Abstract:

According to the chemostratigraphy and lithostratigraphy of the Ordovician Liangjiashan section in Qinhuangdao of North China, the Liangjiashan Formation was divided into the lower, middle and upper members. We chose the Fe/Ca and Ti/Ca ratios as the paleoclimate proxies and carried out the timeseries analysis. The timeseries analysis of the Fe/Ca and Ti/Ca data was performed by means of Multi Taper Method (MTM) and Fourier Transform (FT), from which two obvious cycles were identified: long eccentricity (E) 405 ka and short eccentricity (e) 90 ka. The float point time scale (based on the long eccentricity cycle) indicates that the duration of the Liangjiashan Formation is 6.2 Ma, the mean sediment accumulation rate in the Liangjiashan Formation is 14.68 m/Ma, and the sedimentation rate of the lower member and the middleupper members are 12.00 m/Ma and 19.55 m/Ma respectively; the sedimentation rate in the Majiagou Formation is 18.00 m/Ma. The Ordovician radiation seemed to result in the changing of carbonate production from marldominated to biodetritusdominated, which accelerated the sediment accumulation rate during the transition from the lower to the middleupper members of the Liangjiashan Formation. Our cyclostratigraphical data show that the Ordovician radiation may be regulated by the earth's climate changes caused by the orbit cycle variations.

Key words: cyclostratigraphy, chemostratigraphy, X-ray fluorescence scanning analysis (XRF), Liangjiashan Formation, Ordovician, Ordovician radiation, Qinhuangdao, North China