Palaeogeographic,climatic and tectonic change in southeastern Australia: the Late Neogene evolution of the Murray Basin

The Murray Basin is a low-lying but extensive intracratonic depocentre in southeastern Australia, preserving an extraordinary record of Late Neogene sedimentation. New stratigraphic and sedimentologic data allow the long-term evolution of the basin to be re-evaluated and suggest a significant role for: (1) tectonism in controlling basin evolution, and (2) progressive and step-wise climatic change beginning in the early Pleistocene. Tectonic change is associated with regional uplift, occurring at approximately the same rate from the early Pliocene until the present day, and possibly associated with changing mantle circulation patterns or plate boundary processes. This uplift led to the defeat and re-routing of the Murray River, Australia’s major continental drainage system. Key to our interpretation is recognition of timing relationships between four prominent palaeogeographic features – the Loxton-Parilla Sands strandplain, the Gambier coastal plain, palaeo megalake Bungunnia and the Kanawinka Escarpment. Geomorphic and stratigraphic evidence suggest that during the Early Pliocene the ancestral Murray River was located in western Victoria, flowing south along the Douglas Depression. Relatively small amounts of regional uplift (<200 m) defeated this drainage system, dramatically changing the palaeogeography of southeastern Australia and forming Plio-Pleistocene megalake Bungunnia. At its maximum extent Lake Bungunnia covered more than 50,000 km², making it one of the largest known palaeo- or modern-lakes in an intracontinental setting. Magnetostratigraphic constraints suggest lake formation c. 2.4 Ma. The formation of Lake Bungunnia influenced the Pliocene coastal dynamics, depriving the coastline of a sediment source and changing the coastal system from a prograding strandline system to an erosional one. Erosion during this period formed the Kanawinka Escarpment, a palaeo sea-cliff and one of the most prominent and laterally extensive geomorphic features in southeastern Australia. Marine sediments c. 800 ka to c. 1.16 Ma represent the time of re-establishment of depositional coastal dynamics and of a permanent outlet for the Murray River. This age range is consistent with our best estimate of the age of the youngest Lake Bungunnia sediments and points towards an early Pleistocene age for the demise of the lake system. The youngest Lake Bungunnia sediment, present on a number of distinct terraces, suggests that progressive, step-wise climatic change played a role in the demise of the lake. However, in order for the ancestral Murray River system to have been able to breach the pre-existing tectonic dam, it is likely that tectonic change and/or temporarily enhanced discharge was also significant. This scenario indicates that the modern Murray River has only been in existence for at most 700 ka.     

Near real time satellite imagery to support and verify timely flood modelling

The study investigates the capability of coarse resolution synthetic aperture radar (SAR) imagery to support flood inundation models. A hydraulic model of a 98‐km reach of the River Po (Northern Italy) was calibrated on the October 2000 high‐magnitude flood event with extensive and high‐quality field data. During the June 2008, low‐magnitude flood event a SAR image was acquired and processed in near real time (NRT) in order to provide adequate data for quick verification and recalibration of the hydraulic model. Copyright © 2009 John Wiley & Sons, Ltd.     

Downscaling the hydrological cycle in the Mackenzie basin with the Canadian regional climate model

Abstract

The Canadian Regional Climate Model (CRCM) has been nested within the Canadian Centre for Climate Modelling and Analysis ‘ second generation General Circulation Model (GCM), for a single month simulation over the Mackenzie River Basin and environs. The purpose of the study is to assess the ability of the higher resolution CRCM to downscale the hydrological cycle of the nesting GCM. A second 1‐month experiment, in which the CRCM was nested within analyzed fields of a global data assimilation system, was also performed to examine the sensitivity of the basin moisture budget to atmospheric lateral boundary forcing.

We have found that the CRCM can produce realistic lee cyclogenesis, preferentially in the Liard sub‐basin, along with associated circulation and precipitation patterns, as well as an improved rainshadow in the lee of the Rocky Mountains compared to the GCM. While these features do quantitatively affect the monthly average climate statistics, the basin scale moisture budgets of the models were remarkably similar, though some of this agreement is due to compensating errors in the GCM. Both models produced excessive precipitation compared to a recent climatology for the region, the cause of which is traced to lateral boundary forcing. A second experiment, identical to the first except that the CRCM was forced with analyzed fields at the lateral boundaries, produced a qualitatively different basin moisture budget, including a much more realistic precipitation field. Errors in the moisture budget of the first experiment appear to be associated with the poor representation of the Aleutian Low in the GCM, and do not appear to be strongly connected to (local) surface processes within the models. This suggests that an effective strategy for modelling the hydrological cycle of the Mackenzie Basin on the fast climate timescale ‐ a major requirement of the Mackenzie GEWEX Study ‐ will involve nesting the CRCM within analyzed (or re‐analyzed) atmospheric fields.     

Long-term modeling of alteration-transport coupling: Application to a fractured Roman glass

To improve confidence in glass alteration models, as used in nuclear and natural applications, their long-term predictive capacity has to be validated. For this purpose, we develop a new model that couples geochemical reactions with transport and use a fractured archaeological glass block that has been altered for 1800 years under well-constrained conditions in order to test the capacity of the model.The chemical model considers three steps in the alteration process: (1) formation of a hydrated glass by interdiffusion, whose kinetics are controlled by a pH and temperature dependent diffusion coefficient; (2) the dissolution of the hydrated glass, whose kinetics are based on an affinity law; (3) the precipitation of secondary phases if thermodynamic saturation is reached. All kinetic parameters were determined from experiments. The model was initially tested on alteration experiments in different solutions (pure water, Tris, seawater). It was then coupled with diffusive transport in solution to simulate alteration in cracks within the glass. Results of the simulations run over 1800 years are in good agreement with archaeological glass block observations concerning the nature of alteration products (hydrated glass, smectites, and carbonates) and crack alteration thicknesses. External cracks in direct contact with renewed seawater were altered at the forward dissolution rate and are filled with smectites (400−500 μm). Internal cracks are less altered (by 1 or 2 orders of magnitude) because of the strong coupling between alteration chemistry and transport. The initial crack aperture, the distance to the surface, and sealing by secondary phases account for these low alteration thicknesses. The agreement between simulations and observations thus validates the predictive capacity of this coupled geochemical model and increases more generally the robustness and confidence in glass alteration models to predict long-term behavior of nuclear waste in geological disposal or natural glass in the environment.     

Bacteria-Induced Cementation Process in Loose Sand Medium

Several conventional methods for treatment of soil are available for engineers. The most widely used method includes solution/grout, but they alter the ground pH level and could be toxic. In order to avoid the potential environmental harms and make use of naturally occurring microorganisms, biological methods to improve the engineering properties of soils have been intensely studied. This article presents the results of a research project in which Sporosarcina pasteurii (formerly known as Bacillus pasteurii) was used to induce biological cementation in loose sand medium. The bacteria was injected into sand, which led to the development of cementation (calcium carbonate crystal) between sand grains. The calcification was observed using a scanning electron microscope (SEM).     

General relativistic magnetohydrodynamic and Monte Carlo Modeling of sagittarius A*

Using the tunneling method we derive the Hawking temperature of the nonextremal rotating charged black hole in the Gödel universe of five-dimensional minimal supergravity theory found by Wu. We successfully recovered the tunneling probability of charged Dirac particles and the expected Hawking temperature of the black hole, which is exactly consistent with that obtained by other methods.     

The reef builder gastropod Dendropomapetreaum - A proxy of short and long term climatic events in the Eastern Mediterranean

High-resolution δ¹⁸O and δ¹³C records obtained from seven cores were drilled from ledges of the reef builder gastropod Dendropomapetreaum and used to reconstruct variations in the Levantine basin sea surface temperature, hydrology and productivity during the past 500 years. The δ¹⁸O of the aragonite shell of living D. petreaum indicate that skeletal deposition occurs under isotopic equilibrium and faithfully record the temperature and surface water δ¹⁸O during summer and autumn. The mean down core δ¹⁸O record clearly captures global and local climatic events, such as the Little Ice Age (LIA) and the recent warming of surface waters in the Eastern Mediterranean. Comparison to the Western Mediterranean vermetid δ¹⁸O record reveals changes in the freshwater/evaporation budgets of the two basins during cold and warm periods. The Eastern basin had lower surface temperatures and excess evaporation during the LIA and experienced a relatively larger warming and/or a decrease in freshwater/evaporation during the past 70 years. The D. petraeum δ¹³C is strongly related to δ¹³C of dissolved inorganic carbon and to the primary productivity of the surface water. The mean down core δ¹³C record exhibits enrichment during the LIA maximum and a strong depletion trend during the last century. The LIA δ¹³C enrichment is attributed to an increase in primary production and high nutrient levels which resulted from increased vertical mixing and upwelling. The last century δ¹³C depletion is mostly related to the increased anthropogenic emissions of ¹³C depleted carbon dioxide and to a certain decrease in primary production. The data indicate that D. petraeum isotopic signatures are unique proxies for last 500 years high-resolution reconstruction of paleo-oceanographic environments in the Mediterranean and potentially in the sub-tropical Atlantic regions.     

Magnetic classification of stony meteorites: 3. Achondrites

Abstract— A database of magnetic susceptibility measurements of stony achondrites (acapulcoite‐lodranite clan, winonaites, ureilites, angrites, aubrites, brachinites, howardite‐eucrite‐diogenite (HED) clan, and Martian meteorites, except lunar meteorites) is presented and compared to our previous work on chondrites. This database provides an exhaustive study of the amount of iron‐nickel magnetic phases (essentially metal and more rarely pyrrhotite and titanomagnetite) in these meteorites. Except for ureilites, achondrites appear much more heterogeneous than chondrites in metal content, both at the meteorite scale and at the parent body scale. We propose a model to explain the lack of or inefficient metal segregation in a low gravity context. The relationship between grain density and magnetic susceptibility is discussed. Saturation remanence appears quite weak in most metal‐bearing achondrites (HED and aubrites) compared to Martian meteorites. Ureilites are a notable exception and can carry a strong remanence, similar to most chondrites.