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

stable isotope geochemistry and phase equilibria of coesite bearing whiteschists dora maira massif western alps peak metamorphic temperatures for the coesite pyrope bearing whiteschists from the dora maira massif western alps were determined with oxygen isotope thermometry the 18o smow values of the quartz after coesite 18o 8 1 to 8 6 n 6 phengite 6 2 to 6 4 n 3 kyanite 6 1 n 2 garnet 5 5 to 5 8 n 9 ellenbergerite 6 3 n 1 and rutile 3 3 to 3 6 n 3 reflect isotopic equilibrium temperature estimates based on quartz garnet rutile fractionation are 700 750 c minimum pressures are 31 32 kb based on the pressure sensitive reaction pyrope coesite kyanite enstatite in order to stabilize pyrope and coesite by the temperature sensitive dehydration reaction talc kyanite pyrope coesite h2o the a h2o must be reduced to 0 4 0 75 at 700 750 c the reduced a h2o cannot be due to dilution by co2 as pyrope is not stable at x co2 0 02 t 750 c p 30 kb in the absence of a more exotic fluid diluent e g ch4 or n2 a melt phase is required granite solidus temperatures are 680 c 30 kb at a h2o 1 0 and are calculated to be 70 c higher at a h2o 0 7 consistent with this hypothesis kyanite jadeite quartz bands may represent a relict melt phase peak p t f h2o estimates for the whiteschist are 34 2 kb 700 750 c and 0 4 0 75 the oxygen isotope fractionation between quartz 18o 11 6 and garnet 18o 8 7 in the surrounding orthognesiss is identical to that in the coesitebearing unit suggesting that the two units shared a common final metamorphic history hydrogen isotope measurements were made on primary talc and phengite d smow 27 to 32 on secondary talc and chlorite rite after pyrope d 39 to 44 and on the surrounding biotite d 64 and phengite d 44 gneiss all phases appear to be in nearequilibrium the very high d values for the primary hydrous phases is consistent with an initial oceanicderived connate fluid source the fluid source for the retrograde talc chlorite after pyrope may be fluids evolved locally during retrograde melt crystallization the similar d but dissimilar 18o values of the coesite bearing whiteschists and hosting orthogneiss suggest that the two were in hydrogen isotope equilibrium but not oxygen isotope equilibrium the unusual hydrogen and oxygen isotope compositions of the coesite bearing unit can be explained as the result of metasomatism from slab derived fluids at depth

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 natural calibration of 18o16o geothermometers application to the quartz rutile mineral pair published data on 18o16o fractionation between quartz rutile and other minerals in rocks are used to calibrate the quartz rutile geothermometer the concordance of temperatures deduced from different geothermometers is used to check the preservation of equilibrium among the coexisting minerals there exists a significant at the 99 level linear relationship between 103ln quartz rutile and the equilibrium temperature 106t2 showing that 18o16o fractionation between quartz and rutile is a reliable measure of the equilibrium temperature for temperatures ranging from 450 to 800 c the following thermometric equation is determined 103ln quartz rutile 4 78 0 08 106t2 this calibration agrees with the theoretical relationship for anhydrous mineral mineral fractionation in addition it is shown that correlated errors in 103ln and 106t2 is favourable to the natural calibration method of the oxygen isotope geothermometers

oxygen diffusion in quartz diffusional oxygen exchange between quartz and water was studied by determining 18o profiles in the quartz using an ion microprobe inverse error function plots of the data are linear as required for a diffusion mechanism one natural and two synthetic samples were used and although they had different impurity concentrations oh na and al per 106 si atoms are 7 4000 35 835 and 67 127 respectively the d values were the same within experimental uncertainty diffusion parallel to c is about 2 orders of magnitude faster than that normal to c at 700 c and diffusion normal to the rhombohedron is intermediate the data indicate a change in slope on an arrhenius plot at the boundary at 100 mpa 1 kbar water pressure the preexponential factors do in square centimeters per second and activation energies q in kilojoules per mole for quartz 500 550 c are as follows do 190 and q 284 parallel to c and do 8 10 2 and q 238 normal to the rhombohedron for quartz 600 800 c do 4 10 7 and q 142 parallel to c do 9 10 7 and q 155 normal to the rhombohedron and do 1 10 4 and q 234 normal to c d increases with ph 2 o and between 25 and 350 mpa log d versus log h 2 o has a slope of approximately 1 1 these d values are all several orders of magnitude larger than previously reported values for oxygen diffusion in water free systems

non carbonate intrabasinal grains in arenites their recognition significance and relationship to eustatic cycles and tectonic setting abstract arenites contain several types of non carbonate intrabasinal nci grains which are seldom given specific attention in petrographic studies however recognition and analysis of these particles may be of invaluable help for stratigraphic paleogeographic and even metamorphic reconstructions rip up clasts are the most common nci grains in various depositional environments concentration of other nci types such as green peloids ferruginous ooids reworked phosphates chert soil fragments black pebbles or pyrite clasts occurs at times of reduced sedimentation rates during major transgressions a wealth of iron phosphorus silica and organic matter of both terrestrial and marine origin is provided by rapid flooding of coastal plains erosion of tropical soils developed during previous lowstand stages and plankton blooms in nutrient rich waters prolonged periods of starved detrital supply foster authigenesis and formation of sediments rich in iron phosphorus and silica in shallow encroaching seas eventually a variety of nci grains from terrestrial paralic and mar ne sources are reworked during stepwise coastal retreat and left as lags on ravinement surfaces or deposited in accreting sandwaves by storm or tidal currents on passive margins nci rich arenite intervals are typically found in the basal transgressive tract of depositional supersequences when a rapid short term eustatic rise is superimposed on regional thermo tectonic subsidence associated with waning rift volcanism break up and reorganization of plate motion ironstone deposition is also favored by global polytaxic conditions and expanded oxygen minimum layer in the oceans various types of nci grains are also found in active margins and foreland basins where they are generally diluted due to higher sedimentation rates other nci grains including plant debris siliceous tests clastic gypsum and even rarer particles may occur as framework components in arenites

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

equilibrium oxygen hydrogen and carbon isotope fractionation factors applicable to geologic systems as demonstrated by the chapters in this short course stable isotope techniques are an important tool in almost every branch of the earth sciences central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances indeed it was harold urey s 1947 thermodynamically based estimate of the temperature dependence of 18o 16o fractionation between calcium carbonate and water and a recognition of how this information might be used to determine the temperatures of ancient oceans that launched the science of stable isotope geochemistry the approach pioneered by urey has since been used to estimate temperatures for a wide range of geological processes e g emiliani 1955 anderson et al 1971 clayton 1986 valley this volume in addition to their geothermometric applications equilibrium fractionation data are also important in the study of fluid rock interactions including those associated with diagenetic hydrothermal and metamorphic processes baumgartner and valley this volume shanks this volume finally a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems cole and chakraborty this volume in the fifty four years since the publication of urey s paper equilibrium fractionation data have been reported for many minerals and fluids of geological interest these data were derived from 1 theoretical calculations following the methods developed by urey 1947 and bigeleisen and mayer 1947 2 direct laboratory experiments 3 semi empirical bond strength models and 4 measurement of fractionations in natural samples each of these methods has its advantages and disadvantages however the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations not all of which are in agreement in this chapter we evaluate the major methods for determining fractionation factors

petrology and geochronology of rutile rutile tio2 is an important accessory mineral that when present offers a rich source of information about the rock units in which it is incorporated it occurs in a variety of specific microstructural settings contains significant amounts of several trace elements and is one of the classical minerals used for u pb age determination here we focus on information obtainable from rutile in its original textural context we do not present an exhaustive review on detrital rutile in clastic sediments but note that an understanding of the petrochronology of rutile in its source rocks will aid interpretation of data obtained from detrital rutile for further information on the important role of rutile in provenance studies the reader is referred to previous reviews e g zack et al 2004b meinhold 2010 triebold et al 2012 coarse rutile is the only stable tio2 polymorph under all crustal and upper mantle conditions with the exception of certain hydrothermal environments smith et al 2009 as such we will focus on rutile rather than the polymorphs brookite anatase and ultrahigh pressure modifications in this chapter we first review rutile occurrences trace element geochemistry and u pb geochronology individually to illustrate the insights that can be gained from microstructures chemistry and ages then in the spirit of petrochronology we show the interpretational power of combining these approaches using the ivrea zone italy as a case study finally we suggest some areas of future research that would improve petrochronologic research using rutile rutile is a characteristic mineral in moderate to high pressure metapelitic rocks in high pressure metamorphosed mafic rocks and in sedimentary rocks e g force 1980 frost 1991 zack et al 2004b triebold et al 2012 rutile also occurs rarely in magmatic rocks e g anorthosites as well as in some hydrothermal systems coarse grained

correlation of gulf coast provincial paleogene stages with european standard stages one of the chief goals of stratigraphy is to correlate the provincial stages used in many countries with the standard chronostratigraphic scale based on european stages in this study united states gulf coast provincial paleogene stages in their type area are correlated with the european standard paleogene stages by use of calcareous nannoplankton gulf coast provincial stage boundaries can be placed in martini9s standard calcareous nannoplankton zonation as follows midwayan sabinian boundary mid np 5 sabinian claibornian boundary base np 12 claibornian jacksonian boundary mid np 17 jacksonian vicksburgian boundary mid np 21 vicksburgian chickasawhayan boundary base np 24 upper chickasawhayan boundary mid np 24 gulf coast stages therefore correlate with the european stages as follows the midwayan stage corresponds to all of the danian stage and the lowest part of the selandian stage the sabinian stage corresponds to the rest of the selandian and the lower half of the ypresian stage the claiboraian stage includes the upper half of the ypresian all of the lutetian and approximately the lower two thirds of the bartonian the jacksonian includes the upper third of the bartonian all of the priabonian and the lower part of the rupelian the vicksburgian corresponds to all but the lowermost and uppermost fractions of the rupelian and the chickasawhayan to the upper one tenth of the rupelian and the lower one fifth of the chattian

