late cenozoic evolution of the east china continental margin insights from seismic gravity and magnetic analyses abstract seismic reflection profiles reveal the structural characteristics beneath the east china sea shelf margin and the okinawa trough and provide new constraints on the late cenozoic evolution of the east china continental margin the frontal shelf basin between the taiwan sinzi uplift and the trough axis occupies the western half of the northern middle okinawa trough in this basin the middle late miocene sediments are confined to grabens or half grabens dominated by listric faults whereas the overlying pliocene quaternary sequence is characterized by a uniform thickness and dense planar type faults suggesting that rifting of the northern middle okinawa trough initiated during the middle miocene but slowed down during the earliest pliocene since that time the opening of the okinawa trough has been dominated by diffuse rifting the southern okinawa trough is predominately filled by quaternary sediments indicating that its back arc rifting began during the earliest pleistocene contractional structures identified in the pre quaternary sequence beneath the continental slope along with an erosional pleistocene pre pleistocene unconformity in the southern okinawa trough demonstrate the existence of pre rifting compression and uplifting in this region we use this evidence and previously published results to propose an evolutionary model of the east china continental margin during the late cenozoic the northern middle okinawa trough began rifting during the middle miocene on a paleo uplift the luzon arc initially impinged upon the eurasian continental margin during the late miocene near the southeastern end of the miyako fault belt and activated the proto taiwan orogeny in today s southern okinawa trough and adjacent regions during the late miocene pliocene the orogeny quickly propagated southwestward along with the west northwest moving philippine sea plate subsequently the rifting of the southern okinawa trough was initiated during the earliest pleistocene and propagated southwestward following the post collisional collapse of the proto taiwan orogen this geodynamic scenario resembles that of present day northern taiwan

a deforming plate tectonic model of the south china block since the jurassic abstract the south china block has experienced multiple phases of tectonic deformation since the middle jurassic understanding this deformation history helps reveal the driving mechanisms responsible and sheds light on the associated magmatism and mineralization here we construct deformable plate tectonic reconstructions for the south china block from 170 ma to the present using gplates the deformation starts with a nw se oriented shortening phase from 170 to 136 ma subsequently south china experienced two episodes of extension in the cretaceous during 136 118 ma and 100 80 ma respectively the cenozoic extension occurred mostly along the southeast continental margin including the east china sea shelf basin and rift basins in the northern south china sea margin and the taiwan margin segment the rifting was initiated nearly simultaneously along the continental margin at 65 ma and ceased at 34 30 ma the northern portion of the okinawa trough started rifting at 15 ma while the southern portion rifted in the last few million years the luzon volcanic arc thrusting onto the southeasternmost south china block since 6 5 ma caused the still active taiwan orogeny the predicted accumulated deformation at present day is characterized by overall shortening onshore with contraction factors mostly between 0 8 and 1 and extension offshore with stretching factors generally between 1 and 2 the central china orogen and taiwan orogen experienced more intense shortening relative to the interior south china by factors down to 0 6 the okinawa trough experienced intense stretching by factors up to 2 5 in its central part the intraplate deformation in the south china block is closely related to the subduction of the izanagi and pacific plates the jurassic and earliest cretaceous shortening was likely induced by trench advance and the extension during the cretaceous and the cenozoic was mostly driven by subduction retreat

is taiwan the result of arc continent or arc arc collision abstract conventionally it has been accepted that the formation of taiwan results from the collision of the luzon arc with the eurasian continental margin we suggest that taiwan results from the collision of the luzon arc with the former ryukyu subduction zone before the collision the latter extended a few hundred kilometres southwest of its present day termination in the early to middle miocene the subduction became inactive in its southwest portion and the manila trench migrated northeastward giving rise to the formation of the luzon arc the collision started in the late miocene by closing the oceanic domain located between the luzon arc and the former ryukyu arc because the luzon arc moved northwestward with respect to the former ne sw trending ryukyu arc the oblique collision first resulted in the indentation on the south ryukyu arc west of 123 5 e and the narrowing of the corresponding portion of the okinawa trough prior to the uplift of taiwan today the hsuehshan and backbone ranges represent the uplifted portion of the backarc basin and the longitudinal valley corresponds to the suture zone between the former ryukyu and the luzon arcs in this model we propose to link although they are not of the same age two truncated backarc basins the active okinawa trough to the northeast and the former active tainan backarc basin to the southwest the former backarc basin extended from southwest of taiwan to southern japan and could have been initiated near the paleo location of taiwan as early as the eocene oligocene the result of the collision is the truncation of the ancient backarc basin associated with the shortening deformation and uplift of the ancient outer arc and related backarc region which provides the fundamental mechanism of the taiwan mountain building this model is in agreement with a counterclockwise rotation of the portion of taiwan located west of the coastal range belonging to the luzon arc and a clockwise rotation of the south ryukyu arc earthquake focal mechanisms geodetic observations and the distribution of the petrologic and structural features are also consistent with the proposed arc arc collision model

new insights on 3 d plates interaction near taiwan from tomography and tectonic implications abstract recent tomographic results are used to trace the south china sea and philippine sea subducting slabs south and northeast of taiwan along the manila and ryukyu trenches respectively in particular the 3 d plates interaction beneath taiwan is discussed based on a close up view of the tomographic sections together with earthquake hypocenters distribution our study indicates that 1 the east dipping south china sea slab can be followed to the north up to the latitude of hualien 2 the eurasian plate subducts beneath most part of the taiwan island down to the 670 km depth discontinuity 3 the north dipping philippine sea slab can be followed slightly west of the longitude of hualien both plates thus interact beneath northern taiwan where the arc continent collision is paroxysmal 4 slab detachment is envisaged at the northern edge of the subducted eurasian plate beneath the coastal range of taiwan which may facilitate the northwestward motion of the philippine sea plate with respect to eurasia slabs geometries obtained from tomographic sections allow us to reconstruct the late neogene plate kinematics and dynamics in this region our main conclusions are 1 the size of the original south china sea was about twice its present size 2 the subducted part of the west philippine basin i e the largest oceanic basin of the philippine sea plate extends only 400 km north of the ryukyu trench 3 slab detachment might have occurred 3 5 my ago beneath the central and northern ryukyu arc along a weak zone that is aligned with the gagua ridge an ancient plate boundary 4 the ryukyu trench has propagated westward from 126 e of longitude southeast of miyako island to the locus of the present arc continent collision along a major lithospheric tear that cut through the continent ocean boundary first and then through the continental lithosphere as a consequence the southern ryukyu margin developed progressively from east to west as a subduction zone during the last 8 my it has been elaborated onto a passive margin which corresponded to the edge of the eurasian continental shelf bordering the south china sea prior to pliocene 5 the southern okinawa trough rifted during the last 2 1 ma following the propagation of the subduction zone 6 subduction of the eurasian margin probably stopped recently beneath northern taiwan and a flip of subduction from west to east is being initiated near hualien

qualifying mass failures on loess gully sidewalls using laboratory experimentation abstract the morphology of the failure scar has been a long debated issue concerning the loess plateau of china and the lack of normative data has hampered vital research in this area in this study a series of laboratory experiments were conducted to observe failure geometries and volumes under rainfall simulations the following six failure scar types occurred the sequence of the types described here may be same to that of the following text namely tf cd cu ia ps and co the number of failure masses in the experiment for scar types tf cd cu ia ps and co amounted to 45 26 23 3 2 and 1 of the total and the corresponding volumes were 58 16 20 2 3 and 1 of the total respectively this implies that tf cd and cu were the three major types of failure scars during the process of gravity erosion on a steep loess slope and the scar tf was the most significant the sensitivity coefficient the degree of variation in the target value caused by a change in a crucial factor when other conditions remain unchanged of the slope gradient and rainfall intensity for the total volume of the tf scar were 4 5 and 3 7 respectively in other words a relatively dangerous failure scar tf might appear if the slope became steeper or if the rainfall became more intensive in addition the sensitivity coefficients of the rainfall duration for the total volume of the cu scar was significant being 12 4 this shows that a long duration storm could easily induce a large volume failure with a cu scar the experimental results obtained here provide a morphogenic insight into the gravity erosion control on a loess gully sidewall

determination of the isostatic and gravity moho in the east china sea and its implications abstract the east china sea ecs is located among the eurasian pacific and philippine sea plates whose crustal structure and evolution are very complex elevation geoid and gravity anomaly data are used in this study to determine the isostatic and gravity moho topography of the ecs and surroundings the gravity effects of sediments and subducting slabs are computed using recent datasets during estimation of the gravity moho and the results show good agreement between the gravity moho and seismic results the crustal isostatic implications of the difference between the isostatic and gravity moho are discussed and the decreasing moho depth from the coast of the mainland china to the western margin of the okinawa trough suggests continental crust type features similar to the yellow sea a combined isostatic analysis which takes the difference between the isostatic and gravity moho into account indicates that the shallower moho beneath the okinawa trough and the depressed moho beneath the ryukyu arc may have implications for rifting in the okinawa trough the steep moho along the ryukyu trench marks the continent ocean boundary at the crustal scale which is consistent with the subduction of the philippine sea plate taking the eastward extension of the ecs into account it is expected that this would be steeper if it was generated by the isostatic over and under compensation beneath the ryukyu arc and trench respectively

failure mechanism of a slope with a thin soft band triggered by intensive rainfall rainfall is considered as one of the paramount factors for slope failures in many regions around the world particularly in tropical and subtropical regions to study the effect of rainfall storm and its duration on the stability of slopes with a thin soft band layer a 2d seepage numerical analysis and experimental investigation were implemented on an unsaturated model consisting of clayey sand soils with a thin soft layer inclined to the horizontal level by 30 at a slope angle of 50 it was subjected to intensive rainfall 20 mm h for 8 h positive pore water pressures and horizontal earth pressures were monitored during the rainstorm using sensors distributed inside the experimental model both the experimental and numerical simulation results showed that the stability of the slope decreased during the time of the rainfall storm infiltration of rainwater resulted in reduction of soil shear strength due to the loss occurring in soil suction after 1 h of rainstorm the tension cracks appeared at the top of the slope and a certain displacement was observed in the sliding blocks during the time of rainstorm the infiltrated water flowed out from the slope through the weak interlayer near to the toe causing piping and local failure so the formed cracks at the top of slope grew and expanded due to sliding of the failed soil blocks moreover the ground water table rose and the positive pore water pressures increased resulting in a reduction of effective stress which is considered as a main factor in soil shear strength a surface runoff was also present following the full saturation of the slope leading to dragging the fine particles with water flow causing erosion the combination of piping and erosion effects led to a quick local failure at the toe as well as sliding of the failed blocks and spreading of the cracks

interaction between landsliding materials and the underlying erodible bed in a loess flowslide abstract loess landslides exhibit strong interactions with the terrace sediments of the jing river on the south jingyang platform jingyang xi an china analysis of past landslide events revealed that the sand layer of this terrace was thrust up to the surface accompanied by other terrace sediments of carrying this led to the formation of a thrust nappe structure over a long distance we performed ring shear tests to examine the shear behavior of this sand layer with the finding that saturated sand was highly susceptible to liquefaction induced failure the groundwater level of the study area is high resulting in near saturation of the sand layer therefore topographic interferences contributed additional variables and increased interaction complexities simulations indicated that the liquefied sand layer was compressed and forced due to the absence of constraints the sand layer near the bottom of the slope was sheared out over a relatively short distance on the other hand particle interia and constraints of the stable layer resulted in the sand layer near the distal part of the deposits being sheared upward to the ground finally an initiation movement model of loess flowslides is proposed it describes static liquefaction of the loess layer of the slope resulted in occurrence of flowslides collisions between the deposits from the platform edge slope and terrace sediments resulted in the shear liquefaction of sands the landslide experienced four stages as they moved scraping collisions floating scrapes folded thrusts and nappe accumulation

