This journal is available online at Wiley Online Library.Visit wileyonlinelibrary.com/journal/ter to search thearticles and register for table of contents e-mail alerts.

vo

lu

me

24

, n

um

be

r 4

,A

ug

ust

20

12

pp

25

5–

33

8

volume 24 number 4 august 2012

TE

RR

A N

OV

A

TERRA NOVA Contentsvolume 24 number 4

August 2012

Cover: A 1.5 m-thick debris-flow breccia from the palaeocanyon-fill of the Ediacaran-aged Wonoka Formation, South Australia,

dominated by tabular clasts (1–75 cm long) of micritic marine limestone. Carbonate clasts like these pictured exhibit the full range

of δ¹³C values - -12 to +4 permil - observed in intact canyon-shoulder sections throughout the basin. The results of this ‘isotope

conglomerate test’ require a syn-depositional age for the extraordinary range of δ¹³C observed in the Wonoka Formation.

Photograph credit: Jon M. Husson (See the article by Husson et al., pp. 318–325).

REVIEW ARTICLES

255 Review of submarine cold seep plumbing systems: leakage to seepage and ventingA. R. Talukder

273 Internal waves vs. surface storm waves: a review on the origin of hummocky cross-stratificationM. Morsilli and L. Pomar

ORIGINAL ARTICLES

283 The Bazar Ophiolite of NW Iberia: a relic of the Iapetus–Tornquist Ocean in the Variscan sutureS. S. Martínez, A. Gerdes, R. Arenas and J. Abati

295 Coseismic and postseismic crustal deformations of the Korean Peninsula caused by the 2011 Mw 9.0 Tohoku earthquake, Japan, from global positioning system dataJ. Baek, Y.-H. Shin, S.-H. Na, N. V. Shestakov, P.-H. Park and S. Cho

301 Constraining clastic input controls on magnetic susceptibility and trace element anomalies duringthe Late Devonian punctata Event in the Western Canada Sedimentary BasinM. G. Śliwiński, M. T. Whalen, F. J. Meyer and F. Majs

310 The Palaeocene/Eocene boundary section at Zumaia (Basque-Cantabric Basin) revisited: new insightsfrom high-resolution magnetic susceptibility and carbon isotope chemostratigraphy on organicmatter (δ13Corg)J.-Y. Storme, X. Devleeschouwer, J. Schnyder, G. Cambier, J. I. Baceta, V. Pujalte, A. Di Matteo, P. Iacumin and J. Yans

318 A syn-depositional age for Earth’s deepest δ13C excursion required by isotope conglomerate testsJ. M. Husson, A. C. Maloof and B. Schoene

326 A distant magmatic source for Cretaceous karst bauxites of Southern Apennines (Italy), revealedthrough SHRIMP zircon age datingM. Boni, S. M. Reddy, N. Mondillo, G. Balassone and R. Taylor

333 Uppermost Lower Aptian transgressive records in Mexico and Spain: chronostratigraphicimplications for the Tethyan sequencesJ. A. Moreno-Bedmar, T. Bover-Arnal, R. Barragán and R. Salas

ter_24_4_oc_Layout 1 6/29/2012 1:53 PM Page 1

A syn-depositional age for Earth�s deepest d13C excursionrequired by isotope conglomerate tests

Jon M. Husson, Adam C. Maloof and Blair SchoeneDepartment of Geosciences, Princeton University, Guyot Hall, Washington Road, Princeton, NJ 08544, USA

Introduction

The Ediacaran Period (Knoll et al.,2006) is the bridge between the Prote-rozoic world and the animal-abundantPhanerozoic. Sponges (Love et al.,2009; Maloof et al., 2010; Sperlinget al., 2010; Brain et al., 2012) appearbefore the �635 Ma (Hoffmann et al.,2004; Condon et al., 2005) terminal–Cryogenian ice age, but decimetre-scale organisms (animals, giantprotists and macro-algae known asthe Ediacaran Biota (Xiao and Lafl-amme, 2009)) do not appear until�579 Ma (Bowring et al., 2003).Broadly synchronous with these firstappearances, the deepest carbon iso-tope excursion in Earth history isrecorded in carbonates from at leastfour continents – most famously fromOman (Burns and Matter, 1993),South Australia (Calver, 2000), SouthChina (McFadden et al., 2008) andsouthwestern USA (Corsetti andKaufman, 2003). The extreme isotopicdepletion seen in these Ediacaranbasins is colloquially referred to asthe �Shuram� anomaly, although globalsynchroneity has not been establishedindependently (Grotzinger et al.,2011). Chemostratigraphic (Prave etal., 2009) and sparse geochronological

(Condon et al., 2005; Bowring et al.,2007) data suggest that the globallyobserved anomalies, synchronous ornot, are hosted in sediments youngerthan the �580 Ma Gaskiers glaciation(Bowring et al., 2003) and older than�551 Ma (Condon et al., 2005).The dominant paradigm among

chemostratigraphers is that d13Ccarb

in carbonate rocks reflects the d13C ofdissolved inorganic carbon (DIC) incontemporaneous sea water, which isvirtually uniform around the worlddue to the long residence time of DICand the short mixing time of theoceans (Kump and Arthur, 1999).Similarities in shape and magnitude,and the broadly Ediacaran age, havebeen used to argue that the �Shuram�anomaly fits this model, and is there-fore globally synchronous and can beused for global stratigraphic correla-tion (Halverson et al., 2005). A pri-mary DIC origin for the �Shuram� isalso the foundation for models involv-ing stepwise oxidation of the terminalNeoproterozoic ocean (Rothmanet al., 2003; Fike et al., 2006; McFad-den et al., 2008) that resulted inpulsed inputs of light carbon to theocean-atmosphere system (Rothmanet al. (2003), and references therein).Absolute time constraints, althoughnot available, are necessary to quan-tify the light carbon fluxes and oxi-dant budget required, and thus testthe model�s viability.Alternatives to the global-DIC

hypothesis have sought to explainthe �Shuram� anomaly, and include

(1) meteoric and (2) burial diagenesismodels. Under the meteoric model,the depleted d13Ccarb values and co-varying d13Ccarb–d

