Saar-Nahe Basin Research Articles

Ökostratigraphische Bioevents im Grenzbereich Stephanium/ Autunium (höchstes Karbon) des Saar-Nahe-Beckens (SW-Deutschland) und benachbarter Gebiete

Ökostratigraphische Bioevents im Grenzbereich Stephanium/ Autunium (höchstes Karbon) des Saar-Nahe-Beckens (SW-Deutschland) und benachbarter Gebiete

Heat flow evolution, subsidence and erosion in the Rheno-Hercynian orogenic wedge of central Europe

Abstract Numerical, thermal and rheological modelling techniques are applied to unravel the basin-forming processes and the heat flow and burial history of the Rheno-Hercynian fold belt (Rhenish Massif), the adjacent Subvariscan foreland (Ruhr Basin), and the intramontane Saar-Nahe Basin. Thermal history and crustal architecture in the study areas were affected mainly by the Variscan Orogeny during late Palaeozoic times. Calibration of the simulated thermal histories is primarily based on vitrinite reflectance and fission-track data. Mechanical modelling reveals average β values of 1.7, reaching a maximum of 2.4 in the central basin (Mosel Graben) and at the transition to the Giessen Ocean to the south during Early Devonian rifting. This stage was associated with tholeitic magmatism and an elevated heat flow of up to 110 mW m −2 , preserved in weakly overprinted syn-rift sediments. Average basal heat flow during maximum burial at the end of the Carboniferous period (i.e. the end of crustal shortening) was between 50 and 70 mW m −2 with a slight decrease from the Subvarian foreland basins towards the Rheno-Hercynian in the south. The values suggest average crustal thicknesses of between 32 and 36 km during late Carboniferous time. For the Saar-Nahe Basin, values between 50 and 75 mW/m 2 represent the thermal regime in the upper crust during the late Stephanian and early Permian time. Estimated eroded thicknesses of Palaeozoic sediments vary between 2500 m in the northern and central Ruhr Basin and more than 6000 m in the Osteifel and the Siegen Anticline within the Rheno-Hercynian, and between 1800 and 3600 m in the Saar-Nahe Basin. Fission-track data provide evidence for significant reheating during the Mesozoic era within the entire study area. This phase of heating, probably linked to North Atlantic rifting, coincides with post-Variscan ore formation and with major tectono-magmatic events in central Europe.

Turbidite basin and mass dynamics related to orogenic wedge growth; the Rheno-Hercynian case

Abstract Investigation of the Rheno-Hercynian Turbidite Basin suggests an interrelation between orogenic wedge migration and changes of the basin architecture, facies types and progradation rates of turbidite systems. The orogenic wedge was built dominantly by the Mid-German Crystalline Rise and accreted older parts of the Rheno-Hercynian Turbidite Basin. Turbidite sequences seem to have developed in stepwise prograding sub-basins. They show systematic trends of widely correlative (tens of kilometres) large-scale cycles that show an upward transition from coarse-grained clastics to highly diluted mud turbidites with highstand shedding of carbonates. These observations suggest the existence of accommodation cycles on the assumed shelf along the Mid-German Crystalline Rise. Exposure of the shelf above sea level was associated with bypass and transport of coarse-grained clastics into the basin, whereas flooding is thought to have caused storage of clastic deposits on the shelf and the simultaneous deposition of mud turbidites in the basin. Accommodation cycles, estimated to reflect an average duration of 10 5 –10 6 a, were probably related to cyclic changes of underthrusting in the internal parts of the orogenic wedge with concomitant uplift. The lifetime and onset of new sub-basins, of the order of a few million years, may show stages of imbricate fan formation. A pattern of major change in sedimentation rates, basin geometry and subsidence style of the Rheno-Hercynian Turbidite Basin and the Sub-Variscan Molasse Basin was interpreted to reflect the different change in crustal strength. This occurred because the hinge line between previously rifted and unrifted crust was overrun during wedge progradation. Numerical mass balance that compares exhumed and intra-basinal masses of the Rheno-Hercynian Turbidite Basin, including the proportional fill of the Sub-Variscan Molasse Basin and the Saar-Nahe Basin, indicates a significant lack of sediment mass (i.e. more than one-third of the exhumed masses). In this estimate, syn- to post-depositional truncation was included. As extension in the internal parts of the orogenic wedge has only a minor role, the above deficit is probably related to subduction of sediment during the early stages of convergence.

