The Megamonsoon and the Great Western Rivers of the Dockum/Chinle in the Last of Pangaea

The Triassic Dockum/Chinle fluvial system, preserves the megamoonsonal fluvial system that drained latest Pangea from the Ouachita front to the PaleoPacific ocean. New insights from the Dockum Group of West Texas and Eastern New Mexico show more studied sections of the Chinle Formation in the Four Corners area link with these strata to record a single large western-flowing system. Outcrop and Zircon data show these sections were likely contemporary Norian units. Detrital zircons from the Dockum Group show strong imprints from Ouachita and Grenvillian basement in modern east and central Texas. Most importantly, these strata have poor signature from the Midcontinent and Yavapai sources to the north, collectively supporting a dominate source from the Ouachita mts of Texas. Both common dates and provenance signatures argue the Dockum hosts the updip drainage that is equivalent to the Chinle to the west. In addition, stratigraphy argues the Dockum rivers record dominantly upper-flow-regime channel deposition from extreme flashiness driven by storm activity in an otherwise dry environment that drained west. Analysis from climate models indicate enhanced heavy precipitation in the continental interior of western Pangaea at this interval as part of a continental entrainment of megamonsoons. These findings collectively argue that the Dockum/Chinle system records a pattern of megamonsoonal storms pulled in against the prevailing easterlies which clashed with the Ouachita front and sent large floods through Dockum channels down dip to a broader Chinle basin, forming an extensive Chinle river system draining Pangaea westward from the Ouachita to the Pacific.