塔里木“东河砂岩”的沉积相分异和孢子化石新资料

FACIES DIFFERENTIATION AND NEW SPORE DATA OF THE DONGHETANG FORMATION IN THE TARIM BLOCK,XINJIANG,NW CHINA

根据东河塘组的原始定义、井下孢子化石组合以及与下伏克孜尔塔格组和上覆巴楚组的相变关系,本文进一步论证东河塘组具有明显穿时性,并厘定了岩相的识别标志及其在塔里木板块的3种展示类型,即3段式、2段式与1段式。早海西期(或加里东期与海西期)构造运动不整合面作为东河塘组之底界,巴楚组底界为含砾砂岩段(或泥岩段)之底,东河塘组与巴楚组之间在多个地点表现为角度不整合式的超覆,仅西部的巴楚局部地点可见两组之间为整合或平行不整合接触。据新井所获得的丰富孢粉化石,可将东河塘组划分出两个孢子组合,即下部的Apiculiretusispora hunanensis-Aneurospora tarimensis(HT组合)和上部的Ancyrospora furcula-Cymbosporites tarimensis(FT组合),时代主要归属于晚泥盆世法门中期,泥盆-石炭系界线可置于巴楚组下泥岩段中部的碳酸盐岩夹层之顶。

The present study redefines the lithological indicators as well as their spatial distributions of the Devonian Donghetang Formation in the Tarim Block based on the aspects of original definition of the units,spore assemblages and the contact relationships to its underlain Kerziertag Formation and overlain Bachu Formation.The sequences of the Donghetang Formation is obviously diachronic and diverse in the block,and shown as Three-Member Type,Two-Member Type or One-Member Type.The base of the Donghetang Formation is considered as an unconformity caused by the Early Hercynian （or Caledonian plus Hercynian） Orogeny.The top of the Donghetang Formation is assigned to the base of the Conglomerate Sandstone Member （or Mudstone Member） of the Bachu Formation.Disconformable onlap is very common between the Bachu and Donghetang formations,and conformable or unconformable contact between them only occurs from the Bachu region,western margin of the block.Two spore assemblages are recognized from the Donghetang Formation.They are the Apiculiretusispora hunanensis-Aneurospora tarimensis（HT） assemblage from the lower part and Ancyrospora furcula-Cymbosporites tarimensis（FT） assemblage from the upper part based on rich fossils analyzed from several new wells.The age of the formation thus mostly belongs to the Middle Famennian,Late Devonian.The Devonian and Carboniferous Boundary is assigned to the top of the carbonate layer,middle part of the Lower Mudstone Member,Bachu Formation.