verdine and other associated authigenic glaucony phosphate facies from the surficial sediments of the southwestern continental margin of india abstract green grains pale green brown infillings of foraminifer tests and brown friable aggregates occur in the coarse fraction of the surface sediments from the southwestern continental margin of india between the periyar river in the north and quilon in the south study of the nature distribution mineralogy and internal structure of these particles resulted in 1 the discovery of a verdine facies and 2 determination of the relationships of phosphate with glaucony and verdine in these sediments two distinct verdine facies associated zones a shelf zone at about 40 m and a slope zone between 100 and 280 m water depth are distinguished verdine grains are abundant up to 30 where biogenic debris dominates in the sediments and are rare glaucony and phosphate predominantly occur as pale green to brown infillings of foraminifers and as phosphatic friable aggregates in the sediments of the terrace at 330 m water depth glauconitic smectite and carbonate fluorapatite are the respective mineral phases the terrace sediments are sandy and often associated with non glauconitized and non phosphatized mollusc shells phosphatized verdine grains occur at 170 m water depth scanning electron microscopy studies indicate that phosphate is in the form of globular to rod shaped bacteria like structures or microbial filaments or both this type of phosphate occurs within the foraminifer tests and as cement in the friable aggregates glauconitized foraminifers are enclosed in phosphatic matrix and phosphate occurs within the glaucony matrix the intergrowth of green clays and phosphatic globules is observed locally in phosphatized glaucony aggregates and also in phosphatized verdine grains the formation of verdine glaucony and phosphate in these sediments is relict the age of their formation is difficult to estimate precisely but appears to be older than mollusc shells dated at 5710 yrs b p planktonic foraminifers from the terrace indicate a quaternary age verdine formation on the shelf and on the slope is diachronous the shelf verdine facies most probably formed during the late pleistocene high sea level stands or during the early holocene the slope verdine may have formed contemporaneously with glaucony and phosphate on the terrace during low sea level stands the terrace most probably acted as a sort of hardground facilitating glauconitization and phosphatization of the sediments upwelling oxygen minimum zone and low terrigenous sediment accumulation provided adequate conditions for phosphatization which was mediated by microbial processes the intergrowth of phosphate with the authigenic clays of verdine and glaucony may be due to the local confinement of the microenvironment which was probably controlled by microorganisms

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

sea level changes in a back arc foreland transition the late carboniferous permian karoo basin of south africa abstract the late carboniferous to early permian succession in the karoo basin consists in ascending stratigraphic order of diamictites mudrocks greywackes and immature sandstones the diamictites are interpreted as glacigene deposits laid down by a marine ice sheet on a shelf post glacial suspension settling of predominantly mud occurred on the basin floor during open marine and later brackish conditions basin floor fan deposits accumulated in the foredeep whereas deltaic mud silt and sand finally infilled the basin glacigene sedimentation occurred in a back arc basin during the late carboniferous and early permian the post glacial succession accumulated in a foreland basin in which the rising orogenic belt was the predominant sediment source relative sea levels following the major namurian regression apparently remained low during the extensive gondwana glaciation marine ice sheets are highly sensitive to sea level fluctuations and minor sea level rises probably climatically controlled were recorded as interglacials when parts of the marine ice sheet collapsed final collapse of the marine ice sheet was associated with a major transgression post glacial mudrock deposition was characterised by relatively high sea levels except for the period of basin floor fan deposition when there was a sea level lowstand final infilling of the basin by prograding deltas was accompanied by a major regression the late carboniferous to early permian sea level fluctuations in the karoo basin show correspondence with global eustatic cycles reflecting low tectonic interference with sea level patterns however late permian sea levels were predominantly tectonically controlled as a result of foreland basin evolution possible global eustatic events complemented apparent sea level changes within the basin during this period

