tem study of in situ organic matter on continental margins occurrence and the monolayer hypothesis abstract tem photomicrographs show that organic matter in the continental margin sediments that we have examined is primarily patchy in distribution and occurs as 1 discrete discontinuous blebs and micro blebs of differentiated and undifferentiated protoplasm 2 bacterial cells and associated muco polysaccharide networks and 3 localized smears generally associated with clay minerals and domain junctions in clay rich flocs not as thin uniform grain coatings or as infillings of nicks or etch pits on sediment grains with high degrees of surface roughness this occurrence contradicts recent assertions that most organic matter in continental margins occurs as monolayer or monolayer equivalent coatings on mineral grains and inorganic bioclastic particles our results are based on tem photomicrographs of samples from the northern california continental slope that fall within the monolayer equivalent envelope defined by mayer 1994 marine snow from the overlying nepheloid layer and sediments from eckernforde bay in the baltic sea these samples were prepared specifically to preserve and image in situ sediment fabric and organic constituents textural evidence suggests that low permeabilities caused by the interaction between the organic inorganic and biologic components of the clay size fraction play a major role in determining organic matter preservation on continental margins

evaluating fossil charcoal representation in small peat bogs detailed holocene fire records from southern sweden in this study we assess how representative a single charcoal record from a peat profile in small bogs 1 5 2 ha in area is for the reconstruction of holocene fire history we use high resolution

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

astronomically controlled cycles in the lower tertiary of gubbio italy abstract a grouping of marl limestone beds in the tertiary of gubbio is interpreted in terms of sedimentary cycles two methods of recording are used subjective mapping of cycle boundaries in the field and power spectral analysis of bed thickness measurements both result in cycle thicknesses of between 30 and 70 cm the cycle record is compared with the known magnetic stratigraphy and this gives an absolute time estimate of 100 kyr for the cycle it therefore seems likely that the earth s eccentricity period is the ultimate cause of the cycle

a 3400 year paleolimnological record of prehispanic human environment interactions in the holmul region of the southern maya lowlands abstract the timing magnitude and drivers of late holocene environmental change in the holmul region of the southern maya lowlands are examined by combining paleoenvironmental and archeological data environmental proxy analyses on a 3350 cal yr lacustrine sediment record include pollen charcoal loss on ignition magnetic susceptibility and elemental geochemistry archeological evidence is derived from extensive settlement surveys conducted near the study site results indicate nearby settlement and agricultural activity taking place in an environment characterized by open forest from around 3350 to 950 cal yr bp the fire history shows a dramatic increase in burning during the classic period possibly reflecting changing agricultural strategies a distinct band of carbonate deposited from 1270 to 1040 cal yr bp suggests decreased hydrologic input associated with drier conditions abrupt changes in proxy data around 940 cal yr bp indicate a cessation of human disturbance and local abandonment of the area

a signal to noise index to quantify the potential for peak detection in sediment charcoal records article i nfo charcoal peaks in lake sediment records are commonly used to reconstruct fire histories spanning thousands of years but quantitative methods for evaluating the suitability of records for peak detection are largely lacking we present a signal to noise index sni that quantifies the separation of charcoal peaks signal from other variability in a record noise we validate the sni with simulated and empirical charcoal records and show that an sni n3 consistently identifies records appropriate for peak detection the sni thus offers a means to evaluate the suitability of sediment charcoal records for reconstructing local fires matlab and r functions for calculating sni are provided

palaeoenvironmental control on sponge microbialite reefs and contemporaneous deep shelf marl limestone deposition late oxfordian southern germany abstract the late oxfordian bimammatum zone deep shelf deposits of southern germany are characterised by abundant reefs that laterally pass into marl limestone alternations the bioconstructions are made from three main components sponges microbialites and allochthonous sediment a detailed morphological analysis of sponge microbialite reefs in the plettenberg section swabian alb southern germany is combined with investigation of calcareous nannofossil assemblages in laterally correspondent marl limestone alternations in order to trace the evolution of palaeoenvironmental conditions during reef development fluctuations of caco3 content in deep shelf deposits provides evidence of a succession of small scale lithological units generally formed by five to six marl limestone couplets within a small scale lithological unit a close link is observed between growth patterns of sponge microbialite reefs and the changes in the nannofossil assemblage composition phases of expansion of the build ups correspond to carbonate deposits characterised by a relative dominance of large oligotrophic nannoplankton species large watznaueria britannica watznaueria manivitiae and schizosphaerella spp marly intervals reveal a high relative abundance of small sized taxa mainly lotharingius hauffii small w britannica and subordinated biscutum dorsetensis and bioconstructions show a net reduction in size or a total demise this suggests that the same palaeoenvironmental parameters controlled at the same time marl versus limestone deposition reef growth phases and calcareous nannofossil assemblage composition successive reef growth phases recognized within a bioherm are correlated to the limestone hemi couplets each reef growth phase is composed of several stacked elementary sequences comprising the following succession i sponge ii microbialites and iii carbonate mud in turn the microbialitic crust is formed of three successive microbial layers 1 a fine crust of dense to clotted micrite 2 a centimetre scale to multicentimetric columnar layer of clotted to peloidal micrite 3 a centimetre scale stromatolitic crust the passage from an initial dense microbial layer with numerous microencrusters to a final stromatolitic crust is interpreted as resulting from an increase of the microbial growth rate mainly driven by changes in the accumulation rate deep shelf deposits resulted from changes in platform carbonate production and export basinwards controlled both by sea level and climate changes climate controlled the intensity of carbonate production in shallow platform environments and export towards the deep shelf as well as the trophic conditions of the deep shelf marine waters low trophic conditions favoured platform carbonate production and export basinwards and a large development of the sponge microbialite reefs in the deep shelf however a high carbonate accumulation rate in the deep shelf was also commonly responsible for the demise of sponge microbialite reefs during unfavourable and higher trophic conditions during marl deposition reduced development and frequent demise of the sponge microbialite reefs is observed

holocene fire regime changes from multiple site sedimentary charcoal analyses in the lourdes basin pyrenees france one lake and three peat bogs from the lourdes glacial basin france were used for macrocharcoal analyses and fire frequency reconstruction over the entire holocene 11700 years the chronology was based upon thirty three 14c ams dates comparison of the distribution of both charcoal accumulation rate char and fire return intervals showed that charcoal accumulation significantly differs between the lake and the peat bogs but that frequency calculation overcomes the disparity between these site types a composite frequency was built from the four individual records to assess regional versus local variability and fire regime controls by comparisons with regional fire activity holocene climatic oscillations and vegetation history the millennial variability can be depicted as follows relatively high frequency between 8000 and 5000 cal a bp up to 5 fires 500 yrs relatively low frequency between 5000 and 3000 cal a bp down to 0 fires 500 yrs and an increase between 3000 and 500 cal a bp up to 4 fires 500 yrs from 8000 to 5000 cal a bp fire frequency displays strong synchrony between sites and appears to be mostly driven by increased summer temperature characterizing the holocene thermal maximum htm on the contrary during the last 3000 years fire frequency was heterogeneous between sites and most probably human driven however higher frequency at the millennial scale during the mid holocene strongly suggests that the perception of human driven fire regime depends on the strength of natural controls

environmental cycles in the late jurassic northwest european epeiric basin interaction with atmospheric and hydrospheric circulations abstract despite the large size and the heterogeneity of the northwest european late jurassic kimmeridgian lower tithonian epeiric basin the sedimentary environment was rather uniform in general deposition of mudstones and the microlaminated organic rich sediments took place under low oxic to anoxic conditions detailed environmental analysis clearly points to a seasonal alternation of aerobic with anaerobic conditions in substrate and bottom water resulting in one year life cycles in the benthic environment the widespread uniformity of facies and the seasonal alternation in the oxygen budget of the benthic environments are best explained by a summer to winter change in the atmospheric circulation of the northern hemisphere this change strongly influenced the oceanographic situation in the northwestern european epeiric basin superposed on this one year cyclicity three more hierarchical levels of cycles are stratigraphically recorded they reflect a complex history of orbital forced and non orbital forced climatic changes and or eustatic sea level fluctuations in the late jurassic

centers of organic carbon burial and oxidation at the land ocean interface abstract continental margin systems collectively receive and store vast amounts of organic carbon oc derived from primary productivity both on land and in the ocean thereby playing a central role in the global carbon cycle the land ocean interface is however extremely heterogeneous in terms of terrigenous input marine primary productivity sediment transport processes and depositional conditions e g such as bottom water oxygen level continental margins are also highly dynamic with processes occurring over a broad range of spatial and temporal scales the rates of oc burial and oxidation are consequently variable over both space and time hindering our ability to derive a global picture of oc cycling at the land ocean interface here we review the processes controlling the fate of organic matter in continental margin sediments with a special emphasis on hot spots and hot moments of oc burial and oxidation we present a compilation of compositional data from a set of illustrative settings including fjords small mountainous river margins large deltaic systems and upwelling areas bulk oc stable isotope and radiocarbon compositions reveal the diversity and complexity characteristic of oc buried in marginal seas this primarily relates to differences in marine and terrestrial inputs the composition of the terrestrial component e g vascular plant oc soil and petrogenic oc inputs and processes modulating the fate of oc within the marine environment e g priming this widely contrasting behavior of oc among these systems illustrates that the reactivity of oc is a product of its chemical composition and regional conditions interpreted in the context of bulk compositional data as well as that obtained on specific molecular markers e g lignin derived phenols the possibility exists to tease apart complex mixtures of terrestrial and marine inputs and to shed light on the role of the myriad of depositional and post depositional processes finally we discuss a set of hot topics that warrant further investigation such as the role of photochemistry fungi halogenation and reactive iron in dictating the fate of oc in the changing coastal ocean

charcoal recognition taphonomy and uses in palaeoenvironmental analysis abstract charcoal predominantly the product of wildfires is abundant in many sedimentary rocks deposited in a wide range of environments from terrestrial to marine it also occurs in some volcanic rocks this paper outlines aspects of charcoal formation both natural and experimental and briefly considers the taphonomic processes leading to a final assemblage this is done using examples from recent fires and through experimentation the ways in which charcoal assemblages are recognized in the field and extraction in the laboratory are also considered methods of charcoal identification are presented the range of charcoalified plant organs that can be found is discussed and a wide range of study methods outlined including light microscopy dark field light microscopy reflectance microscopy scanning electron microscopy and synchrotron radiation x ray tomographic microscopy emphasis in this paper is on the study of macro and meso charcoal above180 m finally there is a consideration of the broad use of charcoal from plant evolution studies fire history studies vegetation studies anatomical studies climate and atmospheric studies and the wider importance of charcoal for the earth and biological sciences charcoal is information rich but yet is an under utilized resource

relationships between charcoal particles in air and sediments in west central siberia production and size of charred particles determine transport and deposition in lakes lack of such data is a principal obstacle to interpretation of past fire from charcoal profiles our two part a

cyclic sedimentation in the shallow marine upper permian kennedy group carnarvon basin western australia abstract the upper permian kennedy group of the carnarvon basin western australia was deposited while the merlinleigh sub basin was undergoing thermal subsidence and the global climate was warming from the carboniferous permian glaciation to the mesozoic greenhouse conditions the kennedy group comprises siliciclastic sedimentary rocks dominated by sandstones in the lower part with coarsening up cycles from mudstones to very coarse sandstones and granule conglomerates in the upper part cycles were observed and logged in the field and although many types of cycles were found three main motifs describe most of the cycles cycle motifs are defined based on the dominance of the various facies mooka motif cycles are dominated by fine grained and bioturbated facies interpreted as deposition during relative sea level highstand with only thin laminated or cross bedded sandstones interpreted as deposited during relative sea level fall binthalya motif cycles are dominated by laminated and cross bedded sandstones and coolkilya motif cycles consist of alternating laminated and bioturbated beds a hierarchy of cycles was observed in the field and this correlated well with spectral analysis of logged parameters spectral analysis of section log data and data sets corrected for the effects of compaction and sedimentation rates detected regular cyclicity geochronology of the kennedy group is not well enough constrained to allow the cycle periods in time to be calculated but ratios of the different scale cycle thicknesses correlate well with ratios of the milankovitch orbital cycles that have been calculated for the permian the presence of regular cyclicity and even bed thicknesses across large distances are not consistent with tectonic or autocyclic models of cycle formation the cycles are more likely to have been caused by fluctuating eustatic sea levels perhaps enhanced by changing amounts or seasonality of precipitation both sea levels and climatic fluctuations would ultimately be controlled by the milankovitch orbital cycles

burial of terrestrial organic matter in marine sediments a re assessment 1 calculations based on recent observations indicate that approximately one third of the organic matter presently being buried in marine sediments may be of terrestrial origin with the majority of this terrestrial organic matter tom burial occurring in muddy deltaic sediments these calculations further suggest that the remineralization of terrestrial organic matter in the oceans is also much less efficient than that of marine organic matter these two underappreciated observations have important implications in terms of our understanding of the controls on the global carbon cycle from a paleoceanographic perspective the results presented here also suggest that changes in tom burial on glacial interglacial timescales have the potential to impact the global carbon cycle i e atmospheric co2 levels

