palustrine carbonates and the florida everglades towards an exposure index for the fresh water environment abstract palustrine carbonates are shallow fresh water deposits showing evidence of subaqueous deposition and subaerial exposure these facies are common in the geological record the intensity of modification is highly variable depending on the climate and the length of emergence palustrine limestones have previously been interpreted as marginal lacustrine deposits from fluctuating low salinity carbonate lakes but several problems remain with existing facies models 1 palustrine carbonates possess a lacustrine biota but commonly display fabrics similar to those of calcretes and peritidal carbonates 2 the co occurrence of calcrete horizons and karst like cavities is somewhat unusual and appears to indicate contemporaneous carbonate precipitation and dissolution in the vadose zone 3 the dominance of gray colors indicates water saturation apparently inconsistent with the evidence for strong desiccation overprint 4 profundal lake deposits are generally absent from palustrine sequences and sublittoral facies commonly make up only a small proportion of total thicknesses 5 no good modern analogue has been identified for the palustrine environment analogy with the florida everglades suggests a re interpretation of palustrine limestones not as pedogenically modified lake margin facies but as the deposits of extensive very shallow carbonate marshes the distribution of environments in the everglades is determined by the local hydrology reflecting the control of seasonal water level fluctuations and topography climate and topography were the main controls on deposition of ancient palustrine carbonates as in peritidal sequences aggradational cycles are capped by a range of lithologies evaporites desiccation and microkarst breccias calcretes lignite or coal horizons etc permitting interpretation of the climate careful analysis of lateral facies variations may permit reconstruction of subtle topography consideration of the florida everglades as a modern analogue for the palustrine environment has suggested the development of an exposure index for fresh water carbonates

the deep structure of the north anatolian fault zone abstract multi scale full waveform inversion of complete continental and regional scale seismograms reveals the crustal and upper mantle signature of the north anatolian fault zone which shapes the neotectonics of turkey and the eastern mediterranean within the crust the fault zone is mostly bounded by several high velocity blocks suggesting that it developed along the edges of continental fragments with high rigidity below the crust the surface expression of the eastern and central parts of the north anatolian fault zone correlate with a pronounced low velocity band that extends laterally over 600 km around 100 km depth the low velocity band merges into the shallow anatolian asthenosphere thereby providing a link to the kirka afyon isparta volcanic field and the central anatolian volcanics we interpret the low velocity band beneath the north anatolian fault zone as the upper mantle expression of the tethyan sutures that formed 60 15 ma ago as a result of africa eurasian convergence the structurally weak suture facilitated the formation of the younger less than 10 ma crustal fault zone in this sense the north anatolian fault zone is not only a crustal feature but a narrow zone of weakness that extends into the upper mantle

constraints on palaeoenvironments in the lower cretaceous wealden of southern england from the geochemistry of sphaerosiderites abstract sphaerosiderites are millimetre scale concretions of feco 3 that form predominantly in waterlogged environments and are of use in palaeoenvironmental and palaeohydrological studies we present petrographic elemental and stable isotopic 13 c 18 o data from sphaerosiderites collected from the lower cretaceous wealden sediments of southern england the sphaerosiderites are composed of very pure feco 3 with only small amounts of ca mg and mn present suggesting that they are well preserved and were precipitated from fresh groundwater 13 c values display a relatively large range from about 5 to 30 vpdb in contrast 18 o values are relatively invariant 1 0 83 with an average of 3 01 vpdb the relationship between carbon and oxygen suggests that the sphaerosiderites faithfully record palaeo groundwater 18 o likely 18 o values for groundwater were calculated using a published experimentally derived siderite water fractionation equation and plausible assumed values for palaeotemperature the average estimate was 4 9 smow the wealden sphaerosiderite oxygen isotope values are comparable with other early cretaceous data from similar palaeolatitudes but lower than estimated holocene values for equivalent latitudes this observation may indicate greater rainfall at 30 n during the cretaceous relative to the holocene and also suggests relative stability of palaeoclimatic conditions during the early cretaceous at this palaeolatitude

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

long term seismicity of istanbul and of the marmara sea region we examine the long term seismicity of the marmara sea region in turkey over a period of twenty centuries to attempt to answer two questions 1 how well recorded in history is the earthquake activity of this region and 2 does seismicity over this long period of time differ from that over the present century we study this densely populated and fast developing region because it is one of the most tectonically active regions on the continents that appears today to be relatively quiescent

periodicity of magnetic intensities in magnetic anomaly profiles the cretaceous of the central pacific summary spectral analyses of long magnetic anomaly profiles of cretaceous age in the phoenix and hawaiian lineations within the pacific basin show two to five non harmonic wavelength peaks with probabilities 90 per cent within the range of several tens to hundreds of kilometres for each profile for each profile with four peak wavelengths their ratios correlate strongly r 0 98 with the ratios for the earth s orbital eccentricity periodicities for this time and hence the profile peaks necessarily correlate with each other these observations suggest that the magnetic anomaly signal is influenced by the earth s changing orbital parameters probably through their influence on the internal geomagnetic field this implies that assumptions usually made to convert the magnetic signal to the magnetization of the oceanic crust may be suspect the observations if confirmed indicate that orbital periodicities can assist in improving the age calibration of the global polarity timescale and that the predicted orbital behaviour of the earth is confirmed for the last 150 ma

carbon oxygen and sulphur isotope variations in concretions from the upper lias of n e england carbon oxygen and sulphur isotope data for transects across two pyrite bearmg carbonate concretions and their host sediments from the upper lias of n e england show symmetrical zonation 13cpdb values of the calcite cement 12 9 to 15 4 indicate that most of it originated from organic matter by bacterial reduction of sulphate augmented with marine and to a lesser extent fermentation derived carbonate organic carbon 13cpdb 26 1 to 37 0 reflects the admixture of allochtho nous terrestrial organic matter with marine material and the selective preservation of isotopically light organic material through microbiological degradation two phases of pyrite are present in each concretion the earlier framboidal pyrite formed throughout the sediment prior to concretionary growth and has 34scd values of 22 to 26 indicating formation by open system sulphate reduction the later euhedral phase is more abundant and reaches values of 2 5 to 5 5 at concretion margins this phase of sulphate reduction provided the carbonate source for concretionary growth and occurred in a partially closed system the 13c and 34s data are consistent with mineralogical and chemical evidence which suggest that both concretions formed close to the sediment surface the 18o values of the calcite in one concretion 18opdb 2 3 to 4 8 indicate precipitation in pore waters whose temperature and isotopic composition was close to that of overlying seawater the other concretion is isotopically much lighter 18opdb 8 9 to 9 9 and large 18o differences between concretions in closely spaced horizons imply that local factors control the isotopic composition of pore waters

origin of ultramafic hosted magnesite on margarita island venezuela ultramafic hosted deposits of magnesite mgco3 have been studied on margarita island venezuela to elucidate the source of carbon and conditions of formation for this type of ore petrographic mineralogic and 18o data indicate that magnesite precipitated on margarita in near surface environments at low p and t 13c ranges from 9 to 16 pdb within the magnesite and 8 to 10 pdb within some calcite and dolomite elsewhere on the island the isotopically light dolomite fills karst and the calcite occurs as stock work veins which resemble the magnesite deposits these carbon isotopic ratios are consistent with a deep seated source rather than an overlying source from a zone of surficial weathering however there is not much enrichment of precious metals and no enrichment of heavy rare earth elements as would be expected if the carbon had migrated upward as aqueous carbonate ions the carbon probably has risen as a gaseous mixture of co2 and ch4 which partially dissolved in near surface water before leaching cations and precipitating as magnesite and other carbonates the process probably is ongoing given regional exhalation of carbonaceous gases

