modes of origin and genetic pathways of peloids within the duwi formation late cretaceous in eastern and western deserts of egypt a petrologic perspective abstract peloids are considered as major constituents of modern and ancient sedimentary rocks although their origins and pathways of formation are not yet comprehensively understood based on field and petrologic investigations peloids have been recorded in the duwi formation late cretaceous in both eastern and western deserts of egypt the duwi formation represents the first onset of fully marine conditions in egypt accompanying the major late cretaceous marine transgression it comprises a heterogeneous suite of shallow marine sediments phosphorites oyster limestones shales glauconites and dolomite according to the hosted rock peloids are classified into two types peloids in phosphorites and peloids in limestones which are characterized by different shapes and sizes systematic study indicates that peloids resulted from the interplay between physico chemical and microbial processes accordingly the more important modes of origin are peloids derived from coprolites by micritization of bivalve shells fragmentation and abrasion of intraclasts by phosphomicritization of bone fragments peloids derived from internal molds intraskeletal and interskeletal peloids nucleated peloids and peloids within matrices the size and morphology of the studied peloids are mainly controlled by the parent material

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

laminar micrite crusts and associated foreslope processes red sea abstract forereef slopes in the red sea of sudan exhibit a uniform biozonation that is independent from the topography of the slopes below 120 m ledges protrude horizontally from sleep cliffs of barrier reefs and atolls as well as from patches of in situ lithified slope sediment on inclined fringing reef slopes free surfaces and cavities within these ledges are partly covered by laminar micrite crusts of 7 20 mm thickness the ledges are formed by an organic framework of living azooxanthellate corals bryozoans serpulids and fossil red algae they are affected by repeated episodes of boring infilling and cementation which obliterate much of the original fabric concomitant cementation and boring result in asymmetric cement linings which often show geopetal fabrics the laminar m crite crusts however show no significant traces of bioerosion which are a typical feature of fossil deep water stromatolites two types of lamination have been observed 1 vertically stacked irregular anastomosing laminate with ragged outlines and little lateral persistence which are often accentuated by iron staining and 2 0 5 mm thick laminae of light grey micrite rich in fine bioclasts showing smooth thin coatings of dark homogenous micrite which are weakly fluorescent in ultraviolet light no algal films are preserved but micritic tubes 10 30 m in diameter often bifurcated form a dense network on the upper surface of the crusts by overgrowing and binding particles associated aragonitic rosettes 30 40 m in diameter may represent calcified coccoid algae or bacteria if true these organisms suggest a formation of the latter type of crust by biogenic processes not related to the photic zone fenestral porosity and frutexites textures are absent radiocarbon dates from corals within the ledges provide ages of 10 500 ybp from the time related decrease in oxygen isotope ratios versus pdb of boring micrite 18o 3 72 micrite crusts 18o 1 69 and unlithified mud 18o 0 47 within the youngest voids of the hard substrates we conclude that crust formation must have taken place in shallower water when sea level was lower during the early holocene rise of sea level

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

depositional sequences of the duwi sibâiya and phosphate formations egypt phosphogenesis and glauconitization in a late cretaceous epeiric sea

iron isotope variations in holocene sediments of the gotland deep baltic sea holocene sediments from the gotland deep basin in the baltic sea were investigated for their fe isotopic composition in order to assess the impact of changes in redox conditions and a transition from freshwater to brackish water on the isotope signature of iron the sediments display variations in 56fe differences in the 56fe 54fe ratio relative to the irmm 14 standard from 0 27 0 09 to 0 21 0 08 samples deposited in a mainly limnic environment with oxygenated bottom water have a mean 56fe of 0 08 0 13 which is identical to the mean fe isotopic composition of igneous rocks and oxic marine sediments in contrast sediments that formed in brackish water under periodically euxinic conditions display significantly lighter fe isotope signatures with a mean 56fe of 0 14 0 19 negative correlations of the 56fe values with the fe al ratio and s content of the samples suggest that the isotopically light fe in the periodically euxinic samples is associated with reactive fe enrichments and sulfides this is supported by analyses of pyrite separates from this unit that have a mean fe isotopic composition of 1 06 0 20 for 56fe the supply of additional fe with a light fe isotopic signature can be explained with the shelf to basin fe shuttle model according to the fe shuttle model oxides and benthic ferrous fe that is derived from dissimilatory iron reduction from shelves is transported and accumulated in euxinic basins the data furthermore suggest that the euxinic water has a negative dissolved 56fe value of about 1 4 to 0 9 if negative fe isotopic signatures are characteristic for euxinic sediment formation widespread euxinia in the past might have shifted the fe isotopic composition of dissolved fe in the ocean towards more positive 56fe values

late quaternary aeolian activity in the mu us and otindag dune fields north china and lagged response to insolation forcing 1 dune fields in parts of northern china contain important stratigraphic records of late quaternary change in the east asian monsoon in this study 33 new optically stimulated luminescence osl ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet dry climate variation in the mu us and otindag dune fields of north china the results indicate dune activity and dry climate in the last few hundred years 14 ka to about 7 8 ka and 50 ka to 60 ka the dunes were mainly stable implying a wetter climate between about 7 8 ka and 2 4 ka these results imply a lag of several thousand years between peak summer insolation at 10 11 ka and high summer monsoon rainfall after 7 8 ka in the investigated regions the monsoon climate may not respond directly to orbital forcing over millennial time scales land surface feedbacks may account for lagged dune field response

phytoliths as quantitative indicators for the reconstruction of past environmental conditions in china ii palaeoenvironmental reconstruction in the loess plateau abstract quantitative reconstruction of the climatic history of the chinese loess plateau is important for understanding present and past environment and climate changes in the northern hemisphere here we reconstructed mean annual temperature mat and mean annual precipitation map trends during the last 136 ka based on the analysis of phytoliths from the weinan loess section 34 24 n 109 30 e near the southern part of the loess plateau in northern china the reconstructions have been carried out using a chinese phytolith climate calibration model based on weighted averaging partial least squares regression a series of cold and dry events as indicated by the reconstructed mat and map are documented in the loess during the last glacial periods which can be temporally correlated with the north atlantic heinrich events our mat and map estimations show that the coldest and or driest period occurred at the upper part of l2 unit late mis 6 where mat dropped to ca 4 4 c and map to ca 100 mm two other prominent cold dry periods occurred at lower ll 5 ca 77 62 ka and l1 1 ca 23 10 5 ka where the mat and map decreased to about 6 1 6 5 c and 150 370 mm respectively ca 6 6 6 2 c and 400 200 mm lower than today however the highest mat average 14 6 c max 18 1 c and map average 757 mm max 1000 mm occurred at sl interval mis 5 during the interstadial of l1 4 l1 2 mis 3 and during the holocene warm wet period the mat was about 1 2 c and map 100 150 mm higher than today in the weinan region the well dated mat and map reconstructions from the chinese loess plateau presented in this paper are the first quantitatively reconstructed proxy record of climatic changes at the glacial interglacial timescale that is based on phytolith data this study also reveals a causal link between climatic instability in the atlantic ocean and climate variability in the chinese loess plateau

