Record of a nonbarred clastic shoreline

ISLA, MANUEL F.; SCHWARZ E.; VEIGA G.D.

GEOLOGY

GEOLOGICAL SOC AMER, INC

Lugar: Boulder; Año: 2020

0091-7613

The morphology of wave-dominated clastic shorelines (i.e., foreshore and upper-shoreface sediments) can vary from barred to non-barred, though the geological record of non-barred, sand-dominated shorelines has yet to be recognized. A facies and quantitative architecture analysis of a clastic shoreline succession characterized by sandy, inclined beds is presented and interpreted as the record of a high-gradient, non-barred shoreline. Inclined beds dip seaward and have a tangential geometry (< 3 m height, < 40 long, < 11° dip), and they are composed of planar lamination along the foreset and subordinate small-scale trough cross-bedding in the bottomsets. This facies distribution reflects a steep beach profile with a narrow surf zone and development of plane bed both in foreshore and proximal upper-shoreface settings. Successive packages of inclined beds are interpreted as the seaward accretion of this shoreline morphology. The resulting architecture is similar to radar facies interpreted as upper-shoreface/foreshore deposits in sandy Holocene examples, offering outcrop-based ground truth for GPR-based studies. We propose diagnostic criteria for identification in the record of non-barred, clastic shorelines in recent and deep time, and contrast them with classical facies models of barred systems.