Antonio Fernando Menezes Freire (1,2,3), Toshihiko Sugai (1), Ryo Matsumoto (2)fernando@nenv.k.u-tokyo.ac.jp

(1) Department of Natural Environmental Studies, University of Tokyo, 524, Environmental Bldg. 5-1-5, Kashiwanoha Campus, Chiba 277-8563 Japan(2) Department of Earth and Planetary Science, University of Tokyo, 7-3-1, Hongo Campus, Bunkyo-ku, Tokyo 113-0033 - Japan

(3) Petróleo Brasileiro S/A - PETROBRAS/E&P-EXP/GEO/MSP, Av. Chile, 65, sala 1301, 20031-912, Rio de Janeiro - RJ - Brazil

THE STUDY OF THE GAS HYDRATE BEARING-SEDIMENTS FROM JOETSU BASIN, EASTERN MARGIN OF JAPAN SEA

Interbedded dark gray thinly laminites and dark

ke a correlation between samples collected in the Pacific

MAIN PURPOSESA) To understand the sedimentar history of the Late Quaternary using the stratigraphic and geochemical records from piston- cores collected on a gas hydrate area located on the Eastern Margin of Japan Sea, south of the Sado Islands (Figs. 01 and 02)B) To make a correlation between these records on Japan Sea and those observed on the drilling core CK-06 on the Eastern Margin of the Pacifc Ocean, east of Shimokita Peninsula (Fig. 01).C) To infer the methane flux variations along the geologic time using geochemical data.

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So, it is possible to use this criteria

- As organic matter, generated by plankton, removes C selectively from the surface water, planktonic The primary carbon source for marine

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Holocene: Straits more deep and large promoted a

C δCδ13

THE NATURE OF ORGANIC MATTER: MARINE vs. TERRESTRIAL- TOC and C content indicate the origin and intensity of organic matter production. - warming of sea water and rising of sea level.

- Pleistocene: cold temperatures and sea level dropping (~120m at LGM). Few species were available, and the organic matter production was weak. The study area was a big bay with poor sea water circulation conditions (Figure 5);

foraminifera tests becomes enriched in (Burdige, 2006). phytoplankton is seawater bicarbonate, with a of ~0‰. In contrast, land plants use atmospheric

- Terrestrial Plants has relatively high C/N ratios of >12 and marine organic matter have C/N ratio <12 [Lamb, 2006]. Figures 7 and 8 show graphics with these data.

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- As a result of all of these factors, generally has a C of around -17‰ to δ13marine organic matter -22‰ and of around -25‰ to -28‰ [Burdige, 2006] [Lamb, 2006].terrestrial organic matter

better sea water circulation (Figure 5). More species arrived from the Pacific Ocean increasing the organic matter production.

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Cδ13 CO as their carbon source, with of around -7‰.2

ABSTRACTRecently, we recognized active methane venting and gas hydrates, which are widely distributed on just below the sea floor in the Joestu basin, eastern margin of Japan Sea. This study has the intention to give support for future works, understanding the Late Quaternary history of the study area. brown to gray bioturbated units are common throughout the Quaternary sediments of the Japan Sea, and have been often explained in terms of glacio-eustatic sea-level changes. These layers have a very good correlation because they occur in all Japan Sea. We used total organic carbon (TOC), nitrogen content and carbon isotopic composition of the gas hydrates bearing-sediments in order to identify the nature of the organic matters present in the study area and to maOcean. Associated with XRD analysis, these data helped us to locate the Holocene/Pleistocene boundary, to identify key stratigraphic surfaces, and to recognize sulfate-methane interfaces. Different SMI occurs due methane flux variation with the geologic time. Age control was madeby tephra layers identification and correlation.

TOTAL ORGANIC CARBON AND C CONCENTRATIONSThe Holocene/Pleistocene Boundary- Clear TOC and C curves increasing upward;- This shift depth marks the boundary Holocene (higher TOC and heavier d13C isotope)/Pleistocene (lower TOC and lighter d13C isotope);- The pattern is the same along Japan Sea and there is a very good

correlation with the Pacific Ocean. to infer the boundary Holocene/Pelistocene (Figures 3 and 4).