18Ocarb (features ofmost, but not all, Shuram-like anom-aly profiles) are interpreted as a recordof remineralising fluids charged withDIC issued from organic matter res-piration in soils (Knauth and Ken-nedy, 2009; Swart and Kennedy,2012). The burial diagenesis modelinvokes post-burial fluid-rock inter-actions at depth, wherein a high pCO2,low d13C fluid, developed from buriedorganic matter, mixes with an 18O-richbasinal brine (Derry, 2010). Bothdiagenesis models therefore argue foracquisition of negative d13Ccarb afterthe carbonate sediments had beendeposited (although in the meteoriccase, alteration can happen immedi-ately after deposition). If the �Shuram�anomalies are a record of diagenesis,one must ask (1) what type of processwould lead to diagenetic alteration ofd13Ccarb, synchronously or not, inEdiacaran basins around the world,and (2) why might Ediacaran sedi-ments be uniquely predisposed to suchintense alteration (Grotzinger et al.,2011).We present data from six measured

stratigraphic sections (Fig. 1B,C)from the Ediacaran Wonoka Fm. ofthe Adelaide Rift Complex (ARC) ofSouth Australia that (1) demand syn-depositional acquisition of its lowd13Ccarb values (down to )12&) andthe observed covariation betweend13Ccarb and d18Ocarb, (2) rule out the

ABSTRACT

The most negative carbon isotope excursion in Earth history isfound in carbonate rocks of the Ediacaran Period (635–542 Ma).Workers have interpreted the event as the oxidation of theEdiacaran oceans [Rothman et al., Proc. Natl. Acad. Sci. USA 100(2003) 8124; Fike et al., Nature 444 (2006) 744; McFadden et al.,Proc. Natl. Acad. Sci. USA 105 (2008) 3197], or as diageneticalteration of the d13C of carbonates (d13Ccarb) [Knauth andKennedy, Nature 460 (2009) 728; Derry, Earth Planet. Sci. Lett. 294(2010) 152]. Here, we present chemo-stratigraphic data from theEdiacaran-aged Wonoka Formation (Fm.) of South Australia thatrequire a syn-depositional age for the extraordinary range ofd13Ccarb values ()12 to +4&) observed in the formation. In some

locations, the Wonoka Fm. is 700 metres (m) of mixed shelflimestones and siliclastics that record the full 16& d13Ccarb

excursion. In other places, the Wonoka Fm. is host to deep(�1 km) palaeocanyons, which are partly filled by tabular-clastcarbonate breccias that are sourced from eroded Wonokacanyon-shoulders. By measuring the isotopic values of 485carbonate clasts (an isotope conglomerate test), we show thatcanyon-shoulder carbonates acquired their d13Ccarb–d18Ocarb

values before brecciation and redeposition in the palaeocan-yons.

Terra Nova, 24, 318–325, 2012

Correspondence: Jon M. Husson, Depart-

ment of Geosciences, Princeton University,

Guyot Hall, Washington Road, Princeton,

NJ 08544, USA. Tel.: (609) 258-0836; fax:

(609) 258-1274; e-mail: jhusson@princeton.

edu

318 � 2012 Blackwell Publishing Ltd

doi: 10.1111/j.1365-3121.2012.01067.x

burial diagenesis model, and (3) con-strain the styles of meteoric diagenesisthat could be invoked to explain theobservations from Australia.

Geological setting

The ARC (Fig. 1A) was part of acontinental margin formed to the

present-day east of the Stuart Shelf,and the Wonoka Fm. is part of theEdiacaran Wilpena Group (Preiss,2000; Preiss and Robertson, 2002).

–15 0 5–20

Flin

der

s R

ang

es

Gam

mon

Ran

ges

StuartShelf

5,6

9

10

19ADELAIDERIFTCOMPLEX

84

N

67

80

0

100

200

300

400

500

600

POUND

WO

NO

KA F

ORM

ATIO

N

700

800

–15 –10 5

Debris flow brecciaIntraclast brecciaMicrobialite

Grainstone/sandstoneRibbonite/ribbonite with silt interbeds

Siltstone

LITHOFACIES KEY

CANYON-SHOULDER SECTION

CANYON-FILL SECTION

WONOKA SECTION LOCATIONS

Undifferentiated sedimentsCambro-Ordovician volcanic rocksHAWKER – LAKE FROME GROUPS (542–505 Ma)WILPENA GROUP (635–542 Ma)UMBERATANA GROUP (~710–635 Ma)BURRA GROUP (~777–710 Ma)CALLANA GROUP (~840–777 Ma)

Undifferentiated Palaeo-Mesoproterozoic rocksMajor fault

Canyon-shoulder sectionCanyon-fill section

Measured sections

Bunyeroo Gorge section(from Calver 2000)

km

N

δ13C

m

m

MAP LEGEND

(A)

(C)

Basal carbonate brecciaswith clast δ13C range(see Fig. 2C, 5A)

2

3

4

5

6

7

89

10

11

1

900

1000

POUND

WO

NO

KA F

ORM

ATIO

N

0

100

200

300

400

500

600

700

800

1018O, δδ 18O C, δ13

196784

9105, 6

Map areaof Fig. 3

139o 140o

31o

30o

(B)

