Reconnaissance Geology of Lower Taylor Valley, Victoria Land, Antarctica

E. E. ANGINO M. D. TURNER E. J. ZELLER RECONNAISSANCE GEOLOGY OF LOWER TAYLOR VALLEY, VICTORIA LAND, ANTARCTICA Abstract: The central part of Lower Taylor Valley Four systems of lamprophync dikes cut both the consists of a thick, nearly vertical sequence of granitic and metasedimentary rocks, whereas sev- faulted metasedimentary rocks in sharp contact on eral smaller pegmatitic and aphtic dikes are largely the west with banded granitic rock. An Ar40/K40 restricted to the granitic rocks. A sample collected date of 500 + 20 m.y. obtained on biotite separated from one of the lamprophyres gave an Ar40/K4() from carbonate material indicates an Upper date of 458 + 20 m.y. Cambrian-Lower Ordovician period of orogeny. Much of Taylor Valley is blanketed by morainal A monzonitic gneiss sample from the west flank of material deposited by Taylor Glacier and its Mt. Nussbaum yielded an Ar40/K40 age of 425 tributaries. + 20 m.v. Although few meteorological observations Introduction have been made, and these only in summer, it is Geological investigation in Taylor Valley, probable that the climate is typical of coastal re- one of a series of major east-west valleys in gions of Antarctica. Surface temperatures of 20° South Victoria Land (Figs. 1,2), were carried C have been recorded on clear days, and meltwa- out by the writers during the field seasons of ter is surprisingly abundant in midsummer. Small 1959-1961 to provide a framework for thermo- glacial streams have cut gullies to the valley luminescence studies. Much of the detail shown floor, or to small basins behind terminal moraines, on Figures 3 and 4 was refined from field data where the water accumulates and freezes, to be by photogeology. removed later through sublimation and evapo- Earlier workers (David and Priestley, 1914; ration. Some of the deeper lakes, such as Smith and Debenham, 1921; and others) have Bonney, are perennially ice-covered but re- described the geology and geomorphology of main liquid below, despite the very low average this area. Hamilton and Hayes (1959) studied annual temperatures (about —20° C). Further regional structure from McMurdo Sound to details of the unusual limnological features of the head of the Taylor Glacier, and Pewe lakes Bonney and Vanda (Wright Valley) are (1960) has discussed the glacial history of the described by Angino and Armitage (in press). McMurdo region. The authors have also re- There is almost no vegetation or animal life ported on other geologic work in this general in the area. A small amount of lichens and a area (Angino, and others, 1960; Zeller and few insects and mites can be found with per- others, 1961). sistant search. In summer, the ponds and the shallow areas of the larger lakes support some Regional Setting algae accompanied by sparse micrometazoa. The Taylor Valley area is dominated by the 4000-m peaks of the Royal Society Range. The Metamorphic and Igneous Rocf^s valley itself is a nearly 1500-m gorge in the The central part of Taylor Valley is under- vicinity of Mt. Nussbaum and Lake Bonney lain by a series of near-vertical, north-north- but widens eastwardly among the more sub- west-striking metasedimentary rocks of the dued mountains near the sea (Figs. 3, 4). The Ross System (Harrington, 1958) which seem to upper part of the valley is occupied by the have been deposited in the major north-south- . Taylor Glacier, an active outlet glacier drain- trending Ross geosyncline (Harrington, 1958). ing eastwardly from the Polar Ice Cap. Numer- Over 900 m of these units, first described by ous large alpine glaciers flow into the valley Ferrar (1907), were mapped in the vicinity of from the surrounding mountains. Mt. Nussbaum and are here named the Mt. Geological Society of America Bulletin, v. 73, p. 1553-1562, 4 figs., December 1962 1553 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/73/12/1553/3442267/i0016-7606-73-12-1553.pdf by guest on 02 October 2021 1554 ANGINO AND OTHERS—LOWER TAYLOR VALLEY, ANTARCTICA LONGITUDE 90° WEST 65° QJ UJ ROSS SEA ROSS ICE SHELF SOUTH ^._- NAF McMURDO ^ POLE \J> r' M\C i-a \ V GEORGE V COAST AOELIE COAST Kilometers 0 900 0 '«« *~~ ™ LONGITUDE 90° EAST Figure 1. Map of part of Antarctic continent showing major land areas Nussbaum sequence of the Ross System. Indi- and argillites, with few carbonates, are more vidual marble beds up to 60 m thick were prevalent in northern Victoria Land (Smith noted. Associated schists and quartzites are and Priestley, 1921, p. 163; Harrington, 1958). thinner but more numerous, with iron-stained Smith and Debenham (1921) and others be- quartzite forming the summit of Mt. Nuss- lieved the granitic masses in the McMurdo baum. West of the metasedimentary rocks and Sound area to be younger than the sedimentary in sharp contact with them is a mass of light- rocks, and that the sedimentary rocks were gray granitic rock of the