Abstract

This study documents the effects of changing lake level (limnostasy), tectonics, sediment yield, and basin physiography on the facies architecture, sequence stratigraphy, and reservoir quality of three fine-grained deltas deposited along the eastern margin of late Pleistocene Lake Bonneville. Analysis of facies architecture indicates that the Weber and Spanish Fork deltas were strongly wave-modified because they were situated along openly exposed portions of the shoreline. The Bear River delta, nestled in a relatively isolated northeast arm of the lake, records both fluvial and wave processes. These fine-grained deltas were fed by low-gradient rivers that drained large regions that were sparsely glaciated, whereas other contemporaneous, coarse-grained "Gilbert" deltas were fed by steep-gradient rivers that drained local source areas that were strongly influenced by glaciers. Limnostasy, tectonics, and sediment yield were similar for all three fine-grained deltas, implying that the most influential forcing parameter on sequence stratigraphy is basin physiography. Basin physiography (specifically ramp length and accommodation) most strongly controlled the external and internal geometry of the lowstand systems tract of each delta. Potential hydrocarbon reservoir quality (e.g., grain size and sorting) is largely a product of drainage basin size and stream gradient. Relative differences in ramp lengths seemed to determine thickness and lateral continuity of delta front deposits. Relative differences in accommodation appeared to determine the internal geometry of the delta front deposits, especially in the lowstand systems tract. These deltas can serve as analogs for lacustrine exploration and production where many forcing parameters typically are unknown.

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