Palynomorphs from the Devonian Talacasto and Punta Negra Formations, Argentinean Precordillera: New biostratigraphic approach

摘要

Marine and terrestrial palynomorphs from the Loma de los Piojos section of the Precordillera Basin, western Argentina, were analyzed. The studied section embraces the upper part of the Lower Devonian Talacasto Formation and the whole Lower-Middle? Devonian Punta Negra Formation, which constitute the Gualilan Group. Terrestrial palynomorphs dominate the Talacasto Formation whereas marine palynomorphs dominate the Punta Negra Formation. Even though palynomorphs are scarce, poorly preserved, and marked by low diversity, they enable, together with previous palynological data, a new biostratigraphic interpretation for the Devonian units of the Gualilan Group. In addition, an age reassessment of the guide horizon of Keidel (1921), and a correlation of sections from different parts of the basin are provided. Based on palynological data, the age of the Talacasto Formation is constrained to the Lochkovian-late Pragian and the age of the Punta Negra Formation is now considered to be restricted to the late Pragian-Emsian, although a younger age for the uppermost part of Punta Negra is possible.