Deep-Sea Research II 50 (2003) 1529–1562

Plio-Quaternary sedimentation on the Wilkes land continentalrise: preliminary results

M. Busettia,*, A. Caburlottoa, L. Armandb, D. Damianic, G. Giorgettic,R.G. Lucchia, P.G. Quiltyd, G. Villae

a Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Borgo Grotta Gigante 42/c 34010 Sgonico, Trieste, Italyb Institute of Antarctic and Southern Ocean Studies, and Antarctic Cooperative Research Centre, University of Tasmania,

GPO Box 252-80 Hobart, Tasmania 7001, AustraliacDipartimento di Scienze della Terra, Universit "a di Siena, Via Laterina 8, Siena 53100, Italy

dSchool of Earth Sciences, University of Tasmania, GPO Box 252-79 Hobart, Tasmania 7001, AustraliaeDipartimento di Scienze della Terra, Universit "a di Parma, Parco Area delle Scienze, 157, Parma 43100, Italy

Abstract

The Wilkes Land continental rise is characterised by mounds and channels with approximately a north–south

elongation, perpendicular to the margin. Proximal mound relief is up to 1000m, decreasing to about 300m in the

central part. During the geophysical and geological survey conducted on in February–March 2000 by the joint Italian

and Australian WEGA Project, onboard R/V Tangaroa, 11 piston cores were collected along two transects crossing the

channel-mound system. All cores were logged for physical (magnetic susceptibility and density) and acoustic properties

(P-wave velocity). Split cores were X-rayed and samples were analysed for clay mineral assemblages, chemical and

micropaleontological (diatoms, foraminifera and nannofossils) content.

Glacial and interglacial intervals have been recognised in the sediment cores. The interglacial facies consists of

massive mud, distinguished by: (a) bioturbated massive mud occasionally with fine-grained ice-rafted debris (IRD), and

(b) structureless massive mud with abundant fine to coarse-grained IRD, containing well-preserved open-ocean

diatoms. The glacial facies is represented by laminated mud with planar and/or cross laminations, with occasional

isolated dropstones, and rare, poorly preserved, sea-ice diatoms. The sharp boundary, characterizing the limit between

massive to laminated facies, is interpreted to indicate a fast glacial onset. In contrast, the smooth passage presents from

laminated to massive sediments, indicates a gradual glacial waning.

Recent down-slope gravity flows have been identified in a turbidite, a normally graded coarse-grained sand,

recovered in the thalweg of Jussie Canyon, and probably also in the massive debris facies from the steep side of Mound

A. The massive debris is characterised by structureless and unsorted gravel and pebbles within a muddy matrix. Clay

mineral assemblages and grain lithologies indicate a hinterland Wilkes Basin and continental shelf provenance for the

terrigenous fraction.

Crown Copyright r 2003 Published by Elsevier Science Ltd. All rights reserved.

*Corresponding author. Tel.: +39-040-214-0254; fax: +39-040-327307.

E-mail address: mbusetti@ogs.trieste.it (M. Busetti).

0967-0645/03/$ - see front matter Crown Copyright r 2003 Published by Elsevier Science Ltd. All rights reserved.

doi:10.1016/S0967-0645(03)00078-X

1. Introduction

Deep-sea mound deposits around Antarctica arean object of growing interest for their relation tothe behaviour of the ice cap and their record ofpaleo-climatic change. The Wilkes Land conti-nental margin is one location of these morpholo-gical features that can provide informationfor the evolution of the Eastern Antarctic icecoverage.The Wilkes Land continental margin morphol-

ogy is characterised by several submarine canyonscutting the slope, and by mound and channelsystems in the continental rise. The mounds,named from west to east Mounds C, A and B,have approximately north–south elongated axesperpendicular to the margin between 143�E and145�E. They are asymmetrical, with a long gentleeastern side and short steep western side, lyingbetween 2500 and 3600m water depth in the upperand lower part, respectively. The relief is up to1000m in the proximal area, decreasing to about300m in the centre. Mounds C and A areseparated by the Jussie Canyon; Mound C isdelimited on the eastern side by Buffon Canyon.Both canyons reach the shelf break, while theWega Channel, separating Mound A and B,probably starts from the upper rise (Fig. 1). Fromseismic evidence, Donda et al. (2003) suggest thatthe submarine canyons originated by down-slopegravity flows. Hence they represent the mainsediment drainage pattern, supplied by the con-tinental shelf margin ice-sheet, and feeding themound depositional system. Turbidity currents areconsidered the main process for sediment supply tothe rise, although depositional facies suggest theinterplay of turbidity and bottom currents (Escutiaet al., 1997). The initiation of mound deposition isinterpreted as to have started in the EarlyMiocene, by deposition of turbidites, followed bya mound attenuation phase with smoothing andfilling the previous relief (Donda et al., 2003; DeSantis et al., 2003), as elaborated on seismicinterpretation.The canyons cutting the slope are thought

to be the conduits of bottom currents originat-ing on the shelf. The continental shelf of WilkesLand, in particular the Ad!elie Depression close

to the Mertz Glacier, has been identified asone of the main sources of Antarctic BottomWater (AABW) (Gordon and Tchernia, 1972;Rintoul, 1998). Plumes of cold, fresh, densewater flow over the continental slope and rise(Rintoul, 1998), and are probably channelleddown canyons (Bindoff et al., 2000). Furthermore,the down-slope current on the sea floor iswestward and bottom-intensified (Bindoff et al.,2000).Similar mound systems are present elsewhere

around Antarctica. On the continental rise west ofthe Antarctic Peninsula, such ‘‘mounds’’ have beeninterpreted as sediment drifts, constructed bydeposition, from a nepheloid layer, of smallhigh-energy turbiditic currents originating onthe slope, and maintained and developed todayas a result of both turbidity-and bottom-currentaction (Rebesco et al., 1996, 1997). The sedimentdrifts also have been studied in terms of Plio-Quaternary glacial/interglacial fluctuations (Cow-an, 2000; Pudsey, 2000a, b; Lucchi et al., 2002a, b),indicating that a good record of detailedclimatic change is preserved in these deposits.In addition to the two ‘‘end member’’ phases ofglacial and interglacial periods, transitionalfacies have been recognised, which are veryimportant for understanding the mechanism ofgrowth and retreat of the ice shelf on thecontinent.A geophysical and geological survey was carried

out in February–March 2000 by the joint Italianand Australian WEGA Project, onboard the R/VTangaroa. The aim of the project was a multi-disciplinary investigation of the continentalshelf, slope and rise for paleo-climatic studies.About 600 km of multichannel seismic reflectionprofiles, 3.5 kHz acoustic profiles and 11piston cores with trigger cores were acquired onthe continental rise (Fig. 1). The cores werecollected along two transects parallel tothe margin and crossing the channel-moundsystems (Fig. 2).The purpose of this study is to analyse the

sediment piston cores collected to investigate Plio-Quaternary deposition and sedimentary processes,and possibly relate them to glacial/interglacialpaleo-climatic fluctuations.

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621530

Fig. 1. Location map of the continental margin of Wilkes Land showing the eleven piston cores collected along two 3.5 kHz acoustic profiles, during the joint Australian

and Italian WEGA Project in February–March 2000. The morphology of the continental rise is characterized by mound and channel systems with approximately north–

south elongation. Bathymetric contours are in metres.

M.

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Fig. 2. 3.5 kHz acoustic profiles crossing Jussie canyon, Mound A, and WEGA channel, with core locations. In the distal profile (line 26) Mound A is characterized by a

short steep western side and a long gentle eastern side. Maximum relief of the mound is approximately 400m. Morphology of the same mound in the proximal area (line

33) is rough, with low relief. In profile line 26, on the gentle side of the Mound A, it is possible to recognize reflectors pinching-out to the mound crest between the sites of

cores 20 and 21.

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2. Methods

The whole cores were logged for physical andacoustical properties, and after splitting, visuallydescribed on board ship (Brancolini and Harris,2000). Shore-based investigations included: (1) X-radiographs, (2) clay mineral analysis, (3) chemicalanalysis for biogenic opal, organic carbon, totalnitrogen and calcium carbonate content, (4)mineralogy of the sand fraction, and (5) biostrati-graphy using diatoms, nannofossils and foramini-fera.

2.1. Physical and acoustic properties

Physical (wet bulk density (WBD) and magneticsusceptibility (MS)) and acoustic (P-wave velocity)properties were logged on board ship on all thewhole cores using a Multi-sensor Core Logger(Geoteks), with a sampling interval of 1 cm. Thelog acquisition is software-controlled, and the dataare automatically correlated to each other. Wetbulk density is measured using a Caesium-137gamma ray source with a beam of about 1 cm indiameter and 20 s sampling time. The MS wasdetermined using a Bartington MS2 loop sensor(3-cm horizontal resolution), with 1-s samplingtime. The volume magnetic susceptibility (VMS)was then obtained using a correction that takesinto account the loop sensor and sediment corediameters. P-wave velocities (Vp) were obtainedusing two rolling transducers (transmitter with a250 kHz P-wave pulse and receiver) and processedusing in situ conditions provided by CTD mea-surements (temperature and salinity) acquiredduring the survey (Brancolini and Harris, 2000).

2.2. Clay minerals

Cores from PC-18 to PC-27 were sampled every10–15 cm, with higher resolution close to litholo-gical boundaries (total of 242 samples). Sedimentsamples were dispersed in an ultrasonic bath,washed and centrifuged with deionised water andwet-sieved at 63 mm. The clay and silt fractionswere separated using the Stokes’ law settlingprocedure in glass tubes. The clay fraction wassaturated with 50% MgCl2 solution to improve

homogenous charging and d-spacing of the basallattice layers within expandable clays. Smear slidesproduced oriented clay mounts. X-ray diffracto-grams were obtained with a Philips PW 1710instrument, using CuKa radiation (40KV, 40mA).Each sample was analysed between 2� and 40�2y;with a step size of 0.02�2y (Brown and Brindley,1980). A slow scan between 23� and 25.5�2y; withsteps of 0.05�2y; was performed on the glycolatedmounts obtained with ethylene–glycol vapour at atemperature of 60�C for about 18 h.The degree of lattice ordering and crystallite size

of smectite and illite, called the ‘‘crystallinityindex’’, is expressed as the integral breadth (IB)of the glycolated 17 (A (smectite) and 10 (A (illite)peaks, respectively. The IB is the width of therectangle that has the same height and the samearea as the measured peak. We use the samecrystallinity categories as Diekmann et al. (1996):(a) smectite: o1.5=well crystalline, 1.5–2.0=moderately crystalline, >2.0=poorly crys-talline, (b) illite: o0.4=very well crystalline, 0.4–0.6=well crystalline, 0.6–0.8=moderately crystal-line, >0.8=poorly crystalline.Diffractograms were analysed using the ‘‘Mac-

Diff’’ software (Petschick, University of Frank-furt, Germany, unpublished) on an Apple PersonalComputer. The software allowed the determina-tion of the intensity, width and area of peaks fromwhich the semi-quantitative percentages of miner-als were calculated.

2.3. Chemical analysis

Chemical analysis was performed at the Labor-atorio di Biologia Marina (Trieste–Italy) on a totalof 119 samples collected at a sample spacing of10 cm from cores PC-18, -19, -20, and -21.Biogenic opal concentration (SiO2+0.4H2O)

was measured employing the DeMaster method(DeMaster, 1981; Conley, 1998), in which the drysediment is treated with a Na2CO3 solution (1%)at 85�C.Organic carbon (Corg) and total nitrogen (Ntot),

were determined by CHN analysis, performedafter a sequential hydrochloric acid treatment ofdry sediments following the method of Nieuwen-huize et al. (1994), using a Perkin Elmer 2400

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1533

CHNS/O elemental analyser with temperatureranging between 950�C and 1050�C.Calcium carbonate content (CaCO3) was deter-

mined using a modified Bernard calcimeter, thatmeasured the volume of CO2 produced by thereaction CaCO3+HCl (18%). The percentage ofCaCO3 is obtained through a stoichiometriccalculation based on a blank test.

2.4. Biostratigraphy and composition of sand

fraction

Preliminary diatom analysis of core catchersediments was completed on board the ship(Brancolini and Harris, 2000). Additional samplesfor post-cruise study were collected from cores PC-18, -19 and -20, at 20-cm intervals and analysed atthe Antarctic CRC (Hobart, Australia). Smearslides were prepared with standard methods, andviewed at � 1000 magnification under oil immer-sion and phase contrast. All results are qualitativeenabling preliminary age assignments. Diatomoccurrences were documented as present when>3 complete frustules were encounted in thesmear slide, as fragments when only identifiablefrustules were encounted, and rare when only onecomplete frustules was observed. Where identifica-tion was uncertain, the term cf. (compares with)was documented. Criteria for separating reworkedversus in situ deposition of diatom frustulesdepended predominately on three attributes: (i)preservation of frustules, e.g., fragments versuscomplete specimens, the latter suggesting in situ,(ii) abundance, e.g., where the number of completespecimens was >3, suggesting in situ, (iii) totalassemblage, e.g., where a single older specimenappeared allochthonous against the remainingspecies identified, therefore suggesting reworking.Approximately 110 samples were collected from

selected intervals of all cores, and examined for

calcareous nannofossil content. Smear slides wereprepared with standard method and investigatedusing a � 1200 magnification. Counting of cocco-liths was performed on fixed areas of 6mm2.Foraminiferal and compositional studies were

performed on the core catchers from each pistonand trigger core, and from some selected levels incores PC-18, -20, -23, -25 and -28. About 12 g ofsediment were washed and sieved at 63 and125 mm, and the sand fractions investigated formineralogical composition and presence of for-aminifers. The mineralogical composition ofgraded sands, recovered in core PC-28, wasinvestigated in slides obtained by embedding thesediments in araldite before thin sectioning.

3. Results

3.1. Visual logs and X-radiographs

Three geomorphological settings were investi-gated within the studied area, each one with adifferent sedimentary record. The distal easterngentle slope of Mound A (cores PC-18, -19, and -20) and the proximal eastern and upper westernsides of the same mound (core PC-26 and -27)contain a sequence of alternating massive mudwith occasional bioturbation and sparse fine-grained ice-rafted debris (IRD), and laminatedsediments with planar and cross laminations(Fig. 3a). The laminated intervals consist of fineto medium sand in core PC-27 (proximal), whereasthe grain size decreases to silt/silty mud in coresPC-19 and -20 (more distal). IRD pebbles ofdolerite, granite, orthogneiss, marble, and por-phiritic monzonite occur mainly within the mas-sive mud and occasionally in the laminatedintervals.

Fig. 3. Lithostratigraphy of the cores based on visual observation and analysis of X-radiographs. Five main facies are recognized:

massive mud, laminated mud, massive debris, laminated-to-massive mud, and turbidite. Cores along the gentle side of Mound A in the

distal area and cores from proximal sites are characterized by massive mud and laminated mud (Fig. 3a). Cores from the steep side of the

Mound A consist of massive debris overlying the laminated-to-massive mud or the massive mud (Fig. 3b). Correlation from core to core

has been made using volume magnetic susceptibility (VMS) and lithology. Selected marker VMS peaks used for the correlation are

numbered (Fig. 3a). VMS peaks are not correlated in Fig. 3b as they are strongly influenced by gravels and pebbles present in the

massive debris that can obscure the VMS signature of sediment matrix.

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621534

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1535

Along the steep side of Mound A, cores (PC-21,-22, -23 and -24) contain a section of massivecoarse-grained IRD in the upper part (maximum2m-thick). In the lower part, a sequence ofalternating laminated mud and massive mud wereobserved. The boundaries gradually pass fromlaminated to massive mud and a sharp contactbetween massive and laminated sediments(Fig. 3b).Core PC-28, located within the Jussie Canyon

(Fig. 2), recovered a turbidite characterised byabout 1.5m of normally graded coarse sandgradually fining upward to silty clay with sparsemud chips. This turbidite was deposited abovesilty mud interval, suggesting that it may representthe last event of a repeated process.

The combination of visual and X-ray investiga-tion allowed the identification of five sedimentaryfacies (Figs. 3a,b and 4):

(1) Massive mud: distinguished in two sub-facies:(i) bioturbated massive mud occasionally withfine-grained IRD, (ii) structureless massive mudwith abundant fine to coarse-grained IRD;

(2) Laminated mud: characterised by planar and/or cross laminations, with mm- to cm-thick X-ray-light laminae/beds and mm-thick X-ray-dark laminae, with occasional isolated drop-stones (IRD). The boundary from massive tolaminated facies is sharp;

(3) Massive debris: structureless and unsorteddebris (gravel and pebbles) in a muddy matrix;

Fig. 3 (continued).

Fig. 4. Visual and X-radiographs observations allows the recognition of five sedimentary facies: (1) Massive mud: distinguished in two

subfacies: (a) bioturbated massive mud occasionally with fine-grained IRD, (b) structureless massive mud with abundant fine to coarse-

grained IRD, (2) laminated mud: planar and/or cross laminations, with mm to cm-thick X-ray-light laminae/beds and mm-thick X-ray-

dark laminae, and occasional isolated dropstones (IRD), (3) massive debris: structureless and unsorted debris (gravel and pebbles)

within muddy matrix, (4) laminated-to-massive mud: repeated intervals of finely laminated mud gradually passing to structureless mud

with sparse clasts (IRD). The boundary between massive and laminated mud is sharp.

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621536

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1537

(4) Laminated-to-massive mud: dm-repeated inter-vals of finely laminated mud gradually passingto structureless mud with sparse clasts (IRD).The boundary between massive and laminatedmuds is sharp;

(5) Turbidite: normally graded coarse-grainedsand with sparse mud chips.

3.2. Physical and acoustic properties

Physical and acoustic properties respond pre-dictable and coherently to lithological variations,although the response from single units cannot beunequivocally characterised. Ice-rafted debris,particularly isolated clasts, can strongly influencethe logs, causing abrupt increased values in WBD,P-wave velocity, and depending of lithology, alsoin VMS (Fig. 5a).The massive mud usually has consistently higher

values of P-wave velocity (Vp) and WBD thanlaminated facies (Fig. 5a and b). The VMS isgenerally low (up to 70 SI), with sharp variationsat the boundaries with the laminated facies (lowervalues). In contrast, the laminated mud shows ahigher down-core variability of Vp and WBD thatcorrespond to alternating dark and light laminae(higher values correlate with dark laminae). Themassive debris has the highest values of physicaland acoustic properties as they are stronglyinfluenced by the presence of abundant coarseIRD. Finally, the massive-to-laminated mud hascombined properties of the typically massive andlaminated facies (Fig. 5b).The massive mud recovered in core PC-18 and in

the upper 3m of PC-19 shows unusual reverse

down-core trends of Vp and WBD. This isuncommon, as the P-wave velocity is normallydirectly influenced by the density of the sedimentsand hence they should present the same logvariations. We exclude the hypothesis of aninstrumental error for two reasons: (1) the reversetrends of Vp and WBD occur in two cores, and (2)in the lower part of core PC-19 and in all othercores the massive mud shows normal coherenttrends.A preliminary core-to-core correlation has been

obtained combining the VMS logs with identifiedsedimentary facies (Fig. 3a and b). Good resultswere achieved for the cores collected along thegentle side of Mound A, while in cores locatedalong the steeper side, only the uppermostsedimentary facies (massive debris) has beenconfidently correlated. We think that along thisside the deeper units belong to progressively oldersediments as suggested by the 3.5 kHz seismicstratigraphy, and thus that the surface below themassive debris is time transgressive.

3.3. Diatom assemblage and compiled

biostratigraphy

Diatom frustules were recovered in almost allcore-catcher samples and within samples of thethree cores studied. In most cases diatom assem-blages were affected by dissolution bias, meaningheavily silicified genera were dominant and lightlysilicified genera were absent or rare. Core-catcherassemblages were generally largely fragmented anddissolution-biased assemblages. Most core-catchersamples suggested strata penetration was not

Fig. 5. Physical and acoustic properties were logged using the multi-sensor core logger (Geoteks) on whole cores at 1 cm intervals. The

massive mud usually has consistently higher values of P-wave velocity (Vp) and wet bulk density (WBD) than laminated facies, mostly

clearly seen in core 20. Volume magnetic susceptibility (VMS) is generally low (up to 70 SI), with sharp variations at the boundaries

with the laminated facies (lower values). In contrast, laminated mud shows a higher down-core variability of Vp and WBD that

correspond to alternating dark and light laminae (higher values correlate with dark laminae). The massive debris has the highest values

of physical and acoustic properties as they are strongly influenced by the presence of abundant coarse IRD. Finally, the massive-to-

laminated mud has combined properties of the typically massive and laminated facies. The clay mineral assemblage is dominated by

illite with minor percentages of smectite and chlorite. Kaolinite occurs in trace amounts only. In general the laminated mud has a low

content of illite and a relative high content of smectite and chlorite. In contrast, minima in smectite and maxima in illite contents occur

in the massive mud. Illite exhibits a down-core distribution pattern that is reverse to that of smectite. There is a direct correlation

between down core variation of illite content and the wet bulk density, caused by the highest matrix density of illite (2.84 g/cm3) in the

clay mineral assemblage (smectite=2.35 g/cm3), (Hallenburg, 1998).

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621538

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1539

Fig. 5 (continued).

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621540

beyond the Quaternary or late Pliocene (Table 1,Appendix A Table 6). Cores PC-23 and –27 had nobiostratigraphic indicator species to enable apreliminary age assignment. Preservation of dia-tom material in core samples varied from good toexcellent (whole frustules present, limited dissolu-tion, abundant and varied assemblages), poor(whole and fragmented specimens, dissolutionbiased assemblage decreasing assemblage variety),very poor (all specimens fragmented and dissolu-tion affected, rare complete specimens), to barren(no diatoms recovered).Diatom assemblage composition was attributed

to open-ocean or sea-ice cover environments basedon indicator taxa identified in previous ecologicaland statistical association studies undertaken inthe Southern Ocean are shown in Tables 2–4(Appendix A, Tables 6–10). (Pichon et al., 1987;Fryxell and Prasad, 1990; Armand, 1997; Zielinskiand Gersonde, 1997; Armand and Zielinski, 2001).In many cases species representative of bothenvironmental groups were observed in the samesamples (e.g., Fragilariopsis kerguelensis, Thalas-

siosira lentiginosus and Dactyliosolen antarcticus

(open-ocean) with Fragilariopsis curta, F. cylindrus

and Rhizosolenia sima f. silicea (sea-ice)).Specimens or occurrences of ‘‘reworked’’ specieswere difficult to assign due to the nature ofthe highly fragmented and dissolution biasedmaterial. Generally, reworking was identifiedon the basis of fragments of species from thegenus Denticulopsis, which normally predominatein the Miocene (Yanagisawa and Akiba, 1990),

Table 1

Preliminary diatom age assessment from core catcher sediments

Core Preliminary age assessment

PC-18 Quaternary, reworking of Plio-Pleistocene

PC-19 Quaternary, reworking of Plio-Pleistocene

PC-20 ? Pliocene

PC-21 Late Pliocene

PC-22 Early Pliocene/Late Pleistocene

PC-23 No indicator diatoms, no age assignment

PC-24 Late Pliocene

PC-25 Quaternary, no reworked species

PC-26 Late Pleistocene

PC-27 Rare diatoms, no age assignment

Table 2

Down core assessment of PC-18

Depth

(cm)

Diatom assessment

0–40 Good preservation, 18 cm soft layer best preservation

of modern? mixed open-ocean and sea-ice assemblage.

Highly fragmented in other intervals. Very minor

reworking of Miocene-Pliocene species.

60–67 Poor preservation, very highly fragmented. Dissolution

biased assemblage.

80 Poor preservation, very highly fragmented, dissolution

biased. Many E. antarctica terminal cells and presence

of Rh. sima f. silicea suggesting sea-ice conditions.

100–

140

Very poor preservation, very highly fragmented.

Dissolution biased assemblage, LAD of R. leventerae at

140 cm (0.130–0.140Ma).

160 Poor preservation, very highly fragmented. Dissolution

biased assemblage, sea-ice assemblage.

179–

240

Poor preservation, very highly fragmented. Dissolution

biased assemblage. Very minor reworking of Miocene-

Pliocene species at 200 cm.

260 Poor preservation, highly fragmented. Presence of Rh.

sima f. silicea, E. antarctica terminal cells and F.

peragallii suggesting sea-ice conditions.

280–

347

Poor preservation, highly fragmented, dissolution

biased assemblage. Indications of a greater open-ocean

component in samples 300–347 cm. Also increase in

frequency of R. leventerae observations.

Table 3

Down core assessment of PC-19

Depth (cm) Diatom assessment

0–100 Good to poor preservation, fragmented to

highly fragmented. Mixed open-ocean- sea ice

assemblage. Dissolution bias evident. Miocene

reworking at 0–60 cm. R. leventerae observed

at 60 cm.

120–320 Poor preservation, highly fragmented,

dissolution biased assemblage. Less variable

assemblage. Notable increases in E. antarctica

and decrease in Thalassiothrix antarctica from

120 to 320 cm. Reworking through these

intervals. R. leventerae fragments common at

depth until 260 cm.

340–380 Very poor preservation, very highly

fragmented, mostly dissolved specimens. 360–

380 cm fragments only. Suspected sea-ice cover

(laminated mud). Pliocene reworking 360–

380 cm.

400–420 Poor preservation, highly fragmented,

dissolution biased assemblage.

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1541

appearing out of context to the remainder ofspecies encountered.Core PC-18 contains a mostly poorly preserved

diatom assemblage down core with exception tothe first 40 cm of the core where preservation isgood and the assemblage is diversified (Table 2,Appendix A, Table 6). Range charts of selecteddiatom species are illustrated in Fig. 7. Theoccurrence of modern diatom taxa and theappearance of Rouxia leventerae between 140 cm(bsf) and the base of the core places core strata

within the T. lentiginosa/F. kerguelensis Concur-rent Range Zone identified by Zielinski andGersonde (2002). The last abundance datum(LAD) of Rouxia leventerae (0.13–0.14Ma, iso-tope stage 5/6 transition, Zielinski et al., 2002) isidentified at 140 cm (bsf) in PC-18 thereforeindicating the a–b subzone boundary of the T.

lentiginosa/F. kerguelensis Concurrent Range Zone(Zielinski and Gersonde, 2002). Although variousRouxia species were identified in the core (Fig. 7),the last occurrence datum (LOD) of Rouxia

constricta, defining the boundary between the T.

lentiginosa/F. kerguelensis Concurrent Range Zoneand the R. constricta Partial Range Zone, was notidentified because Rouxia constricta was onlyrecently described (Zielinski and Gersonde,2002). Occurrences of Actinocyclus ingens withinthis core were not considered applicable to theLast Occurrence Datum of the species(LOD)=0.38Ma (Zielinski and Gersonde, 2002).Core PC-19, located about 3 km parallel, but up

the Mound A slope from PC-18 (Fig. 2), reveals asimilar diatom sedimentation history to the lattercore. The top section of the core has goodpreservation, diminishing to poorer preservationand increased fragmentation with depth (Table 3,Appendix A, Table 7). Intervals of Miocene orPliocene diatom reworking occur through out thecore (Appendix A, Table 7). Rouxia leventerae issporadic through the core and due to thecontinuous, albeit fragmented, recovery of thisspecies, we have assigned the core within the T.

lentiginosa/F. kerguelensis Concurrent RangeZone. We have furthermore placed the LAD ofR. leventerae at 120 cm (bsf) due to the consistentfragment record. The LOD of Rouxia constricta

was not identified. As in PC-18, we did not applythe LOD of A. ingens to this core. We suspect amajor interval of sea-ice cover occurred between340 and 380 cm (bsf) due to the lack of diatommaterial contained in the sediments.Core PC-20 is located near the axis of Mound A

(Fig. 2). The core contains a variable good-poor-good preservation in the first 200 cm, againdiminishing to generally poor preservation downcore (Table 4, Appendix A, Table 8). A fewobservations of Rouxia leventerae specimens arenoted within the top 130 cm (bsf); these assist in

Table 4

Down core assessment of PC-20

Depth (cm) Diatom assessment

0-20 Good preservation, open ocean-ice edge

assemblage, Miocene reworking, F.

kerguelensis dominated.

40–100 Poor diatom recovery, almost barren at 100 cm

(laminated mud), Miocene reworking, very

highly fragmented, Suspected sea-ice coverage-

comments restricted to laminations in this

interval.

120–180 Good-excellent preservation, open-ocean

assemblage, LAD of R. leventerae (0.130–

0.140Ma) at 120 cm, Miocene reworking,

presence of H. karstenii and other distinct

open-ocean species at 160 cm, suspected warm

conditions. Fragmentation increasing with

depth.

200–220 Poor preservation, highly fragmented,

dissolution affected assemblage, transition

from open-ocean to sea-ice assemblage.

240 Very poor recovery, highly fragmented, biased

towards an open ocean dissolution resistant

species. Suspected sea-ice coverage.

260 Good-poor preservation, highly fragmented,

open-ocean assemblage possible warmer

conditions?

280–389 Poor preservation to barren, Miocene-Pliocene

reworking. No F. kerguelensis or very rare

modern diatoms preserved in any sample

interval. 300 and 360 cm barren. 340 cm

reworking event? and presence of A. ingens

(LAD=0.65Ma). Suspected sea-ice coverage.

400–420 Poor-good preservation, very highly

fragmented. Reappearance of F. kerguelensis.

Pliocene reworking (Th. inura). F. barronii

specimen at 420 cm (LAD=1.350Ma).

440–460 Poor to very poor preservation, very highly

fragmented, Miocene reworking.

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621542

defining the top section to the T. lentiginosa/F.

kerguelensis, Concurrent Range Zone (Fig. 7). Thebase of core PC-20 contains Actinocyclus ingens, asingle specimen of Fragilariopsis barronii, andFragilariopsis kerguelensis, suggesting an age of>1.35Ma, corresponding to the top of the R.

constricta Partial Range Zone and the base of theActinocyclus ingens Partial Range Zone (Fig. 7).The application of the LAD of F. barronii

(Gersonde and B!arcema, 1998) has been noted asdifficult to apply because it has transitional formswith its evolutionary successor F. kerguelensis

(Gersonde and B!arcema, 1998; Zielinski et al.,2002). Therefore, should this diatom zone place-ment be correct, we identify the boundary betweenthe R. constricta Partial Range Zone and the T.

lentiginosa/F. kerguelensis Concurrent Range Zoneat 150 cm (bsf) based on a possible Last AbundantOccurrence Datum (LAOD) of A. ingens at 120 cm(bsf). The observation at 150 cm (bsf) of the warm-water attributed Hemidiscus karstenii in this coresuggests that warm surface waters had intrudedthe Antarctic region during deposition. Thisspecies range is well documented as a Northernand Central Southern Ocean biostratigraphicindicator for the late/middle Pleisotocene(0.19Ma, MIS7, Burckle et al., 1978; Gersondeand B!arcema, 1998; Zielinski et al., 2002). Itsbiostratigraphic use in this core is not warranted,yet nevertheless indicates that core deposition iswithin the middle Pleistocene, presumably border-ing the boundary between the R. constricta PartialRange Zone and the T. lentiginosa/F. kerguelensis

Concurrent Range Zone.Semi-quantitative analyses of all cores revealed

calcareous nannofossils only within the Massive

debris of cores PC-21 and -22 (Table 5). This isconsistent with the onboard observation of for-aminifer-rich intervals within this sedimentaryfacies. In all the other cores there are no calcareousnannofossils. The presence of Emiliania huxleyi inthe uppermost part of core PC21 (0–135 cm)indicates an age of 0.275Ma or younger, whereasthe interval down to 180 cm contains an assem-blage with Pseudoemiliania lacunosa, whose lowabundance could be related to reworking ratherthan indicating an age older then 0.4Ma. A singlespecimen of Coccolithus pelagicus was detected in

sample PC-22, at 15 cm, and believed to bereworked.The foraminiferal fauna in the cores is over-

whelmingly agglutinated (Appendix A, Table 10).A few samples contain planktonic foraminifera,with Neogloboquadrina pachyderma dominant. Asparse calcareous benthic fauna is present spor-adically. Sponge spicules are also present in manysamples.The turbidite recovered in core PC-28 is barren

in the lower part (up to 110 cm). The firstoccurrence of a single foraminifer (N. pachyderma)appears at 80 cm. At 40 cm rare sponge spiculesand large calcareous foraminifera are present,including the planktonic N. pachyderma and afew benthics such as Globocassidulina and apolymorphinid. The fossils are more abundant atthe top of the core, and consist mainly of spongespicules (mostly broken), common/well preservedradiolaria, and minor diatoms.

3.4. Clay minerals

The clay mineral assemblages are dominated byillite with minor smectite and chlorite (Fig. 5a andb). Kaolinite occurs in trace amounts only. Ingeneral the laminated mud has a low content ofillite and a relative by high content of smectite andchlorite. In contrast, minima in smectite andmaxima in illite content occur in the massive

mud. Illite exhibits a down-core distributionpattern that is opposite to that of smectite, andthere is a direct correlation between down-corevariation of illite content and the WBD. Otherminerals detected within the clay fraction are:

Table 5

Down core assessment of PC-21

Depth (cm) Nannofossil assessment

0–1 Poor preservation: of rare nannofossils.;

presence of Emiliania huxleyi, indicating latest

Pleistocene.

60 Poor preservation: very rare nannofossils,

90–180 Good preservation: rare-few nannofossils,

presence of Emiliania huxleyi and of mid-late

Pleistocene reworking

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1543

quartz, plagioclase, and K-feldspar, which arepresent in high concentrations that, however, havenot been quantified.In core PC-18 the upper 40 cm are characterised

by a relatively constant concentration of all clayminerals. Between 40 and 120 cm the smectitecontent falls to 3–6% with a higher content of illite(70–80%) having only small fluctuations. Between120 and 360 cm there are major fluctuations with adecrease of illite (64–78%) and chlorite (11–23%)content and an increase of smectite (4–23%). Thesmectite is well to moderately crystalline(IB ¼ 0:6621:80), and illite is Fe/Mg-rich andwell to moderately crystalline (IB ¼ 0:5520:73).In core PC-19 the upper 135 cm show a

progressive increase of illite content (62–78%),whereas smectite concentration decreases from16% to 5%. The chlorite has a constant concen-tration and kaolinite occurs in traces. Between 130and 265 cm the sediment is characterised by adecrease of illite content (from 78% to 69%) witha pronounced increase of smectite (from 5% to25%). Below 265 cm the illite and smectite showonly minor variations, whereas chlorite andkaolinite have major fluctuations (7–15% and 0–13%, respectively). Illite and chlorite show asimilar down-core distribution, which is oppositeto that of smectite and kaolinite. Smectite is highlyto moderately crystalline (IB ¼ 1:0921:66) as isillite (IB ¼ 0:5420:79), that is Mg/Fe-rich phase.In core PC-20 the down-core clay mineral

concentration has several fluctuations due to thealternation of the massive and laminated facies;the only exception is the interval 180–240 cm thatis characterised by a constant low smectiteconcentration (about 10%). Illite and chloriteexhibit down-core distribution patterns that are

frequently opposite to those of smectite andkaolinite. Smectite is highly crystalline(IB ¼ 0:8621:48), and illite is moderately toohighly crystalline (IB ¼ 0:4720:77).In core PC-21 the down-core clay mineral

distribution presents several small-scale fluctua-tions with a sharp decrease in illite and increase insmectite at the boundary between the massive

debris and the laminate-to-massive mud facies.Smectite is highly to moderately crystalline(IB ¼ 1:0921:70) as is illite (IB ¼ 0:5320:76).Traces of glauconite are present in cores PC-18,

-24 and –28 (Appendix A, Table 10).

3.5. Mineralogical composition of sand fraction

A detailed mineralogical analysis of the sandfraction composition was conducted on the sandyturbidite of core PC-28 and on selected samplescollected from the whole core set.The bottom of the turbidite consists of well

sorted, coarse-grained (about 2mm), rounded tosubrounded grains. The components are 70–80%lithic fragments, consistent with a dominant sourcefrom a gneissic terrane; abundant quartz andfeldspar (microcline/plagioclase), biotite, minorchlorite, and sericite; quartzite, and a variety ofsedimentary rocks are common; 20–25% mono-crystalline quartz with undulose extinction, com-monly well rounded. There is a trace of coarse-grained, sparry carbonate grains (when calcite ordolomite are not determined). At 110 cm thesediment is slightly finer with a few extracarbonate grains. Upward (80 cm) the sediment iscomposed by sand of about 1mm, with markedlymore angular grains, and a higher proportion offine grained lithic fragments (shale or low grade

Fig. 6. Down-core distribution of geochemical parameters are consistent with lithofacies variation. CaCO3 and biogenic silica

percentages are usually o1% and o15%, respectively. Significant fluctuations of CaCO3>1% were recorded within the massive mud

in PC-18 and -19 having a trend similar to the biogenic silica. In core PC-21 the CaCO3 content reaches 35% in the massive debris and

falls too1.5%. Ntot and Corg have low and constant average values of 0.08% and 0.20%, respectively, the only exception being in core

PC-19 which has a sharp increase of Corg at the boundary between massive and laminated facies at 3.4m. The percentage of organic

carbon is generally lower in the massive mud, consistent with the presence of pervasive bioturbation suggesting oxygenated sea-bottom

conditions with degradation of the organic matter. In the laminated mud a slightly higher organic carbon content than the massive

facies due to the absence of bioturbation suggests favourable conditions for organic matter preservation. The C/N ratio is

predominantly lower than 5, indicating a marine origin of the sediments (Stein, 1991). Peaks with values between 5 and 10 or around

10, observed mainly within the laminated mud are an admixture of marine/terrigenous compounds. Very high C/N ratios (up to 240)

within the massive mud in core PC-18 is indicative of terrigenous supply (Stein, 1991).

