History of Oligocene Erosion, Uplift and Unroofing of the Transantarctic Mountains Deduced from Sandstone Detrital Modes in CRP-3 Drillcore, Victoria Land Basin, Antarctica
J.L. SMRLI~II~
Brilish Antarctic Survey. Natural Environment Research Council. l-Iisli Cross, Madinglcy Road - Cambrklgc CB3 OET - UK ([email protected])
Received 26 October 2000: acc~~ptc~/in revised form 23 April 2001
Abstract - Detrital modes determined on 68 sandstone samplcs from CRP-3 drillcore indicate a continuation of the dynamic history of uplift-rclatcd erosion and unroofing previously documented in CRP-l and CRP-212A. Thc source area is identified very strongly with the Transantarctic Mountains (TAM) Dry Valleys block in southern Victoria Land. Initial unroofing of the TAM comprised removal of much of a former capping sequence of Jurassic Kirkpatrick basalts, which preceded the formation of the Victoria Land Basin. Erosion of Beacon Supergroup outcrops took place during progressive uplift of the TAM in the Oligocene. Earliest CRP-3 Oligocene samples above 788 metres below the sea floor (mbsf) were sourced overwhelmingly in Beacon Supergroup strata, including a recognisable contribution from Triassic volcanogenic Lashly Formation sandstones (uppermost Victoria Group). Moving up-section, by 500 mbsf, the CRP-3 samples are depauperate quartz arenites dominantly derived from the quartzose Devonian Taylor Group. Between c. 500 and 450 mbsf, the modal parameters show a distinctive change indicating that small outcrops of basement granitoids and metamorphic rocks were also being eroded along with the remaining Beacon (mainly Taylor Group) sequence. Apart from enigmatic fluctuations in modal indices above 450 mbsf. similar to those displayed by samples in CRP-2/2A, the CRP-3 modes are essentially constant (within a broad data scatter) to the top of CRP-3. The proportion of exposed basement outcrop remained at < 20 %. indicating negligible uplift (i.e.relative stability) throughout that period.
INTRODUCTION mean sample interval of about one every 15-20 m. Twenty two sandstone samples from the Beacon The Cape Roberts Drilling Project used a sea ice Supergroup were also analysed modally, for platform to drill the western margin of the Victoria comparative purposes. Sample treatment included Land Basin in McMurdo Sound, to obtain resin impregnation of weak samples, and staining for fundamental knowledge of Cenozoic palaeoclimates feldspars (method of Houghton, 1980). For each and tectonic history of the Ross Sea region. The sample, 300 sand grains were counted using the background to the project, its detailed aims, methods Gazzi-Dickinson method (Dickinson, 1970). In used and results so far are summarised in Cape reporting the results, all of the detrital modes are Roberts Science Team (1998, 1999. 2000) Hambrey recalculated to exclude matrix (<30 pm). Counts for & Wise (1998) and Barsett & Ricci (2000a, b). In this lithic sedimentary grains (Ls) in the CRP-3 samples paper, the results of a study of sandstone detrital were also excluded by recalculation, because they modes on samples from CRP-3 are described and appear to be intraformational and thus do not preserve interpreted. The modes reveal a continuing dynamic provenance information (Smellie, 2000). However, Ls history of erosional unroofing and accompanying forms only a tiny part of the grain population in those uplift of the Transantarctic Mountains adjacent to the samples and the recalculations to exclude Ls have CRP-3 drillsite. only a trivial effect on the modes. Grain types are described in detail by Smellie (1998). There is no obvious systematic influence of grain size on the METHODS CRP-3 sample modes, other than possibly to increase the data scatter (Cape Roberts Science Team, 2000; Sixty eight CRP-3 samples were selected for see also Smellie, 1998, 2000). However, the use of modal analysis. A mean sample distribution of about the Gazzi-Dickinson method and focus on modal one every 10 m was achieved for most of the core. indices (particularly ratios) that are unaffected by The upper 300 m is most poorly sampled, with a grain size, should minimise that scatter (Ingersoll et al., 1984; Smellie, 2000). As in CRP-l and CRP- grains wit11 angular shapes, whereas coal typically 2/2A, the dominant influence on modal variations is occurs as larger, single grains showing roundin;!,, likely to be provenance. There arc no clear clown-core variations for the minor framework minerals and all are persistent ((';il>e Robcrts Science Team, 2000a). However, below ;iboul RESULTS OF THE DETRITAL MODES 400 mbsf', biotitc occurs mainly as small inclusions within cliiartz (note: only sand-size biotite grains or The CRP-3 samples arc q~~artzofeldspatl~icinclusions were counted for the modes; most hiolite is sandstones similar to sandstones in CRP-land CRP- sub-sand grade and only its presence is recorded in 2/2A. Most are s~ibarkoses(sensu Pettijohn et al., table 1, listed as an accessory phase). By contriisl, 1973). A smaller proportion are arkoses, and several ~n~iscoviteoccurs more commonly as free grains. samples, mainly between 500 and 600 mbsf, are Accessory minerals include zircon, bioclastic ;iiul quartz arenites (Tab. 1). In addition, a few samples possible inorganic carbonate, sphene, garnet, cpiilotc have mud matrix exceeding 15 % and are arkosic (includiiig clinozoisite) and possible celadonite (one wackes; all are situated above 330 mbsf (see Tab. 1 occurrence; Tab. 1). in Wise et al., this volume). The mean value for Lithic grains are a minor detrital component in ;ill quartz (Q) and feldspar (F) is 92.3 % (Q+F), and 32 samples and usually forni < 5 % of the mode (mean % of samples (22 samples) have 2 95 % Q+F. These 2.7 %). They are dominated by fine volcanic types values are significantly higher than for any previous (Lv), typically forming > 90-100 % of the litliic Cape Roberts Project modes (cf. Smellie, 1998, 2000). population. Above 500 mbsf, most samples have < Q and F vary antithetically. Q values show a gradual 3.5 % Lv, whereas below 500 mbsf, the proportion of down-core increase to 98 % at 500 mbsf, falling more Lv increases gradually to about 5 %, with some steeply to 56 % at 700 mbsf before recovering samples reaching 7-9 %. Four types were separately slightly, to about 70 % at the base of the core distinguished: (i) quartz-feldspar aggregates with (Fig. 1). Ratios of rounded to angular quartz grains graphic or myrmekitic textures; (ii) monominer*a l'ic or (QrIQa) fluctuate widely (0.04-1.3) and the values are bimineralic quartz-feldspar aggregates with fine commonly higher than observed in CRP-1 and CRP- patchy (mosaic-like) or "snowflake" textures; (iii) fine 2/2A (Smellie, 1998, 2000). The ratios are highest at lathy-textured grains formed mainly of decussatc 525 mbsf, falling sharply thereafter to much lower plagioclase, rarely with altered pyroxene andlor values (0.08-0.1) at the base of the core. In most of altered glass(?); and (iv) grains with feathery-texturcil the samples, plagioclase (P) is more abundant than plagioclase and/or pyroxene, sometimes with rod-like alkali feldspar (K). K exceeds P in samples between or dendritic opaque oxide, smectite(?)-altered glass or 400 and 620 mbsf, corresponding generally to those prismatic pyroxene. Graphic-textured (type (i) grains samples poorest in F and richest in Q. P and K show relatively high abundances at four positions in abundances apparently show no covariation, except for the core: 0-250, 380-440, about 500 and below the section between 500 and 650 mbsf, where the 580 mbsf (Fig. 1). Lathy-textured (type (iii) grains indices broadly vary sympathetically. K/Q ratios are also show a weak peak at 380-400 mbsf, but no other low (mainly < 0.1; Fig. 1) and are similar to those significant variations with depth. Feathery-textured encountered in the basal 300 m of CRP-2/2A. They (type (iv) grains are more common above 440 mbsf broadly vary antithetically with Qr/Qa ratios, as also and almost non-existent below that depth. By