Multistage deformation of linked fault systems in extensional regions: An example from the northern Perth Basin,Western Australia

Linked fault systems identified in the northern portion of the onshore Perth basin comprise north‐striking normal faults, the dominant structures in the basin, and hard linkages—east‐striking transfer faults. The former are either divided into segments of distinctive character by, or terminate at, the transfer faults. The fault systems were initiated by west‐southwest‐east‐northeast extension in the Early Permian but were reactivated by subsequent rifting with approximately east‐west extension in the Jurassic. They were also reactivated by the oblique extension of northwest‐southeast orientation associated with Gondwana continental breakup in the Late Jurassic ‐ earliest Cretaceous. In addition to reactivation, older structures of the linked fault families controlled the development of younger fractures and folds. During the oblique extension, the linked fault systems define releasing bends, characterised by a rollover anticline in the hangingwall of the Mountain Bridge Fault, and restraining bends where contractional folds are sites of major commercial hydrocarbon fields in the basin.     

In situ stresses and natural fractures in the Northern Perth Basin,Australia

Present-day stress orientations in the Northern Perth Basin have been inferred from borehole breakouts and drilling-induced tensile fractures observed on image logs from eight wells. Stress indicators from these wells give an east – west maximum horizontal stress orientation, consistent with stress-field modelling of the Indo-Australian Plate. Previous interpretations using dipmeter logs indicated anomalous north-directed maximum horizontal stress orientations. However, higher-quality image logs indicate a consistent maximum horizontal stress orientation, perpendicular to dominant north – south and northwest – southeast fault trends in the basin. Vertical stress was calculated from density logs at 21.5 MPa at 1 km depth. Minimum horizontal stress values, estimated from leak-off tests, range from 7.4 MPa at 0.4 km to 21.0 MPa at 0.8 km depth: the greatest values are in excess of the vertical stress. The maximum horizontal stress magnitude was constrained using the relationship between the minimum and maximum horizontal stresses; it ranges from 8.7 MPa at 0.4 km to 21.3 MPa at 1 km depth. These stress magnitudes and evidence of neotectonic reverse faulting indicate a transitional reverse fault to strike-slip fault-stress regime. Two natural fracture sets were interpreted from image logs: (i) a north- to northwest-striking set; and (ii) an east-striking set. The first set is parallel to adjacent north- to northwest-striking faults in the Northern Perth Basin. Several east-striking faults are evident in seismic data, and wells adjacent to east-striking faults exhibit the second east-striking set. Hence, natural fractures are subparallel to seismically resolved faults. Fractures optimally oriented to be critically stressed in the present-day stress regime were probably the cause of fluid losses during drilling. Pre-existing north- to northwest -striking faults that dip moderately have potential for reactivation within the present-day stress regime. Faults that strike north to northwest and have subvertical dips will not reactivate. The east-striking faults and fractures are not critically stressed for reactivation in the Northern Perth Basin.     

Transport properties of rocks from statistics and percolation

Two simplified microstructural models that account for permeability and conductivity of low-porosity rocks are compared. Both models result from statistics and percolation theory. The first model assumes that transport results from the connection of 1D objects or pipes; the second model assumes that transport results from the connection of 2D objects or cracks. In both cases, statistical methods permit calculation of permeability k and conductivity , which are dependent on three independent microvariables: average pipe (crack) length, average pipe radius (crack aperture), and average pipe (crack) spacing. The degree of connection is one aspect of percolation theory. Results show that use of the mathematical concept of percolation and use of the rock physics concept of tortuosity are equivalent. Percolation is used to discuss k and near the threshold where these parameters vanish. Relations between bulk parameters (permeability, conductivity, porosity) are calculated and discussed in terms of microvariables.     

Measurement and Analysis of Thermal Conductivity of Rocks in the Tarim Basin, Northwest China

: As a parameter that describes heat transmission properties of rocks, thermal conductivity is indispensable for studying the thermal regime of sedimentary basins, and retrieving high-quality data of thermal conductivity is the basis for geothermal related studies. The optical scanning method is used here to measure the thermal conductivity of 745 drill-core samples from the Tarim basin, the largest intermontane basin with abundant hydrocarbon potential in China, and water saturation correction is made for clastic rock samples that are of variable porosity. All the measured values, combined with previously published data in this area, are integrated to discuss the distribution characteristics and major controlling factors that affect the thermal conductivity of rocks in the basin. Our results show that the values of thermal conductivity of rocks generally range from 1.500 to 3.000 W/m·K with a mean of 2.304 W/m·K. Thermal conductivity differs considerably between lithological types: the value of a coal sample is found to be the lowest as being only 0.249 W/m·K, while the values for salt rock samples are the highest with a mean of 4.620 W/m·K. Additionally, it is also found that the thermal conductivity of the same or similar lithologic types shows considerable differences, suggesting that thermal conductivity cannot be used for distinguishing the rock types. The thermal conductivity values of mudstone and sandstone generally increase with increasing burial depth and geological age of the formation, reflecting the effect of porosity of rocks on thermal conductivity. In general, the mineral composition, fabric and porosity of rocks are the main factors that affect the thermal conductivity. The research also reveals that the obvious contrast in thermal conductivity of coal and salt rock with other common sedimentary rocks can induce subsurface temperature anomalies in the overlying and underlying formations, which can modify the thermal evolution and maturity of the source rocks concerned. This finding is very important for oil and gas resources assessment and exploration and needs further study in detail. The results reported here are representative of the latest and most complete dataset of thermal conductivity of rocks in the Tarim basin, and will provide a solid foundation for geothermal studies in future.     

Paleodrainage and fault development in the southern Perth Basin,Western Australia during and after the breakup of Gondwana from 3D modelling of the Bunbury Basalt

The evolution of faults and paleodrainage patterns on the southwestern Australian passive margin during and after the breakup of Gondwana in the Early Cretaceous remains poorly understood. This contribution investigates the fault and paleodrainage evolution in the southern Perth Basin with the use of the ‘Bunbury Basalt’, the only lava flows known to be synchronous with continental breakup. New aeromagnetic data have been integrated with well intersections and outcrop constraints to establish the first 3D model of the Bunbury Basalt. The model reveals that flows are up to 100 m thick and are predominantly confined to two north–south-trending paleovalleys and their tributaries situated in the Bunbury Trough in the southern Perth Basin. The Donnybrook Paleovalley flow ponded in a paleovalley proximal to the Darling Fault and is truncated by the two later flows within the Bunbury Paleovalley, which is positioned centrally in the Bunbury Trough. Offsets of the Bunbury Basalt have been used to identify new northeast- and northwest-trending faults in the southern Perth Basin, and broad folding is interpreted as a consequence of drag into the Darling and Busselton faults. The model has been used to determine post-basalt net displacements for the Darling and Busselton faults of 370 and 210 m, respectively, and <175 m for the northeast and northwest-trending faults. The source vents for the Bunbury Basalt were probably located at extensional jogs at intersections between the Darling Fault and subordinate oblique faults. These results challenge the views on longstanding quiescence of the post-breakup western Australian passive margin.     

塔里木盆地东河砂岩沉积和储层特征及综合分析

东河砂岩是一套海侵初期的沉积产物，东河砂岩不是一个等时沉积体，相当于晚泥盆世晚期至早石炭世早期沉积，具体沉积时间各地有差异。由于东河砂岩是覆盖广泛的海侵初期沉积，因此具有海侵初期填平补齐的特征，其沉积相决定于海侵的速度、沉积物的供给和海侵前的古地貌。塔北地区受塔北古隆起的阻挡，海水在古隆起周围滞留时间较长，又有较粗粒的物源供给，其沉积产物主要是滨岸海滩沉积；塔中地区由于地形复杂，沉积类型也比较复杂，底部砾岩段有河流相沉积，而块状砂岩段和砂砾岩段有河口湾和滨岸海滩沉积，不同段在成分、分选性和粒级上有较大的差异；而其它低平地区主要是海侵期快速的滨岸和陆架沉积。受沉积因素影响，东河砂岩有效储层的分布具有地域性；除沉积因素外，低的地温梯度和短期的深埋藏是优质储层发育的重要控制因素。     

漠河盆地东南部中生代火山岩年代学与地球化学研究

漠河盆地东南部中生代火山岩地层主要由光华组和甘河组组成,锆石U--Pb定年结果确定两组火山岩分别形成于128~125 Ma和126~120 Ma。光华组流纹岩高硅富碱、贫钙铁镁;轻重稀土分馏较明显[w(La/Yb)N=13.01~17.99],铕异常中等(δEu=0.49~0.67);富集大离子亲石元素Rb、K、Th、U,亏损高场强元素Nb、Ta、P、Ti;锆石εHf(t)值为-2.5~3.0,两阶段Hf模式年龄为989~1 130 Ma;岩浆源区为中元古代末期的地壳物质。甘河组粗安岩和玄武粗安岩富碱高钾,镁指数较大(Mg#≈48);稀土元素配分曲线为轻稀土富集的右倾型[w(La/Yb)N=12.67~23.21],铕异常不明显(δEu=0.77~0.91);富集Rb、Ba、K、Th、U等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素;锆石εHf(t)值为-1.2~4.1;岩浆源区为俯冲流体交代过的岩石圈地幔,岩浆经历了一定程度分离结晶作用。     

Hydrogeology and hydrochemistry of the Parmelia aquifer,northern Perth Basin,Western Australia

This study aims to characterise the hydrogeology and hydrochemistry of the Parmelia aquifer and to understand controls on recent water-level changes as these are needed to underpin a quantitative analysis of recharge. The Parmelia aquifer, a layered sequence of sand, silt and discontinuous lenses of clay, receives diffuse rainfall recharge on its outcrop and groundwater recharge occurs across the Dandaragan Plateau at different rates. Water levels have risen steadily over the last three decades between 10 and 55 cm/y in response to the replacement of native vegetation with pasture and annual crops. The mean aquifer properties from sediment analyses indicate a very wide range of porosity (8.9 – 49.5 %) with an arithmetic mean of 26% and consequently a very broad range of specific yield (0.0004 – 0.4) with an arithmetic mean of 0.14. Groundwater in the Parmelia aquifer has an underlying meteoric origin with compositional changes due to reactions with silicate minerals and leaching of chloride that has concentrated in the soil by evapotranspiration. The hydrochemistry sampled at different depths and locations in the aquifer indicates that the groundwater is not well mixed, and variations arise due to relatively recent recharge that has undergone evaporation in some areas.     

松辽盆地营城组火山岩成岩作用类型、特征及其对储层物性的影响

通过野外剖面观察、钻井岩心描述、薄片鉴定和扫描电镜分析,松辽盆地营城组火山岩的成岩作用阶段分为早期和晚期。早期成岩作用类型有挥发分逸出、熔蚀作用、等容冷凝结晶、准同生期热液沉淀结晶、熔结作用、冷凝收缩、分熔冷凝结晶和早期压实胶结作用;晚期成岩作用类型为充填作用、脱玻化作用、交代作用、机械压实压溶作用、胶结作用和溶解作用。早期成岩作用主要影响原生孔隙的发育,晚期成岩作用影响次生孔隙的发育。准同生期热液沉淀结晶、早期压实胶结作用、充填作用、机械压实压溶作用和胶结作用是使松辽盆地营城组火山岩储层物性降低的主要成岩作用;挥发分逸出、等容冷凝结晶、冷凝收缩和溶解作用是产生孔隙空间使储层物性变好的主要成岩作用。     

吐哈盆地鄯善弧形构造带碎屑岩的成岩作用

吐哈盆地鄯善弧形构造带三间房组储集层的成岩作用类型主要为压实作用、胶结作用和溶蚀作用。成岩作用改变了砂岩储集层的孔隙结构。压实作用和胶结作用降低了砂岩的原生孔隙度,溶解作用产生的次生孔隙成为主要的汕气储集空间。     

Alternating episodes of extension and contraction during the Triassic: evidence from Mesozoic sedimentary basins in eastern Australia

Triassic to Lower Cretaceous continental sedimentary basins occur in eastern Australia, but the tectonic and structural evolution of these basins is not fully understood. Using gridded aeromagnetic data, seismic reflection data and field observations, we conducted a structural analysis aimed at characterising major faults and deformation style in these sedimentary basins. Our results show evidence for two alternating episodes of rifting during the Triassic. An earlier episode of rifting, which took place in the Early Triassic to early Late Triassic, is inferred based on synsedimentary normal faults in the Nymboida Coal Measures and the boundary West Ipswich Fault System in the Esk Trough. This phase of rifting was followed by a contractional event that resulted in tilting, folding, and thrust faulting. Evidence of synsedimentary normal faults and bimodal volcanism indicates that another rifting phase occurred during the Late Triassic and resulted in the development of the Ipswich Basin. From the latest Late Triassic to the Early Cretaceous, the accumulation of continental sediments in the Clarence-Moreton Basin was accompanied by subsidence. We suggest that the alternating rifting episodes and contraction were ultimately controlled by plate boundary migration and switches between trench retreat and advance during the Triassic.     

Metamorphic grade and gradient from white K-micas of Na-mica bearing sedimentary rocks in the Mosquito Creek Basin,East Pilbara Craton,Western Australia

Shales and phyllites from the turbidite sequences of the 2.9 Ga Mosquito Creek Formation of the East Pilbara, Western Australia contain varying amounts of paragonite and mixed Na–K micas (MNKMs), the 0 0 l X-ray diffraction reflections of which are unresolved from the 10-Å reflections, and only partly resolved from the 5-Å reflections of white K-mica (WKM). The Kübler index (‘crystallinity’), the full width at half maximum (FWHM) of the WKM, obtained from these composite reflections by applying a three-peak deconvolution procedure, reveals a metamorphic zoning of the Mosquito Creek Formation. The highest, “epimetamorphic”, grade occurs in the — largely Na-mica free — southern part, with lower, medium- to high-anchimetamorphic, grades in the central part, notably in a WSW-ENE anticlinal zone extending from Nullagine to the Blue Spec Mine. The Na-mica free metasediments of the Glen Herring Shale of the Fortescue Group, overlying the Mosquito Creek Formation to the W, show only a slightly lower metamorphic grade. The low b₀ lattice parameter of the WKMs indicates a very low metamorphic P/T gradient. The Na-mica bearing metasediments of the Mosquito Creek Formation correspond to a kaolinite-bearing protolith, strongly Al-enriched and K-depleted with respect to the presumably granitic-tonalitic source rock.     

The Mesozoic structural evolution of the Gorgon Platform,North Carnarvon Basin,Australia

The Gorgon Platform is located on the southeastern edge of the Exmouth Plateau in the North Carnarvon Basin, North West Shelf, Australia. A structural analysis using three-dimensional (3D) seismic data has revealed four major sets of extensional faults, namely, (1) the Exmouth Plateau extensional fault system, (2) the basin bounding fault system (Exmouth Plateau–Gorgon Platform Boundary Fault), (3) an intra-rift fault system in the graben between the Exmouth Plateau and the Gorgon Platform and (4) an intra-rift fault system within the graben between the Exmouth Plateau and the Exmouth Sub-basin. Fault throw-length analyses imply that the initial fault segments, which formed the Exmouth Plateau–Gorgon Platform Boundary Fault (EG Boundary Fault), were subsequently connected vertically and laterally by both soft- and hard-linked structures. These major extensional fault systems were controlled by three different extensional events during the Early and Middle Jurassic, Late Jurassic and Early Cretaceous, and illustrate the strong role of structural inheritance in determining fault orientation and linkage. The Lower and Middle Jurassic and Upper Jurassic to Lower Cretaceous syn-kinematic sequences are separated by unconformities.     

Lithostratigraphy and depositional environment of the Permian Nowra Sandstone in the southwestern Sydney Basin,Australia

