channel axis overbank and drift sediment waves in the southern hikurangi trough new zealand abstract in the southern apex of the hikurangi trough east of new zealand swath bathymetry and backscatter seismic profiles and cores from the proximal part of the 2000 km long hikurangi channel show different types of sediment waves in the channel axis and on the levee backslopes these represent different responses to large turbidity currents locally backslope sediment waves merge into sediment waves formed by a deep geostrophic flow in the channel axis and on channel walls sediment waves that have wavelengths of 1 4 km and heights of less than 6 m occur where cores show gravelly and coarse sandy turbidites they are not apparent in layering below the channel axis they are inferred to be thin transitory surface sand bodies migrating across coarser substrates and may have formed in a recent perhaps the last turbidity current their geometry suggests that they probably formed as antidunes in high velocity flows that were much thicker than the channel depth overbank sediment waves also have similar wavelengths of 1 4 km but heights of up to 45 m they have conspicuous sub seabed layering to a depth of at least 400 m beneath the seabed seismic stratigraphy indicates that they have developed for most of the last 2 ma during near vertical aggradation of the channel its levees and overbank slopes at average rates of 0 4 0 7 m ka the sediment waves migrate up levee backslopes towards the levee crest at rates of 3 20 m ka and are inferred to be formed beneath lee waves initiated in overbank flows by the linear perturbation of the levee they are best developed on the outsides of bends where centrifugal outflow of upper overspill parts of large turbidity currents might be concentrated they are particularly well developed at right hand bends on the left bank where centrifugal and southern hemisphere coriolis effects combine poorly developed sediment waves on the inside of some left hand bends may be the result of coriolis effects only overbank sediment waves decrease in height and wavelength away from the channel and continue into a depression along the slope toe deformation front at the landward edge of the turbidite plain where the channel intersects the slope toe depression the absence of a left bank levee suggests that overbank flows re enter the channel along the toe of the chatham rise sediment waves up to 5 m high and 2 5 km in wavelength migrate away from the channel and towards a slope toe moat they are inferred to be part of a drift deposit perhaps associated with a branch of the pacific deep western boundary current

seismic stratigraphic framework and depositional history for cretaceous and cenozoic contourite depositional systems of the mozambique channel sw indian ocean this study describes previously unrecognized contourite depositional systems cdss in the mozambique channel which constrain palaeoceanographic models for this area the stratigraphic stacking patterns record nine seismic units su1 to su9 separated by eight major discontinuities a to h oldest to youngest key seismic markers in cds evolutionary history occur during aptian albian 122 ma late cenomanian 94 ma early 38 2 36 2 ma and late 25 23 ma oligocene and early middle miocene 17 15 ma epochs these record onset 122 to 94 ma growth 94 to 25 23 ma maintenance 25 23 to 17 15 ma and burial 17 15 ma to the actual time stages for cdss cdss first develop during the onset stage which coincides with the opening and deepening of the african southern ocean gateway at 122 and 100 ma respectively the growth stage beginning in the late cenomanian 94 ma correlates with the opening and deepening of the equatorial atlantic gateway during the growth stage two major shifts in sedimentary stacking pattern occur which coincide with palaeoceanographic changes during the early 38 2 36 2 ma and late 25 23 ma oligocene these in turn coincide with the onset and local enhancement of antarctic water masses cds growth continued until the early middle miocene during the maintenance stage 17 15 ma most cds growth ceased at the end of the maintenance stage circulation of the north atlantic water mass into the southern hemisphere led to a deepening of antarctic water masses in the area

a gravity survey across the bourlamaque massif southeastern abitibi greenstone belt quebec canada the relationship between the geometry of tonalite plutons and associated gold mineralization abstract gravity data collected over the bourlamaque massif near val d or quebec are used to obtain a three dimensional image of this pluton the interpretation is based on density measurements of samples of the pluton and its envelope the small gravity anomaly less than 5 mgal over the massif indicates that the pluton is a thin body 1 km pronounced differences between the southern and the northern segments of the gravity profiles suggest that the northern lobe of the pluton is thicker than the southern lobe geometrically the pluton resembles a dyke cutting across the stratigraphic layers at a 80 angle it was apparently emplaced in an extensional environment before being deformed in the kenorean orogeny the location of the lode type gold deposits near the pluton is determined by its shape and the competency contrast at the lower intrusive contact

upb zircon and rutile chronology of archean greenstone formation and gold mineralization in the val d or region quebec abstract u pb geochronology provides an absolute time framework for the evolution of the sigma gold deposit and surrounding rocks at val d or southern abitibi subprovince the bourlamaque batholith the largest pluton in the area gives a 2699 8 1 0 ma u pb zircon age this pluton cuts the val d or formation which hosts the mineralization a u pb zircon age of 2704 9 1 1 ma on a felsic volcanic rock the colombiere rhyolite 13 km east of the mine dates that formation the gold bearing quartz vein system at sigma is hosted by andesites and two generations of porphyry intrusions all metamorphosed to the greenschist facies the oldest porphyry porphyritic diorite shows the same deformation as the volcanic rocks and has a 2703 7 2 5 ma u pb zircon age the porphyritic diorite and volcanic rocks are cut by feldspar porphyry dykes which post date regional folding and have a 2694 0 2 2 ma u pb zircon age regional greenschist metamorphism has been dated directly with a u pb date of 2684 7 ma on rutile in the colombiere rhyolite the mineralization and hydrothermal alteration in the mine are superimposed on the metamorphic minerals hydrothermal rutile from an alteration halo around the veins in andesite has a 2599 9 ma u pb age textural evidence clearly indicates that the wall rock alteration and vein filling are contemporaneous and hence the vein system and gold mineralization appear to have developed at least 80 m y after the formation and metamorphism of host greenstones

