palynofacies and stable c and n isotopes of holocene sediments from lake macuco linhares espirito santo southeastern brazil depositional settings and palaeoenvironmental evolution particulate organic matter in sediments constitutes a valuable proxy for paleoenvironmental reconstructions a 192 cm lacustrine sediment core 7521 cal yr b p from the northern coast of the state of espirito santo southeastern brazil was radiocarbon dated and then analyzed for palynofacies stable isotopes c and n and grain size the values for total organic carbon toc 1 91 to 20 89 total nitrogen tn 0 08 to 1 1 13c 27 10 to 29 01 15n 1 92 to 5 09 and c n 12 87 to 50 11 suggest predominance of c3 plants and changing mixtures of terrestrial and aquatic organic matter in the sediments palynofacies and cluster analyses were used to identify four palynofacies associations that reflect different phases in the lake macuco evolution palynofacies 1 192 to 106 cm 7521 cal yr b p to 7054 cal yr b p interpolated age is characterized mainly by amorphous organic matter aom non opaque phytoclasts nops mangrove pollen grains rhizophora sp l 1753 and avicennia sp l 1753 and foraminiferal test linings palynofacies 2 106 to 65 cm 7054 cal yr b p interpolated age to 4847 cal yr b p is dominated by nops and aom with an increase in the values of mangrove pollen grains relative to palynofacies 1 both palynofacies reflect marine and fluvial influences in a depositional environment related to the development of an estuarine system during the mid holocene transgressive stage palynofacies 3 65 to 27 cm 4847 cal yr b p to 3800 cal yr b p interpolated age comprises high abundances of fluvial elements nop and opaque phytoclasts op and low values of aom the depositional environment is interpreted as being an estuary during the marine regression with the displacement of the estuarine basin and mangroves towards the sea palynofacies 4 27 to 0 cm 3800 cal yr b p is characterized by the predominance of aom and nop increase in the values of freshwater algae and no evidence of marine influence this last phase reflects the beginning of the establishment of lake macuco and floodplain of the barra seca river under conditions similar to the present day

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

comparative study of organic matter preservation in immature sediments along the continental margins of peru and oman part i results of petrographical and bulk geochemical data abstract detailed petrographical and bulk geochemical investigations of organic matter om have been performed on sediments deposited below or close to upwelling areas offshore peru odp leg 112 sites 679 681 688 and oman odp leg 117 sites 720 723 724 in order to obtain a quantitative understanding of its accumulation and degradation microscopical as well as nanoscopical investigations reveal that the om in sediments affected by upwelling mechanisms mainly up to 98 consists of unstructured amorphous organic aggregates without any apparent biological structures in sediments which are not or to a lesser extent affected by upwelling site 720 terrestrial om predominates organic carbon toc contents are highly variable and range between 9 8 in sediments deposited below upwelling cells and 0 2 in sediments outside the upwelling zone the toc sulphur ratios of the sediments scatter widely the samples from the deep water locations sites 688 and 720 show c s ratios of normal marine sediments whereas at the other locations no correlation or even a negative correlation between sulphur and toc concentration exists in most of the upwelling influenced sediments om contains a significant amount of sulphur the incorporation of sulphur into the om followed microbial sulphate reduction and occurred in the upper meters of the sedimentary column below om is still present in vast amounts and relatively hydrogen rich but is nevertheless non metabolizable and becomes the limiting factor for bacterial sulphate reduction according to mass balance calculations 90 99 of the om produced in the photic zone was remineralized and 1 3 was consumed by microbial sulphate reduction the aerobic and anaerobic processes have greatly affected degradation and conservation of om

