Ancient hydrocarbon seepsfrom the Mesozoic ...

(2002)2 , 63-91

Ancient hydrocarbon seeps from the Mesozoicconvergent margin of California:carbonategeochemistry, fluids and palaeoenvironmentsK A CAMPBELL', J D A N D D DES

Stare USA,'NASA CA, USA

ABSTRACT

than a dozen hydrocarbon seep-carbonateOccurrencesin lateJurassic to late Cretaceous and accretion-ary strata, western Caiifornia.accumulated in turbiditelfault-hosted serpentinediapir-related settings. Threesites. Paskenta,Cold Fork Cottonwood Creek and Wilbur Springs. were analyzed for their petrographic. geochem-ical and attributes,andeach showed a three-stage development that recorded the of fluidsthrough reducing-oxidizing-reducing conditions. The first stage constituted diffusive, reduced fluid seepage

through seafloor sediments, as indicated by micrite. corroded surfaces encrustedwith framboidalpyrite, yellow calcite and negative cement stable isotopic signatures as low as -35.5% as

as -10.8% Mega-invertebrates, adapted to reduced conditions bacterial chemosymbiosis,nized the sites during this earliest period fluid seepage. A second, early stage Of centralized venting at the seafloorfollowed. which was coincident with hydrocarbon migration. as evidenced by nonluminescent fibrous cements with

as low as -43.7%. elevated (up to petroleum inclusions, marine andpyrite. Throughout these early phases hydrocarbonseepage. microbial sediments were as layered

and clotted. nondetrital micrites. A late-stage of development marked a return to reducing conditions duringburial diageneris. as implied by pore-associated Mn-rich cement phases with bright patterns.and negative signatures as These recurring patterns sites highlight similarities inthe hydrogeological evolution of the Mesozoic convergent margin of California, which influenced local geochemicalconditions and organism responses. A Comparison of stable carbon and oxygen isotopic data for 33 globally distrib-uted seep-carbonates, ranging in age from Devonian Recent, delineated three groupings that reflect variable fluidinput, different regimes and time-temperature-dependent burial diagenesis.

Key-words: ancient hydrocarbonseeps. California carbonate geochemistry, carbonate paragenesis, stableisotopes

Received 23 June 2001; accepted November 2001

Corresponding author: Kathleen A. Campbell. Geology Department, University. of Private Bag 92019,Auckiand, NewE-mail: Tel: 7599. ext. Fax: 7435.

INTRODUCTION

Modern hydrocarbon hydrothermal(Fig. 1) arc situated at

and biological where andfluids arc discharged at t h e scafloor, sustaining lush

Modern biota areby and recurring of

2002 Ltd

biotic bactcria in Van Dover 2000).bactcria oxidize fluids, which are gcncratcd

along boundaries spreading subductionzones), diapirism undersealandslidesorganic-rich porcu'atcrsk Moore 1990; Schumacher Abrams

form from fluids, ranging

to hydrocarbon

64 A. CAMPBELL

.. . . ... . . . . . , ,., ., ,, .

Fig. map of modern and ancient to hydrothermal vent and hydrocarbon with

Plate boundary double tooth Data fromCampbell Link et Dover

with watereta!. 1995; 1987).

and hydrothermal vent depositsrcponed from

dcposirs and world-wide(Fig. 1) Campbell dc Rondc

1996).Microorganisms have occupied marine settings d c

Rondc 1996; andin volcanic deposits

since a t 1997). Seep-carbonatesabundant have in

rocks old as Devonian (Peckmann 2000).Criteria in the

arc in elsewhere 1994,2000,1989;

1999; ctIn general, deposits arc rccognizcd

by their and associations, rhcir

and and rhcir body fossil, textural or biomarkcrof organism activity In the

sequence of phases ordeposits provides a for

chemical of forand wirh

organism activity (cf. Cook Stakes 1995).within of

isoropic of fabricand mineral phases can be to

fluid-diagenctic of an ancienr orand

(cf. 1996; Sample 1993).To more than a dozen Upper to

hydrocarbonin

Group) and accretionary prism Group)of and central California (Fig. study

2002 2 , 62-94

Mesozoic hydrocarbon seeps, California 65

I.

50 100

Fig.2. and map seep-carbonatecircler) of western California. The three

study the Cold Fork of Creek, andgeology of

margin from Accretionary Complexto broken and

of Croup lo

- and Sierra Nevada batholith

present-day indicate rock typesunrelated study.

is first to an ofrhcand three of

as a andThe Upper

Springsand Cold ForkCretaceous) seep dcposirs (Fig. California,chosen derailed study because rhey span a considerable

of 70 Myr fluid andin

addition, in of two knownof that

carbon this margin -and

(Fig.3; Campbell 1993). Thefossil Sauna of rhe localities pan

2002 2, 63-94

Fig.3. three seep-carbonate 01study. (A) The deposit is situated within a

Compare with photograph4A)

el The Cold Cottonwood Creeksituated near the the Fork and

Map and ages of unit5madihed The deposit

with theGreat Valley Map

(19846.

66 K. A. CAMPBELL e t

in vent-step world-wide (Camp-.% rhc had

nor, this study, analyzed for their andattributes.

GEOLOGICAL A N D PALAEONTOLOGICALCONTEXT OF STUDY SITES

ofthc Group,California, as a forearc basin was recognized in

early years of tectonic reconstruction ofgeology (Dickinson 1971; 1970; Hamilton 1969).

up to 15 thickdites were deposited the Jurassicgene, in a north-sourh axial forearc basin .%

1981).The petrofacies and tectono-chronologicallinks among forearc Group),

(Franciscan Complex) arc(Sierra arc now1983). places along western margin of outcrop

Great forearc strata and ofthe crust (Coast Ophiolirc) wcrc

juxtaposed ahovc highly deformedand mctamorphozed Franciscan subductionBailey 1964; Dickinson 1996).

For pods and of anomalouswith ahundanr wcrc known

from fossil-poor Grcat Anderson 1945; Bcrkiand 1973; Campbell 1993;son Gabh 1369; 1956; 1395)

2) . was undersrood thar enclosingtic had offshore origins, most early

assignedto shallow reef and brachiopod coquinas from arc

Campbell2001; Campbell 1994).

Also abundant arc tuhcs and fossilof lucinid, and

(including up 25 in length), which arc nowrccognizcd to bc living ehcmosymbiodc groups

1993).deposits predominarc among the

Mesozoic seep-carbonares of California.fluid migration and

fluid expulsion in an forcarc basin, fromJurassic (Tithonian) to Creraceous (Campanian).

from Paskenta and Cold Fork of Cortonwood limestone deposits, whichoccur along large-scale,norrh-cast-trending, regional

features and Sulphur Springs Faults, Fig. and Moxon (1990) used

and stratigraphic to a

and similar faults

during the of Great Valley Faultsoffcrcd pathways for

the prism and fluidfrom depth. considered within rhc

overall Latearc-trench system, Greatcarbonates formed more or less continuously, in patchydistributions along for (Fig. during aspan ofat offorcarc history.

Sedimentary foliatehost seep-carbonatcs of the Springssrudysitc which are part unusual,and spatially restricted rcctonic of Early Cretaceous

Alhian). This cvcnt rcpresenrsand expulsion in seafloor diapirs of

and dcepiy narcd fluids from oceanic crustOphiolirc; Campbell 1993; Carlson

exposed at Wilbur Springs is an of a

possibly a al.

and i s analogousmud andfound in Marianas forearc basin1992; 1991). Wilbur Springs carho-nares of this study formed seeps aropor on the flanks of source protrusion, fluids

diapir breaching seafloor (Campbell 1993). the carbonarcs raked from

protrusion mobile flows thatwith

along floor of the forearc basin ct

1993;

METHODS OF STUDY

thin sections were examined byzed, cross-polarized, W and light microscopy.

a(10-13

strucred of thin sections aid in rhc selection of for analysis.

alizarin red and1994) to among

Rock-chip preparation for analysisincluded in discillcd anddrilling of a binocular microscope. samples (1 and roasted at

for h. from hy reac-tion with orthophosphoric acid and in an

carbonate attached to a I1the

To in carho-narc, micrirc run at CarolinaStare on a Finnigan MAT 251 mass


spectromercr, had throughtrap internal

laboratory samples andruns. For both carbon and

tory precision than and(NCSU).

Ira of carbon-coatcd, thinon a SX-51 dis-

persive electron probe a t

of California, (UCB). conditionsas follows: angle, 40.0'; width of

bcam, bcam voltage, bcam current,count times for To dctcrnminc

precision and limits during microprobe runs, spots were analyzed on a standard

(UCB die same conditions as theaccuracy of measurements was

by correction of acquired standard inaccordance with measured on

srandard calcite (by plasma-massX-ray

spectroscopy Online data andreduction pcrformcd by Probe for

an applied KO

for clement (Donovan 1993)o-factor

addition,- based a n a atom of Ca,

and corrected measurements of foreffecr of the ion, further improving

accuracy. were corrected fordrift, count standard count drift,off-peak backgrounds (linear and

height analysis.

RESULTS OF FIELD STUDIES

outcrop of Paskenta, Cold Fork ofCotronwood and Wilbur Springs can bcfound in (1993, Campbell

(1993) and Campbell (19951.in pods or lenses Fig. which

into broad types Fig.( i ) dark calcite containingand grains; and various lighter

Commonly, thcsc carbonarc spa-tially irregular, pyrite-coated surfaces(Fig.4C). to

a fill ofinternaltals or spar. I n addiuon, s m a l l (up a

in diamctcr), nodular of carbo-nate could be into the for short distances from central areas of

2002

Fig.4. Typical hand and petrographicheld locality.

Digger Creek and and county road A9;

geology seep-carbonaleby Valley

(broken andRange Outcrop block from

by andrestricted CampbellCoin= in Entire long.of typical broadly into dirk and

separated by dark. pyrite-coated

accumulation lens m long, Fig.4A) andCold Fork lens long) along

lengths, the Wilbur Springs deposin quarriedand broken float blocks could he

sampled 1995).

68 K . A . CAMPBELL

RESULTS OF LABORATORY STUDIES

A isotopic and analysiscollected from three srudy sites

recognition of a recurring stratigraphy, and aninferred w a s broadly similar

frameworkthe of evolving geochemical condi-

tions nature and timing of seep organismand

arc i n following sections, the

and discussion of peuographic, isotopic and compositional dara.

Petrography and paragenesis of three CalifornianMesozoic seep deposits

OverviewA recurring sequence was identified for

including four major carbonate phases, onephasc, 10 phases carbonarc or

and corrosion(carbonate phases in

Corrosion eithcr an mineralphasc coating, or was

for allsummarized in Fig. 5 .only and textural phases

the Californian deposits inFig. 5; Figs 6 and 7A). A similar was

from of rhcCanadian (Beauchamp 1989; Beauchamp

1992; Savard 1996). For Californian sites,sequence of (Fig. 5 ) may

main diagcnetic stages: early1-7; Fig. 7) with organism and

( 2 ) port-associated, burial-diagcncticFig. S), with no biouc associarions. In addition,

and of fossil worm(Fig. 9) Thcsc were imporranrin acting conduits for fluid dur-ing burial long after seeping had been by Thus, die oftube worm animals early in influenced

fluid-diagcnetic record that in theCalifornian deposits. Finally, with to cement

we and relativeposition of probable (Fig. 10).

of occurredcolonization by afluid i s inferred have a t or near

In particular, most fossilsassociared wirh micrirc phase (micrirc 1,1, and abundant,

mega-fossils,foraminifera, and1 also contained and

detritus from corrosionand posr-dating the micritc, vugs

and which, in places, with pyrite (event 2; Fig. Following corrosion,

and pyrite-encrusred islands com-monly all that remained micrirc phase; sub-

residual regions by6 and 7Aj.

Worm rubes 3) and othcrcoated by a distinctive carbonarc 4 ) diatin thin as an

(cf. Beauchamp 8; 1992). This ubiquitous Cementtypically contained of organic and pyrirc,and either filled spaces or existing grains (Figs6and 7A). The likely formed an

in of the early micrirc, probably dissolution associated with indicated bygencc and growth of yellow crystals from

regions. Both carbonare phases displayed similar under CL ro brighr orange). A

phasc that both as primary cement andspar has been documented in

Foukc 1994).The next major phasc o f a

fibrous cement (fibrous 1 which formedradiating horizons (event 5)

from, arc intcrlaycrcd with, cal-cite above (Figs6 and 7A). Fan-likc offibrous cement displayed undulosc in

light, and wcrc under CL. Atlocality, fibrous dark inclusions

appcarcd to yellow-brown globules or blackin plane-polarized light (Fig.7C-E). The dart inclu-

sions (Fig.and hydrocarbons. Fibrous

from Cold Fork Wilbur Springs sites donot contain inclusions, either ofmodification, or liquid hydrocarbons nor

in fluids from localities. A final,characteristic of the fibrous i s an inferred boring structure of a marine organism (Fig. which

CL (Fig.7F). prescncc(event through micrirc and fibrous

a hard ground on scafloorprior burial.

fillings or linings of (micritc 2,poor, 7 ) common at

and diagenctic stages and 6) .

2002


3 ' 3u

3 3u

3

70 K . A. CAMPBELL

I

3 3ud

In pore-associated,or was with fibrous cements

Late stagephases and events of diagcncsis wcrc

in pores and or by lare-stage dissolution/of selected fabrics onset of

was marked by corrosion cvcnt8)along margins Fig. 6), and formation of

rim cement types. For example, a

locking, 9 ) rimmed(Fig. and splays ofNrc in some fibrous both of which thesame dark SB). rim fabric con-sistcd of thin horizons rhick) of an inclusion-rich,isopachous calcite 10; Fig. which was asso-

ciated with cavity margins, or outermost offibrous ccmcnrs. isopachous exhibited a grainy

bright orange which isof probably from formcd

fibrous 1or cements rhat spatially affiliated withthis later, inclusion-rich

was by carbonarc,ciclastic and 11-14; Fig. 5). In

Fig. inclusion-rich isopachous by calcite 11).Many

filled or lined with a whichappeared golden-yellow in hand sampler (Fig. orgolden-brown dark-brown in thin section and This contained variableamounts of angular quartz and feldspar grains, and prcccdcd

was with the precipitation ofiatc calcitc(calcite spars Fig. and (event 14).Calcite spars 1 and 2 by dark-orangcorange CL, spar homo-geneous or mottled, or zonationFig. occurred as fine admixturcs silt-clay fill, or strongly prismatic

(Fig. which wedged among

The youngest cvcnt16) was fabric and

particularly calciteand addition, with

within the 1that a (fibrous 2 ,

17; Fig. 5), nor conspicuous in plane-polarized lightfibrous 2

easily distinguished by its brighr whcrc i r unaltered, nonluminesccnt, early

fibrous (Fig. Commonly, rhcbands of the late fibrous were spatially connccrcd

small dissolution with

spar

... ...

72 K . A. CAMPBELL

Fig.6. Entire thin illustratingcarbonate Cement in 1

1 and 2 The threearc by CE3. Large formed during

recrystallized light.

for decay or priorIn rare examples (Fig. originalas thin, brown by calcite rims.However, more walls away

only theOriginal walls probabiy were of an

organic, and chitinous material (cf.a!. Internal are visible in larger speci-

mens and worm with(Fig.9C). In light

oxidation rinds, illuminated asthin, darker rims around unalteredOnce animals died, both and tubefaces wcrc coated and by tha t post-datedpyrite and yellow calcitc (Figs and 9).

Microbial sedimentary textures2) occuncd in unusual

and spatial relationships to

nctic phascs at all Californian Mesozoic(Fig. 10). These included: (i)micritc, which coated corrosion horizons Fig.or lined pores and Fig.with indistinct margins, surrounded by translucent microspar

and anddraped walls of worm

Fig. or encrusting Fig.The Californian examples similar to putativemicrobial fabrics in Italian of Mio-cene age 1999, Fig. p. 263, andFigs9 and 10, p. 266-267; 2000). A

analysis of thc Iralianorigin

a!. 1999).The infcrrcd microbial fabrics ofthe Californian seep-carhonatcs occurred through.our stage, and arc study.

Stable isotopes of carbonate carbon and oxygen

The isotopic analysisCalifornian dcposirs Fig. indicarc a

origin. This is based ondepiction in Aharon 2000;

Kauffmaii a!. 1996; 1987;of as low as (PDB). In

addition, carbonate phases formrd isoto-pic groups, and could be discriminatedby analyzed included major carbonatc phases fibrouscalcitc spar), shell-carbonate samples earlyphascs and a concretion from nearby

carbonarc phascs were norbecause spatial resolution of the was to

contamination of powders by adjacent phascs.A carbon versus isotopic cross-plot (Fig.11)

a grouping ofthc into four fields, com-

prising the authigenic carbonatcs from of rhrcclocalities and shell-carbonate. carbonatc carbonwas the depleted across allphascs with -17

PDB. Possible carbon sources for range ofinclude sourced methane,

mired (thermogcnic ordissolved carbon (DIC) in or

fractions (cf. Aharon 1997). In comparison, the ColdFork Wilbur Springs carbonate carbon values weresimilar to each other -19 to

PDB), and suggest mixing of hydrocarbon andwater D I C 1991)during

signatures all clustered in anear PDB for both and This pattern is

shell near isotopic equilibrium bicarbonarc (Anderson Arthur 1963). Specifically,

2002 63-94

74 K. A. CAMPBELL

Fig. Petrographic of late Cavity lined with dentate cement inclusion-rich and blocky calcitedentate cement light view and as CL.

character of dentate and cements, dull orange Ct and of calcite bothdark orange 1, and orange 2, 2

biocky calcite rill-ciay ID) view as in in CL.no: detected and calcite (El radially cement and pore cemented

with Same view and Cl .1 with pyramidaland tabula; character barite. formed in

radially Cement, filled with 3 A. plane-polarized Same view andCL. early cement by bright cement band spatially with

iate 3.

2002 2 , 63-94

El+

LO+

ox-€*-


Table 3 Mean elemental data for major three Of this Fc, Ai. K,

and shown tor probe Carbonate baedon a one-to-one atom of Ca. High for early 1 are by particularly high content for

Carbonate M g el M n el el el K el el Ti el el el

M g

Detection limit .

SD 1030

Micrite 1 361863Anhedral yellow 384902

1 376455Fibrous 2 (bright CLI 376104Spar 2 (orange 386567

388858

99%

3 (yellow

Fork of Creek1 3792032 381792

Anhedral yellow 385768Fibrous 1 (dark 381553Dentate Calcite 381233

Rhombohedra1 396787

1 (dark orange 387828

393839

Spar 2 (orange 391497

3 (yellow

Wilbur1 339015

Fibrous 1 [dark 389652Fibrous 2 (bright 389117Spar 2 (orange 386442Spar 1 (dk (7) 387050Spar 3 (yellow 385632

386435

90

80

40

20 10

40

20

20 50

10 10 10 10 50

20

10

170

110

66895084

13150122124391259

42335238

11951

40272198249

2352890

2.82.1

239536951d.

438498

796

1084

7291207

1346830

58662

6903212

605455480

5864

1209916

1269

19387 5076 1192 1384 219161 25 47 227275 24 49 776455 20 36 48596 19 4771 12 38

1381029888

106.698.499.198.998.498.2

5 45.01.80.1

9367429825442159

27898

855

2578 5733223723

54

b.d261125

25421647913778

b.d62

179114

5453

1.72.22.54.94.41.7

0.110.4

15771372

13170

148453

28191286

482507602981

4533625 M485293328

193135198

766083

b db d3742

103.899.099.999.1

103.0l w . o98.3

1653351333

b d.1218308

3904344318553120'

1359

2.51.61.4

1.3

0.6

6213148277

1156645332268

113616721239

1747

2701154

324b.d103

623026

41076 12128 2880 620 553155 16 52 72 b d173 39 77 120 b d

3839 1341 57 b d123 13 41 34 b d277 35 85 59 b d128 32 137 858 b d

1162451

b db d32

170

116.1

98.7103.298.297.2

standard deviation. dk. dark. below detection limit: el elemental percent

and high ohraincd forwerc caused by a mixture of phases

calcite + grains),the of interaction for the electron

beam and the sample. Thus, inover-corrected rhc normal-

ized (assumed bomogcncous) intensitiesfrom what were actually minute in

Donovan, personal communication, 2001). Compared1, calcites from the and Cold Fork

showed a drop in Fe and Mn480 Rorh the

fibrous (fibrous 1)and wercrelatively high and content, hut extremely low Fc

and Mn concentrations, early cementscalcite). The fibrous

(fibrous 2 , CL) werc similar in their elementalcomposiuons compared early fibrous from

2002 Lrd, 2,63-94

they werc derived,and Fe concentrations, bur yielded Mntions. Isopachous and rhombohedral rim conraincdmodcratc and Sr, but low in Fe and Mnconrcnr compared phases. latespars displayed and Sr lowS and generally high Mn concentrations, especially for

latest spar 3 (to Mn) thatporosity.

in and Mn concentrations are evidentfor all with respect(Fig. 13) .Early displayed conrcnr andhigh Fe concentrations, all carbonare

contained Fibrous arc situated a

poinr in Mn content, with How-ever, Mn the various

spars. Early ofthc Cold andcontained iron

80 K. A. CAMPBELL

4000

3000a

2000

1

2

spar 2

5000

0 1000 2000 3000 4000 5000

M n

+yellow

fibrous 1

0 500 1500 2000

Mn

1

2spar 1

spar 2

concentrations Par-Cold Fork of Creek and

Springsdeviations about

of variabilityrecorded each cement

4000

3000

2000

0 1000 2000 3000

Mn

( m a x i m u ma abundance of

corrosion surfaces. Broadly in and M g

versus are for allto (Figs 14 and 15).follow a withCa and Mn followed

consistently lower Mn A occurred in fibrousto relatively hut

canccntrations. A turning point in Mn is inlate-phase with

spars appear occurred in ‘jumps’with each phase was

highly in these spars. All preservedas low-Mg content

2002 2, 63-94

Mesozoic hydrocarbon seeps, California

m

micrite

1

spar 3

3

m

0 1000 2000 3000 4000 5000

Mn

fibrous 1

+ isopachous

rhomb

spar 1

spar 2

0 500 1000 1500 2000

M n

14. Mn forCold fork of Creek

and WilburStandard about theare graphical of the

recorded for each

5

early3

2

Springsfibrous 1

2spar

spar 2

late

-x-

0 1000 2000 3000 4000

Mn

occurred in the spars, inyellow calcites with and Cold Fork fib-rous yielding Mg concentrations

15) .Some studies been

modern or hydrocarbonwhich allow comparisons with the Californian data

and yellow Canadian

2 , 63-94

Arctic sites the same ofand as Californian Meso-

zoic examples, bur a lowera!. 1996). Jurassic Pass

stones, Antarctica displayed and that

in early fibrous cement well as ina!. 1995). Both early and

'OW

0

ieds

iedsVieds

0

+

9


subduction system of California (Fig.2). ForCanadian associated with

and (Bcauchamp SavardCalifornian wcrc found

with micritc, for worm which encrustedwith anhcdral calcirc in Evidence for early, sulphidc-rich fluid anaerobic conditionsis in this study by rhe of

micritc, corrosion surfaces with pyrirc coatings andcalcite In modcrn hydrothermal vcnr and

hydrocarbon mussels and wormsa fluids (rich in forof their internal chemosymbiotic bacteria

in 2000). the metazoans aretcd spatially or around active

1989). (2000)sccp as anoxic by

bottom waters,precipitate of concenuated anaerobic rnethanc

coupled with rcduction. Together,produce high of

and DIC in porc fluids (Aharon 2000;1992; 1987). of pyrirc

and is explained by activitiesof hydro-gen which, in turn, with iron inscafloor to Fc-monosulphidcs

formation of pyrite 1970;Barnes 1996, 1997).

In a for mound formation inCanadian Arctic, Beauchamp Savard (1992, fig. 17, p.448) both and anhcdral calcite

beneath sulphidc-oxidizing bacterialmats under localized anaerobic conditions. n ophysical remnants of microbial features for

At the Cold Fork of Cottonwoodsite in California, nor only did worm surfaces

anhedral yellow calcirc and pyritebut, in addition, clotted micritc linings orcoatings which likely microbial in origin Fig.

association worm and microbialfabrics phases from

sccp in reducingbacterial to flourish, and pyrite and yellow

calcitc to prccipitatc (cf. Savard 1992;1998). However, at all Californian

of deposits. Even biasestowards appears that microbial

on the scafloor volu-minous prrcipiration of micritc and yellow calcite in

deposits It likely that rhe ofthese ccmcnt phases occurred in porc-

within seafloor via coupled

2002 2,63-94

mcthanc oxidation and rcduction. distinctconditions that controlled precipitation

ofthc different reduced ccnicnrs micritcsus yellow calcite) are unknown, butwcrc to fluid associarcd with

The early carbonate phases of all Californian sccpdeposits similar Mnimply and yellow formation in

of porcwaterr, which was byinteraction and fibrous 1

aragonirc?) formation under aerated conditions14 1990,

Fig. 7.41, p . fibrous cements also cxhibircdsignatures, lacked pyrirc or dctrital and

bored by which mayformation in association with aerobic

by using in ambicnr(cold) .bottom Beauchamp Savard 1992,Fig. 13, p. 444). In addition, of fluid flow throughmodcrn accretionary prisms have revealed that micrite slabsand develop flow seafloor

fibrous or dcnratc cements commonly are associated with chimney or

flow in cold, scafloor condi-tions 1990, 1987).We infersimilar flow conditions in association with ofmicrite 1 and fibrous 1 The spatial

major carbonate by(1995, p. who presented

rock sampling from throughcarbonate deposit. carbonate margins wcrc domi-nated micrite and fossils, but the

of containrd abundant fibrous cements and lacked fossils. This reflect fluid flow through seafloor at margins of thc sccp, whcrc conditions optimal for organism andflow the central area perhaps near or con-duits.

Conditions during phases of burial diagenesis

dirgcnctic of paragcnctic scqucncc forCalifornian seep-carbonares is typified by porc-associarcd phases that burial conditions. particularly

evolution or input of fluids implyactions distinct from scawatcr or fromearly, hgdracarbon-rich isotopic and com-positional clearly indicated at

point from early phascs and (1-7) to phascsand for and Cold Fork deposits.

