SHINARUMP INCISED VALLEY CUT-AND-FILL DEPOSITS, PALEOSOLS, AND ICHNOFOSSILS IN THE LOWER PART OF THE UPPER TRIASSIC CHINLE FORMATION, PETRIFIED FOREST NATIONAL PARK, ARIZONA: IT REALLY DOES EXIST, AND IT HAS REGIONAL STRATIGRAPHIC IMPLICATIONS

Sedimentologic and stratigraphic analysis of the entire Upper Triassic Chinle Formation exposed in Petrified Forest National Park (PEFO) has yielded a complete measured section that includes several successions of incised valley cut-and-fill complexes in the lower part of the Chinle Formation. These lower most Late Triassic deposits represent the "mottled strata" and Shinarump Member of Stewart et al. (1972) described elsewhere on the Colorado Plateau, but also in the vicinity of PEFO. The mottled strata represent the interfluves of paleovalleys cut into the Lower Triassic Moenkopi Formation, while stratigraphically higher Shinarump conglomerates and sandstones occur with laterally equivalent, pedogenically-modified (e.g., mottled) terrace deposits. Stratigraphic relations demonstrate that the "mottled strata" is genetically related to the Shinarump Member and are treated as one sequence set. Recent work in the central portion of PEFO has located more outcrops of the Shinarump. These outcrops are of lenticular channel deposits containing coarse to granular quartzose sandstones cut into older, pedogenically modified mudrock (mottled strata), or contemporaneous purple-mottled overbank deposits that represent slight to moderate pedogenesis. North and south of the Haystacks are the stratigraphically lowest units in PEFO--pedogenically modified (earliest Late Triassic event=mottled strata=Shinarump Member) Lower Triassic Moenkopi Formation and channel deposits of the Shinarump. These units contain ichnofossils of 1) rhizoliths that represent ground covering plants and small, upright woody plants; 2) crayfish burrows assigned to Camborygma eumekenomos; 3) adhesive meniscate burrows; 4) termite nests assigned to Archeoentomichnus isp.; and 5) small, quasi-vertical and horizontal burrows. Recognition of Shinarump paleovalley cut-and-fill complexes in PEFO demonstrates that tributaries of the major Shinarump incised valley system documented by previous workers are present throughout this region. The facies relationships are complicated by their occurrence within incised valleys characterized by significant paleotopography; physical correlation of lithostratigraphic units without recognition of these features could and has lead to misinterpretation of the local and regional stratigraphy.