failure mechanisms in loess and the effects of moisture content changes on remoulded strength abstract investigations into the failure mechanisms of loess slopes in the loess region of north central china have shown that a majority of mass movements are associated with shallow slab slides predominantly moving under tension the effects of soil moisture content are of paramount importance when dry vertical slopes in loess may exceed 15 m in height but under conditions close to saturation the structural strength of loess rapidly decreases causing failure of the slopes mass failure of loess occurs as collapse due to hydroconsolidation and disintegration of the loess fabric as a result of liquefaction or fluidization and can be associated with progressive failure processes local destruction of the openwork fabric of the loess can lead to small plastic movements within the loess deposits this is as close as loess can come to creep

topographic controls on evolution of shallow landslides in pastoral wairarapa new zealand 1979 2003 abstract this study aims to identify topographic influence on shallow landslides and their evolution during 1979 2003 in the pastoral lower north island new zealand landslide affected sites were mapped from aerial photographs and an aster satellite image the two landslide maps were overlaid in a geographic information system arcgis to detect the changes that have taken place in landslide affected areas the change map and the landslide distribution maps were overlaid with three topographic layers of slope gradient slope position and slope aspect that had been derived from a digital elevation model in arcgis the overlay analysis revealed that landslides affected area increased from 23 75 ha in 1979 to 110 97 ha in 2003 the distribution of landslide affected sites is inversely correlated with slope gradient but positively with slope position northern aspects are the most vulnerable to landsliding containing about 78 of the total affected sites moderate slope gradients suffered the most severe landsliding in the lower to middle slopes the overall magnitude and frequency of landsliding is also related to northern and eastern octants on the moderate slope gradients in the low to moderate slope positions although the same topographic setting is conducive to landsliding in both 1979 and 2003 the rate of landsliding varies with topographic setting hence topography is critical not only to landsliding but also to the evolution of sites already affected by landslides such an understanding over large spatial scales is possible only with the use of multitemporal remote sensing data and gis that are able to speed up data collection and analysis

cenozoic sill intrusion in the central and southern east china sea shelf basin abstract cenozoic igneous rocks dominated by basalts are exposed sporadically onshore east china and they provide important information about the cenozoic evolution of the region importantly their geometries and distribution are still not well constrained in the 200 600 km wide offshore continental shelf region based on seismic profiles this study presents the geometric characteristics of 133 igneous sills that are widely distributed in the central and southern regions of the east china sea shelf basin ecssb sills in high amplitude continuous seismic reflections mostly occur in a time interval of 1 1 3 3 s in multiple seismic profiles corresponding to a depth range of 1 1 4 8 km they can be classified into five types saucer shaped sills strata concordant sills laccoliths inclined sheets and hybrid sills of these the saucer shaped sills predominate strata deformation associated with these igneous sills indicate that sill intrusion has become intense since the miocene and it potentially affected petroleum systems in the ecssb forced folds induced by the sills are prospective petroleum traps we infer that sill intrusion in the ecssb was due to magma upwelling caused by dehydration and or small scale convection in a large mantle wedge above the stagnant pacific slab the subduction of the philippine sea plate resulted in tectonic inversion in the ecssb and extension in the okinawa trough since the early miocene triggered more magmatism in the tectonically thinned ecssb thick sedimentary strata over a thin crust in the ecssb may have induced more intrusive than extrusive cenozoic magmatism

structural and engineering geology of the east gate landslide purcell mountains british columbia canada the east gate landslide is a prehistoric landslide that was reactivated in january 1997 the slope failure took place in the lower greenschist metasedimentary units of the precambrian horsethief creek group the grizzly creek thrust is a regional overturned fault that coincides with the location of the headscarp of the east gate landslide four discontinuity sets were recognised from detailed engineering geological mapping of the headscarp and surrounding area the main scarp of the section reactivated in 1997 was sub divided into three structural domains based on its position within the landslide lithology and orientation of the discontinuity sets limit equilibrium techniques finite difference flac and distinct element udec codes were used to investigate the failure mechanism of the 1997 event the results of the field observations and numerical models suggest that the 1997 failure involved a complex mechanism incorporating components of rock slumping bi planar and pseudo circular failure that was controlled by both the orientation of the discontinuity sets and reduced rock mass quality due to tectonic deformation

petroleum systems in the offshore xihu basin on the continental shelf of the east china sea xihu basin is one of the cenozoic sedimentary basins within the continental shelf of the east china sea within which eight oil and gas fields and four hydrocarbon bearing structures have been found our systematic analysis of potential petroleum systems in the basin has identified the eocene pinghu formation as the most important source rock in the basin the eocene pinghu formation consists of mudstone and coal deposited in an embayment and tidal flat environment and is characterized as containing type iii kerogen the pinghu formation is mature and at the present time is within the oil and wet gas windows with determined vitrinite reflectance values in the range of 0 55 2 2 measured vitrinite reflectance rom modeling results suggest that the main stage of hydrocarbon expulsion occurred during the miocene the main reservoir consists of fine grained sandstones of the huagang and pinghu formations deposited within shallow lacustrine and estuarine environments the measured porosity from core samples of reservoir rock ranges from 10 to 35 whereas permeability values range from 1 to 4000 md both porosity and permeability decrease with depth the mudstones of the upper huagang and longjing formations also occur as regional seals which developed overpressure zones as determined by two way sonic transit times the overburden includes all the oligocene miocene pliocene and quaternary strata the hydrocarbon traps in the basin are mainly structural traps including faulted blocks faulted structural noses and anticlines most traps were developed at the ends of the eocene or oligocene hydrocarbons produced from the xihu basin are predominantly natural gases with minor amounts of crude oil the crude oil in the basin is characterized by a low density low sulfur low wax low vanadium nickel ratio a low resin and asphaltene content and a high proportion of saturated hydrocarbons the natural gas in the basin is composed predominantly of methane with an average c1 c1 5 ratio of 0 89 and a c1 c2 5 ratio of 8 6 two petroleum systems have been identified in the basin the known pinghu huagang and the hypothetical huagang huagang systems the pinghu huagang is the major petroleum system and most important for oil and natural gas exploration in the basin

structural characteristics of the northern okinawa trough and adjacent areas from regional seismic reflection data geologic and tectonic implications abstract analysis of regional multi channel seismic data from the northern okinawa trough and adjacent shelf provides some important constraints on the structural development of the area the sedimentary strata in the northern east china sea shelf basin separated from the okinawa trough by the taiwan sinzi belt are affected by the miocene compressional tectonism and truncated by the late miocene unconformity in contrast those in the western margin of the northern okinawa trough are cut by numerous normal faults and the late miocene horizon forms a conformable surface this suggests that the taiwan sinzi belt acted as a buttress for the northern okinawa trough against the compressional tectonism our data also reveal the ho basin in the western margin of the northern okinawa trough previously known only from proprietary industry data the longwan ridge lying between the ho basin and the northern okinawa trough may be the youngest of the relict arcs or buried ridges in the area the abrupt along strike change in the fault polarity near the northern margin of the depocenter of the ho basin suggests a nw trending left lateral transfer zone or fault the western boundary of the northern okinawa trough is characterized by the gently deepening seafloor whereas that of the southern okinawa trough is marked by steep border faults suggesting more rapid subsidence in the south this together with the well developed symmetric axial faults in the south and the greater width and the lack of well developed axial zone in the north may suggest focused rifting extension in the southern okinawa trough and diffuse rifting extension in the northern okinawa trough we postulate that the diffuse rifting extension in the northern okinawa trough is due to the tectonic perturbation caused by the convergence or subduction of the topographically high and buoyant amami plateau at the northern ryukyu arc

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

seismic record of tectonic evolution and backarc rifting in the southern ryukyu island arc system abstract the southern ryukyu island arc system is located at a convergent plate margin where the philippine sea plate is subducting under the eurasia plate we have conducted multi channel seismic reflection surveys to study tectonic evolution and backarc rifting of the southern ryukyu island arc system using the r v tansei maru of the ocean research institute university of tokyo in june 1993 and 1994 we describe systematically a complete cross section from the east china sea continental shelf to the ryukyu trench from the viewpoint of seismic stratigraphy seven major seismic units and three stages in the tectonic evolution of the system are identified 1 during stage 1 from late miocene to earliest pleistocene pre rift deposits of the shimajiri group accumulated over a wide region from the east china sea continental shelf to the forearc region 2 stage 2 is defined by a series of tectonic processes involving crustal doming erosion subsidence and sedimentation in association with initial rifting of the southern okinawa trough during most of early pleistocene time and 3 the backarc rifting is still in progress and syn rift sedimentation has been under way since the late pleistocene stage 3 a new significant observation lies in the fact that the pliocene shimajiri group is not distributed in most of the present day southern okinawa trough this implies that the backarc rifting of the southern okinawa trough was probably initiated after the deposition of the shimajiri group that is during the early pleistocene crustal scale simple shear allowing an asymmetrical half graben structure rather than pure shear governed the initial rifting of the southern okinawa trough the possibility however cannot be excluded that pure shear associated with symmetrical rifting may be predominant in the present day rifting of the southern okinawa trough as a result of northwestward migration of the rifting axis the average extension rate of the southern okinawa trough is estimated to be approximately 1 2 cm year on the basis of fault geometry observed on the acoustic basement

okinawa trough genesis structure and evolution of a backarc basin developed in a continent abstract the okinawa marginal basin was opened by crustal extension into the asian continent north of the taiwan collision zone it is located behind the ryukyu trench subduction zone and the ryukyu active volcanic arc if we except the andaman sea the okinawa trough is the only example of marginal backarc basin type opened into a continent at an early stage of evolution active rifting and spreading can be observed synthesis of siesmic reflection seismic refraction drilling dredging and geological field data has resulted in interpretative geological cross sections and a structural map of the ryukyu okinawa area the main conclusions of the reconstruction of this backarc basin volcanic arc evolution are 1 backarc rifting was initiated in the volcanic arc and propagated along it during the neogene it is still active at both ends of the basin remnants of volcanic arc are found on the continental side of the basin 2 there was synchronism between opening and subsidence of the okinawa trough and tilting and subsidence of the forearc terrace the late miocene erosional surface is now 4000 m below sea level in the forearc terrace above the trench slope retreat and subsidence of the ryukyu trench line relative to the asian continental plate could be one of the causes of tilting of the forearc and extension in the backarc area 3 a major phase of crustal spreading occurred in pliocene times 1 9 my ago in the south and central okinawa trough 4 en echelon rifting and spreading structures of the central axes of the okinawa trough are oblique to the general trend of the arc and trench the ryukyu arc sub plate cannot be considered as a rigid plate rotation of 45 to 50 of the southern ryukyu arc since the late miocene is inferred the timing and kinematic evolution of the taiwan collision and the south okinawa trough opening suggest a connection between these two events the indentation process due to the collision of the north luzon arc with the china margin could have provoked lateral extrusion clockwise rotation 45 to 50 according to palaeomagnetic data and buckling of the south ryukyu non volcanic arc tension in the weak crustal zone constituted by the south ryukyu volcanic arc and opening of the south okinawa trough similar lateral extrusions rotations buckling and tensional gaps have been observed in indentation experiments additional phenomena such as thermal convection retreating trench model or anchored slab model could maintain extension in the backarc basin such a hypothetical collision lateral backarc opening model could explain the initiation of opening of backarc basins such as the mariana trough bonin trough parece vela shikoku basin and sea of japan a new late cenozoic palaeogeographic evolution model of the philippine sea plate and surrounding areas is proposed

