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

surficial geology of the continental shelf northwestern vancouver island abstract the vancouver island continental margin lies along the convergent boundary between the explorer and juan de fuca plates and the america plate off northwestern vancouver island this tectonic regime is manifested in major thrust faults and folds which dislocate volcanic and sedimentary rocks of tertiary age beneath a relatively undeformed wedge of late neogene mudstones surficial sedimentation reflects both the tectonic and high latitude settings of the area predominance of lithic arenites and graywackes high wave and current energy restricting modern sedimentation to the outer shelf deeper than 110 m and resulting in the formation of large oscillation bedforms to depths of 100 110 m trapping of terrigenous sediments in fjords leading to low sediment accumulation rates on the shelf which in turn favor the formation of abundant glauconie gravel lags and extensive areas of biogenic sediments dominated by molluscs and bryozoa and the presence of pleistocene glaciomarine sandy muds and muddy sands beneath the mid and outer shelf

glauconitic sediments on the continental shelf off vancouver island british columbia canada abstract the tectonically active vancouver island continental margin is characterized by a very narrow 80 km continental shelf and an extremely steep continental slope the shelf is marked by high wave and current energies on the inner nondepositional shelf and very slow rates of sediment accumulation on the outer shelf within the muddy sands of the outer shelf and slope glauconitic grains are frequently an important constituent of the sand fraction occurring in four principal forms a locally abundant pale green infillings of benthic foraminifera b very abundant pale to moderately dark green dull grains displaying varying degrees of fracturing of the external surfaces c scarce moderately dark green altered and expanded mica grains and d scarce very dark green small 200 m grains with polished highly fractured surfaces mineralogically the grains mainly reflect their origins as detrital sediments they consist most commonly of quartz plagioclase minerals chlorite smectite and illite also a mixed layer mineral smectite illite occurs in significant amounts in glauconitic grams but is absent in unaltered mud fragments and in the clay fraction of sediments from the outer shelf the appearance of this mineral reflects the first stages of glauconite authigenesis bulk analyses of glauconitic grains yielded k2o values of less than 2 reflecting their very early stage of evolution but 19 28 fe2o3 several times the level in the surrounding matrix sediments microprobe analyses and scanning electron microscopy show that glauconitic smectite forms in the pores and along fractures in the host grains commonly as a boxwork arrangement or rosette clusters of blades fe2o3 and k2o values at these sites can reach 32 5 and 7 5 respectively several lines of evidence including radiocarbon age determinations on glauconitized foraminifera tests indicate a recent age for the vancouver island shelf glauconitic grains

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

geochemical and paleoenvironmental variations across the cretaceous tertiary boundary at braggs alabama abstract the cretaceous tertiary k t boundary in southern alabama occurs in a sequence of interbedded shallow marine limestones and marls deposited during a late maastrichtian regression and subsequent danian transgression the presence of a diverse assemblage of cretaceous and paleocene benthic micro and macrofossils has allowed detailed examination of paleoenvironmental changes in this shallow marine setting at the time of the k t boundary extinctions although extensive diagenesis has resulted in the recrystallization and cementation of whole rock carbonate a few molluscan macrofossils have retained their original calcitic structure the oxygen isotopic record of these macrofossils shows a gradual cooling of 2 3 c over a 3 m y period which began in the late maastrichtian and continued into the danian the characteristic depletion in 13 c across the k t boundary displayed by planktonic microfossils from pelagic sequences is not recorded at braggs major changes in whole rock trace and minor element chemistry reflect the decrease in terrigenous mineral fluxes to this location brought about by the rapid early paleocene transgression

excess k ar ages of glauconite from the upper marine molasse and evidence for glauconitization of mica k ar age determinations along with optical investigations were used to examine whether glauconite from the upper marine molasse omm is of authigenic allogenic or transformed origin for this purpose 16 glauconite samples from 14 different localities were investigated from the burdigalian muschelsandstein collected along a traverse from lake constance to west of geneva

whence the gosport sand upper middle eocene alabama the origin of glauconitic shell beds in the paleogene of the u s gulf coastal plain abstract an explanation for the depositional history of the gosport sand has proven to be as puzzling as its diverse mollusk fossils is beguiling we propose that shifting delta lobes produced patchy environments which accumulated to form the gosport sand and likely other glauconite and fossil rich shell beds of the gulf coastal plain of the paleogene we present facies and mineralogical data to suggest glauconite in the gosport sand was deposited during relatively stable environmental conditions increased glauconite maturity and taphonomic alteration in the gosport sand are attributed to eustatic transgression resulting in decreased deposition enhanced winnowing and increased exposure at the sediment water interface increased fossil diversity and abundance likely result from time averaging and accumulation of shells from ancient patchy habitats analogous to modern inner shallow shelf and open sound environments delta progradation and subsidence would have determined the migration of these environments we evoke a similar depositional model for glauconite rich shell beds distributed throughout the paleocene and eocene of the gulf coastal plain based on their transgressive nature and roughly equivalent facies these shifting environmental conditions may have played a partial role in generating the high molluscan diversity of the gulf coastal plain of the paleogene

glaucony from the cretaceous of the sierra de guadarrama central spain and its application in a sequence stratigraphic context detailed sedimentological and geochemical analyses of upper cretaceous glaucony bearing deposits from the middle portion of the castro de fuentiduena formation in central spain enable identification of a multiphase history of glaucony accumulation despite its relatively high maturity k2o 7 glaucony from the transgressive subtidal sandstones has anomalously low concentration in the host rock generally 10 suggesting remobilization from a different source the remarkable thickness of the glaucony bearing horizons concurrently with concentration of glaucony in laminae small size and high degree of roundness and sorting provide further evidence for an allochthonous origin of the green grains in contrast authigenic glaucony from the overlying offshore clays exhibits higher abundance up to 45 and lower maturity k2o 7 and is interpreted to have formed in situ allochthonous glaucony originally developed in more distal areas during a prolonged period of sediment starvation the green grains were then swept away from their place of origin and concentrated into tidal bars and channels within the upper transgressive systems tract of the third order depositional sequence maximum concentration of autochthonous glaucony is recorded at the transition from tidal influenced to offshore deposits this glaucony which is relatively less evolved due to lower time available for maturation is interpreted to reflect the turnaround from transgressive to highstand conditions marking the condensed section of the depositional sequence as postulated by previous sequence stratigraphic models this study documents that allochthonous glaucony can be widespread throughout the transgressive systems tract tst while the condensed section cs typically hosts autochthonous glaucony contrary to the existing literature however this study shows that glaucony from the tst may be even more mature than glaucony from the cs if enough time for maturation during transgression is allowed before the ultimate concentration of the green grains identification of spatial and temporal characteristics of glaucony thus is critical to a reliable sequence stratigraphic interpretation of the glaucony bearing deposits

compositional variation within some glauconites and illites and implications for their stability and origins textural mineralogical and chemical data are presented for glauconites and illites from the lower cretaceous glauconitic sand formation alberta canada single crystal analyses by scanning transmission electron microscopy stem indicate that both glauconite 29 analyses and illite 44 analyses correspond very closely to ideal dioctahedral structures al dominates the octahedral sheet in illite very extensive a1 for feiii substitution was also found in some of the glauconites much more than previously recorded the dioctahedral mica structure is clearly very stable and flexible with respect to a1 for feiii substitution iron poor glauconites were found associated with pyrite we believe that glauconites tend to lose iron progressively during burial diagenesis especially where pore water iron activities are low high hs activity and low eh it seems probable that a1 for si tetrahedral substitution also takes place during diagenesis with consequent loss of swelling properties this is the same trend which is responsible for conversion of smectite to illite glauconite forms only where sediments reside for lengthy periods at the interface between oxidizing and reducing environments where fe3 is transiently available in solution related marine and terrestrial nontronites also form only in similar interface environments

secular variation in the isotopic composition of nd in tethys seawater abstract this preliminary nd isotopic study of authigenic glauconites that are mineralogically chemically isotopically rb sr k ar and stratigraphically well characterized suggests that these minerals can be used to determine the nd isotopic evolution of ancient ocean water generally glauconites indicate the same evolutionary history of nd in tethys seawater as published data for marine phosphates e g fish remains mn ores and fossil debris the initial nd values define a smooth curve with lowest values of 9 to 10 for the cretaceous and lower tertiary highest nd values have been found for 150 200 ma tethys seawater that was influenced by both a nonradiogenic continental component and a greater input of young mantle derived material

temperate skeletal carbonate sediments on scott shelf northwestren vancouver island canada abstract scott shelf 2000 km 2 centred at scott islands northwestern vancouver island is mainly shallower than 150 m topographically diversified and floored by bedrock outcrops and terrigenous lithic gravels and sands left stranded following the post glacial rise in sea level 13 000 yrs b p it lies in a zone of vigorous wind wave currents and strong tidal flows but is largely starved of modern terrigenous sediment as a consequence it is slowly accumulating a thin discontinuous blanket of clean skeletal carbonate sands and gravels admixed to varying degrees with the underlying terrigenous deposits principal skeletal contributors are infaunal bivalves on coarse sandy and gravelly substrates barnacles on low amplitude gravelly ridges bryozoans on bedrock outcrops and boulders and benthic foraminifera on fine sands in deep 100 m waters south of the scott islands living carbonate benthos are scattered and generally sparse occupying specific ecologic niches and the shelf wide rate of carbonate production is low skeletons are fragmented transported and mixed during storms and are concentrated within bedrock hollows and crevices and shallow depressions between gravel ridges where infaunal bivalves are abundant the carbonates are dominated by aragonite but otherwise the skeletal hashes are predominantly calcitic many grains and especially aragonitic ones are corroded and weakened by epilithic and endolithic bioerosion and probably also by marine and dissolution the most corroded shells have ages of only about 1000 yrs so that their preservation potential is low the character of scott shelf skeletal carbonate deposits reflects their temperate latitude cold water heritage

syndepositional shallow water precipitation of glauconitic minerals abstract numerous studies have demonstrated that glauconitic minerals predominantly form in water depths of mid shelf to upper slope in modern oceans these areas tend to have slow sedimentation rates another commonly cited requisite for glauconitic mineral precipitation cambro ordovician strata from the southwestern us are rich in glauconitic minerals stratigraphic sedimentological and petrographic constraints indicate that the glauconitic minerals are autochthonous in marked contrast to the modern environments of deposition these cambro ordovician strata formed under very shallow water to tidal flat conditions the trough cross stratified deposits of the most glauconitic mineral rich accumulations glaucarenites indicate a high energy environment and probably a normal to high rate of sedimentation the presence of fibroradiated rims of glauconitic minerals on glauconitic mineral pellets echinoderm fragments and quartz grains demonstrates that the cambro ordovician glauconitic minerals precipitated on or in close proximity to the sea floor and prior to calcite precipitation consequently glauconitic minerals must have formed under markedly different conditions in the lower paleozoic than they do today thus the occurrence of glauconitic minerals in the rock record cannot be used a priori as an environmental indicator of either mid shelf and deeper water and or a slow rate of sedimentation

