豫西地区下二叠统太原组遗迹组构及其沉积环境

豫西下二叠统太原组中发育丰富的遗迹化石,常见有Zoophycos,Taenidium,Thalassinoides,Teichichnus,Gordia,Nereites,Chondrites和Planolites等,部分灰岩层中还发育生物扰动构造。根据遗迹化石的形态、组成、产状、分布特征以及丰度、分异度、生物扰动程度的不同,在研究区太原组碳酸盐岩中共识别出5种遗迹组构,包括类型A--Gordia-Planolites遗迹组构、类型B--Rhizocorallium-Thalassinoides遗迹组构、类型C--Zoophycos-Taenidium遗迹组构、类型D--Zoophycos-Speckle burrow强生物扰动遗迹组构、类型E--Chondrites-Nereites遗迹组构。其中类型C根据Zoophycos在剖面上所展现的各种特征,又可细分为3种类型,即类型C-1,C-2和C-3。通过分析宿主岩的沉积特征,表明太原组碳酸盐岩中的遗迹组构主要分布于潟湖潮坪和台内浅滩(类型A)、正常天气浪基面之上的浅海上部或局限台地(类型B,类型C-1和类型C-2)、正常天气浪基面之下的开阔台地(类型C-3,类型D)和风暴浪基面之下的浅海下部或水动力条件类似的较闭塞的沉积环境中(类型E)。

Ichnofabrics and their environment in carbonates from the Lower Permian Taiyuan Formation, Jiaozuo city, Henan

The abundant trace fossils were developed in the Lower Permian Taiyuan Formation of western Henan,in which common components include Zoophycos,Taenidium,Thalassinoides,Teichichnus,Gordia,Nereites,Chondrites,Planolites and so on,and strong bioturbation structures were found in part of limestone beds.Based on the differences of trace fossil characteristics in morphology,composition,occurrence,distribution,aboundance,biotaldiversity and bioturbation degree,five types of ichnofabrics have been recognized in the carbonates of the Taiyuan Formation in this study area,and they are named as follows:Type A,Gordia-Planolites ichnofabric;Type B,Rhizocorallium-Thalassinoides ichnofabric;Type C,Zoophycos-Taenidium ichnofabric;Type D,Zoophycos-speckle burrow(strong bioturbation) ichnofabric;Type E,Chondrites-Nereites ichnofabric.According to the diameter size,colours of back-filled sediments and burial depth of the Zoophycos in vertical section,the Zoophycos-Taenidium ichnofabric can be further divided into 3 subtypes,i.e.,Type C-1,Type C-2 and Type C-3.The sedimentary characteristics of the host rock show that:these types of ichnofabrics in carbonate of the Taiyuan Formation mainly distributed in lagoons-tidal flat and shoals within carbonate plateform(type A),the upper shallow sea or restricted platform over fair-weather wave base(type B,type C-1 and type C-2),the open platform located under the fair-weather wave base(type C-3,type D) and the lower shallow sea under the storm wave base or partly landlocked sedimentary environment(type E).