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The geochemistry of the late Cambrian carbonate in North China: the Steptoean Positive Carbon Isotope Excursion (SPICE) record suppressed in a coastal condition?

Published online by Cambridge University Press:  08 March 2019

Jing Huang Open the ORCID record for Jing Huang [Opens in a new window] ,
Yali Chen ,
Xuelei Chu  and
Tao Sun
Jing Huang*
Affiliation:
CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China CAS Center for Excellence in Comparative Planetology, China
Yali Chen
Affiliation:
Agro-Environmental Protection Institute/Key Laboratory for Environmental Factors Control of Agro-product Quality Safety, Ministry of Agriculture and Rural Affairs, Tianjin 300191, China
Xuelei Chu
Affiliation:
Institute of Geology and Geophysics, Key Laboratory for Mineral Resources, Chinese Academy of Sciences, Beijing 100029, China University of Chinese Academy of Sciences, Beijing 100049, China
Tao Sun
Affiliation:
Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, USA
*
Email: [email protected]
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Abstract

The Steptoean Positive Carbon Isotope Excursion (SPICE) is globally distributed in late Cambrian sedimentary records but controversially heterogeneous in its magnitudes. Here we use multiple geochemical proxies to investigate the late Cambrian carbonates from the Tangwangzhai section in North China, which were deposited in a shallow coastal environment with three depositional sequences (S1–S3). Each sequence comprises a transgressive systems tract (TST) and a highstand systems tract (HST). The REE + Y and trace element records are consistent with the depositional condition and indicate that terrigenous influence was more significant in the TST than HST. δ13Ccarb and δ34SCAS are low in the TST relative to HST, consistent with the scenario that terrigenous inputs were profoundly aggressive to seawater by introducing 13C-depleted and 34S-depleted materials. Within the TST of S2, the SPICE excursion shows a scaled-down δ13Ccarb positive shift (∼1.7 ‰) relative to its general records (∼4–6 ‰); the corresponding δ34SCAS show no positive excursion. This ‘atypical’ SPICE record is attributed to enhanced 13C-depleted and 34S-depleted terrigenous influence during the TST, which would reduce the amplitude of δ13Ccarb excursion, and even obscure δ34SCAS excursion. Meanwhile the subaerial unconformity at the base of TST would also cause a partially missing and a ‘snapshot’ preservation. Our study confirms significant local influence to the SPICE records, and further supports the heterogeneity and low sulphate concentrations of the late Cambrian seawater, because of which the SPICE records may be vulnerable to specific depositional conditions (e.g. sea-level, terrigenous input).

Keywords

carbon isotopesulphur isotopeterrigenous inputtrace element
Type
Original Article
Information
Geological Magazine , Volume 156 , Issue 10 , October 2019 , pp. 1805 - 1819
Copyright
© Cambridge University Press 2019 

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