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Drones and Detrital Zircons:APaleogeographical Reconstructionofa Long Lived Mega-Valley in the Ferron Sandstone, Utah.


Provenance analysis of valley terraces in the youngest non-marine sequence of late Turonian Notom Delta in the Ferron Sandstone Member of the Mancos Shale Formation challenges the decade old theory that this ancient delta was fed by a single trunk valley in response to high frequency changes in base level. The single trunk theory was based on grainsize trends and similarity of sedimentary structures, tidal signatures, fluvial style and internal valley architecture; which in turn compared the Ferron-Notom Delta to modern moderate sized rivers such as the Po, Rhône and Ebbro rivers, all of which are single trunk systems.

Using quadrupole Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) of detrital zircons extracted from Incised Valley (IV) terrace samples; distinct provenances were determined for each terrace deposit. Previously published data and new measured sections correlated with the use of drone photography, photogrammetry software and 3D outcrop models were used to identify valley terraces along strike and dip which were then sampled in 13 individual terraces in the attempt to correlate these deposits. 3900 individual zircons were measured, of which 2983 concordant U-Pb age dates were obtained. Plotting the age spectra of these samples in a Multidimensional Scaling analysis (MDS) reveals two distinct population and therefore 2 separate catchment sources.

The resulting paleogeography is that of a multi-trunk, compound incised Mega-valley that evolved to span 30 km along strike and over 30 km down dip. Such a system may be more analogous to the Brazos Delta, and may show similarity with the paleo geographical extent of the McMurray Formation, Alberta, Canada .