内蒙古鄂托克早白垩世恐龙足迹化石8号点风化机理研究*

内蒙古鄂托克旗查布地区是罕见的恐龙足迹等遗迹化石分布区，分布着大量白垩纪恐龙足迹化石。这些足迹化石在野外遭受着不同程度的风化破坏, 为此在足迹密集的核心区8号点建立了野外地质遗迹博物馆保护原址。跟踪观察后发现室内足迹化石的风化程度相较于露天保存更加严重, 尤其在馆内靠近四周围墙的区域, 足痕表面酥粉破碎, 有的足迹甚至完全消失。为研究8号点足迹化石的风化原因, 本文对8号点馆内外赋存于同一层位的岩石进行取样, 使用偏光显微镜(PM)、X射线衍射(XRD)、压汞(MIP)、离子色谱(IC)、拉曼光谱(Raman)、傅里叶变换红外光谱(FTIR)以及扫描电子显微镜能谱 (SEM-EDS)等方法进行分析, 结果发现室内岩石的孔隙率更高, 孔径更大, 可溶盐含量是室外上层的2倍, 室外下层的约11倍, 种类以NaCl和Na2SO4为主。模拟实验显示, 相比冻融作用, Na2SO4更具有破坏性。由此认为导致鄂托克遗迹博物馆内恐龙足迹化石风化的机理是由地下水和降雨形成的地表水共同作用的结果, 尤以Na2SO4为主的可溶盐产生强烈的水盐活动。同时, 之前用作加固的硝基清漆保护效果不明显, 并尝试提出保护性建议。

Study on weathering mechanism of dinosaur tracks from Early Cretaceous in tracksite No. 8, Otog, Inner Mongolia

The Chabu area in Otog Qi, Inner Mongolia, is one of the few places in the world that yield rare, abundant Early Cretaceous dinosaur footprints and tracks. However, these footprint fossils are experiencing different degrees of weathering in the field. In order to protect these in-situ fossils, the Otog Field Museum of Geological Vestige was built on the Tracksite No. 8. However, it has been discovered that the degree of weathering of the indoor footprints, especially those in the area near the surrounding walls within the museum, is much higher than that of the footprints in the field. The surface of the footprints gradually became efflorescent and broken, and in some cases, the entire footprint completely disappeared. In order to understand this phenomenon, rock specimens from the same stratum, both inside and outside of the museum, were studied by means of polarized light microscope (PM)n, X-ray diffraction (XRD) analysis, mercury intrusion test (MIP), ion chromatography (IC) analysis, Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS). The results show that the indoor rock has a higher porosity and a larger pore size, and the soluble salt content is two times of that in the surface samples and 11 times of that in the subsurface samples of the rocks in the field. The soluble salts are mainly NaCl and Na2SO4. Simulated aging tests show that the damage resulted from soluble salt is greater than freeze-thaw cycles and that Na2SO4 is the most damaging salt. Therefore, the weathering of the dinosaur footprints inside the museum is the combined effect of groundwater and surface rainwater, which leads to strong water-salt activity of Na2SO4. Nitrocellulose varnish, which was used as a consolidant and sealing material, does not offer good protection against weathering. Some suggestions are provided for future protection of the dinosaur footprints and tracks at this site.