the white stone band of the kimmeridge clay formation an integrated high resolution approach to understanding environmental change the kimmeridge clay is a jurassic mudrock succession that shows milankovitch band climatic cyclicity a key issue is to determine how the subtle changes that define this cyclicity result from climatic change using material from the natural environment research council rapid global geological events rgge kimmeridge drilling project boreholes the white stone band was investigated at the lamination scale using backscattered electron imagery and quantitative palynofacies fabric analysis shows the lamination to represent successive deposition of coccolith rich and organic matter rich layers individual laminae contain unsorted palynological debris with a consistent ratio of marine and terrestrial components such mixed organic matter input is interpreted as the result of storm transport linking water column processes to laminae deposition suggests seasonal input with a coccolith bloom followed by a more diverse assemblage including dinoflagellates and photosynthetic chlorobiacean bacteria as the photic zone extended into the euxinic water column organic matter export to the sea bed underwent minimal cycling through oxidation and subsequently became preserved through sulphurization with greatly increased sequestration of carbon this was significantly increased by late season storm driven mixing of euxinic water into the photic zone increased frequency of storm systems would therefore dilute the coccolith input to give an oil shale hence climatically induced changes in storm frequency would progressively vary the organic content of the sediment and generate the climate cycle signal

the sedimentary expression of oceanic anoxic event 1b in the north atlantic abstract the aptian albian oceanic anoxic event 1b contains the record of severalperturbations in the global carbon cycle and multiple black shale levels particularly in the western tethys the local lithological expression of anoceanic anoxic event depends on palaeogeographical and depositional settingas well as on regional palaeoclimate marine sediments at a particular locationmay therefore be more or less organic rich or not at all and they may consistof different lithologies in most studies however much of the lithologicalvariability associated with oceanic anoxic events is left unaccounted for and thus the exact processes leading to the enrichment of organic matter in thesemarine sediments and their subsequent preservation in the geological recordare unknown this study focuses on the local sedimentary processes behindthe deposition of organic rich sediments at deep sea drilling project site 545and ocean drilling program sites 1049 and 1276 in the north atlantic duringoceanic anoxic event 1b although speci cally dealing with the sedimentsdeposited during this particular event at these localities it is expected that thesame processes were responsible for determining the exact sedimentaryproducts at localities in similar settings as well as during other similar eventsin the mesozoic here it is shown that the deposition of organic richsediments during oceanic anoxic event 1b was a consequence of theenhanced productivity favoured by upwelling and by riverine nutrientinput or aeolian fertilization of the euphotic zone depending ongeographical location slope instability processes resulted in the transfer ofpart of these organic rich sediments from the shelf to deep sea depocentres asmud laden organic rich turbidites especially in the northern north atlantic the so called black shales are much more varied than their name implies the end product of sedimentation during an oceanic anoxic event at aparticular location is commonly the result of several equi nal processes actingon a local scale rather than the direct result of basinal or even globalmechanisms keywords aptian albian kilian event north atlantic oae 1b oceandrilling program oceanic anoxic event paquier event

microfabric analysis of mn carbonate laminae deposition and mn sulfide formation in the gotland deep baltic sea the manganese carbonate deposits of the anoxic littorina sediments of the gotland deep have been commonly related to the periodic renewal of deep water by inflowing saline water from the north sea the use of scanning electron microscopy based techniques allows identification of small scale sedimentary and geochemical features associated with mn carbonate laminae which has significant implications for models of mn carbonate formation varves occurring in the littorina sequence contain up to four laminae that may be placed in a seasonal cycle and kutnahorite laminae occur within varves only as a winter early spring deposit this kutnahorite laminae seasonality is in agreement with the seasonal distribution of major baltic inflow events recorded in historical records and a direct causal link between inflows and kutnahorite deposition is implied benthic foraminifera tests are found to be heavily encrusted in kutnahorite implying that benthic recolonization during oxidation events occurs concurrently with kutnahorite formation the relatively common occurrence of small 50 to 100 m hexagonal mn sulfide pseudomorphs associated with 13 of kutnahorite laminae studied is reported in gotland deep sediments for the first time although mn sulfide crystals are not usually preserved in the sediment the discovery of mn sulfide pseudomorphs suggests that initial formation of mn sulfide in the gotland deep may occur much more commonly during the process of kutnahorite formation than previous reports of mn sulfide occurrence have implied

multiple monsoon controlled breakdown of oxygen minimum conditions during the past 30 000 years documented in laminated sediments off pakistan abstract late holocene laminated sediments from a core transect centred in the oxygen minimum zone omz impinging at the continental slope off pakistan indicate stable oxygen minimum conditions for the past 7000 calendar years high sw monsoon controlled biological productivity and enhanced organic matter preservation during this period is reflected in high contents of total organic carbon toc and redox sensitive elements ni v as well as by a low diversity high abundance benthic foraminiferal buliminacea association and high abundance of the planktonic species globigerina bulloides indicative of upwelling conditions surface water productivity was strongest during sw monsoon maxima stable omz conditions reflected by laminated sediments were found also during warm interstadial events preboreal bolling allerod and dansgaard oeschger events as well as during peak glacial times 17 22 5 ka all ages in calendar years sediment mass accumulation rates were at a maximum during the preboreal and younger dryas periods due to strong riverine input and mobilisation of fine grained sediment coinciding with rapid deglacial sea level rise whereas eolian input generally decreased from glacial to interglacial times in contrast the occurrence of bioturbated intervals from 7 to 10 5 ka early holocene in the younger dryas 11 7 13 ka from 15 to 17 ka heinrich event 1 and from 22 5 to 25 ka heinrich event 2 suggests completely different conditions of oxygen rich bottom waters extremely low mass and organic carbon accumulation rates a high diversity benthic fauna all indicating lowered surface water productivity during these intervals the omz was very poorly developed or absent and a sharp fall of the aragonite compensation depth favoured the preservation of pteropods the abundance of lithogenic proxies suggests aridity and wind transport by northwesterly or northeasterly winds during these periods coinciding with the north atlantic heinrich events and dust peaks in the tibetan loess records the correlation of the monsoon driven omz variability in the arabian sea with the rapid climatic fluctuations in the high northern latitudes suggests a close coupling between the climates of the high and low latitudes at a global scale

variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore namibia results from sediment archives the coastal upwelling system offshore namibia is ideally suited to address a focal question of the integrated marine biogeochemistry and ecosystem research programme what are the mechanisms that drive long term changes in ecosystems considerable interannual variability in climatic forcing is indicated by long time series of meteorological and remote sensing observation these accompany considerable interannual to interdecadal changes in the upwelling intensity over the last 100 years as well as a centennial trend on longer time scales the only archives available are sediment records spanning the late holocene to decipher the sediment record we mapped surface sediment patterns of proxies for physical sea surface temperature sst from alkenone unsaturation indexes and nutrient 15n on bulk sedimentary n variables their present day surface sediment patterns outline the coastal upwelling cells and filaments and associated high productivity area analysed in an array of dated sediment cores the spatial patterns of sst suggest long term 100 years variability in the location and intensity of individual upwelling cells the patterns of 15n outline an area of intense denitrification near the coast and advection of water with low oxygen concentrations in the undercurrent from the north 15n exhibits considerable downcore variability in particular over the last 50 years the variability appears to be governed by differences in extent of denitrification and thus of the shelf oxygen balance which appears to have deteriorated in the last 50 years together the data suggest that sst and denitrification conditions have remained in the narrow bounds outlined by today s patterns in surface sediments but that spatially small variability in upwelling intensity and make up of upwelling feed waters induced considerable changes in the lower trophic levels of the coastal upwelling ecosystem over the last 6 000 years attempts to correlate proxy records from sediments with observational time series and regional climate reconstructions were not successful possibly because annual to interannual environmental signals are erased in the process of sediment formation

physicochemical and biological influences on sedimentary fabric formation in a salinity and oxygen restricted semi enclosed sea gotland deep baltic sea two ca 8000 year long sediment cores from the gotland deep the central sub basin of the baltic sea were studied by means of digital images x radiographs and scanning electron microscopy energy dispersive x ray mineralogical analysis to gain understanding of the physicochemical and biological influences on sedimentary fabric formation in modern and ancient seas with a high flux of organic carbon and associated oxygen stress and depauperate ichnofauna four lithofacies were recognized i sharply laminated mud ii biodeformed mud iii burrow mottled mud and iv sedimentation event bed the sharply laminated and burrow mottled facies dominate the cores as alternating long intervals whereas the biodeformed and sedimentation event facies occur as thin interbeds within the sharply laminated intervals the sharply laminated mud comprises alternating diatom rich and lithic laminae with occasional mn carbonate laminae lamination discontinuity horizons within the laminites where the regular lamination is overlain sharply by gently inclined lamination challenge the traditional view of mud accumulation by settling from suspension but indicate localized accumulation by particle trapping microbial mats and potentially by the rapid lateral accretion of mud from bedload transport the biodeformed interbeds record brief few years to few decades oxic dysoxic conditions that punctuated the anoxic background conditions and permitted sediment surface grazing and feeding by a very immature benthic community restricted to the surface mixed tier the likely biodeformers were meiofauna and nectobenthic pioneers passively imported with currents the sedimentation event interbeds are distal mud turbidites deposited from turbidity currents probably triggered by severe storms on the adjacent coastal areas the turbidite preservation was favoured by the anoxic background conditions the long burrow mottled intervals are characterized by intensely bioturbated fabrics with discrete planolites rare arenicolites polykladichnus and very rare lockeia trace fossils as well as bivalve biodeformational structures which represent shallowly penetrating endobenthic feeding and grazing strategies and permanent dwellings these burrowed intervals represent longer periods several years to few centuries of oxic dysoxic conditions that permitted maturation in the benthos by means of larval settling of opportunistic worm like macrofauna and bivalves resulting in the development of a transition tier these observations imply more dynamic and oxic depositional conditions in gotland deep than previously thought comparison to previous zoobenthic studies in the area allowed discussion of the benthic dynamics and the identification of probable biodeforming and trace producing species implications for current biofacies and trace fossil models are discussed

controls on detrital sedimentation in the cariaco basin during the last climatic cycle insight from clay minerals abstract a high resolution analysis of the clay mineral content of sediments of the cariaco basin spanning the last climatic cycle was performed in order to determine how the detrital sedimentation in the basin records climatic oscillations at various timescales at the scale of glacial interglacial cycles the clay mineral content records changes in the geographic origin of the detrital supply from a dominantly kaolinite and smectite rich southern source during glacial to a more illite rich northerly source during interglacials though possibly influenced by eustatic variations these changes mostly reflect the latitudinal fluctuations of the intertropical convergence zone itcz the eemian shows an increased contribution from the northern source compared to the holocene during mis3 seasonality modulates the effect of itcz position and leads to increased smectite contribution fluctuations of the smectite and kaolinite contents during dansgaard oeschger cycles reflect changes of runoff intensity enhanced supplies in kaolinite during heinrich like events and stadials also suggest remobilizations of sediments deposited on the unare platform resulting from rapid sea level variations the younger dryas is characterized by a significantly different clay mineral association reflecting a drastic modification of terrigenous supply an eolian contribution would explain this peculiar mineralogy although local contributions cannot be ruled out a similar event is noted at the mis6 5 transition pointing for the occurrence of a younger dryas like episode during termination ii

the role of diagenetic carbonate concretions in the preservation of the original sedimentary record the upper cretaceous organic rich limestones and marls of the tarfaya basin of southwest morocco contain numerous calcite concretions which formed during early diagenesis relative textural similarities are observed both in the concretions and in the host sediments however the biological content of the concretions is considerably higher than in the host marls and limestones evidence for fossil dissolution in the host marls and the absence of concretions in some fossil rich zones suggest that the difference in fossil abundance between the concretions and host rock is a function of dissolution rather than preferential precipitation in fossil rich areas consequently the carbonate concretions appear to represent the memory of the sediment and allow quantification of the original biological components and are potential tools for estimating the original biological material deposited in the soft sediments

tropical ocean atmosphere controls on inter annual climate variability in the cretaceous arctic 1 the first annually resolved sedimentary record from the cretaceous is used to develop time series of inter annual and decadal scale climate variability from the arctic ocean analysis of records spanning 1000 years reveals strong periodicities in the quasi biennial oscillation and el nino southern oscillation enso band as well as a 14 year period which all closely match periodicities typical of modern high latitude climate variability this supports the view that an arctic ocean free of permanent sea ice would be driven by similar forcing to the present state implicating tropical ocean atmosphere interaction and demonstrating that stratosphere troposphere coupling likely played a prominent role in the transmission of cretaceous equatorial climate forcing to polar latitudes as has recently been established for the modern earth system on the other hand the prominent enso periodicities in our records argue against the hypothesized link between past warm climates and permanent el nino states

