Marine Geology 373 (2016) 26–38 Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margo Pockmarks and methanogenic carbonates above the giant Troll gas ﬁeld in the Norwegian North Sea A. Mazzini a,⁎, H.H. Svensen a, S. Planke a,b, C.F. Forsberg c, T.I. Tjelta d a CEED, University of Oslo, Oslo, Norway VBPR, Oslo, Norway NGI, Oslo, Norway d Statoil, Stavanger, Norway b c a r t i c l e i n f o Article history: Received 25 May 2015 Received in revised form 19 November 2015 Accepted 21 December 2015 Available online 28 December 2015 Keywords: Norwegian North Sea Troll Methanogenic carbonates Pockmarks Gas hydrates a b s t r a c t Acoustic imaging has revealed more than 7000 pockmarks on the seaﬂoor above the Troll East gas ﬁeld in the Norwegian North Sea. We present the ﬁrst comprehensive study conducted on one of the World's largest pockmark ﬁelds complementing the acoustic data with extensive sampling, geochemical and petrographical studies. Speciﬁcally, we aimed at detecting possible active seepage still present over this vast area. The pockmarks are present as isolated structures, on average ~35 m wide and up to 100 m in size. In addition, smaller satellite pockmarks surround some of the pockmarks. In contrast to the muddy surroundings, parts of the investigated pockmarks contain laterally extensive carbonate deposits or meter sized carbonate blocks. These blocks provide shelter to abundant colonies of benthic megafauna. The carbonate blocks are comprised of micritic Mg-calcite and calcite, micritic aragonite, and botryoidal aragonite. Framboidal pyrite is also commonly present. Carbon isotopic values of the carbonates are 13C-depleted (δ13C as low as −59.7‰) and with δ18O up to 4.5‰, indicating a methanogenic origin, possibly linked to gas hydrate dissociation. Pore water extracted from shallow cores from the centre and the ﬂanks of the pockmarks show similar Cl and SO4 proﬁles as the reference cores outside the pockmarks, ruling out active methane seepage. This conclusion is also supported by seaﬂoor video observations that did not reveal any evidence of visual ﬂuid seepage, and by the absence of microbial mats and by the fact that the carbonate blocks are exposed on the seaﬂoor and party oxidized on the surface. We conclude that methane seepage formed this extensive gas ﬁeld following to gas hydrate dissociation. © 2015 Elsevier B.V. All rights reserved. 1. Introduction There are three main settings where pockmarks are commonly present: 1) in offshore hydrocarbon provinces where ﬂuids leaking from reservoirs reach the seaﬂoor; 2) in gas hydrate regions as the result of ongoing or paleao dissociation of clathrates, and 3) in estuarine and delta regions where the constantly deposited organic-rich sediments or drowned wetlands trigger the production of shallow gas. Comparative studies show that the ﬁelds with the highest density of pockmarks are usually located at shallow depth associated with deltaic and estuarine settings (e.g. Kelley et al., 1994; Rogers et al., 2006; Brothers et al., 2012; Riboulot et al., 2013 and refs. therein). At these localities the presence of microbial methane is mostly recorded as opposed to thermogenic methane that is common at greater water depths especially in hydrocarbon-rich provinces (e.g. Nickel et al., 2013; Smith et al., 2014). ⁎ Corresponding author at: Centre for Earth Evolution and Dynamics (CEED) University of Oslo, ZEB-bygningen Sem Saelandsvei 2A, Blindern 0371 Oslo Norway. E-mail address: email@example.com (A. Mazzini). http://dx.doi.org/10.1016/j.margeo.2015.12.012 0025-3227/© 2015 Elsevier B.V. All rights reserved. Former or ongoing methane seepage in pockmarks is commonly coupled to anaerobic methane oxidation operated by microbial colonies ions that bind with of archea and bacteria. This reaction releases CO2− 3 Ca present in the seawater ultimately resulting in authigenic carbonate precipitation (Valentine and Reeburgh, 2000; Boetius and Suess, 2004; Boetius and Wenzhöfer, 2013). Methanogenic carbonates are indeed common features at many pockmarks and seepage sites (Kocherla et al., 2015; Magalhães et al., 2012; Hovland et al., 1987; Naehr et al., 2000; Greinert et al., 2001; Gontharet et al., 2007; Akhmetzhanov et al., 2008; Greinert et al., 2010; Haas et al., 2010). The presence of pockmarks in the North and Norwegian Seas and all the way north to the Barents Sea has been documented by several authors (e.g. Hovland and Judd, 1988; Andreassen et al., 2000; Bouriak et al., 2000; Bünz et al., 2003; Berndt et al., 2004; Hovland et al., 2005; Mazzini et al., 2005, 2006; Forsberg et al., 2007; Paull et al., 2008; Chand et al., 2012; Nickel et al., 2012). One of the largest pockmark ﬁelds is located at Nyegga, in the southern part of the Vøring Plateau. The ﬁrst discovery of authigenic carbonates from this locality was reported by Mazzini et al. (2005). The ﬁrst discovery of gas hydrates in the area was reported more recently (Ivanov et al., 2007). Although A. Mazzini et al. / Marine Geology 373 (2016) 26–38 the features in the Nyegga region have always been described as pockmarks, a large part of them are not morphological depressions but rather positive structures containing large carbonate ediﬁces in the central area. In order to describe these “seeping positive structure” Ivanov et al. (2010) coined the new term “seep mounds”. Large pockmark ﬁelds represent a window into the subsurface plumbing systems. They have been targeted for extensive geological and geophysical explorations offshore Norway in order to investigate the gas origin and if they are currently active or not. Active pockmarks and mud volcanoes represent oasis of unique chemosynthetic life (Olu et al., 1997; Sibuet and Olu, 1998; Menot et al., 2010; Ritt et al., 2011). However, numerous questions remain unanswered in particular for the pockmarks at northern latitudes. For example, is the seepage entirely related to gas hydrate dissociation? Or could the leakage from underlying gas and oil reservoirs represent the source of gas? Was the gas release catastrophic or did the ﬂuid migration occur at 27 slow mode? The climatic consequences of palaeo and modern seepgas release to the shallow ocean and atmosphere is still an open question (Westbrook et al., 2009; Smith et al., 2014) and the discovery of new large pockmark ﬁelds is of relevance for future studies and global estimates. In this