CADIC   02618
CENTRO AUSTRAL DE INVESTIGACIONES CIENTIFICAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
PALAEOENVIRONMENTAL CONDITIONS DURING THE HOLOCENE TRANSGRESSIVE-REGRESSIVE EVENT IN THE BEAGLE CHANNEL, TIERRA DEL FUEGO, SOUTHERN ARGENTINA
Autor/es:
SOLEDAD CANDEL; STEPHEN LOUWYE
Lugar:
Ushuaia
Reunión:
Congreso; VI CONGRESO ARGENTINO DE GEOMORFOLOGÍA Y CUATERNARIO; 2015
Institución organizadora:
CADIC-CONICET
Resumen:
A palynological analysis of 53 sediment samples from two Holocene outcrops located in the bahía Lapataia area, Beagle channel (Tierra del Fuego, southern Argentina), were carried out for the reconstruction of the palaeoenvironmental conditions during the Holocene transgressive-regressive cycle in the Beagle channel. This channel is a former tectonic valley that was completely covered by ice during the Last Glacial Maximum (ca. 24,000 yr BP). After the ice-melting around 8200 14C yr BP, the valley was occupied by lakes, peat bogs and rivers. During the Holocene transgression, the valley was submerged by the sea and a marine environment was fully established by at least by 7900 14C yr BP (Rabassa et al. 1986). The fossil marine sequences are: Aserradero-Lapataia 2 (54º 51´ 22.7" S, 68º 34´ 22.8" W), and arroyo Baliza (54º 51´ 36" S, 68º 33´ 43.2" W) sites. The sediments consist of dark gray clayey silt with presence of abundant mollusks such as Mulinia edulis, Yoldia sp., Venus antiqua, Aulacomya atra, Mytilus chilensis, among others (Rabassa et al. 2009). The palynological analysis from Aserradero-Lapataia 2 site (8167 14C yr BP) shows a dominance of arboreal pollen of Nothofagus dombeyi type associated with shrubs and herbs such as Poaceae, Asteraceae, Empetrum rubrum and Gunnera. The aquatic palynomorph assemblages consists of fifteen dinoflagellate cysts taxa (mainly Brigantedinium simplex, Echinidinium granulatum, Selenopemphix quanta, Polykrikos schwartzii, a.o.), acritarchs (Halodinium sp., Palaeostomocystis fritilla and P. subtilitheca), foraminiferal linings, copepod eggs and freshwater to brackish-marine algae (Botryococcus sp., Zygnema sp., Spirogyra sp., Debarya sp., Cymatiosphaera sp., Tasmanites sp.). The terrestrial palynomorph assemblage identified in the arroyo Baliza site (2844 14C yr BP) is dominated by Nothofagus dombeyi type and shrubs and herbs (Misodendrum, Empetrum rubrum, Poaceae, and Asteraceae). The aquatic palynomorphs are represented by eighteen marine dinoflagellate cysts, mainly Brigantedinium simplex, Brigantedinium spp., Polykrikos schwartzii, Echinidinium granulatum, Dubridinium sp., Polykrikos kofoidii, Selenopemphix nephroides, S. quanta and Islandinium cezare. Acritarchs (Halodinium sp., Palaeostomocystis fritilla, P. subtilitheca and P. sp1) are also present together with foraminiferal linings, copepod eggs and freshwater to brackish-marine algae (Zygnema sp., Spirogyra sp., Cymatiosphaera sp., Tasmanites sp.). The palynological assemblage from Aserradero-Lapataia 2 (8167 14C yr BP) suggests the presence of a closed-canopy Nothofagus forest under cold and highly effective moisture conditions during the Early Holocene transgressive phase. The dinoflagellate cyst species diversity could indicate the development of estuarine environments affected by glacier meltwater discharge resulting in anomalously low salinities. On the other hand, the palynological records of arroyo Baliza site during the Late Holocene, have a similar composition to those observed in the surface samples from the Beagle channel (Candel et al. 2012), with higher diversity of dinoflagellate cyst species suggesting that the environmental conditions during the Mid-Late Holocene are comparable to today. This study completes the preliminary results documented by Rabassa et al. (2009). The new data will allow the comparison of the palynomorph assemblages from the fuegian archipelago with assemblages from other localities of the Northern and Southern Hemispheres.