Flow processes and sedimentation in a low-sinuosity high net-sand content fluvial channel belt: 3D outcrop study of the Cedar Mountain Formation, Utah

Abstract

This thesis documents the locations and proportions of lithofacies, morphometric characteristics and continuity of sandstone of a 3D exposure of an ancient fluvial channel belt in the Cedar Mountain Formation. Morphometric measurements include: width (80m), thickness (6.3 m), sinuosity (1.2), radius of curvature (right: 175 m, left: 220 m) bend curvature (right: 2.2, left: 2.8), and aspect ratio (12.7). Additionally, using cross-cutting relations, superposition, and facies type, the sequential evolution of the channel belt is interpreted. Using photopanels and measured sections, three primary lithofacies are documented. Facies within the channel belt are cross-stratified sandstone, conglomerate, and ripple-to-planar laminated sandstone. Lithofacies are quantified by geomorphic position (outside bend, inside bend, and inflection point) in the studied channel belt. Sandstone is continuous across the entire outcrop, however, bedsets and stories do not longitudinally persist the entire wavelength of the channel belt. Furthermore, we interpret that high-energy flows incised into the adjacent mudstone to create channel for fluid and sediment to flow through. Next, a high-energy conglomerate was deposited across the base of the channel as it began to migrate laterally although conglomerate is thickest at inflection points. Finally, using superposition and low-flow regime structures, we interpret that laterally accreting and downstream accreting bars filled the channel belt to the point of avulsion. These results can be used to update previous fluvial reservoir models to predict the spatial location and proportions of lithofacies within a reservoir. Updated reservoir model helps predict flow units and preferential fluid migration pathways in the subsurface.