Sedimentary processes on the Crimean continental margin in the Black Sea

Structural specific features of the sedimentary succession on the continental margin of the South Crimea in the Black Sea have been examined in the Yalta Area using geomorphologic, acoustic, and lithologic methods. Alternation of regressive and transgressive sequences has been ascertained in sediment sections formed on the shelf and in the Yalta deep-sea fan due to Quaternary oscillations of the basin level. The analysis of sediment sections resulted in revealing a leading role of sedimentary material transference from upper hypsometric levels to lower ones in the sediment accumulation.     

Tectonic and magmatic evolution of the eastern Karakoram,India

Abstract

The Shyok suture zone separates the Ladakh terrane to the SW from the Karakoram terrane to the NE. Six tectonic units have been distinguished. From south to north these are; 1. Saltoro formation; 2. Shyok volcanites; 3. Saltoro molasse; 4. Ophiolitic melange; 5. Tirit granitoids; 6. Karakoram terrane including the Karakoram batholith. Albian—Aptian Orbitolina-bearing lime-stones and turbidites of the Saltoro formation tectonically overlie high-Mg-tholeiites similar to the tectonically overlying Shyok volcanites. The high-Mg tholeiitic basalts and calcalkaline andesites of the Shyok volcanites show an active margin signature. The Saltoro molasse is an apron-like, moderately folded association of redgreen shales and sandstones that are interbedded with ~ 50 m porphyritic andesite. Desiccation cracks and rain-drop imprints indicate deposition in a subaerial fluvial environment. Rudist fragments from a polygenic conglomerate of the Saltoro molasse document a post-Middle Cretaceous age. The calcalkaline andesites of the Shyok volcanites are intruded by the Tirit granitoids, which are located immediately south of the Ophiolitic melange and belong to a weakly deformed trondhjemite-tonalite-granodiorite-granite suite. These granitoids are subalkaline, I-type and were emplaced in a volcanic arc setting. The subalkaline to calcalkaline granitoids of the Karakoram batholith are I-and S-type granitoid. The I-type granitoids represent a typical calcalkaline magmatism of a subduction zone environment whereas the S-type granitoids are crustderived, anatectic peraluminous granites. New data suggest that the volcano-plutonic and sedimentary successions of the Shyok suture zone exposed in northern Ladakh are equivalent to the successions exposed along the Northern suture in Kohistan. It is likely that the o istan and Ladakh blocks evolved as one single tectonic domain uring the Cretaceous-Palaeogene. Subsequently, collision, suturing and accretion of the Indian plate along the Indus suture (50–60 Ma) together with tectonic activity along the Nanga Parbataramosh divided Kohistan and Ladakh into two arealy distinct magmatic arc terranes. The activity and a dextral offset along the Karakoram fault (Holocene-Recent) disrupted the original tectonic relationships. © 1999 Éditions scientifiques et médicales Elsevier SAS     

Morphology and evolution of an anastomosed channel network where saline underflow enters the Black Sea

The Bosphorus Strait accommodates two‐way flow between the Aegean and Black Seas. The Aegean (Mediterranean) inflow has speeds of 5 to 15 cm sec^?1 in the strait and a salinity contrast of ～12‰ to 16‰ with the Black Sea surface waters on the shelf. An anastomosed channel network crosses the shelf and in water deeper than 70 m is characterized by first‐order channels 5 to 10 m deep, local lateral accretion bedding, muddy in‐channel barforms, and a variety of sediment waves both on channel floors and bar crests, crevasse channels entering the overbank area and levée/overbank deposits which are radiocarbon‐dated in cores to be younger than ～7·5 to 8·0 ka. This channel network accommodates the saline density current formed by the Mediterranean inflow. The density contrast between the density underflow and the ambient water mass is ～0·01 g cm^?3, similar to the density contrast ascribed to low‐concentration turbidity currents in the deep sea. Channel‐floor deposits are sandy to gravelly with local shell concentrations. Low‐relief bedforms on the channel floor have relatively straight crests, upflow‐dipping cross‐stratification, heights 1 to 1·5 m and wavelengths 85 to 155 m. Bankfull flows are subcritical, so these probably are not antidunes. Bar tops are ornamented locally with mudwaves having heights 1 to 2 m and wavelengths ～20 to 100 m; these are potentially antidunes formed under shallow overbank flows. Towards the shelf edge, the degree of channel bifurcation increases dramatically and bar tops are dissected locally by secondary channels, some of which terminate in hanging valleys. Conical mounds on the shelf (possibly mud volcanoes or sites of fluid seepage) interact with the channel network by promoting accretion of muddy streamlined macroforms in their lee. This channel network may be one of the largest and most accessible natural laboratories on Earth for the study of continuously flowing density currents. Although the driver is salinity contrast, the underflow transports sufficient sediment to form levée wedges and large streamlined barforms, and presumably transports sediment into deep water.     