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

mid cretaceous sequence stratigraphy and sedimentary cyclicity in the western paris basin abstract cenomanian and turonian depositional patterns of the western paris basin are interpreted in terms of sequence stratigraphy a system tract analysis of the epicontinental normandie basin with pelagic chalks and of the maine platform covered by clastics provides evidence for relative changes in coastal onlap various minor uncomformities are related to these changes of sea level the four global cycles uza or zc 2 2 2 5 of haq et al 1987 1988 are recognised while an additional one is proposed for the geslinianum zone in addition periodic rhythmic cycles are commonly registered within the chalk expressed by the repitition of various facies enhanced both by biosedimentary processes and diagenetic alteration these elementary climatic cycles allow accurate lithostratigraphic correlations during this period when the sea level peaked on the tectonically passive border of the armorican block the paris basin appears to record a detailed set of events which can be correlated with those in the atlantic boreal and tethyan provinces

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

authigenesis of impact spheroids in the k t boundary clay from italy new constraints for high resolution stratigraphy of terminal cretaceous events abstract detailed chemical and mineralogical analyses of authigenically altered impact spheroids contained in the cretaceous tertiary k t boundary clay of the northeastern apennines provide information about the chemical conditions on the sea floor of a deep pelagic basin immediately after the impact of a large extraterrestrial object against the earth s surface the temporal alteration of global meterologic conditions resulting from this catastrophic event caused the death of most planktonic and nektonic biomass of the oceans dead organisms settled on the seafloor creating low ph low eh conditions at the water sediment interface reducing and slightly acidic waters percolated in the top sediment causing reduction and leaching of iron and dissolution of the top surface of the calcareous o ze the suppression of biogenic calcium carbonate production in the upper water column and the reducing conditions in the seafloor lasted for a period not longer than 50 ka during this time only detrital silt and clay were deposited in the basin along with the fallout material derived from the impact cloud the fallout included spherules of sub millimeter size which condensed from vaporized and or molten terrestrial target rock admixed with the vaporized impactor the heterogeneous chemical composition of the spherules and the wide range of shapes of relict crystals preserved in them suggest that they were originally made of a suite of high temperature quenched minerals ranging in composition from silica rich iron poor ones plagioclase to iron rich silica poor ones spinel beat ng clinopyroxene and olivine the slightly reducing conditions of the seafloor favored the authigenic growth of k feldspar in si rich spherules and of glaucony in the fe rich ones in some parts of the paleobasin characterized by stronger reducing conditions k feldspar authigenesis did not occur and spheroids were preferentially altered to pyrite and glaucony the resumption of carbonate deposition resulting from the post k t plankton bloom coincided with the restoration of normal oxidizing conditions in most parts of the paleobasin such conditions caused the arrest of glauconitic growth and the alteration of the most fe rich spherules to goethite bioturbation activity also resumed in the top sediment causing slight vertical mixing in the k t boundary clay layer in addition to the mineralogical and chemical description and the interpretation of the authigenic phases contained in the italian k t boundary clay this paper includes a high resolution stratigraphic analysis of the boundary clay in the petriccio section which is the best preserved among the several k t sections studied in the northeastern apennines the most relevant discovery from this study is that the impact spherules are concentrated in the central part of the clay layer along with the peak of an iridium anomaly whereas grains of quartz with multisets of parallel lamellae which are considered a product of impact shock metamorphism are mostly concentrated in the bottom part of the layer this clear decoupling may represent several thousands of years of delay in deposition of ridium and spheroids with respect to shocked quartz and suggests two impact events closely spaced in time however further high resolution analyses in other sections in the northeastern apennines and elsewhere around the world is advised for more definitive confirmation for a terminal cretaceous multiple impact hypothesis