hydrothermal metal supplies enhance the benthic methane filter in oceans an example from the okinawa trough abstract anaerobic oxidation of methane aom is an important process that regulates methane budget in the global carbon cycle sulfate is traditionally regarded as the most important electron acceptor for aom however recent studies reveal that reactive metal reduction driven aom metal aom may also present on natural environments partitioning the methane c sink from anaerobic oxidation between sulfate reduction driven aom sulfate aom and metal aom is thus becoming a scientific challenge to be addressed this study aimed to show that metal aom has a potential to complement sulfate aom especially when methane seeps met sediments enriched in iron and manganese oxides supplied by hydrothermal plumes samples of authigenic carbonate were collected from the cold seeps on the western slope of the okinawa trough ot a semi enclosed back arc basin with cold seeps and hydrothermal activities coexist spatially petrologic and mineralogical observations provided faithful evidence of a close genetic relationship between goethite and authigenic carbonates likely indicating the presence of metal aom although some contributions of organoclastic fe reduction cannot be ruled out the most possible place of metal aom was between the lower part of the sulfate methane transition zone smtz and the immediate upper part of the methanogenic zone the characteristics of 13ccarb 53 7 to 3 3 vienna peedee belemnite vpdb also point to our carbonate samples as the products of aom these authigenic carbonates was further identified as three possible types of carbonate of different sources sulfate aom metal aom and hydrothermal carbonates depending on the correlations among concentrations of carbonate associated sulfate cas 13ccarb and 18ocarb based on these findings we tentatively suggested that the reduction of reactive metals carried by hydrothermal plumes might drive the methane oxidation in the adjacent cold seep areas resulting in the precipitation of unique carbonates and enhancement the efficiency of the benthic methane filter this study reported the coupling or interaction between the two extreme submarine environments by metal aom for the first time which might help in understanding and improving the global carbon and metal cycles now and in the past

two phase opening model for the okinawa trough inferred from paleomagnetic study of the ryukyu arc tertiary volcanic and sedimentary rocks were collected at 50 sites of both the central ryukyu arc and the southern ryukyu arc for a paleomagnetic and geochronological study in an attempt to understand the opening of the okinawa trough back arc basin stable primary components of remanent magnetization were isolated through both thermal and alternating field demagnetization experiments from 12 sites of three geological units of the central ryukyu arc and from 12 sites of two geological units of the southern ryukyu arc the paleomagnetic results were compared with the tertiary apparent pole wander path of eurasia in order to investigate the tectonic movement of the ryukyu arc with respect to the asian continent the comparison and the radiometric ages indicate that the southern ryukyu arc rotated clockwise through 25 between 10 ma and 6 ma in contrast the central ryukyu arc experienced little rotational motion since 17 ma we propose the following two phase opening model for the okinawa trough opening the first stage took place between 10 ma and 6 ma the southern part of the trough opened by means of a wedge mode to cause the clockwise rotation of the southern ryukyu arc in the central part the parallel opening occurred and the ryukyu arc drifted without any rotation the second phase started recently in the whole okinawa trough it is observed as the present activities in the trough

geology and tectonics of the ryukyu islands abstract the ryukyu islands are divided morphologically and geologically into three island groups north central and south ryukyus north central ryukyu represents the geological continuation of the outer belt of southwest japan composed of mesozoic eocene sedimentary sequences whereas south ryukyu is characterized by high pressure metamorphic rocks eocene volcanics and limestone and lower miocene sediments the geological and structural contrasts between north central and south ryukyus are conspicuous before the late miocene transgression covered the whole area the ryukyu islands have been established since then the successive developments of the goto tunghai senkaku basins since the paleogene of the okinawa trough since the miocene and of the grabens near the island group since the pliocene signify a southeastward shift of the basins in relation to the activity in the granite diapir zones accompanied by volcanism

the stratigraphical position and the use of the term eopleistocene in serbian geological literature abstract when the calabrian stage was included in the quaternary frame by the decision of the 18th igc 1948 it implied changes in the stratigraphical scale subdivision at the beginning of the 1970s after the addition of the calabrian stage to the quaternary and the lowering of the quaternary boundary it became evident that in the new scheme a gap of nearly 1 my was created in the case of fluvial and fluvio lacustrine formations the time frame of the pleistocene could not include the oldest quaternary fluvial and fluvio lacustrine formations because of the lowering the quaternary boundary to nearly 1 8 ma as was done in marine calabrian stage and terrestrial formations villafranchian stage this was one of the main reasons why the term eopleistocene was implemented into the serbian quaternary stratigraphical terminology in 1972 and it was used in a semi official way until 2010 in 2009 with the official ratification of the ics iugs of the lowering of the neogene quaternary i e pliocene pleistocene boundary to 2 58 ma the use of the eopleistocene in the serbian stratigraphical terminology lost its meaning the use of the term eopleistocene in the serbian stratigraphical scheme cannot be accepted in the sense of modern stratigraphical principles because the mixing of the discriminatory concepts of the alpine morphostratigraphical model with regional exussr climatostratigraphic and or biostratigraphical units was obvious as a term eopleistocene also caused a number of unclear and undefined problems misunderstandings with regard to relations eopleistocene pleistocene eopleistocene lower pleistocene eopleistocene alpine morphostratigraphical stages with the developments and changes in the quaternary stratigraphy the serbian eopleistocene should be interpreted and replaced with upper part of lower pleistocene because the base of the eopleistocene had been identified at nearly 1 8 ma and the lower middle pleistocene brunhes matuyama boundary does not correspond with the eopleistocene neopleistocene boundary

stratigraphic revision of the quaternary material from the vicinity of belgrade and the serbian segment of the tisza valley analysed by v d laskarev abstract in his studies of the quaternary deposits in the vicinity of belgrade and vojvodina v d laskarev clearly identified the main quaternary facies and lithostratigraphic units loess series corbicula fluminalis beds holocene sands etc since the period of the publication of his research there has been development in quaternary stratigraphy and palaeogeography in compliance with these changes the following elements of his studies should be corrected 1 the age of the loess series in the zemun loess plateau and the belgrade plateau corresponds to the younger part of the middle and late pleistocene 2 the pleistocene corbicula beds represent temperate fluvial stages of the younger part of the lower and middle pleistocene the viviparus boeckhi horizon was defined as a subunit of the pleistocene corbicula beds that corresponds to the younger part of the lower pleistocene fluvial temperate stages the makis beds should be defined as a local term for the pleistocene corbicula beds in the sava valley in the vicinity of belgrade 3 laskarev generally recognized the main features of the quaternary palaeogeographic evolution however they cannot be applied to the whole area of the serbian segment of the pannonian plain there are still no reliable geological data for the lower and middle pleistocene parts of the quaternary geological sections such as the zrenjanin titel loess plateau it is evident that up to now the pleistocene corbicula beds have not been identified in the basement of the titel loess plateau only the aeolo lacustrine and lacustrine palustrine silts underlying the loess series 4 geomorphological investigations have identified four terraces in the valley of the danube and the tisza in vojvodina in this case the first terrace level of laskarev should be divided into the lower ia or t1 and upper ib or t2 terraces

fossils from quaternary fluvial archives sources of biostratigraphical biogeographical and palaeoclimatic evidence fluvial sedimentary archives have the potential to preserve a wide variety of palaeontological evidence ranging from robust bones and teeth found in coarse gravel aggradations to delicate insect remains and plant macrofossils from fine grained deposits over the last decade advances in quaternary biostratigraphy based on vertebrate and invertebrate fossils primarily mammals and molluscs have been made in many parts of the world resulting in improved relative chronologies for fluviatile sequences complementary fossil groups such as insects ostracods and plant macrofossils are also increasingly used in multi proxy palaeoclimatic and palaeoenvironmental reconstructions allowing direct comparison of the climates and environments that prevailed at different times across widely separated regions this paper reviews these topics on a regional basis with an emphasis on the latest published information and represents an update to the 2007 review compiled by the flag inspired igcp 449 biostratigraphy subgroup disparities in the level of detail available for different regions can largely be attributed to varying potential for preservation of fossil material which is especially poor in areas of non calcareous bedrock but to some extent also reflect research priorities in different parts of the world recognition of the value of biostratigraphical and palaeoclimatic frameworks which have been refined over many decades in the core regions for such research particularly for the late middle and late pleistocene of nw europe has focussed attention on the need to accumulate similar palaeontological datasets in areas lacking such long research histories although the emerging datasets from these understudied regions currently allow only tentative conclusions to be drawn they represent an important stage in the development of independent biostratigraphical and palaeoenvironmental schemes which can then be compared and contrasted

a study of critical state on an unsaturated silty soil critical state models for unsaturated soils have been proposed in recent years however the proposed models have been based on limited experimental data compacted specimens have generally been used for research and the complications of soil fabric resulting from the compaction procedures have brought difficulties into the interpretation of fundamental soil behavior there is a need to undertake further laboratory research studies on unsaturated soils particularly to obtain a fundamental understanding of the shear strength and critical state of unsaturated soils by testing soil specimens with simple soil structures suction controlled triaxial drained shear tests on an unsaturated silt were carried out as part of this research program specimens were prepared by gradually consolidating the initially slurried soil the resulting specimens had a relatively simple soil fabric and stress history the results showed that applying suction to an initially saturated specimen has a similar influence on the stre

the effects of slope length and slope gradient on the size distributions of loess slides field observations and simulations abstract in this study we characterize and consider the effects of slope length and slope gradient on the size distributions of loess slides to carry out this study we employ data on 275 loess slides within zhidan county central loess plateau china these data were collected in the field and supplemented by the interpretation of remote sensing images both the field observations and slope stability analysis show that loess slide size increases with the slope length slide sizes is significantly correlated with slope length showing a power law relationship in both cases however the simulation results show that slope gradient is not associated with loess slide size the main part of the link between slope gradient and slide size seen in the observations is only apparent as indicated by the strong connection between slope gradient and length statistical analysis of the field observations reveals that slope gradient decreases with increasing slope length and this correlation interferes with the potential relationship between landslide sizes and slope gradient seen in the field observations in addition the probability densities of the areas of loess slides occurring on slopes of different slope lengths are determined using kernel density estimation this analysis shows that slope length controls the rollover of the frequency size distribution of loess slides the scaling exponent increases with slope length

evolution of the southern taiwan sinzi folded zone and opening of the southern okinawa trough abstract recent interpretation of seismic sections and free air gravity anomalies in offshore northern taiwan reveals that the southern taiwan sinzi folded zone began to form in late middle miocene though it was mainly constructed in the late pliocene with strong reverse faulting and folding two westward progradational sequences were deposited in the shelf basin with sediments supplied from the southern taiwan sinzi folded zone and the southern ryukyu arc these two structures are displaced by several northwest striking dextral strike slip faults that were active in the early quaternary when the clockwise rotated southern ryukyu arc and the folded southern taiwan sinzi folded zone were broken it is believed that recent extension in the southern okinawa trough started in the early quaternary because uplift on the southern taiwan sinzi folded zone continued to latest pliocene early quaternary paleogene miocene sediments of the east china sea shelf in the western part of the southern okinawa trough basin are interpreted to indicate that the east china sea shelf basin extended to the east of the southern taiwan sinzi folded zone

post collisional magmatism around northern taiwan and its relation with opening of the okinawa trough being part of an active mountain belt formed by oblique collision of the luzon arc with asia northern taiwan and the offshore islets are marked by a series of latest pliocene quaternary volcanoes whose eruptions have been conventionally ascribed to westward propagation of the ryukyu volcanic arc on the basis of new geochemical data along with supporting geologic and geophysical evidence we propose instead that this young volcanism resulted from post collisional lithospheric extension in the northern taiwan mountain belt and the mantle source regions involved in the melt generation have been significantly modified by the nearby ryukyu subduction related processes magmas thus produced through the northeast to the southwest in the northern taiwan volcanic zone ntvz vary from low k to calc alkaline and then shoshonitic compositions such a spatial geochemical variation characterized by southwestward increase in enrichments of potassium and incompatible trace elements runs subparallel to the southwestern part of the present day ryukyu trench the geochemical variation that can be explained by southwestward decrease in degrees of partial melting of the mantle sources is reconciled with a southwestward weakening extensional regime observed in the ntvz the post collisional extension in northern taiwan furthermore might have played a role in reactivation of the opening in the middle okinawa trough and gave way to its rapid southwestward propagation with associated development of the ryukyu subduction zone west of124oe this nascent subduction in turn resulted in abundant submarine volcanoes which delineate an embryo volcanic front along the southern margin of the trough therefore the southwestern okinawa trough is not a fore arc basin as had been previously alleged but represents an atypical back arc basin which developed broadly synchronously or prior to its arc trench system in this particular collision extension subduction tectonic environment 1999 elsevier science b v all rights reserved

