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PALEOECOLOGÍA, COMUNIDADES BENTÓNICAS Y SUCESIÓN PALEOAMBIENTAL EN EL GRUPO RÍO CACHIRI, DEVÓNICO, SIERRA DE PERIJA, VENEZUELA

1983; Asociación Paleontológica Argentina; Volume: 20; Linguagem: Inglês

1851-8044

Teresa M. Sánchez, Juan L. Benedetto,

Space Exploration and Technology

PALAEOECOLOG,BENTHIC COMMUNITIES AND PALAEOENVIRONMENTAL SUCCESSION IN THE RIO CACHIRI GROUP, DEVONIAN, SIERRA DE PERIJA, VENEZUELA.- The Rio Cachiri Group provides a good example of a marine transgressive sequence followed by a main regressive cycle produced by a prograding delta complex. The transgressive sequence begins with unfossiliferous black shales and interbedded quartzitic sandstones with many coquinoid horizons. This facies of shallow water, wave agitated deposits is dominated by the Leptocoelia-Acrospirifer Community. The climax of the transgression, which was reached during Emsian-Early Eifelian times, includes very fossiliferous dark argillaceous limestones and calcareous siltstones deposited in an open marine platform with moderate circulation. This environment was inhabited by two distinct bryozoan communities dominated by fenestrate and ramose forms, brachiopods, crinoids and scattered solitary and colonial Rugosa corals. The prograding deltaic sequence at Eifelian-Civetian time is related with a regional uplift of the region to the southeast of the ancient shoreline. The Leptocoelia, Devonochonetes -Mediospirifer, Longispina and Mediospirifer-Atrypa-Camarotoechia communities fluorished in a shallow subtidal-prodelta environment. The upper part of the regressive marine sequence is characterized by influx of terrigenous sediments which consist of coarse sandstones, green siltstones and carbonaceous shales with much vegetal debris, suggesting a delta platform environment. This zone was inhabited by Tropidoleptus and Devonochonetes-Tylothyris-pelecypods communities, in which the percentage and diversity of molluscan fauna reached a maximum. The Devonian sedimentary cycle culminated with a thick alluvial plants-bearing sequence.