Thessaloniki Mud Volcano, the Shallowest Gas Hydrate-Bearing Mud Volcano in the Anaximander ...

12 Pages·2014·10.59 MB·English

HindawiPublishingCorporation
JournalofGeologicalResearch
Volume2011,ArticleID247983,11pages
doi:10.1155/2011/247983
Research Article
Thessaloniki Mud Volcano, the Shallowest Gas Hydrate-Bearing
Mud Volcano in the Anaximander Mountains, Eastern
Mediterranean
C.Perissoratis,1Chr.Ioakim,1S.Alexandri,2J.Woodside,3P.Nomikou,2A.Da¨hlmann,4
D.Casas,5K.Heeschen,6H.Amman,7G.Rousakis,2andV.Lykousis2
1InstituteofGeologyandMineralExploration,EntranceC,SpyrouLouis1,OlympicVillage,Acharne,13677Athens,Greece
2HellenicCentreforMarineResearch,46thkmAthens-SounionBP712,19013Anavyssos,Greece
3Department of Sedimentary and Marine Geology, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The
Netherlands
4DepartmentofGeochemistry,FacultyofEarthSciences,UtrechtUniversity,80021Budapestla-an4,3508TAUtrecht,TheNetherlands
5InstitutdeSciencesdelMar,PaseoMaritimodelaBarceloneta37-49,08003Barcelona,Spain
6Bundesanstaltfu¨rGeowissenschaftenundRohstoffeGeozentrumHannover,Stilleweg2,D-30655Hannover,Germany
7TechnischeUniversita¨tBerlin,MullervBresslauStrasse,10623Berlin,Germany
CorrespondenceshouldbeaddressedtoC.Perissoratis,[email protected]
Received2June2011;Revised16August2011;Accepted12September2011
AcademicEditor:MichelaGiustiniani
Copyright©2011C.Perissoratisetal.ThisisanopenaccessarticledistributedundertheCreativeCommonsAttributionLicense,
whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.
A detailed multibeam survey and the subsequent gravity coring carried out in the Anaximander Mountains, Eastern
Mediterranean, detected a new active gas hydrate-bearing mud volcano (MV) that was named Thessaloniki. It is outlined by
the1315mbathymetriccontour,is1.67km2 inarea,andhasasummitdepthof1260m.Theseabottomwatertemperatureis
13.7◦C.Thegashydratecrystalsgenerallyhavetheformofflakesorrice,somelargeraggregatesofthemareupto2cmacross.
A pressure core taken at the site contained 3.1 lt. of hydrocarbon gases composed of methane, nearly devoid of propane and
butane.Thesedimenthadagashydrateoccupancyof0.7%ofthecorevolume.Thesecharacteristicsplacethegashydratefieldat
ThessalonikiMVattheupperboundaryofthegashydratestabilityzone,pronetodissociationwiththeslightestincreaseinsea
watertemperature,decreaseinhydrostaticpressure,orchangeinthetemperatureoftheadvectingfluids.
1.Introduction:PurposeofThisStudy theirdiscoveryinthelate1970s[13].Mudvolcanoesarealso
known for their high methane fluxes, advecting methane-
The occurrence of mud volcanoes (MVs), mud diapirs, richfluidsatseafloorseeps,gashydrates,andfavorableenvi-
and fluid seeps has long been known in various different ronmentsforchemosyntheticsymbioticfauna[5,10,12].