middle to late holocene environmental changes in the depositional system of the tropical brackish bolgoda lake coastal southwest sri lanka abstract the tropical bolgoda lake is one of the largest lagoonal estuaries in sri lanka organic constituents in this lake were investigated using 28 surface sediments three cores from the lake and four short cores from mangrove mud elemental and molecular compositions of sediments and living organic matter om were determined using cns elemental analysis and gas chromatography mass spectrometry respectively chronology of events was determined using accelerated mass spectrometry ams 14 c data for bulk oms woods and mollusk shells the history of bolgoda lake can be divided into two major chrono stratigraphic divisions namely a lower sedimentary succession from ca 7 0 cal ky b p to 2 5 cal ky b p and an upper sedimentary succession from ca 2 5 cal ky b p to the recent according to the sapropelic depositional system concentrations of the mangrove biomarker taraxone increased significantly at ca 7 0 cal ky b p the lower part of the sediment sequence had moderate productivity and was mainly deposited under marine terrestrial influence in oxygen poor anoxic conditions during mid holocene sea level highstands a drastic increase in total organic carbon toc content reaching 29 was found in one of the bolgoda cores this increase occurred because of sea level regression at about 2 5 cal ky b p this change was probably caused by development of a beach rock sandbar and the estuary system changed to a semi closed lake due to the sea level regression as a result aquatic vascular plants predominate in this depositional system after ca 2 5 cal ky b p toc content decreased slightly but relatively high toc contents were maintained in the muddy sediments in moderately sized and shallow 1 2 m tropical estuaries lagoons such as bolgoda lake drastic changes in toc contents may be the most sensitive indicator of sea level variations increase in higher plant om with higher n c 29 n c all and n c 37 n c all alkane ratios also suggest a climatic transition from wetter to somewhat drier after the middle holocene accumulations of pyrogenic polycyclic aromatic hydrocarbons pahs in the modern sediments record anthropogenic activity after european settlement in the 15th century

the application of δ13c and c n ratios as indicators of organic carbon sources and paleoenvironmental change of the mangrove ecosystem from ba lat estuary red river vietnam in this study two sediment cores 70 cm were collected from separate mangrove forests straddling the ba lat estuary red river of northern vietnam to examine the origins of sedimentary organic carbon soc and reconstruct the paleoenvironment in addition mangrove leaves and particulate organic matter were collected and measured for 13c to trace the origins of soc the cores were analyzed by high resolution sections for 13c toc c n ratios sediment grain size water content and porosity with values of 13c toc and c n ratios ranging from 28 19 to 22 5 2 14 30 94 mg g and 10 29 18 32 respectively the 13c and toc relationship indicated that there were some small residual effects of diagenetic processes on toc and 13c values in mangrove sediments however the shifts of 13c and c n ratios from the bottom to the surface sediment of the cores explained the change in organic matter sources with values of c n 12 and 13c 25 indicated terrestrial e g mangrove litter and marine phytoplankton sources respectively the covarying 13c c n ratios and sediment grain sizes during the past 100 years in sediment cores showed that the paleoenvironment may be reconstructed into three environments subtidal tidal flat and intertidal mangrove general trends in 13c and c n followed a gradual increase in the c n ratio and a concomitant decrease in 13c from the subtidal through to tidal flat and to the intertidal mangrove 13c and c n ratios are therefore effective in measuring the continuum of environmental change in mangrove ecosystem

relationships between environmental conditions and the diagenetic evolution of organic matter derived from higher plants in a modern mangrove swamp system guadeloupe french west indies abstract the sedimentary organic matter content of a series of 2 m deep cores was investigated along a sea land transect at five sites representing five species of mangrove and salt marsh vegetation the vegetation was settled at the same place for at least 1000 years and therefore sedimentary organic matter deriving from the decay of higher plants has accumulated in large amounts the global morphological and chemical preservation of the organic matter attested by various sedimentary parameters including the proportions of cellulose bearing tissues the toc contents the c n ratios the total sulphur contents and the 13 c compositions reveals that the sedimentary organic matter is less degraded when it has been under the influence of the marine water table for a long time this is indicated by a good correlation between the salinities of interstitial waters the redox potentials measured in the wet sediments and the chemical composition of the organic matter moreover the concentration of organic sulphur shows a positive correlation with the hydrogen index hi only under the marine water table influence suggesting the very local presence of sulphur hc compounds