Turb

iditi

c sa

ndst

ones

–20

Fig. 1 (A) Simplified geological map (adapted from Preiss and Robertson (2002) and Rose and Maloof (2010)) of the study areawithin the Adelaide Rift Complex (ARC). Locations of measured stratigraphic sections are denoted by yellow symbols andlabelled with numbered white squares. Representative physical stratigraphy of (B) a canyon-shoulder section and (C) a canyon-fillsection, paired with d13Ccarb and d18Ocarb (in & notation reported relative to the Vienna Pee Dee Belemnite carbon isotopestandard) data from six localities. (canyon-shoulder sections: 19 – Parachilna, 67 – Saint Ronan, 84 – Black Range Spring; canyon-fill sections: 5–6 – Mount Thomas, 9 – Oodnapanicken, 10 – Mount Goddard). Wonoka Fm. carbonates consist mostly oflimestone; dolomite only is found at its base as the thin (0.1)1 m), but persistent, �Wearing Dolomite� (Haines, 1988), and in theuppermost 150–200 m (units 9 and 11). Haines (1988) subdivided the Wonoka Formation into 11 informal lithological units, whichare broadly recognisable throughout the central Flinders Ranges and labelled here on our canyon-shoulder sections. The chemo–and lithostratigraphies of canyon-shoulder and canyon-fill sections are remarkably similar from locality to locality, although thethickness of canyon-fill sections (500–1000 m) is more variable than canyon-shoulder sections (�700 ± 100 m), depending uponthe depth of canyon incision.

Terra Nova, Vol 24, No. 4, 318–325 J. M. Husson et al. • Isotope conglomerate test

.............................................................................................................................................................

� 2012 Blackwell Publishing Ltd 319

The Nuccaleena Formation, the dis-tinctive cap dolostone to the glacialElatina Formation (Plummer, 1979;Williams, 1979; Rose and Maloof,2010), forms the base of the WilpenaGp., and frequently is correlated withthe younger Cryogenian glacial capunits found around the world (Halv-erson et al., 2005) (dated to be�635 Ma in Namibia (Hoffmannet al., 2004) and South China (Con-don et al., 2005)). The Wonoka Fm.varies between 400 and 1500 metres(m) thick, and coarsens and shallowsupwards into the siliclastic, EdiacaraBiota-bearing Pound Subgroup. At itsbase in the central Flinders Ranges(e.g., 19, 67, and 84 in Figs 1B and2D), the Wonoka Fm. is a deep-shelfsequence of turbidites with climbing-rippled sands and allodapic (i.e.,transported down-slope) carbonatebeds. The Wonoka Fm. transitionsupwards into a shallower, storm-dom-inated mid-shelf sequence containing

abundant hummocky and swaleycross-stratified sands (Fig. 2E), andwavy limestone laminites and grain-stones. At the top of these units, theWonoka Fm. coarsens abruptly intothick (�50–100 m), trough cross–bed-ded fine-to-medium grained sand-stones (unit 10 under the terminologyof Haines (1988); see Fig. 1 caption).In contrast, the northern Flinders (5,6, 9, 10 in Fig. 1C) record deeperoutermost-shelf and slope settings,with �1000-m deep palaeocanyonsthat cut into the underlying Bunyerooand Brachina formations (Fig. 2A,B)(Haines, 1988; Christie-Blick et al.,1990; DiBona and von der Borch,1993; Giddings et al., 2010) and arefilled with mixed carbonate and silic-iclastic turbidites and tabular-clastlimestone breccias (Fig. 2C). Hence-forth, we refer to outer shelf sectionsas �canyon-shoulders�, and sectionswith palaeocanyons as �canyon-fill.�The uppermost Wonoka Fm. is char-

acterised by �80–100 m of microbia-lite and stromatolite bioherms (unit 11of Haines (1988)), which blanket thecanyon-shoulders and some canyon-fill sections (Fig. 3).

Methods

Carbonates were sampled at 1.0 mresolution whilst measuring six strati-graphic sections from across theAdelaide Rift Complex (ARC; Fig. 1A). Clean limestones and dolostoneswith minimal siliciclastic componentswere targeted. A total of 1049 sam-ples were slabbed and polished per-pendicular to bedding and 5 mg ofpowder were micro-drilled from indi-vidual laminations for isotopic anal-ysis. Sections 5–6, 9, 10, and 19(Fig. 1B,C) were measured at theUniversity of Michigan Stable Iso-tope Laboratory on a Finnigan MATKiel I preparation device coupleddirectly to the inlet of a Finnigan-

(E)

100 m

Wonoka Fm

Bunyeroo Fm

10 cm

(F)

Paleaeocurrentdirections

(A)

2m

Brachina Fm

Wonoka Fm

(B)

(C) (D)

N

5 kmWonoka

Brachina

Fig. 2 (A) Google Earth image (acquired 2 ⁄26 ⁄2010) of a �1000-m-deep Wonoka palaeocanyon, with palaeocurrent directionsfrom Eickhoff et al. (1988) – photos B and C are located on the north side of the palaeocanyon near the �W� in the Wonoka Fm.label in (A); (B) angular and erosive contact (black line) between Brachina Formation canyon wall and Wonoka Formationcanyon-fill (white dashed lines depict change in bedding attitude) at Mount Thomas (sections 5–6); (C) a 2-m-thick debris flowbreccia, dominated by tabular clasts (1–75-cm long) of micritic marine limestone; (D) canyon-shoulder outcrop near ParachilnaGorge (19); (E) small-scale hummocky cross-stratified (HCS) carbonate grainstone typical of canyon-shoulder outer shelf faciesfrom Saint Ronan (67); (F) 20–40-cm thick grainstone (red in colour)-to-microbialite (yellow) couplet typical of upper WonokaFm. stratigraphy at Parachilna Gorge (19).

Isotope conglomerate test • J. M. Husson et al. Terra Nova, Vol 24, No. 4, 318–325

.............................................................................................................................................................

320 � 2012 Blackwell Publishing Ltd

MAT 251 triple collector isotoperatio mass spectrometer. All othersamples were measured at PrincetonUniversity on a GasBench II prepa-ration device coupled directly to theinlet of a Thermo DeltaPlus contin-uous flow isotope ratio mass spec-trometer. d13C and d18O data arereported in the standard delta nota-tion as the difference from the VPDBstandard (Vienna Pee Dee Belemnite),

and measured precision is 0.1 (1r)for both values. For a more thoroughdiscussion of these methods, see Roseet al. (2012).

Results

The canyon-shoulder sections of Para-chilna Gorge, Saint Ronan and BlackRange Spring (19, 67, and 84 inFig. 1B) exhibit very low d13Ccarb

values and d13Ccarb–d18Ocarb covaria-

tion (see Fig. 4A). Isotopic values aremost negative at the base of unit 3(down to )12&), and the profilerecovers smoothly and gradually to-wards positive d13Ccarb values. At thetop of unit 8, the curve crosses 0&,and d13Ccarb remains positive in units9–11. The isotopic profiles of canyon-shoulder units 1–11 are remarkablyconsistent between sections over

Canyon-shoulder1 km

N Pound subgroup

Basal breccias with silt interbeds

Upper unit 11

sandstonecanyon

Wonoka Fm.

Bunyeroo Fm

. Bunyeroo Fm.

Pound subgroup

Unit 10Unit 11

Units 1 - 7

Wonoka Fm.

6780

Fig. 3 Bing Maps image (acquired 11 ⁄17 ⁄2004) of the Saint Ronan canyon-fill and canyon-shoulder complex (map area markedwith black outline in Fig. 1A). Black lines indicate conformable contacts between units or formations, while white lines indicatesequence boundaries. Isotope conglomerate data of section 80 (Fig. 5B) come from breccias located within the red box in thebottom–left of the figure. Field mapping shows that the microbialite reef facies of unit 11 caps both the canyon-fill and canyon-shoulder sequences, thus indicating that canyon cutting and filling occurred before terminal Wonoka deposition.

n

C

S

P

Fi

1 mm

GIMW

W

C

(A) (B)

(C)

Fig. 4 (A) d13Ccarb – d18Ocarb cross plot showing data from all stratigraphic sections, coded by section number, lithofacies, andlithology (�ls� stands for limestone; �dl� for dolomite). All canyon-shoulder sections show d13Ccarb–d

18Ocarb correlation, especiallyfor d13Ccarb values less than )5& (r2 = 0.49, 0.49 and 0.44 for 19, 67 and 84 respectively; for all sections, P<<0.001). Suchcorrelation is not observed in the fine-grained, allodapic carbonates of the canyon-fill sections (r2 = 0.003 and P = 0.285 for allthree sections combined). In the figure legend, lithofacies are organised in order of increasing permeability (i.e., ranging from fine-grained micritic wavy laminites to coarse grainstones and sandy carbonates). No pattern of dependence between isotopic valuesand lithofacies is observed. (B) Photomicrograph of a cm-scale fining–upward carbonate turbidite from the base of the SaintRonan canyon-shoulder section (67; see Fig. 1B) that shows the lack of coarse recrystallisation observed in Wonoka Fm.carbonates. Even the fine-sand fraction of carbonate grains, which are most susceptible to recrystallisation are preserved inprimary sedimentary textures (e.g., the dashed white line marks the erosive beginning of another turbiditic sequence). These fabricscontrast with rocks from unit 11 (C), where the first evidence of recrystallisation and growth of dolomite rhomboids is observed(one such crystal is outlined (C), with dashed lines depicting orientation of cleavage). Dolomites are only found in the upper 150–200 m of the Wonoka Fm., where carbon isotopic values are at their most positive (+2 to +8&). The isotopic values of (B) and(C) are depicted in panel (A) with lettered symbols; both samples are �85% carbonate by weight.

Terra Nova, Vol 24, No. 4, 318–325 J. M. Husson et al. • Isotope conglomerate test

.............................................................................................................................................................

� 2012 Blackwell Publishing Ltd 321

50 kilometres distant (Fig. 1B). Thelower half of most canyon-fill units iscarbonate poor, except for the fre-quent tabular-clast carbonate breccias(Fig. 2C). Fine-grained allodapic car-bonate beds are common above 300–400 m of basal canyon-fill, andd13Ccarb values from Mount Thomas,Mount Goddard and Oodnapanicken(5–6, 9, 10 on Fig. 1C) vary between)8.5 and )5&. Canyon-fill sectionstherefore do not record (1) the nadirseen in the canyon-shoulders, (2)d13Ccarb–d

18Ocarb covariation (r2 =0.003 and P = 0.285 for all threedatasets combined), or (3) the recov-ery to positive d13Ccarb values.In palaeomagnetics, a conglomerate

test is used to determine whether clastsin a conglomerate were magnetisedprior to transport and deposition(preserving random magnetic direc-tions) or after deposition (preservinguniform magnetic directions, despiterandom clast orientations). Analo-gously, we performed an isotope con-glomerate test on the breccia units ofMount Thomas, Oodnapanicken, andSaint Ronan canyon-fill (5–6, 9, and80, respectively, on Fig. 5A,B) toassess the provenance and relativetiming of acquisition of d13Ccarb and

d18Ocarb by measuring the isotopicvalues of carbonate clasts. The brecciaunits range from 0.2 to 11 m inthickness, are clast-supported in amatrix of fine sand (Fig. 2C), and aremost common at the base of thecanyon-fill stratigraphy. At MountThomas and Oodnapanicken, the tab-ular, 1–100-cm long carbonate clastsconsist of two dominant lithologies:grey, micritic limestone and browndolostone. At Saint Ronan, the clastsare distinctly different from MountThomas and Oodnapanicken brecciaclasts, and identical to the green, wavylaminites and coarse red limestonegrainstones from the adjacent can-yon-shoulder strata (Fig. 4). Individ-ual breccia units record d13Ccarb

variability of 6 and 16& and signifi-cant d13Ccarb–d

18Ocarb covariation(Fig. 5A,B). The d13Ccarb range ofcanyon-shoulder units 1–9 ()12 to+4&; 19, 67 and 84; Fig. 1B) is seenin the breccia units of the more distalcanyon-fill of Mount Thomas andOodnapanicken (5–6 and 9 on Fig. 5A), while the range ()9 to )3&) of themore proximal canyon-fill of SaintRonan (Fig. 5B) matches that of thelocally eroded canyon-shoulder (thefirst �550 m (units 1–7) of J67 on

Fig. 1B). More distal sourcing cannotbe ruled out, however, because thecanyon-shoulder d13Ccarb profile isremarkably reproducible across20 000 km2 of basin map-area (Fig. 1A,B).

