Quantification du contrôle des séquences par la tectonique et l’eustatisme dans le bassin du Dniepr-Donets et sur la plate-forme russe pendant le Carbonifère et le Permien

Introduction. – Une analyse quantitative comparative de la subsidence dans les bassins d’âge paléozoïque supérieur de Moscou (MB) et du Dniepr-Donets (DDB) apporte une vision nouvelle sur l’importance relative de la tectonique et de l’eustatisme comme contrôle de la sédimentation et du fonctionnement de ces bassins. Les résultats publiés sur le segment du Dniepr [Stovba et al., 1995 ; van Wees et al., 1996] sont comparés à de nouveaux résultats provenant du MB et de la partie orientale du DDB (segments du Donets et du Donbass) en utilisant le programme AQUASUB du BRGM. Le bassin de Moscou (MB). – Le MB est situé dans la partie occidentale de la plate-forme russe (fig. 1). Le Carbonifère (fig. 2) y est représenté par environ 650 m de sédiments principalement carbonatés d’origine marine. Une lacune stratigraphique et une érosion importante y sont connues entre le Serpukhovien et le Bashkirien supérieur. La figure 2 présente les séquences du second ordre du MB [Briand et al., 1998] et leur corrélation avec les séquences glaciaires et interglaciaires du Gondwana [Lopez-Gamundi, 1997]. La subsidence totale du Carbonifère (courbe SUTO, fig. 3A) est d’environ 750 m et la subsidence tectonique sous eau (courbe SUTE, fig. 3A) est d’environ la moitié de cette valeur. Deux phases de subsidence sont identifiables : la première du Tournaisien au Bashkirien inférieur avec un faible taux de subsidence tectonique (2 m/Ma) et la seconde du Bashkirien supérieur à l’Assélien avec un taux un peu plus important de subsidence tectonique (22 m/Ma). La méthode proposée par Middleton [1980] pour les bassins intracratoniques américains fut utilisée pour modéliser la subsidence tectonique observée dans le MB (fig. 3B). Le modèle est caractérisé par une phase de subsidence initiale plus faible pendant la période de chauffage de la lithosphère que lors de la seconde phase de subsidence thermique pendant le refroidissement de la lithosphère. Le rapport entre la variation eustatique du niveau marin (DSLE, fig. 3A) et la subsidence tectonique à l’air libre (SUAL) permet de calculer le rapport eustatisme/ tectonique (E/T) qui est égal à 4 en faveur de l’eustatisme pendant la première phase et à 0,3 à l’avantage de la tectonique pendant la deuxième phase. La phase de subsidence 1 correspond aux séquences du second ordre D, 0 et I et la phase 2 aux séquences II à VII. Le bassin du Dniepr-Donets (DDB). – Le DDB est un rift situé entre deux massifs précambriens et est divisé en différents segments, appelés Pripyat, Dniepr, Donets et Donbass (fig. 1). Le DDB présente environ 14 km de sédiments principalement terrigènes dans le segment du Dniepr et environ 21 km dans le Donets et Donbass, d’âge dévonien moyen à sakmarien [Izart et al., 1996 ; 1998]. La couverture d’âge mésozoïque et cénozoïque a une épaisseur de 2 km excepté dans le Donbass où elle a été érodée. Une subsidence tectonique maximale d’environ 3,4 km fut calculée dans le Dniepr par van Wees et al., [1996]. Selon ces auteurs, le segment du Dniepr présente une phase de rifting initiale pendant le Dévonien supérieur et une phase post-rifting du Carbonifère inférieur à la base du Mésozoïque avec quelques rajeunissements, suivie par une inversion tectonique. A la limite entre le segment du Donets et du Donbass nous avons calculé une subsidence totale de 22,8 km et une subsidence tectonique d’environ 6,1 km (fig. 3C). Deux phases tectoniques peuvent être distinguées : la première du Dévonien au Carbonifère inférieur qui présente un taux moyen de subsidence tectonique de 40 m/Ma correspond à la phase du rifting initial et du début de la phase post-rifting du Dniepr et la seconde phase de rifting du Viséen supérieur à l’Assélien qui présente un taux important de subsidence tectonique de 90 m/Ma correspond aux rajeunissements du segment du Dniepr. Un soulèvement a lieu au Sakmarien, puis une compression pendant le Trias supérieur et à la limite Crétacé-Tertiaire [Stovba et Stephenson, 1999]. La subsidence tectonique fut modélisée (fig. 3D) en utilisant la méthode de Royden et Keen [1980]. Les deux phases tectoniques, appelées rifting 1 et 2, furent modélisées successivement. Les facteurs d’extension crustale (δ) sont respectivement pour les deux phases de 1,18 et 3,5 et les facteurs d’extension sous-crustale (β) de 1,1. Le rapport E/T est de 0,24 en faveur de la tectonique pendant la phase 1 et de 0,03 pendant la phase 2. La phase 1 correspond aux séquences du second ordre D et 0 et la phase 2 aux séquences I à VII (fig. 2). Les segments du Dniepr, Donets et Donbass possèdent donc les mêmes caractéristiques tectoniques, avec une intensité plus importante dans le Donets et le Donbass. Conclusion. – Le rifting d’âge dévonien supérieur a existé dans le DDB et probablement aussi dans le MB. L’histoire de ces deux bassins diverge ensuite avec la poursuite du rifting dans le seul DDB. Le MB est un bassin intracratonique qui peut être modélisé avec une phase de chauffage du Dévonien au Bashkirien et une phase de refroidissement engendrant une subsidence thermique du Moscovien à l’Assélien. Le DDB est un rift montrant une première phase de rifting durant le Dévonien supérieur, une phase post-rift jusqu’au Viséen supérieur et une deuxième phase de rifting jusqu’à l’Assélien uniquement dans les segments du Donets et Donbass. Si l’eustatisme contrôle la sédimentation dans le MB, la tectonique prévaut dans le DDB

Limits of the seismogenic zone in the epicentral region of the 26 December 2004 great Sumatra-Andaman earthquake: Results from seismic refraction and wide-angle reflection surveys and thermal modeling

The 26 December 2004 Sumatra earthquake (Mw = 9.1) initiated around 30 km depth and ruptured 1300 km of the Indo-Australian Sunda plate boundary. During the Sumatra OBS (ocean bottom seismometer) survey, a wide angle seismic profile was acquired across the epicentral region. A seismic velocity model was obtained from combined travel time tomography and forward modeling. Together with reflection seismic data from the SeaCause II cruise, the deep structure of the source region of the great earthquake is revealed. Four to five kilometers of sediments overlie the oceanic crust at the trench, and the subducting slab can be imaged down to a depth of 35 km. We find a crystalline backstop 120 km from the trench axis, below the fore arc basin. A high velocity zone at the lower landward limit of the raycovered domain, at 22 km depth, marks a shallow continental Moho, 170 km from the trench. The deep structure obtained from the seismic data was used to construct a thermal model of the fore arc in order to predict the limits of the seismogenic zone along the plate boundary fault. Assuming 100C-150C as its updip limit, the seismogenic zone is predicted to begin 530 km from the trench. The downdip limit of the 2004 rupture as inferred from aftershocks is within the 350C 450C temperature range, but this limit is 210-250 km from the trench axis and is much deeper than the fore arc Moho. The deeper part of the rupture occurred along the contact between the mantle wedge and the downgoing plate

Le permien de l'île d'Hydra (Grèce), micropaléontologie, sédimentologie et paléoenvironnements.

The Permian deposits of Hydra Island (Greece), micropaleontology, sedimentology and paleoenvironments, - This study presents severa! analyses in micropaleontology and scdimentology of four sections of permian deposits in the Hydra Island (Grecce). The micropaleontological study is an inventory of foraminifers and aigne, which allow securnte datations to precise age assigncmcnts. Rcprcscntaûvc facies have bccn dcfined for the Permian deposits. Summary of these data pcrmitted to eharacterize successive paleocnvironments and to propose a reconstruction of Permian sequences in this are

Paleoclimate reconstruction from petrography and biomarker geochemistry from Permian humic coals in Sydney Coal Basin (Australia)

International audienceThe character of the coal in Tomago and Greta coal measures are similar to other coals from the Sydney Coal Basin, with variation from vitrinite-rich to inertinite-rich coal. A type III organic matter (OM) linked to continental higher plants and a perhydrous type III similar to type II were found by Rock-Eval analysis. The coexistence of inertinite with algae (Botryococcus) in the Greta coals explains the high HI in the perhydrous type. The Gangamopteris flora that is reported in the Greta coal measures, grew after plants in a taiga like the recent birch forests in Russia (Retallack, 1980). The Glossopteris flora that is reported in the Tomago coal measures, grew in a swamp forest. Based upon the botanic zonation, this flora was located in the cold temperate biome that was located in Gondwanaland, except for Antarctica which was in the glacial biome. Diterpane analysis results reveal alternation of wet and dry periods existed during the deposition of Lewis coals in the Greta coal measures during the Kungurian, and an increase of dryness is noted from Upper Donaldson to Beresfield in the Tomago coal measures during the Capitanian. Based on analysis of aromatics and diterpanes, the same periods of dryness and wetness alternate during the coal deposition in the Sydney Coal Basin. These climatic changes correspond to high frequency cycles (<100 ka, Goldhammer et al., 1994). The presence of aromatics linked with combustion in the studied samples confirms the hypothesis of fire in peat land to explain high inertinite content. A low to medium biodegradation by bacteria was observed for saturates and aromatics from the studied samples as noted previously in the Sydney and Bowen Basins. This biodegradation concerns short chain n-alkanes, naphtalenes and phenanthrenes and does not alter the paleoenvironmental and paleodimatic interpretation. The comparison between biomarkers from coals and isotopes from marine (Birgenheier et al., 2010) and terrestrial (Retallack et al., 2011) deposits allow us to identify precise dry/wet climate and glacial/interglacial periods during the Permian

