© Terra Antartica Publication 2008-2009

Geology of the Nilsen Plateau, Queen Maud Mountains, Transantarctic Mountains

W.E. Long1, D. McLelland2, J.W. Collinson3 & D.H. Elliot3

1Matanuska-Susitna College, University of Alaska Anchorage, Palmer, AK 99645 - USA 2 Present address unknown 3School of Earth Sciences and Byrd Polar Research Center, The Ohio State University, Columbus, Ohio 43210 - USA *Corresponding author ([email protected])

Abstract - The western escarpment of the Nilsen Plateau, Queen Maud Mountains, Antarctica, consists of basement igneous and low-grade metasedimentary and metavolcanic rocks overlain by a near-horizontal Permian-Triassic sedimentary sequence intruded by Jurassic diabase sills. The basement comprises metasedimentary rocks of Neoproterozoic to earliest Cambrian age and Lower Cambrian metavolcanic rocks intruded by Cambrian to Lower Ordovician granitoids. An erosion surface cut across the basement is overlain by 600+ m of strata comprising Lower Permian glacial beds (Scott Glacier Formation) and overlying post-glacial shales (Mackellar Formation) that are succeeded by fluvial-deltaic beds of the Fairchild Formation and the Upper Permian fluvial, coal-bearing Queen Maud Formation. Some of the glacial beds and the post-glacial shales were deposited in a large fresh to brackish water sea with probable marine connections. Deposition initially filled topographic lows on the basement surface. Increased subsidence and a reversal in paleoslope occurred during the deposition of the Queen Maud Formation as the region developed into a foreland basin resulting from tectonic activity along the Panthalassan margin of West Antarctica. The Queen Maud Formation is overlain disconformably by non-carbonaceous, fluvial beds of the Fremouw Formation. Silicified wood, probably Permian Glossopteris, in the lower part of the formation, and a report of Triassic vertebrate fossils, suggests that the Permian-Triassic boundary is within the lower Fremouw Formation. Ferrar diabase sills, cumulatively as much as 500 m in thickness, were intruded into the sedimentary sequence in the Jurassic. Basement rocks are cut by pre-Permian faults and the whole succession is displaced by post-Jurassic, probably Cenozoic, faults.

INTRODUCTION

This paper is based on fieldwork conducted by William E. Long and Douglas McLelland in the 1963-64 field season at the Nilsen Plateau in the Queen Maud Mountains of the Transantarctic Mountains (Fig. 1). A geological sketch map was compiled by Long and McLelland (1964). Subsequently a draft manuscript on the Permian-Triassic Beacon strata was prepared by Long (1965), and the basement geology was described in McLelland’s MS thesis (1967). Both the draft manuscript and the geological sketch map are lodged in The Ohio State University’s Knowledge Bank. There has been no comprehensive survey of the Nilsen Plateau since that time, and therefore this information fills a gap in the regional geology between the Scott Glacier and Shackleton Glacier regions. Like much of the Transantarctic Mountains south of the Byrd Glacier, the Nilsen Plateau exposes a pre-Devonian basement overlain by Permian-Triassic sedimentary strata that have been intruded by Jurassic sills (Fig. 2).

Fig. 1 - Location map for the Nilsen Plateau, Transantarctic Mountains. CTM: central Transantarctic Mountains. NVL: north Victoria Land. SVL: south Victoria Land. ©240 Terra Antartica PublicationLong et al. 2008-2009 METAVOLCANIC ROCKS

Metavolcanic rocks crop out principally in the central part of the map area around “Cougar Canyon” but also at the head of the Blackwall Glacier and at Crack Bluff (Fig. 3A, 3B). The rocks have a relict porphyritic texture with phenocrysts of quartz and feldspar in a very fine-grained matrix. They have been strongly altered and metamorphosed to the greenschist facies, but they were probably rhyodacite to quartz latite in composition. The rocks exhibit deformational textures and have acquired a NW-SE foliation. Metavolcanic rocks, locally, have an igneous (chilled, i.e. intrusive) contact with the quartzose sandstone unit. The volcanic rocks are intruded by the North quartz monzonite. Compositionally they correlate with the Wyatt Formation in the Scott Glacier region (Minshew, 1966, 1967). Fig. 2 - View to the northeast of Lindstrøm Peak (section 2, Fig. 3A). Photograph annotated to show rock units (symbols as in PLUTONIC ROCKS Fig. 3). (Photo: D.H. Elliot). Several plutonic bodies are recognized and BASEMENT ROCKS differentiated. Most constitute parts of a composite batholith, which is well exposed in the central and McLelland (1967) provided descriptions of the southern map area. various basement rock units. His information is summarized first. Subsequent investigations at the North quartz monzonite Nilsen Plateau by Stump (1985) and Encarnación & These plutons or stocks, which crop out in the Grunow (1996) are discussed in a later section along vicinity of Blackwall Glacier, are porphyritic with a with correlation of the units in this general region. medium- to coarse-grained groundmass. K-feldspar phenocrysts are set in a groundmass of quartz, METASEDIMENTARY ROCKS plagioclase, biotite and accessory minerals. Rapakivi A greywacke-shale/slate sequence comprises most texture is present sporadically. Large angular blocks of the basement rock in the northwestern part of the of country rock and mafic inclusions are present. The map area (Fig. 3A) in the vicinity of the Blackwall rocks lack foliation and show only minor flow banding, Glacier. Individual greywacke beds are 0.3-3 m and on this basis are regarded as post-tectonic and (1-9 ft) thick whereas the fine-grained beds are 15 late in the intrusive history. cm (< 6 in) thick. The measured thickness is about 300 m (1,000 ft), but the true stratigraphic thickness Lonely Ridge granodiorite is probably greater given the outcrop distribution and Rocks assigned to this unit crop out at “Lonely the asymmetric folding. Fold axes trend north to Ridge” and adjacent to “Roaring Valley”. They are north-northwest and are approximately horizontal. medium-grained granodiorites comprising quartz, The greywacke-shale lithology occurs as a small plagioclase and microcline together with biotite and outcrop at the southwestern end of “Lonely Ridge” other accessory minerals. The granodiorite shows where it also is present as rafts in the Lonely Ridge cataclastic textures, and locally where the deformation granodiorite. is more intense exhibits a gneissic texture and locally The minor component of the sedimentary strata passes into mylonitic zones, which are up to 10 m is formed of a single outcrop, near the mouth (30 ft) wide. The foliation and mylonite fabrics are of the Blackwall Glacier, of a metasandstone- oriented vertically and trend 040±10°, and small metasiltstone-slate sequence about 60 m (180 ft) mafic inclusions are similarly aligned. thick. The sandstones are quartzose and exhibit cross The Lonely Ridge granodiorite is in fault contact stratification. The sequence clearly differs from the along its northern margin with the Cougar Canyon alternating greywackes and shales, but its relationship quartz monzonite, whereas along its southern margin to those rocks is unknown. it is intruded by apophyses of the South leuco quartz Lithologically the greywacke-shale sequence has monzonite (see below). These apophyses are generally been correlated with the La Gorce Formation in the oriented parallel to the foliation in the Lonely Ridge Scott Glacier region (Minshew, 1966) and the Goldie granodiorite, and large blocks and slabs of the latter Formation in the Beardmore Glacier region (Grindley, are incorporated in the South leuco quartz monzonite 1963). itself. These fabrics and the parallel orientation of © Terra GeologyAntartica of the Nilsen Plateau, PublicationQueen Maud Mountains, Transantarctic 2008-2009 Mountains 241 A

