Reconstructing the Late Mississippian Paleoclimate: Stratigraphy and XRD Analysis of the Pennington Formation, Sparta, Tennessee

Abstract

The Late Mississippian represents a time when Earth was thought to be an icehouse and was experiencing eustatic sea level changes similar to today. While there’s been a wealth of research done in the western equatorial Pangea for the Late Carboniferous and Permian, this study of the Pennington Formation, Tennessee, offers an opportunity to study less focused upon terrestrial early Carboniferous paleoenvironments from central equatorial Pangea, including the effects of diagenesis on paleoenvironmental proxies employed for paleosol research. New fieldwork of an outcrop outside Sparta, TN shows interbedded limestone and mudstone layers including four paleosol profiles that have been described and analyzed for their principle clay mineralogy. The paleosols preserve typical vertic features including slickensides, mukkara and wedge-shaped peds as well as low chroma color and are thus gleyed Vertisols. The gleyed nature of these paleosols is either the result of forming under waterlogged conditions seen today in soils forming proximal to shorelines or the result of diagenesis associated with sea level rising. The presence of Vertisols intercalated between limestones suggests a persistent influence of glacioeustacy in conjunction with highly seasonal climates during base-level lowstands and soil development which gave rise to pedoturbation and the characteristic suite of vertic morphologies seen in outcrop. Clay mineralogy dominated by illite and vermiculite suggests burial diagenesis. This contrasts sites from the upper Pennsylvanian which contain evidence for eustatic sea level change but are suggestive of more ever-wet conditions and recorded by the common occurrence of thick coal layers atop mineral-dominated paleosol profiles.