The Cretaceous Songliao Basin: Volcanogenic Succession, Sedimentary Sequence and Tectonic Evolution, NE China

The Songliao basin (SB) is a superposed basin with two different kinds of basin fills. The lower one is characterized by a fault-bounded volcanogenic succession comprising of intercalated volcanic, pyroclastic and epiclastic rocks. The volcanic rocks, dating from 110 Ma to 130 Ma, are of geochemically active continental margin type. Fast northward migration of the SB block occurred during the major episodes of the volcanism inferred from their paleomagnetic information. The upper one of the basin fill is dominated by non-marine sag-style sedimentary sequence of siliciclastics and minor carbonates. The basin center shifted westwards from the early to late Cretaceous revealed by the GGT seismic velocity structure suggesting dynamic change in the basin evolution. Thus, a superposed basin model is proposed. Evolution of the SB involves three periods including (1) Alptian and pre-Aptian: a retroarc basin and range system of Andes type related to Mongolia-Okhotsk collisional belt (MOCB); (2) Albian to Companian: a sag-like strike-slip basin under transtension related to oblique subduction of the Pacific plate along the eastern margin of the Eurasian plate; (3) since Maastrichtian: a tectonic inverse basin under compression related to normal subduction of the Pacific plate under the Eurasian plate, characterized by overthrust, westward migration of the depocenter and eastward uplifting of the basin margin.     

Dickite‐ and kaolinite‐bearing sandstones and conglomerates in Illawarra Coal Measures of the Sydney Basin,New South Wales

The recent discovery of dickite, intimately associated with ordered and disordered kaolinite, in quartzose sandstones and conglomerates of the Illawarra Coal Measures is of interest since in terms of the phase rule the co‐existence of two or more of these polytypes is evidence of either an unstable or metastable assemblage. A study has, therefore, been undertaken of the host rocks and accompanying strata in an attempt to gain insight into the mechanism of formation of the dickite and the reason for its development in preference to either of the other generally more abundant polytypes. From the results it would appear that although much still remains unresolved, the dickite is authigenic and precipitated from migrating groundwaters. Due probably to unusually low concentrations of silica in the groundwaters the rate of precipitation was inordinately slow and this apparently facilitated growth of relatively coarse crystals and development of the most stable phase.     

Sequence Stratigraphic Modeling of Sedimentary Basin: Conceptual Model and Application to Erlian and Yinggehai Basins, China

INTRODUCTIONQuantitativebasinmodelinghasbecomeoneofthefrontiersinsedimentarybasinanalySis.Alargevarietyofnumericalmodelsconcerningbasinformation,basinfillingprocess,thermalhistory,hydrocarbongenerationandaCCUmulationhavebeenformulatedoverthelastdecadetondAnctheprocessesandevollltionofsedimentarybasins(Mckenzie,1978,signeretal.,1990;Ungereretal.,1990).Thebasinmodeling,utilizingcomputersimulationtechnique,isapowerfultoolforbasinanalySisandhasincreasinglybeenintegratedintoconventionalbasi…     

Attenuated basin‐margin sequence stratigraphy of the Palaeoproterozoic Calvert and Isa Superbasins: The Fickling Group,southern Murphy Inlier,Queensland

Sedimentary rocks of the Palaeoproterozoic Calvert and Isa Superbasins are exposed across a large area of northern Australia. Despite the extent of the exposures there is little to indicate the nature of the basin margins as most outcrop boundaries are structurally or erosionally defined, or the margins, where preserved, are concealed beneath younger basins. The Murphy Inlier, which forms the boundary between the Mt Isa and McArthur Basins, is unique in that on its southern flanks a basin‐margin succession is well‐preserved as the Fickling Group. A detailed sequence‐stratigraphic analysis of outcrop sections and well logs, supplemented by seismic reflection profiles and SHRIMP U–Pb zircon ages, shows that all seven supersequences of the Isa Superbasin and one supersequence from the older Calvert Superbasin are represented in the Fickling Group. Through this high‐resolution sequence‐stratigraphic framework, it is possible to accurately correlate chronostratigraphically equivalent strata from the McNamara Group on the central Lawn Hill Platform to the Fickling Group on the southern Murphy Inlier. Each supersequence thins substantially from the McNamara Group (～11 km thick) to the Fickling Group (<1 km thick). The combined effects of truncation and onlap of sequences over the Murphy Inlier basement high are responsible for the thinning. Major time breaks of up to 25 million years occur between supersequences in the Fickling Group. Erosional hiatuses are often manifested at the base of supersequences as conglomerate beds composed of silicified detritus from older strata. Sequences in the Fickling Group were generally deposited in a proximal basin‐margin setting, while sequences in the McNamara Group were deposited in distal basin depocentres. The proximal depositional setting of Fickling Group sequences reduces the number of thick carbonaceous shale and siltstone intervals, which often host Zn–Pb–Ag and Cu deposits in the McNamara Group. Many host sequences from the McNamara Group are also absent in the Fickling Group due to truncation and onlap pinchout. Consequently, the economic potential of Palaeoproterozoic strata on the southern Murphy Inlier is less than equivalent strata from the central Lawn Hill Platform. Despite this, potential does exist for future discoveries of economic mineral deposits in the Mt Les Siltstone and Walford Dolomite units of the Fickling Group.     

The variation in thickness and composition of coal seams and its use in interpretation of palaeocurrents — A case study from the Raniganj Coalfield,West Bengal,India

The petrological and chemical composition of a coal reflects all its inherent characters. Together with the variation in thickness of the coal seams, these aspects have been studied in detail around Salanpur (Raniganj Coalfield), India. The data reveal that any coal seam having its mother material supplied continuously from the same source will show a variation in its composition, the resultant being closely related to the environmental factors of the site of deposition, namely its morphology, including the disposition of its channel axis, and the palaeocurrent direction. Thus, it is suggested that these coal-seam properties may be used just as other sedimentary parameters in interpreting the characteristics of the site of deposition and depositing current.     

Corrigendum: Geological setting and origin of fuchsite‐bearing rocks near Menzies,Western Australia

Quartz‐andalusite‐fuchsite rocks in an Archaean greenstone belt at Menzies, Western Australia, are described in their geological setting. They are shown to have developed from intense metasomatism of layered rocks of komatiitic composition. Ratios of the immobile components Al₂O₃, TiO₂, Cr, V and Zr are consistent, despite wide variations in their absolute values, and compare closely with those of an underlying komatiite suite. Marked depletion of Ca, Na, Mg and Fe has led to a strongly peraluminous composition and enhanced Cr values. Silicification and introduction of K has also occurred. Most of the metasomatism took place before peak metamorphism, and the mineral assemblage is now dominated by andalusite, fuchsite, and recrystallized quartz. Schlieren or vein‐like segregations rich in andalusite, chromite, rutile and minor sulphides and tourmaline are interpreted as the original fluid pathways, where concentration of immobiles was achieved through solution of mobile components, and volume loss. They have been termed residual veins. Metasomatism is believed to have taken place by synvolcanic processes analogous to those operating in modern hot spring systems. The rocks were severely modified by metamorphism and tectonism. The fuchsitic rocks at Menzies are compared to similar rocks in other areas.     

The distribution of trace elements and Sr isotopes across the coal and its partings in the Wyodak sea, Powder River Basin, Wyoming, USA

The spatial distribution of major, minor and trace elements in a coal basin is important for exploitation strategy and for the understanding of processes of coal formation and diagenesis. The 35400 km2 intermontane Powder River Basin, NW USA, is a major s…     

The high‐K calc‐alkaline Alagoinhas pluton: anisotropy of magnetic susceptibility,geochemistry, emplacement setting,and implications for the evolution of Borborema Province,NE Brazil

The Alagoinhas pluton is a member of the widespread high‐K calc‐alkaline association of northeastern Brazil. Some authors suggest that this region represents an amalgamation of distinct tectonic terranes assembled during the Brasiliano (Pan‐African) orogeny. Our work compares geochemical data (major, trace and REE) of the Alagoinhas with other plutons of same petrotectonic association (Caruaru‐Arcoverde batholith). These plutons apparently intrude several distinct tectonic terranes, separated by a major E‐W dextral transcurrent system, the East Pernambuco shear zone (EPSZ). Anisotropy of magnetic susceptibility and structural data for the Alagoinhas pluton are used to compare tectonic regimes across the EPSZ. The results indicate that the Caruaru‐Arcoverde batholith and the Alagoinhas pluton evolved from similar sources and were subjected to the same tectonic regime during emplacement, placing severe restrictions on use of the EPSZ as a suture zone between distinct tectonic terranes.     

