RIDGE EVENTS ✦ OCTOBER 2001 5

ARTICLES

Introduction

The Monterey BayAquarium Research Institute(MBARI) conducted a jointmultidisciplinary cruise withscientists funded through theNational Undersea ResearchProgram to the Gorda Ridge inAugust 2000 using theR/V Western Flyer. Sixteen diveswere completed (Figure 1) in 14days utilizing MBARI’s ROVTiburon to explore and sample at anumber of hydrothermal andgeologic targets along and near theGorda Ridge. Four dives were atthe active Seacliff hydrothermal site(Rona et al., 1990) and three wereat the northern Escanabahydrothermal site (NESCA,Morton et al., 1994). The NESCAsite was drilled by ODP Leg 169 in1996 (Fouquet, Zierenberg, Miller,et al., 1998). Neither of these siteshad been visited by a submersiblevehicle since 1994 and we plannedto document changes at these sites.Other hydrothermal objectivesincluded locating and determiningif some of the ODP sites drilled inthe NESCA area had become activehydrothermal recharge ordischarge sites (as observed atMiddle Valley, Zierenberg et al.,1998), mapping the deposits fromthe southern Escanaba site(SESCA, Morton et al., 1994),exploring another sill complexsouth of SESCA to determine if it had anactive or fossil hydrothermal system, andcollection of fauna and bacterial matsfrom active hydrothermal sites.

MBARI’s 2000 Expedition to the Gorda RidgeDavid Clague1, Rob Zierenberg2, Alicé Davis1, Shana Goffredi1, James

McClain2, Norm Maher1, Eric Olsen3, Victoria Orphan1 , Stephanie Ross4,and Karen Von Damm5

1 Monterey Bay Aquarium Research Institute, Moss Landing, CA2 Dept. Geology and Geophysics, University of California at Davis3 School of Oceanography, University of Washington4 U. S. Geological Survey, Menlo Park, CA5 Dept. of Earth Sciences, University of New Hampshire

Geologic and petrologic objectivesincluded a detailed sampling of axiallavas between the shallowest part of thenorthern ridge axis at Narrowgate and

Figure 1. Sixteendives, T185 throughT200, completed byMBARI’s ROV Tiburonalong and near theGorda Ridge.

RIDGE EVENTS ✦ OCTOBER 20016

ARTICLESthe inferred southern end of the 1996eruption site at 42.61°N (Chadwick et al.,1998), sampling of a scattered group ofsmall volcanic cones southeast of thePresident Jackson Seamounts (Clague etal., 2000; Davis and Clague, 2000) andexposed along seafloor faults in thatregion, collection of samples from thelarge sill complexes and associated lavaflows at NESCA and SESCA to furtherevaluate the assimilation of sediment bythese lavas (Davis et al.,1994, 1998), andmapping and sample collection from agroup of volcanic cones in the axis of theridge at the northernmost end of theEscanaba Trough. Two dives were alsospent exploring the western walls of theaxial valley near the largest transformoffset in the ridge and near the northernend of the Escanaba Trough.

During these 16 dives, the ROVTiburon collected 213 samples of lava,hydrothermal deposits (some verydelicate) and lithified sediments; 61 pushcores of sediments, fine-grainedunconsolidated hydrothermal deposits,

and fine-grained volcanic debris; 5scoops of coarser unconsolidatedvolcanic debris; 46 animals; and 23 watersamples (11 gas-tight samplers and 12major samplers). In addition, wemeasured temperatures of hydrothermalfluids at the Seacliff and NESCA sites and

tested and collected 5 samples with a newsuction sampler designed to samplevolcanic glass from young flows.Observations and digital video recordingswere made along slightly more than 52 kmof transits during the dives. The dives alltook place between 2590 m and 3375 mdepth. We also collected 8 gravity coresand 30 wax-tipped rock cores during nightoperations on the cruise.

Seacliff Hydrothermal SiteThe Seacliff hydrothermal field was

discovered during dives using the Seacliffsubmersible in 1988 (Rona et al., 1990)following detailed sampling and mappingusing towed camera systems (Rona andClague, 1989, Clague and Rona, 1990) thatin turn had focussed on a region where achronic hydrothermal plume wasdiscovered (Baker et al., 1987). Thehydrothermal vent field is located about300 m above and 2.6 km east of theneovolcanic zone of the northern GordaRidge. The Seacliff measured thetemperature of the vent fluid at 247°C, but

was unable to collectwater samples. A sampleof the hydrothermalchimney consisted mainlyof barite and amorphoussilica, with minor sulfidephases with an outer zoneof mainly anhydrite andstevensite (a trioctahedralsmectite) and sphalerite(Zierenberg et al., 1995).

We were able tomap the entire Seacliffhydrothermal vent fieldduring the four dives(T186, T188, T191, andT192 on Figure 1) to thearea. We observed manymore active vents thanwere seen in 1988,perhaps because oftemporal changes in thefield, or because of thelimited bottom time

available in the original cruise. Wemeasured temperatures at severalvigorous chimneys emitting clear fluids ofup to 304°C and collected vent watersamples using both major an gas-tightbottles (Figure 2). The fluids have lower-than-seawater salinities and low metal and

Figure 2. One ofseveral vigorouschimneys ventingclear fluids.

RIDGE EVENTS ✦ OCTOBER 2001 7

ARTICLESsulfide contents. We also collected lavaand sediment samples, hydrothermaldeposits, and vent fauna and bacterialmats. The active chimneys consist mainlyof anhydrite and pale green smectite withminor sulfide phases including pyrrhotite,wurtzite and isocubanite. The chimneysare very fragile and were difficult tosample. They are surrounded by debrisderived from collapse of former chimneysand dissolution of the anhydrite. Theselight-colored sediments appear to consistmainly of amorphous silica. Withinseveral m of the vigorously ventingchimneys are extensive zones withshimmering water leaking through baritecrusts and low mounds covered bytubeworm colonies.

The biologic community includes agreat variety of vent-specific and otherfauna. There wereno animals presentin the talus as weapproached theSeacliff site fromthe south. Wemoved from talusinto debris fromthe hydrothermalmounds where wesaw deadtubewormsclumps covered inironoxyhydroxides. Arelatively barrenzone in whichvery few animalswere foundsurrounds themost vigorousvents, theexception beinglimpets(Lepetodrilus sp.),palm worms(mostlyParalvinellapalmiformis), andbright blue mat-like foliculinidciliates, whichcovered much ofthe hydrothermalarea.Temperatureswithin the ciliate

mats measured 3-6°C and the polychaeteAmphisamytha galapagensis that wasfound in close proximity to thefoliculinid mats had bright purple heads,indicative of consumption of the ciliates.Approximately 10-20 m south of thecentral area of venting, we found largemounds of Ridgeia piscesae tubeworms,limpets, pycnogonids, and more blueciliate mat, with associated nematodes.Most animals were associated withdiffuse flow areas, although limpets andparalvinellids were again in directcontact with shimmering water. Largetubeworm clumps, with red-armedanemones (Acitnostolidae?), were veryextensive, up to 80 m from the area ofmost venting. A list of species identifiedin our collections from the crusts and low

