climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

origins and paleoceanographic significance of laminated muds from the ulleung basin east sea sea of japan abstract a detailed facies analysis of long piston core sediments from the ulleung basin reveals four mud facies laminated mud crudely laminated mud bioturbated mud and homogenous mud the laminated and homogeneous muds were most likely deposited from turbidity currents whereas the bioturbated and crudely laminated muds were formed by hemipelagic pelagic sedimentation under well oxygenated and poorly oxygenated bottom water conditions respectively a detailed analysis of vertical distribution of the mud facies together with a chronostratigraphic framework derived from correlative tephra layers with known eruption ages reveals paleoenvironmental changes during the late quaternary during the period between 49 and 23 ka eustatic lowering of sea level facilitated frequent slope failure resulting in repeated deposition of fine grained turbidites on the basin floor normal hemipelagic sediments were intensively bioturbated under well oxygenated bottom water conditions during the period between 23 and 13 to 11 ka deposition from turbidity currents continued but hemipelagic sediments were non bioturbated under poorly oxygenated bottom water conditions the bottom water deoxygenation is attributed to further lowering of sea level during the last glacial period and consequent intensified stratification in the water column by freshwater supply to the nearly isolated sea primary laminae preserved in the crudely laminated mud generally exhibit low compositional bimodality in backscattered electron images which suggests low surface primary productivity and presence of superficial micro bioturbation after rapid rise of sea level at 13 to 11 ka the slopes were stabilized and pelagic sedimentation has prevailed under well oxygenated bottom water conditions

extreme climatic conditions recorded in santa barbara basin laminated sediments the 1835 1840macoma event abstract the santa barbara basin sbb record of laminated sediment well known for its excellent time resolution shows the presence of an unusual once in a millenium event in the period 1835 1840 at a depth of 55 57 cm below the surface of the seafloor this macoma event is the brief flourishing of a macrofaunal community in the deep center of the sbb from which large organisms are normally excluded by the lack of oxygen shells of the pelecypodmacoma leptonoidea dall and associated fossils which congregate in a thin layer dated at 1840 provide evidence for a sudden local extinction of macrobenthos by suffocation various stratigraphic evidence suggests thatm leptonoidea colonized the basin floor for a few years prior to 1840 as a result of temporarily decreased productivity and increased oxygen content in the water spilling over the sill into the basin historical eyewitness reports indicate unusually severe winter storms from southeasterly directions during the 1830s in the sbb we suggest that coastal upwelling was severely reduced during 1835 1839 with the effect of reducing the intensity of the oxygen minimum layer themacoma event apparently is one manifestation of large scale climatic anomalies felt throughout north america and which were possibly linked to the major volcanic eruption of cosiguina nicaragua in 1835

biological forcing of hemipelagic sedimentary laminae evidence from odp site 893 santa barbara basin california core observation x radiography and scanning electron microanalysis of distinctly laminated indistinctly laminated and nonlaminated sediments from odp site 893 show that laminated as well as nonlaminated i e massive hemipelagic sediments can form in the absence of bioturbation this view contrasts with conventional sedimentological interpretations equating laminated hemipelagic sediments with anoxic water masses i e absence of bioturbation and nonlaminated sedimentary intervals exclusively with oxygenation episodes that permitted infaunal colonization we conclude that heterogeneities in the texture and or composition of sediment supply are necessary for the production of laminated sediments the absence of hydraulic and biological reworking permits their preservation laminae at site 893 have two prominent components biosilica and terrigenous detritus compositional contrasts between adjacent laminae in x radiographs reflect short term seasonal and subseasonal heterogeneities in sediment flux core intervals with large contrasts in density and or composition between adjacent laminae are termed as having high bimodality hb hb couplets produce distinctly laminated sediments that intergrade vertically with indistinctly laminated and nonlaminated sediments adjacent laminae in indistinctly laminated sediments possess minimal contrasts in bulk density and composition nonlaminated sediments are compositionally and texturally homogeneous many biosiliceous laminae responsible for distinctly laminated hb couplets record mass flocculation and sedimentation of ungrazed diatom frustules formed during discrete bloom events ecological interpretation of diatomite laminae suggests that many were effectively self sedimenting i e the production of gelatinous exudates by phytoplankton facilitated their aggregation and rapid sedimentation the results indicate that lamination style preserves meaningful ocean climate data concerning episodicity heterogeneity and export efficiency of biologically mediated sedimentary flux in upwelling dominated coastal ecosystems

climatically controlled marker layers in santa barbara basin sediments and fine scale core to core correlation varved sediments with annual layering can provide a detailed history of environmental conditions of marginal ocean basins and of lakes to reconstruct this history requires fine scale correlation and correct age assignment in the santa barbara basin a combination of x radiography water content profiles and microfossil stratigraphy yields correlations of the desired resolution x radiography permits identification of individual layers 1 2 mm thick that differ in porosity or pore water content and hence x ray absorption microfossils and sedimentological parameters provide the clues to the presence for el nino years e g in a d 1984 1959 and 1942 varves allowing the tie in to absolute years within this century el nino layers once identified are readily recognized on the radiographs and within the porosity profiles counting of laminae in x radiographs and core to core correlation via water content then allow establishing age scales for other cores a prominent shell layer in the first half of the 19th century is dated at a d 1838 this event macoma i is of supraregional significance

seismic reflector imaging using internal multiples with marchenko type equations we present an imaging method that creates a map of reflection coefficients in correct one way time with no contamination from internal multiples using purely a filtering approach the filter is computed from the measured reflection response and does not require a background model we demonstrate that the filter is a focusing wavefield that focuses inside a layered medium and removes all internal multiples between the surface and the focus depth the reflection response and the focusing wavefield can then be used for retrieving virtual vertical seismic profile data thereby redatuming the source to the focus depth deconvolving the upgoing by the downgoing vertical seismic profile data redatums the receiver to the focus depth and gives the desired image we then show that for oblique angles of incidence in horizontally layered media the image of the same quality as for 1d waves can be constructed this step can be followed by a linear operation to determine velocity and density as a function of depth numerical simulations show the method can handle finite frequency bandwidth data and the effect of tunneling through thin layers

archaeological sedimentology of overbank silt deposits on the floodplain of the ohio river near louisville kentucky abstract the surface of the floodplain of the ohio river about 20km southwest of louisville kentucky is a series of linear ridges and swales that are subparallel to the channel of the river which here is relatively straight and flows southward numerous prehistoric occupational sites are located on these ridges the sediments that underlie the ridges which were examined in four archaeological excavations as deep as 8 m are predominantly sandy silt and silty fine to very fine sand and appear to be mainly the product of overbank deposition from suspended load abundant cultural material and occupational sites dating as early as 10 000 years bp are found in the sediments at depths as great as 6 5 m the fine sediments of the floodplain are underlain by sand and gravel the context of the cultural materials and the stratigraphy and morphology of the deposits indicate that the ridged deposits began as linear riverside sand and gravel bars these were succeeded upward by fine grained overbank deposits in which the ridged morphology was maintained because the overbank silt and fine sand were deposited as prograding elongate bars at high water as the floodplain ridge built upward the sedimentation rate decreased and the sand content of the sediments diminished and as the river channel occasionally shifted the ridged deposits were built in successive subparallel sequences two archaeological consequences are implicit in this depositional model of orderly growth of the floodplain first available archaeological data from floodplain segments along other parts of the river should confirm the model and second the model should make it possible to search the floodplains of the ohio river for stratified sites of any desired age

