Late Quaternary marginal marine deposits and palaeoenvironments from northeastern Buenos Aires Province, Argentina: A review

Abstract

The late Quaternary marginal marine deposits along eastern Argentina (Southwestern Atlantic) are reviewed according to our present knowledge. In the northeastern coastal area of Buenos Aires Province they have been assigned to a series of transgressions and regressions ranging from the late Pliocene to the late Quaternary. The most widely accepted model is Frenguelli's (1957) classical chronostratigraphical scheme of: ‘Belgranense’, late Pleistocene marine sediments at 3–6 m above m.s.l. and ca. 26,000−>35,000 14C years BP, the ‘Querandinense’, Pleistocene-Holocene estuarine sediments below or at present m.s.l., and the most extensive ‘Platense’, mid-Holocene marine deposits at 4.5−2 m above m.s.l. dated at ca. 8000-1340 14C years BP. The restricted ‘Belgranense’ deposits, recorded in Samborombon Bay, in Magdalena at ca. 32,000 BP, near Mar Chiquita at ca. 24,900 and 30,500 BP and southwards in Bahía Blanca at ca. 26,000–35,500 BP, may belong to an interstadial (González et al., 1986). The molluscan composition suggests a marine invasion of the area but not a typical interglacial cycle characterized by euhaline and warm water elements. However, the oxygen isotope record argues against an interstadial during the interval 34−27 ka and the chronological control for these deposits is very poor, suggesting that they most probably have been elevated neotectonically. The Pleistocene-Holocene ‘Querandinense’ deposits, extensively distributed along the Bonaerensian coastal plain and continental shelf (ca. 11,000 14C years BP), with very low faunal diversity, abundance of freshwater ostracods and absence of the warm water molluscs characteristic of the Holocene ridges, indicate low salinity and cool water conditions. Further dating and isotope analysis of these deposits are required for a better understanding of the chronology of climatic events by the end of the Pleistocene in this area and to establish whether or not they could correspond to the Younger Dryas event of the northern hemisphere. ‘Platense’ littoral ridges formed between ca. 7600 and 2500 BP extend in several subparallel rows from ca. 34° S to ca. 39° S. They formed either as beaches or possibly as sublittoral bars in Samborombon Bay, where they reach 120 km long, 10–30 m wide and up to 5 m thick at 4.5–5 m above m.s.l., or in the supratidal and intertidal zones in Mar Chiquita at 2–4 m above m.s.l. Molluscs and ostracods suggest a brackish marine to marine brackish environment of lower salinity than the modern Atlantic littoral. During the mid-Holocene, the oceanic waters were mixing with large amounts of Antarctic ice melting in the South Atlantic (Isla, 1990) probably reducing salinity along the Bonaerensian littoral. The oldest littoral ridges accumulated during the Hypsithermal and in the Punta Indio area, their different geometry and alignment, greatest age, highest diversity and warmer affinity of the molluscan fauna suggest a short interval of reversal of the atmospheric circulation pattern. Further research is necessary for a better understanding of the chronology of the marine late Quaternary deposits, coastal evolution and climatic changes in this area.