Major fracture zones of Morocco: The South Atlas and the Transalboran fault systems

Within the fracturai pattern of Morocco, 35–45° and 70–90° directions are predominant. Most of the faults originated already during the Upper Palaeozoic and were repeatedly reactivated, later on. Two of the large fracture systems are considered here.The South Atlas fault system (SAF) is composed of different faults with directions varying between 45–90°. They were not functionally connected to the southern hinge of the High Atlas until its Miocene uplift. Today, it seems to be inactive on the whole. Both the tectonic data and the facies distribution of Mesozoic strata contradict clearly the interpretation that the SAF is a huge wrench-fault or even the Mesozoic plate margin of Africa. The SW striking Transalboran fault system (TAF) is still active. It crosses Morocco from Melilla to Agadir, showing again singular faults which are unified to extended lineaments only in a few areas. The intervals between the faults are bridged by linear arrangements of earthquake hypocenters. Sinistral massflow within the deeper parts of the lithosphere seems to be compensated at the surface by movements along pre-existing faults. For the Moroccan segment of the TAF, a sinsitral displacement is testified at least since the Oligocene, while the northeastern segments from the Rif to Spain did not even originate until the Pliocene. This would mean that sinistral shear was transmitted from Africa into the accreted Alboran and Iberia blocks after the Miocene collision.

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Zusammenfassung Unter den großen Störungen Marokkos dominieren die Richtungen 35–45° und 70–90°. Sie wurden zumeist im Jungpaläozoikum angelegt und später wiederholt reaktiviert. Zwei der großen Bruchsysteme wurden näher untersucht:Die Südatlas-Störungszone (SAF) besteht aus unzusammenhängenden Brüchen unterschiedlichen Alters, deren Streichrichtung von 45–90° variiert. Diese wurden erst bei der miozänen Heraushebung des Hohen Atlas zu dessen südlichem Scharnier umfunktioniert. Heute sind nur wenige Störungen des Systems aktiv. Diese Befunde und ebenso die stratigraphisch-fazielle Entwicklung im Mesozoikum Marokkos verbieten, die SAF als bedeutende Lateralverschiebungszone oder gar als nördliche Plattengrenze Afrikas zu interpretieren.Das noch heute aktive, SW-streichende Transalboran-Störungssystem (TAF) setzt sich durch Marokko von Melilla bis Agadir fort. Es besteht an der Oberfläche ebenfals aus singulären Brüchen, die sich nur bereichsweise zu längeren Linien zusammenschließen. Zwischen den Störungen vermitteln linear angeordnete Herde rezenter Erdbeben: Sinistraler Massentransport an einer Tiefenstörung wird an der Oberfläche durch Teilbewegungen an präexistenten Störungen kompensiert. Während in Marokko südlich des Rifs sinistraler Versatz mindestens seit dem Oligozän nachgewiesen ist, entstand die TAF vom Rif bis nach Spanien erst im Pliozän. Die sinistrale Scherung tritt also erst nach der miozänen Kollision von Afrika aus auf die nunmehr akkretierten Mikroplatten- Alboran-Block und Iberia - über.

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Résumé Les grandes fractures du Maroc présentent les deux directions prédominantes de 35°-40° et 70°–90°. La plupart de ces fractures datent du Paléozoïque supérieur et ont été réactivées plusieurs fois au Mésozoïque et au Cénozoïque. Deux de ces grands systèmes de fractures sont considérés ici.L'accident sud-atlasien (SAF) est composé de fractures indépendantes d'âges divers dont la direction varie entre 45° et 90°. Ces fractures ne se sont connectées à la charnière du Haut Atlas qu'après le soulèvement miocène de celui-ci. Aujourd'hui, quelques failles seulement sont encore actives. Ces observations, ainsi que la distribution des faciès du Mésozoïque au Maroc sont en contradiction avec le modèle qui voit dans le SAF une grande zone de décrochement ou même la marge nord de la plaque africaine.L'accident transalboran (TAF), encore actif aujourd'hui, traverse le Maroc en direction sudouest de Mélilla à Agadir. Il est composé de failles discontinues, connectées entre elles seulement à quelques endroits. Les intervalles qui séparent ces failles sont jalonnés par des alignements rectilignes d'hypocentres de séismes récents. L'ensemble correspond à un décrochement sénestre profond compensé en surface par des mouvements le long de failles préexistantes. Ce décrochement sénestre, dans le segment du TAF situé au sud du Rif, s'est manifesté au moins depuis l'Oligocène, tandis que la partie qui s'étend du Rif à l'Espagne méridionale n'a été active qu'à partir du Pliocène. Ceci signifie que ce cisaillement sénestre ne s'est transmis de l'Afrique vers l'Europe qu'après l'accrétion, au Miocène, de la microplaque Alboran et du bloc ibérique.

