the 1996 ad delta collapse and large turbidite in lake brienz abstract in spring 1996 ad the occurrence of a large mass transport was detected by a series of events which happened in lake brienz switzerland turbidity increase and oxygen depletion in deep waters release of an old corpse into surface waters and occurrence of a small tsunami like wave this mass transport generated a large turbidite deposit which is studied here by combining high resolution seismic and sedimentary cores this turbidite deposit correlates to a prominent onlapping unit in the seismic record attaining a maximum of 90 cm in thickness it is longitudinally graded and thins out towards the end of the lake basin thickness distribution map shows that the turbidite extends over 8 5 km2 and has a total volume of 2 72 106 m3 which amounts to 8 7 yr of the lake s annual sediment input it consists of normally graded sand to silt sized sediment containing clasts of hemipelagic sediments topped by a thin white clay sized layer the source area the exact dating and the possible trigger of this turbidite deposit as well as its flow mechanism and ecological impact are presented along with environmental data river inflow wind and lake level measurements the combined results indicate that no particular cause i e earthquake explosion flood wind storm lake level change seiche or sediment dredging triggered the 1996 ad large turbidite deposit instead it was due to a delta slope failure most likely caused by normal sediment accumulation

peraluminous xenoliths in kimberlite metamorphosed restites produced by partial melting of pelites abstract three new varieties of aluminous assemblages from the jagersfontein kimberlite are recognized as xenoliths consisting of garnet spinel alkremite corundum garnet corganite and corundum garnet spinel corgaspinite accessory minerals include phlogopite k pargasite fassaitic pyroxene and secondary spinel bulk rock major elements are depleted in sio2 and enriched in al2o3 and mgo relative to basalt the compatible trace elements ni cr zn ga and v reflect the modal mineralogy and the incompatible trace elements k rb and ba vary as a function of metasomatism chondrite normalized ree patterns are characterized by fanning light and heavy ree variations calculations show that the patterns are consistent with partial melting of pelitic rocks from which a granitic low temperature portion has been removed by anatexis to produce a restite containing the observed geochemical variations sr isotopic ratios of garnet separates are high 0 780 0 804 and also indicate a sedimentary origin for the assemblages a two stage process involving partial melting of archean sediments followed by prograde metamorphism of the residual restite is tentatively proposed initiated by exotic terrain accretion or subduction at the edge of the kaapvaal craton

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

from foreland to forearc domains new multichannel seismic reflection survey of the mediterranean ridge accretionary complex eastern mediterranean abstract the mediterranean ridge of the eastern mediterranean sea is a huge accretionary wedge emplaced as a consequence of the africa aegean plate convergence that has a rate estimated at 40 mm yr processing of recent multichannel seismic data and integration with previous results seismic profiling swath bathymetry sonar have facilitated the study of the overall deformation pattern of the area which includes three distinct major structural domains facing various forelands 1 1 the outer domain is bounded southward by the present day wedge toe and towards the north by topographic slope breaks and clear changes in deformational style beneath the ionian and levantine mediterranean ridge branches the base of messinian evaporites seems to act as a major decollement level 2 2 the central or crestal domain the shallowest one shows evidence of mud diapiric and mud volcano activity and is overthrusting northward over the inner domain facing the libyan margin this area which displays spectacular mud volcano fields appears much wider and shallower 3 3 the less deformed inner domain is bounded northward by the hellenic trench system beneath its ionian inner area seismic velocities characteristic of continental crust have been recorded while within its levantine region it is made of a series of disconnected and uplifted basement blocks strabo seamounts along the matapan and pliny trenches structures which could be caused by transpressive deformation are locally observed we believe that both the north south structural arrangement and the clear west east lateral variations of the mediterranean ridge relate to its progressive collision against the libyan margin promontory this event which may have initiated 5 6 myr ago may have induced a a differentiated paleogeography of messinian evaporites later available for tectonic accretion leading to the further lateral structural variations of the outer domain and b strain partitioning between the central mediterranean ridge and the hellenic trench system

origin and chronology of the augias deposit in the ionian sea central mediterranean sea based on new regional sedimentological data abstract in the ionian sea central mediterranean sea several thick acoustically transparent layers are present including the augias deposit the augias deposit is the most recent thick layer covering the entire floor of the ionian abyssal plain with an average thickness of 10 12 m and a maximum thickness of up to 24 m in the sirte abyssal plain this deposit has also been observed in several adjacent smaller basins in waters deeper than 3000 m its estimated volume is 65 km 3 there are multiple plausible hypotheses regarding its age and triggering event which include the 1600 bc santorini volcanic caldera collapse the 365 ad crete m 8 5 earthquake and other smaller earthquakes such as the 374 ad calabria m 6 3 earthquake and the 361 ad sicily m 6 6 earthquake understanding the cause of this mass transport deposit is crucial for improving the natural hazard assessment of a vast area between southern italy and western greece in this study we propose a new interpretation of the augias deposit in terms of sedimentary processes and origin based on sediment cores collected in the nw ionian sea during the circee cruise onboard r v le suroit in october 2013 the sedimentological analysis of seven piston cores reveals three sedimentary facies corresponding to the augias deposit 1 homogenite 2 megaturbidite and 3 thick sandy turbidite these sedimentary facies are distributed within specific morpho tectonic regions as defined by newly acquired bathymetric data indicating a strong control by transport and depositional processes sixteen radiocarbon dates obtained above and below the augias deposit indicate a possible time window of about 500 years this means that we cannot definitively prove a link to the 365 ad crete earthquake but we regard it as the most likely trigger other depositional models may be plausible but here we propose a sequence of events as follows 1 earthquake shock and possible triggering of submarine mass flow in the eastern part of the ionian sea western hellenic subduction zone 2 tsunami waves amplified by the confined morphology of the sicily and calabria continental shelves inducing an intense re suspension of fine grained sediment and massive destabilization at the heads of submarine canyons triggering turbidity currents 3 gravity driven downslope transport of suspended sediment toward the deep basin and decantation and 4 a final stage of decantation from seiche waves forming the majority of the homogenite facies in the ionian abyssal plain

