Nature and growth of nonmarine-to-marine clastic wedges: Examples from the Upper Cretaceous Iles Formation, Western Interior (Colorado) and the lower paleogene Wilcox Group of the Gulf of Mexico Basin (Texas)

Sequential stratigraphic analyses of third-order, nonmarine-to-marine; clastic wedges provide insights on their growth. Examples studied are the Campanian, Iles Formation, Western Interior Basin (a foreland basin); and the upper Paleocene-lower Eocene Wilcox Group, northwest Gulf of Mexico Basin (a passive-margin basin). In the Iles Formation, the geometry and architecture of fourth-order (0.08–0.5 m.y.) marine-sandstone tongues appear to have a relationship to third-order (0.5–5.0 m.y.) shoreline trajectory. These relationships include a positive correlation between low angles of third-order shoreline trajectory, increasing sandstone-tongue length, and the presence of sharp-based shoreface sandstones, incised valley fills, and gutter casts.; The Iles wedge of the Sand Wash Basin displays a regressive-transgressive pattern of shoreline trajectory that spans 3.3 m.y. It is proposed that this third-order sedimentary cycle can be recognized across the region of northwest Colorado and southern Wyoming. The Campanian of the southern Wyoming/northern Colorado sector of the WIB contains four, large-scale third-order clastic-wedge intervals, or sequences (2.8–3.5 m.y.). These clastic wedges can be identified based on a combination of shoreline trajectory and the presence of regional erosion-surfaces created by relative falls in sea level. Inferred climatic warming coincides with transgressive bases of three Campanian wedges (wedges 1, 2, and 4).; In the Wilcox Group of Texas, four clastic-wedges have recurrence intervals ranging from 2.5–3.3 m.y. It is proposed that clastic wedges with recurrence intervals of 2.5–3.5 m.y. represent a commonly recurring scale of sedimentary sequence. Published accounts of recurring, abrupt warming events (interregional to global in scale) show a close correspondence in timing with the transgressive maxima defining boundaries of the four Wilcox clastic wedges.; Cross-cutting relationships of thrust-faults at the margin of the greater Green River Basin (Laramide foreland of Wyoming) show evidence of thrust motion that corresponds to strong regression to early transgression in the Wilcox Group (Texas Gulf of Mexico Basin). Motion on these faults ceased at times equivalent to the transgressions bounding Wilcox clastic wedges. This relationship provides evidence to suggest that deformational episodes in the thrust belt and greater broken-foreland correspond to episodes of increased generation of sediment that fed continental-scale rivers and associated delta complexes at the passive margin.