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Hydrochemical and isotopic characteristics of groundwater in the Souss Upstream Basin, southwestern Morocco

Heterogeneous shallow Plio-Quaternary formations of the Souss Plain represent the most important aquifer in southern High Atlas Mountains in Morocco. The present work was conducted in the Souss Upstream Basin to identify the chemical characteristics and the origin of groundwater in an aquifer under semi-arid climate. Isotopic and hydrochemical compositions combined with geological and hydrogeological data were used for this purpose. The total dissolved solids vary from 239 to 997 mg l⁻¹, and the following groundwater types are recognized: Ca²⁺–Mg²⁺–HCO₃⁻, Ca²⁺–Mg²⁺–SO₄²⁻ and Ca²⁺–Mg²⁺–Cl⁻. The groundwater is saturated and slightly supersaturated with respect to carbonate minerals and undersaturated with respect to evaporite minerals, which means that the groundwater composition is largely controlled by the dissolution of carbonate rocks known in the basin. The isotopic contents of groundwaters ranged from −8‰ to −5.2‰ for δ¹⁸O, from −52‰ to −34‰ for δD, and from 0 to 5.5 TU for tritium. The hydrogen (δD) and oxygen (δ¹⁸O) isotope signatures reveal a significant infiltration before evaporation takes place, indicating a major recharge directly from fractures in the crystalline and limestone formations of Atlas Mountains (above 800 m a.s.l.) and infiltration of surface water in the alluvial cones at the border of the Atlas basins. The very low tritium values suggest that the groundwater recharge follows a long flow path and a mixing between old and modern water is shown. However, a slight evaporation effect is noted in the southern part of the basin close to the Anti-Atlas Mountains.     

Petroleum source rocks of the Tarfaya Basin and adjacent areas, Morocco

This work characterizes the source rock potential of the Tarfaya Basin and enabled us to reconstruct its geochemical history. Outcrop samples covering different stratigraphic intervals, plus the northwestern part of the Zag/Tindouf Basin (Bas Draa area), were analyzed for total organic carbon (C_org) and total inorganic carbon contents and total sulfur content. Rock-Eval analysis and vitrinite reflectance measurements were performed on 56 samples chosen on the basis C_org content. A set of 45 samples were extracted and non-aromatic hydrocarbons were analyzed by way of gas chromatography-flame ionization detection (GC-FID) and GC-mass spectrometry (GC-MS). Non-isothermal open system pyrolysis at different heating rates was applied to obtain kinetic parameters for modelling petroleum generation from four different source rocks.High quality petroleum source rocks with high C_org content and hydrogen index (HI) values were found for samples of Eocene, Coniacian, Turonian and Cenomanian age. Most samples were carbonate rich and organic/sulfur values were high to moderate. Various maturity parameters indicated immature or possibly early mature organic matter. Based on organic geochemical and petrological data, the organic matter is of marine/aquatic origin (Cenomanian) or a mixture of aquatic and terrigenous material (Eocene). The Early Cretaceous interval did not contain high quality source rocks, but indications of petroleum impregnation were found.     

Oceanic events and biotic effects of the Cenomanian-Turonian anoxic event, Tarfaya Basin, Morocco

Profound biotic changes accompanied the late Cenomanian δ¹³C excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of Morocco. Planktic foraminifera experienced a severe turnover, though no mass extinction, beginning with the rapid δ¹³C excursion and accelerating with the influx of oxic bottom waters during the first peak and trough of the excursion. Species extinctions equaled the number of evolving species, though only the disaster opportunists Guembelitria and Hedbergella thrived along with a low oxygen tolerant benthic assemblage. The succeeding δ¹³C plateau and organic-rich black shale deposition marks the anoxic event and maximum biotic stress accompanied by a prolonged drop in diversity to just two species, the dominant (80–90%) low oxygen tolerant Heterohelix moremani and surface dweller Hedbergella planispira. After the anoxic event other species returned, but remained rare and sporadically present well into the lower Turonian, whereas Heterohelix moremani remained the single dominant species. The OAE2 biotic turnover suggests that the stress to calcareous plankton was related to changes in the watermass stratification, intensity of upwelling, nutrient flux and oxic levels in the water column driven by changes in climate and oceanic circulation. Results presented here demonstrate a 4-stage pattern of biotic response to the onset, duration, and recovery of OAE2 that is observed widely across the Tethys and its bordering epicontinental seas.     

Petrography and geochemistry of Cretaceous to quaternary siliciclastic rocks in the Tarfaya basin,SW Morocco: implications for tectonic setting,weathering, and provenance

The petrography, heavy mineral analysis, major element geochemical compositions and mineral chemistry of Early Cretaceous to Miocene–Pliocene rocks, and recent sediments of the Tarfaya basin, SW Morocco, have been studied to reveal their depositional tectonic setting, weathering history, and provenance. Bulk sediment compositional and mineral chemical data suggest that these rocks were derived from heterogeneous sources in the Reguibat Shield (West African Craton) including the Mauritanides and the western Anti-Atlas, which likely form the basement in this area. The Early Cretaceous sandstones are subarkosic in composition, while the Miocene–Pliocene sandstones and the recent sediments from Wadis are generally carbonate-rich feldspathic or lithic arenites, which is also reflected in their major element geochemical compositions. The studied samples are characterized by moderate SiO₂ contents and variable abundances of Al₂O₃, K₂O, Na₂O, and ferromagnesian elements. Binary tectonic discrimination diagrams demonstrate that most samples can be characterized as passive continental marginal deposits. Al₂O₃/Na₂O ratios indicate more intense chemical weathering during the Early Cretaceous and a variable intensity of weathering during the Late Cretaceous, Early Eocene, Oligocene–Early Miocene, Miocene–Pliocene and recent times. Moreover, weathered marls of the Late Cretaceous and Miocene–Pliocene horizons also exhibit relatively low but variable intensity of chemical weathering. Our results indicate that siliciclastics of the Early Cretaceous were primarily derived from the Reguibat Shield and the Mauritanides, in the SW of the basin, whereas those of the Miocene–Pliocene had varying sources that probably included western Anti-Atlas (NE part of the basin) in addition to the Reguibat Shield and the Mauritanides.     

Calcareous nannofossil biostratigraphy and paleoecology of the Cenomanian – Turonian transition in the Tarfaya Basin, southern Morocco

An abundant and diverse nannoflora occurs across the Cenomanian/Turonian (C/T) boundary at Tazra in the Tarfaya Basin of southern Morocco. The nannoflora of this sequence permits recognition of three biozones (CC10-CC12), three subzones (CC10a, CC10b and CC10c), and thirteen important nannolith bioevents previously reported from this interval elsewhere. The floral record shows erratic species abundance fluctuations that clearly vary with lithology and reflect at least in part preservational bias and diagenetic processes. In general, four dissolution resistant taxa are dominant: Watznaueria barnesae, Eiffellithus turriseiffelii, Eprolithus floralis, and Zeugrhabdotus spp. The late Cenomanian Zone CC10 marks a rapid excursion in ∂¹³C and is characterized by the successive extinction of four taxa, which are widely recognized as reliable biomarkers: Corollithion kennedyi, Axopodorhabdus albianus, Lithraphidites acutus, and Helenea chiastia. This interval is also marked by high species richness and high abundance of the tropical species Watznaueria barnesae, suggesting warm tropical waters. The subsequent ∂¹³C plateau and organic carbon-rich black shale deposition of the oceanic anoxic event (OAE2) is characterized by low species richness, but high nannofossil abundance, and peak abundance of the cool water and high productivity indicator Zeugrhabdotus spp., followed by the first peak abundance of cool water Eprolithus floralis. This interval correlates with the planktic foraminiferal diversity minimum and the Heterohelix shift, which marks the expansion of the oxygen minimum zone (OMZ). The C/T boundary is identified based on the FO of Quadrum gartneri, which is <1 m below the FO of the planktic foraminifer C/T marker Helvetoglobotruncana helvetica. In the early and middle Turonian, the two dominant species, tropical W. barnesae and cool water E. floralis, alternate in abundance and suggest fluctuating climatic conditions.     

Pseudotachylitic breccias from fault zones in the Witwatersrand Basin, South Africa: evidence of autometasomatism and post-brecciation alteration processes

Summary Pseudotachylitic breccias, associated with either bedding-parallel or normal faults, are abundant in the northern and northwestern parts of the gold- and uranium-rich Witwatersrand Basin in South Africa. They are particularly abundant in a zone tangential to the Vredefort Dome, a structure which is now widely accepted to be the eroded remnant of the central uplift of the originally 250 to 300 km wide Vredefort impact structure.Several of these fault zones were sampled along vertical traverses that included both fault breccias and host rocks. Geochemical analyses were undertaken to investigate the processes involved in fault rock formation. In addition, the temporal relationships of fault activity to regional geological events was studied. Detailed petrographic analysis shows evidence for strong hydrothermal overprints of the faults related to breccia formation (thus termed autometasomatism), as well as post-formational alteration. Mixing between two or more precursor lithologies and fluid alteration affected both the fault zones and their wall-rocks. A wide spectrum of trace elements, including Au and U, has been locally mobilised and redeposited by these processes.These fault zones, some of which are of basin-wide significance, were important channels for fluids that also modified the distribution of base metals in the Witwatersrand Basin. The regionally separated locations of our study areas suggest that these processes affected at least a major part of the basin. However, as the chemical characteristics determined for the fault zones differ from site to site, it is likely that the metals were only locally remobilised in the vicinity of fault zones or to previously hydrothermally altered country rock. Subsequent redeposition of metals was limited to the regimes in and around such fault zones.

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Pseudotachylitische Brekzien aus Störungszonen des Witwatersrand-Beckens: Hinweise auf Autometasomatose und Alteration nach der Brekzienbildung

Zusammenfassung Pseudotachylitische Brekzien, entweder an schicht-parallelen oder normalen Verwerfungen, kommen häufig im nördlichen und nordwestlichen Teil des Gold- und Uranreichen Witwatersrand Beckens in Südafrika vor. Man hat sie hauptsächlich von einem tangentialen Bereich um den Vredefort Dom beschrieben. Der Dom ist der tieferodierte Rest der zentralen Aufwölbung der Vredefort Impaktstruktur, die ursprünglich linen Durchmesser von mindestens 250 Km hatte.Einige dieser Verwerfungszonen wurden entlang von Traversen beprobt, die Verwerfungsbrekzien sowie deren Nebengesteine beinhalteten, und geochemisch mit dem Ziel untersucht, die Prozesse bei der Brekzien-Bildung und die zeitlichen Verhältnisse von Verwerfungen und regionalgeologischen Ereignissen zu erfassen. Petrographische Analysen zeigten, daß die Verwerfungszonen im Zusammenhang mit der Brekzierungsphase stark hydrothermal überprägt wurden (ein Prozess, der daher als Autometasomatose bezeichnet wird) und eine zweite Überprägungsphase erfahren haben, die nach der Brekzierung stattfand. Es wird gezeigt, daß sowohl Mischung von wenigstens zwei Mutter-Gesteinskomponenten und Flüssigkeitsüberprägung, die Verwerfungszonen und Nebengesteine betraf, wichtige Rollen in der Bestimmung der chemischen Charakteristiken der untersuchten Zonen spielten. Viele Elemente, darunter Gold und Uran, wurden durch diese Prozesse lokal mobilisiert und wieder abgelagert.Diese Verwerfungszonen, von denen einige eine beckenweite Bedeutung besitzen, agierten als wichtige Kanäle für Flüssigkeiten, die die Verbreitung von wichtigen Metallen im Witwatersrand Becken modifizieren konnten. Da unsere Untersuchungsorte weit voneinander getrennt liegen, muß angenommen werden, daß diese Prozesse wenigstens weite Teile des Beckens beeinflußten. Da jedoch die chemischen Charakteristika der untersuchten Zonen von Fall zu Fall unterschiedlich sind, liegt die Vermutung nahe, daß Metalle höchstens lokal mobilisiert und umgelagert wurden und daß dies vermutlich im wesentlichen in der Nähe von existierenden Reefs stattfand. Es ist ferner klar, daß die Umlagerung von Metallen auf die unmittelbaren Bereiche dieser Verwerfungszonen beschränkt war.

     

Neoproterozoic tectonic evolution of the Hongseong area, southwestern Gyeonggi Massif, South Korea; implication for the tectonic evolution of Northeast Asia

Two types of Neoproterozoic metabasites occur together with regionally intruded arc-related Neoproterozoic granitoids (ca. 850–830 Ma) in the Hongseong area, southwestern Gyeonggi Massif, South Korea, which is the extension of the Dabie–Sulu collision belt in China. The first type of metabasite (the Bibong and Baekdong metabasites) is a MORB-like back-arc basin basalt or gabbro formed at ca. 890–860 Ma. The Bibong and Baekdong metabasites may have formed during back-arc opening by diapiric upwelling of deep asthenospheric mantle which was metasomatized by large ion lithophile element (LILE) enriched melt or fluid derived from the subducted slab and/or subducted sediment beneath the arc axis. The second type of metabasite (the Gwangcheon metabasite) formed in a plume-related intra-continental rift setting at 763.5 ± 18.3 Ma and is geochemically similar to oceanic island basalt (OIB). These data indicate a transition in tectonic setting in the Hongseong area from arc to intra-continental rift between ca. 830 and 760 Ma. This transition is well correlated to the Neoproterozoic transition from arc to intra-continental rift tectonic setting at the margin of the Yangtze Craton and corresponds to the amalgamation and breakup of Rodinia Supercontinent.     

塔里木盆地塔中低凸起北斜坡古生代断裂展布与构造演化

通过对塔中低凸起北斜坡4500km2三维地震数据体的精细解析,根据不整合面和生长地层分析以及断层与地层之间的接触关系,厘定划分出四期不同应力性质的断裂体系,分别为寒武-早奥陶世拉张断裂,晚奥陶世冲断挤压和北西向走断裂,志留-泥盆纪北东向走滑断裂以及二叠纪的岩浆刺穿。寒武-早奥陶世拉张断裂展布形态和发育规模奠定了后期构造活动的基础;晚奥陶世断裂呈发散的帚状,向东南方向收敛,断裂分布具有明显的分带和分段性,东部主要为逆冲断裂,中西部发育北西向走滑断裂,晚奥陶世断裂体系可划分为六组呈北西向展布的弧型断裂带,各弧形断裂带由多条断裂组成,其形成可能与古生代阿尔金北缘北西向冲断挤压有关;塔中志留-泥盆纪走滑断裂体系主要是在挤压应力环境下形成的,呈北东向展布,走滑断裂体系由三部分组成：主干边界断裂、尾端羽列断裂和拉分地堑,其中主干断裂剖面上表现为高角度近似直立断面,直插基底,延伸较远,剖面上呈花状构造,尾端羽列断裂在主干断层的尾端发育,主要位于主干断裂的北端,拉分地堑平面上呈菱形,受多级断层控制;二叠纪岩浆刺穿在塔中三维区呈点状或条带状,岩浆刺穿对早期断裂进行叠置和改造,岩浆侵入和底辟作用致使地层隆升,形成一系列逆断层性质的“正花状构造”。构造活动决定了断裂发育,早古生代塔里木盆地及其周缘地区伸展－聚敛构造演化构成了一个较为完整的威尔逊旋回,寒武纪－早奥陶世塔里木周缘古大洋拉张裂解,早奥陶世末－晚奥陶世部分古大洋俯冲消减,晚奥陶世－泥盆纪周缘大洋部分闭合,发生弧陆或陆陆碰撞,二叠纪岩浆活动代表了另一个构造旋回的开始。     

A Middle Jurassic sauropod tracksite in the Argana Basin,Western High Atlas,Morocco: an example of paleoichnological heritage for sustainable geotourism

A Middle Jurassic site at Tafaytour area (Argana Basin, Morocco) with trackways of six large sauropod dinosaurs is regarded as having high scientific and touristic value. The new dinosaur track site is extremely vulnerable, and suffers from continuous degradation caused by weathering and human activity. Documentation and protection of this tracksite is still a necessity for its integration into local geotourism activities, where it may have a socio-economic impact on the local population. Taking into consideration many similar tracksites, and strata of great paleontological interest in Morocco, including the Tafaytour tracksite, the implementation of legislation for the protection of Morocco's geological heritage, especially the paleoichnological heritage, to protect against destruction, is strongly recommended. This is necessary to cement geoheritage impact, both for scientific reasons and to value add to the socio-economic activities of the local people.     

Magnetostratigraphy of the Ouarzazate Basin: Implications for the timing of deformation and mountain building in the High Atlas Mountains of Morocco.

