iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids abstract volcanogenic sediments are typically rich in fe and mn bearing minerals that undergo substantial alteration during early marine diagenesis however their impact on the global biogeochemical cycling of fe and mn has not been widely addressed this study compares the near surface 0 20 cm below sea floor cmbsf aqueous no 3 and solid phase reactive fe distributions between two volcanogenic sediment settings 1 a deep sea tephra rich deposit neighbouring the volcanically active island of montserrat and 2 mixed biosiliceous volcanogenic sediments from abyssal depths near the volcanically inactive crozet islands archipelago shallow penetration of o2 aq into montserrat sediments was observed 5 cmbsf and largely controlled by the oxidation of organic matter dissolved fe and mn distributions in montserrat pore waters were lowest in the surface oxic layer 0 3 m fe 32 m mn with maxima 20 m fe 200 m mn in the upper 1 15 cmbsf unlike montserrat fe and mn in crozet pore waters were ubiquitously partitioned between 0 2 m and 0 02 m filtrations indicating that the pore water distributions of fe and mn in the traditionally termed dissolved size fraction are dominated by colloids with respective mean abundances of 80 and 61 plausible mechanisms for the origin and composition of pore water colloids are discussed and include prolonged exposure of crozet surface sediments to early diagenesis compared to montserrat favouring nano particulate goethite formation and the elevated dissolved si concentrations which are shown to encourage fine grained smectite formation in addition organic matter may stabilise authigenic fe and mn in the crozet pore waters we conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water which may impact significantly on deep ocean biogeochemistry diffusive flux estimates from montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved mn to the bottom waters and therefore a source for the widespread hydrogenous mnox deposits found in the caribbean region

the brittle plastic transition and the depth of seismic faulting a simple rheological model of shearing of the lithosphere that has gained wide acceptance is a two layer model with an upper brittle zone in which deformation takes place by frictional sliding on discrete fault surfaces and a lower plastic zone in which deformation takes place by bulk plastic flow the two are separated by an abrupt brittle plastic transition which is assumed to be indicated by the lower limit of seismicity experimental studies however as well as the deformation structures of mylonites indicate that a broad transitional field of semi brittle behavior lies between these extremes this is a field of mixed mode deformation with a strength that can be expected to be considerably higher than that predicted from the extrapolation of high temperature flow laws for quartzofeldspathic rocks the semi brittle field lies between t1 the onset of quartz plasticity at about 300 c and t2 feldspar plasticity at about 450 c a model is presented in which the transition t1 does not correspond to a transition to bulk flow but to a change from unstable velocity weakening friction to stable velocity strengthening friction t1 thus marks the depth limit of earthquake nucleation but large earthquakes can propagate to a greater depth t3 t3 t2 which corresponds to the lower limit of dynamic frictional behavior in the semi brittle field and approximately to the peak in strength the zone between t1 and t3 is one of alternating behavior with flow occurring m the interseismic period and with co seismic dynamic slip occurring during large earthquakes this zone is characterized by mylonites interlaced by pseudotachylytes and other signs of dynamic faulting the transition t1 is also marked by a change in the generation mechanism of fault rocks from abrasive wear above which produces cataclastites to adhesive wear below which is proposed as an important generation mechanism of mylonites in the upper part of the semi brittle field

the impact of the 1991 mount pinatubo tephra fallout on the geochemical environment of the deep sea sediments in the south china sea abstract seven years after the 1991 mount pinatubo eruption the current geochemical environment of ash covered deep sea sediments in the south china sea was investigated the depth distributions of o2 no3 mn2 corg and porosity at six representative sites covered with varying thicknesses of tephra are reported the shapes of the depth profiles reveal that o2 is totally exhausted within ash layers thicker than 3 cm while thinner layers are penetrated by oxygen followed by linear downcore profiles with depletion between 8 and 12 cm hence the zone between ash layer and total depletion of oxygen represents a zone of negligible oxygen consumption various multi layer models were developed to explain the observed oxygen concentration profiles these mathematical simulations also serve to assess both the development since the surface sediments were sealed by the ash fallout as well as the future evolution whereas thick tephra layers provoke a nearly stationary situation i e are capable of preventing oxygen from penetrating into the underlying sediments oxygenation of sediments below thin layers increases rapidly in these sediments the effect of oxygen diffusion velocity is drastically reduced by the reaction with dissolved manganese and therefore explains the linear profiles besides this study is suitable as a case study to assess the effects of human interventions in the deep sea ecosystem such as mining and waste dumping

earthquake depths and the relation to strain accumulation and stress near strike slip faults in southern california earthquakes in the major fault zones are predominantly deep earthquakes in the crustal blocks bounding the fault zones are predominantly shallow in the san jacinto fault zone maximum earthquake depths correlate with surface heat flow these relations together with focal mechanisms geodetic strain measurements and fault zone models are consistent with the following ideas 1 interseismic plate motion is accommodated by aseismic slip along an extension of the major fault zone below a brittle zone that is locked between large earthquakes 2 the aseismic slip in a narrow fault zone in the brittle plastic transition region concentrates strain at the base of the brittle fault zone 3 deep earthquakes occur in thelower part of the brittle fault zone due to stick slip failure of highly stressed patches 4 background earhtquakes and aftershocks that occur several kilometers deeper than large earthquake hypocenters suggest that a zone of mixed slip behavior may exist between the stable sliding deep and stick slip shallow regions of the fault zone furthermore the difference in seismicity between the san jacinto and southern san andreas faults suggests that the nature of this mixed zone may evolve as total displacement in the fault zone increases 5 shear stress may be lessmore in the crustal blocks than in the deep brittle fault zones and generally at a level sufficient to cause brittle failure only shallow in the crustal blocks 6 in the stress field produced by plate motion and slip in the deep fault zone the upper brittle fault zone is not oriented favorably for shear failure lack of shallow earthquakes in the fault zones and the predominance of shallow earthquakes on favorably oriented fractures in the adjacent crustal blocks suggest that either stress in the upper brittle fault zone is relatively low or the upper fault zone is effectively strong due to its orientation less

fallout of volcanic ash to the deep south china sea induced by the 1991 eruption of mount pinatubo philippines an ongoing sediment trap experiment in the central south china sea provided the opportunity to investigate directly the mode and rates of a medial fallout of volcanic ash following the june 15 1991 eruption of mount pinatubo philippines within less than three days after the release of the major eruption plume ash accumulation 9 kg m 2 was simultaneously recorded by traps positioned in 1190 and 3730 m water depth at a distance of 586 km to the west of the volcano a numerical simulation of the fallout reveals that the vertical trajectories of the pyroclasts in both the atmosphere and ocean were controlled by particle aggregation the aggregation process caused a premature subaerial fallout of fine grained ash after crossing the air sea interface vertical settling of the ash clusters was enhanced by absorption of water leading to settling rates of more than 1670 m d aggregates were observed at all depths and their rapid settling is reflected in identical pyroclast spectra in intermediate and deep water this implies that particle sorting must have been complete in the upper water column and that the fallout was not perturbed by oceanic currents the tephra blankets an area of 37 10 4 km 2 in a fan shaped westward distribution which reflects the prevailing direction of the upper level winds our data show that atmospheric tephra dispersal patterns are recorded almost instantaneously on the deep sea floor and corroborate the key role of deep sea ash layers as highly reliable chronostratigraphic markers and as a geological tool to infer ancient wind fields

topographic height dependence of internal wave generation by tidal flow over random topography internal waves iws generated by tidal flow over the seafloor play a critical role in ocean circulation and climate we determine the dependence of the radiated iw power on topographic parameters in numerical simulations of tidal flow over two dimensional random topographic profiles that have the spectrum of oceanic abyssal hills the iw power increases as the horizontal spatial resolution scale is decreased but below a certain spatial scale the power saturates at a level less than the linear theory prediction for increasing topographic rms height hrms the emergent interference of the tide and the iws from different generation sites leads to a transition in the iw power dependence on hrms from quadratic to linear this transition in the scaling of the iw power depends on the slopes of a valley s nearest neighboring peaks our results should guide the modeling of iw generation by tidal flow over small scale ocean topography

