observations and geologic significance of marine snow in a shallow water partially enclosed marine embayment because of their fragile nature marine snow sized aggregates aggregates 0 5 mm in longest dimension have been generally overlooked in shallow water environments we report in situ observations and measurements in cape lookout bight north carolina that indicate that marine snow is probably always present and usually abundant underwater photographs show that over a period of hours marine snow varies in size from 8 to 71 10 5 ml and in abundance from 291 to 489 l 1 but that such variations in size and abundance are not obviously related to tide total suspended sediment concentration or current speeds in the 10 to 20 cm s 1 range photographs and concurrent transmissometer records suggest that variations in size shape and abundance of marine snow may be sufficiently great that particulates do not remain optically constant and thus affect beam transmission irrespective of total suspended sediment concentration levels marine snow is significant geologically in that it has high settling rates 50 to 200 m per day and may be the package in which much of the vertical mass flux occurs if so it offers an explanation for the high accumulation rates observed in coastal and estuarine fluid mud deposits

geochemistry and provenance of the middle ordovician austin glen member normanskill formation and the taconian orogeny in new england the austin glen member of the upper middle ordovician normanskill formation is a sandstone shale ysch succession deposited in the foreland of the taconian orogen petrographic major and trace element and nd pb isotopic data provide substantial constraints on its provenance lack of k feldspar and paucity of plagioclase in addition to the dominance of sedimentary rock fragments indicate that the source was dominated by recycled sedimentary components major and trace element data support this conclusion and indicate that the provenance of both shales and sandstones was the same no evidence of an ophiolitic or volcanic component was observed interpretation of nd isotopic characteristics are complicated by a partial resetting of the nd isotope system at about the time of sedimentation but indicate that the provenance of the austin glen member had a long term history of light rare earth element lree enrichment average tdm 1a8 ga furthermore nd isotopic compositions are extremely homogeneous end 8a1 0a6 1 s d n 23 at 450 ma the approximate depositional age indicating either a single source or very well mixed sources 207pb 204pb ratios are variable but within the range of pb isotopic compositions typically described as grenvillian the range of 207pb 204pb is greater than expected for the range of 206pb 204pb and suggests an additional component of pb possibly introduced during diagenesis the immediate source of the austin glen member may have been the accretionary prism that developed as older sediments of the laurentian margin were scraped off the basin oor incorporated within the accretionary prism and shed into the basin no evidence indicating the arrival of an undifferentiated island arc or continental fragment during the taconian orogeny has been found the data acquired during this study can be explained almost exclusively by grenville province source components but with possible additional contributions from older laurentian terranes and late proterozoic rift volcanics that are not readily quanti ed but likely to have been minor accordingly we conclude that the taconian orogeny in new england involved either 1 a continental arc that involved exclusively laurentia 2 collision of a continental block with identical geochemical characteristics as laurentia or 3 essentially no detritus from any exotic colliding block island arc or continental fragment reached the foreland basin at the time of austin glen deposition

effect of regional topography and hydrology on the lacustrine isotopic record of miocene paleoclimate in the rocky mountains drummond c n wilkinson b h lohmann k c and smith g r 1993 effect of regional topography and hydrology on the lacustrine isotopic record of miocene paleoclimate in the rocky mountains palaeogeogr palaeoclimatol palaeoecol 101 67 79 oxygen isotopic compositions of upper miocene 9 2 m y lacustrine limestone from northwestern wyoming range from 21 5 to 35 2 0 pdb and are the lightest yet reported for a non marine carbonate sequence these values require that lake water was greatly depleted in 180 relative to modern meteoric precipitation and indicate that most inflow was sourced as meltwater from glaciers in the adjacent gros ventre range assessment of climatic factors influencing the isotopic composition of global meteoric water indicates either that nearly all of miocene precipitation in the southern rocky mountains was derived from large lake systems in the snake river plain and northern great basin to the west or that gros ventre catchment elevations were up to 2300 m higher than at present because erosion rates in modern alpine regions suggest that subaerial denudation could only account for up to 1200 m of post miocene elevation reduction any additional lowering must reflect the influence of post laramide epeirogeny during basin and range extensional tectonism lacustrine isotopic data therefore provide boundary conditions on the timing and magnitude of changes in late cenozoic paleoclimate topography hydrology and tectonism in the western wyoming portion of the rocky mountains

