Structure of the Sunda Trench lower slope off sumatra from multichannel seismic reflection data

Multichannel seismic reflection profiles across the Sunda Trench slope off central Sumatra reveal details of subduction zone structure. Normal faults formed on the outer ridge of the trench offset deep strate and the oceanic crust, but die out upsection under the trench sediments. At the base of the inner trench slope, shallow reflectors are tilted seaward, while deeper reflectors dip landward parallel to the underlying oceanic crustal reflector. Intermediate depth reflectors can be traced landward through a seaward-dipping monocline. We interpret this fold as the shallow expression of a landward-dipping thrust fault at depth. Landward of this flexure, relatively undeformed strata have been stripped off the oceanic plate, uplifted 700 meters, and accreted to the base of the slope. The oceanic crust is not involved in the deformation at the toe of the slope, and it can be observed dipping landward about 25 km under the toe of the accretionary prism.The middle portion of the trench slope is underlain by deformed accreted strata. Shallow reflectors define anticlinal structures, but coherent deep reflectors are lacking. Reflectors 45 to 55 km landward of the base of the slope dip 4°-5° landward beneath a steep slope, suggesting structural imbrication.A significant sediment apron is absent from the trench slope. Instead, slope basins are developed in 375–1500 m water depths, with an especially large one at about 1500 m water depth that is filled with more than 1.1 seconds of relatively undeformed sediments. The seaward flank of the basin has recently been uplifted, as indicated by shallow landward-dipping reflectors. Earlier periods of uplift also appear to have coincided with sedimentation in this basin, as indicated by numerous angular unconformities in the basin strata.Contribution of the Scripps Institution of Oceanography, new series.     

Morphology and Late Quaternary sedimentation in the Gulf of Oman Basin

The morphology of the Gulf of Oman Basin, a 3,400 m deep oceanic basin between Oman and southern Pakistan and southern Iran, ranges from a convergent margin (Makran margin) along the north side, a passive type (Oman margin) along the south side, translation types along the basin's west (Zendan Fault-Oman Line) and east (Murray Ridge) sides and a narrow continental rise and a wide abyssal plain in the centre of the basin. Sediment input into the basin during the Late Quaternary has been mainly from the north as a result of the uplift of the Coast Makran Mountains in the Late Miocene-Pliocene. Today most of this detritrus is deposited on the shelf and upper continental slope and perched basins behind the fold/fault ridges on the lower slope. The presence of fans and channels on the continental rise on the north side of the basin indicate, however, that continental derived debris was, and possibly is, being transported to the deep-sea by turbidity currents via gaps in the ridges on the lower slope. In addition to land derived terrigenous sediments, the basin deposits also contain biogenic (organic matter and calcium carbonate), eolian detritus and hydrates and authigenic carbonates from the tectonic dewatering of the Makran accretionary wedge. The eolian sediment is carried into the Gulf of Oman Basin from Arabia and the Mesopotamia Valley by the northwesterly Shamal winds. This type of detritus was particularly abundant during the glacial arid periods 21,000–20,000 and 11,000 (Younger Dryas) years ago when exposure of the Persian (Arabian) Gulf increased the area of dust entrainment and shifted the position of the source of the eolian sediments closer to the basin.     

Sedimentation in a tropical fjord: Golfo Dulce, Costa Rica

Sedimentation processes in Golfo Dulce, a periodically anoxic fjord-like embayment on the Pacific coast of Costa Rica, have been investigated by analyses of surface sediments and 3.5-m-long sediment cores. The large proportion of non-biogenic material (>90%) reflects the dominance of terrigenous sediment input to Golfo Dulce. Biogenic components such as organic carbon and carbonate are also supplied from terrigenous sources. The two components, however, originate from different parts of the coast surrounding the gulf. The sediment cores did not show any laminated sections. The sediments can be divided into turbiditic basin deposits and almost undisturbed, hemipelagic slope deposits.     

Sedimentological processes in the southern margin of the Cretan Sea (NE Mediterranean)

The Cretan Basin can be characterized as a back-arc basin of the Hellenic Trench System, that is related to the subduction zone of the African Plate under the Eurasia Plate. The study area includes the narrow and relatively steep (gradient 1.5°) continental shelf of the island of Crete followed by the steep slope (2°–4°) and the rather flat deeper part of the Cretan basin (water depths >1700 m).Surficial sediments of the coastal zone are coarser and of terrigenous origin, while in deeper waters finer sediments, of biogenic origin, are more abundant. Sand-sized calcareous sediment accumulations, identified in middle-lower slope, may be attributed to the aggregation of seabed biogenic material related to the near bed current activity.High resolution profiles (3.5 kHz) taken from the inner shelf shows a typical sigmoid-oblique progradational configuration, implying prodelta sediment accumulation during the Holocene. In the upper-middle slope, sub-bottom reflectors indicate continuous sedimentation of alternating fine and/or coarse grained material. Small-scale gravity induced synsedimentary faults appeared, locally. In contrast, a series of gravity induced faults, identified in the lower slope, are associated with sediment instabilities due to seismotectonic activity. Sediment cores taken from the shelf-break consists of calcareous muddy sand with small amounts of terrigenous silt and fine sand, while the cores recovered from the middle slope has revealed a more homogeneous fine sediment texture of hemipelagic deposition.The prevailing accumulation processes in the southern margin of the Cretan basin are: (i) prodelta deposition in the inner-middle shelf; (ii) settling from bottom nepheloid layers in the shelf and upper slope; (iii) calcareous sediment formation due to settling from suspension and post accumulation aggregation (middle-lower slope); (iv) long-term episodic sediment gravity processes in the lower slope; and (v) to a lesser extent, redeposition from resuspension due to gravity processes and bottom currents.     

Morphology and tectonics of the Yap Trench

We conducted swath bathymetry and gravity surveys the whole-length of the Yap Trench, lying on the southeastern boundary of the Philippine Sea Plate. These surveys provided a detailed morphology and substantial insight into the tectonics of this area subsequent the Caroline Ridge colliding with this trench. Horst and graben structures and other indications of normal faulting were observed in the sea-ward trench seafloor, suggesting bending of the subducting oceanic plate. Major two slope breaks were commonly observed in the arc-ward trench slope. The origin of these slope breaks is thought to be thrust faults and lithological boundaries. No flat lying layered sediments were found in the trench axis. These morphological characteristics suggest that the trench is tectonically active and that subduction is presently occurring. Negative peaks of Bouguer anomalies were observed over the arc-ward trench slope. This indicates that the crust is thickest beneath the arc-ward trench slope because the crustal layers on the convergent two plates overlap. Bouguer gravity anomalies over the northern portion of the Yap Arc are positive. These gravity signals show that the Yap Arc is uplifted by dynamic force, even though dense crustal layers underlie the arc. This overlying high density arc possibly forces the trench to have great water depths of nearly 9000 m. We propose a tectonic evolution of the trench. Subduction along the Yap Trench has continued with very slow rates of convergence, although the cessation of volcanism at the Yap Arc was contemporaneous with collision of the Caroline Ridge. The Yap Trench migrated westward with respect to the Philippine Sea Plate after collision, then consumption of the volcanic arc crust occurred, caused by tectonic erosion, and the distance between the arc and the trench consequently narrowed. Lower crustal sections of the Philippine Sea Plate were exposed on the arc-ward trench slope by overthrusting. Intense shearing caused deformation of the accumulated rocks, resulting in their metamorphism in the Yap Arc.     

Holocene climate in the Persian Gulf as deduced from grain-size and pteropod distribution

Detailed coarse-fraction analyses have been made of twelve sediment cores from the Persian Gulf (40–100 m water depth) in order to detect Holocene climatic changes.The only indication of such a change was provided by the terrigenous material (i.e., the < 63 μ fraction) carried into the Gulf by rivers. All cores show characteristic variations in the quantity of terrigenous material and alternating fine- and coarse-grained layers.There was no other parameter which could point to variations in climate. This might be due to the fact that the sediments are sorted as a result of reworking by tidal currents (velocities 25–50 cm/sec): fine and light particles are removed. Any climatically-produced variations in amount or size of benthonic and planktonic organisms have probably been obliterated by tidal currents. The importance of this factor varied with time: during increased terrigenous supply, tidal currents modified the sediment surface for only short periods and a fine-grained layer was, therefore, deposited. A lesser supply of terrigenous material, on the other hand, resulted in the deposition of a coarse-grained layer.Contemporaneous sedimentation of layers with much terrigenous material (fine-grained layer) and with little terrigenous material (coarse-grained layer) is suggested. Observed petrographic variations are presumably due to large-scale changes of climate and not to local sedimentary variations (including shifts of river-mouth processes).Accordingly, the cores were correlated by examining the percentage of coarse fraction and the median diameter of the sand fraction. The assumption is that the higher the percentage of coarsegrained material, the lower the amount of terrigenous material transported into the Persian Gulf.In support of this correlation, another parameter - varying independently from grain size within one core - was examined: the species composition of pteropod shells. These quantitative changes could also be correlated, because there were different core sections with different species compositions.Correlation of the cores by grain size and by pteropod species provides the same results.Four different climatic zones could be distinguished between the lower and the upper part of the Holocene: a relatively arid period at about 9000 years B.P. was succeeded by a more humid period; this then was followed by a period of less rainfall and finally a period during the Late Holocene when rainfall increased again. This sequence is comparable to the established European climate chronology.     

