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Miocene tubular concretions in East Coast Basin, New Zealand: Analogue for the subsurface plumbing of cold seeps
Abstract
The uplifted accretionary prism of East Coast Basin, in Hikurangi Margin, North Island, New Zealand, exposes late Miocene slope mudrocks (Whangaehu Mudstone, < 10% carbonate) in coastal cliffs north of Cape Turnagain that contain conspicuous tubular carbonate concretions (50–85% carbonate) supporting near-central conduits. Pipe and bulbous morphologies dominate, ranging in exposed length up to 5 m and up to 1 m in diameter. The concretions were formed by the precipitation of micritic dolomite (and calcite) cement within the host mudstone at shallow burial depths (< 100 m). δ13C values of the cement range from − 22 to + 13‰ PDB and are interpreted to reflect carbonate precipitation from either the extensive anaerobic oxidation of methane (AOM) and/or mixing of microbial methane and methanogenic CO2. AOM is confirmed by lipid biomarker evidence indicating that methane oxidation occurred in the sediments at the time of carbonate precipitation. The mixed dolomite/calcite mineralogies and the trend of δ13C in the tubular concretions from strongly negative to strongly positive values are interpreted to reflect methane oxidation from the onset of ascent through to the end of a migration event. Depleted and enriched δ18O values suggest an evolved fluid source influenced by the dissociation of gas hydrates. Collectively, our results indicate that the tubular concretions within the upper slope mudstones delineate parts of the subsurface plumbing network of a cold seep system on the late Miocene paleo-Hikurangi Margin in which the fluids were sourced from ascending methane. The intermediate location of the Whangaehu concretions between older (early Miocene) seep carbonates to the west and modern ones offshore to the east indicates a progressive eastwards shift with time of a long-lived, if only periodically active, seep system. The concretionary plumbing features at Whangaehu provide a conceptual model for subsurface fluid pathways and seep-related processes beneath the modern Hikurangi Margin seabed, and possibly also for other modern and ancient cold seep carbonate systems.
... Several fossil examples have been documented worldwide: in New Zealand [2,[5][6][7], Colorado (USA) [8], Japan [9], the Outer Carpathians (Poland) [10], on the Montenegrin margin in the southern Adriatic Sea [11], and in the area of Pobiti Kamani (Varna, northeast Bulgaria) [12][13][14]. Several sites are also known in Italy: in the Northern Apennines [15]; at the Stirone River natural park [16][17][18]; on the Enza River bed near San Polo d'Enza, Reggio Emilia [19][20][21]; in the Badlands of Mt. ...
... The large dolomite-rich doughnut concretions were associated by [2] with intermittent fluid ascent (CO2 in the present case), where fluid periodically becomes trapped by relatively more impervious (perhaps clay-enriched) stratigraphic layers. The authors of [6] suggested that seep-related tubular (conduit) concretion formation occurred in the subsurface, from cement precipitation, starting at the outer rims of concretions and continuing toward the centre of their conduits. ...
... In our case, the centre of each structure is very open (as shown in Figure 4), unlike those reported by [2,6], which had completely filled central areas (mouths). ...
Early Pleistocene marine deposits in southwestern Umbria (Orvieto–Allerona area, Italy)
recently revealed the presence of more than forty carbonate conduits distributed over 2 km along the Paglia riverbed. In order to investigate their origins, analyses of their mineralogy, δ18O and δ13C stable isotopes, and organic geochemistry were conducted. All the carbonate conduits are made of euhedral microcrystals of dolomite with subordinate quartz, plagioclases, and micas. The stable carbon and oxygen isotope values of the bulk concretionary carbonates range from −0.57 to +4.79‰ (δ13C) and from +1.58 to +4.07‰ (δ18O), respectively. The lack of organic geochemical biomarkers of
anaerobic methane oxidation (AOM) and the very low values of extractable organic matter suggest a non-biological origin for the dolomite precipitation. The latter is probably related to the rise of volcanic carbon dioxide due to the incipient Vulsini magmatism recorded in Early Pleistocene marine deposits all around the study site. The spatial distribution of the structures indicates that the upward migration of the CO2 was controlled by the fault system, while the vertical development of the conduits suggests that carbon dioxide degassing occurred, with multiple events. Carbon dioxide
was probably stored in pockets within the clayey sediments until the pressure exceeded the eruptive threshold. These structures represent the first documentation of a volcanic carbon dioxide marine seepage event in the Umbria region.
... We also draw upon a body of work on the chemistry of active fluid seeps within the Hikurangi Margin (Figure 1), including saline springs on land (e.g., Barnes et al., 2019;Giggenbach et al., 1995) and cold seeps at sites offshore (Lewis & Marshall, 1996). In addition, we draw upon published work on fossil seafloor cold seep limestone formed atop fluid vents that were buried by ongoing Miocene and Pliocene sedimentation within the East Coast forearc basin (Campbell et al., 2008;Nelson et al., 2019;Nyman & Nelson, 2011;Nyman et al., 2010). ...
... CH4 + SO 2− 4 → HCO − 3 + HS − + H2O anaerobic oxidation AOM-style carbonate mineralization has been widely documented within Miocene cold seep carbonates in the eastern Raukumara Peninsula (Campbell et al., 2008;Nelson et al., 2019), in tubular concretions within a late Miocene succession resulting from fluid migration tens of meters beneath the contemporary seafloor (Nyman et al., 2010), and in Late Cretaceous concretions (Kiel et al., 2013). There are numerous examples of modern gas seeps and saline springs on land and offshore Raukumara Peninsula, conveying aqueous fluids and dissolved gases to the surface (Barnes et al., 2019;Francis, 1995;Nyman et al., 2010). ...
... CH4 + SO 2− 4 → HCO − 3 + HS − + H2O anaerobic oxidation AOM-style carbonate mineralization has been widely documented within Miocene cold seep carbonates in the eastern Raukumara Peninsula (Campbell et al., 2008;Nelson et al., 2019), in tubular concretions within a late Miocene succession resulting from fluid migration tens of meters beneath the contemporary seafloor (Nyman et al., 2010), and in Late Cretaceous concretions (Kiel et al., 2013). There are numerous examples of modern gas seeps and saline springs on land and offshore Raukumara Peninsula, conveying aqueous fluids and dissolved gases to the surface (Barnes et al., 2019;Francis, 1995;Nyman et al., 2010). ...
We document the geochemistry of calcite veins in the Late Cretaceous Tikihore Formation (Raukumara Peninsula, New Zealand) to characterize their fluid composition and source and to help establish the age of subduction initiation at the Hikurangi margin of the Australia-Pacific plate boundary. The calcite veins occur within normal faults offsetting turbidites that accumulated in a lower slope basin. Vein calcite trace metal content and rare earth element patterns are consistent with a seawater-derived brine composition. Oxygen isotope (δ18O) values range from −6.1 to +8.4‰ and are −0.2‰ VPDB on average; positive δ13C values of up to +28‰ VDPB reflect methanogenesis. Oxygen isotope temperature data indicate that calcite vein mineralization occurred at temperatures in the range of 29°C–48°C. This is markedly less than the maximum burial temperature experienced by the host rocks, which we estimate to be 104 ± 10°C at 30–27 Ma from the inverse modeling of apatite fission track data. The vein calcite has a 28.5 ± 4.9 Ma U-Pb age. From these data, we infer that the succession above Tikihore Formation was removed by slumping, thereby resulting in fluid overpressure in the reservoir, followed by hydraulic fracturing and the precipitation of the vein calcite. Ultimately, the data presented here from the Tikihore veins are consistent with subduction initiation at 30–27 Ma, based on the U-Pb age of the vein calcite and modeling of apatite fission track data for the host sandstone, corroborated by the 30–27 Ma timing of back thrusting on the Taranaki Fault and related foredeep development in eastern Taranaki Basin.
... Such conduits are called chimneys, pipes and columns (Capozzi et al., 2015). A number of those carbonate conduits and marine cold seep systems have been identified for over 25 years all around the world from Mesozoic up to present (Suess, 2014), lot of them belonging to convergent settings (Lewis and Marshall, 1996;Orpin, 1997;Aiello et al., 2001;Suess et al., 2001;Torres et al., 2002Torres et al., , 2003Díaz del-río et al., 2003;Ledésert et al., 2003;Aiello, 2005;De boever et al., 2006aDe boever et al., , 2006bDe boever et al., , 2009aDe boever et al., , 2009bDe boever et al., , 2011Nyman et al., 2006Nyman et al., , 2010Campbell et al., 2008Campbell et al., , 2010Sahling et al., 2008;Sellanes et al., 2008;Aggirezabala, 2009;Hoareau et al., 2009;DelaPierre et al., 2010;Feng et al., 2010;Pearson et al., 2010;Aggirezabala et al., 2013;Han et al., 2013;Zapatahernandez et al., 2013;Suess, 2014;Blouet et al., 2017;Malié et al., 2017;Wang et al., 2017;Watson et al., 2020). ...
... Most of the previous works dedicated to tubular carbonate concretions have demonstrated that they correspond to the shallow subsurface plumbing systems of conveying mainly biogenic (e.g., Aiello et al., 2001;De boever et al., 2009b;Blouet et al., 2017)but also thermogenic gas (e. g., Díaz del-río et al., 2003, for the Gulf of Cádiz (Spain); Nyman et al., 2010 andPearson et al., 2010, for the East Coast Basin of New Zealand) toward the seafloor. This study presents new results from the analysis of samples coming from source rocks, fault gouges, tubular carbonate concretions and their host rocks that are exposed within the emerged part of the Hikurangi subduction wedge in the East Coast Basin petroleum province of New Zealand. ...
... In the onshore Coastal Ranges, even if a biogenic component is present in some sampling point (Hollis et al., 2005), CH 4 is predominantly derived from thermogenic sources indicating complex migration pathways. Paleo-methane seeps or their plumbing systems are also reported in Cretaceous to Miocene rocks (Figs. 1 and 2;Ledésert et al., 2003;Campbell et al., 2008;Nyman et al., 2010;Kiel et al., 2013;Malie et al., 2017) and indicate that fluid expulsion and thus migration Fig. 1. Locality map of the active and fossil indicators of oil and gas seeps, North Island, New Zealand. ...
In the Hikurangi subduction wedge (New Zealand), a strong relationship exists between tectonic structures and fluid migrations. In the study area, outcropping tubular carbonate concretions, corresponding to the shallow subsurface plumbing systems of paleo-cold seeps, are hosted by Miocene syn-subduction mudstones. New observations demonstrate the presence of migrated solid bitumen within the tubular concretions and in the fault gouge of a major fault zone. A multi-proxy approach was performed to determine the organic matter thermal maturity in the study area (organic matter petrography and solid bitumen reflectance (BR) Rr% (Rr: random reflectance)). We also used Rock-Eval pyrolysis, vitrinite reflectance (VR) Rr%, and clay mineral reaction progress (illite Kübler-Index and clay mineral paragenesis) to determine the diagenesis grade of the rocks. Low Tmax values and clay minerals indicate a thermally immature sedimentary cover. The main source rock of the region, the Waipawa Formation is locally thermally mature (VR = 0.86 Rr%) suggesting that tectonic thrust-sheet stacking isresponsible for a structural thickening causing local organic maturation. The seaward propagation of out-of-sequence thrusts at base of intra-slope basins could be responsible for the inititation of biogenic fluid flows sourced in the shallow sedimentary cover that is subjected to deformation above the blind thrusts, leading to the earlier generation of the first carbonate tubular concretions. With the continuation of blind thrusting, deep thermogenic fluids then migrated laterally through fault planes (primary migration) and finally vertically through the intrabasinal pre-existing tubular concretions (secondary migration). In this paper, solid bitumen is used for the identification of a fossil thermogenic fluid migration from the source rock, along faults and through tubular carbonate conduits within a subduction thrust-wedge. The study evidences a multi-genetic tubular concretion formation, related with the timing and style of the deformation, being therefore a potential reliable indicator for the evolution of tectonic activity.
... Methane leakage is considered one of the main formation mechanisms of early diagenetic calcareous concretions (Clari et al., 2004;Tong and Chen, 2012;Ou et al., 2013;Liang et al., 2016). Tubular concretions are the most common prod-uct of seafloor methane leakage and are often used as migration channels for underground fluids and liquefied sediments (Nyman et al., 2010). These channels the main evidence to supporting the identification of ancient seafloor methane leakage and even mud volcano activities (Aiello et al., 2001;Campbell, 2002;Schwartz et al., 2003;Clari et al., 2004;Liang et al., 2016). ...
... Concretions formed by methane leakage usually have obvious morphological features and mostly form in the shape of mounds, nodules, tabs, chimneys, and tubes (Peckmann et al., 2001;Nyman et al., 2010;Liang et al., 2016). Chimneys and tubules are unique morphological characteristics associated with methane leakage (Pang et al., 2017). ...
... These tubular concretions have analogous appearances and internal textures to methane-derived carbonates formed by the methane leakage process reported previously. In addition, their microscopic features are even more consistent (Campbell et al., 2002;Clari et al., 2004;Nyman et al., 2010;Liang et al., 2016). In the diagram of carbon and oxygen isotopes (Fig. 10), the isotope compositions of the samples are also consistent with methane-derived authigenic carbonates obtained by previous researchers (Liang et al., 2016). ...
... Tubular carbonates exhibit various sizes but are typically some centimeters in diameter and a few decimeters in length (e.g., [9,13]). Some tubular carbonates, however, are up to 5 m in length and up to 1 m in diameter [14]. They are typically hosted within sediments in a vertical or subvertical position [15]. ...
... Formation mechanisms for tubular carbonates have been proposed, including (i) tubeworm fossilization, (ii) the lithification of subsurface sediment around fluid conduits such as burrows or fractures, and (iii) chimneys projecting into seawater (e.g., [5,9,10,14,17]). Tubular carbonates surrounding tubeworm fossils typically exhibit small diameters (less than 1 cm; [18]). ...
... Tubular carbonates surrounding tubeworm fossils typically exhibit small diameters (less than 1 cm; [18]). Larger tubular carbonates, particularly those with diameters above 1 m, likely represent the subsurface plumbing systems of ancient seeps [14], enabling fluid flux over long distances upward through the sedimentary column. Many of the carbonate pipes found at seeps, typically several centimeters in diameter, derive from the cementation of burrows produced by the local megafauna (e.g., [9]). ...
A remarkable exposure of tubular authigenic carbonates was found on the seafloor in the Dongsha area of the South China Sea (SCS). The tubular carbonates, around 2–3 cm in diameter and usually less than 10 cm in length, represent broken fragments of once-larger pipes that now protrude from muddy sediments. The morphology, carbon and oxygen stable isotope compositions, and trace and rare earth element contents of the carbonates were analyzed to decipher the mode of carbonate formation. The tubular carbonates exhibit a dark brown coating of iron and manganese hydrous oxides, indicating prolonged exposure to oxic bottom waters. The carbonate content of the micritic pipes falls between 12.5 and 67.3 wt.% with an average of 42.0 wt.%, suggesting formation within the sediment. This inference is supported by trace and rare earth element patterns including a moderate enrichment of middle rare earth elements. Low d13C values (as low as −50.3‰, Vienna Pee Dee Belemnite (VPDB)) suggest that carbonate precipitation was induced by the anaerobic oxidation of methane. The unusually positive δ18O values of the carbonates (as high as +5.3‰, VPDB) are believed to reflect the destabilization of locally abundant gas hydrate. Taken together, it is suggested that pipe formation was initiated by sediment-dwelling organisms, such as crustaceans or bivalves. The burrows subsequently acted as conduits for upward fluid migration. The lithification of the sediment directly surrounding the conduits and the partial filling of the conduits with carbonate cement resulted in the formation of tubular carbonates. Turbidity currents, sediment slumps, or the vigorous emission of fluids probably induced the fragmentation of tubular carbonates within the sediment. The carbonate fragments had been further subjected to winnowing by bottom currents. This study provides insight into the interaction of megafauna burrowing with fluid migration and carbonate formation at hydrocarbon seeps, highlighting the role of bottom currents and mass wasting on the formation of fragmented tubular carbonates.
... Fluid escape features are manifest in various forms in the geological record and exhibit a range of sedimentary and stratigraphic styles in seismic and outcrop. These include mud and sand volcanoes formed at the contemporaneous sea floor (Clari et al. 2004;Delisle 2004), chimneys or vertical pipe conduits (Løseth et al. 2009;Ilg et al. 2012;Cartwright and Santamarina 2015;Singh et al. 2016;Bertoni et al. 2018), pockmarks (Hovland et al. 1987;Agirrezabala et al. 2013;Chenrai and Huuse 2017) and concretions representing fluid flow conduits (Orpin 1997;Nyman et al. 2010;Nyman and Nelson 2011;Nelson et al. 2019). Sometimes these features may be genetically linked such as pipes and chimney structures with mud volcanoes developed where these features subcrop on the sea floor (Cartwright and Santamarina 2015). ...
... Pockmark features in the general north Taranaki area have recently been described by Chenrai and Huuse (2017) from Pliocene sediments. Methane release concretions from the Urenui Formation have been described in outcrop from both Taranaki and East Coast North Island (Nelson et al. 2004(Nelson et al. , 2007Nyman et al. 2010;Nyman and Nelson 2011;Nelson et al. 2019). Locally, some of these have been referred to as "paramoudra", vertical and sub-horizontal carbonate-cemented (typically dolomitic) concretions common in the Urenui Formation (Schellenberg 2002;Nelson et al. 2004;Nyman and Nelson 2011). ...
... This is interpreted to be a conduit for fluid escape filled with mud, sand and angular cobble-sized material migration of fluids described by others in the north Taranaki outcrop section and general area. For example, Schellenberg (2002), Nelson et al. (2004Nelson et al. ( , 2007, Nyman et al. (2010), Nyman and Nelson (2011) and Nelson et al. (2019) describe distinctive concretions and concretion bodies within slope siltstone outcrops of the Urenui Formation. These include in situ, sub-vertical authigenic carbonate concretions ("paramoudra") exposed in the coastal cliffs and concentric ring concretions exposed in plan view in modern shore platforms fig. ...
Many sedimentary structures are the manifestation of fluid escape in sedimentary basins. This paper examines outcrop and seismic examples in upper Miocene deep-water sandstones and siltstones of north Taranaki, New Zealand. In outcrop examples of fluid escape features comprise discordant bodies within otherwise uniformly bedded surrounding stratigraphy, features characterized by steep sided, over-hanging, vertical or near-vertical margins, infilled with an assortment of poorly sorted or chaotically arranged sandstone and siltstone. Typically, these features are several metres wide and up to 20 m high in outcrop and always occur stratigraphically below a mass transport deposit (MTD). Examples of similar features from nearby 2D and 3D seismic reflection data consist of localized vertical to sub-vertical zones of disrupted reflectivity and are as much as 300 m in height and 10’s–100’s of metres in width. The structures occur in close association with the basal slide planes of seismic-scale MTDs. The close association of fluid escape structures with MTDs suggests that these features formed by the sudden loading of the sedimentary succession by the emplacement of several metre-thick overlying MTDs. We suggest recurring phases whereby the emplacement of MTDs triggered fluid escape within underlying strata and, in turn, the fluid escape contributed to further instability with potential for mobilization and transport of subsequent MTDs in a dynamic deep-water setting.
... The concentration of gas hydrate-associated carbonates in specific interval of the Miocene and their relationships with soft-sediment deformations may contribute to the understanding of factors that lead to their destabilization. Moreover, the investigation of paleo-gas hydrate in the sedimentary record may shed light into their long-term evolution and the interplay with sea level changes and tectonics [45,51]. peculiar structures such as vacuolar or vuggy-like fabrics, association of pure aragonitic and gas hydrate layers (zebra-like structures) and breccias produced by the destabilization of gas hydrates [18,[24][25][26]. ...
... Compared to the abundant literature on present-day gas hydrates, only few studies deal with their past occurrence [36][37][38] or with fossil seep-carbonates recording the dissociation of gas hydrates [39][40][41][42][43][44][45][46]. In fossil sediments, the paleo-occurrence of gas hydrates is particularly challenging to assess, due to the lack of well-established proxies and to the uncertainties on the reconstruction of paleoenvironmental conditions (pressure, temperature, depth) controlling the hydrate stability field. ...
... The concentration of gas hydrate-associated carbonates in specific interval of the Miocene and their relationships with soft-sediment deformations may contribute to the understanding of factors that lead to their destabilization. Moreover, the investigation of paleo-gas hydrate in the sedimentary record may shed light into their long-term evolution and the interplay with sea level changes and tectonics [45,51]. ...
The occurrence of seep-carbonates associated with shallow gas hydrates is increasingly documented in modern continental margins but in fossil sediments the recognition of gas hydrates is still challenging for the lack of unequivocal proxies. Here, we combined multiple field and geochemical indicators for paleo-gas hydrate occurrence based on present-day analogues to investigate fossil seeps located in the northern Apennines. We recognized clathrite-like structures such as thin-layered, spongy and vuggy textures and microbreccias. Non-gravitational cementation fabrics and pinch-out terminations in cavities within the seep-carbonate deposits are ascribed to irregularly oriented dissociation of gas hydrates. Additional evidences for paleo-gas hydrates are provided by the large dimensions of seep-carbonate masses and by the association with sedimentary instability in the host sediments. We report heavy oxygen isotopic values in the examined seep-carbonates up to +6 that are indicative of a contribution of isotopically heavier fluids released by gas hydrate decomposition. The calculation of the stability field of methane hydrates for the northern Apennine wedge-foredeep system during the Miocene indicated the potential occurrence of shallow gas hydrates in the upper few tens of meters of sedimentary column.
... They usually form early in the shallow subsurface by precipitation of minerals (commonly calcite or quartz), within the sediment, as, for example, chert nodules in limestone. In contrast, "concretions" tend to form some sort of more erratic "components" within sediment (e.g., Campbell et al. 2002;Conti et al. 2004;Pierre and Rouchy 2004;De Boever et al. 2006;Campbell et al. 2008;Nyman et al. 2010;Oppo et al. 2015;Viola et al. 2017). Concretions can be assigned to a specific origin because they either show a distinct nucleus in the center such as a fossil, or they are somehow related to specific pathways of fluid, e.g., seep-related carbonate concretions, well documented from many recent marine settings (e.g., Stakes et al. 1999;Dìaz-del-Rìo et al. 2003;Campbell et al. 2010;Roberts et al. 2010;Wehrmann et al. 2011;Nehza et al. 2012;Pierre et al. 2014). ...
... Carbonate concretions are made up essentially of a micritic matrix that contains detrital components represented by silty to sandy grains and plant debris. This indicates that the growth of these concretions results from precipitation of authigenic micrite-sized carbonate within the interparticle pores of the host sediment close to and below the seafloor (Clari et al. 2004;Nyman et al. 2010). The marl inclusions observed in some concretions (Fig. 7g) represent relics of the host sediment which were not cemented. ...
... Tubular concretions have been mentioned as being present both in association with cold seeps (Orpin 1997;Stakes et al. 1999;Dìaz-del-Rìo et al. 2003) and in other situations (Aiello et al. 2001;Pierre et al. 2002;Lédesert et al. 2003;Clari et al. 2004;De Boever et al. 2009;Nyman et al. 2010;Liang et al. 2016;Viola et al. 2017;Oppo et al. 2017). No evidence of exposure to seawater such as epifaunal overgrowth or associated chemoautotrophic organisms has been observed in the studied tubular concretions. ...
Carbonate concretions have been recorded in many recent and ancient marine sediments around the world. The Middle Miocene marl of the Tenes area, situated in the northeast of the Lower Chelif Basin in NW-Algeria, contains such carbonate concretions but with a variety of different structures and morphologies. Three different basic types are distinguished: nodular (spheroidal, ellipsoidal, disc, and irregular), stratiform, and tubular concretions, the last locally have a central conduit. The close association between carbonate concretions and synsedimentary deformation structures (synsedimentary faults, slumps) and normal faults, pronounced in the Ounsour Anhas outcrop, indicates synsedimentary instability related to upward fluid movement. The concretions were formed by precipitation of micritic carbonate within the host marl at shallow burial depth, probably in the active microbial methanogenesis zone. Strongly varying δ¹³C values (− 9.82 to + 5.85‰ PDB) are interpreted as the result of the balance between ¹³C-enriched (residual CO2 from methanogenesis) and ¹³C-depleted (microbial organic matter decomposition) CO2 added to the pore solutions. δ¹⁸O values (− 2.39 to + 1.71‰ PDB) indicate that carbonate concretion growth occurred during early diagenesis conditions, from marine-derived pore-water.
... However, only a few field analogues (e.g. Agirrezabala et al., 2008Agirrezabala et al., , 2013Aiello, 2005;De Boever et al., 2009a, 2009bDela Pierre et al., 2010;Nyman et al., 2006Nyman et al., , 2010Sakellariou et al., 2010) of paleo fluid expulsion have been described to better understand the controlling factors of fluid expulsion and migration (e.g. tectonic activity). ...
... Seep carbonates identified in the East Coast basin prove that a fluid system has existed along the margin since at least 22 Ma (Campbell et al., 2008). Tubular carbonate concretions have also been described by different authors in late Miocene to Pliocene strata of Cape Turnagain and interpreted as shallow subsurface plumbing systems of cold seeps (Ledésert et al., 2003;Nyman et al., 2006Nyman et al., , 2010. ...
... The tubular concretions of Cape Turnagain area crop out along the coastline and are hosted by the Late Miocene to Early Pliocene Whangaehu Mudstone (Fig. 3) (Moore, 1981;Ledésert et al., 2003;Nyman et al., 2006Nyman et al., , 2010. The Whangaehu Mudstone dips seaward and is conformable on undifferentiated Fig. 1. ...
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.
... We follow this dual-level convention in this paper, using conduit concretion as a collective name for all concretions possessing conduits, and more specific morphological terms when referring to particular geometric varieties. Formed predominantly from the precipitation of very fine-grained carbonate minerals (automicrite) in host sediments, they have often been shown to mark the subsurface ascent pathways towards the seafloor of hydrocarbon-enriched seepages derived from any of microbial methane, thermogenic oil and gas, or gas hydrate dissociation sources (Aiello et al. 2001;Greinert et al. 2001;Clari et al. 2004;Conti et al. 2004;De Boever et al. 2006;Judd and Hovland 2007;Nyman et al. 2010;Nyman and Nelson 2011;Capozzi et al. 2015, and papers therein). At the seafloor itself, such seepages may further support the development of cold seep carbonate build-ups involving a variety of chemosynthetic organisms (Campbell 2006;Campbell et al. 2010;Suess 2010). ...
... Formed predominantly from the precipitation of very fine-grained carbonate minerals (automicrite) in host sediments, they have often been shown to mark the subsurface ascent pathways towards the seafloor of hydrocarbon-enriched seepages derived from any of microbial methane, thermogenic oil and gas, or gas hydrate dissociation sources (Aiello et al. 2001;Greinert et al. 2001;Clari et al. 2004;Conti et al. 2004;De Boever et al. 2006;Judd and Hovland 2007;Nyman et al. 2010;Nyman and Nelson 2011;Capozzi et al. 2015, and papers therein). At the seafloor itself, such seepages may further support the development of cold seep carbonate build-ups involving a variety of chemosynthetic organisms (Campbell 2006;Campbell et al. 2010;Suess 2010). ...
... Data sources come from Francis (1995), Lewis and Marshall (1996), Francis and Murray (1997), Tonkin (2003), personal communication with Dave Francis (Geological Research Ltd, Lower Hutt), and our own observations. sporadic occurrence of seafloor-related fossiliferous seep limestones (Campbell et al. 2008), as well as more widely distributed occurrences of seep-related conduit carbonate concretions (Nyman 2009;Nyman et al. 2010;Pearson et al. 2010) ( Figure 1A). Today, extensive hydrocarbon seepage is recorded both onshore and offshore along the length of the Hikurangi Margin, and methane-derived authigenic carbonates and gas hydrates are actively being formed in the offshore (Lewis and Marshall 1996;Francis and Murray 1997;Faure et al. 2006;Pecher et al. 2007;Campbell et al. 2010;Greinert et al. 2010aGreinert et al. , 2010b. ...
An intertidal shore platform in bathyal mudstones of the Late Miocene Pohutu Formation near East Cape, North Island, New Zealand, hosts many impressive dolomitic conduit concretions having predominantly doughnut morphologies up to 6 m across. Carbon isotope values (δ¹³C + 6 to + 9‰ PDB) are interpreted to show that the carbon for dolomite precipitation was derived from extensive anaerobic oxidation of thermogenic methane, while oxygen isotope values (δ¹⁸O + 2 to + 6‰ PDB) implicate the dissociation of gas hydrates at the time of carbonate precipitation. The concretions are inferred to mark the shallow sub-seafloor locations of upward migrating hydrocarbon-enriched fluids in a fossil cold seep system on a convergent margin. The distribution of concretions and faults are intimately associated. We propose that doughnut concretion growth was related to a periodically active fault-valve mechanism involving fluid pressure increase, fault rupture and fluid discharge, followed by fluid pressure decrease, mineral precipitation and fault sealing.
... A common occurrence of carbonate chimneys and mounds at the seafloor is related to the burial of dead organic matter in the sediments and its subsequent degradation mediated by a consortium of microorganisms under oxic to anoxic conditions (Díaz-del-Río et al., 2003;De Boever et al., 2006;Chen et al., 2007;Takeuchi et al., 2007;Nyman et al., 2010;Bayon et al., 2013). In the zone of anoxia ([O 2 ] = 0) within the sediment the organic matter degradation results in methane (CH 4 ) formation. ...
... HCO 3 − + Ca 2+ →CaCO 3 + H + Thus, the continental margins are zones of high CH 4 flux and carbonate precipitation due to the tremendous amount of dead organic matter accumulation. Morphologically, the precipitated carbonates form chimney-and mound-like structures that cluster at the seafloor of the continental margins (Díaz-del-Río et al., 2003;De Boever et al., 2006;Chen et al., 2007;Takeuchi et al., 2007;Nyman et al., 2010;Bayon et al., 2013). ...
A seafloor hydrothermal system located at the Iheya Ridge (Okinawa Trough), named CLAM, deposits Mn-carbonate chimneys that have no analogue found so far on the seafloor. The chimneys are composed of Mn-calcite and Ca-rhodochrosite. The crystallographic differences between these carbonates appear to control the rare earth elements (REE) partitioning between them that results in enrichment of the Ca-rhodochrosite in middle and heavy REE, and enrichment of the Mn-calcite in light REE. Chemistry of the CLAM hydrothermal fluids suggests: (1) low water/rock ratio of the hydrothermal system; (2) phase separation and dominance of low-chlorinity vapor phase; (3) sub-seafloor formation of Na-rich alteration minerals during fluid/rock reactions; (4) removal of some elements from the seawater to the host rocks during the seawater/rock interaction; (5) high Mn/Ca ratio of the basement rocks is responsible for the high Mn concentration in the hydrothermal fluids. C-O-isotope compositions of the CLAM Mn-carbonates suggest they precipitated through binary mixing of end-member hydrothermal fluid and seawater accompanied by progressive degassing and cooling of the fluid. Mn-calcite precipitated from almost pure end-member hydrothermal fluid, whereas Ca-rhodochrosite precipitated from seawater-dominated vent fluid. Mg-isotope fractionation during Mn-carbonate precipitation is assumed to depend on carbonate growth conditions and resulting carbonate mineralogy. S-isotope composition of the CLAM Mn-carbonates suggests that the Ca-rhodochrosite precipitated in oxic conditions through rapid mixing of hydrothermal fluid and seawater, whereas the Mn-calcite precipitated in reduced conditions (thermochemical or microbial sulfate reduction) through slow mixing of hydrothermal fluid and seawater. Sr-isotope composition of the CLAM hydrothermal fluids is close to that of Okinawa Trough deep seawater. In contrast, Sr-isotopes in the CLAM Mn-carbonates are more variable, indicating that Sr was derived from seawater, local lavas and sediments. Nd-isotope composition of the Mn-carbonates indicates that Nd was derived from the local lavas and sediments. Pb in the majority of the CLAM Mn-carbonates is of sedimentary origin (Pb isotope data), but involvement of anthropogenic Pb in the hydrothermal system is inferred for some Mn-calcite samples. Stability phase diagram modeling coupled with C-O-S-Sr-isotope data suggest that in the CLAM vent fluid the rhodochrosite is stable in a narrow Eh-pH range (6<pH<10; Eh>0) and in a wide range of [Mn] and [Ca] activities, whereas calcite precipitates from a close to the end-member hydrothermal fluid in reduced conditions (Eh<0).
... Low-temperature fluids escaping from the seabed produce cylindrically shaped chimney structures of marine sediments cemented by authigenic carbonate and/or iron oxides in a range of marine environments. Most of these chimney structures have been found at seafloor settings associated with active continental margins in the modern ocean (Ritger et al., 1987;Faugères et al., 1990;Orpin, 1997;Stakes et al., 1999;Derkachev et al., 2000;Michaelis et al., 2002;Diaz-del-Rio et al., 2003;Somoza et al., 2003;Takeuchi et al., 2007;Zitter et al., 2008;Chevalier et al., 2011;Magalhães et al., 2012;Angeletti et al., 2015;Oppo et al., 2015;Astakhov et al., 2017) and the rock record (Aiello et al., 2001;Ledesert et al., 2003;De Boever et al., 2006;Martinez-Frias et al., 2007;Nyman et al., 2010;Nyman and Nelson, 2011). However, chimneys have also been found in passive margin settings of the modern Gulf of Mexico Fu et al., 1994;Fu and Aharon, 1997), Nile deep-sea fan (Gontharet et al., 2007;Bayon et al., 2009;Mascle et al., 2014), the Congo deep-sea fan (Haas et al., 2010), and South China Sea (Liang et al., 2017), as well as rocks deposited in the early Atlantic Ocean (Bodin and Rose, 2018). ...
... The δ 13 C values of carbonate minerals precipitated in the modern ocean seawater typically fall within the overall range of − 3 to +6‰ (e. g., Milliman, 1974;Hudson, 1977), which reflects the δ 13 C of ambient dissolved inorganic carbon (DIC), the carbonate mineralogy, biological processes, and other factors. However, the ranges of δ 13 C values of carbonate minerals measured previously in chimney structures range from − 67 to +12‰, with average center and minimum values of − 24‰ and − 35‰, respectively; chimneys with the lowest detrital carbonate contents at each site have the lowest δ 13 C values (Ritger et al., 1987;Roberts and Aharon, 1994;Orpin, 1997;Stakes et al., 1999;Derkachev et al., 2000;Aiello et al., 2001;Michaelis et al., 2002;Diaz-del-Rio et al., 2003;De Boever et al., 2006;Gontharet et al., 2007;Martinez-Frias et al., 2007;Takeuchi et al., 2007;Haas et al., 2010;Nyman et al., 2010;Nyman and Nelson, 2011;Chevalier et al., 2011;Magalhães et al., 2012;Angeletti et al., 2015;Oppo et al., 2015;Liang et al., 2017;Bodin and Rose, 2018). Thus, the δ 13 C values of authigenic carbonate minerals in chimneys are typically much lower than those of other marine carbonates. ...
We discovered a large field of cylindrically-shaped sediment chimneys at the seafloor along the flank of Farnella Canyon (water depth ∼2775 m) at the base of the Sigsbee Escarpment in the northwestern Gulf of Mexico. The chimneys are about 10 cm in diameter with 1 cm wide axial cavities; they rise about 0.5–1 m above the seafloor and continue down into the seabed. Their composition and fabric were characterized using X-ray diffraction, carbonate content, stable oxygen and carbon isotopes, and scanning electron microscopy and microanalysis. Seismic profiles and bathymetric data from the location were analyzed to seek links between the chimneys and seabed geological structures. Results indicate that the vented liquids were warm seawater with brine and there is no evidence of hydrocarbons. These chimneys are residual sediment-filled fluid-escape conduits formed in the seabed from hemi-pelagic sediments that were locally consolidated by the pressure of fluid moving upward through the seabed in adjacent conduits and bound together by iron oxide and amorphous silica precipitates, as well as authigenic dolomite. The chimneys were subsequently exposed at the seafloor when bottom currents eroded the surrounding seabed. Concentric and crosscut bands evident in chimney cross sections indicate venting occurred episodically (venting is not currently active). The chimney field is situated at the toe of the Jurassic salt massif that extends beneath much of the continental slope. Salt movement created a pressure gradient within the seabed, directing porewater flow toward the base of the slope where the chimneys occur; thus, venting most likely occurred during times of salt mobility and shortly thereafter.
... Whereas chemoherms and stromatolites are associated with AOM-activity at or above the sediment-water interface under oxygen-deprived bottom water conditions (e.g. Michaelis et al., 2002;Bayon et al., 2013;Himmler et al., 2018), breccias and tubular carbonate conduits (TCC) are typical of sub-seabed formation conditions (De Boever et al., 2006;Nyman et al., 2010;Conti et al., 2014;Zwicker et al., 2015). ...
... TCCs described as pseudo-chimneys or sub-seafloor tubular concretions show sizes and morphology (i.e. De Boever et al., 2006;Nyman et al., 2010;Angeletti et al., 2015) referable to deeper portions of a seepage system, excluding this as potential explanation for the formation of the TCC from Athina MV. Chimneys in sensu stricto have an internal structure and specific conditions of formation (i.e. ...
... Scattered or isolated MDAC deposits occur in thick bathyal mudstones of Miocene age in North Island, New Zealand, especially in the East Coast Basin ( Figure 1A). In at least 16 different localities the MDAC is represented by seafloor fossiliferous seep limestone deposits with varied textures and mineralogy (Campbell et al. 2008), while in as many as 21 separate locations the MDAC is expressed as morphologically diverse subseafloor conduit concretions of mainly microcrystalline carbonate and often with central conduits ( Figure 1A) (Lédesert et al. 2003;Nyman et al. 2010;Nyman and Nelson 2011;Nelson et al. 2017). However, only rarely (e.g. at Tauwharepare, Karikarihauata and the largest at Rocky Knob; see Campbell et al. 2008, their figure 1 for locations) do both these carbonate types occur at the same locality, and so any direct genetic link between the seafloor and sub-seafloor environments of methane seepage is uncertain, and usually inferred. ...
... Alternatively, enrichment of δ 18 O values by +2‰ to +3‰ VPDB compared to middle Miocene New Zealand seawater could be accounted for by gas hydrate dissociation, a process invoked for many seep carbonate occurrences (e.g. Bohrmann et al. 1998;Aloisi et al. 2000;Greinert et al. 2001;Díaz-del-Río et al. 2003;Clari et al. 2004Clari et al. , 2009Pierre and Rouchy 2004;Pierre et al. 2010;Nyman et al. 2010;Cau et al. 2015; see also Table S1). During gas hydrate formation, heavy oxygen is preferentially included into the hydrate molecule, and upon dissociation of large volumes of gas hydrates, heavy oxygen can be released into sediment pore fluids, thereby increasing δ 18 O values by up to 3‰ VPDB (Davidson et al. 1983;Ussler and Paull 1995). ...
Methane-derived authigenic carbonates (MDACs) in Miocene bathyal mudstones in North Island, New Zealand are typically expressed as either sub-seafloor conduit concretions or as seafloor seep limestones, but rarely are both types exposed in outcrop at one locality. Consequently, any potential genetic link between them is usually inferred. This also appears to be the case for global occurrences of MDAC. At the Rocky Knob seep complex near Gisborne both seep limestones and conduit concretions co-occur. The petrography and stable carbon (δ13C) and oxygen (δ18O) isotope compositions of their various authigenic carbonate components (automicrite, fibrous aragonite crystals, and granular, blocky and bladed calcite crystals) show that distinctive isotope and petrographic groupings for precipitates within the conduit concretions match or “correlate” with several of those in the seep limestones. This corroborates their genetic tie and derivation from the same fluids, albeit in different parts (i.e. sub-seafloor vs. seafloor) of the seep complex.
... It is documented in modern and ancient marine sedimentary basins worldwide and linked to different tectonic regimes at convergent and passive margins (e.g. Taviani, 2001;Pinheiro et al., 2003;Ge et al., 2010;Nyman et al., 2010;Capozzi et al., 2012;Van Landeghem et al., 2015 and references therein; Marzec et al., 2016;Mazzini et al., 2016 and references therein;Roy et al., 2016). The occurrence of seep carbonates corresponds to present and past hydrocarbon vents, which contribute to the gas budget of the marine environment and the atmosphere. ...
... Pipe-like conduits, also named chimneys, are less commonly reported in the literature and their formation mechanisms are still under debate (e.g. Nyman et al., 2010;Magalhães et al., 2012;Talukder, 2012;Oppo et al., 2015;Reitner et al., 2015;Andrews et al., 2016). The case study from the Secchia River succession provides new insights into the relationships between the formation of authigenic carbonates, which occurred in a shelf environment during the Early Pleistocene, the geologic evolution of the marine basin and the concurrent hydrocarbon migration processes in the petroleum system of the Northern Apennines. ...
Understanding authigenic seep carbonate formation provides clues for hydrocarbon exploration and insights into contributions to gas budgets of marine environments and the atmosphere. Seep carbonates discovered in the outcropping succession along the Secchia riverbanks (near Modena, Italy) belong to the Argille Azzurre Formation of Early Pleistocene age deposited in an upper shelf environment overlying the Miocene foredeep successions, which include hydrocarbon fields. The fluid migration from the hydrocarbon fields, up to the surface, is presently active on land and started in the marine succession during the Late Miocene.
... It is documented in modern and ancient marine sedimentary basins worldwide and linked to different tectonic regimes at convergent and passive margins (e.g. Taviani, 2001;Pinheiro et al., 2003;Ge et al., 2010;Nyman et al., 2010;Capozzi et al., 2012;Van Landeghem et al., 2015 and references therein; Marzec et al., 2016;Mazzini et al., 2016 and references therein;Roy et al., 2016). The occurrence of seep carbonates corresponds to present and past hydrocarbon vents, which contribute to the gas budget of the marine environment and the atmosphere. ...
... Pipe-like conduits, also named chimneys, are less commonly reported in the literature and their formation mechanisms are still under debate (e.g. Nyman et al., 2010;Magalhães et al., 2012;Talukder, 2012;Oppo et al., 2015;Reitner et al., 2015;Andrews et al., 2016). The case study from the Secchia River succession provides new insights into the relationships between the formation of authigenic carbonates, which occurred in a shelf environment during the Early Pleistocene, the geologic evolution of the marine basin and the concurrent hydrocarbon migration processes in the petroleum system of the Northern Apennines. ...
Winter floods and river incisions exposed a new authigenic carbonates (ACs) field across the Secchia River (near Modena, Italy). The outcropping succession belongs to the Argille Azzurre Formation, is Early Pleistocene in age and was deposited in an upper shelf environment. Authigenic carbonate globular concretions (GC) and carbonate chimney are interspersed along the strata beds in the whole thickness of the section. Five GC and one chimney have been sampled with the aim to achieve an exhaustive geochemical characterization of the carbonates coming from this new discovered site. Starting from a morphological description, each sample has been divided in subsamples in order to have a micro characterization of petrography, SEM-EDX observation, together with XRD and XRF analyses. The samples are mainly composed by microcristalline dolomite, above 50%; the remaining silicoclastic grains are composed by quarts, chlorite, biotite and feldspars. Carbon, oxygen and strontium isotope signatures have been analysed on all the samples. The δ13C signatures divide the samples in two groups according to the morphology, possibly corresponding to two different type of formation processes: globular concretion have positive values that suggest an influence of CO2 reduction processes, also observed in active seepages in the area. Whereas the chimney, with negative δ13C values, has been interpreted as former conduit where carbonate precipitation is promoted by anaerobic oxidation of methane coupled with sulphate reduction processes. The δ18O range of temperature formation, coupled with 87Sr/86Sr signatures, give the information to discern the different contribution of connate water respect to the seawater in the carbonates formation.
