part page item. This article discusses the International Stratigraphic Guidelines and Australian practices relating to stratigraphic unit names, when there is a change to the name of the geographic feature that the unit is named after. Australian examples demonstrate both the advice of the Stratigraphic Guidelines not to change the unit name, and a particular case where it was more appropriate to change the unit name for local reasons.

Weather conditions during the survey were generally very good with only a few days of seas of about two metres. Technically and scientifically, the balance of the program changed when the seismic (and magnetic) program was reduced to one third of the expected kilometres because of the failure of the compressor. Fortunately, two of four critical lines running WNW-ESE were acquired (Table 1). Data acquisition rates (average of 200 km/day) were tolerable and seismic data quality was good. A whale watch was kept in accord with the requirements of the Department of the Environment and Heritage, but no whales were seen. The dredging program was increased to take advantage of the reduced seismic program, and most Mellish Rise sites were located either on the two new seismic lines or on pre-existing BMR continental margin survey seismic lines. A number of sites on the Kenn Plateau made use of seismic data from last year's Southern Surveyor Cruise SS5/04. The need to use BMR seismic lines moved the dredging balance to the western half of the area. Of the 44 dredges attempted, 37 (85 %) produced valuable results (Table 3). The swath-mapper was invaluable in designing dredge plans. The coring program of 5 cores (Table 2) produced three moderately successful cores, but was disappointing overall. The two seismic lines extend right across the Mellish Rise and reveal how the area has been affected by tension but not compression, with high blocks 50-100 km across separated by heavily sedimented graben of similar width. Satellite bathymetry and gravity maps, and the total seismic data set show that structural trends bounding the blocks are NW-SE, N-S and NE-SW. Numerous smaller horsts rise above the broad highs. Dredges from the Coriolis Ridge and the Selfridge Rise, both on the northern Kenn Plateau, are dominated by silicic volcanics of continental origin, siliciclastic sediments, and shallow marine carbonates (some reefal). Basaltic volcanics are rare. The continental volcanics may be rift-related (Upper Cretaceous to early Eocene). The calcarenites may be Eocene and Oligocene in age. Dredges from the generally deeper water (thinner crust) Mellish Rise are different, being dominated by basaltic volcanics and hyaloclastites, although silicic volcanics, siliciclastic sediments, and shallow marine carbonates (some reefal) occur. Two phases of volcanism, rift related (Upper Cretaceous to early Eocene) and hotspot related (late Eocene-Oligocene) may well be present. Three dredges from a southern protrusion of the Louisiade Plateau, which is not necessarily genetically related to that plateau, contain basaltic volcanics and hyaloclastites, silicic volcanics, siliciclastic rocks, and shallow marine carbonates in an assemblage like that of the Mellish Rise. Until exhaustive laboratory studies of the rocks are carried out, the above generalisations remain speculative. In the end, the volcanics could be related to any of four known periods of volcanism: ? The Late Jurassic (145-135 Ma) subduction-related volcanism of the Graham?s Creek Formation in the Maryborough Basin: tuffs, agglomerates and volcanic breccias, overlain by trachyte and rhyolite flows, overlain by basaltic andesite and dacite. ? The Early Cretaceous (125-115 Ma) explosive rift-related volcanism of the Whitsunday and Cumberland Islands: dacite, rhyolite, and andesitic ignimbrite. ? The assumed Late Cretaceous to Paleocene rift-related volcanism of the Marion Plateau (drilled in ODP Leg 194): altered basalt flows and volcaniclastic breccias and conglomerate. ? The Late Eocene to Early Oligocene hotspot volcanism of the Tasmantid chain: basalts and hyaloclastites.

Part-page item of matters related to stratigraphy. This column discusses informal units, the role of authors and reviewers, and is the 50th Stratigraphic Column produced by the Australian Stratigraphy Commission. Journal ISSN 0312 4711

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A Late Jurassic (Tithonian) suite of marine microplankton is present in the Flamingo Formation and its equivalents in the Timor Sea, offshore north-western Australia and adjacent regions. It includes three dinoflagellate cyst genera, Aidelacysta, Ampulladinium and Belowia, and ten species of dinoflagellate cysts which are described as new. The genera Balcattia, Biorbifera and Dissimulidinium are emended to note key morphological features observed in the material studied. The new dinoflagellate cyst species are Aidelacysta clavata, Ampulladinium variabile, Balcattia cheleusa, Batioladinium paeminosum, Belowia baltea, Biorbifera aggressiva, Cassiculosphaeridia solida, Dissimulidinium purattiense, Gardodinium angustum and Pseudoceratium robustum. An additional morphotype of Belowia, B. sp. A. is informally described and Meiourogonyaulax bulloidea is emended to note the microreticulate nature of the autophragm. Stanfordella granulosa is reported from the Southern Hemisphere for the first time. A new acritarch species, Nummus tithonica, is also described. These microplankton taxa have stratigraphical utility in the Tithonian Cribroperidinium perforans Zone to the upper Pseudoceratium iehiense Zone.

A suite of hitherto unpublished Late Jurassic (Oxfordian) dinoflagellate cysts which have restricted stratigraphical ranges has been recorded from offshore exploration wells in the north-western Australian region. Three genera and eight species of dinoflagellate cysts are formally described as new. The genera are Cygnusicysta, Fosteria and Tringadinium; the species are Cygnusicysta taltarniana, Fosteria eclipsiana, Fusiformacysta challisiana, Microdinium jurassicum, Systematophora gemina, Tringadinium bjaerkei, T. comptum and Woodinia bensonii. The dinoflagellate cyst genus Systematophora is emended to include forms with paired, slender solid processes within the paracingulum, in order to accommodate S. gemina. With the exception of Tringadinium bjaerkei, which ranges from late Callovian to Tithonian, all these new dinoflagellate cyst taxa have stratigraphical utility in the Oxfordian Wanaea spectabilis Zone of the north-western Australian region.

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The Wallareenya extensional jog developed between c. 2955 and 2940 Ma at a releasing bend in the northeast-trending Tabba Tabba Shear Zone, in the Archaean Pilbara Craton of northwestern Australia. The extensional jog, or pull-apart, formed during transtensional movement along the shear zone, and was simultaneously filled by a sequence of magmas that range in composition from gabbro to monzogranite. Magmas were emplaced through fractures which conform to Riedal R1 and R2 and P fracture directions and that segment the area into diamond-shaped blocks. Some of these conduits were utilised by up to five magma generations. Space for emplacement was created primarily through active extension within the evolving jog, and the emplacement age of the magmas decreases systematically westwards, tracking a paralleled migration in the main focus of extension. Away from fractures and magma conduits, horizontal sheeting shows that the magmas spread out laterally at suitable horizons such as the contact with overlying metasedimentary country rocks.