empirical and theoretical comparisons of the chicxulub and sudbury impact structures chicxulub and sudbury are 2 of the largest impact structures on earth research at the buried but well preserved chicxulub crater in mexico has identified 6 concentric structural rings in an analysis of the preserved structural elements in the eroded and tectonically deformed sudbury structure in canada we identified ring like structures corresponding in both radius and nature to 5 out of the 6 rings at chicxulub at sudbury the inner topographic peak ring is missing which if it existed has been eroded reconstructions of the transient cavities for each crater produce the same range of possible diameters 80110 km the close correspondence of structural elements between chicxulub and sudbury suggests that these 2 impact structures are approximately the same size both having a main structural basin diameter of 150 km and outer ring diameters of 200 km and 260 km this similarity in size and structure allows us to combine information from the 2 structures to assess the production of shock melt melt produced directly upon decompression from high pressure impact and impact melt shock melt and melt derived from the digestion of entrained clasts and erosion of the crater wall in large impacts our empirical comparisons suggest that sudbury has 70 more impact melt than does chicxulub 31 000 versus 18 000 km3 and 85 more shock melt 27 000 km3 versus 14 500 km3 to examine possible causes for this difference we develop an empirical method for estimating the amount of shock melt at each crater and then model the formation of shock melt in both comet and asteroid impacts we use an analytical model that gives energy scaling of shock melt production in close agreement with more computationally intense numerical models the results demonstrate that the differences in melt volumes can be readily explained if chicxulub was an asteroid impact and sudbury was a comet impact the estimated 70 difference in melt volumes can be explained by crater size differences only if the extremes in the possible range of melt volumes and crater sizes are invoked preheating of the target rocks at sudbury by the penokean orogeny cannot explain the excess melt at sudbury the majority of which resides in the suevite the greater amount of suevite at sudbury compared to chicxulub may be due to the dispersal of shock melt by cometary volatiles at sudbury

late pleistocene uplift history along the southwestern marmara sea determined from raised coastal deposits and global sea level variations pleistocene raised coastal deposits characterized by locally abundant shells aragonite cemented beachrock and associated nearshore deposits border the western marmara sea at elevations of 0 50 m field observations confirm that these deposits formed during a series of transgressive and regressive events u th dates in 16 in situ shells from four localities show that the peak of the transgressions occurred during the highstands of oxygen isotopic stages 7 and 5 between 53 and 210 ka the elevations of these dated deposits can be used to quantify their post depositional uplift and indicate that the entire western marmara shelf including the strait of canakkale dardanelles has been rising at an average rate of 0 40 mm yr 1 since 225 ka the primary cause of uplift is the local compression associated with a restraining bend in the western segment of the north anatolian fault paleogeographic maps constructed using the average rate of tectonic uplift and detailed topographic and bathymetric maps reveal that prior to glacial oxygen isotopic stage 8 the marmara sea was never isolated from the aegean sea even when global sea level was low because the floor of the strait of canakkale was too deep early in its uplift history the dominance of mytilus edulis in raised coastal terraces dating from the lowstand of glacial oxygen isotopic stage 8 suggests that the degree of communication between the aegean sea and marmara sea was comparable to that of the present during the peak of glacial oxygen isotopic stage 6 the floor of the strait was subaerially exposed isolating the marmara sea for the first time in the pleistocene from the higher salinity mediterranean water inflow and possibly causing it to become a blackish water lake during interglacial isotopic stages 9 7 and 5 the strait of canakkale was very wide and deep 100 125 m and there were two subsidiary channels bolayir and eceabat channels providing additional links between the aegean sea the marmara sea further promoting significant water exchange between these basins the dominance of ostrea edulis in the raised terraces dating from isotopic stages 5 and 7 confirms an enhanced penetration of the mediterranean water mass into the marmara sea the history of communication between the black sea fed by central and northern european drainage systems and the low latitude mediterranean sea is of fundamental importance in understanding the genesis of organic rich sapropel deposits throughout the region the results presented in this paper caution against the simple assumption that sea level change alone controlled the degree of connection across this oceanographic gateway instead the physiography and paleoceanography of the region were controlled both by variations in global sea level and the rate of uplift in an area of active transpression

organic geochemistry and origin of late glacial holocene sapropelic layers and associated sediments in marmara sea abstract organic geochemistry of two sapropel sapropelic sediment units dated 10 6 6 4 and 3 8 3 2 kyr bp and associated sediments in two gravity cores from the marmara sea were studied to characterize the organic matter and discuss its paleoceanographic implications vertical trends of c n ratio 13c and hydrogen indices show that the flooding of the marmara sea by the mediterranean waters at 12 kyr bp and onset of deposition of the lower sapropelic layer at 10 6 yr bp are characterized with a high input of terrestrial organic matter this terrestrial input decreased and marine organic matter contribution increased in time towards the top of the upper sapropelic layer at 3 2 kyr bp the lower sapropelic layer is broadly the same age and has a similar distribution of organic matter type as the s1 sapropel of the aegean sea suggesting their depositions may have been controlled by the same events both the lower marmara sapropelic layer and the aegean s1 sapropel were probably deposited during a time of high influx of organic rich river waters from the black sea this influx of black sea water could have induced water stratification in the marmara sea and aegean sea and lead to the deposition of the sapropels

was the black sea catastrophically flooded in the early holocene abstract a catastrophic flooding of the black sea basin was proposed to have occurred during its reconnection to the ocean in the early holocene possible cultural consequences of the flood include the migration of neolithic farmers from around the black sea towards central europe as well as the creation of flood myths stratigraphic and paleo geomorphologic information from danube delta aided by radiocarbon ages on articulated mollusks constrain the level in the black sea before the marine reconnection to ca 30 m below the present sea level rather than 80 m or lower if the flood occurred at all the sea level increase and the flooded area during the reconnection were significantly smaller than previously proposed

post impact alteration of surficial suevites in ries crater germany hydrothermal modification or weathering processes alteration of surficial suevites at ries crater germany was studied by means of x ray diffraction and scanning electron microscopy here we discuss the origin of hydrous silicate clay phases in these suevites that have been previously interpreted as resulting from post impact hydrothermal processes the results of this study indicate that the dominant alteration phases are dioctahedral al fe montmorillonite and halloysite which are typical low temperature clay minerals we suggest that the surficial suevites are not altered by hydrothermal processes and that alteration occurred by low temperature subsurface weathering processes if the surficial suevites were indeed hydrothermally modified during the early stages of post impact cooling then the alteration was of limited character and is completely masked by later weathering

wind effects on a front over the continental shelf slope a continuously stratified two dimensional vertical and seaward model is used to study the effects of alongshore wind on a front between lighter water over the continental shelf and heavier water in the offshore ocean the model produces three components of alongshore flows one component associated with the horizontal density front and two wind driven components one near the coast and one over the shelf break the cross shore circulation has two near surface features a seaward component resulting from the offshore density gradient and a shoreward seaward component resulting from the right hand left hand alongshore wind stress which has the coast to the right left facing downstream these two components contribute to the maintenance of the front with no wind low density water over the shelf tends to move toward the offshore ocean associated with the near surface seaward flow resulting in flatter isopycnal surfaces a moderate right hand alongshore wind suppresses the density driven surface flow and constrains the shelf water while a strong wind in the same direction pushes the front shoreward and makes isopycnal surfaces steeper resulting in increased exchange of the shelf water a left hand alongshore wind contributes to more rapid frontal relaxation and a seaward shift in its position these results are applied to the labrador shelf

vitric compositions in the onaping formation and their relationship to the sudbury igneous complex sudbury structure the 1 85 ga sudbury structure is the largest well preserved exposed example of a terrestrial impact crater it contains world class ni cu platinum group element pge ores associated with the igneous component a new understanding of the geology and geochemistry of the vitric crater fill sequence the onaping formation provides constraints on the evolution of 1 85 ga igneous rocks in the sudbury structure the onaping formation has a well defined mappable stratigraphy composed of three members seven stratigraphic units and two types of intraformational dikes that are overprinted by an impact generated hydrothermal system stratigraphic and alteration mapping provided a basis for well constrained sampling and allowed the definition of the geochemical characteristics of the less altered rocks from each unit including vitric bombs and blocks and intraformational vitric dikes significantly the identification of a least altered composition of the vitric onaping formation enabled an investigation of the link between the early formed vitric melt phase in the impact crater fill sequence and the sudbury igneous complex and offset dikes the least altered vitric onaping formation represented by the massive xenolith poor cores of vitric bombs blocks and intraformational dikes is andesitic in composition consistent with a crustally derived melt the melt composition 61 6 wt sio 2 4 28 mgo 60 ppm ni is remarkably uniform throughout the onaping formation with a typical enrichment of large ion lithophile and light rare earth elements and pronounced negative nb and ti anomalies incompatible trace element ratios and bulk concentrations of the onaping formation coincide with the main mass norite and offset quartz diorite compositions of the underlying sudbury igneous complex but differ distinctly from the granophyre and quartz gabbro root mean squared differences in composition of the vitric onaping formation with the units of the sudbury igneous complex and quartz diorite offset dikes show that the vitric onaping formation does not directly match any of these igneous units but more closely resembles the composition of the ministic and manchester offset dikes the quartz diorite offset dikes have been proposed as representative of the bulk composition of the original melt of the sudbury igneous complex in detail there are small compositional differences between north and south range offset dikes and between these offset dikes and the concentric manchester offset dike however such differences are lacking in the onaping formation we propose that the least altered vitric composition of the onaping formation represents the best estimate of the bulk composition of an initial quenched melt or shock melt formed early in the evolution of the sudbury structure and is a logical starting liquid to model the evolution of the sudbury main mass and offset dikes the offset dike compositions can be derived from onaping formation vitric shock melt by assimilation of progressively greater amounts of mafic material at deeper levels in the crater this mafic contaminated melt or impact melt developed at the base of the melt sheet and was injected into the offset dikes both prior to and contemporaneously with the earliest stages of sulfide precipitation from the sudbury complex fractionation of the mafic contaminated melt by plagioclase and pyroxene accumulation produced the north range felsic and mafic norite and the south range norites the chalcophile metal content of the onaping formation vitric phase closely reflects the overall metal ratios of the magmatic sulfide ores the vitric onaping formation and unmineralized offset dikes have low liquidus temperatures 1 115 1 125 c and if these units represent the source of metals in the sulfide deposits unusually high mass distribution coefficients for cu and ni and high r factors are necessary to account for the metal endowment

chicxulub impactites geochemical clues to the precursor rocks the 65 ma chicxulub impact structure mexico with a diameter of 180 km is the focus of geoscientific research because of its link to the mass extinction event at the cretaceous tertiary k t boundary chicxulub now buried beneath thick post impact sediments is probably one of the best preserved terrestrial impact structures known because of its inaccessibility only limited samples on the impact lithologies from a few drill cores are available we report major element and sr nd o and c isotopic data for chicxulub impact melt lithologies and basement clasts in impact breccias of drill cores c 1 and y 6 and for melt particles in the chicxulub ejecta horizon at the k t boundary in beloc haiti the melt lithologies with sio2 ranging from 58 to 63 wt show significant variations in the content of al ca and the alkalies in the melt matrix samples 13c of the calcite is about 3 o the 18o values for the siliceous melt matrices of y 6 samples range from 9 9 to 12 4 o melt lithologies and the black haitian glass have rather uniform 87sr 86sr ratios 0 7079 to 0 7094 only one lithic fragment displays 87sr 86sr of 0 7141 the sr model ages tsrur for most lithologies range from 830 to 1833 ma unrealistic negative model ages point to an open rb sr system with loss of rb in a hydrothermal process the 143nd 144nd ratios for all samples except one basement clast with 143nd 144nd of 0 5121 cluster at 0 5123 to 0 5124 in an nd sr diagram impactites plot in a field delimited by nd of 2 to 6 and sr of 55 to 69 this field is not defined by the basement lithologies described to occur as lithic clasts in impact breccias and cretaceous sediments at least one additional intermediate to mafic precursor component is required to explain the data

late quaternary stratigraphy of laurentian fan a record of events off the eastern canadian continental margin during the last deglacial period abstract examination and correlation of 10 piston cores from laurentian fan off the eastern canadian continental margin revealed a high resolution stratigraphic record of events since the last glacial maximum lgm the five lithofacies identified in the cores are 1 bioturbated olive grey silty mud with varying amounts of biogenic carbonate 2 olive grey and reddish brown silt laminated mud with rare fine to very fine sand beds 3 poorly sorted light grey and brick red gravelly sandy mud 4 colour banded silty mud with colours alternating at a centimetre scale between olive grey and reddish brown and 5 brown silty mud commonly massive but occasionally silt laminated the dominant depositional processes include hemipelagic sedimentation turbidity currents and ice rafting in these sediments colour is diagnostic of the sediment source area with reddish sediment being delivered to the fan from the gulf of st lawrence and laurentian channel whereas greenish sediment arrives on the fan from st pierre bank through grand banks valley turbidites are the most volumetrically significant facies conversely ice rafted beds are volumetrically minor but they are the most chronostratigraphically significant facies and include heinrich layers h0 h1 and h2 the chronological control provided by radiocarbon dating and stable oxygen isotopes suggests that sedimentation rates for the reddish brown turbidites deposited between the lgm and 14 ka exceeded 10 m kyr 1 mapping of the units together with a simple sediment deposition model suggest that these beds resulted from deposition by turbidity currents over 1 km thick that lasted on the order of weeks less information can be ascertained from the olive grey turbidites that interbed with h2 and directly overlie h1 because of a lack of sampling except that they had a lower sedimentation rate and include sediment derived from newfoundland and the grand banks comparison of the stratigraphy on laurentian fan with that of other deep water areas further north southwest grand banks margin flemish pass and the labrador sea shows striking similarities over the late quaternary with the deglacial period characterized by rapid sediment accumulation however only on laurentian fan does sediment gravity flow deposition occur during the lgm reddish brown turbidites deposited on laurentian fan during the deglacial period have no equivalent facies further north these unique features suggest important glaciological differences between the ice stream occupying laurentian channel and ice streams farther north the onset of widespread hemipelagic deposition occurred after ca 12 ka on laurentian fan and in flemish pass but not until ca 8 2 ka in the labrador sea consistent with the earlier retreat of glacial ice out of laurentian channel as compared to hudson strait

late glacial holocene palaeoceanography of the sea of marmara timing of connections with the mediterranean and the black seas abstract stratigraphic analysis of late quaternary sediments of the sea of marmara basin smb indicates that it was a freshwater lake during the late glacial to ca 12 000 yr bp depositing sediments with a neoeuxinian fauna characteristic of the black sea basin at ca 12 000 yr bp it was inundated by the mediterranean waters and gradually converted into a marine realm as indicated by the presence above the neoeuxinian sediments of a mixed layer containing both marine and freshwater fauna a sapropelic sediment layer was deposited between 10 600 and 6400 yr bp under suboxic bottom water conditions this layer roughly corresponds in time to s1 sapropel unit of the eastern mediterranean suggesting a common origin its presence in the smb therefore supports the hypothesis that a large influx of freshwaters from the black sea was an important factor in sapropel formation in the eastern mediterranean a second sapropelic layer formed in the smb during 4750 to 3200 yr bp the earliest known record of mediterranean water in the bosphorus is at ca 5300 yr bp suggesting a later marine inundation than the 7150 yr bp event suggested by ryan and co workers an abrupt drowning of black sea shelf at 7 5 kyr bp geo eco marina 2 proc int workshop on fluvial marine interactions mainas romania 1 7 october 1997 pp 115 125 and ryan w b f pitman iii w c major c o shimkus k moskalenko v jones j a dimitrov p gorur n sakinc m yuce h 1997b an abrupt drowning of black sea shelf mar geol 138 1997 119 126 this implies that either earlier marine connections with the black sea were through a different waterway or the earlier marine record in the strait has been eroded the present two layer flow system was established at 4000 yr bp

three dimensional magnetic imaging of the chicxulub crater although few magnetization measurements are available for the structural elements of the chicxulub impact crater the magnetization intensities of the melt sheet upper breccia unit and central uplift are 3 4 orders of magnitude greater than the 3 to 4 km thick carbonate and evaporite stratigraphy covering the yucatan block this allows three dimensional modeling of the crater s structure by inversion using a two layer model two layers are separately inverted by dividing the crater s magnetic field expression into 40 km wavelength components the upper layer average depth 2 km models the distribution of highly magnetized zones in the crater s melt sheet the lower layer average depth 5 km represents relief on the yucatan block s basement surface and effectively maps the crater s 50 km diameter central uplift and possibly the expression of the surrounding collapsed disruption cavity fill the shallower magnetized zones consist of two generally concentric distributions at radii of 20 and 45 km these highly magnetized zones are thought to result from hydrothermal systems localized at the edge of the central uplift and the collapsed disruption cavity having produced magnetic phases during alteration of the melt sheet

lithogeochemical patterns related to sedex mineralization sudbury basin canada abstract distal sediments stratigraphically equivalent to sedex zn cu pb deposits at the base of the proterozoic onwatin argillite formation sudbury basin are depleted in s and enriched in mn occurring as kutnohorite manganosiderite and spessartine and in ba in the form of the k ba feldspar hyalophane fluid inclusion data indicate deposition of the distal sediments at 125 c and of the sedex carbonate gangue at 170 c the overlying onwatin argillites deposited at 60 c are characterized by a distinctive pattern of s c org 0 36 indicative of diagenetic s alternating with s c org 0 36 probably reflecting episodic expulsion of s bearing fluids into the water column during the waning stages of hydrothermal activity similar to the s c org pattern are patterns of rhythmically alternating low and high zn pb as re ni and pd values in the onwatin argillite coinciding with the onset of hydrothermal activity 34 s values in pyrite decrease abruptly from 7 at the top of the onaping formation to 3 at the base of the overlying onwatin argillites 13 c values in the carbonate gangue of the sedex deposits 8 9 to 2 4 lie in or close to the range for magmatic carbon in contrast to values of 18 7 to 14 9 in carbonate derived by oxidation of organic carbon in the overlying and underlying rocks low 34 s values in the sedex deposits and basal onwatin rocks and enrichment of the onwatin argillite in s ni re and pd suggest derivation of these metals at least part of the s and possibly cu zn pb from the magmatic ni cu ores and or associated sudbury igneous complex which probably also provided the energy to drive the convective exhalative system responsible for the sedex mineralization the model implies potential for further sedex deposits along the 110 km of the onwatin onaping contact

