Lava trees and tree moulds are common in many areas where fluid basaltic lava has moved rapidly over forested terrain. Lava trees are formed only by thin flows, but tree moulds are preserved in both thin and thick flows. Both structures may indicate the direction of flow of the lava in which they are preserved. The usefulness of lava trees in this regard is limited to recent flows; tree moulds, however, have been described in rocks as old as middle Tertiary. Features commonly well preserved on the inner walls of moulds indicate the local flow direction. When found in sufficient number, tree moulds provide information on the palaeoslope and vent location.

The area to the N and NE of the Amadeus Basin in central Australia is currently being studied by the Bureau of Mineral Resources as part of a detailed investigation of the Georgina Basin. This has led to the recognition of numerous rock units within a previously undifferentiated latest Precambrian to early Cambrian sequence, and preliminary correlations with the Amadeus Basin are possible. The sequence starts with the lower of the 2 late Precambrian tillites, and includes stromatolitic carbonates and ichnofossiliferous sandstones. These outcrop on the Hay River, Tobermory and Huckitta 1:250000 sheet areas. No early Cambrian carbonates are yet known from the eastern region, but occur on Huckitta in the Mount Baldwin Formation and in the Amadeus Basin in the Todd River Dolomite. These contain early Cambrian shelly fossils. It is tentatively suggested that the late Precambrian–early Cambrian sediments of the SW Georgina Basin are the platform equivalents of the basinal sediments of the Amadeus Basin, with fully marine sediments of this age occurring in the Georgina Basin only in NW–SE trending grabens that cut across the platform.

Structures formed during wind deflation of poorly sorted beach sediments have rarely been described in the literature. However, a number of distinct forms exist including capped pedestals, asymmetrical ‘tear’ structures and scoured or impacted crusts. All these phenomena result from differential spatial erosion of the beach surface by wind, caused by textural or compositional variations. Ephemeral structures are indicative of rapidly changing geomorphological conditions and their presence may also exert control over continuing aeolian processes.

A magnetostratigraphic study of Upper Proterozoic to early Cambrian sediments at 4 localities in Central Australia reveals the presence of a magnetic polarity pattern composed of 2 long quiet intervals, first of reversed then of normal polarity, which is then succeeded by a long mixed interval. Lithologic comparisons suggest that this pattern is a reflection of the behaviour of the geomagnetic field at that time, and probably is not a result of varying sedimentation rates. Two sampled sections in the Arumbera Sandstone separated by 80 km both contain the long normal interval followed by the interval of mixed polarity, the detailed comparison of which demonstrates that the Arumbera-Box Hole boundary is unconformable. Elements from the late Precambrian Mt Skinner fauna in the Arumbera Sandstone indicate that the long normal interval is entirely pre-Cambrian, and that the base of the Cambrian occurs within the interval of mixed polarity.

A comparison with an additional site sampled across a fossil occurrence in the Central Mount Stuart Formation at Central Mount Stuart indicates that at least 1 of the Upper Proterozoic fossils, Hallidaya brueri, has a considerable vertical distribution in time.

If used properly, the magnetic polarity pattern discussed herein offers the possibility of precise intercontinental correlations of stratigraphic sequences near the base of the Cambrian. It is suggested that a stratotype sequence for the base of the Cambrian be chosen in such a manner that the boundary position corresponds to a geomagnetic reversal.

Nineteen members of the Working Group attended the meeting and constituted a good representation in experience, variety of specialist knowledge of disciplines within geology, and first-hand knowledge of appropriate global stratigraphy. The following resolutions as a whole were accepted, as an account of the meeting by those present, with a large majority. The minority of four who did not accept Resolution I requested that the Minority View (see below) should be recorded but it was decided not to include it in the Resolutions.