the impact of hydrodynamics authigenesis and basin morphology on sediment accumulation in an upwelling environment the miocene monterey formation at shell beach and mussel rock pismo and santa maria basins central california u s a abstract in the sections at shell beach pismo basin and mussel rock santa maria basin both along the central california coast the miocene monterey formation is composed of laminated biosiliceous organic rich and phosphate rich sediments which are intercalated with carbonates and volcanogenic deposits the presence of small and large scale scours conglomerates gravity flow deposits slumps and condensed intervals reveals the importance of sediment reworking which is related to the presence of bottom currents the general morphology of the basins and recurrent high energy events of likely seismic origin the lithologies reflect strong upwelling enhanced primary productivity and the presence of an oxygen minimum zone which is indicated by ubiquitous lamination a general absence of bioturbation with the rare exception of traces related to the gravity flow displacement of trace makers high pyrite mo and u concentrations and molar ratios of total organic carbon and organic phosphorus toc p org of up to 2000 oxygen depletion was particularly severe during the early langhian and the late serravallian and early tortonian and favored the preservation of organic matter episodes of deposition of organic rich sediment were followed by longer phases of subdued sediment accumulation and early diagenetic phosphogenesis which resulted in the formation of a low porosity less permeable lid in the near surface sediments that assisted in preserving organic matter phosphogenesis occurred throughout the time interval considered approximately 17 5 6 5 ma and phosphate rich sediments formed especially during periods of sedimentary condensation in the langhian and earliest serravallian and the latest tortonian and early messinian a comparison of temporal trends in the type and quantity of deposited sediments between the two sections at shell beach and mussel rock and three sections of the santa barbara basin el capitan state beach naples beach and haskell beach confirms that towards the top of the monterey formation sediments become enriched in biosilica in all three basins the transition into this lithology occurred diachronously during the serravallian in the pismo and santa maria basins and tortonian in the santa barbara basin and was probably related to a diachronous shift to more intense upwelling in all three basins a phase of important condensation and phosphogenesis terminated monterey type sedimentation during the latest tortonian and early messinian in both the santa maria and santa barbara basins the uniform expression of this phase is interpreted as the result of improved connections between the two basins

dinoflagellate cysts from sediment traps deployed in the bellingshausen weddell and scotia seas antarctica dinoflagellate cysts have been recovered from six long term 1 2 yr sediment trap moorings deployed in the bellingshausen weddell and scotia seas antarctica these traps mostly moored near the sea bed to sample the nepheloid layer were located both within and to the north of the maximum sea ice limit the numbers of cysts together with the composition of the assemblages reinforce the importance of the maximum sea ice limit as a modern biogeographic boundary for the distribution of dinoflagellate cysts cysts derived from heterotrophic dinoflagellates make up the highest proportions within the assemblages recovered from the traps one trap sampled the export production revealing little difference in cyst flux over those sampling the nepheloid layer cyst flux appears to be highest in areas closest to the antarctic convergence north of the maximum sea ice limit and to high nutrient availability there are however differences between the sediment trap assemblages and those recovered from core top samples at the same or nearby sites these differences in the greater number of cysts and in the higher numbers of round brown protoperidinium cysts in the traps may reflect annual differences in the primary productivity and or cyst production in the area in some areas the sediment record may preserve little information about local surface water productivity because of the activity of bottom water currents for example those arising from the antarctic circumpolar current

a depositional model for organic rich duvernay formation mudstones abstract the upper devonian duvernay formation of western canada is an organic rich shale formation now targeted as a hydrocarbon reservoir we present a detailed sedimentological analysis of the duvernay formation in order to better understand organic rich mudstone depositional processes and conditions and to characterize the vertical and lateral heterogeneity of mudstone lithofacies that affect petrophysical and geomechanical rock properties organic rich mudstone facies of the duvernay formation were deposited in a dynamic depositional environment by a variety of sediment transport mechanisms including suspension settling turbidity currents and bottom water currents in variably oxygenated bottom waters suspension settling dominated in distal relatively deep areas of the basin but evidence for weak turbidity currents and bottom water currents was observed in the form of graded beds and thin grain supported siltstone laminae organic enrichment primarily occurred in distal areas as a result of bottom water anoxia and low depositional rates of inorganic sediment in deep water locations near platform margins alternating silty sandy contourite beds and organic rich mudstone beds are present the former interpreted to have been deposited and reworked by bottom water currents flowing parallel to slope in shallower more oxygenated settings mudstone lithologies vary from calcareous to argillaceous these sediments were deposited from suspension settling turbidity currents and bottom water currents although primary sedimentary structures are often obscured by extensive bioturbation locally organic enrichment in dysoxic rather than anoxic bottom waters was driven by a slightly increased sedimentation rate and possibly also by aggregation of sedimentary particles in the water column due to interaction between organic matter and clay minerals large variations observed in sediment composition from siliceous to calcareous to argillaceous reflect multiple biogenic carbonate and clastic sediment sources sediment composition is influenced by basin morphology circulation patterns sea level variation and proximity to sediment sources

cellularly preserved microbial fossils from 3 4 ga deposits of south africa a testimony of early appearance of oxygenic life abstract fossil record of earliest earth s life is scant and restricted to simple kerogenous filaments spheres and lenticular microfossils which origin and taxonomic affiliation are still ambiguous here we report clusters of cell like bodies found in massive and weakly laminated black cherts of the 3 4 ga kromberg formation onverwacht group barberton greenstone belt south africa known earlier for benthic microbial mats and microfossils morphological traits and mineralization of the kromberg microfossils match those known from modern and fossil cyanobacteria micro raman and sem eds analyses showed that the cell like bodies fossilized mostly due to early mineralization with al silicates enclosing dispersed carbonaceous kerogenous matter derived from their thermally altered cell remains although in widespread opinion the early archean life is predominantly represented by benthic microbial mats the random non laminated distribution of the studied cyanobacteria like microfossils in the kromberg cherts is suggestive for probably benthic planktonic life cycle of these microbiota the paper also discusses how the morphological similarity of the kromberg fm cell like microfossils to geologically much younger and extant coccoidal cyanobacteria may influence the debate concerning the time of origin of earth s oxic atmosphere