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

turbidity current sediment waves on the submarine slopes of the western canary islands two sediment wave fields have been identified on the flanks of the western canary islands of la palma and el hierro using a high quality 2 d and 3 d dataset that includes geosea and tobi imagery 3 5 khz profiles and short sediment cores the la palma sediment wave field covers some 20 000 km2 of the continental slope and rise and consists of sediment waves with wave heights of up to 70 m and wavelengths of up to 2 4 km the wave crestlines have a complex morphology with common bifurcation and a clear sinuosity waves have migrated upslope through time cores recovered from the wave field contain volcaniclastic turbidites interbedded with pelagic hemipelagic layers the wave field is interpreted as having formed beneath unconfined turbidity currents a simple previously published two layer model is applied to the waves revealing that they formed beneath turbidity currents flowing at 10 100 cm s 1 with a flow thickness of 60 400 m and a sediment concentration of 26 427 mg l the el julan sediment wave field lies within a turbidity current channel on the southwest flank of el hierro the sediment waves display wave heights of about 6 m and wavelengths of up to 1 2 km the waves are migrating upslope and migration is most rapid in the centre of the channel where the flow velocity is highest this wave field has been formed by channelised turbidity currents originating on the flanks of el hierro

accretion of archean oceanic plateau fragments in the abitibi greenstone belt canada the arc arc collision model is often applied to the evolution of archean greenstone belts this model predicts concordant stratigraphic relations among the various lithologies evolving generally from komatiitic tholeiitic affinities toward calc alkalic affinities new geological data from the malartic composite block of the abitibi greenstone belt indicate that this volcanic pile rather than representing a conformable sequence is composed of four distinct mafic lithotectonic domains that are overlain by a calc alkalic sequence the mafic domains are thought to be examples of accreted archean oceanic plateau material that were deformed during their collage state the younger calc alkalic sequence represents extension related volcanism that erupted through the ac creted and deformed plateau material possibly as a consequence of ridge subduction in a regime of oblique convergence the relations described here may represent a common feature of archean terranes

40ar 39ar geochronological evidence for multiple postmetamorphic hydrothermal events focused along faults in the southern abitibi greenstone belt thermal histories in the abitibi and pontiac subprovinces vary for three general domains 1 zones of impermeable rock with cooling rates of 8 c ma 2 zones of impermeable rock that are spatially associated with monzogranite plutons with apparent cooling rates of 1 2 cima and 3 permeable high strain zones with apparent cooling rates of 2594 ma from the volcanogenic massive sulphide related sericite alteration with the coarser mica yielding the younger date based on radiometric dating impermeable rocks were affected weakly by postmetamorphic hydrothermal events minerals in zones of higher permeability were reset during the intrusion of monzogranite plutons highly permeable zones such as the larder lake cadillac and porcupine destor faults were overprinted repeatedly this produces a drawn out series of dates from minerals with varying closure temperatures radiometric ages from fault zones or ore deposits cannot be used to interpret the cooling history and evolution of the abitibi belt as a whole

internal structure of the cadillac tectonic zone southeast of val d or abitibi greenstone belt quebec the kirkland lake larder lake cadillac break is a major fault zone of the abitibi greenstone belt well known for its spatially associated gold camps a detailed structural analysis of this fault zone in the val d or area has shown the presence of a 200 750 m wide zone of high strain defined here as the cadillac tectonic zone ctz which includes the narrower schist zone generally regarded as the cadillac break the boundaries of the ctz which coincide with major lithologic contacts strike approximately east west and dip 80 to the north the internal structure of the ctz is best analysed in terms of two increments of the same progressive deformation the d1 strain increment is characterized by an east west striking subvertical s1 foliation at low angle in strike to the bound aries of the ctz and containing subvertical elongation lineation primary lithological contacts have been transposed into s1 and folded by f1a folds f1b intrafolial folds of s1 ranging from noncylindrical subhorizontal f

the influence of dikes on auriferous shear zone development within granitoid intrusions the bourlamaque pluton val d or district abitibi greenstone belt shear zone related gold quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes which may have a profound influence on the localization orientation and kinematics of auriferous shear zones the bourlamaque pluton of the val d or district contains several economic auriferous shear zones most of which follow and overprint diorite dikes mineralization in all deposits consists of quartz tourmaline pyrite veins in reverse oblique orientation with a significant range of strike dip and slip direction the geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion the stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly directed compression recorded by similar shear zones outside the pluton this indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes which

postmineralization faults in the beaufor gold deposit abitibi greenstone belt canada geometry origin and tectonic implications for the val d or mining district the beaufor mine is a mesothermal vein type gold deposit hosted by the bourlamaque pluton a synvolcanic intrusion crosscutting archean volcanic rocks of the abitibi greenstone belt in the val d or mining district the auriferous system is related to south dipping reverse shear zones and consists of up to 2 m wide sheared and extensional sulfide rich quartz veins the auriferous veins system is crosscut by two generations of faults east west trending south dipping 60 brittle ductile reverse faults e g the dike 01 central fault system and subvertical to steeply north dipping brittle faults e g the beaufor fault system the dike 01 central fault system presents structural fabrics kinematic and hydrothermal characteristics similar to those of auriferous shear zones both are interpreted as master faults and secondary structures respectively with the dike 01 central fault system acting as a channelway for the updip draining of ore fluids that were mainly trapped in low angle synthetic shear zones incremental deformation and progressive decrease of bulk fluid pressure led to strain localization and faulting of auriferous quartz veins by the dike 01 central fault system the beaufor fault system crosscuts all structures of the beaufor deposit it consists of a series of oblique reverse dextral faults that lack evidence for pervasive hydrothermal alteration the main structure of that system is the east west trending north dipping beaufor fault which is associated with northeast southwest trending synthetic i e west shear faults and north south trending antithetic faults i e post ore faults fault zones of the beaufor mine are reminiscent of large scale tectonics in the val d or mining camp auriferous quartz tourmaline vein deposits are commonly associated with east west trending high angle reverse shear zones and hydrothermal events coeval with or slightly postdating peak metamorphism and regional deformation several fault zones of the val d or area preserve evidence for both reverse shearing and dextral strike slip faulting structures recorded in the beaufor mine suggest that reverse and dextral trancurrent faulting is genetically unrelated and probably resulted from sequential faulting rather than transpression