influence of paleoenvironmental factors on preservation of organic matter in middle cretaceous greenhorn formation pueblo colorado sedimentological and geochemical studies of the upper cretaceous hartland shale and overlying bridge creek limestone members of the greenhorn formation reveal close associations between abundance of current induced sedimentary structures extent of bioturbation and type of preserved organic matter abundant hydrogen rich organic matter 4 5 wt and low sulfur to organic carbon ratios are characteristic of the laminated facies which lack current induced sedimentary structures sparse hydrogen poor organic matter 0 1 0 5 wt and relatively high sulfur to organic carbon ratios are characteristic of the bioturbated facies which contain numerous sedimentary structures indicative of currents the concentration of oxygen in the benthic environment and the degree of bio urbation of the sediment apparently were determined principally by the rate that oxygen was supplied advectively by currents rather than by the rate of oxygen consumption by decomposition thus paleoclimatic and paleo oceanographic factors that influenced mixing and current strength in the water column profoundly affected the amount and type of organic matter preserved in these units it is proposed that episodes of high river discharge lead to density stratification of the water column and in turn to quiescent oxygen depleted bottom water and high preservation of organic matter thus accounting for the intermittent widespread deposition of organic rich strata during maximum transgression and depth of the greenhorn sea the lateral association of voluminous deltaic deposits with dee water black shales in other elongate or restricted marine basins may have causes similar to those envisioned for the hartland shale and bridge creek limestone members

application of backscattered electron imaging to the study of source rocks microtextures abstract scanning electron microscope sem used in backscattered electron bse mode is a powerful tool for the sedimentological study of source rocks owing to its spatial and chemical resolutions ease and speed of operating the obtained imaging is dependent on atomic number contrasts between the different constituents of the sample using the bse mode combined with energy dispersive x ray spectrometry minerals and organic matter can be distinguished more clearly than with the light microscope classically used by organic petrologists in order to describe microtextures of organic rich sediments particularly the disposition of the organic matter this technique has been tested on source rocks having various sedimentological and geochemical characteristics accordingly two patterns of organic matter disposition have been recognized laminated and particulate these dispositions can be put back into their sedimentary context by considering the depositional environment and diagenesis the organic matter disposition suggests the existence of organic networks which are suspected to be a major control for hydrocarbon expulsion

origin of eolian sand mobilization during the past 2300 years in the mu us desert china abstract eolian sand dunes and sand sheets are extensive in the semiarid regions of northern central china previous studies indicated that these eolian sands mainly formed during historical times however the sand sources and their reworking processes have not been well studied and even the reasons for their occurrence are still controversial field investigation and sedimentary evidence indicate that both the inner mu us desert and its southern marginal region both sources of modern eolian sand are largely associated with reworking of sands of the last glaciation based on geological documentary and archaeological data three phases of land cultivation during the past 2300 years together with historical droughts high wind energy and the easily reworked sand sources largely account for the occurrence of active sand dunes and sand sheets in the mu us desert

the coexistence approach a method for quantitative reconstructions of tertiary terrestrial palaeoclimate data using plant fossils abstract the coexistence approach is introduced as a method for quantitative terrestrial palaeoclimate reconstructions in the tertiary it is based on the assumption that tertiary plant taxa have similar climatic requirements to their nearest living relatives the aim of the coexistence approach is to find for a given fossil flora and a given climate parameter the climatic interval in which all nearest living relatives of the fossil flora can coexist for this purpose we have developed a data base climbot containing for over 800 tertiary plant taxa the nearest living relatives and their climatic requirements and an algorithm for analysis climst for all types of fossil floras the coexistence approach thus allows the rapid quantitative reconstruction of 10 different climate parameters including the mean annual temperature temperature of the warmest month temperature of the coldest month mean annual precipitation maximum monthly precipitation minimum monthly precipitation precipitation of the warmest month relative humidity potential evaporation as well as the ratio of mean annual precipitation over potential evaporation the reliability and resolution of the coexistence approach are tested with various techniques and proved to be reasonably good for instance the resolution with respect to the mean annual temperature can be up to 1 c applications to various modern and fossil floras are illustrated and the advantages and disadvantages of the coexistence approach are discussed

petrology and major element geochemistry of peru margin phosphorites and associated diagenetic minerals authigenesis in modern organic rich sediments abstract new petrographic and major element geochemical data from modern peru margin upper slope outer shelf phosphorites are presented which provide insight into their origin and paragenetic relationship with other authigenic minerals glauconite pyrite and dolomite occurring in organic rich sediments glauconites are precipitated relatively early following the partial reduction of ferric iron and following this process phosphate pyrite and then dolomite precipitation take place at progressively deeper levels in the sediment in association with microbial reduction of sulfate as in many ancient economic phosphorite deposits the phosphatic facies here consist of nodules crusts coatings and strata composed of phosphatic pelletal grains ooids structureless grains intraclasts clumps and biogenic grains in association with organic rich biosiliceous sediments all are considered to have formed within a few centimeters or within a few tens of centimeters below the sediment water interface important factors that influence which morphology will tend to develop include the amount of available pore space the presence of suitable nucleation sites the amount and size of siliciclastic detritus incorporated as inclusions and the relative solution chemistries of the precipitating solutions bacterial mediation may play an important but as yet unspecified role in the precipitation process textural data and factor analysis of chemical data suggest that structureless pellets are relatively inclusion free na f mg co3 substituted pore water precipitates whereas ooids are inclusion rich pore water precipitates poor in lattice substituted components variations in nodular cement birefringence and crystallinity are suggested to have been produced by similar lattice substitutions that directly reflect pore water carbonate ion concentrations and thus relative degrees of organic matter degradation phosphate and dolomite are intimately mixed yet mineralogically distinct phases in phosphatized dolomicrites depth stratified threshold carbonate ion concentrations may control the lower limit at which phosphatic minerals may precipitate below depths of a few centimeters excessive carbonate ion concentrations and diminished reactive iron and sulfate concentrations favor the development of dolomite while precluding further development of phosphatic minerals and pyrite periodic sediment reorganization bioturbation current winnowing and erosion mass wasting etc plays an important role in both concentrating pelletal grains and maintaining nodules and crusts at critical depth levels in the sediment as well as mixing ordered mineral parageneses into complicated sequences

sedimentary organic carbon to phosphorus ratios as a redox proxy in quaternary records from the mediterranean abstract in this study organic carbon to organic phosphorus c org p org and total phosphorus c org p tot ratios as bottom water redox proxies are explored for two eastern mediterranean sediment records extending back 600 700 kyrs cores kc19c 19 6 m long 2750 m water depth and kc01b 37 0 m long 3643 m water depth contain numerous organic rich layers sapropels throughout the two cores variations found in the c org p ratios correspond to those for other redox proxies such as total s contents and v al ratios accordingly these are interpreted as variations in bottom water oxygenation and inter sapropel redox variability in core kc19c the original c org p signals seem to have been preserved despite intense post depositional sulfidization high resolution p fractionation data of sapropel s5 from a third core ps25pc 3304 m water depth showing high and relatively stable c org p org ratios indicate that sapropel s5 at this deep location was deposited under permanently reducing conditions while p regeneration from organic matter was intense net p burial increased in the sapropel due to enhanced burial of inorganic calcium phosphate likely biogenic ca p sediment p contents and c org p tot ratios in s5 are variable reflecting short term changes in marine conditions productivity redox and sediment chemistry the c org p org and c org p tot ratios thus provide valuable insight into paleoceanographic conditions and pathways of p cycling for mediterranean sediment records extending back at least 600 700 kyrs

bacterial origin of east australian continental margin phosphorites many models of the origin of marine phosphorites require a sediment rich in organic matter which by decomposition releases phosphorus for the precipitation of carbonate fluorapatite1 7 this concept is useful in explaining contemporary phosphorite in areas of very high productivity off the coasts of peru chile and south west africa8 10 where there are high organic matter fluxes to the sea floor4 7 11 it does not explain the origin of marine phosphorite deposits which formed in regions of limited oceanic upwelling and productivity12 14 the east australian continental margin an area of phosphogenesis throughout the late pleistocene and holocene13 14 is a modern analogue of an east coast phosphogenic province15 17 with low productivity over the upper slope region where the most recent phosphorites have been found18 evidence is reported here for the carbonate fluorapatite in the east australian phosphorites being located within bacterial cellular structures and a model proposed for the origin of these deposits through the slow bacterial assimilation of phosphorus from seawater in an area of restricted sedimentation

organic rich sediments in ventilated deep sea environments relationship to climate sea level and trophic changes sediments on the namibian margin in the se atlantic between water depths of 1000 and 3600 m are highly enriched in hydrocarbon prone organic matter such sedimentation has occurred for more than 2 million years and is geographically distributed over hundreds of kilometers along the margin so that the sediments of this region contain a huge concentrated stock of organic carbon it is shown here that most of the variability in organic content is due to relative dilution by buried carbonates this reflects both export productivity and diagenetic dissolution not differences in either water column or bottom water anoxia and related enhanced preservation of organic matter these observations offer a new mechanism for the formation of potential source rocks in a well ventilated open ocean in this case the south atlantic the organic richness is discussed in terms of a suite of probable controls including local wind driven productivity upwelling trophic conditions transfer efficiency diagenetic processes and climate related sea level and deep circulation the probability of past occurrences of such organic rich facies in equivalent oceanographic settings at the edge of large oceanic basins should be carefully considered in deep offshore exploration

dolomitization in a mixing zone of near seawater composition late pleistocene northeastern yucatan peninsula abstract patches of dolomite occur in cores of reefal limestone from the shallow subsurface on the northeastern coast of the yucatan peninsula this limestone accumulated during an interglacial high stand of sea level about 200 000 years ago dolomitization was preceded by freshwater diagenesis including precipitation of sparry calcite cement stabilization of mg calcitic skeletal fragments and partial dissolution of aragonitic components this suggests a predolomitization lowering of sea level with the consequent freshening of pore water the subsequent precipitation of dolomite indicates a return to high sea level with the consequent increase in mg ca ratio of pore water dolomitization took place during a brief high stand of sea level either shortly after deposition about 200 000 yr bp r more likely about 125 000 yr bp dolomite occurs both as microcrystalline replacement dolomite and as cement the cement is part of the following diagenetic sequence 1 limpid euhedral subhedral calcian dolomite crystals 2 zoned dolomite crystals with zones formed by variations of the calcium magnesium ratio in dolomite 3 layers of alternating calcian dolomite and magnesian calcite or calcite and 4 calcite this sequence represents the progressive freshening of ground water during the initial stage of a fall in sea level average cation composition of the limpid dolomite cement is ca57mg43 electron microprobe analysis zoned cement crystals are composed of ca57 59mg43 41 layers and ca62mg38 layers most of the higher calcium dolomite layers are dissolved forming hollow zone crystals in cement with alternating dolomite and calcite zones the calcite is ca99 97mg1 3 low mg calcite and ca96 93mg4 7 mg calcite the dolomite and mg calcite zones are partially to totally leached 18o compositions of yucatecan dolomite and of modern ground water suggest dolomite precipitation from mixed water ranging from about 75 seawater 25 freshwater to nearly all seawater isotope analyses are for the most stable calcian dolomites more soluble calcium rich dolomite presumably is analyzed with calcite and thought to be isotopically lighter than the less soluble dolomite in the cement sequence the most stable dolomite is followed by more soluble dolomite as ground water becomes less saline isotope analyses together with position of dolomite in the cement sequence suggest the most stable calcian dolomite including limpid dolomite precipitated from mixed water with large proportions of seawater and the less stable more calcian dolomite precipitated from fresher mixed water

phosphate regeneration from sediments of the peru continental margin by dissolution of fish debris generally oxidative regeneration of phosphate from anoxic sediments is by microbially mediated sulfate reduction processes stoichiometric modelling of such reactions takes into consideration varying proportions of decomposable organically bound p to account for the ratios among nutrients in depth concentration profiles of near surface sediments new results of interstitial water composition from sediments underlying the water masses influenced by coastal upwelling of the eastern boundary current system off peru indicate that dissolution of phosphatic fish debris represents a mechanism for remineralization of phosphate comparable to or larger in magnitude than that by oxidative regeneration of organically bound p dissolved interstitial phosphate from fish debris is revealed by an excess amount of phosphate over that predicted from a simple stoichiometric oxidative regeneration model and by anomalously high dissolved interstitial fluoride concentrations phosphate flux estimates based on diffusion from the sediment suggest that this mechanism may generate up to 10 of the nutrient pool in the waters of the peru undercurrent partitioning of p among the two sources reveals further that fish debris phosphate is about four times more important than organically bound p in nutrient generation from sediments of the peru continental margin not only does this mechanism of regeneration affect the nutrient cycling but may also control widespread phosphorite formation in this area

active diagenetic formation of metal rich layers in n e atlantic sediments sediment cores from the porcupine abyssal plain exhibit an indurated layer 0 5 3 cm thick at depths of approximately 50 cm this is some 15 20 cm below the glacial holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of ruddiman and mcintyre 1981 the layer is forming currently at the oxic post oxic boundary in the sediments as revealed by pore water data o2 and no 3 are present in solution above the layer while fe2 mn2 po3 4 and nh 4 are present in solution below and all these species show concentration gradients indicating fluxes into the layer these data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by wilsonet al 1986a b the elements mn ni co fe p v cu zn and u are all enriched to varying degrees in the vicinity of the layer some differential stratification of these elements in the vertical consistent with a redox control is observed at one site with a 0 5 cm layer with mn ni and co above fe p v and cu in the layer and u below at another site the metal rich layer has higher fe and p concentrations and is more indurated here all enrichments except co are contained within a single layer sample 3 cm thick

nonskeletal peloidal precipitates in upper triassic reefs yukon territory canada abstract peloidal sediments and crusts form up to 75 percent of framework limestones in upper triassic reefs in the yukon territory the peloids are spherical to irregular in shape 20 250 m in size and are commonly surrounded by one or more rims of sparry calcite the peloidal sediments occur in confined cavities and in open spaces between reef framebuilders the peloidal crusts generally coat calcareous sponges and tabulozoans internal evidence suggests that the peloids are not detrital grains or fecal pellets and comparisons with mg calcite peloids and peloidal crusts in modern environments suggest that they are precipitates possibly resulting from bacterial activity

geochemical evidence for lacustrine microbial blooms in the vast permian main karoo parana falkland islands and huab basins of southwestern gondwana early permian black pyritic shale units i e the whitehill irati and huab formations and black rock member in southwestern gondwana basins have elevated 13c values of total organic carbon up to 17 pdb hydrogen indices between 300 and 1000 mg co2 g c and oxygen indices 30 mg co2 g c these data suggest a manifestation of a microbial bloom event values for 13c between 26 and 22 pdb hydrogen 100 mg co2 g c and oxygen indices of total organic carbon above and below these rock units are typical for palaeozoic terrestrial type iii organic matter carbon 13 isotope stratigraphy concur with palaeontological evidence that these formations are stratigraphical equivalents and therefore that the microbial blooms covered a vast area 5 million km2 possibly earth s most expansive microbial bloom the palaeoenvironment of the rock units preceding and including the black shales was most likely lacustrine with fresh to brackish water as shown by stable isotope c o and s evidence from organic matter carbonates and pyrite the implication is that a broad tectonic belt which formed as a result of compressional tectonics during the late carboniferous to early permian from the palaeo west must have been sufficiently well developed to cut off any contact with seawater earlier than predicted late permian from previous stratigraphic and sedimentological studies stable isotope data supported by mineralogical evidence indicate that conditions particularly in the upper portions of the lacustrine oil shales were brackish and locally may have been evaporitic we envisage that the microbial blooms possibly botryococcus peaked in the upper half of the black shale units conditions rapidly became unfavourable for microbial blooms across the entire basin in the overlying formations manifested by a change from oil shales type i organic matter to organic poor type iii shales this may possibly have been a consequence of tectonic activity and interrelated causes stable isotope data of carbonates in the overlying sediments indicate that in the palaeo north the basin became evaporitic drying up and in the palaeo southern part of the basin high latitude altitude water flooded the basin and so brought to a close the microbial blooms

model for prediction of organic carbon content in possible source rocks abstract a quantitative model has been developed to improve the prediction of the occurrence of marine siliciclastic source rocks and their likely organic carbon content the input parameters of this quantitative model are organic matter supply in the surface layer of the ocean photic zone water depth calculation of the carbon flux sedimentation rate and preservation conditions presence or absence of oxygen at the sediment water interface to handle the difficulties in the quantification of input parameters a probabilistic approach is applied depending on the available data or the interpretation of the kind of environment different risk distribution functions are used to describe the possible range of each input parameter the calculation is then carried out using the monte carlo simulation technique resulting in a probability distribution of the total organic carbon content which forms the basis of the analysis different scenarios currently under debate e g high primary productivity or the possible effects of enhanced preservation under anoxic bottom water conditions and the influence of varying water depth and sedimentation rate can be tested very quickly using examples of recent peru continental margin and ancient lower toarcian shale germany organic rich marine shales the potential of this tool is demonstrated firstly to quantify souce rock quality in this case total organic carbon content only secondly to assess quantitatively the uncertainties in source rock prediction e g evaluation of organic matter supply water depth and sedimentation rates and thirdly to determine source quality risk values to be used in the appraisal of sedimentary basins and prospects

geochemical characteristics of chilean upwelling sediments at 36 s abstract we examined the cycling of c s fe and the trace elements te ag cd mo mn re and se in chilean upwelling sediments from water depths of 127 2744 m at 36 s the sediments are clay rich with moderate total organic carbon toc and low biogenic caco3 contents for the shallow site within oxygen minimum zone omz which shows some thioploca biomass highest observed toc contents correspond to highest productivity induced toc flux and or enhanced preservation under o2 deficient conditions pyrite formation may be restricted by the concurrent presence of elemental s in thioploca and or the availability of reactive iron in the other sediments 370 m water depth pyrite formation is strongly restricted due to the low availability of metabolizable toc for sulfate reduction calculations of the degree of bacterially mediated remineralization suggest that more nitrogen than toc was remineralized by sulfate reduction than expected from redfield c n relationship manganese is significantly depleted due to reductive dissolution of mn hydr oxides within all sediments mo is only significantly enriched vs the lithogenic background in the shallow core implying anoxic conditions contents of re and mo as well as re mo ratios indicate suboxic conditions for the other cores cd and re contents decrease with increasing water depth reflecting decreasing reducing conditions in contrast authigenic ag contents increase with water depth suggesting enrichment controlled by seawater availability and or opaline input and not redox conditions elevated se contents in all cores may be either due to bio detrital input or diffusion from seawater accumulation rates of toc ts and te off chile are in the same order as those from the gulf of california and lower than those off peru distinct seasonality in upwelling and dilution of chilean sediments with terrigenous material lead to rather low metabolizable toc contents and lower te trapping capacity

a study of the organic matter in tunisian phosphates series relevance to phosphorite genesis in the gafsa basin tunisia abstract in the gafsa basin tunisia peloidal fracolite is interbedded with shales limestones and rocks of intermediate lithology the rocks were deposited in an epicontinental sea and have been buried no more than 500 m the organic matter they contain is therefore thermally immature and in all units derived mainly from marine plankton particularly dinoflagellates the organic matter in the phosphorite units is composed predominantly of humic acids ha which are essentially located within the pellets these pellets are surrounded by an outer matrix in which the organic matter is similar to the kerogen comprised in the shally strata alternating with the phosphorite and limestone beds during weathering the content of the organic matter assocciated with the matrix decreases more rapidly than that of the organic matter entrapped within the pellets geochemical and palynological study of the organic matter in interbedded rocks of different lithology shale limestone phosphorite suggest that the shales were deposited in a reducing environment the limestones in one that was oxic whilst the phosphorites were formed in a redox environment inermediate between the two the interpretation of the data presented in this paper is that the genesis of shales phosphate and some carbonate beds excluding coquinas did not result from the deposition of initially sharply differentiated sediments but resulted from differences in diagenesis of sediments initially containing planktonic organic matter associated with clay and carbonate minerals

origin sequence stratigraphy and depositional environment of an upper ordovician hirnantian deglacial black shale jordan the upper ordovician succession of jordan was located 60 s less than 100 km from the hirnantian ice sheet margin new graptolite dates indicate glaciation ended in jordan in the late hirnantian persculptus biozone the succession records two glacial advances within the ammar formation and the subsequent deglaciations organic rich black shales batra formation form part of the final deglacial transgressive succession that in filled an existing low stand glacial continental shelf topography the base of the black shale is coincident with the maximum flooding surface during transgression interfluves and sub basin margins were breached and black shale deposition expanded rapidly across the region the top of the black shales coincides with peak highstand the expanding puddle model sensu wignall for black shale deposition adapted for the peri glacial setting provides the best explanation for this sequence of events we propose a hypothesis in which anoxic conditions were initiated beneath the halocline in a salinity stratified water column a fresher surface layer resulted from ice meltwater generated during early deglaciation during the initial stages of marine incursion nutrients in the monimolimnion were isolated from the euphotic zone by the halocline increasing total organic carbon toc and 13corg up section indicates the organic carbon content of the shales was controlled mainly by increasing bioproductivity in the mixolimnion the strakhov model mixolimnion nutrient levels were sustained by a continual and increasing supply of meltwater derived nutrients modulated by obliquity changes in high latitude insolation anoxia was sustained over tens to hundreds of thousands of years the formation of black shales on the north gondwana shelf was little different to those observed in modern black shale environments suggesting that it was the nature of the ordovician seas that pre disposed them to anoxia

variations in kerogen densities of sediments from the orinoco delta venezuela abstract a method employing the coulter counter technique was used in determining kerogen density for recent sediments of the orinoco delta these sediments contain essentially terrestrial humic organic matter and have kerogen densities ranging from 1 32 to 1 72 g ml 1 with an average of 1 48 g ml 1 a strong correlation was found to exist between kerogen density and offshore distance and depth in the orinoco delta kerogen density varies with offshore distance and depth decreasing consistently at the rates of 0 015 and 4 g ml 1 km 1 respectively the heavy kerogens are associated with shallow near shore areas while lighter kerogens are found in the deep offshore hence offshore distance and depth could be said to be a function of kerogen density