南海南部海域主要沉积盆地构造演化特征

南海南部海域主要沉积盆地沿南沙块体南部、西部两条不同的边界分布，其成盆时代、盆地类型、盆地演化历史以及油气资源效应都有较大的差异，它们的发生发展均与南海的两次海底扩张有关；构造演化具有明显的阶段性，早期均与区域拉张作用有关，都经历了中中新世末期的变形、改造和随后的区域沉降过程，并受到礼乐运动、西卫运动和南沙运动的影响。万安、曾母和北康盆地是南海南部海域具有代表性的新生代沉积盆地，分属于不同的盆地类型。万安盆地是叠置在较薄地壳和高热流值背景之上的一个新生代走滑拉张盆地，经历了三个构造演化阶段。曾母盆地是南沙块体向南俯冲与婆罗洲块体发生软碰撞而形成的一个周缘前陆盆地，经历了四个不同的构造演化阶段。北康盆地是在南沙块体上于白垩纪末一第三纪早期由于地壳拉伸、裂陷而形成的一个陆缘张裂盆地，经历了三个构造演化阶段。     

Principal faults in the Shatsky Rise and their influence upon the evolution of the geological structure in the East Black Sea Region

A fault was traced along the southwestern margin of the Shatsky Rise. It extends to land where it crosses the Mountainous Crimea. Interpretation and analysis of marine seismic and magnetic survey data, as well as geological data on land, allow stating that the fault originated during the rift evolution stage of the East Black Sea Basin. Currently, the fault is in the sea and is a channel for migrating hydrocarbon fluids. Another fault was traced from the West Caucasus into the sea, where it separates the Shatsky Rise into two structural units.     

Stratigraphic and structural characteristics of the Romanian Black Sea shelf

The Western Black Sea basin opened during Cretaceous times by back-arc rifting in association with a north dipping subduction at the rear of the Cretaceous–Early Tertiary Pontide volcanic arc. The sedimentary wedge developed on the shelf of the Romanian Black Sea sector reflects a complex interplay between large scale rifting, uplift of the orogenic flanks, large-scale post-rift subsidence and sea level changes. We examine the detailed structural configuration of this sector for a regional correlation with the adjacent offshore in Ukraine and Bulgaria. The evolution of the western Black Sea basin started in the Albian–Cenomanian times, when two extensional phases with significantly different directions (N–S and subsequently E–W) lead to the formation of a complex interplay between isolated blocks organised in horsts and grabens generally deepening eastwards. Superposition of normal faults footwall blocks from the two extensional episodes generated a deeply subsided area with enhanced accommodation space, i.e., the Histria Depression, and, consequently, recorded a larger thickness of Paleogene sediments in the post-rift stage. (Re)activation of faults and associated folding reflects repeated inversion during the Late Cretaceous–Oligocene times, associated with subsequent periods of non-deposition and/or erosion during moments of basin fill exposure. These periods of inversion recorded in the Black Sea are controlled by coeval orogenic deformations taking place in the Balkans, Pontides and the Crimean thrust belt. Sea level fluctuations during the Neogene and late Alpine tectonics in the neighbouring orogens caused massive sedimentation followed by sediment starvation and/or significant erosion. Large thicknesses of sediments accumulated during the Pontian, presumably associated with an extensional episode deepening the distal parts of the basin and with differential compaction structures. The interpretation of a high-quality seismic dataset combined with published data allowed the correlation of major structural units and lineaments defined onshore towards the Carpathians with the ones deeply buried below the western Black Sea basin sediments. Unit correlations are furthermore used to derive an integrated tectonic image of the western Black Sea area.     

南海北部陆缘盆地形成的构造动力学背景

摘要：南海北部陆缘盆地处于印度板块与太平洋及菲律宾海板块之间,但三大板块对南海北部陆缘盆地的影响是不同的。通过对三大板块及古南海演化的研究,可知南海北部陆缘地区应力环境于晚白垩世发生改变。早白垩世处于挤压环境,晚白垩世以来转变为伸展环境并且不同时期的成因不同。晚白垩世-始新世,华南陆缘早期造山带的应力松弛、古南海向南俯冲及太平洋俯冲板块的滚动后退导致其处于张应力环境。始新世时南海北部陆缘裂陷盆地开始产生,伸展环境没有变,但因其是由太平洋板块向西俯冲速率的持续降低及古南海向南俯冲引起的,南海北部陆缘盆地继续裂陷。渐新世-早中新世,地幔物质向南运动及古南海向南俯冲导致南海北部陆缘地区处于持续的张应力环境;渐新世早期南海海底扩张;中中新世开始,三大板块开始共同影响着南海北部陆缘盆地的发展演化。     

North Atlantic control on precipitation pattern in the eastern Mediterranean/Black Sea region during the last glacial

Based on proxy records from western Black Sea cores, we provide a comprehensive study of climate change during the last glacial maximum and late-glacial period in the Black Sea region. For the first time we present a record of relative changes in precipitation for NW Anatolia based on variations in the terrigenous supply expressed as detrital carbonate concentration. The good correspondence between reconstructed rainfall intensity in NW Anatolia and past western Mediterranean sea surface temperatures (SSTs) implies that during the glacial period the precipitation variability was controlled, like today, by Mediterranean cyclonic disturbances. Periods of reduced precipitation correlate well with low SSTs in the Mediterranean related to Heinrich events H1 and H2. Stable oxygen isotopes and lithological and mineralogical data point to a significant modification in the dominant freshwater/sediment source concomitant to the meltwater inflow after 16.4 cal ka BP. This change implies intensification of the northern sediment source and, with other records from the Mediterranean region, consistently suggests a reorganization of the atmospheric circulation pattern affecting the hydrology of the European continent. The early deglacial northward retreat of both atmospheric and oceanic polar fronts was responsible for the warming in the Mediterranean region, leading simultaneously to more humid conditions in central and northern Europe.     

Regional and local geothermal conditions in the northern Black Sea

More than 100 new heat flow measurements have been collected in recent years (2002–2004) in different tectonic environments of the northern Black Sea. The northern periphery of the Black Sea is characterized by strong geodynamic and seismic activity, high sedimentation rates, diapiric structures, mud volcanism, and fluid and gas escape at the sea floor. We present new thermal data from the shelf, continental slope and deep-water basin, measured off-shore using a marine thermo-probe and on-shore in drill holes. Heat flow density ranges from 20 to more than 2,000 mW/m². For two local areas (the Dnieper gas seeps and the Dvurechenski mud volcano area), we discuss the relation between heat flow variability and the geological and physical processes in the near-bottom sediment layer. The Dnieper gas seeps area is characterized by strong small-scale heat flow variability and is controlled by fluid and gas migration. In the Dvurechenski active mud volcano, the near-bottom temperature in sediments is anomalously elevated because additional heat is carried out by mass flows of fluids and clay minerals. Away from the mud volcano heat flow quickly decreases to background values.     

Geochemistry of the Pegmatitic Rocks and Minerals in the Kenticha Belt, Southern Ethiopia: Implication to Geological Setting

Trace element distribution patterns are reported for whole rocks (granites, aplites, greisens, pegmatites, alaskites) and minerals from the Kenticha pegmatite field. The data shed light on the evolution, regional and local zonal pattern of the granitepegmatites and associated mineralization in the Kenticha belt. The complex mineralization of commercial concentrations of Ta, Nb, Hf, Zr, REE, U and Th is related to Be, Li, Cs, Rbbearing zones of pegmatites and is structurally controlled. Whole rock chemical signatures of the suite of felsic rocks of the Kenticha belt are predominantly similar to those generated by subduction in modern magmatic arcs and indicate a mantle derivation. Columbotantalite concentrates extracted from the pegmatitic ores represent the basic raw materials from which a number of possible byproducts can be recovered.     

