the major ion composition of carboniferous seawater abstract the major ion chemistry na mg 2 ca 2 k so 4 2 and cl of carboniferous seawater was determined from chemical analyses of fluid inclusions in marine halites using the cryo scanning electron microscopy cryo sem x ray energy dispersive spectrometry eds technique fluid inclusions in halite from the mississippian windsor and mabou groups shubenacadie basin nova scotia canada asbian and pendleian substages 335 5 330 ma and from the pennsylvanian paradox formation utah usa desmoinesian stage 309 305 ma contain na mg 2 k ca 2 cl brines with no measurable so 4 2 which shows that the carboniferous ocean was a cacl 2 sea relatively enriched in ca 2 and low in so 4 2 with equivalents ca 2 so 4 2 hco 3 34 s values from anhydrite in the mississippian shubenacadie basin 13 2 14 0 and the pennsylvanian paradox formation 11 2 12 6 support seawater sources br in halite from the shubenacadie basin 53 111 ppm and the paradox basin 68 147 ppm also indicate seawater parentages carboniferous seawater modeled from fluid inclusions contained 22 mmol ca 2 kg h 2 o mississippian and 24 mmol ca 2 kg h 2 o pennsylvanian estimated sulfate concentrations are 14 mmol so 4 2 kg h 2 o mississippian and 12 mmol so 4 2 kg h 2 o pennsylvanian calculated mg 2 ca 2 ratios are 2 5 mississippian and 2 3 pennsylvanian with an estimated range of 2 0 3 2 the fluid inclusion record of seawater chemistry shows a long period of cacl 2 seas in the paleozoic from the early cambrian through the carboniferous when seawater was enriched in ca 2 and relatively depleted in so 4 2 during this 200 myr interval ca 2 decreased and so 4 2 increased but did not cross the ca 2 so 4 2 chemical divide to become a mgso 4 sea when so 4 2 in seawater became greater than ca 2 until the latest pennsylvanian or earliest permian 309 295 ma seawater remained a mgso 4 sea during the permian and triassic for 100 myr fluid inclusions also record a long interval from the early cambrian to the middle devonian when seawater had low mg 2 ca 2 ratios 2 ca 2 ratio of seawater rose from 0 9 in the middle devonian to 2 5 in the middle late mississippian 2 3 in the middle pennsylvanian and 3 5 in the early permian the transition from calcite seas to aragonite seas established from the mineralogy of oolites and early marine cements occurred in the late mississippian fluid inclusions show that seawater mg 2 ca 2 ratios rose above 2 by the middle to late mississippian coinciding exactly with the shift to aragonite seas aragonite seas existed for 100 myr from the late mississippian until the late triassic early jurassic

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

diagenetic history and reservoir properties of the cenomanian turonian carbonates in southwestern iran and the persian gulf abstract shallow marine carbonates of the mid cretaceous sarvak formation are important reservoir rocks in southern iran and the persian gulf region these carbonates were deposited on the margin of the arabian plate and rest on the kazhdumi formation which is one of the major hydrocarbon source rocks in the region the top of the sarvak formation coincides with the regional turonian unconformity most of the observed diagenetic features are genetically related to meteoric waters entering the sarvak formation during cenomanian turonian and mid turonian uplift and the subsequent paleoexposure integration of field and petrographic studies and isotope geochemistry reveals the history of a variety of diagenetic processes which include dissolution and development of secondary porosity which enhance reservoir properties of the upper sarvak carbonates various types of calcite cements were identified as the main cause for porosity loss in these carbonates their diagenetic environment is discussed using the geochemical data acquired as part of the present study the 18 o and 13 c values 12 3 to 0 6 and 5 8 3 6 vpdb respectively of the cements indicate precipitation from marine meteoric and or mixed meteoric marine fluids some drusy calcite cements exhibit 18 o and 13 c values 5 1 and 0 8 vpdb respectively and higher 87 sr 86 sr ratios comparing to mid cretaceous carbonates i e 0 70747 which may indicate precipitation from meteoric waters lower 18 o and 13 c values e g 5 1 0 8 vpdb combined with higher 87 sr 86 sr ratios e g 0 70747 of some drusy calcite could confirm their precipitation from meteoric waters lower 18 o values of some blocky calcite cements e g 12 3 vpdb and matrix replacive compression related dolomites i e 7 3 to 3 4 vpdb suggest their precipitation at rising temperatures during burial the range of 13 c values 5 8 3 6 vpdb suggests that the main source of carbon in the calcite cements was primarily marine mixed with isotopically more negative carbon from atmospheric soil derived co 2

aragonite calcite seas quantifying the gray area oscillations between the dominance of aragonite and calcite in abiotic marine caco3 precipitates throughout earth history are closely coupled with the evolution of earth s seawater composition and represent the environmental context in which organisms evolved their ability to biomineralize the most important factor controlling these phanerozoic oscillations in caco3 polymorph composition is the ratio of mg ca in seawater which is thought to separate aragonite and calcite precipitation along a distinct temperature controlled threshold a sharp threshold however is contradicted by overlapping aragonite and calcite precipitation fields at a range of experimental conditions here we present experimental data that enable us to quantify the proportions of caco3 polymorphs as a function of mg ca ratio and temperature this allows us to convert published mg ca ratio proxy data and models of the phanerozoic mg ca ratio into proportions of abiotic caco3 polymorphs at a given temperature and thus provides a temperature corrected view of aragonite calcite sea conditions in this revised view abiotic calcite precipitation was inhibited during aragonite sea intervals at temperatures above 20 c whereas calcite sea intervals were characterized by the co precipitation of aragonite and calcite in environments above 20 c this continuous prominence of aragonite precipitation in phanerozoic warm water environments explains the phanerozoic increase of aragonite over calcite skeletal composition in calcifying organisms

compositional variations at ultra structure length scales in coral skeleton distributions of mg and sr in the skeletons of a deep sea coral caryophyllia ambrosia and a shallow water reef building coral pavona clavus have been obtained with a spatial resolution of 150 nm using the nanosims ion microprobe at the museum national d histoire naturelle in paris these trace element analyses focus on the two primary ultra structural components in the skeleton centers of calcification coc and fibrous aragonite in fibrous aragonite the trace element variations are typically on the order of 10 or more on length scales on the order of 1 10 mu m sr ca and mg ca variations are not correlated however mg ca variations in pavona are strongly correlated with the layered organization of the skeleton

