Ephemeral landform development following rapid coastal uplift in the southern orogen of Taiwan

Newly emerged landscapes above sea level are characterized by rapidly evolving geomorphic systems where the initial fluvial pattern adapts to a former submarine topography. Such an early formed fluvial system establishes drainage basins and unstable landforms that characterize high topographic asymmetry which are prone to fast removal or reorganization. Transitional landscapes might form depositional systems as lakes or ponds that subsequently are incised, captured and incorporated into drainage basins. In this study we focus on the recently emerged Hengchun Peninsula to survey its paleoenvironment evolution. Three drillings performed in the Gangkou basin with fieldwork revealed several indicators that reconstructed stages of the landscape reorganization. The major finding shows an ephemeral large lake in the central part of the Hengchun Peninsula that was drained to the Pacific c. 6000 bp . The lake belonged to an ephemeral lakeland that was created after the emergence of the peninsula. Currently, several areas as relict landforms indicate this stage of topography evolution that through high rates of incision and subsequent captures, transforms into drainage basins. Furthermore, two drillings show brackish waters at the present estuary of the Gangkou basin. These two different paleoenvironments today build one system – Gangkou catchment. Long-term uplift rates show that a hanging wall of the Hengchun Fault plays a significant role in the creation of a lakeland by tilting the peninsula's surface. The tilt impacts on asymmetrical emergence of the peninsula and catchment development. Our study shows that a new geomorphic system might create depositional ephemeral landforms (lakes) that represent phases of early topography evolution after emergence above a sea level that are subjected to instantaneous rearrangement and evolves through large-scale phases before it reaches a topographic steady-state.     

Geomorphology and seismotectonic elements in the giarre area,sicily

A morphostructural analysis has been performed on the eastern flank of Mt Etna, located between the towns of St. Alfio and Linera and the Ionian Sea. The research has been carried out through analysis of aerial photographs, and has allowed recognition of morphoneotectonic elements such as: some scarps with rectilinear trend, laterally becoming morphological flexures, according to the lithology; anomalies in the hydrographic network, such as rectilinear tracts of drainage, valleys with simple or double bends, hanging valleys and truncated valleys, narrow deeply engraved valleys with meanders and fluvial captures. All these elements are caused by a fault system oriented NNW–SSE, with a mainly vertical component. Seismic events with very shallow foci have been recorded in the study area; these earthquakes triggered several small landslides on the fault scarps and large series of coseismic and coaxial fractures. It is possible to show that the morphostructures examined have been reactivated during many of the seismic events that have occurred in the area. The combination of these elements verifies that the morphostructures have a real neotectonic cause, which is associated with uplifts which have occurred in the area at different times.     

Fission track dating of the Cenozoic uplift in Mabian area, southern Sichuan Province, China

The apparent ages of samples are obtained from fission track dating of apatite samples collected from the fault zones in Mabian area, southern Sichuan Province. In addition, thermal history is simulated from the obtained data by applying AFT Solve Program, to acquire the thermal evolution history of the samples. The result shows that tectonically the Mabian area was relatively stable between 25 and 3 Ma, compared to the inner parts and other marginal areas of the Tibetan Plateau. The studied area had little response to the rapid uplift events that occurred for several times in the Tibetan Plateau during 25-3 Ma. The latest thermal event related to the activity of the Lidian fault zone (about 8 Ma ) is later than that of the Ebian fault zone (18-15 Ma ) to the west, indicating to some extent that the evolution of fault activity in the Mabian area has migrated from west to east. The latest extensive tectonic uplift occurred since about 3 Ma. As compared with the Xianshuihe fault zone, the Mabian area is closer to the east- ern margin of the plateau, while the time of fast cooling event in this area is later than that in the southeast segment of the Xianshuihe fault zone (3.6-3.46 Ma ). It appears to support the assumption of episodic uplift and stepwise outward extension of the eastern boundary of the Tibetan Plateau in late Cenozoic.     

