ON PSEUDOGYMNOSOLENIDAE OF LATE PRECAMBRIAN IN CHINA
中国晚前寒武纪 Pseudogymnosolenidae

A new group of stromatolites-Pseudogymnosolen which occurs in thelower member of Wumishan Formation, Jixian System, was reported first in1974 from the stratotype section of Upper Precambrian in Jixian County,North China (Cao Ruiji and Liang Yuzuo, 1974). The members of this groupwere discovered in recent years in many other regions at home. A numberof new groups of stromatolites which both resemble Pseudogymnosolen in morphological feature and bear distinct difference were discovered at thesame time. The authors consider that the original Pseudogymnosolen (Correspond to genus) ought to be promoted to Pseudogymnosolenidae (Correspondto family) because of sufficient evidence. These Pseudogymnosolenidae takestable shape of columns and part of the columns themselves are formed bya series of closely linked pseudo-columns. Therefore their position of classification should belong to columnar-stratiform stromatolites. Since they aresmall columns (diameter of the columns commonly<1cm) and frequentlyparallel or slightly divergent, they can be differentiated prominently withthe other stromatolites of the columnar-stratiform kind. In the Yanshan area,part of this supergroup is fromed by black chert, in which well preserved microflora belonging to Eomycetopsis Schopf, Animikiea Barghoorn, RhicnoemaHofmann and some straight filaments were found. It has proved that theseblue-green algae take part in the process of formation. Based on the materials at hand, Pseudogymnosolen identified as this supergroup contains nine groups and about thirty-eight forms, distributed innine provinces and more than ten localities (Fig.1,). They occur in stablehorizon with isotopic time-range 1200-1400 m.y..The minority of this supergroup might present in the lower Proterozoic era, but we have not foundany from the rock younger than 1200 m. y. .Therefore it is the important fossiliferous evidence of the Wumishan Formation, Jixian System. The materials studied in China indicate that Pseudogymnosolenidae is asuseful in stratigraphic division and correlation of Precambrian as other columnar stromatolites and it is playing an important role in stratigraphic division and correlation of those such as Kunyang, Liaohe and Shinagan groupsthat have been discussed. Scholars of U. S. S. R, Australia, France and India had been engaged widely in studying biostratigraphy of stromatolites in Precambrian from theearly 60's to 70's and published a great many memoirs and treatises,but theirmain object was concentrated on researching into bigger columnar stromatoliteswhile the study of small columnar-stratiform stromatolites was neglected.They did not pay enough attention to the potential biostratigraphic significance, though a few of them did describe occasionally the stromatoliteswhich resemble Pseudogymnosolidae in shape. This paper reports briefly our achievements in recent years. We hopethat it will attract the wide attention of scholars at home and abroad.Weshall discuss togerther the real value