Palynomorphs from the SiriusFormation, Dominion Range,

Antarctica

R.A. AsKIN

Geology DepartmentColorado School of Mint'sGolden, Colorado 80401

V. MARKGRAF

INSTAARUniversity of Colorado

RiilI'; (elevido S03()

A low-diversity assemblage of fossil palynomorphs has beenrecovered from the Sirius Formation in the Dominion Range,Antarctica. Associated recycled marine diatoms are believed tobe of Pliocene age (2.5 to 5 million years, Harwood, AntarcticJournal, this issue; or 3.1 to 2.5 and 6.6 to 4.2 million years,Harwood 1985), suggesting the existence of a species-poor landvegetation during the late Pliocene (younger than 3.1 to 2.5million years) in this part of Antarctica.

Six rock samples were provided for palynological study.These were collected by Webb et al. (1987) from Oliver Bluffs,Dominion Range. Sample 1 was from unit 4, section 5; andsamples 2 to 6 from unit 2, section 8. Samples 2, 5, and 6 wereassociated with fossil wood, and 2 and 4 with foliage remains(Webb et al. 1987).

Organic material recovered in palynological preparations ofthese six samples consists almost entirely of parenchymatousand woody tissue. The abundant parenchymatous tissue sug-gests herbaceous vegetation (Upchurch, personal communica-tion). Palynomorphs are sparse (samples 1-3), to extremely rare(Samples 4-6). The dominant type of palynomorph comprisessmooth, thin-walled bodies, some differentially thickened (seefigure, block 4), which are believed to be algal in origin. Some ofthese nondescript palynomorphs may be fungal. Hall (1975)illustrated similar algal "spheres" from core material collectedfrom Dry Valley Drilling Project (DVDP) 4, (Lake Vanda), WrightValley.

Fossil pollen grains of Nothofagus (fusca group) are relativelycommom in these samples. (see figure, block 3.) They are thinand somewhat corroded, however, and are all probably re-cycled from older Tertiary deposits where such forms wereapparently abundant. Harwood (1983; Antarctic Journal, thisissue) and Webb et al. (1983, 1984) have noted the presence ofolder Tertiary recycled diatoms, foraminifera and other micro-fossils in Sirius Formation samples from several localities. Rarerecycled bisaccate pollen, more characteristic of but not re-stricted to the Mesozoic, also occur in the Oliver Bluffs samples.

Specimens of a thick-walled microreticulate tricolp(or)ate totetracolp(or)ate angiosperm pollen species (see figure, blocks 2and 5) occur in samples 1-4 and are relatively common in 2 and3. These may be assignable to plants of the families Poly-gonaceae or Labiatae. The predominance of this species andpresence of its tetrads in sample 2, suggests short distance or notransport and therefore local derivation. Some specimens re-semble pollen referred to as Tricolpites sp. 2 by Truswell (1983),found recycled into Recent seafloor sediments of the Ross Sea.

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Photomicrographs of palynomorphs from the Sirius Formation, Do-minion Range. Magnification x 900. 1. ?Dacrydium sp., sample 2; 2.Tetrad of ?Polygonaceae/Labiatae pollen, sample 2; 3. Nothofagussp. (fusca group), sample 2; 4. ?Alga, sample 2; 5. Pollen of ?Poly-gonaceae/Labiatae, sample 1.

Other palynomorphs recovered include rare podocarpaceousconifer pollen (?Dacrydium, see figure, block 1) in samples I and2; rare indeterminate angiosperm pollen (possibly two species)in samples 2 and 3; and rare palynomorphs of uncertain origin(inaperturate, with two-layered wall) in samples 2, 3, and 4.

The sampled intervals represent lacustrine-fluvial sedimentsinterbedded with glacially derived diamictites. These sedi-ments are believed to represent interglacials (units 2 and 4),while units I and 3 represent glacial episodes (Webb et al.(Antarctic Journal, this issue). The sampled rock units includeabundant wood, some of which is coniferous (Cariquist, per-sonal communication), conifer-derived resin and foliage includ-ing possible coniferous material (Snider, personal communica-tion). The dwarf scale-leaved conifers of the possibly similar"Pilgerodendron uvifera Dwarf-Heath" and "Creeping Dacrydiufnfonckii Heath" communities described from the present-dayMagellanic Tundra (Pisano 1983) produce little pollen, possiblyexplaining the rarity of conifer pollen in these samples.

The presumed in-place palynomorphs, together with otherplant material, reflect an extremely species-poor and probablyspecialized flora which, assuming diatom ages are correct (thepalynomorphs are not age-diagnostic), survived in the Transan-tarctic Mountains until the Late Pliocene. The presence of pal-eosols with root remains, plus foliage and abundant wood,support the contention that at least some of the palynomorphswere produced by plants growing while these Pliocene per-iglacial/interglacial lacustrine and fluvial sediments were ac-cumulating. The occurrence of plants in the Dominion Range asrecently as approximately 2.5 million years suggests thatpockets of vegetation survived in unglaciated areas ("refugia")of the Transantarctic Mountains during Miocene and middlePliocene glacial episodes, and also presupposes adequate melt-

34 ANTARCTIC JOURNAL

water or moisture was available for plant survival during theseepisodes. The apparently low number of surviving speciesprobably represents the last vestiges of land-plant vegetation inAntarctica before the Pleistocene to present-day essentiallynonvegetated scenario.

This palynological research was supported by National Sci-ence Foundation grant DPI 83-14186.