variation of east asian monsoon precipitation during the past 21 k y and potential co2 forcing paleoclimatic research can provide critical insight on causes of change in the east asian monsoon which influences the lives of 1 6 billion people today in this study we use paleoclimatic indexes from chinese loess deposits which have clear climatic implications and are independently dated to reconstruct the monsoon precipitation since 21 ka our results show that monsoon precipitation persistently decreased from 21 ka to ca 8 ka and increased after ca 8 ka with a precipitation peak at 8 3 ka these changes in east asian summer monsoon precipitation are synchronous with changes in high northern latitude ice volume ice cover and atmospheric co2 these new data suggest that variation of the monsoon precipitation was probably driven by co2 forced high northern latitude temperature changes shifting the location of the intertropical convergence zone that dominates monsoon precipitation our trace 21000 modeling experiment supports this interpretation

stromatolite reef crusts early cretaceous spain bacterial origin of in situ precipitated peloid microspar peloidal crusts are significant components of early cretaceous aptian reef carbonates in eastern spain the crusts form steep sided laminated deposits on coral and other skeletal surfaces their microfabric consists almost entirely of silt sized peloids in fenestral microspar matrix this microfabric contrasts with more poorly sorted and generally finer grained detrital wackestone packstone fabrics of the adjacent reef matrix scarcity of incorporated grains indicates that the crusts did not trap many particles it is proposed that the crusts are stromatolites and that peloids and inter peloid space were created concurrently by bacterial degradation of organic matter as they developed inter peloid voids were protected from infiltration of extraneous sediment by the organic rich exterior surface of the stromatolite even spacing of the peloids within microspar may reflect self organization of bacterial colonies in the decaying organic matrix compressed and partly amalgamated peloids marginal to burrows in the stromatolites suggest that the peloid fabrics were initially only partially lithified the grainstone like peloid fabric is therefore interpreted as having formed in situ by very early diagenetic processes driven by heterotrophic bacteria

pore water fluoride in peru continental margin sediments uptake from seawater abstract fluoride analyses display downward decreasing pore water gradients in peru shelf phosphatic muds that require diffusion from the overlying seawater into the sediment column and removal by reaction within the upper few tens of centimeters presumably by incorporation into carbonate fluorapatite the profiles can be modeled as first order f removal with rate constants of 3 yr 1 and asymptotic f concentrations deep in the cores of 35 45 m almost one half the seawater value the integrated flux of fluoride from seawater into organic rich shelf sediments in coastal upwelling zones phosphatic muds yields a contemporaneous global f burial of 0 54 10 10 mol f yr 1 about one fifth the burial in other sinks mostly carbonates and opal the associated burial flux of phosphorus in shelf phosphorites is about 1 6 10 10 mol p yr 1 comparable to p burial in the deep sea with organic matter 1 4 10 10 mol yr 1 and biogenic carbonates 1 4 10 10 mol yr 1 thus phosphorite formation on the peru shelf is a significant contemporaneous process

global and local controls influencing the deposition of the la luna formation cenomanian campanian western venezuela bulk and molecular geochemical micropalaeontological and carbon isotopic data are used to address the different local and global factors influencing the environment of sedimentation of the la luna formation cenomanian campanian approximate palaeolatitude 15 n in a single section in western venezuela based on the constructed chronostratigraphic framework oxygen depleted bottom water conditions and black shale deposition started in western venezuela well before the widespread occurrence of organic rich sediments in higher palaeolatitude regions such as the tethys and the north atlantic near or at the cenomanian turonian boundary in the la luna formation palaeoenvironmental conditions that allowed the preservation of organic matter mainly of marine origin prevailed until santonian times in a distal platform facies with very low siliciclastic input changes in lithology appear to reflect the local response to eustatic sea level variations and the presence of a migrating upwelling belt affecting the bioproductivity of silica and carbonate a marked 13corg isotopic excursion is recognised in the middle part of the section and is apparently unrelated to local palaeoenvironmental changes in bioproductivity and oxygen depletion biological marker data show no variations in association with the isotopic excursion being mainly controlled by local fluctuations in organic matter input and preservation

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

holocene climatic reconstructions from the fossil pollen record at qigai nuur in the southern mongolian plateau this study focuses on the reconstructions of vegetation and climate changes during the past 11 000 years on the basis of 222 fossil pollen samples from qigai nuur core qgn 2004 in the southern p

sedimentation distribution and diagenesis of organic matter in a recent carbonate environment abu dhabi u a e abstract in the modern hypersaline carbonate lagoon and sabkha sedimentary environments of abu dhabi united arab emirates three types of organic matter originate respectively from microbial mat avicennia mangrove and halodule lagoonal seagrass the study of recent sedimentary processes and cross sections through the sabkha sediments lead to the definition of organo sedimentary facies based on geochemical and sedimentological criteria this permits the construction of an organo sedimentary sequence which expresses the holocene sedimentary record involving a transgressive and a regressive sequence the various organic facies occur in both sequences heterogeneity within the individual organic facies reflects several factors including sedimentation dynamics mineral matrix oxidation and reduction and selective organic and mineral diagenesis these parameters are discussed in terms of depositional environment and location within the organo sedimentary sequence changes in distribution quantity and preservation potential of the buried organic matter are discussed in terms of sea level changes and sedimentary accretion rates

phosphorus speciation in the sediment and mass balance for the central region of the great barrier reef continental shelf australia abstract solid phase p speciation has been determined in sediments from a transect across the central section of the continental shelf and slope of the great barrier reef gbr lagoon this region is characterized by a gradient of riverine aluminosilicate clay and silt nearshore seawards of which biogenic carbonate sediment predominates phosphorus speciation results show large variations along this transect organic p and authigenic apatite p are the major chemical forms of phosphorus in the central gbr continental shelf sediments post depositional reorganization of p was also observed converting organic p and iron bound p fe p to authigenic apatite p phosphorus burial rate was estimated from measurements of total p concentration and excess 210pb sediment mass accumulation rates burial efficiency varies significantly over the shelf inshore areas showed significant p remobilization from sediments to the water column up to 50 the mid and the outer shelf showed little evidence for remobilization except for coral reef platform sediments with more of the sediment p being in the less reactive authigenic apatite phases an appreciable fraction of this non labile authigenic apatite phase was identified as fish bone p sources and sinks over the central part of the gbr shelf were quantified using a mass balance approach this showed that coral sea shelf edge upwelling events are essential to satisfy the large p nutrient demand of the whole gbr lagoon p inputs due to upwelling events were greater than those contributed by local rivers over an average year

quantitative reconstruction of holocene millennial scale precipitation in the asian monsoon margin of northwest china revealed by phytolith assemblages from calcareous root tubes in the tengger desert the spatio temporal characteristics and driving mechanisms of the asian summer monsoon asm during the early and middle holocene remain unclear moreover the timing of maximum monsoon precipitation in the asian monsoon margin of northwest china during this period is also a subject of considerable debate herein we analyzed phytolith assemblages within 55 calcareous root tube crt samples from the hinterland of the tengger desert to quantitatively reconstruct holocene millennial scale precipitation changes and discuss the potential forcing mechanisms our results revealed that the mean annual precipitation map was 138 53 to 149 18 mm during 10 0 7 0 cal kyr bp 179 26 to 192 26 mm during 7 0 5 0 cal kyr bp and 129 20 to 161 13 mm during 5 0 1 0 cal kyr bp the quantitative reconstruction results suggested that precipitation in this area was low in the early holocene then increased to a maximum in the middle holocene 30 higher precipitation than present and gradually decreased in the late holocene maximum monsoon precipitation did not occur until the middle holocene in this area because the northernmost margin of the asm reached its northernmost latitude lagging behind its maximum monsoon intensity suppressed by high northern latitude ice volume forcing during the early holocene despite high summer insolation in addition to quantifying the holocene millennial scale precipitation changes in the northwestern margin of the asm this study also provides new evidence for spatial and temporal variations of the asm during the holocene

