Age and origin of laterite and silcrete duricrusts and their relationship to episodic tectonism in the mid‐north of South Australia∗

Differential earth movements occurred during Eocene, Miocene, and late Caino‐zoic times. The faulting formed basins of sedimentation, led to dissection of land‐surfaces in some localities and burial in others, and faulted the Cainozoic sediments.

Laterite and silcrete cap remnants of relict landsurfaces of two different ages. Laterite formed before the Eocene; it was faulted and dissected during the Eocene in the north but continued to develop until the Miocene in the south. Silcrete formed from Eocene to Miocene times; its dissection was promoted by late Cainozoic tectonism.

Since laterite and silcrete formed on the same strata in warm, very moist environments, lithology and climate are not important genetic factors causing laterite to form at one time and silcrete at another. Only base levels of erosion differed. The silcrete surface was largely developed by streams flowing into mid‐Cainozoic lacustrine basins, whereas there is no evidence that these drainage conditions prevailed for laterite formation.     

Middle and Late Tertiary Palaeogeography and Palaeoenvironment on the Northern Continental Margin of the South China Sea

Based essentially on research results of calcareous nannofossils, combined with some other microfossil da-ta and several secondary depositional breaks, this paper discusses the criteria of division and comparison of themiddle and late Tertiary marine sediments, palaeogeographical and palaeoenvironmental evolution andpalaeoclimates on the northern continental margin of the South China Sea, comprising the Tainan basin, PearlRiver Mouth basin. Southeast Hainan basin and Beibu Gulf basin. Study shows that the upper Oligocene toPliocene strata in the whole area consist essentially of marine sediments except in the Beibu Gulf basin. Theyinclude littoral. neritic and deltaic sediments as well as carbonate rock-bioherm limestone. The sea advancedfrom southeast to northwest. During the transgression there appeared three culminations coinciding to thestages of deposition of nannofossil zones NN4-5, NN11 and 13-15.     

U–Pb age and origin of gem zircon from the New England sapphire fields,New South Wales,Australia

Chemical compositions and geochronological data utilising the laser ablation ICP-MS technique are presented for zircon megacrysts found in alluvial gem corundum deposits associated with Upper Cretaceous–Cenozoic alkali basalts in the Inverell district-New England field, New South Wales, eastern Australia. Three localities, Kings Plains, Swan Brook and Mary Anne Gully, produce gem-quality transparent dark brown and yellow zircon megacrysts, mostly under 10 mm in size. Although brown zircon shows relative enrichment in Hf and REE, there are no differences in relative transition metal concentrations between the colours. Chemical homogeneity within a single crystal indicates stable crystallisation conditions. The ²⁰⁶Pb/²³⁸U age of zircon megacrysts from these three localities define older and younger groups of 216–174 Ma and 45–37.7 Ma, respectively. The ?_Hf values of zircon megacrysts from Kings Plains show +7.51±0.34 in the older group and +10.72±0.31 in the younger group. Swan Brook zircons give +11.54±0.47 and +8.32±0.58, and Mary Anne Gully zircons are +13.67±0.63 and +8.50±0.48, respectively. These zircons from New England alluvial gem deposits have two main formational events around Upper Triassic–Lower Jurassic and Eocene episodes. Most originated from lithospheric mantle and all were brought-up by later host basaltic magmas.     

Tertiary Calcareous Nannofossil Biostratigraphy in the North Part of the South China Sea

The marine Tertiary sequence in the north part of the South China Sea may be divided into 18 LateOligocene to Pliocene calcareous nannofossil zones and one unnamed Eocene assemblage based on an analysisof calcareous nannofossils from 40 offshore boreholes. The unnamed Eocene assemblage has been found onlyon the northeast margin of the Zhujiangkou basin. The 18 cakareous nannofossil zones of the Late Oligoceneto Pliocene were deposited in succession, but their development degrees are different. Among the 18 calcareousnannofossil zones, those corresponding to Martini's (1971) NN4- NN5 zones, NN11 zone and NN13-NN15zones are well developed, relatively persistent laterally and also widely distributed. They are the importantmarkers for the stratigraphical subdivision and correlation of the Upper Tertiary between the various basins inthe north part of the South China Sea. Based on the calcareous nannofossils and the sedimentsry features coup-led with the foraminifer zonation in certain basins, the present paper discusses the sedimentary characteristicsof the marine Tertiary and as well as the distribution and development of the sedimentary hiatus in the region.The calcareous nannofossil markers for the Upper / Lower Tertiary and the Quaternary / Tertiary boundaries,and the characteristics and geological significance of the reworked calcareous nannofossils are also discussed inthe paper.     