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

paragenesis of the morgan creek limestone late cambrian central texas constraints on the formation of glauconite abstract deposition of the morgan creek limestone a member of the cambrian wilberns formation began a few meters above a disconformable surface and displays abundant indicators of accumulation in shallow marine to tidal flat environments these indicators include intercalation of a lithologic variety of thin beds e g biosparites biomicrites oosparites intrasparites which display rapid vertical and lateral lithologic changes numerous stromatolitic horizons channels filled with graded oosparites and intrasparites that cut through micrite accumulations and finely laminated non burrowed siltstones glauconite is a ubiquitous minor constituent throughout in the form of pellets replaced skeletal material and mica books and most informatively as an authigenic precipitate in the form of fibroradiating rims on carbonate allochems and siliciclastic grains fibroradiating glauconite rims were disrupted and pushed away from the pelmatozoan nuclei on which they precipitated combined sedimentological and paragenetic constraints indicate that the glauconite was the earliest diagenetic event to affect these sediments and occurred essentially at the sediment water interface within these relatively high energy shallow marine deposits precipitation of glauconite was closely followed by precipitation of carbonate cement as well as dissolution of aragonitic constituents later diagenetic processes included selective dolomitization and silicification in modern seas glauconite is reported to form at and below mid shelf water depths thus the constraints pertaining to the origin of modern glauconite are not valid for late cambrian deposits and probably are also not applicable for late cretaceous through early paleogene glauconites

erosion rates and sediment sources in madagascar inferred from 10be analysis of lavaka slope and river sediment abstract the central highlands of madagascar are characterized by rolling hills thickly mantled with saprolite and cut in many areas by dramatic gullies known as lavakas this landscape generates sediment to rivers via diffusive downslope movement of colluvium and event driven advection of material from active lavakas these two sediment sources have very different 10be signatures analyzed lavaka sediment has very little 10be documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 0 8 mbox 10 times 10 5 end document atoms

tectonic cycles in southern africa abstract the recurrence of major geological events within the 3600 ma stratigraphic record of southern africa suggests a periodicity of320 25ma for at least the last 3200 ma this periodicity is reflected in major episodes of continental volcanism granitoid plutonism orogeny reciprocity of terrestrial and marine dominated sequences platform carbonate sedimentation glaciation and first order changes in sea level these serve to define 11 completed megacycles each introduced by a major rifting event accompanied by listric faulting alluvial sedimentation in restricted fault bound troughs volcanism and a type granitoid plutonism prior to 3200 ma continental rift magmatism occurred subaqueously due to very high early archean sea levels resulting in pillow lavas and a lack of interbedded terrigenous siliciclastics the long term reciprocity of terrestrial and marine dominated sequences records eustatic first order changes in sea level with highstands characterized by generally humid warm continental climates low relief and tropical afforestation on the other hand lowstand climates were hot and arid with high relief and widespread desertification thick marine sequences accumulate in areally extensive epeirogenic basins without significant volcanism or faulting and commonly are divided into an early phase of open shelf sedimentation followed by deposition in a brackish marine foreland basin within openshelf environments an early phase of biochemical precipitation and or siliciclastic reworking along linear shorelines is separated from a later phase involving rapid deposition of immature siliciclastics along lobate shorelines evolution of the foreland basin is related to orogenic activity and the isolation of an epeiric sea which sometimes developed the characters of a barred basin marine dominated sequences display a deterministic stacking of lithofacies important glacial epochs commonly occur midway through first order regression sometimes with lesser events closely following peak transgression potentially they display 320 ma periodicity but with an unexplained mid proterozoic gap glaciation is related to the combined effect of climatic cooling associated with first order regression and depletion of atmospheric co2 by biological uptake associated with platform carbonate development terrestrial volcanism is believed to be the main contributor of atmospheric co2 climatic change is accompanied by cyclical patterns of cratonic weathering and pedogenesis

slipstream an early holocene slump and turbidite record from the frontal ridge of the cascadia accretionary wedge off western canada and paleoseismic implications slipstream slump a well preserved 3 km wide sedimentary failure from the frontal ridge of the cascadia accretionary wedge 85 km off vancouver island canada was sampled during canadian coast guar

the distinctive compositional evolution of glauconite in the cretaceous ukra hill member kutch basin india and its implications abstract an integrated study involving sedimentology mineral chemistry and spectroscopy highlights a distinctive compositional evolution of cretaceous glauconite within the ukra hill member glauconite occurs at the top part of transgressive systems tract deposits built on a marine shelf the concentration of glauconite steadily increases towards the maximum flooding surface maximizing around 50 and sharply falls at the onset of progradation unlike most phanerozoic examples ukra glauconite forms by the variable degree of replacement of quartz feldspar and mica grains xrd feg sem and spectroscopy of glauconite pellets indicate an evolved stage of maturation mossbauer spectroscopy reflects a minor substitution of al3 fe3 total in tetrahedral sites and significant substitution of the same in octahedral sites a consistently high value of k2o as well as fe2o3 contradicts the two popular theories layer lattice and verdissement and support replacement origin of glauconite in a high asi and high ak pore water environment incipiently formed glauconite records a marginal increase in k2o content accompanied by release of al2o3 and sio2 to form evolved glauconite pellets those forming within quartz grains involve an addition of fe2o3 total content during maturation the minimal increase in k2o content of incipiently formed glauconite best exhibited by those formed within quartz grains is possibly related to stratigraphic condensation compositional evolution like this is exhibited by precambrian glauconites involving abiotic substrates but is unusual for the phanerozoic original k2o and fe2o3 total content of glauconites is reduced around peripheries and fractures during diagenesis adding to compositional variability

