Alluvial, eolian and lacustrine sedimentology of a Paleoproterozoic half-graben, Baker Lake Basin, Nunavut, Canada

The northeast-trending Baker Lake sub-basin was a volcanically active, half-graben during deposition of ca. 1.85–1.76 Ga Baker Lake Group. Drainage was oriented along transverse and axial directions with flow to playa lake and deeper perennial lacustrine depocentres. Basin marginal, streamflow-dominated alluvial fans were concentrated along the southern margin, and provided sediment from Archean crystalline basement rocks. These fed transverse gravel- and sand-bed braided streams. Alluvial dynamics were characterized by channel aggradation and abandonment. Abandoned channel belts were sites of floodplain and eolian deposition. Basin axial braided streams fed northeast and southwest to a depocentre near Christopher Island, where eolian, playa and lacustrine environments were intimately linked. Felsic minette flows were initially erupted from localized centres; contemporaneous sedimentary deposits typically contain minor volcaniclastic components that increase in abundance basinward. Voluminous and widespread younger minette flows prograded outward from volcanic centres contributing significant additional basin-infill.     

Stratigraphy,sedimentology, structure and tectonics of Lower Ordovician and Devonian strata of South Mootwingee,Darling Basin,western New South Wales

K‐Ar age measurements using the ⁴⁰Ar/³⁹Ar total fusion technique on nephrite from two occurrences in the Great Serpentine Belt southeast of Tamworth yielded ages of 273 ± 5.8 and 280 ± 5.6 m.y. The K‐Ar ages indicate that tectonic emplacement, during which the nephrite was produced as a reaction product between ultra‐mafic rock and country rock, occurred early in the Permian about 275–280 m.y. ago.     

Stratigraphy,structure and tectonics of Lower Ordovician and Devonian strata of the central part of the Wonominta Block,western New South Wales

K‐Ar age determinations on granites from Central Queensland support the conclusions of field mapping, that the intrusives of the Anakie High are generally older than the rocks of the Drummond Basin. Results on granites from the Bowen‐Collinsville region indicate that they pre‐date most of the Bowen Basin sediments. Four ages are reported for basement rock from bore‐cores in the Great Artesian Basin. They confirm Precambrian basement to the south of the Mt. Isa‐Cloncurry area, and suggest possible Precambrian in the Long‐reach Spur. Two samples from the Nebine Ridge give Lower Carboniferous results. A previous report of Permian basement in the Surat Basin has been shown to be incorrect.     

Sedimentology of the Middle Devonian Timor Limestone,northeastern New South Wales,Australia

The microfacies assemblages and their distribution within the Middle Devonian Timor Limestone, exposed in the Timor Valley of northeastern New South Wales, Australia are described, and a depositional model for the carbonate buildup presented.Two broad lithological divisions are clearly recognizable within this thick (345 m) but lensoidal mass. Lime wackestones/packstones dominate the lower 200–215 m of the buildup while lime grainstones characterize the upper 130 m. Using cluster-sorting techniques on 697 modally analysed limestone samples, five microfacies and several subgroups each characterized by a unique combination of allochems have been recognized within this gross subdivision.The microfacies data and field observations suggest that carbonate sedimentation was initiated in an open marine shelf environment. It began simply because local conditions were favourable for calcareous organisms to become established. The benthos flourished ultimately spreading out over an area of 25 km². Although reefal in outline, the limestone is a bedded deposit containing chiefly comminuted skeletal debris and never had the ecologic potential to form a wave-resistant mass.Lime mud sedimentation began in a sublittoral environment. Abundant calcareous algae throughout most of the lower two-thirds of the buildup suggest that deposition occurred within the photic zone. In succeeding horizons, pellet and intraclast lime grainstones gradually replace the lime mud dominated microfacies, indicating that carbonate deposition slowly outpaced basin subsidence and shoal-water conditions developed over the buildup. During the buildup's final stage, a transgression occurred resulting in quieter marine conditions and the deposition of coral lime wackestones in the former shoal area.Carbonate sedimentation was terminated by an extensive marine tuff killing the calcareous benthos. No further extensive carbonate sedimentation during the Middle Devonian is recorded in the Timor Valley.     