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

cyclic geomagnetic changes in mid cretaceous rhythmites italy magnetic secular variation is recorded as a quasi rhythmical process of uncertain origin rhythmic changes recorded in the scisti a fucoidi in the central apennines of italy pelagic sediments of mid cretaceous late albian age show strong correspondence to patterns of orbital variation in the same strata cyclic magnetic variations are found with peaks in the same range 105 40 26 19 kyr these results appear to support earlier suggestions that secular variations may be related to these astronomical patterns

paleogene stable isotope events the oxygen isotope record in paleogene benthic foraminifera shows that at the base of the paleogene the ocean deep waters had a temperature of about 10 c rising to about 12 c at the base of the eocene and cooling between 51 ma and 49 ma to about 9 c the most dramatic event occurred just after the eocene oligocene boundary at about 35 8 ma when ocean deep waters cooled by several degrees within 104 105 yr probably in association with temporary glaciation in the antarctic region another more intense glacial event in antarctica may have occurred later in the oligocene at about 31 ma and a third near the top of the oligocene at 24 ma in the marine carbon isotope record a very rapid negative excursion occurred precisely at the cretaceous tertiary boundary a recovery to unusually positive values in the late paleocene was followed by a second negative excursion close to the paleocene eocene boundary that was even more extreme in magnitude although it was not as rapid these major carbon isotope events permit very accurate stratigraphic correlation there are many other smaller features in the carbon isotope record that will also prove useful for this purpose

orbital forcing and sedimentary sequences abstract the variation of eccentricity is connected with the most celebrated attempts to determine a limited portion of geologic time in the elaboration of the theory of the ice age that bears his name croll correlated two important epochs of glaciation with epochs of eccentricity computed to have occurred 100 000 and 210 000 years ago as the analysis of the glacial history progresses these correlations will eventually be established or disproved and should they be established it is possible that similar connections may be made between events far more remote gilbert 1900 p 15 16 but the precessional motion pulses steadily on through the ages like the swing of a frictionless pendulum its throb may or may not be caught by the geological process which obtains in a particular province and in a particular era but whenever the conditions are favorable and the connection is made the record should reflect the persistence and the regularity of the inciting rhythm gilbert 1900 p 18

geological evolution of the late mesozoic continental margin of northwestern anatolia abstract the armutlu peninsula is a composite tectonic entity made up of sections of the sakarya continent the rhodope pontide fragment and an ophiolite these were assembled following a continental collision between gondwanaland and laurasia during the late cretaceous the northern margin of the sakarya continent underwent progressively increasing deformation prior to and during the advancing collision due to continued convergence between the two continents initially the leading edge of the continent subsided under the load of an approaching ophiolitic slab following this a north directed thrusting and folding occurred during the turonian progressive elimination and eventual closure of the ocean preceded the thrusting of northerly situated collisiondashinduced nappe packages over the leading edge of the sakarya continent the nappe laden edge of the continental margin then collapsed and steadily subsided under the heavy load of the ophiolitic slab and the northern continental fragment consequently the nappe packages and the ophiolite were collectively metamorphosed during the coniaciandashsantonian interval during the subsidence the main body of the sakarya continent partially detached from its collapsed edge along a fault zone and thus suffered an independent but less severe deformation which lasted until the uplift of the collapsed edge in the campanian from the late campanian onward throughout later orogenic stages the metamorphic and nondashmetamorphic units amalgamated into a single tectonic entity forming a basement for younger cover rocks

tectonic evolution of the marmara sea and its surroundings abstract the basins in the marmara sea are the products of a superimposed evolutionary history defined by two different aged fault systems the early miocene early pliocene thrace eskisehir fault zone and its branches and the late pliocene recent north anatolian fault and its branches the thrace eskisehir fault and its westward branching secondary fault systems define the early neotectonic signature in the region the late neotectonic period started at the end of the early pliocene when the north anatolian fault divided the thrace eskisehir fault into four parts during the late neotectonic period the north anatolian fault extended westward as a number of splays by joining with the ganos bandirma behramkale and manyas edremit fault zones the branches of the north anatolian fault zone nafz caused the evolution of a number of basins which differ in character depending on the trend and past characteristics of the older branches that became connected since the northern branch of the north anatolian fault is connected to the n80 e trending ganos fault zone gfz in the west a single buried fault has developed in the marmara sea causing the well known troughs and ridges superimposed onto the negative flower structure formed by the gfz in the early neotectonic period the middle strand which extends from iznik lake to bandirma is oriented east west up to the n60 e trending bandirma behramkale fault zone then turns southward in the vicinity of bandirma forming a region dominated by compressional tectonics this bending caused n30 e trending tension in addition to the strike slip motion between the eastern part of gemlik bay and bandirma bay the southern branch of the nafz on the other hand produced three pull apart basins with different characteristics along the yenisehir bursa and manyas segments the southern branch of the nafz connected to the manyas edremit fault zone which is oriented n45 e to the south of manyas and the associated bending and rotation caused a n15 e trending extension in addition to the strike slip regime between manyas and uluabat the branches of north anatolian fault cut through the thrace eskisehir fault at three places the east marmara sea region in gemlik bay and to the east of bursa giving lateral offsets of 58 59 7 8 and 10 11 km respectively the cumulative motion is 75 78 km corresponding to the total lateral offset of the north anatolian fault in the region the correlation of these offsets with global positioning system slip vectors and with stratigraphic results implies that the north anatolian fault reached into the marmara sea region about 3 5 million yr ago tectonic processes forming the marmara sea and its environs were initiated by the thrace eskisehir fault and its splays have been most recently controlled by the north anatolian fault and its splays during the last 3 5 million yr

quantitative extraction and analysis of carriers of magnetization in sediments we have applied an integrated procedure for quantitative magnetic mineral extraction based on the separation method of petersen von dobeneck vali 1986 to a range of sediment types to examine the efficiency and representative nature of the extraction process carriers of magnetization have been identified by rock magnetic measurements microscopy and x ray diffraction quantification of the extraction efficiencies is achieved by before and after extraction rock magnetic measurements susceptibility anhysteretic and isothermal remanences these magnetic measurements show that our modified extraction method extracts large proportions of the magnetization carriers in a range of sediment types e g over 75 per cent for magnetite dominated sediments the extraction efficiency is dependent on the sample magnetic mineralogy and whether the magnetic grains occur as discrete grains or as inclusions within host grains susceptibility extraction efficiencies are strongly dependent on whether the susceptibility is of paramagnetic or ferrimagnetic origin the amount of material recovered in the extract shows some inverse correlation with the density of the sediment suspension used during extraction in terms of the mineralogies extracted we identify a diverse and complex range of mineral assemblages all sizes of discrete grains of magnetite are extracted including single domain and superparamagnetic grains and chains of bacterial magnetite other commonly extracted iron and titanium oxides are haematite and ilmenite ferrimagnetic chromites and sulphides were also obtained from some samples considerable amounts of quartz and feldspar are extracted due to the presence of magnetic inclusions within these diamagnetic host grains in the deep sea sediments we examined feldspars constitute a large proportion of the extracts but are significantly less abundant in other sediments where quartz is dominant a wide variety of paramagnetic minerals was identified in the extracts including pyroxenes amphiboles chlorites micas mg cr spinels garnets ti oxides apatites tourmaline and zircon many of which contain ferrimagnetic inclusions possibly less than 0 1 m in grain size dissolution of ultrafine grains of magnetite during pre extraction carbonate dissolution as suggested by sun jackson 1994 does not occur in our samples