马里亚纳“沟−盆”深水沉积环境稀土元素特征与物源约束

通过对西太平洋帕里西维拉海盆东南部的C-P19柱状样和马里亚纳海沟南坡的L3柱状样进行粒度和稀土元素地球化学分析,探讨了二者物源的异同。结果表明:研究区沉积物的稀土元素含量基本不受沉积物粒度控制,主要受控于物源变化。物源判别结果指示二者的物源具有同源性,其中西马里亚纳海脊剥蚀下来的火山物质对研究区的物质来源贡献最大。火山物质中的重矿物可以影响到稀土元素的含量,例如锆石的含量和稀土元素总量(ΣREY)的相关系数可达0.86。来自中国内陆黄土的陆源风尘物质对两个研究区的物源供给也有一定贡献,但其贡献程度较小。由于马里亚纳海沟南坡更加远离大陆且纬度更低,其接受的亚洲风尘也比帕里西维拉海盆和挑战者深渊更少。此外,南极底层水流经研究区,对海盆和海沟的沉积物都造成一定影响,而且在马里亚纳海沟南坡更加活跃,因而帕里西维拉海盆东南部的沉积物比马里亚纳海沟南坡更易于保存。     

南海中央海盆之东部次海盆后扩张期地层特征与影响因素

海底扩张形成的边缘海盆构造演化可划分为前扩张期、同扩张期与后扩张期等阶段。南海中央海盆巨厚的沉积地层大部分是扩张结束之后形成的,尤以东部次海盆地层厚度为最大。因受到不同因素的影响,在该次海盆不同的区域后扩张期发育的地层特征差别较大。这些现象反映海底扩张结束之后所发育的厚层地层中蕴含了大量南海构造演化的信息,因此深入分析该次海盆后扩张期的地层特征与影响因素是南海构造演化研究中不容忽略的环节。利用若干大洋钻孔年代地层资料,在过井剖面上进行合成地震记录标定、划分层序地层并确定其年代属性,并以此为依据分析讨论了本区的地层特征和相关的影响因素。结果表明,东部次海盆北部持续均衡的基底沉降和充足的陆缘物质形成厚度稳定的地层沉积;东部以微板块向马尼拉海沟俯冲为主要影响因素,使不同年代的地层各具特征;中部和西部岩浆活动是主要的影响因素,形成以火山碎屑物质为主的地层沉积;南部因当时的陆坡沉积环境和浊流活动的影响形成具有沉积物波特征的地层沉积。     

渤海湾盆地庙西南洼古近纪沟谷特征及对近源碎屑沉积的控制

为了更好地预测低勘探区有利砂体的展布,在综合利用测井、钻井、地震等资料的基础上,对渤海湾盆地庙西南洼古近系的沟谷特征及其对近源碎屑沉积的控制作用进行了研究。结果表明：与郯庐断裂近EW向垂直相交的大型基底断裂在古近纪表现为长期拉张沉降特征,形成区域性的大型沟谷,多控制着次级洼陷的发育;而与郯庐断裂NW向、NNW向相交的派生断层一般处于挤压应力状态,多发育小型挤压断裂型沟谷。这些小型沟谷在缓坡带和陡坡带的表现特征具有明显差异。通过地震反射、地震相、属性分析和钻井资料相结合的手段,识别并确定不同层段的近源碎屑沉积体的展布,对比发现：NE向或近EW向的区域性大型沟谷往往成为陆源碎屑物质的宏观进积方向,规模相对偏小的大型沟谷,对碎屑物质进积方向的控制作用更为明显;而NW向的小型挤压性断沟,只能控制局部陆源碎屑物质的进积,沿着这些小型沟谷进入盆地的方向,往往能够准确寻找到各类近源碎屑沉积体的位置,这将有利于指导庙西南洼古近系的勘探部署。     