ichnology of an eocene shallow marine passive margin condensed section eastern gulf coastal plain alabama u s a abstract exposures of the eocene tallahatta formation in southern alabama u s a provided the opportunity to document the ichnologic character of a highly condensed passive margin transgressive systems tract and its two component parasequences the studied succession is dominated by variably glauconitic fossiliferous muddy sands deposited in shallow marine shelf settings thorough bioturbation and abundance of mud indicate quiet background conditions whereas admixed sand and localized scour features indicate periodic influence by bottom currents parasequences delineated based on vertical trends in glauconite abundance are bounded at their bases by flooding surfaces marked by thalassinoides dominated firmground ichnofabrics but internally host moderately diverse cruziana ichnofacies assemblages recurring softground ichnofossils include asterosoma chondrites diopatrichnus ophiomorpha planolites rosselia teichichnus thalassinoides and enigmatic composite structures the distributions and abundances of which vary within and between parasequences increasing prominence of diopatrichnus and rosselia towards parasequence tops reflects organismal responses to environmental changes associated with shallowing and or enhanced preservation potential of shallow tier structures in response to increased sedimentation rates maximum sediment starvation during deposition of the uppermost parasequence is reflected by peaks in burrow density softground ichnofossil diversity and concentrations of entobia bored shells and teredolites bored logs enigmatic composite burrows and common thalassinoides with linings and or meniscate backfills are ubiquitous and may be diagnostic of sediment starvation and prolonged habitation of slowly accreting substrates

a shallow marine volcaniclastic facies model an example from sedimentary rocks bounding the subaqueously welded ordovician garth tuff north wales u k abstract volcaniclastic sedimentary rocks bounding the ordovician garth tuff in north wales were deposited in a shallow marine setting adjacent to a magmatic arc the volcaniclastic sedimentary rocks are primarily of angular to euhedral quartz angular euhedral feldspar and volcanic rock fragments these grains are of a pyroclastic origin but have been reworked to various degrees sedimentary rock fragments rounded quartz muscovite biotite iron rich chlorite and various clay minerals occur in lesser amounts the sedimentary rocks can be divided into a proximal offshore to foreshore facies association poffa and an offshore to lower shoreface facies association olsfa the sand dominated poffa exposed near capel curig is characterized by large wave ripples hummocky cross stratification co sets of trough cross beds reactivation surfaces plane beds and graded turbidite layers in suspension deposited mudstone water depths calculated from bedding plane exposure of large wave ripples and determined by the presence of hummocky cross stratification and by facies association vary from a few meters to around 30 m 45 50 m theoretical maximum in a 45 m thick stratigraphic section beneath the tuff eight kilometers to the southeast the garth tuff is bounded by a thick sequence of suspension deposited laminated mudstone with thin graded beds of siltstone and fine grained sandstone this facies association olsfa represents the introduction of material by distal turbidites and by pelagic sedimentation the olsfa was deposited in water depths well below storm wave base possibly in excess of 200 m no evidence of storm waves or surface generated currents occur until over 40 m above the tuff this study documents marine sedimentary rocks deposited in water depths ranging from foreshore to offshore as the bounding facies of the garth tuff it is thus reasonable to conclude that the garth tuff was emplaced and welded in water depths greater than the thickness of the tuff in the area of this study

potential use of the e center as an indicator of initial resetting in tl esr dating of volcanic materials abstract quartz inclusions embedded in volcanic materials can be used for dating quaternary volcanoes by tl or esr methods for these techniques the initial zeroing by heat is assumed however this assumption can sometimes be questioned either because the temperature was not high like in phreatomagmatic deposits or because of contamination like in thin tephra layers preliminary observations suggested that the presence of the e center could be an indicator of poor initial zeroing this possibility was investigated in the present work quartz grains from various geological contexts were studied for comparison annealing and regeneration of the e center was explored

petrology and palaeoenvironmental significance of glaucony in the eocene succession at whitecliff bay hampshire basin uk following the investigations of odin and others into the distribution of green granules glaucony has been widely assumed to be a reliable indicator of a fully marine open shelf environment with a low sedimentation rate we have investigated the value of glaucony as a palaeoenvironmental indicator through an investigation of the pellets and their distribution and reworking in the predominantly brackish to shallow marine tertiary sediments of the hampshire basin together with a re evaluation of the sedimentology glaucony has apparently formed in situ in all lithofacies from shallow marine to estuarine of the three highest glaucony concentrations all dominated by in situ glaucony two occur within highstand system tracts the third is at a sequence boundary several important surfaces do not have more than a few percent glaucony with very variable proportions of mature and in situ pellets the correlation between glaucony concentration and sequence stratigraphy is most obvious in the london clay and wittering formations where least reworking of pellets has occurred in the barton group there are no major concentrations of glaucony at any of the important stratal surfaces we believe this more random glaucony distribution is due to limited glaucony formation and reworking of older glaucony in these sediments ideal conditions for glaucony formation are interpreted to have been fully marine 10 30 m water depth a warm temperature plus low sedimentation rate with periodic winnowing to concentrate the pellets although most of these conditions for glaucony formation occurred in the selsey formation and barton group a factor or factors mitigated against glauconitization we suggest that this was lowering of the water temperature the london clay and wittering formations were deposited relatively rapidly 50 60 m ma 1 and include intervals of estuarine sedimentation both factors that we believe inhibited glaucony formation glaucony maturity reflects the minimum length of time spent in surface sediments close to the oxic sub oxic interface point count data and chemical data for glaucony indicate widespread reworking and an overall increase in reworking with time possibly due to uplift on the isle of wight monocline the apparently wide range of conditions in which glaucony will form and the frequency with which it is reworked suggest that it is a less useful indicator palaeo environmental indicator than is commonly supposed

