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

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

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

recent sedimentation on the new jersey slope and rise radiocarbon dating and sedimentological studies of closely spaced cores indicate movement during the holocene of sediments on the new jersey continental slope and upper rise between wilmington and lindenkohl canyons the uneven time stratigraphic thickness of the late quaternary sediment sections between cores and the nonuniform deposition rate at any given core site and among core sites show that the sediment blanket in canyon and intercanyon areas has been affected by downslope gravity driven pocesses during the holocene to the present the reduced rate of deposition on the slope and upper rise between the late pleistocene and the present is largely due to decreased off shelf transport in response to the eustatic rise in sea level very old radiocarbon dates at core tops result from emplacement of older reworked materials from upslope or from truncation of sections by mass wasting processes exposing older material at the sea floor these processes also account for an irregular sequence of dated sections within cores and stratigraphic irregularities of the surficial cover from core to core marked variability in deposition rates on the slope and upper rise is largely a function of topographic configuration proximity and accessibility to sediment source and transport processes seaward of the shelf break moreover higher accumulation rates on the upper rise are attributed primarily to slope bypassing bypassing prevalent during the late pleistocene has continued periodically to the present

seismic stratigraphy of the fault controlled submarine canyon valley system on the shelf and upper slope of anamur bay northeastern mediterranean sea abstract high resolution shallow seismic reflection uniboom and echosounding profiles obtained on the shelf and upper slope areas of anamur bay turkey northeastern mediterranean were studied together with previous data on the onshore geology of the area to investigate the origin and related seismic stratigraphy of the submarine anamur canyon it was found that the main axial trend of the submarine anamur canyon is aligned with the offshore projection of the n s orientated onshore anamur thrust fault of late cretaceous senonian to early tertiary age interpretation of the distinct reflection configurations observed on the seismic profiles reveals the presence of various seismic facies comparable with the depositional sequences resulting from the relative sea level changes during the late quaternary the acoustic basement probably miocene in age is overlain by a sedimentary column mainly plio quaternary which in turn can be divided into two major seismic sequences and 12 seismic facies that show considerable variations in both their lateral and horizontal extent a palaeo deltaic environment sequence i with its typical topset and foreset facies was recognized and the corresponding deposits are interpreted to be indications of coastal deltaic progradation during late pleistocene sea level highstands or during the early phases of the last major eustatic lowering reflections of sequence ii which includes nine distinct facies are marked by onlap configuration and are believed to be marine deposits of the flandrian transgression at least four transgressive cycles are evident from the seismic profiles at 70 90 60 45 and 40 m water depths the two sequences i and ii are now covered with the most recent facies

holocene climate changes over the desert loess transition of north central china a 2 m trench section at the desert loess transition of north central china was analyzed at 2 cm intervals for grain size distribution md m and total organic carbon toc ams 14c time series of the md and toc records provides direct information on variations of the east asian monsoon climate during the last 10 000 yr md is considered to represent the wind strength and high md reflects strong winter monsoon winds toc denotes the degree of vegetation cover a function of the intensity of summer monsoon circulations from ca 10 000 to 7000 cal yr bp the climate was dominated by a strong winter monsoon and a very weak summer monsoon as indicated by high md and low toc values subsequently climatic conditions became warmer gradually from ca 7000 to 5500 cal yr bp the period between ca 5500 and 2700 cal yr bp displayed the highest toc and lowest md values over the last 10 000 yr marking a stable state of a warm humid climate i e the holocene climatic optimum of china during the interval of ca 2700 1500 cal yr bp the expansion and intensification of agrarian activities could have led to desertification and acceleration of deposition of coarse grained particles resulting in a decreased organic carbon accumulation rate however the toc during this interval still has values as high as during the episode of ca 7000 5500 cal yr bp reflecting a relatively stronger summer monsoon circulation since ca 1500 cal yr ago high amplitude fluctuations of toc that fluctuate in phase with the clay size fraction imply that the climate experienced three major oscillations with a prominent peak of enhanced summer monsoon circulation at ca 1300 cal yr ago and with two intervals of increased winter monsoon strength occurring around ca 1000 and 300 cal yr ago the md and toc records over the past 5000 yr demonstrate a good correlation with the archaeological phenological and historical records of china climate changes in the east asian monsoon region were not only related to the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but were also controlled by the pattern and intensity of the atmospheric circulation

mapping of serpentinites in the eastern desert of egypt by using landsat thematic mapper data serpentinites in the eastern desert of egypt were mapped from landsat thematic mapper tm data by using procedures that take advantage of the distinctive spectral reflectance of these rocks caused by the abundance of antigorite lizardite clinochrysotile and magnetite the method employs a threshold classifier based on three reflectance ratios 1 band 5 7 for estimating the abundance of hydroxyl bearing phases 2 band 5 1 for magnetite content and 3 the calculated value of reflectance for band 4 based on a linear interpolation between bands 3 and 5 divided by the observed band 4 reflectance the third ratio was used to identify rocks in iron bearing aluminosilicates and thereby to distinguish mafic rocks containing substantial amounts of magnetite and hydroxyl bearing phases from serpentinites the method was first successfully tested over the meatiq dome and wadi ghadir areas where serpentinites and ophiolitic melanges dominated by serpentinites have been mapped during the course of field work a tm based map was then generated the map covered about 60 000 km sup 2 in the eastern desert results demonstrate that tm data can be used with reliability to distinguish serpentinites from surrounding rocks in arid regions and to generate detailed maps over wide regions by using quantitative reproducible mapping criteria more possibilities for locating suture zones over the less well known parts of arid continents are clear less

benthic prokaryotic community dynamics along the ardencaple canyon western greenland sea abstract the ardencaple canyon emanating from the eastern greenland continental rise over a distance of about 200 km towards the greenland basin was investigated to determine the effect of enhanced down slope transport mechanisms on deep sea benthic prokaryotic communities the concentration of viable bacterial cells live dead baclight and prokaryotic incorporation rates 3 h thymidine 14 c leucine increased with increasing distance from the continental shelf multidimensional scaling mds results from terminal restriction fragment length polymorphism t rflp analysis indicated a spatial coherence between the benthic bacterial community structure prokaryotic incorporation rates water content protein concentration and the total organic matter in the sediments the community complexity in sediments at 4 5 cm depth was lower in the central parts of the channel compared with the northern and the southern levees while richness in surface sediments of all stations was similar lacking any clear indications for a recent mass sediment transport or funneled shelf drainage flows high similarities between bacterial assemblages in sediments along the canyon course may thus be governed by a combination of an ice edge induced particle flux episodic down slope and canyon guided transport mechanisms

plutonium and210pb distributions in northeast atlantic sediments subsurface anomalies caused by non local mixing abstract the depth distributions of 210 pb and 239 240 pu measured in a suite of box cores collected from water depths of 4000 5000 m in the northeast atlantic ocean exhibit pronounced subsurface maxima caused by sediment reworking by benthic infauna small scale spatial heterogeneity in bioturbation rates is indicated by large differences in tracer profiles from duplicate cores separated only by a few centimeters 210 pb and 239 240 pu activity distributions from each subcore exhibit a high degree of correlation and most tracer profiles exhibit one or more subsurface maxima one dimensional biodiffusion analogue models do not adequately simulate the principal features of this data set however an inverse conveyer belt mixing model which simulates subsurface egestion or a functionally equivalent process of surficial material which is enriched both in organic debris and radioactive tracers can reproduce the subsurface tracer maxima single event and continuous subsurface egestion models have been formulated and solved for different feeding rates and background biodiffusive fields the single event model provides a better fit to the data and in particular ensures the observed high degree of correlation between the 210 pb and 239 240 pu activity profiles regardless of the different tracer input functions the most likely candidate responsible for subsurface tracer egestion is a large infaunal worm of the phylum sipunculida which dominates the biomass below a depth of 3 cm

