Gas-generation potential of shales in small and medium-sized basins: a case study from the Xuanhua Basin,north China

Abstract

Small- and medium-sized basins are widely distributed, and some contain commercial gas reservoirs demonstrating their gas-generation potential. The Xuanhua Basin, which is a small-sized coal-bearing basin in north China, includes a promising target for shale-gas exploration in the Xiahuayuan Formation. In this study, we used this basin as a case study to assess the critical geochemical features for small or medium-sized basins to form commercial gas reservoirs. Total organic carbon (TOC) analysis, Rock-Eval pyrolysis, microscopic observation of macerals, vitrinite reflectance measurement and kerogen stable carbon isotope analysis were performed to characterise the organic geochemistry of the Xiahuayuan shales. The original total organic carbon (TOC_o) content and hydrocarbon-generative potential (S_2o) were reconstructed to further evaluate the gas-generation potential of these shales. In addition, geochemical data of shales from other similar-sized basins with gas discoveries were compared. The results showed that the kerogen from the Xiahuayuan Formation is Type III (gas-prone), and macerals are dominated by vitrinite. TOC values showed a strong heterogeneity in the vertical profiles, with most higher than 1.5?wt%. The measured R_o values ranged from 1.4 to 2.0%. However, thermal maturity was not correlated with the present-day burial depth with higher maturity in the wells closest to the diabase intrusion centre. The remaining generation potential (S₂) averaged 0.91?mg HC/g rock, equal to 1.4?cm³ CH₄/g rock, and the average amount of hydrocarbon generated was 4.33?cm³ CH₄/g rock. In small and medium-sized basins, the TOC content of commercially developed gas shales ranged from 0.5 to 2.5?wt%, organic matter was mainly humic (gas-prone), and the burial depth was generally shallow. Biogenic gas reservoirs for commercial exploitation tend to have larger shale thicknesses (120–800?m) than thermogenic gas reservoirs (60–90?m).

1. The Xiahuayuan Formation is a good gas-source rock with gas-prone kerogen type, relatively high TOC values and moderate thermal maturity.

2. The average amount of hydrocarbon generated from the Xiahuayuan shales is about 4.33?cm³ CH₄/g rock, indicating a potential to form a shale gas reservoir.

3. Owing to the influence of diabase intrusions, the Xiahuayuan shales have entered the dry gas window at relatively shallow-buried depths.

4. Small- and medium-sized basins have the potential to generate commercial gas reservoirs with the generated volume mainly a product of the thickness and maturity of black shales.

     

A 1642 Ma age for the Fraynes Formation,Birrindudu Basin,confirms correlation with the economically significant Barney Creek Formation,McArthur Basin,Northern Territory

Abstract

An interpreted CA–IDTIMS age of 1642.2?±?3.9?Ma for a volcanogenic tuffaceous siltstone from the previously undated Fraynes Formation of the Birrindudu Basin in the northwestern Northern Territory enables a rigorous chronostratigraphic correlation to be made with the economically important Barney Creek Formation of the southern McArthur Basin. This result supports previous interpretations that these geographically widely separated formations are probably linked in the subsurface. It also establishes the stratigraphic interval encompassing the Fraynes and Barney Creek formations as a potential target for greenfields base metals and petroleum exploration programs across the greater McArthur Basin.

• KEY POINTS

• A new interpreted CA–IDTIMS age provides a chronostratigraphic link between the Fraynes Formation of the Birrindudu Basin and the economically important Barney Creek Formation of the southern McArthur Basin.

• The Fraynes and Barney Creek formations are probably linked in the subsurface.

• This stratigraphic level is a potential target for greenfields base metals and petroleum exploration across the greater McArthur Basin.

     

Provenance analysis of the Cretaceous Laiyang Group on Lingshan Island (western Yellow Sea,China) and its tectono-sedimentary implications

Abstract

Longstanding debates on the tectonic setting and provenance of the Lower Cretaceous Lingshandao Formation have hindered basin analysis and tectonic studies of the collision of the Yangtze Craton and the North China Craton, and thus the evolution of the Sulu Orogen. Thin-section analysis, identification of rock particles, cathodoluminescence, heavy minerals and trace-element analysis have, in addition to field investigations, been applied to reconstruct the source area and transport pathways of the sediments that build the Lower Cretaceous Laiyang Group on the Lingshan Island, western Yellow Sea. These analyses indicate that the Laiyang Group consists mainly of material derived from a recycled orogen and from transitional continental sediments. The Laiyang Group on Lingshan Island has been sourced from igneous and metamorphic rocks. Comparing analyses of detrital minerals with rocks from surrounding areas leads to the conclusion that the main source area is the Sulu Orogen that supplied sediment to rift basin rather than a residual basin between the Yangtze Craton and the North China Craton.

1. A recycled orogenic belt is the source area for the Laiyang Group on Linshan Island.

2. Felsic metamorphic and igneous rocks form the most probable sources.

3. The rift basin was filled by sediments supplied from the Sulu Orogen on both sides.

     

Coal seam development characteristics and distribution predictions in marginal sea basins: Oligocene Yacheng Formation coal measures,Qiongdongnan Basin,northern region of the South China Sea

Abstract

Coal measures located in marginal sea basins are important hydrocarbon source rocks. For the purpose of effectively guiding future oil and gas exploration, the characteristics and distribution patterns of coal seams in coal measures of a marginal sea basin are systematically outlined. Coal measures in marginal sea basins can have large thicknesses, but the individual coal seams can be very thin and lack lateral continuity. In the study area, the organic micro-components of the coal are dominated by vitrinite, with very low amounts of inertinite and liptinite. The amount of inorganic microscopic components is large, but with limited drilling results, few cores and thin coal seams, which are easily overlooked during logging activities, a comprehensive analysis of the logging data may improve efficiency in coal-seam identification and thickness determination. The development and distribution of coal seams in marginal sea basins are controlled by various factors, including (1) paleoclimatic and paleobotanic conditions, which could fundamentally limit coal formation, (2) coal-forming sedimentary environmental conditions that may limit the scope of coal-seam development from a macroscopic perspective, and (3) paleotectonic and paleotopographic conditions that define the coal-forming structures. Therefore, the descending and rising cycles of base-levels, along with changes in the growth rates of the accommodation spaces, can be used to determine the horizons that are potentially favourable for coal formation and can also indicate the migration trends of coal-forming environments on the structural plane. Seismic wave impedance inversion methods could be utilised for semi-quantitative assistance for prediction of coal seams. In summary, for models of coal-seam development in marginal sea basins, the grades should be divided according to reliability, and the different reliability levels should be predicted separately.

1. The characteristics of coal seams developed in marginal sea basins are described.

2. The macerals of coals developed in marginal sea basins have been ascertained.

3. A development model and distribution prediction method for coal seams are assessed according to the control factors.

4. A model for the prediction of coal-seam distribution is presented.

     

Geology of the Acropolis prospect,South Australia,constrained by high-precision CA-TIMS ages

Abstract

Acropolis is an Fe-oxide–copper–gold prospect ～20?km from Olympic Dam, South Australia, and marked by near-coincident gravity and magnetic anomalies. Prospective Fe-oxide–apatite?±?sulfide veins occur in Mesoproterozoic and Paleoproterozoic volcanic and granitoid host units beneath unmineralised sedimentary formations. We have produced a geological map and history of the prospect using data from 16 diamond drill holes, including LA-ICPMS and high-precision CA-TIMS ages. The oldest unit is megacrystic granite of the Donington Suite (ca 1850?Ma). A non-conformity spanning ca 250 My separates the Donington Suite and felsic lavas and ignimbrites of the Gawler Range Volcanics (GRV; 1594.03?±?0.68?Ma). The GRV were intruded by granite of the Hiltaba Suite (1594.88?±?0.50?Ma) and felsic dykes (1593.88?±?0.56?Ma; same age as the Roxby Downs Granite at Olympic Dam). The felsic dykes are weakly altered and lack Fe-oxide–apatite–sulfide veins, suggesting that they post-date the main hydrothermal event. If correct, this relationship implies that the main hydrothermal event at Acropolis was ca 1594?Ma and pre-dated the main hydrothermal event at Olympic Dam. The GRV at Acropolis are the same age as the GRV at Olympic Dam and ca 3–7 My older than the GRV exposed in the Gawler Ranges. The gravity and magnetic anomalies coincide with sections through the GRV, Hiltaba Suite and Donington Suite that contain abundant, wide, Fe-oxide veins. The GRV, Hiltaba Suite and Donington Suite are unconformably overlain by the Mesoproterozoic Pandurra Formation or Neoproterozoic Stuart Shelf sedimentary formations. The Pandurra Formation shows marked lateral variations in thickness related to paleotopography on the underlying units and post-Pandurra Formation pre-Neoproterozoic faults. The Stuart Shelf sedimentary formations have uniform thicknesses.

1. KEY POINTS

2. Fe-oxide–apatite?±?sulfide veins are hosted by the Gawler Range Volcanics (1594.03?±?0.68?Ma), the Hiltaba Suite granite (1594.88?±?0.50?Ma) and Donington Suite granite (ca 1850?Ma).