Table 1. Gorda / Escanaba taxaPhylum Family Genus Species Site Class

Ciliophora Spirotrichea Folliculinidae Folliculina ? SCnidaria Anthozoa Actinostolidae S, NEAnnelida Polychaeta Sibloginidae?? Ridgeia piscesae S, NE Polychaeta Hesionidae Hesiospina* vestimentifera S Polychaeta Polynoidae Lepidonotopodium piscesae S, NE Polychaeta Polynoidae Levensteiniella kincaidi S, NE Polychaeta Polynoidae Opisthotrochopodus tunnicliffeae S Polychaeta Alvinellidae Paralvinella palmiformis S, NE Polychaeta Alvinellidae Paralvinella sulfincola S, NE Polychaeta Ampharetidae Amphisamytha galapagensis S, NEMollusca Solenogaster Simrothiellidae Helicoradomenia* juani S Gastropoda Peltospiridae Depressigyra globulus S Gastropoda Peltospiridae Melanodrymia brightae SE Gastropoda Neolepetopsidae Neolepetopsis gordensis S, NE Gastropoda Pseudococculinidae Amphiplica gordensis S, NE Gastropoda Pyropeltidae Pyropelta* sp. NE, SE Gastropoda Clypeosectidae Clypeosectus curvus S Gastropoda Lepetodrilidae Lepetodrilus fucensis S, NE Gastropoda Provannidae Provanna laevis S Gastropoda Provannidae Provanna variabilis S, NE Bivalvia Solemyidae Solemya^ sp. NE Bivalvia Vesicomyidae Calyptogena^ sp. NEArthropoda Pycnogonida Ammotheidae Ammothea verenae S, NE Crustacea Philomedidae Euphilomedes climax S

S=Sea Cliff Site (GR14), NE = NESCA, SE = SESCA * tentative identification, ^ only shellscollected, observed. Additional small polychaetes and cnidarians have not been identified.

RIDGE EVENTS ✦ OCTOBER 20018

ARTICLESmounds around the most active vents ispresented in Table 1.

Northern Gorda Ridge AxisWe conducted two dives (T185

and T187 on Figure 1) and collected 18wax-tipped rock cores along the axis ofthe ridge near the Narrowgate region,just south of the region studied by Davisand Clague (1990). The first (northernmost) dive was aborted after only a shorttime on the bottom due to technicalproblems with the vehicle and the secondsearched for the proposed southern lavaflow from the 1996 eruption (Chadwicket al., 1998). This southern dive alsoexplored and sampled one of the largerof the flat-topped volcanic cones in theaxis of the Gorda Ridge. No young glassyflows or active or inactive hydrothermalfields were observed. The proposedsouthern lava flow for the 1996 eruption

at 42.61°N does not correspond to thesmall depth anomalies identified byChadwick et al. (1998) and may not exist.The samples are currently being studiedas part of an MS thesis evaluating thevariation in lava composition at theNarrowgate region of the North Gordasegment.

President Jackson SeamountsThe eight seamounts that

comprise the President JacksonSeamounts form a linear chain that

formed near the Jackson segment of theGorda Ridge; they are now located oncrust between 2.18 and 3.97 Ma old(Clague et al., 2000). The seamounts rangein volume from 24 to 68 km3. To thesoutheast of the southeastern seamount,the seafloor is dotted with small volcaniccones that may represent an incipientninth seamount, but one that neverdeveloped into a single large edifice. Wedid two dives in this region (dives T189and T190 on Figure 1) and collected lavaserupted from at least 9 of these scatteredvents. All the recovered samples are N-MORB, most quite primitive (MgO>8%)like the majority of lavas from thePresident Jackson Seamounts (Davis andClague, 2000). In addition, we collected asuite of samples from a 200-m tall ridge-parallel fault to sample crustal rockserupted along the ridge axiscontemporaneous with the largerseamounts. These too are all N-MORB.

Samples from the small volcanic conesinclude hyaloclastite and a light-coloredash deposit draping the top of the faultscarp, apparently the ash is derivedfrom one of the nearby cones or largervolcanoes since it contains small glassfragments of MORB composition.

West Wall of the Axial Valley

We also did two dives on thewestern scarp of the axial valley, onenear the southern end of the Centralsegment and the other near the northernend of the Escanaba segment (divesT193 and T194 on Figure 1). Thenorthern dive site (T193) was of interestbecause prior to several hundredthousand years ago, the Gorda Ridgewas morphologically more like other

spreading centers in the Pacific and lackedthe deep axial valley. The recoveredsamples were selected to sample lavas thatpredate the formation of the present-daydeep axial valley, and will be compared tothose erupted during the current period ofmagma starvation that has formed thedeep valley. The dive progressed up astair-step slope of alternating blocks ofgreenstone and glassy pillow lavas. Thegreenstone has planar fault surfaces(Figure 3) and is mainly volcanic brecciawith abundant secondary quartz, chlorite,and albite. Quartz veins up to 4 mm thick

Figure 3. The planarfault surfaces of thegreenstone blocks.

RIDGE EVENTS ✦ OCTOBER 2001 9

ARTICLESoccur within the breccia samples.Sediment scoops collected volcanic glassand also recovered small fragments ofvein quartz, often including small crystals.Some of the analyzed glasses have up to0.53 wt.% K2O and fall outside the rangeof previously described samples fromGorda Ridge (Davis and Clague, 1987).

The second dive on the valleywalls (dive T194 on Figure 1) explored anarea of bright acoustic backscatter on sidescan sonar map of the valley floor in thenorthern Escanaba Trough that wasthough to represent a recent volcaniceruption. The area was entirely covered insediment and no lava was seen, nor wereany fissures. The high backscatter may becaused by a young lava flow, but it is nolonger exposed on the surface and couldnot be sampled. The dive continued upthe eastern 660-m high wall of theEscanaba Trough where we encounteredthick, well-indurated sedimentary rocks.Atwater and Mudie (1968, 1973) had usedgeophysical data to hypothesize that thevalley wall in this region consisted offaulted sedimentary rocks. The wall, asthey proposed, consists of a stairstep ofdiscrete fault blocks. The more massive ofthese units are sand to siltstone withvertical tabular joints. This is apparentlythe same sediment sequence that fillsthe Escanaba Trough and was emplacedduring the late Pleistocene Missoulafloods (Zuffa et al., 2000). The 660 m ofuplift of the axial valley wall, althoughaccomplished with movement on aseries of ridge-parallel faults, hasapparently mostly taken place withinthe past 10 ka. Lava flows crop out inthe uppermost wall, indicating that theoutermost and now uppermost faultblock predates the sediment filling ofthe valley.

Volcanic Cones at north end ofEscanaba Trough

One dive explored a cluster ofconical volcanic vent structures near thenorthern end of Escanaba Trough (diveT196 on Figure 1 and the cover). Thesecones appear to be older to the west andeach has a distinct composition. Thewesternmost cone has a large summitcrater that is breached to the east. Lavasfrom all the cones are N-MORB, including

a few moderately vesicular lavas (25%vesicles) from the breached cone.

NESCAWe did three dives at NESCA

including two to explore thehydrothermal vents and ODP drill sites(dives T195 and T197 on Figure 1) andone to explore the extensive lava flowthat covers about 12 km2 in the region(dive T198). A few samples from thisflow were recovered previously (Davis etal., 1994,1998), but no systematiccollection of samples from the differentparts of the flow had been attempted, norwere there but minimal visualobservations of the flow. We not onlymapped and collected these flows duringthe three dives, but also collected 9samples of glass from the distal edges ofthe flow field using a wax-tipped rockcorer. The compositions of all the 43samples analyzed to date are similardespite some parts of the flow predatinguplift of the sediment hills and otherparts post-dating the deformation. Onearea that we had inferred to be the ventcomplex for the flows based on detailedbathymetric and sidescan coverage,

turned out to be lava flows disruptedand broken during uplift above a deepsill.

The main high-temperature venthad essentially an identical 215°Ctemperature it had when discovered in

Figure 4. ODP hole1038A drilled to adepth of 115 mthrough the sulfidestructure which is hostto the main high-temperature vent.

RIDGE EVENTS ✦ OCTOBER 200110

ARTICLES1988 (217°C, Campbell et al., 1994)despite the fact that ODP hole 1038A(Figure 4), located approximately 4 maway, was drilled to a depth of 115 mthrough the sulfide structure on whichthe venting occurs. The drill hole itselfwas diffusely venting hydrothermal fluidand was colonized by palm worms andother hydrothermal fauna. Although thetemperature of venting at this moundhad remained stable, the hydrothermalfield had all but shut down, and thenumerous mounds venting lowtemperature fluids and supportingextensive colonies of tube worms in 1988were inactive with essentially no signsindicating the former abundance of ventfauna.