Petrography and geochemistry of manganiferous rocks in the Mankwadzi area in the southern Kibi‐Winneba metavolcanic belt,Ghana: Implications for genesis of Mn formations in the Birimian of West Africa

Manganiferous rocks in the Mankwadzi area in the southernmost portion of the Kibi‐Winneba metavolcanic belt, one of several Mn occurrences in the Paleoproterozoic Birimian of Ghana, are hosted in hornblende schist and amphibolite. These rocks are, in places, intruded by hornblende dyke. In outcrop, the manganiferous rocks appear to be conformable with the host schist and amphibolite, are macroscopically dark, fine‐grained and structurally massive to distinctly banded. Observed alternating light and dark occasionally macro‐folded bands suggest post‐depositional deformation of both light and dark bands. Microscopic observations revealed that the light bands are dominantly Si‐rich and the dark bands mainly of opaque minerals. Whole rock analyses of the manganiferous rocks show high contents of MnO (16.75–27.4 wt%) suggesting that the opaque minerals are likely rich in Mn. The analyzed rock samples show moderate to strong enrichments in light rare earth elements compared to heavy rare earth elements. Whereas the manganiferous rocks show perceptibly negative Eu anomaly, host hornblende schist and hornblende dyke do not. Eu anomaly in amphibolite samples is, however, uncertain as the three samples analyzed gave positive, negative and no Eu anomalies. Based on the field characteristics, microscopic and geochemical features, we suggest that the Mn occurrence in the Mankwadzi area originated via sedimentary deposition and was later modified by metamorphism, hydrothermal and/or supergene processes similar to manganiferous occurrences at Nsuta and Tambao in the Birimian of West Africa.     

松原前郭地震区孕震构造的地震层析成像研究

本文选取2013年10月到2018年12月期间松原市周边17个地震台记录到的515个地震事件的2926条P波和2665条S波到时数据,采用双差成像方法联合反演松原地震区震源参数和中上地壳(0~25 km)高分辨率三维体波速度和波速比结构,进而利用O'Connell-Budiansky理论估计了该区岩石介质的裂缝密度和饱和度参数.重定位后的震源参数精度有了显著提高.松原震区P波和S波的速度、波速比结构均表现出明显的不均匀特性,主要表现为低P波、低S波、低波速比结构,推测松原地震区发生更大地震的可能性较低.松原震群区浅地表区域(< 5 km)整体表现为低P波、低S波和高波速比结构,而岩石介质的裂缝密度和饱和度表现为高值.浅层高波速比、高裂缝密度和高饱和度结构可能与流体有关;从区域构造出发表明松原地震发震构造与东北地区的区域构造应力场密切相关.松原震区的三维精细速度和高精度震源位置信息为深入了解该地区的地壳结构、孕震构造和地震活动性提供重要参考.

     

Holocene yardangs in volcanic terrains in the southern Andes,Argentina

Yardangs of different sizes were developed in the Payun Matru Volcanic Field, a semiarid area east of the southern Andes mountains. Yardangs from volcanic terrains have not been described previously from Earth, although studies from Mars interpreted linear ridges found by Mariner and Viking images as yardangs. The Payun Matru Volcanic Field is an extensive plateau at 2000 m a.s.l. covered by basaltic lava and ignimbrite flows. Strong westerly winds affect the extensive plateau. Micro‐ and mesoyardangs are formed on the ignimbrite rock blanket, and macroforms or megayardangs, several kilometres in length, are developed in the basaltic lava flows as long parallel troughs. They all have a distinctive 320° azimuth, which is the prevailing wind direction. No yardang features are noted in the more recent lava flows, younger than 1000 years, indicating that their formation needed a longer time or they developed in earlier periods with stronger winds. The yardang development is explained by the strong unidirectional winds, the poor vegetational cover due to the aridity of the region, the available quartz sand and volcanic ash particles as abrasive agents, and the volcanic lithology texture and flow structure. Copyright © 2001 John Wiley & Sons, Ltd.     

Crustal velocity,density structure,and seismogenic environment in the southern segment of the North-South Seismic Belt,China

The southern segment of the North-South Seismic Belt in China is a critical region for earthquake preparedness and risk reduction efforts. However, limited by the low density of seismic stations and the use of single-parameter physical structural models, the deep tectonic features and seismogenic environment in this area remain controversial. Thus, a comprehensive analysis based on high-resolution crustal structures and multiple physical parameters is required. In this study, we applied the ambient noise tomography method to obtain the three-dimensional (3D) crustal S-wave velocity structure using continuous waveform data from 112 permanent stations and 350 densely distributed temporary stations in the southern segment of the North-South Seismic Belt. Then, we obtained the high-resolution 3D density structure through wavenumber-domain 3D gravity imaging constrained by the velocity structure. The low-velocity and low-density anomalies in the upper crust of the study area were mainly distributed in the Sichuan Basin and around Dali and Simao, while the high-velocity and high-density anomalies were primarily distributed in the Panxi region, corresponding to the surface geological features. Two prominent low-velocity and low-density anomalies were observed in the middle and lower crust: one to the west of the Songpan-Garzê block and Sichuan-Yunnan diamond-shaped block, and the other near the Anninghe-Xiaojiang fault. Combined with the spatial distribution of seismic events in the study area, we found that previous earthquakes predominantly occurred in the transition zones between high and low anomaly regions and in the low-velocity and low-density zones in the upper crust. In contrast, moderate-to-strong earthquakes mainly occurred within the transition zones between high and low anomaly regions and close to the high-velocity and high-density regions, often with low-velocity and low-density layers below their hypocenters. Fluids play a critical role in the seismogenic process by reducing fault strength and destabilizing the stress state, which may be a triggering factor for earthquakes in the study area. Additionally, the upwelling of molten materials from the mantle may lead to energy accumulation and stress concentration, providing an important seismogenic background for moderate-to-strong earthquakes in this area.     

Major earthquakes of the southern Gornyi Altai in the Holocene

The paper describes geological and geomorphological features of ancient major earthquakes that occurred in the Holocene in the zone of the Altai earthquake of September 27, 2003 (southern Gornyi Altai). Fossil earthquakes occurred in the regions of the Northern and Southern Chuya ridges and Chuya and Kurai basins; their sources reached the surface and formed systems of coseismic ruptures oriented SE-NW or E-W. Secondary (gravitational and vibrational) paleoseismic deformations were represented by rockfalls, landslides, and gryphons in near-field zones of these paleoevents. They were spread in an area of about 2000–2500 km² coinciding, on the whole, with the position of source zones. Paleoseismogeological investigations showed that, apart from earthquakes of the 20th and 21st centuries, eight seismic events with magnitudes M = 7.0–8.0 occurred in the region over the last 8500 years. Ancient strong earthquakes that produced the observed paleoseismic ruptures occurred approximately 230–300, 1000, 1700, 2300, 3500, 4500, 5200, and 8500 years ago. Therefore, the recurrence interval averaged 1400 yr for earthquakes with a magnitude of about 7.0 and 2100 yr for events with a magnitude of about 7.5.     

Dispersion in the Yucatan coastal zone: Implications for red tide events

The mechanisms governing dispersion processes in the northern Yucatan coast are investigated using a barotropic numerical model of coastal circulation, which includes wind-generated and large scale currents (i.e. Yucatan Current). This work provides the foundations for studying the dispersion of harmful algal blooms (HABs) in the area. Modelling experiments include effects of climatic wind (from long term monthly mean NCEP reanalysis), short term wind events (from in situ point measurements), and Yucatan Current (YC) characteristics. Its magnitude was approximated from published reports, and its trajectory from geostrophic current fields derived from altimeter data. These provided a range of real and climatic conditions to study the routes in which phytoplankton blooms may travel. The 2-D model results show that a synthetic and conservative bloom seeded in the Cabo Catoche (CC) region (where it usually grows), moves along the coast to the west up to San Felipe (SF), where it can either move offshore, or carry on travelling westwards. The transport to the west up to SF is greatly influenced by the trajectory, intensity and proximity of the YC jet to the peninsula, which enhances the westward circulation in the Yucatan Shelf. Numerical experiments show that patch dispersion is consistently to the west even under the influence of northerly winds. When the YC flows westward towards the Campeche Bank, momentum transfer caused by the YC jet dominates the dispersion processes over wind stress. On the other hand, when it flows closer to Cuba, the local processes (i.e. wind and bathymetry) become dominant. Coastal orientation and the Coriolis force may be responsible for driving the patch offshore at SF if external forcing decreases.     

Late Anisian radiolarian assemblages from the Yarlung‐Tsangpo Suture Zone in the Jinlu area,Zedong, southern Tibet: Implications for the evolution of Neotethys

Abundant Triassic radiolarian fossils were obtained from varicolored bedded cherts exposed in the Buruocang section near Jinlu village, Zedong, southern Tibet. The radiolarian‐bearing rocks represent fragmented remnants of the Neotethys oceanic sediments belonging to the mélange complex of the east part of the Yarlung‐Tsangpo Suture Zone. Two new middle Late Anisian radiolarian assemblages recognized from this section named Oertlispongus inaequispinosus and Triassocampe deweveri, respectively, are compared with those known from Europe, Far East Russia, Japan, and Turkey. These Anisian radiolarian fossils are the first reported in southern Tibet and the oldest radiolarian record within the Yarlung‐Tsangpo Suture Zone. They improve time constraints for the evolution of Neotethys in southern Tibet.     

青海门源地区地震活动时空分布特征和孕震环境研究

位于青藏高原东北缘的青海门源地区地震活动频繁, 自1986年以来先后发生了三次6级以上的强震活动.研究门源地区的地震活动特征、发震构造和孕震环境可以为地震发生机理的分析和未来地震危险性的判定提供重要依据.本文基于中国地震台网中心提供的地震目录和震相数据, 使用波速比一致性约束的双差层析成像方法获得了门源地区2009年以来的地震精定位结果和高分辨率的三维VP、VS和VP/VS模型.使用"剪切-黏贴"方法计算了门源MS6.9地震和MS4.5以上余震的震源机制解, 并收集了该区域历史中强地震的震源机制解.结果显示: 2013年门源MS5.3地震和2016年门源MS6.4地震的余震序列沿着冷龙岭北侧断裂展布, 2022年门源MS6.9地震的余震序列沿着托莱山断裂和冷龙岭断裂展布, 其展布方向与附近断裂的走向一致.1986年门源MS6.4地震、2013年门源MS5.3地震和2016年门源MS6.4地震的震源机制解均为逆冲型, 而2022年门源MS6.9地震及其余震的震源机制解以走滑型为主.结合地震定位结果, 本次门源MS6.9地震与之前的三次中强地震的发震构造不属于同一条断层.研究区内断裂分布、中强地震的震源位置与三维速度结构具有对应关系, 托莱山断裂和冷龙岭断裂两侧的介质性质存在明显差异, 应力在刚性介质边缘累积, 导致门源地区中强地震沿着异常体边缘的断裂频繁发生.     

Mesozoic uplift of the Dabashan and Micangshan-Hannan Dome in the South Qinling orogenic belt

The topographic evolution of continental orogens is important for understanding continental orogenic processes,geodynamic mechanisms,and climatic and environmental changes.The Qinling Orogen is a major orogenic belt in China,and its uplift history can provide insights into the tectonic configuration and geodynamics of China and East Asia.Previous studies have shown that the Dabashan and Micangshan-Hannan Dome(MHD)in the South Qinling orogenic belt were uplifted during the Mesozoic.However,the magnitude of the uplift remains unclear.In this study,using sedimentary records in the northern Sichuan Basin and lithospheric flexural modeling,we estimated the magnitude of Mesozoic uplift of the Dabashan and MHD,along with the effective elastic thickness(Te)of the Sichuan Basin.The Dabashan and MHD were uplifted by approximately 1220 and 880 m during the Middle Jurassic and Early Cretaceous,respectively.Therefore,we propose that the present-day elevation of the Dabashan and MHD is primarily the result of Mesozoic uplift.The differences in the duration and amount of uplift between different tectonic units indicate that the uplift processes and driving mechanisms in the South Qinling orogenic belt were different in the Mesozoic and Cenozoic.Mesozoic uplift was the result of convergence of the North China and South China blocks advanced from east to west,whereas Cenozoic uplift was driven by ongoing indentation of the Indian Plate into Eurasia from southwest to northeast.The lithospheric strength of the northern Sichuan Basin was weakened from the Middle Jurassic to Early Cretaceous,and Tedecreased from 73 to 57 km.This may have been caused by the flexure-related bending stresses in the lithosphere that developed due to the large topographic loading.     

Mercury in coastal and estuarine sediments of the northeastern Irish sea

Mercury concentrations in surface intertidal sediments from estuarine and coastal environments of the Northeastern Irish Sea are reported. This region has two inputs of mercury contaminated effluents from chlor-alkali factories, and localized mercury contamination of sediments fairly similar to that reported for the Rhine has been found in the Wyre estuary. The present results for the Mersey estuary agree well with others reported in the lierature. Coastal sediments are much less contaminated than the estuarine deposits, and in all the environments studied strong correlations between mercury concentration, total organic carbon and < 63 μm grainsize fraction contents have been found.     

羌塘中央隆起带深部结构特征研究及其意义

羌塘含油气盆地是我国境内最大的中新生代海相沉积盆地.羌塘地体内的中央隆起将盆地分为南北两个盆地.中央隆起带构造属性认识存在两种截然不同的分歧,一是伸展环境下形成,整个羌塘盆地有着同一的基底.而另一认识其是一古特提斯缝合带,其两侧盆地具有不同的演化机制.调查羌塘中央隆起的深部结构特征及其与南北两侧的盆地间的构造关系是认识羌塘盆地基底性质及其油气远景之关键科学问题.尽管羌塘地体在青藏高原形成演化过程中遭到了强烈改造,但在收集并分析已有地球物理资料基础上认为其深部结构仍有可能被完整保存.因此,利用密集宽频带流动台网观测,获取其深部结构,进而研究其与两侧盆地关系,是当前羌塘含油气盆地研究之重要突破口,同时该项研究符合我国当前国家油气资源战略评估政策.     

Macroseismic attenuation in the Campanian area, southern Italy

The main objective of the present study is to evaluate seismic attenuation relationships for the Campanian area (southern Italy) using the felt intensity report data obtained from comprehensive historical databases (DOM 4.1). We focused our attention on the Campania region because it is characterized by a high seismic hazard and risk, particularly in the Naples area and its suburbs. In order to derive an attenuation relationship for the area, we fitted the observed data by using several functions. We found that a linear plus logarithmic model gives the best fits for the data in the Campanian region. Most of the attenuation relationships proposed up to now for the Italian Peninsula have an isotropic behavior and do not always properly describe the macroseismic attenuation. Therefore, in order to check the possible dependence of the attenuation on the azimuth of the seismic rays, we divided our data set in octants and performed for each of them the same analysis we carried out for the whole data set. The obtained results differ from octant to octant and the differences, besides being associated with the source effects, could be interpreted as probably due to the existence of lateral variations in the lithological and physical features of the crust at different depths, which could affect the patterns of attenuation.     

Early Cretaceous uplift history of the Dabie orogenic belt: Evidence from pluton emplacement depths

The North Dabie complex unit(NDC)is a widely exposed petro-tectonic unit.To understand post-orogenic uplift history and mechanism of the Dabie orogenic belt,many samples of granite,granodiorite,diorite,and alkali feldspar granite with precise zircon U-Pb ages were collected for electron microprobe analysis of hornblende.Emplacement pressure values were then calculated by using an Al-in-hornblende geobarometer.The result shows that total Al(AlT)values in hornblende range from 1.17to 1.97 p.f.u.,XFe(=Fe/(Fe+Mg))from 0.4 to 0.65,and corresponding pressure values from 256.8 to 676.2 MPa for AlT greater than 1.17.It is suggested that although the main mechanism for the uplift is tectonic extension,inhomogeneous uplift related to the pluton emplacement is also important during post-orogenic evolution of the Dabie orogenic belt.Emplacement depth distribution of the plutons shows that uplift in the NDC is affected by horst-graben structures since 120 Ma.     

Pliocene cyprinids (Cypriniformes,Teleostei) from Kunlun Pass Basin,northeastern Tibetan Plateau and their bearings on development of water system and uplift of the area

Here described are the cyprinid fossils from the Pliocene Lower Member of Qiangtang Formation of the Kunlun Pass Basin,northeastern Tibetan Plateau,collected at a locality 4769 m above the sea level(asl).The materials consist of numerous disarticulated and incomplete bones as well as thousands of pharyngeal teeth,fin rays,and vertebrae.The fossils were referred to the genus Gymnocypris,lineage Schizothoracini,family Cyprinidae;the lineage Schizothoracini;and the family Cyprinidae respectively.The Schizothor...     

Human-induced changes in recent sedimentation rates in Bohai Bay,China: Implications for coastal development

In many countries, coastal planners strive to balance the demands between civil, commercial strategy and environmental conversation interests for future development, particularly given the sea level rise in the 21 st century. Achieving a sustainable balance is often a dilemma, especially in low-lying coastal areas where dams in inland river basin are trapping significant amounts of fluvial sediments. We recently investigated the shore of Bohai Bay in northern China where there has been a severe increase in sea level following a program of large-scale coastal reclamation and infrastructure development over the last five decades. To investigate this trend, we obtained sediment cores from near-shore in Bohai Bay, which were dated by ~(137)Cs and ~(210)Pb radionuclides to determine the sedimentation rates for the last 50 years. The average sedimentation rates of Bohai Bay exceeded 10 mm yr~(-1) before 1963, which was much higher than the rate of local sea-level rise. However, our results showed an overall decreasing sedimentation rate after 1963, which was not able to compensate for the increasing relative sea-level rise in that period. In addition, our results revealed that erosion occurred after the 1980 s in the shallow sea area of Bohai Bay. We suggest that this situation places the Bohai Bay coast at a greater risk of inundation and erosion within the next few decades than previously thought, especially in the large new reclamation area. This study may be a case study for many other shallow sea areas of the muddy coast if the sea level continues to rise rapidly and the sediment delivered by rivers continues to decrease.     

Investigation of historical earthquakes in the northeastern Fujian area

Taking the northeastern Fujian area as an example, we provide some new technological ideas and contents for the historical earthquake investigation of significant engineering construction sites. ① Make sure the integrity of earthquake materials with reference to the regional histories of culture and disasters; ② Evaluate the influence of historical earthquakes on the basis of actual records, review and identify the epicenter location and magnitude of destructive earthquakes. The research by the new technological ideas will endue the investigation of historical earthquakes with new meanings in the cultural phylogeny and credible time domain, so as to make the results of historical earthquake research more scientific. The aim of the paper is to improve the level of historical earthquake investigation for a better service to the engineering construction.     

Tafoni in the El Chorro area,Andalucia, southern Spain

Using a combination of field, laboratory and micromorphological evidence, this study examines tafoni (singular, tafone) in the El Chorro area of Andalucia, southern Spain, and makes inferences concerning the processes responsible for their formation. Twenty-five tafoni were randomly selected for field examination. The morphology of these cavernous rock domes is characterized by a helmet-shaped outer roof and an arched-shaped cavern, often with a partially overhanging visor; measurements of height, width and depth of the caverns revealed marked variations in size. The presence or absence of lichen cover, surface varnish, overhanging visor, cavern backwall stripes, rock flaking, weathering pits and cavern floor sediments was also noted. Surface hardness values, obtained using a Schmidt hammer, are relatively low but significantly higher on the outer roof of the tafoni than on the inner cavern walls. Analysis of sediment samples collected from the cavern backwalls and floors indicates predominantly sandy textures, alkaline pH values and some base cation enrichment. Micromorphological analysis of thin sections, prepared from undisturbed blocks, reveals large quantities of pore-filling cement, consisting mainly of calcite, mineral grains affected by weathering and pseudomorphic replacement, and dark, rounded nodules with a metallic appearance. In terms of their formation, different processes appear to act on different parts of the landform. On the outer roof surfaces, case hardening, resulting from near-surface cementation and surface varnish development, is dominant. On the inner cavern surfaces, however, core softening, resulting from granular disintegration and flaking, dominates. Exfoliation weathering, running water and wind deflation also appear to play an important role in tafone formation. A phased model of tafone evolution is proposed whereby the features pass through four phases of development–initiation, enlargement, amalgamation and degradation; in the study area there are examples of tafoni in each of these phases. Much of the evidence suggests that the tafoni are actively developing under current environmental conditions. © 1997 by John Wiley & Sons, Ltd.