benthic recycling of biogenic debris in the eastern tropical atlantic ocean abstract distributions of pore water o2 no 2 no 3 nh 4 si oh 4 po3 4 mn2 f and t a were determined at 15 stations in the eastern equatorial atlantic while overall profile characteristics are consistent with previous models of organic matter diagenesis profile shapes suggest that a deep reaction layer rich in organic c is also present at many sites while it is unlikely that the oxidation of organic c in this layer has had a major effect on the ocean c cycle pore water profile shapes are significantly altered despite exposure to seawater so2 4 concentrations for 1000 years decomposition of the organic matter in the layer appears to be restricted to oxic and suboxic processes these results suggest major differences in organic carbon decomposition and preservation under oxic suboxic and anoxic conditions present day benthic fluxes are largest adjacent to the eastern boundary coastal upwelling region and similar in magnitude to values reported for the eastern pacific preliminary estimates suggest that the benthic respiration in the eastern 1 3 of the north atlantic south of 20 n may alone account for 20 of the total deep north atlantic respiration combining these results with estimates of organic c burial and deep water column decomposition suggests that this region is a major location of organic c input into the deep sea

effects of the santorini thera eruption on manganese behavior in holocene sediments of the eastern mediterranean the explosive eruption on the island of santorini in 1630 b c in minoan times had a large environmental impact over the eastern mediterranean region it has even been suggested that the mn enriched layer the marker bed above the most recent sapropel s1 in sediments of a crestal area of the mediterranean ridge gained mn from a hydrothermal source related to the santorini eruption radiocarbon dating of two cores from this area sampled at high resolution demonstrate that this large mn peak in fact pre dates the santorini event by 2 8 ky and forms part of a pattern seen in mn profiles from all over the eastern mediterranean this same mn profile shape is altered in areas that experienced substantial deposits of either the tephra layer emitted by the santorini eruption or the turbidites that were triggered by it evidence of both of these perturbations is readily identified from compositional element al and sr ca profiles that are distinct from those of the enclosing sediments in one core with a 37 cm thick santorini ash layer an oxidation front succeeded in penetrating the whole ash layer after emplacement to form a mn peak but is now retreating in cores where thin 15 cm santorini turbidites or ash layers lie above s1 oxidation fronts initially form additional mn peaks on top of the turbidites and subsequently alter the characteristic double peaked mn profile shape usually observed above sapropel s1

late palaeozoic to early mesozoic geodynamic evolution of the circum pacific orogenic belt in south korea and southwest japan abstract a review of the overall features of the late palaeozoic early mesozoic orogen of southwest japan and its korean hinterland allows a new geodynamic model for the building of the east asian margin to be proposed during middle carboniferous to early permian times an oceanic basin formed in a passive margin environment at a moderate spreading rate as the honshu continental block drifted away from the sino korean continent during that period paralic platform conditions and extensional synsedimentary tectonics prevailed in korea in middle permian times the closure of the oceanic area was responsible for yakuno ophiolite obduction and high pressure metamorphism while highly subsiding coal basins developed in the emerged korean hinterland thereafter in late permian times when the honshu block collided with the asian margin akiyoshi orogeny locally derived terrestrial clastic sedimentation in korea has succeeded coal measure deposition with local unconformity in early triassic times the collision was completed and regional uplift of the thickened crust resulted in the deposition of thick distal siliciclastic rocks in rapidly subsiding hinterland troughs korea and flyschoid deposition in the tamba foreland basin outer zone of southwest japan middle to late triassic medium to low pressure metamorphism large scale transcurrent tectonics and associated calc alkaline synkinematic plutonism in the hida and ogcheon belts represent a post collisional feature of the akiyoshi orogenic event post tectonic intrusives and terrestrial deposits post date intracratonic tectonics at ca 200 ma thus the akiyoshi orogeny of southwest japan is a result of continental drift and ensuing collisional rewelding of a fragment of sino korea the honshu microcontinent

mechanical erosion and reheating of the lithosphere a numerical model for hotspot swells it is currently debated if either thermal erosion of the lithosphere or dynamical support is the source of topography and geoid anomalies the origin of tins controversy lies probably in the difficulty to model simultaneously these two effects for this purpose we have studied the time dependent behavior of two dimensional convection with a temperature and pressure dependent viscosity the use of a control volume method allows us to define a rigid zone simulating the mechanical lithosphere the interface between the lithosphere and the convective mantle is determined by a viscosity cutoff first some experiments model the rise of a plume below the lithosphere in order to observe the evolution of the uplift and thus to appreciate the various processes involved in the swell formation before the plume reaches the base of the thermal lithosphere an uplift a few hundred meters in amplitude develops which can only be ascribed to a pure dynamical support the major uplift occurs when the ductile part of the lithosphere the convective boundary layer is squeezed by the plume the reheating of the mechanical lithosphere takes place after this transient stage of dynamical erosion however this late process is very slow but can magnify the amplitude of the swell if the lithosphere stays long enough above the plume these results shed some light on the different mechanisms occurring during the swell formation but the configuration modeled does not correspond to the one expected for actual hotspot swells they feature plume rising up to the lithosphere while natural situations correspond to lithosphere drifting above preexisting plumes an experiment with a moving lithosphere was run and shows that thermal erosion does not affect significantly a moving lithosphere even for relatively slow drifting velocities few centimeters year indeed the thermal structure of the lithosphere is not modified above the 800 c isotherm except for a motionless plate in this case the resulting swell should be greater this could explain why azores crozet or cap verde swells are so high on the other hand the shape of a swell over a moving lithosphere is strikingly reminiscent of the hawaiian swell

the former presence of organic matter caused its later absence burn down of organic matter in oceanic red beds enhanced by bioturbation eocene variegated shale carpathians eocene oceanic red beds that formed in a well oxygenated setting at low sedimentation rates below the calcite compensation depth are effectively barren of organic carbon in the present state recurrent distal low erosive turbidites preserve the bioturbated zone underneath that documents seasonal and long term fluctuating accumulation of considerable amounts of organic matter on the sea floor as evidenced by scolicia the producers of this trace fossil exploited nutritious organic matter conserved in turbidite buried sea floor deposits over the long term slow average sedimentation of hemi pelagic oxic red mud led to long oxygen exposure times and low burial of organic matter consequently trace fossils representing persistent sediment feeding modes are of small size although the food limited setting appears appropriate for producers of graphoglyptids such stationary burrows have not been encountered because seasonal deposition of organic matter fostered at least temporary surface layer feeding organisms for instance producers of nereites irregularis that intensively reworked the sediment and hence hindered graphoglyptid production these findings confirm palaeoceanographic modelling results that suggest upwelling in the study area during the eocene this article is protected by copyright all rights reserved

deep sea benthic foraminiferal recolonization of the 1991 mt pinatubo ash layer in the south china sea a census count of rose bengal stained benthic foraminifera from the surface area on top of a 2 to 6 cm thick ashfall layer at three deep water stations along the western margin of the philippines exhibits a unique assemblage composition of benthic foraminifera the total number of benthic foraminifera is low and the ratio of living individuals to empty tests is high specific diversity is low with a significant dominance of infaunal morphotypes including species of the genus reophax r scorpiurus r bilocularis and r dentaliniformis which are regarded as successful recolonizers assemblages below the ash layers are diverse and contain many epifaunal suspension feeding agglutinated and calcareous foraminifera the 1991 mt pinatubo eruption caused mass mortality of benthic foraminifera in a vast area of the eastern south china sea followed by step wise recolonization of the ash substrate three years after the eruption the benthic foraminiferal community structure is still far from recovery to background levels

