| Description |
Spatial point pattern analyses (PPAs) such as Ripley's K-function and the quadrat method are commonly used to quantify clustering, randomness, and uniformity of the distribution of channel belts in fluvial strata. These point patterns may reflect various controls on fluvial architecture, e.g., uniform compensational stacking and avulsiongenerated clustering. To build upon these methods and to statistically compare point patterns with other architectural metrics, a moving window analysis was performed on extensive outcrops of the Cretaceous John Henry Member of the Straight Cliffs Formation. Digital terrain models (DTMs) produced using unmanned aerial vehicle-based stereophotogrammetry form the basis of detailed interpretations of a 200 m-thick fluvial succession over a total outcrop length of 4.5 km. We developed a workflow that uses variable-length moving window averages to analyze spatial point patterns, and architectural metrics such as net sand to gross rock volume (NTG), amalgamation, and channel belt width and thickness. Results indicate that the K-function requires significant correction for edge effects, leading to the use of the quadrat as the primary PPA method in this study, although the latter is not without its own limitations. We used high widthto- thickness aspect ratio quadrat cells in order to investigate point patterns with laterlly elongate geometry. When analyzed at small scales, quadrat point patterns and NTG correlate positively and broadly match previously observed stratigraphic trends in the fluvial John Henry Member, indicating that these trends are regional in nature. There are iv deviations from these trends in architectural statistics over small distances (100s of meters) and large distances (kilometers), which are interpreted to be caused by the autogenic processes of avulsion, and the migration of a distributive fluvial system respectively. At large analytical scales, point patterns and NTG correlate negatively, which is a result of using centroid-based PPA on a dataset with disparately-sized channel belts. |
