Late Quaternary benthic foraminifera from the Argentine coastal shelf: a review.

LAPRIDA, C. GARCIA CHAPORI, N., WATANABE, S., TOTAH, V. AND COMPAGNUCCI, R.

Córdoba

Congreso; 9º Congreso Argentino de Paleontología y Bioestratigrafía,; 2006

The Argentina continental shelf (ACS) is one of the largest shelves in the world in which Quaternary sea-level fluctuations prevailed over tectonic and isostatic factors. Since the pioneer study of Boltovskoy (1954), some benthic foraminiferal studies have been performed in short cores from the ACS (core length between 1 and 7 m) retrieving Late Pleistocene to Holocene sediments. Recently, this kind of studies have been intensified with the aim to understand the paleoclimatic implications of the post-LGM (Late Glacial Maximum) evolution of passive continental margins. We present here a brief summary of the results of studies carried out in the ACS in these 50 years of work. In the northern shelf (35 to 41°S), outer shelf cores (> 100 m water depth, core length ~4.5-6m) retrieved late Pleistocene and Holocene sediments. Lowermost samples correspond to pre-LGM inner shelf environments; littoral to upper sublittoral environments related to LGM lowstand are recognized between ~3-4 m depth in the cores; above it, coastal and inner shelf environments dominated by  Malvinas Current (MC) fauna are documented in relation to the early Holocene transgression (Boltovskoy, 1973). Cores from -50 to -100 m (core length ~1 to 4.5 m) contained littoral and inner shelf faunas associated with the beginning of the Late Glacial transgression (Boltovskoy, 1954, 1973, Ferrero, 2005). Isolated specimens of MC species were found in cores at ~-70 to -100 m, related to short-term variations of its western boundary during the early Holocene (Boltovskoy, 1973). Cores from depths shallower than -50 m (core length ~1-6 m) retrieved Holocene sequences (Boltovskoy, 1973, Bernasconi and Cusminsky, in press). Benthic foraminifers indicate coastal settings related to successive positions of the coastline prior to 6000 BP and reflect the rapid sea level rise during the early Holocene. Salt marsh deposits and tidal flats were recognized at -12 m in Colorado Basin for the last 6500 years (Gómez et al., 2000). In the Salado Basin, two pulses of climatic deterioration were detected in nearshore cores reflected in sudden sea level falls which, according to the ages proposed by Vilanova et al. (2006), coincide with the Neoglaciation between 5400 and 4900 BP, and with the cold water invasion on the shelf  (Laprida et al., 2004). In the northern Patagonian shelf (41 to 46°30'S, water depth ~50-100 m), foraminiferal assemblages indicate late Pleistocene lowstand deposits below ~4m depth in the cores, and early Holocene inner shelf facies above it (Boltovskoy, 1973). Isolated MC specimens were found in cores at ~75-100 m water depth. Shorter cores from 45 to 47°S (water depth ~40-143 m) retrieved only Holocene sediments dominated by inner shelf species, with no outstanding variations in faunal composition (Boltovskoy, 1954, Bernasconi and Cusminsky, 2005).