MAGNETOSTRATIGRAPHY OF THE MORRISON FORMATION, NORTHERN BIGHORN BASIN, WYOMING

Several paleoecological studies have been conducted on the Morrison Formation, including recent efforts by Turner and Peterson (2004) and Foster (2003). Most of the conclusions in these studies are based on lithostratigraphic correlations from the Colorado Plateau region, with the generalized stratigraphy extrapolated to the entire formation. The facies in the Morrison Fm. are time transgressive, as are most terrestrial deposits. Lithologic correlation of units from Colorado to Wyoming or New Mexico may represent similar sedimentary environments, not temporally similar facies. In order to draw specific conclusions about the ecology of the plants and animals preserved within the formation, temporal control of facies is necessary.

Field investigations within the Coyote Basin region of the Bighorn Basin have yielded fossilized vertebrate and plant material making a detailed paleoecologic study desirable. Using paleomagnetics, Swierc and Johnson (1996) were able to develop a preliminary magnetostratigraphy near this field area. I returned to the specific bonebeds in the field area—the Big Al, Siber, and VMNH quarries—and collected paleomagnetic samples from sections through the digsites. Preliminary results demonstrate that paleomagnetic samples obtained from the paleosols in the stratigraphic sections are viable, and I have identified reversals in the samples initially processed. I will present the expanded results of my paleomagnetic study comparing previous lithostratigraphic interpretations with the developed magnetostratigraphy, and showing the chronologic correlations of lithologies and dinosaur quarries within the Coyote Basin.