羌塘盆地半岛湖地区上侏罗—下白垩统生物礁相碳酸盐岩对海水信息的保存性评估

The Upper Jurassic-Lower Cretaceous biohermal carbonate rocks from the Bandaohu region, Qiangtang Basin: Preservation of coeval sea water information

关键词:  海水信息  成岩蚀变  礁相碳酸盐岩  上侏罗－下白垩统  羌塘盆地

Key words:  sea water information  diagenetic alteration  biohermal carbonate rock  Upper Jurassic-Lower Cretaceous  Qiangtang Basin

摘要:

有关海相碳酸盐成岩蚀变性及其对海水信息保存性的研究是一个未曾被人们重视的领域,从而限制了古海洋学及其相关学科的研究水平。近年来,这一研究领域逐渐得到学者们的重视。本文对羌塘盆地半岛湖地区上侏罗统-下白垩统生物礁相碳酸盐岩样品的微观组构观察、阴极发光分析、化学分析和同位素分析等研究表明,大部分样品都具有较低的Mn含量和较高的Sr含量,所有样品均具有较低的Mn/Sr比值,样品δ¹³C值和δ¹⁸O值分布范围波动较小。不同类型岩性对海水信息的保存性按含生屑泥晶灰岩→泥晶粒屑灰岩→粒屑泥晶灰岩→礁灰岩围岩部分→礁灰岩生物骨架部分的顺序依次变差。

Abstract:

The evaluation of diagenetic alteration of marine carbonate rocks and the preservation of coeval sea water information has long been a negligible field. The examination of microscopic fabrics, cathodoluminescence images, trace elements and isotopes in the Upper Jurassic-Lower Cretaceous biohermal carbonate rock samples from the Bandaohu region, Qiangtang Basin has disclosed that these samples are characterized by low Mn and high Sr contents, low Mn/Sr ratios, and limited range of δ¹³C and δ¹⁸O values. The preservation of coeval sea water information tends to become progressively worse in the sequence of bioclastic micritic limestone→micritic grainy limestone→grainy micritic limestone→wall rocks of reefal limestone→skeletal frameworks of reefal limestone.