lead 210 sediment geochronology in a changing coastal environment abstract sediment accumulation rate studies utilizing excess 210 pb and 137 cs were conducted as part of recent investigations of biogeochemical cycling at a single site in cape lookout bight a rapidly changing coastal basin on the outer banks of north carolina u s a cores three meters in length reveal a depositional history for the bight interior characterized by a gradual transition in texture from coarse grained to fine grained material over the period 1946 1979 this transition is controlled by progressive enclosure of the bight by an active northerly migrating recurved spit the textural gradation is periodically interrupted by layers of well sorted sand associated with major storm events lead 210 data indicate that the upper meter of the sediment has accumulated at a rate of 3 35 to 4 71 g cm 2 yr 1 or approximately 8 4 to 11 8 cm yr 1 at o 0 84 below 120 cm depth dilution of clay and silt by low activity sand necessitates correction of the 210 pb profile in order to establish a geochronology grain size 210 pb distribution measurements at three depths reveal that the specific activity dpm g 1 of clay is 3 2 times that of silt and 24 7 times that of sand corrections of bulk sediment excess 210 pb activities based on these measurements lead to dates for textural changes which are consistent with charted changes in basin morphology and major storm events sixteen 137 cs measurements between 33 241 cm depth reveal a peak activity at 105 115 cm and indicate a minimum sedimentation rate of approximately 2 7 g cm 2 yr 1

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

mixing of siliciclastic and carbonate sediments in shallow shelf environments the inhibiting effect that siliciclastic material has on carbonate secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form however many modern and ancient shelf deposits contain a spectrum of sediments that are of mixed composition the processes responsible for this mixing can be grouped into four categories 1 punctuated mixing where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another 2 facies mixing where sediments are mixed along the diffuse boundaries between contrasting facies 3 in situ mixing where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates and 4 source mixing where admixtures are formed by the uplift and erosion of nearby carbonate source terranes the allochemical constituents of mixed sediments are both coralgal and foram mollusc in composition the foram mollusc assemblage is the most common because of the effects of increased turbidity unstable substrates and the clogging of filter feeding mechanisms associated with a siliciclastic influx

measurement of size and settling velocity of suspended aggregates on the northern california continental shelf abstract a high resolution video camera attached to a miniature sediment trap was used to make time lapse images of suspended aggregates settling through the water column the video trap system was placed 2 m above the seabed in the strataform study area off eureka california and was programmed to take a 7 second time sequence of settling particles every 6 h over a 4 month period the camera field of view within the trap is 15 mm and the minimum particle resolution is approximately 130 m data analysis was carried out with a video frame grabber and digital imaging software to determine the particle size shape and settling velocity results of the first deployment of this system september 1995 show that particle sizes elliptical nominal diameter determined from the video images ranged from 130 to 740 m with a modal size of 300 m the average form factor ratio of short to long semi axis of the aggregates was 0 71 measured settling velocities varied from 0 09 to 8 13 mm s in terms of weight percent or mass the median size of the aggregate distribution is 600 m analysis of settled particles collected from the sediment trap shows disaggregated or component grains ranging from 1 0 to 63 m with a modal size of 26 m and a median size of 11 m additionally an analysis was carried out to separate the relative importance of particle shape and excess density on settling velocity and these results were compared to observations using the equations for settling velocity of spheres and prolate spheroids and substituting published relationships for size versus excess density into these equations the settling velocity for combinations of shape and excess density has been calculated results show that differences between sphere and prolate spheroid with major axis both parallel and perpendicular to flow approximations caused less than a 13 difference in computed settling velocity in contrast the various size excess density relationships used to compute settling velocity caused order of magnitude deviations from measured values in all cases however the approximations of settling velocity for aggregates provide a significantly better fit to data than approximations based on disaggregated sediment size distribution

