diagenetic matrix in proterozoic graywackes from sweden abstract four diagenetic mechanisms of matrix formation were recognized in graywacke sandstones from the visingso group upper proterozoic southern sweden these mechanisms are 1 chemical alteration of detrital silicate minerals 2 authigenesis crystallization from pore solutions 3 pseudoplastic flow of soft argillaceous fragments forming pseudomatrix and 4 alteration of pseudomatrix either through fixation or leaching of cations compared to the previously published studies dealing with graywacke matrix the new contribution in the present study is 1 alteration of detrital unstable particles is shown to occur through dissolution and replacement by clay minerals and 2 the microprobe and x ray diffraction analyses scanning electron and petrographic microscopes were used together in the mineralogical and textural investigation

the geologic record of climatic change this paper reviews the principal results from paleoclimate studies and includes background material slanted toward climate modelers the inferred temperature history of the last 4 6 billion years indicates major changes in the components of the earth s climate system a secular change in global insolation receipt is due to a 20 30 increase in solar luminosity since the formation of the earth a co2 h2o greenhouse effect may have offset the lower luminosity during early earth history inferred fluctuations of global temperature have occurred over a broad range of time scales on time scales of 106 108 years paleogeographic factors e g continental drift and sea level changes have contributed significantly to temperature changes associated with transitions between nonglacial and glacial states preliminary modeling efforts indicate that additional factors e g co2 changes in atmospheric circulation must also be considered in order to explain the origin of nonglacial climates the origin of polar ice caps may result from ocean circulation changes that were caused by plate tectonic processes fluctuations of ice volume on a time scale of 10 105 years correlate with insolation variations caused by orbital perturbations feedback interactions within the land sea air ice system e g ocean circulation changes and bedrock dynamics have been responsible for a significant modulation of the orbital signal ice ages may be due to orbitally induced temperature changes superimposed on a global cooling of terrestrial origin

pyrite chlorite and pyrite biotite relations in sandstones abstract authigenic euhedral pyrite in feldspathic sandstones of the visingso group upper proterozoic southern sweden is observed to be closely associated with authigenic fine crystalline interstitial chlorite and or sand sized chlorite or biotite microprobe analyses revealed that chlorites which are accompanied by relatively large amounts 3 vol of pyrite are characterized by a lower fe fe mg ratio than chlorites with lesser amounts 0 5 vol of associated pyrite the lower fe fe mg ratio of the former chlorites might have resulted from subsequent substitution of fe 2 by mg 2 in an initially fe rich chlorite the released fe 2 would then react with sulfide ions in an anoxic sulfidic environment to form pyrite another alternative is that the chlorites with lower fe fe mg ratio were crystallized from solutions characterized by a higher activity of mg 2 than chlorites with higher fe fe mg ratio iron from the biotite grains became available due to diagenetic illitization kaolinization and or chloritization

methane origin and oxygen fugacity evolution of the baogutu reduced porphyry cu deposit in the west junggar terrain china most porphyry copper deposits worldwide contain magnetite hematite and anhydrite in equilibrium with hypogene copper iron sulfides chalcopyrite bornite and have fluid inclusions with co2 ch4 that are indicative of high fo2 in contrast the baogutu porphyry cu deposit in the west junggar terrain xinjiang china lacks hematite and anhydrite contains abundant pyrrhotite and ilmenite in equilibrium with copper iron sulfides chalcopyrite and has fluid inclusions with ch4 co2 that are indicative of low fo2 the mineralized intrusive phases at baogutu include the main stage diorite stock and minor late stage diorite porphyry dikes the main stage stock underwent fractional crystallization and country rock assimilation contamination and consists of dominant diorite and minor gabbro and tonalite porphyry the country rocks contain organic carbons 0 21 0 79 wt the 13cvpdb values of the whole rocks 23 1 to 25 8 in the wall rocks suggest a sedimentary organic carbon source the 13cvpdb values of ch4 28 2 to 36 0 and co2 6 8 to 20 0 in fluid inclusions require an organic source of external carbon and equilibration of their 13cco2 ch4 values 8 2 25 0 at elevated temperatures 294 830 c suggesting a significant contribution of thermogenic ch4 mineral composition data on the main stage intrusions such as clinopyroxene hornblende biotite magnetite ilmenite sphene apatite and pyrrhotite suggest that the primary magma at baogutu was oxidized and became reduced after emplacement by contamination with country rocks mineral compositions and fluid inclusion gas compositions suggest that the redox state of the system evolved from logfo2 fmq 1 in the magma stage to logfo2 fmq in the hydrothermal stage though oxidized magma was emplaced initially assimilation contamination of carbonaceous country rocks decreased its fo2 such that exsolved fluids contained abundant ch4 and deposited a reduced assemblage of minerals

