Sedimentology and Chronology of Paleogene Coarse Clastic Rocks in East-Central Tibet and Their Relationship to Early Tectonic Uplift

A systematic sedimentological and chronological study of typical Paleogene basins in eastcentral Tibet suggests that the depositional characteristics of extensively developed huge-bedded, purplish-red coarse clastic rocks formed in a tectonic setting of regional thrusting and strike-slipping represent a typical dry and hot subaerial alluvial fan environment formed in a proximal and rapidaccumulating sediment body in debris flows and a fan-surface braided river. Combining results from basin-fill sequences, sequences of coarse clastic rocks, fauna and sporo-pollen associations and thermochronological data, it is conduded that the coarse clastic rocks formed in the period of 54.2- 24.1 Ma, nearly coeval with the formation of Paleogene basins in the northern （Nangqen-Yushu thrust belt）, middle （Batang-Lijiang fault belt）, and disintegration of large basins in the southern （LanpingSimao fold belt） segments of Tibet. The widespread massive-bedded coarse clastic rocks, fold thrusting and strike-slip, thrust shortening, and igneous activities in the Paleogene basins of eastcentral Tibet indicate that an early diachronous tectonic uplift might have occurred in the Tibetan Plateau from Middle Eocene to Oligocene, related to the initial stage of collision of the Indian and Asian plates.

Cenozoic Evolution of Sediments and Climate Change and Response to Tectonic Uplift of the Northeastern Tibetan Plateau

Through a comprehensive study of magnetostratigraphy and sedimentology of several basins in the northeastern Tibetan Plateau,we reveal that the study area mainly experienced six tectonic uplift stages at approximately 52 Ma,34-30 Ma,24-20 Ma,16-12 Ma,8-6 Ma,and 3.6-2.6 Ma.Comprehensive analyses of pollen assemblages from the Qaidam,Linxia,Xining,and West Jiuquan Basins show that the northeastern Tibetan Plateau has undergone six major changes in vegetation types and climate：50-40 Ma for the warm-humid forest vegetation,40-23 Ma for the warm-arid and temperate-arid forest steppe vegetation,23-18.6 Ma for the warm-humid and temperate-humid forest vegetation,18.6-8.5 Ma for the warm-humid and cool-humid forest steppe vegetation,8.6-5 Ma for the temperate sub-humid savanna steppe vegetation,and 5-1.8 Ma for the cold-arid steppe vegetation.Comprehensive comparisons of tectonic uplift events inferred from sedimentary records,climatic changes inferred from pollen,and global climate changes show that in the northeastern Tibetan Plateau the climate in the Paleogene at low altitude was mainly controlled by the global climate change,while that in the Neogene interval with high altitude landscapes of mountains and basins is more controlled by altitude and morphology.

Geomorphic indices and relative tectonic uplift in the Guerrero sector of the Mexican forearc

Tectonically active areas,such as forearc regions,commonly show contrasting relief,differential tectonic uplift,variations in erosion rates,in river incision,and in channel gradient produced by ongoing tectonic deformation.Thus,information on the tectonic activity of a defined area could be derived via landscape analysis.This study uses topography and geomorphic indices to extract signals of ongoing tectonic deformation along the Mexican subduction forearc within the Guerrero sector.For this purpose,we use field data,topographical data,knickpoints,the ratio of volume to area（Rva）.the stream-length gradient index（St）,and the normalized channel steepness index（k_（sn））.The results of the applied landscape analysis reveal considerable variations in relief,topography and geomorphic indices values along the Guerrero sector of the Mexican subduction zone.We argue that the reported differences are indicative of tectonic deformation and of variations in relative tectonic uplift along the studied forearc.A significant drop from central and eastern parts of the study area towards the west in values of R_（VA）（from ~500 to^300）,St（from ~500 to ca.400）,maximum St（from ~1500-2500 to ~ 1000） and k_（sn）（from ~150 to ~100） denotes a decrease in relative tectonic uplift in the same direction.We suggest that applied geomorphic indices values and forearc topography are independent of climate and lithology.Actual mechanisms responsible for the observed variations and inferred changes in relative forearc tectonic uplift call for further studies that explain the physical processes that control the forearc along strike uplift variations and that determine the rates of uplift.The proposed methodology and results obtained through this study could prove useful to scientists who study the geomorphology of forearc regions and active subduction zones.

