Surficial Geology of the Naper 7.5 Minute Quadrangle, Nebraska Portion R.M. Joeckel1, S.T. Tucker2, L.M. Howard1 and M.S. Kuzila1 1Conservation and Survey Division, University of Nebraska-Lincoln 2Highway Paleontology Program, University of Nebraska State Museum, University of Nebraska-Lincoln Kp Pierre Shale (Upper Cretaceous, Campanian-Maastrichtian) Qakp2 Young Quaternary alluvium of the Keya Paha River (Late Holocene) Qapc4 Older Quaternary alluvium of Ponca Creek (Holocene) Overview of the Nebraska Portion of the Naper Quadrangle Version 1.0, September 2013 Gray to dark gray (weathering light gray, olive gray, olive brown, grayish brown, pale brown, Very pale brown, pale brown, brownish gray, and grayish brown, well-sorted very fine sand and Gray, light brownish gray, very pale brown, and brown sandy silt, silty fine sand and fine to Geographic Setting and Geomorphology and pale yellow) silt shale to clay shale, with rare, very thin to thin beds of siltstone, very fine silty very fine sand. coarse sand. sandstone, and bentonite, as well as some beds of chalky limestone. The Naper Quadrangle lies almost entirely within northern Boyd County, Nebraska (a very small 99°07'30" 490000mE 491 492 493 5' 494 495 496 2'30" 497 498 0499 99°00' These deposits are associated in most places with visible meander scrolls and flood channels. Areas mapped as Qapc4 are comparatively smooth-surfaced and have been in long-term part of it lies within Gregory County in southern South Dakota). Only that portion of the 43°00' 43°00' The Pierre Shale is mapped on the slopes of the river valleys. Approximately 200 ft (61 m) of Most areas mapped at Qakp2 were wooded in the late 1930s and remain at least partially wooded agricultural use (likely more than a century). These areas probably never experience overbank quadrangle lying in Nebraska is presented as a geologic map in this document. T. 95 N. T. 95 N. GREGORY CO SOUTH DAKOTA GREGORY CO flooding. Since the entrenchment of Ponca Creek, these deposits are now part of one or more 1 upper Pierre Shale strata underlie the north valley wall of the Keya Paha River. These steep today, indicating that these areas have been stable for several dec ades at minimum. Areas 8 BOYD CO 1 5 9 NEBRASKA BOYD CO T. 35 N. T. 35 N. 5 0 0 alluvial terraces. The Naper Quadrangle lies southward and westward of the Laurentide glacial limit, on the Nov slopes are prone to mass wasting. mapped as Qakp2 were indeed present at the time of the first aerial photography of the region in 1 Qal Kp W W 8 Qal 5 1938, but General Land Office (GLO) maps from the 1890s do not show the course of the Keya eastern Great Plains. The northern half and southern one-quarter of the Naper Quadrangle lie 0 1 5 4 80 Kp 0 1 1 1 Qp1 1 8 1 R R within the United States Department of Agriculture Natural Resources Conservation Service 9 Paha in sufficient detail to allow an early historic qualification of the age of these deposits. 0 8 Alluvial sands on high terraces (Pleistocene) 0 0 Qas 1 0 0 8 0 0 Qapc2 Qf 0 W Broadwater Formation (Neogene; Pliocene) These deposits may be as young as early historic, but additional age control is available. Areas (NRCS) Major Land Resource Area (MLRA) 66 Dakota-Nebraska Eroded Tableland, whereas Nov 1 Nb 8 0 19 20 21 22 23 24 19 0 mapped as Qakp2 consist of silty surface strata underlain by sands and they may be flooded at Very pale brown, well- to moderately sorted, very fine to fine sands containing granules and the slopes along the valleys of the Keya Paha and Niobrara rivers are included in MLRA 63B 000m 20 1 47 50 9 47 60 N 5 60 Southern Rolling Pierre Shale Plains (United States Department of Agriculture, Natural 0 White and light brown, medium to very coarse sands and pebbly to cobbly sands, as well as high flow stages of the Keya Paha River. Mapping units Qakp2 and Qakp3 (below) include a pebbles. 0 5 8 a few, very low terraces. Resources Conservation Service, 2006). 1 1 c 1 9 1 n gravels. 