Presented during the 6th International Conference on Gas Hydrates, Vancouver, Canada, 2008

1. ENVIRONMENTAL CHANGES OF THE LAST 30,000 YEARS
IN THE GAS HYDRATE AREA OF JOETSU BASIN
EASTERN MARGIN OF JAPAN SEA
6th International Conference on Gas Hydrates
The Fairmont Hotel Vancouver Antonio Fernando Menezes Freire*1,2, Eiichi Takeuchi*2, Akinori Nagasaka*2, Akihiro Hiruta*2, Osamu Ishizaki*2, Toshihiko Sugai*1, Ryo Matsumoto*2
Vancouver, BC, CANADA July 6-10, 2008 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
1/2
CORE LOCATIONS
CORE LOCATIONS MAP GAS HYDRATE STUDY AREA
MAIN PURPOSES
A) 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
JAPAN SEA CK-06 Margin of the Pacifc Ocean, east of Shimokita Peninsula (Fig. 01).
(SHIMOKITA PENINSULA ) C) To infer the methane flux variations along the geologic time
UT-07/NT-07-20 using geochemical data.
PC-701
PACIFIC OCEAN
Fig. 02: Map of the study area showing Joetsu Knoll and
Umitaka Spur gas hydrate areas. Also this map shows
piston coring location.
Fig. 01: Core location map. UT-07 (Umitaka Maru) cruise and NT-07-20 (Natsushima Cruise) are located
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over Umitaka Spur and Joetsu Knoll gas hydrate areas. PC-701 is a reference site and belongs to UT-07
cruise. CK-06 (Chikyo) cruise is located at Pacific Ocean and is a refence to make correlation.
TOTAL ORGANIC CARBON AND d C CONCENTRATIONS
The Holocene/Pleistocene Boundary
Piston cores data from the study area shows a clear upward increasing of both TOC and
ABSTRACT d13C contents. It is possible to identify a shift on TOC curve, from 1.3% to 2.0% and from
Recently, we recognized active methane venting and gas hydrates, which are widely distributed on just below -26‰ to -22‰ on d13C curve, around 3.5 m depth in reference piston core PC-701 graph
the sea floor in the Joestu basin, eastern margin of Japan Sea. This study has the intention to give support (Figure 03a). The same increased pattern can be observed in piston cores PC-702
for future works, understanding the Late Quaternary history of the study area. (Figure 03b) and PC-706 (Figure 03c), respectively located over Joetsu Knoll and Umitaka
Interbedded dark gray thinly laminites and dark brown to gray bioturbated units are common throughout the Spur gas hydrate areas, but at different depths. These shift depths represent important
Quaternary sediments of Japan Sea, and have been often explained in terms of glacio-eustatic sea-level changes on environmental conditions in the study area: Below occurs a relative small TOC
changes. These layers have a very good correlation because they occur in all Japan Sea. We used total production with d13C values around -26‰ and, above this shift, occurs a higher TOC
organic carbon (TOC) content and carbon isotopic composition of the gas hydrates bearing-sediments in production with heavier d13C isotopic composition.
order to identify the nature of the organic matters present in the study area and to make a correlation with CK-06 and GISP-2 (Figure 04) TOC and d13C profiles have very similar pattern and are
samples collected in the Pacific Ocean. Associated with XRD analysis, these data helped us to locate the very easily correlated with Japan Sea study area. The conclusion is that both Japan Sea
Holocene/Pleistocene boundary, to identify key stratigraphic surfaces, and to recognize sulfate-methane and Pacific Ocean had the same changes on organic matter production, and the
interfaces. Different SMI occurs due methane flux variation with the geologic time. boundary Holocene/Pleistocene is very well marked using this criteria.
d d d
d
d
TL-1 14
Foraminifera C (10.9~7.4Ka) d
TL-1
TL-1
TL-2
TL-2
Foraminifera C14 (19.6~15.8Ka)
TL-2 Fig. 03c: PC-706 located over Umitaka Spur gas hydrate
Vvvvv AT ash layer (~30Ka) site. Curves show the same pattern.
Fig. 03b: PC-702 located over Joetsu Knoll gas hydrate d d
site.The same pattern can be seen in both TOC and d13C
Fig. 03a: PC-701 reference piston core. Both TOC and d13C curves show and both thin laminated -1 (TL-1) and TL-2 are present.
a shift around 3.5m and it represents changes on organic matter production.
This depth is here interpretated like the boundary between Holocene and
Pleistocene and it is confirmed by C14 dating from foraminifera tests and
the occurrence of AT tephra layer (~30Ka).
THE NATURE OF ORGANIC MATTER: MARINE vs. TERRESTRIAL Fig. 04: Correlation between CK-06 drilling core and GISP-2 ice core. The same increased pattern
on both TOC and d13C curves, associated with foraminifera C14 dating indicate the boundary
TOC and d13C content indicate the origin and intensity of organic matter production. The warmer of the sea water and the rise
Holocene/Pleistocene. The d18O curve from GISP-2 indicates warmer conditions at Holocene
of the sea level during Holocene induced the free communication between Japan Sea and the Pacific Ocean because the time and the TOC curve shows that a more effective organic matter production occurs. Also,
straits are more deep and large. Because this condition, more warm-water species of diatom and radiolaria became more the d13C curve indicate heavier isotope compositions and, according Burdige, 2006, it reflects a
12 marine organic matter production. Pacific Ocean curves are very easily correlated with Japan Sea
present at Japan Sea [Oba et al. 1991]. As organic matter, generated by plankton, removes C selectively from the surface
13 13 curves and both have the same signature.
water, the d C of planktonic foraminiferal tests becomes heavier. According Burdige [2006], d C of TOC, in association with
nitrogen content can potentially be used to differentiate sources of organic matter. Organic matter produced by phytoplankton
has very different d13C values from that produced by land plants because of differences in the isotopic composition of their
carbon source [Burdige, 2006]. The primary carbon source for marine phytoplankton is seawater bicarbonate, with a d13C of
~0‰. In contrast, land plants use atmospheric CO2 as their carbon source, with d13C of around -7‰ [Burdige, 2006]. Differences
in the mechanisms of CO2 uptake by terrestrial plants (CO2 diffusion) versus marine plants (active uptake of bicarbonate in most
cases) also lead to some additional amounts of carbon fractionation during photosynthesis. As a result of all of these factors,
13
marine organic matter generally has a d C of around -17‰ to -22‰ and terrestrial organic matter of around -25‰ to -28‰
[Burdige, 2006].
Marine organic matter generally has a C/N ratio between 5 and 10 and fresh terrestrial organic matter has a C/N ratio >20.
These differences are a result of dissimilarities in the structural components of marine versus terrestrial plants: carbon-rich
lignocelluloses in the latter and nitrogen-containing proteins in the former.
While the Holocene is characterized by a higher marine organic matter production, Pleistocene is characterized by lower
13
organic matter production with lighter d C isotopic composition due to terrestrial organic matter source. The anoxic layer
TL-2 in this time are due the lower water circulation because sea level drops on LGM. During this time, when the sea level was
120m below present sea level, the coastal line was very close present shelf broken and the shallow and narrow straits (Figure
05) reduced drastically the sea water circulation causing clay minerals and organic matter to stay more time at suspension
inducing strong anoxic conditions and the occurrence of dark-gray thin laminated mud. The crossplot with data from both CK-06
and UT-07 cruise shows three groups of organic matter values (Figure 06a) and, according Burdige [2006] criteria, it is possible
to infer the nature of organic matter production at each geologic time. Comparing to Japan Sea study area, the samples from
Pacific Ocean have more relation with marine production. Crossplot with samples only from Japan Sea study area (Figure 06b)
shows that, excepting PC-701, organic matter has a terrestrial or mixing source. Umitaka Spur and Joetsu Knoll (Figures 02
and 05) are closer to shore line than PC-701 and, at Pleistocene, the “bay” stage induced weak circulation.
Fig. 05: Coastal and bathymetric map of Joetsu basin, south of Sado Islands frompresent and
during the LGM time, when the sea level dropped around 120m than present sea level. The
narrow and shallow strait between Sado Islands and the western coast of Japan limited the
circulation of sea water currents making Joetsu basin like a big bay.
FIGURE XX
Fig. 06:a) Crossplot TOC x d13C data from CK-06 (crosses) and UT-07 (squares). Three groups can be seen: relative higher TOC values and d13C heavier than ~-22‰
(marine phytoplankton production); relative medium TOC and d13C between ~-22‰ and ~-25‰ (mixed or non determinate); and relative lower TOC and d13C lighter
than ~-25‰ (vascular land plants). According Burdige, 2006. b) Crossplot TOC x d13C 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].

2. ENVIRONMENTAL CHANGES OF THE LAST 30,000 YEARS
IN THE GAS HYDRATE AREA OF JOETSU BASIN
EASTERN MARGIN OF JAPAN SEA
6th International Conference on Gas Hydrates
The Fairmont Hotel Vancouver Antonio Fernando Menezes Freire*1,2, Eiichi Takeuchi*2, Akinori Nagasaka*2, Akihiro Hiruta*2, Osamu Ishizaki*2, Toshihiko Sugai*1, Ryo Matsumoto*2
Vancouver, BC, CANADA July 6-10, 2008 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
2/2
TERRIGENOUS MATERIAL INPUT
The boundary between the Holocene and Pleistocene could be marked by TOC and d13C isotopic
concentration how discussed before but, also, this boundary could be identified using clay minerals,
quartz and feldspars content (Figures 08a and 08b). During the LGM, eustatic sea level lowering 120m
below present sea level and would have severely restricted or completely blocked the inflow into the study
area [Oba et al. 1991] (Figure 05). Because of this sea level dropping, the river`s mouths were very close to
the edge of the shelf and the discharge form ice melting with sediments in suspension occurred directly on
the slope. In particular, Joetsu basin coastal line was more than 20km sea ward during the LGM (Figure 05),
and a very shallow and narrow strait was formed between the Sado Islands and the western Japan coastal
line. The sea water flow through this pathway was very low and Joestu basin was a big bay. The poor sea
water circulation 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. On the other hand, at the Holocene, the sea level rising
vvvv
induced a good 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. Quartz and feldspars have no porosity while
clay minerals have a lot of porous. Because this, quartz and feldspars can not float for a long time and Figure 08. PC-701 clay minerals (a) and quartz, feldspars and quartz/feldspars ratio profiles. The boundary between the
rapidly sink to the sea floor. The lower clay minerals content at Pleistocene coincides with the lower TOC Holocene and Pleistocene could be marked by TOC and d13C isotopic concentration how discussed before but, also, this
boundary could be identified using clay minerals, quartz and feldspars content.
content (Figure 03a). It is because LGM time, when the weather was very cold and dry and, also, river’s
mouth were more far from due low sea level condition.
SULFATE OXIDATION OF METHANE
Sea water and sediment pore water have a lot of ions dissolved. The sediment particles also have cations and
anions adsorbed mainly on clay minerals. When a methane flux comes to the sea floor, both thermogenic or
2- 2-
biogenic origin, an oxidation of methane occurs (Figure 10). So4 , Co3 and H2S are not stable and the presence
of cations dissolved in the interstitial water react with them and forming sulfates, carbonates and sulfides. Barite,
calcaite, aragonite, dolomite and pyrite are commom authigenic minerals that precipitate around the sulfate-
methane interface (SMI).
Samples collected from UT-07 cruise shows some “fronts” of barite, calcite and pyrite (Figures 11, 12 and 13).
Instead calcite and toral inorganic carbon (TIC) values can have association with foraminifera, sulfur, pyrite and
barite have no relation with them and are good indicators of SMI. 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 inducing more chemical precipitation. On the other hand, if methane
flux oscillates very quickly, the reaction is not so strong and a poor amount of authigenic minerals will be formed.
Figure 10. Diagarm about sulfate-oxidation of methane oxidation and the formation
of the sulfate-methane interface (SMI).
Figure 11. PC-701 SMI profile. TIC, calcite, barite, pyrire and sulfur curves show peaks at similar depths. Note that the present SMI is located
at the depth where SO4 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 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 d13C around -87‰
indicates biogenic origin.
Figure 12. PC-702 SMI profile. This is a gas hydrate site located over Joetsu Knoll. Plumes and gas hydrate are present and were recovered
and analysed. Also, gas chymineis and faults have been see on seismic data. A d13C 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.
Figure 13. PC-707 SMI profile. Located over Umitaka Spur gas hydrate site, this piston core shows a very shallow present SMI. The same
features occurred at Joetsu Knoll are present here and shallower positioning of present SMI and no occurrence of the upper fossil SMI indicate
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.
CONCLUSIONS
REFERENCES
Burdige D. Geochemistry of Marine Sediments. New Jersey, Princeton University press, 2006.
The late Quaternary correlation between Japan Sea and the Pacific Ocean is possible using piston-
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coring data. TOC and d C increased pattern is very similar in both sites. It indicates more organic Dickens G. R. Sulfate Profiles and Barium Fronts in Sediment on the Blake Ridge: Present and
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matter production during Holocene and the d C increased pattern upward suggests a phytoplankton Past Methane Flux Trough a Large Gas Hydrate Reservoir. Geochimica et Cosmochimica Acta.
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melt on the mountains located near the shoreline of Niigata Prefecture, causing the increasing of Hypotesis. Washington DC: American Geophysical Union, 2003.
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AKNOWLEDGEMENTS Washington DC: American Geophysical Union. Paleoceanography. V.6, n.4, p.499-518, 1991.
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.