age models for pelagites and turbidites from the cap timiris canyon off mauritania abstract this study of sediments from the cap timiris canyon demonstrates that geochemical data can provide reliable age depth correlation even of highly turbiditic cores and attempts to improve our understanding of how turbidite emplacement is linked to climatic related sea level changes the canyon incises the continental margin off nw africa and is an active conduit for turbidity currents in sediment cores from levee and intrachannel sites turbidites make up 6 42 of sediment columns age models were fitted to all studied cores by correlating downcore element data to dated reference cores once turbidite beds had been removed from the dataset these age models enabled us to determine turbidite emplacement times the cap timiris canyon has been active at least over the last 245 kyr with turbidite deposition seemingly linked to stage boundaries and glacial stages the highly turbiditic core from the intrachannel site postdates to 15 kyr and comprises holocene and late pleistocene sediments turbidite deposition at this site was associated especially with the rapid sea level rise at the pleistocene holocene transition during the holocene turbidity current activity decreased but did not cease

an ams radiocarbon method to determine the emplacement time of recent deep sea turbidites abstract this paper reports the evaluation of a novel method based on accelerator mass spectrometer ams radiocarbon dating of planktonic foraminifera to evaluate the times of emplacement of recent deep sea turbidites it assumes that the standing stock of relatively large 150 m planktonic foraminifera in the bioturbated surface mixed layer of box cores represents an integration of the flux from the water column since the turbidite was emplaced and exploits the potential of the ams method to analyse the resultant small samples which can be readily separated the method is evaluated by application to three atlantic turbidites which form the present day sediment surfaces on the horseshoe madeira and tagus abyssal plains the time of emplacement of madeira abyssal plain turbidite is estimated at 1120 730 and 870 years before present each 120 140 years in three different cores the resultant weighted mean emplacement time 930 76 years before present is somewhat older than previous estimates by geochemical methods the times of emplacement for the horseshoe 240 and 140 years before present each 120 years and tagus 300 120 years before present abyssal plains are both consistent with initiation by the lisbon earthquake of 1755

redox zonation of elements at an oxic post oxic boundary in deep sea sediments abstract deep sea sediments generally provide limited evidence of redox control on the post depositional redistributions of elements this is because only a fraction of any element is reactive and observed elemental distributions are the result of a number of competing processes which are simultaneously active so that redox effects are not dominant a detailed investigation is reported of a core which is unusual in showing unequivocal evidence of direct redox control operating in a homogeneous environment that is relatively free from competing processes a progressive oxidation front has migrated slowly downwards into a uniform turbidite over a long period ca 250 ky the reactive fractions of several redox sensitive elements now show a remarkable degree of organisation around the redox boundary of this front with the different elements exhibiting individual responses solid phase enrichments are not coincident but are arranged in a clear succession of concentration peaks along the redox gradient from oxic to postoxic conditions the succession is mn i fe se and pt cu and pb v zn and sb and u the movement directions of most elements can be inferred from the peak shapes against the homogeneous turbidite background composition the system seems to have been essentially isolated within the sediment for most elements so that no loss or gain can be ascribed to redox processes exceptions are u and v which have been augmented by uptake from ocean bottom waters into the sediments by an efficient redox trap mechanism

corundum inclusions in diamonds discriminatory criteria and a corundum compositional dataset abstract mineral inclusions of corundum are reported from diamonds from alluvial deposits of tributaries of the rio aripuana juina brazil we present the first recorded occurrence of sapphire as an inclusion in diamond and expand on the database of ruby and white corundum inclusions ruby inclusions are found to occur both as isolated and touching grains with aluminous pyroxene and associated with ferropericlase mineral chemistry and phase relations place the origin of such ruby bearing diamonds within the lower mantle at 770 km mineral associations indaving other corundum inclusions were not observed hence their depth of origin is less certain compositions of corundum samples were characterised by electron and ion microprobe given the scarcity of literature data corundum samples from a variety of other geological settings were also analysed samples comprised corundums associated with granitic emplacement metasomatism amphibolite facies and granulite facies rocks gem and industrial synthetic origins and carmine coloured corundums recovered from kimberlite drill cores in addition to variable amounts of cr fe ti mg and si measurable quantities of other transition elements and high field strength elements were also detected corundums from similar geological settings show very similar compositions and are easily distinguishable from other settings irrespective of locality rubies from norwegian tanzanian and kenyan amphibolite facies rocks are compositionally indistinguishable additionally corundums from metasomatised zones associated with contact metamorphism from arizona and japan were very similar particularly characterised by unusually high abundance of mobile zr and nb tens of ppm all juina inclusions are particularly distinguishable from other corundums by high concentrations of ni 18 171 ppm weight typically at least an order of magnitude enriched over the same corundum varietal types from elsewhere furthermore the sapphire inclusion exhibited much larger ratios of ga and ge to hfse elements compared to otherwise similar samples and ruby inclusions are distinguished by high mg fe ratios 0 27 1 56 by weight compositional differences between inclusions in diamonds and corundums from other settings in addition to corundum s physical and chemical durability suggest that with the employment of rapid identification tools such as energy dispersive spectrometry eds and laser icpms corundum has promise as an indicator of diamond prospectivity