distinguishing similar volcanic source areas from an integrated provenance analysis implications for foreland andean basins abstract the mata amarilla formation marks the onset of the foreland stage of the austral basin which is composed of mostly nonmarine and littoral siliciclastic sediments thus providing an opportunity to study the detrital record of the late cretaceous southern foreland andes our dataset provides for the first time a comprehensive picture of the late cretaceous evolution of the austral foreland basin constituting a possible analogue to other foreland basins at the foot of the andes sandstones from the mata amarilla formation testify to variable contributions from jurassic bimodal volcanic rocks of the deseado massif and the patagonian fold and thrust belt in the context of an eastward advancing orogen sandstone petrography shows an overall feldspathic litharenite composition whereas sandstones coming from the northeast deseado massif have higher lv and lower qp proportions than samples coming from the west patagonian fold and thrust belt in the central part of the study area sandstones are characterized by higher proportions of qt associated with a greater distance and time of transport relating to its position in the austral foreland basin in spite of the increased maturity of sandstone in the central area x ray analyses permit recognition of the compositional signature of mata amarilla formation in which four clay mineral assemblages were identified s rich in smectite s k rich in smectite and kaolinite pg rich in palygorskite and i s rich in illite smectite mixed layers s assemblage evidences well crystallized smectite characteristic of volcaniclastic origin most smectite was formed during early diagenesis through alteration of labile tuffaceous material derived from the southern andes the stratigraphic variations in clay mineral assemblages reveal a strong environmental control on their distribution the transformation of smectite into illite and kaolinite is considered as product of pedogenesis whereas the presence of palygorskite indicates a coastal environment with paleosol development under poorly drained conditions

paleoceanography of the eastern indian ocean from odp leg 121 drilling on broken ridge broken ridge in the eastern indian ocean is overlain by about 1 600 m of middle cretaceous to pleistocene tuffaceous and carbonate sediments that record the oceanographic history of southern hemisphere mid to high latitude regions prior to about 42 ma broken ridge formed the northern part of the broad kerguelen broken ridge plateau during the middle eocene this feature was split by the newly forming southeast indian ocean ridge since then broken ridge has drifted north from about 55 to 31 s the lower part of the sedimentary section is characterized by turonian to santonian tuffs that contain abundant glauconite and some carbonate the tuffs record a large but apparently local volcanic input that characterized the central part of broken ridge into the early tertiary maestrichtian shallow water several hundred to 1 000 m depth limestones and cherts accumulated at some of the highest rates ever documented from the open ocean 4 to 5 g cm 2 10 3 yr 1 a complete with all biostratigraphic zones cretaceous tertiary boundary section was recovered from site 752 the first 1 5 m y of the tertiary is characterized by an order of magnitude reduction in the flux of biogenic sediments indicating a period of sharply reduced biological productivity at 55 s following which the carbonate and silica sedimentation rates almost reach the previous high values of the latest cretaceous we recovered a complete section through the paleocene that contains all major fossil groups and is more than 300 m thick perhaps the best pelagic paleocene section encountered in ocean drilling about 42 ma broken ridge was uplifted 2 500 m in response to the intra plateau rifting event subsequent erosion and deposition has resulted in a prominent eocene angular unconformity atop the ridge an oligocene disconformity characterized by a widespread pebble layer probably represents the 30 ma sea level fall the neogene pelagic ooze on broken ridge has been winnowed and thus its grain size provides a direct physical record of the energy of the southern hemisphere drift current in the indian ocean for the past 30 m y

the problem of glaucony from the shannon sandstone campanian wyoming terra nova 23 100 107 2011 abstract the shannon sandstone one of the most controversial units in the field of stratigraphy was first interpreted as a shelf sand ridge deposit but subsequent studies have furnished different interpretations from lowstand shoreface to incised valley models despite a general consensus among previous workers about the significance of glaucony for shannon interpretation mineralogical characterization of the green grains has never been undertaken identification of glaucony has been restricted to visual inspection accurate characterization of highly glauconitic deposits from the shannon sandstone powder river basin of wyoming section w3 reveals that sedimentological interpretation of the greensands relies mostly upon mistaken mineral identity glaucony appears as a minor component of the rock and proves to be poorly mature and significantly less abundant 0 6 than previously inferred up to 85 characterization of the glauconitic minerals however provides data that contribute to shannon interpretation

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

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

middle wisconsin glaciation in the genesee valley ny a stratigraphic record contemporaneous with heinrich event h4 abstract two lacustrine deformation tills with ages corresponding closely to north atlantic heinrich event h4 are preserved in the genesee valley on the western edge of the finger lakes region of new york state the locality is at the convergence of a major north flowing river with the laurentide ice sheet and results in unusual preservation of datable organics intact middle and late wisconsin glacial sequences are preserved above a middle wisconsin interstadial disconformity within a bedrock trough that has dimensions similar to those of the larger finger lakes the shallow burial depth and age of the disconformity circa 35 000 14 c years bp demonstrate that deep erosion of finger lakes bedrock troughs cannot be presumed to have occurred during all major glacial advances the preserved glacial stratigraphy indicates that proglacial and substrate conditions as well as the rate of ice advance may cause a wide variation in the ability of ice sheets to cause deep basal erosion during major glacial stadials the evidence also demonstrates that middle wisconsin ice advanced more than 30 km south of the lake ontario shoreline in west central new york other buried wood of middle wisconsin age in the genesee valley suggests that the recoverable record of early and middle wisconsin glaciations in new york is more diverse than is documented in the existing literature

inversion of a transfer system into lateral ramps an example from the south central pyrenees spain field work in the south central pyrenees suggests that omission contacts i e younger over older rocks occur at the base of the cadi unit cadi thrust and pass laterally into thrusts this change occurs across tear faults which are present in the hangingwall of the cadi thrust sheet and which controlled the deposition of upper cretaceous sediments adraen formation detailed mapping in the contact area between the nogueres and cadi units has shown that the actual thrust geometry in the study area is controlled by preexisting normal and transfer faults which developed in an already compressional context lateral ramps or tear faults develop depending on the angle between the pre existing extensional transfer fault and the thrust transport direction

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

reappraisal of the cambrian glauconite bearing anse maranda formation quebec appalachians from deep sea turbidites to clastic shelf deposits the cambrian anse maranda formation is a glauconite bearing clastic succession within the quebec reentrant it is part of the appalachians humber zone particularly of the shale feldspathic sandstone assemblage which represents the rift to drift deposits of the laurentian margin the massive sandstones of the anse maranda were originally interpreted as the proximal turbidites of a deep sea fan the occurrence of glauconite and the high degree of bioturbation which give the sandstones a massive aspect suggest a different depositional environment detailed ichnology and lithofacies descriptions indicate that the anse maranda predominantly represents shelf sediments deposited in storm influenced environment and that intense bioturbation destroyed most of the sedimentary structures the paleo geographic reconstruction suggests that the anse maranda was deposited seaward of a headland identified as the montmorency promontory along a narrow shelf with an irregular topography some coeval turbidites of sim

eustasy versus subsidence lower paleocene depositional sequences from southern alabama eastern gulf coastal plain four distinct sequences of rise and fall in relative sea level may be inferred from the lower paleocene strata in southern alabama southern alabama is part of the eastern gulf coastal plain a passive continental margin these third order sequences are traceable from the western part of the study area where a thick section of deltaic influenced siliciclastic sediments was deposited in a subsiding salt withdrawal basin to the eastern part of the study area where a somewhat thinner sequence of carbonate and siliciclastic deposits accumulated on a stable platform formed over paleozoic basement rocks the fact that these sequences and their component systems tracts can be recognized and traced throughout southern alabama considering the significant differences in subsidence and sedimentation rates from the western part to the eastern part of the study area indicates that some factor other than subsidence rates or sediment supply controls the cyclicity exhibited by these sequences eustasy is interpreted as that controlling factor this interpretation is consistent with the observations of previous writers that the conditions of differential subsidence climate and sediment supply may overprint the effects of global sea level change but that these factors usually do not mask the impacts of eustasy

rb sr ages of glauconite recrystallization dating times of regional emergence above sea level abstract rb sr ages of glauconite pellets commonly fall short of the presumed age of deposition by 10 20 according to current estimates of the geologic time scale in part the young ages are the result of preferential loss of exchangeable radiogenic sr consequently in pellets where tightly bound nonexchangeable rb and sr have remained a closed chemical system since deposition removal of the exchangeable cations with ammonium acetate nh4oac can raise the apparent age to coincide with the expected depositional age in other cases the age of pelletal glauconite remains younger than the depositional age after chemical treatment analyses of nh4oac treated disaggregated clay size fractions invariably yield young but rather consistent apparent ages these are interpre ed as recording the time of diagenetic recrystallization of the glauconite crystallites which compose the pellets glauconite recrystallization appears to have taken place in the llano uplift of central texas at 428 350 328 and 265 280 my ago these ages do not coincide with times of elevated temperatures deep burial or tectonism instead they correlate with times of regional emergence above sea level apparently a change in pore water chemistry due to an influx of meteoric water promoted recrystallization and this inference is supported by the oxygen isotope composition of the glauconite diagenesis of glauconite by this mechanism offers an opportunity to date sea level changes by isotopic methods

