Authigenic Greigite as an Indicator of Methane Diffusion in Gas Hydrate-Bearing Sediments of the Hikurangi Margin, New Zealand

Authigenic ferrimagnetic iron sulfides, essentially greigite (Fe$_{3}$S$_{4}$), are commonly found in gas hydrate-bearing marine sediments of active accretionary prisms. Greigite is a by-product, either intracellular or extracellular, of microbial activity, and therefore provides good indication of microbial processes which are closely related to the occurrence of gas hydrate. A high-resolution rock magnetic study was conducted at Site U1518 of International Ocean Discovery Program Expedition 375, located in the frontal accretionary wedge of the Hikurangi Margin, offshore New Zealand. Samples were collected throughout the entire recovered stratigraphic sequence, from the surface to ∼492 m below seafloor (mbsf) which includes the Pāpaku fault zone. This study aims to document the rock magnetic properties and the composition of the magnetic mineral assemblage at Site U1518. Based on downhole magnetic coercivity variations, the studied interval is divided into five consecutive zones. Most of the samples have high remanent coercivity (above 50 mT) and first-order reversal curves (FORC) diagrams typical of single-domain greigite. The top of the hanging wall has intervals that display a lower remanent coercivity, similar to lower coercivities measured on samples from the fault zone and footwall. The widespread distribution of greigite at Site U1518 is linked to methane diffusion and methane hydrate which is mainly disseminated within sediments. In three footwall gas hydrate-bearing intervals, investigated at higher resolution, an improved magnetic signal, especially a stronger FORC signature, is likely related to enhanced microbial activity which favors the formation and preservation of greigite. Our findings at the Hikurangi Margin show a close linkage between greigite, methane hydrate and microbial activity

Influence of Early Low-Temperature and Later High-Temperature Diagenesis on Magnetic Mineral Assemblages in Marine Sediments From the Nankai Trough

Funding Information: This research used samples and data provided by the International Ocean Discovery Program (IODP). The authors thank the Marine Works Japan staff at the Kochi Core Center for support during sampling. This work was supported by the Japan Society for the Promotion of Science Grant-in-Aid for Science Research (grant 17K05681 to Myriam Kars), the German Research Foundation (DFG grants 388260220 to Male Koster and Susann Henkel, and 408178672 to Florence Schubotz), and the Australian Research Council (grant DP200100765 to Andrew P. Roberts). The authors also thank two anonymous reviewers for their constructive comments and Editor Joshua Feinberg for handling the manuscript.Peer reviewedPublisher PD

Hot fluids, burial metamorphism and thermal histories in the underthrust sediments at IODP 370 site C0023, Nankai Accretionary Complex

This research used samples and data provided by the International Ocean Discovery Program (IODP). The authors are grateful to the IODP and the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT). We thank crew, drilling team, geologists and lab technicians on D/V Chikyu and the staff of the Kochi Institute for Core Sample Research for supporting operations. This work was supported by the ECORD research grant [2017 to MYT]; and the NERC grant [NE/P015182/1 2017 to SAB]. ZW acknowledges technical support provided by Colin Taylor at the University of Aberdeen. Petromod 2017 was provided by Schlumberger. VBH and KUH acknowledge funding from the Deutsche Forschungsgemeinschaft through the Cluster of Excellence, The Ocean Floor – Earth’s Uncharted Interface“ and Project Grant HE8034/1-1 2019. This is a contribution to the Deep Carbon Observatory.Peer reviewedPublisher PD

Izu-Bonin-Mariana Rear Arc: The Missing Half of the Subduction Factory

4GT) lies in the western part of the Izu fore-arc basin, ~60 km east of the arc-front volcano Aogashima, ~170 km west of the axis of the Izu-Bonin Trench, 1.5 km west of Ocean Drilling Program (ODP) Site 792, and at 1776 meters below sea level (mbsl). It was drilled as a 150 m deep geotechnical test hole for potential future deep drilling (5500 meters below seafloor [mbsf]) at proposed Site IBM-4 using the D/V Chikyu. Core from Site U1436 yielded a rich record of Late Pleistocene explosive volcanism, including distinctive black glassy mafic ash layers that may record large-volume eruptions on the Izu arc front. Because of the importance of this discovery, Site U1436 was drilled in three additional holes (U1436B, U1436C, and U1436D), as part of a contingency operation, in an attempt to get better recovery on the black glassy mafic ash layers and enclosing sediments and to better constrain the thickness of the mafic ash layers. IODP Site U1437 is located in the Izu rear arc, ~330 km west of the axis of the IzuBonin Trench and ~90 km west of the arc-front volcanoes Myojinsho and Myojin Knoll, at 2117 mbsl. The primary scientific objective for Site U1437 was to characterize “the missing half of the subduction factory”; this was because numerous ODP/Integrated Ocean Drilling Program sites had been drilled in the arc to fore-arc region (i.e., ODP Site 782A Leg 126), but this was the first site to be drilled in the rear part of the Izu arc. A complete view of the arc system is needed to understand the formation of oceanic arc crust and its evolution into continental crust. Site U1437 on the rear arc had excellent core recovery in Holes U1437B and U1437D, and we succeeded in hanging the longest casing ever in the history of R/V JOIDES Resolution scientific drilling (1085.6 m) in Hole U1437E and cored to 1806.5 mbsf

