ML18229A321
| ML18229A321 | |
| Person / Time | |
|---|---|
| Site: | 04008943 |
| Issue date: | 12/31/1985 |
| From: | NRC/OGC |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| References | |
| RAS 54407, ASLBP 13-926-01-MLA-BD01, 40-8943-MLA2 | |
| Download: ML18229A321 (5) | |
Text
UNITED STATES OF A MERICA NUCLEAR REGULATORY COMMISSION ATOMIC SAFETY AND LICENSING BOARD In the Matter of CROW BUTTE RESOURCES, INC. (Marsland Expansion Area) Docket No. 40-8943-MLA-2 ASLBP No. 13-926-01-MLA-BD01 Hearing Exhibit Exhibit Number: Exhibit Title:
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SJ/ ~EST-CENTRAL UNITED ST ATES R. M. FLORES AND S. S. KAPLAN , EDITORS DENVER, CO LORADO 1985 CENOZOIC PALEOGEOGRAPHY OF WESTERN NEBRASKA \ James B. Swinehart Vernon L. *souders Harold M. O e Graw Robert F. Diffendal, Jr. Conservation and Survey Division-IANR University of N ebras ka--L-incoln
- L inc oln, NE 68588-0517 ABSTRACT The Cenozoic strata of western Nebraska are an extensive sequence of continental depos i ts that extend eastward from th e Hart vi 1 le, Laramie, and Front Range uplifts and southeast from the Black Hills. The oldest Cenozoic sediments (Chadron Formation, Wh ite River Gfoup) are Early Ol i gocene al l uv i al val l ey fil l s. Subsequent to filling of these drainages and continuing for about the next 7 m.y., landscape dev elopment in western Nebraska was dominated by eol i an deposition of tremendous volumes of rhy olitic volcanic ash derived from western eruptions. A p 1 a in of 1 ow relief, with only an occasional narrow drainage heading in the wes te r n high l ands, was maintained during most of this per iod. Upl ift in the Rocky Mountains and Great Plains (pre-Gering Formation, Arika r ee Group) cau sed erosion and brought epicla stic detritus into the area about 28 m.y. ago. Eol ian sediment consist i ng mostly of pyroclastic detritus continued building the plains during and after Gering alluvial deposition until about 19 m.y. ago when Arikaree deposition ceased. About this time, western volcanic activi ty declined for several mi 1 lion years and was followed by a marked decrease in the volume of rhyolitic volcan ism for the remai nde r of the Cenozoic.
At the end of Arikaree deposition in western Nebraska, a major pu l se of eros ion (p r e-Runn i ngwater Formation, Ogallala Group) was fol lowed by a fundamental change in depositional style and landscape evo lution, terized by a heterogeneous mixture of epiclastic valley fi 1 ls. Sands and grave l s from Rocky Mountain sources were f irst deposited in a major valley in the northern half of the area and later in valleys to the south. Episodic regional and local structural ments influenced the size and position of many Ogallala valleys. For the past 5 m.y. degradation, in response to major regional uplift, has great l y exceeded aggradation as the dominant factor affecting landscape evolution in western Nebraska.
INTRODUCTIO N This report is a genera 1 out 1 i ne of successive cha n ges in the Cenozoic landscape of western Nebraska.
209 It also pres en ts some new interpretations on the r o le of structure in inf l uencing regional depos i tional and eros io nal patterns in this area. Lugo and Lugo ll956) presirnted the first attempt at a regional synthesis of Tertiary paleogeography of Nebraska.
Since 1956, many outcrop studies and paleonto l ogic invest ig at ions have modiified understa n ding of the geology of western Nebraska.
In addition, ana ly s i s of a large amount of subsurface information has provided new insights into the stratigraphy of the region and furnished a data base for paleogeographic interpretations which would be ioopossible to achieve from outcrop studies alone. The surface of Cenozoic rocks in the study area forms an eastward sloping plain from the Laramie Rangii-Hartv i lle Uplift in Wyoming (Fig. 1) that has been deeply eroded in the North Platte River valley and a 1 ong the Pine Ridge (Fig. 2). Dune sand covers most of the east central part of the area. face da t a used in this report came from electric logs of approximately 11,600 oi 1 and gas tests and from samples and electric logs of about 500 test holes WYOMING SO U T H DAKO T A C O L ORA D O I OO MIL ES ,........,_.
....,...~
50 ICIO l(I LOMETfRS K enn e dy O o s i n KANSAS vs Fi gu re 1. Index map of study area and major regional uplifts and basins.
