安徽齐云山晚白垩世兽脚类恐龙足迹点沉积环境

安徽齐云山兽脚类足迹群是目前中国晚白垩世保存最好的恐龙足迹群之一,对其沉积环境的研究为恢复白垩纪末期恐龙动物群的生活环境提供了证据。研究区足迹全部为兽脚类凸型足迹,与无脊椎动物遗迹Palaeophycus tubularis和Scoyenia sp.保存在一起,指示陆相沉积中的浅水沉积。通过薄片鉴定,足迹层位主要为岩屑砂岩,其平均粒径、标准偏差、偏度和峰度4个粒度参数特征与典型的河相砂一致;粒级分布直方图、概率累积曲线图及散点图表明,足迹层位从下到上颗粒逐渐变细,水动力条件变弱,沉积环境由河床沉积转变为边滩沉积。综上,齐云山兽脚类足迹点沉积环境为大型曲流河沉积,足迹保存在边滩沉积的下部,是白垩纪末期干旱气候条件下兽脚类恐龙动物群的水源地。

Sedimentary environment of Late Cretaceous theropod tracksite in Qiyun Mountain, Anhui Province

Qiyun Mountain theropod tracks from Anhui Province seem to be the best preserved tracks in several kinds of Late Creta-ceous tracks. The study of their sedimentary environment provides evidence for restoring the habitats of dinosaur fauna. All of the tracks are natural theropod casts, preserving Palaeophycus tubularis and Scoyenia sp., which indicates a shallow water in continental deposits. The thin section analysis reveals that the footprint layers are dominated by lithic sandstones. The four grain characteristic pa-rameters consisting of average size, standard deviation, skewness and kurtosis for the sandstones are consistent with features of the typi-cal fluvial deposits. Grain size distribution histogram, probability cumulative curves and scatter plots of footprint layers present the smaller particles and weaker hydrodynamic conditions upwards. The sedimentary environment displays the transformation from river-beddeposits to point bar deposits. Therefore, the sedimentary environment of Qiyun Mountain theropod tracksite was large meander-ing river deposition. Tracks were preserved in the lower part of point bar deposits which was the water source of the theropod fauna under the Late Cretaceous dry climate conditions.