Cyclostratigraphic correlation of Middle–Late Ordovician sedimentary successions between the South China Block and Tarim Basin with paleoclimatic and geochronological implications

Abstract

The Middle−Late Ordovician transition was one of the most critical periods throughout the Earth's history, and it involved paleoclimate changes and biological turnover. Here, we conducted cyclostratigraphic analysis on the magnetic susceptibility (MS) from the Kuniutan and Miaopo formations in the Zhenjin section and the Pagoda and Linhsiang formations in the Puxihe section in Yichang, South China. We constructed an astronomical time scale to understand the astronomically forced paleoclimate changes during this key interval. Spectral analyses on the MS series show that the thickness ratios of different sedimentary cycles in the studied sections are consistent with those of Milankovitch cycles during the Middle and Late Ordovician. The floating astronomical time scale of the studied sections was constructed based on astronomical tuning to 405-kyr eccentricity cycles, providing an estimated duration of ∼0.82 Myr for the Guttenberg isotopic carbon excursion (GICE). A high-precision and continuous astronomical time scale has previously been established in the Ordovician marine sediments in the Tarim Basin. The cyclostratigraphic correlation of sedimentary successions between the South China Block and Tarim Basin reveals that the duration of the Middle Ordovician gap in South China is ∼1.38 Myr. Alignment of the maxima of the ∼1.2-Myr obliquity cycle and the 405-kyr eccentricity cycle may have resulted in increased weathering inputs and prolonged periods of ocean anoxia, pacing the enhanced organic carbon burials and the positive isotopic carbon excursion during the middle Darriwilian isotope carbon excursion (MDICE) and GICE.