柴西地区上油砂山组咸化湖沼沉积与微生物岩

Saline lacustrine palustrine sediments and microbialite in the upper Youshashan Formation in the western Qaidam basin

利用大量岩芯、薄片、地震及分析化验资料,围绕南翼山—大风山地区的上新统上油砂山组(N^22)咸化湖沼沉积,研究沉积特征及成因机制,建立沉积模式,分析控制因素。研究表明:(1)上新统上油砂山组(N^22)沉积时期,南翼山—大风山地区为咸化湖沼环境,因咸水与淡水频繁融合,构成独特的生态系统,发育适应性的水生生物与微生物等,由生物、化学、物理沉积作用共同影响,形成咸化沼泽沉积组合。(2)明确了咸化湖沼相识别标志,主要包括沼泽土以及大量近地表暴露标志等,并伴生湖沼相微生物岩与微体化石组合等。(3)沼泽环境共发育7类岩相,进一步分析主要岩相的沉积特征及控制因素。(4)沼泽环境可分为滨岸带、植被带及浸没区,不同环境可形成不同的沉积层序、发育不同沉积岩相组合。咸化湖沼相的沉积层序主要包括退积型准层序,进积型准层序以及加积型准层序等。

Focussing on saline lacustrine palustrine sediments in the Pliocene upper Youshashan Formation(N^22)in the Nanyishan-Dafengshan area,a large of number of cores,thin sections,seismic and test data were used to study the sedimentary characteristics and genetic mechanism with the objective of analyzing the controlling factors and establishing a sedimentary model.The results show that:(1)in the sedimentary period of the Pliocene upper Youshashan Formation(N^22),saline lacustrine palustrine sedimentary environment developed in the Nanyishan-Dafengshan area.Saltwater and freshwater frequently merged to form a unique ecosystem,developing adaptive aquatic organisms and microorganisms.The sedimentary assemblage of saline palustrine sediment was finally formed by the combined impact of biological,chemical,and physical sedimentation processes.(2)The identification marks of saline lacustrine palustrine facies were clearly expressed mainly including bog soil and a large number of near-surface exposed marks,accompanied by a combination of lacustrine palustrine facies microbialite and microfossils.(3)Seven types of lithofacies were developed in palustrine environment,and the sedimentary characteristics and controlling factors of main lithofacies were further analyzed.(4)The palustrine environment was divided into beach area,vegetative area and inundated area.Different sedimentary environments formed different sedimentary sequences and developed individual lithofacies assemblages.The sedimentary sequence of saline lacustrine palustrine facies was mainly composed of prograding parasequence,retrograding parasequence,and aggradation parasequence.