Evidence for two pulses of glaciation during the late Proterozoic in northern Utah and southeastern Idaho MAX D. CRITTENDEN, JR.* u.s. Geological Survey. Menlo Park. Cal(lornia 94025 NICHOLAS CHRISTIE-BLICK Exxon Produclion Research Co .. P.o. Box 2189. How·lOn. Texas 77001 PAUL KARL LINK Deparlmelll olGeologl'. Idaho Slale Universily. Pocalello. Idaho 83029 ABSTRACT Correlation of the allochthonous, miogeo­ tochthonous structural settings (center right clinal glacial deposits with the single glacial edge in Fig. I) are parts of thin and locally A record of glaciation during late Prot­ unit present in autochthonous and parau­ deposited sequences in which mUltiple un­ erozoic time is preserved in a number of tochthonous platform sites is uncertain, but conformities attest to interruptions of sedi­ localities extending from the Sheep rock our interpretation of sedimentary facies and mentation, whereas most occurrences in the Mountains, Utah, to Pocatello, Idaho, and paleogeography suggests that only the allochthon (A in Fig. I) are parts of thicker from the Park City area 40 km east of Salt younger of the two episodes recorded in the sequences in which deposition apparently Lake City to the Deep Creek Range along allochthon is represented by the diamictites continued without major tectonic distur­ the Utah-Nevada line. Over much of this of the autochthon. bance into Cambrian time. In the au­ area, the glacial deposits and associated tochchthon, glacial sediments I accumulated rocks thicken westward and form the basal INTRODUCTION above thick trough deposits of Proterozoic part of a miogeoclinal wedge that accumu­ Y age or were deposited directly on crystal­ lated near the late Proterozoic and early Since Hintze (1913) and Blackwelder line basement of Archean and early Proter­ Paleozoic continental margin. In the east, (1910, 1925, 1932) first described them, the ozoic age. In the allochthon, similar and such deposits are thin and rest on Archean distinctive boulder-bearing black diamic­ apparently correlative glacial deposits are basement or rocks of Proterozoic Y age; in tites of northern Utah and southeastern intercalated with thick non-glacial sedi­ the west, they are part of thicker sequences Idaho have been ascribed alternately to gla­ ments and locally with submarine volcanic in which deposition apparently continued cial (Calkins and Butler, 1943; Crittenden rocks. In many areas, the base of these without significant interruption from late and others, 1952) and non-glacial processes allochthonous sections either is not exposed Proterozoic into Cambrian time. In many (Condie, 1967; Schermerhorn, 1974). The or is cut out by thrusts, but locally these places, the original continuity between the most recent studies by Varney (1976), Blick rocks unconformably overlie units of Pro­ western and eastern parts of the deposi­ (1979), and Ojakangas and Matsch (1980) terozoic X age not present within the tional wedge has been obscured by thrusting have provided definitive evidence of glacial autochthon. of Cretaceous and early Tertiary age that activity in the form of striated and faceted In the autochthon, and in some areas carried the thick basinal sequences eastward clasts, dropstones, isolated sand and gravel of the Charleston-Nebo allochthon (in over those deposited on the continental clots, and a striated glacial pavement. American Fork Canyon, for example) only platform. Recent mapping of Fremont Although interpretations differ as to the one unit of glacially related rocks has been Island in Great Salt Lake, the Wasatch details of paleogeographic setting and depo­ recognized, although there is evidence for Range between Ogden and Brigham City, sitional mechanisms, most authors now repeated fluctuations of the ice margin dur­ and the Sheeprock Mountains shows that agree that much of the diamictite was de­ ing over-all retreat (Blick, 1979; Christie­ glacial episodes represented either by dia­ posited in a glaciomarine environment. Sim­ Blick, 1980a). In several areas in the mictite or by dropstones enclosed in fine­ ilar rocks constitute the earliest deposits of allochthon, however, two glacial episodes grained laminated beds are separated by as the late Proterozoic and early Paleozoic can be recognized, separated by a sufficient much as 1,000 m of non-glacial deposits, miogeocline in many parts of the Cordillera thickness of non-glacial deposits to suggest including black slate, alternating graywacke (Crittenden and others, 1972; Stewart, 1972; that the two episodes were separated by a and siltstone, quartzite, and conglomerate. Christie-Blick and others, 1980). time interval perhaps as long as the Pleisto­ Using reasonable sedimentation rates for The diamictites are present in many areas cene. This paper presents the evidence for such deposits and by comparison with mod­ of northern Utah and southeastern Idaho ern analogues, we infer that two episodes of (Fig. I), and it was evident some time ago lin this paper. "glacial sediments" are ones that glaciation, each probably consisting of mul­ (Crittenden and others, 1971) that the dis­ accumulate