de glauconiarum origine the glauconitic facies is widespread on present day continental shelves from 50 s to 65 n and at water depths between 50 and 500 m and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m it is also common in many ancient rocks of post late precambrian age it occurs as sand to pebble sized essentially green particles granular facies but also as a surface coating on particles and hardgrounds and as a diffuse impregnation film and diffuse facies we suggest the replacement of the term glauconite which has been interchangeably used to designate a morphological form and a specific mineral by glaucony facies and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family the widely accepted model of burst and hower for glauconitization requires a degraded micaceous 2 1 layer lattice structure parent clay mineral however detailed analysis of numerous samples of recent glaucony reveals that such a parent substrate is exceptional the model therefore requires modification generally the parent material is carbonate particles argillaceous kaolinitic faecal pellets infillings of foraminiferal tests various mineral grains and rock fragments that pass gradually into the commonly occurring green grains we show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate accompanied by progressive alteration and replacement of the substrate it is this two fold evolution that causes the verdissement of granular substrates macrofossils and hardgrounds the authigenic mineral is an iron rich and potassium poor glauconitic smectite while new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium producing decreasingly expandable minerals with a non expandable glauconitic mica as the end member this mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony four categories nascent little evolved evolved and highly evolved glaucony are distinguished glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro environment and ambient open marine sea water the optimum conditions for glauconitization are those of semi confinement as a result the interior of a grain is more glauconitized than its less confined periphery similarly for identical substrate types large grains 500 m provide more favourable substrates for glauconitization than lesser confined small grains on a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing low accumulation rates expose grains to the open marine environment for sufficiently long times 105 106 years for highly evolved glaucony

iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids abstract volcanogenic sediments are typically rich in fe and mn bearing minerals that undergo substantial alteration during early marine diagenesis however their impact on the global biogeochemical cycling of fe and mn has not been widely addressed this study compares the near surface 0 20 cm below sea floor cmbsf aqueous no 3 and solid phase reactive fe distributions between two volcanogenic sediment settings 1 a deep sea tephra rich deposit neighbouring the volcanically active island of montserrat and 2 mixed biosiliceous volcanogenic sediments from abyssal depths near the volcanically inactive crozet islands archipelago shallow penetration of o2 aq into montserrat sediments was observed 5 cmbsf and largely controlled by the oxidation of organic matter dissolved fe and mn distributions in montserrat pore waters were lowest in the surface oxic layer 0 3 m fe 32 m mn with maxima 20 m fe 200 m mn in the upper 1 15 cmbsf unlike montserrat fe and mn in crozet pore waters were ubiquitously partitioned between 0 2 m and 0 02 m filtrations indicating that the pore water distributions of fe and mn in the traditionally termed dissolved size fraction are dominated by colloids with respective mean abundances of 80 and 61 plausible mechanisms for the origin and composition of pore water colloids are discussed and include prolonged exposure of crozet surface sediments to early diagenesis compared to montserrat favouring nano particulate goethite formation and the elevated dissolved si concentrations which are shown to encourage fine grained smectite formation in addition organic matter may stabilise authigenic fe and mn in the crozet pore waters we conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water which may impact significantly on deep ocean biogeochemistry diffusive flux estimates from montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved mn to the bottom waters and therefore a source for the widespread hydrogenous mnox deposits found in the caribbean region

salinity history of the earth s early ocean it is commonly thought that the oceans are becoming saltier with time as sodium and chlorine are weathered out of continental rocks and transported to the sea here we argue that the salinity of the early ocean was 1 5 to 2 times the modern value and that it did not decline significantly until surprisingly late in the earth s history if correct this theory could help explain why the evolution of higher life took so long

the glauconite fe illite fe smectite problem a critical review iron silicate minerals are a significant component of sedimentary systems but their modes of formation remain controversial our analysis of published data identifies end member compositions and mixtures and allows us to recognize controls of formation of different mineral species the compositional fields of glaucony fe illite fe al smectites are determined in the m 4si vs fe sum of octahedral cations m interlayer charge solid solutions could exist between these phases the fe al and fe rich clay minerals form two distinct solid solutions the earliest phases to be formed are fe al smectites or berthierine depending on the sedimentation rate reductive microsystems appear in the vicinity of organic debris in unconsolidated sediments the fe is incorporated first in pyrite and then in silicates after oxidation potassium ions diffuse from the sea water sediment interface if not interrupted the diffusion process is active until reaction completion is reached i e formation of fe illite or glauconite or a mineral assemblage berthierine nontronite according to the available al ion amounts in the microsystem mixed layer minerals are formed when the diffusion process is interrupted because of sedimentation compaction or cementation despite the common belief of their value as palaeoenvironment indicators these minerals can form in a variety of environments and over a period of millions of years during sediment burial

