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.     

Spherical harmonic analysis of earth’s conductive heat flow

A reappraisal of the international heat flow database has been carried out and the corrected data set was employed in spherical harmonic analysis of the conductive component of global heat flow. Procedures used prior to harmonic analysis include analysis of the heat flow data and determination of representative mean values for a set of discretized area elements of the surface of the earth. Estimated heat flow values were assigned to area elements for which experimental data are not available. However, no corrections were made to account for the hypothetical effects of regional-scale convection heat transfer in areas of oceanic crust. New sets of coefficients for 12° spherical harmonic expansion were calculated on the basis of the revised and homogenized data set. Maps derived on the basis of these coefficients reveal several new features in the global heat flow distribution. The magnitudes of heat flow anomalies of the ocean ridge segments are found to have mean values of less than 150 mW/m². Also, the mean global heat flow values for the raw and binned data are found to fall in the range of 56–67 mW/m², down by nearly 25% compared to the previous estimate of 1993, but similar to earlier assessments based on raw data alone. To improve the spatial resolution of the heat flow anomalies, the spherical harmonic expansions have been extended to higher degrees. Maps derived using coefficients for 36° harmonic expansion have allowed identification of new features in regional heat flow fields of several oceanic and continental segments. For example, lateral extensions of heat flow anomalies of active spreading centers have been outlined with better resolution than was possible in earlier studies. Also, the characteristics of heat flow variations in oceanic crust away from ridge systems are found to be typical of conductive cooling of the lithosphere, there being little need to invoke the hypothesis of unconfined hydrothermal circulation on regional scales. Calculations of global conductive heat loss, compatible with the observational data set, are found to fall in the range of 29–34 TW, nearly 25% less than the 1993 estimate, which rely on one-dimensional conductive cooling models.     

Heat flow–heat production relationship not found: what drives heat flow variability of the Western Canadian foreland basin?

International Journal of Earth Sciences - Heat flow high −80 ± 10 mW/m2 in the northern western parts of the Western Canadian foreland basin is in large...     

Estimates of heat flow and heat production and a thermal model of the São Francisco craton

An updated analysis of geothermal data from the highland area of eastern Brazil has been carried out and the characteristics of regional variations in geothermal gradients and heat flow examined. The database employed includes results of geothermal measurements at 45 localities. The results indicate that the Salvador craton and the adjacent metamorphic fold belts northeastern parts of the study area are characterized by geothermal gradients in the range of 6–17°C/km. The estimated heat flow values fall in the range of 28–53 mW/m², with low values in the cratonic area relative to the fold belts. On the other hand, the São Francisco craton and the intracratonic São Francisco sedimentary basin in the southwestern parts are characterized by relatively higher gradient values, in the range of 14–42°C/km, with the corresponding heat flow values falling in the range of 36–89 mW/m². Maps of regional variations indicate that high heat flow anomaly in the São Francisco craton is limited to areas of sedimentary cover, to the west of the Espinhaço mountain belt. Crustal thermal models have been developed to examine the implications of the observed intracratonic variations in heat flow. The thermal models take into consideration variation of thermal conductivity with temperature as well as change of radiogenic heat generation with depth. Vertical distributions of seismic velocities were used in obtaining estimates of radiogenic heat production in crustal layers. Crustal temperatures are calculated based on a procedure that makes simultaneous use of the Kirchoff and Generalized Integral Transforms, providing thereby analytical solutions in 2D and 3D geometry. The results point to temperature variations of up to 300°C at the Moho depth, between the northern Salvador and southern São Francisco cratons. There are indications that differences in rheological properties, related to thermal field, are responsible for the contrasting styles of deformation patterns in the adjacent metamorphic fold belts.     

A dynamic network model for two‐phase immiscible flow

A dynamic pore‐scale network model is formulated for two‐phase immiscible flow. Interfaces are tracked through the pore throats using a modified Poiseuille equation, whereas special displacement rules are used at the pore bodies. The model allows interfaces to move over several pore‐lengths within a time step. Initial computational results are presented for a drainage experiment to demonstrate some of the features of the model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physical characteristics of a lava flow determined from thermal measurements at the lava’s surface

We consider the problem about determination of characteristics of a lava flow from the physical parameters measured on its surface. The problem is formulated as an inverse boundary problem for the model simulating the dynamics of a viscous heat-conducting incompressible inhomogeneous fluid, where, on the basis of additional data at one part of the model boundary, the missing conditions at another part of the boundary have to be determined, and then the characteristics of fluid in the entire model domain have to be reconstructed. The considered problem is ill-posed. We develop a numerical approach to the solution of the problem in the case of a steady-state flow. Assuming that the temperature and the heat flow are known at the upper surface of the lava, we determine the flow characteristics inside the lava. We compute model examples and show that the lava temperature and flow velocity can be determined with a high precision when the initial data are smooth or slightly noisy.     

The lower Devonian Kowmung volcaniclastics: A deep‐water succession of mass‐flow origin,northeastern Lachlan Fold Belt,N.S.W.

The Lower to ?Middle Devonian Kowmung Volcaniclastics form the upper part of a succession of Upper Siluran to mid‐Devonian flyschoid rocks in the Yerranderie area of N.S.W., and contain two major facies associations. (1) A mudstone facies association represents the ambient, background sedimentation, comprising predominantly buff mudstone that is host to an assemblage of coarser‐grained sediments, including graded‐bedded to massive siltstone, sandstone, conglomerate, allodapic limestone, and large allochthonous limestone blocks and associated limestone breccia. Bouma sequences are common, sole structures occur and maximum bed thickness is about 3 m. (2) A volcaniclastic facies association intrudes and interrupts the accumulation of the ambient mudstone facies association, and contains massive to partly graded, quartzofeldspathic siltstone, sandstone, breccia and conglomerate. Sedimentation units in the volcaniclastic facies association are up to 120 m thick. The two facies associations interfinger. Stratigraphically, the base of the Kowmung Volcaniclastics is taken as the first sedimentation unit of the volcaniclastic facies association. The mudstone facies association below this level is part of the Siluro‐Devonian Taralga Group.

Both facies associations were deposited in relatively deep‐water. The dominant transport process in both associations was mass‐flow, involving granular mass‐flows (turbidity currents, grain flows), debris flows and avalanches. Massive mudstone is hemipelagic in origin. The volcaniclastic facies association probably represents a submarine volcanic apron around the emergent, volcanic Bindook Complex. Grossly, the succession coarsens upwards, and there is evidence of several sources of sediment, rather than a single point at the head of a submarine fan.

Provenance is diverse. In the mudstone facies association, framework grains in sandstone are microlitic volcanic‐rock fragments with a mafic to intermediate volcanic source. Clasts in conglomerate and breccia are consistent with derivation from the regionally extensive, quartzose Ordovician flyschoid successions. Clasts of ?penecontemporaneous limestone also occur. The volcaniclastic facies association was probably derived largely from the nearby, coeval Bindook Complex, which consists of silicic ash‐flow and ash‐fall tuff, lava, associated sediment and granitoids. Detritus was either derived directly from volcanic eruptions or was worked in fringing littoral and fluvial environments prior to redeposition by mass‐flow. Quartzite boulders mixed with volcanic clasts in the conglomerate suggest that Ordovician quartzarenite was also exposed around the volcanic complex. Tentative provenance correlations have been made between the different rock units in the Kowmung Volcaniclastics and their possible sources in the northern part of the Bindook Complex.     

Model or measurements? A discussion of the key issue in Chapman and Pollack’s critique of Hamza et al.’s re-evaluation of oceanic heat flux and the global power

Chapman and Pollack (C and P)[2007, Int J Earth Sci] criticize Hamza et al. [2007, Int J Earth Sci] for using actual heat flux measurements in young oceanic crust instead of values from 1-D cooling models. The rationalization of C and P and previous authors is that hydrothermal circulation causes the discrepancy between model and measurement. However, the discrepancy between model values and measured heat flux exists over the entire ocean floor and is opposite to the perturbations that hydrothermal circulation would superimpose on a conductive system [Hofmeister and Criss (2005) Tectonophysics 409:199–203]. The error lies in force-fitting a 1-D cooling model to the 3-D oceanic crust [Hofmeister and Criss (2005) Tectonophysics 395:159–177]. Shortcomings of the 1-D model include mathematical errors, such as use of volumetric rather than linear thermal expansivity to describe contraction which, by assumption, is limited only to the Z -direction [Hofmeister and Criss (2006) Tectonophysics]. This 3× error, traceable to McKenzie and Sclater [1969, Bull Vocanol 33–1:101–118], accidentally provides good agreement of model values with globally averaged seafloor depths for young, but not old ages, and is the sole rationale for using the simplistic cooling model. There is no justification for selective substitution of erroneous 1-D model values for measurements only for the younger half of the 3-D oceanic crust, as stridently and arbitrarily promoted by C and P. Hamza et al. [2007, Int J Earth Sci], in contrast, use the scientific method, which calls for discarding models that do not well describe physical phenomena. The remainder of this report summarizes the shortcomings of cooling models, particularly the half-space cooling (HSC) model touted by C and P, and explains how hydrothermal circulation affects heat flux. We focus on the basics, as these have been misunderstood. With the key issues of C and P being erroneous, it is not necessary to address their remaining comments, many of which enumerate the vote for an imagined, gargantuan circulation of hot fluid through oceanic basins that is somehow warmed without removing heat from the rocks. The use of “consensus” to belittle valid challenge is the enemy of the scientific method.     

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.     

A digitized global flood inventory (1998–2008): compilation and preliminary results

Floods have profound impacts on populations worldwide in terms of both loss of life and property. A global inventory of floods is an important tool for quantifying the spatial and temporal distribution of floods and for evaluating global flood prediction models. Several global hazard inventories currently exist; however, their utility for spatiotemporal analysis of global floods is limited. The existing flood catalogs either fail to record the geospatial area over which the flood impacted or restrict the types of flood events included in the database according to a set of criteria, limiting the scope of the inventory. To improve upon existing databases, and make it more comprehensive, we have compiled a digitized Global Flood Inventory (GFI) for the period 1998–2008 which also geo-references each flood event by latitude and longitude. This technical report presents the methodology used to compile the GFI and preliminary findings on the spatial and temporal distributions of the flooding events that are contained in the inventory.     

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.     

The age of orogenesis in the Nambucca Slate Belt: A K‐Ar study of low‐grade regional metamorphic rocks

K‐Ar ages of biotite and hornblende from undeformed granodiorite plutons and of slaty and phyllitic rocks, ranging from prehnite‐pumpellyite metagreywacke to greenschist fades, have been determined in an attempt to define the age of orogenesis in the eastern part of the Nambucca Slate Belt. The plutons have K‐Ar ages of 226–227 m.y. (biotite) and 228–231 m.y. (hornblende) that provide a younger age limit for deformation. The lower grade metamorphic rocks yield a range of ages including some comparable with the depositional age of the rocks as indicated by fossils. Rocks of pumpellyite‐actinolite and greenschist facies give a more coherent group of ages which suggest orogenesis at about 250–255 m.y. Specimens of these latter rocks that have been affected by a later structural episode than that during which slaty cleavage formed, yield slightly older ages, which may result from the inclusion of minor amounts of environmental excess ⁴⁰Ar.

Support for the 250–255 m.y. age comes from previously determined radiometric ages from the western part of the Slate Belt, although the presence of granitic bodies perhaps as old as 289 m.y., some closely associated with high‐grade regional metamorphic rocks, may indicate the presence of additional earlier orogenic movements in this region.     

Simultaneous transport of water and solutes under transient unsaturated flow conditions — A case study

The imbalance between incoming and outgoing salt causes salinization of soils and sub-soils that result in increasing the salinity of stream-flows and agriculture land. This salinization is a serious environmental hazard particularly in semi-arid and arid lands. In order to estimate the magnitude of the hazard posed by salinity, it is important to understand and identify the processes that control salt movement from the soil surface through the root zone to the ground water and stream flows. In the present study, Malaprabha sub-basin (up to dam site) has been selected which has two distinct climatic zones, sub-humid (upstream of Khanapur) and semi-arid region (downstream of Khanapur). In the upstream, both surface and ground waters are used for irrigation, whereas in the downstream mostly groundwater is used. Both soils and ground waters are more saline in downstream parts of the study area. In this study we characterized the soil salinity and groundwater quality in both areas. An attempt is also made to model the distribution of potassium concentration in the soil profile in response to varying irrigation conditions using the SWIM (Soil-Water Infiltration and Movement) model. Fair agreement was obtained between predicted and measured results indicating the applicability of the model.     

Experimental measurements of the diffusion parameters of light hydrocarbons in water-saturated sedimentary rocks—I. A new experimental procedure

An automatic experimental set-up has been developed for the determination of diffusion parameters of hydrocarbon gases through water-saturated rock samples. Diffusive flow of hydrocarbons through rock slices is monitored by gas chromatography. Experiments are carried out according to the time lag method yielding diffusion coefficients, solubility coefficients, and diffusion permeabilities. Diffusion coefficients down to 10⁻¹² m² s⁻¹ (10⁻⁸ cm⁻² s⁻¹) may be determined routinely on rock samples of 2–10 mm thickness. Maximum errors in diffusion coefficients are estimated around 20% and reproducibility was found to range between 10 and 20%. Specific features of this set-up are automatic sampling and data acquistion, high sampling frequency, and maintenance of water-saturation of the rock samples throughout the experiment.     

Architecture of the Central Andes—a compilation of geoscientific data along a transect at 21°S

Based on numerous geoscientific data a section through the Central Andean active continental margin at 21°S has been compiled which shows the structure of the South American upper plate and the downgoing Nazca Plate.     

An upscaling method for one‐phase flow in heterogeneous reservoirs. A weighted output least squares (WOLS) approach

In this paper we study the problem of determining the effective permeability on a coarse scale level of problems with strongly varying and discontinuous coefficients defined on a fine scale. The upscaled permeability is defined as the solution of an optimization problem, where the difference between the fine scale and the coarse scale velocity field is minimized. We show that it is not necessary to solve the fine scale pressure equation in order to minimize the associated cost‐functional. Furthermore, we derive a simple technique for computing the derivatives of the cost‐functional needed in the fix‐point iteration used to compute the optimal permeability on the coarse mesh. Finally, the method is illustrated by several analytical examples and numerical experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sea‐rafted pumice on the Australian east coast: Numerical classification and stratigraphy

Sixteen elements (Ca, K, Mg, Na, Al, Fe, Mn, P, Co, Cu, Li, Ni, Rb, Sr, Ti, Zn, determined by atomic absorption) were identified in 453 pumice fragments recovered from Holocene strandplains in southeast Queensland and New South Wales. Eight pumice groups and 13 subgroups are recognised by numerical analysis. Some pumices record known eruptions. Others come from known centres in Tonga and Vanuatu. Several pumice eruptions have occurred from some centres, but there are instances of single episodes. The numerical analyses, combined with carbon dating and soil identification, identify marker horizons in the development of the strandplains. These horizons provide a time‐scale for soil development. Pumice that occurs in middens has an archaeological value. Coke was found with recent pumice. It conveniently identifies the modern industrial age.     

Felsic tuff from Rutland Island — A pyroclastic flow deposit in Miocene-sediments of Andaman-Java subduction complex

The bedded felsic tuff exposed in Rutland Island, Andaman, consists of two facies:

Principles of Precambrian time‐stratigraphy

Two approaches to the time‐stratigraphic subdivision of the Australian Pre‐cambrian are possible. In one, bodies of rock are referred, by means of radio‐metric dates, to periods defined by chosen points on the absolute time‐scale. In the second, the boundaries of time‐rock units are defined at selected reference points on the ground, and these reference points are dated as accurately as possible by radiometric means. Geographically distant bodies of rock are correlated with “type” time‐rock units by radiometric dates.

The second approach is preferred since: (a) it leads to a geological time‐scale homogeneous in concept; (b) it implies that there is no difference in principle between Precambrian and Phanerozoic time‐stratigraphy; and (c) the time‐rock units so created are directly comparable with those that might be established by lithological, palaeontological, magnetometric, or climatic‐litho‐logical correlation. Criteria and procedures for the definition of time‐rock units and their boundaries are suggested.     

Bender-based G0 measurements: A coupled numerical–experimental approach

Bender elements are shear wave transducers, widely used for the experimental identification of the small-strain shear moduli of geomaterials. They offer good coupling with the sample and controllable loading signal and frequency, but some of their design and signal interpretation features are still under investigation. The research of these features has been approached mainly on experimental grounds and, in most cases, the conclusions were not consensual. This study aims at laying the foundations for a coupled, numerical–experimental approach to the problem. It uses hybrid-Trefftz finite elements to model the bender element test and the output signal obtained in the laboratory to validate the model.Two main reasons justify the choice of the hybrid-Trefftz finite elements. First, hybrid-Trefftz elements are considerably less wavelength-sensitive than conforming displacement elements. This feature endorses the use of the same (coarse) mesh for modelling waves of very different types and frequencies, thus eliminating the need for time-consuming mesh refinements. Second, hybrid-Trefftz elements use physically meaningful approximation bases. This feature enables the numerical filtration of the spurious compression waves propagating laterally from the emitter and of their reflections from the envelope of the sample. Hybrid-Trefftz finite elements are shown to recover adequately the output signal obtained experimentally, for pulse excitations of various frequencies and two sets of boundary conditions. The decomposition of the output signal into its shear and compression components endorses the clear identification of the shear wave arrival and the amount of compression wave pollution.