Tectonic and liquefaction structures in the Loreto basin,Baja California (Mexico) : synsedimentary deformation along a fossil fault plane

Abstract

Complex fault assemblages associated to liquefaction structures have been analyzed in a Pliocene basin located along the Gulf of California. The studied outcrop shows a fossil fault plane formed ill soft flat lying sediments. The liquefaction and fluidification structures have been recognized in voleaniclastic layers deposited ill a lagoonal environment and are potentially related to seismic wave shaking and to successive dewatering along fractures. This strati-graphic record is explained by the progressive development of a seismic fault zone, related to the transtensional regime still active in the Gulf. The present analysis can he considered as an useful case study for the reconnaissance of the different types of structures formed during synsedimentary deformation in hydroplastic conditions.     

贵州丹寨,三都,都匀地区低温成矿系列的成矿物质来源和分异条件

位于扬子地块西南缘的丹寨、三都、都匀地区有两个主要的矿源层-容矿层-屏闭层组合，它们分别是汞、金和铅锌的生储层序，它们排放的含硫油气则可能是低温热液矿化中硫的来源或主要来源。由于矿源层-容矿层-屏闭层组合的不同，古地热场的水平和垂直梯度，成矿时期和构造环境，成矿溶液的成分和性质的差异使该区出现低温热液矿化的分界现象。     

准南前陆冲断带构造分段及其与油气关系

通过大量地面地质、地震和非地震资料的综合解释,分析了准南前陆冲断带的构造分段特征.认为乌鲁木齐-米泉断裂和红车断裂等盆内大型基底断裂是控制构造分段的主要因素,其形成演化决定了构造分段特征的出现或消失;盆缘调节构造是造成次级构造分段的主要原因.准南前陆冲断带构造分段对该区主要烃源岩与生储盖组合的形成及分布、对油气成藏期等方面具有重要的控制作用.     

Tectono-sedimentary analysis of a complex,extensional, Neogene basin formed on thrust-faulted,Northern Apennines hinterland: Radicofani Basin,Italy

Large NW–SE oriented, Neogene–Quaternary structural depressions, up to about 200 km long and 25 km wide, have developed on the western side (hinterland) of the Northern Apennines over thrust substrate. The depressions are now, for the most part, laterally bounded by normal faults and are longitudinally separated into basins by transfer zones. A debate exists in the literature as to whether these basins have developed as half-graben under a predominantly extensional regime since late Miocene, or as thrust-top basins under a predominantly compressional regime that has continued until the Pleistocene. The Radicofani Basin is one of the best-preserved basins. It developed mainly during the late Miocene–Early Pliocene in the southern half of the Siena–Radicofani structural depression, and is now bounded on the east by normal faults that transect a thrust anticline “nose“ in the substrate, to the north by a substrate high or transfer zone, and to the south and west by Quaternary igneous/volcanic edifices. The basin experienced variable differential tectonic and associated sedimentation along linking, normal boundary faults. Along its eastern margin it shows the development of thick (∼600 m) alluvial fans that developed in relay areas between boundary faults and transverse faults and transfer zones. Well-exposed sections generally show upward transitions from conglomeratic alluvial fans, to shoreface sandstone, to offshore mudstones. Locally, the transition is marked by deltas primarily characterised by thick gravelly, sandy, stacked cross-sets The thicker, sandy-gravel to gravelly-sand cross-sets (5–8 m thick) are interpreted as Gilbert-type deltas; interstratified thinner (0.5–1 m thick), generally openwork gravelly strata are part of delta topset assemblages and probably represent prograding fluvial bars. Tectonic movements provided the accommodation space for the total, ∼2700 m thick basin fill. Sea level fluctuations that led to the repeated development of the cross-sets may also have been influenced by climatic or eustatic changes, possibly related to the effects of early Antarctic glaciations.Some features of the Radicofani Basin can be found in both extensional and compressional basins. However, the position of the basin in the mountain chain and the development of alluvial fans, fandeltas and associated deposits along the main boundary fault, combined with structural evidence from seismic lines, show that during the early Pliocene this basin best conforms to existing models of half-graben.     

3D seismic analysis of gravity-driven and basement influenced normal fault growth in the deepwater Otway Basin,Australia

We use three-dimensional (3D) seismic reflection data to analyse the structural style and growth of a normal fault array located at the present-day shelf-edge break and into the deepwater province of the Otway Basin, southern Australia. The Otway Basin is a Late Jurassic to Cenozoic, rift-to-passive margin basin. The seismic reflection data images a NW-SE (128–308) striking, normal fault array, located within Upper Cretaceous clastic sediments and which consists of ten fault segments. The fault array contains two hard-linked fault assemblages, separated by only 2 km in the dip direction. The gravity-driven, down-dip fault assemblage is entirely contained within the 3D seismic survey, is located over a basement plateau and displays growth commencing and terminating during the Campanian-Maastrichtian, with up to 1.45 km of accumulated throw (vertical displacement). The up-dip normal fault assemblage penetrates deeper than the base of the seismic survey, but is interpreted to be partially linked along strike at depth to major basement-involved normal faults that can be observed on regional 2D seismic lines. This fault assemblage displays growth initiating in the Turonian-Santonian and has accumulated up to 1.74 km of throw.Our detailed analysis of the 3D seismic data constraints post-Cenomanian fault growth of both fault assemblages into four evolutionary stages: [1] Turonian-Santonian basement reactivation during crustal extension between Australia and Antarctica. This either caused the upward propagation of basement-involved normal faults or the nucleation of a vertically isolated normal fault array in shallow cover sediments directly above the reactivated basement-involved faults; [2] continued Campanian-Maastrichtian crustal extension and sediment loading eventually created gravitational instability on the basement plateau, nucleating a second, vertically isolated normal fault array in the cover sediments; [3] eventual hard-linkage of fault segments in both fault arrays to form two along-strike, NW-SE striking fault assemblages, and; [4] termination of fault growth in the latest Maastrichtian. We document high variability of throw along-strike and down-dip for both fault assemblages, thereby providing evidence for lateral and vertical segment linkage. Our results highlight the complexities involved in the growth of both gravity-driven normal fault arrays (such as those present in the Niger Delta and Gulf of Mexico) and basement-linked normal fault arrays (such as those present in the North Sea and Suez Rift) with the interaction of an underlying and reactivating basement framework. This study provides an excellent example of spatial variability in growth of two normal fault assemblages over relatively short spatial scales (∼2 km separation down-dip).     

Integrated Reservoir Characterization and Petrophysical Analysis of Cretaceous Sands in Lower Indus Basin,Pakistan

The reservoir character of the Cretaceous sand is evaluated in Lower Indus Basin, Pakistan where water flooding is very common. Thus, prediction of subsurface structure, lithology and reservoir characterization is fundamental for a successful oil or gas discovery. Seismic reflective response is an important tool to detect sub-surface structure. Seismic reflection response is not enough to highlight geological boundaries and fluids in the pore space therefore, the use of integrated approach is vital to map sub-surface heterogeneities with high level of confidence. Based on seismic character and continuity of prominent reflectors four seismic horizons are marked on the seismic sections. All the strata is highly disturbed and distorted with presence of a network of fault bounded horst and graben structures, which indicate that the area was under compressional tectonic regime. These fault bounded geological structure formed structural traps favorable for the accumulation of hydrocarbon. The petrophysical analysis reveals that the Cretaceous sand formation has four types of sand: Sand A, B, C and D with good porosity (15 % average) and low volume of shale. Although complete petroleum system is present with structural traps and reservoir character of sand interval is very good but these sands are highly saturated with water thus are water flooded, which is the main reason of the abundant wells in the study area.     

Seismotectonics of the passive continental margin of Egypt

The results of focal mechanisms determination for the recent seismic activity (earthquakes of 1951, 1955, 1987, 1988, and 1998) in the passive continental margin of Egypt may shed some light on the local stress field in this area. Moreover, studying the source mechanism of these events provides an opportunity to understand the structural style of the passive margin of Egypt, as well as the tectonic setting beside its variation in space and time. This study reveals that there are two types of tectonic regimes which caused these mechanisms. The first is a tensional regime, represented by NW oblique (normal-dextral) faults and the second is a compressive one represented by E–W to ENE (reverse-sinstral) faults. These fault trends probably indicate rejuvenation of inherited E–W Mesozoic and NW Oligo-Miocene faults.     

西昆仑—西南天山地区断裂活动性研究

利用多时相、多波段卫星图像，对西昆仑-西南天山地区大约500000km^2范围的断裂活动性进行分析判读。根据卫星图像上显示的地貌、微地貌特征，构造组合形态，将所判读的断裂分为全新世活动、晚更新世活动以及活动不明显的3类，结合地震活动性，对该地区强震危险性进行了分析，提出西昆仑布伦口组合构造带活动，可能是形成20世纪南天山前缘乌恰、阿图什、伽师一系列强烈地震的原因。     

Fohn lamproite and a possible Late Eocene — pre‐Miocene diatreme field,Northern Bonaparte Basin,Timor Sea

Seismic profiles in the Northern Bonaparte Basin, Timor Sea, northern Australia, disclose an east‐northeast‐trending 120 × 25 km swathe of over 40 circular to subcircular features excavated in the pre‐Miocene erosional surface and buried by Lower Miocene sediments. The larger structures, typified by the Fohn Structure, include central structural highs overlying narrow vertical corridors of upward‐bulging seismic horizons (bulge‐forms). Associated with these structural highs are troughs that overlie broader vertical zones of slower seismic velocity (crater‐form features). Smaller circular features (Dc <2.0 km) include both crater‐form and bulge‐form structures. The first type shows zones of seismic velocity crater‐form structures under craters excavated below the base‐Miocene horizon. The second type exhibits vertical seismic bulge‐form features directly beneath palaeotopographic highs developed at the same horizon. Identification in drill cuttings of fragments of olivine‐leucite lamproite at Fohn 1, at depths of 690–880 m, suggests that this structure is a lamproite diatreme consisting of a massive volcanic plug ringed by pyroclastics, analogous to the classic champagne‐glass structure of alkaline volcanic diatremes. The seismic morphometry of several of the larger structures of the field is analogous to Fohn, suggesting that they too may be diatremes. The smaller bulge‐form features may represent deeply eroded diatreme feeder necks. Crater‐like structures underlain by seismic velocity crater‐forms are interpreted as relatively little‐eroded maars with low‐velocity infill, probably consisting of volcanic and country rock breccia as at Fohn 1, as well as unconsolidated clastics of the transgressive Lower Miocene Oliver Sandstone Member. Lamproite fragments at Fohn 1 are dominated by apatite‐rich assemblages consisting of saponite‐altered olivine, analcime and nontronite‐altered zoned leucite, high‐Ti K‐bearing diopside, Ti‐rich richterite, Ti‐rich phlogopite, Mg‐rich ilmenite, Cr‐bearing priderite, Ba and Sr‐rich fluorapatite and rare‐earth element‐rich apatite. Textural relations suggest early crystallisation of olivine, leucite and K‐bearing diopside followed by crystallisation of alkali amphibole, priderite, ilmenite and apatite in alkali‐Tindash;Fe–rich groundmass. Fohn 1 lamproites have very high whole‐rock P levels, high Na,Sr and Y and low K,Ba,Zr and Nb levels compared to Early Miocene West Kimberley lamproites. The mineral paragenesis suggests crystallisation of olivine‐leucite assemblages at temperatures >1100°C and pressures <0.1 GPa, followed by crystallisation of amphibole and phlogopite under water‐saturated conditions at temperatures below ～1020°C.     

伸展断陷盆地的演化特征——以海拉尔盆地贝尔凹陷为例

贝尔凹陷是海拉尔盆地中一个早白垩世的伸展断陷,通过综合应用地震、钻井等资料对贝尔凹陷的形成及演化进行深入分析,认为伸展作用和缩短作用的交替进行贯穿了凹陷的演化过程,白垩纪发育的3个伸展作用幕和3个缩短作用幕控制了凹陷的3期沉积旋回、伸展构造与反转构造的叠加和油藏的形成。伸展作用和缩短作用控制着贝尔凹陷内的构造样式和沉积样式的形成与演化。从而影响着烃源岩、储集层的发育与分布,并制约着油气的运移、聚集和保存。     

Garnet‐controlled very low velocities in the lower mantle transition zone at sites of mantle upwelling

Deep mantle plumes and associated increased geotherms are expected to cause an upward deflection of the lower–upper mantle boundary and an overall thinning of the mantle transition zone between about 410 and 660 km depth. We use subsequent forward modelling of mineral assemblages, seismic velocities, and receiver functions to explain the common paucity of such observations in receiver function data. In the lower mantle transition zone, large horizontal differences in seismic velocities may result from temperature‐dependent assemblage variations. At this depth, primitive mantle compositions are dominated by majoritic garnet at high temperatures. Associated seismic velocities are expected to be much lower than for ringwoodite‐rich assemblages at undisturbed thermal conditions. Neglecting this ultralow‐velocity zone at upwelling sites can cause a miscalculation of the lower–upper mantle boundary on the order of 20 km.     

Paleogene biostratigraphy of the North Caspian region based on dinocysts and nannofossils from the Novouzensk borehole. Article 2: Biotic events and paleoecological settings

The relatively complete late Danian-initial Lutetian succession of biotic events, which are suitable to serve as biostratigraphic reference levels for interregional correlations are defined in the section of the Novouzensk reference borehole based on dinocyst and nannoplankton assemblages. The analysis of palynological and nannofossil assemblages allows dynamics of basin development and sea-level fluctuations to be traced. Three major stages reflecting different sedimentation regimes are established in the borehole section: (1) Danian with terrigenous-carbonate sedimentation regime corresponding to the Algai and Tsyganovka formations; (2) Selandian-Thanetian (initial Eocene included) characterized largely by siliceous-terrigenous sediments of the Syzran, Novouzensk, and, partly, Bostandyk formations; (3) Ypresian-Lutetian with the carbonate-terrigenous sedimentation regime corresponding to the upper part of the Ypresian Bostandyk and Lutetian Kopterek formations. The composition of dinoflagellate and nannoplankton assemblages characterizes the North Caspian basin as an internal largely shallow sea with a changeable temperature regime. The paleoecological analysis of phytocoenoses made it possible to define basin fluctuations comparable with third-order rhythms. Four Danian rhythms definable in the Algai and Tsyganovka formations indicate conditions of an open warm-water basin. Dynamics of the step-wise shoaling of the basin was characteristic of the Selandian-early Thanetian ages with subsequent restoration of the marine regime in the late Thanetian. The Syzran Formation corresponds to two Selandian rhythms, which were formed in shallower settings of the restricted sea basin. Four Thanetian rhythms are established in the Novouzensk Formation. The early Thanetian basin was characterized by the shallowest disturbed marine conditions, which were followed by the restored normal marine regime in the late Thanetian. Six Ypresian rhythms correspond to the Bostandyk Formation (Yp-0, Yp-1, Yp-5-Yp-8) reflecting transition from initial Ypresian coastal (Yp-0, Yp-1) to normal marine conditions during the Yp-5 rhythm. The early (Yp-2-Yp-4) and late (Yp-9-Yp-10) Ypresian corresponded to the sedimentation break. Most abundant and diverse microbiotic assemblages characteristic of the Yp-7 rhythm are correlative with the EECO event. The marly Kopterek Formation corresponding to the early Lutetian rhythm (Lu-1) is characterized by diverse thermophilic biota.     

Structural interpretation and hydrocarbon potential of Balkassar oil field,eastern Potwar,Pakistan, using seismic 2D data and petrophysical analysis

The Balkassar oil field is situated in the eastern Potwar sub-basin, lies on the southern flank of Soan syncline in Himalayan collisional regime. The area represents Indo-Pak and Eurasian blocks of Precambrian to recent time. Thrusting and folding of Himalayan, Indo-Pak plate movement and Salt Range uplift form the structural trap in Balkassar sub-surface (Balkassar anticline). On the basis of information from eleven seismic 2D lines and wells data six reflectors well data, four faults were identified and marked. The structural trend is northeast southwest. Interpretation of seismic 2D data reveals that the study area has undergone intense deformation as a consequence of development of thrusts and backthrusts.The Balkassar anticline is bounded by two thrust faults one from southeast and the other from northwest. Time and depth contour models shows that anticline limbs at north-western side are steep as compared to south-eastern limbs. Seismic interpretation indicates the presence of well-developed anticline bounded by three faults in the cover sequence and one fault in basement and thus the structure may act as a trap for hydrocarbons. The petrophysical analysis of Balkassar-OXY-1 well shows about 83.1% hydrocarbons saturation in the reservoir rocks, hence this study suggest that Balkassar Oilfield has potential to produce hydrocarbons.     

岔西地区浊积岩的发现及其油气勘探意义

通过对岔河集西部地区东三段的骨架砂岩分布特征、岩性组合、岩芯观察、粒度分析和地震反射特征等研究,认为储油砂体主要为浊流成因。浊积岩的形成与控凹断层-牛东断裂的发生、发展直至消亡的全过程密切相关。经分析该区东三段存在雄古1岔39、岔76及岔107雄21三个浊积扇,由于后期差异压实作用形成三个对应的鼻状构造,均已获得工业油流,对于油田的增储上产来讲,是进行滚动勘探的有利地区。     

Numerical models of tectonic deformation at the Baltica–Avalonia transition zone during the Paleocene phase of inversion

Predictions from dynamic modelling of the lithospheric deformation are presented for Northern Europe, where several basins underwent inversion during the Late Cretaceous and Early Cenozoic and contemporary uplift and erosion of sediments occurred. In order to analyse the evolution of the continental lithosphere, the equations for the deformation of a continuum are solved numerically under thin sheet assumption for the lithosphere. The most important stress sources are assumed to be the Late Cretaceous Alpine tectonics; localized rheological heterogeneities can also affect local deformation and stress patterns. Present-day observations available in the studied region and coming from seismic structural interpretations and stress measurements have been used to constrain the model. Our modelling results show that lateral variation in lithospheric strength below the basin systems in Central Europe strongly controls the regional deformation and the stress regime. Furthermore, we have demonstrated that the geometry of the boundary between Baltica and Avalonia, together with different rheological characteristics of the two plates, had a crucial role on local crustal deformation and faulting regime resulting in the Baltica–Avalonia transition zone from the S–N Alpine convergence.     

Fault-block structures in the eastern margin of the Amur lithospheric plate,their seismicity,and fluid regimes

The results of long-term studies of the neotectonic processes and related phenomena such as the Earth’s interior degassing, the fluid discharge, and the high seismicity in the zone of interaction between the Amur and Okhotsk lithospheric plates at the transition between the Verkhnii and Srednii Amur regions were used for defining the separate structural blocks with different geodynamics and analyzing their relations with the seismic events during the periods of high seismic activity and quiescence. The heliometric and atmochemical studies in the Zeya-Bureya basin revealed zones of high permeability. Long-term observations of the fluid dynamics at the Konstantinovka mineral water deposit demonstrate a correlation between the variations in the water-soluble helium contents and the changes in the stress-deformed state of the blocks located up to 200 km away from regime observation sites.     

Foraminiferids from the London Clay at Lower Swanwick and their palaeoecological interpretation

Sixteen foraminiferid assemblages have been studied from the London Clay succession at Lower Swanwick brickyard. These are divided into three faunules which are interpreted as indicating a shallow shelf regime with strong deltaic influences.     

Precambrian granulites of the Aldan shield, eastern Siberia, USSR

Abstract Precambrian granulites of the Aldan shield in southern Yakutia, USSR, form a massif of 200,000 km² bounded by younger fold-belts to the south, west and east. The massif consists of several blocks that reflect a primary heterogeneity of composition and differences in structural and thermodynamic evolution of different parts of the area. According to structural and petrological data the massif can be divided into two megablocks: eastern Aldan and western Aldan. They are separated by a narrow meridional fold-belt. Structural evolution of this central zone was determined by the geodynamics of the mega-blocks and was completed in the late Archaean. Towards the south, this central zone is ‘transformed’into the relatively small Sutam block adjoining the Stanovoy fold-belt that bounds the Aldan shield on the south. The Sutam block is separated from the other structural units of the Aldan shield by a system of north trending grabens filled by post-Archaean sediments. The Aldan shield is composed of Archaean high-grade granulites, while the Stanovoy fold-belt, to the south, consists of highly foliated Proterozoic rocks metamorphosed under relatively lower-grade conditions. However, relics of the granulites are mapped within the fold-belt. They contain high-grade assemblages (e.g. Opx + Sil + Qz, Sap + Qz, Opx + Gr + Sil, etc.). One of the relics, the Tokskii block, which is only slightly touched by diaphthoresis, is located in the southeastern part of the Stanovoy fold-belt. Metamorphic conditions of the Tokskii block are compared with those of the Sutam block and a similar evolution of the units is revealed. Mineral assemblages and mineral compositions do not vary within each unit, but they change in a north-south direction. The Opx + Sil + Qz assemblage has been found only in Sutam and Tok, but not in eastern Aldan and western Aldan. The Sap + Qz assemblage has been found in the Tokskii block but has not yet been found in the Sutam block. The pyrope content in garnets, from metapelites of both blocks, is significantly higher than that from the Aldan (eastern and western blocks) rocks to the north. The most important assemblages from different units of the Aldan shield have been studied using the electron microprobe in order to unravel the metamorphic evolution of the granulites and thus to deduce the thermodynamic regime of this evolution. A geodynamic model for the Aldan shield is discussed in terms of Archaean island arc development.     

The Muruntau Deposit: Geodynamic Position and a Variant of Genetic Model of the Ore-Forming System

The paper presents the results of original structural studies conducted over a long time within the Kyzylkum ore province and at the Muruntau deposit (Central Asia), including the period when the central part of the deposit, as well as horizons at the eastern and southeastern flanks (abandoned or inaccessible at present), were available to visit. Owing to the geodynamic and structural analysis of the region and the deposit itself, several stages of deformation that created the Muruntau interference structure have been identified. These stages were attributed to the Caledonian (subduction, collision, and transpression regimes), Hercynian (subduction, collision, and transpression regimes), and Cimmerian (transpression regime) cycles of tectonogenesis. The fault–fracture structures of these stages are accompanied by the development of various newly formed (vein–veinlet-metasomatic) mineral assemblages. Based on the averaged characteristics of gold mineralization in various mineral formations, a morphogenetic classification of orebodies was developed and their role in the deposit was revealed. The morphological features of the Main Muruntau ore deposit are considered. A critical review of the results of isochron age dating was made. The subduction–hydrothermal model of the formation of the giant Muruntau gold ore deposit is discussed.