西秦岭甘南地区上二叠统毛毛隆组古环境演变:基于遗迹网络分析

Palaeoenvironmental evolution of the Upper Permian Maomaolong Formation in Gannan area of the West Qinling:Based on ichnonetwork analysis

西秦岭地区是二叠系—三叠系之交深水相保存较为连续的地区,西秦岭甘南地区上二叠统毛毛隆组发育丰富的遗迹化石(12属17种)。遗迹网络分析作为新兴的研究方法,侧重于用相互连接的遗迹分类群来重建遗迹群落系统,这为研究遗迹群落的行为学和生态学提供了丰富的手段。笔者以西秦岭甘南地区上二叠统毛毛隆组发现的遗迹化石为数据源,运用遗迹网络分析方法,揭示出毛毛隆组遗迹群落具结构化特征,遗迹群落体现出环境驱动的遗迹组合面貌特征:Palaeophycus-Lockeia-Arenicolites-Dictyodora-Planolites-Protovirgularia-Chondrites组合(C1,近源浊流区),Palaeophycus-Lockeia-Arenicolites-Dictyodora-Protovirgularia-Phycodes-Chondrites-Helminthopsis组合(C2,浊流过渡区—浊流远源区),和Palaeophycus-Nereites-Scolicia-Protovirgularia-Helminthopsis组合(C3,远源浊流区)。该遗迹群落由C1演变至C3的过程,揭示了古环境从近源浊流区至远源浊流区的演变历程。

The continuous Permian-Triassic strata in West Qinling represent deep-marine deposits.In this paper,abundant trace fossils(seventeen ichnospecies,twelve ichnogenera)have been identified in the Upper Permian Maomaolong Formation in the Gannan area of the western Qinling orogen.As a new ichnologic method,ichnonetwork analysis focuses on the reconstruction of the community system composed of interconnected ichnotaxa,which provides useful means for studying the behavior and ecology of ichnocoenosis.In this study,an ichnonetwork analysis is conducted with trace fossils data obtained from the first hand filed trip.The results show that ichnocoenosisis structured in the Maomaolong Formaiton,and three ichnoassociations were controlled by palaeoenvironments:Palaeophycus-Lockeia-Arenicolites-Dictyodora-Planolites-Protovirgularia-Chondrites(C1,proximal turbidite zone),Palaeophycus-Lockeia-Arenicolites-Dictyodora-Protovirgularia-Phycodes-Chondrites-Helminthopsis(C2,turbidite transition zone-distal turbidite zone),and Palaeophycus-Nereites-Scolicia-Protovirgularia-Helminthopsis(C3,distal turbidite zone).The evolution from C1 to C3 in the Upper Permian Maomaolong Formation from the Gannan area of the West Qinling reveals the palaeoenvironmental changes from proximal turbidite zone to distal turbidite zone.