Rift Destabilization of a Proterozoic Epicontinental Pediment: A Model for the Belt–Purcell Basin, North America
Published:January 01, 2007
James W. Sears, 2007. "Rift Destabilization of a Proterozoic Epicontinental Pediment: A Model for the Belt–Purcell Basin, North America", Proterozoic Geology of Western North America and Siberia, Paul K. Link, Reed S. Lewis
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In the absence of land plants, broad pediments may have formed stable landforms that beveled Proterozoic continents. Braided streams would have transported a thin layer of clastic sediment across such Proterozoic epicontinental pediments. The Proterozoic pediment–braidplain system may be represented by extremely flat regional unconformities beneath locally preserved, supermature, braidplain sandstones. Continental rifting would have destabilized Proterozoic epicontinental pediments by funneling runoff along rift axes to create large rivers, which otherwise were not favored in the Proterozoic landscape. The sedimentological history and detrital–zircon provenance of the intracratonic Mesoproterozoic Belt–Purcell basin of western North America may be described in terms of destabilization of a late Paleoproterozoic to early Mesoproterozoic epicontinental pediment by a three–armed rift system with the Belt–Purcell basin at its center. A model using a Siberia–Laurentia–Australia paleocontinental reconstruction implies that the sedimentary veneer of the pediment washed down the western branch of the rift system to enter the Belt–Purcell basin at a point source on its western side. Capture of clastic sediment in delta fans on the western side of the basin permitted clean carbonate to precipitate on the northeast side. Reconfiguration of the basin by renewed rifting appears to have changed composition, grain size, and sedimentary provenance during deposition of the Missoula Group (upper Belt–Purcell Supergroup).
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Proterozoic Geology of Western North America and Siberia
This volume is a compendium of research on the Belt Supergroup. It is an outgrowth of Belt Symposium IV, held in Salmon, Idaho, in July, 2003, in conjunction with the Tobacco Root Geological Society annual field conference. Because of the geographic extent and great thickness of the Belt Supergroup, years of work have been required before conclusions are “bona fide”. The Mesoproterozoic Belt Supergroup of western Montana and adjacent areas is geologically and economically important, but it has been frustratingly hard to understand. The previous Belt Symposium volumes offer an historical view of the progress of the science of geology in the western United States. The advent of U-Pb geochronology, especially using the ion microprobe (SHRIMP) and laser-ablation ICPMS, has injected geochronometric reality into long-standing arguments about Belt stratigraphy. Several papers in this volume utilize these new tools to provide constraints on age and correlation of Belt strata (Chamberlain et al., Lewis et al., Link et al., and Doherty et al.)