Fig. 3 - Geologic sketch maps of the western escarpment of the Nilsen Plateau. A. Northwestern outcrops. B. Southeastern outcrops. The two maps overlap fractionally. Slightly modified from geologic map of Long and McLelland (1964), and with basement age assignments updated. Names in parentheses are unofficial. The original map names “Black Rock Glacier” and “South Ridge” officially are now, respectively, Blackwall Glacier and Crack Bluff. ©242 Terra Antartica PublicationLong et al. 2008-2009 the metasedimentary rocks suggest the younger North quartz monzonite lacks deformational fabrics South leuco quartz monzonite was intruded along the and hence has been interpreted as post-tectonic. southern contact of the Lonely Ridge granodiorite. McLelland (1967) reported a Neoproterozoic Rb-Sr and an Ordovician K-Ar date for biotite from the Lonely South leuco quartz monzonite Ridge granodiorite From “Windy Ridge” southward, the plutonic rocks More recent field and geochronologic studies on are all assigned to the South leuco quartz monzonite. basement units from the Scott Glacier and elsewhere It is sparsely porphyritic with phenocrysts of K-feldspar have refined the correlations and age assignments. set in a medium- to coarse- grained groundmass Stump (1985) presented additional detail on the of feldspars, quartz, and accessory minerals. The stratified basement rocks at Nilsen Plateau, as well margin of the pluton contains xenoliths of Lonely as data on those units from other locations in this Ridge granodiorite and metasedimentary rocks. sector of the Transantarctic Mountains (see also The pluton intrudes the Lonely Ridge granodiorite Stump, 1995). The greywacke-shale/slate sequence, and is itself cut by aplite and pegmatite dikes. A correlated with the La Gorce Formation and having rock of slightly differing grain size and composition a discordant contact with the Wyatt Formation, has is interpreted as a border phase, and tabular and a minimum thickness of 2000 m at Hanson Spur lens-shaped bodies of similar composition occur in in the Queen Maud Mountains (Stump, 1985). On the Lonely Ridge granodiorite east of “Windy Ridge.” the basis of lithology, the quartzose sandstone unit The pluton exhibits widespread foliation. might be correlated with the Ackerman Formation from the Scott Glacier region (Stump, 1983). La Cougar Canyon quartz monzonite Gorce rocks were deformed and metamorphosed This pluton is similar to the other quartz prior to emplacement of the Wyatt Formation and monzonites, having K-feldspar phenocrysts in a were assigned a Neoproterozoic to Early Cambrian medium- to coarse-grained groundmass of quartz, age (Stump et al., 1986). Recent analysis of detrital feldspars and biotite together with accessory minerals. zircons suggest that the La Gorce Formation is no The rock has a variably developed foliation, defined older than 581 Ma (Stump et al., 2007). An upper age by mineral alignment, which is essentially vertical. limit is provided by Wyatt samples from the La Gorce The pluton, which lacks inclusions and xenoliths, Mountains, which yielded a U/Pb zircon age of 526±2 is in fault contact with metavolcanic rocks along its Ma (Encarnación & Grunow, 1996), or the earliest northern margin and with the South leuco quartz epoch (Fortunian) in the Cambrian (International monzonite at “Lonely Ridge”. Commission on Stratigraphy, 2008). The Wyatt Formation, consisting of both intrusive and extrusive U-1 quartz monzonite phases (Stump, 1985), is overlain conformably, in the Quartz monzonite, compositionally very similar to Scott Glacier region, by the Ackerman Formation which the Cougar Canyon pluton but showing strong foliation, consists of shallow marine strata with interbedded crops out at the south western end of “Lonely Ridge.” volcanic rocks (Stump, 1983). A volcanic unit in the It may be part of the Cougar Canyon pluton but has Ackerman Formation has given a Pb-Pb age of 524±2 been given a separate designation because of the Ma (Encarnación & Grunow, 1996), which, given foliation. It intrudes, and has a chilled contact against, the uncertainty, is indistinguishable from that of the an apophysis of the South leuco quartz monzonite. Wyatt Formation. Stump (1985) reported a sheared It also encloses large rafts of metasedimentary rocks but concordant contact between Wyatt rocks and the that are aligned parallel to the NW-striking steeply cross-bedded sandstone unit in the Blackwall Glacier dipping foliation in the pluton. region (c.f., McLelland, 1967), which is consistent with correlation of those sedimentary rocks with the Ackerman Formation. AGE AND CORRELATION OF BASEMENT UNITS Rb-Sr dates were reported by Faure et al. (1979) The field relations and structural data (McLelland, for basement rocks, but the most precise age data 1967) suggested that the metasedimentary rocks are have been provided by more recent zircon U/Pb the oldest basement rock unit, and the quartzose dating. Zircons from the Lonely Ridge granodiorite sandstone unit was deposited prior to emplacement have yielded a Pb-Pb age of 521±9 Ma and a 206Pb/238U of the metavolcanic rocks. The metasedimentary and age of 527±6 Ma (Encarnación & Grunow, 1996). metavolcanic rocks, correlated respectively with the The Pb-Pb age is similar to an age for a foliated La Gorce and Wyatt formations of the Scott Glacier granitoid from Mt. Zanuck in the Scott Glacier region region, were intruded by plutonic bodies associated (Encarnación & Grunow, 1996). These ages fall in with the Ross orogen. Field data suggested that 1) the the range of zircon SHRIMP ages for Ross intrusive Lonely Ridge granodiorite was emplaced first, prior rocks in the La Gorce Mountains (Vogel et al., 2002), to regional deformation and thus was interpreted as although no information is given for fabrics in the pre-tectonic; 2) the South leuco quartz monzonite dated rocks. The plutons comprising the composite was emplaced syn-tectonically; and 3) the Cougar batholith in the southern Nilsen Plateau, all of which Canyon pluton, which has only minor foliation, was show deformational fabrics, can be assigned an emplaced late in the deformational history. The Early Cambrian age. The undeformed North quartz © Terra GeologyAntartica of the Nilsen Plateau, PublicationQueen Maud Mountains, Transantarctic 2008-2009 Mountains 243 monzonite is post-tectonic, and thus is inferred to be the central Transantarctic Mountains. Late Cambrian to Early Ordovician in age (>480 Ma) Some of the stratigraphic names in the unpublished based on dating of two undeformed granitoids in the report (Long, 1965), based on fieldwork in 1963- Scott Glacier region (van Schmus et al., 1997). 1964, were never formally established, although they have been used in other publications (e.g., Elliot, 1975; Kyle and Schopf, 1982). We are using PERMIAN-TRIASSIC STRATIGRAPHY the stratigraphic names established by Minshew (1966, 1967), who worked in the Scott Glacier region The stratigraphy of the Beacon Group in the including Mount Weaver. Informally named units Transantarctic Mountains south of the Byrd Glacier to from the field report (Long, 1965) are replaced with the Amundsen Glacier is relatively well known from names from the Beardmore Glacier region. Formation the many expeditions that have taken place from the names, ages, correlations, and thicknesses are early 1960’s until present. However, the region south summarized in table 1. Stratigraphic sections are of the Amundsen Glacier, including the Wisconsin shown in figure 4. and Ohio ranges (Horlick Mountains), has had few stratigraphic studies since the early 1960’s. This study, SCOTT GLACIER FORMATION although based on fieldwork from 1963-64, has been reinterpreted to reflect the knowledge gained from Minshew (1966) proposed the name Scott Glacier more recent studies in the Shackleton Glacier and Formation for glacial deposits in the Scott Glacier Beardmore Glacier regions. The Permian-Triassic region. The unit is correlative with the Pagoda sedimentary sequence exposed along the escarpment Formation in the Beardmore and Shackleton Glacier of the Nilsen Plateau bridges the gap between two regions (Coates, 1985). large regions of the central Transantarctic Mountains. In the Nilsen Plateau the Scott Glacier Formation Unquestionably more detailed fieldwork needs to be ranges in thickness from 3 to 34 m (10 to 110 ft). It done, but the Permian-Triassic stratigraphic units is primarily a diamictite composed of poorly sorted, can be correlated through a distance of 1200 km matrix-supported conglomerate interbedded with along the Transantarctic Mountains. The revision of sandstone, siltstone, shale and rhythmite. Resistant the stratigraphic nomenclature in this report helps coarse-grained units form prominent ledges. The to clarify the stratigraphic relationships throughout formation overlies a basement erosional surface