a comparison of charcoal measurements for reconstruction of mediterranean paleo fire frequency in the mountains of corsica fire history reconstructions inferred from sedimentary charcoal records are based on measuring sieved charcoal fragment area estimating fragment volume or counting fragments similar fire histories are reconstructed from these three approaches for boreal lake sediment cores using locally defined thresholds here we test the same approach for a montane mediterranean lake in which taphonomical processes might differ from boreal lakes through fragmentation of charcoal particles the mediterranean charcoal series are characterized by highly variable charcoal accumulation rates results there indicate that the three proxies do not provide comparable fire histories the differences are attributable to charcoal fragmentation this could be linked to fire type crown or surface fires or taphonomical processes including charcoal transportation in the catchment area or in the sediment the lack of correlation between the concentration of charcoal and of mineral matter suggests that fragmentation is not linked to erosion reconstructions based on charcoal area are more robust and stable than those based on fragment counts area based reconstructions should therefore be used instead of the particle counting method when fragmentation may influence the fragment abundance

on the periodicity and magnitude of late carboniferous glacio eustatie sea level changes data from sedimentary cycles in basins from northern england the appalachians and midcontinent us afford an insight into periodicities and controls of late carboniferous glacio eustatic sea level changes lithofacies with identifiable palaeobathymetry are used to assess the magnitude of sea level change in the pennine basin of northern england the method yields a minimum value of 42m walsh power spectral analysis is employed to resolve periodicities of about 120ka within the pennine basin of northern england 212 140 and 93 ka within the midcontinent us succession and 109 84 67 63 ka within the appalachian basin within the pennine basin periodicities and magnitudes are found to be independent of their position within the basin thus any tectonism can be assumed to have had a negligible effect on the transgressions a simplified modelled climatic curve is derived from milankovitch parameters and pleistocene 18 o data this is used in a basin fill model that simulates the thermally subsiding pennine basin the resulting distribution of marine deposits is seen to depend upon both the steady regional subsidence and the magnitude and extent of glacio eustatic transgressions

signal analysis of cyclicity in maastrichtian pelagic chalks from the danish north sea abstract low field bulk magnetic susceptibility has been determined on maastrichtian chalk samples from a drill core from the dan field in the danish north sea fast fourier transformations fft have been used to detect possible cycles in the magnetic susceptibility data power spectra from the complete section and from sub sections of the magnetic susceptibility reveal two cyclicities of ca 0 4 cycles m and ca 1 7 cycles m which are present on a 90 confidence level signal analysis of natural gamma ray wire line log data supports these findings sedimentation rate estimates place the cycles in the milankovitch frequency band artificial time series are used to study the applicability of the fft to identifying cyclicity in chalks expected geological distortions e g hiati and sedimentation rate variations are introduced into the time series to investigate the response of the frequency spectra different methods of handling missing data intervals are also examined

a continuous record of fire covering the last 10 500 calendar years from southern sweden the role of climate and human activities a high resolution continuous 10 500 cal yrs long macroscopic charcoal record from a peat and lake sediment deposit at storasjo in the hemiboreal vegetation zone of southern sweden is presented

geochemical anomalies at the cenomanian turonian boundary northwest new mexico a high resolution section of 64 carbonates and calcareous shales from northwest new mexico spanning the cenomanian turonian c t boundary is examined for selected elemental concentrations as well as carbon isotopic and molecular distributions spatial and temporal sampling resolutions for the entire sample set are 1 spl 19 cm and 1 spl 33 ka respectively in proximity to the c t boundary respective spatial and temporal resolutions increase to 1 spl 10 cm and 1 spl 17 ka results show the occurrence of several geochemical anomalies all with coincident maxima at about 0 5 m below the c t boundary stable carbon isotope ratios of the kerogen and the aliphatic and aromatic hydrocarbon fractions increase by approximately 4 within 20 m of the boundary this entire c t boundary event isotope anomaly occured over approximately 2 5 ma a 5 fold increase in the concentrations of u and th occurs synchronous with the isotope excursion although this u th spike occurs over a period of only 0 2 0 3 ma elevated u and th concentrations at this spike co occur with a the highest 20s 20s 20r sterane epimer ratios b c27 c27 30 sterane homolog ratios and c the lowest n alkane yields in kerogen pyrolyzates these observations suggest an effect of radiogenic heat production on the organic matter in the section the origin of the carbon isotope excursion is attributed as in previous studies to atmospheric co2 drawdown in latest cenomanian time caused by rapid burial of organic matter due to a global marine transgression the u and th spike is probably secondary perhaps resulting from adsorption of these elements onto clays concentrated at the c t boundary although the occurrence of coeval maxima for these isotopic and elemental anomalies suggests a common cause extrapolation of the co2 drawdown model to explain the u th anomaly is unwarranted at this time ongoing mineralogical analysis of clays and carbonates close to the c t boundary in the red wash section may ultimately explain the occurrence of this u and th spike

fluvial processes and cyclicity in terminal fan deposits an example from the late devonian of southwest ireland abstract the gun point formation is a sandstone dominated sequence approximately 1 5 2 5 km thick which forms part of a major 6 km late devonian alluvial basin fill succession in southwest ireland it is interpreted as the deposits of a southerly flowing terminal fan system which operated under a semi arid climate the proximal zone was characterized by low sinuosity gravelly feeder channels which passed downstream into a medial zone dominated by a sandy braidplain further south in the distal zone phases of high energy flood activity were centred on transient low sinuosity ephemeral channels and were separated by more quiescent periods of shallow sheetflooding subaerial exposure and non deposition sedimentary parameters such as set thickness coset thickness channel sand body density and maximum sand body thickness all exhibit regular cyclic fluctuations with a periodicity of 160 180 m the cycles are interpreted as evidence of regular discharge variations which may have been a response to the 412 ka orbital eccentricity cycle a second periodicity of approximately 700 m has also been detected and is thought to reflect long term variations in basin subsidence

