Section Measuring

Sections were measured at numerous localities in the Darwin Glacier area, the Devonian sections show the lower half of the Taylor Group (below Hatherton Sandstone) to be of similar 0 thickness in both the Darwin Glacier and Knobhead areas. The upper part of the Taylor Group (Hatherton Sandstone and above) is significantly thinner in the Darwin Glacier area. A number of sections were also measured through the Victoria Group and these will be compared with strata in the central part of the basin following the 1989-90 field season.

Taylor Group New Correlations

The reappearance of abundant pebbles near the top of Junction Sandstone (?Lower Hatherton Sandstone, Haskell et al 1965) is correlated to the appearance of scattered pebbles near the top of Altar Mountain Formation in the Knobhead area. A platform developed at the boundary between Junction and Hatherton Sandstone is littered with well rounded quartz pebbles which are very similar to the quartz pebbles that litter the platform identified at the Attar Mountain Formation Arena Sandstone boundary in the Knobhead area. Field characteristics (including trace fossil assemblage) of the Hatherton Sandstone are very similar to those of the Arena Sandstone and the units are inferred to be equivalent. The discovery of Aztec Siltstone by a party led by Margaret Bradshaw page 22 from Canterbury Museum (K221) supports this correlation and shows the correlation suggested by Haskell et al (1965) is incorrect.

Paleoenvironments of the Taylor Group

The presence of paleosols, desiccation polygons, red beds, small scale channels, intraformational conglomerate, plant fossils and carbonaceous shale in all formations except the Hatherton Sandstone indicates the Taylor Group to be non-marine. The absence of many of these features in the Hatherton Sandstone makes this part of the Taylor Group harder to interpret, but the presence of dominantly unidirectional trough cross bed axes and similarity to the Arena Sandstone and Beacon Heights Orthoquartzite suggests that the Hatherton Sandstone is also non-marine. This interpretation is supported by trace fossil evidence, the trace fossil assemblage in the lower part of Hatherton Sandstone is very similar to assemblage found in the Junction Sandstone which is considered to be fluvial.

New Fossil Fish Locality

Abundant fish plates, scales and spines were found in the Aztec Siltstone near the summit of peak 1960 m, 5 km southeast of Mt Hughes in the Cook Mountains. Preliminary investigation by J.A. Long has indicated an unusual association of sharks and phylloioids. Further work on this association will be conducted in order to determine both paleoenvironmental and biostratigraphic significance.

Trace Fossils

A systematic study of the relationships between trace fossil distributions and sedimentological controls was conducted in the Darwin Glacier area. Initial results confirm observations made in 1988-89 which indicated that ichnogenera which have formerly been used as marine indicators were in fact occurring in non-marine strata. Skolithos in the Taylor Group is generally closely associated with ephemeral pond deposits and massive green sandstone beds interpreted as overbank deposits.

Diplichnites is restricted to large trough and tabular cross-bed surfaces in the Junction and Hatherton Sandstones. We believe that these tracks were made by terrestrial arthropods walking on exposed bed forms during periods of low flow and consider it unlikely that the tracks could be preserved if they were made in submerged or saturated sand.

Darwin Tillite

Two previously undescribed facies sequences were recorded in the Darwin Tillite in the Hatherton Glacier area. At one locality, a red shale sequence overlies an erosion surface cut in Hatherton Sandstone, abundant sand blebs indicate periodic influxes of sand and up section sand beds become increasingly common and the unit passes upwards into a bluff forming sandstone. The sand beds are up to 40 cm thick and grade from medium to fine sand, load casts occur at the base of beds and ripples are preserved on the top surfaces. The sandstone units are inferred to have been deposited by turbidity flows in a glacio-lacustrine setting. The slumped sandstone unit is truncated by an erosion surface containing glacial striations and is overlain by a green diamictite phase of the Darwin Tillite. The sequence is 150 m thick and records a glacial advance prior to diamictite emplacement.

On the south side of the Hatherton Glacier a similar red shale with thin sandstone beds and blebs occurs above the green diamictite. The interbedded sandstone and shale grades upwards into varved black shale containing scattered (probably ice rafted) pebbles. The unit is directly overlain by the basal Misthound Coal Measures and records glacial retreat following diamictite emplacement.

Misthound Coal Measures and Ellis Formation

Section measuring and facies description was conducted with in the Victoria Group at a number of locations in the Darwin and Hatherton Glacier area. Comparison with the Victoria Group in the central part of McMurdo basin will be carried out following the 1989-90 field season.

Beacon Heights Orthoquartzite

Exposures of Beacon Heights Orthoquartzite in the Fry Glacier area were examined and found to be similar to exposures at the type section and at knobhead.

Metschel Tillite

The Metschel Tillite does not occur in any of the sections visited in the Towle and Northwind Valleys and the Weller Coal Measures directly overlie the Maya Erosion Surface in this area.

Slump Folding

Large slump folds have been described in the Beacon Heights Orthoquartzite from several locations in the Convoy Range (Burgess et al 1981), only one such occurrence was observed on Elkhorn Ridge. About 50 m of Beacon Heights Orthoquartzite is incorporated in a slump fold on the southside of Elkhorn Ridge, however, the presence of a thin sliver of Weller Coal Measures within the slump shows it is not the result of soft sediment deformation. Geometry of adjacent dolerite bodies suggests that the folding is associated with the intrusion of Ferrar Dolerite.

Allan Hills Section Measuring

Sections were measured though all the Victoria Group formations exposed at Allan Hills. The section data along with similar data collected in the Darwin Glacier area will be compared with the sequence in the Skelton Neve following field work in 1989-90. Facies descriptions and paleocurrent measurements were collected during section measuring. The ten degree unconformity reported by Ballance (1977) was found to result from the juxtaposition of very large dipping point bars and horizontal channel floor deposits.

Hummocky Cross-Stratification

Structures resembling hummocky cross-stratification were observed in the upper part of the Weller Coal Measures at Allan Hills. Further work will be required before the significance of the discovery can be fully evaluated. HCS is normally considered a marine indicator its occurrence in an acknowledged alluvial setting (Weller Coal Measures) is likely to be significant.