Heavy metal pollution in the Black Sea shore and offshore of Turkey

Land-locked seas were polluted mainly by land-based pollutants. The Black Sea is the largest enclosed sea in the world and widely perceived to be heavily polluted. In order to determine the impact of marine activities on heavy metal pollution, shore (500 m distance from edge)–offshore (5,555 m distance from edge) samples of various stations through the Sinop, Samsun and Ordu cities located in the Middle Black Sea region between May 2000 and October 2001 were taken. In addition, samples were taken between April–May 2000 in order to designate the heavy metal pollution of certain rivers, streams, harbor and shores in Samsun’s boundary and 32 sampling stations for the routine pollution monitoring studies are selected including rivers, streams, industrial and domestic discharge points along the Black Sea coast of Turkey in the year 1996. Heavy metal concentrations of whole samples were measured and compared with “Quality Criteria of General Marine and Continental Inside Water Sources” currently effective in Turkey so as to bring up the levels of pollution in marine, rivers and streams.     

Subduction,ophiolite genesis and collision history of Tethys adjacent to the Eurasian continental margin: new evidence from the Eastern Pontides,Turkey

This paper presents several types of new information including U–Pb radiometric dating of ophiolitic rocks and an intrusive granite, micropalaeontological dating of siliceous and calcareous sedimentary rocks, together with sedimentological, petrographic and structural data. The new information is synthesised with existing results from the study area and adjacent regions (Central Pontides and Lesser Caucasus) to produce a new tectonic model for the Mesozoic–Cenozoic tectonic development of this key Tethyan suture zone.

The Tethyan suture zone in NE Turkey (Ankara–Erzincan–Kars suture zone) exemplifies stages in the subduction, suturing and post-collisional deformation of a Mesozoic ocean basin that existed between the Eurasian (Pontide) and Gondwanan (Tauride) continents. Ophiolitic rocks, both as intact and as dismembered sequences, together with an intrusive granite (tonalite), formed during the Early Jurassic in a supra-subduction zone (SSZ) setting within the ?zmir–Ankara–Erzincan ocean. Basalts also occur as blocks and dismembered thrust sheets within Cretaceous accretionary melange. During the Early Jurassic, these basalts erupted in both a SSZ-type setting and in an intra-plate (seamount-type) setting. The volcanic-sedimentary melange accreted in an open-ocean setting in response to Cretaceous northward subduction beneath a backstop made up of Early Jurassic forearc ophiolitic crust. The Early Jurassic SSZ basalts in the melange were later detached from the overriding Early Jurassic ophiolitic crust.

Sedimentary melange (debris-flow deposits) locally includes ophiolitic extrusive rocks of boninitic composition that were metamorphosed under high-pressure low-temperature conditions. Slices of mainly Cretaceous clastic sedimentary rocks within the suture zone are interpreted as a deformed forearc basin that bordered the Eurasian active margin. The basin received a copious supply of sediments derived from Late Cretaceous arc volcanism together with input of ophiolitic detritus from accreted oceanic crust.

Accretionary melange was emplaced southwards onto the leading edge of the Tauride continent (Munzur Massif) during latest Cretaceous time. Accretionary melange was also emplaced northwards over the collapsed southern edge of the Eurasian continental margin (continental backstop) during the latest Cretaceous. Sedimentation persisted into the Early Eocene in more northerly areas of the Eurasian margin.

Collision of the Tauride and Eurasian continents took place progressively during latest Late Palaeocene–Early Eocene. The Jurassic SSZ ophiolites and the Cretaceous accretionary melange finally docked with the Eurasian margin. Coarse clastic sediments were shed from the uplifted Eurasian margin and infilled a narrow peripheral basin. Gravity flows accumulated in thrust-top piggyback basins above accretionary melange and dismembered ophiolites and also in a post-collisional peripheral basin above Eurasian crust. Thickening of the accretionary wedge triggered large-scale out-of-sequence thrusting and re-thrusting of continental margin and ophiolitic units. Collision culminated in detachment and northward thrusting on a regional scale.

