Chemostratigraphy of the Uppermost Cambrian Below the Ordovician GSSP

• Main Author: Wang, Lisha
• Other Authors: Department of Earth Sciences
• Format: Thesis
• Language: English
• Published: Brock University 2018
• Subjects: Ordovician GSSP; carbon isotope values; Cambrian‒Ordovician; Newfoundland; chemostratigraphy; Canada; Cow Head; Green Point
• Online Access: http://hdl.handle.net/10464/13331

Chemostratigraphy is an important tool for correlating layered sedimentary rock successions. Preserved/near primary carbon isotope signatures in marine carbonates can provide high-resolution profiles for sedimentary sequences supplementing the need for distinguishing fossils from different depositional environments and those lacking fossil materials. The Global Boundary Stratotype Section and Point (GSSP) of the Cambrian‒Ordovician boundary is located at Green Point in the Green Point Formation of the Cow Head Group in western Newfoundland, Canada. To reconstruct a continuous and high-resolution chemostratigraphy from the Cambrian‒Ordovician boundary to the Furongian Series Stage 10, we included the δ13C results of the Green Point Formation covering the Ordovician GSSP interval (Azmy et al., 2014). The Green Point Formation through the base of Ordovician GSSP consists of alternating dark gray to black shale and thin ribbon limestone rhythmites, with few fossils. The samples are micritic limestone, dolomitic limestone, and dolostone. They were determined to be in primary to near-primary condition based on multiple screening tests. Cathodoluminescence screening reveals dull to bright luminescence of the samples indicative of good preservation for many of them. The δ13Ccarb and δ18O values of the Green Point carbonates range from -6.44‰ to +0.33‰ (VPDB) and from -8.63‰ to -5.67‰ (VPDB), respectively, with poor correlation. Mn/Sr ratios range from 0.63 to 9.82, with no correlation to δ13Ccarb, but with ratios supporting the near primary nature of the δ13C values. Carbon isotope compositions of the Green Point Formation below the Ordovician GSSP fluctuate but remaine essentially invariantly negative. The δ13C values reveal a negative excursion at and below the Cambrian‒Ordovician boundary, which may correlate with the Top of Cambrian Carbon Isotope Excursion (TOCE) and its significant negative excursion. A nadir of -6.44 ‰ at the base of the Eoconodontus conodont zone marks the proposed GSSP for the base of the ...