科研之友
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摘要
A marine molluscan assemblage is described from four fossil concentrations in the Coastal Plain of Rio Grande do Sul State, southern Brazil. The concentrations were found at the same stratigraphic interval, some 7.5 m above present sea-level, in a layer deposited in a shallow marine environment during the penultimate marine transgression around 230 ka BP and currently exposed along the banks of Chui Creek, located some 11 km landwards of the present coastline. The assemblage is composed of a mixture of highly fragmented, unidentifiable shells and well-preserved bivalves and gastropods. Many bivalve remains are complete, including juveniles and thin-shelled taxa, lacking signs of abrasion or bioerosion. The origin of the shell concentrations is interpreted as a short-term depositional event, generated by storms, in shallow water settings under a marine transgressive regime. The predominant taxa in the assemblage are infaunal, stenohaline bivalves that inhabit shallow sandy bottoms, with few gastropods and epifaunal organisms. Most of the taxa have living representatives today in the southern Brazilian coast, indicating a mixture of Argentinean and Caribbean (or Brazilian) malacological provinces. The presence of taxa that are not found living in the coast of Rio Grande do Sul today (Anomalocardia brasiliana, Chione paphia, C. cancellata, Anadara brasiliana and Arcinella brasiliana), suggests wanner oceanographic conditions coinciding with past sea-level highstands, also indicated by similar taxa found in fossil concentrations in the Uruguayan and Argentinean coasts. A discussion of the stratigraphic position, age and correlation of this assemblage with other outcrops is also presented.
- 出版日期2013-12