Two series arc bydata (Figs 13-15). The first is carbonarc

and/or rim cement precipitation along

K. A . CAMPBELL

dcntatc, isopachous, rhombohcdral cal-cites) or bands phases (fibrous 2calcites). of smoothlydecreasing and Mg contents, as to precedingfibrous cements, Fc and Mn concentrations remained similarly low. second oflate-stagesisted of pore-filing precipitation spars 1-3, barite) and silt-clay The calcite spars cxhibitcd

values, contents and highThey also showed distinctive, discrete, upward

shifts in Mn concentrations, and lowest Mg concentra-tions of all The jumps in contcntthe suggest a to reducing

conditions during burial (coniparcFig. 14 with Morse Mackenzic 1990, Fig.7.41,and contributions from individual burial fluid packages with compositions.

The corrosion Fig. 5 )during three shifts in fluid com-position-pH during step-carbonate development. occurred in near scafloor, inwith diffusive, acidic infused with dis-solved and iron. Organisms utilized

fluids of to produc-tion, and pyrite precipitated directly upon corrosion

CEI, an episode of sccp fluidoccurred, as as contact normal seawater, as

by fibrous characteristics andDuring CE2, corrosion was associatcd

with fracturing and vein formation, as as the onset ofpore-associated fluid evolution, locally

fibrous or partially dissolved 2petals in Fig.6). Fracturing associated with CE2may localfault or by overpressuring andwith increasing occlusion of porosiry during continued sub-surface fluid flow through deposit (cf. Fontana1999). CE3, by

dissolution that secondaryin yellow calcites. Corrosion was

driven by input of burial fluids that undersaturated inbicarbonarc.

In general, stabilization of carbonatestypically in

precipitated phases form via fluid input and/or localized of precursor carbo-nate components The latter

fluids to partially individualinternal phascs and thcir

Once thehas transformed calcite, and residual

occluded, generally behavea Thus, the dis-

tinctive characteristics of

Californian Mcsozoic a rich birth-to-burial history of unusual deposits and their faunas,and of not

in the

Phanerozoic trends in stable isotopic signatures of seep-carbonates

16 rangc of stablc carbon andisotopic distributions of 33 rcponcd dcporits of authigcnicmarine which precipitated in association with sub-marine fluid-sccpagc from Phanerozoic continental and cpicontincntal seaways around world.14 modern, Ccnowic and 10 Palacowic-Mesozoicseep-carbonate for which stablc

measured. Table4 the data andfor each occurrence, whereas Fig. 16 displays

trends and highlights onlybroad stablc isotopic fields arc (Fig.16): a

field most and(Group I); (ii) a variably

but Ceno-zoic and modem seep-carbonarcs (Group and a

field, with ranging from dcplctcd to (Group

Mesozoic from California (Fig. 16) arc situated indcplctcd quadrant (Group I), along with mostother and Mesozoic deposits.

compared to most of examples, Paskentacarbonates dcplctcd in andCalifornian wcrc more in

occurrence in this quadrant is from mod.Oregon front whcrc carbonatc

and associated with faults wcrc exccpin and with Cold Fork and

Paskcnta (Fig. For the unusualisotopic signatures of modern wcrc

explained by tapping warm fluidsduring active fault-ing, and by of minerals (Sam.

1993; Reid 1998).Othcr Mesozoic sccp from Colorado and the Canadian

(Fig. 16) had somewhat similar isotopic comparedCalifornian sites. Howcvcr, their phascs wcrc

strongly in byhigher formation tcmpcraturcs and/or distinctive fluidsciatcd with burial diagcncsis. An isotopically unusual zoic was from calcitic of

Jurassic Formation, southern France(Fig. 16, Group III),which exhibited a

of values (-26.5 PDB), and tovalues -7 to PDB)

Thecarbonate carbon contcnt French

2002

Mesozoic hydrocarbon seeps. California 85

SOURCES

0

Carbon and oxygen for 33 seep-carbonates worldwide. Data and for the 14

and Table4 With few data clustered three Group I,

11, Cenozoic-Modem Group Unaltered. seep-associated are

aggregated about PDS lor both carbon and oxygen. of Cottonwood Creek and Wilbur from areShown for the isotopic of seep-carbonates potential carbon right: 19801.and

temperature of on oxygen (horizontal. lop. 1983; Land

L Cement, Oregon: Eel River: Say;Cn Canadian (Cretaceous). French carbonates An=

equilibration produced during bacterial1992).

One factor that could explain clustering of mostPalaeozoic and Mesozoic deposits in a

isotopic field (Group I, Fig. 16)isand during diagcn-.

