Detrital Zircon Signal Inversion in the Cretaceous Southwestern U.S. Interior Seaway - A Case Study from the Gallup System New Mexico

Abstract

Sedimentary provenance analysis has been revolutionized by U-Pb age dating of detrital zircons. This geochronological technique allows researchers the ability to track sediment dispersal from its source to its ultimate sink. A compilation of 13,165 U-Pb zircon ages from 131 samples from the Late Jurassic to Late Cretaceous of the southwestern interior U.S. has shown a distinct change in sedimentary provenance. This study utilizes zircon ages from both sources and sinks to reconstruct the sediment routing systems throughout this period. The uplift of the Mogollon Highlands rift terrane in the Early Cretaceous caused a spike in Yavapai-Mazatzal (1.8-1.6 Ga) zircons in the Late Cretaceous once the sedimentary cover had been exhumed. This spike in Precambrian grains is found as far north as the Ferron Notom delta in south-central Utah, with a more pronounced increase in the nearby San Juan Basin. A total of 4 new samples were collected from the San Juan Basin in northwestern New Mexico to test changes in sediment provenance across a hypothesized sequence boundary determined by recent high-resolution sequence stratigraphy. A statistically significant shift in zircon signal was found between the Gallup Sandstone Formation and the overlying Torrivio Sandstone Member of the Crevasse Canyon Formation. This data, combined with petrographic analysis, has identified a major sediment provenance change, which is attributed to tectonic forcing and a subsequent increase in sediment supply occurring contemporaneously with a eustatic drop in sea level. Changes in sediment provenance across this sequence boundary between these two units resolves the decades-long debate of whether or not the Torrivio and Gallup are associated units and has implications for future sequence stratigraphic correlations of fluvial sediments which are notoriously difficult to correlate.