Lithofacies in the mid‐Permian Nowra Sandstone indicate a middle/upper shoreface to foreshore environment of deposition under the influence of storm‐generated waves and north‐northeasterly directed longshore currents. Palaeogeographic reconstruction for the Nowra Sandstone portrays a sand‐dominated high energy shelf and offshore shoal forming a sequence thickening seaward away from the western shore of the Sydney Basin. The shoal‐crest at the outer edge of the shelf trends north‐northeast. It is characterized by fine‐ to medium‐grained sandstone with upper flow regime structures and a high proportion of conglomerate, whereas coarser sandstone with lower energy bedforms occurs along the seaward side of the shoal. In the deeper water to the east, the lower Nowra Sandstone becomes rapidly thinner as it passes seaward, via bioturbated storm redeposited sandstone beds, into the shelf deposits of the Wandrawandian Siltstone. This sequence accumulated during a regressive event and the base of the formation becomes progressively younger eastward. The sand may have been supplied by rivers along the western coast but the major source was south of the study area. The lower Nowra Sandstone is separated from the upper part of the formation by an extensive ravinement surface overlain by the Purnoo Conglomerate Member. In contrast to the lower unit, the upper Nowra Sandstone forms a westward thickening wedge that represents a backstepping nearshore sand facies that accumulated during a transgression. The upper Nowra Sandstone passes vertically and laterally eastward into the Berry Siltstone. Thus both boundaries of the Nowra Sandstone are diachronous, first younging eastward and then westward as a response to a regressive‐transgressive episode.     

柴达木盆地西部中生界原型盆地及其演化

柴达木中生界盆地形成时间及其盆地原型研究存在很大争议,主要原因在于对盆地内有无三叠系陆相沉积及其与上覆下侏罗统地层接触关系和中生界原型盆地形成的构造背景等问题认识不清.区域地质调查在盆地西部月牙山北发现中、上三叠统陆相地层与上覆下侏罗统地层整合接触,在此基础上,结合地表露头、古流分析及地震解释资料研究认为:柴达木中生界盆地起始于中三叠世.中生代在古阿拉巴斯套山与古昆仑山间发育一个大的近东西向展布的活动型山间盆地,盆地经历了中-晚三叠世、早-中侏罗世和晚侏罗世-白垩纪三个演化阶段,分别对应发育了中-晚三叠世坳陷型盆地、早-中侏罗世断陷型盆地和晚侏罗世-白垩纪坳陷型盆地三种原型盆地类型.中-晚三叠世盆地分布比较局限,沉积以氧化环境下的红色碎屑岩建造为主,不具生烃能力;早-中侏罗世盆地范围扩大,沉积物以暗色含煤建造为主,主要分布于现今的阿尔金山地区及其山前地带,沉积中心在阿尔金山地区.晚侏罗世-白垩纪阿尔金山快速隆升,成为主要物源区,开始分割塔里木和柴达木盆地沉积,沉积物为红色磨拉石建造.该研究对于准确评价柴达木盆地生烃潜力及合理进行勘探部署具有重要意义.     

鸡西盆地下白垩统含煤层系低孔低渗砂岩的成因探讨

黑龙江鸡西盆地下白垩统城子河组和穆棱组是主要的含煤系地层,岩石类型为长石岩屑砂岩和岩屑长石砂岩,成岩作用主要为压实作用、胶结作用、溶蚀溶解作用及交代作用等,露头砂岩经历了表生成岩作用。压实作用和胶结作用是储层砂岩物性差的重要原因,二者相比,前者对该区孔隙度减少贡献更大。对比露头砂岩与岩芯砂岩,露头砂岩的储层物性更好。     

柴达木盆地西部西岔沟剖面湖相碳酸盐岩岩石学特征与沉积环境分析

湖相碳酸盐岩在柴达木盆地西部古、新近系地层中广泛出露,在研究区西岔沟地区主要分布在下干柴沟组、上干柴沟组的顶部,下油砂山组及上油砂山组的底部。通过实测西岔沟剖面、岩性分析、岩相组合特征、生物特征、沉积构造、室内薄片鉴定等研究对西岔沟剖面的碳酸盐岩进行了分析,识别出西岔沟剖面的碳酸盐岩的类型主要有鲕粒灰岩、介壳灰岩、藻叠层石灰岩、泥晶灰岩、砂质灰岩等,沉积环境主要属滨浅湖,并在岩石学特征的基础上对其成因进行了研究。     

Petrophysical characterisation of tight sandstone gas reservoirs using nuclear magnetic resonance: a case study of the upper Paleozoic strata in the Kangning area,eastern margin of the Ordos Basin,China