Modelling of the thermal history of the Carboniferous Lorraine Coal Basin: Consequences for coal bed methane

International audienceThis paper proposes a new scenario for the thermal history of the Carboniferous Lorraine Coal Basin following the tectonic model developed by Averbuch et al. (2012) and establishes some consequences for the coal bed methane (CBM) exploitation. Organic matter maturation data (Vitrinite Reflectance) determined on eleven boreholes in the eastern Lorraine have been used to characterize the Lorraine Coal Basin evolution. Paleozoic and Mesozoic overburials have been calculated using a thermal modelling software (Petromod). Results show that (1) Paleozoic erosion may be estimated at a maximum of 1200 m which represents a low amplitude event, (2) a little erosion occurred between Upper Paleozoic and Lower Mesozoic: paleotemperature offset is about 20 °C and VR data range from 0.7 (Westphalian D) to 0.5 (Lower Triassic), (3) Cretaceous cover overburial reaches a maximum of 300 m and decreases eastwards and (4) the variation of heat flows is in agreement with the compressive and extensive phases of Paleozoic and the extensive phase of Mesozoic. Consequences on the petroleum system are the following: organic matter is immature in the Jurassic and Triassic sedimentary rocks, mature (oil window) in the Permian, Stephanian and Westphalian C-D, highly mature (gas window) in Westphalian A-B-C and overmature in Namurian-Westphalian A. The high methane adsorption capacity of coal and the presence of natural fractures inside coal seams demonstrated by coal tomography allow a high CBM potential in this basin. The Lorraine Coal Basin is therefore a target for coal gas

НОВА ТЕКТОНІЧНА МОДЕЛЬ ПІЗНЬОПАЛЕОЗОЙСЬКОЇ ЕВОЛЮЦІЇ ЛОТАРИНЗЬКО-СААРСЬКОГО ВУГЛЕНОСНОГО БАСЕЙНУ (ФРАНЦІЯ / НІМЕЧЧИНА)

 The extensive database of published geologic information, structural maps and sections, combined with results of seismic surveys have been used to elaborate a new tectonic model of evolution for both French and German parts of the entire Lorraine-Saar Basin (LSB). In our interpretation the LSB is a thin-skinned asymmetrical parallelogram-shaped pull-apart basin. It has been settled and developed on the basal detachment of the listric Metz Fault within megablock on junction of two overlapping sublatitudinal master wrench faults. Our model implies that styles of sedimentation, further deformation and magmatic patterns in the LSB were governed by interplay of local extension-compression environments resulted from translational and rotational responses of the megablock to multiple dextral-sinistral strike-slip reactivations of master wrench faults. The strata in basin lie within a regional scale domain of present-day tensile stress state where cleat systems should be open and we expect that coal seams here must possess higher permeability and hence higher potential for coalbed methane production.  Для розробки нової тектонічної моделі еволюції французької та німецької частин єдиного Лотаринзько-Саарського басейну (ЛСБ) було проаналізовано велику базу даних, що включає опубліковану геологічну інформацію, структурні карти і розрізи, результати сейсмічних зйомок. У нашій інтерпретації ЛСБ являє собою тонкопластинчастий асиметричний басейн призсувного розтягу (пул–апарт) паралелограмоподібної форми. Він був закладений і розвивався на базальній поверхні лістричного Мецького розлому в межах мегаблоку на стику двох трансрегіональних зсувних зон, що перекриваються. Наша модель передбачає, що характер осадконагромадження, наступні деформаційні процеси і магматична активність в різних частинах єдиного басейну контролювалися ефектами локального розтягу або стиску, котрі виникали як реакція на поступальні і обертальні рухи мегаблоку за умов знакозмінної зсувної активізації північної і південної зон субширотних розривів. На сучасному етапі розвитку басейну його осадовой чохол знаходиться у стані локального розтягу з відкритими системи кліважу; отже, ми очікуємо, що вугільні пласти тут мають більш високу проникність і, таким чином, більш високий потенціал для промислового видобування вугільного метану.

