Abstract

BOREL, C. Marcela  and  GOMEZ, Eduardo A.. Palynology from the Holocene of Canal del Medio, Bahía Blanca estuary, Buenos Aires, Argentina. Ameghiniana [online]. 2006, vol.43, n.2, pp.399-412. ISSN 1851-8044.

Holocene palynological samples from the Canal del Medio (38° 49' S; 62° 17' W), Bahía Blanca inner estuary, south of Buenos Aires province, contain pollen, spores, remains of algae (Dinoflagellata, Chlorophyta and Cyanophyta) and acritarchs. The pollen spectra are dominated by Chenopodiineae and Poaceae, along with Asteraceae and Ephedra. The dinophycean algae are represented by cysts of estuarine dinoflagellates of the order Gonyaulacales (Operculodinium centrocarpum (Deflandre and Cookson) Wall, Spiniferites bulloideus (Deflandre and Cookson) Sarjeant, S. sp. cf. S. pachydermus (Rossignol) Reid, S. bentorii (Rossignol) Wall and Dale and S. ramosus (Ehrenberg) Loeblich and Loeblich). The chlorophycean algae consist of cenobia of Pediastrum boryanum (Turpin) Meneghini and colonies of Botryococcus braunii Kützing. The assemblages also contain sheets of Gloeotrichia sp. The acritarchs are represented by Micrhystridium sp., Cymatiosphaera sp., Halodinium minus Bujak, Acritarch sp. F, Acritarch sp. G and Acritarch sp. H. Three palynological zones are distinguished in the sequence. The lowermost zone, dated in 3,500 ¹⁴C yr B.P., represents an ancient tidal plain in close relation with a channel of turbid water and variable energy. The intermediate zone suggests better conditions for the development of autotrophic dinoflagellates, in a restricted estuarine environment. For the top zone, the low frequencies of dinocysts and acritarchs indicate similar conditions to those currently present in the inner Bahía Blanca estuary. Along the profile, the pollen reflects the development in the surrounding areas of halophytic communities, with the presence of xerophytic woodland. The characteristics of these deposits indicate that ca. 3,500 ¹⁴C yr B.P., the mean sea level was located at a similar position than the current one.

Keywords : Palynology; Algae; Acritarchs; Pollen; Holocene; Buenos Aires; Argentina.