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

sedimentation in the albemarle pamlico lagoonal system synthesis and hypotheses abstract relative to its size and in terms of its sedimentary processes the albemarle pamlico lagoonal system is one of the least studied coastal lagoons in the united states a synthesis of the current knowledge about sedimentation in the albemarle pamlico system is presented based on archived data published over the last 30 years and new unpublished data collected over the past two years the literature reflects considerable past research effort on sediment grain size and mineralogy but very little on sediment dynamics or flux of suspended particulate material the physiographic complexity of the system which includes barrier islands a deep central basin four river systems and extensive fringing embayments does not appear to be reflected in the form of sedimentologic complexity in general the surficial cover of sediments ranges from medium sands in the inlets and on the shoals of the outer banks to fine silts and organic rich clays in the central basin and embayed river mouths and channels the transition zones from sands to muds are typically sharp and are usually related to bathymetry it is concluded that 1 parts of the albemarle pamlico lagoonal system may have high sedimentation rates relative to rates of sediment input and that rapid vertical flux by large aggregates offers an explanation for the fluid mud deposits that would otherwise be absent 2 fine grained sediments that escape the estuarine sediment trap are confined to pamlico sound by the outer banks barrier islands and are simply recycled until finally coming to rest in the deep basin 3 short term advective processes are secondary to longer term processes such as sea level rise and barrier island migration in the net advection of albemarle pamlico sediments and 4 at the present rate of terrigenous sediment input and relative sea level rise the albemarle pamlico lagoonal system will never reach a sediment filled state

on gulf stream variability and meanders over the blake plateau at 30 n current and temperature variability of the gulf stream at 30 sup 0 n was observed with a subsurface array of current meter moorings from august 1980 to october 1981 energetic current fluctuations in the 2 14 day period band accounted for 45 70 of the total observed variability flow perturbations in the cyclonic shear zone tended to have a cyclonic sense of rotation and were 180 sup 0 out of phase from anticyclonic flow perturbations within the anticyclonic shear region these fluctuations appear to result from northward propagating wave like meanders of the gulf stream axis the fluctuations do not appear to be directly related to local wind forcing observations of near bottom flow on the blake plateau east of the gulf stream showed periods of prolonged southward currents lasting up to 40 days with speeds in excess of 30 cm s sup 1 the mean flow was also southward due to these strong events the source of the southward flow is unknown it may be connected to cold core eddies that are not detectable in the surface with remote sensing or possibly a remnant of the southward undercurrent that has been observed beneath the gulf stream off cape hatteas and on the deep slope of the blake escarpment

characterization of lacustrine mixed fine grained sedimentary rocks using coupled chemostratigraphic petrographic analysis a case study from a tight oil reservoir in the jimusar sag junggar basin abstract mixed deposits are sediments consisting of external clastic epiclastic or terrigenous intrabasinal components and pyroclastic components the mixture comprising variable amounts of the three components is defined as mixed sedimentary rocks the permian lucaogou formation p2l in the jimusar sag of the junggar basin is a promising tight oil target in western china the fine grained mixed sedimentary rocks of which are rich in organic matter om and two sweet spot intervals with relatively high porosity however the sediment composition provenance and deposition environmental settings have not been studied in detail in this study coupled chemostratigraphic petrographic analysis were used to reconstruct their depositional environments the results show that the fine grained sedimentary rocks have three major sediment sources external clastic input terrigenous clastics intrabasinal autochthonous to parautochthonous components carbonates siliceous skeletal debris and om and pyroclastic input main lithofacies include siltstone fine sandstone mudstone dolomite and tuffite the silt sandstones were mainly sourced from rocks with calc alkaline composition while the tuffaceous sedimentary rocks were sourced from high k calc alkaline rocks elemental proxies suggest that the carbonate rocks were generally deposited under warm and arid conditions whereas the fine grained clastic sediments were deposited under relatively humid conditions the muddy or silty tuffaceous mixed rocks were deposited under relatively reducing conditions compared with carbonates and sandstones variations of lithofacies and om accumulation of different intervals reflect changing deposition environmental settings and the frequently altered high toc content rocks and good reservoirs are benefit for tight oil formation the work may provide some useful insights and serve as a reference for studying other mixed fine grained sedimentary rocks and tight oil plays in similar lacustrine basins elsewhere

pore types and pore size distributions across thermal maturity eagle ford formation southern texas pore types pore size and pore abundance vary systematically across thermal maturity in the eagle ford formation maverick basin southern texas scanning electron imaging of 20 samples from four wells is used to assess the complex response of pores to chemical and mechanical processes entailing both destruction of primary porosity and generation of secondary pores primary mineral associated pores are destroyed by compaction cementation and infill of secondary organic matter whereas secondary pores are generated within organic matter om destruction of primary pores during early burial to 0 5 occurs by compaction of ductile detrital om and clays and to a lesser degree as a result of cementation and infill of secondary om larger pores are associated with coccolith debris the dominant om is spatially isolated detrital om stringers porosity is volumetrically dominated average 6 2 by relatively large mostly interparticle mineral associated pores median size 51 6 nm 0 000002 in detection limit near 3 4 nm 0 00000012 0 00000015 in at low maturity porosity and pore size correlate directly with calcite abundance and inversely with om volumes at higher maturity further destruction of primary pores occurs through cementation secondary om infill and greater compaction mineral associated pores are present at high maturity 1 2 1 3 but are smaller median size 30 2 nm 0 0000011 in and less abundant average of 2 5 than at low maturity a large portion of om within high maturity samples is diagenetic in origin and has pervaded into primary pore space coating cement crystals and filling intraparticle pores substantial mineral associated porosity is locally present in samples where incursion of primary pore space by secondary om has not occurred abundant secondary porosity is generated as om matures into the wet gas window porosity in most high maturity samples is volumetrically dominated average of 1 3 by smaller om hosted pores median size 13 2 nm 0 00000051 in

