柳永清, 旷红伟, 彭楠, 许欢, 陈军, 徐加林, 刘海, 章朋. (2015)冀西北尚义上侏罗统—下白垩统后城组恐龙足迹新发现及生物古地理意义* [J]. 古地理学报, 14(5): 617-627
Liu Yongqing, Kuang Hongwei, Peng Nan, Xu Huan, Chen Jun, Xu Jialin, Liu Hai, Zhang Peng. (2015)New discovery of dinosaur footprints in the UpperJurassic-Lower Cretaceous Houcheng Formation at Shangyi,northwestern Hebei Province and its biogeographical implications[J]. Journal Of Palaeogeography, 14(5): 617-627. DOI:  
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冀西北尚义上侏罗统—下白垩统后城组恐龙足迹新发现及生物古地理意义*
柳永清, 旷红伟, 彭楠, 许欢, 陈军, 徐加林, 刘海, 章朋
中国地质科学院地质研究所,北京 100037

第一作者简介 柳永清,男,1960年生,研究员,主要从事沉积地质学,沉积古地理和古生态学研究。E-mail:liuyongqing@cags.ac.cn。

收稿日期:2012-06-20
基金:*国家自然科学基金项目(编号:90914003,41272021),中国地质调查局项目(编号:1212011085477),中国地质科学院地质研究所基本业务费项目(编号:J1106)联合资助
摘要

简要报道了新近首次在冀西北张家口尚义地区发现的恐龙足迹。野外地质调查发现,恐龙足迹赋存于尚义晚中生代盆地侏罗系—白垩系后城组顶部。恐龙行迹呈近东西向展布,由数十个足迹构成。初步研究表明,造迹者分别属于兽脚类和蜥脚类恐龙,由西向东行进。足迹中包括兽脚类足迹 70余个,组成数个行迹;蜥脚类足迹 15个,构成 1列行迹。蜥脚类足迹特征显示其可能属于游泳状的行迹。华北北部土城子组 /后城组发育于燕辽生物群—热河生物群更替演化时期(晚侏罗世—早白垩世早期),以往在该时期沉积物中罕见脊椎动物骨骼化石。近年来华北北部土城子组 /后城组中频繁发现的恐龙足迹表明,燕辽生物群—热河生物群更替演化时期发育着以恐龙为代表的脊椎动物群。该发现将有助于进一步了解土城子组 /后城组沉积时期恐龙属种的多样性及其生物古地理环境。晚侏罗世—早白垩世早期沉积古地理和古生态环境及其与恐龙动物群发育的研究有助于揭示陆地生物群更替演化和环境的关系。

关键词: 上侏罗统—下白垩统; 后城组; 恐龙足迹; 古地理; 尚义
中图分类号:Q915.5 文献标志码:文章编号:1671-1505(2012)05-0617-11 文章编号:1671-1505(2012)05-0617-11
New discovery of dinosaur footprints in the UpperJurassic-Lower Cretaceous Houcheng Formation at Shangyi,northwestern Hebei Province and its biogeographical implications
Liu Yongqing, Kuang Hongwei, Peng Nan, Xu Huan, Chen Jun, Xu Jialin, Liu Hai, Zhang Peng
Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037

About the first author Liu Yongqing,born in 1960,is a research professor of sedimentology,palaeogeology and palaeoecology at Institute of Geology,Chinese Academy of Geological Sciences.E-mail:liuyongqing@cags.ac.cn.

Abstract

A number of dinosaur footprints have been discovered recently from the Upper Jurassic-Lower Cretaceous Houcheng Formation in Shangyi,Zhangjiakou,northwestern Hebei Province.The trackways and footprints display a east-west trend on the rock surface of the top of the Houcheng Formation.The preliminary research indicates that these trackways comprise theropod and probably swimming sauropod footprints.One trackway consisted of fifteen sauropod footprints and the other footprints cluster including more than seventy theropod footprints were both recognized.The Tuchengzi/Houcheng Formation was deposited in the transitional period from the Yanliao Biota to the Jehol Biota,which was previously considered as poor palaeogeography and palaeoecology and rare dinosaur bone fossils have been found.Frequent discoveries of dinosaur footprints from the Tuchengzi/Houcheng Formation in northern areas of North China suggest that vertebrate of dinosaur mainly was the survival in the transitional period from the Yanliao Biota to the Jehol Biota in the Late Jurassic-Early Cretaceous,and greatly enrich the knowledge on the diversity of dinosaur species and biogeography of the Tuchengzi/Houcheng Formation.Study on the palaeogeography,palaeoecology and dinosaurs in the Late Jurassic-Early Cretaceous is beneficial to reveal the enigma of replacement of terrestrial biotas and environment.