U-OKI Tephra Layer (~10.7Ka)

TERRIGENOUS MATERIAL INPUT-The boundary Holocene/Pleistocene can be marked by using clay minerals, quartz and feldspars content (Figure 6); -During the LGM, eustatic sea level lowering120m and restricted or completely blocked the inflow into the study area [Oba et al. 1991]. River`s mouths were close to the slope and the discharge form ice melting with sediments in suspension occurred directly over this location (Figure 5);-At Pleistocene, the poor sea water circulation on the study area could not spread fine grain floated sediments and it stays at suspension for more time. Little by little, clay minerals sunk to the sea floor. -At the Holocene, the sea level rising induced a good sea water circulation and clay minerals were washed over. At the same time, the increasing of the weathering because to the melt of ice in response of warmer climate, induced quartz and feldspars transportation by rivers and rapidly precipitate to the sea floor.

Figure 06. PC-701 clay minerals, quartz, feldspars and quartz/feldspars ratio profiles.The boundary between the Holocene and Pleistocene could be marked by TOC and C isotopic concentration how discussed before but, also, this boundary can be identified using clay minerals, quartz and feldspars content.

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vvvv

Fig. 07:a) Crossplot TOC x C data from CK-06 (crosses) and UT-07 (squares). Three groups can be seen: relative higher TOC values and heavier than~-22‰ (marine phytoplankton production); relative medium TOC and between ~-22‰ and ~-25‰ (mixed or non determinate); and relative lower TOC and lighter than ~-25‰ (vascular land plants). Crossplot TOC x data from UT-07 samples. PC-701, located far from the coastal line and into a typically depositional site, shows a large range of values and indicate both terrestrial and marine organic matter source. The other cores have a small range between terrestrial to mixed organic matter, according Burdige [2006].

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CC

C C

Note that some samples are located on a non determineted source because highnitrogen content, tipically of marine environments. The mixed and terrestrial

Figure 08 - Typical C and C/N ranges for organic inputs to coastal environments.

nature at Pleistocene is also clear. Modified from Lamb et al. 2006.

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SULFATE-METHANE INTERFACE- Sea water and sediment pore water have a lot of ions dissolved (Figure 9);- The sediment particles also have cations and anions adsorbed mainly on clay minerals; - When a methane flux occurs at the sea floor, an oxidation of methane occurs. So , Co and H S are not stable and the presence of disponible ions induce the reaction. Barite, calcite, aragonite, dolomite and pyrite are commom authigenic minerals that precipitate around the sulfate-methane interface (SMI) The region where sulfate becomes to zero is called SMI (Figure 10) (Dickens, 2001).- Samples collected from UT-07 cruise shows some “fronts” of barite, calcite and pyrite (Figures 11, 12, 13) - Because methane flux can vary with time, SMI can be shallower or deeper accoding the flux intensity- Depending on the time that SMI is stable at the same depth, the reaction will be more effective.

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CONCLUSIONSThe late Quaternary correlation between Japan Sea and the Pacific Ocean is possible using TOC and C increased pattern. This pattern indicates more organic matter production during Holocene and the

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δ13C increased pattern upward suggests a phytoplankton organic matter production. The poor sea water circulation at Pleistocene, due to the drop of sea level at LGM, caused a poor spreading of clay minerals, and, little by little, it was sunk to the sea bottom. At Holocene, the rising of the sea level induced a good sea water circulation and clay minerals were easily washed over seaward. At the same time, the climate warm increasing induced the snow melt on the mountains located near the shoreline of Niigata Prefecture, causing the increasing of weathering. Because this, quartz and feldspars were delivered by rivers, arriving to Joetsu Basin and sinking to sea floor faster than clay minerals.Geochemical records of sulfate-oxidation of methane is present by several peaks of calcite, barite, pyrite and sulfur. At least two sets of peaks are present and represent different stages of the sulfate methane interface (SMI). Present SMI and fossil SMI can be infered and it can infer that the flux of methane was not constant with the geologic time. The peaks above and below present SMI indicates that methane flux was stronger (upper) and weaker (lower) than present level.