role of large particles in the transport of elements and organic compounds through the oceanic water column abstract during the past decade data from a variety of sources have been obtained which show conclusively that the relatively rare large particles sinking through the water column are responsible for the majority of the downward vertical mass flux in the sea this finding has important implications for understanding the transfer distribution and fate of elements and organic compounds in marine waters the large 100 m detrital particles responsible for vertical flux are primarily biogenic and range in size and composition from small discrete fecal pellets and plankton hard parts to large amorphous aggregates or snow which contain both organic and inorganic constituents depending on size shape and density these particles sink at rates ranging from 1000 m day 1 several methods have been developed for sampling these particles of which in situ sediment trapping has probably furnished the most comprehensive qualitative and quantitative information on the role large particles play in material transport flux studies have highlighted the importance of marine heterotrophs in packaging fine suspended particulate matter into large rapidly sinking particles which accelerate the movement of incorporated materials to depth large particle production via biological packaging is not restricted to the euphotic zone but can occur at all depths and information is now accruing on rates of production of large particles in the water column chemical analyses of sedimenting particles collected in sediment traps and those sampled by other means have allowed quantifying vertical fluxes and residence times of elements radionuclides and organic compounds natural and anthropogenic in various oceanic regimes pertinent studies dealing with the above aspects are reviewed and several areas for future research are suggested

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

rare earth element mobility in the oceanic lower sheeted dyke complex evidence from geochemical data and leaching experiments hydrothermally altered rocks from the base metal depleted reaction zone in the lower sheeted dyke complex odp hole 504b show significant losses of rare earth elements ree in extensively altered domains alteration patches while very similar in major element composition and alteration mineralogy the alteration patches have up to 50 lower ree concentrations than the surrounding weakly altered diabases in order to test if there is a dependence of ree mobility on the alteration history we carried out leaching experiments on a weakly altered diabase and an adjacent alteration patch the leaching experiments are used as a probe to identify the hosting phases of major and trace elements before and after alteration they are not designed to simulate natural alteration processes major element compositions of the leaching solutions show that small amounts 9 to 14 of the rocks and similar proportions of plagioclase amphibole and chlorite were dissolved from both rock types in contrast to the major elements up to 100 of the ree could be leached from the strongly recrystallised alteration patch after 20 h all leaching solutions were light ree enriched and had negative eu anomalies compared to the host rock geochemical modelling suggests that mainly interstitial material formerly late stage magmatic liquids and probably some apatite are the main ree sources in the rocks affected during experimental leaching dissolution of plagioclase amphibole clinopyroxene and chlorite cannot explain the ree compositions of the leachates the higher ree leachability of the heavily altered rock suggests that the extensive hydrothermal alteration resulted in a complete redistribution of the ree from lattices of the magmatic minerals to the grain boundaries of secondary minerals this can explain the marked increase in ree accessibility during ongoing alteration which finally led to ree depletions in the highly altered rock we propose that late stage interstitial material provides the most important ree source of rocks in the oceanic crust this interpretation is in contrast to a model by klinkhammer et al klinkhammer g p elderfield h edmond j m mitra a 1994 geochemical implications of rare earth element patterns in hydrothermal fluids from mid ocean ridges geochim cosmochim acta vol 58 pp 5105 5113 who suggested that the similarity in the ree patterns of plagioclase and that of hydrothermal vent fluids is a result of chemical exchange between plagioclase and hot fluids in the ocean crust our leaching results indicate that although dramatic dissolution of plagioclase occurred it did not control the ree patterns of the leachates moreover ree patterns inferred for fluids that mobilised ree from the highly altered rock are different from those of vent fluids we therefore propose that the characteristic ree pattern of vent fluids may result from differences in aqueous chloride complex stabilities sorption controlled ree fractionation during fluid migration and mineral precipitation in the discharge zone