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

shannon sandstone in wyoming a shelf ridge complex reinterpreted as lowstand shoreface deposits abstract the shannon sandstone campanian of wyoming was formerly interpreted as two stacked shelf ridge complexes sand was believed to have been transported from a time equivalent shoreline 110 150 km to the west and reworked or molded into ridges at the depositional site we show that this time equivalent shoreline section at lucerne wyoming consists of not one shoreface sandbody but two superimposed they are both storm dominated and the lower one terminates in beach facies capped by root traces there must have been a rise in relative sea level of at least 14 m to make accommodation space for the second shoreface sandbody in the salt creek area and the adjacent subsurface teapot dome there are two sandier upward facies successions in the lower succession there are abrupt vertical acies contacts between offshore bioturbated sandstones thicker hummocky cross stratified sandstones and coarser cross bedded sandstones there is also evidence that the cross bedded sandstones rest erosively on underlying facies the trace fauna in the sandstones includes macaronichnus segregatis rosselia socialis and ophiomorpha the m segregatis suggests a foreshore or upper shoreface depositional environment and r socialis indicates a lower to middle shoreface neither are characteristic of a shelf ridge complex the abrupt and probably erosive facies contacts along with the trace fauna suggest that the cross bedded sandstones in this succession represent a shoreface deposit that formed during a stage of actively falling relative sea level overlyi g muddy bioturbated sandstones indicate that shoreface deposition was terminated by a transgression the upper sandier upward succession contains facies and trace fauna similar to those of the lower succession and is also interpreted as a prograding shoreface rather than the sand moving 110 150 km from the shoreline and then being molded into shelf ridge complexes at salt creek we suggest that the shoreline moved into the salt creek area as the result of a fall in relative sea level it was transgressed and moved back westward a second fall of relative sea level moved the shoreline back to salt creek and a final transgression terminated shannon deposition

sequence stratigraphic significance of sedimentary cycles and shell concentrations in the aitamir formation albian cenomanian kopet dagh basin northeastern iran abstract albian cenomanian siliciclastic shallow marine sediments of the aitamir formation kopet dagh basin northeastern iran form strongly asymmetric fining coarsening upward cycles which are interpreted as recording changes in relative sea level deepening shallowing cycles these cycles correspond to depositional sequences in which deposits of the lowstand systems tract are not present the sequence boundary coinciding with the transgressive surface shell concentrations are found in distinct positions within the depositional sequence as transgressive lags at the base of the transgressive systems tract tst in the maximum flooding zone mfz and at or close to the top of the highstand systems tract hst they are dominated by bivalves mainly oysters and or ammonites and differ from each other in a number of stratigraphic sedimentologic palaeoecological and taphonomic features such as species diversity preservation quality orientation percentage of disarticulation and degree of biogenic alteration characteristic features of concentrations at the base of the tsts are moderate time averaging distinct basal erosional surface sorting a chaotic to preferred convex up orientation and nearly total disarticulation of shells they are suggestive of an environment in which reworking and local transport was frequent events similar features are shown by concentrations near the tops of the hsts except that the shells were largely concentrated in lenses rather than in beds as in the transgressive lags associated sedimentary structures indicate deposition above fair weather wave base in a high energy environment concentrations occurring in the mfz in contrast are autochthonous and highly time averaged having accumulated during times of low rates of sedimentation below storm wave base this is supported by their high preservation quality comparatively high percentage of articulated shells shells of infaunal organisms commonly preserved in life position high glauconite content and biogenic alteration being the most important taphonomic features

