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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Robert F. Diffendal, Jr., Publications Natural Resources, School of 1984 Cenozoic Geology of the Southern Nebraska Panhandle: Old Valleys, Volcaniclastics, and Vertebrates: 1984 Fall Field Trip, Nebraska Geological Society James B. Swinehart University of Nebraska-Lincoln, [email protected] Robert F. Diffendal Jr. University of Nebraska-Lincoln, [email protected] Mary Rebone University of Nebraska-Lincoln Robert Hunt University of Nebraska-Lincoln, [email protected] Follow this and additional works at: http://digitalcommons.unl.edu/diffendal Part of the Geology Commons, Geomorphology Commons, Hydrology Commons, and the Stratigraphy Commons Swinehart, James B.; Diffendal, Robert F. Jr.; Rebone, Mary; and Hunt, Robert, "Cenozoic Geology of the Southern Nebraska Panhandle: Old Valleys, Volcaniclastics, and Vertebrates: 1984 Fall Field Trip, Nebraska Geological Society" (1984). Robert F. Diffendal, Jr., Publications. 47. http://digitalcommons.unl.edu/diffendal/47 This Article is brought to you for free and open access by the Natural Resources, School of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Robert F. Diffendal, Jr., Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. CENOZOIC GEOLOGY OF THE SOUTHERN NEBRASKA PANHANDLE Tbrr Tah - (:...• Tb w....... "r- ) ................ ~ .... ' ..... Tbrr - -~-~~ ~ ............. ~; : .:.~ .. ~. ~~.~}.~ ::. '. :::.:;.::. ~ ,., .. +••••• .r ••••~... "0 0. ~. --' .. ' .'. .... ~ .' ... .., ......... s.:.............. .... Tbw __----- '. 0, ............ ~:.,:~ ... .... ·····.4 ... OLD VALLEYS, VOLCANICLASTICS, AND VERTEBRATE! 1984 Fall Field Trip Nebraska Geological Society LEADERS: JAMES SWINEHART MARY REBONE R.F. DIFFENDAL, JR. - 'V' Scale 1: 500,000 10 0 10 20 MU.. fS • ECHHHHI I I I 10 0 10 20kM H H H H H I I ---, Contour Interval 200 feet LOCCfho't) or Smps NEBRASKA GEOLOGICAL SOCIETY 1984 FALL FIELD TRIP LIST OF PARTICIPANTS Damon Brown Jim Kearney 812 W. ~1yrtle 4226 Locust St. Fort Collins, CO 80521 Lincoln, NE 68516 Colorado State University SCS George F. Engelmann Mi ke Leite Geog/Geol, UNO 1635 F St., No.6 Omaha, NE Lincoln, NE 68508 UNO - Geology UNL - Geology Al Fagerstrom Nan Lindsley-Griffin 420 Morrill Hall 433 Morrill Hall UNL - Geology Lincoln, NE Lincoln, NE 68588 UNL - Geology Robert Goodwin Dave Loope 433 Morrill Hall 1263 So. 20th, #2 Lincoln, NE 68588 Lincoln, NE UNL - Geology UNL - Geology John R. Griffin Greg Ludvi gson 4920 Woodland Ave. 123 North Capital St. Lincoln, NE 68516 Iowa City, IA 52240 Geo 1ogi c Consul tant Iowa Geological Survey Ann Guhman Ginny Maciel P.O. Box 94814 6208 Parker St. Lincoln, NE 68509 Omaha, NE68104 UNL - Geology UNO - Geology Joel Haverland Dave May 830 N' 36 601 E. Eagle Heights Lincoln, NE Madison, WI 53705 UNL - Geology University of Wisconsin Eric Hubbard Michael T. McCawley 328 West St. 4035 S. 30th Fort Collins, CO 80521 Lincoln, NE 68502 Colorado State University USDA - SCS Bob Hunt Mary Rebone 433 Morrill Hall 433 Morrill Hall Lincoln, NE Lincoln, NE 68588 UNL - Geology and UNSM UNL - Geology Denny L. Jorgenson Richard S. Rhodes II 4948 N. 113th 2014 Rochester