Growth faults at the prodelta to delta-front transition, Cretaceous Ferronsandstone, Utah

Cliff exposures of synsedimentary growth faults at the base of the Cretaceo us Ferron sandstone in central Utah represent outcrop analogs to subsurface growth faults. Delta front sands prograded over and deformed less dense pr odelta muds of the underlying Tununk Shale. Detailed fault patterns and ass ociated facies changes demonstrate a complex fault history and style for gr owth fault development rather than a simple progressive development of faul ts in a basinward position. The most proximal and most distal fault sets we re the earliest active faults, Growth faulting was initiated by deposition of cross-bedded distributary channel and mouth bar sandstones that reach 9 m thick in the hangingwalls of the faults. Curvature of the beds in the han gingwall of the faults nucleates smaller conjugate fault sets. Cross-bed se ts in the hangingwalls of faults decrease from meter to decimeter scale awa y from the faults suggesting decreasing flow velocity or decreased preserva tion of cross sets as a result of decreasing accommodation in distal hangin gwalls. Shifts in depositional loci, including upstream and downstream accr etion of mouth bar sands contribute to the complex faults history and inter nal heterogeneity and development of potentially isolated sandy reservoir c ompartments. (C) 2001 Elsevier Science Ltd. All rights reserved.