Magnetostratigraphy of the Upper Jurassic Morrison Formation at Dinosaur National Monument, Utah, and Prospects for Using Magnetostratigraphy as a Correlative Tool in the Morrison Formation

Abstract

The terrestrial deposits of the Upper Jurassic Morrison Formation, western USA, have been intensively studied since the discovery of their well-preserved and diverse dinosaurian fauna. The broad geographic area and large time interval represented by the formation makes it an ideal candidate for the study of biodiversity patterns, population ecology, and morphological evolution through time, with environment and with latitude, but attempts to use it for such studies have been hampered by a lack of long-range correlation. We collected magnetostratigraphic samples near Dinosaur National Monument, Utah, in order to examine the magnetostratigraphy of this heavily studied area, and assess the prospects of using magnetostratigraphy as a correlative tool in the Morrison Formation. A magnetic reversal immediately above the quarry sand at Dinosaur National Monument, in combination with an existing radiometric date, allows us to constrain the age of the historic dinosaur quarry to 150.91–150.04 million years. Along with radiometric dating, magnetostratigraphy is useful for tightly constraining the ages of dinosaur quarries to allow faunal comparisons through space and time. Problems encountered during sampling might be alleviated by collecting hand specimens in Morrison mudstones.