by P. Allen Macfarlane, Alan Wade, and John H. Doveton
Kansas Geological Survey
Shell Western Exploration and Production
Kansas Geological Survey Open-file Report 91-1A
Recent coring and geophysical logging of test holes penetrating pre-Graneros Cretaceous strata in north-central Kansas were undertaken to assist ongoing research directed at updating our understanding of the stratigraphy of these units. These strata were deposited in environments that shifted laterally great distances in relatively short intervals of geologic time because of the low depositional slopes of the ramplike eastern margin of the Western Interior seaway (Hamilton, 1989). The results of this response to transgression and regression are sedimentary rocks deposited over wide areas that are of similar lithologies but of different age. Traditional description of these strata as lithostratigraphic formations, complicated by a sparsity of outcrops, the complex mosaic of lithofacies exhibited vertically and laterally, and the lack of stratigraphic markers has promoted correlation of strata of different age. The work reported here is directed toward developing a more consistent stratigraphic framework for these units. This research effort is being conducted as part of the Kansas Geological Survey's research program to evaluate the long-term water resources potential of the Dakota aquifer in Kansas.
The Dakota aquifer consists of strata from the Dakota Formation, Kiowa Formation and Cheyenne Sandstone. An integral part of the Dakota aquifer program is the definition of hydrostratigraphic units within this aquifer. A hydrostratigraphic unit is defined as a formation, portion of a formation, or group of formation that possess similar hydrologic properties and that can be grouped into aquifers, aquitards, or aquicludes (Maxey, 1964). Hydrostratigraphic units are used to understand regional ground-water flow patterns, which are an important constraint on the quantity and quality of ground water available to wells. Discussion is not limited here to the three formations that make up the Dakota aquifer but also includes the Graneros Shale, which is, in part, laterally equivalent to the uppermost part of the Dakota Formation.
Our purpose is to present and interpret the data collected from three test holes that were drilled by the Kansas Geological Survey in FY90 in Lincoln, Republic, and Washington counties and to include a stratigraphic interpretation of each core. Detailed descriptions of each core can be found in Appendix 1, Appendix 2, and Appendix 3. This FY90 data and other test-hole data from earlier test-hole drilling of the Haberer, Braun #1, and #1 Brungardt test holes, Russell and Ellis counties, are used to describe the stratigraphy of the units that make up the Dakota aquifer and to make comparisons between the subsurface sections. These earlier test holes are discussed by Macfarlane et al. (1990), Hamilton (1989), and Macfarlane and Hamilton (1990). Comparisons are also made with surface sections reported by Hamilton (1989) and others. Appendix 4 contains the geophysical logging data from the Braun #1 and #1 Brungardt test holes. Appendix 5 contains a description of the Haberer core.
Last, from these comparisons we make inferences concerning the paleogeography of Kansas at the time that these units were being deposited. Paleogeographic reconstruction is important because the major fluvial and deltaic systems controlled the deposition of sandstones, which are the principal water-producing porous media in the Dakota aquifer (Leblanc, 1972). Information on the location of stream valleys and delta systems at the time of deposition is a key element in the prediction of sandstone body trend and distribution and thus of hydraulic continuity. Locally, the more permeable aquifer units consist of sandstones that were deposited in stream valleys and in deltas. River and delta distributary channel sandstones differ hydrostratigraphically from other types of deltaic sandstones in their sandstone body geometry and in their permeability (Weber, 1982). River and delta distributary channel sandstones tend to be highly permeable, discontinuous, and ribbonlike in contrast to deltaic sands, which tend to be less permeable, continuous, and sheetlike. These sandstone aquifer units are embedded in finer grained shaly sediments, which are much less permeable and act as an aquitard.
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