Two magnetostratigraphic profiles (450 samples) have been carried out to constrain the age of synorogenic formations in the southern foreland of the High Atlas of Morocco. The Amekchoud profile covers the Aït Ouglif and Aït Kandoula alluvial formations that form the bulk of the Ouarzazate basin fill, indicating an age between the upper Langhian and the Messinian (Miocene). Data obtained in the previously unexplored Hadida formation profile covers the oldest terms of the foreland basin succession, but the low quality of the magnetic record only allows proposing a tentative age between the middle Lutetian and an undetermined middle to late Eocene. The correlation of the Amekchoud profile is based on the recognition of the long C5n chron (Tortonian) in the middle part of the section studied and a new vertebrate locality of upper Tortonian age found in the upper part. These results indicate a discontinuous record of foreland basin development in the southern Atlas domain from mid Eocene to late Miocene times, punctuated by an intermediate large hiatus of 20-25 ma (late Eocene to mid Miocene). Thrusting in the Sub-Atlas frontal thrust belt began before the Aït Ouglif and Kandoula formations, probably during the Oligocene, and extends up to recent times. The alternation of periods of deposition with others of no sedimentary record, which does not coincide with specific tectonic events, results probably from the interference of orogenic deformation and the mantle-related thermal uplift events that have been described for the Moroccan Atlas.     

四川盆地中部主干走滑断裂带及伴生构造特征与演化

根据下—中三叠统嘉陵江组和雷口坡组膏盐岩层内的伴生构造及上震旦统灯影组台缘带被错动的位置、方向与距离,判定川中及北斜坡地区主干走滑断裂带的性质与分布规律。嘉陵江组和雷口坡组膏盐岩层内发育多排呈左阶排列的NW向雁列式构造,与深部(盐下)走滑断裂构成2种伴生组合。第1种组合主要发育在磨溪地区,膏盐岩层内的雁列式构造位于深部走滑断裂的正上方;第2种组合主要发育在北斜坡地区,膏盐岩层内的雁列式构造发育在2条主干走滑断裂带之间。根据这2种组合及灯影组台缘带的错动位置,共识别出6条主干走滑断裂带。在盆地整体演化格架的制约下,通过川中地区代表性生长构造的定量解析,将走滑断裂演化划分为3个阶段:(1)晚奥陶世—志留纪右行走滑阶段;(2)晚古生代—三叠纪走滑断裂沉寂阶段;(3)中侏罗世至今左行走滑阶段。其中,上震旦统灯影组二段台缘带呈现出有规律的向东逐段错动(错动距离20~40 km)的特征,可作为加里东期右行走滑活动的间接证据;川中及北斜坡地区在晚三叠世处于扬子地块北缘和雪峰山前陆盆地前缘隆起的隆后稳定地区,而中侏罗世以来周缘造山带的急剧隆升与差异性演化使得川中地区遭受持续的挤压和抬升,激发了基底断裂与早期走滑断裂的再次活动。     

青藏高原东缘鲜水河断裂带磁组构特征及构造意义

为了探究鲜水河断裂带的几何学、运动学特征,在野外构造、显微构造分析基础上,研究了鲜水河断裂带296块构造岩定向样品的磁组构特征和热磁特征,结果显示样品的平均磁化率km值总体较小,属微弱磁性到弱磁性;热磁实验及其显微构造表明顺磁性的页硅酸盐(如黑云母)等矿物对糜棱岩类样品磁化率贡献较大;磁化率各向异性度PJ总体较大,表明鲜水河断裂带构造变形强烈;磁化率椭球体形状参数T总体大于0,扁率E总体在1附近分布,说明鲜水河断裂带磁化率椭球体以扁圆形为主,整体上磁面理较磁线理发育,进一步显示出鲜水河断裂带构造变形样式以剪切、压扁为主,伴有拉伸的构造变形,同时也反映出鲜水河断裂带多次变形的综合特征;最小磁化率主轴Kmin方位表明鲜水河断裂带北段和南段分别受近EW向和NE-SW向主压应力控制;同时Kmin方位及其倾伏角特征显示鲜水河断裂带总体以左行走滑剪切为主,北段两侧块体在鲜水河断裂带两次不同的构造活动时期,各自有一定的相对抬升,但抬升幅度均不大;南段则是SW块体相对NE块体抬升,抬升幅度较大;整个断裂带特征显示出鲜水河断裂带在向南发展逐渐转化为挤压构造,这可能与青藏高原物质的向东逃逸受阻以及鲜水河断裂带与龙门山断裂带在此交接的地质背景不无关系.     

