northland ophiolite new zealand and implications for plate tectonic evolution of the southwest pacific the northland ophiolite and coeval ocean floor sedimentary rock form the northland allochthon obducted from the northeast onto new zealand in the late oligocene the ophiolite was probably emplaced as a single sheet and separated into individual massifs during subse quent movement of the allochthon chemically the bulk of the igneous rocks are normal mid ocean ridge basalts but the ophiolite also includes a younger suite of hornblende modal within plate alkalic rocks believed to represent seamounts two alternative models one involving a subduction flip the other involving continuous westward subduction are proposed to account for the obduction of the upper part of the northland ophiolite the oceanic crust from which the ophiolite originated was formed simultaneously with tasman sea spreading on the western rim of a once much larger south fiji plate assemblage

a late cretaceous and cenozoic reconstruction of the southwest pacific region tectonics controlled by subduction and slab rollback processes abstract a cenozoic tectonic reconstruction is presented for the southwest pacific region located east of australia the reconstruction is constrained by large geological and geophysical datasets and recalculated rotation parameters for pacific australia and lord howe rise pacific relative plate motion the reconstruction is based on a conceptual tectonic model in which the large scale structures of the region are manifestations of slab rollback and backarc extension processes the current paradigm proclaims that the southwestern pacific plate boundary was a west dipping subduction boundary only since the middle eocene the new reconstruction provides kinematic evidence that this configuration was already established in the late cretaceous and early paleogene from 82 to 52 ma subduction was primarily accomplished by east and northeast directed rollback of the pacific slab accommodating opening of the new caledonia south loyalty coral sea and pocklington backarc basins and partly accommodating spreading in the tasman sea the total amount of east directed rollback of the pacific slab that took place from 82 ma to 52 ma is estimated to be at least 1200 km a large percentage of this rollback accommodated opening of the south loyalty basin a north south trending backarc basin it is estimated from kinematic and geological constraints that the east west width of the basin was at least 750 km the south loyalty and pocklington backarc basins were subducted in the eocene to earliest miocene along the newly formed new caledonia and pocklington subduction zones this culminated in southwestward and southward obduction of ophiolites in new caledonia northland and new guinea in the latest eocene to earliest miocene it is suggested that the formation of these new subduction zones was triggered by a change in pacific australia relative motion at 50 ma two additional phases of eastward rollback of the pacific slab followed one during opening of the south fiji basin and norfolk basin in the oligocene to early miocene up to 650 km of rollback and one during opening of the lau basin in the latest miocene to present up to 400 km of rollback two new subduction zones formed in the miocene the south dipping trobriand subduction zone along which the solomon sea backarc basin subducted and the north dipping new britain san cristobal new hebrides subduction zone along which the solomon sea backarc basin subducted in the west and the north loyalty south fiji backarc basin and remnants of the south loyalty santa cruz backarc basin subducted in the east clockwise rollback of the new hebrides section resulted in formation of the north fiji basin the reconstruction provides explanations for the formation of new subduction zones and for the initiation and termination of opening of the marginal basins by either initiation of subduction of buoyant lithosphere a change in plate kinematics or slab mantle interaction

human impact and slope dynamics evolutionary trends in the monoclinal relief of adriatic area of central italy abstract the present work deals with a large area of the marche abruzzi monoclinal relief which is made up of a clayey sediment succession with sandy conglomeratic levels alternating at varying stratigraphic heights the east verging monocline was generated by an intense quaternary tectonic uplifting it differs approximately in the west east and in the southern directions forming three wide morphostructures the deep fluvial down cutting disjointed the monoclinal relief into a succession of high hills which give the area a typical cuesta morphology with fronts facing the western quadrants the present study aims at contributing to the knowledge of recent slope morphodynamics by analyzing the spatial distribution and state of activity of fast hydro erosion processes and superficial mass movements correlations are made between these phenomena and the morphotectonic and lithological features of the various sectors in the area with particular reference to agricultural land use the present research underlines how the badlands represent the most spectacular form of fast erosion whereas the landslide phenomena which affect the prevalently loamy clayey eluvial colluvial covers are the most widespread processes despite the distribution density and recent or current evolutionary trends are generally associated with different morphostructural features of the various sectors of the area they prove to be strictly controlled by agricultural exploitation and by the connected techniques and types of cultivation

erosion processes in calanchi in the upper orcia valley southern tuscany italy based on multitemporal high resolution terrestrial lidar and uav surveys a 125 000 m2 calanchi badland in the province of siena tuscany was monitored with an unmanned aerial vehicle uav and terrestrial laser scanning over the period of one year tls terrestrial laser scanning was carried out on two sample slopes whereas the image acquisition of the uav covered the entire catchment in combination with ground control points the uav images were used to create orthophotos and 3d point clouds using the structure from motion sfm software photoscan the tls surface models indicate seasonal differences in erosion and deposition the surface change measured with sfm showed nearly 6 700 m3 of net material loss resulting from 8 700 m3 erosion and 2 000 m3 deposition these values reveal a mean annual surface lowering of 5 3 cm for the catchment additionally several geomorphological processes such as rill erosion slope wash and translational slides could be detected in the one year monitoring period a comparison of tls and sfm results showed differences in the calculated volumes of mobilised material these discrepancies resulted from shadowing effects and low point densities of the tls point clouds

composition of back arc basin volcanics valu fa ridge lau basin evidence for a slab derived component in their mantle source abstract samples dredged from 2 localities near the crest of the valu fa ridge an active back arc basin spreading centre in the lau basin consist of highly vesicular lava fragments of andesitic composition the samples are characterized by rare euhedral an 85 plagioclase phenocrysts in a hypocrystalline groundmass of an 60 plagioclase laths brown glass and rare subhedral clinopyroxene samples from within and to a lesser extent between the dredge hauls show remarkable isotopic and chemical homogeneity with 87 sr 86 sr 0 70330 2 143 nd 144 nd 0 51303 2 206 pb 204 pb 18 65 2 207 pb 204 pb 15 55 1 208 pb 204 pb 38 34 4 sr 165 ppm rb 7 ppm cs 0 17 ppm k 3300 to 4200 ppm ba 96 ppm and ree lree depleted with 12 18 chondritic abundances on sr nd pb pb and sr pb plots the volcanics lie just within or on the edge of the morb fields overlapping with island arc volcanics from the marianas and tonga compared with morb and ocean island basalts the samples show alkali element enrichment relative to ree and higher cs relative to rb the isotopic and geochemical characteristics of the valu fa ridge volcanics clearly indicate a minor but significant slab derived component in the back arc basin mantle source

geologic and kinematic constraints on late cretaceous to mid eocene plate boundaries in the southwest pacific abstract starkly contrasting tectonic reconstructions have been proposed for the late cretaceous to mid eocene 85 45 ma evolution of the southwest pacific reflecting sparse and ambiguous data furthermore uncertainty in the timing of and motion at plate boundaries in the region has led to controversy around how to implement a robust southwest pacific plate circuit it is agreed that the southwest pacific comprised three spreading ridges during this time in the southeast indian ocean tasman sea and amundsen sea however one and possibly two other plate boundaries also accommodated relative plate motions in the west antarctic rift system wars and between the lord howe rise lhr and pacific relevant geologic and kinematic data from the region are reviewed to better constrain its plate motion history during this period and determine the time dependent evolution of the southwest pacific regional plate circuit a model of 1 west dipping subduction and basin opening to the east of the lhr from 85 55 ma and 2 initiation of northeast dipping subduction and basin closure east of new caledonia at 55 ma is supported west dipping subduction and basin opening were not driven by convergence as has previously been proposed our plate circuit analysis suggests that between at least 74 ma and subduction initiation at 55 ma there was little net relative motion between the pacific plate and lhr

geochemistry of the mian lue ophiolites in the qinling mountains central china constraints on the evolution of the qinling orogenic belt and collision of the north and south china cratons abstract the anzishan ophiolite a typical ophiolitic block of early carboniferous age in the mian lue suture zone of the qinling mountains central china consists of amphibolites metabasalts gabbros and gabbroic cumulates all of these rocks as well as those in the hunshuiguan zhuangke hz block have compositions similar to normal morb and back arc basin basalts babb with high end t values indicating that they were derived from a depleted mantle source the mian lue suture zone also contains blocks of other lithologies e g rift volcanic rocks in the heigouxia block and arc volcanic rocks in the sanchazi block although they are in fault contact with each other the presence of these different blocks in the mian lue suture zone may represent a complete wilson cycle from initial rifting to open ocean basin to final subduction and continent continent collision during the late paleozoic early triassic in this region the north and south china cratons were separated by paleo tethys at least until the early carboniferous and final amalgamation of both cratons along the qinling orogenic belt took place in the triassic

intact phospholipids microbial life markers in marine deep subsurface sediments abstract deep subsurface sediments from the nankai trough japan sea odp leg 190 sites 1173 1174 1177 and near surface sediments from hydrate ridge ne pacific have been analysed by high performance liquid chromatography hplc electrospray ionisation esi mass spectrometry ms the main objective was to utilize the presence of intact phospholipids as a direct indicator of viable microorganisms the extracts of nankai trough sediments were found to contain a variety of phospholipid pl structures well known to stem from microorganisms to depths as great as 745 mbsf and in situ temperatures as high as 85 c in addition high relative amounts of lysophospholipids e g lysophosphatidylcholines exceeding those of the regular phospholipids were detected diglyceride mass fragments of various pls have been assigned to fatty acyl side chains of typical chain length c14 c16 c18 c20 and degree of unsaturation zero one or two double bonds similar results were obtained for the phospholipid distribution in extracts of organic matter rich hydrate ridge sediments to date the enhanced occurrence of lysophospholipids cannot be explained completely but a response to increasing thermal and ecological stress seems probable

a review of prokaryotic populations and processes in sub seafloor sediments including biosphere geosphere interactions article i nfo sub seafloor biosphere marine microbiology prokaryotic diversity dark energy biosphere geosphere interactions a general review of the sub seafloor biosphere is presented this includes an update and assessment of prokary otic cell distributions within marine sediments current deepest 1922 m and the impact of this on global sub seafloor biomass estimates these global estimates appear relatively robust to different calculation approaches and our updated estimate is 5 39 10 29 cells taking into consideration new data from very low organic matter south pacific gyre sediments this is higher than other recent estimates which is justified as several sediments such as gas hydrate deposits and oil reservoirs can have elevated cell concentrations the proposed relationship between elevated cell concentrations and milankovitch cycles in sequential diatom rich layers at some sites demonstratesnotonlyadynamicdeepbiosphere butalsothatthedeepbiosphereisanintegralpartofearthsys tem processes over geological time scales cell depth distributions vary in different oceanographic provinces and this is also reflected in contrasting biodiversity despite this there are some clear common sub seafloor prokary otes for bacteria these are the phyla chloroflexi gammaproteobacteria planctomycetes and the candidate phylum js1 and for archaea uncultivated lineages within the phylum crenarchaeota miscellaneous crenarchaeotal group and marine benthic group b euryarchaeota sagmeg marine benthic group d thermoplasmatales associated groups and thaumarchaeota marine group i in addition spores viruses and fungi have been detected but their importance is not yet clear consistent with the direct demonstration of active prokaryotic cells prokaryotes have been enriched and isolated from deep sediments and these reflect a subset of the total diversity including spore formers that are rarely detected in dna analyses activities are generally low in deep marine sediments 10 000 times lower than in near surface sediments however depth integrated activity calculations demonstrate that sub surface sediments can be responsible for the majority of sediment activity up to 90 and hence are biogeochemically important unlike near surface sediments competitive metabolisms can occur together and metabolism per cell can be 1000 times lower than

