modern sedimentary processes in the wilmington canyon area u s east coast abstract sedimentary processes active in the wilmington canyon area during the past century are documented from geochronologic sedimentologic and radiographic analysis of sediment cores collected using primarily d s r v alvin site selection for the alvin dives and for collection of box and kasten cores was achieved using sea marc and seabeam data allowing accurate sampling of numerous subenvironments from this extensively dissected area of the continental margin 210 pb sediment accumulation rates from intercanyon areas are highest on the upper slope 1 7 mm yr 140 mg cm 2 yr and decrease with water depth to about 0 4 mm yr 36 mg cm 2 yr on the upper rise within submarine canyons accumulation rates vary dramatically from a maximum of 6 mm yr 500 mg cm 2 yr to less than 0 3 mm yr 22 mg cm 2 yr higher accumulation rates in canyons occur as a result of additional supply of older sediment probably from bioerosion of the canyon walls this is supported by observations from d s r v alvin reduced 210 pb activities and indurated mud clasts observed in several canyon cores extremely low accumulation rates in wilmington and south wilmington canyons are probably the result of strong episodic boundary currents non steady state 210 pb profiles and sedimentologic data indicate small scale mass wasting in south heyes canyon and on the lower slope and rise just north of wilmington canyon

imaging subduction from the trench to 300 km depth beneath the central north island new zealand with vp and vp vs summary recent dense deployments of portable digital seismographs have provided excellent control on earthquakes beneath the central north island of new zealand here we use a subset of the best recorded earthquakes in an inversion for the 3 d vp and vp vs structure the data set includes 39 123 p observations and 18 331 s observations from 1239 earthquakes and nine explosions the subducted plate is imaged as a high vp low vp vs feature vp within the mantle of the subducted slab is almost always 8 5 km s 1 which requires the ca 120 myr slab to be unusually cold the low vp vs within the subducted plate closely parallels the lower plane of the dipping seismic zone it most likely indicates fluid resulting from dehydration of serpentine in the slab mantle and the earthquakes themselves are likely to be promoted by dehydration embrittlement we identify a region with vp 8 0 km s 1 directly above the dipping seismic zone can be interpreted as sinking entrained with the motion of the subducted slab and forming a viscous blanket that insulates the slab from the high temperature mantle wedge material in the overlying low vp region can be interpreted as rising within a return flow within the wedge the volcanic front appears to be controlled by where this dipping low vp region meets the base of the crust the thickness of the backarc crust also shows significant variation along strike in the central taupo volcanic zone tvz the crust is ca 35 km thick while southwest of mt ruapehu the crust thickens by ca 10 km there is no significant low vp zone in the mantle wedge in this southwestern region suggesting that this thicker crust has choked off mantle return flow the seismic tomography results when combined with constraints on mantle flow from previous shear wave splitting results provide a plausible model for both the distribution of volcanism in the central north island and the exceptional magmatic productivity of the central tvz

chronology and petrogenesis of a 1 8 g lunar granitic clast 14321 1062 abstract a study was undertaken to determine the chronology of a pristine granite clast 1062 from apollo 14 breccia 14321 using rb sr sm nd and 39ar 40ar methods the genesis of the granite as constrained by the isotopic results and trace element characteristics is discussed chronology the rb sr internal isochron is slightly disturbed and yields an age of 4 09 0 11 ae 87 rb 0 0139 ae 1 and an imprecise initial i sr 0 702 008 if two data are excluded the age becomes 4 13 0 03 ae and i sr 0 698 003 the whole rock and mineral separates are extremely radiogenic they yield model ages which are relatively well defined the average model age is 4 12 0 03 ae relative to babi 0 69898 the sm nd internal isochron is also slightly disturbed and gives an age of 4 11 0 20 ae 147 sm 0 00654 ae 1 the 39ar 40ar average age of the non magnetic fraction of the sample yields a slightly younger age of 3 88 0 03 ae k ar constants from steiger and a 1977 the concordancy of rb sr and sm nd internal isochrons with the rb sr model age strongly suggests that the granitic clast formed at 4 1 ae ago in the shallow crust and was later excavated and brecciated about 3 88 ae ago petrogenesis isotopic and trace element data of the lunar granite show large k la and rb sr fractionations small sm nd fractionation and the distinct v shaped ree distribution pattern at the time of crystallization a two stage model involving crystal fractionation followed by silicate liquid immiscibility sli is proposed for lunar granite genesis we propose that the granite can be the immiscible acidic liquid produced by sli from a residual liquid which underwent fractionation of ca 3 of phases with ree distribution coefficients similar to those of phosphate minerals from a highly evolved parental magma with ree contents about twice those of the 15405 85 quartz monzodiorite qmd the extreme scarcity of lunar granitic samples and their young formation ages suggest that they are probably not directly crystallized from the differentiation of the primordial magma ocean our isotopic results and trace elements data from other workers suggest that granites qmd and probably mggabbronorites may be genetically related and may have formed in a plutonic environment similar to gabbro granophyre associations in terrestrial layered intrusions such as the skaergaard intrusions

geomorphic characterization of four shelf sourced submarine canyons along the u s mid atlantic continental margin abstract shelf sourced submarine canyons are common features of continental margins and are fundamental to deep sea sedimentary systems despite their geomorphic and geologic significance relatively few passive margin shelf breaching canyons worldwide have been mapped using modern geophysical methods between 2007 and 2012 a series of geophysical surveys was conducted across four major canyons of the us mid atlantic margin wilmington baltimore washington and norfolk canyons more than 5700 km2 of high resolution multibeam bathymetry and 890 line km of sub bottom chirp profiles were collected along the outer shelf and uppermost slope depths of 80 1200 m the data allowed us to compare and contrast the fine scale morphology of each canyon system the canyons have marked differences in the morphology and orientation of canyon heads steepness and density of sidewall gullies and the character of the continental shelf surrounding canyon rims down canyon axial profiles for washington baltimore and wilmington canyons have linear shapes and each canyon thalweg exhibits morphological evidence for recent relatively small scale sediment transport for example washington canyon displays extremely steep wall gradients and contains 100 m wide 5 10 m deep v shaped incisions down the canyon axis suggesting modern or recent sediment transport in contrast the convex axial thalweg profile the absence of thalweg incision and evidence for sediment infilling at the canyon head suggest that depositional processes strongly influence norfolk canyon during the current sea level high stand the north walls of wilmington washington and norfolk canyons are steeper than the south walls due to differential erosion though the underlying cause for this asymmetry is not clear furthermore we speculate that most of the geomorphic features observed within the canyons e g terraces tributary canyons gullies and hanging valleys were formed during the pleistocene and show only subtle modification by holocene processes active during the present sea level high stand