Calibration et Application du géothermomètre magnétique MagEval dans les roches sédimentaire

Pour évaluer la température d’enfouissement subie par les roches sédimentaires, une large gamme de géothermomètres est disponible, basés sur les constituants organiques ou minéralogiques de ces roches. Comme pour toutes les techniques expérimentales, elles présentent des avantages et des inconvénients. Dans cette thèse, nous utilisons une approche magnétique pour estimer la température d’enfouissement. Dans une première partie, nous avons étudié l’assemblage magnétique de puits sélectionnés à travers le monde pour mieux caractériser le géothermomètre magnétique MagEval. Deux calibrations ont pu être établies. Pour décrire la relation entre la température maximale d’enfouissement subie par les roches et leur assemblage magnétique, nous avons réalisé des expériences de chauffe en laboratoire de 50 à 130°C sur des argilites non métamorphosées. Les chauffes expérimentales ont montré que des nanominéraux magnétiques sont continuellement produits avec la température. Dans une deuxième partie, nous avons étudié les propriétés magnétiques des roches sédimentaires dans deux sites géologiques analogues pétroliers : le bassin des Grès d’Annot dans le SE de la France (température d’enfouissement 60-250°C) et les chaînes plissées de la Valley & Ridge Province dans les Appalaches, Etats-Unis (température d’enfouissement _120-200°C). Ces études suggèrent une évolution des principaux minéraux magnétiques avec la température. Magnétite, nanogoethite et pyrrhotite sont principalement formées. Les différents résultats obtenus dans cette thèse nous ont permis de proposer une évolution des minéraux magnétiques en fonction de la maturité des roches et de la température.To evaluate the burial temperature experienced by sedimentary rocks, a wide range of geothermometers is available, based on both organic and inorganic constituents of these rocks. Like all experimental techniques, they show limitations. In this thesis, we used a magnetic approach to estimate burial temperature. In a first part, we studied the magnetic assemblage of selected boreholes over the world to better characterize the magnetic geothermometer MagEval. Two calibrations were established. To assess the relationship between the peak burial temperature experienced by the rocks and their constitutive magnetic minerals, we conducted laboratory heating experiments from 50 to 130°C on unmetamorphosed claystones. The experimental heating showed that nano magnetic minerals are continuously produced with temperature. In a second part, we investigated rockmagnetic properties of sedimentary rocks from two geological plays of petroleum interest : the Grès d’Annot basin in SE France (burial temperature 60-250°C) and the fold-and-thrust belts of the Valley & Ridge Province in the Appalachians, USA (burial temperature _120-200°C). These studies suggested an evolution of the main magnetic minerals with temperature. Magnetite, nanogoethite and pyrrhotite are mainly formed. All the conducted analyses lead us to propose an evolution of the magnetic minerals as a function of the maturity of the rocks and temperature

Rock magnetic data of IODP Hole 370-C0023A

Hemipelagic sediments contained in 7 cc plastic cubes were analyzed for paleomagnetic and rock magnetic properties. Samples were collected from Hole C0023A drilled during International Ocean Discovery Program (IODP) Expedition 370, off Cape Muroto, Shikoku Island, Japan, which took place in 2016 (Heuer et al., 2017, https://doi.org/10.14379/iodp.proc.370.2017). A series of magnetic measurements were carried out at the Center for Advanced Marine Core Research, Kochi University, Japan. These analyses include magnetic susceptibility, natural remanent magnetization and its alternating field demagnetization, anhysteretic remanent magnetization, and isothermal remanent magnetization. Detailed rock magnetic measurements, which include hysteresis parameters, characterize magnetic mineral assemblages in terms of abundance, grain size, and composition. For further information on the methodology, please refer to “Read Me” document

Rock magnetic properties of IODP Holes 375-U1518E and 375-U1518F

Hemipelagic sediments contained in 7 cc plastic cubes were analyzed for paleomagnetic and rock magnetic properties. Samples were collected from Holes U1518E and U1518F drilled during International Ocean Discovery Program (IODP) Expedition 375, northern Hikurangi Margin, New Zealand, which took place in 2018 (Wallace et al., 2019, https://doi.org/10.14379/iodp.proc.372B375.2019). These analyses include magnetic susceptibility, natural remanent magnetization (NRM) and its alternating field (AF) demagnetization, anhysteretic remanent magnetization (ARM), and isothermal remanent magnetization (IRM). Detailed rock magnetic measurements, which include hysteresis parameters, aim at characterizing the magnetic mineral assemblages. For further information on the methodology, please refer to “Read Me” document

