鄂尔多斯盆地上三叠统延长组震积岩识别标志研究

Study on the recognition marks of seismites in Upper Triassic Yanchang Formation,Ordos Basin,China

震积岩主要通过地震驱动形成的软沉积物变形构造来识别。鄂尔多斯盆地南部中生界延长组长6-长8中发育大量软沉积物变形构造,包括微同沉积断裂、震裂缝、液化砂岩脉、沙侵蘑菇、振动液化卷曲变形构造、负荷构造及枕状层、地震角砾岩、震塌岩等。这些变形构造常沿限定的岩层发育,上、下均为未变形的岩层,显示事件变形特征。同时在塔17井中发现完整的震积岩垂向序列,序列自下而上分为下伏未震层、微断裂层、微褶皱层、碎块层及液化均一层、上覆未震层。该震积岩的发现,表明晚三叠世随着秦岭、南祁连海槽的封闭,南北向逆冲带发生强烈活动;并且为盆地西南部延长组长6-长8发育的大规模浊积岩的外界触发机制是由地震活动引起的提供了有力证据。

Seismites are identified mainly by soft-sediment deformation structures. Many earthquake- related seismites have been discovered in the Chang 6 -- Chang 8 of the Upper Triassic Yanehang Formation in the south of Ordos Basin. Having surveyed the eores of wells, many typieal deformation struetures are diseovered, sueh as syn sedimentary miero faetures, stone veins, vibrational liquefaetion, deformation strueture, earthquake breeeia and load-easts and balls-and pillows-types, ere. They develop in eonst-rained horizons bounded by undeformed strata, suggesting that they are syndepositional. The eomplete vertieal sequenee of seismite of Well Ta 17, ineludes a shattered roek bed, ladder shaped faulted bed, vibrational liquefaction deformation structure bed, liquefied sandstone vein bed, rubble bed and homogenized bed. The discovery of seismite can be used to interpret the teetonie evolution of the basin. In Late Triassie, with the dosing of Qinling and the sea slot of the southern Qilian, strong aetivities oeeurred in the south-north thrust belt. They are the direet indueing faetors of the seismo-deposition in the Yanehang Formation and provide the evidenee for the turbidite of Chang 6 -- Chang 8 of the Yanehang Formation in the southwest of Ordos Basin, that is, the outside trigger meehanism of the turbidite is earthquake aetivity.