Cenozoic Tectonic Uplift History of Western Qinling: Evidence from Sedimentary and Fission-Track Data

The western Qinling （秦岭） orogenic belt is one of the outermost ranges in the northeas- tern Tibetan Plateau. Its tectonic uplift history is therefore essential to insight on the evolution history of the plateau. However, the timing of deformation and uplift history is still poorly known. Fortunately, its Cenozoic orogenic history is recorded in an excellent synorogenic sedimentary sequence exposed in the Tianshui （天水）Ba- sin, the northeastern foot of western Qinling. Ac- cording to sedimentary-tectonic analysis of the Yaodian （尧店） and Lamashan （喇嘛山） sections based on the previous magnetostratigraphy stu- dies, we speculated that two stages （occurred at 9.2-7.4 and -3.6 Ma） of variation in depositional facies were attributed to the uplift and deforma- tion of the western Qinling, and the modern structure geomorphic frame of the northeastern Tibet formed after 2.6 Ma. Furthermore, four stages of active processes along the western Qinling occurred at 49--41, 34-27, 25-19 and -13 Ma, are deciphered from an integrated detrital apatite fission-track data of the Ganquan （甘泉）, Yaodian main sections and seven small ones. The former two are represents the exhumation episodes triggered by tectonism and the others attributed to the volcanic signals.

Impact of long term uplift on stream networks in tectonically active Northern Hill Range, Kachchh palaeo-rift basin, western India

The study deals with stream response to sustained tectonic during the Cenozoic and development of two parallel scarps in the western Kachchh. The study encompasses fluvial networks developed over the Jara and Jumara domes, which are a part of the laterally extensive belt of flexures bounded by the Kachchh Mainland Fault(KMF) to their north and called as Northern Hill Range(NHR). Parameters such as longitudinal profile, Hack profile, stream length gradient index(SL), hypsometric curve, hypsometric integral(HI), valley floor width to height ratio(Vf), elongation ratio(Re) and escarpment sinuosity(ES) were analysed. Hack profiles of the major rivers draining through the area show similar convex up nature suggesting primary influence of the tectonics in controlling and shaping the landscape of the region. Elongation ratio <6 and undergone higher degree of fluvial erosion indicated by the low values of hypsometric integral suggest the tendency of river systems to increase the basin area longitudinally rather than laterally. The study suggests that higher net uplift in the eastern half(Jumara dome) caused the rivers to overcome the structural control and to carve out generally straight north oriented channels. The rivers of western part(Jara dome) show more prominent structural control of cuesta girdles formed in compact lithologies and attributed to the domal structure. The ~10 km long Jaramara scarp believed to the remnant of older KMF scarp, is a product of headward erosion of the fluvial channels through different hard and soft litho-units of the area. The similar orientation of Jaramara scarp and morphology of the Ukra intrusive body suggests that the Ukra intrusive played a significant role in controlling the formation and morphology of the Jaramara scarp.

An integrated north–south paleo-Dadu-Anning River: New insights from bulk major and trace element analyses of the Xigeda Formation

The Xianshuihe-Anninghe fault extends SE–S and constitutes the southeastern margin of the Tibetan Plateau.However,the Dadu River which is associated with the fault does not flow following the path,but makes a 90ºturn within a distance of 1 km at Shimian,heading east,and joins the Yangtze River,finally flowing into the East China Sea.Adjacent to the abrupt turn,a low and wide pass near the Daqiao reservoir at Mianning separates the N–S course of the Dadu River from the headwater of the Anning River which then flows south into the Yunnan Province along the Anninghe fault.Therefore,many previous studies assumed southward flow of the paleo-Dadu River from the Shimian to the Anning River.However,evidences for the capture of the integrated N–S paleo-Dadu-Anning River,its timing,and causes are still insufficient.This study explored the paleo-drainage pattern of the Dadu and Anning Rivers based on bulk mineral and geochemical analyses of the large quantities of fluvial/lacustrine sediments along the trunk of the Dadu and Anning Rivers.Similar with sands in the modern Dadu River,the Xigeda sediments also exhibit a granitoid affinity with the bulk major mineral compositions of quartz(>50%),anorthite(about 10%),orthoclase(about 5%),muscovite(about 5%),and clinochlore(about 4%).Correspondingly,bulk major elements show high SiO_(2),with all samples>60%,and some of them>70%,low TiO_(2)(≤0.75%),P_(2)O_(5)(≤0.55%),FeO*(≤5%),and relatively high CaO(1.02%–8.51%),Na_(2)O(1.60%–2.52%),and K_(2)O(2.17%–2.71%),with a uniform REE patterns.Therefore,synthesizing all these results indicate that these lacustrine sediments have similar material sources,which are mainly derived from its course in the Songpan-Ganzi flysch block,implying that the paleo-Dadu originally flowed southward into the Anning River and provided materials to the Xigeda ancient lake.The rearrangement of the paleo-Dadu River appears to be closely related to the locally focused uplift driven by strong activities of the XianshuiheXiaojiang fault system.

