Fluvial fans and megafans are recognized as important depositional systems accountable for the accumulation of large volumes of terrestrial clastic sediments in continental basins. Fluvial fans are normally present in the proximity of topographic highs, where a radiating network of channels develops outward from an apex on a low-gradient sedimentary basin. Albeit the planform geometry of fluvial fans can vary, typically these geomorphic forms are recognized by a broad fan-shaped deposit with a gentle convex upward profile. Recent studies in fluvial geomorphology and sedimentology show that thick successions of largely alluvial origin can be attributed to the long-term progradation of large fluvial fans in various climate contexts and in all tectonic settings characterized by prolonged subsidence and steady sediment supply. River avulsion and bifurcations, commonly observed on active fluvial fans, are the sedimentological mechanisms driving the spatial distribution of runoff and driving the sediment transport on alluvial surfaces over long timespans. These processes not only control the deposition of sediment on fluvial fans but also contribute to the gradual build-up of a network of channels radiating downstream from the apex of the system.

This study focuses on the stratigraphy of Paleocene-Eocene fluvial succession outcropping across the southern margin of the Uinta Basin (central Utah, U.S.A.). The stratigraphic interval comprises the Colton and Wasatch formations, presented as a downdip-oriented transect that outcrops over 100 km from proximal to distal sectors and records the continental sedimentation in the Uinta Basin during the Laramide orogenic phase. The studied deposits have been attributed to the long term evolution of a fluvial fan that interacted, towards the distal end of the system, with a shallow lacustrine environment. General observation of the system-scale sedimentological trends and distribution of architectural elements allowed the identification of two distinct depositional trends, with a firt order progradation and the fluvial system, followed by a retrogradational backstepping of the fan margin likely due to the initial transgression of Lake Uinta.

This work also presents a detrital zircon U-Pb study followed by detailed geochemical and petrographic analysis. Geochronology observations contribute to a refinement of the source-to-sink model of the fluvial-dominated Wasatch and Colton formations and the reconstruction of the the local paleodrainage during the Laramide orogenic phase. Distinctive geochemical and mineralogical signatures in sandstone and mudstones within the Wasatch-Colton formations also allowed the establishment of a chemostratigraphic framework that can be laterally traced for tens of kilometers. Autogenic dynamics and a weathering-prone depositional environment in the distal sector of the depositional system are considered to be responsible for minor mineralogical variations.

In addition, this study explored the viability of a numerical modelling approach to qualitatively evaluate the connection between several depositional parameters and the spatial organization of fluvial architectural elements. This is achieved via the evaluatuation of system-scale grain-size distribution, channel-belt density, and the general geomorphic characteristic of the synthetic fans.