authigenic uranium relationship to oxygen penetration depth and organic carbon rain we have measured u in benthic incubation chambers sediment pore waters and in sediments along the california continental margin sedimentary u uptake rates based on a combination of sediment pore water profiles and benthic incubation chambers generally agree with those predicted from sediment accumulation rate data this agreement supports the view that most of the continental margin sedimentary u is delivered by diffusion across the seawater sediment boundary the average rate of authigenic u accumulation for all the sites examined here is 0 2 nmol cm 2 y 1 which is consistent with published global estimates of sedimentary u uptake in addition the accumulation rate of u in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate these relationships highlight the potential utility for the u accumulation rate as a proxy for these processes

germanium geochemistry in the southern california borderlands abstract concentrations of ge oh 4 denoted as ge i or inorganic germanium and si oh 4 were measured in water column and pore water samples from san pedro and san nicolas basins in the southern california borderlands there is a characteristic linear relationship between ge i and si in the water column which implies that the distributions of germanium and silica are controlled by similar processes in contrast the pore water chemistry of germanium appears to differ from that of silica particularly in the reducing organic rich sediments of san pedro basin silica concentrations in san pedro basin pore water asymptotically increase to 480 m at 35 40 cm depth ge i concentrations in the topmost 2 cm of pore water from san pedro basin are an order of magnitude greater than bottom water concentrations below 2 cm ge i concentrations decrease exponentially with a half distance of about 8 cm cycling of ferric oxyhydroxides at a redox boundary is the most likely cause of the ge i enrichment in san pedro basin pore water while authigenic pyrite formation with the concomitant inclusion of germanium is a probable but undocumented cause of the downcore decrease in ge i pore water ge i and silica concentrations in sediments of san nicolas basin are generally greater than bottom water concentrations but vary irregularly with depth probably due to irrigation

seismic expression of pleistocene paleoceanographic changes in the california borderland from digitally acquired 3 5 khz subbottom profiles and ocean drilling program leg 167 drilling 1 we correlate processed 3 5 khz seismic profiles with physical properties of cores collected during odp leg 167 from the tanner east cortes and san nicolas basins through much of the pleistocene succession results indicate that seismic horizons in the unconsolidated pleistocene sediments top 50 m are mainly controlled by density contrasts removing of the compaction trend from the density reveals a very interesting relationship between density and composition the density closely and inversely correlates with organic carbon indicating that large scale variations in organic carbon are responsible for seismic reflections through their influence on density this is a significant discovery since there apparently is no other paleoceanographic setting that we know of where such a close linkage between acoustic properties and organic carbon has been established the variations in organic carbon are mainly marine in origin and derive from variations in primary productivity associated with upwelling and the preservation regime related to oxygenation of water pleistocene reflections on 3 5 khz profiles in the borderland province thus record regional cyclical fluctuations in the paleoclimatic signals the close resemblance in the density profiles at the three different basins indicates that the sedimentary regime was similar in those basins through the pleistocene these common density patterns produce regional seismic horizons that correlate well among the basins it is likely these correlated and dated horizons could be extrapolated to other borderland basins e g san clemente where they can potentially be used as time markers for neotectonic studies in the region

nicolas and eel submarine fans california continental borderland nicolas and eel submarine fans occur in the san nicolas basin an outer basin of the california continental borderland that has a low sedimentation rate nicolas fan lies southeast of san nicolas island and the broad san nicolas bank the upper fan is characterized by numerous channels the midfan region may be divided into three distinct areas a central midfan and two subfans the central midfan depositional system is typical of normark s suprafan the subfans are essentially flat sandy lobes eel fan lies west of san clemente island and is fed by an erosional valley its midfan region may also be characterized as a flat sandy lobe box core data show that holocene turbidity currents have occurred on the central nicolas fan whereas the subfans and eel fan are nearly nactive the local tectonic regime influences these fans by determining slope trends creating bathymetric obstacles controlling canyon location and triggering mass movements sea level changes affect sedimentation patterns of the fans by increasing the mean grain size and the amount of sediment delivered to the fan during lowstands these changes may in turn affect the morphology of the fan the characteristics of these fans represent variations of the generalized fan models described in the literature

constraining assembly time of some blocks on eastern margin of pangea using permo triassic non marine tetrapod records abstract the supercontinent pangea was mainly formed during the permian but when it reached maximum land is unsure because the configuration of the east asian blocks during the permo triassic is still highly debated fossil tetrapods provide one of the best calibrations to the time of connection between continents but the data of permo triassic tetrapods have rarely been applied in the previous reconstructions here we review the oldest records of non marine tetrapods on the east asia blocks and use them to discuss the timing of connection between continents during the permian and triassic the distribution of seymouriamorpha shows the kazakhstanian was connected to the baltica by land from the cisuralian the diverse dashankou fauna indicates that the alxa block amalgamated to pangea at least in the guadalupian older than 266 ma the questionable footprints and late permian dicynodont assemblage from the north china show the north china craton may have been connected to the main part of pangea from the guadalupian and became part of pangea at least by 256 ma the late permian laotian tetrapods support the hypothesis that the south china block already collided with the north china and the indochina blocks by the end of the permian and there was a land route for the migration of non marine tetrapods

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

germanium silicon fractionation in a river influenced continental margin the northern gulf of mexico abstract in this study we have sampled the water column and sediments of the gulf of mexico to investigate the effects of high riverine terrigenous load and sediment redox conditions on the cycling of ge and si water column ge si ratios across the gulf of mexico continental shelf range from 1 9 to 25 mol mol which is elevated compared to the global ocean value of 0 7 mol mol the ge enrichment in the gulf of mexico seawater is primarily due to anthropogenic contamination of the mississippi river which is the main ge and si source to the area and to a smaller extent due to discrimination against ge during biogenic silica bsi production ge si 1 2 1 8 mol mol especially by radiolarians and siliceous sponges ge si 0 6 1 1 mol mol most sediment pore waters ge si 0 3 4 5 mol mol and sediment incubation experiments benthic flux ge si 0 9 1 2 mol mol indicate precipitation of authigenic phases that sequester ge from pore waters non opal sink this process appears to be independent of oxidation reduction reactions and suggests that authigenic aluminosilicate formation reverse weathering may be the dominant ge sink in marine sediments compilation of previously published data shows that in continental margins non opal ge burial flux is controlled by bsi supply while in open ocean sediments it is 10 100 times lower and most likely limited by the supply of lithogenic material we provide a measurement based estimate of the global non opal ge burial flux as 4 32 mmol yr 1 encompassing the 2 16 mmol yr 1 needed to keep the global marine ge cycle at steady state

morphology and sedimentology of two contemporary fan deltas on the southeastern baja california peninsula mexico abstract the san juan de los planes drainage basin is located on the southeastern margin of the baja california peninsula approximately 20 km southeast of the city of la paz pleistocene alluvial fans have been built into the basin from the surrounding areas of high relief and are presently being eroded at the fan apex the dissection depth ranges from 20 to 40 m and is 6 to 15 m at the coast the sediments have been redeposited in several active modern fan deltas built out into the narrow shelf of la ventana bay shelf width ranges from 0 to 5 km average 3 km wave energy is delivered from southeasterly storms and from the local sea breeze winds the respective wave heights average 2 and 1 m the agua caliente and las canoas fan deltas the subjects of this paper are located on the active el sargento fault zone and are fed by channels that deeply dissect the older fan surfaces the agua caliente fan delta is a classic gilbert type delta with a steeply inclined delta front wave reworking and redistribution of the sediments at the delta face are important and a wave cut terrace has developed at about 6 m depth the las canoas fan delta is a shoal water profile hjulstrom type with a gently inclined delta front wave energy is less important the alignments of the coasts of both fans are controlled by the fault line sediment supply is largest for the las canoas fan delta the fan deltas are examples of this depositional form as it has developed in an arid tectonically active high relief and narrow neo trailing edge margin