diagenetic alterations related to marine transgression and regression in fluvial and shallow marine sandstones of the triassic buntsandstein and keuper sequence the paris basin france abstract the distribution of diagenetic alterations in triassic fluvio deltaic quartzarenitic to sublitharenitic lowstand systems tract lst sandstones of the gres a voltzia formation anastomosing fluvial quartzarenitic transgressive systems tract tst sandstones of the gres a roseaux formation and shallow marine quartzarenitic to sublitharenitic tst sandstones of the gres coquiller formation the paris basin france can be linked to transgression and regression events and thus to the sequence stratigraphic context near surface eogenetic alterations which display a fairly systematic link to the depositional facies and sequence stratigraphic framework include i cementation by meteoric water calcite 18 o 8 9 and 13 c 9 1 in the fluvio deltaic lst sandstones ii cementation by mixed marine meteoric calcite 18 o 5 3 to 2 6 and 13 c 3 9 to 1 3 and dolomite 18 o 4 6 to 2 6 and 13 c 2 9 to 2 3 in the foreshore tst sandstones and below parasequence boundaries pb and transgressive surface ts and in the shoreface tst sandstones below maximum flooding surfaces mfs being facilitated by the presence of carbonate bioclasts iii dissolution of detrital silicates and precipitation of k feldspar overgrowths and kaolinite particularly in the fluvio deltaic lst sandstones owing to effective meteoric water circulation and vi formation of autochthonous glauconite which is increases in abundance towards the top of the fluvio deltaic lst sandstones and along ts and in the shoreface tst sandstones by alteration of micas owing to the flux of seawaters into the sandstones during transgression whereas parautochthonous glauconite is restricted to the ts sandstones owing to marine reworking mesogenetic alterations which include cementation by quartz overgrowths and illite display fairly systematic link to fluvio deltaic lst sandstones this study has revealed that linking of diagenesis to transgression and regression events enables a better understanding of the parameters that control the spatial and temporal distribution of diagenetic alterations in sandstones and of their impact on reservoir quality evolution

late cretaceous transgression on a cimmerian high neka valley eastern alborz iran a geodynamic event recorded by glauconitic sands abstract in the neka valley eastern alborz iran glaucony bearing marine sediments of early middle santonian age directly overlie palaeozoic to triassic units deformed during the eo cimmerian orogenic event late triassic the upper cretaceous open marine sediments were deposited on a flat surface lacking any evidence of pedogenesis the geochemical and morphological features of glaucony grains which characterize the base 1 to 1 5 m of the upper cretaceous succession indicate an autochthonous origin of the highly evolved glaucony denoting a long lasting period of low sedimentation rate the development of glaucony in the observed stratigraphic position is indicative of a rapid drowning of the former cimmerian relief that cannot be explained by a eustatic rise alone the palaeo depth needed for the development of glaucony and for the presence of the observed bathyal foraminifera assemblages is greater than the maximum eustatic excursion documented in the cretaceous the occurrence of glaucony in this stratigraphic position reflects thus an important episode of increased subsidence rates related to a geodynamic event framed in a time interval of major plate reorganization in the complex puzzle of the iranian plates the subsidence event that caused the development of the glauconitic horizon in the neka valley could likely represent the effect of a santonian stage of the complex and long lasting story of the opening of the caspian sea

