Patterns of mixed siliciclastic‐carbonate sedimentation adjacent to a large dry‐tropics river on the central Great Barrier Reef shelf,Australia

The Great Barrier Reef represents the largest modern example of a mixed siliciclastic‐carbonate system. The Burdekin River is the largest source of terrigenous sediment to the lagoon and is therefore an ideal location to investigate regional patterns of mixed sedimentation. Sediments become coarser grained and more poorly sorted away from the protection of eastern headlands, with mud accumulation focused in localised ‘hot spots‘ in the eastern portion of embayments protected from southeast trade winds. The middle shelf has a variable facies distribution but is dominated by coarse carbonate sand. North of Bowling Green Bay, modern coarse carbonate sand and relict quartzose sand occur. Shore‐normal compositional changes show Ca‐enrichment and Al‐dilution seawards towards the reef, and shore‐parallel trends show Al‐dilution westwards (across bays) along a Ca‐depleted mixing line. Intermediate siliciclastic‐carbonate sediment compositions occur on the middle shelf due to the abundance of relict terrigenous sand, a pattern that is less developed on the narrow northern Great Barrier Reef shelf. Rates of sediment deposition from seismic evidence and radiochemical tracers suggest that despite the magnitude of riverine input, 80–90% of the Burdekin‐derived sediment is effectively captured in Bowling Green Bay. Over millennial time‐scales, stratigraphic controls suggest that sediment is being preferentially accreted back to the coast.     

A proposal for time‐stratigraphic subdivision of the Australian Precambrian

Sufficient stratigraphic and radiometric data are now available to provide the basis for a time‐stratigraphic subdivision of the Precambrian in Australia.

The data show that a major stratigraphic break occurred from about 2,600 to 2,300 m.y. and another at about 1,800 m.y., and that igneous activity was widespread from 2,700 to 2,600 m.y., and at about 1,800 m.y. and 1,500 m.y. Three largely unmetamorphosed rock sequences represent most of the time‐interval from 2,300 m.y., to the start of the Cambrian.

The terms Archaean and Proterozoic are tentatively retained with a boundary dated at or before about 2,300 m.y. Time‐rock subdivision of the Proterozoic is proposed in terms of the three unmetamorphosed rock sequences deposited after 2,300 m.y. The oldest time‐rock unit is to be defined from the Hamersley Range area of Western Australia and is tentatively named the Lower Proterozoic ("Nullaginian") System with a base dated at about 2,300 m.y. The other units are the Carpentarian and Adelaidean Systems which have bases dated at about 1,800 m.y. and 1,400 m.y., respectively. The top of the Adelaidean System is defined by the base of the Cambrian.

The boundaries between the proposed time‐rock units have ages comparable with those of boundaries between some overseas Precambrian subdivisions based on plutonic events.     

Plio‐Pleistocene tectonics and eustasy in the Gippsland Basin,southeast Australia: Evidence from magnetic imagery and marine geological data