internal structure of a contourite drift generated by the antarctic circumpolar current 1 we describe the internal structure and stratigraphy of a well imaged contourite drift from the southern ocean this drift which we have named the south falkland slope drift lies on the northern flank of the falkland trough due south of the falkland islands drifts which occur directly in the path of the antarctic circumpolar current acc downstream of the drake passage gateway are of considerable paleoceanographic significance since their detailed stratigraphic record will help to constrain the history of the acc we have reprocessed a grid of seismic reflection profiles generously provided by westerngeco ltd in order to enhance imaging of the south falkland slope drift and of drift deposits within the trough the resultant high quality images enable us to map the internal architecture of these drifts in unprecedented detail by combining seismic stratigraphic mapping with measured sedimentation rates from nearby boreholes we have inferred ages of the principal mappable horizons with minor adjustments to sedimentation rates through time we can show that these ages correspond to significant southern ocean events we propose that the south falkland slope drift initiated at 24 5 20 5 ma in accordance with some but not all published estimates of acc establishment a highly reflective horizon with an estimated age of 14 5 ma corresponds to growth of the east antarctic ice sheet which led to a period of significant global cooling a similarly bright reflective horizon with an estimated age of 9 ma is thought to be related to a reorganization of bottom current flow which just predated establishment of grounded ice sheets on the antarctic peninsular shelf finally a prominent early pliocene unconformity at 4 5 ma may be linked with the onset of major northern hemisphere glaciation or with antarctic ice sheet expansion we conclude that this well imaged drift is an important and largely continuous stratigraphic record of acc activity and suggest that it would be an excellent drilling target

a model for the growth of mudwaves in the presence of time varying currents abstract mudwaves are produced in a model when a periodic current produces lee waves that alter the deposition erosion rates of sediment at the bottom of an ocean a technique analogous to using a lagrangian representation for calculating the velocity perturbations associated with these lee waves is determined and then applied to a situation typical of one observed in the argentine basin the fact that the imposed current is variable results in the perturbation velocities also being time dependent with two major time scales one of these time scales is the period of the variable current which is taken to be on the order of weeks this is consistent with the dominant periods indicated in the data the other time scale is on the order of a day or two and is associated with the time required for the time dependent part of the imposed current total current minus its time averaged part to cross a ridge waves on this time scale are excited when the imposed current passes through a value that changes the character of the lee waves from vertically propagating to bottom trapped or vice versa the long term erosion deposition and mudwave growth rates are insensitive to the details of these shorter time scale variations

archean wrench fault tectonics and structural evolution of the blake river group abitibi belt quebec structural analysis of the blake river group volcanic rocks in the rouyn noranda region shows the formations to be distributed largely in z shapes resulting from the interference of two early fold systems oriented west northwest east southeast and east west respectively the first of these two fold systems is probably related to the shortening associated with left lateral movement along the two major fractures in the region namely the porcupine destor and larder lake cadillac faults the second system appears to be the result of north south compression perpendicular to the two major fractures the two major faults the first system of early folding the normal and reverse faults and the minor dextral and sinistral strike slip faults that have been observed in the blake river group rocks can all be integrated into one tectonic system that of wrench fault tectonics the orientations of the principal structures recognized in the abitibi belt major shear zones folding and faulting suggest that the d

gold bearing fault zones related to late archean orogenic folding of upper and middle crust in the abitibi granite greenstone belt ontario abstract this work investigates the structures of the abitibi granite greenstone belt ontario with a focus on regional scale folds and on regional scale auriferous fault zones the folds and the fault zones resulted from late archean orogenesis the analysis is based on studies of surface geology and on modelling of the gravity field amphibolite grade orthogneiss was involved in the regional folding that also deformed the overlying greenstones folding resulted in uplift of the orthogneiss that preserves the metamorphic mineral assemblage ferropargasite garnet biotite andesine quartz geothermobarometric calculations indicate recrystallization of a metatonalite sample under peak paleopressures of 7 0 1 2 to 7 9 1 1 kb providing evidence that folding involved crust to depths of at least 18 25 km the regional bouger anomaly map reveals previously unrecognized first order folds interpretation of the bouger anomaly map also confirms that granitic batholiths are hosted by anticlines a wavelet based inversion method was used to determine the locations orientations and continuations at depth of the maxima of density contrasts the maximum density contrasts correspond to steeply dipping geological contacts on the limbs of the open to tight regional scale folds regional scale fault zones only have prominent gravity signatures where they correspond to sheared rocks on the limbs of folds modelled gravity profiles were used to produce profiles that visualize the shapes of batholiths and greenstone bodies within the present day upper crust the granitic batholiths have tabular shapes which are locally folded with preserved main body thicknesses of 1 3 km the greenstones form keels corresponding to synclines some of which reach 5 6 km depth the results of this study confirm that the principal deformational response of the abitibi granite greenstone belt to late archean collisional tectonics was large half wavelength 10 40 km folding of the upper and middle crust our results and interpretations also strongly suggest the regional scale fault zones which are loci for orogenic gold deposits are fold related structures they represent quasi continuous lineaments of shearing and faulting on the limbs of regional folds and locally in the cores of detachment anticlines as shown in a previous paper

