first report of oribatid mite arthropod borings and coprolites in permian woods from the helan mountains of northern china abstract oribatid mite borings and coprolites are described for the first time from the permian of the northern helan mountains in the inner mongolia nei mongol and ningxia huizu autonomous regions northern china to our knowledge they are the first reported mite borings and coprolites from the cathaysian palaeozoic they occur in petrified gymnospermous woods from five stratigraphic horizons within three formations the cisuralian shanxi guadalupian lower shihhotse and the lopingian sunjiagou formations the borings and galleries are interpreted as trunk tunnels and their secondary branches which are interconnected to form a complicated maze like network two kinds of coprolite can be recognized based on their dimensions shape and density of composition one form is about 20 65 m in diameter and of spheroidal shape whereas the other is about 37 5 70 m 55 145 m and ovoid in shape the smaller form of coprolite is densely compacted and occurs in all five horizons the larger form shows a fairly loosely organized texture and occurs only in the cisuralian age wood this report of palaeozoic wood borers and their coprolites from the cathaysian flora is consistent with previous data on the palaeogeographical distribution and stratigraphic occurrences of plant arthropod interactions

the blanketing effect of sediments in basins formed by extension a numerical model application to the gulf of lion and viking graben abstract a numerical finite difference model is employed to reconstruct the time temperature history of sediments in basins formed by extension in which crustal thinning by stretching as well as the effects associated with sedimentation and compaction are taken into account two extreme cases of basins were investigated to identify the scale of this mechanism the gulf of lion illustrates a case of a young basin in which the average sedimentation rate is high 620 m ma and the viking graben in the north sea offers a case of a basin formed in the triassic but where average sedimentation rate is much less 37 m ma in the former the sediments absorb 30 of the surface heat flow while in the latter the effect is only 10

erosional troughs in deep sea carbonates and their relationship to basement structure abstract a detailed survey of a small area in the eastern equatorial pacific with the marine physical laboratory s deep tow instrument package reveals erosionally excavated troughs in an area of relatively rapid accumulation of carbonate the troughs lie on top of a basement high implying a relationship between the troughs and the basement feature differential accumulation and compaction may explain the origin of the troughs sediment deposited around the basement high preferentially accumulates on gentle slopes and in troughs this results in a thick sequence of sediment on the flanks of the basement high and a thin sequence above on top of the hill unstable sediment masses and differential compaction generate a tensile stress field above the peak of the basement high which causes slumping and faulting the steep slopes generated by faulting and slumping may then serve to intensify tidal currents or act as spillways and locally generate increased turbulence this increased turbulence results in local erosion by dissolution a trough will form above a basement high however only when a combination of 1 basement steepness 2 high sedimentation rate 3 sediment thickness and 4 sediment erodibility are present

permian sedimentary record of the turpan hami basin and adjacent regions northwest china constraints on postamalgamation tectonic evolution the permian marks an important yet poorly understood tectonic transition in the tian shan region of northwestern china between devonian carboniferous continental amalgamation and recurrent mesozoic cenozoic intracontinental orogenic reactivation the turpan hami basin accommodated up to 3000 m of sediment and is ideally positioned to provide constraints on this transition new stratigraphic data and mapping indicate that extension dominated early permian tectonics in the region whereas flexural foreland subsidence controlled late permian basin evolution lower permian strata in the northwestern turpan hami basin consist of coarse grained debris flow and alluvial fan deposits interbedded with mafic to intermediate volcanic sills and flows in contrast lower permian rocks in the north central and northeastern turpan hami basin unconformably overlie a late carboniferous volcanic arc sequence these lower permian strata include possible shallow marine carbonate rocks and thick volcanic and volcaniclastic rocks that are in turn overlain by littoral to profundal lacustrine facies above a regional lower permian upper permian unconformity regional sedimentation patterns record the development of a more integrated sedimentary basin the upper permian is entirely nonmarine and can be correlated east west along the depositional strike of the basin the lower upper permian consists of a broad belt of braided fluvial deposits shed northward these strata are overlain by fluctuating littoral and profundal lacustrine facies and associated fluvial facies the uppermost permian is characterized by shallow lake plain and fluvial environments the early permian association of diffuse volcanism and partitioning of subbasins by normal faulting is consistent with an early phase of lithospheric extension local relationships indicate west east extension in the turpan hami basin along faults oriented normal to late devonian carboniferous collisional sutures within the tian shan the cause of extension in the wake of carboniferous orogenesis remains enigmatic however the temporal and spatial relationships of the two strain regimes suggest that they are genetically related upper permian stratigraphy and unconformities and local late permian triassic contractional deformation record foreland basin development when the turpan hami region became a wedge top basin with respect to the north tian shan fold and thrust belt flexurally induced late permian subsidence is also manifested in the larger junggar basin to the north where 4000 m of strata are preserved in the foredeep region the turpan hami and junggar basins were depositionally connected for much of the late permian when a vast lacustrine system developed across northwestern china this lacustrine paleogeography was only occasionally interrupted possibly by structural damming during uplift of the orogenic wedge

heat flow morphology pore fluids and hydrothermal circulation in a typical mid atlantic ridge flank near oceanographer fracture zone hydrothermal circulation affects heat and mass transfers in the oceanic lithosphere not only at the ridge axis but also on their flanks where the magnitude of this process has been related to sediment blanket and seamounts density this was documented in several areas of the pacific ocean by heat flow measurements and pore water analysis however as the morphology of atlantic and indian ridge flanks is generally rougher than in the pacific these regions of slow and ultra slow accretion may be affected by hydrothermal processes of different regimes we carried out a survey of two regions on the eastern and western flanks of the mid atlantic ridge between oceanographer and hayes fracture zones two hundred and eight new heat flow measurements were obtained along six seismic profiles on 5 to 14 ma old seafloor thirty sediment cores from which porewaters have been extracted have been collected with a kullenberg corer equipped with thermistors thus allowing simultaneous heat flow measurement most heat flow values are lower than those predicted by purely conductive cooling models with some local variations and exceptions heat flow values on the eastern flank of the study area are more variable than on the western flank where they tend to increase westward as the sedimentary cover in the basins becomes thicker and more continuous heat flow is also higher on average on the northern sides of both the western and eastern field regions and includes values close to conductive predictions near the oceanographer fracture zone all the sediment porewaters have a chemical composition similar to that of bottom seawater no anomaly linked to fluid circulation has been detected heat flow values and pore fluid compositions are consistent with fluid circulation in volcanic rocks below the sediment the short distances between seamounts and short fluid pathways explain that fluids flowing in the basaltic aquifer below the sediment have remained cool and unaltered finally relief at small scale is calculated using variogram of bathymetry and compared for different regions affected by hydrothermal circulation

analysis of a conductive heat flow profile in the ecuador fracture zone abstract we report 18 new conductive heat flow measurements collected from a sediment pond located in the inactive part of the ecuador fracture zone in the panama basin the data were collected along an east west transect coincident with a multi channel seismic reflection profile that extends from odp hole 504b to west of the sediment pond conductive models indicate that heat flow should decrease from 400 mw m 2 on the 1 5 ma western plate to 200 mw m 2 on the 6 ma eastern plate however the observed heat flow increases nearly linearly toward the east from approximately 140 mw m 2 to 190 mw m 2 the mean value of 160 mw m 2 represents an average heat flow deficit of 50 which we attribute to lateral advective heat transfer between exposed outcrops on the western and eastern margins of the sediment pond we apply the well mixed aquifer model to explain this eastwardly flow and estimate a volumetric flow rate per unit length in the north south direction of 400 250 m 2 yr 1 through the basement aquifer using a darcy flow model with the mean flow rate we estimate permeabilities of 10 11 and 10 12 m 2 for aquifer thicknesses of 100 and 1000 m respectively the estimated permeabilities are similar to other estimates in young oceanic upper crust and suggest that vigorous convection within the basement significantly modifies the thermal regime of fracture zones additional heat flow data are needed to determine the prevalence and importance of advective heat transfer in fracture zones on a global scale

three dimensional models of hydrothermal circulation through a seamount network on fast spreading crust abstract we present results from three dimensional transient fully coupled simulations of fluid and heat transport on a ridge flank in fast spread ocean crust the simulations quantify relationships between rates of fluid flow the extent of advective heat extraction the geometry of crustal aquifers and outcrops and crustal hydrologic parameters with the goal of simulating conditions similar to those seen on 18 24 m y old seafloor of the cocos plate offshore costa rica extensive surveys of this region documented a 14 500 km2 area of the seafloor with heat flux values that are 10 35 of those predicted from conductive cooling models and identified basement outcrops that serve as pathways for hydrothermal circulation via recharge of bottom water and discharge of cool hydrothermal fluid simulations suggest that in order for rapid hydrothermal circulation to achieve observed seafloor heat flux values upper crustal permeability is likely to be 10 10 to 10 9 m 2 with more simulations matching observations at the upper end of this range these permeabilities are at the upper end of values measured in boreholes elsewhere in the volcanic ocean crust and higher than inferred from three dimensional modeling of another ridge flank field site where there is less fluid flow and lower advective power output the simulations also show that in a region with high crustal permeability and variable sized outcrops hydrothermal outcrop to outcrop circulation is likely to constitute a small fraction of total fluid circulation with most of fluid flow occurring locally through individual outcrops that both recharge and discharge hydrothermal fluid

heat flow variations correlated with buried basement topography on the juan de fuca ridge flank systematic heat flow variations are commonly observed on sedimented flanks of mid ocean ridges these variations have been attributed to the convective circulation of pore fluids within the oceanic crust and have been used to estimate the scale and pattern of this circulation here we report similar systematic variations observed in a detailed heat flow and seismic reflection survey over sediment covered 3 myr old sea floor on the eastern flank of the juan de fuca ridge we find that heat flow peaks are located above buried basement ridges and adjacent to two minor basement outcrops heat flow lows are found where thick sediments fill basement valleys the simple inverse relationship between heat flow and sediment thickness defined by the data indicates that hydrothermal circulation sealed within the permeable portion of the oceanic crust is vigorous enough to maintain approximately isothermal 10 k conditions at the sediment crust interface as no systematic variations in estimated basement temperatures are observed it seems that at this location the heat flow variations result only from sediment thickness variations and do not reflect a particular convective pattern

structure of a corystosperm fossil forest from the late triassic of argentina abstract a palaeoecological study of a standing late triassic forest containing 150 silicified stumps from the rio blanco formation of mendoza province argentina is described a mapped portion of the forest floor provides quantitative data tree density mean separation of trees and basal area per stump which along with taxonomic and sedimentologic information allowed the reconstruction of a plant community that grew along river banks and within proximal floodplain environments analysis of architectural and phenological data from monotypic forest indicates an evergreen community composed of a corystosperm genus with a canopy height of c 13 21 m the corystosperm taxon elchaxylon like rhexoxylon has polyxylic axes with centripetal secondary xylem but does not generate perimedullar bundles and the centrifugal secondary xylem produces an undivided solid pycnoxylic cylinder vegetation analysis shows that the forest has a clustered distribution pattern with high density forest density ranges between 727 and 1504 trees ha but there are first order clusters with elevated density mean nearest neighbour distance of 1 85 m the histogram of diameter classes based on 131 stumps suggests an earlier colonization by few older pioneers the largest ones followed by establishment of a large younger cohort of coeval trees based on 9 series and 139 rings the mean ring width and mean sensitivity ms were 3 47 mm and 0 31 respectively ms values and the presence of false rings indicate the forest community responded to stressed ecosystems the growth rings are very erratic and range from 0 27 to 8 94 mm for fossil growth analysis it was assumed that wider rings would suggest a warmer climate and the considerable range in growth rates would indicate variability in the limiting factors among subsequent cycles

