DEVELOPMENT OF A 3-DIMENSIONAL SEQUENCE STRATIGRAPHIC MODEL FOR THE LATE TRIASSIC (NORIAN) OWL ROCK MEMBER LOCATED AT PETRIFIED FOREST NATIONAL PARK, ARIZONA: A RECONSTRUCTION OF PALEODEPOSITIONAL ENVIRONMENTS AND PALEOCLIMATIC CONDITIONS
Alluvial depositional cycles within the Chinle Formation at PEFO have previously been recognized as being organized within a cyclic hierarchy of meter-scale fluvial aggradational cycles (FAC’s), decameter-scale fluvial aggradational cycle sets (FAC-sets), and deca- to hectometer-scale fluvial sequences. FAC’s occur as either fining-upward terrestrial deposits that have a paleosol weathered into their upper boundary, or have an upper boundary that lacks a paleosol and is abruptly overlain by coarser-grained deposits of the overlying FAC. Measured sections of the Owl Rock Member at Chinde Mesa are accompanied by map-oriented, high-resolution, digital photopans that highlight the distribution of FAC surfaces and inferred fluvial architectural elements.
The interplay between sedimentation and climate during the time interval preceding the Triassic-Jurassic biotic crisis is also examined in this study. Important climatic factors considered include atmospheric carbon dioxide concentrations (based on stable carbon isotope analysis of pedogenic carbonate), and mean annual temperatures (based on stable oxygen isotope analysis of both pedogenic and lacustrine carbonate). Carbonate specimens collected along measured sections are evaluated in terms of isotopic reliability using petrographic microscopy. Calculated atmospheric carbon dioxide concentrations and mean annual temperatures are compared to elucidate temporal relationships.