Journal of Conference Abstracts

Session D08:5A

D08 : 5A/01 : F6

Cenozoic Kinematics of Basin Formation in Northeast Asia

Paul Wheeler (wheeler@esc.cam.ac.uk) &

Nicky White (nwhite@esc.cam.ac.uk)

Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, UK

Northeast Asia consists of a number of major sedimentary basins which include the Bohai, Yellow Sea, Japan Sea (Yamato and Ulleung), Cheju and East China Sea (ECS) basins. The kinematics, that is, rift duration, total strain, strain rate and uplift periods, for these basins are poorly known. A Late Cretaceous drop in Pacific/Eurasia convergence rate (Northrup et al., 1995) coincides with the onset of extension in the ECS and Yellow sea. With a further drop in convergence rate extension was transferred ~1500 km inboard from the subduction zone to the Bohai area. The first Bohai rift event initiating at 50-45 Ma (av. ß1.28) lasted c.20 Ma, followed by 3-500 m of uplift concentrated in the north. A second rift event (c. 8 Ma to present) is spatially coincident with increased seismicity and, relative to the first rift event, has its locus offset to the south. The transferral of extension inboard may be related to thermal heterogeneity generated by an earlier orogeny. Compression in the Bohai, ECS and Yellow Sea is coincident with the initiation of extension in the Japan sea (32-28 Ma). Extensional strain rates from the Japan Sea (5x10^-15) are a half to a full order of magnitude higher than other intracontinental rift basins but are of the same order as the Aegean and are probably characteristic of backarc basins in general. There is good evidence for extensional strain rate being influenced by proximity to the source of the extensional force (i.e. the subducting slab). Large clockwise rotation of southeast Japan may have driven Mid-Miocenetectonic inversion in the north ECS. A switch to compression in the Japan Sea occurred during the Late Miocene at the same time as extension began in the Okinawa trough. It is a general observation that along the ECS/Japan sea subduction zone the initiation of compression in one portion of the subduction zones length tends to facilitate the initiation of extension in the adjacent zone.

Northrup C, Royden L, & Burchfiel B, Geology, 23, 719-722

D08 : 5A/02 : F6

Triassic-Jurassic Evolution and Palynostratigraphy of the Junggar Basin ­ one of the Major Hydrocarbon Basins of China

A. Rahman Ashraf (epias01@uni-tuebingen.de)¹,

Che Li²,

Volker Mosbrugger (volker.mosbrugger@uni-tuebingen.de)³,

Yu-Ke Shang⁴,

Ge Sun (gsun@jlonline.com) &

Xinfu Wang (wangxinf@jlonline.com)

¹ Institut f. Geologie u. Paläontologie, Sigwartstr.10, 72076 Tübingen, Germany

² Regional Geological Surveying Party, Bureau of Prospecting and Development of Geology and Mineral Resources of Xinjiang, Ministry of Geology and Mineral Resources, 8 North Tianjin Road, Urumqi, Xinjiang, China

³ Institut u. Museum f. Geologie und Paläontologie, Sigwartstr.10, 72076 Tübingen, Germany

⁴ Nanjing Institute of Geology and Paleontology, Academia Sinica, Chi-Ming Ssu, Nanjing 21008, China

Beside the Tarim and Turpan basins, the Junggar basin is one of the three great hydrocarbon basins located in the Xinjiang Uygur Autonomous Region of Northwest China containing about 1.3 billion tons of oil and abundant coal and gas. The basin is bounded on the Northwest by the West Junggar Mountains, on the Northeast by the Altay Shan, and on the South by the Tian Shan. The Junggar basin was cut off from marine sedimentation during the Carboniferous to Early Permian due to the collision of the Tarim craton with the Southern margin of central Asia and the uplift of the "palaeo-Tian Shan". The Permian-Tertiary sediments may attain a thickness of approximately 16 km in the centre of the basin; the Mesozoic sediments are up to 6 km in thickness and were deposited in a lacustrine and fluvial to deltaic environment. In addition, the palaeolatitudinal position of the Junggar Basin remained more or less constant during the Mesozoic and is comparable to the present-day position (44° to 46° N). Therefore, climate change due to plate movements across latitudes cannot played a major role in the evolution of the Junggar basin and in the formation of its oil, gas and coal resources.

Despite its economic importance, its excellent outcrops and abundant plant and vertebrate fossils, surprisingly little is known about the stratigraphy, sedimentology and evolution of the basin as well as about the climatic and geodynamic boundary conditions under which the hydrocarbon reservoirs were formed. Here we present results of an interdisciplinary sino-german research project on the environmental, sedimentary and climatic evolution of the Junggar Basin in the Triassic and Jurassic. As a first step a palynostratigraphic scheme is established which allows to correlate the Junggar basin with time-equivalent basins in Afghanistan, Iran and Germany. Based on this information the general sedimentary evolution in these basins is compared and a preliminary environmental and climatic model for the formation of a typical "coal cycle" in the Junggar basins is presented.

D08 : 5A/03 : F6

Stratigraphic Developments in Coeval Rift and Post-Rift Basins: An Example from Late Oligocene to Miocene Series of Taiwan

Tien-Shun Lin (andrew.lin@earth.ox.ac.uk),

Stephen P. Hesselbo (stephen.hesselbo@earth.ox.ac.uk) &

Antony B. Watts (tony@earth.ox.ac.uk)

Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR, UK

Adjacent and coeval basins, the Taihsi-Taichung and Tainan Basins, existed in Taiwan in a rift-type continental margin during Late Oligocene to Miocene that now underlies a foreland basin sequence. Over these time intervals, the basins were subject to post-rift subsidence and intermittent rift tectonics respectively. The objectives of this study are to document the stratigraphic architecture of these coeval rift and post-rift sediments and to determine the spatial and temporal variations of the rift tectonics within the Tainan Basin. A sequence stratigraphic correlation on wireline logs from approximately 200 boreholes was carried out in the present work.

This analysis shows that whilst two rift phases with an intervening tectonically quiescent period occurred in the Tainan Basin, the Taihsi-Taichung Basin was undergoing continuous post-rift thermal subsidence. The rifting history of the Tainan Basin has been confirmed by backstripping the stratigraphic data used Airy-type and flexural models.

During the first rift phase, from Late Oligocene to Early Miocene (NP24 to early NN2), the Tainan Basin began its development on Mesozoic basement. Rift tectonics mainly occurred in the area which now corresponds to the Central Uplift Zone of the Tainan Basin. Three subsidiary rift stages (early, climax and late rift stages) of the first rift phase signal a marine rift succession, with an overall fining-upward to coarsening-upward rift signature in the rift basin centre. The principal reservoir and source rocks of the Tainan Basin are interpreted as being formed during early rift and rift climax stages respectively. Meanwhile, sediments (NP25 to early NN2) penetrated by drilling in the Taihsi-Taichung Basin were fluvial to coastal in origin and onlapped onto its neighbouring basement highs along a pronounced break-up unconformity. The break-up unconformity is interpreted as a result of oceanic spreading of South China Sea initiated in the Oligocene.

During Early to Middle Miocene (late NN2 to NN6) all the basins and platforms experienced tectonic quiescence. Stratigraphic sequences can be correlated inter-regionally. In particular, three maximum flooding surfaces, namely the Mollusc Limestone, Orbitoid Limestone and Operculina Limestone exist pervasively in the study area. Sequences comprise a suite of sediments deposited in coastal to shallow marine environments except in the Taihsi-Taichung Basin where few fluvial and deltaic excursions occurred.

From Middle to Late Miocene (NN7 to NN11), probably extending into Plio-Pleistocene, another rift episode occurred in the Tainan Basin while all other regions remained in tectonic quiescence. The rift centre was in the northern Tainan Basin, where a major graben, the Northern Depression of the Tainan Basin developed. Sediments deposited in the Tainan Basin were mainly marine mudstone and the coeval sediments in the Taihsi-Taichung Basin were mainly fluvial in origin.

D08 : 5A/04 : F6

Geological Evolution of the Precaucasus Hydrocarbon Basins

Alexandr Konyuokhov (koshchug@geol.msu.ru),

Boris Sokolov &

Nourdin Iandarbiev (eaablia@geol.msu.ru)

Geological Faculty, Moscow State University, Vorobievy Gory, Moscow, Russia

There were several stages in the geological history of the Precaucasus sedimentary basins (Azov - Kuban and Eastern Precaucasus), that we can distinguish. Their development started in the Late Permian and was going on during the Mesozoic when these basins were included in the southern continental margin of the Russian craton. Large river deltas evolved there in Early and Middle Jurassic times. A chain of salt lagoons occurred in the Tithonian to the south of the modern Stavropol dome and Nogai step. The thick salt successions were deposited in those lagoons. During the Cretaceous and Paleogene a wide carbonate platform formed in these places, with biomorphic, detrital, algal and oolitic limestones that compose the successions with a thickness of about 1500-2500 m. At the final stades of the closure of the Tethys, the old continental margin became to break down quickly. Many tectonic blocks which were included into the Mesozoic - Paleogene carbonate platform previously, subsided to the depth of about 500-1000 m, forming the sea floor of the very wide Maykop Basin. The new submarine slope extended from the Tuapse Trough to the North Caspian area. Many slides and slumps bodies, that can be seen on seismic profiles in these regions, confirm such a point. Clayey and muddy sediments were accumulated during the Late Oligocene and Early Miocene. The thickness of the Maykop Formation which is composed of mild water-saturated shales, change from 2 to 5 or even 6 km in the Precaucasus. As a result of the emergence of the Caucasus Mountains, which began in the Middle-Late Miocene, thick successions of mainly sandstones and siltstones were formed. Due to difficulties with the sedimentary and interlayered waters to escape from the thin-grained deposits, the Maykop shales began to move up forming the diapiric folds and then mud volcanoes that are wide spread in the Azov - Kuban and Terek - Caspian foredeeps. The great oil and gas fields were discovered in these areas. For example, we can mention the Terek and Sunzha rises. A great number of diapiric structures occur in the neighbouring parts of the Caucasus region, first of all in the Kura and Rioni depressions and on the Apsheron threshold and in the South Caspian Sea depression where they have the same origin. Thus, various successions evolved at different tectonic stades of the evolution of the Precaucasus sedimentary basins. More over, due to quick deposition and burying of thin-grained sediments with great thickness, the multiple tectonic deformations took place in the upper part of the sedimentary cover. Their development was related with the dia - and catagenetic transformations that occurred within shales and other deposits when they subsided to a depth of about 2 - 4 km.

D08 : 5A/05 : F6

Tectonic Evolution of the Northern Part of the Precaspian Basin During the Devonian Time

Alexandre Konyukhov (koshchug@geol.msu.ru),

Tran Hao &

Sergey Frolov

Geological Faculty, Moscow State University, Vorobievy Gory, Moscow, Russia

The northern margin of the Precaspian Basin was a part of the wide Sakmara land that extended from Pachelma Trough to the Paleo-Ural Ocean during the Early Paleozoic. At the beginning of the Devonian, this mainland started to break down quickly. By the Emsian only two uplifts, the Pugachev and Salt-Ilezk domes, remained in this area. Between them there was a sea inlet stretching from north-west to south-east. During the Early Eifelian time, the great Karachaganak lagoon evolved on the eastern side of this sea inlet. It was protected from the sea waves action by a chain of small bioherms and reefs. On the other side of the sea inlet, a narrow tidal flats were situated with submarine accumulative bars in of front them. The latters were formed by coarse-grained siliciclastic and calcareous sands while lime oozes and black clayey muds deposited in the lagoon and on the tidal flats. During the Late Eifelian, many reefal edifices originated in the northern part of the sea inlet along the latitudinal faults that separated neighbouring tectonic blocks. During the Givetian and Early Fransian, the input of siliciclastic material increased sharply, and a wide river delta with several lobes occupied the whole sea inlet. A thick succession of quartzose sandstones, siltstones and minor shales accumulated in the northern part of the Precaspian basin in this time. At the beginning of the Middle Fransian, the strong tectonic activation happened in this region. Some of blocks started to rise and deposits, that were formed earlier, were partially removed, mainly those of Givetian and Early Fransian age. The new marine transgression expanded from the South, rather than from the East and shallowsea water flooded the whole area soon. However, the tops of Pugachev and Salt-Ilezk domes as well as the Chinarevski and Karpovski swells rose above sea level as an archipelago of islands. Between them, several large lagoones developed in the Middle Fransian. The gipsum, anhydrite and clays with large content of organic matter accumulated there. In the first half of the Famenian, palygorskitic clays were deposited in the lagoones. One of them was protected from the sea waves by small reefs, others by the long shore bars. Thus, the distribution of various facies that were accumulated in the northern part of the Precaspian Basin in the Devonian was tightly related to tectonic movements.

