observations of a cut off low over southern australia the structure and evolution of an intense cut off low is documented in detail unprecedented for the australian region by combining high time resolution radiosonde profiles with co located wind profiler observations and routine australian bureau of meteorology analyses the cut off low develops over the ocean south of australia and subsequently interacts with a subtropical frontal system over the central part of the continent throughout the period of observation the strongest temperature gradients lay through the subtropics moreover the subtropical temperature gradients strengthened while the midlatitude temperature gradients associated with the cut off low weakened the australian bureau of meteorology s 150 km regional assimilation and prognosis system analyses capture the broad scale structure and evolution of the system reasonably well the system documented here is similar in structure to the instant occlusion investigated by browning and hill 1985 the major difference being that our cut off low develops poleward of a subtropical front the cut off low was cold cored and produced a very deep tropopause fold over adelaide the tropopause descended to an altitude of about 5 km and the temperature at 500 hpa fell to 30 c the western edge of the low level cold dome was marked by a strong secondary warm front which passed over adelaide about 8 hours after the tropopause height minimum the warm front was characterized at the surface by an absolute minimum in the pressure and a temperature rise of about 7 c significantly this increase in temperature took place in the early hours of the morning against the diurnal trend the cut off low produced very high rainfalls resulting in flash flooding and much damage in the adelaide hills area the most severe convection took place in the region behind the lowered tropopause around the passage of the warm front

glaucony and sequence stratigraphy a conceptual framework of distribution in siliciclastic sequences abstract detailed analysis of recent literature on glaucony and selected case studies eocene isle of wight miocene northern apennines shows that the presence of glaucony alone is not diagnostic of a specific systems tract of a depositional sequence a reliable sequence stratigraphic interpretation of glaucony bearing units requires additional information on glaucony including 1 spatial distribution 2 maturity distinction between nascent slightly evolved evolved and highly evolved glaucony and 3 genetic attributes differentiation of autochtonous from allochthonous and intrasequential from extrasequential glaucony autochthonous glaucony is common at various stratigraphic levels in the transgressive systems tract tst and the lower highstand systems tract hst showing an upward increase tst and then decrease hst in abundance and maturity the condensed section can be distinguished from the overlying and underlying deposits by the higher concentration and maturity of glaucony allochthonous intrasequential parautochthonous glaucony can be present in the entire tst hst and lowstand systems tract lst generally showing lower concentration and maturity than its autochthonous counterpart allochthonous extrasequential detrital glaucony is present mainly in the lst its concentration and composition depending on the characteristics of the source horizon the associa ion between autochthonous and allochthonous intrasequential and extrasequential glaucony commonly exists in the lst and in the lower tst

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

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

a retreating fan delta system in the neoproterozoic chattisgarh rift basin central india major controls on its evolution a thick wedge of immature siliciclastics characterizes the basal part of the basin fill succession in the eastern part of the neoproterozoic chattisgarh basin it comprises a mosaic of mass flow deposited conglomerate and pebbly sandstone coarse grained sandy braided stream deposits wave lag pebble sheets high energy wave dominated foreshore and upper shoreface facies and wave and tide dominated lower shoreface facies the succession is characterized by strong lateral and vertical facies variation the facies associations and stacking pattern point to the development of an alluvial fan to fan delta complex with outbuilding of delta lobes onto a high energy shallow marine shelf via a high gradient narrow delta plain the delta front deposits of coarse grained sand interfinger and grade into prodelta mud in the seaward direction the dominance of coarse grained sandy detritus with a high content of fresh feldspar grains points to mechanical weathering of granites and gneisses of the cratonic basement and a semiarid climate the sediment caliber and the climate exerted a major control on the facies and on processes of sediment transfer from the fan to the shelf a critical balance between progradation aggradation and retrogradation controlled the evolution of delta successions within an overall transgressive regime related to the extension of a cratonic rift basin repeated fault controlled uplift of the source followed by subsidence and transgression generated multiple fining upward cycles and a retreating fan delta system the marked variations in thickness of the delta succession and the stacking pattern in different measured profiles reflect the overriding tectonic controls on delta evolution the accumulated fault displacement in active sectors created higher accommodation and thicker delta sequences intermittent uplift of fault blocks exposed fresh bedrock to mechanical weathering generated a large amount of detritus and resulted in forced regressions repeatedly disrupting the fining upward pattern the controls of source rock lithology or climate were of secondary importance to tectonic effects retreating fan deltas are rarely reported and may be a stratigraphic response of marine connected rift basins at the early stage of extension the delta stratigraphy is analogous to the submarine fan stratigraphy in the case where basin shales act as hydrocarbon sources the fan deltas are potential hydrocarbon reservoirs the coarse grained lobes can be excellent reservoirs with the enclosing prodelta muds acting as seals to vertical migration of hydrocarbon the coarse grained deposits of the delta plain and proximal delta front occurring as laterally coalesced large sand bodies blanketed by transgressive prodelta mud might also form good reservoirs

