Sedimentology and kinematics of a large, retrogressive growth-fault system in Upper Carboniferous deltaic sediments, western Ireland

Growth faulting is a common feature of many deltaic environments and is vital in determining local sediment dispersal and accumulation, and hence in controlling the resultant sedimentary facies distribution and architecture. Growth faults occur on a range of scales, from a few centimetres to hundreds of metres, with the largest growth faults frequently being under‐represented in outcrops that are often smaller than the scale of feature under investigation. This paper presents data from the exceptionally large outcrops of the Cliffs of Moher, western Ireland, where a growth‐fault complex affects strata up to 60 m in thickness and extends laterally for ≈ 3 km. Study of this Namurian (Upper Carboniferous) growth‐fault system enables the relationship between growth faulting and sedimentation to be detailed and permits reconstruction of the kinematic history of faulting. Growth faulting was initiated with the onset of sandstone deposition on a succession of silty mudstones that overlie a thin, marine shale. The decollement horizon developed at the top of the marine shale contact for the first nine faults, by which time aggradation in the hangingwall exceeded 60 m in thickness. After this time, failure planes developed at higher stratigraphic levels and were associated with smaller scale faults. The fault complex shows a dominantly landward retrogressive movement, in which only one fault was largely active at any one time. There is no evidence of compressional features at the base of the growth faults, thus suggesting open‐ended slides, and the faults display both disintegrative and non‐disintegrative structure. Thin‐bedded, distal mouth bar facies dominate the hangingwall stratigraphy and, in the final stages of growth‐fault movement, erosion of the crests of rollover structures resulted in the highest strata being restricted to the proximity of the fault. These upper erosion surfaces on the fault scarp developed erosive chutes that were cut parallel to flow and are downlapped by the distal hangingwall strata of younger growth faults.     

Permo-Carboniferous Radiolarians from the Wupata''''erkan Group,Western South Tianshan, Xinjiang, China

1 IntroductionThe Wupata'erkan Group, also called Wupata'erkanFormation (Wang et al., 1990), in the western SouthTianshan, China (Fig. 1), mainly comprises gray and darkgray fine-grained clastic rocks, interlayered with medium-acidic volcanic rocks (andesite and quartz porphyry),carbonates, cherts and variegated tuffaceousconglomerates. The chert in the formation was firstly foundin our field trip along sections of the Qiqi'erjianakesu Riverand Kekebiele Daban. Deformation of the group is…     

Modélisation géométrique 3D des granites stéphaniens du massif du Pelvoux (Alpes,France)

The structural analysis and the 3D modelling of Stephanian granites of the Pelvoux Massif characterize an emplacement along sinistral NW–SE- and dextral NE–SW-trending shear zones in the Pelvoux and in the Aiguilles Rouges–Mont Blanc Massifs, respectively. This Carboniferous shear system is consistent with a north–south extension direction known in the whole Variscan belt at this time. To cite this article: P. Strzerzynski et al., C. R. Geoscience 337 (2005).     

Permo-Carboniferous Radiolarians from the Wupata＇erkan Group, Western South Tianshan, Xinjiang, China

The Wupata‘erkan Group, also called Wupata‘erkan Formation, distributed in the South Tianshan, Xinjiang,China, mainly consists of gray and dark gray fine-grained clastic rocks, interlayered with volcanic rocks, carbonates and cherts. Some ultra-basic rocks (blocks) punctuate the formation. The formation was variously assigned to Silurian-Middle Devonian, Silurian-Lower Devonian, and pre-Devonian, mainly based on Atrypa bodini Mansuy, Hypothyridina parallelepipedia (Brour.) and Prismatophyllum hexagonum Yoh collected from the limestone interlayers, respectively.However, radiolarian fossils obtained from 24 chert specimens of the Wupata‘erkan Group, mainly include Albaillella sp.cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon, Albaillella sp. cf. A. indensis Won, Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto, Albaillella sp. and Latentifistulidae gen. et. sp.indet., are earliest Carboniferous and Late Permian. The earliest Carboniferous assemblage is characterized by Albaillella sp. cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon and Albaillella sp. cf. A. indensis Won, and the Late Permian assemblage by Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto. This new stratigraphic evidence indicates that the Wupata‘erkan Group is possibly composed of rocks with different ages from Silurian to Permian, and therefore, it is probably an ophiolite mrlange. The discovery of Late Permian Albaillella sp. cf. A. excelsa provides more reliable evidence supporting the existence of a Permian relic ancient oceanic basin in the western part of Xinjiang South Tianshan.     

