Carboniferous Sarcopterygian Fossils and the Marine Paleoenvironment of the Joggins Formation, Nova Scotia, Canada

Abstract

Joggins Fossil Cliffs, a UNESCO World Heritage Site in Nova Scotia, Canada, is known for its Late Carboniferous (Pennsylvanian) coal seams and remarkably preserved ecosystems that represent terrestrial tropical Pangea. Of the five formations present, the most significant is the Joggins Formation (Fm) which is divided into approximately 15 sedimentary cycles based on the alternation of flooding plains, coals, and channel bodies. While the site records cyclic terrestrial and marine deposits, the marine influence of the Joggins Fm has rarely been studied. As a result, many fish fossils in the Joggins Fm collection remain unidentified, and there are ongoing debates about the source of the marine influence. I aim to (1) identify five unidentified sarcopterygian fish fossils from the Joggins Fm, and (2) determine their habitat and depositional environment. I have selected seven sarcopterygian fish fossils, most of which are scales, and I identified them to the family level using relevant literature. To learn more about the marine influence at a specific location within the formation, a carbonaceous limestone was chosen as a representative specimen for the marine depositional environment based on its thickness and history of producing determinate fish fossils. Thin sections were made for a vertical representation of the limestone band as well as a sedimentary log for greater marine influence context. Both thin section and microfossil analysis shows extensive bivalve and ostracod fossils layered in organic matter. Phosphate and bone fragments can also be seen in thin sections. The fossil assemblage for this location within the Joggins Fm suggests a paleoenvironment with moderate marine influence, likely a brackish or estuarine environment. Lastly, this work contributes to our complete understanding of both the terrestrial and marine environments of this important site and the animals that lived within it.