Late Permian Coal Measures Research Articles

Petro-chemical characterization and depositional setting of a late Permian high ash coal deposit, Central Mongolia

Pan global Permian coal measures are unique in the evolution of the Earth, not matched in any period before or since. Middle and late Permian coal-bearing strata are widely distributed in Mongolia. In particular, a large concentration of transtensive coal-bearing sub-basins is located in southern Mongolia, some of which are well documented. However, the late Permian coal measures developed along the shores of the Mongol-Transbaikalian Seaway in central Mongolia, the focus of this contribution, has received very limited attention. This study focuses on the c. 420 m thick coal-bearing middle part of a c. 2,600 m thick Permo-Triassic succession in the Bayanjargalan district. The study draws on data from 38 drillholes, 3 km of trenches, mapping, petrological analysis of sandstone samples, analysis of macroflora, fauna and trace fossils, 82 coal quality samples as well as washability and ash XRD analysis from a 3t coal bulk sample. The unstable and wedge-shaped architecture of the coal seams strongly suggest a syn-tectonic influence on their development. Paleoclimatic indicators suggest the peat mire ecosystem developed during relatively cold - temperate climatic conditions. Peat-forming plants such as Cordaites, Rufloria and Koretrophyllites probably benefited from moist air currents along the seaway. Plant-arthropod interactions are reported from two sites, in particular DT228 and DT246 oviposition lesions, the latter being almost twice the size of a previous report from North America. Results from 82 proximate analyses returned consistent very high ash yields of 46.95% (db) and 43.45% (adb) from the 3t bulk sample, which are unusual for Permian coals in Mongolia.

Enrichment Factors and Metallogenic Models of Critical Metals in Late Permian Coal Measures from Yunnan, Guizhou, and Guangxi Provinces

The Late Permian coal measures in eastern Yunnan, western Guizhou, and central Guangxi are significantly enriched in critical metals that could serve as important supplements to conventional critical metal deposits in China. This study collected previous geochronological and geochemical data from the Late Permian coal measures to evaluate the distribution characteristics and enrichment factors of critical metals. Moreover, metallogenic models for critical metals were also developed. The results showed that Late Permian coal measures in Yunnan, Guizhou, and Guangxi provinces exhibited abnormal enrichment in Nb, Zr, and rare earth elements (REY, or REE if Y is excluded). The Emeishan mafic rocks and intermediate-felsic volcanic ash from the Truong Son orogenic belt underwent chemical weathering, with Nb and Zr selectively preserved in situ in the form of heavy minerals (e.g., rutile, zircon, and anatase), which subsequently led to the enrichment of Nb and Zr in bauxite and Al-claystone at the bottom of the Late Permian coal measures. Intermediate-felsic volcanic ash from the Emeishan large igneous province (ELIP) and the Truong Son orogenic belt supplied Nb, Zr, and REY for the middle and upper parts of the Late Permian coal measures. The intermediate-felsic mineral material of the coal measures in the intermediate zone, outer zone, and outside zone of ELIP are derived mainly from the ELIP, the mixture from ELIP and the Truong Son orogenic belt, and the Truong Son orogenic belts, respectively. Nb, Zr, and REY were leached by acidic aqueous solutions and from the parting and roof into underlying coal seams, where they deposited as authigenic minerals or adsorbed ions on organic matter during early coalification.

Tectonic evolution of a sequence of related late Permian transtensive coal-bearing sub-basins, Mongolia: A global wrench tectonics portrait

During the late Permian in Mongolia, inertia-driven transtensive reactivation of primordial fracture zones gave rise to the development of a sequence of related, but isolated, fault-bounded sub-basins; some of these became the locus of substantial peat accumulation that evolved into economically important coal deposits. The present study focuses on late Permian coal measures in two widely separated areas: Area 1: located in central Mongolia, developed along the southern margin of the Mongol-Transbaikalian Seaway. The late Permian coal sequence forms a c. 420 m thick middle part of a Permo-Triassic succession which spans c. 2,600 m. The V-shaped, fault-bounded NE oriented sub-basin evolved under transtensive conditions. The thick infill records a transition from shallow marine and humid coal forming depositional environments during the late Permian to relatively arid desolate terrestrial conditions during early Triassic times, considered here to mark the dramatic drainage of the Mongol-Transbaikalian Seaway across the Permo-Triassic boundary. Area 2: situated in southern Mongolia, is a NE oriented elongate sub-basin, bounded by two wrench faults, which formed under transtensive conditions. Thickness of the late Permian coal-bearing strata is c. 650 m. The sedimentary strata record a transition from a humid coal-bearing environment to predominantly marine conditions. Both study areas are located proximal to two controversial suture zones. However, the zones do not show the presumed shortening, major thrusting, regional metamorphism and given the complete absence of tuffs within the studied Permo-Triassic successions it could be argued that the sutures are not only cryptic but non-existent.

Evidence for an Early-Middle Jurassic fluid event constrained by Sm–Nd, Sr isotopes, rare earth elements and yttrium in the Bowen Basin, Australia

The Late Permian coal measures in the Bowen Basin, Australia, are extensively mineralized with calcite as cleat infilling and veins. This study utilised strontium and samarium‑neodymium isotope analyses as well as rare earth element and yttrium (REY) composition of vein calcites, from two boreholes in a faulted and intruded area within the Jellinbah Thrust Zone, to investigate the origin and timing of calcite precipitation. All samples showed low Sr isotopic ratios that overlapped the range typical of mantle materials, suggesting that fluids were derived from the mantle. The calcite veins in core from Dingonose 14, with two exceptions, exhibit very similar Sr isotopic ratios yet have large variations in REY patterns and a wide range in Sm–Nd ratios. These samples defined an isochron corresponding to an age of 174 ± 11 Ma, which may record the timing of fluid mobilization from the deeply buried part of the foreland basin during the Early and Middle Jurassic, prior to subsequent extension and uplift in the Late Cretaceous. This fluid event may be a response to the Gondwana supercontinent break-up during the Early-Middle Jurassic. Various thermal and chemical conditions resulted in the different REY patterns of calcite in Dingonose 14 core. Calcite veins in Summit 3 core showed extremely similar REY patterns and Sr isotopic ratios but different Sm–Nd isotopic compositions relative to Dingonose 14 core, with no Sm–Nd isochron able to be resolved. The structural geology of the Summit 3 locality is complex, having overturned beds and large veins of prismatic quartz present in addition to calcite, and potential for multiple periods of veining to have occurred. Hence the lack of Sm–Nd isotopic equilibrium for the Summit 3 samples is most likely due to multiple fluid events.

Origin of the alkali tonsteins from southwest China: Implications for alkaline magmatism associated with the waning stages of the Emeishan Large Igneous Province

ABSTRACTA unique type of Nb–Zr–REE–Ga-enriched alkali tonstein of pyroclastic origin occurs exclusively within the late Permian coal measures of southwest China. The alkali tonsteins are located within the lowest Xuanwei or Longtan formations of Wuchiapingian age, indicating that their age is later than the main episode of Emeishan Large Igneous Province (ELIP) magmatism. The alkali tonsteins have intermediate–felsic Al2O3/TiO2 values (12.6–34.2, mean 22.0), light rare earth element-enriched chondrite-normalised patterns, negative δEu and incompatible element ratios similar to those of ELIP alkaline Nb–Ta-enriched syenites. All available evidence shows that the alkali tonsteins from southwest China originated from coeval ELIP alkaline magmatism. The enrichment of Nb–Zr–REE–Ga in alkali tonsteins is derived from the ELIP alkaline Nb–Ta-enriched volcanic ashes and may represent the last stage of mineralisation associated with the Emeishan mantle plume activity.

Electrofacies analysis using high-resolution wireline geophysical data as a proxy for inertinite-rich coal distribution in Late Permian Coal Seams, Bowen Basin

This paper examines the stratigraphic and geographic distribution of coal composition in main Late Permian coal measures in the Bowen Basin, using coal electrofacies as a proxy for inertinite maceral group content. Data for this research were derived from some 26 wells in the northern part of the Bowen Basin. A companion paper (Roslin and Esterle, 2015, in review) introduced the methodology, which is based on electrofacies analysis and uses high-resolution wireline data (including microresistivity from Compact Micro-Image (CMI) tool and Photoelectric Factor (PEF) data in addition to conventional gamma ray, density and laterolog resistivity) to obtain coal electrofacies. Validation of the methodology was performed by comparison of the weighted average proportion of coal electrofacies to the weighted average proportion of the corresponding coal lithotypes obtained from millimetre scale logging and to the percentage gathered from maceral content analysis. The weighted average proportion of the interpreted dull inertinite-rich coal electrofacies (independent of rank and heat effects) was then analysed to determine their stratigraphic and geographic distribution.From the base upward, the main Late Permian coal bearing units are the Moranbah Coal Measure (MCM), Fort Cooper Coal Measure (FCCM), and Rangal Coal Measure (RCM) and their stratigraphic equivalents across the basin. The proportion of inertinite-rich dull coal electrofacies increases upwards in the RCM, with some thick and merged seams showing distinctive electrofacies signatures. Within the study area, the coal measures and individual seams split from north to south, reflecting increased subsidence and sediment influx into basin depocentres. As the seams split, the proportion of inertinite-rich dull coal electrofacies decreases in the tested sample set.

