U-Th-Pb LA-ICP-MS Detrital Zircon Analysis of the Triassic Chinle and Moenkopi Formations and Permian Coconino Sandstone of Chinde Point, Petrified Forest National Park, Arizona

Abstract

The Petrified Forest National Park (PEFO) of Arizona preserves outstanding exposures of the Triassic Chinle and Moenkopi Formations that are underlain by upper Paleozoic strata of the Coconino Sandstone. In 2013, drill core was collected from these strata in an effort to establish links with the astrochronological time scale developed in the Newark basin. Other workers involved in this project are using this core to refine and improve an absolute time scale employing Milankovitch cycles. To improve constraints on provenance and depositional ages of the Coconino, Moenkopi, and Chinle formations, we acquired 7,511 individual U-Pb detrital zircon dates from 29 samples from the core. Comparison of U-Pb ages with ages of rocks in various potential source terranes suggests that our samples were shed from rocks of the Archean (2.7-2.5 Ga) Wyoming Province and Paleoproterozoic terranes (2.1-2.0 Ga) of the Canadian Shield, the Yavapai and Mazatzal Provinces (1.8-1.6 Ga), Ancestral Rocky Mountains (1.8-1.4 Ga), midcontinent basement and overlying platformal strata (1.5-1.3 Ga), Grenvillian orogen (1.3-0.95 Ga), Yucatán-Campeche block (720-420 Ma) and Amarillo-Wichita uplift (600-500 Ma), Appalachian orogen (450-350 Ma), eastern Mexico magmatic arc (310-232 Ma), and Triassic magmatic arc of western North America (230-210 Ma). The youngest peak age of the Permian Coconino sandstone is 260 Ma, whereas the youngest peak age for the Early-Middle Triassic Moenkopi Formation is 250 Ma. All samples from the Late Triassic Chinle Formation have youngest peak ages from 224-214 Ma. These maximum depositional ages compare well with CA-TIMS and ID-TIMS dates from strata of the Moenkopi and Chinle Formations, as well as the Adamanian-Revueltian land vertebrate faunachron (LVF) from Lucas (1998) and Parker and Martz (2011). U-Pb detrital zircon ages document a depositional hiatus/erosional period of ~250-225 Ma between the Moenkopi and Chinle Formations.