3. The age of felsic dykes (1593.88?±?0.56?Ma) interpreted to be post-mineralisation implies that the main hydrothermal event at Acropolis was ca 1594?Ma.

4. The Gawler Range Volcanics at Acropolis are the same age as the Gawler Range Volcanics at Olympic Dam and ca 3 to 7 My older than the Gawler Range Volcanics exposed in the Gawler Ranges.

     

Neogene Billa Kalina Basin and Stuart Creek silicified floras,northern South Australia: a reassessment of their stratigraphy,age and environments

Abstract

Silicified fossil macrofloras of the Willalinchina Sandstone, at Stuart Creek in the Billa Kalina Basin of northern South Australia, are most likely early Miocene–early Pliocene with preference for the younger age, based on reinterpretation of published evidence including basin stratigraphy, paleogeography, isotopic and other dating. The macrofloras include Eucalyptus and occur in fluvial channel sandstones. The Willalinchina Sandstone is equated with the Danae Conglomerate Member of the Mirikata Formation, interpreted as older than the Watchie Sandstone, Millers Creek Dolomite Member and Billa Kalina Clay Member, and here regarded as of upper Neogene age. The Billa Kalina Basin lies between Lake Eyre, Torrens and Eucla basins, and has affinities with all three. The Kingoonya Paleochannel, peripheral to the Eucla Basin, joins the southern margin of the Billa Kalina Basin across the Stuart Range Divide, and contains the Garford Formation of mid-Miocene to Pliocene age (palynological dating), here partly equated with the Mirikata Formation. Interpretations of paleolake Billa Kalina and associated paleochannel environments are made, based on a new assessment of stratigraphic and paleogeographic relationships.

1. KEY POINTS

2. The Billa Kalina Basin sediments in northern South Australia are equated with the later Neogene ‘upper’ Garford Formation of the Kingoonya Paleochannel, which flowed into the Eucla Basin, and depositional processes are clarified.

3. A variety of consistent age data from adjacent basins and the Kingoonya Paleochannel indicate the Stuart Creek ‘silcrete floras’, associated with the Willalinchina Sandstone channel deposits, are Neogene, probably early Pliocene, but the possibility remains that they may be incised into the Watchie Sandstone and therefore late Pliocene.

4. The Billa Kalina Basin was linked to the Kingoonya Paleochannel through much of its history, with flow disrupted by the Stuart Range Divide, local tectonics, and regional tilting.

     

Metamorphism in the New England Orogen,eastern Australia: a review

Abstract

This paper summarises current knowledge on metamorphism within the entire New England Orogen (NEO) of eastern Australia. Rocks recording metamorphic assemblages characteristic of each of the three metamorphic facies series (high, medium and low P/T) have been identified within the orogen. These include high P/T blueschists and eclogites, mid P/T orogenic metamorphism and low P/T contact aureoles and sub-regional high-temperature–low-pressure (HTLP) metamorphism (regional aureoles). Metamorphism is described as it relates to six tectonic phases of development of the NEO that together comprise two major cycles of compression–extension. Medium–high-grade contact metamorphism spans all six tectonic phases while low-grade burial and/or orogenic metamorphism has been identified for four of the six phases. In contrast, exposure of high P/T eclogites and blueschists, and generation of sub-regional low P/T metamorphism is restricted to extensional phases of the orogen. Hallmarks of the orogen are two newly identified zones of HTLP metamorphism, the older of which extends for almost the entire length of the orogen.

1. KEY POINTS

2. The orogen is dominated by low-temperature rocks while high-temperature amphibolite to granulite facies rocks are restricted to small exposures in HTLP complexes and contact aureoles.

3. Blueschist metamorphism falls into two categories; that associated with subduction during the Currabubula-Connors continental arc phase occurring at depths of ～13–30?km; and the other of Cambrian–Ordovician age, exposed within a serpentinite melange and associated with blocks of eclogite. The eclogite, initially from depths of ～75–90?km, appears to have been entrained in the deep crust for an extended period of geological time.

4. A comprehensive review of contact metamorphism in the orogen is lacking and as studies on low-grade metamorphism are more extensive in the southern part of the orogen than the north, this highlights a second research gap.

     

Two belts of HTLP sub-regional metamorphism in the New England Orogen,eastern Australia: occurrence and characteristics exemplified by the Wongwibinda Metamorphic Complex

Abstract

Two north–south-trending belts of high-temperature–low-pressure (HTLP) sub-regional metamorphism have been identified in the New England Orogen of eastern Australia. Metamorphic complexes in the ～1300?km long Early-Permian Inland belt have ages ca 300–290?Ma, and those of the ～400?km long Mid-Permian Coastal belt ca 275–270?Ma. These periods correspond to the beginning and end of an extended (early–mid Permian) phase of subduction rollback and crustal thinning in eastern Australia. This paper describes and incorporates recent work on the Wongwibinda Metamorphic Complex in the southern New England Orogen as a basis for comparison with thirteen other HTLP sub-regional occurrences within the orogen. These are described in as much detail as is currently available. Some outcrops of HTLP rocks in difficult terrain have been subject to limited study and only conditional comparisons can be made. However, a significant number of characteristics shared between the complexes including: their location at the higher-temperature end of broad areas of very low-grade to greenschist facies metamorphic rocks, indicative of tilted crustal blocks; their association with major shear zones; the presence of migmatite at the high-temperature end of a steep metamorphic field gradient; the presence of two-mica granite formed by the melting of the local sedimentary pile; and temporal association with S-type granites; imply a common extension-related mechanism of formation for these HTLP belts. The connection with major faults and shear zones suggests the belts trace major crustal-scale extensional structures that migrated eastwards from ca 300 to 270?Ma.

1. KEY POINTS

2. Two previously undocumented belts of HTLP subregional metamorphism are identified within the NEO.

3. Available dating indicates that metamorphism occurred along the belts at the beginning and end of a major early–mid Permian extensional phase in eastern Gondwana/Australia.

4. The characteristics of the HTLP complexes including their association with shear zones indicates they may delineate major loci of extension.

     

Luminescence dating of Quaternary alluvial successions,Sellicks Creek,South Mount Lofty Ranges,southern Australia

Abstract

Quaternary alluvial and colluvial sediments infill major river valleys and form alluvial fans and colluvium-filled bedrock depressions on the range fronts and within the Mount Lofty Ranges of southern Australia. A complex association of alluvial successions occurs in the Sellicks Creek drainage basin, as revealed from lithostratigraphy, physical landscape setting and optically stimulated luminescence (OSL) ages. Correlation of OSL ages with the Marine Oxygen Isotope record reveals that the alluvial successions represent multiple episodes of alluvial sedimentation since the penultimate glaciation (Marine Isotope Stage 6; MIS 6). The successions include a penultimate glacial maximum alluvium (Taringa Formation; 160?±?15?ka; MIS 6), an unnamed alluvial succession (42?±?3.2?ka; MIS 3), a late last glacial colluvial succession within bedrock depressions (ca 15?ka; MIS 2) and a late last glacial alluvium (ca 15?ka; MIS 2) in the lowest, distal portion of Sellicks Creek. In addition, the Waldeila Formation, a Holocene alluvium (3.5?±?0.3?ka; MIS 1), and sediments deposited during a phase of Post-European Settlement Aggradation (PESA) are also identified. The age and spatial distribution of the red/brown successions, mapped as the Upper Pleistocene Pooraka Formation, directly relate to different topographic and tectonic settings. Neotectonic uplift locally enhanced erosion and sedimentation, while differences in drainage basin sizes along the margin of the ranges have influenced the timing and delivery of sediment in downstream locations. Close to the Willunga Fault Scarp at Sellicks Creek, sediments resembling the Pooraka Formation have yielded a pooled mean OSL age of 83.9?±?7?ka (MIS 5a) corroborating the previously identified extended time range for deposition of the formation. Elsewhere, within major river valleys, the Pooraka Formation was deposited during the last interglacial maximum (128–118?ka; MIS 5e). In general, alluviation occurred during interglacial and interstadial pluvial events, while erosion predominated during drier glacial episodes. In both cases, contemporaneous erosion and sedimentation continued to affect the landscape. For example, in the Sellicks Creek drainage basin, which lies across an actively uplifting fault zone, late glacial age sediments (MIS 2) occur within the ranges and near the distal margin of the alluvial fan complex. OSL dating of the alluvial successions reported in this paper highlights linkages between the terrestrial and marine environments in association with sea-level (base-level) and climatic perturbations. While the alluvial successions relate largely to climatically driven changes, especially in major river valleys, tectonics, eustasy, geomorphic setting and topography have influenced erosion and sedimentation, especially on steep-sloped alluvial fan environments.

1. KEY POINTS

2. Luminescence dating of the Sellicks Creek alluvial fan complex reveals that sedimentation occurred predominantly during the later stages of glacial cycles accompanying lower sea-levels than present.

3. Luminescence dating confirms that the stratigraphically lower portions of the Pooraka Formation are beyond the range of radiocarbon dating.