References

Carlquist, S. 1986. Personal communication.Hall, S.A. 1975. Palynologic investigation of Quaternary sediment from

Lake Vanda. Antarctic Journal of the U.S., 10(4), 173-174.Harwood, D.M. 1983. Diatoms from the Sirius Formation, Transan-

tarctic Mountains. Antarctic Journal of the U.S., 18(5), 98-100.Harwood, D.M. 1985. Late Neogene climatic fluctuations in the south-

ern high-latitudes: Implications of a warm Pliocene and deglaciatedAntarctic continent. South African Journal of Science, 81, 239-241.

Harwood, D.M. 1986. Recycled siliceous microfossils from the SiriusFormation. Antarctic Journal of the U.S., 21(5).

Pisano, E. 1983. The Magellanic tundra complex. In A.J.P. Gore (Ed.),Mire: Swamp hog, fen, and moor—Regional studies, ecosystems of theworld, 413,Amsterdam: Elsevier.

Snider, J. 1986. Personal communication.Truswell, E.M. 1983. Recycled Cretaceous and Tertiary pollen and spo-

res in Antarctic marine sediments: A catalogue. Palaeontographica,186(4-6)B, 121-174.

Upchurch, G. 1986. Personal communication.Webb, P-N., D.M. Harwood, B.C. McKelvey, J.H. Mercer, and L.D.

Stott. 1983. Late Neogene and older Cenozoic microfossils in highelevation deposits of the Transantarctic Mountains: Evidence for ma-rine sedimentation and ice volume variation on the east antarcticcraton. Antarctic Journal of the U.S., 18(5), 96-97.

Webb, P-N., D.M. Harwood, B.C. McKelvey, and L.D. Stott. 1984.Cenozoic marine sedimentation and ice-volume variation on the EastAntarctic craton. Geology, 12, 287-291.

Webb, P-N., D.M. Harwood, B.C. McKelvey, M.C.G. Mabin, and J.H.Mercer. 1987. Sirius Formation of the Beardmore Glacier region. Ant-arctic Journal of the U.S.

Structural geological investigationsin the

Nimrod Glacier area

E. STUMP and D.C. EDGERTON

Department of GeologyArizona State University

Tempe, Arizona 85287

R.J. KORSCH

Bureau of Mineral Resources, Geology, and GeophysicsCanberra, AC. T. 2601, Australia

A folded unconformity crops out in the Nimrod Glacier areaof the Transantarctic Mountains (Laird, Mansergh, and Chap-pell 1971). Lower Cambrian Shackleton Limestone overlies anerosion surface on late Precambrian Coldie Formation, which istruncated at a high angle, demonstrating a Precambrian episodeof folding. The Shackleton Limestone and, presumably, theGoldie Formation beneath it, were folded during the Cambro-Ordovician Ross Orogeny. However, previous descriptions ofColdie Formation deformation identified only one episode offolding (Gunn and Walcott 1962; Grindley 1963; Laird, Man-sergh, and Chappell 1971). Our objective was to identify andcharacterize the two episodes of deformation in the NimrodGlacier area that seemed required by reported field relations.

During the 1985-1986 field season, our party occupied threebase camps placed by helicopter out of the Beardmore Southcamp (figure). The campsite at Mount Markham was reached bysnowmobile from a helicopter put-in at 3,000 meters in thesaddle of the Markham Plateau. We had 1 day of helicopterreconnaissance in the Miller Range examining Nimrod Groupmetamorphics, and Edgerton spent 2 additional weeks in theMiller Range with the party of Borg et al. (Antarctic Journal, thisissue).

Our first camp was on Cotton Plateau where a syncline ofShackleton Limestone overlying Coldie Formation associatedwith the younger cleavage verge to the west (east over westfolding). The older cleavage in Coldie Formation is clearly ex-posed at Panorama Point. We found that throughout the north-ern end of Cotton Plateau, Goldie Formation contains two setsof intersecting cleavage and two sets of mesoscopic folds withopposite vergences (directions of overturning). The youngercleavage has a northwesterly strike corresponding to the axial-planar orientation of the syncline of Shackleton Limestone. Thefolds in Coldie Formation associated with the younger cleavageverge to the west (east over west folding). The older cleavage inGoldie Formation is oriented north to northeast; folds associ-ated with it verge eastward.

We systematically collected all formations visited during theseason. In addition to the typical graywacke-shale associationpreviously reported for Goldie Formation, we found within it athick sequence of mafic pillow lavas containing portions ofcoarse-grained gabbro. This crops out at Panorama Point and atthe head of Prince Edward Glacier. In addition, we found fourunits of diamictite (pebbly mudstone) within the Coldie Forma-tion. The possibility exists that these units are of glacial origin, ifthis proves to be true, it will be the first known locality inAntarctica of an episode of late Precambrian glaciation that isrecorded on all of the other continents.

Beneath the summit peaks that are composed of Beacon Su-pergroup and Ferrar Dolerite, the northern end of the MarkhamPlateau is underlain entirely by steeply dipping ShackletonLimestone. Rocks that appear on air photos to resemble GoldieFormation are in fact a dark portion of Shackleton Limestone.

From our third camp we examined the sole locality of theCobham Formation, a metamorphic assemblage containingcalc-schists and marbles, which Laird, Mansergh, and Chappell(1971) reported is conformably overlain by Coldie Formation.We affirmed this relationship and found two generations ofstructures within both Cobham and Coldie formations, similarto those at Cotton Plateau.

Based upon field observations of both lithology and structure,it may be suggested that the Cobham Formation is correlative

1986 REVIEW 35