the agglutinated foraminifera from the sw pacific bathyal sediments of the last 550kyr relationship with the deposition of tephra layers abstract the agglutinated foraminiferal content from the last 550 kyr record of the images core md 97 2114 chatham rise new zealand was analysed in order to detect the possible linkage existing between the composition of the grains forming the agglutinated tests and the deposition of tephras the core was collected east of new zealand about 680 km from the active taupo volcanic zone tvz located on the north island thus it contains numerous macro and microscopic tephra layers scanning electron microscopy and energy dispersive spectroscopy analyses were carried out on entire agglutinated foraminifera as well as on sectioned specimens sampled around and within the tephra layers the analyses show that the studied foraminifera built structurally complex tests picking and selecting mineral and biogenic particles on the basis of their availability and abundance in the substratum as well as their composition size and shape in most of the studied species belonging to the order textulariida the composition of the agglutinated grains does not change when the deposition of the tephra layer strongly enriched the substratum in volcanic glass shards only the species karreriella novangliae changed significantly its grain composition mostly selecting volcanic glass fragments to cover the test surface nevertheless the tephra deposition seems to influence the wall microstructure of the agglutinated tests textulariid specimens coming from the volcanoclastic layers have a thinner wall which is also characterised by a less abundant calcareous matrix with respect to the specimens sampled above or below the tephra layer we hypothesise that the volcanic ash deposition probably interfered with the normal agglutinating process by causing the development of more aggressive waters at the sea floor which in turn could have induced carbonate dissolution our observations therefore suggest that the sediment type of the substratum is not the only controlling factor in the construction of the agglutinated foraminiferal test and grain selection which appears to be species dependent

grain size areal thickness distribution and controls on sedimentation of the 1991 mount pinatubo tephra layer in the south china sea the june 15 1991 climactic eruption of mt pinatubo produced an extensive largely co ignimbrite derived airfall ash layer on luzon island and across the central south china sea the layer covers an area of 4 105 km2 with a volume of 5 5 km3 near the coast of luzon the deposit consists of two units a normally graded basal ash bed unimodal in grain size and a finer grained internally structureless upper ash bed showing grain size bimodality with increasing distance from the source the coarse particle populations of the two units merge and migrate towards a near constant fine population 11 m the distal region is covered by a fine mode dominated virtually ungraded single ash layer the reversal of the winds from easterly directions at upper tropospheric and stratospheric levels to westerly directions in the middle and lower troposphere indicates that both the coarse and fine mode components fell out from high altitude eruption clouds the high velocity upper level winds however would have transported fine grained ash particles far beyond the south china sea which suggests that their settling was accelerated by aggregation the boundary between the units thus marks a change from fallout of predominantly discrete pyroclasts to simultaneous fallout of aggregated fines and freely falling coarse grained particles the particle populations composing the upper ash bed were almost completely removed from the proximal areas by the upper level winds at lower elevations the counterclockwise circulation of a typhoon over the coastal area advected the ash south and eastward producing a thickness maximum in the medial region at about 160 km from source the strong displacement of fines possibly aided by wind turbulence led to a break in bulk tephra thinning rates close to the coastline in the distal region outside the influence of the typhoon southwest monsoonal winds caused a distinct lobe axis inflection and thickness asymmetry within this region at about 420 km from source fallout of particle aggregates created a second thickness maximum comparison of the field data with previous experimental observations and tephra flux records in the deep sea wiesner et al 1995 carey 1997 mccool 2002 implies that the transport of ash in the water column was largely determined by vertical density currents differences in the reaction of coarse and fine particles to turbulence in the descending plumes probably suppressed the segregation of fines but allowed the coarser pyroclasts to maintain their initial order of arrival at the sea surface considering typical fall rates of convective plumes modifications of the initial fallout position of the particles by the south china sea current system are on the order of only a few kilometers the results suggest that convective sedimentation processes ensure the preservation of atmospheric particle transport directions distances and fallout modes in the deep sea

historical seismicity of korea the korean peninsula lies in the eurasian plate neighboring seismically active china and the japanese islands instrumental observation of earthquakes began in korea in 1905 and about one thousand events of mostly small magnitude less than 4 0 have been detected to date in and near the peninsula strain release due to these earthquakes is almost negligible compared to that due to about 2186 historical earthquakes that occurred from 2 to 1904 a d in the peninsula in this study these historical earthquakes are cataloged from korean historical documents and their epicenters and intensities are estimated as best as possible temporal variations of the historical seismicity of korea clearly reveal a very irregular strain release pattern over the nineteen centuries with low to moderate seismicity most of the time except for the unusually high seismicity from the fifteenth to the eighteenth centuries this highly irregular strain release pattern clearly indicates the characteristics of intraplate seismicity of the peninsula epicenters of large earthquakes appear to be well associated with the major faults and the boundaries of major geological units in the peninsula it is to be noted that the major faults associated with large historical earthquakes were created by the mesozoic tectonic activities that severely disrupted crustal layers of the peninsula historical earthquakes occurred all over the peninsula however the northeastern part appears relatively less seismic probably due to the area being less disrupted during the mesozoic the b value in the magnitude frequency relation determined from historical korean earthquakes is 0 71 which is between those of the japanese islands and eastern china and is lower than in many stable intraplate regions online material catalog of historical seismicity of korea 2 1904 a d

the effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the skafta river iceland abstract this study describes the chemical composition of dissolved degased and suspended fluxes of the 2002 skafta glacial flood which emerged from one of the skafta subglacial lake due to geothermal activity beneath the icelandic vatnajokull glacier the dissolved and suspended fluxes during the flood are compared with those normally observed in the skafta river to determine the effect of such floods on the annual fluxes of material delivered to the coastal waters concentrations of most dissolved elements during the flood were significantly higher than those normally observed in the skafta river in addition dissolved concentrations of nutrients such as sio 2 fe and v increased more than an order of magnitude during the flood these will affect biological processes on a local scale the 34 s composition in the flood water suggests that the dissolved so 4 was derived from the oxidation of h 2 s and the geothermal fluid the total suspended particulate load measured in the skafta river during the 8 day 2002 flood was approximately half of the non flood total annual skafta suspended load as particles carry the bulk of limiting nutrients to the oceans this demonstrates the importance of glacial floods for primary production of coastal waters the composition of the flood water and the skafta subglacial lake together with reaction path modelling suggest that substantial degasing of co 2 and h 2 s occurred at the glacial outlet during the flood this degasing may have released as much as 262 000 and 7 980 tonnes of co 2 and h 2 s respectively to the atmosphere having a considerable impact on the local carbon and sulphur cycles during the flood event

recognition of the minoan tephra in the acigol basin western turkey implications for inter archive correlations and fine ash dispersal here we report the recognition of the minoan tephra layer in the acigol basin western turkey which represents the most eastward occurrence of this tephra on land and the first in continental deposits out of lacustrine sediments in mainland turkey the correlation is supported by glass and mineral geochemistry which includes solution and laser ablation icp ms data for trace and rare earth elements thickness and grain size data allow the extension of already described occurrences to an area of about 359 000 km 2 from the eastern mediterranean to black sea throughout central western turkey coupling dispersal area and grain size data suggests the joint influence of high and low atmosphere dynamics in dispersal of fine ash during volcanic eruptions the thickness and lateral continuity of the minoan tephra in the acigol basin testifies to the widespread impact on the late bronze age environment of mainland turkey of this important ash deposit copyright 2013 john wiley sons ltd

