Rocky shore-gravelly beach transition, and storm/post-storm changes of a holocene gravelly beach (Kos island, Aegean sea): Stratigraphic significance

Summary  On Kos island, Greece, along an investigated coastal segment 3 km in length, four adjacent sectors were distinguished, (1) Empros beach, a rocky shore with plunging cliffs and a steeply dipping, submarine talus, (2) Thermi beach, a „coarse-clastic beach” with a subaerial cliff fringed by a bouldery to coarse gravelly beach with poorly developed zonation, (3) Dimitra beach, a gravelly beach with well-developed zonation, and (4) Phokas beach, a gravelly beach characterized by finer mean grain size. The lateral variation in Holocene coastal morphology would lead to different transgressive records: „rapid” sea-level rise that may be suggested by transgression of the rocky shore is contemporaneous with „gradual” rise recorded by transgression of the gravelly beaches. Dimitra beach is an about 500 m long, cuspate, microtidal, wave-dominated gravelly beach. From land offshore, in its fairweather configuration it shows

(a)	a backshore of rounded gravels to small, rounded boulders,
(b)	a winter storm berm paved by disc-shaped clasts,
(c)	a belt of beach cusps each centered by an oblique-triangular foreshore sand flat, and flanked by gravel ridges of roughly triangular shape in plan view,
(d)	a fairweather plunge step,
(e)	a. „relic storm/swell beachface” (uppermost shoreface during fairweather) of clean, rounded coarse gravels to cobbles,
(f)	a storm/swell plunge step, and
(g)	a vencer of gravels to boulders that, farther seaward, grades into submarine sand flats.

During storm upbuilding, the foreshore sand flats disappeared, the gravel ridges were eroded and an even, more gently dipping storm beachface developed. Beach restoration in a swell regime proceeded in feedback with the emergent fairweather beach morphology. During ensuing fairweather, the foreshore sand flats were partly winnowed. On Dimitra beach the layer involved in beach face to uppermost shoreface dynamics was about 1 m thick and 10–15 m wide. In fossil gravelly beach successions, features formed during highenergy events include both berms and master bedding surfaces. Features of the waning stage are fairweather plunge steps and relic storm/swell beachfaces (lower beachface). From cuspate gravel ridges of the upper beachface probably only the basal part is preserved.