Collisional deformation of the suture zone ended prior to the Mid-Eocene (~45?Ma) when the Eurasian margin was transgressed by non-marine and/or shallow-marine sediments. The foreland became volcanically active and subsided strongly during Mid-Eocene, possibly related to post-collisional slab rollback and/or delamination. The present structure and morphology of the suture zone was strongly influenced by several phases of mostly S-directed suture zone tightening (Late Eocene; pre-Pliocene), possible slab break-off and right-lateral strike-slip along the North Anatolian Transform Fault.

In the wider regional context, a double subduction zone model is preferred, in which northward subduction was active during the Jurassic and Cretaceous, both within the Tethyan ocean and bordering the Eurasian continental margin.     

Palaeoseismic Events in Karst Terrains along the Northern Bulgarian Black Sea Coast

The study of the palaoseismic events in the karst terrains of the Bulgarian Black Sea coast is a very important up-to-date problem. The investigated region is one of the highest-energy regions in Bulgaria with established and recorded catastrophic historic and contemporary earthquakes. The terrain is subjected to the influence not only of its own earthquake foci but also of those in Romania and Russia. The palaeoearthquakes that caused considerable disturbances in the karst terrains along the Northern Bulgarian Black Sea coast have left significant traces. They caused disturbances in the environment and the relief (rearrangement of the surface and ground water karst basins, partially or entirely collapsed caves, deformed caves, oil, gas and salt intrusions and gravitationally formed caves). The ecological consequences in historic and contemporary aspects were catastrophic. The palaeoseismic dislocations were formed as a result of global, regional and local geodynamic events related with the destruction     

Active right-lateral strike-slip fault zone along the southern margin of the Japan Sea

We describe an active right-lateral strike-slip fault zone along the southern margin of the Japan Sea, named the Southern Japan Sea Fault Zone (SJSFZ). Onshore segments of the fault zone are delineated on the basis of aerial photograph interpretations and field observations of tectonic geomorphic features, whereas the offshore parts are interpreted from single-/multichannel seismic data combined with borehole information. In an effort to evaluate late Quaternary activity along the fault zone, four active segments separated by uplifting structures are identified in this study. The east–northeast-trending SJSFZ constitutes paired arc-parallel strike-slip faults together with the Median Tectonic Line (MTL), both of which have been activated by oblique subduction of the Philippine Sea plate during the Quaternary. They act as the boundaries of three neotectonic stress domains around the eastern margin of the Eurasian plate: the near-trench Outer zone and NW–SE compressive Inner zone of southwest Japan arc, and the southern Japan Sea deformed under E–W compression from south to north.     

Asteroid impact in the Black Sea. Death by drowning or asphyxiation?

Normally the consequences of an impact of an asteroid in a water body are discussed in terms of the beach run up of impact-generated waves. If even a small asteroid would hit the Black Sea, however, the potential emissions of toxic and flammable gases could be more disastrous to the region (comprised of Romania, Ukraine, Russia, Georgia, Turkey and Bulgaria) than the tsunami caused by the impact.     

黑海天然气水合物地质调查现状分析

黑海天然气水合物资源丰富,是我国未来开展国际合作的重要区域.论文系统地总结、分析了黑海地区天然气水合物近50年的地质调查结果,包括天然气水合物的分布、资源潜力和地质调查特点等.分析归纳要点包括:黑海地区天然气水合物类型以Ⅰ型为主,主要赋存在细粒沉积储层中,甲烷资源量最高可达850万亿m3;除俄罗斯外,黑海周边其他各国的调查能力和装备实力相对较弱,各专属海域水合物调查程度较低,资源分布不明;土耳其积极参与国际合作项目,具备一定的调查能力和装备实力,是我国未来合作的重点.     