4. Upper Pleistocene alluvial fan sedimentation at Sellicks Creek correlates with pluvial events in southeastern Australia.

     

GC profiles of oils reflect organic maturity rather than depositional environment of parent source rock: examples from Central Australia

Abstract

Review and analysis of 1332 gas chromatography (GC) n-alkane traces of oils from the Cooper and Eromanga basins indicate the shape of any GC trace profile is primarily controlled by the degree of organic maturity (early, peak or late) at which the oils were expelled from the parent source rock, rather than indicating the depositional environment, and hence organic composition, of that source rock. The depositional environment of a source rock may still be inferred, however, from the position of the n-alkane maximum on the GC traces of early expulsion oils in association with the pour point of the oil. Departures of GC trace profiles from the standard early, peak or late expulsion profiles can indicate mixing of oils of different maturities, while variations in the GC trace profiles of oils within adjacent reservoir units may indicate phase separation of the parent liquid, or possible seal breach by an accumulation that exceeds the capacity of its overlying seal.

1. KEY POINTS

2. GC trace profiles of 1332 oils from across the Cooper and Eromanga basins of central Australia have been reviewed.

3. Organic maturity, rather than organic composition, of the parent source rock controls the shape of any GC trace profile.

4. All early maturity oils display a consistent GC trace profile shape that is different from all peak maturity oils and different again from all late maturity oils.

5. Depositional environment of the source rocks within a basin can be inferred from the relative pour points of the resultant oils.

     

辽东苏子河盆地聂尔库组沉积相与沉积环境研究

辽东苏子河盆地是早白垩世形成的小型断陷盆地,盆地内发育了相对连续的陆相沉积,是研究白垩纪陆地环境及气候演化的理想地区。早白垩世晚期沉积的聂尔库组地层出露连续,沉积现象典型。通过分析聂尔库组沉积岩类型、沉积构造、古生物化石及垂向沉积序列,可识别出扇三角洲相和湖泊相,其中扇三角洲相包括扇三角洲平原亚相、扇三角洲前缘亚相和前扇三角洲亚相,湖泊相主要为滨浅湖泥砂沉积。研究表明,聂尔库组形成于断陷盆地边缘陡坡带,属于间歇性洪水控制的扇三角洲—湖泊沉积体系,经历了扇三角洲—湖泊—扇三角洲的沉积环境变化,代表了断陷湖盆由深陷扩张期—抬升收缩早期的沉积充填过程。根据沉积岩与沉积相特征,结合古生物、特殊沉积、黏土矿物及地球化学资料,认为早白垩世晚期辽东地区总体与当时全球"温室气候"的大背景相一致,处于高温干旱/潮湿的气候条件,但这种高温气候具有不均一性,存在气候波动。     

二连盆地白音查干凹陷下白垩统都红木组沉积特征及演化

通过详细的岩芯观察、录测井资料分析,并结合区域地质资料和前人研究成果,对白音查干凹陷下白垩统都红木组的沉积相特征和沉积演化进行了深入研究。结果表明,白音查干凹陷主要发育扇三角洲相、辫状河三角洲相、浊积扇相和湖泊相4种沉积相类型。其中,扇三角洲和浊积扇在陡峭的北坡发育,辫状河三角洲在宽缓的南坡沉积,湖泊相分布在扇三角洲和辫状河三角洲的侧翼及凹陷的中心。都红木组沉积时期白音查干凹陷处于强裂陷向坳陷转化阶段。根据残留地层分布特征,其沉积演化可分为早、中、晚3个时期,从早期至晚期,扇三角洲和辫状河三角洲的面积不断缩小,分别后退了约3km和4-11km,湖泊沉积成为主体。     

Structural development of the Hastings Block and tectonic implications for the southern New England Orogen

Abstract

The shape and structural development of the box-like Parrabel Dome (PD) within the Hastings Block is poorly understood because it has only been weakly cleaved, complexly folded and extensively faulted in comparison to the adjoining blocks. Better characterising this block will provide important controls on the tectonics of the southern New England Orogen. The structural development of the PD and southern Hastings Block (SHB) provides evidence of the degree of rotation, translation and deformation of the Hastings Block, a key terrane within the southern New England Orogen. A major decollement under the Hastings Block–Nambucca Block was suggested to facilitate south-directed deformation caused by the developing Coffs Harbour Orocline. The orientation of bedding and the stratigraphic facing of some fault blocks within the northern Hastings Block (NHB) are consistent with development of the PD, while other fault blocks indicate significant disruption of the NHB prior to, during and after dome development. A deep-seated fault is suggested by the gravity worm analysis consistent with the boundary zone between the PD, NHB-Yarrowitch Block and the east-dipping and younging sequences in the SHB. The eastern limb of the PD underwent clockwise rotation after formation. Fault blocks have been rotated and translated within a restraining bend as the NHB moved post-PD formation northwest along the interface between the NHB and SHB.