submarine canyons and channels in the lower st lawrence estuary eastern canada morphology classification and recent sediment dynamics abstract series of submarine canyons and channels observed in the lower st lawrence estuary lsle provide an opportunity to analyze in great detail the morphology spatial distribution and modern activity of such systems in a relatively shallow 300 m semi enclosed basin based on their geomorphology and physical settings the canyons and channels were classified into four categories according to their feeding sources ancient or recent glacially fed river fed longshore drift fed and sediment starved systems their activity was interpreted based on geomorphological characteristics such as the presence of bedforms related to gravity flows backscatter intensity axial incision and the presence of rapidly deposited layers in surficial sediments river fed deltas were interpreted as inactive mainly because suspended sediment concentrations at river mouths are low preventing the generation of hyperpycnal currents or delta lip failures related to high sediment supply longshore drift fed canyons present where the coastal shelf narrows were found to be episodically active probably due to earthquakes or extreme storm events unlike other longshore drift fed canyons observed elsewhere in the world they are active infrequently because of the modern low rates of sediment supply to their heads the most active canyons are the sediment starved type and were observed near pointe des monts their activity is probably due to slope failures and to the presence of strong hydrodynamic processes therefore sediment supply is not the main mechanism responsible for modern canyon and channel activity in the lsle however sediment supply has been an important factor during the formation of the submarine channels and canyons their quasi exclusive occurrence on the quebec north shore is attributed to its larger watershed and important sedimentary delivery during deglaciation the quebec north shore watershed is 20 times greater than the quebec south shore watershed which favored the transport of greater volumes of sediment during the early holocene moreover the slope proximity to the shore led to the formation of longshore drift fed systems on the north shore when sediment supplied to rivers were transferred on a narrow shelf

sedimentary processes on the atlantic continental slope of the united states abstract until recently the sedimentary processes on the united states atlantic continental slope were inferred mainly from descriptive studies based on the bathymetry and on widely spaced grab samples bottom photographs and seismic reflection profiles over the past 6 years however much additional information has been collected on the bottom morphology characteristics of shallow subbottom strata velocity of bottom currents and transport of suspended and bottom sediments a review of these new data provides a much clearer understanding of the kinds and relative importance of gravitational and hydrodynamic processes that affect the surface sediments on the rugged slope between georges bank and cape lookout n c these processes include 1 small scale mass wasting within submarine canyons and peripheral gullies 2 density flows within some submarine valleys 3 sand spillover near the shelf break 4 sediment creep on the upper slope and 5 hemipelagic sedimentation on the middle and lower slope the area between georges bank and hudson canyon is further distinguished by the relative abundance of large scale slump scars and deposits on the open slope the presence of ice rafted debris and the transport of sand within the heads of some submarine canyons between cape lookout and southern florida the slope divides into two physiographic units and the topography is smooth and featureless on the florida hatteras slope offshelf sand spillover and sediment winnowing related to gulf stream flow and possibly to storm driven currents are the major processes whereas hemipelagic sedimentation is dominant over the offshore slope along the seaward edge of the blake plateau north of the blake spur slumping generally is absent south of cape lookout although one large slump scarp related to uplift over salt diapirs has been identified east of cape romain future studies concerning sedimentary processes on the atlantic slope need to resolve 1 the ages and mechanisms of mass wasting 2 the accumulation rates and thicknesses of hemipelagic sediments and 3 the causes and variability of offshelf sand spillover sediment winnowing and canyon transport

petrology and chemistry of two large granite clasts from the moon abstract pristine granite clasts in apollo 14 breccias 14321 and 14303 have estimated masses of 1 8 and 0 17 g respectively the 14321 clast is 60 k feldspar and 40 quartz with traces of extremely mg poor mafic silicates and ilmenite the 14303 clast is roughly 33 plagioclase 32 k feldspar 23 quartz 11 pyroxene and 1 ilmenite pyroxene and ilmenite are moderately mg rich plagioclase and pyroxene are strongly zoned both clasts are severely brecciated but monomict pristine both have abundant graphic intergrowths of k feldspar with quartz unlike the majority of similar earth rocks both clasts are devoid of hydrous phases the bulk composition of the 14321 clast is similar to those of several other lunar granitic samples but the 14303 clast is unique it bears as close a resemblance to kreep as it does to other lunar granites silicate liquid immiscibility may explain why the granites are low in ree relative to kreep

sm nd age of lherzolite 67667 implications for the processes involved in lunar crustal formation abstract pristine samples from the lunar highlands potentially offer important information bearing on the nature of early crustal development on all the terrestrial planets one apparently unique sample of this group of lunar crustal rocks the feldspathic lherzolite 67667 was studied utilizing the sm nd radiometric system in an attempt to define its age and the implications of that age for the evolution of the lunar highlands data for 67667 precisely define an isochron corresponding to an age of 4 18 0 07 ae the observed lack of disturbance of the sm nd system of this sample may suggest that this time marks its crystallization at shallow depth in the lunar crust however the possibility that this age as well as those of other highland rocks indicate the time of their impact induced excavation from regions deep enough in the lunar crust to allow subsolidus isotopic equilibrium to be produced or maintained between their constituent minerals is also considered taken together bulk rock sm nd data for four high mg rocks including 67667 indicate that the chemical characteristics of all their source materials were established 4 33 0 08 ae ago and were intimately associated with the parent materials of kreep this finding provides more support for the concept of a large scale differentiation episode early in lunar history the possible roles of the crystallization of a global magma ocean endogenous igneous activity and of planetesimal impact in producing the observed geochemical and chronological aspects of lunar highland rocks are discussed

