摘要
皖南蓝田剖面皮园村组为一套埃迪卡拉纪-寒武纪过渡期(约550～532 Ma)沉积的黑色硅岩.皮园村组硅岩样品的w(Ce)/w(Ce*)为0.68～1.08(平均0.85),w(La N)/w(Ce N)为0.56～1.52(平均1.10),指示它们可能形成于大陆边缘环境.剖面下部与剖面上部样品具有明显不同的稀土配分:剖面下部样品的REE低,具有与现代海水非常相似的稀土配分,表明受陆源碎屑物质影响很小.虽然剖面上部样品依然保留了海水的某些特征,如Ce的负异常和Y的正异常,但总体显示出平坦的REE配分形态,且REE高,接近平均页岩,表明剖面上部样品受陆源碎屑影响大.w(Al2O3)也表现出下部样品低(0.03%～0.94%,平均0.41%)、上部样品高(0.74%～5.04%,平均2.98%)的特征.这些地球化学特征表明:皖南皮园村组硅岩很可能沉积于大陆边缘环境,其沉积水体由于海退的影响逐渐变浅,由深水盆地边缘环境转变为斜坡环境.硅岩沉积古地理环境的变化可能造成水体氧化还原环境的变化,从而对早期生命的出现、演化和分布产生影响.
The black Piyuancun chert in Southern Anhui Province was deposited in terminal ediacaran to early cambrian transition period （about 550–532 Ma）. The w（Ce）/w（Ce＊） and w（LaN）/w（CeN） of the Piyuancun chert samples were 0.68–1.08 （avg. 0.85） and 0.56–1.52 （avg. 1.10）, respectively, which indicates that the chert was deposited in the continental margin. Chert samples from the lower part and the upper part of the Lantian section have different rare earth elements （REE） patterns： REE concentrations for chert samples in the lower section are low relative to post-Archean Australian shale （PAAS）, and their REE patterns are similar to that of the modern seawater, indicating that the influence of terrigenous detrital has been trivial. Although REE patterns for the chert samples in the upper section maintain some seawater characteristics, such as negative Ce anomaly and positive Y anomaly, they have flat REE patterns that are similar to PAAS, and their REE concentrations are close to that of PAAS, indicating that the influence of terrigenous detrital has been huge. Al2O3 content also displays the characteristics that the content are low in the lower section （0.03%–0.94%, avg. 0.41%） and are high in the upper section （0.74%–5.04%, avg. 2.98%）. These geochemical characteristics show that the Piyuancun chert was probably deposited in the continental margin, and the water column became shallow （from basin margin to slope） for regression. The depth of the water column in which the Piyuancun chert deposited probably prompted the water column redox condition to change, and therefore affected the survival, evolution and distribution of early life.
出处
《兰州大学学报（自然科学版）》
CAS
CSCD
北大核心
2014年第6期802-808,共7页
Journal of Lanzhou University(Natural Sciences)
基金
国家自然科学基金项目(41002011
41372003
41172029)
关键词
硅岩
古地理环境
埃迪卡拉纪-寒武纪过渡期
皮园村组
chert
paleogeographic environment
Ediacaran-Cambrian transition period
Piyuancun Formation