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

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

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

deep sea tsunami deposits in the eastern mediterranean new evidence and depositional models the tsunami wave induced by the collapse of the santorini caldera after the bronze age minoan eruption 3500 bp produced turbidites and large volume mega turbidites in the abyssal plains of the ionian sea as well as on the floor of small basins of the mediterranean and calabrian ridges characterized by the so called cobblestone topography since the first discovery in 1978 a holocene mud layer which has been termed homogenite and which typically shows a graded interval at its base has been identified and correlated in over 50 deep sea cores recovered in the eastern mediterranean four types of homogenite can be distinguished each related to a particular depositional setting 1 a closed cobblestone these are from a few decimetres to several metres thick pelagic turbidites of local provenance exclusively found at the bottom of small sized ponded basins of the mediterranean and calabrian ridges a debris flow may be present at the base of the turbidite where the vertical relief of the basins is over 200 m 2 b abyssal plain a 10 to 20 m thick megaturbidite recorded in the ionian and sirte abyssal plains the source area is the african continental margin possibly the continental shelf it can be easily identified as a transparent acoustic layer that shows recent deformation across the deformation front of the mediterranean ridge accretionary prism the volume of the minoan homogenite in the ionian abyssal plain has been calculated at a minimum of 11 km3 3 c open cobblestone this type is exclusively found on the outer slope of the mediterranean ridge near the deformation front unlike types a and b the base of the turbidite here is erosional instead of depositional this homogenite has been deposited in small basins and occasionally on topographic highs of the mediterranean ridge by the up slope flow of turbidity currents of african provenance that formed the abyssal plain deposit type b 4 d a fourth depositional model has been identified homogenites present in deep anoxic basins of the mediterranean ridge this setting is substantially similar to type a but the vertical relief of the basin is much higher up to 800 m and the deposition occurs in high density anoxic brines which modify the settling rate and hence the resulting sedimentological characters

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

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

eustatic control of calciclastic turbidites abstract global changes in sea level can be recognized in seismic sections by establishing the relationship between sea level changes and the timing of potential deep sea carbonate reservoir facies of turbidity current and debris flow origin their occurrence may be predicted prior to drilling compilation of published data suggests that throughout the phanerozoic most calciclastic turbidites tend to correspond to lowering episodes of sea level calciclastic turbidites therefore should occur primarily in association with major uncorformities caused by lowstands of sea level the data also suggest a possible lowstand of sea level during the late cretaceous campanian maastrichtian

late quaternary turbidite emplacement on the horseshoe abyssal plain iberian margin abstract the horseshoe abyssal plain hap is located on the iberian margin at approximately 4800 m water depth and is confined within topographic elevations with a relief of about 3000 m with the exception of gorringe bank which rises to only 20 m below sealevel the plain is built up by an alternation of turbidites of the order of meter thick beds numbered h2 h3 h8 and h13 contrasting with sets of thinner beds of the order of decimeters thick h4 5 6 7 and h9 10 11 12 and pelagites centimeters in thickness an intensive study of eight piston cores using visual observation color and thickness relative stratigraphic position of units magnetic susceptibility logs calcium carbonate content and mineralogy of turbid te bases concludes in a bed by bed correlation of all individual turbidites the major source of terrigenous material feeding the hap is the sao vicente canyon which incises the portuguese shelf while minor sources are the surrounding seamounts the elongate geometry of the abyssal plain with its single dominant source of sediments produced laterally continuous deposits from both large and small flows these covered the entire 356 km length of the plain grain size analysis of the four thickest turbidites h2 h3 h8 and h9 demonstrates only slight downcurrent fining and vertical grading expressed best in the ratio of coarse silt to fine silt plus clay a small amount of sand is carried the length of the plain the thicker units all show the same pattern of thickness with a maximum in the middle of the plain around a topographic constriction and bend this is most plausibly explained as due to reduction in flow speed of an initially supercritical flow causing enhanced deposition some of the beds appear to have a double coarse layer in the base which may indicate partial reflection of flows from the side of the basin it is suggested by application of equations for flow behavior that both thick 3 m and thin 0 3 m beds are due to supercritical flows a few tens of meters high however the thick beds resulted from high concentration flows cv 4 by volume whereas thinner beds require low concentration cv 1 to run out over the full length of the basin the stratigraphy is tied into the dated oceanic pelagic record by analysis of foraminifera in the pelagic layers above the turbidites and through recognition of two heinrich layers h 1 and h 2 ages 14 3 and 21 ka the resulting age framework shows higher turbidite frequency in the glacial 2 7 kyr than interglacial holocene 1 0 kyr this also gives higher mass flux during the glacial emplacement of turbidites cannot be clearly related to sea level changes but may well be due to seismic activity however one of the largest earthquakes in human experience lisbon in 1755 triggered only a thin turbidite invalidating the term seismite for thick turbidites