Slump structures in quaternary slope sediments of the northern Derbent Basin (Caspian Sea)

During Cruise 20–3 of the R/V Rift (April, 2006), the area that includes the shelf and slope of the Derbent Basin in the northern Middle Caspian was studied using the continuous seismoacoustic profiling method. In accordance with the previous standpoint, two Pleistocene deltaic complexes formed in the Enotaevian and Mangyshlakian time are defined in this area. The seismoacoustic records obtained for the northern slope of the Derbent Basin demonstrate the development of specific rootless exogenic-gravitational fold structures in the upper (～150–200 m) Quaternary part of the sedimentary sequence. The Quaternary section encloses angular unconformities indicating the pulsating mode of gravitational processes in the northern slope of the basin. South-dipping gravitational normal faults (and/or normal fault-related flexures) displacing the bottom surface and uppermost sedimentary layers (with vertical amplitudes up to 5–6 m) were defined in the southern part of the study area. Several impulses of the submarine slump structures predated and accompanied the deposition of the upper deltaic sequence (Mangyshlakian), although their most intense formation took place later during the Novocaspian (Holocene) time. Thus, the structural analysis of the seismoacoustic data revealed intense development of different-origin and different-age gravitational structures within the Quaternary sediments in the northern slope of the Derbent Basin. These results should be taken into consideration when designing, building, and operating submarine constructions in order to prevent potential natural hazards and reduce their consequences.     

Composition and conditions for formation of neogene deposits at the Primorye continental slope in the area of Vladimir Bay in the Sea of Japan

The petrographic and micropaleontological studies of the rocks in the sedimentary cover of the Primorye continental slope in the area of Vladimir Bay in the Sea of Japan made it possible to establish that the sedimentary cover is represented in this area by two different facial complexes of Late Miocene rocks. The first facial complex consists of terrigenous rocks (siltstones, sandstones, and conglomerates) that were accumulated under relatively shallow-water conditions of the shelf and the uppermost part of the continental slope. The second one is formed by diatomaceous-clayey rocks under more deep-water conditions, mainly in the upper part of the continental slope. The carbonate nodules that are widely distributed among the deposits of the first complex but are also recorded in the second one were formed as a result of diagenetic processes in the terrigenous or silicious-terrigenous sediments that had been formed. With respect to their age, the Late Miocene deposits are characterized by a full succession of diatomaceous zones over 10.0–5.5 mln yr. The sediments of the first facial complex accumulated during the first third of the Late Miocene (10.0–8.5 mln yr), while those of the second began to accumulate somewhat later, but their accumulation continued until the late Miocene (9.2–5.5 mln yr).     

A seismic reflection study of the External Calabrian Arc in the northern Ionian Sea (eastern Mediterranean)

The External Calabrian Arc is located off the convex side of the Calabro-Peloritanian Arc in the northern Ionian Sea. A systematic reflection seismic survey indicates that it is made of different structural elements whose characters seem consistent with an active accretionary margin. The main structures are the Crotone-Spartivento slope (comparable to an inner trench slope) and the intermediate depressions (comparable to a trench area). Internal to these elements, the Crotone-Spartivento basin may represent a fore-arc basin. This partly outcrops in Calabria and its structure suggests that the accretionary margin developed at least since middle-upper Miocene.Subduction processes do not affect a true oceanic crust, because of the great thickness of sediments covering the whole eastern Mediterranean. Hence some peculiar features occur in the system. as the cobblestone topography, or are lacking, as a typical and continuous trench zone.In the areas with cobblestone topography we distinguish a Calabrian Ridge sensu stricto from a Calabrian Ridge sensu lato. The former is a N-S trending swell, external to the supposed trench zone, interpreted as a sedimentary outer-arc ridge produced by rather surficial tectonic accumulation of sediments further chaoticized by gravitative mechanisms. The Ridge s.l. is a very wide area with low relief and little or no seismic penetration. Tectonization seems gentler than in the Ridge s.s. and structural axes seem to possess different orientations. These areas are interpreted as due to a widespread surficial chaoticization above presumed decollement layers occurring within the sedimentary column of the Ionian bathyal plain.The pattern of deformations of the Calabrian Ridge seems consistent with the Calabro-Peloritanian Arc actively overriding the eastern Mediterranean, with a resultant direction of movement essentially towards the East.     

