Acritarchs from Ponta Grossa Formation and Their Stratigraphic Significance--Devonian of Parana Basin: ABSTRACT

Abstract

The Devonian fossil record in the Parana basin of Brazil is End_Page 450------------------------------ restricted to the Ponta Grossa Formation, a potential source rock unit. The subsurface distribution, the character and the stratigraphic limits of this formation are not precisely known yet. Paleontological studies of the macrofauna from this formation indicated an Early Devonian age. Previous palynological analysis has been exclusively based on chitinozoans, spores, and the acritarchs of the leiofusidae group and the Maranhites genera. Other microplankton have not been considered. This paper intends to fill this lack in the palynological record of the Devonian for the Parana basin. For this paper a wide range of surface samples and core samples from eight wells drilled by PAULIPETRO (a CESP-IPT joint venture) have been studied. Microplankton from the Devonian of the Parana basin never before described are presented here, together with their biostratigraphical and paleoecological implications. Intrabasinal and interbasinal correlations are also made. From a total of 60 species identified until now, twenty forms having well-defined stratigraphic ranges and broad (intercontinental) geographic representation are described herein. This assemblage is marked by the presence and diversity of the Subgroups Polygonomorphitae and Pteromorphitae. The Subgroup Acanthomorphitae is also well represented. The Emsian-Frasnian age previously established for the Ponta Grossa Formation through other palynological studies is further confirmed by the paleomicroplankton evidence. Moreover, the chronostratigraphic limits of these sediments may now be refined even further. Thus, despite the presence of long-ranging forms, other species, such as Triangulina alargada, which is restricted to the Emsian in the La Vid Formation in northern Spain, allow a better chronostratigraphic subdivision of the Ponta Grossa Formation. The microplankton assemblage is very similar to others known from the Maranhao basin, Brazil; the province of Leon, Spain; and Ghana, Africa. The abundance of forms of Tasmanites together with a large quantity and diversity of microplankton provides the basis for the paleoecologic interpretations. End_of_Article - Last_Page 451------------