Key words: Houcheng Formation; Upper Jurassic-Lower Cretaceous; dinosaur footprints; palaeogeography; Shangyi
1 前言

华北北部广泛分布上侏罗统— 下白垩统(大青山组/后城组/土城子组/三台组)浅紫色粗碎屑岩沉积建造, 它也恰好位于含燕辽生物群(道虎沟生物群)的中侏罗统(九龙山组— 髫髻山组)和含热河生物群的下白垩统(张家口组— 大北沟组— 义县组— 九佛堂组)火山— 沉积岩系之间。热河生物群以产带羽毛恐龙、原始鸟类、哺乳动物、翼龙类、鱼、昆虫和早期被子植物而著名(Sun et al., 1993, 1998, 2001, 2002, 2011; Jin et al., 1995; Chen et al., 1998; Ji et al., 1998; Xu et al., 1999a, 1999b, 2001, 2003, 2004; Zhang et al., 2000, 2004, 2008; Lu, 2002; Zhou and Zhang, 2002, 2003; Chang et al., 2003; Luo et al., 2003, 2007a; Zhou et al., 2003; Xu and Norell, 2004; Zhou, 2004, 2006; Wang et al., 2005; Wang and Zhou, 2006; Zhang and Zhou, 2008; Ren et al., 2009), 燕辽生物群也以丰富的带羽毛恐龙、哺乳动物、昆虫和过渡性翼龙的发育为特征(Ji and Yuan, 2002; Xu and Zhang, 2005; Ji et al., 2006; Meng et al., 2006; Luo et al., 2007b, 2011; Hu et al., 2009; Lü et al., 2009, 2011; Ren et al., 2009; Xu et al., 2009b, 2010, 2011)。虽然燕辽生物群(道虎沟生物群)和热河生物群的更替演化发育在晚侏罗世— 早白垩世期间, 但它们之间的更替演化规律与特征始终是未解之谜, 这也是古生物学家与地质学家长期探索的内容。因此, 该时期的古生态环境、尤其是动植物(群)繁衍生存及发育和演化特征是备受学术界关注的核心科学问题之一。

土城子组/后城组沉积特征和岩石组合表明, 它们是干旱炎热的古气候和古地理环境中较浅湖泊— 辫状河— 冲积扇以及沙漠沉积的产物(许欢等, 2011)。长期以来, 土城子组/后城组中罕见脊椎动物化石, 少量的发现也仅限于1例蜥脚类(董枝明, 2001), 2例原始角龙类— 朝阳龙(Chaoyangsaurus)(Zhao et al., 1999)和宣化角龙(Xuanhuaceratops)(Zhao et al., 2006)。故此, 前期研究多认为, 土城子组/后城组沉积期古地理环境十分恶劣, 燕辽生物群几近“ 消亡” , 热河生物群也尚处萌生早期, 因此, 陆生动植物群落非常“ 匮乏” , 古生态环境极为“ 脆弱” (柳永清等, 2009, 2010; 许欢等, 2011; Liu et al., 2012)。

然而, 早在20世纪40年代, Yabe等(1940)就描述了产于辽宁朝阳羊山土城子组的4000余个兽脚类足迹(Grallator)。这似乎表明虽然土城子组/后城组中保存或被发现的脊椎动物骨骼化石很少, 但该地出现的大量兽脚类足迹可能暗示着土城子组/后城组沉积期仍存在着以恐龙动物群为代表的庞大陆地脊椎动物群。近年来华北北部土城子组/后城组中频繁报道的大量以兽脚类为主, 包括蜥脚类、鸟脚类以及鸟类等的脊椎动物足迹, 使得这一科学疑问更加得到了广大古生物学家与地质学家们的关注与探索。