paper we document the structure and nature of a giant pockmark ﬁeld in the Norwegian North Sea (Fig. 1) where large carbonate blocks have been identiﬁed and sampled. These results are part of a large Statoil-funded project aiming at investigating gas migration around the Troll A platform. The aim of the paper is to describe the characteristics of this new discovery and to determine if active seepage is occurring in the region based on a large sampling campaign inside and outside the pockmarks. This issue has important implications for the ﬂuid ﬂow and hazard aspects of the area. If the pockmarks are actively leaking, there is a potential risk for formation of new pockmarks with a possible inﬂuence on platform stability. The second important Fig. 1. (A) Inset map of Norwegian channel and North Sea, framed the Troll study area. (B) Detail of the Troll East gas ﬁeld (yellow) covered with an extensive multibeam survey (purple line). (C) Troll ﬁeld multibeam data. Note the large number of pockmarks (about 7500 in total). UTM Zone 31, WGS84 datum. Indicated the Troll A platform and the location of the three main ROV pockmark study areas: in red (Septagram), green (Peanut), and blue (Arch). (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.) 28 A. Mazzini et al. / Marine Geology 373 (2016) 26–38 aim is to ﬁnd evidence of former seep activity and hydrocarbon ﬂow through the sea ﬂoor via pockmarks. 2. Troll A shallow gas migration project The main objective of the Statoil “Troll A shallow gas migration project” was to understand the cause of high pressures in the outer annuli of the wells and in the foundation skirt compartments of the Troll A platform (Tjelta et al., 2007). The Toll A platform is a large concrete gravity base structure located in the Norwegian trench. High pressures have to be bleed-off routinely since the installation of the platform in 1995, typically once a month for the well annuli and more irregularly for the foundation skirt compartments. This routine procedure raised a number of questions about the potential for natural gas seepage in the Troll area, in particular if the numerous pockmarks in the region could be sites for active focused ﬂuid ﬂow and thereby representing a potential hazard. One of the main goals of the project was therefore to search for evidence of active ﬂuid seepage. 3. Geological setting The giant Troll oil and gas ﬁeld are located in the northern North Sea, about 50 km west of Norway, in the 300 m deep Norwegian Channel. The ﬁeld extends over more than 700 km2, and is situated on the Horda Platform between the northern Viking Graben to the west and the Øygarden Fault Zone to the east. The reservoir consists of faulted Jurassic sandstones of the Viking Group about 1.5 km below the sea ﬂoor. Two major crustal extensional events, a Permo-Triassic and a late Jurassic–early Cretaceous event, lead to the formation of the northern North Sea rift system (Christiansson et al., 2000; Faleide et al., 2010; Holgate et al., 2013). The rift basin was subsequently inﬁlled with late Cretaceous and Paleogene sediments during post-rift subsidence. Southern Norway and the eastern ﬂank of the North Sea were subsequently uplifted and eroded, in particular from mid-Miocene times. Repeated ice stream activity during the Pleistocene formed the Norwegian Channel (Sejrup et al., 2003). The stratigraphy of the Horda Platform is dominated by Mesozoic and Cenozoic clastic sediments above a Paleozoic basement. Two major angular unconformities are apparent in seismic reﬂection data — the Base Cretaceous Unconformity (BCU) and the Upper Regional Unconformity (URU) (Faleide et al., 2010). Sub-horizontal Quaternary glacial and marine sediments, and a few tens of meters thick sequence of post-glacial marine sediments, overlie the URU. 4. Methods 4.1. Marine expeditions and acoustic survey After an initial multibeam survey to cover a large area around the Troll ﬁeld (~ 15,000 km2), four different main ROV cruises were conducted in 2005 and 2006 to map in more detail the structure of six complex pockmarks (Fig. 1). Initial surveying took place in March 2005 in the Septagram region using the vessel Edda Fonn. This survey was followed up in July 2006 and October 2006 in the Septagram and Peanut regions, and in December 2006 in the Arch region, using R/V Normand Tonjer, Edda Fonn, and Normand Tonjer, respectively. The ROV survey equipment for the two survey vessels were similar, providing high-quality bathymetry (the DTM bin size is 0.5 by 0.5 m for all except the high-resolution grid of Septagram which is 0.1 by 0.1 m), side-scan sonar (325 kHz), and sub-bottom proﬁler (4.5 to 10 kHz) data. Typically, a constant ﬂight height of 10–15 m above the regional sea ﬂoor was used. Video record and high resolution image stills were collected during each ROV dive in order to document the presence of ﬂuid activity, chemosyinthetic fauna, and possible authigenic carbonates. 4.2. Sampling Sixteen ~ 6 m long cores and one 12 m core have been collected in the Septagram region (i.e. from the Septagram pockmark and two buried pockmarks) during two separate expeditions in 2005 and 2006. In addition, 28 short (0.5 m) ROV cores were taken (19 in the Septagram region, 4 in the Peanut region, 3 in Arch D, and 2 in Arch E). A collection of biological samples and carbonate blocks was sampled using an ROV grabber at the pockmark sites (Fig. A1, Tables A1–A2). 4.3. Petrography Thin sections of the carbonate samples were studied using both optical and electronic microscopes, including UV light, secondary electron and backscattered electron modes. A set of XRD analyses was conducted on carbonate fractions in order to identify the carbonate phases. A total of 42 individual mineral analyses were performed with a CAMECA SX 100 electron microprobe (EMP) in order to determine the composition of the authigenic carbonate. The results are presented in Table A3, both as weight percent oxides and the calculated structural formulas. 3D CT scanning was conducted on one of the carbonate blocks in order to determine the internal structure. Images were acquired using a GE Lightspeed Ultra CT 99_OC0 spiral computed tomography scanner, with an 8 sensor system (Majorstuen Røntgen Capio, Oslo, Norway). The thickness of the scanned slices was 0.625 mm, and 247 scans were made throughout the sample. 