CHARACTERIZATION OF ALLUVIAL CYCLICITY USING TERRESTRIAL LIDAR SCANNING: PALEOCENE NACIMIENTO FORMATION, SAN JUAN BASIN, NEW MEXICO

Numerous studies on mud-rich alluvial successions containing intercalated paleosols have documented a hierarchy of cyclic aggradational deposits associated with specific thicknesses and time durations (e.g., Atchley et al., 2004; Cleveland et al. 2007). Atchley et al. (2004) used accommodation plots, originally devised to identify cyclic marine stacking patterns from vertical successions, as a method to examine cyclic alluvial strata. This applied technique identified fining-upward meter-scale fluvial aggradation cycles (FACs) which in turn stack into decameter-scale fluvial aggradational cycle sets (FACSETs). The majority of FACs are paleosol-capped and are attributed to periods of aggradation during river avulsion, followed by channel stability and mature soil development. Fining-upward FACSETs are associated with avulsive channel migration in which thickness and grain-size is directly dependent on relative channel position. In our work, we question how these FACs and FACSETs vary laterally across continuous sections and apply lidar and high-resolution photography to address this variability.

Our study focuses on the early to middle Paleocene Nacimiento Formation located in the northwest San Juan Basin of New Mexico. This unit is composed of up to 500 m of paleosol-bearing alluvial deposits (Williamson & Lucas, 1992). At Kutz Canyon the Nacimiento Formation is exposed as badlands eroded into a series of amphitheaters that provide wide-view outcrop perspectives. High-resolution terrestrial lidar scans and digital photos obtained from a portion of this area (~0.85 km²) allow facies boundaries to be traced in 3D. Using these data any apparent alluvial cycles can also be statistically evaluated across the study area. Results derived from field and remotely sensed data will be compared to assess the alluvial cyclicity in these strata and to determine the overall viability of terrestrial laser scanning in alluvial stratigraphic studies.