turbidity current sediment waves on irregular slopes observations from the orinoco sediment wave field abstract the orinoco sediment wave field covers an area of at least 29 000 km2 on the southern margin of the orinoco valley at a water depth of 4400 4825 m wave dimensions are highly variable across the wave field with wavelengths of 110 2600 m and wave heights of 1 15 m slope gradients are also very variable with values of 0 14 0 48 overall the sedimentary sequence on the upslope wave flanks is about 40 thicker than that on the downslope flanks leading to upslope wave migration in the manner of antidunes in addition reflectors on the upslope flanks generally display higher reflectivity than those on the downslope flanks suggesting that a higher proportion of coarser sediment occurs on the upslope flank an unconfined turbidity current origin is proposed for the orinoco sediment waves based upon detailed analysis of regional stratigraphic seismic facies and sediment wave distribution morphology and dimensions sediment waves are not related to flows passing along or spilling out of the orinoco valley or to bottom currents flowing parallel to the slope turbidity currents responsible for wave generation are interpreted as originating from slope failures on the adjacent venezuela guyana and suriname continental margins simple numerical modelling has enabled turbidity current flow characteristics across the orinoco sediment waves to be estimated internal froude number 0 7 1 1 flow thickness 24 645 m and flow velocity 31 82 cm s 1 a key finding of this study is that there appears to be a close relationship between the changes in slope gradient and those in wave dimensions across the wave field the irregular gradient of the present day wave field is partly a reflection of the irregular bounding surface of the sediment waves which is represented by mass flow deposits and associated mud diapirs the changes in slope gradient along this lower boundary lead to variations in the flow thickness and flow velocity of passing turbidity currents which in turn control the wave dimensions generally on lower gradients beyond minor breaks of slope flow thickness increases and flow velocity decreases leading to an increase in wavelength and a decrease in height

geologic evolution of the late archean abitibi greenstone belt of canada the southern volcanic zone svz of the late archean abitibi belt of the superior province of canada is dominated by komatiitic to tholeiitic volcanic plateaus and large bimodal mafic felsic volcanic centers these volcanic rocks were erupted between about 2717 and 2700 ma in a series of rift basins that formed as a result of wrench fault tectonics they overlie and juxtapose a volcano plutonic assemblage characterized in the northern abitibi belt the age of the assemblage is about 2720 ma or older and it comprises basaltic to andesitic and dacitic subaqueous massive volcanics cored by comagmatic sills and layered anorthositic complexes and overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 2 ma a tectonic model is proposed in which the svz formed in a series of rift basins that dissected an earlier formed volcanic arc comparisons are made with rift environments that have been postulated for phanerozoic areas such as the hokuroko basin of japan the taupo volcanic zone of new zealand and the sumatra and nicaragua arcs

structural evolution and early accretion of the archean malartic composite block southern abitibi greenstone belt quebec canada the malartic composite block of the southern abitibi belt underwent at least two phases of ductile deformation over a period of 25 ma during the late archean it is divided into seven tectono stratigraphic domains on the basis of their lithologicai content structural styles and geochemical affinities of the volcanic and plutonic rocks the malartic composite block is bounded to the south by the sedimentary rocks of the kewagama group that have been also affected by deformation the crosscutting relationships between the structural elements along with precise geochronological data provide a basis for evaluation of the evolution of the deformation in this part of the southern abitibi the d1 tectonic event produced ductile thrust faults and folds in the mafic and ultramafic domains of the malartic composite block the calc alkalic rocks of the val d or domain 2705 ma were erupted on top of these deformed domains thus establishing the minimum age for d1 the d2 event is divided into three increments t

the tectonic evolution of the abitibi greenstone belt of canada based on structural geochemical sedimentological and geochronological studies we have formulated a model for the evolution of the late archaean abitibi greenstone belt of the superior province of canada the southern volcanic zone svz of the belt is dominated by komatiitic to tholeiitic volcanic plateaux and large bimodal mafic felsic volcanic centres these volcanic rocks were erupted between approximately 2710 ma and 2700 ma in a series of rift basins formed as a result of wrench fault tectonics the svz superimposes an older volcanic terrane which is characterized in the northern volcanic zone nvz of the abitibi belt and is approximately 2720 ma or older the nvz comprises basaltic to andesitic and dacitic subaqueous massive volcanics which are cored by comagmatic sill complexes and layered mafic anorthositic plutonic complexes these volcanics are overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 2 ma the tectonic model envisages the svz to have formed in a series of rift basins which dissected an earlier formed volcanic arc the nvz analogous rift environments have been postulated for the hokuroko basin of japan the taupo volcanic zone of new zealand and the sumatra and nicaragua arcs the difference between rift related submergent volcanism in the svz and emergent volcanism in the nvz resulted in the contrasting metallogenic styles the former being characterized by syngenetic massive sulphide deposits whilst the latter was dominated by epigenetic porphyry type cu au deposits

morphology of abyssal mudwaves at project mudwaves sites in the argentine basin abstract extensive fields of mudwaves are present in the argentine basin mudwaves and water parameters at three sites were studied to provide detailed information on bathymetry mudwave structure sediment parameters and bottom water flow characteristics two sites 5 and 6 are discussed in this paper crests of mudwaves at site 5 on the north flank of the zapiola drift are oriented 45 anti clockwise from the measured westward flow direction and migrate to the left of the flow direction mudwaves at site 6 on the south flank of the zapiola drift are oriented 20 anti clockwise from the inferred southeast bottom flow direction and also migrate to the left of direction evidence from current meters and surface sediments suggests that the mudwaves at site 5 are active today while those at site 6 have been active in the holocene but perhaps not within the last 100 years mudwave orientation anti clockwise to mean flow preferential sediment accumulation on the left wave flank and apparent sediment accumulation on the wave crest agree with a model for mudwave growth presented by blumsack and weatherly 1989 deep sea research 36 1327 1339 cross wave asymmetry in sediment accumulation pattern is sufficient to cause a 10 change in surface sediment bulk density over the wave profile the record of mudwave migration obtained from sites 5 and 6 in the southern argentine basin and from site 7 in the northern argentine basin suggests that bottom water flow has changed over a number of time scales during the last 200 000 years thus the analysis of abyssal bed forms can provide independent evidence about past changes in bottom flow

