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

Weiguo Li, Chris Campbell, and Janok P. Bhattacharya
University of Houston, Houston, TX

Despite the importance of incised valley system reservoirs, good 3D outcrop examples are relatively rare. The Notom fluvial-deltaic complex, of the Turonian Ferron Sandstone Member, in Central Utah, contains a superbly exposed example of a wide compound valley fill. The Ferron was deposited into a rapidly subsiding foreland basin of the Western Interior Seaway. The delta complex is built upon highly burrowed shelf mudstones of the Tununk Shale. Sixty measured sections oriented along both depositional dip and strike directions show that the Notom delta complex consists of 12 north- to northeast-ward-prograding parasequences, ranging from heterolithic river-influenced deltas to homogeneous, marine- influenced shorefaces. These are erosively overlain by pebbly fluvial sandstones and their associated floodplain mudstones and coals. A transgressive lag caps the wedge, which is in turn overlain by shelf mudstone of the Blue Gate Shale.

Regional correlation shows a major valley system. In the distal part, fluvial deposits erosively cut into lower shoreface deposits. Local terraces are mapped and indicate branching, with a 50 degrees angle between trunk and tributary branches. The basal erosional surface has been traced continuously for 4 km along depositional strike and 9km updip. Updip areas show that the valley cuts down into older coal- and bentonitic floodplain deposits. The valley reaches a maximum thickness of 25 m and is filled with dominantly multistory, multilateral fluvial deposits. The terraces indicate multiple episodes of incision and filling, suggesting a compound valley. The occurrence of inclined heterolithic strata and shallow marine burrows in the top parts indicate marine influence during the late-stage filling of the valley forming a flood-capped valley system.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas