The core of borehole 1209/78 west of Doberlug–Kirchhain and south of Herzberg in the Torgau–Doberlug Syncline records an atypical lower part of the Tröbitz Formation with thin limestone horizons. These limestone layers include the remains of a low to moderately diverse fauna with the trilobites Protolenus ( Hupeolenus ) bergstroemi n. sp., Cambrunicornia saxonica n. sp., Ornamentaspis ? aff. todraensis Geyer 1990a , Calodiscus ? n. sp., the remains of two undetermined olenelloid? and paradoxidid? species, at least two brachiopods ( Trematobolus , undetermined acrotretoid), and one hyolith. The fauna clearly suggests a position in the lower Agdzian stage of the West Gondwana chronostratigraphic scheme and correlation with the lowermost to lower Middle Cambrian strata in regions such as the Moroccan Atlas ranges and northern Spain, so the assemblages represent the oldest Middle Cambrian fauna known from the Saxothuringian domain and reconfirm the palaeogeographic position in the Perigondwanan segment. The lithological differences of the fossiliferous cores from those of the typical Tröbitz Formation and the recorded high-energy conditions indicate high-frequency sea-level changes suggesting that this part of the succession may be a late stage of the subglobally recognizable eustatic sea-level fluctuations at the traditional Lower–Middle Cambrian boundary interval.

The steep biogeochemical gradients near deep sea hydrothermal vents provide various niches for microbial life. Here we present biosignatures of such organisms enclosed in a modern and an ancient hydrothermal sulfide deposit (Turtle Pits, Mid-Atlantic Ridge, Recent; Yaman Kasy, Russia, Silurian). In the modern sulfide we found high amounts of specific bacterial and archaeal biomarkers with δ13C values between −8 and −37‰ VPDB. Our data indicate the presence of thermophilic members of the autotrophic Aquificales using the reductive tricarboxylic acid (rTCA) cycle as well as of methanogenic and chemolithoheterotrophic Archaea. In the ancient sample, most potential biomarkers of thermophiles were obscured by compounds derived from allochthonous organic matter (OM), except for an acyclic C40 biphytane and its C39 breakdown product. Both samples contained high amounts of unresolved complex mixtures (UCM) of hydrocarbons. Apparently, OM in the sulfides had to withstand high thermal stress, indicated by highly mature hopanes, steranes, and cheilanthanes with up to 41 carbon atoms.

Ultramafic–mafic- and ultramafic-hosted Cu (Co, Ni, Au) volcanogenic massive sulfide (VMS) deposits from ophiolite complexes of the Main Uralian Fault, Southern Urals, are associated with island arc-type igneous rocks. Trace element analyses show that these rocks are geochemically analogous to Early Devonian boninitic and island arc tholeiitic rocks found at the base of the adjacent Magnitogorsk volcanic arc system, while they are distinguished both from earlier, pre-subduction volcanic rocks and from later volcanic products that were erupted in progressively more internal arc settings. The correlation between the sulfide host-rocks and the earliest volcanic units of the Magnitogorsk arc suggests a connection between VMS formation and infant subduction-driven intraoceanic magmatism.

In the southern Uralides, Permian magmatism, tectonism and metamorphism concentrate in the East Uralian Zone, such that this zone provides the key for understanding of the late phase of the Uralian orogeny. Carboniferous distal marine sediments and lenses of amphibolite–serpentinite associations show that the lithospheric precursor of the East Uralian Zone was largely oceanic. In the Latest Carboniferous, the Kazakhstanides collided with the Uralides, but relics of the oceanic basin between both units were conserved and accommodated a large part of Permian deformation. Structural data provide evidence that a NW-directed plate convergence was partitioned in W-directed compression and N-directed strike-slip. Additionally, they show that granitic melts, which had formed in the thickened crust of the Uralides, migrated eastward into the strike-slip belt of the East Uralian Zone. Also the exhumation of the plutonic rocks occurred eastward, oblique to the direction of regional extension, indicating that upper crust and lower crust deformed mainly decoupled from one another. We suggest that the emplacement of the granite–gneiss complexes contributed significantly to the consolidation of the orogenic crust in the eastern Urals.

The Urals are characterized by a depression of the Moho to a depth of 57 km. This structure is interpreted as a relic orogenic root, which has been conserved because no significant post-collisional processes occurred. However, there is evidence that voluminous post-collisional magmatism affected the lower crust. In this paper, we use thermal finite element models to quantify the influence of the post-collisional magmatism on the stabilization of the root. We show that at least 70% of the heat producing elements migrated in granitic melts from the lower crust to the upper crust. As a result the crustal heat flow reduced and the lithosphere could stabilize at a thickness of 180 km. Furthermore, we propose that a granulite metamorphic event during the thermal relaxation of the collision zone prevented the 57 km thick crust from delamination. These results strongly indicate that post-collisional processes were necessary for the stabilization of the Uralian crust and lithosphere. (c) 2008 Elsevier B.V. All rights reserved.