nanoscale evidence for uranium mobility in zircon and the discordance of u pb chronometers scanning transmission electron microscopy stem images coupled with u pb isotopic analysis give new insight into mobility of u and pb in zircon zircon crystals included in xenotime and in plagioclase of a pegmatitic assemblage comprising euxenite correspond to irradiation related alteration of zircon with amorphization microporosity swelling radial cracking and uptake of non formula cations like ca leading to increased discordance of the u pb system fractures and pores represent the vectors for fluid mediated open system behavior stem images demonstrate the presence of u rich clusters 70 nm with uraninite structure within the porosity at high magnification pores are surrounded by a low density halo 100 nm and are coated by a high density wall 50 nm enriched in u or ca or both we interpret the spatial link between u ca and porosity as evidence for u uptake alteration of euxenite crystals into pyrochlore in the rock led to liberation of u and ca these elements were transported by fluids through cracks and incorporated within zircon thanks to porosity by a diffusion reaction process the data on this uncommon sample demonstrate that discordance of the u pb system in zircon affected by radiation damage includes a component of u mobility u gain u loss superimposed on pb mobility pb loss pb gain

aragonitic scleractinian corals in the cretaceous calcitic sea changes in seawater chemistry have affected the evolution of calcifying marine organisms including their skeletal polymorph calcite versus aragonite which is believed to have been strongly influenced by the mg ca ratio at the time these animals first emerged however we show that micrabaciids a scleractinian coral clade that first appeared in the fossil record of the cretaceous when the ocean mg ca ratio was near the lowest in the phanerozoic thus a priori favoring calcitic mineralogy formed skeletons composed exclusively of aragonite exceptionally preserved aragonitic coralla of micrabacia from the late cretaceous ripley formation southeastern usa have skeletal microstructures identical to their modern representatives in addition skeletons of micrabacia from cretaceous chalk deposits of eastern poland are clearly diagenetically altered in a manner consistent with originally aragonitic mineralogy these deposits have also preserved fossils of the scleractinian coelosmilia the skeleton of which is interpreted as originally calcitic these findings show that if changes in seawater mg ca ratio influenced the mineralogy of scleractinian corals the outcome was taxon specific the aragonitic mineralogy unique skeletal microstructures and ultrastructures and low mg ca ratios in both fossil and living micrabaciids indicate that their biomineralization process is strongly controlled and has withstood major fluctuations in seawater chemistry during the past 70 m y

self induced fracture generation in zircon the mineral zircon has particular geological significance because of its use in the age determination of rocks and as a structural analogue phase for radioactive waste forms despite its widespread utility however radiation damage of the crystal structure metamictization causes a volume expansion of the crystal lattice and the generation of internal stresses which can induce fractures in the crystal a model has been developed which describes the state of stress in n concentric spherical shells each of which may have different material properties the case of a three shelled composite sphere has been examined explicitly in combination with fracture mechanics theory the model predicts that spatially distinct radial and or concentric fracture sets can be produced and such fracture patterns accurately describe the distribution and types of self induced fractures observed in natural zircons in general the formation of such microfractures in zircon is a function of the degree of metamictization shell thickness and the confining pressure the model predicts that the maximum depths in the earth s crust at which radial versus concentric fractures can form in a crystal are different suggesting that the types of fractures found in a suite of zircons from a particular rock might be potential indicators of the depth of burial because metamictization induced fractures may serve as potential pathways for the rapid leaching of various elements from the zircon crystal this may also have important implications in interpreting the u pb ages of fractured zircons or in evaluating the suitability of related crystalline phases as hosts for nuclear waste

cathodoluminescene at low fe and mn concentrations a sims study of zones in natural calcites abstract point analyses of natural calcite cements by sims confirm the earlier suggestions that 20 ppm mn is required to activate luminescence whereas fe concentrations in excess of 1400 ppm quench it partly independently of the mn content below this fe threshold luminescence is bright at mn concentrations in excess of 225 ppm in the range 20 225 mn all types of luminescence dull luminescent and nonluminescent can occur this undifferentiated domain is evident also from a compilation of literature data the type of luminescence is not a simple function of fe and mn concentrations other parameters influence cl sinc most diagenetic calcite cements have fe and mn concentrations that place them within the field of mixed cathodoluminescence these results force reassessment of models that equate the type of luminescence with the redox state of the diagenetic environment

the chemistry of quartz in granitic pegmatites of southern norway petrogenetic and economic implications trace element concentrations in quartz from 188 granitic pegmatites in the froland and evje iveland pegmatite fields southern norway have been determined to establish exploration targets for high purity quartz and to gain a better understanding of the genesis of pegmatites hosting these deposits both pegmatite fields were formed during the sveconorwegian grenvillian orogeny 1145 900 ma at the western margin of the fennoscandian shield in situ raster analyses within single quartz crystals were undertaken by laser ablation inductively coupled plasma mass spectrometry la icp ms spot size 75 m to assess levels of lattice bound impurities rather than mineral and fluid inclusions that are relatively easily removed during high purity quartz processing quartz in the froland pegmatites has relatively pure and homogeneous compositions containing 46 24 gg 1 al 8 3 gg 1 ti 1 4 0 8 gg 1 ge and 11 7 gg 1 li the ti in quartz geothermobarometer gives an average pegmatite crystallization temperature of 537 39 c temperature estimates are highest along the northwestern margin of the pegmatite field 550 c whereas the most differentiated pegmatites occur toward the northeast the area of greatest economic potential for high purity quartz lies just north of the central part of the field where individual pegmatites contain 1 million metric tons mt quartz with low average trace element contents of 67 11 gg 1 from mineral chemical criteria and a range of other geologic factors we propose that pegmatite melts in the froland field were generated by fluid present crustal melting at about 1060 ma in zones of localized high strain deformation during progressive thrusting along the porsgrunn kristiansand fault zone quartz in the evje iveland pegmatites has more variable compositions with 69 57 gg 1 al 19 11 gg 1 ti 2 3 1 8 gg 1 ge and 7 5 gg 1 li from its ti content it crystallized at temperatures of 613 70 c the regional spatial distribution of ti in quartz temperatures appears irregular mainly due to the scattered distributions of chemical evolved pegmatites with amazonite cleavelandite replacement zones which show crystallization temperatures down to 442 c quartz from the evje iveland pegmatites is unlikely to be of current economic interest due to its moderate to high trace element contents heterogeneous chemistry and low volume the evje iveland pegmatites show no apparent genetic link to a granite intrusion instead they probably formed as a result of partial melting at the depth of their amphibolite country rocks at around 910 ma this is related to a regional low pressure high temperature metamorphic event at about 930 to 920 ma

