New carbon isotope stratigraphy of the Ediacaran–Cambrian boundary interval from SW China: implications for global correlation

Abstract

The Yangtze Platform preserves relatively thick carbonate successions and excellent fossil records across the Ediacaran–Cambrian boundary interval. The intensely studied Meishucun section in East Yunnan was one of the Global Stratotype Section candidates for the Precambrian–Cambrian boundary. However, depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified. The Laolin section located in NE Yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the Precambrian–Cambrian boundary. However, the stratigraphic framework and correlations were controversial. We studied and systematically sampled the Laolin section and present here new carbon isotope data for this section. The Laolin section consists of, in ascending order, the Baiyanshao dolostone of the Dengying Formation, the Daibu siliceous dolostone, Zhongyicun dolomitic phosphorite, lower Dahai dolostone and upper Dahai limestone of the Zhujiaqing Formation, and the black siltstone of the Shiyantou Formation. Our data reveal a large negative δ13C excursion (−7.2‰, L1′) in the Daibu Member, which matches the previously published data for the Laolin section, and a large positive excursion (+3.5‰, L4) in the Dahai Member, which was not shown in the published data. The excursion L1′ correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in Siberia and Mongolia. Similar magnitude excursions are also known from Morocco and Oman, for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 Ma, thus confirming a global biogeochemical event near the Ediacaran–Cambrian boundary. Our data also indicate that deposition was more continuous at the Laolin section compared with the Meishucun section, where there are no records of a comparable negative excursion near the Ediacaran–Cambrian boundary, nor any comparable positive excursion in the Dahai Member. Therefore, the Laolin section has proven potential to be a supplementary Global Stratotype Section for the Ediacaran–Cambrian boundary on the Yangtze Platform.

The study on the source of the oil seeps and bitumens in the Tianjingshan structure of the northern Longmen Mountain structure of Sichuan Basin, China

“…Similar isotopic compositions of kerogen, carbonates and oil from Infracambrian-Cambrian strata are also reported in numerous areas including Oman, Pakistan, North West Indian, Morocco, Siberia and USA (Hoering, 1967;Welte et al, 1975;Tucker, 1986;Fowler and Douglas, 1987;Brasier et al, 1990;Summons and Powell, 1992;Peters et al, 1995;Bazhenova and Arefiev, 1998;Li et al, 2009a;Kaufman and Knoll, 1995;Walter et al, 2000). Summons and Powell (1992) suggested that during Cambrian, elevated atmospheric carbon dioxide levels resulted in higher fractionation during photosynthesis.…”

Chronology of early Cambrian biomineralization

“…The majority of bilaterian skeletal fossils of the Terreneuvian Series belong to these latter groups. Their first appearances occurred in beds younger than the Precambrian-Cambrian boundary and the carbon isotope negative anomaly associated with this boundary (Narbonne, Kaufman & Knoll, 1994;Brasier et al 1996;Kimura et al 1997;Li et al 2009), but not younger than those with Siberian δ 13 C feature Z and attributed to the upper Anabarites trisulcatus-lower Purella zones of the NemakitDaldynian Stage (Brasier, Khomentovsky & Corfield, 1993;Brasier, et al 1994a,b). These first appearances can be correlated with the Anabarites trisulcatusProtohertzina anabarica (SSF1) Assemblage Zone of the lower Meishucunian Stage of South China, where all of them except shells of molluscs occur in beds older than the tuffite with a combined depositional age of 535.2 ± 1.7 Ma (Zhu et al 2009).…”

“…They are correlated bio-and chemostratigraphically with the Nemakit-Daldynian Stage of Siberia (Qian et al 2002;Li et al 2007Li et al , 2009Li & Xiao, 2004;Steiner et al 2007) and comprise in ascending order the assemblage zones Anabarites trisulcatusProtohertzina anabarica (SSF1) of the lower Meishucunian Stage, Paragloborilus subglobosus-Purella squamulosa (SSF2) and Watsonella crosbyi (SSF3) of the middle Meishucunian Stage (Fig. 3).…”

“…Porcauricula hypsilippis (Jiang, 1980) is known from lower SSF2 beds (Qian & Bengtson, 1989), in the rising trend towards a prominent positive peak ZHUCE in China (Brasier et al 1990;Li et al 2009). Lapworthella ludvigseni Landing, 1984 and Eccentrotheca kanesia Landing, Nowlan & Fletcher, 1980 occur in the lower Watsonella crosbyi Zone of SE Newfoundland (Landing et al 1989).…”

Significant carbon isotope excursions in the Cambrian and their implications for global correlations

“…The earliest records might be the work in Morocco [1], Siberia [2], and subsequently South China [3]. So far, data of the carbon chemostratigraphy have covered most of the continents [2,[4][5][6][7][8][9][10][11][12][13]. Most of the results are regional, the sampled sections or drilling cores are always limited to parts of the Cambrian System, so carbon isotope data in the Cambrian are inevitably scattered.…”