南海礼乐盆地新生代构造层序界面特征及油气地质意义

礼乐盆地是中国南海深水领域一个重要的含油气盆地,具有较好的油气资源前景。应用沉积学和层序地层学的原理和方法,结合区域构造演化特征,详细研究了礼乐盆地新生代沉积充填过程中关键构造层序界面（S100、S70、S50）在钻井岩性、测井曲线、古生物及地震剖面上的特征。结果表明,构造层序界面为岩性、电性的突变面,在构造层序界面附近,古生物演化过程中存在标志生物种属和数量的突变。在地震剖面上,构造层序界面是区域性的不整合界面,表现为明显的上超、下超或削截特征。进而详细论述了这3个构造层序界面形成的油气地质意义,具体表现为：（1）反映了关键时期礼乐盆地性质的转化;（2）有利于形成优质储集空间;（3）层序不整合面既是油气横向长距离运移的重要通道,也是礼乐盆地油气藏成藏的关键。     

High-yielding aquifers in crystalline basement: insights about the role of fault zones,exemplified by Armorican Massif,France

While groundwater constitutes a crucial resource in many crystalline-rock regions worldwide, well-yield conditions are highly variable and barely understood. Nevertheless, it is well known that fault zones may have the capacity to ensure sustainable yield in crystalline media, but there are only a few and disparate examples in the literature that describe high-yield conditions related to fault zones in crystalline rock basements. By investigating structural and hydraulic properties of remarkable yielding sites identified in the Armorican Massif, western France, this study discusses the main factors that may explain such exceptional hydrogeological properties. Twenty-three sites, identified through analysis of databases available for the region, are investigated. Results show that: (1) the highly transmissive fractures are related to fault zones which ensure the main water inflow in the pumped wells; (2) the probability of intersecting such transmissive fault zones does not vary significantly with depth, at least within the range investigated in this study (0–200 m); and (3) high yield is mainly controlled by the structural features of the fault zones, in particular the fault dip and the presence of a connected storage reservoir. Conceptual models that summarize the hydrological properties of high-yield groundwater resources related to fault zones in crystalline basement are shown and discussed.     

中国南海礼乐盆地新生代断裂体系的发育与演化

断裂体系发育特征是礼乐盆地新生代构造演化的重要表现形式。运用研究区丰富的二维地震资料,在详细刻画主干断裂和次级断裂的几何学特征基础上,厘定了断裂体系各时期的活动规律,明确了断裂体系演化的时空差异性：古新世-早渐新世断裂体系以NNE向和NEE向主干断裂为主,早期整体断裂活动速率低且NNE向断裂占主导,后期NNE和NEE向断裂活动均大幅增强;晚渐新世-早中新世断裂体系表现为NNE和NEE向主干断裂继承性活动、NW向主干断裂和NEE-近EW向次级断裂形成;中中新世以来断裂体系活动微弱、消亡。响应于太平洋板块、欧亚板块和印澳板块交汇碰撞、古南海消亡以及新南海扩张的区域地质背景,礼乐盆地的新生代演化过程可分为陆缘裂陷(包括陆缘初始裂陷和陆缘强烈裂陷)、漂移裂陷及前陆拗陷三个阶段;古新世至早中新世拉张应力场由NWWSEE到SN向的顺时针转变和中中新世以来拗陷背景下来自东、南侧的挤压控制了礼乐盆地断裂体系的发育与演化。     

A revised ammonoid biostratigraphy for the Aptian of NW Africa: Essaouira-Agadir Basin,Morocco

A revised ammonoid biostratigraphy is presented for the Aptian of NW Africa, Essaouira-Agadir Basin (EAB), Morocco, based on detailed analysis of 5 key sections. A number of bio-events are documented and 26 genus and 43 species fully documented, forming the largest published Aptian ammonite collection made from NW Africa. The section at Tiskatine is documented as the type section, and 8 zones and subzones are defined, of which 5 are new. This work allows correlation of the Aptian of the EAB to the Standard Mediterranean Ammonite Scale (SMAS).Two main hiatuses are identified at the scale of the basin scale: a major one that includes most of the lower Aptian and the base of the upper Aptian and a second one encompass the top of the upper Aptian and the base of the lower Albian. The ammonite fauna displays a clear Tethyan palaeobiogeographic character affected by a fairly high degree of endemism at the genus and species level. The new genus and species Elsaisabellia tiskatinensis is introduced.     