radiation damage in diopside and calcite crystals from uranothorianite inclusions combining observation and simulation radiohalos formed around urano thorianite uth from the tranomaro granulitic skarns se madagascar were studied these structures consist of uth grains surrounded by both aluminous diopside cpx and calcite cc1 crystals optical microscope and scanning electron microscope sem images revealed 1 the presence of radiating cracks around the uth probably due to swelling of the metamict uth 2 a diffuse optical halo at the cc1 uth interface and 3 a wide reaction zone at the cpx uth interface composed of secondary calcite cc2 with low temperature sheet silicate from the smectite group samples prepared across various interfaces using focused ion beam fib were investigated by transmission electron microscope tem in contrast to sem observations there is no direct contact between cc1 and uth from cc1 to uth we found 1 a large 200 300 nm amorphous zone a enriched in u th and ca but without si 2 a chain b of very small 20 nm tho2 crystals 3 another amorphous zone c which in contrast to zone a is enriched in si and 4 another zone d made of small amorphous si rich bubbles the organization is similar for the uth cc2 interface the presence of hydrous minerals smectite and carbonate calcite in reaction zone and in cracks the presence of pb rich inclusions in secondary calcite the abundance of fluid inclusions in the porous layer in calcite the dissociation of u and th in the calcite uranothorianite layer and the tho2 chains along interfaces are strong indications that low temperature crystallization was promoted by a fluid phase srim simulation was used to calculate the effect of and recoil particles of the three decay chains in cpx cc and uth the thickness of the damaged area calculated for in cpx and cc are similar to the widths of the recrystallized areas observed in thin section 30 m corrected with the wandering recoil effect the size of the damaged area calculated for recoil nuclei in cc 50 60 nm is multiplied by 3 and is in rather good agreement with the thickness of the totally amorphous layer at the cc uth interface 200 nm finally it is emphasized that radiohalos are a point of chemical and physical weakness in a rock and probably a starting point for alteration

a cretaceous scleractinian coral with a calcitic skeleton it has been generally thought that scleractinian corals form purely aragonitic skeletons we show that a well preserved fossil coral coelosmilia sp from the upper cretaceous about 70 million years ago has preserved skeletal structural features identical to those observed in present day scleractinians however the skeleton of coelosmilia sp is entirely calcitic its fine scale structure and chemistry indicate that the calcite is primary and did not form from the diagenetic alteration of aragonite this result implies that corals like other groups of marine calcium carbonate producing organisms can form skeletons of different carbonate polymorphs

new data on sequence stratigraphy of the sarvak formation in malekshahi city ilam province zagros basin iran abstract two surface sections of the sarvak formation late albian late turonian named tange e bawlek and shahnakhjir were studied these sections are about 24 km apart located in the flanks of the kabirkuh and shahnakhjir anticlines in ilam province in the western part of the zagros fold thrust belt zftb the sarvak formation is 845 m and 412 m thick in these sections respectively the lower contact with the garau formation is erosional with karst features and abundant glauconite at the first section whereas it isn t exposed at the last section field evidences and laboratory examinations on thin sections of collected samples revealed five 3rd order depositional sequences in the sarvak formation of which the four lower sequences were deposited in a carbonate platform whereas the last one was deposited in a foreland basin the lower contact of the first and last sequences are type whereas rest of the boundaries are type ii in compare with the arabian plate lower boundary of the topmost sequence is assumed to coincide with the boundary between ap8 and ap9 sequences 1 and 2 predominantly comprising neritic facies whereas sequences 3 and 4 are composed of pelagic facies although the topmost sequence basically varies in biota content lithology and depositional setting from the rest of the formation overwhelming shale lithofacies in contrast to the other part of the formation along with unconformity in lower contact of this sequence strongly support to consider this part as separate lithostratigraphic unit hence we suggest this part to be considered as a potential new formation after further complementary studies

distribution and petrogenetic behaviour of trace elements in granitic pegmatite quartz from south norway the present study documents that the trace element distribution in granitic quartz is highly sensitive to cafc processes in granitic melts igneous quartz efficiently records both the origin and the evolution of the granitic pegmatites aluminium p li ti ge and na in that order of abundance comprises 95 of the trace elements most samples feature 1 ppm of any of these elements the remnant 5 includes k fe be b ba and sr whereas the other elements are present at concentrations lower than the detection limit potassium fe be and ti are relatively compatible hence obtain the highest concentrations in early formed quartz phosphorous ge li and al are relatively incompatible and generally obtain the highest concentrations in quartz that formed at lower temperatures from more evolved granitic melts the ge ti the ge be the p ge and the p be ratios of quartz are strongly sensitive to the origin and evolution of the granitic melts and similarly the rb sr and the rb k ratios of k feldspars may be utilised in petrogenetic interpretations however the quartz trace element ratios are better at distinguishing similarities and differences in the origin and evolution of granitic melts after evaluating the different trace element ratios the ge ti ratio appears to be most robust during subsolidus processes in the igneous systems hence probably should be the preferred ratio for analysing and understanding petrogenetic processes in granitic igneous rocks

a critical assessment of mollusk 18 o 16 o mg ca and 44 ca 40 ca ratios as proxies for cretaceous seawater temperature seasonality seasonal temperature fluctuations of tethyan coastal water are recorded in a pristine 80 my old rudist shell from turkey in order to critically assess factors other than seawater temperature that might have influenced the shell geochemical record three different paleo temperature proxies 18o mg ca and 44ca were applied in a qualitative manner all three proxies reflect the same cyclical trends and thus yield robust evidence for seasonal fluctuations in late cretaceous surficial seawater temperature this suggests the successful application of the new 44ca temperature proxy to fossil mollusk calcite the direct comparison of the three data sets however demonstrates that all proxies are fraught with problems similar to other studies 18o 16o ratios point to warmer summer temperature maxima than those in comparable costal settings today nevertheless the 18o 16o proxy is subject to environmental factors that might lead to an overestimation of peak temperatures moreover mg ca molar ratios are less sensitive to environmental factors but were strongly affected by the ion regulating capability of the rudist bivalve that responded to the low mg ca ratio of cretaceous seawater similarly uncertainties of the 44ca composition of cretaceous seawater and the complex bio calcification of mollusks presently limit the interpretation of 44ca values in terms of absolute seawater temperature the multiproxy approach applied here however documents that these limitations do not obscure the dominant patterns of seasonal sea surface temperature variations recorded in the biogeochemical rudist archive