biological mixing intensity and rates of organic carbon accumulation in north carolina slope sediments sediment accumulation rates and biological mixing intensities were determined at three sites on the north carolina slope based on profiles of naturally occurring14c 210pb and234th the three sites all were at a water depth of 850 m with a spacing of 150 180 km between sites sediment accumulation rates increase from south to north from values of 7 cm ky 1 at site i to 160 cm ky 1 at site ii to 1100 cm ky 1 at site iii the organic carbon burial rate at these sites also increases in the northward direction from 0 65 site i to 20 site ii to 150 g corg m 2 year 1 site iii these data indicate that continental margin environment can exhibit highly variable carbon fluxes over relatively small distances on the seafloor the rate of organic carbon accumulation at site iii is one of the highest values reported for the marine environment based on these accumulation rates and dissolved inorganic carbon flux estimates from each site the seabed organic carbon preservation efficiency i e the ratio of corg accumulation rate to corg deposition rate times 100 was estimated to vary from 6 0 to 54 to 88 at sites i ii and iii respectively the14c age of organic matter in surface sediments was older at site iii 1800 years bp than at sites i and ii 800 years bp indicating that site iii receives a greater proportion of old sediment from either up slope areas or from terrigenous sources inventories of excess234th half life of 24 days were used as a tracer for particle flux covering the 100 days prior to the october 1989 july august 1990 and august 1991 cruises the mean234th inventories at the three sites were 4 7 1 9 8 4 6 3and23 1 7 3dpm cm 2 for sites i ii and iii respectively profiles of excess234th activity reveal that the biological mixing intensity is greater at site iii meandb 19 11cm2year 1 n 5 than at either site i meandb 6 0 6 2cm2year 1 n 6 or site ii meandb 4 6 5 2cm2year 1 n 9 in addition to the trend in mixing coefficients the depth of particle mixing on a 100 day time scale generally is greater at site iii than at the other two sites these observations of particle mixing intensity are consistent with the northward increase in the mean abundance of macrofauna 300microns from mean values of 9400 m 2 at site i to 21 400 m 2 at site ii to 55 500 m 2 at site iii for the three study sites off north carolina a strong correlation r2 0 99 p 0 06 exists between macrofaunal abundance and the organic carbon deposition rate an equally strong correlation r2 0 99 p 0 04 occurs between macrofaunal abundance and the234th inventories index of 100 day particle flux fine sand size glass tracer beads were dispersed at these three sites by submersible and then the field plots were sampled 1 year later the vertical distributions of beads at the three sites are consistent with a higher mixing intensity at site iii than at the other two sites but the estimated mixing coefficients generally are lower than those determined from the profiles of234th the slower mixing of the glass beads may be the result of their low food value and or their relatively large size compared to the surrounding fine grained sediments

impact of local morphology on sedimentation in a submarine canyon rov studies in eel canyon northern california u s a abstract despite existing paradigms about marine sedimentation some submarine canyons are receiving large amounts of sediment during the present highstand of sea level these modern examples can be used to unlock secrets of past canyon sedimentation however submarine canyons have complex morphology and consequently dramatic variations in sedimentary processes and deposits can occur over a range of spatial scales as small as meters to tens of meters operations from surface ships usually cannot place sampling devices on the canyon seabed with this level of accuracy the purpose of the present study was to investigate the variability of sedimentation over a range of scales in order to delineate accurate trends along and among channels at the head of a canyon sampling with the rov ventana facilitated detailed examination of microenvironments i e wall thalweg in eel submarine canyon the combination of intense sedimentation from nepheloid layers and gravity flows in a complicated morphologic system leads to clear distinctions between microenvironments as well as some recognizable and unifying trends in sedimentation inherent small scale variability due to canyon morphology is evident in narrow and steep channels at 1 m horizontal resolution cores exhibit consistent sediment fabric but laminae can differ between cores at the 10 m horizontal scale the fabric is not consistent broader more gently sloping channels reveal consistent sediment fabric at the 10 m scale in most cases physical stratification decreases along the thalwegs of channels as water depths increase in contrast channel walls generally exhibit elevated impacts of bioturbation and variable amounts of physical stratification radiochemical profiles 210pb 137cs and the predominance of physical stratification including discrete laminae with high sand content suggest that the northern entrants are receiving more sediment than their southern counterparts however 210pb profiles in this study demonstrate rapid accumulation of sediment everywhere in the head of eel canyon with the highest rates of accumulation 40 mm yr found in the channel thalwegs in thalwegs evidence from sedimentary structures e g erosional bases cross bedded sand layers demonstrates that gravity flows occur frequently many times each year and have been linked by other investigations to storm impacts on the adjacent continental shelf on decadal timescales these processes are temporarily depositing sediment in the head of the canyon which is removed over longer timescales probably as larger gravity flows triggered by earthquakes the radiochemical and sedimentological data collected at the base of entrant channels confirm that modern sediment is moving to deeper portions of the canyon

a long square barrel gravity corer for sedimentological and geochemical investigation of fine grained sediments abstract large volume undisturbed sediment cores 3 m long are obtained using a modified gravity corer the corer is square in cross section 12 7 12 7 cm and is designed to facilitate acquisition and subsampling of fine grained sediments sedimentological and geochemical data demonstrate that the modified gravity corer obtains undisturbed cores and preserves the sediment water interface

modern sediment dispersal and accumulation in quinault submarine canyon a summary abstract quinault canyon off the coast of washington intersects the dispersal path of modern columbia river sediments on the continental shelf study of the dynamics dispersal and accumulation of these deposits in the canyon indicates that no systematic down canyon transport occurs rather sediment dispersal is controlled primarily by the regional flow pattern suspended particulate matter is resuspended on the shelf primarily during winter storm events and advected northward as a bottom nepheloid layer bnl over the shelf cross canyon advection produces an intermediate nepheloid layer inl over the upper slope and canyon from which the suspended particulate matter settles rapidly probably in amorphous aggregates rapid short term deposition 10 1 g cm 2 yr 1 and enhanced modern accumulation generally 10 10 2 g cm 2 yr 1 are confined to the upper canyon 1600 m where fluctuations in deposition rates and grain size are related to specific shelf sediment resuspension events in the lower canyon 1600 m accumulation is slow and temporally uniform

significance of primary hilltop loess in reconstructing dust chronology accretion rates and sources an example from the negev desert israel 1 although high latitude loess sequences have been studied extensively for reconstructing past climates loess in desert margins has been mostly overlooked moreover many low latitude loess studies have focused on secondary reworked sequences for which paleoclimatic inferences are complicated owing to postdepositional processes acting under local control in this respect the spatial distribution of the loess and its different types are crucial in this study we differentiate primary and secondary loess using remote sensing and field criteria we present remote sensing and geographic information system procedures for mapping loess distribution in general and for identifying pristine hilltop loess sequences in particular then we present the mineralogical and textural analyses combined with optically stimulated luminescence ages of one such primary hilltop loess sequence in the negev desert that show that the late pleistocene negev loess started accumulating at 95 ka much earlier than previously proposed 70 ka it was preceded by a previously unknown middle pleistocene period of loess formation at 180 130 ka the ages also suggest that the threshold of dust accretion rate needed for loess formation is 0 02 mm a 1 30 g m 2 a 1 a factor of 2 or more lower than previously thought 0 04 to 1 0 mm a 1 our results also provide insights into causes of late pleistocene loess accretion and its close association with regional dune field activity the methodology for mapping the loess distribution may potentially be generalized to help understanding loess formation in other more remote desert areas

the geochemistry of fallout plutonium in the north atlantic i a pore water study in shelf slope and deep sea sediments abstract the distribution of fallout plutonium between pore waters and sediments in the northwest atlantic is examined in order better to define the potential for pu migration from and within marine sediments along a transect of seven cores collected between woods hole and bermuda the solid phase 239 240pu 210pbex and 137cs results do not suggest that any of these tracers are preferentially mobile within the cores pore water pu activities appear to be controlled primarily by the distribution of pu in the solid phase with an operationally determined distribution coefficient kd in the range of 0 2 23 104 there is a trend in the kds along the transect with higher values in the 104 105 range on the shelf and slope to lower values 239 240 pu cm 2 year sediment mixing models are not significantly altered by the inclusion of pu diffusion terms since the pore water terms are so small relative to typical sediment mixing rates

environmental changes recorded in the upper pleistocene along the desert boundary southern israel abstract most paleoclimatic studies in the middle east and africa suggest large changes in climate during the last 100 000 years a specific area of interest is the record of environmental changes along the desert boundary this study was conducted in such a boundary in the northern negev israel sedimentological evidence and the 18 o 16 o 13 c 12 c and 14 c content of carbonate nodules formed within the sediments were examined data obtained in two study areas 35 km apart suggest that while soil formation was occurring in the northwest only fluviatile and lake deposition occurred to the southeast the results of this study suggest that during the late pleistocene the boundary was much steeper than in the holocene the period before 35 000 yr b p periodically was wetter than at present with freshwater lakes and soil covered by c 3 plants a change to a more arid condition occurred during the last glacial maximum in europe 18 000 yr b p a second wet period not as wet as the earlier one occurred with the retreat of the glaciers in europe at this time decrease of loess supply and formation of the top soil occurred at both study locations in the southern area this wet period ended with highly evaporated sabkha deposits about 11 000 yr b p the holocene record suggests progressive aridity which was accompanied in the southeast location by covering the area with dunes

