--> Links Between Short-Term Beach Evolution and Resulting Heterogeneities in Wave-Dominated, Upper-Shoreface-Foreshore Sandstone Bodies
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AAPG ACE 2018

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Links Between Short-Term Beach Evolution and Resulting Heterogeneities in Previous HitWaveNext Hit-Dominated, Upper-Shoreface-Foreshore Sandstone Bodies

Abstract

Despite the knowledge on morphodynamics of regressive, Previous HitwaveNext Hit-dominated barrier/strandplain systems, processes responsible for sand accretion and seaward migration operating at 102-103 year scale in the upper-shoreface and foreshore regions are far from been understood. In this contribution we analyze architectural styles of foreshore-to-upper-shoreface sand bodies of microtidal, barrier/strandplain systems, in order to reconstruct depositional processes and discuss preservation of morphological features, and possible controlling factors. Selected cases studies include Cainozoic and Cretaceous examples with a narrow grain size range (very fine to medium sand), in which facies and architectural styles allow for reconstructions on gradients and morphological configurations.

Three main architectural styles were recognized. Type 1 and Type 2 styles are characterized by preservation of upper-shoreface (US), cross-bedded sandstones and foreshore (FS) parallel planar laminated, but with contrasting depositional gradients. Type 1 shows FS deposits downlapping (seaward) onto upper-shoreface strata with a clear slope break (> 5° to < 1°), whereas Type 2 shows subhorizontal transitions between FS and US deposits. Type 3 style is characterized by large-scale, seaward dipping foreset beds (11°-2°) with a tangential geometry, and weak discrimination between foreshore and upper-shoreface sediments. Parallel planar lamination and small-scale trough cross-stratification are common, the latter becoming dominant at the bottomsets.

Previous HitTypesNext Hit 1 and 2 are interpreted to represent long-lived, bar-trough systems in gentle to moderate beach profiles, whereas Type 3 reflects bar-less, steeper beachfaces. Bar-related deposits (e.g., swash or longshore bars) are uncommon, suggesting low preservation of these features in regressive, microtidal systems. The analyzed dataset suggests that the generation and preservation of any single architectural style seems unrelated to the Previous HitwaveNext Hit-dominated system type or shoreline trajectory. In contrast, they likely reflect preferential sediment accumulation in the US or FS settings over 102-1003-year periods, which eventually could be linked to the associated beach profiles (from dissipative to reflective beaches).

The identification of different architectural styles in these US-FS deposits as a result of contrasting mid-term evolution of the Previous HitwaveTop-dominated, regressive system may provide an innovative insight for the characterization of paralic reservoirs.