Fig. 4 - Stratigraphic sections on the Nilsen Plateau. Section numbers are the same as in the field report (Long, 1965) and locations are noted on the geologic map (Fig. 3). Thicknesses of stratigraphic units, including diabase sills, were plotted in feet and in greater detail in the field report. Here we have converted thicknesses to meters and extracted sills in order to make it easier to compare formations from one section to another. The sections are hung on the contact between the Fairchild and Queen Maud formations. Letter symbols below each stratigraphic column denote basement units (see Fig. 3) at that location. Along the base of the figure are direct distances between locations of stratigraphic columns. ©244 Terra Antartica PublicationLong et al. 2008-2009 Tab. 1 - Correlations and thicknesses of formations in the central Transantarctic Mountains. Sources: Beardmore Glacier region – Barrett et al. (1986), Collinson et al. (2006); Nilsen Plateau – this paper; Mount Weaver – Minshew (1967); Ohio Range – Long (1965).

Beardmore Gl. Age Nilsen Plateau Mount Weaver Ohio Range Region Falla Fm. Late Triassic (285 m) Early to Middle Fremouw Fm. Fremouw Fm. Triassic1 (620-800 m) (340+ m) Middle to Late Buckley Fm. Queen Maud Fm. Queen Maud Fm. Upper Mt. Glossopteris Fm. Permian (745+ m) (275+ m) (600+ m) (450+ m) Fairchild Fm. Fairchild Fm. U. Weaver Fm. Lower Mt. Glossopteris Fm. (120-200 m) (100-250 m) (90 m) (150 m) Mackellar Fm. Mackellar Fm. L & M Weaver Fm. Discovery Ridge Fm. Early Permian (55-140 m) (0-50 m) (110 m) (165 m) Pagoda Fm. Scott Glacier Fm. Scott Glacier Fm. Buckeye Fm. (126-390 m) (3-34 m) (0-20 m) (225-300 m) 1Basal Fremouw is uppermost Permian locally.

Tab. 2 - Boulder counts.

Metasedimentary Granite Gneiss Metavolcanic rocks Location rocks (%) (%) (%) (%) Section 6 1 0 64 35 “Wildcat Pass” NE side low 47 21 17 15 “Wildcast Pass” SW side 72 0 9 19 “Lonely Ridge” SE corner 77 7 6 10 “Lonely Ridge” 90 3 44 3 “Lonely Ridge” NW corner 60 12 21 7 Section 1 56 6 31 7

with 3 to 10 m (10 to 30 ft) of local relief. At most counts from several localities are shown in table 2. localities the ancient erosion surface is clean and in Large clasts from metavolcanic and metasedimentary some cases polished and grooved (Fig. 5). Boulders rocks were derived from the local basement complex. from local basement rock appear to have moved only Boulders are faceted and angular, and in some cases a short distance. At the base of sections 4 and 7, striated, showing evidence of glacial transport or diamictite, which lies directly on the basement, locally abrasion. Matrix composes 50-65% of the diamictite. fills fissures in basement rock. The best exposure of Thin-sections show poorly sorted grains of angular the entire unit is in section 4. quartz, feldspar, and metamorphic and igneous rock The basal diamictite is composed of medium- to fragments in a matrix of silt and clay. dark-gray silty mudstone with abundant randomly A light-yellow-gray weathering siltstone or scattered pebbles, cobbles and boulders. Boulder mudstone, which is locally laminated, commonly rests on boulder beds (Figs. 6 & 7). Mudstone with or without laminae occurs in contorted beds (Fig. 8) between undisturbed beds, suggesting deformation prior to lithification, probably caused by slumping. Thin diamictite units are locally interbedded with mudstone. Individual rhythmites range in thickness from 1.8 to 4.1 cm (0.7 to 1.6 in). A single rhythmite grades from light-gray silt at the base to medium- dark-gray clay at the top. Unit boundaries are sharp along the contact with coarser material above the clay-sized fraction of the underlying unit. One unusual unit contains numerous angular sand grains scattered in the medium-dark-gray argillaceous, fine part of the rhythmite. These scattered grains are larger than Fig. 5 - Striated pavement on Cambrian basement rock under the the silt at the base of the rhythmite and were likely Lower Permian Scott Glacier Formation. deposited independently and simultaneously with © Terra GeologyAntartica of the Nilsen Plateau, PublicationQueen Maud Mountains, Transantarctic 2008-2009 Mountains 245