petrology of impact melt rocks at the chicxulub multiring basin yucatan mexico compositions and textures of melt rocks from the upper part of the chicxulub structure are typical of melt rocks at other large terrestrial impact structures apart from variably elevated iridium concentrations less than 1 5 to 13 5 0 9 ppb indicating nonuniform dissemination of a meteoritic component bulk rock and phenocryst compositions imply that these melt rocks were derived exclusively from continental crust and platform sediment target lithologies modest differences in bulk chemistry among samples from wells located approximately 40 km apart suggest minor variations in relative contributions of these target lithologies to the melts subtle variations in the compositions of early formed pyroxene and plagioclase also support minor primary differences in chemistry between the melts evidence for pervasive hydrothermal alteration of the porous mesostasis includes albite k feldspar quartz epidote chlorite and other phyllosilicates as well as siderophile element enriched sulfides suggesting the possibility that chicxulub like sudbury may host important ore deposits

holocene slip rate of the north anatolian fault beneath the sea of marmara abstract the north anatolian fault naf is a major continental transform system that extends e w across turkey for over 1600 km separating the anatolian and eurasian plates a portion of its northern branch runs below the sea of marmara this portion constitutes a seismic gap because the last destructive earthquakes occurred at the western 1912 ganos earthquake m 7 4 and eastern 1999 izmit and duzce earthquakes m w 7 4 7 2 edges of the marmara basin it is likely that fault ruptures will fill this gap in the next decades this region of the north anatolian fault is critical to our understanding of fault interactions stress buildup during seismic cycle and seismic hazard in the istanbul area we obtained high resolution acoustic images of the naf in the floor of the eastern marmara sea gulf of izmit and measured fault related offsets of 14 c dated subseafloor channels and paleoshorelines the resulting average slip rate on the fault is 10 mm year for the last 10 kyr this is less than half the total anatolia eurasia relative motion estimated at 24 mm year for the last 10 years from satellite geodetic measurements we conclude that either much of the strike slip motion along this branch of the naf did not occur on the main fault segment or the slip rate increased recently or both these results affect kinematic models of the naf and assessments of seismic hazard for the city of istanbul and the surrounding region

the timing and evolution of the post glacial transgression across the sea of marmara shelf south of istanbul high resolution reflection seismic profiles with core analyses of sedimentary sequence near the sea of marmara som entrance to the strait of istanbul soi bosphorus provide detailed record of sealevel changes since the late glacial maximum lgm the sequence is deposited over the lgm erosional surface at a maximum depth of 105 m it includes seven seismic units that can be confidently correlated with 14c dated sedimentary units in the cores unit 6 represents levee deposits of the paleo soi channel that was deposited by a black sea outflow during 11 2 10 6 kyr bp the reflection surfaces at base of unit 5 and 4 correspond to wave cut terraces at 71and 63 m respectively and are estimated to be 10 6 and 9 8 kyr bp the seismic unit 2 overlaying a mud drape unit 3 comprises deltaic sediments that was deposited during 6 400 3200 yr 14c bp isopach map and

low frequency current variability on the labrador shelf current meter measurements from two locations on the northern part of the labrador shelf have been analyzed using empirical orthogonal function eof analysis in the three frequency bands 0 09 0 18 cpd 0 18 0 36 cpd and 0 36 0 54 cpd to describe the measurements in each frequency band a numerical circulation model was developed for the shelf driven by alongshore and onshore wind stresses and by flow through hudson strait the latter flow is taken to arise from the atmospheric pressure variations over hudson bay and from the along static wind stress over hudson strait the model appears to be quite successful in describing the circulation in the center frequency band this suggests that the forcing within this band is primarily due to the alongshore wind stress over the shelf and to the flow through hudson strait the model indicates that in the region of study the mode 1 shelf wave dominates the velocity field over the upper part of the shelf whereas mode 2 dominates the flow near the shelf break in the first and third frequency bands the model is less successful in describing the measured currents it is likely that this failure is at least in part due to the neglect of other forcing mechanisms such as shelf waves propagating southward out of baffin bay

ice seawater turbulent boundary layer interaction with melting or freezing abstract a second moment turbulence closure model is applied to the problem of the dynamic and thermodynamic interaction of sea ice and the ocean surface mixed layer in the case of ice moving over a warm ocean surface layer melting is intrinsically a transient process that is melting is rapid when warm surface water initially contacts the ice then the process slows when surface water is insulated from deeper water due to the stabilizing effect of the melt water and the thermal energy stored in the surface layer is depleted effectively the same process prevails when ocean surface water flows under stationary ice in which case after an initial rapid increase the melting process decreases with downstream distance accompanying the stabilizing effect of the melt water is a reduction in the ice seawater interfacial shear stress this process and model simulators are used to explain field observations wherein ice near the marginal ice zone diverges from the main pack when the surface ice layer is m

reply to comment on the timing and evolution of the post glacial transgression across the sea of marmara shelf south of istanbul by hiscott et al marine geology 248 228 236 in their comment hiscott and co authors adhere rigidly to ages and sources for sedimentary units in the subsurface of the marmara shelf that they have previously reported in their publications from 2002 through 2007 this adherence is in spite of a superior age depth model from our 13 m long sediment core that penetrated deeply into the deposits under consideration and in disregard to the results of subsequent more detailed and full coverage mapping of the region under scrutiny the age revisions are dismissed by the authors of the comment as representing sediments severely disturbed during coring we rebut this criticism the bosporus source attributed by them to the sedimentary units sampled and dated by us appears to be driven by their conception that the black sea had a persistent outflow prior to its two way connection with marmara irrespective of whether the outflow was persistent our reply shows that the drawing of the isopachs of the sedimentary units by hiscott and co authors was accomplished in a fashion to promote the bosporus source hypothesis regardless of the geographic limits of their survey the ages assigned to the units are equally indeterminate because the cores used by them have missing core tops of unknown lengths that are not discussed in their publications furthermore the sub bottom reflectors at the sites where the reflectors were calibrated to their only core without a missing top are actually hidden by the finite width of the bottom reflecting wavelet

an abrupt drowning of the black sea shelf abstract during latest quaternary glaciation the black sea became a giant freshwater lake the surface of this lake drew down to levels more than 100 m below its outlet when the mediterranean rose to the bosporus sill at 7 150 yr bp 1 saltwater poured through this spillway to refill the lake and submerge catastrophically more than 100 000 km2 of its exposed continental shelf the permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of europe at that time

early holocene age and provenance of a mid shelf delta lobe south of the strait of bosphorus turkey and its link to vigorous black sea outflow abstract the chronology of an abandoned holocene delta lobe present water depth 40 70 m on the northeastern shelf of the marmara sea south of the strait of bosphorus was revised from the early holocene 11 0 9 7 cal ka to the middle holocene 6 65 3 75 cal ka by eris et al eris k k ryan w b f cagatay m n sancar u lericolais g menot g bard e 2007 the timing and evolution of the post glacial transgression across the sea of marmara shelf south of istanbul marine geology 243 57 76 three independent seismic and multibeam surveys and replotting of navigational fixes for the 1992 1993 vintage survey lines which eris et al correlated to their md04 2750 giant piston core confirm that they misplotted the location of the md04 2750 core site on seismic profiles by a minimum of 200 m because of rapid convergence of seismic reflections in this critical area the assessment of the age of the holocene delta proposed by eris et al is incorrect instead existing and new data allow the age of this delta lobe to be refined to 11 1 10 2 cal ka 200 300 years each using several dated cores and the md04 2750 chronology itself a dense grid of previously unpublished seismic data shows that the lobe emanates from the strait of bosphorus and not from any of the local small streams mineralogy of the very fine sand fraction of the delta excludes the kurbagalidere stream as a source of the detritus as does the composition of detrital hornblendes it is concluded that the early holocene delta lobe indeed records a period of strong black sea outflow as advocated by co authors rnh and aea in 2002 re examination of multibeam imagery from the strait itself provides support for strong southward flow that potentially coincided with accumulation of the delta lobe at the southern exit of the strait

petrogenesis of an augite bearing melt rock in the chicxulub structure and its relationship to k t impact spherules in haiti geophysical anomalies on the yucatan peninsula define a buried circular structure with an approximate diameter of 180 km refs 1 3 these anomalies along with stratigraphic and petrological data including evidence for shock metamorphism have been used to interpret the structure as an impact crater4 this structure known as chicxulub is particularly interesting because it formed at or near the end of the cretaceous period in the geographical region where an impact is believed to have occurred in large part because of a thick ejecta deposit found on haiti5 glassy tektite like relics in this deposit6 9 are unusually calcic up to 31 wt cao ref 7 providing a further circumstantial link with the chicxulub structure which penetrates a carbonate and evaporite sequence7 8 here we strengthen this link by showing that a simple chemical relationship exists between the glasses and an augite bearing melt rock found within the chicxulub structure and argue that the composition of this melt rock could not easily have been produced by volcanic processes

a case study of impact induced hydrothermal activity the haughton impact structure devon island canadian high arctic the well preserved state and excellent exposure at the 39 ma haughton impact structure 23 km in diameter allows a clearer picture to be made of the nature and distribution of hydrothermal deposits within mid size complex impact craters a moderate to low temperature hydrothermal system was generated at haughton by the interaction of groundwaters with the hot impact melt breccias that filled the interior of the crater four distinct settings and styles of hydrothermal mineralization are recognized at haughton a vugs and veins within the impact melt breccias with an increase in intensity of alteration towards the base b cementation of brecciated lithologies in the interior of the central uplift c intense veining around the heavily faulted and fractured outer margin of the central uplift and d hydrothermal pipe structures or gossans and mineralization along fault surfaces around the faulted crater rim each setting is associated with a different suite of hydrothermal minerals that were deposited at different stages in the development of the hydrothermal system minor early quartz precipitation in the impact melt breccias was followed by the deposition of calcite and marcasite within cavities and fractures plus minor celestite barite and fluorite this occurred at temperatures of at least 200 c and down to 100 120 c hydrothermal circulation through the faulted crater rim with the deposition of calcite quartz marcasite and pyrite occurred at similar temperatures quartz mineralization within breccias of the interior of the central uplift occurred in two distinct episodes 250 down to 90 c and 80 c appreciation of the structural features of impact craters has proven to be key to understanding the distribution of hydrothermal deposits at haughton

comment on the timing and evolution of the post glacial transgression across the sea of marmara shelf south of istanbul by eris et al marine geology 243 57 76 abstract in their recent paper eris and co authors attempt to refute much of our work on deltaic sediments at the southern exit of the bosphorus strait turkey first their age model is completely inconsistent with the well constrained chronology of our cores mar02 110 and mar02 111 their calypso core md 2750 must have seriously oversampled the holocene section giving an erroneous impression of true thicknesses and ties to seismic data and therefore leading to an incorrect assessment of the timing of deltaic sedimentation second they have ignored evaporative drawdown in the marmara sea from 14 7 11 3 ka lowering of the sea surface by evaporation is a better explanation for a lowstand shoreline at 83 m elevation than their proposal that the dardanelles sill was this deep at the time of reconnection with the global ocean third we contest their conclusion that the uppermost delta in this area was sourced from the kurbagalidere river the sediment flux of this river is too little it cannot account for the strong upward climb of the topset to foreset transition into a rapidly rising ocean and eris et al make no attempt to explain the absence of a precursor shelf edge delta that would be mandatory if this river had the water and sediment discharge that they suggest

black sea impact on the formation of eastern mediterranean sapropel s1 evidence from the marmara sea abstract water exchange between the black sea and the mediterranean sea has been a major focus of the paleohydrography of the eastern mediterranean glacial melt water released from the black sea is a potential factor in the formation of sapropel s1 an organic rich sediment layer that accumulated during the early holocene a high resolution study done on sediments from the marmara sea the gateway between the mediterranean and the black sea sheds light on the holocene exchange processes past sea surface temperature and sea surface salinity sss were derived from stable oxygen isotope ratios 18o of foraminiferal calcite and alkenone unsaturation ratios uk 37 heavy 18o values and high sss in the marmara sea suggest absence of low salinity water from the black sea during s1 the comparison with data from the levantine basin and southern aegean sea outlines gradients of freshening in the eastern mediterranean sea whereby the major sources of freshwater were closer to the levantine basin it is thus concluded that the black sea was not a major freshwater source contributing to formation of s1 given the absence of a low salinity layer the deposition of organic rich sediments corresponding to s1 in the marmara sea is likely the result of the global transgression and the concomitant re organization of biogeochemical cycles leading to enhanced productivity as shown by globigerina bulloides

mobile element analysis by secondary ion mass spectrometry sims of impactite matrix samples from the yaxcopoil 1 drill core in the chicxulub impact structure the concentrations of the fluid mobile trace elements lithium beryllium boron and barium were measured in samples of the altered matrix of several impactite breccias of the yaxcopoil 1 drill core using secondary ion mass spectrometry sims to determine the extent of transport due to aqueous or hydrothermal processes three of the elements li be and b have higher concentrations in the upper suevite impact breccias than in the lower impact melt deposits by factors of 3 5 2 2 and 1 5 respectively lithium and b are the most enriched elements up section and appear to have had the greatest mobility the similar fractionation of li and b is consistent with fluid transport and alteration under low temperature conditions of less than 150 c based on published experimental studies in contrast to li be and b the concentration of ba in the altered matrix materials decreases upward in the section and the concentration of ba in the matrix is an order of magnitude less than the bulk concentrations likely due to the presence of barite the origin of the elemental variations with depth may be related to different protolith compositions in the upper versus the lower impactite units a different protolith in the altered matrix is suggested by the mg rich composition of the lower units versus the al rich composition of the upper units which largely correlates with the mobile element variations the possibility that vertical transport of mobile elements is due to a postimpact hydrothermal system is supported by published data showing that the sediments immediately overlying the impactites are enriched in mobile elements derived from a hydrothermal system however the mobile elements in the sediments do not have to originate from the underlying impactites in conclusion our data suggests that the impactites at this location did not experience extensive high temperature hydrothermal processing and that only limited transport of some elements including li be and b occurred

geophysical characterization of the chicxulub impact crater 1 geophysical data indicate that the 65 5 million years ago chicxulub impact structure is a multi ring basin with three sets of semicontinuous arcuate ring faults and a topographic peak ring pr slump blocks define a terrace zone which steps down from the inner rim into the annular trough fault blocks underlie the pr which exhibits variable relief due to target asymmetries the central structural uplift is 10 km and the moho is displaced by 1 2 km the working hypothesis for the formation of chicxulub is a 50 km radius transient cavity lined with melt and impact breccia formed within 10 s of the impact and within minutes weakened rebounding crust rose kilometers above the surface the transient crater rim underwent localized deformation and collapsed into large slump blocks resulting in a inner rim at 70 85 km radius and outer ring faults at 70 130 km radius the overheightened structural uplift collapsed outward buried the inner slump blocks and formed the pr most of the impact melt was ultimately emplaced as a coherent 3 km thick melt sheet within the central basin that shallows within the inner regions of the pr smaller pockets of melt flowed into the annular trough subsequently slope collapse ejecta ground surge and tsunami waves infilled the annular trough and annular basin with sediments up to 3 km and 900 m thick respectively testing this working hypothesis requires direct observation of the impactites within and adjacent to the pr and central basin

secondary alteration of the impactite and mineralization in the basal tertiary sequence yaxcopoil 1 chicxulub impact crater mexico the 65 ma chicxulub impact crater formed in the shallow coastal marine shelf of the yucatn platform in mexico impacts into water rich environments provide heat and geological structures that generate and focus sub seafloor convective hydrothermal systems core from the yaxcopoil 1 yax 1 hole drilled by the chicxulub scientific drilling project csdp allowed testing for the presence of an impact induced hydrothermal system by a characterizing the secondary alteration of the 100 m thick impactite sequence and b testing for a chemical input into the lower tertiary sediments that would reflect aquagene hydrothermal plume deposition interaction of the yax 1 impactites with seawater is evident through redeposition of the suevites unit 1 secondary alteration mineral assemblages and the subaqueous depositional environment for the lower tertiary carbonates immediately overlying the impactites the least altered silicate melt composition intersected in yax 1 is that of a calc alkaline basaltic andesite with 53 4 56 wt sio2 volatile free the primary mineralogy consists of fine microlites of diopside plagioclase mainly ab 47 ternary feldspar ab 37 to 77 and trace apatite titanite and zircon the overprinting alteration mineral assemblage is characterized by mg saponite kmontmorillonite celadonite k feldspar albite fe oxides and late ca and mg carbonates mg and k metasomatism resulted from seawater interaction with the suevitic rocks producing smectite kfeldspar assemblages in the absence of any mixed layer clay minerals illite or chlorite rare pyrite sphalerite galena and chalcopyrite occur near the base of the impactites these secondary alteration minerals formed by low temperature 0 150 c oxidation and fixation of alkalis due to the interaction of glass rich suevite with down welling seawater in the outer annular trough intersected at yax 1 the alteration represents a cold mg k rich seawater recharge zone possibly recharging higher temperature hydrothermal activity proposed in the central impact basin hydrothermal metal input into the tertiary ocean is shown by elevated ni ag au bi and te concentrations in marcasite and cd and ga in sphalerite in the basal 25 m of the tertiary carbonates in yax 1 the lower tertiary trace element signature reflects hydrothermal metal remobilization from a mafic source rock and is indicative of hydrothermal venting of evolved seawater into the tertiary ocean from an impactgenerated hydrothermal convective system

wind effects on the buoyancy driven general circulation in a closed basin using a two level model abstract wind effects on buoyancy driven circulation in a two level rectangular basin are studied the ocean is driven by positive and negative buoyancy fluxes in the northern and southern portions as well as wind stress of constant curl in a model with a flat and frictionless bottom a barotropic component is determined only by wind forcing a baroclinic component of the wind driven circulation associated with horizontal density gradient is reduced by horizontal diffusion i e the wind driven circulation is more barotropic with stronger diffusion meridional overturn induced by buoyancy fluxes is modified by the wind driven circulation for example the southward upper level flow produced by positive and negative buoyancy fluxes in the northern and southern portions greatly shifts to the western eastern boundary by cyclonic anticyclonic wind driven circulation with realistic intensity relative importance of the wind driven circulation to the buoyancy driven circulation for meridional density

hydrothermal alteration in the core of the yaxcopoil 1 borehole chicxulub impact structure mexico petrographic electron microprobe and raman spectrometric analyses of yaxcopoil 1 core samples from the chicxulub crater indicate that the impact generated a hydrothermal system relative textural and vein crosscutting relations and systematic distribution of alteration products reveal a progression of the hydrothermal event in space and time and provide constraints on the nature of the fluids the earliest calcite halite and gaylussite suggest that the impactite sequence was initially permeated by a low temperature saline brine subsequent development of a higher temperature hydrothermal regime is indicated by thermal metamorphic diopside hedenbergite aeg3fs 18 33 en32 11wo 47 53 after primary augite and widespread na k for ca metasomatic alkali exchange in plagioclase hydrothermal sphene apatite magnetite bornite as well as early calcite combined 3 to 8 vol were introduced with metasomatic feldspar a lower temperature regime characterized by smectite after probable primary glass secondary chlorite and other pre existing mafic minerals as well as very abundant calcite veins and open space fillings extensively overprinted the early hydrothermal stage the composition of early and late hydrothermal minerals show that the solution was chlorine rich cl f 10 and that its fe mg ratio and oxidation state increased substantially 4 to 5 logo2 units as temperature decreased through time the most altered zone in the impactite sequence occurs 30 m above the impact melt the lack of mineralogical zoning about the impact melt and convective modeling constraints suggest that this unit was too thin at yaxcopoil 1 to provide the necessary heat to drive fluids and implies that the hydrothermal system resulted from the combined effects of a pre existing saline brine and heat that traveled to the yaxcopoil 1 site from adjacent areas where the melt sheet was thicker limonite after iron oxides is more common toward the top of the sequence and suggests that the impactite section was subjected to weathering before deposition of the tertiary marine cover in addition scarce latest anatase stringers chalcopyrite and barite in vugs francolite after apatite and recrystallized halite are the likely products of limited post ydrothermal ambient temperature diagenesis or ocean and or meteoric water circulation

origin of the strait of canakkale dardanelles regional tectonics and the mediterranean marmara incursion abstract the regional tectonics and the mid to late quaternary seismic stratigraphy of the strait of canakkale dardanelles and its opening towards the aegean sea were interpreted by using shallow seismic profiles this strait is a narrow valley that resulted from regional uplift of the gelibolu and biga peninsulas in the pliocene as a consequence of compressional events generated by strike slip faulting activity of the ganos fault a northern strand of the north anatolian fault a nne ssw trending fault system between eceabat and canakkale believed to result from the left lateral displacement of the ganos fault on the gelibolu peninsula cut this valley into different segments the connection between the marmara basin and the aegean sea has been achieved after flooding of the connected valleys during the mid to late pleistocene three major sea level lowstands 130 150 m during this period 600 kyear bp interrupted the sea water connection at least twice three main seismic unconformities detected in the sediments of the strait of canakkale represent these lowstands minor sea level lowstands could have induced narrowing of the strait and erosion of depositional units the recent geological history of the strait of canakkale appears as deduced from the gelibolu peninsula and its western regions strongly related to escape tectonics influenced by the compressional forcing of the anatolian block in addition it also shows a morphological evolution which carries the effects of the global sea level variations

magnetic mineralogy of the yaxcopoil 1 core chicxulub core from the yaxcopoil 1 yax 1 hole drilled as a result of the chicxulub scientific drilling project csdp has been analyzed to investigate the relationship between opaque mineralogy and rock magnetic properties twenty one samples of suevite recovered from the depth range 818 894 m are generally paramagnetic with an average susceptibility of 2000 x 10 6 si and have weak remanent magnetization intensities average 0 1 a m the predominant magnetic phase is secondary magnetite formed as a result of low temperature 45000 x 10 6 si and a remanent magnetization of 77 5 a m magnetic mafic basement clasts are a common component in the yax 1 impactite sequence the high susceptibility and remanence in the mafic basement clasts are caused by the replacement of amphiboles and pyroxenes by an assemblage with fine 1 m magnetite ilmenite k feldspar and stilpnomelane replacement of the mafic minerals by the magnetic alteration assemblage occurred before impact similar alteration mechanisms if operative within the melt sheet could explain the presence of the high amplitude magnetic anomalies observed at chicxulub

sea level changes and depositional environments in the izmit gulf eastern marmara sea during the late glacial holocene period abstract offshore and onshore stratigraphic studies together with high resolution shallow seismic reflection profiling and multibeam bathymetric mapping were carried out in the western and central part of the izmit gulf these studies indicate that the izmit gulf was a lacustrine environment as part of the marmara lake during the late glaciation and early deglaciation until 12 kyr bp when the marmara basin was inundated by the mediterranean waters correlation of 14 c dated onshore and offshore stratigraphic units in the western izmit gulf indicates that generally coarse late glacial sediments overlie a marked erosional surface formed during the low water level of the marmara lake these coarse sediments are succeeded by 10 4 7 kyr bp old transgressive and by late holocene post transgression mud units the bathymetry and sub bottom chirp profiles clearly show that the paleoshoreline of the gulf was located at 85 m having been controlled by the bedrock sill depth of the canakkale strait another paleoshoreline observed at 65 m on the northern margin of the western izmit and karamursel basins was probably formed during the younger dryas sea level stillstand the shelf areas during this time were colonized by bioherms which were subsequently drowned and disappeared after a further rise of the sea level the presence of a 65 m marine paleoshoreline in the karamursel basin indicates that the sill restricting this basin to the west was much deeper than its present 55 m level and was located further south the golcuk basin restricted by a 38 m sill to its west was probably not flooded by marine waters until 9 kyr bp

multiple hydrothermal processes in footwall units of the north range sudbury igneous complex canada and implications for the genesis of vein type cu ni pge deposits systematic regional sampling along the contact zone of the 1 85 ga age sudbury igneous complex with the archean levack gneiss footwall in the north range of the sudbury structure revealed textural mineralogical and fluid inclusion systematics of post sudbury igneous complex hydrothermal processes that affected the various lithologies at late stages of emplacement of the sudbury igneous complex and formation of magmatic fe ni cu sulfide deposits a partial melt from the levack gneiss invaded the contact zone this partial melt is revealed by small microdikes and irregular bodies of granophyric quartz plagioclase with megacrysts of hornblende clinopyroxene and titanite plagioclase hornblende equilibrium was established at 750 to 800 c and 1 10 to 1 55 kbars pressure corresponding to about a 4 to 6 km depth under lithostatic conditions f cl wt percent ratios around 15 for accessory apatite and hornblende indicate that a cl rich fluid phase separated during the crystallization of the footwall granophyre this is expressed as miarolites the cl rich fluid 50 wt nacl equiv salinity was trapped as primary fluid inclusions in quartz at around 480 c minimum temperature and around 1 1 kbars minimum pressure during supercooling these inclusions are rich in ca fe mn and k as well as na chloride this fluid may have interacted with earlier primary magmatic sulfide causing remobilization and reprecipitation of cu ni platinum group elements pge in veins and disseminations in the footwall these veins are parallel to the sudbury igneous complex footwall contact and are characterized by chalcopyrite pentlandite millerite magnetite stilpnomelane ferropyrosmalite epidote and chlorite michenerite moncheite merenskyite froodite insizwaite sobolevskite gold and bi ni sulfides are associated with sulfides epidote quartz actinolite and chlorite are common in the alteration selvages of the veins compositions and assemblages of platinum group minerals pgm indicate their precipitation below 575 to 485 c primary highly saline fluid inclusions about 40 wt nacl equiv in quartz indicate crystallization at 400 to 480 c and around 1 6 kbars minimum t and p respectively late carbonate epidote actinolite chlorite veins and alteration overprinted the earlier assemblages at about 300 to 400 c with some bornite millerite native silver and other bi sulfides the second stage of hydrothermal activity is characterized by regional carbonic aqueous nacl co 2 ch 4 h 2 o type immiscible fluids that were trapped as secondary inclusions in quartz from various lithologies no mineralization is related to this stage along the north range boiling of these fluids took place during a pressure drop from lithostatic to hydrostatic conditions during uplift from about a 5 to 6 to a 3 to 4 km depth at 300 to 350 c high 20 26 wt nacl equiv and low salinity 6 12 wt nacl equiv fluids coexisted with different carbonic species contents the predominant north south and northwest southeast orientations of fluid inclusion planes reveal that mobilization of carbonic aqueous solutions may be related to the northwesterly oriented thrusting in the sudbury structure during the late stages 1 8 1 7 ga of the penokean orogeny and to predominantly north south faulting in the north range the third stage of fluid mobilization also took place mostly along northerly and northwesterly oriented fractures aqueous fluids were ca rich brines 20 40 wt salinity with temperatures between 150 and 250 c some of these fluids also circulated in fractures parallel to the sudbury igneous complex footwall contact ne sw thus they locally may have interacted with the earlier sulfide assemblages and are also responsible for formation of late veinlets with chalcopyrite epidote quartz chlorite assemblages mobilization of these fluids took place under litho and hydrostatic conditions at about a 4 to 6 km depth this hydrothermal activity is related to a regional tectonothermal event during emplacement of northwesterly oriented sudbury dikes 1 24 ga regional scale fluid inclusion studies along the north range highlight the role of multiple hydrothermal processes in the metallogenic evolution of the sudbury igneous complex and especially in the distribution of copper and precious metals in the footwall units

petrographic investigation of melt and matrix relationships in chicxulub crater yaxcopoil 1 brecciated melt rock and melt rock bearing suevite 846 885 m units 4 and 5 abstract the drill core from the international continental drill program s chicxulub scientific drilling project yaxcopoil 1 yax 1 borehole in the annular trough of the chicxulub crater exhibits from 794 to 895 m a continuous sequence of impactites consisting of reworked fallout fallout suevite and brecciated impact melt rock these impact breccias exhibit a complex history of deposition fracturing matrix emplacement and hydrothermal alteration detailed investigation of the mineralogy and chemistry of these breccias has led to a better understanding of the complex events involved in their formation we find that the paragenesis of the brecciated impact melt rock unit 5 861 885 m involved fracturing of melt rock and early k metasomatism during a hydrothermal alteration episode as suggested by earlier work however the present work has identified the role of multiple episodes of precipitation of mg rich phyllosilicates and formation and dissolution of accessory minerals in a relatively high temperature 300 c hydrothermal event the earliest matrix formation event involved precipitation of mg rich phyllosilicate accessory quartz calcite apatite and andradite garnet from a hydrothermal fluid with a brine or seawater component the fluid could have partly incorporated elements and shock metamorphosed mineral phases derived from sedimentary lithologies including calcite and dolomite that underwent complex phase transformations such as melting decomposition and possible back reactions the discovery of andradite garnet in the matrix confirms the presence of an early high temperature hydrothermal event previously identified by mineralogical stable isotope and fluid inclusion studies the mineral assemblage including mg rich saponite suggests the involvement of seawater by comparison with similar alteration assemblages in hydrothermal systems involving seawater around the world the presence of a later low temperature phase of the hydrothermal system with different fluid chemistry is indicated by the partial dissolution of andradite garnet and continued precipitation of matrix phyllosilicate minerals but without the accessory quartz abundant calcite or andradite and without an accompanying k metasomatism event

impact melt sheet formation on mars and its implication for hydrothermal systems and exobiology abstract hydrothermal deposits are a prime exobiological research target on mars and impact craters are potentially a significant source for these deposits key factors in the longevity of terrestrial impact crater hydrothermal systems are the volume of shock melt produced and the degree to which this melt is quenched by mixing with un melted clasts mixing occurs when the shock melt is smeared along the crater floor and the degree of mixing is inversely proportional to the thickness of this smeared layer to investigate the potential development of thick melt sheets on mars we apply an analytical impact model to asteroid and long period lp comet impacts that produces martian craters with final diameters of 30 640 km we combine our model shock melt volumes with estimates of the surface area of the transient cavity to estimate initial shock melt thickness which we use as a proxy measure of the amount of mixing between shock melt and un melted clasts we calculate this shock melt thickness parameter for a range terrestrial craters with and without thick melt sheets from which we infer the melt sheet characteristics for the model mars craters the results demonstrate that most asteroid impacts on mars do not produce thick clast free melt sheets only asteroid impact craters 580 km in diameter on mars produce shock melt thicknesses comparable to earth s 200 km diameter sudbury crater and martian craters 65 km in diameter produce shock melt thicknesses comparable to terrestrial craters that lack melts sheets entirely lp comet impacts on mars are more likely to produce thick melt sheets lp comet impact craters 280 km in diameter on mars produce shock melt thicknesses comparable to that of the sudbury crater given that lp comet impacts on mars are rare compared to asteroid impacts we conclude that large long lived impact hydrothermal systems are likewise rare on mars comparisons of the mars asteroid impact rate with the potential longevity of impact hydrothermal systems indicate that such systems were active 1 of the time in the last 3 5 ga which raises questions about the exobiological importance of impact crater hydrothermal systems on mars after the noachian

a mesoscale ocean feature study using synthetic aperture radar imagery in the labrador ice margin experiment 1989 four synthetic aperture radar sar images were collected during the labrador ice margin experiment limex in march 1989 to study mesoscale ocean features over the newfoundland shelf ice floe movement is detected by displacement in the first two images collected on consecutive days streamfunction maps of ocean currents are drawn using an objective method after direct wind driven components are removed the general flow pattern shows the inshore branch of the labrador current to be isolated from the seaward flow over the northern edge of the grand banks in agreement with the mean circulation detected in noaa satellite images for 3 years by the same method ice distribution in the sar images implies mesoscale features much richer than those in the objectively drawn flow field it is difficult to detect ice movement in the images with two day separation because no persistent ice feature is identified in the study area it is suggested during the ers 1 ice mission to take airborne sar images one day before or after a satellite pass for ocean current detection from ice floe movement

shocked titanite records chicxulub hydrothermal alteration and impact age abstract hydrothermal activity is a common phenomenon in the wake of impact events yet identifying and dating impact hydrothermal systems can be challenging this study provides the first detailed assessment of the effects of shock microstructures and impact related alteration on the u pb systematics and trace elements of titanite catisio5 focusing on shocked granite target rocks from the peak ring of the chicxulub impact structure mexico a 1 mm long shock twinned titanite grain preserves a dense network of irregular microcracks some of which exploit shock twin interfaces secondary microcrystalline anatase and pyrite are heterogeneously distributed along some microcracks in situ laser ablation multi collector inductively coupled plasma mass spectrometry la mc icpms analysis reveals a mixture of three end member pb components the pb components are 1 common pb consistent with the pb isotopic signature of adjacent alkali feldspar 2 radiogenic pb accumulated since magmatic crystallization and 3 a secondary younger pb signature due to impact related complete radiogenic pb loss the youngest derived ages define a regression from common pb that intersects concordia at 67 4 ma in agreement with the established age of 66 04 0 05 ma for the chicxulub impact event contour maps of la mc icpms data reveal that the young ages are spatially restricted to microstructurally complex domains that correlate with significant depletion in trace elements ree y zr nb mo sn th and reduction in magnitude of the eu eu anomaly mapping by time of flight secondary ion mass spectrometry tof sims show that patterns of localised element depletion in titanite are spatially related to microcracks which are enriched in al the spatial correlation of ages and trace element abundance is consistent with localised removal of pb and other trace elements from a pervasive network of fast fluid pathways in fractured domains via a fluid mediated element transport process associated with the impact event here we interpret the 67 4 ma u pb age to represent hydrothermal pb loss in the chicxulub peak ring in the wake of the impact event these results highlight the potential of our analytical approach using titanite geochronology and geochemistry for dating post impact hydrothermal activity in impact structures elsewhere

origin and emplacement of the impact formations at chicxulub mexico as revealed by the icdp deep drilling at yaxcopoil 1 and by numerical modeling we present and interpret results of petrographic mineralogical and chemical analyses of the 1511 m deep icdp yaxcopoil 1 yax 1 drill core with special emphasis on the impactite units using numerical model calculations of the formation excavation and dynamic modification of the chicxulub crater constrained by laboratory data a model of the origin and emplacement of the impact formations of yax 1 and of the impact structure as a whole is derived the lower part of yax 1 is formed by displaced cretaceous target rocks 610 m thick while the upper part comprises six suevite type allochthonous breccia units 100 m thick from the texture and composition of these lithological units and from numerical model calculations we were able to link the seven distinct impact induced units of yax 1 to the corresponding successive phases of the crater formation and modification which are as follows 1 transient cavity formation including displacement and deposition of cretaceous megablocks 2 ground surging and mixing of impact melt and lithic clasts at the base of the ejecta curtain and deposition of the lower suevite right after the formation of the transient cavity 3 deposition of a thin veneer of melt on top of the lower suevite and lateral transport and brecciation of this melt toward the end of the collapse of the transient cavity brecciated impact melt rock 4 collapse of the ejecta plume and deposition of fall back material from the lower part of the ejecta plume to form the middle suevite near the end of the dynamic crater modification 5 continued collapse of the ejecta plume and deposition of the upper suevite 6 late phase of the collapse and deposition of the lower sorted suevite after interaction with the inward flowing atmosphere 7 final phase of fall back from the highest part of the ejecta plume and settling of melt and solid particles through the reestablished atmosphere to form the upper sorted suevite and 8 return of the ocean into the crater after some time and minor reworking of the uppermost suevite under aquatic conditions our results are compatible with a 180 km and 100 km for the diameters of the final crater and the transient cavity of chicxulub respectively as previously proposed by several authors and b the interpretation of chicxulub as a peak ring impact basin that is at the transition to a multi ring basin

deltas south of the bosphorus strait record persistent black sea outflow to the marmara sea since 10 ka at the southern exit of the bosphorus strait in the northeastern marmara sea high resolution seismic profiles reveal two lobate progradational delta lobes in modern water depths of v40 65 m the younger delta was active from v10 to 9 ka based on radiocarbon dates of equivalent prodelta deposits and the elevation of its topset to foreset transition the topset to foreset transition climbs in the seaward direction because the delta prograded into a rising sea low abundances of marine fauna and flora in the 10 9 ka interval support a deltaic interpretation there are no rivers in the area that could have fed the delta instead all evidence points to the strait itself as the source of sediment and water when this outflow was strongest v10 6 6 0 ka sapropels accumulated in basinal areas of both the aegean and marmara seas benthic foraminiferal and dinoflagellate cyst data from contemporary deposits elsewhere in the marmara sea point to the continual presence through the holocene of a surface layer of brackish water that we ascribe to this same outflow from the black sea through the bosphorus strait by v9 1 8 5 ka two layer flow developed in the bosphorus strait as global sea level continued to rise and the sediment supply to the younger delta was cut off because the outflowing black sea water ceased to be in contact with the floor of the strait the older delta lobe lies below a prominent lowstand unconformity and is tentatively interpreted to have formed from v29 5 to 23 5 ka oxygen isotopic stage 3 when the marmara sea stood at v355 m and a second sapropel accumulated in deep basinal areas crown copyright 2002 elsevier science b v all rights reserved

an assessment of sediment loss and distortion at the top of short gravity cores abstract examination of laminated bottom sediment cores from two glacier fed lakes in the canadian rocky mountains allows an assessment of the amount of material lost or badly distorted by open barrel gravity corer impact analysis of sediment 137cs content indicates that the laminae are of annual periodicity and allows precise dating of individual laminae examination of 8 cores from hector lake indicates that a mean of 4 6 mm of sediment was missing from the top of each using sedimentation rates in the recovered sections of core and lake wide sedimentation rate variations to approximate sedimentation rates in the missing sections of the core an additional mean thickness of 3 6 mm was strongly distorted analysis of 14 cores from bow lake indicates that on average 6 4 mm of sediment was lost at core tops and an additional 11 4 mm or less suffered severe distortion these data suggest that at least in the lakes studied high impact velocity gravity coring has less of an effect on core top sediment than has previously been reported

north anatolian fault in the gulf of izmit turkey rapid vertical motion in response to minor bends of a nonvertical continental transform 1 the catastrophic rupture of the north anatolian fault east of the marmara sea on 17 august 1999 highlighted a need for mapping the underwater extension of that continental transform a new bathymetric map of izmit gulf indicates that the fault follows the axis of the gulf with a few minor bends submerged shorelines and shelf breaks that formed during the last glacial maximum provide markers to quantify vertical deformation variable tilting of these horizons reveals that vertical deformation is highest just south of the fault a correlation between vertical deformation of the southern fault block and distance to fault bends can be accounted for by a fault dipping steeply to the south hence subsidence uplift of the southern hanging wall block would be expected where the fault strikes at a slightly transtensional transpressional orientation to relative plate motion subsidence reaches about 8 mm yr west of the town of golcuk and might be accommodated in 1 2 m subsidence events during large earthquakes that scenario is compatible with the tsunami runups and the coseismic subsidence of the southern shore that occurred in 1999 seafloor morphology also suggests that earthquakes are accompanied by widespread gas and fluid release the periphery of the deepest basin displays a hummocky texture diagnostic of sediment fluidization and mud volcanoes occur west of hersek peninsula that might be activated by earthquakes finally the backscatter imagery reveals a series of lineaments midway through the gulf that are interpreted as products of the 1999 surface rupture the seafloor is undisturbed farther west suggesting that surface slip decreased to an insignificant level beyond hersek possibly the stress shadow from the 10 july 1894 earthquake which was felt strongly along the western izmit gulf contributed to arrest the 1999 surface rupture

hydrothermal alteration associated with the chicxulub impact crater upper peak ring breccias abstract the 66 ma 180 km chicxulub impact structure in the northern yucatan peninsula and southern gulf of mexico is the best preserved large impact crater on earth with a well developed peak ring the most recent drilling campaign took place offshore during the joint international ocean discovery program international continental scientific drilling program iodp icdp expedition 364 at site m0077a 21 45 n 89 95 w and recovered 830 m of continuous core initial examination revealed that the peak ring comprises four main lithological units from the base upwards crystalline basement granitoid rocks unit 4 a thin layer of impact melt rocks units 3a and b melt bearing breccias units 2a c and post impact sedimentary rocks unit 1 preliminary analysis of the drill core indicated that hydrothermal alteration has affected all lithologies and is especially pervasive in the melt bearing breccias of unit 2 721 6 to 617 33 meters below sea floor mbsf here we present the first detailed investigation of hydrothermal alteration within the melt bearing breccias alteration phases are predominantly fe mg clay minerals zeolites alkali feldspars calcite and minor sulfides sulfates opal and fe ti oxides alteration is especially intense proximal to lithologic contacts particularly at the base of subunit 2b where there is an abrupt increase in host rock porosity 30 m above the impact melt rocks the pervasiveness of clay minerals and zeolites is attributed to the high amounts of devitrified silicate glass throughout unit 2 the phases preserved here are consistent with the findings of previous hydrothermal studies in other areas of the chicxulub structure and suggest an evolving water rock system that was alkaline saline comparable to seawater volcanic glass alteration

late quaternary co seismic sedimentation in the sea of marmara s deep basins the deep northern part of the sea of marmara northwestern turkey is composed of several aligned actively subsiding basins which are the direct structural and morphological expression of the north anatolian fault s northern branch the last 20 kyr of their sedimentary fill lacustrine before 12 kyr bp have been investigated through giant piston coring onboard r v marion dufresne marmacore cruise 2001 and chirp subbottom profiler onboard r v atalante during marmarascarps cruise 2002 especially during the lacustrine stage the infilling of the deep basins tekirda central kumburgaz and cinarcic basins up to 1250 m depth was dominated by turbidites with coarse mixed siliciclastic and bioclastic basal part intercalated in hemipelagic type finegrained calcareous and slightly siliceous clays often especially in the thickest ones the turbidites show strong segregation and a sharp boundary between coarse part and suspendedload part in the central basin 8 m of a unique sedimentary event include a 5 to 8m thick homogenite well imaged on seismic profiles the latter is interpreted as related to a major possibly triggered tsunami effect as described in the eastern mediterranean by kastens and cita 1981 in the marine holocene upper part of the sedimentary fill repeated to and from structures affecting silt or fine sand are evidencing seiche like effects and thus earthquake triggering detailed correlations between two deep coring sites 1250 and 1200 m indicate more than 100 overthickening in the deepest one this implies specific processes of distribution of terrigenous input by dense hyperpycnal currents high kinetic energy seiche effect complex reflections on steep slopes the peculiar sedimentary infilling of the sea of marmara s central basin and by extrapolation of the whole set is tentatively interpreted as a direct consequence of the strong seismic activity the imprint of the latter is more obvious prior to the base of the holocene as environmental conditions favoured marginal accumulation especially on the southern shelf of large amounts of erosion products available for mass wasting

modeling interpretation of mesoscale meanders of the ice edge off the labrador coast observed in noaa satellite imagery abstract noaa satellite visible images exhibit two alternative ice edge patterns off labrador one is a straight pattern and the other is a large meander pattern with alongshore wavelengths of 200 300 km and offshore extensions corresponding to banks over the continental shelf as strong northwesterly wind events occurred the straight patterns changed into the large meander patterns assimilating results from both a continental shelf model driven by alongshore wind and a reduced gravity model constrained by a vertical wall with alongshore variation this progression is interpreted as follows the strong wind induces downwelling and a resultant alongshore flow over the shelf break and then the intensified labrador current interacts with alongshore variation in the shelf break more effectively than the weak one does the topography produces propagating meanders of the labrador current and is enhanced by offshore and offshore extensions corresponding to banks and saddles respectively several days after

chicxulub central crater structure initial results from physical property measurements and combined velocity and gravity modeling the chicxulub crater in mexico is a nearly pristine example of a large impact crater its slow burial has left the central impact basin intact within which there is an apparently uneroded topographic peak ring its burial however means that we must rely on drill holes and geophysical data to interpret the crater form interpretations of crater structures using geophysical data are often guided by numerical modeling and observations at other large terrestrial craters however such endeavors are hindered by uncertainties in current numerical models and the lack of any obvious progressive change in structure with increasing crater size for this reason proposed structural models across chicxulub remain divergent particularly within the central crater region where the deepest well is only 1 6 km deep the shape and precise location of the stratigraphic uplift are disputed the spatial extent and distribution of the allogenic impact breccias and melt rocks remain unknown as do the lithological nature of the peak ring and the mechanism for its formation the objective of our research is to provide a well constrained 3d structural and lithological model across the central region of the chicxulub crater that is consistent with combined geophysical data sets and drill core samples with this in mind we present initial physical property measurements made on 18 core samples from the yaxcopoil 1 yax 1 drill hole between 400 and 1500 m deep and present a new density model that is in agreement with both the 3d velocity and gravity data future collation of petrophysical and geochemical data from yax 1 core as well as further seismic surveys and drilling will allow us to calibrate our geophysical models assigning a suite of physical properties to each lithology an accurate 3d model of chicxulub is critical to our understanding of large craters and to the constraining of the environmental effects of this impact