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

evolution of the blueschist and greenschist facies rocks of sifnos cyclades greece the metamorphism on the island of sifnos is characterized by the eocene development of a coherent highpressure blueschist terrane and an early miocene greenschist facies overprint this study documents the metamorphic evolution of the blueschist assemblages still preserved in the northern parts of the island and their subsequent transformation into greenschists in the central and southern parts the oxygen isotope geothermometry is based on calibrations for quartz pyroxenes and magnetite matthews et al 1983a augmented by revised calibrations for the minerals muscovite qz mu 1 55 106 t 2 epidote qz ep 1 56 1 92 ps 106 t 2 and rutile qz ru 4 54 106 t 2 oxygen isotope analyses of minerals from the blueschist unit of northern sifnos give consistent fractionations which are independent of rock type an average temperature of 455 c was obtained although the scatter in temperatures deduced from the various geothermometers suggests that equilibration occurs under slightly changing physicochemical conditions analyses of minerals and whole rocks shows that pervasive equilibration in the presence of a common metamorphic fluid has not occurred the minerals and whole rocks of the greenschists of central sifnos are systematically enriched in 18o relative to the blueschist assemblages chemical data indicate that the greenschist overprint was accompanied by a metasomatic enrichment of ca2 and co2 the petrologic isotopic and chemical evidence favour a metamorphism governed by the infiltration of 18o co2 enriched aqueous solutions it is reasonable to assume that this is connected with the miocene magmatic activity observed throughout the cyclades the marbles separating the blueschist from the greenschist unit probably acted as barriers to fluid infiltration into the blueschists and were responsible for their preservation the pressure of the blueschist metamorphism is estimated at 14 2 kbar corresponding to a depth of ca 50 km the structural style and stratigraphy of sifnos are suggestive of the subduction of a continental margin sequence it is clear that the considerable tectonic depression may be associated with continental collision and underthrusting

cenozoic evolution of sediment accumulation in deltaic and shore zone depositional systems northern gulf of mexico basin abstract paleogeographic and volumetric lithofacies mapping of 18 cenozoic genetic sequences within the northern gulf of mexico basin quantifies the proportional sequestering of sediment within wave dominated shore zone vs deltaic systems through time three long term depositional phases are revealed by plots based on paleogeographic and sediment isochore maps of total shore zone system area and volume to total delta system area and volume sz d 1 sz d area and volume ratios are highly variable in paleocene through eocene sequences however typical volume ratios for major genetic sequences upper middle and lower wilcox queen city qc and yegua range between 0 2 and 0 6 minor sequences sparta sp jackson js which record very low rates and volumes of sediment accumulation have the greatest variability in their ratios 2 oligocene and miocene sequences display consistently high proportions of shore zone sediment sz d area ratios range from 0 6 to 1 0 and volume ratios cluster between 0 4 and 0 8 3 a substantial late neogene decrease in sz d ratios is presaged in the late miocene sequence pliocene and pleistocene sequences are uniformly characterized by very low ratios of

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

petrology and palaeoenvironmental significance of authigenic iron rich clays carbonates and apatite in the claiborne group middle eocene ne texas the claiborne group eocene in north east texas consists of clayey sandstones and mudrocks both with variable proportions of dark green to brown clay pellets deposited in a marginal to open marine setting on the gulf coast margin the composition of concretionary carbonate and clay pellets from 5 localities has been investigated using a wide variety of analytical techniques our palaeontological sedimentological c s and stable isotope data support an interpretation of marginal marine facies with limited freshwater input for the claiborne group dark green mature pellets are predominantly associated with transgressive bioturbated marine sediments from the weches formation through to the youngest crockett formation there is a trend from pellets composed mostly of dark green serpentine rich mixed layer clay to those of mostly brown immature nontronite rich mixed layer clay the serpentine is intermediate between odinite and berthierine and may have been originally odinite that has undergone partial transformation to berthierine pellet maturity apparently corresponds with the degree of winnowing and sedimentation rate it does not appear to correspond with global temperature fluctuations though the serpentine rich rather than glauconite rich composition may do siderite cement mostly in the form of concretions post dates the iron rich clay pellets and pre dates calcite cement carbonate and apatite concretions show a wide range of mineral cement textures reflecting variation in sedimentary environment and early diagenetic processes based on water temperatures derived from verneriacardia bivalves a precipitation temperature of 20 c is assumed for the concretionary siderite using this temperature we surmise that the siderite precipitated from marine pore waters with intermittent meteoric water mixing