attempts at dating ancient volcanoes using the red tl of quartz abstract the suitability of the red tl peak of quartz for long range dating is tested by application to some volcanic events of the french massif central see map fig 1 having assumed ages in the range 14 150 ka the samples are sediments heated by lava flows and pyroclastic products in most cases the results fit with the geological evidence no direct comparison can yet be made with other dating methods on the other hand for two events having ages of 2 and 14 ma the growth curve using the additive dose technique had an abnormal shape which could not be reproduced with a sample zeroed in the laboratory this effect which is not yet properly understood may prevent the use of the tl regeneration technique for evaluation of the palaeodose for very old samples

distinctive compositional characteristics and evolutionary trend of precambrian glaucony example from bhalukona formation chhattisgarh basin india abstract up to 20 of framework quartz and feldspar grains in wave reworked sandstones in the precambrian bhalukona formation central india are replaced by glaucony which is characterized by high k2o al2o3 mgo and low total fe2o3 content textural evidence indicates that incipient glaucony within cleavages and fractures of detrital grains evolved to pellets k2o content of glaucony remains high av 8 despite its low total fe2o3 content glaucony evolved with addition of total fe2o3 at a constant k2o during the course of maturation al2o3 was released while total fe2o3 mgo and sio2 were added to the glaucony structure glaucony originated in a high ak and high asi pore water environment by pseudomorphic replacement of grains continental weathering related supply of fe mg k and si facilitated glaucony formation in shallow marine sediments the origin evolution and geochemistry of shallow marine originated precambrian glaucony completely differ from those of their phanerozoic counterpart

is the rarity of glauconite in precambrian bhima basin in india related to its chloritization abstract an integrated textural mineralogical and chemical investigation reveals the origin of authigenic glauconite within the mesoproterozoic rabanpalli formation in the bhima basin and its subsequent alteration to chlorite glauconite forms within the transgressive shallow shelf deposits in the rabanpalli formation it primarily occurs in two modes as thoroughly replaced form of detrital grains and as altered zones along cleavages and fractures of quartz k feldspar and mica all varieties of glauconites exhibit high contents of k2o the fe2o3 t content is highest in glauconite formed within mica while it is least in glauconite formed by the replacement of feldspars pseudomorphic replacement of substrates by glauconite best explains the origin of glauconite in the rabanpalli formation diagenetic chlorite mostly occurring as thick rims on grains and along the grain margin fractures replaces glauconite chloritization predominantly takes place in the glauconite variety forming within the mica the mineral chemistry of chlorite is characterized by high mgo and fe2o3 t chloritization involves the simultaneous removal of fe mg and si from the glauconite structure to form brucite type sheets the high contents of fe2o3 t and mgo reducing porewater and the high thermal maturation of sediments facilitate the formation of chlorite within the rabanpalli formation this study therefore indicates that the rarity of glauconite in the precambrian is related to its alteration to chlorite

a subaqueous welded tuff from the ordovician of county waterford ireland abstract the metal man tuff mmt from the ordovician of county waterford ireland was emplaced and welded in water depths greater than the thickness of the pyroclastic flow the mmt is the basal member of the middle tramore volcanic formation mtvf of the 5 km thick tramore group the mmt consists of a 10 m thick basal graded zone that represents a pyroclastic flow consisting of angular clasts of black mudstone pumice gray flow banded rhyolite and pink massive rhyolite set in a matrix of non deformed ash shards and pumice maximum grain size grades from large cobbles and small boulders to pebbles the basal 10 30 cm is depleted with respect to the largest boulders resulting in an inversely graded basal layer the basal graded zone passes upward into a transition zone with a strong eutaxitic foliation defined by elongated fiamme of mudstone and flattened pumice overlying this is an upper welded zone with a pronounced eutaxitic foliation columnar jointing flattened ash shards and shards deformed around phenocrysts and spheroids the presence of these features indicate that the deposit is welded was hot and was in motion as the shards deformed the mmt represents a pyroclastic flow that was a hot primary product of an eruption rather than re mobilized cold pyroclastic debris the mmt is bounded by suspension deposited fine grained tuff tuffaceous mudstone and terrigenous mudstone deposited below storm wave base many of the mudstone horizons contain brachipod faunas from shelf depth water nowhere in the 5 km thick tramore group is there terrigenous sandstone evidence of unidirectional flowing water nor any indication of shoreline alluvial environments or subaerial exposure it thus seems reasonable to conclude that the mmt was emplaced and welded subaqueously the geochemistry of the mmt is typical of other high silica 70 78 wt sio2 rhyolite from the ordovician of ireland the chemistry of the mmt is consistent from top to bottom allowing it to be distinguished from associated syndepositional intrusive rock and fine grained tuffs

