Influence of lithologic erodibility on alluvial fan area,western white mountains,California and Nevada

Differences in lithologic erodibility and sediment storage within a drainage basin affect the relationship between alluvial fan area and drainage basin area along the western White Mountains. Large fans are produced by basins underlain by resistant rocks, which have steep and narrow trunk stream canyons with little sediment in storage. Small fans are produced by basins composed of erodible lithologic units, which have wider valley floors, lower valley-side slopes, and considerably more sediment stored along trunk stream canyons than is the case in basins underlain by resistant rocks.     

Seismogenic destruction of the Kamenka medieval fortress, northern Issyk-Kul region, Tien Shan (Kyrgyzstan)

A paleoseismological study of the medieval Kamenka fortress in the northern part of the Issyk-Kul Lake depression, northern Tien Shan in Kyrgyzstan, revealed an oblique slip thrust fault scarp offsetting the fortification walls. This 700 m long scarp is not related to the 1911 Kebin Earthquake (Ms 8.2) fault scarps which are widespread in the region. As analysis of stratigraphy in a paleoseismic trench and archaeological evidence reveal, it can be assigned to a major twelfth century a.d. earthquake which produced up to 4 m of oblique slip thrusting antithetic to that of the nearby dominant faults. The inferred surface rupturing earthquake apparently caused the fortress destruction and was likely the primary reason for its abandonment, not the Mongolian–Tatar invasions as previously thought.     

Large-scale Basement-involved Landslides, California Continental Borderland

— Large seafloor relief, shallow metamorphic basement, and seismic activity in the California Continental Borderland combine to produce major submarine slides capable of generating local tsunamis. The Catalina Schist basement complex of the Borderland contains melange units, faults between metamorphic facies, and foliation derived from a history of deep subduction underthrusting and subsequent tectonic exhumation along regional low-angle fault systems. Neogene volcanic and sedimentary rocks covered the exhumed metamorphic basement forming an interface with a strong contrast in material properties. Neogene transtensional block-faulting formed steep escarpments that cut through and elevated the low-angle detachment surface, providing slip surfaces with free faces susceptible to failure along the rheological boundary. Two basement-involved slope failure examples west of San Diego are described, including large block-glides and progressive rotational slumps along the steep northeast-facing Thirtymile Bank escarpment and along the southwest flank of Fortymile Bank.     

FIRST REPORT OF BERO ZECO ACTIVE FAULT IN GÊRZÊ, NORTHERN TIBET

In the interior of the Tibetan Plateau, the active tectonics are primarily marked by conjugate strike slip faults and north-trending rifts, which represent the E-W extension since late Cenozoic of the plateau. The conjugate faults are mainly composed of NE-trending left-lateral strike-slip faults in Qiangtang terrane and NW-trending right-lateral strike-slip faults in Lhasa terrane. While, the rifts mainly strike N, NNW and NNE within southern Tibet. However, it is still a debate on the deformational style and specific adjustment mechanism of E-W extension. One of key reasons causing this debate is the lack of detailed investigation of these active faults, especially within the northwestern plateau. Recently, we found a 20km long, NNW-trending active fault at Bero Zeco in northwestern Tibet. This fault is presented as fault sag ponds, channel offsets and fault scarps. Displacement of channels and geomorphic features suggested that the Bero Zeco Fault(BZF)is a dextral strike-slip fault with a small amount of normal slip component, which may result from the E-W extensional deformation in the interior of Tibet. BZF strikes N330°~340°W, as shown on the satellite image. The main Quaternary strata in the studied area are two stages alluvial fans around the Bero Zeco. From the satellite images, the old alluvial fans were cut by the lake shoreline leaving many of lake terraces. And the young fans cut across the lake terraces and the old fans. By contrasting to the "Paleo-Qiangtang Huge Lake" since late Quaternary, these old alluvial fans could be late Pleistocene with age ranging from 40ka to 50ka. And the young fans could be Holocene. The sag ponds along the BZF are distributed in the late Pleistocene alluvial fans. Also, the BZF displaced the late Pleistocene fans without traces within Holocene fans, suggesting that the BZF is a late Pleistocene active fault. The fault scarps are gentler with the slope angle of around 10° and the vertical offset is about 2m by field measurement. Reconstruction of the offset of channels suggested that the accumulated dextral offset could be about 44m on the late Pleistocene alluvial fans. Therefore, we infer that the dextral slip-rate could be around 1mm/a showing a low-rate deformation characteristic. The angle between the strike of BZF and principal compressive stress axis(σ₁)is around 30°, which is significantly different to the other faults within the conjugate strike-slip fault zones that is 60°~75°. Now, the deformation mechanisms on these conjugate faults are mainly proposed in the studies of obtuse angle between the faults and σ₁, which is likely not applicable for the BZF. We infer that the BZF could be the northward prolongation of the north-trending rifts based on the geometry. This difference suggests that the conjugate strike-slip faults may be formed by two different groups:one is obtuse angle, which is related to block extrusion or shear zones in Lhasa and Qiangtang terranes possibly; the other is acute angle, which may represent the characteristics of new-born fractures. And more studies are needed on their deformation mechanisms.     