contrast, observed in CRP-2/2A, and show a significant steady the quartzo-feldspathic mosaic grains (type (ii) show a increase in samples below 500 mbsf. striking increase below c. 550 mbsf (Fig. 1). It is Pyroxene is the only other common framework- principally the variation in the type (ii) grains that is grain constituent, with abundances generally varying responsible for the overall down-core increase in Lv between 1 and 6 % (mean: 4.1 %). Highest noted above. Other lithic grains are uncommon. In abundances (9-12 %) occur in samples above 170 addition to mudrocks, there are also sporadic mbsf, diminishing to minimum values (< 1 %) at 500 occurrences of fine quartz-mica tectonite (Lm) and mbsf, then rising to about 6 % at the base of the core polycrystalline quartz (Qp). Dolerite and granitoid (Fig. 1). grains are also present but, because of the Gazzi- Minor framework minerals include hornblende Dickinson methodology used, they are not counted as (pale green, pale brown), brown biotite, muscovite, such (cf. Dickinson, 1970). opaque oxide and coal, with a combined mode between 0.3 and 7 % (mean: 0.9 %). Of these, opaque grains (opaque oxide and coal) are PROVENANCE commonest, as in CRP-2/2A samples (Smellie, 2000). The two opaque grain types can often be All samples contain the same grain types, and distinguished empirically: opaque oxide commonly none are diagnostic of individual parts of the section. occurs as an interstitial phase within dolerite grains, Moreover, despite the presence of significant down- as fine granular aggregates or as individual small core variations in modal abundances, the data show - 2 >l,. <. . ,. - $2, 7:.-, , + ,.:z g .ca= 2 . .- cl - U-* - 2 z .L c - - :D U, - ,- . E G> : - m. :; - - - 2 /= : :J :; L-< .:.. 2 "cL -g. L U ; :g, :g, ,. :- L ::F? = :. , .S, -.* OCL " -. . - -, &g -? La = = , <.E s*2 ts;~gz<<<: c2 'd /J-S.. - "
KIQ Pyroxene Lithic volcanic grains (1) Lithic volcanic grains (2) 00 01 02 03 04 05 0 5 10 15 20 0 1 ? 3 4 5 0 2 4 6 8
Fig. 1 - Down-core distribution of selected modal indices for sandstone samples in CRP-3. All values plotted are percentages. Also superimposed are mean values determined for representative groups of samples from the different provenance types (Beacon Supergroup (Taylor and Victoria groups: unpublished modal data of the author) and basement (mainly granitoids: calculated from Talarico & Sandroni. 1998). Note that detritus derived from Ferrar dolerite will have no effect on these ratios but is the likely primary control on the pyroxene abundances shown. Curves drawn in each diagram are based on 5-point runningaaverages. See Tab.1 for explanation of modal abbreviations. Lithic volcanic grain types (i-iv). and their provenance interpretation, are described in the text.
noted above, although dolerite and granitoid are too DISCUSSION coarse-grained to be included in the modes. Together, they have a persistent down-core distribution (Cape EROSIONAL HISTORY AND LOCATION OF THE Roberts Science Team, 2000). Only dolerite grains SOURCE TERAIN show a few obvious zones of greater abundance, located mainly within the upper 180 mbsf, but also at It is possible to estimate the relative contributions 370-400 and 480-540 mbsf (see also Sandroni & from the different lithological provenance "types" (i.e. Talarico, this volume). Qp and Lm also occur as a granitoid and metamorphic basement, Beacon, Ferrar detrital component in Beacon sandstones and need not dolerite, Kirkpatrick basalt) by comparing the indicate a basement provenance. different modal contributions of those sources (cf. Smellie, 2000). QrIQa ratios are a particularly useful evidence for a ma.jor influence of a Victori;~(ii.0111) discriminant. Because of the short distance between source is lacking above 500 mbsf, the sponulir hiit the TAM source terrain and the CRP-3 drillsite (30- persistent presence of Permo-Triassic palynof'ossil~. 