micritized skeletal grains in northern belize lagoon a major source of mg calcite mud abstract lime mud in northern belize lagoon is composed predominantly of silt size cryptocrystalline grains and clay size clumps both of which consist of anhedral equant crystals less than 0 5 m in size this mud is 70 90 mg calcite containing 9 10 mole mgco3 detailed petrographic morphologic and mineralogic analyses suggest that the cryptocrystalline grains are micritized skeletal grains and that the mud formed by abrasion and bioerosion of these altered grains micritization of skeletal grains occurred primarily by recrystallization of original skeletal carbonate laths prisms and blades of mg calcite aragonite and calcite to equant crystals of micritic mg calcite with additional alteration by micritic infilling of microborings and skeletal cavities because of d fferences between crystal morphologies and mineralogies of original skeletal components and their micritized counterparts mud produced by diminution of micritized grains is distinct from that produced by skeletal breakdown the abundance of cryptocrystalline grains in the bahamas and other shallow carbonate environments suggests that micritized grains are potentially an important source of lime mud that has not previously been identified

using phytolith assemblages to reconstruct the origin and spread of grass dominated habitats in the great plains of north america during the late eocene to early miocene abstract this paper outlines a general approach for analyzing siliceous microfossils from plants phytoliths in geologic sediments and uses this method to reconstruct the evolution of grasslands in the central great plains during the late tertiary phytolith assemblage analysis is widely employed for reconstructing vegetation types in pleistocene holocene paleoecology and archaeology but no standardized methodology is currently available published phytolith studies are often system specific and tailored after specific modern analogues as a result they vary in extraction technique classification scheme and method of inference for ancient phytolith assemblages whose modern analogues are not well understood a more general analytic approach is necessary this analytic approach includes studying all size fractions 2 250 mm using a classification scheme based on the available literature and a comprehensive modern phytolith reference collection and comparing relative frequencies through time of all diagnostic phytoliths to interpret changes in habitat structure this general method was applied to late eocene to early miocene sediment samples from northwestern nebraska to deduce vegetation history and the results were compared to those obtained using a more specific technique stromberg paleogeogr paleoclimatol paleoecol 177 2002 59 in both studies phytoliths were extracted by means of heavy liquid separation from the following lithostratigraphic units 1 the late eocene chadron formation and the early oligocene brule formation white river group 2 the late oligocene early miocene monroe creek formation the early miocene harrison formation and anderson ranch formation arikaree group and 3 the early miocene runningwater formation and box butte formation ogallala group the two techniques general vs specific produced results that differ markedly data from the general approach indicate the presence of relatively closed habitats in late eocene to early oligocene typified by the presence of phytoliths from bambusoid grasses woody and herbaceous dicotyledons and palms the introduction and spread of modern open habitat grasses such as pooids arundinoids and panicoids occurred between the late oligocene and early miocene this resulted in a savanna or woodland type habitat by the early miocene in contrast analysis using the specific method suggested the presence of open habitats in northwestern nebraska from the late eocene onward the difference in interpretation based on the two approaches is principally due to inclusion of phytoliths 50 mm and the use of an expanded reference collection in the current study general analytic approach these results point to the importance of methodological choices in phytolith analysis and emphasize the usefulness of phytoliths as paleoecological indicators in the fossil record

anatomy and origin of a cretaceous phosphorite greensand giant egypt late cretaceous epicontinental phosphorites porcelanites cherts dark coloured shales glauconitic sandstones and bioclastic and fine grained carbonate rocks in egypt are examined in terms of their overall depositional and diagenetic framework and stable isotopic and organic geochemical characteristics two main depositional realms are interpreted and correlated through sequence stratigraphic analysis 1 a shallow hemipelagic environment accompanying initial stages of marine transgression and conducive to the formation of organic carbon rich shales biosiliceous sediments and thick phosphorites and 2 a relatively high energy depositional regime accompanying sea level fall during which deltas advanced glauconites were reworked seaward and prograding oyster banks became periodically exposed to episodes of fresh water diagenesis thereby promoting solution collapse phenomena in associated cherts lenticular to massive phosphorites are viewed as the result of current winnowing and concentration of authigenic grains initially precipitated in associated reducing shales and biosiliceous sediments in eastern egypt the phosphorites form winnowed lag layers some of which may have been redeposited down slope in structural lows in the west these sands were concentrated into giant phosphorite sand waves built by reworking of penecontemporaneously deposited phosphatic muds during marine transgression carbon isotopic results substantiate interpretations from modern deposits for limitation of phosphate mineral precipitation with depth in sediments as a result of lattice poisoning however direct desorption of phosphorus to pore waters from detrital iron oxyhydroxide phases also may have been important in the cretaceous setting the iron reduced in this process being available for incorporation in glauconites the main locus for authigenic glauconite precipitation appears to be where iron fluxes from regions of lateritic weathering were highest and near the boundary between oxygenated and reduced waters this study suggests a model for the common coexistence of glauconites and phosphorites in the geological record although upwelling is often advocated as the origin of nearly all giant phosphorite deposits we suggest that some of these may have been strongly influenced by fluvially derived phosphorus borne on particulates and desorbed from these compounds upon flocculation and or reduction in bottom waters or pore waters

organic matter preservation on the pakistan continental margin as revealed by biomarker geochemistry in order to assess whether the oxygen minimum zone omz in the arabian sea has an eaect on the preservation and composition of organic matter in surface sediments we investigated samples from three diaerent transects on the pakistan continental margin across the omz in addition to determining the total amount of organic carbon toc we analyzed the extractable lipids by gas chromatography combined gas chromatography mass spectrometry and compound specific stable carbon isotope measurements the extractable lipids are dominated by marine organic matter as indicated by the abundance of lipids typical of marine biota and by the bulk and molecular isotopic composition sediments from within the omz are enriched in organic carbon and in several extractable lipids i e phytol n alcohols total sterols n c35 alkane relative to stations above and below this zone other lipid concentrations such as those of total n fatty acids and total n alkanes fail to show any relation to the omz only a weak correlation of toc with mineral surface area was found in sediments deposited within the omz in contrast sediments from outside the omz do not show any relationship between toc and surface area among the extractable lipids only the n alkane concentration is highly correlated with surface area in sediments from the hab and makran transects in sediments from outside the omz the phytol and sterol concentrations are also weakly correlated with mineral surface area the depositional environment of the indus fan oaers the best conditions for an enhanced preservation of organic matter the omz together with the undisturbed sedimentation at moderate rates seems to be mainly responsible for the high toc values in this area overall the type of organic matter and its lability toward oxic degradation the mineral surface area the mineral composition and possibly the secondary productivity by sedimentary bacteria also appear to have an influence on organic matter accumulation and composition 2000 elsevier science ltd all rights reserved