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

u pb age constraints for the magmatic and tectonic evolution of the pontiac subprovince quebec new u pb zircon titanite and monazite ages help constrain the history of magmatism and tectonism within the pontiac subprovince of western quebec the pontiac subprovince resembles other metasedimentary belts of the superior province however the stratigraphic relationships between the dominantly sedimentary rocks of the pontiac and the adjacent volcanic dominated abitibi belt to the north and west remain controversial volcanic rocks of the belleterre volcanic zone in the southern part of the pontiac subprovince have been interpreted by other workers as klippen of abitibi strata that were thrust southward onto the pontiac subprovince however volcanic rocks in the belleterre zone give crystallization ages of 2689 2682 ma which are younger than any extrusive rocks dated thus far from the abitibi belt single detrital zircon grains from pontiac sedimentary rocks give ages as young as 2683 ma indicating that the sediments are similar in age or younger than the volcanic units the volcanic rocks pro

structural analysis and vein episode of the penjom gold deposit malaysia implications for gold mineralisation and tectonic history in the central belt of malaysia abstract gold mineralisation at the penjom gold deposit in the central belt of peninsular malaysia is dominantly hosted in structurally controlled quartz carbonate veins that display a variable degree of overprinting events under a ductile brittle regime mineralised veins are categorised into two main episodes fold and thrust related veins mainly comprised of bedding and penjom thrust parallel shear veins and associated extension veins developed during a d2 event in addition ne to nne trending splays and penjom thrust parallel reverse dextral and locally nnw to ns reverse sinistral faults overprint earlier vein events forming a new episode of extensional veins during d3 event mostly at the fault contacts of intrusives either as shallow dipping or vertical sheeted stockwork or brecciated veins at least two episodes of faulting d4 d5 are evident which postdates the main episodes of veining and mineralisation this is indicated by a series of late episodes ns trending sinistral and oblique to normal faults which transect and displace the penjom thrust and the folded footwall sequence at low angles and responsible for intensive vein deformation along the penjom thrust and displacement of ore body structural interpretations of mineralised veins suggest that the veins were formed under a compressional to transpressional regime with later post vein displacement in a transtensional to extensional regime vein formation in response to deformation observed at penjom reflects regional structural deformation within the central belt of peninsular malaysia and specifically along the bentong raub suture zone

channel related sediment waves on the eastern slope offshore dongsha islands northern south china sea abstract the characteristics and origin of the sediment waves on the eastern slope offshore dongsha islands northern south china sea scs were analyzed by integrating high resolution multibeam bathymetric seismic and piston core data four sediment wave fields were identified which are the west dongsha channel wdsw west taiwan channel wtsw south taiwan channel stsw and west penghu channel wpsw sediment wave fields respectively they are distributed on the right levees looking downstream and adjacent overbank areas of related channels wdsw wtsw and stsw or developed outside the channel mouths wpsw each sediment wave field consists of several to tens of rows of sediment waves these sediment waves are up to 2 8 7 2 km in wavelength and 30 60 m in wave height with wave crests orthogonal to or oblique to the orientation of the channels the sediment waves gradually decrease in dimension both in downslope direction and with the distance increasing away from the channel most sediment waves are asymmetric in cross sections with a thicker upslope flank and a thinner downslope flank and therefore migrate upslope piston cores suggest that sandy turbidites developed with normal size grading dominate the channels while massive muds with thin sandy or silty turbidite interbeds prevail in the inter channel regions on which the sediment waves situated the sediment waves on the channel levees and related overbank areas wdsw wtsw and stwd were presumably built by the turbidity currents overspilled from the channels while those in wpsw located outside the mouth of the west penghu channel are suggested generated by unconfined sheet like turbidity currents outside the channel mouth

consonorm_lg new normative minerals and alteration indexes for low grade metamorphic rocks the consonorm lg method provides a standardized solution for approximating metamorphic parageneses as well as indexes for estimating chemical and mineralogical changes caused by hydrothermal alteration consonorm lg is designed for rocks dominated by silicates fe ti oxides and or carbonates and it approximates the main parageneses of greenschist and lower amphibolite grade metamorphic rocks for three sets of temperature and pressure conditions 350 c and 2 5 kbars 450 c and 2 5 kbars 575 c and 2 kbars for each model the norm calculates the main paragenesis using an acfmnk tetrahedron a convenient way of representing a large number of silicate assemblages in addition to silicate minerals consonorm lg calculates fe ti oxides and other accessory minerals from minor elements as well as sulfides from analyzed s or from analyzed metals and carbonates from analyzed co2 or from normative co2 estimated from loss on ignition loi consonorm lg also calculates several alteration indexes to estimate fe mg e g chloritization ca e g propylitic alteration na and k acid alterations e g sericitization phyllic alterations and al gain e g argillization carbonatation indexes are also calculated using the amount of normative minerals formed by this type of alteration i e carbonates chlorite and muscovite the normative calculation is validated using published whole rock analyses and petrographic descriptions alteration indexes are validated using several natural samples of alteration halos around base metal and gold deposits

shock metamorphism of clay minerals on mars by meteor impact a large fraction of clay minerals detected on mars by infrared remote sensing represent materials exhumed from the subsurface by meteor impact begging the question of whether the infrared features used to detect the clays are affected by shock associated with the impacts we used x ray diffraction and infrared and mossbauer spectroscopy to evaluate the mineralogy of five clay minerals after experimentally shocking them to six shock pressures from 10 40 gpa the shocked clays exhibit three main relevant shock effects 1 an overall decrease in infrared spectral contrast in the impact fragmented materials 2 oxidation of fe in ferrous clays and 3 loss of some spectral structure in relatively well ordered clays such as kaolinite other than the widespread oxidation of ferrous clays shock metamorphism likely has little effect on the accurate interpretation of clay mineralogy on mars from remote sensing data however we are able to identify rare cases of extreme shock in some martian clay deposits

evolution of the south central segment of the archean abitibi belt quebec part ii tectonic evolution and geomechanical model in this paper we describe the relations between the paleogeographic and tectonic evolution of the southwestern part of the archean abitibi and bellecombe belts volcanism in the abitibi belt created a very thick anisotropic plate composed of competent volcanic rocks and broken by the duparquet destor break the depocenters of the upper division of diverse volcanic rocks subsided about 10 km relative to their surroundings and some central volcanic complexes within this division were consolidated by synvolcanic plutons and their thermal metamorphic aureole the cadillac break a normal fault separated the abitibi and bellecombe belts the latter consisted of comparatively incompetent sedimentary rocks on top of a basement composed of ultramafic mafic flows north south compression of the volcanic terrain during the kenoran orogeny produced a set of flexure folds f1 that curve around the consolidated cores of central volcanic complexes generally in an easterly direction synclinoria nucleated at the dee

