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Stratigraphy and Correlation of Glacial Deposits of the Rocky Mountains, the Colorado Plateau and the Ranges of the Great Basin

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STRATIGRAPHY AND CORRELATION OF GLACIAL DEPOSITS OF THE ROCKY MOUNTAINS, THE COLORADO PLATEAU AND THE RANGES OF THE GREAT BASIN Gerald M. Richmond u.s. Geological Survey, Box 25046, Federal Center, MS 913, Denver, Colorado 80225, U.S.A. INTRODUCTION glaciations (Charts lA, 1B) see Fullerton and Rich- mond, Comparison of the marine oxygen isotope The Rocky Mountains, Colorado Plateau, and Basin record, the eustatic sea level record, and the chronology and Range Provinces (Fig. 1) together occupy much of of glaciation in the United States of America (this the western interior United States. These regions volume). include approximately 140 mountain ranges that were glaciated during the Pleistocene. Most of the glaciers Historical Perspective were valley glaciers, but ice caps formed on uplands Following early recognition of deposits of two alpine locally. Discussion of the deposits of all of these ranges glaciations (Gilbert, 1890; Ball, 1908; Capps, 1909; would require monographic analysis. To avoid this, Atwood, 1909), deposits of three glaciations gradually representative ranges in each province are reviewed. became widely recognized (Alden, 1912, 1932, 1953; Atwood and Mather, 1912, 1932; Alden and Stebinger, Purpose and Scope 1913; Blackwelder, 1915; Atwood, 1915; Fryxell, 1930; This report summarizes the evidence for correlation Bradley, 1936). Subsequently drift of the intermediate of the Quaternary glacial deposits in 26 broadly glaciation was shown to represent two glacial advances distributed mountain ranges selected on the basis of (Fryxell, 1930; Horberg, 1938; Richmond, 1948, 1962a; availability of detailed information and length of glacial Moss, 1951a; Nelson, 1954; Holmes and Moss, 1955), record. and the older drift was shown to include deposits of Because the glacial deposits rarely are traceable from three glaciations (Richmond, 1957, 1962a, 1964a). one range to another, time-parallel criteria such as Deposits of two glacial advances during the last reliable radiometric ages, identifiable tephra, and glaciation were recognized initially (Ives, 1938; Sharp, paleomagnetic reversals are most useful for correlation. 1938; Moss, 1951a; Horberg, 1954; Holmes and Moss, However, such criteria presently are not available in 1955; Eschman, 1955). Then three were delineated most ranges, and therefore many correlations are based (Singewald, 1950; Nelson, 1954; Richmond, 1960, on relative age criteria. A great variety of relative age 1962a, 1964a, 1965a) and subsequently four were criteria currently are being explored and tested. They differentiated (Kiver, 1968, 1972; Graf, 1971). Many of are referred to here without evaluation. For some the publications cited above include regional corre- ranges I suggest correlations on the basis of chronologie lations based on stratigraphic, morphologic, pedologic, controls from other ranges, as shown on Charts 1A and and weathering criteria. The names of glaciations in the lB. Wind River Mountains (Washakie Point (oldest), The text is intended as an expanded explanation of Cedar Ridge, Sacagawea Ridge, Bull lake, and Pine- the stratigraphic columns shown in Charts 1A and lB. dale) were applied as a standard throughout the Rocky The bases for the time divisions and the time scale are Mountains in order to reduce the complexity of discussed in Introduction to Quaternary Glaciations of nomenclature (Richmond, 1965). Currently these units the United States ofAmerica (Richmond and Fullerton, are undergoing revision and subdivision (Charts lA, this volume). The glacial deposits in each range are 1B). treated individually to emphasize, from range to range, Until the advent of radiometric dating, the ages differences in the character of the deposits, the number assigned to glaciations in the western mountains were of glaciations or glacial advances recognized, and the conjectural. Few workers attempted correlation with criteria for correlation utilized by different investi- the continental glaciations. The Wisconsin 'stage' was gators. The columns for Yellowstone National Park considered to be no older than 25 ka, and the term and for the Sierra Nevada are included for purposes of early Wisconsin was applied to the earliest 'substage' of chronologie correlation. For discussions of those areas the Wisconsin 'stage' (Horberg, 1954). In this sense, see Richmond, Yellowstone National Park, and Fuller- the Bull Lake glaciation in the Rocky Mountains was ton, Sierra Nevada, this volume. For discussion of the considered to be early Wisconsin (or 'Iowan') in age correlation of marine oxygen isotope stages with and the Pinedale glaciation was considered to be late 99 100 Quaternar y Sc ience Reviews . \ '":.. - -. - 100 laO III(ILO ME TEA S FI G . 1. Inde x map o f th e western interior U nited States showing A , Northe rn R ock y M ountainssouthof th e limit o f Co rdille ra n ice sheetglaciation;B,MiddleRockyMou nta ins ; C , Sou thern R ocky Mountains ; D , Colo rado Pl ateau; E, Ranges in th e Great Basin. Numbered dotsrepresent a reas of al pine glaciation d iscu ssed in text a nd shown o n C ha rts lA and lB. Area s of alpine glaciation on Figure 1 1: Glacier National Park , Montana. 