科研之友
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摘要
Current sequence stratigraphic models deal with stratal packages almost exclusively along depositional-dip. A high-resolution outcrop example detailing sequence stratigraphic architecture along depositional-strike is largely lacking. This outcrop study provides a detailed sequence stratigraphic correlation along depositional-strike for a length of similar to 50 km. Moreover, this study focuses on the facies and statigraphic relationships particularly at the very transition between coeval marine and nonmarine strata, which is relatively underdocumented. Within the Mesaverde Group of central and eastern Utah, the Upper Cretaceous shallow-marine Star Point Sandstone and paralic Blackhawk Formation are relatively well studied along depositional-dip in the Book Cliffs, but the nature of their spatio-temporal transition particularly along depositional-strike in the NNE-SSW trending Wasatch Plateau remains poorly documented. Fades-scale to stratigraphic-scale data were gathered from ten outcrop "windows" along the eastern margin of the Wasatch Plateau. The vertical and lateral transition between marine and nonmarine strata varies in complexity within the study area. In the southern part of the study area near the central Wasatch Plateau, the shallow-marine Star Point Sandstone passes stratigraphically upward into the nonmarine Blackhawk Formation in one simple transition without any intercalation of marine and nonmarine strata. In the northern part of the study area, however, where the Star Point Sandstone to Blackhawk Formation transition is complex, aggradationally stacked shallow-marine sandbodies (i.e., parasequences) taper and completely pinch-out within coastal-plain mudstones in a paleo-landward direction over short distances (<1 km), representing potential stratigraphic traps. These marine sandbodies are intercalated with coeval nonmarine strata within the Blackhawk Formation. Fourth-order sequence boundaries and flooding surfaces were correlated along the lower Campanian depositional-strike. The results reveal along-strike undulations in the early Campanian depositional topography, which was characterized by alternating incised valleys, interfluvial topographic highs with mature soil development, and shoreline embayments. In particular, the variable along-strike transition-complexity from shallow-marine to coastal-plain strata is the result of differential tectonic subsidence, where the transition-complexity increases and the stacking pattern is more aggradational towards an early Campanian depocenter in the north of the study area. This study reveals that differential subsidence is the key in controlling along-strike variability of sequence stratigraphy and that correlation of sequence stratigraphic surfaces are far more challenging in nonmarine strata than in adjacent marine strata.
- 出版日期2015-7-15