structural setting textures and timing of hydrothermal vein systems in the val d or camp abitibi canada implications for the evolution of transcrustal second and third order fault zones and gold mineralization in the val d or camp archean abitibi greenstone belt canada numerous gold mineralized second and third order fault zones are spatially associated with the transcrustal cadillac tectonic zone ctz this situation is used to test whether fluid systems in the ctz have a similar structural timing to those in the gold hosting structures and hence the ctz could represent the main fluid conduit in the camp the transcrustal ctz at orenada no 2 contains structurally complex vein systems with mineralized quartz tourmaline veins related to both d2 oblique reverse faulting and f3 dextral asymmetric folding both of which have been overprinted by unmineralized subhorizontal and subvertical quartz veins quartz tourmaline veins within second and third order shear zones at paramaque and riviere heva also formed during d2 deformation and have been at least at riviere heva deformed by f3 asymmetric folding in contrast mineralized quartz vein systems at cartier malartic are controlled by f3 folding and over

geophysical evidence for widespread cenozoic bottom current activity from the continental margin of nova scotia canada abstract two dimensional and three dimensional multichannel seismic reflection data are utilized to examine previously unrecognized contourite depositional systems along the continental margin of nova scotia canada prior to this study these features were thought to be of limited extent in the study area the new data show that contourite drifts are widespread with greatest drift development during the late miocene to pliocene giant sediment waves form stacked aggrading sequences of bedforms and their development is linked to pre existing seafloor morphology small sediment drifts developed locally throughout the late paleogene and neogene either southwest and down current of seafloor obstacles or form channel fills major erosional pulses form regional seismic markers first along the continental rise in the early oligocene then along the continental slope during the late miocene and pliocene three dimensional seismic data show that erosion surfaces preserve along slope amplitude anomalies two dimensional low relief sediment waves and barchanoid bedforms the geophysical evidence implies that a northeast to southwest along slope bottom current influenced cenozoic depositional patterns throughout the study area

interactions among adriatic continental margin morphology deep circulation and bedform patterns abstract within the mediterranean region the adriatic basin is one of the key sites for the formation and spreading of dense shelf water once formed in the northern shallow region as a response to strong wintry cold air outbreaks dense water masses move southeastwards as bottom hugging gravity currents eventually reaching the south adriatic continental margin a fraction of the dense water mass is thus intercepted by the shelf break whence it flows down the continental slope driven by its negative buoyancy and interacting with ambient water and seafloor topography this process generates a wide variety of dynamics and morphological features such as erosional moats furrows giant comet marks sediment drifts and sediment waves in this study we merge the outcomes of a state of the art wave ocean coupled numerical model with the geological evidence from the analysis of southern adriatic bedform patterns the model was run to reproduce an exceptional cold event that occurred in winter 2012 and benefits from a high resolution bottom topography produced from data collected during recent bathymetric surveys model results allow the identification of flow pathways along and across the continental shelf and slope with particular emphasis on the role of large scale margin geometry in controlling morphodynamic processes and its implications in terms of resolution requirements for modelling purposes although modelled overall water fluxes and basin renewal ratios are mostly controlled by regional circulation and large scale morphology local topographic features and singularities appear crucial in triggering concentrating and modulating bottom currents dynamics and sediment transport towards the south adriatic pit as well as enhancing mixing and entrainment of ambient water as long as this degree of information is provided within the bathymetric constraint modelled hydrodynamic pathways in the study case are consistent with observed bedform morphology and their spatial pattern for different zones in the continental slope temporal variability of the flows has been investigated permitting to disentangle the relative contribution of dense water cascading and background circulation at the basin and sub basin scale in controlling bedform dynamics this study gives a first quantitative insight on the hydrodynamic mechanisms responsible for south adriatic margin reshaping suggesting a modelling approach to the interpretation of the high resolution bathymetric and stratigraphic data made available by recent survey technologies

the structural controls of gold mineralisation within the bardoc tectonic zone eastern goldfields province western australia implications for gold endowment in shear systems the bardoc tectonic zone btz of the late archaean eastern goldfields province yilgarn craton western australia is physically linked along strike to the boulder lefroy shear zone blsz one of the richest orogenic gold shear systems in the world however gold production in the btz has only been one order of magnitude smaller than that of the blsz 100 t au vs 1 500 t au the reasons for this difference can be found in the relative timing distribution and style s of deformation that controlled gold deposition in the two shear systems deformation within the btz was relatively simple and is associated with tight to iso clinal folding and reverse to transpressive shear zones over a 12 km wide area of high straining where lithological contacts have been rotated towards the plane of maximum shortening these structures control gold mineralisation and also correspond to the second major shortening phase of the province d2 in contrast shearing within the blsz is concentrated to narrow shear zones 2 km wide cutting through rocks at a range of orientations that underwent more complex dip and strike slip deformation possibly developed throughout the different deformation phases recorded in the region d1 d4 independent of other physico chemical factors these differences provided for effective fluid localisation to host units with greater competency contrasts during a prolonged mineralisation process in the blsz as compared to the more simple structural history of the btz

tectonic evolution of the northern volcanic zone abitibi belt quebec the archean abitibi subprovince has been divided formally into a northern volcanic zone nvz including the entire northern part of the subprovince and a southern volcanic zone svz on the basis of distinct volcano sedimentary successions related plutonic suites and precise u pb age determinations the nvz has been further formally subdivided into i a monocyclic volcanic segment mvs composed of an extensive subaqueous basalt plain with scattered felsic volcanic complexes 2730 2725 ma interstratified with or overlain by linear volcaniclastic sedimentary basins and ii a polycyclic volcanic segment pvs comprising a second mafic felsic volcanic cycle 2722 2711 ma and a sedimentary assemblage with local shoshonitic volcanic rocks a sequence of deformational events d1 d6 over a period of 25 ma in the nvz is consistent with a major compressional event north south shortening was first accommodated by near vertical east trending folds and with continued deformation was concentrated along ma

