沙井子地区奥陶系碳酸盐岩地球化学特征研究

Study on Geochemical Characteristics of Ordovician Carbonate Rock in Shajingzi Area

探讨鄂尔多斯西缘沙井子地区奥陶系碳酸盐岩地球化学特征和沉积环境。对研究区内的25块碳酸盐岩岩心样品进行常量元素和微量元素分析,利用相关性分析对其元素和组分的富集规律及环境意义进行探讨。论述碳酸盐岩中各氧化物含量之间的相关关系,SiO2、Al2O3、P2O5与K2O、TFe2O3、TiO2呈正相关而与CaO呈负相关;Na2O与MgO呈正相关,与CaO呈负相关;V与SiO2、TiO2、P2O5正相关,与CaO负相关,较为全面地反映出研究区奥陶系碳酸盐岩特殊的地化特征及其所蕴含的环境意义。元素地球化学特征分析有助于反演古环境、古气候条件。沙井子地区早奥陶世晚期至中奥陶世早期,沙井子地区主要为氧化环境下的浅水开阔台地,气候干热,发育泥晶粒屑灰岩、亮晶砂屑灰岩、生物碎屑灰岩、云斑泥晶灰岩呈不等厚互层。平凉组为弱还原的深水斜坡环境,发育一套以陆源碎屑为主、砂质白云岩、灰质白云岩、含泥灰岩次之的沉积组合。

To have a clear awareness of the geochemical characteristics and sedimentary environment of Ordovician carbon- ate rock in Shajingzi area, the west margin of Ordos basin, the paper makes a research on macroelements and microelements in the twenty - five core samples, and makes a study on the elements enrichment mechanism and its environmental significance. The analysis of relationship between content of various oxides in carbonate rock shows that Si02, A1203 and P205 have positive correlation with K20, TFe203 and Ti02, while a negative correlation with CaO. Moreover, there is a positive correlation be- tween content of Na20 and content of MgO, while a negative correlation between Na20 content and CaO content. Content of V is positive correlated to it of SiO2 ,TiO2 ,P205, and is negative correlated to it of CaO. The result show that geochemical charac- teristics analysis is helpful for the study on palaeoenvironment and paleoclimate. During late stage of early Ordovician and early stage of late Ordovician, Shajingzi area is a meseta in hot heat oxidation environment. The main rock at that time are micrite limestones, sparry areinte limestones and bioclastic limeston, which are interbedded with each other. In an environment of weak reduction, Pingliang Formation, located in a deep - water slope, is a combination of sandy dolomite, calcite dolomite and marlite.