transport equation for suspended sediment based on two fluid model of solid liquid two phase flows most theoretical and numerical studies employ diffusion theory to investigate suspended sediment distributions in fluvial rivers yet diffusion theory based descriptions are strictly valid only in the limit of small particle inertia and low concentrations this paper presents a transport equation for sediment in suspension based on a two fluid model of solid liquid two phase flows the transport equation is derived from the consideration of mass conservation for solid particles the velocity of the solid phase is obtained from an asymptotic solution of the momentum conservation equation for solid phase moreover this transport equation is a typical convection diffusion equation that includes the conventional diffusion equation as a special case when particle inertia is small and concentrations are low retaining the essential features of two fluid models the transport equation is applicable to sediment laden flows with a wide range of particle inertia and sediment concentrations comparisons of the results with available experimental observations are presented and fairly good agreement is obtained doi 10 1061 asce hy 1943 7900 0000331 2011 american society of civil engineers ce database subject headings suspended sediment two phase flow open channels solids flow author keywords suspended sediments sediment concentration two phase flow open channels

automated upscaling of river networks for macroscale hydrological modeling 1 we developed a hierarchical dominant river tracing drt algorithm for automated extraction and spatial upscaling of basin flow directions and river networks using fine scale hydrography inputs e g flow direction river networks and flow accumulation in contrast with previous upscaling methods the drt algorithm utilizes information on global and local drainage patterns from baseline fine scale hydrography to determine upscaled flow directions and other critical variables including upscaled basin area basin shape and river lengths the drt algorithm preserves the original baseline hierarchical drainage structure by tracing each entire flow path from headwater to river mouth at fine scale while prioritizing successively higher order basins and rivers for tracing we applied the algorithm to produce a series of global hydrography data sets from 1 16 to 2 spatial scales in two geographic projections wgs84 and lambert azimuthal equal area the drt results were evaluated against other alternative upscaling methods and hydrography data sets for continental u s and global domains these results show favorable drt upscaling performance in preserving baseline fine scale river network information including 1 improved automated extraction of flow directions and river networks at any spatial scale without the need for manual correction 2 consistency of river network basin shape basin area river length and basin internal drainage structure between upscaled and baseline fine scale hydrography and 3 performance largely independent of spatial scale geographic region and projection the results of this study include an initial set of drt upscaled global hydrography maps derived from hydro1k baseline fine scale hydrography inputs these digital data are available online for public access at ftp ftp ntsg umt edu pub data drt

fluid methane and energy flux in an active margin gas hydrate province offshore costa rica joint analysis of seafloor temperature data borehole temperature measurements and observations that constrain the position of the top and base of the gas hydrate zone ghz at sites on the non accretionary costa rican margin provide quantitative constraints on the flux of energy fluid and methane through the sediments on the overriding plate a comparison of borehole temperature data obtained in the trench at the toe of the deformed sedimentary wedge and at a midslope location indicates that the thermal regimes are perturbed by appreciable advective flux at 1 km oceanward 19 mm yr 1 and 1 4 km landward 5 7 mm yr 1 of the deformation front this observation is loosely consistent with models that predict the most rapid dewatering and highest rates of fluid expulsion within a few kilometers of the deformation front using data that constrain the thickness of the ghz at three sites on the forearc we estimate methane and fluid flux rates through application of a one dimensional analytical model that constrains the nature of the plumbing system for the gas hydrate reservoir our results indicate a two fold decrease in methane flux between a site located 400 m from the toe of the wedge and a site 12 km from the toe an intermediate site located 1 4 km from the toe of the wedge has a thick ghz extends to at least 340 365 m below seafloor that requires a very high methane supply rate 345 mol m 2 kyr 1 for a mass flux of 5 mm yr 1 we conclude that this site has the most two dimensional fluid flux regime with fluids being fed into the zone laterally by conduits and fractures and vertically by expulsion during compaction of underthrusting sediments

flankflux an experiment to study the nature of hydrothermal circulation in young oceanic crust the sediment buried eastern flank of the juan de fuca ridge provides a unique environment for studying the thermal nature and geochemical consequences of hydrothermal circulation in young ocean crust just 18 km east of the spreading axis where the sea floor age is 0 62 ma sediments lap onto the ridge flank and create a sharp boundary between sediment free and sediment covered igneous crust farther east beneath the nearly continuous turbidite sediment cover of cascadia basin the buried basement topography is extremely smooth in some areas and rough in others at a few isolated locations small volcanic edifices penetrate the sediment surface an initial cruise in 1978 and two subsequent cruises in 1988 and 1990 on this sedimented ridge flank have produced extensive single channel seismic coverage detailed heat flow surveys co located with seismic lines and pore fluid geochemical profiles of piston and gravity cores taken over heat flow anomalies complementary multichannel seismic reflection data w

the nicoya convergent margin a region of exceptionally low heat flow over 100 measurements of seafloor heat flow reveal that the accretionary complex adjacent to the nicoya peninsula is characterized by remarkably low heat flow values over the accretionary prism average 28 mw m and values in the trench and the ocean crust seaward of the trench average 14 mw m we attribute the low heat flow to effective hydrothermal cooling of the upper crust on the subducting plate and suggest that extensional faults created by flexure of the lithosphere enhance hydrothermal circulation thermal models show that subduction of low temperature crust combined with significant frictional heating at the decollement can explain the low and uniform heat flow disparity between heat flow values observed on the lower trench slope with model results suggests upward advection of heat by porewater flux through broadly distributed conduits

pore fluid advection and reaction in sediments of the eastern flank juan de fuca ridge 48 n abstract pore water data collected during ocean drilling program odp leg 168 provide an opportunity to study advection and reaction in hemipelagic sediments in an off axis hydrothermal setting we have modelled the pore water so42 profiles to obtain estimates of vertical advective darcy velocities strong downwelling at rates of 0 3 0 9 mm a 1 occurs at a site 4 km from the boundary between sediment free and sediment covered ridge downwelling velocities weaken away from the boundary twenty kilometres to the east strong upwelling at 2 mm a 1 is indicated at two sites 1030 and 1031 drilled above a basement high further eastwards where sediment thicknesses are in excess of 200 m vertical advective pore fluid flow through the sediment column is weak confining flow to the basement aquifer extension of the so42 model to pore fluid alkalinity mg2 and ca2 profiles enables the effects of reactions within the sediment column to be examined sulfate reduction leads to the production of alkalinity but the alk so42 ratios are less than the theoretical ratio of 2 at all the sites studied the discrepancy is largely explained by the precipitation of calcium carbonate and by the diagenetic reactivity of magnesium in the pore fluids alkalinity results are consistent with both sources and sinks for mg2 within the sediment column dependent on the direction of pore fluid advection

dilemma of late palaeozoic mixed floras in gondwana abstract during carboniferous and permian periods the plant fossil assemblages of northern and southern hemispheres were distributed in four floral provinces and each flora had its own characteristics pteridosperms were dominant in the euramerian floras of europe and america cordaitales and equisetales along with angaridium angaropteris represent the angara flora of russia russian federation and far east provinces gigantopteris flora characterizes the cathaysian province of china japan and south east asian countries and glossopteris flora are present in southern hemispheric land masses of gondwana which includes india australia africa south america and antarctica well defined floral provinces quite often show the intermixing of different floristic elements exemplifying the presence of mixed floras the occurrence of mixed floras suggests that they have two modes of distribution one distribution pattern shows mixed floras along the marginal basins of the tethyan region during the middle and late permian another pattern is evident in the gondwana floras where glossopteris floras contain a number of extra gondwanic elements likewise some euramerian cathaysian and angaran floras show the possible presence of glossopterid related elements having comparative morphological features as part of the flora mixed floral elements of northern and southern floras have been examined in detail and it is suggested that in all probability the so called elements of the mixed floras had their ancestry or affiliation with carboniferous floras and during the early permian they duped due to severity of climatic conditions but developed again during late permian when climate became more hospitable for their development the cathaysian and euramerian forms discovered with gondwanan forms in the mixed floras of tethyan region i e hazro saudi arabia new guinea oman jordan kashmir central tibet and southern tibet belong to middle and upper permian sequences and during this time the warm humid and temperate climate helped to revive the northern hemispheric forms which had their endurance in a relatively similar climate of the late carboniferous the morphological conservatism flexibility radiation relationship and analogous features of mixed floral elements have been examined and attempts are made to sort out their disputed presence in different floral provinces

zalesskioxylon xiaheyanense sp nov a gymnospermous wood of the stephanian late pennsylvanian from ningxia northwestern china abstract a new late pennsylvanian species of gymnospermous fossil wood zalesskioxylon xiaheyanense sp nov is described from the lower taiyuan formation stephanian b c near the village of xiaheyan ningxia hui autonomous region northwestern china the specimen consists only of silicified secondary xylem the tracheids are pycnoxylic with 2 3 seriate bordered pits arranged in subcircular or hexagonal alternate araucaroid pattern the pores of the pits are small linear and regularly tilted xylem rays are homogeneous uniseriate 1 25 cells high cross fields are filled with numerous mixed simple pits of various sizes growth rings axial parenchymatous elements and resin canals are absent the geographic distribution of zalesskioxylon woods is reviewed zalesskioxylon xiaheyanense sp nov grew at low latitudes and because of the lack of growth rings probably lived under relatively uniform climatic conditions our new species supplements the poorly known distribution of carboniferous wood in china

heat and fluid flux through sediment on the western flank of the mid atlantic ridge a hydrogeological study of north pond a comprehensive survey of heat flow sediment thickness and bathymetry in a large intermontane sediment pond on the western flank of the mid atlantic ridge north pond shows that only 20 to 25 of the heat escaping from the lithosphere flows through the sediments in the pond even though they completely cover a 70 km2 area of the seafloor three in situ pore pressure gradient measurements gave values that were negative relative to hydrostatic indicating that there is drawdown of water through the sediment at rates of 1 to 5 mm yr north pond is a recharge zone for hydrothermal circulation that is probably driven by lateral pressure gradients produced by topographic relief

provenance stratigraphic architecture and hydrogeologic influence of turbidites on the mid ocean ridge flank of northwestern cascadia basin pacific ocean abstract the northwestern edge of cascadia basin north pacific ocean is unusual because late pliocene to holocene turbidites lap onto juvenile oceanic crust of the juan de fuca ridge subsidence of the ridge flank combines with irregular westward progradation of the turbidite facies to create a stratigraphic section that coarsens and thickens upward the sand provenance is mixed individual turbidity currents have funneled into the area through several shelf slope and abyssal floor conduits including vancouver valley juan de fuca channel barkley canyon and nitinat canyon local bathymetric blockage deflection and reflection of flow paths by basement relief remobilization by intrabasinal submarine slides and debris flows episodic channel switching and sporadic overbank flooding have combined to produce erratic recurrence intervals for the turbidity currents only the tallest basement highs have remained isolated from turbidite deposition during the last 500 000 years spatial and temporal differences in sediment accumulation are important because they modulate the three dimensional responses of compaction and consolidation those changes in physical properties govern where and when hydraulic communication with the underlying basement shuts down the basal hemipelagic layer of cascadia basin transforms to an effective hydrologic seal seepage rates 1 mm yr once the sediment basalt interface is buried by 100 150 m of strata rapid accumulation of turbidites therefore accelerates the hydrogeologic conversion of igneous basement from open to sealed

evolution of heat flow hydrothermal circulation and permeability on the young southern flank of the costa rica rift we analyze 67 new conductive heat flow measurements on the southern flank of the costa rica rift crr heat flow measurements cover five sites ranging in oceanic crustal age between approximately 1 6 and 5 7 ma and are co located with a high resolution multi channel seismic line that extends from slightly north of the first heat flow site 1 6 ma to beyond odp hole 504b in 6 9 ma crust for the five heat flow sites the mean observed conductive heat flow is 85 mwm 2 this value is approximately 30 per cent of the mean lithospheric heat flux expected from a half space conductive cooling model indicating that hydrothermal processes account for about 70 per cent of the heat loss the advective heat loss fraction varies from site to site and is explained by a combination of outcrop to outcrop circulation through exposed basement outcrops and discharge through faults super critical convection in layer 2a extrusives occurs between 1 6 and 3 5 ma and flow through a thinly sedimented basement high occurs at 4 6 ma advective heat loss diminishes rapidly between 4 5 and 5 7 ma which contrasts with plate cooling reference models that predict a significant deficit in conductive heat flow up to ages 65 10 ma at 5 7 ma the crr topography is buried under sediment with an average thickness 150 m and hydrothermal circulation in the basement becomes sub critical or perhaps marginally critical the absence of significant advective heat loss at 5 7 ma at the crr is thus a function of both burial of basement exposure under the sediment load and a reduction in basement permeability that possibly occurs as result of mineral precipitation and original permeability at the time of formation permeability is a non monotonic function of age along the southern flank of the crr in general agreement with seismic velocity tomography interpretations that reflect variations in the degree of ridge axis magma supply and tectonic extension hydrothermal circulation in the young oceanic crust at southern flank of crr is affected by the interplay and complex interconnectedness of variations in permeability sediment thickness topographical structure and tectonic and magmatic activities with age

the marine permian of east and northeast asia an overview of biostratigraphy palaeobiogeography and palaeogeographical implications abstract the permian marine biostratigraphy faunal successions and mutual correlations where possible throughout east and northeast asia are synthesized region by region based on both published literature and the author s field observations in certain parts of the region the correlation of the permian marine successions of ne asia with the permian international timescale and in particular with gondwanan permian marine sequences remains a major challenge due to profound marine provincialism during the permian however by employing biogeographically mixed faunas from east asia se mongolia ne china south primorye of far east russia and the south kitakami terrane of japan as biostratigraphic gateways coupled with some bipolarly and bi temperately shared permian marine taxa and faunas it has been possible to correlate with reasonable confidence some of the high palaeolatitude permian marine rock units and faunas of ne asia with those of the tethyan region and gondwana palaeobiogeographically the permian marine faunas of east and ne asia are assigned to four major provinces verkolyman sino mongolian japanese cathaysian and panthalassan provinces on the basis of their palaeogeographical distribution patterns and characteristics of faunal assemblages of these the sino mongolian japanese province has considerable significance for regional palaeogeographical plate tectonic and palaeoceanographical reconstructions during the middle permian because of its conspicuously mixed cool and warm water marine biota the origin of this biogeographically mixed marine biota is interpreted to have resulted from a combination of some key factors including the increased tectonic convergence between the bureya jiamusi terrane and the sino korean platform during the permian and the intermingling of both warm and cold water ocean currents off the eastern coastal areas of the bureya jiamusi terrane and the sino korean platform during the middle permian

evidence for a western extension of the angaran phytogeographic province in the early permian abstract a newly described early permian fossil plant assemblage in the mt dall conglomerate in the farewell terrane alaska range usa is analyzed from a paleobiogeographic perspective these data constitute the youngest paleontological dataset yet discovered in this terrane represent the terrane s only predominantly terrestrial fossil assemblage and are the only plant macrofossil remains of early permian age within a 1500 km radius today a suite of multivariate statistical analyses comparing the mt dall paleoflora to similar age asselian artinskian collections from the angaran euramerican and cathaysian permian phytogeographic provinces reveals that the mt dall paleoflora has a paleobiogeographic affinity with sub angaran plant fossil assemblages collected from mongolia and the primorye region of southeastern russia the paleoflora has dual importance in the construction and testing of hypotheses for which there are geographically and temporally few controls first these data may be used in association with other faunal and floral remains to test models of the assembly of alaska which seek in part an understanding of the paleogeographic and lithological origins of accreted terranes that the mt dall paleoflora indicates mixed eurasia north america paleobiogeographic affinity among individual taxa and plots in multivariate space with mid latitude assemblages on northern pangea may suggest deposition in that latitudinal belt second contrary to the well sampled fossil plant bearing permo carboniferous of the paleotropics and the northeastern temperate pangean regions angaraland terrestrial biome structure and vegetation type of northwestern pangea are poorly known this lack of understanding is due to the paucity of paleofloral collections from this region in this time period and the paleogeographic uncertainty of their position along the ancient active margin of laurentia the mt dall paleoflora s phytogeographic affinity to paleobotanical collections from the northeastern pangea therefore suggests that the angaran province extended meridionally westward in the early permian into what is now northern north america

late paleozoic macrofloral assemblages from weibei coalfield with reference to vegetational change through the late paleozoic ice age in the north china block abstract based on investigations of seven stratigraphic sections in the weibei coalfield a typical coal basin in the north china block the succession of late paleozoic plant macrofossil assemblages from the benxi or penchi in old spelling taiyuan shanxi lower shihhotse and upper shihhotse formations were redefined these zones are the paripteris spp linopteris spp conchophyllum richthofenii assemblage benxi fm neuropteris pseudovata lepidodendron posthumii assemblage taiyuan and lower shanxi fms emplectopteridium alatum emplectopteris triangularis cathaysiopteris whitei assemblage upper shanxi and lower shihhotse fms gigantonoclea lagrelii fascipteris hallei lobatannularia heianensis assemblage upper shihhotse fm as a result of this biostratigraphic reanalysis it has become clear that biostratigraphic boundaries do not exactly correlate to lithostratigraphic boundaries as has been thought the biostratigraphy of the terrestrial deposits in the north china block were correlated to the iugs global chronostratigraphy the more precise chronostratigraphic constraints that were obtained as a result of this study make it possible to more precisely correlate the vegetational successions to the concurrent waxing and waning of the late paleozoic ice sheets

physical properties of young 3 5 ma oceanic crust from the eastern flank of the juan de fuca ridge comparison of wireline and core measurements with global data 1 we compile and compare petrophysical data from the upper oceanic crust in hole u1301b on 3 5 ma seafloor on the eastern flank of the juan de fuca ridge measurements include core scale lab based and in situ wireline measurements of formation porosity electrical resistivity bulk density p wave velocity and gamma ray emission a comparison between hole u1301b data and those from other sites ranging in age from 5 9 to 167 ma demonstrates some important differences hole u1301b samples tend to have lower bulk density values for a given porosity than do other young crustal sites hole u1301b samples also tend to have higher values of formation factor the ratio of fluid conductivity to saturated rock conductivity which may indicate development of tortuous microporosity that is more consistent with samples from older seafloor evaluation of global trends of petrophysical properties versus crustal age indicates that hole u1301b in situ data is consistent with global trends but core scale p wave velocity and bulk density values fall below global trend values predicted for young crust this last observation is likely related to basement topography and the regional exposure until relatively recently of basement outcrops around site u1301 until most of the exposed basement in this area was buried hydrothermal circulation extracted much of the lithospheric heat kept basement fluid temperatures low and limited the rate and extent of alteration a subsequent period of higher temperature fluid circulation with more restricted and less oxidative conditions resulted in enhanced and pervasive alteration of crustal rocks

the galapagos spreading center at 86 w a detailed geothermal field study appendix is available with entire article on microfiche orderfrom american geophysical union 2000 florida avenue n w washington d c 20009 document j80 013 01 00 payment mustaccompany order we report here measurements of the heat flow field of the galapagos spreading center on crust of age less than 1 0 m y the 443 measurements in an area of about 570 km2 reveal the general planform of the geothermal flux and permit the first truly areal estimate of the near axis conductive heat flux the intrusion process and associated hydrothermal circulation dominate the surface heat flow pattern with circulation apparently continuing beyond the limits of our survey the areal average of the conductive heat flux is 7 1 0 8 hfu 295 33 mw m2 about one third the heat flux predicted by plate models the remaining heat is apparently removed by venting of hydrothermal waters at the spreading axis and through basalt outcrops and hydrothermal mounds off axis the pattern of surface heat flux is lineated parallel to the axis and the strongly lineated topography sharp lateral gradients in the heat flow greater than 10 hfu km near escarpments and commonly expressed as high heat flow at the tops of the scarps and lower heat flow in the valleys may indicate a local concentration of the circulation by surface fault systems and or variable sediment thickness

thermal models of the middle america trench at the nicoya peninsula costa rica 1 we present thermal models of the 24 ma cocos plate subducting under the caribbean plate at the nicoya peninsula costa rica our modeling incorporates the effect of hydrothermal cooling of the seafloor and the absence of an accretionary prism initial geotherms of the incoming plate representing different effective cooling depths of hydrothermal circulation affect the thermal structure and temperatures along the main subduction thrust excluding the deforming prism results in a higher heat flow immediately landward of the trench than previous models and therefore significant frictional heating is not required conductive plate cooling over predicts heat flow across the frontal forearc with no or very low frictional heating models with hydrothermal cooling to depths of 2 km under predicts the heat flow comparisons with recently determined hypocenter locations indicate that the updip limit of seismicity is consistent with temperatures between 100 150 c but there are large along strike variations in both the seismicity and thermal regime

hydrothermal pits in the biogenic sediments of the equatorial pacific ocean 1 a recent expedition to the equatorial pacific surveyed over 60 000 km2 of seafloor using swath map imaging and high resolution seismic profiling this survey revealed the common occurrence of large pits in the biogenic sediments that are usually associated with basement highs the pits range in size up to a few kilometers across and are on the order of 50 m 100 m deep they were found on seafloor ranging in age from 15 ma to 55 ma with overlying sediment cover up to 500 m thick we link their origin with hydrothermal discharge through conduits created by differential compaction and fracturing over basement highs and by basement faulting that penetrates the overlying sediments although carbonate dissolution is likely to be associated with the formation of the pits their occurrence shows no consistent relationship with the present calcite compensation depth ccd

extent of the microbial biosphere in the oceanic crust we estimate the depth of the 120 c isotherm by constructing crustal thermal gradients based on theoretical and observed conductive heat flux as a function of lithospheric age we chose the 120 c isotherm because it is close to the upper limit for prokaryotic life and therefore the isotherm approximates the maximum depth at which life can persist in the ocean crust the depth of the potential microbial biosphere increases with lithospheric age from approximately 0 5 to 1 km for 1 ma lithosphere to as much as 5 km at a subduction age of 180 ma we use global models of oceanic plate creation to estimate the volume of crust occupied by the biosphere today and throughout geologic time presently the volume of the ocean crust that is capable of containing life is similar to the volume of the oceans 1018 m3 depending on the model used for the growth of continental crust the volume of rock available to house the subsurface biosphere may have remained constant or doubled since the archean although the thermal models presented here provide estimates for the potential depth and volume of rock in which microbes may live the biomass in this volume is not well constrained using a previously published model the prokaryotic biomass in the igneous ocean crust is estimated to exceed that in all aquatic and soil environments and is similar to that in the continental subsurface and in marine sediment most of the crustal biomass beneath the sediments is likely contained within the extrusive layer and this has probably been the case since microbes first colonized the oceanic crust in the archean

distribution and characteristics of mixed transitional mid permian late artinskian ufimian marine faunas in asia and their palaeogeographical implications abstract the permian marine biogeography of the asian region is characterised by the development of three broad realms boreal tethyan and gondwanan in the early early permian asselian to early artinskian there seems to have existed sharp biogeographical boundaries with no transitional zones between the realms presumably due to the effect of gondwanan glaciation and sharp climatic zonation the mid permian late artinskian to ufimian of the asian region is distinguished by the rise of two broad transitional zones in which mixed marine faunas flourished the northern transitional zone north and northeast china sikhote alin central and northeast japan is characterised by an admixture of both warm water cathaysian and cold temperate boreal genera the southern transitional zone arabian peninsula iran afghanistan the karakorum southeast and central pamir salt range central and northwest tibet shan thai terrane timor and western irian jaya on the other hand is distinguished by incorporating faunal elements of both gondwanan and cathaysian origin the mixed faunas of both transitional zones share several antitropically distributed genera e g monodiexodina lytvolasma and spiriferella and are succeeded by palaeotropical tethyan faunas of late permian age it has been postulated that the mixed mid permian fauna of the northern transitional zone was probably formed in an epicontinental sea which was connected to both the asian tethys and the arctic which facilitated the migration of cathaysian and boreal forms into the epicontinental sea and subsequent faunal mixing the formation of the mixed faunas of the southern transitional zone on the other hand is probably related to the breaking off of the cimmerian blocks from northern gondwana and subsequent drifting into a lower latitudinal zone with geographical proximity to both gondwana and cathaysia during the mid permian

drilling to gabbro in intact ocean crust sampling an intact sequence of oceanic crust through lavas dikes and gabbros is necessary to advance the understanding of the formation and evolution of crust formed at mid ocean ridges but it has been an elusive goal of scientific ocean drilling for decades recent drilling in the eastern pacific ocean in hole 1256d reached gabbro within seismic layer 2 1157 meters into crust formed at a superfast spreading rate the gabbros are the crystallized melt lenses that formed beneath a mid ocean ridge the depth at which gabbro was reached confirms predictions extrapolated from seismic experiments at modern mid ocean ridges melt lenses occur at shallower depths at faster spreading rates the gabbros intrude metamorphosed sheeted dikes and have compositions similar to the overlying lavas precluding formation of the cumulate lower oceanic crust from melt lenses so far penetrated by hole 1256d

fluid sources and pathways of the costa rica erosional convergent margin 1 the margins community has only relatively recently begun to examine the tectonics and associated hydrologic systems of erosive convergent margins which are substantially different as compared with accretionary margins in this respect the type example erosive margin is the costa rica system which has been the subject of numerous recent large scale investigations here pore fluids expelled at the wedge toe and at midslope mounds and mud volcanoes have been interpreted to have a common deep source of dehydrating clays analogous to that at accretionary margins however we report unusually high b li molar ratios in pore fluids from a recent mudflow on mound 11 offshore costa rica which together with unusually low b li ratios previously reported at the wedge toe reveal that alternative fluid sources and or processes must be operating at the costa rica margin as serpentine formation is the only subduction zone process that significantly fractionates b and li we propose that the difference in fluid chemical composition is the result of erosion of upper plate serpentinites ongoing serpentinization and serpentine mineral phase transitions in the subduction channel these processes provide both a source of fluids and fluid pathways that lead to the unique geochemical signature observed at this erosional margin this conclusion is compatible with and supported by the current view of the tectonics geology and hydrogeology of the costa rica margin and the similarity of the pore fluid to that of two other convergent margins both with known fluid serpentinite interactions

chemical plumes from low temperature hydrothermal venting on the eastern flank of the juan de fuca ridge we report evidence for chemical anomalies in the water column from low temperature ridge flank hydrothermal venting during cruises in 1992 and 1994 samples were taken from the water column for trace metals nutrients dissolved gases and particles near each of three basaltic outcrops overlying 3 5 m y old crust on the eastern flank of the juan de fuca ridge in cascadia basin the water column above one of these outcrops baby bare which rises about 70 m above a flat turbidite plain was the most thoroughly sampled thermal chemical mn fe 3he ch4 and o2 and particulate anomalies in the water column confirm the existence of 1 early diagenesis of organic matter in seafloor sediment which produces a flux of dissolved metals and nutrients to bottom seawater 2 hydrothermal emissions which are both focused spring like and diffuse and 3 resuspension of sediment by turbulent flow of tidal currents about a topographical high on the basis of data from the water column and thermal and chemical pore water data from 46 piston and gravity sediment cores near and on baby bare flankflux 90 and 92 we constrain the composition of seawater in basement and thus the composition of spring like water given this composition no measurable dissolved silica or phosphate hydrothermal anomalies are expected in the water column

a dynamic approach to sediment laden turbulent flows an approach that studies the effects of the dynamic coupling between turbulent flow and sediment in suspension on the mean velocity and the sediment concentration profiles of sediment laden open channel flows is systematically developed the analysis is based on the boussinesq approximation to the governing equations that treats the mixture of the liquid and sediment as a single fluid with changing density over the flow depth as a result it permits the direct systematic comparison between the turbulent flow of clear water and that with suspended sediment by further employing the mixing length approach for the related turbulent closure problem the coupling effects on mean velocity and concentration profiles are evaluated and the resulting distributions are compared with available experimental data the derived mean velocity distribution contains profiles of existing models as special cases and thus unifies the results of existing major models conceptually and quantitatively moreover the analysis clearly demonstrates the importance of the coupling effect on the suspended sediment concentration profile and consequently a more generalized formula of concentration profile is obtained although the mean velocity and concentration profiles are the main concern of this paper the approach establishes a framework for further study of the effects of the dynamic interaction on other physical quantities

thermal effects of marine sedimentation in hydrothermally active areas summary a hydrothermally active ocean basin vigorous hydrothermal circulation in highly permeable basement rocks maintains a nearly constant temperature at the base of the overlying accumulating sediment section to investigate the thermal effects of sedimentation in such geological settings we have developed a simple onedimensional finite element model and applied it to cases in the northeast pacific the model accounts for differential motion of fluids and sediment grains during compaction and can be used with any porosity depth function results demonstrate clearly that the constant basal temperature of an accumulating sediment section maintained by convective heat transfer in the basement causes the section to remain thermally near steady state for even very high rates of accumulation particularly when compared to conditions estimated for a section where heat is transported in the basement by conduction a 10 kyr period of thermal recovery due to the highly diminished sediment supply during the post pleistocene further reduces the thermal effects of sedimentation by a significant amount only in rare cases where rates of accumulation exceed 10 mm yr l and sediment thicknesses exceed 1 km are the sea floor heat flow and temperatures at depth diminished significantly an example is found in middle valley of the juan de fuca ridge in a part of which over 2 km of sediment has accumulated in the past 200 kyr even in this extreme case the heat flow is estimated to be lower than that of the steady state by about only 15 per cent while rates of accumulation are also high in other parts of middle valley and in many other hydrothermally active areas such as guayamas basin escanaba trough and the eastern flank of the juan de fuca ridge these rates and the accumulated sediment thicknesses are found to be insufficient to cause appreciable thermal anomalies

fluvial sedimentology of an upper jurassic petrified forest assemblage shishu formation junggar basin xinjiang china abstract a remarkable petrified forest assemblage is preserved in the upper jurassic shishu formation of the northeastern junggar basin xinjiang uygur autonomous region china discovered in 1965 the silicified wood occurs as two horizons of fallen logs and a group of rooted stumps in growth position coincident with the upper log horizon the largest log is 25 3 m in length the largest stump is 2 5 m in diameter the enclosing strata are fluvial silts sands and gravels wood characteristics indicate that climate was mild with seasonal variation in precipitation temperature or light paleohydrology and stratigraphy of the shishu formation suggest a wide shallow low sinuosity mixed load meandering stream regime that drained southward into the junggar basin during the late jurassic

origin of elevated sediment permeability in a hydrothermal seepage zone eastern flank of the juan de fuca ridge and implications for transport of fluid and heat elevated sediment porosity and permeability may help to focus upward fluid seepage observed over a buried basement high on the eastern flank of the juan de fuca ridge consolidation and permeability tests of fine grained hemipelagic and turbidite sediments from the seepage site and from nearby sites that are not experiencing seepage indicate that sediments at the seepage site primarily hemipelagic have 10 15 higher porosity and 10 higher permeability at a given depth and 10 100 lower hydraulic impedance for the 40 m thick sediment column the correlation of consolidation and permeability properties with sediment type rather than location indicates that the relatively high porosity and permeability do not result from fluid flow but are intrinsic properties of the hemipelagic sediment on the basis of measured sediment properties fluid pressure at the top of basement is 5 kpa greater than hydrostatic a simple circulation model that incorporates this estimate and proximity to the nearest basement outcrops 4 20 km suggests that local basement permeability is between 3 10 13 and 3 10 11 m2 within the range measured in nearby boreholes the measured sediment properties combined with other published data indicate that a few tens of meters of fine grained terrigenous hemipelagic or calcareous marine sediment effectively seal the basement aquifer whereas much thicker siliceous or pelagic sediment may support thermally and chemically significant fluid flow the large contrast in hydraulic impedance among sediment columns of different types could cause regional variation in the evolution of ridge flank hydrothermal systems and in the contribution of seepage to ridge flank fluxes

a depth averaged two dimensional model for flow sediment transport and bed topography in curved channels with riparian vegetation 1 a depth averaged two dimensional numerical model has been developed to simulate flow sediment transport and bed topography in river channels with emergent and submerged rigid vegetation and large woody debris the effect of helical flow in bends is considered by adopting an algebraic model for the dispersion terms in the depth averaged two dimensional momentum and suspended sediment transport equations and by adjusting the bed load transport angle the governing equations are discretized using the finite volume method on a nonstaggered curvilinear grid model validity has been assessed using experimental data observed in both fixed and movable bed laboratory flumes and a natural channel with submerged and emergent rigid vegetation in general mean flow velocities sediment transport rates and changes in bed topography predicted by the model agree well with the experimental observations for laboratory and field cases root mean square relative errors for velocities were less than about 13 and 44 respectively and about 50 of errors for changes in bed topography were less than 14 5 and 8 of the flow depth respectively

influence of sedimentation local and regional hydrothermal circulation and thermal rebound on measurements of seafloor heat flux 1 we quantify the influence of environmental processes on measurements of seafloor heat flux with a new one dimensional thermal model that includes time varying sedimentation and boundary conditions represents several scales of hydrothermal and transient conductive processes within basement and allows fluid seepage through accumulating sediments variations in basement thermal conductivity the extent of hydrothermal mixing in upper basement and fluid seepage through sediments each influence seafloor heat flux by 2 8 conductive thermal rebound following the cessation of advective heat loss from the crust may lower seafloor heat flux values by 5 10 even after several to several tens of million years the new models indicate that thermal rebound takes much longer than suggested by earlier analytical calculations mainly because earlier models did not account for the heat capacitance of the conductive lithosphere application of the new model to 3 5 3 6 ma seafloor on the eastern flank of the juan de fuca ridge suggests that anomalously low heat flux in this area is best explained by incomplete conductive thermal rebound in the last 100 200 ka following the burial of numerous basement outcrops application of the new model to the eastern flank of the east pacific rise and extrapolation out to the age of some of the oldest remaining seafloor indicate that sedimentation corrections may be important even where accumulation rates are typical of global values model results also suggest that conductive thermal rebound through thick sediments may bias measurements made on moderate to old seafloor even where there is little evidence at present for ridge flank hydrothermal circulation