pleistocene environmental dynamics recorded in the loess of the middle and lower danube basin abstract the substantial loess deposits of the middle and lower danube basin in southeastern europe represent one of the thickest and most comprehensive terrestrial palaeoenvironmental records on the continent yet are also the least well understood environmental conditions over the last million years have resulted in relatively continuous deposits uninterrupted by glaciation and tundra conditions which nevertheless reflect oscillations between relatively warm humid interglacial and cold dry glacial intervals this relative environmental stability may have proven important for hominins migrating into and through the region the loess stratigraphy comprises distinct loess paleosol sequences reflecting glacial interglacial phases which can be quantified for intensity using environmental magnetism and geochemistry these phases are emphasised by variations in vegetation and malacofauna which respond to climatic change the loess deposits demonstrate broadly similar sedimentological characteristics across the basin danubian loess deposits initiated in response to the tectonic formation of the pannonian basin retreat of the large palaeolakes and increased sediment supply from the danube the period from 1 ma 500 ka mis 27 13 was characterised by alternating loess deposition and pedogenesis during glacial and interglacial periods respectively in response to relatively humid forested conditions this period represents the opening of the danube corridor and provides the backdrop for initial hominin arrival into europe after 500 ka and particularly after mis 9 loess accumulation rates increased in response to relatively more steppic arid environments mis 9 and 13 15 were the most humid phases of the last 600 ky the mis 5 interglacial period was the warmest and relatively most humid period preceding the holocene and was followed by substantially increased loess accumulation during mis 4 which may be linked to north atlantic circulation the complexity of the mis 3 interstadial paleosol suggests that conditions were not uniformly warm and wet during this time mis 3 corresponds with the first arrival of anatomically modern humans to europe the last glacial maximum and younger dryas of mis 2 were characterised by substantially increased loess accumulation indicating cold steppe environments most likely influenced by the north atlantic although conditions were sufficiently mild that the region acted as a refugium for thermophilic biota as may also have been the case for most of the pleistocene glacial cycles the holocene soil represents relatively wamer and more humid conditions corresponding to the current interglacial

erosion rates in the southern oregon coast range evidence for an equilibrium between hillslope erosion and sediment yield the relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes in landscapes containing hillslopes crenulated by alternating topographic noses and hollows estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows hollows act as local traps for a portion of the colluvium transported down hillslopes and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area analysis of colluvial deposits in nine oregon coast range hollows has yielded average colluvial transport rates into the hollows of about 35 cm3cm 1yr 1 and average bedrock lowering rates of about 007 mm yr for the last 4000 to 15000 yr these rates are consistent with maximum bedrock exfoliation rates of about 0 09 mm yr calculated from six of the hollows supporting the interpretation that exfoliation rates limit erosion rates on these slopes sediment yield measurements from nine coast range streams provide similar basin wide denudation rates of between 0 05 and 0 08 mm yr 1 suggesting an approximate steady state between sediment production on hillslopes and sediment yield in addition modern sediment yields are similar in basins varying in size from 1 to 1500 km2 suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape

hydrothermal fluid flow system around the iheya north knoll in the mid okinawa trough based on seismic reflection data seismic reflection data around the iheya north knoll hydrothermal field provide insights into geological structures that control subseafloor hydrothermal fluid flow in the sediment covered continental backarc basin of the mid okinawa trough we identified the seismic expression of widespread porous volcaniclastic pumiceous deposits and intrusions as a result of silicic arc volcanism the porous and permeable volcanic deposits are distributed in an area extending updip from the thick succession of the deep trough to the seafloor at the hydrothermal field their regional structure focuses the flow of hydrothermal fluids derived from the surrounding trough fill sediments and directs them to the vents of the hydrothermal field the high concentrations of ch4 and nh4 in the fluids of the hydrothermal field are likely derived from the interaction of migrating fluids with trough fill sediments

neogene clay and its relation to landslides in the southwestern loess plateau china loess occurs widely in northwestern china covering neogene clay and other sedimentary units that overlie the bedrock the neogene clays of the baoji region of shaanxi province north china including the eolian hipparion and paleo sanmen lake fluvial deposits are typical clays of the southern chinese loess plateau these clays are also sensitive key strata controlling the development of large scale landslides along the slope of the loess tableland surrounding the guanzhong basin to investigate the neogene clay types and landslides in the region soil samples were tested and the macro and micro structures of the clay strata were analyzed comprehensive analysis methods including the pipette method and fine x ray diffraction were applied to quantitatively analyze the sample composition and determine the clay mineral types the neogene clays are mainly composed of illite and montmorillonite mixed layer minerals on the williams discrimination diagram of swelling potential both types of clay are medium to strongly expansive soil two case studies illustrate that rainfall reduces the shear strength of the neogene clay and raises the groundwater level rainfall has gradually destroyed the structure of the neogene clay transforming it to sliding belt soil the sliding belt lies mainly within the neogene clay layers significantly affecting the occurrence and characteristics of landslides in baoji the rise in groundwater level and weakening of the shear strength of the neogene clay are important factors in the occurrence of landslides the long term strength is a key factor affecting the development of loess landslides along the loess tableland in baoji

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

the crustal deformation of the ilan plain acted as a westernmost extension of the okinawa trough abstract we analyze the current deformation in ilan plain of northeastern taiwan considered as the western extension of okinawa trough based on 34 geodetic sites observed between 2002 and 2006 the station velocities are between 1 9 mm yr and 43 0 mm yr in a direction between 38 and 143 relative to stable continent margin of eurasian plate this largest velocity is moving southeastward 143 at a rate of 43 mm yr was enhanced by a seismic doublet that occurred on march 6 2005 the station velocities at the northern margin of ilan plain are insignificant with a magnitude of 1 9 mm yr to 7 5 mm yr on the contrary the station velocities increase approximately southward along the southern margin of ilan plain the stations are moving roughly e w with a magnitude of 5 8 mm yr to 21 8 mm yr further southward the station velocities increase to a value of 43 0 mm yr in a direction of 143 the most prominent feature of the strain distribution patterns in ilan plain are the remarkable extensional strain rates observed in central and southern flank of the ilan plain the largest extensional rate is found 2 66 strain yr in 147 with a shortening rate in the perpendicular direction 1 28 strain yr in 57 indicating transtensional deformation mode in the northeastern flank of ilan plain insignificant or minor deformations are observed overall the extensional rates in this area clearly increase from north to south the extension directions in study area mostly trend e w to nw se directions using the velocity field of 34 gps stations and its strain rate filed we suggest the lateral extrusion process towards mechanically weak domain adjacent ryukyu subduction zone the lateral extrusion is facilitated by the opening of the okinawa trough we conclude that the northeast taiwan is subjected to both the compressional force exerted by the indentation of philippine sea plate and the tensile force induced by trench retreat related to the suction force at the ryukyu trench due to the interaction of two forces the stress regime rapidly changes from pure compression in the taiwan collision belt to transtension near ilan plain and its offshore area

okinawa trough backarc basin early tectonic and magmatic evolution the okinawa trough lying between japan and taiwan is a backarc basin formed by extension within the continental lithosphere behind the ryukyu trench arc system stress directions associated with the two last extensional phases in the southwestern okinawa trough have been deduced from a comparison with analog modeling the direction of extension is n 150 o for the pleistocene phase of extension 2 0 1 ma and n 170 o for the late pleistocene holocene phase of extension 0 1 0 ma the present day ryukyu volcanic arc a narrow continuous feature extending from japan to taiwan is located on the eastern side of the okinawa trough 80 100 km above the wadati benioff zone the minimum depth for emplacement of arc magmatism scarce present day backarc volcanism appears in the middle and southern okinawa trough within linear en echelon bathymetric depressions a n045 o oriented seamount volcanic chain cuts across obliquely the southwestern okinawa trough and lies in the direct line of extension of the gagua ridge a n s linear volcanic feature of the philippine sea plate associated with this extension of the gagua ridge a large reentrant located at the base of the ryukyu prism the uplift of part of the nanao forearc basin and the deformation of the sedimentary arc suggest that the voluminous cross backarc volcanism could be tied to the subduction of the gagua ridge located there at a depth of 80 100 km beneath the backarc basin a second area of anomalous volcanism has been identified in the middle okinawa trough in the ene extension of the daito ridge a wnw ese 400 km long volcanic feature of the philippine sea plate we suggest that the gagua and daito ridges initially induced stress at the base of the arc which is still brittle and cracks propagated through the overlying brittle lithosphere allowing magmas with arc affinities to erupt at the seafloor this excessive magmatism reaches the seafloor through conduits which preferentially follow in their shallowest portion the crustal normal faults of the backarc rifts the okinawa trough is consequently still in an early stage of evolving from arc type to backarc activity

a stochastic hydro geomorphological model for shallow landsliding due to rainstorm abstract a prediction model of shallow landsliding is proposed it considers not only the deterministic aspects containing slope stability saturated throughflow and a soil regolith depth development but also the stochastic aspects of intensity and duration of rainfall it turns out that the probability of saturated throughflow which is the direct trigger mechanism to shallow landsliding can be expressed by a log normal distribution the short term probability of landsliding is defined as the excess probability that the depth of saturated throughflow surpasses the critical value the average recurrence interval t av of landsliding can be calculated as the expected value this model was applied to a test field where a lot of shallow landsliding occurred at a heavy rainstorm in 1988 then a dem of 5 m grid interval was utilized to calculate t av at every grid point consequently it was found that the percentage of the landslide grid number to the total grid number for every t av rank increases when t av decreases therefore it is confirmed that t av is an index of the susceptibility to shallow landsliding and the distribution map of t av can be regarded as a kind of hazard map the spatial distribution of t av reveals its significant dependence on the topography

the stratigraphy of the serbian pleistocene corbicula beds abstract fossils of non marine molluscs are among the most prominent in continental pleistocene deposits of europe with stabilization of taxonomies in the 19th century numerous publications appeared with faunal lists of warm temperate stage taxa but few attempts were made to interpret the data the goal of recent work along with the re evaluation of sites and their molluscan assemblages described in the literature is to enable non marine molluscan faunas to be used as guide fossils for the analysed fluvial sequences in the classification of climato lithostratigraphic principles the biostratigraphic scheme developed in this work is comparable with parallel investigations of other fossil records and climato lithostratigraphy combined with geochronologic methods in earlier literature the pleistocene corbicula record was mentioned in makis beds makiski slojevi in the corbicula fluminalis beds slojevi sa c fluminalis of szentes deposits senteski slojevi as well as being associated with the viviparus boeckhi horizon as defined by halavats in the late 19th century in serbian records the most important locations of the pleistocene corbicula beds are in the south eastern part of the pannonian plain which corresponds to the lowland river valleys of the paleo danube paleo sava and paleo tisza and the western margin of the dacian realm pleistocene corbicula beds were formed as warm stage fluvial and palustrine deposits and they are climate lithostratigraphic units pleistocene corbicula beds are younger than upper paludina beds defined as the lower part of the lower pleistocene in the pannonian realm or the romanian stage in the dacian realm according to the molluscan assemblage palaeogeographical features and other paleontological contents vertebrate fauna ostracods they are older than the upper pleistocene according to the reference data and the composition of the molluscan assemblage the v boeckhi horizon has been identified as a biostratigraphic unit fortunately the v boeckhi horizon can be adopted to the serbian climato lithostratigraphy model of the fluvial warm stages and represents the lowermost part subunit of the pleistocene corbicula beds of lower pleistocene age