Palynofacies changes and their reflection on preservation of peat accumulation stages in the Late Permian coal measures of the Bowen Basin, Australia: A new system for coal palynofacies characterisation

A high-resolution study (n=66) was conducted on Late Permian coal measures of the Bowen Basin, Australia, to observe palynofacies changes during peat accumulation over time. Palynofacies were determined using polytopic vector analysis (PVA) to derive end members with variable compositions that reflected fine scale environmental changes, within and between seams, of the Kaloola Member. Palynofacies reflect a three-stage succession within the palaeo- peat-forming environments from stable, anoxic conditions at the base, progressing to variable, oxic conditions toward the top of each seam. In cases where a seam was capped by tuff, rather than siliciclastic sediment, anoxic conditions similar to the bottom of each seam occurred. The results corroborate previous interpretations of palaeofloral communities and provide a new palynofacies model that integrates environmental progression within the coal seams in the Late Permian coal measures of the Bowen Basin. A complementary study of palynological assemblages recognised a shift from Dulhuntyspora sp., to Protohaploxypinus sp. in the lower Kaloola Member, indicating a change in pollen/spore source. Associations between dispersed palynomorphs and coal phyterals of parent flora remain tenuous beyond class rank, due to poor preservation and taxonomic bias inherent within the sample space. This is the first such palynofacies study to be conducted in the Bowen–Sydney–Gunnedah basin complex, thus opening the way for future work examining regional changes in palynofacies, expressed in both coal and siliciclastic sediments.

Decoupling δ13C response to palaeoflora cycles and climatic variation in coal: A case study from the Late Permian Bowen Basin, Queensland, Australia

The Late Permian coal measures of the Bowen Basin, Australia express both environmental and climatic changes that occurred prior to the Permian Triassic (P–T) boundary. In order to decouple the influence of environmental factors (salinity, pH, base level and temperature) from depositional and climatic factors (atmospheric CO2) in organic δ13C, a high resolution study was performed on 24 coal seams (total 24.6m) in the Late Permian stratigraphy in the northern Bowen Basin. The Late Permian stratigraphy of the Bowen Basin records a transition from deltaic and lacustrine conditions within the Tinowan Formation and Black Alley Shale Formation, to fluvial deposition in the Kaloola and Bandanna Formations. Intermittent volcanism is recorded by tuff layers during periods of peat accumulation. Variations of coal lithotypes were recorded and formed the basis of sampling for petrography and isotope analysis. Coal samples were etched to expose cellular anatomy, and systematically identified to recognise palaeoflora assemblages. When observed within seam, δ13C of the coal varied cyclically (13C enriched-depleted-enriched) as a response to environmental changes expressed in palaeoflora communities. The total range of δ13C was −26.6‰ to −21.9‰. The overall trend of δ13C progresses to increasing 13C enrichment, corresponding with dull lithotypes (rich in inertinite) which indicate fluctuations in base level. The 13C enrichment peaks at −22.5‰ within the Kaloola Member and shifting rapidly toward a depletion (maximum −26.6‰) of 13C in the upper Bandanna Formation, prior to the P–T boundary. These changes are expressed in palaeoflora communities where ecosystems shifted from dominant Glossopteris flora, to climax community flora including Palaeosmunda, Cycadales and Ginkgo, suited to temperate, early Mesozoic climates. The results of this study represent an insight into the effects of environmental variables on 13C uptake of plants. The identification of flora within coal gives an insight into palaeowetland evolution, and can be partnered with classic petrographical techniques for integrated analysis in coals. Both the geochemistry and the anatomical aspects of coal represent an important tool for future palaeowetland research.

Study on REEs as tracers for late permian coal measures in Bijie City, Guizhou Province, China

Analyses of Rare Earth Elements (REEs) in 13 coal samples collected from Late Permian coal measures of Bijie City in western Guizhou Province were conducted using Inductively Coupled Plasma-Mass-Spectrometry (ICP-MS). The results indicated that REEs patterns were not controlled by materials from the sea, whereas the contribution of land plants was about 1%. The major sources of REEs were from terrigenous material as indicated by negative Eu anomaly. There were similar distribution curves of REEs between Bijie's coal and Emeishan basalt. M12 coal seam, which had the highest ΣREE, appeared near the boundary between Longtan Formation and Changxing Formation, which was closely correlated to the eruption of Emeishan basalt. The Emeishan basalt contributed to REEs enrichment of M12. So the sources of REEs were controlled by terrigenous material, and the Emeishan basalt was the predominant source of terrigenous material, which dominated the enrichment and pattern of REEs in Late Permian coal measure from Bijie.

Influence of localised igneous activity on cleat dawsonite formation in Late Permian coal measures, Upper Hunter Valley, Australia

Abstract Stable ( δ 13 C and δ 18 O) and radiogenic 87 Sr/ 86 Sr isotopic data have been used to investigate the origin of cleat dawsonite (NaAlCO 3 (OH) 2 ) in the Late Permian Wittingham Coal Measures of the Upper Hunter region in the Sydney Basin, New South Wales. The δ 13 C PDB values have a narrow range (− 1.7‰ to + 2.4‰), with an average of + 0.3‰, suggesting a magmatic source for the carbon. In contrast, δ 18 O SMOW values have a wide range (+ 13.6‰ to + 19.8‰), and decrease systematically with decreasing distance from a major intrusion. This systematic variation reflects establishment of localised hydrothermal cells. Water–rock interaction between fluids associated with these hydrothermal cells, and Rb-poor volcaniclastic detritus in the coal measures, produced mantle-like 87 Sr/ 86 Sr (0.705032 to 0.706464) in the dawsonite.

AN INTEGRATED GEOLOGICAL AND GEOPHYSICAL INTERPRETATION OF A PORTION OF THE OFFSHORE SYDNEY BASIN, NEW SOUTH WALES

The study area is within PEP 11, which is more than 200 km in length, covers an area over 8,200 km2 and lies immediately offshore of Sydney, Australia’s largest gas and petroleum market on the east coast of New South Wales. Permit water depths range from 40 m to 200 m. While the onshore Sydney Basin has received episodic interest in petroleum exploration drilling, no deep exploration wells have been drilled offshore.A reappraisal of available data indicates the presence of suitable oil- and wet gas-prone source rocks of the Late Permian coal measure succession and gas-prone source rocks of the middle to early Permian marine outer shelf mudstone successions within PEP 11. Reservoir quality is an issue within the onshore Permian succession and, while adequate reservoir quality exists in the lower Triassic succession, this interval is inferred to be absent over much of PEP 11. Quartz-rich arenites of the Late Permian basal Sydney Subgroup are inferred to be present in the western part of PEP 11 and these may form suitable reservoirs. Seismic mapping indicates the presence of suitable structures for hydrocarbon accumulation within the Permian succession of PEP 11, but evidence points to significant structuring post-dating peak hydrocarbon generation. Uplift and erosion of the order of 4 km (based on onshore vitrinite reflectance studies and offshore seismic truncation geometries) is inferred to have taken place over the NE portion of the study area within PEP 11. Published burial history modelling indicates hydrocarbon generation from the Late Permian coal measures commenced by or before the mid-Triassic and terminated during a mid-Cretaceous compressional uplift prior to the opening of the Tasman Sea.Structural plays identified in the western and southwestern portion of PEP 11 are well positioned to contain Late Permian clean, quartz-rich, fluvial to nearshore marine reservoir facies of the coal measures. These were sourced from the western Tasman Fold Belt. The reservoir facies are also well positioned to receive hydrocarbons expelled from adjacent coal and carbonaceous mudstone source rock facies, but must rely on early trap integrity or re-migrated hydrocarbons and, being relatively shallow, have a risk of biodegradation. Structural closures along the main offshore uplift appear to have been stripped of the Late Permian coal measure succession and must rely on mid-Permian to Early Permian petroleum systems for hydrocarbon generation and accumulation.