progradational holocene carbonate tidal flats of crooked island south east bahamas an alternative to the humid channelled belt model the stratigraphic record of many cratonic carbonate sequences includes thick successions of stacked peritidal deposits representing accumulation at or near sea level these deposits have provided insights into past palaeoenvironments sea level and climate change to expand understanding of carbonate peritidal systems this study describes the geomorphology sedimentology and stratigraphy of the tidal flats on the crooked acklins platform south east bahamas the crooked island tidal flats extend continuously for ca 18 km on the platformward flank of crooked island reaching up to 2 km across tidal flats include four environmental zones with specific faunal and floral associations and depositional characteristics i supratidal continuous supratidal crust and pavement ii upper intertidal with the mangrove avicennia germinans and the cyanobacteria scytonema iii lower intertidal with the mangrove rhizophora mangal and iv non vegetated heavily burrowed subtidal submarine these zones have gradational boundaries but follow shore parallel belts coring reveals that the thickness of this mud dominated sediment package generally is 2 m with depth to pleistocene bedrock gradually shallowing landward the facies succession under much of the tidal flat includes a basal compacted organic rich skeletal lithoclast lag above the bedrock contact suggesting initial flooding this unit grades upward into rhizoturbated skeletal sandy mud subtidal overlain by coarsening upward peloid foraminifera gastropod muddy sand reflecting shallowing to intertidal elevations cores from landward positions include stacked thin indurated layers with autoclastic breccia root tubules and fenestrae interpreted as supratidal conditions collectively the data reveal an offlapping pattern on this prograding low energy shoreline and these holocene tidal flats may represent an actualistic analogue for ancient humid progradational tidal flats nonetheless their vertical facies succession is akin to that present beneath channelled belt examples suggesting that facies successions alone may not provide unambiguous criteria for prediction of the palaeogeomorphology lateral facies changes and heterogeneity in stratigraphic analogues

effect of surface waves on charnock coefficient under tropical cyclones 1 the dependence of the air sea momentum flux on surface wave fields is investigated at very high winds under tropical cyclones a coupled wave wind model is applied to estimate the momentum flux under ten hurricanes in the western atlantic ocean during 1998 2003 the model explicitly calculates the wave induced stress vector and the total wind stress vector from a given wind speed vector and a calculated wave spectrum it is found that the neutral drag coefficient levels off at high wind speeds under tropical cyclones being consistent with recent observations and previous modeling studies the most important finding of this study is that the charnock coefficient is mainly determined by two parameters the input wave age wave age determined by the peak frequency of wind energy input and the wind speed regardless of the complexity of the wave field under a real hurricane and that the charnock coefficient increases with the input wave age at very high winds

microfacies characteristics of a tropical mangrove fringed shoreline cleveland bay queensland australia sedimentary and taphonomic controls on mangrove facies development mangrove ecosystems strongly influence the sedimentology and geomorphology of contemporary intertidal environments and are known to have occupied similar ecological niches at least as far back as the early cenozoic given this it is remarkable how few records of mangrove occurrence have been reported in the geologic record here a microfacies approach is adopted to examine the characteristics of a contemporary mangrove colonized intertidal succession along an active prograding shoreline in north queensland australia and compared with a proximal mid late holocene preserved intertidal succession this enables a comparison of microfacies development and preservation potential in like for like depositional environments over short temporal and spatial scales in the contemporary intertidal system active shoreline progradation has produced a highly gradational shallowing upward succession mid to low intertidal substrates characterized by an abundant and diverse bioclast especially molluscan fauna and a rich calcareous foraminiferal assemblage are overlain by organic rich upper intertidal mangrove facies characterized by abundant organic material especially wood and bark fragments and a distinct fauna of agglutinated foraminifera the major sedimentary effects of mangrove progradation are to introduce substantial amounts of organic matter into the substrate effectively overprinting the mudflat facies to mix and re texture due to root network development and infaunal bioturbation the sediment substrate and to modify the depth ranges over which infaunal molluscs and foraminifera occur variations in the relative abundance of constituents permit however the clear delineation of mangrove and intertidal mudflat facies whilst an essentially similar facies succession is identifiable in the sub recent many of the diagnostic facies constituents are either not preserved or are present in far lower abundances than in the modern in particular the inferred mangrove units contain far less organic material most wood and root material is absent are essentially devoid of bioclastic material and contain a depauperate agglutinated foraminiferal fauna the primary drivers of this are 1 loss of calcareous foraminifera and bioclasts due to carbonate dissolution 2 loss of agglutinated foraminifera due primarily to biological fiddler crab test degradation and mineralization of their organic binding agents and 3 aerobic and anaerobic degradation of organic material consequently actual criteria for identifying the presence of a former mangrove in this succession are limited such poor preservation even within sub recent mangrove deposits suggest that the longer term preservation potential of key diagnostic criteria is likely to be extremely poor within similar terrigenoclastic dominated organically enriched successions thus whilst mangroves significantly modify and re texture intertidal substrates use may often need to be made of sparsely preserved faunal or floral remains or traces interpreted in the context of the broader intertidal depositional succession to infer the presence of mangrove colonized substrates in the rock record

