Geological Mapping

Field mapping at a scale of 1:20,000 was completed as planned. The Weller Coal Measures being mapped to member level. A draft map and text was completed in the field, and it is expected that this will be submitted for publication later this year (woolfe et al. in prep). Additional geographical control was established using a total station and three GPS sites established by the USGS-DOSLI program. Three cairns were established near the head of Manhaul Bay and tied into the GPS network. Details of these sites will be included in a volume of geological data to be published later this year.

Enigmatic Sandstone Geometries

Field relationships and paleocurrent analysis has shown that the apparently enigmatic sandstone geometries resulted from the interaction of two different sedimentary systems. Some of the sheetlike geometries probably represent episodic advances of a sandy alluvial fan originating in highland to the east while other originated within the meandering system itself.

This interpretation leads to two significant findings. Firstly, paleocurrent analysis of the fan derived sheets show that highlands of crystalline basement rocks existed to the East of Allan Hills during the Permian. Of more significance is the finding that meandering rivers can deposit extensive sandstone sheets with internally complex geometries and diverse paleocurrent directions. This contrasts strongly with accepted models of meandering river deposition and suggests that a previously unrecognised process was occurring.

Further work is required to fully document an alternative model. However, it is envisaged that the sheet sandstones were deposited by blind swamp-draining meandering rivers. The unusual bed geometry results from biogenic aggradation of the flood plain (swamp) exceeding the clastic accumulation of the meandering system (Woolfe et al submitted).

Paleobotanical Studies

Paleobotanical studies revealed evidence for the in situ formation of Gondwana Coals a previously unrecognised feature (Francis et al. accepted). This evidence included the presence of Vertebraria roots in shaly units both within and at the base of major coal seams and the occurrence of upright stumps within coal seams.

Further laboratory studies are required to document fully the climate record contained in the fossil wood, but the occurrence of outsized clasts, ice needle impressions and a striated boulder in associated strata suggest that the climate was at least cold enough for the formation of winter ice locally, and perminent ice fields with glaciers higher in the drainage basin. Wide growth rings in the trees indicate that conditions were favourable during the growing season.

Hummocky and Swaley Cross Stratification

Paleocurrent determinations, facies associations and geometric considerations show that many of the structures resembling HCS and SCS within the Weller Coal Measures are drape features. Where pre-existing channel floor topography has been mantled by planar or ripple laminated sediment deposited in waning flood stage. It is believed that drape features of this type have not been previously documented.

Permian Glaciation

Several lines of evidence have led to the conclusion that glaciers still occupied highlands to the east of Allan Hills during the deposition of the Weller Coal Measures (Barrett et al. submitted). These include:

a)	Rhythmically laminated muddy sandstone and sandy mudstone. Rhythmic lamination is unusual in fluvial systems other that those controlled by seasonal ice melting.page break
b)	Pockets of outsized clasts, these are typically pebbles 2-5cm in diameter contained within sandy or muddy horizons. These grouped pebbles are interpreted as having been ice rafted by lake or glacier ice floating down current during of after major thaws.
c)	A large striated boulder was found in WCl in "Camp Valley". Multidirectional striae show that the boulder was striated prior to its inclusion in the surrounding sediment and the fine preservation suggests limited fluvial transport.

Paleocurrent Relationships

An extensive suite of paleocurrent measurements (about 10,000) were made during the field season. Primary data processing was conducted in the field using at Toshiba T1600 laptop and a tailor made software package (PC 0.1, Zwartz in prep).

Further processing of this data base is required. However, initial results indicate that the relationships between ripples, crossbeds, bar sets, paleochannel directions and sinuosity are probably more complex than previously thought. It is anticipated that the data set will allow, possibly for the first time, a quantative analysis of preservation potential and bias within a meandering river complex. The entire data set will be made available in published form later this year (Woolfe (ed) in prep).

Jurassic Glaciation

The Mawson Formation was subdivided into two lithostratigraphic members based on clast composition and textural differences. The lower of these members, Mawson A (Woolfe et al. in prep), is interpreted as being of glacial origin. This interpretation is supported by:

a)	An extensive erosion surface (Mawson Erosion Surface (Woolfe et al in prep)) which page break separates Beacon and Ferrar rocks at Allan Hills. This surface has over 400 m of sharp relief at Allan Hills and indicates a period of uplift and erosion prior to the main magmatic phase of the Ferrar event.
b)	Mawson A is directly underlain by locally intensely folded sediments of the Beacon Supergroup. The intensity of folding decreases downwards from the erosion surface over a few tens of metres. Within the zone of most intense folding, metre and decametre scale isoclinal folds have formed during complex brittle failure of interbedded sandstone and shale while cataclastic flow occurred in some coal seams. Strain is partitioned into a zone subparallel with the Mawson Erosion Surface. The style and distribution of deformation is closely analogous to that observed locally beneath the Sirius Formation, a known glacial deposit. This suggests that both the sub-Mawson and sub-Sirius strain resulted from similar processes. We believe that the deformation resulted from ice contact drag folding at the base of a dry-based glacier.
c)	Several striated clasts were found within Mawson A. It is unlikely that these could have survived prolonged transportation and they are taken as direct evidence that diamictite and the sub-erosion surface deformation were glacially produced.

Sirius Formation

Extensive exposures of the Sirius Formation occur through Allan Hills. Although the formation was not studied in detail during the 1990-91 a number of features were recorded which could form the basis of a more detailed study in the future.

a)	Glacial striae are preserved in several locations both adjacent to and beneath the Sirius Formation. These could be used to supplement geomorphic and fabric studies in order to constrain paleo-ice flow directions.page break
b)	At a number of localities Sirius Formation directly overlies well exposed deformed Beacon sediments. It is believed that these underlying rocks were deformed by ice contact drag folding. A study of the structural styles of both the sub-Sirius and sub-Mawson deformed zone could provide a better understanding of ice-rock interactions.
c)	Several different emplacement mechanisms are suggested by the geomorphic position of the diamictite exposures. These include valley floor, valley wall and ridge line deposits.