climate and vegetation in southeastern australia respond to southern hemisphere insolation forcing in the late pliocene early pleistocene terrestrial climate responses to orbital forcing during the late pliocene early pleistocene are poorly understood particularly in the southern hemisphere but are important for determination of the timing of regional climate evolution early in the history of the glaciated quaternary world we present a pollen record from southeastern australia that shows marked cyclic change over some 280 000 yr straddling the pliocene pleistocene boundary rainforest communities responded to climate forcing primarily within the precession and eccentricity bands suggesting that major vegetation changes were driven directly by summer insolation rather than by obliquity dominated glacial cycles

stromatolites the challenge of a term in space and time abstract several definitions of stromatolites are discussed and kalkowsky s most important statements about stromatolites are translated from german to english a new definition for stromatolites is proposed namely stromatolites are laminated rocks the origin of which can clearly be related to the activity of microbial communities which by their morphology physiology and arrangement in space and time interact with the physical and chemical environment to produce a laminated pattern which is retained in the final rock structure unconsolidated laminated systems clearly related to the activity of microbial communities and often called recent stromatolites or living stromatolites are defined as potential stromatolites the main microbial activities which are important in the formation of potential stromatolites and stromatolites are described and examples of stromatolites of various types including iron stromatolites are also described

taphonomic variations in eocene fish bearing varves at horsefly british columbia reveal 10 000 years of environmental change the eocene horsefly locality in british columbia has yielded many fossil fishes insects and plants its varved sediments make it ideal for study of temporal changes in environment and fish morphology several intervals of diatomaceous varves indicate a deep stratified lake setting earlier studies focused on morphological and taphonomic change during the 700 year h2 interval and morphological change during the 10 000 year h3 interval the present study uses taphonomy as an index for environmental change during the ten millennia represented by h3 comparing taphonomic changes with the morphologic changes found earlier the h3 interval records deposition in deep water indicated by dominance of the fish genera amyzon and eohiodon quiet water conditions are indicated by minimal fin disarticulation hypoxia at the time of fish death is confirmed by open mouths of most fish specimens while cool water on the lake floor prevented full flotation of fish carcasses water depth temperature and oxygenation fl

evolutionary and geologic consequences of organic carbon fixing in the primitive anoxic ocean steps leading to development of the modern photic based marine food web are postulated as the result of modifications of the environment enhanced by the activity of archean sulfur chemoautotrophs such organisms anoxium evolved in an anoxic ocean prior to 3 9 10 9 yr ago at archean analogs of modern oceanic hydrothermal vents at this time geothermal energy was more readily available to organisms than photic energy given atmospheric conditions at the surface similar to venus where intensity is low and only middle and red visible wavelengths penetrate the cloudy co 2 rich atmosphere competition for the reduced sulfur developed due to oxidation and loss of sulfur to sediments consequently evolutionary advantage shifted to anoxium isolates that could use alternate energy sources such as light to supplement the diminished supplies of reduced sulfur initially photo sulfur organisms evolved similar to modern purple bacteria that absorb in the red visible spectra subsequent carbon fixing and oxidation improved both the quantity and range of light reaching the ocean surface this permitted absorption in the blue visible range so that water splitting was now feasible releasing free oxygen and accelerating oxidation eventually reducing environments became restricted completing the shift in the principal marine carbon fixing activity from anoxic chemoautotrophic to aerobic photosynthetic organisms

facies architecture and sequence stratigraphy of fine grained lacustrine deltas along the eastern margin of late pleistocene lake bonneville northern utah and southern idaho this study documents the effects of changing lake level limnostasy tectonics sediment yield and basin physiography on the facies architecture sequence stratigraphy and reservoir quality of three fine grained deltas deposited along the eastern margin of late pleistocene lake bonneville analysis of facies architecture indicates that the weber and spanish fork deltas were strongly wave modified because they were situated along openly exposed portions of the shoreline the bear river delta nestled in a relatively isolated northeast arm of the lake records both fluvial and wave processes these fine grained deltas were fed by low gradient rivers that drained large regions that were sparsely glaciated whereas other contemporaneous coarse grained gilbert deltas were fed by steep gradient rivers that drained local source areas that were strongly influenced by glaciers limnostasy tectonics and sediment yield were similar for all three fine grained deltas implying that the most influential forcing parameter on sequence stratigraphy is basin physiography basin physiography specifically ramp length and accommodation most strongly controlled the external and internal geometry of the lowstand systems tract of each delta potential hydrocarbon reservoir quality e g grain size and sorting is largely a product of drainage basin size and stream gradient relative differences in ramp lengths seemed to determine thickness and lateral continuity of delta front deposits relative differences in accommodation appeared to determine the internal geometry of the delta front deposits especially in the lowstand systems tract these deltas can serve as analogs for lacustrine exploration and production where many forcing parameters typically are unknown

sunspot periods in the late precambrian glacial climate and solar planetary relations cycles conspicuous in late precambrian 680 myr glacial varves in australia reveal strong climatic periods of about 11 22 145 and 290 yr and a weaker period near 90 yr the 11 22 and 90 yr cycles equate with sunspot periods and the longer cycles with solar and climatic periods as indicated by tree ring studies the varve cycles provide clear evidence of 11 and 22 yr climatic periods in the geological record and may carry important implications for solar physics and planetary science

sedimentology and isotope geochemistry of lacustrine carbonates of the oligocene campins basin north east spain the non marine campins basin developed in the oligocene during a period of early rifting of the catalan coastal ranges lacustrine deposits interbedded between two alluvial units comprise shallow and deep lacustrine facies the lower shallow lacustrine facies are made up of microbialite buildups and thin limestone beds in the studied area these facies are overlain by deep lacustrine facies which consist of alternations of several metre thick carbonate and mudstone dominated intervals in addition to calcite which is characteristic of the shallow lacustrine facies aragonite and abundant dolomite are present in the deep lacustrine facies this mineralogical change in the sequence reflects an overall increase in the mg ca ratio of the lake waters the deep lacustrine sequences are interpreted as having formed in a hydrologically closed basin that was subject to changes in the mg ca ratio of the water probably related to variations in the evaporation precipitation rate the sedimentological mineralogical and isotopic characteristics of the campins basin dolomites suggest that in general they are primary in origin the stable isotope data show an approximate covariance between 13c and 18o in the lower shallow lacustrine carbonates calcite which suggests that they formed during the onset of closure of the lake the 13c and 18o values of the deep lacustrine carbonates display three different clusters that are roughly related to the carbonate mineralogy normalisation with respect to calcite of the isotopic compositions of dolomite and aragonite from the deep lacustrine carbonates allows the integration of all these isotope values into one covariant trend the sequential appearance of different carbonate minerals and the isotopic covariant trend may indicate an overall evaporative concentration of the lake waters the change in slope of the covariant trend for the isotope values between the shallow and the deep lacustrine carbonates might reflect the change in the waterbody morphology recorded in the basin fill sequence

a 2 3 million year lacustrine record of orbital forcing from the devonian of northern scotland detailed sedimentological examination of onshore sections through cyclic lacustrine deposits of the middle devonian succession of northern scotland has been augmented with offshore data to allow the construction of a continuous 2 3 myr record of orbital forcing these data provide an important record of climatic variance through the devonian which by comparison with other records from this time can significantly improve our understanding of the devonian global climatic system precessional and eccentricity cycles are shown to be dominant by the direct measurement and extrapolation of depositional rates in well exposed sections as well as the analysis of ratios between primary and modulating cycles spectral analysis has confirmed the presence of regular cycles throughout the offshore data which provide a far longer record of orbitally forced cyclicity than previously available the presence of a half precession cycle is also suggested similar up section variations in cycle thicknesses are recorded from both the onshore and offshore succession these variations and those in cycle symmetry are related to a trend from an underfilled to a balanced fill basin state of further importance in controlling cycle thickness is the period of each cycle during which lacustrine conditions and therefore lake level controlled accommodation existed

syneruptive and intereruptive lithofacies in lacustrine environments the cretaceous beolkeum member wido island korea abstract the cretaceous beolkeum member was deposited in a lacustrine environment affected by explosive volcanism and a number of syneruptive lithofacies are intercalated with lacustrine mudstones the syneruptive lithofacies were formed by primary volcanic processes and resedimented depositional processes during and after eruptions and exhibit unique depositional features which can be grouped into four syneruptive lithofacies assemblages sla 1 to sla 4 from bottom to top primary syneruptive lithofacies are represented by welded massive lapilli tuff in sla 1 and a normally graded lapilli tuff in sla 2 in sla 1 sustained pyroclastic density currents were able to displace lake water and rarely interacted with lake water resulting in the formation of a welded texture and columnar joints in sla 2 unsteady pyroclastic density currents rapidly disintegrated mixed with ambient water and transformed into high density turbidity currents depositing thick normally graded lapilli tuff resedimented syneruptive lithofacies were primarily controlled by volcaniclastic sediment supply after eruptions when volcaniclastic sediments were continuously supplied into the lake by debris flows a volcaniclastic fan can be formed sla 1 resulting in a coarsening upward trend and progradational geometry in case of relatively small amounts of volcaniclastic sediment supply turbidity currents would be a main depositional process depositing a series of normally graded tuff on the primary syneruptive lithofacies sla 2 showing a fining upward trend in sla 3 and sla 4 there are only a few cm thick normally graded tuff reflecting minor volcaniclastic sediment supply however overlying normally graded sandstones in sla 3 showing a coarsening upward trend and a thick normally graded sandstone in sla 4 suggest favorable conditions for the generation of the sediment gravity flows probably due to an increase in volcaniclastic sediment supply after eruptions