Fig. 7. Rhythmite overlain by diamictite. Deposition was subaqueous. A possible interpretation is that the boulder was ice rafted and dropped into water-saturated rhythmite. Tape measure is 45 cm long. Fig. 6 - Interbedded rhythmite and diamictite. Deposition was subaqueous. A possible interpretation is that the fine sediment settled from a distal meltwater plume and that the coarse material marks on the striated pavement at section 12 suggest was ice-rafted. Some of the dropstones penetrate the rhythmite, that the direction of ice motion was 150°. In the suggesting that it was water-saturated at the time. Tape measure same area, a polished surface is preserved on the is 45 cm long. northwest side of a small roche moutonée. In addition to the Pagoda Formation in the the silt and clay fraction of the specimen, perhaps Beardmore Glacier and Shackleton Glacier regions, by melting of floating ice. The uppermost part of the Scott Glacier Formation can be correlated with the the formation is composed of medium-dark-gray Buckeye Formation (Long, 1962) in the Ohio Range mudstone containing sparse randomly scattered 400 km to the east. No direct evidence of the age of pebbles and cobbles. All the above features suggest the Scott Glacier Formation was found in the Nilsen deposition by glacial and subaqueous processes. Plateau, but palynomorph assemblages from the Direction of ice movement appears to have been equivalent Pagoda Formation in the Nimrod Glacier generally from the present Ross Sea and Queen Maud area indicate an Early Permian (Asselian-Tastubian) Range because of the following criteria: 1. Striae and age (Askin, 1998). groove directions on the glacial pavement at the base of section 12 range from 150° to 165°; 2. Possible MACKELLAR FORMATION grooves near the base of section 5 are oriented 115°, and questionable striae on the basement at section 13 The Mackellar Formation was named for Mount strike 110°; 3. Long axes of 13 elongate cobbles and Mackellar in the Queen Alexandra Range by Grindley boulders at the base of section 16 show a preferred (1963). The type section is at the base of Mount orientation of about 130°, with a secondary preference Mackellar along the Tillite Glacier. In the field report at about 90° to the dominant direction, in agreement (Long, 1965), the name “Roaring Formation” was with the striae directions above; 4. Crescent-shaped named after “Roaring Valley” where the unit is well exposed. However, the name “Roaring Valley” has since been formally given to a feature in southern Victoria Land. The lithologic unit is identical to the Mackellar Formation in the Beardmore and Shackleton glacier areas, so we find it unnecessary to propose a new name. The best reference sections in the Nilsen Plateau are 4 and 6. In the Nilsen Plateau the Mackellar ranges in thickness from about 50 m in the northernmost section (16) to about 20 m in the southernmost section (18). Mackellar strata are absent in section 14, which may be located on a local basement high. However, a major sill at this horizon may have complicated that interpretation. The overlying Fairchild Formation is Fig. 8 - Contorted rhythmite. The folds appear to have multiple also thinner in this section (see Fig. 3). noses, probably the result of slumping by water-saturated sediment The dominant lithology for Mackellar strata is in a subaqueous environment. The scale of the folding and the fact that shear planes are not developed argues against overriding very-dark-gray carbonaceous and micaceous shale. by a glacier. Minor lithologies include dark-greenish-gray siltstone, ©246 Terra Antartica PublicationLong et al. 2008-2009 mudstone, and very fine-grained sandstone as well Shackleton Glacier areas, so we find it unnecessary as medium-gray, well-bedded, silty shale, medium- to to propose a new name. The best reference sections light-greenish-gray mudstone with a blocky fracture, in the Nilsen Plateau are 6 and 7. and lenticular light-gray, silty, calcareous beds. Several The formation ranges from 100 to 250 m thick, beds of calcareous rocks in section 5 range from generally thickening to the north. North of Crown light- to dark-gray and contain variable amounts of Mountain on the northwest-facing escarpment clay, silt, and fine sand with calcite fracture fillings. (sections 14 and 16), it ranges from 60 m to 190 m The basal contact with the underlying Scott Glacier thick. The base of the formation is a disconformity with Formation is not clear owing to diabase intrusions evidence of minor local erosion into the underlying along the contact at most localities. Mackellar Formation. In section 14, where the Vertical burrows occur in the upper half of the formation is thinnest, it appears to lie directly on formation in sections 2 and 7. Trails or horizontal the Scott Glacier Formation, although a thick sill has burrows were found on bedding planes in the intruded along this contact. uppermost layers of the formation in sections 10, Most of the formation is fine- to medium-grained 13, and 16. These are similar to those reported by feldspathic sandstone. Bedding ranges from thin to Lindsay (1969), Barrett (1969), Barrett et al. (1986), massive with abundant cross-bedding. Minor beds and Miller and Collinson (1994a) from the Mackellar consist of micaceous shale, siltstone, and mudstone. Formation in the Beardmore Glacier area. Fine-grained beds locally contain ripple marks. The Mackellar Formation can be correlated with the Outcrops are very light gray, light yellowish gray, lower and middle members of the Weaver Formation reddish brown, or dark gray. Thin-section analyses described by Minshew (1966) in the Wisconsin Range show framework grains of quartz, feldspar (10- and the Scott Glacier area and the Discovery Ridge 25%) and minor detrital minerals in an argillaceous, Formation in the Ohio Range (Long, 1962) (see siliceous, micaceous or limonitic matrix. Orthoclase is Tab. 1). The Mackellar Formation and its correlatives the dominant feldspar, suggesting a granite source. have been interpreted as deposits in a large lacustrine Trace amounts of metamorphic minerals indicate a or marine body of water (e.g., Barrett et al, 1986; metamorphic source similar to that of local basement Miller and Collinson, 1994b). rocks. Kyle and Schopf (1982) reported a poorly preserved In the northern part of the escarpment, rounded assemblage of palynomorphs from this formation in limonitic spots make a distinctive pattern on the the Nilsen Plateau. Masood et al. (1994) described outcrop (Fig. 9). Small yellow spots, 6-12 mm (0.25- a similar but more extensive assemblage from the 0.5 in) in diameter, and amoeboid carbonaceous Mackellar Formation in the Beardmore Glacier area. bodies, about 25-50 mm (1-2 in) across, are distinctive Askin (1998) described these palynomorphs as features of the sandstone on northern exposures. representing periglacial vegetation correlated with A southeasterly paleoslope was determined from upper Stage 2 (Evans, 1969) of eastern Australia, 30 paleocurrent measurements of large-scale cross- which is thought to be Early Permian (Asselian- beds and ripple marks throughout the study area. This Tastubian) based on correlations with palynomorph is in agreement with paleocurrent directions from the and marine assemblages from western Australia Beardmore Glacier area (Barrett et al., 1986). (Foster and Waterhouse, 1988). This age is not much different than that reported from the underlying glacial deposits elsewhere in Antarctica. Although the Mackellar Formation does not contain evidence for the presence of extensive glacial ice, the periglacial palynoflora suggests continuing cold, perhaps tundra conditions on land.