Discussion

We interpret the breccia clasts to becarbonates sourced from units 1–9 ofcanyon-shoulder localities (e.g., 19,67, and 84 on Fig. 1B). In certainpalaeocanyons, 0.05 to 5 m-thickgrey-to-yellow micritic limestone lay-ers are found along the edge of thecanyon wall (Fig. 2A,B). This carbon-ate is of debated origin (Eickhoffet al., 1988; Giddings et al., 2010),and it may represent an additionalsource of clasts for the basal brecciabeds of Mount Thomas and Oodna-panicken, although the observedd13Ccarb range of this in situ carbonate()6.5 to )9.3&) (Giddings et al.,2010) covers less than one-fourth ofthe full range observed in the carbon-ate breccias. These limestone beds arenot present at Saint Ronan, where thelithofacies, colour and isotopic com-position of the clasts are identical tounits 1–7 (Fig. 1B) of the canyon-

Range of locallyeroded shoulder

–15

–10

0

5

δ13C

carb

(‰)

5,69 –15 –5 0δ18Ocarb (‰)

n = 108r 2= 0.593P<<0.01

relative to the base of palaeocanyons

n = 377 P<<0.01r 2= 0.457

14.113.112.211.310.39.48.95.24.23.32.81.90.5

Basin-widerange of canyon shoulder(units 1 – 9)

80–15

–10

0

5

δ13C

carb

(‰)

–15 –5 0δ18Ocarb (‰)

Stratigraphic heights*(in m)

(A) (B)

(see 67on Fig. 1B)

Range of allodapic

upper canyon

(see 5–6;9; 10 on Fig. 1C)

67; see Fig. 1BSaint ronan shoulder

Parachilna shoulder19; see Fig. 1B

Stratigraphic heights*

574.1328.2105.14.7

176.298.044.311.3

LimestoneDolomite

(in m)

Fig. 5 Results of isotope conglomerate tests from Mount Thomas and Oodnapanicken canyon-fill [labelled 5–6 ⁄blue and 9 ⁄ redrespectively, in (A)] and Saint Ronan canyon-fill (labelled 80 ⁄green in (B)). If the clasts acquired their d13Ccarb values and d13Ccarb –d18Ocarb correlation in situ on canyon-shoulders, then they should exhibit a random collection of values representing the fullisotopic range present on the canyon-shoulder at the time of canyon filling. In contrast, if the extremely negative d13Ccarb (downto )12&) and d13Ccarb–d

18Ocarb correlation in canyon-shoulders are a result of post-depositional diagenesis, then clasts fromindividual breccia beds should either (1) reflect the original pre-diagenetic isotopic values in the shoulder (i.e., not extremelydepleted in d13Ccarb), or (2) a consistent diagenetic value homogenous within breccia units. The clasts of the more distal,Oodnapanicken and Mount Thomas canyon-fill exhibit the full range of d13Ccarb values observed in units 1–9 in canyon-shouldersections throughout the basin (19 and 84; Fig. 1B). The more proximal Saint Ronan canyon-fill appears to have sampled a smallercanyon-shoulder range; breccias exhibit a smaller d13Ccarb range, but the clasts match the colour, lithologies and isotopic rangeobserved in units 1–7 of the immediately adjacent canyon-shoulder (67; Fig. 1B; Fig. 3). More distal sourcing, however, is stillpossible because the canyon-shoulder d13Ccarb profile is remarkably consistent across the ARC (Fig. 1A,B).

Isotope conglomerate test • J. M. Husson et al. Terra Nova, Vol 24, No. 4, 318–325

.............................................................................................................................................................

322 � 2012 Blackwell Publishing Ltd

shoulder section 6.5 km distant. Thus,these observations require that boththe negative d13Ccarb values and thed13C–d18O covariation were acquiredin Wonoka Fm. canyon-shoulder car-bonates before those carbonates werebrecciated and redeposited in the pal-aeocanyons.While the mechanism for the for-

mation of the Wonoka canyons re-mains controversial [subaerial(Christie-Blick et al., 1995) vs. sub-marine (Giddings et al., 2010)], therehas been broad agreement that can-yon incision occurred early duringWonoka Fm. deposition (placed var-iously at a cryptic unconformity with-in Haines� canyon-shoulder units 1–5(Christie-Blick et al., 1995; Giddingset al., 2010); see Fig. 1B). Given thepresence of carbonate clasts withpositive d13Ccarb values in canyon-fillbreccia units, our results require ahigher surface (i.e., above unit 8) to beresponsible for at least some of thecanyon cutting at Mount Thomas andOodnapanicken. We do not claim,however, that this proposed surfacerepresents all canyon cut–fill se-quences within the Wonoka Fm., asworkers have documented numerousintervals of canyon incision through-out Wonoka Fm. deposition (DiBonaand von der Borch, 1993). We there-fore propose placing a sequence

boundary at the abrupt appearanceof unit 10 sandstones, where units 8and 9 are variably absent (Fig. 3) andthe d13Ccarb profile first recovers topositive d13Ccarb values. Thus, thecanyon-fill sampled units 1–9 of intactcanyon-shoulder stratigraphy, whosecarbon isotopic range ()12 to +4&)matches that of the tabular-clast brec-cias. The most positive d13Ccarb ob-served from the Saint Ronan brecciasis )3&, corresponding isotopically tothe top of unit 7 of the intact canyon-shoulder stratigraphy. Thus, the can-yon cutting surface could be placedlower at Saint Ronan, so long as thecanyon remained open to sedimentinfill throughout the deposition of unit7 on the canyon-shoulder.As the canyons filled completely,