geostatistical analysis of seafloor depressions on the southeast margin of new zealand s south island investigating the impact of dynamic near seafloor processes on geomorphology abstract seafloor depressions are widespread on the present day continental slope along the southeast coast of new zealand s south island the depressions appear to be bathymetrically constrained to depths below 500 m correlating to the top of the gas hydrate stability zone and above 1100 m similar depressions observed on the chatham rise are interpreted to have formed as a result of gas hydrate dissociation leading to the hypothesis that a similar origin can be applied for the depressions investigated in this study our investigation however has found limited geophysical or geochemical evidence to support this hypothesis the objective of this paper is to examine whether a causal relationship can be established between potential mechanisms of depression formation and the present day seafloor geomorphology geostatistical analysis methods applied to multibeam bathymetry and interpretation of 3d seismic data have been used to empirically describe the geomorphology of the seafloor depressions and investigate potential correlations between geomorphology and other processes such as current flow along the shelf and slope in this region and underlying polygonal fault systems although the results of our analysis do not preclude that the seafloor depressions formed as a result of gas hydrate dissociation neither does our geophysical or geochemical evidence support the theory therefore we propose an alternative mechanism that may have been responsible for the formation of these structures based on the evidence presented in this study the most likely mechanism responsible for the formation of these seafloor depressions is groundwater flux related to the interaction of current systems and the complex geomorphology of submarine canyons on the southeast coast of the south island

evolution of veatch washington and norfolk submarine canyons inferences from strata and morphology abstract investigations of veatch washington and norfolk submarine canyons on the eastern continental margin of the united states resulted in a detailed assessment of their past and present geologic processes norfolk and washington canyons share such characteristics as similar levee geometry stratigraphy and mineralogy veatch canyon differs from norfolk and washington canyons in these respects seismic reflection profiles of all three submarine canyon heads indicate an erosional origin seismic profiles of veatch canyon s lower continental slope indicate a formation by depositional processes in contrast the continental slope profiles of washington and norfolk canyons reveal a history of alternating episodes of deposition and erosion cored sediments from washington and norfolk canyons disclose recent intermittent down canyon transport of sand to the continental rise bathymetric and seismic profiles suggest veatch washington and norfolk canyons have all been subjected to a minimum of two periods of development similar axial trends of washington and norfolk canyons imply a common structural influence

characterization of benthic biogeochemistry and ecology at three methane seep sites on the northern u s atlantic margin abstract several hundred methane seeps were recently discovered along the u s atlantic margin a passive margin without a major hydrocarbon basin these seeps represent a compelling opportunity to compare and contrast geochemical parameters as well as the distribution and composition of associated chemosynthetic ecosystems across geologically distinct seeps specifically this study characterized the physical chemical geological and biological features at veatch canyon new england and shallop canyon methane seep sites using a suite of state of the art sampling and communication tools auv sentry hov alvin a video equipped multicore and a real time telepresence connection to the inner space center isc at the university of rhode island water column backscatter data collected by auv sentry confirmed previously detected gas emission and further indicated the presence of 13 actively emitting gas seeps within the veatch canyon survey area 5 within the new england survey area and 15 within the shallop canyon survey area complementary high resolution seafloor bathymetry and backscatter mapping data indicated highly rugose morphology at all surveyed seep sites including the presence of extensive rock outcrops and bivalve beds video collected by hov alvin provided visual confirmation of gas plumes and the presence of chemosynthetic communities including microbial mats and mussel beds as well as large outcrops of authigenic carbonate rock surrounding locations of discrete gas emission bathymodiolus was the dominant species observed at the veatch canyon methane seep site while the deep sea red crab chaceon quinquedens dominated the new england and shallop canyon seep sites elevated pore water sulfide concentrations suggested stimulation of sulfate coupled anaerobic oxidation of methane aom and or degradation of organic matter in seep sediments relative to non seep sediments aom was observed directly within overlying authigenic carbonate rocks dna sequencing of the surface sediments revealed diverse sulfide oxidizing bacteria similar to the taxa described previously at other methane seeps including members of the thiotrichales and campylobacterales together these analyses provide one of the first interdisciplinary descriptions of sites within this massive seep system setting the stage for more targeted hypothesis driven investigations in this context telepresence facilitated interdisciplinary research between specialists at the isc and scientists and engineers at sea enabling researchers to transfer data and maximize research efforts with sampling tools at sea our findings suggest that although the geological setting is distinct the surficial microbial and macrofaunal communities closely resemble those of previously described methane seeps