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

mg rich ferric illite in marine transgressive and highstand systems tracts examples from the paleoproterozoic semri group central india this paper focusses upon two glauconitic sandstones in the paleoproterozoic deoland formation and chorhat sandstone both belonging to the semri group central india in both the cases glauconitic minerals occur in sandstones deposited in the marine realm within a transgressive systems tract tst for the former unit and within a highstand systems tract hst for the latter the proportion of glauconitic minerals increases in the paleo offshore direction petrography reveals selective early glauconitization of detrital k feldspars along their fringes cleavages and the fractures created by volume expansion during progressive alteration leading to the generation of peloids with small relics of the precursors xrd and mineral chemistry reveal a structure typical of glauconite and more akin to mg rich ferric illite the mineral chemistry of the glauconitic mineral phases remains the same whether the glauconitization process was incipient or at an advanced

unusual seawater composition of the late cretaceous tethys imprinted in glauconite of narmada basin central indiaunusual seawater composition of the late cretaceous tethysu bansal et al a detailed investigation of a glauconite bed within the late cretaceous bryozoan limestone formation of the bagh group in central india as well as the study of existing records reveals the existence of a glauconitic sea along the margins of the palaeo tethys ocean during the late cretaceous epoch the authigenic green mineral formed abundantly on shallow seafloors unlike in its modern deep sea counterpart we present an integrated petrographical geochemical and mineralogical investigation of the glauconite within late cretaceous transgressive deposits to highlight its unique geochemistry with moderate fe 2 o 3 and high al 2 o 3 sio 2 mgo as well as k 2 o contents x ray diffractional parameters identify the evolved to high evolved nature of the glauconite while mossbauer spectroscopic study reveals the dominance of fe 3 compared to fe 2 in the atomic structure the rare earth elements ree pattern of glauconite reveals moderate light ree heavy ree lree hree fractionation and weak negative eu anomaly the ce anomaly of the glauconite indicates a sub oxic diagenetic condition we propose that late cretaceous glauconites formed within a shallow marine depositional setting across the tethyan belt because of enhanced supply of k si al fe mg cations through continental weathering under the extant greenhouse climate

convective mixing in a tropopause fold we present a case study of the passage of a tropopause fold over the uk behind a cold front with emphasis on the mixing caused by convection extending into the fold the event took place on 15 16 january 1999 and was the subject of intensive observations using the met office c130 aircraft and the mesosphere stratosphere troposphere mst radar at aberystwyth here we concentrate on radar and satellite observations during the afternoon of 16 january when the surface cold front had passed over the uk a tongue of moist air moved north eastwards over wales at 700 hpa at this time which because of the very dry air in the fold above resulted in potential instability the resulting convection was clearly observed in noaa satellite images the mst radar depicted the passage of the cold front and tropopause fold as a layer of high echo power and vertical wind shear ascending with time spectral widths showed the fold to be free of turbulence until 1200 utc on 16 january when convection was observed reaching into the frontal zone and generating turbulence eddy dissipation and diffusivity rates of 8 6 mw kg 1 and 8 5 m2s 1 respectively were derived for this event to place these figures in context they are compared with corresponding rates derived for sixteen other passages of tropopause folds over the radar each resulting from shear rather than convective instability the convective event is found to be comparable to the strongest shear events and to correspond to moderate turbulence as experienced by an aircraft this process is of potential importance for atmospheric chemistry because it mixes boundary layer air directly with stratospheric air over a timescale of 1 2 hours copyright 2004 royal meteorological society

combination of mesoscale and synoptic mechanisms for triggering an isolated thunderstorm observational case study of csip iop 1 abstract an isolated thunderstorm formed in the southern united kingdom on 15 june 2005 and moved through the area where a large number of observational instruments were deployed as part of the convective storm initiation project earlier a convergence line had formed downstream of devon in the southwest of the united kingdom in a southwesterly airflow along which a series of light showers had formed the depth of these showers was limited by a capping inversion or lid at around 2 5 km the deep thunderstorm convection developed from one of these showers when the convection broke through the lid and ascended up to the next inversion associated with a tropopause fold at around 6 km a series of clear air reflectivity rhis are used to map the height of the capping inversion and its lifting resulting from the ascent along the convergence line the origins of the lid are tracked back to some descent from the midtroposphere along dry adiabats the strength of the lid was weaker along a northwest to southe