K–Ar and Rb–Sr dating of authigenic illite–smectite in Late Permian coal measures, Queensland, Australia: implication for thermal history

K–Ar and Rb–Sr isotopic studies were carried out on authigenic illitic clay minerals in Late Permian coal measures from the Bowen Basin (Australia), in order to determine the timing of maximum paleotemperatures, which were responsible for coal maturation and coal seam gas generation. The results indicate two major thermal events affected the Bowen Basin region, at 205–215 and 140–155 Ma. The narrow range of age data from different size fractions, lithologies and stratigraphic depths indicates episodic, short-lived thermal events, rather than gradual temperature increase due to progressive burial as previously believed. The earlier, thermal event in the latest Triassic postdates maximum burial of the Bowen Basin strata, which occurred during the Middle to Late Triassic. The ages of 205–215 Ma correspond with the published evidence for regional Late Triassic extension in eastern Australia. The younger (140–155 Ma), thermal phase during the Late Jurassic–Early Cretaceous is related to the initial rifting and associated widespread igneous activities prior to break-up of Gondwana. The K–Ar dates in conjunction with vitrinite reflectance data as paleotemperature indicators indicate that the younger thermal event occurred at lower temperatures than the earlier one, except in the shallow part of the southern Bowen Basin. This event is recorded exclusively in less illitic, R=0 illite–smectite (I–S) mixed-layer samples mainly in the shallow part of the southern Bowen Basin (Baralaba Coal Measures).

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.

Stable isotope geochemistry of authigenic clay minerals from Late Permian coal measures, Queensland, Australia: implications for the evolution of the Bowen Basin

Oxygen and hydrogen isotope analyses were carried out on authigenic clay minerals from Late Permian coal measures of the Bowen Basin (Australia). In the northern Bowen Basin, the oxygen isotope compositions of the mixed-layer illite/smectite show significant irregular variations with respect to depth, which parallel the changes in the extent of the illitisation reaction and are interpreted as reflecting changes in water/rock ratio in turn related to permeability. The δ 18O and δD values of illite–smectite and kaolinite in the northern Bowen Basin and the calculated fluid isotopic composition ( δ 18O=−3‰ to +1‰; δD=−70‰ to −90‰) in equilibrium with these clays are considerably lower than those typically reported for deeply buried sedimentary basins. These stable isotope data, together with relatively high inferred palaeotemperatures (up to 235°C) and abnormally high geothermal gradients are consistent with a hydrothermal origin for clay mineral formation in the northern Bowen Basin. The hydrothermal system is interpreted to be a result of the Late Triassic extensional tectonic regime, which developed in large parts of eastern Australia and affected the northern part of the Bowen Basin. In the southern Bowen Basin, by contrast, clays are more enriched in 18O and deuterium, which is explained by lower temperatures (in the shallow coal measures) and a significant enrichment in the fluid isotopic composition ( δ 18O=−3.6‰ to +5.6‰, δD=−66‰ to −35‰) under low water/rock ratio conditions, especially in deeper pelitic rocks.

Clay-Mineral Authigenesis in the Late Permian Coal Measures, Bowen Basin, Queensland, Australia

AbstractMineralogical studies were performed on authigenic clay minerals of mudrocks, sandstones, and bentonites from 38 boreholes in the Late Permian coal measures of the Bowen Basin. Clay-mineral separations of samples from the northern Bowen Basin consist mainly of (Reichweite, R) R = 1 and R ≥ 3 interstratified illite-smectite (I-S), chlorite, and kaolinite. In the southern Bowen Basin, samples from higher stratigraphie sections are characterized by randomly ordered (R = 0) I-S mixed layers, and kaolinite and chlorite in smaller amounts. Samples from the lower sections consist of (R ≥ 3) I-S, chlorite, chlorite-rich chlorite-smectite (C-S), and laumontite.Examination of the mineralogy and distribution of authigenic clay minerals from the Late Permian coal measures in the northern part of the Bowen Basin indicated that the presence of clay minerals is not systematically related to depth and clay occurrences do not occur regularly. These mineralogical variations of clay in volcaniclastic sediments are incompatible with thermal control. Variations in the rate of fluid flow and potassium supply owing to permeability exert major influences on clay-mineral paragenesis and the reaction of illitization. In more permeable zones (possibly faults or fracture zones), highly illitic clays with lath-shaped morphologies may have precipitated directly from potassium-rich fluids migrating from deeper parts of the basin. In addition, abundant chlorite precipitated contemporaneously with illitic clays, which may have resulted from sufficient magnesium and iron occurring in the fluids as a result of dissolution of intermediate or mafic-rock fragments. At the same time, clay paragenesis with less illitic I-S, kaolinite, and minor chlorite occurs outside the channelized zones of high fluid flow, where a diffusive-flow regime may have predominated with lower ratios of the activities of K+ and H+ (i.e., αK+/αH+) in the solutions.In the southern Bowen Basin, depth-related changes in the distribution of clay minerals are evident and may be indicative of thermal control on clay-mineral reactions. Zeolites are present locally in the Late Permian volcaniclastic rocks in the southern Bowen Basin, but not in the north. This is attributed to a low ratio of αCO2/αH2O (where α = activity) and/or more saline and alkaline solutions.