last glacial maximum to holocene sea surface conditions at umnak plateau bering sea as inferred from diatom alkenone and stable isotope records 1 the bering sea gateway between the pacific and arctic oceans impacts global climate when glacial interglacial shifts in shore line position and ice coverage change regional albedo previous work has shown that during the last glacial termination and into the holocene sea level rises and sea ice coverage diminishes from perennial to absent yet existing work has not quantified sea ice duration or sea surface temperatures sst during this transition here we combine diatom assemblages with the first alkenone record from the bering sea to provide a semiquantitative record of sea ice duration sst and productivity change since the last glacial maximum lgm during the lgm diatom assemblages indicate that sea ice covered the southeastern bering sea perennially at 15 1 cal ka b p the diatom assemblage shifts to one more characteristic of seasonal sea ice and alkenones occur in the sediments in low concentrations deglaciation is characterized by laminated intervals with highly productive and diverse diatom assemblages and inferred high coccolithophorid production at 11 3 cal ka b p the diatom assemblage shifts from one dominated by sea ice species to one dominated by a warmer water north pacific species simultaneously the sst increases by 3 c and the southeastern bering sea becomes ice free year round productivity and temperature proxies are positively correlated with independently dated records from elsewhere in the bering sea the sea of okhotsk and the north pacific indicating that productivity and sst changes are coeval across the region

sediment geochemical records of productivity and oxygen depletion along the margin of western north america during the past 60 000 years teleconnections with greenland ice and the cariaco basin abstract many sediment records from the margins of the californias alta and baja collected in water depths between 60 and 1200 m contain anoxic intervals laminated sediments that can be correlated with interstadial intervals as defined by the oxygen isotope composition of greenland ice dansgaard oeschger d o cycles these intervals include all or parts of oxygen isotope stage 3 ois3 60 24 cal ka the bolling allerod warm interval b a 15 13 cal ka and the holocene this study uses organic carbon corg and trace element proxies for anoxia and productivity namely elevated concentrations and accumulation rates of molybdenum and cadmium in these laminated sediments to suggest that productivity may be more important than ventilation in producing changes in bottom water oxygen bwo conditions on open highly productive continental margins the main conclusion from these proxies is that during the last glacial interval lgi 24 15 cal ka and the younger dryas cold interval yd 13 11 6 cal ka productivity was lower and bwo levels were higher than during ois3 the b a and the holocene on all margins of the californias the corg and trace element profiles in the lgi b a holocene transition in the cariaco basin on the margin of northern venezuela are remarkably similar to those in the transition on the northern california margin correlation between d o cycles in greenland ice with gray scale measurements in varved sediments in the cariaco basin also is well established synchronous climate driven changes as recorded in the sediments on the margins of the californias sediments from the cariaco basin and in the gisp 2 greenland ice core support the hypothesis that changes in atmospheric dynamics played a major role in abrupt climate change during the last 60 ka millennial scale cycles in productivity and oxygen depletion on the margins of the californias demonstrate that the california current system was poised at a threshold whereby perturbations of atmospheric circulation produced rapid changes in circulation in the eastern north pacific ocean it is likely that the pacific and atlantic oceans were linked through the atmosphere warmer air temperatures during interstadials would have strengthened hadley and walker circulations which in turn would have strengthened the subtropical high pressure systems in both the north pacific and the north atlantic producing increased rainfall over the cariaco basin and increased upwelling along the margins of the californias

a mid holocene geochemical record of saline inflow to the gotland deep baltic sea the formation of mn enrichments in gotland deep sediments has been linked to the occurrence of periodic inflows of saline water from the north sea in turn these saline inflow events are very strongly linked to variation in north atlantic atmospheric conditions here sedimentary mn concentrations in mid holocene sediments are measured with a 0 5 mm sampling resolution using scanning electron microscope techniques as the sedimentation rate in core 20001 5 was estimated to be approximately 0 5 1 mm per year examining the variation in mn enrichments may potentially provide an annual record of variation in saline inflow and by extension north atlantic climate on interannual timescales there are many processes that can affect mn cycling in the gotland deep when considered together these processes could potentially act to remove or significantly weaken the transmission of the primary saline inflow signal to the measured geochemical record producing an effectively random mn record analysis of the mn rec

independent component analysis as a tool for ground deformation analysis summary independent component analysis ica is a recent and well known technique used to separate mixtures of signals this technique has been applied to the ground deformation time series recorded at the permanent gps network of the osservatorio vesuviano ingv in order to characterize the deformation background level in the neapolitan volcanic area the analysis revealed the presence of five independent periodic signals common at all the gps stations some of them are interpreted as effects of earth tides the residual signal at each station represent the local ground deformation unfortunately the ica cannot provide the absolute amplitude of the components indeed we are not able to obtain a residual amplitude at each station then we used a stationarity analysis in order to investigate the eventual presence of local transient deformations the ica technique combined with the stationarity analysis has shown to be a very interesting tool for individuating ground deformation trends and could be very useful in volcanic areas monitoring

fine grained sediment flocculation below the hubbard glacier meltwater plume disenchantment bay alaska a study in disenchantment bay alaska demonstrates that fine sediment beneath a meltwater plume is flocculated and that floc sizes and fraction of mass bound within flocs exhibit a pronounced increase with depth rather than down fjord this spatial pattern of variability likely is due to the longer depositional timescale of flocs compared to their horizontal advection timescale within the meltwater plume the flux of mass within flocs also increases with depth these observations have implications for sedimentation models as sedimentation rates estimated from surface waters underestimate those at depth and could result in the inaccurate prediction of the position of suspension depocenters the results also may explain the behavior of fine sediment in more complex environments where floc properties are difficult to observe