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

compositional characteristics of glauconitic alterations of k feldspar from india and their implications abstract chemical characteristics of glauconite and ferric illite derived from alteration of k feldspar in three proterozoic formations of india are studied the phases show widely varying octahedral and tetrahedral cation contents but k content is nearly constant co existence of glauconite and ferric illite is interpreted as due to influx of fresh water in a marine dominated sequence a continuum in composition between illitic and glauconitic minerals at high alkali content is established no correlation between composition of glauconite and environment of deposition or degree of diagenesis is deduced ferric illite in fluvial environment contains less mg than that in a marine dominated one direct pseudomorphism of k feldspars by glauconite and ferric illite in their respective chemical en ironments controlled largely by the availability of fe and mg is indicated in this study chemical characteristics of glauconite and ferric illite in an environment with high ak induced by dissolution of k feldspar are markedly different from those described earlier

mechanical twinning in quartz shock experiments impact pseudotachylites and fault breccias abstract increasing use of diffraction methods to study preferred orientation of minerals has established that quartz in deformed rocks not only displays characteristic c axis orientation patterns but that there is also generally a distinct difference in the orientation of positive and negative rhombs in the trigonal quartz crystal structure positive and negative rhombs are structurally different and particularly negative rhombs e g 01 1 1 are much stiffer than positive rhombs e g 10 1 1 here we focus on the role of mechanical dauphine twinning under stress as a cause of this difference and illustrate with ebsd measurements ubiquitous twinning in quartz bearing rocks subjected to high stresses characteristic twinning is observed in experimentally shocked sandstones and stishovite bearing quartzites from the vredefort meteorite impact site in south africa similar twinning is documented for quartz associated with pseudotachylites from the santa rosa mylonite zone in southern california whereas quartz in underlying ductile mylonites are more or less twin free it suggests that twinning was produced by local seismic stresses that caused fracture and frictional melting on fault surfaces quartz bearing breccias from the safod san andreas fault observatory at depth drilling project also show evidence of twinning and suggest high seismic stresses in the currently creeping segment of the san andreas fault at parkfield from these observations it appears that dauphine twin microstructures can be diagnostic of high local and transient stresses

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

apatite glaucony association in the ediacaran doushantuo formation south china and implications for marine redox conditions abstract major phosphogenic events took place in the late paleoproterozoic and the ediacaran both of which followed an episode of atmospheric oxygenation these apparent coincidences have led to suggestions that the precambrian phosphorus cycle was partly regulated by oceanic redox conditions although direct evidence is lacking in this paper we report the discovery of glaucony in drill cores from the phosphorite rich ediacaran doushantuo formation at weng an south china which provides new insights into redox conditions and geochemical cycles during the deposition and early diagenesis of the lower doushantuo formation the presence of flaser and lenticular bedding in the sandstones suggests deposition in a tidally influenced shallow water environment apatite is present as millimeter scale flasers in sandstones but more commonly as intraclastic grains glaucony typically occurs as interstitial aggregates cementing and replacing detrital minerals and phosphatic grains with an upsection decrease in abundance the doushantuo glauconies have consistently high k2o 7 6 9 6 wt in particular phosphorite hosted glaucony has generally higher total iron tfe2o3 than sandstone hosted glaucony consistent with al3 fe3 substitution in the octahedral site as supported by raman peaks slightly shifted towards lower wavenumbers for higher fe content a decrease in detrital input probably resulted in limited al availability during early diagenesis which in turn led to the waning of glaucony upsection the phosphate grains do not show any negative ce anomalies consistent with precipitation of authigenic apatite in suboxic environments with insignificant preferential remobilisation of ce during deposition and early diagenesis ree y features show variable diagenetic ree enrichment in phosphorites but identical concave down patterns the wide occurrence of glaucony cement further documents the presence of a generally suboxic early diagenetic environment on the seafloor which was in active exchange with bottom seawater slight fluctuations of redox states in the porewater and bottom water would have promoted the cycling of fe enrichment of phosphate and ree and extensive glaucony authigenesis therefore the glaucony bearing phosphorites in the doushantuo formation are a direct result of fe redox driven diagenesis apatite glaucony association likely forms in suboxic environments and is considered as a useful mineralogical proxy for paleoredox conditions on the precambrian ocean floors

