early diagenesis of terrigenous triterpenoids and its implications for petroleum geochemistry abstract the distribution of triterpanes in sediments and crude oils is commonly used for oil oil and oil source rock correlation in petroleum geochemistry while isomer ratios of such compounds are applied as maturity parameters the triterpane pattern in terrestrially influenced geological samples is however remarkably less diverse than the triterpenoid skeletons occurring in the extant higher plant biosphere natural observations laboratory experiments and molecular mechanics calculations have revealed that acid catalysed double bond isomerization and skeletal rearrangement reactions of terrigenous triterpenoids during early diagenesis are the key to understanding the triterpane patterns in more matured geological materials examples studied in detail are the double bond isomerization of oleanenes and the subsequent hydrogenation of the products into oleanane and 18 oleanane and the transformation of taraxer 14 ene and lup 20 29 ene into oleanenes although the reactions are likely to be kinetically controlled the main products formed and ultimately preserved are the thermodynamically most stable ones the experimental results and natural observations have significant implications for the use of terrigenous triterpenoid compounds in petroleum geochemistry

biomarkers as proxies for plant inputs to peats an example from a sub boreal ombrotrophic bog lipid distributions in modern peat forming plants were determined and compared to biomarkers recovered from a ca 2800 year old peat deposited in a dutch ombrotrophic bog the peat section spans a well constrained shift in local hydrology and vegetation and potential molecular proxies for plant inputs were directly tested against the macrofossil record based on the analyses of modern plants low molecular weight lmw n alkanes c23 c25 and high molecular weight n alkanes c33 are proposed as potential biomarkers for sphagnum and non sphagnum inputs respectively consistent with this in the bargerveen peat core lmw n alkane abundances increase and hmw n alkane abundances decrease coincident with the shift to sphagnum dominated peat additional potential proxies include the abundances of c22 alkanedioic acid and phytenyl phytenoate as sphagnum indicators and the abundances of the triterpenoids taraxer 14 ene and taraxast 20 ene as biomarkers for ericaceae rootlets

a thermo chemical regime in the upper mantle in the early earth inferred from a numerical model of magma migration in a convecting upper mantle abstract a numerical model of mantle magmatism in a convecting upper mantle has been developed to study the thermo chemical evolution of the upper mantle of the early earth the solid state convection in the upper mantle is modeled by a convection of a binary eutectic material with a newtonian temperature dependent rheology in a two dimensional rectangular box placed on a heat bath as a model of the lower mantle the density depends on the chemical composition and melt content as well as temperature of the material the material contains heat producing elements that are incompatible and exponentially decay with time mantle magmatism is modeled by a permeable flow of melt generated by a pressure release melting induced by the solid state convection through matrix the permeable flow is driven by a buoyancy due to the density difference between the melt and the matrix the thermo chemical evolution in the box occurs in two stages if the deeper part of the box is not so strongly depleted in heat producing elements in spite of the upward migration and concentration of heat producing elements into a crustal layer along the top surface boundary due to magmatism in the earlier stage active magmatism occurs because of a strong internal heating due to the heat producing elements a chemically stratified structure develops well in the box with dense magmatic products in the deeper part and less dense residual materials in the shallower part and the temperature distribution becomes strongly superadiabatic over the entire box the temperature at the base of the box becomes as high as the solidus temperature the chemically stratified structure is however suddenly destroyed by convective mixing and the temperature in the deeper part of the box suddenly drops by several hundred degrees when the internal heat source becomes too weak owing to the decay of heat producing elements which sustain the active magmatism and hence keep the effect of chemical differentiation due to the magmatism stronger than the effect of convective mixing in the later stage of the evolution the box becomes chemically homogeneous and magmatism occurs only mildly if heat producing elements are efficiently transported into the crustal layer and the deeper part of the box becomes strongly depleted in heat producing elements owing to the magmatism only a mild magmatism occurs even at the beginning a chemically stratified structure does not develop well and the temperature in the box rapidly decreases to a stationary value the regime of hot and chemically stratified upper mantle suggested from the earlier stage of the case with mild depletion of heat producing elements at depth fits in with many observations of the archean continental crust

the diagenetic fate of taraxer 14 ene and oleanene isomers abstract the extractable organic matter in holocene to early miocene deep sea sediments from site 645 odp leg 105 in baffin bay contains almost exclusively biological markers of terrigenous origin pentacyclic triterpenoids of the ursene and amyrin oleanene type often occur as the most abundant compounds in the aliphatic hydrocarbon ketone and alcohol fractions of the sediment extract a specific diagenetic reaction involves the conversion of taraxer 14 ene into olean 12 ene in the upper 700 metres of the sedimentary sequence the taraxerene to oleanene conversion is complete before the onset of isomerisation of diasterenes at c 20 in the sediment as well as in laboratory simulation experiments olean 12 ene further isomerises to olean 13 18 ene and olean 18 ene the latter of which may be the direct precursor of 18 h and 18 h oleanane found in sediments containing more mature organic matter and in crude oils the subsurface interconversion of these triterpenoid skeletons indicate that oleanane does not necessarily start life as an oleanoid

models for the archean thermal regime a variety of different regionalized thermal evolution models are presented all models include an oceanic style of heat loss in which mantle convection penetrates to the surface in the form of spreading and subducting plates in continental regions the lithosphere is assumed to act as a conductive lid on mantle convection that can be either layered or mantle wide the continental lithosphere is defined in different ways it can be of fixed thickness insensitive to temperature or extend to some fixed cutoff temperature a thermally controlled rheological lithosphere when a fixed temperature is used widespread melting occurs in the archean and one has the further option of allowing these melts to erupt onto the surface thus providing a new heat transfer mechanism and also a general subsidence of the continental lithosphere due to the continuous volcanic loading the models are first used to determine the concentration of heat producing elements required to have a present day mantle potential temperature of 1350 c starting from a high temperature 2000 c 4 5 billion years ago the results depend primarily on whether the mantle is layered if layered 15 30 ppb uranium normalized to the silicate portion of the earth and withk u 104 th u 3 8 are needed while mantle wide cases need uranium concentrations in excess of 35 ppb the models are also used to calculate the thermal structure of continental lithosphere through time only lithospheres of fixed thickness 175 km can explain the recent discovery of diamonds with model ages of 3 2 3 4 billion years for a thick lithosphere to have existed in the archean it would seem most likely that its thickness be the result of some chemical distinction rather than simply its rheological properties such chemically distinct lithosphere would have greater likelihood of surviving to the present which raises the issue of biased preservation

numerical experiments on coupled magmatism mantle convection system implications for mantle evolution and archean continental crusts numerical experiments on the simple models of coupled mantle magmatism mantle convection system were made to study the thermal and chemical evolution of the earth s mantle mantle convection is modeled by the convection of a two component newtonian constant viscosity fluid in an internally heated two dimensional rectangular region the density of the convecting fluid is assumed to depend on its chemical composition as well as its temperature the two components of the convecting fluid are assumed to constitute an eutectic system mantle magmatism i e magma segregation in the mantle is modeled by differentiation of the eutectic mixture from the convecting fluid this chemical differentiation is assumed to occur when the temperature t increases to the solidus temperature ts assumed to increase linearly with depth owing to convective heat transport taking into account the change in density distribution due to this chemical differentiation we solve the basic equations for convection numerically as an initial value problem we find that how the mantle evolves depends strongly on two quantities h internal heating rate and r m e m is the density of undifferentiated mantle material at 0 c e is the density of the eutectic mixture at 0 c and 0 is a measure of density change in the mantle due to thermal expansion r represents the magnitude of the dependence of density on chemical composition 1 when 4 r 2 and h hc tav increases with time while q continues to be nearly constant magmatism occurs to produce a residue which occupies the uppermost part of mantle throughout the evolutionary history of the mantle 3 when 1 1 and h hc tav increases with time while q decreases with time mantle magmatism occurs to produce a residue which accumulates at the bottom of mantle throughout the evolutionary history of the mantle we also find that mantle magmatism occurs episodically when r 1 and r 2 while mantle magmatism occurs continuously when 1 r 1 from an estimate of r appropriate for the earth s mantle and known features of the archean continental crusts we conclude that the type 1 mantle evolution occurs beneath the continental crusts many features of the archean continental crusts fit in with the framework of the type 1 mantle evolution

the structure of the kythira antikythira strait offshore sw greece 35 7 36 6 n the kythira antikythira strait within the sw hellenic arc forms a 100 km long nnw sse trending ridge between peloponnesus and crete and represents the submarine continu ation of the hellenic alpine belt in order to present the shallow as well as the deeper structure of kythira antikythira strait we studied five seismic sections oriented either parallel or perpendicu lar to the inner part of the hellenic arc this information was complemented with velocity analyses from a dense network of seismic lines and information concerning the bathymetry contractional structures recognized on the seismic profiles indicate that this part of the gavrovo tripolitza geo tectonic zone was involved in the miocene shortening related to the westward propagation of the hellenic fold and thrust system east dipping thrust faults which root in the top of the crystalline basement were identified on the seismic profiles the deepest reflector identified on the profiles cor responds to the crystalline basement shallower reflectors include those corresponding to the con tacts between the mesozoic miocene upper miocene lower pliocene and pliocene pleistocene sedimentary sequences the upper cenozoic to quaternary sequence rests unconformably upon mesozoic carbonates messinian intrusions forming small scale domes deform the pliocene quaternary sedimentary succession west and east dipping normal faults were also recognised both within the palaeozoic and cenozoic successions and are related to regional extension during sedimentation

molecular characterization of fossil and extant dammar resin extracts insights into diagenetic fate of sesqui and triterpenoids abstract the composition of sesquiterpenoids and triterpenoids in the solvent extract of extant miocene and eocene dammar i e class ii resins has been determined and compared to investigate the vulnerability of these biomarkers to diagenesis molecular evidence e g absence of bicadinanes and low rock eval maturity values tmax

molecular characterisation of soil surface horizons with different vegetation in the vosges massif france the total lipid extracts tles from a series of 13 soil surface samples from sites covered by a stable vegetation for at least 150 years and located in the vosges massif france have been investigated in order to establish a molecular reference for soil surface horizons the tles are dominated by plant n alkyl lipids with distributions homologue predominance clearly discriminant with regard to the vegetation cover higher plant terpenoids present in varying relative abundances allow distinction between soils from grassland and oak fir and beech forests to be made furthermore the occurrence of some specific terpenoids seems to be restricted to a particular vegetation cover so they may therefore be used as diagnostic markers for tracing back past vegetation in ancient soils

biomarkers of holocene buried conifer logs from bella coola and north vancouver british columbia canada abstract the biomarker compositions of a holocene seep oil liquefied resin originating from a buried log of douglas fir pseudotsuga menziesii from bella coola bc canada and a holocene pine wood pinus sp sample from north vancouver bc canada were analyzed using gas chromatography mass spectrometry gc ms the total extract of the bella coola sample contains the sesquiterpenoid derivative calamenene and diterpenoids of the labdane abietane pimarane and phyllocladane classes a novel series of successively degraded labdane derivatives labdan 15 oic acid norlabdanoic acids drimenoic acid was detected in the polar fraction and a diagenetic pathway is proposed aromatic abietanes are the major components in the neutral fraction the neutral fraction of the pine wood contains two sesquiterpenoids calamenene cadalene diterpenoids of the abietane pimarane isopimarane and kaurane classes and a series of steroids 18 norabieta 8 11 13 triene dehydroabietin is the major component among the predominantly aromatic abietanes based on the compositions of the terpenoids it is concluded that the diagenesis of the pine and douglas fir logs probably occurred under anaerobic conditions leading to reductive reactions such as decarboxylation of resin acids with concurrent oxidation reactions to form the aromatic derivatives

cooling of the earth in the archaean consequences of pressure release melting in a hotter mantle a model is presented to describe the cooling of the earth in the archaean at the higher archaean mantle temperatures pressure release melting starts deeper and generates a thicker basaltic or komatiitic crust and depleted harzburgite layer compared with the present day situation intrinsic compositional stability and lack of mechanical coherency renders the mechanism of plate tectonics ineffective it is proposed that the archaean continents stabilised early on top of a compositionally stratified root in the archaean oceanic lithosphere hydrated upper crust can founder and recycle through its high pressure phase eclogite eclogite remelting and new pressure release melting generates new crustal material migration of magma and latent heat release by solidification at the surface provides an efficient mechanism to cool the mantle by several hundreds of degrees during the archaean this can satisfactorily explain the occurrence of high extrusion temperature komatiites and lower extrusion temperature basalts in greenstone belts as being derived from the same source by different mechanisms