varve microfabric record of seasonal sedimentation and bottom flow modulated mud deposition in the coastal northern baltic sea abstract eutrophication induced hypoxia has resulted in preservation of laminated sedimentary fabric in coastal areas of the northern baltic sea these laminites offer a potential technique for dating recently deposited organic rich muds but their formation mechanisms have been inadequately understood in this study microfabric of the modern laminated sediments in the coastal gulf of finland and archipelago sea was investigated through x radiography and scanning electron microscopy of samples embedded in epoxy resin the sedimentary fabric comprises rhythmic biogenic and lithogenic lamina successions reflecting seasonal changes in the composition of accumulating material the diatom rich biogenic lamina succession is formed during the vernal phytoplankton bloom through rapid sedimentation of aggregates composed of intact diatom frustules and minor proportions of clay rich lithic material that are enclosed in a sticky matrix of amorphous phytodetritus analogous to the formation of the marine snow accumulation of the lithogenic lamina succession results from decline in primary production towards late summer enhanced recycling of organic carbon due to grazing by zooplankton and intensified resuspension of lithic rich terrigenous material concomitantly with increased cyclonic activity towards late autumn and winter the inclusion of silt grains and isolated diatoms and faecal pellets in the lithogenic laminae attests to lateral transport and deposition from near bottom flows contradicting the generally accepted view that laminated sediments accumulate by suspension settling under quiescent conditions only accumulation rates inferred from 137 cs dating are consistent with the biogenic lithogenic lamina succession couplet thickness supporting the interpretation that the couplets reflect an annual cycle of deposition the results indicate that these modern laminated sediments provide a high resolution archive for assessing recent human induced environmental changes as well as a robust tool for evaluating the lateral expansion of seafloor oxygen deficiency due to anthropogenic eutrophication in the area during the past decades

apparent synchroneity of submillennial scale climate events between greenland and santa barbara basin california from 30 10 ka abstract evidence is presented from odp hole 893a santa barbara basin for possible synchroneity between greenland and california margin submillennial climate change records during termination 1 and the last glacial maximum lgm planktonic foraminiferal isotope and faunal records are compared to the gisp2 18o records greenland for the interval between 30 and 10 ka using a new chronology based on 38 planktonic 14c dates apparent synchronous climatic events include interstadial is events 2 3 and 4 a broad warming trend between 21 and 19 ka and a broad cooling trend between 19 and 17 ka bolling and allerod warm episodes separated by the cooler older dryas event younger dryas cool episode and the preboreal the resulting tight correlation supports an intimate teleconnection between santa barbara basin surface waters and greenland air temperatures differences between greenland and santa barbara basin suggest that some regional variations were superimposed on the global pattern of climate change e g the pre bolling warming

modern climate forcing of terrigenous deposition in the tropics cariaco basin venezuela one approach to deciphering tropical quaternary paleoclimate records has been to study the composition of terrigenous material in order to infer past changes in hydrologic and atmospheric conditions here we present the inorganic geochemistry major and trace elements of modern sediment traps and shelf sediments in the tropical cariaco basin venezuela in order to characterize seasonal variation in deposition of the terrigenous component and to document linkages within the ocean atmosphere climate system we show that variation in the chemistry of terrigenous input to the basin is a sensitive monitor of the annual meridional migration of the intertropical convergence zone itcz additionally seasonal terrigenous relative abundances are decoupled from terrigenous absolute fluxes showing that abundances are not directly related to terrigenous delivery changes in mixing between local fluvial sediments fluvial and or eolian mafic material and saharan dust explains the observed seasonality the modern seasonal variations are significantly smaller than those observed in the glacial interglacial paleorecord indicating that climate sensitivity at the two time scales is very different a striking contrast in the behavior of ti al between the longer glacial interglacial time scale and the modern seasonality also suggests that long term terrigenous deposition is not linked simply to 100kyr shifting of the itcz the modern data can be reconciled with the glacial interglacial record by invoking generally drier conditions during glacial periods over tropical latitudes combined with intermittent wet conditions caused by precessional forcing 2007 elsevier b v all rights reserved

sedimentary facies and high resolution primary production inferences from laminated diatomacous sediments off northern chile 23 s the oceanographic conditions at the mejillones bay 23 s are strongly influenced by an important wind driven upwelling cell of the humboldt current system hcs as well as by the presence of the oxygen minimum zone omz in this region laminated diatomaceous sediments in this bay were analysed using different qualitative and quantitative techniques on the sediment cores 33c and 32b to interpret the main physical ocean climate factors driving sedimentation processes the composition of these sediments is dominated by the high concentration of resting spores of the genus chaetoceros sp which denotes the strong influence of the upwelling events and primary production on hemipelagic sedimentation processes within the basin the laminae characterized by thickness ranging from 1 mm to several cm are associated with changes in density porosity due to the different concentration and composition of phytoplankton remains and organic matter dark laminae are generally characterized by higher concentration of chaetoceros r s toc organic matter carbonates and lithic minerals with respect to the adjacent lighter laminae representing periods of strong upwelling events high primary production rates and intensified hypoxia contrarily relatively lighter laminae are characterized by diminished concentration of chaetoceros r s and relative increases of the concentration of centric and pennate diatoms producing a more porous sediment some of these light laminae could be associated with short lived major oceanographic enso like events the variability of the sedimentary fluxes observed in both cores represents mostly ocean climate trends at decadal interdecadal and secular time periods the secular trends of the sedimentary fluxes suggest an intensification of the upwelling events and primary production from the second half of the 19th century as well as intensified processes during the 20th century these changes seem to occur contemporaneously with ocean climate variations in the southwestern tropical pacific ocean suggesting a major basin scale climate change during this period

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

variation in biogenic and detrital fluxes and formation of laminae in late quaternary sediments from the peruvian coastal upwelling zone abstract studies of laminated sediments from the peru margin using back scattered electron imagery bsei provide a high resolution record of variation in detrital and biogenic fluxes and highlight the uncertainty involved in preserving a record of surface processes in bottom sediments intermittently laminated sediments which predominate in the peru forearc basins record episodic major diatom bloom events from which there was adequate flux to counteract water column processes of dissolution and comminution a distinctive sub millimetre lamination with a limited occurrence during isotope stage 5 comprises a regular alternation between silt rich and clay rich couplets which may represent annual deposition with irregularly interlaminated diatom ooze containing near monospecific bloom assemblages the absence of diatom ooze layers between silt clay couplets may be controlled by variation of either the intensity of upwelling and or the nutrient content of upwelled waters macroscopically obvious 0 5 3 cm thick pelleted or homogeneous zones which occur throughout the sub millimetre laminated sequence represent periods of increased oxygenation with a probable 8 16 year duration occurring at irregular intervals of a few years to a few hundred years a slight but pervasive microscopic bioturbation is common within laminated intervals which would macroscopically be described as anaerobic sediments

non annual laminations and expansion of anoxic basin floor conditions in santa monica basin california borderland over the past four centuries sediments from box cores in the deep portion of santa monica basin have been examined by x radiography and the upper 10 20 cm are characterized by laminations 1 5 mm in thickness age dating of 9 cores by 210pb analysis has shown that accumulation rates on the central basin floor have been remarkably constant during the past century averaging 16 0 0 4 mg cm2 yr densitometer analysis of the x radiography films from 7 cores and spectral analysis of the resulting time series indicates that most lamination couplets have a periodicity in the 3 7 year range a range matching that of the el nino southern oscillation periodicity the median periodicity appears to have decreased slightly during the past 3 centuries from 7 0 years during 200 300 yrs b p to 5 2 yrs during 0 100 yrs b p this trend could be due to a decreasing sedimentation rate an increasing forcing frequency or an increasingly faithful response of the basin in more recent years multiple processes have contributed to creation of the laminations in santa monica basin the principal factors appear to be 1 variations in porosity due to the relative abundance of organic filaments probably formed by beggiatoa mats and 2 compositional variations that reflect variations in carbonate lithogenous ratios and in grain size both of these are expected to respond to enso events the presence of near anoxic bottom waters has prevented bioturbation permitting laminations to be preserved basin bottom waters became nearly anoxic about 350 years ago at the onset of warming as the little ice age waned expansion of the near anoxic area during the past century may have been augmented by 20th century anthropogenic effects the style of these non annual laminations in santa monica basin matches that of the annual laminations in the adjacent santa barbara basin and demonstrates the need for caution in interpreting all laminations as representing annual varves

millennial scale variability to 735 ka high resolution climate records from santa barbara basin ca 1 determining the ultimate cause and effect of millennial scale climate variability remains an outstanding problem in paleoceanography partly due to the lack of high resolution records predating the last glaciation recent cores from santa barbara basin provide 2500 5700 year windows of climate with 10 50 year resolution ages for three cores determined by seismic stratigraphic correlation oxygen isotope stratigraphy and biostratigraphy date to 293 ka mis 8 450 ka mis 12 and 735 ka mis 18 these records sample the late pleistocene during which the 100 kyr cycle strengthened and the magnitude of glacial interglacial cyclicity increased thus these records provide a test of the dependence of millennial scale behavior on variations in glacial interglacial cyclicity the stable isotopic 18o composition of planktonic foraminifera shows millennial scale variability in all three intervals with similar characteristics duration cyclicity to those previously documented during mis 3 at this site stadial g bulloides 18o values are 2 75 1 75 average 2 25 and interstadial values are 1 75 0 5 average 1 with rapid decadal scale interstadial and stadial initiations of 1 2 as in mis 3 interstadials lasted 250 1600 years and occurred every 650 1900 years stadial paleotemperatures were 3 5 9 5 c and interstadial paleotemperatures were 7 5 13 c upwelling evidenced by planktonic foraminiferal assemblages and 13c increased during interstadials similar to mis 3 high productivity during some stadials was reminiscent of the last glacial maximum this study builds upon previous records in showing that millennial scale shifts were an inherent feature of northern hemisphere glacial climates since 735 ka and they remained remarkably constant in the details of their amplitude cyclicity and temperature variability

the relationship between annual varve thickness and maximum annual discharge 1909 1971 annually laminated varved sediments from the river angermanalven mid central sweden have been used to construct an annual 2000 year long record of varve thickness maximum daily annual discharge and mean varve thickness for the years 1909 1971 are significantly correlated r 0 87 a relationship between maximum daily annual discharge for the observed period 1909 1971 and varve thickness was determined the return time of two exceptionally thick varves in the 2000 year long record at the years 658 and 492 ad were estimated and their likelihood estimated based on a gumbel frequency analysis c 2002 elsevier science b v all rights reserved

sediment fabrics oxygenation history and circulation modes of japan sea during the late quaternary abstract the quaternary hemipelagic sediments of the japan sea are characterized by centimeter to decimeter scale alternations of heavily bioturbated organic poor light layers and finely laminated organic rich dark layers these dark and light layers which can be correlated throughout the deeper part of the basin are considered to reflect changes in bottom water oxygenation however depositional mechanisms responsible for individual dark layers and causes of oxygen depletion are not fully understood two possible settings for deposition of organic rich dark layers are recognized one is a stratified ocean like the black sea where limited vertical advection results in euxinic conditions in the deeper parts of the basin the other is an upwelling region like the arabian sea where the oxygen minimum zone is intensified by enhanced nutrient upwelling and surface productivity in this study fabrics of hemipelagic sediments deposited in the japan sea during the last 160 ka were studied in three cores collected from different latitudes and water depths fabrics were classified into 4 classes based on corresponding bottom water oxygenation level five dark layer types were defined based on the distribution patterns of sediment fabric classes within each dark layer comparison of dark layer types at shallower and deeper sites in a chronologic framework provided evidence for five different modes of deep water circulation these circulation modes which reflect relative intensities of upwelling and density stratification appear to be related to global sea level changes as well as climate impact on the nature of water influx through the tsushima strait

diagenetic origin of quartz silt in mudstones and implications for silica cycling mudstone the most abundant sedimentary rock type1 composed primarily of clay or silt sized particles contains most of the quartz found in sedimentary rocks2 these quartz grains which are chemically and mechanically resistant and therefore preserve their characteristics well have long been considered to be derived from the continental crust1 here we analyse quartz silt from black shales in the eastern usa dating back to the late devonian period about 370 million years ago using backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe our results indicate that up to 100 of the quartz silt in our samples does not originate from the continental crust instead it appears to have precipitated early in diagenesis in algal cysts and other pore spaces3 with silica derived from the dissolution of opaline skeletons of planktonic organisms such as radiolaria and diatoms transformation of early diatoms into in situ quartz silt might explain the time gap between the earliest fossil occurrences of diatoms about 120 myr ago4 and molecular evidence for a much earlier appearance between 266 or even 500 myr ago5 6 moreover if many other mudstone successions show similarly high proportions of in situ precipitated rather than detrital quartz silt the sedimentary record in mudstones may have been misinterpreted in the past with consequences for our estimates of palaeoproductivity as well as our perceptions of the dynamics and magnitude of global biogeochemical cycling of silica

