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The architecture of alluvial suites is governed by a variety of autocyclic and allocyclic mechanisms that work in concert. Careful evaluation of source lithologies, climatic conditions, and tectonic setting must be combined with sedimentologic analysis of three-dimensional exposures of fluvial rocks to rigorously determine controls on the architecture of individual sequences. Consequently, although study of alluvial architecture is a potentially effective and important means of elucidating the depositional and tectonic history of continental basins, there are few well documented field studies.

The lower Eocene Willwood Formation of Wyoming and the Plio-Pleistocene Glenns Ferry Formation of Idaho offer contrasting examples of alluvial architecture even though both sequences were generated by meandering streams in tectonically active intermontane basins. Independent evidence for the chronostratigraphy, provenance, climate, and tectonic setting is documented for each unit. Evaluation of these parameters demonstrates that differences in tectonic framework, specifically differences in the rate of basin subsidence, were responsible for the contrasting architectures. Decreasing rates in the Bighorn Basin produced a sequence with a thick and strongly multistory sand body plus mature paleosols in the Willwood Formation. In contrast, single or weakly multistory channel deposits, encased by vast quantities of overbank sediments, characterize the Glenns Ferry Formation and reflect more rapid rates of subsidence and sediment accumulation in the Snake River Plain of Idaho.

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