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621544

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1545

metamorphic grains originating from shale) andtraces of individual garnet grains. At 40 cm thesandy fraction is notably finer with subrounded-subangular grains, and includes traces of garnet.The top of the core contains mostly angular-subangular markedly finer grains, but otherwise itis compositionally similar to those above.

3.6. Chemical analysis

Down-core distribution of geochemical para-meters is coherent with lithofacies variation(Fig. 6). The biogenic silica varies between 1.8%and 15%. In the cores located along the gentle sideof Mound A (cores PC-18, -19, and -20) thepercentages generally decrease in the deeper unitsshowing local minor fluctuations. In core PC-19 asharp decrease occurs at 340 cm (bsf), correspond-ing to the massive/laminated facies boundary.Along the steep side of Mound A (core PC-21)the values are consistently low within the massive

debris (up to 4.3%), with an abrupt increaseobserved in the overlying laminated-to-massive

mud facies (up to 9.8%) (Figs. 6 and 7).The calcium carbonate percentages are usually

o1%. Significant fluctuations above 1% arerecorded within the massive mud in PC-18 and -19, having a trend similar to that of biogenic silica.In core PC-21 the CaCO3 content reaches 35%within the massive debris that falls too1.5% in thelaminated-to-massive mud facies.Total nitrogen and the organic carbon have low

and constant averages of 0.08% and 0.20%,respectively, with the exception of core PC-19,which has a sharp increase of Corg at the boundarybetween the massive and laminated facies at340 cm (bsf). The C/N ratio measured in coresPC-18, -19, -20 and -21 is dominantly o5,indicating a marine origin of the organic matter(Stein, 1991). Peaks with values of 5–10 or around10 (admixture of marine/terrigenous compounds)were observed mainly within the laminated faciesof cores PC-19, -20 and -21. A very high C/N ratio

(up to 240), which according to Stein (1991) isrelated to land plants, hence indicative of terrige-nous supply, was observed within the massive mud

of core PC-18.

4. Discussion

4.1. Sedimentary facies

In this section we synthesise the sedimentologi-cal characteristics of the sedimentary facies identi-fied in the WEGA cores and suggest a preliminaryinterpretation of climatic significance.The massive mud is characterised as being

structureless. The fine-grained sediment, the lackof laminations, grading, and the presence ofpervasive bioturbation suggest hemipelagic sedi-mentation. A similar sedimentary facies has beendescribed on the continental rise of the AntarcticPeninsula (Pudsey and Camerlenghi, 1998; Pudsey,2000a, b; Lucchi et al., 2002a, b) and interpreted asan interglacial deposit. Evidence of interglacialsedimentation for the massive mud is: (1) gooddiatom preservation, with a species assemblagecharacteristic of open-ocean environment, (2) highvalues of biogenic silica (up to 15%), indicating aperiod of increased bio-productivity (Stein, 1991;Nijenhuis and de Lange, 2000), (3) presence ofbioturbation, suggesting a low-energy environ-ment with low accumulation rate, (4) presence ofsparse fine to coarse grained IRD, representing thecontinuous sediment input from icebergs.The two sub-facies (bioturbated massive mud

occasionally with fine-grained IRD, and structure-less massive mud with abundant fine- to coarse-grained IRD) probably represent different pa-leoenvironmental conditions within the intergla-cial periods. This is supported by the variability inclay minerals and diatom assemblages, physicaland acoustic properties (e.g., diatom assemblagesindicate episodes of different sea-ice extent withinthe interglacial period).

Fig. 7. Ranges of selected diatom species and their assigned zones in cores PC-18, -19, -20. Volume magnetic susceptibility (VSM) and

the main facies types as in Fig. 3a. Thin range lines refer to fragments and thick lines refer to presence of species occurrence down core.

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621546

massive m

udlam

inated mud

PC

-19

depth (m bsf)

1234

Diatom Zones

Marker Species Ranges

VM

S (S

I)20

4060

T.lentiginosa / F. kerguelensis

a b

Rouxia spp.

R. leventerae

A. ingensF. kerguelensis

PLEISTOCENE

PC

-20

depth (m bsf)

1234

Diatom Zones

Chronostratigraphic units

T.lentiginosa / F. kerguelensisA. ingens

a b

R. constricta

F. kerguelensis

PLEISTOCENE

A. ingens

H. karesteniiR. leventerae

Rouxia spp.

?

F. baronii

?

VM

S (S

I)20

4060

?

?

Marker Species Ranges

PC

-18

VM

S (S

I)30

5070

F. kerguelensisA. ingens

R. leventerae

Rouxia spp.

depth (m bsf)

123

Diatom Zones

T.lentiginosa / F. kerguelensisa b

PLEISTOCENE

Marker Species Ranges

Chronostratigraphic units

Chronostratigraphic units

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1547

The massive mud is characterised by similardown-core trends of WBD and illite content. Illiteis the heaviest clay mineral of the presentassemblage, with a matrix density of 2.84 g/cm3

(Hallenburg, 1998). Hence the percentage of illitestrongly influences the values of WBD, and this isparticularly evident in the massive facies where theclay grain size fraction is predominant.In PC-18, and in the upper part of PC-19, the

opposite trends of WBD and P-wave velocity(Fig. 8) may be due to a relatively high content ofbiogenic opal (up to 15%). The biogenic opal haslower grain density (estimate by Weber (1998) in2.2 g/cm3) compare to that of the terrigenousfraction (2.6–2.75 g/cm3), and has higher rigiditythat causes an increasing of P-wave velocity(Weber, 1998). Similar opposite trends wereobserved by Weber et al. (1997), who distinguishedbiogenic-opal rich sediments (up to 90%, withWBD of 1.1–1.3 g/cm3) from terrigenous sedi-ments (WBD of 1.4–1.8 g/cm3). In contrast, theminor content of opal in our records induces smallchanges in the WBD, hence our data plot with adifferent trend but in the same area (Fig. 8). Thevery low percentage of organic carbon corre-sponds with the presence of pervasive bioturba-tion, suggesting oxygenated sea-bottom conditionswith degradation of organic matter.

The laminated mud is characterised by alterna-tion of laminated mud (light-grey in X-radio-graphs) and silt/silty-mud laminae/layers (dark-grey in X-radiographs), related to traction cur-rents. Cross-laminations occur locally in the coresimplying intervals of stronger current activity.This facies has been interpreted as a glacial depositas suggested by: (1) absence/rare and poorpreserved diatoms indicating unfavourablepaleo-environmental conditions, (2) absence ofbioturbation, (3) rare drop stones suggestingextended sea-ice cover with sporadic release fromicebergs.A similar facies was described in the continental

rise of the Antarctic Peninsula and interpreted as aglacial deposit (Pudsey and Camerlenghi, 1998;Pudsey, 2000a, b; O’Cofaigh et al., 2001; Lucchiet al., 2002a, b), with laminations related to eitherturbiditic and contouritic processes.The sharp boundary between massive to lami-

nated facies is interpreted to indicate a fast glacialonset. In contrast the smooth passage fromlaminated to massive sediments indicates a gradualglacial waning. The laminated mud has a slightlyhigher organic carbon content than the massivefacies. This is consistent with the absence ofbioturbation, suggesting favourable conditionsfor organic matter preservation.

Fig. 8. The massive mud recovered in core PC-18 and in the upper 3m of PC-19 show an unusual reverse correlation between P-wave

velocity and wet bulk density (a). The massive mud in the lower part of core PC-19 and in all the other cores shows a normal direct

correlation between P-wave velocity and wet bulk density (b). The reverse correlation observed could be due to a relatively high content

of biogenic material (up to 15%). The biogenic opal has lower grain density (estimate by Weber (1998) in 2.2 g/cm3) compare to that of

the terrigenous fraction (2.6–2.75 g/cm3), and has higher rigidity that causes an increasing of P-wave velocity (Weber, 1998).

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621548

The massive debris is characterised by structure-less mud with unsorted debris (gravel and peb-bles). This facies is present in the upper part(maximum 200 cm) of all cores collected fromthe steep side of the Mound A (PC-21, -22, -23and -24). This sediment has the highest CaCO3

values (up to 35%) and contains calcareousnannofossils, used as a proxy of ‘‘warm’’conditions. Nannofossil age attribution (0.07–0.23Ma) suggests that this facies is coevalwith the massive mud of core PC-18 and the upperpart of PC-19 collected from the gentle side ofMound A.The high concentration of the coarse-grained

fraction chaotically distributed in the massive

debris could suggest a massive iceberg rainoutevent (IRD). The absence of such a deposit incores recovered from the gentle side of the mound,however, suggests that this hypothesis is not likely.Alternatively, this deposit represents a debris flowfrom shallower areas located above the CCD.Massive transport and fast deposition wouldprevent dissolution of calcareous fossils in theareas below the CCD. In this latter case, however,the potential source area of the debris flow is notobvious.The laminated-to-massive mud is present in the

deeper part of cores PC-21 and -22, from the steepside of Mound A, overlain by the massive debris

facies. This facies could represent (a) the record ofa series of glacial/interglacial changes with asmooth transition from the laminated glacialdeposits to the massive interglacials, or (b) theglacial deposition of laminated sediments occa-sionally interrupted by local mass-slope instabilityprocesses (massive debris intervals).

Turbidite facies recovered from Core PC-28 in asmall terrace close to the Jussie canyon thalweg,indicates that this channel is still active. Thecomposition of the sand indicates different sourceareas. The terrigenous fraction is originate toderive from either coastal Precambrian basement,the Beacon Supergroup of the TransantarcticMountains, and from possibly mid Proterozoicred-sandstone equivalents of South Australiansandstone. In the bioclastic fraction the presenceof broken spicules indicates a continental shelfprovenance.

4.2. Biostratigraphy and paleoecological

reconstruction

Diatoms in the cores provide an initial ageassignment. Recent diatom biostratigraphic stu-dies close to the region are limited to the CapeRoberts Quaternary biostratigraphy in the RossSea (Bohaty et al., 1998), and Southern Oceanbiostratigraphy from Kerguelen Plateau (Baldaufand Barron, 1991; Harwood and Maruyama,1992; Ramsay and Baldauf, 1999). However,refined diatom zonations in the southern Atlanticsector of the Southern Ocean (ODP Leg 177) havebeen advanced by Zielinski and Gersonde (2002).Key marine Quaternary and Neogene species wereidentified, but of the three cores currently studied(PC-18, -19 and -20) strata recovered is limited tothe Thalassiosira lentiginosa/Fragilariopsis kergue-

lensis Concurrent Range Zone (0.28Ma to pre-sent), the Rouxia constricta Partial Range Zone(0.65–0.28Ma) and possibly the Actinocyclus

ingens Partial Range Zone (1.8–0.65Ma) (zona-tions from Zielinski and Gersonde, 2002).Diatoms in PC-18 and -19 indicate that the two

cores have similar Pleistocene depositional ages.Both core catcher samples record modern open-ocean to sea-ice diatom assemblages with Rouxia

leventerae in fragments and/or as complete speci-mens (Tables 2 and 3, Appendix A, Tables 6 and7). Reworked Pliocene and Miocene species alsooccur in both cores (e.g., Thalassiosira inura,

Denticulopsis simonsenii, and other Denticulopsis

species).The upper 120 cm of PC-20 contain a diatom

assemblage indicating a potential loss of recentLate Pleistocene sedimentation compared withPC-18 and -19. PC-20 may extend into the earlyPleistocene, based on the appearance of a singlespecimen of Fragilariopsis barronii (suggested ageof ca. 1.35Ma, Gersonde and Burckle, 1990). Wecannot discount the possibility of Fragilariopsis

barronii being allochthonous, since other typicallower Pleistocene species such as Thalassiosira

elliptipora (a multiple sourced Last AppearanceDatum (LAD)=0.70Ma, acme between 1.15 and0.75Ma (Bohaty et al., 1998); South Atlantic FirstAbundant Occurrence Datum (FAOD)=1.01–1.13Ma (Zielinski and Gersonde, 2002) are

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1549

absent in the succeeding intervals. Evidence ofdown-core reworking is indicated by thepresence of fragments of Miocene taxa, especiallyDenticulopsis simonsenii (Table 4, Appendix A,Table 7).Diatom assemblages encountered in the core

sediments of PC-20 indicate an older age (earlyPleistocene) than those observed in the corecatcher (late Pleistocene) (Fig. 7). The core catcherof PC-20 contains fragments of Rouxia leventerae

indicating a stratigraphic juxtaposition of youngersediments into older. We suggest two possibleexplanations to justify the chronological discre-pancy between the base of the core and the corecatcher sample of PC-20. The first involves atechnical problem due to sediment re-penetrationoccurring during coring, and the second impliesthe presence of a sediment slide related to localslope instability. In this case, core PC-20 containsthe sedimentary sequence of the slide whereas thecore catcher penetrated the in situ sediments.Similar Pleistocene diatom age assignment isattributed by Escutia et al. (2003) to all the pistoncores collected in the lower rise, eastward of thestudy area.The massive mud facies contains the best

preserved diatom material. This observation cor-respond to high biogenic silica content (up to14%), which is similar to the values measured inmodern deposits on the Antarctic Peninsulacontinental rise (Pudsey, 2000b). The laminatedfacies is associated with periods of barren or poordiatom preservation. We interpret this to indicateglacial periods with extended sea-ice cover in thestudy area. This hypothesis is also supported bythe presence of a clear sea-ice assemblage in theintervals preceding and following these diatompoor sections. Sediments overlying the laminatedfacies contain a higher percentage of IRD, whichsupports ice retreat.The nannofossil chronostratigraphic control is

provided only by the presence of Emiliana huxleyi

in the massive debris of the upper 180 cm of corePC-21. We believe that the absence of calcareousnannofossils in the underlying interval is due tounfavourable paleoecological conditions at thetime rather than indicating sediments older than0.285–0.230Ma (E. huxleyi first occurrence). The

rarity of nannofossils may be due to: (1) lowproductivity in cold surface sea-water, sea-icecover extension, and poor nutrient availability,or (2) to poor preservation caused by carbonatedissolution (Villa and Wise, 1998). The presence ofnannofossils in our cores corresponds to thehighest carbonate content (up to 35%) recordedin the entire set of cores (usually CaCO3=0–4%).The absence of the E. huxleyi acme indicates thatthe massive debris sediments are, however, olderthan 0.06–0.07Ma.Foraminifera are not common in the studied

cores and the species recovered are mostly longranging with little biostratigraphic significance.The planktonic assemblage is dominated byNeogloboquadrina pachyderma, showing clear signsof dissolution. This observation is consistent withthe comments on nannofossil preservation (seeabove) and supports the second hypothesis ofcarbonate dissolution below the CCD.The foraminiferal assemblage found in our cores

is similar to that described by Lindenberg andAuras (1984) in the Kerguelen Plateau west ofHeard Island and on the Antarctic slope at theouter edge of Prydz Bay with benthic Psammo-

sphaera, Cyclammina and Martinottiella species incommon. According to Quilty (1985) and Poissonet al. (1987), the CCD off Prydz Bay is expected tobe at about 1500m-depth the continental shelfedge. A higher content of N. pachyderma has beenobserved in core PC-27 and in the trigger cores ofPC-21 and -24 at water depths of 2659, 3034 and3260m, respectively. Samples collected from corePC-18, -19, -20, and -25 at 3194, 3014, 3236,3363m depth, respectively, are barren of calcar-eous fauna. This suggests that the CCD is deeperthan near the continental shelf edge and may havebeen fluctuating with time in a range of 2660–3300m.

4.3. Clay minerals: climatic significance and

provenance

The composition of the clay mineral assem-blages in marine sediment depends on the climaticand weathering conditions on land as well as thelithology of source rocks. In Antarctic Quaternarymarine sediments, the clay minerals show minor

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621550

fluctuations in contrast with those of the earliestOligocene (Ehrmann, 1998b; Ehrmann and Mack-ensen, 1992), indicating that the main shift inweathering regime was completed at that time(Anderson et al., 1980; Ehrmann et al., 1992;Pudsey and Camerlenghi, 1998). Once the Antarc-tic continent was covered by ice and dominated byphysical weathering processes, the clay mineralcomposition of the sediments did not changesignificantly in response to further cooling events.For this reason, changes of individual clay mineralconcentration should be related to variations inthe source rather than to fluctuations in theintensity of glaciation (Ehrmann et al., 1992;Petschick et al., 1996; Ehrmann, 1998a).In the cores studied, the main changes in clay

mineral distribution can be correlated with themain lithological variations. Higher smectite andkaolinite contents occur in the laminated mud,whereas illite and chlorite are more abundant inthe massive mud. Clay mineral variations also canoccur within single sedimentary facies. Smectiteand illite are well-crystallised, suggesting lowchemical alteration and a nearby source area,respectively.Smectite in marine sediments around Antarctica

is considered to be detrital resulting from thechemical weathering of volcanic rocks (Ehrmannet al., 1992). The high percentages of smectite inthe laminated facies could be related to erosion ofolder pre-glacial smectite-rich material (Ehrmannet al., 1992) from the continental shelf bygrounded ice during glacial periods.Illite and chlorite in Antarctic sediments usually

are derived from sub-glacial erosion of crystallineand metamorphic rocks (Ehrmann et al., 1992). Inthe cores studied, illite and chlorite probablyoriginate from the intrusive and high-grademetamorphic rocks of the hinterland of WilkesLand (Marinoni et al., 2000). This is confirmed bythe mineralogical composition of the sand fraction(see results section and below).Kaolinite is found only in traces throughout all

cores, with a slightly higher percentage within thelaminated facies. As kaolinite derives by weath-ering in warm and humid climates (Chamley,1989), we argue that it was probably producedduring pre-Oligocene time, before the onset of the

ice sheet, and stored locally in ancient sedimentaryrocks.

4.4. Provenance of sand fraction

The composition of the sand and sandstonerecovered in the area indicates the presence ofmore than one source. Sand assemblages come inseveral forms. One type is fresh and angular withmany different minerals and represents eitherfreshly physically eroded basement rock or somequartz grains could derive from physically eroded‘red sandstone’ discussed below. Modern glacialaction could be the transport mechanism to theshelf area, whereas melting ice or down-slopegravity flows could be the transport mechanism tothe deeper areas of the continental rise. A secondsuite of quartz grains that is very well rounded andof high sphericity. Some grains also occur aslarger, slightly porous sandstone fragments in thecoarser grain size. These are similar to Permo-Triassic sandstone from the Prince Charles Moun-tains. This occurrence may suggest that Permo-Triassic sandstone is one of the sedimentary rocksin the Wilkes Basin, representing part of theBeacon Supergroup from the TransantarcticMountains. Very little coal is present in this areato suggest a sub-ice section with coal measures, inmarked contrast with the situation in Prydz Baywhere recycled coal is an ever-present constituent,accompanied by rounded sand grains (ShipboardScientific Party, 2001).Red sandstone occurs as both large clasts and

single red grains. Thin sections of the redsandstone from the nearby coast (CommonwealthBay–Cape Denison) (Fig. 1) show that here thesandstone has very low porosity and the individualgrains are regularly overgrown, bearing clearevidence of pressure cementation. No simpleround grains are present. This looks quite differentfrom the rounded sand grains discussed above,and it has been suggested that it is similar to mid-Proterozoic sandstone from South Australia. Thesimilarity with South Australia is suggestedbecause of the Gondwana paleogeography thathas South Australia juxtaposed against this part ofthe Antarctic coast.