geological environments of the Eastern Mediterranean [1] The Anaximander Mountains are situated between the
and in the Aegean Sea [2]. They occur not only in regions Hellenic and Cyprus Arcs at the junction of the African
of compressional stress present in subduction zones (e.g., Plate with the Anatolian and the Aegean microplates,
Calabrian Arc [3], Mediterranean Ridge [4], and orogenic an area accommodating the relative motion between the
belts[1,5–7]),butalsoonpassiveriftedmarginssuchasthe African and Eurasian plates [6,10,14]. The mountains
Egyptianoffshore[8,9]andareasofmixedtectonicsignature have thus undergone a complex deformation including
liketheANAXIMANDERMountainswheremudvolcanism southwarddirectedthrusting,northeast-southwestshearing
is related to faults with normal and transcurrent faulting in the west (Strabo Trough trend) and northwest-southeast
components [10–12]. Especially the accretionary prism of shearingintheeast(FlorenceRisetrend),andcross-cutting
the Hellenic Arc (Mediterranean Ridge) is an area where a normal faulting, all defining the current structure of the
largenumberofmudvolcanoeshavebeenstudiedfollowing mountains [10,12,15,16]. They are comprised of three
2 JournalofGeologicalResearch
mainseamounts:Anaximander,Anaximenes,andAnaxago- deck the autoclave corer was placed upright for controlled
ras(Figure1(a)). degassing and kept in an ice bath to prevent warming
The setting of the Anaximander Mountains is clearly to deck temperatures. The degassing, gas collection, and
favorable for the occurrence of mud volcanoes (Figure1) gas-subsampling were carried out using a valve system as
thanks to the presence of overpressured fluids and faults described by Heeschen et al. [19], a method used and
that act as conduits for the fluids to escape [12, 17, 18]. described also by others [18]. The pressure was constantly
Discovered during the Dutch ANAXIPROBE project by monitored and the increasing volume of released gas was
multibeam surveying in 1995, seven large mud volcanoes read off from a converted graduated cylinder. Gas sub-
were sampled in 1996 [6, 7, 11] when the first gas hydrates samples were taken via a three-port valve and were stored
samplesintheMediterraneanSeawerecollectedfromKula for analysis in the laboratory [22]. A total of four gravity
MV. By 2002 the Amsterdam and Kazan MVs were also cores and one autoclave core were collected at Thessaloniki
discovered to have hydrates. Between 2003 and 2005 the MV (Figure2, Table1). The trace and main elements were
EC-funded project ANAXIMANDER targeted these mud analyzedbytheX-raydiffractionmethodusingaSIEMENS
volcanoes in a study of the gas hydrates and associated D-500 instrument. The crystalline phases were determined
deep biosphere in the area, and this was followed by the using the Joint Committee Power Diffraction Standards
HERMES project (2005–2009). During these projects gas and their final semiquantitative analyses by using the EVA
hydrates from Amsterdam and Kazan MVs were collected programfromSiemens/Bruker/Socabimo.
and studied, and two new mud volcanoes named Athina
andThessalonikiwerealsodiscovered,sampled,andstudied
3.ResultsandDiscussion
(Figure1(b)[17,19–21]).
Since Thessaloniki MV is the shallowest known GH
3.1. Bathymetry and Backscattering Imaging. Anaximenes
bearing MV in the Eastern Mediterranean, very briefly
Mountain (Figure1) is a slightly northwestward concave
describedearlier[17,21],thepurposeofthisstudyistocarry
feature occupying the shallowest (680m) and smallest area
outdetailedanalysesandexaminationofalldatacollectedin
in the Anaximander Complex, and therefore is character-
thisareaanddiscusstheconditionsandcharacteristicsofthe
ized by steep slopes and rugged relief. To the south the
GHpresent.
Mediterranean Ridge is terminated in the form of a flat
slightly wavy or folded area lying at a water depth of about
2.MaterialsandMethods 2800m. It is separated from Anaximenes Mountain by a
deep valley (>3000m). The study of the combined 3D
The data examined in this study were acquired mainly seabed morphology and backscatter intensity revealed in
during two cruises of the R/V Aegaeo in May 2003 and the southeastern slope of Anaximenes Mountain numerous
October-November 2004. During the first cruise detailed dome-like morphological features with strong backscatter
swath bathymetry and backscatter imagery of the study thatconstitutepotentialmudvolcanosites.Followingimage
area was obtained using a hull-mounted SEABEAM 2120 processing of the backscatter data, a number of high
swath system operating at 20KHz. It has an angular sector backscatter areas implying potential active mud volcanism
of 150◦, with 159 beams and a swath width from 7.5- to wereidentified.Oneofthesesitesatadepthof1798mwas
11.5- times the water depth, for depths from 1 to 5km subsequently surveyed in 2003 and discovered to be a mud
respectively. Navigation was carried out with a Trimble volcano which was named Athina MV (Figure1, [17, 20]).
4000 GPS providing the ships position to within ±10m. Inthesamearea,about9kmnortheastofAthinaMV(at35◦
The bathymetric map of Thessaloniki MV (Figure2) was 28.60N–30◦15.06E),andatwaterdepthsbetween1320and
produced using a 20m grid interval and plotted with a 1260mtheThessalonikiMVwasdiscoveredaftersurveying
Mercatorprojectionatascaleof1:20.000with5mcontours. andsamplinginNovember2004(Figures1and2[17,21]).