the isotopic record of lunar volcanism abstract the timing and extent of lunar volcanism was determined primarily by the internal thermal evolution of the moon a late heavy bombardment produced most of the observable lunar basins easily recognized stratigraphic markers and also may have influenced lunar volcanism most of the nearside basins seem to have been produced 3 8 4 0 ga ago during a period often referred to as the lunar cataclysm the pre cataclysm period was characterized by formation of the lunar crust plutonic rocks within the crust and pre mare volcanism isotopic analysis of breccia clasts pre dating the cataclysm has yielded an outline of this period the isotopic record of post cataclysm mare volcanism is clear but incomplete because samples from the youngest mare areas are lacking specifically the isotopic data show that some lunar anorthosites formed 4 45 ga ago consistent with early formation of an anorthositic lunar crust some mg suite norites troctolites and dunites also formed approximately contemporaneously with the oldest anorthosites but others are up to 200 300 ma younger more evolved rocks granites and quartz monzodiorites also formed between 4 4 and 4 0 ga ago the earliest known pre mare volcanism at 4 25 ga ago included aluminous mare like basalts and an olivine gabbronorite similar to apollo 12 basalts kreep basalt volcanism began at least 4 1 ga ago approximately contemporaneously with that of the ancient mare like basalts and continued during the cataclysm recorded instances of high ti mare basalt volcanism began during or immediately after the cataclysm low ti mare basalt volcanism is the most recent for which samples are available the isotopic data record an early primary lunar differentiation during which mare basalt sources formed probably by crystallization of cumulus minerals from a lunar magma ocean the isotopic record of post cataclysm basalts indicates a heterogeneous lunar mantle and can be explained by partial melting of cumulate sources but more complex petrogenesis also has been suggested more complex petrogenetic processes including assimilation and assimilation fractional crystallization afc seem to be required for pre mare volcanics the isotopic data contain a hint that petrogenesis of the oldest pre mare volcanics may be linked to formation of the so called procellarum basin possibly the oldest and largest lunar basin such a basin would provide a geologic context for the pre mare volcanics and its formation may have been a defining moment in lunar history

the shaping of continental slopes by internal tides the angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins 2 to 4 degrees intensification of near bottom water velocities and bottom shear stresses caused by reflection of semi diurnal internal tides affects sedimentation patterns and bottom gradients as indicated by recent studies of continental slopes off northern california and new jersey estimates of bottom shear velocities caused by semi diurnal internal tides are high enough to inhibit deposition of fine grained sediment onto the slopes

the role of erosion by fish in shaping topography around hudson submarine canyon abstract an 800 km2 area of rough topography around the head of hudson canyon off the eastern united states is attributed to erosion by tilefish lopholatilus chamaeleonticeps and associated species of crustaceans the rough topography has a relief of 1 10 m occurs in water depths of 120 500 m and has been cut into a semilithified silty clay substrate since the onset of the holocene transgression commercial fishing activity indicates that a large population of tilefish which dig burrows in the sea floor occupy the area of the rough topography average tilefish burrows are 1 6 m in diameter and 1 7 m in depth they have a clustered not uniform distribution and their average density is 2 500 per km2 the close match of areas of rough topography and high til fish populations the active burrowing of the sea floor and the clustered distribution of the burrows suggest that the hummocky topography in this area may be the result of continuous erosion by tilefish and associated crustaceans during the holocene an erosion rate of 13 cm per 1 000 years is necessary to create this topography during the past 13 000 years and 18 cm per 1 000 years if as is more likely based on the depths at which tilefish presently are found the erosion started 9 000 years ago

subdivision of the mg suite noritic rocks into mg gabbronorites and mg norites mg suite noritic rocks can be divided into two groups the mg gabbronorites and the mg norites the rocks of these groups differ in ratios of high ca pyroxene to total pyroxene compositions of pyroxene and plagioclase assemblages of ti nb and zr bearing minerals compositions of chrome spinel bulk rock ti sm and sc sm and measured ages the two groups probably crystallized from different types of parent magmas two hypotheses are offered for the differences in composition of the parent magmas one hypothesis ascribes the differences to compositional heterogeneity of the mantle source areas the other hypothesis ascribes the differences to variations in extent of partial melting of the mantle source regions and variations in extent of assimilation of the anorthosite and the highly differentiated residual liquid that were produced during the primordial lunar differentiation

submarine canyon head morphologies and inferred sediment transport processes in the alias almanzora canyon system sw mediterranean on the role of the sediment supply abstract canyon head regions are key areas for understanding the shelf to canyon sedimentary dynamics and assessing the predominant hydrodynamic and sedimentary processes shaping their morphology high resolution multibeam bathymetry surveys conducted on the shelf upper slope and along the main thalwegs of the alias almanzora submarine canyon system were used to recognize the specific morphological features of the various canyon heads and infer the main sediment transport mechanism operating through them off the almanzora river different canyon head morphologies were observed at 65 90 m water depth incising the outer prodeltaic deposits a direct connection from the river supply is evidenced by the presence of a large radial field of sediment waves on the prodelta presumably related to hyperpycnal flows during flash flood events and their continuation towards trains of cyclic steps that merge into the almanzora canyon head processes linked to seepage and groundwater sapping also seems apparent in the prodeltaic deposits which results in pockmark alignments and formation of elongated narrow canyon heads at the southern limit of the almanzora prodelta another type of canyon head results from the formation and merging of linear gullies these have been interpreted as the morphological expression of the distal off shelf transport of flood related hyperycnal flows however most of the canyon heads of the main tributaries of this canyon system i e garrucha cabrera and alias are found at much shallower water depths 7 20 m they generally show a continuation in land with rivers or intermittent creeks known as ramblas that also experience flash flood events but some of them are disconnected from any river source these canyon heads cut into the infralittoral prograding wedge displaying feeder channels that tend to oriented against the direction of the prevalent long shore current some canyon head tributaries show sediment waves along their axis interpreted as the result of hyperpycnal flood events or storm induced turbidity flows this study focusses on the diversity of sediment transport processes that can co exist in the various canyon tributaries of a given submarine canyon system stressing on the importance of the canyon heads location with respect to the principal sedimentary source which ultimately determines their main geomorphological traits

size distribution of submarine landslides along the u s atlantic margin abstract assessment of the probability for destructive landslide generated tsunamis depends on the knowledge of the number size and frequency of large submarine landslides this paper investigates the size distribution of submarine landslides along the u s atlantic continental slope and rise using the size of the landslide source regions landslide failure scars landslide scars along the margin identified in a detailed bathymetric digital elevation model dem have areas that range between 0 89 km2 and 2410 km2 and volumes between 0 002 km3 and 179 km3 the area to volume relationship of these failure scars is almost linear inverse power law exponent close to 1 suggesting a fairly uniform failure thickness of a few 10s of meters in each event with only rare deep excavating landslides the cumulative volume distribution of the failure scars is very well described by a log normal distribution rather than by an inverse power law the most commonly used distribution for both subaerial and submarine landslides a log normal distribution centered on a volume of 0 86 km3 may indicate that landslides preferentially mobilize a moderate amount of material on the order of 1 km3 rather than large landslides or very small ones alternatively the log normal distribution may reflect an inverse power law distribution modified by a size dependent probability of observing landslide scars in the bathymetry data if the latter is the case an inverse power law distribution with an exponent of 1 3 0 3 modified by a size dependent conditional probability of identifying more failure scars with increasing landslide size fits the observed size distribution this exponent value is similar to the predicted exponent of 1 2 0 3 for subaerial landslides in unconsolidated material both the log normal and modified inverse power law distributions of the observed failure scar volumes suggest that large landslides which have the greatest potential to generate damaging tsunamis occur infrequently along the margin

the age and pb loss behaviour of zircons from the isua supracrustal belt as determined by ion microprobe ion microprobe uthpb analyses of zircons from a conglomeratic metavolcanic unit in the isua supracrustal belt of west greenland show that their magmatic age is3807 1ma and failed to detect any older zircon cores or xenocrysts low u areas within zircons at a 30 m scale lost only small amounts of radiogenic pb and only in the recent past whereas high u areas within grains lost much greater proportions of their pb both recently and as early as the archaean some areas in the zircons have concordant upb and thpb ages the ion probe results agree with earlier determinations for the isua supracrustals and clarify minor discrepancies between previous multigrain and single crystal analyses

the case for a younger imbrium basin new 40ar 39ar ages of apollo 14 rocks petrographically and chemically well characterized rocks of the apollo 14 landing site 12 impact melt breccias 3 clast free impact melt rocks 2 granulitic rocks 1 cataclastic noritic anorthosite 1 shocked gabbronorite 1 mare basalt and 1 plagioclase single crystal have been dated by the 40ar 39ar technique the samples represent two different formations at the apollo 14 site 1 small lithic clasts 10 specimens from fragmental breccia 14063 ejected from the 26 ma old cone crater and one clast mare basalt from cone crater soil 14140 and 2 large rock samples 10 specimens collected throughout the regolith of the landing site the first group of samples has exposure ages close to 26 ma and 40ar 39ar ages ranging from 3 86 to 4 09 ga which indicates that breccia 14063 was assembled 3 86 ga ago the second group of samples displays lower 40ar 39ar ages ranging from 3 73 to 3 85 ga we interpret breccia 14063 as part of a nectarian megabreccia unit which was incorporated into the fra mauro formation as a megablock by secondary mass wasting of the ejecta blanket of a local pre imbrian crater the remaining samples are thought to represent clasts of the apollo 14 subregolith basement megabreccia defined as the fra mauro formation consequently the reported ages of these clasts confirm previous suggestions that the fra mauro formation and therefore the imbrium basin is only 3 75 ga old and not 3 85 ga as commonly assumed

in situ measurements of velocity structure within turbidity currents 1 turbidity currents are thought to be the main mechanism to move 500 000 m3 of sediments annually from the head of the monterey submarine canyon to the deep sea fan indirect evidence has shown frequent occurrences of such turbidity currents in the canyon but the dynamic properties of the turbidity currents such as maximum speed duration and dimensions are still unknown here we present the first ever in situ measurements of velocity profiles of four turbidity currents whose maximum along canyon velocity reached 190 cm s two turbidity currents coincided with storms that produced the highest swells and the biggest stream flows during the year long deployment

ancient channels of the susquehanna river beneath chesapeake bay and the delmarva peninsula three generations of the ancestral susquehanna river system have been mapped beneath chesapeake bay and the southern delmarva peninsula closely spaced seismic reflection profiles in the bay and boreholes in the bay and on the southern delmarva peninsula allow detailed reconstruction of each paleochannel system the channel systems were formed during glacial low sea level stands and each contains a channel fill sequence that records the subsequent transgression the trunk channels of each system are 2 to 4 km wide and are incised 30 to 50 m into underlying strata they have irregular longitudinal profiles and very low gradients within the chesapeake bay area the three main stem channels diverge from the head of the bay toward the southeast the channels are rarely coincident although they commonly intersect all three main channels pass beneath the southern delmarva peninsula forming an age progression from north oldest to south youngest beneath the peninsula and from east oldest to west youngest beneath chesapeake bay southward progradation of the tip of the delmarva peninsula during interglacial high sea level stands caused southward migration of the mouth of the bay so that the next generation of channels were incised progressively further towards the southwest the youngest paleochannel is clearly of late wisconsinan age about 18 ka and the intermediate one appears to be late illinoian in age or about 150 ka the age of the oldest paleochannel is not well constrained but it is in the range of about 200 to 400 ka the three paleochannel systems imply a dynamic coastal plain environment and at least two previous generations of the chesapeake bay both the chesapeake bay and the southern delmarva peninsula have changed considerably in the past half million years

