| Description |
A detailed understanding of spatial and temporal changes in alluvial architecture is essential in deciphering the mechanisms controlling stratigraphic trends, and their relative influence throughout a sedimentary basin. In this study, nonmarine exposures of the John Henry Member (Upper Cretaceous Straight Cliffs Formation) are characterized by measured stratigraphic sections, paleocurrent measurements, lateral facies mapping, and channel belt dimension measurements along a three km wide by ~200 m tall outcrop in Bull Canyon of the southwest Kaiparowits Plateau, Utah. Seven depositional units (DU) are interpreted, which define intervals with distinct alluvial architecture. The DUs are grouped into three stratigraphic intervals, each of which represents a large-scale trend in alluvial architecture. The lower stratigraphic interval includes a trend of upward decreasing grain size and channel belt width, thickness, and amalgamation, with isolated tidal influence. The middle stratigraphic interval is composed of consistently thick floodplain and coal mire deposits with laterally restricted channel belts. The upper stratigraphic interval includes vertical trends of increasing grain size, channel belt widths and amalgamation. These data are combined with previously published sections to produce a ~60 km long, dip-oriented correlation of the stratigraphic intervals, which is used to investigate variability within the depositional system. Paleomorphodynamic parameters are calculated from measurements made in fluvial strata at Bull Canyon and Rock House Cove, located ~20 km to the west (paleo-landward). The regional stratigraphy and paleomorphodynamic parameters indicate that the impact of tectonic activity is the primary driver of preserved alluvial architecture. Although some effect of sea level change, climate, and fluvial autogenic processes may be identifiable, they exert lower order control on the preserved system. In the proposed depositional model, changes in alluvial architecture represent the dynamic responses of fluvial fan systems (or distributive fluvial systems) to changes in accommodation and sediment supply resulting from episodic tectonic activity. This study contributes to the evolving paradigm that is transiting from an emphasis on downstream controls on fluvial systems (i.e., accommodation due to relative sea level changes) to more accurately account for hinterland controls (i.e., the interaction of accommodation and sediment supply due factors such as tectonic activity). These concepts are more broadly applicable to the understanding of depositional cyclicity in terrestrial (fluvial) deposits and are particularly relevant to foreland basin systems, which are common in the Cretaceous strata of western North America. iv |