Facies architecture of the Early Devonian Ural Volcanics,New South Wales

The Ural Volcanics are a early Devonian, submarine, felsic lava-sill complex, exposed in the western central Lachlan Orogen, New South Wales. The Ural Volcanics and underlying Upper Silurian, deepwater, basin-fill sedimentary rocks make up the Rast Group. The Ural Range study area, centrally located in the Cargelligo 1:100 000 map sheet area, was mapped at 1:10 000 scale. Seventeen principal volcanic facies were identified in the study area, dominated by felsic coherent facies (rhyolite and dacite) and associated monomictic breccia and siltstone-matrix monomictic breccia facies. Subordinate volcaniclastic facies include the pumice-rich breccia facies association, rhyolite – dacite – siltstone breccia facies and fiamme – siltstone breccia facies. The sedimentary facies association includes mixed-provenance and non-volcanic sandstone to conglomerate, black mudstone, micaceous quartz sandstone and foliated mudstone. The succession was derived from at least two intrabasinal volcanic centres. One, in the north, was largely effusive and intrusive, building a lava – sill complex. Another, in the south, was effusive, intrusive and explosive, generating lavas and moderate-volume (～3 km³) pyroclastic facies. The presence of turbidites, marine fossils, very thick massive to graded volcaniclastic units and black mudstone, and the lack of large-scale cross-beds and erosional scours, provide evidence for deposition in a submarine environment below storm wave-base. The Ural Volcanics have potential for seafloor or sub-seafloor replacement massive sulfide deposits, although no massive sulfide prospects or related altered zones have yet been defined. Sparse, disseminated sulfides occur in sericite-altered, steeply dipping shear zones.     

从脊椎动物化石角度论云南曲靖下、中泥盆统界线

根据早期脊椎动物化石证据及生物地层对比,云南曲靖穿洞组的时代为晚Emsian期。该地区下、中泥盆统界线应划在穿洞组与海口组之间,或从穿洞组顶部穿过。     

Palaeokarst development in a lower Frasnian (Devonian) platform succession,Canning Basin,northwestern Australia

Recognition of palaeokarst in the oldest exposed Devonian (Givetian ‐ lower Frasnian) platform successions of the Canning Basin reef complexes has eluded investigators for over forty years. The first evidence for palaeokarst, developed on microbial mud‐mounds in a single stratigraphic horizon, is documented and records an episode of exposure during early carbonate platform development. Surface palaeokarst features are scalloped surfaces, solution pits and a pipe, underlain by fenestral limestone with sediment‐filled fossil moulds and vugs. The platform succession has variably developed metre‐scale cycles which are composed predominantly of shallowing‐upward subtidal facies, with some cycles having fenestral peloidal mudstone caps. Changes in facies type and stratigraphic arrangement up the succession define two deepening‐upward units (～70 and 180 m thick), with the palaeokarst surface representing emergence following rapid shallowing at the top of the lower unit. The stratigraphic position of the palaeokarst between these two units suggests it may represent a sequence boundary. This may have been caused by a low‐magnitude eustatic fall or footwall‐uplift event superimposed on a rapidly subsiding basin margin.     

藏北龙木错东部三岔口地区下奥陶统与泥盆系的不整合界面

在北羌塘三岔口一带采获丰富的腕足类：汉伯矮正形贝及比较种Nanorthis cf.hamburgensis（Walcott）。建立了早奥陶世岩石地层单位——三岔口组,是羌塘地区目前有化石控制的最低层位。中、晚泥盆世拉竹龙组与下伏志留系、奥陶系不整合接触关系的进一步确定,证明了羌北-昌都板块与扬子板块的亲缘性,为羌北-昌都板块属性的确定提供了重要证据。     

Early Devonian synorogenic alluvial-fan deposits of the Maccullochs Range,western New South Wales

