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Victoria University Antarctic Research Expedition Science and Logistics Reports 1978-79: VUWAE 23

Bottom sediment Paleontology of the proposed MSSTS sites in Western McMurdo Sound (David B. Waghorn and Jeffrey N. Ashby)

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Bottom sediment Paleontology of the proposed MSSTS sites in Western McMurdo Sound (David B. Waghorn and Jeffrey N. Ashby)

Bottom sediments from the proposed MSSTS Sites at New Harbour (NH) and off Butter Point (BP) were obtained by members of VUWAE 23, Event 12, using a NZOI McIntyre grab. Two 10 cm3 subsamples were taken from each grab sample, at depths of 0-1 m (1/A) and 3-5 cm (1/B) below the top of the sample.

Results

The biota includes planktonic and benthonic foraminifera, ostracods, diatoms, radiolaria, sponge spicules and small gastropods (Plate XI). No difference was observed in faunal abundance or diversity between the top and bottom subsamples at each site. Mottling and the presence of ? worm tubes in the sand indicate extensive bioturbation, resulting in homogenity of sediments and samples.

Calcareous Microfossils

A significant difference is apparent, both in species abundance and test composition, in assemblages between the two sites. At New Harbour, sample NH 1/A is dominated by arenaceous benthonic foraminifera, sponge spicules and centric (planktonic) diatoms. Common arenaceous foraminifera include Rhabdammina cf. linearis Brady, Rhizammina indivisa Brady, Reophax nodulosus Brady, Haplophragmoides rotulatum (Brady) cf. sphaeriloculus Cushman, Textularia earlandi Parker, Rzehakinidae sp, and Miliammina arenacea (Chapman). A small number of calcareous benthonic foraminiferal taxa including Trifarina earlandi Parr, Fursenkoina daviesi (Chapman & Parr), Robertina sp. and Globocassidulina crassa rossensis Kennett, occur. Also, two juvenile specimens (ostracod) Echinocytheris cf. dasyderma (Brady) have been identified. Sample NH 1/B is dominated by arenaceous taxa, but reduced in diversity compared to sample NH 1/A. Both samples lack Neogloboquadrina pachyderma (Ehrenberg).

In contrast, both Butter Point samples (BP 1/A & BP 1/B) are dominated by calcareous benthonic taxa. Species present include Trifarina earlandi Parr, Ehrenbergina glabra Heron-Allen & Earland, Astrononion antarcticum Parr, Pyrgo williamsoni (Silvestri), Globocassidulina sp. and Fursenkoina daviesi (Chapman & Parr). Most of the New Harbour arenaceous taxa also occur in abundance in the Butter Point samples. Sinstrally coiled Neogloboquadrina pachyderma (Ehrenberg) are common. Ostracod taxa present are Australicythereis polylyca (Muller), Xestoleberis sp, Krithe 2 spp, Australicythereis sp and Trachyleberis sp. cf. Cythere polytrema Brady.

Siliceous Microfossils

Very low radiolarian abundance was encountered at both sites. The New Harbour assemblage is dominated by Lithelius nautiloides Popofsky, the remaining taxa being Antarctic strelkovi Petrushevskay, Spongotrochus glacialis Popofsky and Spongodiscus cf. favus Ehrenberg. At Butter Point, Radiolaria were of even lower abundance than at New Harbour. The New Harbour assemblage is dominated by Lithelius nautiloides Popofsky, with Spongotrochus glacialis Popofsky and Antarctissa cf. denticulata (Ehrenberg) present. The diatom taxa, Coscinodiscus lentiginosus McCollum, Eucampia balustrum McCollum, C. sellaris McCollum, Charcotia irregularis Peragallow, Pseudoenotia sp and Denticula sp occur in the Butter Point sample.

Discussion

The age of young marine sediments in the shallow parts of the Ross Sea is as yet difficult to determine paleontologically. Of the seventeen Brunhes and Gauss age diagnostic taxa described by Fillon (1972) twelve are restricted to depths greater than 450 metres. The remaining five taxa occur at shallower depths. Two of these, page 13 Globocassidulina crassa rossensis Kennett and Cassidulina porrechis Heron-Allen & Earland, are found at New Harbour and Butter Point respectively. Both species indicate a Brunhes age (Fillon 1972, 1974). The presence at Butter Point of the diatom taxon Eucampia balustrum McCollum found in Gilbert to Brunhes sediments, but more commonly restricted to the Brunhes, also supports a Brunhes age for the Butter Point assemblage. Radiolarian species found have extended age ranges and precise age determinations cannot be made. Present day (Recent) Ross Sea taxa are typically endemic and similar to Gauss assemblages (Fillon 1973).

