Middle Jurassic Flora From Shiguai Basin, Inner Mongolia Of China With New Material Of Ginkgoales And Czekanowskiales

The Shiguai Basin, one of the well-know Mesozoic coal-bearing basins in northern China, is located in the central part of Inner Mongolia ( N40°35′-40°45′,E109°45′-109°50′). It is a typical small scale non-marine coal-bearing basin of Jurassic age and extends from east to west for about 90km long by 20km wide in the widest part. In this basin, the Jurassic sediments are well developed and especially well exposed at the Toudaogou-Erdaogou Section. The Jurassic deposits are divided into four formations in ascending order: the Lower Jurassic Wudanggou Formation, the Middle Jurassic Zhaogou Formation and Changhangou Formation, and the Upper Jurassic Daqingshan Formation. Specimens of fossil plants were collected from the Zhaogou Formation at the Toudaogou-Erdaogou section. Lithologically, the Zhaogou Formation can be subdivided into two members based on the field investigation made by the author. The lower member is represented by fluvial and swamp sediments consisting of conglomerates, sandstones, siltstones, shales and coal layers. Abundant fossil plants described in this paper were collected from the fine-graded sandstone bed from the lower part of this member. Some bivalves have been found in this member. The upper member is composed of sandstones, siltstones, shales and coal beds indicating lacustrine and swamp sediments. This member is mainly coal bearing deposits.To our knowledge, fossil plants from this basin have not been studied in detail. From 2004 to 2006, a lot of fossil plant specimens were collected from Zhaogou Formation by the author and his colleagues. The preliminary examination shows that this is a larger and diverse flora containing Filicopsida, Cycadopsida, Ginkgopsida, Czekanoskiopsida, Coniferopsida, and it is mainly dominance of the Filicopsida, Ginkgopsida, Czekanoskiopsida and Coniferopsida. Detailed studies on the fossil plant specimens reveal that the flora of the Zhaogou Formation are composed of 18 genera and 31 species, The list of the identified fossils is as follows:Filicopsida ( 3 genera and 10 species) Coniopteris burejensis(Zalessky)Seward Coniopteris hymenophylloides(Brongniart)Seward Coniopteris sp. Todites williamsoni(Brongniart)Seward Cladophlebis shansiensis Sze Cladophlebis hsiehiana Sze Cladophlebis argutula(Heer)Fontaine Cladophlebis angusta(Li)Wu comb.n. Cladophlebis haiburnensis(L.et H.)Brongn Cladophlebis sp.Cycadopsida(3 genera and 3 species) Pterophyllum baotoum Chang Anomozamites major (Brongniart) Nilssonia compta(Phillips)Ginkgopsida (2 genera and 4 species) Ginkgo shiguaiensis sp. nov. Gingko longifolius (Phillips) Harris Ginkgo sp. Baiera furcata (L. et H.) BraunCzekanoskiopsida (4 genera and 6 species) Czekanowskia (Harrisalla) chinensis sp. nov. Czekanowskia (Vachrameevia) shiguaiensis sp. nov. Phoenicopsis (Phoenicopsis) cf.angustifolia Heer Phoenicopsis speciosa Heer Sphenarion paucipartita (Nathorst) Harris Ixostrobus lepidus(Heer)HarrisConiferopsida(5 genera and 6 species) Pityophyllum lindstroemi Nath. Pityophyllum nordenskioldi Heer Storgaardia sp. Podozamites sp. Lindleycladus lanceolatus (L.et H.)Harris Elatocladus manchurica Yabe et OishiPlantae insertae sedis(1 genera and 2 species): Taeniopteris tenuinervis Braun Taeniopteris sp.The flora is characterized by prosporous and diverse Filicopsida, Ginkgopsida, Czekanoskiopsida and Coniferopsida. The occurence of Coniopteris burejensis, Coniopteris hymenophylloides marks the difference between the present flora and the Early Jurassic flora. The known species of Ginkgopsida formed during the Early Mesozoic with a relatively high variation have been identified in the flora. They are mostly the important element of the Early and Middle Jurassic in North China. The present elements of Coniferopsida are not quite different from those of the Early Jurassic. Cycadopsids with low variation are mostly the common species of the Middle Jurassic flora in North China, Central Asia and Siberia. All these mark the Early Assemblage of the Middle Jurassic and indicate the age of Middle Jurassic in North China. Fossil bivalves associated with the flora also support the Middle Jurassic age.The existence of the large amount of Filicopsida and the absence of the typical members of dipteridaceae and matoniaceae of the tropical and subtropical floras in the south China indicate the flora were under relatively warm and moisture climate; the high percentages of the Gingkgopsida, Czekanoskiopsida reveals a temperate seasonal climate relatively cool. The mass existence of Coniferopsida is also an indicator of temperate climate. Hence, the flora indicate climate of warm or slightly warm temperate-temperate zones with apparent season variations.Systematic comparison of the flora in the area with those of the same was made. The results showed that the flora is similar to those found in the Yinmagou Formation, Dameigou Formation of the Northeast Part of the Caidamu Basin in Qinghai, the Haifanggou Formation of West Liaoning Province, Mentougou Formation of Beijing, Yima Formation of West Henan, They might be under similar environments and probably form at the same period. Meanwhile, the present flora are quite similar to those of the Middle Jurassic in the central Asia and Siberia, especially some genera and species are same as those in the Yorkshire flora of the Middle Jurassic in England where some marine intercalations are found. This also supports the flora in the Zhaogou Formation are Middle Jurassic in age.For the first time, the study has conducted a detailed dissecting study on leaves as compression .The cuticle was first immersed in 40% HF solution for about 8-24 hours depending on the different degrees of carbonization. Then the cuticle was washed a few times using distilled water before transferring to the Schulze's solution. When the color of the cuticle in the Schulze's solution changes into light brown, the cuticle was washed using distilled water and then treated with 5% NH4OH. Wash with distilled water a few times before mounting on SEM stubs. SEM samples were air dried and coated with platinum. All samples were examined using a JSM-6700 scanning electron microscope at an acceleration voltage of 10kv. All specimens and preparations are stored in the Research Center of Paleontology and Stratigraphy of Jilin University, Changchun, China.By using scanning electron microscope. According to their leaf-shapes and well-preserved cuticulae, this thesis has carefully described the newly found Ginkgo shiguaiensis species, Czekanowskia (Harrisalla) chinensis sp.nov., and Czekanowskia (Vachrameevia) shiguaiensis sp.nov.. This thesis has also studied the structures of leaf-cuticulae of the two previously found Ginkgo longifolius and Ginkgo sp. in the study area. The appearance of these species in Middle Jurassic strata in Daqingshan area, Inner Mongolia is an important extension of Ginkgoales and Czekanowskiales in Northern Hemisphere strata and geographical distribution areas, which significantly improved the study level of the abovementioned two kinds of fossils.The thesis has systematically described Mesozoic Ginkgoales and Czekanowskiales fossils in northern China, reported their detailed classifications, and discussed classification principle,suborder and species. This study will play a positive role in enhancing the study level of Ginkgoales and Czekanowskiales of China, and provide new reference materials for studying middle Jurassic flora in Shiguai basin and other northern China areas, for contrasting of Coal-bearing strata, and for restoring palaeo-geography and palaeo-climate etc.