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Palynomorphs from the Sirius Formation, Dominion Range, Antarctica \% I Palynomorphs from the Sirius Formation, Dominion Range, Antarctica \% I R.A. AsKIN Geology Department Colorado School of Mints Golden, Colorado 80401 75 V. MARKGRAF 2 INSTAAR University of Colorado RiilI; (elevido S03() - 1 A low-diversity assemblage of fossil palynomorphs has been recovered from the Sirius Formation in the Dominion Range, Antarctica. Associated recycled marine diatoms are believed to be of Pliocene age (2.5 to 5 million years, Harwood, Antarctic Nik; "_41ef" 7 Journal, this issue; or 3.1 to 2.5 and 6.6 to 4.2 million years, w5 Harwood 1985), suggesting the existence of a species-poor land 3 4 vegetation during the late Pliocene (younger than 3.1 to 2.5 million years) in this part of Antarctica. Photomicrographs of palynomorphs from the Sirius Formation, Do- Six rock samples were provided for palynological study. minion Range. Magnification x 900. 1. ?Dacrydium sp., sample 2; 2. These were collected by Webb et al. (1987) from Oliver Bluffs, Tetrad of ?Polygonaceae/Labiatae pollen, sample 2; 3. Nothofagus Dominion Range. Sample 1 was from unit 4, section 5; and sp. (fusca group), sample 2; 4. ?Alga, sample 2; 5. Pollen of ?Poly- samples 2 to 6 from unit 2, section 8. Samples 2, 5, and 6 were gonaceae/Labiatae, sample 1. associated with fossil wood, and 2 and 4 with foliage remains (Webb et al. 1987). Other palynomorphs recovered include rare podocarpaceous Organic material recovered in palynological preparations of conifer pollen (?Dacrydium, see figure, block 1) in samples I and these six samples consists almost entirely of parenchymatous 2; rare indeterminate angiosperm pollen (possibly two species) and woody tissue. The abundant parenchymatous tissue sug- in samples 2 and 3; and rare palynomorphs of uncertain origin gests herbaceous vegetation (Upchurch, personal communica- (inaperturate, with two-layered wall) in samples 2, 3, and 4. tion). Palynomorphs are sparse (samples 1-3), to extremely rare The sampled intervals represent lacustrine-fluvial sediments (Samples 4-6). The dominant type of palynomorph comprises interbedded with glacially derived diamictites. These sedi- smooth, thin-walled bodies, some differentially thickened (see ments are believed to represent interglacials (units 2 and 4), figure, block 4), which are believed to be algal in origin. Some of while units I and 3 represent glacial episodes (Webb et al. these nondescript palynomorphs may be fungal. Hall (1975) (Antarctic Journal, this issue). The sampled rock units include illustrated similar algal "spheres" from core material collected abundant wood, some of which is coniferous (Cariquist, per- from Dry Valley Drilling Project (DVDP) 4, (Lake Vanda), Wright sonal communication), conifer-derived resin and foliage includ- Valley. ing possible coniferous material (Snider, personal communica- Fossil pollen grains of Nothofagus (fusca group) are relatively tion). The dwarf scale-leaved conifers of the possibly similar commom in these samples. (see figure, block 3.) They are thin "Pilgerodendron uvifera Dwarf-Heath" and "Creeping Dacrydiufn and somewhat corroded, however, and are all probably re- fonckii Heath" communities described from the present-day cycled from older Tertiary deposits where such forms were Magellanic Tundra (Pisano 1983) produce little pollen, possibly apparently abundant. Harwood (1983; Antarctic Journal, this explaining the rarity of conifer pollen in these samples. issue) and Webb et al. (1983, 1984) have noted the presence of The presumed in-place palynomorphs, together with other older Tertiary recycled diatoms, foraminifera and other micro- plant material, reflect an extremely species-poor and probably fossils in Sirius Formation samples from several localities. Rare specialized flora which, assuming diatom ages are correct (the recycled bisaccate pollen, more characteristic of but not re- palynomorphs are not age-diagnostic), survived in the Transan- stricted to the Mesozoic, also occur in the Oliver Bluffs samples. tarctic Mountains until the Late Pliocene. The presence of pal- Specimens of a thick-walled microreticulate tricolp(or)ate to eosols with root remains, plus foliage and abundant wood, tetracolp(or)ate angiosperm pollen species (see figure, blocks 2 support the contention that at least some of the palynomorphs and 5) occur in samples 1-4 and are relatively common in 2 and were produced by plants growing while these Pliocene per- 3. These may be assignable to plants of the families Poly- iglacial/interglacial lacustrine and fluvial sediments were ac- gonaceae or Labiatae. The predominance of this species and cumulating. The occurrence of plants in the Dominion Range as presence of its tetrads in