the fine-grained, allodapic carbonatebeds of the upper canyon-fill (upper700 m of Fig 1C) represent a recycledand homogenised canyon-shouldersection, producing d13Ccarb profiles(5–6, 9, and 10 in Fig. 1C) that arestratigraphic averages of a canyon-shoulder profile (Fig. 6). To test thishypothesis, linearly interpolated data-sets were created for representativecanyon-shoulder (units 1–9; 19 –Parachilna; see Fig. 6A) and fine-grained canyon-fill d13Ccarb curves(10 – Mount Goddard; Fig. 6B). Lin-ear interpolation serves to weight

d13Ccarb values by the stratigraphicthickness over which they occur, thusaccounting for the stratigraphicweighting that occurs during breccia-tion (i.e., thicker units will contributemore breccia clasts). The distributionsof the Parachilna and Mount God-dard interpolated datasets overlap,with the variance of Mount Goddardbeing much smaller. This result isexpected, as mixing and homogenisa-tion of a canyon-shoulder profile at ascale below that sampled for isotopicmeasurement should decrease the var-iance, but produce a similar mean;where canyon-fill is not well mixed atthe scale of isotopic measurement (i.e.,breccia clasts), the variance of thedistribution is much larger (Fig. 6C).These results are thus consistent withthe model that the fine-grained, al-lodapic carbonates of Mount Thomas,Oodnapanicken, and Mount Goddard(5–6, 9, and 10 on Fig. 1C) representrecycled, redeposited canyon-shoulderunits 1–9.These stratigraphic and isotopic

observations preclude burial diagene-sis models for the negative isotopicvalues (Derry, 2010) in South Austra-lia. The low d13Ccarb values andd13Ccarb–d

18Ocarb covariation of theWonoka Fm. must either be primaryor a relatively early meteoric diage-netic signal (i.e., before the Wonoka

–10 –5 0 50

100

200

500

600

700

Met

res

Interpolated dataMeasureddata

δ13Ccarb

–10 –5 0 5δ13Ccarb

Canyon-shoulder(A) (B)

Interpolated dataMeasureddata 0

0.1

0.2

0.3

0.4

0.5

0.6

Pro

babi

lity

–15 –10 –5 0 5

Canyon clastsFine−grained canyon fillCanyon shoulder

µ = –6.3σ = 3.8 n = 108

µ = −6.7 σ = 2.5n = 573

µ = −7.4

σ = 0.7n= 472

(C)

δ13Ccarb

Fine-grained canyon-fill

Fig. 6 The distribution of stratigraphically weighted d13Ccarb values for representative (A) canyon-shoulder (units 1–9; 19–Parachilna; see Fig. 1B) and (B) fine-grained canyon-fill (10 – Mount Goddard; Fig. 1C). The resulting distributions (C) overlapwith a similar mean, and are thus consistent with the fine-grained canyon-fill consisting of recycled, homogenised and redepositedcanyon-shoulder carbonates. Also displayed is the observed distribution of breccia clast d13Ccarb (Fig. 5A), which representsdiscrete sampling of a canyon-shoulder isotopic profile. Its histogram distribution looks very similar to the canyon-shoulder profilefor d13Ccarb values less than )7.5&, but the breccia clasts have a long tail into positive values that is not as well developed in thecanyon-shoulder. We interpret this observation as a sampling bias; the rarer dolostone clasts were over-sampled to gain clastdiversity in our sampled population, and it is dolomite that carries the most positive d13Ccarb values. A second contributing factormay be that unit 9 of the canyon-shoulder is truncated in places by unit 10 sandstones (Fig. 4). Thus, unit 9, and its associatedpositive d13Ccarb values, may be under represented in the interpolated canyon-shoulder profile.

Terra Nova, Vol 24, No. 4, 318–325 J. M. Husson et al. • Isotope conglomerate test

.............................................................................................................................................................

� 2012 Blackwell Publishing Ltd 323

canyons began to fill, and certainlyprior to burial). In classic examples ofmeteoric diagenesis, negatively alteredd13Ccarb values are associated withexposure surfaces, indicative of top-down diffusion of the altering fluid(e.g., 18O-depleted rainwater chargedwith isotopically light DIC originatingfrom remineralised organic carbon(Allan and Matthews, 1982; Swartand Kennedy, 2012)). In the WonokaFm., the only physical evidence forsubaerial exposure is fenestral carbon-ate fabrics in themicrobialite reef faciesof the uppermost unit 11. At SaintRonan, however, we see this unit devel-oped at the top of both canyon-shoul-der and canyon-fill sections, thusindicating that the canyons were cutand filled before unit 11 deposition(Fig. 3). This observation requires thatcanyon formation occurred duringongoing Wonoka sedimentation, andtherefore demands a syn-depositionalage for the low d13Ccarb values of thecanyon breccia clasts and associatedshoulder stratigraphy. If subaerialexposure of unit 11 resulted inmeteoricdiagenesis, it cannot be invoked toexplain the isotopic values of underly-ing units 1–9 of the Wonoka Fm.Although our proposed sequence

boundary at the base of unit 10 couldbe submarine, with canyon cutting andfilling being a subaqueous process ofmass wasting (Giddings et al. (2010),and references therein), some haveargued that the Wonoka canyonsformed subaerially, with the base levelfall accomplished by basin isolationand Messinian-style evaporitic draw-down (Christie-Blick et al., 1990). Thisscenario would leave the canyon-shoulders as much as 1.5 km abovelocal sea level and susceptible to mete-oric diagenesis. However, based on theisotope conglomerate test (Fig. 5A,B),in this scenario, diagenesis would needto occur after the basin was exposed,but before any substantial canyoncutting and redeposition of shoulderrocks into canyon-fill had occurred.Although our data do not rule out thispossibility, there is no visible evidenceof such alteration in the form ofwidespread recrystallisation (primarysedimentary fabrics (Haines, 1988;Giddings et al., 2010) are exception-ally well preserved in theWonoka Fm.;see Figs 2E,F and 4B). Recrystallisa-tion is only pervasively observed inunit 11 dolomites, where d13Ccarb val-