We searched for and found fiveother ODP drill holes, including Hole1038I which was drilled to a depth of404 m stopping in basaltic basement, but

found no evidence for fluid flow in anyof these holes. The drill string that waslost at the conclusion of Leg 169 wasobserved to be folded on itself once andlaid out across the seafloor about 0.5 kmfrom the location where it was lost.

Hydrothermally derived asphalticpetroleum was recovered in several ofthe push cores, impregnating several ofthe sulfide samples, and as a roundedmound of tar (Figure 5). The material in

the push cores and sulfide samples, whichcommonly had a strong diesel smell,appears similar to materials describedpreviously (Kvenvolden et al., 1987, 1994).The tar mound appears to be a hollowchimney structure formed when hot tarerupted onto the sea floor and is unlikeany previously collected sample.

After exploring numerous massivesulfide mounds, we found one still-activesite (6X), out of the many that were activein 1988 and 1994. The temperature of 6Xvent was 207-212°C. There was only onemoderately sized clump of Ridgeia piscesaepresent in the area and the temperaturesurrounding these animals was 11-45°C.Paralvinellids (Paralvinella sulfincola) werevery abundant, as well as various bacterialmats mat types (which we collected viapushcore). Vesicomyid shells werespotted at the top of Central Hill but theencounter with the lost ODP drill string

prevented further exploration ofpotential clam/bacterial mat areason the east side of the Central Hill.Likewise, solemya shells wereseen on sulfide mounds in thearea, although we never saw anyliving individuals.

SESCAA single dive at SESCA

(T199 on Figure 1) discoveredabundant large hydrothermaldeposits, mainly on top of thelarge flat-lying sill complex. Noactive hydrothermal vents werefound and all the deposits have asimilar appearance in terms ofalteration and degradation.Sixteen previous camera tows, 9dredge hauls, and 5 submersibledives (Morton et al., 1994) hadobserved far less hydrothermaldeposits and lava flows than we

encountered on our one dive. Highlyweathered sulfides were observed withdead Ridgeia tubes encrusted with ironoxides and orange-brown iron oxidizingfilamentous microbial mats. Closermicroscopic inspection of the mat revealedheavily encrusted interwoven twistedfilaments resembling Gallionella spp. Filterfeeding animals were very abundant onold sulfide mounds. In general the faunaon the old lava flows is typical for the

Figure 5: A mound ofh y d r o t h e r m a l l yderived tar.

RIDGE EVENTS ✦ OCTOBER 2001 11

ARTICLESdeep-sea: sponges, gorgonians, sea stars,and anemones. However there were somevent associated limpets (Pyropelta sp.) inthe area.

The margin of a shallowlyemplaced sill is exposed where slumpingof sediment has exposed it. Fifteen lavasamples from the exposed sill and fromthe surficial flows are similar incomposition to the 2 samples describedpreviously (Davis et al., 1994,1998), butvary in MgO from 7.7 to 8.2%. These flowsare cut by numerous fissures, someseveral m wide, indicating that thevolcanic activity here is quite old. Thisobservation is consistent with theapparent old age of the hydrothermaldeposits and suggests that their formationwas directly tied to a single period of sillemplacement and eruption. There are twotypes of sills in the area-large shallow sillsthat have the outline of lava flows, but areroughly 30 m thick, and deep sills thatuplift small steep-sided hills of sediment(Denlinger and Holmes, 1994). Much ofthe hydrothermal activity was associatedwith the large shallow sills which suggeststhat the hydrothermal convective cellspenetrated only to shallow depths (tens ofmeters) in the sediment above the sill.