FAIRCHILD FORMATION

Barrett (1969) named the Fairchild Formation after Mount Fairchild in the Queen Alexandra Range. The type section is near the base of the north face of Mount Mackellar near the head of the Tillite Glacier. Grindley (1963) originally included this unit in the lower part of the Buckley Coal Measures. Barrett (1969) recognized it as a distinctive sandstone unit with little or no coal. In the Nilsen Plateau field report (Long, 1965) this unit was informally called the “Amundsen Formation,” because it together with Jurassic sills forms prominent cliffs (Fig. 4) facing the Amundsen Glacier. This stratigraphic unit is identical Fig. 9 - Typical ledge-forming sandstone in the Fairchild Formation. to the Fairchild Formation in the Beardmore and The spots on the outcrop are probably limonite concretions. © Terra GeologyAntartica of the Nilsen Plateau, PublicationQueen Maud Mountains, Transantarctic 2008-2009 Mountains 247 The Fairchild Formation can be correlated with the with the majority less than 1 m (3 ft) thick. Coal is more upper member of the Weaver Formation described common in the southern part of the Nilsen Plateau. in the Wisconsin Range and the Scott Glacier region Rank of all samples is low volatile bituminous (ASTM by Minshew (1966) and the lower part of the Mount Standards on Coal and Coke, 1959). Rank increases Glossopteris Formation in the Ohio Range named by upward toward a 300-m-thick (950 ft) sill about 26 Long (1962) (see Tab. 1). The Fairchild Formation m (85 ft) above the highest of three coal beds in the has been interpreted as a braided stream and deltaic upper part of section 13. Thermal metamorphic effects plain deposit that prograded into the Mackellar sea on Antarctic coal from sills have been discussed by (e.g., Collinson et al., 1994). Schopf and Long (1966) and Rose and McElroy (1987), Lower Permian palynomorph assemblages similar who concluded that much of the coal in Antarctica had to those from the underlying Mackellar Formation also attained at least bituminous rank prior to intrusion of occur in the lower Fairchild (“Amundsen”) Formation diabase sills in the Early Jurassic. Subsequent heating (Kyle and Schopf, 1982). These are similar to by intrusions has caused increase in rank to as high assemblages from the base of the Mount Glossopteris as meta-anthracite, and some of the coal has been Formation in the Ohio Range. Other fossils include coked, yet retains a banded appearance. poorly preserved stems and burrows and trails. In the field report (Long, 1965) section 12 is described as a complete Queen Maud section QUEEN MAUD FORMATION underlain, with an intervening diabase sill, by the Fairchild Formation and overlain by the Fremouw This formation was named by Minshew (1966) Formation. This 110-m-thick section is significantly for the Queen Maud Mountains, which extend from thinner than the 275-m-thick incomplete section 5, the Beardmore Glacier to the Reedy Glacier. A type- which is 25 km to the northwest. This anomaly is section was designated on Mount Weaver at the head difficult to explain because the thicknesses of the of the Scott Glacier. underlying Permian Formations are within the normal The Queen Maud Formation is composed of range of variation. Our re-interpretation is that the fining-upward cycles of sandstone, siltstone, sandstone capping section 12 was originally identified mudstone, and coal (Fig. 10). Fine-grained beds are as Fremouw Formation but in fact belongs to the composed of carbonaceous blocky mudstone that Queen Maud Formation. Accepting this interpretation, weathers very light gray. The mudstone is composed no complete section of the Queen Maud Formation of a microcrystalline matrix, hardened by contact is present in the Nilsen Plateau. With existing data, metamorphism from sills, with scattered grains of a true thickness of the Queen Maud Formation in silt-sized quartz and feldspar. Coaly fragments and the Nilsen Plateau cannot be determined. However, other plant material are scattered along bedding thicknesses of the coal measures in other areas are surfaces. Carbonaceous material content ranges considerably greater (Tab. 1). from less than 5 percent in gray shale to more than The lower contact of the Queen Maud Formation is 90 percent in coal. gradational and difficult to identify in some sections. Coal beds are lenticular and up to 2 m (6 ft) thick The underlying Fairchild Formation contains much more sandstone and is more resistant than the overlying coal measures. Several criteria were used to place the contact, which vary from section to section. Doumani and Minshew (1965) identified a quartz-pebble conglomerate at the base of the formation at the type section on Mount Weaver. This unit is widespread and is generally at the base of the coal measures. It occurs in sections 14, 1, 3, 4, and 8 in the Nilsen Plateau as well as at the base of the Buckley Formation in the Beardmore- Shackleton Glacier region (Barrett, 1969). Where the conglomerate was not found, the contact was placed at the lowest occurrence of Glossopteris or fine-grained carbonaceous beds and coal. The Queen Maud Formation is the same lithologic unit as the Buckley Formation in the Beardmore and Shackleton Glacier areas. It is equivalent to the upper part of the Mount Glossopteris Formation in the Ohio Range (Long, 1962)(see Table 1). The Queen Maud Formation and its correlatives were all deposited in a fluvial environment (e.g., Collinson et al., 1994). Fig. 10 - Coal and carbonaceous shale at the top of a fining-upward In the Beardmore Glacier region the coal measures cycle overlain disconformably by channel-form sandstone of the have been divided informally into lower and upper cycle above. members. Sandstone in the lower member is quartz- ©248 Terra Antartica PublicationLong et al. 2008-2009 of conglomerate, overlain by fine-grained beds of greenish-gray mudstone and interbedded siltstone and fine-grained sandstone. Sandstone outcrops are light yellowish gray, forming moderately steep, nearly uniform slopes with ledges of cross-bedded, coarse- grained sandstone and conglomerate. Sandstone units are as much as 50 m (150 ft) thick. Quartz, feldspar, and volcanic and sedimentary rock fragments occur in a poorly cemented clay or silt matrix. Conglomerate lenses include pebbles, cobbles, and boulders of sedimentary, metamorphic, volcanic, and pegmatitic rocks and vein quartz. Sedimentary clasts from the underlying Queen Maud Formation, some containing Glossopteris, occur near the base of the formation. Fine-grained units are composed of light- to medium- greenish-gray siltstone and mudstone with some interbedded sandstone, forming units up to 40 m thick. Fig. 11 - In situ fossil tree stump, probably Glossopteris, in the A northwesterly paleoslope toward Victoria Land Queen Maud Formation. is suggested by 3 measurements of large-scale cross-beds. This direction agrees with abundant rich in contrast to the upper member that is dominated paleocurrent determinations from the Fremouw by volcanic lithic sandstone (Barrett, 1969; Barrett Formation in other areas (Collinson et al., 1994). et al., 1986). This change in provenance occurs Incomplete Fremouw sequences were measured approximately at the same horizon as an almost 180º in sections 11 and 9 at the southern end of the reversal in paleocurrent directions (Isbell, 1990; 1991; escarpment. The contact with the underlying Queen Collinson et al., 1994). No palaeocurrent directions Maud Formation is an erosional disconformity. The and insufficient data were collected from the Queen thickest section of 340 m (11) is less than half of the Maud Formation to identify this change. Paleocurrent 735+ m thickness of the Fremouw Formation in the directions from the overlying Fremouw Formation Shackleton Glacier area (Collinson and Elliot, 1984). are opposite to those of the underlying Fairchild, At the northern end of the study area an estimated indicating that the paleoslope reversal probably 500 m (1500 ft) of Triassic strata appear to crop out occurred in the Nilsen Plateau during the deposition on the slopes above section 16, but the field party of the coal measures. did not reach this area. It is possible that a more Kyle and Schopf (1982) noted that bisaccate complete Fremouw section and the overlying Falla pollen dominate the palynomorph assemblages in Formation occur higher on the Nilsen Plateau. the formation on the Nilsen Plateau. They suggested A Lower Triassic Lystrosaurus Zone assemblage a Late Permian age based on a similarity to Stage was described from the Fremouw Formation in the 5 (Evans, 1969) assemblages in Eastern Australia. Shackleton Glacier area (Kitching et al., 1972). James Farabee et al. (1991) described a similar, but more Kitching and John Ruben, who searched for vertebrate extensive palynomorph assemblage of the same Late Permian age in the Beardmore Glacier area. The abundance of the Glossopteris flora, including leaves and wood, agrees with this general age assignment. In situ fossil stumps are remnants of a Glossopteris forest (Fig. 11).

