延庆千家店地区硅化木赋存层位及形成时代分析
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摘要
北京延庆千家店土城子组中的硅化木自发现以来,得到了众多学者的关注,但关于硅化木的赋存层位和形成时代一直未有定论,目前主流观点认为硅化木广泛发育于土城子组一段和二段的下部,关于其形成时代则自侏罗纪早期至白垩纪早期的论述均有,这种争论显然不利于木化石的保护、科普和进一步深化认识。在千家店土城子组进行的考察结果展现出与前人观点不同的线索。实地考察、剖面测量和年龄测试结果显示:原位埋藏硅化木形成时代应为晚侏罗世早期,赋存层位为土城子组一段下部,而土城子组二段下部的沉积特征反应出当时水位频繁升降,水体能量剧烈变化,火山活动暂时陷入沉寂的沉积环境,较难满足形成木化石的基本要求。
The petrified wood of Tuchengzi Formation in Qianjiadian area of Yanqing County, has attracted received many scholars' attention since it was discovered. However, its hosting strata and formation age are uncertain. At present, the main view is that the petrified wood is widely developed in lower part of the first and second unit of Tuchengzi Formation. However, its formation age is discussed from the Early Jurassic to the Early Cretaceous. These arguments are clearly not conducive for the wood fossil protection and further study. Profile measurement and fieldworks show that the petrified wood likely formed in the early stage of Late Jurassic, and it developed likely in lower part of the first unit of Tuchengzi Formation. The sedimentary characteristics of lower part of the second unit of Tuchengzi Formation reflect an inapposite environment, which presented as frequent water lift, dramatic changes in the energy of water, a temporary silence of volcanic activity. The environment is difficult to meet the basic requirements of the formation of wood fossil.
The petrified wood of Tuchengzi Formation in Qianjiadian area of Yanqing County, has attracted received many scholars' attention since it was discovered. However, its hosting strata and formation age are uncertain. At present, the main view is that the petrified wood is widely developed in lower part of the first and second unit of Tuchengzi Formation. However, its formation age is discussed from the Early Jurassic to the Early Cretaceous. These arguments are clearly not conducive for the wood fossil protection and further study. Profile measurement and fieldworks show that the petrified wood likely formed in the early stage of Late Jurassic, and it developed likely in lower part of the first unit of Tuchengzi Formation. The sedimentary characteristics of lower part of the second unit of Tuchengzi Formation reflect an inapposite environment, which presented as frequent water lift, dramatic changes in the energy of water, a temporary silence of volcanic activity. The environment is difficult to meet the basic requirements of the formation of wood fossil.
引文
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[7]张元福,魏小洁,徐杰,等.北京延庆硅化木公园地质剖面陆相层序地层特征分析[J].地学前缘,2012,19(1):68~77.
[8]王荣荣.千家店火山沉积盆地地层特征及古地理环境分析[D].北京:中国地质大学(北京),2015.
[9]北京市地质研究所.北京市地质遗迹详查评价与保护对策研究成果报告[R].2014.
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[12]刘永清,季强,姬书安,等.华北东北部晚中生代陆相地层、生物群及其年代学研究[J].地球学报,2010,31(S1):42~45.
[13]郑月娟,陈树旺,丁秋红,等.冀北—辽西地区侏罗纪土城子组的时代归属[J].地质与资源,2010,19(4):292~295.
[14]王思恩,高林志,万晓樵,等.辽西—冀北地区土城子组的地质时代、年龄及其国际地层对比[J].地质通报,2013,32(11):1673~1690.