present day surface deformation and tectonic insights of the extensional ilan plain ne taiwan abstract taiwan s mountain belt is an ideal location to address major questions regarding mechanisms of lithospheric deformation in convergent settings mountain building processes from oceanic subduction to continental subduction and post orogenic extension in the northeast of this belt the ilan plain is a triangular deltaic plain characterized by a flat topography close to the sea level and surrounded by the high mountains of the hsuehshan range to the northwest and the central range to the southeast its eastern coast faces the western tip of the okinawa trough the back arc basin of the ryukyu subduction zone in this study we analyzed the present day surface deformation of the ilan plain aiming at deciphering its relationships with basement faults and the regional geodynamic setting our approach is mainly based on surface vertical displacements revealed by persistent scatterer interferometry synthetic aperture radar psi which indicate that there is an area of active subsidence 18 mm yr located in the southern part of the plain in probable connection with active basement faults and in agreement with previous geodetic measurements and existing geophysical data our psi results also suggest that the subsidence occurring in the ilan plain has moved from north to south during quaternary in relation with extrusion of the belt due to the westward propagation of the okinawa trough through the taiwan mountains

irrigation induced loess flow failure in heifangtai platform north west china because the construction of dams and hydro electric power stations of liujiaxia and yanguoxia across the yellow river in west gansu province north west china inhabitants in the reservoir areas were resettled in heifangtai loess platform irrigation thus started in 1968 perched water table was significantly raised and resulted in many loess flow failures in the past 30 years this type of landslide was often featured by long runout distance high speed and recurrence laboratory tests along icu and csd stress paths were performed it is shown that the loess has a strong strain softening behavior and instability can occur in drained condition before undrained liquefaction the failure mechanism of loess flow can be interpreted as the following process with increasing perched water table collapse in loess was first triggered in drained condition and led to undrained loading to adjacent soil in the lower saturated part of the loess platform under gravity loading applied by upper dry loess undrained flow failure mobilized eventually

influence of man made cuts on the stability of pyroclastic covers campania southern italy a numerical modelling approach intense rainfall in may 1998 and december 1999 caused disastrous landslides in the sarno quindici and cervinara areas campania southern italy the landslides began with slips of the local pyroclastic covers mantling the carbonate relief and then evolved into debris flows avalanches the study discussed in this paper used a numerical modelling approach to assess the influence of man made cuts on the stability conditions of pyroclastic covers the model that was developed took into account initial failure conditions in order to better simulate the impact of man made cuts along the slopes with or without water seepage into the permeable pumiceous layers of the pyroclastic multilayer numerical analysis of stress strain field clearly showed that tracks or geomorphological discontinuities had a negative impact on the multilayer stability conditions consequently preservation of this vulnerable environment requires correct forest management practices

opening mode of the okinawa trough paleomagnetic evidence from the south ryukyu arc more than 250 samples of volcanics and sedimentary rocks were collected from the south ryukyu arc for paleomagnetic study and k ar dating stable primary components of magnetization were isolated from 18 sites after thermal demagnetization the mean paleomagnetic direction for 15 eocene volcanic sites d 30 1 i 40 3 95 10 3 indicates a direction which is deflected 18 6 11 6 clockwise from the expected field direction calculated from the 40 ma pole of eurasia the clockwise deflection is observed also in the dike rock d 144 0 i 32 1 the age of which is determined to be 9 6 0 8 ma by the conventional k ar dating method these results indicate that with respect to eurasia the southern part of the ryukyu arc has rotated clockwise 19 during the past 10 m y we attribute this rotation to the back arc opening of the southern part of the okinawa trough which occurred by means of the wedge mode later than 10 ma

seismotectonics of northeastern taiwan kinematics of the transition from waning collision to subduction and postcollisional extension 1 the northeastern region of taiwan is one of the few places on earth that experienced a transition from collision to subduction and back arc opening in a young orogenic belt this provides us a rare opportunity to study the structural characteristics in such a transition we attempt to analyze the seismicity and stress patterns in this transitional region using data obtained from a dense and high quality seismic network our results show that from south to north fault types change from thrust to strike slip then to normal faulting the transitional domain between ilan and hualien is dominated by left lateral strike slip faulting with a nnw sse minimum principal stress axis consistent with the opening of the okinawa trough to the north the ilan plain is formed by structural activities of a series of normal fault systems to the south the spatial distribution of an earthquake cluster north of taiwan s coastal range appears to parallel the subducting interface between the philippine sea and eurasian plates this implies the northern extension of the coastal range has subducted consequently the opening of the okinawa trough becomes an important tectonic driving force in northeastern taiwan the westernmost ryukyu arc is pushed by the opening okinawa trough and moves southward the northern part of taiwan s central range moves with the arc to bend southeastward and the ilan plain forms in the space north of the range the bending of the central range belt results in bedding plane slip with left lateral strike slip earthquakes in the transitional domain to accommodate the deformation

correlation of european glaciations and their relation to the deep sea record north european scandinavian glaciations quaternary glaciations in europe may be studied in two areas the first area from west to the east corresponds with the area of scandinavian glaciations that formed coherent ice sheets from northwestern europe as far as the ural mountains correlations from north to south involve comparison of stratigraphic sequences from the area of the scandinavian glaciations by way of the extraglacial zone to the mountain glaciations of the alpine chain a stratigraphic review of the different areas is given in preceding chapters correlation of scandinavian glaciations has in general more basic information available and the nature of the glacial deposits makes correlation easier but stratigraphic comparison of that area with the alps faces difficulties and is possible in rough outline only many problems persist in the alpine area and are derived from surviving quadriglacial concepts which contrast with generally accepted polyglacial schemes correlation of european glaciations and their relation to the deep sea record

stability assessment of jinlong village landslide sichuan the jinlong village landslide is located in zitong county sichuan and approximately 150 km east of wenchuan the landslide has exhibited creep deformation for nearly 30 years field investigations indicated that the slope deformation was caused by the combined effects of unfavorable topographic and geological conditions and earthquakes the sliding surface is along a contact between silty clay and mudstone the wenchuan earthquake accelerated the creep causing bulging of the ground surface shear test results of the silty clay near the sliding surface indicated that the residual strength is consistent with the stability state of the landslide the factors of safety were calculated using the limit equilibrium method lem and the method of fast lagrangian analysis of continua in two dimensions the results using the lem indicate that the stability is clearly affected by seismic shaking and when the peak ground acceleration is 0 08g the slope reaches the limit state the shear failure surface given by numerical simulation develops on the contact between the clay and silty mudstone which confirmed the assumed sliding surfaces location using the lem

neogene subsidence pattern in the multi episodic extension systems insights from backstripping modelling of the okinawa trough abstract extensional systems of back arc basins have been widely recognized and studied in se asia however the interactions between extensional tectonics and spatial temporal distributions of tectonic subsidence in an active back arc basin are poorly known using a backstripping technique we analysed 33 multichannel seismic profiles to calculate the neogene tectonic subsidence across the entire okinawa trough ot for the first time reconstruction of the tectonic subsidence shows that the ot can be roughly divided into four subsidence stages with variable rate by comparing the temporal spatial distribution of the intensive subsidence area we confirmed that rifting events first occurred in the northern segment not and middle segment mot from the miocene to late pliocene and then propagated to the southern segment sot after the late pliocene the factors controlling the rapid tectonic subsidence over the entire ot can be classified into two categories 1 ne to nne trending normal faulting related to extension of the ot and nw to nww trending strike slip faulting i e the tokara fault and the miyako fault related to subduction of the philippine sea plate under the eurasian plate 2 the anomalous rapid subsidence occurred in the southernmost part of the sot is likely related to the subducted gagua ridge which caused magma intrusion resulting from partial melting we suggest that magmatic bodies produced by partial melting of subducted materials intruded into the crust and created a dense lithosphere causing this rapid tectonic subsidence

the 2005 ilan earthquake doublet and seismic crisis in northeastern taiwan evidence for dyke intrusion associated with on land propagation of the okinawa trough summary northern taiwan underwent mountain building in the early stage of the taiwan orogeny but is currently subjected to post collisional crustal extension it may be related to gravitational collapse or to the rifting of the okinawa trough which lies offshore northeastern taiwan the ilan plain northeastern taiwan which is bounded by the normal fault systems and filled up with thick pliocene pleistocene sedimentary sequences formed under such an extension environment over there on 2005 march 5 two earthquakes with about the same magnitude m l 5 9 occurred within 68 s and produced intense aftershocks activity according to the records of central weather bureau seismic network of taiwan we relocated the earthquake sequence by the three dimension earthquake location algorithm with the newly published 3d vp and vp vs velocity model and determined the first polarity focal mechanisms of the earthquake doublet one major cluster of aftershocks which trends e w and dips steeply to the south can be identified and picked up as a potential fault plane the focal mechanisms of the two main shocks are both classified as normal type by first polarity but strike slip by centroid moment tensor inversion however two methods both yield consistent e w strike static coseismic deformation was additionally determined from global positioning system gps daily solutions at a set of continuous gps stations and from strong motion seismographs these data show nw se extension at high angle to the fault plane which cannot be explained from a simple strike slip double couple mechanism on the other hand the small vertical displacements and steep fault plane cannot be explained from a simple normal event as well we present from elastic dislocation modelling that the geodetic data are best explained by significant component of tensile source with centimetre scale of opening on a 15 km long fault extending from 1 to 13 km depth we therefore interpret the crisis as the result of dyke intrusion at the very tip of the okinawa trough which is reasonably driven by backarc spreading

size distribution of loess slides in relation to local slope height within different slope morphologies abstract loess slides are widespread and dangerous gravity induced surface processes on the loess plateau of north central china the local slope height and slope morphology have been considered as important conditioning factors for landslide susceptibility mapping however the quantitative relationship between landslide size and local slope height within different slope morphologies is not very clear in this study an inventory of 155 loess slides was developed based on detailed field investigation and remote sensing image interpretation statistical analysis and gis were applied to find the quantitative relationships between the size of these loess slides and local slope height in different types of slope morphologies the analysis shows that the relationship between the loess slides volume and area exhibits a similar trend within different types of slope morphologies in addition the analysis demonstrated that loess slides are more frequent on local slope height from 40 to 100 m stepped slopes with higher pore water pressure are prone to sliding and approximate 34 19 of total loess slides occur in these stepped slopes moreover the analysis shows that the mean loess slide area and volume rapidly increase with increasing local slope height furthermore the result underlines the fact that both the local slope height and the slope morphology are two fundamental factors that control the occurrence as well as size distribution of loess slides the loess slide size remarkably increases with increasing local slope height within every type of slope morphologies these findings indicate that local slope height can limit the loess slide size and their spatial extent moreover we quantified the correlation between the loess slide size and local slope height using power law form and the scaling exponents of the correlations are different within different slope morphologies

a view on some hydrological triggering systems in landslides abstract in this paper different types of hydrological triggering systems for debris flows shallow and deeper landslides are described the generation of surface run off and high peak discharges in first order alpine catchments is an important triggering mechanism for debris flows failure conditions in shallow landslides can occur when at a critical depth which is determined by the cohesion of the soil and the slope angle the moisture content in the soil becomes close to saturation resulting in a considerable reduction of soil strength deeper landslides 5 20 m depth are in most cases triggered by positive pore pressures on the slip plane induced by a rising ground water level the assessment of meteorological threshold conditions for shallow landslides 1 2 m needs more detailed meteorological information than for deeper landslides in the analyses of the hydrological triggering systems of deeper landslides the presence of a permeable top layer and fissures has to be taken into consideration

