典型韵律互层式灰岩与泥灰岩的地球化学特征对比

通过对德国南部地区上侏罗统麻姆组典型韵律互层式灰岩与泥灰岩进行逐层采样,并进行不溶残余物分析和地球化学测定对比,发现两者所含非碳酸盐物质没有区别。SiO₂、Al₂O₃、Fe₂O₃、K₂O和TiO₂等来源于陆源碎屑物,在灰岩与泥灰岩中的比例完全相同,其含量的不同完全由碳酸盐物质的稀释所引起。元素Sr、Zn、Mn和Mg归为成岩作用控制元素,最先存在形式与碳酸盐有关,但成岩阶段变化极大,Mg的含量主要受白云岩化作用程度控制。另一组元素如S、Ba、Rb和P等介于以上两组元素之间,表现为部分受陆源碎屑物含量控制,部分受成岩作用影响。研究表明,灰岩与泥灰岩韵律互层形成的原因主要是由于碳酸盐物质的沉积速率变化所致,成岩阶段的压溶作用加大了两者的差异,但这种差异只表现在于碳酸盐物质与酸不溶残余物的比例上,而地球化学组成没有本质区别。

The Geochemical Feature' s Comparison between the Typical Rhythmic Bedding Iimestone and Marl of Upper Jurassic Malm in Southern Germany

The ty pical rhy thmic bedding limestone and marl of upper Jurassic M alm in southern Germany were d4posited in typical epicontinental platfo rm envirnment. The rocks in the sectio n were bed by bed sampled, their residues were obtained by isolation with monochlo acid (CH₂ClOO H). The mineral assemblage in residues m ainaly consists of quartz, K-feldspar and clay minerals according to X-ray diffraction analy sis. The analy sis of residues bo th in mineral assemblage and in chemical composition show s that the non-carbo nate m a-terials in limestone and in marl are no essential difference. The geochemical analy sis with XRFS (X -ray Fluo-rescence Spectrometry) w as taken both on rocks and on the residues. SiO₂, Al₂O₃, Fe₂O₃, K₂O and TiO₂ are related to detritus, and demonstrate the same relationships in limestone and in marl, moreover, they all have a g ood positive relationship to the residues content and are classified to the so-called detritus elements group. They rem ained in the sediments and had no change after deposition. Their different concentrations in lime-stonse and in marl are only due to the effect of carbonate sediments, dilution during deposition. The elements Sr, Zn, Mn, and Mg are controlled by diagenesis. They exist fi rstly in the carbonate form, but change much in the period of diagenesis. Dolomitization in some posme posi tion of the section leads to high Mg-content in the rocks. These elements are classified to the group of diagenesis elements. The elements in this g roup have no clear relationship to the residues-contents. However, the behavio r of elements such as S, Ba, Rb and P is be-tween the two groups of elements. They were controlled partly by the detritus and partly by the diagenesis, and they are somerelationship to the residues-contents. The fo rmation of rhy thmic bedding limes tone and marl is the result result of the variation of carbo nate sedimentation rat and then compressed w ith pressure solution. But the differences of them are only in residues content but not essentially in the mineral assemblage and geo-chemical composition of non-carbo nate material in the rocks.