中国陆相侏罗系建阶研究

全国地层工作与地层学研究新进展成果交流会

论中国陆相侏罗－白垩系界线

季强、柳永清等

中国地质科学院地质研究所

　　中国陆相侏罗－白垩系界线问题长期来一直是困扰中国地质学家的争论比较激烈的科学问题之一，而且总是与热河生物群的时代归属问题关联在一起。归纳一下，大致有三种不同的观点：（The issue about the Terrestrial Jurassic-Cretaceous Boundary in China (TJCBC) has long been one of the hot debated, complicated problems among Chinese geologists, and it is always related to the problem of the geological age of the Jehol Biota in China. In general, three opinions on this problem are summarized as follows: ）

　　1.一些学者认为热河生物群的时代应该为晚侏罗世，因此我国陆相侏罗－白垩系界线应当放在义县组顶部或九佛堂组下部。（1. Some scholars hold that the Jurassic-Cretaceous Boundary should be placed on the top of the Yixian Formation or within the lower part of the Jiufotang Formation, because the Jehol Biota is considered to be of an age of Late Jurassic. ）

　　2.另外一些地质学家认为热河生物群的时代为早白垩世，因此我国陆相侏罗－白垩系界线应当放在土城子组（后城组）与张家口组或义县组之间，界线位置与冀北－辽西地区的区域不整合相一致。（2. Some geologists think that the Jurassic-Cretaceous Boundary should be placed between the Tuchengzi Formation and Zhangjiakou Formation，which is consistent with the distinct regional unconformity in the northern Hebei and the western Liaoning, because the Jehol Biota is considered to be of Early Cretaceous in age.）

　　3.还有一部分古生物学家认为热河生物群的时代为晚侏罗世－早白垩世，因此我国陆相侏罗－白垩系界线应当位于义县组内部。（3. Other palaeontologists consider that the Jurassic-Cretaceous Boundary should be placed within the Yixian Formation, because the Jehol Biota is considered to be of Late Jurassic-Early Cretaceous in age. ）

　　非常明显，产生不同观点的主要原因是我国专家对于热河生物群的性质、特征、组成和国际对比，以及侏罗－白垩系界线的定义和标准各自有着不同的认识和理解。（It is very clear that their different opinions are mainly caused by their different understanding of the nature, components and international correlation of the Jehol Biota, as well as the criteria of the Jurassic-Cretaceous boundary.）

　　首先，中国地质学家传统上采用135Ma或137Ma作为侏罗－白垩系界线的年龄值，主要考虑到我国冀北－辽西地区热河生物群的地层分布和土城子组与张家口组之间的区域不整合的存在。但是，欧美学者通常采用144Ma或145Ma作为侏罗－白垩系界线的年龄值。很显然，二者之间就存在7－10Ma的误差。（Firstly, Chinese scholars traditionally adopt 135Ma or 137Ma as the age value of the Jurassic-Cretaceous boundary, mainly considering the stratigraphic distribution of the Jehol Biota and the regional unconformity between the Tuchengzi Formation and the Zhangjiakou Formation or between the Tuchengzi Formation and the Yixian Formation in the northern Hebei and the western Liaoning, China. However, European and American scholars are generally used to adopting 144Ma or 145Ma as the age value of the Jurassic-Cretaceous boundary. It is obvious that there exists an error of 7-10Ma between the two boundary age values used by them.）

　　其次，国际侏罗－白垩系界线主要根据海相化石（菊石等）来定义的，界线层型（GSSP）将来肯定选择在海相地层分布区。众所周知，中国的海相侏罗系和白垩系分布极为有限，主要在西藏地区，但是我国陆相侏罗系和白垩系极为发育，分布也非常广泛。我们面临的一个很大困难在于如何才能保证海相与陆相生物群之间的精确对比。即使我们根据陆相化石选择了一条自己认为是界线的“侏罗－白垩系界线”，但是我们仍然不清楚这条所谓的J－K界线是否与国际上用海相化石定义的J－K界线等时。（Secondly, the global definition of the Jurassic-Cretaceous Boundary is mainly based on the marine fossils, and the boundary stratotype (GSSP) will be certainly selected in the regions of marine strata. The marine Jurassic and Cretaceous deposits are very limited in China and mainly distributed in Tibet, but the terrestrial Jurassic and Cretaceous deposits are widely developed in China. As we know, it is very difficult to make an exact correlation between the marine and terrestrial biota. In such a case, even if we select a possible level for the Jurassic-Cretaceous Boundary mainly based on some terrestrial fossils in China, we would wonder whether this level is equivalent to the Jurassic-Cretaceous Boundary defined by marine fossils or not. ）