a framework for unsaturated soil behaviour a framework is put forward which explains the shear behaviour of an unsaturated soil in terms of the total stresses and suctions acting within the soil it is based on the critical state model for

numerical modeling of late miocene tectonic inversion in the xihu sag east china sea shelf basin china abstract the east china sea shelf basin is an important oil and gas bearing basin in the west pacific continental margin this region was affected by subduction of the pacific plate and the philippine plate in cenozoic and experienced multi stage tectonic inversions this paper presents results from a numerical simulation by finite element method to the xihu sag in the east china sea shelf basin and neighboring areas in an attempt to evaluate the wnw directed compression on the sag during late miocene based on comprehensive structural analysis of a large number of seismic profiles we determine the structural geometry of the sag including the basement of the basin the sedimentary cover and 29 major faults in the xihu sag simulation results show that under continuous wnw directed compression tectonic inversion occurred firstly in the longjing and yuquan tectonic zones in the sag based on quantitative analysis of vertical displacement field of the xihu sag and peripheral areas and its stress intensity evolution we identify a compressional regime in the longjing anticline zone with a gradually propagated uplifting from south to north whereas the propagation of uplifting in the yuquan anticline zone is from north to south the inversion intensity decreases from north to south the formation of the tectonic inversion zone in the xihu sag is not only correlated to the direction of compression and fault patterns in the basin but also closely related to the spatial configuration of fault surfaces of the xihu jilong fault in the xihu sag

geologic evolution and aspects of the petroleum geology of the northern east china sea shelf basin analysis of multichannel seismic reflection profiles reveals that the northern east china sea shelf basin experienced two phases of rifting followed by regional subsidence the initial rifting in the late cretaceous created a series of grabens and half grabens filled by alluvial and fluviolacustrine deposits regional uplift and folding yuquan movement in the late eocene early oligocene terminated the initial rifting rifting resumed in the early oligocene while alluvial and fluviolacustrine deposition continued to prevail a second phase of uplift in the early miocene terminated the rifting marking the transition to the postrift phase the early postrift phase early miocene late miocene is characterized by regional subsidence and westward and northwestward marine transgression inversion longjing movement in the late miocene interrupted the postrift subsidence resulting in an extensive thrust fold belt in the eastern part of the area the entire area entered a stage of regional subsidence again and has become a broad continental shelf source rocks include synrift lacustrine facies fluvial shales and coal beds synrift fluvial lacustrine and deltaic deposits postrift littoral and or shallow marine sandstones and fractured basement have the potential to provide reservoirs various types of hydrocarbon traps e g faulted anticlines overthrusts rollover anticlines faults unconformity traps combination structural stratigraphic traps weathered basement and stratigraphic traps are recognized but many of these traps have not been tested

extensional collapse of the northern taiwan mountain belt as an active collision zone between the luzon arc and the china continental margin the taiwan mountain belt particularly its south central part is undergoing crustal shortening and rapid uplift the northern part of the orogen is however subjected to crustal stretching and rifting as a result of flipping of subduction from the northwest facing luzon arc system to the south facing ryukyu arc system taiwan and its neighboring southern ryukyu used to be part of the rifted china continental margin before the collision started in late miocene time engineered by the northwest movement of the philippine sea plate in the past 5 m y the north south trending luzon arc obliquely overrode the northeast southwest trending continental margin and tectonized it into a collision orogen that progressively enlarged and migrated from northeast to southwest following the southwest propagating collision the north dipping philippine sea plate which was subducting beneath the ryukyu arc also extended westward and caused flipping of subduction in the northern part of the collision orogen in consequence the orogen lost the compressive support by the colliding plates and became subjected to lithospheric stretching induced by the trench suction the collision orogen collapsed as a result of crustal thinning and its central part foundered into a deep submerged basin a whole spectrum of active tectonic scenarios ranging from orogenic buildup by collision to orogenic collapse by rifting and subsidence can be readily observed in the taiwan ryukyu area and provides a vivid example for the process of orogenic collapse

formation and development of the structure of collapsing loess in china abstract gao g 1988 formation and development of the structure of collapsing loess in china eng geol 25 235 245 it is well known that in china the regional variations in microstructure of loess are in phase with the overall tendency for collapsibility gradually decreasing from the northwest to the southeast these differences are consistent with variations in climatic conditions this indicates that the structure of collapsing loess is closely related to the climatic condition and geological environment based on the microstructure analyses it can be assumed that the formation and development of the structure of collapsing loess in china has undergone five stages the loessization stage the formation stage the development stage the degeneration stage and the clayization stage the five stages of loess regularly exist in different regions of the loess plateau this also shows that under the modern climatic condition the collapsing loess in the northwest of the loess plateau in china is still developing however the feature of collapsing loess is gradually disappearing in the southeast of the loess plateau

mineralogy geochemistry and sr pb and in situ s isotopic compositions of hydrothermal precipitates from the tangyin hydrothermal field southern okinawa trough evaluation of the contribution of magmatic fluids and sediments to hydrothermal systems abstract the okinawa trough ot is a back arc basin where rifting is in its initial stages and where hydrothermal fields htfs have developed above terrigenous sediments and volcaniclastics layers of variable thickness the source of ore forming materials within the hydrothermal systems of the ot is complex and may include seawater magmatic rock magmatic fluid and sediments the contribution of magmatic fluids and sediments to the hydrothermal systems of the ot is still uncertain at least 10 modern seafloor htfs have been reported from the ot including the jade hakurei iheya north knoll clam tangyin yonaguni knoll iv hatoma and irabu here we report results of mineralogical geochemical and whole rock sr pb and in situ s isotopic analyses of hydrothermal precipitates from the tangyin htf in the southern ot this field was discovered during the hobab3 cruise in 2014 and contains four types of hydrothermal precipitates fe zn and zn pb rich massive sulfides silica rich precipitates and native sulfur rich samples sulfates in zn pb fe zn and silica rich samples have 87sr 86sr ratios of 0 71068 0 71750 which are higher than those of modern seawater and magmatic rocks and indicate that the sr is derived mainly from seawater and sediments the zn pb fe zn and silica rich samples have 206pb 204pb 18 5129 18 5307 207pb 204pb 15 6374 15 6489 and 208pb 204pb 38 8759 38 9113 ratios that are intermediate between sediments and magmatic rocks suggesting the pb is a mixture of sediment and magmatic rock derived pb the in situ s isotopic data indicate that the ore forming fluids associated with all sample types had low 34s values with the fe zn mean 34s 1 27 1 38 sd n 12 and zn pb rich mean 34s 0 93 0 32 n 36 massive sulfides and silica rich precipitates mean 34s 2 85 1 14 n 58 having lower 34s values than those of native sulfur rich samples mean 34s 4 23 0 72 n 5 the zn pb and fe zn rich massive sulfides and silica rich precipitates represent the medium high temperature 120 c early middle stages of mineralization formed under reducing conditions at low sulfur fugacity fs2 based on the occurrence of low fs2 mineral assemblages e g high fe sphalerite isocubanite pyrrhotite the low 34s values of these three types of samples and of the hakurei and clam htfs with low fs2 mineral assemblages and low concentrations of cu bi and au most likely reflect the incorporation of biological sulfur previously formed by msr within the sediments the native sulfur rich samples of the tangyin htf formed at low temperatures

east asia plate tectonics since 15 ma constraints from the taiwan region abstract 15 ma ago a major plate reorganization occurred in east asia seafloor spreading ceased in the south china sea japan sea taiwan sea sulu sea and shikoku and parece vela basins simultaneously shear motions also ceased along the taiwan sinzi zone the gagua ridge and the luzon ryukyu transform plate boundary the complex system of thirteen plates suddenly evolved in a simple three plate system eu ph and pa beneath the manila accretionary prism and in the huatung basin we have determined magnetic lineation patterns as well as spreading rates deduced from the identification of magnetic lineations these two patterns are rotated by 15 they were formed by seafloor spreading before 15 ma and belonged to the same ocean named the taiwan sea half spreading rate in the taiwan sea was 2 cm year from chron 23 to 20 51 to 43 ma and 1 cm year from chron 20 43 ma to 5b 15 ma five plate kinematic reconstructions spanning from 15 ma to present show implications concerning the geodynamic evolution of east asia amongst them the 1000 km long linear gagua ridge was a major plate boundary which accommodated the northwestward shear motion of the ph sea plate the formation of taiwan was driven by two simple lithospheric motions i the subduction of the ph sea plate beneath eurasia with a relative westward motion of the western end a of the ryukyu subduction zone ii the subduction of eurasia beneath the philippine sea plate with a relative southwestward motion of the northern end b of the manila subduction zone the luzon arc only formed south of b the collision of the luzon arc with eurasia occurred between a and b east of a the luzon arc probably accreted against the ryukyu forearc

stability investigation and stabilization of a heavily fractured and loosened rock slope during construction of a strategic hydropower station in china abstract this paper presents a case history of the 205 m high intake slope at the huangjinping hjp hydropower station on the dadu river deformation and cracks developed on the cut slope during excavation and the deformation extended onto the natural slope above the cut giving rise to serious safety concerns research was conducted to study the engineering geological conditions and the deformation characteristics of the slope during excavation in situ monitoring data and possible causes of cracking were analyzed the results show that the zone of loosened rock mass extended much deeper into the rock mass than it did at other sites in the region because of the tectonic history of the site and cutting the empirically designed cable anchors with lengths of 40 m or 45 m were insufficient to stabilize the slope while the remedial cable anchors as long as 100 m successfully stabilized the slope the analytic method and procedure used in this paper could be useful to similar projects

laboratory characterization of rainfall induced loess slope failure loess slopes are widely distributed throughout the northwestern region of china and are prone to slope failure in response to heavy rainfall we undertook three groups of flume experiments in the laboratory to study loess slope dynamics under artificial rainfall conditions additionally a laser scanner was used to observe loess landslide deformation characteristics and failure development a numerical analysis of unsaturated seepage in loess slopes because of rainfall infiltration was performed moisture content pore water pressure and slope deformation were monitored to quantify the relationship between rainfall infiltration and loess slope stability movement of the wetting front near the slope surface was triggered by rainfall and related to rainfall intensity and duration which is consistent with the numerical solution rainfall infiltration increased pore water pressure producing gravity driven landslides we observed that landslide development began with local failure in the toe slope that gradually retreated toward the crown forming a multi sliding displacement and eventually resulting in total slope failure

the stratigraphical importance of the viviparus boeckhi horizon of serbia fossils of non marine molluscs are among the most prominent in pleistocene deposits with stabilization of taxonomies in the 19th century numerous publications appeared with faunal lists of quaternary warm stage molluscs but few attempts were made to use those data for interpretation the purpose of this work along with reevaluation of sites and their molluscan assemblages described in the literature is to make it possible for non marine molluscan faunas to be used as biostratigraphic indicators biostratigraphic data obtained in this work are comparable with parallel investigation of other fossil records and lithostratigraphy combined with geochronologic methods the four most important localities with viviparus boeckhi in serbia are subotica sombor zrenjanin and the vicinity of belgrade according to the available data the molluscan assemblage of the v boeckhi horizon is identified as fluvial warm stage assemblage which corresponds to the oldest part of the pleistocene corbicula beds it is generally considered that the age of the v boeckhi horizon s corresponds to the younger parts of the early pleistocene however according to the regional data the v boeckhi horizon of serbia is younger than the paludina beds of plioceneeearly lower pleistocene age according to the vertebrate fauna it is older than the upper biharian stage younger part of the middle pleistocene

stratigraphy and spatial and temporal paleoclimatic trends in southeastern eastern european loess paleosol sequences abstract the loess paleosol sections batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine are presently located in areas of different types of steppe and are highly sensitive for recording climatic changes a stratigraphy for these three southeastern eastern european sections is presented based on pedostratigraphy and correlation of recently obtained susceptibility records with susceptibility data of other sections of the area koriten mostistea vyazivok of the chinese loess plateau and with the benthic 18o record of odp 677 six pedocomplexes were studied at the serbian and romanian sections and five at the ukrainian section the oldest are related to marine isotope stage mis 17 batajnica stari slankamen and mircea voda and mis 13 15 stary kaydaky some points concerning the existing loess chronostratigraphies of bulgaria ukraine and china are discussed comparative study of the profiles allows the tracing of paleoclimatic and paleoenvironmental changes in southeastern eastern europe in time and space reconstruction of paleoprecipitation based on susceptibility rainfall relationships and calculations of sedimentation rates are evaluated

three dimensional geological structures and sliding factors and modes of loess landslides loess environments such as the chinese loess plateau are geologically fragile because of their great thickness loose structure crisscrossing ravines and gullies broken terrain dry climate severe erosion and unevenly distributed rainfall as a consequence loess areas are highly prone to environmental problems and geological hazards the geological structure of the loess is one of the main factors that controls occurrence of these geohazards this study investigated the mechanism of loess landslides and their sliding control mode from the perspective of their geological structure using this mechanism a three dimensional geological model of loess landslides was established the study shows that the structural planes in loess divide a complete slope into separate blocks which enables the fast and deep infiltration of surface water via seepage channels and reduces the shear strength of the soil mass inducing landslides the development and formation of loess landslides are primarily controlled by structural planes and influenced by infiltrated water softening the structural plains various types of structural planes may combine and form structural bodies of different types and scales which control the type depth and scale of loess landslides

the formation and evolution of the east china sea shelf basin a new view abstract back arc basins and the related subduction systems have been extensively studied however back arc basins exhibiting episodic jumps of extension centers by the subduction of different ocean slabs are poorly known the east china sea shelf basin ecssb comprises two eastward younging subparallel depression zones and its formation and evolution is accompanied by a complicated subduction history and regional tectonic events offer an excellent opportunity to decipher the various geological features of back arc basins here we review the tectonic and sedimentary features of the subbasins in the ecssb and its adjacent regions and then reconstruct the evolution of the sedimentary paleogeography the west depression zone wdz of the ecssb experienced rifting in the late cretaceous during the subduction of the izanagi plate at the eastern continental boundary in the northern wdz the changjiang depression was mainly dominated by fluvial to lacustrine deposits this depression experienced strong compression characterized by folds and erosion during the transition from a synrift to postrift setting at the end of the paleocene then another compression event occurred that resulted in extensive folds and uplift accompanied by a large scale alluvial fan in the eastern changjiang depression coinciding with the subparallel subduction of the izanagi pacific ridge in the early eocene however the lishui jiaojiang sag characterized by diffuse extension rather than focused rifting in its late rifting period this sag was mainly covered by paralic to marine deposits and experienced extensive erosion caused by tilted sequences from the late eocene to oligocene which shared the same characteristics as basins around the taiwan region it is widely accepted that the formation and evolution of basins around taiwan were controlled by the evolving of the south china sea scs and the related regional tectonics considering the eastward extent of scs it would seem that the southern ecssb was part of the passive margin of scs accordingly the southern ecssb might be significantly influenced by the scs the east depression zone edz commenced rifting in approximately the middle eocene as inferred from the absence of the compressional event that occurred in the early eocene and the existence of a thick layer reflection below the pinghu fm late eocene due to the subduction of the pacific plate the depocenters of the ecssb and the okinawa trough jumped eastward successively triggered by the three oceanic slabs of the izanagi plate at 72 ma the pacific plate at 50 ma and the philippine sea plate at 15 ma thus a new model for the formation and evolution of the ecssb is suggested in which a back arc basin of episodic extension with jumping depocenters in respond to subduction of three oceanic slabs meanwhile its differences between northern and southern part are caused by the dominant subduction and opening of scs respectively the ecssb and okinawa trough might formed mainly by rollback of the oceanic slab possibly due to slab stagnation and toroidal flow related to the subduction however the effects of large scale mantle flow cannot be exclusively identified in this research in addition further research in this region will give new insights into both the formation and evolution of the scs and the continental breakup process

back arc rifting in the okinawa trough abstract geological and geophysical data reveal that the okinawa trough shows incipient continental rifting and crustal separation started from about 2 ma the early extensional movements in the trough are probably of miocene age in addition to the miocene phase two main periods of extension are recognized a pleistocene phase between 1 9 and 0 5 ma and the present day phase during the stage short central rifts central grabens were formed the opening however may have occurred only in the southern part of the trough basin having an average half spreading rate of 2 cm yr 1 since early pleistocene time producing its present width of several tens of kilometres these activities were well represented by igneous intrusions sedimentary facies and sedimentary structures in and around the okinawa trough the width of the zone affected by back arc extension defined as greater okinawa trough is larger than the present okinawa trough whose width is 200 250 km the present form of the greater okinawa trough started to form at the same time as that of the okinawa trough

three dimensional stability evaluation of a preexisting landslide with multiple sliding directions by the strength reduction technique landslide 1 is located on the right bank of the downstream side of the dam for hongjiadu hydropower station in guizhou province china in view of its close proximity to important workings the stability of the slide is of great concern ground investigation showed that the slide is potentially unstable and has two sliding directions reinforcement mainly by piles was proposed as the stabilization measure but two key questions were raised during the design of the piles 1 how could the stability of the slope be evaluated as there are two major sliding directions 2 how could the shear strength parameters of the slip band be determined as it contains a significant proportion of coarse particles in this paper we demonstrate how these issues can be addressed by the strength reduction technique first the strength parameters of the slip band are back analyzed by assuming a factor of safety of unity second the major sliding directions are determined by carrying out finite difference analyses third

back arc extension in the okinawa trough the okinawa trough lying to the east of china is a back arc basin formed by extension within continental lithosphere behind the ryukyu trench arc system middle to late miocene uplift associated with normal faulting of the initially adjacent ryukyu nonvolcanic arc and the taiwan sinzi folded belt corresponds to the first rifting phase the timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern okinawa trough the rifting occurred after a major early miocene change in the motion of the philippine plate with respect to eurasia and ceased during the pliocene a second rifting phase started about 2 m y ago at the plio pleistocene boundary and has continued until the present time it has proceeded to a more advanced stage in the middle and southern okinawa trough than it has farther north detailed bathymetric sea beam seismic reflection and magnetics data collected during the pop 1 cruise of the r v jean charcot reveal the principal features of the extensional processes the back arc spreading phase started very recently in the southern and middle okinawa trough as exemplified by several en echelon and in some cases overlapping active central graben oriented n70 e n80 e some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies transform faults between these en echelon active rifts are not obvious we suggest that the major part of the southern okinawa trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern okinawa trough the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough the system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of okinawa island whereas active volcanoes in the ryukyu arc occur only north of okinawa island we refer to this transition between active arc and back arc volcanism as the volcanic arc rift migration phenomenon vamp globally back arc volcanism propagated from the southern okinawa trough to the okinawa vamp area rifting continues to occur in the northern okinawa trough but is not yet accompanied by associated volcanism the okinawa vamp area is characterized by a series of parallel basaltic ridges oriented n75 e with associated linear magnetic anomalies characteristic of dyke intrusions we suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending n75 e and that this zone presently ends at the southern extremity of the active volcanic chain the initial phase of formation of back arc basin oceanic crust is non steady state and is characterized by the lack of a developed fracture zone pattern the termination of the vamp area in the direction of the volcanic zone of the arc is consistent with the suggestion of molnar and atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs apparently back arc extension initially occurred within the continental lithosphere located westward of the ryukyu arc along its whole length but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward this migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc it is this transfer of volcanism that we call the vamp process thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc this interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence since the plate motion in the phillippine sea is oblique to the trench at least in the southern part of the okinawa trough we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc the motion of the ryukyu platelet with respect to eurasia is consequently an extensional strike slip motion trending roughly parallel to the okinawa trough

how was taiwan created abstract since the beginning of formation of proto taiwan during late miocene 9 ma the subducting philippine ph sea plate moved continuously through time in the n307 direction at a 5 6 cm year velocity with respect to eurasia eu tearing the eurasian plate strain states within the eu crust are different on each side of the western ph sea plate boundary extensional in the okinawa trough and northeastern taiwan versus contractional for the rest of taiwan island the b feature corresponds to the boundary between the continental and oceanic parts of the subducting eurasian plate and lies in the prolongation of the ocean continent boundary of the northern south china sea strain rates in the philippines to northern taiwan accretionary prism are similar on each side of b contractional though with different strain directions perhaps in relation with the change of nature of the eu slab across b consequently in the process of taiwan mountain building the deformation style was probably not changing continuously from the manila to the ryukyu subduction zones the luzon intra oceanic arc only formed south of b above the subducting eurasian oceanic lithosphere north of b the luzon arc collided with eu simultaneously with the eastward subduction of a portion of eu continental lithosphere beneath the luzon arc in its northern portion the lower part of the luzon arc was subducting beneath eurasia while the upper part accreted against the ryukyu forearc among the consequences of such a simple geodynamic model i the notion of continuum from subduction to collision might be questioned ii traces of the miocene volcanic arc were never found in the southwestern ryukyu arc we suggest that the portion of eu continental lithosphere which has subducted beneath the coastal range might include the miocene ryukyu arc volcanoes formed west of 126 e longitude and which are missing today iii the 150 km wide oceanic domain located south of b between the luzon arc and the manila trench above the subducting oceanic eu plate south china sea was progressively incorporated into the eu plate north of b

gold enrichment in hydrothermal sulfides from the okinawa trough an in situ la icp ms study abstract we assess the distribution of gold and investigate the physicochemical controls on gold enrichment in the okinawa trough an immature back arc basin we conducted a systematic study of gold and other trace element concentrations using in situ laser ablation inductively coupled plasma mass spectrometry la icp ms for various minerals in hydrothermal sulfide samples from the iheya north knoll and the yonaguni knoll iv hydrothermal fields orpiment colloform pyrite and colloform sphalerite are relatively enriched in au mean contents of 30 60 17 48 and 8 68 ppm respectively compared with gold poor massive chalcopyrite sphalerite and pyrite based on gold budget estimation colloform pyrite is the most important au host followed by colloform sphalerite and orpiment with these three minerals containing the majority of gold in hydrothermal sulfides gold occurs as invisible in host minerals as lattice bound and submicron inclusions in colloform pyrite as homogeneously distributed lattice bound or nano inclusions in colloform sphalerite and generally as lattice bound in orpiment and tetrahedrite three sets of gold host minerals are identified with distinct ore formation temperatures colloform sulfides and orpiment incorporate the majority of gold at low temperatures whereas tetrahedrite and massive sulfides incorporate only minor or trace amounts of gold at medium and high temperatures respectively our results show that gold enrichment in si ba fe rich hydrothermal sulfides at low temperatures is a significant contributor to gold enrichment in hydrothermal sulfide deposits in the okinawa trough along with the more common zn and cu rich hydrothermal sulfides thermodynamic modeling calculations suggest that the near neutral ph of hydrothermal fluids and the dominant transport species namely au hs complexes rather than au cl complexes are likely responsible for gold enrichment in low temperature mineral assemblages in hydrothermal precipitates from the okinawa trough

initiation of arc magmatism in an embryonic continental rifting zone of the southernmost part of okinawa trough the okinawa trough is a young intracontinental backarc basin that has formed behind the ryukyu arc trench system since late miocene time in the southernmost part of the okinawa trough spot a cluster of active submarine volcanoes delineates a volcanic belt which is located only 100 km above the wadati benioff zone we report herein new major and trace element data for the spot volcanic rocks these rocks show a compositional range from medium k andesite to rhyolite their geochemical characteristics are similar to those of pre backarc rifting volcanic rocks from the central ryukyu arc and different from those of backarc basin lavas from the middle okinawa trough and the post backarc rifting ryukyu arc volcanics therefore despite being topographically contiguous with the rest of the trough the spot that developed in the quaternary is not a simple backarc basin but instead an embryonic rift zone in which early arc volcanism occurs as a result of the ryukyu subduction

formation mechanism analysis of irrigation induced retrogressive loess landslides abstract the loess plateau covers about 6 6 of the total land area of china landslides are serious concerns in loess plateau of china and the south jingyang tableland on the loess plateau of china has received significant attention because of frequent occurrence of gradual retrogressive loess landslides grll there however the characteristics and mechanism of grll are largely unknown in this study three typical landslide groups namely miaodian zaitou landslide group jiangliu landslide group and dabuzi landslide group are chosen as examples to analyze the characteristics of grll by performing a field survey and undrained triaxial shear tests loess fissures are found to play a key role in controlling the evolution of landslides on the one hand the mechanical properties of loess surrounding fissures rapidly weaken due to water infiltration into loess fissures on the other hand the self weight of the overlying loess increases since water infiltrates into fissures the undrained triaxial shear tests results indicate that loess specimen shows either strain hardening or strain softening behavior depending on its initial moisture content furthermore reduction in the shear strength of loess samples is observed as moisture content increases three factors associated with the characteristics and mechanism of grll group including strata lithology slope shape irrigation and rainfall are discussed finally the formation mechanism and evolution of grll are summarized into three stages namely a creep tensional stage a localized liquefaction stage and a sliding stage this study provides important insights on gradual retrogressive characteristics of loess landslides and facilitates appropriate safeguards to reduce the risk of such landslide hazards

collapsibility and deformation characteristics of deep seated loess in china abstract lin z g and wang s j 1988 collapsibility and deformation characteristics of deep seated loess in china eng geol 25 271 282 as part of a comprehensive research program laboratory tests were conducted on samples of deep seated loess from different locations of the loessial regions of northern china including shaanxi gansu shanxi and honan provinces the information thus acquired on some aspects of the engineering properties of the samples such as the unit collapse pressure relationships the initial collapse pressure versus the preconsolidation pressure and deformation pressure characteristics is interesting and may prove useful to geotechnical engineers who work on projects on water poor plateaux or high river terraces in loessial regions throughout the world

geodynamic processes of taiwan arc continent collision and comparison with analogs in timor papua new guinea urals and corsica abstract the taiwan arc continent collision involves four geodynamic processes intra oceanic subduction initial arc continent collision advanced arc continent collision and arc collapse subduction these processes now occur simultaneously in 19 24 30 n but have operated sequentially southward since the late miocene although the geological and geophysical features appear to change progressively from north to south across the island they are distinct within individual tectonic regimes using the present scenario as a basis for comparison it is suggested that timor is at the initial arc continent collision stage while papua new guinea and urals proceeded to the advanced arc continent collision stage however corsica represents an even more advanced stage than in taiwan where a previously accreted arc has collapsed and been totally removed

the mechanical behaviour of an unsaturated compacted silty clay a comprehensive experimental study has been carried out to investigate the volumetric and shear strength behaviour of a compacted silty clay which exhibited collapse on wetting behaviour the experiments consisted mainly of suction monitored triaxial tests carried out in a new apparatus the test results are interpreted on the basis of an elasto plastic framework using the conventional stress variable approach net stress and suction as well as an approach that takes into account the degree of saturation within two modified stress variables the evidence for critical states was examined based on the stress dilatancy relationships it was found that a critical state was observed experimentally in cases where the samples contracted over much of their stress paths but was not truly established in other cases relationships between the shear strength and specific volume at the ultimate state were established for samples over a wide range of degrees of saturation from fully saturated to the air dried state

the revision of quaternary stratigraphy of the sombor and subotica artesian well borehole profiles backa vojvodina serbia abstract the results of stratigraphy of the sombor and subotica boreholes were first results of geological examination of borehole material from vojvodina published by halavats in 1895 these geological profiles alongside the borehole profile in zrenjanin were recognized as standard profiles for quaternary geology and stratigraphic correlation pertaining to vojvodina however the results of taxonomical revisions for malacologic material published in 1977 by krolopp and which presented significant changes in stratigraphy have not been implemented in the results of geological mapping surveying according to new advances and results regarding quaternary stratigraphy lower pleistocene sediments can be better defined using pleistocene corbicula beds the viviparus boeckhi horizon and the results yielded by this paper in the case of the sombor borehole the lower pleistocene was defined at a depth from 48 13 m to 149 5 m according to its palaeonological record molluscan assemblage the lower and or middle pleistocene were defined as the interval between a 35 45 m and 48 13 m depth based on sedimentology lignite and malacology the interval from 15 21 m to 35 45 m depth was identified as pleistocene based on superposition and palaeontological material the yellow quartz sand horizon at 9 74 m 15 21 m remains undefined the holocene yellow silty clay horizon which ascends to a 9 74 m depth was identified as holocene according to the palaeontological content of the same sediments found in the brickyard in the vicinity of sombor in the case of the subotica borehole the lower pleistocene based on palaeontological records was defined at a depth between 99 6 m and 124 5 m the depth from 2 2 m to 99 6 m could not be exactly identified as pleistocene while holocene quicksand ascended to a 2 2 m depth

spatial variation of saturated hydraulic conductivity of a loess slope in the south jingyang plateau china abstract water infiltration in loess soils is an important trigger causing landslides in which the hydraulic conductivity of the loess plays an important role by analyzing a soil trench and soil samples from the south jingyang plateau northwest china a loess slope was investigated a horizontal adit in a lishi loess layer was also analyzed using variable head permeability tests the saturated horizontal hydraulic conductivity k h and saturated vertical hydraulic conductivity k v of the loess samples were measured results showed that the majority of the k h values are larger than the k v values indicating that the loess exhibits permeability anisotropy lilliefors test was used to determine the normality of the k h and k v results test results indicate that k h and k v measurements of the loess samples collected in the trench and adit all show log normal distribution while a number of the k h and k v values also reflect a normal distribution geo statistical analysis shows that the spherical model and the gaussian model provide the best fit variograms of k h and k v values along the trench analysis along the adit indicated the opposite results the variogram range values suggest that the spatial correlation of loess k v is greater in the vertical direction in a horizontal plane while the spatial correlation of k h in the adit is greater than that in the vertical direction loess structure rather than randomness decides the spatial variation of k h and k v measurements except for k h variation along the adit which depends on both structural factor and randomness k h and k v values of loess tend to decrease with depth results which can be described by an exponential decay model

late pleistocene loess palaeosol sequences in the vojvodina region north serbia late pleistocene loess palaeosol sequences are widespread in the vojvodina region with thicknesses reaching a maximum of about 20 m our investigations include more than 40 of these loess sections geochronology of the last glacial loess palaeosol sequences based on lumines cence dating and amino acid racemisation provides correlations between upper pleistocene loess palaeosol sediments in vojvodina and comparable deposits at other european localities sedimentary logs of magnetic susceptibility grain size measurements and carbonate content combined with malacological evidence indicate two main relatively cold and arid phases during the last glacial period related to intensive accumulation of loess units l1l1 and l1l2 as well as many brief episodes of dry and windy climatic conditions suggesting a possible relationship with cold events recorded in the north atlantic region generally late pleistocene climate in the region was dry and relatively warm compared with glacial period sites in central europe and was characterised by sharp differences between glacial and interglacial modes new data and interpretations presented in this study emphasise the significance of loess palaeosol sequences in vojvodina for the reconstruction of the temporal and spatial evolution of late pleistocene palaeoclimate in this part of europe copyright 2007 john wiley sons ltd

occurrence of landsliding on slopes where flowsliding had previously occurred an investigation in a loess platform north west china abstract loess slides in south jingyang platform shaanxi province usually occur on slopes where loess flowslides had previously occurred numerical modeling shows that flowslide occurrence causes conditions that increase shear stress and water content in the subsequent slopes both of these factors move the soil stress states towards its theoretical failure line under these conditions only small increases in water content can cause soil collapse this leads to the backscarps of former flowslides being much more prone to landsliding wetting test results show that the loess can collapse suddenly as the water content gradually increases therefore the wetting process induced by continued irrigation may result in the subsequent slides during constant water content tests of the loess material soil shear strength increases with the development of specimen deformation therefore slide mobilization which may be a relatively slow process is dependent on whether the wetting conditions exist finally a slope evolution model for loess platforms is proposed in this study

an introduction to the middle and upper pleistocene loess paleosol sequence at ruma brickyard vojvodina serbia abstract six loess units and five paleosols are preserved in the 20 m thick exposure of middle and late pleistocene sediments at ruma brickyard vojvodina serbia amino acid geochronology provides stratigraphic correlations between loess paleosol units sl l1 s1 sl l2 s2 sl l3 s3 and sl l4 at ruma with loess of glacial cycles b c and d and e respectively at other central and southeastern european localities the profile represents one of the best potential sections in the region for reconstructing detailed paleoclimates and paleoenvironments of the last ca 350 000 yr initial sedimentological magnetic and malacological evidence indicate many episodes of drier conditions in the region than in other parts of central and southeastern europe during the later part of the middle and late pleistocene

magnetic inversion in the east china sea and okinawa trough tectonic implications abstract in order to better understand continental rifting along the eastern margin of the eurasian plate we have performed a magnetic inversion to reveal the distribution and characteristics of the belts and basins in the east china sea and okinawa trough equivalent magnetizations are obtained by assuming a constant thickness of 5 km of the magnetized layer whose top surface is assigned to the sea floor and taking into account the present day geomagnetic field because of absence of magnetic reversals in the study area a high magnetization zone can reflect a shallow and or highly magnetized basement in contrast a low magnetization zone generally corresponds to a rifted basin with thick sediments the belts in the east china sea shelf basin are in general below sea level and correspond to shallow basement with thin sediments the inversion results show that the belts are parallel and trending about n075 this regular trend suggests a simple southeastward rifting pattern of the east china sea shelf basin the belt trend changes from n075 to n095 at the eastern side of the taiwan sinzi belt southwest of the taiwan sinzi belt the belts in the ryukyu subduction system are parallel to the ryukyu trench it implies that rifting of the middle and northern okinawa trough was initiated along the eastern side of the taiwan sinzi belt then the rifting has been mainly controlled by the oblique subduction of the philippine sea plate beneath the ryukyu arc the southern end of the taiwan sinzi belt terminates at the nw se trending miyako yandang high magnetization zone the southern okinawa trough rifted since early pleistocene is distinct from the middle and northern okinawa trough by the miyako yandang high magnetization zone the southern okinawa trough consists of two rifting patterns east of 123 5 e the backarc rifting is quasi symmetric as evidenced by symmetrically high magnetization zones on both sides of the yaeyama depression in contrast west of 123 5 e the volcanism or high magnetization zones developed along existing nw se trending strike slip faults have generally occurred at the northern margin of the southern okinawa trough the ryukyu arc west of 123 5 e exhibits low magnetization reflecting its non volcanic nature of the upper crust east of 123 5 e the present day ryukyu arc volcanism is expressed by relatively high magnetization

analysis of the distributions of stress in natural ridge forms implications for the deformation mechanisms of rock slopes and the formation of sackung abstract stress distributions in general asymmetric ridge forms derived from 13 ridges in british columbia and colorado are modelled in two dimensions with a finite difference method in each of the 13 ridges sackung scarps tension cracks trenches can be found spatial correlations between stress concentrations and these sackungen landforms are investigated for the mean ridge forms rock mass properties for the modelled ridges are developed using the hoek brown criterion and the geological strength index gsi gravity loading and combined gravity tectonic loading on the ridge forms are considered the importance of representing in situ rock masses with an elastoplastic as opposed to elastic constitutive criterion is discussed the resulting stress distributions for the three general ridge classes indicate that different processes are responsible for the formation of sackungen landforms and slope deformations in each type of ridge