4.4. Geochemistry Carbon, oxygen, and strontium stable isotopic analyses were done at the Institute for Energy Technology (IFE, Norway) on both shell fragments incorporated in the carbonate blocks and the carbonate cements from ﬁve different blocks from four pockmarks. The carbonate cements were ground and digested with a 0.1 ml 100% H3PO4 solution for 2 h at 30.0 °C in a vacuumed environment. The released CO2 was transferred to a Finnigan MAT DeltaXP isotope ratio mass spectrometer (IRMS), for determination of δ13C and δ18O. The analyses were controlled by in-house standards of calcite and aragonite. Results are reported in ‰ relative to the PDB standard. The precision for δ13C is ± 0.1‰ and for δ18O ± 0.2‰. Three bulk crushed carbonate samples (10–20 mg) were used for Sr isotope analysis. The isotopic composition of Sr was determined by thermal ionization mass spectrometry (TIMS) on a Finnigan MAT 261. Pore water extraction was done on thirteen cores and the main cation and anion concentration was analyzed on a total of 140 pore water samples. Isotope analyses were measured on 23 selected water samples. The extracted pore waters were analyzed for Na, Cl, SO4, Ca, Br and K at the Dept. of Geosciences at the University of Oslo. Cations were analyzed on a Varian 300 ﬂame atomic absorption spectroscope, whereas the anions were analyzed on a Dionex QIC analyzer ion chromatograph with a Ionpac AS4A-SC column. Cation and anion analyses were performed on highly diluted samples, thus the uncertainty of the results is in the order of 5–10%. Oxygen, carbon, and hydrogen isotope water analyses were performed at IFE. The water δ18O and δ13C of the dissolved inorganic carbon (DIC) composition was measured using a using a Finnigan DeltaXP isotope mass spectrometer, and is reported as permil VSMOW. The δD composition was determined by a Micromass Optima isotope mass spectrometer. TOC and TIC analyses were done on dried bulk clay samples from the cores in order to determine differences in the sedimentary environments inside and outside the pockmarks. The analyses were done at the Dept. of Geosciences, University of Oslo. Both acid treated (HCl) and original samples were analyzed using a LECO Karbonanalyzer CR-412 instrument. The samples were heated in a CO2 free atmosphere to 1350 °C where the oxidized carbon (CO2) was measured with a CO2 A. Mazzini et al. / Marine Geology 373 (2016) 26–38 IR detector. The inorganic carbon is calculated as the difference between the acid treated sample (TOC) and the bulk sample. 5. Results 5.1. Multibeam and ROV surveys An extensive multibeam survey in the area above the Troll ﬁeld revealed the presence of a huge pockmark ﬁeld. More than 7000 pockmarks have been identiﬁed and most likely many more could be mapped with a more extensive bathymetry study. More detailed ROV multibeam bathymetry surveys (MBE) have provided excellent images of the pockmarks morphology. The pockmarks targeted for more comprehensive studies (Septagram, Peanut, Arch B–E) have similar dimensions. The 0.5 m grid showed that the pockmarks are up to 100 m wide and 15 m deep and that the satellite pockmarks make the complexes bigger (about 300 m in diameter) (Fig. 2). The high resolution bathymetry allows mapping of the pockmarks in great detail. Commonly, the pockmark ﬂoors are ﬂat with 29 occasional carbonate blocks in the central part. The western ﬂanks are typically steeper (up to 35°) and smoother, than the eastern ﬂanks. The latter often have small canyon-like structures. Small, meter-sized so-called unit pockmarks are common both on the ﬂanks or may be scattered over a surrounding distance of at least 100 m from the center of the structure. Very small unit pockmarks may be also clustered along trawling scars. The ROV sub-bottom proﬁler data also revealed the presence of buried pockmarks that are present just a few meters below the surface. ROV video observations did not show any evidence of ﬂuids seepage, bubbling nor microbial mats present at these sites. 5.2. Structure and mineralogy of the carbonate blocks The carbonates from the Septagram and the Arch E pockmarks host a variety of ﬁlter feeders and colonies of various fauna including epibenthic fauna, large sponges, gorgonian corals, anemons, feather stars, tube worms and bivalves (Fig. 3A–D) that typically populated hard substratum environments. The carbonate blocks within the Fig. 2. Example of multibeam lines acquired during the ROV dive over the (A) Arch, (B) Peanuts, and (C) Septagram. Note the distribution of the satellite smaller pockmarks around a central “parent pockmark”. The location of three examples of cores sampled from centre, ﬂank and outside the pockmark is marked in the Septagram image C. 30 A. Mazzini et al. / Marine Geology 373 (2016) 26–38 Fig. 3. (A–D) Large carbonate blocks covered with epibenthic fauna, large sponges, gorgonian corals observed in the craters of the studied pockmarks. (E) Large carbonate blocks sampled from the Septagram and Arch E pockmarks. (F) CT scans of Sample B67-4. The series of pictures represent different x-ray slices through the sample. Of particular interest is the distribution of cavities within the sample (seen in black and dark gray), and the presence of small spherical cavities within the carbonate lobes. Similar features (small circular cavities) were identiﬁed in the G11 Nyegga carbonates (see Mazzini et al., 2006). pockmarks are generally large (meter size) and the retrieved samples represent smaller portions of these. The carbonate samples share many of the same macro and micro characteristics. Some consists of carbonate-cemented shell debris, very similar to those from Nyegga described by Mazzini et al. (2005), others have faint laminations within the massive carbonate blocks suggesting distinct periods of carbonate precipitation or possible different exhumation cycles (additional research and further analyses on these carbonates are planned). We focussed our detailed analyses on the larger blocks that were collected (some reaching the size of ~ 40 cm). Macroscopic observations show A. Mazzini et al. / Marine Geology 373 (2016) 26–38 that the carbonates have a rusty and pitted external surface with abundant shell fragments, tube worms remains, and attached living organisms (Fig. 1A–D). When split, the altered rim can easily be observed as a 3–4 cm thick pitted and discolored zone. The discoloration is due to oxidation of pyrite to iron hydroxides. The internal structure of the samples (Fig. 3E) consists of a dendritic high porosity 31 carbonate framework with numerous clay-ﬁlled cavities. The intricate carbonate-rich network of interconnected conduits and voids cements detrital siliciclastic sediment with varying amounts of carbonate content. No bivalves were observed in the internal part of this speciﬁc carbonate type, suggesting that their formation occurred entirely in the subsurface. Overall this type of carbonates Fig. 4. A) Thin section scan showing the different carbonate growth stages. Note the rimming of the cavities ﬁlled by aragonite. Note the presence of clastic grains in the ﬁrst two phases. B–H: SEM backscatter images. B) The two stages deﬁning the bulk of the sample, with a Mg-Calcite-dominated ﬁrst zone and a aragonite-dominated second zone. Also indicated the last stage of botryoidal aragonite. C) The transition between micritic (Phase 2) and botryoidal aragonite (Phase 3). D) The ﬁrst phase of mineral growth contains abundant Mg-calcite intergrown with aragonite. Both cavities and clastic silicates are common. E) Micritic aragonite with clastic grains (quartz). F) The matrix aragonite phase contains numerous clay-ﬁlled cavities (dark). G) Small botryoidal aragonite along one of the cavities seen in F. H) Close-up of the last phase of botryoidal aragonite crystals. 32 A. Mazzini et al. / Marine Geology 373 (2016) 26–38 strikingly resemble to the authigenic carbonates type G11-C described by Mazzini et al. (2006) from the Nyegga region that is located to the north of Troll. Based on mineralogy and textures three distinct carbonate zones can be identiﬁed in the samples (respectively from older to younger) (Fig. 4): • Zone 1: dark gray to very dark gray inner zone, sometimes containing pelletoids and siliciclastic grains, with abundant micritic Mg calcite (up to 5.3 wt.% MgO) and, in lesser amount, micritic aragonite. Occasional calcite grains were also identiﬁed. • Zone 2: gray to light gray matrix minerals, dominated by micritic aragonite and some Mg calcite. Mg-calcite is intergrown with aragonite and minor calcite is also observed. Occasionally aragonite crystals are larger than those present in zone 1, and the porosity is higher. In both zone 1 and 2 siliciclastic grains (clay minerals, micas, quartz, and feldspar) are present within the carbonate matrix. • Zone 3: represents the last carbonate stage consisting of ﬁbrous/botryoidal white aragonite (as conﬁrmed by XRD and EMP analyses) commonly rimming cavities. Pyrite is also abundant. No siliciclastic grains were observed. Interestingly, an outer rim of ﬁbrous/botryoidal white aragonite was also observed in the Nyegga samples described by Mazzini et al. (2005) from the Tobic seep mound. Fig. 5. Carbon and oxygen isotope values for the Troll carbonates in comparison with Nyegga carbonates: (compilation of data from: Mazzini et al., 2005, 2006; Ivanov et al., 2010). All the Troll samples have 13C very depleted values, whereas there is a spread in the δ18O values. Note that the shells analyzed show gradually decreasing 13C depletion, but that some of them cannot be explained by a sea water carbon source. The trend indicates mixing between carbonate with a seep origin and sea water origin. 5.4. Carbon content in the cores The transition from zone 2 to zone 3 is sharp (Fig. 4) and Mg-calcite is never present in this last stage of growth. Zones 1 and 2 occur in fairly equal proportions in the samples, whereas the zone 3 generation is volumetrically minor. Framboidal pyrite is commonly present in the micritic and botryoidal carbonate. CT scan images of the selected samples conﬁrm that the internal structure of the carbonate block consists of inter-ﬁngered structures with numerous clay ﬁlled cavities. 5.3. Isotope geochemistry The results of the carbon, oxygen, and strontium isotope analyses are presented in Table 1. The shells gave δ13C values between 1.6 and − 8.1 ‰ VPDB and δ18O in the range 0–1.7 ‰ VPDB (Fig. 5). The bulk carbonate samples have δ13C and δ18O values in the range of −54.1 to −59.7 ‰ and 3.6 to 4.0 ‰, respectively. Three samples have been analyzed for bulk 87Sr/86Sr. Although the samples were taken from different carbonate blocks and pockmarks, their ratio is similar. The B53-2 sample has a slightly higher ratio (0.7093) than the B67-4 (0.7092) and the B67-6 (0.7092). The sea water 87Sr/86Sr is for comparison 0.7091. Bulk clay samples were analyzed for TOC and TIC, and the results are presented in Fig. A2.A and Table 2. All four analyzed cores show consistent results, with a slight decrease in TOC from 0.7 in the top to 0.55 wt.% in the deepest levels. There is a spread in TIC within the top sections of the cores (2.5–3 wt.%) and a decrease to 1.1 wt.% at 3–4 m depth. Below 5 m, there is an apparent increase in TIC which is not matched by the TOC content. Authigenic carbonates have only been identiﬁed in the central parts of the pockmarks and not in the analyzed cores. The TIC content thus normally reﬂects the abundance of calcareous microfossils and shell fragments. The similarities between TOC/TIC values inside and outside the pockmarks rule out signiﬁcant differences in sedimentation and accumulation. This also means that there is no obvious indication of an enhanced organic productivity within the pockmarks. 5.5. Water geochemistry The results of the pore water analyses are presented in Tables 2 and A4. The sulfate content (Fig. 6 upper part) gradually lowers from sea water values in all the cores. Note that some of the irregularities in the Table 1 Isotope analyses of Troll carbonate samples. Sample Type δ13C (‰ V-PDB) δ18O (‰ V-PDB) 87 Sr/86 Sr B53-2 B67-4 B67-4 B67-4 B67-4 B67-4 B67-4 B67-4 B67-4 Shell B67-6 B610-8 (1) B610-8 (2) B610-8 (3) B610-8 (4) B612-1 (1) B612-1 (2) B612-1 (3) B612-1 (4) Bulk sample Bulk sample Late stage aragonite Late stage carbonate cement Matrix carbonate. Centre Shell A from surface Shell B from surface Tube from surface Shell in carbonate cement Bulk sample Late stage aragonite Aragonite from inside shell Black carbonate from centre Bulk gray carbonate from centre Black carbonate Brownish carbonate (altered) Light gray carbonate Late stage white aragonite −56.4 −55.1 −59.7 −57.2 −55.9 1.6 −8.1 −0.7 −1.3 −54.1 −59.2 −57.0 −57.3 −56.8 −57.5 −59.4 −56.1 −52.7 4.0 4.5 2.7 2.7 3.7 0.0 1.7 1.7 0.3 3.6 3.5 3.6 3.6 4.0 3.9 3.8 3.9 1.7 0.709316 0.709210 0.709200 A. Mazzini et al. / Marine Geology 373 (2016) 26–38 33 Table 2 Pore water geochemistry (A-series) and bulk sample carbon content. Sample 201A-2E 201A-2F 201A-3B 201A-3F 201A-4B 201A-4D 201A-4F 201A-5F 201A-Ret 201A-ShoeA 201A-ShoeF 202A-2B 202A-2E 202A-3B 202A-3F 202A-4B 202A-4F 202A-5A 202A-5E 202A Shoe A 202A Shoe E 203A-2B 203A-2F 203A-3B 203A-3F 203A-4B 203A-4F 203A-5B 203A-5F 203A Shoe B 203A Shoe F 210A-2B 210A-2F 210A-3B 210A-3F 210A-4B 210A-4F 210A-5B 210A-5F 210A Shoe B 210A Shoe F Troll1 Troll2 Position Depth from Depth to Median TC TOC TIC Cl Br SO4 Na Ca K δ18O δD δ13C TIC m m m wt.