fossil whale preservation implies high diatom accumulation rate in the miocene pliocene pisco formation of peru diatomaceous deposits in the miocene pliocene pisco for mation contain abundant whales preserved in pristine condition bones articulated or at least closely associated in some cases in cluding preserved baleen the well preserved whales indicate rapid burial the 346 whales within 1 5 km 2 of surveyed surface were not buried as an event but were distributed uninterrupted through an 80 m thick sedimentary section the diatomaceous sediment lacks repeating primary laminations but instead is mostly massive with irregular laminations and speckles there is no evidence for bioturbation by invertebrates in the whale bearing sediment cur rent depositional models do not account for the volume of diato maceous sediments or the taphonomic features of the whales these taphonomic and sedimentary features suggest that rapid burial due to high diatom accumulation in part by lateral advection into pro tected shallow embayments is responsible for the superb preser vation of these whales leading to a higher upper limit on phyto plankton accumulation rates than previously documented

sedimentology and high frequency sequence stratigraphy of a forearc extensional basin the miocene caleta herradura formation mejillones peninsula northern chile abstract facies and sequence stratigraphic interpretation for the 380 m thick caleta herradura formation miocene are presented based on detailed and comprehensive outcrop data from the caleta herradura half graben mejillones peninsula northern chile the caleta herradura formation contains an array of lithofacies comprising sandstones sandy mudstones diatomites and breccio conglomerates that are interpreted as the products of inner shelf to non marine depositional settings complete exposure allows for recognition of a number of distinct and laterally persistent key stratal surfaces that permitted the identification of twenty five high frequency meter to tens of meters scale sequences based on their internal organization two main motifs of such unconformity bounded depositional packages can be distinguished deepening and deepening to shallowing upwards transgressive and highstand systems tracts were resolved based on such facies stacking patterns the origin of sequences is difficult to decipher and remains somewhat uncertain however several lines of direct and indirect evidence constrain interpretations for both the sequence architecture and bounding unconformities and help to discriminate between the various mechanisms that may have driven their development in essence these demonstrate that neither tectonically driven sea level oscillations nor climatically induced changes in sediment supply can adequately explain the distinctive features of unconformities and the facies architecture of sediments they delimit instead these high frequency changes in relative sea level are best explained as a consequence of glacio eustatic oscillations the contemporaneous deep ocean proxy records appear to support a causal link between the observed stratigraphic cyclicity and glacio eustatic changes in sea level due to modulation of short term milankovitch scale events by longer period astronomical variations however the type of astronomical forcing remains elusive hindered by lack of adequate age controls and a poor understanding of pacing mechanisms of high frequency climate changes during the middle to late miocene

inssev an instrument to measure the size and settling velocity of flocs in situ abstract an instrument has been developed to observe the settling of individual flocs in turbid water in order to measure size and settling velocity spectra of estuarine cohesive suspended sediments inssev in situ settling velocity instrument is bed mounted and comprises a computer controlled decelerator chamber that collects a sample of water from which some of the suspended matter is allowed to enter the top of a settling column the settling flocs are viewed using a miniature video system subsequent analysis of video tapes can provide direct measurements of size and settling velocity of individual flocs down to 20 m from this information floc density can be estimated the main feature of the instrument is its ability to video flocs in situ irrespective of the concentration in the estuary with as little disturbance to their hydrodynamic environment as possible preliminary field testing in the tamar estuary has given useful results in flow velocities up to 0 4 m s 1 and in concentrations up to 200 mg 1 1 the video recordings show large numbers of low density flocs with multiple structures linked by fine organic fibres

