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Late Proterozoic Paleogeography of the Eastern Great Basin

LEVY, MARJORIE, and NICHOLAS CHRISTIE-BLICK, Lamont-Doherty Geological Observatory, Palisades, NY

Detailed facies interpretation, sequence stratigraphy, and palinspastic reconstruction lead to insights into the Late Proterozoic paleogeographic evolution of the eastern Great Basin. Palinspastic reconstruction of Mesozoic to early Cenozoic crustal shortening and middle to late Cenozoic crustal extension indicate that the late Proterozoic basin of the western United States was only about 60% of its present-day width. More than 3 km of late Proterozoic predominantly siliciclastic strata were deposited in this basin in southeastern Idaho, western Utah, and eastern Nevada prior to continental separation in the latest Proterozoic or Early Cambrian, and represent a variety of depositional environments including basinal

marine, shallow marine, braid delta, braided fluvial, and eolian. These strata can be divided into four depositional sequences bounded by regional unconformities, or sequence boundaries, that permit regional time correlation. Two of these sequence boundaries, at or near the top of the Caddy Canyon Quartzite and at the base of the Mutual Formation, can be traced regionally from southeastern Idaho to southern Utah and from the Wasatch front to eastern Nevada. A widespread paleodrainage system was incised into an extensive braidplain more than 90,000 km2 (after palinspastic reconstruction) underlying the upper Caddy Canyon sequence boundary in response to a relative fall in sea level. Immediately below this sequence boundary, at approximately a single time horizon, the braidplain facies hange laterally from proximal (Huntsville) to medial (Canyon Range, Sheeprock Mountains) to distal braidplain (Dugway Range, Drum Mountains). In the Egan Range in eastern Nevada, correlative strata represent a shallow-marine environment. Above this sequence boundary, a broad muddy shelf more than 200 km wide developed as relative sea level rose. The presence of incised valleys at several horizons within this shelf sequence suggests short-term falls in relative sea level were superimposed on the longer term sea level trend. The base Mutual sequence boundary represents a time when relative sea level once again fell and braided fluvial deposits spread across the entire region. The late Proterozoic paleogeography is portrayed on the palinspastic base map.


AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)