A note on the subsidence history of the northern margin of the Alboran Basin

Backstripping of four marine wells on the northern margin of the Alboran Basin reveals a tectonic subsidence history that varies laterally along the margin from east to west. The well on the eastern margin (AndA1) records a fairly steady, continuous subsidence for most of its history, whereas wells on the western margin (AndG1 and AlbA1) show two distinct phases in their subsidence curves. The form of the subsidence curve for DSDP well 121 reflects its position on a structural high. Beta values for the tectonic subsidence curves range between 1.3 and 1.6.     

礼乐盆地碳酸盐岩时空分布特征及构造意义

对碳酸盐岩(台地与生物礁)的研究具有重要的油气地质意义和科学价值。渐新世以来, 礼乐盆地及周缘开始了大规模的碳酸盐建造, 至今还有一定规模生物礁持续发育。文章通过拖网约束、井震对比和地震相类比方法对礼乐盆地周缘碳酸盐岩的发育特征、构造背景和时空分布规律进行系统研究。结果表明, 礼乐盆地主要发育孤立、前隆、掀斜断块型台地及生物礁。碳酸盐岩时空发育特征为: 1) 渐新世—早中新世以构造前隆和掀斜断块控制的开阔台地为主, 生物礁零星发育; 2) 早中新世—中中新世表现为大量孤立台地和生物礁; 3) 中中新世之后, 发生台地和礁的淹没, 盆地内主要发育点礁。结合构造背景和重磁特征分析表明, 古隆起、掀斜断块、前隆迁移和岩浆活动为控制礼乐盆地不同时期碳酸盐岩发育的主要构造要素。现今礼乐盆地及周缘大量生长的珊瑚礁, 主要发育在上新世—更新世岩浆活动形成的海山之上。     

Growth patterns of a proximal terrigenous margin offshore the Guadalfeo River, northern Alboran Sea (SW Mediterranean Sea): glacio-eustatic control and disturbing tectonic factors

The shelf-upper slope stratigraphy offshore and around the Guadalfeo River on the northern continental margin of the Alboran Sea, Western Mediterranean Basin, has been defined through the interpretation of a grid of Sparker seismic profiles. We tried to identify evolutionary trends in shelf growth, as well as to determine the regional/local factors that may modify the influence of glacio-eustatic fluctuations. Four major depositional sequences are identified in the sedimentary record by a detailed seismic interpretation, which defines three significant intervals of shelf-upper slope progradation, dominated by deposition of shelf-margin wedges, which resulted in uniform patterns of shelf-margin growth in response to significant sea-level falls. In contrast, the record of transgressive intervals is more variable, mainly as the result of distinct patterns of regressive-to-transgressive transitions. Major progradational wedges are internally composed of seaward-prograding, landward-thinning wedges, interpreted to represent shelf-margin deltaic deposits. In contrast, the last aggradational interval is composed of shelf-prograding wedges that show distinct characteristics, in terms of seismic facies, morphology and distribution when compared with previous shelf-margin wedges. These shelf wedges are thought to represent the particular case of Regressive Systems or Shelf Margin Systems Tracts, and their development seems to be controlled by a drastic change in main depocenter location, which moved from the upper slope to the shelf during the Pleistocene. The stacking pattern of seismic units, the shallowness of the acoustic basement and the migration of the shelf break are used to infer spatial and temporal changes in tectonic subsidence-uplift rates, which interact with low-order glacio-eustatic changes. For much of the Pliocene-Quaternary, uplifted sectors alternated laterally with sectors experiencing more subsidence. Subsequently, a significant change from lateral outgrowth to vertical accretion is recognised. This stratigraphic change could be related to the combined influence of increased subsidence rates on the shelf and the onset of higher-frequency glacio-eustatic cyclicity after the Mid Pleistocene Revolution that occurred around 1 Ma.     

Lower Miocene structural evolution of the central Vienna Basin (Austria)

The tectonic evolution of the Vienna Basin overlying the Alpine-Carpathian fold and thrust belt includes two stages of distinct basin subsidence and deformation. The earlier phase contemporaneous with thrusting of the Alpine-Carpathian floor thrust is related to the formation of a wedge-top basin (“piggy-back”), which was connected to the evolving foreland basin (Lower Miocene; c. 18.5–16 Ma). This stage is followed by the formation of a pull-apart basin (Middle to Upper Miocene; c. 16–8 Ma). Sediments of the latter unconformably overly wedge-top basin strata and protected them against erosion.     

Onshore Neogene stratigraphy in the North of the Alboran Sea (Betic Internal Zones): Paleogeographic implications

The Neogene is the period in which the Betic Cordillera, the Rif, and the Alboran Sea acquired their present configuration. The Neogene sediments of the Betic Internal Zones (located directly to the North of the Alboran Sea) show the effects of important periods of deformation. Deposition was clearly controlled by tectonics. Therefore the generation, evolution, and total or partial destruction of basins and the formation of new, often superimposed, basins are common phenomena, according to the locations of the basins in the Betic Cordillera and to the different geodynamic situations.     

Strike-slip tectonic processes in the northern Caribbean between Cuba and Hispaniola (Windward Passage)

Marine geophysical data including Seabeam, seismic reflection, magnetics, gravimetry and side-scan sonar have been recently collected along the northern Caribbean strike-slip plate boundary between Cuba and Hispaniola, in the Windward Passage area. The analysis of this comprehensive data set allows us to illustrate active strike-slip tectonic processes in relation to the kinematics of the Caribbean Plate. We show that the transcurrent plate boundary trace runs straight across the Windward Passage, from the southern Cuban Margin in the west (Oriente Fault) to the Tortue Channel in the east. The Windward Passage Deep is thus not an active pull-apart basin, as previously suggested. The plate boundary geometry implies that the motion of the Caribbean Plate relative to the North American Plate is partitioned between a strike-slip component, accommodated by the Windward Passage active fault zone, and a convergence component, accommodated by compression at the bottom of the Northern Hispaniola Margin. On the basis of a correlation with onland geological data, an age is given to the stratigraphic sequences identified on seismic profiles. A kinematic reconstruction is proposed that follows the tectonic unconformities recognized at sea and on land (Late Eocene, Early Miocene, Middle Miocene and Late Pliocene). Each one of these tectonic events corresponds to a drastic reorganization of the plate boundary geometry. We propose to correlate these events with successive collisions of the northern Caribbean mobile terranes against the Bahamas Bank. During each event, the plate boundary trace is shifted to the south and a part of the Caribbean Plate is accreted to North America.     

Gravity modeling of the Muertos Trough and tectonic implications (north-eastern Caribbean)

The Muertos Trough in the northeast Caribbean has been interpreted as a subduction zone from seismicity, leading to infer a possible reversal subduction polarity. However, the distribution of the seismicity is very diffuse and makes definition of the plate geometry difficult. In addition, the compressive deformational features observed in the upper crust and sandbox kinematic modeling do not necessarily suggest a subduction process. We tested the hypothesized subduction of the Caribbean plate’s interior beneath the eastern Greater Antilles island arc using gravity modeling. Gravity models simulating a subduction process yield a regional mass deficit beneath the island arc independently of the geometry and depth of the subducted slab used in the models. This mass deficit results from sinking of the less dense Caribbean slab beneath the lithospheric mantle replacing denser mantle materials and suggests that there is not a subducted Caribbean plateau beneath the island arc. The geologically more realistic gravity model which would explain the N–S shortening observed in the upper crust requires an overthrusted Caribbean slab extending at least 60 km northward from the deformation front, a progressive increase in the thrusting angle from 8° to 30° reaching a maximum depth of 22 km beneath the insular slope. This new tectonic model for the Muertos Margin, defined as a retroarc thrusting, will help to assess the seismic and tsunami hazard in the region. The use of gravity modeling has provided targets for future wide-angle seismic surveys in the Muertos Margin.     

Influence of lithosphere and basement properties on the stretching factor and development of extensional faults across the Otway Basin,southeast Australia

The NW-SE striking Otway Basin in southeastern Australia is part of the continental rift system that formed during the separation of Australia from Antarctica. The development of this sedimentary basin occurred in two phases of Late Jurassic-Early Cretaceous and Late Cretaceous rifting. The evolution of this basin is mainly associated with extensional processes that took place in a pre-existing basement of Archean, Proterozoic to Paleozoic age. In this study, the total amounts of extension and stretching factor (β factor) have been measured for six transects across the entire passive margin of the Otway Basin region. The results show significant variation in extensional stretching along the basin, with the smallest stretching factors in the easternmost (β = 1.73, 1.9) and westernmost part of the basin (β = 2.09), and the largest stretching factors in the central part (β = 2.14 to 2.44). The domain with the lowest β factor is underlain mostly by thicker lithosphere of the Delamerian Orogen and older crustal fragments of the Selwyn Block. In contrast, the region with the largest β factor and amount of extension is related to younger and thinner lithosphere of the Lachlan Orogen. The main basement structures have been mapped throughout eastern South Australia and Victoria to examine the possible relationships between the younger pattern of extensional faults and the older basement fabrics. The pattern of normal faults varies considerably along onshore and offshore components of the Otway Basin from west to east. It appears that the orientation of pre-existing structures in the basement has some control on the geometry of the younger normal faults across the Otway Basin, but only in a limited number of places. In most areas the basement fabric has no control on the younger faulting pattern. Basement structure such as the north-south Coorong Shear Zone seems to affect the geometry of normal faults by changing their strike from E-W to NW-SE and also, in the easternmost part of the basin, the Bambra Fault changes the strike of normal faults from NW-SE to the NE-SW. Our results imply that the properties of the continental lithosphere exert a major influence on the β factor and amount of crustal extension but only a minor influence on the geometry of extensional faults.     

Petrography,petrology and tectonic implications of Mitre Island,northern Fiji Plateau

Mitre Island samples, Pliocene in age, can be classified together with Anuda samples, of unknown age, as island-arc basaltic andesites with tholeiitic tendencies. The presence of morphologically unusual iron—titanium oxides and of probably xenocrystic plagioclase suggest that at least part of the observed minerals crystallized in a magma chamber underlying the island. The samples apparently represent a mixture of magma fluid, cumulate plagioclase, pyroxene, and iron—titanium oxides which were ponded in a crater lava lake where they were reheated by subsequent eruptions. Many of them show symplectic magnetite formed by high-temperature oxidation of olivine. The morphological complexity and compositional homogeneity of the iron—titanium oxides cannot be explained at present.The presence of sulfide droplets inside olivine, magnetite and ilmenite crystals suggests a formation of an immiscible sulfide liquid in the magma chamber. Droplets of this liquid were overgrown by minerals crystallizing at that time and thus protected against oxidation during and after eruption.Mitre Island is a part of a currently inactive Vitiaz island arc associated in the past with a westward subduction of Pacific plate along the Vitiaz trench. Increased difficulty in subducting the large mass of the Pacific Border Plateau under the northern Fiji Plateau apparently produced counterclockwise rotation of the Vitiaz island arc. Oblique subduction was active until a steep angle was reached between the Vitiaz trench and the motion vector of the Pacific plate. Then a strike-slip fault developed in the Vitiaz trench and the subducted plate was sheared off. Recently the strike-slip zone migrated south from the Vitiaz trench across the northern Fiji Plateau and is presently extending from Aoba Island, in the New Hebrides, northeastward toward the Pacific Border Plateau.     

Zircon U-Pb geochronology,Hf isotopes,and geochemistry constraints on the age and tectonic affinity of the basement granitoids from the Qiongdongnan Basin,northern South China Sea

Studies in the northern South China Sea(SCS) basement remain important for understanding the evolution of the Southeast Asian continental margin. Due to a thick cover of sediments and scarce borehole penetration, little is known about the age and tectonic affinity of this basement. In this study, an integrated study of zircon U-Pb geochronology, Hf isotopes, and whole-rock major and trace elements on seven basement granitoids from seven boreholes of Qiongdongnan Basin has been carried out. New z...     

The distribution and characteristics of the igneous complexes in the northern East China Sea Shelf Basin and their implications for hydrocarbon potential

This paper presents results of two-dimensional seismic mapping of the northern East China Sea Shelf Basin. Various igneous features such as sills, volcanic edifices and stocks were identified by the geophysical exploration. The sills are most common, and are observed at more than 90 locations. Most mapped sills in the study area are characterized by high-amplitude continuous reflections with distinct terminations. Saucer- and cup-shaped sills are observed locally. The stocks are discordant (nearly vertical) igneous bodies and they are characterized by seismic transparency, with upturned host rocks and uplifted overburden. The volcanic edifices and/or necks consist of irregular mounds and peaks and are characterized by strong positive top reflections with chaotic internal facies. The oldest igneous activity in the northern East China Sea Shelf Basin is Early Cretaceous (123.3 ± 3.7). This igneous activity coincides with those observed in eastern China which has been related mainly to the subduction of the Pacific Plate beneath Eurasia Plate. The Miocene igneous activity is well constrained based on seismic stratigraphic relationships within the folded stratigraphy, age dating, and the occurrence of igneous sills. The timing of this intrusion is coincident with the intensive igneous activity as previously suggested for the eastern China. Igneous rocks can produce hydrocarbon traps, reservoirs and they can act as a seal, and therefore are of great importance in petroleum study.     

