Age and Timing of the Permian Mass Extinctions: U/Pb Geochronology of Closed-System Zircons
The age and timing of the Permian-Triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts. Zircons from nine ash beds within the Shangsi and Meishan sections (China), pretreated by annealing followed by partial attack with hydrofluoric acid, result in suites of consistent and concordant uranium/lead (U/Pb) ages, eliminating the effects of lead loss. The U/Pb age of the main pulse of the extinction is 252.6 ± 0.2 million years, synchronous with the Siberian flood volcanism, and it occurred within the quoted uncertainty.
Migration and Security: Political, Social and Economic Contexts of Migration
The current immigration debate in labour-importing countries such as Malaysia centres largely on whether migrants are an asset or a threat. On the one hand, migrant labour is an important economic asset in meeting labour shortages, keeping down labour costs and providing a range of skills not available locally. On the other, there are concerns that migrants put pressure on health and educational services and affect national security. It is also increasingly evident that many people move in disregard of the borders that delineate nations because they aspire to achieve a better life. This movement is perceived to undermine national structures since some migrants operate outside official channels and it is thus in local situations and contexts that the impact of migration is experienced, debated, and contested most directly. The current debate suggests that Southeast Asia is facing an important change of direction due to migration contributing to the reinvention and reconstruction of increasingly impenetrable borders. With the aim of contributing to this ongoing debate in Southeast Asia and the wider Asia-Pacific region, the Malaysia and Singapore Society of Australia addressed these and other issues at its Fourteenth Colloquium in December 2006. The Colloquium theme - Boundaries and Shifting Sovereignties: Migration, Security and Regional Cooperation In Asia - was tackled from a variety of perspectives. Seven papers from the interdisciplinary colloquium were selected for this special issue and provide new insights into the debates around migration and security in the region. In this volume we first examine migration issues focussing on state and societal perceptions towards migrant workers in Malaysia, the migration-trafficking-refugee nexus and the role of the Jesuit Refugee Service, a faith-based organisation that works with refugee groups in the Asia-Pacific. Second, in the context of rethinking about borders, we examine the key issue of security and how Malaysia in particular deals with regional security issues and conflict at its borders with Thailand and the Philippines. The question of suicide bombers in Indonesia is also considered in the wider context of national and regional security.
Using high precision CA-IDTIMS zircon age determinations to interpret correlation and depositional rates in Permian coal sediments of the Sydney, Gunnedah and Bowen basins
The chronostratigraphic framework of the Sydney, Gunnedah and Bowen basins using CA-IDTIMS geochronology is enhancing correlation of stratigraphic units and providing a better understanding of local and regional sedimentation patterns. Ages range from 271.45 Ma (Rowan Formation) to 247.71 Ma (Garie Formation). Two examples demonstrate these studies. Firstly, depositional rates in coal sequences are demonstrated. In the Ulan Coal (Sydney Basin), both the C Ply (256.05 Ma) and the F Ply (257.03 Ma) tuffs have been dated and are separated by about 5 m, giving a depositional rate of about 5.1 m/my. In the Yebna 1 well (Bowen Basin) tuff beds from the top and bottom of a coal interval of the Kaloola Member of the Bandanna Formation, separated by 8.9 m, were dated as 252.49 Ma and 252.97 Ma indicating a depositional rate of 18.6 m/my. The Trinkey Formation (Gunnedah Basin), with 2 thin coal beds, has a maximum thickness of 258 m. Tuff beds near the top and bottom have ages of 253.27 Ma (Blackville 1) and 255.57 Ma (Brawboy 1), a depositional rate of 255 m/my. Secondly, precise local and regional stratigraphic correlation can be demonstrated. Examples are the Awaba Tuff and the Nalleen Tuff; the Hoskinsons Formation of the Gunnedah Basin with the Ulan Coal of the Western Sydney Basin and the Woonona Coal Member of the Wilton Formation of the Southern Sydney Basin. A previously suggested correlation that we can demonstrate as incorrect is that of the Watermark Formation with the Nowra Sandstone.
