Bulletin de la Societe Geologique de France最新文献

{"title":"Pseudotachylyte in the Monte Maggiore ophiolitic unit (Alpine Corsica): a possible lateral extension of the Cima di Gratera intermediate-depth Wadati-Benioff paleo-seismic zone","authors":"O. Fabbri, R. Magott, M. Fournier, Lucas Etienne","doi":"10.1051/BSGF/2018020","DOIUrl":"https://doi.org/10.1051/BSGF/2018020","url":null,"abstract":"At the northern end of the Cap Corse peninsula, several klippes of ultramafic rocks (peridotite and serpentinite), among which the Monte Maggiore klippe is the least serpentinized one, rest upon continental-crust derived rocks (Centuri gneisses) and basic or metasedimentary schists (Schistes Lustres). The Monte Maggiore ophiolitic klippe shares several characteristics with the Cima di Gratera klippe located 30 km further south. First, the two units are composed of a lherzolitic peridotite. Second, they record the same succession of metamorphic events. Third, in the Cap Corse tectonic pile, the two units occupy the highest structural position. Several differences are also observed. First, mafic rocks are significantly less abundant in the Monte Maggiore unit, where they are restricted to dykes cross-cutting the peridotite, than in the Cima di Gratera unit, where they constitute an entire sub-unit. Second, pyroxenite layers are more common at Monte Maggiore than at Cima di Gratera. Despite these differences, the Monte Maggiore and Cima di Gratera klippes can be considered as possible lateral equivalents of a single ophiolitic unit having covered the entire Cap Corse before subsequent erosion. Pseudotachylyte of seismic origin is newly discovered in the Monte Maggiore klippe. The host rock is a cataclastic serpentinized peridotite affected by a cataclastic foliation that is either flat-lying or steeply dipping. Pseudotachylyte fault veins are parallel to the host rock cataclastic foliation. The small lateral extension and the small thickness of fault veins along with frequent cross-cutting relationships suggest that the exposed pseudotachylyte most likely results from numerous small magnitude seismic events such as swarms or aftershocks rather than from large magnitude shocks. All these characteristics are also observed at the Cima di Gratera klippe where they are interpreted as the testimonies of a fossil intermediate-depth Wadati-Benioff zone at the time of subduction of the Ligurian Tethys oceanic lithosphere. Mineral assemblages that could constrain the depth of formation of the pseudotachylyte lack in the Monte Maggiore area. Despite this uncertainty, and given the similarities with the Cima di Gratera occurrences, the pseudotachylyte veins newly discovered at Monte Maggiore are tentatively related to the seismic activity linked with the subduction of the Piemonte-Ligurian oceanic lithosphere in Eocene times. This interpretation suggests that the fossil Wadati-Benioff zone could be traced further south in Alpine Corsica and further north in the Piemontese zone of the western Alps.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"5 1","pages":"18"},"PeriodicalIF":0.0,"publicationDate":"2018-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85425129","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Vertical strain partitioning in hot Variscan crust: Syn-convergence escape of the Pyrenees in the Iberian-Armorican syntax","authors":"B. Cochelin, D. Chardon, Y. Denèle, C. Gumiaux, B. Bayon","doi":"10.1051/BSGF/2017206","DOIUrl":"https://doi.org/10.1051/BSGF/2017206","url":null,"abstract":"A new structural map of the Paleozoic crust of the Pyrenees based on an extensive compilation and new kinematic data allows for the evaluation of the mechanical coupling between the upper and lower crust of the abnormally hot foreland of the Variscan orogen of SW Europe. We document partitioning between coeval lower crustal lateral flow and upper crustal thickening between 310 and 290 Ma under an overall dextral transpressive regime. Partitioning also involved syn-convergence transtensional gneiss domes emplacement during this period. Late orogen-normal shortening of the domes and strain localization in steep crustal-scale transpressive shear zones reflects increasing coupling between the lower crust and the upper crust. The combination of dextral transpression and eastward flow in the Pyrenees results from the shortening and lateral escape of a hot buoyant crust along the inner northern limb of the closing Cantabrian orocline at the core of the Iberian-Armorican arc between ca. 305 and 295 Ma. Delamination or thermal erosion of the lithosphere enhanced orocline closure and explains (1) the switch from crust-to mantle-derived magmatism in the Iberian-Armorican arc and (2) the abnormally hot and soft character of the Pyrenean crust that escaped the closing syntax.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"26 1","pages":"39"},"PeriodicalIF":0.0,"publicationDate":"2017-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83686123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Small-scaled lateral variations of an organic-rich formation in a ramp-type depositional environment (the Late Jurassic of the Boulonnais, France): impact of the clastic supply","authors":"E. Hatem, N. Tribovillard, O. Averbuch, V. Bout‐Roumazeilles, A. Trentesaux, J. Deconinck, F. Baudin, T. Adatte","doi":"10.1051/BSGF/2017193","DOIUrl":"https://doi.org/10.1051/BSGF/2017193","url":null,"abstract":"We studied a potential petroleum source rock deposited in a clastic-dominated ramp environment: the Argiles de Châtillon Formation (Kimmeridgian-Tithonian, Boulonnais area, northern France). The formation was deposited along a proximal-distal gradient on this ramp affected by synsedimentary fault movements. A sedimentological, mineralogical and geochemical study was conducted to decipher the distribution patterns of sedimentary parameters along such a depth increase over the ramp. It comes out that smectite distribution unexpectedly mimics the lateral depth evolution despite the good floatability of the mineral. It is also observed that the Argiles de Châtillon could accumulate noticeable amounts of organic matter in spite of paleoenvironmental conditions that were not specifically prone to organic matter preservation and burial (sedimentation rate, mineral particle grain size, productivity, oxygenation level…). Conversely, reactive iron, when being present in limited abundance, must have allowed sulfide ions to react with organic molecules instead of forming iron sulfides, which fostered organic matter preservation and accumulation. This protecting role of organic sulfide incorporation (additional to other favorable factors) cannot exist if reactive iron is relatively abundant. Lastly, our results (still fragmentary) suggest that smectite minerals could carry reactive iron, which would have occasionally hampered organic-matter preservation.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"24 1","pages":"31"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85178096","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleoenvironmental evolution of the southern Neuquèn basin (Argentina) during the Tithonian-Berriasian (Vaca Muerta and Picún Leufú Formations): a multi-proxy approach","authors":"N. Krim, C. Bonnel, N. Tribovillard, P. Imbert, C. Aubourg, A. Riboulleau, V. Bout‐Roumazeilles, G. Hoareau, B. Fasentieux","doi":"10.1051/BSGF/2017196","DOIUrl":"https://doi.org/10.1051/BSGF/2017196","url":null,"abstract":"The Tithonian-Berriasian interval in the southern part of the Neuquen Basin is represented by the Vaca Muerta and the Picun Leufu Formations. Facies analysis and correlation of the Vaca Muerta Formation and the lower part of the Picun Leufu Formation in the Picun Leufu Anticline allow us to characterize the evolution of successive facies belts representing siliciclastic shelf and mixed ramp environments. Shoreface and offshore facies are developed on the siliciclastic shelf in the western and southern parts of the Picun Leufu Anticline. The offshore transition domain is characterized by storm beds and slump features, whereas the offshore domain corresponds to black to grey shales and turbidites. The mixed siliciclastic-carbonate ramp is characterized by the development of a lagoon and high-energy shoal in the proximal part of the inner ramp, whereas the distal part comprises a tidal complex. The mid-ramp zone is characterized by storm influence and the outer ramp by fine-grained deposits. Two major transgressive-regressive sequences and five high-frequency transgressive-regressive sequences are recognized. The high-frequency transgressive-regressive sequences make up three progradational sequences, an aggradational-progradational sequence and an aggradational sequence. The geochemical characteristics and clay mineralogy of the Tithonian-Berriasian interval in the southern Neuquen Basin indicate that (1) climate played a key role in the evolution of the sedimentary environment, (2) a “normal marine” depositional environment with oxic sea water and sediment pore waters, rapidly changing to suboxic conditions at shallow depth below the seabed and (3) the occurrence of episodically restricted water-mass circulation at the onset of deposition of the Vaca Muerta Formation.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"79 1","pages":"34"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81481593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Palaeoenvironmental control on primary fluids characteristics of lacustrine source rocks in the Autun Permian Basin (France)","authors":"Sylvain Garel, F. Behar, J. Schnyder, F. Baudin","doi":"10.1051/BSGF/2017187","DOIUrl":"https://doi.org/10.1051/BSGF/2017187","url":null,"abstract":"The Autunian (Late Gzhelian-Sakmarian, ∼295 Ma) of the Autun Basin (Saone-et-Loire, France) is well known for its lacustrine oil-shales and boghead that were exploited during the 19th and 20th centuries. A study of the kerogen geochemistry, palynofacies, hydrocarbon (HC) distribution of pyrolysates and kinetics on these organic-rich sediments gave indications on the control of lacustrine primary fluid characteristics by palaeoenvironmental settings. Palynofacies results have shown a Botryococcus algae dominance in the boghead, whereas the oil-shales were dominated either by a mixing of terrestrial particles and lacustrine phytoplanktonic/bacterial organic matter (OM), or by a lacustrine OM that suffered biodegradation within the water column. During the Autunian, an increasing trend of degraded lacustrine OM concentration is observed in the successive oil-shales. Geochemical and kinetics analyses showed that, except for the boghead, hydrogen index values were n -alkanes with ( n -C 6 - n -C 14 ) / n -C 14+ n -alkanes ratio depending on the proportion of terrestrial OM. They were only encountered in the three oldest oil-shales. On the other hand, the HC profile of fluids originating from samples dominated by degraded lacustrine OM, which was obtained for the first time in this study, show low n -alkanes concentrations and a relatively prominent hump. These samples were only present in the three youngest oil-shale levels. Finally, the boghead showed a link between strong concentration of the Pila genus of Botryococcus algae and a primary fluid dominated by n -C 6 - n -C 14 n -alkanes.By comparing these data with published palaeoenvironmental studies, it appears that the kind of dominant OM, and thus the HC distribution of primary fluids, is controlled by the lake level: a lower depth preventing the settlement of anoxic conditions in the bottom waters, and the subsequent good preservation of the OM. During the Autunian, the lake level decreased, consequence of a reduced tectonic activity and of the beginning of a dryer period. Finally, these changes will have caused a strong decrease of the nutrient influx to the lake, favoring the bloom of Botryococcus algae that accumulated to form the boghead.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"59 1","pages":"29"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89009754","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Worldwide shale-oil reserves: towards a global approach based on the principles of Petroleum System and the Petroleum System Yield","authors":"M. Blaizot","doi":"10.1051/BSGF/2017199","DOIUrl":"https://doi.org/10.1051/BSGF/2017199","url":null,"abstract":"Global inventory of shale-oil resources and reserves are far from being complete even in mature basins which have been intensively drilled and produced and in which the main parameters of the regional or local oil-prone source rocks are known. But even in these cases, difficulties still occur for deriving reserves from resources: reaching a plausible recovery factor is actually a complex task because of the lack of production history in many shale-oil ventures. This exercise is in progress in several institutions (EIA, USGS, AAPG) or private oil and gas companies on a basin-by-basin basis in order to estimate the global potential. This analytical method is very useful and accurate but also very time consuming. In the last EIA report in 2013 “only” 95 basins had been surveyed whereas for example, no Middle-East or Caspian basins have been taken into account. In order to accelerate the process and to reach an order of magnitude of worldwide shale-oil reserves, we propose hereafter a method based on the Petroleum System principle as defined by Demaison and Huizinga (Demaison G and Huizinga B. 1991. Genetic classification