D08 : 5A/06 : F6

Quartzite Occurrences in Mugla-Milas, Kocayayla Region Southwestern Anatolia, Turkey

Murat Budakoglu (budakoglu@itu.edu.tr),

Ahmet Celenli (celenli@itu.edu.tr),

Mustafa Kumral (kumral@itu.edu.tr) &

Fikret Suner (suner@itu.edu.tr)

Istanbul Technical University, Faculty of Mines, Geology Dept. 80626 Maslak-Istanbul Turkey

The objective of this study is to investigate the geological properties and distribution pattern of quartzite occurrences in Kocayayla district which is situated about 12 km toward the north-east of the western - Anatolia -Mugla city- Milas town. The study area is located in Menderes Massif which has formed by the effect of major tectonic events during the period of Late Paroterozoic and later periods. The target are was studied to prepeare a detailed geological map in scale of 1/10.000 and thus the quartzite-micashist-albite formation borders are found in the host rock gneiss. In the study area, quartzite zones are scattered within an area of about 20km² and extend towards northeast-southwest direction and albite and mica-shist veins accompany to these units along the same direction.

The main quartzite occurrence is observed around Kucukcakmak Crest which is located in southwest of the study area and have 3 km length and 10-30 meters width in the N-E direction. The visible reserve of these occurrences is about 25 million metric tons. Additionally another quartzite vein, which is less important and parallel to the main quartzite zone, exposed at 100 m. west of Kurttasi district. In polarizing microscope, it is observed that quartzite samples consist of quartz minerals in siliceous cement. On the other hand, some iron oxide remarks can be seen in hand specimens.

The mineralogical examinations using polarizing microscope shows that this unit has granoblastic texture. Rose diagram, which has done by using a number of dip and strike data clearly revealed that the main pressure direction is toward northeast and quartzite-albite occurrences formed as parallel to this structure.

Quartzite has a wide spectrum of industrial use such as glass, ceramic, paint, detergent, construction and refractory. In Turkey, three big flotation establishments are currently in function.

D08 : 5A/09 : F6

Eocene Regional Uplift West of Ireland

Steve Jones (jones@esc.cam.ac.uk)

Bullard Laboratories, Madingley Road, Cambridge CB3 0EZ, UK

The distribution of sediments through the Cenozoic in the Porcupine Basin, west of Ireland, has been determined from a regional grid of seismic lines tied to wells. This basin had a sediment starved, deep water environment throughout the Paleocene. During the Eocene a series of deltas prograded into the basin from the north and west; well developed delta top facies show that water depths were extremely shallow at this time. There was a gradual return to deep water sedimentation through the Eocene and Oligocene. However this cannot be explained by stretching as there is no significant faulting during the Cenozoic. Subsidence modelling of the well data shows that the only way to explain all of these observations is to include a phase of regional uplift which begins abruptly in the early Eocene and then decays gradually. This transient uplift was caused by mantle convection associated with the Iceland Plume. Thus the subsidence modelling places constraints on the development of mantle convection through space and time.

D08 : 5A/10 : F6

Geodynamic and Geothermal Correlations in Sedimentary Basins. Impact on Hydrocarbon Formation (As Revealed in Saharan Basins)

Monzer Makhous (makhous@geodyn.pvt.msu.su)¹ &

Yurii Galushkin (gal@geodyn.pvt.msu.su)²

¹ Moscow State University, Geology faculty Department of Petroleum geochemistry, 119899 Moscow Russia, Russia

² Moscow state university, museum of earth, 119899 Moscow Russia, Russia

The relation between heat flux and the tectonics of sedimentary formations becomes more evident if one compares the maps of isogeothermal gradients with the structure of the Paleozoic complex of Saharan basins. It has been established that the isolines of geothermal gradients and the isotherms follow, in a broad outline, the relief lines of the crystalline basement.

Lithosphere thinning and thermal regime evolution at the rift stage of the basin development are computed with respect to space and time scales in the framework of lithospheric plate extension assuming an extreme limit of placticity. The modeling results including the variation of tectonic subsidence suggest, that the duration of thermal activation of lithosphere on the rift stage (as well as on reactivation stages) considerably exeeds that estimated in a model of instantaneous stretching of the lithosphere.

Models which consider formation of the instrusive body over time (as distinct from instantaneous intrusion) and especially models of emplacement of the intrusive body in the shell of relatively cool magnatic rocks show better agreement between computed and observed data. Hydrothermal heat transport can explain the different aureoles above and below some sills.

High vitrinite reflectance (Ro) values showing abrupt and sudden rise on Ro profiles could not be explained by simple subsidence. Our simulation showed that even an erosion amplitude as high as 1.5-2.5 km could not explain such sudden rise in Ro values. It is explained by convective heat flow due to simultaneous effect of intrusion and the induced hydrothermal activity in the sedimentary cover.

Modeling show that the ratio between sedimantation rates and thermal regime density determine the early maturation of organic matter (OM) in sediments on the rift stage of the basin development. Higher sedimentation rates considerably contribute to higher catagenesis level of organic matter (OM), including a secondary cracking of liquid hydrocarbons to gas ond coke.

The reliability of geodynamical modelling depends to a large extent on the reliability of delimitation of zones with distinct thermal regimes. To solve this problem, a comprehensive approach based on independent thermal criteria has been used. Thus, the thermal modeling is based on the following criteria:- vitrinite reflectance (Ro), which is a reliable parameter for paleogeothermal reconstructions because it is irreversible during the course of geological processes;- actual temperatures measured in bareholes or obtained by logging and properly corrected;- temperatures estimated from an analysis of the crystal structure features of clay minerals and zeolites (occurrence of definite structural polytypes, structural ordering of mixed-layer minerals, etc.). The crystal characteristics of clay minerals are, like the Ro parameter, irreversible with respect to geological inversions. For this reason, the temperatures, obtained on the basis of clay minerals, are reliable enough for paleogeothermal modeling. In distinction from the Ro parameter, which can be measured mainly in source rocks rich in kerogen (that is, starting from the Devonian), the thermal criteria, derived from the crystallinity of clay minerals, can be made readily available for all stratigraphic units.- kinetic simulation of the chemical reactions of maturation of organic matter. This points the way for evaluating the rate of tectonic subsidence using alternative methods, based on the rock density distribution due to temperature variations in the basement.

Modeled calculations of vitrinite reflectance (Ro, %) are achieved by kinetic model of kerogen maturation. The comparison of measured Ro and temperatures with respective calculated values and analysis of the variations of the basement tectonic subsidence amplitude are used as principal tools for reconstruction and control of basin modeling parameters as well as to control the sequence of tectonic and thermal events during the basin development (Makhous et al. 1997).

Makhous M, Galushkin Y, Lopatin N, AAPG Bulletin N°10, 81, 1660-1678, (1997).

D08 : 5A/11 : F6

A Coupled Petrological and Tectonic Model for Basin Evolution: The Influence of Metamorphic Reactions on Basin Subsidence

Katja Petrini (katja@erdw.ethz.ch),

James Connolly &

Yuri Podladchikov

ETH Zurich, Sonneggstr.5, 8092 Zurich, Switzerland

Variations in rock density influence loads in the lithosphere and hence basin subsidence and stress distributions. It is therefore of primary importance for models to use realistic density distributions in both space and time. This need has prompted the introduction of corrections for density variations due to thermal effects. However, density varies more strongly in response to continuous and discontinuous metamorphic reactions and this effect has been largely overlooked. In part this oversight can be attributed to the complexity of the relevant phase relations, and the difficulty of representing these phase relations in a form that can be incorporated in numerical models. To overcome these problems we have developed a program to calculate phase diagram sections. The program enables us to obtain a digital phase diagram section for a system with specified non-volatile chemistry. We are therefore able to incorporate thermodynamic properties, e.g. enthalpy and density, of the equilibrium mineral assemblages of a model rock as a function of pressure and temperature.

We have applied this technique in a 2D finite difference basin model. Such a tectonic setting is particularly appropriate to study the effects of metamorphic reactions because extension produces significant perturbations to the thermal regime. Our petrologic model allows us to continuously update the crustal and sedimentary load with the density changes related to metamorphic reactions (in particular devolatilization reactions) occurring as a result of the evolution of the thermal gradient. Our model produces realistic subsidence curves and reveals that density changes associated with metamorphic reactions play a significant role in the evolution of sedimentary basins.

D08 : 5A/12 : F6

A Three Dimensional Modelling Approach for the Manipulation of Stratigraphic Data in Potential Hydrocarbon Basins

Andrew John Richards (ggd19@keele.ac.uk) &

Graham Williams (gga41@keele.ac.uk)

¹ Department of Earth Sciences, Keele University, Keele, ST5 5BG, UK

Sequence stratigraphy in three dimensions presents a complex geometric problem when stratal patterns, lithologies and chronostratigraphic data are considered. A new technique for the display and analysis of sequence stratigraphic models in three dimensions is presented. A new data structure has been developed that allows for such manipulations to be made. The basis for this is a data structure based on the representation of stratigraphic and structural surfaces (faults and unconformities) as a series of triangles with shared nodes in x,y,z space. At each node an infinite number of attributes may be assigned such as chronostratigraphic age, lithology, porosity, density, permeability, grain size, etc., and each attribute may be incorporated into the three dimensional model and visualised in 3D. Utilising this data structure, attribute values may vary both vertically and laterally within the model, to allow a more accurate representation of the geological volume. Once the 3D model has been populated with attribute data, a number of manipulations are feasible. For one dimensional stratigraphic analysis, different types of burial history curves are used to analyse vertical stratigraphic development at any point in the model. This gives a predictive capability. Extended to 3D, the same algorithms can be used to visualise the compaction or decompaction of a sedimentary sequence. The isostatic response to the removal or addition of sediment may be modelled in 3D and this is useful in predicting palaeobathymetry in a sequential basin reconstruction. The data structure allows for the relationship between stratigraphic and structural surfaces to be visualised. Onlap and downlap patterns can be mapped on unconformity surfaces, whilst the associated ages of stratal lapout and truncation are used to define the ages of various unconformities within the model. The age attribute is used to plot the 3D model in terms of time (absolute age) as a chronostratigraphic model.

D08 : 5A/13 : F6

Mathematical Modelling of Compaction and Diagenesis in Hydrocarbon Basins

Xin-she Yang (yang_xinshe@uqar.uquebec.ca)

INRS-Oceanography, University of Quebec, 310 Allee des Ursulines, Rimouski (Qc), Canada

Sedimentary basins are prime locations for the formation of hydrocarbons, and are thus important in the oil industry as well as in geosciences. One particular problem in hydrocarbonexploration which affects drilling operations is the occasional occurrence of abnormally high pore fluid pressures, which, if encountered suddenly, can cause drilling collapse and failure. The modelling of compaction and diagenesis is thus vitally important to the understanding of how such high pore pressures occur and the evolutionary processes of hydrocarbon generation, migration and accumulations in sedimentary basins. Compaction due to pressure solution and diagenesis due to the transformation of smetite to illite have been considered as the two important processes in deformation and porosity change during compaction and diagenesis in sedimentary rocks. Mathematical models of sedimentary basins typically assume a relationship between effective pressure and porosity which is of a non-linear type (Audet and Fowler, 1992; Yang, 1997). However, at depths greater than a kilometre, pressure solution becomes important and causes this relationship to become more akin to a viscous one. A new mathematical model for compaction and diagenesis in sedimentary basins is presented and numerical simulations together with some mathematical analysis show how the model suggests radically different styles of behaviour in slow and fast compacting basins.

Audet DM & Fowler AC, Geophys. J. Int, 110, 577-590, (1992).

Yang XS, Computational Physics,Chemistry and Biology, Verlag Wissenschaft & Technik Berlin, 611-614, (1997).