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

large scale potential vorticity anomalies and deep convection the effect on deep convection of large scale potential vorticity pv anomalies and their associated tropospheric stable layers is complex and not well understood this article examines the meteorological events of 9 july 2007 iop7b of the convective and orographically induced precipitation study cops which was dominated by an upper level pv anomaly that stretched from the uk to southern france and as far northeast as denmark three precipitation regions were identified from the case lines of intense storms beneath the pv anomaly less intense more widespread convective precipitation to the east of the pv anomaly and in between a region of no precipitation the latter of these coincided with the high resolution measurements and model analyses from cops the extensive and varied data analyzed in this investigation show that convective available potential energy cape was present in this region the distribution of cape and convective inhibition cin is presented via an innovative pseudo 3d visualization that allows horizontal and vertical interactions to be considered however convection was capped by a complex arrangement of dry layers the base of the key layer was at 750 hpa these dry layers descended separately from the upper troposphere moving around the pv anomaly as it developed from a breaking rossby wave to the west during the seven days before the iop this case adds to other studies that show that descent of complex dry layers is an important mechanism for forming convection inhibiting atmospheric lids in western europe a simple conceptual model is developed that synthesizes the effect of large scale pv anomalies on deep convection from a series of consistent case studies this model has significant implications for storm forecasting and projections of storminess in future climates as it highlights the importance of thin structures that can advect hundreds of km before having an impact copyright 2012 royal meteorological society

alluvial fan to storm dominated shelf transition in the mesoproterozoic singhora group chattisgarh supergroup central india abstract mesoproterozoic siliciclastic strata at the basal part of the singhora group central india provide an example of a pre vegetation alluvial fan and braid delta depositional system detailed process based facies and paleoenvironmental analysis have led to the identification of 15 facies types grouped under four different facies associations which record paleoenvironmental settings ranging between continental alluvial fan and distal marine shelf two formations investigated are the rehtikhol formation formed in a conglomeratic or coarse arenaceous alluvial fan braid plain and delta setting and the overlying saraipalli formation which preserved the sedimentation record of a storm infested inner to distal shelf setting the preponderance of granular and sandy sediment gravity flow products with subordinate rock fall deposits within the alluvial fan system together with a pervasive west northwesterly paleocurrent is suggestive of a gently sloping beveled source area in the east southeast distal to the inferred fan a braid plain system developed with the decrease in the depositional slope streams within the braid plain had widths up to several hundred meters the braid plain system at the margin of the marine basin developed a delta with the deposition of wave reworked fluvial dominated sediments the crest trends of wave generated bedforms within the inferred delta sediments depict the northeast southwest shoreline interpreted for the singhora sea the prodeltaic basinal part of the singhora braid delta was storm infested the inner shelf acted as a zone of throughput with high velocity storm flows eroding deep narrow scours gutter casts and is interpreted as a zone of bypass operation of geostrophic currents on the singhora shelf has been inferred from the directional relationship of gutters with the inferred orientation of the shoreline a proximal distal relationship has been established within the shelf products based on the relative dominance of erosional and depositional features the singhora alluvial fan and braid delta facies are arranged in a fining upward sequence denudation of the source area increasing bathymetry with relative rise in sea level or a combination of both is inferred both extrabasinal and intrabasinal forcings possibly contributed to the deepening upward trend

fe illites in a proterozoic deep marine slope deposit in the penganga group of the pranhita godavari valley their origin and environmental significance ferric illite fe illite developed extensively in a siliciclastic submarine fan sequence within a lime mud succession in the proterozoic penganga group at adilabad south india the minerals formed as de novo by preferentially replacing high k minerals like alkali feldspar and mica it is compositionally intermediate between glauconite and illite in a continuously varying chemical spectrum the mineral exhibits an r1 or r3 type stacking sequence with low 10 interlayering of illite and smectite i s all the analyzed grains are characterized by high potash content and it has been inferred that the maturity is dictated by high ak in the microenvironment this occurrence strongly calls into question the environmental significance that has so far been attributed to glauconitic minerals

mesoscale analysis of arc rainbands in a dry slot a series of almost concentric are shaped narrow rainbands was observed travelling at 140 km h 1 and producing severe wind gusts over parts of england their structure and environment have been analysed using radar and satellite imagery mesoscale model diagnostics surface observations and additional rawinsonde ascents obtained during the fronts and atlantic storm track experiment fastex the multiple rainband event is shown to have been associated with part of a dry intrusion characterized by a mesoscale vortex cold pool the event occurred within the dry slot region of a small frontal cyclone where the mesoscale pool of cold dry air was overrunning warm sector air continuous wind profiles from a uhf radar together with a well located rawinsonde at the epicentre of the arc rainbands showed that the major anomaly in the cold pool was an area of locally stronger winds 40 m s 1 at 800 hpa colocated with the temperature minimum at that level the observed orientation of the rainbands is explained in terms of the cold frontal structure at this level triggering ascent of the underlying warm moist air the multiple nature of the arc rainbands remains unexplained the possibilities of mesoscale gravity waves and conditional symmetric instability are both considered