Residual and movable porosity are significant parameters for characterising petrophysical properties, especially in tight reservoirs. Eight tight sandstone samples from the upper Paleozoic gas-bearing strata in the Kangning area, from the eastern margin of the Ordos Basin, were analysed using nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), petrography, and porosity and permeability tests. The lithology and pore types were identified and classified using petrography and SEM. The residual and movable porosity were obtained with NMR. In addition, NMR was used to visualise pore structure and pore size distribution. The results suggest that the upper Paleozoic sandstones in the study area mainly comprise feldspathic litharenite and litharenite. The sandstone porosity and permeability are low, with means of 5.9% and 0.549 mD, respectively. Four pore types exist in the tight sandstones: residual primary pores, grain dissolution pores, micropores (clay-dominated) and microfractures. The T₂ spectra under water-saturated conditions correlate with pore size and can be used to distinguish small and large pores based on the transverse relaxation time cutoff value of 10 ms, which corresponds to a pore diameter of 0.232 μm. Small pores account for 72% of the pores in the tight sandstones. The continuous bimodal T₂ spectra suggest good connectivity between small and large pores, despite the low porosity and permeability. In this study, the movable porosity of the major tight sandstone gas reservoirs is higher than the residual porosity, which confirms the effective evaluation of movable porosity to tight sandstone reservoirs, based on NMR experiments.     

Sulphide minerals in early Archean chemical sedimentary rocks of the eastern Pilbara district, Western Australia

Summary The occurrence and paragenesis of sulphide minerals in chemical sedimentary rocks from the McPhee and the Towers Formations of the Warrawoona Group, eastern Pilbara Craton were examined, in order to evaluate the Archean sedimentary environment. The chemical sedimentary facies of both formations are comprised of chert or chertcarbonate units, which are highly depleted in detrital materials. The cherty rocks are mostly composed of microcrystalline quartz, containing significant types of syndepositional (or diagenetic) sulphide minerals. In particular, the cherty rocks in the Towers Formation (North Pole Chert, Marble Bar Chert) include primary sulphide minerals, such as pyrite, chalcopyrite, sphalerite, monoclinic pyrrhotite, pentlandite, gersdorffite and millerite. This assemblage and the measured FeS content (8.4–10.4 mol%) of sphalerite associated with the Fe-sulphide minerals suggest that the cherty rocks were formed under reducing conditions at temperatures below 200°C (about 150°C), and also that the metamorphic temperature of the rocks was less than 325 °C. Furthermore, the virtual absence of detrital materials and the minor element compositions imply that the cherty rocks of the eastern Pilbara Block were formed by rapid precipitation from reducing hydrothermal solutions.

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Sulfide in chemischen sedimentgesteinen des älteren Archaikums im östlichen Pilbara block, Westaustralien

Zusammenfassung Das Auftreten und die Paragenese von Sulfiden in chemischen Sedimentgesteinen der McPhee und der Towers Formation der Warrawoona Gruppe, östlicher Pilbara Block, wurden untersucht, um das sedimentäre Milieu im Archaikum besser abschätzen zu können. Die chemisch-sedimentäre Fazies beider Formationen besteht aus Chert- oder Chert-Karbonat-Einheiten, die hochgradig an detritärem Material verarmt sind. Die Cherts bestehen aus mikrokristallinem Quartz, der beträchtliche Mengen an syngenetischen bzw. syndiagenetischen Sulfiden enthält. Vor allem die Cherts der Towers Formation (North Pole Chert, Marble Bar Chert) führen Pyrit, Kupferkies, Zinkblende, monoklinen Magnetkies, Pentlandit, Gersdorffit und Millerit als primäre Sulfide. Diese Vergesellschaftung und die gemessenen FeS-Gehalte der mit den Fe-Sulfiden assoziierten Zinkblende (8.4–10.4 Mol%), weisen darauf hin, daß die Cherts unter reduzierenden Bedingungen bei Temperaturen unter 200°C entstanden sind und daß die Matamorphosetemperatur 325 °C nicht überschritten hat. Das Fehlen detritärer Sedimentkomponenten und die Spurenelementzusammensetzungen lassen darauf schließen, daß die Cherts im östlichen Pilbara Block durch rasche Ausfällung aus reduzierenden hydrothermalen Lösungen entstanden sind.