An epeiric ramp: low-energy, cool-water carbonate facies in a Tertiary inland sea, Murray Basin, South Australia

The Murray Supergroup records temperate‐water carbonate deposition within a shallow, mesotrophic, Oligo‐Miocene inland sea protected from high‐energy waves and swells of the open ocean by a granitic archipelago at its southern margin. Rocks are very well preserved and exposed in nearly continuous outcrop along the River Murray in South Australia. Most facies are rich in carbonate silt, contain a background assemblage of gastropods (especially turritellids) and infaunal bivalves, and are packaged on a decimetre‐scale defined by firmground and hardground omission surfaces. Bioturbation is pervasive and overprinted, resulting in rare preservation of physical sedimentary structures. Facies are grouped into four associations (large foraminiferan–bryozoan, echinoid–bryozoan, mollusc and clay facies) interpreted to represent shallow‐water (<50 m) deposition under progressively higher trophic resource levels (from low mesotrophy to eutrophy), and restricted marine conditions from relatively offshore to nearshore regions. A large‐scale shift from high‐ to low‐mesotrophic conditions within lower Miocene strata reflects a change in climate from wet to seasonally dry conditions and highlights the influence terrestrially derived nutrients had upon this shallow, land‐locked sea. Overall, low trophic resource levels during periods of seasonally dry climate resulted in a deepening of the euphotic zone, a widespread proliferation of foraminiferan photozoan fauna and a relatively high carbonate productivity. Inshore, heterozoan facies became progressively muddier and restricted towards the shoreline. In contrast, periods of wet climate led to rising trophic resource levels, resulting in a shallowing of the euphotic zone, a decrease in epifaunal and seagrass cover and widespread development of a mostly heterozoan biota dominated by infaunal echinoids. Rates of carbonate production and accumulation were relatively low. The Murray Basin is best described as an epeiric ramp. Wide facies belts developed in a shallow sea on a low‐angled slope reaching many hundreds of kilometres in length. Grainy shoal and back‐barrier facies were absent. Internally generated waves impinged the sea floor in offshore regions and, because of friction along a wide and shallow sea floor, created a low‐energy expanse of waters across the proximal ramp. Storms were the dominating depositional process capable of disrupting the entire sea floor.     

Detailed Study of Three Contiguous Segments of the Mid-Atlantic Ridge,South of the Azores (37° N to 38°30′ N), Using Acoustic Imaging Coupled with Submersible Observations

Using a new tool of seafloor characterisation (sonar images from FARA-SIGMA cruise; Needham et al., 1992), coupled with submersible observations (DIVA1 cruise) we compare, at different scales of observation, three contiguous segments of the Mid-Atlantic Ridge, South of the Azores Triple Junction, between 37° N and 38°30 N.The two northernmost segments (38°20 N and Menez-Gwen) show unusual morphological features for the MAR; the rift valley is absent and the present-day magmatism is focused on shallow axial volcanoes. On the third segment (Lucky Strike), the morphology is the one usually found on the MAR. On the Menez-Gwen and 38°20 N segments, volcanic constructional activity can obliterate, during periods of high magmatic supply, the morphology inherited from tectonic activity. The dive results constrain the recent evolution of each segment and show that a temporal variability in volcanic dynamics exists. On the three segments, outcrops of eruptive lavas alternate with large areas of explosive volcanic ejecta. This cycle in volcanic activity is influenced by changes in water depth, both spatially (i.e. between segments) and temporally (i.e. for the same segment through time).Each segment has known a specific history in its accretionary processes with a succession of tectonic and volcanic predominance and changes in its volcanic phases between volcanic ejecta and effusive dynamics.The hydrothermal activity is focused at the central part of each segment and is controlled by the presence of fresh lava and major tectonic features.     

Chemical characteristics of groundwater around two massive sulphide deposits in an area of previous mining contamination, Iberian Pyrite Belt, Spain

A detailed chemical study of groundwater was carried out to elucidate the processes controlling the oxidation and dissolution of sulphide minerals at two massive sulphide deposits in the Iberian Pyrite Belt (IPB), i.e. the mined La Zarza deposit and the unmined Masa Valverde deposit. It was found that major-element compositions varied according to the hydrological regime, La Zarza being in a relatively high area with groundwater recharge (and disturbance due to the human factor) and Masa Valverde being in a relatively low area with groundwater discharge. The variations mainly concern pH, Eh, SO₄ and Na concentrations. Metal concentrations were determined (a) by ICP-MS after filtration, and (b) in some cases by voltammetric measurement of Cu, Pb, Zn, Cd and Mn using the Voltammetric In situ Profiling (VIP) System, which allows detection of only the mobile fractions of trace elements (i.e., free metal ions and small labile complexes a few nanometers in size). If one compares the results obtained by each of the two methods, it would appear that the groundwater shows significant enhancement of metal solubility through complexing with organic matter and/or adsorption onto colloids and/or small particles. In areas of sulphide oxidation, however, this solubility enhancement decreases according to Cu>Zn>Cd>Pb. Under very low redox conditions, the attained metal concentrations can be several orders of magnitude (up to 10⁸–10⁹ for Cu and 10²–10³ for Pb) larger than those expected from equilibrium with respect to sulphide minerals as calculated with the EQ3NR geochemical code; Zn concentrations, however, are close to equilibrium with respect to sphalerite. The implication of these results is discussed with respect both to mineral exploration and to environmental issues.     

Solute transfer across the sediment surface of a eutrophic lake: I. Porewater profiles from dialysis samplers

Porewater profiles often are used to identify and quantify important biogeochemical processes occurring in lake sediments. In this study, multiple porewater profiles were obtained from two eutrophic Swiss lakes using porewater equilibrators (peepers) in order to examine spatial and seasonal trends in biogeochemical processes. Variability in profile shapes and concentrations was small on spatial scales of a few meters, but the uncertainty in calculated diffusive fluxes across the sediment surface was, on average, 35%. Focusing of Fe and Mn oxides toward the lake center resulted in systematic increases in porewater concentrations and diffusive fluxes of Fe²⁺ and Mn²⁺ with increasing water depth; these fluxes are postulated to be regulated by the pH-dependent dissolution of reduced-metal phases. Despite higher concentrations of inorganic carbon, NH ₄ ⁺ , Si and P in pelagic compared to littoral sites, diffusive fluxes of these substances across the sediment surface increased only slightly or not at all with increasing water depth. Porewater profiles did reveal temporal changes in Fe²⁺, Mn²⁺, Ca²⁺ and Mg²⁺ that were an indirect result of the large, seasonal changes in seston deposition, but no clear seasonal variations were found in diffusive fluxes of nutrients across the sediment surface. The intense mineralization occurring at the sediment surface was not reflected in the porewater profiles nor in the calculated diffusive fluxes. Calculated diffusive fluxes across the sediment surface resulted from decomposition occurring primarily in the top 5–7 cm of sediment. Diffusive fluxes from this subsurface mineralization were equal to the solute release from mineralization occurring at the sediment-water interface. Buried organic matter acts as a memory of previous lake conditons; it will require at least a decade before reductions in nutrient inputs to lakes fully reduce the diffusive fluxes into the lake from the buried reservoir of organic matter.     

Reviews

CUL DE SAC: The Question of New Zealand's Future by H. Franklin. 13 x 19 cm, 184 pages. Allen & Unwin: Sydney 1985 (ISBN 0 86861 514 5) $A12.95 (soft).

SHOPPING CENTRE DEVELOPMENT: Policies and Prospects edited by J. A. Dawson and J. D. Lord. 14 x 22 cm, 269 pages. Croom Helm: London 1985 (ISBN 0 7099 0845 8) $A49.95 (hard).

GENTRIFICATION OF THE CITY edited by N. Smith and P. Williams. 13 x 22 cm, xiii and 257 pages. Allen & Unwin: Boston 1986 (ISBN 0 04 301201 9) $A59.00 (hard); (ISBN 0 04 301202 7) $A26.95 (soft).

EUROPE TODAY: Countries and Issues by D. J. Davis and D. C. Flint. 19 x 27 cm, 256 pages. Bell & Hyman: London 1986 (ISBN 0 7135 2518 5) £5.95 (soft).

THE WORLD NOW (Australian edition) by A. Reed and R. Pask. 21 x 30 cm, 96 pages. Edward Arnold: Melbourne 1986 (ISBN 0 7131 8225 3) $A12.95 (soft).

THE INDO‐PACIFIC LIBRARY: Set Two — Ten Titles (11 Australia, 12 Burma, 13 French Polynesia, 14 India, 15 Laos and Kampuchea, 16 North and South Korea, 17 Pakistan and Bangladesh, 18 Sri Lanka, 19 Thailand, 20 Vietnam) by G. Houghton and J. Wakefield. 19 x 25 cm, 32 pages each. Macmillan: Melbourne 1987 $A9.95 (hard) each title.

THE INDO‐PACIFIC LIBRARY: Set Two — Macmillan Black Line Masters by G. Houghton and J. Wakefield. Macmillan: Melbourne 1987 (ISBN 0 333 43059 X) $A19.95 (soft).

QUEENSLAND: A Geographical Interpretation (Queensland Geographical Journal, 4th Series, Volume 1) edited by J. H. Holmes. 18 x 24 cm, 343 pages. Boolarong Publications: Brisbane 1986 (ISBN 0817 489X) $A25.00 (soft).

THE ROAD TO BOTANY BAY: An Essay in Spatial History by P. Carter. 14 x 22 cm, xv and 384 pages. Faber and Faber: London 1987 (ISBN 0 571 14551 5) $A29.95 (hard).

AN EVALUATION OF LOCAL AREA ECONOMIC STRATEGY STUDIES (Australian Regional Developments, No. 6) edited by J. D. Conroy. 30 x 21 cm, vii and 102 pages. Australian Government Publishing Service: Canberra 1987 (ISBN 0 644 06161 8).

PRODUCTION, WORK, TERRITORY: The Geographical Anatomy of Industrial Capitalism edited by A. J. Scott and M. Storper. 15 x 23 cm, xix and 344 pages. Allen & Unwin Inc: Boston 1986 (ISBN 0 04 338126 X) $A90.00 (hard); (ISBN 0 04 338127 8) $A38.95 (soft).

ANALYTICAL BEHAVIOURAL GEOGRAPHY by R. G. Golledge and R. J. Stimson. 16 x 24 cm, 345 pages. Croom Helm: London 1987 (ISBN 0 7099 3844 6) $A122.95 (hard).

AMBIGUOUS ALTERNATIVE: Tourism in Small Developing Countries edited by S. Britton and W. C. Clarke. 20 x 21 cm, 194 pages. University of the South Pacific: Suva 1987 (ISBN 982 01 0009); available from Geography Department, University of the South Pacific, Box 1168, Suva, Fiji.

AN ATLAS OF ENVIRONMENTAL AND RUMINANT POPULATION CHARACTERISTICS OF JAVA: A Multivariate Analysis Approach by J. M. Perkins, Armiadi Semali, P. W. Orchard and Rach‐met Rachman. 46 x 31 cm, 71 pages. Forage Research Project, University of New England: Armidale 1986 (ISBN 0 85834 691 5) $A50.00 plus postage (developed countries); $A20.00 plus postage (developing countries).

ANTARCTICA: THE NEXT DECADE. Report of a Study Group (Studies in Polar Research) by A. Parsons et al. 15 x 23 cm, xii and 164 pages. Cambridge University Press: Cambridge 1987 (ISBN 0521 331811) $A65.00 (hard).

THE HUMAN IMPACT ON THE NATURAL ENVIRONMENT by A. Goudie, 25 x 17 cm, x and 338 pages. Basil Blackwell: Oxford 1986 (ISBN 0 631 13758 0) $A29.50 (soft).

ATMOSPHERIC POLLUTION: Causes, Effects and Control Policies by D. Elsom. 15 x 23 cm, x and 319 pages. Basil Blackwell: Oxford 1987 (ISBN 0 631 13813 3) $A122.50 (hard); (ISBN 0 631 15674 7) $A43.95 (soft).

SEA SURFACE STUDIES: A Global View edited by R. J. N. Devoy. 16 x 24 cm, 649 pages. Croom Helm: London 1987 (ISBN 0 7099 0871 7) £55.00 (hard).     

The Jason-1 Mission

On December 7, 2001, the Jason-1 satellite was successfully launched by a Boeing Delta II rocket from the Vandenberg site in California, USA. Its main mission was to maintain the high accuracy altimeter measurements, provided since 1992 by TOPEX/Poseidon (T/P), ensuring continuity in observing and monitoring the ocean for intraseasonal to interannual changes, mean sea level, tides, and so forth. Despite four times less mass and power, the Jason-1 system has been designed to have the same performances as T/P, measuring sea surface topography at the centimeter level. This new Centre National d'Etudes Spatiales/National Aeronautics and Space Administration (CNES/NASA) mission also provides near real-time data for sea state and ocean forecast. The first 10 months of the Jason mission were dedicated to the verification of the system performance and cross-calibration with T/P measurements. A complete CALVAL plan was conducted by the Science and Project Teams of the mission based on in situ and regional experiments, global statistical approaches, and multisatellite comparisons, taking advantage of the T/P-Jason overlap during the first months of the mission. CALVAL and first science results showed that the Jason-1 performances were compliant with prelaunch specifications. This was a needed preamble before starting the routine phase of the mission in July 2003 with generation and distribution of validated geophysical data records to the whole user community.     

Chemistry of fluids from a natural analogue for a geological CO2 storage site (Montmiral, France): Lessons for CO2–water–rock interaction assessment and monitoring

Chemical and isotope studies of natural CO₂ accumulations aid in assessing the chemical effects of CO₂ on rock and thus provide a potential for understanding the long-term geochemical processes involved in CO₂ geological storage. Several natural CO₂ accumulations were discovered during gas and oil exploration in France’s carbogaseous peri-Alpine province (south-eastern France) in the 1960s. One of these, the Montmiral accumulation at a depth of more than 2400 m, is currently being exploited. The chemical composition of the water collected at the wellhead has changed in time and the final salinity exceeds 75 g/L. These changes in time can be explained by assuming that the fraction of the reservoir brine in the recovered brine–CO₂–H₂O mixture varies, resulting in variable proportions of H₂O and brine in the sampled water. The proportions can be estimated in selected samples due to the availability of gas and water flowrate data. These data enabled the reconstruction of the chemical and isotope composition of the brine. The proportions of H₂O and brine can also be estimated from isotope (δ²H, δ¹⁸O) composition of collected water and δ¹⁸O of the sulfates or CO₂. The reconstituted brine has a salinity of more than 85 g/L and, according to its Br⁻ content and isotope (δ²H, δ¹⁸O, δ³⁴S) composition, originates from an evaporated Triassic seawater that underwent dilution by meteoric water. The reconstitution of the brine’s chemical composition enabled an evaluation of the CO₂–water–rock interactions based on: (1) mineral saturation indices; and (2) comparison with initial evaporated Triassic seawater. Dissolution of K- and SO₄-containing minerals such as K-feldspar and anhydrite, and precipitation of Ca and Mg containing minerals that are able to trap CO₂ (carbonates) are highlighted. The changes in concentration of these elements in the brine, which are attributed to CO₂ interactions, illustrate the relevance of monitoring the water quality at future industrial CO₂ storage sites.     

Palaeozoic oolitic ironstone of the French Armorican Massif: a chemical and structural trap for orogenic base metal–As–Sb–Au mineralisation during Hercynian strike-slip deformation

In the Saint-Aubin-des-Chateaux quarry (Armorican Hercynian belt, western France), an epigenetic hydrothermal alteration affects an oolitic ironstone layer intercalated within the Lower Ordovician Grès armoricain Formation. The hydrothermal overprint produced pervasive and massive sulphidation with stratoid pyritised lenticular bodies within the oolitic ironstone layer. These sulphide lenses are spatially associated with strike-slip faults and extend laterally from them. After the massive sulphidation stage (Fe–As, stage 1), subsequent fracturing allowed the deposition of base metals (stage 2) and Pb–Sb–Au (stage 3) parageneses in veins. The dominant brittle structures are vertical extension veins, conjugate shear veins and strike-slip faults of various orders. All these structures are filled with the same paragenetic sequence. Deformation analysis allows the identification of structures that developed incrementally via right-lateral simple shear compatible with bulk strain affecting the Central Armorican Domain. Each increment corresponds to a fracture set filled with specific parageneses. Successive hydrothermal pulses reflect clockwise rotation of the horizontal shortening direction. Geothermometry on chlorite and arsenopyrite shows an input of hot hydrothermal fluids (maximum of 390–350°C) during the main sulphide stage 1. The subsequent stages present a marked temperature drop (300–275°C). Lead isotopes suggest that the lead source is similar for all hydrothermal stages and corresponds to the underlying Neo-Proterozoic basement. Lead isotope data, relative ages of deformation and comparison with neighbouring deposits suggest that large-scale fluid pulses occurred during the whole Hercynian orogeny rather than pulses restricted to the late Hercynian period. The vicinity of the Hercynian internal domain appears as a key control for deformation and fluid flow in the oolitic ironstones, which acted as a chemical and structural trap for the hydrothermal fluids. The epigenetic mineralisation of Saint-Aubin-des-Chateaux appears to be very similar to epigenetic sulphidation described in banded iron formation-hosted gold deposits.