SEDIMENTOLOGY AND CONTROLS ON FLUVIAL ARCHITECTURE OF THE JURASSIC KAYENTA FORMATION, NORTHEASTERN ARIZONA

Examination of the interplay between contrasting depositional systems allows for a characterization and analysis of the impacts that each has on the other and the creation of facies sequences useful in environmental interpretations. The upper Jurassic Kayenta Formation crops out throughout the southern Colorado Plateau and in northeastern Arizona where excellent 3-D exposures, both parallel and perpendicular to paleoflow, permit detailed architectural reconstructions. The fluvial-dominated upper Kayenta comprises both meso- and macro-scale facies sequences. The meso-scale sequences typically are a few meters to several decimeters thick, and represent two types of ephemeral stream complexes based on sedimentary structures, textures, and geometries. One is dominated by fine-grained, horizontal to low-angle laminated sandstones and rip up clasts of mudstone that form tabular bodies. A second is composed of trough and planar cross-stratified, fine- to medium grained sandstone bodies that commonly have lenticular geometries with scoured bases. The first reflects short-lived, flooding events in abandoned channels and the second more sustained flow, low sinuosity systems that traversed the proximal portions of the Kayenta floodplain. The connectedness of the latter is established through lateral facies mapping over several kilometers. Interbedded with both are laminated, sandy carbonate units and mudstones of lacustrine and floodplain origin, respectively. Mega facies sequences are several decimeters thick and consist of rhythmically alternations of both types of meso-sequences. Mapping of these mega-sequences permits development of a detailed 3-D facies model. Climate was the primary control on sedimentation with periodic episodes of flooding that resulted in the inundation of interdunal corridors and ponding of ephemeral lakes. Both the streams and lakes interrupted the onset of widespread erg of the Navajo Sandsone.