tank Formation of southern Nevada was deposited in the foredeep of the Sevier retroarc foreland basin. This unit represents a multi-channel, aggradational, fluvial system that drained the Sevier highlands to the west. High amounts of volcaniclastic input have preserved a "snapshot" of a Late Cretaceous (Cenomanian) flora in situ. Representative taxa include the ferns Cladophlebis, cf. Matonia, and Tempskya; the horsetail Equisetites; the angiosperms Magnolia sp., Sapindopsis magnifolia; as well as unidentified taxa. These taxa are represented by various organs (leaves and stems) and are preserved in a manner which suggests rapid burial, likely in less than a year. This floral record aids in paleoecological reconstructions of an area very proximal to the Sevier fold and thrust front, a region not nearly as well documented as the backbuldge of the Sevier fold and thrust front (i.e., Cedar Mountain Fm of Utah) of this time interval.

Second, the Newark Canyon Formation of east-central Nevada has been interpreted as the deposits of an Early Cretaceous (Aptian) piggy-back basin. This study identifies a diverse vertebrate assemblage which includes fish, turtles, crocodilians, armored dinosaurs, iguanodontid dinosaurs, and theropod dinosaurs. This fauna is hosted within small-channel sandstones, lacustrine mudrocks, debris-flow conglomerates, and hyperconcentrated-flow cobbly mudrocks. These depositional settings indicate a region with some internal drainage, as well as significant topography, but similar in elevation to the foreland, based upon similar small vertebrate taxa.

Finally, the Sheep Pass Formation [Late Cretaceous (Maastrichtian)-Eocene] is interpreted as Sevier hinterland deposits. Unlike the Newark Canyon Formation, the Sheep Pass Formation is considered to be deposits of a basin analogous to those of the modern, highland Altiplano of South America, in this case Nevadaplano. This is a long lived lake basin, with debris flow deposits and occasional fluvial input. From this formation I have recovered a diverse invertebrate fauna, a limited flora, and a vertebrate fauna consisting exclusively of frogs. The frogs are preserved in various taphonomic modes, including attritional assemblages, reworked elements, and a frog bonebed. The biological remains suggest an environment which was cool, at least seasonally. Occurring during a global climatic optimum, the inferred cool climate reinforces the conclusion that the Sevier hinterland was a high elevation plateau, which agrees with the stable isotope data from another study, as well as with structural studies.

Keywords

Cretaceous Geologic Period; Newark Canyon Formation; Paleobiology; Paleoecology; Sevier hinterland; Sheep Pass Formation; Taphonomy; Willow Tank Formation

Disciplines

Geology | Paleobiology | Paleontology

Language

English


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