characterisation of fe bearing particles and colloids in the lena river basin ne russia abstract rivers are significant contributors of fe to the ocean however the characteristics of chemically reactive fe remain poorly constrained especially in large arctic rivers which drain landscapes highly susceptible to climate change and carbon cycle alteration the aim of this study was a detailed characterisation size mineralogy and speciation of riverine fe bearing particles 0 22 m and colloids 1 kda 0 22 m and their association with organic carbon oc in the lena river and tributaries which drain a catchment almost entirely underlain by permafrost samples from the main channel and tributaries representing watersheds that span a wide range in topography and lithology were taken after the spring flood in june 2013 and summer baseflow in july 2012 fe bearing particles were identified using transmission electron microscopy as large 200 nm 1 m aggregates of smaller 20 30 nm spherical colloids of chemically reactive ferrihydrite in contrast there were also large 500 nm 1 m aggregates of clay illite particles and smaller 100 200 nm iron oxide particles dominantly hematite that contain poorly reactive fe tem imaging and scanning transmission x ray microscopy stxm indicated that the ferrihydrite is present as discrete particles within networks of amorphous particulate organic carbon poc and attached to the surface of primary produced organic matter and clay particles together these larger particles act as the main carriers of nanoscale ferrihydrite in the lena river basin the chemically reactive ferrihydrite accounts for on average 70 15 of the total suspended fe in the lena river and tributaries these observations place important constraints on fe and oc cycling in the lena river catchment area and fe bearing particle transport to the arctic ocean

late cenozoic fire enhancement response to aridification in mid latitude asia evidence from microcharcoal records fire provides an important indicator of paleoclimatic change however little information relating to late cenozoic fire history has been gathered in mid latitude asia including inner asia and east asia a key region for understanding the development of the arid monsoon climate system as well as the driving forces behind it here we first report the records of microcharcoal concentrations mc covering the holocene 10 0 ica and late pleistocene 0 8 0 ma which we use to analyze the fire activity patterns at an orbital time scale then we compile the late cenozoic mc record to investigate the long term fire history by analyzing four cores from the yangtze river delta yrd area east asia representing 8 0 ma and three sites in inner asia representing 18 2 ma the results show that the i mc remained higher during the relatively dry late holocene glacial stages than that during the humid middle holocene interglacial stages at individual sites ii mc increased with time in both inner asia and east asia after 18 and 8 ma respectively and iii mc always remained higher in the dry inner asia than in the contemporaneous wet east asia all these characteristics imply that late cenozoic fire occurrence in mid latitude asia experienced a gradual increasing trend along with the global temperature ice volume change and indicates a continuous aridification trend across mid latitude asia the global cooling rather than the tibetan plateau uplift might have played a key role in this observed trend c 2016 elsevier ltd all rights reserved

determinants of fire activity during the last 3500 yr at a wildland urban interface alberta canada abstract long term records of wildfires and their controlling factors are important sources of information for informing land management practices here dendrochronology and lake sediment analyses are used to develop a 3500 yr fire and vegetation history for a montane forest in jasper national park alberta canada the tree ring record ad 1771 2012 indicates that this region historically experienced a mixed severity fire regime and that effective fire suppression excluded widespread fire events from the study area during the 20th century a sediment core collected from little trefoil lake located near the jasper townsite is analyzed for subfossil pollen and macroscopic charcoal 150 m when comparing the tree ring record to the 3500 yr record of sediment derived fire events only high severity fires are represented in the charcoal record comparisons between the charcoal record and historical climate and pollen data indicate that climate and vegetation composition have been important controls on the fire regime for most of the last 3500 yr although fire frequency is presently within the historical range of variability the fire return interval of the last 150 yr is longer than expected given modern climate and vegetation conditions indicating that humans have become the main control on fire activity around little trefoil lake

chemical and physical characteristics of iron oxides in riverine and glacial meltwater sediments abstract the speciation and grain size distribution of iron have been examined in several riverine and glacial sediments in order to evaluate controls on the concentrations and modes of occurrence of iron oxides in weathering derived particulates three operationally defined fractions have been recognised relating to the reactivity of iron towards dissolved sulphide 1 highly reactive iron fe hr consisting of ferric oxides 2 poorly reactive iron fe pr consisting of magnetite and some sheet silicate iron and 3 unreactive residual silicate iron fe u the finer fractions of each riverine and glacial suite are enriched in fe hr and usually also have higher fe hr fet ratios however coarser fractions may also have elevated fe hr contents and relationships of fe hr to both surface area and al indicate that iron oxides dominantly occur in association with the surfaces of aluminosilicate minerals which are common in finer grained fractions but may also be relatively enriched in coarser fractions a similar range of fe hr surface loadings is evident in the riverine and glacial meltwater suites from 0 6 to 1 8 mg fe m 2 for the riverine sediments and 0 5 to 1 5 mg fe m 2 for the glacial meltwater sediments despite wide variations in catchment bedrock lithology and climatic conditions significantly lower iron oxide loadings 0 1 mg fe m 2 were found in subglacial sediments most fe hr is closely associated with organic c although the latter occurs as blebs or smears rather than continuous coatings e g ransom et al 1997 ransom b bennett r h baerwald r shea k 1997 tem study of in situ organic matter on continental margins occurrence and the monolayer hypothesis mar geol 138 1 9 electron microscope observations show that iron oxides may occur as nanoparticulate 10 20 nm spheres at the edges of sheet aluminosilicate minerals as crystalline oxides infilling surface pits in coarser grained aluminosilicate minerals and occasionally as discrete crystalline oxides the similar occurrences of iron oxides in both riverine and glacial environments indicates that the delivery of reactive iron oxides to the oceans during glacial interglacial cycles will be affected by the masses and grain size characteristics of sediments delivered by glacial and riverine fluxes rather than by differences in iron mineralogy these delivery rates will be modified by behaviour of the oxide nanoparticles during transport from the continents

evaluating the extent to which wildfire history can be interpreted from inertinite distribution in coal pillars an example from the late permian kuznetsk basin russia abstract inertinite charcoal distributions in two randomly sampled in situ coal pillars seams 78 and 88 from the late permian kuznetsk basin siberia were analysed using petrographic techniques to determine palaeowildfire histories fire occurrence type and return interval in situ coal pillars are judged to be essential for this type of research as they retain information on the original inertinite distribution and maceral clast size ranges which can never be obtained from the crushed coals typically used for petrographic analysis the seams represent an ombrotrophic mire seam 78 and mire with mire lake seam 88 depositional settings but both environments show the same pattern of fire history charcoal is present in all lithotype units in both pillars both pillars contain episodic charcoal horizons representing local surface fires within the peat forming environment interspersed with frequent regional background fire events as shown by small scattered inertinite this paper presents an approach to calculating fire return intervals fri in these coal pillars by removing the thickness of less compactable charcoal horizons before calculating original duration of peat formation this is achieved by using a range of peat accumulation rates and peat to coal compaction ratios resultant mean fri ranges from 7 years extremes 0 5 to 143 years for a lithotype unit containing 4 horizons to 70 years extremes 5 to 1550 years for a lithotype unit with 2 horizons the mid range values both suggest shorter fire return intervals than seen in modern peat forming environments