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

deglacial seasonal and sub seasonal diatom record from palmer deep antarctica the antarctic peninsula is one of the most sensitive regions of antarctica to climate change here ecological and cryospheric systems respond rapidly to climate fluctuations a 4 4m thick laminated diatom ooze deposited during the last deglaciation is examined from a marine sediment core odp site 1098 recovered from basin i palmer deep western antarctic peninsula this deglacial laminated interval was deposited directly over a glaciomarine diamict hence during a globally recognised period of rapid climate change the ultra high resolution deglacial record is analysed using sem backscattered electron imagery and secondary electron imagery laminated to thinly bedded orange brown diatom ooze near monogeneric hyalochaete chaetoceros spp resting spores alternates with blue grey terrigenous sediments open water diatom species these discrete laminae are interpreted as austral spring and summer signals respectively with negligible winter deposition sub seasonal sub laminae are observed repeatedly through the summer laminae suggesting variations in shelf waters throughout the summer tidal cycles high storm intensities and or intrusion of circumpolar deep water onto the continental shelf introduced conditions which enhanced specific species productivity through the season

quantitative and qualitative relationships between planktonic diatom communities and diatom assemblages in sedimenting material and surface sediments in lake baikal siberia endemic planktonic diatoms are a major component of lake baikal sediments during interglacial periods to investigate how these diatom assemblages are altered during sediment formation quantitative plankton monitoring 1995 1998 was integrated with sediment trapping over 2 yr 1996 1997 in baikal s southern basin depth 1 400 m the traps consisted of both open 6 monthly and sequential 2 weekly collectors deployed throughout the water column sedimentation was seasonal with diatom species composition valve abundance and total dry mass reflecting changes in the planktonic communities sedimented assemblages were transmitted largely intact to the deepest traps 1 300 1 390 m some compositional blurring occurred from differential sinking rates and dissolution of diatom valves a rapid mass flux event of aulacoseira skvortzowii and a baicalensis was recorded in summer 1997 with particle sinking rates between 60 and 100 m d 21 and dry mass fluxes 5gm 22 d 21 although dissolution was evident for all species more delicate taxa were preferentially affected e g a skvortzowii vegetative cells and finesynedra species whereas nitzschia acicularis valves were almost entirely dissolved within the water column comparing trap and plankton diatom assemblages with those in nearby core tops demonstrated that a fundamental taphonomic change occurs in the surface sediment with sedimentary diatom accumulation rates being only about 1 of trap deposition and plankton production rates dissolution was significant in explaining 5 30 of species variance between all taphonomic levels plankton trap samples and surface sediments results indicate that diatom based paleoclimatic records in lake baikal sediments could be improved and refined by taking taphonomic considerations into account

aeolian particles in marine cores as a tool for quantitative high resolution reconstruction of upwelling favorable winds along coastal atacama desert northern chile upwelling areas play a major role in ocean biogeochemical cycles and ultimately in global climate especially in higly productive regions as the south eastern pacific this work is based on the analysis of the aeolian lithic particles accumulated in laminated sediments off mejillones 23 s in the eastern boundary humboldt current system it proposes a high resolution quantitative reconstruction of the upwelling favorable southerly wind strength in the past 250 years comparing its variability with changes in organic carbon export preserved changes to the sea bottom the increase of the intensity and variability in fluxes of particles larger than 35 m and 100 m since the second half of the 19th century and during the 20th century confirms a general strengthening of southerly winds in the region spectral analysis on the complete time series of yearly depositional fluxes indicates that sedimentary variability can be explained by a combination of interannual enso to decadal pdo oscillations similar to the ones yielded by the analysis of the interdecadal pacific oscillation index however when applied separately to the lithic fluxes of the first and last centuries of the time series the method shows that relative to the one of the interannual mode of variability the influence of the decadal mode has increased in the recent period based on the presence absence of particles with sizes larger than 35 100 m each year of the time series is classified as a low wind 12 m s year from the ad 1754 1820 period to the ad 1878 1998 one the proportion of low and intermediate wind years decreased from 12 and 74 to 3 and 68 respectively whereas the proportion of strong wind years increased from 14 to 29 for these periods the mean organic carbon also increased 22 stating the strong relation between export preservation productivity rate and southerly wind intensity in the recent period from ad 1950 on for which the oceanic nino index is available the strong wind years ad 1982 1983 1994 and 1997 correspond to large values of this index suggesting that constructive interferences that result from the interplay between interannual and decadal oscillations modes might explain in part the reinforcement of the winds along the north chilean coast

deglacial ocean and climate seasonality in laminated diatom sediments mac robertson shelf antarctica the palaeoceanography and climate history of the east antarctic margin eam are less well understood than those of west antarctica yet the eam plays an important role in deep ocean circulation and the global ocean system and has likely done so in the past deglacial age marine sediments from the eam provide clues about its past role during this critical period of rapid climate change several deep basins across the eam such as iceberg alley 67 s 63 e on the mac robertson shelf mrs accommodate thick marine sequences that archive the deglaciation in the form of diatom rich continuously laminated varved sediments these laminated sediments are pristinely preserved and contain seasonal and long term information on the cryospheric and palaeoceanographic changes associated with the rapid retreat of the glacial ice sheet across the mrs we present results of microfabric analysis of the lower 2 m of deglacial varves from jumbo piston core jpc43b iceberg alley backscattered electron imagery bsei of polished thin sections and scanning electron microscope secondary electron imagery sei of lamina parallel fracture surfaces are used to analyze the varves one hundred and ninety two laminations are investigated and their nature and temporal significance are discussed in terms of seasonal deposition and cyclicity of diatom species our high resolution palaeodata record exceptionally high diatom production and silica flux associated with the retreat of the east antarctic ice sheet and seasonal sea ice changes along the eam this information is invaluable for assessing cryospheric oceanographic variation and therefore the local and regional response to this period of rapid climate change varves are made up of lamina couplets comprising i thickly laminated to thinly bedded orange orange brown very pure diatom ooze dominated by hyalochaete chaetoceros spp vegetative cells and resting spores and ii brown blue grey terrigenous angular quartz sand silt and clay with an abundant mixed diatom flora the colour variation between these two types of lamination is striking using floristic and textural information we interpret the diatom oozes as spring flux and the terrigenous laminae as summer flux each couplet pair represents one annual cycle and reflects seasonal changes in nutrient availability and stratification associated with the cyclical advance and retreat of seasonal sea ice the diatom oozes can reach up to 7 5 cm in thickness indicating enormous silica flux to the sea floor associated with ice sheet retreat