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

anatomy and origin of a cretaceous phosphorite greensand giant egypt late cretaceous epicontinental phosphorites porcelanites cherts dark coloured shales glauconitic sandstones and bioclastic and fine grained carbonate rocks in egypt are examined in terms of their overall depositional and diagenetic framework and stable isotopic and organic geochemical characteristics two main depositional realms are interpreted and correlated through sequence stratigraphic analysis 1 a shallow hemipelagic environment accompanying initial stages of marine transgression and conducive to the formation of organic carbon rich shales biosiliceous sediments and thick phosphorites and 2 a relatively high energy depositional regime accompanying sea level fall during which deltas advanced glauconites were reworked seaward and prograding oyster banks became periodically exposed to episodes of fresh water diagenesis thereby promoting solution collapse phenomena in associated cherts lenticular to massive phosphorites are viewed as the result of current winnowing and concentration of authigenic grains initially precipitated in associated reducing shales and biosiliceous sediments in eastern egypt the phosphorites form winnowed lag layers some of which may have been redeposited down slope in structural lows in the west these sands were concentrated into giant phosphorite sand waves built by reworking of penecontemporaneously deposited phosphatic muds during marine transgression carbon isotopic results substantiate interpretations from modern deposits for limitation of phosphate mineral precipitation with depth in sediments as a result of lattice poisoning however direct desorption of phosphorus to pore waters from detrital iron oxyhydroxide phases also may have been important in the cretaceous setting the iron reduced in this process being available for incorporation in glauconites the main locus for authigenic glauconite precipitation appears to be where iron fluxes from regions of lateritic weathering were highest and near the boundary between oxygenated and reduced waters this study suggests a model for the common coexistence of glauconites and phosphorites in the geological record although upwelling is often advocated as the origin of nearly all giant phosphorite deposits we suggest that some of these may have been strongly influenced by fluvially derived phosphorus borne on particulates and desorbed from these compounds upon flocculation and or reduction in bottom waters or pore waters

environmental evolution and geological significance of the miocene carbonates of the eratosthenes seamount odp leg 160 abstract miocene carbonates of the eratosthenes seamount located offshore from cyprus in the eastern mediterranean odp leg 160 site 966 have been re analysed the use of sedex sequential extraction to evaluate the nutrient concentrations and of ct scan for the identification of large benthic foraminifera has resulted in a more detailed palaeoenvironmental reconstruction and an improved stratigraphic framework three intervals are recognised in the succession and are attributed to the lower middle and upper miocene respectively the lower miocene interval is dominated by large benthic foraminifera and echinoids this association colonized the top of the seamount following its uplift from deep water to the photic zone the middle miocene interval is characterised by rhodoliths and corals at its base and near the top whereas seagrass seaweed assemblages with epiphytic foraminifera and hooked coralline algal crusts dominate its central part the upper miocene is represented by coral reef facies near its base and lagoonal facies toward its top the succession was deposited in an oligotrophic environment and exhibits a general shallowing upward trend that was mainly controlled by tectonic activity related to the northward subduction of the african plate the succession of the eratosthenes seamount is characterised by a diverse large benthic foraminifera assemblage in its lower part and by corals in its uppermost part whereas corallines characterise the central interval this trend is common in miocene mediterranean carbonates and its occurrence on an isolated seamount confirms its connection with the general evolution of the basin the decline of miogypsinids and lepidocyclinids after the early miocene is notable because the eratosthenes seamount was geographically close to the indo pacific ocean where both groups also thrived during the middle miocene this decline was probably caused by the early miocene closure of the deep water connection between the indo pacific and the mediterranean

diagenesis and quartz cement distribution of low permeability upper triassic middle jurassic reservoir sandstones longyearbyen co2 lab well site in svalbard norway reservoir properties of upper triassic middle jurassic sandstones spitsbergen are studied as part of a co2 storage pilot project in longyearbyen the reservoir formations show large contrasts in sandstone compositions with unexpected low permeability despite moderate porosity values petrographic analyses were performed to investigate the influence and distribution of diagenesis it is concluded that because of various compaction cementation and dissolution processes the sandstone porosity is mainly isolated molds and micropores and associated with fibrous illite and chamosite explaining the low permeability diagenesis and the distribution of quartz cement is influenced by lithofacies and detrital compositions mineralogically immature sandstones de geerdalen formation show a homogeneous distribution of quartz cement overgrowths on quartz grains distributed interstitial to labile grains and other cements e g late calcite the main silica source was from the dissolution of adjacent feldspar and labile grains as part of the chemical compaction in contrast quartz dominated sandstones knorringfjellet formation show a heterogeneous patchy distribution of quartz cement influenced by the sedimentary bioturbation pattern with silica sourced also from dissolution at clay rich microstylolites phosphatic beds at the base and top of the formation are strongly influenced by marine eogenesis and reworking processes and associated with concentration of iron rich authigenic minerals the highest porosity appears in sand supported conglomerate where moldic clay mineral ooids contributed to reduce quartz cementation the stratigraphic change from mineralogical immature triassic to mature uppermost triassic jurassic sandstone compositions is detected in wide areas of the barents shelf and has considerable implications for the distribution of sandstone reservoir properties

