科研之友
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摘要
New, high-resolution, regional correlation and isopach maps provide evidence that (1) Laramide-style deformation began as early as ca. 77 Ma in central Utah, and (2) rapid (208 km m.y.(-1)) and extensive (400 km) progradation of a clastic wedge was facilitated by reduced subsidence during the transition from Sevier- to Laramide-style deformation. This study defines three Campanian, alluvial-to-marine clastic wedges that traversed 200400 km eastward across the Utah-Colorado segment of the Cordilleran foreland basin. Wedges A and C are thicker successions with rising-trajectory shoreline stacking patterns (Blackhawk Formation and Lower Castlegate Sandstone, Bluecastle Tongue and Rollins Sandstone) that reflect relatively slow overall progradation (50-81 km m.y.(-1)) of narrow (10-20 km wide), wave-dominated shorelines. In contrast, wedge B consists of lower-volume successions with a flat to falling shoreline stacking pattern (Middle Castlegate Sandstone, Sego Sandstone, Neslen Formation, Corcoran and Cozzette Members of the Iles Formation) that suggests rapid progradation (similar to 208 km m.y.(-1)) of embayed (60-80 km wide), mixed-energy (wave-and tide-influenced) shore-lines. Wedges A and C prograded 200-250 km in more than similar to 3 m.y., whereas wedge B prograded 340-400 km in similar to 2 m.y. (similar to 170 km m.y.(-1)). The anomalously extensive wedge B is unique in the Utah-Colorado segment because of its long extent, rapid progradation rate, dominance of tidally influenced facies, long-transit transgressions/regressions, and low-accommodation, nested sequence architecture. Stratigraphic relationships indicate development of wedge B coeval with both Sevier- and Laramide-style deformation in Utah. Assuming a constant sediment supply, the extensive (> 300-400 km) "sheet-like" amalgamated wedge (wedge B) may have been caused by (1) reduced subsidence driven by a flexural interference pattern, whereby two short-wavelength (+/- 200 km) flexural profiles are superimposed during the uplift of both basement-cored and thin-skinned thrust belt, (2) an increase in, or eastward migration of, dynamic subsidence during tectonic transitions associated with slab flattening or roll-back (i.e., long-wavelength flexure), or (3) reduced subsidence due to short-wavelength flexural interference augmented by the reduction, or migration, of long-wavelength flexure.
- 出版日期2011-10
