The Main Seam in the Greymouth coalfield (Upper Cretaceous Paparoa Coal Measures) is exceptionally thick (>25m) and occurs in three locally thick pods, termed north, middle, and south. These pods are separated by areas of thin or absent (“barren”) coal. The barren zone between the north and middle coal pods is characterized by a sequence that is 60 m thick comprising relatively thin (1–2.5 m thick) but laterally extensive (up to 500 m) sandstone units. The orientation of both the thin and the barren coal zones is approximately east to west. This is coincident with basement fault systems that occur in the region. Therefore, the stacked nature of the sandstones within this narrow zone may be a result of differential subsidence across basement fault blocks. The Main Seam, like the sandstone units in the “barren” zone, is inferred to represent a stacked sequence. Two zones of thin partings (<20 cm in thickness) occur in the coal, and even where these zones do not occur, an interval of abundant vitrain bands is present. As has been suggested for other coal beds, intervals with high vitrain content may represent a demarcation between different paleomire systems, or, as in the case of the Main Seam, periods where the paleomire was rejuvenated with plant nutrients, allowing continued aggradation of the mire. The low ash yield (<5% dry basis) indicates that the Main Seam was rarely affected by flood incursions. This may have been the result of both doming of the peat surface as well as restriction of the dominant sediment flow by syn-sedimentary faulting. Palynological analyses indicate that the Main Seam mire throughout most of its time was dominated by gymnosperms, particularly a relative of the Huron pine (Lagarostrobus franklinii). However, a distinct floral change to a Gleichenia -dominated mire occurs in the upper few meters of the Main Seam. This vegetation change may have resulted from basinwide environmental or climatic change. Gleichenia does not produce much biomass, and if it was the dominant mire plant it may not have been able to keep peat accumulation rates higher than subsidence. Whether the cause was a decrease in peat accumulation or a drying of mire, the result would have been lowering of the surface to a degree that flooding and final termination would be likely.

Abstract A review of evidence for deformation and terrane accretion on the Late Triassic-Early Jurassic margins of Pangaea and the mid-Cretaceous margins of the palaeo-Pacific ocean shows that deformation was global and synchronous with probable superplume events. Late Triassic-Early Jurassic deformation appears to be concentrated in the period 202–197 Ma and was coeval with eruption of the Central Atlantic Magmatic Province, onset of Pangaea break-up, a period of extended normal magnetic polarity and a major mass extinction event, all possible expressions of a superplume event. Mid-Cretaceous deformation occurred in two brief periods, the first from approximately 116 Ma to 110 Ma in the west palaeo-Pacific and the second from roughly 105 Ma to 99 Ma in the east palaeo-Pacific, with both events possibly represented in northeast Siberia. This deformation was coeval with eruption of major oceanic plateaux, core-complex formation and rifting of New Zealand from Gondwana, the Cretaceous normal polarity epoch, and a major radiation of flowering plants and several animal groups, all linked with the mid-Cretaceous superplume event. A simple unifying mechanism is presented suggesting that large continental or oceanic plates, when impacted by a superplume, tend to break-up/reorganize, associated with gravitational spreading away from a broad, thermally generated topographic high and with a resulting short-lived pulse of plate-marginal deformation and terrane accretion.

Abstract The active margin of Gondwana is presently preserved in the southwest Pacific region in the formerly continuous Gondwana fragments of Australia, Antarctica and New Zealand. The Phanerozoic tectonic history of New Zealand is interpreted in terms of progressive Pacific-ward growth by accretion of arc-trench systems and the basement rocks are described in terms of a number of volcano-sedimentary accreted terranes, suites and batholiths that intrude the terranes. The age of these basement rocks ranges from Early Cambrian to late Early Cretaceous. The origin of the magmatic and sedimentary rocks and the time of accretion of the New Zealand terranes to the Gondwana margin are important for the understanding of Phanerozoic Pacific tectonics. Geochronological research over the last decade on igneous rocks and conglomeratic units shows that the Tutoko Complex/Amundsen Province plutons are major contributors of detritus to the Pahau depositional basin and that the Antarctic sector of the Panthalassan Gondwana margin has to be (re)considered as the likely source for the Permo-Triassic Rakaia sediments. Igneous clast data have greatly improved understanding of the evolution of the New Zealand microcontinent and have put tighter constraints on its Mesozoic tectonic setting within the southwest Pacific margin of Gondwana.

The Western Province is a fragment of the c. 500 Ma SE Gondwana active continental margin. The Eastern Province is a terrane assemblage, which is partly stitched by the Median Batholith. Fragments of the batholith are preserved in the adjacent Drumduan and Brook Street terranes. Permian arc magmatism of the Brook Street Terrane involved both oceanic and continental margin settings. The Permian ( c. 285–275 Ma) supra-subduction zone Dun Mountain ophiolite records subduction initiation and subsequent oceanic-arc magmatism. The Permian Patuki and Croisilles melanges represent detachment of the ophiolitic forearc and trench–seamount accretion. The Murihiku Terrane, a proximal continental margin forearc basin, received detritus from the Median Batholith (or equivalent). The south coast, Early–Late Triassic Willsher Group is another proximal forearc basin unit. The sediments of the Dun Mountain–Maitai Terrane (Maitai basin) represent a distal segment of a continental margin forearc basin. The Caples Terrane is a mainly Triassic trench accretionary complex, dominantly sourced from a continental margin arc, similar to the Median Batholith. The outboard (older) Torlesse and Waipapa terranes are composite subduction complexes. Successively more outboard terranes may restore farther north along the SE Gondwana continental margin. Subduction and terrane assembly were terminated by collision (at c. 100 Ma), followed by rifting of the Tasman Sea Basin.