Sediment was sampled with a 3m long 73cm i.d. Benthos Thismudvolcanohadnotbeenfullyexaminedinprevious
InstrumentsGravityCorerwithpresplitsleevestoreducethe cruisesbecauseofitssmallsizeandlocationatthebaseofa
timeneededtoopenandsamplethecores.Thetimebetween very steep sloping cliff (Figure2), although its eastern side
coring the seafloor and on board sampling of cores from was crossed during the ANAXIPROBE ORETech side scan
a depth of 2000m was thus reduced to between 20 and 25 survey [7] (Figure2). It is an oval submarine hill with its
minutestoensuretheleastpossiblegashydratedissociation long axis about 1750m as defined by the 1315m isobath,
andsedimentdistortion.Assoonasthecoreswereopened, withsteepnorthernandeasternslopesandanareaofabout
the temperature of the sediments was measured, and any 1.67km2. In the inner part, near the summit, it becomes
gashydrateswerecollectedandplacedinafreezerat–70◦C. morecircularwherethreepeaksaredistinguished,twointhe
Detailedsamplingofthesedimentfollowed. west outlined by the 1260m contour and one in the east at
The pressure coring was carried out using the APCA 1265m. Its small size and location on a steep slope made
(Autoclave Piston Corer Anaximander) [22] designed and it a lower priority for investigation during earlier research
fabricated by Technical University of Berlin as part of projects.
the ANAXIMANDER project. The APCA retrieves cores of
10cm diameter and up to a length of 250cm in water
depths of up to 2500m. It preserves the sediment cores 3.2. Sedimentology. Five cores were collected from Thes-
under in situ pressure conditions [22]. Upon retrieval on saloniki MV: four gravity cores (AX46-GC1, AX47-GC1,
JournalofGeologicalResearch 3
29◦00 29◦20 29◦40 30◦00 30◦20 30◦40 31◦00
Kastelorizo TurkishContinentalMargin Antalya
Island Basin
36◦00 B asin 36◦00
Finik e
2500
3000
Rhodes
Basin
35◦40 2500 1500 35◦40
3500 The Great Slid e Fold
3000 A n a x2i0m00a n d e r menes Anaxagoras 2000 Belt
xi
35◦20 Ana Florence 35◦20
Rise
40◦20◦ 25◦ 30◦ 40◦ Mediterranean Ridge Province
Turkey 2500 PREOCJcoEnCtraTctEVAKN3-CAT-X20I0M2−A00N06D8ER
35◦00 Greece ChiefscientistV.Likousis 35◦00
Swath bathymetry map
35◦ Anaximander 35◦ S.Alexandri,P.Nomikou,D.Ballas
Mountains Cyprus PErlloipjescotiido:nW:MGeSr-c8a4torat35◦N MSyisntedmepUthse:d6:0S0EmABMEaAxMde2p1t2h0:3(02000kmHz)
Gridinterval:100meters Datacollectedby:R/VAEGAEO
30◦20◦ Africa25◦ 30◦ −30◦4500 −3500 −2500 −1500 −500Isobaths:100HmelleniccentreformInaMrinaeyr2e0s0e3aracnhdOctober-November2004
29◦00 29◦20 29◦40 30◦00 30◦20 30◦40 31◦00
(a)
Kula
N
◦ 5 6
3 5
Thessaloniki Kazan
◦ 4 8
3 5
Athina
◦ 4 0
3 5
Amsterdam
◦ 3 2
3 5
3 5◦ 2345◦ 1365◦ 0 8 29◦−43800029◦ 5−6260300◦ 04− 23200◦012 −310◦80200 3−0◦124800 30◦−31600030◦ 44− 60300◦ 52 31◦ 00
(b)
Figure 1: Bathymetry-physiography of the Anaximander complex (a), and swath bathymetry with locations of the five surveyed mud
volcanoes((b)from[17]supplementedwithANAXIPROBEdatatooutlineeachMVarea[11]).
