Correlation of the Silurian Rocks of Australia, New Zealand, and New Guinea
Published:January 01, 1975
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J. A. Talent, W.B.N. Berry, A. J. Boucot, G. H. Packham, G.C.O. Bischoff, 1975. "Correlation of the Silurian Rocks of Australia, New Zealand, and New Guinea", Correlation of the Silurian Rocks of Australia, New Zealand, and New Guinea, J. A. Talent, W.B.N. Berry, A. J. Boucot, G. H. Packham, G.C.O. Bischoff
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The changing patterns and episodic nature of diastrophism, sedimentation, and volcanism from Late Ordovician through Early Devonian time in Australia, New Guinea, and New Zealand is presented with the aid of a correlation chart and two paleogeographic-lithofacies maps for late Llandovery and Ludlow-Pridoli times; such analysis proved impractical for the early Llandovery and Wenlock owing to the paucity of preserved sequences, a reflection of significant diastrophism at those times. The criteria for correlation, patterns of paleocommunities, and the applicability of local series’ names are examined; plutonism and the contribution of radiometric dating, particularly with regard to estimates of the age of system boundaries, using Australian sequences, are briefly probed. Graptolites have been used as the primary basis of correlation, supplemented by conodonts, corals, and brachiopods.
Marine sediments of definite Llandovery and Wenlock age are known only from the Tasman Mobile Belt of eastern Australia and its extension through New Guinea.
Paleontological control is poor for sequences accumulated in basins within the craton. Evaporitic sedimentation was widespread in the South Canning Basin of Western Australia. Continental, predominantly aeolian, sedimentation occurred in the Amadeus Basin of central Australia; minor marine incursions, the paleogeography as presently known, and the pattern of Silurian orogenesis (Rodingan Movement) in central Australia suggest connection intermittently through the South Canning Basin rather than eastward to the Tasman Mobile Belt. Connection between the South Canning sequence and the Ludlow carbonate-evaporite sequences in the Carnarvon Basin of Western Australia was offshore with respect to the present coastline.
Following the wane of Late Ordovician volcanism, most of the Tasman Mobile Belt in southeastern Australia underwent a major diastrophic revolution, the Benambran Orogeny. Three phases are discernible stratigraphically: the first in early Llandovery time, the second in middle or early late Llandovery, and the third during the Wenlock, probably not including latest Wenlock time (Quarry Creek phase). Owing to the severity of deformation and perhaps to its continuity in time over most of the area, the first two phases have not been widely distinguished from each other; they are commonly lumped together as the Canberra orogenic phase. A pattern of two longitudinal troughs and two highs, the Cowra Trough and Molong High–Yass Shelf, the Hill End Trough and Capertee High, perhaps initiated earlier, became pronounced in central and southern New South Wales and eastern Victoria following the Benambran events. Platform sequences accumulated on these highs during late Wenlock-Pridoli time; carbonate buildup was particularly prominent during Ludlow time. Relative diastrophic quiescence persisted from latest Wenlock through Ludlow and Pridoli time when southeastern Australia underwent a new cycle of diastrophic events, the Bowning Orogeny. Although formerly regarded as having taken place toward the close of Silurian time and extending into the Early Devonian, recent paleontologic and stratigraphic work indicates an onset not earlier than the Gedinnian. Effects of the Bowning and Benambran Orogenies are less pronounced in the Melbourne Trough of Tasmania and central Victoria than they are in eastern Victoria and in southern and central New South Wales. Contraction of the Melbourne Trough through Late Ordovician into Silurian time seems apparent from the record as preserved. Orogenic events contemporaneous with the Benambran and Bowning events have not been distinguished in northern Queensland or New Guinea, although diastrophic events of Wenlock age have been documented for the former.
Volcanism was conspicuously rare or absent during Llandovery time. Acid and andesitic volcanism was widespread in southeastern Australia following the Quarry Creek phase of the Benambran Orogeny, then contracted during Ludlow time to the Canberra and adjacent areas. Predominantly acid volcanism became widespread following the onset of the Bowning Orogeny. The acme of volcanism appreciably postdates the main deformational episodes for both orogenies in eastern Victoria and southern New South Wales.