文中报道和简要描述了新发现的冀西北尚义晚侏罗世— 早白垩世地层中的恐龙足迹。该发现不仅增加了华北北部土城子组/后城组恐龙足迹产地, 也使得这一时期恐龙足迹(恐龙动物群生活)的空间范围进一步向西(阴山地区)扩展, 足迹内容也得到进一步的丰富。同时, 通过简要分析晚中生代末期华北北部(大青山组/后城组/土城子组/三台组)沉积古地理环境和古气候环境特征, 以及它们与恐龙动物群更替演化、古生态环境和古地理环境的相互关系, 进一步佐证了中国北方燕辽生物群— 热河生物群的更替演化时期发育着以恐龙为主的脊椎动物群, 这对于探讨陆地生物群、尤其是中国北方燕辽生物群— 热河生物群的更替演化以及其与环境演化的关系等方面具有极其重要的科学研究意义。

2 地质背景

新发现的恐龙足迹位于冀西北张家口市尚义县城东20, km的小蒜沟镇, 地理坐标为N40° 44'— N41° 32', E113° 49'— E114° 26'(图 1, 图2)。尚义盆地是晚中生代以来的小型陆相盆地, 盆地内太古界— 元古界、中生代及新生代地层发育。侏罗系主要发育下花园组— 龙门组, 由下部煤系及上部巨砾岩夹粗砂岩组成, 角度不整合于太古代— 元古代变质岩之上。上侏罗统— 下白垩统后城组(上部以往称阎家窑组, 二者呈整合接触, 1:20万和1︰5万区域地质调查)平行不整合于下侏罗统龙门组之上。

图1 华北北部区域地质与构造略图Fig.1 Schematic map showing geology and tectonic in northern North China

图2 冀西北尚义盆地地质略图及恐龙足迹与骨骼化石产地Fig.2 Schematic geological map and localities of dinosaur footprints and bone fossils in Shangyi Basin of northwestern Hebei Province

从尚义盆地北部边缘向东南、西南部, 后城组下部表现出明显的时空相变特征。盆地北部边缘为(冲积扇根)巨、粗砾岩(砾石成分以深成变质岩为主)或中粗砾岩夹砂岩, 向盆地东南、西南部逐渐相变为细砾岩夹砂岩、含砾粗砂岩(扇中辫状河相)和钙质结核钙质粉砂岩(滨浅湖相)。后城组上部由下至上为灰绿色、灰黄色含砾粗砂岩及薄层粉砂岩, 其中灰绿色、灰黄色含砾粗砂岩、砾岩与灰绿色粉砂岩互层, 中厚— 中薄层细砂岩、中砂岩与紫红色薄层粉砂岩互层, 夹钙质结核。恐龙足迹发育在该组顶部粉砂岩和细砂岩韵律层段内(图 3)。

图3 冀西北尚义盆地上侏罗统— 下白垩统后城组顶部沉积序列及恐龙足迹Fig.3 Dinosaur footprints on the top of the Upper Jurassic-Lower Cretaceous Houcheng Formation in Shangyi Basin of northwestern Hebei Province

3 恐龙足迹特征描述

恐龙足迹产出的地层位置以及共生的沉积构造等宏观特征如图3所示。层面上与足迹共生发育的是大量不规则状与马蹄状的波痕、不同规模的泥裂构造、生物遗迹(爬迹和潜穴)和不明成因的丘疹状(凸起)沉积构造(疑似雨痕构造)等, 未见任何植物碎屑或遗迹(图 3)。沉积相标志表明它们形成于干旱炎热气候条件下宽而浅的湖滨环境。

足迹出露在百余平方米的缓倾斜岩层面上, 可明显识别出A和B两类足迹群(图 3)。A类足迹群为小型蜥脚类行迹, 层面上清晰可见15个近圆形的足迹(图 3, 图4)。单个足迹大小基本一致, 直径约14~15 cm。相邻足迹间距最大为68, cm, 最小46, cm, 平均为50 cm。它们组成1列行迹, 行进方向为92~145° (表 1; 图3; 图4; 图5-1, 5-2, 5-5)。从该蜥脚类足迹呈浑圆状、大部分趾垫不清晰、足跟部痕迹凹陷较浅等特征推测, 它们可能是蜥脚类恐龙在浮水或半游泳状态下留下的行进足迹。

图4 A类蜥脚类行迹和足迹特征Fig.4 Characters of sauropod trackway and footprints of A type

图5 A, B类恐龙足迹特征Fig.5 Characters of dinosaur footprints of A and B types

表1 A类足迹群足迹观测数据 Table1 Measurement data of footprints of A type

B类足迹群相距A类足迹群大约3, m, 由71个兽脚类足迹构成(图 6)。足迹平均长15.5, cm, 宽10.5 cm(图 5-3, 5-4, 5-6, 5-7; 图6)。7个足迹趾长数据统计显示(表 2), 平均中趾长11, cm, 宽2.8, cm; 右侧趾长7.0, cm, 宽3.0, cm; 左侧趾长7.0, cm, 宽2.9 cm。70个脚印足迹要素统计表明(表 3; 图5-3, 5-4, 5-6), 足迹平均长15.5, cm, 宽10.5, cm, 长宽比为1.5; 趾间角为30° ~31° ; 大致的行迹走向约为145° (表 3; 图5-3, 5-4; 图6)。

图6 B类兽脚类足迹特征(方框30 cm × 30 cm)Fig.6 Characters of theropod footprints of B type(frames=30 cm × 30 cm)

表2 B类足迹群中部分兽脚类足迹观测数据 Table2 Measurement data of theropod footprints of B type
表3 B类足迹群中足迹观测数据 Table3 Measurement data of footprints of B type
4 华北北部晚侏罗世— 早白垩世过渡期恐龙动物群及其生物古地理意义

从华北北部上侏罗统— 下白垩统后城组/土城子组岩石地层— 年代学格架与恐龙足迹发育层位对比图(图 7)中可见, 尚义盆地后城组整体应对比阴山— 燕山地区的后城组/土城子组/大青山组以及鲁东地区的三台组。更大范围上它们可能对比鄂尔多斯盆地西缘的芬芳河组、河西走廊的享堂组— 河口群底部、北疆地区的齐古组— 卡拉扎组(石树沟群、五彩湾群)。燕山地区除辽西朝阳和冀北承德在后城组/土城子组下部见有恐龙足迹外, 其余大部分地区, 如冀西北尚义和赤城、北京延庆、辽西北票和朝阳等地的恐龙足迹都几乎产于后城组/土城子组3段中(图 7)。辽西北票、朝阳土城子组3段足迹化石层之上的风成砂层夹凝灰岩的SHRIMP锆石U-Pb 年龄为137 Ma(Xu et al., 2012, in press)。Swisher等(1999)也曾在辽西北票恐龙足迹层之下的凝灰岩夹层中获得斜长石Ar-Ar年龄(139 Ma)。因此, 尚义盆地后城组足迹化石的形成时代应为早白垩世早期。

图7 华北北部后城组/土城子组岩石地层— 年代学格架与恐龙足迹层位对比Fig.7 Correlation of lithostratigraphic and chronological framework of dinosaur footprints and bone fossils of the Upper Jurassic-Lower Cretaceous Houcheng/Tuchengzi Formation in northern North China

后城组/土城子组发育于燕辽生物群— 热河生物群更替演化时期。长期以来, 华北北部土城子组/后城组中罕见脊椎动物化石, 因此前期研究多认为土城子组/后城组沉积时期的古地理环境较“ 恶劣” , 古生态环境较为“ 脆弱” 。但从20世纪40年代 Yabe等(1940)描述辽西土城子组的4000 余个兽脚类足迹(Grallator)以来, 特别是2000年以来, 华北北部上侏罗统— 下白垩统土城子组/后城组中又陆续发现至少10余个恐龙足迹化石点(张永忠等, 2004; Chen et al., 2006; Sullivan et al., 2009; Xing et al., 2011, 2012)。这些恐龙足迹包括兽脚类 Grallator morphotype(Yabe et al., 1940; 张永忠等, 2004; Lockley et al., 2006; Fujita et al., 2007; Sullivan et al., 2009; Xing et al., 2009, 2011, 2012), Therangospodus isp.(Xing et al., 2011), Megalosauripus isp.(Xing et al., 2011)和Menglongipus (Xing et al., 2009), 而且还具有罕见的兽脚类游泳迹(Xing et al., 2011)和蹲伏迹(Xing et al., 2012)。此外, 土城子组/后城组中古鸟类足迹(Pullornipes)(Lockley et al., 2006)也被发现。2012年, Zhang等(2012)又首次在北京延庆后城组中发现大量覆盾甲龙类(cf.Deltapodus isp.)、兽脚类、鸟脚类及疑似蜥脚类的恐龙足迹。此外, 李日辉(2002)也报道过华北东部的鲁西地区上侏罗统— 下白垩统三台组(对比土城子组/后城组)中的恐龙足迹; 纪友亮等(2008)报道过滦平盆地上侏罗统— 下白垩统西瓜园组暗色泥岩中的蜥脚类和兽脚类恐龙足迹。不仅如此, 冀西北尚义盆地后城组(姬书安私人通讯, 2012)、宣化(Zhao et al., 2006)以及辽西北票土城子组(董枝明, 2001; Zhao et al., 1999)中还在不同时期都发现过蜥脚类以及食肉类恐龙骨骼化石。中国北方的西部地区, Li等(2012)在陕西神木中侏罗统安定组中也发现大量鸟脚类足迹; 新疆鄯善中侏罗统三间房组出露大型兽脚类足迹, 最近在上覆中上侏罗统齐古组中还正在发掘可能是目前世界上最大的植食类恐龙化石。

