| 库车前陆盆地古近纪—新近纪盐湖环境变迁及其成钾效应探讨 |
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| 引用本文：刘成林,曹养同,杨海军,焦鹏程,顾乔元.2013.库车前陆盆地古近纪—新近纪盐湖环境变迁及其成钾效应探讨[J].地球学报,34(5):547-558. |
| DOI：10.3975/cagsb.2013.05.05 |
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| 基金项目:国家“973”计划项目(编号: 2011CB403007)；国家科技支撑计划课题(编号: 2006BAB07B06)；塔里木油田公司科技项目(编号: 41005050002) |
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| 中文摘要:库车前陆盆地古近纪—新近纪发育巨厚的蒸发岩沉积。古新世, 盐湖沉积主要集中在库车盆地西部拜城凹陷的中东部; 始新世, 盐湖沉积扩展至整个拜城凹陷, 沉积中心和蒸发浓缩中心位于其北部; 渐新世, 盐湖沉积仍然分布于拜城凹陷, 但沉积和浓缩中心已从北部迁移到南部, 改变了此前“南浅北深”的箕状盆地构造格局; 中新世, 盆地沉积中心已从西部的拜城凹陷转移到东部的阳霞凹陷, 盐湖沉积区也随之迁移到东部, 浓缩中心呈串珠状分布。库车前陆盆地古近纪—新近纪环境变迁显示, 盆地次级凹陷的发育、迁移明显受控于盆地构造演化; 而盆地构造活动在制约盐湖岩相古地理面貌(沉积中心、物质来源与浓缩中心等)变迁的同时, 亦对盐湖晚期富钾卤水的再汇集过程具有明显的控制作用, 进而对随后可能的钾盐沉积起到决定性作用。进一步分析表明, 库车前陆盆地古近系—新近系蒸发岩序列中钾离子在横向上的富集势亦明显受控于这一时期盆地岩相古地理的变迁, 即在盐岩沉积面积、厚度大的凹地出现钾离子相对富集。而西部拜城凹陷, 钻孔(始新统)盐岩岩屑的钾离子含量从下向上逐渐增高的趋势, 峰值分别为1.07%、1.43%、3.05%; 东部凹陷钻孔(中新统)盐岩岩屑钾离子含量由下向上亦呈增高趋势, 最低值0.008%, 最高值为0.152%等证据表明, 地层中钾离子纵向上的富集趋势, 则正是始于对岩相古地理面貌变迁的地球化学响应。综上所述, 认为库车前陆盆地具有钾盐成矿远景: 始新世时期, 库车盆地西部凹陷的蒸发浓缩中心区成钾远景相对较好; 中新世时期, 有利的成钾区可能转移到东部凹陷的浓缩中心区。 |
| 中文关键词:塔里木 库车前陆盆地 古近纪 新近纪 蒸发岩 |
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| Discussion on Paleogene-Neogene Environmental Change of Salt Lakes in Kuqa Foreland Basin and Its Potash-forming Effect |
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| Abstract:Evaporites with large thickness were formed in Kuqa foreland basin during Paleogene-Neogene period.The paleo-salt lake deposits during Paleocene were mainly distributed in central and estern Baicheng depression in the west of Kuqa Basin; then the paleo-salt lake deposits expanded into almost entire Baicheng depression and both depocenter and brine enrichment center of salt lake located in the north part during Eocene; after that the salt lake deposits were still distributed in the most of the depression during Oligocene, but evaporites and brine enrichment center had already moved to its south, and hence the previous tectonic pattern of the half-graben basin characterized by “deep in the north and shallow in the south” was remarkably altered; finally, with the migration of the depocenter from Baicheng depression to Yangxia depression in the east of the basin during Miocene, the salt lake sediments also moved eastward. The brine enrichment centers occured as bead distribution during Paleocene to Miocene. The evolution of paleogeography of Kuqa basin indicated that the development and migration of sub-depression was strongly influenced by tectonic activities in the baisn, which controled the paleogeography of salt lake (e.g. depocenter, material source and brine enrichment center) and might have played an important role in the later potential formation of potash deposits. Further analysis reveals that enrichment tendency for potassium in evaporite sequence also controlled obviously by the paleogeographic changes of the Basin, namely, potassium enrichments should have occurred in the regions with large area and great thickness of the salt deposits. The fact that, potassium content of salt rock cuttings in some oil drill holes gradually increased from the bottom to the top, for example, in the western Baicheng depression, the maximum values of potassium content are 1.07%, 1.43%, 3.05% upward in one drill hole, and in the eastern Yangxia depression, the potassium content varies from 0.008% to 0.152%, was just the geochemical response to the enrichment trend of potassium content controlled by change of lithofacies and paleogeography in the paleo-salt lake. From the above, it can predict that the Kuqa foreland basin has good potash metallogenic prospects, which might exist in brine enrichment center of Baicheng depression in Eocene time and probably migrate to the center of Yangxia depression in Miocene time. |
| keywords:Tarim Kuqa foreland basin Paleogene Neogene evaporite |
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