In-situ Strontium Isotopes Analysis on Single Conodont Apatite by LA-MC-ICP-MS

Abstract:

Strontium isotope played an important role in stratigraphic chronology and sedimentary geochemistry research (McArthur et al., 2001). Conodonts is a kind of extinct species of marine animals and widely distributed in marine sediments all over the world. Rich in radiogenic Sr contents and difficulty to be affected during diagenesis alteration makes conodonts a good choice in seawater Sr isotope composition studies (John et al., 2008). Conodont samples were collected from 24^th to 39^th layer across Permian-Triassic boundary at Meishan D section (GSSP), Zhejiang Province, South China (Yin et al., 2001). Conodonts was originated from fresh limestone and only conodont elements with CAI<2 were chosen for in-situ strontium isotope analysis using laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Conodont samples are from totally 25 layers in seven conodont zones making it possible for a high resolution ⁸⁷Sr/ ⁸⁶Sr curve reconstruction during the Permian-Triassic transition. ⁸⁷Sr/ ⁸⁶Sr ratio kept a relatively high value (0.70752) in the middle part of the Clarkina yini zone and a lower value (0.70634) in the upperpart of Clarkina taylorae zone. Of which, ⁸⁷Sr/ ⁸⁶Sr ratio emerged a rapid decrease within the Clarkina taylorae zone. After a subsequent increase, ⁸⁷Sr/ ⁸⁶Sr ratio dropped to 0.70777 in the Isarcicella staeschei zone. These results helps providing reference data for the biological mass extinction events during the Permian-Triassic transition. Our study also makes is possible for high resolution ⁸⁷Sr/ ⁸⁶Sr ratio testing on the single conodont apatite and riched the in-situ studies on the conodont apatite, which of great significance for the future conodont Sr isotope research (Zhao et al., 2009; Zhao et al., 2013).

Keywords: Conodonts, Strontium isotope, LA-MC-ICP-MS, Permian-Triassic transition, Meishan D section

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