biogeochemical processes controlling oxygen and carbon isotopes of diatom silica in late glacial to holocene lacustrine rhythmites biogeochemical cycles and sedimentary records in lakes are related to climate controls on hydrology and catchment processes changes in the isotopic composition of the diatom frustules 18odiatom and 13cdiatom in lacustrine sediments can be used to reconstruct palaeoclimatic and palaeoenvironmental changes the lago chungara andean altiplano 18 15 s 69 10 w 4520 masl diatomaceous laminated sediments are made up of white and green multiannual rhythmites white laminae were formed during short term diatom super blooms and are composed almost exclusively of large sized cyclostephanos andinus these diatoms bloom during mixing events when recycled nutrients from the bottom waters are brought to the surface and or when nutrients are introduced from the catchment during periods of strong runoff conversely the green laminae are thought to have been deposited over several years and are composed of a mixture of diatoms mainly smaller valves of c andinus and discostella stelligera and organic matter these green laminae reflect the lake s hydrological recovery from a status favouring the diatom super blooms white laminae towards baseline conditions 18odiatom and 13cdiatom from 11 990 to 11 530 cal years bp allow us to reconstruct shifts in the precipitation evaporation ratio and changes in the lake water dissolved carbon concentration respectively 18odiatom values indicate that white laminae formation occurred mainly during low lake level stages whereas green laminae formation generally occurred during high lake level stages the isotope and chronostratigraphical data together suggest that white laminae deposition is caused by extraordinary environmental events el nino southern oscillation and changes in solar activity are the most likely climate forcing mechanisms that could trigger such events favouring hydrological changes at interannual to decadal scale this study demonstrates the potential for laminated lake sediments to document extreme pluriannual events

annual layering in the upper jurassic kimmeridge clay formation uk quantified using an ultra high resolution sem edx investigation abstract this paper reports the results of an ultra high resolution investigation of the geochemistry of the late jurassic kimmeridge clay formation kcf using scanning electron microscope energy dispersive x ray analysis sem edx sub millimetre banding is revealed in which each band approximately 112 m thick comprises a couplet of coccolith rich and coccolith poor sediment major element analysis reveals that regularly spaced peaks in the relative amount of calcium are associated with coccolith rich bands it is argued that each couplet represents an annual layer the calcium peaks corresponding to an annual bloom of coccolithophorids there is also a broad correlation between the calcium aluminium ratio and the ratios of sodium aluminium phosphorus aluminium and potassium aluminium to calcium aluminium ratios we tentatively suggest that there may be a link here sodium phosphorous and potassium today being key nutrients for coccolith productivity aluminium is taken as representing the background terrigenous clay fraction if each banded couplet is indeed annual and if the thickness of such bands were to be representative of the kcf as a whole then the post compactional thickness is broadly in agreement with sedimentation rates of 100 m per year calculated by oschmann 1990 this study confirms the view that the kcf in southern england accumulated in a predominantly anoxic environment that favoured the preservation of organic material within the bottom sediment bundles of bands clustering in groups of about 8 10 are tentatively related to short term changes in insolation possibly sun spot cycles

petrographic and geochemical study of organic matter in surficial laminated sediments from an upwelling system mejillones del sur bay northern chile a study of recent laminated sediments accumulated in the oxygen minimum zone of mejillones bay northern chile shows that the organic matter is autochthonous and deposited under varying oceanographic conditions sedimentary units dominated by light laminations have low values of total organic carbon total nitrogen and sulphur and chaotoceros content coupled with high values of yellow amorphous organic matter these were deposited under conditions of low primary productivity favoring the recycling of the major part of metabolizable organic matter in the water column and the accumulation only of non metabolizable organic matter in the bottom sediments in contrast a unit rich in dark laminations with high values of total organic carbon total nitrogen and sulphur shows high values of brown and black aom and chaetoceros content this sedimentary unit reflects increased flocculation of organic particles during a period of high productivity and fast transit of organic material through the column water thus diminishing the recycling of metabolizable organic matter and its accumulation with non metabolizable organic matter in the sediments finally a unit characterized by presence of both light and dark laminations was formed by abrupt alternations of the two oceanographic states described previously

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

self sedimented diatom mats as agents of exceptional fossil preservation in the oligocene florissant lake beds colorado united states microbial mats play a major role in the formation of exceptionally preserved fossil deposits by overgrowing and binding organic remains and sedimentary particles this minimizes hydrodynamic and biological disruption of dead organisms and sedimentary laminae but published works all implicate prokaryotic cyanobacteria as the microbial agent however exceptionally well preserved macrofossils of the oligocene florissant lake beds colorado united states are enveloped in matted aggregations of mucous secreting pennate diatom frustules it is suggested that the macrobiota became entrapped in mucous secreting mats of surface water blooms of planktonic diatoms in lake florissant as the mats and the incorporated macrobiota were sedimented out of the water column the mucosic mats and their associated bacterial communities arrested decay and promoted preservation of refractory tissues thus by a completely different mechanism the diatom mats fulfilled the same preservational role previously suggested for cyanobacterial mats this hitherto unrecognized mode of preservation may be an important causative factor in the formation of exceptionally preserved lacustrine fossil biotas

ice retreat in the eastern antarctic peninsula region the application of diatoms for understanding climate change abstract climate driven retreat of ice shelves on the eastern side of the antarctic peninsula has opened up new coastal marine environments enabling the development of primary productivity diatom assemblages in surface sediment samples from the eastern side of the antarctic peninsula were analyzed to investigate the use of diatoms as paleoenvironmental indicators of changes in glacial and sea ice extent here we present surface sediment diatom assemblage data from samples taken on 5 cruises between 2000 2012 from the northeastern most tip of the antarctic peninsula prince gustav channel larsen a and larsen b embayments and a single sample from just east of larsen c ice shelf absolute diatom abundance increases to the northeast reflecting greater contribution of diatom valves originating from surface waters that are ice free for a longer period of time this trend is mirrored by the relative abundance of chaetoceros subg hyalochaete a spring bloom indicator group the genus fragilariopsis is dominated by sea ice associated species including fragilariopsis curta fragilariopsis cylindrus fragilariopsis obliquecostata fragilariopsis sublinearis and fragilariopsis vanheurckii fragilariopsis spp relative abundance varies inversely with chaetoceros subg hyalochaete distributions of thalassiosira antarctica t1 and thalassiosira antarctica t2 interpreted as a cooler and warmer forms respectively while generally inverse to one another with the t antarctica t2 more common to the northeast are not straightforward with a pocket of high relative abundance in larsen b embayment these diatom data and their comparison to modern oceanography of the eastern antarctic peninsula provide a basis for further paleoceanographic work in the region

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

gas hydrate occurrences and their relation to host sediment properties results from second ulleung basin gas hydrate drilling expedition east sea the second ulleung basin gas hydrate drilling expedition ubgh2 recovered various forms of gas hydrate bearing sediments from 10 drill sites in the lower slope and basin floor of the ulleung basin to characterize the gas hydrate occurrences and the properties of the host sediments whole round core samples were taken from portions of recovered cores determined to be hydrate bearing based on infrared ir scanning these samples were further characterized by a variety of shipboard experiments such as imaging of the sediments with hand held ir and visual cameras measurements of pore water chlorinity within and around ir inferred cold regions in the core and grain size analysis of pore water squeeze cakes sediment compositions of selected samples were further characterized by x ray diffraction and scanning electron microscopes during post cruise analysis the shipboard and post cruise analysis results collectively indicate that the recovered gas hydrates mainly occur as 1 pore filling type bounded by discrete silty sand to sandy silt layers 2 fracture filling veins and nodules or 3 disseminated type in silt in addition minor but significant variation in gas hydrate concentrations were observed in diatomaceous silt where gas hydrates occur as pore filling material in layers dominated by intact diatom frustules gas hydrate accumulations of fracture filling type occur predominantly in regions where acoustic blanking features in the seismic record suggest gas migration from below the gas hydrate stability zone results from the ubgh2 core studies along with the analysis of similar samples from other expeditions including those executed by the ocean drilling program the integrated ocean drilling program and the first ulleung basin gas hydrate drilling expedition greatly improved our understanding of lithologic controls on marine gas hydrate occurrences

