EPEIRIC SEAS: A CONTINENTAL EXTENSION OF SHELF BIOTAS
1. Overview 1.1. Controls 1.2. Temporal Distribution 1.3. Geographic Distribution 1.4. Sedimentology 1.5. Climatic Impact 2. The Environment of Epeiric Seaways 3. Origin and Evolution of the Epicontinental Sea Biota 3.1. Nature of the Epicontinental Fossil Record 3.2. Measuring Biodiversity in Epicontinental Seas 3.3. The Endemism Question 3.4. Precambrian 3.5. Paleozoic 3.5.1. Cambrian 3.5.2. Ordovician–Permian 3.6. Mesoand Cenozoic 3.6.1. Triassic–Cretaceous 3.6.2. Paleocene–Recent 3.7. Mass Extinctions Glossary Bibliography Biographical Sketch
Evidence of oxygenic phototrophy in ancient phosphatic stromatolites from the Paleoproterozoic Vindhyan and Aravalli Supergroups, India
Fossil microbiotas are rare in the early rock record, limiting the type of ecological information extractable from ancient microbialites. In the absence of body fossils, emphasis may instead be given to microbially derived features, such as microbialite growth patterns, microbial mat morphologies, and the presence of fossilized gas bubbles in lithified mats. The metabolic affinity of micro‐organisms associated with phosphatization may reveal important clues to the nature and accretion of apatite‐rich microbialites. Stromatolites from the 1.6 Ga Chitrakoot Formation (Semri Group, Vindhyan Supergroup) in central India contain abundant fossilized bubbles interspersed within fine‐grained in situ‐precipitated apatite mats with average δ13Corg indicative of carbon fixation by the Calvin cycle. In addition, the mats hold a synsedimentary fossil biota characteristic of cyanobacterial and rhodophyte morphotypes. Phosphatic oncoid cone‐like stromatolites from the Paleoproterozoic Aravalli Supergroup (Jhamarkotra Formation) comprise abundant mineralized bubbles enmeshed within tufted filamentous mat fabrics. Construction of these tufts is considered to be the result of filamentous bacteria gliding within microbial mats, and as fossilized bubbles within pristine mat laminae can be used as a proxy for oxygenic phototrophy, this provides a strong indication for cyanobacterial activity in the Aravalli mounds. We suggest that the activity of oxygenic phototrophs may have been significant for the formation of apatite in both Vindhyan and Aravalli stromatolites, mainly by concentrating phosphate and creating steep diurnal redox gradients within mat pore spaces, promoting apatite precipitation. The presence in the Indian stromatolites of alternating apatite‐carbonate lamina may result from local variations in pH and oxygen levels caused by photosynthesis–respiration in the mats. Altogether, this study presents new insights into the ecology of ancient phosphatic stromatolites and warrants further exploration into the role of oxygen‐producing biotas in the formation of Paleoproterozoic shallow‐basin phosphorites.
Pre-Waterways Paleozoic Stratigraphy of Alberta Plains
Detailed study based on sample determinations of 12 wells, one of which is in Saskatchewan and 11 in the plains of Alberta shows a sequence of strata of questionable age that is herein referred to as the Elk Point formation. The formation underlies a thick section of Upper Devonian strata and in turn lies on Ordovician, Cambrian, or pre-Cambrian rocks. It generally consists of two conspicuous red shales, anhydritic dolomites, and thin slightly fossiliferous argillaceous silty limestones, in addition to one to three salt members. Maximum thickness of the entire formation is 1,557 (plus or minus) feet. The age of the Elk Point formation is considered Silurian. However, recent evidence suggests at least the upper part of the formation to be Middle Devonian. A detailed composite geological log of Elk Point area is presented.