The Luda Group in Southern Liaodong Peninsula,Liaoning Province is characterized in the clastic rocks of land facies and shallow sea facies and vocanic rocks.So,it may be correlated with the Changcheng System in Jixian County,Tianjin City,China.The Gezhenpu Group may be correlated with the Jixian System in Jixian County by the carbonate rocks of platform facies rich in stromatolites with Paraconophyton-Conophyton assemblage and Baicalia-Chihsienella assemblage.According to the stromatolites with Linella-Gymnosolen-Katavia-Cuijiatunia-Ximincunella assemblage and using reported new U-Pb age(SHRIPM),the Jinxian Group may be correlated with Xiamaling Formation yielding a weighted mean 206Pb/U238 of 1 368 Ma in Yanshan Mountain area.According to the age of the Xiamaling Formation,the Luda Group is limited in 1 800 ~ 1 600 Ma,the Gezhenpu Group is in 1 600 ~ 1 400 Ma,and the Jinxian Group is in 1400 ~ 1000 Ma.The Yongning Group,Xihe Group and Wuxingshan Group rich in megascopic algal fossils with Chuaria-Tawuia-Longfengshania assemblage and worm fossils with Pararenicola-Paleolina assemblage in Southern Liaodong Peninsula may be correlated with the Little Dal Group,yielding megascopic algal fossils with Chuaria-Tawuia-Longfengshania assemblage(Neoproterozoic) from Mackenzie Mountains,northwestern Canada.Therefore,the Yongning Group,Xihe Group and Wuxingshan Group is Neoproterozoic Era in age.Put together,the Late Precambrian strata divided from below to above into the Luda Group,Gezhenpu Group,and Jinxian Group of Mesoproterozoic,and Yongning Group,Xihe Group and Wuxingshan Group of Neoproterozoic.So,the collation and Stipulation of subdivision and correlation of Late Precambrian strata in Southern Liaodong Peninsula is of important significance in study of the geostratigraphy and geochronology.
Parachuaria discovered from the Chuanlinggou Formation of the Changcheng System in the Yanshan region are clear in the outline and well preserved. A study on the Parachuaria fossils by means of HF acid-resistant maceration, fossil maceration and petrologic section methods indicates that Laminarites in the fossil bed may be remains and fragments of macro-algal Parachuaria fossils. Besides, there are a lot of Leiominuscula and Trachysphaeridium minor and other multicellular algae fragments. The carbonaceous macro-algal Parachuaria fossils may be ancient multicellular brown algae. Parachuaria is an important criterion of the evolution of primitive algae and is a representation of unique features and characteristics of bioassemblage of the distinctive Precambrian stage of China. Parachuaria provides a basis for stratigraphic division and correlation of the Changcheng System as a result of the constancy of the fossil bed. The discovery of Parachuaria not only enriches the substance of the research of Precambrian biostratigraphy but also provides material for the research of the evolution of algae and its characteristics. Description of new species Chuariaceae (Wenz), 1938 emed Duan, 1982 Parachuaria Zhu et Sun, 2002, Parachuaria glabra sp. nov. Description fossils are discoid in outline, carbonaceous. Periphery smooth, diameter is generally 3～6 mm, minimum 0.5 mm, maximum 10 mm. Shield surface smooth, covex lens in cross section. Comparison This species is like Chuaria circularis in shape, but, the individual is larger, periphery smooth, no-concentric ring. Occurrence Chuanlinggou Formation of in the Changcheng System in Jixian, Xinglong County.
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