metamict fergusonite y in a spessartine bearing granitic pegmatite from adamello italy abstract a granitic pegmatite associated with the monte bruffione granodiorite in the tertiary adamello massif italy consists primarily of albite potassium feldspar muscovite quartz and spessartine graphic intergrowths with quartz as accessory minerals the pegmatite contains magnetite pyrophanite monazite ce uraninite xenotime y zircon and fergusonite y this yttrium niobate mineral contains inclusions of th rich uraninite and is itself rich in uo 2 average 7 1 1 1 wt n 34 and tho 2 average 3 5 1 0 wt many fergusonite crystals display growth zoning characterized by a general increase towards the rim in the contents of y and rare earth elements at the expense of u and th irregular or patchy zoning as well as sector zoning are also observed in some of the crystals due to the alpha decay of the u and th fergusonite is metamict as documented by transmission electron microscopy tem and micro raman spectroscopy nevertheless the mineral could be identified as fergusonite y on the basis of a canonical discriminant analysis of its chemical composition and on the basis of the close similarity of its raman spectrum with that of a reference fergusonite the crystalline to metamict transformation was associated with macroscopic swelling as indicated by microfractures that are arranged radially around fergusonite inclusions in pyrophanite the tem data revealed that the amorphous fergusonite contains u rich nanocrystals 5 15 nm across which in most cases are distributed randomly and which probably nucleated after metamictization the tem investigations further revealed the ubiquitous presence of nano sized typically 5 25 nm across nearly circular features which exhibit a low diffraction contrast and which we interpret as nanopores we propose that these nanopores represent former bubbles of radiogenic helium the data presented here allowed us to determine that the critical amorphization dose of fergusonite is 0 97 10 16 alphas mg i e lower than that of other actinide rich oxide minerals e g pyrochlore the presence of the u rich nanocrystals indicates that fergusonite is able to retain actinides even when it is entirely metamict and even if it is surrounded by microfractures which represent potential fluid pathways this result suggests that fergusonite could be a phase suitable to be included in ceramics designed for the immobilization of high level nuclear waste

diagenetic stabilization of aragonite and low mg calcite ii stable isotopes in rudists abstract cretaceous rudists having thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of phreatic vadose meteoric diagenesis on their microstructural and isotopic attributes rudist skeletal components with preserved original mineralogy of aragonite and low mg calcite and with preserved microstructures have isotopic signatures analogous to holocene marine bivalves this similarity argues for a comparable isotopic composition of the cretaceous and holocene seawater as well as for a similar mode of incorporation of stable isotopes into their shells diagenetic stabilization of rudist shells appears to have been a two stage process with low mg calcite diagenetic calcite lmc dlmc and particularly aragonite diagenetic calcite a dlmc transformation as the first step and cementation as a later development the direct a dlmc mineralogical transformation calcitization results in initial depletion in 18o of 2 and the subsequent diagenetic precipitation of ferroan calcite spar causes depletion in 13c as well as an additional decrease in 18o the former due to introduction of organically derived co2 into the diagenetic aquifer in contrast 13o and 13c isotopic depletions in the originally lmc skeletal components are both related to the precipitation of the late diagenetic ferroan sparry calcite cement the earlier calcitization stage being of subordinate importance only

zigzag microstructure in rugose corals a possible indicator of relative seawater mg ca ratios low mg calcite lmc and high mg calcite hmc have been identified confidently as original biominerals in different rugose corals devonian tabulophyllum had a lmc skeleton whereas pennsylvanian lophophyllidium had a hmc skeleton zigzag microstructure a diagenetic microstructure in rugose corals may be related to early migration of mg2 ions during transformation of hmc into lmc therefore zigzag microstructure may indicate that the original mineral was hmc even in specimens that subsequently converted to lmc stratigraphically corals with zigzag microstructure are confined to the late paleozoic which is coincident with the aragonite sea of p a sandberg hence fluctuating mg ca ratios may have directly controlled oscillations in marine carbonate chemistry and the mineral composition of rugose corals so that hmc skeletons as indicated by zigzag microstructure formed during intervals with aragonite seas and lmc skeletons e g tabulophyllum formed during intervals with calcite seas

the major ion composition of cenozoic seawater the past 36 million years from fluid inclusions in marine halite fluid inclusions from ten cenozoic eocene miocene marine halites are used to quantify the major ion composition mg2 ca2 k na so42 and cl of seawater over the past 36 my criteria used to determine a seawater origin of the halites include 1 stratigraphic sedimentologic and paleontologic observations 2 br in halite 3 34s of sulfate minerals 4 87sr 86sr of carbonates and sulfates and 5 fluid inclusion brine compositions and evaporation paths which must overlap from geographically separated basins of the same age to confirm a global seawater chemical signal changes in the major ion chemistry of cenozoic seawater record the end of a systematic long term 150 my shift from the ca2 rich mg2 and so42 poor seawater of the mesozoic cacl2 seas to the mgso4 seas with higher mg2 and so42 ca2 of the cenozoic the major ion composition of cenozoic seawater is calculated for the eocene oligocene 36 34 ma serravallian tortonian 13 5 11 8 ma and the messinian 6 5 ma assuming chlorinity 565 mmolal salinity and the k concentration 11 mmolal are constant and the same as in modern seawater fluid inclusions from cenozoic marine halites show that the concentrations of mg2 and so42 have increased in seawater over the past 36 my and the concentration of ca2 has decreased mg2 concentrations increased from 36 mmolal in eocene oligocene seawater 36 34 ma to 55 mmolal in modern seawater the mg2 ca2 ratio of seawater has risen from 2 3 at the end of the eocene to 3 4 and 4 0 respectively at 13 5 to 11 8 ma and 6 to 5 ma and to 5 in modern seawater eocene oligocene seawater 36 34 ma has estimated ranges of so42 14 23 mmolal and ca2 11 20 mmolal if the ca2 so42 product is assumed to be the same as in modern seawater 300 mmolal2 eocene oligocene seawater had ca2 16 mmolal and so42 19 mmolal the same estimates of ca2 and so42 for serravallian tortonian seawater 13 5 11 8 ma are so42 19 27 mmolal and ca2 8 16 mmolal and so42 24 mmolal and ca2 13 mmolal if the ca2 so42 product is equal to that in modern seawater messinian seawater has an estimated range of so42 21 29 mmolal and ca2 7 15 mmolal with so42 26 mmolal and ca2 12 mmolal assuming the ca2 so42 product is equal to that in modern seawater regardless of the estimation procedure so42 shows progressively increasing concentrations from 36 ma to the present values which are the highest of the cenozoic

diagenesis of carbonate cements in permo triassic sandstones from the iberian range spain evidence from chemical composition and stable isotopes petrographic chemical and stable isotope investigations have been made on calcite dolomite and fe dolomite ankerite from permian triassic clastic sequences from the iberian range spain calcite and dolomite cements have precipitated before the fe dolomite ankerite calcite however has also formed by calcitization of dolomite due to uplift the negative 13cpdb values 9 51 to 2 13 in these carbonates suggest derivation of carbon from oxidation of organic matter in the early carbonates and from decarboxylation of organic matter in the late fe dolomite ankerite early diagenetic dolomitic cements have heavier 13c 3 54 higher mn mn fe and mn mn mg and lower fe fe mg ratios than later diagenetic dolomitic cements the latters are also characterized by lighter 18opdb 10 64 than the early cements due to increase in temperature and to pore water mineral reactions

