吉林大阳岔寒武系-奥陶系界线剖面冶里组海绿石化海绵骨针化石  

GLAUCONITIZED SPONGE SPICULES FROM THE YELI FORMATION AT THE DAYANGCHA CAMBRIAN-ORDOVICIAN BOUNDARY SECTION,JILIN

作　　者：李国祥[1] 赵鑫[1] 

机构地区：[1]现代古生物学与地层学国家重点实验室,中国科学院南京地质古生物研究所,南京210008

出　　处：《古生物学报》2009年第1期23-30,共8页Acta Palaeontologica Sinica

基　　金：国家自然科学基金(Nos.20572006,40872012);国家重点基础研究发展规划项目(2006CB806401)联合资助

摘　　要：大阳岔寒武系-奥陶系界线剖面的界线附近地层(冶里组下部)中富含海绵骨针化石,其中部分骨针化石以次生海绿石化方式保存。海绵骨针的海绿石化与骨针的原始成分蛋白石有关,蛋白石不稳定,常脱水后在成岩过程中转变为石英;在寒武纪-奥陶纪过渡时期,此地的沉积速率较小,沉积了一套海绿石凝缩层,在局部弱碱性环境中,蛋白石质的海绵骨针易于溶解,且被海绿石所替代,蛋白石的溶解与海绿石的晶出替代近为同步,致使骨针形态完好保存。海绿石化海绵骨针共有4种类型:单轴骨针,四射二轴骨针(或十字骨针),五射三轴骨针及六射三轴骨针;其中四射二轴骨针丰度相对较高。单轴骨针可能为普通海绵纲的骨针,其余骨针都为六射海绵纲的特征骨针。The sponge spicules occur commonly in Palaeozoic marine carbonate rocks.Under microscope,the spicules could be discerned in thin sections by their distinct external morphology and optical characters.The glauconitized spicules were scarcely documented in literatures.Eisenack(1978) reported the finding of a fragmentary glauconite mold of sponge spicules from the Lower Ordovician of Sweden.Although the siliceous spicules of the Dayangcha section have been well examined through thin sections(Zhang and Chen,1986),the glauconitized spicules have not been mentioned.When collecting conodont specimens after acetic acid maceration of carbonate samples,the authors recovered dozens of well-preserved glauconitized sponge spicules,including monaxons(Text-figure 2-A—C2),tetractines or(stauractines)(Text-figure 2-D—F),pentactines(Text-figure 3-A),hexactines(Text-figure 3-B1—E).This paper briefly describes the glauconitized spicules and analyzes the glauconitization mechanism.All the fossils under present investigation were collected from the Cambrian-Ordovician transition interval [from HDA11 to HDA14-1(Chen,1986),or from 16.7m to 21.8m(Zhang et al.,1996)] at the Dayangcha section,which is located at 1.5km NE of Dayangcha Town and 25km NE of Baishan(formerly called Hunjiang) City,Jilin Province(Text-figure 1).Lithostratigraphically,the interval belongs to the lower Yeli Formation.The Dayangcha section has been well-known for formerly being one of the candidate sections for the Global Cambrian-Ordovician boundary stratotype more than ten years,and further,it had been accepted as the only candidate section for Global Cambrian-Ordovician boundary stratotype by the International Cambrian-Ordovician Boundary Work-ing Group since 1991.Although the Cambrian-Ordovician Boundary GSSP was finally chosen at the Green Point section in Newfoundland,the Dayangcha is still an important section for regional and interregional correlations across the Cambrian-Ordovician transition interval.The glauconitized spicules documented herein were e

关 键 词：海绵骨针 海绿石化 寒武纪-奥陶纪过渡时期 冶里组 大阳岔 

分 类 号：Q915[天文地球—古生物学与地层学]