青海南部治多-杂多地区早石炭世珊瑚组合和生物地理特征

青海南部下石炭统杂多群珊瑚化石丰富,下部为维宪阶Siphonodendron scitulus - Lithostrotionella zadoensis组合,产于下碳酸盐岩组和碎屑岩组,以群体的Siphonodendron属和Lithostrotionella属最为常见,以地方性属种为主;上部为维宪阶-谢尔普霍夫阶L...     

基于ICESat块域分析法探测2003～2008年南极冰盖质量变化

利用2003～2008年间的ICESat卫星激光测高数据,通过块域交叉点分析提取南极大陆冰盖表面高程变化信息,同时探讨了卫星激光测高不同任务间的系统偏差,结合冰盖地表粒雪密度模型探测南极大陆冰盖质量变化,并对其原因做了初步分析.结果显示南极大陆冰盖高度变化具有明显的年周期信号,平均周年振幅为2.21 cm.在南极大陆的...     

Stratigraphy,sedimentology, structure and tectonics of Lower Ordovician and Devonian strata of South Mootwingee,Darling Basin,western New South Wales

K‐Ar age measurements using the ⁴⁰Ar/³⁹Ar total fusion technique on nephrite from two occurrences in the Great Serpentine Belt southeast of Tamworth yielded ages of 273 ± 5.8 and 280 ± 5.6 m.y. The K‐Ar ages indicate that tectonic emplacement, during which the nephrite was produced as a reaction product between ultra‐mafic rock and country rock, occurred early in the Permian about 275–280 m.y. ago.     

Esk Trough—Yarraman Block contact,an unconformity: Its nature and implications for regional tectonics

Detailed field study in southeast Queensland has resulted in the interpretation of an unconformity at the base of the Esk Trough sequence at its contact with the Yarraman Block (Maronghi Creek beds and associated intrusions). Previously this contact had been considered to be faulted. The nature of the unconformity is very variable with the Esk Formation resting on freshly eroded surfaces, on mature palaeosols and on an immature palaeosol. Immediately above the unconformity, the Esk Formation variably comprises scree breccia, fluvial conglomerate and arenite, and alluvial fan conglomerate and arenite. North‐northwest‐south‐southeast‐striking faults are associated with the unconformity. Where the unconformity parallels these faults, it retains a relatively constant character, but where it is cut by these faults, it shows greater variability, a relationship interpreted to result from contemporaneous tectonism. The Glen Howden Fault extends into structurally disturbed areas previously described as ‘fractured anticlines’ and ‘complex anticlines’, which are here interpreted as flower structures and associated features. The south‐southeast extension of the Glen Howden Fault strikes obliquely across the Esk Trough to finally pass into the South Moreton Anticline previously interpreted as a positive flower structure, and resolves structural and stratigraphic observations that previously appeared anomalous. Inferred strike‐slip movement in the Esk Trough resulted from Early to Middle Triassic north‐northwest‐south‐southeast oblique transtension followed by Late Triassic transpression, and similar tectonism probably affected adjacent portions of the Yarraman Block.     

Carboniferous palaeogeography of the Yarrol and New England Orogens,eastern Australia

During the Carboniferous Period the Yarrol and New England Orogens comprised an active depositional margin east of cratonised parts of Australia. Patterns of deposition within the orogens were probably controlled by dextral shear systems believed responsible for tectonism and the positions of the various depositional elements (volcanic chain, shelf, slope and basin, pull‐apart troughs and graben), and global changes in sea level. These patterns are illustrated by a series of non‐palin‐spastic palaeogeographic reconstructions.

In the Early Carboniferous, similar patterns of deposition existed within the western volcanic chain, marine shelf, and eastern slope and basin provinces of both orogens. Sediments were deposited in two cycles. They range from volcanic fluvial and marine sandstone to siltstone, mudstone and turbidites. Complex depositional patterns within shelfal regions are shown in detailed palaeogeographic reconstructions.

This uniform pattern changed during the latest Visean and Namurian, with the uplift of the New England Arch, subsidence of a non‐marine graben (Werrie Trough) to the west, and development of a new shelf in the east. The Werrie Trough received volcanics as well as fluvial and glacigene sediments, and the shelf marine sandstone and siltstone. The Yarrol Orogen was unaffected by tectonism but there was a change in provenance.

Late in the Carboniferous the Yarrol Orogen was restructured by the intrusion of granitoids into the former volcanic chain, and development of the Yarrol and North D'Aguilar Troughs as probable pull‐apart basins. In the New England Arch, deformation and metamorphism were followed by intrusion of S‐type granitoids. A comparable episode of deformation and metamorphism affected the southeastern part of the Yarrol Orogen at the end of the Carboniferous Period. This partial cratonisation of the mobile zone was a prelude to widespread basin formation during the Permian Period.     