D08 : 5A/14 : F6

Three-Dimensional Dynamic Models of Fault-Controlled Basin Formation ­ Application to Half-Grabens and Strike-Slip Basins

Andreas Henk

(andreas.henk@mail.uni-wuerzburg.de)

Institut fuer Geologie, Pleicherwall 1, 97070 Wuerzburg, Germany

Three-dimensional thermo-mechanical finite element models are used to study the formation and evolution of fault-controlled sedimentary basins. The study aims towards an improved understanding of basin subsidence on the basis of rheology and forces in the lithosphere. Special emphasis is laid on the question how extensional strain is partitioned between the different levels of the lithosphere, e.g. the genetic relation between surface deformation (uplift, subsidence) and deep crustal deformation (lower crustal flow). The numerical model comprises three layers with distinct thermal and mechanical material parameters: upper crust, lower crust and the strong part of the mantle lithosphere. Thermal calculations consider, among others, temperature-dependent conductivities and radiogenic heat production and assume a constant surface temperature and a constant basal heat flow, respectively. Lithospheric deformation is calculated assuming an elastic - perfectly plastic flow law with pressure-dependent yield strength in the brittle domain and temperature- and strain rate dependent power law creep in the viscous domain. A special feature of the modeling approach is the use of so-called contact elements to describe preexisting weaknesses in the crust, i.e. fault zones. This allows to model large differential movements between the independently meshed parts of the finite element model.

The numerical simulations are applied to two case studies from different geodynamic settings: the interaction of basin-bounding normal faults and transfer faults in a half-graben (Saar-Nahe Basin, SW-Germany) and basement subsidence and uplift in relation to movement along a strike-slip fault (Hanmer Basin, South Island, New Zealand).

Session D08:5B

D08 : 5B/21 : F6

Multichannel Reflection Study of the Southern Part of the Dead Sea Basin

Birgitte Larsen (Larsen@jupiter1.tau.ac.il) &

Zvi Ben-Avraham (zvi@jupiter1.tau.ac.il)

Tel Aviv, University, Department of Geophysics and Planetary Sciences, Ramat Aviv, 69978 Tel Aviv, Israel

The Dead Sea basin is a large strike-slip basin, (110 km long, 16 km wide and 6-12 km deep) located within the Dead Sea transform. The Dead Sea transform is a plate boundary separating the Arabian plate from the African plate and connects the divergent plate boundary in the Red Sea to the convergent plate boundary in the Taurus Mountains in southern Turkey. The basin is divided into two sub-basins. The northern basin is covered by a ~300 m deep lake and the southern basin is subareal. Over the years numerous multichannel seismic profiles have been obtained by the oil industry in the southern basin. These profiles reveal much detail about the internal anatomy of the basin and the active tectonic processes.The seismic reflection profiles were used to construct a series of two-way time structural maps and two-way time isochore maps, using the computer program ZYCOR, for the different reflectors and sequences recognized in the area. The electrical and geophysical logs were then used to relate the mapped reflectors and sequences with geological units. One of the new findings is that north of the large Amaziahu fault, that cut across the southern basin, the detailed seismic study shows movement of the depocenter towards the southeast probably in conjunction with movement of the fault. This is an interesting aspect since earlier studies suggest that on a larger scale, movements of the depocenter was towards the north. Another finding is the much larger amount of salt in the Dead Sea basin than earlier assumed. Also the close relationship between the movement on the large Sedom fault, a large normal fault striking north-south with offset up to 1000 m, and the salt tectonics is clearly visualized by this study. It shows that a large subsidence along the Sedom fault caused salt migration up the fault plane because of the extra load of sediments on the hanging wall.

D08 : 5B/22 : F6

Complexities of Basin Evolution in a Simple "Shelf" Setting

Helen Lewis (helen.lewis@pet.hw.ac.uk) &

Gary Couples

Dept of Petroleum Engineering, Heriot-Watt Univ, Edinburgh EH14 4AS, UK

The Carboniferous rocks of central Ireland were deposited onto a "basement" composed of slightly-metamorphosed lower Paleozoic rocks that were deformed in the Caledonian orogeny. In central Ireland, the carbonates and shales of this middle Paleozoic succession, once considered to be quite simple, in fact reveal a great deal of complexity in the sequence of motions that produced the accommodation space that was infilled. The basement surface (which was nearly planar before the Carboniferous depositional cycle) is now broken into an array of fault-bounded blocks that have been variously tilted and translated. Although there is a general subsidence of the basement across central Ireland, individual blocks changed their movement sense during deposition. Some blocks reversed their motion and actually moved upwards. Regions that were tilting became dormant, and unrelated regions began to tilt and subside in different patterns. Depositional variations are related to these changes in motion, and to the differences in compactional subsidence related to earlier Carboniferous variations in deposition. Although popular geodynamic paradigms can be applied to the central Ireland rock succession, the reasonable fit that can be achieved in many 1-D sites is often invalidated by evidence from a nearby locality. We believe that another geodynamic paradigm is needed to address the development of this setting, and perhaps other supposedly simple shelf settings as well. Within this region, fluid flow (during Carboniferous base-metal mineralization) was strongly influenced or controlled by the evolving tectonic pattern. Similar fluid flows may have occurred in many such shelf settings in other localities.

D08 : 5B/23 : F6

Interaction of Erosion and Tectonics at the Top Chalk Surface in the Danish Area

Ole R. Clausen (geolorc@aau.dk) &

Mads Huuse

Department of Earth Sciences, University of Aarhus, DK-8000 Aarhus C, Denmark

The Danish area comprises the eastern part of the North Sea Basin, bounded by the Sorgenfrei-Tornquist Zone to the east and the Central Graben to the west. The Top Chalk surface marks the change in deposition from carbonates (the Chalk Group) to the deposition of siliciclastic deposits, a change taking place during the Paleocene. The morphology of the Top Chalk surface reflects the accumulated post-Danian tectonics, but also the effect of erosion of the Chalk Group. The Chalk Group is generally overlain by fine grained clays, but in the eastern part of Denmark glauconitic greensand overlies the Chalk Group. However, in the western part Late Paleocene silty and sandy intervals are present within the clay dominated Late Paleocene succession (Danielsen et al. 1995).The overall dip of the Top Chalk surface in the Danish area is westward. The dip reflects the Cenozoic subsidence centred over the Mesozoic Central Graben and uplift at the eastern margin of the North Sea Basin. Superposed on the overall westward tilt: late Cenozoic erosion, mid Paleocene erosion, faulting along minor faults aligned in approx. E-W to ESE-WNW striking fault trends, reactivated salt-structures and flexures located above deep crustal faults all affected the present topography of the Top Chalk surface. A number of valleys cutting into the Chalk Group have been mapped across the Danish area. The valleys are filled with Late Paleocene siliciclastic deposits and a relation to the sandy intervals in the centre of the basin is suggested. The position of the valleys was highly influenced by the underlying structures. As an example: a major valley, the Ibenholt Valley is mapped continuously across the Danish North Sea and suggested to continue across the Danish onshore area. The position of the Ibenholt Valley was controlled by an interaction of the Ringkøbing-Fyn High and the previous mentioned fault trends, which are related to the pinch out of mobile Zechstein salt onto the Ringkøbing-Fyn High. Another example is the position of the Poul Valley, which was controlled by the Paleocene inversion of major crustal faults in the south-eastern Danish Central Graben.It is thus shown that the pattern of erosion observed at and the character of the sediments overlying the Top Chalk surface was controlled by regional tectonic movements, which reactivated deep crustal structures. A prominent effect of the reactivated older structural elements was the reactivation of salt-structures, which also affected the pattern of erosion.

Danielsen M, Clausen OR & Michelsen O, Terra Nova, 7, 518-527, (1995).

D08 : 5B/24 : F6

Architectural Elements in Sand-Rich Deep-Water Clastic Systems: Examples of Non-Lobe, Non-Channel Sand-Bodies from the Grès d'Annot (Eocene) of SE France

Simon A. Lomas (s.lomas@abdn.ac.uk),

Bryan T. Cronin (cronin@abdn.ac.uk),

Andrew Hurst (a.hurst@abdn.ac.uk) &

Xavier L. N. Dellamonica (x.dellamonica@abdn.ac.uk)

Geology & Petroleum Geology Department, University of Aberdeen, Aberdeen AB24 3UE, United Kingdom

How useful are the concepts of 'channel' and 'lobe' in the analysis of ancient sand-rich deep-water clastic depositional systems? It is becoming increasingly apparent that, for many sand-rich reservoirs and reservoir analogues, the key architectural elements may be fairway-filling sand-bodies, 15-80 m thick. In outcrop, such sand-bodies occur as prominent, laterally persistent topographic features that have been informally referred to as 'big monsters'. These 'big monsters' do not have characteristics attributable to lobes and can be considered channelised only in an extremely loose sense. They are discernible on 3D seismic data and have recently been recognised in modern confined deep-water systems in the Mediterranean. From outcrop studies it is clear that the 'big monsters' may be sedimentologically complex but relatively uniform in terms of reservoir properties. This contribution addresses the origins, stratigraphic significance and reservoir implications of such sand-bodies, focusing principally on well-exposed examples from the sand-rich Grès d'Annot turbidite system in the Trois Evêchés area of SE France.

D08 : 5B/25 : F6

The Onshore Mesozoic Erosion History of the NE Greenland Margin and its Implications for Offshore Basin Evolution

Kit Johnson (kit.johnson@ic.ac.uk) &

Kerry Gallagher (kerry@ic.ac.uk)

T.H. Huxley School of Environment, Earth Sciences and Engineering, Imperial College of Science, Technology and Medicine, London, England

The frontier areas of the North Atlantic margins are of major prospective importance although little is known about their petroleum systems. This is due in part to the very large thickness of Mesozoic strata that accumulated in the early rift axis prior to break-up between Greenland and Norway/Shetland in the late Thanetian - early Ypresian (57-55 Ma). Before break-up three of the most important frontier regions in the NE Atlantic, the Vøring, Møre, and Faroes-Shetland Basins, were adjacent to the NE Greenland continental margin between latitudes 66° and 75°N. The distribution of reservoir quality sands in the currently distal parts of these basins was controlled by the nature of the eroding source region on the east Greenland margin during the Mesozoic and Tertiary. The spatial and temporal distribution of onshore erosion can be constrained with apatite fission track thermochronology. Approximately 200 samples have been collected from NE Greenland between 68° and 75°N from the coast to 200 km into the continental interior. Initial results indicate two phases of rapid erosion, one in the mid Jurassic and another in the mid-Cretaceous. Further work is focused on resolving the detail of the late Cretaceous and Palaeocene erosion. The results can be integrated with regional scale structural data and what is known of the record of Mesozoic and early Tertiary sedimentation to provide a detailed picture of the onshore erosion and offshore deposition of the North Atlantic margins prior to break-up.

D08 : 5B/26 : F6

Constraining Relationships between an Evolving Hinterland and Basin Sedimentation Using a Combined Approach to U-Pb and Fission-Track Detrital Zircon Dating

Andrew Carter (a.carter@ucl.ac.uk)

Dept. of Geological Sciences, University College, Gower Street, London, U.K.

Correlation between changes in sedimentation and geodynamic processes operating in a source terrain are integral to the formulation of robust sedimentary basin models. Fission-track (FT) analysis, an ideal method for recording denudation history, can be used to extract source information directly from single detrital mineral grains contained within basin sediments. Apatite, the most commonly used mineral in FT analysis, has the highest level of thermal sensitivity (~60-110°C) but its widespread use in provenance studies is restricted by the effects of burial and post deposition heating which can modify or remove the original inherited FT provenance signature. Zircon the other widely used detrital mineral, although more stable (fission tracks in zircon are totally reset by temperatures >300°C), remains sufficiently sensitive to record changes in thermal regime in the uppermost parts of the Earth's crust.

The use of detrital zircon FT data as a tool for monitoring the geodynamic evolution of source is explored. A major limiting factor concerns what a measured zircon FT age actually records, does it relate to source cooling or zircon formation age? It is suggested that by adopting a combined approach to detrital zircon dating, using both U-Pb and FT methods preferably on the same grains, it is possible to discriminate between zircons that record metamorphic cooling and those that have a formation age. An example from the Mesozoic Khorat Group continental sediments of eastern Thailand is used to illustrate the advantage in adopting a dual method approach to detrital grain dating.