% wt.% wt.% ppm ppm ppm ppm ppm ppm permil SMOW permil permil V-PDB 0.74 0.84 1.34 1.84 2.34 2.64 2.94 3.84 5.235 5.33 6.03 0.17 0.57 1.07 1.57 2.07 2.57 2.97 3.47 5.06 5.76 0.52 1.02 1.52 2.02 2.52 3.02 3.52 4.02 5.61 6.21 0.35 0.85 1.35 1.85 2.35 2.85 3.35 3.85 5.44 6.04 3.32 3.66 2.82 2.77 2.43 2.28 2.24 1.96 1.77 1.89 1.98 3.74 2.88 2.8 2.54 2.37 2.54 1.84 2.06 2.13 2.38 3.14 2.61 2.44 2.19 2.08 1.87 1.71 1.89 2.46 2.42 3.24 2.45 2.32 2.2 1.85 1.65 1.92 2.45 2.36 2.36 0.73 0.68 0.69 0.72 0.76 0.66 0.63 0.66 0.64 0.7 0.64 0.79 0.69 0.69 0.76 0.66 0.76 0.6 0.59 0.55 0.55 0.65 0.69 0.72 0.61 0.6 0.6 0.64 0.6 0.57 0.58 0.75 0.71 0.59 0.71 0.59 0.59 0.64 0.61 0.6 0.58 2.59 2.98 2.13 2.05 1.67 1.62 1.61 1.3 1.13 1.19 1.34 2.95 2.19 2.11 1.78 1.71 1.78 1.24 1.47 1.58 1.83 2.49 1.92 1.72 1.58 1.48 1.27 1.07 1.29 1.89 1.84 2.49 1.74 1.73 1.49 1.26 1.06 1.28 1.84 1.76 1.78 20,686 19,524 20,742 22,747 21,899 19,570 19,290 19,574 23,653 18,860 19,774 19,953 20,481 19,967 20,181 23,315 20,367 20,584 19,469 18,786 20,913 20,251 19,868 19,988 20,482 21,065 20,103 18,927 20,986 18,560 66 80 67 84 70 62 62 63 71 55 79 64 72 71 64 73 69 72 58 61 66 64 72 61 57 70 55 62 59 61 3164 3096 3360 3835 4175 3207 3125 3183 2190 1456 1472 2861 3234 3368 3399 4093 3203 2941 2326 1655 1820 3049 3406 3528 3263 3467 2865 2306 2223 1867 420 420 470 3.7 −12.5 0.9 1.4 −9.7 0.6 −0.7 −8.3 0.3 2.0 −12.6 1.1 2.6 −11.4 1.0 2.2 −11.1 0.8 0.8 2.3 0.7 −9.1 −9.5 0.5 −0.8 −10.7 60 55 62 60 70 67 54 54 61 60 60 77 3288 3314 3548 3152 3369 3158 2439 2235 1587 1584 2754 2660 660 620 620 660 690 590 520 540 660 450 450 590 610 580 590 640 560 530 510 470 490 590 550 610 550 570 510 490 530 460 470 640 540 530 510 560 590 550 490 450 440 320 320 0.9 21,347 19,548 19,473 18,981 20,554 22,856 20,166 18,703 19,155 18,780 18,685 19,208 11,500 10,600 10,400 12,300 11,100 10,300 10,000 10,300 12,700 9900 9400 10,500 10,700 10,000 10,300 12,700 10,600 10,800 10,300 9900 10,600 10,500 10,000 10,600 10,500 11,300 10,300 9800 10,200 9900 9800 11,000 10,400 10,300 10,000 10,100 11,900 10,400 9800 9300 9700 10,200 10,600 1.4 0.8 −11.4 0.8 1.4 −7.2 0.5 0.8 0.9 2.1 −7.9 −11.5 0.1 −1.4 −11.7 Centre 0.69 Centre 0.79 Centre 1.29 Centre 1.79 Centre 2.29 Centre 2.59 Centre 2.89 Centre 3.79 Centre 5.19 Centre 5.28 Centre 5.98 Centre 0.12 Centre 0.52 Centre 1.02 Centre 1.52 Centre 2.02 Centre 2.52 Centre 2.92 Centre 3.42 Centre 5.01 Centre 5.71 Flank 0.47 Flank 0.97 Flank 1.47 Flank 1.97 Flank 2.47 Flank 2.97 Flank 3.47 Flank 3.97 Flank 5.56 Flank 6.16 Reference 0.30 Reference 0.80 Reference 1.30 Reference 1.80 Reference 2.30 Reference 2.80 Reference 3.30 Reference 3.80 Reference 5.39 Reference 5.99 Sea water sample Peanut Sea water sample Septagram 0.79 0.89 1.39 1.89 2.39 2.69 2.99 3.89 5.28 5.38 6.08 0.22 0.62 1.12 1.62 2.12 2.62 3.02 3.52 5.11 5.81 0.57 1.07 1.57 2.07 2.57 3.07 3.57 4.07 5.66 6.26 0.40 0.90 1.40 1.90 2.40 2.90 3.40 3.90 5.49 6.09 curves, e.g., the increase at 1.8–2.3 m depth for the central sites, are possibly caused by post-sampling alteration of the samples. Cl proﬁles also reveal similarities between center, ﬂank, and outside the pockmarks with values fairly constant ﬂuctuating around 1900 ppm (Fig. 6 lower part). The interpretation of these proﬁles is however more ambiguous due to the presence of peaks of higher chlorinity. The origin of the high Cl waters could be due to post-sampling effects (such as evaporation/drying). Similarly to the sulfate content, the chlorinity trends show that the samples from the centre of the pockmarks versus reference cores have similar proﬁles. The pore water isotope data (Fig. A3) show a slight decrease in δ18O with depth. There is no difference between centre, ﬂank, and reference cores. The values overall ﬂuctuate between − 9‰ and − 12‰ with some peaks reaching values as high as − 7‰. This implies that the pore waters essentially represent sea water with a slight diagenetic overprint that increases with depth. The δD values are more scattered, but there is a tendency towards lower δD values (e.g. shifting respectively from 2.6‰ to −0.8‰) with depth. The δ13C of the dissolved inorganic carbon in the pore ﬂuids shows enrichment in 13C from shallow depths (δ13C from ~− 12‰ to ~− 8‰) between 1 and 4 m. The lowermost waters from the 5–6 m interval have comparable values to the upper meter waters. 610 520 470 480 410 300 270 410 410 470 450 600 460 430 360 300 320 390 470 460 490 500 440 360 330 320 270 410 480 520 460 470 450 360 330 250 280 402 406 6. Discussion 6.1. Methane seepage and carbonate precipitation From the carbon isotope data, we may ultimately address the possible ﬂuid and carbon sources. The overall low δ13C values (as low as − 59.7 ‰) support the hypothesis that the carbonates formed at shallow subsurface from hydrocarbon-rich ﬂuid seepage at the sea ﬂoor. Compared to the Nyegga authigenic carbonates (Mazzini et al., 2005, 2006; Ivanov et al., 2010), the Troll samples have similar δ13C values although the Nyegga carbonates are more enriched in 18O (Fig. 5). The ﬁgure also shows the mixing trend between the marine carbon and oxygen isotope signatures, in the top left part of the plot, towards seep signatures in the lower part. The substantial spread in δ18O values reﬂects both the temperature of precipitation (higher δ18O equals colder precipitation water temperatures) and the composition of the source ﬂuids. Very 18O enriched ﬂuids are usually interpreted to have a gas hydrate or clay dehydration origin (Savin and Epstein, 1970; Kastner et al., 1993; Aloisi et al., 2000; Dählmann and de Lange, 2003). The colder temperature (i.e. N δ18O) signature of the Nyegga samples can be attributed to deeper and colder waters at that locality compared to the Troll