electrically conducting ca rich brines rather than water expected in the martian subsurface 1 if mars ever possessed a salty liquid hydrosphere which later partly evaporated and froze down then any aqueous fluids left near the surface could have evolved to become dense eutectic brines eutectic brines by definition are the last to freeze and the first to melt if cacl2 rich such brines can remain liquid until temperatures below 220 k close to the average surface temperature of mars in the martian subsurface in intimate contact with the ca rich basaltic regolith nacl rich early brines should have reacted to become ca rich fractional crystallization freezing and partial melting would also drive brines toward cacl2 rich compositions in other words eutectic brine compositions could be present in the shallow subsurface of mars for the same reasons that eutectic magma compositions are common on earth don juan pond antarctica a cacl2 rich eutectic brine provides a possible terrestrial analog particularly because it is fed from a basaltic aquifer owing to their relative density and fluid nature brines in the martian regolith should eventually become sandwiched between ice above and salts beneath a thawing brine sandwich provides one explanation among many for the young gullies recently attributed to seepage of liquid water on mars whether or not brine seepage explains the gullies phenomenon dense cacl2 rich brines are to be expected in the deep subsurface of mars although they might be somewhat diluted temperatures permitting and of variable salt composition in any case they should be good conductors of electricity

ideas about the surface runoff features on mars in their report evidence of recent groundwater seepage and surface runoff on mars 30 june p 2330 1 malin and edgett propose that the seepage and flow of water may have occurred on mars in the recent geologic past on the basis of the observation of a large number of channel features on

analyses of fluid inclusions in neoproterozoic marine halite provide oldest measurement of seawater chemistry we analyzed primary fluid inclusions in halite from marine evaporites in the ca 830 ma browne formation of the officer basin in western australia using the cryogenic scanning electron microscopy energy dispersive x ray spectrometry analysis technique the concentrations of the major ions except k and possibly so 4 2 fall within the range of phanerozoic seawater this is the first direct measurement of the composition of mid neoproterozoic seawater and extends present day knowledge of seawater chemistry by 300 m y our estimates suggest that mid neoproterozoic marine sulfate concentrations were lower 90 than modern values by the terminal neoproterozoic fluid inclusions in halite and evaporite mineralogy indicate seawater sulfate levels rose significantly to 50 80 of modern concentrations which parallels increases in atmospheric and oceanic oxygen

the enigma of prokaryotic life in deep hypersaline anoxic basins deep hypersaline anoxic basins in the mediterranean sea are a legacy of dissolution of ancient subterranean salt deposits from the miocene period our study revealed that these hypersaline basins are not biogeochemical dead ends but support in situ sulfate reduction methanogenesis and heterotrophic activity a wide diversity of prokaryotes was observed including a new abundant deeply branching order within the euryarchaeota furthermore we demonstrated the presence of a unique metabolically active microbial community in the discovery basin which is one of the most extreme terrestrial saline environments known as it is almost saturated with mgcl2 5 m

iceberg hosted nanoparticulate fe in the southern ocean mineralogy origin dissolution kinetics and source of bioavailable fe abstract sediments from icebergs and glaciers contain nanopartculate fe iii oxyhydroxides including ferrihydrite which form in aqueous oxic micro environments where fe ii bearing rock minerals oxidise and high degrees of supersaturation are promoted by freezing and thawing an ascorbic acid extraction dissolves only labile fe present in fresh loosely aggregated ferrihydrite that is directly or indirectly bioavailable glacial and iceberg sediments contain ferrihydrite aggregates that provide 0 04 to 0 17 fe soluble in ascorbic acid rather larger than the concentrations in a limited suite of atmospheric dusts the dissolution behaviour of labile fe from glacial and iceberg sediments by ascorbic acid is controlled by the access of reactant or removal of solute through micropores to or from active sites in the interior of ferrihydrite aggregates a first order kinetic model is presented to examine the rates at which bioavailable fe can be supplied by melting icebergs in the weddell sea the model utilizes rate constants from the literature for the processes which solubilise fe from nanoparticulate ferrihydrite dissolution photochemical reduction and grazing and the processes that remove fe nanoparticulates sinking scavenging and incorporation in faecal material and render them less reactive transformation aging model results demonstrate that icebergs can supply bioavailable fe to the weddell sea by the dissolution of nanoparticulate ferrihydrite despite loss removal of nanoparticles by sinking aging transformation scavenging and incorporation into faecal pellets at rates that are comparable to atmospheric dust dissolution enhanced by photochemical reduction and grazing provides the most rapid rates of bioavailable fe production