archean foreland basin tectonics in the witwatersrand south africa the witwatersrand basin of south africa is the best known of archean sedimentary basins and contains some of the largest gold reserves in the world sediments in the basin include a lower flysch type sequence and an upper molassic facies both of which contain abundant silicic volcanic detritus the strata are thicker and more proximal on the northwestern side of the basin which is at least locally bound by thrust faults these features indicate that the witwatersrand strata may have been deposited in a foreland basin and a regional geologic synthesis suggests that this basin developed initially on the cratonward side of an andean type arc remarkably similar phanerozoic basins may be found in the southern andes we suggest that the continental collision between the kaapvaal and zimbabwe cratons at about 2 7 ga caused further subsidence and deposition in the witwatersrand basin regional uplift during this later phase of development placed the basin on the cratonward edge of a collision related plateau now represented by the limpopo province similarities are seen between this phase of witwatersrand basin evolution and that of active basins north of the tibetan plateau e g the tarim and tsaidam basins the geologic evidence does not appear so compatible with earlier suggestions that the witwatersrand strata were deposited in a rift or half graben

composition of the earth s inner core from high pressure sound velocity measurements in fe ni si alloys article i nfo we performed room temperature sound velocity and density measurements on a polycrystalline alloy fe0 89ni0 04si0 07 in the hexagonal close packed hcp phase up to 108 gpa over the investigated pressure range the aggregate compressional sound velocity is 9 higher than in pure iron at the same density the measured aggregate compressional vp and shear vs sound velocities extrapolated to core densities and corrected for anharmonic temperature effects are compared with seismic profiles our results provide constraints on the silicon abundance in the core suggesting a model that simultaneously matches the primary seismic observables density p wave and s wave velocities for an inner core containing 4 to 5 wt of ni and 1 to 2 wt of si

ab initio calculations of the elasticity of iron and iron alloys at inner core conditions evidence for a partially molten inner core abstract ab initio finite temperature molecular dynamics simulations have been used to calculate the elasticity of hcp fe bcc fe fes and fesi at core conditions the calculated compressional wave velocities are in excellent agreement with the most recent experimental data however the calculated shear wave velocities of all phases studied are significantly higher than those inferred from seismology this discrepancy can only be explained if the inner core is partially molten containing more than 8 liquid

potential distribution of methane hydrate beneath the european continental margins gridded datasets have been constructed for the physical parameters controlling the formation of gas hydrate simultaneous solutions to the gas hydrate phase and pressure temperature equations were obtained for each node of these grids the results show sub bottom depths of potential methane hydrate bsrs these are presented as colour contoured grids for the thickness of the hydrate stability zone for the european margins the chart proposes that if gas hydrates exist over these areas then this is the potential depth to the bsr this depth is generally greater along the continental margins and also increases with increasing age of the margin shallowing of the bsr can be seen over areas of thinned continental crust and plateaus the geological factors controlling gas hydrate formation determine areas of likely occurrence so the apparent paucity of identified hydrate layer bsrs off the european margins particularly in the mediterranean is most notable

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

metaconglomerate preserves evidence for kimberlite diamondiferous root and medium grade terrane of a pre 2 7ga southern superior protocraton article i nfo we studied heavy minerals extracted from a diamondiferous metaconglomerate that formed 2697 2701 ma in a successor basin within the michipicoten greenstone belt mgb of the wawa abitibi terrane southern superior craton the conglomerate is metamorphosed in the greenschist facies and contains mainly locally derived igneous mafic to felsic detritus but also very minor components of medium grade metamorphic minerals diamonds and paragenetic diamond indicator minerals comparison of the size distribution resorb tion and n aggregation of diamonds in nearby wawa lamprophyres and the metaconglomerate diamonds confirms that the latter were not derived from the proximal lamprophyric source the heavy minerals in the metaconglomerate include diopside olivine corundum chromite almandine pyrope with kelyphitic rims picroilmenite amphibole and anorthite low abundances of the heavy minerals several grains per 4 70 tons of the metaconglomerate are in part explained by their complete or partial replacement by the greenschist mineral assemblage detrital almandine and amphibole are inferred to originate in amphibolite facies rocks cr diopside olivine chromite and anorthite were sourced from mafic ultramafic anorthosite and chromitite bearing layered complexes mapped in the mgb the presence of pyrope with more than 6 wt cr2o3 suggests derivation from a cratonic root picroilmenite has compositions typical of kimberlite and unlike that of ultramafic lamprophyres and other unconventional diamondiferous volcanics the wawa metaconglomerate therefore should be considered analogous to the witwatersrand successor basin conglomerate in recording indirect evidence for archean kimberlites the tight localization of the diamondif erous conglomerate in time and space was controlled by a quick 3 ma erosion of the source kimberlite body the location of the kimberlite bearing n2 7 ga superior protocraton was inferred from the provenance of the metaconglomerate detrital material the clasts could have originated as close as the northern wawa abitibi terrane or as distant as the opatica terrane the pre 2 7 ga diamonondiferous cratonic root below the southern superior was removed in the neoarchean proterozoic the existence of archean kimberlites and deep diamondiferous roots below smaller pre 2 7 ga protocratons emphasizes the similarity of neoarchean and phanerozoic mantle processes

