granite geomorphology and its geological controls serra da estrela portugal abstract serra da estrela is an elevated granite massif in central portugal characterized by extensive plateau surfaces incised by deep valleys affected by quaternary glaciation bounded by steep fault generated escarpments the presence of seven major textural variants of granite provides an opportunity to study the relationships between lithology and relief whereas dem analysis helped to show the relationships between lithology and topography objectively the higher ground is associated with fine to medium grained granites and is typified by planar surfaces of low gradient with occasional angular tors and rock pedestals block fields built by angular material are common in the parts that were not previously glaciated less elevated parts of the plateau are supported by medium to coarse grained granites and show more varied topography with an abundance of tors boulder piles and depressions lithological boundaries locally coincide with slope breaks but this is not the rule in the northern part of the massif a deep topographic basin has evolved in biotite granite whereas deeply incised valleys follow major fault lines geological controls show a hierarchy in that gross relief reflects the pattern of tectonic uplift and subsidence whereas lithology and then fracture patterns become more and more important if one focuses on smaller and smaller landforms

development of offset channels across the san andreas fault the san andreas fault offsets some small gullies incising the relatively flat surfaces in the carrizo plain california among these gullies those with larger drainage basins have larger offsets probably because gullies that have larger floods can keep the channels entrenched and subjected to the fault displacement longer on the other hand older offset channels in the area which have much larger offsets indicate that the gradual shift to straighter courses seems probable only for offset channels able to keep and accumulate the offset for a long time the strike slip fault displacement offsets a channel as much as the channel can follow with some modification by fluvial processes until overbank floods at the upper bend induce channel avulsion to a straighter course or until the channel is captured by the beheaded and abandoned downstream reach of the adjacent channel moved with the fault displacement the offset channel promotes aggradation upstream from the upper bend and this makes the channel increasingly susceptible to overbank floods the older offset channels are confined in valleys and this condition is apparently preventive of channel avulsion or capture the strike slip fault displacement also deforms longitudinal profiles of channels assuming that the elimination of discontinuities in the longitudinal profile is the main response of fluvial processes to the deformation by fault displacement nearly continuous longitudinal profiles of some old offset channels seem to indicate the full adjustment the condition in which no more changes will occur as a response to fault displacement until the next fault slip deforms them the irregularities in longitudinal profiles of other offset channels indicate that the channel adjustment by fluvial processes may be occurring but not enough to eliminate the irregularities an offset river can attain a continuous longitudinal profile if it has enough time to adjust its longitudinal profile after the fault displacement otherwise the discontinuity reflecting a various degree of adjustment would remain in the longitudinal profile until channel avulsion or capture occurs the degree of adjustment and the probability of channel avulsion or capture depend highly on the fluvial ability and condition of each river as well as the time after the deformation

tectonic control of the tejo river fluvial incision during the late cenozoic in rodao central portugal atlantic iberian border staircases of strath terraces and strongly incised valleys are the most typical landscape features of portuguese rivers this paper examines the incision achieved during the late cenozoic in an area crossed by the tejo river between the border with spain and the small town of gaviao in the more upstream reach of this area the tejo crosses the rodao tectonic depression where four levels of terraces are distinguished during the late cenozoic fluvial incision stage the rodao depression underwent less uplift than the adjacent areas along the river this is reflected by the greater thicknesses and spatial extent of the terraces terrace genesis was promoted by impoundment of alluvium behind a quartzitic ridge and the local presence of a soft substratum outside this tectonic depression the tejo has a narrow valley incised in the hercynian basement with some straight reaches that probably correspond to ne swand nnw sse faults the terraces being nearly absent geomorphological evidence of tectonic displacements affecting the rodao dissected terrace remnants is described geochronological dating of the two younger and lower terrace levels of this depression suggests a time averaged incision rate for the tejo in the rodao area of ca 1 0 m ka over the last 60 thousand years a clear discrepancy exists between this rate and the 0 1 m ka estimated for the longer period since the end of the pliocene although episodes of valley incision may be conditioned by climate and base level changes they may also have been controlled by local factors such as movement of small fault bounded blocks lithology and structure regional crustal uplift is considered to be the main control of the episodes of valley incision identified for this large long lived river a model is proposed in which successive regional uplift events tectonic phases essentially determined the long periods of rapid river downcutting that were punctuated by short periods of lateral erosion and later by some aggradation producing strath terraces d 2004 elsevier b v all rights reserved

anisotropy of magnetic susceptibility studies in tertiary ridge parallel dykes iceland tertiary margin normal aishihik dykes yukon and proterozoic kenora kabetogama composite dykes minnesota and ontario abstract mafic dykes of different ages were collected from three different tectonic settings and analyzed using anisotropy of magnetic susceptibility ams as a proxy for magmatic flow during intrusion in iceland ridge parallel basaltic dykes were sampled on each side of the active tectonic boundary the dykes are k max orientation indicating vertical emplacement the eocene aishihik dyke swarm intrudes the yukon tanana terrane in the yukon province canada over an area 200 by 60 km these dykes were intruded normal to the accretionary margin are porphyritic andesites and have an intermediate geochemical signature based on major and trace element analyses ten dykes were sampled and 111 cores analyzed using ams and the dykes preserve a vertical k max orientation indicating intrusion was vertical through 30 km of continental crust the 2 06 ga kenora kabetogama dykes in northern minnesota and western ontario crosscut a variety of archean terranes thickness 50 km in a radiating pattern the unmetamorphosed basaltic dykes are 1 120 m wide 10 110 km in length are vertical in orientation and can be grouped as either being single intrusion or multiple intrusion composite dykes ams data preserve a vertical k max orientation for the southerly locations 2 dykes n 53 and horizontal k max for the remainder to the northwest 15 dykes n 194 maximum magnetic susceptibility axes 4 dykes n 92 for composite dykes are scattered and yield inconsistent flow directions with regard to the dyke margin almost all of our results are normal in that the magnetic foliation the plane containing k max and k int normal to k min is parallel to the dyke planes which gives us confidence that the magnetic lineations i e k max orientations are parallel to magmatic flow

morphologic patterns of stream channels on the active yishi fault southern shandong province eastern china implications for repeated great earthquakes in the holocene abstract stream channels totaling 427 on the active yishu fault were systematically measured in the field three categories of deflected stream channels were identified these were the r l and u groups which correspond to channels that are right laterally deflected left laterally deflected and those from which fault displacement cannot be determined respectively of the measured channels 48 7 are group u 37 7 group r and 13 6 group l each group has four different patterns that are strongly affected by local conditions such as channel density width of crush zone slope angle and stream incision and sedimentation by introducing a parameter the deflection angle which is defined as the angle between the fault slip direction on the downstream block and the downstream flow direction at least three paleoslip events preceding the 1668 m 8 5 earthquake at zuoshan were identified and their occurrence times estimated they were all within holocene time but the recurrence intervals seem to have become longer over the past 10 000 years the recurrence intervals appeared to be doubled from 2000 years to about 4000 years over the same period each faulting event was associated with 4 9 m right lateral displacement on the fault if the typical maximum displacement associated with each event is 8 m then the slip rate has decreased from 4 mm yr to about 2 mm yr however considering the possibility that the maximum displacement during each event may not be located at the same place then the recurrence interval on the whole rupture section could be underestimated because in that case the recurrence interval would not be a simple inverse relationship of the average slip rate

anatomy of turbidites and linked debrites based on long distance 120 x 30 km bed correlation marnoso arenacea formation northern apennines italy much of our understanding of submarine sediment laden density flows that transport very large volumes ca 1 to 100 km3 of sediment into the deep ocean comes from careful analysis of their deposits direct monitoring of these destructive and relatively inaccessible and infrequent flows is problematic in order to understand how submarine sediment laden density flows evolve in space and time lateral changes within individual flow deposits need to be documented the geometry of beds and lithofacies intervals can be used to test existing depositional models and to assess the validity of experimental and numerical modelling of submarine flow events this study of the miocene marnoso arenacea formation italy provides the most extensive correlation of individual turbidity current and submarine debris flow deposits yet achieved in any ancient sequence one hundred and nine sections were logged through a ca 30 m thick interval of time equivalent strata between the contessa mega bed and an overlying columbine marker bed correlations extend for 120 km along the axis of the foreland basin in a direction parallel to flow and for 30 km across the foredeep outcrop as a result of post depositional thrust faulting and shortening this represents an across flow distance of over 60 km at the time of deposition the correlation of beds containing thick 40 cm sandstone intervals are documented almost all thick beds extend across the entire outcrop area most becoming thinly bedded 40 cm in distal sections palaeocurrent directions for flow deposits are sub parallel and indicate confinement by the lateral margins of the elongate foredeep flows were able to traverse the basin in opposing directions suggesting a basin plain with a very low gradient small fractional changes in stratal thickness define several depocentres on either side of the verghereto high area the extensive bed continuity and limited evidence for flow defection suggest that intrabasinal bathymetric relief was subtle substantially less than the thickness of flows thick beds contain two distinct types of sandstone ungraded mud rich sandstone intervals record evidence of en masse debrite deposition graded mud poor sandstone intervals are inferred to result from progressive grain by grain turbidite deposition clast rich muddy sandstone intervals pinch out abruptly in downflow and crossflow directions in a fashion consistent with en masse debrite deposition the tapered shape of mud poor sandstone intervals is consistent with an origin through progressive grain by grain turbidite deposition most correlated beds comprise both turbidite and debrite sandstone intervals intrabed transitions from exclusive turbidite sandstone to turbidite sandstone overlain by debrite sandstone are common in the downflow and crossflow directions this spatial arrangement suggests either i bypass of an initial debris flow past proximal sections ii localized input of debris flows away from available sections or iii generation of debris flows by transformation of turbidity currents on the basin plain because of seafloor erosion and or abrupt flow deceleration a single submarine flow event can comprise multiple flow phases and deposit a bed with complex lateral changes between mud rich and mud poor sandstone

megaturbidite deposits in the holocene basin fill of lake como southern alps italy abstract for the first time limnogeological investigations have been carried out in lake como the deepest lake of the alps combining a bathymetric survey multibeam simrad 3000 with a high resolution seismic reflection study single channel 3 5 khz sub bottom profiler and a coring campaign gravity corer this data set enables detailed characterization of the sedimentary subsurface in the western branch of the lake the como branch which has a typical fjord morphology this paper focuses on the deepest part of the como branch argegno basin in which up to 3 5 m thick turbidite deposits are identified the basin fill of the como branch is characterized by well layered draping and onlapping pelagic sediments that are locally affected by creeping and that are intercalated with mass wasting deposits in particular with two large debris flow deposits evolving into megaturbidites in the deepest part of the basin the multibeam data together with the acoustic facies distributions and the volumes of these two major sedimentary deposits mt1 3 106 m3 and mt2 10 5 106 m3 indicate that they resulted from large slides at the northern tip of the como branch along the steep slopes of a sub lacustrine plateau the estimated ages of these events around the mid 12th mt1 and early 6th mt2 centuries are extrapolated from mean sedimentation rates based on radiocarbon 14c and radionuclide 137cs analyses from short cores in the argegno basin possible trigger mechanisms leading to these catastrophic events in the como branch include a combination of steep slope overloading with significant lake level fluctuations related to holocene climate change and or earthquake shaking the tentative age assignment places the age of both major mass movements near two other events mt1 near the occurrence of a major earthquake in the po plain in 1222 ad intensity ix mcs macroseismically derived magnitude 6 2 and mt2 near a megaturbidite triggered in 700 ad in a proglacial lake in southeastern switzerland blass a anselmetti f grosjean m sturm m 2005 the last 1300 years of environmental history in the sediments of lake sils engadine switzerland eclogae geologicae helvetiae 98 319 332 since dangerous tsunami like waves seiches can be generated by large sub aqueous landslides leading to such megaturbidites in this fjord like basin future studies are required 1 to constrain the age of these catastrophic events 2 to document the stabilities of the steep slopes in the como branch 3 to assess the expected frequency of such catastrophic events and 4 to model the propagation of large waves in the como branch and their potential damage along the highly populated lake shore

neotectonics and intraplate continental topography of the northern alpine foreland research on neotectonics and related seismicity has hitherto been mostly focused on active plate boundaries that are characterized by generally high levels of earthquake activity current seismic hazard estimates for intraplate domains are mainly based on probabilistic analyses of historical and instrumental earthquake catalogues the accuracy of such hazard estimates is limited by the fact that available catalogues are restricted to a few hundred years which on geological time scales is insignificant and not suitable for the assessment of tectonic processes controlling the observed earthquake activity more reliable hazard prediction requires access to high quality data sets covering a geologically significant time span in order to obtain a better understanding of processes controlling on going intraplate deformation the alpine orogen and the intraplate sedimentary basins and rifts in its northern foreland are associated with a much higher level of neotectonic activity than hitherto assumed seismicity and stress indicator data combined with geodetic and geomorphologic observations demonstrate that deformation of the northern alpine foreland is still on going and will continue in the future this has major implications for the assessment of natural hazards and the environmental degradation potential of this densely populated area we examine relationships between deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland and their implications for tectonically induced topography for the environmental tectonics project entec the upper and lower rhine graben urg and lrg and the vienna basin vb were selected as natural laboratories the vienna basin developed during the middle miocene as a sinistral pull apart structure on top of the east alpine nappe stack whereas the upper and lower rhine grabens are typical intracontinental rifts the upper rhine graben opened during its late eocene and oligocene initial rifting phase by nearly orthogonal crustal extension whereas its neogene evolution was controlled by oblique extension seismic tomography suggests that during extension the mantle lithosphere was partially decoupled from the upper crust at the level of the lower crust however whole lithospheric folding controlled the mid miocene to pliocene uplift of the vosges black forest arch whereas thermal thinning of the mantle lithosphere above a mantle plume contributed substantially to the past and present uplift of the rhenish massif by contrast oblique crustal extension controlling the late oligocene initial subsidence stage of the lower rhine graben gave way to orthogonal extension at the transition to the neogene the entec project integrated geological geophysical geomorphologic geodetic and seismological data and developed dynamic models to quantify the societal impact of neotectonics in areas hosting major urban and industrial activity concentrations the response of europe s intraplate lithosphere to late neogene compressional stresses depends largely on its thermo mechanical structure which in turn controls vertical motions topography evolution and related surface processes

river patterns and their meaning abstract rivers are largely responsible for shaping the earth s continental landscapes river patterns the spatial arrangements of channels in the landscape are determined by slope and structure at site and sector scale channel morphology varies spatially and in time but river patterns and drainage texture or the frequency of stream lines per unit area together determine the intricacy or otherwise of topography most river patterns evolve through natural selection slope induces the formation of such patterns as parallel radial and distributary while structure produces straight angular trellis and annular arrangements once established patterns tend to persist nevertheless at many sites the usual patterns have been disturbed and patterns that are anomalous in terms of slope and structure have been produced by diversion tectonism volcanism glaciation mass movements and human activities by antecedence superimposition inheritance or underprinting by the persistence of deeply eroding rivers which encounter alien structures and by climatic change river patterns provide clues to underlying structure and to the chronology of events they have also proved significant in the search for minerals

complex tectonic and tectonostratigraphic evolution of an alpine foreland basin the western duero basin and the related tertiary depressions of the nw iberian peninsula abstract the tectonic and tectonostratigaphic evolution of foreland basins and related tertiary depressions are the key to investigate deformation history and the uplifting of the continental lithosphere of the alpine pyrenean orogeny the northern part of the duero basin is the foreland basin of the cantabrian mountains which are in turn the western part of the pyrenean orogen we have studied the western sharp end of the duero foreland basin and its relation to the tertiary deposits of the nw iberian peninsula and the topography evolution in order to propose a coherent tectonic and tectonosedimentary model that could explain all tertiary deposits we have analysed the depositional environment stratigraphic sequences paleocurrents and established a correlation of the main outcrops besides a detailed structural mapping of the alpine structures that limit and affect the main tertiary outcrops has been carried out the tertiary deposits of the nw iberian peninsula depressions are affected and fragmented by alpine structures that limit their extensions and locations the stratigraphic succession is similar in the nw tertiary outcrops they are mainly terrigenous and carbonated continental deposits formed by assemblage of alluvial fans developed at the mountains front in arid or semiarid conditions three formations can be identified in the main depressions toral fm santalla fm and medulas fm the nw tertiary outcrops were the western deposits of the duero foreland basin that surrounded the lateral termination of the pyrenean orogen these deposits were fragmented and eroded by the subsequent uplift of the galaico leoneses mountains and the ne sw strike slip faults activity broken foreland basin only the latest stages of some of these outcrops can be considered as intramontane basins as traditionally have been interpreted the sedimentation started in the northeast oviedo infiesto during the eocene and migrated to the west as pontes during the late oligocene early miocene times meanwhile southern areas were far away from the tectonic activity el bierzo o barco monforte sarria depressions

the xiong er volcanic belt at the southern margin of the north china craton petrographic and geochemical evidence for its outboard position in the paleo mesoproterozoic columbia supercontinent abstract the xiong er volcanic belt covering an area of more than 60 000 km 2 along the southern margin of the north china craton has long been considered an intra continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the paleo mesoproterozoic supercontinent columbia however such interpretations cannot be accommodated by lithology mineralogy geochemistry and geochronology of the volcanic rocks in the belt lithologically the xiong er volcanic belt is dominated by basaltic andesite and andesite with minor dacite and rhyolite different from rock associations related to continental rifts or mantle plumes which are generally bimodal and dominated by mafic components however they are remarkably similar to those rock associations in modern continental margin arcs in some of the basaltic andesites and andesites amphibole is a common phenocryst phase suggesting the involvement of h 2 o rich fluids in the petrogenesis of the xiong er volcanic rocks geochemically the xiong er volcanic rocks fall in the calc alkaline series and in most tectono magmatic discrimination diagrams the majority of the xiong er volcanic rocks show affinities to magmatic arcs in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative nb ta ti anomalies similar to arc related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge nd isotope compositions of the xiong er volcanic rocks suggest that 5 15 older crust has been transferred into the upper lithospheric mantle by subduction related recycling during archean to paleoproterozoic time available shrimp and la icp ms u pb zircon age data indicate that the xiong er volcanic rocks erupted intermittently over a protracted interval from 1 78 ga through 1 76 1 75 ga and 1 65 ga to 1 45 ga though the major phase of the volcanism occurred at 1 78 1 75 ga such multiple and intermittent volcanism is inconsistent with a mantle plume driven rifting event but is not uncommon in ancient and existing continental margin arcs taken together the xiong er volcanic belt was most likely a paleo mesoproterozoic continental magmatic arc that formed at the southern margin of the north china craton similar paleo mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of laurentia the southern margin of baltica the northwestern margin of amonzonia and the southern and eastern margins of the north australia craton which are considered to represent subduction related episodic outbuilding on the continental margins of the paleo mesoproterozoic supercontinent columbia therefore in any configuration of the supercontinent columbia the southern margin of the north china craton could not have been connected to any other continental block as proposed in a recent configuration but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the north china craton

late quaternary turbidite input into the east mediterranean basin new radiocarbon constraints on climate and sea level control the late pleistocene holocene 0 30 ka bp allochthonous sedimentation in the herodotus basin of the eastern mediterranean has been controlled in part by a combination of regional climatic change and eustatic sea level fluctuation a new series of radiocarbon dates made on planktonic foraminifers and pteropod shells taken from the pelagic and hemipelagic intervals between individual turbidite units has given bracketing dates for each major turbidity current event that deposited sand and mud on the herodotus basin plain two partly independent cycles are evident climate induced cycles have lead to an alternation of periods of turbidites sourced from the nile delta fan system with those from the north african shelf and anatolian rise these correlate with pluvial and inter pluvial climatic periods recognized in the nile hinterland sea level cycles have tended to focus turbidite emplacement from whatever source at periods of sea level fall within the latest wisconsin and sea level rise from the wisconsin holocene period in addition to the herodotus basin megaturbidite hbm described previously six other beds with volumes in excess of 25 km3 and wide lateral extent across the basin can be termed megaturbidites there is no simple sea level or climate control on the timing of these events so we must conclude that triggering and emplacement of megaturbidites is independent and variable

local stress fields and intraplate deformation of iberia variations in spatial and temporal interplay of regional stress sources tertiary to present deformation in the interior of the iberian peninsula reflects spatial and temporal variations of the activity of the plate boundaries local deformation patterns observed in many of the numerous intraplate tertiary basins and their borders such as the madrid basin and the sierra de altomira are at first sight incompatible with the regional stress field under which they were formed we demonstrate however that they can be explained as the effect of several stress fields that acted on the iberian peninsula from earliest tertiary onward data on local deformation can constrain both magnitudes and directions of forces acting on the plate boundaries of iberia enabling us to estimate the relative importance of the different plate driving and deforming mechanisms providing further constraints on the tectonic evolution of iberia

active tectonics seismicity and geomorphology with special reference to normandy france integrated studies based on tectonic seismotectonic and geomorphological analyses indicate that normandy northwest france has been an active area during the quaternary topography and landform discontinuities reflect the dislocation and differential uplift of a late cenozoic platform the tectonic activity is represented by i active faults indicated by linear scarps and seismic activity ii offsetting of pre existing surfaces iii plio pleistocene sedimen tation restricted within narrow subsiding zones and iv morphometric properties of drainage basins that indicate zones of differential uplift the inferred strain pattern involves i a shortening direction that strikes nw se as expected in the european context of alpine compression and ii a ne sw trending extension accommodated by nw se normal faults the geomorphological systems encountered in normandy preferentially record differential vertical displacements copy right 2000 john wiley sons ltd

modelling the impact of regional uplift and local tectonics on fluvial terrace preservation abstract a terrace formation model terrace combined with a longitudinal river profile model fluver was used to simulate fluvial terrace formation and preservation in the northwest iberian lower mino river basin under the influence of three tectonic conditions namely regional vertical uplift local basin subsidence and localised differential uplift the simulation results were compared against mapped terrace altitudes and deposit thicknesses the best results were achieved by combining all three tectonic factors indicating that specific terrace formation is a complex interplay of regional and local tectonics the best fit regional uplift rate of 0 10 m ka 1 over the past 600 ka is higher than the 0 08 m ka 1 previously estimated for a section farther to the west which can be attributed to an increase in tectonic uplift from the nw iberian atlantic margin toward the east local relative subsidence causes sediment accumulation in the local basin and less sedimentation in the fluvial terraces on the surrounding uplifting blocks different uplift rates on both sides of the valley caused preservation of unpaired terraces which are fill terraces on one side of the valley and strath terraces on the other side usually the formation of fill or strath terraces is considered to be only climate dependent our results indicate that local tectonics can be important in the terrace formation and preservation this suggests that terrace correlations in other river systems based on deposit thicknesses only might be over simplified

rate of outward growth of the mediterranean ridge accretionary complex abstract the position as a function time of the deformation front on the southwest flank of the mediterranean ridge accretionary complex is constrained as follows 1 a the deformation front is now active 2 b the site of core ban84 05gc was still near the abyssal plain when displaced shallow water benthic foraminifera of inferred african provenance were redeposited within an upper pliocene age unit 3 c the site of core ban84 05gc on the outer flank of the mediterranean ridge was already within the topographically rugged accretionary complex when a pliocene debris flow was emplaced 4 d dsdp site 125 had already been uplifted into a topographically elevated position when lower pliocene pelagic ooze was deposited 5 e a gypsum bearing breccia in dsdp site 125 requires that the site was either on the abyssal plain or within the tectonically active outer perimeter of the accretionary complex during the messinian salinity crisis 6 f dsdp site 377 had already been uplifted into a topographically elevated position when middle miocene age pelagic marl was deposited 7 g dsdp site 377 was still on or near the abyssal plain when early to lower middle miocene age smectite bearing turbidites of inferred african provenance were deposited and 8 h the mediterranean ridge began to grow by offscraping against a backstop formed by the alpine nappes of the hellenic arc at the time that subduction began 33 ma together these constraints define a range of potential growth curves for the mediterranean ridge with a rate of outward growth of approximately 0 5 to 2 cm yr this growth rate is faster than that inferred for most other modern accretionary prisms both as an absolute value and as a fraction of the subduction velocity an unusually thick incoming section and or an unusually weak evaporitic decollement may contribute to the rapid growth rate the inferred age of accretion does not increase linearly with distance from the deformation front rather there is an apparent acceleration of the rate of outward growth through time this observation may reflect a true acceleration of growth rate in response to the onset of back arc extension in the overriding plate aegean sea and or in response to the development of a weak basal decollement following the introduction of halite into the incoming stratigraphic section alternatively the non linearity of the age vs distance curve may indicate that shortening of the offscraped sediments continues across the breadth of the mediterranean ridge rather than being confined to the outer flank

a new conceptual model for the deposition process of homogenite application to a cretaceous megaturbidite of the western pyrenees basque region sw france abstract the north pyrenean megaturbidite is a 19 63 m exceptional thick bed deposited during the late turonian and extending over more than 90 km in the basque region country sw france its thickness varies from more than 63 m to about 19 m from east mauleon area to west basque coast it represents a total compacted volume of about 90 km3 of carbonates on the field rare sedimentary structures are visible in the turbidite bed they consist of laminar planar lamination and rare cross laminations in the eastern region and antidune like structures in the western region five sites have been sampled with a vertical step of 50 cm to 1 m thin sections have been quantitatively analyzed for counting the terrigeneous fraction the quartz grain size and the mineral orientation the deposits fine westward which suggests a source located in the east of the mauleon basin this is consistent with the quartz grain orientation in the lower part of the megaturbidite the deposits fine upward from medium sand to clayey silt this is consistent with the classical definition of homogenites and suggests that these kinds of deposits are turbidites these observations also suggest that the term megaturbidite is appropriated for these deposits the sedimentary analysis indicates that the deposit results from a single event the volume of sediment involved in the process as well as the quartz grain orientation indicating flow motion in the opposite direction of the initial flow and the antidune like structure suggest the formation of reflected flows and the formation of standing waves over the complete water column in the basque flysch sub basins corresponding to a seiche effect the origin of the megaturbidite is probably an earthquake generated collapse on the carbonate platform this example allows providing a new conceptual model for the process of homogenite deposition this model explains the deposition of thick fine grained crudely graded megaturbidites