Carboniferous eclogite and garnet–omphacite granulite from northeastern Hainan Island,South China: Implications for the evolution of the eastern Palaeo‐Tethys

High‐P (HP) eclogite and associated garnet–omphacite granulite have recently been discovered in the Mulantou area, northeastern Hainan Island, South China. These rocks consist mainly of garnet, omphacite, hornblende, quartz and rutile/ilmenite, with or without zoisite and plagioclase. Textural relationships, mineral compositions and thermobarometric calculations demonstrate that the eclogite and garnet–omphacite granulite share the same three‐stage metamorphic evolution, with prograde, peak and retrograde P?T conditions of 620–680°C and 8.7–11.1 kbar, 820–860°C and 17.0–18.2 kbar, and 700–730°C and 7.1–8.5 kbar respectively. Sensitive high‐resolution ion microprobe U–Pb zircon dating, coupled with the identification of mineral inclusions in zircon, reveals the formation of mafic protoliths before 355 Ma, prograde metamorphism at c. 340–330 Ma, peak to retrograde metamorphism at c. 310–300 Ma, and subsequent pegmatite intrusion at 295 Ma. Trace element geochemistry shows that most of the rocks have a MORB affinity, with initial ε_Nd values of +2.4 to +6.7. As with similar transitional eclogite–HP granulite facies rocks in the thickened root in the European Variscan orogen, the occurrence of relatively high P?T metamorphic rocks of oceanic origin in northeastern Hainan Island suggests Carboniferous oceanic subduction leading to collision of the Hainan continental block, or at least part of it, with the South China Block in the eastern Palaeo‐Tethyan tectonic domain.     

广西隆安下石炭统都结微生物岩微相特征与沉积环境研究

广西隆安县都结乡发育的微生物岩产于下石炭统都安组中—上部地层,分布广、厚度大,是中国南方早石炭世报道较少的碳酸盐岩建造类型,具有较高的研究价值。该微生物岩以颗粒灰岩和粘结岩为主,生物含量丰富,包括微生物、有孔虫、棘皮类、钙球、腕足等。通过岩相分析,可识别出以下8种微相类型:MF1含亮晶胶结物的泥晶包壳生屑灰岩、MF2含腕足似球粒灰岩、MF3无纹层似球粒颗粒灰岩、MF4集合颗粒灰岩、MF5细密纹层状粘结岩、MF6内碎屑鲕粒灰岩、MF7鲕粒灰岩、MF8白云质鲕粒灰岩。伴随海平面升降变化,都结微生物岩沉积环境先后经历了FZ1台地边缘浅滩相、FZ2开阔台地相与FZ3局限台地相这三种沉积相带之间往复变化的沉积相模式。结合前人基础地质资料,该沉积相模式表明该微生物岩发育于低纬度孤立碳酸盐岩台地浅水环境,并经历了初期、主体时期和消亡期3个发育阶段,海平面虽伴有小幅波动,但整体呈下降趋势。微生物岩发育于晚古生代冰期与谢尔普霍夫生物灭绝事件前夕,该时期南盘江盆地微生物岩的富集与后生动物礁的缺失相耦合,海洋生态系统中生物组成发生显著变化。在此基础上,本文从微生物岩的角度初步探讨了冈瓦纳大陆冰川作用对北半球低纬度地区的影响。     

Paleomagnetism of the Carboniferous Rouchel Block,Tamworth Belt,and pole path revision for the New England Orogen,eastern Australia