site. The late stage aragonite precipitation is 34 A. Mazzini et al. / Marine Geology 373 (2016) 26–38 Fig. 6. Sediment pore water proﬁles for sulfate (upper three) and chlorine (lower three). systematically more depleted in 13C compared to the bulk samples, with δ13C values as low as −59.7 ‰ VPDB. This likely represents a combination of ﬂuid isotopic composition variations during precipitation and fractionation effects between calcite and aragonite. The Sr isotope results are consistent with a seawater source for the strontium, and thus the major source of cations such as Na and Ca. Interestingly, isotopic data from shells may show a signiﬁcant 13C depletion suggesting that methane-rich ﬂuids were also metabolized by the clams within the pockmarks. Given that Troll and Nyegga carbonates share similar δ13C values, we may suggest a similar origin for the hydrocarbons fueling both systems. Based on isotopic studies and ﬂuid inclusion analyses Mazzini et al. (2005) suggested that the gas leaking through the pockmarks could be a mix of thermogenic (e.g. gas originating from the deep reserves conﬁned to Tertiary domes) and more recent microbial (shallow production) methane. Similar conclusions were suggested also by Ivanov et al. (2010) combining the results of a large carbonate collection coupled with gas hydrate geochemistry and gas headspace analyses from cores. The available data thus suggest that the signature of more recent microbial gas (i.e. generated by microbial alteration of organic matter and gas in shallow sediments) is coupled to the migration of ancient thermogenic gas. Similar conclusions were later conﬁrmed by Vaular et al. (2010) that sampled another pockmark in the Nyegga region. The less 13C depleted (older) carbonate phases and A. Mazzini et al. / Marine Geology 373 (2016) 26–38 the more 13C depleted (latest) aragonite coating further supports this scenario. The hydrocarbons trapped in the Troll reservoir provide important information regarding the gas composition migrating from the Viking Graben (Horstad and Larter, 1997). We therefore suggest that a thermogenic methane with composition similar to the one present in the Troll reservoir (i.e. δ13C = − 44.5‰ Thomas et al., 1985) migrated in the whole region of the Norwegian Channel and was mixed with shallower microbial methane. This would explain the depletion values recorded in the Troll carbonates. The presence of thousands of pockmarks over a large area, suggests formation during a major gas release event. Therefore, given that the Troll δ13C carbonate values are fairly clustered, we hypothesize that the mix of deeper and older thermogenic gas with the younger and shallower microbial gas, occurred prior to the main gas pulse that triggered the formation of the pockmarks. A possible analogy to this scenario is provided by the Peon shallow gas reservoir located on the Tampen Spur to the North of Troll. Despite its shallow depth (165 mbsf), Peon is estimated to hold 15 to 30 billion standard cubic meters of mostly microbial gas (δ13C ~ − 72.‰). Like for the Troll pockmarks ﬁeld, this gas is likely to be the result of deeper thermogenic and shallower microbial gas that is now trapped in a thin 18.7 m unit in a 37.8 m think formation of porous sands (NPD, 2005). 6.2. Insights of pockmarks activity from petrography and carbonate precipitation The methanogenic origin for the studied blocks is also consistent with the petrographic observations showing typical carbonate phases paired with pyrite. This conﬁrms that the carbonates formed by anaerobic oxidation of methane coupled with seawater sulfate reduction, and that the main cations are seawater-derived. The mineralogy and the textures reﬂect the evolution during growth. Thus we can trace the evolution of the samples from initial precipitation within the sulfate reduction zone to exhumation and exposure to sea water and oxidizing conditions. The diagenetic evolution of the different cement zones is summarized in Fig. 7. The carbonates present in Zone 1 (micritic Mg-calcite) precipitated in the subsurface, as indicated by the abundance of siliciclastic material. The signiﬁcant amount of pelletoids could represent carbonate remnants of microbial mats as also indicated by several authors (e.g. Peckmann and Thiel, 2004; Riding and Tomas, 2006). During the gradual decrease in seepage and slow exhumation of the blocks, the cement phase became predominantly micritic aragonite (Zone 2). As the exhumation of the carbonates continued and the pockmarks activity declined the last carbonate Zone 3 35 precipitated ﬁlling the pores with acicular crystals. Once the carbonates were fully exposed on the seaﬂoor (see next paragraph on exhumation of the blocks), a later stage of carbonate oxidation occurred (oxidation of pyrite to iron hydroxides), as highlighted by the reddish oxidation front present within the dendritic features. As also pointed out by other authors (Naehr et al., 2000; Aloisi et al., 2002; Mazzini et al., 2006; Himmler et al., 2011) the different carbonate phases reﬂect the varying geochemistry of the ﬂuids during the various stages of the pockmarks seepage activity. Like also observed at other localities, even in the Troll case, the last carbonate phase is represented by aragonite. This is most probably related to 1) the less vigorous gas seepage during the last stages of the pockmarks activity resulting in a sulfate-rich diagenetic environment and 2) to the gradual expose of the carbonate closer to the sea ﬂoor. The internal structure of the carbonate blocks, consisting of interconnected voids and cavities, could be ascribed to different factors and alternative scenarios could be depicted. For example Haas et al. (2010) documented the recovery of porous carbonates whose shape was inﬂuenced by the presence of Vestimentiferan tube worms populating the seepage sites. At these sites the carbonate precipitation occurs in the subsurface around sediments surrounding the posterior ‘root’ tubes of the colonies. As video survey revealed the presence of tube worms at Troll, they could have strongly affected the shapes of the resulting carbonate. Similar shaped carbonates have also been described by Himmler et al. (2011). The authors suggest a model implying a gradual erosion of the sediments to expose the carbonates followed by carbonate corrosion resulting from acidity locally produced by aerobic