... However, ancient carbonates are commonly affected by late burial diagenesis, resulting in a change in mineralogical composition and alteration of primary oxygen isotope signatures. For this reason, most ancient seep carbonates are composed of calcite and dolomite, rather than aragonite (e.g., Beauchamp and Savard, 1992;Nyman et al., 2010). Furthermore, where Cenozoic (and a few Mesozoic) seep carbonates do retain their aragonite mineralogy, the aragonite is often only preserved as acicular or fibrous crystal aggregates or botryoids in void spaces or cavities (Terzi et al., 1994;Savard et al., 1996;Peckmann et al., 1999Peckmann et al., , 2002Campbell et al., 2008;Amano et al., 2010;Smrzka et al., 2015). ...
... The cracks seen in some globular botryoids (Fig. 6F) may relate to an increase in cavity pressure during intense fluid flow and subsequent hydrofracturing. Such an increase in pressure could have been caused by the precipitation of botryoids that filled and plugged the cavities through which the seepage fluids flowed Nyman et al., 2010;Hryniewicz et al., 2012). In addition, the presence of the bathymodiolin mussel, B. akanudaensis, may also be linked to intense fluid flow, as extant bathymodiolin mussels, some species of which harbor methanotrophic symbionts (Fisher, 1990), are known to live in hydrocarbon seeps with rising gas bubbles and relatively high fluid flux (MacDonald et al., 1989;Olu et al., 1996;Wagner et al., 2013). ...
The modern Japan Sea is characterized by active methane seeps associated with gas hydrates, but its ancient counterparts are not fully understood. This study describes a newly discovered methane-seep carbonate block, the ‘Nakanomata Seep Deposit’, from the upper Miocene Nodani Formation in Joetsu City, central Japan. The age of this deposit is constrained to 7.5–6.5 Ma based on its fossil diatom assemblage. The deposit contains molluscan fossils typical of methane seeps, including vesicomyid and bathymodiolin bivalves, and provannid gastropods, and it retains an almost entirely aragonitic mineralogy, despite its Miocene age. It is composed of clotted microcrystalline aragonite containing nodules and intraclasts, and is crosscut by vein-like networks of voids and cavities rimmed with acicular aragonite. The δ13C values of the carbonate phases are as low as − 41.1‰ and the presence of lipid biomarkers (pentamethylicosane and crocetane) suggests that the deposit originated from the anaerobic oxidation of methane. It is suggested that an initially diffuse methane seepage formed the micritic nodules, followed by a more rapid and intense methane seepage that led to the development of abundant voids in the sediment; finally, the sediment was cemented by microcrystalline aragonite and void-lining acicular aragonite. The seep deposit also contains peculiar globular silica minerals and authigenic quartz. During their precipitation, these globular silica minerals may have trapped methane gas bubbles, and the minerals may be pseudomorphs after silica clathrate. Sufficient increase in pH and supersaturation of silica, which led to the dissolution and subsequent precipitation of these silica minerals, could have resulted from the degassing of carbon dioxide, promoted by an effective supply of methane, and its supersaturation, thus forming gas bubbles.
... However, the underlying geological mechanisms leading to spatial-temporal variability of gas seepage often remain elusive, and there are a number of important interrelationships that need to be considered between processes including hydrate formation dynamics, authigenic carbonate precipitation, and focused flow along faults, fractures, and high-porosity lithologies (Crutchley et al., 2013;Milkov et al., 2005;Teichert et al., 2003;Tréhu et al., 2004a). In addition, typical geological archives, such as seep carbonates (e.g., Han et al., 2014;Nyman et al., 2010), may only reveal partial stages of fluid seepage, while identifying seepage histories from seismic data is difficult because fluid migration patterns are typically concealed by poor image quality at depth and/or overprinting from successive gas migration episodes. Still, seismic images can potentially provide spatial relationships that could be linked to time constraints by seismic stratigraphy. ...
The Formosa Ridge cold seep is among the first documented active seeps on the northern South China Sea passive margin slope. Although this system has been the focus of scientific studies for decades, the geological factors controlling gas release are not well understood due to a lack of constraints of the subsurface structure and seepage history. Here, we use high‐resolution 3D seismic data to image stratigraphic and structural relationships associated with fluid expulsion, which provide spatio‐temporal constraints on the gas hydrate system at depth and methane seepage at modern and paleo seafloors. Gas has accumulated beneath the base of gas hydrate stability to a critical thickness, causing hydraulic fracturing, propagation of a vertical gas conduit, and morphological features (mounds) at paleo‐seafloor horizons. These mounds record multiple distinct gas migration episodes between 300,000 and 127,000 years ago, separated by periods of dormancy. Episodic seepage still seems to occur at the present day, as evidenced by two separate fronts of ascending gas imaged within the conduit. We propose that episodic seepage is associated with enhanced seafloor sedimentation. The increasing overburden leads to an increase in effective horizontal stress that exceeds the gas pressure at the top of the gas reservoir. As a result, the conduit closes off until the gas reservoir is replenished to a new (greater) critical thickness to reopen hydraulic fractures. Our results provide intricate detail of long‐term methane flux through sub‐seabed seep systems, which is important for assessing its impact on seafloor and ocean biogeochemistry.
... By far, the largest of these deposits, at least in exposure, is at Rocky Knob in the Raukumara Peninsula, which also harbors the widest diversity of seep taxa and characteristic seep geological features such as tubular conduit concretions (e.g., Nelson et al. 2019). There is also evidence for other potential late Miocene seepage from the presence of tubular conduit concretions without associated development of seafloor seep carbonate at other sites in East Coast Basin (e.g., Nyman et al. 2010;Nelson et al. 2017), as well as in Taranaki Basin on the west coast of North Island (Nyman and Nelson 2011). ...
The East Coast Basin of eastern North Island, New Zealand, is one of a few places globally that offers the opportunity to reconstruct a spatiotemporal record of long-lived (ca. 25 Ma duration) hydrocarbon seepage from both onshore, exhumed accretionary prism and forearc rocks and their adjacent, offshore, modern convergent tectonic settings. Comparable settings, with analogous ancient and modern seeps, are found elsewhere on the Pacific Rim, including Japan, northwestern USA, and western South America. North Island’s East Coast is also host to much older, Late Cretaceous seep deposits, which are less numerous than the Miocene seeps, and not as widely studied, but are similar lithologically and also contain noteworthy faunal assemblages. This chapter lists the known localities, with descriptions of their lithology and fauna.KeywordsNew ZealandEast Coast BasinNorth IslandHawke(’s) BayRaukumara PeninsulaGisborneDannevirkeHikurangi marginEarly MioceneLate CretaceousAutochthonousMicrobialiteExhumed forearc
... Van der Lingen and Pettinga 1980;Pettinga 1982;Van der Lingen 1982;Neef 1992Neef , 1999Lewis and Pettinga 1993;Reid 1998;Field 2005;Bailleul et al. 2007Bailleul et al. , 2013Burgreen and Graham 2014;Buckeridge et al. 2018;McArthur and McCaffrey 2019;Caron et al. 2022;Claussmann et al. 2021Claussmann et al. , 2022McArthur et al. , 2022. In addition to active onland mud volcanoes and oil and gas seeps (Field et al. 1997;Pettinga 2003;Hollis et al. 2005;Sykes et al. 2012;Malié et al. 2022), that part of the margin displays outcropping paleomethane seeps and expressions of their plumbing systems (tubular carbonate concretions) hosted by Cretaceous to Miocene rocks (Ledésert et al., 2003;Campbell et al., 2008;Nyman et al., 2010;Kiel et al., 2013;Malié et al., 2017Malié et al., , 2022 and Edwards 1984; Harmsen 1985;Haywick et al. 1991;Ballance 1993;Beu 1995;Field et al. 1997;Begg and Johnston 2000;Mazengarb and Speden 2000;Lee and Begg 2002;Nelson et al. 2003;Bland et al. 2004Bland et al. , 2013Caron et al. 2004aCaron et al. , 2004bCaron et al. , 2005Lee et al. 2011;Bertaud-Gandar et al. 2018). The forearc basin is back-stopped by uplifted faultbounded Mesozoic metasedimentary basement rocks of North Island's Axial Ranges, which are closely associated with many active crustal-scale strikeslip faults (North Island fault system) (e.g. ...
This is the first of a two-part New Zealand Journal of Geology and Geophysics Special Issue that focuses on improving our understanding of sedimentary systems of the Hikurangi Subduction Margin, Aotearoa-New Zealand. It is amongst the world’s youngest and most accessible active subduction margins and its sedimentary basins preserve a rich history of inception and ongoing evolution, spanning trench to back-arc positions. These sediments and sedimentary rocks provide a record of surface processes from the latest Paleogene to today, and reflect the spatio-temporal variability of the effects of subduction, seismicity, volcanism, evolving sediment sources, routing systems and processes, all imprinted upon by glacio-eustatic sea-level changes. The papers in this volume focus on the interplay between controlling mechanisms and the dynamics of these systems, from both onshore and offshore sedimentary environments. This issue is divided into two themes, distinguished by geological age: 1. Miocene Sedimentary Systems and intra-slope basin evolution, and 2. Insights from Quaternary Sedimentary Systems from the trench to the inner margin. Collectively, these papers represent significant advances into our understanding of sedimentary systems within the Hikurangi Subduction Margin, with innovative results that may find applications to other convergent settings.
... The δ 13 C values of the studied tubular concretion (Fig. 7) broadly match the data obtained for numerous other concretions at Chiahsien seep site (Chien et al., 2013) and other tubular concretions worldwide (Cavagna et al., 2105;Nyman et al., 2010). They are diagnostic of the anaerobic oxidation of methane (AOM). ...
... The δ 13 C values of the studied tubular concretion (Fig. 7) broadly match the data obtained for numerous other concretions at Chiahsien seep site (Chien et al., 2013) and other tubular concretions worldwide (Cavagna et al., 2105;Nyman et al., 2010). They are diagnostic of the anaerobic oxidation of methane (AOM). ...
At a Pliocene methane seep site in Taiwan, an about half meter-long dolomitic concretion hosting a lucinid bivalve Anodontia goliath, ∼11 cm in diameter reveals the impact of chemosymbiotic bivalves on fluid migration through the shallow sediment. The concretion consists of a central channel filled with sparite and varying amounts of brecciated material derived from the channel walls. The studied bivalve is preserved with the hinge upward. When restored to life position, the central channel of the upper, ∼10 cm-long concretion segment is connected to the shell above the anterior side of the umbos. For the lower, ∼30 cm-long concretion segment, the central channel is connected to the shell underneath the posterior sector of the bivalve. The channels are interpreted as anterior tube for supply of respiration water and posterior tube, mining sulphide generated in the sulphate-methane transition zone of the sediment, respectively. The dolomitic cortex surrounding the central channel is characterized by δ¹³C values as low as -29‰ VPDB, indicating that the rate of anaerobic oxidation of methane was enhanced around the conduit. At the base of the central channel, upward soft sediment deformation structures likely resulted from the dragging effect when fluids migrated out of the sediment and entered the channel. Brecciation of the channel walls indicates pulsating seepage during the incipient stages of cementation. The burrow, thus, acted as a highly permeable conduit channeling upstreaming methane-charged fluid for a substantial period of time. This example illustrates that burrows are efficient in pre-determining the formation of preferential fluid migration conduits at seep sites, most likely with an important impact on fluid mixing and diagenetic reaction rates in the sediment, and ultimately the rate of methane release to the ocean.
... The negative δ 13 C value recorded in Toarcian Aïn Rhezala Limestone suggests that the 13 C-depleted carbon excursion resulted from the rapid release to the ocean and atmosphere of (biogenic) methane from methane hydrate in sediments: because biogenic methane is depleted in 13 C relative to 12 C (δ 13 C −60‰), its oxidation to CO 2 in the oceans and atmosphere imparts a light carbonenriched isotope signal in the pool of dissolved inorganic carbon (DIC) (Hesselbo et al., 2000). The spherical carbonate concretions are associated with normal faults and synsedimentary instability structures in the Theniet El Kelakh Formation and indicate an upward fluid migration (methane or residual CO 2 from the methanogenesis pathway) (Nyman, Nelson, & Campbell, 2010). The concretions show carbon isotope values (δ 13 C of −5.14‰, VPDB) suggesting precipitation below the sulphate reduction zone from pore water and methanederived CO 2 or a post-methanic origin from subsurface connate waters possibly with freshwater influence. ...
The Jurassic Lower Carbonate Group in the Aïn Ouarka area of Western Saharan Atlas, Algeria, is represented by six formations, from base to top: Hettangian Chemarikh Dolostone, Early Sinemurian–Pliensbachian Aïn Ouarka Limestone, Toarcian Aïn Rhezala Limestone, Aalenian–Late Bajocian Raknet El Kahla Limestone Breccia, Late Bajocian Theniet El Klakh, and Late Bajocian–Bathonian Tifkirt Limestone formations. From the microfacies analysis, six microfacies types (MF1–MF6) have been recognized and grouped into three associations developed during a transgressive–regressive cycle: (a) inner ramp facies association; (b) middle ramp facies association; and (c) outer ramp facies association. The mineralogical analysis of the carbonate rocks reveals that they contain mostly low‐Mg calcite associated with ankerite, pyrite, and other detrital minerals such as quartz, chlorite, illite, feldspar (albite), and a few clay minerals. These minerals could be related to the deep fluid and hydrocarbon circulations during deposition. The isotopic data display a variation of δ13C isotopic values between −5.14‰ and +2.21‰ (VPDB) and between −8.12‰ and −4.95‰ for δ18O values (VPDB). The set of δ13C values is similar to the signature of marine dissolved inorganic carbon. First of all, the positive values of δ13C show that the origin of carbon is not from the organic‐rich zone (microbial zone), but probably derived from pore‐water and/or biogenic carbonate precursors. On the other hand, the negative values of δ13C indicate that the carbon may result from organic sources linked to the sulphate reduction bacteria activity, or by a heightened volcanic and/or hydrothermal activities releasing light carbon (12C). The negative δ18O values are not consistent with marine water ambient temperature, but with a possible influence of diagenesis or increasing of temperature by hydrothermal water. This hydrothermal activity is controlled by synsedimentary faults during the Early Jurassic and related to a late pulse of the Central Atlantic Magmatic Province (CAMP) volcanism and by regional volcanism during the Middle Jurassic (Bajocian–Bathonian).