Geochemistry,mineralogy and tectonic setting of deerite‐bearing meta‐ironstones from the Emo Metamorphics of Papua New Guinea

The geochemistry of two deerite‐bearing meta‐ironstones from the Emo Metamorphics of Papua New Guinea suggests that they were deposited as metalliferous cherts enriched in manganese and iron by hydrothermal exhalative activity in an ocean ridge system. Subsequent blueschist facies metamorphism resulted in the formation of the assemblage deerite‐quartz‐albite‐iron oxides‐alkali amphiboles‐spessar‐tine‐stilpnomelane‐apatite, with calcium‐manganese carbonates in one specimen. Assemblages in associated metabasites suggest P‐T conditions of 7 kb at 320°C, which overlap with the P‐T field defined by one of the meta‐ironstones. Oxygen fugacity was probably an important control in determining variations in mineralogy and mineral chemistry. Preliminary data on the trace element geochemistry of associated metabasites are consistent with an ocean ridge environment for the formation of the meta‐ironstones.     

The petrology of the Mt Manypeaks Adamellite and associated high‐grade metamorphic rocks near Albany,Western Australia

The Mt Manypeaks Adamellite is a composite, regionally concordant pluton at least 22 km long and 3 km wide, associated with Precambrian amphibolite facies gneisses of the Albany‐Esperance Block, and situated about 35 km east of Albany, Western Australia. The pluton is surrounded by a granitised aureole, and shows structural and mineralogical harmony with the country rocks. Contacts vary from grada‐tional to sharp. Hence field relations are consistent with syn‐ or late‐kinematic emplacement in the catazone. The normative composition of the pluton corresponds with the thermal trough in the system An‐Ab‐Or‐Q‐H2O at 7 kb PH2O, suggesting an origin involving crystal‐melt equilibria. The pluton is believed to have formed almost in situ by partial anatexis of the country rocks at 700–750°C and a depth of about 25 km during the orogenic episode responsible for regional metamorphism and deformation.     

The genesis of sandstone‐type uranium deposits in the Ordos Basin,NW China: constraints provided by fluid inclusions and stable isotopes

Quartz from sandstone‐type uranium deposits in the east part of the Ordos Basin contains abundant secondary fluid inclusions hosted along sealed fractures or in overgrowths. These inclusions consist mainly of water with NaCl, KCl, CO₂ (135–913 ppm) and trace amounts of CO (0.22–16.8 ppm), CH₄ (0.10–1.38 ppm) and [SO₄]^2? (0.35–111 ppm). Homogenization temperatures of the studied fluid inclusions range from 90 to 210°C, with salinities varying from 0.35 to 12.6 wt‐% (converted to NaCl wt%), implying multiple stages of thermal alteration. Although high U is associated with a high homogenization temperature in one case, overall U mineralization is not correlated with homogenization temperature nor with salinity. The H and O isotopic compositions of fluid inclusions show typical characteristics of formation water, with δ¹⁸O ranging from 9.8 to 12.3‰ and δD from 26.9 to ?48.6‰, indicating that these fluid inclusions are mixtures of magmatic and meteoric waters. The oxygen isotope ratios of carbonates in cement are systematically higher than those of the fluid inclusions. Limited fluid inclusion‐cement pairs show that the oxygen closely approaches equilibrium between water and aragonite at 150°C. Highly varied and overall negative δ¹³C in calcite from cement implies different degrees of biogenetic carbon involvement. Correlations between U in bulk rocks and trace components in fluid inclusions are lacking; however, high U contents are typically coupled with high [SO₄]^2?, implying pre‐enrichment of oxidized materials in the U mineralization layer. All these relationships can be plausibly interpreted to indicate that U (IV), [SO₄]^2? as well as Na, K were washed out from the overlying thick sandstone by oxidizing meteoric water, and then were reduced by reducing agents, such as CH₄ and petroleum, likely from underlying coal and petroleum deposits, and possibly also in situ microbes at low temperatures.     

