Palynological record of the Silurian/Devonian boundary in the Argentine Precordillera, western Gondwana

Abstract

The palynological assemblages of the upper part of the Los Espejos Formation and the lower part of the Talacasto Formation, in the northern outcrops of San Juan Precordillera, Argentina, were studied. This section spans the Silurian/Devonian boundary. Therefore the palynological analysis helps to constrain the age and to identify the position of the system boundary. This age interval has been much discussed owing to the scarcity of stratigraphically valuable fossils. The miospores and marine phytoplankton present in the upper part of the Los Espejos Formation, point to a Late Ludlow/ Přídolí? to early Lochkovian age. The occurrence of relevant biostratigraphic species such as Dictyotriletes cf. emsiensis Morphon, Cymbosporits proteus, Amicospopites streeli and the possible presence of Streelispora newportensis, permit the identification of the Silurian/Devonian boundary within the Los Espejos Formation. This system boundary is recorded for the first time in the Precordillera based on palynological assemblages. The position of this limit coincides with that established based on faunal data. A Lochkovian age is also confirmed in the lower part of the overlaying Talacasto Formation in the studied section, thus supporting previous palynological and fauna data.