holocene glacial history and sea-level changes on james

JOURNAL OF QUATERNARY SCIENCE (1997) 12 (4) 259–273 CCC 0267-8179/97/040259–15$17.50 1997 by John Wiley & Sons, Ltd.

Holocene glacial history and sea-levelchanges on James Ross Island, AntarcticPeninsulaCHRISTIAN HJORT1*, OLAFUR INGOLFSSON2, PER MOLLER1 and JUAN MANUEL LIRIO3

1 Department of Quaternary Geology, Lund University, Solvegatan 13, S-223 62 Lund, Sweden2 Department of Geology, Earth Sciences Centre, Gothenburg University, Guldhedsgatan 5a, S-413 81 Gothenburg, Sweden3 Instituto Antartico Argentino, Cerrito 1248, Buenos Aires (1010), Argentina

Hjort, C., Ingolfsson, O, Moller, P. and Lirio, J. M. 1997. Holocene glacial history and sea level changes on James Ross Island, Antarctic Peninsula. J.Quaternary Sci., Vol. 12, pp. 259–273. ISSN 0267–8179. (No. of Figures: 15 No. of Tables: 2 No. of References: 45)

Received 6 December 1996; revised 30 March 1997; accepted 2 April 1997

ABSTRACT: A reconstruction of deglaciation and associated sea-level changes on northernJames Ross Island, Antarctic Peninsula, based on lithostratigraphical and geomorphologicalstudies, shows that the initial deglaciation of presently ice-free areas occurred slightly before7400 14C yr BP. Sea-level in connection with the deglaciation was around 30 m a.s.l. A glacierreadvance in Brandy Bay, of at least 7 km, with the initial 3 km over land, reached a positionoff the present coast at ca. 4600 yr BP. The culmination of the advance was of short duration,and by 4300 yr BP the coastal lowlands again were ice-free. A distinct marine level at 16–18 m a.s.l. was contemporaneous with or slightly post-dates the Brandy Bay advance, thusindicating the relative sea-level around 4600–4500 yr BP. Our results from James Ross Islandconfirm that over large areas in this part of Antarctica the last deglaciation occurred late. 1997 by John Wiley & Sons, Ltd.

KEYWORDS: Quaternary geology; glaciation; sea-levels; palaeoclimatology; James Ross Island; Antarctica

Introduction

James Ross Island is the largest island in the western WeddellSea (Fig. 1). It is, to more than 80%, covered by the MountHaddington ice-cap and its outlets, but relatively extensiveice-free areas occur in the northern part of the island (Fig. 2).

Quaternary studies on James Ross Island were pioneeredby Argentinian geologists (Rabassa, 1983, 1987), who sug-gested a broad framework for Pleistocene and Holocenedevelopments on the northern part of the island. That workwas followed by a recent attempt by Ingolfsson et al. (1992)to reconstruct in greater detail the Late Pleistocene andHolocene glaciation history. Despite that effort, the timingand pattern of the final deglaciation and associated sea-level changes on northern James Ross Island could not bereconstructed satisfactorily. The status of the so-called BahıaBonita Drift, supposedly deposited in connection with a mid-Holocene glacial advance in Brandy Bay (Rabassa, 1983,1987), remained problematic, owing to the unclear strati-graphical relationship of the 14C-dated mollusc samples usedto constrain the advance chronologically.

* Correspondence to: C. Hjort, Department of Quaternary Geology, LundUniversity, Solvegatan 13, S-223 62 Lund, Sweden

Figure 1 Overview map of the Antarctic Peninsula region.Contract grant sponsor: Swedish Natural Science Research Council (NFR)Contract grant sponsor: University of LundContract grant sponsor: Instituto Antartico Argentino

260 JOURNAL OF QUATERNARY SCIENCE

Figure 2 (A) James Ross Island and Vega Island, showing the location of the main working areas (The Naze and Brandy Bay) andgeographic names mentioned in the text. (B) The Naze, based on air-photo interpretation and showing sediment distribution andgeomorphological features. Sections investigated are indicated by arrows and numbered 1–5.

The possibility of a major glacial advance in the mid- reference to the high-tide mark. The maximum estimatederror in measuring altitude of raised beaches this way isHolocene, which most recent studies indicate was a period

of regional deglaciation (Mausbacher et al., 1989; Clap- ±2 m. Some raised beach deposits were levelled with ahand-held mirror altimeter, where the maximum estimatedperton, 1990; Bjorck et al., 1991a, b; Hjort et al., 1992;

Ingolfsson et al., 1992), motivated us to revisit James Ross error is ±1 m. Sediments were logged to a scale of 1:10 andsections drawn in the field, at a scale of 1:50. LithofaciesIsland in January–February 1993. This paper presents the

results of our work in Brandy Bay and on The Naze penin- codes used are according to Table 1.Geomorphological mapping was carried out using thesula (Fig. 2), where we studied the lithostratigraphy of glacial

and marine sediments in coastal sections, as well as glacial British Antarctic Survey (BAS) 1:250 000 maps SP-21-22and BAS air-photographs from 1979 and 1980 at a scaleand marine landforms and sediments further inland. Prelimi-

nary results were given by Hjort et al. (1995). Bjorck et al. of 1:25 000.When radiocarbon (14C) dating marine organisms we have(1996a) have thereafter discussed the late Holocene environ-

mental development in the area, based on studies of lake used the sea correction of 1200 yr, suggested by Bjorck etal. (1991c) and Domack (1992) for the Antarctic Peninsulasediment cores.(see also Gordon and Harkness, 1992).

Methods Stratigraphy of The Naze

The Naze is a narrow lowland peninsula pointing northwardsBase altitudes of all sections and some altitudes of raisedbeaches were determined by a Leitz digital altimeter, with into Herbert Sound, with the ca. 100 m high Fortress Hill

J. Quaternary Sci., Vol. 12(4) 259–273 (1997) 1997 by John Wiley & Sons, Ltd.

261GLACIAL HISTORY ON JAMES ROSS ISLAND, ANTARCTIC PENINSULA

Table 1 Lithofacies codes and their descriptions as used in thiswork

Lithofacies Lithofacies type descriptioncode (grain size, grain support system, internal

structures)

Co-- Cobble, - - (as below)Gmm Gravel, matrix-supported, massiveGcm Gravel, clast-supported, massiveSm Sand, massiveSng Sand, normally gradedSs Sand, vaguely stratified/laminatedSpp Sand, planar parallel-laminatedSpc Sand, planar cross-laminatedStc Sand, trough cross-laminatedSr Sand, ripple laminatedSr Sand, subcritically (A) or supercritically (B)(A, alt. B) cross-laminatedSd Sand, draped laminationSim Silt, massiveSm, Sim(b) Sand or silt, massive, bioturbated, burrowsSil Silt, laminatedSid Silt, draped laminationCm Clay, massiveCl Clay, laminatedSs(d); Sand or silt, laminated,Sil(d) deformedD(G/S/Si/C)- Diamict, gravelly, sandy, silty or clayey.

One or more grain-size code letters withinbrackets

D( )mm Diamict, matrix-supported, massiveD( )ms Diamict, matrix-supported, stratified

at its base, the ca. 100 m high Dagger Peak near its end,Figure 3 Log of section 1 in the western cliff of The Nazeand with the Comb Ridge beach ridges at its point (Fig. 2).(Fig. 2), ca. 75 m south of the main section (Fig. 4).

Along the western coast a cliff 15 m high, actively erodedby the sea, exposes Cretaceous strata overlain by Quaternarysediments. Some coastal cliffs also occur on the northeastern Sediment descriptions and interpretationsside, but they flatten out south of Dagger Peak, graduallybeing replaced by a broad accretional beach, with a shallowlagoon separated from the sea by a low active beach ridge. Unit AThe central part of The Naze has an altitude of 15–20 ma.s.l. and is covered by an abrasion lag of cobbles and The base of the cliff along the western side of The Naze

peninsula consists of a poorly consolidated stratified marinegravel, as well as a set of raised beach ridges, trendingsiltstone of Cretaceous age (del Valle et al., 1982). TheENE–WSW. South of these the surface is undulating, with aexposed part of that succession is up to 5 m high. Theclast residual on top of glaciomarine sediments.sediment is highly fossiliferous, with an abundance ofThe western cliff sections were described by Ingolfsson etammonites and molluscs, wood and various calcareous con-al. (1992, Fig. 7), based on investigations made during acretions.short ground stop by helicopter in 1987. We reinvestigated

three sections along the cliff (Fig. 2). Two of them arepresented as sediment logs (sections 1 and 3; Figs 3 and 5)

Unit Band one of them as a section drawing (section 2, Fig. 4).Above the Cretaceous strata (unit A) four major Quaternary

Unit B is a grey, clayey-silty, matrix-supported, massive tosedimentary units (B–E) were recognised, each consisting ofstratified diamict (Figs 3 and 4). It has a sharp but undulatingone or more lithofacies. Additional work was done at Combboundary to unit A and is up to 50 cm thick. There is aRidge (section 4), and on the ‘Lundqua Foreland’ ca. 5 kmdispersed, low-frequency occurrence of predominantly gra-southeast of the base of The Naze peninsula (section 5).vel-grade clasts (mean particle size (MPS) 15 cm). Most areThese two localities are not documented here with logs,striated basalt, but semiconsolidated sandstone clasts alsoonly with 14C dates from sediment units that are brieflyoccur. The stratified appearance of some parts of the unitdescribed and tentatively correlated with sections 1–3.is due to thin (0.1–1 cm) yellowish sand beds, some of

1997 by John Wiley & Sons, Ltd. J. Quaternary Sci., Vol. 12(4) 259–273 (1997)


Figure 4 Section 2 in the western cliff of The Naze (Fig. 2).

them seen to emanate from cores of poorly consolidated unit B and with a higher clast content along the base, atCretaceous sandstone clasts. places forming pebble to cobble pavements. The diamict is

Unit B is interpreted as a deforming bed till, the boundary sandy along the base, more silty upwards. Most clasts arebetween unit A and B being the lowermost decollement 4–10 cm in diameter, although some boulders occur (MPSplane of the once subglacially deforming sediment bed (cf. 30 cm). A few thin (0.2–1 cm) beds of yellowish sand wereHart and Boulton, 1991; Hart and Roberts, 1994). This observed, which could usually be traced backwards tointerpretation is supported by the very similar grain size of poorly consolidated sandstone clasts.the unit B matrix and the underlying Cretaceous siltstone, The coarser matrix of unit C and the higher content ofand by the low frequency of exotic rock clasts. It is suggested basalt and sandstone clasts indicate that the material hasthat underlying Cretaceous siltstones were incorporated in a predominantly been brought in by glacier ice. The overalldeforming layer beneath the glacier, which also introduced fine-grained nature of the unit, yielding a low hydraulicbasalt and sandstone clasts into the deforming bed by passive conductivity and thus high pore water pressures during depo-melt release at the ice bed interface. High shear strain within sition, suggests that the process of deposition for the mainthe deforming bed produced tectonic lamination due to part of the unit C diamict was by gradual stiffening of asmear-out of poorly consolidated sandstone clasts (cf. Hart subglacially deforming bed with sediment input from theand Roberts, 1994). This is a different interpretation from melting glacier sole, and not by a lodgement process. Thethat proposed originally by Ingolfsson et al. (1992), who clast pavement at the base of unit C supports a deforminginterpreted unit B as a glaciomarine sediment. bed interpretation, as clasts entering a deforming bed can

sink to a level governed by shearing velocity, clast densityand matrix viscosity and be preserved as a coherent clast

Unit Cpavement when the bed stiffens due to dewatering (Clark,1991; Hicock, 1991).Unit C is a brownish, sandy-silty, matrix-supported diamict

(section 2, Fig. 4). It has a sharp, undulating boundary to



Unit D facies deposited in a proglacial marine environment, thusruling out a subglacial depositional/deformational origin ofthese sediments. The subunit D1 sediments are interpreted asIn section 1 (Fig. 3) unit D consists of a massive sandy silt

with occasional outsized clasts. It is intrabedded with thin deposited in a proximal glaciomarine environment. Sedimentgravity flows from the glacier grounding line and/or slumping(0.5–2 cm) beds of massive sand, sometimes slightly pebbly.