Ave. Omaha, NE 68164 Iowa Ci ty, IA 52240 UNO - Geology University of Iowa Christin Scholting 4510 South 18th St. ()naha, NE 68107 UNO - Geology Rob Skolnick W436 Nebraska Hall Lincoln, NE 68588 UNL - Vert. Paleo. Mark C. Spencer 1302 Marbee Dr., #6 Omaha, NE 68124 UNO - Geology Jim Swinehart 113 Nebraska Hall, UNL Lincoln, NE 68588-0517 Conservation & Survey Div. LLoyd Tanner RR#2, P.O. Box 469 North Platte, NE 69101 130~ fI:t~e5c.St Wayne Vanek Scottsbluff Soil Survey Office 4502 Ave. I,· Scottsbluff, NE 69361 Soil Conservation Service Mike Voorhies W428 NH, UNL Lincoln, NE 68588 Univ. Neb. State Museum Michael Walter 3474 S. 82nd St., Apt. #1 Omaha, NE 68124 UNO - Geology Stephen White ASH 228, UNO . ()naha, NE UNO - Geology Janet L. Wright 3715 So. 33rd St. Lincoln, NE UNL - Geology NEBRASKA GEOLOGICAL SOCIETY FIELD TRIP CENOZOIC GEOLOGY OF THE SOUTHERN NEBRASKA PANHANDLE Sept-ember 8, 1984 Cumulative Mi leage 0.0 7:00 a.m. assemble at Bell Diner, Bridgeport. Drive north on U.S. 26 0.2 Cross North Platte River 0.7 Jct of U.S. 26, 385 and Union Pacific Railroad, keep right 14.9 Broadwater 15.2 Jct U.S. 26 and Neb. 92, continue southeast on 26 20.9 Road to Rush Creek Land and Cattle Company, Foremans Ranch, of the Duer Ranch locality. 22.1 STOP 1 - Duer Ranch. Park on north si de of road east of sand dr aw and ins i de gate. DUER RANCH LOCALITY, MORRILL COUNTY, NEBRASKA James B. Swinehart and R. F. Diffendal, Jr. Conservation and Survey Division University of Nebraska-Lincoln Lincoln, Nebraska 68588-0517 The Duer Ranch locality contains some of the finest and most easily accessible examples of different styles of alluvial cuts and fills in the Cenozoic of Nebraska. It offers a unique area in which to examine the geometries and alluvial fills of several Miocene and Pliocene age paleovalleys and paleogullies. Good exposures of eolian volcaniclastic siltstones and a regionally important volcanic ash of the Oligocene age Brule Formation are also present at the Duer Ranch locality. Deposits of Oligocene through Quaternary age are exposed along the deeply incised intermittent stream valleys on the Duer Ranch (fig. D-1 and 2). The oldest of these units is the Whitney Member of the Bru 1e Formation, White River Group. The Whitney is usually considered the uppermost of the two Brule members recognized in western Nebraska (the other being the Orella). However, recently Souders et al (1980) have presented evi dence that another uni t, i nforma lly named the Brown 2. Siltstone beds, can be recognized above the Whitney in many places in western Nebraska. ~.- .~ -R 47 W I---"""'---~",~,",~ .." ..----.", }-~---.,,",""""""~!-~~'--' ...... -~;.-.. --... 23 ..", - Figure 0-1. Ouer Ranch locality. Base is from U.S. Geological Survey Tar Valley SW (contour interval 20 ft) and Broadwater (contour interval 10 ft) 7.5' quadrangles. The Whitney Member is a massive to crudely bedded volcaniclastic siltstone containing abundant smectite and carbonate cement. There are at least two prominent vitric ash beds (tuffs) exposed in the Whitney (fig. 0-2). The lowest of these ashes, easily visible from Highway 26 in the NE! sec. 10, T. 18 N., R. 47 W., is the Upper Ash of the Whitney, a regional marker bed for much