Evidence for two pulses of glaciation during the late Proterozoic in northern Utah and southeastern Idaho

Abstract

A record of glaciation during late Proterozoic time is preserved in a number of localities extending from the Sheep rock Mountains, Utah, to Pocatello, Idaho, and from the Park City area 40 km east of Salt Lake City to the Deep Creek Range along the Utah-Nevada line. Over much of this area, the glacial deposits and associated rocks thicken westward and form the basal part of a miogeoclinal wedge that accumulated near the late Proterozoic and early Paleozoic continental margin. In the east, such deposits are thin and rest on Archean basement or rocks of Proterozoic Y age; in the west, they are part of thicker sequences in which deposition apparently continued without significant interruption from late Proterozoic into Cambrian time. In many places, the original continuity between the western and eastern parts of the depositional wedge has been obscured by thrusting of Cretaceous and early Tertiary age that carried the thick basinal sequences eastward over those deposited on the continental platform. Recent mapping of Fremont Island in Great Salt Lake, the Wasatch Range between Ogden and Brigham City, and the Sheeprock Mountains shows that glacial episodes represented either by diamictite or by dropstones enclosed in finegrained laminated beds are separated by as much as 1,000 m of non-glacial deposits, including black slate, alternating graywacke and siltstone, quartzite, and conglomerate. Using reasonable sedimentation rates for such deposits and by comparison with modern analogues, we infer that two episodes of glaciation, each probably consisting of multiple advances and retreats, were separated by a non-glacial interval of a few hundred thousand to a few million years' duration. *Deceased. November 1982. Correlation of the allochthonous, miogeoclinal glacial deposits with the single glacial unit present in autochthonous and parautochthonous platform sites is uncertain, but our interpretation of sedimentary facies and paleogeography suggests that only the younger of the two episodes recorded in the allochthon is represented by the diamictites of the autochthon.

Chapter 7: Middle and Late Proterozoic rocks and Late Proterozoic tectonics in the southern Beaverhead Mountains, Idaho and Montana: A preliminary report

“…Correlation chart of Late Proterozoic and Cambrian rocks in the southern Lemhi Range (Derstler and McCandless, 1981;McCandless, 1982;Ruppel and Lopez, 1988;Kuntz and others, 1992), southern Beaverhead Mountains (this chapter), and Pocatello area (Link, 1983;Link and others, 1987;Kellogg and others, 1989).…”

“…11;Harper and Link, 1986;Link, 1986;Link and others, 1987; Levy, 1989). The distinctive volcanic and diamictitebearing strata of the Pocatello Formation (Link, 1983) at the base of the Late Proterozoic section near Pocatello (Fig. 2) are absent in the southern Beaverhead Mountains.…”

Discussion on chemostratigraphy of predominantly siliciclastic Neoproterozoic successions: a case study of the Pocatello Formation and Lower Brigham Group, Idaho, USA

“…In light of the latest available information, Shield's interpretation of the Sr-isotopic data and our interpretation of the C-isotopic data are both inconsistent with post-Varanger sedimentation. Our respective interpretations of the isotopic data do not, in and of themselves, preclude an interglacial Varanger age for the succession, but the fact that uppermost Pocatello and lower Brigham strata lie above the younger of two Pocatello glacial pulses (Crittenden, Christie-Blick & Link, 1983) makes this correlation unlikely. Further, such a correlation would require the deposition of more than 2000 m of shallow marine and braided fluvial strata between stades of Varanger glaciation; in fact, these strata contain several orders of depositional sequence and sequence boundaries, including one interpreted as the eustatic signature of Varanger glaciation (Levy, Christie-Blick & Link, 1994).…”

Global synchronous initiation of the 2nd episode of Sturtian glaciation: SIMS zircon U–Pb and O isotope evidence from the Jiangkou Group, South China

“…The diamictite of the Scout Mountain Member was regarded as a stratigraphic equivalent of the Sturtian glacial successions in South Australia. Therein, the Scout Mountain Member comprises also two diamictite units separated by a thick siliciclastic succession intercalated with tuff beds, in particular the lower and upper diamictite units are also an indication of two episodes of Sturtian glaciation (Crittenden et al, 1983), a case exceedingly resembling the Jiangkou glacial succession in South China. Fanning and Link (2004) sampled from three horizons below, within and over the upper diamictite in order to bracket its depositional age.…”

“…In contrast, the timing, number, and duration of the Sturtian glaciation remain disputable and unresolved (Allen and Etienne, 2008;Hoffman and Li, 2009), which continues to hamper our understanding of ice sheet dynamics during the snowball Earth interval. Within the framework of Sturtian glaciation, two episodes of glaciation as represented by two glaciogenic diamictites have been recognized (Crittenden et al, 1983;Link et al, 1994;Keeley et al, 2012;Balgord et al, 2013). Recent zircon U-Pb ages documented from northwestern Canada and South China have constrained the onset age of Sturtian glaciation to ca.…”