Journal and Proceedings of The Royal Society of New South Wales Volume 120 Parts 3 and 4 [Issued May, 1988]
Earth History of the Southeast Indian Ocean and the Conjugate Margins of Australia and Antarctica
J. J. Veevers
[Clarke Memorial Lecture, delivered to the Royal Society of New South Wales, 5th August, 1997, at Macquarie University.]
Potassium-Argon Ages, Petrology and Geochemistry of some Mesozoic Igneous Rocks in Northeastern New South Wales
J.A. Dulhunty, E.A. Middlemost and R.W. Beck
Abstract. Twelve specimens of volcanic and subvolcanic rocks were collected from outliers in the Wellington-Muswellbrook-Narrabri region of northeastern N.S.W. They were originally assumed to be of Tertiary age as they occurred in close field association with volcanic rocks of established Tertiary age. However, anomalies were perceived as to their possible misconceived age relative to ages of erosion surfaces onto which they were extruded, and sediments into which they were intruded. K-Ar dating proved all specimens collected to be of Mesozoic age, and the establishment of high-level Mesozoic erosion surfaces, previously regarded as Tertiary, has simplified some aspects of landscape development in northeastern N.S.W.
The 12 specimens are all silica undersaturated alkaline rocks that have many geochemical, mineralogical and petrographic similarities. The more primitive basanites, alkali basalts, hawaiites and tephrites all plot as a coherent group in the "within-plate" field on the Ti-Y-Zr discriminant diagram. Spidergrams illustrate the broad chemical similarities among the least differentiated specimens. This study augments the concept that there was widespread alkaline volcanism in northeastern N.S.W. over an extensive period during the Mesozoic.
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The Mineralogical Relationship between some Arid Zone Soils and their Underlying Bedrocks at Fowlers Gap Station, New South Wales (N.S.W.) Australia
E. G. Akpokodje
Abstract. The clay mineralogy of metasedimentary quartzites, phyllitic shales and their overlying desert loam soils from Fowlers Gap Station, Australia, were studied. The mineralogic variations in the rock sequence may be attributed to broad changes in both provenance and the environment of deposition. The smectite, illite and chlorite found in the soils formed on the phyllitic shales were all inherited from the bedrock. Kaolinite, on the other hand, is the weathering product developed under a subtropical climate in the Tertiary. The same clay minerals, except chlorite, also occur in the soils developed on the crest and colluvial slopes of the quartzites. Kaolinite was inherited from the bedrock, whereas significant proportions of the smectite and illite are considered to have been partly formed from the intercalated clay and the closely associated phyllitic shales, where they occur as relics on the weathered Tertiary surface.
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A Geophysical Survey of Culoul and Mellong Creek Valley Fills: Implications for Valley Development in Sandstone Terrain
S.J. Riley and H.M. Henry
Abstract. Geophysical surveys of the Mellong Plateau valley fills supplemented and calibrated against limited drilling revealed a system of wide valleys with up to 10 metres of fill. Streams with dimensions similar to those that presently occupy the valley floors may have excavated the valleys. If they did then there has been a complex history of valley aggradation and incision with the most recent period being one of aggradation.
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Mellong Plateau, Central Eastern New South Wales: An Anomalous Landform
Abstract. The Mellong Plateau, between Colo Heights and Putty in central eastern New South Wales, lies east of the topographically higher Lapstone Monocline (Fig. 1); through the latter the plateau's creeks drain west in transverse valleys against the regional topographic gradient. In spite of its location on top of the Macdonald River – Wollemi Creek drainage divide, the plateau is extensively alluviated, large swamps occurring on all main creeks and tributaries. The plateau's anomalously low relief; wide, shallowly incised valleys; valley-side embayments; and westerly-flowing transverse drainage are described. More than 200 samples of fill were collected to depths up to 10 m; 71 of these were analysed granulometrically. Clay beds were less common in the fill than anticipated; clayey and muddy sand predominated. Difficulties were experienced in determining the alluvium/colluvium and bedrock boundaries, so seismic and resistivity methods were used to supplement drilling, and a limited coring programme was undertaken with thin-section examination of core fabrics. Alternative explanations of Mellong Plateau transverse drainage are discussed. Gaps in present knowledge, e.g. the age of the Lapstone Monocline, speculative existence of a vanished former cover, do not permit any positive conclusion, but genetic diversity seems indicated.
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Volatile Leaf Oils of the Two Subspecies of Melaleuca acacioides R Muell.
J.J. Brophy, E.V. Lassak and D.J. Bolland
Abstract. An examination of the volatile leaf oils of two recently described subspecies of Melaleuca acacioides, ssp. acacioides and ssp. alsophila, has shown substantial chemical differences between them. Subspecies acaciaides from northern Queensland is almost exclusively sesquiterpenic with α- and β-selinenes accounting for about 80% of the oil, whilst subspecies alsophila from northern Western Australia is almost entirely monoterpenoid in character with p-cymene, geranial and terpinen-4-ol, each approximately 20%, as its main oil components.
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Analysis of a Small-Scale Fault at Bingi Bingi, N.S.W., and Speculations on its Relationship to a Large-Scale Transform Fault of the Tasman Sea
Abstract. South of Moruya, at Bingi Bingi Point, N.S.W., a NW trending aplite dyke of the Devonian Tuross Head Complex has been sinistrally drag folded by a ENE steeply dipping fault. A structural analysis of the faulted, drag folded dyke provides a preliminary solution that speculates by scale transfer, that the fault may be part of a Riedel shear system related to movements along a transform fault developed during the opening of the Tasman Sea which subsequently controlled later mafic dykes emplaced during the rifting of Australia from Antarctica.
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