3D Allostratigraphic Mapping and Facies Heterogeneity of a Compound Tributary Incised Valley System, Turonian Ferron Sandstone, Notom Delta, South-Central Utah
Hilton, Benjamin David 1985-
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Incised valley systems are important for sequence stratigraphic and exploration purposes. The tributary component of these systems may inherit complicated, self-similar, plan-view morphologies from the drainage networks that form them. Incised valley depositional models often exclusively focus on fill facies within trunk valleys and either ignore or poorly document facies within tributary valleys. The Notom Fluvio-Deltaic complex, a component of the Turonian (Late Cretaceous) Ferron Sandstone Member of the Mancos Shale Formation, outcrops along Neilson Wash, Utah, and provides the opportunity to study in 3D, facies heterogeneity of compound incised valley fills, including both trunk and tributary components. Using traditional field methodologies (56 measured sections) and remote sensing (aerial LiDAR survey), several objectives have been completed: 1) previous 2D outcrop work / interpretations have been updated and described in 3D space using allostratigraphic principles; 2) Isopach maps and paleogeographic reconstructions show north-east oriented channel belts with both braided and meandering plan view patterns within their respective valley fills; 3) younger cut and fill sequences (unaccounted for in previous studies) are documented; and 4) Interpretation of remnant terraces / interfluves suggest high diachroneity associated with the higher and lower order erosion surfaces that form the composite sequence boundary. Valley allomembers V2B and V2A are shown to be tributary in nature compared with larger or trunk valley allomembers based on stratigraphic valley width to thickness ratio’s, grain size differences, scale of sedimentary structures, preserved thickness of channel elements and abundance of facies types. Confined valleys appear more sand dominated while less confined to unconfined valleys preserve significant floodplain facies, as predicted by traditional incised valley models. Tributary fills appear linked to valley-specific hydrologic conditions, distance to estuarine/tidal processes, river style (braided or meandering), and sediment supply. This outcrop-based study gives a less common 3-dimensional insight to the evolution of a compound incised valley system, which may prove useful for subsurface exploration and for the advancement of oversimplified incised valley facies models.