喀木斯特区晚古生代沉积相及弧缘盆地演化

SEDIMENTARY FACIESOF LATE PALEOZOIC AND EVOLUTION OF ARC-MARGIN BASIN IN KAMISTI REGION

新疆北部准噶尔喀木斯特区在晚古生代是一发育在介于大陆—大洋过渡性质地壳为基底的边缘盆地。以下泥盆统和下石炭统为主的上古生界 ,以岛弧造山带为主要物源区的碎屑岩为主要组成岩石 ,碎屑岩主要视粒度差别划分为 A— E五类 ,依组分再分成亚相 ;碳酸盐岩或硅质岩依成分划分为 G相 ;熔岩火山碎屑岩划为 V相。较大范围内两个或两个以上岩相组成斜坡—海底峡谷、海底扇、盆地平原三个相组合。区内岩相特征和沉积相演化综合表明 :下泥盆统由下而上沉积环境从斜坡上部过渡为下部 ,沉积序列为退积型 ;下石炭统沉积环境由外扇—盆地平原 ,中扇下部 ,中扇上部再过渡为中扇下部 ,沉积序列为进积退积型。弧缘盆地演化经历了孕育期、发展期。

A marginal basin of transitional continental- oceanic crustal basement was developed in the Kamisti region of the northern Xinjiang during the late Paleozoic.The Upper Paleozoic ( mainly of L ower De- vonian and L ower Carboniferous) mainly consists of clastic rocks derived from island- arc orogenic belts.The clastic rocks are divided into A,B,C,D and E types according to grainsize,and subdivided according to com- positions.The carbonates or silicalites are classified as G- facies according to compositions,and lava and vol- caniclastic rocks as V- facies. Two or over two lithofacies make up three facies association including slope- submarine valley,submarine fan and basinal plain. The lithofacies and sedimentary evolution in the region show that L ower Devonian,from bottom up,changes from upper slope to lower slope in terms of its sedi- mentary environment,implying a retrogressional sedimentary sequence.While L ower Carboniferous changes from outer fan- basinal plain,lower mid- fan,upper mid- fan to lower mid- fan in terms of its sedimentary envi- ronment,implying a gressional- retrogressional sedimentary sequence. The arc- margin basin underwent four evolution stages of pregnancy,development,maturity and shrinkage.