1. KEY POINTS

2. The Hastings Block was translated and rotated into its current position from the southeastern end of the Tamworth Belt.

3. Gravity worm data indicate a boundary between northern and southern Hastings Block.

4. The Hastings and Nambucca blocks have been detached from the basement Gondwana rocks.

5. Fault block analysis within the Parrabel Dome, northern Hastings Block indicates relocation of some blocks by faulting.

     

New information on the giant Devonian lobe-finned fish Edenopteron from the New South Wales south coast

Abstract

Edenopteron, with a lower jaw some 48?cm long, and total length perhaps exceeding 3 m, is the largest Devonian lobe-fin known from semi-articulated remains. New material described from the type locality (Boyds Tower, south of Eden) includes three slightly smaller articulated skulls and jaws, and additional bones of the shoulder girdle. Another articulated skull roof, shoulder girdle and palate is described from a second locality (Hegarty Bay), about 10?km south of Boyds Tower. Both localities represent the upper part of the Worange Point Formation, of late Famennian age (uppermost Upper Devonian). The new morphological evidence supports a close relationship to the tristichopterids Mandageria and Cabonnichthys, from the slightly older (Frasnian, Upper Devonian) fossil fish assemblage at Canowindra, New South Wales. Features of the shoulder girdle (supracleithrum, anocleithrum) suggest that Edenopteron is more closely related to Mandageria than Cabonnichthys. Eight characters are used to define a tristichopterid subfamily Mandageriinae, to which Notorhizodon from the Middle Devonian of Antarctica is also referred. The Mandageriinae is endemic to East Gondwana (Australia–Antarctica). In combination with possibly the most primitive tristichopterid, Marsdenichthys from the Frasnian of Victoria, these distributions implicate East Gondwana as a likely place of origin for the entire group. This relates to the major but unresolved question of a possible Gondwana origin for all the land vertebrates (tetrapods).

• An endemic Gondwanan sub-group (Mandageriinae) of the Devonian fishes closest to land animals (tetrapodomorph tristichopterids) is confirmed.

• Retention of primitive features (e.g. accessory vomers) points to an earlier origin of the Mandageriinae in East Gondwana, consistent with the Victorian occurrence of another primitive tristichopterid (Marsdenichthys).

• Edenopteron is confirmed from a second south coast fossil site, and new characters indicate its closest relative is Mandageria from Canowindra, NSW.

• Congruent evidence of older Gondwanan occurrences in other groups (basal tetrapodomorphs, rhizodontids, canowindrids), and previously dismissed trace fossil evidence (Grampians trackways), implicate South China and East Gondwana as the likely place of origin for all land vertebrates.

     

西湖凹陷渐新统花港组大型沿岸砂坝沉积特征及主控因素*

西湖凹陷位于东海陆架盆地东部坳陷带,是该盆地最大的富生烃凹陷,其主力储集层渐新统花港组的沉积环境与沉积体系类型一直存在较大争议。以岩心为基础,结合测井响应与地震反射特征,识别出西湖凹陷中东部花港组厚层砂岩主要有块状含砾中砂岩、冲洗层理中细砂岩、沙纹层理粉细砂岩共3种典型岩石类型,并通过统计分析沉积构造参数,明确花港组厚层砂岩主要发育在岸线附近的冲洗带,水动力强,波浪作用明显;该厚层砂岩在伽马测井曲线上整体表现为下部低幅锯齿箱状、顶部逐渐过渡为高幅锯齿状特征,地震上主要为中等振幅与连续性的、底平顶凸的丘状反射,为大型沿岸砂坝沉积。最后结合测井曲线样式、地震属性与含砂率拟合,刻画了沿岸砂坝的叠置样式与空间展布,确定西湖凹陷花港组大型沿岸砂坝主要分布在研究区东部三角洲前缘外侧,是由于基准面下降、水体变浅,早期形成的辫状河三角洲前缘受波浪作用改造而成。     

