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Re-Evaluating the Asymmetry of Subsurface Wave-Influenced Deltaic Systems

Abstract

This study focuses on re-evaluating the asymmetry of a subsurface wave-influenced deltaic system from the Cretaceous Ferron Sandstone, South-Central Utah. The asymmetric delta model was initially proposed in 2003, primarily based on studies of modern wave-influenced systems. This model has been applied to interpret many subsurface deltaic systems and provided significant guidance for hydrocarbon exploration and development. However, most of the previous studies were based only 2-D along-strike data, where important regional context information and detailed facies architectural analysis at the transitional zone between fluvial-dominated deltaic and wave-dominate shoreface are largely lacking. In addition, the documentation of lateral transition from fluvial- to wave-dominated facies is probably not enough to define the asymmetry of the delta. Integration of regional sequence stratigraphy and detailed facies architectural analysis allows to re-evaluate the Notom Delta in the Cretaceous Ferron Sandstone. This study is based on previous studies on the Notom Delta and newly collected data including 18 detailed measured sections, nine high-resolution photomosaics, 10 clinoform dips and over 1500 paleocurrent measurements. The highly fluvial-dominated nature of the deltaic deposits, nearly opposite direction of paleo-river flow to the approaching waves, updrift barrier system, lacking of muddy lagoon facies under a positive shoreline trajectory and lacking of downdrift-deflected mouth bars all indicate a symmetric delta protected by a barrier system, which is different from previous interpretations. This study suggest that geologist should be more cautious in applying the asymmetric deltaic model to subsurface deltaic systems and if possible more data can be incorporated into the analysis.