山东诸城早白垩世莱阳期古地震事件与恐龙迁移

在诸城断陷皇华镇大山村黄龙沟存在丰富的、多样的恐龙足迹化石,在紧邻化石埋藏层下伏及上覆地层中发现了下白垩统莱阳群杨庄组多套古地震记录,主要包含波状褶皱、底劈构造、液化砂岩脉、液化角砾岩、粒序断层、卷曲变形和震积不整合等塑性、脆性软沉积物变形构造。分析表明初始沉积物、沉积相及构造作用确定了地震活动作用时形成的软沉积物变形构造类型。在早白垩世莱阳群沉积中期,地震活动具有阶段性及频发性,以单向挤压的丘-槽构造及双向挤压的波状变形为主,且后期有构造活动强度加大的特征。根据已识别的古地震记录发育及古地震活动强度分析,推测此时期发震断裂可能是断陷的南缘断裂——五莲断裂。区域构造作用使得该时期沉积环境发生变化,由湖相逐渐过渡到河流相,在突发古地震事件发生之后,在滨浅湖区域留下了丰富的恐龙迁徙足迹。古地震记录的研究,可建立古地震事件与沉积、构造演化的联系,约束构造作用的属性、频次及时限,为确定盆地及周缘构造-沉积演化历史提供证据。

Paleoearthquake event and the migration of dinosaur on Laiyang Phase of Early Cretaceous, Zhucheng, Shandong Province, East of China

Unusual and abundant dinosaur track had been discovered on Yangzhuang Formation of Laiyang Group in Early Cretaceous, at Huanglonggou site in the southern of Zhucheng faulted depression in Jiaolai basin, which located in Jiaodong peninsula, east of China. In this study, we found variety soft-sediment deformation structure proximately under and above these tracks. Soft-sediment deformation structures include undulate fold, diapir, liquefied sand vein, liquefied breccias, convolute deformation and seismite unconformity, and graded faults. Soft-sediments deformation structure style subjected to initial sediments and facies, so dome-trough deformation resulted from unilateral compressing and undulate fold deformation structure resulted from polydirectional compressing along surface. From distribution of deformation records and magnitude of paleo-seismic, suggested seismogenic fault is Wulan Fault, south border fault of Zhucheng faulted depression. Under regional tectonic movement and seismic events, this area changed from lacustrine to fluvial facies, and depocenter migrated. Paleo-earthquake happened after while, dinosaur migration tracks with the approximate orientation kept back on offshore of lacustrine. Paleo-seismic records have been systematic study, contribute to establish relationship between paleo-earthquake events, deposit environment and tectonic evolution, constrain attributes, frequencies, and time-limit of tectonism.