4 JournalofGeologicalResearch
Thessalonikimudvolcano
30◦15 30◦16
N
−−11130000 1 3 6 0 35◦29
−1500
60 0 1340
5 8 0
1 4 0 0
− −1 −14 132 240 60 0 35◦30 35◦30
35◦28− −1 −11 −108 −1000 1320 1300 1216208 0 3355◦◦2298 1100 1150 12130000 12501300 1350 114400510500 3355◦◦2298
30◦15 1300
4gravitycores 35◦27 1300 35◦27
30◦14 30◦15 30◦16
GHsites
Figure2:SwathbathymetrymapofThessalonikiMVandlocationofthecollectedcores(blackdots).Upperleft,greaterswathmapwith
thevolcanoatthecenter,lowerright,ORETechsidescanimagefromANAXIPROBEcruiseontopofSEABEAMbackscatterintensitymap.
GravitycoresAX46-GC1,AX47-GC1,andautoclavecoreAX49-AP1wereretrievedfromthenorthernpeak,nearlyatthesamelocation.
GravitycoresAX-48andAX-49wereretrievedfromthesouthernpeak(from[17]supplementedwithbackscatterdataandlocationof
APCAcore).
Table1:(a)Gravitycores.(b)Autoclavecore.
(a)
Waterdepth Sediment Length G.H.presence Smellof
Coreno. Latitude Longitude
(m) temperature (cm) (visualidentification) H2Sgas
AX46-GC1 35◦28.603(cid:3) 30◦15.113(cid:3) 1263 14,4◦C 110 No Yes
AX47-GC1 35◦28.562(cid:3) 30◦15.123(cid:3) 1265 12,3◦C 167 No Yes
AX48-GG1 35◦28.729(cid:3) 30◦15.052(cid:3) 1264 8.4–10.7◦C 130 Yes Yes
AX49-GC1 35◦28.728(cid:3) 30◦15.060(cid:3) 1264 Nodata 228 Yes Yes
(b)
Waterdepth Length Pressure Gasvol.
Coreno. Latitude Longitude GHpresence
(m) (cm) (bars) (litres)
AX49-AP1 35◦28.728(cid:3) 30◦15.060(cid:3) 1.264 0.70 105 Yes 3.1
AX48-GC1,andAX49-GC1)andoneautoclavecore(AX49- been dissociating gas hydrates present). These observations
AP1).Theyarelocatedinsimilarsedimentaryenvironments confirmedthatthisMVisanactivegashydratebearingmud
on the two western highs on the summit of Thessaloniki volcano,thefourthdiscoveredintheMediterranean.
MV(Figure2),inwaterdepthsfrom1263to1265m.Table1 The general appearance of typical mud breccia cores
presents the details of the core locations and characteris- (Figure3) is of a very poorly sorted sediment with muddy
tics, with the initial deck observations made to determine matrix-supported angular to subangular clasts (xenoliths)
whether there were gas hydrates (even if not actually of different compositions and grain sizes (0.5 to 2.5cm).
observed; for example, with sediment temperatures below The clasts reflect the geological units through which the
the seafloor temperature, ∼13.7◦C, there is likely to have overpressured sediment passed before erupting on the
JournalofGeologicalResearch 5
seafloorasmudbreccia.Inthiscasetheyrepresentbasement
units associated with the Lycian Nappes and Bey Dag˘ları
to the north in Turkey [6, 7, 23–25]. Porous gas-release
structuresarecommoninthesedimentweobservedbecause
Thessalonikimudvolcano
much of the disseminated gas hydrates, associated with
AX46-GC1 AX47-GC1 AX48-GC1 AX49-GC this type of sediment, dissociated during the sampling
0
operationorminuteslateronboard,wheretheambientP-T
5
10 conditions indicate that gas hydrates are unstable [26, 27].
15 Similar sediment has been described in other mud volca-
20 noes(Amsterdam,Kula,andKazan)inthearea[17,24,28].
25
Core AX46-GC1 (Figure3) was retrieved from the
30
southernpeak(1263mwaterdepth;corelengthof119cm).