100 km), angular quartz grains are unlikely to become coal debris and evolved-Lv (cf. Cape Roberts Sciciicr significantly rounded by normal fluvial or glacial 'rc;im. 2000a) indicates that Victoria Group str;it;i irocesses. Very short transport distances for CRP-3 continued to be exposed, but that they formed only n sediments were also inferred by Atkins (this volume), small part of the outcrop being eroded. based on clast shapes and surface features. Thus, Lithic grains derived from the Kirkpatrick biisiilts rounded-well rounded quartz grains will be derived (L,v lypcs (iii) and (iv), above) are slightly commoii~-r exclusively by erosion from Beacon sandstones. (c. 2 %) above c. 430 mbsf, in a section of the corr Moreover, only Beacon sandstones and basement in which Kirkpatrick basalt clasts arc also granitoids will contribute angular quartz. In addition, conspicuous (Cape Roberts Science Team, 2000;i; there are significant differences in QrIQa ratios for Sandroni & Talarico, this volume). They become different parts of the Beacon Supergroup: high QrIQa scarcer below that depth. However, they always f'orm ratios are characteristic of the Devonian Taylor Group, a minor part of the grain population (range of modiil with much lower ratios for Victoria Group sandstones values: 0-2.3 %). The general paucity of detritus from (Fig. 1). Similarly, KIQ ratios are very low in the that source suggests that the Kirkpatrick basalt if Taylor Group, higher in the Victoria Group and very outcrop was largely removed at some time prior to high in basement granitoids (Fig. 1); neither Ferrar the depositional period represented within CRP-3. dolerites nor Kirkpatrick basalts contribute to KIQ The modes for samples within CRP-3, parlicukirly ratios. Smellie (2000) used a combination of QrIQa those obtained close to 500 mbsf. indicate ;I and KIQ ratios to distinguish between Beacon and dominance of sand-grade sediment derived from ;L basement sources: basement sources have very low source dominated by the Taylor Group of the Beacon QrIQa ratios combined with high KIQ, whereas the Supergroup. This implies that strata of the Taylor converse is true for Beacon sources. In figure 1, Group formed a major part of the source terrain. This modal data for the different sources are conclusion provides a strong clue about the locution superimposed for comparison with CRP-3 samples. of the source area that fed the Oligocene Victoria For QrIQa and KIQ ratios, there is excellent Land Basin. The TAM are divided into several crustal antithetic agreement. In particular, from the base of blocks on a range of scales, which probably the core up to c. 500 inbsf, the dominant source experienced different rates and periods of uplift (ç,i,' apparently changes from dominantly Victoria Group Wrenn & Webb, 1982; Stump & Fitzgerald. 1992; to dominantly Taylor Group. This is also consistent Huybrechts, 1993; Fitzgerald, 1994; Busetti et al., with the observed decrease in evolved volcanic lithic 1999; van del- Wateren et al., 1999). Major criistal grains from 800 to 500 mbsf, a trend that a basement lineaments probably exist at the sites of the Mackay source cannot emulate: the sole known source of and Ferrar glaciers. The Dry Valleys block in southern evolved-Lv detritus (Lv type (ii), above) is by Victoria Land is the major outcrop area of the recycling from the upper Victoria Group. Above 500 Devonian Taylor Group, which reaches thicknesses of mbsf, observed trends of (diminishing) QrIQa and 750-1 100 m (Gunn & Warren, 1962; McElroy & (increasing) KIQ ratios either indicate an increasing Rose, 1987; Allibone et al., 1991; Isaac et al., 1996). influx of Victoria Group detritus or else detritus The Taylor Group thins rapidly to the north, south derived from basement rocks. However, the much and west (0-300 m in the central TAM, absent in lower and roughly unchanging proportion of evolved- northern Victoria Land; Barrett et al., 1986; Collinson Lv grains above 500 mbsf suggests that the trends are et al., 1986). Moreover, outcrops in the Convoy much more likely to be an effect of contributions Range, north of the