Introduction to 'Mobility, Labour Migration And Border Controls In Asia'
Migration is regarded as the earliest form of globalisation and human migrations have been a constant theme throughout history. Because there were no political boundaries, the movements of people were usually referred to as migration. According to Bohning (1984) the international migration of human beings dates back only to when the 'nation-state' took hold in Europe during the Industrial Revolution, and as a result of colonialism spread in all directions throughout the world. The nation state brought along with it a 'we-they' or 'in-out' distinction and people become identified with a particular nation. Movement from one nation to another or international migration required a change in allegiance and citizenship. In Asia and elsewhere colonial powers carved out new states with precisely delineated boundaries but kept borders open to trade, investment and labour flows in keeping with the growth of the international economy. In the post Second World War period, decolonisation and the dissolution of empires resulted in the emergence of independent nation states in the Asian region. The East Asian states embraced the 'new' globalisation via trade liberalisation strategies and export-led growth. Concurrently, a new form of the international division of labour brought opportunities for export-oriented industrialisation in East Asia. These countries' comparative advantage lay mainly in lower labour costs, and the labour market thus became one of the main channels through which globalisation impacted on the Asian economies.
Geochemistry of axial lavas from the mid-and southern Mariana Trough, and implications for back-arc magmatic processes
The Mariana Trough, a relatively simple intra-oceanic back-arc basin, is ideal for investigating magmatic processes and mantle- crust interaction in a subduction setting. We present new major- and trace element compositions for 31 basaltic lava and glass samples from the Mariana Trough back-arc spreading center. The studied lavas include phenocrysts of plagioclase, olivine and pyroxene. Major element compositions show that these lavas range from tholeiitic basalt to basaltic andesite, and belong to a sub- alkali tholeiitic series produced by fluid-influenced fractional crystallization of primary basaltic melts. Trace element composi- tions show that these lavas are transitional between typical normal mid-ocean ridge basalts (MORB) and island arc basalt (IAB), and are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs). Trace element ratios, e.g., Ba/Th, Pb/Ce, Th/Nd, La/Sm, Th/Nb, Ba/Nb and Th/Nb, indicate that the mantle from which these lavas were derived underwent modification resulting from the addition of multiple subduction components. Some typical trace element ratios (e.g., Ba/Nb- total subduction component, Ba/Th- shallow subduction, and Th/Nb-deep subduction component) from our new data and the literature suggest that a latitudinal variation exists in addition to subduction components, and indicates a more complex and heterogeneous distribution of subduction components in the Mariana back-arc region. We suggest that, (1) compared to back-arc locations at 18° N and 15.5° N, lavas from back-arc locations at 17° N indicate higher levels of modification by hydrous fluid released from the subducted slab, and (2) compared to back-arc locations at 17° N and 15.5° N, petrogenesis of lavas from back-arc locations at 18° N indicates a greater influence of sediment melt.
Palaeobiogeographic implications of Middle Permian brachiopods from Johore (Peninsular Malaysia)
A new Middle Permian locality in northern Johore, Peninsular Malaysia, yields a small-sized, but compositionally unique, brachiopod fauna consisting of eight species: 'Pseudoleptodus' sp., 'Caricula' cf. 'salebrosa' Grant, 'Neochonetes' ('Nongtaia') aff. 'arabicus' (Hudson & Sudbury), 'Karavankina' sp., 'Transennatia' cf. 'insculpta' (Grant), 'Hustedia' sp., 'Orthothetina' sp., and martiniid indet. The first four genera are new records for Malaysia; in particular, the rare taxa 'Pseudoleptodus' and 'Caricula' characterize the fauna. The brachiopods occur together with the ammonoid 'Agathiceras' sp., the nautiloid 'Foordiceras'? sp., bivalves, and crinoid stems. The locality belongs to the East Malaya terrane of the Cathaysian biotic region, but some affinities to species of the Sibumasu province are recognized. The Malaysian forms of 'Pseudoleptodus', 'Caricula' and 'Transennatia' are similar to those of the Ratburi Limestone (southern Thailand). A Roadian–early Wordian age is interpreted for the Johore fauna. The similarity of brachiopods reported here with those from the Ratburi Limestone suggests that there was species interchange or one-way migration between shallow waters of East Malaya and Sibumasu across the main Palaeo-Tethys. The Tethyan seaway between the two terranes must have been narrower than previously interpreted by some authors to allow such faunal traffic during the Roadian–Wordian time period.
High-precision U-Pb CA-TIMS calibration of Middle Permian to Lower Triassic sequences, mass extinction and extreme climate-change in eastern Australian Gondwana
Twenty-eight new high-precision Chemical Abrasion Isotope Dilution Thermal Ionisation Mass Spectrometry U-Pb zircon dates for tuffs in the Sydney and Bowen Basins are reported. Based on these new dates, the Guadalupian-Lopingian/Capitanian-Wuchiapingian boundary is tentatively placed at the level of the Thirroul Sandstone in the lower part of the Illawarra Coal Measures in the Sydney Basin. The Wuchiapingian-Changhsingian boundary is at or close to the Kembla Sandstone horizon in the Illawarra Coal Measures, southern Sydney Basin, in the middle part of the Newcastle Coal Measures in the northern Sydney Basin, and in the middle of the Black Alley Shale in the southern Bowen Basin. The end-Permian mass extinction is recognised at the base of the Coal Cliff Sandstone in the southern Sydney Basin, at the top of the Newcastle Coal Measures in the northern Sydney Basin, and close to the base of the Rewan Group in the Bowen Basin and is dated at c. 252.2 Ma. The end-Permian mass extinction is interpreted to be synchronous globally in both marine and terrestrial environments, and in high and low latitudes (resolution <0.5 my). The GSSP-defined Permian-Triassic boundary is interpreted to be approximately at the level of the Scarborough Sandstone in the lower Narrabeen Group, Sydney Basin, and in the lower Rewan Group, Bowen Basin. Newdates presented here suggest that the P3 and P4 glacial episodes in the Permian of eastern Australia are early Roadian to early Capitanian, and late Capitanian to mid Wuchiapingian in age respectively. The greenhouse crisis in the uppermost Pebbly Beach and Rowan Formations of the Sydney Basin is interpreted as early mid Roadian, a mid-Capitanian age for the crisis at the base of the Illawarra/Whittingham Coal Measures is confirmed. Greenhouse crises in the upper Illawarra/ Newcastle Coal Measures and lower Narrabeen Group of the Sydney Basin are dated as upper Changhsingian-Induan, and in the upper Narrabeen Group/lower Hawksbury Sandstone as upper Olenekian.
Late Palaeozoic and Mesozoic tectonic and palaeogeographical evolution of SE Asia
SE Asia comprises a collage of continental terranes derived directly or indirectly from the India–Australian margin of eastern Gondwana. The Late Palaeozoic and Mesozoic evolution of the region involved the rifting and separation of three elongate continental slivers from eastern Gondwana and the successive opening and closure of three ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. The Sukhothai Island Arc System, including the Linchang, Sukhothai and Chanthaburi terranes, is identified between the Sibumasu and Indochina–East Malaya terranes in SE Asia and was formed by back-arc spreading in the Permian. The Jinghong, Nan–Uttaradit and Sra Kaeo sutures represent the closed back-arc basin. The Palaeo-Tethys is represented to the west by the Changning–Menglian, Chiang Mai/Inthanon and Bentong–Raub suture zones. The West Sumatra and West Burma blocks rifted and separated from Gondwana, along with Indochina and East Malaya in the Devonian, and together with South China formed a composite terrane 'Cathaysialand' in the Permian. They were translated westwards to their positions outboard of the Sibumasu Terrane by strike-slip tectonics in the Late Permian–Early Triassic at the zone of convergence between the Meso-Tethys and Palaeo-Pacific plates. SW Borneo is tentatively identified as possibly being the missing 'Argoland' that separated from NW Australia in the Jurassic. Palaeogeographical reconstructions for the Late Palaeozoic and Mesozoic illustrating the tectonic and palaeogeographical evolution of SE Asia are presented.
Tectonic evolution of the Malay Peninsula
The Malay Peninsula is characterised by three north-south belts, the Western, Central, and Eastern belts based on distinct differences in stratigraphy, structure, magmatism, geophysical signatures and geological evolution. The Western Belt forms part of the Sibumasu Terrane, derived from the NW Australian Gondwana margin in the late Early Permian. The Central and Eastern Belts represent the Sukhothai Arc constructed in the Late Carboniferous-Early Permian on the margin of the Indochina Block (derived from the Gondwana margin in the Early Devonian). This arc was then separated from Indochina by back-arc spreading in the Permian. The Bentong-Raub suture zone forms the boundary between the Sibumasu Terrane (Western Belt) and Sukhothai Arc (Central and Eastern Belts) and preserves remnants of the Devonian-Permian main Palaeo-Tethys ocean basin destroyed by subduction beneath the Indochina Block/Sukhothai Arc, which produced the Permian-Triassic andesitic volcanism and I-Type granitoids observed in the Central and Eastern Belts of the Malay Peninsula. The collision between Sibumasu and the Sukhothai Arc began in Early Triassic times and was completed by the Late Triassic. Triassic cherts, turbidites and conglomerates of the Semanggol "Formation" were deposited in a fore-deep basin constructed on the leading edge of Sibumasu and the uplifted accretionary complex. Collisional crustal thickening, coupled with slab break off and rising hot asthenosphere produced the Main Range Late Triassic-earliest Jurassic S-Type granitoids that intrude the Western Belt and Bentong-Raub suture zone. The Sukhothai back-arc basin opened in the Early Permian and collapsed and closed in the Middle-Late Triassic. Marine sedimentation ceased in the Late Triassic in the Malay Peninsula due to tectonic and isostatic uplift, and Jurassic-Cretaceous continental red beds form a cover sequence. A significant Late Cretaceous tectono-thermal event affected the Peninsula with major faulting, granitoid intrusion and re-setting of palaeomagnetic signatures.
The Chanthaburi terrane of southeastern Thailand: Stratigraphic confirmation as a disrupted segment of the Sukhothai Arc
A Permo-Triassic volcanic arc system, the Sukhothai Arc, is recognised between the Indochina and Sibumasu continental blocks. The Chanthaburi terrane is here interpreted as a fault-detached, highly disrupted southern segment of the Sukhothai Arc, occupying part of southeastern Thailand and extending into Cambodia. The Klaeng tectonic line is defined as the boundary between the Chanthaburi terrane and Sibumasu block. The stratigraphy of the Chanthaburi terrane is compared with that of the Sukhothai terrane in Northern Thailand. The Late Palaeozoic-Mesozoic sequences of these two volcanic arc terranes in the Sukhothai Zone share important similarities, but show marked contrasts to those of the Sibumasu and Indochina blocks, where the Late Permian-Triassic is largely absent due to the Indosinian I unconformity (western Indochina) or is dominantly carbonates with little terrigenous clastic input (Sibumasu). There is no clear evidence of pre-Carboniferous sedimentary rocks for either the Sukhothai or Chanthaburi terranes. Late Permian lyttoniid brachiopod shale near Klaeng in the Chanthaburi terrane was revisited. The brachiopod, previously reported as 'Leptodus', is re-identified to 'Oldhamina', the genus previously known, elsewhere in Southeast Asia, only in the Huai Tak Formation of the Sukhothai terrane. 'Oldhamina' in Thailand is confined to the Sukhothai Arc. The marine stratigraphy of the Sukhothai Arc is represented by a Permian-Triassic lithological succession of mixed carbonates and siliciclastics, with common volcanic material. The Late Permian and Triassic litho- and biostratigraphy of the Chanthaburi terrane are comparable with the upper Ngao and Lampang groups of the Sukhothai terrane; in particular, they share similar successions from 'Oldhamina' brachiopod bearing shale to 'Palaeofusulina-Colaniella' foraminifer bearing limestone in the latest Permian. Marine depositional conditions were terminated on the Sukhothai Arc by end-Triassic times, later than on the Indochina block (Late Permian) but earlier than on the Sibumasu block (Jurassic/Cretaceous).