Controls of sandstone body geometry and architecture in the Chinle Formation (Upper Triassic), Colorado Plateau

Abstract

The Upper Triassic Chinle Formation forms a widespread continental deposit across the Colorado Plateau. Varying sandstone/mudstone ratios and resulting architectural differences throughout the formation provide the basis for recognition of six formal members and one informal unit in southeastern Utah and adjacent northern Arizona. The Shinarump and Moss Back Members consist of very broad thin sheets of interconnected sandstone bodies that formed in braided stream environments. The Monitor Butte and Petrified Forest Members consist of disconnected ribbon and narrow sheet sandstone bodies enclosed in thick mudstone sequences. The sandstone bodies formed in chiefly meandering streams. The Owl Rock and Churck Rock Members and Kane Springs strata are more variable packages of sandstone, mudstone and limestone that formed by various fluvial and lacustrine processes. Analysis of sandstone-body geometry and interconnectedness of the Shinarump, Moss Back, Monitor Butte, and Petrified Forest Members suggests that changing regional subsidence rates were major causes for their architectural patterns. These conclusions are supported by a comparison of Chinle sandstone-body geometry with sandstone-body geometry produced by quantitative models in the literature. The alternating sheet and ribbon geometry of the calcarenite and calcirudite channel deposits in the Kane Springs strata is related to diapiric salt activity in the Salt Anticline region. Controls that affected the sandstone-body geometry in the Church Rock Member are not fully understood but are probably related to increased aridity at the close of Chinle deposition.