The difference in foraminiferal test composition between the New Harbour and Butter Point Sites, dominantly arenaceous and dominally calcareous species respectively has been described in other regions of McMurdo Sound and the Ross Sea (McKnight, 1962; Kennett, 1966; Fillon, 1972, 1974). Kennett (1966) suggested that a calcium carbonate solution boundary (CCD) occurred at 500-550 metres, separating arenaceous faunas below from calcareous faunas above. Fillon (1972) described 'relic Gauss' and Brunhes sediments which contain dominantly calcareous and arenaceous taxa respectively. He explained the latter as due to an increased undersaturation of calcium carbonate associated with a late Gauss - early Matuyama expansion of the Ross Ice Shelf.(Fillon, 1974. The four samples studied are well above the present day CCD.

Butter Point foraminiferal assemblages lack both the characteristic Brunhes taxon Globocassidulina crassa rossensis Kennett and its Gauss ancestor G. biora (Crespin). A possible intermediate form, Globocassidulina sp., which has a typical G. crassa rossensis shape but lacking the distinctive L-shaped aperture, is common.

High salinities, low temperature and possibly low photosynthetic activity related to the presence of semi-permanent sea ice cover may explain a calcium carbonate depletion of waters at New Harbour, though none of these parameters have been measured yet at the New Harbour Site. Arenaceous taxa may be better adapted than calcareous taxa to oligotrophic areas such as New Harbour where there is no current activity.

Neogloboquadina pachyderma (Ehrenberg) is absent from New Harbour, although photosynthetic planktonic diatoms are common. This suggests that photosynthetic activity is present at New Harbour, but not high enough to support higher trophic groups.

we thank Dr M.A. Harper for identifying the diatoms and Mr S.H. Eager for the ostracods. Mr P.H. Robinson reviewed the manuscript.

References

Fillon, R.H., 1972. Evidence from the Ross Sea of widespread submarine erosion. Nature Phys. Sci. vol 238, no. 81. pp 40-42. text figs. 1-2, tables 1-2.

Fillon, R.H., 1973. Radiolarian Evidence of Late Cenozoic Oceanic Paleotemperatures, Ross Sea, Antarctica. Palaeogeography, Paleoclimatology, Palaeoecology vol 14. pp 171-185.

Fillon, R.H., 1974. Late Cenozoic foraminiferal paleoecology of teh Ross Sea, Antarctica. Micropaleontology vol 20, no 2. pp 129-151, pls. 1-6.

Kennett, J.P., 1966. Foraminiferal evidence of a shallow calcium carbonate solution boundary, Ross Sea, Antarctica. Science vol 153, no. 3732. pp. 193, text figs. 1-2.

McKnight, W.R.M., 1962. The distribution of foraminifera off parts of the Antarctic coast. Bull. Amer. Pal., vol 44, no. 201. pp 65-158, pls. 9-23 text figs. 1-7, tables 1-5.

Thomas, C.W., 1968. Antarctic ocean-floor fossils: Their environments and possible significance as indicators of ice conditions. Pacific Sci., vol 22 no. 1. pp 45-51, text fig 1.

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FIG. 3. Sections traversed for paleomagnetic sampling at Mount Bastion (A) and west Beacon (B). Traverse line ⋰; campsites ΔΔ; D - dolerite; UL, ML, LL - upper, middle and lower Lashly Formation; WCM - Weller Coal Measures; AzS - Aztec Siltstone; BHO - Beacon Heights Orthoquartzite; AR - Arena Sandstone; AMF Altar Mountain Formation NMS - New Mountain Sandstone; FG - Feather Conglomerate.

FIG. 3. Sections traversed for paleomagnetic sampling at Mount Bastion (A) and west Beacon (B). Traverse line ⋰; campsites ΔΔ; D - dolerite; UL, ML, LL - upper, middle and lower Lashly Formation; WCM - Weller Coal Measures; AzS - Aztec Siltstone; BHO - Beacon Heights Orthoquartzite; AR - Arena Sandstone; AMF Altar Mountain Formation NMS - New Mountain Sandstone; FG - Feather Conglomerate.