The geochemistry of coastal wetlands in the Townsville region, north Queensland, is described from a geological perspective, using the mineral stability and diagenesis of mangrove and salt flat sediments. A total of 186 porewater samples were collected from Cape Bowling Green, Gordon Creek, the Townsville Town Common, and the adjacent area of Mt. Low, dissolved concentrations of Fe², Mn², Ca², Na+, K+, Sr², Rb+ and Ba² were measured. The mangrove swamp sediments have a neutral pH (ca.pH 6.9) and reducing (ca. Eh – 250mV) and the salt flats are very slightly basic (ca. pH 7.3) and oxidizing (ca. Eh +100mV), reflecting a general increase of redox potential with increasing elevation. Similarly, increasing salinity landward across the intertidal region is reflected in the porewater sale (Ca², Mg²+, Na+, K+) concentrations and associated presence of evaporate minerals (halite , gypsum, jarosite). However, early depletion of salts indicate that evaporation trends do not simply reflect seawater concentration, but also clay mineral absorption and metabolic uptake by mangrove and samphire vegetation. Overall, geochemical trends across the intertidal zone reflect a continuum of physical (e.g. transport and evaporation) and superimposed chemical (diagenetic) processes between the marine and terrestrial environments. The unstable mineralogy and non-linear evaporation trends, indicate that the intertidal zone is more complex than expected from simple thermodynamic modeling.

The structure of aragonite was first determined by Lawrence Bragg in 1924 in what is the now standard space-group setting Pnma (No. 62). Subsequent studies have all taken his structure as their starting points, despite Bragg's own stated doubts and some earlier etching studies which indicated that the underlying symmetry may really be polar. We have reinvestigated the structure and found that there are many reflections with significant intensity among those that should be systematically extinct in Pnma. Some of these reflections have been subjected to further experimental analysis and have been shown not to be due to Renninger effects. A possible model that satisfies these observations is one where the true structure is in space group P1; and the structure is twinned about the three axial twofold rotation axes of Pnma. The space group P1 cannot be ruled out. Evidence for these conclusions is presented. The crystal chemistry of aragonite is revisited and described in terms of the stuffed alloy CaC. The carbonate group is confirmed to be non-planar in the crystal.

The thermal decomposition of calcium and dicalcium magnesium aconitate hydrates were studied by TG/DTG, DTA, EGA, SEM and other physico-chemical techniques. The decomposition proceeds in four stages: dehydration; oxidation of the carboxylic acid portion of the salt; complete fragmentation of the hydrocarbon portion; and finally, decarboxylation of the metal carbonate to the oxide. The crystal morphologies of the hydrate and anhydrous salts of each compound are very similar. Tricalcium aconitate consists of well-developed twinned crystals and stellate clusters intergrown with flat platy crystals. On the other hand, dicalcium magnesium aconitate crystals are monoclinic with well-developed pinacoidal faces.

Cleveland Bay and Halifax Bay are adjacent embayments, situated on the inner-shelf region (0-20 m) of the central Great Barrier Reef shelf off Townsville, northeast Australia. These bays contain Holocene sediments up to 5 m in thickness, deposited during the last stages of the post-glacial sea-level rise. X-ray diffraction and X-ray fluorescence techniques were used to examine the mineralogy and geochemistry of the main Holocene facies, sampled in 40 vibrocores.The sediments of southern Halifax Bay and Cleveland Bay consist mainly of quartz (ca. 50%), alkali feldspars (ca. 20%), clay minerals (ca. 20%) consisting of mixed-layer clays, smectite, kaolinite and illite, and carbonate (ca. 10%) including aragonite and calcite. The Holocene facies sequence comprises, in order of increasing age, modern bay, shoreline and mangrove sediments.The oxides of the major components (SiO2, Al2O3, Fe2O3, MgO, CaO, K2O, Na2O, P2O5) in Halifax Bay show the predicted linear correlations with geochemically related minor elements (Pb, Rb, Sr, Y, Zr, Ga, Zn, Ni, Co, Mn, Cr, Ti, Sc, V, Ba), and can be used to discriminate Holocene facies. However, in Cleveland Bay these elements are poorly correlated within each facies and provide very poor facies discrimination. These findings probably result from the presence of sandy shoreline sediments up to 2 m in thickness in the Holocene sequence of Cleveland Bay, with the consequent development of a weak oxic zone and migration of elements between adjacent facies. A similar oxic zone is poorly developed in Halifax Bay because the shoreline facies there is either thin or absent. That the chemical signatures of Holocene inner-shelf facies are spatially-variable, and are strongly influenced by the stratigraphy, has wide implications for geochemical studies of marine sediments.

The effect on shell formation of Tridacna gigas by sea water supplemented for 3 mo with ammonium (5, 10 μM, N) and phosphate (2, 5, 10 μM, P), separately or in combination, was examined. Exposure to N and N+P significantly enhanced shell-extension rates, but significantly reduced shell weights at equivalent size. Scanning-electron microscopy further revealed structural alterations in the outer shell layer, such as misshapen aragonite crystals, irregular crossed-lamellar orientation, and relatively porous shell microstructure. These observations are consistent with results of X-ray diffractometry on the shells which show distinct shifts in the positions of reflections from the (012) and (200) crystal planes relative to the control, indicating changes in crystal lattice parameters following addition of nutrients.

