辽东半岛南部中新元古界地层的重新厘定

Collation on the Subdivision and Correlation of Meso-Neoproterozoic Strata in Southern Liaodong Peninsula,Liaoning Province,China

近年来,燕山地区原青白口系下马岭组的年代学研究取得了突破性进展(其年龄为1 368±12 Ma,1 370±11 Ma,1 366±9 Ma);在研究区金州大和尚山侵入于"桥头组"辉绿岩也获得新元古代锆石U-Pb年龄(904±15Ma～1 125±38 Ma)。这些年代数据使我们认为对于辽南地区前人所划"震旦系"地层的划分与对比应进行重新考虑。本文以岩石地层和旋回地层为实际材料,生物地层和事件地层以及年代地层为手段,从长岭子组能否作为标志层入手,对辽南地区中-新元古界进行了系统研究,否定了长岭子组在地层对比中的标志层意义,首次提出葛屯组才是金县地区与复县地区进行地层对比的标志,并将复县地区的五行山群置于金县群之上,从而将辽南地区"震旦系"由老到新重新厘定为中元古界旅大群、革镇堡群和金县群与新元古界永宁群、细河群和五行山群。以碎屑岩为主要特征的岩石组合与海底火山喷发事件,将辽东半岛南部旅大群与蓟县剖面长城系进行了对比;以碳酸盐岩为主要特征并含丰富的叠层石Paraconophyton-Conophyton-Baicalia-Chihsienia等组合的革镇堡群与蓟县剖面蓟县系对比;富含叠层石Linella-Gymnosolen-Katavia-Cuijiatunia-Xingmincunella组合的金县群可与下马岭组对比,从而将金县群首次置于中元古界上部。含宏观藻类化石Chuaria-Tawuia-Longfengshania组合和蠕形类化石Pararenicola-Paleolina组合的永宁群-细河群-五行山群与加拿大新元古界小达尔群-含铜白云岩对比,永宁群-五行山群的时代应为新元古代早期。据此,笔者全面调整了徐淮胶辽吉中-新元古界的地层划分与对比,为在我国建立中-新元古界系一级的地层单元打下良好的基础,具有重要的地层学和年代学意义。同时,由于对该区中-新元古界重新进行了划分与对比,确认了大连上升是中元古界与新元古界的分界面,并大体相当于北美格林威尔运动在华北地块上的响应,为探讨燕山地区与徐淮胶辽吉中-新元古代的沉积特征,海水进退归程,构造运动以及重建Rodinia超大陆提供了地层资料,具有重要的古地理学和古构造学理论意义。

The Luda Group in Southern Liaodong Peninsula, Liaoning Province is characterized in the clastic rocks of land facies and shallow sea facies and vocanic rocks. So, it may be correlated with the Changcheng System in Jixian County, Tianjin City, China. The Gezhenpu Group may be correlated with the Jixian System in Jixian County by the carbonate rocks of platform facies rich in stromatolites with Paraconophyton Conophyton assemblage and Baicalia Chihsienella assemblage. According to the stromatolites with Linella Gymnosolen Katavia Cuijiatunia Ximincunella assemblage and using reported new UPb age （SHRIPM）, the Jinxian Group may be correlated with Xiamaling Formation yielding a weighted mean ^206pb/U^238 of 1 368 Ma in Yanshan Mountain area. According to the age of the Xiamaling Formation, the Luda Group is limited in 1 800 - 1 600 Ma, the Gezhenpu Group is in 1 600 - 1 400 Ma, and the Jinxian Group is in 1400 - 1000 Ma. The Yongning Group, Xihe Group and Wuxingshan Group rich in megascopic algal fossils with Chuaria Tawuia Longfengshania assemblage and worm fossils with Pararenicola Paleolina assemblage in Southern Liaodong Peninsula may be correlated with the Little Dal Group, yielding megascopic algal fossils with Chuaria Tawuia Longfengshania assemblage （Neoproterozoic） from Mackenzie Mountains, northwestern Canada. Therefore, the Yongning Group, Xihe Group and Wuxingshan Group is Neoproterozoic Era in age. Put together, the Late Precambrian strata divided from below to above into the Luda Group, Gezhenpu Group, and Jinxian Group of Mesoproterozoic, and Yongning Group, Xihe Group and Wuxingshan Group of Neoproterozoic. So, the collation and Stipulation of subdivision and correlation of Late Precambrian strata in Southern Liaodong Peninsula is of important significance in study of the geostratigraphy and geochronology.