首页> 外文期刊>Proceedings of the Indian Academy of Sciences. Earth and Planetary Sciences >Origin of Cretaceous phosphorites from the onshore of Tamil Nadu, India
【24h】

Origin of Cretaceous phosphorites from the onshore of Tamil Nadu, India

机译:印度泰米尔纳德邦陆上白垩纪磷矿的起源

获取原文
获取原文并翻译 | 示例
       

摘要

Cretaceous phosphorites from the onshore of Tamil Nadu have been investigated for their origin and compared with those in the offshore. Cretaceous phosphorites occur as light brown to yellowish brown or white nodules in Karai Shale of the Uttatur Group in the onshore Cauvery basin. Nodules exhibit phosphatic nucleus encrusted by a chalky shell of carbonate. The nucleus of the nodules consists of light and dark coloured laminae, phosphate peloids/coated grains and detri-tal particles interspersed between the laminae. Scanning electron microscope (SEM) studies reveal trapping and binding activity of microbial filaments. A mat structure with linearly arranged micro-bial filaments and hollow, cell-based coccoid cyanobacterial mat are present. Nodules contain abundant carbonate fluorapatite, followed by minor calcite, quartz and feldspar. The P_2O_5 content of the phosphorites ranges from 18 to 26%. The CaO/P_2O_5, Sr and F contents are higher than that of pure carbonate fluorapatite. Concentrations of Si, Al, K, Fe, and Ti are low. We suggest that the nuclei of the nodules represent phosphate clasts related to phosphate stromatolites formed at inter-tidal conditions. At high energy levels the microbial mats were disintegrated into phosphate clasts, coated with carbonate and then reworked into Karai Shale. On the other hand, Quaternary phosphorites occur as irregular to rounded, grey coloured phosphate clasts at water depths between 180 and 320 m on the continental shelf of Tamil Nadu. They exhibit grain-supported texture. Despite Quaternary in age, they also resemble phosphate stromatolites of intertidal origin and reworked as phosphate clasts onto the shelf margin depressions. Benthic microbial mats probably supplied high phosphorus to the sediments. Availability of excess phosphorus seems to be a pre-requisite for the formation of phosphate stromatolites.
机译:已经对泰米尔纳德邦陆上白垩纪磷矿的来源进行了调查,并与近海白磷岩进行了比较。在陆上Cauvery盆地的Uttatur Group的Karai页岩中,白垩纪的磷矿以浅棕色到黄棕色或白色的结节状存在。结节显示出磷酸核,被碳酸盐的白垩状壳包裹。结节的核由浅色和深色薄片,磷酸盐类/涂层颗粒和散布在薄片之间的碎屑颗粒组成。扫描电子显微镜(SEM)研究揭示了微生物细丝的捕获和结合活性。存在具有线性排列的微生物细丝和基于细胞的空心球状球状蓝细菌垫的垫结构。结核中含有丰富的碳酸盐氟磷灰石,其次是方解石,石英和长石。磷矿的P_2O_5含量为18%至26%。 CaO / P_2O_5,Sr和F含量均高于纯碳酸盐氟磷灰石。 Si,Al,K,Fe和Ti的浓度低。我们建议结节的核代表与潮间条件下形成的磷酸盐叠层石有关的磷酸盐碎片。在高能级下,将微生物垫分解成磷酸盐块,涂上碳酸盐,然后重新加工成Karai页岩。另一方面,在泰米尔纳德邦大陆架上,水深在180至320 m之间时,第四纪磷矿以不规则至圆形,灰色磷酸盐碎屑存在。它们表现出谷物支撑的质地。尽管处于第四纪,但它们也类似于潮间带起源的磷酸盐叠层石,并且在磷酸盐堆积到陆架边缘凹陷处时进行了重新加工。底栖微生物垫可能向沉积物中提供了高磷。过量磷的可用性似乎是形成磷酸盐叠层石的先决条件。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱:kefu@zhangqiaokeyan.com

京公网安备:11010802029741号 ICP备案号:京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有
  • 客服微信

  • 服务号