Authigenic greigite as an indicator of methane diffusion in gas hydrate- bearing sediments of the Hikurangi Margin, New Zealand

Authigenic ferrimagnetic iron sulfides, essentially greigite (Fe3S4), are commonly found in gas hydrate-bearing marine sediments of active accretionary prisms. Greigite is a by-product, either intracellular or extracellular, of microbial activity, and therefore provides good indication of microbial processes which are closely related to the occurrence of gas hydrate. A high-resolution rock magnetic study was conducted at Site U1518 of International Ocean Discovery Program Expedition 375, located in the frontal accretionary wedge of the Hikurangi Margin, offshore New Zealand. Samples were collected throughout the entire recovered stratigraphic sequence, from the surface to ∼492 m below seafloor (mbsf) which includes the Pāpaku fault zone. This study aims to document the rock magnetic properties and the composition of the magnetic mineral assemblage at Site U1518. Based on downhole magnetic coercivity variations, the studied interval is divided into five consecutive zones. Most of the samples have high remanent coercivity (above 50 mT) and first-order reversal curves (FORC) diagrams typical of single-domain greigite. The top of the hanging wall has intervals that display a lower remanent coercivity, similar to lower coercivities measured on samples from the fault zone and footwall. The widespread distribution of greigite at Site U1518 is linked to methane diffusion and methane hydrate which is mainly disseminated within sediments. In three footwall gas hydrate-bearing intervals, investigated at higher resolution, an improved magnetic signal, especially a stronger FORC signature, is likely related to enhanced microbial activity which favors the formation and preservation of greigite. Our findings at the Hikurangi Margin show a close linkage between greigite, methane hydrate and microbial activity

Investigating the effects of high temperature and a deep SMTZ on rock magnetic properties at Site C0023, IODP Expedition 370

In 2016, International Ocean Discovery Program (IODP) Expedition 370 drilled Site C0023 in the Nankai Trough, off Cape Muroto (Shikoku Island, Japan, NW Pacific Ocean) [1]. The aim of this expedition was to explore the limits of life in the deep subseafloor sediments in a high temperature environment (up to 120°C), and to investigate, among other objectives, the processes at the biotic-abiotic transition. A deep sulfate-methane transition zone (SMTZ) was identified between 630 and 750 meters below sea floor (mbsf). Based on the magnetic data profiles and results from previous ODP expeditions in the area, four magnetic zones were defined mostly reflecting changes in detrital supply and alteration/diagenetic features. Here, a rock magnetic study is conducted in order to document the downhole changes in magnetic properties and magnetic mineralogy (content, grain size and composition of the magnetic mineral assemblage) related to post-depositional diagenetic processes from 200 to 1100 mbsf, with a focus on the deep SMTZ. Natural remanent magnetization and its alternating-field demagnetization, magnetic susceptibility and acquisition of isothermal remanent magnetization are measured on 225 discrete samples for concentration and composition of the magnetic assemblage. Hysteresis properties and first order reversal curves are measured on respective dry powders for magnetic grain size study and composition of the magnetic assemblage. The preliminary rock magnetic results are presented and discussed based on the shipboard inorganic geochemical data. They will be compared to another identified deep SMTZ at IODP Expedition 350 Site U1437 in the Izu Bonin rear arc (NW Pacific Ocean). [1] Heuer, V. et al. (2017) Expedition 370 Preliminary Report. International Ocean Discovery Program. http://dx.doi.org/10.14379/iodp.pr.370.201

Burial, claystones remagnetization and some consequences for magnetostratigraphy

International audienceWe investigate the broad lines of magnetic mineral formation for non-metamorphic claystones. More particularly, we focus on the formation of magnetite from c. 20 day-experiments aiming to reproduce burial conditions. It is shown that the sole action of temperature from 50 °C to 250 °C leads to the formation of magnetite. The neoformed magnetites carry a chemical remanent magnetization which equates at least the natural remanent magnetization. We propose a schematic of burial with three magnetic windows where a chemical remanent magnetization superimposed the natural remanent magnetization. These are the greigite window (subsurface), the magnetite window (depth > 2 km) and the pyrrhotite window (depth > 6 km). The formation of magnetic minerals has profound consequences for the magnetostratigraphy record. We propose a conceptual model that shows that the continuous production of magnetite during burial may result in magnetozones that have no relation to the age of the sediment