changes in sediment composition during seasonal resuspension in small shallow dimictic inland lakes abstract resuspension at edinboro lake pennsylvania usa and east twin lake ohio usa was studied with the aid of sediment traps with special time marking capabilities resuspension resulted from both seasonal holomictic circulation and from continual entrainment of material from the shallow portions of the lake by the circulating epilimnion rainstorms appeared to have negligible effects on trapping rates trapping rates varied widely through the year with minimum sedimentation rates noted at time of winter ice cover and maximum rates noted during autumn circulation most material collected by the sediment traps was material which had been resuspended from the lake bottom the process of resuspension was active through almost the entire year with the exception being the time period under winter ice cover compositional variations in the suspended sediment are seasonal and include enrichment of si in winter ca p s mg na zn ni and cr in summer and mn and to a lesser extent fe and al in late summer and autumn the sediment is generally enriched in detrital minerals during spring and autumn and in amorphous mineraloids mainly diatomaceous silica in winter and complex particles containing ca p s and some fe and mn in summer during times of reduced circulation endogenic minerals include calcite pyrite and possibly some kaolinite most of the mineral fraction present is detrital trap sample differs in composition from bottom sediment but samples collected in traps in early winter closely resemble bottom material trapping rates in early winter appear closest to true rates of fill

diatomaceous origin of siliceous shale in eocene lake beds of central british columbia the abundance of diatoms in neogene lacustrine sediments and their apparent scarcity in paleogene deposits have long perplexed geoscientists but siliceous shales from eocene lake beds of central british columbia provide new insights major element geochemistry x ray diffraction patterns and relict diatom frustules suggest that eocene beds at horsefly mcabee and princeton originated as lacustrine diatomite that underwent diagenetic alteration to produce siliceous shale the combination of high sio2 and low al2o3 values and the presence of opal ct x ray diffraction peaks provide a distinctive geochemical fingerprint for biogenic silica deposits that have been remineralized the discovery of diatomaceous geochemical signatures in siliceous shales may prove to be a useful tool for extending the geologic record of diatoms perhaps helping to reduce the apparent discrepancy between fossil evidence and evolutionary interpretations based extant species

seasonal to sub seasonal palaeoenvironmental changes in lake sihetun lower cretaceous yixian formation ne china sedimentary properties of the fossil bearing deposits of lake sihetun yixian formation lower cretaceous were investigated on a high resolution sub millimetric scale data were obtained from three excavations and 50 thin sections lake evolution is subdivided into four phases of which phases 2 and 3 provided suitable conditions for excellent fossil preservation six microfacies are recognized within these two phases 1 allochthonous siliciclastic laminae 26 1 m thick on average 2 chrysophycean cyst accumulations 3 tuffaceous silt 4 lacustrine chemical precipitates 5 tuff and 6 normal graded sandy to silty siliciclastics phase 2 is characterized by microfacies 1 5 and phase 3 by microfacies 6 biofilms are common and mass occurrences of framboids pyrite pseudomorphs are occurring in sediments of phase 2 varves can be verified for microfacies 2 and 4 179 m thick thicknesses of microfacies 2 highly fluctuate depending on the occurrence of seasonal heavier rains which led to deposition of tuffaceous silt layers microfacies 3 meromictic conditions dominated phase 2 but recurrent mixing is demonstrated by short lived colonization events by a benthic invertebrate fauna the transition of phase 2 to holomictic phase 3 is marked by a dramatic increase in sediment yield associated with a change from dry to humid climates fossil preservation differs according to the diverse physical and chemical conditions during lake evolution phase 2 yields framboid replacement of organic tissue and excellent preservation of growth increments of clam shrimp carapaces which are poorly preserved in phase 3 conversely though exhibiting a different mode of preservation insect fossils are superbly preserved as dark stains sealed by silica coatings during phase 3

seasonal and interannual particle export in an african rift valley lake a 5 yr record from lake malawi southern east africa a time sequencing sediment trap was deployed at 300 350 m in lake malawi east africa from 1987 to 1992 to measure particulate export to the deep anoxic hypolimnion in the northern and central lake regions the monthly settling particulate samples provide a data set of seasonal and interannual export fluxes of organic carbon biogenic opal calcium carbonate and lithogenic material maximum total particle fluxes 50 400 mg m 2 d 1 occurred primarily during the dry windy season april through october when algal productivity is high because of wind induced upwelling of nutrient enriched metalimnion and hypolimnion waters peak flux particulates contained an abundance of aulacoseira and stephanodiscus diatom valves and chains the total particle mass flux during the wet austral summer months november through march was consistently one to three orders of magnitude less than that measured during the dry months and consisted of mineral shards terrestrial plant debris and scattered diatom tests the 5 yr trap data provide support for the claim that the light dark lamination couplets abundant in northern and central lake cores reflect seasonal delivery to the sediments of diatom rich particulates during the windy months and diatom poor material during the wet season however interannual and spatial variability in upwelling and productivity patterns as well as el nino southern oscillation enso related rainfall and drought cycles appears to exert a strong influence over the magnitude and geochemical composition of particle export to the deep hypolimnion of lake malawi

seasonal signals in lake malawi sediments the sedimentary record of lake malawi one of the large rift valley lakes of east africa contains thick sequences of biologically undisturbed finely laminated muds and silts laminated sequences were recovered in cores from the extensive diatom ooze and silty diatom clay facies of the lake basin that is permanently anoxic below 250 m the sequences consist of light dark laminae couplets with average thickness of 1 mm the light laminae are completely dominated by the diatom genus melosira with a relatively minor contribution from the genus stephanodiscus the dark laminae consist of 50 diatoms equal proportions of melosira and stephanodiscus few nitzschia and occasional littoral diatom genera and 50 terrestrial plant debris mineral grains and fine clay and organic material based on a 210pb and 14c calculated sedimentation rate of 1 mm yr 1 for lake malawi basin sediments and the well defined seasonal variations in fluvial input and diatom productivity levels our data suggest that the lamination couplets are annual varves representing biannual sedimentation sequences the light laminae result from diatom blooms occurring during the dry windy season april october when the upper 250 m of the lake is well mixed localized upwelling occurs and the epilimnion becomes enriched with nutrients the dark laminae represent sedimentation in the rainy low wind velocity season november march when runoff and allochthonous terrestrial input are at a maximum and primary productivity is at a minimum

soft sediment deformation structures interpreted as seismites in lacustrine sediments of the prebetic zone se spain and their potential use as indicators of earthquake magnitudes during the late miocene lacustrine formations of late miocene age in the prebetic area se spain show several types of deformational structures that are interpreted as seismites they are present in both marginal and deep lacustrine facies seismites formed in marginal lake environments comprise sand dikes pillows and intruded and fractured gravels in deep lacustrine facies the seismites are represented by pseudonodules mushroom like silts protruding into laminites mixed layers disturbed varved lamination and loop bedding the measured orientations of these structures are consistent with the orientations of the main faults limiting the basins showing that their origin is clearly related to the tectonic stress field that prevailed in the region during the late miocene the magnitudes of the earthquakes that deformed the sediments have been estimated after published data from both ancient and recent lake deposits accumulated in tectonic active regions elsewhere a rank of earthquake magnitudes with two end members i e the lowest magnitudes recorded by loop bedding in laminites and the highest magnitudes represented by intruded and fractured gravels is proposed

caradocian land plant microfossils from libya the oldest paleontologically well dated spore tetrads and cuti clelike sheets of cells have been recovered from beds of caradoc mid ordovician age from boreholes in the murzuk murzuq and rhadames ghad mis basins of western libya these microfossils together with late llandovery early wenlock vascular plant megafossils lycophytes and psilophyton known from libya lead us to conclude that land plants including vascular plants probably had a long pre silurian record extending at least into the basal caradocian additonal evidence suggests that this record does not extend as far back as the earlier late cambrian dresbachian

comments on anti phase oscillation of asian monsoons during the younger dryas period evidence from peat cellulose δ13c of hani northeast china by b hong y t hong q h lin yasuyuki shibata masao uchida y x zhu x t leng y wang and c c cai palaeogeography palaeoclimatology palaeoecology 297 2010 214 222 abstract in their recent paper hong et al 2010 anti phase oscillation of asian monsoons during the younger dryas period evidence from peat cellulose 13 c of hani northeast china palaeogeography palaeoclimatology palaeoecology 297 214 222 discuss bulk peat sample cellulose 13 c data from a fen in northeast china as a proxy for east asian summer monsoon intensity during the late glacial period based on their own results cited papers and an extensive re interpretation of sedimentological and palynological data from nearby lake sihailongwan hong et al 2010 construct a hypothesis of contrasting moisture conditions in northern and southern china with wet conditions in the north during the younger dryas period and an anti phase behaviour of indian and east asian summer monsoon intensity however we do not approve of the re interpretation of our lake sihailongwan data by hong et al 2010 and must strongly reject it we show here that neither the hong et al 2010 fen data nor the lake sihailongwan data or any other cited data allow for the sound assumption of an intensified east asian summer monsoon in northeastern china during the younger dryas the late glacial variability of the fen data found by hong et al 2010 can be easily explained by changes in the plant assemblage down core and thus by the composition of the peat furthermore the use of bulk peat cellulose 13 c data as a precipitation proxy remains unproven for that area hence there is no basis for a model contrasting indian and east asian summer monsoons during that period