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

compositional variations in deep sea gravity flow deposits a case study from the voirons flysch voirons wagital complex chablais prealps france abstract grain size control is frequently invoked to explain the compositional variation of detrital sediments in fluvial sediments a similar possibility is here investigated in the fossil deep sea gravity flow deposits from the voirons flysch voirons wagital complex chablais prealps about 270 samples of diverse depositional settings were analysed using the framework composition including cement and porosity mutti facies and grain size measurements six lithofacies have been identified from cluster analysis they correspond to channel l1 to l3 and lobe l4 and l5 depositional settings and to reworked turbidites l6 our results emphasize the close relationship between petrography and grain size which alters the detrital signal from extrabasinal sources the abundant polycrystalline component of proximal deposits is progressively removed while skeletal grains and additional intrabasinal grains become more abundant in distal deposits alongside porosity is reduced by the simultaneous increase of cement which constrains subsequent diagenetic modifications hence proximal depositional settings keep most of the inherited signal from extrabasinal sources whereas distal deposits will be homogenised when plotted in provenance analysis diagrams the successive depositional settings show distinct fields possibly corresponding to different tectonic settings of the dickinson model this compositional variation thus creates a bias in provenance interpretation resulting from both grain size control and flow mechanisms finally our results emphasize that petrographic data must be handled with care in provenance analyses especially when comparing various deep sea gravity flow systems with different grain size ranges

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

traps associated with paleovalleys and interfluves in an unconformity bounded sequence lower cretaceous glauconitic member southern alberta canada the glauconitic member in badger little bow retlaw and turin fields is an unconformity bounded sequence that formed on an ancient coastal plain in response to relative sea level fluctuations the member consists of valley fill and inter valley strata valley fill sandstone bodies are thick elongate pods that formed from inner estuarine bars when sedimentation was laterally confined between valley margins inter valley sandstone bodies are thin discontinuous sheets that accumulated during highstands when outer estuarine embayments covered interfluvial areas adjacent to associated valleys numerous oil pools are stratigraphically trapped within quartzose sandstones in valley fill and inter valley strata of the glauconitic member in the study area common updip seals for these reservoirs are 1 intra sequence facies changes from sandstone to shale and 2 low permeability lithic sandstones that fill the cross cutting paleovalleys of a younger sequence traps associated with many valley fill pools are enhanced by differential compaction anticlines several oil pools in the study area are hosted by discrete quartzose sandstone bodies that lie beneath a valley filled with low permeability lithic sandstone these quartzose sandstone bodies are interpreted to be remnants of older glauconitic deposits that escaped erosion when a younger valley incised into and followed the trend of one or more older glauconitic valleys

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

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

sand composition changes across key boundaries of siliciclastic and hybrid depositional sequences abstract sand composition of arenite successions is sensitive to a suite of factors operating between initial grain production and final diagenesis on a variety of spatial and temporal scales seven allogenic factors the relative importance of which relies upon the complex interaction between tectonics eustasy and climate play a decisive role in dictating petrofacies distribution within siliciclastic to hybrid depositional sequences these factors include i tectonic exhumation ii physical and chemical rock breakdown iii change in sediment flux iv change in source basin physiography v shelf colonization by organisms vi generation of chemical grains and vii volcanism autogenic processes may locally have a considerable influence on the type and amount of sediment supplied to the basin thus interfering with the external control based upon literature data a conceptual framework of expected compositional changes across the key surfaces for sequence stratigraphic interpretation is outlined two case histories from the miocene shelf to turbidite deposits of the northern apennines and the quaternary alluvial to nearshore succession of the adriatic coast respectively are used as references to illustrate how arenite petrofacies changes can be framed into a sequence stratigraphic scheme on multiple timescales