Mackay Glacier, are dominated from a basement source. by Ferrar dolerite (Pocknall et al., 1994). Any The low KIQ ratios (mostly < 0.08) compared to significant sediment contribution derived from that mean values for KIQ in granitoid basement (0.84) source would thus have a dominant dolerite signature, imply that the proportion of detritus contributed by which is not obvious in CRP-3 samples (except basement was small, suggesting only a small possibly the very high Ferrar-derived pyroxene input basement outcrop. Antithetic fluctuations in QrIQa above 170 mbsf). Absence of lithologically distinctive and KIQ ratios can also be interpreted to suggest that metagreywacke and carbonate clasts and grains in different periods experienced inputs of sediment with CRP-3 sandstones is also a source terrain indicator. different source-proportions, very similar to the These are relatively uncommon lithologies in Victoria variable modes for those ratios observed in CRP-212A Land but are thickly developed and well exposed in (Smellie, 2000). Applying a simple lever rule to the the central TAM (Archaeocyathid-bearing Shackleton modal values suggests that the proportion of detritus Limestone (c. 8 km thick; Cambrian; Byrd Group) derived from basement outcrops generally fluctuated and thermally metamorphosed greywacke and argillite between about 5 and 20 % in alternate periods of of the Goldie Formation (c. 7 km thick; late reduced and enhanced influx, respectively. Although Precambrian; Beardmore Group); Laird et al., 197 1). Finally. the virtual absence of low-pi';i(lcmetamorphic Tiiylor (iroiip strat;i. Usi~igpyroxene modal variations clasts mid lithic grains in CRP-3 (and ('RP-212A;) as ii proxy for Fcrrar doleritc input, it also appears samples suggest that the Protcrozoic low-gsaclc that thc propor~ionof l^cn'ar dolcrite in the source n~etaniorphicterrain of the Skelton Group. which is area diminished up-core during that period. In other restricted 10 the area between the I'ei~ar and Skclton words, from :I source comprising Victoria Group glaciers, was also not contributing significant clctri[us intrnded by sheds of doleritc. the source terrain to the ('RP-3 sequence. changecl to one ilominated by Taylor Group largely lacking clolcritc. In the Dry Valleys block today, UPLIFT AND UNROOFING HISTORY mapping indicates that the Victoria Group contains about 50 % by thickness of I-'errar dolerite, whereas The sequential trends for modal indices the Taylor Group is largely free of dolerite (Isaac et documented above are a clear indication of a dynamic al., 1996). Conversely. the hinterland of Cape Roberts, evolving provenance, which, in the Ross Sea region. crossed by the Mackay Glacier, contains abundant can be interpreted in terms of TAM uplift and erosion dolerite that would swamp the modes with dolerite- in southern Victoria Land. At least three episodes can derived detritus, which is not observed. These be identified from the CRP-3 Oligocene sequence: observations are consistent with the modal data and also support interpretation of the TAM in southern Period I (pe-CRP-3). The paucity of distinctive Victoria Land as the likely CRP-3 provenance area. detritus derived from a Kirkpatrick basalt source The subsequent up-core change (particularly above implies that the Kirkpatrick basalt outcrop had already 400 mbsf) to much higher pyroxene contents could be been largely removed prior to the Oligocene period correlated with the unroofing of the peneplain sill represented by CRP-3. The period of removal of the (also known as the upper sill: Turnbull et al., 1994). Kirkpatrick basalt outcrop may have coincided with The sill is a laterally very extensive and thick (300- the erosion of about 3 km of Beacon Supergroup 500 m) dolerite mainly emplaced along the Kukri strata, down to the lower few hundred metres at Erosion Surface unconformity that separates the CRP-3 (P.J. Barren, personal communication). This Beacon Supergroup from basement (Gunn & Warren, period of erosion is unrepresented