comparison of covalently bound aliphatic biomarkers released via hydropyrolysis with their solvent extractable counterparts for a suite of kimmeridge clays abstract fixed bed hydropyrolysis at pressures greater than 10 mpa has the unique ability to maximise the yields of covalently bound alkanes without adversely affecting their stereochemistries in order to compare the yields and compositions of the solvent extractable and kerogen bound hopanes and steranes for source rocks of varying maturity six kimmeridge clay samples jurassic type ii kerogen have been subjected to successive dichloromethane extraction and hydropyrolysis the ratios of free to kerogen bound aliphatic biomarkers increase markedly at relatively low vitrinite reflectance ca 0 45 0 50 with large reductions occurring in the concentrations of bound hopanes and steranes however the fact that the total concentrations of observable hopanes and steranes i e free plus kerogen bound do not decrease until the vitrinite reflectance is greater than ca 0 50 provides evidence that neither oil migration nor aromatisation has begun to occur to a significant extent below this maturity level to the authors knowledge this represents the first study to observe a systematic change in epimer ratios with increasing maturity for hopanes and steranes covalently bound in kerogens indeed the kerogen bound hopanes and steranes undergo the same epimerisation reaction pathways as their free counterparts in the bitumen but they are generally less mature in terms of isomerisation at both ring and side chain chiral centres indeed the range of the moretane hopane index for the hydropyrolysis oils is much larger than that for the bitumens ca 5 times indicating a much greater sensitivity to relatively small changes in maturity the covalently bound hopanes and steranes released via hydropyrolysis have enabled the maturity of a contaminated core from the north sea central graben maturity to be assessed and have showed that it is compatible with the kimmeridge formation

well preserved palaeogene and cretaceous biomarkers from the kilwa area tanzania we have investigated the biomarker composition of sediments ranging in age from 30 to 70 ma from the kilwa area of tanzania they are dominated by material of terrestrial n alkanols n alkanoic acids n alkanes and triterpenoids and bacterial hopanoids and a dipentadecyl glycerol diether dgd origin with only a minor contribution of marine origin crenarchaeol and some algal steroids this indicates a marine setting dominated by higher plant input which most likely stimulated sedimentary microbial activity including sulfate reduction the lipid composition specifically the presence of bacteriohopanepolyols bhps and the stereochemistry of hopanoids suggests a low degree of thermal maturity many biomarkers have still retained functionality even after 30 70 million years this is in good agreement with the exceptional preservation of foraminifera and nannofossils and can probably be attributed to the very low sediment permeability and burial depth there is a clear distinction in the biomarker distributions between the oligocene age sediments collected at the end of the peninsula near kilwa masoko and the older sediments collected from elsewhere indicating differences in depositional environment sediments from the end of the peninsula have higher branched and isoprenoid tetraether index values indicating a relatively higher terrestrial input they also contain two tentatively assigned c28 hopenes 28 30 dinorneohop 13 18 ene and 28 30 dinorhop 17 21 ene aromatic des a triterpenes des e hopenes aromatic pentacyclic triterpenoids c33 dgd archaeol and bhps which are absent from or only present in small amounts in the other sediments these differences likely reflect an evolution of the depositional area from a relative open shelf environment with substantial water depth to a shallower setting during the early oligocene

core and intact polar glycerol dialkyl glycerol tetraethers gdgts in sand pond warwick rhode island usa insights into the origin of lacustrine gdgts branched and isoprenoidal glycerol dialkyl glycerol tetraethers gdgts are abundant in lake sediments and have potential use for determining past changes in climate and limnology however emerging evidence suggests that both classes of gdgts can be associated with both allochthonous soil organic matter and in situ production potentially complicating interpretation of these compounds in lacustrine sedimentary environments here we investigate the dual source issue surrounding lacustrine gdgts with an emphasis on the branched gdgts by studying both core and intact polar gdgts within a pond and its watershed in warwick ri significant differences in both absolute concentrations of branched gdgts and the percent of branched gdgts present as ipls between the soils and shallow lake sediments suggests in situ production of these compounds within the lake environment principal components analysis of gdgt lipid concentrations and environmental parameters in sand pond sediments and soils highlights two prominent trends in the data one related to the absolute concentrations of type i branched gdgts brgdgt i ib ic and the majority of the isoprenoidal gdgts and another related to the concentration of the more methylated type iii branched gdgts brgdgt iii iiib iiic and isoprenoidal gdgt 0 the latter trend exhibits a subsurface maximum in the sediment column potentially indicating in situ production of more highly methylated branched gdgts and gdgt 0 within the lacustrine sediment column trends in the distributions of branched gdgts as reflected by the mbt and cbt indices imply mixing of two distinct sources of branched gdgts soil derived and in situ or alternatively two or more different microbial producers both possibilities present a challenge to the application of brgdgt based paleoenvironmental proxies in lakes this study highlights the importance of determining the sources of gdgts to the lacustrine environment prior to paleoenvironmental application

african monsoon variability during the previous interglacial maximum abstract little is known about centennial to millennial scale climate variability during interglacial times other than the holocene we here present high resolution evidence from anoxic unbioturbated sediments in the eastern mediterranean sea that demonstrates a sustained 800 yr climate disturbance in the monsoonal latitudes during the eemian interglacial maximum 125 ka bp results imply that before and after this event the intertropical convergence zone itcz penetrated sufficiently beyond the central saharan watershed 21 n during the summer monsoon to fuel flooding into the mediterranean along the wider north african margin through fossil river wadi systems that to date have been considered only within a holocene context relaxation in the itcz penetration during the intra eemian event curtailed this flux but flow from the nile with its vast catchment area was not affected previous work suggests a concomitant eurasian cooling event with intensified impact of the higher latitude climate on the mediterranean basin the combined signals are very similar to those described for the holocene cooling event around 8 ka bp the apparent type of concurrent changes in the monsoon and higher latitude climate may reflect a fundamental mechanism for variability in the transfer of energy latent heat between the tropics and higher latitudes

reconstruction of sea surface temperature variations in the arabian sea over the last 23 kyr using organic proxies tex86 and u37k well established u37 0 based on long chain unsaturated ketones synthesized by haptophyte algae and the newly proposed tex86 derived from the membrane lipids of crenarchaeota comparison of niop905 and 74kl core top data with present day sst 0 10 m values indicates that both proxies yield temperatures similar to local annual mean ssts however tex86 and u37 0 sst down core records derived from the same cores differ in magnitude and phasing the alkenone sst record of niop905 shows small changes in sst 0 5 c over the last 23 kyr while that of core 74kl shows a 2 c increase from the last glacial maximum lgm 23 19 calendar cal kyr b p through the holocene the last 11 5 cal kyr b p synchronous with changes in the northern hemisphere in contrast the tex86 records of both cores show a large increase in sst from 22 23 c in the lgm to 28 30 c during termination i 19 11 5 cal kyr b p decreasing to present day annual means of 26 c a cold phase between 14 5 and 12 cal kyr b p that may correspond to the antarctic cold reversal is also observed this implies a southern hemisphere control on tropical sst reconstructed by the tex86 possibly related to sw monsoon our results suggest that the application of both tex86 and u37 0 give different but complementary information on sst developments in past marine environments

the volcanic stratigraphy and petrogenesis of the oman ophiolite complex the volcanic stratigraphy and trace element geochemistry of the oman ophiolite complex indicate a multistage magmatic origin comprising 1 magmatism due to sea floor spreading in a marginal basin 2 magmatism associated with discrete submarine volcanic centres or seamounts 3 magmatism associated with crustal uplift and rifting and 4 magmatism associated with continent arc collision trace element petrogenetic modelling is used to investigate the nature of the mantle source region and the partial melting and fractional crystallization history for each magmatic event the petrogenetic pathway for the sea floor spreading lavas requires a high degree of melting of a mantle that was depleted in incompatible elements prior to subduction but subsequently selectively enriched in certain elements mostly lil elements and h2o from an underlying subduction zone it also requires magma mixing in an open system magma chamber prior to eruption the seamount lavas were probably derived by a similar degree of partial melting of a similar source but fractional crystallization was restricted to smaller high level magma chambers the rifting lavas were derived from a mantle source that was more depleted than the seamount lavas prior to subduction but which was later modified by a larger subduction zone component the syn collision lavas were however derived from an enriched mantle source which probably underlay the passive continental margin rather than the marginal basin complex results such as these may provide considerable insight into the petrogenetic changes accompanying the transitions from spreading to arc volcanism in a supra subduction zone setting

geochemical evidence for variations in delivery and deposition of sediment in pleistocene light dark color cycles under the benguela current upwelling system abstract distinctive light dark color cycles in sediment beneath the benguela current upwelling system indicate repetitive alternations in sediment delivery and deposition geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in three mid pleistocene intervals from odp sites 1082 and 1084 concentrations of total organic carbon toc vary between 3 5 and 17 1 concentrations of caco3 vary inversely to toc and al which suggests that both carbonate dissolution and terrigenous dilution contribute to the light dark cycles opal concentrations are independent of both toc and caco3 therefore eliminating diatom production and lateral transport of shelf material as causes of the light dark cycles 13corg and 15ntot values do not vary across light dark sediment intervals implying that the extent of relative nutrient utilization did not change the stable 15ntot values represent a balanced change in nitrate supply and export production and therefore indicate that productivity was elevated during deposition of the toc rich layers parallel changes in concentrations of indicator trace elements and toc imply that changes in organic matter delivery influenced geochemical processes on the seafloor by controlling consumption of pore water oxygen cu ni and zn are enriched in the darker sediment as a consequence of greater organic matter delivery redox sensitive metals vary due to loss mn and ba or enrichment mo under reducing conditions created by toc oxidation organic matter delivery impacts subsequent geochemical changes such as carbonate dissolution sulfate reduction and the concentration of metals thus export production is considered ultimately responsible for the generation of the color cycles

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

evidence for constriction and pliocene acceleration of east west extension in the north lunggar rift region of west central tibet 1 the active north trending north lunggar rift in west central southern tibet exposes an extensional metamorphic core complex bounded by an east dipping low angle normal fault apatite and zircon u th he thermochronology and thermal modeling of the north lunggar rift document a minimum timing for rift inception at 10 ma and rapid footwall exhumation between 5 and 2 ma miocene footwall cooling and exhumation rates were initially slow to moderate at 400 c ma 1 and 4 10 mm a 1 footwall isotherms were significantly compressed during rapid exhumation resulting in an elevated transient geothermal gradient between 50 and 90 c km 1 the minimum magnitude of horizontal extension for the north lunggar rift is 8 1 12 8 km maximum is 15 20 km less in the south at 10 km mean pliocene extension rate is 1 2 2 4 mm a 1 in the 120 direction results for the north lunggar rift are similar in magnitude rate and orientation of slip to the kinematically linked lamu co dextral strike slip fault to the north this suggests a state of constrictional strain during pliocene time along this stretch of the bangong nujiang suture from which the lamu co fault emanates the onset of extension in this region may be explained by crustal thickening and gravitational orogenic collapse followed by accelerated rifting resulting from localized crustal stretching and increased magmatic activity potentially driven by the position and northward extent of underthrusting indian lithosphere

impact of dia and catagenesis on sulphur and oxygen sequestration of biomarkers as revealed by artificial maturation of an immature sedimentary rock hydrous pyrolysis of an immature ro 0 25 sulphur rich marl from the gessoso solfifera formation messinian in the vena del gesso basin was carried out at 160 c t 330 c for 72 h to study the effect of progressive diagenesis and early catagenesis on the abundance and distribution of sulphur containing and sulphur and oxygen linked carbon skeletons in low molecular weight and high molecular weight fractions e g kerogen to this end compounds in the saturated hydrocarbon fraction monoaromatic hydrocarbon fraction polyaromatic hydrocarbon fraction alkylsulphide fraction and ketone fraction were quantified as well as compounds released after desulphurisation of the polar fraction and hilialh4 treatment of the desulphurised polar fraction sulphur bound phytane and 20r 5 14 17 h and 20r 5 14 17 h c27 c29 steranes in the polar fraction become less abundant with increasing maturation temperature whereas the amount of their corresponding hydrocarbons increases in the saturated hydrocarbon fraction carbon skeletons that are bound in the kerogen by multiple bonds e g c38n alkane and isorenieratane are first released into the polar fraction and then as free hydrocarbons these changes occur at relatively low levels of thermal maturity ro 0 6 as evidenced by the immature values of biomarker maturity parameters such as the c35 hopane ratio and the 22s 22s 22r 17 21 h c35 hopane ratio sulphur and oxygen bound moieties present in the polar fraction are not stable with increasing thermal maturation however alkylthiophenes ketones 1 2 di n alkylbenzenes and free n alkanes seem to be stable thermal degradation products of these sulphur and oxygen bound moieties thus apart from free n alkanes which are abundantly present in more mature sedimentary rocks and crude oils alkylthiophenes 1 2 di n alkylbenzenes and ketones can also be expected to occur the positions of the thiophene moiety and the carbonyl group coincide with the original positions of the functional groups of their precursors thus important information about palaeobiochemicals is retained throughout the sequestration degradation process

n2 fixing cyanobacteria supplied nutrient n for cretaceous oceanic anoxic events the abundance of specific membrane lipids 2 methylhopanoids indicates that cyanobacteria played a key role in the seemingly global deposition of black shales during the early aptian ca 120 5 ma and late cenomanian ca 93 5 ma oceanic anoxic events organic matter rich sediments deposited during these events are characterized by a 15n content typical of newly fixed n2 indicating that cyanobacterial n2 fixation was the main source for nutrient n we propose that denitrification and anaerobic ammonium oxidation effectively cut off the return of nutrient n from the anoxic deep waters to the photic zone in the oceans giving n2 fixing cyanobacteria a competitive advantage over algae during these oceanic anoxic events

rapid palaeoceanographic changes in the benguela upwelling system for the last 160 000 years as indicated by abundances of planktonic foraminifera abstract two sediment cores retrieved from the continental slope in the benguela upwelling system geob 1706 19 33 7 s 11 10 5 e and geob 1711 23 18 9 s 12 22 6 e reveal striking variations in planktonic foraminiferal abundances during the last 160 000 years these fluctuations are investigated to assess changes in the intensity and position of the upwelling centres off namibia four species make up over 95 of the variation within the core and enable the record to be divided into episodes characterized by particular planktonic foraminiferal assemblages the fossil assemblages have meaningful ecological significance when compared to those of the modern day and the relationship to their environment the cold water planktonic foraminifer neogloboquadrina pachyderma sinistral n pachyderma s dominates the modern day coastal upwelling centres and neogloboquadrina pachyderma dextral and globigerina bulloides characterize the fringes of the upwelling cells globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional reduced nutrient levels of the subtropical waters in the fossil record episodes of high n pachyderma s abundances are interpreted as evidence of increased upwelling intensity and the associated increase in nutrients the n pachyderma s record suggests temporal shifts in the intensity of upwelling and corresponding trophic domains that do not follow the typical glacial interglacial pattern periods of high n pachyderma s abundance describe rapid discrete events dominating isotope stages 3 and 2 the timing of these events correlates to the temporal shifts of the angola benguela front jansen et al 1997 situated to the north of the walvis ridge absence of high abundances of n pachyderma s from the continental slope of the southern cape basin indicates that southern ocean surface water advection has not exerted a major influence on the benguela current system the coincidence of increased upwelling intensity with the movement of the angola benguela front can be interpreted mainly by changes in strength and zonality of the trade wind system

biological productivity during sapropel s5 formation in the eastern mediterranean sea evidence from stable isotopes of nitrogen and carbon we determined 15n 14n ratios in modern surface and sapropel s5 sediments of the mediterranean sea to clarify differences in the nutrient regime associated with sapropel formation in the modern situation high 15n of unused nitrate 15 20 remaining in the surface waters during the winter phytoplankton bloom evidences p limitation of biological production in winter 15n of surface sediments decrease towards the east of the basin 5 to 2 5 this is a consequence of either eastward increasing nitrogen fixation during the summer months or of particulate matter being supplied predominantly by the p limited winter bloom very low 1 1 15n values in sapropel s 5 from four locations require a very light source of nutrient n assimilated at a minimum of ten times the modern export flux because the isochronous records show no spatial gradient in 15n we exclude both ekman type upwelling and direct riverine discharge as likely sources of nutrients our data are consistent with an anti estuarine thermohaline circulation in the upper 500m during s5 time allowing for the trapping of nutrients in the eastern basin the most likely scenario for s5 is that phosphorus release from a relatively shallow redox boundary resulted in an imbalanced supply of n p 16 1 to the photic zone the result was a slow assimilation of carbon during summer stratification and extensive n2 fixation providing the majority of the export flux from a n limited system

archaea in black sea water column particulate matter and sediments evidence from ether lipid derivatives abstract phytane and long chain c40 head to head acyclic c40 0cy and cyclic isoprenoids with 1 3 cyclopentyl rings c40 1cy c40 2cy and c40 3cy derived from archaeal core lipids are present in black sea particulate matter from both the oxic and anoxic zones and in sediment cores from the central basin and the western continental margin the occurrence of these ether linked isoprenoids throughout the water column and sediments suggests that archaea are widely distributed in the black sea methanogens are the probable source of ether linked phytane and some of the acyclic c40 compounds while psychrophilic archaea related to hyperthermophiles are the likely sources of the cyclic isoprenoids

release of bound aromatic hydrocarbons from late archean and mesoproterozoic kerogens via hydropyrolysis hydrogen lean kerogens atomic h c 0 4 isolated from the 2 5 billion year old ga mt mcrae shale hamersley group at tom price western australia were studied via hydropyrolysis a continuous flow technique that degrades organic matter in a stream of high pressure hydrogen assisted by a dispersed mo catalyst the hydropyrolysates yielded predominantly phenanthrene and pyrene and higher polyaromatic hydrocarbons and alkylated homologues were generated in low relative concentrations saturated hydrocarbons were not detected the molecular and carbon isotopic compositions of the hydropyrolysates are very similar to aromatic hydrocarbons obtained by solvent extraction of the host rocks because molecular structures covalently attached to kerogen are unaffected by contamination this indicates that both the bound and extractable aromatic fractions are syngenetic with the host rocks therefore the results of the hydropyrolysis experiments provide compelling evidence for preserved bitumen of archean age the very high proportion of nonalkylated polyaromatic hydrocarbons in the hydropyrolysates is consistent with hydrothermal dehydrogenation of the kerogen and a marked concentration difference of pyrene in rock extracts and hydropyrolysates might be explained by hydrothermal redistribution of the bitumen the kerogen and bitumen composition is therefore consistent with models suggesting a hydrothermal origin for the giant iron ore deposits at mt tom price comparison of the archean samples with hydropyrolysates from immature mesoproterozoic kerogens from the roper group mcarthur basin northern territory and with pyrolysis experiments on proterozoic kerogens in the literature suggests that precambrian kerogens are frequently highly aromatic and lipid poor regardless of their degree of thermal preservation

tectonic setting for the genesis of oceanic plagiogranites evidence from a paleo spreading structure in the oman ophiolite abstract in the oman ophiolite detailed structural and lithological mapping of the 60 45 km maqsad area has revealed several plagiogranite intrusions ranging from metre scale dykes to hectometre scale bodies these plagiogranites are spatially related to kilometre scale mafic plutons displaying generally pegmatitic textures and locally deformed in amphibolite facies conditions along shear zones up to a few hundred metres thick isotope data demonstrate the mantle origin of these pegmatites and plagiogranites nd ranges from 6 3 to 9 9 and has an average value 26 samples of 8 1 within the field of present day morbs and similar to the average nd 7 8 of the oman ophiolite primary igneous sequence these intrusions are not restricted to a given structural level their paleovertical extent exceeds 5 6 km from 2 km below the moho up to the base of the sheeted dyke complex their modal composition evolves up section from predominantly pyroxenites and gabbro norites in the mantle harzburgites to gabbro norites diorites and quartz diorites at crustal level petrography whole rock and mineral chemistry show that this vertical succession of lithologies can be simply explained by low pressure fractional crystallization of a hydrated basaltic melt plagiogranites although more abundant at upper crustal level are not restricted to this horizon plagioclase composition in plagiogranites presents a remarkable evolution with paleodepth from highly calcic 70 95 an in the mantle section intermediate and highly scattered in the lower crust 10 85 an to quite sodic at upper crustal level 5 20 an highly calcic plagioclases in quartz bearing rocks is a puzzling character inconsistent with fractional crystallization even if high degrees of fractional crystallization of a hydrated basaltic melt remain the simplest way to account for the chemistry of the upper crustal plagiogranites processes such as fluid induced remelting or assimilation of country rocks must be invoked to account for the chemistry and field characteristics of the deeper plagiogranites mantle and crustal structures in the maqsad area indicate that the pegmatites and plagiogranites emplaced in an ocean ridge setting when a mantle diapir soaked with basaltic melt intruded a cool hydrothermally altered lithosphere they were eventually transposed in an off axis setting as the ascension of the diapir progressed up to moho level it is concluded that the formation of large volumes of buoyant leucocratic rocks is possible at ocean ridges provided periods of amagmatic spreading are long enough to induce the growth and alteration of an axial lithospheric lid this is likely more frequent at slow spreading centres where mantle upwelling is discontinuous in space and time

biogeochemical controls on glycerol dialkyl glycerol tetraether lipid distributions in sediments characterized by diffusive methane flux the tex86 tetraether index of tetraethers consisting of 86 carbon atoms is a proxy for sea surface temperature sst based on the distribution of isoprenoidal glycerol dialkyl glycerol tetraether gdgt membrane lipids synthesized by marine pelagic thaumarchaeota one of the caveats of this proxy is the production of additional gdgts by sedimentary euryarchaeota involved in anaerobic oxidation of methane aom that occurs at deep sea methane seeps but is also widespread in many continental shelf settings here gdgt distributions are investigated through the sulfate methane transition zone smtz in aarhus bay denmark to examine the extent the tex86 proxy is compromised in such a continental shelf setting where aom is characterized by a diffusive rather than rapid advective methane flux both free extractable and non extractable lipid fractions were analyzed as it was expected that pelagic derived and sediment derived gdgts could become incorporated into the molecular and sedimentary matrix to a different extent the results show a large change of tex86 values mainly due to the relative high amounts of gdgt 2 produced by aom related archaea both in the free and non extractable lipid fractions this additional gdgt input renders calculation of ssts based on tex86 inappropriate at the smtz the aom related gdgt signature however did not persist into deeper sediments perhaps reflecting rapid remineralization of the gdgts at the smtz although the process of aom at aarhus bay might not be representative for all continental margin settings it illustrates that aom in a variety of settings not just cold seeps can influence sedimentary gdgt distributions

the subduction initiation rule a key for linking ophiolites intra oceanic forearcs and subduction initiation we establish the subduction initiation rule sir which predicts that most ophiolites form during subduction initiation si and that the diagnostic magmatic chemostratigraphic progression for sir ophiolites is from less to more hfse depleted and lile enriched composi tions this chemostratigraphic evolution reflects formation of what ultimately becomes forearc lithosphere as a result of mantle melting that is progressively influenced by subduction zone enrichment during si the magmatic chemostratigraphic progression for the izu bonin mariana ibm forearc and most tethyan ophiolites is specifically from morb like to arc like volcanic arc basalts or vab boninites or bon because si progressed until establishment of a mature subduction zone morb like lavas result from decompression melting of upwelling asthenosphere and are the first magmatic expression of si the contribution of fluids from dehydrating oceanic crust and sediments on the sinking slab is negligible in early si but continued melting results in a depleted harzburgitic residue that is progressively metasomatized by fluids from the sinking slab subsequent partial melting of this residue yields typical ssz like lavas in the latter stages of si if si is arrested early e g as a result of collision morb only ophiolites might be expected consequently morb and ssz only ophiolites may represent end members of the si ophiolite spectrum the chemostratigraphic similarity of the mariana forearc with that of ophiolites that follow the sir intimates that a model linking such ophiolites oceanic forearcs and si is globally applicable

origin and transformation of organic matter in pliocene pleistocene mediterranean sapropels organic geochemical evidence reviewed abstract drilling of deep water post messinian sedimentary sequences by odp legs 160 and 161 in the mediterranean sea has shown that occurrence of organic carbon rich sapropels and sapropel like sediments extends from the levantine basin westward into the alboran basin in the eastern mediterranean sapropel deposition started in the early pliocene whereas in the western basin the onset of sapropel formation occurred later in the early pleistocene precessional cycles are apparently the primary external forcing for sapropel formation nevertheless the pattern of sapropel occurrence suggests that the precessional influence is modulated by the glaciation cycles large differences were observed in the organic carbon contents of sapropels recovered in the eastern and western mediterranean correspondence between organic carbon contents rock eval hydrogen index values and elemental c n ratios indicate that both variations in the production and preservation of marine organic matter have led to the accumulation of high amounts of organic matter in sapropels molecular organic geochemical compositions of sapropels from the eastern mediterranean further confirm that the major fraction of organic matter in sapropels is derived from marine algal sources and has undergone variable oxidation enhanced marine productivity and improved preservation of organic matter is central to sapropel formation accumulation of increased amounts of land derived material at times of sapropel formation is also evidenced supporting the hypothesis of significant periodic freshwater discharges

moist morb axial magmatism in the oman ophiolite the evidence against a mid ocean ridge origin the oman ophiolite has an axial volcanic suite and associated sheeted dike complex similar in composition to modern mid oceanic ridge basalt morb its internal structure is regarded by many as being directly comparable to ocean lithosphere from the east pacific rise however there has long been controversy over the geodynamic setting in which the ophiolite formed and the extent to which the analogy can be drawn because the morb like axial volcanics are overlain by lavas that include depleted arc tholeiites and boninites to some this implies that the entire ophiolite formed above a subduction zone others maintain that it formed at a true open ocean mor and that the water required to generate the arc like magmas derived from descending near axis hydrothermal fluids or from ancient subduction a popular compromise posits that the axial suite formed at a true mor and the later magmatism documents the initiation of obduction we test these models by reexamining the morb like character of the early axial lavas and dikes we show that fractionation trends require the presence of water at concentrations significantly higher than any open ocean morb instead trends are identical to those of backarc basin and intraoceanic forearc volcanics by showing that the entire ophiolite formed in a hydrous system we rule out all models in which the oman ophiolite was generated at an open ocean mor instead it formed at a submarine spreading center above a probably newly initiated subduction zone

the petrogenesis of leucogranitic dykes intruding the northern semail ophiolite united arab emirates field relationships geochemistry and sr nd isotope systematics the khawr fakkan block of the semail ophiolite united arab emirates exhibits a suite of 10 100 m scale metaluminous to peraluminous granitic intrusions ranging from cordierite andalusite biotite monzogranites to garnet tourmaline leucogranites which intrude mantle sequence harzburgites and lower crustal sequence cumulate gabbros structural constraints suggest that the subduction of continental sedimentary material beneath the hot proto ophiolite in an intra oceanic arc environment led to granulite facies metamorphism at the subduction front and the generation of granitic melts which were emplaced up to the level of the ophiolite moho compositions indicate the analysed granitoids were largely minimum melts that crystallised at variable a h2o and pressures of 3 to 5 kbar the lile sr rb and ba covariation modelling suggests that the granitoids formed largely by the dehydration melting of muscovite rich metasediments initial 87sr 86sr ratios of analysed dykes vary between 0 710 and 0 706 at initial nd values of between 6 3 and 0 5 cogenetic units of a composite sill from ra s dadnah yield a sm nd isochron age of 98 8 9 5 ma mswd 1 18 geochemical and isotopic characteristics of the analysed granitic intrusions indicate that the subducted continental material was derived from oceanic trench fill haybi complex sediments preserved as greenschist asimah area to granulite facies bani hamid area ophiolitic metamorphic sole terranes the sr nd isotope systematics suggest that hybrid granitic melts were derived from pre magmatic mixing of two contrasting subduction zone sources

archaeal remains dominate marine organic matter from the early albian oceanic anoxic event 1b abstract the sources for both soluble and insoluble organic matter of the early albian 112 myr oceanic anoxic event oae 1b black shales of the ocean drilling program odp site 1049c north atlantic ocean off the coast of florida and the ravel section of the southeast france basin sefb were determined using optical chemical stable carbon and nitrogen isotopic analyses archaea derived isoprenoidal tetraether membrane lipids and free and macromolecularly bound isoprenoid alkanes are abundant in these black shales more specifically the presence of certain ether lipids bi tricyclic biphytane tetraethers indicates an important contribution of representatives of marine planktonic archaea the large difference up to 12 in 13c 12c ratios between algal biomarkers and the much more abundant planktonic archaea derived biomarkers indicates that the latter were living chemoautotrophically this offset in 13c 12c ratios was used to estimate that up to 40 of the organic matter of the sefb and up to 80 of the organic matter of odp site 1049c preserved in the black shales is derived from archaea furthermore it is shown that even though there are apparent similarities high organic carbon oc content distinct lamination 13c enrichment of oc between the black shales of oae1b and the cenomanian turonian 94 myr oae the origin of the organic matter archaeal versus phytoplanktonic and causes for 13c enrichment of oc are completely different

tectonic development of the samail ophiolite high precision u pb zircon geochronology and sm nd isotopic constraints on crustal growth and emplacement 1 new high precision single grain u pb zircon geochronology and whole rock nd isotopic data provide insight into the magmatic and tectonic development of the samail ophiolite the analyzed rocks can be broadly divided into two groups based on their structural position dates and isotopic composition an older group related to on axis magmatism and a younger group of post ridge dikes sills and stocks on axis gabbros tonalites and trondhjemites yielded th corrected 206pb 238u dates from 96 441 0 062 to 95 478 0 056 ma these dates combined with dates from rioux et al 2012 suggest that most of the ophiolite crust formed at an oceanic spreading center in 1 ma the post ridge intrusions come from all depths in the crust the upper mantle and the metamorphic sole post ridge gabbros tonalites and trondhjemites from the crust and mantle yielded th corrected 206pb 238u dates of 95 405 0 062 to 95 077 0 062 ma a small trondhjemitic pod from the metamorphic sole yielded younger th corrected 206pb 238u dates of 94 90 0 38 to 94 69 0 12 ma isotopic data suggest two distinct sources for the post ridge magmas five of the gabbros and tonalites from the crust have end 96 ma 6 90 0 12 to 7 88 0 16 and two trondhjemites from the upper mantle and metamorphic sole have end 96 ma 7 77 0 08 and 7 01 0 16 the negative end t and u pb dates from the mantle dike require that subduction or thrusting was established below the ophiolite 0 25 0 5 ma after formation of the crust the bimodal isotopic composition of post ridge magmas may reflect coeval decompression and or fluid fluxed melting of the mantle and melting dehydration or assimilation of sediment in the down going plate at this time the new data place temporal constraints on mid ocean ridge and supra subduction zone models for ophiolite formation

geochemical studies of the recent sapropel and associated sediment from the hellenic outer ridge eastern mediterranean sea i mineralogy and chemical composition abstract the mineralogy major and minor element geochemistry and the accumulation rate of a single kastenlot core from the eastern mediterranean is reported the sapropel is similar mineralogically and in its major element composition to the associated marl ooze and calcareous clay it differs from these sediments in having higher concentrations of ba cr cu mo ni sr and zn and lower concentrations of mn the enrichments are explained by increased fertility ba organic matter or sulphide association cr cu mo ni and zn and the presence of aragonitic pteropods sr the organic material has a marine origin based on the carbon isotopic value 13 c 20 and c n ratio 10 the sapropel accumulated 3 to 5 times faster than the associated sediments in this particular core the evidence is consistent with the formation of this sapropel by an increased flux of carbon to the sea floor this would have been caused by increased marine primary production in the eastern mediterranean during periods of reversed circulation brought about by high post glacial runoff primarily from northern africa the additional carbon flux would have lowered the oxygen levels of the bottom waters but it is not known whether anoxic conditions ensued or whether they would have been necessary to preserve the deposited carbon

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

geochemical constraints on the bimodal origin of high himalayan leucogranites major and trace element and rb sr isotope systematics of the manaslu leucogranite central nepal have been examined to constrain the role of mineral fractionation and fluids in peraluminous granite petrogenesis biotite and tourmaline are for the most part mutually exclusive with a predominance of two mica leucogranites over tourmaline leucogranites the 87sr86sr initial isotopic ratios sri indicate that leucogranitic melts were derived from two different sources the two mica leucogranites having a metagreywacke origin with sri 0 752 nd 15 such a bimodal nature of the source zone does not directly influence the magmatic evolution except that probably the higher initial boron content in the metapelitic rocks may increase the na2ok2o ratio in contrast the amount of water present during melting principally controls in part anatectic processes and element behaviour water saturated conditions probably occured during melting of metagreywackeous rocks and favoured crystallization of two mica leucogranites whereas water absent conditions prevailed during melting of metapelitic layers and favoured biotite plagioclase and monazite fractionation in the source zone and tourmaline crystallization in the leucogranite

deep sulfate reduction completely mediated by anaerobic methane oxidation in sediments of the upwelling area off namibia abstract porewater concentrations of sulfate methane and other relevant constituents were determined on four sediment cores from the high productivity upwelling area off namibia which were recovered from the continental slope at water depths of 1300 and 2000 m at all four stations a distinct sulfate methane transition zone was observed several meters below the seafloor in which both sulfate and methane are consumed nutrient porewater concentration profiles do not show gradient slope changes at the depths of the transition zones flux calculations carried out on the basis of the determined porewater profiles revealed that anaerobic methane oxidation accounts for 100 of deep sulfate reduction within the sulfate methane transition zone and consumes the total net diffusive sulfate flux a significant contribution of organic carbon oxidation to the reduction of sulfate at these depths could therefore be excluded we state that porewater profiles of sulfate with constant gradients above the transition zones are indicative for anaerobic methane oxidation controlling sulfate reduction

a 35 000 year record of terrigenous and marine lipids in amazon fan sediments elemental and lipid analyses were carried out on sediments recovered from ocean drilling program odp site 942 to provide a 35 kyr record of organic matter input to amazon fan sediments total organic carbon toc and higher plant biomarker mass accumulation rates were an order of magnitude greater during the last glacial period compared to the current interglacial due to sea level controlled variations in amazon river sediment supply large maxima were also seen at similar to 12 ka which are most likely due to discharge events higher plant n alkane average chain lengths did not change throughout the record suggesting consistency in the source vegetation type the abundance of taraxerol relative to other plant biomarkers increased at similar to 12 ka indicating increased mangrove input due to either higher mangrove productivity or increased erosion of mangrove deposits the mass accumulation rates mars of some bacterial and eustigmatophyte biomarkers varied closely with those of higher plant biomarkers and so seem to have a non marine source long chain alkenones were present in some of the sediments generally in very low concentration indicating dilution of the marine signal with terrestrial organic matter c 2005 elsevier ltd all rights reserved

recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach study of organic matter in immature sediments from a messinian evaporitic basin shows that consideration of structures modes of occurrence and carbon isotopic compositions of free and sulfur bound carbon skeletons allow identification of biochemical precursors detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way moreover unprecedented biochemicals were recognized these extend the horizon of biomarker geochemistry

carbon isotopic composition of isoprenoid tetraether in surface sediments of lake qinghai and surrounding soils abstract isoprenoid gdgts i gdgts along with their constituent biphytanyl moieties are biomarkers for archaea in order to obtain more information on identifying the carbon source and potential carbon assimilation pathway of archaea in surface sediments of lake qinghai and the surrounding soils the stable carbon isotopic composition of i gdgt derived biphytanes as well as its relationship with 13 c values of total organic carbon toc and dissolved inorganic carbon dic was investigated the 13 c values of i gdgt derived biphytanes ranged from 42 7 to 20 3 for example the values for acyclic biphytanes bp 0 the most abundant varied from 25 0 to 22 1 in offshore sediments 30 5 to 25 4 in surrounding soils and 42 7 to 32 0 in nearshore sediments the wider variation than that of 13 c toc 26 9 to 25 1 in offshore sediments and that in surrounding soils indicated that 13 c values of bp 0 may be a sensitive indicator for examining the depositional environments between terrestrial and lacustrine systems with average 13 c values of 23 6 crenarchaeol derived biphytanes bp cren in offshore sediments were enriched in 13 c ca 3 6 relative to toc in addition the carbon isotopic fractionation between bp cren and dic was 21 3 consistent with that reported for marine thaumarchaeota the enrichment in 13 c relative to toc and the similar carbon isotopic fractionation indicated that thaumarchaeota in offshore sediments of qinghai lake are autotrophic with average 13 c values of 29 2 bp cren in surrounding soils was depleted by 0 9 to 12 8 in 13 c relative to dic the quite large scatter in carbon isotopic fractionation between bp cren and dic indicated that the biomass of soil thaumarchaeota originated from inorganic and organic carbon sources suggesting a mixotrophic lifestyle

massive expansion of marine archaea during a mid cretaceous oceanic anoxic event biogeochemical and stable carbon isotopic analysis of black shale sequences deposited during an albian oceanic anoxic event 112 million years ago indicate that up to 80 weight percent of sedimentary organic carbon is derived from marine nonthermophilic archaea the carbon 13 content of archaeal molecular fossils indicates that these archaea were living chemoautotrophically their massive expansion may have been a response to the strong stratification of the ocean during this anoxic event indeed the sedimentary record of archaeal membrane lipids suggests that this anoxic event marks a time in earth history at which certain hyperthermophilic archaea adapted to low temperature environments

a diatomaceous origin for long chain diols and mid chain hydroxy methyl alkanoates widely occurring in quaternary marine sediments indicators for high nutrient conditions for the first time a biological source for the long chain alkyl 1 14 diols and 12 hydroxy methyl alkanoates lipids widely occurring in the marine water column and sediments has been identified cultures of proboscia indica and proboscia alata rhizosolenoid diatoms belonging to the widespread diatom genus proboscia contain c28 c28 1 c30 and c30 1 alkyl 1 14 diols and c27 and c29 12 hydroxy methyl alkanoates as major neutral lipids these components form a substantial fraction of lipid fractions from sediment traps or sediments especially in areas with an elevated primary production such as upwelling regions examination of literature data reveals that as much as 20 to 35 of the total lipid flux in the arabian sea is derived from proboscia diatoms during the start of the upwelling season their rapid transfer to the water sediment interface may explain why corresponding 1 14 keto ols inferred oxidation products of diols are hardly formed these interpretations are supported by compound specific carbon isotopic analysis of long chain keto ols and diols in surface sediments of the arabian sea the data indicate that long chain alkyl 1 14 diols and 12 hydroxy methyl alkanoates can be applied as indicators for high nutrient conditions in the photic zone

polyphasic carbonate precipitation in the shallow subsurface insights from microbially formed authigenic carbonate beds in upper miocene sediments of the tertiary piedmont basin nw italy article i nfo authigenic methane derived carbonates hosted in upper miocene slope sediments of the tertiary piedmont basin nw italy are studied by a multidisciplinary approach including petrography stable oxygen and car bon isotopes of carbonates as well as lipid biomarkers in order to explore the relationship between microbial activity and carbonate precipitation in the shallow subsurface the studied rocks show a bed parallel geom etry and are characterized by dolomitic intergranular cement which is typified by positive 13 c values as high as 6 2 vpdb a striking feature of some dolomite beds is an intricate network of septarian like cracks filled with both injected sediments and polyphasic carbonate cements prokaryotic molecular fossils in the dolomite beds comprise archaeol 13 c 40 vpdb and various bacterial dialkyl glycerol diethers dages 13 c 30 vpdb strongly suggesting that dolomite precipitation took place at the interface of the zones of archaeal methanogenesis and bacterial sulphate reduction in contrast extremely negative 13 c values of carbonate cements as low as 56 3 vpdb and various archaeal and bacterial molecular fossils e g pentamethylicosane pmi 106 vpdb are recorded in the crack filling carbonate cements these cements precipitated due to anaerobic oxidation of methane coupled to sulphate reduction we pro pose a scenario for the formation of the diagenetic beds suggesting that carbonate precipitation was the re sult of three microbially driven processes sulphate reduction methanogenesis and finally anaerobic oxidation of methane this unusual sequence was a consequence of a dynamic change of environmental geo chemical conditions and fluid circulation patterns that prevailed in the ancient subseafloor during early dia genesis of the unconsolidated sediments anaerobic oxidation of methane which usually predates methanogenesis during increasing burial postdates methanogenesis in case of the septarian like beds after the beds were affected by crack formation induced by overcritical pore pressure allowing the ingress of sulphate rich water from above and methane rich water from below

descent toward the icehouse eocene sea surface cooling inferred from gdgt distributions the tex86 proxy based on the distribution of marine isoprenoidal glycerol dialkyl glycerol tetraether lipids gdgts is increasingly used to reconstruct sea surface temperature sst during the eocene epoch 56 0 33 9 ma here we compile published tex86 records critically reevaluate them in light of new understandings in tex86 palaeothermometry and supplement them with new data in order to evaluate long term temperature trends in the eocene we investigate the effect of archaea other than marine thaumarchaeota upon tex86 values using the branched to isoprenoid tetraether index bit the abundance of gdgt 0 relative to crenarchaeol gdgt 0 and the methane index mi we also introduce a new ratio gdgtrs which may help identify red sea type gdgt distributions in the geological record using the offset between tex86h and tex86l h l and the ratio between gdgt 2 and gdgt 3 2 3 we evaluate different tex86 calibrations and present the first integrated sst compilation for the eocene 55 to 34 ma although the available data are still sparse some geographic trends can now be resolved in the high latitudes 55 there was substantial cooling during the eocene 6 c our compiled record also indicates tropical cooling of 2 5 c during the same interval using an ensemble of climate model simulations that span the eocene our results indicate that only a small percentage 10 of the reconstructed temperature change can be ascribed to ocean gateway reorganization or paleogeographic change collectively this indicates that atmospheric carbon dioxide pco2 was the likely driver of surface water cooling during the descent toward the icehouse

kerogen bound glycerol dialkyl tetraether lipids released by hydropyrolysis of marine sediments a bias against incorporation of sedimentary organisms over the past 10 years the membrane lipids of archaea particular glycerol dialkyl glycerol tetraethers gdgts have been recognised as significant components of marine sediments and as potentially powerful tools in palaeoclimate reconstruction however relatively little is known about their preservation and in particular their incorporation into macromolecular organic matter fractions here we examine abundances distributions and stable carbon isotope ratio 13c values of gdgts and the diether archaeol in sediments from the benguela upwelling region ocean drilling program odp site 1084 and a mediterranean sapropel s5 these are compared with distributions of biphytanes released from the kerogen solvent extracted residue fraction using hydropyrolysis hypy gdgts likely derived from pelagic crenarchaeota are amongst the most abundant extractable components in both benguela and s5 sediments but are an order of magnitude more abundant in the former moreover the benguela sediments have far greater concentrations of the acyclic gdgt than expected consistent with the presence of methane in core 1084 co occurring archaeol and variable gdgt 13c values the excess acyclic gdgt probably arises from a contribution from sedimentary methanogens hypy released biphytanes have similar abundances in benguela and sapropel sediments and represent a significant proportion of the total tetraether lipid pool at the latter site however the distributions of hypy released biphytanes especially in benguela sediments do not always match those of the free gdgts at both sites hypy released biphytane 13c values are relatively invariant consistent with a single source again likely to be pelagic crenarchaeota these observations suggest that gdgts can be incorporated into sedimentary geomacromolecules relatively rapidly with those derived from pelagic crenarchaeota more likely to be incorporated than those derived from sedimentary methanogens it is likely that this bias arises from a lack of reactive substrates i e oxygen radicals in deeper anoxic sediments consistent with an important role for oxidative cross linking in kerogen formation

the effect of maturity and depositional redox conditions on archaeal tetraether lipid palaeothermometry recently we proposed a new organic sea surface temperature proxy tex86 based on the distribution of archaeal tetraether lipids here we have examined the effect of oxic degradation and maturity on this new temperature proxy our results show that oxic degradation does not appear to affect the tex86 values within the analytical error hydrous pyrolysis experiments suggest that thermal maturity does have an effect on tex86 sediments with relatively high amounts of 22s hopanes 22s 22s 22r ratios 0 1 or 17 21 h hopanes ratios 0 5 may have tex86 values which are biased towards lower values and thus lower sea surface temperatures

archaeal lipids in neogene dolomites monterey and sisquoc formations california planktic versus benthic archaeal sources abstract the distribution of archaeal lipids including archaeol and glycerol dibiphytanyl glycerol tetraethers gdgts in dolomite concretions and surrounding sediment from the monterey formation miocene and the sisquoc formation miocene pliocene were examined to distinguish planktic from benthic contributions for this purpose dolomites with positive 13 c values 7 to 13 were chosen such highly positive values point to pronounced methanogenesis of benthic archaea in the sedimentary column at first glance distributions and relative abundances of gdgts in both dolomites and background sediment were similar resembling patterns of marine planktic crenarchaea a contribution of benthic euryarchaea to the gdgt pool became evident only from variations in the 13 c values of different biphytanes obtained after ether cleavage of gdgts whereas bi and tricyclic biphytanes had an isotopic signal typical of planktic archaea 13 c 23 6 to 20 5 and 23 4 to 21 2 respectively for both dolomite and background sediment acyclic and monocyclic biphytanes showed lower values for dolomite samples 25 1 to 22 6 and 27 6 to 24 7 respectively indicating a contribution of lipids from benthic archaea the isoprenoid diether archaeol 13 c 23 9 to 22 9 assigned to euryarchaea was only detected in dolomite samples also reflecting additional input from sedimentary archaea probably autotrophic methanogens the occurrence of lipids derived from methanogenic archaea agrees with the strong 13 c enrichment of dolomites and with mineral formation taking place in the zone of archaeal methanogenesis this implies that the lipid biomarker inventory of sedimentary strata needs to be interpreted carefully as it is often not straightforward to discriminate between input from the water column and sedimentary microbial activity

aging of marine organic matter during cross shelf lateral transport in the benguela upwelling system revealed by compound specific radiocarbon dating organic matter accumulation and burial on the namibian shelf and upper slope are spatially heterogeneous and strongly controlled by lateral transport in subsurface nepheloid layers much of the material deposited in depo centers on the slope ultimately derives from the shelf supply of organic matter from the shelf involves selective transport of organic matter we studied these selective transport processes by analyzing the radiocarbon content of co occurring sediment fractions here we present radiocarbon data for total organic carbon as well as three tracers of surface ocean productivity phytoplankton derived alkenones membrane lipids of pelagic crenarchaeota crenarchaeol and calcareous microfossils of planktic foraminifera in core top and near surface sediment samples the samples were collected on the namibian margin along a shelf slope transect 85 to 1040 m at 24 s and from the upper slope depo center at 25 5 s in core top sediments alkenone ages gradually increased from modern to 3490 radiocarbon years with distance from shore and with water depth crenarchaeol while younger than alkenones also increased in age with distance offshore it was concluded that the observed ages were a consequence of cross shelf transport and associated aging of organic matter radiocarbon ages of preserved lipid biomarkers in sediments thus at least partially depend on the relative amount of laterally supplied pre aged material present in a sample highlighting the importance of nepheloid transport for the sedimentation of organic matter over the namibian margin

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

melts of sediments in the mantle wedge of the oman ophiolite the rocks in the crustal section of the oman ophiolite show an increasing input of a subduction component with time most likely reflecting the generation of the ophiolite above a subducting slab field relations new geochemical data and nd hf isotope data for felsic to mafic intrusive rocks in the mantle harzburgite from the haylayn block in the oman ophiolite suggest late magmatic events in a mantle wedge shortly before obduction of the ophiolite incompatible element contents and low end and ehf of the felsic rocks exclude differentiation from mafic magmas but are consistent with an origin by partial melting of pelagic sediments similar to leucogranites in continental collision zones these melts apparently mixed with mafic magmas resembling enriched late stage lavas from the ophiolite the leucogranitic intrusions into the mantle wedge confirm the transfer of melts of sediments from the subducted plate into the mantle at subduction zones we suggest that the enrichment of rb k and pb observed in the oman boninites is caused by addition of melts of sediments similar to those from the haylayn block to the boninite source in the mantle wedge

methane index a tetraether archaeal lipid biomarker indicator for detecting the instability of marine gas hydrates abstract gas hydrates represent one of the largest pools of readily exchangeable carbon on earth s surface releases of the greenhouse gas methane from hydrates are proposed to be responsible for climate change at numerous events in geological history many of these inferred events however were based on carbonate carbon isotopes which are susceptible to diagenetic alterations here we propose a molecular fossil proxy i e the methane index mi to detect and document the destabilization and dissociation of marine gas hydrates mi consists of the relative distribution of glycerol dibiphytanyl glycerol tetraethers gdgts the core membrane lipids of archaea the rational behind mi is that in hydrate impacted environments the pool of archaeal tetraether lipids is dominated by gdgt 1 2 and 3 due to the large contribution of signals from the methanotrophic archaeal community our study in the gulf of mexico cold seep sediments demonstrates a correlation between mi and the compound specific carbon isotope of gdgts which is strong evidence supporting the mi methane consumption relationship preliminary applications of mi in a number of hydrate impacted and or methane rich environments show diagnostic mi values corroborating the idea that mi may serve as a robust indicator for hydrate dissociation that is useful for studies of global carbon cycling and paleoclimate change

a long term high latitude record of eocene hydrological change in the greenland region abstract a range of proxy approaches have been used to reconstruct short term changes to earth s hydrological cycle during the early eocene hyperthermals however little is known about the response of earth s hydrological and biogeochemical systems to long term cenozoic cooling which began following the early eocene climatic optimum 53 3 49 4 million years ago ma here we use the molecular distribution and isotopic composition of terrestrial biomarkers preserved in marine sediments of odp site 913 east greenland to develop a long term record of high latitude hydrological change between 50 and 34 ma there is a marked decline in the concentration of conifer derived diterpenoids and angiosperm derived triterpenoids during the eocene as the input of wind blown conifer pollen remains stable during this interval this implies that decreasing di and triterpenoid concentrations reflect declining influence of fluvial inputs and perhaps terrestrial runoff throughout the eocene branched gdgts and bacterial derived hopanes indicate an increased input of soil and kerogen derived organic matter respectively after 38 ma this coincides with evidence for ice rafted debris and suggests input of organic matter via glacial processes this also implies some continental glaciation occurred on east greenland in the middle to late eocene leaf wax hydrogen isotopes extending throughout this section the first such long term record from the paleogene indicate that precipitation 2h was persistently higher than that of modern coastal greenland consistent with warmer ocean source waters and enhanced poleward moisture transport non intuitively however this effect appears to have been smallest during the warmest part of the record and higher 2h values occur in the middle eocene although interpretation of these hydrogen isotope trends is unclear they clearly indicate alongside the changes in biomarker abundances a perturbed hydrological cycle through the eocene in coastal greenland more long term records are required to ascertain if this represents regional or global hydrological reorganisation