peak analysis of sedimentary charcoal records some underlying assumptions and potential pitfalls abstract fire histories are derived from sedimentary charcoal sequences using a suite of statistical techniques that has become increasingly complex here we outline the various assumptions that underpin these methods and highlight potential sources of error that must be considered we hope to spur debate on the circumstances in which such methods are appropriate and highlight areas needing further research

stratigraphic charcoal analysis on petrographic thin sections application to fire history in northwestern minnesota results of stratigraphic charcoal analysis from thin sections of varved lake sediments have been compared with fire scars on red pine trees in northwestern minnesota to determine if charcoal data accurately reflect fire regimes pollen and opaque spherule analyses were completed from a short core to confirm that laminations were annual over the last 350 yr a good correspondence was found between fossil charcoal and fire scar data individual fires could be identified as specific peaks in the charcoal curves and times of reduced fire frequency were reflected in the charcoal data charcoal was absent during the fire suppression era from 1920 a d to the present distinct charcoal maxima from 1864 to 1920 occurred at times of fire within the lake catchment fire was less frequent during the 19th century and charcoal was substantially less abundant fire was frequent from 1760 to 1815 and charcoal was abundant continuously fire scars and fossil charcoal indicate that fires did not occur during 1730 1750 and 1670 1700 several fires occurred from 1640 to 1670 and 1700 to 1730 charcoal counted from pollen preparations in the area generally do not show this changing fire regime simulated sampling of the thin section data in a fashion comparable to pollen slide methods suggests that sampling alone is not sufficient to account for differences between the two methods integrating annual charcoal values in this fashion still produced much higher resolution than the pollen slide method and the postfire suppression decline of charcoal characteristic of my method but not of pollen slides is still evident consideration of the differences in size of fragments counted by the two methods is necessary to explain charcoal representation in lake sediments

forest vegetation change and disturbance interactions over the past 7500 years at sasquatch lake columbia mountains western canada abstract fire is the most important abiotic disturbance in the interior cedar hemlock ich and engelmann spruce subalpine fir essf forest zone of southeastern british columbia canada other disturbances are also important such as defoliator and boring insect outbreaks windthrow diseases and rapid mass movements few studies have examined the interaction between multiple types of disturbances in these forests over long timescales here we present high resolution analyses of biomass burning erosion and vegetation assemblage changes at sasquatch lake nel02 a valley lake in the columbia mountains the 531 5 cm sediment core was radiocarbon dated and provided a 7500 year stratigraphy that was used for pollen macroscopic charcoal 150 m and sedimentologic analyses pollen and charcoal data provided evidence of forest composition changes and fire activity magnetic susceptibility loss on ignition and particle size distribution analyses characterised changes in erosion into the basin the results show that coniferous forests with a high abundance of pinus pollen had established in the catchment by the beginning of the record and were subject to intermittent burning and high energy erosive events tsuga heterophylla expanded by 4400 cal bp and the modern interior cedar hemlock forests expanded throughout the lower elevations due to increased regional continentality since 4500 cal bp high energy erosional inputs to the lake were less frequent from 3500 to 750 cal bp and rapid mass movements may have increased in frequency during the little ice age dendrochronological evidence in these stands suggests a mixed severity fire regime during past 300 years which has not been fully examined for charcoal based fire event reconstruction here we use identified peaks as an indicator of increased biomass burning and charcoal movement in the catchment in relation to peaks in allochthonous clastic material to understand the potential relationships between biomass burning and erosion events at multiple temporal scales in the catchment this suggests that post fire conditions up to several decades were subject to increased erosion to the lake and erosion events were more common during the early holocene establishment of dense essf and ich forests decreased siliciclastic input to the lake throughout the mid holocene until a recent rockslide the high resolution sampling of this lake sediment record provides long term evidence of variability in the relationships between vegetation cover fire and erosion at a catchment scale

effects of syn pandemic fire reduction and reforestation in the tropical americas on atmospheric co2 during european conquest abstract a new reconstruction of late holocene biomass burning in the tropical americas is consistent with the expansion of fire use by mesoamerican and amazonian agriculturalists and a subsequent period of fire reduction beginning 500 years bp the marked reduction of biomass burning after 500 years bp a unique feature of the fire history of the tropical americas relative to other regions of the globe is synchronous with the collapse of the american indigenous population during pandemics accompanying european conquest we predict that fire reduction contemporaneous with pandemics in the tropical americas was associated with massive forest regeneration on 5 105 km2 of land and sequestration of 5 10 gt c into the terrestrial biosphere which contributed to the 2 global reduction in atmospheric co2 levels and the 0 1 increase in 13c of atmospheric co2 from 1500 to 1750 a d this study 1 builds upon prior fire history reconstructions by synthesizing a substantially greater number of stratigraphic charcoal accumulation records and soil charcoal 14c dates to resolve features of the late holocene biomass burning record in the tropical americas and 2 corroborates the hypothesis advanced by ruddiman ruddiman w f 2003 the anthropogenic era began thousands of years ago climatic change 61 261 293 ruddiman w f 2005 plows plagues and petroleum princeton university press princeton new jersey that biospheric carbon sequestration via reforestation of cropland abandoned during pandemics contributed to changes in atmospheric co2 concentration during the past millennium

the low temperature geochemical cycle of iron from continental fluxes to marine sediment deposition suspended sediments from 34 major rivers geographically wide spread and 36 glacial meltwater streams have been examined for their variations in different operationally defined iron fractions fehr iron oxides soluble in dithionite fepr iron soluble in boiling hcl but not in dithionite and feu total iron less that soluble in boiling hcl river particulates show a close association between fehr and total iron fet reflecting the effects of chemical weathering which derive oxide iron from and retain it in close association with total iron consistent with this continental scale average fehr fet ratios vary with runoff ratios average river runoff per unit area average precipitation per unit area by contrast the diminished effects of chemical weathering produce no recognizable association of fehr with fet in glacial particulates and instead both fepr and feu are closely correlated with fet reflecting essentially pristine mineralogy a comparison of the globally averaged compositions of riverine particulates and marine sediments reveals that the latter are depleted in fehr fepr and fet but enriched in feu the river and glacial particulate data are combined with estimates of authigenic hydrothermal atmospheric and coastal erosive iron fluxes from the literature to produce a global budget for fehr f e pr f e u and fet this budget suggests that the differences between riverine particulates and marine sediments can be explained by i preferentially removing fehr from the riverine particulate flux by deposition into inner shore reservoirs such as floodplains salt marshes and estuaries and ii mixing the resulting riverine particulates with fehr depleted glacial particulates preliminary measurements of inner shore sediments are consistent with i above phanerozoic and modern normal marine sediments have similar iron speciation characteristics which implies the existence of a long term steady state for the iron cycle this steady state could be maintained by a glacioeustatic feedback where fehr enriched riverine particulates are either more effectively trapped when sealevel is high small ice masses diminished glacial erosion or are mixed with greater masses of fehr depleted glacial particulates when sealevel is low large ice masses enhanced glacial erosion further important controls on the steady state for fehr operate through the formation of euxinic sediments and ironstones which also provide sealevel dependent sinks for fehr enriched sediment

