COUPLING OF CAMBRIAN TRILOBITE EXTINCTION EVENTS AND CARBON ISOTOPE ANOMALIES: A CASE STUDY OF CAMBRIAN SERIES 2-3 BOUNDARY CANDIDATE SECTIONS IN GUIZHOU CHINA

The Wuliu-Zengjiayan section of the Kaili Formation is one of the GSSP candidate sections for defining the base of Cambrian Stage 5 that is coincided with the base of Series 3. In addition to the well-documented biostratigraphy, some studies focused on the prospect of achieving international correlation based on geochemistry. Recently, a new work provided a comprehensive study on the chemostratigraphy of the Kaili Formation and reported a robust negative carbon isotopic excursion. However, this has not been validated by another independent research group. The main objective of this study was to investigate a new section in the Kaili Formation to confirm or refute the presence of a robust negative carbon isotopic excursion. Studied samples came from the Miaobanpo section, which yields the most abundant well-preserved Burgess Shale-type taxa. A 4-m thick barren zone in between the last occurrences of Bathynotus/Redlichia trilobites and the first occurrence of Oryctocephalus indicus is noted. Samples were collected from this barren interval and fresh powders were collected using a Dremel drill and/or a dental drill. On average, 200 μg of each sample was weighed out for both stable carbon (δ¹³C) and oxygen (δ¹⁸O) analyses, following standard preparation procedures, with the Thermo Delta^PlusXP system at the Earth Systems Center for Stable Isotopic Studies of Yale University (ESCSIS). Plotted results are based on the average values from two sets of the data. The results show that the data obtained from ESCSIS and the commercial lab are consistent; thus, the instrumental errors are minimized. Correlation of Kaili sections is based on the robust signatures of carbon isotopes. To summarize, this study shows that robust negative δ¹³C_carb values (-6‰ or less) occurred in the barren zone at the Miaobanpo section and the results is similar to the Jianshan data reported in the lieturature. The negative carbon excursion probably resulted from a major faunal turnover event, but not the trigger of the end-lower Cambrian (or Cambrian Series 2) extinction event.