in CRP-3 but 1962; Turnbull et al., 1994: Isaac et al., 1996). presumably corresponds to a major phase of early, pre-Oligocene uplift and unroofing of the TAM. Period 3 (above c. 450 mbsf). The modal indices also show a significant change at c. 450 nibsf. Above Period 2 (788 to c. 450 mbsf). From the base of that depth, most of the indices show a comparatively the CRP-3 core to c. 500 mbsf, progressive changes wide scatter superimposed on only very gradual up- in the modal indices indicate that the source terrain core variations (e.g. diminution in Q, antithetic changed from one dominated by Victoria Group increase in P). The scatter can be resolved statistically strata, initially uppermost Victoria Group (Lashly into a series of weakly-defined peaks and troughs, Formation), to one dominated by the Taylor Group. which may have importance for uplift and erosion. At c. 500 mbsf, the modal trends alter direction (e.g. For example, QrIQa and KIQ ratios, and pyroxene from higher to lower QrIQa ratios; Fig. 1). The modes, show several peaks, which cross-correlate (in change corresponds to an abrupt influx of detritus the case of QrIQa and KIQ ratios, they correlate from the basement outcrop, which was either exposed antithetically). Despite greater data scatter for CRP-3 for the first time. or else the area of basement samples, the patterns broadly resemble those outcrop available for erosion was significantly previously described for CRP-212A samples increased by uplift. As the change occurs within a (particularly below c. 300 mbsf in that core; Smellie, period of rapidly varying modes caused by uplift, and 2000). However, the origin of the CRP-212A modal the upper surface of the basement outcrop is a gently variations is still enigmatic. It remains hard to ascribe dipping homoclinal surface (Kukri Erosion Surface), the variations to an entirely sedimentological origin the former seems more likely. The modes continue to e.g. by varying the transport paths between source change rapidly up to c. 450 mbsf, indicating an and basin, to alternately tap lithologically different increasing contribution from the basement outcrops. provenances). However, the peaks and troughs are In terms of simple homoclinal uplift of the TAM, a superimposed on a more general pattern of only slight period of progressive upward movement and erosion up-core provenance variation. The modes remain is envisaged. Had it been abrupt uplift, exposing (for dominated by Beacon sandstone detritus (probably example) Victoria and Taylor groups more or less mainly Taylor Group), together with material shed simultaneously along steep scarps, we would expect from a relatively small basement outcrop representing to see a more homogeneous mixture of detritus rather probably < 20 % of the provenance area, and some than the progressive modal trends observed. The up- Ferrar dolerite. The proportion of basement outcrop core diminution of Victoria Group detritus also apparently changed little to the top of CRP-3, suggests that the Victoria Group strata were back- implying that uplift was either extremely slow or had stripped by scarp retreat relative to the underlying possibly ceased during that period. 488 J.L. Smellie
CONCLUSIONS Victoria 1,:md Basin. A11t:ircticn. This voiumc. Barren P.J. & Ricci C.A.. 2000:i. S~ud~sI'roul the C:ip Knlu-11s Detrital modes were determined on 68 samples Project. Ross Sea. Autarctic~i.Scienlific Report of <'l certainly the Dry Valleys block of southern Victoria Busetti M,. Spadini G.. van dcr Wiiteren F.M.. Cloctii~gl~S, g<Â Land. The modal variations indicate that the earliest Zanolla C.. 1999. Kinematic modelling of the West Aiit:~rcl'n. sediments were derived overwhelmingly from a Rift System. Ross Sea. Antarctica. Glol~aland Planciai Y Change, 23. 79-104. Beacon source, initially Victoria Group strata Cape Roberts Science Team. 1998. Initial Report on CRP-1. C7:ipr (including a distinctive contribution from the Triassic Roberts Project. Antarctica. Terra Amrtica. 