关于辽西北票组地质时代及区域对比的再讨论

Rediscussion on Geologic Age and Regional Correlation about Beipiao Formation in Western Liaoning

北票组是辽西侏罗纪主要含煤地层,大部分学者从植物化石角度论述其时代为早侏罗世,区域上与窑坡组、永定庄组、富县组、三工河组对比。本文从地层层序、岩性、构造演化、古气候演化等角度对北票组的地质时代和区域对比进行了讨论,认为该组为印支期后地壳伸展阶段早侏罗世早—中期兴隆沟组火山喷发之后和中侏罗世中晚期海房沟组、蓝旗组燕山期火山活动之前的含煤盆地沉积产物。前者火山活动在冀北、京西形成南大岭组,在北疆三工河组局部形成火山岩夹层;后者火山活动在冀北、京西形成九龙山组、髫髻山组,晋北形成云岗组、天池河组,北疆形成头屯河组。北票组底部杂色地层化石稀少,有机质含量低,气候应相对干热,北票组(杂色地层以上部分)、海房沟组、蓝旗组植物化石和孢粉证明古气候由温湿向干热逐渐演化,而该特征和中国北方以至全球早侏罗世晚期干热、中侏罗世从早期到晚期由温湿向干热的演化规律—致。从而,北票组底部杂色地层属于早侏罗世晚期并和三工河组、富县组、永定庄组、阳眷组、窑坡组底部对比;北票组杂色地层以上部分属于中侏罗世早期,与西山窑组、延安组、大同组、下花园组、窑坡组(K1砂岩以上部分)对比。

Objectives：The Beipiao Formation is major Jurassic coal-bearing stratum in Western Liaoning.Most scholars believe that the Beipiao Formation is belonged to the Early Jurassic and can be correlated with Yaopo, Yongdingzhuang,Fuxian and Sangonghe Formation.But we think there are contradictions in the conclusions,so this article attempts to solve the above problems. Methods：Based on the comprehensive analysis about the stratigraphic sequence,lithology,tectonic evolution and paleoclimate evolution,we discuss the geologic age and regional correlation about the Beipiao Formation. Results：We think that the Beipiao Formation is the coal-bearing basin deposits between the early—middle period of Early Jurassic Xinglonggou Formation erupted in the crustal extension stage after indosinian and the middle—late perod of Middle Jurassic Haifanggou,Lanqi Formation erupted in Yanshanian.The former volcanic activity formed Nandaling Formation in Northern Hebei and Western Beijing,volcanic rock interlayer in part of Northern Sinkiang;The latter volcanic activity formed Jiulongshan—Tiaojishan Formation in Northern Hebei and Western Beijing,Yungang—Tianchihe Formation in Northern Shanxi,Toutunhe Formation in Northern Sinkiang. At the bottom of Beipiao Formation is motley and there are not more fossils,low organic matter,and the climate was relatively dry.The plant fossils and sporopollen in Beipiao（above the motley part）,Haifanggou,Lanqi Formation prove that the ancient climate evolved from humid cool to dry heat gradually.The characteristic is same to the Northern China and the global in Jurassic. Conclusions：The motley stratum at the bottom of Beipiao Formation belongs to the late Early Jurassic and can be correlated with Sangonghe, Fuxian, Yongdingzhuang, Yangjuan Formation and the basal bed of Yaopo Formation;Beipiao Formation（above the motley part）belongs to the early Middle Jurassic and can be correlated with Xishanyao,Yanan,Datong,Xiahuayuan Formation and Yaopo （above the K1 sandstone）Formation.