terpenoids in surface soils from different ecosystems on the tibetan plateau abstract realizing the potential of terpenoid biomarkers as an unequivocal land ecosystem and floral diversity indicator calls for work to establish a direct link between the terpenoids extracted from the plants and those found in the underlying soils to this end we have characterized the triterpenoid profile of soils and vegetation along two altitudinal transects representing very different ecosystems the first transect comprising 31 sample sites was on the eastern slopes of mt gongga eastern tibetan plateau rising from 1230 m to 4500 m above sea level an area with a temperate monsoonal climate the second transect sampling 29 sites was on the northern slopes of mt west kunlun a region characterized by montane desert meadow and alpine steppe located between 1300 m and 5050 m above sea level the dominant terpenoid biomarkers polycyclic triterpenoids of the taraxerane oleanane friedelane ursane lupane glutinane and lanostane series identified in the soils were found to be consistent with the overlying vegetation however the discovery of some unusual triterpenoids including the pentacyclic triterpene 3 methyl ethers ptmes d a friedo 2 3 secoolean 2 3 dioic acid methyl 3 acetoxylup 20 29 en 28 oate 24 methylenecycloartan 3 one 9 19 cyclolanostan 3 yl 24 methylene acetate 3 methoxy 9 lanosta 7 24 dien 26 23 olide and 3 methoxy 9 lanost 7 en 26 23 olide in the gongga soils does not match the current vegetation and may be indicative of a long vanished forest type vegetation thus soil biomarkers may be a useful tool in the reconstruction of palaeo vegetation

carbon isotope evidence for sedimentary miliacin as a tracer of panicum miliaceum broomcorn millet in the sediments of lake le bourget french alps abstract we report the determination of the carbon isotopic composition of miliacin olean 18 en 3 ol methyl ether extracted from the sediments of lake le bourget french alps it is compared with the 13 c value of miliacin extracted from panicum miliaceum broomcorn millet a c 4 plant and chionochloa sp a c 3 plant the 13 c value of sedimentary miliacin 21 5 is very close to that of miliacin extracted from bran 23 and seeds 23 5 of p miliaceum and significantly different from that of chionochloa sp 33 these results provide additional support for the use of sedimentary miliacin as a tracer of broomcorn millet a c 4 cereal cultivated since the bronze age around lake le bourget these findings illustrate the potential of this compound to reconstruct past agriculture from lake sediment archives finally considering the high abundance of miliacin in the bran of p miliaceum the compound could have been wind transported to the sediment during threshing and winnowing on the lake shore

archean komatiites and geotherms solution to an apparent contradiction the high liquidus temperatures of archean komatiites and the low geothermal gradients in archean continents appear to give contradictory indications of temperatures in the archean mantle we resolve this contradiction in terms of an idealized model of convection in the archean mantle we suggest that temperatures in the archean mantle were no more than 100 c higher than at present that komatiites originate from the hot lower boundary layer of a non steady convection cell and that archean continents were formed near subduction zones where near surface temperature gradients were lower than elsewhere in the convecting mantle

stable isotopic variations in west china a consideration of moisture sources 1 in this study individual precipitation samples collected over 2 years at stations in different climatic regions of west china tibetan plateau region tianshan region and altay were analyzed for the stable isotopes of precipitation to improve our understanding of how vapor transport impacts the modern stable isotopic distribution our results identify regional patterns in both 18o and deuterium excess d excess defined as d 8 18o and in particular we have identified the northward maximum extent of the southwest monsoon over the tibetan plateau this demarcation is also the boundary for the fractionation effect of temperature on stable isotopes in precipitation the patterns we have identified are as follows 1 in the southern tibetan plateau along the southern slope of the himalayas our results show a distinct seasonality for both 18o and d excess as a result of the shift of summer monsoon moisture and winter westerly moisture transport the signals of 18o in the western tibetan plateau reveal that the region receives southwest monsoonal moisture in the east of the plateau stable isotopic variation shows alternation between monsoon intrusion and recycling of northern moisture 2 in contrast in tianshan there is an apparent temperature effect in 18o with enriched values occurring in summer and depleted values occurring in winter seasonal d excess values opposite to those observed in the southern tibetan plateau are controlled by differing seasonal evaporation conditions 3 in altay the most northern mountain region the seasonal 18o shows the same variation with that in tianshan region however d excess shows no apparent seasonal variation