Structural, magnetic and gravity trends of the southern New England Orogen (SNEO) indicate four oroclinal structures, none conclusively confirmed paleomagnetically. Curved structures of the Tamworth Belt (TB)—a continental forearc exposed across six tectono-stratigraphic blocks with interlinked Carboniferous stratigraphies and extensive ignimbritic rocks known to retain primary magnetisations despite prevalent overprinting—are prospective to oroclinal testing through comparison of Carboniferous pole paths for individual blocks. Pole paths (a) have been established for the Rocky Creek and Werrie blocks (northwestern/western TB), (b) are described herein for the Rouchel Block (southwestern TB), and (c) are forthcoming for the Gresford and Myall blocks (southern/southeastern TB). The Rouchel path derives from detailed paleomagnetic, rock magnetic and magnetic fabric studies. Thermal, alternating field and liquid nitrogen demagnetisations show a low-temperature overprint, attributed to late Oligocene weathering, and high-temperature (HT) primary and overprint components in both magnetite and hematite carriers, showing slight, systematic, directional differences with hematite providing the better cleaned site poles. Seven primary mean-site poles of Tournaisian and mainly Visean age and three overprint poles show six positive fold tests, five at 95% or higher confidence levels. Two dispersed groupings of intermediate (IT) and HT overprint site poles of Permian and Permo-Triassic age are attributed to early and late phases in oroclinal evolution of the SNEO. HT and IT/HT overprint site poles of mid-Carboniferous age are attributed to Variscan Australia–Asia convergence. Individual pole paths for the Rocky Creek, Werrie and Rouchel blocks show no noticeable rotation between them, indicating primary curvature for the southwestern TB. Their integrated SNEO pole path establishes a reference frame for determining rotations of the southern and southeastern TB.     

Petrogenesis of a late-Variscan rhyodacite at the Ossa Morena-Central Iberian zones boundary,Iberian Massif,Central Portugal: Evidence for the involvement of lithospheric mantle and meta-igneous lower crust

A late-Variscan rhyodacite is exposed at the contact between the Ossa Morena Zone and the Central Iberian Zone of the Iberian Massif, Central Portugal. Dykes of rhyodacite intruded the Série Negra Unit and the Sardoal Complex that are part of the Cadomian basement. The igneous crystallization age of the rhyodacite (308 ± 1 Ma) was obtained on igneous monazite by the ID-TIMS U-Pb method. It is broadly coeval with the emplacement of late-Variscan granitoids during the last deformation phase of the Variscan Orogeny (ca. 304–314 Ma) and with the development of the large late-Variscan strike-slip shear zones (ca. 307 Ma). The rhyodacite samples are calc-alkaline, show identical composition and belong to the same magmatic sequence. The rhyodacite isotopic signatures (Sm-Nd and δ¹⁸O) are consistent with depleted-mantle juvenile sources and the contribution of the meta-igneous lower crust. The input of mantle juvenile sources is related to Variscan reactivation of lithospheric fractures. The inherited Neoproterozoic (ca. 619 Ma) and Mesoproterozoic (ca. 1054 Ma) zircon ages, are similar to those of the Central Iberian Zone. This suggests that lower crust of the Central Iberian Zone was involved in the magma generation of the rhyodacite. Coeval late-Variscan magmatic rocks display a larger contribution from ancient crustal components, which may be attributed to the smaller volume and faster cooling rate of the rhyodacite and consequent lower melting of the crust. Mixing of juvenile mantle-derived melts with melts from the lower continental crust was followed by fractional crystallization of garnet and amphibole that remained in the source. Fractional crystallization of plagioclase, biotite, quartz and zircon occurred in shallower magma chambers. Fractional crystallization of zircon was not significant.     

新疆西准噶尔玛依勒山地区阔依塔斯杂岩体地球化学特征及锆石U-Pb年龄

新疆西准噶尔北部广泛发育中酸性侵入岩,其形成时代为晚石炭世—早二叠世,岩石类型为辉石闪长岩、石英闪长岩和花岗闪长岩。阔依塔斯杂岩体的形成年龄为(297±2)Ma,Si O2为52.40%~67.53%;高Al2O3,14.92%~17.85%;里特曼指数(δ)小于3.3,介于1.47~1.98;富钠贫钾,K2O/Na2O为0.15~0.49;铁高而镁低,Fe OT/Mg O为1.01~1.69。其稀土配分模式右倾,轻重稀土分馏明显,具有微弱铕正异常。地球化学和年代学特征表明:岩体形成于后碰撞演化的晚期阶段,这一时间早于东准噶尔后碰撞的时间(二叠纪末)。该杂岩体主体可能为幔源岩浆底侵镁铁质下地壳,导致发生部分熔融的产物。