grass habitat analysis and phytolith based quantitative reconstruction of asian monsoon climate change in the sand loess transitional zone northern china we investigated climate niches of grasses at regional scales and quantitatively reconstruct asian monsoon precipitation at the sand loess transitional zone in northern china our results provide direct evidence that certain grass lineages have been specialized in specific habitats pooideae grasses stand out and occupy a much cooler environment than all other subfamilies pooideae aristidoideae and chloridoieae occupy dry environments pooideae grasses occupy the coldest and driest environments compared to all other subfamilies with a mean annual temperature mat and precipitation map of 13 6 to 15 3 c and 224 to 1674 mm respectively at a regional scale we built a database for grasses and their corresponding climate parameters based on this database past climate parameters at the margin of the asian summer monsoon since 70 ka were quantitatively reconstructed by phytolith assemblages they show that this area was dominated by cold and dry adapted grasses since 70 ka with a mat and map of 3 3 to 11 0 c and 442 to 900 mm respectively generally consistent with the results of phytolith based transfer function reconstructions and with the results of previous nearby pollen based quantitative reconstructions with the improvement of the species climate and ecosystem dataset our database based method is a promising quantitative reconstruction approach to past climatic change in the monsoon region

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

role of upper cretaceous oyster bioherms in the deposition and accumulation of high grade phosphorites in central jordan abstract phosphorite grains were authigenically precipitated within precursor marl and biosiliceous deposits during high water level and intense upwelling within the tethys ocean to the north of jordan with falling sea level the oyster lopha villei colonized bathymetric highs in the shallow shelfal environments in east central jordan during the uppermost campanian lower maastrichtian late cretaceous the oyster bioherms in the epeiric southern shelf of the tethys formed small basins several hundreds of meters across and about 40 50 m deep under these lowstand conditions oyster shells were shed off the bioherms and deposited as large cross bedded units on the flanks of the basins at the same time precursor phosphatic sediments were reworked and winnowed to form high grade phosphorite sand more than 250 million metric tons 250 109 kilograms of phosphorite sand were deposited basinward of the oyster beds as sea level continued to fall the oyster bioherms formed partially silled basins with low biological diversity in which marl and or bituminous marl was deposited the marls are overlain by the transgressive phosphatic marl and chalk of the muwaggar formation which were deposited under open marine conditions

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

pollen based quantitative reconstruction of holocene climate changes in the daihai lake area inner mongolia china vegetation around the daihai lake northern china is very sensitive to climate changes in this paper pollen based quantitative climate reconstructions using three methods weighted averaging partial least squares method wapls modern analog technique mat and pollen response surface method prs were conducted to obtain robust reconstructions of holocene climate changes in the daihai lake area the result obtained by the three methods all consistently show the annual precipitation to have been 50 100 mm lower in the early holocene 100 200 mm higher in the mid holocene and 50 100 mm lower again in the late holocene than at present the wapls and the mat methods also show quasi synchronous oscillations of the mean annual temperature ta 18 28c lower in the early holocene and 18 38c higher in the midholocene than today the time period from 6200 to 5100 cal yr bp was the wettest and the warmest interval with an annual precipitation pa greater than 550 mm and mean annual temperature ta higher than 6 58c several cold and dry events can be identified to occur about 8200 6000 and 4400 cal yr bp with an annual precipitation less than 400 mm and a mean annual temperature colder than 4 58c respectively the mean temperature of the warmest month tw as reconstructed using both wapls and mat methods was relatively stable during the holocene fluctuating about 628c relative to the present level but the prs method suggests more varied tw values in both amplitude and frequency after 1500 cal yr bp no consistent pattern can be observed from these three different analyses probably because of the impact of intensified human disturbances on the natural vegetation the fluctuations of annual precipitation pa correspond to that observed in dongge cave in southern china the differences might be linked to indian monsoon and east asia monsoon climates or caused by the different degree of dating precision different temporal resolution and different sensitive response of climate proxies to the climate variations

aspects of depositional processes of organic matter in sedimentary basins abstract quantitative evaluation of source rocks is a prerequisite for assessing realistic petroleum potential in target basins such an evaluation includes information about the actual occurrence of organic rich beds their stratigraphic placement specific locations in sedimentary sequences lateral extension geometry at the scale of the basin and their organic facies variations richness and quality to achieve this evaluation current methods rely on analytical data alone for several years an attempt has been made to elaborate a predictive approach based on the integration of the various factors controlling the accumulation and distribution of organic matter in sedimentary basins in order to try to model the process the main effort has been devoted to the control of the production of biomass according to paleogeography and paleoclimatology and to the control of the degradation of organic matter according to the development of oxygen starved water bodies depositional processes which are certainly a key factor to understand the internal variations and the distribution of organic bearing sediments have been largely overlooked examples of modern environments e g black sea caspian sea lake bogoria show that the distribution of the organic matter in anoxic basins is generally organized in a concentric pattern with a centripetal increase of organic content towards the depocenters where the sediment thickness is the greatest such a feature which can be related to the hydrodynamic properties of the organic particles is of paramount importance as far as the distribution of petroleum potential is concerned this centripetal concept with its implications for source rocks evaluation is well exemplified in the lower jurassic of the north sea and in the lias of the paris basin however this pattern can be strongly affected in anoxic basins when extensive gravity transport mechanisms cause redeposition of sediments in such a situation sediments including their specific organic contents are redistributed along transit pathways in lake tanganyika these modes of transport drive a significant amount of altered organic matter towards the deepest parts of the basin resulting in a marked lateral heterogeneity of the organic facies in the bottom sediments similar processes might contribute to the complex pattern of the distribution of organic facies seen in the upper jurassic of the north sea on the other hand gravity flows can introduce organic rich sediments into basins where environmental conditions would otherwise have been unfavorable for organic accumulation a dramatic example of such a situation is provided by the several hundred metres thick sequence of organic rich turbidites and debris flows deposited since the late miocene at the base of the continental slope off south west africa

peloidal fabrics in upper jurassic reefal limestones weald basin southern england abstract coraliferous limestones from the corallian group upper jurassic of subsurface of the weald basin southern england record the localized development of superimposed patch reefs and banks the reefal limestones exhibit a variety of peloidal fabrics in particular well sorted peloids 10 60 m in diameter with a well developed euhedral rim of fibrous sparry calcite around a micritic anhedral nucleus they occur in confined intraskeletal pores corals molluscs and borings growth cavities between framebuilders and as stromatolitic crusts the peloids in interskeletal cavities and as crusts resemble microbial precipitates and merge into spongiostromate fabrics the distribution of these peloidal fabrics seems to be facies related and is best developed in zones which had relatively low framework growth rates low sedimentation rates and moderate energy levels the peloids are identical in form and occurrence to those in some ancient and quaternary reefs the association of the peloids with stromatolitic coatings and spongiostromate fabrics leads us to interpret the peloids as microbial precipitates either by direct precipitation or by induction the abundance of microbial carbonate in these reefal limestones places them in an intermediate category between frame built reefs and microbial mud mounds

