Microstructure Of Cordaites From The Early Permian Of Yongchang In Gansu And Paleoenvironment Research

A cuticular structure is one of the important characteristics to identify fossil plants, and it was recently used to reconstruct the paleoclimate. The author collected fossil materials of three species of Cordaites Ung. from the Lower Permian of Yongchang in Gansu Province and analyzed their cuticular characteristics. The fossils were identified mainly based on cuticular features, combined with gross morphology. One of the fossils was named Cordaites yongchangensis sp. nov. as a new species. The key characteristic identification of the new species is hypostomatic and the cells of upper epidermis are often rectangle; papillaes are well developed on the surface of ordinary epidermic cells in the abaxial cuticle and the pairs of guard cells are reniform. They are usually surrounded by two lateral subsidiary cells and two polar subsidiary cells. Two large lateral subsidiary cells are long-rectangle or long-oval; two smaller polar subsidiary cells are close to rhombus and the two adjacent stomatal apparatus usually shared a polar subsidiary cell. The papillae were not found on the surface of subsidiary cells.The other two fossils were identified as Cordaites huainanensis Chen and Cordaites radvanicensis Simunek respectively. The former has the following characteristics:leaves are hypostomatic; epidermal cells of adaxial cuticle are rectangular; abaxial cuticle composed of non-stomatal areas and stomatal-band areas; cells of the non-stomatal areas are rectangular; the pairs of guard cells are reniform or half round; lateral subsidiary cells are rhombic nearly and polar subsidiary cells are rounded or long oblong; stomata in the same stomatal area are very closely arranged, usually sharing one common polar subsidiary cell; papillae absent in the ordinary cells and the lateral subsidiary cells. The latter is characterized by leaves amphistomatic and stomata aligned in bands on both abaxial and adaxial cuticles; cells of the adaxial epidermis similar to that of abaxial epidermis but stomatal density of abaxial cuticles is higher than those of adaxial; typical cells of epidermis generally elliptic and regularly rectangular; guard cells elliptic; two polar subsidiary cells similar to but a bit smaller than typical cells; lateral subsidiary cells, 2-4, soybean form or elliptic in shape; papillae poor developed in the ordinary cells and the subsidiary cells.Macro-and micro-characteristics of Cordaites huainanensis and Cordaites yongchangensis sp. nov. suggest their relevancy with the extant genus Podocarpus, particularly with Podocarpus fleuryi Hickel. Then the CO2 concentration of the Early Permian is reconstructed by performing stomatal frequency analysis of these Cordaites fossils. The pCO2 value estimated by C. yongchangensis sp. nov. is 337.98×10-6-675.96×10-6, and the vaule estimated by C. huainanensis is 376.98×10-6-753.96×10-6. Compared with the atmospheric CO2 concentration from Berner and Kothavala (2001),the results suggest the Recent Standardization is more suitable for Cordaites when reconstructing the pCO2 of the Early Permian. The main reasons can be that the CO2 concentration of the Early Permian in this area is very close to the present condition.The author also reconstructed the paleoenvironment in this area at that time by stable carbon isotope technique, which is another distinctive feature of this thesis. We investigated the stable carbon isotope composition, carbon isotope discrimination and water use efficiencies of Cordaites leaves. In combination with the cuticluar characters of the Cordaites materials from the Yongchang, we concluded that the past climate environment is more hot and humid on the whole, and may be associated with short-term drought.Finally, the cuticles of Cordaites from the world are compared in this thesis, with an identification key of them provided. These Cordaites materials can be easily subdivided into five morphotypes and they are listed as follows. Type 1 includes species with stomata dispersed relatively regularly or sparsely in poorly defined, or irregular and rare stomatal. Type 2 represents species with stomata arranged in well defined single or double stomatal rows. Type 3 comprises species with stomata arranged in double or multiple stomatal rows that form stomatiferous bands separated by non-stomatiferous bands. Type 4 contains species with irregular stomatal shape and a varying number of subsidiary cells. Type 5 includes species with poorly preserved cuticles.