Exhumed Shoreface and Tidal-Delta Complexes in Lower Cretaceous Ferron Delta (Central Utah): ABSTRACT

Abstract

Numerous studies of modern shoreface and tidal-delta complexes have appeared in the literature, but few well-documented ancient examples are known. In the Lower Cretaceous (Turonian) Ferron delta complex of the Mancos Shale in central Utah, such a system has been recognized in outcrop. This complex is part of the transgressive destructional phase of the Ferron delta and represents a shoreface setting overstepped by rapid transgression, buried and preserved within fine-grained, shallow shelf sediments. The facies tract is now exposed by erosion and the exhumed surface has been examined in detail. The exposed parts of the shoreface complex consist of 9 km of upper-shoreface and foreshore settings, tidal inlets with recurved accretionary spits, ebb-tidal delta bodies, and extensive washover fans. Within the outcrop belt, two inlet complexes have been positively recognized and parts of a third complex may be present. Behind the shoreface complex are shallow and restricted lagoons with locally extensive tidal channels. Geometry of the ebb-tidal delta bodies and their suites of preserved sedimentary features support a model of strong longshore current systems from south to north along the edge of a large embayment. Studies of basin geometry, shelf width, probable nature of the adjacent land surface, and paleocirculation patterns have all combined to provide data for this model of a mesotidal setting with associated shoreface, lagoonal, and tidal-facies tracts. End_of_Article - Last_Page 294------------