中国陆相侏罗系—白垩系界线及其国际地层对比——以冀北—辽西地区侏罗系—白垩纪年代地层为例

Boundary between Jurassic and Cretaceous in Chinese Non-marine Basin and with International Stratigraphic Correlation:a Case Study of Biostratigraphic and Isotopic Dating in Luanping,Hebei Province

冀北—辽西地区陆相侏罗系—白垩系发育,各类生物化石丰富,并夹有火山岩,是利用岩石地层、生物地层、同位素测年和磁性年代地层综合研究侏罗系\白垩系界线的理想地区。冀北滦平盆地侏罗系\白垩系界线附近的地层为大北沟组和大店子组,辽西义县—北票地区侏罗系\白垩系界线附近的地层为土城子组和义县组。大店子组含有孢粉Cicatricosisporites-Luanpingspora-Jugella组合;介形类Yanshanina-Cypridea-Rhinocypris组合,Cypridea-Yanshanina-Timiriasevia组合,Cypridea sulcata亚组合和叶肢介Eosestheria-Abrestheria组合等各类化石,这些生物组合与国内、外的对比,尤其是孢粉和介形类与英、法、德、俄和加拿大等地相关地层同类化石组合的对比,其时代为早白垩世早期(Berriasian)。辽宁西部义县组下部的孢粉、介形类和叶肢介与国内、外的对比,也得出与大店子组的时代大致相同的结论。大北沟组含孢粉Poceites-Podocarpidites-Schizaeoisporites组合,介形类Luanpingella-Torinina-Eoparacypris组合以及叶肢介Nestoria-Keratestheria组合等,这些生物组合与国内、外同类生物组合的对比,得出的时代结论是晚侏罗世晚期(Tithonian)。土城子组含有孢粉、介形类及叶肢介等6大门类化石,根据已有的研究成果,得出的时代结论是晚侏罗世。因此,侏罗系\白垩系的界线划在大北沟组与大店子组之间。生物地层的国际对比表明:此界线与国际侏罗系\白垩系界线,即Tithonian\Berriasian界线是一致的。根据冀北—辽西地区一系列同位素测年数据推断,侏罗系\白垩系界线年龄应接近130.7Ma。

Northern Hebei-Western Liaoning, developing in boundary between Jurassic and Cretaceous with various fossils and volcanic ash bedding, is the marvelous region for the study of lithological, biostratigraphic, isotopic dating and Magnetic chronostratigraphy. The boundary of Jurassic and Cretaceous strata are between the Dabeigou and Dadianzi formations in the Luanping Basin, Northern Hebei and the Tuchengzi and Yixian formations in Yixian-Beipiao area in Western Liaoning. The Dadianzi Formation consists of spore ＆ pollen assemblages, such as Cicatricosisporites-Luanpingspora-Jugella; Ostracoda： Yanshanina-Cypridea-Rhinocypris assemblages, Cypridea-Yanshanina-Timiriasevia assemblages, Cypridea suleata sub-assemblages and conchostraca： Eosestheria-Abrestheria assemblages and so on. Those fossils can be correlated in home and aboard, especially, spore ＆ pollen and ostracoda are the same fossils in the correlation strata in England, French, Germany, Russia and Canada, with age of Early Early Cretaceous （Berriasian）. However, the spore ＆ pollen and conchostracain developed mainly in the lower part of the Yixian Formation are same as those assemblages in the Dadianzi Formation. Then, the Dabeigou Formation with spore ＆ pollen assemblages： Poceites-Podocarpidites-Schizaeoisporites assemblages, Ostracoda. Luanpingella-Torinina-Eoparacypris assemblages and conchostraea： Nestoria-Keratestheria assemblages show the Late Late Jurassic period （Tithonian） in the eorrelation with home and aboard. However, the boundary of Jurassic and Cretaceous is just developed in between the Dabeigou and Dadianzi formations. In the International biostratigraphic correlation shows the boundary between Jurassic and Cretaceous, e.g. the boundary of the Tithonian and Berriasian. According to the isotopic data in North Hebei-Western Liaoning region, the boundary age of Jurassic and Cretaceous is at 130.7 Ma.