Early Cretaceous Fossil Plants In West Fujian And Northeast Jiangxi And Their Paleoenvironmental Analysis

Some fossil plants were collected from the Bantou and Junkou Formations of West Fujian Province, and the Zhoujiadian Formation of Northeast Jiangxi Province. Through detailed description and identification, these fossils are assigned to 20 genus and 41 species, involved of 5 new species. Of the three formations, fossils from the Bantou Formation are the most abundant in species and quantities, and all the species discovered in the Junkou and Zhoujiadian Formations are almost occurred in the Bantou Formation. By analyzing the floral composition characteristics and age range of all the species in the Bantou formation, it is supported the view that the age of the Bantou flora is the Early Cretaceous, as the component elements of the flora are similar to those of the Early Cretaceous floras. The paleofloristic province in which the Early Cretaceous Flora of the studied area is situated belongs to the southeast coastal subprovince, south province in China, which is assigned to the Euro-Sinian region. Additionally, the studied areas are situated in the tropic or subtropic zone, and the paleoclimate is generally hot and arid. Comparing the component characteristic between the Bantou flora and the late Early Cretaceous Junkou and Zhoujiadian floras, it can be seen that the proportions of fossil conifers are different among three of them. For example, Cupressinocladus, the typical representative element of early Early Cretaceous, which are very commonly found in the Bantou Formation; whereas, the genus Pseudofrenelopsis generally occurred in the upper Lower Cretaceous, which are abundant in the Junkou and Zhoujiadian Formations while scattered in the Bantou Formation, and these differences in component elements among them reflect the age character of the three floras. Furthermore, besides of multitudinous drought enduring fossil plants, a certain amount of plants apt to moist and warm conditions are occurred in the Bantou Formation whereas which are almost absent from the Junkou and Zhoujiadian Formations. It is concluded that the decrease in hygrophilous plants from the early to late Early Cretaceous maybe indicates the tendency of a hot and arid paleoclimate existed in late early Cretaceous of South China. According to the floral composition and age characteristics, we divide the three floras into two assemblages, namely. Cupressonocladus-Pagiophyllum Assemblage represented by the Bantou flora, and Pseudofrenelopsis-Brachyphyllum Assemblage composed of fossil plants from the Junkou and Zhoujiadian Formations, and which show the vegetation scenery of early and mid-late Early Cretaceous respectively in west Fujian and East Jiangxi Province of China.The anatomical microstructure features of some compressed fossils are investigated here, involving of the genus Cladophlebis, Elatides, Brachyphyllum and Pseudofrenelopsis. The cuticular features of Cladophlebis studied here fill in a gap of the epidermic structure about this form genus, therefore, a new species Cladophlebis yonganensis Dai et B. N. Sun, sp. nov. is proposed. By comparing of the epidermic features between this new species and resembled fossil natural genus, as well as that of the living ferns, we discuss the stomatal evolutionary trends of ferns, and included that the new species studied here represent a certain extinct plant of Filices.As stomatal frequency of fossil conifers are considered as potential indicators of pCO2 values during the geological history, the species Pseudofrenelopsis papillosa (Cheirolepidiaceae) from the Bantou, Junkou and Zhoujiadian Formations are used to reconstruct atmospheric CO2 of the late Hauterivian, late Aptian and late Albian age, based on the ratios between stomatal indices of fossil cuticles and those from four modern analogs (nearest living equivalent), using Carboniferous and Recent standardizations to explore ranges. The CO2 content estimated from P. papillosa is between 600-1300 ppmv, and implies a 1.6-3.5 times higher than present. The results show a low of 611-981 ppmv in the late Hauterivian, and a high of 799-1283 ppmv in the late Albian, which is only slightly higher than that of 753-1208 ppmv in the late Aptian. This CO2 range during the three intervals is consistent with those predicted worldwide by previous studies (stomatal indices, biogeochemical models and carbon isotopes). Moreover, applying the values of atmospheric CO2 into the transfer functionδT=4×1nRCO2, the change ratio of the global mean land surface temperature, from present day values, indicate an increased temperature of 2.8-4.7℃during the late Hauterivian,3.6-5.5℃during the late Albian and 3.8-5.7℃during the late Aptian, these values are consistent with the warm temperatures predicted for mid-Cretaceous (90-125Ma), and therefore support the view through analysis of floral component characteristics above that the paleoclimate is becoming hotter from early to late Early Cretaceous.