D08 : 5B/29 : F6

The Distribution of Potential Pre-Westphalian Hydrocarbon Source Rock in the North German Basin Derived from Magnetotelluric Data

Norbert Hoffmann (norbert.hoffmann@bgr.de)¹,

Hartmut Jödicke (jodicke@uni-muenster.de)² &

Wolfgang Müller (wm@bgr.de)³

¹ BGR 3.16, Wilhelmstr. 25-30, 13593 Berlin, Germany

² Institut für Geophysik, Corrensstr. 24, 48149 Muenster, Germany

³ BGR 3.13, Stillweg 2, 30655 Hannover, Germany

Magnetotellurics, a geophysical method applied for revealing the distribution of the electrical conductivity in the subsurface, is particularly appropriate for encountering and delineating deep good conductors, which may be due to TOC and pyrite-rich black shale (alum shale), commonly considered potential hydrocarbon source rock.

From an integrated geological and geophysical interpretation of 88 magnetotelluric soundings in the North German Basin, the authors have modeled the structural and paleogeographical development of the deep subsurface and, in particular, of the regional distribution of potential source rock in the pre-Westphalian.

Good electrical conductors have been found on the islands of Rügen and Usedom as well as on the northern mainland up to the Anklam fault in depths of 8 - 11 km. There, the good conductor is probably identical with the Early Paleozoic black shale (Scandinavian alum shale), encountered at a depth of 1.6 km in the Baltic Sea offshore well G 14, about 40 km north east of Rügen.

South of the Lower Elbe Line, good conductors appear at depths of 7 - 10 km in northern Brandenburg, southwestern Mecklenburg and northeastern Lower Saxony, i.e. in the external Variscan zone. They are correlated with Lower Carboniferous and Early Namurian black shale (Rhenohercynian alum shale), encountered for example in the Pröttlin 1 well (stillwater facies).

In the area between the Anklam fault and the Lower Elbe Line, any indications of good conductors within the pre-Westphalian sediments are missing, thus excluding the occurrence of source rock in this area. Scandinavian alum shale is probably missing because this area is part of the Caledonian magmatic arc, originating from the collision of East Avalonia with Baltica in the period between Ordovician and Early Devonian and characterized by positive magnetic and gravity anomalies (East Elbian Massif). The absence of Rhenohercynian alum shale is probably due to the fact that, in the Lower Carboniferous era, this area was not a stillwater (starved) basin, but probably a carbonate platform (Kohlenkalk facies).

D08 : 5B/30 : F6

Origin of Solid Bitumens on the Western Spitsbergen and on the Franz Josef Land

Nadezhda Cherevko (konanova@geo.komi.ru)

Institute of Geology, RAS, Pervomayskaya St, 54, Syktyvkar, 167610, Russia

The solid bitumens of the region of a ridge Vurmbrandegg on a southern coast of a gulf Hornsund on the Western Spitsbergen is observed in a triassic rocks. Solid bitumen is an anthraxolitewith distinctly expressed fluide texture. It is formed the balls in a containing rocks. Their sizes are about 0,8 cm in a diameter. Bitumen density is 1,81 g/cm³. Its element structure (%): C - 95,52; H - 0,99; S+O+N - 3,49.

The region on the Franz Josef Land when the bitumens are found is combined by triassic terrigenous formations, submitted by argillites, alevrolites and sand rocks. Sarface alevrolites-sand rocks are penetrated dikes of dolerites and basalts, consisting from strips dark-grey high density dolerites and grey irregular-porefirous-bubbly dolerites and basaltes. Dikes, in turn, are penetrated numerous cross veins of an hydrothermal origin. Near the dikes of dolerite-basalte the viscous bitumens -asphaltes-asphaltites is observed. Solid bitumen as kerite fill the pore and bubbies-chambers in containing rocks.

Three generations of asphaltes-asphaltites are allocated . There are the black viscous bitumen, viscous brown bitumen, solid brown bitumen. Their formation is connected with the halsedon-quartz-siliceous, calcit-opul-halsedonous and calcit-halcedonous mineralisation. Solid bitumens are submitted two kerite generations. Kerite of the first generation fills the bubbles-chambers in containing rocks. It has a spherical surface, on which the inflated spherical microhillocks are observed. On them the microcracks of dried volume is observed. These microcracks are filled of hematite. Thus hematete and bitumen form the continuous hematite-kerite of allocation. Kerite of the second generation is black solid scrap bitumen. It is observed in a containing rocks or as fragments of the wrong form, space between of which is filled by carbonate cement, or it is formed the independent formations.

The origin of solid bitumens on the Western Spitsbergen and on the Franz Josef Land is explaned by the hydrothermal inject of solutions with the oil hydrocarbons in postintruzious stage on zones of contacts of bodies dolerites contacting with the sedimentary rocks. Thus the solid bitumens carry out an information not only about hydrothermal, but also of hypergen changes. The presence solid bitumens on the Arctic Islands, obviously, is connected with the oil-gas-bearing basins of the Barents-North-Kara Area.

D08 : 5B/31 : F6

OF-Mod: A new Approach to Simulate the Deposition of Source Rocks at a Basin Scale

Ute Mann (ute.mann@iku.sintef.no) &

Are Tømmerås (are.tommeras@iku.sintef.no)

N-7034 Trondheim, Norway

Reservoir rocks are modelled successfully at a basin scale already, taking heterogeneity in the reservoir architecture and distribution of the reservoir unit in a sedimentary basin into account. Simulating the basin fill using stratigraphic models does this. But also source rock formations, e.g. the Kimmeridge Clay Formation in the Viking Graben, may vary significantly in their thickness, exceeding several hundreds of metres in the central parts of a basin, but may be missing to the outer edges due to erosion or non deposition. Large variations within a source rock interval in kerogen type and source rock quality can be observed laterally on a basin scale, but also along a vertical dimension in individual bore holes. These heterogeneities have to be considered carefully when source rocks are evaluated for petroleum potential. In terms of organic facies variations much more information is needed on the time-space distribution of kerogen composition and quantity. Although several conceptual models describing the spatial organic facies distribution at a basin scale have been developed in the last years, the development of a simulation tool for predicting variations in source rock quality/organic facies lags behind this development. So far, models estimating the organic carbon content of a source rock interval from wire-line log characterisation are only 1-D and they are not able to take quality variations within a source rock interval into account (e.g. Passey et al., 1990; Mallick and Raju, 1995).

A completely new aspect in discussing TOC predicting models is the combination of the organic facies concept with a stratigraphic basin fill simulation program. This combination enables not only to improve the prediction of quality changes within a source rock interval over a vertical scale. It will provide a better understanding of lateral facies changes and, moreover, it will enable quantitative predictions of source rock potential. And finally, it considers much better the aspects of organic matter preservation, sensitivity to variations in sedimentation rate, sediment dilution effects, and anoxia than existing TOC predictive models.

The processes controlling the deposition of the organic matter are key factors in understanding the distribution of the organic facies types. The OF-Mod simulator accounts for these processes, as they are numerically described in a 2-D computer simulation program developed in Java. This application is combined with stratigraphic basin fill simulation program Demostrat, which is a process-based, dynamic slope type model for siliciclastic settings. From Demostrat the "sedimentation related parameters", which are effecting the organic sedimentation are extracted (e.g., sedimentation rate, sediment density, sand/shale fraction, water depth, sea level fluctuations etc.). Here, we like to demonstrate first results of the capabilities of the OF-Mod simulator.

Passey QR, Creaney S, Kulla JB, Moretti FJ & Stroud JD, AAPG Bulletin, 74, 1777-1794, (1990).

Mallick RK & Raju SV, The Log Analyst, 49-63, (1995).

D08 : 5B/32 : F6

Fractured Reservoirs - Distributions Controlled by the Flexural-Slip Process

Gary Couples (gary.couples@pet.hw.ac.uk) &

Helen Lewis (helen.lewis@pet.hw.ac.uk)

Dept of Petroleum Engineering, Heriot-Watt Univ, Edinburgh EH14 4AS, UK

All petroleum reservoirs contain material discontinuities (joints, fractures, small faults, bedding-plane slip, etc). In some cases, their effects on flow are not noticed until late in the producing life of the field. In other situations, the flow heterogeneities associated with these features are recognized at the initial stages of development. In either circumstance, reservoir management requires an understanding of the distribution of both the discontinuities, and how individual discontinuity types affect the flow of fluids.

Our research indicates that the flexural-slip process is important in determining the sizes, orientations, intensities, and clustering of natural discontinuities (here referred to as fractures) in layered rock sequences. Heterogeneous stress states characterize domains that vary in time and space, leading to overprinting of deformation fabrics, and making interpretation difficult. During deformation, the material responses of rocks vary with lithology, porosity, grain size, and cementation. The deformation can also produce fractures that both enhance and degrade fluid flow within the same flexural structure. Although this complexity is often too great to resolve via data-driven methods, the process-based model can be used to explain and integrate the deformation fabrics observed through the usual sampling methods.

D08 : 5B/33 : F6

A Comparison between a Completely Dolomitized and Partially Dolomitized Devonian oil Reservoir: Simonette (Leduc Formation) Versus Ante Creek A & B (Swan Hills Formation)

Luc Rock (rock@geosci.lan.mcgill.ca) &

Eric W. Mountjoy (Eric_M@geosci.lan.mcgill.ca)

Earth & Planetary Sciences, McGill University, 3450 University Street, H3A-2A7 Montreal, QC, Canada

The Simonette and Ante Creek reservoirs are part of a series of extensive Upper Devonian reef complexes or buildups in the West-central Alberta Basin. Buried at depths of about 3510 and 3380 m, they are one of the few places in the Alberta basin where dolostone and limestone reef reservoirs can be compared, especially their similarities and differences in reservoir characteristics.

Ante Creek's lithofacies are similar to other Swan Hills buildups (Fischbuch, 1968). The Ante Creek buildup can be subdivided into two platform cycles and five reef cycles. In the Simonette Leduc reservoir, facies recognition is difficult as primary textures are obliterated by pervasive replacement dolomitization.

Similar diagenetic processes were observed in Ante Creek and Simonette. Commonly, the pores/vugs in the Simonette field are filled with saddle dolomite crystals coated by bitumen. A major difference is the greater amount of anhydrite in Simonette, a common feature in most Devonian dolomite reservoirs.

Vuggy, moldic, intercrystalline, and fracture porosity types predominate in the dolomite Simonette reservoir. Interparticle and intrafossil pore types were mainly observed in the limestones of Ante Creek. Following is a summary of porosity and permeability data from the three pools. Simonette has the highest average porosities and permeabilities with an average porosity ranging between 1.5 and 12.3% (mean of 5.2). In Ante Creek A, the average ranges between 0.5 to 10.9% (mean of 3.6) versus 0.8 to 10.7% (mean of 4.3) for Ante Creek B. The average horizontal permeability for Simonette ranges from 0.5 to 893 md (mean of 62). For Ante Creek A, it varies between 0 to 139 md (mean of 6) versus 0.8 to 409 md (mean of 125) for Ante Creek B. The average vertical permeability for Simonette ranges from 0.3 to 193 md (mean of 12). For Ante Creek A, it varies between 0 to 41 md (mean of 2) versus 0 to 21 md (mean of 3) for Ante Creek B.

Porosity and permeability is distributed almost uniformly throughout the Simonette pool. In the Ante Creek pool, reef stages two and three have the best reservoir characteristics. High porosity values are associated with the reef margin/reef interior facies. The highest permeability values are observed in dolomitized intervals.

Comparing these fields shows that depositional facies and diagenesis affect the distribution of porosity and permeability, as has been shown for other Leduc and Swan Hills reservoirs (Walls and Burrowes, 1985, 1990). At burial depths >2 km, porosity and permeability are reduced more in limestone than dolostone, as the latter are more resistant to pressure solution (Amthor et al., 1994). Porosity is mainly controlled by the depositional facies, whereas permeability is mainly affected by diagenetic processes, especially dolomitization (Mountjoy and Marquez, 1997).

Fischbuch NR, Bull Can Petrol Geol, 16, 444-556, (1968).

Walls RA & Burrowes OG, SEPM Sp Publ, 36, 185-220, (1985).

