塔里木盆地晚古生代古盐度与古环境探讨

目的利用古盐度数据为有争议的塔里木盆地上古生界地层的沉积环境研究提供判定依据。方法对盆地巴楚、塔中、塔北地区的上古生界泥岩样品进行B,Ba,Sr,Ga等微量元素及K2O含量测试,开展古盐度地球化学分析,使用多指标恢复出研究区晚古生代水体的古盐度。结果本研究测试的古盐度数据分布于4.7‰～55.2‰,变化范围较大,涵盖了淡水、半咸水、咸水、超咸水各种类型。其中,以半咸水—咸水样品多见,超咸水样品集中出现于巴楚地区二叠系南闸组及库普库兹曼组,淡水样品出现于塔中地区砂泥岩段。结论古盐度测试显示,塔河地区"东河塘组"具半咸水特征,这一结果与该区钻、测井揭示的三角洲沉积吻合;石炭系巴楚组—卡拉沙依组各泥岩段的古盐度具半咸水特点,反映了该时期为有河流注入的淡化泻湖环境;砂泥岩段沉积期,淡水河流注入对古盐度控制作用较为明显。巴楚地区二叠系南闸组—库普库兹曼组泥岩为咸水浅海陆棚—半咸水泻湖与潮坪沉积,个别样品的古盐度偏高可能与样品含火山凝灰质有关。

Analysis on paleosalinity and paleoenvironment of Late Paleozoic in Tarim Basin

Aim The paleosalinity was used to offer useful information for identifying and restoring depositional environments of Late Paleozoic which has disputes.Methods Content of element B,Ba,Sr,Ga and K2O in the Upper Paleozoic shale and mudstone samples collected from Tazhong,Bachu and Tahe area in Tarim Basin was measured to make geochemical analysis and was the water paleosainity of Upper Paleozoic restored with multiple indexes.Results The paleosalinity data distribute from 4.7‰ to 55.2‰,have a great varying range,and contain of various types including fresh water,semi-saline,saline,ultra saline.Most samples are semi-saline or saline.Ultra saline data appear mainly in the samples of Permian Nanzha-Kupukuzman Formation in Bachu area.Fresh water data appear in the samples of sand-mud member of Carboniferous Kalashayi Formation in Tazhong area.Conclusion Paleosalinity data show Donghetang Formation in Tahe area is semi-saline,which coincides with the delta deposit revealed by drilling core and logging data.The paleosalinity of mudstone members in BaChu-Kalashayi Formation all belongs to semi-saline environment,suggesting a probable lagoon deposition injected by fresh water rivers.The paleosalinity of sand-mud members is the lowest in comparation with the other lithilogic members,which reflects the fluvial injections of fresh water and mud-sand loads during the related depositional period.The saline to semi-saline paleosalinity of Permian Nanzha-Kupukuzman Formation in Bachu area may respectively indicate neritic shelf and lagoon or tidal flat environment affected by fresh water rivers.Rare samples with abnormally high paleosainity might have been caused by tuffaceous material contained in shale samples.