early proterozoic oceanic crust and the evolution of subcontinental mantle eclogites and related rocks from southern africa seven eclogitic nodules from kimberlites in southern africa have been studied in detail for whole rock major and trace element geochemistry petrography and mineral chemistry by electron microprobe high purity mineral separates from six of these samples have been analyzed for trace elements and for the isotopic composition of sr nd and oxygen three eclogite groups are recognized group a eclogites have very high mg fe low na in pyroxene moderate 18o 4 7 to 5 3 and low 87sr 86sr and 143 144nd olivine and enstatite may also be present as accessory phases in this group group b eclogites have moderate to high mg fe ratios high na in pyroxene low 18o 3 0 to 3 4 high 87sr 86sr and 143nd 144nd ratios and extremely lree depleted hree enriched garnets with no eu anomalies group c eclogites have low mg fe ratios high na in pyroxene and variable sr nd and o isotope compositions accessory feldspar is present in one sample that may be of crustal origin mineral separates of garnet and pyroxene have positive eu anomalies the group a eclogites are too refractory to represent magma compositions and must have formed as cumulate dike rocks in the upper mantle that contain a minor trapped liquid component this is supported by the presence of accessory olivine and enstatite and by their ksm and knd which are similar to empirical pyroxene garnet partition coefficients the group b eclogites are extremely depleted in incompatible elements and have ndvalues 10x to 20x morb the high 87sr 86sr of these eclogites is not consistent with their strongly depleted lree and high nd and cannot be primary it must have been imposed on the protolith the low 18o of these eclogites cannot form by mantle fractionation processes and must also be inherited from the protolith both the sr and oxygen isotope data are consistent with high temperature hydrothermal alteration of a basaltic protolith followed by partial melting to form the refractory compositions observed now the hydrothermal fluid may have been sea water but secondary enrichment of the protolith in rb is required to generate the observed high sr ratios the high na content of the pyroxenes supports a spilitic alteration event the major and trace element characteristics of the group c eclogites are consistent with recrystallization of a cumulate gabbro protolith one group c rock is probably a garnet granulite derived from the lower crust the other may represent the plutonic portion of oceanic crust a reconstructed whole rock isochron for the three bellsbank eclogites yields an age of 2 1 0 1 b y this implies that plate tectonic processes involving the generation and subduction of oceanic crust have been active since the early proterozoic the early proterozoic ocean crust consisted of two components a plutonic section of gabbro cumulates group c eclogites and a volcanic section of basalt group b eclogites the volcanic component has undergone substantial hydro thermal alteration and subsequent partial melting to form a refractory residue the plutonic component is less modified

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

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

eocene seismicity in the pyrenees from megaturbidites of the south pyrenean basin spain abstract the triggering mechanism for emplacement of nine calcareous megaturbidites mt in the clastic turbidite eocene basin of the pyrenees is examined the thickness of each mt is 10 to 200 m and their volume may reach 200 km 3 their mobilization is thought to result from seismic activity related to thrust faults along the northern border of the basin we attempt to define the seismic characteristics for a volume of 100 km 3 the dimensions of the slope failures are estimated to be 100 5 10 0 1 0 2 km and related to a fault rupture length of about 50 100 km and liquefaction of basal clayey layers given these two constraints superficial earthquakes of m 7 would be required to initiate landslides

gordo megabed a possible seismite in a tortonian submarine fan tabernas basin province almeria southeast spain abstract the mainly tortonian sediments of the tabernas basin contain the elements of a well developed small submarine fan synsedimentary unconformities and randomly intercalated megabeds in both basin plain and fan lobe deposits indicate tectonic activity during fan growth one of the megabeds the gordo megabed overlies dislocated and deformed fan lobe and basin plain deposits the megabed with a thickness of up to 40 m has a sheet like geometry and consists of four superimposed sedimentary units unit i is a matrix supported conglomerate and contains reefal limestone debris metamorphic rocks and mainly at its top large slabs of ripped up fan sediments up to 60 m across the irregular surface of the unit is filled in by unit ii a cobble pebble conglomerate this conglomerate is covered by unit iii a sandstone layer of 6 8 m thickness which grades into unit iv a normal graded to massive mudstone the extra basinal content of the megabed is conservatively estimated at 0 9 km3 its total volume at 6 km3 from sedimentary structures and textures it is inferred that unit i represents a deposit from a debris flow while unit ii consists of a complex mixture of deposits of debris flow and turbulent flow and units iii and iv are deposits from a turbulent flow the megabed is interpreted to originate from a single catastrophic collapse along the basin margin because of its exceptional volume the sheet like geometry and the random position within the fan sequence the megabed is referred to as a seismite the depositional history succeeding a tectonic triggering is envisioned as follows the collapse of the basin border evolved through stages of sliding and slumping into a debris flow body transformation of the debris flow produced turbulent flow it is tentatively assumed that the debris flow outraced its turbidite

correlation frequency of emplacement and source directions of megaturbidites on the madeira abyssal plain abstract this paper describes the sediments of the whole madeira abyssal plain including the madcap area to the south previous studies have centred on the central sub basin which occupies most of the plain and which has become one of the most studied areas of seafloor the plain is made up of a series of large turbidites separated by thin pelagic layers which can be used to provide a high resolution stratigraphy back to about 750 000 years many of the turbidites were deposited close to oxygen isotope stage boundaries suggesting a strong relationship to sea level climate change although the exact initiation mechanism for the flows is not known data from the northern and southern extensions of the plain shows the effects of different entry points for the four main turbidite groups volcanic rich turbidites enter from the ne and e calcareous turbidites from the w one group of organic rich turbidites enters from the se and one group from the ne and e different turbidite sources operate for limited periods before switching to one of the other source areas it is very rare for two sources to provide turbidites at the same isotope stage boundary

