Fluvial-lacustrine sequence stratigraphy, provenance, ichnology, and sandstone reservoir modeling of the tertiary Uinta and Duchesne River Formation, northern Uinta Basin, Utah

The Tertiary Uinta and Duchesne River Formations exhibit spectacular outcrop exposures in the Uinta Basin, northeastern Utah. This paper documents four different geological topics/subjects resulting from field and laboratory studies: 1) fluvial-lacustrine sequence stratigraphy, 2) source-to-sink fluvial system, 3) ichnology and paleoenvironment implications, and 4) sandstone reservoir models and characterization. Chapter 1 highlights a sequence stratigraphic framework and basin-scale facies architecture of the Duchesne River Formation. An upward-fining sequence of the lower three members was heavily influenced by uplift in the Uinta Mountains. Its internal fluvial-lacustrine deposits show marked contrasts between the western and eastern part of the basin due to irregular allogenic controls of tectonic subsidence and water discharge (climate and source terrain input controls). Chapter 2 highlights a source-to-sink fluvial system of the basal member of the Duchesne River Formation, which preserves a high net-sand-to-gross-thickness ratio (NTG) system in the western sink (basin) and a low NTG system in the eastern sink. Petrographic data and drainage patterns indicate a high discharge from multiple source terrains with a long sediment transport along the E-W basin axis in the western part of the basin. These factors were important for development of large-volume and high-quality (porous) fluvial sandstone reservoirs in the sink. Chapter 3 focuses on distinct trace fossil assemblages within the fluvial-lacustrine sequence of the uppermost Uinta and the overlying Duchesne River Formations. The study demonstrates the important relationships of depositional facies and trace fossils: 1) lacustrine deposits with the dominant horizontal grazing trace fossil assemblage, 2) fluvial deposits with the dominant insect trace fossil assemblage, and 3) transitional (wetland) deposits with intermediate trace fossil assemblage. Chapter 4 emphasizes the outcrop-based geological/reservoir modeling of fluvial and lacustrine deposits of the Uinta and Duchesne River Formations. The study provides statistical inputs of fluvial channel geometry for reservoir modeling applications, and demonstrates which stochastic modeling techniques best represent observed depositional patterns derived from outcrop data. The Uinta and Duchesne River Formations exhibit the important aspects of coarse-grained deposits in the late-stage lacustrine basin fill.