low p metamorphism following a barrovian type evolution complex tectonic controls for a common transition as deduced in the mondonedo thrust sheet nw iberian massif the mondonedo thrust sheet has been studied to investigate the complex dynamic relationships that may be involved in the development of low and medium p metamorphic domains this unit underwent an initial medium p event during the initial stages of variscan convergence related to crustal thickening subsequently the thrust sheet evolved to a low p baric type of metamorphism related to syn convergence thinning and exhumation its footwall cropping out in two tectonic windows registered a different evolution with a low p history that evolved from low to high t under a high geothermal gradient several different p t paths of the mondon edo thrust sheet and its relative autochthon are traced and interpreted according to the structural evolution of the area following the initial crustal thickening two main syn convergence extensional shear zones developed one of them occurs in the hangingwall whereas the other affects the footwall unit both extensional shear zones were contemporaneous with ductile thrusting in the inner parts of the thrust sheet and their activity is viewed as a consequence of the need for gravitational re equilibration within the orogenic wedge the most commonly accepted models of tectonothermal evolution in regions of thickened continental crust assume that low p metamorphism is essentially a late phenomenon and is linked to late orogenic tectonic activity in the mondon edo thrust sheet our conclusions indicate that low p metamorphism may also develop during convergence and that this may occur in at least two cases one is tectonic denudation of an allochthonous unit during its emplacement and the other thinning and extension at the footwall unit of an advancing thrust sheet as a consequence the low p evolution may show different characteristics in different units of an orogenic nappe pile

interaction of two successive alpine deformation fronts constraints from low temperature thermochronology and structural mapping nw iberian peninsula the lateral termination of the alpine pyrenean orogen relief onshore is located in the nw iberian peninsula it overlies a variscan basement iberian massif where the sedimentary record of the alpine tectonic is very scarce thus the characterisation of the tectonic evolution of the lateral termination is difficult and timing and geometries of the main tectonic structures remain unclear combining the tectonothermal histories obtained by modelling of the apatite fission track data aft with structural mapping allows for a comparative study of the different tectonic scenarios and deformation transfer in the lateral termination of an orogen aft ages for the studied area vary from 53 5 12 9 and 222 12 ma from late triassic to early eocene the beginning of the cenozoic cooling episodes is in agreement with the infilling of the tertiary basins late eocene or oligocene calculated uplift for the alpine orogeny is around 2 400 m the cantabrian mountains were uplifted and emplaced southwards and the main period of exhumation began in the palaeogene at rates of 0 02 mm a and continued during the neogene at rates of 0 06 mm a however the galaico leoneses mountains located to the south of the studied area were uplifted and emplaced northwards during the neogene showing more rapid uplift rates of 0 08 mm a suggesting that the western termination of the alpine pyrenean orogen relief is the result of the successive interaction of two alpine deformation fronts

inversion of moment tensor focal mechanisms for active stresses around the microcontinent iberia tectonic implications the iberian microcontinent and its connected oceanic crust are affected by deformations related to the eurasian african plate boundary active stress inversions from populations of moment tensor focal mechanisms have been performed around and inside the iberian peninsula using a total of 213 moment tensor estimates main results are 1 the tensorial solutions show better consistency and lower misfits compared to those obtained previously from first p arrival focal mechanisms 2 along the eurasia africa western boundary the type of active stresses progressively changes easternwards from triaxial extension to uniaxial compression along the terceira ridge the gloria fault zone and the gulf of cadiz 3 in the betics alboran rif zone uniaxial extension predominates with shmax n155oe trending 4 in n algeria uniaxial compression reappears 5 the iberian foreland is currently under strike slip to uniaxial extension tensorial conditions

insights into the tectonic topography of the present day landscape of the central iberian peninsula spain abstract the landscape of today s central iberian peninsula has been shaped by ongoing tectonic activity since the tertiary this landscape comprises a mountain ridge trending e w to nw se the central system separating two regions of smooth topography the basins of the rivers duero and tajo in this study we explore interrelationships between topography and tectonics in the central iberian peninsula regional landscape features were analysed using a digital elevation model dem slope gradients and slope orientations derived from the dem were combined to describe topographic surface roughness topography trend surfaces inferred from harmonic analysis were used to define regional topographic features low roughness emphasizes the smooth nature of the basins topography where surfaces of homogeneous slope gradient and orientation dominate high roughness was associated with abrupt changes in gradient and slope orientation such as those affecting crests valley bottoms and scarp edges present in the mountain chain and in some deep incised valleys in the basins one of the applications of roughness mapping was its capacity to isolate incised valley segments the area distribution of incised rivers shows their prevalence in the east on a regional scale the topographic surface can be described as a train of ne sw undulations or waves of 20 km wavelength these undulations undergo changes in direction and interruptions limited by n s trending breaks e w and ne sw troughs and ridges clearly mark structural uplifts and depressions within the central system these structures are transverse to the compressive nw se stress field that controlled the deformation of the central iberian peninsula from the neogene to the present they represent the upper crustal folding that accommodates alpine shortening n s breaks coincide with late miocene faults that control the basins sedimentation further associated palaeoseismic structures suggest the recent tectonic activity of n s faults in the eastern part of the tajo basin apatite fission track analysis data for this area suggest the occurrence of a significant uplift episode from 7 to 10 ma which induced the river incisions appearing in the roughness map n s and ne sw faults could be seismogenic sources for the current moderate to low seismic activity of the east tajo basin and southeast central system although n s fault activity has already been established we propose its significant contribution to shaping the landscape

a thick holocene homogenite from the ionian abyssal plain eastern mediterranean abstract a homogenite layer thicker than 12 m holocene in age occurs in the ionian abyssal plain the graded sandy base is 1 3 m thick most of the layer is structureless and homogeneous in grain size and mineral composition the most remarkable components are siltsized grains composed of aragonite needles they are interpreted as skeleton fragments of the green alga halimeda sp the homogenite covers an area of at least 1100 km 2 and assuming a minimum thickness of 10 m comprises a volume of 11 km 3 the source of the material of the homogenite is a matter of speculation very likely it has been remobilized from different areas around the ionian abyssal plain as triggering event a tsunami generated by the collapse of the santorini caldera about 3500 yrs b p is assumed

seismic image of the cantabrian mountains in the western extension of the pyrenees from integrated escin reflection and refraction data abstract integrated analysis of normal incidence and large aperture seismic reflection data collected in 1992 and 1993 within the spanish escin and complementary projects provide a first complete n s crustal transect across the northern iberian peninsula and continental margin images of the crustal structure of the cantabrian mountains and their transition to the duero basin and to the cantabrian margin are obtained from a a 65 km long vertical reflection profile escin 2 on land b a 200 km long reversed refraction profile and c wide angle recordings of the marine escin 4 profile consistent results between reflectivity pattern and velocity depth distribution reveal important lateral variations in the deep structure the reflective crust imaged in the escin 2 profile changes its attitude from sub horizontal beneath the duero basin to north dipping beyond the mountain front basement thrusts are observed in the upper crust merging into a detachment at 6 s twt and may have triggered the alpine uplift of the range the moho is identified at the bottom of the reflective lower crust and deepens from 12 to 15 s at the northern end of the profile about 35 km inland modelling of the refraction data laterally extends the seismic image and provides evidence for variscan crustal features beneath the duero basin northwards the velocity in the lower crust decreases and the moho constrained by the wide angle data from profile escin 2 deepens to about 60 km ending abruptly at the shoreline the velocity depth model is constrained along the asturian platform up to the continental slope where the crust mantle boundary is located at 24 km depth this margin moho shows a progressive deepening southwards and extends to the coast where it is found at 30 km depth the present seismic data support an important alpine reworking and thickening of the crust under the cantabrian mountains the onshore offshore transition is marked by an imbrication of two crusts of very different thicknesses this signature offers a strong parallelism with the one previously observed further east across the pyrenees in the ecors seismic profile

evidence of relief inversion from the rim syncline of bannock basin abstract the last steps in the geological exploration of bannock basin cruises ban 88 and ban 89 of r v bannock provided direct evidence of an inversion of relief that was long suspected but hitherto never recorded dolostones and dolomitic mudstones of probable messinian age subcropping beneath the brine in the northern part of bannock basin and zanclean oozes recorded on the sill separating two narrow and elongate satellite basins along the eastern part of the rim syncline record a relief inversion during their evolution from cylindric folds to collapse structures in particular the core from the eastern intrabasin sill contains two major unconformities one separates early zanclean oozes from late piacenzian pelagic sediments characterized by winnowed layers inclined bedding and incipient hardgrounds and the second separates the latter from middle pleistocene pelagic sediments the deepening is certainly post late piacenzian post m pl 6 biozone because sediments of that age record an actively uplifting structure another argument in favour of the relief inversion and of the youthful age of the deepening is derived from a core raised from the northern part of the major western basins large sill separating maestro from borea basins which contains a coarse turbidite of north african origin representing an upflow turbidite similar to others recorded on the outer slopes of the mediterranean ridge this unique finding in the area of bannock basin is preserved in the central part of the collapse basin whereas in other settings an erosional gap is noticed at the equivalent stratigraphic position

sedimentological and geochemical evidence for seismoturbidite generation in the kumburgaz basin sea of marmara implications for earthquake recurrence along the central high segment of the north anatolian fault abstract holocene earthquake history of the central high segment of the north anatolian fault is examined here for the first time based on analysis of seismoturbidites within a 21 m long piston core recovered from the kumburgaz basin in the sea of marmara the visual lithological description combined with detailed grainsize analyses indicate that the deep basin hemipelagic sediments are interrupted by 28 turbidite units during the last 6 1 cal kyrs bp the turbidites show strong segregation and a sharp boundary between a coarse basal part and overlying homogenite as inferred from detailed sedimentological and geochemical data several amalgamated turbidites are recognized by repeated fining upward sequences with no intervening homogenite indicating multiple episodes of traction and deposition as a result of various slope failures and turbidity currents each amalgamated unit was possibly triggered by the same earthquake event rupturing in the sea of marmara the most common sedimentary feature is the continuous parallel lamination that was presumably introduced by long lasting water oscillations on suspended sediments due to the seiche effect the establishment of geochemical criteria and exclusive sedimentary processes distinguish earthquake triggered turbidites seismoturbidites from other trigger factors moreover such distinction allows us to evaluate hydrodynamic sedimentary conditions and processes in the kumburgaz basin the base of most seismoturbidites are associated with a sharp increase in mn concentration that can be explained by a diagenetic enrichment of mn at the oxic anoxic interface of the sediments near the seafloor prior to the deposition of the turbidite an age depth model of the studied core based on seven ams 14c ages allows correlation between historical earthquakes and seismoturbidites in the kumburgaz basin at least the latest nine of them fit well with the previously recorded major earthquake events between ca 500 cal yrs bp and 2 5 cal kyrs bp

influence of sea level and basin physiography on emplacement of the late pleistocene herodotus basin megaturbidite se mediterranean sea radiocarbon 14c dates from pelagic intervals above a megaturbidite in the herodotus basin give direct evidence of emplacement at the beginning of the last glacial period approximately 27 125 calendar years before present as sea level lowered rapidly and entered a low stand phase the herodotus basin megaturbidite is a basinwide deposit that forms a recognisable acoustically transparent layer on 3 5 khz high resolution seismic profiles and covers an area of approximately 40 000 km2 it thins from about 20 m in thickness proximally to some 10 m distally over a basin length in excess of 400 km the total volume is estimated at around 400 km3 which is significantly more than the volume of sediment that could have been displaced from its most likely source area the funnel shaped marginal embayment of the gulf of salum to the west of the nile cone the additional material may have been derived in part from synchronous failures on other parts of the libyan egyptian shelf and slope but most is believed to have come from large scale erosion at the base of the very large volume turbidity current that was generated from the original slide detailed sedimentary analyses of cores recovered from the megaturbidite show its distinctive characteristics graded sand silt mud and bioturbated mud units poorly developed structures proximally becoming more distinct and ordered distally variation in grain size and structures that suggest either flow separation reflection around topographic highs and or an inherently unstable flow and a mixed source bioclastic terrigenous composition these features together with its size and lateral extent would make any similar megabed an excellent marker horizon in basin analysis a combination of factors was responsible for triggering the initial slide debris flow event that evolved downslope into this mega turbidity current these include lowered sea level that destabilised the outer shelf upper slope sediments tectonic oversteepening of the margin relatively high rates of sedimentation and seismic activity

a dynamic concept for eastern mediterranean circulation and oxygenation during sapropel formation we propose that intermittent bottom water ventilation occurred throughout periods of sapropel deposition and that the recently reported sapropel interruptions represent centennial scale episodes of enhanced frequency intensity of that process in essence the modern high frequency variability in deep water formation affected by climatic variability over the northern basins on seasonal to longer time scales prevailed also at times of sapropel deposition although the overall ventilation state was much reduced this concept is supported by detailed multiple species isotope records for three aegean cores the presence of abundant globorotalia truncatulinoides within especially sapropels s7 and s8 in the western levantine basin observations of three rapid benthic repopulations within sapropel s6 in the deep western levantine basin a report of continuous benthic presence through sapropel s1 at intermediate deep locations offshore libya and further supporting information from the literature in the aegean records concomitant abundance of low oxygen tolerant benthic foraminifera and presence of the more oxyphilic benthic foraminifer uvigerina mediterranea with surface similar 13c values indicate repeated deep water re oxygenation events throughout the deposition of s1 the observations of a continuous benthic presence through s1 offshore from libya imply that no persistent anoxia developed at mid depth levels in that region which is far removed from direct deep ventilation influences the abundance of deep mesopelagic g truncatulinoides through several sapropels from the western levantine basin also suggests the presence of bio available oxygen at many hundreds of meters of depth moreover the rapid intermittent benthic repopulations within sapropels from the deep eastern mediterranean imply that bottom water anoxia was spatially restricted and or of a highly intermittent nature the short time scales of these repopulation events are incompatible with titration of an extensively anoxic water column and subsequent re establishment of water column anoxia we suggest that where anoxic azoic conditions were present they most likely were restricted to a veneer at the sediment water interface the extent of such an anoxic blanket depends on the balance between advective oxygen supply into the deep sea and biological and chemical oxygen demand the demand functions imply a decoupling of oxygenation from water mass advection allowing export production and corg posting rates to the sea floor to delimit the extent of the anoxic blanket in both space and time low productivity regions would develop no anoxic blanket allowing for the observed persistence of deep dwelling planktonic and bottom dwelling benthic faunas

slope instabilities from echo character mapping along the french guiana transform margin and demerara abyssal plain the french guiana transform margin and demerara abyssal plain have been recently surveyed in the framework of the extraplac french program of extension of the continental shelf guyaplac survey ifremer ifp shom ipev based on the interpretation of some of the data collected during the guyaplac survey simrad em12 multibeam bathymetric data backscatter imagery and 3 5 khz profiles the area can be divided into three morphostructural domains 1 the western guiana margin including a part of the demerara plateau an important bathymetric relief prolonging the continental platform off guiana and surinam this domain is bounded by 1a the nw se trending northern border of the demerara plateau which appears quite steep and corresponds to a transform segment of the margin 1b the n s eastern border of the demerara plateau which corresponds to a divergent segment of the margin the demerara plateau shows a segmented morphology lowslope gradients and a very rough surface ripples perpendicular to the slope direction nnw sse structural steps seem to correspond to collapses of 100 km long blocs towards the east slumps initiate along these directions the observed rough bathymetry seems to be related to creeping processes at a greater scale seismic data this part of the margin has been totally destabilized numerous imbricate transparent masses rooted at about 0 5 s t w t t belowseafloor thenw se trending northern border of the demerara plateau corresponds to a cliff like continental slope probably slightly smoother than other transform margins ghana co te d ivoire margin the n s eastern border of demerara plateau is characterized by numerous small scale imbricate slumps some of these failures seem to be emplaced in the prolongation of the nnw sse structural steps identified on the demerara plateau 2 the eastern guiana margin corresponds to a nw se oriented gullied transform margin segment the associated continental slope is very steep and characterized by numerous imbricate slumps and related debris lows some undulated masses probably corresponding to creeping sediments or to older mass wasting events are still imprinted on bathymetry this transform margin segment is nearly entirely destabilized and eroded 3 the demerara abyssal plain this domain is characterized eastwards by channels belonging to the amazon turbidite system and westwards at the foot of demerara continental slope by sediment waves probably created by contour currents to conclude it seems that there is a strong relationship between the structure transform and divergent segments and the emplacement of recurrent slope instabilities these are probably related to the steepness of the slopes but also to subsidence histories generating in some cases huge deep seated collapses of the whole margin fluid ascents are common everywhere in the area probably enhancing slope instability their origin is not constrained but the black shales or cretaceous organic rich layers could be good candidates

a computer interfaced sedigraph for modal size analysis of fine grained sediment a system has been developed allowing the direct storage on disc of size data from the x ray scanning settling tube sedigraph 5000et processing of the cumulative percentage data output to produce smooth frequency curves is described this allows rapid 15 min and precise m 0 1o discrimination of size modes peak heights median and silt and clay percentages of fine grained sediments an example of a mud turbidite is given showing systematic changes in bulk and modal properties not visible by eye lack of size segregation in the 1 m thickness of this turbidite shows that it may have been deposited from a highly concentrated flow rather than from a dilute waning turbidity current such flows may explain ungraded poorly graded muddy sediments also known as homogenites unifites or megaturbidites by other authors

isotopic and sedimentary signature of megathrust ruptures along the japan subduction margin abstract the m9 3 2004 sumatra and m9 0 2011 tohoku earthquakes and tsunamis had devastating consequences for the adjacent heavily populated coasts they had large shallow coseismic slip that reached the trench which is thought to be a key factor in generating the huge tsunamis the sedimentary record contains unique spatial and temporal information on the effects of megathrust earthquakes it can provide a better understanding of earthquake related tectono sedimentary processes and of the earthquakes themselves we present new results obtained from high resolution multibeam bathymetry subbottom profiles acquired with parasound and ten 10 m long piston cores recently collected from the japan trench margin during r v sonne so251 expedition we identify the 2011 tohoku event deposit extending for 250 km along the japan trench basins from the enrichment and concentrations of short lived radioisotopes excess xs210pb 137cs and 134cs in all ten cores the high enrichment of xs210pb points to surficial sediment remobilization as the main source in three cores from the northern central and southern segments of the japan trench for the first time we identify sediment remobilization by its 87 86sr end and pb isotope signatures and the composition and texture of the sediment with this new approach we fingerprint older sedimentation events potentially linked to earthquakes and infer processes responsible for their deposition thick acoustically transparent and homogeneous units we name homogenites characterize these event deposits physical geochemical and acoustic properties link homogenites to the 2011 tohoku and previous earthquakes we propose a multi stage entrainment and depositional process related with both the high frequency and the exceptionally large low frequency and long duration motions expected from ruptures of the shallow megathrust below the compliant outer upper plate these large long period motions could propagate along the outer upper plate beyond the rupture zone and could generate widespread entrainment of surficial sediment

configuration of the late paleoproterozoic supercontinent columbia insights from radiating mafic dyke swarms abstract remnants of 2 1 1 8 ga orogens can be recognized in nearly every craton assembled within reconstructions of the rodinia supercontinent although no particular pattern of laterally extensive orogenic belts emerges these cratons may be the fragments of an older supercontinent formed in response to the collision and accretion of even older cratons during the early earth history paleomagnetic constraints have played a limited role in many previous reconstructions of the early precambrian supercontinent mainly because of the poor age control and a large scatter of the paleomagnetic poles the geometry of giant radiating dyke swarms and orogenic belts provide important constraints for the reconstruction of the pre rodinian supercontinent some early unmetamorphosed and undeformed mafic dyke swarms in north china southern peninsular india and north america share coeval age of 1 85 ga if these continents are assembled the overall pattern exhibited by the mafic dyke swarms appears to constitute a giant radiating swarm with a piercing point between the cuddapah rift in south india and the xiong er aulacogen in north china this suggests that the north china craton indian craton and canadian shield may be fragmented from the same landmass the reconstruction of 1 85 ga giant radiating dyke swarm attempted in this paper suggests that the north china craton india craton and canadian shield were united together to form a landmass within the columbia supercontinent before its extension and break up the 1 90 1 85 ga andean style north orogenic belt suggests that a subduction zone existed on the northern margin of the north china craton wopmay orogenic belt developed in a 1 88 1 84 ga continental volcano plutonic arc which is interpreted as the product of eastward subduction of oceanic lithosphere the transantarctica orogenic belt in east antarctica may be another candidate to be linked with the subduction zone the north orogenic wopmay orogenic and transantarctica orogenic belts could be connected to form a continuous subduction zone the orogenic comparison strengthens the configuration of the columbia supercontinent proposed by the reconstruction of the giant radiating dyke swarm the laurentia west australia and east antarctica were relatively stable from 1 85 ga to 1 20 ga as inferred from the data on dyke swarms magmatism and the paleomagnetism these continents constituted the core of the columbia supercontinent in the late paleoproterozoic time the north china craton and indian craton were however separated from the columbia supercontinent during the mesoproterozoic time

the recent upper miocene to quaternary and present tectonic stress distributions in the iberian peninsula a general synthesis of the recent and present stress situation and evolution in the iberian peninsula was obtained from microstructural and seismological analysis the stress evolution was deduced from 1 fault population analysis fpa from 409 sites distributed throughout the iberian peninsula 2 paleostress indicators given by 324 stations taken from the bibliography and 3 seismic data corresponding to 161 focal mechanisms evenly spread in the studied region the application of fpa together with the determination of stress tensors and focal mechanisms for the whole iberian microplate has provided two main results 1 the iberian peninsula is undergoing a nw se oriented compression except for the northeastern part pyrenees ebro basin and iberian chain where it is n s to ne sw and the gulf of cadiz where it seems to be e w and 2 the main trends of the stress field have remained almost constant since the upper miocene the analysis performed by zones suggests the presence of local heterogeneities in the stress field

facies analysis of pleistocene sediments from the bannock basin area a key to the reconstruction of its tectonic evolution abstract facies analysis was carried out on 21 selected cores from the bannock area in order to investigate the relationships between sedimentation and tectonism bannock basin is a large 3500 m uncorrected deep subcircular depression near the deformation front of the mediterranean ridge facing the sirte abyssal plain the basin is divided into several sub basins aligned along a rim syncline surrounding a central elevated area salt dome high density brines and anoxic sediments occupy the deepest part of the depressions the facies distribution is controlled by the bottom configuration in that pelagic facies typically occur on plateaus and domes debris flow deposits in base of slope settings and turbidites in basinal settings the facies distribution may therefore be used to reconstruct the evolution of the various parts of the rim syncline erosional gaps may be related to tectonism or may be features created by the passage of major turbiditic events the results of our study of the facies associations and of the rates of sediment accumulation indicate that the collapse of the eastern part of the rim syncline pre dates the collapse of the western part the western basins are deeper and larger than the eastern ones and unlike the latter are aligned at the foot of a strike slip fault with a vertical offset of at least 700 m

assessment of recent tectonic activity on the nw iberian atlantic margin by means of geomorphic indices and field studies of the lower mino river terraces abstract until recently nw iberia was assumed to be tectonically quiescent stable however a combination of tectono morphological analyses demonstrates that neotectonic movements do occur which are in agreement with recent findings by other workers we use a dem based tectono geomorphic approach in combination with field work to assess the presence and nature of neotectonics in the lower mino catchment in nw iberia the area is characterized by clearly developed lineaments coinciding with paleozoic and mesozoic faults and fractures and remnants of a peneplain stepping down towards the coast longitudinal river profiles show knick points where lithological control can be excluded valley shapes show that some valleys have recently been rejuvenated systematic asymmetry tendencies of river catchments indicate tilting of fault bounded blocks finally at several locations faulted terrace deposits of the mino river have been found the types of motions that can clearly be evidenced by our analyses are normal faulting and tilting of fault bounded blocks little clear evidence exists for strike slip faulting whereas reverse faulting has not been found in this study a striking morphological feature of the study area is the presence of small fault bounded basins along the course of the river mino the tectonic movements take place along inherited paleozoic and mesozoic faults which apparently act as weakness zones the reactivation of these faults under the present day stress conditions is probably the reason for the complicated pattern and style of present day tectonic motions that we find the small basins are particularly difficult to explain they could result from the interaction of partially obliquely reactivated strike slip faults step over and normal faults

recent fold growth and drainage development the janauri and chandigarh anticlines in the siwalik foothills northwest india the active growth of a fault and thrust belt in frontal zones of himalaya is a prominent topographical feature extending 2500 km from assam to pakistan in this paper kinematical analysis of frontal anticlines and spatial mapping of active faults based on geomorphological features such as drainage pattern development fault scarps and uplifted quaternary alluvial fans are presented we analyse the geomorphic and hydrographic expressions of the chandigarh and the janauri active anticlines in the nw india siwaliks to investigate the morphological scenario during the folding process we used spatial imagery geomorphometric parameters extracted from digital elevation models and fieldwork folding between the beas and sutlej rivers gives clear geomorphological evidence of recent fold growth presumably driven by movements of blind thrust faults structural style within the janauri and chandigarh anticlines is highly variable fault propagation folds pop up structures and transfer faults the approach presented here involves analysis of topography and drainage incision of selected landforms to detect growth of active anticlines and transfer faults landforms that indicate active folding above a southwest dipping frontal thrust and a northeast dipping back thrust are described along strike differences in ridge morphology are measured to describe the interaction of river channel patterns with folds and thrust faults and to define history of anticline growth the evolution of the apparently continuous janauri ridge has occurred by the coalescence of independent segments growing towards each other by contrast systematic drainage basin asymmetry shows that the chandigarh anticline ridge has propagated laterally from nw to se