Volcanic rocks as discriminants in evaluating tectonic versus climatic control on depositional sequences, Permo-Carboniferous continental Saar-Nahe Basin

The third- and fourth-order sequential arrangement of continental sedimentary strata in the Permo-Carboniferous Saar–Nahe Basin preserves a detailed record of contemporaneous faulting and volcanism. Transgressive lacustrine facies of the Upper Carboniferous coincide with the stratigraphic position of extrabasinally derived pyroclastic fallout layers and features of synsedimentary tectonism such as unconformities, thickness and facies changes across faults, and seismogenic deformation structures. The tectonic imprint on fourth-order cycle initiation is further documented by abrupt vertical facies transitions during lake transgression, implying rapid and episodic rather than gradual basin subsidence. This interaction becomes much more pronounced within the fluvially dominated Lower Permian, when tectonism controlled both the ascent of large volumes of magma within the basin as well as episodic enlargement of accommodation space and depositional area. Major extrusive volcanic units are preferentially associated with sequences recording transgression that are only preserved in fault-bounded hanging wall traps starved from clastic sediment input. It is suggested that the stratigraphic position of pyroclastic fallout within the sequential framework of basins elsewhere, provides an important analytical tool for the identification of contemporaneous tectonic events and as such form a discriminant between purely climatically induced Milankovitch band cycles versus those involving a tectonic control.

Geochemistry and isotope systematics of calc-alkaline volcanic rocks from the Saar-Nahe basin (SW Germany) – implications for Late-Variscan orogenic development

Late Carboniferous (300–290 Ma) calc-alkaline basalts, andesites, and rhyolites typical of volcanic arc settings occur in the intermontane Saar-Nahe basin (SW Germany) within the Variscan orogenic belt. The volcanic rock suite was emplaced under a regime of tensional tectonics during orogenic collapse and its origin has been explained by melting of mantle and crust in the course of limited lithospheric rifting. We report major, trace and rare-earth-element data (REE), and Nd-Pb-Sr-O isotope ratios for a representative sample suite, which are fully consistent with an origin closely related to plate subduction. Major and trace element data define continuous melt differentiation trends from a precursor basaltic magma involving fractional crystallization of olivine, pyroxene, plagioclase, and magnetite typical of magma evolution in a volcanic arc. This finding precludes an origin of the andesitic compositions by mixing of mafic and felsic melts as can be expected in anorogenic settings. The mafic samples have high Mg numbers (Mg# = 65–73), and high Cr (up to 330 ppm) and Ni (up to 200 ppm) contents indicating derivation from a primitive parental melt that was formed in equilibrium with mantle peridotite. We interpret the geochemical characteristics of the near-primary basalts as reflecting their mantle source. The volcanic rocks are characterized by enrichment in the large ion lithophile elements (LILE), negative Nb and Ti, and positive Pb anomalies relative to the neighboring REE, suggesting melting of a subduction-modified mantle. Initial Nd values of −0.7 to −4.6, Pb, and 87Sr/86Sr(t) isotope ratios for mafic and felsic volcanics are similar and indicate partial melting of an isotopically heterogeneous and enriched mantle reservoir. The enrichment in incompatible trace elements and radiogenic isotopes of a precursor depleted mantle may be attributed to addition of an old sedimentary component. The geochemical characteristics of the Saar-Nahe volcanic rocks are distinct from typical post-collisional rock suites and they may be interpreted as geochemical evidence for ongoing plate subduction at the margin of the Variscan orogenic belt not obvious from the regional geologic context.

Abstract: 3D Modelling of Burial and Temperature History in the Permo-Carboniferous Saar-Nahe Basin (SW-Germany) 

Abstract: 3D Modelling of Burial and Temperature History in the Permo-Carboniferous Saar-Nahe Basin (SW-Germany) 

Formation and sediment fill of the Saar-Nahe Basin (Permo-Carboniferous, Germany)

Formation and sediment fill of the Saar-Nahe Basin (Permo-Carboniferous, Germany)

Facies architecture variations and seismogenic structures in the Carboniferous–Permian Saar–Nahe Basin (SW Germany): evidence for extension-related transfer fault activity

Sedimentary and volcanic strata in the late-orogenic intermontane Saar–Nahe Basin preserve a record of sedimentary responses to motion on contemporaneously active faults. Studies of such deposits can constrain both concepts for lateral and vertical sedimentary facies development and geometric and kinematic models of intrabasinal extension. During Carboniferous–Permian syn-rift development, the Saar–Nahe Basin underwent a marked intrabasinal segmentation generated by the offsets of longitudinal normal faults and dextral (oblique) strike-slip faults which were developed perpendicular to the SW–NE basin elongation. The latter are interpreted as transtensional transfer faults which compartmentalized the basin into segments of differing structural style, bed thickness and facies development. The fault zones themselves bound an assemblage of variously sized uplifted and downthrown blocks showing variable magnitudes and senses of displacement. Their activities are recorded by the contrasting depositional histories of tephrostratigraphically constrained sedimentary units occupying footwall and hanging wall block positions during basin filling. The influence of faults on the depositional system is seen in their effect as topographic barriers, thus restricting free dispersal and mixing of sediment. Particular sedimentary facies, such as coals and biogenic limestones, are confined to the immediate vicinity of the fault zones, indicating the isolation of sediment-starved areas near downthrown hanging walls. Other fault-generated depressions acted as depositional traps favouring considerable accumulations of basaltic lavas, volcaniclastic mass flows and fluvial channel deposits. In contrast, uplifted footwalls are characterized by the formation of unconformities and pedogenic features. The abundance of syn-tectonic deformation structures such as sediment-filled fissures, intraformational breccias, series of micro-faults, clastic dykes and other water-escape features within syn-rift strata and their distinct spatial linkage to fault zones implies considerable seismically triggered processes associated with faulting. The combined occurrence of abrupt variations in facies architecture across faults and seismotectonic structures suggests that the basin subsidence history involved a series of events rather than gradual change.

New discoveries of xenacanth sharks from the Late Carboniferous of Spain (Puertollano Basin) and Early Permian of Germany (Saar-Nahe Basin): Implications for the phylogeny of xenacanthiform and anacanthous sharks

New discoveries of xenacanth sharks from the Late Carboniferous of Spain (Puertollano Basin) and Early Permian of Germany (Saar-Nahe Basin): Implications for the phylogeny of xenacanthiform and anacanthous sharks

Dermal skeletal elements ofLissodus (Chondrichthyes: Hybodontoidea) from the Lower Permian of the Saar-Nahe-Basin

The appearance ofLissodus sp. NM in the Rotliegend of the NE Saar-Nahe basin extends the knowledge of this genus of the superfamily Hybodontoidea. Additional to some isolated teeth, which represent the most important diagnostic feature, many scales and a spine fragment could be described from the Niedermoschel locality. The functional morphology of the scales will be discussed on the basis of wellknown results from Recent sharks.

Borosilicate alteration associated with U-Mo-Zn and Ag-Au-Zn deposits in volcanic rocks

Borosilicate alteration is developed in many uranium-molybdenum-zinc deposits in volcanic piles such as at Novazza (Italy), Novoveska Huta (Slovakia), Ben Lomond (Queensland, Australia), the Saar-Nahe basin (Germany), the Shengyuan district (China), and at many deposits in Russia. These uranium-molybdenum-zinc deposits share similar styles of alteration with silver-gold-zinc deposits in volcanic rocks, like those of the Humboldt Range (Nevada, USA), the Basin district (Montana, USA) and Equity Mine (British Columbia, Canada). In thick volcanic piles, fluid-rock interaction commonly develops under the influence of convective hydrothermal systems. In borosilicate-bearing systems the alteration is characterized by changes in borosilicate mineralogy and chemistry under mesothermal conditions. Zonal distribution of different compositions of tourmaline can be observed including regular increases of alkali deficiency in the X(3a) site from peripheral (chlorite-epidote-prehnite) to internal (sericite and/or pyrophyllite) alteration zones. In the central part of these systems tourmaline is absent and the alteration assemblage is characterized by an andalusitedumortierite-quartz association. Such changes in mineral assemblage are related to an increase in temperature from 250 to 350–400 °C and to decreases in pH and Eh, from the outer toward the inner parts of the hydrothermal system. The zonation of the borosilicate-bearing alteration systems is similar to that of aluminosilicate-bearing hydrothermal systems (muscovite, pyrophyllite, andalusite) developed in volcanic rocks. A kaolinite-alunitejasperoid assemblage is generally associated with the borosilicate alteration, and seems related to a late hydrothermal phase mainly located in graben structures.

Rekonstruktion des Florensprungs an der Westfalian/Stefan-Grenze im Saar-Nahe-Becken über die Analytik von Biomarkern

Rekonstruktion des Florensprungs an der Westfalian/Stefan-Grenze im Saar-Nahe-Becken über die Analytik von Biomarkern

The Permo-Carboniferous Saar-Nahe Basin, south-west Germany and north-east France: basin formation and deformation in a strike-slip regime

The Permo-Carboniferous Saar-Nahe Basin in south-west Germany and north-east France formed at the boundary between the Rhenohercynian and Saxothuringian zones within the Variscan orogen, where non-marine sediments were deposited in a narrow, structurally controlled basin. The basin has an asymmetrical geometry perpendicular to the South Hunsruck Fault. However, there is a lack of growth of the sediment pile into the fault, and isopach maps show the depocentre always located adjacent to the South Hunsruck Fault, but migrating towards the north-east with time. This pattern is typical of a strike-slip basin, indicating that the South Hunsruck Fault was a dextral strike-slip fault during sedimentation. Tectonic subsidence curves indicate that, during the Middle Devonian to Early Carboniferous, the basin subsided due to thermal relaxation of the lithosphere. A change to very rapid subsidence at the start of the Westphalian continued until late in the Autunian. This was due to mechanical subsidence associated with strike-slip movement on the South Hunsruck Fault. Towards the end of subsidence in the Saar-Nahe Basin, the Grenzlager volcanics introduced a thermal pulse into the crust, leading to thermal cooling and relaxation of the lithosphere.

The Permo-Carboniferous Saar-Nahe Basin, south-west Germany and north-east France: basin formation and deformation in a strike-slip regime

The Permo-Carboniferous Saar-Nahe Basin, south-west Germany and north-east France: basin formation and deformation in a strike-slip regime

Aromatized arborane/fernane hydrocarbons as molecular indicators of floral changes in Upper Carboniferous/Lower Permian strata of the Saar-Nahe Basin, southwestern Germany

Thirty-seven coal samples of Upper Carboniferous and Lower Permian age from three boreholes in the Saar-Nahe Basin, Germany, have been studied by organic geochemical and coal petrological methods. The investigations were aimed at the recognition of floral changes in the Upper Carboniferous and Lower Permian strata. The results show that compositional changes in the extracts are only partly caused by variations in coalification. Specific aromatic hydrocarbons appear in Upper Westphalian D coal seams and increase in concentration up to the Rotliegendes. The dominant compound has been identified by mass spectrometry and NMR-spectroscopy as 5-methyl-10-(4-methylpentyl)-des- A-25-norarbora(ferna)-5,7,9-triene (MATH) and always occurs associated with 25-norarbora(ferna)-5,7,9-triene. Both compounds are thought to originate from isoarborinol, fernene-3β-ol, or fernenes. The strongly acidic conditions during deposition of the coals might have induced the 4,5-cleavage combined with a methyl-shift in an arborane/fernane-type pentacyclic precursor yielding the MATH. Based on petrological investigations, palynomorphs related to early Gymnospermopsida such as Pteridospermales and Coniferophytes ( Cordaitales and Coniferales) increased in abundance in the strata beginning with the Upper Westphalian D concomitant with the above mentioned biomarkers. The results suggest the arborane/fernane derivatives originate from the plant communities producing these palynomorphs.

Late orogenic Basin evolution in the Variscan internides: the Saar-Nahe Basin, southwest Germany

The late Variscan evolution of the Saar-Nahe Basin in southwest Germany is closely controlled by the kinematics of the Hunsrück Boundary Fault, which also separates two main tectonostratigraphic units of the Variscides. The Saar-Nahe Basin comprises a half-graben structure, which formed due to extensional reactivation of a Variscan thrust. Between the early Westphalian and late Rotliegend, about 8.5 km of alluvial fan, fluvial and lacustrine sediments accumulated. During the Permo-Carboniferous, W-E oriented extension was accommodated by a system of NW-SE trending transfer faults and orthogonal normal faults. Balanced cross-section construction and subsidence analyses suggest a 35% extension of the previously thickened crust in the late stage of the orogeny. The subsidence analyses show discontinuous depth-dependent extension, with laterally varying extension factors in the crust and mantle. The offset between syn- and post-rift depocentres is explained by a mantle stretching zone, shifted laterally with respect to the area of maximum crustal extension. Finally, a geodynamic model for the evolution of the Saar-Nahe Basin, with special reference to the earlier Variscan development and the general evolution of Permo-Carboniferous basins in Central Europe is presented.

Phaenocompsopogon pustulatus n.gen.n. sp., a calcareous alga from the lacustrine rotliegend of the Saar-Nahe Basin (SW-Germany)

Phaenocompsopogon pustulatus n. gen. n. sp. is a calcareous freshwater alga, probably of rhodophycean affinity. The fossils are mainly known from one locality in the Lower Permian of the Saar-Nahe Basin. The algal remains form a packstone in the Reckweilerhof-Bank of the Altenglan Formation. The simple thallus branches irregularly y-shaped and is covered with abundant pustules. An axial canal is characteristic, as are distinct cell features of an inner and outer cortex surrounding a structureless medulla. Most fossils are silicified and often three-dimensionally preserved. The algae lived in a wave-dominated environment, probably in offshore shallow water. The limited occurrence suggests special ecological restrictions.

Results of the DEKORP 1 (BELCORP-DEKORP) deep seismic reflection studies in the western part of the Rhenish Massif

Summary Within the DEKORP project (DEKORP: Deutsches Kontinentales Reflexionsseismisches Programm) a joint deep seismic reflection venture with the BELCORP (Belgian Continental Reflection Seismic Programme) group of the Belgian Geological Survey was carried out in 1987 across the Rhenish Massif, a part of the mid-European Variscides. This orogenic belt developed in the Upper Devonian/Carboniferous. Mostly Devonian rocks crop out at the surface. The Rhenish Massif is bordered by two sedimentary troughs: the sub-Variscan Foredeep in the north and the Permo-Carboniferous Saar-Nahe Basin in the south. In the east-west direction it is subdivided by the axial depression of the Eifel Nord-Sud Zone. The aim of the survey which totals almost 220 km of seismic profiling, was to investigate the crustal structure of the western part of the Rhenish Massif and to compare it with the line DEKORP 2-N which crosses the eastern portion of the massif. The results indicate the presence of NW-vergent tectonics of various styles that can often be traced down to deep parts of the crust. Horizontal Variscan compression plays a dominant role in the northern part while post-Variscan extension seems to dominate in the Saar-Nahe Basin, although even there traces of Variscan compression seem to be preserved in the middle crust. Common characteristics of the pre-Palaeozoic basement, differences between the western and eastern parts of the Rhenish Massif, and the deep extension of the Aachen Thrust (Faille du Midi) have been clearly observed. This prominent thrust in the north with its characteristic ramp and flat structure has been followed over 100 km length down

Geological interpretation of DEKORP deep seismic reflection profiles 1C and 9N across the variscan Saar-Nahe Basin southwest Germany

Deep seismic reflection results across the Variscan Saar-Nahe Basin in southwest Germany, recorded as parts of DEKORP lines 1C and 9N, provide excellent images of the geometry of the basin and also of the structures in the underlying basement. This basement consists of several discrete units, some of which are highly-reflective, whereas others are essentially non-reflective; two of these units consist of well-layered dipping reflectors that are interpreted as having been telescoped by thrusting. Adjacent to the South Hunsrück Fault, the sedimentary pile within the Saar-Nahe Basin is over 8 km thick, but it thins dramatically towards the southeast and east. The position of continuous reflectors, both in the basin and the basement, indicate that the South Hunsruck Fault is subvertical and not a listric normal fault as proposed in several earlier interpretations. This implies that the basin did not form by normal extension but that it is transtensional in character, its geometry predominantly being controlled by strike-slip movements on the South Hunsruck Fault.

Aspects of Permian Palaeobotany and Palynology. IX. Conifer-dominated Rotliegend floras from the Saar-Nahe basin (? Late carboniferous-early permian; SW-Germany) with special reference to the reproductive biology of early conifers

A conifer-dominated Rotliegend flora (? Late Carboniferous-Early Permian) from a newly discovered locality near Oberhausen (Saar-Nahe area; SW-Germany) is described and figured. This flora is compared with fossil plant associations previously recorded from two other localities in the immediate vicinity. All three floras are dominated by conifers. The most common element is Walchia hypnoides (Brongniart) Brongniart. Apart from vegetative remains, reproductive structures have also been found. A new reconstruction of the ovuliferous cone of W. hypnoides is given. Because the species appears to differ in some fundamental respects from other Walchia's, W. hypnoides is transferred to the newly established natural genus Otovicia. tOtovicia hypnoides (Brongniart) nov. comb. is compared with other Late Palaeozoic conifers. The nomenclature of Ernestiodendron filiciforme (Sternberg) Florin is discussed. The diagnosis of the family Walchiaceae is emended to accommodate forms with more than a single ovule per ovuliferous dwarf-shoot. Special attention is given to the reproductive biology of the earliest conifers, which appear to have been zoidogamous and well adapted for wind pollination. Relevant other taxa known from the Oberhausen area are figured and briefly annotated. This selection includes several very rare elements. Some remarks on the environment, mode of deposition and palaeoecology of the plants under consideration are given.