再论台湾造山带构造格架与演化过程SCIEI北大核心CSCD

台湾造山带是中新世晚期以来相邻菲律宾海板块往北西方向移动,导致北吕宋岛弧系统及弧前增生楔与欧亚大陆边缘斜碰撞形成的。目前该造山带仍在活动,虽然规模很小,但形成了多数大型碰撞造山带中的所有构造单元,是研究年轻造山系统的理想野外实验室,为理解西太平洋弧-陆碰撞过程和边缘海演化提供了一个独特的窗口。本文总结了二十一世纪以来对台湾造山带的诸多研究进展,讨论了其构造单元划分及演化过程。我们将台湾造山带重新划分为6个构造单元,由西至东分依次为:(1)西部前陆盆地;(2)中央山脉褶皱逆冲带;(3)太鲁阁带;(4)玉里-利吉蛇绿混杂岩带;(5)纵谷磨拉石盆地;(6)海岸山脉岛弧系统。其中,西部前陆盆地为6.5Ma以来伴随台湾造山带的隆升剥蚀形成沉积盆地。中央山脉褶皱逆冲带为新生代(57~5.3Ma)欧亚大陆东缘伸展盆地沉积物由于弧-陆碰撞受褶皱、逆冲及变质作用改造形成的。太鲁阁带是造山带中的古老陆块,主要记录中生代古太平洋俯冲在欧亚大陆活动边缘形成的岩浆、沉积和变质岩作用。玉里-利吉蛇绿混杂岩带和海岸山脉岛弧系统分别为中新世中期(~18Ma)以来南中国海板块向菲律宾海板块之下俯冲形成的岛弧和弧前增生楔,其中玉里混杂岩中有典型低温高压变质作用记录,变质年龄为11~9Ma;岛弧火山作用的主要时限为9.2~4.2Ma。纵谷磨拉石盆地记录1.1Ma以来的山间盆地沉积。台湾造山带的构造演化可划分为4个阶段:(a)古太平洋板块俯冲与欧亚大陆边缘增生阶段(200~60Ma);(b)欧亚大陆东缘伸展和南中国海扩张阶段(60~18Ma);(c)南中国海俯冲阶段(18~4Ma);(d)弧-陆碰撞阶段(<6Ma)。台湾弧-陆碰撞造山带是一个特殊案例,其弧-陆碰撞并不伴随着弧-陆之间的洋盆消亡,而是由于北吕宋岛弧及弧前增生楔伴随菲律宾海板块运动向西北方走滑,仰冲到欧亚大陆边缘,形成现今的台湾造山带。     

Black Sea chemocline oscillations during the Holocene: molecular and isotopic studies of marginal sediments

We measured δ¹³C values of free and sulfur-bound lipids and framboidal pyrite-size distributions in three sediment cores from the southern margins of the Black Sea. The margin cores show a marked difference in the occurrence of biomarkers from green sulfur bacteria compared with the deep-basin cores, as a result of deepening of the chemocline resulting from enhanced mixing and/or decreased light-penetration as a consequence of high turbidity and productivity in shelf waters. Quantitation of biomarkers suggests that photic-zone anoxia along the shelf margin was generally absent during the deposition of unit I, although occurred during the deposition of Unit IIb at two sites.     

南海北部—东海南部中生代盆地演化与油气资源潜力

目前的勘探成果表明,南海北部到东海南部的广阔海域普遍发育中生代地层,但是除了在台西南盆地发现工业油气藏之外,其他地区的中生界尚未有大的勘探突破。本次研究将中生代南海北部—东海南部作为一个整体,开展大地构造背景分析,厘清各构造时期盆地的性质及其形成演化机制,探讨油气资源潜力。结果表明:南海北部—东海南部从晚三叠世到白垩纪整体为一个大型盆地,盆地的演化受其周围板块相互运动所控制;晚三叠世(T₃)主要受特提斯构造域控制,发育被动陆缘边缘海沉积盆地;从早侏罗世(J₁)到早白垩世均受古太平洋板块(伊泽奈崎板块)向欧亚板块俯冲机制的控制,其中早—中侏罗世(J_1-2)发育弧前坳陷盆地,晚侏罗—早白垩世(J₃—K₁)盆地性质为弧后断陷盆地;晚白垩世(K₂)受太平洋板块、欧亚板块和印度板块的联合控制,性质依然为弧后断陷盆地,与前期相比,裂陷强度加大;海水由东南方向侵入,地层垂向上由海相向陆相逐渐过渡,由东南向西北和东北方向,水体逐渐变浅,亦由海相向陆相逐渐演变;中生界在南海北部潮汕坳陷等地区发育深海相和海湾相泥岩,在东海南部基隆坳陷也发育良好的海湾相泥岩,生烃潜力大,具有形成大型油气藏的物质基础和地质条件,勘探潜力巨大。本次研究结果可以为南海北部—东海南部中生界的油气资源勘探提供依据。