35
Thetop5cmiscomposedofayellowishgrayoxidizedmud
40
layer with faint laminae supporting dispersed small clasts
45
50 <1.5cm in diameter. There is a gradual change in color
55 downwards toward the next 5 to 19cm section which is a
60 greenish-gray reduced mud containing a few clasts up to
65 3cm in diameter. The following 19–119 section is simi-
70 lar in color with the overlying section but with larger
75
clasts, up to 5cm in diameter and increasing in the
80
lower 10cm. Evidence of dewatering features associated
85
with a strong gas smell were also noted. The sediment
90
temperature upon opening of the core was 14.4◦C, roughly
95
100 (actually, just above) seafloor temperature. No gas hydrates
105 weredetected.
cm) 110 Gassmell On the same southern peak at a distance of about 80m
pth ( 111250 T=14.4◦C to the north and at a depth of 1265m core AX47-GC1 was
De collected with a length of 167cm (Figure3). The sediment
125
temperature upon opening was 12.3◦C. At the top of the
130
135 PresenceofGH core there was a 3cm thick yellowish gray oxidized layer
140 T=8.4◦C− followed by a 3–78cm section of dark reduced greenish-
145 10.7◦C graymudwithoccasionalclasts.Thesedimentismoresoupy
150 in the top 41cm of the section becoming stiffer below,
155 withfaintlaminaeat64to65cm.Thenext78to167cmsec-
160 Gassmell tioncontainslargerrockclasts,upto2.5cmacross,andtwo
165
T=12.3◦C dark gray-colored laminated layers at 79–85cm and at 96–
170 99cm.Thesedimentbecomesstiffatthebottomofthelayer.
175
NoGHwerefound.
180
185 On the northern peak a 130cm long core (AX48-GC1,
190 Figure3) was retrieved from a water depth of 1264cm.
195 The sediment temperature when measured on deck varied
200 between 8.4 and 10.7◦C. No oxidized layer was observed
205
at the top of the core, indicating relatively recent mud
210
volcanic activity in this area (because the upper part of the
215
mud breccias had not had time to oxidize nor to be over-
220
225 lain by semipelagic sediment typical of the local seafloor).
230 Thesedimentconsistsofgreenish-graymudwithlargerock
PresenceofGH
clasts dispersed throughout the whole length of the core.
The GH were observed mainly between 110 and 120cm
Yellowish mud - oxidized layer where their dissociation produced many degassing features
Greenish gray mud resulting in the soft and sometimes soupy texture of the
Clasts sediment (Figure4). Most of the large rock clasts occur in
the lower section of the core, where the sediment becomes
GH dissociation features
stifferbelowacoredepthof55cm.
Gradual change in color or composition
Core AX49-GC1 (Figure3) was the longest core taken
Sharp change in color or composition
(228cm)andalsocomesfromthenorthernpeakatthesame
Presence of gas hydrates
location and water depth as core AX48-GC1. It consists of
Figure3:Descriptionofthegravitycores. gray mud with foamy mousse-like texture and consistency,
6 JournalofGeologicalResearch
It is possible that observations of gas hydrates in one core,
butnotinanotherwithsimilarconcentrationsofmethane,
canbeexplainedbydifferencesinthesizeofthegashydrate
depositsbetweenthetwocores,withthesmallerGHcrystals
disappearingmorequickly.
Theinsitumethaneconcentrationintheautoclavecore
at northern site AX49 (core AX49-AP1) was calculated to
be about 180mmoL/kg pore water at depths where there is
no sulfate present. To calculate gas hydrate volumes from
methane concentrations in(cid:2)relation to the core volume, the
amount of collected gas ( CH = 3.1L) is related to the
4
4cm corevolumebetweenthebottomofthecoreandthesulfate
depletiondepth,assuminganevendistributionthroughout
Figure 4: Section 99–124cm of core AX48-GC1. Note the soft
this depth range with dissolved and hydrate-bound CH to
characterofsection110–120cmwhichcontainedgashydrates. 4
be present. The saturation concentration (c ) of CH is
eq 4
subtractedbeforecalculatinggashydratevolumes.Fordetails
see[30].IncoreAX49-AP1gashydratesoccupyabout0.7%
withmanydegassingfeaturesproducedfromthedissociation
of the core volume. The gas collected from the pressure
ofGHdispersedthroughoutthewholelengthofthecore.
core is nearly devoid of propane and butane thus allowing
structureIgashydratestobeformed[19].Nopressurecorer
3.3. Geochemical Results. A geochemical analysis was made wastakenonthesouthernpeakofthiswesternhigh.
of both the mud flow (trace element) and the rock clasts
(mainelement)ofthegravitycores.
