Poster presented during the AAPG 2008 at Cape Town, South Africa

1. Antonio Fernando Menezes Freire (1,2,3), Toshihiko Sugai (1), Ryo Matsumoto (2)
THE STUDY OF THE GAS HYDRATE BEARING-SEDIMENTS 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
FROM JOETSU BASIN, EASTERN MARGIN OF JAPAN SEA (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
PRESENT AND FOSSIL SMI: THE GEOCHEMICAL RECORD
ABSTRACT THE NATURE OF ORGANIC MATTER: MARINE vs. TERRESTRIAL
Recently, we recognized active methane venting and gas hydrates, which are widely - TOC and δ C content indicate the origin and intensity of organic matter production.
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distributed on just below the sea floor in the Joestu basin, eastern margin of Japan Sea. SULFATE-METHANE INTERFACE
-Holocene: warming of sea water and rising of sea level. Straits more deep and large promoted a - Sea water and sediment pore water have a lot of ions dissolved (Figure 9);
This study has the intention to give support for future works, understanding the Late better sea water circulation (Figure 5). More species arrived from the Pacific Ocean increasing the
Quaternary history of the study area. Interbedded dark gray thinly laminites and dark - The sediment particles also have cations and anions adsorbed mainly on clay minerals;
organic matter production. - When a methane flux occurs at the sea floor, an oxidation of methane occurs. So4 , Co3 and H2S are
2- 2-
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 - Pleistocene: cold temperatures and sea level dropping (~120m at LGM). not stable and the presence of disponible ions induce the reaction. Barite, calcite, aragonite, dolomite
Few species were available, and the organic matter production was weak. The study area was a big and pyrite are commom authigenic minerals that precipitate around the sulfate-methane interface (SMI)
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 bay with poor sea water circulation conditions (Figure 5); The region where sulfate becomes to zero is called SMI (Figure 10) (Dickens, 2001).
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the gas hydrates bearing-sediments in order to identify the nature of the organic matters - As organic matter, generated by plankton, removes C selectively from the surface water, planktonic - Samples collected from UT-07 cruise shows some “fronts” of barite, calcite and pyrite (Figures 11, 12, 13)
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present in the study area and to ma ke a correlation between samples collected in the Pacific foraminifera tests becomes enriched in δ C (Burdige, 2006). The primary carbon source for marine - Because methane flux can vary with time, SMI can be shallower or deeper accoding the flux intensity
Ocean. Associated with XRD analysis, these data helped us to locate the Holocene/Pleistocene phytoplankton is seawater bicarbonate, with a δ13C of ~0‰. In contrast, land plants use atmospheric - Depending on the time that SMI is stable at the same depth, the reaction will be more effective.
boundary, to identify key stratigraphic surfaces, and to recognize sulfate-methane interfaces. CO2 as their carbon source, with δ13C of around -7‰.
Different SMI occurs due methane flux variation with the geologic time. Age control was made - As a result of all of these factors, marine organic matter generally has a δ13 C of around -17‰ to Fig.11. PC-701 SMI profile. TIC, calcite, barite, pyrire and sulfur curves show peaks at similar depths. Note that the present SMI is located
by tephra layers identification and correlation. -22‰ and terrestrial organic matter of around -25‰ to -28‰ [Burdige, 2006] [Lamb, 2006].
at the depth where SΟ 4 content is near zero and CH4 becomes high. A strong coincidence with this SMI with chemical peaks indicates
that it is agood parameter to identify SMI. TIC and calcite can have influence of foraminifera, but barite, pyrite and sulfur have no
- Terrestrial Plants has relatively high C/N ratios of >12 and marine organic matter have C/N ratio 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
<12 [Lamb, 2006]. Figures 7 and 8 show graphics with these data. and its δ C around -87‰indicates biogenic origin.
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TOTAL ORGANIC CARBON AND δ C CONCENTRATIONS 13
Figure 9. Diagarm about anaerobic oxidation of methane and the formation of the
of the sulfate-methane interface (SMI). Fig.12. PC-702 SMI profile. This is a gas hydrate site located over Joetsu Knoll. Plumes and gas hydrate are present and were recovered
The Holocene/Pleistocene Boundary and analysed. Also, gas chymineis and faults have been see on seismic data. A δ13C 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.
- Clear TOC and δ13C curves increasing upward;
Fig.13. PC-707 SMI profile. Located over Umitaka Spur gas hydrate site, this piston core shows a very shallow present SMI. The same
- This shift depth marks the boundary Holocene (higher TOC and heavier features occurred at Joetsu Knoll are present here and the shallower positioning of present SMI indicates that methane flux is now stronger
d13C isotope)/Pleistocene (lower TOC and lighter d13C isotope); 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.
- The pattern is the same along Japan Sea and there is a very good Fig.10 - Scheme of SMI formation
(Dickens, 2001).
correlation with the Pacific Ocean. So, it is possible to use this criteria
to infer the boundary Holocene/Pelistocene (Figures 3 and 4).