the preservation potential of ash layers in the deep sea the example of the 1991 pinatubo ash in the south china sea following the eruption of mount pinatubo on 15 june 1991 volcanic ash was transported westward to the south china sea in an atmospheric plume falling out and settling to the sea floor within days and forming an up to 10 cm thick layer on an area 400 000 km 2 immediately after deposition surviving deepburrowing animals re opened their connection to the sea floor to obtain water for respiration and or food take up later small sized meiofauna and then macrofauna re colonized the sea floor mixing newly deposited organic fluff with the underlying ash consequently ash deposits thinner than 1 mm have not often been observed as a continuous layer when cored six years after the eruption while ash about 2 mm thick is now patchily bioturbated in areas covered by ash thicker than 5 mm mixing by benthic animals is controlled mainly by the adaptation of the burrowing fauna to variations in grain size the rate of background sedimentation the availability of benthic food on and within the sediment and pore water oxygen levels with respect to these factors four provinces can be distinguished i along the philippines margin run off from land fuels primary production that in turn leads to a high benthic food content the benthic fauna is adapted to a variable grain size and rapid sedimentation therefore mixing is intense and the preservation potential of the ash layer is low ii in areas affected by deposition of hyperpycnites and turbidites i e in canyons in front of river mouths and in the manila trench the ash layer is preserved due to rapid burial iii the area to the west to about 116 e receives low amounts of benthic food benthic mixing is less intense and the preservation potential of the ash is high iv the central south china sea where the ash is thinner than 3 cm is affected by intense wind mixing and upwelling and the benthic food content is high thus the chance that the ash will be preserved as a sharp based layer is low consequently the style of ash preservation has palaeo environmental significance older buried and burrowed event layers provide further information to elucidate the fate of the 1991 pinatubo ash layer in general their appearance fits with observations in the recent

th u pb monazite geochronology of the luliang and wutai complexes constraints on the tectonothermal evolution of the trans north china orogen abstract recent lithological metamorphic and geochronological studies show that the basement of the north china craton ncc formed by collision of two discrete archean to paleoproterozoic blocks eastern and western blocks along a paleoproterozoic orogen named the trans north china orogen however the timing of the collision is controversial and post collisional exhumation has not been precisely dated this study applies the electron microprobe th u pb monazite dating technique to determine the ages of the peak metamorphic event and subsequent exhumation of the low to medium grade luliang and wutai complexes in the trans north china orogen electron microprobe th u pb monazite data for the luliang complex reveal five tho 2 pbo age ranges 1 1940 1938 ma 2 1880 1847 ma 3 1795 1755 ma 4 1720 1703 ma and 5 1648 ma of these age ranges the first four have also been recorded in the wutai complex which yields tho 2 pbo ages of 1 1930 ma 2 1838 1822 ma 3 1793 ma and 4 1719 ma the oldest age range of 1940 1930 ma is interpreted to record the widespread emplacement of mafic dikes in rocks of the luliang and wutai complexes the age range of 1882 1822 ma is in accord with the shrimp u pb ages of metamorphic zircons and mineral sm nd and 40 ar 39 ar ages obtained for other complexes in the orogen and is interpreted as the age of the major metamorphic event caused by amalgamation between the eastern and the western blocks the age range of 1795 1755 ma is consistent with emplacement of large scale unmetamorphosed mafic swarms at 1800 1765 ma interpreted as the time of post orogenic extension the 1720 1703 ma and 1648 ma ages are considered to date later multiple stages of hydrothermal alteration since monazites with such young ages only occur along fractures in older monazite grains and at the rims these new monazite tho 2 pbo ages support the tectonic model for the evolution of the north china craton that envisages discrete eastern and western blocks colliding along the trans north china orogen at 1 85 ga and then undergoing post collisional extension in the period 1795 1755 ma

depth dependent seismic scattering attenuation in the nuevo cuyo region southern central andes 1 in the present work we separated intrinsic from scattering attenuation coefficients both for the crust and the upper mantle in the tectonically highly active areas of the southern central andes nuevo cuyo region analyzing two groups of earthquakes well separated in depth this region is characterized by the presence of flat subduction we apply mltwa multiple lapse time window analysis coda normalization and q coda techniques to measure the scattering and intrinsic attenuation coefficient and the total q for s waves we find that intrinsic attenuation does not decrease with depth whereas scattering attenuation is higher in the crust than in the upper mantle and that intrinsic attenuation predominates over scattering attenuation we interpret this observation in terms of the release of water and other fluids into the overlying lithosphere due to the dynamics of the subduction process in agreement with most of the prevalent geodynamic models

pore water profiles and numerical modelling of biogeochemical processes in peru basin deep sea sediments abstract an extensive set of pore water profiles including o 2 no 3 no 2 nh 4 po 4 3 fe 2 mn 2 so 4 2 sio 4 4 ph and alkalinity as well as solid phase data on organic carbon content and porosity in 18 sediment cores obtained from five areas in the peru basin rv sonne 106 expedition in 1996 is presented the pore water profiles indicate that early diagenesis progresses through oxygen respiration denitrification and manganese iv reduction while the subsequent redox states iron iii reduction sulphate reduction and methanogenesis cannot be observed from the dissolved phase in these deep sea sediments a numerical diagenetic model was applied to the data in order to derive parameters such as the depositional flux of metabolizable organic matter or the bioturbation intensity that control the geochemical conditions in the deep sea floor and could not be obtained directly by measurements moreover the numerical simulations show that even those pore water no 3 profiles that decline non linearly to zero concentration are not compatible with a steady state assumption they can be explained only by transient downward progression of a nitrate front

long term mobilisation of chemical elements in tephra rich peat ne iceland this paper presents geochemical profiles of a tephra bearing minerotrophic peat column from ne iceland obtained using various elemental analyses of the solid phase and the pore water the influence of tephra grain size thickness and composition of each tephra on the peat geochemistry was investigated interpretations are supported by a statistical approach in particular by autocorrelation and by microscopy observations minerotrophic peat geochemistry may be strongly dependent upon post depositional mobilization and possible leaching of elements as demonstrated by fe and trace metal concentration profiles chemical elements and more specifically potentially harmful metals can be slowly leached out of volcanic falls during their weathering and re accumulate downwards it is emphasised that a tephra deposit can act as an active geochemical barrier blocking downward elemental movements and leading to the formation of enriched layers in this study the formation of poorly amorphous fe phases above the hekla 3 tephra is shown these poorly crystalline fe phases scavenged ni

relationship of pyroclastic volcanism and lake water acidification to jehol biota mass mortality events early cretaceous northeastern china abstract geochemical analysis of the 14 4 m thick lacustrine succession of the lower cretaceous yixian formation jehol group has yielded new insights concerning vertebrate mass mortality events in the lake sihetun volcanic caldera in western liaoning province northeastern china that produced the jehol biota fossil lagerstatten the long term evolution of the caldera system resulted in a shift from felsic to mafic magma chemistry accompanied by a reduced frequency of pyroclastic eruptions declining hydrothermal activity and lower lacustrine productivity the basal tetrapod beds exhibit strong hydrothermal influence as indicated by enrichments of boron b certain alkalis rb cs rare earth elements rees yttrium y and many metals e g co cr cu ge mo ni sb u v and w and by strongly negative molybdenum isotope compositions 98mo to 2 50 that may record large fractionations between molybdate and thiomolybdate species in the sihetun caldera hydrothermal system in contrast the overlying fish beds and non fossiliferous beds have an elemental and mo isotopic composition similar to calc alkaline basalts 98mo 0 29 0 04 in the surrounding watershed suggesting weathering of yixian formation volcanic rocks as the major source of sediment during its