evidence of a quaternary dammed lake in the mawat chwarta area western zagros kurdistan region ne iraq abstract the mawat chwarta valley is located north of the sulaimania city at northern iraq and is surrounded by high mountains on all sides white laminated sediments with annual varves on a millimetre scale have been recorded at eight localities on the valley gentle slopes sedimentological palaeontological and geomorphological data of these sediments suggest that a lake occupied the valley during the quaternary the sediments are of two types purely fine grained and fine grained with coarse interbeds the two types occur at an elevation difference of about 62 m the two types are interpreted as representing deep abyssal and shoreline deposits respectively and indicate the approximate depth of the lake the sediments contain the fresh water green algae of the genus botryococcus in addition to a few leaves scattered plant debris and some pollen grains mainly of herbaceous plants contrary to the general south western drainage pattern in northern iraq the mawat chwarta valley is drained to the north where the mawat river passes now through deep and narrow gorges along which rock slides and debris plugs are known to have occurred in the past these mass wasting events are considered here to have blogged the runoff of the valley in the past and eventually led to the formation of a large dammed lake numerical chronology work failed which requires further investigation in the future

multi proxy evidence of late holocene human induced environmental changes at lake pupuke auckland new zealand abstract new zealand was the last major landmass in the world to be colonised by people despite the short time depth of human presence in the country there is ongoing debate about the date of earliest arrival of people that resulted in the emergence of two contrasting colonisation hypotheses the early hypothesis and the short prehistory to decide between both hypotheses we employed a range of multi proxy investigations geochemistry stable isotopes and mineral magnetism on a lacustrine sequence from lake pupuke a maar lake in the city of auckland and an area potentially among the first places in new zealand to have been colonised by early people the environmental history reconstructed from the multi proxy evidence identified a clear lack of catchment disturbance from c 2000 b p until several decades before the eruption of the rangitoto volcano the nature and abruptness of disturbance unambiguously point to anthropogenic forcings and are likely to mark the onset of prehistoric human colonisation at the site linear interpolation between independently dated tephrochronostratigraphic marker beds present in the sediments allowed to date this event to c 610 cal yr b p this date is in compliance with the short prehistory for this region

are light dark coupled laminae in lacustrine shale seasonally controlled a case study using astronomical tuning from 42 2 to 45 4 ma in the dongying depression bohai bay basin eastern china abstract as a typical sedimentary structure in fine grained rocks laminae are widely distributed in shales and mudstones in sedimentary basins the shahejie formation 42 2 45 4 ma formed during the eocene of the paleogene in the dongying depression of china is recognized as a typical area to study lacustrine shale according to the composition of different lamina four types of couplets are identified including carbonate clay couplets carbonate organic couplets clay organic couplets and carbonate clay organic triplets all couplets are composed of light and dark layers a combination of core images microscopic observations mineral compositions geochemical data carbon and oxygen isotopes and strontium isotopes verifies that the laminae are primarily developed in a saline and anoxic or even euxinic environment with a high organic matter om flux through astronomical cycle analysis of the natural gamma ray gr curve from sample site well ny1 the data suggest that the lacustrine shale laminae are formed annually with an average duration of 1 34 yr the formation of laminae is affected by the season which is closely related to the seasonal growth and death of algae during the period of algae growth a large number of light colored carbonate laminae are deposited whereas when the algae dies organic matter accumulates at the bottom of lakes and forms dark organic rich laminae the interbedded and lenticular laminae which are subdivided by layering characteristics are primarily affected by diagenesis in postdepositional processes study of the laminae is helpful in understanding the formation process of lacustrine shale and it provides invaluable sources of information for paleoclimate reconstruction

anatomy of a lacustrine stratigraphic sequence within the fourth member of the eocene shahejie formation along the steep margin of the dongying depression eastern china a comprehensive study on rift stratigraphy requires a solid understanding of sequence architecture along the steep margins of rift basins this study analyzes an eocene lacustrine sequence along the steep margin of the dongying depression in eastern china through integrated core well log and three dimensional seismic analyses the lacustrine sequence is bounded by unconformities and their correlative conformities at the base and top and consists of three systems tracts namely an early expansion systems tract eest late expansion early contraction systems tract leecst and late contraction systems tract lcst which record a lake expansion contraction cycle these systems tracts differ in thickness and development of depositional systems the eest is the thickest and contains well developed marginal and basinal fan systems with an overall retrogradational stacking pattern the well developed fan systems are the most striking features within the sequence the leecst is the most widespread and contains dominantly profundal sublittoral deposits the lcst is the thinnest with poorly developed fan systems and is characterized by significant erosion by fluvial incision the variable thickness and development of depositional systems in the three systems tracts are the responses to the interplay of sediment supply and accommodation space accommodation space establishes the framework for sedimentary infill and sediment supply determines spatial distribution and temporal evolution of depositional systems within each systems tract this study provides a lake expansion contraction scheme to divide a lacustrine stratigraphic sequence into systems tracts and highlights the feasibility of applying this approach in studying sequence stratigraphy along the steep margin of a lacustrine rift basin the results also provide understandings for the development distribution and evolution of depositional systems and their controlling factors along the steep margin of other rift basins in the world

oligo miocene lacustrine microbial and metazoan buildups from the limagne basin french massif central the limagne basin french massif central is an extensive continental lacustrine system accommodating microbial and metazoan buildups from chattian to aquitanian age a description of these buildups and their associated biotic components in grand gandaillat and crechy quarries provides insights into their spatio temporal distribution patterns flats cauliflowers domes cones and coalescent columnar morphologies have been identified with a main laminated mesofabric and laminated columnar filamentous and caddisfly coated microfabrics two low gradient margin models emerged based on the changes in the distribution morphology and size of the microbial and metazoan rich deposits through time the first model applies to the chattian deposits in the grand gandaillat quarry and the second to the aquitanian deposits in the crechy quarry this study emphasizes the heterogeneity of marginal lacustrine carbonate siliciclastic cycles the lacustrine palustrine cycles of the limagne basin record i lacustrine deposits composed of microbial and metazoan buildups and organic matter rich marls indicating periods of high accommodation and ii palustrine deposits composed of mudstone and clayey paleosoils indicative of periods of low accommodation the cycles differ with thin and symmetrical deposits that dominate the chattian cycles whereas thicker and asymmetrical deposits mark the aquitanian cycles in addition the chattian buildups are exclusively microbial and only a few centimeters thick whereas the aquitanian ones are multiple meters in height and are composed of both microbes and metazoans climatic tectonism volcanic and local parameters are involved in the deposition of buildups and their organization in each different cycle climate may control the long term arid humid sedimentary succession tectonic may explain the difference in the deposit thickness between two cycles of different ages and localizations as well as the specific distribution of the buildups throughout the basin volcanism may control the chemical lacustrine conditions and local physiography may impact the soil removal ability of the lake margin

taphonomy of jack s birthday site a diverse dinosaur bonebed from the upper cretaceous two medicine formation of montana jack s birthday site is a diverse vertebrate assemblage from the upper two medicine formation of western montana age is roughly 74 ma the site covers roughly 3000 m2 and excavations over 140 m2 a large bone sample 1600 skeletal elements allowed statistical evaluation of the preservational and compositional variation within the site evidence including sedimentary facies plant and invertebrate fossils and bone orientation and condition indicates jack s birthday site represents part of a small shallow floodplain lake lithologies and fossil preservation vary from northwest to southeast over a distance of 50 m this variation represents a transition from lake through shoreline to marginal shoreline floodplain environments containing ten dinosaur taxa and a variety of non dinosaurs jack s birthday site provides one of the best single faunal samples of the region the vertebrate assemblage includes two taphonomic fractions the first consisting of attritional predominantly isolated and allochthonous elements represents a time averaged assemblage the other consists of associated parautochthonous remains restricted to a single horizon taxa represented by associated remains include three iguanodontoids hypacrosaurus prosaurolophus and gryposaurus and the theropod troodon associated individuals of these taxa have non random distributions within the site fisher s exact test p 0 01 and observed taxonomic clustering may reflect group behavior and or event mortality the four or more troodon represent the first described multi individual troodontid occurrence the diversity and spatial complexity of the parautochthonous fraction of the birthday site assemblage is difficult to explain discussion of possible event mortality mechanisms focuses on three drought botulism and cyanobacterial toxicosis these share an ability to act over an ecologically significant period of time affect a variety of species and concentrate mortality along water sources aspects that may have been important in generating the birthday site assemblage evidence at the site favors drought or perhaps a drought botulism hypothesis however taxonomic clusters could represent completely separate events with a variety of causes