deposit scale structural architecture of the sigma lamaque gold deposit canada insights from a newly proposed 3d method for assessing structural controls from drill hole data deposit scale structural analysis is a practical method of structurally analyzing 3d drilling data this interpretation method uses readily available distributed 3d data at the most relevant scale for mining and exploration this method does not depend on collecting traditional structural data from core such as orientation of planar and linear data but relies on the premise that grade distributions sampled from drilling provide insight into the structural control of the deposit with the interpretation of structural geometry done using a computer 3d viewer this method is applied to the well studied archean sigma lamaque gold deposit which features late orogenic vein mineralization and which is controlled by three orders of structural features the first order control is the easterly plunging pipe like conduit parallel to f2 fold plunge defined by the intersection of bedding s0 and foliation s2 1 5 km radius 3 km down plunge the second order controls nested within the first order are the younger subvertical late diorite plugs that intruded vertically into the host rocks along the established s2 foliation anisotropy 1250 400 150 m dimension for main plug the third order control laterally limited by first and second order structural controls is the well documented gold bearing vein sets 1 10 m thick and up to 1 5 km in extent that developed in the late diorites and in the older folded volcanogenic stratigraphy and diorites it is proposed that the first order control defined by the moderately plunging f2 fold is the main fluid pathway resulting from structural permeability formed during earlier folding the second order late diorite plugs and other competent lithological units which intersected and fractured during late stage d2 compression served as chemically reactive sites causing gold to precipitate along this first order pathway it is predicted that intrusions that do not intersect the first order structural conduits are less likely to be mineralized greenfield orogenic gold exploration requires that the first order controls are identified and the geometry of hydrothermal alteration is best understood in the context of the structural architecture of the host rocks

formation of voids and veins during faulting abstract we have developed a quantitative model of void and vein development in fault zones based on observations of fault roughness and the contact characteristics of rough directionally anisotropic fractal surfaces this model includes progressive dilation of the fault during slip events and the elastic deformation of the surfaces normal to the fault plane closure as new void space develops the model predicts vein geometries that are qualitatively similar to those observed in fault controlled mineral deposits the statistics of the vein system are described and strategies for sampling of such structures by drilling are developed the results have significant implications for evaluation of ore reserves and evaluating the fluid transport properties of faults

geochemical and mineralogical diagnosis on gold ores a case study from the cadillac larder lake fault zone abitibi canada abstract numerous orogenic gold deposits have been discovered within the archean abitibi greenstone belt of canada these include the francoeur wasamac astoria zulapa goldex lamaque lac herbin and beaufor deposits all of which are located within the cadillac larder lake fault zone cllfz these gold deposits are hosted by various lithologies and vary in terms of style of mineralization sulfide abundance and hydrothermal alteration these variations mean that exploration for new deposits has been difficult in this area using common exploration criteria this study presents the results of a principal component analysis pca based approach combining geochemical and mineralogical data to quickly identify different types of gold mineralization within the cllfz including assessing the use of this approach in mineral exploration the first principal components in both classification methods used during this study pce1 and pcm1 representing element geochemical and mineralogical classification respectively can efficiently discriminate between mineralization and barren altered rocks the second principal components pce2 and pcm2 can be used to constrain the host rocks altered vs barren and style of mineralization disseminated vs vein hosted respectively finally pce3 and pcm3 give more detailed information on the nature of the mineralization in an area possible reflecting variations in the composition of ore forming fluids all of the above indicates that the two pce and pcm classification methods are complementary which means that using approaches that combine these methods will provide a comprehensive understanding of the nature of studied samples and or deposits information extracted from the results of the pca undertaken during this study may be beneficial for mineral exploration in unknown districts such as glaciated areas where traditional geological fieldwork is challenging this study also defines element and mineral mineralization indices based on pce1 and pcm1 which enables evaluation of the extent and style of gold mineralization in an area this study indicates that pca based automated mineralogical and geochemical classification methods could be highly useful in exploration for gold deposits

timing of gold mineralization in the val d or district southern abitibi belt evidence for two distinct mineralizing events gold bearing quartz vein deposits in the val d or area of the southern abitibi greenstone belt are classified in two categories based on structural and chronologic relationships young deposits 2690 ma feature commonly deformed orebodies that are cut by dikes of various composition such deposits occur at the siscoe kiena orion and norlartic mines the norlartic main orebody is crosscut by a tonalite dike which has been dated by u pb at 2692 or 2 ma in agreement with structural data these observations show that gold mineralization in the val d or area occurs in at least two different settings and was emplaced at different times

crustal structure and kinematic framework of the northwestern pontiac subprovince quebec an integrated structural and geophysical study structural mapping gravity and magnetic modelling and interpretation of a deep seismic profile in the northwestern pontiac subprovince outline the crustal structure and early structural developme

