Journal of Conference Abstracts

Session D04:5A

D04 : 5A/01 : G3

Deep Structure and Basin Evolution Along the Trans-European Suture Zone: Introduction

Tim Pharaoh (t.pharaoh@bgs.ac.uk)¹ &

Ulf Bayer (bayer@gfz-potsdam.de)²

¹ British Geological Survey, Nottingham, UK

² Geo Forschungs Zentrum, Potsdam, Germany

EUROPROBE's Trans-European Suture Zone (TESZ) project is a coordinated multidisciplinary investigation into the nature and history of the most fundamental lithospheric boundary in Europe, separating mobile Phanerozoic terranes (Caledonide-Variscide orogens) in the SW, from the ancient Precambrian crust of the East European Craton (EEC) and Baltic Shield in the NE, over a distance of 2000 km, from the North Sea to the Black Sea. The project involves the collaboration of over 120 geoscientists from 65 institutes in 15 countries, working on 22 carefully coordinated sub-projects. Due to the thick post-Palaeozoic cover throughout this region, geophysical experiments e.g. seismic reflection and magnetotelluric profiling, teleseismic tomography and studies of core material from deep boreholes, are the research priorities. Project highlights include: teleseismic tomography experiments to investigate the complex suture extending through the whole lithosphere into the asthenosphere; deep seismic reflection and magnetotelluric experiments to correlate deep and shallow structure of the Proterozoic and Phanerozoic lithosphere; determination of the depth to Moho and lithospheric velocity structure across the zone using refraction-wide angle reflection experiments; deciphering the tectonothermal history of Palaeozoic terrane accretion by multidisciplinary analysis of drillcores and outcrops; and comparison of Permian-Mesozoic subsidence and Cenozoic inversion of sedimentary basins overlying the contrasting lithospheres on either side of the suture.

In the North Sea and N Germany, crust of Avalonian affinity is juxtaposed with older, thicker lithosphere of Baltica along a southward-dipping suture (Caledonian Deformation Front). Docking of Avalonia against Baltica occurred in latest Ordovician or earliest Silurian time, with further oblique-slip during early Devonian deformation. The superimposed Permian-Mesozoic basins in this region are tectonically decoupled from the Caledonian basement by the presence of a thick salt layer, and the effect of basement control on the cover is therefore difficult to evaluate. In central Europe, the suture is obscured by overriding orogenic complexes in the west (Variscides) and east (Carpathians). The evidence for the early Palaeozoic history of the TESZ here is difficult to decipher but the Tornquist-Teisseyre Zone forms a persistent tectonic element throughout Poland and has clearly played a significant role in the extension and subsequent inversion of the superimposed Polish Trough. Towards the Black Sea, Variscide internide terranes, accreted in late Palaeozoic time, directly abut the edge of the EEC and crust of Avalonian type is absent. Here the basement structures were strongly reactivated during rifting of the Tethyan margin and during subsequent Alpine-Carpathian inversion. Thus the TESZ has a complex history and is certainly composite in origin. EUROPROBE geophysical experiments aim to characterise lithospheric structure in the contrasting segments of the zone.

D04 : 5A/02 : G3

Seismic Crustal Models of the Polish Basin Based on the POLONAISE'97 Data

POLONAISE Working Group &

Aleksander Guterch (aguterch@igf.edu.pl)

¹ Institute of Geophysics, PAS, Ks. Janusza 64, 01-452 Warsaw, Poland

The Polish Basin forms the eastern most part of the Permian Central European Basin, bordered by the East European Craton (EEC) to the east and by the Bohemian Massif to the south-west. The axis of the Basin, the Mid - Polish Trough (MPT), parallels the edge of the EEC along the boundary between the Phanerozoic and Proterozoic European custal domains. The Polish Trough coincides approximately with the Teisseyre - Tornquist Zone (TTZ), which is a part of the Trans - European - Suture Zone (TESZ), a first order geotectonic unit, stretching from the Black Sea to the British Islands. A large seismic experiment was conducted in Poland during May of 1997 and targeted the deep structure of the TESZ and the complex series of upper crustal features associated with it. This international cooperative effort, is known as the POLONAISE'97 Project. POLONAISE included contributions from the geophysical communities in Poland, Denmark, the USA, Lithuania, Germany, Finland, Sweden and Canada. The large, entirely land-based lithospheric seismic experiment involved deployment of 613 instruments to record 63 shot points along 5 profiles with a total lenght of about 2000 km. Moreover, 5 multichannel seismic reflection stations (90 and 120 channels) recorded all shots. Two dimensional P-wave tomographic crustal velocity models and ray-tracing crustal modelling along POLONAISE profiles are presented. At this early stage of interpretation we may formulate a few significant seismic and tectonic observations. One of the most important is a very distinct asymmetry between the maximal thickness of the sedimentary cover in the Polish Trough (15-20 km), the location of the tectonic inversion zone, and the crustal root (50 km deep) associated with TESZ/TTZ. Preliminary seismic models of the crust has implications for Caledonian and Variscan collision tectonics and for subsequent basin formation in the area.

D04 : 5A/03 : G3

MONA LISA Deep Seismic Data Reveals a Tectonic Mantle Shear Zone in the Southeastern North Sea

Mireille Laigle (mlm@seis.geol.ku.dk),

Hans Thybo (ht@seis.geol.ku.dk) &

Tanni Abramovitz (tanni@seis.geol.ku.dk)

Geological Institute, Oester Voldgade 10, DK 1350 Copenhagen, Denmark

Caledonian collision structures are imaged in many seismic profiles which have been collected during different surveys in the Baltic Sea (BABEL, DEKORP) and in the southern North Sea (BIRPS and MONA LISA). By integrated geological and other geophysical interpretation, the seismic structures imaged from the whole crust allow to define and locate the Caledonian deformation front and the suture zone between the two plates Baltica and Eastern Avalonia, characterized by different seismic velocities and reflectivity patterns. In order to better constrain the geometry of possible Caledonian thrust planes across the deformation front, new advanced seismic processing applied on selected samples is in progress.

The four normal-incidence reflection profiles image a southward to westward dipping reflective band in the mantle down to 22 s twt (70-80 km). The real geometry of these reflectors has been constrained by depth migration of line-drawings. Coincident wide-angle reflection and refraction modeling indicate the presence of high seismic velocities in the mantle (>8.6 km/s) within a 5 km thick layer along this dipping structure. These high velocities are observed along profile 2, which deviates by 35° from profile 1 and by 60° from profile 3, but not along these two latter profiles. This suggests then the existence of strong anisotropy in the layer, consistent with "frozen-in" alignment of olivine crystals in a 200°N direction.

We interpret this southward dipping layer as a tectonic mantle shear zone, and not as an old Caledonian subducted slab in eclogite facies, which would be inconsistent with the strong azimuthal anisotropy indicated in this layer. Moreover, the deep reflections revealed from the other surveys suggest a northward directed Caledonian subduction structure in the mantle. This tectonic mantle shear zone developed during Caledonian collision and post-orogenic collapse or Late Carboniferous to Early Permian basin formation in the area.

D04 : 5A/04 : G3

Reflection Seismic Mapping of Regional Orogenic Structures Below the Southwestern Baltic Sea

Alexander Lassen (la080164@geo.geol.ku.dk),

Hans Thybo &

Asger Berthelsen

Geological Institute, Ostervoldgade 10, 1350 Copenhagen-K, Denmark

A large dense network of commercial reflection seismic data to 4sTWT from the SW part of the Baltic Sea have been used to map Cambro-Silurian sediments next to an allochtonous Caledonian thrust complex. Intra crystalline thrusts and shear zones in the Precambrian basement represent the southward continuation of the Sveconorwegian orogen in SW Sweden. Focusing on the area between the islands of Moen and Ruegen four prominent structural features are distinguished: (1) An E-W striking set of S to SW dipping reflections in the Cambro-Silurian foreland seqence is interpreted as compressional structures caused by accretion of a "suspect" Caledonian terrain, Avalonia. (2) The base of the Cambro-Silurian sequence is marked by a distinct regional marker, the "O-reflection", which is generated by the sharp lithological transition from black Ordovician shales to the Cambrian Nexoe/Hardeberga sandstone. The top of the Cambrian sandstone acted as decollement for the Caledonian northward thrust movements and constitute a clear seismic boundary between the Phanerozoic sedimentary seqences and the Precambrian basement. (3) North dipping reflections below the Cambrian sandstone are interpreted as a late Precambrian graben structure. The grabenfill is correlated with clastics of the Vendian Visingsjoe Fm in the Vaettern graben, southern Sweden. (4) N-S oriented, W-dipping intracrystalline reflections observed below the O-reflection and presumed Vendian sediments are interpreted as ductile thrusts and shear zones of Sveconorwegian origin. The commercial reflection seismic data was acquired for imaging Mesozoic bassins. However this study demonstrates its potential use for interpretations of the Sveconorwegian and Caledonian evolution on the southwestern edge of the Baltic Shield.