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

depositional sequences in the cretaceous post rift sediments on the new jersey atlantic margin abstract deposition of the cretaceous post rift sediments of the new jersey atlantic margin was controlled by numerous cycles of sea level change the strata deposited within each cycle constitute the depositional sequence of the cycle two types of deposits are identified in the depositional sequences of the new jersey coastal plain transgressive deposits and highstand deposits the transgressive deposits formed when sea level was rising at its greatest rate which led to rapid inundation of the margin the highstand deposits formed when sea level rise slowed and began to fall unconformities developed in the coastal plain during lowstand of sea level at the end of a cycle and during the initial slow rise of sea level at the beginning of the next cycle as a consequence the depositional sequences are unconformity bounded and are separated by hiatuses of varying time dimensions in the coastal plain the transgressive deposits are characterized by their fine grained nature and by containing authigenic glauconite often in abundance they have sharp basal contacts where they unconformably overlie a lower sequence the highstand deposits are sands and silts that grade from the underlying transgressive deposits nine depositional sequences are recognized in the lower and upper cretaceous on the basis of these criteria each of these sequences is time constrained by biostratigraphic distribution of various microfossil groups foraminifera pollen and spores dinoflagellates and coccoliths an additional four depositional sequences are suggested in the non marine lower cretaceous on the basis of the interpretation of highstand deposits two major unconformities five minor unconformities and their accompanying hiatuses are recognized a major coniacian to early santonian hiatus can be traced from the coastal plain to wells in the baltimore canyon trough

synconvergent ductile flow in variable strength continental crust numerical models with application to the western grenville orogen 1 we present results from numerical models for a convergent orogen with laterally variable lower crustal strength representing a simplified orogenic system in which a strong craton flanked by progressively weaker terranes collides with another continent with progressive convergence crustal thickening and thermal relaxation lower crust becomes decoupled from upper and middle crust forming a ductile orogenic infrastructure beneath a stronger superstructure collision with strong external crust results in uplift and expulsion of ductile nappes from the orogenic core creating allochthonous terranes overlying a lower crustal indentor the extent of transport and exhumation of lower crustal nappes over the indentor reflects the amount of convergence and the erosion rate the western grenville orogen displays across strike variations in age tectonic history and protolith association suggesting a systematic variation in precollision crustal strength the laurentian craton margin and accreted terranes were variably reworked at synorogenic depths of 25 35 km during the ottawan orogeny deformation propagated from younger monocyclic rocks in the southeast into older polycyclic rocks flanking the craton on the northwest a comparison between numerical model results and crustal scale cross sections from the georgian bay and montreal val d or transects shows close correspondence between crustal structure and model geometry this indicates that the models produce geologically realistic results and provides a context for interpreting the tectonic evolution of the western grenville orogen contrasts between the results of homogeneous channel flow models and the present ductile nappe models suggest that the effects of different styles of ductile flow can be distinguished in the geologic record

coesite in clinopyroxene in the caledonides and its implications for geodynamics coesite is reported for the first time from the caledonide orogen it occurs as inclusions in clinopyroxene in the dolomite eclogite at grytting norway and provides valuable new evidence to support the hypothesis of extremely high pressure 30 kbar in certain norwegian eclogites this finding has implications for the geodynamics and kinetics of the concepts of microscale intracrystalline tectonic overpressure and of macroscale local or regional tectonic overpressure and for the hypotheses of subduction and obduction involving a more than 100km vertical component of transport

verdinized fecal pellets as indicators of prodelta and delta front deposits in the nile delta egypt abstract green and yellow peloids interpreted as verdinized fecal pellets and a few interpreted as glauconitized fecal pellets are concentrated in marine lithofacies of holocene age in cores of the northeastern nile delta these pellets occur primarily in mud rich prodelta and delta front deposits mineralogically and chemically they are closely comparable to pellets observed in upper holocene to modern delta front deposits seaward of the rosetta branch of the nile the modern delta front in this region is shallow and influenced by bottom currents and burrowing organisms the formation of the pellets suggests a marine setting typified by large fluxes of freshwater and terrestrial organic matter and high rates of sediment accumulation in view of their distinct distribution in time and space it is proposed that these grains serve as valuable indicators of specific depositional environments and can be used to more precisely interpret and correlate subsurface sequences in the nile delta