in a glacial environment as defined by tiple advances and retreats, were separated tribution of these and overlying Paleozoic Boulton and Deynoux (1981). The term "non­ by a non-glacial interval of a few hundred rocks has been modified by tectonic trans­ glacial" is applied to sediments in which no gla­ cial influence has been detected. even though thousand to a few million years' duration. port that took place during the development some may have been derived by glacial activity or of the Cordilleran fold belt (King, 1969). As may have accumulated in an environment appre­ *Deceased. November 1982. a result, the rocks exposed in eastern au- ciably influenced by glacial meltwater. Geological Society of America Bulletin. v. 94. p. 437-450, 8 figs .. April 1983. 437 438 CRITTENDEN AND OTHERS Figure 1. Map of northern Utah and southeastern Idaho showing extent of Precambrian rocks and localities referred to in text. (I) Willard-Paris thrust; (2) Charleston-Nebo thrust; (3) concealed trace of inferred connection between 1 and 2; (A) area of allochthon referred to in text. this conclusion and assesses its significance for regional correlation of the upper Prot­ erozoic rocks. GLACIAL RECORD IN THE AUTOCHTHON Antelope Island Antelope Island (Fig. 1) is underlain tfl Area of Figure 2 mainly by granite gneiss inferred to be of Archean or early Proterozoic age (Bryant, 1980; Bryant and Graff, 1980; Hedge and others, 1983) and assigned to the Farming­ ton Canyon Complex (Eardley and Hatch, 0> 1940a). These crystalline rocks are overlain c::'" o Q:c unconformably by little-metamorphosed rocks of Proterozoic Z age, consisting of 45 m of diamictite, 40 m of pinkish-tan­ weathering laminated dolomite, and 35 m of EXPLANATION argillite (only partly exposed). These units are in turn overlain disconformably by an PhanerozoIc (0-570m.y.) \ D '" \\' indeterminate thickness, at least several tens @........ ~ Sail Lake Cily of metres, of light tan to pale gray cobble ~ Prole,ozoic Z (570-800m.y.) ". and pebble conglomerate and quartzite, representing the basal part of the Tintic D Prole,ozoic Y (800-1600 m.y.) Quartzite (Cambrian). That coarse-grained n:;\~~ A,chean (>2500 'fly) quartzite was, we believe, correctly identi­ fied as Cambrian by Eardley and Hatch z (1940b) but later was assigned to the Pre­ cambrian Mutual Formation by Larsen (1957), and this assignment was adopted for the geologic map of Utah by Stokes (1963). More recent comparisons with units ex­ posed in the Wasatch Range in both .he allochthon and autochthon confirm Eard­ ley's identification as the Tintic Quartzite and emphasize a close relationship to the exposures in the Farmington-Bountiful sec­ tion of the Wasatch Range (between Salt Lake City and Ogden) (Fig. 1), where the Tintic Quartzite rests directly on the Far­ mington Canyon Complex without any intervening rocks of Proterozoic Z age (Crittenden, 1972). These relations indicate that the line of zero thickness for Protero­ zoic Z rocks lies between Antelope Island EVIDENCE FOR PULSES OF GLACIATION 439 and the Farmington-Bountiful section of the margin of an ice sheet that reached the port on the Willard thrust (Crittenden, the Wasatch. sea. Christie-Blick (I 980a) cited evidence of 1961; Blick, 1979). The tectonic position of Antelope Island repeated glacial fluctuations during over-all The stratigraphically lowest and thickest is uncertain. Rocks exposed there are struc­ retreat but did not find evidence of pro­ section of the formation of Perry Canyon is turally beneath the Willard thrust (Fig. I; longed periods of entirely non-glacial depo­ in the upper plate of the Willard thrust, Crittenden, 1972), but they may be structur­ sition. An obvious problem is that in the beginning just south of the mouth of Perry ally above several thrusts that crop out in postulated glaciomarine environment the Canyon (Fig. 2), where the formation con­ southwestern Wyoming (see Royse and oth­ time interval represented by any particular sists of three units. The lower and upper ers, 1975; Blick, 1979). We therefore regard hiatus is difficult to evaluate. The most that units are composed of diamictite and the Antelope Island as autochthonous or can be said is that there is no evidence that intervening unit is interbedded graywacke parautochthonous. early glacial deposits within the Mineral and siltstone (see column 5 of Fig. 4 beloW). Fork had consolidated sufficiently to yield The lower diamictite, here about 365 m Mineral Fork Area clasts of diamictite to later glacial advances. thick, rests directly on the Facer Formation. Its thickness is variable along strike, how­ Glacial rocks older than the Cambrian GLACIAL RECORD IN ever; only 2 km to the east, it is a maximum Tintic Quartzite were recognized in the Cot­ THE ALLOCHTHON of 60 m thick and is locally absent. Where tonwood area (Fig. I) by Hintze (1913) and diamicite is missing, the base of the Perry by Calkins and Butler (1943) during map­ Mouth of Perry Canyon Canyon is marked by I to 5 m of coarse ping of the Alta and American Fork mining arkosic grit that grades upward into alter­ districts.