dolomitization and chertification of the early eocene rus formation in abu dhabi united arab emirates abstract the early eocene carbonates of the rus formation in the jabal hafit area near al ain united arab emirates were sampled to study their diagenetic history these carbonates were cyclically deposited in a shallow water environment alternating with marls or marly limestones and are characterized by extensive dolomitization and chertification with associated glauconitization the cyclic nature of sedimentation suggests that deposition was eustatically driven the diagenetic history of the limestones proceeded through the following path 1 marine cementation of allochems concomitant with formation of micrite envelopes 2 micritization of peloids ooids and skeletal grains 3 neomorphism of formerly high mg calcite and aragonite grains to low mg calcite 4 partial to complete dolomitization 5 partial chertification of both calcite and dolomite 6 glauconitization of chert 7 fracturing during shallow burial and 8 precipitation of late coarse calcite spar or mosaic and saddle baroque dolomite spar filling voids and fractures porosity is virtually nil in these rocks except for infrequent unfilled fractures vugs and oomolds due primarily to cementation and chertification biogenic grains are abundant in the limestones with nummulites sp alveolinid and miliolid foraminifera and crinoid ossicles and other echinoderm fragments being most common the tests of nummulites sp are commonly replaced by length fast chalcedony fibers which are occasionally later replaced by glauconite spherulitic and zebraic chalcedony and more rarely megaquartz occur as void filling cements and fringing chalcedonic fibers frequently rim the tests of skeletal grains all except the fringing chalcedonic fibers were subject to glauconitization prior to the chertification process is an extensive dolomitization period rhombic and sucrosic dolomite partially to completely replaced calcite at a relatively early diagenetic stage silicification caused the replacement of calcite by chert at a much more rapid rate than that of dolomite which was found floating within a chertified matrix fractures occurred both early and late in the rus and are usually filled by a late coarse mosaic calcite spar or coarse mosaic and saddle dolomite spar in completely dolomitized samples

substrate control on formation and maturation of glauconites in the middle eocene harudi formation western kutch india formation and maturation of glauconites within the early middle eocene harudi formation built up in a lagoon to shelf transition in western kutch india is addressed taking recourse to a combined sedimentological micropalaeontological and mineralogical investigation the glauconite is authigenic and its occurrence coincides with maximum flooding the glauconite is more matured within the fecal pellets and is less matured within the intra particle pores of bioclasts namely foraminifera ostracoda gastropoda and bryozoa sem eds xrd and geochemical studies clearly document that the infilling within the intra particle pores of bioclasts belong to nascent to slightly evolved glauconite 5 wt k2o while the pellet belongs to slightly evolved to evolved glauconite 5 7 wt k2o based on chemical characteristics and sem investigations the glauconitization process can be best explained by the verdissement theory the glauconite possibly formed as initial authigenic glauconitic smectite precipitates while the pellet matured subsequently by addition of k the process was hindered in case of infillings the maturation process also involved addition of si and release of al with or without release of mg the glauconite maturation was facilitated in case of fecal pellets because of higher porosity inter granular nature of pores and availability of necessary elements in semi confined micro environments in contrast the maturation was aborted at an early stage in case of infillings because of the minute closed nature of the pores and prevalent alkaline conditions not allowing dissolution of calcitic tests a low negative cerium anomaly suggests glauconite formation in sub oxic micro environments created by decay of organic matters within the fecal pellets and bioclasts a clear case of substratum control on glauconitization becomes apparent

glaciation and post glacial history of the continental shelf off southwestern vancouver island british columbia abstract bathymetry sediment distribution and seismic stratigraphy are used to interpret the pattern of glaciation of the continental shelf off southwestern vancouver island canada four seismostratigraphic units are distinguished and mapped in relation to sediments and sedimentary rocks present on the shelf they are 1 undivided tertiary bedrock 2 a unit composed mainly of pleistocene outwash 3 pleistocene morainal deposits and 4 holocene marine sediments a large piedmont glacier is envisaged formed by the coalescence of glaciers emanating from juan de fuca strait and barkley sound it cut a system of deep troughs into the tertiary bedrock built up a complex of morainal ridges and built out an extensive outwash plain on the unglaciated shelf to the northwest during glacial maxima the piedmont glacier extended right across the shelf particularly high discharge of debris from the seaward ends of the glacial troughs may have caused the erosion of adjacent submarine canyons during the final deglaciation the ice withdrew somewhat faster than the sea advanced although masses of downwasting ice may have persisted in many of the troughs the glacial topography including moraines and tertiary bedrock were levelled by the advancing sea but many of the troughs were preserved from burial perhaps because they were still ice filled or because the coastal system was sediment starved strong currents sweep the present shelf redistributing sand and mud winnowed from the tops of the truncated moraines into low lying areas and leaving concentrations of gravel behind

evolution patterns of glaucony maturity a mineralogical and geochemical approach abstract integrated mineralogical and geochemical analyses were carried out on a wide variety of glauconitic grains from 25 western european localities covering the whole range of glaucony maturity and ranging in age between the cretaceous and the pliocene a comprehensive data set documents the major evolution patterns of glaucony and the relationships between glauconitic minerals and their substrate components increasing glaucony maturity involves potassium and rubidium enrichment the progressive evolution from a k poor glauconitic smectite to a k rich glauconitic mica is accompanied by the overall decrease of distance between peaks 001 and 020 the width of basal reflection 001 however is proposed here as a more powerful tool for the discrimination of glauconitic minerals at different stages of maturity this parameter is especially efficient for the differentiation of evolved and highly evolved glaucony the range of initial substrate composition appears to control significantly major and trace element variations during glaucony maturation contrasting patterns are observed in glauconitic grains as a function of the proportion of carbonate versus siliciclastic substrate components particularly the distribution patterns of mgo and sio2 in glaucony associated with carbonate host rocks suggest progressive uptake of these elements in the structure of glauconitic minerals with increasing degree of maturation by contrast a decrease in sio2 and ai2o3 with increasing maturity may be observed when the substrate for glauconitization is represented by siliciclastic material fe shows a positive correlation with k2o in glaucony with low maturity but an opposite trend in evolved glaucony therefore fe cannot be regarded as a reliable indicator of glaucony maturity maturation of glauconitic minerals results invariably in ca and sr depletion irrespective of the original composition of the precursor material as a consequence the proportion of ca and sr may be considered as an inverse relative criterion of glauconitic mineral evolution for a given source area