Sediment provenances and magmatic events of Late Neoproterozoic (Ediacaran) and Cambro-Ordovician rock complexes from the Saxo-Thuringian zone are constrained by new laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating of detrital zircons from five sandstones and magmatic zircons from an ignimbrite and one tuffite. These geochronological results in combination with the analysis of the plate-tectonic setting constrained from field observations, sedimentological and geochemical data, and trends of the basin development are used to reconstruct Cadomian orogenic processes during the Late Neoproterozoic and the earliest Cambrian. A continuum between Cadomian orogenesis and the opening of the Rheic Ocean in the Cambro-Ordovician is supported by the data set.In our model, the early stage of the Cadomian evolution is characterized by a Cordilleran-type continental magmatic arc, which was established at the periphery of the West African craton between ca. 650 and 600 Ma. Subsequently, at ca. 590-560 Ma, a back-arc basin was formed behind the Cadomian magmatic arc. The back-arc basin was closed between ca. 545 and 540 Ma, leading to the development of a short-lived Cadomian retroarc basin. Subsequently, a mid-oceanic ridge was subducted underneath the Cadomian orogen. Slab break-off of the subducted oceanic plate resulted in increased heat flow, leading to voluminous magmatic and anatectic events that culminated at ca. 540 Ma. Oblique incision of the oceanic ridge into the continent caused the formation of rift basins during the Lower to Middle Cambrian. This process continued from the Middle to Upper Cambrian, finally caused the opening of the Rheic Ocean in the Lower Ordovician.

The most complete Ediacaran (terminal Neoproterozoic) to Early Cambrian record in the Saxo-Thuringian Zone is provided by the Cadomian-deformed Ediacaran Rothstein Formation and the unconformably overlying Early Cambrian Zwethau Formation in the Torgau-Doberlug Syncline (TDS). Conglomerates and greywackes of the marine Rothstein Formation are of continental magmatic arc provenance and record detrital zircon SHRIMP ages that indicate a Late Cryogenian to Early Ediacaran (700-580 Ma) age for the arc source and its emplacement into Palaeoproterozoic (2000 Ma) crust. Tuffaceous intercalations record extrabasinal eruptions of evolved calc-alkaline lavas that point to ongoing Cadomian continental arc magmatism. SHRIMP zircon ages from a tuffaceous layer date this volcanic activity and the formation's deposition as Late Ediacaran (566 10 Ma). Close correlation in provenance and age to other Ediacaran units of the Saxo-Thuringian Zone points to a common palaeogeographic setting in the Avalonian-Cadomian belt. Detrital and inherited zircon ages, and Nd-isotopic ratios from these Ediacaran siliciclastic rocks suggest a position on the active margin of Gondwana near the West African craton.The Early Cambrian Zwethau Formation records the erosion of the underlying Ediacaran rocks followed by the successive evolution of: (i) a carbonate-dominated subtidal ramp with calcimicrobial-archaeocyathan buildups, (ii) a shallow-subtidal to intertidal mixed ramp with peritidal sediments, and oolite shoal complexes, and (iii) a more siliciclastic depositional environment. Calcimicrobial-archaeocyathan buildups, oolite shoals, and sulfate nodules in intertidal sediments indicate warm, and to semi-arid climatic conditions and a palaeogeographic setting in equatorial to sub-equatorial latitudes. Archaeocyaths, the trilobite taxon Dolerolichia, and the sedimentary facies assemblages compare closely to those of the "Mediterranean" Early Cambrian, constraining the palaeogeographic setting to the European, sub-equatorial, western Gondwana shelf realm. Archaeocyaths record a mid-Early Cambrian (Middle Issendalenian/Ovetian) age, making these the oldest Cambrian sediments in both the Saxo-Thuringian Zone and the Bohemian Massif. The Middle Cambrian lithological and palaeontological records of the TDS closely resemble those of the Frankenwald area of the Saxo-Thuringian Zone as well as those of other fragments of the western Gondwana shelf in Spain, Morocco, and Bohemia.Archaeocyaths, Early Cambrian trilobites, and correlations with Morocco suggest Cambrian deposition commenced at ca. 520 Ma, such that the Cadomian unconformity represents a time gap of about 35-55 Ma (latest Ediacaran to Early Lower Cambrian). This gap, which is related to the Cadomian orogeny and so common to all areas of the Cadomian belt, obscures some of palaeobiological, palaeogeographic, and climatic change that marks the Precambrian-Cambrian transition. (c) 2006 Elsevier B.V. All rights reserved.

