An Integrated Lower Triassic Sequence in Chaohu, Anhui Province
TONG Jin-nan~1, ZHAO Lai-shi~1, ZUO Jing-xun~1, Hans J. Hansen~2, Yuri D. Zakharov~31.State Key Laboratory of Geo-Processes and Mineral Resources, China University of Geosciences, Wuhan430074, China2.Geological Institute, Copenhagen University, DK-1350 Copenhagen, Denmark3.Far Eastern Geological Institute, Russian Academy of Sciences, Vladivostok690022, Russia
One of the GSSP (Global Stratotype Section and Point) candidates for the Induan-Olenekian boundary is situated in Chaohu, central Anhui Province, southeast China. Chaohu also has a representative and well-expressed Lower Triassic sequence that has been better studied in various aspects. This paper presents an integrated and comprehensive Lower Triassic sequence of Chaohu to serve for a standard regional stratigraphical sequence, based upon up-to-date achievements in the (studies) of lithostratigraphy, biostratigraphy and carbon isotope stratigraphy at three sections in the area. Eight conodont zones and six ammonoid zones are consequently well distinguished in the Lower Triassic of Chaohu, and most of them are (regionally) or even globally correlative. The δ~(13)C_(carb) excursion shows two characteristic shifting periods, and this carbon isotope sequence is not only of a stratigraphic value but also of great importance to understanding the biotic recovery and ecosystem reconstruction at the beginning of the Triassic. In the light of the integrated Lower Triassic sequence, a complete Lower Triassic magnetic stratigraphic sequence is established from the data at the three sections. The Lower Triassic covers five major normal polarity zones and five reversed polarity zones, and both the Permian-Triassic boundary and the Induan-Olenekian boundary are located inside normal polarity zones.