mesoscale analysis of a polar trough interacting with a polar front the interaction of a polar trough with a polar front can lead to a characteristic satellite cloud pattern commonly referred to as an instant occlusion the detailed structure and development of an event rather resembling an instant occlusion is analysed in this paper using routine data supplemented by additional radiosondes soundings and cloud imagery from noaa 7 and meteosat and radar network pictures the event presented differs from an instant occlusion as described by anderson and others in that a band of polar front cloud developed simultaneously with the band of cloud associated with the polar trough rather than being a pre existing feature thus we refer to it under the different name of pseudo occlusion in order to keep this distinction in mind a conceptual model of the pseudo occlusion is developed in which the key elements are i a moist relatively warm low level jet associated with the polar trough referred to as the polar trough conveyor belt and ii a major upper level jet streak associated with the polar front referred to as the polar front conveyor belt the two conveyor belts intersect almost at right angles precipitation associated with the polar front is predominantly from stratiform cloud whereas that associated with the polar trough is a mixture of stratiform and convective just on the poleward side of the upper jet the cloud top drops abruptly here dry air having recently descended beneath the tropopause fold suppresses the depth of the moist air associated with the polar trough conveyor belt this leads to a minimum in the intensity of precipitation between the rain areas associated with the trough and the front although the air overrunning the trough just on the poleward side of the polar front is dry as a result of earlier descent the air in this location is likely to have begun ascending as part of the indirect circulation in the exit region of the upper level jet streak the polar trough low level jet probably forms part of this circulation

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

origin and sequence stratigraphic implications of high alumina glauconite within the lower quartzite vindhyan supergroup abstract an integrated field petrographical and geochemical investigation reveals a shallow marine dys oxic depositional setting for the glauconite at the top of the mesoproterozoic lower quartzite member of the vindhyan supergroup a thorough facies and paleogeographic analysis indicates a storm influenced shallow subtidal depositional condition for the glauconitic sandstone occupying the mid level of a transgressive systems tract tst deposit which is capped by the maximum flooding zone mfz the x ray diffractional parameters confirm the evolved character of the glauconite the mineral chemical analysis indicates the glauconite is enriched in k2o mgo and al2o3 and depleted in fe2o3 total compared to the phanerozoic variety it formed by the pseudomorphic replacement of the k feldspar by the addition of fe2o3 at consistently high content of k2o unlike most phanerozoic examples the elevated level of h3sio4 cl k na mg and fe possibly derived by the continental weathering and or contemporary volcanism facilitated the glauconitization process the high content of mg in the glauconite corresponds to the mg rich mesoproterozoic seawater a dys oxic depositional condition associated with a major marine flooding surface favoured the formation of glauconite while the onset of anoxic regime caused the disappearance of glauconite and the deposition of pyritiferous and carbonaceous shale in the overlying condensed zone deposits

constraints on the development of proterozoic basins in central india from 40ar 39ar analysis of authigenic glauconitic minerals ages of some key stratigraphic sequences in central indian proterozoic basins are based predominantly on lithostratigraphic relationships that have been constrained by only a few radioisotopic dates to help improve age constraints single grains of glauconitic minerals taken from sandstone and limestone in two proterozoic sequences in the pranhita godavari valley and the chattisgarh basin were analyzed by the 40 ar 39 ar incremental heating method analysis of the age spectra distinguishes between ages that are interpreted to reflect the time of glauconite formation and anomalous ages that result from inherited argon or postcrystallization heating the analyses indicate an age of 1686 6 ma for the pandikunta limestone and 1566 6 ma for the ramgundam sandstone two units in the western belt of proterozoic sequences in pranhita godavari valley glauconite from the chanda limestone in the upper part of this sequence contains inherited 40 ar but is interpreted to reflect an age of ca 1200 ma glauconite from the somanpalli group in the eastern belt of the pranhita godavari valley gives an age of 1620 6 ma in the chattisgarh basin glauconite from two units gives disturbed ages that suggest a period of regional heating in the chattisgarh basin at ca 960 1000 ma these new ages indicate that these sequences are 200 400 m y older than previously recognized which has important implications for geochemical studies of mesoproterozoic ocean redox conditions in addition to providing important constraints on regional tectonics and lithostratigraphy

