成都金沙遗址区全新统震积岩的发现及其地质意义

Discovery and geological significance of the Holocene seismites in the Jinsha site in Chengdu,Sichuan

震积岩是灾变性事件岩的典型代表,是具有震积构造和震积岩序列有一定成因联系的一组岩石的总称。成都金沙遗址区全新统地层中首次发现震积岩,该地层自下而上为底部砾石层、中部暗色（含炭）泥质层、上部褐黄色土壤层,整体属河流冲积物。通过野外观察,研究区发育一组走向SE120°的正断层,断层两盘的底部砾石层顶界面有明显的错断。构成地垒构造;在IT6511、IT6610层位中的断层带中见明显阶梯状断裂,其以张性正断层为主,断距约为10-90cm。在靠近阶梯状断裂的IT6512、IT6613-6614层位中发现一系列地震成因的软沉积物变形标志及破裂构造,包括砂土液化（脉）、液化卷曲变形构造、负载构造、微断裂、地裂缝、震塌岩等。分析认为这些软沉积物变形标志及破裂构造是由同期地壳活动引起的地震作用形成的。金沙遗址区震积岩的发现,对研究四川盆地全新世以来的古环境有重要意义。

The seismites are interpreted as a typical representative of catastrophic event deposits,and a general term for a group of genetically related rocks with the structures and sequences of the seismites. The seismites and seismic deposition are recognized for the first time in the Holocene strata in the Jinsha site,Chengdu,Sichuan.These strata are assigned to the alluvial deposits,and display gravel layers at the base,dark（ carbonaceous）argillaceous layers（ shale layers） in the middle part,and brown yellow soil layers in the upper part. There occurs a series of SE-trending normal faults on both sides of which well-defined faults at the top interface of the basal gravel layers constitute the horst structures. In the IT6511 and IT6610 horizons,there occur stepped faults composed of extensional normal faults with the slips of faults from 10 to 90 cm. In the IT6512,IT6613 and IT6614 horizons,there are many deformational indicators and fracture structures in the soft sediments such as sand liquefied veins,liquefied convolute deformational structures,load structures,microfaults,microfractures,and seismites.The above-mentioned soft sediment deformational structures and fracture structures are believed to be caused by the crustal movement-induced earthquakes. The discovery of the seismites in the Jinsha site in Chengdu is of great value for the approaches to the palaeoenvironments of the Sichuan Basin from the Holocene onwards.