SURFACE FIELD RECONNAISSANCE FOR BURIED LARGE VERTEBRATE FOSSILS AND DETERMINATION OF PETROPHYSICAL CHARACTERISTICS DIFFERENTIATED BY GEOPHYSICAL INSTRUMENTS SUCH AS A MAGNETOMETER: EXAMPLES FROM THE LANCE FORMATION OF EASTERN WYOMING

The Lance Formation of eastern Wyoming, Late Cretaceous (Maastrichtian) has yielded abundant vertebrate fossils, including dinosaurs, since the 19^th century. Buried fossil materials are often exposed by weathering and erosion and discovered protruding from outcrops or on the weathered surface of hills. There are, no doubt, many fossils still buried. Some of the partial skeletons that have been excavated may have additional disarticulated elements remaining buried a short distance away. Location and discovery of these missing parts could add substantially to the knowledge of such specimens. The Lance Formation of eastern Wyoming is renowned for its ironstone concretions that resemble large tree trunks. Some of the concretions contain vertebrate fossils. The sedimentary rocks are iron rich generally. The strata in parts of the section have iron concentrated in concretions or along fractures and joints, while in other areas the iron may be more evenly disseminated through the stratum. Not only are the distribution patterns of iron different in different parts of the stratigraphic section vertically and laterally, but the specific chemical state of the iron compounds varies as well. Fossils may contain iron compounds also. The factors that control the chemistry and distribution of the iron compounds are complex and related to depositional environment as well as post-depositional diagenetic conditions. Dinosaur excavation sites were chosen for their differing distribution modes of iron compounds. Field reconnaissance was conducted with a proton magnetometer. Contrasting patterns were encountered at the sites. Two sites were selected from which vertical cores and lateral extent samples were taken for petrophysical properties analysis in the laboratory in order to enable correlation with field data. This technique will not only facilitate the full recovery of disparate parts of disarticulated skeletons, but also new discoveries.