formation of shallow water glaucony in weakly oxygenated precambrian ocean an example from the mesoproterozoic tieling formation in north china abstract authigenic glaucony precipitation in phanerozoic oceans takes place mostly in middle shelf to upper slope environments with low depositional rate or sediment starvation precambrian glaucony however is more common in stratigraphic successions deposited from shallower water environments with high and variable depositional rates this phenomenon has long been noticed in literature but the controlling factors of shallow water glaucony precipitation in precambrian oceans have not been adequately investigated to better understand the glauconitization processes in precambrian oceans we have conducted an integrated study of the glaucony in stromatolitic carbonates of the mesoproterozoic tieling formation ca 1437 ma in north china using sedimentological mineralogical and geochemical data obtained from field observations petrography xrd sem quantitative eds and icp ms analyses macro and microscopic observations show that the tieling glaucony fills voids of varying sizes and shapes and records different maturation stages of glauconitization geochemical analyses show that the tieling glaucony has high k 2 o avg 8 but low and variable total fe 2 o 3 tfe 2 o 3 contents 1 92 13 65 wt the tfe 2 o 3 contents increase with maturation of glaucony titration results show that the tieling glaucony contains both fe 3 and fe 2 ions but has fe 2 fe 3 ratios much higher than that of the phanerozoic glaucony ree results of glaucony hosting carbonates show weak negative and positive ce anomalies with average ce ce ratio close to 1 0 suggesting carbonate precipitation near the redoxcline of fe mn oxides all these features suggest that the tieling glaucony was precipitated in seawater around the fe redoxcline where both fe 2 and fe 3 were available throughout the glaucony maturation stages high fe 2 fe 3 ratios in the depositional environments led to fe 2 occupation at octahedral sites of glaucony and negative charges on octahedrons which resulted in high k content to balance the negative charges on octahedrons and low tfe 2 o 3 limited by dioctahedral structure the formation of the tieling glaucony and other similar precambrian glauconies is likely controlled by low oxygen concentration in seawater and a shallow redoxcline that controls the availability of fe and k cations during initial precipitation and maturation of glaucony the shift of authigenic glaucony precipitation from shallow water in the precambrian to deep water in the phanerozoic may record the deepening of ocean chemocline in response to increased ocean oxygenation

glaucony from the eocene of the isle of wight southern uk implications for basin analysis and sequence stratigraphic interpretation the lower middle eocene sequence of the hampshire basin which includes an alternation of sands silts and clays interpreted as fluvial to open marine deposits is exposed at two locations on the western alum bay and eastern whitecliff bay margin of the isle of wight glaucony is encountered throughout the study units sand clay alternations of lagoonal origin and estuarine channel fill sands include less than 10 of predominantly poorly evolved allochthonous glaucony shelf silts and sands generally comprise more than 20 of evolved mostly autochthonous glaucony vertical changes in maturity of glaucony confirm the trend predicted by recent models indicating an overall upward increase in the transgressive systems tracts and decrease in the highstand systems tracts with maximum values in coincidence with the condensed sections where a remarkable peak in glaucony concentration is invariably recorded comparison of glaucony characteristics at different sites of depositional sequences shows a slight increase in maturity and abundance from the proximal to the distal areas this lateral tendency is interpreted to reflect more suitable conditions for glauconitization in open marine environments than in shallow waters despite documented intrasequential variability of glaucony characteristics glaucony assemblages from distinct depositional sequences may be generally identified on the basis of more pronounced differences in maturity consequently glaucony attributes can be used as an index for characterization of third order sedimentary cycles

an oxygen minimum palaeoceanographic signal from early toarcian cavity fills moderately deep marine toarcian sedimentary rocks of the medianes nappe alpine front ranges switzerland comprise calcarenites and lime mudstones they were deposited under storm and fairweather conditions in the dysaerobic zone near the storm wave base these remnants of the northern margin of the tethyan ocean show facies where primary sediment 9deep water9 stromatolitic micrite was reworked during early diagenesis stromatactis like cavities were formed by carbonate dissolution near the sediment water interface suboxic early diagenetic conditions are indicated by corroded pyrite and newly formed glauconitic oncoids carbon and oxygen stable isotope data indicate cavity stabilization and cementation above the sulphate reducing zone oceanographic conditions during the time of cavity development are reconstructed from the carbon and oxygen isotope composition of cavity cements of bulk sediment and of associated ammonites 13 c values of up to 4 are related to the oceanic anoxic event of the early toarcian and oxygen isotope values from cements and ammonites define a shallow toarcian thermocline

sedimentary dynamics and tecto volcanism in the venosa basin basilicata italia direct tecto volcanism is the main process involved in the sedimentary filling of the venosa lacustrine basin two formations have been distinguished the tufarelle formation and the piano regio formation in the sedimentary series exposed at the notarchirico middle pleistocene prehistoric site several volcanic episodes represented by pumice falls coarse and fine ash falls and subsequent epiclastic processes have interrupted the lacustrine sedimentation and induced specific environmental changes hominids were present immediatly after every volcanic event to exploit the new environment on an opportunistic basis

compositional variability of glauconites within the upper cretaceous karai shale formation cauvery basin india implications for evaluation of stratigraphic condensation abstract a detailed mineral chemical investigation of glauconite within the condensed section deposits of the cretaceous karai shale formation cauvery basin india reflects a wide spectrum in chemical composition related to origin and evolution in different substrates stratigraphic condensation and post depositional alteration fe and mg rich glauconite comprising up to 60 of the sedimentary rocks occurs as replaced forms of fecal pellets as infillings within pores and chambers of bioclasts including those of foraminifera ostracoda bryozoa and algae and as altered forms of mica exhibiting vermiforms authigenic precipitation of k and fe poor glauconite followed by addition of fe and k into the lattice and concomitant release of al and si explains the origin of glauconite pellets and infillings the origin of glauconite vermiforms in partly degraded mica involves only the second stage of fe and k addition glauconite pellets and vermiforms exhibit sharply defined alteration zones along peripheries to form rims and in proximity to cracks or cleavages with reduced k2o and fe2o3 total and enhanced al2o3 and sio2 related to late stage meteoric water actions cores of glauconite pellets and unaltered zones of vermiforms reflect evolved characteristics with 6 k2o typical of a condensed section while other glauconite varieties occurring at the same stratigraphic level exhibit slightly evolved nature not consonant with stratigraphic condensation increasing abundance of glauconite pellets from the bottom to the top of the transgressive systems tract accompanied by slight increase in k2o within their cores reflects the effect of stratigraphic condensation on the evolution of glauconite high fe2o3 total content of glauconite in the karai shale formation may be related to upwelling although the fe may be contributed partly by the biotite substrate mossbauer spectroscopy of glauconites reveals significant total fe substitution in both tetrahedral and octahedral sites detailed mineral chemical analysis enables us to distinguish stratigraphically significant glauconite within the karai shale formation from the rest of the glauconite notwithstanding its wide compositional range

the significance of iron stained foraminifera off se trinidad west indies western central atlantic ocean eleven samples of seafloor sediment were taken from water depths of 78 90 m within the savonette field off se trinidad western atlantic ocean this surface sediment is relict having been deposited during an early holocene transgression the samples yielded much iron stained quartz and a rich assemblage of dead foraminifera of which 75 of planktonic foraminifera were stained with iron as was 66 5 of the calcareous benthonic foraminiferal assemblage the fauna both iron stained and unstained was dominated by cibicidoides ex gr pseudoungerianus and is concluded despite the proximity of the orinoco delta to be equivalent to a relict cibicidoides biofacies in carbonate rich areas of the gulf of mexico staining was by limonite and hematite differing percentages of calcareous benthonic species had been stained with iron anova revealing three groups of species within which the mean percentage of iron stained specimens per sample did not differ a globocassidulina subglobosa and hanzawaia concentrica b amphistegina gibbosa cassidulina norcrossi australis cibicioides ex gr pseudoungerianus c io elphidium translucens and quinqueloculina lamarckiana and c eponides antillarum and e repandus it is concluded that species differ in their susceptibility to iron staining and that planktonic foraminifera are more susceptible than most benthonic species although waters off northern south america are turbid and the photic zone only 25 m deep the relict assemblage contained 8 4 algal symbiont bearing foraminifera especially a gibbosa and e translucens that would be limited to the photic zone these are thought to have lived at a time early in the holocene transgression when sequestration of sediment within the orinoco delta rendered the water sufficiently clear for viable populations of symbiont bearing foraminifera should iron stained foraminifera prove to be restricted to transgressive systems tracts this would make them a useful sequence stratigraphic tool

the magnetic susceptibility of continental shelf sediments west coast vancouver island canada abstract measurements of magnetic susceptibility of continental shelf sands off central vancouver island revealed two areas of anomalously high values 1 at the mouths of coastal inlets suggesting a reworking of glacial and glacio fluvial sediments and 2 the outer shelf downslope from outcropping deformed tertiary pleistocene strata resulting from the winnowing of these older sediments during periods of lowered sea level magnetic susceptibility was highest within the silt and fine sand fractions and lowest in the clay and coarse sand fractions though because of the grain size distributions the fine sand invariably contributed more to the overall sample susceptibility than the other size fractions although no apparent relationships were found between magnetic susceptibility and commonly measured grain size statistics the highest values were concentrated within a narrow range of size sorting skewness and kurtosis magnetic susceptibility is a readily determined parameter of marine sediments which can contribute to the interpretation of the depositional history of a region and which may have direct economic applications because of the association between magnetite and heavy mineral placers

tephro stratigraphy and the age of ancient southern italian acheulean settlements the sites of loreto and notarchirico venosa basilicata italy the stratigraphic and chronological positions of the palaeolithic sites of loreto and notarchirico have been revised by adopting a litho tephro stratigraphic approach applied to the deposits of the venosa basin relating them to the evolution of volcanic eruptions of mount vulture the notarchirico tephra dated to around 640 ka is a geological marker of paramount importance in the study of ancient southern italia settlements and identifies the assemblage from level f at notarchirico as one of the oldest acheulean in europe