carbon burial rates in sediments and a carbon mass balance for the herbert river region of the great barrier reef continental shelf north queensland australia the largest century scale carbon reservoir in the herbert river sector of the great barrier reef continental shelf is carbonate carbon this carbonate carbon is produced by corals coralline algae and other benthic organisms and is stored on less than 13 of the area of the shelf maximum organic carbon burial rates 1 28 mol m 2 yr 1 occur within a wind protected 20 m water depth embayment 1 area of the shelf where the highest bulk sedimentation rates 1 12 kg m 2 yr 1 were determined from 210pb and137 cs profiles in 1 4 m cores sediment organic carbon oc and carbonate carbon cc accumulation rates are very low in the great barrier reef lagoon shelf and slope where most annual productivity 8 15 mol oc m 2 yr 1 is decomposed by algal and microbial respiration a carbon mass balance indicated that approximately 1 of combined river and marine organic carbon production was preserved in across shelf sedimentation but 3 of river and mangrove organic carbon input was preserved in this small wind protected embayment an across shelf carbon mass balance model predicted average shelf organic matter respiration correctly and the ratio of organic carbon fixation to respiration corrected for burial losses was 1 06

the organic geochemistry of coal from plant materials to coal coalification is a process that transforms plant remains under the influence of time temperature and possibly pressure to a black generally lustrous solid organic fossil fuel having a very complex chemistry although much has been learned in the past two centuries on coal chemistry we still have little knowledge of the way plant materials undergo these transformations the problem has been the existence of adequate characterization tools the advent of some new tools for structural elucidation of macromolecules has led to some revised thinking on coalification originally thought to be a process involving the full degradation of plant remains and subsequent reconstitution of these remains the general consensus today is that the process involves a selective preservation of certain resistant plant components followed by some minor reorganization of the biopolymers that survive the major components of plants do degrade and the resistant ones often constitute only a small fraction of the original mass of the plant materials this paper examines the most recent literature concerning coalification and focuses on the chemistry associated with coalification of certain recognizable plant remains that have been at the center of research activity for the past two decades thus we examine the recent knowledge of the chemistry of resistant biopolymers in extant and fossil wood cuticles resins spores and algae knowledge that has been assembled to establish the reaction pathways towards coal macromolecules

environmental changes recorded in the holocene sedimentary infill of a tropical estuary abstract early to late holocene sedimentary infill of the potengi jundiai estuary brazil was studied in a 31 5 m long sediment core the borehole was drilled in a mangrove area within the central part of the flood tide delta the sedimentary record encompassing the last 10 kyr was studied for sediment texture and for the n alkanes composition of organic matter om sediments rich in om and bivalve shells accumulated during the period of sea level rise mostly in an intertidal environment of mangrove forest mudflat and subtidal estuarine flood delta the characterization of n alkanes c10 c33 and lignin methoxyphenols by means of direct analytical pyrolysis py gc ms technique allowed determining the sources of the extant om downcore fluctuations were observed in n alkanes and in several n alkane based indices such as long chain carbon preference index cpi c24 c33 long to short chain ratio l s and average chain length acl as well as in the relative proportion of lignin derived compounds the n alkanes distribution points to changing sources of om input to the estuarine sediments over most of the holocene period major inputs of terrestrial vegetation alternated with periods of mixed input from aquatic macrophytes as the rate of sea level rise changed over time the n alkanes distribution and the lignin markers were useful for reconstructing paleoenvironmental conditions particularly during the early holocene when the lower potengi river valley now an estuarine area could accommodate terrestrial forest vegetation before switching to halophytic mangroves as sea levels rose