deposition of megabeds megaturbidites and sea level change in a proximal part of the eocene miocene flysch of central dalmatia croatia some carbonate megabeds of the proximal part of the dalmatian eocene miocene flysch basin eastern adriatic sea are underlain and overlain by conglomeratic fan deltas whereas thinner bedded turbidites interfinger with fan delta conglomerates fan deltas and interfingering turbidites are interpreted as having been deposited during lowstand s and early sea level rise s whereas deposition of megabeds is attributed to periods of accelerated sea level rises that aborted growth of fan deltas attribution of megabeds to periods of sea level rise is based on the following observations 1 they overlie some conglomeratic fan deltas 2 skeletal and lithic debris in megabeds originated by subaerial weathering of older sediments and 3 their large thickness indicates considerable primary accumulation 0f debris and low frequency of hows sea level changes inferred from mega beds are different from those related to thinner classical turbidites and distinction of the two is important for sequence stratigraphy in deep marine sediments

seismoturbidites a new group of resedimented deposits abstract turbidite beds of exceptionally large volume and areal extent occur in both modern and ancient deep water basins these beds which may reach individual volumes in excess of 100 km3 are apparently the product of catastrophic gravity flows triggered by earthquakes along the margins of highly mobile basins most commonly elongate flysch troughs turbidite beds produced by these catastrophic events are generally characterized by very distinctive geometry internal structures and composition and are termed herein seismoturbidites characteristically these sediments lack time persistent features of deep sea fans such as channels and lobes seismoturbidites may occur as scattered intercalations diluted within otherwise normal turbidite sequences thus forming generally excellent markers for basin wide correlations or as closely spaced repetitive units comprising the bulk of the sedimentary fill of certain flysch basins in both cases they may offer a tremendously useful tool for a better understanding of the distribution of paleoseismic zones in time and space

linking continental slope failures and climate change testing the clathrate gun hypothesis it has been suggested that the release of clathrates rather than expansion of wetlands is the primary cause of the rapid increases observed in the ice core atmospheric methane record during the pleistocene because submarine sediment failures can involve as much as 5000 gt of sediment and have the capacity to release vast quantities of methane hydrates one of the major tests of the clathrate gun hypothesis is determining whether the periods of enhanced continental slope failure and atmospheric methane correlate to test the clathrate gun hypothesis we have collated published dates for submarine sediment failures in the north atlantic sector and correlated them with climatic change for the past 45 k y more than 70 by volume of continental slope failures during the past 45 k y was displaced in two periods between 15 and 13 ka and between 11 and 8 ka both these intervals correlate with rising sea level and peaks in the methane record during the bolling allerod and preboreal periods these data support the clathrate gun hypothesis for glacial interglacial transitions the data do not however support the clathrate gun hypothesis for glacial millennial scale climate cycles because the occurrence of sediment failures correlates with heinrich events i e lows in sea level and atmospheric methane a secondary use of this data set is the insight into the possible cause of continental slope failures glacial period slope failures occur mainly in the low latitudes and are associated with lowering sea level this finding suggests that reduced hydrostatic pressure and the associated destabilization of gas hydrates may be the primary cause the bolling allerod sediment failures were predominantly low latitude suggesting an early tropical response to deglaciation e g enhanced precipitation and sediment load to the continental shelf or warming of intermediate waters in contrast sediment failures during the preboreal period and the majority of the holocene occurred in the high latitudes suggesting either isostatic rebound related earthquake activity or reduced hydrostatic pressure caused by isostatic rebound causing destabilization of gas hydrates

eustatic control of turbidites and winnowed turbidites global changes in sea level primarily the results of tectonism and glaciation control deep sea sedimentation during periods of low sea level the frequency of turbidity currents is greatly increased episodes of low sea level also cause vigorous contour currents which winnow away the fines of turbidites in the rock record the occurrence of most turbidites and winnowed turbidites closely corresponds to global lowstands of paleo sea level this observation may be useful in predicting the occurrence of deep sea reservoir facies in the geologic record

nd and sr isotope systematics of clastic metasediments from isua west greenland identification of pre 3 8 ga differentiated crustal components recent field work on the isua metasediments has established that there are two lithological sequences a and b which are divided into a number of distinct formations each clastic metasedimentary unit has a relatively unique trace element signature the depleted mantle sm nd model ages of samples from all major units range from 3 59 to 3 98 ga whereas rb sr model ages cover a very wide range 1 9 4 6 ga the samples from the sequence a felsic gneiss formation a6 yield a relatively good rb sr isochron age of t 3 71 0 07 ga the sequence b samples do not yield a rb sr isochron however some of the samples plot close to the a6 rb sr isochron and sequences a and b appear to have essentially the same deposition age the sm nd data for both sequences yield initial end values in the range 1 to 3 for a deposition age tstrat 3 64 ga if tstrat 3 81 ga the range is 0 4 this range appears to reflect real variability of initial end values corresponding to the time of deposition data trends in end versus 1 nd diagrams suggest at least three distinct components in each of sequences a and b model age calculations suggest that some of these components must be derived from continental crustal sources that predate the time of deposition of these sediments by as much as 0 4 b y other components appear to be derived from volcanic sources that are roughly coeval with sediment deposition the very high initial end values implied for early depleted mantle sources 2 to 4 suggest a very large pre 3 8 ga continental crust alternatively these high values could reflect an early terrestrial mantle with highly fractionated cumulate layers that formed in a 4 5 ga magma ocean