蒙古国塔木察格盆地塔南凹陷早白垩世构造古地貌控砂机制*

构造活动是源-汇系统中形成古地貌和砂分散体系的重要影响因素。塔木察格盆地塔南凹陷在早白垩世是一个典型的断陷湖盆,经历了多期幕式断陷活动,但同沉积构造活动及其配置所产生的古地貌对层序结构特征、沉积体系及砂体分布的控制作用仍不明确。文中以地震、测井、岩心资料为基础,以层序地层学理论和古地貌控砂理论为指导,建立了塔南凹陷下白垩统层序地层格架;结合断层活动性分析,阐明了不同类型古地貌对沉积体系和砂体分布的控制作用和规律。构造演化和沉积充填的综合研究表明: 受控盆主断裂的幕式断陷活动及同沉积断裂的差异断陷活动影响,塔南凹陷发育横向凸起和走向斜坡2种类型的构造调节带,这些构造调节带是水系入盆的通道,控制着盆地的主体物源方向、沉积体系类型与分布特征;根据断层的几何形态及发育部位,共识别出4种类型构造坡折带,分别是陡坡断崖型坡折带、陡坡断阶型坡折带、缓坡反向断阶型坡折带和盆内坡折带,它们各自控制了不同类型沉积体系的形成与分布;沉积物入盆后,沉积物分散体系和砂体的分布特征受同沉积断裂的组合样式控制,研究区共发育梳状断裂系、叉状断裂系和平行断裂系3种同沉积断裂平面组合;与构造调节带相对应的断裂坡折带低部位是大型储层砂体,特别是低位扇三角洲或盆底扇砂体发育的有利部位,是寻找砂岩油气藏的有利区带。研究成果对于深化断陷湖盆源-汇系统理论、指导断陷湖盆砂体分布预测具有重要的理论意义和实际价值。     

Jurassic uplift and erosion of the northeast Queensland continental margin: evidence from (U–Th)/He thermochronology combined with U–Pb detrital zircon age spectra

Abstract

The Jurassic–Cretaceous Great Artesian Basin is the most extensive, and largest volume, sedimentary feature of continental Australia. The source of its mud-dominated Cretaceous infill is attributed largely to contemporary magmatism along the continental margin to the east, but the source of its Jurassic infill, dominated by quartz sandstone, remains unconstrained. This paper investigates the question of a Jurassic sediment source for the northern part of the basin. Jurassic uplift and exhumation of the continental margin crustal sector to the east provided the primary Jurassic sediment source. (U–Th)/He data are presented for zircon and apatite from Pennsylvanian to mid Permian granitoids of the Kennedy Igneous Association distributed within the northern Tasmanides between the Townsville and Cairns regions and for coeval granites of the Urannha batholith from the Mount Carlton district (N Bowen Basin), also within the northern Tasmanides. The data from zircon indicate widespread Jurassic exhumation of a crustal tract located to the east of the northern Great Artesian Basin and largely occupied by rocks of the Tasmanides. Detrital zircon age spectra for samples of the Jurassic Hutton and Blantyre sandstones from the northeastern margin of the Great Artesian Basin show their derivation to be largely from rocks of the northern Tasmanides. In combination, the detrital age spectra and (U–Th)/He data from zircon indicate exhumation owing to uplift generating appreciable physiographic relief along the north Queensland continental margin during the Jurassic, shedding sediment westward into the Great Artesian Basin during its early development. A portion of (U–Th)/He data for zircon are consistent with late Permian–mid Triassic exhumation within the Tasmanides, attributable to the influence of the Hunter--Bowen Orogeny. Evidence of Cretaceous and Paleocene exhumation episodes is also indicated for some samples, mainly by apatite (U–Th)/He analysis, consistent with data previously published from fission track studies. Overall, new data from the present study reveal that the exhumation related to Jurassic regional uplift and the subsequent erosional reworking of the northeast Australian continental margin is critical for the evolution and development of the northern side of the Great Artesian Basin in eastern Australia. Apart from this, another two previously suggested Permian–Triassic and Cretaceous exhumation and uplift episodes along the northeast Australian continental margin are also confirmed by the dataset of this study.

1. KEY POINTS

2. U–Pb detrital zircon ages of sandstone samples from the northeastern Eromanga Basin reveal Paleozoic (480–280 Ma) and Proterozoic (1800–1400 Ma) age clusters.

3. (U–Th)/He zircon and apatite dating results of granitoids samples from Cairns, Townsville and the Mount Carlton districts are dominated by Jurassic (198–164 Ma) and Permian–Triassic (272–238 Ma) age clusters.

4. Combination of above two datasets proves the regional uplift-driving Jurassic exhumation episode in the northeast Australian continental is vital for the development of the northern Great Artesian Basin.