oxidation of methane and hydrogen sulﬁde. The internal structure of the Troll carbonates does not show the presence of e.g. shells or other easily identiﬁable features and this hypothesis cannot be easily validated. Thin sections do not reveal obvious indication of carbonate dissolution zones, in addition the presence of methanogenic aragonite ﬁlling the numerous vesicles and conduits might rule out this scenario. Alternatively the cavernous structure present in the blocks could represent the carbonate precipitation casting portions of free gas bubbles or tubular ﬂuids conduits in the subsurface sediments created during the vigorous methane seepage. With the present data, this seems to be the most likely explanation. The obtained CT scan images are strikingly similar to that observed by Mazzini et al. (2006). Therefore, considering these macrostructures, the formation model similar to that suggested by Mazzini et al. (2006) could be applied. Some general considerations can be obtained from the results of the EMP analyses. In contrast to the carbonates from the G11 pockmark at Fig. 7. Summary of the petrographic and textural evolution of the carbonate samples. The two ﬁrst stages are characterized by micritic Mg-Calcite and aragonite, where the aragonite is more extensive with time. Aragonite dominance during the last stage can be explained by shallower precipitation relative to the sulfate reduction zone (lowers the stability of Mg-Calcite), but still within reducing condition (pyrite is present). The ﬁnal exhumation of the samples led to pervasive pyrite oxidation along the margins of the carbonates. 36 A. Mazzini et al. / Marine Geology 373 (2016) 26–38 Nyegga, dolomite was not identiﬁed in any of the studied Troll samples. The Sr and Mg contents of the carbonates are shown in Fig. A2.B in molar values relative to the end member structural formulas. Strontium is conﬁned to aragonite, which contains up to 1.8 wt.% SrO (corresponding to 0.034 mol per formula unit). The SrO content in aragonite is always higher than 0.7 wt.%. The chemical formula for that particular mineral analysis (the ﬁrst analysis from B612-1 in Table A3) is accordingly Ca1.964Mn0.002 Sr0.034(CO3)2 compared to Ca(CO3) for pure aragonite. The Sr concentrations in the Troll aragonites are very similar to the aragonites from the G11 pockmark at Nyegga suggesting similar formation conditions. The calcites do not contain any strontium, and plot along the x-axis in Fig. A2.B. Foraminifera shells have the lowest Mg concentrations. The absence of strontium in the calcite is evidence for a precipitation of calcite directly from pore ﬂuids and not from recrystallization of aragonite which normally takes place during deeper burial and results in some Sr entering the calcite structure. Similarly the 87Sr/86Sr of bulk carbonate from the G11 pockmark (Mazzini et al., 2006) had a ratio of 0.7092 that overlaps that of the Troll samples. The Troll samples have a signiﬁcant clastic component which likely contributed to increasing the 87Sr/86Sr up to 0.7093 in one sample. However, the results are still consistent with a seawater source for the strontium, and thus the major source of cations. Our conclusion about no current seep activity at Troll is further supported by seismic interpretations that showed no evidence for deep roots of the pockmarks in the study area. There is further no evidence of structural control on the location of the pockmarks. 6.4. Pockmark formation It is remarkable that numerous pockmarks are surrounded by smaller satellite pockmarks on the outskirts of the crater (Fig. 2). Interestingly these pockmark complexes seem to have the thickest and most laterally extensive distribution of authigenic carbonates. A model that could explain this was initially proposed by Mazzini et al. (2006), suggesting that an initial vigorous burst created the major pockmark crater followed by carbonate precipitation; once the methanogenic carbonates reach a signiﬁcant thickness, the rising ﬂuids are deﬂected laterally thus contributing to a progressive extension and precipitation of carbonates (see Fig. 8 G11-C in Mazzini et al., 2006). Once the full surface of the pockmark crater is covered by thick authigenic carbonates, the ﬂuids rising in the more permeable vertical conduit will be buffered. The overpressure gathered in the subsurface of the “parent pockmark” 6.3. The sulfate reduction zone as a proxy for methane seepage The systematic pore water extraction from reference cores and cores collected for the centre and the ﬂanks of pockmarks was completed in order to trace the presence of active seepage at pockmark sites. Of − particular relevance are the SO2− 4 and Cl values that commonly reﬂect the presence of ﬂuids seepage thus affecting the depth of the sulfate reduction zone (Fig. 6). More speciﬁcally, pore water sulfate concentrations in the cores can be used as a proxy for methane ﬂux (e.g. Treude et al., 2005; Dale et al., 2008; Knab et al., 2009; Treude et al., 2014). If the sediment pore water sulfate proﬁles in the pockmarks are shallower compared to the background cores, it suggests the presence of methane seepage (sulfate reduction to sulﬁde induced by microbial methane oxidation) (Borowski et al., 1996). Deeper sulfate reduction levels in the pockmarks would require a different explanation, like permeability variations. Overall, the sulfate is lowered in concentration by up to 63% compared to the upper parts of the cores. Even though this is a signiﬁcant depletion, it is evident that the cores were not deep enough to penetrate the level of sulfate reduction. Of relevance is the comparison between the three sites. Fig. 6 shows the virtual similar sulfate proﬁles when comparing the centre with the ﬂank and the reference stations. The presence of a regional and uniform sulfate reduction proﬁle suggests that there are no indications that the pockmarks are currently active conduits for methane bearing ﬂuids. Similar proﬁles are indeed collected form cores collected at exposed or buried pockmarks. It is reasonable to conclude that the similar proﬁles inside and outside the pockmarks indicate that, after a period of widespread seepage, the region re-equilibrated the vertical distribution of chemical reactions and ﬂuids composition. Similar cores from active pockmarks in Nyegga, reveal instead drastic sulfate decrease in the top 50 cm bsf