... Fossil analogous to modern systems have been recognized in exposed sedimentary successions on all continents (except Antarctica) and have allowed the investigation of the long-term evolution of hydrocarbon seepage in relation to tectonic processes and climate change [12]. Spectacular seep-carbonate examples have been reported from Miocene outer shelf and upper slope deposits at Hikurangi Margin, New Zealand [10,19,20] and in Cretaceous deposits linked to cold seepage in forebulge setting (Tepee Buttes carbonate mounds) cropping out in Colorado, USA. [21]. ...
The natural emission of methane-rich fluids from the seafloor, known as cold seepage, is a widespread process at modern continental margins. The studies on present-day cold seepages provide high-resolution datasets regarding the fluid plumbing system, biogeochemical processes in the sediment, seafloor seepage distribution and ecosystems. However, the long-term (hundreds of thousands to millions of years) evolution of cold seepage remains elusive. The identification and study of outcrop analogous now exposed on land represent a valuable method for better understanding the effects of geological processes and climate forcing on the development of cold seepage systems. Here, we provide an overview on Miocene seep-carbonate deposits of the northern Apen-nines (from Emilia to the Umbria-Marchean sector, Italy), based on decades of field research integrated with detailed sedimentological and geochemical investigations. We report a total of 13 seep-carbonate outcrops, which formed in three different structural settings of the paleo-accretionary wedge corresponding to wedge-top basins, outer slope and intrabasinal highs at the deformational front. We discuss the recurring lithostratigraphic occurrence of seep deposits and the main compo-sitional features (carbonate facies, carbon and oxygen stable isotopes) in order to interpret the seep-age dynamics, duration and infer the contribution of methane-rich fluids released by paleo-gas hy-drates. The datasets presented in this study represent a valuable complete record of cold seepage spanning ~12 Myr, that can be used to better understand factors controlling the regional-scale spatial and temporal evolution of cold seepage systems at modern active continental margins.
... Clearly an evolution of the deformation mechanisms occurred from a penetrative ductile process to a brittle behavior (faulting overimposed on early penetrative deformation). This event corresponds to the period of development of the carbonate pipes which are interpreted as former fluid conduits comparable to similar structures described in different places (Deville et al., 2006(Deville et al., , 2020De Boever et al., 2009;Nyman et al., 2010;Conti et al., 2014;Zwicker et al., 2015;Tamborrino et al., 2019). This event corresponds also to the period of development of the syn-kinematic calcite veins. ...
Major decollements located within buried overpressured shale commonly develop in thrust fronts, accretionary prisms and sedimentary deltas controlled by gravity tectonics. In seismic data, it is possible to observe only large scale deformation of what is commonly designed as mobile shale but the precise geometry and the dynamic evolution of these bodies remains poorly understood. It is often difficult to define if we are dealing with ductile or brittle deformation and to understand the role of the fluids in time and space during deformation. For this reason, large scale outcrops were studied in the Parras Basin (Mexico), which makes possible a direct observation of the shale tectonic processes. This work suggests changes in space and time of the deformation processes which occurred within the shale formation hosting the decollement. Distributed deformation was observed within the shale formation hosting the decollement compared to more localized deformation above. Also a change of the rheology of the shale over time occurred progressively toward brittle processes in the whole sedimentary pile. XRD and microscopic studies have shown that diagenetic processes are favored in the shear zones of penetrative deformation leading notably to reverse gradient of illitization. The isotopic analysis of cements in veins and the study of associated fluid inclusions have shown that fluid dynamics also evolved during time showing notably evidence for widespread fluid migration issued from rocks located below the decollement during the beginning of the deformation. Progressively, the tectonic system located above the decollement tends to be preserved from fluid migration coming from below the decollement and to be influenced only by local fluid migration (closed system).
... Processes that can also occur in seep environments include aerobic and nitrate-driven organic matter remineralization, as well as iron reduction, manganese reduction, organoclastic sulfate reduction, methanogenesis, and marine silicate weathering (Stakes et al., 1999;Aloisi et al., 2000;Peckmann et al., 2001;Jørgensen and Kasten, 2006;Wallmann et al., 2008). Seep carbonates can exhibit various types of morphologies ranging from nodular, tubular, and grapestone concretions to chimneys, as well as laterally extensive crusts on the seafloor and large, stacked crusts forming mounds (Díaz-del-Río et al., 2003;Nyman et al., 2010;De Boever et al., 2011;Zwicker et al., 2015;Sahling et al., 2016;Smrzka et al., 2017Smrzka et al., , 2019b. Sulfate-driven AOM is the key process at seeps, providing chemical energy for benthic ecosystems (Boetius et al., 2000) and increasing pore water alkalinity and the saturation state of carbonate minerals (Kulm et al., 1986;Ritger et al., 1987;Bohrmann et al., 1998). ...
Marine authigenic carbonates form shallow-water microbialites, mud mounds, and hydrocarbon-seep deposits and contain appreciable amounts of trace elements that yield information on paleoenvironments. Element patterns of some of these carbonates archive metabolic processes through geologic time since many trace elements are redox-sensitive and participate in biological cycling. Trace element distributions in microbial carbonates not only yield information on the redox state of ancient oceans, but also on the chemical evolution of Earth’s hydrosphere and atmosphere. Trace element patterns can be used to distinguish marine from freshwater sources, to estimate water depth, and can help identify microbial metabolisms through time. A major issue concerning the use of marine carbonates as a paleoenvironmental archive is assessing the degree of early and late diagenetic alteration, which can modify or even reset the original content and distribution of trace elements. The degree and effect of early and late diagenetic alteration can be evaluated by comparing element contents to organic and other inorganic geochemical proxies. Authigenic hydrocarbon-seep carbonates forming in seafloor sediments are the product of microbial oxidation of methane and other hydrocarbon compounds. Seep carbonates are excellent archives, whose trace element contents yield information on sedimentary redox processes, as well as information on seepage intensity and fluid composition. Trace elements serve as proxies in these highly dynamic environments shaped by fluid seepage and chemosynthesis, and can help to reconstruct the evolution of chemosynthesis-based life at seeps through the Phanerozoic.
... (1) Chimneys could be cemented by carbonate precipitation, as has been observed for other chimneys, thus enhancing the mechanical properties of the sediment. Indeed, outcrop observations in a number of sedimentary basins have shown tubular carbonate pipes underneath fluid venting features (Aiello et al., 2001;Gay et al., 2007;Nyman et al., 2010;Nyman et al., 2006). (Hustoft et al., 2007). ...
Fluid migration within the sedimentary column contributes significantly to slope failure and pockmark formation and can be an effective triggering mechanism to generate submarine landslides. Pockmarks are thus commonly listed among geohazards. Contrary to these accepted notions, we propose here an alternative view of pockmarks with an example from the Eastern Niger Submarine Delta: Pockmarks and associated chimneys may increase or modify the shear strength of sedimentary layers and locally enhance seafloor stability. The analysis of two 3D seismic volumes shows that a landslide deposit divides into two branches around a cluster of three pockmark chimneys, interpreted to impede its further development. The morphological characteristics of a slide constrained by fluid seepage features show the potential role of fluid escape in marine sediment strengthening. This article is protected by copyright. All rights reserved.
... Different amounts of carbonate can be generated by the AOM resulting in a few millimeters of carbonate precipitation or a few meters of carbonate slab. In addition, carbonate concretion, carbonate, carbonate chimneys, and even carbonate pavement measuring a few hundred square meters can be formed (Nyman et al., 2010). At the SHC site, the precipitation of carbonates via AOM occur primarily as cement and their growth in the sediments will serve as a trap for the upward migrated methane. ...
... Plaza-Faverola et al., 2011;Crutchley et al., 2015;Klaucke et al., 2015;Mohammedyasin et al., 2016), while the identification of buried authigenic carbonates may be difficult on seismic data due to resolution limits (Andresen, 2012;Ho et al., 2012). On the other hand, seismic and seafloor data from modern analogues allow observations at a basinwide scale and the recognition of fluid migration pathways that are rarely identified in the geological record (Nyman et al., 2010;Nelson et al., 2017). ...
We present new field data from three outcrops of Miocene methane-derived authigenic carbonates in the foredeep of the northern Apennines that contain chemosynthetic fauna and record a long history (∼1 Ma) of shallow fluid seepage linked to seafloor anaerobic oxidation of methane. The studied outcrops show similar features in terms of carbonate morphology, facies, spatial distribution and lateral and vertical contacts with the enclosing sediments. Methane-derived carbonates occur in two structural positions: 1) on the slope of the ac-cretionary wedge in hemipelagites draping buried thrust-related anticlines, and 2) at the leading edge of the deformation front in the inner foredeep, within fault-related anticlines standing above the adjacent deep seafloor as intrabasinal ridges. We compare fossil seeps with two extensively investigated modern analogues: the Hikurangi Margin, offshore New Zealand and Hydrate Ridge, on the Cascadia margin, offshore the U.S.A. These analogues share a similar compressive structural setting and are marked by the presence of variably extensive and voluminous methane-derived carbonate bodies and chemosynthetic fauna on the present-day seafloor. The comparison allows us to propose a model for the evolution of fluid seeps on thrust-related ridges. At the deformation front, uplift and geometry of the anticlinal ridges are controlled by the growth of splay faults, mostly blind, connected to the basal detachment, favoring the migration of fluids toward the incipient anticline. Fold development generates extensional stresses in the hinge zone of the anticline, promoting the development of normal faults; fluid migration pathways and seafloor seeps shift from the forelimb toward the crest of the ridge as the structures evolve. In the slope setting, far from the deformation front, thrust faults and extensional faults in buried anticlines remain the main fluid migration pathways to sustain seepage at the seafloor. After reaching a mature stage within the wedge, the structure is less active and buried in the slope environment of the evolved prism.
... Plaza-Faverola et al., 2011;Crutchley et al., 2015;Klaucke et al., 2015;Mohammedyasin et al., 2016), while the identification of buried authigenic carbonates may be difficult on seismic data due to resolution limits (Andresen, 2012;Ho et al., 2012). On the other hand, seismic and seafloor data from modern analogues allow observations at a basinwide scale and the recognition of fluid migration pathways that are rarely identified in the geological record (Nyman et al., 2010;Nelson et al., 2017). ...
We present new field data from three outcrops of Miocene methane-derived authigenic carbonates in the foredeep of the northern Apennines that contain chemosynthetic fauna and record a long history (∼1 Ma) of shallow fluid seepage linked to seafloor anaerobic oxidation of methane. The studied outcrops show similar features in terms of carbonate morphology, facies, spatial distribution and lateral and vertical contacts with the enclosing sediments. Methane-derived carbonates occur in two structural positions: 1) on the slope of the accretionary wedge in hemipelagites draping buried thrust-related anticlines, and 2) at the leading edge of the deformation front in the inner foredeep, within fault-related anticlines standing above the adjacent deep seafloor as intrabasinal ridges. We compare fossil seeps with two extensively investigated modern analogues: the Hikurangi Margin, offshore New Zealand and Hydrate Ridge, on the Cascadia margin, offshore the U.S.A. These analogues share a similar compressive structural setting and are marked by the presence of variably extensive and voluminous methane-derived carbonate bodies and chemosynthetic fauna on the present-day seafloor. The comparison allows us to propose a model for the evolution of fluid seeps on thrust-related ridges. At the deformation front, uplift and geometry of the anticlinal ridges are controlled by the growth of splay faults, mostly blind, connected to the basal detachment, favoring the migration of fluids toward the incipient anticline. Fold development generates extensional stresses in the hinge zone of the anticline, promoting the development of normal faults; fluid migration pathways and seafloor seeps shift from the forelimb toward the crest of the ridge as the structures evolve. In the slope setting, far from the deformation front, thrust faults and extensional faults in buried anticlines remain the main fluid migration pathways to sustain seepage at the seafloor. After reaching a mature stage within the wedge, the structure is less active and buried in the slope environment of the evolved prism.
... The mechanisms of the formation of these pipes are still controversial. It has been suggested that a relatively steady and focused migration of methane-rich fluids through vertical or near vertical conduits is the most probable formation mechanism (Nyman et al., 2010;Chen and Han, 2013). Burrows beneath the seafloor may play an important role in forming conduits and may become an integral part of the plumbing system close to the seafloor (e.g., Zwicker et al., 2015). ...
Three decades after the discovery of cold seep systems, various sites of hydrocarbon seepage have been found in the South China Sea (SCS). Over the past decade, these sites have become model systems for understanding the variability of hydrocarbon seepage and associated biogeochemical processes. In this review, we describe the cold seep systems of the SCS with an emphasis on seafloor manifestations, fluid sources, biogeochemical processes, and macroecology. Seafloor features associated with seeps include mud volcanoes, pockmarks, and carbonate deposits. A common characteristic of cold seeps is the occurrence of authigenic (i.e., in situ precipitated) carbonate minerals. These carbonates commonly exhibit low δ¹³C and high δ¹⁸O values, suggesting the incorporation of methane-derived carbon and oxygen derived from gas hydrate water. Biogeochemical processes such as sulfate-driven anaerobic oxidation of methane (SD-AOM), the key process at seeps, have been studied in detail with the aim of establishing geochemical proxies to trace these processes into the geological past. We also detail the features characterizing seep ecosystems. Understanding the impact of decomposing methane hydrate on the marine carbon budget remains challenging and requires additional seafloor observations as well as models predicting how gas hydrate responds to changing conditions such as temperature increase, sea level rise, and episodic mass wasting.
... Moreover, from a morphological point of view, the tubular concretions below the second and third authigenic levels are reminiscent to feederpipes acting as fluid conduits in seep systems (e.g. De Boever et al., 2006;Nyman et al., 2010;van de Schootbrugge et al., 2010;Oppo et al., 2015;Reitner et al., 2015;Zwicker et al., 2015;Li et al., 2018). Their overall morphological and lithological characteristics are furthermore similar to late Albian seep carbonates of the Basque Country that have been identified as burrow structures by Wiese et al. (2015). ...
In the Lower Bajocian of the Jebel Bou Kendill section (Central High Atlas Mountain), three peculiar levels of authigenic carbonates are observed within the carbonate-poor Agoudim III Member. Morphological, sedimentological and geochemical evidences indicate that the two upper levels have been deposited at a hydrocarbon seep site, whereas the lowermost level likely underlines the zone where hydrocarbon fluids were generated. The first seep carbonate level is made of mineralized burrows that have acted as fluid conduits leading to a conspicuous cap carbonate bed on top of which several chimneys and chemoherm structures are embedded. Hence, this carbonate bed is a fossilized sea-floor carbonate crust. The second seep carbonate level is made of chemoherm structures buttressed against the first carbonate beds of the Agoudim IV Member. They were probably formed within the sedimentary column, close to the sea floor. Similar seep carbonates are observed regionally within the Agoudim III Member in the highly subsiding Central High Atlas troughs. A relationship between these seep carbonates occurrence and the late Early Bajocian global environmental perturbation can be deduced, as this latter has led to the deposition of a relatively organic-matter rich sedimentary sequence in these troughs via seawater eutrophication. The decomposition by bacterial activity of this organic matter, aided by rapid burial rates, has led to the generation of alkaline-rich fluids promoting the precipitation of the seep carbonates. A similar relationship between transient environmental perturbations and seep carbonates occurrence is observed in numerous Mesozoic examples and can be explained by the fact that hydrocarbon-seeps are supply-limited systems. Transient deviation from the Mesozoic greenhouse climate norm, either toward hothouse or coldhouse climates, favours the deposition of organic-rich sediments or transient methane storage, respectively, hence increasing the likelihood for the formation of hydrocarbon seepage.