J. B. SWINEHART, V. L SOUDERS, H. M. DEGRAW, AND R. F. DIFFENDAL, JR. I JoJ Ogo lla lo Group
- Ar i k or ee G r o up White R ive r Group 0 Crefoceous rocks 1111111111 F a ult (down-thr o wn side /Joch11red)
Figure 2. Ge nera l iz ed geo l ogic map of we s t ern Nebraska. Pos t-O gal l ala rocks (Plioc ene and yo ung er) not shovm. C re ta ceou s rocks refer to P i erre Sha le in t he north an d F ox Hills Sandstone in Scotts Bluff County. O nl y known f a u lts wi th appa r e nt t hr ows in exces s of 100 f t (30 m) are shown. 210 G:>' I t dri i t s tic GE beE Ger For Int Net anc ho, ca, re Cl, 2) gr , yo, del Wh OV* ro va lo di Ne an se SU sp se gr of Or mi Fe Bt S( We G I WI f al 1 t d 1 g w 1 f n J. B. SWINEHART , V. L. SOUDER S, H. M. DEGRAW , AND R. F. DIFFENDA JL, JR. I I A l SOUTH "' A' I ... ... NORTH \> "' I :,. -o ,) "' ~* =>:.:: I \3 ... 0<( "' :,. G 0:: V>c, ii: w w I C z V) 0:: I Ow 0 ,_ ,_ ! w I w :;; w li ... 0 w w 0 0 I 0 0 ::, ::, st ,_ t !: ;:: T r ans itio n zone, Pierre Shale -' ,_ Sha l e <I -' I <I 0 P i erre Sho l e 0 0 2 0 \i 0 I "' vs ... B "' ... ., i \3 "' SOUTH :,. ., I f 0 V, ii: s' -' <( 0 1 0:: ., NOR T H ... <->1~ I.) .... -0 t 0 z ! ... V) ., 0 :,. ,_ 0 ii: 0:: *r w w w 0 ,_ ... st w :::. w 0 w ::, 0 t-0::, ;:: 0 ,_ 0--' -,_ <( P ierre -' <I P i err e Shole Shale 0 0 0 VS ... "' ., C :,. "' ii: c' SOU T H *:::: t Sond H i l ls NORTH Cl Cl ,_ 0 o-w 0 V, w 0 -0: ... 0 w 0 t-w "' w 0 :;; ::, [ ,_ ? w ' t-0 -' ::, <( ,_ 0 0 :i 0 0 <( "' P i erre Sha l e [ ', J S Figure 5. Geo l ogic sections across study area. Br u le Fo r mation, Arikaree**troup and Og a llala Group are subdivided i n selected areas as fol l ows: A-B r ow n Siltsto n e beds; B-Ge ri ng F ormation; C-M on r oe .. , 214
~I [l] Wj CJ 1-w w .... O* W EST 0 0 0 "' -o w O c,O ::::, <t I-I-..J c,: 0 0 0 "' E WEST 0 0 0 "' -o I-0 WO w <t .... w 0 ::::, I-I-0 ..J 0 c,: 0 "' 0 CENOWIC PALEOGEOGRAPHY OF ~7ES TERN N E BRASKA I ~,t Tro n si t io/1 zo n e, Pierre '$h o l e P ie rre Sho l e P i erre Shale E' EAST 0-Q*(/) N 0:: -*w 1-w ::;; w a ::::, I-g~ O'.) o* E A ST 0 0 >J;) (/) a; w 1-w 0::;; N W -o ::::, I-..J c,: ~..1..Ve_r.11
,-. cl.o-1 -e x_o..J g Lg-e-ro-t-io_n _x_l_0_6 ___ 0 ____________ 4_o_M_I L-E-S--------'----'."', 8' Sou th Dakota C' O ua lerna r y de posits Plio cene depos i ts Og a ll ala Group I I I 0 4 0 KI LO M ETE R S 11111 Arikaree Grou p L ii! Br ul e F or mol ion 1111 C h a dr o n F o rmatio n L o wer A sh of Whitney M emb er, Brule Formation
~It F a u lt Arrows indicG*t e direct i on of relat i ve mo,,ement.
Oas/Jed w he r e in fer red. E E o,__..,___, >, 3: A B Colorado Creek-Harrison formations; 0-Upper Harrison beds; E-Runnin9water Formation; F-S h eep Creek and Olcott formations; G-Ash Hollow Formation.
215 C i' ; o'