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Structural and taphonomic analysis of a columnar coralline algal build-up from SE Sicily
Institution:1. UPMC Univ Paris 06, UMR 7144, Equipe ABICE, Station Biologique de Roscoff, 29680 Roscoff, France;2. Laboratorio de Ecología Molecular, Instituto de Ecología y Biodiversidad (IEB), Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras, 3425 Santiago, Chile;3. Instituto de Ciencias Ambientales y Evolutivas, Facultad de Ciencias, Universidad Austral de Chile, Isla Teja S/N, Casilla 567, Valdivia, Chile;4. CNRS, UMR 7144, Adaptation et Diversité en Milieu Marin, Station Biologique de Roscoff, 29680 Roscoff, France;1. University of Vigo, Spain;2. Pereiro de Aguiar Prison, Ourense, Spain
Abstract:Unusual “coralligenous” build-ups were found at the infra–circalittoral boundary from SE Sicily. They are columnar, rising up perpendicularly from the bottom, and consist of an inter-growth of encrusting algae and invertebrates. A selected build-up and its longitudinal section, together with some thin sections of selected parts, were studied to detail the growth structures, composition and fabric of the trapped sediments. The coralline algae show a succession of “concentric”, “fruticulose” and “foliaceous” structures. The framework delineates cavities bounded by algal thalli, sometimes filled by sediments. The organisms constituting the framework were grouped into functional guilds (Fagerström, 1991): “primary frame builders” (mainly coralline algae); “secondary frame builders” (vermetids, serpulids and some bryozoans); “bafflers” (erect, flexible bryozoans, some sponges and soft algae); “binders” (encrusting bryozoans, some crustose coralline algae and serpulids); “destroyers” (a few endolithic algae, rare sponges and bivalves); “dwellers” (brachiopods, foraminifers, bivalves, small bryozoans and some motile organisms). The distribution pattern of taphonomic features (composition, grain size and distribution of sediments filling cavities; presence of cement and its location; mineralogical composition and crystal size), together with interactions between growth structures and functional guilds, allowed one to distinguish three taphofacies, each recording different environmental conditions. They have been tentatively related with cyclic sequences testifying to local hydrodynamic regimes, with subsequent slighter and stronger intensity phases, during the last 2200 years.
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