THE ROLE OF CLIMATE IN DETERMINING THE ARCHITECTURE AND STACKING PATTERNS OF COASTAL-PLAIN FLUVIAL SYSTEMS: AN ANALYSIS OF THE CAMPANIAN MASUK FORMATION

Climate change over geological timeframes can cause variations in relative water discharge (RQW), or the ratio of water to sediment discharge. While many sequence stratigraphic models are based around the premise that relative changes in sea level (RSL) control stacking patterns in continental-margin settings, ancient examples of upstream controlled systems are largely undocumented in scientific literature. Analyses of the Masuk Formation in southern Utah provides a unique opportunity to study a tidally influenced fluvial system that appears to be controlled predominantly by upstream factors.

There are two key features observed in sequence boundaries of RQW-driven systems that differentiate them from RSL-driven systems: (1) the depth of incision increases updip, and (2) rates of erosion are spatially uniform, leading to the formation of widespread, planar sequence boundaries. To test whether or not the Masuk Formation meets the criteria, the lateral extent and geometry of the sequence boundaries was established. This study combines unmanned aerial vehicle based photogrammetry and three-dimensional, high-resolution digital geological data from outcrops with standard field investigation techniques to thoroughly analyze the Masuk Formation.

Preliminary analyses indicates that allogenic forces distinct from the traditional RSL dominated system controlled the Masuk Formation’s stacking pattern. Major composite sandstone bodies display planar, sheet-like geometry and are laterally continuous in a significantly greater extent than would be expected based on empirical relations. Together, these bodies record a series of high-frequency sequences, formed along the western margin of the Western Interior Seaway. Within the individual sequences appears to be a trend in facies change from a basal chaotic sandstone with admixed mudrock and sandstone transitioning upward to a more organized cross-bedded and stratified sandstone. This trend may be representative of cyclical variations in RQW, or cycles from high to low periods of precipitation. Recognizing the diversity of forces that control architecture in coastal-plain fluvial settings could help to expand on the currently limited range of sequence stratigraphic models.