geochemistry of fine grained clastic sedimentary rocks of the neoproterozoic ikorongo group ne tanzania implications for provenance and source rock weathering abstract the neoproterozoic ikorongo group which lies unconformably on the late archaean nyanzian supergroup of the tanzania craton is comprised of conglomerates quartzites shales siltstones red sandstones with rare flagstones and gritstones and is regionally subdivided into four litho stratigraphic units namely the makobo kinenge sumuji and masati formations we report geochemical data for the mudrocks i e shales and siltstones from the ikorongo basin in an attempt to constrain their provenance and source rock weathering these mudrocks are compositionally similar to paas and ps indicating derivation from mixed mafic felsic sources however the siltstones show depletion in the transition elements cr ni cu sc and v and attest to a more felsic protolith than those for paas and ps the chemical index of alteration cia 52 82 reveal a moderately weathered protolith for the mudrocks the consistent ree patterns with lree enriched and hree depleted patterns la yb cn 7 3 38 3 coupled with negative eu anomalies eu eu 0 71 on average which characteristics are similar to the average paas and ps illustrate cratonic sources that formed by intra crustal differentiation geochemical considerations and palaeocurrent indications suggest that the provenance of the ikorongo group include high mg basaltic andesites dacites rhyolites and granitoids from the neoarchaean musoma mara greenstone belt to the north of the ikorongo basin mass balance calculations suggest relative contributions of 47 42 and 11 from granitoids high magnesium basaltic andesites and dacites respectively to the detritus that formed the shales corresponding contributions to the siltstones detritus are 53 43 and 4

the structure of shelf and gulf stream motions in the georgia bight abstract the structure of the current and temperature fields along 30 n over the mid shelf and western blake plateau in the south atlantic bight has been investigated by combining two moored instrument experiments in the summer of 1981 the shelf moorings were part of the second georgia bight experiment gabex ii and the gulf stream mooring data on the blake plateau have been described by lee and waddell 1983 empirical orthogonal functions eof in the frequency domain are used to extract shelf and gulf stream coherent current and temperature fluctuations in the two to 14 day period band three modes are found of which the first two are interpreted as gulf stream meander and frontal eddy circulations the difference between them is chiefly in the shelf motions the first mode is primarily restricted to the shelf edge whereas the second mode penetrates to the 40m isobath the third mode dominates at mid shelf and is the only mode that shows strong coherence with the windstress and local sea level fluctuations the relationship of the modes to the occurrence of mid and inner shelf cold sub surface intrusions generated by shelf edge gulf stream frontal eddies is examined all three modes are found to play a role in the initiation growth and decay of these structures

temperature and velocity structure of the gulf stream northeast of cape hatteras modes of variability thirty five expendable bathythermograph sections and 10 pegasus velocity sections taken approximately normal to the gulf stream northeast of cape hatteras were used to examine the variability of the current s structure the regridded profiles were superimposed in a stream coordinate system such that the temperature variance associated with the superposition was minimized the resulting variance field was examined using empirical orthogonal functions the temperature variability is heavily weighted by seasonal warming hence the following results exclude temperatures from the upper 200 m the first mode 48 of the variance is due to a deepening of the thermocline relative to the mean on the offshore side of the gulf stream and a shoaling on the inshore edge associated with a change of geostrophic velocity and baroclinic transport the amplitudes of this transport mode indicate a slight downstream increase in baroclinic transport 2 per 100 km and a seasonal modulation 5 sverdrups rms that peaks in may june the second temperature mode below 200 m 13 21 of the variance is associated with a change in horizontal shear a vorticity mode and is positively correlated with measured path curvature and layer thickness the directly observed pegasus velocity sections were combined with corresponding temperature sections to compute their joint empirical modes the dominant combined mode has a thermocline structure change as in the transport mode that is coupled with an increase in alongstream velocity and for levels above the main thermocline an inflow from both sides toward the center both temperature and velocity data indicate that high transport in the gulf stream is associated with lateral displacement offshore of its mean position

trace elements as palaeoenvironmental markers in strongly mature hydrocarbon source rocks the cretaceous la luna formation of venezuela abstract the late cretaceous la luna formation is the main hydrocarbon source rock formation in venezuela in the lake maracaibo area the formation shows a steep maturation gradient affecting sedimentary organic matter om and clay minerals related to local burial history and thrusting events the influence of the gradient is examined through geochemical organic and inorganic and mineralogical investigations carried out on samples from five cored boreholes in the maracaibo basin the analytical procedure comprises rock eval pyrolysis vitrinite reflectance measurement palynofacies observation major and trace element content determination performed on bulk rock samples or after a sequential leach protocol dop calculation and the examination and analysis of clay mineral assemblages the maturation gradient seems to have had no effect upon the distribution of the trace elements referred to as proxy indicators for palaeodepositional conditions of om rich sediments ba p v mo ni co cu cd cr and mn consequently trace elements appear to be reliable palaeoenvironmental markers they indicate that during the la luna fm deposition the water column must have had variable conditions with high primary production near the surface and the correlative development of euxinic conditions at the bottom this provides further arguments for an upwelling system affecting the northern platform of south america during late cretaceous time the relative scarcity of reactive iron in the depositional environment must have taken an active part in a process involving sulphur and acting on the environmental conditions as well as on om vulcanisation this process favours aliphatic om storage and may be relevant for many other om rich facies or hydrocarbon source rocks

