Halle-Exkursion 2010 des Geowissenschaftlichen Vereins Neubrandenburg e.V.

Die Herbstexkursion der Sammlergruppe führte 21 Mitglieder und Freunde des Geowissenschaftlichen Vereins Neubrandenburg vom 30. September bis 3. Oktober 2010 in die Geologie von Halle/Saale und Umgebung. Im Stadtgebiet selbst besichtigten wir neben den Baudenkmälern vor allem Zeugnisse der Salzsiedekunst, das Geiseltalmuseum sowie Aufschlüsse rhyolithischer Gesteine des halleschen Vulkanitkomplexes (HVK). Exkursionsziele in der nördlichen Umgebung waren Zeugnisse des historischen und aktuellen Bergbaus auf Steinkohle, Kupferschiefer und Hartgestein.researc

Germanium and precious metals (Ag–Au–Pt–Pd) at low temperature: the hematite–carbonate–selenide vein system of Tilkerode, Harz Mountains, Germany

At the historical Eskeborner Berg underground workings at Tilkerode (Eastern Harz Mountains, Germany), Fe was mined from a carbonate–hematite vein system that was locally enriched in selenide minerals. Clausthalite [PbSe] was the most abundant selenide mineral in a carbonate matrix with laths of specular hematite. To date, the selenide-bearing carbonate–hematite vein system at Tilkerode has not been geochemically investigated. Here, we present the first whole-rock chemical data for a wide suite of trace elements. The following metals are enriched relative to bulk continental crust (orders of magnitude in parentheses): Se (>105), Hg (>104), Ag and Pb (103), Au, Bi, Pt, Ge, Te, Pd and Cd (102). Samples from Tilkerode have up to 2640 ppm Ag, 338 ppm Ge, 1560 ppb Au, 970 ppb Pt and 365 ppb Pd, with Pt/Pd > 1, and a significant positive correlation of Ge vs. (Pd+Pt). The selenide mineralisation took place below 112 °C, the maximum temperature stability of umangite [Cu3Se2]. Our data indicate there is potential for prospecting Ge and precious metals in low-temperature vein systems

Zur Oberkarbonflora in der Bohrung Jessen 1Z/62 bei Wittenberg (Sachsen-Anhalt)

Die Nachuntersuchung der Bohrung Jessen 1 Z/62 im Rahmen der Tiefenkartierung im südöstlichen Sachsen-Anhalt ergab, dass die fossilführenden Schichten zwischen Teufe 1050,40 m und 1202,0 m in das höhere Westfal D eingestuft werden müssen. Damit wird eine Neudefinition der Roitzsch-Formation notwendig. Floristisch kann Stefan nicht belegt werden, ist aber aus lithologischer Sicht höchst wahrscheinlich. Eine paläobotanische Beziehung zum Zwickauer Becken liegt nahe. Paralische Einflüsse in diesem Teilbecken des Saale-Senkungsgebietes zwischen Wittenberg und Torgau sind nicht belegbar. Die Obergrenze des Westfals dürfte bereits bei 1050,40 m und nicht erst bei 1065,30 m Teufe liegen, d.h. erstmalig konnte (sekundär?) rotgefärbtes Westfal D im Bereich der Saale-Senke nachgewiesen werden. The sediments of the drilling Jessen 1Z/62 between 1050,40 m and 1202,0 m are of Westphalian D age. Therefore it is necessary to redefine the so called Roitzsch formation. Stephanian is not verified by plant fossils but is most likely by lithological reasons. Palaeontological relationships to the Zwickau Basin are obvious; therefore paralic influence is unverifiable in this part of the Saale depression between Wittenberg and Torgau. The upper boundary of the Westphalian is located by 1050,40 m, while former authors were opting for the depth of 1065,30 m. So at the first time reddish (secondary coloration) Westphalian D is demonstrated around the Saale depression

Der Erstnachweis von Namur A in der Umgebung von Prettin: Ein Beitrag zur Tiefenkartierung von Sachsen- Anhalt