Formation of the Yalong Downstream Terraces in the SE Tibetan Plateau and Its Implication for the Uplift of the Plateau

The Yalong River is an important river that runs across the abruptly changing terrain of the SE Tibetan Plateau. The terraces and Quaternary sediments in its valleys preserve the information of tectonic uplift, climate changes, and landform evolution since the Middle Pleistocene. Based on geomorphological, sedimentological, and chronological investigations, 6-8 terraces are identified in the lower reaches of Yalong catchment and its tributary--the Anning River. The electron spin resonance （ESR） or optically stimulated luminescence （OSL） data on the alluvial sediments in the upper portion of terraces indicate that they formed in 1.10, 0.90, 0.72, 0.06-0.04, 0.03-0.02, and 0.01 Ma. Tectonic uplift and the climatic cycle controlled the formation of the Yalong River terraces. The former dominated the dissection depths and incision rates, whereas the latter controlled the transformation between accumulation, which developed during the glacial period, and incision, which developed during the glacial-interglacial transition. The Yalong downstream incised rapidly from 1.10 to 0.72 Ma and rapidly from 0.06 Ma until the present; the terraces developed during these two periods. The incision rates in space during the two periods indicate the uplifting extent of the Jinpingshan area, which decreases toward the east and the south. The results reveal two rapidly uplifting stages in the SE Tibetan Plateau, including an accelerated uplifting since 0.06 Ma. Since the Middle Pleistocene, the tectonic uplift of the SE and NE parts of the Tibetan Plateau is synchronous, according to the same development stages of the river terraces of the Yalong downstream and the Yellow River in the Lanzhou area of the NE Tibetan Plateau. The difference in the horizontal displacement between the Xianshuihe Fault and the Anninghe Fault bend resulted in the rapid uplift of the Jinpingshan area. The incision rate for the spatial distribution of the Yalong downstream is the geomorphologicai response of crustal shortening and uplift differences in the SE margin block of the Tibetan Plateau. The southeastward diffusion process of the Tibetan Plateau was recorded.

Mixing Deposition of Upper Carboniferous in Jiangshan,Zhejiang Province and its Tectonic Significance

The Outangdi Formation in Jiangshan, Zhejiang, is the mixing deposit of terrigenous clastics and carbonates in Weiningian of the late Carboniferous. The mixing deposits include interbeddings, which constitute a series of alternated clastic and carbonate beds and mixing within the same bed which forms ＂hunji rock＂. The Outangdi Formation has the features of intercalated marine and terrestrial deposits with the progradational sequences, which are lower fine and upper coarse sedimentary granularity in the section. Hunji rock is formed in a seashore environment. It is a mixed carbonate sediment found in beaches or tideland facies with quartz sand taken from a bayou or beach by coastwise flow and circumfluence. There are two kinds of hunji sequences： （1） interbeds of sandstone and carbonate rock in seashore environments; and （2） interbeds of clastics in river facies and carbonate rock in ocean facies. It is indicated that mixing depositions belong to ＂facies mixing＂, affected mainly by regional tectonic uplift, rise of the global sea level, and the dynamics of water medium in the basin. Regional sea level periodic changes and progradational sequences probably resulted from the intense uplift of the old land called Cathaysia. The classification and name of mixed sediments are also discussed in the present study. Interbeds and alternated beds of clastic and carbonate beds are named ＂hunji sequence＂, a new genetic term. It is suggested that hunji rock means a special sediment event of mixing terrigenous clastics and carbonates instead of a name of a specific rock.

Chronological Link Between the Abrupt Change of the Loess Grain Size Sequence and the Formation of River Terraces on the Eastern Margin of the Qinghai-Tibetan Plateau Since the Late Early-Pleistocene

Based on the study of magnetostratigraphy,magnetic susceptibility and grain size of Garze A section on the southeastern margin of the Qinghai-Tibetan Plateau since the late early-Pleistocene,the basal age of Garze loess is located at～1.16 MaBP and a series of abrupt paleoclimatic changes is detected.The times of abrupt changes are of distinct series features,and the interval between each two adjacent abrupt changes is～50 kyr or～100 kyr.The most significant abrupt changes occur at around 1.06,0.85,0.6,0.46,0.39 and 0.14 MaBP.There is a chronological link between the abrupt changes of paleoclimate and the formation of river terraces and it is almost simultaneous with a strengthening trend of neotectonic activities.Therefore,maybe the climatic transition controll the timing of terrace formation,and the tectonic uplift originate potential energy and has a direct effect on channel incision, both the climatic transition and the tectonic uplift are important.Terraces are the products of the interaction of instable climatic variations and tectonic uplift.Like the loess-paleosol sequences,river terrace sequences are also controlled by the climate-tectonic coupling system and are ruled by climate-tectonic gyration with a～100 kyr paracycle,which may be the short eccentricity period of the earth.

