USING GIS AND PHOTOGRAMMETRIC METHODS TO INTERPRET AND DIGITALLY PRESERVE FLUVIAL ICHNOFOSSIL ASSEMBLAGES, OLIGOCENE BRULE FM, NORTHWEST NEBRASKA, USA

An extensive suite of tracks and trackways is preserved in sheet sandstones of the Orella Member, Brule Formation (Oligocene) at Toadstool Park in northwestern Nebraska. We interpret the sheet sandstone as the result of an avulsion flood event which swept over the floodplain, leaving up to 1 meter of medium coarse sand. Most primary sedimentary structures have been destroyed by bioturbation. Upper parts of the sandstone preserve tracks and trackways of Subhyracodon, Poebrotherium, Mesohippus, entelodonts, oreodonts, birds and invertebrates. The period during which tracks were actively being preserved was likely short as burial would have taken place rapidly. The Toadstool trackways thus preserve a snapshot of life on an active floodplain. The various track morphologies combined with textural differences within the sheet sandstone offers a rich source of detailed information about the geologic environment in which they were formed. Experimental photogrammetric documentation of the trackways is proposed as a technique allowing their detailed study by multiple researchers while effectively preserving fragile ichnological information whose primary sources are being destroyed by weathering, erosion, and vandalism. Further study using methods adapted from LIDAR laser scanning and geographic information systems is hoped to reveal ichnological details unavailable by traditional means.