5, 1 - 187. Lashly Formation), whereas by c. 500 mbsf the Cape Roberts Science Team. 1999. Studies from the Cape Rol~ei~s source was almost entirely Taylor Group strata. Project, Ross Sea. Antarctica. Initial Report on CRP 212A. Above 500 mbsf, an important contribution was Terra Antariica. 6. 1- 173. Cape Roberts Science Team. 2000. Studies from the Cape Roln-r1-i introduced from a source identified as basement. The Project. Ross Sea. Antarctica. Initial Report on CRP-3. 'I'crrii basement contribution increased upward to Antartica. 7. 1-209. c. 450 mbsf, but thereafter the proportion of basement Collinson. J.W.. Pennington. D.C. & Kemp. N.R.. l(IS0. outcrop being eroded remained roughly constant (at Stratigraphy and petrology of Permian and Triassic l'luvi;iI < 20%) to the top of the core. Interpretation of the deposits in northern Victoria Land. Antarctica. In: Stinnp. l;, (ed.) Geological investigations in northern Victoria 1,and. modal trends indicates that progressive rather than American Geo~~/~ysicalUnion, Antarctic Research Scric'.~.46. sudden uplift occurred during the period represented 21 1-242. up to c. 450 mbsf, after which the remainder of the Dickinson W.R.. 1970. Interpreting detrital modes of graywackc CRP-3 sequence accumulated in a period of relative and arkose. Jour: of Sedim. Petrol.. 40. 695-707. stability or only slight uplift. Although not Elliot D.H.. 1996. The Hanson Formation: a new stratigi-aphical unit in the Transantarctic Mountains. Antarctic Science, 8. 380- represented by samples in the CRP-3 sequence, it is 394. also evident that a major episode of uplift and erosion Elliot D.H., Fleming T.. Haban M.A. & Siders M.A.. 1995. of the TAM must also have preceded the formation of Petrology and mineralogy of the Kirkpatrick Basalt and I-'crrar the Victoria Land Basin. Dolerite. Mesa Range region. north Victoria Land, Antarctic:!. AGU Antarctic Research Series. 67 103-141. Fitzgerald. P.G., 1994. Thermochronologic constraints on posi- Paleozoic tectonic evolution of the central Tra~isantarctic ACKNOWLEDGEMENTS - I am particularly grateful to Mountains. Antarctica. Tectonics, 13. 818-836. Jim Collinson for Beacon sandstone samples, numerous George A.. 1989. Sand provenance. In: Barrett P.J. (ed.) Antarctic reprints of papers on Beacon stratigraphy and petrology, and Cen~oicHistory from the CIROS-1 Drillhole, McMiirilo Sound. DSIR Bulletin. 245. 159-167. access to unpublished detrital modes of Beacon sandstones; Gunn B.M. & Warren G.. 1962. Geology of Victoria Land between to Bill Hammer and the late Ken Woolfe for additional Mawson and Mulock Glaciers, Antarctica. Bulletin o,f tin' reference samples of Beacon sandstones; to Massimo Geological Survey of New Zealand, 71. 157 pp. Pompilio and Hannes Grobe for help with obtaining CRP-3 Hambrey M. & Wise S.. 1998. 1998. Studies from the Cape samples; and to Stewart Bush and Mike Tabecki for making Roberts Project. Ross Sea. Antarctica, Scientific Report of and staining thin sections from difficult core material. CRP-1. Terra Antartica. 5. 460 p. Finally. my grateful thanks are extended to all involved in Houghton H.F., 1980. Refined techniques for staining plagioclase the Cape Roberts Project. from inception to completion, for and alkali feldspars in thin section. Jour of Sedim Petrol., 50. their invaluable help and constructive discussions during the 629-63 1. course of three drilling seasons and workshops, and to all Huybrechts P,. 1993. Glaciological modelling of the Late Cenozoic East Antarctic ice sheet: stability or dynamism? Geografiska n~enibersof Scott Base and McMurdo Station for their Annaler. 75A, 221-238. unstinting hospitality. Constructive comments on this paper Ingersoll R.V., Bullard T.F., Ford R.L.. Grimm J.P.. Pickle J.D. & by Werner Ehrmann and David Elliot are also greatly Sares S.W., 1984. The effect of grain size on detrital modes: a appreciated. test of the Gazzi-Dickinson point-counting method. Jour. of Sedim. Petrol.. 54. 