assessing the spatial fidelity of sedimentary charcoal size fractions as fire history proxies with a high resolution sediment record and historical data abstract fire reconstructions provide context for modern rates of burning and inform predictions of fire regimes responses to climate and or ecological changes charcoal particles preserved in lake sediments are a widely employed fire proxy although many studies have calibrated the charcoal proxy the spatial scales of charcoal dispersal and source area remain disputed understanding the spatial fidelity of charcoal accumulation is increasingly important in light of recent efforts to aggregate multiple charcoal records to infer changes in regional continental and global scale fire regimes using a high resolution sediment record from swamp lake california we compare charcoal accumulation rate char variations of three size fractions of sedimentary charcoal 63 150 150 and 250 m to historical area burned data we find that macroscopic 250 and 150 m and mesoscopic 63 150 m charcoal source areas are within 25 35 and 150 km of swamp lake respectively we also use a dispersal model to confirm these findings our estimates of charcoal source area fall within the large range of estimates for forest fires in the literature further our methodology shows potential for constraining source areas of charcoal in sedimentary records which is requisite for the reliable inference of the spatial extent of fire in paleorecords

pollen representation source area and basin size toward a unified theory of pollen analysis abstract the concepts of pollen source area and of production and dispersal biases in pollen representation are quantified by means of a simple theoretical model source areas and relative pollen representation are shown to depend on basin size according to functions that describe the amount of pollen remaining airborne at increasing distances from single pollen sources the form of these functions is determined by physical processes standard formulas for elevated sources do not apply but the integrated form of sutton s equation for particle dispersal from a ground level source gives useful approximations applicable to pollen transport over a forest canopy simulations using this equation yielded source areas that increased realistically with basin size showed substantial differences between source areas for pollen grains with different deposition velocities and predicted that lighter pollen grains should become better represented with increasing basin size all of these predictions are qualitatively consistent with present knowledge of the characteristics of pollen assemblages in different depositional environments the model further allows parameters that can be estimated by statistical calibration methods to be predicted from underlying physical quantities this extension suggests procedures for testing the theory with quantitative data on surface pollen and forest composition preliminary results showed reasonable agreement between estimated and predicted values of dispersal indices for the most abundant taxa in pollen spectra from the northern midwestern united states

climate vegetation and human influences on late holocene fire regimes in the sanjiang plain northeastern china abstract understanding the fire evolution history and its driving mechanisms can provide useful insights into the fire regimes and their potential impacts in the future here we present a well dated peat profile with high resolution charcoal and pollen records to reconstruct the fire and vegetation history in the sanjiang plain over the last 6000 yr the regional and local fire frequencies were reconstructed with the microscopic 125 m charcoal fractions respectively during the interval 6 0 4 5 ka bp both the regional and local fires exhibited much low frequencies responding to the strong summer monsoon thereafter the fire frequencies increased significantly with the decline of the summer monsoon and the highest frequencies corresponded well with the weak monsoon intervals around 4 0 2 7 and 0 8 ka bp as for the local fires in addition to the climate changes the local vegetation conditions have also served an important role in driving their occurrences during the last 300 yr the gradually increased fire frequencies were attributed to the intensified human activities instead of the climate and vegetation influences

pronounced variations in fagus grandifolia abundances in the great lakes region during the holocene mesic tree species such as fagus grandifolia and tsuga canadensis experienced multiple abundance declines in eastern north america during the last 8000 years but the causes remain unclear this paper presents a new sub centennial record of holocene vegetation fire and sedimentological changes at spicer lake in to test hypotheses about the role of fire and hydrological variations on shifts in vegetation composition four pollen zones are reported abies picea forests 15 11 8 ka bp pinus dominated mixed forest 11 8 10 6 ka bp transitional mixed forest 10 6 6 8 ka bp and deciduous forest characterized by the expansion and high variability of f grandifolia after 6 8 ka bp macroscopic charcoal indicates five to seven fires between 6 1 and 4 4 ka bp and no fires between 4 4 and 2 ka bp despite several large declines in f grandifolia and more fires after 1 8 ka bp likely linked to declining f grandifolia abundances after 1 1 ka bp six peaks in mineralogenic sediments are suggestive of hydro

eocene magnetic stratigraphy at gubbio italy and its implications for paleogene geochronology the sequence of polarity zones established by alvarez and others for the cretaceous and paleocene in the scaglia formation in the bottaccione gorge at gubbio has now been extended through the uppermost paleocene into the upper eocene globigerinatheka semiinvoluta zone anomaly 18 the relationships between the standard paleogene foraminiferal zones and the sea floor anomalies are defined with the exception of the mid eocene zones of morozovella lehneri orbulinoides beckmanni and the base of the truncorota loides rohri zone which are obscured by inadequate preservation and a fault gap the base of the eocene lies above anomaly 25 the lower to middle eocene contact base lutetian lies in the upper part of anomaly 22 the base of the bartonian lies below the base of anomaly 18 and the base of the priabonian upper eocene lies within anomaly 18 radiometric ages appear to diverge systematically from a geochronology based on steady sea floor spreading rates suggesting that spreading may have been as much as a factor of 3 slower in the paleocene and the late eocene than in the early and middle eocene

whither cyclostratigraphy testing the gamma method on upper pleistocene deep sea sediments north atlantic deep sea drilling project site 609 1 abstract gamma analysis a procedure for tuning cyclic sediments in which gamma is defined as 1 sedimentation rate was applied to the upper pleistocene gray scale record of deep sea drilling project site 609 from the north atlantic the spectrum of the gamma tuned time series produces eccentricity obliquity and precession index signals when the primary periodicity is tuned to the precessional beat frequency however the timescales are significantly too long suggesting that some of the primary cycles used in the gamma tuning procedure have higher frequency than the precessional beat by filtering the specmap calibrated time series at i 0 12 kyr the spurious cy cles are removed from the tuning procedure in this case the resulting gamma corrected spectra look much more like that of the specmap tuned time series however the time series remains slightly too long forward modeling is consistent with the results from modeling the core that is the gamma method is quite robust at revealing orbital periodicity in an orbitally controlled re cord for which sedimentation rates are facies dependent however the method does not produce an accurate time series criteria for complete rejection of gamma results are clarified as either 1 least squares results include negative gamma values or 2 the resulting spectrum does not show an or bital signature variation on sedimentation rates greater than 5 result in incorrect time series however variations on sedimentation rates as high as 15 generally reproduce strong orbital spectra and occasionally the method can also generate an orbital spectrum with up to 25 noise the method is not as robust in predicting gamma values or sedimentation rates although it generally distinguishes facies with relatively high sedimentation rates from facies with relatively low sedimentation rates the values predicted may be incorrect by a factor of2 thus while gamma tuning of the time series is an improvement over observed thicknesses the resulting timescale is not correct the implications of these results for cyclostratigraphy are significant the generation of an orbital spectrum from a time series that is demonstrably incorrect casts doubt on cyclicity as a dating tool

