Incised Valley Systems and Sequence Stratigraphy of the Ferron Sandstone, Notom Delta, Henry Mountains Region, Utah

The Notom Delta is one of the Ferron wedges deposited in a foreland basin of the Western Interior Seaway during Turonian and it is exposed three dimensionally in the Henry Mountains region, Utah. The complex is built upon dark colored, unlaminated, and highly burrowed shelf mudstone and culminates in pebbly coarse sandstone sourced mainly from the northwest. The wedge is capped by a transgressive lag which is in turn overlain by shelf mudstone. Measured sections show that the whole wedge is compoosed of 12 north- to northeast-ward-prograding small-scale parasequences. Five high-order sequences are recognized based on tracing key surfaces, interpreting lap-out relations, and the stacking patterns of parasequences.

Two incised valleys are developed in these high-order sequences. The upper valley is especially well exposed along the canynon cliffs in the study area. Regional correlation and mapping recognized and characterized two continuous erosional surfaces in the valley, each of which is with considerable erosional relief and is regionally important. These surfaces are interpreted as unconformities which partition the valley into two unconformity-bounced sequences, marking as VI and VII respectively according to their stratigraphic position. The compound nature of the incised valley is further indicated by the occurrence of terraces due to multiple incision and filling. Field studies recognized a major change in valley sedimentology from V1 to VII as indicated by the difference in grain size, change in paleocurrent current direction, and change in overall facies characteristics and their internal organization from the former to the later. The observation strongly support the development of valleys within a high accommodation foreland setting. The development of higher-order sequences in the deltaic complex is most probably controlled by higher-order relative sea level fluctuations.