clearly in contrast with the results reported herein (Ivanov et al., 2010). Cl content supports the conclusion that there is no indication of ﬂow of low salinity pore ﬂuids through the pockmark sediments, which would have been the case if gas hydrates were actively dissociating. This conclusion is supported also by the similarities in the Na, Ca, and K trends. Insights about pockmarks inactivity also come from the metagenomics studies to characterize the prokaryotic communities inhabiting the surface sediments in the Troll area in relation to geochemical parameters (Havelsrud et al., 2012). The sampled locations show no obvious evidence of methane seepage. Fig. 8. Correlation between pore water sulfate concentrations and pockmark activity. With no signiﬁcant active seepage, the depth of the sulfate reduction zone will be similar outside and inside the pockmark (upper case). With active methane seepage, the methane will reduce the sulfate and thus result in a shallower sulfate reduction zone within the pockmark (middle case). The lower case represents a potentially deeper sulfate reduction zone inside the pockmark. Here deep penetration of sea water into the sediments is likely occurring possibly due to high permeabilities in the pockmark sediments. A. Mazzini et al. / Marine Geology 373 (2016) 26–38 will then be radially released triggering the formation of “satellite pockmarks” framing the main crater. 6.5. Pockmarks dynamics We do not exclude that the diffusive methane seepage at pockmarks sites might have encountered period of more vigorous or explosive activity as suggested by the presence of isolated and angular large carbonate blocks. Similar isolated blocks have also been observed at Nyegga (Mazzini et al., 2006; Ivanov et al., 2010). In any case, the fact that meter sized carbonates remained exposed on the seaﬂoor after an ancient period of seepage suggest that signiﬁcant sediment erosion must have occurred after the subsurface carbonate precipitation. Moreover the deposits inside the pockmarks consist mainly of ice-rafted clasts and coarse-grained sands. This additional piece of evidence suggests that two mechanisms are involved in the pockmarks formation and preservation. Initially the seeping gas transports in suspension preferentially the ﬁne-grained sediments. These particles are constantly washed away by the currents leaving behind the coarser fraction. The strong N–S currents swiping the area also explain why the pockmarks have not been buried by hemipelagic deposition until now. The direction of the currents matches that of the main axis of the pockmarks that are statistically mostly elongated towards the NNW–SSE. The degraded N slope of the pockmarks compared to the southern slope also supports inﬂuence from a dominating current direction. Laboratory and numerical simulations support this scenario and reveal that typical bottom currents are efﬁcient to prevent the sedimentation of particles up to ﬁne sand (Hammer et al., 2009; Pau et al., 2014) and may be efﬁcient mechanisms for sediment erosion. Thus the oxidation rims present around the collected carbonates, are the result of their exposure on the seaﬂoor. 7. Conclusions • A large pockmark ﬁeld was mapped and investigated in the Troll region. More than 7000 pockmarks are found in the Troll East gas ﬁeld region. • Large blocks of carbonate deposits were observed and sampled at pockmarks sites. The presence of these carbonates uniquely inside the pockmarks indicates widespread carbonate precipitation occurring only at these location. • The methanogenic origin of these carbonates is conﬁrmed by their 12C enrichment (i.e. δ13C as low as −59.7‰). The methane oxidation coupled with seawater sulfate reduction is supported by abundant framboidal pyrite observed within the carbonate cements. • Three main phases of carbonate growth are recorded in the samples, including one initial phase of Mg calcite and micritic aragonite, and intermediate phase of micritic aragonite and a third, ﬁnal phase of botryoidal aragonite devoid of siliciclastic sediment. The macroscopic texture of these carbonates strongly resemble to those collected from Nyegga pockmarks. • 18O enrichment in the carbonates suggests that the source of methane might have originated by the dissociation of gas hydrates ongoing at the moment of carbonate precipitation. • The 87Sr/86Sr is consistent with a seawater source for the strontium, and thus the major source of cations. • The carbonates have been exposed to seawater for a long time, as highlighted by the abundant outer surface alteration and pyrite oxidation. This suggests ancient carbonate precipitation that is not occurring any longer. • Further evidence of paleao seepage is provided by water analyses extracted from cores sampled inside and outside the pockmarks. The results show no difference between pockmark and background pore water sulfate concentrations, indicating that the pockmarks are currently not active ﬂuid ﬂow conduits. • Seaﬂoor observations showed no evidence of bubbles, ﬂuids seepage, microbial colonies or other typical chemosymbiotic alive assemblages present at active seepage sites. 37 Although active pockmarks are reported elsewhere in the North Sea and in the Nyegga area to the north, the evidences collected reveal that there is no activity in the Troll area and that the retrieved carbonates are the result of a palaeo methane seepage. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.margeo.2015.12.012. Acknowledgments We thank the editor Gert J. De Lange, Luca Martire and two anonymous reviewers for their constrictive comments that helped to improve the manuscript. We are very grateful to Statoil and the Troll license partners for giving access to data used in this study. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013)/ERC Grant agreement n° 308126. The Centre for Earth Evolution and Dynamics (CEED) is thanked for the support during this work. References Akhmetzhanov, A.M., Kenyon, N.H., Ivanov, M.K., Westbrook, G., Mazzini, A., 2008. Deep-water depositional systems and cold seeps of the Western Mediterranean, Gulf of Cadiz and Norwegian continental margins. IOC Technical Series No. 76. UNESCO. Aloisi, G., Bouloubassi, I., Heijs, S.K., Pancost, R.D., Pierre, C., Sinninghe Damste, J.S., Gottschal, J.C., Forney, L.J., Rouchy, J.-M., 2002. 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