diffusion effects on oxygen isotope temperatures of slowly cooled igneous and metamorphic rocks recently obtained data on oxygen diffusion in feldspars quartz and hornblende permit the prediction of the apparent18o16o temperatures that would be measured in a rock that consisted only of those three minerals and cooled slowly from high temperature the computed temperatures would be based on the differences in the18o16o ratios between coexisting pairs of minerals the present calculation takes into account the diffusion rates for oxygen as a function of temperature the cooling rate of the rock the mineral grain sizes and the mode of the rock for mineral grains 1 mm in radius and a cooling rate of 10 c m y the minimum difference in apparent temperature between quartz feldspar and feldspar hornblende pairs will be 115 c despite the assumption of a normal uneventful slow cooling history to room temperature further the apparent quartz hornblende temperature will range over 30 c 590 620 c depending on the mode of the rock for a cooling rate of 1000 c m y the apparent difference in temperature can be as much as 400 c consequently consistency in temperatures obtained by oxygen isotope analysis should not be expected in most high grade metamorphic rocks or igneous rocks which are cooled slowly departures from the pattern of temperatures obtained in this model would imply a very rapid quench from high temperature or a complex history for the rock for some minerals including hornblende the relation between temperature and the equilibrium fractionation of oxygen isotopes between coexisting phases has been derived from observed relations in natural specimens the choice of the specimens used for such calibrations needs to be re evaluated in light of these findings this may result in a change in the equilibrium equation constants an example from the literature the san jose tonalite baja california mexico was modelled and yields 18o concentrations in the minerals that correspond closely with the measured values this suggests that the model used is appropriate that the rock has had a simple thermal history and that it cooled at 100 200 c m y over the temperature range 800 500 c the set of paleotemperatures obtained for a rock will in general yield neither the mineral closure temperatures nor the formation or crystallization temperatures on the other hand the cooling rate of the rock may be derived from the data this in turn may have important tectonic implications with regard to denudation and uplift rates

time averaging taphonomy and their impact on paleocommunity reconstruction death assemblages in texas bays the death assemblages in upper copano bay and upper laguna madre texas were compared with the living communities as sampled over a two year period in order to determine how taphonomy and time averaging affect paleocommunity reconstruction the living and death assemblages were compared using taxonomic composition numerical abundance diversity biomass and trophic and habitat proportions taxonomic composition particularly adult taxonomic composition and the biomass of the death assemblage more accurately reflect the characteristics of the living community than do numerical abundance and other community attributes based upon numerical abundance such as diversity taxonomic composition and biomass are less modified by taphonomy and time averaging because they are temporally more persistent characteristics of the community community and paleocommunity attributes are not equivalent because the paleocommunity is described using time averaged data ecological theory must be supplanted by paleoecological theory that takes into account this temporal component

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

the genesis of glaucony in the oligo miocene torquay group southeastern australia petrographic and geochemical evidence abstract the oligo miocene torquay group at bird rock in southeastern australia comprises a sequence of fine grained skeletal carbonates and argillaceous and glauconitic sandstones which were deposited in a cool water mid shelf environment the bird rock glaucony consists predominantly of randomly interstratified glauconitic smectite which constitutes bioclast infills and faecal pellet replacements petrographic and geochemical evidence indicates that the glaucony is autochthonous and comprises chemical components derived primarily from argillaceous matrix material seawater is unlikely to be a significant source of ions the glauconitization of the bird rock sediments occurred under sub oxic partially reducing conditions in the very shallow burial environment and involved local iron redistribution sub oxic conditions favour glauconitization because iron is stable in the soluble ferrous state and can be fixed in authigenic silicates due to the negligible concentrations of hydrogen sulphide it is likely that localised acidic conditions were initiated during the glauconitization process this acidity appears to have been buffered by the dissolution of bioclastic carbonate the fact that glaucony predominantly occurs as bioclast infills and faecal pellet replacements implies that the physico chemical conditions appropriate for glauconitization develop preferentially in such biogenic detritus the development of appropriate micro environments within such sediments probably relates to their physical confinement and or high organic matter content the bird rock glaucony developed during intervals of slow sedimentation and environmental quiescence associated with marine flooding events these conditions facilitated glauconitization by allowing the favoured clay rich sediments to accumulate and remain in the appropriate physico chemical regime sufficiently long for the complex glauconitic structures to form

oxygen isotope fractionation in zinc oxides and implications for zinc mineralization in the sterling hill deposit usa oxygen isotope fractionation in the zinc oxides has been calculated by means of the modified increment method the results suggest that zincite is slightly enriched in 18o relative to the franklinite of the spinel type structure but considerably depleted in 18o relative to the franklinite of the inverse spinel type structure the zinc oxides are significantly depleted in 18o relative to water under hydrothermal and metamorphic conditions the oxygen isotope analyses of mineral pairs including the zinc oxides and the common gangue minerals such as calcite and quartz can constitute a sensitive isotope geothermometer application of oxygen isotope geothermometry to natural assemblages is attempted for the calcite zinc ore mineral pairs from the sterling hill deposit in usa the results indicate that the temperature of the zinc mineralization may be in the range from 410 to 630 c and thus lower than the metamorphic temperatures of granulite facies a metamorphic fluid could have been involved in the formation of the zinc ore minerals franklinite would structurally be an inverse spinel in the infancy of its formation and thus could have originally evolved from zn2 substitution to fe2 of magnetite at the high temperatures

