DEFLEXED BALTOGRAPTUS SPECIES IN THE EARLY TO MID ARENIG GRAPTOLITE BIOSTRATIGRAPHY OF NORTHWESTERN ARGENTINA

摘要

1 INTRODUCTIONGraptolites constitute one of the most important groups of fossils used to define the biostratigraphic framework of the Lower to Middle Ordovician sedimentary succession of Northwestern Argentina. As a result of a more intensive taxonomic study during the last decade several biozones were proposed mainly for the Early Ordovician of the Eastern Cordillera. Nevertheless, little is known of the proximal end development of the biostratigraphically important species in this succession (e.g., Baltograptus, Corymbograptus). The aim of this paper is to provide an accurate understanding of a number of expansograptids, including Baltograptus sp. nov., B.