从模拟研究看青藏高原的隆升形式与亚洲季风——干旱环境演化的区域差异（英文）

Tectonic uplift of the Tibetan Plateau(TP) is a major event in the recent geological history of the earth,which produced far-reaching impacts on the Asian and global climates and environments.Since the 1970 s,with the development of theories in planetary fluid dynamics and the improvement of computational environment,numerical simulation based on general circulation models(GCMs) has become an increasingly effective tool in investigations of the physical mechanisms and evolutionary processes of paleoclimate associated with the TP uplift.In this paper,we provide a timely review on representative works in the past four decades on the paleoclimatic responses to the plateau uplift.Numerical simulations to study the paleoclimatic effects of the plateau uplift experienced three stages with increasing complexity:1) plateau uplift as a whole in a single episode,as represented by the no-mountain/with-mountain experiments;2) phased uplift in which the uplifting process was divided into multiple stages and within each the plateau rose by a certain proportion of its current height;and3) sub-regional uplift,in which the focus was the effects of the uplift of a certain area within the TP,such as the northern Tibetan Plateau.These studies discovered the cause-effect relations between the plateau uplift and paleoclimate change,especially for the effects on the evolution of Asian monsoon system and aridification of inland Asia.In this review,we also included examples of current on-going studies,such as the relative impacts of the Himalayas vs.those of the TP as the rain barrier and comparative studies on the paleoclimatic effects of the uplifts of the TP and African highland.Toward the end,we identified five areas as the focus of future research regarding the TP uplift:1) the differences in the evolutionary processes of the South Asian and East Asian monsoons in response to the Himalayas-TP uplift at the regional and sub-regional scales;2) climatic feedbacks;3) long-distance effects(teleconnections) of the TP uplift;4) abrupt climatic changes;and 5) comparisons between the results of numerical simulations and geological evidences.

Mapping of geomorphic dynamic parameters for analysis of landslide hazards:A case of Yangbi river basin on the upper Lancang-Mekong of China

Landslides are common hazards in orogenic belt areas.However,it is difficult to quantitatively express the driving effects of tectonic uplift and stream erosion on the occurrence of landslides on large spatial scales by conducting field investigations.In this study,we analyzed a relatively large region that extends over the Yangbi River basin on the upper Lancang-Mekong in China.A series of quantitative indices,including kernel density of the landslide(KDL),hypsometric integral(HI),steepness index(ksn),stream power(?),and stream power gradient(ω)were used to explore the promoting effects of tectonic uplift and stream action intensity on landslides by mapping geomorphic dynamic parameters combined with actual landslide data.The analysis showed that the HI value in the highest landslide risk area was approximately 0.47,and that the KDL in the region can be expressed as a function of steepness or stream power gradient of the channel network,namely,KDL=0.0127 Ln ksn-0.0167(R2=0.72,P<0.001)and KDL=0.0219 Lnω-0.0558(R2=0.21,P<0.02).Therefore,the lower reach of the Yangbi River basin,with higher steepness and stream power gradient,usually has a high uplifting rate and stream incision that drives landslides and causes the entire river network system to be in a stage of longterm active erosion.Furthermore,the results suggest that sediments were being rapidly discharged from the steep tributary channels to the mainstream.This practical situation highlights that the downstream area of the river basin is a high-risk area for landslide hazards,especially in association with heavy rainfall and earthquakes.

Quaternary Neotectonic Configuration of the Southwestern Peloponnese, Greece, Based on Luminescence Ages of Marine Terraces

This project studies marine terraces in western Messenia, southwestern Peloponnese, Greece, to propose a model of neotectonic configuration and paleogeographic evolution of western Messenia during the Quaternary. GIS analysis of topographic data and geological mapping revealed flanks of raised terraces created on Quaternary marine deposits. Luminescence ages of sediments from the three westernmost marine terraces tend to be consistent OIS-5, OIS-7 and OIS-9, respectively, thus agreeing with the three latest warm stages of the Pleistocene. Moreover, the type and the extent of deformation of the dated marine terraces allowed us to reflect on the neotectonic configuration of western Messenia as well as to conclude that progressive differential uplift over the last 300 ka has induced a dome-like structure to the upper crust of western Messenia.