The proximal part of the giant submarine Wailau landslide, Molokai, Hawaii

The main break-in-slope on the northern submarine flank of Molokai at −1500 to −1250 m is a shoreline feature that has been only modestly modified by the Wailau landslide. Submarine canyons above the break-in-slope, including one meandering stream, were subaerially carved. Where such canyons cross the break-in-slope, plunge pools may form by erosion from bedload sediment carried down the canyons. West Molokai Volcano continued infrequent volcanic activity that formed a series of small coastal sea cliffs, now submerged, as the island subsided. Lavas exposed at the break-in-slope are subaerially erupted and emplaced tholeiitic shield lavas. Submarine rejuvenated-stage volcanic cones formed after the landslide took place and following at least 400–500 m of subsidence after the main break-in-slope had formed. The sea cliff on east Molokai is not the headwall of the landslide, nor did it form entirely by erosion. It may mark the location of a listric fault similar to the Hilina faults on present-day Kilauea Volcano. The Wailau landslide occurred about 1.5 Ma and the Kalaupapa Peninsula most likely formed 330±5 ka. Molokai is presently stable relative to sea level and has subsided no more than 30 m in the last 330 ka. At their peak, West and East Molokai stood 1.6 and 3 km above sea level. High rainfall causes high surface runoff and formation of canyons, and increases groundwater pressure that during dike intrusions may lead to flank failure. Active shield or postshield volcanism (with dikes injected along rift zones) and high rainfall appear to be two components needed to trigger the deep-seated giant Hawaiian landslides.     

An outline of the petrology, structure and age of the Pompangeo Schist Complex of central Sulawesi, Indonesia

Variably dismembered and metamorphosed accretionary complexes constitute the basement of much of the Indonesian island of Sulawesi. The most extensive of these is the Pompangeo Schist Complex, which crops out over ∼ 5000 km² in central Sulawesi, and is predominantly composed of interbanded phyllitic marble, calcareous phyllite, graphitic schist and quartzite; rocks of terrigenous to shallow marine origin. Along the eastern margin of the complex, schists are interthrust with unmetamorphosed Jurassic sandstone, which may represent parental material of the complex. The schists are unconformably overlain by pelagic sediments with an Albian–Cenomanian biostratigraphy. Synmetamorphic progressive deformation of the Pompangeo Schist Complex has resulted in repeated isoclinal folding and a strong transposition foliation striking north-northwest/south-southeast and dipping west, subparallel to the compositional banding of the complex; microstructural fabrics indicate a top-to-east sense of shear. On a regional scale the Pompangeo Schist Complex is lithostratigraphically coherent and an east-to-west metamorphic field gradient is recognizable, which, if continuous, represents a relatively low thermal gradient of ∼ 15 °C/km. K–Ar dating yielded ages of ca 111 Ma. Correlative metamorphic rocks appear to underlie the entire Neogene magmatic province, since they occur sporadically throughout western Sulawesi, including the Bantimala region of the South Arm. The Pompangeo schist metamorphism cannot be correlated with arc magmatism in western Sulawesi, which is of Neogene age. The Pompangeo and Bantimala schists, as well as other accretionary complexes in western Sulawesi, were probably generated in the same subduction system that was responsible for the extensive Mesozoic continental arc in central Kalimantan, at the eastern margin of Sundaland.     

