The Middle Jurassic Stratiqraphy And Flora In Northeastern Margin Of Erdos Basin

The present thesis is focused on the paleonbotany and stratigraphy. The stratigraphy of the Erdos basin is introduced briefly at first. Detailed field geological survey was carried out on the Mid-Jurassic Yan'an Formation at the Northeast margin of the basin. A cross section of 175.36m was measured and large number of fossil plants and fossil insects were collected. Based on the lithological features of the Yan'an Formation, the Mesozoic stratigraphic succession was discussed. The strata formerly considered to be the Late Triassic and the Early Jurassic were demonstrated to be Middle Jurassic in age by the fossil flora. Thus no Late Triassic and the Early Jurassic strata are developed in the area. The Middle Triassic and Middle Jurassic strata are in disconformable contact. This supports the view that Indo-sinia Orogeny is only shown by the vertical uplift movement in this area.Since the Middle Jurassic, the area subsided continually and relatively complete Middle Jurassic strata were deposited under the continued effect of the Yanshan Orogeny. Preliminary sedimentary analysis of the Early Middle Jurassic Strata indicate the sedimentary facies are mainly fluvial, lacustrine and swamp peat facies in which coal beds were developed. Detailed studies on the hundred of fossil plant specimens reveal that the flora of the Yan'an Formation are composed of 20 genera and 39 species, and the main taxa are Sphenopsida, Filicopsida. Cycadopsida, Ginkgopsida and Coniferopsida. The list of the identified fossils is as follows:Sphenopsida (1 genera and 1 specie)Radicites sp.Filicopsida ( 5 genera and 16 species)Coniopteris burejensis(Zalessky)Seward Coniopteris hymenophylloides(Brongniart)SewardConiopteris qinghaiensis He Coniopteris tatungensis Sze,1933,emend.nov.WanEboracia lobifolia(Phillips)Thomas Todites williamsoni(Brongniart)SewardTodites princeps(Presl)GothanCladophlepis argutula(Heer)FontaineCladophlepis asiatica Chow et Yeh Cladophlepis fangtzuensis SzeCladophlepis cf. gigantea Oishi Cladophlepis hirta Moeller Cladophlepis punctata (Thomas)Cladophlepis tsaidamensis SzeCladophlepis sp.Sphenopteris modesta Leckenby Cycadopsida(2 genera and 3 species)Pterophyllum cf. richthofeni SchenkPterophyllum sp.Anomozamites sp.Ginkgopsida (7genera and 12 species)Ginkgoites sibiricus(Heer)SewardGinkgoites cf. ferganensis (Brick)GemkinaSphenobaiera huangi(Sze)HsüSphenobaiera longifolia(Pomel)FlorinCzekanowskia rigida HeerCzekanowskia setacea HeerPhoeniopsis.angustifolia HeerPhoeniopsis manchurica Yabe et ōishiPhoeniopsis speciosa Heer,Sphenarion latifolia(Turutanova—ketova)HarrisIxostrobus lepidus(Heer)HarrisVittifoliolum sp.Coniferopsida(5genera and 7 species):Pityospermum sp. Storgaardia mentoukouensis (Stockmans et Mathieu)DuanPodozamites lanceolatus (L. et H.)HeerPodozamites sp.Ferganiella Podozamioides Elatocladus manchurica Yabe et Oishi Elatocladus patens HarrisThe flora is Characterized by prosporous and diverse Filicopsida, Ginkgopsida and Coniferopsida. The extreme richment of Coniopteris burejensis,Coniopteris hymenophylloides, Coniopteris tatungensis and Eboracia lobifolia mark 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 Coniopteris—Phoenicopsis flora 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 late assemblage of the Coniopteris—Phoenicopsis Flora and indicate the age of Middle Jurassic in North China. Fossil insects associated with the flora also support the Middle Jurassic age. The existence of the large amount of Filic...