badland susceptibility assessment in volterra municipality tuscany italy by means of gis and statistical analysis badlands can be defined as complex and peculiar types of erosional formations that develop in clayey environments and are mainly favoured by lithological and topographic features as well as by markedly seasonal climate this work aims at assessing badland susceptibility in volterra municipality located in tuscany region italy by means of bivariate statistical analysis implemented in a geographic information system the volterra municipality is affected by intense soil erosion processes including rill and gully erosion usually turned out as badland forms mostly occurring on pliocene pleistocene clayey sediments firstly an inventory of 234 badland areas was produced on the basis of an available pre existing database integrated with the interpretation of aerial photographs and supported by a field survey badlands were distinguished in type a and type b according to different evolutional stage vegetation presence and consequently different landforms then nine geoenvironmental factors supposed to be predisposing for badland occurrence were chosen and combined with the spatial frequency of badland areas derived from the inventory through information value statistic approach the result was a badland susceptibility map that highlights a strong control of lithology slope gradient and land use in conditioning badland development in the investigated area the effectiveness of the performed model was demonstrated by a validation test computed through a receiver operating characteristics analysis the outcomes of this work provide an updated badland database that is useful for soil erosion management and further land use planning within the volterra municipality

morphological analysis and erosion rate evaluation in badlands of radicofani area southern tuscany italy abstract since 1988 geomorphologic research based on field surveys and photo geological analysis has been conducted in southern tuscany italy in areas characterised by very rapid morphological evolution in the area outcrop pliocene marine claystones uplifted during the quaternary up to 750 m above sea level now undergoing intense erosion processes leading to considerable badlands formation morphodynamic analysis conduced by direct and indirect measurements in a sample area were taken in order to quantify the erosion rate in badland areas the torrente piantrafolla sample area was chosen as representative of the study area it was most recently monitored during the period nov 2000 feb 2004 at this time morphographic and morphometric analyses carried out in selected measurement stations located on slopes identified gravity as the main morphogenetic process responsible for slope shaping the calanchi badland areas are characterised by constant and rapid shrinking of their edges resulting from landslides which occur in autumn and winter as a consequence of intense rainstorms selected measurement stations indicate an erosion rate value range from 5 to 7 5 cm y the comparison between 1976 and 1994 digital elevation models dem obtained from photogrammetric restitution indicated a mean erosion rate of about 5 cm y in a nineteen year period this value considerably higher than the values measured in other italian basins indicate a very rapid evolution of the slopes due mainly to small earth flows inside calanchi badlands

assessment of calanchi and rill interrill erosion susceptibilities using terrain analysis and geostochastics a case study in the oltrepo pavese northern apennines italy

a comparative study of late cretaceous ophiolitic basalts from new zealand and new caledonia implications for the tectonic evolution of the sw pacific abstract our understanding of the tectonic evolution of the sw pacific between the cretaceous and the miocene is incomplete during this period there were a number of ophiolitic complexes formed and emplaced including the tangihua ophiolite complex of new zealand and the poya terrane ophiolites of new caledonia both ophiolitic complexes contain rocks from only the uppermost levels of the oceanic crust have a similar age of formation and were emplaced during the eocene consequently it is thought that the two systems are somehow related however the poya terrane and the tangihua ophiolite complex have significantly different geochemistry the poya terrane basalts are predominantly p and n morb tholeiites generated during the opening of a small marginal basin north east of new caledonia whereas the tangihua basalts range from back arc tholeiites to calc alkaline arc basalts suggesting formation in an arc back arc setting the similarities in age emplacement and stratigraphy between the two systems must be a result of the tectonic regime operating within the sw pacific as the new geochemical information clearly shows that the poya terrane and the tangihua ophiolite complex are not directly related

space time variability of denudation rates at the catchment and hillslope scales on the tyrrhenian side of central italy studies on denudation rates can provide insight into the influence of climate change tectonics and human activities on landscape evolution research performed in central italy has shown considerable spatial variability of denudation rates in the major river basins these studies have focused mainly on the tyrrhenian side of the italian peninsula where plio pleistocene marine deposits filling nw se elongated sedimentary basins have been uplifted during the quaternary up to several hundreds of meters above present sea level small sub catchments developed on clays are affected by sharp and or rounded edged badlands i e calanchi and biancane representing denudation hot spots in the present day morphoclimatic framework in this paper we analyze the relationships between indirectly estimated denudation rates at the catchment scale and field monitoring data at the hillslope scale we attempt to better understand and quantify all hillslope processes that contribute to seasonal variability of denudation to help with predicting the net input from hot spots to the overall estimated sediment yield at the basin outlets at the hillslope scale we discuss in particular the variability of denudation rates at calanchi and biancane badlands as a function of their different morphoevolution

tectono magmatic evolution of the west philippine mariana region and the origin of boninites re examination of published data on the tectomagmatic evolution of the west philippine mariana region indicate that arc magmatism and back arc extensional pulses are not synchronous but are largely asynchronous arc volcanism ceases within a few million years of the development of a back arc basin and recommences oceanward on a new arc during the final stages in the development of the back arc basin following karig s model we believe that ascent beneath the arc axial chain of a line of diapirs of morb source mantle interferes with processes of arc magma generation and arc magmatism wanes partial melting of the diapirs produces voluminous morb type tholeiites which split the arc and form the crust of a widening back arc basin we show for both the west philippine mariana region and occurrences of boninite like lavas in ophiolites that boninites appear to be erupted after arc magmatism and immediately before eruption of morb type lavas passage of a diapir of hot morb source mantle through refractory sub arc peridotite which has been enriched in lile and h2o will result in limited partial melting of the hydrous peridotite and the restricted production of boninitic magmas these are more likely to erupt modified or only slightly modified by crystal fractionation through the thin forearc crust continued ascent of the morb source mantle diapir will result in it partially melting to yield morb tholeiites which erupt shortly after and in considerably more voluminous amounts than the boninites finally we suggest that forearcs regions are likely to be incorporated into foldbelts and that boninite or low ti lava bearing ophiolites may characterize such regions

water extraction of coals potential for estimating low molecular weight organic acids as carbon feedstock for the deep terrestrial biosphere abstract with the recent increasing interest in the deep biosphere the question arises as to where the carbon sources that support deep microbial communities are derived from our research was focussed on the water soluble low molecular weight lmw organic acids that are potentially available from different sedimentary lithologies to serve as a carbon source to feed the deep biosphere a series of eocene pleistocene coals mudstones and sandstones of varying rank maturity and total organic carbon toc content from the waikato basin new zealand has been soxhlet extracted using water the combined concentration of recovered formate acetate and oxalate range from 366 to 2499 g g sediment and appear to be dependent on rank organofacies and toc the yields indicate the potential of carbonaceous sediments to feed the local deep terrestrial biosphere over geological periods of time the existence of living microbial organisms in the mudstones and sandstones was proved by the identification of intact phospholipids pls

new sw pacific tectonic model cyclical intraoceanic magmatic arc construction and near coeval emplacement along the australia pacific margin in the cenozoic various reconstructions of the sw pacific for the late cretaceous and cenozoic suggest that northeast dipping subduction began in the south loyalty basin slb at 55 50 ma and that subsequent closure of the slb resulted in the diachronous emplacement of cretaceous paleocene ophiolitic nappes onto the norfolk ridge in new caledonia at 40 34 ma and in northland new zealand around 24 21 ma a fundamental problem with these models is that they do not account for the fact that ne dipping subduction had already been established offshore papua new guinea by at least 65 60 ma which resulted in the emplacement of the papuan ultramafic belt pub ophiolite at 59 58 ma a second issue is that the reconstructions are based largely upon unfounded assumptions as to the age and nature of the basement beneath the loyalty arc and three kings ridge finally reconstructions of the northland region are based upon the erroneous assumption that the age of the majority of the igneous component comprising the northland allochthon is late cretaceous paleocene when in fact it is oligocene a new model is presented whereby the pub new caledonia and northland ophiolites formed and were emplaced in a cyclical fashion above an extensive ne dipping cenozoic intraoceanic arc system which diachronously propagated n s along the entire eastern margin of the australian plate these infant arc ophiolites represent fragments of suprasubduction zone lithosphere sszl generated in the earliest stages of magmatic arc formation that were emplaced shortly after 20 m y as a result of forearc australian plate collision subduction inception was the result of subsidence of older morb like lithosphere generated within an extensive back arc basin to the east of the norfolk ridge during the earliest stages of slb formation above a southwest dipping pacific plate during emplacement of each ophiolite a crustal fragment of the older lithosphere was scraped off the ne dipping slab and subsequently back thrust beneath each ophiolite during its emplacement

the role of the hillside in determining the morphometric characteristics of calanchi the example of adriatic central italy abstract a typical example of badlands in the italian peninsula is the calanchi plural of calanco which may be defined as rapidly evolving very dense and hierarchical drainage systems whose genesis is controlled by mineralogical characteristics the granulometric composition of local lithotypes structural conditions hillside gradient and climate in this work some of the morphometric characteristics of the hillside were compared on a statistical basis with those of the drainage network of the calanchi for two large sample areas in adriatic central italy it was possible to demonstrate how the hillside environment strongly affects the activation of the process and the characteristics of the calanchi depending on their morphometric morphometric characteristics in particular the length inclination ratio of the hillside conditions the hydrographic pattern of the calanco system