along strike variability in the seismogenic zone below nicoya peninsula costa rica 1 at the subduction zone in northwestern costa rica the seismogenic zone lies directly beneath the nicoya peninsula allowing for near source seismic studies of earthquake activity we located 650 earthquakes along the seismogenic plate interface using a dense seismic network in the vicinity of the nicoya peninsula using these data we constrained the updip limit of the seismogenic zone there and found a transition in depth 10 km in the south to 20 km in the north that occurs where the subducting oceanic crust changes from warmer cocos nazca spreading center cns origin to colder east pacific rise epr origin we argue that the temperature of the incoming oceanic crust controls the seismogenic updip limit beneath nicoya costa rica subducting colder oceanic crust deepens the seismogenic updip limit

fossil wood from the middle cretaceous moreno hill formation unique expressions of wood mineralization and implications for the processes of wood preservation abstract the cretaceous turonian moreno hill formation of west central new mexico provides an opportune isotaphonomic setting to study wood preservation because both carbonized and mineralized wood are commonly found within the same sediments and often within individual specimens petrographic reflectance maceral and chemical analyses were used to compare and characterize mineralized and carbonized wood from the study site to investigate biases which influence mode of preservation coal in the form of coal inclusions is the most common form of fossil wood and mineralized wood is also widespread in the formation two striking specimens of in situ coalified stumps are particularly informative because each includes a mineralized ring that appears to represent the former location of sapwood most of the mineralized samples are primarily composed of quartz but a few specimens are predominantly mineralized with apatite calcite is present in charcoal samples where it permineralized but never replaced organic carbon this study points to two key factors that influence mineralization wood permeability and the chemical alteration of the wood prior to incorporation into the sediment the patterns of mineralization are consistent with hypothesized microbial involvement in the mineralization process the coexistence of coal and mineralized tissues in some samples suggests that the processes of silicification and phosphatization co occurred with coalification and that these processes are competitive within individual pieces of wood as such various stages of wood degradation have been preserved in mineralized samples from the moreno hill formation the study suggests that coal inclusions and mineralized wood coal associations may also be common in other ancient sediments even though weathering may obscure their presence such information is important for paleoecological and paleoenvironmental studies which utilize the occurrence of fossil wood to help reconstruct floral composition or climatic conditions

xenoxylon junggarensis sp nov a new gymnospermous fossil wood from the norian triassic huangshanjie formation in northwestern china and its palaeoclimatic implications abstract a permineralized gymnospermous wood xenoxylon junggarensis sp nov is described from the norian upper triassic huangshanjie formation in dalongkou section jimsar county xinjiang uygur autonomous region northwestern china the pycnoxylic wood consists of thick walled tracheids and thin walled rays it is characterized by commonly rounded to very compressed contiguous or sometimes separated uniseriate occasionally rounded and alternate biseriate radial pits and one or two simple large pits in each cross field the fossil wood genus xenoxylon gothan is known to be an indicator of cooler and or wetter climates in the boreal hemisphere during the mesozoic its occurrence in the huangshanjie formation from junggar basin together with the palaeobotanical and palynological data indicates that a wet and temperate climate prevailed in the northern xinjiang during the norian interval the mean sensitivity of analysis of 22 growth rings is 0 36 suggesting a seasonal response to climate growth rings in the fossil woods are large 2 3 mm average with a maximum of 5 44 mm representing either a longer growing season or more favorable conditions for growth including readily available water and higher temperature based on a considerable amount of earlywood and a small percentage of latewood and some indirect evidence it is hypothesized that growth of x junggarensis in the high latitude junggar basin in the late triassic was limited by light levels

quantitative estimate of heat flow from a mid ocean ridge axial valley raven field juan de fuca ridge observations and inferences a systematic heat flow survey using thermal blankets within the endeavour segment of the juan de fuca ridge axial valley provides quantitative estimates of the magnitude and distribution of conductive heat flow at a mid ocean ridge with the goal of testing current models of hydrothermal circulation present within newly formed oceanic crust thermal blankets were deployed covering an area of 700 by 450 m in the raven hydrothermal vent field area located 400 m north of the main endeavour hydrothermal field a total of 176 successful blanket deployment sites measured heat flow values that ranged from 0 to 31 w m 2 approximately 53 of the sites recorded values lower than 100 mw m 2 suggesting large areas of seawater recharge and advective extraction of lithospheric heat high heat flow values were concentrated around relatively small hot spots integration of heat flow values over the raven survey area gives an estimate of conductive heat output of 0 3 mw an average of 0 95 w m 2 over the survey area fluid circulation cell dimensions and scaling equations allow calculation of a rayleigh number of approximately 700 in layer 2a the close proximity of high and low heat flow areas coupled with previous estimates of surficial seafloor permeability argues for the presence of small scale hydrothermal fluid circulation cells within the high porosity uppermost crustal layer of the axial seafloor

near axis heat flow measurements on the northern juan de fuca ridge implications for fluid circulation in oceanic crust present models of the cooling of oceanic crust suggest that convection of hydrothermal fluid is a major component of the process in axial regions abundant faults and open fissures are associated with the venting of high temperature hydrothermal fluid in older crust where the insulating sediment cover is thick previous studies have shown that basement topography is the dominant forcing factor for within crust fluid circulation in the intermediate region where young crust is lightly sedimented heat flow data are difficult to obtain with traditional techniques to determine whether topography or permeability is the dominant process controlling fluid circulation in the near axis region we conducted a profile of heat flow measurements using the submersible alvin on the endeavour segment of the juan de fuca ridge our data indicate that topographic forcing is responsible for the long wavelength variations with high heat flow at the ridge summits and low values in the inter ridge valleys the locations of the extreme values of heat flow taken within the context of subsurface faulting are consistent with a model where a ridge valley topographic pair comprises a single circulation cell this model predicts that the source area for the high temperature axial vents may be in the flanking inter ridge valleys

hydrothermal circulation juan de fuca ridge eastern flank factors controlling basement water composition pore water has been analyzed from sediment cores taken from three areas on the eastern flank of the juan de fuca ridge as part of flankflux 90 a study of hydrothermal circulation through mid ocean ridge flanks seismic reflection and heat flow surveys davis et al 1992a indicate that the three areas differ in sediment thickness basement topography abundance of outcrops basement temperature and fraction of heat lost by advection versus conduction area 1 is on 0 6 ma crust with nearly continuous basement outcrop area 2 is on 1 3 ma crust over the first buried ridge parallel to the present ridge axis and area 3 is on 3 5 3 8 ma crust over two axis parallel buried ridges that penetrate the sediment cover in three locations each area includes a hydrothermal system in which seawater flows into basement reacts with crustal basalt and then exits basement either through the sediment or directly into the overlying water column as constrained by concentrations of sulfate and lithium in the pore waters at least some seawater enters basement in all three areas without reacting fully with the overlying sediment even where no outcrops are known nearby speeds of up welling of pore water through the sediment have been estimated by fitting profiles of dissolved magnesium and chlorinity which behave conservatively in these areas to numerical time dependent transport models the estimated velocities range from 0 1 to 7 4 cm yr faster flows probably occur but were not sampled upwelling speed correlates positively with heat flow and basement highs and negatively with sediment thickness the correlation with heat flow differs from area 2 to area 3 along with differences in physical properties of the turbidite sediment we have documented pore water upwelling through sediment up to 100 m thick we estimate that upwelling continues at decreasing speeds through sediment up to 160 m thick corresponding to a heat flow of 0 44 w m2 in area 2 and 0 3 w m2 in area 3 concentrations of magnesium and chlorinity in the altered seawater upwelling from basement are uniform within each area but differ from one area to the next both species remain at the bottom seawater concentration in area 1 where basement is cooled to 10 c at the base of the sediments mainly by advection the concentration of magnesium decreases with increasing basement temperature in areas 2 and 3 to a minimum of 2 5 mmol kg at about 90 c in area 3 the transition from largely advective to largely conductive heat loss occurs over only 20 km between areas 1 and 2 and corresponds to a dramatic change in the composition of fluid circulating through basement as the uppermost basement is heated from 10 to 40 50 c chlorinity of the basement fluid increases above the present day bottom seawater concentration in areas 2 and 3 and in nearly all other mid ocean ridge flanks studied to date as a result of rock hydration and the higher chlorinity of bottom seawater during the last glacial period while chlorinity generally correlates positively with uppermost basement temperature in various ridge flank hydrothermal systems it reaches a maximum in area 2 at only 40 c probably because alteration there occurs at a lower water rock ratio than elsewhere for all mid ocean ridge flanks studied to date the temperature at the basement interface correlates better with the fraction of heat lost by advection versus conduction and with the average thickness of the sediment cover than with crustal age

palaeosol stratigraphy across the permian triassic boundary bogda mountains nw china implications for palaeoenvironmental transition through earth s largest mass extinction abstract upper permian and lower triassic palaeosols from northeastern tethyan localities exposed within the bogda mountains nw china provide a wealth of information regarding long term palaeoclimatic and palaeoenvironmental variations wuchiapingian palaeosols are characterized by intense redoximorphy accumulation of vascular plant matter accumulation of clay minerals and fe oxides slickensides and clastic dikes suggesting a soil moisture regime that ranged from perennially wet to distinctly seasonal in soil moisture budget changsinghian to early induan palaeosols include subsurface accumulations of clay and carbonate as well as surficial accumulations of organic matter indicative of sub humid to sub arid soil moisture and variable soil moisture regimes induan to olenekian palaeosols contain pedogenic caco 3 accumulations and gypsum pseudomorphs indicating a drier environment characterized by net soil moisture deficiency elemental composition of palaeosol matrix was used to estimate palaeoprecipitation through the chemical index of alteration minus potassium cia k proxy estimates from various wuchiapingian strata indicate relatively stable palaeoprecipitation during the late changsinghian and early induan palaeoprecipitation appears to have decreased from 1100 to 230 180 mm year over less than 100 m of vertical stratigraphic section in the induan and olenekian palaeoprecipitation appears much less stable than in wuchiapingian with values vacillating from 290 to 1014 mm year the transition to a relatively unstable precipitation state coincides generally with the permian triassic boundary and may reflect climatic disturbances associated with the end permian extinction event in addition to altered atmospheric circulation patterns resulting from regional tectonics moisture availability and expansion of the subtropical high pressure belt

hydrothermal venting and geothermal heating in cascadia basin observations in cascadia basin on the eastern flank of the northern juan de fuca ridge reveal significant bottom water modification as a result of regional conductive heating and local hydrothermal venting seafloor conductive heating occurs throughout the sedimented basin while hydrothermal fluid discharge is confined to small 1 km2 isolated igneous basement outcrops in the northern sector of the plateaulike basin the vertical fluxes of heat and mass associated with these seafloor processes lead to the formation of a 250 to 350 m thick geothermal boundary layer characterized by anomalously high temperature reduced vertical stability and high dissolved silicate concentration using a basinwide average lithospheric heat flux of 0 3 w m 2 and the observed thermal anomaly structure of the water column we obtain a mean residence time of 1 to 2 years for the deep water over cascadia basin detailed water property data collected in 1992 and 1993 within the immediate vicinity of three isolated igneous basement outcrops in the north central sector of the basin indicate that local bottom water heating arises from low temperature venting through the summit and flanks of the outcrops near the smallest edifice especially well defined layers of anomalously warm particle laden water were found within 20 m of the outcrop summit depth of 2610 m maximum anomalies of temperature light attenuation coefficient and dissolved silicate concentration in the layers were 0 040 c 0 015 m 1 and 5 mol l 1 respectively we estimate the local heat flux fo from the smallest outcrop to be 2 4 0 8 u 109 w where u m s 1 is the mean horizontal current at the venting depth for reasonable mean currents in the range 10 3 to 10 2 m s 1 we find fo 0 2 to 2 4 107 w assuming that the depressed conductive heat flow of 0 05 w m 2 observed through the sedimented seafloor surrounding the smallest outcrop reflects the advective loss of heat through the outcrop the radial distance over which crustal fluids must collect heat and converge on the outcrop is about 10 km