MAIN PURPOSES
A) To understand the sedimentar history of the Late Quaternary
U-OKI Tephra Layer (~10.7Ka) 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 Fig. 07:a) Crossplot TOC x δ 13 C data from CK-06 (crosses) and UT-07 (squares). Three groups can be seen: relative higher TOC values and δ13C heavier than
and those observed on the drilling core CK-06 on the Eastern ~-22‰ (marine phytoplankton production); relative medium TOC and δ C between ~-22‰ and ~-25‰ (mixed or non determinate); and relative lower TOC
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Fig. 11 Fig. 12 Fig. 13
Margin of the Pacifc Ocean, east of Shimokita Peninsula (Fig. 01). and δ13C lighter than ~-25‰ (vascular land plants). Crossplot TOC x δ13C data from UT-07 samples. PC-701, located far from the coastal line and into a typically
C) To infer the methane flux variations along the geologic time 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]. AKNOWLEDGEMENTS
using geochemical data. For 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 Umitaka
Maru and Natsushima.
REFERENCES
CONCLUSIONS Burdige D. Geochemistry of Marine Sediments. New Jersey, Princeton University press, 2006.
The late Quaternary correlation between Japan Sea and the Pacific Ocean is
Dickens G. R. Sulfate Profiles and Barium Fronts in Sediment on the Blake Ridge: Present and
possible using TOC and δ C increased pattern. This pattern indicates more organic
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Past Methane Flux Trough a Large Gas Hydrate Reservoir. Geochimica et Cosmochimica Acta.
TERRIGENOUS MATERIAL INPUT matter production during Holocene and the δ13C increased pattern upward suggests Elsevier Science Ltd. V.65, n.65, n.4, p.529-543, 2001.
-The boundary Holocene/Pleistocene can be marked by using clay minerals, quartz and a phytoplankton organic matter production. Ken I. et al. C Age of Core Samples from Middle to South East Japan Sea by AMS. Bull. Geol.
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feldspars content (Figure 6); The poor sea water circulation at Pleistocene, due to the drop of sea level at LGM, Survey Japan. V.47(6), p.309-316, 1996.
-During the LGM, eustatic sea level lowering120m and restricted or completely blocked caused a poor spreading of clay minerals, and, little by little, it was sunk to the Kennett J.P. et al. Methane Hydrates in Quaternary Climate Changes: The Clathrate Gum
the inflow into the study area [Oba et al. 1991]. River`s mouths were close to the sea bottom. At Holocene, the rising of the sea level induced a good sea water Hypotesis. Washington DC: American Geophysical Union, 2003.
slope and the discharge form ice melting with sediments in suspension occurred circulation and clay minerals were easily washed over seaward. At the same time,
Lamb L et al. A Review of Coastal Paleoclimate and Relative Sea-Level Reconstructions
directly over this location (Figure 5); the climate warm increasing induced the snow melt on the mountains located near Using d13C and C/N ratios in Organic Materials. Earth-Sciences Reviews, v.75, p.29-57
-At Pleistocene, the poor sea water circulation on the study area could not spread fine the shoreline of Niigata Prefecture, causing the increasing of weathering. Because 2006.
grain floated sediments and it stays at suspension for more time. Little by little, clay this, quartz and feldspars were delivered by rivers, arriving to Joetsu Basin and
Matsumoto R., Ishida Y. Environmental Impact of Methane Seeps in Cold Waters: An Example
minerals sunk to the sea floor. sinking to sea floor faster than clay minerals. of Giant Methane Plumes from Eastern Margin of Japan Sea. 17th International Sedimentolo-
-At the Holocene, the sea level rising induced a good sea water circulation and clay Geochemical records of sulfate-oxidation of methane is present by several peaks gical Congress. Fukuoka, Japan. V.B, p.7, 2006.
minerals were washed over. At the same time, the increasing of the weathering
vvvv
of calcite, barite, pyrite and sulfur. At least two sets of peaks are present and Nakada M. et al. Late Pleistocene and Holocene Sea-Level Changes in Japan: Implications
because to the melt of ice in response of warmer climate, induced quartz and represent different stages of the sulfate methane interface (SMI). Present SMI and for Tectonic Histories and Mantle Rheology. Paleogeography, Paleoclimatology, Paleoecology.
feldspars transportation by rivers and rapidly precipitate to the sea floor. Figure 08 - Typical δ13 C and C/N ranges for organic inputs to coastal environments. fossil SMI can be infered and it can infer that the flux of methane was not constant V.85, Elsevier. P.107-122, 1991.
Figure 06. PC-701 clay minerals, quartz, feldspars and quartz/feldspars ratio profiles.The boundary between the Note that some samples are located on a non determineted source because high
nitrogen content, tipically of marine environments. The mixed and terrestrial
with the geologic time. The peaks above and below present SMI indicates that Oba T. et al. Paleoenvironmental Changes in the Japan Sea During the Last 85,000 Yeras.
Holocene and Pleistocene could be marked by TOC and δ C isotopic concentration how discussed before but,
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also, this boundary can be identified using clay minerals, quartz and feldspars content. nature at Pleistocene is also clear. Modified from Lamb et al. 2006. methane flux was stronger (upper) and weaker (lower) than present level. Washington DC: American Geophysical Union. Paleoceanography. V.6, n.4, p.499-518, 1991.