The Glyde Sub‐basin: A volcaniclastic‐bearing pull‐apart basin coeval with the McArthur River base‐metal deposit,Northern Territory

Sedimentological, geochemical and tectonic studies have been carried out on the Glyde Sub‐basin, a fault‐bounded depocentre adjacent to the margin of the Batten Trough, 80 km south of the HYC Pb‐Zn‐Ag ore deposit, in the mid‐Proterozoic McArthur Basin. Although it is unmineralized, the basin is, in some aspects, morphologically similar to the HYC Sub‐basin and provides an insight into processes which occurred coevally along strike from a giant shale‐hosted base‐metal deposit. The geometry of the sub‐basin supports an origin in a releasing bend of the Emu Fault during oblique right‐lateral extension of the Emu Fault Zone, resulting in the deposition of a very thick sequence of below wave‐base Barney Creek Formation carbonaceous siltstone. Prior to sub‐basin development the area was covered by hypersaline carbonate tidal flats of the Coxco Dolomite Member of the Teena Dolomite.

Internal syn‐sedimentary normal faulting fractured the sub‐basin into seven major blocks, establishing a basic geometry of northern and southern depressions, into which the W‐Fold and HYC Pyritic Shale Members were successively deposited, separated by a non‐depositional horst. During the subsequent deposition of undivided Barney Creek Formation the horst was submerged and greater water circulation was established. The horst continued to be an east‐west barrier to clastic and volcaniclastic gravity flows, evidenced by the confinement to the northern depocentre of prograding easterly‐derived carbonate‐dominated turbidites.

Rhyolitic volcanism in the Glyde Sub‐basin commenced in the W‐Fold Shale Member, and became common in the overlying Barney Creek Formation. The measurable volcanic component increases from 4.4 to 17.5% of the total sediment package southwards over 18 km, implying a southern rhyolitic source within 6–30 km. A geochemical comparison of these relatively unaltered tuffs with those intercalated in the HYC ore sequence identified a comagmatic relationship on the basis of immobile element contents, supporting a common volcanic source. This conclusion was only possible after a preliminary study found Ti, Zr, Y and Nb to be relatively immobile in the severely potassium‐altered tuff of the HYC hydrothermal ore environment. Low‐grade (as distinct from high temperature hydrothermal) potassium‐alteration of felsic tuff throughout the McArthur Basin may have resulted from diagenetic interaction with very evolved lacustrine saline brines, whereas brines in the diagenetic environment of the Glyde Sub‐basin, in which unaltered or sodically‐altered tuff predominates, were comparatively less evolved.     

The R��o de la Plata Craton: a review of units, boundaries, ages and isotopic signature

A review of the lithostratigraphic units in the Río de la Plata Craton and of new and previously published geochronological, isotopic and geophysical data is presented. Sm?CNd T_DM model ages between 2.6 and 2.2?Ga characterize the Piedra Alta Terrane of this craton. Crystallization ages between 2.2 and 2.1?Ga for the metamorphic protoliths and 2.1?C2.0?Ga for the post-orogenic granitoids indicate juvenile crust, followed by a short period of crustal recycling. Cratonization of this terrane occurred during the late Paleoproterozoic. Younger overprinting is not observed, suggesting it had a thick and strong lithosphere in the Neoproterozoic. A similar scenario is indicated for the Tandilia Belt of Argentina. Sm?CNd T_DM model ages for the Nico Pérez Terrane show two main events of crustal growth (3.0?C2.6?and 2.3?C1.6?Ga). The crystallization ages on zircon ranges between 3.1 and 0.57?Ga, which is evidence for long-lived crustal reworking. The age for cratonization is still uncertain. In the Taquarembó Block, which is considered the prolongation of the Nico Pérez Terrane in southern Brazil, a similar scenario can be observed. These differences together with contrasting geophysical signatures support the redefinition of the Río de la Plata Craton comprising only the Piedra Alta Terrane and the Tandilia Belt. The Sarandí del Yí Shear Zone is regarded as the eastern margin of this Craton.     