15a: Front Range . Co lorado - east. 2: Elkh orn Mount ains, Montana. 15b: Front Range, Colorado - west. 3: North Bould er Mountains. Mont ana. 16a: Sawatch Range. Colorado - east. 4: Bull Mountain , Mont ana. 16b: Sawatch Range , Colora do - west. 5: Bitterroot Range, Montana. 17: San Juan Mount ains, Colorado. 6: Pioneer Mount ains, Montan a. 18: Sangre de Cristo Range , Colo rado- New Mexico. 7: Lemhi Rang e, Idaho. 19: Sierra Blanca, New Mexico. 8: Southwestern, Salmon River Mountains, Idaho. 20: Grand Mesa. Colorado. 9a: Wind River Range , Wyoming - east. 21: La Sal Mountains, Utah . 9b: Wind River Range , Wyoming - west. 22: Aquarius Plateau. Utah . 10: Bighorn Mountains, Wyomi ng. 23: San Francisco Peaks. Arizona. II : Northern Medic ine Bow Range , Wyoming . 24: White Mountains, Arizona. 12: Southern Medicine Bow Range , Colorado . 25: Ruby-East Humbolt Range . Nevada . 13: Uinta Mountains, Utah- Wyoming . 26: Wallowa Mount ains, O regon. 14: Wasatch Range , Utah . Quaternary Glaciations in the Northern Hemisphere IIII Wisconsin in age (Blackwelder, 1915, 1931; Alden, Colorado Front Range. Henry Schwarcz, McMasters 1932; Atwood and Mather, 1932; Bradley, 1936; Sharp, University, and Barney Szabo, U.S. Geological 1938; Horberg, 1954). Bryan and Ray (1940), in a Survey, determined a number of 234U/23oTh ages, and pioneering attempt to correlate glaciations with vari- Meyer Rubin provided a 14C age from the Wind River ations in the earth's insolation proposed by Milan- Range. John N. Rosholt, Jr., determined a uranium- kovitch (1930), suggested that a succession of moraines trend age from the Glacier National Park area. Helpful in Colorado, which they assigned to 'substages' of the discussions of specific areas with Richard F. Madole, Wisconsin, might be 122-111 ka, 78-67 ka, 29.5-19.5 Ralph R. Shroba, Kenneth L. Pierce, Glenn R. Scott, ka and 10 ka old, but they pointed out the lack of David W. Moore, Paul E. Carrara, Chester A. substantive evidence for those age assignments. The Wallace, Bruce H. Bryant, Edward T. Ruppel, William characteristics of the two oldest moraines of the M. Weber, and William C. Mahaney are gratefully succession are those that typify moraines of the Bull acknowledged. I am indebted to Richard F. Madole Lake glaciation (Richmond, 1962b). and David S. Fullerton for comment and suggestions Documentation of a post-Sangamon glacial advance for improvement of the manuscript. earlier than the Wisconsin 'stage' in the midcontinent region, based on 'greater-than' 14C ages (Flint and Rubin, 1955), was followed by assignment of its NORTHERN ROCKY MOUNTAINS deposits to an early Wisconsin 'substage' (Dreimanis, 1960a, b) or to an Altonian 'substage' (Frye and The Northern Rocky Mountains, south of the Willman, 1960) of a redefined 'Wisconsinan stage' southern limit of Cordilleran ice sheet glaciation, (Frye et al., 1968). The youngest Bull Lake Till in the include approximately 58 ranges in which alpine Rocky Mountains was correlated with till of the glaciers developed during the Pleistocene. Most were Altonian 'substage' (Richmond, 1965a, Table 2), from valley glaciers, but ice caps or coalescent glacier which 14C ages from about 35,000 BP to about 38,000 complexes formed on the uplands of at least four BP had been obtained (Frye et al., 1968). Morrison and ranges. The largest ice cap was in the unnamed broad Frye (1965) estimated that the Bull Lake glaciation mountainous area along the Continental Divide south occurred between about 72,000 and 32,000 BP. Later of Glacier National Park (Fig. 1, area 1). The glacial correlations of glacial deposits in the western U.S.A. deposits of most of the ranges have received very little (Birkeland et al., 1971; Porter, 1971; Flint, 1971) study. Those of eight are discussed here. utilized the sparsely available radiometric ages, dated tephra, and paleomagnetic reversals. Subsequently, till Glacier National Park, Montana in the Yellowstone Park area, correlated with the Bull Glacier National Park, in the Lewis Range, Mon- Lake Till in the Wind River Range, has been shown to tana, (Fig. 1, area 1), extends southward from the be lllinoian in age (Pierce et al., 1976; Richmond, International Boundary with Canada on both sides of Yellowstone Park, this volume). Two extensive post- the Continental Divide. The area is significant because Sangamon, pre-Wisconsin glacial advances of 'Eowis- the relationships of alpine glacial deposits to deposits of consin' age have been identified (Richmond, Yellow- both Laurentide ice sheet glaciation to the east (see stone Park, this volume) and an early Wisconsin Fullerton and Colton, Montana Plains, this volume) advance has been postulated (Pierce et al., 1976; and Cordilleran ice sheet glaciation to the west (see Richmond, Yellowstone Park, this volume). Thus, at Richmond, Cordilleran ice sheet, this volume) are least two, and probably three, glacial advances inter- demonstrable. vened between the Bull Lake and the Pinedale glaci- Deposits of seven alpine glaciations and two Lauren- ations in Yellowstone Park (Chart lA).
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