鄂尔多斯盆地东胜东三叠系—侏罗系湖泊风暴沉积的发现及其意义

鄂尔多斯盆地东北部东胜—纳林河一带出露的中生界三叠系—侏罗系—白垩系地层,为一套河湖相沉积(白垩系可能有风成沉积).在三叠系—侏罗系地层中发育完好的风暴沉积和风暴岩.在东纳林煤矿—德胜西岔路口的109国道两侧长约40 km的三叠系—侏罗系地层中发育风暴沉积,该德胜西剖面连续长度达548 m.这套风暴沉积主要为一套河流—...

Discovery and Significance of Lake Storm Deposits in the Triassic-Jurassic of Eastern Dongsheng,Ordos Basin

Mesozoic rocks are exposed in the northeastern corner of Ordos City.The main strata consist of a set of Triassic-Jurassic lacustrine deposits.Well-developed storm deposits and tempestites are found in the Triassic-Jurassic.The main site of the study is in the Triassic-Jurassic on both sides of National Highway 109 from Nalinhe coal mine to western Desheng,a distance of about 40 km.The western Desheng profile shows well-developed storm deposits and tempestites over a continuous length of 548 m.These are mainly a fluvial-delta-lacustrine deposit(with a few peat bogs),which is remarkable for its type-perfect HCS and SCS.Preliminary studies suggest that this set of storm deposits and storm rocks mainly developed in shallow lakes.The main features are as follows.(1)Where there are storm deposits or storm rocks,the stratification is very poor,and the strata are mostly lenticular,or lenticular/wavy.(2)The mounds and depressions form perfect medium-and large-scale continuous sinusoidal curves of wavelength ranging from several meters to nearly 100 meters,and amplitude ranging from tens of centimeters to 1-2 meters.(3)The lithology and its combinations are mainly a set of yellow-brown conglomerate+sandstone+gray mudstone.It has an obvious binary structure(lower coarse/upper fine).Stratification has developed in the upper part of the lower block.Conglomerate dominated by coarse debris is a common bottom deposit in the storm deposits.Storm deposits and tempestites have been formed by coal seams near the Nalinhe coal mine.(4)Gray gravel-bearing block mudstone with floating gravel reveals that it was deposited rapidly,similar to debris flows formed by storms rather than hydrostatic deposits formed in normal weather.The pebbly mudstone is tens of centimeters thick,which indicates a considerable rate of deposition at the time.(5)In western Desheng,a prominent profile of storm sediments and rock,the bottom developing the 1 to 3 thick gravel layers,with a middle layer tens of centimeters to 1-2 m thick and large amounts gravel 30-40 cm in diameter,most with imbricate structure.The former may be instructed the backflow storm in the direction of the lake,which indicates flushing flow to the lake shore caused by very strong storms.(6)Oscillatory flow is dominant,but has clear characteristics of composite and oscillatory flow in some places.(7)The overall sedimentary background is that of a broad,shallow lake environment,with mainly in situ oscillatory vertical deposition.Lake storm deposits and tempestites in the Triassic-Jurassic in Ordos is not usual;to date,no such large HCS and SCS have been reported anywhere worldwide.This study has shown that the lacustrine water in which these storm deposits and tempestites were formed was about 50 meters deep.