The Pliocene and Pleistocene sediments of the Gippsland shelf are dominated by mixed carbonates and siliciclastics. From a detailed stratigraphic study that combines conventional marine geology techniques with magnetic imagery, the Late Neogene tectonic and eustatic history can be interpreted and correlated to the onshore section. Stratigraphic analyses of eight oil and gasfield foundation bores drilled to 150 m below the seabed revealed three principal facies types: (i) Facies A is fine‐grained limestone and limey marl deeper than 50 m below the seabed, of Late Pliocene age (nannofossil zones CN11–12); (ii) Facies B is a fine‐coarse pebble quartz‐carbonate sand that occurs 10–50 m below the seabed in the inner shelf, grading down into Facies A in wells in the outer shelf, and is of Early‐Middle Pleistocene age (nannofossil subzones CN13a-14b: ca 1.95–0.26 Ma); and (iii) discontinuous horizons of Facies C composed of carbonate‐poor carbonaceous and micaceous fine quartz sand occurring 10–50 m below the seabed. The sparse benthic foraminifers in Facies C are inner shelf or Gippsland (euryhaline) Lakes forms. Holocene sands dominate the upper 1.5–2.5 m of the Gippsland shelf and disconformably overlie cemented limestones with aragonite dissolution, indicating previous exposure to meteoric water. Nannofossil dating of the limestones indicates ages within subzone CN14b (dated between ca 0.26 and 0.47 Ma). Airborne magnetic imaging across the Gippsland shelf and onshore provides details of buried magnetic palaeoriver channels and barrier systems. The river systems trend south‐southeast from the Snowy, Tambo, Mitchell, Avon, Macalister and Latrobe Rivers across the shelf. Sparker seismic surveys show the magnetic palaeochannels as seismic ‘smudges’ 20–40 m below the seabed. They appear to correspond to Facies C lenses (i.e. are Early to Middle Pleistocene features). Magnetic palaeobarrier systems trending south‐southwest in the inner shelf and onshore beneath the Gippsland Lakes are orientated 15° different to the modern Ninety Mile Beach barrier trend. Offshore, they correlate stratigraphically to progradation packages of Facies B. Analysis of bore data in the adjacent onshore Gippsland Lakes suggests that a Pliocene barrier sequence 100–120 m below surface is overlain by fluvial sand‐gravel and lacustrine mud facies. The ferruginous sandstone beds resemble offshore Facies C, and are located where magnetic palaeoriver channel systems occur, implying Early to Middle Pleistocene ages. Presence of the estuarine bivalve Anadara trapezia in the upper lacustrine mud facies suggests that the Gippsland Lakes/Ninety Mile Beach‐type barriers developed over the past 0.2 million years. Further inland, magnetic river channels that cut across present‐day uplifted structures, such as the Baragwanath Anticline, suggest that onshore Gippsland uplift continued into the Middle Pleistocene.     

A compilation of Australian heat‐flow measurements

A map is presented based on all known Australian heat‐flow estimates, including five new ones. A second map, based on the first, also is presented, but excludes any determinations judged for any reason to be unreliable. The data show that heat flow over large areas of the continent is effectively uniform to within 0.5 heat flow units (i.e. to within 20 mW m^‐2), with perhaps three major regional heat‐flow provinces being defined in western, central, and eastern Australia.     

Assessment of the relative importance of major sediment‐transport mechanisms in the central Great Barrier Reef lagoon

The delivery, flux and fate of terrigenous sediment entering the Great Barrier Reef lagoon has been a focus of recent studies and represents an ongoing environmental concern. Wave‐induced bed stress is the most significant mechanism of sediment resuspension in the Great Barrier Reef, and field data and mathematical modelling indicates that the combined effects of short‐period wind waves, longer period swell waves, and tidal and wind‐driven currents can often exceed the critical bed stress for resuspension. Suspended‐sediment concentrations at 20 m water depth indicate resuspension seldom occurs on the middle shelf under normal wave conditions. Non‐cyclonic turbidity events are generally confined to the inner shelf. The wave climate in the southern sector of the central Great Barrier Reef lagoon is the most erosive, and resuspension of outer shelf sediments was hindcast for recorded cyclones. Wind‐driven, longshore currents are fundamental to the northward movement of sediment, and the annual northward mass flux from embayments undergoing resuspension in the Burdekin region is estimated to be one order of magnitude larger than the mass of sediment introduced by a moderate flood plume. Strong onshore winds are estimated to generate significant three‐dimensional bottom return currents on approximately 30–70 days per year, forming a potentially significant offshore‐directed sediment flux during high suspended‐sediment concentration events on the inner shelf.     

Fore‐arc evolution in the Tasman Geosyncline: The origin of the southeast Australian continental crust

A new general model describing the extended evolution of fore‐arc terrains is used to analyse the evolution of the southern Tasman Geosyncline and the concomitant growth and kratonisation of the continental crust of southeast Australia during the Palaeozoic. The southern Tasman Geosyncline comprises ten arc terrains (here defined), most of which are east‐facing, and several features formed by crustal extension. Each arc terrain consists of several strato‐tectonic units: a volcanic arc, subduction complex and fore‐arc sequence formed during subduction; and an overlying post‐arc sequence which post‐dates subduction and is composed of flysch, neritic sediments or subaerial volcanics.

When these materials attained a thickness of c. 20 km their internal heat‐balance caused partial melting of the subduction complex and the hydrated oceanic lithosphere trapped beneath it, to yield S‐ and I‐type granitic magma. The magma rose, inducing pervasive deformation of each arc terrain and emplacement of granitoid plutons at high levels in the evolving crust. Transitional basins then developed in many terrains on top of their volcanic arcs or the thinner parts of the buried accretionary prisms. After deformation of the transitional sequences, platform cover accumulated, marking the completion of kratonisation.

Analysis of each arc terrain in terms of the above units leads to a predicted ‘stratigraphy’ for the continental crust of southeast Australia. The crust is complexly layered, with lateral discontinuities reflecting the boundaries of arc terrains which were successively accreted, principally back‐arc to fore‐arc, during crustal development.     

Key section of the Preobrazhenka productive horizon in the Vendian–Lower Cambrian carbonate complex (Lena–Tunguska petroliferous province)

We present results of lithofacies, reservoir, geochemical, well logging, and petrophysical studies of the key section of the Vendian–Lower Cambrian Preobrazhenka productive horizon in the Lena–Tunguska province. We have considered the composition, structure, and formation conditions of the deposits as well as the intensity of postsedimentation processes and the rock geochemistry, petrophysics, and reservoir properties.     

Geological note: Authigenic Sr‐Ba‐Ca carbonate minerals in coals of the Hunter Valley,New South Wales

Strontianite (SrCO₃), witherite (BaCO₃) and alstonite (CaBa[CO₃]₂) were among the range of epigenetic coal cleat/fracture carbonates identified within the Wittingham Coal Measures, Jerrys Plains Subgroup in the Hunter Valley. Three stages of diagenetic cement development, all related to basin evolution, are postulated. Material for the development of the various carbonates was derived from: basinal pore fluids, surrounding rock and organic matrix as a result of diagenetic exchange, active mass transport or devolatilization of basement rocks during metamorphism, including plutonic intrusion.     

Chemostratigraphy of the Vendian–Cambrian carbonate sedimentary cover of the Tuva-Mongolian microcontinent

The carbonate sediments from the Vendian–Cambrian shelf of the Tuva-Mongolian microcontinent were dated by Sr and C isotope chemostratigraphy. Analysis of the Sr-isotopic characteristics (0.70725–0.70873) and δ¹³C variations (+ 10.5 to –3.5‰), as well as their comparison with the data on the key sections of Siberia, Africa, Central Asia, Australia, South America, and Spitsbergen, showed that the carbonate sedimentary cover of the Tuva-Mongolian microcontinent accumulated at 600–520 Ma and the carbonate sediments of the Muren Formation and the basal beds of the Bokson Group near the Ukha-Gol River are the oldest. Their sedimentation followed the Marinoan global glaciation.     

Integrated magnetobiochronology of the Pliocene–Pleistocene Miyazaki succession,southern Kyushu,southwest Japan: Implications for an Early Pleistocene hiatus and defining the base of the Gelasian (P/P boundary type section) in Japan

An integrated magnetobiochronology of the Miyazaki Pliocene–Pleistocene succession in the Miyazaki area, southwest Japan, was established using planktic foraminiferal and calcareous nannofossil biostratigraphy together with paleomagnetic data. The upper Miyazaki succession in the northern Miyazaki region can be divided into the Takanabe, Hisamine (redefined), and Higoyashiki (new) Formations, in ascending order. A depositional hiatus between the Hisamine Formation and the Takanabe and/or older formations was also identified based on integrated magnetobiostratigraphy from five sections including the Nagatani River (NGT) section through the uppermost Miyazaki succession. The hiatus, herein called the Hisamine unconformity, is equivalent to the Kurotaki unconformity between the Miura and Kazusa groups of the Boso Peninsula in central Japan. The depositional hiatus recognised in the lower Pleistocene of Pacific coastal areas in southwestern and central Japan may have resulted from tectonic activity associated with a change in the subduction direction of the Philippine Sea plate, which commenced prior to ca. 2.2 Ma. The youngest unit just below the hiatus is the upper part of the Takanabe Formation in the NGT section. The NGT section represents the continuous Late Pliocene to earliest Pleistocene sequence including the Gauss/Matuyama boundary and is here proposed as the type section for the Pliocene/Pleistocene boundary in Japan, which the IUGS ratified as the base of the Gelasian in 2009.     

Lower Boundary of the Marine Pleistocene in Northern Shelf of the South China Sea

A marine stratigraphic sequence across the Pliocene / Pleistocene boundary has been found in the north-ern continental shelf of the South China Sea. The marine Quaternary deposits in the Yinggehai Basin may ex-ceed 2,000 m in thickness, probably providing the best section for studying the lower boundary of the marinePleistocene in South China. The vertical succession with planktonic foraminifers and nannofossils revealed inboreholes in the basin has been well correlated with that in the international stratotype section of thePliocene / Pleistocene boundary at Vrica, Italy, resulting in the acquirement of a biostratigraphic boundary at1.64 Ma. This boundary, however, does not coincide with any prominent lithological palaeoenvironmentalchanges in the study area and can hardly be used in geological practice. There are, in contrast, significantchanges at the level of LAD of Globorotalia multicamerata sensu lato located below the above-mentionedboundary. The percentage of planktonic foraminifers in the total population and preservation of foraminiferaltests display great changes at this level corresponding to a clear onlap on the seismic profiles and indicating adepositional hiatus at ca. 2.0-2.5 Ma. Since the level can be widely traced in the Pearl River Mouth Basin andthe Beibu Gulf Basin and well corresponds with the marked depositional environmental changes recorded inthe west Pacific and other regions, it is recommended that the Plio / Pleistocene boundary be drawn at the levelof Gr. multicamerata sensu lato LAD, roughly concurrent with the Gauss / Matuyama turn.     

Some features of the evolution of carbonate accumulation in the earth’s history: Communication 1. Evolution of the intensity, mechanism, and setting of carbonate accumulation

Marine and oceanic carbonate accumulation during the Vendian-Cambrian was mostly controlled by the life activity of organisms, which either constructed skeletons and directly transferred carbonates into sediments or created geochemical environments favorable for the precipitation of the carbonate substance. During the first third of the Paleozoic, the chemogenic and biochemogenic mechanisms of limestone formation were replaced by the biogenic one. In the dolomite formation, to the contrary, the chemogenic mechanism progressively replaced the biochemogenic mechanism and its pseudobiogenic modification. The carbonate accumulation occurred in the cyclic mode and its intensity increased with time to reach its peak in the Late Cretaceous. The main paleogeographic domains of carbonate accumulation also experienced changes. They were mainly represented by spacious shelf seas in the Paleozoic; by intraoceanic shoals, reefs and pelagic realm in the Mesozoic; and by the pelagic realm and, to a lesser extent, reefs in the main Cenozoic.     

Magnetostratigraphy and lithostratigraphy of the Laño vertebrate-site: Implications in the uppermost Cretaceous chronostratigraphy of the Basque-Cantabrian Region

Here we present the magnetostratigraphic dating of the Laño locality (Condado de Treviño, northern Iberian Peninsula), one of the most noteworthy Campanian-Maastrichtian vertebrate sites of Europe. A composite section of 75 m thickness (Laño quarry) constructed from multiple, overlapping profiles and a continuous one (Faido) have been sampled for magnetostratigraphy. Thermal demagnetization techniques were systematically applied to 161 standard specimens and allowed characterizing the characteristic remanent magnetism, mostly carried out by magnetite. The palaeomagnetic signal is slightly scattered due to variety of lithologies, but the primary character can be guaranteed, since the normal and reverse directions are pseudo antiparallel; 346, 28 (α₉₅: 11.9°, k: 5.3) and 175, −35 (α₉₅: 16.4°, k: 4.6). Reliable samples allowed us to build the local polarity sequence made of eight magnetozones that has been used to correlate to the Global Polarity Time Scale. The age of the lower part of the Laño-village succession is basal late Campanian (Hoplitoplacenticeras marroti ammonite zone) and fits with the long reversed zone that must correlate to Chron C33r. The pattern of magnetozones allows tracking the section up to C30r at the upper part of the profile. In this correlation, the Laño vertebrate site is regarded as latest Campanian in age as it falls within the C32n (≈72–73.5 Ma). The combined lithostratigraphic and magnetostratigraphic analyses have yielded additional conclusions regarding the vertebrate assemblages that are representative of the Late Campanian of the Iberian Peninsula, in addition to highlight an older occurrence in Europe of some vertebrate groups such as salamandrid lissamphians and anguid lizards (or amphisbaenians).     

Magnetostratigraphy of the Campanian–Maastrichtian Bakchar Basin (southeastern West Siberia)

In this paper the results of magnetostratigraphic studies of the Upper Cretaceous penetrated by two wells (S-124 and S-114) drilled in the Tomsk structural-facies zone (Bakchar iron ore deposit) are presented. The obtained biostratigraphic data show that the sediments formed in the Campanian–Maastrichtian time interval. The high-temperature component of the remanent magnetization identified in the rocks allowed us to compile paleomagnetic columns for each well and correlate the columns, using paleontological data, with each other and with the general magnetostratigraphic and magnetochronological scales. In magnetostratigraphic sections of two wells, the Campanian reverse-polarity Slavgorod Formation (R(km)) with a normal-polarity horizon is correlated with Chron C33(r) (top) and C33(n) (bottom) of the Gradstein scale, and the Maastrichtian normal-polarity Gan’kino Formation with a thin reverse-polarity horizon (N(mt)) is correlated with Chron C30 of this scale.     

The Phosphates of Pleistocene–Holocene Sediments of the Eastern Gallery of Denisova Cave

Authigenic phosphate mineralization was first studied on the territory of Russia on the basis of the Holocene and Pleistocene deposits of Denisova Cave. The formation of phosphates in the eastern gallery is related to biodegradation of the horizons of guano of insectivorous bats, which inhabited the cave in the absence man. The results confirmed the archaeological record of the Holocene and the upper part of Pleistocene sequences of the eastern gallery.     

Ground‐penetrating radar imaging of Pleistocene sediments,Boco Plain,western Tasmania

Ground‐penetrating radar surveys across the southern end of the Boco Plain, western Tasmania, revealed a complex sequence of Quaternary glacial and non‐glacial sediments. The subsurface imaging supported previous suggestions of a complex Boco Plain palaeotopography that incorporates a range of depositional environments and multiple constructional events. The ground‐penetrating radar technique enabled imaging of the sediments to 20 m depth, and permitted identification of different sedimentary facies and constructional events due to the significant contrast in dielectric constant within and between the sediments and bedrock. The bedrock and sediment stratigraphy are in broad agreement with drillcore records from the southern end of the Boco Plain and indicate the utility of the method in the initial stages in the investigation of Pleistocene sedimentary sequences of this type.     

Evolution of the Landscape of the Western Part of the Turan–Uyuk Basin (Tuva Highland) in the Late Pleistocene

Doklady Earth Sciences - A complex of works including geomorphological deciphering, field survey, drilling, electric prospecting, and dating of deposits using the radiocarbon method and optically...     

South Australian farmers’ markets: tools for enhancing the multifunctionality of Australian agriculture

This paper critically examines the role of farmers’ markets in Australian agriculture. A case study is undertaken in South Australia, where all stallholders at three farmers’ markets situated in Adelaide, Willunga and Berri were surveyed regarding their production and marketing techniques. Overall responses supported literature highlighting the importance of farmers’ markets to the producers who chose to exploit this marketing niche. A strong co-reliance on ‘wholesale sales’ was also recognised, suggesting an important integration of productivist and post-productivist approaches to agricultural development. Of most promise for long-term agricultural sustainability was evidence that certain groups of farmers were found to be realising the potential of these and other alternative markets, in terms of their risk reducing capacity, and diversifying to include various conservation values into their agricultural enterprises. These groups were less concerned about market fluctuations and more concerned with issues of social equity, environmental health and having fun, which meant they unwittingly epitomised the goals of political ecology, by challenging the dominant agricultural methods of production and marketing. It seems these groups also recognised that the direct nature of their transactions would sow beneficial social, environmental and economic ‘seeds’ for change. Finally, it is argued that policies to improve access to farmers’ markets and reduce the cost of participation would assist small scale Australian agricultural producers to evolve smoothly into a multifunctional era.     

Experimental modeling of the immobilization of heavy metals at the carbonate adsorption–precipitation geochemical barrier

Experimental data obtained on the adsorption–precipitation immobilization of heavy metals (Cu, Zn, Pb, Cd, Co, and Ni) from acidic and neutral solutions by calcite and dolomite demonstrate that interaction of solutions of heavy metals with these minerals at pH > 7.8–8.1 leads to a significant decrease in the concentrations of the metals because of the crystallization of carbonates of these metals. Except Pb, which is equally removed from solutions by both minerals, the immobilization efficiency of the metals on dolomite is greater than on calculate at the same pH. Residual Zn, Cd, Co, and Ni concentrations are immobilized by chemosorption, which is the most efficient for Cd and less significant for Co, Ni, and Zn. It is proved that artificial geochemical barriers on the basis of carbonate rocks can be efficiently applied to protect environment from contamination with heavy metals.     

Plio–Pleistocene basalts from the Meseta del Lago Buenos Aires,Argentina: evidence for asthenosphere–lithosphere interactions during slab window magmatism

Plio–Pleistocene (3.4–0.125 Ma) post-plateau magmatism in the Meseta del Lago Buenos Aires (MLBA; 46.7°S) in southern Patagonia is linked with the formation of asthenospheric slab windows due to ridge collision along the Andean margin ∼6 Ma ago. MLBA post-plateau lavas are highly alkaline (43–49% SiO₂; 5–8% Na₂O+K₂O), relatively primitive (6–10% MgO) mafic volcanics that have strong OIB-like geochemical signatures. Their relatively enriched Sr–Nd isotope ratios (⁸⁷Sr/⁸⁶Sr=0.7041–0.7049; ¹⁴³Nd/¹⁴⁴Nd=0.51264–0.51279), low ²⁰⁶Pb/²⁰⁴Pb (18.13–18.45), steep REE patterns (La/Yb=11–54), and low LILE/LREE and LILE/HFSE ratios (Ba/La<15, La/Ta<15, Ba/Ta<180; Sr/La=15–22; Th/La<0.13; Ce/Pb>15) are distinctive from most other Neogene Patagonian slab window lavas. These data are interpreted to indicate contamination of OIB-like asthenosphere-derived slab window magmas with an EM1-type component derived from the Patagonian continental lithospheric mantle (CLM). The EM1-type signature in Patagonian slab window lavas are geographically associated with the Deseado Massif and indicate important regional differences in lithospheric mantle chemistry beneath southern Patagonia. We propose that hot, upwelling subslab asthenosphere in slab window tectonic settings can cause significant thermo-mechanical erosion and thinning of the continental lithospheric mantle and, thus, may be an important process in slab window magma petrogenesis.