Although signatures of arcsomewhat resistant modification Aharon

this can valuesat low water-rock interactions, in studies of nor-mal and burial carbonarcs &1977; Given 1985; Patterson 1994;

1983). Seep-carbonates, in particular, form asdeposits from point ofhydrocarbon in basinsdominated by sediments.ing of these during burial would sub-jected carbonates passage of of

combined of andisotopic

seep-carbonates and incoming pore fluids, and thus substantially the values of somc

phases (cf. 1983). clear isotopic andtrends are in and

Mesozoic seep-carbonarc phases Figs 12-15;man 1996, 1983,p.dcspitc the overall shift Group values com-pared Cenozoic and For

early and phases are as distinct

2002 Lrd, 2, 63-94

isotopic subgroups in many Group IL Fig.

low of Palaeozoic andseep-carbonates ingcn isotopic composition and/or throughEarth's as has to explainpattern found in sedimcnrary deposits

(cf. 1999, p. 357-359).isotopic signatures of

the Californian Mesozoic (Fig. 11)arc modern values, and no sig-nificant in content.

In second isotopic field (Group Fig. mostand modern -0 and PDB, and formed in cold at

shelf depths (see for In addition,deposirs associarcd with gas

isotopic signatures ofits to by

in comparisonGroup The

Cenozoic and step-carbonates ranged from -SO to PDB, and are to

carbon reservoirs of content, impnnredby of biogcnic or oxidation,

and/or matteresis 16 with Aharon 1994, Fig.9,p. 146).

86 K . A. CAMPBELL

E E

2002

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90 K. A. CAMPBELL

distinct withand highly variable signals thirdisotopic field (Group Fig. 16). Thcsc

unusual carbonarcs include sonic modern Oregon dolo-mite and sccp-carbonates with

carbonate carbon, attributed toin by

1990; Lorenson 1999;addition, from modern

display values, attributedformation in association with decomposition

Lorenson 1999; Naehr 1999). Finally,somc precipitates with dcplctcd signatures

to formedsomc late ccmcnts from and

modern Montercy Bay (Fig.16; Stakes1999; 1999; Terzi 1994).

I n Californian Mesozoic thisarc from one another isotopically, but

range ofmost seep-carbonates world-wide. Thcsc older clearly preserved a distinctsignal of phases.

values a

overprint, to their oldcr age andof significant mod-

ification during burial. In contrast, Cenozoic andsccp-carbonates were: (i) isotopically from

older deposits; (ii) rccordcd variableand generally ambient seafloor conditions; and

significant isotopicFinally, fluids cnrichcd in residual or fluids

,with waters, havc occasionally formedsccp-carbonates in niarinc but their to

formation and migration, if any, havc norbeen studied in any derail.

CONCLUSIONS

Three studied instrata (Upper Jurassic Upper

or diapir-related), California,contain recurring parageneric Stable iso-tope valuer and compositions of rhe carbonates

co-varied carbonate phase, and these the onset and of scafloor seepage, fol-

lowed by iate-stage fluids invoduccd during burialsignificant among

fluids in particular original (orpartially and chemical were

in these Mesozoic Arfossil chemosgmbiotic, to

of sccp and they contact and/or methanr-rich

fluids sediment-wirer Microbialis byand clotted which havc

activity inA broadly consistent in stratigraphy

for both Canadian Arctic and Californian Mesozoic implies that fluid and

similar for two geographically anddisjunct hydrocarbon sccp

in the Californianrecorded in and phases

ncarcd the of contact normal conditionsdue Two divisions of this late arcapparent: ( i ) corrosion andof carbonate cements; andfill by three of spar, and silt-clay.compositions smooth inthe former grouping phases, but in dis-crete in the inputs of distinct fluid packages during

Global comparisons of isotopic for 33Phancrozoic, carbonates with submar-ine fluid define distinct Californianexamples of study plotting with olderMesozoic In general, younger

less likely burialwill havc an on isotopicCarbon for Phanerozoic as a

variable isotopically but are have affected bymigration, of scdimcnrary organic

and Several carbonatcdisplay isotopic orfreshened fluids in offshore

ACKNOWLEDGEMENTS

We financial support K.A.C. from Fund of Chemical

administcrcd through of EarthUniversity of Southern California; a NationalCouncil Rcscarch adminisrcrcdNASA Rcscarch and the ofland Committee. support from

Exobiology Program and the NASAD.J.D. support from

A. C. and L. conrriburcd draft.crpcrtisc. Field and/or laboratory assistance was

provided by D. J. M. L. M.Discipulo. Donovan, B. W. Fouke and For

discussions, thank D. J. Bottjer, C.Donovan, A. G. Fischcr, B. W. T. L. C.

D. L. and K. A. J. and Rsuggestions t h a t improved quality

of manuscript.

2002 2 , 63-94


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2001 2, 63-94

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