Permian stratigraphy of the Woolaga creek area, Mingenew District, Western Australia

Six units are distinguished in the Permian sequence, and are considered to belong to the Sakmarian and Artinskian stages.

Petrographic and isotope constraints on the origin of authigenic carbonate minerals and the associated fluid evolution in Late Permian coal measures, Bowen Basin (Queensland), Australia

Authigenic carbonate minerals are ubiquitous throughout the Late Permian coal measures of the Bowen Basin, Queensland, Australia. In the northern Bowen Basin, carbonates include the following assemblages: siderite I (delta O-18(SMOW) = +11.4 to + 17%, delta C-13(PDB) = - 5.3 to + 120), Fe-Mg calcite-ankerite-siderite II mineral association (delta O-18(SMOW) = +7.2 to + 10.20, delta C-13(PDB) = 10.9 to - 1.80 for ankerite) and a later calcite (delta O-18(SMOW) = +5.9 to + 14.60, delta C-13(PDB) = -11.4 to + 4.40). In the southern Bowen Basin, the carbonate phase consists only of calcite (delta O-18(SMOW) = +12.5 to + 14.80, delta C-13(PDB) = -19.4 to + 0.80), where it occurs extensively throughout all stratigraphic levels. Siderite I occurs in mudrocks and sandstones and predates all other carbonate minerals. This carbonate phase is interpreted to have formed as an early diagenetic mineral from meteoric waters under cold climate and reducing conditions. Fe-Mg calcite-ankerite-siderite Il occur in sandstones as replacement of volcanic rock fragments. Clay minerals (illite-smectite, chlorite and kaolinite) postdate Ca-Fe-Mg carbonates, and precipitation of the later calcite is associated with clay mineral formation. The Ca-Fe-Mg carbonates and later calcite of the northern Bowen Basin are regarded as having formed as a result of hydrothermal activity during the latest Triassic extensional tectonic event which affected this part of the basin, rather than deep burial diagenesis during the Middle to Late Triassic as previously reported. This hypothesis is based on the timing relationships of the authigenic mineral phases and the low delta O-18 values of ankerite and calcite, together with radiometric dating of illitic clays and recently published regional geological evidence. Following the precipitation of the Ca-Fe-Mg carbonates from strongly O-18-depleted meteoric-hydrothermal fluids, continuing fluid circulation and water-rock interaction resulted in dissolution of these carbonate phases as well as labile fragments of volcaniclastic rocks. Subsequently, the later calcite and day minerals precipitated from relatively evolved (O-18-enriched) fluids. The nearly uniform delta O-18 values of the southern Bowen Basin calcite have been attributed to very low water/rock ratio in the system, where the fluid isotropic composition was buffered by the delta O-18 values of rocks. (C) 2000 Elsevier Science B.V. All rights reserved.

Laser-derived particle size data from CRP-3, Victoria Land Basin, Antarctica: Implications for sequence and seismic stratigraphy

Seven hundred and nineteen samples from throughout the Cainozoic section in CRP-3 were analysed by a Malvern Mastersizer laser particle analyser, in order to derive a stratigraphic distribution of grain-size parameters downhole. Entropy analysis of these data (using the method of Woolfe and Michibayashi, 1995) allowed recognition of four groups of samples, each group characterised by a distinctive grain-size distribution. Group 1, which shows a multi-modal distribution, corresponds to mudrocks, interbedded mudrock/sandstone facies, muddy sandstones and diamictites. Group 2, with a sand-grade mode but showing wide dispersion of particle size, corresponds to muddy sandstones, a few cleaner sandstones and some conglomerates. Group 3 and Group 4 are also sand-dominated, with better grain-size sorting, and correspond to clean, well-washed sandstones of varying mean grain-size (medium and fine modes, respectively). The downhole disappearance of Group 1, and dominance of Groups 3 and 4 reflect a concomitant change from mudrock- and diamictite-rich lithology to a section dominated by clean, well-washed sandstones with minor conglomerates. Progressive downhole increases in percentage sand and principal mode also reflect these changes. Significant shifts in grain-size parameters and entropy group membership were noted across sequence boundaries and seismic reflectors, as recognised in others studies.

Permian Palynofloral Assemblages of the Chaco-Paraná Basin (Argentina): Systematics and Stratigraphic Significance

Core samples from an upper Palaeozoic, partly glaciogene borehole section (Ordóñez: YPF Cd O es-1) in the southern Chaco-Paraná Basin (Córdoba Province, northeastern Argentina) have produced variable palynological results. Samples from the lower part of the section (i.e., from the diamictite-bearing upper Ordóñez Formation) proved non-palyniferous. Those from the overlying, essentially post-glacial Victoriano Rodríguez Formation yielded spore-pollen assemblages in varying concentrations and in good to excellent states of preservation, thus providing the material basis for the present account. The palynomorph taxa represented in the assemblages comprise 20 species of spores (distributed among 14 genera) and 25 species of pollen grains (14 genera). The majority of the species are described in systematic detail. One trilete spore species -Convolutispora archangelskyi- is newly proposed. Several other, possibly new species (three of trilete spores, one of monosaccate pollen) are represented insufficiently for other than informal naming. The following new combinations, also of trilete spore species, are instituted: Converrucosisporites confluens (Archangelsky & Gamerro, 1979), C. micronodosus (Balme & Hennelly, 1956), and Anapiculatisporites tereteangulatus (Balme & Hennelly, 1956). Sculptural intergradation (granulate through verrucate) among three species -Granulatisporites austroamericanus Archangelsky & Gamerro, 1979, C. confluens, and C. micronodosus- prompts their informal grouping, proposed herein, as the Converrucosisporites confluens Morphon, which is also recognizable elsewhere in the Gondwanan Permian. The possibility, if not the likelihood, that G. austroamericanus is conspecific with Microbaculispora tentula Tiwari, 1965 is canvassed. The palynologically productive borehole section of the Victoriano Rodríguez Formation studied here is assignable to the middle to upper Cristatisporites Zone and to the succeeding Striatites Zone, thus signifying an Early Permian age for this section and facilitating correlation with strata of the Paraná and Paganzo Basins. From this and prior work, the Ordóñez well sequence embracing the Ordóñez and Victoriano Rodríguez Formations includes, in addition to the latter two zones, the preceding (late Pennsylvanian) Potonieisporites-Lundbladispora Zone which is known from the lower to mid-upper part of the Ordóñez Formation. Thus, the Carboniferous-Permian boundary can be inferred to lie within the upper part of the latter formation

Stratigraphy, facies architecture and tectonic implications of the Upper Devonian to Lower Carboniferous Campwyn Volcanics of the northern New England Fold Belt

Upper Devonian to Lower Carboniferous strata of the Campwyn Volcanics of east central Queensland preserve a substantial sequence of first-cycle volcaniclastic sedimentary and coeval volcanic rocks that record prolonged volcanic activity along the northern New England Fold Belt. The style and scale of volcanism varied with time, producing an Upper Devonian sequence of mafic volcano-sedimentary rocks overlain by a rhyolitic ignimbrite-dominated sequence that passes upward into a Lower Carboniferous limestone-bearing sedimentary sequence. We define two facies associations for the Campwyn Volcanics. A lower facies association is dominated by mafic volcanic-derived sedimentary breccias with subordinate primary mafic volcanic rocks comprising predominantly hyaloclastite and peperite. Sedimentary breccias record episodic and high energy, subaqueous depositional events with clastic material sourced from a mafic lava-dominated terrain. Some breccias contain a high proportion of attenuated dense, glassy mafic juvenile clasts, suggesting a syn-eruptive origin. The lower facies association coarsens upwards from a lithic sand-dominated sequence through a thick interval of pebble- to boulder-grade polymict volcaniclastic breccias, culminating in facies that demonstrate subaerial exposure. The silicic upper facies association marks a significant change in eruptive style, magma composition and the nature of eruptive sources, as well as the widespread development of subaerial depositional conditions. Crystal-rich, high-grade, low- to high-silica rhyolite ignimbrites dominate the base of this facies association. Biostratigraphic age controls indicate that the ignimbrite-bearing sequences are Famennian to lower-mid Tournaisian in age. The ignimbrites represent extra-caldera facies with individual units up to 40 m thick and mostly lacking coarse lithic breccias. Thick deposits of pyroclastic material interbedded with fine-grained siliceous sandstone and mudstone (locally radiolarian-bearing) were deposited from pyroclastic flows that crossed palaeoshorelines or represent syn-eruptive, resedimented pyroclastic material. Some block-bearing lithic-pumice-crystal breccias may also reflect more proximal subaqueous silicic explosive eruptions. Crystal-lithic sandstones interbedded with, and overlying the ignimbrites, contain abundant detrital volcanic quartz and feldspar derived from the pyroclastic deposits. Limestone is common in the upper part of the upper facies association, and several beds are oolitic (cf. Rockhampton Group of the Yarrol terrane). Overall, the upper facies association fines upward and is transgressive, recording a return to shallow-marine conditions. Palaeocurrent data from all stratigraphic levels in the Campwyn Volcanics indicate that the regional sediment-dispersal direction was to the northwest, and opposed to the generally accepted notion of easterly sediment dispersal from a volcanic arc source. The silicic upper facies association correlates in age and lithology to Early Carboniferous silicic volcanism in the Drummond (Cycle 1) and Burdekin Basins, Connors Arch, and in the Yarrol terranes of eastern Queensland. The widespread development of silicic volcanism in the Early Carboniferous indicates that silicic (rift-related) magmatism was not restricted to the Drummond Basin, but was part of a more substantial silicic igneous province.

Rare earth element fractionation in authigenic illite–smectite from Late Permian clastic rocks, Bowen Basin, Australia: implications for physico-chemical environments of fluids during illitization

REE analyses were performed on authigenic illitic clay. minerals from Late Permian mudrocks, sandstones and bentonites from the Bowen Basin (Australia). The mixed-layer illite-smectite exhibit REE patterns with an obvious fractionation of the HREE from the LREE and MREE, which is an apparent function of degree of illitization reaction. The highly illitic (R greater than or equal to 3) illite-smectite from the northern Bowen Basin show a depletion of LREE relative to the less illitic (R=0 and 1) clays. In contrast, an enrichment of HREE for the illite-rich clays relative to less. illitic clays is evident for the southern Bowen Basin samples. The North American Shale Composite-normalized (La/Lu)(sn) ratios show negative correlations with the illite content in illite-smectite and positive correlations with the delta(18)O values of the clays for both the northern and southern Bowen Basin samples. These correlations indicate that the increasing depletion of LREE in hydrothermal fluids is a function of increasing water/rock ratios in the northern Bowen Basin. Good negative correlations between (La/Lu)(sn) ratios and illite content in illite-smectite from the southern Bowen Basin suggest the involvement of fluids with higher alkalinity and higher pH in low water/ rock ratio conditions. Increasing HREE enrichment with delta(18)O decrease indicates the effect of increasing temperature at low water/rock ratios in the southern Bowen Basin. Results of the present study confirm the conclusions of some earlier studies suggesting that REE in illitic clay minerals are mobile and fractionated during illitization and that this fact should be considered in studies of sedimentary processes and in identifying provenance. Moreover, our results show that REE systematic of illitic clay minerals can be applied as an useful technique to gain information about physico-chemical conditions during thermal and fluid flow events in certain sedimentary basins. (C) 2003 Elsevier Science B.V. All rights reserved.

Early-Middle Jurassic stratigraphy of the Fortrose-Chaslands region, southernmost South Island, New Zealand

The 40 km of coastline from Fortrose to Chaslands Mistake (southeastern South Island, New Zealand) comprises sediments that are part of the Early-Middle Jurassic of the Murihiku Terrane. The sediments are dominantly fluvial with some marine beds and alluvial fan deposition, and display an evolution of fluvial style which progresses from perennial flow to seasonal flow. The McPhee Cove Conglomerate is a prominent unit to the north. It has been used to separate two formations which would otherwise, on inherent lithological grounds, be difficult to distinguish. This paper discusses several similar conglomerates which occur in the south, but which are separated from the type area of the McPhee Conglomerate by major tectonic disruption. Hence, the existing lithostratigraphic nomenclature to the north, including the McPhee Cove Conglomerate, cannot be simply extended southwards. The Fortrose-Chaslands area appears to consist of two tectonic blocks, the Slope Point Block and the Brothers Block, which are separated from each other and from the adjacent Papatowai Block by major strike faults (or fault zones). A change is proposed to the existing stratigraphy which involves recognising all terrestrial sediments as part of the False Island Formation. Four prominent clast-supported conglomerate horizons are named as members of the False Islet Formation: the White Head Conglomerate, Black Bluff Conglomerate. Hoiho Conglomerate, and Slope Point Conglomerate Members. The latter contains five named conglomerate beds.