Beachrock litorale Morphodynamik und Meeresspiegeländerungen nach Befunden auf Euboa (Griechenland). in Beiträge zur Geomorphologie und Länderkunde. Prof. Dr. Harmut Valentin zum Gedächtnis.. (Beachrock. Littoral morphodynamics and sea level
Beachrocks are beach materials lithified above high tide level. The beach material will be cemented under the prevailing conditions of Mediterranean climate there. Before being cemented beach materials must have been wetted, and this process
is linked to rare oceanographic-climatic conditions, such as wind-tides lifting up the sea level and extending the swash zone landward. Under even these conditions beachrocks are destroyed by backswash and breakers, too. Formation and destruction of beach
rock occur at the same time. Periods of months, years or 10 years are required for beachrock formation, whereas beachrocks may be destroyed in periods of 10-10 years. The authors working on beachrock up to now agree beachrock to be an excellent
The coast of Lebanon lends itself particulary well to the development of beach-rock, whatever the pluviometry, the nature of sediments, or the size of its constitutive elements. If the beach-rock does not appear in areas where the coastline
is stable, it is present where the coast is receding. Beach-rock does not originate in the material which composes the present beach, but in fossil marine deposits which may be several millenia old (Bronze Age, for example).
Beach-rocks of coastal beaches or of sand reef cays could be considered as witnesses: 1) of the coastal morphology, of the sedimentary conditions and of the altitudinal sea level| 2) of the wave-exposure. It's in this view that are analysed: 1
) the fossilized organisms into the beach-rocks| 2) the organisms that could be fossilized or apt to leave a matrix or a print, that colonize beach-rocks when they are exposed and when they form hard-substrates.
Numerous examples all along the Mediterranean coastline show that beach-rock frequently originates inside soft fossil holocene marine deposits and is exposed only when the coast recedes. The present beach often hides it during the summer, thus
making it possible for a veil of sand to cement itself unconformably on the slabs of beach-rock. The phenomenon of receding coastlines being general in the Mediterranean, it is quite natural that beach-rock forms in this ancient sedimentary stock
the problem of whether the beach-rock is associated with Holocene fossil beaches. The result of the review varies according to sites. The second series intends to insist upon the value of beach-rock in the study of the variation of sandy beach outlines
Essai de synthèse sur le beach-rock in Le beach-rock.
Beachrock ; Géographie physique ; Géomorphogenèse ; Littoral ; Milieu marin ; Niveau marin ; PICG 200 ; Sédimentologie
A l'issue du colloque sur le beach-rock, les participants ont élaboré la définition suivante: le beach-rock est une formation sédimentaire indurée sous l'effet d'une cimentation carbonatée, réalisée au niveau de l'étage médiolittoral. Il existe des
beach-rocks fossiles, situés à des altitudes supérieures ou au contraire inférieures au niveau actuel de la mer.
In tropical regions beach-rock in the best tool for the study of the variations of sandy beach outlines during the last 6 000 years. In Madagascar, it is very frequent, especially in the coral reef areas. It provides possibilities to obtain data
concerning the evolution, often very complicated, of littoral spits, sand cays, and motu. Arrecifes, on the SE, S and SW coasts of Madagascar, are not Flandrian beachrocks, but probably contemporaneous with the post Eemian regression.
Beach-rocks, which are common in tropical regions, may be capped by coral reefs, or conversely develop upon reef flats, depending on the variations of sea level and coastal profile in recent times. Some good examples of these complex relationships
are presented here from the Northeastern coasts of Brazil where they are particularly conspicuous due to the thinness of coral formations and to the great development of the beachrocks.
Recent studies of littoral geomorphology in Sardinia have showed the existence of numerous beach-rock outcrops. These can be classified into two generations: the first one which goes up to 50 cm, whose emerged part is often corroded and whose
immerged part is broken into polygonal paving-flags. The second lays on the tidal zone and sometimes contains Roman or Punic artefacts. On the other hand, different oceanographic missions and diving operations have discovered several beach-rocks spread over
of a streamlet. This sandstone does not seem to be an actual beach-rock despite some analogies.
On Verdicio beach, in Penas cape, on the northern Spanish coast, an holocene littoral sandy deposit is transformed into sandstone. It is protected from the sea water by a present sandy littoral formation, and it is in contact with the fresh water
Sur la plage de Pattaya, sur la côte E du golfe de Siam, les sédiments de l'estran consistent en un mélange de grains de quartz et de feldspath et de bioclastes marins consolidés par un ciment marin et transformés en beach-rock (microphotographies).
are precipitated in a marine or fresh-water, phreatic or vadose environment close to the water table. Oblique beach stratification and keystone vugs (typical for the swash zone) are thus preserved. Coastal erosion exposes this preferentially cemented layer
, and marine cementation in the intertidal zone further indurates the rock. Wave action often washes away the underlying non consolidated sediments. This causes the beachrock to break into blocks which may glide into the subtidal zone.
Beach-rock development is based on successive stages of microbial activity, crystal growth, mechanical and biological erosion, etc. The combined study of such events could be a helpful way to recognize and differentiate shoreline variations.
The radiocarbon dating of a beach-rock from the Ligurian coast (Italy) has given an apparent 14 C age of 3330 95 yr B.P. In spite of the uncertainty on the actual age, the beach-rock seems to have been developing even after the Post-glacial climatic
optimum. Nine horary pH measurements have been done donc during 26 hours in 4 solution pits developed on the emerged beach-rock. High variations are observed. These observations are the same for each pit and this corroborates the importance of biochemical
Les beach-rocks de la baie de Funtanamare (Sardaigne sud-occidentale) in Le beach-rock.
Ancien rivage ; Beachrock ; Funtanamare, baie ; Géographie de l'Europe ; Géomorphogenèse ; Géomorphologie littorale ; Italie ; Littoral ; Niveau marin ; PICG 200 ; Plate-forme continentale ; Pléistocène supérieur ; Quaternaire marin ; Sardegna
Dynamique littorale actuelle de la plage submergée| formes et dépôts attribués à la transgression versilienne. En particulier un beach-rock versilien, qui s'étire sur 3 km, ferme la baie à une profondeur qui va de 8 m sur les bords jusqu'à 20 m dans
la partie centrale. La comparaison avec les autres dépôts de plage submergés observés le long de la côte sarde, montre que le stationnement de la mer à la profondeur de ce beach-rock est un des plus importants de la transgression versilienne.