crustal velocity structure across the southern korean peninsula from seismic refraction survey 1 the first crustal scale controlled source seismic refraction experiment in the southern korean peninsula kcrust2002 was carried out along a 300 km long profile across this peninsula in december 2002 iterative processing and modeling produced a laterally varying layered crustal velocity model the crust is thickest 34 km below the okcheon fold belt in the middle of the transect and thinnest 28 km at the eastern end where the cretaceous gyeongsang basin is characterized by 5 km of low velocity material that constitutes the upper crust the p velocities in upper and lower crust range from 5 4 to 6 0 km s and from 6 4 to 6 7 km s respectively the average crustal poisson s ratio is found to be 0 25 0 27 vp vs 1 73 1 78 along the profile a mid crustal velocity discontinuity is recognized in the northwestern part of the transect the underlying mantle has velocities in the range of 7 9 8 1 km s

the impact of the 1991 mt pinatubo eruption on deep sea foraminiferal communities a model for the cretaceous tertiary k t boundary the ash layer from the 1991 mt pinatubo eruption provided a natural laboratory to assess mass mortality and the rates of recovery of deep marine ecosystems after a catastrophic event and to draw a parallel with the environmental impact of the k t boundary event on deep sea foraminiferal communities the first recolonization assemblages of benthic foraminifers after the mt pinatubo ash fall exhibit surprising similarities with benthic foraminiferal communities established following the k t boundary event i e comparatively low abundance and diversity absence of suspension feeders dominance of mobile infaunal taxa and a high proportion of agglutinated foraminifers the first foraminifers to recolonize the deep sea after both catastrophic events were opportunistic forms with high capability for rapid dispersal however major differences are evident in the timing and duration of the faunal transitions post eruption assemblages with high proportions of epibenthic suspension feeders became established after a short initial recolonization phase of approx 6 7 years on the mt pinatubo ash layer in the k t sections comparatively stable new benthic foraminiferal assemblages including suspension feeders only became established several thousand years after the event delayed recovery of the pelagic ecosystem and poor deep water ventilation probably slowed down the recovery of the benthic community structure after the k t boundary c 2005 elsevier b v all rights reserved

uptake of dissolved oxygen during marine diagenesis of fresh volcanic material convergent plate volcanism typically occurs close to the oceans hence a high proportion of fresh highly reactive volcanogenic material is rapidly deposited onto the seafloor previous studies haeckel et al 2001 have shown that dissolved oxygen o2 is extensively depleted in the pore waters of ash deposited in the south china sea from the 1991 pinatubo eruption here we report the results of an extensive field laboratory and modelling study of dissolved o2 concentrations and ancillary geochemical data pore water no2 no3 and solid phase feii feiii and organic carbon in the sediments surrounding the volcanic island of montserrat lesser antilles dissolved o2 is depleted to zero within 0 3 cm of the sediment water interface in sites containing the thickest layers of volcanogenic material 35 cm compared to a penetration depth of 6 cm in sites with minimal ash loading of 0 5 cm experimental studies using volcanogenic sediment in a flow through cell obtained similar o2 consumption rates to those observed in studies of individual minerals and basalt white and yee 1985 these results and comparison with other geochemical data lead us to conclude that the dominant mechanism for dissolved o2 uptake in volcanogenic sediments is oxidation of silicate bound feii by a coupled electron transfer reaction the observation that rapid dissolved o2 uptake by volcanogenic sediments is a ubiquitous feature of deposition of fresh volcanic material in the oceans may have global implications while the global amount of dissolved o2 consumed by this process is trivial compared to that resulting from oxidation of organic carbon the widespread deposition of volcanic ash from massive explosive eruptions may lead to enhanced preservation of organic carbon in marine sediments and thus lowering of atmospheric co2 concentrations during critical periods in earth history

the immediate environmental effects of tephra emission the earth s history is punctuated by large explosive eruptions that eject large quantities of magma and silicate rock fragments into the atmosphere these tephra particles can sometimes be dispersed across millions of square kilometres or even entire continents the interaction of tephra with or in receiving environments may induce an array of physical chemical and biological effects the consequences for affected systems and any dependent communities may be chronic and localised in the event of frequent small eruptions while larger and rarer events may have acute regional scale impacts it is therefore necessary to document the range of possible impacts that tephra may induce in receiving environments and any resulting effects in interconnected systems we collate results from many studies to offer a detailed multidisciplinary and interdisciplinary review of the immediate post eruptive effects of tephra emission into the atmosphere onto vegetation soil or ice snow surfaces and in aquatic systems we further consider the repercussions that may be induced in the weeks to years afterwards in the atmosphere tephra can influence cloud properties and air chemistry by acting as ice nuclei in or by offering sites for heterogeneous reactions respectively tephra on vegetation causes physical damage and sustained coverage may elicit longer term physiological responses tephra deposits on soils may alter their capacity to exchange gas water and heat with the atmosphere or may have a specific chemical effect such as nutrient input or acidification on sensitive soils tephra deposition onto snow or ice may affect ablation rates rivers and lakes may experience turbidity increases and changes in their morphology as a result of fallout and prolonged months or years erosion from the tephra covered catchment in the first weeks after deposition tephra leaching may affect river chemistry the abundance and speciation of phytoplankton populations in lakes may be altered by tephra induced changes in water chemistry or sediment water nutrient cycling in the oceans tephra deposition may fertilise fe limited waters with potential impacts on the global carbon cycle embracing the full complexity of environmental effects caused by tephra fall demands a renewed investigative effort drawing on interdisciplinary field and laboratory studies combined with consideration of the interconnectivity of induced impacts within and between different receiving environments

biologically mediated dissolution of volcanic glass in seawater we studied the effects of biological mediation on the dissolution of basaltic glass in seawater experiments with typical seawater microbial populations were contrasted with a sterile control and reactions were monitored chemically and isotopically biologically mediated experiments produce twice the mass of authigenic phases than abiotic experiments and the phases are different abiotic alteration of glass dissolves basaltic si and ca and scavenges seawater mg while biotic alteration removes ca from seawater such opposing behavior of ca and mg in biotic and abiotic alteration of basaltic glass may have important implications for the carbon cycle and the exchange processes between ocean crust and seawater 87sr 86sr data of glass and alteration products suggest that biological mediation enhances both the diffusion of seawater sr into glass by a factor of 3 4 and the dissolution of basaltic sr into seawater by a factor of 20 40 the dependence of chemical exchange processes between seawater and glass on biological activity implies that chemical fluxes from water rock interaction at low temperatures may change as life on earth evolves

iron reduction through the tan green color transition in deep sea sediments mossbauer spectroscopic investigations of deep sea sediments from the peru basin revealed a prominent downcore increase of the bulk sediment fe ii fe iii ratio across the well known tan green color transition this increase occurs along a continuous gradient extending over a 3 cm zone at the two deep sea sites that we report remarkably constant values of the fe ii fe iii ratios above 11 2 89 2 and below 37 2 63 2 the iron redox transition zone delimit the gradient clearly a minor peak of diagenetic iron enrichment is manifest at the redox front this fe enrichment has accumulated in a redox cycle and amounts to 16 4 of the total fe at the peak maximum the data imply that 26 4 of the detrital iron has experienced in situ redox transition from fe iii to fe ii within the iron redox transition zone

reactive fe ii layers in deep sea sediments the percentage of the structural fe ii in clay minerals that is readily oxidized to fe iii upon contact with atmospheric oxygen was determined across the downcore tan green color change in peru basin sediments this latent fraction of reactive fe ii was only found in the green strata where it proved to be large enough to constitute a deep reaction layer with respect to the pore water o2 and no3 large variations were detected in the proportion of the reactive fe ii concentration to the organic matter content along core profiles hence the commonly observed tan green color change in marine sediments marks the top of a reactive fe ii layer which may represent the major barrier to the movement of oxidation fronts in pelagic subsurface sediments this is also demonstrated by numerical model simulations the findings imply that geochemical barriers to pore water oxidation fronts form diagenetically in the sea floor wherever the stage of iron reduction is reached provided that the sediments contain a significant amount of structural iron in clay minerals