rare earth and major element geochemistry of eocene fine grained sediments in oil shale and coal bearing layers of the meihe basin northeast china abstract the meihe basin is a paleogene pull apart basin long flame coal lignite and oil shale are coexisting energy resources deposited in this basin ninety seven samples including oil shales coals brown to gray silt and mudstone have been collected from the oil shale and coal bearing layers to discover the rare earth element geochemistry the total ree contents of oil shales and coals are 137 256 g g and 64 152 g g respectively the chondrite normalized patterns of oil shales and coals show lree enrichments hree deficits negative eu anomalies and negligible ce anomalies the chemical index of alteration cia as well as some trace elements is often used to reflect the paleoenvironment at the time of deposition the results show that fine grained sediments in both layers were deposited in dysoxic to oxic conditions and in a warm and humid climate and coals were deposited in a warmer and more humid climate than oil shales oil shales and coals are both in the early stage of diagenesis and of terrigenous origin besides diagrams of some major trace and rare earth elements show that the fine grained sediments of both layers in the meihe basin are mainly from the felsic volcanic rocks and granite and that their source rocks are mostly deposited in the continental inland arc setting the analysis of major elements shows that si al k and ti in both layers are found mainly in a mixed clay mineral assemblage and that si is also found in quartz sodium occurs primarily in clay minerals whereas ca is found mainly in the organic matter in the coal bearing layer iron is mainly controlled by organic matter rather than detrital minerals in contrast in the oil shale bearing layer neither detrital minerals nor organic matter exert a control on the iron content analyzing the relationship between rare earth elements and major elements shows that rees in the oil shales and the coals are both of terrigenous origin and are mainly controlled by detrital minerals rather than by organic matter in both layers rees have no relationship with fine grained phosphates and during the weathering process the rees were not very mobile and were resistant to fractionation

kinematics and correlation of the surface wind field in the south atlantic bight surface winds observed at charleston south carolina and at an offshore buoy located some 300 km to the east of charleston are analyzed to determine operational transformations for estimating the offshore winds from the coastal winds both the statistics describing the wind field at each station along with those describing the correlation between stations are found to be seasonally modulated ensemble averaged by season transfer functions computed by using the first 3 years of available data are applied to a fourth independent data year for assessing their predictive utility the transfer functions and predictability are both seasonally modulated and the transformation matrix is nondiagonal each offshore wind velocity component depends upon both coastal components

gulf stream fluctuations and meanders over the onslow bay upper continental slope abstract gulf stream fluctuations observed over the 200 and 400 m isobaths off onslow bay north carolina have a prominent weekly time scale the principal fluctuations observed during the 4 month winter experiment are consistent with webster s 1961a description of downstream propagating skewed lateral meanders of the gulf stream over the upper continental slope the subtidal velocity fluctuations were highly coherent over the vertical extent 120 m and over the horizontal extent 64 km of our array the implied downstream propagation speed was 30 km day 1 for the weekly period meanders concurrent satellite images of a sea surface temperature sst meander pattern indicate that subsurface temperature salinity velocity and relative vorticity maxima occurred as meander crests shoreward sst front excursions passed over the experiment site the meandering currents were not coherent with nearby wind stress or coastal sea level fluctuations eddy flux estimates indicate energy conversion from the f

an assessment of a time of transition laser sizer in measuring suspended particles in the ocean abstract an assessment of the performance of the laser sizer cis 1 by galai for the size range of 0 5 150 m was conducted in a cruise across the continental shelf north of taiwan two types of measurements for the laser sizer were compared with the sizes analyzed by microscopic examination the measurements of cis 1 were performed with 1 a liquid flow pump system and 2 a small volume cuvette system the results of this study showed that although the liquid flow system analyzed a larger volume of water sample its measurements compared badly with that of microscopic examination but occasionally accurate results did appear when the particles were less fragile the measurements with the cuvette system generally agreed well with that of microscopy the mean value of the average deviation between the measurements of microscopy and the cuvette system was 33 it was also found that the narrower the particle size spectrum the more accurate the cis 1 s measurements were