stable isotope geochemistry and formation mechanisms of quartz veins extreme paleoaltitudes of the central alps in the neogene quartzveins ranging in size from less than 50 cm length and 5 cm width to greater than 10 m in length and 5 m in width are found throughout the central swiss alps in some cases the veins are completely filled with milky quartz while in others sometimes spectacular void filling quartz crystals are found the style of vein filling and size is controlled by host rock composition and deformation history temperatures of vein formation estimated using stable isotope thermometry and mineral equilibria cover a range of 450 c down to 150 c vein formation started at 18 to 20 ma and continued for over 10 my the oxygen isotope values of quartz veins range from 10 to 20 permil and in almost all cases are equal to those of the hosting lithology the strongly rock buffered veins imply a low fluid rock ratio and minimal fluid flow in order to explain massive nearly monomineralic quartz formation without exceptionally large fluid fluxes a mechanism of differential pressure and silica diffusion combined with pressure solution is proposed for early vein formation fluid inclusions and hydrous minerals in late formed veins have extremely low d values consistent with meteoric water infiltration the change from rock buffered static fluid to infiltration from above can be explained in terms of changes in the large scale deformation style occurring between 20 and 15 ma the rapid cooling of the central alps identified in previous studies may be explained in part by infiltration of cold meteoric waters along fracture systems down to depths of 10 km or more an average water flux of 0 15 cm3 cm 2yr 1 entering the rock and reemerging heated by 40 c is sufficient to cool rock at 10 km depth by 100 c in 5 million years the very negative d values of

thermodynamics and lattice vibrations of minerals 5 applications to phase equilibria isotopic fractionation and high pressure thermodynamic properties in previous papers in this series a model that uses available elastic structural and spectroscopic data on minerals has been used to predict the thermodynamic functions cv heat capacity s entropy e internal energy and f helmholtz free energy in this paper four applications to problems of current geochemical and geophysical interest are presented 1 interpretation of complex trends of calorimetric data 2 calculation of phase equilibria 3 calculation of oxygen isotopic fractionation factors and 4 estimation of the effect of pressure on thermodynamic functions the model demonstrates that trends in high temperature thermodynamic properties of silicates are determined by the position and relative numbers of high frequency modes generally antisymmetric si al o stretching modes the position of these modes varies systematically with degree of polymerization of tetrahedra and therefore high temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition trends at low frequency are much more complex because the low frequency optic modes that most strongly influence the low temperature thermodynamic functions depend in a complex way on the size coordination and mass of cations and various polyhedra in the minerals the heat capacity curves of kyanite andalusite and sillimanite and of quartz coesite and stishovite show crossovers that cannot be explained by debye theory which accounts only for acoustic mode behavior but can be explained by the model spectra proposed because proper account is taken of the changing low and high frequency optic modes upon polymorphic transformations the proposed model is sufficiently accurate that phase equilibrium problems can be addressed the quartz coesite stishovite equilibrium curves the kyanite andalusite sillimanite triple point and the breakdown of albite to jadeite plus quartz are cited as specific examples for each example predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally the calculated slopes are sensitive to spectroscopic parameters particularly to the distribution of optic modes in the far infrared this sensitivity is discussed in detail for the albite breakdown reaction the model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated a simple set of rules for generating hypothetical spectra of 18o minerals from measured spectra of the 16o forms is given reduced partition functions are calculated for 13 minerals at 298 k the model values of reduced partition function 1000 ln of these minerals decrease in the order quartz calcite albite muscovite clinoenstatite anorthite diopside pyrope grossular zircon forsterite andradite rutile in good agreement with experimental data at 1000 k the first six minerals show small crossovers so that the order becomes calcite muscovite albite quartz anorthite and clinoenstatite the differences in 1000 ln at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends the model clearly defines the region in which the fractionation factors do not follow a 1 t trend and should be useful for extrapolation of experimental data to low temperatures finally a modified gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression and thermodynamic properties to 1000 kbar 1000 k are given for nine minerals at 1 mbar the predicted decrease in entropy at 298 k ranges from 54 of the 1 bar value for periclase to 25 for stishovite

