云南晋宁梅树村剖面研究新进展

<正> 1984年初,我们曾将梅树村剖面近四十年来的研究成果作了系统总结 (罗惠麟等,1984)。同年1月,该剖面被国际地科联前寒武系-寒武系界线工作组表决通过为唯一的全球界线层型候选剖面,并提交国际地层委员会予以确认。为了进一步提高剖面的研究程度,1984—1986年间,我们着重在生物地层、岩石地层、同位素地质及磁性地层等方面加深研究,又取得了一批新成果,这些成果无疑将会使该剖面处于领先地位,现作一简单报道。

New advances in the study of Meishucun section of Jinning, Yunnan

New advances in the study of petrostrata, biostrata, isotope age, stable isotopic dating as well as palaeomagnetism are briefly summarized in the present paper. In order to justify the precise position of boundary point of Precambrian-Cambrian (Point "B"), an additional section was measured at the southern sector of Xiaowaitoushan. In so doing, the contents of the small shelly fossils near the Point "B" were enhanced. Our studies were emphasized oa the Tannuolina, Lapworthella, Chancellorida and Sachites occurring at the bottom of Unit 13 of the section. For the sake of showing the primitive composition and texture of shell as well as its evolutional patterns, by means of polarization microscope and SEM, the components and microtextures and microstructures of small shelly fossils collected from the strata between late Sinian and Meishucunianian age have been carefully studied. The isotope age for the black shale in the Lower Badaowan Member is determined at 570.7±4.7Ma, and the phosphorite of the Upper Zongyicun Member at 596.9±4.6Ma. According to the recently measured data on palaeomagnetism, the palaeolatitude of Meishucun district during late Sinian to early Cambrian should not be over 18° beyond equator northward and southward. The new data have also demonstrated that there must be at least six reversed magnetized layers appearing in the column of Meishucun section.