Geologic Studies of the Platte River, South-Central Nebraska and Adjacent Areas—Geologic Maps, Subsurface Study, and Geologic History
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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Publications of the US Geological Survey US Geological Survey 2005 Geologic Studies of the Platte River, South-Central Nebraska and Adjacent Areas—Geologic Maps, Subsurface Study, and Geologic History Steven M. Condon Follow this and additional works at: https://digitalcommons.unl.edu/usgspubs Part of the Earth Sciences Commons Condon, Steven M., "Geologic Studies of the Platte River, South-Central Nebraska and Adjacent Areas—Geologic Maps, Subsurface Study, and Geologic History" (2005). Publications of the US Geological Survey. 22. https://digitalcommons.unl.edu/usgspubs/22 This Article is brought to you for free and open access by the US Geological Survey at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Publications of the US Geological Survey by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Geologic Studies of the Platte River, South- Central Nebraska and Adjacent Areas—Geologic Maps, Subsurface Study, and Geologic History Professional Paper 1706 U.S. Department of the Interior U.S. Geological Survey Geologic Studies of the Platte River, South-Central Nebraska and Adjacent Areas—Geologic Maps, Subsurface Study, and Geologic History By Steven M. Condon Professional Paper 1706 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey Charles G. Groat, Director Version 1.0, 2005 This publication and any updates to it are available online at: http://pubs.usgs.gov/pp/pp1706/ Manuscript approved for publication, March 3, 2005 Text edited by James W. Hendley II Layout and design by Stephen L. Scott Any use of trade, product, or fi rm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government Cover—View from the bridge over the Platte River just south of Overton, Nebraska, looking downstream (to the east). (USGS photo taken in 2002 by Steven M. Condon.) III Contents Abstract ------------------------------------------------------------------------------------------------------ 1 Introduction -------------------------------------------------------------------------------------------------- 1 Acknowledgments ------------------------------------------------------------------------------ 3 I. Geologic maps of the Elm Creek West and Newark 7.5 minute quadrangles ---------------------- 3 Introduction -------------------------------------------------------------------------------------------- 3 Methods ------------------------------------------------------------------------------------------------ 3 Elm Creek West quadrangle ------------------------------------------------------------------------- 4 Description of map units ----------------------------------------------------------------------- 4 Discussion --------------------------------------------------------------------------------------- 5 Logs of test holes in the Elm Creek West quadrangle -------------------------------------- 7 Newark quadrangle ---------------------------------------------------------------------------------- 12 Description of map units ---------------------------------------------------------------------- 12 Discussion -------------------------------------------------------------------------------------- 13 Logs of test holes in the Newark quadrangle ----------------------------------------------- 16 II. Subsurface Cenozoic geology of south-central Nebraska ----------------------------------------- 22 Introduction ------------------------------------------------------------------------------------------- 22 Methods ----------------------------------------------------------------------------------------------- 22 Subsurface geology --------------------------------------------------------------------------------- 23 III. The development of the Cenozoic Platte River drainage system --------------------------------- 31 Introduction ------------------------------------------------------------------------------------------- 31 Structural setting ------------------------------------------------------------------------------------- 32 Precursor events ------------------------------------------------------------------------------- 32 Laramide orogeny ------------------------------------------------------------------------------ 33 Geologic history of the Tertiary and Quaternary ------------------------------------------------- 34 Paleocene --------------------------------------------------------------------------------------- 34 Eocene ------------------------------------------------------------------------------------------ 35 Oligocene --------------------------------------------------------------------------------------- 39 Miocene ----------------------------------------------------------------------------------------- 40 Pliocene ----------------------------------------------------------------------------------------- 43 Pleistocene ------------------------------------------------------------------------------------- 45 Holocene ---------------------------------------------------------------------------------------- 49 Discussion and Summary --------------------------------------------------------------------- 51 References Cited ------------------------------------------------------------------------------------------- 54 Figures 1. Regional map of study area in parts of Wyoming, Colorado, Nebraska, and Kansas ------------ 2 2. Location map of the subsurface study area in south-central Nebraska -------------------------- 22 3. Structure contour map drawn on top of Precambrian rocks --------------------------------------- 23 4. Chart showing Cenozoic stratigraphic units in south-central Nebraska, northeastern Colorado, and southeastern Wyoming ----------------------------------------------- 24 5. Unconformity surface on top of Cretaceous rocks in south-central Nebraska ------------------ 25 IV Figures 6. Isopach map of the Ogallala Group ----------------------------------------------------------------- 26 7. Unconformity surface on top of the Ogallala Group or Cretaceous rocks in south-central Nebraska ------------------------------------------------------------------------------ 27 8. Isopach map of fluvial Pliocene and Pleistocene sediments in south-central Nebraska ---- 28 9. Isopach map of loess intervals in the Pliocene and Pleistocene section in south-central Nebraska ------------------------------------------------------------------------------ 29 10. Isopach map of all Pliocene and Pleistocene alluvium in south-central Nebraska ----------- 30 11. Paleogeography in Paleocene time ----------------------------------------------------------------- 33 12. Paleogeography in Eocene time --------------------------------------------------------------------- 36 13. Photo of middle-Eocene erosion surface in the Front Range. View is northeast from Green Mountain --------------------------------------------------------------------------------- 37 14. Paleogeography in Oligocene time ----------------------------------------------------------------- 38 15. Paleogeography in Miocene time ------------------------------------------------------------------- 42 16. Paleogeography in Pliocene time ------------------------------------------------------------------- 44 17. Paleogeography in Pleistocene time --------------------------------------------------------------- 47 Plates 1. Geologic map and topographic profile of the Elm Creek West 7.5 minute quadrangle 2. Geologic map and topographic profile of the Newark 7.5 minute quadrangle 1 Geologic Studies of the Platte River, South-Central Nebraska and Adjacent Areas—Geologic Maps, Subsurface Study, and Geologic History By Steven M. Condon Abstract recognized on the west side of the Medicine Bow Mountains of Wyoming in the Miocene, and the presence of distinctive rock clasts indicates that the Laramie River fl owed from the The Platte River of south-central Nebraska was studied at North Park area of Colorado northeast across a fi lled Laramie three scales to place the river in its geological context and to Basin and the Laramie Range of southeastern Wyoming in the trace its evolution through geologic time. At the largest scale Miocene. The present drainage system developed in the late the Elm Creek West and the Newark 7.5 minute quadrangles Miocene to the Pliocene and included the capture and diver- were mapped. These quadrangles are located just west and sion of the South Platte River into its present channel. The just east of Kearney and serve to illustrate the main geomor- combined North and South Platte Rivers deposited gravel and phic elements of the present Platte River Valley. The central sand across Nebraska and fl owed southeast from Kearney, elements of the quadrangles are the Platte River channels, Nebraska through the middle to late Pleistocene. Within the islands, and bottomlands, which are fl anked by terraces that past 25,000 years the Platte River below Kearney was cap- step up away from the river to the north and south. Signifi - tured and diverted into its present course and confi ned there by cant other elements of the landscape are eolian sand and loess bounding valley walls of loess. deposits. The geologic maps are supplemented by topographic profi les of the mapped terraces and graphical representations of subsurface units in test wells that occur within the quad- rangles. Introduction An intermediate-scale study consisted of