Journal Article

Structure and paleoecology of Lower Cambrian reefs

Rowland, Stephen M, Gangloff, Roland A

1988

Overview

Lower Cambrian buildups were constructed by a consortium of calcareous cyanobacteria(?) and archaeocyaths in varying proportions. The earliest are small Renalcis-cored bioherms in the Tommotian of the Siberian Platform. During the Atdabanian Stage archaeocyaths diversified and assumed a more active constructional role. A barrier complex of bioherms and associated facies developed in equatorial latitudes on the Siberian Plate. Here termed the \"Great Siberian Barrier Complex,\"this carbonate barrier was over 800 km long and up to 300 km wide. The first paleoecologic studies of Lower Cambrian buildups were carried out by Soviet workers in the rocks of the Great Siberian Barrier Complex: During the Botomian Stage archaeocyathan diversity increased dramatically and the distribution and variety of buildups also increased. Botomian buildups of western North America display a complex morphology and four-stage community replacement sequence previously documented in younger Phanerozoic framework reefs. Botomian reefs of Antarctica display an especially wide variety of textures and show that archaeocyaths were not an essential component of framework reefs in the Lower Cambrian. Following a more-or-less continuous marine transgression during the first three stages of the Early Cambrian, the end of the Early Cambrian was a time of worldwide regression, here termed the Toyonian Regression. During this regression archaeocyathan diversity plummeted, while the associated fauna experienced a dramatic increase in diversity. Lower Cambrian reefs display a complex trophic web in which archaeocyaths with algal symbionts probably played an important energetic role. We present evidence that Renalcis and Epiphyton were cyanobacteria that could live autotrophically in well-lit settings, photoheterotrophically in dim light, and perhaps chemoheterotrophically in complete darkness. The diversity of reef morphologies and boundstone fabrics in Lower Cambrian reefs has been underappreciated, as has the faunal diversity of the reef community. Lower Cambrian reefs have much to teach us about the reef ecosystem generally, and the Lower Cambrian reef-building fauna, including archaeocyaths, could be an important source of data on the evolutionary paleoecology of the Cambrian fauna.

• Publisher: Society of Economic Paleontologists and Mineralogists
• Subject: Algae / Antarctic regions / Antarctica / Asia / Atdabanian / Australasia / Australia / Cambrian / Canada / Carbonates / Commonwealth of Independent States / Community structure / Cyanobacteria / Earth sciences / Earth, ocean, space / Exact sciences and technology / Fauna / Geological facies / Geology / Invertebrate paleontology / Lena River / Limestones / lithofacies / Lower Cambrian / Paleoecology / Paleontology / Paleozoic / reefs / Russian Federation / Russian Republic / Siberia / Siberian Platform / South Australia / Strait of Belle / Stratigraphy / United States / USSR / Western U.S