BIOSTRATIGRAPHY, TAXONOMIC DIVERSITY AND PATTERNS OF MORPHOLOGICAL EVOLUTION OF ORDOVICIAN ACRITARCHS (ORGANIC-WALLED MICROPHYTOPLANKTON) FROM THE NORTHERN GONDWANA MARGIN IN RELATION TO PALAEOCLIMATIC AND PALAEOGEOGRAPHIC CHANGES

Abstract

Acritarchs, the fossilizable, resting cysts of phytoplanktonic algal protists, are the dominant component of marine organic-walled microfossils in the Palaeozoic. The majority of acritarchs show strong similarities with dinoflagellate cysts in morphological and biogeochemical features, as well as distributional patterns in the sediments. The production of these organic-walled microfossils and their distribution and survivorship in the sediments were controlled by differences in ecological tolerances and life cycle (autecology) of the planktonic parent organisms.