3-D Facies Architectural Study of Channel Belt Deposits in the Ferron Sandstone, Hanksville, Utah

Abstract

Two ancient meandering fluvial bodies in the Cretaceous Ferron Sandstone, Hanksville, Utah have been studied with Ground Penetrating Radar (GPR) to evaluate their 3D facies architecture and paleohydrological parameters. Traditional study of fluvial deposits, based on two-dimensional sections, typically involves cores, trenches, and logs but cannot lead to a full 3D characterization of the deposit. Most outcrop studies, lack plan view exposure and requires extrapolation of 3D heterogeneity based on 2D data. In this study, both bodies are exposed extensively in planview. Sand body A has been interpreted as a point bar complex based on planview and cliff exposures. However, sand body B was interpreted as a single point bar based on its crescent shape in the airborne Light Detection and Ranging (LiDAR) images and unidirectional paleoflow directions of cross beds. Lack of cliff exposure in B prohibits complete characterization in three dimensions. GPR data have thus been collected from both outcrops. Radar facies were characterized in point bar A by integrating GPR and surface stratigraphy. Later, this result was extended as an analogue to evaluate the shallow subsurface facies architecture of the point bar B. Three distinct radar facies have been identified, 1) Small trough like reflections, 1-2m long and <0.5m deep, 2) 4-6m long and 0.5m deep inclined reflections, and 3) a single, continuous, >15 m long, and >2.5m deep reflection which truncates facies 1, and 2. Facies 1 lies near the top of the sections and is interpreted as sets and cosets of small scale trough cross-bedding. Facies 2 has been interpreted as trough cross bedding formed by dune migration. Facies 3 has been interpreted as a basal channel scour surface. In cliff sections, point bar complex A shows a fining upward profile with the basal channel scour surface at around 2.5m depth. Radar stratigraphy corroborates that facies 3 coincides with the channel base and point bar bounding surface. Observation of a fining upward profile with a channel scour fill at 2.5m depth in B also supports the interpretation as a single scroll bar in a meandering river. Many previous GPR based sedimentological studies are supported with logs, cores or trench data. However, in this study we have shown that the sub-surface study of sedimentological deposits that are exposed solely in plan-view can be used to interpret subsurface channel geometry and channel thickness and allow 3D reconstruction of fluvial deposits.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016