Nový pohled na genezi ordovické oolitické rudy z ložiska Skalka u Mníšku pod Brdy (pražská pánev, Barrandien)

Q4 Earth and Planetary Sciences

Geological Research in Moravia and Silesia Pub Date : 2019-06-19 DOI:10.5817/gvms2019-1-2-80

D. Buriánek, M. Bubík, Dalibor Všianský

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引用次数: 1

Abstract

The Skalka Deposit near Mníšek pod Brdy currently represents one of the best exposed localities of Ordovician oolitic iron ores in the Barrandian. The studied oolitic iron ores consist mainly of siderite (Fe = 1.47–1.86 apfu) and kaolinite (Si = 7.99–8.06 apfu; VIAl = 7.62–7.67 apfu). This mineral association has been formed as a result of the process of diagenesis and has resulted from the decomposition of chlorite and Fe-(oxo-)hydroxides. Presence of colofane indicates rather low temperatures for this transformation. Paleontological record makes the previous hypothesis, that the iron ore deposit was formed in an isolated depression separated from the Prague Basin by a flat elevation, questionable. The presence of abundant graptolites and agglutinated foraminifers in the shales of the Šárka Formation indicates rather deep-water open-marine conditions. Ferruginous ooids are typically formed on shoals affected by wave action. The presence of these ooids in deep-water shale and existence of oolitic iron ore deposit accompanied by this shale does not need to be explained by sudden shallowing, but more likely by reworking of ooids in gravity flows to sublittoral or bathyal depths. Original position of shoal was most likely situated towards NNW where ore deposit and finally the complete Šárka Formation disappear. The fossil record indicates open-marine realm southeast of the Skalka area.

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关于Mníšek pod Brdy附近Skalka矿床Ordovice鲕粒矿成因的新观点

目前，Mníšek pod Brdy附近的Skalka矿床是Barrandian地区奥陶系鲕粒铁矿暴露最好的地区之一。研究的鲕状铁矿主要由菱铁矿(Fe = 1.47 ~ 1.86 apfu)和高岭石(Si = 7.99 ~ 8.06 apfu)组成;VIAl = 7.62-7.67 apfu)。这种矿物组合是成岩作用的结果，是绿泥石和铁(氧)氢氧化物分解的结果。colofane的存在表明这种转变的温度相当低。古生物学的记录使得先前的假设，即铁矿床形成于一个孤立的洼地，与布拉格盆地隔着一个平坦的高地，这个假设是有问题的。Šárka组页岩中有丰富的笔石和有孔虫凝集，显示出较深的开放海环境。含铁流体通常在受波浪作用影响的浅滩上形成。这些流体在深水页岩中的存在，以及伴随页岩的鲕状铁矿床的存在，不需要用突然变浅来解释，而更有可能是重力流中流体向海底或深海深处的重新加工。浅滩的原始位置很可能位于NNW方向，矿床最终在此消失，整个Šárka组消失。化石记录显示在斯卡尔卡地区东南部的开阔海域。

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来源期刊

Geological Research in Moravia and Silesia Earth and Planetary Sciences-Geology

CiteScore

0.40

自引率

0.00%

发文量

期刊介绍： The Geological research is peer-reviewed open access journal that publishes original research articles. The journal aims principally at quick publication of variety results from different fields of geological sciences and its applied sectors including interdisciplinary topics, laboratory experiments and modelling. Journal is focused on basic data and their simple and clear interpretation. Its aim is to facilitate the systematic development of the scientific body of knowledge in the field of geosciences with a span beyond the region of Central Europe. The form of articles/texts is as concise as possible. There is a section for publication of extended abstracts from conferences and meetings as well.