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1551

Table 6

Core catcher—Qualitative assessment GC-01 GC-03 GC-04 GC-05 GC-06 GC-09 PC-01 PC-18 PC-19 PC-20 PC-21 PC-22 PC-23 PC-24 PC-25 PC-26 PC27 PC28

Notes seea seeb seec seed seee seef

Species Preservation Key vpp hfd, r hfd, r hfd, r hfd, r hfd, r hfd, r vpp,hfd,r hfd, r r vpp,hfd

Actinocyclus actinochilus f p p?

Actinocyclus ingens p

Act. ingens (var. ovalis/var. A Harwood & Maruyama) p p

Actinocyclus karstenii f p

Asteromphalus hookeri p

Chaetoceros atlanticum p p

Chaetoceros vegetative cells p p

Chaetoceros spores p p p p p p p

Chaetoceros spines p

Coconeis fasciolata p

Corethron criophilum f p p

Dactyliosolen antarcticus p p p p

Denticuliopsis spp. f p p p p

Eucampia antarctica intercalary p p p p p p p f

Eucampia antarctica terminal p

Fragilariopsis curta p p p p p p p p p

Fragilariopsis cylindrus p p p p p

Fragilariopsis kerguelensis f p p p p p p f p p

Fragilariopsis obliquecostata p p

Fragilariopsis pseudonana p

Fragilariopsis separanda p p p p p p

Fragilariopsis sublinearis p

Fragilariopsis rhombica p p p p

Fragilariopsis ritscheri p p

Fragilariopsis vanheurkii p p p

Navicula directa p

Nitzschia aff. aurica p

Nitzschia barronii p

Odontella weissfloggii p p

Paralia spp. p p

Pleurosigma spp. p

Porosira glacialis f p

Probsoacia spp. p

Pseudo-nitzschia lineola p p

Pseudo-nitzschiaspp. p p f

Rhizosolenia antennata f. semispina p p p f

Rhizosolenia hebetata group p

Rhizosolenia spp. f

Rouxia antarctica p p p p p

Rouxia diplonoides(Harwood) p

Rouxia leventerae p f f f p

Rouxia cf. naviculoides Schrader p p

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Stellarima microtrias p p

Thalassiosira antarctica p

Thalassiosira gracilis v. gracilis p p p p p f p

Thalassiosira gracilis v. expectata p p p p

Thalassiosira latimarginata(trifulta) p p p

Thalassiosira lentiginosa p p p p p 1 only f p p

Thalassiosira aff. lentiginosa p

Thalassiosira oestrupii p p

Thalassiosira oest. v. oestrupii p

Thalassiosira oliverana p p

Thalassiosira ritscherii p p

Thalassiosira tetraoestrupii var. reimeri (Mahood &Barron) p

Thalassiosira torokina p

Thalassiosira tumida p p p

Thalassiosira spp. p

Thalassiothrix antarctica p p p p p p p f

Tricotoxin reinboldii p p p

Unknown centrics p

Distephanus spp. p p p p p

Dinoflagellate p

Radiolarians p p

Sponge spicules p p p

Notes: f=fragment; p=present; vpp=very poor preservation, rare diatoms; hfd=heavily fragmented/dissolution biased asssemblage; r=reworked species.aTypical modern/late Quaternary sea-ice assemblage and open ocean influence with benthics. No reworked elements observed.bTypical modern/late Quaternary sea-ice assemblage. No reworked elements observed.cSea-ice and open-ocean assemblage with many R. leventerae as reworked elements? very fragmented and dissolution/robust sp. dominated.dModern sea-ice and open-ocean assemblage.eFragments rare.fKnown turbidite.

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Table 7

PC18 p=present, f=fragments

Smear slide qualitative analysis Depth (cm)

Species 0 18 20 39 40 60 67 80 100 120 140 160 179 200 220 240 260 280 300 320 340 347 Core catcher

Actinocyclus actinochilus p p p p p p p p p p p p p p p p p p p p

Actinocyclus curvatulus p p p

Asteromphalus hookeri p p p p p p p p p

Asteromphalus hyalinus p p p p p

Asteromphalus parvulus p p p p p p p p p p

Azpeitia tabularis p p p p p p

Chaetoceros bulbosum complex p p

Chaetoceros criophilum p

Chaetoceros spores p p p p p p p p p p p p p p p p p p p p p

Corethron criophilum p p p

Coscinodiscus oculus-iridis p p

Coscinodiscus spp. p

Dactyliosolen antarctica p p p p p p p p p p p p p p p p p p p

Eucampia antarctica v. recta inter p p p p p p p p p p p p p p p p p p

Eucampia antarctica v. recta term p p p p p p p p p p p p

Fragilariopsis curta p p p p p p p p p p p p p p p p p p p p

Fragilariopsis cylindrus p p p p p p p p p p p p p p p p p

Fragilariopsis kerguelensis p p p p p p p p p p p p p p p p p p p p p p p

Fragilariopsis obliquecostata p p p p p p p p p

Fragilariopsis peragalli p p p p

Fragilariopsis rhombica p p p p p p p p p p p p p p p p p p p

Fragilariopsis ritscheri p p p p p p p p p p p p p

Fragilariopsis separanda p p p p p p p p p p p p

Fragilariopsis sublinearis p p p p p p p p p p

Navicula directa p p p

Navicula sp. p

Nitzschia sicula v. rostrata p p p

Odentella weissflogi p p

Paralia spp. p p p p p p

Pleurosigma/Gyrosigma spp. p p p

Porosira glacialis p p p p p

Porosira pseudodenticulata p p p

Proboscia spp. Dissovled p p

Pseudo-nitzschia turgiduloides p p p

Pseudo-nitzschia lineola p

Rhizosolenia antennata f. semispina p p p p p p p p p p p p p

Rhizosolenia sp A. p p p

Rhizosolenia heavily silicified p p

Rhizosolenia sima f. silicea p

Rhizosolenia spp. Dissolved p p p p p p p p p p

Stellarima microtrias p p p p p p

Thalassiosira antarctica veg. p p p p p p p p

Thalassiosira gracilis v. gracilis p p p p p p p p p p p p p p p p p p

Thalassiosira gracilis v. expectata p p p p p p p p p

Thalassiosira latimarginata p

Thalassiosira lentiginosa p p p p p p p p p p p p p p p p p p p p

Thalassiosira oestrupii p p p p p p p p

Thalassiosira oliverana p p p p p p p p p p p p

Thalassiosira tumida p p

Thalassiosira sp. p p p p p p p p p p p

Thalassiosthrix antarctica p p p p p p p p p p p p p p p p p p p

Trichotoxon reinboldii p p p p p p p p p p p p p p

Rouxia cf. leventerae p p p p p p

Rouxia spp. p p p p p p p

Actinocyclus ingens p p p

Thalassiosira inura p p

Denticulopsis sp. a a p a

Stephanopyxis spp. p

Cestodiscus spp? p

Actinocyclus sp F (Zielinski) p

Distephanus spp. p p p p p p p p p p p p p

a=D. simonsenii to prakataymae lineage.

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621554

Table 8

PC19 p=present, f=fragments

Smear slide qualitative analysis Depth (cm)

Species 0 20 40 60 80 100 120 160 180 200 220 240 260 300 320 340 360 380 400 420 Core catcher

Actinocyclus actinochilus p p p p p p p p p p p p p p p p

Actinocyclus curvatulus p

Asteromphalus hookeri p p

Asteromphalus hyalinus p p p

Asteromphalus parvulus p p p p p

Azpeitia tabularis p p p p p p p p p p

Chaetoceros bulbosum complex p

Chaetoceros spores p p p p p p p p p p p p p p p p p

Cocconeis spp. f

Corethron criophilum p

Coscinodiscus oculus-iridis p

Coscinodiscus spp. p

Dactyliosolen antarctica p p p p p p p p p p p p p p

Eucampia antarctica v. recta inter p p p p p p p p p p p p p p p p p

Eucampia antarctica v. recta term p p p p p p p p p p p p

Fragilariopsis curta p p p p p p p p p p p p p p p p p

Fragilariopsis cylindrus p p p p p p p p

Fragilariopsis kerguelensis p p p p p p p p p p p p p p p p p p p

Fragilariopsis obliquecostata p p p

Fragilariopsis rhombica p p p p p p p p p p p p

Fragilariopsis ritscheri p p p p p p p p p p p

Fragilariopsis separanda p p p p p p p p p p p p p p p

Fragilariopsis sublinearis p p p p p p p p p

Fragilariopsis vanheurcki p

Odentella weissflogi p

Paralia spp. p p p p p p p p

Porosira pseudodenticulata p

Rhizosolenia antennata f. semispina p p p p p

Rhizosolenia antennata f. antennata p

Rhizosolenia sp A. (Armand and Zielinski) p p

Rhizosolenia hebetata group p p

Rhizosolenia heavily silicified p

Rhizosolenia spp. Dissolved p p p p p p p p p

Rhizosolenia cf. sima f. silicea p

Stellarima microtrias p p p p

Thalassiosira antarctica veg. p p p p p

Thalassiosira gracilis v. gracilis p p p p p p p p p p p p

Thalassiosira gracilis v. expectata p p p p p p p

Thalassiosira latimarginata p p p p p

Thalassiosira lentiginosa p p p p p p p p p p p p p p p p p p p

Thalassiosira oestrupii p p p p p p p p p p

Thalassiosira oliverana p p p p p p p p p p

Thalassiosira tumida p

Thalassiosira sp. p p p p p p p p p

Thalassiosthrix antarctica p p p p p p p p p p p p p p p

Trichotoxon reinboldii p p p p p p p p p p

Rouxia leventerae p f f f p f f p p

Rouxia antarctica p

Rouxia spp. 2 p f p f f f

Actinocyclus sp F.(sensu Zielinski) p p

Actinocyclus ingens p p p p p f p

Fragilariopsis interfrigidaria p f

Denticulopsis sp. p p f f f

Trinacria/Triceratium spp. p f f

Distephanus spp. p p p p p p p p p p

*=D. simonsenii to prakataymae lineage.

2=R. isopolica fragment.

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1555

Table 9

PC20 p=present, f=fragments, r=rare, cf=compares withSmear slide qualitative analysis Depth (cm)Species 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 389 400 420 440 460 Core catcher

Actinocyclus actinochilus p p p p pAsteromphalus hookeri p pAzpeitia tabularis p p p pChaetoceros criophilum pChaetoceros spores p p p p p p p p p p p pCocconeis spp. pCoconeis costata p pCorethron criophilum pCoscinodiscus marginatus pCoscinodiscus spp. p pDactyliosolen antarctica p p p p p p pEucampia antarctica v. recta inter p p p p p f p p p p p pEucampia antarctica v. recta term p p p pFragilariopsis curta p p p p p p p p p cfFragilariopsis cylindrus p p pFragilariopsis kerguelensis p p p p p f p p p p p p p p p p p pFragilariopsis obliquecostata p p p p pFragilariopsis rhombica p pFragilariopsis ritscheri p p p pFragilariopsis separanda p p p p p p p p pFragilariopsis sublinearis p p p p p p pNitzschia sicula v. rostrata pOdentella weissflogi p pParalia spp. p p p p p p p f pRhizosolenia antennata f. semispina p p p pRhizosolenia antennata f. antennata pRhizosolenia crassa pRhizosolenia sp A. (Armand and Zielinski) p pRhizosolenia hebetata group pRhizosolenia spp. dissolved p p p p p p p p p p p pStellarima microtrias p p pThalassiosira antarctica veg. p p pThalassiosira gracilis v. gracilis p p p p p pThalassiosira gracilis v. expectata pThalassiosira lentiginosa p p p p p p p p p p p p p rTh. cf. lentiginosa pThalassiosira oestrupii f f p pThalassiosira oliverana p p p p pThalassiosira sp. p p pThalassiosthrix antarctica p p p p p p p p p p p p p f p p p fTrichotoxon reinboldii p p

Hemidiscus karstenii pRouxia leventerae f p fRouxia antarctica p p f p f p p

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5. Conclusions

Plio-Quaternary sedimentation in the continen-tal rise off Wilkes Land, characterised by moundand channel systems, was investigated throughstudies of 11 piston cores collected along twotransects across a mound.Two main depositional modes have been recog-

nised using sedimentary facies analysis and areinterpreted a reflection of glacial-interglacial pa-leoclimatic conditions. Deposits consist of massive

mud interpreted as hemipelagic sedimentation. Thepresence of fine- to coarse-grained IRD suggestsdeposition from retreating sea ice and goodconditions for life as indicated by well preservedopen-ocean diatoms and bioturbation. Smallfluctuations of clay mineral assemblages andphysical and acoustic properties, presence ofintervals with higher concentration of fine IRD,and diatom assemblages from open-ocean to ice-edge or even sea-ice conditions imply that theinterglacial periods were characterised by coolingand warming episodes.Glacial sediments consist of Laminated mud

characterised by laminae/beds associated withtraction currents. Evidence of glacial conditionslies in the poor fossil content, lack of bioturbation,and absence or few poorly preserved diatoms, andvery rare dropstones, suggesting sporadic icebergformation during stable ice cover.Lithological analysis of grains and clay mineral

assemblages indicates that the source of theterrigenous fraction is both the hinterland ofWilkes Land and continental shelf deposits.Terrigenous sediment supply to the continentalrise was by downslope gravity flows along thecanyons, as suggested by the turbidite recovered inthe thalweg of Jussie Canyon, and by the observeddecrease in grain size of sediment from theproximal to the distal area. Bottom currentactivity is also an important process achievingsediment redistribution, as indicated to by planarand cross laminations present especially in theglacial deposits.

Ro

ux

iacf.

iso

poli

cap

Act

inocy

clu

sin

gen

sp

pp

pp

Fra

gil

ari

op

sis

ba

rron

iif

Fra

gil

ari

opsi

sin

terf

rigid

ari

af

Rh

izoso

len

iaco

stata

cfT

ha

lass

iosi

sra

inu

raf

fD

enti

culo

psi

saff.

dim

orp

ha

pD

enti

culo

psi

ssi

mo

nse

nii

pp

fp

pp

pp

pp

pp

pp

Den

ticu

lop

sisspp.

pp

pp

pp

pT

rin

acr

iap

ileo

tus

pT

rin

acr

ia/T

rice

rati

umspp.

ff

Th

ala

ssio

sira

cf.

pra

efra

ga

pN

itzs

chia

gro

ssep

un

cta

taf

Ste

ph

an

op

yx

issp

p.

pp

cf.

Bax

teri

opsi

sbru

nii

p

Dis

teph

an

usspp.

pP

pp

pp

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–1562 1557

Table10

CONTENT

33PC18,

171-172

cm

33PC18,

CC

33TC01,

CC

34PC19,

CC

34TC02,

CC

35PC20,

231-232

cm

35PC20,

463-464

cm

35TC03,

CC

36PC21,

CC

36TC04,

CC

37PC22,

CC

38PC23,

65-66

cm

38PC23,

129-130

cm

38PC23,

CC

39PC24,

CC

39TC07,

CC

40PC25,

191-192

cm

40PC25,

387-388

cm

40TC08,

CC

41PC26,

CC

41TC09,

CC

42PC27,

CC

42TC10,

CC

43PC28,

CC

Waterdepth

(m)

3236

3194

3014

3034

3142

3186

3260

3363

2658

2659

3045

Non-biotic

Volcanicglass

trtr

trtr

trtr

trtr

trtr

trtr

trtr

trtr

Glauconite

trtr

tr

MnOxide

trtr

trtr

trtr

Dominantresidue

Terrigenous

xx

xx

xx

xx

xx

xx

xx

xx

x

Diatoms

xtr

xx

x

Radiolaria

xx

xx

xx

xx

xx

xx

Spongespicules

xx

xx

x

Other

biota

Echinoid

spines

xx

Bone

xx

Spongespicules

trm

cm

mc

trm

mx

mm

trm

ctr

m

Radiolaria

cc

cm

cx

mm

xm

xc

trm

tr

Diatoms

mtr

cm

trtr

xc

Foraminifera

Benthic

?Haplo

phra

gm

oid

essp

.1

Ader

cotr

ym

aglo

mer

ata

3

Alv

eolo

phra

gm

ium

sp.

3

Am

mobacu

lite

sagglu

tinans

2

Am

mola

gen

acl

ava

ta1

Am

phit

rem

oid

essp

.1

Bath

ysi

phonsp

.18

Conotr

ach

am

min

aalt

ernans

2

Cri

bro

stom

oid

esco

nto

rtus

2

Cri

bro

stom

oid

essu

bglo

bosu

m1

88

1

Cycl

am

min

aca

nce

llata

11

Cycl

am

min

ain

cisa

11

Cycl

am

min

aorb

icula

ris

22

13

Cyst

am

min

apauci

locu

lata

1

Epis

tom

inel

laex

igua

8

Glo

boca

ssid

uli

na

crass

a8

Glo

boca

ssid

uli

na

subglo

bosa

8

Glo

mosp

ira

charo

ides

3

Haplo

phra

gm

oid

esbra

dyi

1

Haplo

phra

gm

oid

escf

rotu

latu

m1

Haplo

phra

gm

oid

essp.

1

Lagen

asp

.1

1

Mars

ipel

lacy

lindri

ca1

Mart

inott

iell

abra

dyana

16

77

38

16

22

9

Mel

onis

affi

nis

8

Nutt

all

ides

um

bonif

era

48

Para

fiss

uri

na

lata

8

Port

atr

och

am

min

aanta

rcti

ca2

Psa

mm

osp

haer

acf

fusc

a3

M. Busetti et al. / Deep-Sea Research II 50 (2003) 1529–15621558

Acknowledgements

This research has been carried out as acooperative project supported by the AustralianAntarctic Science Advisory Committee (ASAC)and by the Italian Progetto Nazionale Ricerche inAntartide (PNRA).We thank Captain A. Leachman and the crew of

the R/V Tangaroa of the National Institute ofWater and Atmospheric Research (NIWA) fromNew Zealand, for their cooperation in achievingthe goals of this study. We thank also the ScientificParty in particular those involved in coringoperations onboard.Technical assistance support for the diatom

analysis was provided through Australian Antarc-tic Science Grant 1216, and results from thediatom work are documented as Metadata at theAustralian Antarctic Division.Andrea Caburlotto acknowledges a Ph.D. grant

from PNRA for the WEGA project.The authors thank Steven Bohaty, Carol Pudsey

and an anonymous reviewer whose comments andconstructive suggestions greatly improved thispaper.

Appendix A

This appendix comprises of Tables 6–10.

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osp

haer

afu

sca

11

16

81

6

Psa

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osp

haer

aparv

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bull

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is8

Reo

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aabyss

oru

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7

Rhabdam

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asp.2

2

Rhabdam

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2

Rodlikesp.4

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Toly

pam

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asp.1

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Toly

pam

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1

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31

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1

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glo

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