the reconstruction of boreal forest fire history from lake sediments a comparison of charcoal pollen sedimentological and geochemical indices abstract fossil charcoal fossil pollen sedimentological and geochemical analyses of lake sediments have been used previously to reconstruct a history of local fires and resulting vegetation change the rationale behind these approaches is described and the usefulness of each technique for reconstructing fire history in the boreal forest is assessed empirically historical and dendrochronological records provide regional and local fire histories for a site in wood buffalo national park alberta canada the local and regional history of fires is compared with the microscopic charcoal content macroscopic charcoal content elemental carbon content fossil pollen content sedimentology and geochemistry of annually laminated sediments from a small lake there is no significant correlation between the abundance of microscopic charcoal macroscopic charcoal and total elemental carbon content of the sediments automated measures of microscopic charcoal abundance made with an image analysis system are correlated significantly with optical counts of microscopic charcoal none of the charcoal measures provide unequivocal records of local fire activity and the abundance of microscopic charcoal appears to be influenced by variations in regional fire activity however the highest depositional rate of macrofossil charcoal occurred during the time of a fire that burned within the drainage basin variations in sedimentological measures and geochemistry do not correlate with local fire activity fossil pollen percentages and accumulation rates display a pattern of variation that is consistent with observed vegetation responses to fire in the boreal forest what is likely apparent in the pollen record are the results of a series of burns of sufficient extent and intensity to kill most of the above ground biomass of the vegetation in an area at least as great as the drainage basin the inability of evidence from lake sediments to provide detailed histories of past fire activity is not surprising given the wide range of variation in the spatial extent proximity intensity and impact of individual fires

small scale moisture availability increase during the 8 2 ka climatic event inferred from biotic proxy records in the south carpathians se romania in this paper we present high resolution early holocene pollen plant macrofossil charcoal diatom biogenic silica and loss on ignition records from a mountain lake in the south carpathians in order to reveal ecosystem response to the 8 2 ka climatic oscillation we found significant changes both in terrestrial vegetation and lake diatom assemblages in the northern slope of the retezat mts between c 8300 and 8000 cal yr bp rapid changes in relative frequencies and pollen accumulation rates of the major deciduous pollen types associated with peaks in microcharcoal accumulation rates suggested that vegetation disturbance mainly took place in the mixed deciduous forest zone where woodland fires partially destroyed the populations of fraxinus excelsior quercus and corylus avellana and facilitated the establishment of carpinus betulus in the forest openings the diatom record furthermore showed the spread of a planktonic diatom species aulacoseira valida at 8150 cal yr bp coincidently with a shor

recognition of cyclicity in the petrophysical properties of a maastrichtian pelagic chalk oil field reservoir from the danish north sea subdivision of the maastrichtian chalk from the danish north sea has proven difficult because of its homogenous composition which is caused by a fairly stable depositional environment nevertheless the chalk petrophysical properties show cyclic behavior that potentially can be used for subdivision petrophysical properties of a 23 m long succession of maastrichtian chalk from the dan field were examined for cyclicity by spectral analysis magnetic susceptibility values measured on plug samples together with the neutron porosity and natural gamma radiation well log data were analyzed both as complete data sets and in subsets to survey the general existence of cycles in the chalk all three properties contain consistent cycles at approximately 2 m wavelength as well as additional frequencies where the relative dominance of the different frequencies differs cross spectral analyses of subsets of the petrophysical parameters provide substantial evidence for the coexistence of the approximately 2 m cycles in the maastrichtian chalk furthermore the magnetic susceptibility carries spectral evidence for a higher frequency because most power spectra of the subsets from the magnetic susceptibility have a spectral peak in the 1 8 2 0 cycles m interval i e approximately 0 5 m cycle the cycles can be interpreted as resulting from the eccentricity 94 5 k y and the precession 22 5 k y of the milankovitch cycles assuming a sedimentation rate of 2 6 cm k y the existence and the understanding of cycles at a submeter scale yield possibilities for an advantageously precise subdivision of chalk reservoirs and correlation between wells begin page 2004

particle size evidence for source areas of charcoal accumulation in late holocene sediments of eastern north american lakes abstract two methods of analyzing charcoal in sediment reveal changes in charcoal accumulation across temperate eastern north america during the last several hundred years in one method the analyst counts mostly small particles that reflect regional emissions in the other the analyst counts only larger particles derived mostly from such local sources as catchment fires we used these methods to compare charcoal accumulation at 14 lakes from the prairie forest border in minnesota to eastern maine the two methods gave concordant accumulation rates for sediments of pre 1850 age at each of 4 lakes analyzed by both methods this concordance is consistent with the interpretation that pre 1850 emissions were controlled by broad scale factors such as climatically controlled regional differences in fuels and moisture since 1900 large particles decreased greatly and small particles decreased slightly in minnesota and wisconsin by contrast in the northeast the large particle accumulation has remained at the low values measured in pre 1900 sediments at most sites while small particles increased everywhere east of central new york and pennsylvania the observed patterns suggest that 1 large particles primarily reflect local fires that were common in the midwest before fire suppression became effective 2 large particles were rare in the northeast especially before extensive land clearance 3 small particles reflect regional combustion that increased in the northeast after extensive use of fire for land clearance and wood burning for industrial purposes of the 19th century and 4 small particles remain abundant in the midwest long after effective fire suppression probably because these well dispersed small particles have a large source area that extends beyond the local wildfires that account for large particles before european settlement