Facies relationships and cyclicity of high-latitude, Late Permian coal measures, Bowen Basin, Australia

The Late Permian Moranbah Coal Measures are developed throughout the northern and central Bowen Basin, eastern Australia, and are subject to large-scale opencut coal mining activity. They were deposited in a rapidly subsiding retroarc foreland basin, during frequent base-level changes. Contemporaneous compressive deformation and volcanism facilitated the supply of abundant volcanoclastic sediments, resulting in rapid, but punctuated, basinal aggradation. To the south and east, transgressive–regressive cycles were marked by the inter-digitation of paralic–shallow marine and alluvial strata. Lonestones (dropstones) are common within the marine deposits and are attributed to ice-rafting indicative of a cold-climate depositional regime. Two basin-wide chronostratigraphic units, the P-tuff bed and the Harrow Creek superseam, have been used to evaluate the facies architecture of the stratigraphic interval they enclose. The lithofacies mosaic of the 25–75 m thick sequence has been examined by means of 26 widely distributed coreholes and two detailed district-scale studies based around the Moranbah–Goonyella and German Creek minesites. Eight alluvial–shallow marine facies associations have been recognised. Their architectural and temporal relationships allow the accurate reconstruction of the coal-bearing depositional system. Two dissimilar, stacked, depositional systems tracts, A (organics) and B (clastics) are recognised. The P-tuff bed is enclosed by facies of tract A, forming a thick, low-ash, coal-bearing interval which was emplaced essentially synchronously across the basin. It represents a time of clastic sediment starvation when basin-wide peat mire accumulation prevailed. Four similar extensive coal-bearing intervals within the Moranbah Coal Measures are also considered to represent basin-wide episodes of peat accumulation. This pattern is in strong contrast to traditional views of coal measure development, which argue that coals formed within a contemporary facies mosaic, in which fluvial channels, levees and crevasse splays were also represented. The second depositional systems tract (B) is characterised by clastic packages, dominated by large-scale (up to 4 km wide and 50 m thick), sandstone bodies deposited by low sinuosity trunk river systems, flanked by substantial crevasse splay deposits (up to 3 km wide and 30 m thick). It represents the product of catastrophic flooding events. The cyclothemic succession of systems tracts A and B is interpreted in terms of eustatic sealevel cycles. The tract A coal-bearing intervals represent relative sealevel lowstands. Systems tract B represents relative sea level highstand with its lower interval at German Creek to the south consisting of paralic and marine facies. The cycles had durations in the order of 400 to 600 ky and are considered to represent 4th order sealevel cycles of the Permian Period.

THE WALLOON COAL MEASURES—THE NEXT COAL SEAM GASTARGET?

The Queensland coal seam gas industry has grown over the last 12 years. During this time the vast majority of exploration wells have targeted the Late Permian coal measures in the Bowen and Galilee Basins. These formations have been the major target because they contain coals with a vitrinite reflectance ranging above 0.7%. This range has always been seen as the main period for methane generation.As well as containing vast quantities of Permian coal, Queensland also has vast quantities of Middle Jurassic coals within its Mesozoic Basins. These coals have received little-to-no exploration for their coal seam gas potential as they have always been interpreted as being immature for gas generation.Over 550 petroleum exploration wells drilled in the Mesozoic Surat Basin of eastern Queensland were reviewed to determine the coal volume of the intersected Walloon Coal Measures. A significant number have intersected large volumes of sub-bituminous to high volatile bituminous coals, in seams ranging up to 11.7 m in thickness. While the individual seams are not laterally persistent, the coal packages can be traced over hundreds of kilometres of the eastern Surat Basin.While only one well has tested the gas content, gas quality and saturation of the Walloon Coal Measures, numerous water bores have reported gas flows from the zone, and petroleum wells intersecting the formation have recorded high mud gas readings during drilling.The relatively shallow depth of the unit over much of the basin, the thickness of the coal packages, the proximity to major gas trunk pipelines and markets make the Walloon Coal Measures an ideal target for the next generation of coal seam gas explorers.

Oil-source correlations as a tool in identifying the petroleum systems of the southern Taroom Trough, Australia

A geochemical study of crude oils and samples of various Permian, Triassic and Jurassic organic-rich rock units from the southern Taroom Trough was undertaken to test the prevailing Permian-source hypothesis for the petroleum reserves of the Bowen/Surat Basin. Seventy three core and cuttings samples were screened using organic petrography, total organic carbon analysis, Rock-Eval pyrolysis, and solvent extraction. Saturated and aromatic hydrocarbon fractions of selected source rocks, kerogen hydrous pyrolysates, and thirteen oils were then analysed by gas chromatography, gas chromatography-mass spectrometry and isotope ratio mass spectrometry, for the purpose of oil-to-source correlation. On the basis of their bulk carbon isotopic compositions and terpane, sterane and aromatic biomarker signatures, two oil families were identified. Those oils sourced by the Snake Creek Mudstone and reservoired in the Showgrounds Sandstone (both the Middle Triassic age) at Roswin North and Rednook are assigned to the “Snake Creek-Showgrounds” petroleum system. The remaining oils belong to the “Blackwater-Precipice” system. These originated in the Late Permian coal measures of the Blackwater Group but are produced from the Precipice Sandstone and other reservoir rocks of Permian to Jurassic age along the southeastern and southwestern margins of the trough.

Sequence stratigraphy of the Late Permian Coal Measures in the Sydney Basin

In the Late Permian Newcastle, Tomago and Illawarra Coal Measures of the foreland Sydney Basin, eight 3rd‐order depositional sequences form three sequence sets. The sequence sets constitute the highstand systems tract of a 2nd‐order sequence. Up‐sequence decreasing marine shale thickness and increasing incised‐valley‐fill thickness, coupled with an overall regressive trend from marine to dominantly alluvial environments, indicate that sedimentation was influenced by 3rd‐order relative sea‐level cyclicity superimposed on 2nd‐order falling relative sea‐level. The correlation of sequence boundaries and their overlying incised‐valley‐fills from well to well across the basin implies repeated basin‐wide relative sea‐level falls (involving uplift and/or eustatic sea‐level falls). Angular unconformities coincident with the Sequence D, Sequence E, and end‐Permian sequence boundaries indicate periods of accelerated structural movement during relative sea‐level falls. Basin‐wide coal seams were formed at the top of ...

COALBED METHANE RESOURCES IN THE PERMIAN OF EASTERN AUSTRALIA AND THEIR TECTONIC SETTING

The Bowen and Sydney Basins in eastern Australia contain vast coal resources which provide a source for coalbed methane. Through studies of the spatial and temporal distribution of the sedimentary packages, the structural geometry and tectonic setting of the sedimentary packages, and the maturation and burial history, the Australian Geological Survey Organisation (AGSO) is mapping the distribution and structural styles of the sources of methane, in particular, the Late Permian coal measures. AGSO's results from the Bowen Basin show at least two distinctly different structural styles of potential targets for coalbed methane drainage: on the Comet Ridge, the Permian coal measures are essentially subhorizontal and tectonically undisturbed, whereas in the western Taroom Trough, the coal measures are folded into a series of anticlines, each of which occurs above a thrust fault which in turn forms part of an imbricate thrust fan. Both of these styles occur at depths of less than 1000 m.Calculations by the Bureau of Resource Sciences (BRS) indicate that the inferred coalbed methane resources-in-place are 62 trillion cubic feet (1760 billion m3) for Australia, in which the Bowen and Sydney Basins are currently the only potential provinces of coalbed methane. The low permeability of the coal seams hinders attempts to utilise this vast amount of energy resources.Further exploration is necessary to delineate commercially feasible areas. This delineation is the only process that will be able to determine demonstrated coalbed methane resources.