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首页> 外文期刊>Sedimentary geology >Chloritization of Late Ordovician K-bentonites from the northern Baltic Palaeobasin-influence from source material or diagenetic environment?
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Chloritization of Late Ordovician K-bentonites from the northern Baltic Palaeobasin-influence from source material or diagenetic environment?

机译：来自北波罗的海古盆地的晚奥陶纪钾膨润土的绿化作用是否受原材料或成岩环境的影响？

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摘要

The Baltic Ordovician-Silurian sedimentary succession embodies numerous altered volcanic ash beds that are illite-smectite dominated. Only a few beds rich in chlorite-smectite are known from the Upper Ordovician Pirgu Stage of Estonia. Mixed-layer chlorite-smectite occurs commonly in low-grade metamorphic and hydrothermal environments. However, chloritic K-bentonites of the Pirgu Stage have never been buried deeply and lack signs of metamorphic overprinting. In order to understand the origin of chloritization, three distinct beds were sampled in 14 drillcores from Estonia and Latvia and analysed by means of XRD and SEM. The principal authigenic assemblage of the bulk samples consists of chlorite-smectite (corrensite) together with illite-smectite and K-feldspar. The actual mineral composition of K-bentonites though varies from sample to sample. The clay mineral assemblages range from virtually pure chlorite-smectite to illite-smectite dominated assemblages with minor or no chlorite-smectite. The proportion of chlorite-smectite in K-bentonites shows systematic lateral variations: the share of chloritic phases is highest in the shallower-water part of the palaeobasin and decreases towards the deeper part of the basin. Such regular lateral variations suggest a possible link between chloritization and the configuration of ancient palaeobasin. The present study suggests that the chloritization of primary felsic ashes occurred during early diagenesis and that it was caused by an influx of Mg-rich water probably from a marine sabkha-type environment.
机译：波罗的海奥陶纪-lur柳纪沉积相继体现了许多以伊利石-蒙脱石为主的蚀变火山灰床。从爱沙尼亚的上奥陶纪Pirgu阶段只有几块富含绿泥石-蒙脱石的床。混合层绿泥石-蒙脱石通常发生在低品位变质和热液环境中。然而，皮尔古期的氯酸钾膨润土从未被深埋，也没有变质叠印的迹象。为了了解氯化的起源，在爱沙尼亚和拉脱维亚的14个钻芯中取样了三个不同的床层，并通过XRD和SEM进行了分析。散装样品的主要自生组合包括绿泥石-蒙脱石（堇青石），伊利石-蒙脱石和钾长石。钾膨润土的实际矿物组成随样品的不同而不同。粘土矿物组合的范围从几乎纯的绿泥石-蒙脱石到伊利石-蒙脱石为主的组合，而次要或没有绿泥石-蒙脱石。钾膨润土中绿泥石-蒙脱石的比例显示出系统的横向变化：在古盆地的浅水部分，绿泥石相的份额最高，而在盆地的深部则减少。这种规则的横向变化表明，在氯化作用与古代古盆地的构造之间可能存在联系。本研究表明，原长生灰烬的氯化发生在早期成岩过程中，这是由可能来自海洋萨布卡型环境的富含镁的水流入引起的。

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