实际上, 近年来在新疆东准噶尔五彩湾中上侏罗统石树沟群中已陆续发现大量恐龙化石, 比较著名的有五彩冠龙(Guanlong)(Xu et al., 2006)、泥潭龙(Limusaurus)(Xu et al., 2009a)等。齐古组中凝灰岩夹层SHRIMP锆石U-Pb测年最新结果为165 Ma(王思恩和高林志, 2012; 王思恩等, 2012)。新疆东北部和华北北部地区在中晚侏罗世(— 早白垩世早期)基本处于同一古纬度区域(Smith et al., 1994), 孢粉等化石组合表明其也都处于干旱炎热的古地理和古气候背景条件下。

尽管华北北部上侏罗统— 下白垩统(大青山组/后城组/土城子组/三台组)很少见到脊椎动物骨骼化石, 但频繁发现的大量兽脚类、鸟脚类及蜥脚类恐龙足迹(群)暗示着土城子组/后城组沉积期应发育着以恐龙动物群为代表的陆地脊椎动物群。前述表明, 新疆东北部— 甘宁地区中晚侏罗世就已经繁育着恐龙动物群, 它们与华北北部晚侏罗世— 早白垩世的恐龙动物群是否具有辐射演化关系, 亦或属于共同的恐龙动物群仍是值得重点研究的科学问题。

恐龙等动物足迹学是恢复其古生态、古环境和生物古地理的重要科学证据。近年来发现的华北北部晚侏罗世— 早白垩世早期沉积物中保存的大量恐龙足迹化石充分说明, 在该时期干旱炎热的古地理和古气候环境背景下仍生存着庞大的恐龙动物群, 即在华北北部和中国西部地区, 于燕辽生物群和热河生物群更替过渡期发育着以恐龙为代表的陆地脊椎动物群。但到目前为止, 华北北部上侏罗统— 下白垩统(后城组/土城子组/三台组)发现的恐龙足迹或以肉食类、或以数千计的兽脚类为主, 对其成因的解释仍待将来开展进一步的深入研究。

无论如何, 中晚侏罗世— 早白垩世早期, 华北北部(由东至西)经宁夏到新疆东北部地区繁育着极为壮观的恐龙动物群。深入分析和对比研究恐龙动物群(骨骼化石)和足迹的发育特征与规律, 对于研究晚侏罗世— 早白垩世恐龙动物群的组成和生活习性、古地理环境、乃至恐龙的分布与迁徙都具有极其重大的科学意义, 同时更有助于认识晚中生代末期中国北方陆生脊椎动物的更替演化、古生态环境以及动物群辐射演化和古地理环境的相互关系。

5 结论

首次在冀西北张家口尚义地区上侏罗统— 下白垩统后城组发现恐龙足迹。造迹者分别属于蜥脚类和兽脚类恐龙。足迹中包括兽脚类足迹70余个, 组成数个行迹; 蜥脚类足迹15个, 构成1列行迹。蜥脚类足迹特征显示其可能属于游泳状的蜥脚类足迹。华北北部土城子组/后城组中兽脚类、蜥脚类或鸟脚类以及鸟类等脊椎动物足迹的发现说明, 华北北部晚侏罗世— 早白垩世早期可能发育着以恐龙为代表的脊椎动物群。对此进行系统研究将有助于揭示晚中生代陆地生物群的灭亡和复苏及其环境约束等规律。

致谢 中国地质科学院地质研究所姬书安和吕君昌研究员在野外考察中给予指导,中国科学院古脊椎动物与古人类研究所尤海鲁研究员对本文提出有益的建议,在此表示衷心感谢!

作者声明没有竞争性利益冲突.

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