of Petroleum Systems. AAPG Bulletin 75 (10): 1626–1643) and more precisely on the Petroleum System Yield (PSY) defined as the ratio (at a source-rock drainage area scale) between the accumulated hydrocarbons in conventional traps (HCA) and hydrocarbons generated by the mature parts of the source-rock (HCG). By knowing the initial oil reserves worldwide we can first derive the global HCA and then the HCG. Using a proxy for amount of the migrated oil from the source-rocks to the trap, one can obtain the retained accumulations within the shales and then their reserves by using assumptions about a possible average recovery factor for shale-oil. As a definition of shale-oil or more precisely LTO (light tight oil), we will follow Jarvie (Jarvie D. 2012. Shale resource systems for oil & gas: part 2 – Shale Oil Resources Systems. In: Breyer J, ed. Shale Reservoirs . AAPG, Memoir 97, pp. 89–119) stating that “shale-oil is oil stored in organic rich intervals (the source rock itself) or migrated into juxtaposed organic lean intervals”. According to several institutes or companies, the worldwide initial recoverable oil reserves should reach around 3000 Gbo, taking into account the already produced oil (1000 Gbo) and the “Yet to Find” oil (500 Gbo). Following a review of more than 50 basins within different geodynamical contexts, the world average PSY value is around 5% except for very special Extra Heavy Oils (EHO) belts like the Orinoco or Alberta foreland basins where PSY can reach 50% (!) because large part of the migrated oils have been trapped and preserved and not destroyed by oxidation as it is so often the case. This 50% PSY figure is here considered as a good proxy for the global amount of expelled and migrated oil as compared to the HCG. Confirmation of such figures can also be achieved when studying the ratio of S1 (in-place hydroca","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"23 1","pages":"33"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84099231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Controlling factors on source rock development: implications from 3D stratigraphic modeling of Triassic deposits in the Western Canada Sedimentary Basin","authors":"V. Crombez, S. Rohais, F. Baudin, B. Chauveau, T. Euzen, D. Granjeon","doi":"10.1051/BSGF/2017188","DOIUrl":"https://doi.org/10.1051/BSGF/2017188","url":null,"abstract":"The recent development of unconventional resources has triggered a regain of interest for source-rocks. The presence of hydrocarbons in these unconventional systems is generally associated with organic-rich sediments. This study aims at better understanding the factors controlling the accumulation of marine organic matter at basin scale, using a process-based approach. This work focuses on the Montney, Doig and Halfway Formations (Lower and Middle Triassic, Alberta and British Columbia, Canada). Recent studies show that the Triassic strata of the Western Canada sedimentary basin can be considered as a transitional period between the Paleozoic passive margin and the Jurassic foreland basin. Based on a 3D regional stratigraphic architecture and on a description of the organic rich interval distribution, a process-based numerical model (DionisosFlow and DORS) has been used to simulate the stratigraphic evolution of the Montney, Doig and Halfway Formations and reproduce the organic distribution in these formations. This modeling approach allowed us to test different scenarios of primary productivity and basin restriction and discuss the regional controls on organic matter accumulation such as dynamic of anoxia or dilution of organic matter by detrital sediments. The reconstruction of the stratigraphic architecture emphasizes a major drop of the water discharge in the basin. In the absence of any evidence supporting a link with a climate change, the drop in water discharge suggests a major modification of the drainage area of the basin, potentially associated with the early stage of the cordilleran orogeny and foreland basin evolution. The numerical simulation also shows that the primary productivity rates in the Montney and Doig Formations are characteristic of a coastal area and that a basin restriction is required to account for the level of anoxia observed in the studied Formations. Lastly, this study investigates the regional controls on organic matter accumulation and emphasizes the impact of regional paleogeographic and geodynamic evolution on the dynamic of anoxia and on the dilution.