Depositional Model for Submarine Fan Deposits of Vedder Sandstone, Eastern San Joaquin Basin: ABSTRACT

Abstract

The Vedder sandstone is an informal subsurface term applied collectively to a series of offlapping clastic wedges of late Oligocene through early Miocene age that subcrop beneath the basal Saucesian unconformity along the southeastern flank of the San Joaquin basin. Although the Vedder has generally been accepted as a shoreface to shallow-water shelf deposit, such an interpretation is inconsistent with the sandstone body geometry, vertical and lateral sequence architecture, and inferred paleobathymetry of foraminiferal assemblages for the interval over the greater part of the northwestern subcrop trend. The Vedder sandstone in that region represents deposition in a series of small submarine fans that coalesced at the base of a fault-controlled slope along the eastern margin of the Zemorrian San Joaquin basin. The Vedder fans exhibit a relatively broad inner fan apron composed of amalgamated, channel-fill deposits that pass quickly downdip into a highly variable midfan belt of channel-levee complexes. The outer fan is characterized by thick, sand-rich depositional lobes with a narrow outer fan fringe. Three periods of fan progradation are recognized in the Vedder interval, each corresponding to a relative sea level drop related to local tectonic pulses in the active forearc setting. A subsequent lowstand coincident with majormore » uplift along the basin margin resulted in a regional unconformity that beheaded the Vedder fans and stripped off much of the equivalent slope and shelf facies. This unconformity juxtaposed the updip Vedder sandstones against an overlying transgressive sandstone, thus reducing the otherwise excellent stratigraphic trap geometries of the Vedder interval.« less