heat transfer in the oceanic crust of the brazil basin a detailed geothermal survey has been made on the western flank of the mid atlantic ridge in the brazil basin where the crust is 20 m y old the area is generally covered by a 150 to 200 m thick layer of foraminiferal ooze but basement outcrops are numerous sedimentary temperature profiles indicate anomalously low temperatures at the base of the sedimentary layer which results from cold bottom water penetrating laterally into the upper igneous crust and absorbing much of the geothermal heat net influx rates of 10 8 m s 1 are implied by a simple aquifer model a negative pressure drop across the sedimentary layer is required by this interpretation refraction studies indicate low seismic velocities 3 3 to 4 5 km s 1 near the top of layer 2 and a large velocity gradient with depth the velocity structure in the upper kilometer of the crust is related to the porosity from which it is inferred that permeabilities there are high many of the 52 temperature profiles show a significant decrease in gradient with depth the curvature can be attributed to one or a combination of the following causes 1 upward advection of pore water at rates of 10 7 s 1 2 bottom water temperature variations 3 variation of conductivity with depth and 4 experimental errors interpretation of curvature in terms of an advective model leads to results hard to reconcile with present knowledge of pressure variations and permeabilities of the oceanic crust

regional heat flow variations across the sedimented juan de fuca ridge eastern flank constraints on lithospheric cooling and lateral hydrothermal heat transport seafloor heat flow has been estimated continuously along a transect on the sedimented eastern flank of the juan de fuca ridge to provide constraints on the scale and rate of lateral heat and fluid transport in the upper igneous crust and on the total flux from the young lithosphere beneath the profile extends from 20 km east of the ridge axis where turbidite sediments lap onto the oceanic crust at an age of less than 1 ma and ends 110 km east of the axis over 3 6 ma crust estimated heat flow is derived from the combination of the depth to igneous basement determined from seismic reflection profiles and basement temperatures measured in nine ocean drilling program boreholes along the transect the strategy is based on the knowledge that in this young area upper basement temperatures are locally homogenized by vigorous hydrothermal circulation and hence vary smoothly between drilling sites at the young end of the transect near the region of extensive outcrop heat flow is only 15 of that predicted for lithosphere of this age heat flow increases systematically to the east reaching the full predicted level about 20 km from the point of sediment basement onlap the anomaly can be accounted for by mixing and or eastward flow of cool water in the upper igneous crust beneath the sediment at a darcian rate of the order of 1 m yr a geochemical signature of fresh seawater in basement is observed many tens of kilometers farther to the east although the thermal signature is no longer present along the remainder of the transect the heat flow conforms very well to that predicted by simple boundary layer cooling theory once the thermal effects of rapid sedimentation on this ridge flank are accounted for

modeling diagnosis of suspended sediment transport in tidal estuarine system a three dimensional time dependent hydrodynamic and suspended sediment transport model was performed and applied to the danshuei river estuarine system and adjacent coastal sea in northern taiwan the model was validated with observed time series salinity in 2001 and with salinity and suspended sediment distributions in 2002 the predicted results quantitatively agreed with the measured data a local turbidity maximum was found in the bottom water of the kuan du station the validated model then was conducted with no salinity gradient no sediment supply from the sediment bed wind stress and different freshwater discharges from upstream boundaries to comprehend the influences on suspended sediment dynamics in the danshuei river estuarine system the results reveal that concentrations of the turbidity maximum simulated without salinity gradient are higher than those of the turbidity maximum simulated with salinity gradient at the kuan du station without bottom resuspension process the estuarine turbidity maximum zone at the kuan du station vanishes this suggests that bottom sediment resuspension is a very important sediment source to the formation of estuarine turbidity maximum the wind stress with northeast and southwest directions may contribute to decrease the suspended sediment concentration when the freshwater discharges increase at the upstream boundaries the limits of salt intrusion pushes downriver toward river mouth suspended sediment concentrations increase at the upriver reaches in the danshuei river to tahan stream while decrease at kuan du station

updip limit of the seismogenic zone beneath the accretionary prism of southwest japan an effect of diagenetic to low grade metamorphic processes and increasing effective stress off southwest japan the seaward limit of coseismic displacement or updip limit of the seismogenic zone of the 1946 mw 8 3 thrust earthquake reaches to 4 km depth and 40 km landward of the trench this limit coincides with the estimated location of the 150 c isotherm and has been linked to changes in physical properties associated with the smectite to illite clay mineral transition here we show that this limit correlates with a suite of diagenetic to low grade metamorphic processes characterized by 1 declining fluid production and decreasing fluid pressure ratio and 2 active clay carbonate and zeolite cementation and the transition to pressure solution and quartz cementation these diagenetic to low grade metamorphic changes cause the onset of velocity weakening during thrust faulting an increase in effective stress and strengthening of the hanging wall which together combine to produce recordable earthquakes

large scale lateral heat and fluid transport in the seafloor revisiting the well mixed aquifer model abstract large scale lateral fluid flow through oceanic crust provides an explanation for regionally low heat flow in several seafloor settings a well mixed aquifer wma model provides a quantitative and conceptual tool for explaining anomalously low heat flow based on an analytical representation of fluid and heat flow assuming lateral fluid flow in basement in a layer directly below the ocean sediments we present an extended well mixed aquifer ewma model that allows fluid flow at greater depths within the oceanic crust flow through a deeper permeable layer extracts more heat than equivalent flow through a shallower layer of equal thickness and may help to reconcile global heat flow and seafloor permeability data since deeper flow does not require velocities as great as shallow flow to account for the same heat loss and thus permeability can be lower numerical simulations that test the hydrodynamic validity of the wma and ewma equations indicate that the analytical models provide reasonable approximations of large scale lateral heat transport when lateral fluid flow in the crust is confined to thin layers the efficiency of lateral heat transport is reduced as vertical mixing within the lateral flow layer increases

influence of continental roots and asthenosphere on plate mantle coupling the shear tractions that mantle flow exerts on the base of earth s lithosphere contribute to plate driving forces and lithospheric stresses we investigate the sensitivity of these tractions to sub lithospheric viscosity variations by comparing shear tractions computed from a mantle flow model featuring laterally varying lithosphere and asthenosphere viscosity with those from a model with layered viscosity lateral viscosity variations generally do not change the direction of shear tractions but deeply penetrating continental roots increase traction magnitudes by a factor of 2 5 compared to 100 km thick lithosphere a low viscosity asthenosphere decreases traction magnitudes by a smaller amount and is important only if 100 km thick increased plate mantle coupling beneath thick continental lithosphere may increase plate driving forces surface deformation and mantle derived lithospheric stresses in these regions by contrast a low viscosity asthenosphere does not decouple the lithosphere from mantle flow highlighting the geological importance of mantle tractions on the lithosphere

widespread seawater circulation in 18 22 ma oceanic crust impact on heat flow and sediment geochemistry on the basis of heat flow measurements seismic mapping and sediment pore water analysis we demonstrate widespread and efficient ventilation of the 18 22 ma oceanic crust of the northeast equatorial pacific ocean recharge and discharge appear to be associated with basement outcrops including seamounts and north south trending faults along which sediment cover thins out and volcanic rocks are exposed low temperature hydrothermal circulation through the volcanic crust leads to the reduction of heat flow through overlying sediments with measured heat flow values that are well below those expected from conductive cooling curves for lithosphere of this age typically dissolved pore water oxygen decreases from the sediment surface downward reaching minimum values at mid depth and rising again in the lower part of the cores investigated clearly indicating oxygen rich seawater circulation through the oceanic crust underneath the sediments if the residence time of the circulating fluids in the upper crust is short or the fluid flux is large oxic conditions may be preserved and oxygen can diffuse upwards into the sediments this process leading to widespread oxic conditions in the near basement sediments may cause the oxidation of residual reduced material stored in the deeper sediments resulting in downward fluxes of the reaction products into the basement and from there back into the oceans considering the widespread existence of this type of off axis ventilation the net effect of the resulting return flow of reaction products on biogeochemical cycles and element fluxes e g carbon and nitrogen may be very large

estimation of the bed shear stress in vegetated and bare channels with smooth beds the shear stress at the bed of a channel influences important benthic processes such as sediment transport several methods exist to estimate the bed shear stress in bare channels without vegetation but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production this study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds the model which is supported by measurements indicates that for both bare and vegetated channels with smooth beds within a viscous sublayer at the bed the viscous stress decreases linearly with increasing distance from the bed resulting in a parabolic velocity profile at the bed for bare channels the model describes the velocity profile in the overlap region of the law of the wall for emergent canopies of sufficient density frontal area per unit canopy volume a 4 3 m 1 the thickness of the linear stress layer is set by the stem diameter leading to a simple estimate for bed shear stress

septomedullopitys szei sp nov a new gymnospermous wood from lower wuchiapingian upper permian continental deposits of nw china and its implication for a weakly seasonal humid climate in mid latitude ne pangaea abstract septomedullopitys szei sp nov is described from the wuchiapingian wutonggou formation of tarlong valley southern bogda mountains xinjiang in northwestern china the stem has a heterogeneous pith ca 15 20 mm in diameter and containing numerous linear secretory ducts and parenchymatous bands primary xylem is endarch and the tracheids contain scalariform thickenings secondary xylem is of the protophyllocladoxylon type comparisons with contemporaneous gymnospermous woods containing either heterogeneous pith with ducts or protophyllocladoxylon type secondary xylem from the angara palaeocontinent indicate that the tarlong stem represents a new permian morphotaxon for the region the presence of coprolites borings and spindle shaped cavities within the stem suggests well developed animal plant fungi interactions the occurrence of numerous growth interruptions and absence of true growth rings within the stem suggest weak seasonality of annual precipitation the interruptions suggest a humid climate with short term nonperiodic droughts

observations of flexure and the rheology of oceanic lithosphere the principal evidence for the long term i e 1 myr mechanical behaviour of the oceanic lithosphere has come from studies of how it deforms in response to large loads such as volcanoes and sediments a model widely used to explain the deformation is an elastic plate in which flexural rigidity depends on the thermal age of the lithosphere at the time of loading an elastic model however is time invariant and does not take into account temporal changes that may occur in the flexural rigidity as a consequence of loading there is evidence for example that the flexural rigidity of the oceanic lithosphere also depends on load age being large at short times and small at long times thus competing effects may exist between thermal cooling which strengthens the lithosphere and some form of load induced stress relaxation which weakens it in order to investigate the relative roles of these processes we have developed a multilayered viscoelastic model which is based on the results of experimental rock mechanics that creep in the lithosphere is a thermally activated process and on a thermal structure that is given by the plate cooling model by comparing the predictions of the model with a new compilation of flexural rigidity estimates we have found that if the upper mantle viscosity is 1020 pa s the activation energy that best describes the long term mechanical behaviour of the oceanic lithosphere is 120 kj mol 1 this parameter pair explains the dependence of flexural rigidity on both plate and load age it also helps account for the subsidence and uplift history of oceanic islands and the stratigraphic patterns that develop in the flexural moats that flank them at atolls a multilayered viscoelastic model explains the rapid subsidence that follows shield building and does not require that the age of the lithosphere that supports a volcano is thermally re set to a younger value our studies suggest that while the oceanic lithosphere has viscoelastic properties the viscosity of its upper layers is so much higher than that of its lower layers that in effect it behaves as a thin elastic plate on long timescales there will therefore be a certain permanence to the observations of oceanic flexure such that they may be used with some confidence to evaluate the tectonic setting of individual features of the seafloor and in some cases their age