　　再者，国际上两大权威机构（IUGS和ICS）先后推荐了两个不同的侏罗－白垩系界线年龄值。IUGS和UNESCCO提出以135Ma作为界线年龄值，而ICS则提出以145Ma作为界线年龄值。同样，二者之间就产生了近10Ma的误差。（Thirdly, the two international authority organizations (IUGS and ICS) recommended different age values of the Jurassic-Cretaceous boundary respectively. IUGS proposed 135Ma as the age value of the Jurassic-Cretaceous boundary, whereas ICS recommended 145Ma as the boundary age value. Clearly, there exists about 10Ma error between these two boundary age values.）

　　此外，国际上一般认为德国巴伐利亚索伦霍芬地区产始祖鸟的地层的时代为晚侏罗世提通阶，主要是根据以菊石为代表的晚侏罗世海相无脊椎动物化石来确定的。但是问题在于，谁能知道索伦霍芬地区这套地层的准确的测年结果。事实上，迄今为止，我们没有见到有关索伦霍芬地区产始祖鸟地层的实际测年数据，主要因为那套地层是泻湖相灰岩，难以进行放射性同位素测年。可以这么讲，产始祖鸟地层的“150Ma”的所谓年龄是从“144Ma”的J－K年龄值推算出来的。（Additionally, the Archaeopteryx –bearing strata in Solnhofen of Bavaria, Germany is considered to be Tithonian of Late Jurassic in age，because rich Late Jurassic marine invertebrates such as ammonites were found there. The question is, however, who knows the exact dating age of the strata in Solnhofen. Up to now, in fact, there is no report about the isotopic dating age of the Archaeopteryx-bearing strata from Solnhofen, because the Archaeopteryx-bearing strata are composed of lagoon limestones that are not suitable for making isotopic dating. The so-called ‘150Ma’ age of the Archaeopteryx-bearing strata is speculated upon the ‘144Ma’ age value of the Jurassic-Cretaceous Boundary. ）

　　事实上，我们中国学者目前面临的最大难处在于国际侏罗－白垩系界线层型（GSSP）仍然没有确定，我们很难选择以135Ma或者145Ma作为J－K界线年龄值。即使这样，我们中国学者还是锲而不舍，为解决中国的陆相侏罗系与白垩系分界问题做了大量工作和尝试。（In fact, the great embarrassment the Chinese scholars are confronted with is the indetermination of the Jurassic-Cretaceous boundary stratotype (GSSP) yet, and it is very difficult for us to choose 135 Ma or 145Ma as the boundary age value for the moment. Even so, Chinese scholars do much work in the northern Hebei and the western Liaoning recently and try to resolve the problem of the terrestrial Jurassic-Cretaceous boundary in China. ）

　　2000年，陈丕基教授对中国陆相侏罗系和白垩系的划分和对比进行了广泛的分析和讨论。他根据多年的研究，将侏罗－白垩系界线置于义县组与九佛堂组之间。（Chen Peiji（2000）made a comprehensive analysis and discussion on the division and correlation of the terrestrial Jurassic and Cretaceous in China. He placed the Jurassic-Cretaceous Boundary between the Yixian Formation and the Jiufotang Formation. ）

　　2003年，田树刚等人，柳永清等人各自发表文章，报道了河北滦平盆地“侏罗－白垩系界线层”层序地层学和地质年代学研究成果。他们倾向于采用130Ma作为J－K界线年龄值，将该界线置于大北沟组与大店子组之间。（Tian Shugang et al. (2003) and Liu Yongqing et al. (2003) did the study on the sequence stratigraphy and geochronology of the Jurassic-Cretaceous boundary beds in the Luanping Basin of Hebei Province, China. They preferred to putting the Jurassic-Cretaceous boundary between the Dabeigou Formation and the Dadianzi Formation, adopting 130Ma as the boundary age value. ）

　　2004年，陈丕基等人对IUGS和ICS以往在国际地层表中推荐的J－K界线年龄值（130Ma、135Ma、137Ma、142Ma和145Ma）的可靠性和正确性提出了严厉的质疑。他们根据热河生物群的地层分布和国际对比，以及从义县组金刚山层中获得的125.2Ma的实测年龄数据，倾向于采用125Ma作为J－K界线年龄值，将热河生物群归于晚侏罗世提通阶。（Chen Peiji et al. (2004) seriously doubted the correctness of the age values of the Jurassic-Cretaceous boundary (such as 130Ma, 135Ma, 137Ma, 142Ma, or 145.5Ma) recommended by IUGS and ICS in the International Stratigraphic Chart. According to the stratigraphic distribution and international correlation of the Jehol Biota and the 125.2Ma dating age from the Jianshangou bed of the Yixian Formation, they were inclined to consider the Jehol Biota to be of Tithonian of Late Jurassic in age, proposing the 125Ma age-value for the Jurassic-Cretaceous boundary. ）