Recent deformation at the junction between the North Luzon block and the Central Philippines from ERS-1 Images

Abstract The transfer of the major part of the motion between the Philippine Sea Plate and the Sunda block is accommodated along a north-west shear wide zone partly on the Philippine Fault and partly on the Sibuyan Verde Passage Fault (SVPF) as indicated by global positioning satellite and geological data. Given the limited motion along the SVPF and the important motion along the Philippine Fault, as well as the necessity of a connection between these faults and the southern Manila Trench, a transtensional motion along the northeast-southwest Macolod Corridor (MC) may be predicted. We used synthetic aperture radar European remote sensing (SAR ERS-1) images to analyze the volcano– tectonic features of this area, because these images are sensitive to minute textural or topographic contrasts resulting from small effects of recent deformation. In addition, they allow us to determine accurately the shape of the base of volcanic edifices and to detect linear clusters of very small adjacent cones. The results presented herein allow us to extend the features recognized earlier to a larger MC. Large faults actually connect the Philippine Fault to the Sibuyan Verde Passage Fault all across the Taal Volcanic Field. In addition to extension along north-east faults, we identify an important component of left-lateral strike–slip underlined by fault scarps, dykes, alignments of volcanoes and pull-apart basins, accompanied by extension along north-south faults. A relative chronology of the fractures and volcanic edifices is proposed. When compared to the existing ages of the volcanics, an evolution scheme of the area may be proposed, according to which extension shifted from a nearly north-south opening between 5 and 2 million years to a direction close to east-west at Present. The early north-south extension existed in the Marinduque Basin and may have migrated northward and rotated to the present MC.     

塔里木西缘明尧勒背斜的弯滑褶皱作用与活动弯滑断层陡坎

塔里木西缘明尧勒活动背斜两翼河流阶地面上多处发育活动弯滑断层陡坎。这些断坎主要分布在活动轴面附近较陡的等斜岩层(地层倾角分别为74°~89°、18°~20°和45°~60°)一翼,往往成排发育在距活动轴面50~1 200m范围内,宽90~1 000m,长40~950m,随着离活动轴面的距离加大弯滑断层陡坎规模渐小。同一阶地面上发育的弯滑断层陡坎几乎以等间距或间距倍数关系产出。这些断坎走向与下伏基岩地层走向一致,基岩地层大多为中-厚层块状砂岩或粉砂岩互层,岩层间力学性质差异较小。明尧勒背斜南翼克孜勒苏河北岸T3阶地面废弃以来,单条弯滑断层的地表最大缩短速率为0.31mm/a,地表最大抬升速率为0.34mm/a。这些弯滑断层的活动具有重复性和新生性。     

哀牢山变质带元江──墨江剖面岩石的纵波波速特征及其地质意义

依据研究区的地热梯度（25℃／km）,在高温高压（最高温度为1050℃,最高压力为1.2GPa）条件下系统测量了横穿红河-哀牢山断裂带的元江-墨江地质剖面上的哀牢山岩群各类变质岩（千枚岩、片岩、浅粒岩、变粒岩、大理岩和片麻岩）的纵波速度．实验结果表明,不同岩类的纵波速度随温度压力变化的趋势不同．在相当于衷牢山岩群变质岩峰期变质温度和压力条件下（P=0．4-0.8GPa,T=35-700℃）,测得大部分岩石的纵波速度为5．50－5．80km／s,这一纵波速度值与区域地球物理测深揭示的中地壳低速层的纵波速度相当因此,结合该区变质岩、地壳内热状态及地球物理测深研究成果可初步认为：组成哀牢山岩群的浅粒岩、变粒岩、酸性片麻岩以及部分千枚岩、片岩为该地区中地壳低速层的主要岩石类型．     