Late Cretaceous – Early Tertiary sedimentation and tectonic inversion in the southern Netherlands

Analysis of the Upper Cretaceous stratigraphy of the Peel Block reveals the basin development of the block to have been influenced by both the inversion of the Roer Valley Graben and Central Netherlands Basin, and the overall Late Cretaceous transgression. Sediments of Santonian to Danian age were deposited on the block. These sediments are compared with the detailed lithostratigraphy of southern Limburg, where Late Cretaceous strata are exposed. Four successions can be recognised in southern Limburg. The two oldest successions, the Santonian Oploo Formation (new name, proposed in the present contribution) and the mainly Early Campanian Vaals Formation, are restricted to the central and northern parts of the block. These siliciclastic formations were deposited under the influence of inversion of the Roer Valley Graben and the Central Netherlands Basin, as well as under the influence of a rising sea level. Towards the north, sands of the Oploo Formation grade into marls and chalks of the Ommelanden Formation. The two youngest successions comprise the largely Late Campanian to Maastrichtian Gulpen and Maastricht Formations and the Danian Houthem Formation. These chalk formations were deposited under the influence of regional subsidence during a sea-level highstand. Subsequent to deposition of the Houthem Formation, a regional regression triggered a change from shallow-marine carbonate to paralic siliciclastic deposition.     

Zircon geochronology constraints on the age and nature of ‘Precambrian metamorphic rocks’ in the Xing’an block of Northeast China

The Great Xing’an Range in Northeast China is located in the eastern part of the Central Asian Orogenic Belt. From north to south, the Great Xing’an Range is divided into the Erguna, Xing’an, and Songliao blocks. Previous U–Pb zircon geochronology results have revealed that some ‘Precambrian metamorphic rocks’ in the Xing’an block have Phanerozoic protolith ages, questioning whether Precambrian basement exists in the Xing’an block. We present laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating results for zircons from suspected Precambrian metamorphic rocks in the Xing’an block. Meta-rhyolites of the Xinkailing Group in Nenjiang yield magmatic ages of 355.8 Ma. Detrital zircons from phyllites of the Xinkailing Group in Duobaoshan yield populations of ca. 1505, ca. 810, and ca. 485 Ma, with the youngest peak constraining its depositional age to be <485 Ma. Zircons from amphibolitic gneisses of the Xinkailing Group in Nenjiang have magmatic ages of 308.6 Ma. Mylonitic granites of the Xinkailing Group in Nenjiang have zircon magmatic ages of 164 Ma. Detrital zircons from two-mica quartz schists of the Luomahu Group in the Galashan Forest yield ca. 2419, ca. 1789, ca. 801, ca. 536, ca. 480, and ca. 420 Ma, with the youngest peak indicating its depositional age as <420 Ma. Detrital zircons from mylonitized sericite–chlorite schist of the Ergunhe Formation in Taerqi yield populations of 982–948, ca. 519, and ca. 410 Ma, with the youngest peak demonstrating that its depositional age is <410 Ma. These zircon ages for a range of lithologies show that the Great Xing’an Range metamorphic rocks formed during the Phanerozoic (164–485 Ma) and that this crust is mostly Palaeozoic. Based on these results and published data, we conclude that there is no evidence of Precambrian metamorphic basement in the Xing’an block. In summary, the age data indicate that Precambrian metamorphic basement may not exist in the Xing’an region.     

Petrography and origin of granulite‐facies rocks in the Western Musgrave Block,Central Australia

The granulite‐facies rocks in the Tomkinson Ranges of central Australia are dominated by layered felsic (quartzofeldspathic) gneisses with minor interbanded mafic, calcareous, ferruginous, and quartzitic granulites. They are regarded as representing a middle Proterozoic metasedimentary and/or metavolcanic sequence which has undergone anhydrous granulite‐facies metamorphism approximately 1200 m.y. ago. Conditions of metamorphism have been derived from a petrogenetic grid based on several experimentally determined reactions and give estimates of 10–11 kb pressure and 950–1000°C. Such metamorphism could take place close to the base of the crust with a moderate geothermal gradient of 25–30°C/km.     