seismic stratigraphy of late quaternary deposits from the southwestern black sea shelf evidence for non catastrophic variations in sea level during the last 10 000 yr abstract detailed interpretation of single channel seismic reflection and huntec deep tow boomer and sparker profiles demonstrates that the southwestern black sea shelf formed by a protracted shelf edge progradation since the miocene pliocene five seismic stratigraphic units are recognized unit 1 represents the last phase of the progradational history and was deposited during the last glacial lowstand and holocene it is divided into four subunits subunit 1a is interpreted as a lowstand systems tract 1b and 1c are interpreted as a transgressive systems tract and subunit 1d is interpreted as a highstand systems tract the lowstand systems tract deposits consist of overlapping and seaward prograding shelf edge wedges deposited during the lowstand and the subsequent initial rise of sea level these shelf edge wedges are best developed along the westernmost and easternmost segments of the study area off the mouths of rivers the transgressive systems tract deposits consist of a set of shingled shore parallel back stepping parasequences deposited during a phase of relatively rapid sea level rise and include a number of prograded sediment bodies including barrier islands beach deposits and thin veneers of seismically transparent muds showing onlap onto the flanks of older sedimentary features a number of radiocarbon dates from gravity cores show that the sedimentary architecture of unit 1 contain a detailed sedimentary record for the post glacial sea level rise along the southwestern black sea shelf these data do not support the catastrophic refilling of the black sea by waters from the mediterranean sea at 7 1 ka postulated by ryan pitman major shimkus maskalenko jones dimitrov gorur sakinc yuce mar geol 138 1997 119 126 ryan pitman touchstone book 1999 319 pp and ballard coleman rosenberg mar geol 170 2000 253 261

a numerical study of mesoscale ocean eddy interaction with a marginal ice zone observations made during the marginal ice zone experiment mizex program indicated the presence of mesoscale eddies in a marginal ice edge ocean front in the east greenland current the eddies range in scale from 5 to 80 km physical mechanisms including barotropic and baroclinic instability may be responsible for their presence although the evolution of isolated eddies at low latitudes has been the focus of many studies the effect of ice cover on eddy evolution and vice versa has had less attention here an examination of the interaction of isolated mesoscale ocean eddies with a marginal ice zone is presented results are obtained with a two layer nonlinear primitive equation ocean model and a coupled free drift ice model in the absence of winds the ice equilibrates rapidly to the ocean eddy velocity resulting in radial ice motion the ocean sea surface slope is found to provide an important force in the ice momentum balance in no wind simulations with along ice edge 10 m s winds the ice responds largely to the wind and to a lesser extent to the ocean eddy under ice the ocean eddy can be rapidly eroded by wind driven ice motion cyclones anticyclones are rapidly destroyed by along ice edge winds with ice on the left right

the effects of the north anatolian fault zone on the latest connection between black sea and sea of marmara abstract the development of the strait of istanbul is also one of the principal results of the tectonics which led to the evolution of the north anatolian fault zone nafz in the marmara region 3 7 ma ago high resolution seismic profiles from the marmara entrance of the strait of istanbul show a folding which occurred after the deposition of the parallel reflected tyrrhenian sediments over the tyrrhenian strata a fondoform zone of a deltaic sequence and marine sediments of the latest sea level rising are present these sediments also display syn depositional folding this situation implies that a local compressional stress field was created over the area probably since the wurm glacial age this recent variation of the tectonic regime in the northern shelf of the sea of marmara may indicate a significant change in the development of the nafz through the sea of marmara this variation of evolution of the nafz affected the latest development of the strait of istanbul via clockwise rotation of the istanbul and kocaeli peninsulas by right lateral shearing between two zone bounding faults this rotation has led to the development of nne ssw left lateral faults in the strait of istanbul and local compressional and tensional areas explaining the compressional structures seen in the southern entrance of the strait of istanbul therefore the latest mediterranean black sea connection was established by means of the sufficient deepening of the bosphorus channel by a variation in the evolution of nafz through the sea of marmara

reliability of core sampling of soft bottom sediment an in situ study the performances of four light weight open sampling devices intended for use in soft sediments the axelsson hakanson gravity corer the kajak gravity corer the jenkin bottom sampler and the ekman grab box corer were examined in situ by direct observation measurement and photographic documentation by a scuba diver restrictions on the reliability of the sediment samples obtained with these devices and sediment coring instruments in general are evaluated separate studies of core shortening show 1 a positive linear relationship between sediment penetration depth at which shortening of cores starts and coring tube inner diameter 2 a tube size related shift of curve pattern in the regressions of the core shortening versus sediment depth and 3 a negative non linear relationship of shortening intensity versus increasing coring tube inner diameter these findings show the great risk when sampling soft sediments of obtaining a sample quantitatively unrepresentative of the in situ stratification an accurate correction factor for the degree of core shortening requires a knowledge of 1 the sediment depth at which core shortening commences and 2 the curve describing the relationship of shortening to depth of penetration

dating of a regional hydrothermal system induced by the 1850 ma sudbury impact event new u pb geochronologic data from the sudbury structure directly link extensive hydrothermal activity in crater fill breccias with the 1850 ma impact event and constrain complex impact induced processes to 4 m y semiconformable alteration of breccias in the onaping formation includes silicification albitization chloritization calcitization and complex feldspathization which directly underlies zn cu pb ore deposits geochronologic data demonstrate a middle to lower crustal source for the crater fill deposit that was subsequently affected by the hydrothermal event at 1848 4 3 8 1 8 ma these and other data confirm that the crater fill breccia hydrothermal system sudbury igneous complex and its sublayer ni ore bearing units were emplaced as a result of impact the ages of events associated with the sudbury structure are now more closely constrained than in any other meteorite impact structure

geochemical and petrographic characteristics of impactites and cretaceous target rocks from the yaxcopoil 1 borehole chicxulub impact structure mexico implications for target composition we present major and trace element data as well as petrographic observations for impactites suevitic groundmass bulk suevite and melt rock particles and target lithologies including cretaceous anhydrite dolomite argillaceous limestone and oil shale from the yaxcopoil 1 borehole chixculub impact structure the suevitic groundmass and bulk suevite have similar compositions largely representing mixtures of carbonate and silicate components the latter are dominated by melt rock particles trace element data indicate that dolomitic rocks represented a significant target component that became incorporated into the suevites in contrast major elements indicate a strong calcitic component in the impactites the siliceous end member requires a mafic component in order to explain the low sio2 content multicomponent mixing of various target rocks the high alteration state and dilution by carbonate complicate the determination of primary melt particle compositions however two overlapping compositional groups can be discerned a high ba low ta group and a high fe high zn and high hf group cretaceous dolomitic rocks argillaceous limestone and shale are typically enriched in u as br and sb whereas anhydrite contains high sr contents the oil shale samples have abundances that are similar to the north american shale composite nasc but with a comparatively high u content clastic sedimentary rocks are characterized by relatively high th hf zr as and sb abundances petrographic observations indicate that the cretaceous rocks in the yaxcopoil 1 drill core likely register a multistage deformation history that spans the period from pre to post impact contrary to previous studies that claimed evidence for the presence of impact melt breccia injection veins we have found no evidence in our samples from a depth of 1347 1348 m for the presence of melt breccia we favor that clastic veinlets occur in a sheared and altered zone that underwent intense diagenetic overprint prior to the impact event

the mean barotropic circulation on the newfoundland shelf and slope we present results of a numerical model calculation of the barotropic mean circulation in the grand banks region of the continental shelf off eastern canada the modeled circulation is compared with available current data and shows qualitative and some quantitative agreement the model accounts for the general flow of the labrador current along the shelf edge its splitting into two branches north of flemish pass and south of cabot strait and the circulation over the grand banks on the other hand it underestimates the strength of the clockwise circulation over flemish cap and the width of the labrador current it is also possible that neglect of the influence of the gulf stream and north atlantic current gives rise to local discrepancies between observed and modeled flows

a review of sea ice and ocean modeling relevant to the labrador and newfoundland shelves numerical and analytical models of sea ice and ocean circulation are reviewed from a viewpoint of their application to the labrador and newfoundland shelves seasonal variabilities of sea ice and ocean circulation have not been reported in numerical models the difficulty comes from the importance of both stratification and bottom topography sea ice should be included for seasonal cycle calculations individual mechanisms of variabilities with time scales ranging from a day to a month have been studied extensively using various models so that the coupling of these models will make it possible to test the predictability of sea ice and ocean circulation the data collected during limex 87 and 89 provide verification of the models

major and trace element compositions of melt particles and associated phases from the yaxcopoil 1 drill core chicxulub impact structure mexico melt particles found at various depths in impactites from the yaxcopoil 1 borehole into the chicxulub impact structure yucatan have been analyzed for their major and trace element abundances a total of 176 electron microprobe and 45 la icp ms analyses from eight different melt particles were investigated the main purpose of this work was to constrain the compositions of precursor materials and secondary alteration characteristics of these melt particles individual melt particles are highly heterogeneous which makes compositional categorization extremely difficult melt particles from the uppermost part of the impactite sequence are ca and na depleted and show negative ce anomalies which is likely a result of seawater interaction various compositional groupings of melt particles are determined with ternary and binary element ratio plots involving major and trace elements this helps distinguish the degree of alteration versus primary heterogeneity of melt phases comparison of the trace element ratios sc zr y zr ba zr ba rb and sr rb with compositions of known target rocks provides some constraints on protolith compositions however the melt compositions analyzed exceed the known compositional diversity of possible target rocks normalized ree patterns are unique for each melt particle likely reflecting precursor mineral or rock compositions the various discrimination techniques indicate that the highly variable compositions are the products of melting of individual minerals or of mixtures of several minerals small angular shards that are particularly abundant in units 2 and 3 represent rapidly quenched melts whereas larger particles 0 5 mm that contain microlites and have fluidal schlieric textures cooled over a protracted period angular shard like particles with microlites in unit 5 likely crystallized below the glass transition temperature or underwent fragmentation during or after deposition