PRESENT AND FOSSIL SMI: THE GEOCHEMICAL RECORD

Figure 9. Diagarm about anaerobic oxidation of methane and the formation of theof the sulfate-methane interface (SMI).

REFERENCESBurdige D. New Jersey, Princeton University press, 2006.

Dickens G. R. Geochimica et Cosmochimica Acta.

Elsevier Science Ltd. V.65, n.65, n.4, p.529-543, 2001.

Ken I. et al. . Bull. Geol.Survey Japan. V.47(6), p.309-316, 1996.

Kennett J.P. et al. . Washington DC: American Geophysical Union, 2003.

Lamb L et al. Earth-Sciences Reviews, v.75, p.29-57

2006.

Matsumoto R., Ishida Y. . 17th International Sedimentolo-

gical Congress. Fukuoka, Japan. V.B, p.7, 2006.

Nakada M. et al. Paleogeography, Paleoclimatology, Paleoecology.

V.85, Elsevier. P.107-122, 1991.

Oba T. et al. .Washington DC: American Geophysical Union. Paleoceanography. V.6, n.4, p.499-518, 1991.

Geochemistry of Marine Sediments.

Sulfate Profiles and Barium Fronts in Sediment on the Blake Ridge: Present andPast Methane Flux Trough a Large Gas Hydrate Reservoir.

C Age of Core Samples from Middle to South East Japan Sea by AMS

Methane Hydrates in Quaternary Climate Changes: The Clathrate GumHypotesis

A Review of Coastal Paleoclimate and Relative Sea-Level ReconstructionsUsing d13C and C/N ratios in Organic Materials.

Environmental Impact of Methane Seeps in Cold Waters: An Exampleof Giant Methane Plumes from Eastern Margin of Japan Sea

Late Pleistocene and Holocene Sea-Level Changes in Japan: Implicationsfor Tectonic Histories and Mantle Rheology.

Paleoenvironmental Changes in the Japan Sea During the Last 85,000 Yeras

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AKNOWLEDGEMENTSFor our colleagues on both Department of Earth and Planetary Science and Department of Natural Environmental Studies that help us on analysis, discussions and other supports. Thanks to the crew of R/V’s UmitakaMaru and Natsushima.

Fig.10 - Scheme of SMI formation(Dickens, 2001).

Fig. 12Fig. 11 Fig. 13

Fig 11. PC-701 SMI profile. TIC, calcite, barite, pyrire and sulfur curves show peaks at similar depths. Note that the present SMI is locatedat the depth where S content is near zero and CH becomes high. A strong coincidence with this SMI with chemical peaks indicatesthat it is agood parameter to identify SMI. TIC and calcite can have influence of foraminifera, but barite, pyrite and sulfur have no contamination and can calibrate the data. Peaks above and below indicate fossil SMI, when methane flux was stronger (upper) and weaker (lower). This location is a refence site and no evidence about gas hydrate was found at this place. Instead of this, methane flux is present and its C around -87 indicates biogenic origin.

Fig 12. PC-702 SMI profile. This is a gas hydrate site located over Joetsu Knoll. Plumes an gas hydrate are present and were recoveredand analysed gas chymineis and faults have been see on seismi data. A

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d. Also, c C around -50 indicates mixed origin. Note that present

SMI is shallower than at PC-701, indicating that methane flux over Joetsu Knoll is stronger than at reference site.

Fig.13. PC-707 SMI profile. Located over Umitaka Spur gas hydrate site, this piston core shows a very shallow present SMI. The samefeatures occurred at Joetsu Knoll are present here and the shallower positioning of present SMI indicates that methane flux is now stronger than at Joetsu Knoll. An erosion can be occurred and cut the upper SMI. High values of pyrite and sulfur near sea floor sugest erosion because the sea floor is predominatily oxidized.

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