origin and diagenesis of lignin and carbohydrates in mangrove sediments of guadeloupe french west indies evidence for a two step evolution of organic deposits the mangroves of grande terre island guadeloupe french west indies are known to store large amounts of organic carbon and organic rich sediments have been described to several meters depth the purpose of the present work was to precisely determine the molecular composition carbohydrates and lignin derived phenols of these organic deposits in relationship with environmental conditions it was found that within the upper meter of the cores geochemical data displayed the classical degradation pattern of organic matter om deriving from higher plants on the one hand carbohydrates from mangrove tissues underwent fast decomposition other compounds being simultaneously synthesized by bacteria on the other hand lignin phenols were lost rather slowly i e at a similar or lower rate than toc their distribution with depth evidencing various lignin decomposition pathways depending on redox conditions the position of the swamp with respect to salt and fresh water tables strongly influenced these conditions at depth results revealed an organic rich layer which was characterized by surprisingly well preserved om with regard to sugar and phenol compositions we speculate that the preservation of these compounds might be explained by a rapid and permanent flooding of the mangrove stands that may have occurred more than a thousand years ago we suggest that the geodynamic context i e the recurrent seismic activity recorded in guadeloupe may have induced such a flooding resulting in the preservation of this om

formation of ultralaminae in marine kerogens via selective preservation of thin resistant outer walls of microalgae abstract transmission electron microscopy tem observations recently revealed the common occurrence of very thin lamellar structures termed ultralaminae in kerogens from source rocks and oil shales so far considered as amorphous ultralaminae in lacustrine kerogens were shown to derive from the selective preservation of the algaenans occurring in the very thin outer walls of various freshwater chlorophyceae the chemical correlation between such algaenans and fossil lacustrine ultralaminae was chiefly based on the production on pyrolysis of n alkylnitriles with a typical distribution bimodal maxima at c 28 and c 16 the origin of marine ultralaminae is investigated in this work to this end spectroscopic and pyrolytic studies were carried out on i the algaenan forming the very thin outer walls of nanochlorum eucaryotum an extant marine chlorophycea and ii two ultralaminae containing marine kerogens from the lower toarcian shales of paris basin fecocourt and bray a high contribution of polymethylenic chains probably linked via ehter bridges was observed in these bio and geopolymers furthermore on pyrolysis they afforded the same n alkylnitriles with the same distribution unimodal maximum at c 13 lack of c 17 compounds fossil ultralaminae in marine kerogens therefore derive from the selective preservation of the algaenan composed very thin outer walls of marine chlorophyceae such as n eucaryotum algaenans from marine and freshwater chlorophyceae and therefore marine and lacustrine ultralaminae should be characterized by sharply distinct n alkylnitrile distributions

coal petrographic genetic units in deltaic plain deposits of the campanian mesa verde group new mexico usa the campanian rocks of the mesa verde group in the san juan basin new mexico usa form a littoral wedge composed of offshore shoreface and onshore facies this siliciclastic wedge was interpreted as a landward to seaward stepping of grouped genetic units i e intermediate term cycles the continental facies consist of coastal plain deposits coals shales and sandstones represented by three main domains progressively distant from the palaeoshoreline the deltaic plain the intermediate plain and the alluvial plain domains in the deltaic plain grouped aggradational retrogradational genetic units consist of preserved coal shale doublets alternating with thick shales although previous works have identified genetic units in the shoreface facies the existence of the latter has not been proven in the coastal plain deposits as coal shale doublets may represent such genetic units an organic petrography study was performed at high resolution on an 80 cm thick 1 5 km long coal seam to demonstrate this hypothesis in this work the depositional environments of the initial peatlands were rebuilt utilizing two complementary methods maceral and microlithotype analyses the results reveal the existence of internal sequences in the coal seam corresponding to recurrent patterns of a palaeogeographical model proposed for a littoral domain the authors interpret this coal sequence as the record of successive progradational and aggradational events furthermore a previous study of the organic content of the shales located above the coal demonstrated that the preservation of these facies is related to higher accommodation peat production and accommodation sedimentary supply ratios coal shale doublets are then interpreted as elemental genetic units of the deltaic plain formation this study demonstrates that contrary to original concepts littoral coal seams are not just markers of stable shoreline conditions at a high time scale but also record landscape migration