accumulation of modern sediment in quinault submarine canyon abstract twenty box cores have been studied from quinault submarine canyon a major pathway between the washington continental shelf and the deep sea for silt and clay originating from the columbia river sediment accumulation rates on a 100 yr time scale are calculated from profiles of excess 210pb and of 137cs accumulation rates decrease with increasing distance downcanyon from 14 10 2 g cm 2 yr 1 in the upper canyon lower head to 3 10 2 g cm 2 yr 1 in the lower canyon in the upper canyon lower head channel floor areas have a higher mean accumulation rate 12 10 2 g cm 2 yr 1 than channel wall areas 5 10 2 g cm 2 yr 1 the difference in accumulation rate between channel floor and channel wall areas indicates preferential accumulation i e focusing in topographic lows the decrease in accumulation rate from high rates in the channel floors of the upper canyon to low rates in the lower canyon may be caused by progressive depletion of a nepheloid layer source and or may be an artifact of sediment focusing in the upper canyon the silty clay and clayey silt accumulating in the canyon show no significant trend in grain size or clay mineralogy with depth in cores or with distance downcanyon the lack of sorting probably results from the transport of sediment in aggregate form with a nearly random distribution of size and mineralogy within aggregates quinault canyon is accumulating approximately 5 5 10 5 mt of sediment yr 1 the lithogenic component 64 accounts for 1 4 of the columbia river discharge similarity of sediment trap deposition rates including storm events and 210pb accumulation rates indicates that the vertical flux is a major input of sediment to quinault canyon and that storms are important in the accumulation of sediment on a 100 yr time scale

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

210pb geochronology of flood events in large tropical river systems floodplain sedimentation removes particles from fluvial transport and constructs stratigraphic records of flooding biogeochemical sequestration and other aspects of the environmental history of ri

the fossil record of igneous rock abstract a growing awareness of life in deep igneous crust expands our appreciation for life s distribution in the upper geosphere through time and space and extends the known inhabitable realm of earth and possibly beyond for most of life s history until plants colonized land in the ordovician the deep biosphere was the largest reservoir of living biomass this suggests that deep crustal habitats played an important role in the evolution and development of the biosphere paradoxically the paleo perspective of deep life has been largely neglected in the exploration of the deep biosphere as well as in paleontology as a whole here we review the collective understanding of the fossil record in igneous crust with the aim to highlight a rising research field with great potential for substantial findings and progress in the near future we include new results that emphasize the importance of direct or indirect dating of fossils and introduction of new techniques into the field currently an incoherent record of morphological fossils and chemofossils stretching from present to 2 4 ga implies the presence of an abundant and rich yet largely unexplored fossil record further investigations of deep paleo environments will most certainly result in substantial insights into the distribution and development of biospheres throughout life s history the early evolution of prokaryotes and eukaryotes and earth s early biogeochemical cycles we emphasize the fossil record of igneous rock to give it the same status as the fossil record in sedimentary rocks and to implement fossil investigations as standard procedures in future international drilling campaigns

ancestral head of wilmington canyon a 12 channel seismic reflection survey over parts of the head of wilmington canyon and the surrounding shelf revealed four major buried valleys and many small channels the data indicate that the ancestral delaware river valley was the most recent of a series of valleys to enter the canyon from the west the head of wilmington canyon probably was eroded and then filled at various times from late miocene to late pleistocene time thick sedimentary sequences indicate a sediment supply from both the north and west a large buried valley entering the canyon from the north was not mapped with the data presented here but it is possible that such a valley exists this is one of the first documentations of the long history of erosion of the united states east coast canyons

clay size minerals as indicators of modern sedimentary processes in submarine canyons application to the wilmington canyon system recent sedimentary processes in the wilmington canyon area u s east coast are interpreted using high resolution profiles of clay size minerals from sediment cores collected using d s r v alvin and the r v atlantis ii modern surficial sediments 100 years old of the wilmington canyon system contain uniformly high relative abundances of illite 55 65 and chlorite 25 35 where these assemblages occur downcore relatively continuous hemipelagic sedimentation is inferred anomalously high concentrations of expandable minerals to 58 and kaolinite to 15 occur at discrete intervals within several cores from the wilmington canyon area these anomalous intervals are bounded by sediments deposited within the past 100 years previous studies of dsdp sites along the u s atlantic margin revealed relatively high abundances of montmorillonite and kaolinite in late cretaceous tertiary strata similar signatures in the wilmington canyon system probably indicate that these sediments are derived from late cretaceous tertiary outcrops on the canyon walls during episodic sediment transport events intervals rich in detrital clay size minerals quartz feldspar pyroxene and amphibole also occur in cores from the wilmington canyon area and are probably derived from pleistocene sediments which were delivered to the continental slope in great quantities during periods of lower sea level the presence of distinct mineral zonations on the floor of the wilmington canyon suggests that local erosional forces rather than large scale turbidity currents probably dominate the canyon area at present surficial sediments from the intercanyon area northeast of wilmington canyon reveal a downslope decrease in illite and corresponding increase in expandable minerals suggesting an increased contribution of pre holocene sediments derived from erosion of the slope

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

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