new findings of bronze age homogenites in the ionian sea geodynamic implications for the mediterranean abstract holocene homogenites similar in character and stratigraphic position to those previously recorded in the ionian basin and related to the gigantic tsunami originating from santorini bronze age eruption are described from a core transect crossing the deformation front of the mediterranean ridge east of victor hensen seahill investigations on grain sizes and carbonate content carried out on three cores from three different areas of the ionian basin encompassing the bronze age homogenite revealed important similarities and some differences the most obvious difference concerns the carbonate content which is minimum at the base of the unit in a core close to the messina abyssal plain whereas it is maximum in cores from the western mediterranean and calabrian ridges characterized by the typical cobblestone topography a terrigenous versus pelagic nature of the components is documented and a distal versus local provenance is inferred homogenites are critically compared with unifites a type of re sediment recently described from the eastern mediterranean comparison includes in particular a source and sediment transport and b triggering mechanism a substantial difference exists between the sedimentation patterns of the ionian and levantine basins seaward of the calabrian and hellenic arcs in the latest quaternary and the difference contains a clear geodynamic message sedimentation rates increase from the late pleistocene to the holocene in the ionian basin whereas they decrease in the levantine basin the glacio eustatic signal is well expressed in the levantine basin where the source areas are situated consistently in the south or on a passive type aseismic continental margin north african margin in the ionian basin on the contrary the glacioeustatic signal is totally obscured by the strong tectonic signal from the active northern continental margin of the mediterranean

cenozoic deformation of iberia a model for intraplate mountain building and basin development based on analogue modeling 1 inferences from analogue models support lithospheric folding as the primary response to large scale shortening manifested in the present day topography of iberia this process was active from the late oligocene early miocene during the alpine orogeny and was probably enhanced by reactivation of inherited variscan faults the modeling results confirm the dependence of fold wavelength on convergence rate and hence the strength of the layers of the lithosphere such that fold wavelength is longest for fast convergence rates favoring whole lithosphere folding folding is associated with the formation of dominantly pop up type mountain ranges in the brittle crust and thickening of the ductile layers in the synforms of the buckle folds by flow the mountain ranges are represented by upper crustal pop ups forming the main topographic relief the wavelengths of the topographic uplifts both in model and nature suggest mechanical decoupling between crust and mantle moreover our modeling results suggest that buckling in iberia took place under rheological conditions where the lithospheric mantle is stronger than the lower crust the presence of an indenter inducing oblique shortening in response to the opening of the king s trough in the north western corner of the atlantic iberian margin controls the spacing and obliquity of structures this leads to the transfer of the deformation from the moving walls towards the inner part of the model creating oblique structures in both brittle and ductile layers the effect of the indenter together with an increase on the convergence rate produced more complex brittle structures these results show close similarities to observations on the general shape and distribution of mountain ranges and basins in iberia including the spanish central system and toledo mountains

an example of intraplate neotectonic activity vilarica basin northeast portugal the vilarica tectonic basin nw iberian peninsula is presented as an example of intraplate neotectonic activity the regional geological setting is first introduced then followed by a brief view on the neotectonic activity in portugal the basin consists of an elongated depression approximately 20 km long and 2 to 3 km wide trending nne ssw it is located astride a late variscan strike slip fault the manteigas braganca fault suggesting that it might correspond to a structural depression related to reactivation movements on that fault mapping of neogene and quaternary cover deposits preserved in the basin and its vicinity was accomplished and numerous evidence of tectonic deformation tilting and faulting affecting the sediments were found other geomorphological criteria are discussed showing the structural origin of the vilarica basin and its neotectonic activity attending to its location on the manteigas braganca fault the vilarica depression is interpreted as a pull apart basin resulting from left lateral strike slip displacement on that fault in the quaternary average fault slip rates are estimated with values comprised between 0 2 mm yr and 0 5 mm yr these slip rates are typical of moderate to moderately high degrees of fault activity and are compatible with the regional faulting geomorphic expression and the relatively important historical and instrumental seismicity affecting the vilarica region finally a geodynamical model is proposed and the studied area is presented in the geodynamic framework

the structural evolution of active fault and fold systems in central otago new zealand evidence revealed by drainage patterns abstract central otago in new zealand is an area of active continental shortening in which a peneplain surface cut into schist has been deformed by folds which are developed above buried reverse faults we use the drainage patterns in this region to demonstrate various processes in fold and fault growth and interaction that would be difficult to identify by other means in particular we show 1 how simple asymmetric folds can develop into box folds 2 how apparently continuous ridges were formed by the coalescing of quite separate propagating fold and fault segments 3 evidence for the relative ages or relative uplift rates of adjacent structures and 4 evidence for the propagation direction of folds or faults as they grow the few quantitative estimates we obtain for fault propagation rates suggest an increase in length of 10 50 m per earthquake on faults about 20 km long these estimates are very uncertain but are similar in magnitude to an estimate made in nevada for a normal fault of similar size and are also similar to predicted estimates from theoretical growth models they raise the question of whether fault growth earthquake recurrence rates and climate change can interact to produce semi regular discrete features in an active landscape

crustal seismic structure beneath portugal and southern galicia western iberia and the role of variscan inheritance abstract the crustal structure in western iberia is the result of a complex geodynamic history most of the surface is covered by rocks dating to the variscan orogeny the coastal ranges dominated by mesozoic structures and mesocenozoic basins covering partially the mainland in this study we present the results of a local earthquake tomographic study performed to image in depth this complex crustal structure down to 24 km depth the obtained tomograms present a good correlation with the surface geology in general with higher vp velocities in the north and lower vp velocities in the south the heterogeneity observed on the surface geology of the galicia tras os montes zone is well marked being a relatively thin layer over the smoother structure of the centro iberia zone ciz the ciz crustal block confined between the porto tomar ferreira do alentejo and the manteigas braganca faults having higher vp values enhancing the contrast to the lusitanian basin to the west the ossa morena zone corresponds to the unit presenting the greater heterogeneity in both vp and vp vs models showing also with a complex transition to the south portuguese zone and a relatively smooth transition to the centro iberian zone unexpectedly the south portuguese zone present an east west velocity variation with no apparent correspondence with the surface geology the transition to the coastal mesocenozoic basins is clearly marked the lower tagus valley corresponding to a 4 km thick low velocity region the relocation inland recorded seismicity in the period 2000 2014 allows cleansing some of the alignments and establish their correlation with some of the active structures in portugal the model features and seismicity pattern reveal the strong role played by the variscan heritage

carbon and oxygen isotope composition of globigerinoides ruber in two deep sea cores from the levantine basin eastern mediterranean abstract carbon and oxygen isotope analyses have been carried out on 114 samples of globigerinoides ruber from two deepsea cores ban 82 15 pc and ban 82 18 gc raised on the outer slopes of the mediterranean ridge these cores 1050 and 462 cm long respectively contain the sedimentary history of the eastern mediterranean in the last 300 000 years and include sapropelitic layers s 1 to s 10 the climatic fluctuations recorded by the isotopic signal are in general well correlatable with those obtained in previous studies on the mediterranean quaternary most sapropelitic intervals correspond to warm climatic conditions with a maximum recorded in core 15 pc at approximately 125 000 yrs b p isotope stage 5e only s 6 and partially s 8 reflect glacial conditions thus indicating the existence of an alternative model for the deposition of organic rich layers the magnitude of fluctuations in oxygen isotope composition about 7 is unusually wide for the eastern mediterranean and the record is generally shifted toward negative values for approximately 1 this is probably due to the nile discharge that strongly affects these levantine basin cores oxygen and carbon curves are in phase showing the large influence of organic productivity on the carbon isotope composition

geomorpho tectonic evolution of the jamaican restraining bend this work applies recent advances in tectonic geomorphology in order to understand the geomorphic evolution of the jamaican restraining bend located along the caribbean gon ve north american plate boundary we propose a classification of landscapes according to their erosional stages the approach is mainly based on the combination of two dem based geomorphic indices the hypsometric integral which highlights elevated surfaces and the surface roughness which increases when the relief is incised by the drainage network river longitudinal profiles were also analyzed as the drainage network responds quickly to base level change triggered by external forcing such as tectonics anomalies in river profiles knickpoints and convex segments were mapped using stream length gradient sl and normalized steepness ksn indices the results provide new insights for understanding the complex evolution of the jamaican restraining bend three main morphotectonic regions were identified in jamaica 1 the blue mountain wagwater unit located at the eastern tip of the island 2 the jamaican highlands plateau which covers most of the northern and central areas and 3 the tilted block province located along the southern part of jamaica each region has a specific morphological signature which marks a different stage in the late miocene to present evolution of the jamaican restraining bend the evolution of the bend is mainly associated with the western propagation of major e trending strike slip faults and nw trending thrusts in the western and central parts of jamaica the present day motion between the caribbean plate and the gon ve microplate is broadly distributed along several structures while in the easternmost part of the island this motion seems to be almost completely accommodated along the blue mountain range and the plantain garden fault

flow direction and magnetic mineralogy of lava flows from the central parts of the peninsula of baja california mexico magnetic properties of two apparently unrelated lava suites one tholeiitic and the other alkalic coexisting in the central parts of the peninsula of baja california mexico were measured in this study macroscopic indicators and measurements of anisotropy of magnetic susceptibility ams were combined to infer the flow direction on those lavas these measurements were used to investigate the likelihood of the existence of an abnormally long tholeiitic lava flow in this part of the peninsula the obtained results indicate that the tholeiitic flows in the region constitute regular length flows and are likely to have been issued through vents located within the area of study additionally comparison of the magnetic signature of tholeiitic and alkalic lavas reveals a systematic difference in some of the magnetic parameters bulk susceptibility and curie temperatures in particular it is proposed that the narrow range of curie temperatures characteristic of each lava type can be used as a reliable proxy for the identification of each lava type in the region all of these findings show that the alkalic and tholeiitic lavas of the region are more closely related to each other than previously suspected

turbidite flux architecture and chemostratigraphy of the herodotus basin levantine sea se mediterranean the herodotus basin is the deepest part of the se mediterranean and receives allochthonous sediments as turbidity currents and debris flows from around its margin during the late quaternary characteristic supply has been from at least four sources these are 1 dark coloured calcium carbonate poor fine grained turbidites derived from the nile cone to the south and south east 2 lighter coloured calcium carbonate rich slightly coarser grained turbidites derived from the libyan egyptian shelf to the south 3 small light brown foraminifer rich muddy silty turbidites derived from the cyprus eratosthenes seamount anatolian rise carbonate shelf to the east and 4 small localized debris flow deposits derived from the mediterranean ridge to the north during the late quaternary 0 60 ka and specifically the period of 0 27 ka the basin has filled predominantly with allochthonous material derived from the nile cone although one megaturbidite of basinwide extent was derived from the libyan egyptian shelf turbidites have been correlated across the herodotus basin using the technique of chemostratigraphy matching the results of geochemical analysis may show whether or not the beds in different cores were deposited by the same mass wasting event for individual turbidites commonly have diagnostic and unique geochemical fingerprints in terms of major minor and trace element composition sediment budgets for the three main turbidite sources are calculated the cumulative volume of the sedimentary input for the nile cone derived turbidites over the last 27 ka is c 500 km3 giving an average sedimentation rate of c 45 cm ka 1 and a volume per unit time of 18 km3 ka 1 a megaturbidite derived from the libyan egyptian shelf is of basinwide extent and has a volume of c 400 km3

synthetic magnetic fabrics in a plasticene medium mixtures of ferrimagnetic grains with a supporting medium of paramagnetic plasticene permit hypotheses concerning the interpretation of assemblages of different minerals to be confirmed the deformation of such plasticene mixtures in pure shear transpression and simple shear emphasize the dominance of the initial anisotropy over the end result for low strains 25 shortening in pure shear for minor amounts of multidomainal ferrimagnetic grains the deformation experiments indicate that the magnetic lineation rotates rapidly into the maximum extension direction for the three strain histories tested although the magnetic fabric directions are reliable kinematic indicators after modest strain in simple shear the symmetry of the fabric is not a plane strain fabric great discrepancies occur in the case of assemblages single domain femmagnetic grains in plasticene in pure shear these produce inverse fabrics in which the magnetic lineation spins towards parallelism with the maximum shortening direction

low sea level stand emplacement of megaturbidites in the western and eastern mediterranean sea piston cores from the balearic and herodotus abyssal plains in the mediterranean sea show that the late pleistocene to holocene sedimentary sequence is dominated by turbidite muds on each plain one turbidite bed is conspicuous by its thickness and this bed can be correlated basinwide on the basis of geochemical compositional analysis and its apparent correspondence with a distinct acoustically transparent layer on high resolution seismic records these megabeds on the two plains represent megaturbidites of very large volume 300 600 km3 each and are shown by ams radiocarbon dating to have been emplaced during the last low stand of sea level at the height of the last glacial maximum the megabed on the balearic abyssal plain is derived from the southern european margin and is the main sedimentation event over the last 120 ka it emplaced as much material as was deposited by smaller flows during the previous 25 ka sedimentation rate curves for the balearic abyssal plain show that falling sea level correlates with increased terrigenous deposition and that gross sedimentation rates in the basin increased as sea level fell from 120 18 ka due to more frequent emplacement of distal turbidites the herodotus abyssal plain megabed is derived from the libyan egyptian continental shelf west of the nile delta and was the dominant sedimentation event in this basin during the past 60 kyr high resolution seismic profiles from the ionian and sirte abyssal plains in the central mediterranean also suggest possible low sea level emplacement of megabeds in these regions available evidence suggests widespread emplacement of megaturbidites throughout the mediterranean at the last glacial maximum although the triggering mechanisms for these events remain speculative catastrophic destabilisation of the margin after a long period of accumulation with an increased rate of sediment supply is suggested

paleoenvironmental changes during sapropel 19 i cycle 90 deposition evidences from geochemical mineralogical and micropaleontological proxies in the mid pleistocene montalbano jonico land section southern italy an integrated micropaleontological geochemical and mineralogical study has been performed across the mid pleistocene sapropel 19 i cycle 90 from the montalbano jonico land section southern italy to reconstruct the paleoenvironmental conditions at time of its formation the sapropel interval is characterized by two oxygen depletion phases phase a and c interrupted by a temporary re oxygenation interval phase b the beginning and the end of sapropel deposition are dated at 957 0 81 kyr and 950 0 86 kyr respectively the duration of the interruption is estimated to 0 350 0 32 kyr the multiproxy approach highlights that deposition of sapropel 19 reflects a period of enhanced freshwater runoff induced by a wetter climate as a consequence of a more efficient fluvial erosion a higher terrigenous input mostly ascribable to a southern apennines source and an increased turbidity of surface waters accompanied most of sapropel deposition biotic and abiotic proxies document that different paleoenvironmental conditions occur through phases a c the beginning of phase a is characterized by warm on land paleoclimate as well as warm and oligotrophic surface water conditions during the upper part of phase a temperature starts decreasing and surface waters appear more productive this change probably represents the prelude to cooler and drier conditions characterizing phase b which displays a river supply reduction and an eolian input increase sahara dust during phase c the restored depleted oxygen environment at the bottom sediments is clearly coupled with the re establishment of humid conditions and increased river supply at the same time enhanced mixing of water column a cooler paleoclimate and increased productivity of surface waters are recorded the latter likely favored by the enhanced mixing of water column and also increased delivery of land derived nutrients the end of phase c is marked by a restored normal run off enhanced productivity in surface waters and low oxygen conditions at the bottom sediments persist slightly above phase c the overall results suggest that the onset of sapropel deposition is related to water stratification that caused low oxygen exchanges with the sea bottom although enhanced productivity characterizes most of the sapropel deposition it was not the primary factor triggering sapropel deposition

long term morphotectonic evolution in sweden abstract a morphotectonic interpretation of the relief of sweden is presented based on an analysis of the gross forms of the topography computer made topographic profiles covering 76 375 km have been examined together with contour maps new maps of relief and layers of height have also been used three main aspects considered are the relation between the surface of the precambrian basement and its cover rocks the erosional new surfaces developed in both caledonian basement and reexposed precambrian basement and the evolution of the valley pattern the analysis produced the following results the surface of the precambrian basement is a mosaic of old exhumed surfaces and new surfaces formed after erosion of the cover rocks the exhumed surfaces include 1 a sub jotnian surface mainly below cover rocks in downfaulted positions 2 the sub cambrian peneplain and 3 sub mesozoic etch surfaces block faulting was identified in relation to the different exhumed surfaces after the formation of the caledonides a post caledonian surface was cut across the caledonian basement and the precambrian basement with its cover the subsequent evolution of the swedish part of this surface has been traced through several new surfaces in stepped sequences and in relation to the exhumed surfaces five main denudation intervals are distinguished that result in characteristic relief they are preceded by intervals of orogeny uplift and faulting and followed by subsidence and or deposition of sedimentary strata the valley patterns the distribution of new and exhumed surfaces as well as remmants of cover rocks give some fundamental clues to where and when uplift and subsidence occurred historical geomorphology has mainly been based on theories of erosion cycles the relief of the cratons are difficult to fit exclusively into such a system the importance of long lasting covers and of exhumed surfaces have not been considered enough neither the movements of uplift and subsidence reconstruction of geomorphic events appears to be more important for understanding relief evolution than any model as every phase is unique the methods used in this study are worth testing within other cratons

palaeoproterozoic indian shield in the global continental assembly evidence from the palaeomagnetism of mafic dyke swarms abstract palaeomagnetic study of palaeoproterozoic mafic dykes in the basement along the margins of the cuddapah basin the largest precambrian sedimentary basin in south india is presented in detail for a general discussion of palaeoproterozoic igneous activity in india the results are compared with all earlier published data on mafic dykes in india and are integrated with recently published high precision u pb baddeleyite ages to provide a comprehensive account of palaeoproterozoic igneous activity in india the analysis consolidates palaeomagnetic poles for six age divisions between 2 45 and 1 85 ga with robust statistical criteria our best estimates of overall mean poles from 241 dykes are situated at 1 17 7 n 106 0 e a95 9 0 7n 24 at c 2 45 ga 2 7 1 n 57 2 e a95 4 5 n 69 at c 2 37 ga 3 41 6 s 5 5 e a95 5 1 n 34 at c 2 22 ga 4 4 7 n 343 0 e a95 4 4 n 31 at 2 18 ga 5 49 2 n 332 9 e a95 4 8 n 24 at 1 99 1 89 ga and 6 73 7 n 282 6 e a95 2 9 n 39 at 1 86 ga the data permit us to construct an apparent polar wander path for the indian shield for an 600 ma interval of the palaeoproterozoic eon 2 45 1 85 ga testing and evaluation of continental reconstructions for this interval which are mostly based on geological correlations reveal many inconsistencies between 2 45 and 2 37 ga the indian shield was situated at higher latitudes similar to the yilgarn craton of australia it was subsequently located near the equator at 2 22 2 18 1 99 and 1 86 ga thus an india australia connection is supported during these times but a proposed australia kaapvaal link in zimvaalbara and a dharwar india slave connection in sclavia or a superior zimbabwe india connection in superia are inconsistent with indian data in addition the close palaeomagnetic comparison between the palaeoproterozoic dykes of dharwar bastar bundelkhand cratons in india indicates an age of 2 45 ga for orogenic activity along the central indian tectonic zone hence matching this zone with the 2 0 1 8 ga trans north china orogenic belt or positioning north china adjacent to india or juxtaposition of the indian shield along the western margin of laurentia in the columbia reconstructions is not supported the indian data appear to be in accord with the essential features of the refined protopangaea model and the original ur configuration finally the results are interpreted in terms of four dyke emplacement events in the age range 2 45 2 18 ga linked to short lived 5 10 ma lips developed over mantle plumes the dykes of 1 99 1 89 ga age probably relate to continued long lived igneous activity while the 1 86 ga dykes are relatively fewer in number and may represent waning stage of a large igneous event related to a major mantle plume

recent depositional patterns of the nile deep sea fan from echo character mapping the nile deep sea fan was surveyed in 1998 using swath multibeam bathymetry backscatter imagery and 3 5 khz and seismic profiling on the basis of this new data set the fan has been divided into three main provinces western central and eastern recent sedimentary patterns as deduced from echo character mapping show that gravity induced sedimentary deposits are predominant and are expressed through either slides debris flows or turbidites turbidity processes are particularly active in the westernmost province through a well developed network of deep sea channels this network controls turbiditic flows that subsequently overflow levees mass wasting processes are extremely efficient all over the nile deep sea fan in the upper central province a broad allochthonous tongue of mass flow deposits generated by slope destabilizations may have led to channel avulsions and migrations in the eastern province a northwest southeast deformed belt resulting from combined deep seated and salt related tectonics contains large proportions of destabilized sediments i e originating from destabilization processes such as mass movements probably settled by recent tectonic activity this article highlights 1 the influence of both thin skinned and thick skinned tectonics on sedimentary distribution and 2 the predominance of gravity induced sediments turbidites slides and mass flows in such submarine fans the distribution of debris flows and sedimentary deposits settled by turbidity currents appears fundamental in predicting reservoir geometry and economic potential

magnetic fabrics and rock magnetism of the xiong er volcanic rocks and their implications for tectonic correlation of the north china craton with other crustal blocks in the nuna columbia supercontinent abstract the tectonic background of the paleoproterozoic xiong er volcanic rocks xvr is important for understanding the tectonic evolution of the north china craton ncc as well as its paleogeographic position during the assembly of the nuna columbia supercontinent here we report the results of the first anisotropy of magnetic susceptibility ams study of the xvr and use the interpreted flow directions to constrain the emplacement mechanism and to assess its geological significance for the reconstruction of the nuna columbia supercontinent thirty lavas were sampled from three sections in western henan province detailed rock magnetic analyses including measurements of hysteresis loops magnetization versus temperature curves and first order reverse curves were performed to identify the main magnetic phases and grain sizes the inferred directions from the ams results reveal a radial flow pattern with an eruption center probably located near xiong er mountain our data suggest that the xvr may have been emplaced in a triple conjugated continental rift on the south margin of the ncc probably initiated from a paleoplume based on this interpretation a comparison of geological and paleomagnetic results among the proposed crustal blocks in the nuna columbia supercontinent suggests a close linkage of the ncc with sao francisco congo rio de la plate and siberia

calcareous nannofossil palaeoenvironmental reconstruction and preservation in sapropel s1 at the eratosthenes seamount eastern mediterranean abstract the most recent organic carbon enriched layer sapropel s1 deposited at the eratosthenes seamount has unique features such as an early lithological interruption fine light silt laminae and an exceptional vertical extent that is over 25 cm thick here we investigate calcareous nannofossil assemblages to reconstruct very high resolution palaeoenvironmental and palaeoceanographic variations recorded before during and after the perturbation episode that involved the eastern mediterranean sea due to the massive freshwater discharge via nile river our results show that the deep chlorophyll maximum development observed in all micropalaeontological groups from previous studies is a gradual process that started well before the base of sapropel s1 a high frequency variability in the nutricline depth is evident at millennial and or centennial scale throughout the sapropel deposition time interval also we highlight the poor preservation of delicate tiny holococcolith crystals while anoxia was occurring at the seafloor and we suggest that such a phenomenon may be used to mark the original thickness of sapropel deposition where oxygen re ventilation fronts were developed finally calcareous nannofossil reworking peaks shed light on the nature of fine silt laminae within the sapropel s1 at the eratosthenes seamount which may be ascribed to fine sediment plumes from the nile river deposited during exceptional runoff events

cenozoic tectonic activity in a variscan basement evidence from geomorphological markers and structural mapping nw iberian massif abstract the nw iberian massif is part of an ancient basement that has been considered a seismically stable area with no outstanding cenozoic tectonics however recent seismic activity revealed the need for better knowledge of the cenozoic structures in the area because of the lack of mesozoic deposits and the scarcity of cenozoic sediments as well as the intense deformation of the pre mesozoic variscan basement it is difficult to study the cenozoic tectonic structures in this work the combination of detailed structural mapping and study of geomorphological markers in the variscan basement has allowed recognition of cenozoic tectonic structures kinematics and processes that otherwise would not have been identified the identified structures have been gathered into three groups a ne sw trending strike slip faults mainly sinistral b nnw vergent thrusts that uplift the caurel mountains and galaico leoneses mountains and c e w and ene wsw thrusts that uplift the ancares mountains in a pop up structure the structures cut the pre cenozoic erosion surface and affect the drainage network that shows patterns characteristic of tectonic activity the three groups of structures define sectors with different relief showing a strong link between geomorphological elements and tectonic structures the intense drainage reorganisations observed in the area and the deformation of miocene pliocene deposits point out to a significant late miocene tectonic activity in the region thus the cenozoic tectonic activity in the northwest of the iberian peninsula takes place during an extensive period of time which started with the episodes of compression in the cantabrian margin and it is identified nowadays by the recent seismic activity recorded in the north western iberian peninsula 1995 and 1997 lugo events the seismicity is related to the cenozoic structures identified in the area which move under the present se nw horizontal maximum compression and coincide with the proposed seismogenic faults