Theresultsofthetraceelementanalysisinthemudflow 3.4.StudyoftheMudBrecciaRockClasts. Thepresenceofa
oftwogravitycores(Table2(a))indicatethatorganiccarbon yellowish-brownoxidizedlayerintheupperfewcentimetres
(C ),Na O,Mg,Rd,Sr,andCudonotvarydowncore.The of the two gravity cores, where there were no gas hydrates
org 2
total carbon (C ) is higher at the top of the cores than in observed,probablyindicatesthatatthesetwositesmudvol-
tot
thelowersectionswhereasthevaluesofSandZnareusually canoactivitywaslowtoabsentduringthelastfewhundred
loweratthetopofthecoresthanbelow. years. Freshly erupted mud breccia is characterised by grey
Calcite is the dominant mineral in the rock clasts from reduced sediment and the lack of an oxidised hemipelagic
gravity core AX 48-GC1 (Table2(b)). This combined with sediment cover. An estimate of the age of eruptions can
thepresenceoftheothermainelementsshowninTable2(b), sometimes be made using the thickness of the overlying
andthelowdolomitecontent,supportearlierinterpretations sedimentandagoodestimateoftherateofsedimentation,in
that bedrock here is related to the Miocene flysch deposits thisareaabout2–5cm/ka[24].Thecompositionofthemud
presentonlandtothenorth([6]seeSection3.4). inallcoreswasmainlysiltyclayswithasandfractionbetween
These results also indicate that the composition of 5 to 7% and a mean grain size between 6.2 and 7.8 phi; it
the Thessaloniki MV sediments are comparable to those is consisted of terrigenous material with minor amounts of
reportedinotherMediterraneanmudvolcanoeslikeAthina biogeniccomponents,mainlyplanktonicforaminifera.
[20]andeventhosefromtheGulfofCadiz[29]. As noted previously, rock clasts that erupted through a
The methane concentration was measured in both mudvolcanoarecomprisedofachaoticmixtureofmaterial
gravitycores.NogashydrateswereobservedincoreAX47- from the overpressurized source formation and the rock
GC1butthesedimentwaswetandinsomeplaces“soupy.” units through which the eruption occurred. This material
On the other hand, gas hydrates were observed throughout can provide significant geological information about the
core AX49-GC1 when it was opened on deck (Figures 3 deepergeologicalunitsunderlyingthemudvolcano,aswell
and 4). Methane concentrations in core AX47-GC1 were as the stratigraphy. A litho-micropalaeontological study of
about 2800µmoL/kg wet sediment, with a maximum of 39samplesofmudbrecciaclastsfromThessalonikiMVwas
4000µmoL/kgwetsedimentatacoredepthbelowseafloorof undertaken.
100cm.IncoreAX49-GC1,themethaneconcentrationwas These rock clasts of various size (2–5cm in length)
3000µmoL/kg wet sediment, decreasing to 2000µmoL/kg andsupportedinahomogeneousmudbrecciamatrixwere
wet sediment below this maximum at 100cm down core sampled from the gravity cores collected during the second
(Figure5).Thusthemethaneconcentrationsatbothwestern cruise of the ANAXIMANDER project. They were subse-
highsonthesummitofthemudvolcanowerehighdespite quentlywashedandclassifiedbytheirgeneralcharacteristics
the apparent differences in gas hydrate content seen in (composition, color, grain size, reaction with HCl, and
the sediment. However, due to the degassing of these roundness). Several clasts were selected then for further
conventionalcoresduringrecovery,andtheconsequentloss thinsectionanalysisusingaNIKONpolarizingpetrographic
ofup to 90% of themethane [19],wecouldnot determine microscope.Themostinformativesampleswerealsowashed
significant differences in methane concentrations because and sieved through a 150µm sieve. This fraction is also
the concentrations are far below methane saturation in the usedforanalyzingtheplanktonicforaminiferaassemblages.
presence of gas hydrates (∼100mmoL/kg pore water [19]). TypicalexamplesofthinsectionsareshowninFigure6.
JournalofGeologicalResearch 7
Table2:(a)TraceelementanalysisofthemudflowincoresAX48GC1andAX49GC1.(b)Mainelementanalysis(%)oftherockclastsfrom
coreAX48-GC1.