0 8 Po 8 0 5 5 0 Qapc2 0 2 Qapc4 Kp In the Naper Quadrangle, deposits mapped as Qas contain few to common granules to pebbles of 0 0 0 Qp1 17 The topography of the Naper Quadrangle is varied and the landscape is scenic. The total relief 50 This unit is mapped in the uplands near the western edge of the quadrangle, where it overlies Qakp3 Quaternary alluvium of the Keya Paha River (Holocene) crystalline rock types (e.g., granitic rocks and vein quartz), as well as clasts of opaline and carbonate-cemented sandstones eroded from the Ogallala Group. Multiple clasts of Ogallala on the land surface within Nebraska portion of the Marty Quadrangle is greater than 450 ft (137 1800 strata of the Ogallala Group. Diffendal et al. (2008) mapped the Broadwater Formation at a very coarse scale of resolution in this part of Boyd County. Very pale brown, pale brown, brownish gray, and grayish brown, well -sorted very fine sand and Group sandstone, with what appear to be spherulitic carbonate cements, were found in a roadcut m), from the lowest elevation in the Niobrara River Valley to the flat summits of hills at the 19 western margin of the map in section 31 of T. 35 N., R. 15 W. and section 6 of T. 34 N., R. 15 00 silty very fine sand. between sections 20 and 21 of T. 34 N., R. 15 W., at the edge of the ancient alluvial terrace 0 5 C Qapc4 W. Topographic subdivisions within the Naper Quadrangle are as follows: 0 1 0 re between the Keya Paha and Niobrara rivers. 2 9 Nov 5 e Fort Randall Formation of the Ogallala Group (Neogene, Middle Miocene) Nb 0 8 k Nofr 0 1 4759 Qal 4759 Areas mapped as Qakp3 are distal floodplain deposits that appear smooth -surfaced in aerial Kp Kp photography dating back to 1938. Alluvial deposits in these areas must be older than those in the Qes1 Eolian sands locally reworked from alluvial terrace sands (Quaternary) 1. The valleys of the Keya Paha and Niobrara rivers (Fig. 1) in the southern half of the map, 20 1 Massive, laminated, and rippled light gray, yellow, pale yellow, and light yellowish brown 5 0 9 18 1 0 5 5 5 8 as well as that of Ponca Creek in the northwestern quarter of the map. The northern 9 0 0 0 more proximal mapping units Qakp1 and Qakp2. Areas mapped as Qakp3 consist of silty 30 1 25 0 weakly-consolidated siltstones, which locally contain nodules of authigenic carbonate; also 29 27 Qp1 valley wall of the Keya Paha River, which is eroded into the Pierre Shale, is steep and 28 26 30 includes beds of light yellowish brown and pale brown well-sorted very fine to fine sands and surface strata underlain by sands and it is likely that they a re very rarely, if ever, flooded. White to very pale brown fine sand. 1 2 9 0 0 5 heavily dissected; it exhibits more than 300 ft (91 m) of relief. Pierre Shale is also 0 Nov 0 lenses of pebble to cobble gravels. Mapping units Qakp2 and Qakp3 include a few, very low terraces. 1950 This unit is mapped in the southern third of the quadrangle atop the ancient fluvial terrace ezposed on the lower slopes of the valley walls of Ponca Creek. 1 This unit is lithologically distinct from the upper part of the Ogallala Group in the area, and we Quaternary alluvium of smaller streams (Holocene to modern) between the Keya Paha and Niobrara rivers. It is interpreted as wind-reworked alluvial terrace Qal 1 9 1 Qal 9 9 5 0 0 2. The dissected flats atop the divide between Ponca Creek and the Keya Paha River, in the 0 1 Qp1 0 0 7 50 have mapped it as the Fort Randall Formation on the basis of a comparison with Skinner and sediment. Qp2 middle of the map area. These flats slope gently southeastward and they are underlain by W Nov Qp1 Taylor (1967), who described the type section of that unit in the Bijou Hills in northeastern Clayey silt, silt, sandy silt, and sand. Nov 4758 4758 Charles Mix County, South Dakota. Our mapping of the Fort Randall Formation can be Qes2 Eolian sands locally reworked from alluvial terrace sands, with a surficial silty component Late Pleistocene loess and the Miocene sediments of the Ogallala Formation, and they considered provisional pending a complete re-examination of Neogene stratigraphy in the Small, low-order streams in the mapped area deposit clayey silt, silt, sandy silt, and fine to (Quaternary) have several, small, ovoid deflation basins that contain water during wet periods. A few, Qf 2 2 0 northwest-to-southeast-oriented erosional remnants of Ogallala Group strata rise from 0 0 0 5 0 1 0 0 0 8 enclosing region of Nebraska. Fossils from the Fort Randall Formation in its type area place it medium sand. Streams draining basins dominated by surficial materials of either Peoria Loess or 0 85 50 2 2 1 these flats, the highest and most prominent being the Twin Buttes (Fig. 2) in the southern 0 0 within the span of the Barstovian North American Land Mammal Age (16.3- 13.6 Ma).