四川峨眉晚侏罗世湖泊沉积中震积岩的发现及其意义

四川峨眉川主乡上侏罗统的震积岩由微型断裂层、微型褶皱层、碎块层、均一层组成,总厚0.69m.上覆和下伏地层皆为受地震影响的、水平层理保存完好的未震动层.上述自下而上的震积岩层序特征,反映了地震震波对水和沉积界面以下的沉积物因压实作用不同和变形能力差异而形成的不同沉积构造.

Features and. Significance of Seismites From Upper Jurasic Lacustrine Deposites of Emei,Sichuan

The rapidly development of event stratigraphy in the past decades strengthen the concept that thestratigraphical record is coined by rare and short-term catastrophic events rather that by "fair weather"con-ditions.The authors focus cn。kind of high-energy events and their geological records, i. e.,the seisnncdeposites ur mute correctly specifical sedimentary structures caused by earthquake. Here is an example in the Upper Jurassic non-marine deposites IProm Emei County Sichuan Provincein which five sedimentary horizons with characteristic sedimentary structures are well developed and arethought to have been produced by seismic events.They are from the bottom to top: 1. undisturbed bed: lamination is left undeformed, while microfaults may be present in the beds at adistance of a few centimeters. 2.microfault bed: three microfaults can be recognized in the section of 2.8 meter long and they are allnormal fault. the thickness of this bed is about 15-30cm. 3.pleated bed: 6-27 cm thick folded lamination is quite clear in this horizon and a recumbent fold canbe seen at the left side of the section. 4.rubble bed: it is characterised by smaller fragments of the original sediments which were broken topieces by earthquake shock and seperated in the soupy matrix with vairying orientations.The thickness of thisbed is 16-28cm. 5.homogenized (soupy) bed: there are no laminations in this uppermost bed.It implies that a kind ofliquefaction caused by seismic shock may have destroyed all the strucl,ures of the uppermost layer.