a typical calanchi landscape on the eastern apennine margin atri central italy geomorphological features and evolution abstract the surroundings of the town of atri abruzzo region central italy situated about 10 km from the adriatic shoreline can be considered as representative of most part of the italian seaward peninsular landscape the subject of this research the calanchi landscape often generally considered as badlands by non italian authors is in fact made up of many singular landforms each of which calanco corresponds to a more or less extended hydrographic unit the dynamics are mainly the result of the action of the particularly aggressive climatic factors such as the mediterranean rainfall regime on weak substrata clay silt and sand of the plio pleistocene marine cycles the morphogenetic activity is not only limited to channel erosion but it is also due to repeated superficial slides so that it should in fact be better to consider the calanco as the result of a combined erosion process sensu zachar d 1982 soil erosion elsevier amsterdam since the mechanism regulating this process remains unclear this work wants to offer a contribution to this research field multitemporal geomorphological analysis has helped us to distinguish the different areas in which the calanchi evolution has been more or less important in the past in such a way it has been possible to characterize the landscape evolution as a function of the parameters that influence soil loss especially in areas such as that of atri where calanchi like landforms are highly developed moreover this analysis coupled with the processing of 40 years rainfall data also taking into account the concurrent land use changes has clearly shown that the areas affected by calanchi erosion on the eastern apennine margin still tectonically active are progressively diminishing

msi morphometric slope index for analyzing activation and evolution of calanchi in italy article i nfo the calanchi singular calanco are a typical example of italian badlands widespread in areas with hills of clay rich sediments and rocks they appear as a very dense and rapidly evolving drainage system characterized by an alternating pattern of narrow furrows and sharp crests the calanchi can be considered as small hydrographical basins characterized by two possible drainage patterns parallel and dendritic the two patterns show both linear and areal erosion processes in this study calanchi with dendritic drainage patterns were analyzed in three different areas representative of the italian peninsular atri in the abruzzi region mount ascensione in the marche region and orcia valley in the tuscany region for each calanchi the pre erosion topographic surface was reconstructed and the value of msi morphometric slope index was calculated for the surface the volume of eroded material was estimated by comparing the pre calanchi and present surfaces we assumed that slope morphometry influences the type of erosion processes and the efficacy of these processes with respect to the amount of eroded material is a func tion of their duration we deduced that calanchi inception was contemporaneous because the duration of the processes was common to all landforms and probably due to a common climate input moreover the relations among msi eroded volume and erosion processes indicate that over a long period areally distributed surface processes contribute more to total sediment yields than channel flows

effects of land use changes on badland erosion in clayey drainage basins radicofani central italy abstract hillslopes of the radicofani area in the upper valley of the orcia river southern tuscany region italy consist mainly of early pliocene clayey sediments and are widely affected by frequent badland erosion reforestation with frugal conifers has been carried out in the area over the last 50 years the goal of the present study is to evaluate the impact of reforestation and land use change on erosion rates in nine small drainage basins through a multidisciplinary approach geological geomorphological hydrological and land use characteristics were analyzed by a diachronic confrontation between pre reforestation 1954 and post reforestation 2007 situations aerial photo interpretation and processing in gis allowed us to quantify changes in areas affected by badland erosion land use and variations in erosion rates moreover dendrometric data were gathered from 18 circular sample plots in forest stands of 40 years old this allowed us to evaluate both the adaptability of different forest species to the clayey substrate and reforestation fragmentation the differences between the pre and post reforestation situations led to increases in arable land and forest areas and considerable decreases in erosion rates and badland areas however no significant correlation between the erosion rates and the forest area emerged due to the excessive fragmentation of reforestation cores and relatively small reforested surfaces land reclamation seems to have played a more important role in reducing erosion in the clayey substrate the integrated method presented here is an important tool useful to understand the morphological dynamics of badlands in relation to forest vegetation and for land planning and management

mulching effects on erosion from steep slopes and sediment particle size distributions of gully colluvial deposits abstract mulching is an effective soil conservation practice for permanent gullies in southern china knowledge of the sediment characteristics that occur in mulched soils of colluvial deposits could improve the utility of mulching for soil conservation a rainfall simulation experiment was designed to evaluate the effects of mulch on the runoff erosion and particle size distribution of eroded sediments straw mulch coverage of 0 25 50 75 and 95 was tested with simulated rainfall the effective particle size distribution of the sediment was compared with the ultimate particle size distribution to investigate the detachment and transport mechanisms involved in sediment mobilization mulching delayed the runoff initiation time and reduced the average runoff rate compared with bare soil the increased mulch coverage decreased the soil loss rate by 13 0 to 90 3 moreover the peak sediment concentration decreased from 80 to 200 g l 1 under the different mulch coverage conditions the optimal straw application rate was 1 5 to 3 0 mg ha 1 in the permanent gully s deposits the relationship between instantaneous kinetic energy of rainfall and the proportion of effective clay and sand sized particles was well represented using an exponential equation the effective clay sized sediments under the different mulch coverage conditions were 2 to 4 times more common than those of the original soil although there were only 13 9 sand sized particles in the sediment when the mulch coverage was 95 the silt sized sediment was transported as primary particles under the different mulch coverage conditions the effective to ultimate ratio of silt sized particles fluctuated around 1 there were depletions of clay and silt in the colluvial deposit soil with mulch cover and the enrichment ratios of clay and silt were larger than 1 while most of the enrichment ratios for sand were

geochemistry and tectonic significance of the tangihua ophiolite complex new zealand abstract the ophiolitic igneous complexes of the tangihua complex of northland new zealand consist of massive and pillowed basaltic lava sequences with intercalated sediments and lesser gabbro microgabbro and basaltic intrusions the complex also includes minor felsic derivatives younger alkalic intrusions which exhibit within plate characteristics and rare ultramafic rocks the lavas are relatively homogeneous and are dominantly tholeiitic basalts with minor calc alkaline and alkaline affinities the complex nature of the chemistry in particular those lavas with transitional arc signatures and the presence of non arc lavas is clear evidence that these volcanics formed in a suprasubduction zone environment the combined geochemical and tectonic constraints suggest that the tangihua complex formed in either a transitional zone between an arc and a back arc setting or in a zone of migration from arc to back arc volcanism as such the field age and geochemical data support the model in which these rocks formed suprasubduction zone crust and are fragments recording some or all stages of arc initiation arc rifting and back arc basin formation the orientation of the arc and back arc volcanic rocks in relation to the over tectonic regime suggests subduction towards the west recent work in the sw pacific shows that late cretaceous ophiolites are present in papua new guinea new caledonia and new zealand the formation of these ophiolitic systems supports the presence of a large scale tectonic regime convergence and consequent westward subduction stretching from papua new guinea to new zealand during the late cretaceous to early palaeocene

assessing the ratio of archaeol to caldarchaeol as a salinity proxy in highland lakes on the northeastern qinghai tibetan plateau abstract the ratio of archaeol to caldarchaeol the ace index has been proposed recently as an index for paleosalinity reconstruction and is based principally on archaeal core lipids cls from coastal salt pans turich c freeman k h 2011 archaeal lipids record paleosalinity in hypersaline systems organic geochemistry 42 1147 1157 we have examined possible relationships between salinity and ace in both cls and intact polar lipids ipls from suspended particulate matter spm and surface sediments of lakes and surrounding soils on the northeastern qinghai tibetan plateau our results showed that ace values were positively correlated with salinity in all samples however cl ace values were systematically higher than ipl ace values probably due to different degradation kinetics of intact polar ip archaeol and ip caldarchaeol on the other hand surface sediment ace values from both cls and ipls were lower than spm ace values probably due to enhanced production of caldarchaeol relative to archaeol in the sediment our results demonstrate that the ace proxy reflects changes in salinity in diverse environments on the qinghai tibetan plateau which is promising for paleosalinity reconstruction however caution should be used when applying the salinity proxy before we have a better understanding of degradation kinetics of archaeal ipls and in situ production of caldarchaeol and archaeol in sediments

microbial lipid markers within and adjacent to challenger mound in the belgica carbonate mound province porcupine basin offshore ireland iodp expedition 307 abstract during the integrated ocean drilling program iodp expedition 307 for the first time a cold water coral carbonate mound was drilled down through its base into the underlying sediments in the current study sample material from within and below challenger mound located in the belgica carbonate mound province in the porcupine basin offshore ireland was investigated for its distribution of microbial communities and gas composition using biogeochemical and geochemical approaches to elucidate the question on the initiation of carbonate mounds past and living microbial populations are lower in the mound section compared to the underlying sediments or sediments of an upslope reference site a reason for this might be a reduced substrate feedstock reflected by low total organic carbon toc contents in the once coral dominated mound sequence in contrast in the reference site a lithostratigraphic sequence with comparatively high toc contents shows higher abundances of both past and present microbial communities indicating favourable living conditions from time of sedimentation until today composition and isotopic values of gases below the mound base seem to point to a mixed gas of biogenic and thermogenic origin with a higher proportion of biogenic gas oil derived hydrocarbons were not detected at the mound site this suggests that at least in the investigated part of the mound base the upward flow of fossil hydrocarbons being one hypothesis for the initiation of the formation of carbonate mounds seems to be only of minor significance

chemical transects across intra oceanic arcs implications for the tectonic setting of ophiolites systematic spatial variations in ti y and zr are found in volcanic sequences sampled as transects from back arc through arc to trench within the western pacific intra oceanic arc systems these correlations occur regardless of eruption age reflecting the retention of relative positions between individual tectonic units concentrations of these incompatible elements are taken to reflect the nature of the underlying mantle at a particular trench volcano distance during the subduction process volcanics become more depleted trenchwards implying that progressively shallower levels melts were extracted from more refractory or harzburgitic mantle a model is proposed whereby a subduction system is superimposed on a compositionally stratified mantle which is a product of an earlier spreading event on the basis of this evidence the trench distance variation model is applied to the troodos ophiolite complex similar spatial changes in lava chemistry are found across the ophiolite providing evidence for the relative position of the troodos trench and direction of subduction beneath the troodos basin these findings have implications for studies in other orogenic terrains where structure and exposure permit their application

theoretical constraints to gully erosion research time for a re evaluation of concepts and assumptions gullies are conceptualized in the literature as essentially fluvial forms with dimensional boundaries arbitrarily defined between rills and river channels this notion is incompatible with the existing variability of form and process as mass movements frequently exert a fundamental control on gully initiation and expansion to the point of features outgrowing their original contributing area the inability of a conceptual framework to incorporate existing observations inevitably constrains methodologies and research results in this commentary several examples of published results are contrasted with the prevailing assumption of an essentially fluvial nature with the purpose of encouraging discussion on the need for a revised conceptual framework in gully erosion research copyright 2011 john wiley sons ltd

metamorphism in oceanic layer 3 gorringe bank eastern atlantic gorringe bank is an anomalously high structure of the eastern part of the north atlantic which was known to be composed of mantle derived peridotites layer 4 and gabbros layer 3 during the submersible cruise cyagor ii in 1981 the contact between layer 4 and layer 3 was observed on mount gettysburg and interpreted as tectonic the overlying series of gabbro was extensively sampled on both mounts composing the bank gettysburg and ormonde coarse grained to pegmatoid clinopyroxene gabbros predominate and are associated with differentiated rocks ferrogabbros and diorites cumulate gabbros are missing the gabbroic section sampled is therefore interpreted as the upper part of the plutonic section most samples were strongly recrystallized during two distinct events metamorphism occurred close to the ridge axis from interaction of a seawater derived fluid with still hot gabbros high temperature shear zones favoured fluid circulation but the water rock ratio estimated from the sodium input was very small in undeformed rocks 1 the low w r ratio explains the strong evolution of the fluid phase and therefore some particular compositions of secondary minerals low temperature alteration occurred when the gabbros were tectonically emplaced close to the sea bottom

bay of islands and little port complexes revisited age geochemical and isotopic evidence confirm suprasubduction zone origin the bay of islands complex of the humber arm allochthon west newfoundland contains the best exposed ophiolite in the appalachian orogen associated structural slices the little port and skinner cove complexes also contain rocks formed in an oceanic domain although their relationship to the bay of islands complex remains controversial to constrain the origin of the complexes and obtain a better understanding of the geology of the humber arm allochthon we have undertaken an integrated geochronological geochemical and isotopic study a u pb zircon age of ma for the little port complex and a zircon and baddeleyite age of 484 5 ma for the bay of islands complex have been obtained geochemical and isotopic data on trondhjemitic rocks from the two complexes indicate that petrogenetic models for these rocks must account for fundamental differences in source materials and mineralogy during differentiation the little port complex trondhjemites are characterized by initial end of 1 to 1 whereas those

flow driven soil erosion processes and the size selectivity of eroded sediment on steep slopes using colluvial deposits in a permanent gully abstract colluvial deposits with loose coarse material are easily erodible in permanent gullies but the mechanisms of erosion and sedimentation during overland flow remain obscure hence the processes and mechanisms of the transportation of soil particles by overland flow were investigated in this study experiments were carried out in a 5 0 m long by 1 0 m wide flume using colluvial deposits the slope gradient varied from 36 to 84 and the flow rate ranged from 0 72 l m 2 min 1 to 2 88 l m 2 min 1 the runoff rate and sediment yield rapidly increased with increasing overland duration runoff and sediment were highly variable when the flume was treated with a high flow rate compared with a low flow rate with the fluctuation of sediment concentration under the high flow rate usually reaching 500 g l 1 the slope gradient and overland flow rate have strong impacts on sediment transport capacity the mean flow velocity and the unit stream power can be an optimal composite force predictor for estimating sediment transport capacity experimental results also revealed that the percentage of gravel sized particles increased with increasing flow rate and slope gradient but silt and clay fractions observed opposite trend the average enrichment ratio er of gravel was usually 2 16 l m 2 min 1 the bed load transport became an important mechanism however the simulation model overestimated these values

bacterial populations and processes in sediments containing gas hydrates odp leg 146 cascadia margin abstract bacterial populations and activity were quantified at three sites in the cascadia margin accretionary wedge off the west canadian american coast odp leg 146 at two sites sediments contained gas hydrates site 889 890 had a discrete zone of hydrate approximately 10 m above a bottom simulating reflector bsr at 225 m below sea floor mbsf and site 892 had disseminated hydrate in the upper 20 mbsf and a bsr at 74 mbsf site 888 was a control site without gas hydrates the control site 888 and top approximately 90 mbsf of site 889 890 had bacterial distributions similar to previous pacific ocean sites in the upper approximately 30 m of site 892 however bacterial populations were much lower suggesting inhibition by the high concentrations of h 2 s within the hydrate zone below this depth bacterial populations rose to concentrations consistent with other sites the control site was dominated by so 4 reduction and rates of ch 4 oxidation in the top 90 m were low 0 002 0 033 nmol cm 3 d 1 at site 889 890 bacterial populations and activity were stimulated in the discrete hydrate zone ch 4 oxidation rates increased in the middle of this zone to 134 5 nmol cm 3 d 1 ca 9 times the average rate at other depths resulting in a significant 10 increase in the total bacterial population the anaerobic process es responsible for this oxidation remain unclear despite so 4 reducing bacteria previously associated with ch 4 oxidation also being stimulated in this zone fluid flux into accretionary wedge sediments may be an important process in providing electron acceptors to maintain these relatively high rates of ch 4 oxidation this first microbiological study of gas hydrates indicates that bacterial processes are influenced by gas and fluid venting and they play a major role in geochemical changes within these deep 200 mbsf sediments

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

basalts erupted along the tongan fore arc during subduction initiation evidence from geochronology of dredged rocks from the tonga fore arc and trench a wide variety of different rock types were dredged from the tonga fore arc and trench between 8000 and 3000 m water depths by the 1996 boomerang voyage 40ar 39ar whole rock and u pb zircon dating suggest that these fore arc rocks were erupted episodically from the cretaceous to the pliocene 102 to 2 ma the geochemistry suggests that mor type basalts and dolerites were erupted in the cretaceous that island arc tholeiites were erupted in the eocene and that back arc basin and island arc tholeiite and boninite were erupted episodically after this time the ages generally become younger northward suggesting that fore arc crust was created in the south at around 48 52 ma and was extended northward between 35 and 28 ma between 9 and 15 ma and continuing to the present day the episodic formation of the fore arc crust suggested by this data is very different to existing models for fore arc formation based on the bonin marianas arc the bonin marianas based models postulate that the basaltic fore arc rocks were created between 52 and 49 ma at the beginning of subduction above a rapidly foundering west dipping slab instead a model where the 52 ma basalts that are presently in a fore arc position were created in the arc back arc transition behind the 57 35 ma loyalty three kings arc and placed into a fore arc setting after arc reversal following the start of collision with new caledonia is proposed for the oldest rocks in tonga this is followed by growth of the fore arc northward with continued eruption of back arc and boninitic magmas after that time

soil genesis and evolution on calanchi badland like landform of central italy abstract calanchi are badland like erosional landforms common in the mediterranean region which form from accelerated erosion processes the calanchi slopes naked or differently vegetated can be considered as formed by different ecological tesserae originated by the mutual interaction of several factors such as erosion geomorphology microclimatic conditions vegetation ground cover and pedogenesis however information about pedogenesis is rather scarce mainly because the soils developing on calanchi slopes are incessantly disturbed by erosion processes to understand the role of soil evolution on landslide erosion we considered three land facets each one made up of four tesserae t1 to t4 which represented the different steps of soil and vegetal evolution of calanchi the soil of each tessera was described sampled by genetic horizons and the samples were characterized for their physical mineralogical and chemical properties field observations and laboratory data suggest that pedogenesis in the calanchi badlands may progress until a critical threshold indeed advanced plant colonization and solum development improve soil structure increase soil organic matter and favor redistribution of nutrients along the profile the improvement of structure at depth fosters water storage and clay dispersion through soil leaching and reduction of ionic strength of the soil solution making soil less stable depending on the slope gradient the soil weight acquired during rainfall events may trigger landsliding mudflows or collapses that rejuvenate the surface

formation and emplacement of the northland ophiolite northern new zealand sw pacific tectonic implications petrological geochemical geochronological and palaeomagnetic data for rocks of the northland ophiolite terrane of northern new zealand suggest that it formed in a suprasubduction zone setting between c 29 and 26 ma at c 35 s close to its late oligocene obduction site cretaceous igneous rocks formerly considered to be part of the ophiolite probably represent the basement upon which the ophiolite was emplaced and are probably part of the mount camel arc related terrane the ophiolite is believed to have been generated in the southeastern south fiji basin close to a nw se oriented transform fault located to the sw of the vening meinesz fracture zone and was probably emplaced in response to the collision of the hikurangi plateau with eastern new zealand at the end of the oligocene this collision would have involved a major adjustment on the transform fault thereby allowing a portion of the upper crustal section of the southern south fiji basin to be emplaced southwestward onto northern new zealand as well as the coeval emplacement of the east cape allochthon to the south concomitant subduction of the lower crust mantle section led to the initiation of arc volcanism that resulted in the northland lower miocene volcanic plutonic suite

relationships between a new slope morphometric index and calanchi erosion in northern sicily italy the italian badlands or calanchi are common landforms in mediterranean areas including central and southern italy calanchi landforms may be compared to small hydrographic basins these landforms are characterised by dense hierarchical and rapidly evolving drainage systems carved into steep clayey slopes and by a sharply alternating pattern of furrows and narrow generally sharp crests this work presents a study of morphometric characteristics and a statistical analysis for two sites in northern sicily italy on outcrops of silty clay deposits affected by active erosion processes which give this area a typical calanchi landscape in particular factors closely linked to the characteristics of the hydrographic network and slope morphometry were considered and analysed the initial geometry of the slopes was reconstructed and statistically compared with that of the current calanchi slopes including the drainage network a new morphometric index morphometric slope index msi was defined to represent the initial slope geometry as a whole this index was found to be effective in defining the structure of hydrographic networks summarising the characteristics and type of slope evolution and quantifying the rate of soil erosion the rate was determined based on both linear gully erosion and areal landslides sheet and rill erosion morphogenetic processes and our analysis based on msi indicates the dominance of areal erosion msi could also be used for basins larger than calanchi to represent the characteristics of geomorphic processes

assessment of calanchi and rill interrill erosion susceptibility in northern liguria italy a case study using a probabilistic modelling framework abstract soils are a vital part of the natural environment and one of the most important natural resources the european mediterranean regions are particularly sensitive to soil degradation especially in italy many landscapes are prone to water related soil erosion processes such as rill interrill erosion sheet erosion gullies and complex processes forming calanchi corresponding to the english term badlands calanchi develop preferentially on plio pleistocene deposits which are highly susceptible to aquatic erosion processes this study focusses on the assessment of rill interrill erosion as well as calanchi erosion forms and features in previously none or very little studied areas of the langhe roero and monferrato located in the liguria and piedmont region northern apennines italy in this study we assess the driving factors and the spatial distribution of rill interrill and calanchi erosion processes using a geostatistical geostochastic modelling framework therefore a maximum entropy model a generalized linear model and a boosted regression tree approach were applied as independent environmental variables we selected dem based morphometric information as well as pedologic and geologic input data moreover we explore remote sensing techniques to derive information on the vegetation density and vitality the stochastic models applied show that the two very different soil erosion phenomena can be differentiated well with the chosen stochastic techniques the main drivers controlling the spatial distribution of aquatic soil erosion in the study area are soil type slope elevation and topographic wetness index the results of the maxent and brt model were confirmed by the glm application in terms of the significance of predictor variables generally the models show an acceptable to excellent performance with brt and glm outperforming maxent the single independent variable response curves gave valuable insights into the process triggering the erosion forms we were able to clearly differentiate between the processes looking at the response curves that show reasonable characteristics with all applied models