FREMOUW FORMATION

The Fremouw Formation was named for a fluvial sequence of cyclical sandstone, siltstone and mudstone on Fremouw Peak along the south side of the mouth of the Prebble Glacier in the Queen Alexandra Range (Barrett, 1969; Barrett et al., 1986). Grindley (1963) may have originally included this unit in the lower part of the Falla Formation. The provisional name proposed for this unit in the field report (Long, 1965) was “Thorvald Nilsen Formation” with section 11 as Fig. 12 - Fossil wood in the lower part of the Fremouw Formation the type section. in section 9. At localities in the Shackleton Glacier area Glossopteris In the Nilsen Plateau the Fremouw Formation is wood and leaves occur in the lowest 36 m of the Fremouw Formation composed of cyclical sandstone with minor lenses (Collinson et al., 2006). © Terra GeologyAntartica of the Nilsen Plateau, PublicationQueen Maud Mountains, Transantarctic 2008-2009 Mountains 249 fossils in the Nilsen Plateau in 1970-1971, recovered to a paleolatitude of 40º (Crowell, 1999). In an probable Lystrosaurus and possible labyrinthodont extensive study and review of glacigenic strata in bones (Ruben, personal communication 2008). Fossil the Transantarctic Mountains, Isbell et al. (2008) wood (Fig. 12) and thin, flat leaves or stems that have concluded that deposition occurred along the occur in mudstone near the base of the formation in margin of a much less extensive ice sheet, marginal section 9 are probably uppermost Permian. The basal to a marine environment in a trough-shaped basin. Fremouw along the Shackleton Glacier contains an They identified two transitional facies, “basin-margin” Upper Permian Glossopteris flora (McManus et al., and “basinal.” The glacigenic sequence in the Nilsen 2002), suggesting that the Permian-Triassic boundary Plateau, resting on a basement high, fits into their occurs above the base of the Fremouw Formation at “basin-margin” facies. some localities (Collinson et al., 2006). Aitchison et al. (1988) interpreted the correlative Buckeye Formation in the Ohio Range as grading REGIONAL RELATIONSHIPS OF THE PERMIAN- upward from lodgement till to glacimarine deposits. TRIASSIC STRATIGRAPHY However, Woodward and Dowdeswell (1994) pointed out that the grooves illustrated in figure 18.10 of The Permian-Triassic stratigraphic sequence in the Aitchison et al. (1988) to support glacier abrasion Nilsen Plateau is similar to that which occurs for 1,100 end abruptly, suggesting that they formed by iceberg km along the Ross Sea sector of the Transantarctic scour. An occurrence of marine acritarchs (Kemp, Mountains from the Byrd Glacier to the Ohio Range. 1975) supports the glacimarine hypothesis. The The lower part comprises Lower Permian glacial equivalent Whiteout Conglomerate in the northern diamictite, post-glacial lacustrine/marine black shale, Ellsworth Mountains and the Gale Mudstone in the and fluvial-deltaic siltstone and sandstone. This Pensacola Mountains are also regarded as probably part of the sequence was deposited in a relatively marine (Frakes et al.,1971). short time, within the span of the Parasaccites The upper contact of the Scott Glacier Formation Assemblage Zone (Kyle, 1977; Kyle and Schopf, in the Nilsen Plateau is obscure because of an 1982; Masood et al., 1994) representing a periglacial intervening diabase sill and poor exposures. The (cold) environment (Askin, 1998). The upper part of Pagoda-Mackellar contact in the Beardmore Glacier the sequence comprises Middle to Upper Permian region is sharp or gradational within a meter where cyclical fluvial sandstone, carbonaceous shale and dropstones disappear, marking the end of local coal with an abundant Glossopteris flora overlain by glacigenic conditions (Miller and Collinson, 1994b). Lower Triassic cyclical fluvial sandstone and green- The disappearance of dropstones is just as abrupt gray mudstone containing vertebrate bones of the in the Ohio Range (Long, 1965) and Ellsworth Lystrosaurus Zone. Mountains (Collinson et al., 1992). Isbell et al. (1997) The stratigraphic sections in figure 3 are hung at interpreted the base of the Mackellar Formation as a the base of the coal measures. This horizon, marking regional flooding surface or timeline marking the end the change from strata with low organic content of Gondwanan glaciation. Receding ice left a broad to strata with high organic content including coal, outwash plain that quickly flooded as post-glacial probably represents a major climate change and sea level rose. therefore a timeline across the region. Differences in The Mackellar Formation in the Nilsen Plateau is thicknesses of units below this horizon suggest that lithologically similar, but generally thinner than in the local paleorelief measured in tens of meters separated Beardmore Glacier area. Miller and Collinson (1994b) Cambrian basement rocks and Permian strata. Isbell interpreted siltstone and fine-grained sandstone beds et al. (1997) have reconstructed regional pre-glacial as distal turbidites deposited in prograding channel- topography using the top of glacigenic deposits and overbank systems. These sediments were derived the base of post-glacial black shale to show that from winnowing of fines from a prograding outwash considerable regional relief existed on the basement plain. The Mackellar Formation appears to have been nonconformity. Regional differences in thickness deposited under freshwater to brackish conditions. suggested two major topographic basins, one from The turbidites probably represented underflow of the Byrd Glacier to the Amundsen Glacier and the cold water perhaps supplied by streams crossing a other from the Scott Glacier to the Ohio Range (Isbell tundra-like landscape. Carbon/sulfur ratios are high, et al., 2008). The Nilsen Plateau lies on a basement also indicative of fresh water. topographic high that separated these two basins. The Mackellar Formation has been traced along Lower Permian glacial deposits in the Nilsen the Transantarctic Mountains from the Beardmore Plateau are similar to those in the Beardmore and Glacier region to Mount Blackburn, Scott Glacier area Shackleton Glacier areas, but much thinner. This led (Coates, 1985). In the Ohio Range, the Discovery Coates (1985) to hypothesize that the Amundsen-Scott Ridge Formation, like the underlying Buckeye Glacier region was a basement high. These diamictites Formation, is likely to have been marginal marine have been traditionally identified as glacial terrestrial or marine (Aitchison et al., 1988). An abundant in origin (Lindsay, 1970; Coates, 1985, Miller, 1989), and diverse trace fossil assemblage in the Polarstar deposited beneath a large ice sheet that covered Formation in the Ellsworth Mountains suggests a much of the southern Gondwana supercontinent marine origin (Collinson et al., 1992). This seaway, ©250 Terra Antartica PublicationLong et al. 2008-2009 which appears to have extended from the central similar to that in the Beardmore-Shackleton Glacier Transantarctic Mountains to the Ellsworth Mountains region. Deposition was by low-sinuosity streams on and possibly into the southern Africa and Brazil parts an aggrading floodplain in a foreland basin (Collinson of Gondwana (Miller and Collinson, 1994b). If the et al., 1994). The basal contact in the Nilsen Plateau Nilsen Plateau area was a topographic high during and elsewhere is a disconformity with a meter or two the Early Permian, it may have served as a barrier of local relief. The change from gray carbonaceous that restricted the circulation of marine water from shale in the coal measures to the green-gray fine- one basin to another. grained beds in the Fremouw was most likely related The Mackellar seaway became shallower to climate warming and drying at the end of the as the fluvial-deltaic sediments of the Fairchild Permian (Retallack and Krull, 1999; Collinson et al., Formation prograded across the basin. The Fairchild 2006). Regionally the Permian-Triassic boundary is at is lithologically similar throughout the central the base or within the lowermost Fremouw Formation Transantarctic Mountains. Paleocurrent directions (Collinson et al., 2006). The boundary is difficult in the Nilsen Plateau are southeasterly toward the to identify at any one horizon. It is typically in an Weddell Sea, which is in general agreement with unfossiliferous sequence between carbonaceous beds those in the Beardmore Glacier region (Barrett et al., with the Glossopteris flora and greenish-gray beds 1986). The equivalent upper member of the Weaver with the Lystrosaurus fauna. In the Nilsen Plateau Formation at Mount Weaver contains an abundance the boundary is somewhere above the occurrence of of burrows, suggesting a possible marine influence. fossil wood and plant material near the base of the Bradshaw et al. (1984) interpreted the equivalent Fremouw in section 9. lower part of the Mount Glossopteris Formation in Regionally, Triassic streams flowed off the orogenic the Ohio Range as marginal marine or marine based belt in West Antarctica and along the axis of the on trace fossils and other sedimentary features. foreland basin toward Victoria Land (Collinson et al., The middle part of the Polarstar Formation in the 1994). The few observations of paleocurrent directions Ellsworth Mountains, which contains a diverse trace in the Nilsen Plateau section agree with this. Volcanic fossil assemblage, was also considered to be marine detritus occurs in lower Fremouw samples from the (Collinson et al., 1992). This sequence consists of Nilsen Plateau and the Shackleton Glacier areas, but multiple coarsening upward sequences interpreted is absent downstream in the Beardmore Glacier area as prodeltaic and deltaic deposits. In summary, the (Vavra et al., 1984). Mackellar-Fairchild basin became increasingly marine toward the present Weddell Sea. The Queen Maud Formation in the Nilsen Plateau FERRAR DOLERITE is similar to the Buckley Formation in the Beardmore Glacier area, which has been interpreted as Diabase sills (McLelland, 1967) are conspicuous in representing low-sinuosity streams on an aggrading the stratigraphic section and thin dikes are scattered floodplain (Isbell, 1991). Paleocurrent data from the widely. As many as five major sills may be present. middle of the Buckley Formation show that stream Most are between 45 and 120 m (150 to 400 ft) directions reversed from toward the Weddell Sea to thick but individually may exceed 300 m (1000 ft) toward Victoria Land. This change in paleoslope also in thickness (Fig. 3A, Section 15). The original marked a new and major influx of volcanic detritus cumulative thickness of sills was probably in excess of (Isbell, 1990). These changes occurred somewhere 500 m. Mineralogically they comprise two pyroxenes, within the Queen Maud Formation, but sections are mainly augite and orthopyroxene, plagioclase, and in incomplete and too few samples are available to some sills minor olivine. Micropegmatite is present, pinpoint a horizon. The reversal in paleoslope has particularly in the upper parts of the sills. These sills been attributed to mountain building in West Antarctica and dikes are part of the Lower Jurassic Ferrar Large and the progradation of a low-gradient alluvial fan Igneous Province (Elliot & Fleming, 2008). into the basin (Isbell, 1991). This also reflects the initiation of a foreland basin and an increased rate of subsidence. STRUCTURE The Nilsen Plateau is the last locality in the Transantarctic Mountains toward the Weddell Sea Two episodes of faulting are recorded along where Triassic rocks are known to cap the Permian the Nilsen Plateau escarpment (McLelland, 1967). sequence. Rather than the low sinuosity braided Basement rocks are cut by faults, most conspicuously streams of the Queen Maud Formation, the coal along the northern contact of the Cougar Canyon measures of the Mount Glossopteris Formation in quartz monzonite (Fig. 3A). Shear zones and fabrics the Ohio Range and the upper Polarstar Formation within the plutonic rocks that have similar orientation in the Ellsworth Mountains were deposited in a delta (approximately NW-SE) suggest this deformation and and delta plain complex prograding into a marine the basement faults were associated with the Early environment (Bradshaw et al., 1984; Collinson et Paleozoic Ross orogen. al., 1992). The second episode of faulting, post-Jurassic in The Fremouw Formation in the Nilsen Plateau is age, is recorded by offsets of the basement rocks and © Terra GeologyAntartica of the Nilsen Plateau, PublicationQueen Maud Mountains, Transantarctic 2008-2009 Mountains 251

