Fossil Plants And Sporopollen From The Lower Cretaceous Of Xiliannaobao Village In Guyang, Inner Mongolia And Its Paleoclimatic Reconstruction

The research on the Cretaceous climate and vegetation is fundamental to understand the present environment. The Early Cretaceous stratum is well-developed in the middle Inner Mongolia, and contains well preserved plant fossils, many of which haven’t been systematically described and reported. In the present paper, the fossil plants and sporopollen collected from the Lower Cretaceous of Xiliannaobao Village, west Guyang County, were studied systematically. According to the systematic identification and description of the fossil plants and the statistical treatment of palynological assemblage, and the geographical distribution of modern plant community and Sporomorph EcoGroup (SEG), the characteristics of the ancient ecological and climate were discussed. The palynoassemblages are diverse, with gymnosperms dominant and ferns abundant, but there are very small amounts of angiosperms. The gymnosperms are predominated by Taxodiaceae, and a large proportion of Cycadophytes and Ginkgopsida; the ferns are dominant of Lygodiaceae and Cyatheaceae. The palynological data show that the Early Cretaceous flora shows large varity in the studied area, which include coniferous on the top mountain, and ferns along the low hill near the lake or swamp, as well as algae in the fresh water of the lake. The fossil plants and the palynoassemblages indicate that the climate in this area is warm and humid during Early Cretaceous.In the meantime, the buried environment is discussed on the basis of the lithologic characters and preservative condictions of the plant fossils. Generally, the mudstone would indicate weak hydrodynamic conditions, while the fossil plants in the ash black mudstone are relatively broken, and the stratum corneum is in a poor state of preservation. These plants generally growth in well-drained mountain. Therefore these fossil plants are likely to be heterochthonous burial; the fossil plants preserved in the silty mudstone are also relatively broken, and silty mudstone indicates stronger hydrodynamic environment. In that case, a long-distance transport would indicate. According to the preservative conditions and lithological characters, heterochthonous burial was purposed in the study area. The researches in the past indicated that the age of this study area is Hauterivian-Barremian, while others argued that the age is Berriasian-Valanginian. And there are large divergences of opinion in the age of this area, which makes a lot of trouble to the study of paleoenvironment and paleoclimate. Thus, we discussed the geological era in this paper, and revealed that the age of this area is Berriasian-Valanginian.