Date of Award:

2002

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Advisor/Chair:

W. David Liddell

Abstract

The Morrison Formation at Como Bluff, Wyoming, has been historically known for containing a rich source of Late Jurassic vertebrate fossils. However, when collected, most of these fossils were not positioned into a stratigraphic or sedimentologic framework. Research shows that the Morrison Formation at Como Bluff can be divided into three members. These members can be identified by lithologic and paleontological characteristics. The lower Morrison members include the Windy Hill Member and the recently described Lake Como Member. The Windy Hill Member primarily contains near-shore marine sandstone. Megavertebrate fauna is lacking. The Lake Como Member contains illitic clay in red and green mottled paleosols with caliche and thin sandstone beds. The fauna typically consists oflarge saurian and ornithischian dinosaurs. The upper Morrison Formation includes the Talking Rocks Member. This member contains gray-green smectite-rich mudstones. The Talking Rocks Member is generally calcareous and appears to have a megavertebrate fauna similar to the Lower Morrison. The upper part of this member is typically non calcareous and the fauna is more aquatic with turtles, crocodiles, fish and smaller ornithischian dinosaurs, including some species thought to be restricted to the Cretaceous Period. The contact between the Morrison Formation and the overlying Cloverly Formation is placed at the base of the Cloverly conglomerates, which are present throughout the region. In some areas, this boundary coincides with the Jurassic/Cretaceous boundary. However, in sections of the study area, a zone of kaolinitic carbonaceous shale with Cretaceous-like plant material can be found just below the Morrison/Cl overly contact. If this bed is Cretaceous in age, then the Morrison Formation at Como Bluff is in part Early Cretaceous and not restricted to the Late Jurassic.

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