Mineralogy and geochemistry of marine glauconitic siliciclasts and phosphates in selected Cenomanian–Turonian units,Bohemian Cretaceous Basin,Czech Republic: Implications for provenance and depositional environment

Glauconitic siliciclastic rocks and phosphate components from the Pecínov Member of the Peruc–Korycany Formation (Upper Cenomanian), the lower part of the Bílá Hora Formation (Lower Turonian) and the lower part of the Teplice Formation (Upper Turonian) are studied. Geochemical indices suggest that the siliciclasts were derived from the weathering and recycling products of variable rock types of the Bohemian Massif, with a pronounced signature of felsic-derived source lithologies and a minor contribution from the sources of a chemically intermediate nature. Geochemical and mineralogical criteria suggest that the climate in the mid-Cretaceous was generally humid with possible intermittent arid episodes, which resulted in a long-term weathering of source rocks and the development of residual clay minerals in the source area. Several geochemical indications point toward highly reducing marine conditions during deposition of the mudstones, which are composed of quartz, glauconite, kaolinite, smectite, apatite and calcite. The glauconites show a highly mature character with >8 wt. % K₂O and bear evidence of long residence time near the sediment–water interface. They are depleted in Fe and rich in Al indicating a mixed layer mica–smectite as a precursor. Carbonate-fluorapatite is the only phosphate phase identified in the phosphate components, with up to 8 wt. % CO₃²⁻, excess F⁻ and significant amounts of Na⁺ and SO₄²⁻ in the apatite structure. A short-lived phosphogenic event(s) took place in the latest Cenomanian and involved large areas of the Bohemian Cretaceous Basin in association with the Oceanic Anoxic Event 2. The phosphate nodules were initially precipitated under suboxic conditions around the Cenomanian–Turonian boundary and were later reworked and emplaced in the earliest Turonian units. Phosphate coprolites mark another phosphogenic event in the early Upper Turonian. The development of the phosphate coprolites took place under variable redox conditions; the release of organically-bound phosphate and subsequent phosphatisation of fecal material took place under suboxic environment, followed by reworking in oxic realms.     

Age and correlations of the Siluro‐Devonian strata in the Yass Basin,New South Wales

An early Ludlovian (early eβ1) to early Gedinnian (early eγ) age is assigned to the Cliftonwood Limestone—Elmside Formation strata of the Yass Basin, New South Wales. Several Australian sequences are correlated with the Yass Basin succession.     

Holocene climate change inferred from stratigraphy and OSL chronology of aeolian sediments in the Qaidam Basin,northeastern Qinghai–Tibetan Plateau

Paleoclimatic reconstruction based on aeolian sediments in the eastern Qaidam Basin (QB) has been hindered by the limited chronological data. Here we present 61 Optically Stimulated Luminescence (OSL) ages. On the basis of these OSL ages and the lithologic stratigraphy, we propose the ‘effective moisture index (EMI)’ for aeolian sediments to reconstruct the effective moisture change. Based on the EMI from twelve sections, the effective moisture change, moisture sources and relevant mechanisms for paleoclimatic change in the eastern QB are discussed. The results indicate that (1) aeolian deposition started at least before 12.4 ± 0.7 ka during the deglaciation, the paleosols developed at the early and mid-Holocene, and aeolian sand and loess accumulated at mid- and late Holocene; (2) effective moisture history was: hyper-arid at 12.8–11.6 ka, humid and variable at 11.6–8.3 ka, moderately humid and stable at 8.3–3.5 ka, and increasingly arid at 3.5–0 ka; (3) the effective moisture change was mainly controlled by the Asian summer monsoon (ASM), which mainly followed the change of Northern Hemispheric summer insolation, and the westerlies strengthened and increased the aridity in the QB when the ASM shrank.     