舟山外钓山海岸边坡泥沙动力与冲淤演变特征

通过对研究区海域的水文泥沙进行现场测验,对比1960-1962年海图、1995年和2001年水下地形图三期地形数据和分析浅地层探测数据等方法,分析了舟山外钓山岛西海岸边坡的水动力、悬浮泥沙及冲淤特征,探讨了海岸边坡发育演变的模式与机制。研究结果表明,在基岩岬角海岸与潮流深槽的边界控制及往复潮流的作用下,舟山外钓山岛西海岸边坡演变是一个"上淤下冲"的模式,即边坡变陡至边坡土体失稳并在不定期外力触发下滑塌堆积坡脚,然后上部重新淤积、下部滑坡体不断被侵蚀的循环过程。     

南海海盆中部表层沉积物地球化学特征

分析了南海海盆中部224个站位表层沉积物的常量组分和微量元素组成,结果表明,这些沉积物与大陆上地壳相比,具有相对贫Si和富Fe、Mg、Na、Ca、Mn的特点,微量元素含量总体与大陆上地壳较为相近。表层沉积物化学组分可以划分为4类组合：硅酸盐碎屑组分、钙质生物碎屑组分、火山碎屑组分和自生矿物组分;硅酸盐碎屑组分和钙质生物碎屑组分占绝对优势,两者含量互为消长,自生矿物和火山碎屑含量较低,仅在局部区域起到相对明显的贡献。南海海盆中部表层沉积物化学组成主要受水深、沉积作用和物质来源3个因素控制;水深和底流搬运作用影响钙质生物碎屑分布,深水海盆碳酸盐溶解作用强烈,海盆中部沉积物钙质生物碎屑含量低,而底流作用则将陆坡区钙质碎屑搬运至海盆边缘区域。沉积物地球化学特征指示,海盆中部沉积物陆源碎屑物质主要来自于西部或西南部,火山碎屑物质可能主要来自于吕宋岛弧火山喷发,并堆积于扩张中心以北和海盆东部区域。     

Geochemistry and organic petrography of Cretaceous sediments of the Calabar Flank,southeastern, Nigeria

Detailed bulk geochemistry and organo-petrography of outcrop Cretaceous sediments (with no significant effects of weathering) from the Calabar Flank, southeast Nigeria were performed to understand the organic carbon source, accumulation and degradation, and paleo-climatic, paleoceanographic and paleoenvironmental conditions in West Africa during Early Cretaceous (Aptian) to Maastrichtian times. This study was based on microscopic, elemental analyses (organic carbon, nitrogen, iron and sulphur), Rock-eval pyrolysis and carbon-isotope analyses. In general, the Calabar Flank shales are characterised by highly variable total organic carbon (TOC) contents, which range between 0.1% in Aptian–Albian Mfamosing Limestone and 9.9% in the Awi Formation sediments. The organic matter (OM) is a mixture of immature to early-mature marine and terrigenous OM of types III and IV. This is indicated by low hydrogen indices (HI value (10–190 mg HC/g TOC), T_max (417–460 °C), vitrinite reflectance %R_o (0.39–0.62 %R_o), low to high C/N ratios (3.4–1158.0) and high amounts of terrigenous macerals (vitrinite + inertinite). Based on carbon isotope, C/N ratios and sulphate reduction index (SRI), OM degradation (up to 70%, SRI > 2.5) is most pronounced for shales deposited in a marine environment. The geochemical and petrographic data indicate that local factors such as low bioproductivity, down slope transport and redeposition of sediments from a fluvial–deltaic basin to nearshore facies, shallower, oxic and mildly oxygen-deficient environments, humid–arid paleogeographic conditions, specifically controlled the amount and quality of the OM during Aptian–Mastrichtian stages where marine sediments have been assumed to be deposited during the global anoxic events. Therefore, the order of the main factors controlling OM content in sediments are: input of terrigenous material transported from the land > low OM productivity by marine photoautotrophs > low preservation.     