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

middle cretaceous carbonate reservoirs fahud field and northwestern oman reservoir facies in fahud field and throughout northwestern oman are in shallow shelf carbonates of the middle cretaceous mishrif and mauddud formations interparticle porosity formed in the mishrif as sand aprons of lithoclast and skeletal grainstones surrounding fault block islands and less commonly in the mauddud as biostromes of rudist packstones moldic porosity after fine rudist debris is more common than interparticle porosity and occurs in thicker stratigraphic units interpreted to have formed locally in meteoric water lenses associated with islands and regionally during subaerial exposure associated with sea level lows

depositional diagenetic thermal and maturation histories of cretaceous mishrif formation fateh field dubai rudist reef associated limestones comprising the cretaceous mishrif formation are the major reservoirs in fateh field a giant oil field in offshore dubai in this study mishrif cores from four wells on the western flank of the field were examined to gain insights into the depositional diagenetic thermal and maturation histories of the mishrif formation in this area the wells lowest on the west flank contain relatively deep water lower fore reef facies bounded by two erosional unconformities the upper unconformity marks the laffan mishrif contact and extends over fateh field throughout the region in fateh field the lower intra mishrif unconformity has been identified only on the western flank but is probably present in other locations low on the fateh structure the identification of the lower unconformity indicates two cycles of mishrif sedimentation the cycles are related to deep seated salt movement and epeiric sea level changes fluid inclusion data maturation calculations and burial history modeling indicate that the timing of cementation by blocky calcite spar and oil migration were approximately synchronous and occurred during the oligocene to miocene

influences of temperature and mg ca ratio on caco3 precipitates from seawater the mg ca ratio at which the calcium carbonate mineral that has pseudohomogeneously precipitated from seawater changes from calcite to aragonite was experimentally determined as a function of temperature results indicate a dramatic change in the critical mg ca ratio over a relatively small temperature range for example in normal seawater with a mg ca of 5 1 the critical temperature is 6 3 c at a temperature of 25 c however mg ca must be less than 1 4 0 1 for calcite to form these data indicate that paleoclimatic conditions at the time of carbonate deposition must be considered when attempting to make inferences about variation in other factors such as paleo p co 2 p pressure and paleo mg ca ratios that may control carbonate mineral formation by abiotic processes however the inverse relation between inferred global paleoclimatic conditions and the dominant type of caco 3 polymorph being abiotically deposited i e warm conditions and low mg calcite versus cool conditions and aragonite suggest that substantial changes must have taken place in ocean chemistry over phanerozoic time

modelling the primary control of paleogeography on cretaceous climate the low thermal gradients and clement winters characterizing climates of the cretaceous period reveal that the climate system has modes of behaviour quite different from the present recent proxy data analyses suggest that some aspects of climate change within the cretaceous appear to be decoupled from co2 evolution at the geological time scale here we investigate the impact of paleogeography on the global climate with the climate model foam using a early mid and late cretaceous continental configuration we find that changes in geography from the early to mid to late cretaceous cause a large decrease of the seasonal cycle first order identified processes are the decreased continentality of the mid to high latitudes from the mid cretaceous and the increase of the latent heat transport into the winter hemisphere which induce a wetter and a cloudier atmosphere capable of diminishing the winter cooling of the continents owing to the modifications of the seasonal cycle in response to the tectonic forcing the equator to pole thermal gradient is reduced from the early to mid to late cretaceous we nevertheless still do not succeed in simulating warm enough polar temperatures and a definitive theory still waits for an integrated approach explicitly accounting for each factor influencing the thermal gradient ocean dynamics stratospheric clouds and vegetation our study also suggests a mechanism that can weaken the correlation between co2 and climate changes during the cretaceous as evolving geography from the early to late cretaceous through the response of the water cycle and the changes in the thermal gradient results in a 3 8 c global warming at a constant atmospheric co2 level this demonstrates that the paleogeography may affect the relation between pco2 and the climate history and consequently has to be accounted for when linking the atmospheric co2 evolution and the climate record at geological time scales

cenomanian turonian composite δ13c curve for western and central europe the role of organic and inorganic carbon fluxes abstract detailed 13 c stratigraphies have been published recently for several cenomanian turonian pelagic sections of southern england and the lower saxony basin of germany the observed changes in the 13 c record provide a useful tool for high resolution stratigraphic correlation and are used here to create a composite cenomanian turonian 13 c curve in a time related framework a best fit curve to 673 carbon isotope data is provided using the lowess regression scatterplot smoother the long term trend of the smoothed composite 13 c profile varies on time scales of 10 6 years and shows stable 13 c values through the lower cenomanian an increase in the middle and upper cenomanian with a major positive excursion around the cenomanian turonian boundary and a decrease through the lower and middle turonian short term fluctuations vary on time scales of 10 5 years and dominated the 13 c signal in the higher middle and upper turonian changes of the cenomanian turonian 13 c record have commonly been explained by variations in the organic carbon flux to the sedimentary reservoir in response to eustatic sea level change however mass balance consideration suggests also an influence of carbonate production and burial rate on the 13 c signal enhanced inorganic carbon burial increased the ratio of the inorganic to organic carbon fluxes and shifted the 13 c 12 c ratio to more negative values this pattern may be observed in the early and middle turonian 13 c long term record and correlates with the spatial expansion of pelagic carbonate deposits in epicontinental seas short term 13 c variations could be either a directly response to short term sea level changes reflecting local conditions in the european epicontinental sea or could represent changes in oceanic 12 c storage in response to the varying intensity of thermohaline circulation

geochemical perspectives on coral mineralization corals open an exceptional window into many phenomena of geological geochemical climatic and paleontological interest from the paleozoic to the present corals provide some of the finest high resolution archives of marine conditions corals are likewise exceptional for chronometric purposes and even the terrestrial 14c timescale has now been calibrated against coral 230th 234u corals also represent a testing ground for basic ideas about mineralogy and geochemistry the shapes sizes and organization of skeletal crystals have been attributed to factors as diverse as mineral supersaturation levels and organic mediation of crystal growth the coupling between calcification and photosynthesis in symbiotic corals is likewise attributed to everything from photosynthetic alkalinization of the water to efforts by the coral to prevent photosynthetic alkalinization corals also leave a significant geochemical imprint on the oceans their aragonite skeletons accept about 10 times more strontium than does calcite hence the proportion of marine aragonite precipitation affects the oceanic chemical balance biological carbonates represent the biosphere s largest carbon reservoir hence calcareous organisms affect the ocean s ph co2 content and ultimately global temperatures through the greenhouse gas connection finally corals present some geochemical puzzles for ecology and conservation how do symbiotic corals obtain nutrients in some of the most nutrient deficient parts of the planet are global geochemical changes partially responsible for the widespread declines in coral reefs during recent decades we will address many of these issues but will concentrate on coral skeletal structure and calcification mechanism these topics bear most directly on the biomineralization process and generally affect the choice of skeletal materials and analytical techniques used in geochemical investigations the coral reef is probably the planet s most spectacular biomineralization product these grand and complex ecosystems build on the accumulated skeletal debris of countless generations of organisms especially calcareous algae and symbiotic

