Analysis of Mn-deposits from the Alps

Near Weissbach - Diessbach southeast of Lofer (Salzburg, Austria), at the western rim of the Steinernes Meer (Northern Calcareous Alps), the sedimentary sequence of a local Jurassic strike slip basin (pull apart basin) is exposed. This basin formed during the Hettangian (Lias) along E-W directed sinistral strike slip faults showing the structure of a halfgraben with a complex basin fill and asymmetric facies distribution. Along the scarp faults, some of which are still well exposed, different types of mass flows were deposited. In the more distal part red bedded liassic limestones with numerous turbidite and debris flow intercalations (Weissbach Formation) are developed. These slope sediments are overlain by large, up to several hundred meter thick synsedimentary Dachsteinkalk-blocks which slid into the basin and mark a phase of extreme high subsidence. The blocks are overlain by thin, grey and red liassic limestones with a hardground and manganese horizon on top. At places hardground and manganese horizon directly rest on top of the blocks and debris flows. The limestones of the slope facies contain a rich and interesting holothurian fauna, which differs significantly from that of the German Lias. Among the numerous holothurian sclerites there are some stratigraphically important and new species like Theelia liassica MOSTLER, Theelia multiundulata MOSTLER (Upper Hettangian-Lower Pliensbachian), Theelia loferensis MOSTLER (Pliensbachian) und Neomicroanlyx ingridae MOSTLER (Lower Toarcian). Laterally the slope facies interfingers with and is overlain by sediments of the Allgäu Formation, which also contains a manganese mineralization. Apart from the scarp faults the Liassic sequence is developed in a different facies: Dachsteinkalk is overlain by a thin sequence of red and grey, nodular cherty limestones, which upward grade into well bedded cherty limestones and into sediments of the Allgäu Formation. Within the sedimentary sequence of the basin manganese mineralisations occur in two different stratigraphic horizons: A manganese mineralization together with the hardground on top of the Dachsteinkalk-blocks and debris flows and overlying condensed limestones (Lower Toarcian), and a stratiform manganese mineralization within the Allgäu Formation (Aalenian-Bajocian). This stratiform mineralization should not be mixed up with manganese nodule mineralizations which are very common in the deep sea environment. Three different orefacies types have been recognized. Cu-, Ba- and SiO2 -content of the manganese ores and the occurring manganese ore sludges indicate a local source from hydrothermal solutions which ascended along a deep fault system.位于奥地利萨尔茨堡州洛弗尔东南的魏斯巴赫-迪施巴赫一带，地处施泰讷迈尔（Steinernes Meer）西缘，隶属于北石灰阿尔卑斯山（Northern Calcareous Alps）区域，此处出露了一套侏罗纪本地走滑拉分盆地的沉积序列。该盆地形成于赫塘期（Hettangian，莱阿斯期（Lias）），沿东西向左旋走滑断裂发育，具有半地堑（halfgraben）构造特征，盆地充填物复杂且相带分布不对称。沿部分仍清晰出露的陡坡断裂，沉积了多种类型的块体流（mass flows）。在盆地远端区域，发育含大量浊积岩（turbidite）与碎屑流（debris flow）夹层的红色莱阿斯期灰岩，即魏斯巴赫组（Weissbach Formation）。这套斜坡沉积之上覆有厚达数百米的同沉积（synsedimentary）达赫施泰因灰岩（Dachsteinkalk）块体，这些块体滑入盆地，代表了一次极端快速沉降阶段。灰岩块体之上又覆有薄层灰色与红色莱阿斯期灰岩，顶部发育硬底层（hardground）与锰质层（manganese horizon）。部分区域中，硬底层与锰质层直接覆于灰岩块体及碎屑流沉积之上。斜坡相灰岩中产出丰富且极具研究价值的海参类（holothurian）动物群，其组合特征与德国莱阿斯期动物群存在显著差异。在大量海参骨片（sclerites）化石中，发现了若干具有重要地层学意义的新物种，包括Theelia liassica MOSTLER、Theelia multiundulata MOSTLER（赫塘期晚期—普林斯巴赫期早期）、Theelia loferensis MOSTLER（普林斯巴赫期）以及Neomicroanlyx ingridae MOSTLER（托阿尔期早期）。斜坡相在侧向上与阿尔高组（Allgäu Formation）沉积交错互层，并被其覆盖，阿尔高组同样发育锰矿化作用。除陡坡断裂带外，莱阿斯期序列还发育另一套相组合：达赫施泰因灰岩之上覆有薄层红色、灰色结核状燧石灰岩，向上逐渐过渡为层理清晰的燧石灰岩，并最终过渡为阿尔高组沉积。该盆地沉积序列中，锰矿化作用发育于两套不同的地层单元内：一套为赋存于达赫施泰因灰岩块体、碎屑流沉积顶部及上覆凝缩灰岩中的锰矿化（对应下托阿尔阶）；另一套为阿尔高组内的层状（stratiform）锰矿化（对应阿伦阶—巴柔阶）。需注意，此类层状锰矿化不应与深海环境中极为常见的锰结核矿化相混淆。目前已识别出三种不同的矿石相（orefacies）类型。锰矿石及伴生锰矿泥的铜、钡、二氧化硅含量特征表明，其物质来源为沿深断裂系统上涌的热液流体（hydrothermal solutions）。