Tucker Granodiorite probably metamorphosed by the intruding type (Harrington, 1958), with parallel banding plutons. Some substantiation for this view is that suggests relict bedding. Similar rock indicated by an Ar40/K40 date of 500 m.y. + 20 types are found in the McMurdo Sound area m.y. obtained from biotite separated from and southward to the Beardmore region. In marble collected at Marble Point and by a 458 contrast, metamorphic rocks derived from m.y. + 20 m.y. date obtained from one of the deeper-water sediments, such as graywackes dikes exposed in Taylor Valley. This suggests Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/73/12/1553/3442267/i0016-7606-73-12-1553.pdf by guest on 02 October 2021 SHORT NOTES 1555 that the marble in the McMurdo Sound region northeast-striking dike series. Later, these were may be the metamorphosed equivalent of the cut by the north-northwest system. Similar Cambrian Archaeocyathus limestone farther dike systems, observed in both Victoria and south in the Beadmore region (David and Wright valleys, have been described by Webb Priestley, 1914, p. 235-243; Skeats, 1916, and McKelvey (1959, p. 133-134) and Allen p. 196-198). The dates supplement a 500-m.y. and Gibson (1962, p. 237-238). age determination obtained by Goldich and others (1958; personal communication) from Structure paragneiss collected at Gneiss Point, McMurdo Field work, supplemented by photogeologic Sound, Antarctica. The authors believe that study, suggests the presence of a major strike- Figure 2. Index map of part of western coast of McMurdo Sound, South Victoria Land, Antarctica the same deformational episode is indicated by slip fault following the axis of the valley to the these age data. A later metamorphic episode north of Mt. Nussbaum. Relative movement may be indicated by an Ar40/K40 age date of on the north side of the fault is to the east and 425 m.y. + 20 m.y. obtained from biotite upward. On the basis of the tentative presence separated from monzonitic gneiss collected on of the Mt. Nussbaum sequence in the drainage the west slope of Mt. Nussbaum. Metamorphic basin of Canada Glacier, the writers believe effects alone, however, may account for the that a lateral movement of the order of several age differentials. kilometers took place. The Mt. Nussbaum The bedrock of the Lower Taylor Valley sequence (?) reappears in the Cape Bernacchi- from Lake Bonney to McMurdo Sound, par- Marble Point area, 3(MO km northeast along ticularly at Mt. Nussbaum, is cut by four the fault line. The similarity of these units lamprophyric dike systems striking east, east- extends to gross appearance, chemical composi- northeast, north-northeast, and north-north- tion, mineralogy, and Ar40/K40 ages. Time of west, although the east-northeast-striking dikes movement on this fault could only be fixed as may be auxiliaries of the east-west system. postdating deposition of the Mt. Nussbaum Light pegmatitic veins cut the granitic rocks, sequence. Physiographic evidence, however, but only rarely the metasedimentary rocks. A suggests that the latest movement may have tentative order of emplacement, worked out in been Tertiary or, possibly, Pleistocene. the field, is that the north-northeast system, Examination of the available maps of the injected first, was cut by the east- and east- region, in conjunction with our limited knowl- Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/73/12/1553/3442267/i0016-7606-73-12-1553.pdf by guest on 02 October 2021 1556 ANGINO AND OTHERS—LOWER TAYLOR VALLEY, ANTARCTICA edge of the geology, suggests that the Ferrar rock amounts to 60-90 cm, in comparison with Glacier may also follow a fault valley. The essentially none in the zone below. The upper Kukri Hills and the two adjacent valleys may 90 m (vertically) of the slope is covered by be a block which, moving as a unit, was dis- considerable bedrock talus. Some morainal placed several kilometers westward. The large material is present; however, this, talus, and east-west faults would be part of the system of bedrock are all deeply weathered, with irregu- major transverse faults in the area suggested lar surface features produced by wind erosion. by Priestley and David (1912). These field data indicate at least three major pulses of the Taylor Glacier, all appreciably Volcanism later than the major glaciations that overrode Relatively small volcanic eruptions took Mt. Nussbaum and the bench to the south. place during the Pleistocene in Taylor Valley However, the obvious differences in the degree and adjacent areas. West and southwest of Mt. of weathering and erosion of the rocks of the Nussbaum some of the later moraines are three drift levels do not necessarily prove three covered by cones and small flows, with many separate glacial advances, separated by minor volcanic bombs visible in the immediate retreats to points west of Lake Bonney.

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