Distribution And Interpretation Of BSR On Central Oregon Margin

In the past 20 years,the gas hydrate sample had been obtained on Hydrate Ridge,Multiple geology,geophysics and geochemistry date and results have been analyzed and published about the gas,gas hydrate and fluid system on Hydrate Ridge.This thesis is focus on the continental slope east of Hydrate Ridge.We compiled the multiple seismic data from geophysics surveys carried on the central Oregon margin,and observed the hydrate relating seismic characteristics(BSR,faults,chimney and so on).The purpose of this study is as follows:acquiring the distribution of BSR(BSRp and BSRs);interpreting the most likely causes of BSRs and comparing the results with Bangs on Hydrate Ridge.Our results could provide new advice for the study of"double BSRs" in marine gas hydrate bearing sediments.The conclusions are as following:(1)"Double BSR" is recognized.The BSRp is widespread under 500?1 300 m water depth as the active base of GHSZ in current P-T condition.And the BSRp shows a discontinuous character,which is highly disturbed and cut by faults and chimneys.The BSRs are 20?50 m lower,patchy beneath the BSPp,on the west flank of southern summit and the east slope of Hydrate Ridge.(2)The heat flow,which derived results from BSRp,was consistent with the ODP(Ocean Drilling Program)leg 146 and leg 204 in situ results.Partly,the anomalies could correlate to the gas and/or fluid upward migration.(3)Based on the interpretation of BSRs on southern summit of Hydrate Ridge,the BSRs of the continental slope east was discussed.Besides,the forming reasons of BSRs in the continental slope east were discussed by the results of geochemistry from leg 146 and 204.The most likely causes of the BSRs is the base of heavier hydrocarbon gas hydrate.About 98%methane and with the variable concentration of mix C2+ and un-hydrocarbon gases formed hydrate could be the basement of stability zone at BSRs depth.(4)Compared the results from the seafloor sonar side-scan study of the Hydrate Ridge region with the seismic reflection characters related to gas hydrate(BSR.fault.blank zone and chimney),the indication of gas and fluid migration was discussed in hydrate bearing sediments.In conclusion,the discussions of BSR,gas and fluid migration on central Oregon margin are related to the gas hydrate.The result of BSR on continental slope east Hydrate Ridge is a new insight for the regional gas hydrate system study,which obtained from the connection with migration of gas and fluid,characteristics of BSR and feature of gas hydrate existance.These results also provided a new example for gas hydrate exploration in China.