中国晚前寒武纪 Pseudogymnosolenidae

<正> 1974年在我国上前寒武系蓟县层型剖面蓟县系雾迷山组下部首次报道了一个新的叠层石群Pseudogymnosolen Liang et Tsao,近数年来在我国许多地区陆续发现该群分子。与此同时,又发现大量的形态上与Pseudogymnosolen具有一定相似性但又有明显区别的新的叠层石群。作者认为原假裸枝叠层石群(相当属)资料十分丰富,已有足够条件提升为超群Pseudogymnosolenidae(相当科)。此超群的叠层石具有固定的柱体形态(表1图2),局部柱体本身是由一系列紧密相连的假柱组成,故它们的分类位置应归于柱-层叠层石大类。但因叠层体微小(柱体直径一般小于1厘米),具较频繁的平行和微散开分叉,它们可以与柱-层叠层石大类的其他叠层石明显区分。

ON PSEUDOGYMNOSOLENIDAE OF LATE PRECAMBRIAN IN CHINA

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 of Pseudogymnosolenidae in stratigraphic application of Precambrian.