华南上奥陶统宝塔组天文年代格架及其地质意义

对华南四川盆地及周缘地区的四川省南江县桥亭剖面、重庆市南川区三泉剖面和贵州省习水县良村剖面上奥陶统宝塔组高分辨率磁化率(MS)数据进行了旋回地层学分析，识别出405 ka长偏心率、100 ka短偏心率、30 ka斜率和20 ka岁差沉积旋回，其中偏心率和岁差旋回信号最强。利用405 ka长偏心率旋回进行天文调谐后得出三条剖面宝塔组的沉积时限分别为4.17 Ma、5.64 Ma和5.05 Ma，平均沉积速率分别为7.67 m·Ma-1、4.68 m·Ma-1 和6.37 m·Ma-1，呈现出从北往南沉积时限变长，沉积速率变小的趋势，指示了北部接受沉积时间要比南部更晚，海侵从南向北推进。良村剖面宝塔组中所产牙形石Hamarodus brevirameus带和Protopanderodus insculptus带的延续时限分别为3.62 Ma和1.43 Ma；桥亭剖面三叶虫Niuchangella angustilimbata间隔带、Dislobosaspis xixiangensis延限带和未建带的延续时限分别是2.83 Ma、0.41 Ma和0.81 Ma。

Astrochronology of the Upper Ordovician Pagoda Formation,South China and its geological implications

We conducted high resolution cyclostratigraphic studies on the magnetic susceptibility (MS) series of the Upper Ordovician Pagoda Formation in three locations including the Qiaoting section in Nanjiang, Sichuan, the Sanquan section in Nanchuan, Chongqing, and the Liangcun section in Xishui, Guizhou. We identified the hierarchy of Milankovitch 405 ka long eccentricity, 100 ka short eccentricity, 30 ka obliquity and 20 ka precession cycles with strong eccentricity and precessional signals. We also established floating astronomical time scales by tuning the 405 ka eccentricity cycles and determined the precise durations of the Pagoda Formation to be 4.17, 5.64 and 5.05 Ma for the Qiaoting, Sanquan and Liangcun sections, respectively. The average sedimentary rates of the Pagoda Formation were calculated to be 7.67, 4.68 and 6.37 m·Ma-1 for the three sections, respectively, decreasing from north to south in the Sichuan Basin, indicating that the studied area uplifted to become continent before the sedimentary time of the Pagoda Formation and transgressed from south to north. The conodont Hamarodus brevirameus and Protopanderodus insculptus zones in the Pagoda Formation lasted 3.62 and 1.43 Ma for the Liangcun section, respectively, while the trilobites Niuchangella angustilimbata, Dislobosaspis xixiangensis and unnamed zones lasted 2.83, 0.41 and 0.81 Ma for the Qiaoting section, respectively.