| 长江三峡地区震旦系的微体植物化石 |
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| 摘 要： | <正> 1980年,笔者同余汶、钱逸、王宗哲、侯先光、赵自强等在宜昌莲沱的王丰岗,南沱至石牌村以及秭归县庙河震旦系剖面采集了岩样(图1)。莲沱砂岩和南沱冰碛层中的化石贫乏,仅发现球形疑源类Leiominuschla sp.Protoleiosphaeridium spp.以及一些微体植物残片。陡山沱组微体植物类型多样化,数量可观。有疑源类(acritarchs)的刺球亚类(Acanthomorphitae)的分子,如微刺藻(Micrhystridium),波罗地藻(Baltishaeridium)和毛发藻(Comasphaeridium)等,其中Micrhystridium的数量多至千万计。有晚前寒武纪常见的球形亚类(sphaeromorphitae)的分子外,出现许多具有各种裂口、开口及至口盖的疑源类属种,如Leiosphaeridia?operculia sp.n.,Stictosphaeridium?apertum sp.n.,Paiaeostomc cystis angoformis,Eoaperturilites monoscissus gen. et sp. n., Eo. gonostomus gen. et sp. n., Tasmanites? sp. A。
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Sinian microfossil plants from the Yangtze Gorges region |
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| Abstract: | The section of the Sinian in the Yangtze Gorges region was established by Li Si-guang (1924). Since then, many authors, based on the studies of their sedimentary sequences, magmatic activities, tectonic frameworks, radiometric age, have expressed a few new views on the subdivision and age determination of the Sinian in the east of the Yangtze Gorges region. Recently, abundant and well preserved microfossils have been obtained from carbonatites, clastic rocks, especially beds and chert nodules in the section of the Sinian in the east of the Yangtze Gorges region. It is of great significance that many members of Acanthomorphitae, such as Micrhystridium, Baltisphacridium and Comasphaeridium, a number of taxa with opening of Sphaeromorphitae, e.g. Leiosphaeridia, Stictosphacridium, Paleostomocystis, Eoapenurilite sand Tasmanitcs. and coccoid and filamentous alga fossils compared with living eukaryo-tic algae and fungi occur in both microfossil assemblages of the Doushantuo Formation and the Dengy-ing Formation. In addition, a lot of microworm fossils were found from petrographic thin sections of chert nodules in the Dengying Formation. Microfossil assemblages of the Doushantuo Formation and the Dengying Formation are nearly similar in members of microfossils and very characteristic in biost-ratigraphy, therefore, we can name these two formations "Xiadong Group" ("Xiadong" means east of Yangtze Gorges). Now, We consider that the Sinian Sytem of the Yangtze Gorges regicn is composed of the Nantuo Formation (tillites) and "Xiadong Group" (including the Doushantuo Formation and the Dengying Formation). It unconformably or paraconformably overlies the Liantuo Formation and is pa-raconformably overlain by the Lower Cambrian Huashandong Formation containing hyolithids, monopla-cophora, cambroscheritids, sponge spicules, etc. Its time span is about 750 ma to 600 ma from now. As mentioned above, the section of the Sinian in the Yangtze Gorges region is very characteristic in biostratigraphy and continuous in sedimentary sequences. So, taking the section of the Yangtze Gorges region as one of the important stratotype sections for creating a new sequence system under the Cambrian is very suitable. |
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