D04 : 5A/05 : G3

A Velocity Model for the Southern Baltic Sea Derived from BASIN 96 Refraction Seismic Measurements between Ruegen and Bornholm

F. Bleibinhaus

(bleibi@seismik.geophysik.uni-muenchen.de)¹,

K. Bram (k.bram@gga-hannover.de)²,

T. Beilecke (tbeilecke@geophysik.uni-kiel.de)³ &

H. Gebrande

(gebrande@seismik.geophysik.uni-muenchen.de)¹

¹ Institut f. Geophysik, Theresienstr. 41, D - 80333 Muenchen, Germany

² Geowissenschaftliche Gemeinschaftsaufgaben, Stilleweg 2, D - 30655 Hannover, Germany

³ Institut f. Geophysik, Otto-Hahn Platz 1, D - 24098 Kiel, Germany

Within the BASIN 96 project (Basin Analyses and Seismic Investigation in North Germany 1996), marine airgun shots in the southern Baltic Sea were observed on land. Special attention was paid to record good quality data on Ruegen island, which is known for adverse acquisition conditions. Therefore a complex star-shaped array of 288 geophones (the "star of Ruegen") was designed to enhance the signal quality. The data from these and other onshore observations in NE-Germany and on Bornholm island offer a sound basis for p-wave velocity modelling. Kinematic forward modelling resulted in a 3D velocity model between Ruegen and Bornholm. Important structures of the transition zone from Paleozoic western Europe to the Precambrian Baltic Shield are reflected in this model: A pronounced basement high north of Ruegen marks the location of the Caledonian Deformation Front (CDF). Other prominent velocity anomalies are related to the Ronne Graben and the basement outcrops around Bornholm. In the investigated area the Moho depth varies between 28 and 31 km depth. A thicker and slower crust is observed below the CDF which is interpreted in connection with the BABEL and BASIN normal incidence observations as remnant of Caledonian subduction.

D04 : 5A/06 : G3

Major Crustal Features from Northern Germany to the Scandinavian Shield Derived from Receiver Functions

Juergen Gossler (gossler@gfz-potsdam.de),

Rainer Kind (kind@gfz-potsdam.de),

Kurt Wylegalla (wyle@gfz-potsdam.de),

Manfred Stiller (manfred@gfz-potsdam.de) &

TOR Working Group

GFZ Potsdam, Telegrafenberg, D-14473 Potsdam, Germany

The TOR (Teleseismic Tomography Tornquist) working group operated a large seismic network consisting of up to 108 short-period and 31 broadband stations in Europe for about one year starting in summer 1996 across the northern segment of the Trans European Suture Zone (TESZ) - the border between the proterozoic and phanerozoic Europe.

Within this international project we focus on P-to-S converted waves (receiver functions) originating from crustal structures and the Moho. Though, thick sedimental layers cover large parts of the investigated area, clear Moho conversions have been observed along the entire about 1000 km long profile.

First results of applying a new technique of the receiver function analysis suggest that the Moho is bent downward to 34-35 km depth under the North German Basin. In the northern part of the North German Basin we see an imbricated Moho structure striking parallel to the TESZ. Underneath the Danish isle of Sealand we see a south-west dipping structure penetrating the entire crust. This structure is interpreted as the Tornquist Suture separating the Scandinavian from the central European crust. North of the Tornquist Suture the Moho is steeply dipping and reaches a depth of more than 50 km south of Stockholm.

We discuss similarities and differences in the Moho structure as seen by the relatively long-period (1-2 sec) teleseismic converted phases and the high frequency steep angle reflection results of the DEKORP experiment in the north-east German Basin.

D04 : 5A/09 : G3

Reflection Seismic Constraints on Palaeozoic Crustal Structure and Moho beneath the NE German Basin

Charlotte Krawczyk (lotte@gfz-potsdam.de),

Tommy McCann (tmc@gfz-potsdam.de) &

The North German Bains Research Group

GFZ Potsdam, Telegrafenberg, D-14473 Potsdam, Germany

A 500 km long, NE-SW trending seimic transect across the NE German Basin, composed of an offshore and an onshore seismic survey, revealed insights into the structural inventory of this intracontinental basin. It is situated between the stable Precambrian Baltic Shield and the weaker Mid-European Variscides, extending from the Tornquist Zone -an inferred Paleozoic suture- to the Harz Mountains, and from the North Sea to Poland.

The initiation and development of intracontinental basins has been a matter of controversy for some time. Such basins have either a short phase of initial rifting or none at all, succeeded by a period of prolonged subsidence, decreasing over time. Pronounced syn-sedimentary structural activity during the subsidence phase is usually absent, despite considerable crustal thinning. Most conceptual models suggest that thermal relaxation of the lithosphere, following plume-generated heating or subsidence due to water and sediment loading, control basin formation rather than intraplate extension. A time lag between the cessation of tectonic activity and the onset of subsidence is a feature of a number of intracratonic basins, only few of which have been studied by integrated geophysical experiments.

The combination of marine reflection seismics, with a land-based high-fold vibroseismics and a low-fold explosive seismics, imaged both upper and lower crustal structures in detail. The outline and infill of the Permian sedimentary basin is shown, and a possibly volcanic Permo-Carboniferous succession underlying the basins depocentre. Distinct faults related with a rift stage are not observed below the Permian basin, but there is evidence of lower crustal thinning. Prominent fault systems in the upper crust at the southern basin margin are correlated with Late Triassic compressional features.

SW-dipping, widespread mid-crustal reflections outline the Caledonian Accretionary Wedge at the northern basin margin, suggesting that the fossil plate boundary between Avalonia and Baltica extends as far as the basins depocentre below the North German mainland.

An almost flat lying Moho may be correlated across the entire seismic section, with weaker reflectivity in the basin centre, possibly explained by magmatic underplating and/or metamorphic phase changes.

D04 : 5A/10 : G3

3D Gravity Field Interpretation in the Northeast German Basin Along the DEKORP NE-Line

H.-J. Götze (hajo@geophysik.fu-berlin.de)¹,

L. Barrio-Alvers¹,

U. Bayer (bayer@gfz-potsdam.de)²,

J. Kuder (kuder@geophysik.fu-berlin.de)¹ &

M. Scheck (scheck@gfz-potsdam.de)²

¹ Freie Universität Berlin, Malteserstr. 74 - 100, 12249 Berlin, Germany

² Geoforschungszentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany

The key for understanding the dynamic evolution of the Northeast German sedimentary basin is the knowledge of its current internal lithospheric structures. Former studies focus on the evolution and subsidence processes of the basin by the aid of numeric modelling. Due to the complex basin structures through space and time we will concentrate hear on 3D density modelling and the investigation of the isostatic state of the present day basin. The principal idea behind this paper is to show the state of gravity data acquisition, processing and recent results of 3D-modelling which is constrained by other independent geophysics. At first, superficial layers of the basin were compiled on the base of industry borehole data, seismic profiles and magnetotelluric modelling. Gravity, horizontal gradients and aeromagnetic data completed the data base as well as long wavelength geopotential. By the help of 3D potential field modelling and a 3D GIS (geoinformation system), an initial model was constructed to fit in the geophysical data sets. Local gravity effects of salt domes and walls concerned with the mobilisation of the Zechstein salt layers, cause strong negative anomalies of gravity. Their gravity effect was eliminated from the measured Bouguer anomaly by 3D gravity stripping. The resulting modified anomaly field is characterized by a smoother gravity distribution which is dominated by regional gravity highs in the central and northern part of the DEKORP NE-profile which seems to be caused by elongated thickened layers of dense material in a depth of some 10 km. Line drawings of the reflection seismic line do not indicate the boundaries of this high density body (Rho > 2.900 kg/m³) neither in the centre nor into the north of the profile. To identify crustal domains in the crust of the basin down to the Moho interface where the geometry of the 3D density model coincide with layering and domains of high reflectivity and transparency in the crust is one of the main goals. Velocity-depth diagrams, results of seismic tomography and formulas for velocity to density conversions help to match the density and velocity model.

D04 : 5A/11 : G3

The Orientation of the Tectonic Stress Field in NE Germany

Frank Roth (roth@gfz-potsdam.de)¹,

Philip Fleckenstein,

Johannes Palmer² &

Uwe Gross³

¹ Section Earthquakes & Volcanoes, GeoForschungsZentrum, Potsdam, Germany

² Rosen GmbH, Geeste, Germany

³ Geotechnik Projekt GmbH, Leipzig, Germany

Knowledge about the acting stresses is of crucial importance for the tectonics of a region. Data about the stress field near the TESZ in north-eastern Germany used to be very rare. In general, it was assumed that the stress orientation is similar to that found for western Germany and central West-Europe, i.e. NW-SE. To check this and to fill this data gap, several borehole logs of the late 1980's were now analysed for information on the orientation of the principal horizontal stress orientations: These include 4-arm-dipmeter and borehole televiewer data from 16 boreholes. They were compared to a few older data, especially from hydro-fractures, and to recent findings on the stresses in the North-West German basin.Different orientations were found for layers above and below the Zechstein salt in the region. The hydrofrac results were in very good agreement with those from the borehole break-outs found in the dipmeter logs. Those above the salt show EW to NW-SE orientations at 4 locations, however those below the salt layers displayed NS to NE-SW orientation. The latter was found at 10 out of 11boreholes between Berlin and the Baltic sea, between the Polish and the former border between East and West Germany. Moreover, this stress rotation in the sub-saline formations seems to be the continuation of a trend found in the NW German basin.

Geomechanical Properties and Deformation Structures of Permocarboniferous Redbeds in the Basins Adjacent to the Elbe-Line, North-East Germany

Christian A. Hecht (hecht@geologie.uni-halle.de)

Institut für Geologische Wissenschaften und Geiseltalmuseum, Martin-Luther-Universität Halle-Wittenberg, Domstr. 5, 06108 Halle/Saale, Germany

This study presents structural analyses and rock mechanical data of the Late Carboniferous and Permian clastic rock units in north-east Germany. The fault controlled intramontane basins south of the Elbe-Line received the coarse grained sediment load from the Variscan Orogen to the south, accompanied by significant volcanic activity. The sequences comprise conglomerates, brecciated agglomerates, sandstones and mudstones that are well exposed for example in the Saale Valley. They show a variety of faults and shear structures related to Late- and Postvariscan brittle deformation and mainly orthogonal joint sets that are either fault controlled or produced by stress relief after uplift and exposure of the rock units.

The NE-German basin north of the Elbe-Line in contrast recieved distal sediments that are fining upwards in the center of the basin and towards its northern parts. The clastic Rotliegend rocks are underlain by Permocarboniferous volcanic rocks that reach considerable thicknesses north of the Elbe-Line in the Altmark region and south of the TEF (Trans European Fault). The Permocaboniferous sequences of the NE-German Basin are not exposed, but well documented by a great number of research and exploration wells and geophysical investigations. In contrast to the intramontane basins to the south the control of major faults on the Permian sedimentation in the NE-German Basin is only dominant during Lower Permian times. Deformation structures within the Permian layers of the NE-German Basin are poorly reflected by the seismic record, for example the seismic section DECORP 2000, which may be due to the Upper Permian, Zechstein salt layers that cover the clastic Rotliegend series.

Three basic lithotypes are being elaborated for the Permocarboniferous redbeds based on grain properties, packing and cementation, the absolute grain sizes not being taken into account in the first place: (a) grain supported dense packings without much cementation e.g fluvial conglomerates, (b) matrix supported packings with wide grain size spectra and considerable cementation e.g. debris flow deposits and (c) loose packings of unisized grains with a high percentage of cements e.g fluvial and aeolian sandstones. The single grain properties considered in terms of internal friction and mechanical resistance, are particle shape and particle petrology. The most abundant cements encountered are carbonates and finegrained phyllosilicates. Quartz, hematite and other cements occur only locally under special conditons.

Cylindrical rock samples of each lithotype were examined by standard rock mechanical experiments, which were in part also applied in the field. The physical parameters measured are, ultrasonic wave velocity, density, water absorption, permeability, specific internal surface area and axial compression. The rock mechanical results are integrated into the regional tectonostratgraphic patterns of selected areas. The presentation outlines correlations of the rock mechanical behaviour of Permocarboniferous lithotypes to the structural development along the transition from the tectonically controlled intramontane terrain across the Elbe-Line into the moderately subsiding NE-German basin.

D04 : 5A/13 : G3

A 2-D Flexural Model for Crustal Deformation Below the NE German Basin

Anna Maria Marotta (marotta@gfz-potsdam) &

Ulf Bayer (bayer@gfz-potsdam.de)

GeoForschungsZentrum Potsdam, PB 3.4 Albert-Einstein-Strasse, D-14473 Potsdam, Germany

The NE German Basin is part of the Southern Permian Basin, located south of the Trans-European Fault Zone and The Elbe Line. Four tectonic phases seem to have affected its deformative history: initial rift during the Late Carboniferous-Early Permian; main face of thermic subsidence, during the Early Permian-Middle Triassic; differentiation face during the Middle Triassic-Jurassic; inversion with regional compression during the Cretaceous. Different models have been developed, taking into account different mechanisms for the basin formation, as stretching and thinning of the crust (Bachmann and Grosse, 1989; Brink et al., 1990), mantle diapirs (Bachmann and Hoffmann, 1989) emplaced in deep in the crust, simple shear model (Brink et al., 1990). However, new sismic data (DEKORP BASIN`96) and studies of the regional gravity anomaly made questionable some of the conclusions on which these models were based. In particular, the Moho appears flat almost throughout the basin (about -32 km). Only in the southern part of the Basin the Moho uplifts untill about -28 km and then sinks again to -37 km under the Harz mountain. This is associated with a non-homogeneous crust thickness that spans from 32 km to about 22 km in the centre of the bacin and with a sediments infill whose morphology suggests that the upper crust could be totally decoupled from the lower crust. We suggest that deep deformation could be the result of lithospheric buckling due to the regional compressive forces during the tectonic inversion occurred in the late Cretaceous-early Terciary. The results of a 2-D flexural model, for a pure elastic and a viscoelastic lithosphere, will be presented. We extend the model in the third dimension by using a thin sheet approximation. A finite element model is built assuming a vertically averaged rheology and including also the elastic component of lithospheric strenght. We present the preliminary results of this model too.

Bachmann & Grosse, Nds. Akad. Geowiss. Verofftl, 2, 23-47, (1989).

Brink et al, The European Geotraverse. Integrative Studies, 195-212, (1990).

Bachmann & Hoffmann, Geol. Jb, D103, 9-31, (1989).

D04 : 5A/14 : G3

Interpretation of the Deep Seismic Line DEKORP 9601 Across the Cratonic North German Basin

Ian Lerche (lerche@geologie.uni-halle.de)¹,

Norbert Hoffmann (norbert.hoffmann@bgr.de)²,

Thomas Rüffer (rueffer@geologie.uni-halle.de)¹ &

Gerhard H. Bachmann (bachmann@geologie.uni-halle.de)¹

¹ Martin-Luther-Universität Halle-Wittenberg, Institut für Geologische Wissenschaften und Geiseltalmuseum, Domstraße 5, D-06108 Halle (Saale), Deutschland

² Bundesanstalt für Geowissenschaften und Rohstoffe, Dienstbereich Berlin, Wilhelmstraße 25-30, D-13593 Berlin, Deutschland

The base of the lower crust is characterized by the 1 sec (2-3 km thick) broad reflexion band of the Moho, which is between 10-12 sec (30-35 km) deep. Crustal sag is visible in the central part of the basin. An interval without distinct Moho reflexions corresponds to the gravimetric and magnetic Pritzwalk anomaly, interpreted as a large intrusive in the lower crust of Late Carboniferous to Early Permian age.

The middle crust, underlying the northern part of the basin, is interpreted to consist of a basement, which was deformed by the Caledonian orogeny, then stretched and overlain by Devonian and by Carboniferous sediments of the Variscan foredeep. The stretching of the crust goes as far north as to the Trans-European Fault (TEF = Stralsund-Anklam fault, which corresponds approximately with the Baltica-Avalonia suture). On the other hand, in the southern part, the basement and sediments are both deformed by the Variscan (Hercynian) orogeny. The northern edge of the Variscan thrusts indicate a triangle zone, a characteristic of many thrust belts.

The upper crust consists of the fill of the cratonic North German Basin, which came into existence after the Variscan orogeny in latest Carboniferous to early Permian times. The fill comprises several kilometres of Rotliegend volcanics in the central parts of the basin which were deposited in pull-apart-like structures. The Rotliegend is overlain by more than 5 km of Zechstein to Quaternary sediments. In the central parts of the basin, the interval between the Moho and the base Permian is much thinner than at the basin flanks, suggesting considerable extension of the crust in the early stages of the basin evolution. The depocenter of the cross-section coincides with the Pritzwalk anomaly and thick Rotliegend volcanics. This extension of the basin is followed by thermal subsidence from the late Permian (uppermost Rotliegend, Zechstein) onwards. Compressive inversion structures of Late Cretaceous age, such as the Harz and Flechtingen blocks, are associated with listric thrusts and are characteristic of the southern part of the North German Basin.

Quantitative modeling of the basinal evolution is currently being developed in an attempt to evaluate the flexural, thermal and isostatic responses with time. Explanation of the procedures used, and preliminary results from the modeled basement motion, will be discussed.

Bachmann GH, Hoffmann, N, Development of the Rotliegend Basin in Northern Germany, Geologisches Jahrbuch, D 103, 9-31, (1997).

Session D04:5B

D04 : 5B/21 : G3

The Evolution of the Northeast German Basin - Results and Open Questions

Magdalena Scheck &

Ulf Bayer

The Northeast German Basin in the eastern part of the TESZ contains about 8 km of deposits and developped in an intracontinental setting, underlain by basement blocks of Variscan, Caledonian and possibly Precambrian deformation ages. A variety of geological and geophysical data permitted the construction of a 3D structural model imaging regional depositional and structural trends. Based on this model, investigations on subsidence history, structural setting and volumetric proportions were performed as well as different 3D numerical studies including calculations of the density distribution in the underlying crust by means of isostatic and gravimetric modelling. Revaluation of the 3D basin model after validation with newly aquired seismic data (DEKORP BASIN 96) and recently released seismic and well data (courtesy of Erdoel Erdgas Gommern) resulted in conclusions concerning basin history. Accordingly, the NEGB underwent a polyphase evolution and does not fit in a classical basin classification scheme. As the Moho is flat below the basin, neither a simple-shear, nore a pure-shear model can be applied. We see a considerable thinning of the crystalline crust and we have indications of a lower crust with an unusual high density. An additional observation is the presence of more than 40 thousand km³ of mainly acid Late Carboniferous volcanics documenting melt generation in the crust prior to basin initiation. Magmatic signature, the absence of major extensional faults in the initial depositis and a long phase of thermal subsidence indicate, that thermal destabilisation of the lower crust played a major role for basin formation. However, initial subsidence patterns reveal arguments for subordinate effective horizontal stresses. From Late Permian to Middle Triassic we observe a periode of tectonic quiescence when cooling of the heated crust explains sufficiently well the subsidence of a broad NW oriented sag basin. Deposits of this phase are a few thousend m thick and include clastics, carbonates and about 1500 m of Zechstein salt. During Late Triassic, regional extension due to Pangea breakup led to a reconfiguration in the southern part of the basin, where new NNE-SSW trending troughs (Rheinsberg and Gifhorn Troughs) developed. Differentiation continued into Cretaceous times when regional compression due to alpidic convergence caused uplift and inversion in the south-eastern part of the basin and at the basin's margins. A final subsidence phase followed in the Cenozoic. Early salt mobilisation accompagnied Triassic extension and was intensified during Cretaceous to Cenozoic. Mesozoic deformation affected only the post-Zechstein deposits in the basinal area, while deformation of the pre-Zechstein layers is restricted to the basin's margins. This indicates that the viscous Zechstein salt decoupled its cover tectonically from its basement leading to thin-skinned deformation in the basinal area and thick-skinned faulting at the basins margins.

However, the correlation between observed crustal structure and tectonic events remains a subject of discussion as the initial thermal event and Mesozoic deformation may have modified the 'crustal memory' with regard to Caledonian and Variscan events.

D04 : 5B/22 : G3

The Trans-European Suture Zone in NE-Germany ­ Implications from Provenance Analysis and Isotope Dating for the Deeper Subsurface of Northern Germany

Uwe Giese (giese@geologie.uni-halle.de)¹,

Robert Handler (robert.handler@sbg.ac.at)²,

Franz Neubauer (frnaz.neubauer@sbg.ac.at)²,

Robert Tschernoster

(tschernoster@rwth-aachen.de)³ &

Marco Veccoli (marco@earthsciences.uq.edu.au)⁴

¹ Inst.f.Geologische Wissenschaften, MLU Halle / Wittenberg, Halle / Saale, Germany

² Inst.f.Geologie u.Paläontologie, Universität Salzburg, Salzburg, Austria

³ Inst.f.Mineralogie u.Lagerstättenkunde, RWTH Aachen, Aachen, Germany

⁴ Dep.of Earth Sciences, University of Queensland, Brisbane, Australia

Palaeomagnetic results show that Baltica and Gondwana were separated by a wide Tornquist Ocean in Early Palaeozoic times. Thus the origin of the TransEuropean Suture Zone (TESZ) can be seen in the closure of the Tornquist Ocean during Caledonian times. The most representative section across the TESZ including the Tornquist-Teisseyre Zone (TTZ), the Caledonian Deformation Front (CDF) and the TransEuropean Fault (TEF) can be found between Bornholm (in the southern Baltic Sea) and NE-Germany.

Provenance analysis and isotope dating of Early Palaeozoic clastic sediments from deep boreholes clearly differentiate between a Baltic and a Perigondwanean source. Detrital material which derived from the Baltic shield shows compositions dominated by K-feldspar, phengitic muscovite and polycyclic zircons, indicating a high-grade crystalline source. New ⁴⁰Ar/³⁹Ar cooling ages of single detrital muscovite grains show a Grenvillian provenance with ages which range between c. 1100 Ma and 850 Ma. Perigondwanean derived clastic material shows a Cadomian aged low-grade source and an Early Palaeozoic magmatic arc provenance. This is demonstrated by new ⁴⁰Ar/³⁹Ar cooling ages of single detrital muscovite grains ranging around 600 - 700 Ma and is confirmed by single zircon U/Pb analysis. Mixing of both sources started from Late Ordovician onwards. According to these results each borehole can be addressed to specific structural domains with different crustal origins. In combination with the recently shot DEKORP-profile a tentative interpretation of the deeper subsurface of the southern Baltic Sea and NE-Germany appears possible. From this the Rügen Palaeozoic appears as an allochthonous nappe complex, which has been thrusted onto the Baltic shield. Therefore, the Baltic shield reaches much further beneath NE Germany than previously thought, while the TEF represents a younger, reactivated fault zone. The results can be extrapolated to the whole area of the Danish-N-German-Polish Caledonides reaching from southern Denmark to NW Poland.

D04 : 5B/23 : G3

Fluid Inclusions as Indicators of Thermal Events in the NE German Basin

Markus Wolfgramm

(gfaco@geologie.uni-halle.de) &

Andreas Schmidt Mumm

(schmidt-mumm@geologie.uni-halle.de)

Institut für Geologische Wissenschaften, Domstrasse 5, D-06108 Halle (Saale), F.R. Germany

Fluid inclusions are analysed in samples from drill holes in the vicinity of the seismic profile "Basin 9601", trans-secting the NE-German Basin from the isle of Ruegen to the Harz Mountains (Mirow 1/74, Parchim 1/68, Salzwedel 2/64, Eldena 1/74, Kotzen 4/74, Penkun 1/71, Pretzier 1/77) to evaluate thermal patterns in the sedimentary basins. Samples are from coarse grained sediments, mineral precipitates in joints and fractures, dehydration structures and concretions. All samples are investigated by conventional and cathodoluminescence microscopy prior to microthermometric analyses; permitting the identification and distinction of different generations of diagenetic mineral phases. Older, weakly luminescent carbonates are intimately intergrown with early generations of euhedral, zoned quartz of blue luminescence. Subsequently these mineral parageneses were deformed and recrystallised, or replaced by secondary, brightly yellow to orange luminescent calcite associated with quartz. An early fluid system, identified in older authigenic quartz and calcite, is characterised by elevated salinities (15 to 30 equiv.wt.% NaCl+CaCl₂) and relatively low temperatures of homogenisation (<220°C). A younger fluid system (present as primary clusters, within growth zones, as well as in secondary trails in diagenetic and hydrothermal carbonate) has distinctly lower combined salinities (5 to 25 equiv.wt. %NaCl+CaCl₂) and higher temperatures of homogenisation (<295°C). These distinctions are most markedly developed in the centre of the basin but are less clear towards the margins. Late, locally developed, calcite-fluorite-barite veins mark an even younger Upper Cretaceous fluid event. Thermal conditions inferred from the older fluid inclusion assemblages suggest a maximum thermal gradient of 35°C/km for the interval from 2500 to 4500 m; deeper, the homogenisation temperatures show little systematic variation, but seem rather constant. The interpretation is a distinctly lowered thermal gradient or increasing convective heat flow, overriding the conductive heat flow. The boundary of these thermal regimes coincides broadly with the Zechstein base. Younger fluid inclusion assemblages generally represent higher temperatures at a similarly low thermal gradient below the Zechstein. Above the Zechstein this fluid system could be identified only locally in newly formed minerals, which may indicate sporadic penetration of these fluids. Evaluation of the existing results demonstrates the chemical and thermal maturation of the involved fluids from low temperature/low salinity to high temperature/high salinity systems accompanying faulting and fracturing during progressive basin subsidence. The peak of this evolution in the central and marginal parts of the basin was established by K/Ar dating of authigenic illite (Brecht et al., 1998) at 156 Ma and 206 Ma (Late Triassic / Jurassic), respectively.

Brecht GA & Wolfgramm M, Scripta Fac. Sci. Nat. Univ. Masaryk. Brun, 26, 30-31, (1998).

D04 : 5B/24 : G3

The Lower Palaeozoic Craton-Margin Depositional Sequences in North Poland: Record of the Caledonian-Stage Tectonic Events

Krzysztof Jaworowski (kjaw@pgi.waw.pl)

Polish Geological Institute, 4 Rakowiecka, 00-975 Warszawa, Poland

In north Poland the Lower Palaeozoic sedimentary cover of the East European Craton (EEC) may be subdivided into four consecutive depositional sequences. They are bounded by subaerial erosional surfaces.

Sequence I: Upper Vendian - Middle Cambrian (without the uppermost part). Facies: continental sandstones and conglomerates representing alluvial fans, braid plain, braid deltas and fan deltas passing upward into marine transgressive sandstones, tidal sandstones and shelf mudstones with sandy tempestites. Maximum thickness: 1 000 metres.

Sequence II: the uppermost Middle Cambrian - Lower Tremadoc. Facies: transgressive conglomerate and sandstone followed by black claystones of deep anaerobic shelf. Maximum thickness: hardly exceeds 20 metres.