stable isotope sclerochronology of rudist bivalves growth rates and late cretaceous seasonality the almost complete translation of shell accretion to vertical growth was a successful morphogenetic adaptation of rudist bivalves which replaced coral algal hydrozoan communities in most tethyan shallow marine environments during the cretaceous growth rates of rudist shells are therefore important in reconstructions of cretaceous shallow marine benthic communities carbon and oxygen isotopic compositions were analyzed in sclerochronological profiles through the shells of two late cretaceous rudist bivalves from greece and turkey values of 13 c vary between 0 8 and 2 2 in the hippuritid vaccinites ultimus and between 0 8 and 2 6 in the radiolitid gorjanovicia cf costata ranges in 18 o are 5 3 to 2 9 and 4 6 to 2 1 respectively a distinct cyclicity of 13 c and 18 o in both shells reflects late cretaceous seasonality and indicates annual vertical growth increments of 45 mm in v ultimus and 54 mm in gorjanovicia the concentrations of minor elements are similar to those of extant bivalves with low mg calcite shells

understanding biomineralization in the fossil record abstract biomineralization the formation of minerals by organisms is a key aspect in the understanding of the fossil record knowing how biominerals form and their properties is important in the correct use of fossils in geochemistry the understanding of evolution and in the interpretation of how geological events have influenced the fossil record throughout the phanerozoic the focus of this contribution rather than a conventional review on the status of this research field is on the importance of highlighting the traditional link between paleontology and biomineralization

compositional and morphological features of aragonite precipitated experimentally from seawater and biogenically by corals abstract the morphology and composition of abiogenic synthetic aragonites precipitated experimentally from seawater and the aragonite accreted by scleractinian corals were characterized at the micron and nano scale the synthetic aragonites precipitated from supersaturated seawater solutions as spherulites typically 20 100 m in diameter with aggregates of sub micron granular materials occupying their centers and elongate fibrous needles radiating out to the edge using sr isotope spikes the formation of the central granular material was shown to be associated with high fluid ph and saturation state whereas needle growth occurred at lower ph and saturation state the granular aggregates have significantly higher mg ca and ba ca ratios than the surrounding fibers two types of crystals are identified in the coral skeleton aggregates of sub micron granular material and bundles of elongate fibrous crystals that radiate out from the aggregates the granular materials are found in centers of calcification and in fine bands that transect the fiber bundles they have significantly higher mg ca and ba ca ratios than the surrounding fibers the observed relationship between seawater saturation state and crystal morphology and composition in the synthetic aragonites was used as a framework to interpret observations of the coral skeleton we propose that coral skeletal growth can be viewed as a cyclical process driven by changes in the saturation state of the coral s calcifying fluids when saturation state is high granular crystals precipitate at the tips of the existing skeletal elements forming the centers of calcification as the saturation state decreases aragonitic fibres grow in bundles that radiate out from the centers of calcification

microstructure of 24 1928 ma concordant monazites implications for geochronology and nuclear waste deposits the microstructure of monazite was studied using scanning electron microscopy sem electron microprobe analysis emp x ray diffraction patterns xrd and transmission electron microscopy tem four well characterized monazites were investigated having very different concordant u pb ages 24 to 1928 ma and up to 15wt tho2 and 0 94wt uo2 the sem and emp analyses of polished single crystal fragments reveal the absence of significant chemical zoning xrd and tem investigations show that the monazites are not metamict despite their old ages very high abundances of radionuclides and hence high time integrated radiation doses except for the youngest one the monazite crystals are composed of a mosaic of crystalline but slightly distorted domains this structure is responsible for the presence of 1 mottled diffraction contrasts on the tem and 2 a second structural phase b with very broad reflections in the xrd patterns older monazites receive higher self irradiation doses and hence they contain higher amounts of this b phase for the 1928 ma monazite xrd reveals only the broad reflections of phase b implying that the whole monazite was affected by radiation damage that resulted in total distortion of the lattice it is concluded that radiation damage in the form of amorphous domains does not accumulate in monazite because selfannealing heals the defects as they are produced by alpha decay damage the only memory of irradiation induced defects is the presence of distorted domains as the diffusion rate of pb in an undisturbed monazite lattice is extremely low pb loss due to volume diffusion out of the monazite lattice is virtually impossible this is considered as one reason why almost all monazites have concordant u th pb ages moreover as long term self irradiation effects are limited in monazite we consider this phase as a good candidate for the storage of high level nuclear waste under the aspect of its high resistance to irradiation

low temperature alteration of monazite fluid mediated coupled dissolution precipitation irradiation damage and disturbance of the u pb and th pb chronometers abstract low temperature alteration of monazite is documented in three centimeter sized monazite crystals from norway arendal madagascar ambato and sri lanka the three crystals have different chemical compositions especially in their u th y and pb contents and have 208 pb 232 th ages ranging from 491 to 900 ma optical microscope om scanning electron microscope sem and transmission electron microscope tem images and electron microprobe analyses epma show that all three preserve a similar patchy texture this texture is interpreted as resulting from an alteration reaction in which unaltered monazite mnz1 reacts to form a secondary th u y depleted high th u monazite mnz2 accompanied by thorite huttonite thsio 4 thorianite tho 2 and xenotime ypo 4 the proportions of which are dependent upon the initial composition of the monazite mnz1 images reveal variably intense internal fracturing with cracks filled with th rich fe rich phases monazite xenotime thermometry demonstrates that the pristine monazites mnz1 interacted with a low temperature fluid the alteration process is interpreted to follow a mechanism of fluid mediated coupled dissolution precipitation chemical dating with the electron microprobe shows no th u pb age differences between primary and secondary monazites except in the case of the ambato monazite in which altered domains yield older 750 ma apparent ages than the pristine mnz1 domains u pb and th pb isotope dating using la icp ms yields ages consistent with electron probe dates for pristine mnz1 zones however disturbance of these systems in the altered monazite domains leads to variable age results for these depending on sample in the case of sri lanka and arendal only 208 pb 232 th dates provide a reasonable estimate of the age of alteration which are constrained to be 450 and 864 ma respectively u pb systems are disturbed due to common pb contamination up to 40 and u fractionation relative to th during alteration responsible for depletion of u in altered monazites and increase of th u in contrast for the ambato monazite both the u pb and th pb systems were affected and yield inconsistent older dates for altered zones this is attributed to significant common pb contamination up to 80 which affects all pb isotopes and explains why electron probe ages are erroneous th u silicate contamination during measurement resulting from the presence of a numerous nano phases and nano fractures filled with th u silicates that are visible only under tem also contributes to the anomalously old ages for these disturbed mnz2 domains these results demonstrate the important role of radiation damage effects in particular swelling induced fracturing and the essential role of porosity and cracks which allow fluid charged with elements migration through monazite during low temperature alteration