laminations from the palmer deep a diatom based interpretation 1 highly laminated holocene age diatomaceous sediments are characteristic of the palmer deep western antarctic peninsula ocean drilling program odp leg 178 site 1098 from 10 000 years b p to the present laminations are comprised of several groups of diatoms chaetoceros resting spores the dominant laminae former result from intense spring blooms rhizosolenia proboscia thalassiothrix and corethron are common also the consequence of summer production marked by a well stratified water column each lamination represents a single productivity event but laminations are not necessarily annual high concentrations of a subpolar form of eucampia antarctica in laminations between 9000 and 6700 years b p suggest early holocene warmth a consequence of southward intrusion of more subpolar waters the glacial interglacial transition is distinguished by pairs of laminae most likely deposited annually laminations with an overwhelming dominance of chaetoceros resting spores alternate with more terrigenous laminae representing alternation of intense spring blooms with more mixed deposition during the summer proximity to retreating glacial ice results in the supply of silt and sand that provides a marker bed between successive blooms

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

southern ocean laminated diatom ooze mat deposits and potential for palaeo flux studies odp leg 177 site 1093 laminated diatom ooze samples collected during odp leg 177 were analysed using scanning electron microscope sem and optical microscopy to test their potential as high resolution records of polar front hydrography surface production and export sem analysis from two intervals marine isotope stage mis 29 and 12 11 respectively recovered from 50 s in the atlantic ocean odp site 1093 hole a sections 13h 4 0 18 cm and 23h 4 0 22 cm show abundant and well preserved thalassiothrix antarctica mats thought to be indicative of rapid export from the surface and deposition in the sediment a preliminary analysis of laminae succession points to a possible annual couplet triplet succession of laminae and suggests exceptionally high local sedimentation rates of 57 and 80 cm kyr 1 for mis 12 11 and 29 respectively such high accumulation rates imply that local export from the surface layer and sequestration of biogenic silica and organic matter to the sediments may have been much higher than previously suggested resume des depot sedimentaires lamines de diatomites recueillis pendant le leg 177 de l ocean drilling program odp ont ete analyses en microscopie electronique a balayage sem et en microscopie optique ces enregistrements sedimentaires presentent un fort potentiel pour reconstituer avec une haute resolution la production de matiere exportee depuis la couche de surface de l ocean au niveau du front polaire l analyse en sem des stades isotopiques 29 et 12 11 sur du materiel collecte a 50 s dans le secteur atlantique de l ocean austral site odp 1093 forage a sections 13h 4 0 18 cm et 23h 0 22 cm revele des depots abondants et bien preserves de tapis de thalassiothrix antarctica suggerant une exportation rapide jusqu au sediment de materiel biogene genere a la surface de l ocean une analyse preliminaire des successions laminees par couple ou triplet indique des vitesses d accumulation sedimentaire exceptionnellement elevees 57 et 80 cm kan 1 respectivement pour les stades 12 11 et 29 de telles vitesses d accumulation suggerent que l exportation de matiere depuis la couche de surface de l ocean et ou la preservation de silice biogene dans le sediment peuvent etre bien plus elevees qu on ne le pensait jusqu a present

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

opal and organic carbon in laminated diatomaceous sediments saanich inlet santa barbara basin and the miocene monterey formation abstract laminated biosiliceous sediments from saanich inlet british columbia si the monterey formation california mf and santa barbara basin california sbb are organic rich and were studied to assess the suitability of si and sbb as modern analogs of the miocene mf and to explore the controls on distributions of opal and organic carbon to this end individual laminae and groups of laminae extracted from odp cores and outcrop samples were analyzed using a multi tracer geochemical approach total organic carbon opal c n ratios 13 c of organic matter om kerogen type and major and minor element abundances were measured si sediments are 52 84 detrital 15 45 opal and 1 2 organic carbon 13 c and c n ratios indicate a marine source of the om present in the sediments samples from the upper siliceous member of the mf are 6 41 detritus 28 87 opal and 1 5 organic carbon kerogen types c n ratios and 13 c data are suggest mixed but predominantly marine om sbb samples are 59 90 detritus 6 34 opal 3 22 calcite and 1 5 percent organic carbon si and sbb have similar bulk compositions with the exception of the presence of calcite in sbb samples mf sediments have significantly lower detrital and higher opal contents than si and sbb samples these large differences suggest that si and sbb are not appropriate modern analogs for the mf in si sediments organic carbon is concentrated in opal rich detritus lean laminae and intervals this distribution suggests that the coupling of opal and om created in the surface ocean by diatom productivity is preserved in the sediment record in the mf opal and toc are negatively correlated implying that the coupling of opal and organic carbon did not survive the processes of settling sedimentation diagenesis and or weathering this decoupling of organic carbon and opal in the mf is attributed to dilution of om by high opal flux rates and or the respiration and or redistribution of om during diagenesis and or weathering

the upper miocene diatomaceous sediments of the northernmost mediterranean region a lamina scale investigation of an overlooked palaeoceanographic archive

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

palaeoceanographic controls on geochemical characteristics of organic rich exshaw mudrocks role of enhanced primary production organic rich source rocks have generally been attributed to enhanced preservation of organic matter under anoxic bottom waters here geochemical analysis of kerogen and whole rock samples of organic rich lithofacies b1 and organic lean lithofacies b2 laminated mudrocks of the devonian carboniferous exshaw formation alberta highlight the importance of primary production in governing the quantity and quality of organic matter lower si al k al ti al and quartz clay ratios in lithofacies b2 similar maceral types and the laminated fabric of the two lithofacies indicate that the quality and quantity of organic matter are not related to grain size redox or organic matter source changes high total organic carbon toc and hydrogen index hi low oxidation index ox i ratio of oxygen functional groups to aliphatic groups derived by ftir lighter 15ntot and heavier 13corg isotopes indicate that kerogen of lithofacies b1 accumulated during periods of high organic carbon production and delivery of relatively fresh labile well preserved organic matter to the sea floor in contrast low toc hi high ox i heavier 15ntot and lighter 13corg isotopes indicate low primary productivity and delivery high recycling and poor preservation of organic matter during accumulation of lithofacies b2