　　2005年，王五力等人对义县阶的时代和陆相侏罗－白垩系界线进行了专题讨论。根据他们的研究和来自义县阶标准剖面的测年数据，认为以往国际地层表中推荐的144Ma、145Ma和135Ma的界线年龄值不能再作为可信的界线标准，倾向于采用124Ma作为J－K界线年龄值。（Wang Wuli et al. (2005) made a special discussion on the age of the Yixian stage and the terrestrial Jurassic-Cretaceous boundary. According to their current study and the isotopic dating data from the type section of the Yixian stage, they thought that the age values of 144Ma, 145Ma and 135Ma for the Jurassic-Cretaceous Boundary recommended in the International Stratigraphic Chart could not be considered as the creditable criterion，and they were inclined to use the 124Ma as the boundary age value. ）

国际侏罗－白垩系界线定义和位置

　
　

　　如上所述，中国目前在陆相侏罗－白垩系界线研究方面有一个明显的倾向，即要根据中国的陆相化石确定一个具有中国特色的界线标准，界线位置越来越高，尽管知道这些所谓的界线年龄值要比国际地层表中推荐的J－K界线年龄值要年轻得多。（As mentioned above, presently there exists an obvious tendency that some of Chinese scholars try to establish some distinct criteria for the terrestrial Jurassic-Cretaceous boundary in China, although the boundary age values proposed by them are much younger than those in the International Stratigraphic Chart.）

　　近十年，我们也在冀北－辽西地区对热河生物群及相关地层进行了综合性研究。特别是近三年，我们加强了地质年代学研究工作，获得了一批有价值的测年数据，有益于我们对陆相侏罗－白垩系界线研究工作的认识和理解。（Recent years, we also carried out the comprehensive geological investigation and research on the Jehol Biota and the related strata in the northern Hebei and western Liaoning. We also do some work of isotopic dating and get a set of dating results. They are given as follows:）

　　1. 164.6Ma：髫髻山组和蓝旗组底部；158.6Ma：髫髻山组最上部，表明髫髻山组和蓝旗组的时代为卡洛夫阶至早牛津阶。（1. 164.6Ma: from the basal part of the Tiaojishan Formation (or the Lanqi Formation), and 158.6Ma: from the uppermost part of the Tiaojishan Formation. It shows that the Tiaojishan Formation (or the Lanqi Formation) ranges from Callovian to Early Oxfordian in age.）

　　2. 139.4Ma：土城子组最上部，表明土城子组的时代为晚牛津阶至贝里亚斯阶。（2. 139.4 Ma: from the uppermost part of the Tuchengzi Formation, showing a range of the Tuchengzi Formation from Late Oxfordian to Berriasian.）

　　3. 135.5Ma：张家口组下部，表明该组的时代大致为欧特里夫阶。（3. 135.5 Ma: from the lower part of the Zhangjiakou Formation，showing an age of Hauterivian.）

　　4. 131.9Ma：大店子组底部，表明该组的时代为早巴柔姆阶。（4. 131.9 Ma: from the basal part of the Dadianzi Formation，showing an age of Early Barremian.）

　　5. 128.6Ma：义县组下部中华龙鸟层之下玄武安山岩，表明其时代为晚巴柔姆阶。（5. 128.6 Ma: from the basaltic andesites under the Sinosauropteryx-bearing beds in the lower part of the Yixian Formation，showing an age of Late Barremian. ）

　　6. 125.6Ma和124.7Ma：义县组下部中华龙鸟层，表明其时代为早阿普丁阶。（6. 125.6Ma and 124.7Ma: from the Sinosauropteryx-bearing beds in the lower part of the Yixian Formation，showing an age of Early Aptian.）

　　7. 122.3Ma：义县组金刚山层之下的玄武岩，120.3Ma：九佛堂组下部，表明其时代为早阿普丁阶晚期。（7. 122.3 Ma: from the basalt beds under the Jingangshan bed of the Yixian Formation, and 120.3 Ma: from the lower part of the Jiufotang Formation，showing an age of late Early Aptian.）

