THE UPPER CAMBRIAN NORTH CHINA SPICE EVENT: NEW STRONTIUM ISOTOPE DATA AND ITS IMPLICATIONS

The upper Cambrian SPICE event is an ongoing topic in terms of global paleo-environmental changes. The nature of this stable carbon isotope positive excursion coincides with one of the most recognizable trilobite turnover events in the Late Cambrian is still under debate. Most stable carbon isotope SPICE signals were reported from deeper water settings and showed an increase in δ¹³C for about 4-5‰. Nonetheless, previous studies indicated that the shallow water North China Platform displayed a lowered peak and reduced difference (∆¹³C) values. Several recent SPICE studies extended into different analytical methods, such as strontium and sulfur isotopes, in order to provide more holistic data to evaluate the oceanic conditions, and, thus, giving more evidences to speculate on any possible explanation on this trilobite turnover event.

The Cambrian North China Platform was believed to be mostly shallow-water deposits. It lacks the biostratigraphic significant agnostids Glyptagnostus recticulatus for global correlation of the base of the Paibian Stage. The onset of the SPICE signals helped to enhance the stratigraphic correlation between North China and the other paleo-continents. Nonetheless, the relationship between these chemical signals and the trilobite turnover event is still not entirely clear.

Here, we combined our published carbon and oxygen isotope data with the new strontium isotope (⁸⁷Sr/⁸⁶Sr) results from the Huangyangshan section, Shandong Province, on the North China Platform. The preliminary results indicate that the strontium isotope values are compatible to the modern ocean and may be even slightly higher. The relatively high values could signify an increase in chemical weathering rate. Besides, other than the published trilobite and carbon isotope information, by comparing with the global seawater ⁸⁷Sr/⁸⁶Sr curve, the new strontium isotope results may also provide an additional constraint on the depositional age of the Huangyangshan section.