Suspended particulate matter and nepheloid layers over the southern margin of the Cretan Sea (N.E. Mediterranean): seasonal distribution and dynamics

Seawater along the southern margin of the Cretan Sea (May 1994–September 1995) has been found to have light transmission values ranging from 79% to 94%, corresponding to SPM values ranging from 1.5 mg l⁻¹ to 0.2 mg l⁻¹. The highest SPM concentrations (mostly of terrigenous origin) were found close to the sea-bed over the shelf-break and upper slope. The origins of SPM in the surface waters (<150 m) is principally biogenic. The occurrence of nepheloid layers at intermediate depths within the upper water column is mostly a result of density stratification. The dynamics of SPM distributions are governed by the 2-gyre system which induces a general onslope flow; and so inhibits the seaward dispersion of the relatively more turbid coastal/shelf waters. This is in agreement with the virtual absence of suspensates of terrigenous origin offshore of the shelf-break. Near bottom nepheloid layers (BNL) and detached intermediate nepheloid layers occur in the vicinity of the shelf-break and over upper slope region; these may be explained by resuspension induced by near-bed current activity and breaking of internal waves. High concentrations of SPM near the seabed may be caused by anthropogenic (trawling) activity. Occasionally, the formation of BNL may result from local seismic activity resulting in gravity-driven mass movements.     

Sedimentation on the continental terrace around New Zealand: A review

The New Zealand continental terrace is mantled mainly by terrigenous and biogenic sediments associated with subordinate but locally important authigenic, volcanogenic and residual components. Modern terrigenous sands and muds prevail off Westland and Hawkes Bay—Wairarapa where tectonically rising landmasses, several major rivers and few coastal sediment traps ensure deliverance of much sediment to the terrace. Relict terrigenous sands and gravels typically occur in zones where modern sedimentation is low like the middle and outer continental shelf off Otago—Canterbury and Waikato—Taranaki. Relict sediments are commonly associated with biogenic sands and gravels which also dominate the terrigenous-starved shelves around northernmost and southernmost New Zealand, and much of the continental slope. Shelf biogenic components are mainly molluscan, bryozoan and foraminiferal clasts, whereas on the slope foraminifers and calcareous nannoplankton prevail. Both glauconite, the main authigenic component, and residual sediments occur on those shelves and upper slopes receiving little modern terrigenous sediment. Volcanogenic grains are prominent in sediments on the eastern terrace marginal to the Central Volcanic Region of the North Island.Typically, terrigenous shelf sediments off the North Island and northeast South Island have been reworked from older sediments or derived directly from volcanic rocks or both. Around the remainder of the South Island a metamorphic and plutonic-derived assemblage prevails. Sediment dispersal is along the shelf primarily under the influence of storm-driven and tidal currents with semi-permanent ocean currents having little effect. Beyond the shelf, dispersal appears to be mainly downslope, partly through redepositional mechanisms including gravity slumps and turbidity currents.     

Neogene geological history of the Tohoku Island Arc system

The Pacific-type orogeny in the Tohoku Island Arc is discussed using marine geological and geophysical data from both Pacific and Japan Sea along the Tohoku region. The Tohoku Arc is divided into three belts; inner volcanic and sedimentary belt, intermediate uplifted belt and outer sedimentary trench belt. Thick Neogene sediments which are distinguished in several layers by continuous seismic reflection profiling occur on both sides of the intermediate belt. The dominant structural trend of the Neogene layers is approximately parallel to the coast line and to the axis of the Japan Trench and has a extension of approximately 100 km in each unit on the Pacific side. The trench slope break is an uplifted zone of Neogene layers. The structural trend of the upper continental slope and outer shelf is relative uplift of the landward side. Tilted block movement toward the west is the dominant structural trend on the Japan Sea side. Structural trends which can be seen in both the inner and outer belts may suggest horizontal compressional stress of east to west. Orogenesis and tectogenesis in the Tohoku Arc has been active since early Miocene or latest Oligocene. It may be implied that the Japan Trench was not present during Late Cretaceous to Paleogene, as is suggested by the volcanism of the Tohoku Arc. The basic framework of the present structure was formed during late Miocene to early Pliocene in both the inner and outer belts. Structural movements were reactivated during late Pleistocene.