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

stable isotope evidence for gradual environmental changes and species survivorship across the cretaceous tertiary boundary high resolution 13c and 18o records have been generated from analyses of the planktonic foraminiferal species heterohelix globulosa and the benthonic foraminiferal taxon lenticulina spp from 3 m of a cored section spanning the cretaceous tertiary k t boundary at brazos river texas these are the first stable isotope records across the k t boundary based on monospecific and monogeneric foraminiferal samples they show a gradual decrease in 13c values of about 2 5 permil beginning at the k t boundary as defined by the first appearance of tertiary planktonic foraminifera and continuing 17 20 cm above the boundary approximately 40 000 years later gradual 13c depletion contrasts with the sudden 13c drop at the k t boundary observed in many deep sea sections the surface to bottom 13c gradient decreased to less than zero approximately 25 000 30 000 years after the k t boundary and remained negative for at least the next 140 000 years concomitant with change in 13c values is a gradual decrease of about 2 5 permil in 18c values which has not been observed at other localities this 18o depletion suggests changes in temperature and or salinity in the earliest paleocene gulf of mexico no extinction of foraminiferal species is associated with the k t boundary or the onset of 18o and 13c depletions instead two phases of cretaceous species extinctions occur one extinction phase is below the k t boundary and below the tsunami bed of bourgeois et al 1988 and may be linked to sea level regression and environmental perturbations the second extinction phase coincides with the minimum in 13c and 18o values in the early danian zone p0 pla and appears directly related to environmental changes reflected in the isotopic record h globulosa which is commonly present in maastrichtian and danian sediments exhibits significantly lower 18o 16o and 13c 12c ratios in tertiary sediments relative to specimens from maastrichtian sediments demonstrating the survival of this important cretaceous taxon after the k t boundary event

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

the giant monazite crystals from manangotry madagascar abstract the manangotry area in the south east of madagascar is famous for its giant monazite crystals the studied occurrence is an outcrop near the manangotry pass were giant cm sized crystals have been found the crystals are embedded in biotitite levels also containing cm sized xenomorphic ilmenite and are associated with a 1 m thick layer of apatite besides giant crystals monazite is also present as abundant small mm sized grains the surrounding rocks are leucogranites and charnockites the monazite giant crystals are chemically homogeneous and thorium rich whereas small crystals tend to be heterogeneous both biotite and apatite are f rich temperature estimates from biotite and apatite yielded 750 to 800 c despite their high radioactivity the giant crystals preserve a high degree of crystallinity electron microprobe u th pb dating produced ages of 537 14 534 10 and 530 10 ma considered to be the age of the main monazite crystallization episode but some minor domains in small grains yielded 482 12 ma the enclosing biotites yielded 453 6 ma ar ar ages more than 98 of radiogenic helium have been retained in the studied monazite samples and kinetic experiments indicates the intrinsic diffusion parameters for high temperature to be ea 53 kcal mol and d0 3085 cm2 s the paragenesis monazite apatite ilmenite biotite is different from any other occurrences of larges monazite elsewhere based on the current data and literature the preferred genetic model for these giant monazites is crystallization from a high temperature fluorine rich fluid possibly originating from surrounding charnockites

scleractinian corals produce calcite and grow more slowly in artificial cretaceous seawater the mineralogies of most biotic and abiotic carbonates have alternated in synchroneity between the calcite hexagonal and aragonite orthorhombic polymorphs of caco3 throughout the phanerozoic eon these intervals of calcite and aragonite production or calcite seas and aragonite seas are thought to be caused primarily by secular variation in the molar magnesium calcium ratio of seawater mmg ca 2 5 aragonite 1 high mg calcite mmg ca 2 5 low mg calcite a ratio that has oscillated between 1 0 and 5 2 throughout the phanerozoic in laboratory experiments we show that three species of scleractinian corals which produce aragonite in modern seawater and which have flourished as important reef builders primarily during aragonite seas of the past began producing calcite in artificial seawater with an ambient mmg ca ratio below that of modern seawater 5 2 the corals produced progressively higher percentages of calcite and calcified at lower rates with further reduction of the ambient mmg ca ratio in artificial seawater of imputed late cretaceous composition mmg ca 5 1 0 which favors the precipitation of the calcite polymorph scleractinian corals produced skeletons containing 30 low mg calcite skeletal mmg ca 0 04 these results indicate that the skeletal mineral used by scleractinian corals is partially determined by seawater chemistry furthermore slow calcification rates resulting from the production of largely aragonitic skeletons in chemically unfavorable seawater mmg ca 2 probably contributed to the scleractinians diminished reef building role in the calcite seas of late cretaceous and early cenozoic time

middle cretaceous greenhouse hydrologic cycle of north america we present a paleolatitudinal precipitation reconstruction for the greenhouse setting of mid latitude north america based on the oxygen isotopic composition of sphaerosiderites found in middle cretaceous wetland paleosols our reconstructed middle cretaceous d 18 o values of precipitation are 4 less than values from comparable modern low elevation coastal settings free of monsoons the data fit a conceptual model in which the precipitation source for the eastern margin of the cretaceous western interior seaway of north america is an 18 o enriched oceanic coastal jet in this subtropical tropical setting midcretaceous precipitation rates are interpreted to range from 2500 to 4100 mm yr