Sequence III: Arenig - Ashgill (without the uppermost part). The sequence is made up of two segments (IIIa + IIIb) separated with a discontinuity surface formed due to submarine erosion. The erosional gap spans the Upper Llanvirn. Facies: (IIIa) - basal conglomerate and shelf mudstones overlain by marly limestones of a deep carbonate ramp; (IIIb) - black claystones of anaerobic shelf and alternating shelf mudstones and marls of a deep carbonate ramp. Maximum total thickness of the sequence: 140 metres.

Sequence IV: Llandovery (without the lowermost part) - Pridoli (without the uppermost part). Facies: black claystones representing a deep anaerobic shelf followed by grey claystones of disaerobic shelf. The grey claystones of Ludlow age contain abundant thin interbeds of siltstones interpreted as distal turbidites. Maximum thickness: 3 765 metres (!).

Marine transgessions and regressions recorded in the sequences discussed, fit fairly well an eustatic sea-level curve (Vail et al., 1977). This may indicate that facial development of these sequences has depended mainly on eustatic global sea-level changes.

Thickness variability of the sequences reflects the evolutionary history of the Lower Palaeozoic sedimentary basin developed in the marginal part of the EEC (Jaworowski, 1971, 1997, Modlinski, 1982, Dadlez et al., 1994, Poprawa et al., 1997). Sequence I may be interpreted as the result of subsidence connected with the extensional basin which has originated during the Precambrian supercontinental break-up. Small thicknesses of Sequences II and III (the uppermost Middle Cambrian - Ordovician) illustrate decreasing subsidence rate characteristic for the thermal sag stage in basin development. At the end of the Ordovician, collision of the EEC and the terrane of East Avalonia took place. Sequence IV (Silurian) showing enormously large thickness, have been deposited in the craton-margin basin which has resulted from an overthrust of the Caledonian accretion wedge on the south-west rim of Baltica.

Dadlez R, Kowalczewski Z & Znosko J, Geol. Quart., 38, 1-21, (1994).

Jaworowski K, Acta Geol. Pol, 21, 519-570, (1971).

Jaworowski K, Biul. Panstw. Inst. Geol, 377, 1-112, (1997).

Modlinski Z, Prace Inst. Geol, 102, 1-66, (1982).

Poprawa P, Narkiewicz M, Sliaupa S, Stephenson RA & Lazauskiene J, Terra Nostra, 97/11, 110-117, (1997).

Vail PR, Mitchum RM & Thompson SIII, Am. Ass. Pet. Geol. Mem, 26, 83-97, (1977).

D04 : 5B/25 : G3

Zechstein Sequences Along the Northern Basin Margin: Subsidence Versus Sea-Level

R Kaiser (rene.kaiser@uni-koeln.de),

S Nöth (sheila.noeth@uni-koeln.de) &

W Ricken (werner.ricken@uni-koeln.de)

Institut für Geologie, Universität zu Köln; Zülpicher Str. 49A, D-50674 Köln, Germany.

Based on sedimentological core analysis a sequence stratigraphic model was developed for the northern margin the southern Zechstein basin of northeast Germany. The morphology of the relatively undifferentiated carbonate-sulfate platform of the basal Zechstein (here the Staßfurt Carbonate of the Zechstein 2) is tectonically dominated by the NW-SE trending Stralsund-Faultzone. The Ca2 platform shows various facies types, including protected lagoonal sediments, shallow subtidal and intertidal to supratidal sabkha deposits, suggesting rimmed platform conditions. The Staßfurt Carbonate (Ca2) can be subdivided into third-order and higher-order sequences (small scale cyles or parasequences). Most of the Ca2 platform, however, is dominated by the highstand systems tract (HST). Four complete parasequences, each showing a shallowing-upward trend, can be recognized. The transgressive systems tract (TST) is represented by thin deposits of mud conglomerates. The Ca2 maximum flooding surface (mfs) corresponds to the complete flooding of the A1/Ca2 platform. The top of the underlying A1 sulfate platform displays a highly erosive surface which is interpreted as a sequence boundary. The overlying sequence boundary is placed in the Anhydrite sequence (A2) overlying the Ca2, and not in the Ca2-carbonates. The Ca2 slope generally displays approximately equal thicknesses of the transgressiv systems tract (TST) and the highstand systems tract (HST). Turbidites located in the middle and upper slope show the onset of carbonate production on the A1/Ca2 platform during the HST, suggesting "highstand shedding". Monotonous laminated carbonates document that relative sea-level-changes and/or autocyclic processes do not influence the sedimentation in the basin (i.e. in water depths higher than 100). Off-platform highs with shallow-water carbonates and varying Ca2- thicknesses probably result from different rates of subsidence along tectonic reactivation zones (i.e. Barth-Grimmener fault zone).

D04 : 5B/26 : G3

The Jurassic Carbonate Sedimentation in the West Ukrainian Carpathian Foredeep

Alexander V. Emetz (geomin@geof.franko.lviv.ua) &

Igor V. Popadyuk (udgri@icmp.lviv.ua)

Ukrainian State Geological Research Institute, Lviv, Ukraine

These work are realised for the hydrocarbon accumulation prospecting moved by UkrDGRI on the Carpathian foredeep region. Earlier here the Jurassic limestones have been explored by Dulub et al.(1986), et al. For the investigation we have utilised emphasising of the standard carbonate microfacies (Wilson (1980)).

The carbonate sedimentation on the territory of the Jurassic palaeoshelf had a beginning for the Callovian time. Here as a result of erosion level hesitations the cyclic sediments formed. The limestone interbeds are enriched by terrigenous material. For the Oxfordian time the shelf was covered by algal, crinoidal and spongian limestones, sometimes there was a growth of the biogerms. The siliceous spongian carbonate sediments have edged the organic carbonate building. Along the continental margin the cyclic terrigenous sediments of caving type were formed. The fast growth of the carbonate banks led to filling and shallowing of the territory. There were the lagoon sedimentation (gypsum, angidrite) and scouring (multicoloured horizon formation) here. Then, for the Kimmeridgian time the progressive plunge of the shelf have happened. At the beginning the Kimmeridgian shelf was open. However for this time gradually the ecological reefs were formed and soon barrier reef has arisen here. The boundary of division between the Kimmeridgian and Tithonian sediments is non-evident. The facies for these ages are similar, between them there are not a large contrast. The intensive plunge has predetermined a closer arrangement of the Tithonian reef than the Kimmeridgian one to the north-east palaeo-coast. The complex of the reefeal facies defined the different scouring intensity of the palaeosurface for the Cretaceous and then for the Paleogene times. During the latest one the most part of the Tithonian back-reef and fore-reef facies was destroyed as a result of the Kalush thrust fault formation.

Cross Section of the Jurassic Carbonate Platform in the Central Part of the West Ukrainian Carpathian Foredeep

Dulub VG, Burova MI, Burov VS, Vishnyakov IB, Explanatory notes to the regional stratigraphic scheme of Jurassic deposits of the Carpathian foredeep and Volin-Podolia margin of the East-European Craton. VSEGEI, Leningrad, (in Russian), 58, (1986).

Wilson JL, Carbonate facies in geological history. Springer-Verlag Berlin-Heidelberg, (1975).

Session D04:5P

D04 : 5P/01 : PO

Rotliegend Sediments in Baltic Region

Jolanta Cyziene (jolanta.ciziene@lgt.lt)¹ &

Saulius Sliaupa (sliaupa@geologin.lt)²

¹ Geological Survey of Lithuania, Konarskio 35, 2600 Vilnius, Lithuania

² Geological Instititute, Sevcenko 13, 2600 Vilnius, Lithuania

Rotliegend sediments in the Baltic Region were deposited in the 30-40 km wide 300 km long Perloja basin (PB) striking west-east along Polish-Kaliningrad District border and further east into southern Lithuania. In tectonic terms, it marks the limit between Mazury-Belarus High and Baltic Depression. The onset of the basin was related to the reactivation of the Middle Proterozoic Mazury Shear zone that cores the PB along the all its length. It associated with the isostatic collapse of prior tectonically buckled lithosphere in the Mazury-Belarus High. The thickness of Rotliegend sediments (Perloja Fm.) reaches 50 m. Mineralogy and structuring style allow to attribute them to the Upper Rotliegend deposited after Late Hercynian faulting and igneous climax in the in the Baltic region. Six litofacies belts are defined in PB ranging from conglomerates to siltstones. Maturity of rocks increases to the north implying main terrigenic supply from Mazury Rise. Lithologies outcropping in the provenance area also strongly controlled sediment composition in PB. Low-mature sediments deposition was confined to the outcropping of the crystalline basement in the west, while they are much mature in the eastern Lithuania with Lower Palaeozoic sediments exposed. Cement composition was controlled 1) by provenance area evolution (sin-sedimentation cement) that supplied most of clay cement in the early stages of the sediments deposition and considerably ceased in the latter part; 2) by overlying lithologies that affected the epigenetic cementation. Thus, clayey cement prevail in the lower portion of the Perloja Fm., and carbonates/gypsum are prominent in the upper part. Gypsum cement developed below the area of distribution of Zechstein anhydrites, while calcite (rare dolomite) dominates below the marginal part of the Zechstein basin where anhydrites are absent.

D04 : 5P/02 : PO

The Continental Upper Rotliegend at the Northern Margin of the Northeast German Basin

Holger Rieke (rieke@gfz-potsdam.de),

Dirk Kossow (kossow@gfz-potsdam.de),

Tommy McCANN (tmc@gfz-potsdam.de) &

Jörg F. W. Negendank (neg@gfz-potsdam.de)

GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany

The intracontinental NE German Basin is located between the stable Precambrian Baltic Shield to the north and the Caledonian/Variscan-influenced areas to the south. It forms part of the southern Rotliegend Basin, a series of interconnected basins extending more than 1500 km from England to Poland. Faulting, beginning in the Upper Carboniferous led to the development of an asymmetric basin with a gently dipping northern margin and a steep southern one. The current database consists of geophysical well logs and selected core material from 15 wells with Rotliegend strata together with newly-obtained deep seismic data (DEKORP Basin'96) and standard industrial profiles. The network of available seismic profiles cover an area of about 120x80 km along the northern margin of the NE German Basin.

The Upper Rotliegend basin infill, comprising predominantly continental sediments, is up to 1400 m thick and was deposited over a period of ca. 8 Ma. Depositional environments include playa lake and sabkha in the basin centre interdigitating with dune fields and alluvial fans at the margins. The sedimentary record shows a cyclicity generated by periodic transgressions and regressions of the pronounced perennial saline lake.

A series of detailed paleogeographic maps were constructed, showing the distribution of the main depositional environments, for the Upper Rotliegend. Of particular interest is the recognition of NE-SW-oriented channels, which acted as sediment transport conduits from the north, especially in the lowermost Upper Rotliegend. Sequence-stratigraphic analysis of geophysical well logs and core material allowed the recognition of a series of distinct sequences within the Upper Rotliegend succession. Control on the occurence of individual sequence cycles was climatic, related to changing lake levels within the basin.

D04 : 5P/03 : PO

Petrology and Sedimentology of Volcanic and Volcanoclastic Rocks in the Marginal Part of the Polish Permian Basin

Magdalena Panczyk (mpanczyk@geo.uw.edu.pl)¹,

Andrzej Barczuk (abarczuk@geo.uw.edu.pl) &

Pawel H. Karnkowski (phkarnk@geo.uw.edu.pl)²

¹ Institute of Geochemistry, Mineralogy and Petrology, University of Warsaw, Zwirki i Wigury 93, 02-089 Warsaw, Poland

² Institute of Geology, University of Warsaw

The Polish Permian Basin is the part of Southern Permian Basin which extended from England to Poland. The studied drills - Paproc-5, Zdroj-1, Ujazd-3, Ujazd-8 and Zielecin-1 are situated at the north-eastern margin of the Wolsztyn Ridge, west of Poznan (Western Wielkopolska).The Rotliegendes is represented by the volcanic rocks series - Wyrzeka Volcanites Formation, and overlying by sedimentary rocks - Ksiaz Wielkopolski Conglomerate Formation (Karnkowski, 1994, 1997). The rocks of those two formations are covered by 2000 m thick succession of Mesozoic and Cenozoic sediments.Thickness of the volcanogenic formation fluctuates between 100 and 200 m, but the volcanic rocks are eroded in many places. The lower part of the volcanic succession is represented by andesites which occures very locally (drill Paproc-5). The upper part of the volcanic series is represented by rhyolites and rhyodacites - lava flows (mainly carapace facies) and pyroclastic deposition (ignimbrites). All of volcanic rocks are highly hydrothermally altered (albitization, chloritization, carbonatization, silification and other processes) (Jackowicz, 1994).During the Upper Rotliegendes, after volcanic event, Wolsztyn Ridge became the alimentary area for adjacent sedimentary basin. Alluvial fans were accumulated at the basin margins, at the base of Wolsztyn Ridge, very close to the source area. Breccias and conglomerates which dominate in lower part of the profile of sedimentary rocks, contain fragments of the volcanic rocks (mainly acid-volcanic rocks) and older Paleozoic rocks like claystones, mudstones and sandstones. Sediments are poorly sorted and poorly rounded (Panczyk, 1998).The lateral and vertical changeability of the succession of the conglomeratic lithofacies resulted from interbedding of streamflow deposits, debrisflow as well as mudflow deposits, i.e. differentiation of volcanic and sedimentary processes.

Jackowicz E, Prace PIG, 145, 1-47, (1994).

Karnkowski PH, Geol. Quart, 38, 27-42, (1994).

Karnkowski PH, J Conf Abs, 1, 7-24, (1997).

Panczyk M, M. Sc. Thesis, 1-108, (1998).

D04 : 5P/04 : PO

2D-Modelling of Thermal History and Simulation of Gas Migration Along the NE German DEKORP Seismic Profile - Initial Results

Lothar Friberg (friberg@lek.rwth-aachen)¹,

Harald S. Poelchau (h.poelchau@fz-juelich)²,

Bernhard Krooß (h.poelchau@fz-juelich)² &

Ralf Littke (lek@lek.rwth-aachen)¹

¹ Lehrstuhl für Geologie,Geochemie und Lagerstätten des Erdöls und der Kohle, RWTH Aachen, Germany

² Institut für Erdöl und Organische Geochemie, Forschungszentrum Jülich, Germany

The Northeast German Basin is generally regarded as long-lived intracontinental sedimentary basin. The evolution started during Late Carboniferous or Early Permian times. Underlying Carboniferous rocks are considered to be the main source rocks for hydrocarbon gases and nitrogen in the basin. Using the DEKORP profile 9601, exploration seismic records and well data from the oil and gas industry, a 2D model of the Northeast German Basin was constructed. Along the profile and for selected deep wells the thermal and burial history was reconstructed, with the goal of modeling the migration of generated hydrocarbons and nitrogen from Carboniferous source rocks for a quantification of masses and volumes of generated gas.The thermal and burial history was calibrated by comparing measured and calculated vitrinite reflectance data. The kinetic Easy%Ro approach was applied for the calculation of vitrinite reflectance values. High paleo-heat flow of possibly 150-170 mW/m² (or even higher) at the initial time of basin evolution (rifting-phase) can be assumed. These high values, however, have no influence on the present-day coalification pattern. For most of the Mesozoic and Cenozoic period, moderate heat flows of about of 60 mW/m² are assumed.To improve the calibration of the thermal history, further investigations of temperature sensitive parameters (fluid inclusions, illite crystallinity) are currently performed. Open system non-isothermal pyrolysis is used to determine the generation potential of methane and nitrogen and the corresponding and kinetic parameters. These experimental data are used in a kinetic model to estimate timing and efficiency of gas generation in the NE German basin and to assess, in a subsequent step, the gas migration-pathways.

D04 : 5P/05 : PO

3D-Backstripping with Salt-Redistribution Exemplified by the NE-German Basin

Bjoern Lewerenz,

Ulf Bayer &

Magdalena Scheck

Albert-Einstein-Strasse, Telegrafenberg, Haus C, Potsdam, Germany

The Mesozoic evolution of the NE-German basin is strongly overprinted by salt tectonics which hide the major elements of the structural development.Here we illustrate a method which allows three-dimensional backstripping together with mass preserving redistribution of the salt dependent on the load of the overlying sediments. The salt is considered as a viscous fluid which is always close to hydrostatic equilibrium with regard to the overburden. This assumption is a rough first approximation, which, however, allows to solve the inverse problem uniquely as can be derived from the basic equations.

Applying this method yields paleotopographies which are in good agreement with facies patterns. In addition, the short wavelength salt tectonics is filtered out and the temporal evolution of the major tectonic elements becomes visible as will be illustrated by a comparison of backstripping results with and without salt redistribution.

D04 : 5P/06 : PO

The Role of Salt for the Development of the NE German Basin: Results from 3D Structural Modelling and Reflection Seismic Data

Ulf Bayer (bayer@gfz-potsdam.de),

Magdalena Scheck &

Bjoern Lewerenz

Albert-Einstein-Strasse, Telegrafenberg Haus C, Potsdam, Germany

The NE German Basin has a WNW trending axis and is located in the south-eastern part of the Southern Permian Basin. It contains 1000-2000 m of mobilised Upper Permian Zechstein salt below a Mesozoic-Cenozoic sedimentary sequence of some thousand meters. While the base of salt represents an almost flat and unfaulted surface in the basin area, the present day structural setting of the cover is strongly determined by a variety of salt structures like domes, pillows and diapirs. We analysed salt structure development using a 3D structural model based on seismic and well data.

Structural analysis and constraints from reflection seismic and well data suggest, that salt-tectonic deformation varied in time and intensity across the basin. The southern and eastern part of the basin is characterised by numerous salt diapirs piercing their cover layers, while the north-western part of the basin is dominated by salt pillows smaller in amplitude. Salt movement started during Late Triassic in the southern and in the eastern part of the basin whereas the basin centre in the NW was not affected by halokinetic deformation till Late Cretaceous and Cenozoic times. Our results indicate that salt movement during Late Triassic-Early Jurassic was slow and probably triggered by regional extension. This resulted in the formation of the NNE trending Rheinsberg Trough, a structure parallel to the Glueckstadt Graben in the NW German Basin and to the general trend of the North Sea Grabens. In contrast to the Graben structures in the western part of the Southern Permian Basin, no considerable normal faults cut the base Zechstein. Furthermore, evidence of dramatic, short wavelength thickness changes and of normal faulting is sparse in Triassic strata above the salt. Instead, we see a long wavelength thickness increase of Late Triassic Upper Keuper and Lower Jurassic sediments. Nevertheless, salt is almost removed below the Rheinsberg Trough. This indicates, that subsidence of the Rheinsberg Trough was balanced by slow lateral salt extrusion, thus accommodating regional extension without necessity of brittle normal faulting. The phase of slow lateral salt movement was followed by a relatively faster, diapiric phase with widespread removal of salt and salt margin formation in Cretaceous- Early Tertiary times. Furthermore, Late Cretaceous to Early Tertiary inversion structures are present in seismic sections. As the base of salt is almost undeformed below the basin, we can conclude that salt played an important role as a ductile decoupling horizon between its underlying basement and its cover layers due to its viscous rheology.

D04 : 5P/07 : PO

The Modeled Conductive Temperature Field of the NE-German Basin in Comparison with Temperature Measurements

Robert Ondrak (ondrak@gfz-potsdam.de),

Magdalena Scheck (leni@gfz-potsdam.de),

Christian Klesper (geochris@gfz-potsdam.de),

Andrea Foerster (for@gfz-potsdam.de),

Tommy McCann (tmc@gfz-potsdam.de) &

Ronald Gerisch (gerisch@gfz-potsdam.de)

Telegrafenberg, Potsdam, Germany

For the past four decades the NE-German Basin has been drilled extensively in the search for natural resources. Part of this dataset has been made available for research and was used to construct a 3D structural model of the region. The model covers an area of 330x230 km and focuses on the post-Carboniferous sedimentary basin fill. Although spatial resolution of this large-scale basin model is limited to a 4x4 km grid and cannot resolve all details, it includes important geological features, for example, large salt diapirs. The digital structural model provided the framework the calculation of the conductive thermal field using a 3D-FEM model. For the simulations, the stratigraphic units of the model were assigned average physical properties according to the dominant lithology of each stratigraphic unit. The resulting physical model was then used to calculate the present day conductive temperature field of the basin. In order to evaluate the simulated temperature distribution, we compared it with temperature data obtained from various wells throughout the basin. Depending on availability and quality of the data, continuos temperature logs or corrected bottom hole temperatures (BHT) were used. The agreement between modeling results and measured temperature data is good but needs to be improved in certain regions. Towards the northeast the model is warmer while in the center it is colder than the measured temperatures. This deviation is partly due to oversimplification of the model in terms of facies distribution, thickness of the pre-Permian sediments and incorrect physical properties of the rocks. As the variation of physical properties of the sediments alone is insufficient to obtain a reasonable fit between measured and calculated data, we also need to analyze the regional error distribution in terms of the physical properties of the underlying crust and the model resolution. The model has thus been improved with respect to the Carboniferous and pre-Carboniferous sediments particularly in the Rügen area. Expansion of the data set to include older units has led to increased refinement of the model. The observed discrepancies between modeled and measured temperatures in the NE part of the region may be elucidated by this more comprehensive model

D04 : 5P/08 : PO

A Case Study of Spatial Analysis of Petrophysical Properties in the Northeast German Basin

André Gardei (gardei@gfz-potsdam.de) &

Ernst Huenges (huenges@gfz-potsdam.de)

GFZ-Potsdam, Telegrafenberg, 14473 Potsdam, Germany

The Basin 96 seismic experiment covers a profile from the island of Rügen to the Harz mountains through the Northeast German Basin.Pre-Permian sedimentary section above the crystalline, which is resolved in the seismic experiment, plays an important role in understanding geological processes which may be influenced by fluids. Fluid transport pathways, are affected by continuous layers of low permeability. This study concentrates on a classification of those low permeability units in a small but important part of the profile. In the vicinity of the profile in the Rügen area 15 boreholes were selected for the study within a radius of 20 km. The boreholes are drilled to depths up to 7.5 km.The objective of this study is to investigate the permeability structure along those borehole profiles. However, only few permeability data are available yet. Therefore indirect methods based on permeability and relationships between other petrophysical properties have to be developed and then to be applied to resolve the permeability changes in the area.In this study, existing borehole measurements are combined with new petrophysical measurements on core samples. Elastic and electric properties as well as radiogenic heat production data are compiled and collected in a database. The data represent selective properties from different depths which have undergone a different geohistory. Preliminary, we concentrate on the upper Carboniferous / Westphalian units, especially on the Jasmunder layers. The sampling started at Barth 1/63, Binz 1/73, Lohme 2/70, Loissin 1/70, Rügen 2/67,and Rügen 4/64 boreholes. 84 core samples of fine-grained sandstone, sandy siltstone ,and claystone were recovered. The microscopic analysis combined with a digital-image-analysis system, is used to verify grain size, pore size and distribution, also the mineral ingredients will be identified. Permeability variations in 1D (at borehole scale) are mainly controlled by differences in material composition, whereas in 3D (in a regional scale) the specific geological history modifies the conditions. We conclude that, for 3D-modelling and interpretation of petrophysical properties knowledge of the burial history is indispensable.

D04 : 5P/09 : PO

Heat Transfer in Northeastern Germany: A Preliminary 3-D Uncertainty Analysis for Parameters in the Sedimentary Basin

Holger Lehmann (holger.lehmann@bgr.de) &

Christoph Clauser (c.clauser@bgr.de)

GGA, Stilleweg 2, 30655 Hannover, Germany

The temperature field in the sedimentary basin of northeastern Germany is studied in respect to disturbances caused by variuos geological conditions. Successful simulations of basin evolution require as input information on the thermal regime corrected for the influence of effects due to lateral refraction of heat, groundwater flow etc. In the northeast German sedimentary basin many 3-D salt structures distort the heat flow regime due to their relatively high thermal conductivity. Therefore, we used an inversion technique based on the Bayesian parameter estimation to constrain parameters involved in heat transfer and their standard deviations. The model area was discretized into a mesh of finite elements along the local DEKORP profile (about 300 km long). This reflection seismic profile crosses NE-Germany from the island of Rügen in the Baltic Sea to the Harz mountains. Structural information from the DEKORP project, temperature measurements in boreholes near this profile, and thermal conductivities from the main geological rock units are combined in a first 'a priori' model. The 3-D inversion algorithm yields 'a posteriori' information for thermal conductivity within the model area, the vertical heat flow density at the base of the model as well as for temperature. The 'a posteriori' standard deviations of these parameters were used for a preliminary uncertainty analysis. An uncertainty range was obtained for the vertical heat flow density at the base of the sedimentary basin. This information is available for other researchers as input for basin evolution models. The influence of advective heat transfer in the upper part of the basin was analysed in a 2-D inversion which treats conductive and advective heat transfer simultaneously. Variations in the 'a priori' constraints of the thermal and hydraulic parameters indicate the significance of different competing heat transport mechanisms.

D04 : 5P/10 : PO

Gravity Images of the Trans-European Suture Zone

Paul Williamson (p.williamson@bgs.ac.uk),

Dirk Banka (d.banka@bgs.ac.uk) &

Tim Pharaoh (t.pharaoh@bgs.ac.uk)

British Geological Survey, Keyworth, Nottingham NG12 5GG, UK

Recent work has concentrated on compiling a consistent gravity data set for the TESZ project area using data contributed by project participants. This poster presents maps of the latest gravity compilation, together with maps derived by applying various transformations to the data, designed to enhance the structural information that is contained in the gravity data. The gravity images highlight the various sedimentary basins that occur along the TESZ and in the southern North Sea. The spatial relationships between the gravity and magnetic anomalies are also displayed. This work contributes to the study of the origin of basins within the TESZ, part of the programme of research to be carried out by the EC-funded PACE TMR Network.

D04 : 5P/11 : PO

Magnetic Images of the Trans-European Suture Zone

Dirk Banka (d.banka@bgs.ac.uk),

Paul Williamson (p.williamson@bgs.ac.uk) &

Tim Pharaoh (t.pharaoh@bgs.ac.uk)

British Geological Survey, Keyworth, Nottingham NG12 5GG, UK

Recent work has concentrated on compiling a consistent magnetic data set for the TESZ project area using data contributed by project participants, supplemented by available data in the public domain. This poster presents maps of the latest magnetic data compilation, together with maps derived by applying various transformations to the data, designed to highlight the structural information contained in the data. The depth to source of the magnetic anomalies is also estimated using a deconvolution technique. The magnetic images show primarily basement and igneous features and provide information on underlying controls on the formation of the sedimentary basins along theTESZ. This work contributes to the study of the origin of basins within the TESZ, part of the programme of research to be carried out by the EC-funded PACE TMR Network.

D04 : 5P/12 : PO

Late Proterozoic-Early Paleozoic Tectonic Evolution of the Central Part of Western Baltica Edge (Lublin-Podlasie Basin) ­ Subsidence Analysis

Pawel Poprawa (ppop@pgi.waw.pl) &

Jolanta Paczesna (jpacz@pgi.waw.pl)

Polish Geological Institute, ul. Rakowiecka 4, 00-975 Warszawa, Poland

Subject of the study is Late Proterozoic-Early Paleozoic Lublin-Podlasie sedimentary basin. Recently this is represented by separate tectonic units, i.e. Lublin slope of East European Craton (EEC) and Podlasie Depression, located in the central part of eastern Poland. During Late Proterozoic-Early Paleozoic the basin constituted central part of Peri-Tornquist basin, developed along south-western margin of EEC. The analysed area constituted also SW prolongation of Proterozoic Volyn-Orsha aulacogen.

For the Lublin-Podlasie basin subsidence analysis was conducted by means of backstripping. The results show coherent pattern of subsidence across the analysed area. This is characterised by two main tectonic subsidence events, in the Late Proterozoic-Early Cambrian and Late Silurian respectively. The first one was initiated in the Late Proterozoic with emplacement of rift-related continental basalt volcanism, after which period of very rapid subsidence started (Late Proterozoic-Early Cambrian). The subsidence started earlier (Neoproterozoic) in the Lublin basin, affecting progressively wider area in time, including Podlasie basin. Subsidence systematically ceased during Middle Cambrian-Middle Ordovician, creating overall curves pattern typical for extensional basins.

Rift model is proposed here to explain observed Late Proterozoic-Middle Ordovician subsidence pattern. The Late Proterozoic-Early Cambrian time span represents syn-rift stage, and is related here to break-up of Rodinia supercontinent and opening of the suspected Tornquist Ocean. Subsequently ceasing subsidence and expanding depocentres during Middle Cambrian-Middle Ordovician are interpreted as post-rift thermal subsidence stage. In this scenario the area constitutes passive continental margin of suspected Tornquist Ocean, which developed to the SW of Baltica edge. This is coherent with subsidence analysis results of Baltic basin further to the NW along Baltica margin (Sliaupa et al., 1997).

Since the Late Ordovician gradual increase in subsidence rate in time is observed, which reaches maximum in the Late Silurian. As a result subsidence curves have shapes characteristic of compressional tectonic regime. This is also paralleled by systematic increase of subsidence from NE to SW across the area, i.e. towards SW Baltica margin, giving a pattern typical for flexural bending of lithosphere. Such character of Silurian subsidence in the Lublin-Podlasie basin is related here to influence of Caledonian orogeny, ongoing further to the west and SW of analysed area, i.e. to collision of Baltica with Eastern Avalonia and other Gondvanian provenience microplates (e.g. Oliver et al., 1993). This is coherent with results of subsidence analysis of Baltic basin further to the NW (Poprawa et al., 1997).

Late Proterozoic-Early Paleozoic tectonic processes of the western Baltica edge, including analysed here SW edge of EEC, contributed to the structure of Trans European Suture Zone (TESZ). Therefore these are of considerable importance for geological interpretation of deep geophysical investigations of this zone, as well as for revealing nature of TESZ.

Oliver GJH, Corfu F & Krogh TE, Journ. Geol. Soc, London, 150, 355-369, (1993).

Poprawa P, Narkiewicz M, Sliaupa S, Stephenson RA & Lazauskiene J, Terra Nostra, 97/11, 95-102, (1997).

Sliaupa S, Poprawa P, Lazauskiene J & Stephenson RA, Geoph. Journ, Kijv, 19, 137-139, (1997).

D04 : 5P/13 : PO

Palaeotectonic Conditions of Mesozoic Basin Development of the Mid-Polish Trough (Holy Cross Segment)

Jolanta Swidrowska (jswidrow@twarda.pan.pl) &

Maciej Hakenberg (mhakenbe@twarda.pan.pl)

Instytut Nauk Geologicznych, Tward A 51/55, 00-818 Warsawa, Poland

Maps of deposit accumulation rates, treated as a reflection of subsidence rates, coupled with the recognition of sedimentary conditions, make possible to distinguish synsedimentary fault patterns characterizing Late Permian-Late Cretaceous basins which developed along the Trans-European Suture Zone (TESZ). Synsedimentary faults, identified as zones of big subsidence gradients, determine the geometry of basin infill and give evidence for palaeostress field evolution controlling basins development. The multiphase tectonic history includes five discrete episodes of accelerated subsidence: Late Permian-Early Triassic, Early Jurassic, Late Jurassic, Late Albian and Turonian (Dadlez et. al., 1995; Hakenberg, Swidrowska, 1997, 1998). The first two and the Turonian one were connected with increasing activity of basin bounding faults. At the beginning (Late Permian-Early Triassic)the pre-existing Holy Cross fault was reactivated as a bounding fault. Only this episode was strong enough to be considered as an early rifting stage devoid of volcanism. Later on,faults parallel to the TESZ gained in importance: as the first one Nowe Miasto Ilza fault during the Early -Middle Jurassic times bounded the trough from the NE, and, as the second one, Przedborz-Mielec fault took over the role of the bounding fault during Turonian. These NW-SE trending synsedimentary fault zones coincide with boundaries of Late Cretaceous-Early Palaeogen inversion.

The Holy Cross segment of the Mid-Polish Trough was probably iniciated under simple shear conditions during Late Permian-Early Triassic times. A strike-slip component can not be proved here or excluded. The role of strike-slip component is more distinct from Early Jurassic and coupled with stages of accelerated subsidence. During Jurassic-Cretaceous times the clockwise rotation of the strike-slip stress field can be suggested. This rotation was followed by variation of character of strike-slip component along TESZ: from sinistral (Early Jurassic-Middle Albian) to dextral one (from the Turonian till inversion time). The basin developed in transtensional regime till the end of Turonian, afterwards in transpressional regime as the result of growing value of the principal maximum stress. The gravitational stress field manifested themselves three times during basin history (Middle-Late Triassic, Late Jurassic-Early Cretaceous, Cenomanian). Except Late Jurassic these episodes were connected with decrease of subsidence rates. The succession of palaeotectonic strike-slip conditions of basin opening seems to be compatible with the relative movements between Africa and Eurasia plates during Eary Jurassic-Late Cretaceous time span.

Dadlez R, Narkiewicz M, Stephenson RA, Wisser MT & Wees van JD, Tectonophysics, 252, 179-196, (1995).

Hakenberg M & Swidrowska J, C. R. Acad. Sci. Paris, 324, 793-803, (1997).

Hakenberg M & Swidrowska J, Geological Quarterly, 42, 239-262, (1998).

D04 : 5P/14 : PO

The Border of East European Craton (EEC) in Southeastern Poland on the Basis of Gravity and Magnetic Data Interpretation

T. Grabowska &

G. Bojdys

Institute of Geophysics, University of Mining and Metallurgy, Cracow, Poland

According to recent geological views (Pozaryski, 1997), the border of the East European Craton (EEC) in southeastern Poland lies in the northeastern foreland of the Holy Cross Mts., in the Radom-Lysogóry subregion of the Malopolska Block. The border is almost parallel to a few dozen km distant front of the Caledonian deformations (CDF) thrust onto the craton. Such location of the deep-seated craton's border is confirmed by preliminary results of electromagnetic sounding made along a profile intersecting the Holy Cross Mts. (Semenov et al., 1998) as well as by results of gravity and magnetic anomaly interpretation presented in this paper.

Results of 3D gravity modeling for the Mazowsze-Lublin Trough show that a regional structure with increased density and increased magnetic properties is present in the crystalline crust. The most elevated portion of this structure reaches the uppermost parts of the crystalline basement; it is located in the southeastern segment of the TTZ where an anomalous zone, caused probably by intrusion of basic rocks from the upper mantle (Guterch et al., 1996), occurs in the crust at a depth of several km. The boundaries of this regional structure, obtained from 3D modeling, clearly shows in the Radzyn-Goczalkowice profile that intersects the main geological units of SE Poland. According to 2D gravity and magnetic modeling made along the Radzyn-Goczalkowice profile, the SW border of this structure lies near a deep fracture delimiting the TTZ to south-west. The origin of a regional magnetic gradient observed there was also explained by this modeling.

As a result of qualitative interpretation of gravity anomalies, two SE-NW belts of positive residual anomalies, delimited by gradient zones, were identified. They point to dislocations occurring in Paleozoic formations. They are also proved by stripping Mesozoic formations, particularly flexure-fault structures and related anticlines identified by geological survey (Zelichowski, Kozlowski 1983, Pozaryski, 1997).

It should be emphasized that the belts of positive residual anomalies are observed very close to the regional magnetic gradient zone, the southwestern border of the TTZ, and the southwestern edge of the regional structure in the crystalline crust.

Guterch A, Lewandowski M, Dadlez R, Pokorski J, Wybraniec S, Zytko K, Grad M, Kutek J, Szulczewski M, & Zelazniewicz A, Publ. Inst. Geophys. Pol. Acad. Sci, M-20 (294), 1-44, (1996).

Pozaryski W, Prz. Geol, 45 No 12, 1265-1270, (1997).

Semenov VYu, Jankowski J, Ernst T, Józwiak W, Pawliszyn J, Lewandowski M, Acta Geophys. Pol, 46 No 2, 171-185, (1998).

Zelichowski AM, Kozlowski S, Atlas Geologiczno-Surowcowy Obszaru Lubelskiego, scale 1 : 500 000 IG. Warszawa, (1983).