Petrogenesis and Geodynamic Implications of Late Jurassic Diorite Porphyry in the Neoproterozoic Ophiolitic Mélange of NE Jiangxi (South China)

Mesozoic magmatism is widespread in the eastern South China Block and has a close genetic relationship with intensive polymetallic mineralization. However, proper tectonic driver remains elusive to reconcile the broad intracontinental magmatic province. This study presents integrated zircon U-Pb dating, Hf isotopes and whole-rock geochemistry of the Xiwan dioritic porphyry in the NE Jiangxi ophiolitic mélange. Zircon U-Pb dating by SIMS and LA-ICP-MS methods yielded an emplacement age of ～160 Ma for the Xiwan diorite, confirming its inclusion into the Mesozoic magmatic province in SE China, instead of a component of the Neoproterozoic ophiolitic mélange genetically. The dioritic rocks have low Si02(58.08 wt%-59.15 wt%), and high Na_2 O(5.00 wt%-5.21 wt%) and MgO(4.60 wt%-5.24 wt%) contents with low TFeO/MgO ratios(1.02-1.09). They show an adakitic geochemical affinity but exhibit relatively low Sr/Y ratios(24.8-31.1) and high Y contents(14.6-18.3 ppm) compared to the Dexing adakitic porphyries. In addition, the Xiwan diorites have moderately evolved zircon Hf isotopic compositions(ε_(Hf)(t)=-6.1--0.1; T_(DM2)=1597-1219 Ma). These elemental and isotopic signatures suggest that the Xiwan diorite formed through partial melting of a remnant arc lower crust(i.e., early Neoproterozoic mafic arc-related rocks) in response to the underplating of coeval mafic magmas. In conjunction with the temporal-spatial distribution and complex geochemical characteristics of the Mesozoic magmatism, our case study attests to the feasibility of a flat-slab subduction model in developing the broad intracontinental magmatic province in SE China. The flat-slab delamination tends to trigger an asthenospheric upwelling and thus results in extensive partial melting of the overlying lithospheric mantle and lower crustal materials in an extensional setting during the Mesozoic.     

Dinosaur material from the Lower Greensand Group of Upware,Cambridgeshire, and the age of ‘Wealden’ vertebrates from the ‘Bedfordshire Straits’

Post-Wealden dinosaur remains are rare in the UK, so any material from late Early or Late Cretaceous deposits is potentially of palaeoecological and palaeobiogeographical significance. Four dinosaur specimens collected from the Woburn Sands Formation (Aptian) of Upware, Cambridgeshire were described briefly by Walter Keeping in 1883, but have not been reappraised since. These specimens are identified herein as a ?turiasaurian sauropod tooth and indeterminate iguanodontian ornithopod remains (a tooth, middle caudal vertebra, pollex ungual). Although collected from the Woburn Sands Formation, it is likely that all of these fossils were reworked from older (now absent) sediments and they have usually been regarded as either ‘Wealden’ or Neocomian in age, presumably due to previous identifications of some of these specimens as Iguanodon. However, consideration of UK dinosaur faunas and regional geology indicates that these fossils could potentially be older. Further work is needed on the derived terrestrial fossils of the Lower Greensand Group in order to constrain their ages more precisely so that they can be incorporated into broader studies of regional diversity and palaeoecology.     

Baseline geochemical studies in Australia with particular reference to geohealth studies in the Gawler Craton of South Australia

Geoscience Australia and the Cooperative Research Centre for Landscape Environments and Mineral Exploration, in collaboration with State agencies are conducting a series of pilot baseline geochemical surveys （BGS）. These aim to characterize regional geochemical patterns and contribute to what is presently a limited research direction in Australia. BGS can help （1） establish baselines to monitor future change; （2） target mineral exploration; （3） develop informed environmental policies; and （4） geomedical studies on plant and animal well being. In 2004-05, sampling at an average density of 1 sample per 1100 km^2, was conducted in the Gawler Craton, South Australia. In contrast to our pilot region in the Riverina of New South Wales and Victoria, the Gawler lacks well-developed drainage systems and is dominated by aeolian dunes in its western sector. One of the key aims of the Gawler study is to determine whether elemental excesses or deficiencies exist in the regolith and the implications of these for plant, animal and human health. Top （0-10 cm depth） and bottom （～55-90 cm depth） sediment samples were collected in the lower parts of 42 catchments. The compositions of the 〈75 um and 〈180 um fractions were analyzed using XRF （major and some trace elements）, ICP-MS （most trace elements） and ISE （F） methods. Preliminary results show that F, Cr and V are locally elevated above national and international guideline concentrations, raising concerns that these elements may pose potential health issues. Heavy mineral fractions （density 〉2.95） in 4 samples （3 sites） are dominated by iron oxides, spinels, rutile, zircon and barite. Some Cr and V may be related to heavy minerals such as spinels, limiting their bioavailability. Cu, Se and Zn are potentially deficient in parts of the region, but once identified in agricultural areas can easily be remedied through the application of suitable fertilizers.     

Comparison of the ‘strike‐slip’ versus the ‘episodic rift‐sag’ models for the origin of the Isa Superbasin

In this paper we assess two competing tectonic models for the development of the Isa Superbasin (ca 1725–1590 Ma) in the Western Fold Belt of the Mt Isa terrane. In the ‘episodic rift‐sag’ tectonic model the basin architecture is envisaged as similar to that of a Basin and Range province characterised by widespread half‐graben development. According to this model, the Isa Superbasin evolved during three stages of the Mt Isa Rift Event. Stage I involved intracontinental extension, half‐graben development, the emergence of fault scarps and tilt‐blocks, and bimodal volcanism. Stage II involved episodic rifting and sag during intervening periods of tectonic quiescence. Stage III was dominated by thermal relaxation of the lithosphere with transient episodes of extension. Sedimentation was controlled by the development of arrays of half‐grabens bounded by intrabasinal transverse or transfer faults. The competing ‘strike‐slip’ model was developed for the Gun Supersequence stratigraphic interval of the Isa Superbasin (during stage II and the beginning of stage III). According to this model, sinistral movements along north‐northeast‐orientated strike‐slip faults took place, with oblique movements along northwest‐orientated faults. This resulted in the deposition of southeast‐thickening ramp sequences with local sub‐basin depocentres forming to the west and north of north‐northeast‐ and northwest‐trending faults, respectively. It is proposed that dilation zones focused magmatism (e.g. Sybella Granite) and transfer of strike‐slip movement resulted in transient uplift along the western margin of the Mt Gordon Arch. Our analysis supports the ‘episodic rift‐sag’ model. We find that the inferred architecture for the strike‐slip model correlates poorly with the observed structural elements. Interpretation is made difficult because there has been significant modification and reorientation of fault geometry during the Isan Orogeny and these effects need to be removed before any assertion as to the basin structure is made. Strike‐slip faulting does not explain the regional‐scale pattern of basin subsidence. The ‘episodic rift‐sag’ model explains the macroscopic geometry of the Isa Superbasin and is consistent with the detailed sedimentological analysis of basin facies architecture, and the structural history and geometry.     

The actinopterygian fish fauna of the Late Kimmeridgian and Early Tithonian ‘Plattenkalke’ near Solnhofen (Bavaria,Germany): state of the art

An overview is presented of the actinopterygian fishes from the Late Jurassic (Late Kimmeridgian and Early Tithonian) ‘Plattenkalke’ near Solnhofen (Solnhofen lithographic limestone), Bavaria, Germany. The fish fauna is very diverse, with the palaeonisciform Coccolepis, halecostomes such as Lepidotes, Heterostrophus, three genera of macrosemiids and six genera of pycnodontiforms, halecomorphs including two genera of caturids, two genera of amiids, Ophiopsis, ‘Furo’, Ionoscopus, Brachyichthys, Callopterus, Liodesmus, ?Lophiurus, five genera of pachycormids, three genera of pholidophorids, Pleuropholis, two genera of aspidorhynchids and eleven genera of basal teleosts. Although several groups have been subject of revision, most of the fauna remains poorly known. Study of this rich fauna will provide a lot of information on the phylogeny and interrelationships of halecostome fishes.

     

On the Age of the Dongtang Formation in the Hengyang Basin of Hunan and the Cretaceous and Tertiary Boundary

Since the coexistence of the Cretaceous and Palaeocene was ascertained in the Hengyang Basin of Hunan in the middle of the 1960's, the Cretaceous and Tertiary boundary has been discussed in several papers, but it still remains controversal. The points at issue are the connotation, stratigraphical position and lateral correlation of the Dongtang (or Chejiang) Formation.     

Birth and death of the Late Cretaceous “La Luna Sea”, and origin of the Tres Esquinas phosphorites

Deposition of organic carbon-rich intervals of the La Luna and Navay formations of northwestern Venezuela was governed by the development of key paleobathymetric barriers (Santa Marta and Santander massifs, Paraguana Block, and ancestral Mérida Andes). These enhanced the development of anoxia in the “La Luna Sea” by causing poor circulation and limited ventilation. Anoxia was also promoted by high evaporation and low precipitation rates (high salinity bottom water), and high levels of marine algal productivity (high organic matter flux). Nutrient supply was augmented by infrequent fluvial sources.Bottom water oxygen levels increased from the Late Santonian through the end of the Cretaceous. Ventilation of anoxic bottom waters may have been enhanced by more frequent or intense seasonal upwelling (caused by higher wind stress) and catastrophic overturn, as well as the removal of a key paleobathymetric barrier. Common byproducts of overturn events were massive phytoplankton blooms, which produced red tides. Fish and marine reptile bone beds within the Tres Esquinas Member (La Luna Formation) are attributed to massive mortality during these events, and are correlative with similar Campanian units in eastern Colombia. During the Maastrichtian, increasing ventilation, combined with siliciclastic dilution, ultimately produced sediments with lower total organic carbon (TOC) content.     

U-Pb zircon age of gabbroids of the Ust’-Belaya mafic-ultramafic massif (Chukotka) and its interpretation

The Ust’-Belaya mafic-ultramafic massif is assigned to the Western Koryak fold belt and largely composed of residual spinel peridotites, layered spinel and plagioclase peridotites, and gabbros. These rocks are crosscut by occasional plagiogranite and diorite veins and exhibit locally a close spatial association with basalts and carbonate-sedimentary deposits of Late Devonian and Early Carboniferous age. Based on this evidence, the massif was ascribed to the pre-Late Devonian ophiolite association. Our study presents new U-Pb SHPIMP II zircon ages and petrographic and mineralogical data on samples of the layered amphibole gabbro and vein diorite from the Ust’-Belaya massif. The approximate concordant U-Pb age corresponding to a timing of of amphibole gabbro crystallization is 799 ± 15 Ma, and the concordant U-Pb age reflecting a timing of of vein diorite crystallization is 575 ± 10 Ma. These ages coupled with geological studies of the massif, petrological and mineralogical investigations of the dated samples, as well as literature data on the petrology of peridotites and the age of formed plagiogranites suggest that the peridotites and layered gabbros of the Ust’-Belaya massif were formed by the Late Riphean, whereas the vein diorite and plagiogranite were resulted from a later (Vendian-Cambrian) magmatic stage. The peridotites and gabbros of the massif display no genetic relationship with spatially associated basalts and sedimentary rocks and, thus, they cannot be considered as members the pre-Late Devonian ophiolitic association. The results of this study will inevitably lead to a significant revision of geological and geodynamic interpretations of the Ust’-Belaya mafic-ultramafic massif. However, uneven study of the Precambrian complexes of the Koryak and Chukchi areas, their evolution in different structures of the region cannot yet be described by a single geodynamic scenario.     

Place,identity and stigma: blocks and the ‘blockies’ of Tara,Queensland, Australia

This article explores the role of geographical context in generating a stigmatised identity among residents of Tara rural subdivisions in the coal seam gas fields in Queensland’s Western Downs. The research was based on qualitative interviews with Tara ‘Blockies’, as these residents are commonly referred to, that revealed how their existence in the middle of an agrarian region resulted in the assignation of a stigma that has marked them as different, and subsequently devalued their status. We explain that this distinction and category division of the normals, referring to Tara’s Agrarian residents, from the ‘stigmatised’ led to an antagonistic relationship that prevented successful socio-cultural assimilation. We demonstrate how an immoral place becomes disadvantaged, resulting in poor well-being, and how imposed labels threaten the self-esteem of its occupants.     

K‐Ar dating of Permian and Tertiary igneous activity in the Southeastern Sydney Basin,New South Wales

The southern part of the Sydney Basin of New South Wales is comprised mainly of Permian and Triassic marine to freshwater clastic sedimentary rocks. Within this sequence there are six latite extrusive units, several medium‐sized monzonite intrusions and a large number of small to medium‐sized basic to intermediate intrusions. Thin basaltic flows were extruded onto the Tertiary topographic surface. All of these rocks are relatively undeformed.

Radiometric (K‐Ar) dating has previously been carried out on Mesozoic and Tertiary intrusions and flows of the southwestern portion of the Sydney Basin. However, relatively few Permian, and no post‐Permian, K‐Ar dates have been published for the southeastern portion of the basin. The present investigation provides nine K‐Ar dates from the latter area.

Four extrusive and intrusive units have been confirmed as Permian in age (238 ± 6; 241 ± 4; 245 ± 6; and 251 ± 5 m.y.). Five post‐Permian (on stratigraphic criteria) intrusions yielded Tertiary ages (26.2 ± 3.0; 47.9 ± 2.5; 49.0 ± 4.0; 49.4 ± 2.0; and 58.8 ± 3.5 m.y.). The Permian ages agree with previously published K‐Ar data from the southeastern Sydney Basin, and the Tertiary ages complement and extend the data from the southwestern portion of the basin. However, no Mesozoic K‐Ar dates were obtained from the southeastern Sydney Basin. The Tertiary intrusions may have been emplaced as a result of rifting between Australia and New Zealand, or between Australia and Antarctica, or both.