Palynostratigraphy of the cretaceous-paleogene in the Austral basin, SW Santa Cruz province, Argentina

Abstract

This paper analyses the palynological assemblages recovered from the Cerro Cazador and Monte Chico formations and is an exhaustive study of the spore-pollen assemblages from the Cerro Dorotea Formation; all units with outcrops out in southwestern Santa Cruz Province, Argentina. Six sections were sampled in two main areas: Estancia San José and Estancia Laguna Salada. The palynological assemblages yielded by the studied formations are integrated with elements of marine (dinoflagellate cysts and acritarchs) and continental (spores and pollen grains) origin, present in different proportions throughout these units. Forty one species of pollen grains and spores were recognized in the Cerro Cazador Formation, 74 genera and 127 species in the Monte Chico Formation and 64 genera and 107 species in the Cerro Dorotea Formation. On the basis of the stratigraphic distribution of the identified species, four palynological assemblages were recognized, which were defined by the exclusive presence of characteristic species and their similarities with other spore-pollen assemblages. The following ages were suggested: (i) Association 1, upper sections of the Cerro Cazador Formation: upper Campanian-lower Maastrichtian; (ii) Association 2, lower and middle levels of the Monte Chico Formation: Maastrichtian, probably upper Maastrichtian; (iii) Association 3, upper levels of the Monte Chico Formation: Maastrichtian-Danian; and (iv) Association 4, Cerro Dorotea Formation: Danian. Based on this analysis, the K/P boundary is located between Associations 2 and 3, within the Monte Chico Formation. These palynological assemblages indicate a near-shore marine depositional environment close to the coastline, with marginal conditions, and a progressive shallowing of the basin.