Current models of alluvial to coastal plain stratigraphy are concept‐driven and focus on relative sea‐level as an allogenic control. These models are tested herein using data from a large (ca 100 km long and 300 m thick), continuous outcrop belt (Upper Cretaceous Blackhawk Formation, central Utah, USA). Many channelized fluvial sandbodies in the Blackhawk Formation have a multilateral and multistorey internal character, and they generally increase in size and abundance (from ca 10% to ca 30% of the strata) from base to top of the formation. These regional, low‐resolution trends exhibit much local variation, but are interpreted to reflect progressively decreasing tectonic subsidence in the upper Blackhawk Formation and overlying Castlegate Sandstone. The trend may also incorporate progressively more frequent channel avulsion during deposition of the lower Blackhawk Formation. Laterally extensive coal zones formed on the coastal plain during shallow‐marine transgressions, and define the high‐resolution stratigraphic framework of the lower Blackhawk Formation. Large (up to 25 m thick and 1 to 6 km wide), multistorey, multilateral, fluvial channel‐complex sandbodies that overlie composite erosion surfaces occur at distinct stratigraphic levels, and are interpreted as fluvial incised valley fills. Low amplitude (<30 m) relative sea‐level variations are interpreted as the dominant control on stratigraphic architecture in the lower Blackhawk Formation, which was deposited up to 50 km inland from the coeval shoreline. In contrast, the high‐resolution stratigraphy of the upper Blackhawk Formation is poorly defined, and channelized fluvial sandbodies are poorly organized. Vertical and laterally offset stacking of a small proportion (<10%) of sandbodies produced ‘clusters’ that are not confined by ‘master’ erosion surfaces. Avulsion is interpreted to dominate the stratigraphic architecture of the upper Blackhawk Formation. This data‐driven analysis indicates that alluvial to coastal plain stratigraphic architecture reflects a combination of various allogenic controls and autogenic behaviours. The relative sea‐level control emphasized in sequence stratigraphic models is only rarely dominant.

Studies of large-scale sedimentary architecture are mainly based on the interpretation of two-dimensional photomosaics. This method cannot account for the natural rugosity of outcrop exposures, introducing errors in the measurement of geobody sizes and orientations. In the past, three-dimensional outcrop studies have relied on time-intensive fieldwork, with irregular sampling and low geometric accuracy. More recently, terrestrial laser scanning, or LiDAR (Light Detection and Ranging), has been widely applied to small-scale outcrops, but range and accessibility preclude its usage on larger-scale outcrops. Oblique helicopter-based laser scanning, however, allows the collection of tens of kilometres of outcrop sections in a relatively short time frame. In this paper, a procedure for collecting and processing such virtual outcrop data is outlined, and the application of the technique for extracting dimensions of fluvial geobodies from two large and otherwise inaccessible outcrops from Utah is presented. The results are compared to interpretations from more conventional photomosaicking of the same outcrops. Results show that the use of helicopter-based laser scanning enables geoscientists to rapidly acquire georeferenced data that can then be used for sedimentological interpretation and analysis on reservoir scales. It is concluded that helicopter-based laser scanning promotes sedimentological research and is well suited to capturing quantitative geometrical data from large outcrops.

There are numerous allocyclic and autocyclic factors which influence fluvial sandbody geometry. Unraveling the relative importance of such factors is challenging because fluvial systems can migrate and avulse across significant distances on the floodplain, so that collecting datasets that cover a large enough area with sufficient detail is difficult. This problem has been addressed by acquiring an oblique helicopter-mounted lidar survey over 16 km of exposed sections from Cretaceous coastalplain deposits cropping out in the Wasatch Plateau of east-central Utah. The exposures of the Blackhawk Formation occur in steep cliffs, which are continuous for several tens of kilometers, and have been previously inaccessible for study.The recorded lidar data were used to build detailed photorealistic models (virtual outcrops) from which quantitative dimensional data on fluvial architectural elements (mostly sandstone channel bodies) were collected. Those channelized bodies show significant variation in width and thickness. 26% of the sandbodies were identified as being multistory channel bodies, with a thickness of 9.1 m (± 4.67 m; 1 s) and a width of 142.6 m (± 180.7 m), which are significantly larger than the measured single-story sandbodies (5.9 m and 96.9 m, respectively). 50% of all sandbodies have aspect ratios smaller 13:1 and the highest values reach 78:1.The spatial constraint of the 397 fluvial sandbodies enabled the recognition of a series of vertical trends within the dataset. These trends include a subtle upward increase in width and thickness of both the mean and maximum values. This is coupled with a general upward decrease in the number of sandbodies and results in a broadly constant channel-to-overbank ratio. A clear correlation between wider channels with increased distance to the shoreline could also be documented.These observations can be explained by considering the entire Blackhawk Formation as the deposits of a large distributive fluvial system. In this model the key control on channel architecture is the distance to the shoreline, contrasting with previous interpretations of the Blackhawk depositional system in which the rate of accommodation creation in the coastal plain was thought to be the key control on channel geometry and stacking patterns.