Walls RA & Burrowes OG, Diagenesis and reservoir development in Devonian limestone and dolostone reefs of western Canada, Can Soc Petrol Geol, 5.1-5.17, (1990).

Mountjoy EW & Marquez X, AAPG Mem 69, 267-306, (1997).

D08 : 5B/34 : F6

Hydrothermal Dolomitization of Triassic Evaporites on the W Margin of the SE Basin of France: A Record of the Seismogenic Activity of the Uzer Growth Fault at the Mesozoic

Claire Ramboz (cramboz@cnrs-orleans.fr)¹,

Choon-Gi Choi (cgchoi@etri.re.kr)²,

Marcel Volfinger (volfinge@cnrs-orleans.fr)¹ &

Ingrid Leost (i.leost@em.uni-frankfurt.de)³

¹ 1A, rue de la Férollerie, 45 071 Orléans-la-Source cedex2, FRANCE

² ETRI, Electronic Packaging Technology Section, 161 Kajong-Dong, Yusong-Gu, Taejon, 305-360, KOREA

³ Institüt für Mineralogie, J.W. Goethe Universität, Senckenberganlage 28, Postfach 11 1932, D 60054 Frankfurt/Main, GERMANY

Two cores were drilled along the Uzer fault on the W margin of the SE basin of France (Bonijoly et al., 1996). The BA1 borehole, located basinward, crosscut the fault in Middle Triassic evaporites at -1624 m, and the top of carboniferous sediments at -1669 m. At BA1, stratabound and fissural anhydrite on both parts of the fault is pervasively replaced by dolomite. We describe the microstructures and Fe-Mn content of dolomites analysed by EPMA over 400 m of sediments from the base of the core to the Rhaetian, together with trace element PIXE data.

Microstructures. In carboniferous beds, dolomites develop either in mm-wide cm-long tension fractures optically unzoned, or in mm-wide crack-seals with various orientations, sometimes zoned or with fibrous growth. In evaporites, en-echelon micro-cracks filled with zoned dolomite materialize the swelling of sediments below shaly seams by overpressured fluids, with local hydraulic fracturing. On top of the evaporites, zoned dolomites develop both in mm-wide tension gashes and as free crystals (=saddle dolomites). The anhydrite cement of overlying sandstones units is pervasively replaced by dolomites with numerous zoned vuggy overgrowths. Dolomite chemistry. The dolomites from Carboniferous beds, homogeneous at the vein scale, are enriched in Fe and Mn (25<Fe<40, 3<Mn<5 mole%). All zoned dolomites analysed in veins, vugs or in the matrix show scattered Fe-Mn values, with Fe-free cores and ankeritic overgrowths. Only the dolomites developed at -1624 m close to the fault show more complex zonings, with Fe-rich cores. At -1683, -1626, -1356 m, the Fe-Mn content of zoned dolomites are positively correlated (0<Fe<40, 0<Mn<4). Dolomites in sandstones overlying the evaporites also exhibit roughly correlated Fe-Mn values, however they show repetive transverse evolutions at constant Fe and decreasing Mn-contents to zero. Finally, trace element data on saddle dolomites at -1594 m show that the dolomitic and ankeritic growth stages occurred under close system and open system conditions, respectively.Interpretation. These results, in good agreement with fluid inclusion data in dolomites (Léost, 1998), show that the BA1 block was feeded by Fe-Mn-bearing hydrothermal fluids, which percolated from below and along the Uzer fault. They mixed with pore fluids, dolomitized and progressively reduced the evaporite environment. Impermeable evaporites acted as a seal which allowed the base of the core to be pressurized. However, due to fluid leakage on top of the seal, the overlying sandstones units were cemented by dolomites and also became pressurized. At BA1, dolomitization is a hydrothermal process related to the periodic weakening of the Uzer fault from the Lias to the Bathonian (Dromart et al., 1998).

Bonijoly D, Perrin J, Roure F, Bergerat F, Courel L, Elmi S, Mignot A & the GPF team, Marine Petrol. Geol., 16, 607-623, (1996).

Léost I., Unpubl. Thesis, Univ. Orléans, 139pp., (1998).

Dromart G, Allemand P & Quiquerez A, Basin Research, 10, 253-260, (1998).

Session D08:5P

D08 : 5P/01 : PO

Structure and Opening Stages of the Gulf of Guayaquil, Neogene Forearc Basin (South Ecuadorian Andes)

Yann Deniaud (ydeniaud@ujf-grenoble.fr)¹,

Patrice Baby (pbaby@pi.pro.ec)²,

Christophe Basile (cbasile@ujf-grenoble.fr)¹,

Georges Mascle (gmascle@ujf-grenoble.fr)¹,

Martha Ordonez³ &

Gallo Montenegro³

¹ Institut Dolomieu, LGCA, UJF, UPRES-A, CNRS 5025,, 15 rue Maurice Gignoux, 38 031 Grenoble, France

² ORSTOM, Apartado 17 12 857, Quito, ECUADOR

³ Labogeo Petroproduccion, Via a Salinas, km 6 1/2, Guayaquil, Ecuador

The Gulf of Guayaquil is the deepest Neogene and Quaternary sedimentary basin of the Ecuadorian Andes. It lies at the southern edge of the Ecuadorian coastal terrane, accreted during Paleocene times to the South American continental margin. The suture follows the Dolores-Guayaquil shear zone, a dextral strike-slip fault zone ending in the Gulf of Guayaquil. The southern termination of this fault zone divides the Gulf in two sedimentary basins separated by transpressional structures: eastward the Jambeli half-graben tilted toward the NW; and westward the Gulf of Guayaquil sedimentary basin (sensu stricto). This basin is limited to the North by the ESE-WNW trending and South dipping Posorja normal fault zone, parallel to an other E-W tilted block developped southward. To the West the basin is bounded by the continental shelf-break (and further West by the subduction zone), to the South by the Zorritos continental shelf, and to the East by N-S folds, related to the Dolores-Guayaquil strike-slip fault zone. The development of the Gulf of Guayaquil, related to ESE-WNW normal faulting and N-S transpressional structures, appears coeval with NE-SW dextral strike-slip movements along the Dolores-Guayaquil fault zone.

In the basin, approximately 5000 meters of Plio-Quaternary deltaic sediments were deposited. The Lower Pleistocene is the main opening stage with sedimentation rates reaching a maximum of more than 8000 m/Million years at the depocenter. The Upper Pleistocene records a fall in the sedimentary rates linked to the world sea-level fall and to a transpressional event also seen onshore with beach sediments uplifted by 300 meters. The Holocene his marked again by elevated rates of sedimentation.

In this way, the Gulf of Guayaquil is a peculiar pull-apart basin forming during the Upper Neogene between the Dolores-Guayaquil strike-slip fault zone eastward and the oblique convergent subduction zone westward. It is directly linked to the northward motion of the ecuadorian coastal terrane during Neogene times. It is opening in a transtensional context with episodic transpressional events probably linked to subduction anomalies off the Ecuadorian Coast. A volume estimation of the sediment infilling will allow to estimate the recent northward migration of the Ecuadorian Coastal terrane, as well as the balance of erosional loss and sediment deposition related to the Ecuadorian Andean uplift.

D08 : 5P/02 : PO

Paleocene Sedimentation Offshore Scotland

Benjamin Clarke (clarke@esc.cam.ac.uk)

14 Madingley Road, Cambridge, Cambridgeshire, UK

The Paleocene sandy submarine fans offshore Scotland have been the focus of intense study since the discovery of hydrocarbons West of Shetland.

Regional sequence stratigraphic analysis has shown that these laterally-variable fans form correlatable units which have durations of between half and one million years. The marine condensed horizons which divide these units are biostratigraphically correlatable between the North Sea and Atlantic Margin, allowing a new regional Paleocene stratigraphy to be set up.

Sediment accumulation can be quantitatively compared in different areas offshore Scotland using this new stratigraphy. There is broad similarity between the areas but subtle differences exist. The broad similarity is explained by a regional model linking sediment supply with observed regional upift, volcanism and lithospheric extension. The subtle differences are explained by landscape evolution, provenance variability and geomorphological changes.

The North Sea and Atlantic Margin basins form a closed system in which all the deposited sediment is eroded from the Scotland-Orkney-Shetland Massif. A volume balance has been attempted to reconstruct the cover of the Scottish hinterland.

D08 : 5P/03 : PO

Compound Specific Isotope Analysis of the N-Alkanes in the Septarian Concretions from the Terres Noires (French Alps): Implications for the Origin of the Fossil Waxes

Jorge E. Spangenberg (Jorge.Spangenberg@imp.unil.ch)¹ &

Nicolas Meisser (Nicolas.Meisser@sst.unil.ch)²

¹ Institut de minéralogie et pétrographie, Université de Lausanne, BFSH-1 CH-1015, Switzerland

² Musée de Géologie, Université de Lausanne, BFSH-1 CH-1015, BFSH-1 CH-1015

Liquid (oil) and solid hydrocarbons occur in septarian limestone concretions within the Callovian-Oxfordian organic carbon-rich Terres Noires formation (Dauphinois subalpine tectonic domain, France). In the interior of these concretions yellowish tabular platelet-like waxy crystals are associated with calcite, celestite, dolomite and quartz. The crystallographic data of this organic solid matches those of straight-chain normal alkanes and of the organic mineral evenkite (type locality: Evenki district, Siberia) which was believed to be a monoclinic modification of normal tetracosane (n-C₂₄H₅₀). The molecular and isotopic data from the saturated fraction of the oil and the organic crystals in the concretions from two localities, Serres (Hautes-Alpes) and Condorcet (Drôme) areas, give further insight into the composition of the "organic mineraloid" and permit the distinction between the two possible origin of the source hydrocarbons: 1) hydrocarbons produced in situ during thermal evolution of organic material trapped in the septarian concretions, or 2) infiltration into the concretions of extrinsic migrated hydrocarbons caused by the passage of formation/metamorphic hot fluids through the Terres Noires. The molecular analyses show that the organic solid is an assemblage of n-alkanes in the range C₂₀ to C₃₀, with no odd-even predominance and highest concentrations in the C₂₃-C₂₅ range. Trace amounts of branched alkanes and cycloalkanes elute between the n-alkanes. The empirical formula calculated from the relative concentrations of the individual n-alkanes is C_24.4H_50.8, with an expected chemical composition of 85.21% C and 14.78% H. These values are very close to the composition of the organic mineral evenkite of the Siberian locality (85.43% C, 14.99% H). These results suggest that evenkite may be an assemblage of solid straight chain alkanes with 20 to 30 carbon atoms, and not a crystalline phase of pure tetracosane as believed previously. The uniform isotopic composition of the bulk organic solid (-28.7‰) and of the individual n-alkanes (-28.0 to -29.6‰) indicate that the hydrocarbons are indigenous, and exsolved from waxy n-alkanes (-27.7 to -31.1‰) of the oil produced by thermal cracking of the organic matter (marine plants and higher organism) trapped in the septarian concretions during burial and tectonic/low-temperature-metamorphism history of the Terres Noires formation.

D08 : 5P/04 : PO

Characterization of Ammonium Illites in Permo-Carboniferous Rocks from the Eastern Part of the North German Basin

Georg A. Brecht (gbrecht@gfz-potsdam.de),

Birgit Mingram (birgit@gfz-potsdam.de),

Daniel Harlov (dharlov@gfz-potsdam.de) &

Peer Hoth (hoth@gfz-potsdam.de)

GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, F.R. Germany

X-ray diffraction and chemical determination of nitrogen indicate that illites are the main NH₄-bearing minerals within the Permo-Carboniferous succession in the eastern part of the North German Basin. Samples were taken from drill cores of Carboniferous shales and siltstones as well as from Upper Carboniferous to Lower Permian volcanic rocks, down to a depth of 7000 meters, from the Peckensen 7/70, Boizenburg 1/74 and Parchim 1/68 boreholes. X-ray diffraction on the clay fraction was carried out using a Siemens D5000 diffractometer (CuK<alpha>-radiation). Nitrogen determination on the same separates was carried out using a Vario el C-H-N analyzer.