ediacaran seawater temperature evidence from inclusions of sinian halite abstract seawater temperatures throughout earth s history have been suggested to illustrate a long term cooling trend from nearly 70 c at 3500 ma to around 20 c at 800 ma the terminal neoproterozoic prior to the cambrian explosion is a key interval in evolutionary history as complex multicellularity appeared with the advent of the ediacara fauna these organisms were likely the first that required higher levels of atmospheric and dissolved marine oxygen for their sustainability it is known that most modern macroinvertebrates are intolerant of temperatures in excess of 45 c perhaps more importantly these high seawater temperatures limit the potential of dissolved oxygen and therefore become an integral part of this evolutionary story previously our understanding of seawater temperature during the terminal neoproterozoic comes only from 18 o 16 o and 30 si 28 si ratios ascertained from a limited number of cherts isotopic ratio methods for assessing seawater temperatures are inherently indirect and have a wide range of oscillation however maximum homogenization temperatures th max of primary fluid inclusions in halite provide a direct means of assessing brine temperature and have been shown to correlate well with average maximum air temperatures the oldest halites date to the neoproterozoic lower paleozoic 700 500 ma and ediacaran representatives can be found in sichuan province china which do preserve primary fluid inclusions for analysis via cooling nucleation methods we utilized halite samples from the changning 2 well correlative to the dengying formation 551 542 ma to provide a direct assessment of terminal neoproterozoic seawater temperature our measurements indicate that seawater temperatures where these halites formed are highly similar to tropical phanerozoic seawater temperature estimates from compiled paleotemperature data the decline in seawater temperatures over the course of the proterozoic accompanied by the reduction of seawater salinity with the sequestration of salt in massive halite deposits in the neoproterozoic allowed the ocean system to accumulate more dissolved oxygen and potentially paved the way for the evolutionary innovation of complex multicellularity

eutectic brines on mars origin and possible relation to young seepage features abstract if the recently observed young gullies on mars represent seeps or outflows of aqueous fluid that fluid must be highly concentrated brine to be even moderately stable under current martian surface conditions such brines are to be expected in the megaregolith if an initial saline hydrosphere underwent evapoconcentration via water escape from the atmosphere evolved into subsurface cacl 2 enriched brines by chemical interaction with mafic rocks and then froze until eutectic compositions were reached although most such brines would tend to sink deep into the megaregolith they could be preserved locally at relatively high elevations as aquifers or frozen paleoaquifers perched between ground ice and crystalline salts

clues to martian brines based on halogens in salts from nakhlites and mer samples 1 chlorine and br abundances in fracture filling secondary salts in nakhla veins determined in this study by synchrotron x ray microprobe br and electron microprobe cl techniques compare well to the halogens determined recently by apxs instruments in soils and rock rinds at the gusev and meridiani sites the salts in these mars rocks arise from martian brines that have undergone evaporative or freezing concentration the halogen abundances in these salts are corrected for dilution effect because of mixing with halogen poor phases to obtain their true abundances which seem to be close to the halogen abundances in terrestrial sea brines consistent with the petrographic evidence for evaporative salt deposition sequence of carbonate sulfate halite in nakhlite meteorites nakhla veins yield high br 250 ppm and low cl br ratios 10 50 suggesting possible salt deposition from concentrated brines whereas lafayette iddingsite with low br 11 ppm and high cl br ratios 250 300 indicates salt deposition from dilute brines on mars the low cl br ratios 20 to 80 in salts from gusev and meridiani rock rinds indicate that they presumably originate from concentrated subsurface martian brines the high cl br ratio 270 in salts deposited by dilute solutions in lafayette and adirondack is similar to the chondritic cl br ratio which seems to characterize the dilute brines on mars prior to halite precipitation including early mars waters noachian or earlier our results seem to be consistent with the burt knauth model involving density stratification during evaporation freezing of brine solutions in martian regolith