saturated and olefinic terrigenous triterpenoid hydrocarbons in a biodegraded tertiary oil of northeast alaska abstract dinorlupanes norlupanes olean 12 ene 18 olean 12 ene and urs 12 ene occur in a heavily biodegraded tertiary oil tested from the ocs y 0849 1 well drilled on the hammerhead prospect in the beaufort sea offshore northeast alaska these indicators and other source related characteristics of the hammerhead oil ring a degraded oleanoids ursanoids and lupanoids v and ni less than 2 0 ppm v v ni less than 0 5 indicate a land plant angiospermous character in the source facies the olefins in the hammerhead and canadian oils are considered to be contributed directly from the source rather than extracted from adjacent immature non source sediments during migration as indicated by a the accompanying presence in the oil of saturated angiosperm markers and b the absence of measurable amounts of other olefins characteristic of immature organic matter e g diasterenes and hopenes

evolution of the archean continental crust some 20 years of plate tectonic theory combined with new insights into the fine structure of the lithosphere the application of multielement geo chemical and isotopic studies paleomagnetism and geophysical modeling of mantle processes have profoundly influenced present thinking on the origin and evolution of the earth s early continental crust previously our knowledge of the continental crust was based almost exclusively on field geological observations although there is now general agreement on how the earth worked for the last 200 m y because of observable evidence in the oceans and continents e g bird 1980 condie 1982 it has proved difficult to extend this history into more ancient times in view of the lost oceanic record and the ambiguity and complexity of the pre mesozoic rock relationships in the continents dewey 1982 however preserved characteristic rock as semblages uniquely identifying modern type wilson cycle processes i e opening and closure of oceans underlain by oceanic crust have now been recognized in continental terranes as old as 900 m y and these assemblages provide strong evidence for the conclusion that the present global tectonic regime has governed the evolution of the lithosphere at least since the late precambrian kroner 1977 1981a b goodwin 1981 profound disagreement on the older crustal history however prevails to the present day since typical features characterizing phanerozoic accretionary terranes such as obducted ophiolites blueschists and franciscan type melanges have not been found in more ancient regions thus two types of evolutionary models have been developed one type postulates uniformitarian development back to the earliest archean burke

conifer and angiosperm biomarkers in clay sediments and fossil plants from the miocene clarkia formation idaho usa the aliphatic lipids and terpenoids of conifer and angiosperm macrofossils and the clay sediment from a new site p 37 of the miocene clarkia formation idaho usa were analyzed to evaluate the preservation of characteristic conifer and angiosperm biomarkers in the sediment series of aliphatic lipids terpenoids and steroids similar to the biomarkers found in type locality clarkia p 33 were the predominant compounds in the sediment and in the fossils long chain aliphatic lipids were major compounds in the fossil plants and the sediment but a differentiation of angiosperm and conifer sources is not possible due to their common distribution among all vascular plants in addition to previously reported terpenoids diterpenoids of a conifer origin and several angiosperm derived polar triterpenoids of the oleanane lupane ursane and friedelane classes are reported here for the first time from the clarkia sediments the conifer shoots taxodium glyptostrobus calocedrus contained characteristic conifer biomarkers such as abietane type diterpenoids while characteristic angiosperm triterpenoids were predominant in the angiosperm leaves betula quercus lithocarpus the biomarker compositions of the taxodium and glyptostrobus shoots match the terpenoid patterns previously reported from fossil seed cones of the same genera although conifer macrofossils contribute about 45 to the flora of site p 37 characteristic conifer biomarkers occurred in the sediment in only low amounts while the angiosperm derived triterpenoids were present in comparatively higher abundances the results indicate that the conifers are under represented compared to the angiosperms according to the terpenoid composition of the sediment extract this may be due to the presence of small angiosperm derived particles leaf detritus wax in the sediment and or migration of leaf waxes from the angiosperm leaves into the sediment in contrast the diterpenoids are trapped in the resinous woody tissue of the conifers and are thus disseminated less into the sediment

effect of precipitation regime on δ d values of soil n alkanes from elevation gradients implications for the study of paleo elevation we measured dd values of long chain n alkanes isolated from 30 surface soil samples along two elevation transects on the tibetan plateau differing in precipitation regime and water source the east asian monsoon precipitation dominates the wetter regime on the eastern slope from 1230 to 4300 m of gongga shan on the eastern tibetan plateau precipitation from the polar westerlies dominates the drier region on the slope from 1900 to 5000 m in the west kunlun shan on the northwestern tibetan plateau the decrease in dd value with elevation in the wetter region greatly exceeded that in drier region by 1 9 0 1 100 m and 1 4 1 0 100 m respectively the apparent fractionation between leaf wax and precipitation ewax p values in the wetter region ca 164 were more negative than those in drier region ca 125 above 3200 m we also measured dd values in leaves of six common living trees values from 287 to 193 from gongga shan ranging from about 2900 4200 m the abundance weighted average values of the nalkanes ddwax show a strong reverse correlation with sample source elevation r 2 0 78 for soils from 2 0 85 for soils from west kunlun shan above 3200 m suggesting that n alkane ddwax faithfully records the precipitation dd and that the isotopic altitude effect of precipitation controls ddwax altitudinal gradients in the mountains the data show a fairly strong monotonic dependency of n alkane dd values on elevation for the eastern plateau but a complex relationship between n alkane dd values and elevation for the northwestern plateau the ddwax values at sites below 3200 m from the kunlun shan area exhibit an unexpected positive correlation with elevation the study confirms the potential for using sediment ddwax values to reconstruct paleo elevation in wetter regions but suggests caution in applying the approach to dry regions our results also show it is essential to consider the intricacy of the pattern of atmospheric circulation and water sources and their influence on the lapse rate of dd values with elevation

oxygenated spiro triterpenoids possibly related to arborenes in sediments of a tropical freshwater lake abstract three novel 3 oxygenated cd spiro triterpenoids were tentatively identified as 13 15 spiro arbor 9 11 en 3 one 3 methoxy 13 15 spiro arbor 9 11 ene and 13 15 spiro arbor 9 11 en 3 ol in solvent extracts of sediments from lake valencia their proposed origin from higher plants is based on structural precursor product relationships and characteristics of the age distributions since the latest pleistocene

tomography the geoid and plate motions the dynamics of the earth s mantle and its relationship to mantle structure as revealed by seismic tomography the geoid and plate motions are discussed in a critical review of u s research from the period 1987 1990 sections are devoted to plates and mantle convection seismic anomalies flow and the geoid subducted slabs and the 670 km discontinuity the physical properties of the mantle plumes and computational and experimental modeling efforts also included is a comprehensive bibliography for the period 248 refs

convective mixing and the fine structure of mantle heterogeneity a simple theoretical model is presented for the statistical distribution of small scale passive heterogeneity in a convecting mantle the important new variables used to characterize the anomaly field are the autocorrelation function r and its fourier transform the energy spectrum e the anomaly variance the sample variance i e the anomaly variance as filtered by the sampling process and the mixing time scale are expressed in terms of e equations governing the time evolution of r and e are derived starting with the transport diffusion equation the energy spectrum equation is solved for deformation models with homogeneous normal and shear strain components the predictions from these models are compared with results of numerical experiments on mixing of slab shaped heterogeneities by benard convection both the numerical experiments and the theory indicate that compositional heterogeneity subjected to convective flow becomes drawn into thin sheets oriented subparallel to the transport direction re mixing of subducted slabs produces a laminated mantle the energy spectrum of the laminate is highly anisotropic where the transport direction is predominantly horizontal the energy at high wave numbers is in the vertical the low wave number energy is in the horizontal plane the shape of the energy spectrum contains information on mean mantle strain rates age of the anomalies and solid state diffusion rates

