NEW BIOSTRATIGRAPHIC PROPOSAL FOR THE TUCUNUCO GROUP (LOWER PALAEOZOIC), SAN JUAN PRECORDILLERA, ARGENTINA,BASED ON MARINE AND TERRESTRIAL PALYNOMORPHS

VICTORIA JOSEFINA GARCÍA; CLAUDIA VIVIANA RUBINSTEIN

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2015 vol. 52 p. 265 - 285

0002-7014

An exhaustive analysis of the palynomorph assemblages (organic-walled marine phytoplankton and miospores) from the Tucunuco Group, San Juan Central Precordillera was made, comprising four localities: Río Jáchal, Río de las Chacritas, Cerro La Chilca and Quebrada Ancha. Previous data concerning several fossils groups, such as graptolites, conodonts and brachiopods, suggest a mainly Llandovery-Wenlock? age for the La Chilca Formation and Ludlow to locally Lochkovian age for the Los Espejos Formation. The predominance of the marine palynomorphs in both formations in all the studied sections is highlighted. Even though the terrestrial palynomorphs are minority, trilete spores are abundant, diverse and biostatigraphically relevant in the Los Espejos Formation. Correlations with marine palynomorph assemblages and trilete spores biozones from all over the world allow constraining the age of both formations. The Wenlock age of the middle-upper part of the La Chilca Formation is confirmed based on the marine phytoplankton. In the Los Espejos Formation, it is possible to distinguish, from the base to the top, a probable Wenlock, Ludlow, Přídolí and the Lochkovian exclusively in the northern outcrop. Therefore, the presence of the Silurian/Devonian boundary in the upper part on the Los Espejos Formation is confirmed.  A north?south correlation scheme of the studied sections is proposed.