Date of Award
2010
Document Type
Honors Thesis (Open Access)
Department
Colby College. Geology Dept.
Advisor(s)
Robert A. Gastaldo
Second Advisor
Valerie Reynolds
Third Advisor
Bruce Rueger
Abstract
Beaufort Group paleosols from the Karoo Basin, South Africa, record the paleoenvironmental conditions that existed prior to and after the Permian-Triassic extinction event. Paleosol exposures from Wapadsberg Pass, Eastern Cape Province, represent a well- preserved forest-floor litter overlying an interpreted inceptisol, a condition unique to the basin. Vegetation that colonized this landscape included a canopy of the gymnosperm Glossopteris and an understory of sphenopsids (Phyllotheca and Trizygia). Wapadsberg Pass paleosol sites were sampled for petrographic and geochemical analyses to constrain interpretations of Late Permian paleoenvironmental conditions that existed ~ 70 m below the Permian-Triassic Boundary (PTB). This project focuses on determining paleosol-nutrient quality to test a hypothesis that plant toxicity may be responsible for the reported decrease in Glossopteris-leaf size prior to the PTB event.
The greenish-grey (5GY 6/1) paleosol is an iron-stained siltstone with intervals of bedded very-fine sand to silt. The paleosol has a maximum thickness of 70 cm, with a coarser interval at ~30 cm depth. The litter horizon is concentrated in the upper 20 cm of the profile, and includes remnants of poorly preserved Glossopteris leaves and Vertebraria roots. Rooting structures penetrate to ~70 cm depth. Tuffite is interspersed in and caps the paleosol.
Primary structures in petrographic section include ripples, parallel bedding, and small- scale soft-sediment deformation. These are partially destroyed due to phytoturbation and bioturbation. All paleosol sites examined contain an identifiable tuffite, characterized as a mix of well-rounded to angular, transparent clasts. These are distributed as irregular pockets cross- cutting bedding and as dispersed isolated clasts within the fine matrix. Analytical results from TOC and TOC:TON obtained using elemental analysis, and geochemical data obtained using ICP-OES and XRF instruments.
High resolution stratigraphic and geochemical investigation of this paleosol reveals that it is an inceptisol, formed on an aggradational floodplain colonized by a Glossopteris forest, and contains elevated concentrations of plant-toxic elements.
Keywords
Late Permian, mass extinction, paleoenvironment, paleosol, Karoo Basin
Recommended Citation
Knight, Cassi, "Late Permian Paleoenvironmental Factors Expounded Through Analysis of a Forest-Floor Paleosol Profile, Karoo Basin, South Africa" (2010). Honors Theses. Paper 584.https://digitalcommons.colby.edu/honorstheses/584
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