compositional variation of glauconites in upper cretaceous paleogene sedimentary iron ore deposits in south eastern western siberia abstract glauconite occurs either as unaltered greenish or as altered brownish variety in upper cretaceous palaeocene sediments in the southeastern corner of western siberia studied section within the bakchar iron ore deposit includes ipatovo slavgorod gan kino and lyulinvor formations which are represented by sandstones siltstones claystones and oolitic ironstones of coastal marine facies the origin of unaltered glauconite is explained by the verdissement theory transgressions during lower coniacian santonian and campanian favored the formation of unaltered glauconites in dysoxic to anoxic conditions subaerial exposure of glauconite resulted in leaching of potassium oxidation of iron and formation of iron hydroxides in upper coniacian maastrichtian and palaeocene glauconite ultimately converts to leptochlorite and hydrogoethite by this alteration abundant microscopic gold inclusions besides sulphides sulphates oxides and silicates characterize this glauconite mineral inclusions include precious rare metals and non ferrous metals the concentration of gold in glauconite may be as high as 42 9 ppb abundant inclusions of various compositions in glauconites indicate enrichment of marine sediments in precious and non precious metals while major element composition of glauconites is affected by subaerial exposure the broadly similar micro inclusions in both altered and unaltered varieties are possibly related to the comparatively immobile nature of ree and trace elements

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

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

glauconitization of detrital silica substrates in the barton formation upper eocene of the hampshire basin southern england upper eocene detrital silica grains chert and quartz of the hampshire basin display alteration and replacement fabrics by glauconite silica grains have etched surfaces due to glauconitization which appear green in reflected light and thin section quartz grains were glauconitized by surface nucleation and replacement which spreads from the margin with progressive glauconitization replacing the quartz grain interior chert grains were glauconitized by surface replacement and nucleation internally along cracks and in pores different forms of glauconite are associated with the two minerals glauconite associated with quartz is generally highly evolved whereas glauconite associated with chert is of the evolved variety this is interpreted as being due to different surface reaction control mechanisms associated with the two forms of silica there is no evidence to suggest that glauconite evolved in stages from a nascent form two crystalline morphological forms of glauconite are found associated with both quartz and chert glauconite growing within a confined space has a laminated morphology whilst glauconite occurring on the surface has a rosette morphology

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

regressive depositional architecture on a mesoproterozoic siliciclastic ramp sequence stratigraphic and nd isotopic evidences from bhalukona formation singhora group chhattisgarh supergroup central india abstract a paleo environmental and sequence stratigraphic study of the mesoproterozoic bhalukona formation singhora group central india provides new interpretations applicable to understanding sedimentation and stratigraphic architecture in the proterozoic siliciclastic ramp settings under falling and lowstand sea level conditions beside delineation of two diachronous surfaces process based facies analysis identified fourteen facies types that are grouped under five different facies associations paleo environments range among continental fluvial beach foreshore upper shoreface lower shoreface and wave dominated delta front from the paleocurrent measurement within the fluvial channel sandstones and measurement of crest line orientations of wave generated swash bedforms it is inferred that the bhalukona sea had nne ssw shoreline trajectory and the south easterly flowing river system carried sediment on the shoreline from a source in the west northwest such inference though in clear discordance with the earlier proposed south southeastern sediment source for the singhora basin finds support in the shift in e nd t t 1 42 ga values from 3 5 3 3 to 9 3 2 2 indicating change in sediment provenance at the early bhalukona sedimentation history sediments in the bhalukona formation derived from more evolved or older continental crustal sources in comparison to those of the underlying saraipalli formation a tectonic forcing behind the shift in sediment provenance and fall in relative sea level is inferred that established the forced regressive and lowstand shoreline in the singhora basin during the bhalukona time abrupt basin ward shift of facies tract and incision on shelf is exhibited by the occurrence of poorly sorted coarse granular bhalukona fluvial system carrying rip up mud clasts directly above the argillaceous highstand saraipalli shelf with 10 m incision and is inferred as the signal for forced regression and development of type i sequence boundary in low gradient proterozoic ramp settings without shelf slope break we interpret that the bhalukona fluvial system incised the coastal prism developed on the saraipalli highstand coastline the low gradient of the ramp however prompted long distance 15 km regression represented by the offlapped and detached delta front lobe away from the shoreline the slow steady rise in sea level onset of lowstand and establishment of a wave dominated coastline caused reworking of fluvial sediments in the basinal part within the wave base and resulted development of ravinement deposit basin ward the surface grades into correlative conformity with aggradational and weak retrogradational stacking the beach foreshore upper and lower shoreface in order of superposition record the lowstand depositional history the basin scale transgression is witnessed with formation of transgressive surface of erosion tse and establishment of the chuipalli shelf system dominantly beyond storm wave base taking into consideration 23 m preserved shoreface succession 1 m per year eustatic rise consistent with present day rate and average rate of shoreface retreat 0 5 m per year 11 5 km retreat for the bhalukona shoreline is estimated in its lowstand history