radium 228 distribution and mixing in san nicolas and san pedro basins southern california borderland sediment profiles of 228ra and 232th and water column profiles of 228ra are presented for san nicolas and san pedro basins located in the southern california borderland these data are used to estimate fluxes of 228ra from the sediments the vertical eddy diffusivity kz in the water column and the upwelling velocity wz the fluxes of 228ra from sediments estimated by integrating the downcore deficiency of 228ra with respect to its parent nuclide 232th are 335 115 atoms m2s for san nicolas basin and 166 50 atoms m2s for san pedro basin san nicolas basin sediments have an excess of 228ra in the upper 4 cm but irrigation and diffusion create a 228ra deficiency from 4 to 30 cm san pedro basin sediments are anoxic and laminated have a 228ra deficiency above 6 12 cm depth and have no surface excess of 228ra basin waters appear to be well mixed horizontally below sill depth and in steady state with respect to 228ra concentrations of 228ra increase from sill depth to the bottom ranging from approximately 1 0 dpm 100 kg to 2 4 dpm 100 kg in san nicolas basin and from 1 6 dpm 100 kg to 3 1 dpm 100 kg in san pedro basin estimates of kz and wz at several horizons in these basins are made by evaluating two steady state mass balance equations one for 228ra and one for heat this approach is hindered by an inability to accurately define the temperature in waters flowing over the sills and the apparent failure of topography to completely restrict horizontal exchange in the upper part of the water column below sill depth in each basin upper limits for kz are 23 cm2 s at 1700 m in san nicolas and 2 8 cm2 s at 850 m in san pedro basin our best estimates for kz and wz for the deeper part of the basins are kz 5 17 cm2 s and wz 50 150 m y in san nicolas basin and kz 1 3 cm2 s and wz 20 50 m y in san pedro basin the differences in kz between basins reflect differences in the buoyancy gradients upwelling velocities increase from the bottom to the sill of each basin

reconstructing morphological and depositional characteristics in subsurface sedimentary systems an example from the maastrichtian danian ormen lange system more basin norwegian sea understanding large scale sediment distribution patterns and morphological characteristics in subsurface sedimentary systems is highly challenging and generally requires regional seismic and well coverage here we test a method that aims to predict first order morphological characteristics and type of sedimentary transport system in ancient source to sink systems based on trends observed in submodern pliocene holocene depositional environments an example from the paleocene ormen lange system more basin norwegian sea demonstrates the application of the method and several descriptive parameters are estimated for this ancient subsurface system in the ormen lange system basin floor fan and distal slope parameters are well constrained from seismic and well control however knowledge of the morphology and relationships between upper slope shelf and catchment characteristics and their relationships to deep water systems is poor and these are the parameters that are discussed in this study estimated parameters of catchment size derived from this technique are in good agreement with preserved remnants of fluvial valleys located onshore predicted sediment transport characteristics are also comparable to the depositional mechanisms interpreted from cores and well logs suggesting a small tectonically active system with high fluvial discharge and low sediment storage potential in the catchment and shelf subenvironments the discussed method is thus capable of predicting first order segment characteristics in subsurface sedimentary systems with an uncertainty of one to two orders of magnitude this information can be used to increase the understanding of unexplored basins or to add data and uncertainty ranges to well known petroleum systems

