THE EARLY PALEOZOIC MINISTROMATOLITES

Abstract

In spite of intensive sedimentological and biostratigraphic investigations of ministromatolites, their assemblages systematically studied are those of Precambrian age. Ministromatolites occurred in abundance in the Early Proterozoic and Early Riphean but disappeared later. After the Early Cambrian diversification, they became components of Paleozoic stromatolitic assemblages of many continents, as it is evident from available data on newly discovered Cambrian and Ordovician taxa. Formal genera of the Early Paleozoic ministromatolite assemblage are nearly as diverse as the Early Proterozoic and Early Riphean ones, but they are, however, of an essentially different taxonomic composition. In distinction from the Precambrian taxa, many younger forms are relatively large in size, and some of their formal genera show immature lamination similar to that of thrombolites. The frequent occurrence of stromatite-forming microfossils (particularly of genera that appeared at the Precambrian-Cambrian boundary time) in Cambrian and Ordovician ministromatolites suggests that the formation of the Early Paleozoic ministromatolite assemblage was closely related to the microbial evolution.