of the Nebraska Panhandle. The Lower Ash of the Whitney (figs. 0-2 and 3), an even more extensive marker bed, was identified in test hole 24-A-53. Siltstones of the Whitney Member are very well sorted and contain an average of 50% relatively unaltered rhyolitic glass shards (fig. 0-4) and an estimated 30% volcanically derived plagioclase and rock fragments in the coarse silt and very fine sand fractions. These characteristics combined with the general lack of stratification and scarcity of fluvial sequences suggest that most of the Whitney was deposited by the wind and accumulated on upland surfaces where organisms and pedogenic processes >­ a:: 8 <X Dune sand an d loe ss z ~ a:: w t­ <X ~ B o Allu vium and colluvi um , und ifferentiat ed 22 0 1/2 1M --------------- I I 0 .5 I "LO MET! w I . I I z w Bro adwa te r Forma ti on u o .. ..... ~ ....J lliETIj· ~Tbrr :: a.. ...•... : ...•. Broadwa ter Format ion, Remsburg--------------- Ranch beds OGALLALA GROUP Ash Hol low Format ion ~ w z w u o· I o Duer Ra nch beds '. :E ~- AR IKAREE GRO UP 0 Tbr Har rison and Monroe Creek formations, undifferentiated 0 ~- w ' . ' Zw { WH ITE RIVER GROUP uo 8"""F bw.':" (.!) " ::::i Bru le Formation , Wh itney Member o Contact exposed (dos!led where opproKimole) Volca ni c- ash bed Sand and grovel channel (on ow indicoles flow direclion) AI lA' Line of geo log ic sect ion ~ Loca tion af mea su red secti on Figure 0-2. Geologic map of the Ouer Ranch locality. destroyed most stratification. The pyroclastic material was derived from volcanic vents in the western U.S. with the San Juan volcanic field of southwestern Colorado one of the most probable sources. Regional studies of the Whitney indicate that it is a blanket with the Upper and Lower ash beds present over thousands of square kilometers of western Nebraska. These studies add additional strength to the concept of a primarily loessic upland origin for the Whitney. The upper 15 to 30 m of Whitney Member mapped in the western quarter of the locality (figs. 4 SOUTH NORTH A A' Tbr. .... Broadwater Formation Loess Tbrr ... Broadwater Formation, Remsburg Ranch beds 122Q 4000 Tah .... Ash Hollow Formation Td ...... Ouer Ranch complex ....J ~ 1190 To ..... Arikaree Group 3900 L;:! w > ....J W oCt ....J W oCt en 1160 3800 W w en > 5t'... /4!.. Fo .. no,Q-r 10 "" W o > CD I3 rouo"" S, I+:sione ~s: o : 1130 3700 ~ a:: w I­ I­ W W W u.. ::::!: 1100 +++Upper Ash . Tbw Brule Formation 3600 Whitney Member 1070 3500 Vertical ..a99&ralion X 20 A o I MILE ~I----------~,----~I o I KILOMETER Present land surface -. 1220 4000 ~ 1190 3900.....J > W w > .....J UJ ....J <t ~ 1160 3800 ~ UJ en > UJ o > aJ ...... o <t 1130 b]• ·.··0·" 3700 ~ en .. t=::.:.::1 a:: So nd and gravel Silly sandstone I­ UJ UJ I­ UJ UJ E:9 ~ Ea . 3600 LL ::::!: 1100 Sandy siltslone Siltstone-mudstone Calcareous Volcanic aah bed and 1070-c~~~~~==~~==~~~ ______________________~.~~~ca~n~ic~la~st~ic~s"~im~.~nt~ __________~ 3500 o I MILE 13 rl----------,,----~I o I KilOMETER Figure 0-3. A. Geologic section along line A-A'. Lower Ash of Whitney projected from Conservation and Survey Division test hole 24-A-53, 1.2 kilometers west of section; B.

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