a review of the ecological and taphonomic controls on foraminiferal assemblage development in intertidal environments intertidal foraminifera from surface sediments are commonly used as a high resolution indicator of sea level change the integrity of this approach is based upon the assumption that surface assemblages are similar in composition to their buried fossil counterparts this assumption may in some cases be inappropriate due to subsurface or infaunal production and taphonomic alteration here we review the current understanding of foraminiferal production and taphonomic loss in intertidal environments and examine the extent to which these processes can affect the development of foraminiferal assemblages in intertidal environments as a sediment layer undergoes burial dead tests are added at a rate proportionate to the standing crop at that depth as a consequence test accumulation within the layer is proportionate to the depth integrated standing crop depending on the nature of its vertical living distribution the upper 1 cm of sediment may therefore not adequately characterise a given species total input instead a comparison of each species contribution to the entire depth integrated living community may offer a better a priori estimate of relative input to the sediment column this provides an improved base line for identifying true taphonomic trends downcore the potential for infauna to create discrepancies between surface and subsurface assemblages may be minimised however where 1 reproduction is concentrated near to the sediment surface transforming an apparent infaunal standing crop into an effective epifaunal production 2 the living fauna is composed similarly at all depths of production and or 3 intense bioturbation homogenises the upper sediment layers the likely decline in the intensity of taphonomic processes with depth may mean that the foraminiferal production from different depths may not experience taphonomic processes uniformly consequently in addition to their possible gradual enrichment due to subsurface production infaunal species may be preferentially preserved by virtue of their production closer to the base of the taphonomically active zone additionally homogenisation of the sediment column by reworking may mix temporally and perhaps environmentally distinct faunas affecting the stratigraphic integrity of the sediment deposit the most important taphonomic processes in intertidal environments are those associated with early diagenesis while the organic cements of agglutinated taxa may be directly oxidised the associated changes in the saturation state of porewaters with respect to calcium carbonate may affect calcareous species the type of diagenetic reaction operating within the sediment provides a quantitative control on agglutinated test degradation but a largely qualitative control on calcareous preservation in addition calcareous test preservation is dependent upon the rate with which organic matter is supplied while agglutinated test preservation is independent of organic matter concentrations although the specific morphological pathways of test degradation for calcareous species are well understood the stages under which agglutinated tests are lost are less clear the combined but varying influences of production infaunal and species composition taphonomic processes and bioturbation may create complex pathways in the transition from live to dead to fossil assemblages understanding the extent to which infauna taphonomic loss and sediment reworking affect assemblage development in different intertidal environments is essential in order to interpret the fossil record

organic carbon sulphur and iron in recent semi euxinic sediments of kau bay indonesia kau bay island of halmahera eastern indonesia is a 470 m deep basin separated from the pacific ocean by a sill that is at present only 40 m below sea level during weichselian time the sea level dropped below the depth of the sill and freshwater sediments were deposited these sediments are rich in organic matter corg 2 6 wt with terrigenous isotope characteristics 13corg 28 to 30 and are also rich in sulphur s 4 wt this sulphur enrichment is interpreted to be a late diagenetic feature related to diffusion of dissolved sulphate and sulphide from the marine sediments into the freshwater sediments the sulphur in these sediments has a 34s value of 15 the overlying holocene sediments consist of marine muds deposited in alternating low oxygen and h2s bearing bottom waters the marine sediments are also rich in organic matter corg 2 6 wt but of mixed terrigenous and marine origin 13c 25 to 19 moreover the sulphur content of these holocene sediments is lower s 1 2 wt and isotopically lighter 34s 20 in addition to pyrite large amounts of acid volatile sulphur avs compounds accumulate in kau bay the reactive iron content of the sediment limits the amount of iron that is sulphidized while the supply of oxidants controls the limited conversion of avs to pyrite total and reactive iron contents are strongly correlated with the amount of terrigenous organic matter as a consequence of their common provenance and depositional histories the marine sediments in kau bay show no simple relation between organic carbon and sulphur