a 2100 year bp record of the pacific decadal oscillation el nino southern oscillation and quasi biennial oscillation in marine production and fluvial input from saanich inlet british columbia exceptional varved sediments of 2100 years bp recovered from saanich inlet have been analysed using high resolution scanning electron microscopy and spectral analysis techniques each varve may contain up to 22 well defined individual laminae which can be attributed to seasonal scale processes sediment flux comprises alternating diatom ooze diatomaceous mud deposited during spring through autumn and a silty clay deposited during winter the latter may be sporadically punctuated by clay rich laminae identification of some 2000 individual consecutive laminae based on fabric and diatom assemblage has allowed the construction of time series data for spectral analysis laminae types analysed include early spring thalassiosira spp late spring early summer skeletonema costatum multiple summer autumn chaetoceros spp diatom oozes and sporadically present clay rich winter flood deposits sub decadal periods have been identified and linked to the quasi biennial oscillation qbo and el nino southern oscillation enso and decadal periods to the pacific decadal oscillation pdo comparison of spectral analysis results with modern analogues suggests associations may exist between early spring thalassiosira spp laminae and stronger la nina events late spring early summer s costatum laminae and el nino events summer autumn chaetoceros spp multiple laminae and negative pacific northwest index pni regimes and sporadically present winter clay rich laminae and pni regimes the average period for an enso cycle was 3 6 years qbo 2 5 years and pdo 14 8 years spectral analysis of the more recent pni record shows similar significant periods of 13 2 3 7 and 2 6 years multi decadal periods recorded include 42 2 and 31 3 years which might suggest multiples of pdo

solar cycles recorded in carboniferous glacimarine rhythmites western argentina relationships between climate and sedimentary environment abstract a carboniferous glacial episode has been widely known in the western part of argentina since ca 1910 in some sections it is associated with rhythmic sedimentation one of those rhythmite successions is interpreted as composed by varves annually deposited sedimentary cycles accumulated in a glacimarine environment it is further analyzed as a time series searching for cyclic signals several localities show varve like successions but only a few of them are not disturbed by reworking of bottom currents the rio francia section san juan argentina is well suited for varve counting as no current produced structures are recognized through the rhythmite interval and outcrops are good enough for counting directly in the field five varve types which show differences mainly in thickness grain size and dropstone frequency are recognized internally they are mostly symmetric distinguishing them from traditional normally graded varves a feature that has also been observed in holocene glacimarine varves the different varve types indicate varying positions with respect to the ice front because of disturbances or lack of well defined textural or colour contrasts only the three varve types with intermediate thicknesses were counted three units including 1028 690 and 465 varves were measured and then analyzed as time series in order to detect cyclic signals some differences in the quality of the cyclic signals can be seen in spectral analyses depending on the main type of the varve that composes the unit however a peak around 12 yrs can be seen in most of the spectra and is interpreted as the sunspot cycle record a secondary peak near 24 26 yr also may be related to this phenomenon hale cycle four major cycles recognized in the field but not in the spectra that represent major glacial advances and retreats can also be related to a solar periodicity of 2500 3000 yr the recognition of sunspot cycles in these carboniferous varves is not unusual as they are found in other ancient varve successions random processes typified by the distribution of dropstones played an important role in disturbing the climatic signal in this sedimentary environment the random process of sediment transport and deposition by ice rafting disturbs the cyclic climatic signal mainly in proximal varve successions increased water motion and distance to the source of sediment toward the open sea tend to produce more homogeneous very fine grained distal varves eventually causing the loss of varve like appearance the remaining varves located at intermediate positions with respect to the glacio related sediment source seem to be the best suited for recording climatic cyclicity as shown by spectral analyses

from extreme rainfall to drought 250 years of annually resolved sediment deposition in santa barbara basin california abstract the mediterranean climate of southern california is marked by droughts and extreme precipitation events here we use elemental variations generated by scanning x ray fluorescence xrf to identify droughts and floods in recently deposited 1755 2008 sediments of santa barbara basin sbb from box core spr0901 04bc the first principal component pc1 of the scanning xrf elements has high loadings for elements associated with the lithogenic component of sbb laminae couplets while the second pc2 is associated with biogenic components we interpret pc1 as a proxy for river runoff and pc2 as a proxy for marine productivity high values of pc1 are associated with el nino events and positive warm phases of the pacific decadal oscillation pdo while low values of pc2 are associated with el nino events and negative cool phases of the pdo droughts such as the 1934 40 1949 56 and 1989 91 events coincide with low pc1 values in addition to distinguishing interannual and decadal variability in the elemental composition of sbb sediments several historic floods can be recognized including a gray flood layer associated with the 1861 62 flood and a peak in pc1 associated with the flood following the st francis dam disaster in 1928

deglacial nitrogen isotope changes in the gulf of mexico evidence from bulk sedimentary and foraminifera bound nitrogen in orca basin sediments 1 constraining variations in marine n2 fixation over glacial interglacial timescales is crucial for determining the role of the marine nitrogen cycle in modifying ocean productivity and climate yet paleo records from n2 fixation regions are sparse here we present new nitrogen isotope 15n records of bulk sediment and foraminifera test bound fb nitrogen extending back to the last ice age from the oligotrophic gulf of mexico gom previous studies indicate a substantial terrestrial input during the last ice age and early deglacial for which we attempt to correct the bulk sediment 15n using its observed relationship with the c n ratio both corrected bulk and fb 15n reveal a substantial glacial to holocene decrease of 15n toward holocene values of around 2 5 similar to observations from the caribbean this 15n change is most likely due to a glacial to holocene increase in regional n2 fixation a deglacial peak in the fb 15n of thermocline dwelling foraminifera orbulina universa probably reflects a whole ocean increase in the 15n of nitrate during deglaciation the 15n of the surface dwelling foraminifera globigerinoides ruber and the corrected bulk 15n show little sign of this deglacial peak both decreasing from last glacial values much earlier than does the 15n of o universa this may indicate that g ruber and bulk n reflect the euphotic zone signal of an early local increase in n2 fixation our results add to the evidence that during the last ice age the larger iron input from dust did not lead to enhanced n2 fixation in this region rather the glacial to holocene decrease in 15n is best explained by a response of n2 fixation within the atlantic to the deglacial increase in global ocean denitrification

