Recognition of cross-shore dynamics of longshore bars in upper-shoreface deposits of prograding sandy coastal barriers

Abstract

In the past decades it has become evident that the often cyclic cross-shore migration of longshore bars is significantly influenced by wave climate. This study demonstrates that this cyclic migration, whether landward or seaward, leads to the formation of low-angle seaward-inclined stratification (SIS) spanning the beach and upper shoreface in ground-penetrating radar (GPR) data from prograding sandy coastal barriers including strandplains. Previously documented radargrams of these systems are reinterpreted using this knowledge of cross-shore dynamics of longshore bars. Five distinct wave-climate-related radar architectures are identified. A notable observation is the prevalence of SIS as the dominant upper-shoreface to beach structure in most radargrams, despite its infrequently described occurrence from outcrop observations. To address this disparity, this paper also focuses on recognizing SIS in outcrop and core data. Compelling evidence of SIS was discovered in a late Messinian coastal barrier parasequence in SE Spain, and the associated sedimentary architecture is described in detail. It is hypothesized that this example holds generic significance, illustrated using core data from Middle Jurassic strata of the Norwegian continental shelf, and suggesting that the sedimentary architectures of numerous other ancient prograding barrier deposits may exhibit variations within a similar SIS framework.