the provenance of low calcic black shales the elemental concentration of sedimentary rocks depends on the varying reactivity of each element as it goes from the source through weathering deposition diagenesis lithification and even low rank metamorphism however non reactive components of detrital particles ideally are characteristic of the original igneous source and thus are useful in provenance studies to determine the source of detrital granitic and volcanic components of low calcic 1 caco3 marine black shales the concentrations of apparently non reactive i e unaffected by diagenetic redox and or low rank metamorphic processes trace elements were examined using standard trace element discrimination diagrams developed for igneous rocks the chemical data was obtained by neutron activation analyses of about 200 stratigraphically well documented black shale samples from the cambrian through the jurassic a la th sc ternary diagram distinguishes among contributions from the upper and bulk continental crust and the oceanic crust taylor and mclennan 1985 all the low calcic black shales cluster within the region of the upper crust th hf co ternary diagrams also are commonly used to distinguish among the upper and bulk continental crust and the oceanic crust taylor and mclennan 1985 as co is redox sensitive in black shale environments it was necessary to substitute an immobile element i e example rb in the diagram with this substitution of black shales all cluster in the region of the upper continental crust to determine the provenance of the granitic component pearce et al 1984 plots of ta vs yb and rb vs yb ta shows a cluster at the junction of the boundaries separating the volcanic arc granite vag syn collision granite syn colg and within plate granite wpg fields the majority fall within the vag field there are no occurrences of ocean ridge granite org the minimal contribution of basalts to marine black shales is confirmed by the ternary wood diagram th hf 3 ta wood et al 1979 the black shales plot in a cluster in a high th region outside the various basalt fields which suggests contribution from the continental crust

depositional events in santa monica basin california borderland over the past five centuries the southern california coastal climate is characterized by decadal and generational floods that discharge one to three orders of magnitude more sediment than the average annual contribution these can produce turbidity currents directly or load the canyons and slopes with sediments that then may fail and form turbidity flows seismic activity is high on this transform margin and can trigger slope failures where slope sedimentation rates are high and sediments are unstable these events produce slope failures and slides and slumps in canyon heads which evolve into turbidity currents of sufficient volume to reach the adjacent margin basin floors such events occur at approximately century frequency this paper describes six basin floor turbidites that have been mapped in box cores sampling roughly the top 40 50 cm from the basin floor or santa monica basin in the california borderland these deposits were laid down during the past 500 years of record their depositional areas have been conservatively estimated to range from 500 to almost 1500 km2 and contain masses of sediment ranging from 10 000 000 to 100 000 000 tons this compares with a long term average annual terrigenous contribution rate of about 4 000 000 tons yr from the adjacent major streams although annual rates vary from 0 to 60 000 000 tons over the last century of record three of the six events have been related to two major floods 1884 6 1969 and to one major seismic event the mission earthquakes of 1822 1812 the older turbidites were deposited before european entry to the area and cannot be assigned to an historic event but from their size were probably seismically triggered and are the largest of the six events it is likely that other smaller events are masked by the more recent turbidites particularly in the area where box cores are dominantly composed of turbidites these features exhibit average outcrop thickness of 2 to 7 cm with maxima of the order of 10 cm thickness yet represent major events and significant volumes of sediment they also document that the two major sources for such events floods and seismic events produce deposits of very different mass and can probably be separated in the record on that basis thus the frequency of major floods and of major earthquakes in the region could be defined from study of such deposits in longer cores these deposits also provide examples of continued turbidity current activity to the basin floors at a time of high sea level this is contrary to the passive models for sequence stratigraphy depositional patterns