proboscideans and paleoenvironments of the pleistocene great lakes landscape vegetation and stable isotopes abstract in this study we review the history of proboscideans in the great lakes region ontario and western new york in the context of local glacial and vegetational histories further we investigate mammoth mammuthus and mastodon mammut environmental niche partitioning using stable isotope analysis of bone and dentin collagen 13 c col 15 n col and structural carbonate in tooth enamel bioapatite 13 c sc 18 o sc and demonstrate that stable isotopes can be used to identify non locals among museum specimens with no contextual records new radiocarbon dates suggest that ontario mastodons lived in tundra like environments as well as their more common spruce forest habitat local ontario new york mammoths and mastodons consumed 100 c 3 plant diets and drank low 18 o waters consistent with colder than modern climates and proximity to glacial meltwater sources mammoths and mastodons occupied distinct environmental niches characterized by different oxygen and nitrogen isotope compositions and geographical locations this suggests that direct competition for resources was not a major factor in their local extinction we suggest that both mammoths and mastodons obtained water from sources formed primarily from precipitation rather than glacial meltwater we describe how high 15 n values in mammoths could have been caused by a combination of preferences for dry environments consumption of low nutrient forage particularly stems and stalks coprophagy geophagy and dung fertilization we argue that low 15 n values in mastodons could have been caused by consumption of trees and shrubs including nitrogen fixing taxa and a preference for recently deglaciated landscapes and or spruce environments finally we raise the possibility that mastodons contributed to the spruce pine transition by browsing directly on spruce trees

upper cretaceous and lower paleocene diatom and silicoflagellate biostratigraphy of seymour island eastern antarctic peninsula

self sedimentation of phytoplankton blooms in the geologic record abstract understanding the formation of laminated organic rich sediments is an essential topic for researchers interested in fossil fuels biogeochemical cycles earth s environmental history and global change biologists have very recently demonstrated that some marine phytoplankton blooms actively govern their own sedimentation by the formation of sticky transparent gels that facilitate rapid aggregation accelerated sinking and efficient export flux here we present fossil evidence of unfragmented low diversity phytoplankton assemblages preserved as sedimentary laminae and irregular flocs that are attributable to a similar phytoplankton driven sedimentary mechanism we term self sedimentation the geological evidence suggests that self sedimentation precludes significant heterotrophic grazing propels the formation of some conspicuous hemipelagic sedimentary laminae and results in efficient carbon and opal flux to the sediments we suggest that the self sedimentation phenomenon may have broad implications for the geological history of biogeochemical cycling oceanic ecological dynamics and abrupt atmospheric environmental change broader recognition of the self sedimentation phenomenon as explicitly defined here is a prerequisite to testing these unconventional hypotheses

major element analysis of cyclic black shales paleoceanographic implications for the early cretaceous deep western tethys lower cretaceous sediments are frequently characterized by a well expressed cyclicity while the processes influencing environments above the carbonate compensation depth ccd are reasonably well understood almost nothing is known about the deep ocean cretaceous sub ccd sediments from the tethys and atlantic oceans typically show rhythmic black green shale successions to gain insight into the nature of these black green shale cycles we performed detailed geochemical analyses x ray fluorescence rock eval and reactive iron analysis on a 3 m long section of latest aptian age the major element distribution of the analyzed shale sequence indicates a periodic change from a high productivity and well oxygenated green shale mode to a low productivity oxygen deficient black shale mode it is proposed here that the preservation of organic matter was dependent on the strength of salinity driven deepwater generation furthermore the data show that the corg content covaries with changes in the detrital composition therefore we hypothesize that tethyan deepwater circulation was sensitive to changes in the monsoonal system time series analysis suggests that these changes are periodic in nature although we are currently unable to prove that the dominant periodicity is related to the precession component of the milankovitch frequencies

vegetation history in central kentucky and tennessee usa during the last glacial and deglacial periods abstract knowledge about vegetation dynamics during the last glacial and deglacial periods in southeastern north america is under constrained owing to low site density and problematic chronologies new pollen records from two classic sites anderson pond tn and jackson pond ky supported by ams 14 c age models span 25 2 13 7 ka and 31 0 15 4 ka respectively a transition from pinus dominance to picea dominance is recorded at jackson pond ca 26 2 ka coincident with heinrich event h2 anderson and jackson ponds record a transition from conifer to deciduous tree dominance 15 9 and 15 4 ka respectively marking the development of no analog vegetation characterized by moderate to high abundances of picea quercus carya ulmus fraxinus ostrya carpinus cyperaceae and poaceae and preceding by 2000 yr the advent of similar no analog vegetation in glaciated terrain to the north no analog vegetation developed as a time transgressive south to north pattern mediated by climatic warming sporormiella abundances are consistently low throughout the jackson and anderson pond records suggesting that megafaunal abundances and effects on vegetation varied regionally or possibly that the sporormiella signal was not well expressed at these sites additional records with well constrained chronologies are necessary to assess patterns and mechanisms of vegetation dynamics during the last glacial and deglacial periods

isotopic paleoecology of clovis mammoths from arizona the causes of megafaunal extinctions in north america have been widely debated but remain poorly understood mammoths mammuthus spp in the american southwest were hunted by clovis people during a period of rapid climate change just before the regional onset of younger dryas cooling and mammoth extirpation thus these mammoths may provide key insights into late pleistocene extinction processes here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the san pedro valley of arizona using the carbon 13c 12c and oxygen 18o 16o isotope compositions of tooth enamel these records suggest that clovis mammoths experienced a warm dry climate with sufficient summer rainfall to support seasonal c4 plant growth monsoon intensity may have been reduced relative to the preceding time period but there is no isotopic evidence for severe drought however it is possible that the clovis drought inferred from stratigraphic evidence occurred suddenly at the end of the animals lives and thus was not recorded in the enamel isotopic compositions unlike mammoths that lived before the last glacial maximum clovis mammoths regularly increased c4 grass consumption during summer probably seeking seasonally green grasslands farther from the river valley this predictable seasonal behavior may have made mammoths easier to locate by clovis hunters furthermore clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

quaternary chronostratigraphy and stable isotope paleoecology of big bone lick kentucky usa abstract big bone lick bbl in northern kentucky usa has been a critical geologic site in the historical development of north american quaternary vertebrate paleontology since the 1700s sedimentology geoarcheology paleontology accelerator mass spectrometry radiocarbon and optically stimulated luminescence dating and stable carbon and nitrogen isotope analyses were undertaken to develop a chronostratigraphy and history of erosion and deposition for the site to provide a foundation for understanding taphonomy and species extinction and adaptation to periods of climatic and environmental change three geomorphic surfaces are recognized at bbl representing significant periods of floodplain aggradation since the last glacial maximum 26 5 19 ka dating to the oldest dryas tazewell 25 19 ka the older dryas cary 14 12 ka and late holocene 5 ka to the present unconformities suggest significant periods of degradation during the transitions from cold and dry to warm and moist climates from the oldest dryas tazewell to bolling oscillation from the older dryas cary to the allerod and from the younger dryas valders to the holocene climatic optimum increased anthropogenic activities since 5 ka may have increased soil upland erosion and floodplain aggradation stable isotopes demonstrate that the landscape has been dominated by c3 vegetation since the last glacial maximum

