Abstract:

Detailed facies-architecture study of a portion of a > 10-kilometer-wide compound incised valley in outcrops of the Turonian Ferron Notom Delta shows three simple incised valleys filled with different facies associations. The valley-fill deposits were mapped with 30 detailed measured sections, photomosaics, and bedding diagrams. The oldest, incised valley 3, forms a terrace deposit that erodes directly into hummocky-cross-bedded lower-shoreface deposits. It is filled with fine- to medium-grained tidally influenced deposits, characterized by abundant mud-draped cross beds, sparse burrowing, and a bimodal paleocurrent-direction pattern. The younger incised valley 2 locally cuts through the valley 3 terrace and also into the lower-shoreface deposits. The valley 2 fill comprises multi-story medium-grained fluvial deposits with minor finer-grained tidally influenced fluvial deposits in the upper 10%. The youngest, incised valley 1, also locally cuts into the lower-shoreface deposits, removing the terraces formed by valleys 2 and 3. Valley 1 is filled entirely with medium-grained fluvial deposits. The composite valley fill records generally increasing fluvial dominance and decreasing tidal influence during successive cut-and-fill episodes associated with each simple valley fill. It is hypothesized to correlate with a longer-term, stepped relative fall of sea level, punctuated by standstills, or minor rises of sea level.

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