ASSESSING LATERAL VARIABILITY IN CYCLIC ALLUVIAL DEPOSITS USING TERRESTRIAL LIDAR DATA: NACIMIENTO FORMATION, SAN JUAN BASIN, NEW MEXICO

The early Tertiary deposits of the San Juan Basin are represented by the alluvial strata of the Nacimiento and San Jose Formations. Notably, the Paleocene Nacimiento Formation contains abundant horizons interpreted as paleosols. Studies conducted on similar paleosol-rich alluvial successions have reported a hierarchy of repetitive depositional units (Cleveland, 2007; Kraus & Aslan, 1999). These studies describe three scales of alluvial cyclicity attributed to: episodic floodplain sedimentation, distance to channel (sedimentation source), and long-term changes in accommodation space.

Our research aims to address how these documented alluvial cycles vary continuously across hundreds of meters of exposure (~0.85 km²) of the Nacimiento Formation at Kutz Canyon, in the northwest San Juan Basin. Data from terrestrial lidar scans and digital photographs are being used to create a virtual outcrop model in order to statistically evaluate identified cyclic units. Measured sections will be compared with the remotely sensed data to assess the viability of the analyses. Initial field results indicate that distinctive horizons can be easily traced between two measured sections recorded ~330 m apart. Exposure of these two paleosol-bearing sections also varies due to incision by sheet and ribbon sandstone bodies.

The three-dimensional nature of the outcrop model also enables contacts to be accurately traced across the study area. The projected surface of these digitized contacts, especially the well-developed paleosols, may provide information on the paleo-topography of this ancient alluvial surface.