Study on weathering mechanism of dinosaur tracks from Early Cretaceous in tracksite No. 8, Otog, Inner Mongolia
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Abstract:
Chabu area in Otog Qi, Inner Mongolia, is a rare fossil producing area of dinosaur footprints in the world, which is rich of dinosaur tracks from Early Cretaceous. However, these footprint fossils are experiencing different degrees of weathering in the field. In order to protect these fossils in-situ , the Otog Field Museum of Geological Vestige was built on the Tracksite No. 8. Whereas, it was found that the weathering degree of indoor footprints was more serious than that in the field, especially the area within the museum near the surrounding walls, and the surface of the footprints gradually became efflorescence and broken, and some even completely disappeared. In order to understand this weathering phenomenon, fossil rocks of the same stratum inside and outside the museum were tested by means of polarized light microscope (PM) observation, X-ray diffraction (XRD) analysis, mercury intrusion test (MIP), ion chromatography (IC) analysis, Raman spectroscopy (Raman) analysis, Fourier transform infrared spectroscopy (FTIR) analysis and scanning electron microscopy (SEM-EDS) analysis in this article. It is found that the indoor rock has a higher porosity and larger pore size, and soluble salts content is 2 times that of the surface rock as well as 11 times of subsurface rock. The soluble salts are mainly NaCl and Na2SO4. Though simulated aging tests, it is found that the damage of soluble salt is greater than freeze-thaw, and Na2SO4 is the most damage salt. Therefore, it is indicated that the weathering mechanism of dinosaur tracks in the museum is the combined action of groundwater and surface water formed by rainfall, which leads to strong water-salt activity of Na2SO4. It is found that the nitrocellulose varnish, which was used as consolidant and sealing material, did not have a good protective effect. Some suggestions are put forward to deal with this problem.