39ar 40ar dating of two lunar granites the age of copernicus previous investigations have suggested that kreep glass found in 12033 and other apollo 12 soils was ejected from the crater copernicus and deposited in a ray across this site soil fragment 12033 507 has been described as having a core of felsite granitic composition with a kreep glass shell 39ar 40ar dating of a sample of this granite material shows almost complete resetting 800 15 ma ago we interpret this age as giving the most precise determination to date for the formation time of copernicus cosmic ray exposure ages of the granite and associated kreep glass in soil 12033 about 250 ma are much less than the k ar age and suggest a complex postejection burial history the 39ar 40ar age of another granite fragment 14303 204 is determined to be in the range 3 80 3 85 ga this age is in agreement with 39ar 40ar ages determined for a few other lunar granites and is interpreted to represent resetting by a large basin forming impact probably imbrium

isotope systematics and shock wave metamorphism ii u pb and rb sr in naturally shocked rocks the haughton impact structure canada minerals and whole rocks from crystalline fragments collected in the allochthonous polymict breccia of the 23 ma old haughton impact crater on devon island arctic canada were analysed for u pb k and rb sr in order to constrain degrees of shock wave induced perturbations in these systems the results show that shock wave metamorphism at 50 gpa with onset of total melting does not significantly affect the u pb chronometers in monazite and zircon monazite preserved its age of crystallization during high grade metamorphism at 1928 2 2 1 2 0 ma 2 errors as dated by the upper intercept of 2 9 discordant monazites the same analyses yield a lower intercept age of 277 5 35 1 35 0 ma in the concordia diagram demonstrating that discordancy is not a direct effect of shock wave metamorphism but a product of time integrated pb diffusion prior to the impact event which occurred 23 ma ago this constrains maximal shock induced pb loss to less than 3 including possible alteration related pb diffusion from the shock damaged grains in 1903 1 1 4 1 1 ma old monazite from an unshocked reference gneiss recent pb loss also reaches 3 corroborating the occurrence of weak alteration related upb fractionation the data substantiate that u pb discordancy patterns are not a reliable chronometer to date impact events small rock fragments and a coherent block of shock stage i to iii vi consist of heterogeneous unequilibrated rb sr sub systems on the 10 m scale with drastically varying isr shock related rbsr fractionation is very limited and in the large block stage iii three biotite fractions yield an rb sr isochron age of 1791 34 ma 2 which is undistinguishable from the 1814 8 ma age of biotite in the unshocked basement gneiss in contrast to this m3 sized fragment rb sr systematics in a fist size sample of shock stage iii do not yield any reliable age information due to small scale 1 cm3 isotopic disequilibrium it appears that such small scale disequilibrium is essentially due to a take up of radiogenic 87sr in feldspar glass from biotite during shock wave passage this prevents dating of the impact events by the rb sr internal isochron method and it can be concluded that total rock melting is the first condition necessary to reset the rb sr chronometer in shocked crystalline rocks

an extended episode of early mesoproterozoic metamorphic fluid flow in the reynolds range central australia the products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the upper calcsilicate unit in the granulite portion of the late palaeoproterozoic reynolds range group northern arunta block central australia the zones of retrogression characterized by minerals such as wollastonite grossular and clinohumite local resetting of oxygen isotopic compositions and local major element metasomatism were channelways for water rich fluids derived from granulite facies metapelites u th pb isotopic ages measured by the shrimp ion microprobe on zircon and monazite from a granulite facies semipelite an early semiconcordant aluminous quartz rich fluid flow segregation and a late discordant quartz rich segregation record some of the extended thermal history of the area zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 11 ma old itself derived from a source containing zircon as old as 2 2 ga low th u overgrowths on the zircon grew during granulite facies metamorphism at 1594 6 ma monazite cooled to its blocking temperature at 1576 8 ma zircon cores from the semiconcordant segregation are dominantly 2 3 ga old indicating that the source of the fluids was not the particular metamorphosed semipelite studied two generations of low th u overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 8 and 1582 8 ma respectively the monazite age is the same 1576 12 ma zircon from the late discordant segregation gave 1568 4 ma fluid flow occurred for at least 18 3 ma and ended 26 3 ma after the peak of metamorphism suggesting a very slow cooling rate of 3 c ma 1 the last regional high grade metamorphism in the reynolds range occurred at 1 6 ga not 1 78 ga as previously thought the high grade event at 1 78 ga is a separate event that affected only the basement to the reynolds range group

general patterns of circulation sediment fluxes and ecology of the palamos la fonera submarine canyon northwestern mediterranean abstract currents particle fluxes and ecology were studied in the palamos submarine canyon also known as the fonera canyon located in the northwestern mediterranean seven mooring arrays equipped with current meters and sediment traps were deployed along the main canyon axis on the canyon walls and on the adjacent slope additionally local and regional hydrographic cruises were carried out current data showed that mean near surface and mid depth currents were oriented along the mean flow direction ne sw although at 400 and 1200 m depth within the canyon current reversals were significant indicating a more closed circulation inside the canyon mean near bottom currents were constrained by the local bathymetry especially at the canyon head the most significant frequency at all levels was the inertial frequency a second frequency of about three days attributed to a topographic wave was observed at all depths suggesting that this wave was probably not trapped near the bottom the current field observed during the most complete survey revealed a meandering pattern with cyclonic vorticity just upstream from and within the canyon the associated vertical velocity ranged between 10 and 20 m day and was constrained to the upper 300 m this latter feature together with other computations suggests that during this survey the meander was not induced by the canyon but by some kind of instability of the mean flow in the canyon suspended sediment concentration downward particle fluxes chlorophyll and particulate c and n were significantly higher up canyon from about 1200 m depth than offshore defining along with the different hydrodynamics two canyon domains one from the canyon head to about 1200 m depth more affected by the canyon confinement and the other deeper than 1200 m depth more controlled by the mean flow and the shelf slope front the higher near bottom downward total mass fluxes were recorded in the canyon axis at 1200 m depth along with sharp turbidity increases and are related to sediment gravity flows during the deployment period the increase in downward particle fluxes occurred by mid november when a severe storm took place on the canyon walls at 1200 m depth suspended sediment concentrations downward particle fluxes chlorophyll and particulate c and n were higher on the southern wall than on the northern wall inversely to the current s energy this could be caused by an upward water supply on the southern canyon wall and or the mean flow interacting with the canyon bathymetry in the swimmers collected by the sediment traps the dominant species was an elasipod holothurian which has not been recorded in other canyons or elsewhere in the mediterranean indicating particular speciation

petrologic and foraminiferal evidence for active downslope transport in wilmington canyon abstract the texture and composition of surficial sediment collected by drsv alvin in a meandering part of wilmington canyon on the upper rise off the mid atlantic states indicate that deposition from gravity flow or bottom current or both has occurred in this sector in recent time the marked petrologic and foraminiferal variations between closely spaced sample sites across the canyon axis show a distinct pattern that is closely related to the configuration of the thalweg the sediment distribution pattern recalls that in sinuous fluvial systems the presence of higher proportions of sand terrigenous grains and displaced shallow water shelf upper slope foraminifera close to the incised part of meanders is a result of active erosion the irregular down core variations of texture terrigenous grains and biogenic components tend to favor a discontinuous stop and go transport process the nature and distribution of mixed assemblages of shallow and deep lower slope and rise benthonic and planktonic foraminifera also indicate a downslope directed transport process involving several pulse like redepositional phases some material was introduced at the head of the canyon but much sediment has also entered the canyon channel by displacement down canyon walls it appears that sediment between the shelf edge and the rise must reside sufficiently long in transit to pick up and incorporate an important mix of deep water faunas as the material is displaced seaward

offshore imaging with complex overburden understanding gather complexity and resulting attribute accuracy through synthetics the objectives of this study are to determine the effect of complex overburden in offshore continental settings on the seismic wavefield and on the resultant seismic images and attributes seismic waves exhibit complex wave paths when propagating through heterogeneous geologic structures a key step in understanding the consequences for imaging and more importantly amplitude versus angle behavior is to model this complexity in a known earth velocity model the earth model used represented by the seismic velocities should exhibit similar behavior to the real data but still remain as simple as possible this is also the case in velocity model building however the inability to include subtle geologic features leads to inaccuracy and uncertainty in the velocity model understanding how this inaccuracy manifests itself is vital in any predictive exercise using seismic attributes to improve this understanding several synthetic data sets were simulated using full wavefield synthetics it is evident from

suspended sediment fluxes and transport processes in the gulf of lions submarine canyons the role of storms and dense water cascading contemporary suspended sediment transport was studied in seven submarine canyons of the gulf of lions gol current meters equipped with turbidity sensors were moored 4 m above bottom at 300 m depth in the canyon axis from november 2003 to may 2004 sediment transport events were monitored and studied in relation to forcing conditions there was a large flood in early december during which discharges from all of the coastal rivers increased by more than one order of magnitude a smaller flood of the rhone river occurred later in mid january followed by a persistent high river discharge that lasted until mid february there were also several e se storm events during the measurement period two of them causing large swell one in early december max hs 8 4 m coinciding with the major river flood andoneinlatefebruary maxhs 7m duringaperiodoflowerriverdischarge mostofthevariabilityindown canyoncurrentspeeds waslinkedtostrongdownwellinginducedbye sestormsandtocascadingofdenseshelfwaterinducedbynandnwwinds theintensity and timing of these processes strongly varied spatially eastern storms generated higher waves and induced stronger downwelling in the western than in the eastern sector of the gol shelf dense water cascading events were enhanced during eastern storms and they were also more intense in the western sector of the gol these events occurred frequently from january to may along the western canyons and from february to april along the eastern canyons from february to april they occurred simultaneously in all the canyons sediment transport was mainly down canyon and mostly concentrated during storm induced downwelling and dense water cascading events during the high river discharge season most of the newly supplied and resuspended sediment remained stored on theshelf however duringthelatefebruarystormandcascadingevent thestoredsedimentwasquicklyresuspendedandtransported mainly through the westernmost submarine canyon cap de creus following a flushing pattern later although minor storms and shelfdensewatercascadinghardlyincreasedsuspendedsedimentconcentrationswithinthecanyons theyinducedstrongnear bottom current velocities increasing down canyon sediment fluxes and generating small but significant sediment transport events most of the shelf canyon transfer took place during the late february storm and cascading event through the cap de creus canyon where the net suspended sediment flux was between one and two orders of magnitude higher than in the other canyons

distributions and habitat associations of deep water corals in norfolk and baltimore canyons mid atlantic bight usa a multi disciplinary study of two major submarine canyons baltimore canyon and norfolk canyon off the us mid atlantic coast focused on the ecology and biology of canyon habitats particularly those supporting deep sea corals historical data on deep sea corals from these canyons were sparse with less than 750 records for the mid atlantic region with most being soft sediment species this study substantially increased the number of deep sea coral records for the target canyons and the region large gorgonians were the dominant structure forming coral taxa on exposed hard substrates but several species of scleractinians were also documented including first observations of lophelia pertusa in the mid atlantic bight region coral distribution varied within and between the two canyons with greater abundance of the octocoral paragorgia arborea in baltimore canyon and higher occurrence of stony corals in norfolk canyon these observations reflect the differences in environmental conditions particularly turbidity between the canyons some species have a wide distribution e g p arborea primnoa resedaeformis anthothela grandiflora while others are limited to certain habitat types and or depth zones e g paramuricea placomus l pertusa solenosmilia variabilis the distribution of a species is driven by a combination of factors which include availability of appropriate physical structure and environmental conditions although the diversity of the structure forming corals gorgonians branching scleractinians and large anemones was low many areas of both canyons supported high coral abundance and a diverse coral associated community the canyons provide suitable habitat for the development of deep sea coral communities that is not readily available elsewhere on the sedimented shelf and slope of the mid atlantic bight

uranium lead ages for lunar zircons evidence for a prolonged period of granophyre formation from 4 32 to 3 88 ga the ages of a number of small fragments of lunar granophyre have been determined by the in situ u th pb isotopic analysis of zircon using a sensitive high mass resolution ion microprobe shrimp i the zircon from lunar granophyre is characterized by consistently high u and th contents most 200 500 ppm and 100 300 ppm respectively compared to zircon from mafic lunar rocks some fragments of lunar granophyre are found to be as old as 4 32 ga supporting other evidence that the original lunar magma ocean crystallized completely within 200 ma of the formation of the moon itself other fragments are as young as 3 88 ga which is much later than the time of formation of most of the lunar crust the older lunar granophyres have rare earth element ree patterns that are similar to lunar kreep whilst the younger granophyres have bow shaped ree patterns that feature a greater relative enrichment in the heavy ree the wide range of ages of numerous lunar zircons lunar granophyres and other rocks indicates that zircon forming magmatism in the lunar highlands was most active prior to 4 3 ga but continuous until at least 3 88 ga the u pb isotopic composition of much lunar zircon is near concordant but the effects of isotopic disturbance as late as 1 0 ga are observed in some zircon both within granophyre fragments recrystallized by reheating and within fragments in which the original delicate silica k feldspar granophyric intergrowth is well preserved it is therefore essential to make multiple analyses of individual zircon grains and preferably analyses of suites of zircons from lunar igneous rocks if they are to be dated reliably by the u pb method it is possible that some of the younger lunar granophyres are the product of large scale silicate liquid immiscibility within late stage differentiates but this remains unproven until remnants of demonstrably cogenetic fe rich immiscible liquid are positively identified

event driven sediment flux in hueneme and mugu submarine canyons southern california vertical sediment fluxes and their dominant controlling processes in hueneme and mugu submarine canyons off south central california were assessed using data from sediment traps and current meters on two moorings that were deployed for 6 months during the winter of 2007 the maxima of total particulate flux which reached as high as 300 g m 2 day in hueneme canyon were recorded during winter storm events when high waves and river floods often coincided during these winter storms wave induced resuspension of shelf sediment was a major source for the elevated sediment fluxes canyon rim morphology rather than physical proximity to an adjacent river mouth appeared to control the magnitude of sediment fluxes in these two submarine canyon systems episodic turbidity currents and internal bores enhanced sediment fluxes particularly in the lower sediment traps positioned 30 m above the canyon floor lower excess 210 pb activities measured in the sediment samples collected during periods of peak total particulate flux further substantiate that reworked shelf rather than newly introduced river borne sediments supply most of the material entering these canyons during storms published by elsevier b v

periodic resuspension in baltimore canyon by focusing of internal waves high concentrations of particulate matter are frequently reported in submarine canyons this study demonstrates that in baltimore submarine canyon elevated concentrations result from periodic resuspension events the sloping bottom and v shaped topography of submarine canyons could accelerate tidal flows in the canyon axis sufficiently to cause resuspension which occurs predominantly at tidal frequencies however current meter and transmissometer data show that resuspension events are often associated with a borelike intrusion of cold water moving upslope near the canyon head an event that is consistent with the focusing of internal wave energy toward the canyon head at tidal frequencies hydrographic conditions for the focusing of energy are most favorable in late winter and early spring when stratification in the canyon is diminished direct observations reveal that the most pronounced resuspension events occur during those seasons bottom stresses generated in the canyon are sufficient to resuspend sediment along the axis at least between 200 and 800 m with little resuspension occurring deeper along the axis on the canyon walls adjacent slope or shelf during a resuspension event the sediment laden water is forced upcanyon then sloshes back down the canyon until it reaches a layer of higher density water detaches from the canyon floor and moves seaward along a density surface this is a means of transferring sediment and associated pollutants intercepted at the canyon head to deeper water across the shelf slope front over geologic time frequent resuspension and seaward transport may aid in the headward erosion of submarine canyons or at least inhibit their infilling during interglacial times

rare earth element selenochemistry of immiscible liquids and zircon at apollo 14 an ion probe study of evolved rocks on the moon abstract secondary ion mass spectrometry sims analyses of trace elements in two zircons from 14001 7003 are similar in most respects to one reported recently hinton and meyer 1991 hinton and upton 1991 the major difference being the lack of a positive ce anomaly in the zircon ree pattern reported here which obviates an oxidizing environment for lunar zircon using recently published ree partition coefficients all three lunar zircons indicate separation from a primitive magma with a large negative eu anomaly which is slightly lree enriched and contains rees 10 30 cl chondrites however this calculated liquid has a ree pattern which is unlike the host material or any lunar granite it is postulated that these lunar zircons were precipitated in the upper crust of the moon from late stage gabbroic to anorthositic magmas which have undergone extensive fractionation the exact nature of these evolved magmas remains uncertain evidence for suspected immiscible liquids has been found as glasses in fragments from sample 14001 7003 though the granitic complement to this immiscible pair is a viable immiscible liquid composition the mafic complement has likely undergone some post immiscibility modification however the original liquid liquid element partitioning has not been grossly affected by the post immiscibility modification analyses of the glasses by sims yields a set of partitioning data for the ree in actual rocks from the moon for the most part the partitioning of the rees between the glasses is consistent with that determined experimentally and indicates the importance of liquid immiscibility in late stage lunar igneous processes

reconnaissance in dsrv alvin of a fluvial like meander system in wilmington canyon and slump features in south wilmington canyon three dives in dsrv alvin on the atlantic continental rise in wilmington and south wilmington canyons off the east coast of the united states allowed examination and sampling of morphological features in water depths of 2 300 to 2 400 m that were observed in midrange sidescan sonar data in wilmington canyon a fluvial like meandering system was confirmed the meandering channel had steep undercut outer banks and gently sloping inner banks localized slumping is inferred from many steplike depressions on the steep outer banks although the meander system is as much as 500 m wide and has many characteristics typical of a fluvial system extreme depth and evidence of episodic ongoing sedimentary processes preclude a true fluvial origin currents of unknown origin that is downcanyon turbidity flows appear to be the only agent capable of sculpturing the observed features a meander system was not observed in south wilmington canyon channel floor features including deformed and displaced sediment support a previous suggestion of large scale slumping in the area these sediments include upturned clay beds disaggregated gravels loosely bound gravel conglomerates in a reddish brown matrix and a tubular structure resembling a tree root cast within a thinly bedded reddish brown sandstone