ues are at their most positive (+2 to+8&; Fig. 4C). Also, as the meteoricmodel hinges upon fluid–rock interac-tions, the lightest isotopic valuesshould be found in horizons mostamenable to fluid flow. Fluid fluxwould be controlled by primary poros-ity and permeability, which is a func-tion of grain size, shape and packing,and thus directly related to lithofacies.Contrary to these predictions, we ob-servenopatternofpermeability-depen-dent isotope modification (Fig. 4A).Furthermore, the d13Ccarb profile ofthe canyon-shoulders (most negatived13Ccarb at the base, and increasing invalue towards unit 9 and the top) isopposite of that expected from top-down buffering with meteoric watercharged with DIC issued from organicmatter remineralisation (Allan andMatthews, 1982). Finally, whetherShuram-style d13Ccarb anomalies areglobally synchronous or not, Messin-ian-style diagenesis would be a localevent, restricted to the Adelaide RiftComplex and the Wonoka Fm., andwould not explain the negative carbonisotope signatures of other Ediacaranbasins.

Conclusions

Based on the isotope conglomeratetests, acquisition of d13Ccarb values()12 to +4&) in South Australiancarbonate sediments was synchronouswith deposition of Wonoka Fm. can-yon-shoulder sediments. The filling ofpalaeocanyons occurred during thelatter stages of Wonoka Fm. deposi-tion, and the canyons were cut andfilled before development of upperWonoka Fm. microbialite reefs (unit11 on Fig. 1B). These findings areinconsistent with a burial diagenesisorigin, and the expected first-orderstratigraphic and microtextural pat-terns predicted by meteoric diagenesisare not observed. Therefore, the bal-ance of evidence supports a syn-sedi-mentary origin for the extraordinaryrange of d13Ccarb values seen in theWonoka Formation of South Austra-lia.

Acknowledgements

J.M.H was supported by the NationalScience Foundation Graduate ResearchFellowship Program (NSF–GRFP);A.C.M. was supported by the Alfred Sloan

Fellowship; A.C.M. and B.S. were sup-ported by NSF grant EAR–1121034 toMaloof and Schoene, and Princeton Uni-versity supported field and laboratorywork. Blake Dyer, Laura Poppick andBrenhin Keller provided assistance in thefield. We thank Jim Gehling for fruitfuldiscussions on Wonoka Formation stratig-raphy. Reviews from Dan Rothman, DavidFike, Frank Corsetti and three anonymousreviewers greatly improved this work. Wethank the landowners and pastoralists ofSouth Australia for land access. RebeccaMarks, Elizabeth Lundstrom, Jake Rez-nick, Steve Shonts, Jenny Piela and MaryVan Dyke helped with sample preparation.Stable isotope measurements were per-formed at Princeton University by LauraPoppick and at the University of Michiganby Lora Wingate and Kacey Lohmann.

Author contributions

Field work was conducted by J.M.H.

and A.C.M. (2 field seasons) and B.S. (1

field season), following initial project

planning by J.M.H. and A.C.M; J.M.H.

analysed the data, wrote the manuscript

and drafted figures, all with input from

A.C.M. and B.S.

References

Allan, J. and Matthews, R., 1982. Isotopesignatures associated with earlymeteoric diagenesis. Sedimentology, 29,797–817.

Bowring, S., Myrow, P., Landing, E.,Ramezani, J., Condon, D. and Hoff-mann, K., 2003. Geochronologicalconstaints on Neoproterozoic glaciationsand the rise of Metazoans. Geol. Soc.Am. (Abstracts with Programs), 35, 516.

Bowring, S.A., Grotzinger, J.P., Condon,D.J., Ramezani, J., Newall, M.J. andAllen, P.A., 2007. Geochronologic con-straints on the chronostratigraphicframework of the Neoproterozoic HuqfSupergroup, Sultanate of Oman. Am. J.Sci., 307, 1097–1145.

Brain, C.K.B., Prave, A.R., Hoffmann,K.H., Fallick, A.E., Botha, A., Herd,D.A., Sturrock, C., Young, I., Condon,D.J. and Allison, S.G., 2012. The firstanimals: ca. 760-million-year-oldsponge-like fossils from Namibia. S. Afr.J. Sci., 108, 1–8.

Burns, S. and Matter, A., 1993. Carbonisotopic record of the latest Proterozoicfrom Oman. Eclogae Geol. Helv., 86,595–607.

Calver, C., 2000. Isotope stratigraphy ofthe Ediacaran (Neoproterozoic III) ofthe Adelaide Rift Complex, Australia,and the overprint of water columnstratification. Precambrian Res., 100,121–150.

Isotope conglomerate test • J. M. Husson et al. Terra Nova, Vol 24, No. 4, 318–325

.............................................................................................................................................................

324 � 2012 Blackwell Publishing Ltd

Christie-Blick, N., von der Borch, C. andDiBona, P., 1990. Working hypothesesfor the origin of the Wonoka canyons(Neoproterozoic), South Australia. Am.J. Sci., 290, 295–332.

Christie-Blick, N., Dyson, I. and Von DerBorch, C., 1995. Sequence stratigraphyand the interpretation of NeoproterozoicEarth history. Precambrian Res., 73, 3–26.

Condon, D., Zhu, M., Bowring, S., Wang,W., Yang, A. and Jin, Y., 2005. U-Pbages from the Neoproterozoic Dou-shantuo Formation, China. Science, 308,95–98.

Corsetti, F.A. and Kaufman, A.J., 2003.Stratigraphic investigations of carbonisotope anomalies and Neoproterozoicice ages in Death Valley, California.Geol. Soc. Am. Bull., 115, 916–932.

Derry, L.A., 2010. A burial diagenesisorigin for the Ediacaran Shuram-Won-oka carbon isotope anomaly. EarthPlanet. Sci. Lett., 294, 152–162.