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

high frequency cyclicity in the latest messinian adriatic foreland basin insight into palaeoclimate and palaeoenvironments of the mediterranean lago mare episode abstract late messinian lago mare deposits show high frequency cyclicity in the whole mediterranean basin both millimeter and centimeter scale cyclicities have been observed in several odp sites as well as in stratigraphic sections from the mediterranean borderland we have analyzed a well exposed late messinian lago mare section from the adriatic side of the central apennines italy at the fonte dei pulcini section se majella mts millimeter and centimeter scale white and dark couplets have been observed in the field a 50 cm regular spaced sampling has been performed in the uppermost 53 m of the late messinian lago mare clays on the 107 collected samples geochemical caco 3 content mineralogical xrd analyses and micropalaeontological investigations have been performed in addition sem and microprobe investigations as well as mineralogical and micropalaeontological analyses have been carried out on single lamina from a 34 cm thick interval of millimeter scale laminites besides the 10 3 cycles m and 10 2 cycles m frequencies observed in the field spectral analyses performed on the caco 3 data set indicated other high frequency cyclicities 0 47 cycles m 0 35 cycles m and 0 17 cycles m taking into account the estimated sedimentation rate these frequencies correspond respectively to periodicities of 1 year 10 years 2 1 kyr 2 8 kyr and 5 6 kyr these sub milankovitch cyclicities have been related to annual and sunspot solar activity the millimeter scale couplets are interpreted as varves sedimented in an ephemeral water environment marginal to a perennial brackish water lagoonal basin these varved sediments reflect a marked seasonality characterized by the alternation of arid and more humid climatic phases the presence of high values of smectite 60 80 in the clay minerals of the analyzed samples could be a consequence of these climatic oscillations from drier to moister conditions the climatic scenario suggested in this paper for the late messinian lago mare episode is in agreement with the monsoon system that according to some authors starting from 5 8 ma developed in the mediterranean area

latest miocene to earliest pliocene sedimentation and climate record derived from paleosinkhole fill deposits gray fossil site northeastern tennessee u s a abstract lacustrine sediments deposited within a paleosinkhole at the gray fossil site gfs in northeastern tennessee usa provide a latest miocene and earliest pliocene 4 5 7 ma record of sedimentation and paleoclimate the basal graded facies consists of mm to cm thick normally graded layers of primarily locally derived terrigenous silts and fine sands with low organic content which record storm flow influxes into a 40 m deep paleosinkhole lake the graded facies is overlain by the laminated facies which is characterized by mm thick non graded a b couplets of abundant macerated terrestrial organic matter and fine to coarse quartz sand a alternating with quartz and carbonate silt b isotopic evidence for establishment of either c4 dominated or mixed c3 c4 terrestrial ecosystems is not evident at this site 13 c values of bulk organic matter from the basal graded facies range from 24 to 26 pdb and decrease upsection to 28 to 30 in the organic rich laminated facies isotope values covary with changes in both total organic content toc 0 25 1 wt in graded facies 2 12 wt in laminated facies and in carbon nitrogen ratio c n 1 2 in graded facies 20 50 in laminated facies these upsection changes in sedimentary facies and organic geochemistry within the gfs are attributed to either 1 a climate shift characterized by increased precipitation and concomitant increased vegetation within the paleosinkhole watershed over time or 2 progressive shallowing and eutrophication of the paleosinkhole lake coupled with organic diagenesis within either the watershed or the paleosinkhole sediments in which there was isotopic discrimination associated with organic matter decomposition subaerial exposure of the paleosinkhole lake is recorded by paleosol development

evidence for plunging river plume deposits in the pahrump hills member of the murray formation gale crater mars recent robotic missions to mars have offered new insights into the extent diversity and habitability of the martian sedimentary rock record since the curiosity rover landed in gale crater in august 2012 the mars science laboratory science team has explored the origins and habitability of ancient fluvial deltaic lacustrine and aeolian deposits preserved within the crater this study describes the sedimentology of a ca 13 m thick succession named the pahrump hills member of the murray formation the first thick fine grained deposit discovered in situ on mars this work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting the pahrump hills succession can be sub divided into four distinct sedimentary facies i thinly laminated mudstone ii low angle cross stratified mudstone iii cross stratified sandstone and iv thickly laminated mudstone sandstone the very fine grain size of the mudstone facies and abundant millimetre scale and sub millimetre scale laminations exhibiting quasi uniform thickness throughout the pahrump hills succession are most consistent with lacustrine deposition low angle geometric discordances in the mudstone facies are interpreted as scour and drape structures and suggest the action of currents such as those associated with hyperpycnal river generated plumes plunging into a lake observation of an overall upward coarsening in grain size and thickening of laminae throughout the pahrump hills succession is consistent with deposition from basinward progradation of a fluvial deltaic system derived from the northern crater rim into the gale crater lake palaeohydraulic modelling constrains the salinity of the ancient lake in gale crater assuming river sediment concentrations typical of floods on earth plunging river plumes and sedimentary structures like those observed at pahrump hills would have required lake densities near freshwater to form the depositional model for the pahrump hills member presented here implies the presence of an ancient sustained habitable freshwater lake in gale crater for at least ca 10 3 to 10 7 earth years

comparison of drier to wetter interval estuarine roof facies in the eastern and western interior coal basins usa abstract many of the carboniferous coals in the eastern interior of the us are associated with siliciclastic roof facies that were deposited within a fluvio estuarine transition these facies include a variety of rhythmites some of which exhibit tidal cycles drier interval coals westphalian b c stephanian tend to be more laterally restricted and more commonly are associated with paleovalleys conversely wetter interval coals westphalian d are very widespread and are not restricted to paleovalleys throughout the lake carboniferous wet paleoclimates associated with these coals lead to valley incision during sea level lowstand when large tropical rivers downcut older sediments deposited during previous sea level highstands during subsequent rise of sea level these fluvial valleys were flooded and converted to estuaries where tidal ranges and sedimentation rates were significantly amplified based on modern analogs and interpretation of many examples of carboniferous tidal rhythmites the localized depositional rates in these settings are exceptionally high the estuaries became sediment sinks trapping sediment that is pumped in from both fluvial and marine sources as a result sedimentation readily keeps pace with rising baselevel extensive intertidal flats and shallow subtidal flats are created and prograde over the valley confined mires thick tidal cycles and upright trees some with attached foliage record rapid burial of mires this model is supported with examples of roof facies from the westphalian b c of the eastern interior basin and the stephanian of the western interior basin in these areas facies within each cycle range from well developed extensive paleosols and coals to widespread marine shales or limestones variations in both sea level and climate resulted in a complex history of valley fill during which coals could be developed at any time except during widespread flooding minable low sulfur and low ash coals occur but the coals are relatively thin and discontinuous conversely the westphalian d coals are very widespread and significant peat accumulations were not confined to paleovalleys nonetheless the lowest sulfur coals are related to rapid deposition of roof facies that occurred within the paleovalley whereas high sulfur coals were formed in areas of lower sedimentation rate of roof facies that occurred beyond the confines of the paleovalley

isotope shifts in the late permian of the delaware basin texas precisely timed by varved sediments closely spaced samples 285 in number of varved sediments from the upper permian in delaware basin texas have been analyzed for 13ccarb 13corg 18ocarb corg ccarb and calcite dolomite 13c records a dramatic rise from 2 8 to 5 7 in only 4400 years detected in three sections across the basin extrapolating smoothly through a 600 year interruption by a local west side of the basin fresh water inflow evidenced by low 18o this continuity and low corg within the basin both indicate that the excess net deposition of corg necessary to generate the rise in 13c took place in the ocean external to the delaware basin correlation with similar records from the zechstein basin suggest that the event was world wide although this poses obvious difficulties for the carbon cycle the rate of rise of 13c and its sustained high level must imply conversions of oxidized carbon to reduced carbon that are very large depending on which reservoirs were involved

depositional depth of laminated carbonate deposits insights from the lower cretaceous valdeprado formation cameros basin northern spain the lower cretaceous berriasian valdeprado formation cameros basin northern spain contains more than 900 m of laminated carbonates and pseudomorphs after sulfates traditionally many sedimentary packages of different ages and lithologies have been interpreted as deep water deposits based essentially on the abundance of laminations and the absence of subaerial exposure features in contrast the valdeprado formation provides an example of a shallow water deposit dominated by laminations with scarce evidence of subaerial exposure and gives criteria to solve the challenge of distinguishing shallow water and deep water ancient laminated deposits the two most abundant facies all along the valdeprado formation are a parallel laminated limestone formed by alternating carbonate mudstone and calcite and quartz pseudomorphs after displacive gypsum and b graded laminated limestone consisting of quartz mica ostracodes and pseudomorphs after detrital gypsum grains at the base which changes gradually upwards to carbonate mudstone parallel laminated limestone and graded laminated limestone could have been deposited in either deep or shallow environments as a result of salinity fluctuations driven by alternation of flooding and evaporation and by sediment resuspension processes respectively subaerial exposure features such as desiccation mudcracks are scarce in most of the succession except in a few meter scale stratigraphic intervals where they are very abundant interestingly in these intervals desiccation cracks are present at the tops of several successive laminae up to 25 mudcracked laminae per meter of deposit indicating that at least during those periods of time deposition occurred in shallow water bodies that were desiccated frequently in the upper part of the stratigraphic section parallel laminated and graded laminated limestones are associated with current ripple and wave ripple cross laminated arenites and ostracode mudstone to wackestone with centimeter size pseudomorphs after lenticular gypsum and abundant desiccation mudcracks and tepees which also suggest sedimentation in shallow water environments moreover the laminated carbonates display continuous parallel layering and the same facies along the 40 km long outcropping area these deposits are directly interbedded with and pass laterally to siliciclastic sandy muddy flat deposits in the western area of the basin without clinoforms slump structures or slide masses in between all of these features suggest deposition in shallow perennial carbonate sulfate water bodies and their peripheral mudflats developed in a flat bottomed basin with no marked gradients