103-1 16. Isaac M.J.. Chinn T.J., Edbrooke S.W. & Forsyth P.J.. 1996. Geology of the Olympus Range area, southern Victoria Land. Antarctica. Scale 1:50 000. Institute of Geological and Nuclear REFERENCES Sciences geological map 20. 1 sheet and 60 p. Institute of Geological and Nuclear Sciences Ltd., Lower Hutt. New Allibone A.H.. Forsyth P.J.. Sewell R.J.. Turnbull I.M. & Bradshaw. Zealand. M.A.. 1991. Geology of the Thundergut area, southern Victoria Korsch R.J.. 1974. Petrographic comparison of the Taylor and Land. Antarctica. Scale 1:50000. New Zealand Geological Victoria Groups (Devonian to Triassic) in south Victoria Land. Survey Miscellaneous Geological Map 21 (map and notes). Antarctica. New Zealand Journal of Geology and Geophysics. Wellington. New Zealand, Department of Scientific and 17, 523-541. Industrial Research. Laird M.G.. Mansergh G.D. & Chappell J.M.A.. 1971. Geology of Atkins C.B., 2001. Glacial influence from clast features in the central Nimrod Glacier area, Antarctica. New Zealand Oligocene and Miocene strata cored in CRP-2/2A and CRP-3. Journal of Geology and Geophysics. 14, 427-468. McElroy, ('.'l'. & Rose. G.. 19x7. (;colo;;y ol' thc Ik-:icon llrights 212A. Koss SW. /\iuiiirctii.'a 'I'm'ii Aii~iir~icii7. 545-552. arc;t, souiihern Victoria 1,:uiuO. Aniitrciic:~.Si-iulc 1 :50000. A'cit, Stump. K. it, Fit/ycr;tlil. I).(;.. 1002. lipisodic uplil'i ol' the Ze(iliifiii1 (.fcologiccil Survey I\~~,\c(~!!(IIIc~oII.s .Sci'ir.\ Map 21 (mq) 'rtnsaiititrciic Mountitins. (.ico/oi'\. 20. I01 - l (d. ancl notes). Wellington. New /c:tliincl. IX'par11nct11ol Scientific ,F'I 1.illno :. 1,'. c<' S:iiulroni S,. 190S. l'etrogr;tpliy. iiiiiier;il clicmistry and Indiistrial Research. am1 [)rim-iiii~icrof hasrnicnt clasis in Ihc CRP-1 clrillcore Pettijohn I-'.,l..Potter P.E. & Siever R.. 1073. S(iin1 adMIIII/MOIIC. (Victori:~I.;iinl H:isin. Aiut;irciic;l). '//';.I.(//\ii~nr/ic(i. 5. 601-610. Spriti~~rVerlag. Heidelberg. 6 18 p. 'rnhull I.M.. Allihom- A.11.. l-'orsyth P.S. & Heron D.\+).. 1094. Pocknall D.'l'.. Chinn T.J., Sykes R. & Skinner D.N.B.. 1094. Cicology of the Hull Pass - St Johns Ran" curca. southern Geology of the Convoy Range area. soutliern Victoria I.anil, Victoria I.anil. Antarctica. Scale 1:50 000. Institute 01' Antarctica. Scale 1 :50 000. Insiiiiite of Cicological and Nuclear C~cologiciulinn1 Ni~cl~itrSciences gco1ogic;il nicip 14. I sheet Sciences geological map 11. 1 sheet and 36 p. Instiiuie of nut 52 p. Instiiutc of Cleolosiccil am1 Nuclecir Sciences Ltd.. Geological and Nuclear Sciences Ltd.. Lower Huti. Ncw Lower Huli. New 7.calnntl. Zcal:tntl Van der Watcren I-'.M,. Duti:ui T.S.. Van Balen R.T.. Klas W.. Ponipilio M.. Arinienti P. & Tamponi M.. 2001. Petrography. Vcrhcrs A.I,.I,.M.. P;isscliicr S, & Herpers U,. 1999. miiicrnl composition and geochemistry of volcanic and Contras~ingNeogcnc tieniidation histories of difl'erent striictural subvolcanic rocks of CRP-3. Victoria Land Basin. Antarctica. regions in tlie Transantarctic Mouiitains rift flank constrained This volume. by cosiiiogciiic isoiope nie:isttremenis. Glo1)al and Planetary Sandroni S. & Talarico F.. 2001. Petro~raphyand provenance of Ch(in,qc. 23. 145- 172, basement elasts and clast variability in CRP-3 drillcore Wise S.W.. Sr,. Smellie J.1,.. Agiiib F,S.. .larrard R.D. & Krissek (Vicioria Land Basin. Antarctica). This volume. L.A.. 2001. Auiluigcnic smectite clay coats in CRP-3 drillcorc. Smellie J.L.. 1998. Sand grain detrital modes in CRP-1: provenance Victoria Land Basin. Antarctica. as a possible indicator of fluici variations and influence of Miocene eruptions on the marine flow: a progress report. This volume. record in the McMui-do Sound region. Term Antartiro. 5. 579- Wrcnn J.H. & Wchb. P.N.. 1982. Physiographic analysis ancl 587. interpretation of the Ferrar Glacier-Victoria Valley area. Sn~ellieJ.L.. 2000. Erosional history of the Traiisantarctic Antarctica. In: Craclclock C. (eel.) Antarctic gemcience. Mountains deduced from sand "rain detrital modes in CRP- Madison. University of Wisconsin Press. 1091-1099.