摘要
四川江油马角坝、北川沙窝子是龙门山上泥盆统、下石炭统区域性主要岩石地层单位的命名地,对这两地及前龙门山北段地区的调查发现:1)前人关于马角坝地区下石炭统的层序和马角坝组主要化石群的记载有与实际不符之处,当地实际缺失杜内期至维宪早、中期地层,总长沟群的时代应属晚维宪—谢尔普霍夫期,重新厘定马角坝组含义,新指定北川桂溪沙窝子的长滩子剖面为该组的参考剖面;2)在长滩子剖面长滩子组顶部Beichuano-phyllum与Cystophrentis珊瑚化石富集层之上、马角坝组Pseudouralinia富集层之下的大套厚层白云岩层组合的中上部层位,发现Cystophrentis等化石,基于这套厚层白云岩组合的岩性特征明显、顶底接触关系清楚、区域展布广泛,建议引用前人提出的黑岩窝组,同时对黑岩窝组的岩性、岩层组合与古生物组合特征、厚度和时代归属等作了补充和修正,根据其中所含生物群认为黑岩窝组时代为晚泥盆世法门晚期;3)通过与周边地区的地层对比,探讨了龙门山石炭纪的古地理格局及环境演变,认为除前龙门山中部的桂溪—沙窝子等狭窄地区因长期地处泥盆纪海水入侵通道,地势低洼,出现了残存式的杜内期沉积外,前龙门山南、北段广大地区杜内期至维宪早、中期已大部抬升露出水面,直到维宪晚期的全球性海侵,前龙门山遂再度没于水下,出现准平原化浅滩相沉积环境,并延续至石炭纪末。
Recent investigation taking on in the area of Majiaoba of Jiangyou County and Shawozi of Beichuan County, Sichuan Province, West China, where the local lithostratigraphic names of Upper Devonian and Lower Carboniferous were derived, and some other localities in the northern part of Pre-Longmenshan area, has received some new recognitions and realizations. 1） Evidence revealed some divergence with previous records of Lower Carboniferous stratigraphic sequence in Majiaoba region and the main faunal constituents in the Majiaoba Formation, in fact, the Tournaisian to early and middle Visean deposits as previously reported, are not developed in this region; and the age of Zongchanggou Group should be referred to the late Visean to Serpukhovian. The definition of Majiaoba Formation is redefined, and the Changtanzi section outcropped in Shawozi, Guixi of Beichuan County is designated as the reference section for the new defined formation. 2） Above the top of Changtanzi Formation yielding aboundant rugose corals referred to Beichuanophyllum, Cystophrentis,etc., and below the bed accumulated with index rugose genus Pseudouralinia in Majiaoba Formation, there existed a thick dolomitic formation; and in the middle-upper part of this formation, it was for the first time that Cystophrentis and some other mega-fossils had been found. Based on the lithological characteristics, the distinct contact plane with the above-and underlying formations and the wide regional distribution as well, it is suggested to quote the Heiyaowo Formation for this thick dolomitic formation, the definition of which is redefined and the age assignment is late Fammenian of Late Devonian. 3） By stratigraphical correlating with surrounding area the palaeogeographic pattern and evolution of environment of Mt. Longmen during Carboniferous time is discussed. Apart from the narrower region in Guixi-Shawozi of middle part of Mt. Longmen, where early Carboniferous Tournaisian residual deposites remained due to marine invasion transgression into the low depressed channel, the wide area covering southern and northern part of pre-Longmenshan region had raised up above the sea in the period ranging from Tournaisian to early and Middle Visean. It was till late Visean, following the global marine transgression, the Pre-Longmenshan region had been subsided again forming shoal sediments under the para-planation environment.
出处
《地层学杂志》
CSCD
北大核心
2010年第4期349-362,共14页
Journal of Stratigraphy
基金
中国石油化工股份有限公司组织的海相前瞻性研究外协项目"中国海相地层研究"课题资助
关键词
岩石地层
生物地层
古地理格局
石炭系
龙门山
四川
biostratigraphy
lithostratigraphy
paleogeography
Caboniferous
Mt.Longmen
Sichuan