biomineralization and global biogeochemical cycles biological activity is a dominant force shaping the chemical structure and evolution of the earth surface environment the presence of an oxygenated atmosphere hydrosphere surrounding an otherwise highly reducing solid earth is the most striking consequence of the rise of life on earth biological evolution and the functioning of ecosystems in turn are to a large degree conditioned by geophysical and geological processes understanding the interactions between organisms and their abiotic environment and the resulting coupled evolution of the biosphere and geosphere is a central theme of research in biogeology biogeochemists contribute to this understanding by studying the transformations and transport of chemical substrates and products of biological activity in the environment biogeochemical cycles provide a general framework in which geochemists organize their knowledge and interpret their data the cycle of a given element or substance maps out the rates of transformation in and transport fluxes between adjoining environmental reservoirs the temporal and spatial scales of interest dictate the selection of reservoirs and processes included in the cycle typically the need for a detailed representation of biological process rates and ecosystem structure decreases as the spatial and temporal time scales considered increase much progress has been made in the development of global scale models of biogeochemical cycles although these models are based on fairly simple representations of the biosphere and hydrosphere they account for the large scale changes in the composition redox state and biological productivity of the earth surface environment that have occurred over geological time since the cambrian explosion mineralized body parts have been secreted in large quantities by biota because calcium carbonate silica and calcium phosphate are the main mineral phases constituting these hard parts biomineralization plays an important role in the global biogeochemical cycles of carbon calcium silicon and phosphorus the chapter starts with introducing the basic concepts of

upper cretaceous campanian phosphorites in jordan implications for the formation of a south tethyan phosphorite giant a record of sedimentary authigenic and biological processes are preserved within the upper cretaceous campanian alhisa phosphorite formation ap in central and northern jordan the ap formed near the eastern extremity of the south tethyan phosphorite province stpp a carbonate dominated upper cretaceous to eocene phosphorite giant that extends from colombia north africa to the middle east multidisciplinary research of the ap and associated cherts chalks and oyster buildups indicate that phosphatic strata formed on a highly productive storm dominated east west trending epeiric platform along the south tethyan margin the onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the ajlun group pristine phosphates are associated with well developed micrite concretionary horizons and contain abundant non keeled spiral planktic foraminifera and a low diversity benthic assemblage of buliminacean foraminifera suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter the bulk sediment composition and absence of fe bearing authigenic phases such as glauconite pyrite including pyrite molds siderite and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that iron pumping played a minimal role in phosphogenesis authigenic precipitation of phosphate occurred in a broad array of sedimentary environments herein termed a phosphorite nursery that spanned the entire platform this is a non uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings wherever the conditions were suitable for phosphogenesis sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing and storm generated shelf parallel geostrophic currents economic phosphorites formed through the amalgamation of storm induced event beds stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite syndepositional phosphogenesis reworking and amalgamation to form phosphorites contrasts sharply with the principles of baturin cycling a transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis storm reworking of pristine

the influence of paleo bathymetry on total organic carbon distribution tested in the cretaceous hammerfest basin barents sea abstract in basin modelling and petroleum system analysis geometries during deposition of sediments paleo water depth and distribution of organic matter are initial parameters used for further interpretation or modelling this paper presents an approach combining backstripping with a probabilistic forward sedimentary model to calibrate paleo water depth pwd the stochastic pwd results serve as an input for organic facies models and the study demonstrates how pwd will influence models for total organic carbon distribution in a sedimentary basin for the early cretaceous hammerfest basin mainly shelfal to upper bathyal bathymetries average pwd values vary between 118 and 318 m result in average total organic carbon toc varying between 0 47 and 5 24 wt across the basin for the different models basin averaged toc values are similar but vertical and lateral distribution pattern change significantly especially towards the shallow end member pwd the results indicate that pwd uncertainties propagate non linearly into source rock distributions

organic microfacies and basinal tectonic control on source rock accumulation a microscopic approach with examples from an intracratonic and extensional basin abstract relationships among organic petrographic maceral assemblages and hydrocarbon source rock depositional environments distinguish broad marine terrestrial and mixed kerogen accumulation settings organic microfacies from paleozoic and mesozoic source rock intervals in the intracratonic williston basin and the extensional sverdrup basin have been studied using incident white and fluorescent light microscopy distinct anoxic organic microfacies are defined in upper ordovician bighorn group subtidal platformal kukersites and middle devonian upper elk point group carbonate lithologies that preserve a progression of depositional environments from platformal to starved basinal paleozoic carbonate platform microfacies are characterized by well preserved cyanophyceae alginite stromatolitic mats displaying upper surface textural features such as pustules pinnacles endolithic algal borings and interlaminated vertical and horizontal alginite resulting from phototactic growth potential source intervals in middle and upper triassic shelf shales from the sverdrup basin and middle devonian carbonate platform marginal mudstones in the williston basin are both characterized by high concentrations of sapropelic bituminite kerogen hosting unicellular marine alginite similar bituminite rich organic microfacies occur in middle devonian basinal settings associated with larger more abundant alginite and significant amounts of dasycladacean calcareous algae the main controls on source rock accumulation are water depth and chemistry as controlled by depositional setting and basin restriction

paleoenvironmental significance of the monospecific biostromes in the campanian maastrichtian duwi formation eastern desert egypt abstract the campanian maastrichtian duwi formation in the eastern desert of egypt is an economic rich part of the middle east phosphorite belt which has been formed during an extensive high productivity and anoxic episode in the southern tethys to understand the consequences of these environmental conditions on the paleo ecosystems the sediments and the benthic macrofauna was analyzed although the macrobenthic elements are poorly represented throughout the studied sections four monospecific biostromes were recognized they included two ambigostrea oyster biostromes which have developed under high energy and fully aerated environments above the storm wave base in contrast the heterodont bivalves integricardium and aphrodina biostromes were deposited under mesotrophic low energy and dysoxic regimes shell orientation shell size frequency and multivariate analysis of other taphonomic features indicated that one of two ambigostra biostromes were partially generated by waves and or storms i e parabiostromes while the other one is mostly in situ i e autoparabiostromes in contrast the heterodont biostromes are intrinsic autochthonous concentrations autobiostromes the link between occurrences of biostromes and cyclicity of deposits suggests a clear association to sea level fluctuations the autobiostromes dominating the maximum flooding and early highstand intervals and were differentiated from the parabiostromes which formed by physical instead of biologic agents during initial transgressions or late highstand the palaeo ecosystem was reconstructed and the environmental factors behind the biostromes were identified the monospecific nature of the biostromes is interpreted to be a consequence of high stress environment e g high productivity and associated anoxia the global climate during the campanian maastrichtian sea level fluctuations and physiography influenced salinity and oxygen levels and played the pivotal role in the formation of the monospecific biostromes of the duwi formation

calculation of petroleum masses generated and expelled from source rocks abstract an algebraic scheme for calculating the masses of petroleum formed in mature source rocks has been constructed the scheme exploits routine geochemical measurements and a basic understanding of the behaviour of sedimentary organic matter at elevated temperatures under both laboratory and subsurface conditions application of these techniques to data from a wide range of source rock types has led to the following general conclusions 1 1 major oil and gas generation from kerogen occurs between 120 and 150 c in the subsurface gas generation continues to temperatures 160 c 2 2 oil prone source rocks with average initial potential 5 kgt 1 of rock and average organic carbon contents 1 5 expel 60 90 of the total oil generated 3 3 oil expulsion from leaner source rocks is less efficient most of the oil generated remains in the source rock it is subsequently converted to lighter components at higher temperatures and expelled in the vapour state 4 4 the major loss of organic carbon from rich oil prone source rocks during generation and expulsion means that the petroleum potential and organic carbon content of mature source rocks are much less than their initial immature values hence the algebraic scheme must be used to calculate the initial values before expelled petroleum masses can be determined