South of SESCA

A single dive was done on anothersill complex south of SESCA (dive T200 onFigure 1 ). Examination of side-scan datasuggested that lava flows were absentfrom this area and our dive found noexposed lava or glass fragments in thesediment to suggest that lava eruptednearby. As at SESCA, however,hydrothermal deposits, all inactive, areabundant on the steep sides and top of theshallow sill complex. These deposits havesimilar degrees of alteration anddegradation, consistent with the idea thatthe deposits form during a relatively shorttime interval after emplacement of thesills. The observations and samplessuggest that this complex is older thanthat at SESCA. Both pyrrhotite-richmassive sulfide and barite-rich sampleswere recovered. Several samples haveabundant sphalerite and galena, similar topreviously described samples fromEscanaba Trough (Koski et al., 1994).Many of the push cores contain asphaltic

petroleum and have a strong dieselsmell, as does one small sulfide chimneyrecovered from the sediment. A secondsmall mound of tar, similar to that fromNESCA, was recovered here.

Summary

The many observations andsamples collected during the cruise arestill being processed. The R/V WesternFlyer and ROV Tiburon were ablecomplete 16 dives in rather poor weatherconditions on the Gorda Ridge. Duringthe cruise we documented the conditionsat two active hydrothermal vent fields onGorda Ridge and sampled high-temperature vent fluids, vent fauna(including a colorful blue ciliate), anddelicate sulfate/clay chimneys. We alsosampled hydrothermal deposits at twoadditional regions where activity hasceased. We searched for the proposedsouthern lava flow for the 1996 eruptionand conclude that no eruption took placeat this location. We sampled the lavas,hydrothermally altered lavas, andsediments that form the steep axial valleywalls on Gorda Ridge and will be able toexamine any changes in lava chemistrythrough time. We collectedcomprehensive suites of lava samplesfrom several flows to evaluate how andwhere sediment assimilation by theselavas occurs. Finally, we collected a suiteof lavas from the Narrowgate region ofthe northern Gorda Ridge to evaluate thesmall-scale variability in magmaticprocesses at this moderate spreading-rateridge.

References

Atwater, T.M., and Mudie, J.D., Block faultingon the Gorda Rise, Science, 159, 729-731,1968.

Atwater, T.M., and Mudie, J.D., Detailed near-bottom geophysical study of the GordaRise, J. Geophys. Res., 78, 8665-8686, 1973.

Baker, E.T., Massoth, G.J., Collier, R.W., Trefry,J.H., Kadko, D., Nelson, T.A., Rona, P.A.,and Lupton, J.E., Evidence for high-temperature hydrothermal venting on theGorda Ridge, northeast Pacific Ocean, Deep-Sea Res., 34, 1461-1476, 1987.

Campbell, A.C., German, C.R., Palmer, M.R.,Gamo, T., and Edmond, J.M., Chemistry of

RIDGE EVENTS ✦ OCTOBER 200112

hydrothermal fluids from EscanabaTrough, Gorda Ridge, Chapter 11 inGeologic, hydrothermal, and biologicstudies at Escanaba Trough, Gorda Ridge,offshore northern California, U.S. Geol.Surv. Bull., 2022, 201-222, 1994.

Chadwick Jr., W.W., Embley, R.W., and Shank,T.M., The 1996 Gorda Ridge eruption:geologic mapping, sidescan sonar, andSeaBeam comparison results, Deep-Sea Res.II, 45, 2547-2569, 1998.

Clague, D.A., and Rona, P.A., Geology of theGR14 site on northern Gorda Ridge, inGorda Ridge: A seafloor spreading center in theUnited States Exclusive Economic Zone, ed.by G.R. McMurray, Springer-Verlag, NewYork, 31-50, 1990.

Clague, D.A., Reynolds, J.R., and Davis, A.D.,Near-ridge seamount chains in thenortheastern Pacific Ocean, J. Geophys. Res.,105, 16,541-16,561, 2000.

Davis, A.S., and Clague, D.A., Geochemistry,mineralogy, and petrogenesis of basalt fromthe Gorda Ridge, J. Geophy. Res.,92, 10,467-10,483, 1987.

Davis, A.S., and Clague, D.A., Gabbroicxenoliths from the northern Gorda Ridge:Implications for magma chamber processesunder slow-spreading centers, J. Geophys.Res., 95, 10,885-10,990, 1990.

Davis, A.S., and Clague, D.A., President JacksonSeamounts, northern Gorda Ridge:Tectonomagmatic relationship between on-and off-axis volcanism, J. Geophys. Res., 105,27,939-27,956, 2000.

Davis, A.S., Clague, D.A., and Friesen, W.B.,Petrology and mineral chemistry of basaltfrom Escanaba Trough, Chapter 9 inGeologic, hydrothermal, and biologicstudies at Escanaba Trough, Gorda Ridge,offshore northern California, U.S. Geol.Surv. Bull., 2022, 153-170, 1994.

Davis, A.S., Clague, D.A., and White, W.M.,Geochemistry of basalt from EscanabaTrough: Evidence for sedimentcontamination, J. Petrol., 39, 841-858, 1998.

Denlinger, R.P., and Holmes, M.L., A thermaland mechanical model for sediment hillsand associated sulfide deposits alongEscanaba Trough, Chapter 4 in Geologic,hydrothermal, and biologic studies atEscanaba Trough, Gorda Ridge, offshorenorthern California, U.S Geol. Surv. Bull.2022, 65-76, 1994.

Fouquet, Y., Zierenberg, R.A., Miller, D.J., andthe Leg 169 Scientific Party, Proc. ODP, Init.Repts., 169, College Station, TX (OceanDrilling Program), 592p., 1998.

Koski, R.A., Benninger, L.M., Zierenberg, R.A.,and Jonasson, I.R., Composition and growthhistory of hydrothermal deposits inEscanaba Trough, southern Gorda Ridge,Chapter 16 in Geologic, hydrothermal, andbiologic studies at Escanaba Trough, GordaRidge, offshore northern California, U. S.Geol. Surv. Bull., 2022, 293-324, 1994.

Kvenvolden, K.A., Rapp, J.B., Hostettler, F.D.,Morton, J.L., King, J.D., and Claypool, G.E.,Petroleum associated with polymetallicsulfide in sediment from Gorda Ridge,Science, 234, 1231-1234, 1987.

Kvenvolden, K.A., Rapp, J.B., and Hostettler,F.D., Hydrocarbons in sediment fromEscanaba Trough, Chapter 15 in Geologic,hydrothermal, and biologic studies atEscanaba Trough, Gorda Ridge, offshorenorthern California, U.S. Geol. Surv. Bull.,2022, 279-292, 1994.

Morton, J.L., Zierenberg, R.A., and Reiss, C.A.,Geologic, hydrologic, and biologic studies atEscanaba Trough: An Introduction, Chapter1 in Geologic, hydrothermal, and biologicstudies at Escanaba Trough, Gorda Ridge,offshore northern California, U.S. Geol. Surv.Bull., 2022, 1-20, 1994.

Rona, P.A., and Clague, D.A., Geologic controlsof hydrothermal discharge on the northernGorda Ridge, Geology, 17, 1097-1101, 1989.

Rona, P.A., Denlinger, R.P., Fisk, M.R., Howard,K.J., Tagon, G.L., Klitgord, K.D., McClain,J.S., McMurray, G.R., and Wiltshire, J.C.,Major off-axis hydrothermal activity on thenorthern Gorda Ridge, Geology, 18, 493-406,1990.

Zierenberg, R.A., Fouquet, Y., Miller, D.J, and theLeg 169 Scientific Party, The deep structureof a sea-floor hydrothermal deposit, Nature,392, 485-488, 1998.

Zierenberg, R.A., Schiffman, P., Jonasson, I.R.,Tosdal, R., Pickthorn, W., and McClain, J.,Alteration of basalt hyaloclastite at the off-axis Sea Cliff hydrothermal field, GordaRidge, Chem. Geology, 126, 77-99, 1995.

Zuffa, G.G., Normark, W.R., Serra, F., andBrunner, C.A., Turbidite megabeds in anoceanic rift valley recording Jokulhlaups ofLate Pleistocene glacial lakes of the westernUnited States, J. Geology, 108, 253-274, 2000.

ARTICLES