identification characterisation and analysis of the oltrepo pavese calanchi in the northern apennines italy abstract badlands are characteristic erosional forms distributed along the entire apennines in the italian context badland areas are called calanchi the plural of the word calanco in this paper we present the first calanchi inventory map of the oltrepo pavese area northern apennines italy in total 263 calanchi were mapped using remote sensing techniques like orthophotos google earth images as well as field recognition moreover calanchi were characterised from a geomorphologic geologic and a morphometric point of view the calanchi of the oltrepo pavese have been categorised in two geomorphological classes based on process related morphologies in the study area calanchi mainly occur in soft sedimentary bedrock materials such as melanges marls claystones and interstratified rocks the results show that calanchi formations are often related to faults and tectonic lineaments present in the study area moreover we analyse a 5 m cell size digital terrain model to detect correlations between calanchi and morphometric indices the calanchi defined and categorised for the first time in the study area show typical morphometric characteristics of apennine calanchi forms and features in particular they occur on concave south facing slopes on soft bedrock formations finally a multitemporal air photo interpretation over a 40 years period indicated a general decrease in calanchi areas the area reduction is mainly correlated to intensive land use changes combined with variations of precipitation pattern the revegetation trend was also confirmed by ndvi analysis based on landsat satellites images the calanchi were digitized and stored in a gis database providing the information for future quantitative modelling assessments

testing gis morphometric analysis of some sicilian badlands abstract calanchi badlands are erosion landforms characterized by areas with scarce or absent vegetation steep slopes knife edge divides and high erosion rates they are originated by a combination of morphogenetic processes partly similar to those shaping bigger fluvial landforms and therefore can be considered as field laboratories this paper presents the results of an investigation carried out in two badland sites located in sicily where the geometry of 25 calanchi has been characterized using digital elevation models having a mesh size equal to 2 m for each landform a power length volume relationship is established this relationship demonstrates that length of calanchi channels can be used as a reliable predictor of eroded volume as already verified for smaller linear erosion landforms such as rills ephemeral and permanent gullies moreover length volume width and depth of calanchi are combined into two dimensionless groups allowing to establish a morphological similarity between rills ephemeral permanent gullies and the studied badlands furthermore the hack s law which relates channel length to drainage basin area is applied to the 25 calanchi basins obtaining an exponent of this power law smaller than 0 5 this result indicates that basins do not become necessarily more elongate with increasing size finally the relationships between maximum length and width of the landforms are analyzed demonstrating that calanchi basins become wider and not longer and narrower when evolving and increasing their size

gas hydrate destabilization enhanced dewatering benthic material turnover and large methane plumes at the cascadia convergent margin mixed methane sulfide hydrates and carbonates are exposed as a pavement at the seafloor along the crest of one of the accretionary ridges of the cascadia convergent margin vent fields from which methane charged low salinity fluids containing sulfide ammonia 4he and isotopically light co2 escape are associated with these exposures they characterize a newly recognized mechanism of dewatering at convergent margins where freshening of pore waters from hydrate destabilization at depth and free gas drives fluids upward this process augments the convergence generated overpressure and leads to local dewatering rates that are much higher than at other margins in the absence of hydrate discharge of fluids stimulates benthic oxygen consumption which is orders of magnitude higher than is normally found at comparable ocean depths the enhanced turnover results from the oxidation of methane hydrogen sulfide and ammonia by vent biota the injection of hydrate methane from the ridge generates a plume hundreds of meters high and several kilometers wide a large fraction of the methane is oxidized within the water column and generates 13c anomalies of the dissolved inorganic carbon pool

tectonic implications of paleomagnetic data from the northland ophiolite new zealand abstract paleomagnetic sampling of 12 sites from two separate massifs of the northland ophiolite new zealand yields consistent results two characteristic nrm directions are recognised one of normal polarity associated with weakly magnetised rocks particularly intrusive dolerites and another of reversed polarity associated with strongly magnetised rocks particularly basaltic pillow lavas thermal and af demagnetisation shows that the normal directions are due to a secondary viscous component which reflects the present day field direction whilst the reversed directions are stable typically to 500 c reflecting either the primary trm or a hard secondary component the declination and inclination of this stable magnetisation differ substantially from that of the present day field implying significant tectonic movement or deformation of the ophiolite since formation anomalous declinations and inclinations are interpreted here in terms of rotations about vertical axes and tentatively latitudinal translation since no widespread significant tilting has been recognised within the massifs declinations are consistent with clockwise rotations of 50 and 120 for the cape reinga and mangakahia massifs respectively probably associated with obduction at a convergent margin with a right lateral slip component situated to the northeast of northland the anomalously low inclination vectors 30 40 are consistent with an origin at lower than present latitudes which if true implies long lived n s translation of oceanic crust in the southwest pacific region between cretaceous and oligocene times

mapping badland areas using landsat tm etm satellite imagery and morphological data abstract soil erosion is the most influential component of land degradation for its strong impacts on both natural and agricultural environments in order to support effective intervention and recovery policies for eroded areas monitoring techniques should take into account the space time variability of the processes involved and make use of assessed mapping methodologies as baseline criteria for studying the dynamics of landform development when using multispectral data for mapping eroded areas low spectral separability is a significant limit in areas with complex features where soil materials are frequently remixed by surface runoff since multispectral satellite images are a valuable data source for multi temporal analyses of erosion processes at the medium scale we assessed how accurately a badland area can be identified from landsat tm and etm data a protocol for an optimal mapping was built up by testing the performance of different supervised algorithms and input layers spectral and morphological tests were carried out in a well known badland area of basilicata italy with an extension of 8000 ha results obtained from the use of spectral bands with and without thermal channel and principal components returned an overall accuracy ranging from 53 for classification on first three components to 72 for classification on all bands from tm with low values for the kappa coefficient 0 30 0 50 showing that the spectral information alone are insufficient to accurately identify badland areas in order to improve mapping we found that the integration of slopes and aspects derived from a digital elevation model dem can overcome problems inherent to the low separability of spectral signatures the use of morphological data was tested for different classification algorithms and integration approaches in discriminating badlands the better performing algorithm was mlc maximum likelihood classifier and the best results were obtained by integrating all seven bands including tir with slope and aspect maps as input within the classifier a 0 85 and k 0 75 for both the sensors we selected such parameters because they play an important role in characterising badlands of study area from a morphological perspective but the proposed approach is also conceptually simple and can be easily exported to other areas the obtained results support the hypothesis that the combined use of remote sensing imagery and auxiliary morphological data significantly improves the mapping of badlands over large areas with heterogeneous features thus providing a useful methodology for long term studies on soil erosion processes

combining 2d basin and structural modelling to constrain heat transport along the muroto transect nankai trough japan abstract the nankai trough located southeast of shikoku island japan exhibits a zone of exceptionally high heat flow in the central part of the nankai trough the fossil spreading centre of the shikoku basin is subducted beneath the southwest japan arc we have modelled the temperature and maturation history along the muroto transect reaching from the tip of the thrust zone out into nearly undeformed quaternary and tertiary sediments seawards of nankai trough we used two balanced cross sections defining the sections before and after overthrusting as input for 2d basin modelling we can show that rapid burial and overthrusting during the quaternary in combination with a heat flow history following the cooling curve of a 15 ma old oceanic plate is not sufficient to explain the measured maturity of organic material in the sediments several heat flow scenarios derived from theoretical concepts yamano m kinoshita m goto s matsubayashi o 2003 extremely high heat flow anomaly in the middle part of the nankai trough physics and chemistry of the earth parts a b c 28 487 497 and previous modelling approaches e g brown k m saffer d m bekins b a 2001 smectite diagenesis pore water freshening and fluid flow at the toe of the nankai wedge earth and planetary science letters 194 97 109 spinelli g a underwood m b 2005 modeling thermal history of subducting crust in nankai trough constraints from in situ sediment temperature and diagenetic reaction progress geophysical research letters 32 l09301 doi 10 1029 2005gl022793 steurer j underwood m b 2003 clay mineralogy of mudstones from the nankai trough reference sites 1173 and 1177 and frontal accretionary prism site 1174 in h mikada et al eds pp 1 37 available from were tested the best match between observed maturity levels temperature and heat flow measurements is reached for a heat flow history which initially assumes the cooling of a 15 ma old oceanic lithosphere but is reheated to 170 180 mw m 2 during the phase of rapid burial in the quaternary this can be achieved either by assuming the onset of hydrothermal circulation in the cooling crust or by reheating caused by off axis volcanism at about 6 ma yamano m kinoshita m goto s matsubayashi o 2003 extremely high heat flow anomaly in the middle part of the nankai trough physics and chemistry of the earth parts a b c 28 487 497

development of concepts concerning the genesis and emplacement of tethyan ophiolites in the eastern mediterranean and oman regions this article uses evidence mainly from the eastern mediterranean and oman to help understand the origin and emplacement of ophiolites field studies in these regions emphasize the diversity of ophiolite related sedimentary and tectonic processes topics to be discussed here include the sedimentary covers of ophiolites their metamorphic soles related melanges and emplaced continental margin slope rise units modes of ophiolite emplacement will also be considered and tectonic reconstructions that have a direct bearing on the origin and emplacement of ophiolites the writer argues that there is compelling evidence that many ophiolites formed by spreading above intraoceanic subduction zones evidence from their intact sedimentary covers however indicates that such subduction was only incipient in most cases as directly associated volcanic arcs or back arc basins are rare metamorphic soles record fragments of oceanic lithosphere derived from settings ranging from open ocean to continental slope rise settings underlying melanges record the subduction of most of the ocean lithosphere formed at spreading ridges continental margin units beneath ophiolites demonstrate that these ophiolites were formed in ocean basins that were mainly initiated by continental rifting in the eastern mediterranean and oman regions ophiolite emplacement was commonly achieved by trench margin collision although strike slip transpression and large scale accretion along subducting margins played a role in some cases taking account of the mesozoic palaeotectonic setting of the eastern mediterranean region it is widely believed that ophiolites of two main ages mid jurassic and late cretaceous were formed in several small oceanic basins separated by rifted microcontinents the history of tethys in pre mesozoic time remains more open to question lastly giant subduction related ophiolites as in oman cyprus or the balkans may not be forming anywhere in the world ocean today but may instead relate to rare events in earth history when regional to global plate boundaries were drastically reorganised

primary relationships of basaltic intrusive rocks and siliceous sedimentary rocks in the northern chichibu belt shikoku island southwest japan abstract understanding the primary relationships between basaltic rocks and fossiliferous sedimentary rocks provides direct information on the timing and geologic setting of past oceanic igneous activity though the basalts associate with cherts in the northern chichibu belt have been petrographically identified as oia oit or morb such primary relationships of them are not well understood this paper provides the primary intrusive relation of basaltic rocks contact with chert and calcareous siliceous shale of sugyo area in the northern chichibu belt on shikoku island the sediments are included within the basalt as xenoliths and in the contact zone with the basalt they have been recrystallized and contain metamorphic minerals possibly produced by contact metamorphism due to the basalt intrusion these indicate that the basalts are sills or dykes that have intruded the sediments the cherts are radiolarian chert which alternate with the calcareous siliceous shale and include minerals of oceanic volcanic origins asselian radiolarian fossils are yielded from a subangular chert xenolith that was intruded by the basalt possibly before the chert had undergone complete diagenesis the petrography of the sills indicates they are alkali basalts x ray fluorescence analyses indicate that the basaltic rocks include subalkaline basalts and oceanic island tholeiite or oceanic island alkaline basalts we have concluded that the basaltic dykes and sills were products of asselian or younger intra plate volcanism at an oceanic area covered by a pile of pelagic siliceous sediments these asselian cherts are earlier than the sakmarian wordian and capitanian limestones that overlie intra plate basalts of ohnogahara part of the northern chichibu belt the basalt sills may therefore represent the early stages of intra plate igneous activity in the paleo pacific ocean

southwest pacific absolute plate kinematic reconstruction reveals major cenozoic tonga kermadec slab dragging tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench parallel slab motion through the mantle recently defined as a form of slab dragging we investigate here long term slab dragging components of the tonga kermadec subduction system driven by absolute pacific plate motion to this end we develop a kinematic restoration of tonga kermadec trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle estimating tonga kermadec subduction initiation is challenging because another new caledonia subduction zone existed during the paleogene between the australia and pacific plates we test partitioning of plate convergence across the paleogene new caledonia and tonga kermadec subduction zones against resulting mantle structure and show that most if not all tonga kermadec subduction occurred after ca 30 ma since then tonga kermadec subduction has accommodated 1 700 to 3 500 km of subduction along the southern and northern ends of the trench respectively when placed in a mantle reference frame the predominantly westward directed subduction evolved while the tonga kermadec trench underwent 1 200 km of northward absolute motion we infer that the entire tonga kermadec slab was laterally transported through the mantle over 1 200 km such slab dragging by the pacific plate may explain observed deep slab deformation and may also have significant effects on surface tectonics both resulting from the resistance to slab dragging by the viscous mantle

thin ophiolites of north island new zealand abstract the subsurface geometry of ophiolite bodies which is indicative of their structural style and hence obduction history is commonly inferred from stratigraphie and structural data however new gravity data reported here illustrate how under favourable circumstances detailed subsurface forms can be modelled ophiolites in northern new zealand are shown to be particularly thin sheets

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

link between ssz ophiolite formation emplacement and arc inception northland new zealand u pb shrimp constraints cenozoic sw pacific tectonic implications abstract new u pb age data from zircons separated from a northland ophiolite gabbro yield a mean 206 pb 238 u age of 31 6 0 2 ma providing support for a recently determined 28 3 0 2 ma shrimp age of an associated plagiogranite and 29 26 ma 40 ar 39 ar ages n 9 of basalts of the ophiolite elsewhere miocene arc related calc alkaline andesite dikes which intrude the ophiolitic rocks contain zircons which yield mean 206 pb 238 u ages of 20 1 0 2 and 19 8 0 2 ma the ophiolite gabbro and the andesites both contain rare inherited zircons ranging from 122 104 ma the early cretaceous zircons in the arc andesites are interpreted as xenocrysts from the mt camel basement terrane through which magmas of the northland miocene arc lavas erupted the inherited zircons in the ophiolite gabbros suggest that a small fraction of this basement was introduced into the suboceanic mantle by subduction and mixed with mantle melts during ophiolite formation we postulate that the tholeiitic suite of the ophiolite represents the crustal segment of ssz lithosphere sszl generated in the southern south fiji basin sfb at a northeast dipping subduction zone that was initiated at about 35 ma the subduction zone nucleated along a pre existing transform boundary separating circa 45 20 ma oceanic lithosphere to the north and west of the northland peninsula from nascent back arc basin lithosphere of the sfb construction of the sszl propagated southward along the transform boundary as the sfb continued to unzip to the southeast after subduction of a large portion of oceanic lithosphere by about 26 ma and collision of the sszl with new zealand compression between the australian plate and the pacific plate was taken up along a new southwest dipping subduction zone behind the sszl renewed volcanism began in the oceanic forearc at 25 ma producing boninitic like ssz and within plate alkalic and calc alkaline rocks rocks of these types temporally overlap ophiolite emplacement and subsequent miocene continental arc construction

the geochemistry of tholeiitic and alkalic plutonic suites within the northland ophiolite northern new zealand magmatism in a back arc basin abstract the northland ophiolite of new zealand consists mainly of tholeiitic basalts with subordinate alkalic volcanic rocks the alkalic rocks occur together with but are generally younger than the tholeiitis both the tholeiitic and alkalic suites include minor plutonic intrusives which range from gabbro to plagiogranite variations within the tholeiitic plutonic suite can be modelled in terms of low pressure crystal fractionation the evolution of the alkalic suite is more problematic because each massif appears to be derived from a slightly different parental magma new trace element chemistry presented in this study shows that the tholeiitic rocks formed from a mantle source that was compositionally modified by supra subduction zone processes but that the alkalic suite has a different chemical signature nevertheless both suites of rocks are interpreted as having formed in a back arc spreading system in this environment the addition of fertile mantle to the supra subduction wedge facilitated by subduction roll back provided a source for the alkalic rocks with mixed geochemical characteristics

late quaternary geomorphological evolution and erosion rates in the clayey peri adriatic belt central italy abstract this study analyses the geomorphological evolution during the last 20 000 years in two areas representative of the peri adriatic belt of central italy mt ascensione in the high hilly sector 600 1100 m a s l and the atri district in the hilly coastal sector up to ca 500 m a s l in both areas the lithostructural setting is characterized by an east verging monocline mainly composed of clayey formations the two areas are compared in relation to their morpho chronological aspects and geomorphological dynamics the results suggest two fundamental evolutionary phases 1 about 20 000 yr bp sedimentation occurred along the main valleys when the middle to upper portions of slopes were covered by colluvial deposits and 2 at the beginning of the holocene the climatic improvement triggered erosion along rivers producing deep and narrow valleys estimated denudation rates during the last 20 000 yr are 7 8 mm yr 1 for the mt ascensione area and 2 4 3 0 mm yr 1 for the atri district reflecting frequent landslides and fluvial erosion the rates are consistent with the data available in literature denudation rates double if we assume most of the erosion process took place after the beginning of the holocenic warming phase

phosphorus cycling in marine sediments advances and challenges abstract phosphorus p is a critical macronutrient for all living cells as it provides the phosphate ester backbone of nucleic acids plays a crucial role in the transmission of chemical energy by the atp molecule and is also a structural constituent in many cell components while p cycling in the marine water column has been the subject of many studies and reviews many aspects of the sedimentary p cycling remain poorly understood this is mainly due to low p concentrations in sediments and analytical difficulties associated with isolating distinct p forms from sediment samples the aim of this review is to highlight the advances made in our understanding of p cycling in marine sediments as a result of improved instrumentation and novel approaches some of these techniques range from sediment sequential extractions sedex to spectroscopic techniques 31p nmr and innovative isotope tracer experiments stable oxygen ratios in phosphate radioactive p isotopes while our understanding of p cycling has considerably improved numerous aspects of sedimentary p cycling including the fate of organic p in sediments as a function of redox conditions organic matter content and burial depth as well as turnover rates of different sedimentary p compounds remain poorly constrained the techniques presented in this review along with yet to be utilized innovative approaches used in soil and lacustrine sediment p research will play an important role in addressing these important questions and in furthering our understanding of this critical component of the p global biogeochemical cycle

soil detachment by overland flow on hillslopes with permanent gullies in the granite area of southeast china abstract permanent gullies are often initiated from rill erosion followed by the formation of abrupt deep and wide gullies when topsoil and subsoil are carried away by fast flowing surface water few studies have been performed to evaluate soil detachment processes on hillslopes with permanent gullies which may significantly affect the further development of gully erosion soil detachment was investigated by using natural undisturbed soil samples collected in different spatial locations upper catchment middle slope lower slope and scour channel of hillslopes with permanent gullies the relationships of soil detachment capacity with soil property root system and hydraulic parameters were quantified selected samples were tested in a hydraulic flume 3 8 m length 0 2 m width under five different shear stresses 3 67 7 81 10 50 13 97 and 17 28 pa soil detachment capacity was found to be significantly greater in the scour channel than in the other three hillslope positions for the initial and stable gullies the soil detachment capacity was notably reduced in the middle slope relative to the upper catchment and lower slope while a different trend was observed in the active gully the variability of soil detachment capacity at different spatial locations showed a negative correlation to bulk density soil cohesion clay organic matter and root density p

comment on geochemistry of the early miocene volcanic succession of northland new zealand and implications for the evolution of subduction in the southwest pacific by m a booden i e m smith p m black and j l mauk in a recent paper booden et al 2011 present new geochemical and petrological data of early miocene volcanics from the northland region northland volcanic belt in new zealand and interpret these data to support a particular regional tectonic model this tectonic model involves early miocene westward subduction of cretaceous pacific oceanic lithosphere below the northland volcanic belt and the authors interpret the volcanic belt as a continental magmatic arc although the new data are not in disagreement with such a tectonic model they provide more support for an alternative interpretation that involves a northeast dipping subduction zone furthermore geometric and plate kinematic data show that the west dipping subduction model is unviable geological and geophysical data contradict the model while geodynamic arguments indicate that the model is implausible here it will be shown that a subduction model involving a northeast dipping southwestward retreating slab made of the late cretaceous paleocene south loyalty backarc basin lithosphere that subsequently detaches is in agreement with the local geology geophysics and geochemistry is geometrically kinematically and geodynamically viable and fits within the regional southwest pacific tectonic framework

assessment of land degradation susceptibility by scenario analysis a case study in southern tuscany italy abstract in the mediterranean area land degradation phenomena are becoming more and more important due to future climate change and increasing climate variability as highlighted in recent global assessment projects such as the millennium ecosystem assessment or the dialogue on water and climate thus there is consistent evidence that extreme events such as droughts and floods are more frequent than before on the other hand the mediterranean area is strongly influenced by human activities such as cultivation over hundreds of years however in the last decades the cultivation methods and techniques are subject to profound changes such as mechanization use of fertilizers and pesticides remodellation of entire hillslopes etc this particular situation leads to and aggravates the existing stress on land resources as a result land degradation and soil erosion phenomena are leading to decreasing soil productivity or the loss of fertile top soil and related water quality and quantity issues the centre for soil erosion studies cres in grosseto tuscany recently started a study to identify and monitor changes of land use in southern tuscany italy the aim of this study is to assess land degradation sensitivity by scenario analysis as a proxi for land degradation surface wash erosion processes such as rill and interill erosion processes are chosen these present day processes are identified by aerial photo interpretation and subsequently modelled with a simple rusle approach on a monthly basis in this study boundary conditions such as future precipitation were taken from the a2 future climate scenario published by the international panel on climate change ipcc special report on emission scenarios sres moreover current land use was identified from aerial photographs and future land use scenarios were developed considering ecological and socio economical issues for present day conditions of the test area subsequently the different climate and land use scenarios were analysed to study soil erosion susceptibility on the landscape scale the study shows that even with a decline in precipitation volume until 2070 in some months higher erosion rates occur due to higher rainfall erosivity furthermore land use changes play an important role for soil erosion susceptibility as shown the various scenarios can effectively reduce or enhance soil erosion

fossilization and degradation of intact polar lipids in deep subsurface sediments a theoretical approach intact polar membrane lipids ipls are frequently used as markers for living microbial cells in sedimentary environments the assumption with these studies is that ipls are rapidly degraded upon cell lysis and therefore ipls present in sediments are derived from in situ microbial production we used a theoretical approach to assess whether ipls in surface sediments can potentially represent fossilized ipls derived from the upper part of the water column and whether ipls can be preserved during sediment burial previous studies which examined the degradation kinetics of ipls show that phospholipids i e ester linked lipids with a phosphor containing head group degrade more rapidly than glycosidic ether lipids i e ether linked lipids with a glycosidically bound sugar moiety based on these studies we calculate that only a minor fraction of phospholipids but a major fraction of glycosidic ether lipids biosynthesized in the upper part of the water column can potentially reach deep sea surface sediments using a simple model and power law kinetic degradation parameters reported in the literature we also evaluated the degradation of ipls during sediment burial our model predicts a log log relationship between ipl concentrations and depth consistent with what has been observed in studies of ipls in subsurface sediments although our results do not exclude production of ipls in subsurface sediment they do suggest that ipls present in the deep biosphere may contain a substantial fossil component potentially masking in situ ipl production

origin of biancane and calanchi in east aliano southern italy abstract areas underlain by plio pleistocene marine mudstone in south italy are severely affected by denudation processes and have been transformed into badlands with two well defined types of landform biancane and calanchi in this paper factors that contributed to the development of the aliano badlands and particularly to the geneses of biancane and calanchi have been studied based on aerospace data field observations on geomorphic processes and geological structure laboratory measurements of soil and bedrock samples and morphometric analysis several maps and spatial data were prepared to describe factors which are thought to be related with landform formations such as lineament distribution elevation slope and pipe distribution morphometric characteristics of biancane and calanchi steepness and slope length dominant active processes and the dip orientation of beddings joints and fault planes were investigated and 71 samples of soils and bedrock were taken to characterise their properties the results of the analyses of the soil bedrock samples show no significant differences in their properties between biancane and calanchi field observations do not support the idea that biancane are the final product of calanchi development but support the hypothesis that biancane and calanchi are formed under different terrain conditions related to structural patterns and denudation processes of highly erodible materials the origin of biancane is associated with highly dissected surfaces along a reticular system of small joints in contrast calanchi are formed on steep wall like slopes along larger lineaments where the rate of incision into the slopes surpasses the denudation of the densely vegetated back slope

geomorphological chemical and physical study of calanchi landforms in nw sicily southern italy abstract this work deals with an integrated geomorphological and chemical physical study of calanchi landforms in two sites ottosalme and catalfimo of nw sicily southern italy developed on dominant silty clay deposits the calanchi fronts are characterized by different morphological features and dominant geomorphic processes sharp knife edged ridges and concentrated water runoff dominate at ottosalme and smoother landforms affected by mass movements mud flows and translational slides prevail at catalfimo we focused on some geochemical and physical parameters such as ph total dissolved salts sodium adsorption ratio sar porosity plastic and liquid limits as possible causes of the above differences with special emphasis on their role in discriminating the behavior of peculiar microforms such as a weathered outer crust and the corresponding inner massive portion unweathered substrate our results show that the main chemical physical features of calanchi morphologies and microforms often display no clear correlations with respect to those reported in the existing literature pointing to a higher complexity of patterns and behaviors in particular all samples consist of dispersive material sar values 10 but a more plastic and liquid behavior at catalfimo can explain a higher occurrence of landslides and smoother morphology than at ottosalme higher sar values at ottosalme well explain the dominance of concentrated water erosion the chemical behavior of the studied microforms is better described by ph being alkaline with higher values in the inner substrate than the outer crust and appears to minimize the effects of all other parameters and their responses to other external controlling factors lower sar values in the crust suggest that clay dispersivity is not the prominent factor controlling its surface detachment and mobility downslope which is more likely promoted by its higher porosity and consequent water absorption than the inner portion with changes in the saturation state shear strength and water pressure

a review of the gas hydrates geology and biology of the nankai trough abstract in this paper we review research conducted during the last 20 years on the active margin that forms the nankai trough off the southwest coast of japan the nankai trough exists along the convergent plate boundary between the philippine sea and eurasian plates an accretionary prism and a forearc basin occur landward of the nankai trough gas hydrates have been acquired through coring in the forearc basin bottom simulating reflectors bsrs an indicator of free gas which often subtends hydrate bearing strata are present throughout the nankai trough slope sediments are mainly composed of fine grained materials with low reflectivity instability possibly caused by uplift or tectonic activity occurs in the nankai trough with sliding being a major factor in the structuring of the terrain clam colonies calyptogena spp have been observed in numerous locations suggesting fluid flow along major thrust faults when first reported these clams represented members of the genus that had not previously been described most of the detailed information regarding the methane hydrates of the nankai trough comes from the drilling of three test wells 50 km off the omaezaki peninsula in water depths of 945 m the sediments from these boreholes were dominated by calcareous dark gray clay silt and siltstone with a tendency to become sandier toward the bottom of the hole cores collected in zones above within and below the hydrate bearing strata in these boreholes show pore water chloride concentrations ranging between 100 and 550 mm with a highly variable interval occurring between 150 and 270 m below sea floor mbsf compared with seawater values of 550 mm the freshening of the porewater extracted from the cores strongly suggests the presence of gas hydrates in sediments pore saturation of gas hydrate estimated from the chloride anomaly was as high as 80 in sandstones in some of the sediments direct counts of microorganisms in the samples show cell density at 105 cells g throughout the hydrate strata consistent with other marine sediments that have been studied clone libraries of the 16s rna gene created from extracted dna from the nankai trough sediments and isolates from sediment microbial enrichments indicate the presence of methanogenic microorganisms sequence analysis suggests that the microbial community in the nankai trough sediments is distinct from those in previously characterized methane hydrate bearing sediments on the cascadia margin and in the gulf of mexico the majority of the sequences from the nankai trough clone library were either of a novel lineage or most closely related to uncultured clones bacterial clones exhibited sequence phylogenetic relatedness to bacteroidetes planctomycetes actinobacteria proteobacteria and green nonsulfur groups whereas the archaeal clones could be classified within the euryarchaeota and crenarchaeota continued investigations of the nankai trough sediments will add to our understanding of the biogeochemical characteristics of this active margin that is so important to the islands of japan

geochemistry and tectonic setting of matakaoa volcanics east coast allochthon new zealand suprasubduction zone affinity regional correlations and origin in north eastern new zealand the late cretaceous to eocene submarine volcanic rocks of the east coast allochthon referred to as matakaoa volcanics formed a dominantly mafic melange with minor abyssal sediments during the subduction of oceanic crust accreted and melanged pillow lavas and dolerites display the geochemical and isotopic features of tholeiites with some diversity referred to as midocean ridge basalts island arc tholeiites and back arc basin basalts the association of supra subduction tholeiitic magmas abyssal sediments and polymetallic volcanogenic sulphide deposits is typical of many back arc basins therefore a correlation with the alkaline and transitional basalts of the hikurangi manihiki ontong java plateau may be ruled out these petrological features and the fossil ages as well are closely similar to those of the tangihua complex northland allochthon and allow matakaoa and tangihua mafic volcanic rocks now separated by the modern havre trough to be correlated within one single late cretaceous to eocene 2 basin the consideration of possible younger ages oligocene is also discussed the occurrence of late cretaceous eocene oceanic crust with supra subduction zone affinities to the east of the norfolk ridge poses the problem of the intervening southwest dipping subduction the missing late cretaceous eocene arc and their relationship with southeast gondwana marginal break up

rill erosion processes on a steep colluvial deposit slope under heavy rainfall in flume experiments with artificial rain abstract understanding rill erosion processes is important in the prediction of soil erosion and the prevention of soil loss however limited information is available concerning the impacts of rainfall on rill erosion on steep slopes colluvial deposits with steep slopes make up the packed material underlying the collapsing walls in benggang which collapse due to hydraulic pressure and gravity they contain loose materials and large amounts of coarse particles the objectives of this study were to investigate the impacts of rainfall intensity and slope gradient on the rill erosion process rill development and rill flow dynamic mechanisms on the steep slopes of colluvial deposits the colluvial soils were subjected to simulated rainfall in a 5 m2 5 m by 1 m flume at heavy rainfall intensities 100 120 and 140 mm h 1 and on five steep slopes 20 25 30 35 and 40 rill erosion contributed significantly to colluvial slope erosion on average rills accounted for 61 of the soil loss and the effects of slope gradient were greater than those of the rainfall intensity after rill development rill density rill length width and depth all significantly increased correspondingly the soil loss rate sharply raised and irregularly fluctuated moreover the collapse of rill heads or sidewalls tended to increase the relative contribution to rill erosion and rill development the rill flow was characterized by transitional and subcritical flow regimes the rill flow velocity was the most sensitive hydraulic parameter and the unit stream power provided the optimal hydrodynamic parameter to characterize the dynamic mechanisms of rill erosion on colluvial deposits the collapse of rill heads or sidewalls could result in negative values for critical shear stress critical stream power and critical unit stream power of rill erosion which were 19 pa 5 3 n m 1 s 1 and 0 09 m s 1 respectively these results provide a better understanding of the mechanism of rill erosion on steep slopes

gully erosion susceptibility assessment by means of gis based logistic regression a case of sicily italy article i nfo article history this research aims at characterizing susceptibility conditions to gully erosion by means of gis and multivariate statistical analysis the study area is a 9 5 km 2 river catchment in central northern sicily where agriculture ac tivities are limited by intense erosion by means of field surveys and interpretation of aerial images we prepared a digitalmap of thespatial distribution of 260 gulliesinthestudy area inaddition fromavailable thematicmaps a 5 m cell size digital elevation model and field checks we derived 27 environmental attributes that describe the variability of lithology land use topography and road position these attributes were selected for their potential influence on erosion processes while the dependent variable was given by presence or absence of gullies within two different types of mapping units 5 m grid cells and slope units average size 2 66 ha the functional re lationships between gully occurrence and the controlling factors were obtained from forward stepwise logistic regression to calculate the probability to host a gully for each mapping unit in order to train and test the predictive models three calibration and three validation subsets of both grid cells and slope units were randomly selected results of validation based on roc receiving operating characteristic curves attest for acceptable to excellent accuracies of the models showing better predictive skill and more stable performance of the susceptibility model based on grid cells

