Incised Valleys and Sequence Stratigraphy of the Ferron Sandstone, Notom Delta, Capital Reef, Utah
Weiguo Li, Chris Campbell, and Janok P. Bhattacharya
Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas ,77204-5007, [email protected]
The Notom fluvial-deltaic complex is one of the wedges of the Ferron Sandstone Member of the Mancos Shale Formation, deposited in the foreland basin of the Western Interior Seaway during Mid-late Turonian and is exposed three dimensionally in the Henry Mountains region, Utah. The complex is built upon dark colored, un-laminated, and highly burrowed shelf mudstone of the Tununk Shale Member and culminates in pebbly coarse sandstone. The wedge is capped by a transgressive lag, which is in turn overlain by shelf mudstone of the Blue Gate Shale Member.
Sixty measured sections along both depositional dip and strike recognized 25 north- to northeast-ward-prograding parasequences within the complex. Four fourth-order sequences are recognized based on continuous tracing of key surfaces and the stacking patterns of parasequences. A wide compound incised valley system is recognized near the top of the deltaic complex. Regional correlation and mapping show two regionally important erosional surfaces, which partition the valley fill into two fifth-order unconformity-bounded sequences, marked as V1and V2 respectively. Within each of the valleys, there is a clear facies transition from fluvial, to tidal, and finally back into fluvial facies, a transition interpreted to be controlled by the change in sediment supply (S) to accommodation (A) ratio as the valleys were filled. Despite this similarity, a major change in valley sedimentology from V1 to V2 is recognized. This is shown by changes in paleocurrent direction, decrease in channel dimension, and change in fluvial style of formative rivers.
The Notom fluvial deltaic complex is formed under a long-term relative sea level fall after the Greenhorn transgression and relative sea level maximum. The 4th and 5th order sequences recognized in this study are interpreted as the product of high-order sea level fluctuations superimposed on this long-term relative sea level fall. While high-order sea-level change plays an important role during the forming and filling of the incised valleys, the major change in valley sedimentology may be the result of a possible climate change.
AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas