A Study of Seismic Events in the Late Sinian Carbonates of Dalian
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P539.1

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    Abstract:

    It was disputed whether the Neoproterozoic in the Dalian (including Lushun) area of the southern Liaodong Peninsula is at the same horizon as that in the northern Liaodong Peninsula because the former has been intensively deformed and "the later" has not been deformed. Recently, the authors have identified, in the carbonate rock strata of the Upper Sinian Nanguanling, Ganjingzi and Yingchengzi Formations in the study area, vibrate liquefied veins, vibrate liquefied breccias and carbonate turbidites with seismite successions resulting from earthquakes. All the new discoveries in the above area have promoted the study of Sinian in southern Liaodong Peninsula and revealed that there existed 4 instead of 3 earthquake-active periods in the Late Sinian there. In addition, the discoveries have also provided new information for regional stratigraphic correlation. The general character of the Upper Sinian seismic events in the study area is observed as that the seismic beds consisting of carbonates with liquefied veins and breccias are alternated with the normal carbonates at the interval of two seismic events. Their similarity with those observed in the Red Sea, Egypt indicates that they are also products of earthquakes. The seismites in the Nanguanling and Yingchenzi Formations are composed of limestones and ooid bearing micrites with liquefied veins and breccias, limestones with cracks and grainstones with grade bedding (turbidites). Those in the Ganjingzi Formation consist of dolomites with liquefied veins and breccias and roll up deformed structures. So the commonest type of seismites in the area are carbonates with liquefied veins and breccias. The liquefied veins are made up of equal sized, purified and crystallized carbonate grains, while the liquefied breccias are simple in composition and can be pieced together. Both of them are often associated with cracks and deformations. The 4 seismic strata in Dalian, an intensively deformed area, can also be observed in corresponding strata in the northern Liaodong Peninsula (Wafangdian City,the Fuzhou area), which indicates that the two areas belong to the same depositional basin. The above fact provides evidence of seismic events for making stratigraphic comparison of the two areas in the Sinian in regional mapping at scales of 1 : 50000 and 1 : 250000. The dolomite liquefied veins and liquefied roll up deformation structures in the Ganjingzi Formation are identified as a result of another new seismic event. So new materials are given in this paper for comparing the strata of this area to those of others. The study of Sinian strata in the Liaodong Penesula are promoted in addition to enrichment of the sorts of seismites and the succession system in theory.

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PENG Yang, YANG Tiannan, QIAO Xiufu, LI Dianzhi, WANG Guozhen, YANG Zhongzhu, YANG Xiaobo) Institute of Geology, Chinese Academy of Geological Sciences, Beijing,) Geological Exploration Team of Liaoning, Jinzhou, Dalian,.2001. A Study of Seismic Events in the Late Sinian Carbonates of Dalian[J]. Acta Geologica Sinica,75(2):221-

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