DiBona, P. and von der Borch, C., 1993.Sedimentary geology and evolution of anoutcropping shelf-margin delta, LateProterozoic Wonoka Formation, SouthAustalia. AAPG Bull., 77, 963–979.

Eickhoff, K.H., Vonderborch, C.C. andGrady, A.E., 1988. Proterozoic canyonsof the Flinders Ranges (South Australia)– submarine canyons or drowned rivervalleys?. Sediment. Geol., 58, 217–235.

Fike, D., Grotzinger, J., Pratt, L. andSummon, R., 2006. Oxidation of theEdiacaran ocean. Nature, 444, 744–747.

Giddings, J., Wallace, M., Haines, P. andMornane, K., 2010. Submarine originfor the Neoproterozoic Wonoka can-yons, South Australia. Sediment. Geol.,223, 35–50.

Grotzinger, J., Fike, D. and Fischer, W.,2011. Enigmatic origin of the largest-known carbon isotope excursion inEarth�s history. Nat. Geosci., 4, 285–292.

Haines, P., 1988. Storm-dominated mixedcarbonate ⁄ siliciclastic shelf sequencedisplaying cycles of hummocky cross-stratification, late Proterozoic WonokaFormation. South Aust. Sediment. Geol.,58, 237–254.

Halverson, G., Hoffman, P., Maloof, A.,Schrag, D., Rice, A.H.N., Bowring, S.and Dudas, F., 2005. Toward a Neo-proterozoic composite carbon-isotoperecord. Geol. Soc. Am. Bull., 117, 1181–1207.

Hoffmann, K., Condon, D., Bowring, S.and Crowley, J., 2004. U-Pb zircon datefrom the Neoproterozoic Ghaub For-mation, Namibia: constraints on Mari-noan glaciation. Geology, 32, 817–820.

Knauth, L.P. and Kennedy, M.J., 2009.The late Precambrian greening of theEarth. Nature, 460, 728–732.

Knoll, A., Walter, M., Narbonne, G. andChristie-Blick, N., 2006. The EdiacaranPeriod: a new addition to the geologictime scale. Lethaia, 39, 13–30.

Kump, L. and Arthur, M., 1999. Inter-preting carbon-isotope excursions: car-bonates and organic matter. Chem.Geol., 161, 181–198.

Love, G., Grosjean, E., Stalvies, C., Fike,D., Grotzinger, J., Bradley, A., Kelly,A., Bhatia, M., Meredith, W., Snape, C.,Bowring, S., Condon, D. and Summons,R., 2009. Fossil steroids record theappearance of Demospongiae during theCryogenian. Nature, 457, 718–721.

Maloof, A.C., Rose, C.V., Beach, R.,Samuels, B.M., Calmet, C.C., Erwin,D.H., Poirier, G.R., Yao, N. and Si-mons, F.J., 2010. Possible animal-bodyfossils in pre-Marinoan limestones fromSouth Australia. Nat. Geosci., 3, 653–659.

McFadden, K., Huang, J., Chu, X., Jiang,G., Kaufman, A., Zhou, C., Yuan, X.and Xiao, S., 2008. Pulsed oxidation andbiological evolution in the EdiacaranDoushantuo Formation. Proc. Natl.Acad. Sci. USA, 105, 3197–3202.

Plummer, P., 1979. Note on the palaeoen-vironmental significance of the Nuccale-ena Formation (upper Precambrian),central Flinders Ranges, South Austra-lia. J. Geol. Soc. Aust., 25, 395–402.

Prave, A., Fallick, A., Thomas, C. andGraham, C., 2009. A composite C-iso-tope profile for the NeoproterozoicDalradian Supergroup of Scotland and

Ireland. J. Geol. Soc. London, 166, 845–857.

Preiss, W., 2000. The Adelaide Geosynclineof South Australia and its significance inNeoproterozoic continental reconstruc-tion. Precambrian Res., 100, 21–63.

Preiss, W. and Robertson, R., 2002. SouthAustralian mineral explorers guide.Tech. Rep., PIRSA.

Rose, C.V. and Maloof, A.C., 2010. Test-ing models for post-glacial �cap dolo-stone� deposition: NuccaleenaFormation, South Australia. EarthPlanet. Sci. Lett., 296, 165–180.

Rose, C.V., Swanson-Hysell, N.L., Hus-son, J.M., Poppick, L.N., Cottle, J.M.,Schoene, B. and Maloof, A.C., 2012.Constraints on the origin and relativetiming of the Trezona d13C anomalybelow the end-Cryogenian glaciation.Earth Planet. Sci. Lett., 319–320, 241–250.

Rothman, D., Hayes, J. and Summons, R.,2003. Dynamics of the Neoproterozoiccarbon cycle. Proc. Natl. Acad. Sci.USA, 100, 8124–8129.

Sperling, E.A., Robinson, J.M., Pisani, D.and Peterson, K.J., 2010. Where�s theglass? Biomarkers, molecular clocks, andmicroRNAs suggest a 200–Myr missingPrecambrian fossil record of siliceoussponge spicules. Geobiology, 8, 24–36.

Swart, P.K. and Kennedy, M.J., 2012.Does the global stratigraphic reproduc-ibility of d13C in Neoproterozoiccarbonates require a marine origin? APliocene–Pleistocene comparison.Geology, 40, 87–89.

Williams, G.E., 1979. Sedimentology,stable-isotope geochemistry and pala-eoenvironment of dolostones cappinglate Precambrian glacial sequences inAustralia. J. Geol. Soc. Aust., 26, 377–386.

Xiao, S. and Laflamme, M., 2009. On theeve of animal radiation: phylogeny,ecology and evolution of the Ediacarabiota. Trends Ecol. Evol., 24, 31–40.

Received 16 December 2011; revised versionaccepted 23 February 2012

Terra Nova, Vol 24, No. 4, 318–325 J. M. Husson et al. • Isotope conglomerate test

.............................................................................................................................................................

� 2012 Blackwell Publishing Ltd 325