Central Santa Catarina coastal dunefields chronology and their relation to relative sea level and climatic changes

During the past decades, there have been contrarian explanations for the formation and stabilization of coastal dunefields: while many authors believe the dunes formation would be enhanced by falling sea level, others argue that a rising or stable sea level context would be favorable. For Brazilian coastal dunefields, the second hypothesis seems to be more consistent with the luminescence ages found so far; however, most of these data were obtained without using the SAR protocol. Another point of concern is the role of climate change in the aeolian system, which is still not very clear. The aim of this paper is to try to clarify these two questions. To this end, five coastal dunefields were selected in central Santa Catarina coast. The remote sensing and dating results allowed the discrimination and mapping of at least four aeolian generations. Their age distribution in relation to the global curve of relative sea level variation during the Late Pleistocene allows us to suggest that the formation of Aeolian dunefields in the coastal context is supported by stable relative sea level. However, relative sea level is not the only determinant for the formation and preservation of the aeolian coastal dunes. Evidences of climatic control indicate that the initiation of dunefields would be favored by periods of less humidity while their stabilization would occur preferably during the periods of rain intensification, connected to monsoon activity

Discussion of: Size grading along a shingle beach in Wicklow, Ireland.

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Rine Point, un cordon de galets et de sable de la baie de Galway (Comté de Clare, Irlande) et formes associées

ABSTRACT Rine Point is a 2,2 km gravel spit on the south coast of Galway Bay in Co. Clare, western Ireland. The spit is composed of Carboniferous Limestone either derived directly from marine erosion of the Burren Limestone cliffs around Black Head and] or from the shore platforms, or, indirectly, from local glacial deposits (mainly periglacial head). Clasts from these sources have moved east into Galway Bay under a unidirectional regime of decaying Atlantic swell. Initially, the material forms a 2 km fringing ridge made up of gravels, cobbles to boulders, but this passes alongshore into the Rine Point spit. The spit is divided into a series of small (up to 250 m) discrete cells or embayments. These are formed either as the spit tries to attain a local quasi-equilibrium with the incident swell (see Carter et al., 1987) or are associated with irregularities in the frontal rock platform. In several places the spit has been breached and the distal extremity has been beheaded, leaving two residual islands. A distinct cross-shore zonation is apparent. The rock platform and pebbles show excellent examples of bioerosion features. The beachface is formed of rounded gravels, with shell sand patches in the updrift parts of the cells. The ridge crest and back barrier slope are capped with a thin, stratified shelly sand, containing occasional molluscs. In places, small, high level storm breaches have occurred creating fan-shaped gravel washovers. The spit encloses a small tidal marsh, which drains east into a tidal flat. The present day sediment input to Rine Point is probably negligible. To the west, sediment suppy to the coast has been impeded by the building of the coast road and the longshore drift reduced after the building of a small harbour near Black Head in the late-nineteenth century. Much of the remaining cliffline is now naturally armoured with boulder deposits. The morphology of Rine Point suggests strongly that it is a mature feature, which may be entering a phase of decay and break-up.RÉSUMÉ La flèche littorale de Rine Point est accolée dans sa partie occidentale, interne, à une colline de calcaire carbonifère en place et à des dépôts glaciaires et péri- glaciaires pleistocenes. Sa partie orientale, en avant d'un marais maritime qu'elle abrite, est affectée d'ondulations dont l'origine est examinée. Sa sédimentologie (sables, galets, dune résiduelle sommitale) est décrite, ainsi que la plateforme rocheuse calcaire sur laquelle elle repose. Son devenir est envisagé.Morel V, Pennober G, Guilcher André, Carter R.W.G. Rine Point, un cordon de galets et de sable de la baie de Galway (Comté de Clare, Irlande) et formes associées. In: Norois, n°160, Octobre-Décembre 1993. pp. 643-652