摘要
化石埋藏学的核心内容就是要研究不同规模生物化石埋藏的沉积相,恢复沉积环境,了解化石形成和被埋藏前、后的古地理背景。大规模化石记录埋藏学的研究代表着目前国际上发展趋势,重点探索集群灭绝的古地理、古环境与保存作用。中国具有丰富的恐龙化石资源,目前已经成为全球命名恐龙属种最多的国家,相继发现了从侏罗纪到白垩纪的若干恐龙化石遗迹或骨骼埋藏点。胶莱盆地发育着完整的白垩纪陆相(莱阳群—青山群—王氏群,130～65 Ma)地层和沉积记录。早白垩世莱阳群以河流及湖泊相沉积物为主;青山群为中酸性火山岩、火山碎屑岩,间夹沉积岩。晚白垩世王氏群下部以冲积扇、泥石流和辫状河道相的沉积物和岩石组合为主;中部则为滨浅湖与河流粉砂岩-细砂岩-泥页岩-灰质土(古土壤)韵律沉积;上部和顶部为冲积扇泥石流、辫状河和洪泛平原粉砂泥质砾岩-砂岩-砾岩的韵律序列,局部夹玄武岩,反映了晚白垩世末期古地理、古沉积环境已从早白垩世相对湿润和温热的冲积、湖泊环境转变为燥热、干旱的冲积环境。胶莱盆地早白垩世的生物群面貌(脊椎动物、昆虫和植物等)与华北北部热河生物群基本相同,除保存少量的小型恐龙(鹦鹉嘴龙)或翼龙骨骼化石外,还保存了大量的兽脚类、蜥脚类和鸟脚类足迹(群)化石(莱阳群)。诸城晚白垩世王氏群中上部发育集群埋藏的恐龙骨骼化石,已发现恐龙属种10余个,包括3种角龙、3种暴龙、2种鸭嘴龙以及甲龙和虚骨龙等,其中鸭嘴龙占绝大多数(95%以上)。恐龙化石多为无关联的各类骨骼,少数半关联的小个体恐龙,分选差,混杂堆积。通过诸城恐龙化石埋藏地地层及其沉积相研究,识别出泥石流、洪泛平原和辫状河道3种恐龙化石埋藏沉积相、微相类型,其中泥石流相是最主要的埋藏-沉积相,代表了晚白垩世中期恐龙集群埋藏-沉积事件和动力机制。莱阳地区王氏群上部和顶部为紫色、砖红色砾岩-砂岩-粉砂岩-灰质土韵律沉积,属于洪泛平原和辫状河道沉积微相组合,代表着晚白垩世末期燥热、干旱的冲积环境。恐龙化石大都埋藏在大型辫状河道微相之下的洪泛平原微相中。化石呈分散或孤立状,有不同程度的磨蚀或破损,关联或半关联者少见,表明经过一定距离的搬运或改造作用。文章最后简述了胶莱盆地以及白垩纪古地理环境、古生态、恐龙动物群的演化或耦合作用。
The core issue of taphonomy is to study the sedimentary facies of fossil-bearing rocks,reconstruct their depositional environments,and understand the paleogeographical background before and after the burying of fossils at different scales.One of current taphonomy interests focuses on the mass extinction or bonebeds of dinosaurs,including their paleogeography,paleoenvironment and preservation.Numerous Jurassic and Cretaceous dinosaur fossil sites have been discovered in China,making it number 1 in the world in terms of richness of dinosaur genera and species.The terrestrial Cretaceous Laiyang,Qingshan and Wangshi groups（130-65 Ma）,in ascending order,are widely distributed in Jiaolai Basin of eastern Shandong Province,China.Lithologically,the Early Cretaceous Laiyang Group consists of fluvial and lacustrine sediments and the Early Cretaceous Qingshan Group is mainly composed of medium or acid volcanic rocks and pyroclastic rocks interbeded with sedimentary rocks.The Late Cretaceous Wangshi Group is mainly deposits of alluvial fan,mud flow and braided-channel facies in the lower part;shallow lacustrine deposits and rhythmic fluvial sediments of mudstone,siltstone,sandstone or soils（palesoil） in the middle part;and rhythmic depositions of silty-muddy conglomerate,sandstone and siltstone of mud flow,braided-channel and flooding plain facies,locally interbeded with basalt in the upper part.Sedimentary successions and facies associations of the Cretaceous Jiaolai Basin indicate an evolution of basin and sedimentary paleogeography,i.e.,from alluvial-lacustrine environment in humid and warm climate in the Early Cretaceous to an alluvial environment in hot and drought climate towards the Late Cretaceous.Biota of the Early Cretaceous in Jiaolai Basin is identical to the Jehol Biota in the northern areas of North China.In the Laiyang Group,a plentiful of dinosaur（theropod,sauropod and ornithopod） footprints were excellently preserved,as well as a few small dinosaurs（Psittacosaurus） or single bones of pterosaurs.A number of dinosaur bonebeds or mass extinction appeared in the middle or upper part of the Late Cretaceous Wangshi Group in Zhucheng.Until now,over ten genera and species of dinosaurs,including three species of horned dinosaurs,three species of tyrannosaurs,two species of hadrosaurs,and some specimens of ankylosaur and coelurosaurs have been unearthed.Among them,hadrosaurs account for the overwhelming majority（at least more than 95%）.Most of dinosaur bones in mud flow deposits are disarticulated,only with a few articulated.Various-sized bones were mixed in and rare sorting.Bone condition variation is believed to represent deposits of mixture of allochthonous faunal elements by geological events.Three types of taphonomic sedimentary microfacies are recognized： mud flow,flooding plain and braided-channel.Mud flow deposits are major taphonomic occurrence among these three taphonomic microfacies,indicating a preferential preservation of dinosaur material,which are believed to represent the end product of mass burying of dinosaurs and dynamic mechanism through which bones were gathered and accumulated in the Late Cretaceous.The top Wangshi Group in Laiyang mainly consists of the rhythmic depositions of purple red conglomerate,sandstone,siltstone and soils interpreted as flooding plain and braided-channel microfacies respectively,indicating a prevailing hot and drought climate at the end of the Late Cretaceous.All bones are,here,disarticulated and rare articulated,isolated and single,highly abraded and preserved within flooding plain microfacies under large scale braided channel sandstones.Bone condition variation is believed to represent re-deposited after a longer transportation by braided-channels and alterations before or after burying.Furthermore,evolution of Jiaolai Basin and its paleogeographic environment,paleoecology and dinosaur fauna in the Cretaceous are briefly discussed as well.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2011年第4期9-24,共16页
Earth Science Frontiers
基金
国家自然科学基金项目(90914003)
中国地质科学院地质研究所中央级公益性基本业务费专项(J1106)
中国地质调查局项目(1212011085477)