p and s wave velocity model along crustal scale refraction and wide angle reflection profile in the southern korean peninsula abstract the onshore seismic experiment kcrt2004 explored the crustal velocity structure of the southern korean peninsula we present an interpretation of seismic data along this 340 km long nnw sse trending profile the crust was found to consist of three layers the upper middle and lower crust with p and s wave velocities ranging 5 50 to 6 95 km s and 2 82 to 3 91 km s respectively the average p wave velocity 6 26 km s and pn velocity 7 82 7 88 km s are lower than the worldwide average of continental crust moho depths are 29 0 34 9 km gradually thickening toward south the vp vs ratio of crustal material is estimated to be 1 73 0 249 for the upper and middle crust and the ratio increases with the depth in the lower crust the gyeonggi massif in the north of the profile has a lower vp vs ratio than other tectonic units the average crustal vp vs ratio of 1 74 0 253 is remarkably lower than the average value 1 78 0 27 for the bulk continental crust the low average crustal vp vs ratio is similar to that measured in eastern china the empirical analysis using both p wave velocity and vp vs ratio shows that the upper and middle crust is dominantly felsic and the lower crust is intermediate in composition the absence of the mafic material in the lower crust that is also found in eastern china contrasts with the generally accepted global model of the mafic lower crust

earthquakes in korea from 1905 to 1945 from 1905 to 1945 earthquakes occurring in and in the vicinity of the korean peninsula were monitored by the meteorological observatory of the government general of tyosen with one to six seismological stations seismological data of 323 earthquakes of the meteorological observatory during the period are analyzed in this study epicenters of earthquakes are estimated by reports in bulletins of the meterological observatory epicenters and magnitudes of events that occurred from 1926 to 1943 were determined previously based on the crustal structures of the peninsula and japanese islands and tsuboi9s formula respectively lee and jung 1980 kim 1980 the b value determined from these events turned out to be about 0 8 which is between those values for earthquakes of the japanese islands and china the epicenter distribution of earthquakes during the period indicates rather diffuse seismicity over the peninsula not well related to major faults and much lower seismicity in the northeastern part of the peninsula compared with other regions previous studies of historical seismicity of the korean peninsula showed that epicenters of destructive large earthquakes are well associated with major faults in the peninsula formed during mesozoic tectonic activities lee 1987 and lower seismicity in the northeastern part of the peninsula the seismic wave energy release during the period was rather steady except for the period 1936 1938 during which the 1936 m 5 1 ssanggyesa earthquake the largest event during the period occurred in the southern part of the peninsula the source mechanism of the ssanggyesa earthquake indicates a thrust fault with a considerable strike slip component shimazaki 1984 one of the nodal planes trending north northeast coincides with the strikes of adjacent faults reliable source mechanisms of earthquakes in the vicinity of the korean peninsula indicate that the korean peninsula is subject to compressive stresses parallel to the great circles from the himalayas to the japan trench it appears that the earthquakes in the korean peninsula occur along the faults formed during the mesozoic by stresses transmitting from plate boundaries between the eurasian plate and the indian plate along the himalayas in the southeast and the pacific and philippine plates along the japan and ryuku trenches in the east respectively the source mechanisms of large earthquakes in the peninsula are likely to be thrust faults with considerable strike slip components in the trends of faults

magnetic susceptibility variations and provenance of surface sediments in the south china sea magnetic susceptibility ms and grain sizes of surface sediments are measured to characterize sediment sources and their distribution in the south china sea scs distribution characteristics of ms of bulk samples msb fine grained fraction msf and coarse grained fraction msc are examined to explore the factors affecting ms values in sediment transport and deposition processes affected by dilution of quartz and carbonate abundance msc is not suitable for tracing sediment sources in the region instead msf provides a good parameter for tracking transport and deposition of complex and coarse grained sediments such as those from luzon island volcanics and from the pearl and mekong rivers which often have high msf values showing a decreasing trend with water depth on the continental shelf water depth 200 m to the west of luzon island kuroshio intrusion into the scs is the predominant factor for sediment transport after high msf volcanic materials from the luzon island are discharged into the sea sediments from the pearl river are transported southwestward under the china coastal current and then deposited between the pearl river mouth and hainan island to the southwest of taiwan island in the northeastern scs where sediments are mainly derived from taiwan island and or the yangtze river both the kuroshio intrusion and the china coastal current are significant in determining sediment transport and deposition in the south most of high msf sediments from the mekong river are transported eastward under the influence of northeastward currents in summer after entering the sea and then deposited on the northern sunda shelf c 2010 elsevier b v all rights reserved

monte carlo simulation of seismogram envelopes in scattering media the analysis of the seismogram coda envelopes of local and regional earthquakes is one of the most effective strategies for investigating the heterogeneous lithospheric structure characterized by the seismic scattering and attenuation in order to synthesize the coda envelope we introduce a numerical scheme called the direct simulation monte carlo method which has been used in the field of the kinetic theory of gases because of the simplicity of the algorithm the method has several advantages over previous methods in terms of the flexibility of the numerical calculation to incorporate various factors required to construct realistic seismogram envelopes on the basis of coda envelope simulations including multiple scattering we show that an increase of seismic velocity with depth severely affects the shape of the coda envelope the effects of ray bending due to the velocity increase at the moho and the reflection at the free surface are clearly found in the synthesized envelope for a shallow earthquake our simulation demonstrates that the amplitude of the envelope is magnified by stagnation of seismic energy at shallow depths due to the positive velocity gradient with depth because of this effect for an a priori assumption of a homogeneous velocity model the measurement of the scattering coefficient by conventional methods may be overestimated

diagenesis in tephra rich sediments from the lesser antilles volcanic arc pore fluid constraints we present sediment pore fluid and sediment solid phase results obtained during iodp expedition 340 from seven sites located within the grenada basin of the southern lesser antilles volcanic arc region these sites are generally characterized as being low in organic carbon content and rich in calcium carbonate and volcanogenic material in addition to the typical reactions related to organic matter diagenesis pore fluid chemistry indicates that the diagenetic reactions fall within two broad categories 1 reactions related to chemical exchange with volcanogenic material and 2 reactions related to carbonate dissolution precipitation or recrystallization for locations dominated by reaction with volcanogenic material these sites exhibit increases in dissolved ca with coeval decreases in mg we interpret this behavior as being driven by sediment water exchange reactions from the alteration of volcanic material that is dispersed throughout the sediment package which likely result in formation of mg rich secondary authigenic clays in contrast to this behavior sediment sequences that exhibit decreases in ca mg mn and sr with depth suggest that carbonate precipitation is an active diagenetic process affecting solute distributions the distributions of pore fluid 87sr 86sr reflect these competitive diagenetic reactions between volcanic material and carbonate which are inferred by the major cation distributions from one site where we have solid phase 87sr 86sr site u1396 the carbonate fraction is found to be generally consistent with the contemporaneous seawater isotope values however the 87sr 86sr of the non carbonate fraction ranges from 0 7074 to 0 7052 and these values likely represent a mixture of local arc volcanic sources and trans atlantic eolian sources even at this site where there is clear evidence for diagenesis of volcanogenic material carbonate diagenesis appears to buffer pore fluid 87sr 86sr from the larger changes that might be expected given the high abundance of tephra in these sediments part of this carbonate buffering at this site as well as throughout the region derives from the fact that the sr concentration in the non carbonate fraction is generally low 200 ppm whereas the carbonate fraction has sr concentrations approaching 1000 ppm

sequential colonization of muddy turbidites in the eocene beloveža formation carpathians poland abstract a 100 350 m thick succession of centimeter thick fine grained turbidites form the lower mud dominated part of a prograding deep sea fan in the eocene belove a formation in the carpathian mountains of poland these strata contain over 50 ichnotaxa only six of which are common phycosiphon nereites chondrites scolicia halopoa ophiomorpha polished slabs and examination of cross cutting relationships show that post event colonization was sequential using modern analogues it can be shown that the colonization of different depth levels in the sediment at different times reflects changing geochemical conditions especially the re adjustment and re establishment of the redox boundary modern analogues allow an assessment of the timing of each colonization phase the phycosiphon producers entered first and occupied the well oxygenated muds 5 40 mm below the sediment surface as the redox boundary reformed nereites producers entered and probably utilized microbial matter just above the redox boundary about 15 30 mm below the sediment surface subsequently chondrites producers penetrated down to the oxygen deficient layers of the event bed or even deeper levels the halopoa producers entered with phycosiphon but reworked coarser layers contemporaneously with this sequential colonization deep permanent bioturbators which were unaffected by the event cross cut the post depositional suite the variability of the resultant ichnofabrics can be attributed in part to a patchy distribution of the benthos and the relative frequency of turbidite events five ichnofabrics which reflect the successive colonization episodes are recognized each was modified by elements of the permanent infauna

volcanic ash hazard in the central mediterranean assessed from geological data volcanic ash produced during explosive eruptions can have very severe impacts on modern technological societies here we use reconstructed patterns of fine ash dispersal recorded in terrestrial and marine geological archives to assess volcanic ash hazards the ash dispersal maps from nine holocene explosive eruptions of italian volcanoes have been used to construct frequency maps of distal ash deposition over a wide area which encompasses central and southern italy the adriatic and tyrrhenian seas and the balkans the maps are presented as two cumulative thickness isopach maps one for nine eruptions from different volcanoes and one for six eruptions from somma vesuvius these maps represent the first use of distal ash layers to construct volcanic hazard maps and the proposed methodology is easily applicable to other volcanic areas worldwide

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

sediment mixing and accumulation rates in the sulu and south china seas implications for organic carbon preservation in deep sea environments abstract recent rates of carbon burial in two deep sea basins the sulu and south china seas are contrasted to determine factors influencing organic carbon preservation in deep sea sediments the sulu sea is an oxygen deficient warm water basin whereas the adjacent south china sea is more typical of open ocean conditions high resolution sea bed profiles of 14c reveal that accumulation rates for the sulu sea are 2 3 times higher than the south china sea at any given water depth e g 1 3 g cm 2 kyr 1 versus 4 3 g cm 1 kyr 1 respectively at 3000 m higher accumulation rates for the sulu sea are attributed to higher terrigenous input and better carbonate preservation in the warmer bottom waters benthic mixing rates determined using 210pb geochronology generally are lower in the sulu sea 0 004 0 254 cm2 yr 1 as compared with the south china sea 0 17 1 57 cm2 yr 1 especially at the 3000 m and 4000 m sites in the sulu sea where benthic mixing is negligible despite the higher bottom water oxygen levels in the south china sea organic carbon concentration profiles are strikingly similar for the two basins at any given water depth with similar concentration profiles higher accumulation rates in the sulu sea result in equivalently higher carbon preservation rates as primary production is thought to be similar for both basins if anything slightly higher for the south china sea the production rate can not explain the observed differences in carbon preservation in addition benthic mixing rates apparently do not play a major role in carbon preservation as extremely low rates at the deeper sulu sea would predict relatively low carbon preservation contrary to our observations we conclude that sediment accumulation rate is the dominant control on carbon preservation in this area of the western equatorial pacific

intrinsic and scattering attenuation of the mt fuji region japan summary mount fuji is the focus of intense study because of its potential hazard signaled by seismic geologic and historical activity based on extensive seismic data recorded in the vicinity of mt fuji coda quality factor q 1c using a single scattering model hypothesis and intrinsic and scattering quality factor q 1i and q 1s using the multiple lapse time window mltw method were measured to focus the study on the magmatic structure below mt fuji the data were separated into two groups a near fuji region of rays traversing an area with radius 5 km around the summit r 20 km this classification shows the largest discrepancy of q 1c at a range of sampling volumes corresponding to overlapped sampling depth of about 80 km further the spatial division shows significant difference of q 1i and q 1s at hypocentral distance of 80 km the large difference of q 1s in bandwidths 2 4 and 4 8 hz indicates lithospheric heterogeneity beneath mt fuji with a characteristic heterogeneity scale length of about 1 km the results have a small error range due to the large data sample showing that all q 1 values in the near fuji area are greater than those of the far fuji area and q 1i for both the near and far fuji areas is higher than q 1s at high frequencies the q 1i and q 1s values for far fuji are in the range of values for typical non volcanic areas the q 1i values of the near fuji area are lower than those of other volcanic areas considered where as values of q 1s are not the low q 1i for the volcanic region of near fuji suggests that the magmatic activity indicated by percent partial melt in the vicinity of mt fuji is not as active as hot spot volcanoes such as kilauea hawaii

early organic diagenesis the significance of progressive subsurface oxidation fronts in pelagic sediments abstract porewater and solid phase geochemical data at two contrasting ne atlantic stations are reported station 10552 on the cape verde abyssal plain is a site of slow pelagic accumulation ca 0 4 cm kyr 1 molecular oxygen is present in the sediment column to at least 2 m and probably much deeper labile organic carbon is almost totally consumed in the upper few centimetres of the sediment by contrast at station 10554 on the madeira abyssal plain the pelagic sequence has been interrupted by the occasional deposition of organic rich turbidites porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column this metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time this phenomenon exerts a controlling influence on the present nutrient profile and redox succession in a less extreme form substrate distributions of this latter type are not uncommon in atlantic sediments a model has been developed which is controlled by both oxygen and nitrate data this model permits a vertical profile of metabolic activity to be derived and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations about 30 of the total activity at station 10554 is located within the turbidite at the deepening reaction front this is a non steady state condition in fact it is found that the integrated metabolic activity at the two stations is not dissimilar ca 1 2 10 13 moles cm 2 sec 1 the striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column

seismological constraints on the collision belt between the north and south china blocks in the yellow sea abstract the korean peninsula eastern china and the yellow sea comprise the eastern eurasian plate and are believed to share considerable tectonic evolution history the tectonic structures in the yellow sea are poorly understood raising difficulty in reconstruction of tectonic evolution history in the eastern eurasian plate the tectonic structures in the yellow sea are constrained by seismicity and fault plane solutions of earthquakes the fault plane solutions are determined by waveform inversions and seismic phase polarity analyses the ambient stress fields are deduced from the fault plane solutions the primary stress field around the yellow sea is composed of ene wsw directional compression and nnw sse directional tension normal faulting earthquakes with ene wsw directional strikes are observed in the central yellow sea between the shandong peninsula and the central korean peninsula the normal faulting region is interpreted to be a northern margin of collision belt between the north and south china blocks the normal faulting system suggests post collisional lithospheric delamination causing reverse activation of paleo thrustal faults that were developed by the collision between the north and south china blocks in the early jurassic period

depth dependent seismicity and crustal heterogeneity in south korea abstract depth dependent seismicity has been suggested in the seismogenic layer which is divided into upper and lower layers by its seismicity boundary since large earthquakes tend to occur in the lower layer the structure of the seismogenic layer which includes the seismicity boundary provides important information for seismic hazard assessment using 107 land based earthquakes the structure of the seismogenic layer in south korea was studied with focal depth determination by identifying the minimum residuals between the observations and several models the same procedure was done for the depth relocation of 138 events associated with the gyeongju earthquake ml 5 8 the largest event in south korea in the last two centuries the geothermal temperature at the focal depth was also estimated for all earthquakes including the gyeongju earthquake cluster and the pohang earthquake ml 5 4 which caused more damage than did the gyeongju earthquake as observed in a large scale averaging of mainland china a 12 km seismicity boundary was suggested due to the frequent seismicity in the upper layer at 12 km depth at the gyeongju earthquake site the geothermal temperature reached 300 c and the occurrence of aftershocks was limited below that depth based on the rigorously estimated depth we separated the scattering attenuation qs 1 by a multiple lapse time window analysis using individual earthquakes and found higher and lower values for events in the upper and lower layers respectively this depth dependent observation suggests differences in heterogeneity between the upper and lower seismogenic layers and supports the hypothesis that the seismicity of a depth dependent seismogenic layer is related to cracks which diminish with depth our results suggest that the upper limit of the focal depth can be predicted from the depth of the seismicity boundary for normal large earthquakes

depth dependence of earthquake frequency magnitude distributions in california implications for rupture initiation statistics of earthquakes in california show linear frequency magnitude relationships in the range of m2 0 to m5 5 for various data sets assuming gutenberg richter distributions there is a systematic decrease in b value with increasing depth of earthquakes we find consistent results for various data sets from northern and southern california that both include and exclude the larger aftershock sequences we suggest that at shallow depth 0 to 6 km conditions with more heterogeneous material properties and lower lithospheric stress prevail rupture initiations are more likely to stop before growing into large earthquakes producing relatively more smaller earthquakes and consequently higher b values these ideas help to explain the depth dependent observations of foreshocks in the western united states the higher occurrence rate of foreshocks preceding shallow earthquakes can be interpreted in terms of rupture initiations that are stopped before growing into the mainshock at greater depth 9 15 km any rupture initiation is more likely to continue growing into a larger event so there are fewer foreshocks if one assumes that frequency magnitude statistics can be used to estimate probabilities of a small rupture initiation growing into a larger earthquake then a small m2 rupture initiation at 9 to 12 km depth is 18 times more likely to grow into a m5 5 or larger event compared to the same small rupture initiation at 0 to 3 km

moho depth seismicity and seismogenic structure in china mainland abstract the study of the crust upper mantle structure based on wide angle seismic profiles performed in china mainland since 1958 has provided tighter constraints on the architecture and deformation of the lithosphere but the link between the seismic velocity structure and the seismogenic layer of the crust is still an open problem in which we are particularly interested starting from the crustal p wave velocity models obtained along numerous seismic profiles we have mapped the moho depth beneath east asia the results demonstrate that the average moho depth is about 35 km in southeast china 38 km in north and northeast china 51 km in northwest china and 65 km in tibet the moho depth varies between 20 and 28 km in the continental margin and sea area most of the earthquakes in china mainland have magnitude lower than 4 0 and generally occur in the uppermost 20 km of the crust and therefore above the moho discontinuity the average focal depth is found at 10 km in southeast china 12 km in north and northeast china 15 km in northwest china and 13 km in the tibetan plateau the ratio of the average focal depth to the moho depth is approximately 0 3 taking the lower bound of the natural seismicity as the depth above which is located 90 of the foci of earthquakes we have found this limit at depths of 21 41 30 and 36 km in each of the mentioned blocks respectively in north and northeast china some earthquakes occur below the moho at 41 km depth on average versus 38 km although the average focal depth observed here is of only 12 km once defined the seismogenic layer as the layer that concentrates 80 of the released seismic energy we have found that the difference in seismic velocity with respect to the other two crustal layers which extend above and below varies from 0 1 to 0 9 km s in east asia this finding enables to discriminate the place with greater or lesser capacity to generate seismic energy a difference in seismic velocity bigger than 0 9 km s would mean that the layer has an earthquake generating capacity lesser than the seismogenic layer as greatly happens in south china and northwest china while a smaller velocity difference would imply that the layer has a comparable seismogenic capacity as happens in tibet

a geochemical model of the peru basin deep sea floor and the response of the system to technical impacts a geochemical model of the peru basin deep sea floor based on an extensive set of field data as well as on numerical simulations is presented the model takes into account the vertical oscillations of the redox zonation that occur in response to both long term glacial interglacial and short term el nino southern oscillation enso time scale variations in the depositional flux of organic matter field evidence of reaction between the pore water no3 and an oxidizable fraction of the structural fe ii in the clay mineral content of the deep sea sediments is provided the conditions of formation and destruction of reactive clay fe ii layers in the sea floor are defined whereby a new paleo redox proxy is established transitional no3 profile shapes are explained by periodic contractions and expansions of the oxic zone ocean bottom respiration on the enso time scale the near surface oscillations of the oxic suboxic boundary constitute a redox pump mechanism of major importance with respect to diagenetic trace metal enrichments and manganese nodule formation which may account for the particularly high nodule growth rates in this ocean basin these conditions are due to the similar depth ranges of both the o2 penetration in the sea floor and the bioturbated high reactivity surface layer hrsl all against the background of enso related large variations in depositional corg flux removal of the hrsl in the course of deep sea mining would result in a massive expansion of the oxic surface layer and thus the shut down of the near surface redox pump for centuries which is demonstrated by numerical modeling

evaluation of the environmental consequences of polymetallic nodule mining based on the results of the tusch research association abstract realising a need for increased general knowledge of the deep sea for environmental impact assessments related to the permanent storage of waste products and mining of metal resources the german bundesministerium fur bildung und forschung has funded targeted research in the deep sea for more than 10 years the research was carried out in an area in the southeast pacific ocean close to and within a german mining claim to match the interests of german deep sea polymetallic nodule mining enterprises and the developing mining code of the preparatory commission for the international seabed authority and the international tribunal for the law of the sea the tusch abbreviation for tiefsee umweltschutz deep sea environmental protection research association with members from various university and governmental institutions was part of the atesepp effects of technical interventions into the ecosystem of the deep sea in the southeast pacific ocean project between 1996 and 1998 geotechnical sedimentological geochemical hydrographic numerical modelling and ecological studies relevant to environmental impact assessment studies of polymetallic nodule mining were undertaken since general oceanographic knowledge of the deep sea is rather limited these various projects also have increased our general understanding of this region this paper describes the potential impacts of mining processes on the seafloor and the near bottom water layer as well as on bathyal and abyssal pelagic zones that will receive processed water sediment and abraded nodule fines tailings discharged after nodule transport to the mining vessel at the ocean surface the tusch research association defined various recommendations to keep the unavoidable impacts to a minimum such as limited penetration of the mining system into the sediment confining intensive resedimentation to the area behind the miner minimising transport of sediment to the ocean surface and discharging all tailings at great depths ideally close to the seafloor the recommendations are not new but the present studies have improved them from precautionary to scientifically based statements

biotic response to explosive volcanism ostracod recovery after ordovician ash falls abstract the impact of two ordovician ash falls of different intensities was studied in order to determine the recovery patterns of benthic ostracods the studied sections are of sandbian age in nw estonia at poosaspea the kinnekulle k bentonite 40 cm derived from a major volcanic event and at ristna the grimstorp bentonite 6 cm in poosaspea important faunal changes are observed the three pre crisis dominant species i e tetrada memorabilis steusloffina sp nov and olbianella braderupensis were not recovered above the bentonite and at least two of them became extinct the post crisis ecosystem shows strong perturbations of diversity and abundance for a long period of time in ristna the impact of the ash fall is less dramatic all of the dominant pre crisis species survived although some changes in abundance and diversity are observed these results show that significant ash falls lead to marked rearrangement of assemblages and extinction of some taxa while less prominent volcanic episodes only result in temporary changes in the assemblage structure in both cases recovery follows several steps post event ecosystem with survival faunas very low abundance low diversity one two species opportunistic taxa e g sigmoopsis rostrata circulinella nuda dominate the assemblage early stages of recolonization with recovery faunas increasing abundance and diversity recolonization by pre event and immigrant species after a short disturbance period return to climax assemblages with specialized taxa high abundance high diversity although assemblages recovered rapidly after the crises the recovery periods still seem much longer than observed in recent foraminiferal assemblages causal links between the volcanic events and subsequent diversifications could not be demonstrated