detecting compositional spatial and temporal attributes of glaucony a tool for provenance research abstract a reliable interpretation of glaucony bearing units requires the characterization of compositional spatial and temporal attributes of glaucony the criteria that can readily determine the differentiation of the various types of glaucony autochthonous parautochthonous or allochthonous intrasequential and detrital or allochthonous extrasequential are discussed in detail autochthonous vs allochthonous glaucony may be often detected on the basis of detailed sedimentological investigations including facies interpretation of glaucony bearing deposits and careful examination of spatial distribution of glaucony textural and morphological features although generally not diagnostic on their own provide a significant contribution to glaucony interpretation the distinction between parautochthonous and detrital glaucony can be sometimes performed by radiometric dating more commonly it requires that compositional attributes of glaucony be matched against those of putative sources glauconies from distinct parent rocks generally have different maturity and carry unique geochemical and mineralogical fingerprints that may contribute definitive data for provenance research previous work on glaucony and examples from units formed in tectonically stable areas cretaceous eocene deposits of paris basin and hampshire basin and active tectonic basin settings miocene strata of southern alps and northern apennines provide the opportunity to discuss the validity of the proposed criteria across different structural domains and emphasize the need for an integrated approach to the study of glaucony

pixe and microthermometric analyses of fluid inclusions in hydrothermal quartz from the 2 2ga ongeluk formation south africa implications for ancient seawater salinity abstract the ongeluk formation mainly consists of submarine volcanics pillow lavas and sheet flows composed of basaltic andesites that are between underlying and overlying glaciogenic deposits i e the makganyene diamictite and a dropstone layer at the base of the hotazel formation respectively the stratigraphic position of the ongeluk formation indicates that the ongeluk volcanism occurred during a period of global glaciation the ongeluk volcanic rocks are host to subseafloor hydrothermal quartz deposits as drainage cavities and interpillow voids the hydrothermal quartz contains many primary type 1 and secondary type 2 liquid vapor fluid inclusions as well as inclusions that are randomly distributed without a trace of secondary healed cracks type 3 all these fluid inclusions types were individually analyzed with microthermometry and particle induced x ray emission pixe methods the results show that type 1 fluid inclusions are highly saline whereas type 2 fluid inclusions are relatively less saline type 3 fluid inclusions have bimodal peaks of salinity corresponding to those of type 1 and type 2 fluid inclusions and thus appear to represent mixtures between latter two inclusion types among the various fluid inclusion salinities of fluid inclusions a wide range in na ca values was identified in the high salinity fluid inclusions i e type 1 and a subset of type 3 which are thought to represent subseafloor fluids circulated by the ongeluk submarine volcanism the wide range in na ca values can be explained by a mixing process between na rich and ca rich fluids associated with albitization of the host basaltic andesites in the albitization process na is removed from the fluids and fixed by the host rocks by contrast ca is released from the host rocks into the fluids pixe analysis also showed two distinct trends i e vertical and horizontal on variation diagram of ca cl versus cu cl and positive correlations between mn cl cu cl zn cl and pb cl these data are best explained by the presence of other mixing processes between 1 a na rich ca and cu poor fluid 2 a ca rich na and cu poor fluid and 3 a na and cu rich ca poor fluid the cu mn zn and pb rich fluid likely represents a high temperature hydrothermal fluid from a deep reaction zone in the ongeluk subseafloor hydrothermal system by contrast the 1 na and k rich ca and cu poor endmember for the high salinity primary inclusions is considered to represent the composition of 2 2 ga ongeluk seawater we propose the estimation of 2 2 ga ongeluk seawater composition is 2237 mmol kg of na 200 1000 mmol kg of k