X-ray diffraction and nitrogen-determination did not reveal a correlation between the illite (005) peak position and the nitrogen content as suggested by Daniels & Altaner (1990) and Sucha et al. (1994). However, samples from the Peckensen borehole show a weak trend between illite-"crystallinity" and the nitrogen content. Comparison of the total nitrogen content with the vitrinite reflectance (VR) data taken from Hoth (1997) indicate a strong correlation between the degree of coalification and the amount of nitrogen. Sample suites from each of the three locations show specific patterns with respect to the degree of metamorphism. VR-data from the Peckensen samples show a characteristic diagenetic pattern without a clear depth dependence. In contrast, the samples from the Parchim and Boizenburg locations reveal anchi- to epimetamorphic conditions. The samples of the Parchim borehole differ from the Boizenburg samples in that the Parchim samples do not show a depth dependence with respect to the VR-data. All of these specific patterns are reflected in the nitrogen content of the analyzed clay fraction as well. The missing correlation between illite-"crystallinity" and nitrogen content in the higher metamorphic samples suggests that the NH₄-emplacement in illites during higher metamorphic conditions does not strongly affect the crystal structure or could be due to the relatively low nitrogen contents in these illites. Illitisation in the Peckensen area may have happened simultaneously with nitrogen migration. Based on our results, we suggest that detailed studies of nitrogen behavior during clay mineral diagenesis can give additional information about metamorphic conditions and gas migration in the North German Basin.

Daniels, EJ & Altaner, SP, Amer. Min, 75, 825-839, (1990).

Hoth, P, Schrifenreihe f. Geowiss, 4, 1-139, (1997).

Sucha, V, Kraus, I & Madejová, J, Clay Min, 29, 369-377, (1994).

D08 : 5P/05 : PO

Diagenetic and Tectonic Evolution of A Lower Jurassic Carbonate-Flint Multilayer

Carlos Ribeiro (cribeiro@uevora.pt)¹ &

Pedro Terrinha (pagt@fc.ul.pt)²

¹ Dep. Geociencias, Univ Evora, Apartado 94, 7002-554 EVORA, Portugal

² Dep. Geologia, F.C.U.Lisboa, Bloco C2, 5º Piso, Campo Grande, 1700 Lisboa, Portugal

Dolomites and dolomitic limestones of Carixian age (Lower Jurassic) of Praia do Belixe (Sagres, SW-Portugal) show a variety of siliceous bodies: 1) flint beds interbedded with the carbonate host-rock; 2) flint nodules; 3) quartz and chalcedony tension gashes perpendicular to bedding; 4) quartz veins with cataclastic textures injected into normal faults.

Petrographic studies showed that intensive dolomitization erased almost every primary structure of the carbonates and also affected the flint. Flint beds and nodules consist mainly of a fine mosaic of microcrystalline quartz and less frequently of chalcedony; remains of radiolarian spicules and planctonic forams indicates an organo-sedimentary origin for the flint (as opposed to a hydrothermal origin). Tension gashes are dominantly filled by chalcedony and lesser quartz; in some veins growth of quartz and dolomite crystals appear to be in chemical equilibrium. The normal fault quartz veins are made up by quartz and minor quantities of chalcedony; typical cataclastic textures and redeposition of undeformed quartz are present.

During dolomitization of the limestones an important part of the flint was substituted by dolomite. Simultaneously, part of the SiO₂ was re-precipitated into tension gashes. Equilibrium of dolomite and quartz phases at tension gashes margins suggests degassification induced by pressure release inside the tension gashes. Same orientation of flint veins and extensional joints, normal faults and tension gashes suggests that diagenesis occurred during extensional faulting and that siliceous fluids were being extracted out of sediments probably by "seismic pumping".

Syn-sedimentary extensional deformation with formation of vertical joint has been established by detailed interpretation of normal faults and unconformities. A transient episode of compressional deformation separated two tectonic extensional episodes of Carixian age. This compressional episode caused necking and pinching out of flint dykes installed in vertical joints.

A later stage of diagenesis is evidenced by precipitation of dolomite within fractures in tension gashes.

Development of bedding parallel pressure solution foliation, folding of quartz tension gashes by vertical compaction and syn-sedimentary activity of normal faults (interrupted by a transient compressive episode) all suggest that deformation and diagenesis occurred during Carixian (possibly Domerian) times. The Toarcian sediments lie on top of an erosion unconformity and do not show any sign of faulting nor of dolomitization.

D08 : 5P/06 : PO

Modelling of the Rapid Subsidence of Black Sea and South Caspian Basins

Maxim Korotaev (mvk@geol.msu.ru)¹,

Andrei Ershov (and@geol.msu.ru)¹,

Anatoly Nikishin (nikishin@geol.msu.ru)¹ &

Marie-Francoise Brunet (brunet@lgs.jussieu.fr)²

¹ Geological Faculty, Moscow State University, Moscow, Russia

² Laboratoire de Tectonique, Universite Pierre et Marie Curie, Paris, France

Deep-water part of the Black Sea consist of two basins - Western Black Sea Basin and Eastern Black Sea Basin, divided by Andrusov ridge. Western Black Sea basin has oceanic crust and Eastern Black Sea basin has very thinned continental crust. Central part of South Caspian basin has oceanic crust.

Back-arc origin of the Black Sea basin is proposed took place in the Mid-Late Cretaceous. The thickness of Cretaceous-Quaternary sedimentary cover of the Black Sea vary from 15 km in the Eastern Black Sea basin till 18 km in the Western Black Sea basin.

Back-arc origin of the South Caspian basin is proposed took place in the Late Jurassic. Thickness of sedimentary cover of the South Caspian is up to 25 km.

The analyses of the tectonic subsidence based on results of 1D and 2D backsripping shows that some tectonic events can't be explained by model of rifting and post-rift thermal subsidence. For Black Sea such event took place in Pliocene-Quaternary (0.4 km of tectonic subsidence) and for South Caspian in Early Pliocene (2 km of tectonic subsidence). During these time stages both basins were in compressional environment. We propose the "lithospheric folding" model for explanation of this rapid syncompressional subsidence.

Lithosphere of the Black Sea and South Caspian is thermally and structurally heterogeneous. Rheological modelling shows that effective elastic plate with mechanical features of lithosphere of Black Sea basin and South Caspian Basin have thickness (EET) in the central part 100 km and 30 km for the margins, down flexure of middle line of effective elastic plate is 25 km. Such great heterogeneity of the lithosphere under compression induce downward flexural movements.

Total applied force 10¹³ N/m induce 2 km of tectonic subsidence (South Caspian Basin) and force 5*10¹² N/m induce 0.4 km of tectonic subsidence (Black Sea Basin).

Those values are corresponded with estimated from backsripping tectonic subsidence.

D08 : 5P/07 : PO

Clay Mineral Assemblages as Markers of Paleotopographic Changes in Siliciclastic Deposits (SW of the Paris Basin)

Magali Geiller (mgeiller@illite.u-strasbg.fr)¹,

Anne-Marie Karpoff (amk@illite.u-strasbg.fr)¹,

Gilles Merzeraud (merze@dstu.univ-montp2.fr)² &

François Verdier³

¹ EOST, CGS, 1 rue Blessig, 67084 Strasbourg, France

² Université de Montpellier II, Place Eugène Bataillon, 34095 Montpellier Cedex 5, France

³ GDF, 361 av. du président Wilson, 93211 La Plaine St Denis Cedex, France

Reservoir properties of the studied deposits are used by Gaz de France for gaz storage in the underground aquifer. A mineralogical study have been applied to characterize mineralogical markers and to understand relationship of mineralogical associations to change in depositional profiles. This work was carried out in collaboration with GDF which have given many borehole data.

In the Sologne sub-basin, in a proximal continental setting, on the eastern margin of the Armorican Massif, the formations have been deposited during Rheatian and Hettangian times in a transgressive context associated to a decreasing rate of subsidence. Two depositional profiles follow one another and characterize the evolution of the sedimentation in Céré-La-Ronde field. Three depositional environments belong to the first depositional profile with, in a proximal position, an alluvial plain with braided channel, in a distal position, an alluvial plain with sinuous channel and in an intermediate position, a distal alluvial plain with braided channel. The second depositional profile consists of a coastal plain with braided channel in a proximal position, a coastal swamp in a distal position and an alluvial plain with ephemeral channels in an intermediate position.

Samples of the most clayey facies were collected from three wells located at the west, east and central part in the field. Quartz, K-feldspar, plagioclase, muscovite, illite and chlorite are considered as detrital minerals. The distribution of quartz, K-feldspar, plagioclase, and muscovite, emphasizes the detrital feature of the formations of Céré-La-Ronde and the variation of sedimentation between a proximal and a distal end-members. Secondary minerals such as dolomite, calcite, palygorskite, and a mixed-layer made of two phases, chlorite-vermiculite and chlorite-smectite, result from pedogenetic processes. Three levels of paleosoil have effectively been identified in the formations of Céré-La-Ronde, associated with a specific mineral assemblage. Formation of pyrite and of iron oxihydroxides results in early processes related to the environmental conditions. The mixed-layer illite-smectite may be the result of early depositional processes from illite degradation. Kaolinite may be in part detrital and in part secondary, formed in the porosity. In the same way, corrensite could be nor detrital nor secondary, formed in confined conditions: the distinction between both origin is difficult to establish.

However, mineral assemblages are modified with each change of depositional profile established for the formation. This can be the result of joint phenomena related to changes of the nature of erodible areas and to environmental modifications and evolution in the basin itself.

D08 : 5P/08 : PO

Organic Matter and Illite-Smectite Diagenesis of the Central Carpathian Paleogene Basin: Implications for Thermal History

Julia Kotulova (Kotulova@gu.bb.sanet.sk),

Adrian Biron (biron@gu.bb.sanet.sk) &

Jan Sotak (sotak@gu.bb.sanet.sk)

Geological Institute Slovak Academz of Sciences, Severna 5, 974 01 Banska Bystrica, Slovak Republic

Central Carpathian Paleogene Basin represents a largest accumulation space of flysch-like deposits in the Central West Carpathians. This fore-arc basin was formed above the southwestward subducting oceanic slab attached to the European Platform. In the Levoèa Mts., the basin-fill sequence comprises of: 1. Late Eocene Sambron Beds (synrift deposits of claystones, muddy turbidites and scarp breccias); 2. Early Oligocene mud-rich subflysch formation; and 3. Late Oligocene - Early Miocene sandy-rich fan deposits. Clay-mineral assemblages and vitrinite reflectance (VR) data have been applied to determine post-sedimentary alteration of the Paleogene flysch formations, using shales and siltstones from 60 outcrops and 7 deep drill-holes. The clay mineral assemblages (<2 mm-size-fractions) are mainly composed of discrete illite, mixed-layer illite/smectite (I/S), kaolinite, chlorite. The most notable diagenetic reaction is smectite-to-illite transition. With increasing stratigraphic age and burial temperature the proportion of smectite layers in I/S decreases and progressive change of R0 to R3 ordering takes place. The smectite-rich I/S (90-45%S) with random ordering was found in the youngest, Late Oligocene - Early Miocene rocks. The underlying Early to Late Oligocene formations are characterized by R1 I/S (40-20%S), and R3 I/S (,15%S) was encountered mainly in oldest, Late Eocene strata. Correlation with VR data can be approximated as follows: R0 to R1 transition occurs at Ro0.5%, and R1 to R3 transition at Ro0.8%. Observed data indicate burial temperatures between 60°C (Early Miocene sediments) up to at least 150°C (Late Eocene sediments). None of the flysch formations studied reached the anchimetamorphic temperature conditions (highest IC=0.65°D2q, Ro=1.5%).A geographical distribution of individual types of I/S phases as well as VR data mostly reflect a present day bottom configuration of the Levoèa Basin or level of erosion and no regular pattern was observed. Rocks with R0 I/S are preserved only in depressional parts (Poprad and Chmiòany Depressions), while shales containing R3 I/S were found above elevations (e.g. Vikartovce-Klèov and Bajerovce Elevations). Situation is even more complicated in the Periklippen area which is caused by strong tectonic deformations. However, due to prevalence of the Late Eocene Sambron Beds, shales with most advanced illitization (R3 I/S) predominate in this part of basin. It is necessary to point out that presented diagenetic model is schematic and generalized. A significant deviation was recorded in the central part of Levoèa Basin where the youngest known Early Miocene formations display more advanced illitization (R1 I/S with 30%S) and VR (Ro=0.6%) than rocks of similar age in the other parts of basin. Taking into account the range of paleothermal gradients 50 - 30°C/km and normal heat flow, this observation implies, that ca. 2 - 3 km thick sequence of sedimentary rocks has been removed after the Miocene uplift.

