Abstract
The outcrop belt of the Upper Jurassic Morrison Formation in the northeastern Uinta Basin and southeastern flank of the Uinta Mountains is particularly rich in dinosaurian and non-dinosaurian faunas, as well as in fossil plants. The discovery of several well-preserved, relatively intact, fossil logs at several locations in Rainbow Draw and one location in Miners Draw, both near Dinosaur National Monument (Utah), has provided an opportunity to study the local paleobotany, stratigraphy, and sedimentology of the Morrison Formation in northeastern Utah.
Highlights
The Upper Jurassic Morrison Formation is a spectacular and recognizable formation across the Colorado Plateau, and is distinctive because of its array of rainbow-colored mudstone, siltstone, and sandstone beds that typically form a “badlands” landscape
The purpose of this study is to describe the Morrison Formation strata, especially those related to the fossil logs, and to place the logs within a stratigraphic framework for the interpretation of the depositional environment of the log-bearing intervals at both locations
The fossil logs in both the Miners Draw and Rainbow Draw areas occur in the Salt Wash Member of the Morrison Formation
Summary
The Upper Jurassic Morrison Formation is a spectacular and recognizable formation across the Colorado Plateau, and is distinctive because of its array of rainbow-colored mudstone, siltstone, and sandstone beds that typically form a “badlands” landscape. Sections of the Morrison Formation were measured at the Miners Draw and Rainbow Draw areas to describe beds and place the fossil log sites in stratigraphic and sedimentological context. At the Miners Draw area, several sections were measured to capture the entire Morrison Formation (Windy Hill, Tidwell, Salt Wash, and Brushy Basin Members) and the stratigraphic horizon of the fossil log site because distance between base and top of the Morrison is large and complicated by being exposed on the nose of a southwest-plunging anticline (figure 4). The measured section of the Salt Wash Member began at the eastern group of logs along a small drainage that contains the top of the Stump Formation to the top of a ridge where the fossil log-bearing interval and the overlying marker bed are exposed (figure 5A). Concurrent systematic work will prompt a nomenclatural transfer of this species to the genus Agathoxylon (Gee and others, 2019)
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