PRODELTAIC QUARTZ-SAND TURBIDITES IN THE UPPER PENNINGTONFORMATION (MISSISSIPPIAN) AT DOUGHERTY GAP, WALKER COUNTY,GEORGIA (U.S.A.)

摘要

Approximately 4.0 m of interbeddedfine-grained quartz sandstone and shale lay-ers are exposed laterally for 100 m along asidewall at Dougherty Gap, Georgia(U.S.A.). These strata have been interpretedas crevasse-splay deposits suggestive of del-taic infill near the close of the MississippianPeriod. However, another depositional set-ting is possible. The multiple sandstone lay-ers within this interval are not bioturbated,have no obvious internal bedding or sedi-mentary features, exhibit predepositionalconvex hypichnial traces along the bed soles,and have postdepositional asymmetric lin-guoid ripples across the top surfaces of thesandstones. Collectively, these features areindicative of turbidites. The limited natureand scale of these siliciclastic deposits sug-gest emplacement in association with stormevents along an unstable delta front. This"sandy turbidite–mud" cycle was repeatedmore than 20 times at this locale.