pore water chemistry in mangrove sediments relationship with species composition and developmental stages french guiana spatial and seasonal variability of sedimentary salinity ph redox potential and solid phase sulphide concentration were investigated in a range of mangrove communities along the coast of french guiana seasonal depth distributions of these parameters and organic content were compared within avicennia rhizophora and mixed mangrove stands at different stages of plant development mangrove communities and variable surface water inputs strongly impact sediment and ground water properties in the upper sediment changes in salinity are mainly controlled by seasonal conditions transpiration and proximity of fresh water influx whereas we suggest that constant basal salinity results from an accumulation of salt that has migrated as a result of density driven convection processes there are no clear differences between the depth distributions of salinity obtained beneath avicennia germinans and rhizophora mangle stands implying that plant zonations are not primarily controlled by soil salinity in this environment nevertheless r mangle grows in places subjected to the greatest variability in freshwater influxes suggesting that rhizophora might require or withstand occasional inundation by fresh water beneath rhizophora stands sediment properties reflect anaerobic and sulphidic conditions close to the sediment surface in contrast beneath avicennia stands sediment geochemistry mostly depends on the stages in forest development on contents in sedimentary organic matter and on seasonal changes in the early stage of avicennia settlement the sediment at the level of radial pneumatophore bearing cable roots displays permanent suboxic conditions with eh values reaching 400 mv these high ehs are interpreted as an effect of the oxidation produced by the cable root system the development of mature avicennia stands results in accumulation of sedimentary organic matter and promotes low ehs and the reduction of pore water sulphate near cable root level the oxidation process observed in pioneer mangroves results in a reoxidation of solid sulphides produced previously during dry conditions the desiccation of the upper sediment adds its oxidation effects to those of root activity as a result suboxic processes dominate in the upper 20 cm thick layer organic matter decomposition and sulphur oxidation strongly acidify the sediment below 20 cm the sediment is anaerobic and sulphidic hence sulphide concentrations depend on the edaphic conditions controlling decay processes and appear to be a consequence rather than a cause of the observed zonation of vegetal species the small size of a germinans propagules might have a significant influence on the extensive development of this plant community along the highly dynamic coastline of the guianas this study demonstrates that the different properties of pore water were intimately linked and that the explanation of the evolution of this forest reflects a combination of multiple parameters moreover it appeared that the organic content played a key role along with the species composition and the seasonal variations waterlogging desiccation

resistivity structure of the central taupo volcanic zone new zealand abstract the taupo fault belt tfb is a 15 km wide zone of active normal faulting which is located in the central portion of the taupo volcanic zone tvz new zealand and is aligned sub parallel to the strike of this zone a large scale multiple source bipole dipole resistivity survey has shown that the tfb is characterised by high resistivity ca 250 m to depths of ca 7 km in contrast to the adjacent regions in the east and west of the tvz where resistivities are much lower 1 ma ignimbrites that have undergone slow diagenetic alteration that has produced clay minerals the volcaniclastics in the tfb have high resistivities which suggests that they have not undergone significant alteration and are thus younger than the volcaniclastics in the regions to both east and west these high resistivities are also consistent with the absence of surface geothermal activity and low heat flow the tfb also exhibits high seismicity and active faulting in contrast with its surrounding it was not possible to determine the depth to basement rocks in the tfb because of the lack of resistivity contrast between the basement and the overlying volcanics but gravity data indicate that the young volcanics are no more than 3 km thick

palynofacies as useful tool to study origins and transfers of particulate organic matter in recent terrestrial environments synopsis and prospects palynofacies analysis is based on transmitted light microscope study of organic constituents isolated and concentrated by acid and basic digestions published results of studies of present day terrestrial environments show that two complementary approaches successfully characterize particulate organic matter om from palynofacies analyses the first method is based on the identification and the quantification of some typical particles optical markers according to their origin i e aquatic or terrestrial their nature i e biogenic anthropogenic fossil and or their formation i e biodegradation combustion oxidation the second approach is based on the use of binary or ternary diagrams in order to define petrographical signatures from the relative proportions of significant organic constituents this approach can be used for tracking i changes in om composition during humification in soil profiles ii transport of reworked terrestrial particles iii diagenesis of peaty deposits or iv weathering of geological substratum the more advanced approach is based on the use of some predefined optical markers and their optical signatures to establish the relation between the om compositions palynofacies and their depositional environments in addition this kind of study aims to define a modern frame of reference that can be applied in paleoenvironmental reconstructions this paper combines a bibliographic review with previously unpublished data from palynofacies analyses the aim is to present some applied examples illustrating 1 the main approaches developed for characterization of the particulate om in surficial deposits and 2 the study of om transfers in terrestrial geosystems