NEW DETRITAL ZIRCON BIG-DATA APPROACH IN CHARACTERIZING ANCESTRAL ROCKY MOUNTAIN BASIN ISOLATION AND TRANSCONTINENTAL SEDIMENT TRANSPORT

This work outlines two novel approaches for interpreting and interrogating big detrital zircon data sets: 1) Combination of inverse- and forward-sediment-source modelling, and 2) sediment-source mapping. Applied in concert, inverse- and forward-source modelling provide guidance in identifying empirical sediment sources and determining the proportions of those sources that contribute to zircon age spectra. However, even in very large data sets, many areas lack sufficient provenance data while others have a high-density of samples. Moreover, detrital zircon data can be non-unique, requiring synoptic consideration of independent data to produce a more robust interpretation. Sediment-source mapping directly addresses these issues of data distribution heterogeneity and non-unique character by integrating provenance and complimentary geologic data (i.e., forward-modelled source contributions, paleocurrents, paleogeography, and sediment thickness maps), and providing an interpretive method to extrapolate provenance information through data-poor and -ambiguous areas.

We demonstrate the efficacy of this approach by applying it to a late Paleozoic–early Mesozoic 329 sample set that stretches across North America and focuses on the core of the Ancestral Rocky Mountains. Sediment-source mapping provides independent evidence for documented episodes of tectonic activity or inactivity by illustrating 5 sediment-routing episodes throughout the study interval. These sediment routing episodes are defined by provenance changes in western Laurentia and include: 1) early Paleozoic–Early Mississippian intercontinental seaway; 2) Late Mississippian–Early Pennsylvanian transcontinental sediment integration; 3) Early Pennsylvanian–early Permian ARM basin isolation; 4) early–middle Permian tectonic quiescence and widespread eolian sediment transport; and 5) Triassic transcontinental fluvial reintegration. These episodes were driven by both plate tectonic activity and climate change, which resulted in changes in dominant sediment-transport pathways and mechanisms.