a 25 000 year record of environmental change from welsby lagoon north stradbroke island in the australian subtropics there are few continuous australian palaeoclimate records that extend beyond the last glacial maximum lgm meaning that knowledge of regional climates before during and after this period is limited understanding late pleistocene climates of the subtropics is important because of the fundamental role the region plays in the large scale global transfer of energy from low latitudes palaeoclimate studies of subtropical regions can help define the extent of warming cooling during the large global climatic events which characterise the late pleistocene here we report the results from a multi proxy analysis of a sediment record from welsby lagoon on north stradbroke island in the eastern australian subtropics spanning the past ca 25 000 years stable c and n isotope analysis and high resolution contiguous records of macrocharcoal deposition and sediment organic content are interpreted in conjunction with a previously published pollen record sediment organic content displayed a very strong correlation with total organic carbon toc content as determined through elemental analysis and given the peaty nature of the sediment is interpreted as indicative of moisture balance the proxies reflect wet subtropical climates in the lead up to the lgm which led to an expansion of the wetland this was followed by a cool dry and windy lgm ca 22 3 19 7 000 years before present kyr bp which was punctuated by a brief wet phase ca 21 7 20 4 kyr bp a salient feature of the deglacial period is a rapid increase in toc around 15 kyr bp coincident with the antarctic cold reversal and bolling allerod warm phase increased fire frequency is evident in the holocene which is characterised by otherwise stable climate and vegetation this study supports the notion of variable climates during the lgm and finds an onset of deglacial warming in the australian subtropics that predates the holocene

informing sedimentary charcoal based fire reconstructions with a kinematic transport model recent changes in global fire activity and future projections can be attributed to a combination of direct human impacts and indirect effects of anthropogenic climate change to understand how and

the potential for rapid determination of charcoal from wetland sediments using infrared spectroscopy abstract wetland sediments archive information about past terrestrial ecosystem change including variations in fire occurrence and terrestrial carbon fluxes the charcoal content of sediments is important for understanding past fire regimes as well as the role this recalcitrant carbon plays in the global carbon cycle infrared ir spectroscopy provides a rapid non destructive and cost effective method for simultaneously analysing numerous organic and inorganic sediment properties the use of ir spectroscopy is well developed for determining concentrations of total organic carbon toc total nitrogen tn biogenic silica and carbonate in lacustrine sediments in soil science ir spectroscopy is also routinely used to determine charcoal content however the potential for analysing charcoal content from lacustrine sediments has yet to be investigated here we develop ir spectroscopy and partial least squares regressions plsr to predict the charcoal and toc content of an organic 130 000 year old sediment sequence from north stradbroke island minjerribah australia charcoal concentrations used for model development were derived using both traditional palaeoecological area measures cm2 g 1 and solid state 13c nuclear magnetic resonance 13c nmr of poly aryl structures the ir plsr models yielded significant correlations for the two charcoal methodologies area measurements r2 0 57 p

the detection and illustration of regular sedimentary cycles using walsh power spectra and filtering with examples from the lias of switzerland power spectral analysis provides an objective method for the detection of regular cyclicity in data recording some oscillating parameter or time series digitization of measured stratigraphic sections is a convenient method for generating long time series during the examination of pelagic sequences for cyclicity related to orbital variations or milankovitch cycles the application of walsh power spectral analysis to stratigraphic sections is outlined and band pass filtering using the walsh transform introduced it is shown that variations in sedimentation rate hiatuses bioturbation and variations in compaction have the effect of damping or destroying spectral peaks the wavelength ratios of spectral peaks are often used during studies of milankovitch cycles to decide which orbital cycles are involved however in some circumstances hiatuses are able to alter wavelength ratios averaged walsh power spectra were generated for three liassic limestone shale sequences from breggia gorge switzerland the 21 000 year 21 ka precession cycle was detected in all three cases the 100 ka eccentricity cycle in two cases and the 41 ka obliquity cycle in one filtering revealed that the supposed 21 ka sedimentary cycles are grouped into packets of four or five small and large amplitude cycles the packets reflect the 100 ka modulation of the 21 ka precession cycle local disruption of the packaging can be used to locate hiatuses in pelagic strata

high resolution organic record of bridge creek deposition northwest new mexico abstract organic and inorganic geochemical data are presented and interpreted for a high resolution sample set from the uppermost portion of a transgressive systems tract condensed interval spanning the cenomanian turonian boundary at red wash northwest new mexico source potential toc rock eval yields thermal maturity vr elemental ca th and u in whole rock and molecular n alkanes steranes terpanes data are presented for a 64 sample 12 4 m composite section of limestones marlstones and shales of the bridge creek member of the greenhorn formation vertical sampling resolutions of 1 spl 19 cm spatial and 1 spl 33 ka temporal are used to monitor the progress of the transgression from the uppermost cenomanian up to the beginning of the highstand systems tract the section is thermally immature and maturity fluctuations are absent indicating that organic parameters are a function of organic matter production and preservation including diagenesis the rhythmic lithologic fluctuation within the bridge creek is not reflected in the source potential elemental or molecular data which show either no obvious pattern e g carbonate content toc or a unidirectional trend toward development of anoxia upsection e g hydrogen index sterane distributions homohopane index the distribution of the triaromatic steroid hydrocarbons c 20 21 26 28 according to side chain length also varies significantly despite the absence of maturity differences all of the unidirectional trends in the data are interpreted as related to either productivity differences e g sterane hopane ratios and changes in the relative concentration of r c 28 and r c 30 desmethylsteranes or the development of anoxia in the lower water column e g decreases in the diasterane regular sterane ratio increases in the homohopane index westward movement of the paleoshoreline during bridge creek time is also monitored by upsection decreasing th u ratios at red wash

high rates of organic carbon burial in fjord sediments globally fjords have been hypothesized to be hotspots of organic carbon burial a global compilation of organic carbon data and sedimentation rates shows that fjords sequester twice as much carbon as other ocean regions

a model of pollen source area for an entire lake surface a model of pollen deposition on the surface of an entire basin is developed to estimate pollen source area and results are compared with those for a point at the center of a basin i c prentice 1985 quaternary research 23 76 86 1988 vegetation history pp 17 42 kluwer academic this model is more appropriate for approximating the source area of pollen in lake sediment since mixing in lake water and focusing of sediment redistribute pollen originally deposited over the entire surface in general the pollen source radius for the entire basin surface is 10 30 smaller than the source radius for a point at the center the difference in the source radius is more profound for heavier pollen types such as spruce and sugar maple than for lighter types such as oak and ragweed the average pollen input to the entire surface is more strongly influenced by nearby pollen sources than pollen deposition at the center the pollen record from a lake may therefore provide different spatial resolution than the record from a bog of similar radius

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control

quantifying the source area of macroscopic charcoal with a particle dispersal model abstract to aid interpreting the source area of charcoal in lake sediment records we compare charcoal deposition from an experimental fire to predictions from a particle dispersal model this provides both a theoretical framework for understanding how lake sediments reflect fire history and a foundation for simulating sediment charcoal records the dispersal model captures the two dimensional patterns in the empirical data predicted vs observed r2 0 67 p

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr