Antarctic Peninsula Late Cretaceous-Early Cenozoic pal˦oenvironments and Gondwana pal˦ogeographies

Journal

of African

Earth Sciences.

Pergamon

All rights

SOSSS-5362(00)00075-O

Vol. 31, No. 1, pp. 91-105, 2000 o 2000 Elsewer Science Ltd reserved. Printed in Great Britain 0899-5362/00 $- see front matter

Antarctic Peninsula Late Cretaceous-Early Cenozoic palaeoenvironments and Gondwana palaeogeographies

‘Geological 2British 3Department

R.V. Institute,

DINGLE’ and M. LAVELLE2f3a* University of Copenhagen, Bster 1350 Copenhagen, Denmark Antarctic Survey, Madingley Road, Cambridge, of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK

Voldgade

10,

CB3 OET, UK Downing Street,

ABSTRACT-A review is made of stratigraphical, geochemical and palazogeographical data from the northern Antarctic Peninsula and the Southern Ocean for Late Mesozoic-Early Cenozoic times. Clay mineral and S/total organic C ratios are used to re-assess earlier scenarios, and it is suggested that eight climatic episodes affected the northern Antarctic Peninsula between Late Aptian and Palaeogene times. Evolving palasogeographies in southern Gondwana allowed the connection of the inter-continental western Weddell Basin to the proto-Indian Ocean during Albian to Cenomanian times, and it is suggested that this caused an initial cooling of ambient temperatures in the northern Antarctic Peninsula area. This situation altered when the South Atlantic seaway was opened to equatorial regions, producing a Campanian warm episode. Throughout this period, the climate was humid and non-seasonal (ever-wet) and the adjacent seas were dominated by mineralwalled phytoplankton. A Maastrichtian to Mid-Palzeocene cool period is postulated following the establishment of more-polar ocean circulation routes along the southern edge of the Pacific Basin, and the climate became seasonally humid with phytoplankton production switching to organicwalled dominant. The global Palaeogene climatic optimum was a warm, ever-wet episode but as it waned from Mid-Eocene times, a further, relatively short, period of marked seasonality is recognised. Later, Eocene climates were again ever-wet and became progressively cooler. The Late Eocene-Early Oligocene opening of the Tasman Sea and Drake Passage seaways caused cold conditions on Seymour Island, followed rapidly by the earliest glacial sediments on King George Island and the establishment of mineral-walled phytoplankton dominance in the seas. o 2000 Elsevier Science Limited. All rights reserved. Rl%UMl!-Les donnees tardi-mesozo’iques a Bo-cenozoi’ques stratigraphiques, geochimiques et paleogeographiques sur la Pdninsule Antarctique nord et I’Ocean Austral sont pas&es en revue. Les mineraux argileux et les rapports S/C organique total servent a r&valuer les scenarios anterieurs et il est suggere que huit episodes climatiques ont affect6 la Peninsule Antarctique nord de I’Aptien final au Paleogene. L’evolution de I’Albien au Cenomanien de la paleogeographie du Gondwana meridional a permis la connection du bassin inter-continental de Weddell ouest avec le proto-Ocean lndien et il est suggere qu’elle a cause le refroidissement initial des temperatures ambiantes dans la zone de la Peninsule Antarctique nord. Cette situation s’est renversee quand s’est ouverte la voie marine de I’Atlantique Sud vers les regions equatoriales, produisant un episode chaud campanien. Au tours de cette periode, le climat etait humide et saris saison (toujours humide) et les mers adjacentes Btaient dominees par un phytoplancton a test mineralise. Une periode fraiche est supposee du Maastrictien au Paleocene moyen a la suite de l’etablissement de circulation d’eaux plus polaires le long de la bordure sud de I’Ocean Pacifique et le climat est

*Corresponding author [email protected]

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R. V. DING1 E and M. LA VEL L E devenu humide avec des saisons et production de phytoplancton passant ti un type a test organique. L’optimum climatique global du Paleogene a ete un episode chaud e. coujours humide, mais il disparut a partir de I’Eocene moyen, air une periode relativement tour re a saisonalite marquee a ete reconnue. Les climats posterieurs de I’Eocene furent de nouveau toujours humides et devinrent progressivement plus frais. L’ouverture tardi-Eocene a eo-oligocene de la Mer de Tasman et du Passage de Drake a induit des conditions froides dans I’jle de Seymour, suivies rapidement les premiers sediments glaciaires de I’jle de King George et I’etablissement dans les mers de la domination du phytoplancton B test mineralise. @2000 Elsevier Science Limited. All rights reserved. (Received

7/7/98:

revised

version

received

1312199:

accepted

20/5/99)

INTRODUCTION Stable isotope studies have suggested that the temperature of Late Cretaceous to Early Palaeogene southern high latitude marine waters fluctuated between warm ( - 18 “C) and cool ( - 7 “C) (Barrera et a/. , 1987; Pirrie and Marshall, 1990; Ditchfield et a/., 1994; Huber et al., 1995; Pirrie et al., 1998). Combining these signals with terrestrial floral data (e.g. Francis, 1986; Dettmann, 1989; Birkenmajer and Zastawniak, 1989; Askin, 1992) and geochemical time series from sediment provenance areas (principally chemical index of alteration ratios), Dingle and Lavelle (1998b) recognised palaaoclimate fluctuations that encompass three warm and two cool episodes in West Antarctica between Late Aptian (- 120 Ma) and Late Palasocene-Early Eocene ( - 55-50 Ma) times. Subsequent palaeoclimates progressively deteriorated, mirroring southern hemisphere oceanic trends (e.g. Wright and Miller, 1993; Zachos eta/., 1993), and culminated in the earliest regional West Antarctic glacial events at - 30 Ma (Dingle and Lavelle, 1998a). Here, modifications are suggested to the previously published palaeoclimate interpretations for the Antarctic Peninsula region, using further palzeoenvironmental proxies that throw light on onshore rainfall seasonality and marine productivity, and these are discussed in relation to published plate tectonic reconstructions of southern Gondwana. An almost complete succession of Mid-Cretaceous to Early Oligocene continental shelf sedimentary rocks occurs in the James Ross/Seymour Island back arc and King George Island fore arc basins at the northern end of the Antarctic Peninsula (Fig. 1) (the only major hiatus is across the Cross Valley/La Meseta Formation boundary). The authors have used a suite of samples collected by themselves and earlier British Antarctic Survey expeditions for geochemical analyses across this succession, which formed the data set used by Dingle and Lavelle (1998a, 1998b) (Fig. 1). The succession consists mainly of nearshore to outer continental shelf fossiliferous mudrocks and muddy sands, and the lithostratigraphy of the areas has been described by Elliot and Trautman

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(1982), Macellari (1988), Pirrie (1991), Crame et al. (1991), Birkenmajer (1992), Pirrie et al, (I 997) and Marenssi et al. (1998), and the reader is referred to these for detailed sedimentological and textural information. In this study, the stratigraphical correlations of Dingle and Lavelle (1998a, 1998b), which were based on the biostratigraphies of Wrenn and Hart (1988) (marine phytoplankton), Askin et a/. (199 1) (terrestrial palynomorphs) and Crame et al. (1996) (marine invertebrates) have been followed. Sediment samples were analysed for major oxides and minor elements (ARL 8420 X-ray fluorescence spectrometer), and clay mineral ratios (~2 ,um fraction on a Phillips PW1710, Cu anode, X-ray diffractometer) at the University of Keele (UK) and total organic carbon (TOC) at Robertson Research International (UK). The ratio of clay mineral species was determined by comparing XRD peak areas under the 5.5 2-theta (smectite), 8.8 2-theta (illite) and 12.5 2-theta (chlorite + kaolinite) glycolated traces. The chlorite/kaolinite ratio was calculated by comparing the glycolated and 5OO’C heat-treated (kaolinite 001 degraded) traces at the 12.5 2-theta position. All dates are referred to the magnetochronology of Cande and Kent (1995). The reader is referred to Dingle and Lavelle (1998b) for the complete XRF geochemical data set and the British Antarctic Survey (BAS) archive sample numbers. Previously unpublished analytical data and BAS sample numbers are given in Table 1.

RATIONALE FOR PROXY MEASURES AND RESULTS In this study, three measures have been used as proxies for palaeoenvironmental variations: il the chemical index of alteration ratio (CIA) (ambient sediment-source temperatures) -values were previously reported by Dingle and Lavelle (1998b); iii the smectite/kaolinite ratio of the clay mineral complexes (degree of sediment-source rainfall seasonality); and

Antarctic

King

Peninsula pala?oenvironments

George

and palazogeographies

Is

,

10km

,

A B

SEYMOUR, COCKBURN, SNOW HILL Is

JAMES ROSS ISLAND

La Meseta

KING GEORGE ISLAND

(I 7)

L. de Bertodano Snow

Kotick

Point

Hill Is

(15) (29)

(2)

Figure 1. IAl Sampling localities for Late Cretaceous-Cenozoic marine sedimentary rocks in the northern Antarctic Peninsula. JRI: James Ross Island. Sections along which samples were collected are shown as thick lines. (B) Stratigraphical positions of sampled sequences. The Weddell, Cross Valley and Sobral Formations are known exclusively from Seymour Island. The number of samples for which geochemical data are available are indicated in parentheses beside each stratigraphical unit. Journal of African Earth Sciences 93

R. V. DINGLE and M. LA VELLE Table

1. Total

Location

Sjte’

P P P P

1 1

DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ

organic

-

2903 2704 2726 2307‘

812 612 812C -Et12 812

80’

carbon,

Sample

17 7 1. 2 11

29 21 13 11 7

DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ DJ

1 15 12 9 8 6 4 1 11. 6 1 1 27 26 1 25 24 20 11 11 5 1 35 31 28 24

DJ DJ DJ DJ

637 633 633 633-

5 20 11 15

-

Stratigraphical unit Weddell Cockburn Cockburn CapeMelv~lle Cape Melville Cape Melville Polonel Cove Polonez Cove P0lonez cove Polonez Cove Polonez Cove Polonez Cove Polonez Cove Polonez Cove Polonez Cove P0lonez Cove Polonez Cove La Meseta La Meseta La Meseta La Meseta La Meseta La Meseta La Meseta La Meseta La Mesefa La Meseta La Meseta La Meseta La Meseta La Meseta La Meseta La Meseta La Meseta Cross Valley Cross Valley Cross Valley Sobral Sobral Sobral Sobral Sobral Sobral Sobral Lopez de Bertodano Lopez de Bertodana Lopez de Bertodano Lopez de Bertodano Loper de Bertodano Lopez de Bertodano Lopez de Bertodano ~Lopez de Benodano Lopez de Bertodano Lopez de Bertodano Lopez de Bertodano Loper de Bertodano Lopez de Bertodano Lopez de Bertodano Loper de Bertodano Snow HIII Island Snow HIII Island Snow HIII Island Snow Hill Island Snow Hill Island Snow Hill Island Snow HIII Island Snow HIII Island Snow Snow Hill Htll Island Island

1.

812 811 811 811 811. 811’ 811’ 811’ 814814 814 ~630 631 631 632: 631 631. 631 632 631 631 631 628 628 628 633

-

sulphur

Snow Snow Snow Snow

HI,, Hill HIII HIII

island Island Island Island

and

XRD

TOC 1%)

clay

S !ppd_

0.31 0.36’ 0.22 0.48’

1475’ 118 177‘ 4061 371

0.13 0.15

84’ 207

_

mineral

S/T?C. 4758 328 605.~ 773

646 1380

.

’

-~

.~

0.310.26’ O.i80.16 0.15. 0.31~ 1.45. 0.09~ 0.16 0.17 0.45 0.67 0.40 0.78 0.57 0.72 0.88 0.34 0.54 0.08 0.12’ 0.18, 0.16 0.31 0.560.34 0.64 1 19’ 0.54 0.53 0.53 0.40 0.57. 0.69 0.52 0.31’ 0.35’ 0.47’

1211 1660 2277. 2034’ 2310’1855’ 3886. 452 16801744 6360 1157 2095. 830, 603 2442 4837 5706. 3157 568. 6142 5185 2346 950 3958 2280. 5257 m%=1468. 2095 1572. 1285’ 1586. 2076 997 2495 2147 2133

-is10 6365 8132 12713 15400 5984. 2680’ 5022 10500 10259’ 14133 1727 5236 ~~1064 1409 3392 5497 16782 5646 7350 51183’ 26806 14663 3065. 7068 6706 8214 74% 2719 ~3953 2966 3213 2762 3009 1917 8048 6134 4536

0.80 0 71

919. 272

1149 383

061. 0.52 0.61 0.42. 0.45

377 2249, 1374 2836 1260

618 4325 2252 6752 2800

0.41 0.28 0.27 0.35. 0.53.

1979 2362 1445’ 2206 3709 3095 3783 4198 4415

4827 8507 5352 6303 6998 7198’ 7566’ 4076 11038

0.43 0.50 1.03 0.40’

data Mite % clay 18.00 3.00. 92.0!< 62.00 4.00. 78.00’ 11 .oo 54.00;~ 24.00. o.oo-~ 96.00 95.00; 1.00 0.00 100.00’~ 84.1 10: 4.00 96.00 0 00 0.00 82.00’ ~69.00’ 0.00 95.00 1 .oo 96.00’ 2.0097.00’ 0.00 0.00. 96.00’ s2.00’ 10.00 33.001 52.00 41 .oo’ 18.00 48.00: ~_~ !4.00 33.00 23 .oo29.06 28.00 10.00 74.00’ 33.00 36.00 74.00 13.00. 4a.o025.00 _ 80.00 12.00 77.00 10.00 84.00 8.00 1 1 .oo’ 76.00. 54.00’ 17.00’

Smectite % clay 43.00

65 .OO 72.00 lOO.( 10. 87.00 95.00’ 71.00 65.00 85.00 86.00 92.00 81.00‘ 86.00 63.00 77 00 66.00 81 .OO 85.00 62.00 76.00 75.00’ 77.00’ 81 .OO’ 72.0074 00’ 90.00’ 66.00’~ 70.00’ 63.00’0.00 14.00 42.00 32.00 48.00 39.00 53.00

50.00~

17.00’ 25 .OO 0.00 1.00 0.00 16.00 19.00 12.00 11 .oo 6.00. 8.00 9.00 8.00.15.00 21 .oo 12.06. 7.00 33.00’ 11 .oo 12.00 11 .oo 8.00. 14.00 17.00 6.00 10.00 15.00 31.00 -24.00’ 25.00’ 54.00. 66.00’ 52.00’ 37.00’ 21 00

17.00

Kaolinite Chlorite Smactitd .-% clay % clay Kaolinite 2.00 1.20 37.00 3.00 ~_ ~~~~ 2.00 ~~ 30.70 ~ 11 .oo .oo’~ 7.50 10.00’ 1.00 7.60 0.00’ 2.50 ~~~~_~ 4.00’ 0.00 _~~ 24.00 0.00 31.70 3.00 0.00’ 0.00’ 100.00 12.00* ~~~~~ 0.00 _~ ~~ 7.00 4 00’ 0.00’ 24.00 18.00’ 0.00. 4.60 31 .oo; 0.00. 2.20 0.00 ~23.80 4.00’ ~3.001 0.00’ 32.00 0.00. -32.30 3.00 ~4.00’ 0.00 *~ -24.00 19.00: 0.00’ 3.80 0.00 2.20 15.00‘ 0.00. 1.00 41 .oo’ 0.00 1.30 38.00’ 45.00 0.00 0.70 39.00 4.000.70 16.00‘ 0.00 4.60 27.00 3.00’ 1.20 0.00. 5.70 13.00 23.00 4.00 2.10 6.00 2.00. 13.30 4.00 8.60 9.00 8.000.00 -10.50 2.00. 7.80 10.00 0.00’ -1 .so 29.00

~~~0~’

3.00 0.00

0.00 0.00’

5.00’ 6.00 3.00’

0.00 6.0013.00’

0 19.00 11.60 21 70

3.00’ 4 oo2.00’ 11 .oo’ 5.00’ 9.00. 9.00 10.00 8.00. 8.00. 5.00 11 .oo 12.00 13.00: 9.00 11 .oo 9 00, 3.00, 4.00 16 OO6.00 68.00 61 .OO 2.00 1.00 0.00 24.00 27.00’

0.00 0 ml 0.00 0.00 -o.ooo.oo0.00 3.00. 0.00 0.00 0.00’ 0.00 0.00’ 0.00’ 2.00 3.00’ 0.00 0.00 or00 0.00’ 0.00 8.00 0.00. 2.00’ 1 .oo’ 0.00 0.00 0.00.

28.30 71 50 46.01 0 7.40 17.20 9.20~~ 8.60 6.60 10.10 10.60 12.40 7.10 6.30 5.90 9.00 6.50 8.20 30.00 21.50 4.40 10.50 0.00 0.20 21.00 32.00 100.00 1.60 2.00

33.00

0.00

1.50

In the smectite/kaolinite ratio, where kaolinite equals 0.0% of the clay fraction, a value of 100 is entered. See Dingle and Lavelle (1998b3 for XRF geochemical data used to compile the chemical index of alteration ratio in Fig. 2. Base, station and sample alpha-numerics refer to British Antarctic Survey sample archive references.

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iii) the sulphur/total organic carbon ratio (S/TOC) (relative organic-walled/mineral-walled phytoplankton pro-ductivity signal). All the time series are presented as plots of twopoint running means, together with the raw data points.

Chemical index of alteration (CIA) The CIA is a measure for the progressive chemical alteration of feldspars (Nesbitt and Young, 1982, 1984; Roser et a/., 1996). It is calculated by measuring variations in the ratio of A&O, to the labile oxides: AI,O, /(AI,O, + CaO +Na,O + K,O) (in which CaO refers to the silicate fraction). Since the samples presented here are not carbonate-free, values reported are minima, although all samples with > 10% CaO were omitted from the data set.) Since chemical weathering of rocks is promoted primarily by the presence of liquid water and an increase in ambient temperature, fluctuations in CIA ratios largely reflect changes in these parameters. The measure was used originally to assess climatic factors in glacially-related sediments by Nesbitt and Young (19821, who compared CIA values to averages from strong, chemically-weathered tropical muds ( > 0.8) through average shales (i.e. temperate environments) (0.70.751, glacial argillites (0.6-0.651, to mechanically weathered Pleistocene tills (-0.5). Published palseobotanical data from the Antarctic Peninsula (e.g. Birkenmajer and Zastawniak, 1989; Dettmann, 1989; Francis, 1991; Askin, 1992) generally indicate that during Late Cretaceous to Palasogene times the area was subject to overall humid to very humid conditions. Dingle and Lavelle (1998b), as a first approximation, used this to equate to long-term ‘ever-wet’ conditions, which translated the CIA signal to fluctuations in ambient temperature (Fig. 2). They also assessed, and discounted, the possibility that major changes in sediment provenance influenced the long-term CIA signal, by comparing the provenance fields at the formation level with CIA and SiO,/AI,O, (sediment maturity). It was suggested that, overall, pre-glacial sediments gave ratios independent of provenance, while post-Eocene sediments (i.e. those deposited under glacial and inter-glacial conditions of strong physical weathering) show a close relationship between CIA ratios and contemporary volcanic sources. The use of smoothed plots further suppresses any short-term signal noise. Clearly, a final resolution of the relationship between provenance and geochemical signature must be made with more comprehensive geochemical analyses, to which end REE analyses are underway. Figure 2 shows fluctuations in the CIA ratio, with three periods with relatively high values (greater than

and pakeogeographies - 0.65) and two periods with relatively low values (less than - 0.65) during Late Aptian to Mid-Eocene times. In their original interpretation of this curve, Dingle and Lavelle (1998b) postulated warm climates in Late Santonian to Early Maastrichtian and Late Paleocene to early Middle Eocene times, separated by a short cool to cold period in the latest Maastrichtian to Mid-Palaaocene. Further, it was suggested that cooler climates re-established themselves in the Late Eocene (CIA <0.65) and that progressive thermal deterioration (values -0.6) resulted in the establishment of glacial conditions in the Antarctic Peninsula by the Early Oligocene. Here, the authors will assess this interpretation in the light of the clay mineral data.

Smectite/kaolinite ratio Kaolinite forms through intense weathering on land, typically in tropical, well-drained soils under moist conditions with a minimum soil temperature of 15°C (e.g. Robert and Kennett, 1994). Smectite also requires intense weathering under warm-hot temperatures to form, but is favoured by poorly-drained soils subject to strong seasonal fluctuations in rainfall (e.g. Robert and Charnley, 1991; Robert and Kennett, 1994). Consequently, fluctuations in the smectite/ kaolinite ratio are potentially a monitor of soil drainage and strength in the seasonality of rainfall in the provenance area. Low smectite/kaolinite values suggest a well-drained hinterland with weak rainfall seasonality, while ratios, which are relatively high, suggest poorly-drained soils with stronger rainfall seasonality (possibly with marked wet/dry periods). Alternatively, a high smectite/kaolinite ratio may indicate the weathering of volcanic ash falls. During Late Aptian to Late Eocene times in the vicinity of the northern Antarctic Peninsula, the smectite/kaolinite time series (Fig. 2) generally lay below 10, but there were four relatively short excursions during which it increased to > 20. Thus, despite the low-resolution botanical data, which point to long-term ‘ever-wet’ conditions, the clay ratio signal suggests that there were periods during which stronger seasonality in rainfall occurred, or ash falls were prevalent. In the Late Cretaceous, the earliest of these short excursions occurs in the Santa Marta Formation (Santonian-Early Campanian), while there is an Early Maastrichtian spike across the upper Snow Hill Island/lower Lopez de Bertodano Formations boundary. There are larger inflexions in the MidPalaeocene-earliest Eocene (Sobral/lower Cross Valley Formations) and at the base of the La Meseta Formation (late Early Eocene?), which is probably partly ‘obscured’ by the Early Eocene stratigraphical break that precedes the earliest La Meseta Formation

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Figure 2. Two-point averaged time Cenozoic marine sedimentary rocks La Meseta Formation, the following

series curves for sulphur/total of the northern Antarctic members are mentioned

organic carbon (S/TOC), Peninsula. Raw data points in the text: A: Acantilados;

chemical index of alteration ICIAI, and smectite/kaolinite shown. Shaded zones in the formation panel are C: Campamento; S: Submeseta.

also

major

ratio

in Late non-sequences.

CretaceousIn the

Antarctic

Peninsula pakeoenvironments

sediments. A further group of higher values is centred on the Acantilados Member of Mid-Eocene? age, although the ratio only temporarily peaks at 10. lllite values increase at the top of the Sobral and La Meseta Formations, suggesting that physical w.eathering became important during Mid-Palseocene and latest Eocene times, respectively (Dingle et al.,

1998). In this study, identification of trends in the Oligocene and younger glacial/interglacial sedi-ments, where local volcanism and low levels of chemical weathering produce a complex picture, has not attempted; but it is worth noting that, despite the regionally cold conditions and cryosphere development, smectite dominates in the King George Island Oligocene sediments. This apparently paradoxical relationship has also previously been noted by Robert and Kennett (1997) in Southern Ocean sediments from ODP 698 on the Maud Rise. It has to be borne in mind that, since the smectite/ kaolinite value is a ratio, no conclusions can be drawn as to the actual percentages of the clay minerals in the samples. Large ratios do not reflect large quantities of either species in the depositional environment. Sulphur/total organic cardbon WTOC) Pedersen and Calvert (1990) and Calvert and Pedersen (I 992) demonstrated that, in modern seas, concentration of organic matter in bottom sediments is related to upper water productivity. Subsequently, Bertrand and Lallier-Verges (1993) developed the S/ TOC ratio as a potential measure in older sediments for linking variations in the ratio of organic-walled (e.g. dinoflagellates) to mineral-walled (e.g. coccoliths and diatoms) relative phytoplankton production in surface waters. The basis for their method relies on bacterial S reduction concentrating S in the organic component of sediments (as Fe sulphides and organic S compounds), so that the S content is controlled mainly by the flux of metabolisable organic matter to the redox interface. On the other hand, the TOC content of sediments is controlled mainly by the flux of refractory organic matter. Consequently, the ratio of the total S to TOC can be treated as a measure of relative variation of metabolisable to refractory flux from the surface water (Bertrand and Lallier-Verges, 1993). In other words, the S/TOC ratio potentially gauges the relative productivity of organic-walled to mineral-walled phytoplankton. Time series of S/TOC ratios (Fig. 2) shows two long periods of relatively low values (mineral-walled dominant) during Aptian to Early Palaeocene, and Oligocene to Pliocene times. There is a period of rapidly fluctuating values in the Late Cretaceous with

and pakogeographies

a prominent short-lived organic-walled spike in the earliest Maastrichtian and a second, less prominent excursion at about the K/T boundary. The period MidPaleocene to Late Eocene was mainly organic-walled dominant with several particularly high values from the upper part of the Sobral Formation (mid- to Late Palaeocene), although throughout this time values fluctuated with high readings in the middle to upper part of the La Meseta Formation (Middle-Upper Eocene). These data suggest that, while there was considerable short-term variation in oceanic conditions, the history of surface water productivity of phytoplankton can be summarised as three extensive episodes whose limits approximate to: il the K/T boundary; and ii) the onset of glacial conditions in the northern Antarctic Peninsula (Fig. 2). Resolution of potentially conflicting signals from CIA and smectite/kaolinite ratios As mentioned above, Dingle and Lavelle (1998b) used botanical indicators for suggesting long-term, everwet conditions to standardise the water availability factor in interpreting the CIA trends. Although the number of botanical samples collected by previous workers is large, no single, collated stratigraphical disposition of these samples is available in the literature. Consequently, the current macrofloral-based palaeorainfall predictions, against which Dingle and Lavelle (I 998b) gauged the long-term levels of humidity, were generalised. Relatively short-term climatic fluctuations may not have been previously detected. Here, the authors attempt to refine the CIA curve, and in particular, look at situations where the assumption of ever-wet conditions (i.e. weak rainfall seasonality) is not necessarily valid. This occurs when a high smectite/kaolinite ratio suggests either that strong rainfall seasonality is likely, or that a high content of volcanic ash has temporarily inflated the smectite component. In the former case, the CIA data may itself reflect variations in temperature and/or water availability (in contrast to predominantly temperature, as assumed). For example, a shorter rainy season with intense precipitation (causing waterlogged conditions) but higher mean annual temperatures would be likely to achieve the same degree of chemical weathering as under ever-wet conditions (e.g. see Robert and Charnley, 1991). Where contemporary volcanic ash flux may have been relatively high, it will not significantly have influenced the range of CIA values that the authors have encountered, as pure smectite and kaolinite both have values >0.75 (Nesbitt and Young, 19821, which is near the maximum of the range that was encountered in this study. Each case in turn will be considered in the

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R. V. DINGLEandM. following discussion, and available sedimentary data will be used (e.g. Pirrie, 1991) to help resolve the issues.

PALROENVIRONMENTS, PALROCLIMATES AND GONDWANA PALAOGEOGRAPHIES The authors have selected four of Lawver et a/.‘~ (1992) plate tectonic reconstructions to illustrate the main features in the geographical isolation of Antarctica (Fig. 3). In early break-up palasogeographies of southern Gondwana, the Seymour-King George Islands area lay in a maritime setting, between the established Pacific Basin and the small, progressively evolving Weddell Basin. Its translation into the present, glacial setting involved several stages, each potentially liable to have caused palaeoclimatic changes in the northern Antarctic Peninsula and to have influenced the depositional environment of the sedimentary succession. In particular, the implications of possible seasonality signals from the smectite/ kaolinite ratio for the previous assumptions of ‘everwet’ environments by Dingle and Lavelle (1998b) will be discussed. Figure 4 is a summary of the authors’ conclusions.

Mid-Cretaceous Sparse coverage for Aptian to Turonian samples permitted Dingle and Lavelle (1998b) only the tentative conclusion that Albian to Turonian times were relatively cool (temperate) and wet following a warmer Aptian episode. The few new clay mineral analyses support the supposition that the rainfall was non-seasonal, while the S/TOC ratios are low, suggesting a dominance of mineral-walled phytoplankton (i.e. coccolithophores) in the adjacent seas. From 0 isotope data, Huber et al. (1995) have predicted cool sea surface temperatures for the South Atlantic for this period, and Ditchfield et al. (1994) have calculated values of - 1 O-l 2OC for the nearshore marine areas. By Albian times (- 110 Ma) there had been considerable relative motion between Antarctica/Australia and the other main Gondwanide continental units with the formation of small, semi-isolated deep ocean basins in the South Atlantic, Weddell and southern Indian Ocean regions. Surface water connections to the equatorial Tethys were possible along western and eastern Indian Ocean routes, but potential deep water pathways are uncertain. There were shallow water connections to the southern South Atlantic, while no links existed to the equatorial Atlantic (see Dingle, 1999). Consequently, extra-Weddell oceanic connections in Albian times are likely to have been relatively restricted along gradually opening seaways.

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LAVELLE The exception was a trans-polar continental shelf seaway linking the southern Weddell area to the Tasman and east Australian seaboards (Lawver et a/. , 1992). By the time a deep water connection was established between the Weddell Basin and the South Atlantic (- 100 Ma), deep water connections in the southern Indian Ocean were probably extensive (Lawver et a/. , 1992).

Turonian through Campanian Dingle and Lavelle (1998b) proposed that from - 90 (Turonian) to - 75 Ma (latest Campanian), CIA data indicated a warm, humid climate with an optimum around mid-Campanian times. The authors’ smectite/kaolinite curve (Fig. 2) has an inflexion suggestive of a Santonian phase of rainfall seasonality or prevalence of fine-grained volcanic debris. This coincides with a time of long-term change in the temperature regime from cool to warm (as predicted by the CIA curve) and could be related to climatic instability as oceanic circulation adjusted to the rapidly altering palasogeography of the southern South Atlantic/Weddell Sea area. In this case, a seasonal episode suggests that dry season maximum temperatures may have been larger than implied by the CIA curve (which approximates to an annual mean) with more intense wet season precipitation than assumed in the ever-wet model. On the other hand, Pirrie (1991) identified this as a period of significant arc magmatism with a large, direct, fine-grained volcanic flux. Also, the S/TOC ratio does not fluctuate markedly, implying no major change in marine productivity in the adjacent seas. Consequently, the balance of evidence suggests that the smectite/kaolinite peak reflects an intense Santonian volcanic episode, coincident with a period of climate warming under ever-wet conditions. The most significant palseogeographical development in the area, during this time interval, was the initiation at - 90 Ma of direct surface and midwater access for South Atlantic equatorial waters into the Weddell Basin (Dingle, 1999), while shortly before, the transpolar shallow seaway had closed (Lawver et al., 1992). According to Winterer (1991) this period was the acme of the trans-equatorial Tethyan seaway and was a time when the planktonic foraminiferal faunas of the palaeoSouthern Ocean (i.e. Weddell Basin) were characterised by tropical elements (Huber, 1992; see Fig. 4). It may be significant that in the Antarctic Peninsula region, inoceramids became extinct and the cool-favouring dimitobelid belemnites suffered a severe reduction in numbers (Crame et al., 1996) at the peak of the Campanian climatic optimum.

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Figure 4. Summary of paheo-environmental Cretaceous-Cenozoic times. Distribution of (199.2). Climatic episodes l-8 are discussed

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Maaetrichtian through Mid-Palaeocene The CIA curve for this period (Fig. 2) led Dingle and Lavelle (1998b) to predict relatively large palaaotemperature changes with a decline from the MidCampanian optimum, though minor Late Maastrichtian perturbations to cool-cold conditions by MidPalaaocene times. This is in general agreement with the Late Cretaceous temperature declines in this region identified by the isotope studies of Barrera et a/. (I 987) and Ditchfield et al. (1994). The smectite/kaolinite curve has three peaks during this period. The first involves samples from a short sequence in the upper Snow Hill Island Formation (Early-Maastrichtian). The authors suspect that this is not a seasonality signal, but a spike reflecting contemporary volcanism because they have evidence for several thin, bedded tuffs at the same level, near the base of the Haslum Crag Member of Pirrie et al. (I 997) (Dingle 1995). The second smectite/kaolinite inflexion is recorded from the lower part of the Mid-Palaeocene Sobral Formation where Dingle and Lavelle (1998b) detected a short ‘warm-to-cool’ CIA spike followed by a longer ‘cool-cold’ CIA excursion. The latter coincides with a return of the smectite/kaolinite curve to values of - 10 (Fig. 2). Although bedded tuffs occur in the middle part of the Sobral Formation (e.g. Elliot et a/. , 1992) these were avoided for the present study (clays analysed at 100% smectite and CIA values 0.1). In the upper Sobral sediments, the combination of low CIA and relatively low and falling smectite/ kaolinite values suggest late Mid-Palaeocene coolcold temperatures and non-seasonal rainfall (illite/ kaolinite values are relatively high during this colder interval). In contrast, signals from the lower Sobral (intermediate CIA and high smectite/kaolinite values) suggest that the earlier Mid-Palaaocene climate may have experienced a relatively short period with strongly seasonal rainfall. Under these conditions, the assumption of an ever-wet regime on which to calibrate the CIA curve would not be valid, and to achieve the commensurate degree of chemical weathering, a higher mean annual temperature than originally assumed by Dingle and Lavelle (i 998b), cool rather than cool-cold, is likely. The third set of high smectite/kaolinite ratios is recorded from the Cross Valley Formation, which is Late Palseocene-earliest Eocene? in age. CIA values are highest in the upper part, while the smectite content is 87-l 00% of total clays in the three samples analysed in this study. As described by several authors (e.g. review in Elliot, 1997a), the Cross Valley Formation is mainly a coarse volcaniclastic unit sourced from local centres. Consequently, the relatively high smectite/kaolinite

and palzogeographies

ratio was interpreted as indicative of its contemporary volcanic origin, rather than signalling a strongly seasonally wet climate affecting hinterland weathering. Dingle and Lavelle’s (1998b) interpretation of the CIA signal as indicating relative warmth and ever-wetness, needs no modification with the new data. The WTOC curve shows several short-term fluctuations during this period. The earliest is a series of spikes in sediments from the Snow Hill Island Formation (latest Campanian-Early Maastrichtian). Relating these to productivity changes suggests that some, at least, may be associated with enigmatic, local carbonate features within the Karsten Cliffs Member (Pirrie et al., 19971, which have the appearance of possible methane seep features (S. Lomas, pers. comm.; Dingle, 1995). A second, small, short inflexion occurs just below the Cretaceous/ Tertiary boundary for which, at present, there is no explanation. It seems to have been a prelude to a long-term switch to mainly organic-walled phytoplankton production that lasted until the end of Eocene times. Possible explanations for changes in the nutrient regime that may have altered the phytoplankton dominance include variations in nearshore circulation and/or mineral flux through the water column. The only major palsaogeographical change that occurred during this time interval according to the reconstructions of Lawver et a/. (I 992) was the separation of the New Zealand-Lord Howe Rise complex from Antarctica/Australia between 80-70 Ma. This would have generated a new, more-polar circulation route along the southern edge of the Pacific Ocean and may have brought colder surface currents to the western side of the Antarctic Peninsula (Fig. 3). In the long-term, the Palsaocene cold-cool episode can be viewed as the culmination of a -20 Ma thermal decline that was reversed by the global Late Palaaocene warming event. Pakogene Despite the relatively large hiatus between the Cross Valley and La Meseta Formations on Seymour Island (probably most of the Early Eocene), Dingle and Lavelle (1998b) suggested that the upper and lowermost sections of the formation, respectively, provide CIA evidence for an extended period of warm, ever-wet climate. This corresponds to the global Palaeogene optimum. Smectite/kaolinite ratios show a moderately high value in the oldest sample from the La Meseta Formation (Fig. 21, but the authors hesitate to infer a seasonal rainfall signal, as the clast-rich facies may retain a residual Cross Valley contemporary volcanic signature. Progressing up the La Meseta succession,

Journal

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R. V. DINGLEand Dingle and Lavelle (1998b) interpreted the curve to indicate declining provenance temperatures through the remainder of Eocene times. These culminated in cold-cool conditions in the uppermost member (Late Eocene, Submeseta, -34 Ma), where relatively high illite values occur within the clays (Dingle et a/., 1998b), and the terrestrial flora became distinctly sparser (Askin, 1997). This is in general agreement with 0 isotope temperature data for the adjacent seas, which give mean values (Ditchfield et al., 1994; Pirrie et a/., of - 7-9°C 1998) for the upper Acantilados-Campamento Members (classification of Marenssi et al,, 1998 is Telm 2-3 of Sadler, 1988). The age of the latter horizon is probably Middle Eocene since it is 150 m above the base of a section dated by Cocozza and Clarke (1992) as no older than late Early Eocene, and possibly younger. This section is itself - 150 m above the base of the La Meseta Formation (Dingle and Lavelle, 1997). The smectite/kaolinite ratio increases to a point approximately mid-way up the La Meseta succession and then declines sharply towards the top. Although the values are not high, the long-term trend and overall lack of evidence for contemporary volcanic deposits, suggests that an interval of marked rainfall seasonality occured within the Middle Eocene. This implies that the assumption of ever-wet humidity as a basis for the CIA interpretation must be modified for this period. To achieve the concomitant degree of chemical weathering, a higher mean annual temperature than implied by Dingle and Lavelle (1998b) seems likely, which would move the shoulder of the CIA curve to a slightly younger position (to mid-way up the Acantilados Member in Fig. 2). Recent palseontological data from sharks and giant penguins (Case, 1992) and crinoids (Meyer and Oji, 1993) have stressed the temperate and productive nature of the seas in the area during the deposition of much of the La Meseta Formation. This interpretation of the clay mineral data would have the effect of implying a sharper decline in ambient temperatures in later Eocene times. Askin (1992) had already suggested an element of rainfall seasonality in the Seymour Island Eocene terrestrial floral signal without specifying any particular stratigraphical interval. The S/TOC curve for the La Meseta Formation shows a preponderance of relatively high values (organic-walled dominance in the phy-toplankton) with a cluster of lower values (mineral-walled dominance) only in the lower part. The latter coincides with the smectite/kaolinite inflexion mentioned above, implying that the suggested period of rainfall seasonality was accompanied by a change in the productivity characteristics of the local marine surface waters.

102 Journal

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M. LAVELLE The short Mid-Palseocene cool episode discussed above was reversed in the Late Palseocene, when Antarctica experienced the start of the Paleaogene global thermal optimum (Zachos et al., 1994; Robert and Kennett, 1994). Causes for the latter event are uncertain (e.g. Sloan and Barron, 1992), but recent evidence suggests massive North Atlantic volcanism and resultant ocean circulation changes (Bralower et a/. , 1997). Southern Ocean deep water temperatures were as high as 15 OC (Zachos et al., 1994) and sea surface temperatures were 18-22OC (Robert and Kennett, 1994). After the climatic optimum, there was a general, high latitude cooling throughout Mid-Late Eocene times (e.g. Zachos et a/. , 1993). However, would this have been sufficient to account for the Mid-Eocene episode of seasonality? Elliot (1997b) considered various models for uplift of the Antarctica Peninsula; and although he favoured a Neogene date, he identified some features that suggest a Palseogene alternative. Amongst these were plausible plate models to account for uplift, the fact that it would have served as an elevated centre for the subsequent Oligocene glaciation, and evidence from the Seymour Island sedimentary succession (e.g. Mid-Palseocene shallowing in the Sobral Formation and a major erosion surface between the Cross Valley and La Meseta Formations). Elliot (1997b: pp. 68-69) concluded that there is currently insufficient evidence to make an unequivocal judgment, but there can be no doubt that initiation of uplift of the Antarctic Peninsula in earliest Eocene times would have altered the local atmospheric circulation and strongly influenced the climate in the vicinity of the James Ross and Seymour Islands and resulted in stronger west to east climatic gradients (as it does at the present, see Elliot, 1997b). Throughout Palasogene times, continental connections progressively loosened between Antarctica and Australia, although the presence of small units in the Tasman Sea area prevented the establishment of a deep water gateway until - 40 Ma (Lawver et al., 1992). Similarly, between South America and the Antarctic Peninsula, the Drake Passage remained closed to deep circulation until slightly later; but by - 30 Ma, deep and shallow circumpolar circulation had been established and the thermal isolation of Antarctica was complete (e.g. Lawver et a/. , 1992; Beu et a/., 1997). Extensive cryospheres rapidly extended to large parts of both East and West Antarctica after - 34 Ma (see Barrett, 1996 for a review). Post-Eocene Extensive East Antarctic glaciation began in Late Eocene times (e.g. Barrett, 1996) and the northern

Antarctic

Peninsula

pakoen

vironments

Antarctic Peninsulawas glaciated - 4 Myr later ( - 30 Ma). No evidence has yet been found for latest Eocene glacial sediments in the northern peninsula. A significant percentage of the Early Oligocene glacial erratics on King George Island were derived from the Antarctic Peninsula, while up to 47% probably came from beyond, indicating an extensive cryosphere (Dingle and Lavelle, 1998a). Since that time, the northern Antarctic Peninsula has experienced either glacial or interglacial climates, although there is considerable uncertainty on the extent, nature and severity of cryosphere cover (Barrett, 1996). PostEocene proxies indicate dominant mineral-walled phytoplankton assemblages(e.g. coccolithophores or diatoms) and low levels of chemical weathering (i.e. provenance dominated). CONCLUSIONS The authors recognise eight main climatic episodes which have affected the northern Antarctic Peninsula in Late Cretaceous to Early Cenozoic times (Fig. 4). (I 1The record commences in a warm, humid period in Late Aptian times when the area was flanked by the southern Pacific in the west and a small isolated inter-continental sea (Weddell Basin) in the east. The climate was probably non-seasonal. (2) During Albian to Coniacian times, temperatures cooled, but the climate remained humid and nonseasonal. This coincided with the progressive establishment of south Indian Ocean seaways connecting into the Weddell Basin. (3) In Santonian times, temperatures began to increase as the transpolar shelf seaway to Australia closed and connection was established along the South Atlantic to equatorial regions. This culminated in an Early- to Mid-Campanian warm episode; when tropical planktonic foraminifera penetrated to the Weddell area and the Tethyan circum-equatorial routes were at their widest. The climate in the northern Antarctic Peninsulawas humid, non-seasonal and coccolithophores dominated the phytoplankton. (4) A period of cooling began in Early Maastrichtian times which culminated in a short Mid-Palaeocenecool episode during which the climate became seasonally humid (with a marked wet/dry regime) and was accompanied by a change to organic-walled dominance in the phytoplankton of the adjacent seas. The latter phenomenonwas heraldedby an earlierspike in organicwalled phyto-plankton in the early Maastrichtian at approximately the sametime as Huber (1992) records the influx of cooler planktonic foraminiferal faunas into the WeddelVproto-Southern Ocean area. The single, most obvious palaeogeographicaldevelopment at this time was the establishmentof a more-polarroute along

and pakogeographies

the southern edge of the Pacific Ocean, and the authors speculate that it brought cooler conditions to the western seaboard of the northern peninsula and affected the local seasonality. (5) The Late Palmeocene-Early Eocene climatic optimum was global, and caused by events in the northern hemisphere. The climate in the Antarctic Peninsulabecame warm, ‘ever-wet’ and non-seasonal. (6) When the effects of the global optimum had dissipated by the Mid-Eocene, temperatures began to decline and the climate temporarily reverted to marked seasonality, although the mean annual temperature is likely to have remained relatively warm. There were no obvious palasogeographical changes to account for this, although the effects of continuing putative peninsula uplift cannot be discounted. (7) In Mid-Late Eocene times, rainfall reverted again to ‘ever-wet’, while there was probably an accelerated decline in temperature to cold-cool conditions in the latest Eocene, where the geological record of the La Meseta Formation on Seymour Island ceases. (8) The geographical and oceanographical isolation of Antarctica was completed with the opening to deep and shallow circulation through the Tasman and Drake Passage seaways ( - 40-30 Ma). This is recorded on the northern peninsula in cold-climate proxies at the top of the La Meseta Formation (Seymour Island), and the earliest glacial sediments on King George Island (Polonez Cove Formation). Despite this rapid deterioration, it remained locally sufficiently warm and wet to support refugia for hardy arboreal species that returned during the interglacial episode preceding the Early Miocene Cape Melville Formation glaciogenic sediments (e.g. Birkenmajerand Zastawniak, 1989). The establishment of glacial/ interglacial climates was accompanied by dominance of mineral-walled phytoplankton in the adjacent seas.

ACKNOWLEDGEMENTS The authors wish to thank colleagues at the British Antarctic Survey for help with field work and the officers and crew of HMS Endurance for logistical support. Geochemical analyses at Keele were undertaken by David Embley. Rene Madsen (Copenhagen) is thanked for draughting the palzao-geographical maps. Three anonymous referees made important and constructive suggestions for improving the manuscript. REFERENCES Askin, R.A., 1992. Late Cretaceous-Early outcrop evidence for past vegetation American Geophysical Union, Antarctic 56, 61-73.

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Tertiary Antarctic and climates. Research Series

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Sciences

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LAVELLE

Askin, R.A., 1997. Eocene-?Earliest Oligocene terrestrial palynology of Seymour Island, Antarctica. In: Ricci, C.A. (Ed.), The Antarctic Region: Geological Evolution and Processes. Terra Antartica, Siena, pp. 993-996. Askin, R.A., Elliot, D.H., Stilwell, J.D., Zinsmeister, W.J., 1991. Stratigraphy and paiaeontology of Campanian and Eocene sediments, Cockburn Island, Antarctic Peninsula. South American Journal Earth Sciences 4, 99-l 17. Barrera, E., Huber, B.T., Savin, S.M., Webb, P.N., 1987. Antarctic marine temperatures: late Campanian through early Palaeocene. Palaeoceanography 2, 2 l-47. Barrett, P.J., 1996. Antarctic palaeoenvironment through Cenozoic times - a review. Terra Antartica 3, 103-I 19. Bertrand, P., Lallier-Verges, E., 1993. Past sedimentary organic matter accumulation and degradation controlled by productivity. Nature 364, 786-788. Beu, A.G., Griffin, M., Maxwell, P.A., 1997. Opening of Drake Passage gateway and Late Miocene to Pleistocene cooling reflected in Southern ocean mollusca dispersal: evidence from New Zealand and Argentina. Tectonophysics 281, 83-97. Birkenmajer, K., 1992. Cenozoic glacial history of the South Shetland Islands and northern Antarctic Peninsula. In: Lopez-Martinez, J. (Ed.), Geologia de la Antartida

Dingle, R.V., 1999. Walvis Ridge barrier: its influence on palaeoenvironments and source rock generation deduced from ostracod distributions in the early South Atlantic Ocean. In: Cameron, N., Bate, R.H., Clure, R. (Eds.), Hydrocarbon Habitats of the South Atlantic. Geological Society London, Special Publication 153, pp. 293-302. Dingle, R.V., Lavelle, M., 1997. Report of field work undertaken on Seymour and King George Islands, Antarctic Peninsula (January-March 1996) and cruise James Clark Ross/l 2 (March-April 1996). British Antarctic Survey, Report R\1995\GL2 (unpubl.), 22~. Dingle, R.V., Lavelle, M., 1998a. Antarctic Peninsular cryosphere: Early Oligocene (c.30 Ma) initiation and a revised glacial chronology. Journal Geological Society London 155, 433-437. Dingle, R.V., Lavelle, M., 1998b. Late CretaceousCenozoic climatic variations of the northern Antarctic Peninsula: new geochemical evidence and review. Palaeogeography, Palaeoclimatology, Palaeoecology 141, 215-232. Dingle, R.V. Marenssi, S.A., Lavelle, M., 1998. High latitude Eocene climatic deterioration: evidence from the northern Antarctic Peninsula. South American Journal

Occidental. III Congreso Geologico de Espana y VIII Congreso Latinoamericano de Geologia, Salamanca, Simposios T3, pp. 251-260. Birkenmajer, K., Zastawniak, E., 1989. Late Cretaceousearly Tertiary floras of King George Island, West Antarctica: their stratigraphic distribution and palaeoclimatic significance. Geological Society London, Special Publication 47, 227-240. Bralower, T.J., Thomas, D.J., Zachos, J.C., Hirschmann, M.M., Rohl, U., Sigurdsson, H., Thomas, E., Whitney, D.L., 1997. High-resolution records of the late Palaeocene thermal maximum and circum-Caribbean volcanism: is there a causal link? Geology 25, 963-966. Calvert, S.E., Pedersen, T.F., 1992. Organtc carbon accumulation and preservation in marine sediments: how important is anoxia. In: Whelan, J.K., Farrington, J.W. (Eds.), Organic Matter: Productivity, Accumulation and Preservation in Recent and Ancient Sediments. Columbia University Press, New York, pp. 221-263. Cande, S.C., Kent, D.V., 1995. Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. Journal Geophysical Research 100, 6093-6095. Case, J.A., 1992. Evidence from fossil vertebrates for a rich Eocene Antarctic marine environment. American Geophysical Union, Antarctic Research Series 56, 119130.

Earth Science 11, 571-579. Ditchfield, P.W., Marshall, J.D., Pirrie, D., 1994. High latitude palaeotemperature variation: new data from the Trthonian to Eocene of James Ross Island, Antarctica. Palaeogeography, Palaeoclimatology, Palaeoecology 107, 79-101. Elliot, D.H., 1997a. Palaeogene volcaniclastic rocks on Seymour Island, northern Antarctic Peninsula. In: Ricci, C.A. (Ed.), The Antarctic Region: Geological Evolution and Processes. Terra Antartica, Siena, pp. 367-372. Elliot, D.H., 1997b. The planar crest of Graham Land, northern Antarctic Peninsula: possible origins and timing of uplift. American Geophysical Union, Antarctic Research Series 71, 51-73.

Cocozza, C.D., Clarke, C.M., 1992. Eocene microplankton from La Meseta Formation, northern Seymour Island. Antarctic Science 4, 355-362. Crame, J.A., Lomas, S.A., Pirrie, D., Luther, A., 1996. Late Cretaceous extinction patterns in Antarctica. Journal Geological Society London 153, 503-506. Crame, J.A., Pirrie, D., Riding, J.B., Thomson, M.R.A., 1991. Campanian-Maastrichtian (Cretaceous) stratigraphy of the James Ross Island area, Antarctica, Journal Geological Society London 148, 1 1 25- 1 140. Dettmann, M.E., 1989. Antarctica: Cretaceous cradle of austral temperate rainforests? Geological Society London, Special Publication 147, 89- 105. Dingle, R.V., 1995. Report of field work undertaken in the Snow Hill-James Ross Islands area and around Low Head, King George Island: December 1994-February 1995. British Antarctic Survey, Report Gen\l994\GLl (unpubl.), 17~.

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Elliot, D.H., Hoffman, S.M., Rieske, D.E., 1992. Provenance of Palaeocene strata, Seymour Island. In: Yoshida, Y. et al. (Eds.), Recent Progress in Antarctic Earth Science. Terra, Tokyo, pp. 347-355. Elliot, D.H., Trautman, T.A., 1982. Lower Tertiary strata on Seymour Island, Antarctic Peninsula. In: Craddock, C. (Ed.), Antarctic Geoscience. University of Wisconsin Press, Wisconsin, pp. 287-297. Francis, J.E., 1986. Growth rings in Cretaceous and Tertiary wood from Antarctica and their palaeoclimatic implications. Palaeontology 29, 665-684. Francis, J.E., 1991. Palaeoclimatic significance of Cretaceous-Early Tertiary fossil forests of the Antarctic Peninsula. In: Thomson, M.R.A, Crame, A.J., Thomson, J.W. (Eds.), Geological Evolution of Antarctica. Cambridge University Press, Cambridge, pp. 623-627. Huber, B.T., 1992. Palaeobiogeography of CampanianMaastrichtian foraminifera in the southern high latitudes. Palaeogeography, Palaeoclimatology, Palaeoecology 92, 325-360. Huber, B.T., Hodell, D.A., Hamilton, C.P., 1995. MiddleLate Cretaceous climate of the southern high latitudes: stable isotope evidence for minimal equator-to-pole thermal gradients. Geological Society America, Bulletin 107, 1164-I 191. Lawver, L.A., Gahagan, L.M., Coffin, M.F., 1992. The development of palaeoseaways around Antarctica. American Geophysical Union, Antarctic Research Series 56. 7-30.

Antarctic

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