Architecture and growth of normal fault zones in multilayer systems: A 3D field analysis in the South-Eastern Basin,France

3D field data on mesoscale normal faults were collected to examine the geometries and growth of faults in multilayer systems. Observation and analysis of the fractures include the collection of geometric attributes such as fault dips and fault zone thicknesses, detailed mapping in cross-sections and plan views, and the construction of individual and cumulative displacement profiles. Fault zone growth is consistent with a “coherent model” and is strongly influenced by the multilayer system. In the limestone layers, faults grew in several steps, including opening and frictional sliding on 80° dipping segments. Faulting in clay layers was in the form of 40° dipping faults and sub-horizontal faults, the latter being mostly early features developed under the same extensional regime as normal faults and disturbing the fault architecture. The fault zone thickness increases with the limestone thickness and the presence of sub-horizontal faults in clay beds. Numerous connections occur in clay units. The moderate (≈0.08) and low (<0.03) mean displacement gradients in clays and in limestones respectively indicate that the vertical propagation of faults is inhibited in clay layers. Analysis of displacement along fault strike indicates that a 0.08 displacement gradient is associated with the horizontal propagation of fault segments in limestones. According to this value, the fault zones are much longer than expected. It is associated with ‘flat topped’ displacement profiles along some fault segments and connection between segments to form complex fault zones.     

A survey of multi-stage diagenesis and dolomitization of Jurassic limestones along a regional shelf-to-basin transect in the Ziz Valley,Central High Atlas Mountains,Morocco

Petrographic and geochemical data from five localities in the Ziz Valley of Morocco indicate that Jurassic limestones have undergone early diagenesis that varied with location from shelf to basinal settings, burial diagenesis that was most pronounced in basinal settings, and late diagenesis caused by compression and uplift of the High Atlas Mountains.Marine cements occur at all five localities from shelf-to-basin center, although cement types vary from peloidal microcrystalline cements updip on the shelf-to-equant calcite in basinal settings. Presence of moldic grains and/or Mg-poor, Fe-poor blocky cements suggest that meteoric waters influenced early diagenesis at all shelf localities and on an upturned fault block in the basinal region, leaving only one locality unaffected by early meteoric processes. ⁸⁷Sr/⁸⁶Sr ratios of 0.70810–0.70895 (greater than ⁸⁷Sr/⁸⁶Sr of coeval limestones), Mg contents that decrease upward from 47.5 to 43.0 mol% MgCO₃, presence of dolomitized marine cements, and dolomite cements that postdate marine cements but predate meteoric-to-burial cements suggest that dolomitization and dolomite cementation at two shelf localities took place in mixed meteoric and marine waters early in diagenesis. However, poorer preservation of depositional fabrics, lower δ¹⁸O values, and larger and more anhedral crystals suggest that dolostones downdip underwent later modification during burial, whereas those updip did not.Compaction during diagenesis generated numerous concavo–convex and sutured intergranular contacts at updip shelf, downdip shelf, and basinal localities where earlier meteoric cementation was not extensive. Compaction was insignificant in more extensively cemented mid-shelf settings. High Sr (1200–3800 ppm) and Fe (1000–2300 ppm) contents in brachiopod grains suggest that LMC components underwent some modification during burial in basinal settings in Sr-rich reducing waters. Fe contents of late intergranular cements increase from 2000 ppm at the basin's edge to as much as 6000 ppm in the basin's center. Bedding-parallel stylolites occur at all localities.The most negative δ¹⁸O values of sparry dolomites near the Tizi n'Firest fault (−6.2‰ vs. PDB) imply diagenetic temperatures of 65–85°C assuming water δ¹⁸O values of 0.0–2.0‰ vs. SMOW. Those temperatures are much less than previous estimates of burial temperatures in the High Atlas basin. An isotopic gradient extrapolating to roughly 5‰/km in diagenetically modified dolostones likewise suggests a geothermal gradient less than gradients previously proposed for at least parts of the area.Comparison of morphologies of transverse stylolites, which are found at all localities, with morphologies of bedding parallel stylolites suggests that transverse stylolites formed due to compression during late diagenesis. Uplift accompanying that compression allowed influx of low-Mg waters that, along with other factors, caused calcitization of dolomites. The Fe concentration of calcite that fills late fractures increases from less than 2000 ppm at the basin center to values in excess of 3000 ppm at the basin edge, opposite trends in earlier cements and reflecting uplift of the High Atlas Mountains and resultant changes in patterns of groundwater flow.