D08 : 5P/09 : PO

Diverse PTt Conditions of the Variscan Metamorphism - Record of a Miocene Core Complex in the Pannonian Basin?

Tivadar M. Tóth (mtoth@geo.u-szeged.hu) &

Félix Schubert (schubert@sol.cc.u-szeged.hu)

Attila József University, Dept. Mineralogy, Geochemistry and Petrology, Hungary

Several geophysical, as well as geochronological (fission track) studies have suggested that during the extension of the Pannonian Basin in the Lower Miocene, simultaneously with the general subsidence also metamorphic core complexes were formed. In this study a region of a crystalline dome (Szeghalom Dome), north from the Békés Basin have been examined petrologically. In the area both the crystalline basement and the overlying sediments are CH reservoirs.The topographical peak of the dome can be found about 2000 m below the surface, while the basement at the northern flank is situated 700 m deeper. Both areas consist of similar metamorphic rock types, biotite gneiss and amphibolite with a subservient role of micaschist. Significant difference is, however, the appearance of anatectic granite close to the top, where gneiss also contains sillimanite. Gneiss may contain garnet in both areas depending on the bulk chemistry. No significant geochemical or petrographical divergence is exhibited by the amphibolite samples from the two areas. Amphibole - plagioclase thermometry, however, yields consequently a 100°C shift in Tmax giving 680°C at the top, while 580°C at the flank. A difference of a similar measure is shown by the K/Ar amphibole ages (around 210 Ma at the top and 310 Ma at the flank, consequently). All these features suggest that the top region of the dome represents a significantly lower part of the crust than the flank. Taking an average geothermic gradient and uplift rate into account, both the difference in Tmax and in the isotopic age suggest a distance close to 8 km between the two units.This configuration can not be explained by the presence of a Variscan syntectonic anticlyne (the model accepted at present), but it is in good correlation with assuming a large scale detachment. The two different areas are separated by an intensively tectonized zone, consists mainly of cataclasite. Detailed study of this zone is under way. Mineralized veins of the whole crystalline dome contain a sequence of qtz+chl+kao+cc+lau vein-fill. Calcite contains one phase fluid inclusions of low salinity suggesting a low temperature meteoric origin as well as pollens and fragments of continental plants of Miocene age. The two areas with the significantly different Variscan metamorphic evolution could take their present place during the Miocene due mostly to vertical movement.

D08 : 5P/10 : PO

Relay Zones on Traill Ø and Geographical Society Ø, East Greenland

Ole R. Clausen (geolorc@aau.dk)¹,

John A. Korstgård (geoljohn@aau.dk)¹ &

Lars Stemmerik (ls@geus.dk)²

¹ Department of Earth Sciences, University of Aarhus, DK-8000 Århus C, Denmark

² GEUS, Thoravej 8, DK-2400 København NV, Denmark

An important major extensional fault system, the Månedal Fault Trend, is located on Traill Ø and Geographical Society Ø in East Greenland in the transition area between the Wollaston Forland Basin and the Jameson Land Basin. The Wollaston Forland Basin is characterised by Mesozoic fault block rotation in contrast to the Jameson Land Basin which is characterised as a Mesozoic sag-basin (Surlyk, 1991). The Traill Ø area is the western counterpart of the east Atlantic margin offshore mid-Norway and interesting as an exposed analogue of the mid-Norwegian shelf.

Cretaceous mudstones interbedded with sandy debris flow units and conglomerates, are exposed in the hangingwall area east of the Månedal Fault Trend The footwall side of the fault trend generally consists of Triassic clastic sediments. Jurassic sediments (Pelion Formation, and Bernberg Formation) occur within the relay zones generated where major fault segments overlap. Intrusion of basaltic sills and dykes took place during the early Cenozoic. The sills were deformed (brecciated) and mineralised along the Månedal Fault Trend during the Cenozoic.

The mapped length of the Månedal Fault Trend is approximately 70 km. The fault trend strikes N-S and individual faults dip approximately 60° to the east. The Månedal Fault Trend consists of at least four major fault segments. Geometrical analysis and field observations show that the fault segments were soft linked across relay zones during most of the Cretaceous period. The analysis also shows that hard linkage of the fault segments was established during latest Cretaceous or earliest Cenozoic times when the relay zones were cut by relay faults.

The deposition of coarse clastic sediments during the Cretaceous is interpreted to be related to the evolution of the relay structures. The faulting across individual fault segments is also suggested to have influenced the deposition of the Cretaceous succession by generating areas with increased subsidence in front of the fault segments.

Surlyk F, AAPG Bull, 75, 1468-1488, (1991).

D08 : 5P/11 : PO

A Subsidence Analysis of the Mid Norwegian Margin

Rudie van der Meer (melchior@caiw.nl)¹,

Jan-Diederik van Wees (weej@geo.vu.nl),

Sierd Cloetingh (cloeting@geo.vu.nl) &

Ridvan Karpuz (ridvan.m.karpuz@nho.hydro.com)²

¹ Oostblok 16, The Netherlands

² Norsk Hydro Centre, Sandsliveien, N-5049 Bergen, Norway

A backstripping analysis has been performed in order to quantify the temporal and spatial variations of tectonic subsidence of the Mid Norwegian margin. This analysis is based on a new and high quality industry database that is formed by 3D stratigraphic horizons from OBS data and constrained by well data from different parts of the study area. Backstripping has been done for an area of 500 x 455 km for an amount of more than 9000 synthetic wells with a spacing of 5 km.The Mid Norwegian margin has experienced a complex tectono-magmatic history that started already in the post Caledonian times. It is characterized by a serie of subsequent rifting phases that prograded from the south to the north coeval with a shift of the rifting axes that migrated in time towards the actual line of break-up. This resulted in a large number of basins and sub-basins where sediments accumulated with maximum thicknesses reaching to more than fifteen km. The results of our subsidence analysis clearly demonstrates that pre-Cretaceous rifting was concentrated below the central Trondelag platform, the Nordland Ridge and Halten Terrace, and during the Lower and Upper Cretaceous a northward subsidence took place in the Voring basin. At the Late Middle Cretaceous a strong subsidence has been recognized along the Gjallar Ridge while local uplift occurs in the Traena Basin. Late Paleocene uplift up to 200 meters is supposed to be the result of magmatic underplating at the time of continental break-up.

D08 : 5P/12 : PO

Hydrocarbon Basins of Eastern Mediterranean

Yuri Ya. Livshits (livshits@bgumail.bgu.ac.il)

Dept. of Geophysics & Plan. Sci., Tel Aviv University Ramat Aviv 69978, Tel Aviv, Israel

Eastern Mediterranean ensemble of bordering lithosphere plates fixes the position of main hydrocarbon basins. African plate in Oligocene - Early Miocene was cut off from Arabian plate (with its enormous hydrocarbon resources) by Red Sea Rift system (DSRS) and its branch Dead Sea Rift zone (DSRZ). Before this separation all hydrocarbon basins have been developed as a part of a single African-Arabian ancient platform. But since Triassic on the ancient platform rim the peculiar Eastern Mediterranean (Levant) basin (EMB) began to develop. Just this basin limits from west and young Israel - Sinai subplate (ISS) - the African plate's wedge between RSRS and DSRZ. Thus on Eastern Mediterranean part of African plate two main structures are presented: marine Eastern Mediterranean basin and terrestrial Israel - Sinai subplate. The boundary between these structures is definite as a separate historical-structural unit - the Marginal Fault Belt - MFB- ("paleodepositional hinge-belt'', "edge of Cretaceous carbonate platform''). MFB extends along the Mediterranean Sea beach on Israel, Sinai, and Egypt Coastal Plains about 500-km. It runs in longitudinal direction in Israel. But in Sinai and Egypt MFB strike is sublatitudinal. In Israel MFB can be divides into some parallel blocks (total width 5- 12 km); its highest part (western horst-anticline) is complicated by series of echelon anticlines with Helez oil field. The difference in the geological development of the main structures of African plate in Eastern Mediterranean have been emerged during of all geological history since formation of the Riphean molasse basin on the present Sinai subplate area. The EMB and especially MFB were vastly more mobile, than subplate. In response to changing of the main platform structures boundaries, morphology and geological history has been developed and the present hydrocarbon basins. The most attractive is the Eastern Mediterranean basin, including MFB. In this basin are known the oil fields Helez and Ashdod in Israel and gas field Sadot in Sinai (onshore), a many oil/gas/condensate fields in Nile delta (onshore and offshore) and a lot of other hydrocarbon discoveries and shows in Egypt, Sinai, Israel (offshore and onshore). The "kitchen" for hydrocarbons is situated probably in EMB marine part. The source rocks likely are represented mainly by the Middle Jurassic bituminous carbonates The second type of hydrocarbon basins is presented by RSRS with well known oil/gas fields in Red Sea area (onshore and offshore), and probably DSRZ. In DSRZ gas and very small oil fields are known only in the graben rim now. The Senonian bituminous shales in deeply buried parts of the Dead Sea graben (under salt) are proposed as a source rocks. The third type is hydrocarbon basin of Israel- Sinai subplate. As a source of oil/gas migration are proposed Triassic- Jurassic and possible Paleozoic rocks from buried and inverted Mesozoic graben.

Thus the very complicated evolution of Eastern Mediterranean caused the genetic variability of hydrocarbon basins of this area.

D08 : 5P/13 : PO

Upper Devonian Domanic - One of the Pechora Basin Source Rock Units

Dmitry Boushnev (boushnev@geo.komi.ru)

54, Pervomaiskaya st., Syktyvkar, 167610 Russia, Russia

For a long time, the Domanic facies deposits of the Pechora basin are known as an excellent oil source rock. The investigation had two main aims: to learn a distribution of the organic matter (OM) within domanic beds itself and to study molecular composition of the dissolved OM for oil - source rock correlation. We have studded both outcrop samples and samples from different wells drilled mainly in the northern part of the Pechora basin.

Domanic beds are represented by calcareous clays, limestones, siliciliths and oil shales. OM is distributed among different lithofacies irregularly: shales are most rich in TOC (8-10%), limestones - most poor (0.5-1.5%), middle position is occupied by calcareous clays and siliciliths (4.6-6.5 and 3-4%, respectively).

The n-alkanes, sulphur aromatic compounds and biomarkers distributions are very similar in the domanic samples from different places. The n-alkane spectra have no local maximums, the Pr+Ph/C17+C18 ratio usually is big (up to 1.5 at Rock-Eval's Tmax equal to 437°C), and Pr/Ph ratio approximately equal to 1.5. Sulphur aromatic compounds are dominated by benzothiophenes, "V-similar" distribution of dibenzothiophenes frequently being observed. The distribution of steranes hydrocarbons has an expressed minimum at C28 (in average C27:C28:C29 as 35.3 : 16.2 : 48.5).

The oil - source rock correlation study was successfully carried out on the example of Upper Devonian oils of Varandey-Adzva zone of the Pechora basin. The oils with genetically related to Domanic are characterised here by low maturation. This indicates that primary migration of the oil from domanic deposits could occur at low degree of OM catagenesis.

D08 : 5P/14 : PO

Microelements in the Oils of the Pechora Basin

Olga Valiaeva (orggeo@geo.komi.ru)

54, Pervomaiskaya st., 167610 Syktyvkar, Russia, Russia

The study of the microelement composition of oils of Khoreyver depresion of the Pechora basin was carried out on the basis of results of emission spectral analysis. For comparison of composition and concentration of microelements in oils and living organic matter (OM) diagram "the fields of concentration" was used. The field of concentration in living organic matter is constructed on data of G.Bowen. Similarity of configurations of the fields of elements concentration in living OM and oils, identical cut character and peculiarities of their location are evedent. However the field of elements concentration in oils lay below or within the corresponding fields in living OM. V and Cr are exceptions. It allows to make a conclusion, that the change in the concentration of microelements in oils is caused by respective change of their concentration in living OM.