... The tortuous, burrow-like morphologies of the small concretions at these sites (Figs. 4,5) suggest that fluids containing methane diffused into the low-permeability silty sediments through animal burrows and other small pore spaces, rather than through more effective fluid conduits such as large pipe-and chimney-like structures (Kulm and Suess 1990;Nyman et al. 2010;Zwicker et al. 2015). Campbell et al. (2008) also inferred that burrows served as relatively permeable fluid pathways through impermeable tight mudstones to deposit carbonate ''blebs.'' ...
Along continental margins, various types of methane seeps with a variety of flux rates, spatial extents, and duration occur. Although numerous studies have investigated spatially extensive high-flux-rate seeps, seeps with ephemeral and/or weak flows, known as diffusive seeps, have received less attention. This study investigated ancient diffusive methane seeps in the Shin’etsu sedimentary basin, central Japan, aiming to deduce their spatial extent and their sedimentological, paleontological, and geochemical properties. The seeps were identified as centimeter-scale carbonate concretions in two outcrops of Neogene siltstones in the basin. A comprehensive examination of the spatial distribution of the carbonates, their associated molluscan fossils, petrography, carbon and oxygen isotopic compositions, and lipid-biomarker contents of the concretions revealed that they originated from the anaerobic oxidation of methane (AOM) and formed via a weak, diffusive fluid flow. The small size and irregular or burrow-shaped morphologies of the concretions indicate that methane-bearing fluids diffused through small pore spaces such as burrows. Associated molluscan fossils consist of vesicomyids and other bivalves typical of methane seeps. Fossils of predator species were also identified, but epifaunal seep organisms are notably absent. The carbonate concretions are composed of strongly 13C-depleted micrite (δ13C values as low as −46.0‰ vs. VPDB) with minor 13C-rich void-filling sparry cements. The presence of lipid biomarkers pentamethylicosane (PMI; with δ13C values as low as −119‰) and biphytane and the absence of crocetane suggests that the AOM was performed by an ANME-1-dominated archaeal community. The insights of diffusive methane seepage in the geological record gained from this study can help to better understand depositional processes of seep deposits and variations in fluid flows in both ancient and modern methane-seeping systems.
... Although the coupled metabolic activities of AOM consortia are usually recorded by distinctively depleted δ 13 C signals in the carbonate by-products (Furnes et al., 2008), less depleted δ 13 C could be produced under AOM conditions either from admixture of residual methanogenic 13 CO 2 (e.g., Claypool and Kaplan, 1974), or alternatively from extensive AOM (Whiticar, 1999;Pancost et al., 2000;Nyman et al., 2010). Importantly, as any suitable redox couple for AOM is progressively depleted, acetoclastic methanogenesis becomes the more likely diagenetic mechanism producing CO 2 in deep AOM zones (Parkes et al., 2005;Bethke, 2011). ...
... Esta reacción se produce en los sedimentos, en la interface entre las zonas OM y SR, donde el metano que proviene de capas subyacentes, se encuentra con el sulfato del agua de mar. Como resultado se origina bicarbonato, lo que aumenta la alcalinidad en el ambiente, favoreciendo la precipitación del carbonato de calcio autigénico (Valentine, 2002;Levin, 2005;Nyman et al., 2010). ...
In this paper the main evidence and features of the first fossil seep, discovered along the emerged coast of Central Chile are documented. The carbonate structure is currently preserved on the Navidad beach and is oriented N45°W, perpendicularly to the coastline. The outcrop is characterized by autigenic carbonate accumulation, containing a variety of fossils, such as bivalves, gastropods, tube worms, teredolites, microbialites and others. Calcite veins (0.4 to ~1.5 cm thick) cross the main outcrop, being indicative of the last stages of hydrocarbon fluid flow through sub-vertical fractures. The obtained values of δ13C vary between -41.4‰ PDB in the matrix and -29.5‰ PDB in bivalve shells being consistent with typical low ranges registered in hydrocarbon seeps
... Methane-rich fluids could have triggered the early lithification of the outer margin encasing the flow along vertical pathways (e.g. Clari et al., 2004;Nyman et al., 2006Nyman et al., , 2010. This phenomenon is therefore strongly dependent by the rate of methane flux toward the sea bottom as also suggested by different 13 C depletion within Stirone River chimneys. ...
... Based on (1) the occurrence of columnar concretions probably representing mineralized fluid-escape conduits, (2) the apparent lack of chemosymbiotic invertebrates and (3) the lack of banded and botryoidal aggregates of fibrous cement, the concretionary carbonates represent the plumbing system of seeps rather than their expressions just below the seafloor (cf. De Boever et al., 2009;Peckmann et al., 2009;Nyman et al., 2010;Zwicker et al., 2015). Thus, it is suggested that the non-stratabound Xigaze concretions originated from focused seepage that resulted in the establishment of an extensive plumbing system (Fig. 4E, F; cf. ...
Seep carbonates provide excellent records of past seepage activities, and have been commonly considered to preserve primary, unaltered stable carbon isotope signatures. However, late diagenetic reactions may overprint original isotopic compositions, but the mode and effect of such alterations are poorly understood. In particular, there are significant uncertainties regarding how carbon and strontium isotopic compositions of seep carbonates respond to diagenesis. This study reports recently discovered Cretaceous hydrocarbon-seep deposits from the Yarlung-Zangbo Suture Zone, Tibet, China that have experienced substantial diagenetic alteration that is shown by recrystallization and secondary veins. Unitary linear recursive analysis was applied to δ¹³C values and ⁸⁷Sr/⁸⁶Sr ratios of the seep carbonates to evaluate the degree of secondary modification and to quantitatively constrain the compositions of primary carbonates and late diagenetic fluids. The δ¹⁸O values range from − 11.8‰ to − 2.2‰, δ¹³C values from − 34.1‰ to − 12.9‰ and ⁸⁷Sr/⁸⁶Sr ratios from 0.706221 to 0.706808. The heterogeneity in isotopic compositions and the observation that the most negative δ¹⁸O values occur in samples with the most extensive recrystallization indicate significant and spatially heterogeneous modification of isotope compositions during late diagenesis. The linear correlations between δ¹³C values and δ¹⁸O values for matrix micrites (R² = 0.54), and between bulk carbonate ⁸⁷Sr/⁸⁶Sr ratios and δ¹⁸O values (R² = 0.85) are best explained by burial diagenetic overprinting of oxygen, strontium, and even carbon isotopic compositions rather than by meteoric water hypergenesis. Extrapolated values of δ¹³C and ratios of ⁸⁷Sr/⁸⁶Sr against a δ¹⁸O value of − 2‰ (average value of calcite precipitated in isotopic equilibrium with coeval Cretaceous seawater) that would characterize the primary carbonate, give an end member δ¹³C value of − 34‰ and an end member ⁸⁷Sr/⁸⁶Sr ratio of 0.7072. The end member isotopic values obtained by this extrapolation suggest that the primary seep carbonates with low δ¹³C values and high ⁸⁷Sr/⁸⁶Sr ratios were formed by anaerobic oxidation of methane near the seafloor. In contrast, the measured δ¹⁸O values and ⁸⁷Sr/⁸⁶Sr ratios reflect late diagenetic fluids represented by burial pore water characterized by a low ⁸⁷Sr/⁸⁶Sr ratio and high temperature. Our findings reveal that δ¹³C values can only be moderately and ⁸⁷Sr/⁸⁶Sr ratios can be significantly altered during late diagenesis, and show that it is possible to quantitatively assess the primary composition of diagenetically altered seep carbonates.
... Fossil seep deposits contain a wide variety of concretionary bodies (Kaufmann et al. 1996;Schwartz et al. 2003;Nyman et al. 2010;Nyman and Nelson 2011;Hendricks et al. 2012;Agirrezabala et al. 2013;Cochran et al. 2015;Wiese et al. 2015). Studies of the morphology of these concretionary bodies, their position in the outcrop, and their carbon and oxygen isotopic composition have helped elucidate the subsurface plumbing systems of seeps. ...
Study of ancient cold-methane seep deposits provides insight into the changes in seep communities over the lifetime of a seep, which are otherwise difficult to observe in modern settings. We studied 24 cold-methane seep deposits in the Upper Cretaceous (Campanian) Pierre Shale of southwestern South Dakota. These deposits were subdivided into three categories depending on their physical characteristics: (1) those with a single main conduit, few secondary pipes and concretionary bodies, and no carbonate cap, implying strong advective flow to the sedimentwater interface; (2) those with a single main conduit, a moderate number of secondary pipes and concretionary bodies, and a small carbonate cap, implying both advective and diffusive flow to the sediment-water interface; and (3) those with a single main conduit, a high number of secondary pipes and concretionary bodies, and a broad carbonate cap, implying extensive flow, but dampening at the sediment-water interface due to the presence of the large carbonate cap. We analyzed the faunal composition at all 24 seeps. The number of species ranges from five to 20. All of the seeps are dominated by baculitid ammonites, inoceramids, and lucinids (''foundation'' organisms). These species are the same as those in time-equivalent non-seep sites in the Pierre Shale and are not seep-obligate. However, in seep categories 2 and 3, the number and kind of secondary organisms increases in association with the development of the large carbonate cap. These organisms include oysters, gastropods, echinoids, sponges, crinoids, and scaphitid ammonites. We infer that these organisms appear because (1) the carbonate hardground provides a more diverse habitat allowing attachment and encrustation and (2) the bottom waters are better oxygenated and/or the level of hydrogen sulfide is reduced because the methane rich fluids are diverted away from the carbonate cap, thus providing a more suitable habitat for organisms such as scaphitid ammonites that require a well-oxygenated environment. However, even at these seeps, the number of secondary organisms usually does not exceed that of foundation organisms.
... Methane-rich fluids could have triggered the early lithification of the outer margin encasing the flow along vertical pathways (e.g. Clari et al., 2004;Nyman et al., 2006Nyman et al., , 2010. This phenomenon is therefore strongly dependent by the rate of methane flux toward the sea bottom as also suggested by different 13 C depletion within Stirone River chimneys. ...
... The PeT conditions in the Silesian basin were favorable for hydrate formation during the Oligocene and clathrites have been recognized in the Grybów unit (Bojanowski, 2007a;Bojanowski et al., in prep.). Water utilized for gas hydrate formation is enriched in 18 O relative to the surrounding pore water (Davidson et al., 1983;Harrison et al., 1982;Hesse, 2003;Hesse and Harrison, 1981) even by 4.5& Matsumoto and Borowski, 2000;Nyman et al., 2010) and depleted in ions due to the ion-exclusion effect (Ussler and Paull, 1995). Therefore, the residual water is depleted in 18 O and enriched in ions, especially in fine-grained sediments where diffusion is rather slow and the system is not perfectly open (Ussler and Paull, 1995). ...
... A number of carbonate conduits situations have been identified and catalogued to date (e.g., Jørgensen, 1992;Lewis and Marshall, 1996;Orpin, 1997;Stakes et al., 1999;Aiello et al., 2001;Díazdel-Río et al., 2003De Boever et al., 2009;Clari et al., 2004;Aiello, 2005;De Boever et al., 2006a,b;Nyman et al., 2006Nyman et al., , 2010Logvina et al., 2007;Takeuchi et al., 2007;Merinero et al., 2008Merinero et al., , 2012Campbell et al., 2010;Magalhães et al., 2012;Somoza et al., 2012;Wirsig et al., 2012;Han et al., 2013; and this issue), but many more are in all likeness still undisclosed. ...
Late Early–Late Cretaceous strata preserved at the northeastern end of the Waiau Toa/Clarence valley, northeastern South Island, New Zealand, have been central to ongoing debates concerning the end of Mesozoic subduction on the Zealandian margin of Gondwana and the initiation of extension. New geological mapping within this area at Coverham, Kekerengu and Wharekiri, has resolved complex relationships between Cretaceous stratigraphic units and faults. Results indicate that, within the interval 110–100 Ma, Champagne and lower Split Rock formations record syn-tectonic deposition by marine mass-transport processes within confined sub-basins with steep seafloor gradients. Upper Split Rock Formation and overlying Nidd Formation record progressive burial of seafloor topography between c. 100–86 Ma. Although uncertainties remain, three or four faults appear to have been low-angle structures with normal displacements that were active within the interval c. 105–89 Ma; one of these faults experienced brief reversal of offset between c. 91 and 87 Ma. The new data are most consistent with a model of subduction shutdown between c. 105–100 Ma, following impact of the Hikurangi Plateau large igneous province at the subduction margin. Widespread uplift along the margin between 97 and 95 Ma may reflect subsequent rebound of the subducted plate.
Cold seeps spread worldwide along the continental margins, which are closely related to the exploration of gas hydrates. Cold-seep carbonates have been reported to record the nature of seepage, including fluid source, sedimentary environment, and variation of seepage activity. We investigated the morphology, mineralogy, element compositions, and carbon and oxygen isotopes of 15 cold-seep carbonates collected from the Shenhu area, and compared them with 2 carbonates from the Haima cold seep, the South China Sea (SCS), to promote our knowledge of cold-seep system in SCS. Most of the Shenhu carbonates exhibit crust morphology, and some are in the form of chimneys and blocks. Their absolute (20%–65%) and relative carbonate mineral contents (mainly aragonite and calcite, with minor samples containing dolomite) vary significantly, indicating the multi-stage methane leakage in our study area. Some samples show a slight negative Ce anomaly, suggesting either the mixing of seawater or variation of the redox condition during the precipitation; the co-occurrence of strongly enriched U and Mo demonstrates anoxic condition during precipitation. The mixed genetic methane source was interpreted by δ13C of the Shenhu carbonates to range from −22.34‰ to −59.30‰ Vienna PeeDee Belemnite (VPDB), and the slight 18O-enrichment imprinted on the carbonates suggests the possible influence from hydrate dissociation. The Haima carbonates, with biogenic methane as the main gas source, were presumably formed in a stronger fluid flux by compared with our Shenhu samples.
Radish concretions exhibit a typical columnar to pear-shaped, stipe downward geometry. In Middle Jurassic mudrock in south-west Germany, radish concretions started to form around an iron-sulphide lined tube by pervasive cementation constituting an ellipsoidal parent domain in uncompacted sediment at burial depths of ≤ 5 to 8 m as recorded by 75 to 80% minus-cement porosity. Thereafter, the concretions grew vertically in compacting sediment as evidenced by laminae within the concretions being increasingly inclined towards the tips, and concomitantly decreasing minus-cement porosity. During early diagenesis, prior to septarian crack formation, bicarbonate generating the microbial cement originated within the sulphate reduction zone chiefly from anaerobic oxidation of methane and to a lesser degree of organoclastic material. Later, at 50 to 70 m burial depth, septarian cracks formed as evaluated by sedimentation–compaction analysis based on minus-cement porosity data and compressibility of similarly composed sediments. The outward-narrowing septarian cracks indicate that they formed when the concretions were still in a plastic state but already cemented sufficiently to be resistant against compaction. In this stage, up to one-quarter of the pore volume of the concretions was still open as suggested by shrinkage experiments. This pore volume, and the septarian cracks, were filled with cement termed late diagenetic. In the study area, the decompacted net-sedimentation rate was low, about 2 to 3 cm kyr⁻¹, for ca 2.5 Myr, allowing the concretions to reside for a long time within the sulphate reduction zone and to grow. Radish concretions formed within the transition zone from thick, rapidly deposited to long-term, slowly accumulating sediment.
The late Neogene marls from the Lorca, Murcia and Vera basins in S-E. Spain contains abundant dolomite nodules that were formed due to intense methane-rich fluid migration. The pathways for these fluids are evidenced by dense networks of fractures that are crossing the sedimentary layers and eventually the dolomite nodules. The fractures are generally filled by secondary fibrous gypsum that form veins of a few cm thick.
The oxygen and sulfur isotopic compositions of the gypsum veins exhibit wide ranges (−2.2 < δ¹⁸O‰ VSMOW <6.7; −22.3 < δ³⁴S‰ VCDT <10.5) that are far away from the average δ values of Tortonian-Messinian gypsum from the basins of Lorca, Fortuna and Sorbas (δ¹⁸O = 13.8 ± 2.3‰; δ³⁴S = 21.3 ± 1.0‰) precipitated from the late Neogene seawater sulfate. These low δ values of the gypsum veins clearly indicate their diagenetic origin that would have resulted from sulfide oxidation with ¹⁸O-depleted water. The isotopic compositions of the diagenetic dolomite nodules close to the gypsum veins (−0.7 < δ¹⁸O‰ VPDB <3.7; −11.9 < δ¹³C‰ VPDB <7.3) are indicative of their formation in methane-rich fluids. In this context, the formation of sulfide is related to the bacterial sulfate reduction that is associated with the anaerobic oxidation of methane. During this process, pyrite coprecipitated with dolomite, either within the dolomite framework or within conduits where the fluids were seeping. The pyrite oxidation occurred later during diagenesis when more or less oxygenated groundwaters circulated within the fractures during the sealevel drawdown of the Messinian Salinity Crisis and after the regional uplift of the sedimentary deposits in relation with the Betic cordillera tectonics.
Dolomitization has traditionally been regarded as being related to the interaction of thermally active Mg-rich fluids with poorly ordered carbonate precursors of elusive origin. Our ideas on how such precursors form have evolved rapidly since the late 1990s, and microbes are now considered key players — i.e., by providing nucleation sites and due to their capacity to regulate pore water alkalinity. Outstanding questions include what triggers the low-temperature reactions conducive to dolomite stabilization and whether or not subsurface chemolithotrophs participate in the catalysis of these reactions. Here these aspects are evaluated throughout three independent but complementary textural and spectroscopic examinations of shallow marine dolomites. First, fine-scale analyses of modern carbonate cements point to biologically mediated manganese and sulfur co-recycling as a necessary control for dolomite stabilization. Second, similar analyses of mid-Cretaceous dolomitic marlstones suggest that in the Aptian-Albian epicontinental sea of northern South America, dolomite precipitation was linked to the utilization of metals and sulfur for organic matter respiration. Reactants were transported to the extended shallow marine setting in association with episodic orbital perturbations, which also triggered high organic matter productivity and burial, and ultimately led to interstitial organogenic dolomite formation. Third, stromatolitic rocks from the Paleoproterozoic Gunflint Formation (Ontario, Canada) were interrogated in order to interpret the variable redox states of pore waters at the time of stromatolite accretion and diagenetic mineral stabilization. This study shows that diagenetic shifts associated with exogenous water mixing, together with variable burial and exhumation histories, led to the development of the temporarily and spatially restricted reaction fronts responsible for the pervasive replacement of early formed carbonate cements. Such diagenetic complexity adds difficulty to the interpretation of paleomarine geochemical conditions. Overall, this work reveals that the trace metal content of shallow marine dolomite provides information useful for the evaluation of redox conditions that govern mineral authigenesis. However, autocycles and their effect on the activity of subsurface microbes, and thus over the saturation state of minerals in coastal sediments should be carefully considered prior to regional scale paleoceanographic interpretations.
Hydrocarbon-seep carbonates were discovered to be hosted within Miocene marine mudstone in the central Western Foothills near the Kuohsing area, Central Taiwan. Here, we present field observations, petrography, mineralogy, stable carbon isotope data, as well as rare earth element compositions. We evaluate the role of diagenetic alteration on the Kuohsing seep carbonates and constrain their fluid sources and formation conditions. Four main morphologies in the field were observed, including cylindrical columns, massive forms, lenticular nodules, and stratiform bodies. Petrographically, the carbonates are predominantly composed of partially recrystallized calcite and dolomite, with abundant amounts of biogenic detritus, pyrite aggregations and unidentified filaments. Isotopic analyses show that carbon isotope values inversely vary with oxygen isotope values, indicating substantial modification of the carbon isotope compositions of the carbonates by diagenetic processes. Extremely negative δ¹³C values as low as -47.6‰ recognized as a near-primary isotopic signature recorded in the carbonates, an end member of the trend, reveals that methane was incorporated during the carbonate precipitation. On the other hand, the carbonates have well preserved primary REE compositions, exhibiting MREE enrichment, no La and Ce anomalies, and supra-chondritic Y/Ho ratios. These REE patterns suggest that the Kuohsing authigenic carbonates were precipitated from reducing seep fluids with limited admixture of seawater.
In Zakynthos Island (Greece), authigenic cementation of marine sediment has formed pipe-like, disc and doughnut-shaped concretions. The concretions are mostly composed of authigenic ferroan dolomite accompanied by pyrite. Samples with >80% dolomite, have stable isotope compositions in two groups. The more indurated concretions have δ18O around +4‰ and δ13C values between -8 and -29‰ indicating dolomite forming from anaerobic oxidation of thermogenic methane (hydrocarbon seep), in the sulphate-methane transition zone. The outer surfaces of some concretions, and the less-cemented concretions, typically have slightly heavier isotopic compositions and may indicate that concretion growth progressed from the outer margin in the ambient microbially-modified marine pore fluids, inward toward the central conduit where the isotopic compositions were more heavily influenced by the seep fluid. Sr isotope data suggest the concretions are fossil features, possibly of Pliocene age and represent an exhumed hydrocarbon seep plumbing system. Exposure on the modern seabed in the shallow subtidal zone has caused confusion, as concretion morphology resembles archaeological stonework of the Hellenic period.
Seabed fluid flow involves the flow of gases and liquids through the seabed. Such fluids have been found to leak through the seabed into the marine environment in seas and oceans around the world - from the coasts to deep ocean trenches. This geological phenomenon has widespread implications for the sub-seabed, seabed, and marine environments. Seabed fluid flow affects seabed morphology, mineralization, and benthic ecology. Natural fluid emissions also have a significant impact on the composition of the oceans and atmosphere; and gas hydrates and hydrothermal minerals are potential future resources. This book describes seabed fluid flow features and processes, and demonstrates their importance to human activities and natural environments. It is targeted at research scientists and professionals with interests in the marine environment. Colour versions of many of the illustrations, and additional material - most notably feature location maps - can be found at www.cambridge.org/9780521819503.
Early Pliocene (Opoitian) coquina limestone at Cape Turnagain rests conformably or disconformably on a thick siltstone sequence of late Miocene to early Pliocene (Kapitean — Opoitian) age.Silt and fine sand were deposited in a somewhat restricted shelf environment which became progressively shallower throughout Kapitean and early Opoitian time. Further lowering of sea level and/or uplift of the shelf during the Opoitian resulted in the formation of a narrow, current-swept barnacle bank; shell debris transported from the bank was deposited, in part, in channels eroded into the underlying sediments. The limestone at Cape Turnagain possibly accumulated at the southern tip of this barnacle bank.
Methane seeps in shallow waters in the northern Kattegat off the Danish coast form spectacular submarine landscapes - the 'bubbling reefs' - due to carbonate-cemented sandstone structures which are colonized by brightly coloured animals and plants. These structures may be 100 m2 in area and consist of pavements, complex formations of overlying slab-type layers, and pillars up to 4 m high. The carbonate cement (high-magnesium calcite, dolomite or aragonite) is C-13-depleted, indicating that it originated as a result of microbial methane oxidation. It is believed that the cementation occurred in the subsurface and that the rocks were exposed by subsequent erosion of the surrounding unconsolidated sediment. The formations are interspersed with gas vents that intermittently release gas, primarily methane, at up to 25 l h-1. The methane most likely originated from the microbial decomposition of plant material deposited during the Eemian and early Weichselian periods, i.e. 100 000 to 125 000 years B.P. Aerobic methane oxidation in the sediment was restricted to the upper 4 cm in muddy sand and to the upper 13 cm in coarse sand, Maximum aerobic methane oxidation rates ranged from 4.8 to 45.6-mu-mol dm-3 d-1. The rock surfaces and epifauna around the seeps were also sites of methane-oxidizing activity. Integrated sulphate reduction rates for the upper 10 cm of muddy sand gave 4.2 to 26.6 mmol SO42- m-1 d-1. These rates are higher than those previously reported from similar water depths in the Kattegat but did not relate to the sediment methane content. Since gas venting occurs over several km2 of the sea floor in the Kattegat it is likely to make a significant local contribution to the cycling of elements in the sediment and the water column. The rocks support a diverse ecosystem ranging from bacteria to macroalgae and anthozoans. Many animals live within the rocks in holes bored by sponges, polychaetes and bivalves. Stable carbon isotope composition (delta-C-13) of tissues of invertebrates from the rocks were in the range -17 to -24 parts per thousand, indicating that methane-derived carbon makes little direct contribution to their nutrition. Within the sediments surrounding the seeps there is a poor metazoan fauna, in terms of abundance, diversity and biomass. This may be a result of toxicity due to hydrogen sulphide input from the gas.
Recent revisions to the geomagnetic time scale indicate that global plate motion model NUVEL-1 should be modified for comparison with other rates of motion including those estimated from space geodetic measurements. The optimal recalibration, which is a compromise among slightly different calibrations appropriate for slow, medium, and fast rates of seafloor spreading, is to multiply NUVEL-1 angular velocities by a constant, α, of 0.9562. We refer to this simply recalibrated plate motion model as NUVEL-1A, and give correspondingly revised tables of angular velocities and uncertainties. Published work indicates that space geodetic rates are slower on average than those calculated from NUVEL-1 by 6±1%. This average discrepancy is reduced to less than 2% when space geodetic rates are instead compared with NUVEL-1A.
Oil seeps and stains from the East Coast Basin, New Zealand have been investigated using biomarker and stable carbon isotope analyses to determine oil-oil correlations. Oils sampled from the Raukumara Peninsula (northern East Coast Basin, North Island) and Marlborough (southern East Coast Basin, South Island) are derived from Late Cretaceous-Paleocene marine source rocks with a minor terrestrial content and are isotopically light. In contrast, oils sampled from Hawke’s Bay and Wairarapa (central and southern East Coast Basin, North Island) are derived from Paleocene marine source rocks, which contain high abundances of C30 regular steranes and 28,30-bisnorhopane, and are isotopically heavier than the other group. Biomarkers and bulk carbon isotopes show that there are at least two distinct sources of hydrocarbons in the basin.
Growth histories of contractional structures at the southern end of New Zealand's Hikurangi forearc basin have been analysed for the last c. 10 m.y. Growth data are from outcrop and seismic‐reflection profiles that contain syntectonic strata and angular unconformities, and from deformed fluvial terrace surfaces. Deformation is described for up to eight intervals of time, spanning c. 12 000 yr to 5 m.y., the ages of which were determined by biostratigraphy and tephrochronology. Reverse faults and related asymmetric folds, which strike parallel to the subduction margin and verge troughwards, experienced variable rates of shortening through time. The current period of deformation commenced at c. 1.8 Ma with displacement rates of c. 0.1–0.7 mm/yr on the main faults (i.e., Martinborough, Huangarua, and Mangaopari Faults). Before this time there were periods of accelerated deformation during the mid Pliocene (c. 3.4–2.4 Ma) and latest Miocene (c. 8.0–6.0 Ma). Therefore, shortening since 10 Ma accumulated mainly during three periods of 1–2 m.y., with structures active in the Quaternary forming in the late Miocene or earlier. Local intervals of accelerated deformation are coincident with the timing of intervals of uplift and faulting along much of the emergent forearc and cannot be attributed to local transfer of displacements between faults. Instead, these intervals of deformation appear to reflect regional changes in the kinematics of the upper plate. These changes could arise due to margin‐normal migration of strain to regions outside the forearc basin or may indicate temporal variations in the dynamics of subduction.
Active fluid venting and its surface manifestations (unique animals and carbonates) occur over the accretionary prism in the Cascadia subduction zone located off central Oregon. A large variety of authigenic carbonate deposits and unique carbonate structures have been observed from submersibles and remotely operated vehicles and recovered with aid of submersibles and bottom trawls from the outermost continental shelf and lower continental slope. The carbonate deposits range from relatively thin crusts and slabs to irregular edifices and well-formed circular chimneys that rise from 1 to 2 m above the seafloor. Mineralogically, the carbonate cement consists of aragonite, calcite, Mg-calcite, or dolomite with varying amounts of detrital constituents. Stable carbon and oxygen isotope data identify four distinct subgroups of methane-derived carbonates from several different vent sites and different fluid source zones. Subgroup I represents one vent site on the lower slope and is characterized by oxygen isotope values ranging from +6.8% to +4.7% PDB. Subgroup II represents another vent site about 1 km away and exhibits oxygen values of +3.4% to +4.9% PDB. Carbon isotopic values range from -40.96 to -30.23% versus -44.26 to -53.44% PDB, respectively, for the two vents. An irregular edifice from the outer shelf has the same isotopic composition as subgroup II. A companion study shows that the expelled fluids contain largely biogenic methane and methane-derived dissolved carbonate; a shallow fluid source zone (
Hydrate Ridge is part of the accretionary complex at the Cascadia margin and is an area of widespread carbonate precipitation induced by the expulsion of methane-rich fluids. All carbonates on Hydrate Ridge are related to the methane-carbon pool either through anaerobic methanotrophy or through methanogenesis. Several petrographically distinct lithologies occur in boulder fields or in massive autochtonous chemoherm complexes which include methane-associated diagenetic mudstones and venting-induced breccias. The mudstones result from methane diagenesis in different sediment horizons and geochemical environ-ments related to very slow methane venting. Cemented bioturbation casts occur as fragments, complex framework or as clasts together with bivalve shells as part of intraformational breccias, which are restricted to chemoherm complexes. Here, fluids ascend from the sub-seafloor and support aragonite-dominated car-bonate precipitation near or at the sediment surface. Voids within mudclast brec-cias are either aragonite-rich indicating a formation near the surface at vent sites or are cemented by dolomite, which indicates formation in deeper parts of the sediment column. Brecciation is caused by tectonic or slump processes. In addi-tion, we recognized a direct relationship between gas hydrates and sediment frac-turing as well as the oxygen isotope composition of carbonate lithologies. Such gas hydrate-associated carbonates either show layered megapores and veins as relics of the original gas hydrate fabric or consist of aragonite-cemented intra-clast breccias formed by growing and decomposing gas hydrate near the sedi-ment surface. Both rock fabrics and the enrichment of 18 O in high Mg-calcite demonstrate carbonate-forming mechanisms of gas hydrate.
The Gambier Limestone, a bryozoan-rich, cool-water car-bonate of Late Eocene to Early Miocene age in the Otway basin of southeastern Australia, is about one-third variably dolomitized lime-stone and dolostone. Individual dolomite crystals range from 10 to 500 m and are of three types: (1) silt-size crystals (4–64 m diameters) having a brightly luminescent core (10–20 m) of nearly stoichiometric dolomite with 1 mol% MnCO 3 and SiO 2 but no Fe, surrounded by a thin, dull or alternating dark and bright CL cortex that is nonstoi-chiometric with 44–46 mol % MgCO 3 but sharp to diffuse zoning in Mn and Fe, (2) sand-size crystals, which also have a brightly lumines-cent and stoichiometric core and dark and bright non-stoichiometric thin inner cortex, but are mostly a thick outer cortex (at ca. 50 m diameter) that is nonluminescent and nonstoichiometric with some Fe but no Mn, and (3) identical sand-size crystals with a variably leached core and inner cortex that is either a void or a void filled with late calcite cement. These three crystal populations represent two distinct dolomites and their alteration product. The smallest of the silt-size crystals, which are rarely preserved, are also the cores of the larger crystals upon which grew an inner and outer cortex of somewhat different composition. The 18 O values of dolomite rhombs (1.6 to 2.9 ‰) correlate positively with 13 C values (0.7 to 3.0‰), with the lowest values from silt-size or small sand-size crystals and the highest values from large sand-size crystals with leached, unfilled cores. Low and variable 18 O and 13 C values in conjunction with high and variable Mn and Fe contents in both the core and inner cortex of all crystals are consistent with for-mation from a mixture of brackish water and seawater. Higher values for the outer cortex in sand-size crystals are typical of those expected for precipitation from normal or near-normal seawater. Low Sr, Mn, and Fe contents in the largest crystals, in conjunction with fluid inclu-sions of seawater salinity in the outer cortex, are also consistent with the bulk of the large crystals having precipitated from seawater. Using the Sr-isotope evolution curve for Cenozoic seawater, Sr-isotope ratios of the dolomites can be divided into four distinct groups, which cor-respond to times of major transgressions. This Cenozoic example, in which dolomite petrography and crystal chemistry can be explained in terms of simple transgression–regression, offers a simple sedimento-logical explanation for many similar dolomites where processes of for-mation cannot be so easily constrained.
Micritic limestone-marl alternations make up the major part of the Silurian strata on Gotland (Sweden). Their position on
the stable Baltic Shield protected them from deep burial and tectonic stress and allowed the preservation of early stages
of burial diagenesis, including lithification. In the micritic limestones certain characteristics have been preserved (e.g.,
pitted microspar crystals, sharp boundaries between microspar and components, lack of deformation phenomena) that offer insights
into their formation. We suppose the formation of these micritic limestones and limestone-marl alternations to be based on
a rhythmic diagenesis within an aragonite solution zone (ASZ) close below the sediment surface. The micritic limestones are
the product of a poikilotopic cementation of carbonate muds which consisted of varying portions of aragonitic, calcitic and
terrigenous matter. Their microspar crystals show the primary size and shape of the cements lithifying the original carbonate
mud. Dissolution of aragonite in the marls provided the carbonate for the lithification of the limestones. By cementation,
the limestone beds evaded further compaction. The marls, which already underwent a volume decrease by aragonite depletion,
lacked cement and became more and more compacted due to increasing sedimentary overburden. Although field observations show
that primary differences in material influence the development of limestone-marl alternations they are not required for their
formation.
In central California, Maastrichtian–Danian shales of the Moreno Formation preserve a fluid migration system that developed along the western margin of the former Great Valley forearc basin. The system consists of a network of interconnected sandstone intrusions linked to overlying fossiliferous carbonates whose geochemistry, fauna, and petrology are characteristic of active cold seeps. The system is approximately 800m thick and represents episodic migration and seafloor expulsion of fluids over at least 0.5106years. This locality has the most extensive exposure yet discovered of a complete seep system, from underlying fluid pathways to seep deposits and associated communities.
A significant fraction of the products of organic matter diagenesis is water soluble. Some products react directly to precipitate sedimentary minerals: carbonates, sulphides and phosphates. Low-temperature reactions are mostly microbial whereas later (deeper) reactions are thermally induced. Most of the soluble products are acidic and do not, by themselves, stimulate carbonate mineral precipitation. Reduction of Fe(III) by organic matter, however, causes massive increase in alkalinity. The balance between this and the microbial reactions is a major controlling influence on patterns of mineral diagenesis. Organic acids are produced during catagenesis and can cause mineral dissolution, both of carbonates and silicates. The permeability and porosity of sedimentary rocks may be modified with obvious consequences for petroleum geology. The amounts and types of acids generated are not well known. Equally poorly documented are the Fe(III)-organic matter reactions, yet these must affect both mineral authigenesis and organic maturation.
The East Coast region is an area ofabout 75 000 km2, about half of which is offshore, extending from East Cape in the northeast to Kaikoura in the southwest, a distance of more than 500 km. The region straddles the active Hikurangi subduction margin between the Australian and Pacific plates. The stratigraphic succession consists of three elements: (1) Cretaceous rocks ranging from paralic sandstones to bathyal mudstones and flysch deposited in a variety of compressional and extensional tectonic settings prior to and during rifting from Australia; (2) latest Cretaceous and Paleogene rocks, mainly mudstone and micrite, reflecting post-rift foundering of the New Zealand region; (3) Miocene rocks dominated by bathyal flysch and mudstone but punctuated by neritic sands and limestones, and Pliocene rocks characterised by alternating siliclastics and coarse bioclastic limestones. Good quality seismic data cover much of the offshore part of the region, but are generally of poorer quality and coverage onshore. The inferred top-Cretaceous seismic reflector, which approximates the position of Late Cretaceous-Paleocene marine source rocks, is at over 3000 m depth over large areas and reaches depths greater than dominantly offshore and in the south. There are few Paleogene structures, reflecting a passive margin phase. In the late Paleogene there was a plate margin to the north which locked in the earliest Miocene, causing obduction of oceanic crust in the north of the region and the emplacement of a series of allochthonous nappes forming the East Coast Allochton. The present Hikurangi oblique subduction margin formed at about this time, and the Neogene records a varied history of strike-slip, compressional and extensional deformation. Numerous oil and gas seeps demonstrate the region's petroleum potential, and significant gas was found in the two offshore wells drilled. The most likely source rock in the deeper parts of the region is the Paleocene Waipawa Formation, a marine black mudstone with TOCs around 2-6% and S2 hydrocarbon yields of 5-20 kg per tonne of rock, with both oil and gas potential. The formation is widespread in outcrop and probably extends offshore. The Cretaceous-Paleocene Whangai Formation, a widespread marine mudstone underlying the Waipawa Formation, also has generative potential, as do some earlier Cretaceous rocks, particulaly those with detrital organic matter. Potential reservoir units are terrestrial fan and alluvial conglomerates, paralic and shelfal sand bodies, slope channel systems, bathyal fan deposits, shallow marine limestones and units with secondary fracture porosity. Late Cretaceous sandstones locally have good porosity and permeability characteristics but most Cretaceous units are generally tighter. Potential Paleogene reservoirs are mainly fractured siliceous shales and a few units of greensand. Miocene sands offer locally excellent reservoir potential, although quality is variable in some bathyal units. The Pliocene limestones all have very good potential although quality decreases with increasing age and burial. Maturation modelling indicates considerable variability in the timing of generation and expulsion within the basin. In some places, Cretaceous marine source rocks may have expelled most of their oil before many of the Neogene potential reservoir sandstones were deposited and before Neogene trap formation. Oils from Cretaceous source rocks in these areas are therefore most likely to be found in Cretaceous plays or as secondary accumulations in Neogene plays. Gas from Cretaceous sources was generated during the Paleogene in some areas, but most was generated during the Neogene. In most places, Paleocene source rocks have started to expel hydrocarbons in only the last few million years, after the main period of reservoir and trap development, and these have higher preservation potential. In some deeper areas, such as below the allochthon and in Cook Strait, modelling suggests that there was a expulsion of oils from Paleocene source rocks during the Middle and Late Miocene. Differences in kinetic parameters are likely in some cases to have caused shallower Paleocene type II source rocks to generate oil and gas before more deeeply buried Cretaceous type III source rocks. Most generation appears to have been only over the last few million years, during or after deposition of reservoir units and the main development of structural closures, some of which are more than 40 km2 in extent. The East Coast region has proven hydrocarbon generation, good reservoir units and large closures, and the timing of expulsion is favourable in many areas. The region warrants further exploration.
Slope forms and inferred erosion processes are found to closely reflect the lithologic characteristics of three groups of Cretaceous mid Tertiary sedimentary rocks. Clay mineralogy, the proportions of clay and other minerals, and the presence or absence of carbonate cement are found to be important in determining both slope form and process in overconsolidated shales and marls and in indurated muddy sandstones. Localised leaching of carbonate cement by acid- sulphate weathering of pyrite appears to be an important control on the location of major isolated complex failures in Cretaceous-Tertiary shales in which the clay fraction is dominated by montmorillonite. -Authors
Dissolution of feldspar and mica and precipitation of kaolinite require a through flow of meteoric water to remove cations such as Na+ and K+ and silica. Compaction driven pore-water flow is in most cases too slow to be significant in terms of transport of solids. The very low solubility of Al suggests that precipitation of new authigenic clay minerals requires unstable Al-bearing precursor minerals. Chlorite may form diagenetically from smectite and from kaolinite when a source of Fe and Mg is present. In the North Sea Basin, the main phase of illite precipitation reducing the quality of Jurassic reservoirs occurs at depths close to 4 km (130-140°C) but the amount of illite depends on the presence of both kaolinite and K-feldspar. Clay mineral reactions in shales and sandstones are very important factors determining mechanical and chemical compaction and are thus critical for realistic basin modelling.
Calcite cement derived intraformationally in seven stratigraphic units of marine origin is distributed heterogeneously at the outcrop scale. Sandstone beds intercalated with calcareous shale older than Pliocene tend to be completely cemented, whereas stacked sandstone beds that lack shale interbeds have calcite cement in the form of tightly cemented concretions that make up only 10-30% of a bed. Patterns of concretions within beds are remarkably varied and include both random and uniform spacing. There is no preference of concretions for shell-rich layers. The lack of strong textural or compositional controls on the localization of calcite cement suggests the preeminence of highly localized hydrologic factors in determining the spatial distribution of authigenic pore-filling calcite. Faults apparently served as fluid conduits and were selectively cemented. In general, only sandstones intercalated with shale are totally cemented. -from Authors
The temperature and salinity of the water at the ocean floor has been estimated by extrapolation of selected serial station data. Plots of extrapolated bottom water temperatures and salinities against bottom depth are presented, together with a chart showing the regional distribution of bottom water temperature. Discussion of the results in terms of water masses is offered.
Oxygen isotope evidence indicates high but variable delta18O values in benthic foraminiferal calcite during the latest Miocene and earliest Pliocene. These high values may represent increases in global ice volume and associated sea-level fall. The delta18O record resembles glacial/interglacial cycles, but with only one-third the amplitude of the late Pleistocene signal. This variability may reflect instability in the Antarctic ice sheet, and palaeomagnetic correlation points to an isotopic event coinciding with the isolation and desiccation of the Mediterranean basin during the latest Messinian.
Chaotic deposits are frequently reported in the geological literature and are commonly interpreted as olistostromes or tectonic melanges. A chaotic complex in the Cenozoic succession of Monferrato (NW Italy) consists of interbedded mud breccia and burrowed silty clays that are pierced by sheared mud breccias and embed carbonate-cemented blocks. These may be represented by microcrystalline limestones or strongly cemented matrix-supported breccias locally containing remains of chemosymbiotic organisms (lucinid bivalves). Moreover, cylindrical concretions, up to 15 cm in diameter and 1 m long, occur in the chaotic complex and crosscut bedding planes at high angles. The cement of all these lithified portions is mainly dolomite characterized by low delta(13)C values (from -10.3 to -23parts per thousand PDB) and delta(18)O values up to + 7parts per thousand PDB. The delta(13)C values testify to precipitation of carbonates induced by microbial oxidation of methane, whereas the markedly positive delta(18)C signature, ubiquitous in the cylindrical concretions, is the evidence for the presence and destabilization of gas hydrates. The studied section provides a well-exposed example of the geological record of the birth, life, and death of a mud volcano. Unsheared, soft mud breccias represent mud flows along the flanks of the volcano, whereas sheared mud breccias are the result of the injection of unconsolidated overpressured fine-grained sediments, both taking place during "eruptive" phases. They were followed by more quiet stages of hemipelagic sedimentation, burrowing, and CH4 seeping. The cylindrical concretions represent the first described ancient example of the chimneys observed in present-day mud-volcano settings. They are the remnants of a cold-seep plumbing network that crosscut the mud volcano edifice. The chimneys were the pathway for the expulsion toward the sea floor of gas- and sediment-charged fluids likely originated from destabilization of methane gas hydrates. The association of mud breccias and methane-derived carbonates may not be due to mass gravity flows but can be primary and, therefore, is a diagnostic criterion for recognizing chaotic deposits due to mud volcano activity in the geological record.