40ar 39ar age constraints on the thermal history of the archean abitibi greenstone belt and the pontiac subprovince implications for terrane collision differential uplift and overprinting of gold deposits 40ar 39ar mineral age spectra of granitic and metamorphic rocks in conjunction with existing conventional zircon geochronology indicate that at least two major late archean thermal events affected tectonic blocks of the abitibi southern volcanic zone svz and the juxtaposed pontiac subprovince the earlier thermal activity 2690 2670 ma was accompanied by the intrusion of voluminous syntectonic plutons and caused low pressure greenschist facies metamorphism in the svz and intermediate pressure metamorphism in the pontiac subprovince the second thermal event 2660 2630 ma was coeval with the emplacement of syncollisional s type garnet muscovite granites in the pontiac subprovince and the higher grade lacorne block of the abitibi svz and reset the k ar systems in preexisting rocks magmatic amphibole from the syntectonic round lake batholith 2695 ma u pb zircon age of the abitibi svz has a slightly disturbed ar release spectrum with an upper plateau age of 2669 6 ma signifying that the low gra

mudwaves on the gardar sediment drift ne atlantic small amplitude 15 m mudwaves were mapped on the gardar sediment drift using the hydrosweep ds multibeam echosounder system on the r v maurice ewing improved data processing techniques allowed the swath mapped bathymetry to image features smaller than the nominal resolution 14 m of hydrosweep mudwave heights wavelengths and orientations were determined from the hydrosweep data and in conjunction with 3 5 khz profiles these mudwave fields were analyzed with regard to present models of mudwave formation mudwave crest orientation was clockwise to mean bottom flow direction and migration was to the right of measured currents for two areas on the drift this is consistent with models developed on large amplitude mudwaves using mudwave orientation and migration direction in a third area bottom current directions were inferred

dynamics of particles along the western margin of the southern adriatic processes involved in transferring particulate matter to the deep basin abstract the southern adriatic is an area of dense shelf water dsw cascading and open ocean convection the impact of dsw cascading events in transferring organic matter to the deep benthic community and in producing a wide range of bedforms along the continental margin has been highlighted in recent years in order to improve our knowledge on the interannual variability of the dsw cascading with the ultimate goal to understand timing of dsw formation and transport as well as the cascading process its variability in intensity and duration and the ultimate impact of the dense water on the deep sea in march 2009 we deployed an instrumented mooring in a field of sediment waves 860 m depth located down current to the bari canyon in march 2010 a second mooring was installed in the northern channel of the canyon winters 2009 2010 and 2011 were mild and particularly wet and the po river discharge remained relatively high throughout the whole winter hence we expected weak dense shelf water formation associated with a shallow shelf water overflowing off the adriatic shelf by contrast in winter 2012 the north adriatic experienced a severe cold wave with ne bora winds and reduced fresh water input these weather conditions allowed the formation of extremely dense shelf water three additional moorings were quickly deployed during this cold event in the southern adriatic sea to investigate the spatial variability of particle and organic matter fluxes exiting from the adriatic continental shelf under the influence of a strong dsw cascading event slow near bottom currents never exceeding 40 cm s 1 were recorded between march 2009 and february 2012 water temperatures depicted minor negative shifts total mass fluxes tmfs were low annual avg 1 7 2 8 g m 2 d 1 and 0 3 0 6 g m 2 d 1 in the canyon and in the sediment wave field respectively and peak values 6 8 g m 2 d 1 but showed significant seasonal and interannual variability fluxes in the canyon were higher than those measured in the sediment wave field at deeper water depth mass flux peaks during the 2112 dsw cascading were up to 5 times higher than the peaks of previous years up to 18 70 g m 2 d 1 with a spatial variability mainly driven by the localized pathways of dsw cascading in the canyon near bottom currents exceeded 70 cm s 1 and temperature dropped to 12 2 c while current speeds were high also at 1200 m depth 60 cm s 1 in the moat surrounding the dauno seamount surprisingly mass flux peaks occurred from the 16th february to the 1st of march 3 4 weeks ahead of the usual dsw occurrence suggesting an early arrival of the dsw the deep dsw cascading was the main process driving the particle transfer across the southern adriatic margin during late winter spring 2012 mooring data showed a nw se gradient of temperature and kinetic energy from upslope to basin floor indicating slope transverse flow modulated by local obstruction caused by the rugged seafloor topography bari canyon is one of the sites of dsw flow and in this area we have the possibility to extend observations back in time using continuous mooring data since 2009 and previous published materials this approach allowed evaluation of additional mechanisms of particle transport e g open ocean convection storm driven downward transport shallow dense water cascading that are particularly relevant in years when the dsw formation is less vigorous and cascading processes are sluggish the small amplitude of total mass flux peaks the weak currents and the relatively high and constant temperatures recorded during 2009 2010 and 2011 springs are consistent with an enhanced vertical particle rain from a mid water nepheloid layer triggered in turn by a shallow cascading of not particularly dense shelf water detaching from the seafloor when reaches its neutral buoyancy thus the intensity of dsw cascading shallow vs deep plays a first order control on the particulate fluxes through the western margin of the southern adriatic while storm induced sediment transport can occasionally be relevant too

initiation and evolution of turbidity current sediment waves in the magdalena turbidite system this study describes an extensive sediment wave field in the magdalena turbidite system caribbean sea colombia which occupies an area of at least 15000 km2 on the continental slope 3330 3800 m the waves display wavelengths up to 1 9 km wave heights up to 18 m and crestlines that are aligned roughly parallel to the regional bathymetric contours preferential deposition on the upslope wave flank has led to upslope migration in the manner of antidunes the magdalena sediment waves are interpreted as forming beneath unconfined turbidity currents which may result from the downslope evolution of slumps and mass flows the unconfined turbidity currents are derived from several point sources along the continental slope and spread laterally as they flow downslope this has led to the formation of a laterally extensive sediment wave field simple numerical modelling estimates that the turbidity currents responsible for wave generation were near or super critical with flow thickness and velocity estimated at 40 160 m and 36 82 cm s 1 respectively however later phases of wave growth were not dependent on specific flow conditions the most important aspect of this study is that the entire sediment wave unit from the basal boundary to the present day seafloor has been investigated using ultra high resolution seismic profiles the sediment wave unit rests upon an irregular discontinuity that marks a recent change in the sedimentary regime of the magdalena turbidite system from channelised to unchannelised gravity flows above this boundary the sediment waves display a growth pattern characterised by an increase in wave dimensions in addition the wave dimensions appear to become more regular through time however breaks of slope in the lower bounding surface of the wave field have produced variations in wave morphology that are still visible at the present day seafloor this indicates that there is a close relationship between variations in slope angle and turbidity current flow characteristics which in turn leads to variations in wave morphology