Rapid uplift,stepped marine terraces and raised shorelines on the Calabrian coast of Messina Strait,Italy

A series of 26 Quaternary shorelines, stepped between present sea level and 556 m, are studied. They are part of the flight of marine terraces of the Aspromonte region. The shorelines were determined using three geomorphological models: wave-cut platforms and gravel-built terraces associated with their sea-cliff foot, and observations of lateral changes between marine terraces and fluvial terraces. The elevation of the sea-cliff foot is either measured directly, by exposure in cross-section, or by estimation from geomorphological patterns. With caution, we connect the different landmarks of the shorelines which are discontinuous because of destruction between interfluves or because they are overlain by torrential deposits. The results of mapping show that there are few differential movements from one transect to another and mean uplift rate is 98 cm ka^?1. This rate is calculated on the basis of a correlation of the area studied with the Ravagnese Tyrrhenian site, 125 m high, whose date is isotopic substage 5e. Middle and Late Quaternary tectonic activity leads to faulting, slight folding and warping but some scarps associated with faults are actually ancient sea cliffs.     

Remote sensing-GIS and GPR studies of two active faults,Western Gangetic Plains,India

Northern parts of the Ganga–Yamuna Interfluve in the Gangetic Plains, India have been investigated by remote sensing and Ground Penetrating Radar (GPR) techniques. Digital analysis of remote sensing data and Geographical Information System (GIS) techniques were used to locate a new active transverse Muzaffarnagar Fault and confirmed an earlier described Solani-II Fault in almost flat or gently sloping terrain. The Solani-II and Muzaffarnagar faults are members of two major systems of surficial faults i.e. longitudinal and transverse faults, respectively. Longitudinal faults are curvilinear in nature, trending N–S in the northern regions and veering to E–W in the southern regions of the plains and transverse faults are normal to the longitudinal faults occurring in the Upper Gangetic plains.GPR survey was carried out by common offset method across the Muzaffarnagar and the Solani-II faults, using a 100 MHz antenna. Our GPR data indicate that both regions around the Solani-II Fault and Muzaffarnagar Fault are characterized by 2–3 major steeply dipping normal faults at shallow depth (< 20 m). One of the major faults is always associated with cliffs on the surface. In addition, a number of smaller synthetic and antithetic faults are present, thus forming members of an array covering wide regions. Also, several small folds observed in all the three radargrams which are probably seismites. Both the Solani-II and Muzaffarnagar faults probably developed at about 2.5 ka and almost at the same time fans were deposited on the downthrown block of the Muzaffarnagar Fault.     

滇西南地区澜沧断裂全新世滑动速率与走滑起始时间探讨

通过卫星影像解译、野外实地调查和地质填图,获得滇西南地区澜沧断裂的基本特征和活动性参数,澜沧断裂属于龙陵—澜沧新生地震断裂带的东南段,北起耿马县联合村,向南东经澜沧县哈卜吗、战马坡、大塘子至澜沧县城东南,总体走向NNW,长度约85km。该断裂为一条全新世活动的右旋走滑断裂,兼具倾滑分量,沿断裂形成了丰富的断错地貌现象,主要表现为断层陡崖、冲沟右旋、断层陡坎、断层沟槽、断层垭口和断陷凹坑等。通过详细的野外考察,选择典型断错地貌进行差分GPS测量,结合所获相应地貌面的年代数据,得到该断裂全新世以来平均右旋走滑速率为(4.2±2.3)mm/a,其结果与现今GPS观测所得速率相当,反映了该断裂长期以来滑动速率的稳定性。同时根据岩体的最大位错量4.6~4.8km,估算断裂开始右旋走滑的时代为距今约1.1 Ma,即早更新世晚期。     

褶皱陡坎中相关断层在缩短量计算中的作用——以东秋里塔格背斜为例

通过对东秋里塔格背斜地区内与褶皱陡坎伴生的次级断层进行的地质调查,确定了该次级断层属于伸出向斜的逆冲断层,也给出了次级断层的发生时间晚于褶皱作用起始时间的1个变形实例。褶皱陡坎中发育的次级断层使得陡坎上盘地层沿断层面整体向上迁移,不仅次级断层使得阶地面发生掀斜并增大褶皱陡坎的坡度,而且直接影响了区域缩短增量计算的真实性。计算结果显示,当不考虑次级断层对褶皱陡坎高度的影响时,计算所得缩短增量为51.42m,考虑次级断层对褶皱陡坎高度的影响时,计算得到的地壳缩短量为45.23m。二者相差6.19m,偏差占总缩短增量的13.7%,是一个不可忽视的量值。东秋里塔格背斜北翼和南翼的褶皱陡坎发育于相同岩性的基岩中而且具有相同的形成机制。但是背斜北翼在水平距离不足300m的范围内发育了3级褶皱陡坎,这表明北翼相对于南翼,其活动枢纽带更为紧闭。这是由于北翼存在更加强烈的挤压应力及更加快速的隆升作用。因此,次级断层的研究对于正确认识区域构造演化、了解褶皱与断层相互作用关系具有重要意义。但是仍存在很多问题:1)受观察剖面范围有限、次级断层分布不连续和断距沿延伸方向不断增大等因素的制约,次级断层对缩短增量造成的影响可能被低估,计算结果应为缩短量的最小值。2)次级断层增加的陡坎高度与断层的断距、倾角具有怎样的定量关系?3)若次级断层只发育于活动枢纽带内,又会产生怎样的影响?这些问题还需更多的研究实例来进行更加深入的研究。     

Structural analysis of the Brigham City-Weber segment boundary zone,Wasatch normal fault,Utah: Implications for fault growth and structure

We investigate the history, kinematics, principal stress orientations and geometry of deformation at the end of a bent normal fault segment of the Wasatch fault zone, Utah. Three fault types, developed in Archean crystalline rocks, reflect progressive uplift of fault-related footwall rocks. Chlorite-breccias and phyllonites reflect deep-level, reaction-assisted plastic deformation along the north-striking part of the segment. Planar, fretted faults which formed by cataclasis cut the phyllonites and breccias and are developed throughout the footwall of the segment. Youngest faults are hematitecoated, extremely narrow polished surfaces. Slip vectors and kinematic analyses of small faults developed in the footwall indicate oblique normal slip along the north-striking portion of the segment. Slip vectors and fault orientation along the northwest-striking portion of the segment reflect complexly oriented slip on faults which strike subparallel and at high angles to the main fault trace, yet slip is confined to a broad fault-parallel zone. Small faults at the southernmost tip of the segment indicate a strong influence of the north-striking Weber segment to the south. Inversion of fault data for principal stress orientations document complexly oriented principal stresses through the segment boundary zone and suggest that ₃ may have reoriented approximately 60° over the life of the segment. Subsurface structure combined with small fault data indicate the segment boundary is comprised of a southwest-plunging bedrock high which is reflected by a sharp bend in the Brigham City segment. The southern end of the Brigham City segment may have started, as a straight, north-striking fault which has bent due to changes in stress orientations and/or interaction with the adjacent Weber segment.     

Recognition of shear heating on a long‐lived major fault using Raman carbonaceous material thermometry: implications for strength and displacement history of the MTL,SW Japan

The extent to which movement on major faults causes long term shear heating is a contentious issue and an important aspect in the debate about the strength of major faults in the crust. Comparing the results of experimental work on the kinetics of crystallization of carbonaceous material with results of thermal modeling show that the Raman carbonaceous material (CM) geothermometer is well suited to studying shear heating on geological time scales in suitable lithologies exposed around exhumed major fault zones. The Median Tectonic Line (MTL), SW Japan, is the largest on‐land fault in Japan with a length of > 800 km. Application of Raman CM thermometry to pelitic schist adjacent to the fault reveals the presence of a rise in peak temperature of around 60 °C over a distance of around 150 m perpendicular to the MTL fault plane. The spatial association of this thermal anomaly with the fault implies it is due to shear heating. Thermal modeling shows the recorded thermal anomaly and steep temperature gradient is compatible with very high rates of displacement over time scales of a few thousand years. However, the implied displacement rates lie outside those generally observed. An alternative explanation is that an originally broader thermal anomaly that developed during strike slip faulting was shortened due to the effects of normal faulting. Constraints on displacement rate, width of the original anomaly, duration of heating and peak temperature imply a coefficient of friction, μ, greater than 0.4.     

Duplex of metamorphic units including ultramafic rocks in the central region of Tokunoshima,Southwest Japan

Geological observations in the central part of Tokunoshima in the Amami Islands, Southwest Japan, reveal that discrete layers of serpentinite, dioritic gneiss, and amphibolite are intercalated into pelitic schist and these rock bodies form a northwest‐dipping tectonic stack. A subhorizontal psammitic schist layer overlies them. These rocks underwent ductile deformation that is denoted by penetrative foliation and mineral lineation. Microstructures of the sheared metamorphic rocks and serpentinite indicate top‐to‐the‐east, ‐southeast or ‐south (hanging‐wall up) displacements. The en echelon array of rock bodies is interpreted as a duplex with the psammitic schist layer on its top and the pelitic schist layer on its bottom. It is inferred that the serpentinite‐bearing duplex was formed due to the tectonic erosion and the subsequent accretionary growth operated in a Cretaceous or older subduction zone. Tokunoshima has been considered to belong to the Shimanto Belt. However, regional low‐pressure and high‐temperature type amphibolite‐facies metamorphism and related ductile deformation have not been recognized in the other areas of the Shimanto Belt. There is no metamorphic rock occurrence comparable to that of Tokunoshima in the neighboring islands. The metamorphic rocks in Tokunoshima can be correlated to any of low‐pressure/temperature type metamorphic regions in Kyushu.     

SLIP RATES OF THE RIYUE MT. FAULT AT DEZHOU SEGMENT SINCE LATE PLEISTOCENE

The Riyue Mt. Fault is a secondary fault controlled by the major regional boundary faults (East Kunlun Fault and Qilian-Haiyuan Fault). It lies in the interior of Qaidam-Qilianshan block and between the major regional boundary faults. The Riyue Mt. fault zone locates in the special tectonic setting which can provide some evidences for recent activity of outward extension of NE Tibetan plateau, so it is of significance to determine the activity of Riyue Mt. Fault since late Pleistocene to Holocene. In this paper, we have obtained some findings along the Dezhou segment of Riyue Mt. Fault by interpreting the piedmont alluvial fans, measuring fault scarps, and excavating trenches across the fault scarp. The findings are as follows:(1) Since the late Pleistocene, there are an alluvial fan f_p and three river terraces T₁-T₃ formed on the Dezhou segment. The abandonment age of f_p is approximately (21.2±0.6) ka, and that of the river terrace T₂ is (12.4±0.11) ka. (2) Since the late Pleistocene, the dextral strike-slip rate of the Riyue Mt. Fault is (2.41±0.25) mm/a. In the Holocene, the dextral strike-slip rate of the fault is (2.18±0.40) mm/a, and its vertical displacement rate is (0.24±0.16) mm/a. This result indicates that the dextral strike-slip rate of the Riyue Mt. Fault has not changed since the late Pleistocene. It is believed that, as one of the dextral strikeslip faults, sandwiched between the the regional big left-lateral strike-slip faults, the Riyue Mt. Fault didn't cut the boundary zone of the large block. What's more, the dextral strike-slip faults play an important role in the coordination of deformation between the sub-blocks during the long term growth and expansion of the northeast Tibetan plateau.     

Thrust geometries in unconsolidated Quaternary sediments and evolution of the Eupchon Fault, southeast Korea

Abstract The Korean peninsula is widely regarded as being located at the relatively stable eastern margin of the Asian continent. However, more than 10 Quaternary faults have recently been discovered in and reported from the southeastern part of the Korean Peninsula. One of these, the Eupchon Fault, was discovered during the construction of a primary school, and it is located close to a nuclear power plant. To understand the nature and characteristics of the Quaternary Eupchon Fault, we carried out two trench surveys near the discovery site. The fault system includes one main reverse fault (N20°E/40°SE) with approximately 4 m displacement, and a series of branch faults, cutting unconsolidated Quaternary sediments. Structures in the fault system include synthetic and antithetic faults, hanging‐wall anticlines, drag folds, back thrusts, pop‐up structures, flat‐ramp geometries and duplexes, which are very similar to those seen in thrust systems in consolidated rocks. In the upper part of the fault system, several tip damage zones are observed, indicating that the fault system propagates upward and terminates in the upper part of the section. Pebbles along the main fault plane show a preferred orientation of long axes, indicating the fault trace. The unconformity surface between the Quaternary deposits and the underlying Tertiary andesites or Cretaceous sedimentary rocks is displaced by this fault with a reverse movement sense. The stratigraphic relationship shows normal slip sense at the lower part of the section, indicating that the fault had a normal slip movement and was reversely reactivated during the Quaternary. The inferred length of the Quaternary thrust fault, based on the relationship between fault length and displacement, is 200–2000 m. The current maximum horizontal compressive stress direction in this area is generally east‐northeast–west‐southwest, which would be expected to produce oblique slip on the Eupchon Fault, with reverse and right‐lateral strike‐slip components.     

祁漫塔格北缘断裂晚第四纪以来活动特征初步研究

祁漫塔格北缘断裂处于青藏高原内部造山带地区,其构造活动反映了青藏高原的构造演化特征。本文采用活动构造和构造地貌相结合的研究方法,对该断裂的活动性进行初步分析研究。首先采用航卫片解译和野外调查,发现该断裂断错了山前全新世冲洪积扇,形成的断层陡坎高度在1.5~2.5m。通过扩散方程,并参考前人研究结果,认为祁漫塔格北缘断裂晚第四纪的抬升速率初步限定在1~2mm/a。我们基于数字高程模型提取的地形高程纵剖面和面积-高程积分,其结果也支持祁漫塔格北缘存在构造活动。     

Nannofossil age constraints for the northern KwaZulu-Natal shelf-edge wedge: Implications for continental margin dynamics, South Africa, SW Indian Ocean

Samples collected from the shelf-edge wedge using surface grab samples and the Jago submersible constrain the KwaZulu-Natal shelf-edge wedge to a late Pliocene age on the basis of the absence of Gephyrocapsa oceanica s.l. and Discoaster brouweri, and the presence of Calcidiscus macintyrei. This correlates with proposed Tertiary sea-level curves for southern Africa and indicates relative sea-level fall during the late Pliocene coupled with hinterland uplift. Exposed failure scarps in the upper portions of submarine canyons yield sediment samples of early Pleistocene ages, indicating the uppermost age of deposition of clinoform topsets exposed in the scarp walls. Partially consolidated, interbedded silty and sandy deposits of similar age outcrop in the thalweg of Leven canyon at a depth of 150 m. These sediments provide an upper age limit of the shelf-edge wedge of early Pleistocene, giving a sedimentation rate of this wedge of 162–309 m/Ma. The distribution of widespread basal-most Pleistocene sediments on the upper slope indicates that these sediments escaped major reworking during sea-level falls associated with Pleistocene glaciations and remain as relict upper slope veneers. The absence of more recent sediments suggests that this area has been a zone of sediment bypass or starvation since the early Pleistocene. Areas where younger sediments mantle deposits of early Pleistocene ages represent areas of offshore bedload parting, re-distributing younger Holocene sediment offshore and downslope.