revised tectonic boundaries in the cocos plate off costa rica implications for the segmentation of the convergent margin and for plate tectonic models the oceanic cocos plate subducting beneath costa rica has a complex plate tectonic history resulting in segmentation new lines of magnetic data clearly define tectonic boundaries which separate lithosphere formed at the east pacific rise from lithosphere formed at the cocos nazca spreading center they also define two early phase cocos nazca spreading regimes and a major propagator in addition to these sharply defined tectonic boundaries are overprinted boundaries from volcanism during passage of cocos plate over the galapagos hot spot the subducted segment boundaries correspond with distinct changes in upper plate tectonic structure and features of the subducted slab newly identified seafloor spreading anomalies show oceanic lithosphere formed during initial breakup of the farallon plate at 22 7 ma and opening of the cocos nazca spreading center a revised regional compilation of magnetic anomalies allows refinement of plate tectonic models for the early history of the cocos nazca spreading center at 19 5 ma a major ridge jump reshaped its geometry and after 14 5 ma multiple southward ridge jumps led to a highly asymmetric accretion of lithosphere a suspected cause of ridge jumps is an interaction of the cocos nazca spreading center with the galapagos hot spot

model for calculating bed load transport of sediment a bed load transport model based on the mechanics of sediment moving by saltation yields predicted values of bed load flux as a function of boundary shear stress grain diameter and density the parameters required to calculate bed load transport particle velocity bed load sediment concentration and the height of the bed load layer can all be determined from our model which computes sequences of trajectories of individual saltating grains as well as the concentration of moving grains that the flow can support the latter is related to the momentum the accelerating grains extract from the flow predicted curves of bed load transport vs boundary shear stress agree well with transport data collected by gilbert meyer peter iet al n and the waterways experimental station measured shear stress was corrected for pressure drag when bed forms were present comparison of predicted bed load transport with common bed load equations reveals considerable similarity among the relationships the best agreement with the data is produced by relationships in which the transport rate vanishes as the shear stress approaches the critical shields number as in our model and yalin s equation

estimating the distribution of suspended sediment concentration in submerged vegetation flow based on gravitational theory abstract vegetation plays a significant role in river ecosystem which has a great influence on hydraulic structures and sediment transport understanding the vertical distribution of suspended sediment concentration ssc in canopy flow is helpful to study the process of riverbed erosion and deposition in vegetated channels aiming at the sediment laden flow in open channel covered with submerged vegetation this study divides the water depth into two layers along the vertical direction with the vegetation height as the boundary and then proposes a new ssc distribution model based on gravitational theory to estimate the vertical distribution of relative ssc in the free water layer and vegetation layer respectively in the meanwhile a new formula is also proposed to evaluate the reynolds shear stress below the submerged vegetation height which has been successfully applied in the derivation of the new ssc distribution model the validation results of the simplified velocity model the new reynolds shear stress formula and the new ssc model compare well with the collected experimental data series on top of that it is found that the uniformity of ssc distribution profile progressively decreases with the increasing sediment particles diameters besides according to the validation results and discussion it is believed that the controversy point about gravitational theory would not have obvious influence on the estimation of ssc distribution so that the gravitational theory can be adopted to investigate suspended sediment transport in vegetation flow that would be benefit for river ecological restoration and better management

along strike variations in underthrust sediment dewatering on the nicoya margin costa rica related to the updip limit of seismicity 1 along the costa rican subduction zone offshore the nicoya peninsula an offset in the updip limit of seismicity coincides with a transition between subduction of warm crust generated at the cocos nazca spreading center and cool crust formed at the east pacific rise we evaluate whether the observed difference in thermal state of incoming crust would result in significant differences in sediment dehydration reaction progress along strike thought to be a control on the updip limit of seismicity we combine thermal models with models of dehydration reaction kinetics for opal and smectite to estimate the distribution of diagenetic fluid sources the modeled distribution of diagenetic fluid sources mimics the pattern of the updip limit of seismicity seismicity begins 15 20 km landward of most of the smectite to illite transition this suggests that the location of the updip limit of seismicity may be influenced by the dissipation of fluid overpressures landward of smectite to illite dehydration

the effects of sedimentation and compaction on oceanic heat flow summary the estimation of environmental effects forms an important part of the interpretation of oceanic heat flow measurements in particular the perturbations associated with sedimentation and surface temperature changes must be taken into account analytical solutions can be obtained only for individual simplified versions of these problems whereas any real example is complicated by the process of sediment compaction which changes the bulk thermal properties with depth a physical model is developed which uses sediment porosity trends to predict the thermal parameters and material advection rates for an evolving sediment basement system these values are then used in a numerical solution to the heat flow equation to give estimates of the perturbed surface heat flux through time in addition to variations in sedimentation rate sediment type radioactive heat production and surface temperature changes are considered heat flow corrections may vary by up to a factor of 2 according to sediment type while radioactive heat production can offset the effects of sedimentation by as much as 40 per cent the results also indicate that alterations determined from simple analytical models tend to over estimate the true perturbation to the flux

global distribution of seamounts inferred from gridded geosat ers 1 altimetry using a forward modeling approach based on an axisymmetric gaussian seamount i characterize the global seamount distribution by locating circular maxima in the gridded vertical gravity gradient field derived from altimetry collected by the geosat and ers 1 satellite missions the global seamount distribution is long tailed and resembles a power law distribution for seamounts in the height range 2 7 km smaller seamounts are not well isolated by my technique nor are they well resolved in the gridded data several factors are likely to influence the height of volcanic seamounts such as melt availability magma driving pressure and plate thickness the observed relationship between seamount gravimetric amplitudes and the age of the underlying seafloor implies that there is an upper limit on seamount heights whether a seamount will reach that height depends most likely on supply side factors such as melt availability and magma driving pressure but the limiting height itself seems more likely to be controlled by the strength of the oceanic plate specifically compressional stresses directly beneath the seamount as a consequence of the lithosphere s flexural response to loading may eventually exceed the magma driving pressure and prevent magma from reaching the surface thus limiting the growth of the seamount because oceanic plate strength primarily is controlled by plate age the limit on seamount height is inferred to be a simple function of plate age at the time of seamount emplacement using analytical solutions i present a simple flexural model that predicts the observed global height age relationship

vertical sediment distribution so far various calculation models for the vertical distribution of suspended sediment concentration have been produced by several investigators from different theories the limitations of all these models imply that it is possible to find a more reasonable model for which each previous model can be included as special case the formulation of a reasonable general model is the purpose of this paper

hydrothermal recharge and discharge across 50 km guided by seamounts on a young ridge flank hydrothermal circulation within the sea floor through lithosphere older than one million years myr is responsible for 30 of the energy released from plate cooling and for 70 of the global heat flow anomaly the difference between observed thermal output and that predicted by conductive cooling models 1 2 hydrothermal fluids remove significant amounts of heat from the oceanic lithosphere for plates typically up to about 65 myr old3 4 but in view of the relatively impermeable sediments that cover most ridge flanks5 it has been difficult to explain how these fluids transport heat from the crust to the ocean here we present results of swath mapping heat flow geochemistry and seismic surveys from the young eastern flank of the juan de fuca ridge which show that isolated basement outcrops penetrating through thick sediments guide hydrothermal discharge and recharge between sites separated by more than 50 km our analyses reveal distinct thermal patterns at the sea floor adjacent to recharging and discharging outcrops we find that such a circulation through basement outcrops can be sustained in a setting of pressure differences and crustal properties as reported in independent observations and modelling studies

mapping the fluid flow of the mariana mounds ridge flank hydrothermal system pore water chemical tracers we present a conceptual model of fluid circulation in a ridge flank hydrothermal system the mariana mounds the model is based on chemical data from pore waters extracted from piston cores and from push cores collected by deep sea research vessel alvin in small meter sized mounds situated on a local topographic high these mounds are located within a region of heat flow exceeding that calculated from a conductive model and are zones of strong pore water upflow we have interpreted the chemical data with time dependent transport reaction models to estimate pore water velocities in the mounds themselves pore water velocities reach several meters per year to kilometers per year within about 100 m from these zones of focused upflow velocities decrease to several centimeters per year up to tens of centimeters per year a larger area of low heat flow surrounds these heat flow and topographic highs with upwelling pore water velocities less than 2 cm yr in some nearby cores downwelling of bottom seawater is evident but at speeds less than 2 cm yr downwelling through the sediments appears to be a minor source of seawater recharge to the basaltic basement we conclude that the principal source of seawater recharge to basement is where basement outcrops exist most likely a scarp about 2 4 km to the east and southeast of the study area

passive off axis convection through the southern flank of the costa rica rift pore fluids are passively convecting through young oceanic sediments and crust around deep sea drilling project dsdp site 504 on the southern flank of the costa rica rift as inferred from a variety of geological geochemical and geothermal observations the presence of a fluid circulation system is supported by new data collected on ocean drilling program odp leg 111 and a predrilling survey cruise over the heavily sedimented 5 9 ma site during the latter elongated heat flow anomalies were mapped subparallel to structural strike with individual measurements of twice the regional mean value and strong lateral and vertical geochemical gradients were detected in pore waters squeezed from sediment cores also there is a strong correlation between heat flow bathymetry sediment thickness and inferred fluid velocities up through the sediments on an earlier dsdp leg an 8 bar underpressure was measured in the upper 200 m of basement beneath thick sediment cover although the forces which drive passive circulation are not well understood it has generally been thought that the length scale of heat flow variations provides a good indication of the depth of hydrothermal circulation within the oceanic crust this assumption was based on analytical and numerical analyses of relatively simple porous media models deep crustal convection had been inferred near site 504 based on the geometry of surface heat flow anomalies with a wavelength of 4 7 km but appears to be precluded by low crustal permeability as measured in dsdp hole 504b the widely varied geothermal and hydrogeological observations near site 504 are readily explained by a model which combines 1 basement relief 2 irregular sediment drape 3 largely conductive heat transfer through the sediments overlying the crust and 4 thermal and geochemical homogenization of pore fluids at the sediment basement interface which results from 5 topographically induced passive hydrothermal circulation with large aspect ratio convection cells this convection involves mainly the permeable upper 200 300 m of crust the deeper crust is not involved this convection is induced through a combination of buoyancy fluxes due to heating from below and topographic variations on the seafloor and at the basement sediment interface this model was designed to incorporate data from both near the sediment surface and deep within boreholes it is successful in duplicating numerous field observations