　　8. 2000年， J. Pálfy等人公布了侏罗系各阶的测年数据，其中贝利亚斯阶底界年龄值为141.8Ma。（1. J. Pálfy et al. (2000) reported a series of the dating data of the Jurassic stages，giving an age of 141.8Ma for Berriasian (Jurassic-Cretaceous). ）

　　9. 2005年， J. J. Mahoney 等人报道了太平洋西北地区夏特斯基隆起贝利亚斯阶最下部沉积物中玄武岩的热年龄值为144.6±0.8Ma, 提供了一个最低界线年龄值。（2. J. J. Mahoney et al. (2005) reported that basalt sills cored in lowermost Berriasian sediments on Shatshy Rise in the northwest Pacific yield a mean 40Ar-39Ar incremental heating age of 144.6±0.8Ma, providing a minimum estimate on the age of the Jurassic-Cretaceous boundary. ）

　　10. 2005年，A. Davis在冀北－辽西地区土城子组（后城组）底部获得了156Ma的年龄，顶部获得了139Ma的年龄，表明土城子组（后城组）的时代大致为晚牛津阶至贝利亚斯阶。（3. G. A. Davis (2005) obtained the age value of 156-139Ma from the Tuchengzi Formation and the Houcheng Formation in the western Liaoning and the northern Hebei. It shows that the Tuchengzi Formation and the Houcheng Formation are of an age of Late Oxfordian to Berriasian.）

　　11. 侏罗－白垩系界线的时间标准全球是统一的。我们可以寻找或选择陆相化石或其他标志来识别陆相侏罗－白垩系界线，但不可能根据陆相化石去确定一个与国际J－K界线不等时的，却要让国际同行们接受的“陆相J－K界线”。（1. The time criterion of the Jurassic-Cretaceous boundary is globally uniform. It is impossible to make a boundary definition based on terrestrial fossils or others, the time of which is not equivalent to the global J-K boundary defined by marine fossils. ）

　　12. 尽管目前国际侏罗－白垩系界线层型（GSSP）还没有确定，但是界线肯定是以海相化石，而不是以陆相化石来确定，而且界线层型肯定选择在海相地层发育区。中国陆相侏罗－白垩系界线问题的解决无疑有待于国际侏罗－白垩系界线层型（GSSP）的确定，其与国际J－K界线层型之间只是一个被动的对比关系。我们没有任何理由，也不可能根据我国的陆相化石或区域地质特征去标新立异或修改国际J－K界线时间标准。（2. At present, although the Jurassic-Cretaceous boundary (GSSP) has not been defined yet, the boundary will be surely defined by marine fossils, rather than terrestrial fossils, and the boundary stratotype (GSSP) will be certainly chosen in the region of marine strata. To resolve the problem of the terrestrial Jurassic-Cretaceous boundary in China is surely after the confirmation of the Jurassic-Cretaceous boundary stratotype (GSSP), and it is only a passive correlation relationship to the Jurassic-Cretaceous boundary stratotype (GSSP). We can not make or modify a global definition of the Jurassic-Cretaceous boundary only based on the terrestrial strata and fossils of China.）

　　13. 如果IUGS或ICS最终决定采用135Ma作为国际侏罗－白垩系界线年龄值，那么中国陆相侏罗－白垩系界线将在土城子组与张家口组（或义县组）之间，与冀北－辽西地区的区域不整合相吻合，表明热河生物群的时代为早白垩世。（3. If IUGS and ICS finally make a decision to adopt the 135Ma as the age value of the Jurassic-Cretaceous Boundary, then the terrestrial Jurassic-Cretaceous boundary will be placed between the Zhangjiakou Formation and the Tuchengzi Formation and consistent with the regional unconformity between the two formations in the northern Hebei and the western Liaoning, indicating the Early Cretaceous age of the Jehol Biota.）

　　14. 如果IUGS和ICS最终决定采用145Ma作为国际侏罗－白垩系界线年龄值，那么中国陆相侏罗－白垩系界线将位于土城子组最上部，意味着土城子组上部有一部分地层归入贝利亚斯阶。如果情况果真如此，那么冀北地区可能缺失凡兰吟阶的地层，辽西地区可能缺失凡兰吟阶和欧特里夫阶的地层。（4. If IUGS and ICS finally make a decision to adopt the 145Ma as the age value of the Jurassic-Cretaceous Boundary, then the Jurassic-Cretaceous boundary will be placed within the uppermost part of the Tuchengzi Formation, implicating the absence of the Valanginian strata in the northern Hebei and the absence of the Valanginian and Hauterivian strata in the western Liaoning.）

冀北－辽西地区J－K界线层的划分和对比

　
　