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

convective inhibition beneath an upper level pv anomaly upper level potential vorticity pv anomalies reduce the convective stability of the troposphere through their impact on the vertical potential temperature profile thus reducing convective inhibition cin and increasing convective available potential energy here by contrast we show the impact of a layer of stable air that was intrinsically linked with an upper level pv anomaly and that increased cin this layer descended and tracked beneath the small upper level pv anomaly which in this case was a shallow upper level trough this low humidity relatively high pv layer originated from the tropopause fold generated by a breaking rossby wave which also produced the upper level pv anomaly two days later despite conditions favourable for deep convection as demonstrated by the development of a single storm the cin produced by this dry layer or lid was largely responsible for capping convection over much of southern england at around 2 5 km during the case presented here which comes from the convective storm initiation project copyright c 2008 royal meteorological society

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

the surprising role of orography in the initiation of an isolated thunderstorm in southern england abstract many factors both mesoscale and larger scale often come together in order for a particular convective initiation to take place the authors describe a modeling study of a case from the convective storms initiation project csip in which a single thunderstorm formed behind a front in the southern united kingdom the key features of the case were a tongue of low level high w air associated with a forward sloping split front overrunning lower w air above a convergence line and a lid of high static stability air which the shower was initially constrained below but later broke through in this paper the authors analyze the initiation of the storm which can be traced back to a region of high ground dartmoor at around 0700 utc in more detail using model sensitivity studies with the met office unified model metum it is established that the convergence line was initially caused by roughness effects but had a significant thermal component later dartmoor had a key role in the developmen

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

high alumina glaucony from the middle cambrian of oeland and bornholm southern baltoscandia abstract two contemporaneous middle cambrian glauconies from different depositional environments in southern baltoscandia the acrothele granulata conglomerate of oland and the exsulans limestone formation of bornholm have been studied by means of xrd emp and sem these glauconies show a characteristic high silica 50 high alumina 10 and low iron the chemical composition is environmentally induced and can be related to formation and deposition in shallow cool water all progressive stages of weathering from glaucony to goethite are found in the kalby member of the exsulans ls fm a new morphological type of glaucony is described molds closely replicating the inorganic pore space where they occur having imprints of crystal faces from the surrounding calcite cement

observations of the development of convection through a series of stable layers during the convective storm initiation project this article describes the development of convection through a series of stable layers on 20 july 2004 during the pilot project of the convective storm initiation project csip convective clouds developed ill south central england as a result of diurnal heating they formed near the south coast and grew gradually as they moved northwards eventually producing light precipitation several stable layers and associated dry layers or lids were observed by sequential radiosondes launched every two hours most of these lids were also detected by the chilbolton l band radar and with a wind profiler as prominent layers of bragg echo one particular lid at 820 mb 1 7 km inhibited the early development of the convection for about an hour delaying the production of precipitation the uppermost lid at 650 mb stopped all convection from intensifying in the csip domain estimates of the growth of convection through the lids were sensitive to the values of temperature and humidity chosen to represent the ascending parcels the development of the thermals in the boundary layer was best explained by using the surface layer average values parcels would not have been sufficiently buoyant to reach the lifting condensation level lcl unless these values were used however such parcels in the absence of mixing would then have been too buoyant to be capped by the main lid at 1 7 km as was observed by the radars in fact the development of the cumulus clouds above the lcl is best represented by using 950 1000 mb average thermodynamic values the results highlight the importance of predicting the altitude strength and persistence of such lids in order to forecast the intensity location and timing of convective precipitation more accurately copyright c 2008 royal meteorological society

