珠江口盆地多期走滑构造与叠合型拉分盆地:以阳江东凹为例

珠江口盆地的成盆机制和构造演化过程探讨是该地区烃源岩研究中不可缺少的环节,也是大家广泛关注的焦点问题.本文以阳江东凹为例,通过整体与局部相结合的分析方法,从整体上确定了研究区走滑断裂的发育特征和展布框架,明确了区域构造运动与走滑断裂的成因联系;并将整体划分成局部,聚焦于阳江东凹古近纪盆地构造演化阶段逐步分解与精细检验,...     

南天山西段南缘断裂构造特征及对乌什凹陷发育的控制

乌什凹陷位于南天山西段以南,新生代受南天山崛起的陆内造山作用制约,与库车坳陷有相同的成盆动力学背景。因乌什凹陷南有温宿凸起阻挡了挤压应力的传播,东与库车坳陷间有北西向的构造变换带(西秋里塔格构造带)所隔,新生代变形与库车地区有不同的特征。以吉迪克组的泥岩层为滑脱面,乌什凹陷的中-新生界可分为上、下两个构造层,总体看上构造层以背冲构造为特征,下构造层则发育基底卷入的对冲构造。乌什凹陷的这一变形特征还与新生代挤压应力场自东向西迁移和走滑作用吸收了部分冲断变形有关,反映了南天山新生代构造对海西-印支期碰撞构造的继承性。文章简述了南天山造山带的构造演化,介绍了乌什凹陷周缘的主要断裂的特征,恢复了乌什凹陷中-新生代的演化并与库车坳陷进行了对比。在此基础上探讨了乌什凹陷的成盆动力学机制,分析了乌什凹陷与南天山造山带的耦合演化,指出该区的油气勘探应以三叠系为主要目的层。     

苏丹Muglad盆地中南部西斜坡沉积层序及有利地层圈闭预测

苏丹Muglad盆地油气资源丰富,是重要的油气探区.盆地中南部西斜坡位于Kaikang坳陷西部斜坡带,是Muglad盆地重要的勘探区之一.研究区在构造转型时期遭受严重剥蚀,目前残余地层厚度约为5 000 m.受区域构造活动的影响,研究区的沉积储层发育演化与构造演化密切相关.随着构造圈闭勘探进入中后期,寻找新的勘探领域和...     

Matt Wilson structure: record of an impact event of possible Early Mesoproterozoic age,Northern Territory

The Matt Wilson structure is a circular 5.5 km-diameter structure in Early Mesoproterozoic or Neoproterozoic rocks of the Victoria Basin, Northern Territory. It lies in regionally horizontal to gently dipping Wondoan Hill and Stubb Formations (Tijunna Group) and Jasper Gorge Sandstone (Auvergne Group). An outer circumferential syncline with dips of 5?–?40° in the limbs surrounds an intermediate zone with faulted sandstone displaying horizontal to low dips, and a central steeply dipping zone about 1.5 km across. Several thrust faults in the outer syncline appear to indicate outward-directed forces. The central zone, marked by steeply dipping to overturned Tijunna Group and possibly Bullita Group sandstone and mudstone, indicates uplift of at least 300 m. The rocks are intensely fractured with some brecciation, and contain numerous planar to subtly undulating surfaces displaying striae which resemble shatter cleavage. Thin-sections of sandstone from the central area show zones of intense microbrecciation and irregular and planar fractures in quartz, but no melt-rocks have been identified. The planar fractures occur in multiple intersecting parallel sets typical of relatively low-level (5?–?10 GPa) shock-pressure effects. Alternative mechanisms, i.e. igneous intrusion, carbonate collapse, diapirism and regional deformation processes, have been discounted. The circular nature, central uplift, faulting, shatter features and planar fractures are all consistent with an impact origin. The Matt Wilson structure is most likely a deeply eroded impact structure in which the more highly shocked rocks of the original crater floor have been removed by erosion. Estimates of the age of the Auvergne and Tijunna Groups range from Early Mesoproterozoic (which we favour) to Late Neoproterozoic. Early Cambrian Antrim Plateau Volcanics near the impact structure show no signs of impact effects, allowing the age of impact to be constrained between Early Mesoproterozoic and Early Cambrian. The presence of widespread soft-sediment deformation features, apparently confined to a single horizon in the Saddle Creek Formation some 700?–?1000 m stratigraphically higher in the Auvergne Group than the rocks at the impact site, and apparently increasing in thickness towards the Matt Wilson structure, lead us to speculate that this probable event horizon is related to the impact event: if correct the impact occurred during deposition of the Saddle Creek Formation.     

Paleoclimate studies and natural-resource management in the Murray-Darling Basin I: past,present and future climates

This paper provides an incisive review of paleoclimate science and its relevance to natural-resource management within the Murray-Darling Basin (MDB). The drought of 1997–2010 focussed scientific, public and media attention on intrinsic climate variability and the confounding effect of human activity, especially in terms of water-resource management. Many policy and research reviews make statements about future planning with little consideration of climate change and without useful actionable knowledge. In order to understand future climate changes, modellers need, and demand, better paleoclimate data to constrain their model projections. Here, we present an insight into a number of existing long-term paleoclimate studies relevant to the MDB. Past records of climate, in response to orbital forcing (glacial–interglacial cycles) are found within, and immediately outside, the MDB. High-resolution temperature records, spanning the last 10⁵ years, exist from floodplains and cave speleothems, as well as evidence from lakes and their associated lunettes. More recently, historical climate records show major changes in relation to El Niño–Southern Oscillation cycles and decadal shifts in rainfall regimes. A considerable body of research currently exists on the past climates of southeastern Australia but, this has not been collated and validated over large spatial scales. It is clear that a number of knowledge gaps still exist, and there is a pressing need for the establishment of new paleoclimatic research within the MDB catchment and within adjacent, sensitive catchments if past climate science is to fulfil its potential to provide policy-relevant information to natural-resource management into the future.     

Preliminary 3–D geological model of the Kalgoorlie region,Yilgarn Craton,Western Australia,based on deep seismic‐reflection and potential‐field data

The granite‐greenstone terranes of the Eastern Goldfields Province, Yilgarn Craton, Western Australia, are a major Australian and world gold and nickel source. The Kalgoorlie region, in particular, hosts several world‐class gold deposits. To attempt to understand why these deposits occur where they do, it is important to understand the crustal architecture in the region and how the major mineral systems operate in this architecture. One way to understand these relationships is to develop a detailed 3–D geological model for the region. The best method to map the 3–D geometry of major geological structures is by acquisition and interpretation of seismic‐reflection profiles. To contribute to this aim, a grid of deep seismic‐reflection traverses was acquired in 1999 to examine the 3–D geometry of the region in an area including the Kalgoorlie mineral region and mineral fields to the north and west. This grid was tied to the 1991 regional deep seismic traverse and 1997 high‐resolution seismic profiles in the same region. The grid covers an area measuring approximately 50 km wide by 50 km long and extended to a depth of approximately 50 km (below the base of the crust in this region). The resulting 3–D geological model was further constrained by both surface geological data and geophysical interpretations, with the seismic interpretations themselves also constrained by gravity and magnetic modelling. The 3–D model was used to investigate the geometric relationships between the major faults and shear zones in the area, the relationship between the granite‐greenstone succession and the basement, and the spatial relationships between the greenstones and the granites. Interpretation of the grid of seismic lines and construction of the 3–D geological model confirmed the existence of the detachment surface and led to the recognition that the granite‐greenstone contact usually occurs at a much shallower level than the detachment. Also, west‐dipping faults in the vicinity of the Golden Mile, including the Abattoir Shear through to Boulder‐Lefroy Fault, appear to be more important than previously thought in controlling the structure of that area. An antiformal thrust stack occurs beneath a triangle zone centred on the Golden Mile. The Black Flag Group was deposited in a probable extensional setting, and late extension was also probably more important than previously thought. The granite‐gneiss domes were uplifted by the formation of antiformal thrust stacks at depth beneath them.     

Potential Influence of a Developing La Niña on the Sea-Ice Reduction in the Barents–Kara Seas

Abstract

The potential influence of a developing La Niña on Arctic sea-ice annual variability is investigated using both observational data and an atmospheric general circulation model. It is found that during the developing phase of an eastern Pacific (EP) La Niña event in June, July, and August (JJA) and September, October, and November (SON), the sea-ice concentration (SIC) over the Barents–Kara Seas declines more than 15%. The local atmospheric circulation pattern associated with the EP La Niña is characterized as a weak decrease in geopotential height over the Barents–Kara Seas, combined with an anticyclone in the North Atlantic. The corresponding southerly winds push warm waters northward into the key sea-ice reduction region and directly accelerate sea-ice melt. Meanwhile, the abundant moisture contained in the lower troposphere is transported into the Arctic region by winds resulting from the local barotropic structure. The humid atmosphere contributes to both net shortwave and longwave radiation and thus indirectly accelerates the decline in sea ice. Simulations by the European Centre Hamburg Model, version 5.4, are forced by observed sea surface temperature anomalies associated with EP La Niña events. The results of the simulations capture the North Atlantic anticyclone and reproduce the moisture transport, which supports the premise that an EP La Niña plays a crucial role in sea-ice reduction over the Barents–Kara sector from the perspective of atmospheric circulation and net surface heat flux.     

Constraining sequence stratigraphy in north Australian basins: SHRIMP U–Pb zircon geochronology between Mt Isa and McArthur River

Fifty‐five new SHRIMP U–Pb zircon ages from samples of northern Australian ‘basement’ and its overlying Proterozoic successions are used to refine and, in places, significantly change previous lithostratigraphic correlations. In conjunction with sequence‐stratigraphic studies, the 1800–1580 Ma rock record between Mt Isa and the Roper River is now classified into three superbasin phases—the Leichhardt, Calvert and Isa. These three major depositional episodes are separated by ～20 million years gaps. The Isa Superbasin can be further subdivided into seven supersequences each 10–15 million years in duration. Gaps in the geological record between these supersequences are variable; they approach several million years in basin‐margin positions, but are much smaller in the depocentres. Arguments based on field setting, petrography, zircon morphology, and U–Pb systematics are used to interpret these U–Pb zircon ages and in most cases to demonstrate that the ages obtained are depositional. In some instances, zircon crystals are reworked and give maximum depositional ages. These give useful provenance information as they fingerprint the source(s) of basin fill. Six new ‘Barramundi’ basement ages (around 1850 Ma) were obtained from crystalline units in the Murphy Inlier (Nicholson Granite and Cliffdale Volcanics), the Urapunga Tectonic Ridge (‘Mt Reid Volcanics’ and ‘Urapunga Granite’), and the central McArthur Basin (Scrutton Volcanics). New ages were also obtained from units assigned to the Calvert Superbasin (ca 1740–1690 Ma). SHRIMP results show that the Wollogorang Formation is not one continuous unit, but two different sequences, one deposited around 1730 Ma and a younger unit deposited around 1722 Ma. Further documentation is given of a regional 1725 Ma felsic event adjacent to the Murphy Inlier (Peters Creek Volcanics and Packsaddle Microgranite) and in the Carrara Range. A younger ca 1710 Ma felsic event is indicated in the southwestern McArthur Basin (Tanumbirini Rhyolite and overlying Nyanantu Formation). Four of the seven supersequences in the Isa Superbasin (ca 1670–1580 Ma) are reasonably well‐constrained by the new SHRIMP results: the Gun Supersequence (ca 1670–1655 Ma) by Paradise Creek Formation, Moondarra Siltstone, Breakaway Shale and Urquhart Shale ages grouped between 1668 and 1652 Ma; the Loretta Supersequence (ca 1655–1645 Ma) by results from the Lady Loretta Formation, Walford Dolomite, the upper part of the Mallapunyah Formation and the Tatoola Sandstone between ca 1653 and 1647 Ma; the River Supersequence (ca 1645–1630 Ma) by ages from the Teena Dolomite, Mt Les and Riversleigh Siltstones, and Barney Creek, Lynott, St Vidgeon and Nagi Formations clustering around 1640 Ma; and the Term Supersequence (ca 1630–1615 Ma) by ages from the Stretton Sandstone, lower Doomadgee Formation and lower part of the Lawn Hill Formation, mostly around 1630–1620 Ma. The next two younger supersequences are less well‐constrained geochronologically, but comprise the Lawn Supersequence (ca 1615–1600 Ma) with ages from the lower Balbirini Dolomite, and lower Doomadgee, Amos and middle Lawn Hill Formations, clustered around 1615–1610 Ma; and the Wide Supersequence (ca 1600–1585 Ma) with only two ages around 1590 Ma, one from the upper Balbirini Dolomite and the other from the upper Lawn Hill Formation. The Doom Supersequence (<1585 Ma) at the top of the Isa Superbasin is essentially unconstrained. The integration of high‐precision SHRIMP dating from continuously analysed stratigraphic sections, within a sequence stratigraphic context, provides an enhanced chronostratigraphic framework leading to more reliable interpretations of basin architecture and evolution.     

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.     

On the magnetic field diffusion in mhd modeling of the inner coma of comet halley

Abstract

Some approaches of one-dimensional time-dependent magneto-hydrodynamic modeling of the structure of the inner coma of comet Halley are considered. The influence of the magnetic field diffusion on this structure is studied. The solution of Cravens (1989) approach containing classic magnetic diffusion is compared with an approach containing a specific diffusion, caused by non-instantaneous mass-loading of new ions. A case with no magnetic field is also considered. Common features of all the solutions are obtained. Special attention is paid to the sharp velocity jump, synchronized with a local density pick. Some differences between two types of magnetic field diffusion are discussed. A possible connection is supposed between this consideration and the large-scale shock fitting modeling of the solar plasma-comet interaction.