The silt is rich in paired in situ-positioned molluscs, mostly and resedimentation from morainal banks and groundeddebris-rich icebergs are indicated from diamict units withLaternula elliptica, but also Yoldia eightsii and Thracia mere-

dionalis. Along section 2 (Fig. 4) the unit D sediments have inclined to sub-horizontal stratification, interfingering withor filling out depressions in massive, more coarse-graineda sharp boundary to unit C. They evolve into a very complex

sediment succession, which can be divided into a lower gravity flow diamicts. Stratified sands with or without raftedclasts indicate traction deposition from turbid density under-(D1) and an upper (D2) subunit. The lower unit shows very

complex and sometimes gradational and/or interfingering flows, sometimes interbedded with muds frominter/overflows, forming rhythmically laminated sedimentsfacies changes between stratified, deformed to non-deformed

silty-sandy sorted sediments, massive matrix-supported diam- (cf. Domack, 1984; Mackiewisz et al., 1984). Molluscs arenot in an in situ position in the unit D1 sediments, alsoicts, at places with large clusters of cobbles and boulders

(MPS 50 cm), and stratified sandy diamicts. All facies contain indicating a high sedimentation rate and vivid reworking ofthe sediments.mollusc fragments. Two 14C datings yielded ages of ca. 7400

and 7300 BP (samples 1 and 2, Table 2) after correction The subunit D2 sediments indicate a more distal glacioma-rine deposition from suspension sedimentation, tractionfor the marine reservoir effect. The upper part of section 2

shows a gradational change towards massive to vaguely deposition from underflow density currents/tidal currents andoccasional drops of ice-rafted debris. The frequently occur-stratified fine sand, silt and clay (subunit D2), with a scat-

tered occurrence of out-sized clasts (MPS 30 cm). The left- ring in situ molluscs also indicate a more distal environmentwith a lower sedimentation rate. The rhythmically laminatedhand corner of the section displayed a well-developed

interbedding of clay and sandy silt, with individual beds sequence in the upper part of section 2 (Fig. 4) has a non-deformed lower part, whereas the upper part is isoclinallybeing 1–5 cm thick. The upper part of this rhythmically

laminated sequence shows isoclinal folding and overthrusting deformed, indicating lateral compression. Lateral faciesrelations indicate that the whole package, resembling sedi-along a lower shear plane, and it cannot be excluded that

the whole sediment package has been dislocated into its ment facies common in the lower part of unit D, was thrustinto its present position due to push from a groundingfinal position. The D2 subunit is rich in paired and mostly

in situ-positioned molluscs, mainly Laternula elliptica. Car- iceberg, after which deposition of the overlying massive siltwith in situ-positioned molluscs continued.bon-14 dating of two samples yielded ages of ca. 7100 and

6700 yr BP (samples 3 and 4, Table 2).A silty sand at section 4 and a sandy diamict at section

5 (Fig. 2), both with paired Laternula, are tentatively corre- Unit Elated with unit D. Carbon-14 datings from these sedimentsgave ca. 6800 and 7000 yr BP, respectively (samples 7 and Unit D sediments are situated just beneath the logged suc-

cession at section 3 (Fig. 5) and show a gradational facies8, Table 2).We interpret unit D as a glaciomarine deposit. Defor- change into the unit E coarsening upwards sequence. The

lowermost part (subunit E1) forms a subhorizontal to low-mation structures at different levels within the complex unitD sediment succession are synsedimentary with sediment angle sediment succession, predominated by planar parallel-

Table 2 Radiocarbon dates on samples from James Ross Island. Samples 2 and 4 are datings from Ingolfsson et al. (1992). A correction of1200 yr for the reservoir effect on marine molluscs is used (Bjorck et al., 1991c). With the exception of one sea urchin (no. 11) all datedsamples are mollusc shells. Samples with Lu- laboratory numbers are conventional datings, those with Ua- numbers are AMS datings

Sample Site Section Sedimentary m a.s.l. Dated material Laboratory 14C age yr 14C age Rcorr d13Cunit number BP yr BP (‰)

(± 1 s) (± 1 s)

1 The Naze 2 D1 5 Mollusc fragments Lu-3605 8560 ± 100 7360 ± 100 −0.32 The Naze 2 D1 (-) Laternula elliptica Lu-2877 8460 ± 90 7260 ± 90 0.13 The Naze 2 D2 7 Laternula elliptica Lu-3607 8260 ± 100 7060 ± 100 −0.34 The Naze 2 D2 8 Laternula elliptica Lu-2876 7920 ± 60 6720 ± 60 0.55 The Naze 3 E1 12.5 Laternula elliptica Lu-3606 7680 ± 90 6480 ± 90 −0.16 The Naze 3 E1 12.9 Nacella concinna Lu-3608 7580 ± 110 6380 ± 110 0.97 The Naze 4 D 2 Laternula elliptica Lu-3603 7980 ± 90 6780 ± 90 −0.48 The Naze 5 D 2 Laternula elliptica Ua-3223 8190 ± 65 6990 ± 65 –9 The Naze 5 E 2.5 Laternula elliptica Lu-3604 7050 ± 90 5850 ± 90 −0.2

10 Brandy Bay 1 A2 1.5 Yoldia eightsii Ua-3218 6570 ± 65 5370 ± 65 –11 Brandy Bay 1 A3 2.4 Sterechinus sp. Ua-3219 6140 ± 80 4940 ± 80 –12 Brandy Bay 1 B 2.8 Yoldia eightsii Ua-3217 6195 ± 70 4995 ± 70 –13 Brandy Bay 2 A3 5 Yoldia eightsii Ua-3220 6165 ± 70 4965 ± 70 –14 Brandy Bay 2 B 7 Laternula elliptica Ua-10126 6080 ± 105 4880 ± 105 1.115 Brandy Bay 3 B 15 Yoldia eightsii Ua-3221 5885 ± 65 4685 ± 65 –16 Brandy Bay 4 C 2 Yoldia eightsii Ua-3222 5455 ± 90 4255 ± 90 –



Unit E is interpreted as prograding beachface sediments,deposited during the gradual emergence of the area. Therewas no abrupt change in sedimentation, rather a gradationalfacies change from offshore muds to lower shoreface sand(subunit E1). Scours may indicate coast-transverse rip currenterosion or storm-induced turbidity current erosion. The verti-cal facies succession in upper subunit E2 resembles thatdescribed from both contemporary barred nearshore depo-sitional systems (e.g. Hunter et al., 1979) and fossil Pleisto-cene coarse-grained spit systems (bar–trough systems, e.g.Nielsen et al., 1988; ‘landward slope facies’, Davidsson-Arnott and Greenwood, 1976). The uppermost sediments arethought to represent a rip-channel scour trough and infillsediment from the foreshore wave-swash, laid down immedi-ately before the emergence of the area.

A laminated sand on top of the diamicton at section 5(Fig. 2), lithologically similar to the subunit E1 sediments butlower in altitude (2.5 m a.s.l.) and with a 14C age on Later-nula shells of ca. 5900 BP (sample 9, Table 2) shouldrepresent a later part of a glacio-isostatic readjustment ofthe area.

Environmental interpretation – The Naze

The lowermost till units (units B and C) were deposited fromand beneath a wet-based glacier, advancing north and eastout of Croft Bay into Herbert Sound and overriding thelow-lying Cretaceous sediments on The Naze. Deglaciationstarted somewhat before 7400 yr BP, and was characterisedby subaquatic deposition of a complex succession of gravityflow, traction, suspension and ice-rafted sediments. Sedimentfacies suggest a water depth of at least 20–30 m. The glacio-marine environment was succeeded by a foreshore–shorefaceone during glacio–isostatic uplift of the area. The radiocar-bon dates around 6400 yr BP from unit E (samples 5 and6, Table 2) give a rough indication of when the emergenceof the present lowlands between 15 and 20 m a.s.l. tookplace. Foreshore bars, trending ENE–WSW, were developedover the central, highest part of the lowland during thisemergence.

Figure 5 Section 3 in the western cliff of The Naze (Fig. 2), ca.100 m north of the main section (Fig. 4).

Stratigraphy of Brandy Baylaminated sand and ripple-laminated sand, the latter withsilt drapings and some out-sized silty clay intraclasts. Minorfacies constituents are massive sandy silts, sand-infilled shal- Brandy Bay is a ca. 4 km long and 2 km wide bay, opening

into Prince Gustav Channel (Fig. 6). Southwards the baylow scour troughs and stringers/thin beds of clast-supportedgravel. The sandy silts have an abundance of in situ-pos- continues into a wide valley, extending towards a glacier

named IJR-45 (Rabassa, 1983). This glacier faces northwardsitioned Laternula elliptica, whereas the sand beds containboth paired and single shells of Laternula, some Nacella and its terminus is heavily loaded with supraglacial debris.

In its present state it is not connected with the large ice-concinna shells and assembled remains of sea urchins(Sterechinus sp.). Two 14C determinations of mollusc samples cap to the south.

Rabassa (1983) defined a drift sheet, the Bahıa Bonitagave ages of ca. 6500–6400 yr BP (samples 5 and 6,Table 2). Drift, of Holocene age (ca. 5000 yr BP; uncorrected) in the

Brandy Bay area. He also (Rabassa, 1983, 1987) describedThe sequence coarsens upwards (subunit E2) into troughcross-laminated sand with coarse, clast-supported basal lags, drumlins associated with this drift sheet, and concluded that

during the Bahıa Bonita stage the IJR-45 glacier was wet-overlain by steeply inclined beds of planar parallel-laminated(gravelly) sand and massive to normally graded, clast-sup- based, sliding over its bed. A prominent feature of the Bahıa

Bonita Drift is a large boulder train, starting at the IJR-45ported gravel beds. These beds are cut by a scour trough,infilled with basal lag gravels and cross-bedded sand. The glacier and following the western side of the valley (Fig. 6).

The boulders are predominantly of local volcanic breccias,sequence ends with two cobble lags with planar parallel-laminated sand in between. A palaeocurrent direction up to 10–15 m in diameter, occurring singly or in clusters

(Fig. 7) and with a decreasing frequency towards the bay.towards east–southeast is indicated from bed inclinationsand ripple lamination. Further out along Brandy Bay these breccia boulders disap-



of the entire section 1 (Fig. 9), and as a detailed sedimentlog from the right hand part of the section (Fig. 10).Additional minor sections (sections 2 and 3; Fig. 6) are notpresented with logs, but only with 14C dates from sedimentunits correlated to units A and B of section 1. Two strati-graphic units (C and D; see Fig. 12) were recognised in asediment succession at the inner part of the bay (section4; Fig. 6).

Unit A

The lowermost unit consists of intensely deformed sedimentsand is subdivided into three subunits. Subunit A1 (Fig. 10)is a laminated succession of clayey silt beds, 2–5 mm thick,interbedded with very thin (0.5–1 mm) fine sandbeds/partings. Massive clay beds, 2–4 cm thick, also occur.There is a low frequency of out-sized clasts (5–10 mm).The bedding is usually highly inclined (60–70°), folded andcontorted into isoclinal folds. The folding increases upwards.

Subunit A2 also consists partly of laminated clayey silts,but has an increasing content of pebbles and cobbles withoccasional boulders (MPS 50 cm) and grades laterally (Fig. 9)and vertically into massive to vaguely stratified sandy siltydiamicts with cobble and boulder clusters. The subunit isintensely deformed, showing upright, inclined, overturnedand isoclinal recumbent folding. Sand, originally belongingto the overlying subunit A3 has been down-folded intosubunit A2, forming cores in overturned folds which arenow separated from subunit A3 by a shear plane formingthe boundary between subunits A2 and A3. Measurementson contact surfaces within folds of subunit A2 indicate amean fold axis orientation of 40°–220°, with a stress direc-tion from ca. 130° (Fig. 11). The subunit contains both singleshells and shell fragments. A 14C dating on Yoldia eightsiigave an age of ca. 5400 yr BP (sample 10, Table 2).

Subunit A3 is a faintly laminated sand with occasionalcoarse sand/fine gravel stringers. It varies in thickness, witha maximum of 1 m, and disappears in the right-hand partof the section (Fig. 9). It also displays some small-scale dragfolds and shear thrusts. The lower part of the sand isinterbedded with 1–4 cm thick, black, silty-clayey tephrabeds. These are not continuous, but are cut by erosive(deformation) surfaces. A 14C date on sea urchin remains(Sterechinus sp.) gave an age of ca. 4900 yr BP (sample 11,

Figure 6 Brandy Bay, showing geomorphological features of the Table 2). A date on Yoldia eightsii from folded sedimentsarea. Sections investigtaed are indicated by arrows and numbered in section 2 (Fig. 6), correlated with subunit A3 in section1–4. The map is compiled from air-photo interpretation and from 1, yielded ca. 5000 yr BP (sample 13, Table 2).a geomorphological map made by O. Humlum (in Bjorck et al.,

The unit A sediments are interpreted as deposited in1996a). Black triangle marks the 1993 camp site.a proglacial glaciomarine environment, with an upwardsincreasing proximity to the glacial source. The subunit A1sediments suggest a combination of suspension depositionpear and are replaced by crystalline boulders, mainly gran-

ites of Antarctic Peninsula provenance. Elongated ridges par- of mud from inter/overflows, deposition of sand from turbidsediment underflows and deposition from ice-rafting. Thealleling the southwestern side of Brandy Bay are considered

by us to be a continuation of the drumlins described from rafting frequency increases upwards, making the subunit A2sediment more clast-rich and diamictic in character. Somefurther inland by Rabassa (1983, 1987) who, however

(Rabassa, 1983), interpreted them as lateral moraines to the of the stratification of the subunit A3 sand is believed torepresent primary sedimentary structures, indicating depo-glacier depositing the Bahıa Bonita Drift.sition from traction underflows. The intrabedded tephras ofsubunit A3 should, however, have been deposited from sus-pension.

The whole unit A succession indicates intense, post-depo-Sediment descriptions and interpretationssitional deformation. The fold structures (Fig. 11) suggest aunidirectional stress from approximately southeast. WeThe main section studied by us at Brandy Bay is a coastal

cliff exposed along the southwestern shore of the bay (Fig. 8; believe that the deformation is due to glacial overridingfrom a glacier extending from Brandy Bay into the Princelocations in Fig. 6). Three stratigraphical units (A, B and E)

were recognised at this site and are presented as a drawing Gustav Channel.



Figure 7 The camp in Brandy Bay 1993, sited close to some huge volcanic-breccia boulders of the Bahıa Bonita Drift. The IJR-45 glacier,with debris-laden terminus, can be seen in the background (arrow).

Figure 8 Section 1 in Brandy Bay.



Figure 9 Section 1 on the southwestern shore of Brandy Bay (Fig. 6). The log in Fig. 10 is a detail of the right-hand part of this section.

Unit B thin beds of clast-supported fine gravel. The succession endswith a surface cobble lag.

Unit E, found at section 1 (Figs 9 and 10), has an erosiveUnit B is a matrix-supported, for the most part massive,clayey silty and very firm diamict. Most clasts are 5–15 cm boundary with the underlying sediments, marked by a more

or less continuous cobble lag. The sediments form a suc-in diameter, although some boulders occur (MPS 30 cm).The diamict varies somewhat in thickness along section 1 cession of predominantly interbedded and interfingering sets

of planar parallel-laminated sands, clast-supported, massive(Fig. 9), being up to 1 m thick. It has a sharp boundary tounit A and the lowermost 10–20 cm shows thin (2–5 mm) gravels and gravel stringers, ca. 2.5 m thick. Minor facies

constituents are sets of trough cross-laminated sand and setssand intrabeds. The diamict carries shell fragments and alsosingle whole shells. A date on Yoldia eightsii gave ca. 5000 of ripple-laminated sand.

Unit C is interpreted as a glaciomarine sediment, theyr BP (sample 12, Table 2). Dates on shells from diamictsat sections 2 and 3 (Fig. 6), correlated with the unit B lowermost part being deposited in a more proximal environ-

ment than the uppermost massive clay. During regressiondiamict in section 1, gave ca. 4900 and 4700 yr BP, respect-ively (samples 14 and 15, Table 2). the overlying unit D was deposited in a lower

shoreface/foreshore position. Unit E at section 1 wasUnit B is interpreted as a subglacial deforming bed till.The boundary between unit A2/A3 and B is suggested to be deposited in a similar stratigraphical position during the

emergence of the area. The latter sediments are, however,a decollement plane between the more slowly deformingsediments beneath it and the penetratively deformed sedi- on the basis of their facies combinations, interpreted to be

of fluvial origin, deposited in a braidplain environment simi-ment above it (cf. Hart and Boulton, 1991). The lowermostpart of unit B shows tectonic lamination due to incorporation lar to that existing today around the small stream that enters

Brandy Bay just north of the exposure. The braidplain depo-and attenuation of sand from subunit A3. Shells from unitB date the same time interval as those from the underlying sition was preceded by a period of fluvial erosion, possibly

here removing glaciomarine sediments equivalent to unit Csubunit A3, thus also they indicate that the main sedimentsource of unit B is the unit A sediments. at site 4 and forming the erosive lag at the boundary between

units B and E.

Units C, D and E

Sediments assigned to unit C are not found in section 1. Environmental interpretation – Brandy BayThis unit is recognised only at section 4 (Fig. 6), a rivercutting at the inner part of Brandy Bay. The unit C sediments The lowermost sediment units in Brandy Bay (A and B)

indicate an increasing proximity to an advancing glacier,(Fig. 12) form a succession of massive silt, interbedded withthin beds of fine sand and grading upwards into massive followed by glacial overriding and deformation of the progla-

cial glaciomarine sediments and deposition of a subglacialclay. The silt has a low-frequency occurrence of pebble-sized clasts and is rich in paired and mostly in situ-pos- till. The sediments were partly moulded into streamlined

landforms, paralleling the flow direction. The flow directionitioned molluscs. A 14C date on Yoldia eightsii gave ca.4300 yr BP (sample 16, Table 2). The unit C clay at section of this wet-based glacier is also indicated by the prominent

boulder train of volcanic breccias (Fig. 6), forming a palaeo-4 is in its upper part interbedded with thin sand beds,forming a gradual continuation into the unit D sediments: a flowline from the IJR-45 glacier inside Brandy Bay. The 14C

dated molluscs from units A and B pre-date this glacialsuccession of alternating planar parallel-laminated sand and



Figure 11 Stereographic plot of contact surfaces within folds ofthe subunit A2 in Brandy Bay. Thin half circles show plungedirections and dip of contacts. Thick half circle shows the meanplunge direction and dip of the structural data (n = 18). Boxesshow poles to planes. Stress direction, indicated by structuraldata, is from ca. 130° towards 310°.

Figure 10 Log of section 1 on the southwestern shore of BrandyBay.

Figure 12 Section 4, exposed along a stream at innermost BrandyBay (Fig. 6).



advance and indicate that it reached the outer part of Brandy slope, ending in a cliff at 16 m a.s.l. The material in thisslope is a crudely cross-stratified beach sand and gravel,Bay after 4700 yr BP. The overlying glaciomarine sediments

(unit C) from the inner part of Brandy Bay, which post-date with a thin lag of pebble–cobble gravel on top.2. Above the cliff there are markedly coarser, massive beachthis mid-Holocene glacial advance, show that its culmination

phase was of very short duration, less than 500 yr. gravels, with a distinct lag of beach cobbles on top. Thisdeposit can be followed up to ca. 30 m a.s.l.Bjorck et al. (1996a) found that lake sediments started to

accumulate in basins inside the present coast of Brandy Bay 3. Above 30 m a.s.l. the lag gradually appears more exten-sively weathered, with a higher frequency of angular andby ca. 4200 yr BP (oldest 14C date 4185 ± 80 yr BP), suggest-

ing that the deglaciation was very rapid. This fits well with frost shattered stones. Unconsolidated beach gravels wereobserved in test pits up to ca. 80 m a.s.l.our youngest radiocarbon date from unit C, 4255 ± 90 yr BP

(Table 2), which gives the maximum age of the emergence of 4. Above 80 m a.s.l., an iron-stained gravelly sediment withwell rounded pebbles and cobbles is found on the sur-the coastal lowland in Brandy Bay.face, resembling a beach deposit. However, this sedimentseems to be a weathering product from a Cretaceousconglomerate, from the Whisky Bay Formation within theGustav Group (Medina et al., 1992), which is found inMarine levelssitu at 90 m a.s.l. on the slope facing Prince Gustav Chan-nel.

Rabassa (1983) suggested that traces of Quaternary marineThe beach deposits occurring below 80 m a.s.l. (Fig. 13)

abrasion could be found up to ca. 100 m a.s.l. on Jamesare probably of Quaternary age. They belong to three age

Ross Island and that these upper marine levels were ofgroups, where the distinct change in surface weathering

considerable age, possibly Middle Pleistocene. Strelin andaround 30 m a.s.l. represents one age-break, and the 16 m

Malagnino (1992) divided marine terraces on James Rosscliff another. The occurrence of Antarctic Peninsula derived

Island into three categories, ‘terrazas inferiores’ (0.75–6 mcrystalline erratics in the terrain would seem to indicate that

a.s.l.), ‘terrazas intermedias’ (10–22 m) and ‘terrazas super-the weathered beach deposits above ca. 30 m a.s.l. have

iores’ (30–120 m), and noted the possible occurrence ofbeen overridden by a glacier flowing north along Prince

even higher marine levels. Ingolfsson et al. (1992) suggestedGustav Channel without much altering the sediments. The

that the Holocene marine limit on James Ross Island andmarine level at 30 m may then be the marine limit associated

surrounding islands in the western Weddell Sea lies betweenwith deglaciation after that event. There are sedimentological

15 and 20 m and post-dates 6700 14C yr BP.indications from the sections on the west side of The Naze(unit D) that the water depth in connection with deglaciationthere shortly before 7400 yr BP was 20–30 m, and wetentatively suggest that the 30 m marine level formed at ca.Brandy Bay 7500 yr BP. The 16 m terrace represents the mid-Holoceneregional marine level identified by Ingolfsson et al. (1992).