The nephelinitic–phonolitic volcanism of the Trindade Island (South Atlantic Ocean): Review of the stratigraphy,and inferences on the volcanic styles and sources of nephelinites

Trindade Island is located in the South Atlantic Ocean, 1170 km from the Brazilian coast, and represents the eastern end of the E–W Vitória–Trindade Chain. It shows the youngest plume-induced (ca. 3.7 to <0.17 Ma) subaerial volcanism on the South American plate, associated with the Trindade plume activity. Almeida (1961) recognized five volcanogenic successions at Trindade (in decreasing age): the Trindade Complex (TC, >2.4 Ma) and the Desejado (DF, ∼2.4 to 1.5 Ma), Morro Vermelho (MV, <0.17 Ma), Valado (VF, no age) and Paredão (PF, no age) formations, composed of effusive–pyroclastic deposits and subvolcanic intrusions associated with nephelinite–phonolite volcanic episodes. We revised the original Almeida's (1961) stratigraphy with additional field work and petrography to recognize eruptive styles and processes within the nephelinite–phonolite volcanism. Also, available geochemical databases were used to improve the stratigraphic correlation between nephelinites from different units and to characterize their mantle sources.The nephelinitic volcanism may represent Strombolian and Hawaiian–type activity of low viscosity and volatile–rich lavas interlayered with pyroclastic successions (fall–out deposits). Phonolitic deposits record explosive Vulcanian–style episodes of volatile–rich and higher–viscosity lavas interlayered with pyroclastic deposits (mostly pyroclastic flows). Geochemical data allowed the individualization of nephelinites as follows: (1) MV olivine–rich nephelinites and all olivine–free varieties are low K₂O/Na₂O, K₂O/TiO₂ and intermediate CaO/Al₂O₃ that may be derived from N–MORB and HIMU mantle components; (2) the VF olivine–rich nephelinites have high K₂O/Na₂O, K₂O/TiO₂ and CaO/Al₂O₃ that indicates both EM and HIMU mantle sources and; (3) the PF olivine–rich nephelinites show high K₂O/TiO₂ similar to those from VF, and intermediate CaO/Al₂O₃ as nephelinites from MV rocks, suggesting a mixed source with EM + HIMU > N–MORB components.We suggest that the HIMU and EM mantle types resulted from metasomatic episode(s) in the peridotitic mantle beneath the Trindade Island during the Brasiliano Orogeny and later, as previously pointed out by Marques et al. (1999). Thus, the major HIMU component would relate to recycled oceanic crust or lithospheric mantle (mostly CO₂–eclogites) whereas the less important EM component to recycled marine or continental sediments.     

U–Pb geochronology and palynology from Lopingian (upper Permian) coal measure strata of the Galilee Basin,Queensland, Australia

This study presents the first chemical abrasion-isotope dilution thermal ionisation mass spectrometry (CA-IDTIMS) U–Pb zircon ages from tuffs in Lopingian (upper Permian) strata of the Galilee Basin, Queensland and reassigns the B coal-seam to the ‘Burngrove Formation equivalent.’ Five Lopingian tuffs were dated: four from the CRD Montani-1 drill hole including three from the ‘Fair Hill Formation equivalent’ (255.13 ± 0.09, 254.41 ± 0.07 and 254.32 ± 0.10 Ma) and one from the ‘Burngrove Formation equivalent’ (252.81 ± 0.07 Ma, approximately the age of the Yarrabee Tuff in the adjacent Bowen Basin); and a single tuff from the Black Alley Shale in the GSQ Tambo-1-1A drill hole (254.09 ± 0.06 Ma). In the Galilee Basin, all three units are constituents of the Betts Creek Group, here formally elevated in nomenclatural status from the Betts Creek beds. On the western margin of the basin, the group thins, and the ‘J and K’ seams (formerly known as the Crossmore and Glenaras sequences, respectively) in the GSQ Muttaburra-1 drill hole have been interpreted through palynology as Cisuralian–early Guadalupian (spore-pollen assemblage APP3.2). This corroborates the exclusion of the ‘J and K’ seams from the overlying Lopingian Betts Creek Group (spore-pollen assemblage APP5), and the underlying lower to mid-Cisuralian Aramac Coal Measures (spore-pollen assemblage APP2.2), which represent the uppermost unit of the Joe Joe Group. It is proposed that the ‘J and K’ seams are restricted to a depocentre in the Hulton–Rand structure. The recognition of these strata containing APP3.2 spore-pollen assemblages suggests that the mid-Permian hiatus is locally reduced to 12–13 My from 30 Ma (where the ‘J and K’ seams are absent). The results of the radiometric dating and palynological analysis in the Galilee Basin support the proposed, albeit informal stratigraphy, that is given in terms of equivalents of formational units in the Bowen Basin and on the intervening Springsure Shelf.