septarian concretions from the oxford clay jurassic england uk involvement of original marine and multiple external pore fluids septarian concretions occur at several horizons within the oxford clay formation a marine mudstone containing pristine aragonite and immature biomarker molecules they record the passage of at least four generations of pore fluids the first of marine origin and the last still present in cavities concretion bodies formed cracked and calcite and pyrite precipitated in and around the cracks within the sulphate reduction zone as demonstrated by c o s and sr isotopic composition pore fluid 1 before major compaction sandstone dykes were intruded locally and baryte precipitated followed by coarse calcite cements with isotopically light oxygen and radiogenic strontium indicating the introduction of meteoric derived water pore fluid 2 later coarse celestine within concretions has distinct sulphur isotopic composition and requires a further geographically restricted water source pore fluid 3 celestine bearing concretions contain water in tight cavities whose isotopic composition is close to that of modern precipitation its chemistry shows that it is equilibrating with pre existing minerals implying a relatively recent origin pore fluid 4 the mineralogy of the oxford clay concretions shows that complex results can follow from a simple burial and uplift history and that multiple generations of pore fluids can pass through a low permeability clay

pore water evolution during sediment burial from isotopic and mineral chemistry of calcite dolomite and siderite concretions abstract coal measures often contain concretions segregations of diagenetic minerals originally formed within unconsolidated sediments three different types calcite pyrite dolomite pyrite and siderite occurring spatially quite close together in the central pennine region of england vary widely in carbon isotope composition 10 35 13c 21 49 and in major cation chemistry ca mg fe mn within some siderite concretions very high mn fe ratios were found in central subsamples these were also most enriched in 13c the fe mg ratio decreases systematically from centre to edge early shallow to deeper later precipitation the calcite pyrite and dolomite pyrite concretions developed completely prior to significant burial both have high mn fe ratios but negative 13c values calcite 21 49 dolomite 8 67 to 10 48 all of these patterns can be equated precisely with theories of pore water evolution developed on the basis of geochemical investigations of modem sediments microbial processes sulphate reduction methanogenesis contributed significantly as did thermal decarboxylation to siderite precipitated at considerable burial depth mn iv and fe iii acted differentially as oxidants producing co2 and increasing alkalinity the interplay of fresh and marine depositional waters is seen most obviously in the presence or absence of sulphate reduction this controlled mineral type iron sulphide or carbonate as well as isotopic and mineral chemistry

constraints on the development of secondary porosity in the subsurface re evaluation of processes abstract secondary porosity formed by the dissolution of grains and cements is of great economic importance in both clastic and carbonate reservoirs a review of the commonly proposed mechanisms for the production of secondary porosity indicates that meteoric water penetration and mixing corrosion may be able to create significant volumes of secondary porosity in the shallow subsurface leaching by acidic fluids generated by solution of co 2 or monocarboxylic acids both derived during the thermal maturation of organic matter or by acidic fluids created by clay mineral reactions in shales are the most commonly proposed mechanisms by which secondary porosity is said to form in the deep subsurface however these mechanisms suffer from great difficulties in producing significant volumes of secondary porosity once mass balance and fluid migration problems are taken into account it is highly likely that the correct mechanism for the creation of economically significant amounts of secondary porosity in the deep subsurface is yet to be found

multidisciplinary research on fault activity in the western part of the north anatolian fault zone abstract westward migration of large earthquakes along the north anatolian fault zone seems to have been suspended after the 1967 mudurnu valley earthquake which may imply the formation of a seismic gap however the westward extension of the north anatolian fault zone has not been clearly defined two branches have been proposed but which one of them is the true extension is a matter of controversy in this paper we review some of the results which we have obtained so far from field work in order to derive some basic information as to the characteristic features of the respective branches the northern branch which we call the izmit sapanca fault zone is characterized by a wide graben like structure in the deformation zone however the topography corresponding to folding prevails which implies compressional deformation in late quaternary the southern branch which we call the iznik mekece fault is a simple continuous strand and is displaced right laterally there also exist holocene offset features indicating that strike slip faulting has been dominant temporary seismic observations were made twice for one month in 1986 and for two months in 1988 during these two observation periods no significant seismic activity was found in the vicinity of the iznik mekece fault whereas many small earthquakes occurring at the izmit sapanca fault zone were recorded although the observation period is rather short we conclude that current seismic activity at the iznik mekece fault is very low in view of some geological evidence showing the past activity of this fault we interpret low seismic activity as indicating that seismicity is currently at the stage of quiescence we attempted to estimate recurrence intervals of large earthquakes at the iznik mekece fault by excavating trenches at two locations we carefully selected trench sites but they were not good enough to provide crucial information the only result is that the latest earthquake at the eastern portion of the iznik mekece fault must have taken place 200 500 years b p trenching was also attempted at a location where the surface rupture associated with the 1967 mudurnu valley earthquake is clearly recognized we found evidence showing the last two faulting events the most marked feature is extensive magnetic anomalies along the iznik mekece fault detailed features of the observed anomalies indicate that they are closely related to the fault structure in particular weak magnetization zones are found to correspond to fractured zones these magnetic anomalies can be interpreted in terms of dyke like structures similar fault related anomalies have been found in the distributions of electric potential and radon concentration in soil gas these anomalies provide important information as to a strategy for continuous measurements fault related anomalies should be taken into consideration when an effective way is pursued for detecting anomalous changes prior to faulting

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

early diagenesis and its relationship to depositional environment and relative sea level fluctuations upper cretaceous marshybank formation alberta and british columbia early diagenesis of the upper cretaceous late coniacian to early santonian marshybank formation was controlled by depositional environment composition of depositional water fe and organic content of the sediment sedimentation rate proximity to the shoreline and influx of meteoric water related to relative sea level fall five depositional environments each characterized by a distinct early diagenetic mineral assemblage have been recognized offshore shelf sediments that were deposited in a dysaerobic environment are characterized by abundant framboidal pyrite and rare septarian concretions composed of early calcite and siderite intense sulphate reduction promoted by the dysaerobic depositional water was the primary influence on early diagenesis offshore shelf sediments deposited under aerobic conditions are characterized by abundant concretions composed of two generations of siderite s1 and s2 in this environment methanogenesis rather than sulphate reduction was more important early diagenesis of the inner shelf sands was generally limited however in sands deposited proximal to the shoreline mixing of marine and meteoric waters promoted crystallization of fe rich chlorite and siderite the shoreface was characterized by dissolution of detrital minerals in the upper portion and precipitation of kaolinite or illite smectite in the lower portion in the coastal plain environment brackish water and early reducing conditions resulted in formation of abundant euhedral pyrite ankerite rather than siderite is the typical early diagenetic carbonate the 18o values of the earliest cements i e early calcite siderite s1 inner shelf siderite indicate crystallization from a low 18o marine derived porewater assuming crystallization at 25 c a 18o value of about 7 smow can be estimated for the seaway during marshybank formation time similar calculations for the overlying dowling member puskwaskau formation suggest that the 18o value of the seaway increased to about 4 smow consistent with its transgressive nature very low 18o values are exhibited by siderite s2 these results indicate crystallization during intermediate diagenesis 60 c from meteoric water 15 smow that entered the marshybank formation during sea level lowstand

calcite cementation during bacterial manganese iron and sulphate reduction in jurassic shallow marine carbonates faunally restricted argillaceous wackestones from the middle jurassic of eastern england contain evidence of early diagenetic skeletal aragonite dissolution and stabilization of the carbonate matrix closely followed by precipitation of zoned calcite cements and precipitation of pyrite distinctive cathodoluminescence and trace element trends through the authigenic calcites their negative 13c compositions and the location of pyrite in the paragenetic sequence indicate that calcite precipitation took place during sequential bacterial mn fe and sulphate reduction calcite 18o values are compatible with cementation from essentially marine pore fluids although compositions vary owing to minor contamination with 18o depleted late cements mg and sr concentrations in the calcites are lower than those in recent marine calcite cements this may be a result of kinetic factors associated with the shallow burial cementation microenvironments bicarbonate for sustained precipitation of the authigenic calcites was derived largely from aragonite remobilization augmented by that produced through anaerobic organic matter oxidation in the metal and sulphate reduction environments aragonite dissolution is thought to have been induced by acidity generated during aerobic bacterial oxidation of organic matter distinction of post oxic metal reduction and anoxic sulphate reduction diagenetic environments in modern carbonate sediments is uncommon outside pelagic settings and early bacterially mediated diagenesis in modern platform carbonates is associated with extensive carbonate dissolution high detrital fe contents of the jurassic sediments and their restricted depositional environment were probably the critical factors promoting early cementation these precipitates constitute a unique example of calcite authigenesis in shallow water limestones during bacterial mn and fe reduction

magnetotelluric imaging of the creeping segment of the san andreas fault near hollister 1 fluids may play a significant role in the earthquake rupture process since fluids can dramatically change the electrical resistivity of crustal rocks electromagnetic exploration methods can image in situ fault zone fluids magnetotelluric mt data has been collected on segments of the san andreas fault saf in central california exhibiting a range of seismic behavior from locked to creeping this paper describes mt data from the creeping segment of the saf near hollister california inversion models image a zone of enhanced conductivity beneath the surface trace of the saf that has similar geometry and greater depth extent than the fault zone conductor at parkfield comparison with geologic and seismic tomographic studies show this zone is bounded by the san andreas and calaveras faults and coincident with a zone of low seismic p wave velocities combined with previous mt studies this indicates a correlation between seismicity and the presence of fault zone fluids

lacustrine carbonates and pedogenesis sedimentology and origin of palustrine deposits from the early cretaceous rupelo formation w cameros basin n spain the berriasian rupelo formation of the w cameros basin consists of a 2 200 m thickness of marginal and open lacustrine carbonate and associated deposits open lacustrine facies contain a non marine biota with abundant charophytes both stems and gyrogonites ostracods gastropods and rare vertebrates carbonate production was mainly biogenic the associated marginal lacustrine palustrine facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history the succession was laid down in a low gradient shallow lake complex characterized by wide fluctuations of the shoreline carbon and oxygen stable isotope analyses from the carbonates show non marine values with ranges of 13 from 7 to 11 and 18 from 3 to 7 5 differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake analyses from the entire sample suite plot on a linear trend isotopic compositions become lighter with increasing evidence of pedogenic modification this suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil derived co2 the stable isotope data thus support evidence from petrography and facies relations that palustrine limestones form through pedogenic modification of lake carbonates

diagenetic siderite and other ferroan carbonates in a modern subsiding marsh sequence abstract mineralogical and carbon and oxygen stable isotope compositions in siderite rich concretions from a marsh within the mississippi river deltaic plain are highly variable the concretions have sideritic interiors and become more calcitic and dolomitic ankeritic near their margins 13c values of these concretions range from 10 0 to 7 4 pdb and 1 o values range from 2 4 to 8 9 pdb the stable isotope compositions exhibit two general trends one is a growth trend that shows 13c an 18o depletion from the centers to the margins of the nodules and bands the other is a progressive burial trend that shows 13c enrichments and 18o depletions at the centers of the concretions with depth a zonal model for carbonate precipitation with emphasis on an early fresh water non sulfidic methanic phase followed by a sulfidic stage associated with marine inundation of the marsh explains much of the observed carbon isotopic variations mixing of fluids plus precipitation in a partially closed chemical microsystem accounts for most of the oxygen isotope fractionations documented between growth layers and casts doubt on the utility of change in 18o shifts as an indicator of depth or relative temperature of concretion formation for concretions that form in coastal environments

shallowing upward sequences in purbeckian peritidal carbonates lowermost cretaceous swiss and french jura mountains purbeckian carbonates in the swiss and french jura goldberg formation lower berriasian comprise shallow subtidal intertidal supratidal low energy high energy marine brackish freshwater and hypersaline facies these facies are arranged in small 0 2 1 5 m thick sequences which display a dominant shallowing upward component and which form the fundamental units of the highly structured purbeckian sedimentary record six types of small scale sequences can be recognized a intertidal to supratidal overprinting of shallow lagoonal facies b algal marsh sequence with frequent dolomitization c sabkha sequence often associated with collapse breccia d tidal flat sequence with desiccation features e lacustrine sequence f terrestrial overprinting of subtidal or intertidal facies episodic event deposits such as tempestites are superimposed thin transgressive beds which rework elements of the underlying facies are frequently found at the base of the sequences green marls and black pebbles are common at the top and indicate long subaerial exposure the sequences are often incomplete as subtidal facies may be absent or their upper part can be eroded lateral facies changes are common which is due to the very shallow and partly emergent purbeckian platform where various depositional environments were juxtaposed however many sequence boundaries are well developed and can be correlated over large parts of the study area the purbeckian shallowing upward sequences were generated by climatically controlled sea level changes autocyclic processes occurred locally but were overprinted by drops of sea level affecting the entire platform the small scale sequences are most probably related to the 20 000 year cycle of the precession of the equinoxes larger sequences with usually well developed emersion surfaces are attributed to the 100 000 and 400 000 year eccentricity cycles of the earth s orbit identification and correlation of sequence boundaries makes it possible to set up a framework of isochronous surfaces which often cut across facies boundaries and thus to interpret in detail the palaeogeographic sedimentological and diagenetic evolution of the purbeckian peritidal carbonate environments

magnetotelluric imaging of fluids in intraplate earthquake zones ne japan back arc intraplate earthquake zones in the back arc of ne japan were imaged by wide band magnetotelluric mt soundings the 90km long mt profile of 34 stations extends over the two topographic features the dewa hills and the ou backbone range which were uplifted by thrust faults mt data show two dimensionality and strong te tm anisotropic responses at the periods around 100 s after tensor decompositions with regional strike of n12 e two dimensional inversion was carried out where static shift was also a model parameter the final model is characterized by conductive blocks in the mid crust to account for the anisotropic responses correlation of the conductors to the seismic scatterers and to the low velocity anomalies suggests that the conductors represent fluids high seismicity clustering near the rims of conductors suggests that the intraplate seismicity results either from the migration of the fluids to less permeable crust or from local stress concentration near the structural boundary

analysis of the early jurassic geomagnetic data recorded at the breggia gorge ticino switzerland abstract geomagnetic directions recorded in a lower jurassic stratigraphic sequence that outcrops at the breggia gorge are analyzed a new method to identify directions suitable for calculating a time averaged dipolar geomagnetic direction has been applied to calculate a hypothetical early jurassic geocentric axial dipole the data were separated to identify normal reverse directions corresponding to periods of stable field and intermediate directions from an analysis of the data in the palaeogeographic coordinates of the breggia gorge at the time of the acquisition of the remanence it is suggested that polarity transitions in the early jurassic behaved in a similar manner to that described for late cenozoic reversals with the vgps preferentially following longitudinal paths the preferred paths coincide with a time averaged location of the jurassic subduction area of pangea this agreement could indicate a connection between the geometry of the reversals and the subduction zones an analysis to test whether both n r and intermediate directions have similar preferred distributions suggests that the underlying structure of the early jurassic geomagnetic field was similar to that observed for the late cenozoic the dispersion of directions with inclinations around 0 is higher than those belonging to n r polarity directions suggesting that there was an enhancement of fluctuations of the geomagnetic field during intermediate states in the early jurassic

deconvolution of long core paleomagnetic data of ocean drilling program by akaike s bayesian information criterion minimization deconvolution of long core paleomagnetic data of the ocean drilling program odp was developed based on bayesian statistics samples of deep sea sediments obtained by drilling with an advanced piston corer are subjected to pass through measurements by a cryogenic magnetometer aboard the odp s research vessel joides resolution which provide continuous paleomagnetic records deconvolution of the magnetometer output was developed in order to obtain more detailed variations of the magnetization than permitted by the spatial resolution of the pickup coil approximately 11 cm the magnetization vector was modeled as a smoothly changing sequence parametrized by l2 norm of second order difference and then deconvolved using a matrix calculation as a smoothness constrained least squares method the optimum smoothness was obtained by minimizing akaike s bayesian information criterion which is a measure of the logarithm of the likelihood this deconvolution scheme was applied to pass through data artificially produced by convolving synthetic reversal record and adding a gaussian noise the amplitude of the noise was estimated and the variations shorter than the spatial resolution of the sensor were obtained the deconvolution also was applied to the real pass through data from holes 769a and 769b measured at intervals of 5 mm the deconvolution revealed variations of the magnetizations with a maximum spatial resolution of about 2 cm the magnetizations after deconvolution were in good agreement with magnetization values measured separately on cube samples taken at intervals of 5 or 10 cm

ophiolite emplacement by strike slip tectonics between the pontide zone and the sakarya zone in northwestern anatolia turkey northwestern anatolia contains three main tectonic units a the pontide zone in the north which consists mainly of the istanbul zonguldak unit in the west and the ballidag kure unit in the east b the sakarya zone or continent in the south which is juxtaposed against the pontide zone due to the closure of paleo tethys prior to late jurassic time and c the armutlu ovacik zone which appears to represent a tectonic mixture of both zones these three major tectonic zones are presently bounded by the two branches of the north anatolian transform fault the two tectonic contacts follow older tectonic lineaments the western pontide fault which formed during the development of the armutlu ovacik zone since the earliest cretaceous an overall extensional regime dominated the region a transpressional tectonic regime of coniacian santonian to campanian age caused the welding of the istanbul zonguldak unit to the sakarya zone by an oblique collision in the late campanian a transtensional tectonic regime developed forming a new basin within the amalgamated tectonic mosaic the different tectonic regimes in the region were caused by activity of the western pontide fault most of the ophiolites within the armutlu ovacik zone belong to the paleo tethyan and or pre ordovician ophiolitic core of the istanbul zonguldak unit the late cretaceous ophiolites in the eastern parts of the armutlu ovacik zone were transported from neo tethyan ophiolites farther east by left lateral strike slip faults along the western pontide fault there is insufficient evidence to indicate the presence of an ocean intra pontide ocean between the istanbul zonguldak unit and the sakarya zone during late cretaceous time

origin and diagenetic evolution of ca mg fe carbonates in some coalfields of japan carbonate concretions lenses and bands in the pleistocene palaeogene and upper triassic coalfields of japan consist of various carbonate minerals with varied chemical compositions authigenic carbonates in freshwater sediments are siderite calcite ankerite dolomite ferroan magnesite in brackish water to marine sediments in the coal measures calcite dolomite ankerite siderite ferroan magnesite and in the overlying marine deposits calcite dolomite siderite most carbonates were formed progressively during burial within a range of depths between the sediment water interface and approximately 3 km the mineral species and the chemical composition of the carbonates are controlled primarily by the initial sedimentary facies of the host sediments and secondarily by the diagenetic evolution of pore water during burial based on the regular sequence and burial depth of precipitation of authigenic carbonates in a specific sedimentary facies three diagenetic stages of carbonates are proposed carbonates formed during stage i 2000 m are fe calcite and extremely high ca mg siderite the latter is exclusively in marine mudstones the supply of ca is partly from the alteration of silicates in the sediments at elevated burial temperatures after uplift calcite with low mg content precipitates from percolating groundwater and fills extensional cracks

optimized sequential extraction for carbonates quantification and δ13c analysis of calcite dolomite and siderite siderite is present in diverse types of rocks and sediments but its quantification is cumbersome when present in relatively low contents a new analytical method for the sequential separation of different carbonate phases is presented the separation quantification and characterization of the carbonates is based on different kinetic reactions during acid digestion in combination with monitoring the solution composition and the concomitant release of co2 trapping the released gasses permits the isotopic characterization 13c of the different phases based on published rate laws an idealized model was built to identify ph and temperature conditions for optimal separation of the various carbonates by taking the size distribution of carbonate particles into consideration results from the theoretical survey were implemented in an extraction scheme which was optimized and evaluated by tests on pure mineral phases and their mixtures further tests on a diverse array of sediment and rock samples validated the specificity and reproducibility of the method

structural interpretation of the marmara region nw turkey from aeromagnetic seismic and gravity data abstract the seismically active marmara region located in nw turkey lies on the westward end of the north anatolian fault naf the naf is well defined on land previous investigations of its extension in the marmara sea include marine bathymetry seismological activity and seismic profiles in this study faults and their configurations identified inland are extended into the marmara sea by means of aeromagnetic anomalies as well as seismic and gravity profiles the deep structure was resolved by constructing a map of the tertiary bottom shallow curie isotherm was determined by spectral analysis indicating a thinner crust in the northern marmara depression area with respect to the continental crust a combination of the geophysical data allows us to propose the existence of subsidence and isostatic equilibrium in the northern marmara sea a less active zone identified in the central high zone dividing the marmara sea into two parts may also be deduced from the seismic data this structural arrangement may play a key role in earthquakes that will affect the surrounding regions

geomagnetic long term secular variations in italian lower cretaceous shallow water carbonates summary the remanent magnetic properties of an 88 m bore core are unrelated to either the dolomite content or the sedimentological textures and are considered to be carried primarily by biogenetic magnetite that was cemented in during very early diagenesis individual readings represent time intervals of c 720 32 yr and after 40 mt partial demagnetization they provide an almost continuous record of averaged geomagnetic secular variations over a period of some 3 17 myr the magnitude of directional secular variation is twice that of the present day despite being smoothed and the secular variations appear to grade into polarity transitions suggesting no diverence in their mechanisms the rates of change in direction between subjacent levels in the core have a log normal distribution which extends smoothly beyond 90 and has a median value of 13 700 yr the same as for unsmoothed european secular variation during the last 2000 yr the intensity of remanence after 40 mt partial demagnetization appears to provide a reasonable approximation to geomagnetic field intensity this tends to be weaker when the direction is moving faster reflecting averaging but is unrelated to the distance of the vector from the mean direction that is it depends on the rate of change and not on the virtual pole latitude the virtual poles after correction for tectonic rotations about horizontal and vertical axes have latitudes that form a strongly platykurtic fisherian distribution while their longitudes have a circular distribution on which are superimposed two gaussian peaks 180 apart this bore core thus provides detailed information of smoothed geomagnetic secular variation in the lower cretaceous 127 3 ma which shows clear regularities in behaviour some related to changes in the earth s orbital parameters

tectonostratigraphic evolution of the basins on the southern branch of the north anatolian fault system in the se marmara region turkey the lithostratigraphy of the mekece iznik corridor the geyve pamukova and the iznik basins on the southern branch of the north anatolian fault system nafs sb was investigated in detail the intra basin deposits carried by sakarya river and the drainage systems in the northern and southern elevated blocks of the iznik and geyve pamukova basins have been classified based on their lithofacies characteristics the geyve pamukova basin which has developed with a nne ssw trending transtensional strain was formed as a lazy z shaped and releasing bend or pure strike slip pull apart basin that is related to simple shear right lateral strike slip faulting the iznik basin was formed by a right lateral strike slip faulting kinematics and nne ssw trending transtension as a result of the step over of the northeast trending dirazali fault from the southern edge to the nw trending gurle fault and the western step over of this fault to the e w trending umurbey fault this strike slip setting is also supported by the nw se trending right lateral oblique normal orhangazi fault on the northern edge of the basin according to this the iznik basin can be described as a more advanced stage of a large scale pull apart basin compared with a lazy z shaped and releasing bend or transtensional strain furthermore it is defined as the former stage of an extreme or rhomboid type transtensional pull apart basin

the parasequence definition are transgressive deposits inadequately addressed abstract in only a few decades sequence stratigraphy has become one of the cornerstones of modern stratigraphy although the sequence is the principal stratigraphic unit parasequences are the fundamental composite building blocks by definition parasequences are typically upward shoaling successions that are bounded by flooding surfaces that form in response to relatively rapid rises of relative sea level in that definition little provision is made for significant transgressive deposition during the time of flooding but transgressive deposits do exist in the geological record because these deposits lie above the flooding surface and derive much of their sediment from transgressive erosion of the underlying progradational succession should the parasequence boundary not be moved from the u derlying flooding surface upward to the top of the transgressive unit by doing so the underlying progradational unit and the overlying transgressive unit would constitute one complete regressive transgressive succession nonetheless although appealing the typical inability to easily accurately and consistently identify the uppermost surface of the transgressive unit makes it an untenable surface for stratigraphic purposes as suggested by earlier workers therefore the flooding surface a readily identifiable surface that caps the progradational package and consistently underlies transgressive deposits is the most appropriate surface to bound the parasequence in any event to ignore transgressive deposits is to ignore an important component of the geological record a record that not only provides insight into transgressive depositional processes but also is one that can be economically important as a result transgressive deposits need to be included in the parasequence definition possibly only implicitly but certainly not explicitly excluded furthermore the notion that sequences typically indicate progradational deposition excludes examples where upward fining transgressive deposits related to upward deepening are present and lie below the upward shoaling progradational part of the same parasequence

origin of ultramafic hosted vein magnesite deposits abstract large deposits of magnesite mgco3 occur either as carbonated ultramafic rocks or as sedimentary beds the origins of both sedimentary and ultramafic hosted deposits remain controversial as does the relationship between them ultramafic hosted deposits are reviewed herein with an emphasis on veins rather than massive bodies magnesium apparently has been supplied to magnesite veins by their ultramafic host uncertainties concerning ultramafic hosted deposits include the source state and mode of transportation of carbon the cause of its precipitation and the mineralogy of the initial precipitate genetic questions about ultramafic hosted vein deposits are summarized with the aid of flow charts the preferred route through these charts attributes most vein magnesite to an influx of metamorphic degassing co2 and ch4 into groundwater which flows through serpentinite or peridotite the source of co2 ch4 is considered to be deeper than 10 km because metamorphism 300 c is required to release carbonaceous volatiles of the type which apparently induced observed magnesite mineralization however vein magnesite precipitation generally has occurred within just a few hundred meters of the earth s surface vein deposits are considered to be genetically related to massive bodies but the massive bodies typically contain less 12c the 12c rich co2 which has produced vein deposits is attributed to a fluid phase variably mixed ch4 co co2 which rose until it reached upper crustal groundwater the hypothetical water poor fluid presumably became slightly oxidized hence richer in soluble co2 as it encountered near surface sulfate bearing water co2 enriched water is envisioned to have been expelled regionally due to tectonic processes leaving little mineralogical evidence of its expulsion through non ultramafic rock co2 rich water which happened to encounter either serpentinite or peridotite presumably has produced magnesite vein deposits and a common silicate byproduct nontronite according to the following reaction 12 mg3si2o5 oh 4 serpentine 36 hco3 4 fe3o4 o2 12 fesi2o5 oh nontronite 36 mgco3 magnesite 36 oh 18h2o

the magnetic polarity stratigraphy of a hauterivian barremian carbonate sequence from southern italy summary remanence directions measured at 2 cm intervals along a composite 88 m bore core enable mean palaeomagnetic poles to be defined at 13 6 s 25 2 w and 13 6 n 154 8 e the directions of remanence vary very smoothly away from each palaeomagnetic pole extending more than 90 from them this raises doubts about the physical meaning of polarity definitions based on the distance between virtual and mean palaeomagnetic poles for practical purposes intermediate polarity is defined as directions whose virtual poles lie more than 25 from the mean pole enabling at least five normal subchrons to be specified within the upper predominately reversed quarter of the core and 11 reversed subchrons within the lower predominantly normal three quarters of the core the stratigraphic thickness between these subchrons shows a very high linear correlation r 0 99 with the stratigraphic thickness of other terrestrial sequences and the distances between marine polarity sequences of comparable age the analysed sequence contains wavelength spectra which when transformed to the temporal realm match periodicities determined for three marine magnetic anomaly profiles of similar age these also match planetary orbital periodicities for the cretaceous these observations suggest that secular variations and polarity transitions are driven by common core processes whose surface expression is influenced by changes in the planetary orbits such detailed geomagnetic features enable far greater reliability in establishing magnetostratigraphic correlations and also enable them to be dated astronomically

formation of secondary pyrite and carbonate minerals in the lower williams lake tailings basin elliot lake ontario canada the lower williams lake tailings which resulted from u milling operations during the late 1950s and early 1960s cover an area of 2 ha in a small bog under partial water cover the tailings are underlain by a sand unit containing decaying organic material above the natural base consisting of sand till and gravel the tailings are composed predominantly of quartz muscovite k feldspar plagioclase and clinochlore residual pyrite grains displaying angular to subangular particles measuring less than 1 to 250 m occur in concentrations ranging from trace to approximately 6 wt framboidal pyrite has formed within the tailings basin in association with organic rich material the appearance of framboidal pyrite in the tailings indicates a reversal of the oxidation process and reprecipitation of fe sulfides in addition the tailings include calcite calcian siderite fe oxyhydroxides and fe si oxyhydroxides as secondary precipitates and replacement products groundwaters in the tailings and the underlying units are saturated with respect to gypsum and siderite these and the other saturation indices calculated for calcite goethite and barite are consistent with the secondary mineralogy of the tailings conditions promoting the formation of pyrite can be described as neutral to weakly alkaline and reducing assisted by microbial activity this study provides the first account of secondary carbonates and framboidal pyrite in the elliot lake tailings the existing environmental conditions at the site are favorable for the desired site rehabilitation

late cretaceous to late eocene palaeogeographic evolution of southwest europe abstract a synthesis of personal research concerning the peri pyrenean region and previously published data is presented as a series of palaeogeographic reconstructions subsequent to the progressive regression at the end of the cretaceous the sea invaded three times parts of the earlier senonian marine domain on both sides of the eastern palaeo pyrenees pre cuisian climatic rewarming combined with cuisian continental epeirogenic deformations resulted in major biogeographic modifications during the cuisian local tectonics forced the sea from the northern pyrenean basin whereas in the southern pyrenean basin the sea retreated much later as a consequence of the pyrenean tectonic phase however the pyrenean tectogenesis seems to have affected a much larger region including the alps shoreline migrations are compared and related to the geodynamic behaviour of the meridional and septentrional european provinces in order to distinguish between tectonic and eustatic causes

catchment processes and the quantity and composition of sediment delivered to terminal basins discussion although the quantities of sediment exported to the sea by large rivers are relatively well known information on mineralogical and geochemical characteristics is less readily available quantity and composition are strongly influenced by tectonic environment and also by both present and past climate an analysis of diagenetic processes in fine grained clastic sediments suggests that bed parallel changes in the intensity of diagenetic modification reflected in phenomena such as cemenstone horizons and marked changes in authigenic mineral assemblages sulphides carbonates silicates could be explained by changes in sediment supply rate driven by climatic fluctuations it is less easy to explain fluctuations in detrital sediment composition diagenetic reorganization would appear to be the most common cause of marked local compositional contrast in mudstones

carbon isotope stratigraphy a tool for basin to carbonate platform correlation the early cretaceous carbonate carbon isotope stratigraphy established in pelagic limestones is marked by several pronounced excursions towards positive 13c values we investigated a biostratigraphically and palaeomagnetically calibrated aptian section to see whether c isotope stratigraphy could be recognized in shallow water carbonates the chosen carbonate platform sections are located in southern italy and have been dated by biostratigraphy bulk samples chosen from the barremian albian part of the sequence were analysed for their o and c isotope compositions the c isotope curve established shows two major positive excursions which can be correlated with the synchronous and globally recognized aptian c isotope events the data provide evidence that c isotope stratigraphy can be used as a powerful correlation tool between pelagic and shallow water limestone sequences

spherulitic siderites in the holocene coastal deposits of korea eastern yellow sea elemental and isotopic composition and depositional environment abstract siderite concretions are recovered from both freshwater unit ii and tidal unit i deposits in the holocene macrotidal flat of kyunggi bay west coast of korea siderites from both units show a spherulitic and well rounded texture and well developed equant rhombs on the external surfaces the size of the concretions in unit ii 50 150 m in diameter is normally larger than that in unit i 10 20 m the siderites in unit ii are chemically pure and highly enriched in fe whereas those of unit i are relatively impure and distinctly zoned demarcating high mn up to 69 1 mol in the core and high fe up to 75 9 mol in the margin within siderites of unit i substitution for fe by ca and mg reaches up to 20 3 mol mean 15 1 mol and 16 1 mol mean 12 6 mol respectively bulk 18 o values 0 7 to 1 3 peedee belemnite pdb for siderites in unit i are relatively higher than those 7 1 to 0 5 pdb in unit ii regardless of units siderite 13 c values 21 3 to 11 2 pdb are persistently low indicating microbially mediated precipitation at shallow burial depth extensive mn ca and mg substitution coupled with enrichment of 18 o in the siderites of unit i seems to reflect marine influence during the holocene transgression the occurrence of early diagenetic siderites provides supporting evidence on the depositional environment marine vs non marine of the holocene muddy coastal deposits of korea eastern yellow sea

significance of localized pore pressures to the genesis of septarian concretions the burial stress and hydrologic conditions existing during concretion formation in mudrocks are evaluated and integrated into a model for the genesis of septarian cracks initial concretion cement formation will lower concretion permeability through the filling of pre existing pore space during progressive burial this may lead to increased excess pore pressure localized within the concretion body causing a reduction of the effective stress analysis of the stress conditions and crack morphology suggests that cracks in septarian concretions result from tensional failure sub critical crack growth as a consequence of this localized excess pore pressure conditions suitable for crack formation will depend upon the magnitude of the excess pore pressure and the stress corrosion limit of the concretion body a review of the likely strength of such concretions indicates that cracking could be initiated at depths less than 10 m a variety of observed crack morphologies can be explained with this model depending upon the spatial distribution of strength and effective stress in the concretion crack orientations mostly reflect stress anisotropy but are also influenced by directional anisotropy in the crack growth rates locally increased pore pressure also likely occurs in non septarian concretions but is not sufficient to cause cracking this enhanced local pressure may assist the crystal surface growth reactions of the carbonate cement through this enhancement process the shape of concretions may be a response to the local anisotropic pore pressure contours which reflect the permeability anisotropy of the concretion and surrounding mudrock

coal deposition in carbonate rich shallow lacustrine systems the calaf and mequinenza sequences oligocene eastern ebro basin ne spain two main coal bearing sequences developed during the oligocene in the tertiary ebro basin the calaf early oligocene and mequinenza late oligocene coal basins coal deposition took place in shallow marsh swamp lake complexes which sometimes became closed and evolved under warm climatic conditions with fluctuating humidity these shallow lacustrine systems are closely interrelated with the terminal parts of the distributive fluvial systems which spread from the tectonically active ebro basin margins laterally extensive lignite bearing sequences including rather thin lenticular autochthonous and or hypautochthonous coal seams with high ash and sulphur contents characterized coal deposition in the shallow lacustrine systems coal seam geometry which makes them nearly subeconomic resulted from the tectonic instability during basin margin evolution and the sometimes closed arid conditions under which the lacustrine systems evolved high ash and sulphur contents resulted from the inadequate isolation of peat forming environments from clastic influx and from the very low acidity and sometimes high sulphate contents of the lacustrine waters coal exploration in shallow lacustrine sequences similar to those described here must take into account that the spread of coal forming environments and maxima of coal deposition are usually coincident with lake expansions and retraction or shifting of the terminal fluvial zones interrelated with the lacustrine areas

new paleomagnetic pole for the upper jurassic chon aike formation of southern argentina south america testing the tectonic stability of patagonia with respect to south america and implications to middle jurassic early cretaceous true polar wander abstract a paleomagnetic pole and a new ar ar date of 156 08 0 05 ma are reported for the chon aike formation an extensive plateau of ignimbrites outcropping in the deseado massif southern patagonia argentina the geographic coordinates and statistical parameters for the paleomagnetic pole validated by a reversal test are lat 84 3 s long 191 3 e a95 8 6 k 13 3 n 23 this pole shows a complete coherence with late jurassic and early to mid cretaceous poles of south america obtained exclusively from igneous rocks avoiding any potential inclination shallowing it is suggested that a southern patagonia was an integral part of south america in the late jurassic b any reported vertical axis tectonic rotations must pre date the late jurassic in this region c according to updated paleomagnetic data from igneous rocks south america had very limited latitudinal drift between about 160 and 140 ma and therefore d its apparent polar wander apw path when compared with global apparent polar wander paths does not support a large global shift or true polar wander tpw between 160 and 140 ma

a strategy of tectonomagnetic observation for monitoring possible precursors to earthquakes in the western part of the north anatolian fault zone turkey abstract in order to investigate changes in the geomagnetic field associated with seismic activity in the western part of the north anatolian fault zone nafz seven continuous measurement stations and eighteen repeated survey sites were set up in the inik geyve region taking into account the fault trace and its features simple differences in the total intensity between these continuous stations have been derived for detecting possible anomalous phenomena associated with earthquake occurrences theoretical studies imply that changes in the total intensity associated with fault activity are larger in the case of non uniform distribution of rock magnetization than those in the uniform case meanwhile inversion analyses of magnetic anomalies at the north anatolian fault zone nafz suggest a dyke like structure extending parallel to the fault strike this structure enables us to test our strategy based on non uniform magnetization for detecting pre and or co seismic changes in the geomagnetic field we made a theoretical estimation of geomagnetic changes for the case of a magnetic dyke structure intruding a non magnetic body parallel to the strike of a fault it turns out that unlike the uniform case the magnetic field arising from stress induced magnetization is enhanced a tectonomagnetic observation system talcing into account such a non uniform magnetization structure in the inik geyve region of the nafz is also described

determination of the deep fault geometry along the southern branch of the north anatolian fault system by using resistivity and magnetic methods abstract the wenner lateral resistivity and magnetic dyke profiles carried out along the southern branch of the north anatolian fault system the use of magnetic dyke method indicates that the faults located in the deep parts of the continental crust were high angled and dipping towards north and the right lateral strike slip faults were the only active main fault types in the plio quaternary deposits besides a high angled strike slip fault and its secondary components form the geological contact between the basement rocks and the basin filling deposits nafs sb that is developed during plio quaternary neotectonic period is the only structural source during the formation of the deposits in the depression areas and recent times this zoning is related to nafs sb and developed depending on both the near vertical and 70 90 dipping strike slip faulting apart from the near vertical fault planes the faults dipping towards the depression areas developed due to the existence of the transtensional stresses in the strike slip faults

