Detrital zircon U-Pb fingerprinting of the Appalachian signature: Early Pennsylvanian sediment routing from highlands to deep-sea fans and the persistence of recycled Appalachian-affiliated zircons

Abstract

Carboniferous sediment dispersal from the Appalachian orogenic system (eastern United States) has become a topic of widespread interest. However, the actual pathways for continental-scale, east-to-west sediment transfer have not been documented. This study presents detrital zircon (DZ) U-Pb ages and Hf isotopic values from the Lower Pennsylvanian Jackfork Group, Johns Valley Shale, and Pottsville Formation of the Ouachita and Black Warrior Basins and DZ U-Pb ages from the Caseyville Formation of the Illinois Basin to delineate the likely sediment-routing systems within the broader context of sediment dispersal across Laurentia. We interpret results to suggest Alleghenian-sourced sediment and water were routed through at least two paleovalleys within the Appalachian foreland-basin foredeep and backbulge depozones to the Ouachita Basin terminal sink. Clearly circumscribed, southward- or southwestward-oriented paleodrainage areas provide a template of the Appalachian foreland-basin system, and as such the central and southern Appalachians were an unlikely source for the Appalachian signature observed in the western United States at this time. Collectively, the Ouachita Basin represents a terminal sink for sediments derived from much of the eastern and central United States. After the closure of the Ouachita Basin and the culmination of the Alleghenian orogen, the DZ U-Pb signature of the Appalachian-Ouachita orogenic system, which includes the Grenville (1250–950 Ma) and Appalachian (500–275 Ma) age groups, dominates the Phanerozoic record of North America. An east-to-west, Pennsylvanian to modern, comparison of DZ samples across North America demonstrates a persistent Appalachian signature for samples, including a recycled Appalachian signature in the West. The presence of this Appalachian signature in western Laurentia is clear, but the actual sediment-routing systems responsible for transferring this signal to the West during the Mississippian through early Triassic remain poorly defined. Lower Pennsylvanian deposits proximal to the Appalachian orogen, composed of 50–75% Appalachian- and Grenville-age DZ, represent the primary Appalachian signature, but it is unlikely this sediment was routed directly from the central and southern Appalachians to western Laurentia. Instead, this signal may have been derived from the northern Appalachians or perhaps the Ellesmerian orogen. By the Triassic, DZ samples in the West display a primary Appalachian signature and represent rivers sourced from the Ouachita-Marathon highlands. DZ sampled from Mesozoic fluvial sandstones, such as along the Front Range, indicate drainage reversal due to the rise of the Western Cordillera; yet a persistent Appalachian signature exists in these western-sourced, eastward-flowing systems—a phenomenon that continues to the present. None of these systems are interpreted to be sourced by primary Appalachian or Grenville terranes, suggesting a recycled Appalachian signature. These western samples frequently are composed of 40% Appalachian- and Grenville-age DZ, accompanied by western age groups (e.g., Yavapai-Mazatzal and Western Cordillera). Although western drainage reorganization reversed the trajectory of Appalachian-sourced sediment routing, WC DZ are typically dwarfed by the recycled Appalachian signal and underrepresented across the continent. The persistent Appalachian signature, originally sourced by the concatenation of two supercontinent orogen terranes, continues to be the dominant contributor in the DZ record of North America.