ferruginous seawater facilitates the transformation of glauconite to chamosite an example from the mesoproterozoic xiamaling formation of north china berthierine and chamosite are iron rich clay minerals that share similar chemical compositions berthierine forms at low temperature 25 45 c during early diagenesis and may transfer to chamosite at temperatures of 70 c because the formation of berthierine and chamosite requires significant amount of fe 2 supply their presence in marine sediments is often used as a mineral proxy for ferruginous conditions in porewater recent studies reveal that the precambrian oceans were characterized by pervasive ferruginous water column conditions that may favor the formation of iron rich clay minerals like berthierine and chamosite to evaluate if ferruginous water column conditions in the precambrian ocean played a role on iron rich clay mineral formation we conducted an integrated petrographic mineralogical and geochemical study on the chamosite and glauconite bearing strata of the mesoproterozoic xiamaling formation 1 40 1 35 ga in north china petrographic xrd sem and eds analyses show that the chamosites of the xiamaling formation was transferred from glauconite with berthierine as an intermediate mineral phase during early diagenesis geochemical analyses indicate that a complete transformation from glauconite dominated to chamosite dominated end members samples requires an addition of a large amount of fe 16 9 wt mg 2 4 wt and a small amount of al 1 4 wt but a simultaneous release of si 11 8 wt and k 6 0 wt considering that the glauconite and chamosite bearing strata are devoid of iron rich detrital minerals e g biotite and iron oxides and lack evidence of hydrothermal alteration the required fe 2 for glauconite berthierine chamosite transformation was most likely from fe 2 rich ferruginous seawater which may have promoted glauconite berthierine transformation at the very early diagenetic stage when fe 2 exchange between porewater and seawater was still available this interpretation is consistent with the high fe hr fe t but low fe py fe hr fe al and v al ratios from the hosting strata that support ferruginous depositional environments because most precambrian strata have passed the oil window temperature 50 150 c the preservation of berthierine would be rare and chamosite should be the representative iron rich clay mineral thus the abundance of chamosite in fine grained marine siliciclastic sediments may be used as a mineral indicator of ferruginous water column conditions

glauconite composition and morphology shocked quartz and the origin of the cretaceous main fossiliferous layer mfl in southern new jersey u s a abstract the main fossiliferous layer mfl is a concentration of vertebrate and invertebrate fossils 20 to 30 cm thick preserved in a sequence of glauconitic sand at or near the cretaceous paleogene boundary in the new jersey usa coastal plain several hypotheses have been proposed to explain the origin and age of the mfl including marine transgression and formation of lag deposits of reworked bones and shells formation of a condensed section and attritional accumulation of fossil material and catastrophic collapse of late cretaceous ecosystems following the end cretaceous bolide impact at chicxulub we use new data on glauconite morphology concentrations geochemistry and presence of shocked quartz coupled with previous data on sedimentology taphonomy and rare earth element geochemistry of fossil vertebrates to interpret the genesis of the mfl glauconite concentration and maturity steadily increases from latest cretaceous sediments of the navesink new egypt formation through the mfl and into the paleogene upper hornerstown formation suggesting that marine transgression and decreasing sedimentation rates were a factor in the formation of the glauconite but not the mfl rare earth element patterns in fossil bones from the mfl which are acquired during fossilization are different from those of cretaceous and paleogene specimens indicating that vertebrate remains in the mfl fossilized in situ and were not reworked from older underlying units vertebrate fossils from the mfl are preserved as isolated to articulated specimens while isolated specimens would be common in a transgressive lag articulated specimens would not articulated specimens could be concentrated by attritional accumulation along a defined surface during a period of slow sedimentation but the lack of a distinct increase in glauconite maturity or concentrations of elements associated with heavy mineral accumulations at the navesink new egypt hornerstown contact or mfl which would be expected during a period of reduced sedimentation hiatus or unconformity are absent at the localities studied shocked quartz was identified in a burrow fill directly beneath the mfl at the contact of the navesink and hornerstown formations clay clasts with latest cretaceous microfossils along with reworked invertebrate fossils with infills of latest cretaceous sediment have been recovered from the mfl the association of shocked quartz mixture of isolated and articulated vertebrates with distinct rare earth signatures lack of a punctuated period of increased glauconite maturity and presence of reworked late cretaceous invertebrates and clay clasts with late cretaceous microfossils suggests that the mfl may represent a thanatocoenosis that was the direct result of environmental disturbance associated with the end cretaceous impact event at chicxulub

late holocene climatic changes as detected by the growth and decay of ice wedges on the southern shore of hudson strait northern quebec canada the dating of cryoturbated palaeosols associated with past ice wedge activity on late holocene sandy fluvial terraces in a region of continuous permafrost leads to an interpretation of periods of ice wedge growth and active cracking that alternated with periods of decay dormancy and active layer deepening the reconstruc tion corresponds with palaeoclimatic information obtained from existing arctic wide and regional proxy rec ords the little ice age stands out as a period of intense ice wedge activity in the study area it was followed by a warm thawing interval during the first half of the twentieth century from ad 1946 to 1991 a well documented cooling of the climate took place which reactivated 94 of the studied ice wedges the pyramidal shape of ice wedge tops and the depths of the upgrowth features could be correlated between sites several kilometres apart clearly indicating a regional climatic response the mean annual air temperature dropped from about 7 8 c in 1946 to 8 9 c in 1991 the t