ABSTRACT Dissolution and solution transfer during deformation/metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components. Progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries.Progressive shortening is accommodated by the cores of most other minerals (including sulphides). These minerals develop strain, and hence dislocation density gradients, on their rims due to progressive shearing along grain boundaries. These gradients are particularly large when the mineral abuts phyllosilicate or graphite. The resulting chemical potential gradients between the core and rim drive dissolution, causing removal of the highly strained grain margins.Removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation. Interlayers and interfaces on boundaries lying at a low angle to the direction of shearing, and oriented relative to the sense of shear such that they can open, gape by small amounts. Water present in these interlayer spaces becomes destructured, considerably enhancing diffusion rates along the foliation.Penetrative volume loss, especially in deforming/metamorphosing pelitic rocks, is large at all metamorphic grades, increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies. Transference of material by fluid flow from deep to high levels in the earth's crust is precluded because thousands to tens of thousands of rock volumes of fluid are required, necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells, unless some extremely large‐scale form of fluid channelling is possible. Reassessment of diffusion mechanisms, and hence rates, during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid, indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required. The amount of fluid can be reduced sufficiently to allow large volume losses by a one‐way flow of fluid to the earth's surface, in deforming/metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure.Deformation partitioning‐controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation/metamorphism because matrix minerals, other than phyllosilicates and graphite, are preferentially removed. The large size of porphyroblasts, if present, tends to preserve them from dissolution. Hence, the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew, in rocks in which bedding is still well preserved.

The general features of the greisen systems include the occurrence of lenticular to massive alteration zones contained within cuspate protruberances from the apical zones of late stage geochemically specialised granitoids. The systems consist of an upper outer zone of minor barren pegmatite development, often associated with fine grained pegmatitic granite. The mineralisation occurs as irregular, to massive, or sheet-like bodies with the zone immediately below the contact extending for some 10–100 m. The bodies are essentially zones of fluorine rich sericitic-silicic alteration with associated cassiterite. The mineralised zone merges downwards into highly altered granite dominated by feldspathic types of alteration which in turn grade into mildly altered “fresh” granite.

Normal splenocytes cultured with Formalin-killed Candida albicans were shown to acquire significant suppressor cell activity in a period of 3 days. These cells were found to suppress both the phytohemagglutinin-induced mitogen response as well as the anti-sheep erythrocyte antibody response. Experiments were carried out to determine the nature of the suppressor cell population. Results showed that these cells were not susceptible to treatment with anti-Thy 1 antibody and complement. Panning experiments showed that the suppressor cells were not plastic-adherent or Mac-1 antigen-positive. The suppressor cells were, however, adherent to anti-mouse immunoglobulin (F(ab′)2-fragment)-coated dishes. Additional experiments showed that the suppressor cell activity was susceptible to treatment with monoclonal anti-Lyb 2.1 antibody and complement. These results suggest that the suppressor cell induced in vitro by Candida is a member of the Blymphocyte lineage.

The crystal structure of the kaolinite: dimethylsulfoxide (DMSO) intercalate (P1, a = 5.187(2), b = 8.964(3), c = 11.838(4) Å, α = 91.53(1)°, β = 108.59(2), γ = 89.92(1)°) has been determined using spectroscopic and X-ray and neutron powder diffraction data. Both the X-ray and neutron powder diffraction patterns were refined. Solid-state 13C, 29Si, and 27Al nuclear magnetic resonance data and previously collected infrared spectroscopic data provided a useful starting model for structural refinement. Due to the extreme overlap of reflections of this low-symmetry unit cell, the Rietveld method proved inadequate, and quasi-single crystal methods were employed. Each DMSO molecule was found to be triply hydrogen bonded above the octahedral vacancy in the gibbsitic sheet of the kaolinite layer. One methyl group is keyed into the ditrigonal hole in the tetrahedral sheet with the other S-C bond parallel to the sheet. The DMSO molecules are accommodated by significant horizontal displacement of individual kaolinite layers to achieve almost perfect overlap of the octahedral vacancy by the adjacent ditrigonal hole.

ABSTRACTHolocene reef development was investigated by coring on Britomart Reef, a mid‐shelf reef, 23 km long and 8 km wide situated 120 km north of Townsville in the central Great Barrier Reef (GBR). Two holes were drilled, Britomart 1 on a lagoon patch reef, and Britomart 2 on the windward reef crest. The Holocene reef (25·5 m) is the thickest yet recorded in the GBR and overlies an uneven substrate of weathered Pleistocene limestone.Mineralogical and geochemical analyses show that magnesian calcite and aragonite were converted to low Mg‐calcite below the Holocene‐Pleistocene disconformity. Corals above the interface have 7500–8500 ppm Sr, but 1650–1500 ppm just below it, decreasing to 400–800 ppm downwards. The intermediate Sr values could be due to partial replacement of aragonite by calcite or higher original Sr content in the corals.Three units are recognized in the Holocene: (1) coral boundstone unit, (2) coral framestone unit, and (3) coral rudstone unit. The coral boundstone unit forms the top 5 m of both cores and is algal‐bound coral rubble similar to the present reef top. The coral framestone unit is composed of massive head corals Diploastrea heliopora and Porites sp., and is currently forming in patch reefs situated in the lagoon and along the reef front. The coral rudstone unit comprises coral rudstone and floatstone with unabraded, and unbound, coral clasts in muddy matrix. This matrix may be up to 30% sponge chips.Radiocarbon dating indicates the reef grew more rapidly under the lagoon than under the reef front from 7000 to 5000 yr BP. The rate of reef growth matched existing estimates of sea‐level rise, but lagged approximately 1000 years (5–10 m) behind it. Most of the reef mass accumulated between 8500 and 5000 yr BP as a mound of debris, perhaps stabilized by seagrasses or algae. Accretion of the reef top in a windward direction between 5000 and 3000 yr BP created the present, steep reef‐front profile.