gravity driven deposits in an active margin ionian sea over the last 330 000 years in the ionian sea the subduction of the nubia plate underneath the eurasia plate leads to an important sediment remobilisation on the calabrian arc and the mediterranean ridge these events are often associated with earthquakes and tsunamis in this study we analyse gravity driven deposits in order to establish their recurrence time on the calabrian arc and the western mediterranean ridge four gravity cores collected on ridges and slope basins of accretionary prisms record turbidites megaturbidites slumping and micro faults over the last 330 000 years these turbidites were dated by correlation with a hemipelagic core with a multi proxy approach radiometric dating 18o b colour curve sapropels and tephrochronology the origin of the gravity driven deposits was studied with a sedimentary approach grain size lithology thin section geochemistry of volcanic glass the results suggest three periods of presence absence of gravity driven deposits a first on the western lobe of the calabrian arc between 330 000 and 250 000 years a second between 120 000 years and present day on the eastern lobe of the calabrian arc and over the last 60 000 years on the western lobe and a third on the mediterranean ridge over the last 37 000 years return times for gravity driven deposits are around 1000 years during the most important record periods the turbidite activity also highlights the presence of volcaniclastic turbidites that seems to be link to the etna changing morphology over the last 320 000 years

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

diapiric features in the southeastern mediterranean sea possible indication of extension in a zone of incipient continental collision abstract several types of diapiric structures were studied in the zone between the nile deep sea fan and the eratosthenes seamount in the se mediterranean sea the study discovered four stages in the structural evolution of the diapiric features starting as a domal piercement structure and developing into initial basin as seawater dissolution starts to effect the diapiric salt subsequently v shaped and then mature u shaped basins formed as products of dissolution sedimentary collapse and sediment deposition the structures both protrusions and depressions are aligned along discrete lineaments most of them trending ne sw and a few nw se the ne sw lineaments are probably a series of normal faults and the nw se ones seem to be strike slip faults the development of extensional structures on the underthrust edge of the african plate as it approaches the subduction zone are commonplace in the mediterranean and elsewhere and the occurrence of normal faults in this area is compatible with the intensive subsidence of the eratosthenes seamount in the plio pleistocene the lithostatic load of the nile deep sea fan could have contributed to the subsidence and thus enhanced the diapirism in the se mediterranean

geochemistry of the 1984 mauna loa eruption implications for magma storage and supply the 1984 eruption of mauna loa volcano hawaii produced about 220 106 m3 of lava of remarkably homogeneous composition no significant compositional changes occurred during the 22 day eruption and along the 20 km vent system even though crystallinity increased substantially accompanying a decline in the eruption rate such homogeneity in lava composition is typical of many historic mauna loa eruptions the 1984 lava along with most other homogeneous mauna loa lavas is multiply saturated crystallizing olivine clinopyroxene and plagioclase bulk compositions are perched at the intersection of an olivine control trend with a trend for more differentiated lavas there is no evidence to indicate that the 1984 lava is a differentiate of the 1975 magma or that it results from mixing a new batch of magma with differentiated melt remaining in the magmatic plumbing system after the 1975 eruption it is proposed that these lavas are erupted directly from a small continuously replenished magma reservoir located about 3 4 km beneath the summit caldera successive eruptions therefore provide a sampling of magma chamber processes and small but discernible changes in lava composition reflect the competing processes of magma supply differentiation and eruption

evidence for long term instability in the storegga slide region off western norway abstract shallow seismic surveys around the storegga slide off western norway have allowed greater understanding of the development of this part of the european margin the northern flank of the scarp is formed of seismically well layered hemipelagic and distal glaciomarine deposits in which a variety of luid escape structures probably due to gas are locally abundant there is evidence of slides that substantially pre date the earliest slide previously recognized surveying on the north sea fan to the southwest of the storegga slide shows the markedly different nature of the autochthonous sediments on the southern flank of the storegga slide there is a predominance of glacigenic debris flows in the upper part of the sequence lesser maximum slopes and an apparent absence of interstitial gas and or hydrates this contrast has had considerable effect on slope stability and has influenced the position of the southwestern storegga slide boundary the north sea fan succession includes at least three major buried slides termed the vigra more and tampen slides all of which substantially pre date the storegga event and probably pre date predominantly glacigenic margin sedimentation post late weichselian slope failure is locally significant the region has a long but as yet chronologically poorly defined history of instability in which seismic triggering is considered to have been important

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

sound velocity and density measurements of liquid iron up to 800 gpa a universal relation between birch s law coefficients for solid and liquid metals abstract we performed compressional sound velocity and density measurements on liquid iron at pressures up to 800 gpa with a newly refined shock compression method using a high power laser we found that sound velocity as a function of density can be fitted to a linear relation following birch s law for hot dense liquid as well as for the solid phase of iron with a slope ratio between the solid and liquid of approximately 1 5 a comparison of birch s law for solid and liquid metals indicates that the sound velocity in the liquid phase is about 10 lower than that in the solid phase at melting point density which is about 1 5 times larger than the initial density we suggest that these relations between birch s law coefficients for solid and liquid phases along the hugoniot are universal for metals

high resolution chemostratigraphy of quaternary distal turbidites a case study of new methods for the analysis and correlation of barren sequences

