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标题：Sedimentology and ichnology of Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków- Silesia Homocline, Poland
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作者：Paulina Leonowicz
期刊名称：Acta geologica Polonica
印刷版ISSN：0001-5709
出版年度：2012
卷号：62
期号：3
页码：281-296
语种：English
出版社：Institute of Geology, University of Warsaw
摘要：The lithology, sedimentary structures and trace fossil association from the Bathonian organic-rich mudstones from Kraków-Silesia Homocline (SW Poland) are described and a preliminary interpretation of the palaeoenvironment is presented. The ore-bearing clays exposed in the Gnaszyn clay-pit are developed as dark grey claysilt deposits with a few horizons of sideritic concretions. Sedimentological analysis has revealed that these deposits originated in the offshore part of a marine basin, below the fair weather wave base. Relict parallel lamination suggests that the predominant mechanism of deposition was quiet settling from suspension. However, locally preserved storm deposits indicate that the sea bottom was affected by offshore flows, deriving coarser material from the nearshore area. The degree of bioturbation is high but the diversity of the trace-fossil association is low. It consists mainly of Chondrites, Trichichnus, pyritized burrows and less common Palaeophycus. Other traces, including Thalassinoides, Planolites, Taenidium and some undetermined burrows, occur mainly in the lower part of the succession. This ichnoassociation combines features of distal Cruziana and Zoophycos ichnofacies, suggesting poor oxygenation of the bottom sediment. Temporary improvements in bottom oxygenation, linked with more intense mixing of water during major storms, resulted in the more diverse trace fossil suite that is found in some intervals of the succession.
关键词：Dark grey mudstones;Trace fossil tiering;Ore-bearing clays;Middle Jurassic;Kraków–Silesia Homocline;Poland.