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

eastern mediterranean sapropel s1 interruption an expression of the onset of climatic deterioration around 7 ka bp we discuss the palaeoclimatic interpretation of unprecedented high resolution micropalaeontological studies of shortterm 2 to 4 centuries interruptions within early holocene organic rich layer sapropel s1 from the eastern mediterranean results for cores from the adriatic and aegean seas that contain double s1 sapropels indicate that these interruptions which are centred roughly around 7000 years 14 cnc bp are genuine and related to climatic deterioration this interpretation is endorsed by a coeval dry event recorded in terrestrial records and indications of climatic deterioration affecting human migration patterns and early societies in egypt the presence of sapropel interruptions in the two major source areas of deep water for the entire eastern mediterranean likely implies that similar intervals may be found throughout the basin provided that sedimentation rates and sampling resolutions allow the detection of events with a duration of only several centuries moreover our results show that the sapropel mode of circulation comprises a delicate balance between reduced ventilation and enhanced productivity which is easily disturbed through surface water cooling triggering a short time of improved deep water ventilation 1999 elsevier science b v all rights reserved

tectonic classification of cenozoic iberian foreland basins abstract the iberian microcontinent stands out because of its intense alpine intraplate deformation this is reflected in a large number of cenozoic basins of very different sizes most of the contacts between topographic highs and basins are thrust or strike slip faults all these basins seem to have undergone a common sedimentary evolution comprising four stages initiation of sedimentation intense syn tectonic infilling change from endorheic to exorheic drainage and accelerated erosion related to fluvial incision this simple evolutionary model shows a migration from east to west in which basins are still tectonically active at the atlantic margin of iberia this common evolution is also found in a series of geometrical characteristics such as the ratio r of length of strike slip fault and length of thrust fault that are very similar in both types of basin border settings thrust related basins are mainly associated with segmented pop downs whereas the main basins have the characteristics of open ramp basins strike slip related basins are mostly transpressive structures although small pull apart basins are usual along the vilarica and messejana faults for basin areas larger than 100 1000 km 2 a constant r value of 0 6 is found including the ebro duero madrid lower tagus and badajoz basins within the iberian microcontinent the total amount of cenozoic contractional deformation was distributed between strike slip and thrust faults with an r ratio close to 0 6 however for small basins this parameter seems to depend on the type of fault range or deformation belt pure strike slip transtension transpression and pop up independently of its local tectonic development

deep water facies processes and models a review and classification scheme for modern and ancient sediments abstract a review of previous work on modern and ancient deep water facies processes and models is presented with a new classification scheme involving 40 distinct facies related to 15 conceptually distinct facies groups these facies are fixed points in a spectrum of facies generated in a process continuum from resedimentation processes through semi permanent bottom currents to pelagic settling in essence the scheme is descriptive of the sedimentary attributes of sediments although it is designed to aid interpretation of possible sediment transport deposition processes the classification scheme is three tier with facies classes groups and constituent facies and is hierarchical to allow flexibility in its use there are seven facies classes with classes a e defined largely on the basis of grain size differences class f on the basis of internal organization and class g on composition the facies classes are class a gravels muddy gravels gravelly muds and pebbly sands with 5 gravel grade class b sands with 80 sand grade and 80 mud 40 silt and 0 20 sand class e muds and clays with 95 mud grade for the purpose of large scale mapping or reconnaissance fieldwork either the level of facies classes or groups may be appropriate whereas for more detailed sedimentology the more detailed facies level will be necessary

duration of s1 the most recent sapropel in the eastern mediterranean sea as indicated by accelerator mass spectrometry radiocarbon and geochemical evidence slowly accumulated 5 cm kyr 1 and rapidly accumulated 5 20 cm kyr 1 sediments have been compared to define the initiation and termnation times of the most recent sapropel s1 in the eastern mediterranean sea the ba a1 ratio has been employed as a more persistent index of productivity than cg accelerator mass spectrometry radiocarbon dating of pelagic foraminifera indicates a maximum duration for increased ba a1 levels in s 1 from 9500 6000 uncorrected radiocarbon convention years b p in the rapidly accumulated sediments and 9500 5300 years b p in the slowly accumulated sediments this difference is ascribed to bioturbation affecting the slower accumulated s1 sediments in the two most rapidly accumulated s1 units from the adriatic and aegean seas there is a saddle of lower values centered on 7500 years b p in the corg and ba ai profiles so that the visual s 1 unit appears as a doublet geochemical evidence indicates that this intervening period is best interpreted as an episode of increased ventilation and bottom water oxygenation during the period of sapropel accumulation

reconstructing the interacting effects of base level climate and tectonic uplift in the lower mino river terrace record a gradient modelling evaluation the origin of the lower mino river terraces in the nw iberian peninsula has been a topic of debate since the 1940s various hypotheses about their main controlling factors have been put forward but general consensus is still lacking field studies of terrace distribution and the weathering of quartzite pebbles in the terrace deposits demonstrated that terrace longitudinal correlation is not parallel to the current river bed in addition the longitudinal profile model fluver2 was used to simulate the profile evolution of the mino river over the past 450 ka a reconstructed longitudinal profile and an offshore climate record were used as inputs several scenarios with variable uplift rates were investigated and evaluated against properties of four selected reaches along the river for a match with the number of terraces their relative altitude timing and sediment thickness an uplift scenario with a net constant vertical uplift rate of 0 08 m ka 1 yielded the best results the best fit scenarios indicate that base level changes from glacioeustatic changes in combination with tectonic uplift are the main driving forces of the observed terrace formation and valley incision contrary to most nw european fluvial systems the timing of upstream controlled sediment supply has a less dominant effect on terrace formation this can be explained by the close proximity to the narrow passive atlantic margin

the form distribution and anisotropy of magnetic susceptibility of jurassic dykes in h u sverdrupfjella dronning maud land antarctica implications for dyke swarm emplacement abstract the mesozoic dyke swarms of western dronning maud land antarctica form a minor intrusive component of the karoo large igneous province five hundred and sixty one dykes were recorded intruding neoproterozoic gneisses and middle jurassic syenite plutons 40 ar 39 ar geochronology data reveal two temporally distinct components the 178 175 ma alkaline straumsvola dyke swarm that predominantly intrudes a nepheline syenite pluton and the 206 204 ma tholeiitic jutulrora dyke swarm found throughout the study area the straumsvola swarm exhibits highly variably dyke trends that display a restricted opening direction interpreted to be the result of high magma pressure equal to the maximum principal stress the jutulrora swarm displays a fan of dyke trends with dyke thickness and spacing increasing away from the inferred point of fan convergence anisotropy of magnetic susceptibility measurements reveal vertical magma transport within both dyke swarms in the straumsvola area with the southern outer exposures of the jutulrora swarm exhibiting lateral magma transport although associated with a long lived local igneous centre comparison of palaeostress estimates for the straumsvola dyke swarm and contemporaneous dykes in ahlmannryggen and vestfjella indicates the presence of a regional scale radial stress system in western dronning maud land between 178 175 ma supporting a mantle plume origin for the karoo large igneous province

the hilt bed an upper cretaceous compound basin plain seismoturbidite in the hornbrook forearc basin of southern oregon and northern california usa abstract the hilt bed is a thick laterally continuous marker bed of fine to medium grained sandstone that crops out for a nw se along strike distance of about 50 km on the southwestern flank of the cretaceous hornbrook forearc basin of northern california and southern oregon the hilt bed forms part of the blue gulch mudstone member of the hornbrook formation and is everywhere underlain and overlain by basin plain mudstone that contains thin interbeds of turbidite sandstone and siltstone the bed is as thick as 4 71 m in the central part of the outcrop belt and thins progressively to the nw and se it was derived from erosion of igneous and metamorphic basement rocks of the klamath mountains which flank the basin to the sw paleocurrents measured from flute casts at the base of the bed indicate sediment transport to the ne the hilt bed can be divided into a compound succession of nine bouma divisions all of which are generally present in outcrop the succession consists in ascending stratigraphic order of bouma abababcde divisions the basal a division is typically the thickest and coarsest layer with overlying divisions generally thinner and more variable in thickness the bed appears to have been deposited as a compound turbidite by at least three separate turbidity currents that appear to have been generated either by the same triggering event or by a rapid succession of related events only the uppermost part of the bed thus contains a complete bouma sequence the unidirectional paleocurrent indicators lateral continuity and extent of the three flows that make up the bed incompleteness of the two lower bouma sequences and absence of interbedded shale or bioturbated levels suggest that the three turbidity currents reached the basin floor at almost the same time to yield the bed the compound nature of the hilt bed suggests that a major seismic event triggered the three large flows which probably originated in either a single submarine canyon or three adjacent canyons

analysis of digital elevation data for palaeosurfaces in south western sweden a 3873 km large rectangular area of the precambrian basement in south western sweden has been investigated regarding gross morphology of palaeosurfaces gis and digital elevation data were used to

origin of a thick redeposited carbonate bed in eocene turbidites of the hecho group south central pyrenees spain large scale carbonate beds interbedded in basin plain turbidites of the eocene hecho group northern spain are interpreted as giant turbidity current deposits because of their internal organization and lateral extent one such bed the roncal unit has been traced down the axis of the basin for 75 km and commonly reaches thicknesses in excess of 100 m internally the roncal unit displays an overall upward decrease in grain size from a basal megabreccia with large slabs of carbonate platform debris to a calcareous mudstone the roncal unit was probably deposited from a highly mobile and competent sediment gravity flow generated by an earthquake shock which led to the catastrophic collapse and subsequent transport of the upper part of a carbonate platform flanking the basin

segmentation and increasing activity in the neogene quaternary teruel basin rift spain revealed by morphotectonic approach abstract the nnw sse trending teruel basin rift is the largest late miocene quaternary extensional intracontinental structure located within the central eastern iberian chain spain the structural and morphotectonic study carried out in the central northern part of this half graben basin north of teruel city has allowed us to analyse rift segmentation deformation partitioning and rift evolution results are based on vertical displacement calculations fault throw and bending of the main border and intrabasin fault zones we use two geomorfological stratigraphical markers the intramiocene erosion surface ies 11 2 ma and the fundamental erosion surface fes 3 5 ma while the first marker reveals rift initiation under an e w extension the late marker records vertical displacements associated to a second late pliocene quaternary rifting stage characterized by a nearly multidirectional extension regime with prevailing ene wsw trending o3 despite the along axis rift segmentation into three structural domains northern central and southern and the distribution of deformation among border and intrabasin faults in the central and southern domains a consistent average slip rate post ies of 0 09 mm a has been calculated on distinct transects across the basin suggesting a homogeneous crustal scale extension process in the region the results also reveal that slip rates during the late pliocene quaternary 0 12 0 16 mm a are higher than the late miocene early pliocene 0 05 0 07 mm a slip rate increase is caused by i a westward propagation of deformation from the valencia through and ii a change in the regional stress field both enhanced by crustal doming affecting central eastern iberia as well as progressive fault linkage throw vs distance graphs suggest that the main faults are in a transient stage towards coalescence less advanced within the southern domain regional late pliocene quaternary uplift concomitant with increasing slip rates in the teruel basin rift has caused the basin to rise so that synrift sedimentation only took place in rapidly subsiding residual basins until the region became exorheic and the basin was incised by the present day fluvial network

setting and tectonic evolution of some eastern mediterranean deep sea basins abstract nine discrete deep sea basins seven from the calabrian and mediterranean ridges and two from the strabo trench were explored geologically during several cruises carried out from 1978 to 1984 in the eastern mediterranean the seven basins displaying similar geological features calabrian and mediterranean ridges may be divided into three groups on the basis of their size 1 very small basins botticelli and raffaello basins whose area ranges from 1 1 to 4 3 km 2 2 small basins ares aphrodite and katia basins from 7 to 13 km 2 and 3 large basins bannock and cleft basins from 22 to 74 km 2 the two basins from the strabo trench tyro and kretheus basins whose areas range from 16 to 20 km 2 are considered separately tectonics is the most important element affecting basin formation processes progressive folding and faulting of messinian pliocene and quaternary sediments in the calabrian and mediterranean ridges allows the infiltration of water into the subbottom and dissolution of messinian evaporites so that collapse of the overlying unconsolidated plio quaternary cover creates local distensive tectonics superimposed on the regional compressive tectonic setting the size of the basins reflects different steps in this process very small basins are related to the fracturing occurring at the top of anticlines small basins originate when anticlines are faulted and large amounts of water are able to reach the evaporites and increase the intensity of leaching finally large basins are related to regional tectonic lineaments both compressive large reverse faults overthrusts and strike slip salt diapirism may be associated with some of these situations the process responsible for the tyro and kretheus basins formation is the pull apart mechanism connected with the strike slip motion occurring in that area the geometric position of subaqueously dissolved evaporites seems to influence the environment on the basin floor brines originating from the dissolution of buried evaporites are thought to disperse in the subbottom whereas brines originating from dissolution of evaporites cropping out on the basin walls can flow to the floor and cause stagnation only if the shape of the basin prevents the action of bottom currents

mobility of a large volume pyroclastic flow emplacement of the campanian ignimbrite italy abstract the trachytic campanian ignimbrite originally exposed over a 30 000 km 2 area around naples italy is the product of a highly energetic gas rich eruption the deposit lies in valleys and isolated watersheds and in its medial and distal extent to the south north and east of naples the campanian pyroclastic current encountered mountains exceeding 1000 meters anisotropy of magnetic susceptibility ams measurements indicate that the campanian pyroclastic current the transport system traveled radially outward from the phlegrean fields area but the ignimbrite forming flow the deposition system that developed from the base of the transport system moved downslope from mountainsides to valleys including slopes facing the eruption source and flowed down drainage systems from intermontane basins the campanian pyroclastic current flowed 35 km over the water of the bay of naples to deposit 43 m of ignimbrite on the south shore and also overtopped a 685 1000 m high ridge of the sorrento peninsula to deposit more on the other side the distribution of the ignimbrite and the measured flow directions suggest that the campanian pyroclastic current moved across the landscape as an expanded and therefore turbulent decompressing flow rather than as a high density nonturbulent sheet like current moving over mountains by momentum acquired by eruption column collapse strong expansion is corroborated by shard morphology that indicates derivation from highly inflated pumice and suggests vesicles must have been at least 80 by volume of the original magma

sedimentary earthquake records in the izmit gulf sea of marmara turkey abstract sedimentary earthquake records of the last 2400 a including that of the devastating 17 august 1999 izmit earthquake mw 7 4 were studied in cores from the 210 m deep central karamursel basin of the izmit gulf in the eastern sea of marmara using laser grain size physical properties stable o and c isotopes and xrf core scanner analyses and dated by radionuclide and radiocarbon methods the earthquake records are represented by turbidite homogenite mass flow units thu that commonly contain a basal coarse layer a middle laminated silt layer and an overlying homogeneous mud layer the coarse basal part has a sharp and sometimes scoured lower boundary and includes multiple coarse sand silt layers or laminae showing normal size grading multiple coarse layers and occasional bi directional cross bedding suggest deposition from a bed load during water column oscillations or seiche effect the grain size characteristics of the overlaying laminated silt and the homogeneous mud units indicate deposition from weak oscillating currents and homogeneous suspension respectively high mn value just below the base of thus suggests diagenetic enrichment at oxic anoxic redox boundary before the mass flow event sharp decrease in mn with very low values within the thus suggests transient redox conditions following the mass flow variable geochemical compositions of the basal coarse layers indicate different sediment sources for different thus eight sedimentary earthquake records observed in the last 2400 a in the izmit gulf can be confidently correlated with the historical earthquakes of 1999 1509 ad ms 7 2 1296 ad i vii 865 ad i viii 740 ad i viii 268 ad i viii 358 ad i ix and 427 bc this gives an earthquake recurrence time of ca 300 a with the interval between consecutive events ranging from 90 to 695 a

turbidites and megaturbidites from the herodotus abyssal plain eastern mediterranean unrelated to seismic events abstract a transect of 9 piston and gravity cores was taken across the southeast flank of the mediterranean ridge the transect extends from the abyssal plain to a location 290 m shallower than the abyssal plain and 50 km north of the edge of the ridge each core contains two or more turbiditic layers which belong to two discrete types here called a and b type a essentially consists of black plastic clays rich in smectite with silt fraction of terrigenous nature source area is the nile cone and age is middle or late pleistocene type b turbidites are pale brown to whitish in color coarse grained carbonate rich and bioclastic in composition with shallow water fossils dominant they are poor in smectite and the silt fraction is very rich in carbonates calcite and aragonite the source area is the north african shelf south of the abyssal plain a megabed belonging to type b turbidites is correlatable from core to core with a thickness in excess of 10 m in the abyssal plain and an estimated volume of 10 km 3 its stratigraphic position in the latest pleistocene suggests that its origin is related to a sudden collapse of bioclastic sediments accumulated in a canyon head during a low sea level stand the source areas of the two discrete turbidite types belong to the essentially aseismic north african continental margin although they are presently recorded on the tectonically active mediterranean ridge no seismic events are required to account for the presence of either type of turbidite

open ocean to trench turbidity current flow in the nankai trough flow collapse and reflection the ocean drilling program leg 131 which drilled in the nankai trough in the western pacific ocean has shown for the first time that turbidity currents are deflected and reflected against the trench slopes such that in the trench outer slope there is a predominant pattern of currents carrying terrigenous sediments apparently coming from the open ocean shikoku basin directly toward the trench landward slope the purpose of this paper is to summarize the evidence for flow rebound at odp leg 131 site 808 and to show that these results have important implications for the interpretation of paleocurrents in ancient linear turbidite systems

deposition of ungraded muds from high density non turbulent turbidity currents turbidity current deposits of mud have recently been found up to 10m in thickness resulting from single depositional events1 2 turbidites 1 5 m thick from the madeira abyssal plain3 4 display long segments with little vertical change of grain size5 6 this suggests that the currents froze in some way making them unable to sort sediment here we suggest that a decline in flow speed of these currents led to a concentration gradient in silt close to the bed that was sufficiently steep to stratify the flow a concentration gradient of 18 kg m 3 over 1 5 m height gives a layer richardson number above the critical value of 0 25 for damping of turbulence we propose that with turbulence severely damped a dense suspension of fine material consolidates like a static suspension while continuing to flow downslope the current changes from a fully turbulent flow to a decelerating flow with suppressed turbulence and increasing density in the latter state interparticle forces prevent differential settling of the coarser grains

origin of mud breccia from the mediterranean ridge accretionary complex based on evidence of the maturity of organic matter and related petrographic and regional tectonic evidence abstract drilling the milano mud dome situated in the olimpi field on the northern flank of the mediterranean ridge accretionary complex has documented episodic eruptive activity over the last 1 to 1 5 million years mud extrusion is related to backthrust faulting due to subduction of the africa plate beneath a relatively rigid backstop of cretan continental crust the mud dome is mainly composed of mud breccia with up to 65 of polymictic clasts embedded in a clayey matrix previously published results from petrography and new maturity data of both clasts and mud matrix presented here allow us to distinguish between two different areas of provenance 1 a northern province characterised by a trimodal maturity distribution of organic material was found for the majority of the mud breccia matrix samples studied similarly some of the clasts studied show the three vitrinite reflectance populations these are carbonate and sandstone clasts inferred to have been eroded from the upper nappes of the cretan thrust stack after exhumation in the late miocene as well as mudstone clasts clay mineralogy of these clasts coincides with earlier results on seafloor samples of a northern provenance recovered in the hellenic trench 2 a southern provenance is proposed for a second group of clasts with a bimodal maturity distribution not showing the second population 0 64 0 82 rm these clasts are litharenites calcilutites and calciturbidites of a proposed southern provenance i e north africa the presence of huminite in all clast and matrix samples studied 0 26 0 45 rm is indicative of a shallow burial history estimates regarding the depth of mobilisation of the mud using the regional thermal gradient indicate burial not deeper than 2 km below the seafloor organoclastic matrix components mirror the northern clast provenance so that prior to subduction and subsequent extrusion deposition of the mud in the northeastern mediterranean can be inferred we propose a model in which sediment from the north was trapped within the forerunner of the pliny trench this sediment was deposited above the backstop of the subduction complex which was later overridden by the accretionary prism as a result of incipient collision density inversion forces then favoured uprise and extrusion of underconsolidated sediments as mud volcanoes the mud matrix was probably largely derived from a messinian succession although alternatives remain possible

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

pleistocene suvero slide paola basin southern italy abstract the suvero slide covers an area of about 225 km 2 in the paola slope basin on the eastern tyrrhenian margin the shape and lateral extent of the deposit reflect topographic confinement of the slide between the continental slope and a morphologic barrier formed by a margin parallel slope ridge no headwall or slide plane comparable in scale with the slide deposit were found suggesting that quasi in situ deformation of semi consolidated sediments took place when the failed materials reached the floor of the slope basin the failure occurred downslope from a basement high originating from local uplift continued uplift after the suvero slide occurred is documented by the presence of steep upper slope gradients within the study area and by the presence of small scale creep and failure events that postdate the suvero slide

stratigraphy and sedimentation in the western strabo trench eastern mediterranean abstract three piston cores ranging in length from 501 to 921 cm raised from the adjacent mediterranean tyro and kretheus basins and their intervening sill confirmed previous findings of persistent anoxia and extended our knowledge of the stratigraphic record the two cores from the basinal settings contain a bronze age homogenite this tsunami induced turbidite is only 28 cm thick in the shallower kretheus basin whereas it has a thickness of 235 cm in the deeper tyro basin the recovery of the homogenite in these subbasins of the western strabo trench demonstrates that the tsunami wave turned west of crete and arrived here with a velocity sufficient to remobilize unconsolidated sediments draping the basin slopes the holocene and uppermost pleistocene sedimentary record is characterized by numerous millimetric to centimetric sand layers containing reworked pliocene and miocene foraminifers the repetitive siliciclastic turbidites interfered with the normal eastern mediterranean succession of sapropels and tephras and document a strong neotectonic activity related to the presence of an active trench on the floor of ponded rimmed basins like the tyro and kretheus basins the sand layers are associated with anoxic sediments whereas they are associated with normal well oxygenated marls on the sill which lies above the anoxic oxic interface basin anoxia is interpreted as the result of submarine dissolution of messinian evaporites giving rise to deep seated brines extraformational reworking documents the occurrence of pre messinian fossiliferous sediments exposed on the trench wall and subject to submarine erosion the stratigraphic time framework is given by nannofossil biostratigraphy corroborated by lithostratigraphic correlation of isochronous lithologies sapropel and tephra chronology a drastic change in sedimentary regime is recorded at approximately 70 ka b p emiliania huxleyi acme e huxleyi zonal boundary older sediments which were only recovered in core 37 from the sill separating the tyro and kretheus basins are pelagic with an almost typical eastern mediterranean succession of sapropels and tephras no siliciclastic turbidites and no extraformational reworking are noticed in sediments older than 70 000 years we conclude that the trench system became active just at that time a thick layer of plurimillimetric pumice bubbles was discovered within sapropel s 6 indicating a strong explosion of a nearby volcano at 180 ka b p but we have no analytical data yet to substantiate the provenance of the volcanogenic deposits

textural and dispersal patterns of thick mud turbidites from the madeira abyssal plain abstract the madeira abyssal plain is the site of a thick sequence of thick pleistocene turbidites that are almost entirely of material less than 63 m in grain size the major turbidites are 1 to 5 m in maximum thickness concentrating on three turbidites cored at 24 locations detailed patterns of thickness and vertical and lateral grain size changes reveal flow paths on the plain in general the bases of the units are of graded silt showing thick and thin planar lamination and occasionally ripple cross lamination a new idealised sequence of changes in size and structures with distance along the flow path is developed closer to source the beds comprise a graded structured silty base overlain by structureless mud which may also be graded down current the silty base becomes thinner with less apparent structure and the upper homogeneous part becomes thicker and more uniform in an overall thickening trend at the distal end uniform beds up to 5 m in thickness are found in one turbidite the modal size structure shows some silt modes which are hydrodynamically sorted and change size vertically and spatially while one particular mode is constant in size due to a particular species of coccolith the turbidites originated from slumps on the northwest african continental margin and from the vicinity of madeira and the canaries some of which exceeded 100 km3 in volume

the seismogenic zone of the continental crust in northwest iberia and its relation to crustal structure the distribution of seismicity at the western end of the cantabrian mountain range nw iberia reflecting current crustal dynamics is investigated integrating seismically active structures long term structures and the topographic features at the surface the thickness of the seismogenic zone within the continental crust is established in 20 km two crustal domains can be distinguished in the study area in terms of the seismicity pattern the style of alpine structures and the relief the presence of crustal fluids arises as a very likely contributing factor to the excessive thickness of the seismogenic zone in the study area more importantly a switch in tectonic style at the transition between crustal domains in coincidence with the lateral termination of orogenic frontal thrusts is envisaged as involving sufficient stress heterogeneity and amplification to explain the current concentration and characteristic pattern of historical seismicity in the region overall the distribution of seismicity in the crust is sensitive to the type and style of crustal structures

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

contained reflected turbidity currents from the middle ordovician cloridorme formation quebec canada an alternative to the antidune hypothesis the parautochthonous cloridorme formation is a syn orogenic flysch succession that was deposited in an elongate foredeep basin as mainly lower middle fan outer fan and basin floor deposits the basin floor deposits about 1 5 km thick are confined to members 1 2 and 1 and are characterized by graded thick 1 10 m mud rich calcareous greywacke beds previously interpreted as deposits of concentrated muddy unidirectional turbidity currents that locally generated backset antidune lamination in internally stratified flows the dominant flow directions were from east to west but west to east transport also occurred as seen in the orientation of ripples climbing ripples flutes consistently overturned flames and grain imbrication we believe that the flows that deposited these thick calcareous greywacke beds reversed by roughly 180 one or more times during deposition of the lower sandy part of the beds flow reversals are consistent with the sharp grain size breaks and mud partings within sandy divisions measurement of grain fabric relative to stratification in the most celebrated antidune bedforms indicates flow from west to east thus the bedforms were produced by west to east migration of megaripples not by the upcurrent migration of antidunes the thick muddy beds were deposited by large volume muddy flows that were deflected and reflected from the side slopes and internal topographic highs of a confined basin floor much like the contessa and similar beds of the italian apennines large quantities of suspended mud were ponded above the irregular basin floor and settled to produce the thick silty mudstone caps seen on each bed because of their mode of emplacement we propose that these beds be called contained turbidites