holocene sediment budgets for the basins of the california continental borderland abstract two holocene sediment budgets have been compiled for the california continental borderland the first detailed budget includes the six northern inshore and central basins that capture almost 40 of the total sediment input to the entire borderland in the second budget the data for the six basins has been added to estimates of accumulation for the remaining borderland area to produce a total regional budget of lower precision than the smaller six basin region natural river influx to the borderland approximates 13 1010 tons for the holocene epoch and biological input has been estimated at about 2 1010 tons eolian and ocean current influx have each been estimated at about 1 1010 tons in sum the total deposited volume for 104 yrs is about 14 1010 tons and the estimated total influx is of the order of 17 1010 tons which suggests that a net of 1 3 101010 tons for the holocene high sea level period the six high accumulation rate basins are located adjacent to the largest river sources the major zones of coastal upwelling and the main northern eddies of the california current these high accumulation sites are typically also areas where mass movement and fan development are localized the sediment accumulation rate is much larger than subsidence rate and flat floored basins are typical in contrast the southern and outer low accumulation basins are areas of draped sediment with accumulation rate less than subsidence rate and are the sites of penecontemporaneous deformation of the accumulating fine hemipelagic sediments few fans or major mass movements are seen significant sedimentation is mainly confined by topography to less than 20 of total margin area thus the moderate to low total sediment influx is amplified by the restricted receiving area to produce locally thick deposits of limited areal extent this pattern is characteristic of neogene southern california basins and illustrates that stratigraphic thickness is not a valid indicator of sediment influx

a time series study of silica production and flux in an eastern boundary region santa barbara basin california a high resolution data set describing the annual silica cycle between january 1994 and august 1999 in the santa barbara basin sbb captures processes and events occurring in both surface and deep basin waters increases in biogenic silica bsi concentrations in the surface waters indicated strong bloom events in the early spring of each year and sporadic blooms during the summer and fall lithogenic silica lsi was present at elevated concentrations in surface waters in the winter and spring at times the siliceous biomass in the sbb is comparable to that in major global upwelling regions however anomalously low annual depth integrated bsi concentrations were observed during the e1 nino conditions of 1997 1998 a 1 5 year time series of biogenic silica production rate measurements was used to calculate the highest resolution estimate of annual silica production to date an estimated 5 5 mol si m 2 yr 1 this silica production rate approaches that estimated for the major global upwelling zones 8 3 mol si m 2 yr 1 eastem boundary regions outside of the major coastal upwelling zones would account for 30 40 of global silica production if the santa barbara basin is representative of these coastal regions since the sediments of the sbb contain a high resolution climate record an understanding of the coupling between surface processes and deep basin sedimentation events is of value fluxes of bsi and lsi to 470 m were not strongly coupled to the seasonal cycle of particulate concentrations or production rates in surface waters continuous sediment trap collections of sedimenting particles indicate that both lsi and bsi tend to be exported at the highest rates during the spring and summer as particles sink lsi becomes enriched relative to bsi and consistently dominates the mass flux of silica at 470 m brief increases in the percent contribution of bsi to si flux may create microlaminae within larger scale laminations which are thought to be annual varves a comparison of annual bsi sedimentation rates with annual silica production estimates reveal that 30 of the annual silica production is exported to a depth of 470 m this export rate is the highest observed to date and suggests the potential for large quantities of silica burial in coastal sediments

emeishan mantle plume activity and carbon isotope responses in the middle permian south china abstract during the permian emeishan mantle plume activity created a large igneous province and deeply impacted carbon isotope records in marine carbonate strata in south china to evaluate the isotopic variations caused by this catastrophic event 140 carbonate samples from four sections were collected and analyzed the 13ccarb values in the upper section of the qixia formation gradually increased stabilized at 4 0 in the lower middle sections of the maokou formation and then abruptly decreased in the upper section of the maokou formation this isotopic evolution trend is likely related to mantle plume geochemical processes occurring during these respective stages large amounts of upwelling heat from the emplacement of the mantle plume triggered large scale decarbonation reactions in the continental crust resulting in co2 production enriched in 13c substantial amounts of 13c enriched co2 directly affected the isotope compositions of marine carbonates during this time temporal and spatial fluctuations in carbon isotopes were also controlled by terrestrial materials as a result of regression and doming caused by plume emplacement the abrupt decrease in 13ccarb in the upper section of the maokou formation reflects the onset of volcanism resulting in the breakdown of organic materials these findings emphasize the contribution of a carbon reservoir with a thermal decarbonation origin in the upper crust particularly against the permian tectono thermal background this mechanism which is similar to biological isotope fractionation in the carbon cycle should not be overlooked

copper isotope signatures in modern marine sediments abstract the development of metal stable isotopes as tools in paleoceanography requires a thorough understanding of their modern marine cycling to date no cu isotope data has been published for modern sediments deposited under low oxygen conditions we present data encompassing a broad spectrum of hydrographic and redox regimes including continental margin and euxinic sulphide containing settings taken together with previously published data from oxic settings these data indicate that the modern oceanic sink for cu has a surprisingly homogeneous isotopic composition of about 0 3 65cu relative to nist srm976 we suggest that this signature reflects one of two specific water column processes 1 an equilibrium isotope fractionation between soluble isotopically heavy cu complexed to strong organic ligands and an isotopically light pool sorbed to particles that deliver cu to the sediment or 2 an equilibrium isotope fractionation between the same isotopically heavy ligand bound pool and the particle reactive free cu2 species with the latter being scavenged by particulates and thereby delivered to the sediment an output flux of about 0 3 into sediments is isotopically light relative to the known inputs to the ocean at around 0 6 and the seawater value of 0 6 to 0 9 suggesting the presence of an as yet unidentified isotopically light source of cu to the oceans we hypothesize that this source may be hydrothermal or may result from the partial dissolution of continentally derived particles

a 9000 year flood history for southern california a revised stratigraphy of varved sediments in santa barbara basin abstract the center of santa barbara basin sbb preserves annual laminations through most of the holocene providing an important locality for high resolution late quaternary paleoclimate and paleoceanography reconstructions an accurate chronology is necessary for these sediment based records and enables comparisons with more distal data time series of similar quality here we present an improved high resolution radiocarbon chronology for the last 9000 yrs based on 89 accelerator mass spectrometric ams 14c dates of mixed planktonic foraminiferal carbonate from three sediment cores collected in sbb mv0811 14jc spr0901 06kc and odp hole 893a accurate core to core correlation is demonstrated using prominent gray flood and olive turbidite layers identified in sbb and dated in multiple cores gray layer deposits were found more frequently in wetter intervals as determined by multi proxy hydroclimate records in southern california e g lake deposits and tree rings mass accumulation rates mars calculated for the sbb depocenter using the improved radiocarbon age model indicate high mars are associated with these gray layers that have been associated with floods thus sediment accumulation in sbb is largely controlled by sediment delivery via river runoff following precipitation events although mars may also be influenced by other factors that enhance erosion in river catchments folded sediment is observed within the basal core section of mv0811 14jc which stratigraphically correlates with 14c age reversals in odp hole 893a we associate this sediment slump feature with the large goleta submarine slide complex in santa barbara channel and estimate the submarine slide event occurred at 9000 200 yrs bp furthermore small olive turbidite layers identified and dated in sbb can be temporally linked with large earthquakes along san andreas fault and can therefore potentially reconstruct earthquake history in southern california

rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the california continental borderland the rock magnetic properties of marine sediments from the california continental borderland san pedro santa catalina and san nicolas basins have been studied in order to quantitatively assess the effects of sediment diagenesis on magnetic minerals previous studies have noted that the natural remanent magnetization in these sediments primarily carried by detrital magnetite decays to 10 or less of its surface value soon after deposition this decrease is caused by magnetite dissolution related to sediment diagenesis and is unrelated to paleoclimatic variations or changes in the regional influx of detrital magnetic material detailed rock magnetic measurements show that shifts to softer remanent coercivity and differences in the rate and degree of magnetic intensity loss with depth can be related to the dissolution process the shift to softer remanent coercivity is related to a coarsening of the magnetic mineral grain sizes with depth due to preferential dissolution of the finest grained magnetic material the intensity decreases which are linearly proportional to magnetite concentration decreases indicate that dissolution occurs with rate constants ranging from 0 3 to 1 6 kyr 1 the rate constants sulfide concentrations and magnetite grain size estimates from the borderland are consistant with previous studies of magnetite dissolution our results demonstrate the importance of both sulfide and magnetite surface area in the dissolution process anomalous peaks in viscous remanence within the sediments suggest the authigenic growth of greigite and its subsequent transformation to pyrite

a budget of marine and terrigenous sediments hanalei bay kauai hawaiian islands abstract the sediment budget of hanalei bay on the north shore of kauai was calculated using sedimentological and geophysical methods the calculations of the budget subsequently allowed an interpretation of the holocene history of the bay the bay sediments are easily separated into marine carbonate and terrigenous siliciclastic grains surficial sediments are dominated by carbonate grains 70 of coralline algae coral and mollusc fragments as well as foraminifera halimeda bryozoa and echinoderm tests however siliciclastic grains e g olivine plagioclase volcanic lithics from the hanalei river watershed draining shield volcanic highlands are the most common individual grain type 27 and form a zone of high concentration from the mouth of the hanalei river into the center of the bay flooding in the bay by the post glacial sea level rise began soon after 11 7 kyears the resulting marine environment caused the net deposition of 45 5 1 5 10 6 m 3 of sediment in the bay and approximately 33 7 11 2 10 6 m 3 of sediment on the hanalei coastal plain the total volume of carbonate sediment stored in the bay and coastal plain is greater than the volume likely to have been produced exclusively within the bay during the same time calculations indicate that approximately 2490 m 3 year 1 have been imported into the bay or coastal plain and deposited since 11 700 years ago the majority of this sediment influx is likely delivered from the east by the strong tradewind driven littoral currents that characterize kauai s north shore net carbonate sediment deposition in hanalei bay peaked at a rate of 15 500 m 3 year 1 between 5000 and 3000 years ago when sea level may have been 2 m above present diminishing to 3890 m 3 year 1 from 1000 years ago to the present this influx is likely to have played a significant role in the mid to late holocene progradation of the hanalei shoreline

hyperpycnal sediment discharge from semiarid southern california rivers implications for coastal sediment budgets southern california rivers discharge hyperpycnal river density greater than ocean density concentrations of suspended sediment 40 g l according to buoyancy theory during flood events mostly during el nino southern oscillation enso conditions because hyperpycnal river discharge commonly occurs during brief periods hours to occasionally days mean daily flow statistics often do not reveal the magnitude of these events hyperpycnal events are particularly important in rivers draining the transverse range and account for 75 of the cumulative sediment load discharged by the santa clara river over the past 50 yr these events are highly pulsed totaling only 30 days 0 15 of the total 50 yr period observations of the fate of sediment discharge although rare are consistent with hyperpycnal river dynamics and the high likelihood of turbidity currents during these events we suggest that much of the sediment load initially bypasses the littoral circulation cells and is directly deposited on the adjacent continental shelf thus potentially representing a loss of immediate beach sand supply during particularly exceptional events 100 yr recurrence intervals flood underflows may extend past the shelf and escape to offshore basins

rock magnetic characteristics of surficial marine sediments from the california continental borderland abstract the rock magnetic variability of surficial marine sediments from the california continental borderland adjacent to southern california is described the data were derived from measurement of the natural nrm anhysteretic arm and isothermal irm remanent magnetization and magnetic susceptibility of 385 samples from 230 cores magnetic mineralogy studies carried out on selected samples indicate that detrital magnetite predominates throughout the borderland but there are also locally important contributions from detrital and authigenic hematite altered glauconite and biogenic magnetite maps of the distributions of various rock magnetic parameters show that 1 the proportion of magnetic material decreases outward from the coastline through dilution by organic material and carbonate 2 the magnetic grain size distribution shifts to finer average grain size outward from the coastline 3 important local contributions to the sediment magnetic material can come from erosion of submerged bank tops or ridges 4 glauconite rich zones on bank tops can be altered to remanent magnetic material that is anomalously strong in intensity and coercivity and 5 that diagenetic processes occur ubiquitously within the deep basins causing large scale dissolution of the magnetic material comparisons of arm and sirm saturation irm indicate that arm is very sensitive to grain size changes and that both the quantity arm 2 2 0 5 and sirm are good indicators of volume of remanent magnetic material in the borderland

the geological setting of santa monica and san pedro basins california continental borderland the california continental borderland s present configuration dates from about 4 to 5 106 years before present bp and is the most recent of several configuration of the southern california margin that have evolved after the north america plate over rode the east pacific rise about 30 106 years ago the present morphology is a series of two to three northwest southeast trending rows of depressions separated by banks and insular ridges two inner basins santa monica and san pedro have been the site for the california basin study cabs funded by the us department of energy the santa monica and san pedro basins contain post miocene sediment thicknesses of about 2 5 and 1 5 km respectively during the holocene past 10 000 years about 10 12m have accumulated the sediment entered the basin by one or a combination of processes including particle infall mainly as bioaggregates from surface waters from nepheloid plumes surface mid depth and near bottom from turbidity currents mass movements and to a very minor degree direct precipitation in santa monica basin during the last century particle infall nepheloid plume transport have been the most common processes the former process has been dominant in thecentral basin at water depths from 900 945m where characteristic silt clay is found with a typical mean particle diameter of about 0 0006mm standard deviation 2 skewness near zero kurtosis is typically 2 platykurtic these values indicate broad near log normal particle size distributions the calcium carbonate content averages about 10 and organic carbon about 4 surficial sediment bulk densities are 1 1 1 2 and accumulation rates range from 16 30mg cm 2yr1 in this central fine deposit bottom water oxygen contents are at or below 0 1 ml 1 1 so that bioturbation is inhibited thus preserving the primary sedimentary stratification there appear to be annual varves but the laminae couplets are not simple wet dry season pairs their formation is related to longer period climatic events el nino cycle of 3 to 4 years is dominant and is also affected by aperiodic bottom water flushing events the anoxic zone of bottom water has expanded over the past 300 to 350 years from a samll area in the northeastern basin floor ca 120km2 at 300 years bp and now covers most of the basin floor below depths of about 850m 1290km2 this expansion may have been primarily relaed to ocean circulation rate changes following the little ice age but is also likely to have been strongly affected by subsequent major changes in the natural drainages post european colonization the bottom water oxygen contents must also reflect the introduction of oxidizable pollutants coincident with the shift to agricultural mission era and then to urban use late 19th century to present of the adjacent mainland such localized effects are also suggested by the contrasting very large increases in the area of low oxygen bottom water in santa monica basin relative to the minimal changes in the area of anoxia in santa barbara basin over the same period and the lack of such zone in san pedro basin in the san pedro basin the bottom waters have remained dysaerobic so its sediments are bioturbated and preserve little or no evidence of primary stratification dumping of oil drilling muds and cuttings during the couple of decades prior to 1970 has left a surficial deposit ranging from 1 to 15cm in thickness forming a bull s eye isopach pattern as seen in radiographs bottom water oxygen content is usually 0 2ml o21 1 bottom infauna and epifauna are sparse central basin floor sediments water depths 800m of san pedro basin have textural characteristics similar to those of santa monica basin with distal basin floor surficial sediments being deposited primarily by particle infall and nepheloid flow at the present time mean diameters 0 006mm standard deviation 2 skewness 0 and kurtosis 2 platykurtic calcium carbonate content averages 8 10 and organic carbon is about 4 an estimate of the contemporary sedimentation rate was determined for a single box core of 25 29mg cm 2 yr1 from the central basin near the present distributary margin it cannot be considered necessarily to be representative mixing is indicated by the data an important climatic factor is the alternation of multi year wet and dry periods the california basin study was conducted during an extended dry period of low river discharge this undoubtedly will have affected the conclusions of the study related to sediment water interactions and pollutant transport by suspended clays