middle eocene paleohydrology of the dongying depression in eastern china from sedimentological and geochemical signatures of lacustrine mudstone previous understanding that stratigraphic variability in lacustrine sequences is primarily caused by depositional processes governed by regional tectonics and climatic change remains to be tested on microscopic scale here we study the upper fourth member es4u of the eocene shahejie formation the major source rock of the dongying depression eastern china in order to understand stratigraphic heterogeneity and tectonic and climate controls on depositional processes in lacustrine mudstone our study integrates core descriptions microscopic observations and studies of mineralogy toc and chemical weathering proxies of cia and ln al2o3 na2o from two full bore cores and correlation of gamma ray logs from six wells across the depression we identified four major lithofacies including the interbedded evaporite and mudstone deposited in a shallow salt lake the silt bearing clay rich mudstone deposited in a pro delta environment within a shallow open lake the laminated calcareous mudstone deposited in a deep stratified meromictic lake with frequent earthquake activities and the massive calcareous mudstone deposited in a shallow and oxygenated lake the es4u member changed from the interbedded evaporite and mudstone dominated lithofacies association to silt bearing clay rich mudstone dominated lithofacies association and then laminated calcareous mudstone dominated lithofacies association suggesting basin wide changes in depositional processes lake level lake water chemistry and paleohydrology we suggest that these changes reflect balance between sediment and water supply and potential accommodation of the lake basin which were governed by paleoclimate in the lake drainage and extensional tectonics we infer that during the deposition of the es4u member the lake basin evolved from an underfilled lake basin with salty lake water under arid climate to a shallow balanced fill lake basin when climate became humid then to a deep balanced fill basin with stratified bottom lake water when climate became more humid and the basin was deepened by tectonic activity this study demonstrates that climate and tectonics both control paleolimnological changes and depositional processes of lacustrine mudstone

varve formation during the past three centuries in three large proglacial lakes in south central alaska the sediments stored in the large deep proglacial lakes of south central alaska are largely unstudied we analyzed sediments in 20 cores up to 160 cm long from eklutna kenai and skilak lakes using a combination of repeated lamination counting radionuclide dating event stratigraphy and tephrochronology we show that the characteristically rhythmic layers were deposited annually most of these glacial varves consist of one coarse grained base and a fine grained top but varves composed of multiple coarse grained turbidite pulses are common too they are likely related to successive episodes of high sediment discharge during flooding and they become more frequent in all three lakes along with increased sedimentation rates during the nineteenth century late phase of the little ice age these flood turbidites were generated by rain events and intense melting of snow and ice other mega turbidites are a result of earthquake triggered slope collapses e g a d 1964 some event layers are present in all three lakes in addition the annual time series of varve thickness normalized annual sedimentation rate are significantly correlated among the three lakes p 0 27 p 0 001 differences between the varve thickness records can be attributed partly to the dam construction at eklutna lake and outbursts from an ice dammed lake at skilak lake geomorphologic differences among the catchments result in further differences in sedimentation patterns in the three lakes

in situ optical measurements of chang e 3 landing site in mare imbrium 2 photometric properties of the regolith the panorama cameras onboard the yutu rover of the chang e 3 lunar mission acquired hundreds of high resolution color images of the lunar surface and captured the first in situ lunar opposition effect oe since the apollo era we extracted the phase curve and the color ratio in three bands with the phase angle range from 2 degrees to 141 degrees photometric inversions using the hapke model reveal that submicroscopic dusts are present in the landing area and both the coherent backscattering and the shadow hiding are responsible for the strong oe compared with spaceborne measurements the grains in the landing site are brighter more transparent and appear to be better crystallized than the average maria basaltic grains the results show that the phase reddening effect appears to be present in the in situ phase curves the current phase curve can be used as the ground truth validations of any future spaceborne phase curve measurement over the landing site region

record of redox status in laminated sediments from lake titicaca a sulfur k edge x ray absorption near edge structure xanes study abstract laminated sediments are commonly used to examine limnological and ecological processes on short time scales here we examine changes in sulfur speciation of lamination couplets from lake titicaca south america using x ray absorption near edge structure xanes spectroscopy the dark colored layer of each lamination couplet contains a significant fraction of reduced organic sulfides with smaller fractions of iron sulfides and sulfate in contrast the light colored layer of each couplet is primarily composed of sulfate in all laminae the sulfate is present as inorganic sulfate substituted in calcite the differences in speciation likely reflect changes in productivity during sediment deposition during the warm productive summer months micritic calcite precipitation was induced in oxidized surface waters due to ph changes induced by consumption of dissolved co 2 this calcite incorporates dissolved sulfate and forms the light colored layers this pulse of productivity creates organic matter that partially decomposes during the austral winter months consuming oxygen and delivering organic rich sediment to the lake bottom this decomposition and the possible presence of a halocline kept bottom waters low in oxygen and lead to the production of organic matter rich in reduced sulfur these data suggest that these laminations are deposited annually and illustrate the utility of s k edge xanes for the analysis of laminated sediments

varves in lake sediments a review abstract downcore counting of laminations in varved sediments offers a direct and incremental dating technique for high resolution climatic and environmental archives with at least annual and sometimes even seasonal resolution the pioneering definition of varves by de geer 1912 had been restricted to rhythmically deposited proglacial clays one century later the meaning of varve has been expanded to include all annually deposited laminae in terrestrial and marine settings under favourable basin configurations and environmental conditions limnic varves are formed due to seasonality of depositional processes from the lake s water column and or transport from the catchment area subsequent to deposition of topmost laminae the physical preservation of the accumulating varved sequence requires the sustained absence of sediment mixing for example via wave action or macrobenthic bioturbation individual sub laminae in varved lake sediments typically express contrasting colours always differ in terms of their organic chemical and or mineralogical compositions and often also differ with regard to grain size various predominating climatic and depositional conditions may result in clastic biogenic or endogenic incl evaporitic varved sediments and their mixtures to reliably establish a varve chronology the annual character of laminations needs to be determined and verified in a multidisciplinary fashion sources and influences of possible errors in varve chronologies are best determined and constrained by repeated varve counts and by including radioisotopes and correlation with historically documented events a well established varve chronology greatly enhances the scientific value of laminated limnic archives by securely anchoring the wealth of multi proxy palaeoenvironmental information in the form of time series for multidisciplinary investigations applications of varved records are discussed with special reference to advances since the 1980s these span fields like calibrating radiometric dating methods reconstructing past changes of the earth s magnetic field or detecting fluctuations in solar forcing once a varve chronology is established it can be applied to precisely date events like volcanic ash layers earthquakes or human impact as well as short and long term climate temperature precipitation wind hydroclimatic conditions or flooding and environmental changes eutrophication pollution due to their exceptional high temporal resolution and in combination with their robust and accurate internal time scale in calendar years annually laminated sediments can be regarded as one of the most precious environmental archives on the continents these records are necessary to extend temporally limited instrumental records back in time as such they have societal relevance with regard to risk assessments related to natural hazards arising from e g flooding or volcanic eruptions

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

origin of precambrian iron formations in the lake superior region the precambrian banded cherty iron formations in the lake superior region were deposited on broad continental shelves and deposits of the supratidal intertidal and subtidal zones can be recognized in the well known facies of the iron formations the supratidal deposits were primarily calcitic aragonitic and sideritic muds other minerals in order of decreasing abundance may have been gypsum anhydrite ankerite dolomite quartz apatite and halite intraclasts were produced by desiccation granulation and some of this material was redeposited in the intertidal and subtidal zones the intertidal zone was characterized by the development of extensive algal reefs and digital sized and larger stromatolitic mounds desiccation granulation and tidal rip of mineralized stromatolites further added to the accumulation of intraclasts the intertidal zone was the domain of granules that were derived by abrasion and rounding of intraclasts the original mineralogy of the intertidal deposits was similar to that of the supratidal zone however because of photosynthesis the sea water was oxygenated lozenge shaped grains are considered to be secondary silicified and iron oxide replicates of original gypsum crystals and by comparison with recent evaporites some anhydrite and halite may also have been present the deposits of the intertidal and subtidal zones are considered to be comparable to the present day abu dhabi complex in the persian gulf spherical microstructures are abundant and well preserved in the chert of the subtidal deposits pyrite which characterizes these deposits probably was formed largely by the bacterial reduction of sulfate derived from the intertidal zone the laminations in the iron formations resulted from several causes that were controlled by chemical and mechanical processes such as the rates and localization of the precipitation of calcitic aragonitic and sideritic muds and the mechanical breakup and redistribution of these sediments as sand silt and mud these processes resulted in compositional and textural laminations the diversity of the banded cherty iron formations recognized in the different facies then can be explained largely in the diagenetic changes the large scale pervasive diagenetic changes were the replacement of calcite and aragonite by chert and the formation of iron silicates by the reactions between ionic silica and siderite and iron bearing dolomite vein like structures and the development of magnetite along stylolites indicate mobility of iron in late diagenetic stages and iron organic chelates are suggested to account for the mobility depending on the composition of the laminae and the chemical environment silicification during diagenesis produced the hematite magnetite siderite pyrite and mixed mineral facies

annually laminated lake sediments and the study of quaternary environmental changes a review abstract annually laminated lake sediments non glacial varves have in recent years been discovered in increasing abundance especially since the development of in situ freezer samplers so far the majority of examples have been found in three main areas eastern north america northern and central europe and east and central africa a much more widespread distribution seems highly probable however the formation of annual laminations in freshwater lakes is governed by a number of factors the most important of which appears to be morphometry seasonality of sediment supply which may be controlled by physical biological or even cultural processes in the lake or in its catchment is also clearly significant four main types of laminations here termed ferrogenic calcareous biogenic and clastic have so far been recorded although it is quite clear that others exist special field and laboratory techniques are needed in order that the particular properties of varved sediments may be fully exploited annually laminated sediments have so far been applied to the investigation of a number of aspects of the quaternary these include the study of a geochronology b climatic change c vegetation history especially the role of fire in forest ecosystems d the calculation of rates of sediment influx to lakes and of rates of erosion from their catchments and e the monitoring of processes in the modern environment such as heavy metal pollution eutrophication and acid rain annually laminated lake sediments combine an internal independent chronology with the preservation of discrete visible increments of seasonal and annual sedimentation given this unique property and the likelihood that many more examples will be discovered the prospects for further applications of studies of these sediments to the investigation of the quaternary seem very good indeed

microdeformation of lacustrine laminite sequences from late miocene formations of se spain an interpretation of loop bedding lacustrine laminated sediments laminites present in late miocene formations of the hijar basin se spain display well developed loop bedding a structure consisting of bundles of laminae that are sharply constricted at intervals giving a morphology of loops or links of a chain the laminite sequences which are interbedded with turbidite marlstones were accumulated on the bottom of a permanently stratified lake developed in a rapidly subsiding basin limited by 010 and 105 normal faults as deduced from both macro and microdeformational analyses the basin evolved under an extensional stress field throughout the late miocene four main types of loops simple and complex loops with subcategories have been recognized within the laminite sequence simple loops of type 1 show the best definite pattern quite similar to pinch and swell structures a type of boudinage typical of stretching of alternating beds where the competence contrast is not strongly marked the remaining loop types display contortion and occasional breakage of laminae microfaulted edges indicative of microdeformation near the boundary between the ductile brittle deformational fields the distribution of the various loop types across the laminite sequence reflects an interplay between progressive lithification of the laminites as sedimentation progressed and tectonic stresses which affected the sediment sequence accordingly a mechanism of deformation under an extensional stress field ultimately related to the creep movement of the main basin faults which resulted in successive seismic shocks of low magnitude is proposed to explain the formation of loop bedding in the laminites

annually laminated lake sediments and environmental changes in bashang plateau north china abstract angulinuo lake is the biggest lake on the bashang plateau north china and is 47 6 km2 in area and 2 6 m in depth a core from the inner part of angulinuo lake was sliced and the sediment was observed by scanning electronic microscope sem annual laminations characterized by variable color and grain size were found and interpreted as recording the cyclic deposition of lacustrine clay and aeolian dust the results of chemical analysis of coarse grains conducted by sem edax and grain size analysis of modern aeolian dust in the ice on angulinuo lake support an aeolian origin for the light coarse layers image analysis technique was used to calculate the size and number of coarse grains in each layer the coarse grains were fractionated into four classes 42 m 14 42 m 14 4 2 m and 1 4 4 2 m in general the abundance of the four classes shows similar temporal variation patterns around angulinuo lake the winter monsoon is strong and transports aeolian dust into the lake when the winter monsoon is strong the size and amount of coarse grains are expected to increase we infer that the winter monsoon was weaker during 8430 5440 year bp and was unstable in the later part of this period from 5440 year bp the winter monsoon became stronger and then weaker from 3250 to 2490 year bp during 2490 1170 year bp the winter monsoon was slightly stronger but since 1170 year bp it has become weaker again the changes of the winter monsoon intensity recorded in the annual laminations in angulinuo lake sediments correspond well to environmental changes in north china and to changes in sea level during the same period periods of weaker winter monsoon correspond to times of higher sea levels while the periods of stronger winter monsoon correspond to the neoglaciation stage in china and the periods of lower sea levels

evaluating iron as a biomarker of rhythmites an example from the last paleozoic ice age of gondwana abstract microorganisms play a significant role in mineral precipitation but detecting them in the fossil record is still a challenge here we offer an example of how the detection of biological activity in the sedimentary environment can modify a classical depositional model this study describes the activity of microorganisms in sedimentary structures and the iron mineral formation during the last paleozoic ice age in southwestern gondwana recorded by the itu rhythmites parana basin brazil the itu rhythmites have been considered to be varve type deposits that present alternating dark laminae clay silt size sediments and light layers sand gravel size sediments of varied thickness forming couplets earlier studies focused on abiotic processes of these structures we applied different techniques and analytical approaches were used such as synchrotron based techniques and rock magnetic techniques in order to test the biogenicity of iron minerals contained in putative microbially induced sedimentary structures by detecting biominerals in this rock succession the depositional model had to be reconsidered taking into account the biological activity the limitations on the specific conditions for bacterial growth and for mineral precipitation therefore we offer a new depositional model that considers the role of microorganisms in formation of these laminae and this model can be considered for other iron rich rhythmic deposits in other places of the world considering the effects of temperature and other factors in the bacterial productivity the deposition of the latest couplets in the outcrop occurred in different seasons and by different depositional processes corroborating with the non periodicity of 1 year per lithological couplet

tephrostratigraphical investigation of lake sediments and a peat bog in northeastern china since 20 000 years this is a detailed tephrostratigraphical investigation of late quaternary deposits in the longgang and changbaishan volcanic fields of northeastern china a total of 45 reference samples which were collected from either side of the chinese korean border showed very similar geochemical characteristics to the millennium eruption of tianchi volcano through comparing the published data of the glass shards detected in gushantun with these reference samples further description is that the glass shards in the sediment of gushantun came from the tianchi volcano eruption in ad 1702 1668 and 1597 a basaltic tephra layer found in the sediment of hanlongwan associated with an eruption of the jinlongdingzi volcano which happened in 1500 2100 cal yr bp by comparing with the published data from sihailongwan and xiaolongwan tianchi and jinlongdingzi volcano are both active and erupted several times during the historical period reference samples and the tephra layers detected in hanlongwan sihailongwan gushantun

testing the precision of bioevents deciding which of two bioevents is the less diachronous is a common problem in biostratigraphy the most accurate correlation uses the finest timescale available chemostratigraphy or cyclostratigraphy offer a potential precision of about 10 ka graphic correlation can then be used to test the precision of bioevents and to quantify any mismatch it can also be used to determine in which section any event occurs earlier application of these ideas to correlation of the cenomanian turonian and coniacian santonian boundaries demonstrates that some bioevents are as precise as chemo and cyclostratigraphy but that most are not two problems occur with bioevents first they may not be recognizable in all sections second where they are recognizable they may be diachronous in the former case calculating confidence intervals on known ranges in sections where the relevant fossil has been recorded is an alternative test large confidence intervals suggest that both first and last occurrences of a fossil may be diachronous bioevents at the cenomanian turonian boundary the following bioevents in stratigraphic order appear to be reliable time planes for international correlation the last occurrences of 1 corolithion kennedyi 2 rotalipora greenhornensis 3 axopodorhabdus albianus 4 rotalipora cushmani 5 lithraphidites acutus 6 microstaurus chiastius and 7 the first occurrence of quadrum gartneri at the coniacian santonian boundary only the first and last occurrences of platyceramus undulatoplicatus and the first occurrences of platyceramus cycloides and lucianorhabdus cayeuxii have been identified as potentially reliable bioevents

holocene fluctuations of a meromictic lake in southern british columbia abstract holocene deposits of mahoney lake a meromictic saline lake located in a closed basin in the semi arid okanagan valley contain evidence of frequent and marked changes in lake depth up to 12 m 10014c yr probably caused by short term changes in effective precipitation we studied a 5 45 m long core comprising a basal layer of inorganic mud overlain by a succession of layers of calcareous laminated and nonlaminated organic mud marl and sand we used mazama tephra to adjust nine radiocarbon ages for the hardwater effect meromixis developed ca 900014c yr b p and the lake has been episodically meromictic for about half the time since because of close linkages between sediments and depositional environments in meromictic and saline lakes we infer that laminated sediments indicate meromictic conditions and high lake levels ca 12 m water depth whereas thick marl layers and nonlaminated sediments indicate nonmeromictic conditions and thus low lake levels

late glacial and holocene development of lake donggi cona north eastern tibetan plateau inferred from sedimentological analysis abstract sediments of lake donggi cona on the northeastern tibetan plateau were studied to infer changes in the lacustrine depositional environment related to climatic and non climatic changes during the last 19 kyr the lake today fills a 30 8 km big and 95 m deep tectonic basin associated with the kunlun fault the study was conducted on a sediment core transect through the lake basin in order to gain a complete picture of spatio temporal environmental change the recovered sediments are partly finely laminated and are composed of calcareous muds with variable amounts of carbonate micrite organic matter detrital silt and clay on the basis of sedimentological geochemical and mineralogical data up to five lithological units lu can be distinguished that document distinct stages in the development of the lake system the onset of the lowermost lu with lacustrine muds above basal sands indicates that lake level was at least 39 m below the present level and started to rise after 19 ka possibly in response to regional deglaciation at this time the lacustrine environment was characterized by detrital sediment influx and the deposition of siliciclastic sediment in two sediment cores upward grain size coarsening documents a lake level fall after 13 cal ka bp possibly associated with the late glacial younger dryas stadial from 11 5 to 4 3 cal ka bp grain size fining in sediment cores from the profundal coring sites and the onset of lacustrine deposition at a litoral core site 2 m water depth in a recent marginal bay of donggi cona document lake level rise during the early to mid holocene to at least modern level in addition high biological productivity and pronounced precipitation of carbonate micrites are consistent with warm and moist climate conditions related to an enhanced influence of summer monsoon at 4 3 cal ka bp the lake system shifted from an aragonite to a calcite dominated system indicating a change towards a fully open hydrological lake system the younger clay rich sediments are moreover non laminated and lack any diagenetic sulphides pointing to fully ventilated conditions and the prevailing absence of lake stratification this turning point in lake history could imply either a threshold response to insolation forced climate cooling or a response to a non climatic trigger such as an erosional event or a tectonic pulse that induced a strong earthquake which is difficult to decide from our data base

sedimentary facies in an extensional and deep lacustrine depositional system the pliocene tiberino basin central italy abstract the tiberino basin was formed during plio pleistocene extensional tectonic activity in central italy the pliocene sediments that fill this structure consist predominately of fine grained clastic lithofacies deposited in a lacustrine system four facies associations have been distinguished facies association a was deposited in a deep offshore lacustrine environment and consists of massive laminated bluish gray marly clays that lack benthonic fauna but have preserved organic matter leaves wood this facies association is the main lacustrine deposit whereas the other three represent marginal facies facies association b is interpreted as a delta system deposit it has gilbert type sandy gravel bodies with foresets up to 50 m high and prodelta bodies consisting of laminated to massive marly clays that alternate with sandy and gravelly mud strata association c corresponds to a coastal environment where two sub environments are recognized 1 a wave dominated coastline characterized by interbedded muddy and sandy strata with sedimentary structures attributed to hummocky cross stratification and 2 clayey silts and lignites interpreted as a coastal wetland a spectacular fossil forest is preserved in situ within this unit association d formed on the distal part of a muddy alluvial fan consists of sheet flood clayey sandy silts that alternate with incipient paleosols rare ribbon channel fills are also present paleoenvironmental reconstruction indicates that the tiberino basin was occupied by a narrow deep meromictic lake during the pliocene the size shape depth and sub environment distribution of this lake were controlled by tectonic phenomena such as the high subsidence rate which caused the lake to be large and deep only in the few coastal areas that had high sedimentary input were wetland or alluvial fan deposits formed

palaeoclimate controlled accumulation of organic matter in oligocene evaporite sediments of the mulhouse basin abstract marl beds of a 30 m thick interval of the oligocene evaporites of the mulhouse basin display a cyclic variation in their organic carbon content that is related to changes in sedimentation rate the construction of a time scale suggests a duration of 58 000 30 yr for the interval studied calculated accumulation rates for organic matter of aquatic origin are used to assess the fluctuation of palaeoproductivity of the system the observed variation of the accumulation rates of terrigenous organic matter throughout the studied interval is most likely linked to variations in palaeoclimate

an abandoned channel fill with exquisitely preserved plants in redbeds of the clear fork formation texas usa an early permian water dependent habitat on the arid plains of pangea abstract a well preserved plant assemblage at the colwell creek pond locality of leonardian kungurian age provides an opportunity to evaluate taphonomic conditions in a dryland alluvial setting a narrow channel body incised to 5 m depth through red paleo vertisols contains 2 m of varicolored laminated mudstone with graded layers and plant material x ray diffraction analysis of individual laminae indicates the presence of chlorite illite kaolinite and mixed layer clay with hematite in red and gray layers and goethite in yellow brown laminae no carbonate was identified and the total organic carbon content is minimal the fine sediment accumulated in a shallow abandoned channel from suspension and gentle underflows probably linked to seasonal inflow and analysis of lamina thickness suggests that standing water may have persisted for up to a few millennia the preservation of lamination is attributed to a lack of bioturbation possibly linked to a paucity of subsurface oxygen low productivity elevated salinity rapid deposition or a combination of these factors minimal bioturbation may also reflect the limited use of freshwater ecospace during the early permian clay rich paleo vertisols complete the fill with drab root traces that indicate growth of vegetation in a strongly seasonal setting abundant plant material in the laminated beds includes branches of walchian conifers the possible cycadophyte taeniopteris spp and the comioid possible peltasperm auritifolia waggoneri they were derived from an adjacent riparian zone and preserved as 3d goethite petrifactions much of the foliage shows evidence of arthropod herbivory although a humid climatic episode cannot be ruled out the exceptional abundance and preservation of the plants probably reflects the persistence of an oxbow lake on a relatively arid alluvial plain where riparian plants experienced periodic moisture stress but had access to groundwater nearly year round rapid burial in standing water the lack of bioturbation in the laminated sediments and early biomineralization probably explain the exceptional preservation of the plant remains

controlling factors on the formation and distribution of sweet spot areas of marine gas shales in south china and a preliminary discussion on unconventional petroleum sedimentology abstract shale gas resources in china are abundant with the marine shales accounting for the largest proportion i e 13 1012 m3 the wufeng longmaxi shale system deposited across the late ordovician and early silurian transition in south china is currently the target for shale gas exploration and development in china its annual output in 2018 reached 10 8 109 m3 making china the largest shale gas production region outside north america within this shale system the sweet spot intervals of shale gas formed vertically and sweet spot areas of shale gas formed regionally the sweet spot intervals occur mainly at the bottom of the wufeng longmaxi shale and are 10 40 m in thickness the sweet spot interval is characterized by high total organic carbon toc and gas contents relatively high porosity high brittle mineral content and abundant lamination fissures and fractures the formation of shale gas sweet spot intervals is mainly controlled by four factors in south china they are anoxic shelf environment abundant nano pores in organic matter sealed roof and floor strata and abundant lamination and high silica content in shale respectively as the regional extension of the sweet spot intervals the formation of the sweet spot area requires all the controlling factors for the sweet spot interval it was born in regional anoxic shelf with stable tectonics and preserved in relatively stable tectonic zones three sweet spot areas are identified for the wufeng longmaxi shale in south china i e fuling weiyuan fushun yongchuan and changning zhaotong areas the total area is about 2 104 km2 with technically recoverable resources of 3 3 1012 m3 in addition with the rapid progresses of exploration and development of unconventional petroleum resources such as shale gas the petroleum industry around the world extends to unconventional petroleum resources gradually accomplishing an important change of petroleum geology research focus from conventional to unconventional unconventional petroleum geology research focuses on continuously or semi continuously distributed sweet spot areas for which the formation would be the result of coupling sedimentology from several geological events such as global or regional tectonic activity volcanic eruption climate change anoxic water biotic mass extinction and radiation and gravity current it is necessary to innovatively construct new insights of unconventional petroleum sedimentology in order to enrich and improve the petroleum sedimentology research and its application therefore the concept of unconventional petroleum sedimentology is proposed and its research task method aim and importance are preliminarily discussed

natural vs human induced facies changes in recent shallow fjord sediments of the store lungegardsvannet in bergen western norway a basin wide change from an older homogeneous bioturbated to a younger laminated facies occurs in sediments from the 26 m deep permanently anoxic store lungegardsvannet fjord the younger facies consists of alternating packages of light and dark layers each containing millimetre scale laminae the composition of the dark layers differs from that of the light layers in the occurrence of predominantly marine benthic diatoms larger grain size lower loss on ignition loi and lower trace metal cu pb zn concentrations total trace metal concentrations correlate with the redox sensitive trace elements mo and v r 0 8 and with loi r 0 6 the correlation of the minerogenic matter and the grain size related elements al and li is poor r 0 2 the shoaling of the sill depth and reduction of the fjord area resulting in the reduction of bottom water exchange accounted for the shift from bioturbated to laminated sediments during the end of the last century the alternating changes within the laminated facies are the result of alternating wind forces during years of calm wind conditions 1908 1919 and 1945 1961 undisturbed sedimentation of organic matter from primary production and an associated accumulation of trace metals prevail years of high wind force 1919 1945 and 1961 1991 trigger shore erosion and an increased influx of minerogenic matter

climate driven paleolimnological change controls lacustrine mudstone depositional process and organic matter accumulation constraints from lithofacies and geochemical studies in the zhanhua depression eastern china abstract the influence of paleoclimate on the depositional process of lacustrine mudstone and organic matter accumulation is important to both paleoclimate reconstruction and hydrocarbon exploration here we study the lower third member es3l of the eocene shahejie formation in the zhanhua depression bohai bay basin eastern china in order to understand how paleoclimate influenced depositional processes and organic matter accumulation of lacustrine organic rich mudstone by combining detailed core descriptions and microscopic observations and high resolution mineralogical and geochemical analyses we identified two major lithofacies including massive calcareous mudstone and laminated calcareous mudstone from the luo 69 drilling core the sedimentologic observations and changes of geochemical proxies including detritus index ln al2o3 na2o b ga and v v ni suggest that the massive calcareous mudstone was deposited in a small shallow salt lake that was dysoxic anoxic and the paleoclimate in the lake catchment was cool and arid and the laminated calcareous mudstone was deposited in a large and deep stratified lake which has anoxic highly saline bottom and oxic less saline surface water and the lake catchment was more humid and warm the dominant lithofacies changed from laminated calcareous mudstone to massive calcareous mudstone in the studied core suggesting that the lake became shallower and smaller when the paleoclimate became cooler and drier through time such a climate trend may be a response to global cooling during the middle eocene the average total organic content toc in both lacustrine highstand and lowstand are comparable even though the lake water chemistry and amount of terrigenous input are different we infer that the accumulation of organic matter within the lacustrine highstand was controlled by the combination of primary productivity carbonate production and preservation in anoxic bottom water while accumulation within lacustrine lowstand was only controlled by primary productivity