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"86 1","pages":"30"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90644375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Space-time evolution of a large field of pockmarks in the Bay of Concarneau (NW Brittany)","authors":"A. Baltzer, M. Reynaud, A. Ehrhold, J. Fournier, C. Cordier, Hélène Clouet","doi":"10.1051/BSGF/2017191","DOIUrl":"https://doi.org/10.1051/BSGF/2017191","url":null,"abstract":"About a decade ago, a large field of pockmarks, covering an overall area of 36 km2 was discovered in water depths of , forming original benthic communities. Two complementary surveys were carried out in April 2011 (Pock and Ploops) and April 2014 (Pock and Tide), on the Oceanographic Vedette (O/V) Haliotis (Ifremer/Genavir), to map the limit of the pockmarks and Haploops fields with the maximum accuracy. The link between the presence of the Haploops nirae communities and the occurrence of pockmarks /gas was then established and the proposed hypothesis was that tidal cycles may provide a good candidate for a short-term (monthly) triggering mechanism of fluid expulsion (Baltzer A, Ehrhold A, Rigolet C, Souron A, Cordier C, Clouet H. 2014. Geophysical exploration of an active pockmark field in the Bay of Concarneau, southern Brittany, and implications for resident suspension feeders. Geo-Marine Letters, 34, 215–230). Due to the high-level precision (50 cm) of the positioning system (Magellan Aquarius Ixsea Hydrins) coupled with the RTK attitude system, these new bathymetric and imagery maps together with the sub-bottom Chirp profiles, allow us to compare the data sets from April 2011 and April 2014. The superimposition of the two data sets shows that the distribution of the pockmarks remains similar between these 2 dates (i.e. for 3 years), for the group of large, widely scattered pockmarks, which are deeply rooted in the Holocene palaeo-valley infills and for the group of pockmarks identified as the trawl-scour pockmarks, initiated by trawling action. Most of the pockmarks present very recent shapes without any infilling but sonar imagery reveals that some of them have been covered by a thin muddy layer, thereby reflecting, at least, a temporary cessation of expulsion or a different activity. Chirp profiles indicate some acoustic flares above the pockmarks, revealing gas/fluid expulsion. Different gas clues within the sedimentary column, such as acoustic turbidity, enhanced gas reflectors (EGR), chimneys pipes, occur at exactly the same places on the chirp seismic profiles from 2011 and 2014. Therefore, contrary to most examples described in the literature, this pockmarks field is still active.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"32 1","pages":"23"},"PeriodicalIF":0.0,"publicationDate":"2017-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89425896","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spider structures: records of fluid venting from methane hydrates on the Congo continental slope","authors":"V. Casenave, P. Imbert","doi":"10.1051/BSGF/2017189","DOIUrl":"https://doi.org/10.1051/BSGF/2017189","url":null,"abstract":"Fluid seepage features on the upper continental slope offshore Congo are investigated using multi-disciplinary datasets acquired during several campaigns at sea carried out over the last 15 years. This datasets includes multibeam bathymetry, seismic data, seafloor videos, seafloor samples and chemical analyses of both carbonate samples and of the water column. Combined use of these datasets allows the identification of two distinctive associations of pockmark-like seabed venting structures, located in water depths of 600–700 m and directly above a buried structural high containing known hydrocarbon reservoirs. These two features are called spiders due to the association of large sub-circular depressions (the body) with smaller elongate depressions (the legs). Seismic reflection data show that these two structures correspond to amplitude anomalies located ca.  60–100 ms below seabed. The burial of these anomalies is consistent with the base of the methane hydrate stability domain, which leads to interpret them as patches of hydrate-related bottom-simulating reflection (BSR). The morphology and seismic character of the two structures clearly contrasts with those of the regional background (Morphotype A). The spider structures are composed of two seafloor morphotypes: Morphotype B and Morphotype C. Morphotype B makes flat-bottomed depressions associated with the presence of large bacterial mats without evidence of carbonates. Morphotype C is made of elongated depressions associated with the presence of carbonate pavements and a prolific chemosynthetic benthic life. On that basis of these observations combined with geochemical analyses, the spider structures are interpreted to be linked with methane leakage. Methane leakage within the spider structures varies from one morphotype to another, with a higher activity within the seafloor of Morphotype C; and a lower activity in the seafloor of Morphotype B, which is interpreted to correspond to a domain of relict fluid leakage. This change of the seepage activity is due to deeper changes in gas (or methane) migration corresponding to the progressive upslope migration of fluids. This phenomenon is due to the local formation of gas hydrates that form a barrier allowing the trapping of free gas below in the particular context of the wedge of hydrates.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"28 1","pages":"27"},"PeriodicalIF":0.0,"publicationDate":"2017-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89487019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatial distribution and tectonic framework of fossil tubular concretions as onshore analogues of cold seep plumbing systems, North Island of New Zealand","authors":"P. Malié, J. Bailleul, F. Chanier, R. Toullec, G. Mahieux, V. Caron, B. Field, R. F. Mählmann, S. Potel","doi":"10.1051/BSGF/2017192","DOIUrl":"https://doi.org/10.1051/BSGF/2017192","url":null,"abstract":"Analysis of offshore seismic lines suggests that a strong relationship exists between tectonic structures and fluid migration in accretionary prisms. However, only few field analogues of plumbing systems and their tectonic frameworks have been investigated in detail until now. The uplifted accretionary prism of the Hikurangi Margin (North Island, New Zealand) exposes early to late Miocene mudrocks in coastal cliffs of Cape Turnagain and in the Akitio syncline, south-east of the Pongaroa city. These outcrops display tubular carbonate concretions corresponding to complex subsurface plumbing networks of paleo-seeps within Miocene trench slope basins. We present here, new results on the spatial distribution of these tubular carbonate concretions, with particular attention to their relation to tectonic structures. In the Pongaroa area, tubular carbonate concretions in lower Miocene mudrocks occur along a N-S trend, while in middle Miocene strata they occur along a NNE-SSW direction. The N-S trend parallels a major fault zone (i.e. the Breakdown fault zone), which separates two wide synclines, the Waihoki and the Akitio synclines. During the Early-Middle Miocene, the Breakdown fault zone controlled the evolution of the Akitio trench slope basin constituting its western edge. The NNE-SSW strike parallels the axis of the Akitio syncline and is also parallel to the present-day subduction front. Our results therefore show that tubular concretions are parallel to post-Middle Miocene second order folding and thrusting in the northeastern limb of the Akitio syncline. In the Cape Turnagain area, tubular concretions occur in the western limb of the Cape Turnagain syncline, in the footwall of the major seaward-verging Cape Turnagain fault. This suggests that fluid migrations may occur not only in the crests of anticlines, as observed offshore for present-day plumbing system of cold seeps, but also in the footwalls of thrust faults. All these observations show that the spatial distribution of tubular concretions is controlled by regional tectonic structures with paleo-fluid migrations related to major deformation episodes of the accretionary prism. Thus, we distinguish three episodes events that likely triggered fluid migration leading to the formation of the tubular concretions: (1) In the Early Miocene, shortly after the onset of development of the Akitio trench slope basin, on its inner (western) edge; (2) During the late Middle Miocene, during an extensional deformation episode on the western limb of the Akitio trench slope basin; (3) At the end of the Late Miocene, during a second major shortening period at the footwall of major thrust fault, such as in the Cape Turnagain area.","PeriodicalId":55978,"journal":{"name":"Bulletin de la Societe Geologique de France","volume":"26 1","pages":"25"},"PeriodicalIF":0.0,"publicationDate":"2017-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77455333","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}