chemical and isotope composition of the oilfield brines from mishrif formation southern iraq diagenesis and geothermometry abstract this paper focuses on the geochemical composition and isotope geochemistry of brines in the cenomanian turonian carbonate mishrif reservoir of southern iraq main dissolved constituents trace elements 2h and 18o 87sr 86sr mineral saturation indices and thermodynamic calculations were investigated in formation waters from the mishrif formation to obtain a better understanding of brine evolution and diagenetic effects over geological time previous published 11b data were also reinterpreted as a geothermometer tool the results are compared with previous published data for local oilfields and coeval formations in the arabian gulf the mishrif brine has a marine origin and is diagenetically modified to ca excess and na deficit formation waters are quartz supersaturated and are in equilibrium with chalcedony and calcite dolomite in the temperatures range of 50 75 c which is also confirmed by calcite water oxygen isotope fractionation and 11b geothermometer the potential role of clays in conditioning brine chemistry during diagenetic processes was highlighted by activity diagrams in particular their adsorption exchange effect on sodium could explain the lower temperature obtained by the na li geothermometer 42 6 c the 2h and 18o values show that oxygen isotope composition of the brines was isotopically more affected by interaction with limestone during diagenesis than seawater evaporation the main effect is an 18o enrichment on the brine starting from the smow value locally dilution by present day meteoric water was also detected rumaila south which is shifted towards the local meteoric water line the strontium isotope ratios range from 0 707713 to 0 707749 and correspond to a marine strontium of late cenomanian early maastrichtian age except for the majnoon sample which shows a more radiogenic value 0 708043 radiogenic strontium and gypsum and anhydride saturation indices of the majnoon sample could indicate the contribution of calcium and sulphate from the strontium rich sulphate minerals of the cambrian salt domes occurring in the oilfields of southern iraq the higher manganese concentration 4 mg l and the slightly higher temperature inferred by geothermometers up to 74 c in comparison with present day could indicate that the majnoon brine is a hot fluid probably related to a deeper structure such as the zagros foredeep fault

depositional sequences diagenesis and structural control of the albian to turonian carbonate platform systems in coastal fars sw iran abstract this study covers a 300 km long ne sw oriented transect including five outcrop sections and provides new biostratigraphic data and a sequence stratigraphic interpretation of the albian cenomanian and turonian sediments kazhdumi and sarvak formations present in coastal fars sw iran two different carbonate depositional systems are distinguished one for the albian and one for the cenomanian turonian during the albian eustatic control was the dominant factor influencing sedimentation while during the cenomanian and turonian large and small scale tectonics were dominant this resulted in significant thickness variations and local diagenetic overprint of the sequence boundaries regional correlations were established constrained by ammonite data as well as sedimentological and sequence stratigraphic considerations in the albian interval including the kazhdumi formation and re dated mauddud member three 3rd order sequences have been distinguished the depositional system consists of muddy carbonate ramps rich in orbitolinid benthic foraminifers which laterally interfinger with green marls albian deposits are present throughout the area and vary in thickness from 100 to 160 m subaerial exposure has only been observed on top of the albian 3 sequence top mauddud member in the upper part of the succession which is of cenomanian turonian age the depositional system changed to rudist rimmed carbonate platforms surrounding local organic rich intra shelf basins the thickness in this interval varies greatly from 0 to 300 m which was controlled by both large scale qatar fars high and local scale salt domes tectonic processes in this tectonically active setting three cenomanian and one turonian 3rd order sequences have been distinguished several sequence boundaries show evidences for long lasted subaerial exposures up to 13 ma with the local preservation of soil sequences and continental deposits the expression of these exposures varies laterally considerably and macroscopic evidences are sometimes lacking petrographic and c o stable isotope investigations supplement classic sedimentology to reveal the record of these exposures

phanerozoic trends in skeletal mineralogy driven by mass extinctions changes in ocean chemistry that favoured the precipitation of aragonite or calcite are thought to have influenced the skeletal mineralogy of marine calcifyers an investigation of the original skeletal mineralogy of large numbers of marine taxa suggests that the selective recovery of marine organisms from mass extinctions has a much greater influence on the overall percentage of aragonitic organisms than the mg ca ratio of the oceans marine calcifying organisms that produce sediments and build reefs generally have skeletons and shells that are composed of either aragonite or calcite long term changes in the estimated mg ca ratios of sea water tend to correspond to changes in the prevailing mineralogy of these creatures1 2 high mg ca ratios are expected to favour the spread of aragonitic organisms whereas calcitic taxa are thought to benefit from low mg ca ratios3 4 5 6 here we test these patterns throughout the phanerozoic eon and assess the relative impacts of changing ocean chemistry and mass extinctions on the evolutionary success of calcifying organisms we find that mass extinctions are more important in regulating long term patterns of skeletal mineralogy than the mg ca ratios of the global oceans furthermore selective recovery from mass extinctions is usually more important than selective extinction in driving the phanerozoic pattern of skeletal mineralogy but even in the recovery phase there is no clear connection between changes in the dominance of aragonite or calcite and the mg ca ratio of the oceans thus providing further evidence for the complexity of biotic recoveries7

stratigraphic architecture and fracture controlled dolomitization of the cretaceous khami and bangestan groups an outcrop case study zagros mountains iran this work has been carried out as part of a joint study between norsk hydro now statoil and nioc national iranian oil company

trapping of helium in nano bubbles in euxenite positive identification and implications abstract the y ree u th nb ta ti oxides like euxenite fergusonite pyrochlore zirconolite are known to contain nanometric spherical cavities or bubbles interpreted to contain radiogenic helium in situ analyses by scanning transmission electron microscopy stem coupled with electron energy loss spectroscopy eels inside nano bubbles from an euxenite crystal sampled in its host c 920 ma old pegmatite in norway deliver for the first time a positive identification of helium and an estimation of helium pressure in such bubbles the chemically unaltered euxenite crystal proves amorphous and homogeneously speckled with bubbles ranging from 5 to 68 nm in diameter around a log normal distribution centered at 19 nm the euxenite contains 9 87 wt uo 2 and 3 15 wt tho 2 it accumulated a theoretical alpha decay dose of 3 46 10 20 g i e 170 he nm 3 at a dose rate of 11 926 g s this corresponds to production of 0 23 wt he the density of helium inside the bubbles estimated from eels data ranges from 2 to 45 he nm 3 leading to a pressure of 8 to 500 mpa the proportion of produced helium trapped in bubbles is about 10 helium bubbles clearly influence helium diffusion they may contribute to the swelling of euxenite during amorphization and to the fracturing of the host rock our results suggest that dose dose rate and structural state seem to be important parameters for the nucleation growth and coalescence of helium bubbles but also demonstrate the crucial need of experimental studies to be able to develop a predictive model of the long term behavior of materials in response to helium irradiation furthermore chemical alteration of euxenite here materialized by fluid driven dissolution precipitation towards silica bearing euxenite removes the bubbles and mobilizes helium into the rock via cracks and grain boundaries it is then suggested that helium rich fluid released from such u th rich sources may percolate into surrounding rock units inducing perturbation of the u th he systematics of apatite and zircon in these units