deep circulation in the late cretaceous oxygen isotope paleotemperatures from inoceramus remains in d s d p cores abstract inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths a survey of all cretaceous sediments from deep sea drilling project legs 1 69 and 75 revealed over 500 inoceramus specimens at twenty sites of these 47 well preserved late cretaceous specimens from the south atlantic pacific and indian oceans were analyzed for oxygen and carbon isotopes the specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep sea habitat paleotemperatures ranging from 5 to 16 c show that late cretaceous oceans were significantly warmer than the present oceans the data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

diagenetic alteration of detrital biotite in proterozoic sedimentary rocks from sweden abstract the alteration of detrital biotites has been studied in two clastic proterozoic sedimentary sequences from southern and central sweden namely the visingso group and the dala sandstone respectively the results showed that the biotites are altered through replacement by clay minerals illite chlorite and less commonly kaolinite biotite may either be replaced pseudomorphically one biotite crystal by one clay mineral crystal or by fine crystalline clay minerals which merge into the interstitial clay matrix in reddish rocks biotite may be associated with pigmentary hematite and in greenish rocks with pyrite the variation in the two textural habits of biotite alteration i e pseudomorphic or fine crystalline is related to physico chemical properties of pore solution and nature of biotite particles

sem study of authigenic rutile anatase and brookite in proterozoic sandstones from sweden abstract scanning electron microscopic examinations revealed interstitial rutile anatase and brookite to be common in upper proterozoic sandstones of the visingso group in southern sweden anatase is observed as either single discrete crystals or as numerous crystals filling and lining pore space rutile and brookite occur predominantly as clusters of crystals within interstitial cements on detrital grains e g feldspar and quartz or as overgrowths on detrital and authigenic titanium oxides these titanium oxides have been formed diagenetically from percolating pore solutions rich in titanium ions the source of titanium ions is suggested to be mainly detrital fe ti oxides sphene and biotite grains

seasonal cycle variations on the supercontinent of pangaea the seasonal cycle of temperatures on pangaea early late permian configuration is simulated with a two dimensional energy balance climate model results indicate that the annual range of temperatures in the southern hemisphere of pangaea was considerably larger than any occurring at present maximum mean monthly summer temperatures are 38 c daytime highs probably exceed 45 c in some regions however summer temperatures in polar regions are considerably lower 0 5 c and are favorable for persistence of ice in eastern australia and glaciation in siberia conditions that receive some support from geologic data these simulations suggest that very high summer temperatures and a large annual range are major features of supercontinent environments such conditions may have significantly influenced the distribution of terrestrial permian biota our results are difficult to reconcile with postulated equable climates for some supercontinent configurations

simulated circulation of an idealized ocean for pangaean time an eight level dynamical ocean model driven by prescribed surface forcing wind stress temperature precipitation minus evaporation from a previously published pangaean time climate simulation is used to study possible features of ocean circulation temperature and salinity for the early mesozoic the simulations are sensitivity experiments rather than estimates of the actual circulation because many simplifying assumptions are made concerning the prescribed surface forcing and the ocean basin s shape and depth simulated features include relatively warm water in high latitudes warm deep water a westward flowing equatorial current across panthalassa and into the tethys sea poleward and eastward flowing currents along the tethys coasts and relatively vigorous meridional and longitudinal vertical overturning cells cool relatively fresh polar water combines with warm saline tethys water to produce the relatively warm deep water there are few geological estimates of early mesozoic pangaean time ocean circulation available for comparison with the simulated circulation

cretaceous climate a comparison of atmospheric simulations with the geologic record abstract atmospheric simulations using realistic cretaceous geography 100 million years ago suggest that paleography is an important factor governing the nature of the circulation the simulated cretaceous atmospheric circulations are markedly different both from the present day atmospheric circulation and from the classical hypotheses of a weaker circulation and poleward displacement of circulation features e g the subtropical high therefore they pose specific questions which can be tested against the geologic record aspects of the cretaceous simulations are verified in comparisons with the geologic record the simulations serve to guide areas of future paleoclimatic research and to formulate better the nature of the problem of warm equable climates

dynamics of anoxia abstract a simple steady state one dimensional advective diffusive model of the ocean s coupled carbon oxygen and phosphorous system is developed the model is an extension of wyrtki s 1962 model of the oxygen distribution the occurrence of anoxia requires two conditions 1 sufficiently high productivity and 2 sufficiently low oxygen concentration in the bottom water it is shown that anoxic layers are most likely to occur fairly high in the water column anoxic events may be associated with timesof vigorous thermohaline circulation in contrast to stagnation arguments often invoked the model results are used to interpret both modern and ancient oceanic anoxic events

packstones and floatstones ambiguous textures and origins in need of critical appraisal abstract the depositional textural classification of allochthonous limestones by dunham 1962 and its modifications by embry iii and klovan 1971 are widely used by carbonate petrologists during petrographic field studies and core examinations the origin and textures of packstones and floatstones used in this classification scheme need re appraisal towards their unified and unequivocal usage by carbonate petrologists in academia and the petroleum industry such usage will help avoiding inadequate interpretations of the depositional sequence stratigraphic or reservoir quality distribution models based on examination of jurassic cretaceous and holocene carbonate deposits from united arab emirates and oman it is suggested here that packstones should not be used to interpret energy of depositional environments because the majority are originally deposited as grainstones i e free of mud matrix thus sand and mud sized particles are expected to be hydraulically separated i e not deposited simultaneously therefore packstones might be originally grainstones that have incorporated variable amounts of mud matrix by various post depositional processes primarily bioturbation and or compaction deformation of peloids known as pseudomatrix dickinson 1970 we further observed that the 2 mm allochems in floatstones float in grainstones and packstones and not in mud wackestone matrix

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

pangaean climates megamonsoons of the megacontinent the climate for a highly idealized geographic representation of the megacontinent of pangaea corresponding to the period 250 200 m y ago is explored using a low resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth with a provision for sea ice formation and decay soil moisture is included as a predicted variable on the continent because there are large uncertainties about key factors that might influence the pangaean climate sensitivity experiments are used to examine the climate for two different mean elevations 0 and 1000 m two different snowcover prescriptions and two different levels of implied greenhouse heating and solar luminosity modern co2 concentration and modern solar luminosity fivefold increase in modern co2 concentration and a 1 decrease in modern solar luminosity in all of the experiments the large bipolar land masses of laurasia and gondwanaland joined near the equator in the west and separated by the tethys sea in the east exhibit extreme continentality with hot summers cold winters and large scale summer and winter monsoon circulations year round or seasonal aridity is simulated for all but the eastern coastal regions the tropical western coast and the regions poleward of 40 latitude the simulated climate of the idealized pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late permian and triassic however the model results serve mainly to indicate the importance of various climate forming factors geography topography heating detailed comparisons will require new experiments with better models and more accurate geologic boundary conditions