sample 2, suggests short distance or no recently as approximately 2.5 million years suggests that transport and therefore local derivation. Some specimens re- pockets of vegetation survived in unglaciated areas ("refugia") semble pollen referred to as Tricolpites sp. 2 by Truswell (1983), of the Transantarctic Mountains during Miocene and middle found recycled into Recent seafloor sediments of the Ross Sea. Pliocene glacial episodes, and also presupposes adequate melt- 34 ANTARCTIC JOURNAL water or moisture was available for plant survival during these Harwood, D.M. 1986. Recycled siliceous microfossils from the Sirius episodes. The apparently low number of surviving species Formation. Antarctic Journal of the U.S., 21(5). probably represents the last vestiges of land-plant vegetation in Pisano, E. 1983. The Magellanic tundra complex. In A.J.P. Gore (Ed.), Antarctica before the Pleistocene to present-day essentially Mire: Swamp hog, fen, and moor—Regional studies, ecosystems of the nonvegetated scenario. world, 413,Amsterdam: Elsevier. Snider, 1986. Personal communication. This palynological research was supported by National Sci- J. Truswell, E.M. 1983. Recycled Cretaceous and Tertiary pollen and spo- ence Foundation grant DPI 83-14186. res in Antarctic marine sediments: A catalogue. Palaeontographica, 186(4-6)B, 121-174. Upchurch, G. 1986. Personal communication. References Webb, P-N., D.M. Harwood, B.C. McKelvey, J.H. Mercer, and L.D. Stott. 1983. Late Neogene and older Cenozoic microfossils in high elevation deposits of the Transantarctic Mountains: Evidence for ma- Carlquist, S. 1986. Personal communication. rine sedimentation and ice volume variation on the east antarctic Hall, S.A. 1975. Palynologic investigation of Quaternary sediment from craton. Antarctic Journal of the U.S., 18(5), 96-97. Lake Vanda. Antarctic Journal of the U.S., 10(4), 173-174. Webb, P-N., D.M. Harwood, B.C. McKelvey, and L.D. Stott. 1984. Harwood, D.M. 1983. Diatoms from the Sirius Formation, Transan- Cenozoic marine sedimentation and ice-volume variation on the East tarctic Mountains. Antarctic Journal of the U.S., 18(5), 98-100. Antarctic craton. Geology, 12, 287-291. Harwood, D.M. 1985. Late Neogene climatic fluctuations in the south- Webb, P-N., D.M. Harwood, B.C. McKelvey, M.C.G. Mabin, and J.H. ern high-latitudes: Implications of a warm Pliocene and deglaciated Mercer. 1987. Sirius Formation of the Beardmore Glacier region. Ant- Antarctic continent. South African Journal of Science, 81, 239-241. arctic Journal of the U.S. Structural geological investigations Our first camp was on Cotton Plateau where a syncline of Shackleton Limestone overlying Coldie Formation associated in the with the younger cleavage verge to the west (east over west Nimrod Glacier area folding). 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 sets of intersecting cleavage and two sets of mesoscopic folds with E. STUMP and D.C. EDGERTON opposite vergences (directions of overturning). The younger Department of Geology cleavage has a northwesterly strike corresponding to the axial- Arizona State University planar orientation of the syncline of Shackleton Limestone. The Tempe, Arizona 85287 folds in Coldie Formation associated with the younger cleavage verge to the west (east over west folding). The older cleavage in R.J. KORSCH Goldie Formation is oriented north to northeast; folds associ- Bureau of Mineral Resources, Geology, and Geophysics ated with it verge eastward. Canberra, AC. T. 2601, Australia We systematically collected all formations visited during the season. In addition to the typical graywacke-shale association previously reported for Goldie Formation, we found within it a A folded unconformity crops out in the Nimrod Glacier area thick sequence of mafic pillow lavas containing portions of of the Transantarctic Mountains (Laird, Mansergh, and Chap- coarse-grained gabbro. This crops out at Panorama Point and at pell 1971). Lower Cambrian Shackleton Limestone overlies an the head of Prince Edward Glacier. In addition, we found four erosion surface on late Precambrian Coldie Formation, which is units of diamictite (pebbly mudstone) within the Coldie Forma- truncated at a high angle, demonstrating a Precambrian episode tion. The possibility exists that these units are of glacial origin, if of folding. The Shackleton Limestone and, presumably, the this proves to be true, it will be the first known locality in Goldie Formation beneath it, were folded during the Cambro- Antarctica of an episode of late Precambrian glaciation that is Ordovician Ross Orogeny. However, previous descriptions of recorded on all of the other continents. Coldie Formation deformation identified only one episode of Beneath the summit peaks that are
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