VMS deposits of the South Urals developed within the evolving Urals palaco-ocean between Silurian and Late Devonian times. Arc-continent collision between Baltica and the Magnitogorsk Zone (arc) in the south-western Urals effectively terminated submarine volcanism in the Magnitogorsk Zone with which the bulk of the VMS deposits are associated. The majority of the Urals VMS deposits formed within volcanic-dominated sequences in deep seawater settings. Preservation of macro and micro vent fauna in the sulphide bodies is both testament to the seafloor setting for much of the sulphides but also the exceptional degree of preservation and lack of metamorphic overprint of the deposits and host rocks. The deposits in the Urals have previously been classified in terms of tectonic setting, host rock associations and metal ratios in line with recent tectono-stratigraphic classifications. In addition to these broad classes, it is clear that in a number of the Urals settings, an evolution of the host volcanic stratigraphy is accompanied by an associated change in the metal ratios of the VMS deposits, a situation previously discussed, for example, in the Noranda district of Canada.Two key structural settings are implicated in the South Urals. The first is seen in a preserved marginal allochthon west of the Main Urals Fault where early are tholeiites host Cu-Zn mineralization in deposits including Yaman Kasy, which is host to the oldest macro vent fauna assembly known to science. The second tectonic setting for the South Urals VMS is the Magnitogorsk arc where study has highlighted the presence of a preserved early forearc assemblage, are tholeiite to calc-alkaline sequences and rifted arc bimodal tholeiite sequences. The boninitc rocks of the forearc host Cu-(Zn) and Cu-Co VMS deposits, the latter hosted in fragments within the Main Urals Fault Zone (MUFZ) which marks the line of are-continent collision in Late Devonian times. The arc tholeiites host Cu-Zn deposits with an evolution to more calc-alkaline felsic volcanic sequences matched with a change to Zn-Pb-Cu polymetallic deposits, often gold-rich. Large rifts in the arc sequence are filled by thick bimodal tholeiite sequences, themselves often showing an evolution to a more calc-alkaline nature. These thick bimodal sequences are host to the largest of the Cu-Zn VMS deposits.The exceptional degree of preservation in the Urals has permitted the identification of early seafloor elastic and hydrolytic modification (here termed halmyrolysis sensu lato) to the sulphide assemblages prior to diagenesis and this results in large-scale modification to the primary VMS body, resulting in distinctive morphological and mineralogical sub-types of sulphide body superimposed upon the tectonic association classification.It is proposed that a better classification of seafloor VMS systems is thus achievable using a three stage classification based on (a) tectonic (hence bulk volcanic chemistry) association, (b) local volcanic chemical evolution within a single edifice and (c) seafloor reworking and halmyrolysis. (c) 2005 Elsevier B.V All rights reserved.

Zircons from two Neoproterozoic tuff layers from the northeastern Saxothuringian Zone were studied by SHRIMP ion microprobe analysis. The tuff layers are from the Rothstein Formation (Doberlug Syncline) and the Lusatian Main Group (Lusatian Anticline) with both units representing fragments of Cadomian marginal basins. Concordant Pb-206/U-238 ages (95 % confidence) of 566 +/- 10 Ma (Rothstein Formation) and 574 +/- 8 Ma (Lusatian Main Group) for the tuff-derived zircons reveal an Upper Vendian age not only for the volcanic activity in the continental are source of the tuffs and associated terrigenous sediments, but also for the contemporaneous depositional processes in the marginal basins. Dating of detrital zircons from a Neoproterozoic graywacke (Rothstein Formation) suggest the occurrence of earlier Cadomian magmatism and a Paleoproterozoic crustal component in the source area.

Abstract Saxo-Thuringia is classified as a tectonostratigraphic terrane belonging to the Armorican Terrane Collage (Cadomia). As a former part of the Avalonian-Cadomian Orogenic Belt, it became (after Cadomian orogenic events, rift-related Cambro-Ordovician geodynamic processes and a northward drift within Late Ordovician to Early Silurian times), during Late Devonian to Early Carboniferous continent-continent collision, a part of the Central European Variscides. By making use of single zircon geochronology, geochemistry and basin analysis, geological processes were reconstructed from latest Neoproterozoic to Ordovician time: (1) 660–540 Ma: subduction, back-arc sedimentation and tectonomagmatic activity in a Cadomian continental island-arc setting marginal to Gondwana; (2) 540 Ma: obduction and deformation of the island arc and marginal basins; (3) 540–530 Ma: widespread plutonism related to the obduction-related Cadomian heating event and crustal extension; (4) 530–500 Ma: transform margin regime connected with strike-slip generated formation of Early to Mid-Cambrian pull-apart basins; (5) 500–490 Ma: Late Cambrian uplift and formation of a chemical weathering crust; (6) 490–470 Ma: Ordovician rift setting with related sedimentation regime and intense igneous activity; (7) 440–435 Ma: division from Gondwana and start of northward drift. The West African and the Amazonian Cratons of Gondwana, as well as parts of Brittany, were singled out by a study of inherited and detrital zircons as potential source areas in the hinterland of Saxo-Thuringia.

This paper deals with compression fossils of two Late Carboniferous herbaceous lycopods. New fertile material of Selaginellites gutbieri (Goppert, 1837) Kidston, 1911 was collected from its type locality Oelsnitz (Westphalian D; Erzgebirge-Basin). The three-dimensionally preserved strobili clearly show micro- and megasporangia. In addition a sterile large-leaved form is described from the Westphalian D of the Saar Basin.