LATE TRIASSIC LAURENTIAN PALEODRAINAGE NETWORKS AND SEDIMENT ROUTING TO THE AULD LANG SYNE BASIN BASED ON DETRITAL ZIRCON U-Pb ANALYSIS

The Upper Triassic Chinle Formation is interpreted as the deposits of a continental-scale fluvial system that traversed southern Laurentia from the Ouachita Mountains of the southcentral USA to the Auld Lang Syne basin (ALSB) of western Nevada. Whereas the Chinle represents an important component of early Mesozoic transcontinental sediment transfer, sediment routing corridors have yet to be fully constrained, and definition of a terminal depositional sink for the Chinle source-to-sink (S2S) sediment-dispersal system remains unclear.

This study presents >9,200 new detrital-zircon (DZ) U-Pb ages from Chinle fluvial sandstones in Utah and correlative Jungo Terrane turbidites in Nevada to document provenance and examine potential sediment routing corridors from the Appalachian-Ouachita Cordillera to the ALSB.DZ U-Pb ages distributions, multidimensional scaling (MDS) analysis, and maximum depositional ages (MDAs) indicate at least three paleodrainage systems during basal Chinle deposition transported sediment through long-lived (ca. 213 to 229 Ma) mixed bedrock-alluvial valleys to the western Laurentian margin. MDS analysis demonstrates DZ U-Pb age distributions from the Chinle cluster with Jungo Terrane samples and we interpret a S2S relationship between Chinle fluvial systems and the deepwater ALSB. DZ samples collected from Jungo turbidites produced a series of MDAs that suggest a ca. 11 Myr (ca. 213 to 224 Ma) window of deposition, indicating a genetic link with basal Chinle fluvial systems. Mixture modeling indicates that Jungo turbidites reflect sediment contributions from only two basal Chinle paleodrainage systems; the Painted Desert (≈78%) and Vermillion Cliffs (≈22%) systems.

We conclude that the Late Triassic climatic shift to a tropical monsoonal regime forced Laurentian sediment routing through basal Chinle paleodrainage systems to the marginal-marine ALSB. Sediment was delivered to the deepwater ALSB during cycles of dynamic topography-driven sea-level fall and lowstands in the Norian, when Chinle fluvial systems extended across an exposed continental shelf to a slope canyon at the shelf margin. The mixed signal in Jungo turbidites is likely due to autogenic processes operating on the shelf delta but may also reflect timing differences of peak discharge for each paleodrainage system.