Comparison of generative capacities for bitumen and gas between Carboniferous coals from Donets Basin (Ukraine) and a Cretaceous coal from Sabinas–Piedras Negras Basin (Mexico) during artificial maturation in confined pyrolysis system

18 pages, 11 figures, 4 tables.-- Available online 17 November 2006.-- Issue title: TSOP 2005 - Papers from the 22nd Annual Meeting of TSOP (Louisville, Kentucky, USA, 11–15 Sep 2005).The goal of this work is to study the ability of two immature Carboniferous coals from Donets Basin (Ukraine) to act as source for oil. Heating experiments in confined medium were performed to compare the thermal behavior of these coals, 1l1 Dim (%Rr = 0.55; H/C at. = 0.79) and 2c10YD (%Rr = 0.65; H/C at. = 0.80), relative to a mature Cretaceous coal from Sabinas Basin (Olmos, %Rr = 0.92, H/C at. = 0.77). Macerals analysis carried out on starting materials showed that Olmos is exhausted in liptinite contrary to 2c10YD (20 vol.%) and 1|1Dim (6 vol.%). The vitrinite content is lower for 2c10YD (59 vol.%) than for Olmos (84 vol.%) and 1|1Dim (80 vol.%). Solid bitumen occurs often dispersed in the raw coals. Both petrographic and geochemical analyses on starting materials revealed that the selected Carboniferous Donets coals have better potentialities for bitumen generation than the Cretaceous Sabinas coal. The presence of long chain n-alkanes (> n-C8) in the pyrolysis-GC chromatograms indicates that the two raw Carboniferous coals from Donets Basin can yield non-volatile hydrocarbons under further thermal maturation. It is speculated that some vitrinite macerals present in hydrogen-rich Carboniferous coals from Donets Basin can act as source rocks for oil. As a matter of fact, results showed that the ‘oil window’ occurs between ~ 1.0%Rr and ~ 2.0%Rr for both Cretaceous Sabinas and Carboniferous Donets coals during confined pyrolysis. As expected from geochemical and petrographic analyses of starting samples, the Carboniferous Donets coals yielded more bitumen and hydrocarbons than Cretaceous Sabinas coal during artificial maturation. Low proportions of solid bitumen (< 12 vol.%) are also formed between 1.1%Rr and 1.5%Rr during confined pyrolysis of coals. Two solid bitumen groups have been identified, which correspond to distinct phases of neo-formation. The drop in the solid bitumen content at higher ranks indicates that it contributes to generation of gas during experimental simulation. Moreover, their morphology and porosity change with the level of maturity. The porosity of the vitrinite matrix increases as well as the pore size with increasing maturity. A relationship has been observed between the porosity and the weight loss: the higher pore content of Carboniferous Donets coals is correlated with a higher generation of gas compared to Cretaceous Sabinas coal.The authors wish to acknowledge the CREGU (France) and the Syria Government for their financial support. This research was also supported by a CSIC-CNRS (Spain-France) Bilateral Agreement (Collaboration Cooperation Accord CNRS/CSIS Project Conjoint 16226).Peer reviewe

Alternating microbial mounds and ooidal shoals as a response to tectonic, eustatic and ecological conditions (late Viséan, Morocco)

The succession in the Tizra Formation shows an excellent exposure of a small open marine platform where alternating microbial boundstones (buildups) and oolitic/bioclastic grainstone (shoals) and packstone facies tempestites occur repetitively for a sort interval only 0.55 Myr, an scenario unknown in the geological record. The relatively small extent of the platform allows a detailed study of facies and ecological variations, to determine the controlling factors for the growth and evolution of the platform (tectonics, glacioeustatism, terrigenous input), as well as the particular environmental/ecological conditions for the formation of microbial buildups and oolitic shoals (turbidity, energy, nutrients, chemical variations). Although microbial mounds are well-known during the Palaeozoic, the close relationship with ooids, as observed in the studied succession, is unusual, particularly for the frequent ooids embedded in the microbial facies, an ecological parameter used by previous authors to identified shallower stages in the microbial growths. Petrographic analysis of the ooids, as well as their ecological conditioning, suggest that less than 40% of samples yield ooids generated in situ, whereas there is a predominance of transported ooids. Ooids formed in situ, which include large irregular and elongated ooids, were generated in calmer water than the typical rounded and egg-shaped ooids. The occurrence of the predominant types of ooids in shallower-water grainstones with in situ generation, and in the deepest-water microbial facies, suggest their ease of transport. The higher production of ooids occurs during the shallowing phases of the cycles, whereas they were more easily transported during the deepening phases, whereas in the microbial buildups, no features of in situ ooid generation are found