Carbon Isotope from Shallow Marine System in North China: Implications for Stratigraphical Correlation and Sea-Level Changes in Cambrian

Cambrian System at the Shatan Section in northern Henan, North China, consists of sedimentary successions of tidal flat and shallow-water carbonate platform facies. Data of carbon isotope (delta 13Ccarb) from this section reveals five positive delta 13Ccarb (Pst-l-Pst-5) and five negative delta 13Ccarb excursions (Nst-l-Nst-5). In the positive excursions, delta 13Ccarb rises to 0.88 parts per thousand, 1.05 parts per thousand, 2.04 parts per thousand, 1.00 parts per thousand and 2.97 parts per thousand, respectively, while in the negative excursions delta 13Ccarb drops to -8.00 parts per thousand, -3.50 parts per thousand, -1.00 parts per thousand, -0.33 parts per thousand and around -2.00 parts per thousand, respectively. On the basis of chronostratigraphy of Cambrian, the most remarkable carbon isotope excursions can be correlated regionally and globally. In addition, one second-order and ten third-order sequences have been recognized at this section. Correlating third-order sequences and chemostratigraphy indicates that carbonates from the basal part of the transgression system tract (TST) and the upper part of the high-water system (LHST) generally have lighter delta 13Ccarb values, whereas massive carbonates with microbialite from the lower part of the high-water system tract (EHST) usually have heavier delta 13Ccarb values. The association of delta 13Ccarb values with sea-level fluctuations suggests that the positive carbon isotope excursions or high delta 13Ccarb values may have been caused by an increase in the marine primary productivity in response to maximum seawater flooding during the transgression.