the role of fe on the formation and diagenesis of interstratified glauconite smectite and illite smectite a case study of upper cretaceous shallow water carbonates abstract the widespread formation of interstratified glauconite smectite gl s and illite smectite i s in modern and ancient diagenetic settings records the physicochemical conditions prevailing during clay mineral authigenesis to date however significant gaps in our knowledge persist in respect to the influence of interstitial solution chemistry temperature and reaction kinetics on the evolution of composition mineralogy and microstructure of gl s and i s herein we present a study on the reaction mechanisms and the physicochemical conditions that led to the precipitation of early diagenetic gl s and late diagenetic i s on a stable carbonate platform during the cenomanian at langenstein in the northern german basin the texture and the k ar age 95 0 1 8 ma of the green glauconitized grains revealed that green clay authigenesis progressed in initially organic rich semi confined micromilieus i e in fecal pellets and in foraminifera close to the sediment seawater interface the composition of gl s varied in the range k 0 20 0 74 na 0 0 10 ca 2 0 0 05 0 28 0 75 fe 3 0 63 1 20 fe 2 0 08 0 24 al 3 0 19 0 97 mg 2 0 29 0 52 2 01 2 12 al 3 0 09 0 35 si 4 3 65 3 91 o 10 oh 2 and depended on the rate of aqueous fe 2 and k ion diffusion the micromilieu of glauconitization and on the bulk sedimentation rate the mineralogical microstructural and chemical changes of the ongoing gl s products revealed the following reaction for green clay authigenesis at langenstein fe iii smectite reacted with monosilicic acid goethite and aqueous k mg 2 and fe 2 to form glauconite and aqueous na ca 2 and h ions this process considers complex mineral transformations commonly associated with glauconitization such as early diagenetic oxidation of organic matter and microbial catalyzed dissolution of fe oxy hydroxides carbonates and detrital silicates in contrast the k ar age of i s 68 0 1 6 ma and its compositional variability k 0 29 0 45 na 0 0 10 ca 2 0 0 06 0 30 0 55 fe 3 0 16 0 29 fe 2 0 0 10 al 3 1 37 1 68 mg 2 0 18 0 43 2 00 2 12 al 3 0 17 0 39 si 4 3 61 3 83 o 10 oh 2 indicate a burial diagenetic origin for this mineral phase rather than transformation of illitic clays into i s during weathering under warm and humid climatic conditions the results from kinetic modelling support a diagenetic origin of i s 50 60 i layers and 50 40 s layers and imply its formation by the replacement of pre existing k feldspar at high pore fluid activity k na ratios and at low fe 2 concentrations we propose that the substitution of al 3 for fe 3 fe 2 and mg 2 in the octahedral sheet shifts the stability field of the kaolinite fe al mg smectite fe al mg illite or glauconite triple point to much lower monosilicic acid activities and stabilizes the i s or gl s structure this reaction supports the idea that the bio availability of fe is the rate limiting factor for glauconitization which is not the case for the diagenetic growth of i s whereby the pore water fe 2 concentration may be limited by the competing formation of fe oxy hydroxides and or fe sulfides

the role of bacterial sulfate reduction during dolomite precipitation implications from upper jurassic platform carbonates the early diagenetic formation of dolomite in modern aquatic environments is limited mostly to evaporitic and marine anoxic organic rich sediments dominated by bacterial sulfate reduction bsr in such environments bacterial activity lowers the energy barriers for the nucleation and growth of dolomite and thus promotes the formation of non stoichiometric highly disordered and metastable proto dolomite although the boundary conditions for the formation of modern proto dolomites are considered to be generally understood the role of bsr during limestone dolomitization in ancient marine environments remains questionable herein we present a study about the physicochemical conditions and processes which led to the formation of partly dolomitized limestone and dolostone in the presence of bsr on a stable carbonate platform during the upper jurassic at oker northern german basin the dolomite textures the spatial trace elemental patterns of the dolomite and of the surrounding limestone and the results of 18o and 13c isotope analyses reveal that the oker dolomite has been formed by the early diagenetic replacement of magnesian calcite precursors at temperatures between 26 c and 37 c we interpret the mineralizing fluids responsible for dolomitization as pristine marine to slightly evaporitic and reducing seawater being modified during shallow seepage reflux and or evaporitic tidal pumping the elevated 34scas values 17 9 to 19 7 v cdt of the oker dolomite compared to ambient upper jurassic seawater indicate that bsr facilitated dolomite formation for the first time we show that a linear anti correlation exists between decreasing carbonate associated sulfate cas contents in dolomite and increasing ordering ratio of the dolomite lattice structure with the degree of cation order in dolomite to be given by degree of cation order dol 0 018 cas dol 68 3 r2 0 98 this correlation implies that the cas content of sedimentary dolomite can be used as a measure for dolomite maturity the relationships between the ambient paleo environmental controls the resultant dolomitization pathways and subsequently the structure and the composition of the precipitating dolomite are presented and discussed in relation to the stability of modern and ancient proto dolomites throughout burial diagenesis

john joly 1857 1933 and his determinations of the age of the earth abstract john joly 1857 1933 was one of ireland s most eminent scientists of the late nineteenth and early twentieth centuries who made important discoveries in physics geology and photography he was also a respected and influential diplomat for trinity college dublin and various irish organizations including the royal dublin society measuring the age of the earth occupied his mind for some considerable time a problem he was to address using a diverse range of methods his sodium method of 1899 for which he is best known was hailed by many as revolutionary but it was later superseded by other techniques including the utilization of radiometric dating methodologies although joly himself carried out much research in this area he never fully accepted the large age estimates that radioactivity yielded nevertheless joly s work in geochronology was innovative and important for it challenged earlier methods of arriving at the earth s age particularly those of lord kelvin although his findings and conclusions were later discredited he should be remembered for his valuable contribution to this important and fundamental debate in the geological sciences

oxygen and stable carbon isotopes from a nautiloid from the middle pennsylvanian late carboniferous impregnation lagerstatte buckhorn asphalt quarry primary paleo environmental signals versus diagenesis abstract two shell fragments one of an undetermined cephalopod and one of an orthoconic nautiloid pseudorthoceratidae gen et sp indet from the pennsylvanian buckhorn asphalt lagerstatte oklahoma were studied to reconstruct paleotemperatures and to explore possible diagenetic alterations for the first time not only parts of the shell of an orthoconic nautiloid but also its cameral deposits were sampled in high resolution the mineralogy geochemistry and microstructure of both shell remains the pseudorthoceratid and the undetermined cephalopod were investigated in detail before high resolution transects for oxygen and stable carbon isotopes were sampled the shell fragment of the undetermined cephalopod showed no or very little diagenetic alteration therefore the measured 18o variation 18o range of 0 68 and the inferred temperature range of 28 to 31 c are interpreted to represent an original signal the temperatures indicate that the specimen lived in shallow warm tropical waters the 13c signal with a 13c range of 3 43 is interpreted to be the consequence of a strong metabolic effect a septum of the phragmocone of the pseudorthoceratid nautiloid was only slightly altered by diagenesis and a largely original 18o signal could be obtained the 18o values exhibit an inferred temperature range of 14 to 15 c indicating that this species lived in deeper and cooler waters the cameral deposits were investigated in detail by energy dispersive x ray edx and by xrd gadds x ray diffraction general area detector diffraction system analyses part of the cameral deposits in the orthoconic nautiloid turned out to originally consist of high mg calcite hmc instead of the estimated aragonite anyhow the massive cameral deposits show signs of strong small scale alteration resulting in a distinct spreading of oxygen values the oxygen and carbon isotope plots show a linear trend for the oxygen carbon correlation this is interpreted as the mixing of two end members with the lightest end members suggesting a meteoric diagenesis with a diagenetic fractionation of the aragonite to low mg calcite lmc respectively the hmc to lmc and dolomite the calculated temperatures of the pseudorthoceratid specimen and the undetermined cephalopod indicate two different paleoenvironments additionally the pseudorthoceratid nautiloid displays the narrow range of temperatures in the deeper parts of the sea and the undetermined cephalopod the more fluctuating temperatures in the shallow areas it is also shown how important a detailed investigation of microstructures and mineralogy of samples with an according cautious interpretation of the achieved dataset is the importance of an intensive examination of samples is pointed out to avoid small scale alterations to be overlooked since this would lead to a misinterpretation of the results

verdine and glaucony facies from surficial sediments of the eastern continental margin of india the present paper reports the first mineralogical description of green grains verdine and glaucony from sediments of the eastern continental margin of india only 24 of the 82 sediment samples studied at depths between 18 and 247 m contain green grains and their percentages in the coarse fraction 125 250 m range from 6 to 40 of these 13 samples from the inner shelf 18 70 m contain irregular dark green grains 6 samples from the outer shelf 70 125 m contain dark green pellets and a few dark green internal moulds of skeletal materials and 5 samples from the continental slope 160 247 m contain dark green moulds and infillings of planktonic and benthic foraminifers the green grains found at depths between 18 and 125 m consist of poorly crystalline phyllite v with very little detrital clay at 170 m depth odinite young phyllite v occurs and further seaward between 200 and 247 m glauconitic smectite is present all verdine and glaucony grains studied show an early stage of evolution and the colour does not reflect their evolution the verdine and glaucony from the slope sediments may correspond to the last glacial maximum and the outer shelf verdine facies formed during the subsequent transgression the inner shelf green grains may represent the present day formation of verdine

unusual occurrence of glauconite in a shallow lagoonal environment lower cretaceous northern aquitaine basin sw france some minerals are considered to be representative of specific natural environments among them glauconite is considered to be formed in marine deep platform conditions however the term glauconitic is misused to designate green minerals formed in marine outer shelf environments x ray diffraction scanning electron microscopy and energy dispersive x ray analyses of individual green materials were carried out leading to the identification of glauconite in the purbeckian facies green glauconite grains predominantly occur as burrow fills and occasionally as faecal pellet replacements two depositional environments have been identified from bottom to top of the succession 1 an argillaceous dolomitic lagoonal sediment formed in saline shallow water 2 a marl limestone alternation deposited in a brackish water estuary the crystallochemical properties of the glauconites change abruptly these findings show that glauconite may form in coastal environments and not only in mid shelf to upper deep water platform environments as classically assumed moreover the glauconite composition changes with the chemical conditions imposed by the local environment

spatial variability in oceanic redox structure 1 8 billion years ago the deposition of iron formations ceased about 1 84 billion years ago reconstructions of ocean chemistry suggest that the advent of euxinic conditions along ocean margins preferentially removed dissolved iron from the water column in the form of the mineral pyrite inhibiting widespread iron oxide mineral deposition

deposition of talc kerolite smectite smectite at seafloor hydrothermal vent fields evidence from mineralogical geochemical and oxygen isotope studies abstract talc kerolite smectite smectite chlorite smectite and chlorite samples from sediments chimneys and massive sulfides from six seafloor hydrothermal areas have been analyzed for mineralogy chemistry and oxygen isotopes samples are from both peridotite and basalt hosted hydrothermal systems and basaltic systems include sediment free and sediment covered sites mg phyllosilicates at seafloor hydrothermal sites have previously been described as talc stevensite or saponite in contrast new data show tri octahedral mg phyllosilicates ranging from pure talc and fe rich talc through kerolite rich kerolite smectite to smectite rich kerolite smectite and tri octahedral smectite the most common occurrence is mixed layer kerolite smectite which shows an almost complete interstratification series with 5 to 85 smectitic layers the smectite interstratified with kerolite is mostly tri octahedral the degree of crystal perfection of the clay sequence decreases generally from talc to kerolite smectite with lower crystalline perfection as the proportion of smectite layers in kerolite smectite increases our studies do not support any dependence of the precipitated minerals on the type subtype of hydrothermal system oxygen isotope geothermometry demonstrates that talc and kerolite smectite precipitated in chimneys massive sulfide mounds at the sediment surface and in open cracks in the sediment near seafloor are high temperature 250 c phases that are most probably the result of focused fluid discharge the other end member of this tri octahedral mg phyllosilicate sequence smectite is a moderate temperature 200 250 c phase forming deep within the sediment 0 8 m chlorite and chlorite smectite which constitute the alteration sediment matrix around the hydrothermal mounds are lower temperature 150 200 c phases produced by diffuse fluid discharge through the sediment around the hydrothermal conduits in addition to temperature other two controls on the precipitation of this sequence are the silica activity and mg al ratio i e the degree of mixing of seawater with hydrothermal fluid higher silica activity favors the formation of talc relative to tri octahedral smectite vent structures and sedimentary cover preclude complete mixing of hydrothermal fluid and ambient seawater resulting in lower mg al ratios in the interior parts of the chimneys and deeper in the sediment which leads to the precipitation of phyllosilicates with lower mg contents talc and kerolite smectite have very low trace and rare earth element contents some exhibit a negative or flat eu anomaly which suggests eu depletion in the original hydrothermal fluid such eu depletion could be caused by precipitation of anhydrite or barite sinks for eu2 deeper in the system ree abundances and distribution patterns indicate that chlorite and chlorite smectite are hydrothermal alteration products of the background turbiditic sediment

composition and evolution of the early oceans evidence from the tagish lake meteorite abstract laboratory leaching studies of the tagish lake meteorite demonstrate that the most readily leached cations of carbonaceous chondrite meteorites are mg ca na and k with the most readily leached anions being so4 cl and po4 in decreasing order of abundances soluble organics were not analyzed due to limited sample sizes magnesium and sulfate the most abundant solutes leached from tagish lake meteorite are also the most abundant ions of salts lining fractures of aqueously altered meteorites these same ions probably were the most abundant solutes of the first permanent oceans which probably formed during or soon after the late heavy bombardment stage 4 2 to 3 7 ga considering the residence time of cl in modern seawater and the composition of the exposed continental crust to at least 3 3 ga evolution of seawater from mg so4 dominated to nacl dominated would have required about 3 105 yr and could not have been complete until about 3 0 to 3 3 ga the calculations also suggest that the first permanent oceans were more saline than modern seawater and as argued by others these aspects have significant implications for evolution of life many solar system bodies besides earth probably derived a significant proportion of their volatile and soluble constituents from carbonaceous chondrite material therefore primordial solutions similar to those presented here were likely important in the early evolution of aqueous systems throughout the solar system including those present on carbonaceous chondrite parent asteroids and icy outer solar system satellites

gold mobility during palaeoarchaean submarine alteration abstract seafloor alteration provides large amounts of solutes to the hydrosphere in order to investigate gold mobility during water rock interaction prior to 3 billion years ago low detection limit analysis of au concentrations was carried out on rocks from marine alteration zones stratiform zones recording low temperature 150 c seafloor alteration are a characteristic feature of greenstone belts older than 3 0 ga hydrothermal processes were operating on and immediately below the seafloor giving rise to extensive silicification of sub seafloor volcanic rocks and silicification of seafloor sediments in order to investigate gold mobility during silicification unaltered and variably silicified volcanic rocks and associated cherts from palaeoarchaean greenstone successions c 3 4 ga of south africa were analyzed results show mobility of gold during silicification of mafic ultramafic rocks and transfer to the archaean ocean some gold was incorporated into carbonaceous marine sediments overlying the alteration zones a combination of pervasive silicification rarity of black shales and low gold content in komatiites can explain the low mineralization potential of palaeoarchaean greenstone belts for orogenic gold deposits

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments

oligocene to pliocene palaeogeographic evolution of the cankiri corum basin central anatolia turkey abstract the cankiri corum basin is one of the largest basins of central anatolia to have developed oligocene to quaternary terrestrial environments the basin contains significant raw materials for industry and energy but the determination of their distribution patterns requires a good knowledge of the stratigraphic and spatial distribution of deposits besides evolving tectonic regimes in the basin and the sedimentary sequences controlled by them can play key roles in revealing the regional paleogeography on the basis of a new chronological framework provided by mammalian fossils and sedimentological data ten sedimentary formations have been identified for the oligocene pleistocene time interval from the oldest to the youngest these are the incik guvendik kizilirmak kilcak kumartas hancili bayindir akkasdagi bozkir and degim formations during early oligocene times an alluvial fan and braided and meandering rivers deposits developed at the northern and eastern rims of the basin whereas lacustrine products dominated by evaporitic deposits occurred in vast areas at the center in late oligocene the lake area contracted and dominant floodplains and braided rivers took place in the central area of the basin during early middle miocene large lacustrine areas dominated by organic clastic deposits developed in the northern and middle parts of the basin lake shore facies were formed in northern parts of the basin and on some paleohighs surrounding the lake in the orta and abanozu regions volcanic activity started during the middle miocene and lasted until the beginning of late miocene during late miocene there were different types of lacustrine environments in the northern and southern parts of the basin a hypersaline lake characterized by evaporitic deposits in the north and carbonate rich shallow lakes and swamps in the south a younger evaporitic lake formed in early pliocene in the northern part of the basin and covered vast areas its deposits are as thick as 400 m from late pliocene the thick sedimentary sequences deposited during the oligocene early pliocene interval become fragmented and deformed by a tectonic wedge bounded by a normal fault in the west and a thrust in the east sedimentary products of this tectonic regime are represented by thick alluvial fan sequences of the degim formation

the tectonic significance of k ar illite fine fraction ages from the san luis formation eastern sierras pampeanas argentina the sierra de san luis forms the southern tip of the eastern sierras pampeanas in central argentina two narrow belts of low grade phyllites and quartz arenites i e the san luis formation have accommodated part of the strain related differential exhumation of the medium to high grade metamorphic domains that constitute to the basement complex of the sierra eleven phyllite samples were subjected to the k ar fine fraction dating technique results are interpreted in relation to the kubler index of the illites which indicate epimetamorphic conditions for the majority of the samples obtained ages between 330 and 290 ma cover a period of compressional tectonics in the late mississippian visean serpukhovian boundary followed by the subsidence during the formation of the paganzo basin in the provinces of la rioja and san luis these tectonic movements are coincident with the toco orogeny in northern chile and southern bolivia this suggests that the older k ar ages document the compressional stage and that younger ages record the cooling of the basement during the subsequent extensional uplift of the basement