Print this page3-D Facies Architecture of a Storm-, Flood-Dominated Deltaic Lobe in the Cretaceous Ferron Notom Delta Complex
Three dimensional facies architectural studies of ancient deltaic systems are critical for developing 3-D models for subsurface reservoir characterization. Variably-oriented exposures of clinoforms within fluvial dominated deltaic parasequences of the Cretaceous Notom Delta complex of the Ferron Sandstone Member, of the Mancos Shale Formation, Utah, allow a 3D reconstruction. The Notom delta complex has been divided into 4 sequences, and 9 parasequence sets. This study focuses on Parasequence 3a. The outcrop consists of three well-exposed cliff faces. Photomosaic interpretation were integrated with detailed sedimentological measured sections to asses the external bed geometry and internal facies variability respectively. A total of seven measured sections were completed on all three cliff faces and each shows a similar coarsening upward facies succession. Sandstone beds in the distal delta front and proximal prodelta are normally graded and show well developed Bouma sequences, with flat lamination passing into climbing current ripples. In places sands show hummocky cross stratification (HCS) and climbing wave ripples, suggesting rapid deposition during storms. Several units show extensive soft sediment deformation, also suggestive of high sedimentation rates. Plant material is abundant, but the parasequence as a whole shows low levels of bioturbation, suggesting stressful conditions. The low bioturbation, and abundance of Bouma sequences suggest river-fed, possibly hyperpycnal delta front turbidites. The locally high levels of fully marine bioturbation on bed tops suggest a return to fully marine conditions . The presence of HCS and aggrading wave rippled beds indicates that the river-flood deposits were at times associated with major oceanic storms. Rapid deposition caused sediment liquefaction and failure, resulting in the abundant soft-sediment deformation features. We this interpret this systems at a storm-, flood-dominated deltaic succession. Externally, the parasequence consists of clinoforms beds dipping at a maximum of about 6°. In strike view they show a mounded, lens-shaped geometry. These are interpreted as mouth bar deposits. Bed boundaries show little evidence of undulation and scours, despite the overall lens-shaped external geometry. Along-strike, lenses are less than a few hundred meters in width. Beds may also be draped with silty mudstones, which may represent flow barriers or baffles indicating a complex reservoir architecture.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009