sedimentary processes of fine grained material and the effect of seawall construction in the daeho macrotidal flat nearshore area northern west coast of korea abstract sedimentary processes on the lower tidal flat of the reclaimed seosan bay daeho tidal flat at the west coast of korea have undergone significant changes since 1984 when seawalls over 8 km long were constructed at the bay mouth comparison of pre and post construction tidal flow models indicates that in general tidal currents have increased considerably in front of the daeho tidal flat with tidal flow directions having changed from shore normal to shore parallel the 12 h measurements of currents and suspended sediment concentrations at four anchored hydrographic stations show nearshore suspended sediments drifting southward throughout the year bypassing the daeho tidal flat cyclic seasonal variations occur prominently in the grain texture of the tidal flat sediments and associated sedimentation rates in summer fine grained sediments deposit at a rate of 2 6 mm month particularly in sheltered places during the winter monsoon erosional processes are greatly enhanced by the interplay of tidal currents and waves up to 30 mm month this sedimentary seasonality is reflected in the variations in the concentration of nearshore suspended matter the concentration of suspended matter is much higher in winter 60 80 mg l because of vigorous resuspension activities compared with the summer concentration 10 30 mg l the direct effect of seawall construction coupled with strong natural seasonality can be seen from the continuous monitoring of sedimentation rates on the tidal flat the 2 year 1993 1995 measurements indicate that the entire daeho tidal flat was eroded during that period at the abnormally high average rate of 10 cm year the causal blocking of bayward sediment and water movements by any artificial structure might lead to similar erosional conditions to many other bays facing the yellow sea on the both chinese and korean coastlines subjected to energetic winter wave attack

late neogene chronology and sequence stratigraphy of mixed carbonate siliciclastic deposits of the cibao basin dominican republic a stratigraphic study of late miocene pliocene mixed carbonate and siliciclastic sediment upper part of the yaque group was conducted in northern hispaniola to refine the chronostratigraphy of uplifted nearshore marine sequences in the cibao basin classic late neogene sections in these sequences include a spectacularly preserved faunal record for the northern caribbean refined ages of the cercado formation 6 6 6 0 ma the gurabo formation ca 5 8 4 0 ma and the mao formation 3 9 3 5 ma allow correlation to regional and global sea level events each of the three formations corresponds to one depositional sequence composed of mixtures at different proportions of skeletal debris mostly coral and mud size silt siliciclastic sediment distinct stratal geometries and lithofacies individualize the three formations each separated by pebble conglomerates the cercado formation depositional sequence consists of prograding inner shelf siliciclastic sands and patch reefs the basal transgressive unit of the gurabo formation is made of seaward prograding low angle clinothems of bedded and burrowed siliciclastic sand with molluscs and free living corals the upper gurabo unit consists of massive middle shelf clinothems of silt with bedded reef debris and in situ branching coral thickets these clinothems grade basinward into massive deeper water silt deposits at the shelf edge and basin slopes the mao formation sequence records the transition from lowstand fluvial deltaic facies to transgressive and highstand marine clinothems made mostly of coral debris in a silt matrix in the mao formation outcrops the coral silt clinothems can be divided into at least 10 high frequency cycles 40 k y based on lithofacies channelized and slumped coarse siliciclastic sand gravel and nonmarine alluvium cap the sequence likely associated with lowered sea level starting at ca 3 3 ma and perhaps the onset of regional uplift the major lithologic and sequence geometry changes in the cibao basin correlate with trends in the oxygen isotope ice volume proxy and likely reflect deposition responding to major periods of marine transgression and highstand an especially prominent feature is the major deepening and margin back step near the miocene pliocene boundary continuing in the early pliocene which resulted in the deposition of the gurabo formation transgression and sea level highstand in the late early pliocene 3 9 3 5 ma produced distinctive margin progradation primarily by coral debris this progradation event was synchronous with progradation in the nearby western great bahama bank the different stratal configurations of the three sequences can be attributed to a combination of factors including 1 shelf morphology and location on the shelf 2 paleoceanographic conditions such as warm sea surface temperatures and reduced upwelling which controlled coral productivity and reef geometry and 3 the influx of siliciclastic mud from the adjacent mountains

estuarine flocs their size settling velocity and density the size and settling velocity of flocs of suspended sediments from the chesapeake bay were measured in laboratory experiments and in the field the curves between floc diameter and settling velocity showed a non stoke s relationship that was best described by the following settling velocity cm s 1 73 floc diameter cm 0 78 furthermore the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size in addition to changing density a cylinder shape was found to be the best shape factor