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首页> 外文期刊>facies >Lacustrine bioherms, spring mounds, and marginal carbonates of the Ries-impact-crater (Miocene, Southern Germany)
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Lacustrine bioherms, spring mounds, and marginal carbonates of the Ries-impact-crater (Miocene, Southern Germany)

机译：里斯撞击坑（中新世，德国南部）的湖泊生物群落、泉丘和边缘碳酸盐岩

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摘要

The petrographic investigation of the Miocene Rieslake-carbonates gave rise to a modifiedDunham-scheme for classifying non-marine carbonates. If the fabric is not exclusively the result of hydromechanical or biogenic effects,Dunham-terms were extended by interpretative attributes describing processes responsible for the secondary fabric development (pedogenesis, early meteoric diagenesis). The lowermost investigated section reveals a distinct zonation of the lake shore during humid stages (carbonates of the infra-, eu-, and supralittoral), interrupted by playa-like interstages of arid conditions (desiccated mudflat). Dolomitic successions of sinter-veneered bioherms, built by green algae and cyanobacteria, form an incomplete ‘reef belt’ at the northern crater rim. Bioherm sequences were controlled by a seasonally oscillating lake level and fluctuations of higher order, which correspond to small-scale climatic fluctuations in the range of several hundreds to thousands of years. A superposed facies trend is recognized, which is the result of the decreasing eutrophy, alkalinity, and carbonate supersaturation. This reflects the climatic change to generally humid conditions at the end of Miocene. Originally thrombolitic sublacustrine spring mounds were caused by upwelling groundwater from permeable bedrock. Cement framestones of the mound core are considered to result from fabric alteration within the upwelling ground water and by emersions. Marginal carbonates of the Ries basin, inclusively bioherms, probably were originally Mg-calcitic. Aragonite was restricted to gastropod shells and sublacustrine spring mounds. Dolomitization is interpreted as essentially due to a fluctuating phreatic mixing-zone caused by meteoric groundwater, which underflowed saline water at the soda lake margin. The algal flora comprises cyanobacteria, possible cyanobacteria, green algae, few charophytes, endoliths, and problematic forms. A Recent contamination by endolithic fungi and lichens is evident. Occasionally preserved insect larval tubes, mass accumulations of pupal cases of flies, and arthropod eggs demonstrate that these groups were once a prominent part of the fossil soda lake ecosystem of the Nördlinger
机译：对中新世里斯莱克碳酸盐岩的岩相学研究产生了一种改进的Dunham方案，用于对非海相碳酸盐进行分类。如果织物不完全是流体力学或生物作用的结果，那么邓纳姆项则通过描述负责次生织物发育过程（土壤发生、早期陨石成岩作用）的解释属性来扩展。最下部的调查部分揭示了在潮湿阶段（地下、欧洲和上层的碳酸盐）湖岸的明显分区，旱条件的类似海滩的间段（干燥的泥滩）打断。由绿藻和蓝藻建造的烧结贴面生物群落的白云岩演替在北部陨石坑边缘形成了一个不完整的“礁带”。生物群落序列受季节性波动的湖泊水位和高阶波动的控制，对应于数百至数千年范围内的小尺度气候波动。认识到叠加相趋势，这是富营养化、碱度和碳酸盐过饱和度降低的结果。这反映了中新世末期气候向一般潮湿条件的变化。最初，血栓形成的湖下泉丘是由来自渗透性基岩的地下水上升流引起的。土墩岩芯的水泥框架石被认为是上升流地下水中织物蚀变和渗流造成的。里斯盆地的边缘碳酸盐岩，包括生物群落，可能最初是镁钙质的。文石仅限于腹足类贝壳和湖相下泉丘。白云石化被解释为主要是由于陨石地下水引起的波动的潜水混合区，地下水在苏打湖边缘潜流了咸水。藻类菌群包括蓝藻、可能的蓝藻、绿藻、少量炭藻、内石和有问题的形式。最近被内石真菌和地衣污染是显而易见的。偶尔保存下来的昆虫幼虫管、苍蝇蛹的大量积累和节肢动物卵表明，这些群体曾经是诺德林格苏打湖化石生态系统的重要组成部分

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  • 来源
    《facies》 |2006年第1期|35-89|共页
  • 作者

    Dipl.-Geol.GernotArp;

  • 作者单位

    Institut und Museum für Geologie und Paläontologie;

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