Mid- to Late Holocene organic-walled dinoflagellate cysts from the northern Argentine shelf

Abstract

A Mid- to Late Holocene dinocyst record from the northern inner shelf of Argentina is described. It is analyzed with respect to the distribution of modern dinocysts, other Holocene records from the Buenos Aires province and the biogeographic distribution of planktonic dinocysts and their motile equivalents. Between ca. 5360 and 3300 14C yr BP the low diversity and abundance of the cyst assemblages can be related to a restricted littoral-subtidal environments. After ca. 3300 14C yr BP a major change is characterized by an increase in dinocyst abundance, indicating a normal inner neritic environment. The dominance of Operculodindium centrocarpum at some levels suggests some influence of continental shelf waters whereas the higher abundances of dinocysts from heterotrophic taxa e.g. Protoperidinium stellatum, Votadinium calvum, V. spinosum in other levels reflects a more inshore-coastal water influence with increased nutrient availability. Both assemblages are consistent with the present day transitional coastal-neritic conditions, suggesting that they were established after ca. 3300 14C yr. These inferences supplement those based on other proxies, reflecting sea-level decrease and the coastal geomorphological evolution post ca. 5360 14C yr BP.