The Impact of Modern Weathering on the Geochemistry of a Marine Permo-Triassic Boundary Section
Date of Award
Open Access Thesis
Master of Science (MS)
Environmental Sciences/Environmental, Earth & Ocean Sciences
Robyn E. Hannigan
Curtis R. Olsen
Allen M. Gontz
The Permian-Triassic Boundary (PTB) marks the end-Permian extinction, the greatest mass extinction recorded in Earth's history. The Attargoo PTB section located in Spiti Valley, Himachal Pradesh, India was situated along the north continental margin of Gondwana-land in the Neo-Tethys Ocean during the end-Permian extinction. In Spiti Valley, PTB sections such as Attargoo are exposed by a thin (~ 2cm) ferruginous layer separating the Permian black shale from Triassic Limestone. Studies that have presented geochemical data to support a theory of the end-Permian extinction lack any interpretation of post-depositional effects on Spiti Valley PTB sections. In order to accurately present a cause for the end Permian extinction one must understand if the Spiti PTB sections contain any original chemical signature. In this study we present the major element geochemistry of the Attargoo PTB section to see if this section has experienced any post-depositional alteration and assess the major element geochemistry of the ferruginous layer. X-ray fluorescence (ED-XRF), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), and Loss on Ignition (LOI) were used to gather major element, organic, and inorganic carbon values for the Attargoo PTB section. From our analysis we suggest that the Attargoo section has experienced intermediate weathering, very little chloritzation, no K-metasomatism, and is diagenetically altered. Intermediate weathering is supported by the CIA values quantified at the Gungri formation. The major element chemistry suggests that the Triassic limestone contains dolomitic characteristics. The extent of chemical weathering and chloritization do not appear to be significant in which samples are altered from the original chemical composition this is reflective in the shale CIA values and both ternary plots. The ferruginous layer can be divided into three sections: lower, middle and upper ferruginous layer. The lower ferruginous layers has shale characteristics, whereas the middle and upper ferruginous layer has characteristics of an ironstone or iron rich shale. The CIA values of the middle and upper ferruginous layer suggest that it formed under arid or dry conditions. The Ca, Fe, P and Corg values suggest that the ferruginous layer formed in situ during a non-depositional event of subaerial origin.
Williams, Jeremy Christopher, "The Impact of Modern Weathering on the Geochemistry of a Marine Permo-Triassic Boundary Section" (2011). Graduate Masters Theses. 49.