Fig. 13 - View from the west of the first bluff northwest of Crack Bluff, annotated to show inferred structural features. Basement rock is the South Leuco Quartz Monzonite. Beacon beds cap the down-dropped fault sliver at the left of the photo. Tilted Beacon strata are in contact with the basement granitoid in the center of the photo; this is also evident on USGS photo TMA854 F-31 129. At A, Beacon strata (in the photograph) appear to have a northeasterly dip, whereas at B the strata appear to be horizontal. The faulting and tilting of Beacon beds (left and center of photo) are post-Permian (possibly post-Jurassic) in age. Relationships between beds at A and B are uncertain. (Photo: D.H. Elliot).

overlying strata in the southern part of the map area documented, they are normal (e.g., Katz, 1982). The (Fig. 3B). Mapped faults have a predominant E-W presence of reverse faults is unusual in an extensional orientation and are high-angle; locally there are N-S setting, however in the Queen Alexandra Range a faults. Normal faults are down to the south. Reverse monocline records reverse motion in the Jurassic, faults place basement rocks against Permian strata which was related to the emplacement of Ferrar rocks which have been tilted and overturned (McLelland, in a rift system associated with Gondwana break-up 1967, Fig. 11) or folded and disrupted (Long, 1965, (Elliot & Larsen, 1993). In major rift systems, such Fig. 23). Several long straight cliffs in the southern as those in Africa, reverse faults may occur in transfer part of the map area have faces covered by quartz- zones (Rosendahl, 1987). The reverse faults at the cemented breccia, suggesting the presence of a Nilsen Plateau may also be associated with Early major fault system parallel to the Nilsen Plateau Jurassic rifting rather than being related to uplift of escarpment. Stump (1985) noted a horizontal breccia the Transantarctic Mountains. zone and deformed Beacon strata at Crack Bluff, and interpreted the structure as part of a post-Beacon monocline (down to the northeast). The northwest SUMMARY point of the un-named bluff (Fig. 13) forming the first major outcrop northwest of Crack Bluff is Stratified sedimentary and volcanic rocks in the displaced by a north-south fault, down to the west; basement are correlative with well-established units from photography, a thin section of horizontal(?) in the Queen Maud Mountains-Scott Glacier region. Beacon strata caps that fault sliver. The contact Plutonic rocks intrusive into those strata are part between basement and Beacon rocks immediately of the extensive Ross orogen granitoids (Granite east of that locality appears, on photography, to be Harbour Intrusive Suite) of Cambrian to earliest faulted, with Beacon beds tilted and dipping to the Ordovician age. east (this may be the site of the reverse faulting The Permian-Triassic stratigraphic sequence in illustrated in McLelland’s fig. 11). Further, Beacon the Nilsen Plateau bridges the gap between the strata on the principal, southwest-facing, outcrop of Queen Maud Mountains and the Horlick Mountains. that bluff, appear to be dipping northeasterly and to Although stratigraphic names change across the be separated by a discontinuity from topographically region, reflecting facies changes and the work of higher and apparently horizontal beds. Although the separate field parties, major stratigraphic units can discontinuity might be of tectonic origin, it is possible be correlated. The Permian section in the Nilsen that the tilted beds form a rotated slide block similar Plateau reflects a transition from a mainly terrestrial to toreva blocks noted in the Queen Alexandra Range sequence to the north to one with greater marine (Elliot, 2002). influence to the south. The exact position of the Post-Jurassic faults relate to the uplift and Permian-Triassic boundary in the Nilsen Plateau section segmentation of the Transantarctic Mountains has not been determined, but as in the Queen Maud that began in the Scott Glacier region in the early Mountains, non-carbonaceous fluvial sediments with Cretaceous (Fitzgerald & Stump, 1997). The overall tetrapod fossils of the Lystrosaurus Zone represent pattern of inferred faults is illustrated in Davis and the Triassic. The Nilsen Plateau is the southernmost Blankenship (2005). Where motion on faults is known occurrence of Triassic rocks. ©252 Terra Antartica PublicationLong et al. 2008-2009 Acknowledgements - The National Science Foundation, doi:10.1130/2005.MCH093. Office of Antarctic Programs (now the Office of Polar Doumani, G.A. & Minshew, V.H., 1965. General geology of the Programs) funded this investigation. The U.S. Navy provided Mount Weaver area, Queen Maud Mountains, Antarctica. In: logistic support and transportation; Air Development Hadley, J.B. (ed.), Geology and Paleontology of the Antarctic. Washington, D.C., Amer. Geophys. Union, Antarctic Res. Series, Squadron 6 supported the fieldwork with critically important 6, 127-139. air transport. Courtney Skinner, geological field assistant, Elliot, D.H., 1975. Gondwana basins in Antarctica. In: Campbell, Larry M. Rychener, laboratory assistant, and Warren Brussee, K.S.W. (ed.), Gondwana Geology. Canberra, Australia, Australian draftsman, greatly aided this report. The late Dr. J.M. National. University Press, 493-536. Schopf, U.S. Geological Survey, provided paleobotanical and Elliot, D.H., 2002. Toreva blocks in the Transantarctic Mountains: stratigraphic advice. Dr. J. Isbell gave invaluable help and implications for Cenozoic paleoclimates. Geol. Soc. Amer., advice on current interpretation of glacial deposits. Reviews Abstracts with Programs, 34(6), 239. by E. Stump and F. Talarico are greatly appreciated. Elliot, D.H. & Larsen, D., 1993. Mesozoic volcanism in the Transantarctic Mountains: Depositional environment and Byrd Polar Research Center contribution number 1393. tectonic setting. In: Findlay, R.H., Banks, M.R., Veevers, J.J. & Unrug, R. (eds), Gondwana 8 - Assembly, Evolution, and Dispersal. Rotterdam, A.A. Balkema, 397-410. REFERENCES Elliot, D.H. & Fleming, T.H., 2008. Physical volcanology and geological relationships of the Jurassic Ferrar Large Igneous Aitchison, J.C., Bradshaw, M.A. & Newman, J., 1988. Lithofacies Province, Antarctica. J. Volc. Geotherm. 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