At the ‘Refugio San Carlos’ cape, at the entrance to BrandyInside the area in Brandy Bay affected by the Bahıa Bonita

Bay (Fig. 6), the following sequence of strandlines and beachglacial advance, marine abrasion is encountered only below

deposits were found, starting from the base (Fig. 13):this level. The age of the 16 m beach should thus be ca.4600–4300 yr BP, based on radiocarbon dates from post-1. Above the recent beach there is a gently rising abrasional

Figure 13 Shoreline diagram, illustrating conditions near Refugio San Carlos, at the southern entrance to Brandy Bay (Fig. 6).



Bahıa Bonita deposits. This fits well with dates published byBjorck et al. (1996a) on the onset of lake sedimentation ataround 4200 yr BP in basins inland from Brandy Bay, andwe suggest that the 16 m marine level formed at around4500 yr BP.

The Naze

As noted above, the marine level at the deglaciation of TheNaze, around 7500 yr BP, was at 20–30 m above thepresent. However, the best developed shoreline on this pen-insula is found at 18 m a.s.l., at Comb Ridge (Fig. 2). It isexpressed as a sharp boundary between a sandy diamictwith angular surface boulders (interpreted as a colluviumderived from the Dagger Peak hills immediately to the west)and a sequence of well-developed beach ridges occurringdown to the present shore (Fig. 14). The central part of thepeninsula, where the main stratigraphic section studied byus lies on the western side, is generally lower than 18 mand has been abraded by the sea over its entire surface (cf.unit E in the sediment description). However, a thicker than5 m section (site 4, Fig. 2) of crudely bedded silty sand, withoccasional dropstones and a profusion of in situ marinemolluscs (Laternula elliptica, Yoldia eightsii; 14C sample 7,Table 2, 6780 ± 90 yr BP) is exposed along the north shoreat Comb Ridge, directly below the 18 m beach. It appears Figure 15 Synthesis of early and mid-Holocene glacial, marinethat the sea – most probably a transgressive sea – eroded and climatological developments on James Ross Island. Climateinto a colluvial cover which had been deposited after ca. data marked by an asterisk are modified from Bjorck et al.6800 yr BP, and formed the sharp boundary at 18 m. (1996a).

We have thus, based on shells from unit E (Fig. 5) in TheNaze sections, concluded that the initial emergence of thecentral lowland of The Naze took place shortly after 6400 1. Lithostratigraphical archives on The Naze and in Brandyyr BP, and we have indications of a somewhat lower sea- Bay contain a record of the deglaciation after the Lastlevel around 5900 yr BP (section 5). We believe, however, Glacial Maximum. The minimum age for the initialthat the marine limit within Brandy Bay (16 m a.s.l.) and deglaciation is ca. 7500 yr BP.the distinct shoreline at Comb Ridge on The Naze (18 m 2. The relative sea-level in connection with that deglaciationa.s.l.) belong to another, younger, marine event dating from was around 30 m a.s.l.as late as ca. 4500 yr BP, transgressive in character and 3. Older Quaternary littoral sediments occur between ca.possibly caused by glacioisostatic depression connected with 30 and 80 m a.s.l., but were probably overridden by icethe Bahıa Bonita glacial event. during the Last Glacial Maximum.

4. A glacier readvance in Brandy Bay culminated at ca.4700 yr BP. Relative sea-level on northern James RossIsland in connection with this advance was 16–18 m a.s.l.Summary and discussion

Our new data from James Ross Island make it necessaryto modify the glacial history reconstruction of Ingolfsson etFrom our investigations on northern James Ross Island, weal. (1992) for this island. Ingolfsson et al. (1992) suggestedconclude the following (Fig. 15).that the initial deglaciation of the coastal areas on northernJames Ross Island occurred about 10 000 yr BP. This assump-tion was based on the 14C age 9525 ± 65 of freshwater moss,sampled from glaciolacustrine sediments at Cape Lachman.It agreed with the age of freshwater algae sampled by Zaleand Karlen (1989) from a site on Vega Island, which theytook to indicate that by 10 000 yr BP glaciers there hadretreated to positions inside the present coast.

Radiocarbon dates on lake sediments from Antarctica ingeneral and the Antarctic Peninsula in particular, often seemto yield ages that are too high. Bjorck et al. (1991c) con-cluded that there were serious contamination problems con-nected with 14C dates of lake sediments in the AntarcticPeninsula area, and pointed out that often the cause of too-high ages seemed to be a combination of different contami-nation sources and processes. Radiocarbon dates on organicremains (microbial mats, algae, water mosses) in sedimentFigure 14 The distinctly marked marine level at 18 m a.s.l.cores sampled from the present Lake Hoare in Taylor Valley,(where the boulder strewn area ends) at Comb Ridge on the

northern part of The Naze peninsula (Fig. 2). southern Victoria Land, revealed large contamination prob-



lems (Squyres et al., 1991). These were expressed in very high Antarctic Peninsula (which gives a significant precipi-tation shadow effect – thus the relatively high ELA); and (ii)high ages of surface sediments (varying between 2000 and

6000 14C yr) and through samples obtained from depth in the anticyclonic cold barrier winds bringing arid air massesfrom the south (Bjorck et al., 1996a). Increased influence ofthe cores yielding the same or younger ages than the surface

material. Squyres et al. (1991) concluded that radiocarbon the cyclonic system would bring more precipitation in theform of snow, leading to a general lowering of the ELA ondates of Lake Hoare sediments were of limited value due

to their high degree of contamination. James Ross Island and thus to glacial advances. Strengtheningthe barrier wind activity, however, could also lead to glacialIngolfsson et al. (1992), from the 14C dating of the fresh-

water moss sample, suggested 9525 ± 65 BP as a maximum advances, by increasing snow drift from the south, e.g. fromthe Mount Haddington ice-cap into Brandy Bay. The glacialage for the initial deglaciation of northern James Ross Island.

Contamination of the dated sample, which emanated from readvance in Brandy Bay, if viewed only from a localperspective, may have been caused by either of these twowhat was probably an ice-marginal lake, could not be

excluded. In the light of the contamination problems encoun- factors.Deglaciation of the presently ice-free areas around thetered with freshwater dates from Antarctica, which, as noted

above, may even be in the range of 6000 yr (Squyres et al., Antarctic Peninsula and in the South Shetland Islands was,generally speaking, slow and occurred relatively late,1991), we now prefer initially to treat such dates as

maximum ages. This also applies to the old age from Vega between 8500–4000 yr BP (Sugden and John, 1973 (withtheir oldest 14C date becoming 8470 ± 230 yr BP whenIsland (10 235 ± 225 yr BP, uncorrected, Ua-925, Zale and

Karlen, 1989), which was made on an algal mat sample corrected for the marine reservoir effect of 1200 yr); Clap-perton and Sugden, 1982; Barsch and Mausbacher, 1986;from a dried out pond between two moraines. The chron-

ology should preferably rely on mollusc dates, for which Mausbacher et al., 1989; Mausbacher, 1991; Ingolfsson etal., 1992; Bjorck et al., 1996b). It coincided roughly withthe reservoir effect seems reasonably similar around Antarc-

tica (e.g. Gordon and Harkness, 1992) and which probably the Milankovichean summer insolation maximum for theselatitudes (e.g. Budd and Smith, 1987; Budd and Rayner,give more reliable (minimum) ages for the initial deglaci-

ation. Thus we now suggest that the initial deglaciation of 1990). A number of recent studies have also shown that thepresent interglacial environment over large areas in coastalnorthern James Ross Island occurred shortly before 7400 yr

BP, which is the approximate age of the oldest mollusc Antarctica dates back only to 6000–5000 yr BP (e.g. Fenton,1982; Fenton and Smith, 1982; Pickard et al., 1986; Bjorcksamples from glaciomarine sediments in the area. This age

happens to be similar to the deglaciation of the inner parts et al., 1991a, b, 1996a; Baroni and Orombelli, 1991, 1994),and Bjorck et al. (1996a) defined the Holocene ‘climateof the Ross Sea (Licht et al., 1996).

Ingolfsson et al. (1992) also, based on a reconnaissance optimum’ for James Ross Island to between 4200 and 3000yr BP, noting indications of similar ‘optimal’ conditionsstudy of the lithostratigraphy of The Naze sections combined

with the data published by Rabassa (1983, 1987), concluded during that time in a number of proxies from around Antarc-tica. We believe that the Brandy Bay (Bahιa Bonita) glacialthat glaciers had expanded into Croft Bay and Brandy Bay

during the period between 7000 and 5000 yr BP. Our advance should be seen as part of a regional response toincreased precipitation, due to warmer and more cyclonicreinvestigations confirm only the readvance into Brandy Bay,

and date it to between 5000 and 4500 yr BP. It was of very conditions in mid-Holocene times. In this we agree withDomack et al. (1991), who suggested that mid-Holoceneshort duration and culminated at ca. 4600 yr BP. We do

not have any firm control on how far the glacier had warming was what caused the glacial advances in EastAntarctica. The late, post-5000 yr BP, deglaciation of Byersoriginally retreated before readvancing, but the distribution

of the Bahıa Bonita Drift (Fig. 6) indicates that the glacier Peninsula on Livingston Island in the South Shetlands (Bjorcket al., 1993, 1996b) is another example of the same pattern.was within its present limits before advancing. This would

mean that the glacier front readvanced at least 7 km, withthe initial 3 km over land. It also means that, initially, it did Acknowledgements Logistics, including air transport southwards

from Buenos Aires, helicopter flights within the field area, food,not have contact with the Mount Haddington ice-cap, whichfuel, tents, radio, etc., plus stays at the Marambio Base and at theexcludes surging as the basic cause of its advance.Rio Gallegos airbase on the way in and out, was cared for by theThe distinct beach level at 16–18 m a.s.l. was suggestedInstituto Antartico Argentino and the Fuerza Aerea Argentina, afteras the Holocene marine limit on James Ross Island byarrangements made by the Swedish Polar Research Secretariat. OtherIngolfsson et al. (1992). We now revise that suggestion andlogistic support, including travel to and from Argentina, was cared

conclude that the marine limit connected with the deglaci- for directly by the Polar Research Secretariat. The Swedish Embassyation around 7500 yr BP was at ca. 30 m a.s.l., and that in Buenos Aires was of great help with transferring equipment intothe 16–18 m beach is connected with the mid-Holocene and out of Argentina. The scientific work sensu stricto was fundedBahıa Bonita glacial advance. by the Swedish Natural Science Research Council (NFR) and by the

Glacial oscillations in those areas within the Antarctic University of Lund and the Instituto Antartico Argentino.Peninsula region not affected directly by fluctuations in sea-level are controlled primarily by the availability of precipi-tation. The annual mean temperature is everywhere at orbelow 0°C and over large areas in maritime Antarctica the ReferencesELA (equilibrium line altitude) even today lies close to sealevel. The annual mean temperature on northern James RossIsland is estimated to between −7 and −10°C (Washburn,

ARISTARAIN, A. J., PINGLOT, J. F. and POURCHET, M. 1987.1974; Fukuda et al., 1992) and the annual precipitationAccumulation and temperature measurements on the James Ross

there is less than 150 mm (Aristarain et al., 1987). The ELA Island, Antarctic Peninsula, Antarctica. Journal of Glaciology, 33,on northern James Ross Island lies relatively high, at ca. 1–6.400 m a.s.l. The island is influenced by two weather systems: BARONI, C. and OROMBELLI, G. 1991. Holocene raised beaches(i) the cyclonic westerly storm-tracks transporting humid, at Terra Nova Bay, Victoria Land, Antarctica. Quaternary

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holocene glacial history and sea-level changes on james

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