Vertical facies successions record the evolution of depositional environments through time; a sequence progressing from poorly-sorted, unimodal-current sandstone (fluvial) upward through sand-mud alternations with bipolar (tidal) currents to well-sorted, bimodal-current sandstone (shoreface) reflects a transgressive (deepening/marine-influence-increasing) succession.
The base of the sequence (poorly-sorted sandstone with unimodal paleocurrent) reflects fluvial deposition, characterized by unidirectional river currents and generally poor sorting. The middle unit...
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