Variation in vertical stress in the Baram Basin, Brunei: tectonic and geomechanical implications

The vertical or lithostatic stress is an important factor in tectonic and geomechanical studies and is commonly used in the prediction of pore pressures and fracture gradients. However, the vertical stress is not always calculated in situ and the approximation of 1.0 psi/ft (22.63 MPa/km) is often used for the vertical stress gradient. Vertical stress has been determined in 24 fields in the Baram Basin, Brunei, using density log and checkshot velocity survey data. The Baram Basin shows a variation in vertical stress gradient between 18.3 and 24.3 MPa/km at 1500 m depth below the surface. This variation has a significant effect on in situ stress related issues in field development such as wellbore stability and fracture stimulation. The variation is caused by a bulk rock density change of 2.48–2.07 g/cm³ from the hinterland of the delta to its front. Differential uplift and erosion of the delta hinterland and undercompaction associated with overpressure are the interpreted causes of the density and hence vertical stress variation.     

Morphological characteristics in the area off eastern Taiwan Island and their tectonic implications

On the basis of bathymetric data and other geological and geophysical data obtained during the first survey conducted by Chinese Mainland in the area off eastern Taiwan Island from May to June in 2000, the morphological features of the region, the tectonic control to the seafloor topography and their tectonic implication are studied and discussed. The results have revealed that both the slope zone of the Ryukyu arc and the Ryukyu Trench present a typical morphotectonic characteristics controlled by the trench-arc system in the West Pacific Ocean. At the slope of eastern Taiwan Island the isobathic lines parallel to the coastline and distribute densely in nearly N-S direction and the slope gradient of topography is large. Such a unique feature is attributed to the collision of the Luzon arc and Eurasia continent. In the Huatung Basin, turbidity fans and submarine canyons are well developed, the formations of which are mainly related to the steep topography of the slope of the Luzon arc and the abundant s     

东海陆架盆地中生代残留地层特征及其构造启示

东海陆架盆地是位于中国东部华南大陆边缘的一个中、新生代叠合盆地,具有较大油气潜力。目前东海陆架盆地油气的发现均来自于新生界,对中生代残留地层的各方面特征认识不足:在空间上通常集中于特定构造单元,且基本位于盆地西部;在时间上主要涉及白垩纪和侏罗纪,且多是定性或半定量的研究。本文在前人研究的基础上,收集、整理了研究区目前最新、最全的反射地震资料和钻井数据,从钻遇中生界井的标定出发,以地震资料的层序划分和解释为基础,进行残留地层的研究,空间上统一盆地东、西两大坳陷带,时间上统揽白垩纪、侏罗纪以及前侏罗纪三个时期。结果表明,东海陆架盆地中生代残留地层遭受了后期严重的剥蚀改造,总体呈现东厚西薄、南厚北薄的特征,残留地层范围随时间不断东扩。对比各时期残留地层平面展布特征,揭示了东海陆架盆地的演变过程:三叠纪时期盆地原型为被动大陆边缘坳陷型盆地,早、中侏罗世时期为活动大陆边缘弧前盆地,晚侏罗世—晚白垩世时期为大陆边缘弧后伸展盆地;与此相对应,古太平洋板块俯冲肇始于晚三叠世—早、中侏罗世时期,板块后撤始于晚侏罗世。东海陆架盆地在中生代的东侧边界位于钓鱼岛隆褶带的东侧。     

Stratigraphic and tectonic evolution of the western Alboran Sea: Late miocene to recent

The western Alboran Sea contains three morphostructural domains: continental margins, structural highs, and basins, some with diapirs. Seven sequences from Tortonian to upper Quaternary, identified on airgun profiles, record a distinct set of depositional events. The tectonic evolution was influenced by the relative movement of the African and Iberian plates. Connections through the Atlantic/Mediterranean gateways and global sea level oscillations are recorded as major unconformities in the depositional record. A Neogene change in tectonic character from transtensional to transpressional regimes is postulated on the basis of changes in the regional stress field orientation.     

Well log interpretation and seismic character of the cenozoic sequence in the northern Alboran Sea

Seismic stratigraphic and main lithological features of the sedimentary cover overlying the basement of the Alboran Sea were established via the analysis of commercial multichannel seismic surveys, geophysical well logs, and well data. Six seismic stratigraphics units (VI to I), bounded by unconformities, form the marine sediments that range in age from early Miocene to Quaternary. They are dated by extrapolation of commercial drilling results from the northern Alboran Sea. Volcanic activity is recorded within sedimentary sequences of units V to II. Undercompaction features are detected in the two basal units.     

东海陆架盆地中生界构造样式及其动力学成因探讨

构造样式为盆内各类构造组合的几何形态表达,反映了盆地所处应力场性质变化与构造演化过程。本文基于近5年来针对东海陆架盆地所取得的地震资料解释成果,并综合盆地构造演化特征及其地球动力学背景,对盆地内中生界构造样式进行了系统的分类与总结,详细划分为5类构造样式:伸展构造样式、挤压构造样式、走滑构造样式、反转构造样式和底辟构造样式,并进一步细化为12种构造组合。同时,对东海陆架盆地内西部坳陷、中部低隆起、东部坳陷3个构造单元内的中生界构造样式发育情况分别进行了总结,各类构造样式自西至东具有各异的展布特征。综合盆内中生界构造样式几何学特点与展布特征可见,由于伊佐奈歧板块的俯冲、碰撞作用,区内处于挤压构造环境,进而形成了挤压背斜、断背斜、正反转等构造组合;大洋板块的后退翻卷及板块碰撞、俯冲的远程效应下,区内构造环境以伸展作用为主,形成了一系列NNE向裂陷盆地,发育了丰富的伸展构造组合;走滑-拉分构造的发育较好体现了构造环境的转变,地震剖面上见有花状断裂发育;岩浆底辟构造多发育于拉张环境下,与断裂展布息息相关,多沿NE-NNE向断裂展布。此外,新生代多期构造运动是影响中生界构造样式发育展布的重要因素。     

Paleomagnetic results from deep-sea sediment of the Korea Deep Ocean Study (KODOS) area (northern equatorial Pacific) and their paleodepositional implications

Paleomagnetic properties of sediment cores were examined to reconstruct paleodepositional conditions in the Korea Deep Ocean Study (KODOS) area, located in the northeastern equatorial Pacific. The studied KODOS sediments have a stable remanent magnetization with both normal and reversed polarities, which are well correlated with the geomagnetic polarity timescale for the late Pliocene and Pleistocene. Average sedimentation rates are 1.56 and 0.88 mm/kiloyear for the Pleistocene and late Pliocene, respectively. Clay mineralogy and scanning electron microscope analyses of the sediments indicate that terrestrial material was transported to the deep-sea floor during these times. The variations of sedimentation rates with age may be explained by the onset of the northern hemisphere glaciation and subsequent climatic deterioration during the Pliocene and Pleistocene. For the Pleistocene, an increasing sedimentation rate implies that input of terrestrial materials was high, and also a high input of biogenic materials was detected as a result of increased primary production in the surface water. The down-core variations in paleomagnetic and rock-magnetic properties of the KODOS sediments were affected by dissolution processes in an oxic depositional regime. As shown by magnetic intensity and hysteresis parameters, the high natural remanent magnetization (NRM) stability in the upper, yellowish brown layers indicates that the magnetic carrier was in pseudo-single domain states. In the lower, dark brown sediments, only coarse magnetic grains survived dissolution and the NRM was carried by more abundant, multi-domain grains of low magnetic stability. The down-core variation of magnetic properties suggests that the KODOS sediments were subjected to dissolution processes resulting in a loss of the more stable components of the magnetic fraction with increasing core depth.     

Methane-derived carbonates and chemosymbiotic communities of Piedmont (Miocene,northern Italy): An update

Stable carbon isotope values of authigenic carbonate rocks in the Miocene terrigenous sediments of Piedmont indicate a methane-related origin. Some of these methane-derived carbonates (Lucina limestone) are characterized by the presence of abundant lucinid remains. Carbonate dissolution/precipitation and development of lucinid communities were related to bacterial methane oxidation, both aerobic and anaerobic. Anaerobic oxidation led to carbonate precipitation and production of sulfide, which sustained lucinid communities through chemosynthetic symbiotic bacteria. Aerobic oxidation of methane likely resulted in dissolution of carbonate skeletal grains. Several phases of carbonate precipitation, characterized by slightly different isotopic compositions, are recognizable in the limestones.     

Cenozoic sedimentary rocks on the northern slopes of the Kuril Deep-Water Basin (Sea of Okhotsk) and conditions of their formation

Sedimentary rocks from the northern slope of the Kuril Deep-Water Basin are examined. Four different-age lithological units are distinguished, and inferences about the probable conditions of their formation are made. The Paleogene-Lower Miocene deposits (lithological units I and II) are represented by the purest varieties of siliceous rocks, which implies their accumulation far away from the source areas under quiet hydrodynamical conditions of the waters. The composition of the microfossils suggests a relatively shallow-water marine basin. The Pliocene-Pleistocene deposits of lithological units III and IV were formed in an active hydrodynamical environment under conditions of synchronous explosive volcanism at bathyal depths. The presence of porcelanite outcrops on the continental slope of the basin, together with the micropaleontological data about the paleodepths of the sedimentation, allows us to assume that, in the region studied, the continental slope was formed as a result of vertical motions in the post-Middle Miocene time.