eustatic cyclicity in the paleocene and eocene data from the brazos river valley texas abstract documentation of the geologic history of global sea level change requires the analysis of numerous geographically diverse sections the paleocene through eocene section of the brazos river valley eastern texas is an area suitable for such analysis which has yet to be studied analysis of the brazos river valley section for sea level changes during the paleocene and eocene was accomplished by the application of sequence stratigraphie analysis using seismic well log and outcrop data the information obtained from this study was then used in evaluating the published sea level record a total of fifteen sequence boundaries and ten maximum flooding surfaces indicating conditions of falling and rising sea level respectively were identified in the paleocene and eocene strata of the brazos river valley results of this study show an excellent correlation with the published record of sea level change in the paleocene poor correlation in the early eocene good correlation in the middle eocene and fair correlation in the late eocene the excellent correlation between the results of this study and the published record during the paleocene provide strong support for eustalic nature of these events poor to fair correlation during the early and late eocene is attributed to the resolution of the data base and neither supports nor refutes the published record results of this study in the middle eocene provide strong support lor the published record with two important exceptions published records show a cycle of sea level change in the earliest part of the middle eocene which was not observed in this study and a rise in sea level near the end of the middle eocene bartonian may have occurred earlier than that indicated by the published record

in situ oxygen isotope and trace element geothermometry of rutilated quartz from alpine fissures finely acicular rutile intergrown with host quartz rutilated quartz is commonly found in hydrothermal veins including the renown cleft mineral locations of the swiss alps these alpine cleft mineralizations reportedly formed between 13 5 and 15 2 ma based on ages of rare hydrothermal monazite and titanite at temperatures t of 150 450 c based on fluid inclusions and bulk quartz mineral oxygen isotope exchange equilibria and pressures p of 0 5 2 5 kbar estimated from a geothermal gradient of 30 c km the potential of rutilated quartz as a thermochronometer however has not been harnessed previously here we present the first results of age and t determinations for rutilated quartz from six locations in the swiss alps with vein country rocks that cover peak metamorphic conditions between 600 and with x zr ppm and r 0 008314 uncertainties scaled by the square root of the mean square of weighted deviates mswd 11 n 9 this relationship supports previously recognized temperature dependent zr uptake in rutile although widely used zr in rutile thermometer calibrations based on high t experiments are at variance with oxygen isotope exchange temperatures by contrast ti in quartz lacks systematic relations with oxygen isotope temperatures the discrepancy between low t ti in quartz thermometry on one side and oxygen isotope and zr in rutile thermometry on the other suggests that ti in quartz thermometry should be applied with caution for low t 500 c rocks 1 embed mml math 1 gif

maceration of calcareous skeletons in the december issue of sedimentology 1979 26 two papers on the disintegration of calcareous skeletons appeared in both articles the authors alexandersson 1979 fitzgerald parmenter milliman 1979 describe skeletal degradation producing fragments and even single calcium carbonate crystallites in the present marine environment at least part of this maceration alexandersson 1978 is attributed to the breakdown of the skeletal organic matrix on the sea bottom both studies were carried out on samples from the sediment surface of marine cold water regions there another destructive process is active etching and dissolution of the calcareous particles by the ambient carbonate under saturated water e g alexandersson 1975 1978 the possible coexistence of these biological and physicochemical destructive processes and the lack of information from cores have left open questions in the above mentioned two studies some of these questions were discussed by me lewy 1975 my observations and conclusions may now have a wider significance

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

comments on stable isotope geothermometry the system quartz water we show that the results of quartz water partial oxygen exchange experiments under hydrothermal conditions are determined primarily by exchange between water and dissolved silica species and not by diffusion in the solid hence these experiments do not provide an accurate value of the variation of fractionation with temperature but only a rough indication of it we conclude that the bottinga and javoy 1 equation relying on this type of information and on the precise calculation of the coefficient a 3 7 in the thermometric equation 1000 ln a b 106 t2 is not seriously questioned by these17o 18o partial exchange experiments

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

paleogene sea levels and climates u s a eastern gulf coastal plain abstract biostratigraphic zonation of the paleogene formations in the eastern gulf coastal plain of the u s a based on calcareous nannoplankton allows a reassessment of the timing and pattern of changing sea levels and climates in the region general similarity is recognizable between the gross pattern of paleogene transgressions regressions in the eastern gulf coastal plain and the recently published vail et al 1977 scheme of eustatic sea level changes local tectonism and sedimentation have however overprinted intra cycle shoreline fluctuations on the eustatic pattern a hiatus spanning at least calcareous nannoplankton zone np 11 exists between the early eocene hatchetigbee and tallahatta formations another significant hiatus representing most or all of np 23 exists between the early oligocene bucatunna clay and the late oligocene chickasawhay limestone nannoplankton assemblages suggest temperate sea surface waters during the early and early late paleocene followed by subtropical sea surface conditions from latest paleocene to earliest oligocene climatic conditions were cooler during the remainder of the early oligocene