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event 1 oceanic anoxic event 2 oae2 spanning the cenomanian turonian boundary ctb represents one of the largest perturbations in the global carbon cycle in the last 100 myr the 13ccarb 13corg and 18o chemostratigraphy of a black shale bearing ctb succession in the vocontian basin of france is described and correlated at high resolution to the european ctb reference section at eastbourne england and to successions in germany the equatorial and midlatitude proto north atlantic and the u s western interior seaway wis 13c offset between 13ccarb and 13corg is shown to be a good pco2 proxy that is consistent with pco2 records obtained using biomarker 13c data from atlantic black shales and leaf stomata data from wis sections boreal chalk 18o records show sea surface temperature sst changes that closely follow the 13c pco2 proxy and confirm tex86 results from deep ocean sites rising pco2 and sst during the late cenomanian is attributed to volcanic degassing pco2 and sst maxima occurred at the onset of black shale deposition followed by falling pco2 and cooling due to carbon sequestration by marine organic productivity and preservation and increased silicate weathering a marked pco2 minimum 25 fall occurred with a sst minimum plenus cold event showing 4 c of cooling in 40 kyr renewed increases in pco2 sst and 13c during latest cenomanian black shale deposition suggest that a continuing volcanogenic co2 flux overrode further drawdown effects maximum pco2 and sst followed the end of oae2 associated with a falling nutrient supply during the early turonian eustatic highstand

varve formation in the gulf of california insights from time series sediment trap sampling and remote sensing the varved sediments that accumulate in the central gulf of california guaymas and carmen basins provide a record that allows for the resolution of annual to decadal scale climate variability in this region time series sediment trapping combined with remotely sensed observations of sea surface temperature avhrr and color czcs have been used to examine the mechanism of varve formation in the central gulf sst and surface pigment concentration records for both the mainland and baja sides of the gulf display similar seasonal trends high temperatures and low pigment concentrations occur synchronously on both sides of the central gulf from june through to october in association with the 1991 92 el nino warm temperatures persist in the central gulf until december low ssts typically occur from december through may with high pigment concentrations marking the period from november through april the summer early fall june october is a time of high terrigenous and biogenic sediment fluxes during this time of year the total flux is dominated by eolian transported lithogenic material and dark laminae are deposited during this period during el nino years high terrigenous fluxes may extend into winter light laminae represent deposition from november through may during which time biogenic material dominates the total sediment flux high opal fluxes beginning in november are attributed to seasonal cooling of surface water and upward mixing of nutrients true upwelling conditions do not develop in the gulf until late winter spring during this time the total flux is still dominated by opal but the magnitude of the flux is reduced this may be an artifact of phytoplankton grazing and not lower production rates

millennial scale climate change and intermediate water circulation in the bering sea from 90 ka a high resolution record from iodp site u1340 1 millennial scale climate events in the north pacific are thought to be related to changes in the circulation of north pacific intermediate water which may have formed in the bering sea in the past to advance our understanding of the mechanisms that underlie millennial scale events bering sea sediment cores from the integrated ocean drilling program site u1340 were used to construct high resolution multiproxy climate records of the last 90 000 years sediment density records show millennial scale events resembling dansgaard oeschger events several of which are laminated interstadials were characterized by 3 5 c warming increased productivity driven by upwelling and reduced benthic oxygenation bering sea intermediate water also changed over longer timescales our records show the presence of intermediate water with lower salinity and higher oxygen content than modern beginning around 60 ka and persisting until the beginning of the deglaciation the bolling allerod was characterized by high productivity laminated sediments and strong denitrification signature our data support the idea that productivity derived changes in oxygenation at intermediate water source regions may have contributed to the intensification of the north pacific wide oxygen minima during the bolling allerod

processes controlling the accumulation of diatoms in sediments a model derived from british columbian fjords the transformation of biocoenosis to taphocoenosis of diatom assemblages was examined using monthly sediment traps over a 3 year period at four sites in the fjords of british columbia the fjords were chosen as a natural laboratory where productivity is high and seasonally variable and where geological rates of sediment accumulation approach the biological rates of production and flux the composition of trap samples from different depths was quantified and compared with the surface sediment recovered by box cores fragmentation caused by zooplankton grazing preferentially destroys 20 50 of the early spring and 50 75 of the late spring and early summer production grazing activity and incorporation into pellets does not otherwise affect preservation differential dissolution occurs during settling through the water column taxa with a high surface to volume ratio are preferentially lost low level lateral advection tends to concentrate heavy robust taxa while strong advection affects all particles equally and has no net biasing effect the interaction of these processes results in a sediment assemblage in which winter and fall taxa are more common than they are in the plankton while the early spring bloom is badly underrepresented multivariate analyses indicate that the sediment is dominated by the early summer bloom but caution must be exercised in this interpretation because the bloom is characterized by a species skeletonema costatum which is common at all seasons of the year and therefore is not a reliable indicator of a single period of production the end result is a decrease in seasonal contrast and at some sites a reordering of seasonal proportion in the sediment while the seasonal composition can still be identified there is also evidence of homogenization of sediment assemblages with some of the original spatial variability obscured taken to an extreme a unique fossil assemblage may be produced which cannot be statistically related to any combination of seasons of production three factors which might affect preservation of deep sea assemblages water depth accumulation rate and degree of bioturbation do not have a measurable effect in fjord environments strong modification of assemblages can occur within the upper 500 m deep sea monitoring programs which do not include this interval may lead to erroneous conclusions concerning production and flux to the sediments

interhemispheric ice sheet synchronicity during the last glacial maximum the timing of the last maximum extent of the antarctic ice sheets relative to those in the northern hemisphere remains poorly understood we develop a chronology for the weddell sea sector of the east antarctic ice sheet that combined with ages from other antarctic ice sheet sectors indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of northern hemisphere ice sheets surface climate forcing of antarctic mass balance would probably cause an opposite response whereby a warming climate would increase accumulation but not surface melting our new data support teleconnections involving sea level forcing from northern hemisphere ice sheets and changes in north atlantic deep water formation and attendant heat flux to antarctic grounding lines to synchronize the hemispheric ice sheets

holocene lake development of two dalmatian lagoons malo and veliko jezero isle of mljet in respect to changes in adriatic sea level and climate abstract within the austrian igbp pages project palaeolimnology of adriatic alpine lakes paal geochemical and diatom analyses were performed on sediment cores of malo and veliko jezero two karstic coastal lakes on the island mljet croatia combined with diatom calibration they provide evidence of remarkable environmental changes during the holocene the formation of the lakes in the early holocene was triggered by a rise in the adriatic sea level from approximately 50 to 30 m which resulted in the transmission of seawater through karst and by a temporary increase in precipitation the onset of this pluvial period was dated in malo jezero at 8 4 kyr b p and had its maximum approximately 7 6 kyr b p it was briefly interrupted by a dryer episode from about 7 2 until 7 1 kyr b p between 6 and 5 5 kyr b p a transition to the present mediterranean climate occurred the marine ingression into veliko jezero through the soline channel with a present depth of 2 5 m took place about 5 kyr b p from 5 to 4 kyr b p the oscillating sea level gradually approached the present value a tephra layer at 7 3 kyr b p in both lakes was related to sudden environmental changes that were probably caused by tectonic movements accompanying italian volcanism

sediment fluxes and varve formation in santa barbara basin offshore california results from a year long sediment trap study provide the first direct observations of seasonal variability in sediment fluxes to the sea floor in santa barbara basin offshore california and are used to evaluate varve formation in this basin sediment fluxes throughout the year are dominated by lithogenic material biogenic sediments primarily silica are of secondary importance we conclude that the combination of high lithogenic fluxes and low biogenic fluxes during the fall winter period results in the deposition of dark laminae the onset of upwelling and high surface productivity in the spring results in high biogenic silica fluxes that last into the summer the relative contribution of silica to the total sediment flux is highest during this spring summer period and we suggest that light laminae are formed at that time this is consistent with previous suggestions that sediment input is the primary factor controlling varve formation in this basin

glacio isostatic control on hypoxia in a high latitude shelf basin in high latitude continental shelf environments late pleistocene glacial overdeepening and early holocene eustatic sea level rise combined to create restricted marine basins with a high vulnerability to oxygen depletion here we show that ongoing glacio isostatic rebound during the holocene may have played an important role in determining the distribution of past hypoxia in these environments by controlling the physical exchange of water masses and the distribution of large scale phosphorus p sinks we focus on the baltic sea where sediment records from a large presently oxic sub basin show evidence for intense hypoxia and cyanobacteria blooms during the holocene thermal maximum using paleobathymetric modeling we show that this period was characterized by enhanced deep water exchange allowing widespread phosphorus regeneration intra basin sills then shoaled over a period of several thousand years enhancing p burial in one of the sub basins together with climate forcing this may have caused the termination of hypoxia throughout the baltic sea similar rearrangements of physical and chemical processes likely occurred in response to glacio isostatic rebound in other high latitude shelf basins during the holocene

cyclic sedimentation produced by fluctuations in meltwater discharge tides and marine productivity in an alaskan fjord glacimarine sediment deposited in the fjord adjacent to muir glacier in south eastern alaska consists of rhythmically laminated muds stratified sandy mud sand and gravelly mud facies cyclicity is recorded by gravelly mud facies deposited during winter by ice rafting black mud laminae formed by spring plankton blooms and variations in tidal rhythmite thickness and texture produced by the interaction of meltwater discharges and tidal currents in the macrotidal fjord regular cyclicity in laminae thickness is tested statistically by fourier transform and can be attributed to a lunar tidal cycle control in the five cores collected up to 6 km from the sediment source cores close to the source can have additional laminae as a result of discharge fluctuations and distal cores may lack full cycles because of variability in the plume path and attenuation with distance cyclic variations in sediment texture are recorded in magnetic susceptibility ms profiles of the cores high ms values are produced by turbidite sand beds or by stratified sandy mud deposited by overflow plumes during peak summer meltwater discharge low values reflect muddy intervals deposited during periods of low meltwater discharge such as during autumn and winter sediment accumulation rates measured by 210pb dating range from 82 cm year 1 2 km from the sediment source at the head of the fjord to 16 cm year 1 6 km away these rates are within the same range as average sediment accumulation rates determined from cyclic seasonal markers within the cores these data show that with careful documentation annual cycles of glacimarine sediment accumulation can be detected within marine cores cores collected from the distal portion of the basin were deposited during the transition of muir glacier from a tidewater terminus ending in deep water to a terrestrial glacier with an ice contact delta deposited in front of the terminus this transition is recorded by a coarsening upward sedimentary sequence formed by turbidite sands originating from the prograding delta above fine grained laminated basin fill deposited by turbid overflow plumes

the significance of diatoms in the formation of laminated sediments of the shaban deep northern red sea laminated sediments spanning the last 20 000 years though not continuously in the shaban deep a brine filled basin in the northern red sea were analyzed microscopically and with backscattered electron imagery in order to determine laminae composition with emphasis on the diatomaceous component based on this detailed study we present schematic models to propose paleoflux scenarios for laminae formation at different time slices the investigated core geob 5836 2 26 12 61 n 35 21 56 e water depth 1475 m shows light and dark alternating laminae that are easily distinguishable in the mid holocene and at the end of the deglaciation 13 15 ka period light layers are mainly composed of coccoliths terrigenous material and diatom fragments while dark layers consist almost exclusively of diatom frustules monospecific or mixed assemblages the regularity in the occurrence of coccolith diatom couplets points to an annual deposition cycle where contrasting seasons and associated plankton blooms are represented diatoms fall winter deposition coccoliths summer signal we propose that for the past 15 000 years the laminations represent two season annual varves strong dissolution of carbonate with the concomitant loss of the coccolith rich layer in sediments older than 15 ka prevents us from presenting a schematic model of annual deposition however the diatomaceous component reveals a marked switch in species composition between last glacial maximum lgm sediments dominated by chaetoceros resting spores and sediments somewhat younger 18 19 ka dominated by rhizosolenia we propose that different diatom assemblages reflect changing conditions in stratification in the northern red sea strong stratification conditions such as during two meltwater pulses at 14 5 and 11 4 ka are reflected in the sediment by rhizosolenia layers while chaetoceros dominated assemblages represent deep convection conditions

reverse engineering mother nature shale sedimentology from an experimental perspective abstract experimental study of the sedimentology of shales can take a variety of forms at its simplest one can experiment with suspensions in a glass jar and try to understand their settling behavior or one can manipulate mud in a tank or bucket to gain insights into its rheology this approach was championed over a century ago by sorby and the insights gained can be quite profound more recently tank and settling tube experiments of animal sediment interactions compaction behavior and sediment unmixing via re suspension have proven to be highly informative in spite of their simplicity flumes can be used to obtain quantitative information about depositional and erosional parameters and to generate fundamental bedforms in flume experiments however it is of critical importance that the flume be designed in a way that flocculated materials move under shear stress conditions that would be reasonable in natural environments although much flume work on muds has been conducted by hydraulic engineers the transfer of that knowledge to sedimentology is hampered by the fact that engineers and sedimentologists are interested in different though not mutually exclusive products from such experiments engineers and hydrologists are commonly concerned with quantifying fluid flow properties whereas sedimentogists are particularly interested in the sedimentary products that result from a variety of flow conditions recent sedimentologically oriented flume studies have shown that muds can form deposits at flow velocities and shear stresses that would suffice to transport and deposit medium grained sand mud suspensions are prone to flocculation and the resulting floccules travel in bedload and form ripples that accrete into beds the latter finding suggests that many laminated shales were deposited from currents rather than by settling from slow moving or still water there are many other sedimentary features in shales that can potentially be reproduced in flume studies and in the future serve to provide a quantitative basis for shale sedimentology

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation