fiamme degassing structures and their implications for the post emplacement temperatures and h2o contents of high grade ignimbrites abstract a new process in post emplacement ignimbrite degassing is proposed from observations of unusual structures in a high grade ignimbrite in sardinia the structures consist of fiamme decorated above and below by vesicles termed here fiamme degassing structures fds the relative volumes of vesicles and fiamme have a positive linear correlation and the ratio between the volume of vesicles above and below fiamme asymmetry ratio is 1 wt at

non newtonian rheology of igneous melts at high stresses and strain rates experimental results for rhyolite andesite basalt and nephelinite the stress strain rate relationships of four silicate melt compositions high silica rhyolite andesite tholeiitic basalt and nephelinite have been studied using the fiber elongation method measurements were conducted in a stress range of 10 400 mpa and a strain rate range of 10 6 to 10 3 s 1 the stress strain rate relationships for all the melts exhibit newtonian behavior at low strain rates but non newtonian nonlinear stress strain rate behavior at higher strain rates with strain rate increasing faster than the applied stress the decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt the decrease in viscosity observed at the high strain rates of the present study ranges from 0 25 to 2 54 log10 pa s the shear relaxation times of these melts have been estimated from the low strain rate newtonian shear viscosity using the maxwell relationship s g non newtonian shear viscosity is observed at strain rates time 1 equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time brittle failure of the fibers occurs 2 log10 units of time above the relaxation time this study illustrates that the occurrence of non newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate high silica rhyolite melts involved in ash flow eruptions are expected to undergo a non newtonian phase of deformation immediately prior to brittle failure

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

a diagnostic gdgt signature for the impact of hydrothermal activity on surface deposits at the southwest indian ridge abstract the impact of hydrothermal activity on wider ocean geochemistry and microbial ecology remains a topic of much interest to explore whether hydrothermal microbial signatures are exported to surrounding marine sediments or if such organisms serve as an important source of sedimentary organic matter we determined the distributions of glycerol dialkyl glycerol tetraether gdgt membrane lipids in surficial normal marine sediments metalliferous sediments and low temperature hydrothermal deposits at newly discovered hydrothermal fields and adjacent areas at the southwest indian ridge swir the gdgts in those samples varied significantly evidently representing a variable influence of the hydrothermal activity gdgt compositions of surficial background sediments in swir were similar to those commonly observed in marine sediments dominated by gdgts associated with marine planktonic archaea and especially gdgt 0 and crenarchaeol in contrast the gdgts of metalliferous sediments strongly impacted by hydrothermal activity and low temperature hydrothermal deposits were markedly different characterized by high relative abundances of isoprenoid gdgts igdgts bearing multiple rings yielding a higher ring index low relative abundances of crenarchaeol and the presence of glycerol monoalkyl glycerol tetraether lipids gmgts so called h tetraethers that were absent in the normal marine sediments sources for these hydrothermal specific tetraether lipids likely include methanogens and anaerobic methanotrophic archaea gdgt 0 and gdgt 1 3 respectively thermoprotei and thermoplasmatales elevated gdgt 3 and 4 and other thermophilic archaea including methanobacteriales gmgts deposits influenced by low temperature hydrothermal activity also contained higher abundances of branched gdgts brgdgts typically attributed to soil bacteria the more distal metalliferous sediments influenced by the neutrally buoyant plume did not contain putative hydrothermal gdgts having the same gdgt distribution as the background sediments this suggests that the neutrally buoyant plume has a limited potential to directly influence the organic matter inputs to surrounding sediments due to a rapidly waning chemosynthetic microbial contribution relative to normal marine contributions as the plume dispersed and was diluted

the clay with flints deposit in northern ireland reassessment of the evidence for an early paleocene ignimbrite reassessment of key geological sections field relationships and petrographical characteristics of the northern ireland clay with flints and donald s hill ignimbrite formation show they formed dominantly by sedimentary processes the involvement of a previously postulated pyroclastic flow during early paleocene time is not recognized and as such the donald s hill ignimbrite formation stratigraphic term is discounted instead a multistage model of formation by sedimentary accumulation and remobilization is presented and the term clay with flints is retained regionally two dominant facies are recognized in most clay with flints sections facies 1 was formed by an initial accumulation of flints on a chalk landscape undergoing karstification and involved deposition of a clay matrix derived predominantly from contemporaneous erosion of subtropical soil horizons formed mainly on basalt in facies 2 evidence is observed for widespread remobilization of facies 1 deposits by high density mudflows driven by the advancement of the antrim lava group which caused the blockage of subsurface and marginalization of surface drainage a stratigraphical constraint imposed by the presence of a supposed ignimbrite in this part of the north atlantic igneous province has been problematic but this is resolved by its identification as a diachronous sedimentary deposit that formed until buried by either the lower or upper formations of the antrim lava group

deposition of rheomorphic ignimbrite d mogan formation gran canaria canary islands spain rheomorphic ignimbrite d 13 4 ma upper mogan formation on gran canaria a multiple flow single cooling unit is divided into four major structural zones that differ in fabric and finite strain of deformed pyroclasts their structural characteristics indicate contrasting deformation mechanisms during rheomorphic flow the zones are a a basal zone vitrophyre with pure uniaxial flattening perpendicular to the foliation b an overlying shear zone characterized by asymmetric fabrics and a significantly higher finite strain with an ellipsoid geometry similar to stretched oblate bodies c a central zone with a finite strain geometry similar to that of the underlying shear zone but without evidence of a rotational strain component and d a slightly deformed to non deformed top zone where the almost random orientation of subspherical pyroclasts suggests preservation of original syn depositional clast shapes rheomorphic flow in d is the result of syn to post depositional remobilization of a hot pyroclastic flow as shown by kinematic modeling based on a the overall vertical structural zonation suggested by finite strain and fabric analysis b the relation of shear sense to topography c the interrelationship of the calculated vertical cooling progression at the base of the flow formation of vitrophyre and the related vertical changes in strain geometry d the complex lithification history and e the consequent mechanisms of deformational flow rheomorphic flow was caused by load pressure due to an increase in the vertical accumulation of pyroclastic material on a slope of generally 6 8 we suggest that every level of newly deposited pyroclastic flow material of d first passed through a welding process that was dominated by compaction pure flattening before rheomorphic deformation started

origin and distribution of terrestrial organic matter in the nw mediterranean gulf of lions exploring the newly developed bit index the branched and isoprenoid tetraether bit index is based on the relative abundance of nonisoprenoidal glycerol dialkyl glycerol tetraethers gdgts derived from organisms living in terrestrial environments versus a structurally related isoprenoid gdgt crenarchaeol produced by marine crenarchaeota the bit index varies between 0 and 1 representing marine and terrestrial organic matter om end members respectively hopmans et al earth planet sci lett 224 107 116 2004 in this study the applicability of the bit index to trace terrestrial om is tested in combination with other organic parameters toc c n ratio 13corg total lipid and n alkane in the gulf of lions a river dominated continental margin of the western mediterranean we analyzed a variety of soils and riverbed sediments from the continent as well as surface sediments from the shelf and canyons the bit index in soils and riverbed sediments shows high values 0 9 while it varies between 0 02 and 0 83 in marine sediments decreasing seaward from the inner shelf to the slope for marine surface sediments high bit values are associated with lower 13corg values as well as higher toc contents and higher n alkane concentrations our results confirm that the bit index can be applied in coastal marine environments in order to characterize terrestrial om as proposed by hopmans et al 2004 therefore the bit index is a useful addition to the proxies presently available for studying the origin and distribution of om in continental margins and especially valuable in multiproxy studies

petrography and geochemistry of impactites and volcanic bedrock in the icdp drill core d1c from lake el gygytgyn ne russia the 3 6 ma old and 18 km diameter el gygytgyn impact structure in ne siberia was drilled in 2008 09 by icdp international continental scientific drilling program a 517 m long core hole d1c was drilled into the outer flank of the central uplift structure with an overall core recovery of approximately 63 thereby approximately 315 m lake sediments and approximately 202 m impactites were recovered here we present a detailed petrographic and geochemical assessment of the impact breccia and bedrock sections in this core the 97 m long lower bedrock unit 517 420 m below lake floor blf consists of an ignimbrite in the overlying upper bedrock unit 420 390 mblf the core recovered a sequence of similar ignimbrite and several decimeters of mafic rocks we interpret these units as rocks that are located close to their former preimpact position but have been somewhat rotated due to collapse of the central uplift i e it represents parautochthonous basement from about 390 to 328 mblf occurs a suevite package with an impact melt poor clast dominated matrix and lithic and mineral clasts that cover the entire range of volcanic target rocks known from the el gygytgyn region all stages of shock metamorphism unshocked to melted were observed in clasts and in microclasts of the matrix of suevite from different depths immediately below this package at the contact to the underlying bedrock occurs a 1 m wide sheared zone within vitrophyric ignimbrite which we consider the actual crater floor the uppermost approximately 12 m from 328 316 mblf depth seem to comprise reworked suevite consisting of a mixture of sediments and suevite with more and on average stronger shocked minerals than found in the main suevite unit this includes a small component of glassy spherules and impact melt fragments toward the top of this unit lake sediments progressively become the dominant material in this section we assume that this unit contains a fallback component from the ejecta plume that was mixed with the first sediments of the postimpact crater lake and possibly some rocks that slumped off the inner crater wall similar to a thin layer at the base of the sediment section of borehole lb 5a recovered in lake bosumtwi ghana

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

viscosity of a teide phonolite in the welding interval abstract the viscosity of a natural phonolitic composition with variable amounts of h2o has been experimentally determined the starting materials were crystal free phonolitic glasses from montana blanca situated within the las canadas caldera of teide dry phonolitic melt viscosities were determined using concentric cylinder viscometry in the low viscosity range the glassy quench products of these runs were then hydrated by high pressure synthesis in a piston cylinder apparatus to generate a suite of samples with water contents ranging from 0 02 to 3 75 wt samples thus hydrated were quenched rapidly and prepared cut and polished for the determination of water contents by infrared spectroscopy before and after experimental viscometry the viscosities of the melts dry and hydrated were determined at 1 bar using a micropenetration technique samples were stable under the measurement conditions up to 3 75 wt h2o homogeneity of water content was confirmed by infrared spectroscopy and total water contents were calculated using absorptivity coefficients for compositions extremely close to that investigated here the variation of viscosity as a function of water content and temperature can be described in the high viscosity interval of relevance to many welding processes by the non arrhenian expression 1 log 10 5 900 0 286 ln h 2 o 10775 4 394 8 h 2 o t 148 7 21 65 ln h 2 o whereas the high viscosity range alone is adequately described by the arrhenian expression 2 log 10 10 622 0 738 ln h 2 o 17114 3 590 4 h 2 o 1 t where is the viscosity in pa s h2o is the water content in wt and t is the temperature in k these results are particularly useful for the scaling of conditions extant during the welding of phonolitic products of montana blanca the welding of glassy phonolitic rocks is enhanced by the lower viscosity of these melts with respect to calcalkaline rhyolites the ratio of viscosities of phonolitic to calcalkaline rhyolitic melts is a complex function of temperature and water content and reaches up to 104 5 at 0 1 wt h2o and 500 c abundant evidence of welding and remobilisation of pyroclastic and spatter products of teide system volcanism are consistent with these experimental observations

tetraether lipids from the southern yellow sea of china implications for the variability of east asia winter monsoon in the holocene to better understand the origin and distribution of organic matter om in the yellow sea ys and to delineate potential interactions between the atmosphere and the marine system during the holocene we reconstructed terrestrial input and temperature variation for the last 8 8 ka bp using glycerol dialkyl glycerol tetraethers gdgts obtained from a 4 4 m sediment core ysc 1 from the southern ys the archaea derived isoprenoid gdgts igdgts were dominated by gdgt 0 and crenarchaeol the igdgts and bacteria derived branched gdgts bgdgts correlated well and varied in opposition to the bit branched vs isoprenoid tetraether index this may be due to varying river runoff and influence of the ys coastal current yscc and ys warm current yswc related to the east asia winter monsoon eawm which made the bit proxy less suitable for tracing soil om input to the ys tex86 tetraether index of tetraethers consisting of 86 carbons derived sea surface temperature values sst varied from 9t o 16c close to the sst in the ys cold season the mbt cbt methylation of branched tetraethers and cyclization of branched tetraethers derived continental temperature ranged from 10 to 19 c indicating an annual mean air temperature for the middle and low drainage basin of the ys these two temperature records were decoupled but both correlated with the variation in the eawm suggesting an intimate link between eawm and temperature variation in east asia

distribution of glycerol dialkyl glycerol tetraethers in surface sediments of lake qinghai and surrounding soil abstract glycerol dialkyl glycerol tetraethers gdgts are increasingly used as proxies for paleoclimate studies of marine and lacustrine environments while gdgt based proxies have been applied to a number of lake environments globally little is known about the distribution of gdgts on the qinghai tibet plateau we have investigated the isoprenoid gdgts igdgts and branched gdgts bgdgts in lake qinghai sediments and the surrounding surface soil in order to examine their potential use as paleoclimate proxies on the qinghai tibet plateau the results show that i the values of the igdgt bgdgt ratio for surrounding soil were at the higher end among globally distributed soils and consequently bit values avg 0 71 at the lower end ii the tex86 values decreased while the mbt and cbt values increased along an onshore soil nearshore sediment offshore sediment transect iii the tex86 values for the offshore sediments were almost identical and their inferred temperatures were close to mean summer surface water temperature and iv the bgdgt inferred mean annual air temperature maat and ph for soil were consistent with measured maat and ph however the cbt inferred ph for offshore sediments seemed inconsistent with the ph of lake water or sediment our results suggest that i the higher ph may be an important factor leading to the higher igdgt bgdgt values and lower bit values in surrounding surface soil ii both igdgts and bgdgts may originate from terrestrial input and in situ production for this saline lake especially for nearshore sediments however for offshore sediments terrestrial igdgt input seems minor and tex86 may be useful for paleoclimate studies of lake qinghai

coupled thermal and hydrological evolution of tropical africa over the last deglaciation we analyzed the distribution of branched tetraether membrane lipids derived from soil bacteria in a marine sediment record that was recovered close to the congo river outflow and the results enabled us to reconstruct large scale continental temperature changes in tropical africa that span the past 25 000 years tropical african temperatures gradually increased from 21 to 25 c over the last deglaciation which is a larger warming than estimated for the tropical atlantic ocean a direct comparison with sea surface temperature estimates from the same core revealed that the land sea temperature difference was through the thermal pressure gradient an important control on central african precipitation patterns

the transition of spatter to lava like body in lava fountain deposits features and examples from the cabezo segura volcano calatrava spain abstract the cabezo segura ii volcanic cone calatrava volcanic province iberian microplate comprises proximal wall deposits with a well defined crater wall unconformity and crater fill deposits the complex volcanic succession that shows evidence of several eruptive episodes was built by magmatic and hydrovolcanic explosions of different styles strombolian hawaiian sub plinian and phreato strombolian generated from a multiple feeder ultrabasic dyke intra crater rock units at the volcano summit include spatter deposits together with up to 10 m thick and more than 200 m long lava like bodies geological logs for the main lava like bodies define a characteristic facies model that involves a central lava like mass which grades vertically into a transition zone of apparently coherent spatter then dense spatter and finally into vuggy spatter deposits these units are inferred to have formed during pulsating lava fountain type explosive eruptions the depicted facies distribution being the result of progressive increase in welding grade and densification of the spatter in response to variations in the accumulation rate their field features may be used as a guide for the precise identification of vent sites in deposits of hawaiian eruptions also structures like those here recognised that might have survived in lava like flows could be of help to identify when lava producing eruptions represented an explosive hawaiian event lava fountains and not a purely effusive event

crenarchaeotal membrane lipids in lake sediments a new paleotemperature proxy for continental paleoclimate reconstruction paleoclimate studies of continental environments have been hampered by the lack of an independent paleotemperature proxy a novel sea surface temperature proxy has been proposed for marine systems based on membrane lipids of marine crenarchaeota this proxy will provide an independent continental paleotemperature tool that will allow paleoclimatologists to address fundamental questions about temperature variability in continental environments and its relationship to climate change

growth destruction and facies architecture of effusive and explosive volcanics in the miocene shama basin southwest of saudi arabia subaqueous subaerial volcanism in a lacustrine setting abstract this paper presents for the first time detailed stratigraphical and petrographical analyses of the harrat shama volcanic basin hsvb of miocene age in sw saudi arabia this basin is filled by abundant volcanics intercalated with fluvio lacustrine sedimentary successions these successions are characterized by a syneruptive intereruptive cycle which results from the intercalation periods of volcanics and volcaniclastic sedimentation along with periods of fluvial incision two depositional sequences showing an overall fining upward trend are preserved within the hsvb the first comprises hyaloclastites zeolite bearing bedded tuffs and bedded accretionary lapilli tuffs interpreted as deep lake whereas the second is made up of extensive pumiceous pyroclastic flows peperitic breccias and basaltic lava flows which are in turn capped by siliciclastic deposits of lacustrine deposits the passage between two sequences is defined by lateral variations of the lithofacies and textural features reflecting a change in paleogeography the fining upward volcaniclastic deposits of the hsvb sequence are interpreted to represent the sedimentation pattern induced by tectonic subsidence with the influence of volcaniclastic sediment input indicating well established proximal distal relationship hsvb was evolved through three stages including pre syn and post caldera stages the first two stages correspond to proximal aggradational syn eruptive event whereas the latter stage refers to distal degradational inter eruptive event these stages overlap in time as shown by the alternation of explosive effusive and their resedimented deposits reflecting diverse eruptive sequences formed by different fragmentation processes the difference in the latter coupled with the variability in the magma water interaction and the nature of substrate are responsible for such diversity resulting in progressive environmental changes from subaqueous to subaerial regime from bottom to top the development of such contrast in the depositional sequences reflects variation in the sediment flux and subsidence rate during the evolution of the hsvb

low temperature hydrothermal alteration of intra caldera tuffs miocene tejeda caldera gran canaria canary islands article i nfo the miocene tejeda caldera on gran canaria erupted 20 rhyolite trachyte ignimbrites mogan group 14 13 3 ma followed by 20 phonolitic lava flows and ignimbrites fataga group 13 8 5 ma upper mogan tuffs have been severelyaltered immediately within the caldera margin whereas extra caldera mogan ignimbrites and overlying fataga units are apparently unaltered the altered intra caldera samples contain minerals characteristic of secondary fluid rock interaction clays zeolites adularia and relics of the primary mineral assemblage identified in unaltered ignimbrites k feldspar plagioclase pyroxene amphibole and groundmass quartz major and trace element data indicate that si na k pb sr and rb were strongly mobilized during fluid rock interaction whereas ti zr and nb behaved in a more refractory manner experiencing only minor mobilization the 18 o values of the altered intra caldera tuffs are significantly higher than in unaltered extra caldera ignimbrites consistent with an overall low temperature alteration environment unaltered extra caldera ignimbrites have d values between 110 and 173 which may reflect rayleigh type magma degassing and or post depositional vapour release the d values of the altered intra caldera tuffs range from 52 to 131 with ambient meteoric water at the alteration site estimated at ca 15 interaction and equilibration of the intra caldera tuffs with ambient meteoric water at low temperature can only account for whole rock d values of around 45 given that dclay water is ca 30 at 100 c and decreases in

welding and rheomorphism of phonolitic fallout deposits from the las canadas caldera tenerife canary islands the las canadas caldera is a nested collapse caldera formed by the successive migration and collapse of shallow magmatic chambers among the pyroclastic products of this caldera are phonolitic fallout deposits that crop out in the caldera wall and on the extracaldera slopes these deposits exhibit an uninterrupted facies gradation from nonwelded to lava like and record continuous volcanic deposition densely welded and lava like facies result from the extreme attenuation and complete homogenization of juvenile clasts that destroy original clast outlines and any evidence of fallout deposition agglutination contributes significantly to the final degree of flattening observed in the welded facies after deposition rheomorphic flowage occurs emplacement temperatures for one of the welding sequences are calculated from magmatic temperatures and a model of tephra cooling during fallout results are 486 c for the nonwelded facies and 740 c for the moderately welded facies for the same welding sequence a cooling time between 25 and 54 days is estimated from published experimental and computational data as the possible duration of welding and rheomorphism following deposition and agglutination the lava like pyroclastic facies had the rheological properties of viscous lavas and flowed down the outer slopes away from the caldera some lava like masses detached from proximal areas to more distal regions during deposition the eruptive style evolved from plinian fallout to fountain fed spatter deposition this evolution was accompanied by a decrease in explosive power and a lower height of the eruptive column which produce higher emplacement temperatures and more effective heat retention of pyroclasts

emplacement and rheomorphic deformation of a large lava like rhyolitic ignimbrite grey s landing southern idaho the miocene grey9s landing ignimbrite reaches 70 m thick and covers at least 400 km 2 in the central region of the snake river plain it shows particularly intense welding and rheomorphic deformation and although parts are eutaxitic most is lava like with flow banding and no fiamme a near ubiquitous penetrative flow lamination associated with a well developed elongation lineation is folded into small intrafolial tight to isoclinal oblique and sheath folds which are refolded by larger folds in the upper parts structural and kinematic analysis reveals that welding and early deformation occurred rapidly during deposition from a very hot 1000 c high mass flux pyroclastic density current that flowed westward across a graben faulted landscape as hot particles were deposited they rapidly agglutinated and coalesced and underwent noncoaxial shear in a subhorizontal ductile shear zone close to the current deposit interface the shear zone is interpreted to have been less than 2 m thick it produced and deformed the rheomorphic fabric and it migrated upward with the rising current deposit interface during aggradation so that it transiently affected all levels of the resultant thick ignimbrite deformation was progressive and after the density current had dissipated viscous spreading and downslope flow continued and involved an increasingly thick portion of the sheet this folded the flow banding and f 1 intrafolial isoclines into larger sheath folds and into more upright periclines near the top of the ignimbrite we demonstrate that structural and kinematic analysis can elucidate the emplacement history of rheomorphic ignimbrites

variability of tetraether lipids in yellow river dominated continental margin during the past eight decades implications for organic matter sources and river channel shifts abstract glycerol dialkyl glycerol tetraethers gdgts and bulk organic geochemical parameters were examined for a short core from the bohai sea a yellow river dominated continental margin a three end member mixing model using branched isoprenoid tetraethers bit index 13c and c n shows that the average fractions of soil marine and plant organic matter om during the period of 1933 2011 are 67 7 38 92 26 1 0 58 and 6 2 0 23 respectively abrupt changes of sedimentary om compositions around 1953 1976 and 1996 are synchronous with the yellow river mouth relocations the bit index values 0 33 0 80 present a stronger correlation with crenarchaeol abundance r2 0 88 than branched gdgts abundance r2 0 27 suggesting that variations of marine thaumarchaeota abundance rather than soil om inputs is the first order factor controlling the bit index values although this proxy has been widely used for soil om the comparison between the bit index nutrient status and historical yellow river sediment load indicates that the high sensitivity of the bit index to the yellow river channel shifts cannot be explained by a nutrient stimulation mechanism but instead is likely caused by the restriction of thaumarchaeota growth in highly turbid water due to the enormous sediment inputs from yellow river our study demonstrates that local conditions should be considered when applying the bit index as an environmental proxy

the emplacement of a large chemically zoned rheomorphic lava like ignimbrite the sgurr of eigg pitchstone nw scotland the sgurr of eigg pitchstone on the isle of eigg nw scotland is a crystal rich trachydacitic partially vitrophyric rock which has previously been interpreted both as a lava and as a sill we interpret this rock as a chemically zoned rheomorphic lava like ignimbrite that formed during a sustained pyroclastic eruption the sgurr of eigg pitchstone can be subdivided into discrete emplacement units distinguished by the following features 1 their present day weathering characteristics 2 the orientation spacing and morphology of the columnar joints 3 sharp undulating boundaries with marked topographic breaks the absence of weathered surfaces palaeosols pyroclastic fall deposits or sedimentary rocks at emplacement unit boundaries suggests deposition from a single eruption the emplacement units some of which display upper and basal vitrophyres represent distinct depositional packages that record several rapidly emplaced ignimbrites which welded cooled and devitrified as a simple essentially single cooling unit during eruption from a sustained low pyroclastic column the sgurr of eigg pitchstone displays a pervasive base parallel flow banding which is folded into intrafolial recumbent isoclinal folds the flow banding and folds indicate that rheomorphism occurred throughout deposition the sgurr of eigg pitchstone is interpreted as an erosional remnant of an extensive ignimbrite sheet the first such unit recorded within the north atlantic igneous province

spatial distributions of core and intact glycerol dialkyl glycerol tetraethers gdgts in the columbia river basin and willapa bay washington insights into origin and implications for the bit index abstract branched and isoprenoid glycerol dialkyl glycerol tetraethers brgdgts and isogdgts respectively are used to reconstruct carbon flow from terrestrial landscapes to the ocean in a proxy called the branched vs isoprenoid tetraether index or bit index the index is based on analysis of core gdgts c gdgts that are produced from intact gdgts i gdgts upon cell death gdgts are a component of the cell membranes of bacteria in soils br and archaea iso primarily in the marine environment however uncertainty as to the identity of the organisms that biosynthesize brgdgts the variation in the extent to which gdgts represent end member carbon pools and the suspected production of brgdgts and isogdgts in both marine and terrigenous environments hinders interpretation of the bit index since brgdgts remain our only tool for measuring the presence of unknown brgdgt producing organisms it is particularly important to use the intact form of brgdgts in living cells rather than c brgdgts in relict biomass to infer the distributions of the likely source organisms in situ production within riverine lacustrine and marine environments is currently thought to be possible yet few measures of i brgdgts are available in these environments to support these claims here we assess the spatial distribution of core and intact gdgts in the columbia river basin and nearby willapa bay washington and oregon in order to elucidate source environments and behavior of i gdgts vs c gdgts the presence of i brgdgts throughout the studied soils rivers and estuaries suggests in situ production across the continuum from soil to marine environments likewise intact crenarchaeol the marine end member isogdgt used in the bit index was present in all samples widespread production of each gdgt class along terrigenous carbon transport paths likely alters the bit index along this continuum core to intact ratios and the weak correlation between i gdgt derived bit values and carbon isotope signatures suggest a mixture of allochthonous and autochthonous sources of gdgts in riverine and marine environments our findings highlight the need for further work into the provenance and behavior of gdgts in order to improve interpretation of the bit index and other environmental proxies that rely on them

warm arctic continents during the palaeocene eocene thermal maximum the palaeocene eocene thermal maximum petm 55 5 ma is a geologically relatively brief episode of extreme warmth both deep and surface ocean temperatures increased by up to 5 c in equatorial waters and up to 8 c in mid and high latitude waters from the continents the annual mean air temperature response during the petm is still largely unknown mainly due to a lack of quantitative temperature proxies and sufficient suitable continuous high resolution records recently a new proxy for continental temperature reconstructions has been proposed based on the distribution of membrane lipids of bacteria in present day soils j w h weijers s schouten j c van den donker e c hopmans j s sinninghe damste 2007 environmental controls on bacterial tetraether membrane lipid distribution in soils geochimica et cosmochimica acta 71 703 713 and shown to reconstruct annual mean air temperature in this study we applied this new proxy in an attempt to reconstruct the air temperature in high latitude continental areas during the petm by analysis of a marine sedimentary sequence obtained from the lomonosov ridge in the central arctic ocean integrated ocean drilling program expedition 302 site 004 hole a the results indicate a warming of 8 c above background values of 17 c this warming is coincident with a similar rise in sea surface temperatures documented earlier our results thus further confirm the warm conditions in the arctic and point to a strongly reduced latitudinal temperature gradient during the petm 2007 elsevier b v all rights reserved

branched glycerol dialkyl glycerol tetraethers in arctic lake sediments sources and implications for paleothermometry at high latitudes branched glycerol dialkyl glycerol tetraethers brgdgts are analyzed in different lakes of the mackenzie canadian arctic and kolyma siberian arctic river basins to evaluate their sources and the implications for brgdgt based paleothermometry in high latitude lakes the comparison of brgdgt distributions and concentrations in the lakes with those in river suspended particulate matter riverbank sediments and permafrost material indicates that brgdgts in arctic lake sediments have mixed sources in contrast to global observations distributional offsets between brgdgts in arctic lakes and elsewhere in the catchment are minor likely due to the extreme seasonality and short window of biological production at high latitudes consequently both soil and lake calibrated brgdgt based temperature proxies return sensible temperature estimates even though the mean air temperature mat in the arctic is below the calibration range the original soil calibrated mbt cbt methylation of branched tetraethers cyclisation of branched tetraethers proxy generates mats similar to those in the studied river basins whereas using the recently revised mbt cbt calibration overestimates mat the application of the two global lake calibrations generating summer air temperatures sat and mat respectively illustrates the influence of seasonality on the production of brgdgts in lakes as the latter overestimates actual mat whereas the sat based lake calibration accounts for this influence and consequently returns more accurate temperatures our results in principle support the application of brgdgt based temperature proxies in high latitude lakes in order to obtain long term paleotemperature records for the arctic although the calibration and associated transfer function have to be selected with care

recognition characterization and implications of high grade silicic ignimbrite facies from the paleoproterozoic bijli rhyolites dongargarh supergroup central india abstract a controversy regarding the distinction between the highly welded lava like ignimbrites sometimes showing strongly rheomorphic characters and the extensive silicic lava flow has been overwhelming in the recent literature however a rethinking after walker 1983 has brought into light the concept of grade referring to the degree and extent of welding between the pyroclasts various parameters and characteristics were suggested for strengthening the idea of densely welded ignimbrites which differentiate them from lava here a comprehensive study on early proterozoic acid magmatic rocks forming lower part of the dongargarh supergroup central india has been made to suggest extensive occurrence of high grade welded rheomorphic tuffs the possibility of their being welded ignimbrite rather than lava flow has been explored in the light of facies analysis as well as detailed microscopic evidences despite having overall monolithologic look various units bear distinction on account of their nature of welding enrichment of phenocrysts and degree of stretching the presence of vitroclastic texture melt inclusions and radial fracturing of phenocrysts suggests pyroclastic nature of these deposits based on these characters four facies a b c and d from bottom to the top respectively have been identified from field studies around salekasa facies a and b represent clast supported matrix supported welded pyroclastic flow deposits facies c represents extremely welded thinly laminated rheomorphic tuffs while lava like tuffs with an autobreccia carapace is represented by facies d a complete gradation of facies a b to d through c exists high to extremely high grade nature of welding in these deposits suggests a low column height subaerial plinian to fissure eruption of a very high temperature silicic magma in a continental setting

low temperature hydrothermal alteration of intra caldera tuffs miocene tejeda caldera gran canaria canary islands abstract the miocene tejeda caldera on gran canaria erupted 20 rhyolite trachyte ignimbrites mogan group 14 13 3 ma followed by 20 phonolitic lava flows and ignimbrites fataga group 13 8 5 ma upper mogan tuffs have been severely altered immediately within the caldera margin whereas extra caldera mogan ignimbrites and overlying fataga units are apparently unaltered the altered intra caldera samples contain minerals characteristic of secondary fluid rock interaction clays zeolites adularia and relics of the primary mineral assemblage identified in unaltered ignimbrites k feldspar plagioclase pyroxene amphibole and groundmass quartz major and trace element data indicate that si na k pb sr and rb were strongly mobilized during fluid rock interaction whereas ti zr and nb behaved in a more refractory manner experiencing only minor mobilization the 18o values of the altered intra caldera tuffs are significantly higher than in unaltered extra caldera ignimbrites consistent with an overall low temperature alteration environment unaltered extra caldera ignimbrites have d values between 110 and 173 which may reflect rayleigh type magma degassing and or post depositional vapour release the d values of the altered intra caldera tuffs range from 52 to 131 with ambient meteoric water at the alteration site estimated at ca 15 interaction and equilibration of the intra caldera tuffs with ambient meteoric water at low temperature can only account for whole rock d values of around 45 given that dclay water is ca 30 at 100 c and decreases in magnitude at higher temperatures all altered tuff samples have d values that are substantially lower than 45 indicating interaction with a meteoric water source with a d value more negative than 15 which may have been produced in low temperature steam fumaroles supported by numerical modeling our gran canaria data reflect the near surface epithermal part of a larger fault controlled hydrothermal system associated with the emplacement of the high level fataga magma chamber system in this near surface environment fluid temperatures probably did not exceed 200 250 c

a model to explain joint patterns found in ignimbrite deposits the study of fracture systems is of paramount importance for economic applications such as co2 storage in rock successions geothermal and hydrocarbon exploration and exploitation and also for a better knowledge of seismogenic fault formation understanding the origin of joints can be useful for tectonic studies and for a geotechnical characterisation of rock masses here we illustrate a joint pattern discovered in ignimbrite deposits of south america which can be confused with conjugate tectonic joint sets but which have another origin the pattern is probably common but recognisable only in plan view and before tectonic deformation obscures and overprints it key sites have been mostly studied by field surveys in bolivia and chile the pattern is represented by hundreds of meters up to kilometre long swarms of master joints which show circular to semi circular geometries and intersections that have x and y patterns inside each swarm joints are systematic rectilinear or curvilinear in plan view and as much as 900 m long in section view they are from sub vertical to vertical and do not affect the underlying deposits joints with different orientation mostly interrupt each other suggesting they have the same age this joint architecture is here interpreted as resulting from differential contraction after emplacement of the ignimbrite deposit above a complex topography the set of the joint pattern that has suitable orientation with respect to tectonic stresses may act to nucleate faults

constraints on the application of the mbt cbt palaeothermometer at high latitude environments svalbard norway abstract branched glycerol dialkyl glycerol tetraethers gdgts are membrane lipids of unknown bacteria that are ubiquitous in soil and peat two indices based on the distribution of these lipids in soils the cyclization of branched tetraethers cbt and the methylation of branched tetraethers mbt indices have been shown to correlate with soil ph and mean annual air temperature mat and soil ph respectively and can be used to reconstruct mat in palaeoenvironments to verify the extent to which branched gdgts in marine sediments reflect the distribution pattern on land and whether these proxies are applicable for palaeoclimate reconstruction in high latitude environments with a mat of

a 30 ma history of the amazon river inferred from terrigenous sediments and organic matter on the ceara rise abstract the history of the amazon river is a much discussed subject and the timing of the development of a transcontinental system in particular is a matter of some controversy with estimations varying between the early miocene and the pliocene or even the pleistocene to shed further light on this we studied the sediment provenance of an oligocene to late pleistocene marine sedimentary section from the ceara rise odp site 925 a topographic high in the central atlantic ocean using major element concentrations and nd isotopic composition in 85 samples in addition the carbon isotopic composition of bulk organic matter and changes in the distribution of glycerol dialkyl glycerol tetraethers gdgts were used to identify periods of increased river outflow on the basis of these results we suggest that the history of the development of the amazon river is characterized by specific steps during the late oligocene early miocene 30 18 3 ma the terrigenous mass accumulation rates tars were high and sediment and gdgt compositions suggest that a large river system existed which at times received weathering products from a younger and probably andean sediment source a shift to a younger andean sediment provenance after 8 7 ma indicates that the amazon river became permanently connected with the andes between 18 3 and 4 5 ma tars were generally low and gdgts were derived for the most part from in situ production in marine waters around 4 5 ma the river expanded probably due to ongoing tectonic activity and uplift in the andes increased andean rock erosion this led to a strong increase in terrigenous sediment deposition and enhanced organic matter preservation on the ceara rise and the delivery of terrestrial both soil and riverine branched gdgts to the ceara rise

sources and transport of terrestrial organic matter in vancouver island fjords and the vancouver washington margin a multiproxy approach using d13corg lignin phenols and the ether lipid bit index the branched and isoprenoid tetraether bit index a ratio of marine and terrestrial glycerol dialkyl glycerol tetraether gdgt membrane lipids was recently introduced as a proxy for the fraction of fluvially derived organic carbon oc buried in marine sediments we investigate the source and distribution of terrestrial oc in marine sediments in a large spatial data set that encompasses the washington vancouver island margin vancouver island fjords and puget sound with the goal of comparing the bit index to other traditional measures of terrestrial oc d13 co f oc d13corg and lignin phenols d13corg values and lignin concentrations indicate that the fjords are a significant trap for undegraded wood derived terrestrial material with surface sediments containing up to 76 terrestrial oc these proxies also show significant terrestrial oc contributions to margin sediments up to 54 with most likely an angiosperm source from the columbia river in contrast to d13corg values and lignin concentrations bit index values indicate extremely low terrestrial carbon throughout the study area bit index values range from 0 to 0 28 and are uncorrelated with the other proxies though the bit index did not correlate with other proxies margin gdgt concentrations varied offshore similarly to other terrestrially derived oc and are well correlated with other proxies we suggest that the bit index is best interpreted as a proxy for soil or peat derived oc the majority of terrestrially derived oc delivered to sediment in this area has a lignin rich nonsoil source the disparity between the bit index and other proxies implies that the bit index significantly underestimates terrestrial relative to marine oc input to sediments in areas in which riverine oc input is not soil or peat derived burial of organic carbon oc on continental margins is estimated to account for the majority of the total carbon burial in the ocean and is a significant sink for terrestrial oc hedges and keil 1995 understanding the sources and fate of this terrestrial oc in marine sediments is thus of importance in understanding global biogeochemical cycles in this study we use two traditional proxies for terrestrial oc input to sediments the d 13 c of bulk sedimentary oc d13corg and the concentration of lignin phenols to examine the sources and quantity of terrestrial oc in sediments throughout the washington vancouver island margin vancouver island fjords and puget sound we compare these results to those obtained using a recently introduced proxy for terrestrial oc in marine sediments the branched and isoprenoid tetraether bit index

seasonal variability of branched glycerol dialkyl glycerol tetraethers brgdgts in a temperate lake system quantitative climate reconstructions are crucial for understanding the magnitude of and mechanisms behind natural and anthropogenic climate change yet there are few proxies that can reliably reconstruct terrestrial temperature branched glycerol dialkyl glycerol tetraethers brgdgts are bacterial membrane lipids that are increasingly used to reconstruct paleotemperature from lake sediments but despite their potential we have a poor understanding of 1 autochthonous vs allochthonous sources of brgdgts in lakes and 2 the seasonality of and environmental controls on brgdgt production within lakes to investigate these factors we examined water column suspended particulate matter spm and settling particles from a sediment trap collected on a biweekly to monthly basis over a period of three years at lower king pond a small kettle lake in northern vermont usa we also compared the concentration and fractional abundances of brgdgts in spm and settling particles with those of catchment soils river sediments and lake surface sediments to constrain the relative importance of brgdgts derived from the landscape versus brgdgts produced within the lake itself we find significant differences in concentrations and fractional abundances of brgdgts between soil and river sediment samples from the catchment and lake sediments indicating a mostly autochthonous source for lacustrine brgdgts brgdgt concentrations fluxes and fractional abundances in spm vary over the annual cycle indicating that brgdgts are produced throughout the year and respond to changes within the water column the total annual flux of brgdgts settling through the water column is comparable to the brgdgt accumulation rates in surface sediments indicating that in this lake brgdgts are mostly produced within the water column not in the sediment itself while brgdgts are produced in all seasons within the water column the flux to the sediments is highest during periods of spring and fall isothermal mixing potentially biasing paleotemperature reconstructions towards mixing season temperature because the seasonal timing and frequency of lake mixing varies as a function of regional climate lacustrine brgdgt calibrations should be regional in nature and comprise lakes with similar mixing regimes

rheology of welding inversion of field constraints at present the mechanisms and rheological behaviour of pyroclastic deposits during welding and compaction are poorly understood here we explore the extent to which the rheological properties of pyroclastic deposits are constrained by physical property distributions in welded ignimbrite physical properties of samples from a 20 m section of the bandelier tuff new mexico are used as proxies for strain the observed strain et is ascribed to a combination of a time dependent viscous compaction ev and a time independent mechanical compaction em described by

impact of mechanical heterogeneity on joint density in a welded ignimbrite joints are conduits for groundwater hydrocarbons and hydrothermal fluids robust fluid flow models rely on accurate characterisation of joint networks in particular joint density it is generally assumed that the predominant factor controlling joint density in layered stratigraphy is the thickness of the mechanical layer where the joints occur mechanical heterogeneity within the layer is considered a lesser influence on joint formation we analysed the frequency and distribution of joints within a single 12 m thick ignimbrite layer to identify the controls on joint geometry and distribution the observed joint distribution is not related to the thickness of the ignimbrite layer rather joint initiation propagation and termination are controlled by the shape spatial distribution and mechanical properties of fiamme which are present within the ignimbrite the observations and analysis presented here demonstrate that models of joint distribution particularly in thicker layers that do not fully account for mechanical heterogeneity are likely to underestimate joint density the spatial variability of joint distribution and the complex joint geometries that result consequently we recommend that characterisation of a layer s compositional and material properties improves predictions of subsurface joint density in rock layers that are mechanically heterogeneous

ranking welding intensity in pyroclastic deposits welding of pyroclastic deposits involves flattening of glassy pyroclasts under a compactional load at temperatures above the glass transition temperature progressive welding is recorded by changes in the petrographic e g fabric and physical e g density properties of the deposits mapping the intensity of welding can be integral to studies of pyroclastic deposits but making systematic comparisons between deposits can be problematical here we develop a scheme for ranking welding intensity in pyroclastic deposits on the basis of petrographic textural observations e g oblateness of pumice lapilli and micro fabric orientation and measurements of physical properties including density porosity point load strength and uniaxial compressive strength our dataset comprises measurements on 100 samples collected from a single cooling unit of the bandelier tuff and parallel measurements on 8 samples of more densely welded deposits the proposed classification comprises six ranks of welding intensity ranging from unconsolidated rank i to obsidian like vitrophyre rank vi and should allow for reproducible mapping of subtle variations in welding intensity between different deposits the application of the ranking scheme is demonstrated by using published physical property data on welded pyroclastic deposits to map the total accumulated strain and to reconstruct their pre welding thicknesses

silver creek caldera the tectonically dismembered source of the peach spring tuff sanidine 40 ar 39 ar geochronology confirms that silver creek caldera which straddles the eastern edge of the colorado river extensional corridor near oatman arizona united states is the source of the peach spring tuff eight new dates five from outflow three from caldera fill are analytically indistinguishable and combined with the most precise previously published date give a weighted mean average age of 18 78 0 02 ma a fragment of the caldera identified in the midst of the extensional corridor is structurally juxtaposed with mesozonal plutons of identical age the implied extension direction 182 225 is compatible with abundant previously published structural data for the region

thermodynamic and rheological properties of rhyolite and andesite melts the heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative enthalpy measurements made between 400 and 1800 k for the glass phases the experimental data agree with empirical models of calculation of the heat capacity for the liquid phases the agreement is less good owing to strong interactions between alkali metals and aluminum which are not currently accounted for by empirical heat capacity models the viscosity of both liquids has been measured from the glass transition to 1800 k the temperature dependence of the viscosity is quantitatively related to the configurational heat capacity determined calorimetrically through the configurational entropy theory of relaxation processes for both rhyolite and andesite melts the heat capacity and viscosity do not differ markedly from those obtained by additive modeling from components with mineral compositions

grain size distribution of volcaniclastic rocks 1 a new technique based on functional stereology the power of explosive volcanic eruptions is reflected in the grain size distribution and dispersal of their pyroclastic deposits grain size also forms part of lithofacies characteristics that are necessary to determine transport and depositional mechanisms responsible for producing pyroclastic deposits however the common process of welding and rock lithification prevents quantification of grain size by traditional sieving methods for deposits in the rock record here we show that functional stereology can be used to obtain actual 3d volume fractions of clast populations from 2d cross sectional images tests made on artificially consolidated rocks demonstrate successful correlations with traditional sieving method we show that the true grain size distribution is finer grained than its representation on a random 2d section our method allows the original size of vesicular pumice clasts to be estimated from their compacted shapes we anticipate that the original grain size distribution of welded ignimbrites can also be characterized by this method our method using functional stereology can be universally applied to any type of consolidated weakly to non deformed clastic material regardless of grain size or age and therefore has a wide application in geology

archaeal and bacterial glycerol dialkyl glycerol tetraethers in sediments from the eastern lau spreading center south pacific ocean abstract the compositions of glycerol dialkyl glycerol tetraethers gdgts in surface sediments and sediment cores from the eastern lau spreading center elsc south pacific ocean were determined isoprenoid gdgts isogdgts and branched gdgts brgdgts are present in all the samples with archaea and bacteria respectively as the sources of these membrane lipids greater concentrations of isogdgts 0 08 38 0 ng g dry weight dw than brgdgts 0 05 27 4 ng g dw indicate that archaea made larger contributions to the gdgt pool in the elsc sediments than bacteria the relative abundance of brgdgts and bit index the branched vs isoprenoid tetraether values are higher in samples taken from the seafloor in the vicinity of or close to hydrothermal vents than in samples taken distant from hydrothermal activity suggesting that brgdgts are likely produced in the elsc hydrothermal vents temperature estimates based on tex 86 tetraether index of tetraethers consisting of 86 carbon atoms appear to reflect local surface water temperatures despite potential in situ hydrothermal input of gdgts to the elsc sediments

rheomorphism of welded tuffs abstract peralkaline welded tuffs from the islands of gran canaria canary islands and pantelleria italy show abundant evidence for post depositional flow it is demonstrated that rheomorphism or secondary mass flowage can occur in welded tuffs of ignimbrite and air fall origin the presence of a linear fabric is taken as the diagnostic criterion for the recognition of the process deposition on a slope is an essential condition for the development of rheomorphism after compaction and welding internal structures produced during rheomorphic flow can be studied by the methods of structural geology and show similar dispositions to comparable features in sedimentary slump sheets it is shown that secondary flowage can occur in welded tuffs emplaced on gentle slopes provided that the apparent viscosity of the magma is sufficiently low compositional factors favor the development of rheomorphism in densely welded tuffs of peralkaline type

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

kinematics of compressional fold development in convergent wrench terranes abstract kinematic models are presented for compressional fold development in wrench and convergent wrench terranes that relate fold shortening axial rotation and axial extension fold shortening may be derived from final fold geometry existing fold geometry and axial orientation two readily measurable quantities provide the data needed to determine the relative components of shearing and convergence within the fold system analyses utilizing these kinematic models indicate that folds developed in sedimentary rocks in the wrench borderlands of both the rineonada and san andreas wrench faults in central california are the product of strongly convergent wrenching the axes of these folds have been rotated no more than a few degrees during the course of their development in contrast folds developed in the alpine schists along the alpine fault in new zealand and in pleistocene sediments along the southern limit of the san andreas fault suggest an almost pure wrench setting and large 25 axial rotations significant axial extension is inherent in wrench related compressional folds this axial extension is commonly manifest in the form of normal and strike slip faults that are internal to the folds and trend at high angles to the fold axes the relative amount of axial extension diminishes as the degree of convergence increases this axial extension and the associated extensional features can be a diagnostic indication of the influence of wrenching

large changes in seasonal sea ice distribution and productivity in the sea of okhotsk during the deglaciations changes in the surface environment of the central sea of okhotsk were reconstructed using tex86 paleothermometry facilitated by the bit index in order to investigate paleoenvironmental changes during the glacial interglacial cycles the core top tex86 derived temperature is the same as the present day summer sea surface temperature sst suggesting that tex86 records seasonal rather than annually averaged ssts in this region the tex86 record reveals 3 c lower summer sst during glacial maxima than during interglacial periods and significant warming during the deglaciations 15 10 ka and 136 130 ka this is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present day and its substantial retreat during the deglaciation timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations the relationship could reflect an increase in the supply of fresh and warm water from the amur river during deglaciation which significantly impacted hydrology by facilitating sea surface stratification which in turn promoted production of coccolithophids

onset of long term cooling of greenland near the eocene oligocene boundary as revealed by branched tetraether lipids the eocene oligocene e o boundary interval is considered to be one of the major transitions in earth s climate witnessing the fi rst major expansion of the east antarctic ice sheet however the extent of the associated climatic cooling especially for high northern latitude continental landmasses is poorly constrained in this study we reconstruct the fi rst mean annual air temperature maat for the greenland landmass during the late eocene and early oligocene by applying a new proxy based on the distribution of branched tetraether lipids derived from soil bacteria preserved in a marine sediment core from the greenland basin the temperature estimates are compared with a composite continental temperature record based on bioclimatic analysis of pollen assemblages both proxies reveal comparable late eocene maats of 13 15 c and a gradual long term cooling of 3 5 c starting near the e o boundary these data are in agreement with other maat reconstructions from northern midlatitude continents and suggest a general cooling of the northern hemisphere during the e o transition

sources and distributions of branched and isoprenoid tetraether lipids on the amazon shelf and fan implications for the use of gdgt based proxies in marine sediments branched glycerol dialkyl glycerol tetraethers brgdgts in river fan sediments have been used successfully to reconstruct mean annual air temperature maat and soil ph of the congo river drainage basin however in a previous study of amazon deep sea fan sediments the reconstructed maats were ca 10 c colder than the actual maat of the amazon basin in this study we investigated this apparent offset by comparing the concentrations and distributions of brgdgts in amazon river suspended particulate matter spm and sediments to those in marine spm and surface sediments the riverine brgdgt input was evident from the elevated brgdgt concentrations in marine spm and surface sediments close to the river mouth the distributions of brgdgts in marine spm and sediments varied widely but generally showed a higher relative abundance of methylated and cyclic brgdgts than those in the river since this difference in brgdgt distribution was also found in intact polar lipid ipl derived brgdgts which were more recently produced the change in the marine brgdgt distribution was most likely due to marine in situ production consequently the maats calculated based on the methylation of branched tetraethers mbt and the cyclisation of branched tetraethers cbt were lower and the cbt derived ph values were higher than those of the amazon basin however spm and sediments from stations close to the river mouth still showed mbt cbt values that were similar to those of the river therefore we recommend caution when applying the mbt cbt proxy it should only be used in sediment cores that were under high river influence the influence of riverine derived isoprenoid gdgt isogdgt on the isogdgt based tex86 temperature proxy was also examined in marine spm and sediments an input of riverine isogdgts from the amazon river was apparent but its influence on the marine tex86 was minor since the tex86 of spm in the amazon river was similar to that in the marine spm and sediments

leaf wax biomarkers in transit record river catchment composition rivers carry organic molecules derived from terrestrial vegetation to sedimentary deposits in lakes and oceans storing information about past climate and erosion as well as representing a component of the carbon cycle it is anticipated that sourcing of organic matter may not be uniform across catchments with substantial environmental variability in topography vegetation zones and climate here we analyze plant leaf wax biomarkers in transit in the madre de dios river peru which drains a forested catchment across 4 5 km of elevation from the tropical montane forests of the andes down into the rainforests of amazonia we find that the hydrogen isotopic composition of leaf wax molecules specifically the c28 n alkanoic acid carried by this tropical mountain river largely records the elevation gradient defined by the isotopic composition of precipitation and this supports the general interpretation of these biomarkers as proxy recorders of catchment conditions however we also find that leaf wax isotopic composition varies with river flow regime over storm and seasonal timescales which could in some cases be quantitatively significant relative to changes in the isotopic composition of precipitation in the past our results inform on the sourcing and transport of material by a major tributary of the amazon river and contribute to the spatial interpretation of sedimentary records of past climate using the leaf wax proxy

temperature changes across the paleocene eocene thermal maximum a new high resolution tex86 temperature record from the eastern north sea basin abstract the paleocene eocene thermal maximum petm 55 9 ma was a hyperthermal event associated with large carbon cycle perturbations sustained global warming and marine and terrestrial environmental changes one possible trigger and or source of the carbon release that initiated the petm is the emplacement of the north atlantic igneous province naip this study focuses on an expanded section of marine clays and diatomite on fur island in northern denmark where the entire petm sequence has been identified by a negative 4 5 13 ctoc excursion this remarkably well preserved section also contains 180 interbedded ash layers sourced from the naip making it an ideal site for investigating the correlations between large scale volcanism and environmental changes this study provides a new and complete high resolution tex86 derived sea surface temperature sst reconstruction over the entire petm and the post petm section up to about 54 6 ma the palaeothermometry record indicates an apparent short lived cooling episode in the late paleocene followed by a pronounced temperature response to the petm carbon cycle perturbations with a 10 c sst increase during the petm onset up to 33 c extreme ssts fall shortly after the petm onset and continue to decrease during the petm body and recovery down to anomalously cool ssts post petm 11 23 c both phases of potential cooling coincide with proxies of active naip volcanism suggesting a causal connection although several overprinting non thermal factors complicate interpretations of the tex86 values indices of effusive and explosive naip volcanism are largely absent from the danish stratigraphy during the petm body though a re emergence toward the end of the petm suggest naip volcanism might have played a role in the petm termination in the north sea this new sst record completes the previous fragmented view of climate changes at this globally important petm site and indicates large temperature variations in the north sea during the earliest eocene that are possibly linked to naip volcanism

rheological controls on the emplacement of extremely high grade ignimbrites extremely high grade lava like welded ignimbrites are produced by many large explosive eruptions with volumes typically 101 103 km3 however understanding of the physical properties of these unusual deposits and their transport and depositional mechanisms is incomplete the lava like and rheomorphic grey s landing ignimbrite idaho western united states provides abundant field evidence supporting the upward migration of a transient 2 m thick sub horizontal ductile shear zone at the interface between the pyroclastic density current and the deposit through which all of the aggrading pyroclastic material passed here we use a combination of rheological experiments and thermo mechanical modeling to test the syndepositional shear zone model we show that syndepositional welding and ductile flow are achievable within a very restricted field of likely temperature strain rate space where rapid deformation is favored by higher emplacement temperatures 850 c the field of ductile deformation is broadened significantly by accounting for strain heating which permits a sustained temperature increase of up to 250 c within the shear zone and helps to explain the enormous extents of lava like lithofacies and the intense rheomorphism recorded in extremely high grade ignimbrites recognition of strain heating within rheomorphic ignimbrites suggests that large pyroclastic density currents may travel over a hot substrate potentially hotter than the density current itself

large scale rheomorphic shear deformation in miocene peralkaline ignimbrite e gran canaria the single ignimbrite cooling unit e average thickness 28 m volume ca 30 km3 forms the uppermost member of the miocene upper mogan formation on gran canaria it is strongly chemically zoned from basal first erupted comendite peralkaline rhyolite to late erupted trachyte and apart from an upper trachytic zone it is densely welded e was emplaced onto a surface inclined ca 2 5 from the source caldera detailed mapping of key sections up to 300 m long exposed in barranco walls ca 10 km from the caldera margin reveals structures that are interpreted to have been produced by rheomorphic deformation of the ignimbrite along shear zones the shear zones formed within the lower viscosity comenditic tuff extensional structures include mega boudinage and decapitated sequences and compression resulted in sequence repitition by overthrusting mechanisms traditionally thought to be important during rheomorphic deformation of welded tuffs compaction lateral creep folding vertical density driven diapirism cannot account for these features which reflect lateral post compactional rheomorphic movement locally in excess of 800 m we suggest the following sequence of events emplacement of the several flow units compaction with little lateral movement rheomorphic deformation during and after compaction layers of secondary porosity developed within the comenditic tuff possibly where upward escape of gas was prevented by overlying relatively impermeable layers of densely compacted ignimbrite these structurally weak layers of high porosity subsequently acted as shear zones

synchronous change of temperature and moisture over the past 50 ka in subtropical southwest china as indicated by biomarker records in a crater lake abstract over the past few decades studies on the indian summer monsoon ism have been mainly based on paleo marine records whilst the sparsity of land records limits our understanding of the ism evolutionary process over continental landscapes here we provide paleoclimate reconstructions based on n alkanes and branched glycerol dialkyl glycerol tetraethers brgdgts from a 50 ka lacustrine sediment core collected from lake tengchong qinghai in southwestern subtropical china our results reveal that the botanical sources of sedimentary n alkanes in this lake are mainly from aquatic macrophytes and terrestrial plants the lake level evolution from the mis 3 to the holocene can be divided into four stages high in the mis 3 low in the lgm high in last deglacial and low in mid and late holocene our brgdgts based climate reconstructions indicate that the mean air temperature differences between the present day and the lgm were up to about 3 4 c from mis 3 to holocene there was a broadly and consistently synchronous trend between precipitation and air temperature in this ism region this is different from the asynchronous temperature and precipitation variations in the east asian summer monsoon easm regions in the period of last glacial termination our study shows that the climate in ism regions was primarily driven by changes in june summer solar insolation at 30 n and those glacial boundary conditions such as ice volume and sea surface temperature might also have affected the ism

extended cooling and viscous flow of large hot rhyolite lavas implications of numerical modeling results abstract a common misconception about rhyolite lava flows is that they cannot advance far from their vents and are constrained to be small due to their high viscosities although a high viscosity lava will indeed flow quite slowly it may advance a great distance if the lava efficiently retains heat and thus mobility and if the available magma supply is large to evaluate this possibility a finite difference numerical model was used to determine the rate of heat loss from units interpreted to be large rhyolite lavas cooling of such 100 300 m thick units is very slow and is further retarded by a vesicular carapace and by evolution of latent heat thermal history alone suggests that large thick lava flows could remain active for several decades to constrain the duration of flow advance of these units their inferred apparent viscosities are compared with those of active lava flows mean flow velocity of some large rhyolites in southwestern idaho usa was estimated based on the observation that the units must still have been advancing by viscous flow at the start of spherulite crystallization indicating perhaps a 10 to 18 year flow duration based on studies of obsidian dome california mean flow velocities would have been roughly 0 59 to 2 5 km yr and calculated average apparent viscosities of the flows ranged from 1 8 to 3 6 orders of magnitude greater than the viscosity of the lava itself this relationship also holds for active andesite and basaltic andesite block lava flows which have apparent viscosities 2 7 to 4 orders of magnitude greater than lava viscosities this implies that large rhyolites may indeed have been emplaced in the same manner as less silicic block lavas and that long distance viscous flow is not unrealistic for rhyolite lavas a good example of a large volume lava is the 15 km 3 rhyolite of the badlands sw idaho where vent relations show that lava effused from a fissure and advanced up to 9 km more extensive rhyolites could also be emplaced solely by effusion extended flow of these lavas may lead to the remelting and removal of basal crumble breccias and to the formation of welded shard textures in their margins both processes tending to obscure the lava flow origin of the units the great dimensions of lava like rhyolitic units with volumes of 10 to at least 200 km 3 are not a sufficient reason to assume they erupted as ignimbrites

mechanistic controls on diverse fates of terrestrial organic components in the east china sea terrestrial carbon transferred from the land to sea is a critical component of the global carbon cycle a range of geochemical proxies has been developed to fingerprint the fate of terrestrial organic matter tom in marine sediments however discrepancies among different proxies limit our ability to quantify and interpret the terrestrial signals in marine sediments with consequences for the investigation of both the modern carbon cycle and past environmental change to mechanistically understand these discrepancies we examined the distributions of a range of terrestrial proxies and their aquatic counterparts i e marine proxies in the yangtze river east china sea yr ecs shelf system where tom experiences extensive modification during transport and burial tom proxies in the yr ecs system collectively fit a power law model but with distinct attenuation rates the a values for individual molecular proxy groups among a range of tom proxies the modeled a values decrease in the order soil marker bhps triterpenols lignin hmw n alkanols branched gdgts hmw n alkanes for biomarkers and rsoil bit tomiso for proxies tracing tom rapid loss of tom components through dissociation in the narrow estuary followed by oxidation over the wide open shelf are best described by power curves inherent chemical reactivity i e the number of functional groups responses to hydraulic sorting and in situ production regulate the individual attenuation rates of them chemical reactivity plays the most important role on proxy behavior supported by a strong correlation between a values and standard molal gibbs energies both physical protection and chemical reactivity fundamentally control the overall behavior of tom components with the relative importance being setting dependant the former is relatively important in the estuary whereas the later is the primary control over the open shelf moreover regional variation of different marine counterparts is also significant over the river ecs shelf system seemingly regulated by regional nutrient distributions therefore for tom estimates using molecular ratio approaches the specific behavior of individual terrestrial components and marine counterparts and the physical biological and chemical characteristics of depositional settings all need to be considered

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

mafic plinian volcanism and ignimbrite emplacement at tofua volcano tonga tofua island is the largest emergent mafic volcano within the tofua arc tonga southwest pacific the volcano is dominated by a distinctive caldera averaging 4 km in diameter containing a freshwater lake in the south and east the latest paroxysmal vei 5 6 explosive volcanism includes two phases of activity each emplacing a high grade ignimbrite the products are basaltic andesites with between 52 wt and 57 wt sio2 the first and largest eruption caused the inward collapse of a stratovolcano and produced the tofua ignimbrite and a sub circular caldera located slightly northwest of the island s centre this ignimbrite was deposited in a radial fashion over the entire island with associated plinian fall deposits up to 0 5 m thick on islands 40 km away common sub rounded and frequently cauliform scoria bombs throughout the ignimbrite attest to a small degree of marginal magma water interaction the common intense welding of the coarse grained eruptive products however suggests that the majority of the erupted magma was hot water undersaturated and supplied at high rates with moderately low fragmentation efficiency and low levels of interaction with external water we propose that the development of a water saturated dacite body at shallow 6 km depth resulted in failure of the chamber roof to cause sudden evacuation of material producing a plinian eruption column following a brief period of quiescence large scale faulting in the southeast of the island produced a second explosive phase believed to result from recharge of a chemically distinct magma depleted in incompatible elements this similar but smaller eruption emplaced the hokula ignimbrite sheet in the northeast of the island a maximum total volume of 8 km3 of juvenile material was erupted by these events the main eruption column is estimated to have reached a height of 12 km and to have produced a major atmospheric injection of gas and tephra recorded in the widespread series of fall deposits found on coral islands 40 80 km to the east in the direction of regional upper tropospheric winds radiocarbon dating of charcoal below the tofua ignimbrite and organic material below the related fall units imply this eruption sequence occurred post 1 000 years bp we estimate an eruption magnitude of 2 24 1013 kg sulphur release of 12 tg and tentatively assign this eruption to the ad 1030 volcanic sulphate spike recorded in antarctic ice sheet records

flow banding in obsidian a record of evolving textural heterogeneity during magma deformation we perform a quantitative textural analysis of banding in obsidian from big glass mountain bgm medicine lake volcano california and from mayor island mi new zealand the samples are compositionally homogeneous with banding defined by variable microlite content bgm or vesicularity mi the spatial distribution of alternating light and dark bands has a 1 wavenumber power spectral density as well as multifractal characteristics through the use of simple mathematical models we demonstrate that formation of the observed banding structure is consistent with a continuous deformational reworking of magma our results indicate that changes in crystallinity vesicularity were concurrent with magma deformation and are random multiples of the total amount of crystallinity vesicularity that was already present at any given time banded obsidian from bgm and mi can be found in close spatial proximity to brittle deformational textures we therefore propose that a key element of banding formation in our samples may be magma brecciation or fragmentation fragmentation can result in variable rates of degassing of fragments which in turn can lead to nonuniform crystal vesicle nucleation and growth rates repeated fragmentation welding and subsequent viscous deformation can thus lead to banding formation

occurrence of tetraether lipids in stalagmites implications for sources and gdgt based proxies lipid biomarkers in stalagmites have potential in palaeoenvironmental reconstruction but glycerol dialkyl glycerol tetraethers gdgts in stalagmites have rarely been investigated we report the occurrence of archaeal isoprenoid gdgts and bacterial branched gdgts in heshang cave stalagmites in central china the archaeal component crenarchaeol dominated bacterial branched gdgts in the stalagmites and on the weathered parent rock surface collected inside the cave in contrast the distribution of gdgts in the overlying soil shows that branched gdgts dominated archaeal gdgts hence the majority of archaeal gdgts in stalagmites may be produced by crenarchaeota inhabiting the cave rather than being inherited from the overlying soil bacterial branched gdgt distributions expressed as mbt and cbt indices showed remarkable differences between stalagmite and soil samples implying that most branched gdgts may also be produced in situ in the cave the tex86 or tex86 values were found to increase with more depleted 18o values representing much stronger monsoon and therefore usually higher temperatures in the study region however the mbt cbt index in stalagmites may be influenced by a variety of factors besides palaeotemperature

recent distribution and accumulation of organic carbon on the continental margin west off spitsbergen the study compiles the controlling factors for organic matter sedimentation patterns from a suite of organogeochemical parameters in surface sediments off spitsbergen and direct seabed observations using a remotely operated vehicle rov in addition we assess its storage rates as well as the potential of carbon sinks on the northwestern margin of the barents sea with short sediment cores from a selected fjord environment storfjord while sedimentation in the fjords is mainly controlled by river meltwater discharge and coastal erosion by sea ice glaciers resulting in high supply of terrigenous organic matter atlantic water inflow and thus enhanced marine organic matter supply characterizes the environment on the outer shelf and slope local deviations from this pattern particularly on the shelf are due to erosion and out washing of fine grained material by bottom currents spots dominated by marine productivity close to the island have been found at the outer isfjord and west off prins karls forland as well as off the kongsfjord krossfjord area and probably reflect local upwelling of nutrient rich atlantic water derived water masses accumulation rates of marine organic carbon as well as reconstructed primary productivities decreased since the middle of the last century negative correlation of the isfjord temperature record with reconstructed productivities in the storfjord could be explained by a reduced annual duration of the marginal ice zone in the area due to global warming extremely high accumulation rates of marine organic carbon between 5 4 and 17 2 g m 2 yr 1 mark the storfjord area and probably high latitude fjord environments in general as a sink for carbon dioxide

groundmass crystallisation and cooling rates of lava like ignimbrites the grey s landing ignimbrite southern idaho usa constraining magmatic and eruptive processes is key to understanding how volcanoes operate however reconstructing eruptive and pre eruptive processes requires the ability to see through any post eruptive modification of the deposit the well preserved grey s landing ignimbrite from the central snake river plain provides an opportunity to systematically investigate the post eruptive processes occurring through a single deposit sheet despite overall compositional homogeneity in both bulk and glass compositions the grey s landing ignimbrite does preserve differences in the abundance of li in plagioclase crystals which are strongly associated with the host lithology li abundances in plagioclase from the quickly cooled upper and basal vitrophyres are typically low average 5 ppm n 262 while plagioclase from the microcrystalline interior of the deposit has higher li contents average 33 ppm n 773 given that no other trace elemental parameter in plagioclase varies we interpret the variability in li to reflect a post depositional process groundmass crystallisation of a rhyolite like grey s landing requires 50 crystallisation of sanidine and variable amounts of a silica rich phase quartz tridymite cristobalite and plagioclase to satisfy mass balance we suggest the low affinity of li for sanidine causes migration of groundmass li into plagioclase during crystallisation even within the microcrystalline interior of the deposit the morphology of the groundmass varies the more marginal finer grained regions are dominated by cristobalite as the sio2 rich phase while tridymite and quartz are additionally found in the more slowly cooled coarser grained portions of thick sections of the ignimbrite numerical models of cooling and crystallisation tested against field observations indicate that the groundmass crystallisation occurred relatively rapidly following emplacement a maximum of a few years where the ignimbrite is thickest these numerical models also illustrate that the time at which the potential for rheomorphism ceases either the ignimbrite is a solid glass or 50 crystalline is diachronous across the deposit

branched glycerol dialkyl glycerol tetraethers in pleistocene loess paleosol sequences three case studies abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are membrane lipids presumably derived from anaerobic heterotrophic soil bacteria empirical studies have shown that the composition of branched gdgts in topsoils varies in degree of cyclization and methylation expressed as cbt and mbt i e cyclization and methylation index of branched tetraethers depending on soil ph and mean annual air temperature mat here we present results from three case studies namely three well studied loess paleosol sequences lpss in which we measured the branched gdgts in order to test the applicability of these biomarkers for paleoclimate reconstruction the results show that major disagreements exist between expectations based on available stratigraphic pedological and geochemical data on the one hand and gdgt derived reconstructions on the other hand caution is therefore advised when interpreting the respective indices in lps studies we discuss several potential directions for future research i some of the target peaks in the hplc chromatograms consist of multiple unidentified compounds this needs to be addressed by way of improved component separation identification and new calibration studies ii factors other than mat and soil ph that could affect membrane composition should be further investigated e g nutrient availability and redox conditions as well as seasonality and changes in bacterial communities iii gdgts may be produced in non negligible amounts at depth and thus overprint the original in situ signal a concern that could be termed growth depth effect iv gdgts should also be analyzed in dust source regions and contemporaneous eolian sediments in order to address a potential redeposition effect

distribution of glycerol dialkyl glycerol tetraethers in soils from two environmental transects in the usa abstract glycerol dialkyl glycerol tetraethers gdgts of both archaeal and bacterial origin form the basis of new temperature proxies applicable to soil and lake and marine sediments in soil branched gdgts are prevalent and their abundance of methyl or cyclic groups has been calibrated to mean annual temperature mat using mbt and cbt indices however soil ph is also known to be an important variable controlling the distribution of branched gdgts precipitation amount helps control soil moisture as well as ph and soil moisture is a leading variable affecting microbial diversity and activity in soil we have evaluated the distribution of gdgts from two soil transects in the usa a dry western transect covering six western states and a wet east coast transect from maine to georgia in order to assess the effect of precipitation on the distribution of soil gdgts our results show distinctly different gdgt distributions across climatic regions with dry western soils characterized predominantly by thaumarchaeotal isoprenoid iso gdgts and as a consequence low bit index values 0 2 0 6 and moist temperate east coast transect soils expressing mostly branched br gdgts and higher bit values 0 9 1 the predominance of iso gdgts in the western soils is related to the degree of aeration which in turn is related to precipitation amount and also to soil ph we also observed a substantial increase in the offset between measured mat and mbt cbt based mat below an annual precipitation of 700 800 mm yr 1 implying an impact of precipitation amount on mbt cbt based temperature reconstruction the data suggest that while soil tetraethers work well as a temperature proxy in moist temperate regimes they do not produce reliable measurements of temperature in sediments sourced from areas with 1 precipitation moreover erosion of soils with low bit values into lacustrine or marginal marine environments will not be detected via the bit index which can potentially affect paleotemperature reconstruction from sediments and so provide erroneous estimates of soil carbon delivery bit index values also show a correlation with precipitation amount the abundance of iso gdgts in western transect soils allowed calculation of tex 86 values but no correlation was found between tex 86 calculated temperature and mean annual temperature

the middle eocene climatic optimum meco a multiproxy record of paleoceanographic changes in the southeast atlantic odp site 1263 walvis ridge the middle eocene climatic optimum meco 40 ma was a transient period of global warming that interrupted the secular cenozoic cooling trend we investigated the paleoceanographic paleoenvironmental and paleoecological repercussions of the meco in the southeast atlantic subtropical gyre ocean drilling program site 1263 tex86 and 18o records support an 4 c increase in surface and deepwater temperatures during the meco there is no long term negative carbon isotope excursion cie associated with the early warming consistent with other sites and there is no short term negative cie 50 kyr during the peak of the meco in contrast to what has been observed at some sites this lack of a cie during the peak of the meco at site 1263 could be due to poor sediment recovery or geographic heterogeneity of the 13c signal benthic and planktic foraminiferal mass accumulation rates markedly declined during meco indicating a reduction of planktic foraminiferal production and export productivity vertical 13c gradients do not indicate major changes in water column stratification and there is no biomarker or micropaleontological evidence that hypoxia developed we suggest that temperature dependency of metabolic rates could explain the observed decrease in foraminiferal productivity during warming the kinetics of biochemical reactions increase with temperature more so for heterotrophs than for autotrophs steady warming during meco may have enhanced heterotroph i e foraminiferal metabolic rates so that they required more nutrients these additional nutrients were not available because of the oligotrophic conditions in the region and the lesser response of primary producers to warming the combination of warming and heterotroph starvation altered pelagic food webs increased water column recycling of organic carbon and decreased the amount of organic carbon available to the benthos

the emplacement history of a remarkable heterogeneous chemically zoned rheomorphic and locally lava like ignimbrite tl on gran canaria abstract ignimbrite tl on gran canaria is a complex compositionally zoned rheomorphic tuff that locally exhibits features previously considered to be diagnostic of lavas it is made up of two locally overlapping lobes of ignimbrite that were emplaced during a single eruptive episode the eastern lobe is high grade with rheomorphic zones and localised patches that are lava like the western lobe is extremely high grade more extensively lava like and welded to its top surface both parts are zoned with a basal comendite rich zone grading up through a mixed zone into an upper trachyte rich zone lithic contents and the relative proportions of comendite and trachyte pyroclasts vary with height each comendite rich zone is vitroclastic whereas each trachyte rich zone is partly lava like with local gradations into vitroclastic ignimbrite mixed zones are intermediate in character and locally show compositional banding gradational zoning in massive ignimbrite best seen in lower strain zones and welding fabrics that are pervasively lineated and oblique to bedding suggest that deposition was sustained agglutination was rapid and rheomorphic deformation began during the sustained deposition the viscosity and porosity of the agglutinate varied with height because successively deposited pyroclast populations varied in grainsize composition and temperature the hot agglutinate continued to compact and shear downslope after the density currents had dissipated causing further rheomorphic folding thrusting attenuation and autobrecciation the western lobe locally overlies the partly welded top of the eastern lobe in part because it advanced rheomorphically across it for at least 300 m hot state loading and auto intrusion occurred due to unstable density layering in the chemically zoned agglutinate deformation behaviour changed during cooling and degassing and because of heat transfer between juxtaposed agglutinates and localised retention of dissolved volatiles where there was an overlying impermeable cap

comparison of instrumental and gdgt based estimates of sea surface and air temperatures from the skagerrak sea surface temperatures ssts and annual mean air temperatures mats are estimated for the last 200 years from glycerol dialkyl glycerol tetraethers gdgts proxies in a marine sediment core from the skagerrak off southern norway the reconstructed values compare well with annual ssts and summer air temperatures obtained from composite regional instrumental records the results provide further confidence in the application of proxies based on gdgts to estimate past temperatures

the late paleozoic felsic lava dominated large igneous province in northeast germany volcanic facies analysis based on drill cores in the deep subsurface of the northeast german basin products of extensive volcanism are present that formed during the waning phase of the variscan orogeny permian carboniferous boundary large volumes 48 000 km3 of dominantly felsic magma were emplaced in the northern foreland of the variscan mountains in a terrestrial semi arid environment most of these units were inferred by previous authors to represent the products of explosive volcanic eruptions such as ignimbrites however a detailed analysis of the volcanic texture and lithofacies association shows that most units are best interpreted as coherent lavas emplaced either as extrusive units or as shallow intrusions with important implications for the reconstruction of the paleo environment this study shows that detailed textural examination of drill cores provide important observations which can be applied as criteria for the interpretation of the mode of volcanic eruptions furthermore phenocryst logging and geochemical fingerprinting based on immobile element ratios can be employed for the classification and discrimination of individual emplacement units

glycerol dialkyl glycerol tetraethers in surficial coastal and open marine sediments around china indicators of sea surface temperature and effects of their sources accurate reconstruction of past sea surface temperature sst is important for the understanding of past climate and its variations recently the tex86 indicator tetraether index of tetraethers consisting of 86 carbon atoms based on glycerol dialkyl glycerol tetraethers gdgts has been developed into a promising proxy for sst reconstruction in this study we investigated the distribution of gdgts in surficial sea bottom sediments from coastal and open marine settings around china between 18 degrees n and 38 degrees n in water depth of either 1000 m as the distribution patterns of gdgts reflect their biological sources and their respective habitats these can be identified from the sediment samples investigated the distributions of branched gdgts brgdgts in the yellow sea ys was found to be similar to that of the lower yellow river basin indicating that the brgdgts in the ys originated from terrestrial soil while the variability of the cyclisation ratio of branched tetraethers cbt derived ph values in the pearl river estuary pre suggested that brgdgts might also be produced in situ in coastal sediments or in the water column in the shallow areas water depth 1000 m the sst86h matched well the mean annual sst determined by satellite indicating the applicability of the tex86 temperatures for paleodimate investigations in these study areas and potentially in similar settings of deep water these findings provide the basis for application of branched isoprenoid index bit and tex86 as indicators for temperature and paleotemperature in coastal and open marine environments around china c 2013 elsevier b v all rights reserved

welding processes in volcanology insights from field experimental and modeling studies this volume is a collection of ten papers largely derived from a special session welding processes in volcanology organized for the 2003 meeting of eug egs agu in nice france and brings together field experimental and modeling studies we briefly review advances in understanding welding as represented by this volume and point to future lines of inquiry with an emphasis on understanding the timescales of welding the metrics of strain and feedback relationships between compaction porosity permeability loss fluid transport and rheology of the deposit our analysis suggests that within the realm of field and textural studies more systematic and quantitative data are necessary to evaluate strain histories related to welding and the timing of welding relative to other processes during eruption and emplacement a new generation of experiments is needed in which load strain rate and volatile pressure can be controlled numerical models are needed to further explore the relationships and feedbacks between processes that contribute to welding d 2004 elsevier b v all rights reserved

using tetraether lipids archived in north sea basin sediments to extract north western european pliocene continental air temperatures the pliocene is often regarded as a suitable analogue for future climate due to an overall warmer climate 2 3 c coupled with atmospheric co2concentrations largely similar to present values 400 ppmv numerous pliocene sea surface temperature sst records are available however little is known about climate in the terrestrial realm here we generated a pliocene continental temperature record for northwestern europe based on branched glycerol dialkyl glycerol tetraether brgdgt membrane lipids stored in a marine sedimentary record from the western netherlands the total organic carbon toc content of the sediments and its stable carbon isotopic composition 13corg indicate a strong transition from primarily marine derived organic matter om during the pliocene to predominantly terrestrially derived om after the transition into the pleistocene this trend is supported by the ratio of branched and isoprenoid tetraethers bit index the marine terrestrial transition indicates a likely change in brgdgt sources in the core which may complicate the applicability of the brgdgt paleotemperature proxy in this setting currently the application of the brgdgt based paleothermometer on coastal marine sediments has been hampered by a marine overprint here we propose a method to disentangle terrestrial and marine sources based on the degree of cyclizationof tetramethylated brgdgts rings using a linear mixing model based on the global soil calibration set and a newly developed coastal marine temperature transfer function application of this method on our brgdgt record resulted in a corrected terrestrial temperature record matterr this latter record indicates that continental temperature were 12 14 c during the early pilocene and 10 5 12 c during the mid pilocene pollen based terrestrial temperatures estimate from nortern and central europe furthermore two colder 5 7 c periods in the pilocene maytterr record show that the influence of pilocene glacials reached well into nw europe

transport of terrestrial organic matter to the deep north atlantic ocean by ice rafting abstract total organic carbon toc 13c values of toc 13corg and glycerol dialkyl glycerol tetraethers gdgts were analysed for a sediment core from the north atlantic covering the last 30 kyr to investigate organic matter deposition due to ice rafting toc content was low in sediments representing glacial times 0 2 0 4 and even lower in holocene sediments

evaluation of glycerol dialkyl glycerol tetraether proxies for reconstruction of the paleo environment on the qinghai tibetan plateau the uplift of the qinghai tibetan plateau has a great effect on local and global climate changes here we report the late holocene climate change in the northern plateau by using a 3490 year sediment core record from kusai lake glycerol dialkyl glycerol tetraethers gdgts collected from the core were examined in combination with other paleo environmental proxies the reconstructed mean annual air temperatures maat using branched gdgt membrane lipids of certain bacteria proxies are higher than the measured maat but much closer to measured summer air temperatures suggesting a possibility of a bias of the reconstructed maat towards summer temperatures the ph values derived from a branched gdgt proxy show a negative correlation with toc a lake productivity indicator in arid regions furthermore both cbt ph and toc show temporal cyclic changes which suggest that the branched gdgt derived ph index may be useful in reconstructing paleo ph values in a lacustrine system lastly the composition of isoprenoid gdgts membrane lipids of archaea shows a major shift around 1400 bp which is in line with a large increase in sediment soluble salts at this time but lags behind the onset of salt mineral precipitation by 600 yr suggesting that change in archaeal community composition and salt mineral precipitation may require different threshold values of salinity the results of this study demonstrate that useful paleo climatic and paleo environmental information can be extracted from the gdgts preserved in lake sediments

source settling and degradation of branched glycerol dialkyl glycerol tetraethers in the marine water column abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are commonly found in distal marine sediments however their presence in the water column source and delivery process are not fully understood in this study we examined seasonal and depth variation in the flux of branched gdgts in sinking particles and underlying sediment at 39 n 147 e in the mid latitude nw pacific from november 1997 to august 1999 branched gdgts showed synchronous variation in their sinking flux at different depths and the variation was similar to that of lithogenic material of eolian dust origin their degrees of cyclization and methylation were nearly constant and bear some resemblance to those of alkaline soils this suggests that westerly winds transport branched gdgts to the study site via the atmosphere from continental asia the sinking flux of branched gdgts was higher in 1999 than in 1998 presumably reflecting changes in the migration path of asian dust in response to the el nino southern oscillation synchronous variation in branched gdgt concentrations at different depths implies rapid vertical transport of branched gdgts to deep water with a sinking velocity exceeding 260 m d 1 the sinking flux of the branched gdgts decreased with increasing depth but the rate of decrease was much smaller than those of other compounds the preservation efficiency of branched gdgts was 3 5 6 4 of surface inputs at the water sediment interface which is much higher than those of isoprenoid gdgts 1 0 1 3 and other compounds the branched and isoprenoid tetraether bit index values were extremely low i e

isoprenoid and branched gdgt based proxies for surface sediments from marine fjord and lake environments in chile abstract proxies based on glycerol dialkyl glycerol tetraether gdgt lipids from archaea isoprenoid gdgts and bacteria branched br gdgts in 33 surface sediments from marine fjord and lake systems between 25 s and 50 s in chile were analyzed the regional texh86 calibration obtained from the marine and fjord sediments and mean annual surface temperature t 59 6 texh86 33 0 r2 0 9 n 23 is statistically identical to the global ocean calibration based on suspended particulate material in terms of slope but not in terms of intercept the regional surface and subsurface texh86 calibrations were statistically different from the existing global ocean core top calibrations the tex86 calibration model based on most of the relatively large lakes studied here t 50 7 tex86 11 8 r2 0 9 n 5 is statistically identical to the global lake calibration the relatively high tex86 values from smaller lakes suggested an additional source for isoprenoid gdgts likely terrestrial or aquatic methanogenic archaea application of the soil calibrated mbt cbt methylation and cyclization of br gdgts respectively temperature proxy to the marine and fjord sediments resulted in an overestimation of continental mean annual air temperature maat suggesting in situ production of certain br gdgts in the water column or surface sediment for the lakes mbt cbt based surface air temperature estimates were 3 6 c below maat however temperature estimates from the lake specific mbt cbt global calibration were in good agreement with mean annual surface temperature for all the lakes the results highlight the need for testing local vs global calibrations of gdgt based proxies before their application for palaeoenvironmental reconstruction