Editor's note

Postcratonization intrusions in the Yilgarn Block of Western Australia are predominantly dykes with high length/width ratios and sharp contacts with minimal thermal metamorphism of country rock. Dyke frequency and number of relative age relationships increase towards the exposed margins of the Yilgarn Block. Dykes in the northern, southern and western margins of the Yilgarn Block are mafic, ranging from gabbro to magnetite‐rich leucodolerite, and have apparently been intruded over a long time interval in response to periodic reactivation of the tectonically active craton margins. Dykes in the central Yilgarn Block range from porphyritic olivine picrite to magnetite‐rich quartz dolerite and display a spectrum of chemical compositions with an overall trend of tholeiitic iron‐enrichment. The concentration of both Archaean and Proterozoic rocks of high‐Mg nature in the central Yilgarn Block is suggestive of a fundamental control, perhaps in the mantle source area, and also indicates that ultramafic magmas were generated in the area over an extensive time interval. Dykes in the central Yilgarn Block were emplaced in tensional fractures from the Late Archaean until the culmination of a major marginal crust‐forming event at about 2000 Ma. On the basis of the limited data available, the dykes are similar to poststabilization swarms in other cratonic nucleii.     

Provenance comparisons between the Nambucca Block,Eastern Australia and the Torlesse Composite Terrane,New Zealand: connections and implications from detrital zircon age patterns

Detrital zircon U–Pb LAM-ICPMS age patterns for sandstones from the mid-Permian –Triassic part (Rakaia Terrane) of the accretionary wedge forming the Torlesse Composite Terrane in Otago, New Zealand, and from the early Permian Nambucca Block of the New England Orogen, eastern Australia, constrain the development of the early Gondwana margin. In Otago, the Triassic Torlesse samples have a major (64%), younger group of Permian–Early Triassic age components at ca 280, 255 and 240 Ma, and a minor (30%) older age group with a Precambrian–early Paleozoic range (ca 1000, 600 and 500 Ma). In Permian sandstones nearby, the younger, Late Permian age components are diminished (30%) with respect to the older Precambrian–early Paleozoic age group, which now also contains major (50%) and unusual Carboniferous age components at ca 350–330 Ma. Sandstones from the Nambucca Block, an early Permian extensional basin in the southern New England Orogen, follow the Torlesse pattern: the youngest. Early Permian age components are minor (<20%) and the overall age patterns are dominated (40%) by Carboniferous age components (ca 350–320 Ma). These latter zircons are inherited from either the adjacent Devonian–Carboniferous accretionary wedge (e.g. Texas-Woolomin and Coffs Harbour Blocks) or the forearc basin (Tamworth Belt) farther to the west, in which volcaniclastic-dominated sandstone units have very similar pre-Permian (principally Carboniferous) age components. This gradual variation in age patterns from Devonian–late Carboniferous time in Australia to Late Permian–mid-Cretaceous time in New Zealand suggests an evolutionary model for the Eastern Gondwanaland plate margin and the repositioning of its subduction zone. (1) A Devonian to Carboniferous accretionary wedge in the New England Orogen developing at a (present-day) Queensland position until late in the Carboniferous. (2) Early Permian outboard repositioning of the primary, magmatic arc allowing formation of extensional basins throughout the New England Orogen. (3) Early to mid-Permian translocation of the accretionary wedge and more inboard active-margin elements, southwards to their present position. This was accompanied by oroclinal bending which allowed the initiation of a new, late Permian to Early Triassic accretionary wedge (eventually the Torlesse Composite Terrane of New Zealand) in an offshore Queensland position. (4) Jurassic–Cretaceous development of this accretionary wedge offshore, in northern Zealandia, with southwards translation of the various constituent terranes of the Torlesse Composite Terrane to their present New Zealand position.     

扬子西缘元古宙峨边群烂包坪组地层归属及其锆石SHRIMP U-Pb年代学证据

扬子西缘峨边群地层序列一直以来存在争议,其时代归属缺乏地质年代学约束。通过对扬子西缘元古宙峨边群各组、段岩石组合特征、沉积充填序列及其沉积接触关系的综合分析,初步确定了峨边群烂包坪组地层归属。该地层应位于原峨边群上部,代表一次新的构造旋回开始,已不属于峨边群地层范畴。在烂包坪组下部凝灰岩中首次获得的(779.3±15.7) Ma锆石SHRIMP U Pb年龄,进一步证实其形成于新元古代,而非中元古代。(2 737±30) Ma和(2 480±29) Ma的两个单颗粒锆石SHRIMP U Pb年龄,表明扬子西缘峨边-金口河地区可能存在古老的新太古代结晶基底。这些研究成果和新的认识将有助于推动扬子西缘峨边群研究工作的深入开展。     

胜利青东区块沙河街组井壁稳定钻井液技术

青东区块位于济阳坳陷青东凹陷北部断阶带.沙河街组的地质构造复杂,局部断层发育,断层以下地应力作用明显,沙三段泥岩硬而脆,层理性强,从而使钻探中井壁失稳严重,曾经多次发生复杂事故,轻者反复划眼,严重者则卡钻,严重地制约该区块的勘探开发进程.通过优选铝胺抑制、封堵、防塌钻井液体系,并且在施工中采用合理的钻井液液柱压力支撑和联合多元协同抑制-强封堵-合理地控制流变性等技术措施,配合相应的现场维护处理工艺,保证了青东古1井沙河街组的井壁稳定,使该井提前完钻,钻井周期缩短了20％.     

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