neural net aided detection of astronomical periodicities in geologic records abstract astronomically controlled variations in the earth s climate induce cyclic trends in the sedimentary process and record milankovitch periodicity one of the main difficulties to be solved in order to choose among the registered periodicities is the conversion from the spatial i e recurrent variations along the stratal sequences to the temporal domains of the astronomically induced frequencies present in the rock record we discuss here how this problem can be circumvented by teaching a neural net how to recognize periodicities in the signal the application to two sequences of shallow water carbonate deposits from the cretaceous of southern italy has shown this approach to be particularly effective confirming the existence of milankovitch type periodicities in the records examined where climate sediments and biota concomitantly react to the variation in the solar constant induced by secular perturbations of the earth s orbital elements

evolution of the middle strand of north anatolian fault and shallow seismic investigation of the southeastern marmara sea gemlik bay abstract the gemlik bay is developed as a pull apart basin during the late pliocene early pleistocene mainly controlled by west trending dextral strike slip faults along the middle strand of the north anatolian fault zone with the nw trending thrace eskisehir fault playing secondary role the north anatolian fault reached the eastern marmara sea 3 5 ma ago where its middle strand intersected the thrace eskisehir fault gps slip vectors measured on the armutlu and mudanya blocks show a displacement of 7 8 km during the last 3 5 ma the middle strand of the north anatolian fault zone has lower tectonic activity than the northern strand because uplift of the southeast marmara sea region has been continuous since the late pliocene the presence of fluviatile lacustrine and deltaic environments in the gemlik pull apart basin over the same period supports a lower lever of tectonic activity the transgressive marmara formation was deposited on top of these fluvio lacustrine deposits following the mediterranean inundation at 600 ka via the strait of canakkale the gemlik basin was affected both by two major sea level falls at 160 132 and 24 11 ka and minor short lived sea level variations as a result of becoming a lacustrine setting five times since 600 ka during these lowstands stacked delta successions were deposited around the lake and on the transgressed shelves of the marmara sea

electrical resistivity structure of the northwestern anatolia and its tectonic implications for the sakarya and bornova zones abstract the crustal structure of the northwestern anatolia was studied by magnetotelluric measurements with periods up to 500 s at 20 locations along a line line ks crossed istanbul sakarya and bornova zones to investigate deep electrical resistivity patterns that contribute to the understanding of tectonic setting of the region the results obtained from the two dimensional 2d inversion of magnetotelluric data for the modes transverse electric te and transverse magnetic tm show that the tectonic structure up to 5 km depth was comparatively complex and that the structural pattern was generally disturbed by the grabens and neogene basins of low resistivity feature the low resistivity

strike slip fault geometry in turkey and its influence on earthquake activity the geometry of turkish strike slip faults has been reviewed and described from this data set it appears that fault geometry the distribution of discontinuities such as bends and stepovers along the main fault trace plays an important role in controlling the location of large earthquake rupture segments along the fault zones large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 more important than the size of each discontinuity however is the total geometric pattern i e the distribution of adjacent bends and stepovers based not only on distance from one another but also on relative discontinuity size certain geometric patterns restraining single or double bends are particularly common and can be viewed as responsible for strain accumulation along portions of the fault zone fault geometry not only plays a role in the extent of earthquake rupture but also in characteristics of earthquake behavior for example large earthquake epicenters often occur near restraining bends or double bends furthermore aftershocks and swarm activity can often be associated with releasing areas areas along the strike slip fault that are undergoing a relatively large amount of extension

manganese fluxes from mississippi delta sediments abstract massive sediment deposition on the mississippi river delta establishes reducing conditions sufficient to bring about mn dissolution in the top millimeters of sediment as a result significant fluxes of dissolved mn pass from the delta sediments to the overlying water column this process is examined by study of chemical partitioning of mn in river particulates and delta sediments and from interstitial water chemistry remobilized mn is actively transported away from the delta area with aluminosilicate detritus thereby providing excess mn to the deep gulf of mexico at the expense of the delta sediments

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

magnetotelluric imaging of the fault rupture area of the 1999 izmit turkey earthquake abstract wide band 320 0 001 hz and long period 0 01 0 0001 hz magnetotelluric mt data were acquired along two profiles crossing the western part of the north anatolian fault zone nafz turkey which consists of two main fault branches the first profile izmit profile crosses the epicentral area of the 17 august 1999 izmit earthquake in fact the mt measurements along this profile started just a few weeks before the occurrence of the mainshock and four instruments happened to be in operation in the vicinity of the fault when the earthquake took place the second profile adapazari profile is located about 30 km east of the first profile two dimensional modeling shows the following results first the hypocenters of mainshock and aftershocks are located on the highly resistive side near the edge of a conductive zone second the long period mt data show a low resistivity zone extending down to 50 km between the two fault branches such a deep conductive zone is interpreted as representing partial melting resulted from the past complex tectonics in this region and it is related to the non seismic after slip in the layer below the seismogenic zone characterized by the highly resistive layer

hierarchy of high frequency orbital cycles in cretaceous carbonate platform strata abstract lower cretaceous valanginian hauterivian carbonate platform strata which are well exposed in the matese mountains of the southern apennines italy have been analyzed on a microstratigraphic cm scale to exemplify the high frequency cyclic nature of the mesozoic shallow water sedimentation in southern italy based on the vertical organization of lithofacies and their early diagenetic signature 46 metre scale cycles are recognized these elementary cycles are hierarchically organized into groups bundles and superbundles the elementary cycles are prevalently formed by subtidal deposits and show emersion related features at the top suggesting repeated sea level fluctuations the number of elementary cycles compared to time as constrained by biostratigraphy and their grouping into sets implying higher order complexity in the environmental oscillation suggest an orbital control on sedimentation spectral analysis of recurrent thickness in stratal features defines and quantifies the cyclicity which is characterized by lithofacies thickness periodicities of 1271 391 159 124 and 69 cm linear correlation of the relative ratio set rrs of these periodicities with the corresponding rrs of the orbital perturbation periodicities shows that 1271 and 391 cm fit the 404 220 and 94 890 year cycles of early cretaceous orbital eccentricity 159 and 124 cm fit the 49 010 and 38 030 year cycles of the earth s axial obliquity whereas 69 cm corresponds to the precession periodicity thus the san lorenzello section required not less than 1 6 ma to form at an average rate of 26 mm ka each 400 ka cycle can be viewed as a depositional sequence in which sequence boundaries maximum flooding surfaces and system tract equivalents have been recognized the microstratigraphic approach is very promising for understanding the fine structure of climate related environmental fluctuation recorded by the 3000 m thick carbonate platform successions of the southern apennines over a time span of about 150 ma upper triassic upper cretaceous and for deriving a more precise chronostratigraphy for global correlation

repeated subaerial exposure of subtidal carbonate platforms triassic northern italy evidence for high frequency sea level oscillations on a 104 year scale triassic carbonate platforms in northern italy ladinian latemar carnian durrenstein norian dolomia principale consist of hundreds of stacked meter scale cycles each made of a subtidal unit with a cap rock that carries vadose cements pisoids and tepee structures these diagenetic caps are interpreted to be due to subaerial exposure of the subtidal sediments the absence of peritidal deposits rules out progradation as the cause of the exposure i e these are not ginsburg autocycles thus the repeated exposure must be the result of relative sea level oscillations which based on the number of cycles and time intervals involved occurred with an average frequency in the 104 year range we postulate a combination of small scale high frequency eustasy and local tectonic movements e g differential subsidence in the norian and infrequent pulses of uplift in the ladinian to explain the cyclicity and its internal variations