ages and stratigraphical architecture of late miocene deposits in the lorca basin betics se spain new insights for the salinity crisis in marginal basins unlike most neogene basins of the betic cordillera where the salinity crisis is dated to the messinian a contradictory tortonian dating was proposed for evaporites of the lorca basin as a consequence complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites in order to integrate the lorca basin into the geological context of the western mediterranean domain during the late miocene new sedimentological and stratigraphical studies coupled with new dating were performed which allow us to propose a messinian age for both diatomite bearing deposits and evaporites of the lorca basin these new ages challenge the idea of a tortonian salinity crisis in the lorca basin three main events of base level drop were evidenced during the messinian each event is correlated with successive steps of basin restriction shallow salina evaporites were deposited after a base level fall during the messinian before a final base level drop which led to the entire exposure of the basin this last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep mediterranean basins the reflooding which allowed the deposition of brackish deposits and a short lived marine incursion occurred at the end of the messinian base level drops occurred during eustatic falls amplified by the gradual uplift of the betic cordillera the exhumation of the tercia ridge along the strike slip alhama de murcia fault system during the messinian probably favoured the gradual restriction of the basin a discussion on correlations of main unconformities between several neogene basins of the betics is proposed suggesting a similar structural evolution at the regional scale

paleohydrological indicators in playas and salt lakes with examples from canada australia and africa abstract the sedimentary records of playas and salt lakes provide some of the best evidence for hydrological change in a region these records are comprised of siliciclastic sediments and chemically precipitated minerals that typically vary temporally and spatially in some cases the interpretation is straightforward with mineralogical sequences related to changing brine concentrations and hydrology as well as to climate in other cases it is difficult to identify the controlling factors which include climate groundwater geological setting and basin morphology in addition diagenesis commonly affects the sedimentary record models of lake level fluctuations are given for basins in the canadian prairies and southeastern australia the lake manitoba model is based mainly on secondary changes associated with pedogenesis that alters the deeper water sediment during low water stages smaller canadian lakes in more arid regions display a larger variety of diagnostic paleohydrological indicators such as specific carbonate and salt mineralogy nature of bedding grain size and secondary alterations decreasing water levels in shallow lakes tend to show a progression from clastics to carbonates to salts and then back to clastics as groundwater levels fall below the lake floor similar parameters are used in australian lakes the hydrological model for the lake tyrrell playa in victoria whose present ionic composition is similar to seawater shows clastics being deposited when average lake levels are high followed by deposition of primary carbonates gypsum and halite once seasonal drying on the lake floor begins secondary gypsum grows within already deposited sediment and clay pelletization in the capillary fringe of surface sediment leads to basin deflation and the accumulation of adjacent eolian lunettes continued water level decline leads to pedogenesis subsequent lake level rises in all of these models may initiate sedimentation in any part of the hydrological cycle and a complete cycle in the sedimentary record appears to be uncommon

laminated sediments as palaeo indicators as society at large becomes increasingly concerned with the issues surrounding global climate change so the pressure on the scientific community to produce models and predictions of climate variability increases in many respects however that branch of science concerned with climate change is in its infancy while recent meteorological and oceanographic studies have shed light on the processes and mechanisms of atmospheric and oceanic circulation this has produced only a snapshot perspective of global change limited by the range of instrumental or historical records on the other hand palaeoclimatic and palaeoceanographic studies have been mainly on coarser millennial timescales that have a more academic and less immediate appeal the palaeorecords which have the required temporal interannual decadal resolution are limited to tree rings ice cores coral records and laminated marine or lacustrine sediments this volume is concerned with the wide ranging application of lacustrine and marine laminated sediments as palaeo indicators

lacustrine varve formation through time abstract studies using sediment traps in lakes reveal that the seasonal flux of sediment regulates both the composition and timing of deposition of materials that reach the bottoms of lakes if the bottom waters of a lake are partly or totally anoxic the seasonally deposited materials are preserved as annual groupings of laminae varves common components that form individual laminae consist of allochthonous clastic material derived from the drainage basin precipitated carbonate minerals diatom frustules iron rich and manganese rich flocs autochthonous organic detritus and autochthonous and allochthonous materials resuspended from the bottom the style of varving has changed over geologic time reflecting changes in biologic evolution and types of materials available precipitated iron rich laminations were common in the middle precambrian graded sets of clastic organic laminations persisted through the precambrian prior to the evolution of bioturbating benthic organisms glaciolacustrine varves appear to have retained their distinctive character through time carbonate rich varves occurred sporadically in the precambrian and phanerozoic with the exception of diatoms major components of modern lacustrine varves were present through the paleozoic and mesozoic and yet varves are rare in strata of these ages and may have accumulated in marine to brackish water environments diatoms were introduced into lacustrine systems in early tertiary time and are common components of varves from then on diatom laminae combined with a greater chance for geologic preservation of younger lake deposits have increased the number of geologically young occurrences of varved sediments however seasonal associations of modern varve components and the processes they represent are present in ancient deposits and provide clues to the interpretation of ancient environments

stratigraphic evidence for a deep eocene lake uinta piceance creek basin colorado relief on a prograding clastic complex is used to estimate the water depth of eocene lake uinta in the piceance creek basin of western colorado relief of as much as 412 in is present today on the complex postdepositional compaction can account for only about 100 m of this relief therefore the remaining 312 m appear to represent paleorelief on the floor of lake uinta the lake was apparently more than 300 m deep authigenic saline minerals were precipitated in the unlithified sediments of the deeper areas of the lake suggesting that at least the lower part of the water column was highly saline the evidence presented here indicates that the deep stratified lake model is more appropriate than the more generally accepted shallow or playa lake model for lake uinta

solar variance recorded in lacustrine deposits from the devonian and proterozoic of scotland abstract continental lacustrine laminites deposited in low latitudes have been examined from the devonian and torridonian mesoproterozoic strata of northern scotland to investigate the consistency of sunspot periodicity through geological time the thicknesses of 2448 annual laminae were measured from the middle devonian c 388 ma achanarras limestone member lower caithness flagstone group and of 2821 laminae from the mesoproterozoic 1 2 ga poll a9mhuilt member of the stoer group time series analysis resolved periodicities of 13 8 and 13 9 years in the complete devonian and mesoproterozoic datasets respectively when sedimentological variance was considered and the data were examined as evolutive spectra those sections consisting of the most robust data consistently yielded periodicities between 8 6 and 13 7 years for the devonian section and 9 2 and 10 6 years for the mesoproterozoic section these correspond well to schwabe cycles evidence for the presence of the longer hale cycles 20 years was also recognized in the devonian time series the sunspot periodicities identified within the devonian and mesoproterozoic show little variance from published examples from the quaternary and eocene and therefore provide evidence for the consistency of solar processes and solar atmospheric interactions for the past 1 2 ga

sedimentation in a blast zone lake at mount st helens washington implications for varve formation sediment collected in traps in a newly formed lake in the blast impact area at mount st helens recorded a sediment yield that is about two orders of magnitude greater than for comparable basins with vegetation and similar precipitation most sediment was mobilized by storms and runoff at the onset of the wet season the sedimentation response to strongly seasonal precipitation in the absence of vegetation produced turbidites and graded annual couplets the style of sedimentation suggests an alternate mechanism for the formation of long sequences of graded clastic varves

high frequency paleoclimate signals from foulden maar waipiata volcanic field southern new zealand an early miocene varved lacustrine diatomite deposit abstract a freshwater diatomite deposit near dunedin south island new zealand provides an exceptional archive of mid latitude seasonal climate variation during latest oligocene early early miocene time the diatomite accumulated in a small 1 5 km diameter maar floored lake that formed during basaltic volcanism except for exposures of basanite dated at 23 2 ma by 40 ar 39 ar and remnants of a paleogene sandstone and conglomerate cover the diatomite body is surrounded by otago schist geophysical profiles indicate that the total diatomaceous sediment thickness may exceed 100 m two depositional facies are described from 15 5 m of weakly consolidated fresh diatomite accessible in two pits a thinly laminated facies comprising 60 of the section consists of dark brown and white couplets of average thickness 0 5 mm both brown and white laminae are composed essentially of frustules of a single pennate diatom along with 1 2 of siliceous sponge spicules dark laminae also contain abundant 5 7 5 m diameter siliceous chrysophycean stomatocysts and organic matter decalcified complete skeletons of galaxias a southern hemisphere group of freshwater or diadromous fish are found throughout diverse well preserved leaves some with attached scale insects are dominated by lauraceae rare flowers are also present trace fossils preserved in the laminated comprise 1 1 5 mm wide pale diatomaceous strings of probable faecal origin and isolated 20 40 mm diameter sand lenses interpreted as faecal remains of swimming waterfowl the second diatomite facies group comprises dark brown speckled beds interpreted as sediment gravity flows up to 14 cm thick and interspersed throughout the study section they incorporate abundant laminated diatomite flecks and leaves and minor woody plant matter and terrigenous silt almost all are capped by 1 8 mm of white diatomite that is interpreted as post flow fall out of resuspended diatom frustules associated breccia and swirly beds up to 8 cm thick are composed of variably contorted clasts of laminated diatomite in a speckled matrix nodules spheroids and films of authigenic framboidal pyrite are commonly associated with plant and fish remains as in modern lakes white laminae likely formed from diatom blooms when light flux temperature or nutrients were optimal during spring early summer dark laminae accumulating during autumn winter months laterally continuous pinstripe lamination absence of bioturbation and excellent fish and plant preservation indicate that the profundal lake and floor were anoxic periodic variations in couplet thickness of 3 10 years compare with quaternary records of el nino southern oscillation variability and indicate that the early early miocene low altitude new zealand climate was seasonal and strongly ocean influenced as it is today