depositional trends in siliciclastic deposits of the stone city transgressive systems tract middle eocene texas abstract strata exposed at stone city bluff texas contain shelf sediments deposited during progressive marine deepening from shallow water depths and then capped by a maximum flooding horizon they are part of the early bartonian np16 cook mountain transgressive systems tract exposed in the type section of the stone city member of the crockett formation this locality lies on the inner portion of a shelf transect about 175 km 110 mi shoreward of the late eocene shelf slope margin and probably never farther than 80 km 50 mi from the shoreline sedimentary structures in the sediments change upward reflecting a shift from tidal current dominated to storm dominated deposition in lower intervals tidal control is dominant the transition interval contains isolated storm sands as sheets with lenses 40 cm 15 in thick in mudstones with tidal bedding these storm beds contain teeth bone concentrates and some gravel size clasts at the bases of larger lenses in higher intervals storm deposition is dominant in all units mostly as thin distal layers of very fine sand or silt amalgamated storm deposits form larger units e g the moseley bed local hardground surfaces are developed where storm washing exposed concretionary layers or on condensed winnowed zones glauconite occurrence and siderite concretion formation are most common in the upper intervals storm deposits have dual sediment sources and contain 1 skeletal remains shells fish bone and glauconite pellets concentrated by in place winnowing or 2 fine quartzose sand washed in from shallower water settings alternation of amalgamated storm deposits and mudstone units with thin storm deposits indicate a cyclic record of storm activity

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

oxygen isotope fractionation in quartz albite anorthite and calcite laboratory measurements of equilibrium oxygen isotope fractionation in quartz albite anorthite and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600 c and above exchange in these systems is as rapid as exchange between silicates and water fractionation factors can be summarized in the following equations qc 0 38 106t 2 abc 0 57 106t 2 anc 1 59 106t 2 from which the silicate pair fractionations are readily obtained these results are compared with published theoretical estimates as well as data derived from hydrothermal experiments some significant differences are found in particular it is difficult to reconcile all of the hydrothermal data either with theoretical calculations or with the present experimental data the new experiments provide an internally consistent set of fractionation factors suitable for isotopic thermometry and for test of disequilibrium in natural systems

growth of normal faults in multilayer sequences a 3d seismic case study from the egersund basin norwegian north sea abstract we investigate the structural style and evolution of a salt influenced extensional fault array in the egersund basin norwegian north sea through analysis of 3d reflection seismic and well data analysis of fault geometry morphology throw distribution and syn kinematic strata reveal an intricate but systematic style of displacement and growth suggesting an evolution of 1 initial syn sedimentary fault growth contemporaneous with salt mobilization initiated during the late triassic 2 cessation of fault activity and burial of the stagnant fault tips and 3 subsequent nucleation of new faults in the cover above contemporaneous salt re mobilization initiated during the late cretaceous with downward propagation and linkage with faults stage 3 was apparently largely controlled by salt mobilization in response to basin inversion as reactivated faults are located where the underlying salt is thick while the non reactivated faults are found where salt is depleted based on the 3d throw analyses we conclude that a combination of basement faulting and salt re mobilization is the driving mechanisms behind fault activation and reactivation even though the sub and supra salt faults are mainly geometrically decoupled through the salt a kinematic coupling must have existed as sub salt faults still affected nucleation and localization of the cover faults

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

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions

coupling of oceanic and continental crust during eocene eclogite facies metamorphism evidence from the monte rosa nappe western alps high precision u pb geochronology of ru tile from quartz carbonate white mica rutile veins that are hosted within eclogite and schist of the monte rosa nappe western alps italy indicate that the monte rosa nappe was at eclogite facies metamorphic conditions at 42 6 0 6 ma the sample area indren glacier furgg zone dal piaz 2001 geology of the monte rosa massif historical review and personal comments smpm consists of eclogite boudins that are exposed inside a south plunging overturned synform within micaceous schist associated with the eclogite and schist are quartz carbonate white mica rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist intrusion of the veins at about 42 6 ma occurred at eclogite facies metamorphic conditions 480 570 c 1 3 1 4 gpa based on textural relations oxygen isotope thermometry and geothermobarometry the

formation of segmented normal faults a 3 d perspective the interpretation of fault kinematics from geometric data is an essential step in developing an understanding of the growth of fault systems constraints on fault geometry are however often restricted to 2 d maps or cross sections in this article we consider the extent to which kinematic interpretations of faulting benefit from a 3 d rather than 2 d geometrical perspective concentrating on relay zones and segmented normal fault arrays we suggest that very different interpretations of their evolution arise from the recognition that the propagation directions of faults and fault segments will rarely be contained within the inspection plane of 2 d data a 3 d perspective favours an interpretation in which the segments of a fault array are kinematically interrelated from their initiation individual segments in such systems may link into a single fault surface out of the plane of inspection or may be unconnected in 3 d we argue that this interpretation which conflicts with the often suggested model of incidental overlap of originally isolated faults should be the preferred model for the generation and growth of segmented normal fault arrays