DEVELOPMENT OF A SCIENTIFIC DRILLING PROGRAM IN CENOZOIC STRATA OF THE GREAT PLAINS IN KANSAS AND NEBRASKA

The Kansas Geological Survey (KU) and the School of Natural Resources (UNL) are partnering on an effort to retrieve long drillcores of unconsolidated Cenozoic terrestrial strata from the Great Plains, including the Miocene Ogallala Formation. Drillcore samples from unsaturated sediments are most effectively cored with hollow-stem auger drill rigs with split spoon samplers. Drillcore samples from deeper water-saturated sediments can only be retrieved using a rotosonic drill rig with hydraulic piston core barrel. The retrieval of long cores provides high-quality samples for detailed sediment characterization with allied laboratory studies, and eliminates many uncertainties about lithology and precise stratigraphic position that have long hampered regional subsurface analyses of Cenozoic units in the Great Plains. Moreover, long-term curation of these research cores will provide continuing opportunities for scientific research long into the future. In central Kansas, drilling activities are now completed in units of the so-called “Equus Beds” – Plio-Pleistocene units filling the McPherson Channel. This resulted in three cross-channel drilling transects consisting of 15 cores with a cumulative thickness of 439 m. In southwest Kansas, the HP1A core in Haskell County has a current depth of 98 m, with more yet to come. Retrieved core samples from the HP1A core have been characterized by sedimentologic analyses, stable isotope chemostratigraphy, magnetostratigraphic analyses, and continuing geochronologic studies that indicate the presence of thick Eocene-Oligocene deposits that were previously unknown in Kansas. A drilling transect across the Cimarron River Valley in southwest Kansas is currently in progress, with 88 m of core already in hand; this drilling is intended to constrain interpretations of Plio-Pleistocene fluvial incision into the High Plains surface. In the Niobrara River Basin of Boyd County, in northern Nebraska, 60 m of core penetrating the Ogallala Fm and underlying Cenozoic units is already in hand. All cores sampled in this program are subject to sedimentologic logging, high-resolution chemostratigraphic studies of organic δ¹³C, and extraction of volcanogenic zircon phenocysts from mudstone paleosols for U/Pb geochronology using LA-ICP-MS equipment at the University of Kansas.