     

Looking beneath the Stawell and Bendigo zones in Victoria,Australia: a view through the granite window

Abstract

Information, mainly from the granitic and silicic volcanic rocks in the Stawell, Bendigo and Melbourne structural zones in the state of Victoria, shows that the sources of both the S- and I-type rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with the sources of similar granitic rocks in the Melbourne Zone, consistent with the absence of the mainly Proterozoic Selwyn Block beneath most of the SBZ. Below a mid-crustal décollement in the SBZ, the crust is evidently highly variable and possibly includes thinned Proterozoic crust. There is geochronological evidence for ca 400 and ca 370?Ma granulite-grade metamorphic events here, and, after this double bout of metamorphism, and depletion in the silicic melt component, the constituents of the entire deep crust of the SBZ would have densities similar to those of overlying, much lower-grade Cambrian metabasaltic to boninitic rocks. Thus, granitic magmas may have formed here by partial melting of a variety of rock types, probably with back-arc affinities, with ages that may extend back to the Proterozoic. Therefore, the basement of the SBZ is unlikely to consist solely of thick ocean-floor rocks, as in some current interpretations.

1. KEY POINTS

2. The sources of the Devonian granitic rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with those of the Melbourne Zone granites.

3. Two Devonian granulite-facies events left the melt-depleted deep SBZ crust with densities similar to those of overlying Cambrian metabasaltic rocks.

4. The SBZ Devonian granitic magmas probably formed by partial melting of heterogeneous Proterozoic to Cambrian arc-related crust, below the mid-crustal décollement.

     

Integrating satellite soil-moisture estimates and hydrological model products over Australia

Abstract

Accurate soil-moisture monitoring is essential for water-resource management and agricultural applications, and is now widely undertaken using satellite remote sensing or terrestrial hydrological models’ products. While both methods have limitations, e.g. the limited soil depth resolution of space-borne data and data deficiencies in models, data-assimilation techniques can provide an alternative approach. Here, we use the recently developed data-driven Kalman–Takens approach to integrate satellite soil-moisture products with those of the Australian Water Resources Assessment system Landscape (AWRA-L) model. This is done to constrain the model’s soil-moisture simulations over Australia with those observed from the Advanced Microwave Scanning Radiometer-Earth Observing System and Soil-Moisture and Ocean Salinity between 2002 and 2017. The main objective is to investigate the ability of the integration framework to improve AWRA-L simulations of soil moisture. The improved estimates are then used to investigate spatiotemporal soil-moisture variations. The results show that the proposed model-satellite data integration approach improves the continental soil-moisture estimates by increasing their correlation to independent in situ measurements (～10% relative to the non-assimilation estimates).

Highlights

• Satellite soil-moisture measurements are used to improve model simulation.

• A data-driven approach based on Kalman–Takens is applied.

• The applied data-integration approach improves soil-moisture estimates.

     

Porphyry fertility in the Northparkes district: indicators from whole-rock geochemistry

Abstract

Four economic porphyry Cu–Au deposits and several prospects have been investigated in the Northparkes district, part of the Ordovician to early Silurian Junee–Narromine Belt of the Macquarie Arc, New whole-rock geochemical data from the Northparkes porphyry Cu–Au district, NSW, indicate that the mineralising intrusive complexes exhibit distinct arc signatures that are transitional from high-K calc-alkaline to silica-saturated alkalic. Based on ratios of Sr/Y vs Y (e.g. Sr/Y > ～20 and Y < ～17?ppm) the mineralising intrusions are interpreted to have crystallised from fractionated hydrous melts indicating the suppression of plagioclase crystallisation in favour of hydrous mineral phases. This interpretation is supported by listric-shaped rare earth element curves and the presence of primary hornblende phenocrysts indicating elevated magmatic water contents. There is an association of mineralising intrusions with a low Zr trend both in the mineralised Northparkes district intrusive rocks and in mineralised porphyry-related intrusive rocks globally. A newly developed fertility indicator ratio Zr/Y ～10% is more accurate at identifying the mineralised rocks at Northparkes than the conventional Sr/Y vs Y fertility indicator diagram, successfully identifying 92% of the mineralising intrusions, mainly owing to the fact that it is less affected by hydrothermal alteration. The insensitivity of Zr–Y to alteration makes this indicator a useful new tool that may lead to enhanced probabilities for future discoveries in the Northparkes district, broader Macquarie Arc and altered rocks globally.

1. KEY POINTS

2. Mineralising intrusions in the Northparkes district have distinct Zr vs Y concentrations.

3. The Zr vs Y indicator of magmatic fertility is less sensitive to alteration than Sr-based indicators.

4. The Zr vs Y magmatic fertility indicator identified at Northparkes is not unique and identifies mineralising intrusions in other porphyry fields.