ORIGIN OF THE CHERT MARKER BED OF THE DINOSAUR CANYON MEMBER, MOENAVE FORMATION, IRON COUNTY, UTAH

The Dinosaur Canyon Member of the Moenave Formation was deposited during the Late Triassic Period in a near-shore marine environment in the area of study is near the mouth of Cedar Canyon, just east of Cedar City, Iron County, Utah. Evidence for this interpretation include abundant sedimentary structures found in the fine-grained sandstone, siltstone, and shale that make-up the unit. Structures consistent with a shallow marine depositional environment include: hummocky crossbedding, small amplitude wave ripple marks, sole marks, invertebrate trails, and multiple episodes of rapid transgression – regression occurring in the upper part of the unit. The chert marker bed that is regionally indicative of the Dinosaur Canyon occurs approximately 150 feet below the upper boundary with the Springdale Sandstone. It is a distinctive white to gray, very fine-grained laminated sandstone or siltstone with carbonate cement and layers of gray to red primary chert. The chert appears to be nonfossiliferous. Even though it shows no evidence of tests of any kind, it does show some sedimentary structures. Within the chert are a few near-perfect calcite rhombs, lending evidence to its primary nature.