22-2/F52-4/2-6 Contour interval: 25

22-2/F52-8/3-3

22-1/F52-07/19 Contour interval: 5

Titles in this newsletter: Lead-isotope-based stratigraphic correlations and ages of Proterozoic sediment-hosted Pb-Zn deposits in the Mount Isa Inlier Potential for magnetostratigraphy as a correlation tool in the Late Permian coal measures of eastern Australian basins New geological and geochronological constraints on volcanogenic massive sulphide prospectivity near Halls Creek (WA) Revision of Late Triassic biostratigraphy of the North West Shelf Permian-Carboniferous magmatism in north Queensland: a new perspective Mineralisation potential of the granites of the Cape York Peninsula Batholith, Cape Weymouth, Coen, and Ebagoola 1:250 000 Sheet areas Implications of Pb-isotope data for tectonostratigraphic correlations in the Proterozoic of central Australia Benthic chamber technology and the sea-floor of Port Phillip Bay, Melbourne Landscape evolution in the East Kimberley region, Western Australia Mapping large-scale hydrothermal systems using coincident magnetic and gamma-ray spectrometric anomalies The 'Keith-Kilkenny Lineament': fault or fiction? A milestone in geomagnetic processing Plate tectonics of the Christmas Island region, northeast Indian Ocean

No abstract available

No abstract available

In the Dalton area, 60 km north of Canberra, Australia, earthquakes are strongly clustered in time, but the presence of multiple events with magnitudes around 2.8 is not a useful criterion for earthquake forecasting. If magnitude ML >2.7 events less than 14 months apart during the period 1960-1993 are grouped together, the magnitude ML(MAX) of the largest event of a group may be forecast from the relationship: ML(MAX) = 0.097 + 2.296 log t, where t months is the quiescent interval preceding the group in question and 2.8<ML(MAX)<4.2.

The multielement structure of the Late Cambrian euconodont Teridontus nakamurai (Nogami, 1967) is shown to be a seximembrate apparatus consisting of Sa, Sc, Sb, Sd, Pb and Pa elements. No M element has been identified and none is expected in this type of conodont. All elements are coniform with a hyaline base and albid tissue in the cusp extending from the apex of the basal cavity to near the cusp tip. The cusp tip is usually hyaline. The albid tissue is dense and the juncture of hyaline and albid tissues at the basal cavity apex is usually abrupt and planar, rather than tapered as found in most coniform element species. Albid tissue fills the entire diameter of the cusp, and there is no outer layer of hyaline tissue. The S elements have a relatively long base and are differentiated by their cross-sectional shape. The P elements have a short base and different cross-sectional shapes. The surface of all elements is covered with a very fine striate ornament, but the elements lack other surface structures, such as keels, carinae, costae and grooves.

The Monaro Volcanic Province in southeastern New South Wales is an Early to Middle Tertiary intraplate volcanic province of lava field style, similar to the Newer Volcanic Province of southwestern Victoria. The lava pile is dominated by nepheline basanite, alkali olivine basalt and transitional basalt with minor olivine tholeiite and nepheline hawaiite. Olivine nephelinite lavas occur near the top of the lava pile. The lavas are interbedded with Tertiary sediments and hyaloclastites, some of which have formed in lakes, probably developed by lava damming the pre-basaltic drainage. Thick weathering profiles, in some cases bauxitic, are developed on many of the flows in the lava pile, suggesting long breaks between eruptions at particular sites. This is consistent with sporadic eruplions from widely scattered vents. Most known eruption sites in the province are represented by volcanic plugs of aphanitic to coarse-grained nepheline basanite, olivine nephelinite, nepheline hawaiite and alkali olivine basalt. Fractionated varieties of these rocks also occur together with minor feldspar-rich and titanian augite-rich cumulates. The predominant plug type is aphanitic to fine-grained nepheline basanite, containing mantle xenoliths and/or kaersutite amphibole. Basement fractures have had a major influence on the position of volcanic centres. Plugs are concentrated along two northwest trending linear zones: the Bemboka Zone in the north; and the Berridale-Towamba Zone in the south. The Berridale Fault-Towamba Lineament is a major crustal feature of the region. Other basement structures, including north-northeast-trending faults , appear to have controlled some eruption centres away from the two major zones.

The Lachlan River rises in the humid highlands of southeastern Australia and flows westward into the Murray Basin. The climate is sub-humid to semi-arid and, as it crosses the Murray Basin, the Lachlan loses most of its discharge through evaporation and infiltration. Unlike most river terminations, the Lachlan ends in the Great Cumbung Swamp without dividing into distributaries; neither are there large fresh-water lakes nor playas. Only during floods, occuring in 15-20% of years, does Lachlan water flow past the swamp into the Murrumbidgee River to the south. The swamp water remains fresh because salt is lost with water that infiltrates into underlying aquifers. This water loss causes the river to terminate because it reduces stream competence and prevents the Lachlan from forming a lake which could then overflow and breach the low topographic barriers that defeat it. The Great Cumbung Swamp is divided into three depositional environments: 1. The Lachlan channel is sinuous and up to 40 m wide. It shows morphology equivalent to cut-bank and point-bar morphology when it first enters the swamp but becomes straight as it reaches the central, lowest part of swamp. Its most distal reach is sinuous with a slight upstream bed gradient. 2. Phragmites Marsh: Most of the Great Cumbung Swamp is marsh colonised by Phragmites australis. Very slight topography controls flood frequency and degree of desiccation, and hence Phragmites growth. The marsh displays a dendritic texture resembling small-scale drainage networks possibly formed by floodwater etching out micro-relief developed on the deep-cracking flood plain clays. Within the Phragmites marsh are bodies of open water less than 0.75 m deep connected to the main channel through breaches in the levees. The lakes grade into the surrounding marsh with a gradual increase in the density of Phragmites clumps. 3. Overflow areas: The Great Cumbung Swamp proper is surrounded by alluvial plain colonised by scrub and eucalypts. It is underlain by black to grey deep-cracking clays. Traversing this plain are anastomosing channels that carry water from the swamp to the Murrumbidgee during floods. These channels are slightly sinuous and up to 20 m wide, 1 m deep, and have symmetrical cross-sections. Great Cumbung Swamp sediments are largely black clays with those deposited in the Phragmites marsh being extensively bioturbated by roots. The development of pedogenic textures and preservation of organic matter depends on the frequency of desiccation. The Lachlan channel accumulates massive black clay with only a few thin sandy beds in the upstream reach. These sandy beds probably drape the channel bottom during the falling stage. The Lachlan River in the Great Cumbung Swamp has a very low gradient and provides an example of fluvial deposition at the lowest end of the energy spectrum. Ancient analogues for this style of river termination will probably be found in fine-grained sediments interpreted as flood plain or lake deposits. Other deposits interpreted as deltaic, but for which no connection with lake or marine depos its can be demonstrated, may also be th e deposits of swa mps. Some sediments in the Triassic to Jurassic basins of the eastern U.S.A. may be good analogies.