(a)
Core Sampledepth(cm) Ctot∗% Corg∗% S% Na2O% Mg% Sr% Rb% Znppm Cuppm
AX48GC1 9cm 2,57 0,37 0,27 1,48 0,142 0,022 0,08 87 56
(cid:3)(cid:3) 30cm 2,05 0,35 0,44 1,75 0,146 0,019 0,10 94 78
(cid:3)(cid:3) 65cm 2,20 0,32 0,48 1,62 0,134 0,027 0,08 100 74
(cid:3)(cid:3) 110cm 1,70 0,32 0,40 1,75 0,137 0,023 0,08 104 78
AX49GC1 12cm 2,85 0,44 0,58 1,75 0,151 0,024 0,09 89 73
(cid:3)(cid:3) 50cm 2,25 0,48 0,62 1,75 0,150 0,023 0,09 102 72
(cid:3)(cid:3) 70cm 1,45 0,39 0,48 1,75 0,158 0,016 0,08 86 69
(cid:3)(cid:3) 105cm 1,75 0,43 0,58 1,62 0,146 0,023 0,08 94 76
(b)
Mineral %
Calcite 57
Quartz 12
Montmorillonite 5
Kaolinite 8
Glaucophane 4
Albite 6
SiO 5
2
Dolomite 3
∗
Ctotistotalcarbon,Corgisorganiccarbon.
Methane(µmol/kgwetsediment) an angular-subangular form, are small in size, have light-
gray colour, are consolidated, and contain (10–60%) well-
0 2000 4000 6000 8000
preserved pelagic foraminifera in a micritic calcite matrix.
0
The foram chambers are usually filled by sparitic calcite or
pyrite.TheplanktonicspeciespresentareOrbulinasuturalis,
50 Globigerinoidestrilobus,Globigerinoidessp.,andGloboquad-
rina dehiscens, which indicate a Lower to Middle Miocene
)
bsf 100 age and an open marine environment [17, 24, 31]. The
m detrital biomicrites are angular-subangular in form, gray-
c
h( brown in colour, contain tests and fragments of planktonic
ept 150 foraminifera,withfinegrainedaggregatesofcalciteandsilty
D
sized angular quartz grains in a micritic arenite matrix.
200 AmongthemainfossilsrecognizedarethespeciesOrbulina
universa, Orbulina suturalis, Globigerinoides trilobus, Globo-
quadrina nepethens, and Globigerinoides obliquus. which
250
indicate an Upper Miocene age [31], and an open marine
AX47GCI depositionalenvironment.
Comparable microfaunal associations of Miocene
AX49GCI
depositswerealsoidentifiedintheclastssampledbygravity
Figure5:Methaneconcentrationsofoneofthesouthern(AX47- coring in the upper parts of mud flows in Amsterdam,
GG1) and northern (AX49-GG1) gravity core stations at Thessa- Athina, Kazan, and Kula MVs. These data support the
lonikiMV. conclusion that part of the basement of the Anaximander
Mountains in this area contains Miocene deposits that
are comparable in age and facies with the geological
units of the neighbouring land area of SW Turkey.
RockclastsfromtheThessalonikiMVcores(AX46GC1, Considering that these units are probably in situ, it can
AX47GC1, AX48GC1, AX49GC1, and AX49AP1) belong be concluded that the onshore Miocene flysch deposits of
to two rock groups: fossiliferous micrites and detrital the Antalya Complex [24, 31] extend southward into the
biomicrites. Both these two groups were recognized also AnaximenesandAnaximanderMountains,thussupporting
in the other ANAXIMANDER mud volcanoes during this similar conclusions by Woodside et al. and other authors
project [24, 25]. The fossiliferous micrites exhibit mainly [6,7,12,32,33].
8 JournalofGeologicalResearch
(a) (b)
(c) (d)
Figure6:(a–d)Polarizedmicroscopepicturesofthinsectionsofmudbrecciarockclasts;bioclasticcarbonatepack/wackestones(grading
intomudstones/claystones)withGlobigerinidaeplanktonicforaminifera.
4.GasHydrateStabilityField forexample,wereashighas2.78◦C/mintheactivecentreof
Isismudvolcano[35].
As noted above, the sediment cores with gas hydrates were Agashydratestabilitydiagram,basedontheparameters
allfromrelativelyrecentlyeruptedmudbreccia,asindicated justdescribed,indicates(Figures7(a)and7(b),[27,36])that
bythelackofhemipelagiccoverorsurfaceoxidationofthe thegashydratesatThessalonikiMVarejustatthelimitfor
mud flow. Thessaloniki MV is the shallowest mud volcano theoccurrenceofstablemethanehydrate,anddonotextend
bearinggashydratesintheMediterranean(1265m).Atthis morethanafewmetersabovetheknownThessaloniki MV
depth the gas hydrates are just within, and near the edge depth.Thismeansthatwithonlysmallchangesintheenvi-
of the gas hydrate stability zone (Figures 7(a) and 7(b)) as ronmental parameters the gas hydrates could disassociate
determinedbythepressure(12.9Mpaat1265mdepth)and releasingwaterandmethane.Suchchangescouldresultfrom
seafloor temperature (∼14◦C). The field data collected at adecreaseinseafloorpressure(e.g.,bytectonicupliftorsea
ThessalonikiMVindicatedthattheGHoccurat1265msea leveldecrease)orbyslightincreaseinthebottomwatertem-
floordepthandinsubbottomsedimentarylayersatleastto perature(e.g.,fromaneventliketherecentincreaseinbot-
220cm below seafloor. The sea bottom water temperature tomwatertemperatureintheIonianSea[37]).Thesesmall
is 13.75◦C and the geothermal gradient is expected to be changes in temperature and sea level are both possible and
30–35◦C/Km or more, based on heat flow measurements sufficienttodestabilizethegashydratesatThessalonikiMV.
made in the Olimpi mud diapir field [34]. During the Although the amount of methane produced from the
MIMEScruisein2004,oneheatflowmeasurementmadeby autoclave core from Thessaloniki MV is minor in quantity,
Feseker and Foucher on Amsterdam Mud Volcano showed andthevolumeofgashydratesisunlikelytobelargeatthis
a significant warming of the sediments by over 3◦C in the site (based on the maximum depth at which gas hydrates
upper10mofmud[35,36].Inothermudvolcanoareasthe in this area can be stable, as indicated in Figures 7(a) and
heatflowimpliesmuchhighergeothermalgradientswhich, 7(b)),wedo not know thepotential arealextent of the GH
JournalofGeologicalResearch 9
Temperature(◦C)
5 10 15 20 25
0
50
Methanegasand
Methanegasand
water
water ice
200
Hydrothermal
curve 100
Permafrost
hydrate
400
Methane
hydrate
andwater ice
600
m) m) 500 Methane
( (
Depth 800 Depth 1000 Xhydrate Oceanic
hydrate
Hydrate
1000 phase +N+aNCalCl N 2N2 ++CCOo22,, CC22HH66
boundary HH22SS,, C C33HH88
1200 5000
Water/sediment
Geothermal BaseofGH
10000
curve −10 0 10 20 30 40
1400
Temperature(◦C)
(a) (b)
Figure7:(a)GashydratestabilitydiagramfortheThessalonikiMVgreaterarea(basedon[36]),(b)gashydratestabilitydiagram[27]
depictingwithanXthelocationofThessalonikigashydratefield.
at these water depths in the Eastern Mediterranean. Since at Thessaloniki MV indicate that the GH there are at the
these GH are at the upper boundary of the GH stability upper limit of the stability zone, and prone to dissociation
diagram their distribution and presence should be studied withtheslightesttemperatureincreaseorpressuredecrease.
morethoroughly. Thereforeitcouldbeaparticularlysuitablesiteforstudying
not only the mud volcano activity, but also the stability
of natural gas hydrates and their potential environmental
5.Conclusion impactshouldtheydissociate.
AnewgashydratebearingmudvolcanonamedThessaloniki Acknowledgments
wasdiscoveredintheAnaximanderMountainsonthebasis
ofitsseafloorexpressionandananalysisofcorescontaining The field and office work was supported by the EC-funded
gas hydrates in a matrix of mud breccia typical of mud projectsANAXIMANDER(EVK-CT-2002-20068)andHER-
volcanoes. It is the shallowest mud volcano there, lying at MES(GOCE-CT-2005-511234-1)whichtheauthorsgreatly
depths between 1315 and 1260m, with an areal extend of appreciate.Theauthorsthanktheofficersandthecrewofthe
about 1.67km2 and comprising three peaks on its summit. R/V Aegaeo for their important and effective contribution
GH were collected from three cores (two conventional during the field work. They also thank the anonymous
gravity cores and one autoclave core). The GH crystals reviewersfortheusefulcommentsandsuggestions.
have the form of flakes or rice. The degassing of the
228cmlongautoclavecoreprovided3.1litersofgas(mostly
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