PRE-PHANEROZOIC STROMATOLITES: THE DIFFERENCES REMAIN

In recent years, the pendulum of investigations on stromatolites (microbialites) has swung from the pre-Phanerozoic to the Phanerozoic. The Phanerozoic record is richer and more varied than previously thought. Renewed interest, intensity of study, and the abundance of strata relative to the pre-Phanerozoic have helped produce a new appreciation of microbialite richness in Phanerozoic ecosystems. The growing record of Recent microbialites is helping to fuel these investigations by providing important microbiological and environmental data.

Still, the pre-Phanerozoic remains as the great bastion of stromatolites. Their abundance and diversity are unparalleled, particularly during the Mesoproterozoic and Neoproterozoic. Unique shapes permit biostratigraphy. When diversity of marine forms is plotted against time, curious patterns emerge: diversity increases through the Paleoproterozoic, reaches a maximum late in the Mesoproterozoic, and early in the Neoproterozoic a steady decline in diversity occurs with few taxa remaining by Precambrian-Cambrian boundary. Columnar branched and coniform stromatolites show the greatest percentages in diversity decreases during the Neoproterozoic. Why are these two types of stromatolites, which epitomize the Proterozoic, so rare in the Phanerozoic? There is no single, simple answer to this question and there are no simple solutions to explaining the Proterozoic record of stromatolites.