diatom assemblages in surface sediments of the northwestern weddell sea antarctic peninsula a study of 42 surface sediment samples from the northwestern weddell sea documents the relationship between the modern distribution of diatom assemblages and present oceanographic conditions in the region three diatom assemblages were identified using r mode principal components analysis and cluster analysis while q mode cluster analysis was used to distinguish two geographically distinct biofacies based on the relative abundance of diatom species the biofacies of the former larsen a ice shelf lais is more closely associated with a sea ice diatom assemblage while the biofacies of the prince gustav channel northern peninsula pgc np is associated with two open coastal diatom assemblages this division is consistent with variance observed in the current oceanographic setting whereby the lais is generally characterized by a longer seasonal duration of sea ice coverage and lower primary productivity relative to the pgc np which is marked by a shorter seasonal duration of sea ice coverage and greater surface water productivity this relationship is further reflected in the distribution of the paleoenvironmentally significant diatom species fragilariopsis curta thalassiosira antarctica and chaetoceros subg hyalochaete spp as well as in absolute abundance data specifically f curta and the morphological form t antarctica t1 are representative of greater seasonal duration of sea ice coverage and lower productivity chaetoceros subg hyalochaete spp and the morphological form t antarctica t2 are associated with decreased seasonal duration of sea ice cover and greater surface water productivity a setting that is further reflected in high absolute diatom abundances these findings provide a basis for future paleoceanographic work in the region especially as studies of surface sediment diatom assemblages are vital to establishing a link between downcore diatom assemblages and those presently found in the water column

evaluating escarpment evolution and bedrock erosion rates in the western guadalupe mountains west texas and new mexico abstract the guadalupe mountains tower above surrounding plains and basins in western texas and southeast new mexico although this mountain range is extensively studied for the permian stratigraphy related to the petroleum reservoirs in the adjacent delaware basin little is known about the geomorphic history the western escarpment in particular rises abruptly from the salt basin to the west of the range and guadalupe peak rises 1600 m above the surrounding landscape this study investigates how geologic processes create and maintain the steep profile of the escarpment on the western boundary of the guadalupe mountain range in situ produced cosmogenic nuclides were used to quantify erosion rates across the steep western front of the range to assess how tectonic climatic and lithologic forces influence the escarpment profile erosion rates range from 1 to 73 m myr faster erosion rates in the southern area of the escarpment coincide with more frequently mapped faults higher elevations at the top of the rim and locations with colder temperatures and higher precipitation topographic profiles across the western escarpment surfaces indicate greater retreat from the original positions of fault surfaces at the north end of the mountain range faster erosion rates in the mountain range are linked to greater uplift and more recent activity in the southern end of the guadalupe mountains

algal bloom episodes and the formation of bituminite and micrinite in hydrocarbon source rocks evidence from the devonian and mississippian northern williston basin canada organic petrology incident light microscopy of middle devonian inter reef laminates and devonian mississippian epicontinental black shales williston basin canada indicates that algal bloom episodes and consequential bacterial activity played a significant role in the accumulation of amorphous bituminite iii rich organic microfacies corpohuminite like algal akinete cells produced by filamentous algae during algal bloom periods are persistent maceral inclusions within the potential hydrocarbon source rock intervals these cells ro mean range 0 24 0 90 are regarded as positive indicators of stressful palaeoenvironmental conditions unicellular tasmanites and leiosphaeridia marine alginite and variably degraded alginite remnants ghosts within the amorphous kerogen may be products of cell lysis photo oxidation and microbial alteration these processes are characteristic of algal bloom periods minute ca 1 m spheroidal and coccoidal bacteria like macerals are dispersed throughout the bituminite iii network attesting to the importance of microbial activity within the water column and sediment during and after organic matter accumulation dispersed granules laminations and replacement textures of micrinite like macerals within bituminite iii are interpreted as remnants of microbial alteration rather than a residual product of thermal maturation and hydrocarbon generation

late wisconsin periglacial environments of the southern margin of the laurentide ice sheet reconstructed from pollen analyses full glacial pollen assemblages from four radiocarbon dated interstadial deposits in southwestern ohio and southeastern indiana imply the presence of herbaceous vegetation tundra or muskeg with subarctic indicator selaginella selaginoides on the southern margin of the miami lobe of the laurentide ice sheet ca 20 000 14c yr bp scattered picea spruce and possibly pinus pine may have developed regionally ca 19 000 14c yr bp and ca 18 000 14c yr bp respectively spruce stumps in growth position support a local source of pollen prior to the ca 14 000 14c yr bp glacial advance small amounts of quercus oak and other deciduous pollen suggest development of regional boreal conifer hardwood forests copyright 2002 john wiley sons ltd

biogenic and abiogenic components of laminated hemipelagic sediments in the central gulf of california abstract alternating light and dark submillimeter to millimeter thick layered sediments rhythmites are found along the slopes of the central and southern gulf of california where a strong oxygen minimum zone intersects the sediment water interface two short intervals of distinct alternations were sampled lamina by lamina from two cores in the central gulf both cores are from the slope of the guaymas basin one core is from the mainland side the other core is from the baja side each lamina sample was analyzed for its opal micro floral assemblage textural character trace metal and bulk chemical cu mn fe ni zn ca k al sio2 and c org content and mineralogy on both sides of the gulf the light laminae contain more diatom frustules up to 90 and less terrigenous and organic material than the dark laminae the sediment is predominantly silt sized the dark laminae contain more terrigenous material which is primarily clay size on both sides of the gulf the light laminae apparently represent sedimentation during the dry winter season of northwesterly winds whereas the dark laminae represent the wet summer season of southeasterly winds

fecal pellet flux to modern bottom sediment of santa barbara basin california based on sediment trapping fecal pellets constituted more than 60 of the material collected during 45 days of deployment of a suitcase type sediment trap in santa barbara basin the flux was 660 g m 2 yr 1 of which 22 g m 2 yr 1 was carbon flux pellet transport can account for about one half of the sediment flux to the central basin floor including the supply of terrigenous matter the clearing activities of pellet producing plankton have important implications for sedimentation and fertility in the coastal ocean