The Early Devonian, Maccullochs Range beds (new) of the Winduck Interval largely comprise non-marine fine-grained sheet-flood-deposited sandstones which lie in the southeast sector of the Darling Basin Conjugate Fault System. Deposition of the >2.5 km-thick sequence occurred on the Wilcannia, Towers and Coolabah Bore alluvial fans, that were sourced largely from lightly indurated sandstone caps overlying a large basement high lying north of the Darling River Lineament, and also from west of Maccullochs Range (Coolabah Bore Fan). Four lithofacies are recognised. Lithofacies 1, massive sandstone, is proximal and was deposited from hyperconcentrated sheet floods. The more distal lithofacies 2 is partly massive, partly laminated and partly affected by soft sediment slumping during its deposition. It contains 1.3 – 3.5 m-thick sheet-flood successions that rarely show cross-bedding. Lithofacies 3 and 4 are minor: lithofacies 3, stream-flood deposited, comprises coarse-grained, pebbly sandstone and lithofacies 4, transient playa lake deposits that are locally intercalated with lithofacies 2. In lithofacies 2, thick massive fine-grained sandstone is commonly overlain by laminated sandstone that was deformed when soft. Incised channel deposits in lithofacies 2 deposits are rare and palaeosols were not discovered. Permanency of the positions of two of the alluvial fans, and by inference their feeder streams, remained unchanged for ～9 million years. The fans overlie probable floodplain deposits observed in a quarry in the easternmost part of the study area. Marine fossils are very minor in the range—the brachiopod Howellella jaqueti at one locality indicates an Early Devonian age for one of the brief marine incursions into what was normally an alluvial-fan environment. Very brief marine incursions elsewhere in the group are deduced from the presence of very rare fossil gastropods.     

藏北龙木错东部三岔口地区下奥陶统与泥盆系的不整合界面

在北羌塘三岔口一带采获丰富的腕足类:汉伯矮正形贝及比较种Nanorthiscf.hamburgensis(Walcott)。建立了早奥陶世岩石地层单位——三岔口组,是羌塘地区目前有化石控制的最低层位。中、晚泥盆世拉竹龙组与下伏志留系、奥陶系不整合接触关系的进一步确定,证明了羌北-昌都板块与扬子板块的亲缘性,为羌北-昌都板块属性的确定提供了重要证据。     

Devonian formations,vertebrate faunas and age control on the far south coast of New South Wales and adjacent Victoria

A diverse fossil vertebrate record in the Devonian of coastal southeastern Australia includes at least 30 genera and species representing all three major groups of extant jawed vertebrates (bony and cartilaginous fishes, and tetrapods), and both extinct groups (placoderm and acanthodian fishes). A bone recorded by W. B. Clarke in 1860 from Twofold Bay is the first published record of a Devonian vertebrate from the Southern Hemisphere. Abundant plant remains at some localities include large impressions of arborescent lycopsids, indicating one of the earliest forest environments for the Gondwana supercontinent. An early terrestrial invertebrate fauna is evidenced by fossil millipede remains. A review of the evidence for age control using paleontology and isotopic dating suggests that the lower part of the Devonian sequence (Bunga beds, Boyd Volcanic Complex) may be somewhat older (Emsian – Eifelian) than recently proposed; the tetrapod trackways at Genoa River in Victoria (lower part of the Combyingbar Formation) may correlate with the lowermost Twofold Bay Formation of the Merrimbula Group, which is overlain by the marine Bellbird Creek Formation, a manifestation of the global late Frasnian marine transgression and extinction event. Abundant placoderm remains at all higher fossil fish horizons in the overlying Worange Point Formation indicate a latest Devonian rather than Carboniferous age for the upper Merrimbula Group.     

晚白垩世中国东南沿岸山系与中南地区的沙漠和盐湖化

晚白垩世在中国东南沿古太平洋西岸地区形成了一条巨大的沿岸山系，其山峰高度在３５００—４０００ｍ之间，东西宽度近５００ｋｍ，挡住了东来的暖湿气流，使中南地区云梦泽内陆水域的广大平原和丘陵地变成了一个热带—亚热带干旱、炎热的半沙漠和盐湖地区，这一古地理和古气候格局一直持续到早第三纪末才开始改变。     

Effect of Pb loss on the ages of reference zircons QGNG and SL13, and of volcanic zircons from the Early Devonian Merrions and Turondale Formations,New South Wales

Recent papers (Black et al. 1997; Jagodzinski & Black 1999) reported that SL13‐referenced SHRIMP zircon ages are ca 1.3% younger than QGNG‐referenced ages. It is shown here that these authors overestimated their analytical errors and as a consequence failed to register the presence of large and variable fractions of Pb loss within both QGNG (median 40% of spots) and SL13 (25%). If only the oldest ²⁰⁶Pb/²³⁸U age groups within each of the same 16 analytical sessions are selected for comparison, the ²⁰⁶Pb/²³⁸U ages of QGNG relative to SL13 agree with the Concordia intersection age by isotope dilution to within 0.4% (standard deviation). This observation eliminates the possibility of systematic bias. Jagodzinski and Black (1999) also overlooked Pb loss in their ages for the Early Devonian Turondale and Merrions Formations, which are corrected here for time‐scale use.     

印支地体泥盆纪牙形石、放射虫和竹节石组合

Devonian faunas including conodonts, radiolari-ans, tentaculitids and other important fossils have re-cently been found at several localities in the Indochina Terrane. These faunas are biostratigraphically and tectonically important.     

Stromatoporoid growth forms and Devonian reef fabrics in the Upper Devonian Alexandra Reef System,Canada – Insight on the challenges of applying Devonian reef facies models

Existing facies models for Devonian reef systems can be divided into high‐energy and low‐energy types. A number of assumptions have been made in the development of these models and, in some cases, criteria that distinguish important aspects of the models are poorly defined. The Upper Devonian Alexandra Reef System contains a variety of reef fabrics from different depositional environments and is ideal for studying the range of environments in which stromatoporoids thrived and the facies from these different environments. A wide variety of stromatoporoid growth forms including laminar, tabular, anastamosing laminar and tabular, domal, bulbous, dendroid, expanding conical, concave‐up whorled‐laminar, concave‐up massive tabular and platy‐multicolumnar are present in the Alexandra Reef System. The whorled‐laminar and massive tabular concave‐up growth forms are virtually undocumented from other Devonian reefs but were common in the reef front of the Alexandra, where they thrived in a low‐energy environment around and below fair‐weather wave base. In contrast, high‐energy parts of the reef margin were dominated by bioclastic rubble deposits with narrow ribbon‐like discontinuous bodies of laminar stromatoporoid framestone. In the lagoon, laminar stromatoporoids formed steep‐sided sediment‐dominated bioherms in response to sea‐level rise and flooding. Relying mostly on the different reef facies in the Alexandra system, a new classification scheme for Devonian reef fabrics has been developed. Devonian reef fabrics can be classified as being: (i) sediment‐laden metazoan dominated; (ii) metazoan–microbial dominated (boundstone); (iii) metazoan dominated (framestone); or (iv) metazoan–marine cement dominated. Distinction of these fabrics carries important sedimentary and palaeoecological implications for reconstructing the depositional environment. With examples from the Alexandra Formation, it is demonstrated that reef facies accumulated in a range of depositional environments and that the simple observation of massive stromatoporoids with or without microbial deposits does not automatically imply a high‐energy reef margin, as otherwise portrayed in a number of the existing facies models for these systems.     

四川宝兴灵关─金台山飞来峰泥盆纪地层古生物

首次详细地描述了灵关一金台山飞来峰泥盆纪地层剖面，将泥盆系划分为平驿铺组、甘溪组、养马坝组和观雾山组４个岩石地层单位，建立了４个腕足类组合带和２个珊瑚类组合带，并与邻区进行了对比。通过年代地层界线的讨论，初步认为该飞来峰内仅有下泥盆统和中泥盆统中下部地层。     

Proximal braidplain deposits in the Middle Devonian Malbaie Formation of Eastern Gaspé, Quebec, Canada

The Middle Devonian Malbaie Formation of Eastern Gaspé, Canada, comprises sharply alternating conglomerate and sandstone units. Their petrography suggests derivation from the same source, but palaeocurrents indicate different dispersal systems for the sand and gravel. The principal conglomerate facies is horizontally stratified, with well-developed imbrication, characteristic of deposition on a high-energy, proximal braidplain. Minor cross-stratified conglomerate shows well-defined size sorting, attributed to avalanching down foresets and sorting within minor bedforms on bar tops. The sandstone units mainly comprise erosion surfaces overlain by mudstone intraclasts, alternating with lineated low-angle to horizontally stratified sandstone or trough cross-stratified sandstone. The sandstone units were deposited on a proximal braidplain with highly variable discharge, but the absence of calcrete indicates that dry periods were not prolonged. The Malbaie is the coarsest, uppermost formation of a Devonian clastic wedge formed during the Acadian Orogeny. The uniformity of facies association and palaeocurrents, particularly in conglomerate units, indicates derivation from a broad upwarp to the south. This implies that the Acadian uplands resulted from straight compression, in contrast to the localized uplifts formed by strike-slip faulting during the Carboniferous.     

Syn-sedimentary hydrothermal dolomites in a lacustrine rift basin: Petrographic and geochemical evidence from the lower Cretaceous Erlian Basin,Northern China

Dolomites occur extensively in the lower Cretaceous along syn-sedimentary fault zones of the Baiyinchagan Sag, westernmost Erlian Basin, within a predominantly fluvial–lacustrine sedimentary sequence. Four types of dolomite are identified, associated with hydrothermal minerals such as natrolite, analcime and Fe-bearing magnesite. The finely-crystalline dolomites consist of anhedral to subhedral crystals (2 to 10 μm), evenly commixed with terrigenous sediments that occur either as matrix-supporting grains (Fd1) or as massive argillaceous dolostone (Fd2). Medium-crystalline (Md) dolomites are composed of subhedral to euhedral crystals aggregates (50 to 250 μm) and occur in syn-sedimentary deformation laminae/bands. Coarse-crystalline (Cd) dolomites consist of non-planar crystals (mean size >1 mm), and occur as fracture infills cross-cutting the other dolomite types. The Fd1, Md and Cd dolomites have similar values of δ¹⁸O (−20·5 to −11·0‰ Vienna PeeDee Belemnite) and δ¹³C (+1·4 to +4·5‰ Vienna PeeDee Belemnite), but Fd2 dolomites are isotopically distinct (δ¹⁸O −8·5 to −2·3‰ Vienna PeeDee Belemnite; δ¹³C +1·4 to +8·6‰ Vienna PeeDee Belemnite). Samples define three groups which differ in light rare-earth elements versus high rare-earth elements enrichment/depletion and significance of Tb, Yb and Dy anomalies. Medium-crystalline dolomites have signatures that indicate formation from brines at very high temperature, with salinities of 11·8 to 23·2 eq. wt. % NaCl and T_h values of 167 to 283°C. The calculated temperatures of Fd1 and Cd dolomites extend to slightly lower values (141 to 282°C), while Fd2 dolomites are distinctly cooler (81 to 124°C). These results suggest that the dolomites formed from hydrothermal fluid during and/or penecontemporaneous with sediment deposition. Faults and fractures bounding the basin were important conduits through which high-temperature Mg-rich fluids discharged, driven by an abnormally high heat flux associated with local volcanism. It is thought that differing amounts of cooling and degassing of these hydrothermal fluids, and of mixing with lake waters, facilitated the precipitation of dolomite and associated minerals, and resulted in the petrographic and geochemical differences between the dolomites.     

四川宝兴灵关─金台山飞来峰泥盆纪地层古生物

首次详细地描述了灵关一金台山飞来峰泥盆纪地层剖面，将泥盆系划分为平驿铺组、甘溪组、养马坝组和观雾山组４个岩石地层单位，建立了４个腕足类组合带和２个珊瑚类组合带，并与邻区进行了对比。通过年代地层界线的讨论，初步认为该飞来峰内仅有下泥盆统和中泥盆统中下部地层。     

滇西南孟连西北部泥盆系的确定

通过 1∶5万孟连县、景信幅的区域地质调查 ,在孟连县北西 1∶2 0万孟连幅原划的“西部拉巴组”(原定为下二叠统 )中 ,采获Entactinia -Entactinosphaera组合共 4个属 6个种的放射虫化石 ,结合岩性组合、沉积相等特征 ,重新更正为中—上泥盆统曼信组。为研究该区的地层展布、大地构造环境、古地理、构造活动等提供了新资料。