Microelements could be combined into few groups according to the ratio of their concentretions in oils and OM. The first group includes the elements, which concentration in oils is lower than in living organisms. There are Al, Fe, Mg, Cu, Pb. The second group is made of elements Ti, Mg, Ni, wich have close concentrations in oils and OM. V and Cr are nited in the third group, with the concentration in oils higher than in living OM. Hence, microelements of oils could be regarded as the evidence of an organic origin of oils, as well as biomarkers.

The main source of Ti, Fe, Cu, Ni in oils is primary organic substance. Al and Mg are likely to enrich oils from primary organic substance and from the host rocks during migration. Host rocks and groundwater are main sourses of V and Cr. The source of Pb is groundwater. It is possible to allocate two basic genetic sources of oils: 1. OM of marine type. It could be regarded as the major sourse for the oils from Siluriun, Lower Devonian and Fameniar ages are belonged there. Such oils are characterized by absence of Ti and Cr and increased contents of Fe in comparison to other elements. 2. OM of a mixed type. The oils from Carboniferous and Permian deposits are characterized by absence of Cr, high contents of V and Ni.

D08 : 5P/15 : PO

Oil and Gas Potential of Local Structures within the Northern Part of the Pre-Urals Foredeep

Sergey Klimenko (klimenko@geo.komi.ru)

54, Pervomaiskaya, Syktyvkar, 167610, Russia

The purpose of our researches consist in revealing on the basis of the statistical analysis of interrelations between various structural - morphological parameters of local structures of northern part Pre-Urals foredeep and probable their oil and gas potential and also paleotectonical of the analysis of a history of immersing in this territory with the subsequent forecast of perspectiv objects on detection of oil and gas. For reception of necessary result we used a principle of the range of parameters with a certain sample by of increasing of perspective of geological objects. The main point of rank classification consists in following: the basis is undertaken by parameters, describing as local structure, and number of parameters, reflecting a geological structure of a larger structural element, in limits of which these structures are located. Each of parameters is broken into certain intervals, which get the ranks it depends on increasing of the perspective of parameters' meanings, about which will be marked below. Then these ranks are summarized and the diagram of their distribution is built on them. For a conclusion of critical meaning of ranks' sums, on which it will be possible to define a degree of perspective of this or that structure, the parameters' meanings of those structures are taken, where the deposits of gas and oil and emrty structures are already revealed. In result, according to the character of distribution the perspective of this or that structures is defined with the help of critical meaning ranks' sums. At realization of rank classification of local structures of Upper Pechora, Bolshesynya and Kosyu-Rogov depressions data on 44 structures were used, on 9 of which already deposits are revealed. The special interest is in structures with a sum of ranks exceeding or equal 14. These structures can be referred, on our data, to prime objects for statement of exploration in oil and gas. They include North Vuktylskaya in Upper Pechora depression, Uldor-Kyrtynskaya - in Bolshesynya depression and Amshorskaya, Voravozhskaya, Kochmeskaya, Povarnitskaya and Ust-Lemvinskaya - in Kosyu-Rogov depression. To poorly perspectiv objects it is possible to attribute structures in Upper Pechora depression - East-Shor`elskaya, Patrakovskaya, in Kosyu-Rogov depression - Verhnelyagskaya and other with sums of ranks equal 8; 9 and 10. Thus, during research works classification model of the forecast oil and gas potential of local structures is created, in a basis of which there must be the range of geological parameters on their oil and gas bearing complexes. Due to this model objects in northern depressions Pre-Urals foredeep, the most perspectiv for detection in their field of oil and gas are planned.

D08 : 5P/16 : PO

Devonian Sin-Rift Clastic Complex in the Pechora-Kolva Aulacogen of the Pechora Basin, Russia

Nikolai Malyshev (malyshev@geo.komi.ru)¹,

Robert Ressetar (ressetar@egi.utah.edu)² &

Zinaida Larionova³

¹ Institute of Geology Komi Science Center, 54 Pervomayskaya st., Syktyvkar, Russia

² Energy & Geoscience Inst., University of Utah, Salt Lake City, USA

³ Timan-Pechora Scientific Research Center, Ukhta, Russia

The most prolific siliciclastic hydrocarbon reservoirs in the Pechora Basin occur in a series of depressions formed during a Devonian rift event that affected most of the continental margin of eastern Europe. The Devonian clastic complex was deposited in a series of half-grabens of the Pechora-Kolva aulacogen. The Usa, Vozey and Kharyaga sub-basins with eastern border faults were structurally separated from each other by synthetic overlapping transfer zones. The Usa sub-basin was probably depositionally isolated from the Vozey and Kharyaga during sea-level lowstands. In the Usa-Kharyaga area, the Devonian clastics generally are thickest (300-700 m) near the border faults, thinning westward toward the Lay swell - a structural paleohigh within the Pechora-Kolva aulacogen. A much thicker section of Devonian clastics accumulated on the western side of the swell in the Pashshor area.

The Devonian clastic complex consists of eight depositional sequences. Log, core and seismic analyses show that the Middle Devonian to lower Frasnian strata represent sedimentary environments ranging from fluvial to nearshore to low-energy shelf. The paleogeographic reconstruction of these settings suggests they are best explained by a structurally controlled estuarine model. The depocenters for the sequences shift both within and between individual half-grabens, migrating generally northwestward in response to changes in relative subsidence rates.

Reservoir sandstones occur in shoreface deposits of the transgressive systems, and in fluvial, deltaic and shoreface deposits of the highstand systems. Relating porosity and permeability data to the log and core interpretations shows that the best reservoir rocks occur in shoreface and deltaic channel sandstone, and, secondarily, in fluvial sandstone.

In the Usa oil field maximum porosity and permeability occur in nearshore bar sandstone of the Kedrovskiy horizon, with lower quality sandstone in Kolvinskiy horizon transgressive estuarine and Starooskolskiy fluvial deposits. The Vozey oil field spans the northern Usa sub-basin and the Vozey sub-basin. In the former the highest reservoir quality sandstone occurs in Kedrovskiy shoreface facies, with lower quality sandstone in Omrinskiy and Kolvinskiy fluvial facies. In the Vozey sub-basin Starooskolskiy fluvial facies have highest porosity and permeability. In the Kharyaga oil field the Kedrovskiy generally has moderate porosity but low permeability. The best reservoirs are in Starooskolskiy shoreface and distributary channel sandstone. Omrinskiy and Kolvinskiy shoreface sandstone and Dzherskiy fluvial sandstone commonly have moderate to high porosity but low permeability.

D08 : 5P/17 : PO

4D Modeling of Hydrocarbon Generation, Migration and Accumulation

Andrew Dodds (a.j.dodds@esci.keele.ac.uk)

Department of Earth Sciences, University of Keele, Staffs, UK

A computer model has been constructed to model the evolution of 3D geological volumes through time. Parameters modeled include temperature, source rock kinetics, expulsion of hydrocarbons, secondary migration of hydrocarbons, entrapment of hydrocarbons with spillage and remigration, sedimentation, fault movement, compaction of sediment and isostatic response to sediment loading. These parameters are modeled through time to show the evolution of the volume of rock and any hydrocarbon accumulations that occur within it.

Models are imported as a set of surfaces made up of triangles; hence each triangle has a dip and dip direction for the modeling of migration pathways, and a volume which acts a a container for generation and entrapment parameters such as the source rock parameters and the porosity. Hence all parameters can vary continuously across the model, so allowing full 3D modeling through time.

The modeling process can be viewed at any stage by means of an OpenGL based viewer built in to the main modeling program. It is possable to step backwards and forwards through time within the model to view the evolution of hydrocarbon accumulations, drainage patterns of generated hydrocarbons, areas of active hydrocarbon generation, temperature fields, position of the geological surfaces, or any other aspect of the model. The model runs on relatively modest computing power; a model containing 8000 triangles can be calculated in 16 minutes on a Celeron 300A PC with 128 Mb of SDRAM.

D08 : 5P/18 : PO

Early Diagenetic Reduction Processes in Anoxic Sulfur-Rich Environments

A. Behrens (Behrens@chimie.u-strasbg.fr)¹,

P. Schaeffer (pschaeffer@chimie.u-strasbg.fr)¹,

P. Adam (padam@chimie.u-strasbg.fr)¹,

S. Bernasconi (stefano@buzzard.ethz.ch)² &

P. Albrecht (albrecht@chimie.u-strasbg.fr)¹

¹ Laboratoire de Géochimie Organique, UMR 7509 du CNRS, ULP, Institut de Chimie, 1 rue Blaise Pascal, 67000 Strasbourg, France

² Geologisches Institut, ETH-Zentrum, CH-8092 Zürich, Switzerland

Early diagenetic reduction processes undergone by functionalized lipids in anoxic, sulfur-rich sediments are widely recognized, but as yet poorly understood. For instance, these processes are thought to be involved in the conversion of phytol to dihydrophytol and phytane, in the transformation of sterols into stanols, in the reduction of the polyfunctionalized side-chains from bacterial hopanepolyols, or in the transformation of carotenoids into their related saturated hydrocarbons widespread in sulfur-rich sediments. Early reduction processes could be biologically-induced, being operative during the earliest stages of diagenesis. Alternatively, abiotic reduction reactions may be envisaged, provided that the redox potential is low enough. Recently, geochemical studies carried out on recent organic-rich sediments from a sulfur-rich lake (lake Cadagno, Switzerland) have shown the presence of numerous partly-reduced carotenoid derivatives, suggesting that reduction processes are highly operative in this ecosystem. In order to better understand the mechanisms involved in the reduction reactions of carotenoids, we have isolated the partly-reduced carotenoids I-III and unambiguously determined their structures by 1D and 2D homonuclear and heteronuclear NMR studies.

It was established that compound I results from the partial reduction of the carotenoid isorenieratene biosynthesized by green sulfur photosynthetic bacteria, whereas compounds II and III are formed by the reduction of carotenoids from purple sulfur photosynthetic bacteria. The fact that compound I and compounds II-III originate from distinct biological precursors, together with the presence of reduction intermediates of carotenoids with additional double bonds in the organic extract of the sediments from lake Cadagno, indicates that these compounds are probably not biosynthetic products from photosynthetic bacteria, but result from the reduction of carotenoid precursors during early diagenesis. Moreover, the splitting of some signals observed in the NMR spectra of II and III suggests the presence of diastereomeric mixtures, and may therefore indicate that the reduction processes did operate without stereoselectivity.

D08 : 5P/19 : PO

The Relationship between the Geochemical Characteristics and Ash Fusion Temperature for Some Lignites from Thrace Basin, NW Turkey

Yüksel Örgün (orgun@itu.edu.tr),

Nurgül Çelik &

Yilmaz Bürküt

ITU, Mining Faculty, Geology Department, , 80626 Maslak - Istanbul, Turkey

There are several coal formations having low reserve in the Thrace basin. Marl and clay units generally cover the coal seams. According to the elementary composition, proximate analyses and calorific values, the Thrace coals have low rank, and they harmonious with ortho-lignitous and peat. The major (wt%) and trace (in ppm) element results of the coal ash samples varies in a large range. For example, Al₂O₃ varies between 3.74 and 33.70; CaO, 1.09 and 16.80; Total alkaline, 0.72 and 14.03; TiO₂, 0.60 and 1.38; Ni, 21 and 900; Pb, 1 and 210; W, 11 and 1980; U, 3 and 270; Ga, 10 and 80. The whole high values belong to the samples taken from southwest part of the basin that was effected by Miocene volcanism. The fusion temperatures of some of the coal ash samples are given in Table 1. The maximum temperatures belong to the samples that have the lowest total alkaline values. Some of the linear correlation coefficients between fusion temperatures and inorganic chemical components of the samples are given in Table 2. The highest correlation coefficients belong to the total alkaline (T.A) and TiO₂.

Table 1 The fusion temperatures of the coal ash (°C)

Samples 1 2 3 4 5 7 8

ST¹ 1090 1010 950 980 1000 1210 1190

MT² 1150 1100 1000 1010 1100 1240 1200

ST¹:Softening Temperature

MT²:Melting Temperature

Table 2 The linear correlation coefficients of the samples

T. A CaO Al₂O₃ TiO₂ Pb U Ga

ST¹ -0.91 -0.44 0.68 0.87 -0.72 -0.63 -0.74

MT² -0.90 -0.61 0.52 0.79 -0.67 -0.55 -0.63

ST¹: Softening Temperature

MT²: Melting Temperature