geochemistry and petrology of recycled orogen derived sediments a case study from upper precambrian siliciclastic rocks of the central iberian zone iberian massif spain abstract two areas of upper precambrian siliciclastic rocks separated from each other by 150 km were selected in the central iberian zone ciz for a petrological and geochemical study the petrology of the coarser grained rocks indicates the absence or scarcity of igneous clasts the presence of extrabasinal and intrabasinal clasts and homogeneous features of sandstones ranging from very fine to fine grained the modal data of these rocks plot close to the qt l and qm lt sides of qtfl and qmflt triangular diagrams suggesting provenance from a recycled orogen the geochemical data on the shales and sandstones from the two areas studied are very uniform both groups of rock show similar ranges of relevant major element ratios such as al 2 o 3 tio 2 17 46 21 51 17 46 21 34 for shale and sandstone respectively al 2 o 3 feo t 2 40 3 79 2 18 3 33 and feo t feo t mgo 0 71 0 77 0 68 0 76 together with parallel average rare earth element ree patterns and similar values for some key trace element ratios la th th yb th u zr hf sm nd and cr sc other trace element ratios la sc th sc cr th and cr zr are uniform in the shales group and also in the sandstones group although minor differences become apparent when both groups are compared these differences are probably related to the quartz dilution effect affecting the relative abundance of phyllosilicates in these rocks and indirectly the sc and cr contents given their covariations with al2o3 the zr yb zr y and zr th ratios of the shales are uniform the sandstones show higher and more variable values and there is no correlation between zr abundance and any of these ratios in the shales or sandstones together with the parallel ree patterns shown by both groups of rock these results suggest the absence of heavy mineral fractionation during the transport of detrital material and or the relative importance of other minerals probably phyllosilicates in the control of yb y and th abundances apparently all the groups of rocks show a remarkable geochemical homogeneity despite the distance between the sampling areas thus the petrological and chemical data are consistent and point to a very extensive homogeneous and stable source region as the most plausible contributor to the upper precambrian siliciclastic rocks in the ciz the possible relationship between this zone and n gondwana is also discussed

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

experimental nucleation and growth of smectite and chlorite coatings on clean feldspar and quartz grain surfaces abstract laboratory experiments were performed to investigate high temperature 100 150 c authigenic formation of clay coatings smectites chlorites on clean feldspar and quartz surfaces artificial formation waters were used with mg concentrations in the range of north sea brines experiments were run for 21 50 days in brines composed of magnesium chloride and sodium carbonate adjusted to circum neutral ph the experiments suggest that the silica activity is the main factor determining if grain coating smectites or chlorite form the clay minerals form easily on both clean quartz and feldspar surfaces but chlorite coatings were formed only on feldspar surfaces while smectite coatings were formed on both feldspar and quartz the chlorite morphology varies between honeycomb edge to face and rosette patterns while all smectite formed with honeycomb like textures the clay coatings produced in this study are morphologically similar to naturally occurring diagenetic clay minerals in natural sediments and sedimentary rocks the formation of clay coatings is promoted by pre existing clay drapings on mineral grains the growth substrates used in this study were not coated with such a natural precursor materials this suggests that the nucleation of clay coatings in nature may be possible on clean quartz and feldspar surfaces but pre existing clay minerals may impact the allowed levels of supersaturations and thereby the formation of the grain coating phases

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

causes of anoxia in the world ocean we examine the hypothesis that global scale episodes of anoxia such as occurred in the cretaceous are due to

atmospheric circulation during warm geologic periods is the equator to pole surface temperature gradient the controlling factor paleoclimatologists have hypothesized that the equator to pole surface temperature gradient is a dominant control on the paleocirculation of the oceans and the atmosphere atmospheric simulations using realistic cretaceous 100 m y ago geography are used to examine quantitatively the relationships between paleogeography surface temperature gradients and the nature of the atmospheric circulation these results raise questions concerning the classical theories and interpretations of warm paleoclimates and suggest that paleogeography is an important factor governing the nature of the circulation