ApreliminaryorganicgeochemicalstudyshowsthatthesulphideoresfromthehydrothermaldepositoftheOkinawaTrougharegenerallylowinthetotalorganiccarbonandextremelylowinthesolubleorganicmatter.Inthealiphatichydrocarbonfraction,then-alkanesrangefromC15toC35,withusualmaximainthemiddlen-C20regionandstrongodd-carbonnumberpredominancewhenn>C25(CPI=1.2).Thedominantanaloginthearomaticfractionisphenanthrene,apolynucleararomatichydrocarbon,whichprovidesevidenceforhydrothermalactivity.Theorganicmatterderivedmainlyfrommarineplanktonicandterrigenousvascularplantsisentrappedinahigh-temperatureregimesuchasanactivechimneyandcooledquicklyinthesulphideoresontheseafloor.Organicmatterandsulphidesaredefinitelyproductsofahigh-temperaturealteration.ThebiomarkercompoundsindicatethattheoresareformedunderlowEhandpHconditions梐reducingtoanoxicenvironment,whichisfavourableforsulphatestobereducedintosulphidesbybiogenic(bacterial)orabiogenicactivity.
