龙门山早—中泥盆世Chondrites类型及其环境意义

摘要

Total 8 ichnospecies of the Chondrites fossil,including Chondrites expansus ,Chondrites cf. fenxiangensis ,Chondrites filiformis ,Chondrites isp.,Chondrites targonii ,Chondrites type-C, Chondrites cf.type-C and Chondrites intricatus are preserved and identified in the early-middle Devonian strata of Guixi-Shawozi section,Sichuan,China.These Chondrites ichnospecies belong to 3 Chondrites ichnocoenoses,single Chondrites ichnospecies type,double Chondrites ichnospecies type and multiple Chondrites ichnospecies type respectively.The Chondrites trace fossils distributed in shore to shelf deposit environment are appertained to Chondrites-Phycodes ichnocoenosis and Chondrites-Lockeia ichnocoenosis,the Chondrites-Phycodes ichnocoenosis represent shallow shelf surrounding with abundant food and relatively low oxygen content.However,the Chondrites-Lockeia ichnocoenosis represent shallow shelf,a normal oxygen condition with plenty of oxygen environment. It reveals that these Chondrites trace fossils lived in 3 kinds of sedimentary environment,including deep water shelf condensed section,shallow shelf and storm deposit environment in the Longmenshan area.Besides,Chondrites fossils in condense section reflect suboxic environment,the rest represents normal oxygen environment.There is no correspondence between Chondrites branch diameter and its palaeo-oxygenation facies.%四川龙门山地区下-中泥盆统有丰富的丛藻迹遗迹化石,可识别出8种类型,包括:Chondrites expansus、Chondrites cf.fenxiangensis、Chondrites filiformis、Chondrites isp.、Chondrites targonii、Chondrites type-C、Chondrites cf.type-C和Chondrites intricatus,它们的组合类型有3种:单一种类型、两种组合类型和多种组合类型.Chondrites遗迹化石分布于滨岸-陆棚的沉积环境中,分属于Chondrites-Phycodes和Chondrites-Lockeia遗迹化石组合.其中Chondrites-Phycodes组合代表食物充足、氧含量相对较低的浅水陆棚环境,而Chon-drites-Lockeia组合代表氧含量充足的常氧环境浅水陆棚环境.Chondrites遗迹化石的沉积环境包括深水陆棚凝缩段环境、浅水陆棚环境和风暴沉积环境等.保存于深水凝缩段中的Chondrites遗迹化石反映贫氧相环境,其余2种则代表常氧相环境.Chondrites虫孔直径大小与古氧相之间并不存在直接的对应关系.