detecting a sequence boundary across different tectonic domains an example from the middle miocene of the northern apennines italy sequence stratigraphic concepts can provide a powerful tool for understanding the tectono sedimentary evolution of areas extending across different tectonic domains an example is provided by the upper serravallian strata of the northern apennines where a sedimentological and biostratigraphic study allows a sequence boundary to be traced across the foredeep and piggy back basin successions turbidite sedimentation of predominantly alpine and subordinate apenninic provenance occurred in the apenninic foreland basin throughout the middle miocene deep water sedimentation in the foredeep was laterally associated with deposition in shelf to slope environments in the piggy back basins in the piggy back basin succession the upper serravallian sequence boundary is a laterally extensive unconformity within homogeneous marly deposits this unconfonnity is laterally correlative with the base of lenticular turbidite bodies a stratigraphic lacuna affecting zone n14 characterizes the marginal areas where glaucony rich deposits assigned to zone n15 unconformably overlie marls displaying association of zone n13 in the depocentres where no significant stratigraphic gap has been detected the sequence boundary is narrowly constrained to lowermost zone n14 the upper serravallian unconformity of the piggy back basins succession is correlative with time equivalent features in two distinct parts inner basin and outer basin of the foredeep in the inner basin the sequence boundary separates basin margin turbidites from overlying slope hemipelagites in a more external position outer basin the sequence boundary is the base of a characteristic mega turbidite of apenninic provenance turrito layer in other sectors of the outer basin where turbidite sedimentation was entirely of alpine provenance the sequence boundary has no clear physical expression the observed facies distribution in the study area suggests that an important thrusting event affected the northern apennines in the late serravallian resulting in submarine channel incision and nondeposition in the piggy back basins compressional activity in the foredeep was responsible for the closure of the inner basin and subsequent shifting of turbidite sedimentation in the outer basin slope instability led to widespread remobilization of previously deposited turbidites triggering turbidite events of huge volume the different characteristics of the sequence boundary in the various parts of the foredeep constitute an example of differential response of a multisourced supply system to tectonic deformation

alkremite garnetite and eclogite xenoliths from bellsbank and jagersfontein south africa alkremites garnet spinel orundum garnetites and eclogites garnet clinopyroxene from bellsbank and jagersfontein kimberlites show textural and mineralogical evidence of crystal fractionation from evolving aluminous magma e g ca and p increase in garnet as cr and ti decrease in most spinels detailed variations of cr and ti in garnet and spinel require several parental magmas corundum in alkremites contains 0 1 0 2 wt vo tioz 0 2 0 5 cr2o3 and 0 5 1 2 fezor mica 0 7 3 4 tioj in grain boundaries is secondary foundering or subduction of al rich sediments perhaps chloritized ocean crust may have generated local al enrichment in the upper mantle to provide diverse source regions for alkremite magmas

the nile deep sea fan preliminary results from a swath bathymetry survey we present and discuss a set of data mainly swath bathymetry backscatter images and a few seismic data that have been recently recorded over large areas of the nile deep sea fan between water depths of 1200 and 3000 m these data demonstrate the presence of at least three distinct morphostructural provinces where interacting sedimentary tectonic and salt tectonic processes control the present day morphology and the recent evolution of the major mediterranean deep sea fan the role of the ongoing collision presently occurring between the continental eratosthenes seamount and the cyprus arc may have been and still is a determining parameter for the development of the nile deep sea fan

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

stable and radiogenic isotope study of eclogite xenoliths from the orapa kimberlite botswana eclogite xenoliths from orapa can be accurately classified as group i or group ii on the basis of na2o in garnet and k2o in clinopyroxene group i xenoliths are commonly diamondiferous while group ii xenoliths are diamond free both xenolith varieties may contain graphite isotopic character is to some degree correlated with major and trace element chemistry group ii samples with ca poor garnet have clinopyroxenes with radiogenic 87sr86sr 0 705 0 709 and the least radiogenic 143nd144nd 0 5122 0 5125 group i eclogites with higher ca and fe in garnets have less radiogenic 87sr86sr 0 702 0 7066 and bulk earth or higher 143nd144nd ratios group i eclogites have more radiogenic 206pb204pb 18 6 19 than group ii xenoliths 16 5 18 6 in contrast group ii xenoliths have more variable and in some cases more radiogenic 206pb204pb 36 6 39 3 than group i xenoliths 38 3 38 4 the sr sm nd and pb concentrations of minerals in orapa group i eclogite xenoliths are much lower than in group ii samples all the group ii xenoliths are inferred to be enriched in light rare earth elements while group i xenoliths are probably characterised in many cases by light rare earth element depletion constituent garnet and clinopyroxene in both group i and ii eclogite xenoliths are essentially in isotopic equilibrium at the time of pipe emplacement mineral as well as calculated whole rock 143nd144nd compositions of most of the group i eclogites are too close to bulk earth and depleted mantle estimates in order to obtain useful model age information depleted mantle model ages derived from the much lower 143nd144nd compositions of the group ii eclogite xenoliths range from 661 to 1248 my with an average clinopyroxene model age of 908 my and an average whole rock model age of 1016 my on the basis of an observed covariation of o and sr isotopic compositions the entire orapa group i eclogite xenolith suite can be modelled as mixtures of oceanic basalt with or without a few percent of ocean floor sediment the group ii xenoliths might have crystallised from a melt which derives from a protolith with time averaged lree depletion their radiogenic sr isotope character could be due to interaction of the melt with metasomatised lithosphere or might be a superimposed metasomatic signature