badlands denudation hot spots the role of parent material properties on geomorphic processes in 20 years monitored sites of southern tuscany italy abstract some monitoring stations have been recording for 20 years the geomorphic processes acting on calanchi and biancane badlands located in the tyrrhenian side of central italy field monitoring was aimed at studying the dynamics of surface processes such as sheet rill and gully erosion shallow landsliding piping and tunneling considering their space time variability as a consequence of both natural factors and human pressure this paper shows the results of grain size geochemical and mineralogical composition of parent materials from upper orcia valley sites southern tuscany to further elucidate the role of their properties on processes acting on both bare and vegetated surfaces parent materials properties are discussed with respect to the initiation and development of different badlands processes in particular clay dispersivity at different depths in the sample sites is examined as a well known controlling factor of accelerated erosion thus providing some interesting clues for understanding the spatial variability of denudation rates in the considered badlands sites

dynamic processes controlling evolution of rifted basins abstract the extension of the lithosphere controlling the development of rifted basins is driven by a combination of plate boundary forces frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system although mantle plumes are not a primary driving force of rifting they play an important secondary role by weakening the lithosphere and by controlling the level of rift related volcanic activity a distinction between active and passive rifting is only conditionally justified the extension of the lithosphere depending on its rate and magnitude and the potential temperature of the asthenosphere can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere in rift systems the level and timing of volcanic activity is highly variable the lack of volcanic activity implies passive rifting an initial passive rifting stage can be followed by a more active one during which magmatism plays an increasingly important role magmatic destabilization of the moho may account for the frequently observed discrepancy between upper and lower crustal extension factors combined with evidence for thermal thinning of the mantle lithosphere this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models the structural style of rifts is controlled by the rheological structure of the lithosphere the availability of crustal discontinuities that can be tensionally reactivated the mode orthogonal or oblique and amount of extension and the lithological composition of pre and syn rift sediments simple shear extension prevails in rifts that subparallel the structural grain of the basement pure shear extension is typical for rifts cross cutting the basement grain pre existing crustal and mantle lithospheric discontinuities contribute to the localization of rift systems the duration of the rifting stage of extensional basins is highly variable stress field changes can cause abrupt termination of rifting in major rift systems progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts depending on constraints on lateral block movements crustal separation can be achieved after as little as 9 my and as much as 280 my of rifting activity syn rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere its magmatic inflation and thermal attenuation of the mantle lithosphere post rift basin subsidence is governed by thermal reequilibration of the lithosphere asthenosphere system deep seated thermal anomalies related to syn rift pull up of the asthenosphere lithosphere boundary have decayed after 60 my by about 65 and after 180 my by about 95 the magnitude of post rift subsidence is a function of the rift induced thermal anomaly and crustal density changes the potential temperature of the asthenosphere and initial water depths intraplate stresses can have an overprinting effect on post rift subsidence stretching factors derived from post rift subsidence analyses must be corrected for such effects

north eastward subduction followed by slab detachment to explain ophiolite obduction and early miocene volcanism in northland new zealand oligocene miocene models for northern new zealand involving south westward subduction to explain early miocene northland volcanism do not fit within the regional southwest pacific tectonic framework a new model is proposed which comprises a north east dipping south loyalty basin slab that retreated south westward in the eocene earliest miocene and was continuous with the north east dipping subduction zone of new caledonia in the latest oligocene the trench reached the northland passive margin which was pulled it into the mantle by the slab resulting in obduction of the northland allochthon during and after obduction the slab detached from the unsubductable continental lithosphere inducing widespread calc alkaline volcanism in northland the new model further explains contemporaneous arc volcanism along the northland plateau seamount chain and sinking of the northland basement followed by uplift and extension in northland

a new empirical model for estimating calanchi erosion in sicily italy abstract calanchi plural of calanco are typical badland landforms of the italian landscape they consist of dense networks of v shaped valleys with a sparse or absent vegetation cover which frequently develop on unconsolidated or poorly consolidated clayey deposits in this paper the dimensional analysis and the incomplete self similarity theory were used to deduce a model relating the volume of sediments eroded from the calanchi area to a set of geometric attributes of their tributary areas the morphometric characteristics of 209 calanchi basins were used to calibrate and validate the model the predictive skill of the model was assessed by calculating the mean square error and the nash sutcliffe model efficiency coefficient the model was found to provide a reliable prediction of eroded volume from basins entirely covered by calanchi landforms as well as from basins only partially affected by badland erosion processes furthermore as the residuals between the calculated and the measured volume of the eroded material are normally distributed the deterministic model may be considered complete meaning that no other variables are necessary to explain the studied physical process in other words the model is able to predict erosion volume in calanchi landforms from a deterministic point of view

living microbial ecosystems within the active zone of catagenesis implications for feeding the deep biosphere earth s largest reactive carbon pool marine sedimentary organic matter becomes increasingly recalcitrant during burial making it almost inaccessible as a substrate for microorganisms and thereby limiting metabolic activity in the deep biosphere because elevated temperature acting over geological time leads to the massive thermal breakdown of the organic matter into volatiles including petroleum the question arises whether microorganisms can directly utilize these maturation products as a substrate while migrated thermogenic fluids are known to sustain microbial consortia in shallow sediments an in situ coupling of abiotic generation and microbial utilization has not been demonstrated here we show using a combination of basin modelling kinetic modelling geomicrobiology and biogeochemistry that microorganisms inhabit the active generation zone in the nankai trough offshore japan three sites from odp leg 190 have been evaluated namely 1173 1174 and 1177 drilled in nearly undeformed quaternary and tertiary sedimentary sequences seaward of the nankai trough itself paleotemperatures were reconstructed based on subsidence profiles compaction modelling present day heat flow downhole temperature measurements and organic maturity parameters today s heat flow distribution can be considered mainly conductive and is extremely high in places reaching 180 mw m2 the kinetic parameters describing total hydrocarbon generation determined by laboratory pyrolysis experiments were utilized by the model in order to predict the timing of generation in time and space the model predicts that the onset of present day generation lies between 300 and 500mbelow sea floor 5100 5300mbelow mean sea level depending on well location in the case of site 1174 5 10 conversion has taken place by a present day temperature of ca 85 c predictions were largely validated by on site hydrocarbon gas measurements viable organisms in the same depth range have been proven using 14c radiolabelled substrates for methanogenesis bacterial cell counts and intact phospholipids altogether these results point to an overlap of abiotic thermal degradation reactions going on in the same part of the sedimentary column as where a deep biosphere exists the organic matter preserved in nankai trough sediments is of the type that generates putative feedstocks for microbial activity namely oxygenated compounds and hydrocarbons furthermore the rates of thermal degradation calculated from the kinetic model closely resemble ratesof respiration and electron donor consumption independently measured in other deep biosphere environments we deduce that abiotically driven degradation reactions have provided substrates for microbial activity in deep sediments at this convergent continental margin

on the evolution of marginal basins this paper presents a critique of the models proposed to explain the formation of back arc basins those marginal basins located behind active or inactive trench systems and whose origin is inferred to be subduction related several marginal basins are not generically back arc but rather are related to the initiation of subduction continental rifting or plate boundary readjustments models of back arc basin formation must be consistent with the observed characteristics of back arc basins which include the following 1 the crustal structure and magnetic lineation patterns of back arc and major ocean basins are similar implying that the processes of crustal accretion in both tectonic environments are also similar 2 arc trench systems without currently spreading back arc basins are in the majority 3 although petrographically similar to and within the compositional range of midocean ridge basalts morb back arc basin basalts babb show consistent geochemical differences from n type morb and are in many respects transitional toward island arc tholeiites iat 4 distinct babb and iat mantle sources may be in extremely close proximity during the initial rifting of an island arc 5 rifting of the volcanic arc may occur on either side of the line of active volcanoes 50 km and may vary from one side to the other along strike 6 a remnant arc is not always developed 7 back arc spreading may be initiated above subducted lithosphere but with time the center of spreading migrates away from the arc and no longer overlies a benioff zone and 8 there is no simple correlation between the timing of global plate reorganizations and the formation of back arc basins the three main classes of models proposed to explain back arc basin formation are mantle diapirism induced aesthenospheric convection and global plate kinematics because the driving mechanism for the first two classes of models is provided by the local subducting slab these models fail to explain the temporal and spatial distribution of back arc basins the third class of models proposes that back arc basins should form whenever global plate interactions require divergence between the overriding plate and the trench line the latter being observed to move only in a seaward direction with respect to a hot spot reference frame however the tectonic setting of several back arc basins suggests that they represent more than just a passive response to kinematic boundary conditions for example some dynamic back arc force seems required to move the new hebrides tonga and south sandwich forearc plates seaward neither the local nor the global models adequately specify the necessary and or sufficient conditions for back arc basin formation a better understanding of the processes associated with the initiation of rifting and of subduction is required arc rifting and back arc spreading are both secondary phenomena to subduction but they are also primary extensional phenomena fundamentally analogous to continental rifting and the initial spreading of major ocean basins

dendrochronological and geomorphological investigations to assess water erosion and mass wasting processes in the apennines of southern tuscany italy abstract the tyrrhenian side of the central apennines is located in a lively geological context in which uplift denudation dynamics played a key role in landscape evolution intense water erosion and gravitational processes led to the development of spectacular badlands on the widespread clayey hillslopes the crete d arbia badlands as part of the crete senesi of southern tuscany represent one of the most beautiful examples of these landforms developed on pliocene clays on the other hand these rapidly evolving landforms endanger the artistic heritage of the area as with the monte oliveto maggiore abbey that was constructed on the top of a badland hillslope and confers additional value to the landscape in the perspective of monitoring and reconstructing some significant phases of the relief evolution of this area an integrated approach has been used which is based on dendrogeomorphology and geomorphological monitoring techniques in particular the correspondence between the data from dendrogeomorphological indicators and the measured denudation rates on badland hillslopes was tested the sampling for dendrogeomorphological analysis has been performed in two stages on 45 trees of the pinus pinea l species on hillslopes affected by soil creep and shallow landslides in order to identify annual ring growth anomalies compression wood and roots exposure trees local behaviour is not homogeneous but some common trends have been detected on the basis of the anomaly index and compression wood since 1993 several monitoring stations at badland denudation hot spots have been equipped with erosion pins quantitative data from monitoring stations compared to pluviometric series indicated critical phases of denudation that were supported by dendrochronological data the integrated approach between dendrogeomorphology and geomorphological monitoring techniques allowed calibration of both tools in order to extend the analysis in the period preceding the field measurements this kind of approach capable of implementation in many contexts could be particularly helpful in order to forecast the relief evolutionary trend