melt segregation from partially molten source regions the importance of melt density and source region size the compressibility of basic melt at 1 atmosphere is about an order of magnitude higher than that of mantle minerals consequently the density contrast between melt and the principal residual crystals in mantle source regions is expected to decrease with increasing source region depth the increasingly olivine normative character of primary melts produced at greater depths is also expected to result in a decrease in this density contrast with increasing source region depth once vertical permeability is established by melt generated during partial melting buoyancy driven melt percolation can under some circumstances segregate melt from the residual crystals in its source region on a geologically rapid time scale limits to this process are provided by cooling of the source region freezing melt in and rigidity of the crystalline matrix mechanically trapping melt source region size influences these limits strongly consequently small partially molten diapirs km in diameter may be able to trap large melt fractions 30 but larger source regions would be unable to do so the reduction in density contrast with pressure reduces the buoyant force driving melt percolation and provides another limit to melt segregation diapirs at depth may thus stably contain large fractions of melt but may decompress and unload their melt during ascent this effect would be enhanced in small diapirs and may be relevant to the genesis of komatiitic magma melt compression may also be a factor in explaining why the very different maximum depths inferred for typical basic melt segregation from source regions on different planets 500 km on the moon 250 km on mars 100 km on earth correspond to similar pressures 25 35 kbar at greater pressures melt may no longer be capable under ordinary conditions of segregating upwards by buoyancy this may also help to explain why depleted peridotites overlie more fertile peridotites and how deep regions of the mantle are able to remain fertile over geologic time

polar aromatic biomarkers of miocene aged chukurovo resinite and correlation with a progenitor macrofossil abstract functionalised aromatic constituents of chukurovo resinite are compared here with the chemical composition of a macrofossil assigned paleobotanically as taxodium dubium sternb heer terpenoids and lipids of fossil wood tissue embedded in a clay sediment were extracted and analyzed for comparison the information was interpreted in relation to the biomarker compositions of different conifer families as well as to the effects of contamination by inward migration of organic matter from the adjacent sediments many of identified geolipids i e alkanes alkanols alkan 2 ones and steranes triterpanes have no chemosystematic value because they are ubiquitous in the plant kingdom ferruginol sugiol and products of their diagenetic transformations were identified as the dominant specific biomarkers in the resinite ferruginol and its analogues were the most abundant diterpenoids in taxodium dubium sample thus the biomarker composition of the extractable matter of the resinite strongly suggests that species of cupressaceae contributed significantly to the chukurovo paleoenvironment

temperature distribution in the crust and mantle in an attempt to understand the temperature distribution in the earth experimental constraints on the geotherm in the crust and mantle are considered the basic form of the geotherm is interpreted on the basis of two dominant mechanisms by which heat is transported in the earth 1 conduction through the rock and 2 advection by thermal flow data reveal that 1 the temperature distributions through continental lithosphere and through oceanic lithosphere more than 60 million years old are practically indistinguishable 2 crustal uplift is instrumental in modifying continental geotherms and 3 the average temperature through the archean crust and mantle was similar to that at present it is noted that current limitations in understanding the constitution of the lower mantle can lead to significant uncertainties in the thermal response time of the planetary interior

palaeoenvironment assessment of pliocene lom lignite bulgaria from bitumen analysis and preparative off line thermochemolysis abstract the dacian coal bearing province is located in nw bulgaria coal formation is thought to be connected with desiccation of the dacian basin during a prolonged regression in the late pontian and pliocene dacian romanian age a lom lignite sample was characterized via micropetrography bulk chemical analysis spectral methods and thermochemolysis the pollen record was poor suggesting coal formation under oxygen rich conditions during peatification straight chain alkanes alkan 2 ones alkanols des a triterpenoids aromatized triterpenoids aromatized hopane hopene hopanes and triterpenoids with a strong dominance of oleanane derived structures were present in the extracted bitumen the residue after extraction was subjected to preparative off line tetramethylammonium hydroxide tmah thermochemolysis the aliphatic products released were c22 c27 fatty acid fa methyl esters i e methoxymethyl esters c22 c28 even numbered diacids dimethyl esters with a smooth distribution and traces of i and ai c15 acid methyl esters trapped and bound fas were distinguished using tetraethylammonium acetate teaac treatment the main thermochemolysis products were phenols structurally related to lignin vanillyl and syringyl units were produced in similar amounts indicating nonwoody angiosperm vegetation as the main plant input to the palaeo swamp probably originating from marsh or grassland sources the bitumen provided unequivocal information for an angiosperm contribution to the mire while the results of the tmah pyrolysis revealed a concomitant angiosperm and gymnosperm input the biomarker assemblage makes the lom lignite unique in bulgaria all the other bulgarian neogene lignites being dominated by coniferous vegetation with only traces of angiosperm contributions

maceral composition and molecular markers of two condensed middle holocene peat profiles in n spain abstract this study deals with the palaeohydrological information obtained from lipids composition and vegetal tissue preservation of two peat cores from asturias north spain the two profiles differ in the type of peatland raised bog in la borbolla and blanket bog in buelna and the type of organic matter being more bryophytic in the raised bog and more herbaceous in the blanket bog the peatlands are located close to the coast on impermeable old flat erosion surfaces which favoured peat accumulation within a distance of 3 5 km from each other the accumulation rate varied between 0 05 and 0 07 mm yr and the records extend from around 9000 to 2500 cal yr bp the main differences between the two peat sites can be summarized as follows the raised bog has lower mineral matter content and h c atomic ratio and higher c n ratio and extraction yields compared to the blanket bog it has also a higher tissue preservation index for huminite macerals and increasing inertodetrinite index with depth regarding biomarkers the raised bog has a relatively higher concentration of n alkane 2 ones compared to the corresponding n alkane of similar carbon number higher concentration of medium vs high molecular weight methyl ketones and higher triterpenoids steroids ratio than the blanket bog alternating humid dry periods have been recorded in both profiles based on lipid concentrations indicating that the sphagnum rich intervals in the raised bog are more sensitive than the herbaceous blanket peat record to climatic variations the main humid intervals identified are dated as 5000 7500 cal yr bp in the blanket bog and as 6000 3500 cal yr bp and last 2500 cal yr bp in the raised bog and correlate with the humid periods traced in other peatlands locations in this region the transition middle to late holocene is characterized by humid conditions in the region which favoured the sphagnum growth in the peats the reflectance of huminite in these records appears to be more related with differences in the oxidative conditions than with variation of peat maturity it is higher in the layers with high mineral matter content at the beginning of organic matter accumulation and also in the upper part of the profile subjected to seasonal desiccation a more intense biochemical gelification coincides with higher concentration of hopanoids derived from bacteria in the upper part of the profile acrotelm high amount of nonadecan 2 one k 19 and high concentrations of triterpenyl acetates which are also determined in other peat profiles from northern spain are also detected in these profiles this indicates that the specific conditions required for the formation of these compounds probably associated to wet temperate climate dominated throughout the region

vascular plant biomarkers as proxies for palaeoflora and palaeoclimatic changes at the dogger malm transition of the paris basin france abstract vascular plant biomarkers are used here as a chemostratigraphic tool for tracing both palaeoflora and palaeoclimatic changes during the callovian and oxfordian in the paris basin the retene cadalene ratio shows low values in claystones from the middle callovian to the end of the lower oxfordian then increases drastically from the end of the lower oxfordian cordatum zone synchronously with the progressive development of the oxfordian carbonate platform the relative proportion of retene a conifer biomarker is strongly correlated with the abundance of some of its diagenetic precursors and with saturated diterpanes some of these are very common and abundant in the pinaceae family while specific markers for non pinaceae conifers are not detected thus the increase in the retene cadalene ratio around the cordatum zone reflects the rising proportion of pinaceae on the london brabant massif which was the nearest land from the locations studied as pinaceae show many morphological adaptations to dry climate compared to the other plants reported in the jurassic taphofloras of the paris basin their increasing proportion indicates an increasing aridity this climatic change is also supported by published geochemical palaeobiogeographical palynological palaeobotanical and mineralogical data a comparable increase in the relative proportion of retene was also described for the oxfordian of western australia which could be an argument for a worldwide increase in aridity at the end of the lower oxfordian