ONE IF BY LAND, TWO IF BY SEA, AND THREE IF BY AIR? SEDIMENT TRANSPORT INTO COLORADO BASINS

By coupling detrital zircon (DZ) U-Pb ages to grain morphologies, we infer the mode and relative distance of sediment transport for several quartzose Paleozoic to Cenozoic sedimentary units in Colorado (USA). DZ in these basins experienced a variety of transport and depositional processes, which resulted in delivery of local, far-traveled, and exotic to Laurentia grains.

DZ populations from a Pennsylvanian-to-Jurassic succession record a transition from locally sourced, Ancestral Rocky Mountains uplift-related (Penn-Perm. Fountain Fm.) to far travelled and exotic (Lyons, Lykins, Jelm, and Sundance/Entrada formations). Shallow marine, fluvial and eolian units above the Fountain have DZ peak ages that coincide with Grenville (~1 Ga), peri-Gondwana (~610 Ma), and Appalachian (~480-260 Ma) terranes. Well rounded DZ with abundant impact structures suggest long transport distances. The far-field Appalachian-Ouachita orogeny associated with the amalgamation of Pangea, and its subsequent erosion, likely supplied sediment that was transported ≥1500 km to the interior of North America. Long distance transport was presumably by large transcontinental rivers and subsequent regional deflation and erg deposition.

A younger DZ population, from the Late Cretaceous Codell Sandstone Member of the Carlile Fm., contains a continuum of ages between ~105-90 Ma (96 Ma peak age). DZ are often delicate, euhedral, needle-like prisms. It is likely that the majority of DZ in the Codell are derived from Cordilleran arc volcanism, which requires transport of 100’s of km over the Sevier highlands and minimal physical abrasion. We hypothesize that the majority of transport was atmospheric, with deposition as ash fall, and minimal reworking in low energy, nearshore environments.

Transport of DZ in this study includes transcontinental rivers, deflation and aeolian transport, volcanic eruption, and local processes. Local and far traveled DZ persist in sedimentary environments for 10’s to 100’s of m.y. depending on tectonic and climatic forcing processes. For example, Cambrian Sawatch and Pliocene Ogalalla fms. have almost identical, locally-derived DZ peak ages despite deposition >500 my apart. Distance of transport and timescales of DZ residence in sedimentary environments has critical implications for DZ provenance studies.