evidence for excess pore pressures in southwest indian ocean sediments brown clay cores from the madagascar and crozet basins show the following evidence of excess pore pressures large amounts of flow in increasing average sedimentation rate with age and nonlinear temperature gradients additionally many hilltops in these basins have no visible sediment cover the bare hilltops may result from periodic slumping caused by excess pore pressures calculated excess pore pressures which equal or exceed the overburden pressure were inferred from water fluxes predicted by nonlinear temperature gradients and laboratory permeability measurements by using darcy s law since pore pressures which exceed the overburden pressure are unreasonable we attribute this discrepancy to laboratory measures which underestimate the in situ permeability the widespread presence of overpressured sediments in areas of irregular topography provides a process for resuspension of clay sized particles this mechanism does not require high current velocities for the erosion of clay and therefore can be applied to many areas where no strong currents are evident carbonate rich sediments from the madagascar ridge the mozambique ridge and the agulhas plateau had almost no flow in and occurred in areas where all topography was thickly draped with sediment since the age and tectonic location of the ridges and plateaus preclude water circulation in the basement wemore attribute these differences between the brown clay and the carbonate rich material to an absence of significant excess pore pressures in the plateau and ridge sediments less

hydrothermal circulation through mid ocean ridge flanks fluxes of heat and magnesium thermally driven convection of seawater occurs through oceanic crust of all ages at the seafloor spreading axis on mid ocean ridge flanks and in the ocean basins at the ridge axis and on the flanks circulating seawater produces a major chemical exchange between the oceans and the crust based on heat budget constraints and the composition of hot springs between 10 and 40 of the river flux of mg can be taken up during high temperature alteration of the basaltic crust along the ridge axis most of the hydrothermal heat loss however occurs on the mid ocean ridge flanks where the temperatures are lower and the seawater flux correspondingly larger the estimated heat loss on the flanks is so large that upwelling must occur over a large fraction 5 30 of the seafloor less than 65 ma in age if temperatures are 20 c and seepage velocities are on the order of 10 to 100 cm y the circulating seawater needs to lose on average less than 1 2 of its mg content in order to solve the mg mass balance for the oceans chemical fluxes through mid ocean ridge flanks are poorly known because of the wide range of crustal conditions that prevail there and the paucity of study to date the most critical parameter for characterizing crustal conditions is temperature in basement which is a function of crustal age basement topography and sediment thickness and permeability basement temperature which can usually be inferred from heat flow and seismic reflection surveys largely determines the change in the composition of seawater circulating through basement this change can be inferred in turn from profiles of sediment porewater chemistry all sites studied to date with temperatures at the sediment basement interface 25 c have a large component of advective heat loss and show only a small 80 mg loss both types of sites may be important for chemical fluxes whether the cooler sites are important depends on how much the seawater changes in composition as it circulates through the crust only small changes are needed whether the warmer sites are important depends on how much heat is lost by advection in this type of setting the warmer sites could produce significant chemical fluxes even if they are scarce they could account for the entire river input of mg to the oceans even if they represent only 8 20 of the total advective heat loss on ridge flanks

first report of coupled early permian paleomagnetic and geochronologic data from the dunhuang block nw china and implications for the tectonic evolution of the paleo asian ocean abstract in order to better understand the tectonic relationship between the dunhuang block dhb and its adjacent blocks and to constrain the timing of the closure of the paleo asian ocean a combined geochronologic and paleomagnetic investigation has been undertaken on early permian tuff basalt flows and sandstones from the shuangbaotang formation in the northwestern part of the dhb u pb zircon dating indicates that the age of the strata is between 280 6 2 9 ma and 291 4 2 6 ma thermal demagnetization of a three component isothermal remanent magnetization irm and curie point experiment suggest that magnetite dominates in the rock samples analyzed in addition there is a minor amount of hematite in some sandstones stepwise thermal demagnetization successfully isolated stable characteristic remanent magnetization chrm from 11 tuff layers two lava flows and nine sandstone beds two components were isolated from all samples a lower temperature component ltc and a higher temperature component htc the ltc is near the direction of the present day geomagnetic field and produced a negative fold test indicating it is a viscous remanent magnetization in the present day geomagnetic field most of the htc are reverse polarity normal 4 reverse 158 which is in accordance with the kiaman reversed superchron that spans the late carboniferous permian interval in addition the htc of all studied sites passed the fold and reverse tests suggesting that they likely represent primary remanent magnetization the tilt corrected mean direction from all sites tuff basalts and sandstones is ds 1 7 is 43 1 ks 403 95 1 5 n 22 the mean paleopole of the site mean direction corresponded vgps lies at 74 5 n 268 5 e with a95 1 6 considering the consistent inclination values recorded among the studied tuff basalts and sandstones and the low degrees of anisotropy within all samples we suggest that there is no significant inclination shallowing caused by depositional compaction in the sedimentary layers of the studied section taking into account the results from this study as well as previous late paleozoic paleomagentic studies from adjacent tectonic blocks we conclude that the dhb formed part of the amalgamated dunhuang north china alxa qaidam mega block during the early permian but was separated from the tarim block by a small ocean here named the qiemo xingxingxia paleo ocean at this time a comparison of the early permian paleolatitudes of these and other adjacent blocks suggest that the paleo asian ocean sensu lato was still open at this time combined with other geological evidence a paleogeographic reconstruction of the paleo asian ocean has been reconstructed for the early permian

the thermal environment of cascadia basin 1 located adjacent to the ne pacific convergent boundary cascadia basin has a global impact well beyond its small geographic size composed of young oceanic crust formed at the juan de fuca ridge igneous rocks underlying the basin are partially insulated from cooling of their initial heat of formation by a thick layer of pelagic and turbidite sediments derived from the adjacent north american margin the igneous seafloor is eventually consumed at the cascadia subduction zone where interactions between the approaching oceanic crust and the north american continental margin are partially controlled by the thermal environment within cascadia basin basement topographic relief varies dramatically and sediments have a wide range of thickness and physical properties this variation produces regional differences in heat flow and basement temperatures for seafloor even of similar age previous studies proposed a north south thermal gradient within cascadia basin with high geothermal flux and crustal temperatures measured in the heavily sedimented northern portion near vancouver island and lower than average heat flux and basement temperatures predicted for the central and southern portions of the basin if confirmed this prediction has implications for processes associated with the cascadia subduction zone including the location of the locked zone of the megathrust fault although existing archival geophysical data in the central and southern basin are sparse nonuniformly distributed and derived from a wide range of historical sources a substantial n s geothermal gradient appears to be confirmed by our present compilation of combined water column and heat flow measurements

abrupt thermal transition reveals hydrothermal boundary and role of seamounts within the cocos plate 1 new thermal data from 18 24 ma lithosphere on the cocos plate delineate contrasting subsurface thermal conditions in adjacent sections of crust heat flow through seafloor created at the east pacific rise is generally suppressed by 70 relative to conductive lithospheric cooling models whereas heat flow through adjacent similarly aged lithosphere generated at the cocos nazca spreading center is consistent with these models the transition between thermal regimes is remarkably abrupt only 2 5 km wide indicating a shallow hydrothermal origin the transition is more closely associated with differences in the distribution of basement outcrops than with tectonic boundaries demonstrating the importance of the former in extracting heat from the lithosphere on a regional basis

unconformity bounded upper paleozoic megasequences in the beishan region nw china and implications for the timing of the paleo asian ocean closure abstract the upper paleozoic sedimentary sequence in the beishan region northwest china provides a complete record of the complex amalgamation and extension history of the central asian orogenic belt caob for this part of china integrating newly obtained stratigraphic paleontological and radiometric data this paper reviews the upper paleozoic stratigraphic sequences of the beishan region the upper paleozoic strata here are divided into three megasequences ms they are in ascending order devonian mississippian guadalupian and lopingian megasequences ms1 ms2 and ms3 separated by two major unconformities each indicative of a huge sedimentary hiatus ms1 is made up of continental and epicontinental marine deposits in the pre rift stage ms2 of transgressive marine and volcanic strata in the syn rift stage and ms3 of continental sediments in the inversion stage the major unconformity between ms1 and ms2 is interpreted to represent the regional uplift and erosion caused by the final amalgamation of caob in the beishan region the syn rift ms2 represented by transgressive marine and volcanic strata in the beishan region can be well correlated with pennsylvanian guadalupian megasequences in inner mongolia where they rest on a major interregional unconformity this correlation suggests the closure of the paleo asian ocean in beishan and inner mongolia before the carboniferous followed by the development of a synchronous marine rift megasequence in the southern part of the caob

first report of a phytogeographically mixed transitional middle late permian fossil wood assemblage from the hami area northwest china and implications for permian phytogeographical paleogeographical and paleoclimatic evolution in central asia abstract a diverse and well preserved fossil wood assemblage is described for the first time from the middle permian taerlang formation and the upper permian quanzijie formation in the vicinity of the tianshan town hami city of northwestern china on the basis of wood microstructure the fossil woods are classified into three genera and five species including one new genus prototianshanoxylon gen nov and two new species prototianshanoxylon erdaogouense sp nov prototianshanoxylon hamiense sp nov the new genus is characterized by window like cross field pitting and mixed tracheid radial wall pitting that suggest a transitional type between araucarioid type and protopinoid type pittings phytogeographically the fossil wood assemblage is characterized by an admixture of elements of both temperate angaran represented by wood specimens with moderately to well defined growth rings in their secondary xylem and tropical subtropical north subregion of the cathaysian floras with wood specimens lacking well defined growth rings such a phytogeographically mixed fossil wood assemblage is interpreted to represent a transitional and complex climate condition between a cool temperate and tropical to subtropical zones showing both seasonal variation and unstable climate conditions previously similarly mixed floras have already been found to exist widely in northern china ranging in age from early to late permian but the mechanisms thought to be responsible for their formation were varied and remain controversial in this study the formation of these mixed permian floras of north china is linked to the closure of the tianshan hingan seaway coupled with the collision and amalgamation of siberia with north china and the tarim block in a manner much like closing a pair of scissors with the closure of the seaway proceeding gradually and progressively from west to the east

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting

tree growth at polar latitudes based on fossil tree ring analysis permineralized trunks and mature wood samples with well preserved growth rings are described and analyzed from the upper permian and middle triassic of the central transantarctic mountains this fossil wood is unique in that the plants lived in an environment with no modern analogue and exhibited luxuriant tree growth above 75 s paleolatitude ring width averages 1 69 2 3 mm with maximum width of 6 83 9 9 mm an order of magnitude larger than ring widths produced at near polar latitudes today tree rings in both the permian and triassic woods show similar structure consisting almost entirely of earlywood spring wood with between 0 12 of each ring classified as latewood summer wood the small amount of latewood 0 6 cells indicates a very rapid transition to seasonal dormancy probably in response to decreasing light levels at these paleolatitudes in order to accurately delimit the earlywood latewood boundary a comparison was done of classical dendroclimatological techniques and alternative techniques utilized primarily by paleobotanists analyzing fossil woods we found that classical wood anatomy techniques provided a more accurate explanation of wood development and tree growth for these high latitude samples the suggested cool temperate late permian glossopteris flora from this area differs substantially from the warm temperate middle triassic corystosperm flora leaf type dicroidium and very different paleoclimates have been reconstructed for these two time periods ring structure and wood growth from both sites however are very similar indicating that these plants were responding to the environment in very similar ways the structure of the tree rings including a large number of earlywood tracheids and a very low number of latewood cells provides evidence that growth at these polar latitudes was limited by light levels rather than water and temperature as occurs in modern high latitude forests these fossil tree rings have important implications for understanding woody shoot growth and cambial function at high latitudes during periods of global warmth 2007 elsevier b v all rights reserved