Die lithologische und paläontologische (paläobotanische) Bewertung von Bohrkernen einschließlich deren geophysikalischen Messergebnissen im Gebiet von Prettin bei Torgau ergab eine stratigraphische Einstufung in das Namur Ae2 (Arnsbergium). Dieses Namur-Alter widerspricht den bisherigen strukturellen Vorstellungen eines Unterrotliegend-Grabens, die damit nicht aufrecht zu erhalten sind. In diesem Raum erstmals nachgewiesene Konglomerate an der Basis des Namurs führen Gerölle, die vermutlich von einem im Liegenden erbohrten Ignimbrit stammen.Lithological and palaeobotanical assessments – including also geophysical measurements – from boreholes in the vicinity of Prettin near Torgau (Sachsen-Anhalt, Germany) indicate a Lower Carboniferous i.e. Namurian Ae2 (Arnsbergium) age. This Namurian age contradicts previous concepts involving the tectonic structure of a rift of Asselian age hypothesized in former publications. Conglomerates from the basis of the Namurian discovered here for the first time have pebbles probably originate from the underlying ignimbrite. This offers important hints about the age of ignimbrites developed in the core

Late Palaeozoic red beds elucidate fluvial architectures preserving large woody debris in the seasonal tropics of central Pangaea

Fluvial red beds containing anatomically preserved large woody debris shed new light on seasonally dry biomes of the Pennsylvanian–Permian transition and elucidate the concurrence of river depositional systems and vegetation. As a result, the occurrence, distribution and preservation of petrified large woody debris accumulations are considered crucial to understanding the role of arborescent vegetation in shaping fluvial environments. This study reports sizeable silicified trunks and corresponding fluvial architectures from the uppermost Pennsylvanian (upper Gzhelian) Siebigerode Formation (Kyffhäuser, central Germany). The origin, taphonomy and depositional environment of the fossil woods are elucidated by using a multidisciplinary approach including geological mapping, lithofacies analysis, sediment petrography, wood anatomical studies and microstructure analyses. Results reflect the gradual burial of a gentle basement elevation by sand-bed to gravel-bed braided rivers at the north-western margin of the perimontane Saale Basin. Facies architectures resulted from a complex interplay of syndepositional tectonics, repeated palaeorelief rejuvenation, high-frequency channel avulsion, seasonally dry climate and woody debris–sediment interactions. The alluvial influx and cut-bank erosion recruited trunks from adjacent semi-riparian slope habitats vegetated by up to 40 m tall cordaitaleans and conifers. High discharge in wide braids facilitated uncongested transport of large woody debris. Trunk entombment and initial preservation resulted from grounding on barforms, anchoring by attached roots and subsequent burial. The post-depositional two-phase silicification was influenced by hydrothermal hematite mineralization and determined a selective wood preservation pattern known as ‘pointstone’. Large woody debris-induced sedimentary structures (‘LWDISS’) are introduced as a class of sediment structures formed by the biogenic impact on terrestrial deposition

An andesitic sill complex in the Southern Permian Basin: volcanogenetic model and stratigraphic implications

Subvolcanic intrusions are highly variable in shape and structure, and occur in nearly all parts of the upper crust, as a result of extensive volcanic activity. Processes of subvolcanics interacting with the host rock are insufficiently understood, as they are rarely exposed. In the southernmost part of the Flechtingen-Altmark Subprovince, (sub)volcanic rocks of the Flechtingen Volcanic Complex (FVC) are exposed in several quarries. It is built up of silicic tuffs, ignimbrites and lava flows, but also of intermediate lavas and extended sill sheets. Additionally, major granitic intrusions exposed by drillings are associated with the FVC. In the Mammendorf quarry, a sill intruded in between lithified turbiditic series of early Carboniferous (Visean–Serphukovian) age at the base, and widely consolidated volcanoclastic deposits of late Carboniferous (late Pennsylvanian) age at the top. Various magma-host rock interactions were found indicating brittle and ductile deformation patterns occurring at the basal contact, and secondary fluidal mixing predominantly occurring at the top contact, most probably caused by fluids accompanying the intruding magma. We present an extended volcanogenetic model for the FVC. Volcanic activity initiated at 302 ± 3 Ma with fallout deposits represented by mostly re-deposited silicic ashfall deposits of the Flechtingen Formation, and cumulated in depositing major ignimbrite series, most likely forming a caldera. Later, the sills intruded at the rheological boundary of the lithified Mississippian turbiditic series and the partly consolidated volcanoclastic series. Finally, major granitic intrusions emplaced in the basement rocks at around 298 ± 4 Ma. The study contributes to clarify stratigraphic constraints of late Carboniferous to early Permian continental deposits and sheds light on stratigraphy of significant late Paleozoic volcanic deposits of the Flechtingen-Altmark Subprovince in the Southern Permian Basin