a multidisciplinary approach in determining the maceral kerogen type and mineralogical composition of upper cretaceous eagle ford formation impact on pore development and pore size distribution abstract maceral kerogen or organic matter type and mineralogical composition with the associated porosity of the upper cretaceous eagle ford formation karnes county texas was investigated in karnes county the calcareous mudstone of the eagle ford formation was deposited in an open marine outer shelf to upper slope environment to adequately characterise all components of this mudrock a multidisciplinary approach was implemented to analyse 26 core samples from a single producing well that completed within the eagle ford formation analyses included organic petrology organic geochemistry light and electron microscopy and spectroscopy pore size distribution analyses and x ray diffraction the bitumen reflectance ranges between 1 94 and 2 08 calculated vr o 1 60 1 69 indicating the mudrock is in the condensate rich gas window the toc content ranges between 1 7 and 7 2 with an average of 3 9 mineral composition is dominated in descending order by calcite clay quartz and plagioclase calcite varies between 32 and 87 with an average of 57 porosity measured by helium pycnometry ranges between 3 5 and 10 3 with an average of 7 5 organic petrology coupled with backscattered and field emission scanning electron microscopy indicates matrix bitumen as the most significant contributor to the toc content and porosity matrix bitumen contains significant meso and microporosity and is enhanced by the secondary cracking of the bitumen an increase in bioclastic mostly foraminifera and siliciclastic components correlates with lower toc content due to the lower volume of organic rich matrix peloids fecal pellets are calcareous organic rich and lack terrigenous sediment indicating a zooplankton source pelagic deposition of peloids is interpreted as a primary mechanism of amorphinite deposition which is converted to hydrocarbons and matrix bitumen the mixed siliciclastic calcareous matrix that surrounds the peloids is comprised of matrix bitumen and dispersed organics from land plants vitrinite fusinite and inertodetrinite the siliciclastic component increases in the middle of the eagle ford and marks the boundary maximum flooding surface between the lower tst and upper hst section of the formation the inorganic and organic components suggest a mixed terrigenous and marine source with both inorganic and organic sediments being derived from the proximal ouachita thrust belt and from pelagic organisms within the overlying water column the lower tst eagle ford formation contains more micro and mesopores than the upper hst eagle ford formation due to higher toc content in the lower eagle formation these results illustrate that a multidisciplinary approach is necessary to identify how pore network are distributed within mudrocks and how this distribution is controlled by organic inorganic deposition and hydrocarbon generation processes

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

iceberg alley east antarctic margin continuously laminated diatomaceous sediments from the late holocene a 24 meter jumbo piston core nbp0101 jpc41 collected from an inner shelf basin in iceberg alley reveals an approximately 2000 year history of unusually high primary productivity iceberg alley an 85 km long and 10 20 km wide cross shelf trough on the mac robertson shelf east antarctica reaches depths of 850 m and is bounded on either side by shallow banks that are lined with grounded icebergs the sediments are laminated on a mm to cm scale throughout and are highly biosiliceous microscopic examination of smear slides quantitative diatom slides and sediment thin sections reveals that the sediments are visually dominated by the diatom corethron pennatum a large and lightly silicified species notable for its long and narrow shape the valves girdle bands and spines are all exceptionally well preserved suggesting rapid sedimentation other common species include sea ice related fragilariopsis such as f curta and f cylindrus with lesser contribution from other large diatoms including rhizosolenia spp and chaetoceros ehrenberg subg chaetoceros chaetoceros ehrenberg subg hyalochaete gran resting spores typically associated with large early season blooms and common in many laminated sedimentary sections around the antarctic margin are surprisingly rare laminae with any significant terrigenous component are also very rare individual laminations appear to represent blooms and in some cases sub seasonal events are likely preserved we suggest that this productive system is associated with the continuous presence of low salinity meltwater derived from a combination of sea ice melt and grounded icebergs which may be a source for a steady supply of micronutrients such as iron to the surface mixed layer

volumetric wavefield recording and wave equation inversion for near surface material properties volumetric recording of the seismic wavefield implies that the local receiver group or array approximately encloses a volume of the earth we show how volumetric recording can be used to measure several spatial derivatives of the wavefield by making use of the full elastic wave equation the free surface condition on elastic wavefields and derivative centering techniques analagous to lax wendroff corrections used in synthetic finite difference modeling these derivative estimates can be inverted for p and s velocities in the near surface directly beneath the receiver group the quantities estimated are the effective velocities of the p and s components experienced by the wavefield at any point in time hence the velocity estimates may vary with both wave type and wavelength the estimates may be useful to aid statics estimation and are exactly the effective velocities required for separation of the wavefield into p and s and up and down going components

modern to late holocene deposition in an anoxic fjord on the west coast of canada implications for regional oceanography climate and paleoseismic history laminated sediments preserved in the anoxic inner basin of effingham inlet on the pacific coast of vancouver island british columbia canada yield a high resolution sediment deposition record spanning about 6000 yr the varying thickness of diatom terrigenous mud varves in sediment cores from the basin can be interpreted in terms of annual changes in surface productivity and freshwater input within the inlet similarly the occurrence of unlaminated mud units homogenites intercalated amongst the laminated sediments can be interpreted in terms of oceanic and climatic changes these units appear to be associated with coastal upwelling events that result infrequently in highly oxygenated oceanic water penetrating to the bottom of the inner and outer basins of the inlet the sedimentary record also contains massive and graded mud units considered to arise from debris flows and turbidity currents some of which were probably initiated by seismic events including a major event about 4500 14 c yr bp which may be earthquake related a total of seventeen oceanographic surveys of the inlet beginning in 1995 characterize the modern seasonal coastal upwelling regime and a unique bottom water oxygenation event which was

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

post glacial seasonal diatom record of the mertz glacier polynya east antarctica an ultra high resolution post glacial laminated sediment record from mertz ninnis trough east antarctic margin eam has been analysed using sem backscattered electron imagery secondary electron imagery and quantitative diatom abundance laminations are classified using visually dominant diatom species and terrigenous content four biogenic diatom ooze laminae types one diatom bearing terrigenous lamina type and one diatom bearing terrigenous sub lamina type have been identified diatom ooze lamina types comprise near monogeneric hyalochaete chaetoceros spp resting spore laminae laminae characterised by corethron pennatum laminae characterised by rhizosolenia spp and mixed diatom assemblage laminae diatom bearing terrigenous lamina and sub lamina types comprise mixed diatom assemblage terrigenous laminae and sub laminae characterised by porosira glacialis resting spores formation of each of these lamina types is controlled by seasonal changes in nutrients oceanographic regimes and the mertz glacier polynya dynamics

algal blooms and marine snow mechanisms that enhance preservation of organic carbon in ancient fine grained sediments abstract combined petrographic and geochemical methods are used to investigate the microfabrics present in thin sections prepared from representative organic carbon rich mudstones collected from three successions the kimmeridge clay formation the jet rock member of the whitby mudstone formation and the pebble shale and hue shale this study was initiated to determine how organic carbon rich materials were being delivered to the sediment water interface and what happened to them after deposition prior to deep burial analyses of the fabrics present shows that they exhibit many common attributes in particular they are all 1 highly heterogeneous on the scale of a thin section 2 organized into thin beds the organomineralic aggregates present in these mudstones are interpreted to be ancient examples of marine snow this marine snow likely formed in the water column particularly during phytoplankton blooms and was then transported rapidly to the seafloor the existence of the thin beds with homogenized tops and an in situ infauna indicates that between blooms there was sufficient oxygen and time for a mixed layer to develop as a result of sediment colonization by diminutive organisms using either aerobic or dysaerobic metabolic pathways these textures suggest that the constituents of these mudstones were delivered neither as a continuous rain of sediment nor were the bottom waters persistently anoxic in addition the presence of thin lags and sharp based beds suggests that the seafloor was being episodically reworked during deposition these fabrics indicate that conditions in the water columns and at the seafloors while these rocks were being deposited were very dynamic and episodic fluxes of high concentrations of organic carbon to the seafloor during phytoplankton blooms likely enhanced preservation of organic carbon