hierarchal genetic stratigraphy a framework for paleoceanography a detailed genetic stratigraphic framework for paleoceanographic studies can be derived by describing correlating interpreting and predicting stratigraphic sequences relative to a hierarchy of their constituent time stratigraphic transgressive regressive units t r units t r unit hierarchies are defined and correlated using lithostratigraphic and paleoecologic data but correlations can be enhanced or checked tested to confirm or deny with objective biostratigraphic magnetostratigraphic or chemostratigraphic data such chronostratigraphies can then be bracketed by radiometric ages so that average periodicities for t r units can be calculated and a hierarchal geochronology derived t r units are inferred to be the net depositional result of eustatic cycles of sea level change and can be differentiated from autocyclic deepening shallowing units because the latter are noncorrelative intrabasinally boundaries between t r units are conformable or unconformable genetic surfaces of two types transgressive surfaces and climate change surfaces the latter are useful for correlating minor transgressive phases through nonmarine intervals thereby deriving information linking paleoclimatic and paleoceanographic processes permo carboniferous sequences can be analyzed relative to a hierarchy of six scales of genetic t r units having periodicities of 225 300 m y first order 20 90 m y second order 7 13 m y third order 0 6 3 6 m y fourth order 300 500 10 years fifth order and 50 130 10 years or less sixth order paleogeographic maps for the time of maximum transgression transgressive apex of successive fifth order t r units 5 25 m thick in the glenshaw formation upper pennsylvanian northern appalachian basin delineate delta lobes embayments islands and linear seaways relative extent of marine inundation on the fifth order maps was used to delineate fourth order t r units and the fourth order t r units constitute the transgressive half of a third order t r unit this third fourth and fifth order hierarchy is correlated more than 1200 km 750 miles to the western interior basin and is confirmed with limited objective biostratigraphy

a new high precision 40ar 39ar age for the rochechouart impact structure at least 5 ma older than the triassic jurassic boundary the rochechourt impact structure in south central france with maximum diameter of 40 50 km has previously been dated to within 1 uncertainty of the triassic jurassic boundary at which time 30 of global genera became extinct to evaluate the temporal relationship between the impact and the triassic jurassic boundary at high precision we have re examined the structure s age using multicollector argus v 40ar 39ar mass spectrometry results from four aliquots of impact melt are highly reproducible and yield an age of 206 92 0 20 0 32 ma 2 full analytical external uncertainties thus the rochechouart impact structure predates the triassic jurassic boundary by 5 6 0 4 ma and so is not temporally linked to the mass extinction rochechouart has formerly been proposed to be part of a multiple impact event but when compared with new ages from the other purported paired structures the results provide no evidence for synchronous impacts in the late triassic the widespread central atlantic magmatic province flood basalts remain the most likely cause of the triassic jurassic mass extinction

search for milankovitch patterns among oolitic ironstones the stratigraphic record of about 175 oolitic ironstones is sparse yet it portrays several meaningful patterns repeated ironstone episodes occurred in only about 10 major sedimentary basins which were marked by relative tectonic stability or subdued orogeny intervals between episodes varied but were mostly a few to several million years long repetitions on this scale are commonly construed as global rise and fall of sea level the pattern persisted for a few tens of million years in fore deeps several tens of million years on unstable cratons and microcontinents and more than 100 m y in intracratonic basins within the congenial habitats an ironstone developed locally between each of several successive shallow marine upward shoaling detrital sequences these asymmetric units normally a few meters to a few tens of meters thick recurred on average every 250 to 500 kyr commonly fewer than 10 ironstone bearing sequences are involved during a very long lapse in normal sedimentation between such sequences stacked ironstones accumulated on the same short time scale speculation about short time scale patterns is poorly constrained but several other repetitive stratigraphic successions with a several hundred thousand year cadence have been attributed tentatively to the 400 000 year milankovitch climate cycle it is unclear how this would exert a eustatic control without the waxing and waning of continental glaciers

intercalibration of 40ar39ar dating standards a number of standards used for k ar and 40ar39ar dating have been intercalibrated multiple splits 15 40 mg each of mmhb 1 sb 3 biotite lp 6 biotite 40 60 ga1550 biotite fish canyon tuff 3 biotite taylor creek rhyolite sanidine bern 4 muscovite bern 4 biotite and pennsylvania state university orthoclase 1a were irradiated in capsules fused and analyzed in replicate analyses most of these standards proved to be homogeneous in 40ar 39ark ratio age k ca and 36ar contents mmhb 1 is inhomogeneous in age at the 15 mg level indicating it is unsuitable for use as an interlaboratory standard using material taken straight from the bottle the orthoclase sample is also inhomogeneous at the 30 mg level quoted relative to an age of 162 9 ma for the sb 3 biotite standard total fusion ages are lp 6 biotite 40 60 128 1 ma ga1550 biotite 97 8 ma fish canyon tuff 3 biotite 27 95 ma taylor creek rhyolite sanidine 28 0 ma bern 4 muscovite 18 51 ma bern 4 biotite 17 21 ma these ages are in good agreement with the absolute k ar ages of these minerals different preparations of biotite and sanidine standards from a welded tuff such as the fish canyon tuff may not be of identical ages tests on submilligram splits reveals that sb 3 biotite ga1550 biotite fish canyon tuff 3 biotite and taylor creek rhyolite sanidine are suitable for use as monitors in laser work the sanidine specimen appears to be the most suitable for use as the primary monitor for 40ar39ar dating

new 40ar 39ar dating of the antrim plateau volcanics australia clarifying an age for the eruptive phase of the kalkarindji continental flood basalt province the kalkarindji flood basalt province of northern australia erupted in the mid cambrian today the province consists of scattered volcanic and intrusive suites the largest being the antrim plateau volcanics apv in northern territory accurate dating of the kalkarindji flood basalt province has proved challenging with previous studies focused on minor volcanic rocks and intrusive dykes in northern territory and western australia these previously published data corrected to the same decay constants range from 512 8 to 509 6 2 5 ma 2 placing the kalkarindji flood basalt province in apparent synchronicity with the cambrian stage 4 5 biotic crisis at 510 1 ma this study utilizes 40ar 39ar dating of basalts from the apv to accurately date the major volcanic eruptions in this province the results yield an age of 508 0 498 3 5 5 ma 2 indicating that the apv is younger than the intrusive rocks these dates allude to a relative timing discrepancy where intrusive activity in the north australian craton preceded the eruption of the apv as the last magmatic activity in the region the determination of these largest eruptions to be later than 510 ma effectively disassociates the kalkarindji lavas from being a major cause of the 510 ma biotic crisis but cannot definitively discount any deleterious effects on the fragile cambrian ecosystem supplementary material 40ar 39ar analysis data tables xrf geochemical data alteration study and photomicrographs of all five samples are available at https doi org 10 6084 m9 figshare c 4176674

hydraulic parameters and solute velocities in triple porosity karstic fissured porous carbonate aquifers case studies in southern poland rock and flow parameters of three karstic fissured porous aquifers in the krakow silesian triassic formations were measured using various methods and compared though cavern and fissure porosities are shown to be very low cavern porosity below 0 5 and fracture porosity below 0 2 they contribute dominantly to the hydraulic conductivity from about 1 3 10 6 to about 11 10 6 m s matrix porosity 2 11 is shown to be the main water reservoir for solute transport and the main or significant contributor to the specific yield 2 though the matrix porosity is shown to be much larger than the sum of the cavern and fissure porosities its contribution to the total hydraulic conductivity is practically negligible hydraulic conductivity of the matrix is from about 5 10 11 m s to about 2 10 8 m s on the other hand the matrix porosity for neglected cavern and fissure porosities when combined with tracer ages or mean travel times is shown to yield proper values of the hydraulic conductivity k by applying the following formula k matrix porosity mean travel distance mean hydraulic gradient mean tracer age confirming earlier findings of the authors this equation is shown to be of great practical importance because matrix porosity is easily measured in the laboratory on rock samples whereas cavern and fracture porosities usually remain unmeasurable

modified expression for bulb tracer depletion effect on argon dating standards 40ar 39ar geochronology depends critically on well calibrated standards often traceable to first principles k ar age calibrations using bulb tracer systems tracer systems also provide precise standards for noble gas studies and interlaboratory calibration the exponential expression long used for calculating isotope tracer concentrations in k ar age dating and calibration of 40ar 39ar age standards may provide a close approximation of those values but is not correct appropriate equations are derived that accurately describe the depletion of tracer reservoirs and concentrations of sequential tracers in the modified expression the depletion constant is not in the exponent which only varies as integers by tracer number evaluation of the expressions demonstrates that systematic error introduced through use of the original expression may be substantial where reservoir volumes are small and resulting depletion constants are large traditional use of large reservoir to tracer volumes and the resulting small depletion constants have kept errors well less than experimental uncertainties in most previous k ar and calibration studies use of the proper expression however permits use of volumes appropriate to the problems addressed

a thermochronological perspective on the morphotectonic evolution of the southeastern tibetan plateau a large part of the southeastern tibetan plateau tp is characterized by low relief surfaces at high elevations 3 5 km the origin of these landscapes and their geodynamic implications with regard to evolution of the southeastern tp has been the subject of considerable debate focusing on this topic this study utilizes fission track and u th he thermochronology to reconstruct the thermal history of the late triassic daocheng granite on which a low relief high elevation landscape has developed results suggest that the plateau surface experienced widespread late jurassic to early cretaceous cooling at a rate of 1 2 c ma followed by minimal regional cooling 0 3 c ma and early miocene enhanced cooling 2 3 c ma along deep valleys at the southern edge of the landscape given the subdued late jurassic to early cretaceous crustal deformation in the study area we relate the coeval cooling to crustal refrigeration and exhumation triggered by northward subduction of the meso tethys ocean along the bangong suture subsequent late cretaceous to cenozoic minimal cooling supports arguments for the formation of a low elevation landform prior to uplift of the southeastern tp the enhanced cooling commenced at the early miocene 15 22 ma along deep valleys and heralded the onset of river incision and surface uplift of the southeastern tp this finding does not support previous proposals claiming that high elevations of the southeastern tp were formed in late miocene time resulting from lower crustal flow but rather supports a model highlighting continental subduction and extrusion along the large tanggula yushu batang red river fault system

postglacial transgressions in late paleozoic basins of western argentina a record of glacioeustatic sea level rise the areas marginal to main glaciated centers are appropriate sites to distinguish the record of glacioeustatic sea level fluctuations the late paleozoic basins of western argentina show a marginal position with respect to the glaciated areas of eastern south america brazil in three of these basins tarija calingasta uspallata and central patagonian widespread glacial marine diamictites and their gravity reworked counterparts pass upward to open marine fine clastics mudstones shales and scarce fine sandstones with fossils of the levipustula zone of middle carboniferous late namurian westphalian age the presence of fine grained marine sequences capping the diamictitic deposits is interpreted as the sedimentary response to a glacioeustatic sea level rise expressed as a transgression in stratigraphic terms the glacioeustatic nature of this sea level rise is confirmed by the interbasinal facies based correlation of the transgressive episode and the paleolatitudinal positioning of this portion of gondwanaland during carboniferous times

statistics for la icp ms based fission track dating abstract despite the conceptual elegance and simplicity of the external detector method edm for fission track dating an increasing number of laboratories are switching to la icp ms as a means of measuring the uranium content of apatite zircon and sphene la icp ms based fission track laft dating offers shorter turnaround times removes the need to handle radioactive materials and hydrofluoric acid and facilitates double dating with the u pb method this paper aims to bring the statistical treatment of laft data on an equal footing with the edm by formulating four different analytical protocols depending on the accuracy and reproducibility of the uranium measurements under the absolute dating approach the spontaneous track densities and uranium concentrations are directly plugged into the fundamental fission track age equation assuming that both of these measured quantities have been determined accurately and that the fission decay constant and equivalent isotopic track length are known the zeta calibration approach avoids making these assumptions by normalisation to a reference material of known age uranium zoning has a detrimental effect on the accuracy of laft ages this effect can be removed by counting only those fission tracks located within the laser ablation pit alternatively the uranium heterogeneity may be quantified by fitting multiple ablation spots in some or all the analysed grains using a lognormal distributional assumption for the uranium concentration laft dating is arguably less well suited than the edm to young and u poor samples that lack sufficient spontaneous fission tracks to reveal visual evidence for uranium zoning such samples occasionally contain no fission tracks at all resulting in infinite analytical uncertainties this paper introduces a pragmatic solution to this problem in which the uranium measurement are converted to virtual induced fission track counts to produce strictly positive ages with finite standard errors with the age equation and zero track strategy in place laft ages can be subjected to more sophisticated statistical analysis using a logarithmic transformation these ages can be visualised on radial plots and deconvolved into finite and continuous mixtures the methods introduced in this paper have been implemented in a software package called isoplotr that is available free of charge at http isoplotr london geochron com

origin and age of saline waters in busko spa southern poland determined by isotope noble gas and hydrochemical methods evidence of interglacial and pre quaternary warm climate recharges abstract in the busko and solec spas saline sulphide and sulphate waters are exploited at different depths the shallow water system in busko is related to an interglacial or interstadial period shown by the lack of tritium and 14 c and its 18 o and d values equal to that of modern water the noble gas temperatures ngt are somewhat lower than the present air temperatures but the 4 he and 40 ar ages of about 90 480 ka confirm a pleistocene recharge the 18 o and d values of the deep system are much heavier than those of local modern waters which may mean the recharge of a warm pre quaternary climate the 4 he 40 ar and 21 ne contents and the ngt values confirm the deep system to be recharged at the pre quaternary stages of the present hydrologic cycle i e after the sea transgression in the badenian high so 4 2 contents indicate that the cl and so 4 2 in both systems originated from simultaneous leaching of nacl and gypsum other components can be explained by cation exchange between water and badenian clay minerals in marls e g ca 2 for mg 2 and na for k and by the decay of marine organic matter supplying br i and b

late paleozoic foraminifera as depth indicators abstract many late paleozoic foraminifera consistently occur in particular rock types for which depths of deposition may be inferred a few genera appear randomly in many different rock types and were possibly pelagic textulariina in the ammodiscacea most genera of hippocrepininae astrorhizidae and ammodiscidae are widespread and end page 542 common in dark gray shales siltstones fine to very fine sandstones and silty calcareous mudstones deposited in basinal slope and deeper shelf setting below effective wave base in the lituolacea the hormosinidae lituolidae textulariidae trochamminidae and ataxophragmiidae include only a few late paleozoic genera which locally are abundant in dark to medium gray silty shales siltstones silty sandstones and carbonate wackestones and packstones all deposited near wave base miliolina late paleozoic representatives are primitive tubular nonseptate genera of hemigordiopsidae fischerinidae and nubeculariidae these occur mainly in shallow warm water calcareous wackestones fusulinina these were the most taxonomically diverse of the late paleozoic foraminifera and were adapted to a wide range of depth habitats parathuramminacea locally were very abundant in deeper water dark gray calcareous wackestones formed in basins and slopes below wave base endothyracea s l included many genera and families that dominated most of the early carboniferous shallow water calcareous depositional environments nodosinellidae preferred open shelf facies and may have extended to depths below wave base colaniellidae ptychocladiidae paleotextulariidae tetrataxidae tournayellidae endothyridae loeblichiidae and lasiodiscidae locally were common in shallow shelf shoal and lagoonal carbonate wackestones packstones and as displaced fossils in some grainstones uch as oolites bradyinidae were globose had pseudoalveolar walls and were widely scattered in a number of different lithologies suggesting a pelagic or planktonic habitat archaediscidae which have recrystallized wall structure were common in shallow water carbonates and calcareous shales fusulinacea most of which probably had photosynthetic symbionts were adapted to shallow carbonate depositional habitat at depths less than 15 to 20 m 49 to 66 ft carboniferous fusulinidae and ozawainellidae apparently occupied most of this depth range because of their adaptation to middle carboniferous cool surface waters permian schubertellidae and oazawainellidae became adapted to shallow warm water lagoons and shelves verbeekinidae and neoschwagerinidae were common in reef cores and upper flank deposits of permian tethyan reefs schwagerinidae also adapted to shallow to very shallow water carbonate environments such as reef edges shallow lagoons tidal flat channels margins of algal shoals and banks and other shallow nearshore areas for example eoparafusulina formed e tensive skeletal grainstones in many cross bedded subtidal deposits several globose lineages within the fusulinacea possibly were pelagic such as robustoschwagerina pseudoschwagerina verbeekina and many of the permian staffellidae end of article last page 543

late paleozoic depositional sequences are synchronous and worldwide more than fifty transgressive regressive depositional sequences are present in carboniferous and permian shallow marine successions on stable cratonic shelves worldwide these were synchronous depositional events resulting from eustatic sea level changes that generally ranged from 100 to 200 m each transgressive regressive sequence is correlatable using current fossil knowledge they average about 2 m y and range from 1 2 to 4 m y in length the presence within these strata of numerous synchronous unconformities of considerable duration and worldwide extent suggests that the fossil record is very incomplete and that we are studying a punctuated fossil record and not a punctuated evolution based on a highly irregular mutation rate these late paleozoic transgressive regressive depositional sequences facilitate correlations because depositional histories of a rock succession can support interpretations of faunal assemblages and faunal similarities in evaluating age relationships

eustatic and far field tectonic control on the development of an intra platform carbonate shoal complex upper tongue of the tanglewood member upper ordovician lexington limestone central kentucky u s a abstract the lexington or trenton limestone is an upper ordovician chatfieldian edenian upper sandbian lower katian temperate water unit averaging about 60 m thick that was deposited in relatively shallow waters across the lexington platform in east central united states during the taconian orogeny lexington trenton shallow water deposition ended across most of the platform in late chatfieldian time and from that point deepened upward into the more shale rich clays ferry point pleasant and kope formations due to apparent sea level rise in central kentucky however deposition of the lexington limestone continued into early edenian time and includes up to 50 m of additional coarse calcarenites and calcirudites at the top which form the tanglewood buildup and reflect locally regressive conditions apparently related to local structural uplift consequently in central kentucky the lexington is more than 100 m thick and lexington deposition on the buildup continued into early edenian time as an intra platform shoal complex that tongues out into deeper water units in all directions in an attempt to understand how this shoal complex developed we examined the last major body of coarse skeletal sands in the central kentucky lexington limestone the upper tongue of the tanglewood member a 12 m thick succession of fossiliferous calcarenite and calcirudite that occurs across an area of 5200 km 2 near the center of the lexington platform although relatively homogeneous the upper tanglewood is divisible into five small scale fining upward sequence like cycles which contain prominent widespread deformed horizons facies analysis indicates that four lithofacies which reflect distinct depositional environments comprise the sequences across the shoal complex lithofacies were correlated across the shoal complex by integrating cyclicity and widespread deformed horizons in order to delineate the locations of major depositional environments facies analysis shows that the thickest and coarsest parts of each sequence and the shallowest depositional environments coincide with basement fault blocks which are known to have experienced uplift during earlier lexington limestone deposition the occurrence of thick coarse facies on the same blocks suggests that the blocks continued to experience uplift into shallow water where tides and waves redistributed sediments during upper tanglewood deposition although eustasy apparently controlled cyclicity taconian far field forces generated by orogeny in the east seem to have influenced facies distribution in each cycle through reactivation of basement fault zones as synsedimentary growth faults the example of the upper tanglewood member shows that tectonic far field forces can exert important influences on the development of carbonate depositional environments even in distal intracratonic settings like the lexington platform

deciphering continental breakup in eastern australia using low temperature thermochronometers 1 first order topographical features at high elevation passive margins have the potential to store information about the early stages of continental rifting which are usually lost in the sediment record in this study we present a new combination of apatite fission track and u th he analyses from two coast perpendicular traverses to decipher the time of formation and evolution of the escarpment at the southeastern australian margin a combination of inverse and forward modeling of the apatite fission track aft and he data indicates that the coast experienced a rapid denudational event starting at 110 10 ma at least 15 myr before seafloor spreading 85 ma in agreement with the hypothesis that rifting at magma poor margins evolves slowly thus the enhanced denudation is not related to the synbreakup base level drop but it may have been related to a thermally driven transient surface uplift considerations on isostatic flexure and rigidity of the lithosphere indicate that unless significant synrift brittle movements are assumed to have occurred along margin parallel faults that are no more visible the coast must have experienced a higher geothermal gradient than normal the evolution of the rest of the coastal plain may have taken up to 90 myr in agreement with numerical models of passive margins evolution the u th he ages across the coastal plain are consistent with an in place excavation scenario of a high rift shoulder and they rule out the possibility of a constant retreat of the escarpment aft he data from the plateau indicate that the highlands remained stable throughout continental breakup experiencing rates of erosion of 5 10 m myr since at least 200 ma

an undulatory discontinuity surface on a gently inclined muddy ramp possible evidence of secondary helical flow from the geological record an unusual somewhat cryptic undulatory discontinuity has been recognized near the basal contact of the wanakah shale member of the middle devonian ludlowville formation in western new york it is in part marked by undulating diagenetic limestone beds and concretionary horizons but can be traced continuously by subtle surfaces of fossil and pyritic lags this surface marks the top of parallel elongate mud ridges trending approximately n s perpendicular to the inferred e w depositional strike of the appalachian basin in western new york these ridges are observed in the field as irregularly spaced mud swells which have up to 1 5 m of relief and vary from 30 to 50 m or more in width the intervening broad flat channel floors are characterized by dense concentrations of diminutive brachiopods with gastropods and styliolinids which are gradually replaced by thin styliolinid horizons with abundant pyrite nodules and pyritized burrows over the tops of the swells traceable shelly horizons are observed to pinch out over the swells suggesting a period of relatively undisturbed sediment filling following the formation of the channellized surface the interval of nearly barren shale below this irregular surface however contains concretionary horizons and rare styliolinid pavements which are themselves irregular possibly indicating a changing topography for this surface through time previous taphonomic and palaeoecological studies of the lower wanakah shale member have disclosed a well defined regressive transgressive cycle with more subtle superimposed subcycles the undulatory surface described here occurs within the early regressive part of this cycle and appears to record an accentuated regressive kick of a lower order subcycle the formation of this surface is therefore interpreted to be a consequence of regressive submarine erosion and sediment bypass together with redeposition from suspension the development of the channels and parallel longitudinal mud ridges was probably controlled by helical flow cells within offshore directed bottom currents they may be the first recorded instance of sedimentary furrows described from the geological record taphonomic and biofacies data indicate relative depths below average storm wave base suggesting that sediment winnowing and redeposition occurred at depths only rarely affected by the direct impact of storm wave agitation

a metrological approach to measuring 40ar concentrations in k ar and 40ar 39ar mineral standards in geochronology isotopic ages are determined from the ratio of parent and daughter nuclide concentrations in minerals for dating of geological material using the k ar system the simultaneous determination of 40ar and 40k concentrations on the same aliquot is not possible therefore a widely used variant the 40ar 39ar technique involves the production of 39ar from 39k by neutron bombardment and the reliance on indirect natural calibrators of the neutron flux referred to as mineral standards many mineral standards still in use rely on decades old determinations of 40ar concentrations resulting uncertainties both systematic and analytical impede the determination of higher accuracy ages using the k ar decay system we discuss the theoretical approach and technical design of a gas delivery system which emits metrologically traceable amounts of 40ar and will allow for the sensitivity calibration of noble gas mass spectrometers the design of this system is based on a rigorous assessment of the uncertainty budget and detailed tests of a prototype system a number of obstacles and proposed resolutions are discussed along with the selection of components and their integration into a pipette system

multi phase cooling of early cretaceous granites on the jiaodong peninsula east china evidence from 40 ar 39 ar and u th he thermochronology abstract the jiaodong peninsula at the southeastern periphery of the north china craton ncc has undergone complex changes since the mesozoic a striking feature of the ncc is the widespread distribution of late mesozoic magmatic rocks predominantly characterized by granitic intrusions these igneous plutons are economically important due to their polymetallic mineralization and significant as geodynamic tracers of the regional tectonic evolution two representative early cretaceous granites the yashan and yuangezhuang plutons on the jiaodong peninsula were selected for multiple thermochronometer studies to constrain a complete thermal history from their emplacement to near surface conditions we obtained biotite 40ar 39ar ages of two granites on the new generation argus vi noble gas mass spectrometer two biotites registered identical 40ar 39ar plateau ages of 117 ma which are consistent within the error with their zircon u pb ages this suggested that the two granites were emplaced at the same time and cooled rapidly to about 300 c the single crystal zircon u th he zhe dating for the two samples gave weighted mean ages of 93 5 4 5 ma and 93 3 5 0 ma combined with previously published geochronological data and the thermal inversion of the zircon low temperature thermochronological data three phases of rapid cooling were identified for the two studied plutons 1 the early cretaceous 117 110 ma 2 the late cretaceous 100 90 ma and 3 the early tertiary 65 50 ma the early cretaceous phase of cooling occurred in a regional extensional regime on the ncc characterized by various extensional structures the late cretaceous cooling is consistent with the third episode of the yanshan movement which caused a regional basin inversion event on the ncc in comparison to the first two phases of rapid cooling the early tertiary cooling was more gradual this phase corresponded to a widely developed eocene rift on the ncc and the reactivation of major boundary faults such as the giant tan lu fault zone and the taihangshan fault

metal rich fluid inclusions provide new insights into unconformity related u deposits athabasca basin and basement canada the paleoproterozoic athabasca basin canada hosts numerous giant unconformity related uranium deposits the scope of this study is to establish the pressure temperature and composition p t x conditions of the brines that circulated at the base of the athabasca basin and in its crystalline basement before during and after uo2 deposition these brines are commonly sampled as fluid inclusions in quartz and dolomite cementing veins and breccias associated with alteration and u mineralization microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms data from five deposits rabbit lake p patch eagle point millennium and shea creek complement previously published data for the mcarthur river deposit in all of the deposits investigated fluid inclusion salinity is between 25 and 40 wt nacl equiv with compositions displaying a continuum between a nacl rich brine end member cl na ca mg k and a cacl2 rich brine end member cl ca mg na k the cacl2 rich brine has the highest salinity and shows evidence for halite saturation at the time of trapping the continuum of compositions between the nacl rich brine and the cacl2 rich brine end members combined with p t reconstructions suggest anisothermal mixing of the two brines nacl rich brine 180 30 c and 800 400 bars cacl2 rich brine 120 30 c and 600 300 bars that occurred under fluctuating pressure conditions hydrostatic to supra hydrostatic however because the two brines were u bearing and therefore oxidized brine mixing was probably not the driving force for uo2 deposition several scenarios are put forward to account for the cl na ca mg k composition of the brines involving combinations of seawater evaporation halite dissolution mixing with a halite dissolution brine mg ca exchange by dolomitization na ca exchange by albitization of plagioclase na k exchange by albitization of k feldspar and mg loss by mg rich alteration finally the metal concentrations in the nacl rich and cacl2 rich brines are among the highest recorded compared to present day sedimentary formation waters and fluid inclusions from basin hosted base metal deposits up to 600 ppm u 3000 ppm mn 4000 ppm zn 6000 ppm cu 8000 ppm pb and 10 000 ppm fe the cacl2 rich brine carries up to one order of magnitude more metal than the nacl rich brine though the exact origin of major cations and metals of the two brines remains uncertain their contrasting compositions indicate that the two brines had distinct flow paths and fluid rock interactions large scale circulation of the brines in the athabasca basin and basement was therefore a key parameter for metal mobility including u and formation of unconformity related u deposits

gradient analysis of faunal distributions associated with rapid transgression and low accommodation space in a late pennsylvanian marine embayment biofacies of the ames member glenshaw formation conemaugh group in the northern appalachian basin usa abstract the ames sea situated in a shallow marine embayment in the appalachian basin was the result of the most extensive marine transgression of the pennsylvanian in this region gradient analysis of the proportional abundance of taxa reveals an environmental continuum across the ames embayment along which four biofacies were distributed biofacies distribution is interpreted to be controlled by salinity turbidity and oxygen gradients associated with the geometry of the ames depositional basin and relative sea level change the eastern portion of the ames sea resembled a foredeep trough located on the detrital slope of the recently uplifted appalachian highlands biofacies 1 and 2 occur exclusively in the eastern part of the ames depositional basin and are dominated by eurytopic molluscs tolerant of terrigenous influx biofacies 3 occurs in both the eastern and western portions of the ames depositional basin this biofacies is dominated by the opportunistic brachiopod neochonetes which would quickly colonize the seafloor in the wake of transgression d biofacies 4 occurs exclusively in the western part of the ames depositional basin and is composed primarily of stenotopic crinoids bryozoans brachiopods and epifaunal bivalves that inhabited a clear water cratonic ramp on the eastern flank of the cincinnati arch vertical variations of faunal assemblages in the ames member were the result of variations in relative sea level associated with glacio eustatic cycles biofacies 3 dominated by neochonetes was deposited at the base of the ames member during the initial rapid transgression in a mostly dysoxic environment with low turbidity and marine salinity during the first regression low density surface water from eastern sources restricted vertical circulation established a stratified water column and promoted estuarine conditions in the ames embayment well oxygenated surface waters were unable to circulate to the benthic habitat which led to periodically dysoxic conditions and the establishment of biofacies 1 and 2 composed of diminutive eurytopic molluscs a second stratigraphically higher occurrence of biofacies 3 is interpreted to represent a second transgression however unlike the first transgression lithologic and faunal data suggest that the benthic habitat was well oxygenated above the mid ames marine zone occurrence of biofacies 3 biofacies 1 and 2 were deposited in the final regressive phase as local terrigenous source areas brought increasing turbidity and fluctuating salinity to the ames embayment previous paleoecological research on the ames member cited freshwater and or clastic influx as the major controls on biotic distribution but the results of the present study suggest that oxygen availability was also a major control stratification of the water column during the ames sea level cycle promoted estuarine circulation that prevented well oxygenated surface waters from reaching the benthic habitat this led to the deposition of dark gray to black fissile shales that contain fossil assemblages dominated by diminutive molluscs and brachiopods that were tolerant of low oxygen conditions

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

origin of natural waters and gases within the upper carboniferous coal bearing and autochthonous miocene strata in south western part of the upper silesian coal basin poland abstract the molecular and stable isotope compositions of coalbed gases from the upper carboniferous strata and natural gases accumulated within the autochthonous upper miocene skawina formation of the debowiec simoradz gas deposit were determined as well as the chemical and stable isotope compositions of waters from the skawina formation and waters at the top of the upper carboniferous strata of the kaczyce ridge the abandoned morcinek coal mine in the south western part of the upper silesian coal basin two genetic types of natural gases within the upper carboniferous coal bearing strata were identified thermogenic ch4 small amounts of higher gaseous hydrocarbons and co2 and microbial ch4 very small amounts of ethane and co2 thermogenic gases were generated during the bituminous stage of coalification and completed at the end of the variscan orogeny degassing desorption of thermogenic gases began at the end of late carboniferous until the late miocene time period and extended to the present day this process took place in the upper carboniferous strata up to a depth of about 550 m under the sealing upper miocene cover a primary accumulation zone of indigenous thermogenic gases is present below the degassing zone up to 200 m depth from the top of the upper carboniferous strata within the weathered complex an accumulation zone of secondary microbial gas occurs waters within these strata are mainly of meteoric origin of the infiltration period just before the last sea transgression in the late miocene and partly of marine origin having migrated from the upper miocene strata then both methanogenic archaebacteria and their nutrients were transported by meteoric water into the near surface carboniferous strata where the generated microbial ch4 saturated coal seams waters within the miocene strata of the debowiec simoradz and zablocie are of marine origin and natural gases accumulated within autochthonous miocene strata of the debowiec simoradz gas deposit were most probably generated by microbial processes of on organic matter dispersed within the strata though some contribution of gases migrating from the carboniferous coal bearing strata cannot be excluded

calibration of ga1550 biotite standard for k ar and 40ar 39ar dating abstract the mineral separate ga1550 biotite has become an international standard for k ar and 40 ar 39 ar dating studies although it was prepared as an intralaboratory standard at anu to monitor tracer depletion from a gas pipette it is one of a small number of samples that has been calibrated against 38 ar tracers some of which had been mixed with known amounts of atmospheric argon so that a so called primary calibration has been performed by measuring ga1550 biotite against additional tracers from the same batch we have determined the radiogenic argon content of this sample as 1 342 0 007 10 9 mol g and together with the measured k content of 7 645 0 050 weight percent we derive a best estimate for the k ar age as 98 5 0 5 ma where the error is derived from averaging the ages determined relative to the 38 ar tracer

unraveling multiple thermotectonic events accommodated by crustal scale faults in northern iberia spain insights from k ar dating of clay gouges

40ar 39ar ages and residual volatile contents in degassed subaerial and subglacial glassy volcanic rocks from iceland abstract major volatile contents h 2 o co 2 f cl and s and 40 ar 39 ar ages have been determined in variably degassed rhyolite obsidians from pleistocene holocene aged subaerial and subglacial eruption environments from the torfajokull volcanic center and the monogenetic volcano at prestahnukur iceland icelandic subglacial rhyolites preserve residual h 2 o contents of 0 08 0 69 wt undetectable co 2 840 1780 ppm f 430 2000 ppm cl and 6 45 ppm s most subglacial obsidians have degassed volatile signatures at the time of their eruption under ice one eruption blahnukur torfajokull showed h 2 o contents which exceed those expected for quenching at atmospheric pressures up to 0 69 wt h 2 o and are consistent with eruption at 40 kbar of pressure or equivalent to under 450 m of ice altered and microcrystalline groundmass in some subglacial rhyolites yield variable volatile contents that are likely the result of micro scale variability and the presence of alteration products two subaerial rhyolite obsidians gave low volatile contents consistent with quenching at the surface new 40 ar 39 ar ages were determined on the subglacially erupted rhyolites and provide broad constraints on the timing and frequency of glacio volcanism during the pleistocene three subglacial eruptions at torfajokull yielded ages of 108 22 ka blahnukur 255 20 ka habarmur and 236 7 ka hasker ingur which fit into a range of previously determined ages at torfajokull of 67 384 ka a new age of 132 19 ka was determined for the monogenetic subglacial eruption at prestahnukur holocene aged subaerial volcanic glass produced no ages due to large amounts of air derived 40 ar 84 93 preliminary apparent 40 ar 39 ar ages from the limited feldspar phenocrysts available in these crystal poor samples yield erroneous apparent plateau ages far older than eruption ages suggesting a homogenously distributed excess ar component disturbances to the 40 ar 39 ar geochronometer are correlated with a heterogeneous distribution of volatiles in glass and linked to hydration e g kaldaklofsfjoll mild alteration e g habarmur and alteration and or recrystallization of glass e g blahnukur our observations indicate however that unaltered subglacially erupted glasses that are partially to wholly degassed are promising materials for the application of the 40 ar 39 ar geochronometer the precision to which we can date these young glassy samples currently limits the use of 40 ar 39 ar geochronometer as a tool for understanding the exact timing and duration of glaciovolcanism in the recent past

the occurrence of a secondary zone of coal bed methane in the southern part of the upper silesian coal basin southern poland potential for methane exploitation abstract coal bed methane cbm exploitation in the upper silesian coal basin has in spite of earlier failures again aroused investor interest carboniferous coal seams at depths of 200 500 m are characterized by coal permeability values estimated at 27 230 md and degrees of methane saturation almost 100 that suggest future successful exploitation based on the results of geological surveys archived in the polish geological institute the shallow cbm zone is defined as a gas horizon distinct from a deep cbm zone the disposition of the shallow zone follows the topography of the upper carboniferous paleorelief and is deemed the most important factor controlling methane distribution within this zone the most favorable places for cbm accumulation within the shallow coal seams are erosional highs and the slopes of upper carboniferous ridges associated with fault zones the thickness of the zone 200 m and methane contents 8 m 3 t coal daf are highest in these places the nearly full saturation of the coal seams with methane reflects the involvement of two genetic types of gas indigenous late stage microbial methane and thermogenic methane derived from the deeper coals the favorable geological characteristic of this shallow cbm zone is a potential source of energy for upper silesia

walchian conifers from the mid late pennsylvanian conemaugh group in the appalachian basin stratigraphic and depositional context and paleoclimatic significance abstract walchian conifers are indicators of seasonally dry habitats of the euramerican subtropics and tropics and are of considerable value in tracking both short term and long term pennsylvanian permian paleoclimatic changes in central pangea walchian conifer macrofossils first appeared in north america during the middle pennsylvanian but are rare in central pangean coal basins until the permian an abrupt climate change occurred near the desmoinesian missourian boundary that was characterized by global warming stronger seasonality and shorter wet phases this change coincided with the regional extinction of most tree lycopsids and the appearance of widespread high chroma calcic vertisols and aridisols only four occurrences of walchia have been reported from the pennsylvanian of the appalachian basin 1 7 11 mine of eastern ohio 2 rennersville in southwest pennsylvania and 3 charleston and 4 cedar run both in southern west virginia this paper uses recently acquired outcrop data to more fully document and reevaluate the depositional and stratigraphic context of the west virginia assemblages and their paleoclimatic and paleogeographic implications the cedar run walchia assemblage occurs in olive mudshale of an abandoned fluvial channel fill 15 8 16 9 m above the base of the ames limestone indicating an early virgilian age it consists of compressions and impressions of branches and branchlets of walchia lepidophylloides cordaites and rare neuropteroid pinnules the channel fill at this location is a component of the grafton sandstone incised valley fill previously described from the study area correlation of paleosol bounded marine cored cyclothems in the study area with their nonmarine cyclothem equivalents at charleston west virginia indicates the walchia previously reported at the mahoning coal horizon occurs between the brush creek and bakerstown coals and is therefore missourian not late desmoinesian and similar to the revised age for the 7 11 mine walchia reported from eastern ohio late pennsylvanian upland or dryland conifer communities were comprised of walchia cordaites and sigillaria which produced a forest with seed ferns as an understory the cedar run assemblage was probably transported into the valley from adjacent well drained coastal plain uplands formed during valley incision and deposited within the early transgressive systems tract it is also possible that walchia expanded into the valleys when drainage became ephemeral during more arid climatic phases the revised correlations of appalachian basin walchia horizons indicate their appearance closely followed rather than predated the abrupt climate change and extinctions at the desmoinesian missourian boundary

origin of brines in the upper silesian coal basin poland inferred from stable isotope and chemical data brines in the miocene formations of the upper silesian coal basin have isotopic composition close to smow which identifies them as the connate marine water however controversies exist on the origin of brines in the carboniferous formations isotopic and hydrochemical data exclude any relationship to marine water and enrichment by evaporation the most common brine which occurs at great depths can be identified as the oldest infiltration in a very hot climate 18o 2 d 20 cl content 34 to 140 g l this brine is free of so42 and u and rich in ba2 and226ra its salinity is probably related to the leaching of evaporites and intensive weathering of rocks during the rotliegendes other brines are difficult to identify because their isotopic contents are within the range of mixing between the oldest brine and the quaternary waters 18o 10 d 70 isotopic and hydrochemical data allow identification of several occurrences of brine formed by meteoric water of a warm tertiary climate after the last marine transgression in the tortonian that brine is rich in so42 and contains moderate contents of226ra and u its salinity is thought to result from leaching of miocene evaporites two other identified types of brines can be related to some infiltration periods before the last marine transgression the sources in salinity of these 2 types remain unknown mining activity results in a common occurrence of mixed brines when the quaternary component dominates its identification is easy from the isotopic composition whereas the end brine component can ususally be identified by chosen ion ratios and the presence or lack of sulphates

record of glacial eustatic sea level fluctuations in complex middle to late pennsylvanian facies in the northern appalachian basin and relation to similar events in the midcontinent basin abstract pennsylvanian cycles in the northern appalachian basin nab were historically considered to result from delta lobe switching and more recently from sea level fluctuation with sandy deltas prograding during highstand these interpretations are revised using new data from cores and outcrop exposures thick 5 m channel deposits with a marked erosion surface at their base cutting down across previous cycles are re interpreted as incised valley fill ivf deposits in paleovalleys because the basal erosion surfaces are widespread and thus reflect a record of lowstand most common are simple paleovalleys that contain mainly sandy fluvial deposits compound paleovalleys with sequence boundaries above the basal erosion surface contain terrestrial estuarine and marine deposits early to late highstand deposits in interfluvial parts of the cycles are dominated by shale and mudstone with paleosols coals and local non marine limestone which reflect floodbasin to lacustrine conditions these reinterpretations are applied to previously and newly recognized cycles in ascending order upper kittanning lower freeport upper freeport leader new upper freeport piedmont new mahoning mason interval locally includes upper new galilee in the north and brush creek across a 300 km arc in the northern appalachian basin these deposits accumulated in a high shelf setting that experienced fewer marine transgressions and were interrupted by more frequent exposure and downcutting in contrast to the thicker and more complete succession with more numerous marine units in the midcontinent magnitudes of highstand transgressions into this basin deduced from the up dip extent of marine and brackish fossil assemblages were greatest for the brush creek less so for the upper kittanning and mahoning and least for the lower freeport upper freeport leader piedmont and mason the anomalous basin wide fresh water roofshales and equivalents of the upper freeport coal may reflect ponding of fresh water to the north by an elevated area that prevented marine encroachment at the southern opening of the basin along the kentucky ohio border maximum thicknesses of ivf deposits in each cycle are used as a proxy for estimating the minimum depth of lowstand incision preceding transgression while the thickness of ivf deposits in most cycles ranges from 6 to 20 m the two thickest are 30 m thick one associated with the pre mahoning paleovalley and the other with the immediately post mahoning paleovalley the extent of transgression of each cycle in the nab is roughly equivalent to those of their age correlative major marine cyclothems pawnee through swope in the midcontinent moreover the amount of incision between them is also roughly equivalent to the amount of regression between each of the roughly coeval cyclothems in the midcontinent with the deepest incisions in the nab pre mahoning and post mahoning corresponding to the greatest southward withdrawals of the sea in the midcontinent memorial and seminole hepler during this same interval

apatite u th he age constraints on the development of the great escarpment on the southeastern australian passive margin the southeast australian margin like other high elevation passive margins is characterised by a steep escarpment that separates a dissected coastal plain from a low relief inland plateau quantitative constraints on the generation of escarpments can be provided by apatite u th he ages here we use a coast perpendicular traverse across the coastal lowlands escarpment and plateau to test the three prevailing models of se australian escarpment formation namely retreat into a downwarped rift shoulder escarpment retreat and down wearing on high elevation rift shoulder with flexural rebound apatites from the coastal plain have he ages of between 87 and 112 ma suggesting that the coastal lowlands developed very rapidly after rifting and continental break up at 85 100 ma the he age data are inconsistent with the erosion of a downwarped rift margin and cannot be explained by a constant post break up rate of lateral escarpment retreat across the coastal plain or by constant down wearing the data require either rapid escarpment retreat or rapid in place excavation of the escarpment soon after break up in response to rifting and the lowering of base levels on the margin of the new continent at break up followed by a period of landscape stability and low erosion combined with the existing apatite fission track record the he data are consistent with erosion of 3 4 km within a maximum of 28 myr of break up at a minimum vertical erosion rate of 130 m myr 1 along the coast the rapid denudation period across the coastal plain in this region took less than 48 myr from the coast to the escarpment base which corresponds to an average vertical erosion rate of 45 m myr 1 this is equivalent to a mean escarpment retreat rate of 5 10 km myr 1 apatite he ages from the plateau 183 247 ma indicate that the highlands remained stable throughout continental break up experiencing average erosion rates of less than 10 m myr 1 since the late palaeozoic early mesozoic

wa1ms a 2 61 ga muscovite standard for 40ar 39ar dating abstract the 40ar 39ar dating technique requires the use of neutron fluence monitors standards to allow calculation of the age of a sample precise calibration of these standards is crucial to obtaining accurate ages and decreasing the uncertainties associated with 40ar 39ar dates few fully intercalibrated 40ar 39ar standards with a sufficient total fusion grain to grain reproducibility are currently in use in the argon community for precambrian samples only hb3gr hornblende 1 08 ga yields sufficient grain to grain reproducibility and has an appropriate age for acceptable argon isotopic ratio measurements here we present chemical and intercalibration results for a new 2 61 ga standard wa1ms is a muscovite extracted from an archaean shear zone in the lake johnston greenstone belt western australia in situ trace element analysis by ela icpms revealed consistent k contents subtle zonation and intra grain and grain to grain heterogeneities in rb sr ti and fe but a lack of mineral inclusions wa1ms has been investigated over 3 irradiations ranging from 25 to 40 h in two reactors with several disc positions and three grains sizes and has been calibrated against fcs and ga1550 and hb3gr overall we carried out 48 total fusion and 4 step heating experiments of wa1ms crystals flat age spectra and average f value 40ar 39ark relative standard deviations ranging from of 0 43 to 0 60 p 0 15 0 83 for 47 48 analyses demonstrate the reproducibility of wa1ms and its suitability as a reliable 40ar 39ar standard we calculated r wa1ms fcs 205 59 0 25 r wa1ms ga1550 57 25 0 06 and r wa1ms hb3gr 3 9713 0 014 all with p 0 14 allowing direct comparison between wa1ms and any standards in used in the community provided that they have been calibrated against any of the three standards used in the calibration and regardless of the age adopted for each of these standards the recently revised decay constant values and standard ages proposed by renne et al 2011 yield a weighted mean age of 2614 2 1 5 ma 0 055 p 0 8 1 for wa1ms against the three standards when calibrated solely against fcs in order to minimize correlated errors between fcs vs ga1550 and hb3gr we calculate a preferred age of 2613 0 2 4 ma 0 09 which is recommended when using this standard additionally this corresponds to a 40ar 40k value of 0 3375 0 0057 10 1 for wa1ms which is independent of the value of the decay constant used for calculation and allows recalculation of the age of wa1ms for any preferred set of decay constants and standard ages using the constants proposed by steiger and jager 1977 directly calculated from the three r values yields an age of 2598 2 3 5 ma corresponding to an identical although less precise 40ar 40k value of 0 3375 0 0086 10 1 benefits of this standard include 1 an increased relative precision per crystal analyzed relative to other standards for proterozoic and archaean samples 2 no post irradiation waiting time due to the absence of ca no need to wait for 37arca decay and 3 loading of standard grains that are optically different from the unknown e g pyroxene or hornblende to avoid standard unknown mixing wa1ms is freely available to the 40ar 39ar community

tracing the interaction of acid mine drainage with coal utilization byproducts in a grouted mine strontium isotope study of the inactive omega coal mine west virginia usa abstract in order to ameliorate acidic discharge the inactive omega coal mine west virginia was partially filled by injection of a grout consisting of 98 coal utilization byproducts cub including fluidized bed combustion ash and fly ash and 2 portland cement in this study discharge chemistry and sr isotope ratios were determined to identify and quantify the extent of interaction between mine waters and the cub cement grout eight sampling sites were monitored around the downdip perimeter of the mine the major and trace element chemistry of the discharges was generally not sufficient to distinguish between discharges that interacted with grout and those that did not elements that showed the most separation include k and as which were elevated in some waters that interacted with cub cement grout in contrast the sr isotope ratios clearly distinguished discharges from grouted and non grouted areas discharges that bypassed the grouted portions had 87 sr 86 sr ratios ranging from 0 71510 to 0 71594 while two discharges that interacted with grout had ratios in the range of 0 71401 0 71456 the treatment inlet which includes both grouted and ungrouted discharges yielded intermediate isotopic ratios leaching experiments on cub cement grout coal and surrounding rocks are consistent with the isotopic trends observed in the discharges based on these results waters that interacted with grout received 30 40 of their sr from the cub cement grout material these results suggest that the grout material is chemically eroding at a rate of approximately 0 04 per year this novel application of the sr isotope system illustrates its ability to sensitively track and quantify fluid interaction with coal and cub based grout

glacier fed sandstone sheets in the weller coal measures permian allan hills antarctica abstract the upper member of the weller coal measures permian at allan hills victoria land antarctica consists of repetitive coal layers separated by sheetlike bodies of predominantly sandstone and subordinate siltstone and conglomerate all of fluvial origin investigation of the lowermost inter coal sheet wc1 reveals abrupt planar basal contacts persistent upward fining and a strong westward palaeocurrent trend three lithofacies are recognized in the wc1 sheet a small scale cross bedded pebbly sandstone which occupies most of the basal portions of the sheet b large scale cross bedded medium coarse sandstone confined to a linear ne sw belt overlying or locally replacing facies a and c siltstone and rippled fine grained sandstone which drapes and overlaps facies a and b and contains glossopteris leaves and vertebraria root traces facies distribution patterns indicate the wc1 body initiated as an abrupt sheetlike incursion of coarse sediment over a low lying mire facies a followed by entrenchment and confinement of flow as the sheet extended distally facies b facies c represents low energy floodplain sedimentation co existing with and later succeeding facies b as deposition evolved toward abandonment and eventual renewal of peat deposition relatively rapid deposition of the sandstone sheet is implied by the lack of any significant hiatus markers outsized clasts up to 45 cm in diameter one observed to display prominent striations occur sporadically throughout the wc1 including within siltstone beds of facies c these are inferred to be ice rafted deposits which together with other evidence suggest meltwater influence possibly glacial on sediment transport and deposition preliminary examination of other sandstone sheets in the upper weller indicates attributes similar to the wc1 including abrupt bases upward fining character and predominantly westward palaeocurrent patterns the allan hills exposures are believed to represent a succession of low lying mire complexes interrupted by abrupt but infrequent incursions of coarse sediment possibly by extreme meltwater floods

the occurrence and behavior of radium in saline formation water of the u s gulf coast region abstract radium has been measured in deep saline formation waters produced from a variety of u s gulf coast subsurface environments including oil reservoirs gas reservoirs and water producing geopressured aquifers a strong positive correlation has been found between formation water salinity and ra activity resulting from the interaction of formation water with aquifer matrix ra isotopes enter the fluid phase after being produced by the decay of parent elements u and th which are located at sites on and within the solid matrix processes that are belived to be primarily responsible for transferring ra from matrix to formation water are chemical leaching and alpha particle recoil factors controlling the observed salinity ra relationship may be one or a combination of the following factors a ion exchange b increased solubility of matrix silica surrounding ra atoms coupled with a salinity controlled rate of reequilibration of silica between solution and quartz grains and c the equilibration of ra in solution with detrial barite within the aquifer no difference was found in the brine ra relation in water produced from oil or gas wells and water produced from wells penetrating only water bearing aquifers although the relation was more highly correlated for water bearing aquifers than hydrocarbon containing reservoirs

depositional environments and sequence stratigraphy of the late carboniferous early permian coal bearing successions shandong province china sequence development in an epicontinental basin abstract this study focuses on the late carboniferous early permian coal bearing successions in shandong province north china in order to understand the depositional processes and sequence stratigraphic framework in an epicontinental basin based on detailed analysis of eleven facies five facies assemblages fas were recognized in the studied succession fa1 3 are present mainly in the benxi and taiyuan formations and consist of mixed siliciclastic and carbonate lithofacies representing eluvial lagoon barrier lagoon and tidal flat environments fa4 occurs in the shanxi formation and consists mainly of interbedded medium to fine sandstone siltstone mudstone and coal lithofacies representing river dominated deltaic environments fa5 is characterized by interbeds of trough cross stratified coarse sandstone and silty mudstone mainly in the lower shihezi formation which was deposited in meandering river channel and floodplain three third order sequences were established based on the vertical arrangement of facies assemblages and identification of physical surfaces i e subaerial unconformity transgressive surface and regressive surface each sequence comprises a transgressive systems tract tst and a highstand systems tract hst tst of sequence 1 is composed of eluvial lagoonal deposits fa1 whereas hst formed in lagoon barrier and tidal flat settings fa2 and fa3 tst of sequence 2 formed in a barrier lagoon system fa2 whereas hst is characterized by repetitive accumulation of interbedded limestone sandstone mudstone and coal deposited under lagoonal and tidal flat settings fa2 and fa3 tst of sequence 3 comprises fa2 and hst mainly fa4 deposited in a river dominated shallow water delta system sequence 3 is overlain by a fluvial sequence fa5 the three third order sequences in the shandong region are generally correlated with those in the taebaeksan basin south korea the eastern part of the north china block the relative sea level curves established in the two regions show a generally similar long term rising trend

composition and origin of coalbed gases in the upper silesian and lublin basins poland abstract coalbed gases in the upper silesian coal basin uscb are highly variable in molecular and stable isotope composition geochemical indices and stable isotope ratios for coalbed gases from uscb vary within the following ranges ch4 c2h6 c3h8 hydrocarbon index from 122 to more than 10 000 cdmi carbon dioxide methane index cdmi co2 co2 ch4 100 from 0 0 to 21 0 13c ch4 from 79 9 to 44 5 d ch4 from 202 to 153 13c c2h6 from 24 6 to 22 3 13c c3h8 24 7 one sample and 13c co2 from 27 2 to 2 8 only two coalbed gases were collected from the lublin coal basin lcb geochemical indices and stable isotope ratios for these samples show the following values hydrocarbon index more than 10 000 cdmi 4 3 and 34 6 13c ch4 67 3 and 52 5 d ch4 201 one sample and 13c co2 13 7 and 11 9 methane higher gaseous hydrocarbons c2 to c5 and carbon dioxide occurring in the coalbed gases in both the uscb and the lcb were generated during the bituminous stage of the coalification process and probably during microbial reduction of carbon dioxide however depth related isotopic fractionation which has resulted from physical e g diffusion and adsorption desorption processes during gas migration cannot be neglected in both basins the coalification process lasted no longer than several ma and was completed at the end of the variscan orogeny at the turn of carboniferous and permian

cyclicity in the middle eocene cayraz carbonate formation haymana basin central anatolia turkey abstract the haymana basin in central anatolia turkey developed on a fore arc accretionary wedge during the late cretaceous and the middle eocene turbidite deposits fill the center of the basin and grade northwestward into shallow marine clastics and carbonates which in turn pass into lacustrine and fluvial deposits toward the margin the middle eocene cayraz formation represents the youngest paleotectonic unit of the haymana basin it is composed of two shelf systems ss each formed by a package of nummulitic banks and intervening calcareous mudstones 150 250 m thick overlying 70 100 m thick monotonous mudstones within each of the two shelf systems two orders of coarsening upward and shallowing upward sequences are recognized the smaller order sequences 3 10 m thick are termed basic units bu four types of basic units have been distinguished these are made up of either calcareous mudstone overlain by a nummulitic bank or silty mudstone overlain by sandy to conglomeratic beds each basic unit represents a specific depositional environment ranging from quiet lagoon or open marine to more energetic bank or sandy bar basic units are vertically associated to form three types of 15 35 m thick basic sequences bs which represent the time and space evolution of the shelf systems owing to their small scale their lateral association and the condensed nature of their bounding surfaces basic units are considered to be allocyclic transgressive regressive cycles tuned to milankovitch bands at the scale of basic sequences bs and shelf systems ss the lateral and vertical distribution of the sequences and the presence of onlap structures strongly suggest sea level changes the sequential organization thicknesses of basic units and basic sequences and an estimated sedimentation rate favour sea level changes controlled by milankovitch climatic cycles amalgamation or condensation of basic units in basic sequences and the existence of locally accentuated onlaps suggest a coupled effect of discontinuous subsidence

characterizing thermogenic coalbed gas from polish coals of different ranks by hydrous pyrolysis abstract to provide a better characterization of origin and volume of thermogenic gas generation from coals hydrous pyrolysis experiments were conducted at 360 c for 72 h on polish coals ranging in rank from lignite 0 3 r r to semi anthracite 2 0 r r under these conditions the lignites attained a medium volatile bituminous rank 1 5 r r high volatile bituminous coals attained a low volatile bituminous rank 1 7 r r and the semi anthracite obtained an anthracite rank 4 0 r r hydrous pyrolysis of a coal irrespective of rank provides a diagnostic 13 c value for its thermogenic hydrocarbon gases this value can be used quantitatively to interpret mixing of indigenous thermogenic gas with microbial methane or exogenous thermogenic gas from other sources thermogenic methane quantities range from 20 dm 3 kg of lignite 0 3 r r to 0 35 dm 3 kg of semi anthracite 2 0 r r at a vitrinite reflectance of 1 7 r r approximately 75 of the maximum potential for a coal to generate thermogenic methane has been expended at a vitrinite reflectance of 1 7 r r more than 90 of the maximum potential for a coal to generate co 2 has been expended assuming that these quantities of generated co 2 remain associated with a sourcing coal bed as uplift or erosion provide conditions conducive for microbial methanogenesis the resulting quantities of microbial methane generated by complete co 2 reduction can exceed the quantities of thermogenic methane generated from the same coal bed by a factor of 2 5

sedimentary cyclicity in the marine pliocene pleistocene of the wanganui basin new zealand sequence stratigraphic motifs characteristic of the past 2 5 m y earth s climatic history since 2 5 ma has been controlled by milankovitch variations in the planetary orbit comprising alternate periods of glaciation and interglaciation with a dominant frequency of 41 000 yr concomitantly eustatic sea level has fluctuated 70 to 130 m causing rapid transgressions and regressions of the shoreline across the world s continental shelves the resulting sedimentary record is cyclothemic each cyclothem corresponding to a single climate and sea level cycle the wanganui basin new zealand contains a 2 km thick almost complete composite record since isotope stage 100 ca 2 5 ma in the form of 47 superposed cyclothems of shelf origin each cyclothem corresponds to an unconformity bound stratigraphic sequence and typically contains a transgressive systems tract sometimes a mid cycle shell bed a highstand systems tract and sometimes a regressive systems tract no advantage accrues from using transgressive regressive units rather than cyclothems and or sequences in description of the succession six basic sequence motifs represent deposition in locations between the shoreline and offshore shelf i e the hawera birdgrove turakina seafield castlecliff and rangitikei motifs a seventh the nukumaru motif which includes dominant coquina limestone represents deposition in shallow water areas of reduced terrigenous sediment on the flank of the basin the sequence motifs represented in any section change systematically in sympathy with basin scale changes in subsidence and sediment supply in contrast with the 41000 year length of individual glacioeustatic sequences these basin wide tectonic cycles have a periodicity of many hundreds of thousands to a few million years i e that of third or fourth order sequences of the exxon type this coupled with the restriction of strongly cyclothemic sediments to geological periods of known glacio eustasy permiancarboniferous pliocene pleistocene suggests that tectonic subsidence cycles rather than glacio eustasy are the driving forces behind the development of the third and fourth order unconformity bound sequences that are reported to occur throughout the stratigraphic record

sedimentary environment dynamics and the formation of coal in the pennsylvanian variscan foreland in the ruhr basin germany western europe during the pennsylvanian formation of coal was a phenomenon that was spread over many continents it is the aim of this paper to illustrate factors that led to the formation of coal seams in paralic clastic sedimentary environments in the ruhr basin german variscan foreland during the pennsylvanian in terms of sequence stratigraphy and the structural evolution of the basin lithostratigraphic sections from exploration wells in the currently explored zone of the coal basin allowed the generation of volumetric lithofacies models using geostastical methods these models support the analysis of sedimentary facies and a sequence stratigraphic interpretation of the successions that are widely correlated throughout the basin we then evaluate the relation of the sequence stratigraphic elements derived from the facies models with the abundance of coal seams

fractionation in a zoned monzonite pluton mount dromedary southeastern australia mount dromedary pluton is one of several predominantly monzonite plutons and smaller intrusive bodies which constitute the dromedary igneous complex in southeastern new south wales the pluton exhibits a striking arrangement of petrographically but not always chemically distinct zones ranging from mafic monzonite at the outside to quartz monzonite in the centre the rocks display a mineralogical and geochemical integrity which indicates a consanguineous relationship minor compositional discontinuities between zones together with observed and inferred minor intrusive zone boundaries suggest that each zone has to some extent evolved independently negative eu anomalies in ree abundance patterns show that some of the zones have been affected by fractionation of feldspar but complementary accumulates are not found at the present levels of exposure the pattern of zoning can be explained by a process of shallow fractional crystallization in which variations within zones are the result of lateral accretion of alkali feldspar as well as settling and or lateral accretion of mafic phases at lower levels in the intrusion and upward displacement of fractionated magma the parental magma of the pluton probaby originated by partial melting of an alkali basalt composition with an amphibolite mineralogy at the base of the crust

assessing the impact of serwis mine tailings site on farmers wells using element and isotope signatures holy cross mountains south central poland this paper presents the results of a geochemical and isotopic study of technogenic soils and acid pool waters in the abandoned mine tailings pile and its potential impact on the adjacent farmers wells at the village of serwis south central poland the acid tailings pools showed strong trace element and ree signals these acid pools were featured by the predominance of medium rare earth elements mree with a strong positive gd anomaly the technogenic soils also revealed a mree roof shaped pattern but with distinct positive excursions in gd sm eu and ce the 34s so42 signatures of acid pool waters mean of 1 3 were close to those of soils and pyrite means of 2 3 and 3 2 respectively the waters of four farmers wells exhibited nearly the same 34s so42 values 0 7 4 0 as the nearby acid pool waters 0 3 3 1 the similar 34s isotope signatures combined with the highest contents of dissolved so42 181 577 mg l in these wells suggest that the tailings pile is a potential source of so42 derived from pyrite weathering this relationship may also be evidenced by a spatial site variable dendrogram that groups these four wells into one cluster at the linkage distance dlink dmax 100 53

geochemistry of highly saline fluids in siliciclastic sequences genetic implications for post variscan fluid flow in the moravosilesian palaeozoic of the czech republic ubiquitous post variscan dolomites occur in zn pb cu veins at the nizk jesenik mountains and the upper silesian basin lower and upper carboniferous siliciclastics at the eastern part of the bohemian massif crush leach stable isotope oxygen and carbon and microthermometry analysis of the fluid inclusions in dolomites enable understanding the geochemistry origin and possible migration pathways of the fluids homogenisation temperatures of fluid inclusions range between 66 and 148 c with generally higher temperatures in the nizk jesenik mountains area than in the upper silesian basin the highest homogenisation temperatures up to 148 c have been found near major regional faults and the lowest in a distant position or at higher stratigraphic levels highly saline 16 6 28 4 eq wt nacl h2o nacl cacl2 mgcl2 fluids occur in inclusions na cl br systematics of trapped fluids and a calculated oxygen isotopic fluid composition between 0 9 and 3 0 v smow indicate that the fluid was derived from evaporated seawater stable isotopic modelling has been used to explain stable isotopic trends isotopic values 13c 6 0 2 0 v pdb 18o 15 5 22 5 v smow of dolomites resulted from fractionation and crystallisation within an open system at temperatures between 80 and 160 c rock buffering explains the isotopic composition at low w r ratios organic matter maturation caused the presence of isotopically light carbon in the fluids and fluid rock interactions largely controlled the fluid chemistry k li br and na contents k cl i cl and li cl molar ratios the fluid chemistry reflects well the interaction between the fluid and underlying limestones as well as with clay and organic rich siliciclastics no regional trends in temperature or fluid geochemistry favour a fluid migration model characterised by an important vertical upward migration along major faults a permeable basement and fractured sedimentary sequence enhanced the general nature of the fluid system fluid characteristics are comparable with the main post variscan fluid flow systems in the polish cracow silesian ore district and german sedimentary basins

correlation of carboniferous strata using a hierarchy of transgressive regressive units carboniferous strata can be described interpreted and correlated using six scales of allocyclic transgressive regressive t r units these t r units are inferred to be the net result of deposition during cycles of sea level change all pennsylvanian and lower permian strata constitute one second order t r unit or synthem the pennsylvanian system contains third fourth fifth and sixth order t r units that can be correlated across both marine and nonmarine facies in the appalachian basin this permits differentiation of allocyclic t r units from autocyclic t r units or fluvial autocyclic units the hierarchical approach is also useful for predicting the location of marine horizons coals claystones and various types of stratigraphic breaks a hierarchical scheme of allocyclic t r units could be combined with biostratigraphic radiometric and magnetostratigraphic data to form a practical chronostratigraphic framework for the carboniferous

40ar 39ar ages of flood basalt provinces in russia and china and their possible link to global faunal extinction events a cautionary tale regarding alteration and loss of 40ar abstract the hypothesis that the permo triassic boundary ptb mass extinctions were caused by flood basalt volcanism in russia siberian traps and or china the emeishan traps is investigated from the point of view of time of occurrence 40 ar 39 ar ages numerous published ages in the literature are rejected as good estimates of the time of crystallization the filters applied in this respect are a statistical reliability of plateau isochron sections of stepheating data and b the alteration state of the material that was dated alteration appears to be ubiquitous unsurprising since most of the material dated was used without acid leaching a procedure that is effective in yielding fresh er samples of 70 ages in the literature for the main pulse of siberian trap volcanism less than ten prove to be reliable ages similar techniques applied to 40 ar 39 ar for the emeishan traps leaves only a single reliable age for the magmatic episode these ages are compared to both published and new 40 ar 39 ar ages for the ptb as based on analysis of minerals from critical ash beds in china there is good overlap in the ages ptb 250 0 0 1 ma siberian trap lavas 250 1 0 4 ma lending credence to a genetic link between the formation of the siberian traps and the faunal extinction event at the ptb a similar link for the formation of the viluy traps russia and the late devonian extinction event is investigated only a single reliable 40 ar 39 ar age is available for the viluy traps and falls close to the interpolated age for the frasnian fammenian boundary the use of the unspiked k ar technique to yield accurate ages for such altered samples is questioned a review of u pb data pertinent to these problems suggests a close temporal link between the formation of the siberian traps and the ptb comparison of u pb and 40 ar 39 ar ages for the ptb raises questions about the accuracy of high precision sanidine ages possibly resulting from very slow leakage of 40 ar from this mineral

geology and 40ar 39ar geochronology of the middle miocene mcdermitt volcanic field oregon and nevada silicic volcanism associated with propagating flood basalt dikes at initiation of the yellowstone hotspot

characterization of the rhyolite of bodie hills and 40ar 39ar intercalibration with ar mineral standards abstract the rhyolite of bodie hills california is characterized compositionally and the geochronology of selected phases is studied sanidine bhs from the rhyolite is well suited as a 40ar 39ar reference material with high k ca and radiogenic yield intercalibration with ga1550 biotite from the dromedary igneous complex new south wales australia yields an age of 9 7946 0 0031 ma for bhs relative to an age of 98 79 0 54 ma for ga1550 and a calibration factor rbhs ga1550 of 0 096719 0 000032 bhs is also intercalibrated with sanidines of the taylor creek rhyolite tcs rtcs bhs of 2 90874 0 00067 fish canyon tuff fcs rfcs bhs of 2 88339 0 00088 and rhyolite of alder creek acs racs bhs of 0 12028 0 00024 these calibration factors yield ages of 28 344 0 011 ma 28 099 0 013 ma and 1 1809 0 0024 ma for tcs fcs and acs respectively relative to ga1550 full propagation of errors increases these uncertainties and that of bhs to 0 9 of their ages calibration of bhs using the astronomically tuned age of fcs determined by kuiper et al 2008 yields an age of 9 8295 0 0036 ma stepwise heating of bhs reveals the same small progressive increase in age across the age spectrum reported for fcs acs and other potassium feldspars e g foland and xu 1990 phillips et al 2017 this increase is consistent with mass fractionation of argon during step heating and favors use of single step fusion ages of all sanidines for monitor and calibration purposes zircons from the rhyolite of bodie hills are strongly zoned in u and th and u pb geochronologic analyses suggest multiple generations of zircon growth the youngest ages indicate a crystallization age of 9 97 0 08 ma 2 arguably similar to the 40ar 39ar results when residence time is considered but previous episodes of zircon growth began at least 400 ka prior to eruption precise u th he thermochronology of these zircons is difficult because crystal to crystal variations in the magnitude and complexity of their u th zoning complicates accurate alpha ejection calculations replicate conventional single crystal u th he ages are more widely dispersed than predicted by analytical uncertainties but laser ablation u th he ages are more reproducible with an inverse variance weighted mean of 9 71 0 58 ma

aqueous sulphates from the stripa groundwater system abstract the isotopic composition of aqueous sulphate in the groundwater in the stripa pluton reflects the geochemical history of the groundwater as well as the origin of the sulphur or sulphate in shallow modern groundwater sulphate originates from fallout and the oxidation of pyrite or other reduced forms of sulphur at intermediate depths sulphate of surface origin is lost through bacterial reduction the origin of sulphate of the deep and more saline water is not clearly defined but could be derived from a sedimentary brine which was subject to substantial modification through rock water interaction bacterial sulphate reduction also occurs locally at depths below about 800 m

diagenetic and other highly mineralized waters in the polish carpathians abstract highly mineralized waters of different chemical types and origin occur in the flysch formations and their bedrocks in the western part of the polish carpathians the marine sedimentation water of the flysch formations is not preserved as the most mineralized and the heaviest isotopic values of flysch waters are characterized by 18 o and 2 h values in the ranges of 5 7 and 20 30 respectively their origin is related to the dehydration of clay minerals during burial diagenesis with molecules of marine water completely removed by molecules of released bound water they are relatively enriched in na in respect to the marine water supposedly due to the release of na during the illitization of smectites and preferable incorporation of other cations from the primary brine into newly formed minerals in some parts of younger formations i e in the badenian sediments brines occur with isotopic composition close to smow and cl contents greatly exceeding the typical marine value of about 19 6 g l supposedly due to ultrafiltration most probably the marine water of the flysch formations was similarly enriched chemically in its initial burial stages final cl contents in diagenetic waters depend on different cl contents in the primary brines and on relationships between diagenetic and further ultrafiltration processes in some areas diagenetic waters migrate to the surface along fault zones and mix with young local meteoric waters becoming diluted with the isotope composition scattering along typical mixing lines in areas with independent co 2 flow from great depths they form chloride co 2 rich waters common co 2 rich waters are formed in areas without near surface occurrences of diagenetic waters they change from the hco 3 ca type for modern waters to hco 3 mg ca hco 3 na ca and other types with elevated tds mg 2 and or na contents for old waters reaching even those of glacial age bedrocks of the flysch are represented by mesozoic and paleozoic mudstones sandstones and carbonates and in some areas by badenian sediments brines of the mesozoic and paleozoic bedrocks are usually significantly enriched in ca 2 and mg 2 in comparison with the badenian brines by analogy to the deepest brines in the adjacent upper silesian coal basin they are supposed to originate from paleometeoric waters of a hot climate

pressure disequilibria induced by rapid valve closure in noble gas extraction lines pressure disequilibria during rapid valve closures can affect calculated molar quantities for a range of gas abundance measurements e g k ar geochronology u th he geochronology noble gas cosmogenic chronology modeling indicates this effect in a system with a 10 l reservoir reaches a bias of 1 before 1000 pipette aliquants have been removed from the system and a bias of 10 before 10 000 aliquants herein we explore the causes and effects of this problem which is the result of volume changes during valve closure we also present a solution in the form of an electropneumatic pressure regulator that can precisely control valve motion this solution reduces the effect to 0 3 even after 10 000 aliquants have been removed from a 10 l reservoir

composite sequence stratigraphic patterns in alluvial to shallow marine successions examples from the piacenzian of the valdelsa basin central italy abstract the sequence stratigraphic analysis of continental and shallow marine successions is a helpful tool for investigating the cyclicity of the sedimentary record a similar approach is adopted in the present study to illustrate the composite cyclothemic facies architecture that characterizes the piacenzian strata of the southern valdelsa basin central italy specifically we integrated facies analysis paleopedology paleobiology of marine mollusk assemblages and biostratigraphy to assess the response of geomorphic sedimentary and biotic systems to piacenzian multifrequency relative sea level fluctuations this integrated approach resulted in the definition of a composite sequence stratigraphic framework that includes a hierarchy of units ranging from the elementary to the composite depositional sequences referred to the 5th to 3rd order cycles of sea level fluctuations respectively a correlation with the piacenzian oxygen isotopic signature of glacial and interglacial stages and related sea level fluctuations associates the cyclic development of fluvial coastal and shallow marine depositional systems to the mid piacenzian warm period and to the subsequent transition to the gelasian thus the glacio eustatic control prevailed on the development of the described multi scale cyclical pattern of sedimentation compared to the role played by the deformation of the northern apennines orogen

storm effects on siliciclastic and carbonate shelf sediments in the medial silurian succession of pennsylvania abstract upper llandoverian through wenlockian strata in the pennsylvania part of the northern appalachian basin formed on a gentle epeiric ramp that extended from marginal tidal flats through coarser grained mid shelf shoals to a muddy basin center over approximately 10 million years the composition of the accumulating sediment evolved from siliciclastic to carbonate while the ramp maintained a relatively similar configuration and position below sea level and while storm generated processes continued as the major producers of sediment characteristics in both siliciclastic and carbonate parts of the succession sedimentary structures and their sequences are generally similar with only a small number of dissimilar features resulting from the differences in composition small scale coarsening and shallowing upward sequences are present in both mid shelf bar and basin transition deposits although specific sequence characteristics are different in siliciclastic and carbonate parts such sequences record cyclic fluctuations of relative sea level while the composition of the sediment evolved over this extended period the gentle ramp gradient was maintained largely by the processes generated by storms such processes were more effective because of the fluctuations of relative sea level

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

episodic deposition of the lias in the medianes nappe western switzerland a record from mineralized ammonite bearing beds abstract sinemurian and pliensbachian depositional sequences from the starved distal northern continental margin of the tethys are preserved in the medianes nappe western swiss prealps they contain mineralized beds which include a variety of facies the northern continental margin of the tethys was broken into blocks less than 50 km wide during an extensional phase the sinemurian and pliensbachian sediments in the study are vary in thickness from less than 50 m in the north to more than 200 m in the south although the upper sinemurian to pliensbachian mineralized beds are thin between 0 10 and 0 50 m thick they commonly contain several distinct faunal horizons stacked one upon another the mineralized beds are localized in the northern and central parts of the prealpes medianes in crinoidal calcarenites or between crinoidal calcarenites and alternating siliceous limestone sand marls petrographical and geochemical analyses of these beds show multiple phases of mineralization within an early oxic to suboxic environment formation of hematite phosphates glauconite and silica locally interlayered with pyrite occurred either during a bacterial oxidation zone or during a bacterial manganese and iron reduction zone the beds may have been reworked as intraformational conglomerates some ammonites in the beds have corroded upper surfaces although these beds can be traced from the northern to the central part of this section of the northern continental margin of the tethys deposition was not uniform the episodic occurrence of these mineralized beds in space and time may be explained by local changes in accomodation potential these changes are governed by differential subsidence and eustasy of the third order cycle scale with an added effect of higher order frequency cycles possibly climatic in origin thus there is an interplay of supraregional i e global effects eustasy regional intraplate stresses regional break up of tethyan margin into moderate scale blocks and local locally derived sediment flux local structural patterns parameters that have affected the deposition of the beds the interplay of these factors leads to a highly complex and unique rock record

paleosols of late pennsylvanian cyclic strata new mexico cyclically deposited siliciclastic and carbonate rocks of the late pennsylvanian virgilian holder formation of south central new mexico were deposited on a narrow shelf between the pedernal uplift and the orogrande basin in the dry canyon area sacramento mountains shelf to basin palaeotopography is indicated by onlapping beds and primary dips calcareous alteration zones are developed on the tops of major carbonate units these detailed studies confirm earlier interpretations that alteration zones represent subaerial exposure events and provide new evidence for and further documentation of a paleosol environment the paleosols contain 1 rhizoliths 2 tangential needle fibres of calcite 3 five types of alveolar texture 4 upward oriented ribbon spar 5 brownish and clear isopachous spar 6 blackened grains 7 random needle fibres of calcite 8 coated grains 9 micritized grains 10 glaebules 11 desiccation cracks 12 possible microcodium and 13 well developed laminated crusts isopachous cements upward oriented cements which mark the former tops of capillary fringes dark colour and shallow depth of penetration of rhizoliths less than 1 m indicate significant paleosol formation in waterlogged hydromorphic and drier conditions pennsylvanian palaeohydrogeology of the system is reflected in the type of paleosol alteration paleosols developed on subtidal strata and paleosols which drape tens of metres of palaeotopography indicate cyclic sedimentation was not controlled by delta lobe switching local tectonic up and down movement would be an unlikely mechanism to explain the repeated tens of metres of relative sea level fluctuation eustatic sea level fluctuations induced by late pennsylvanian gondwana glaciation probably were of the correct magnitude and frequency to have caused the holder cycles

a comparison of k ar and rb sr ages of rapidly cooled igneous rocks two points in the palaeozoic time scale re evaluated k ar and rb sr ages were measured on rapidly cooled igneous rocks from kinnekulle sweden ordovician bentonite the cerberean cauldron australia late devonian felsic volcanics mount dromedary australia cretaceous monzonite and cooma australia jurassic syenite no systematic bias was detected between the ages determined by the two techniques calculated using the constants recommended by the i u g s subcommission on geochronology the k ar and rb sr ages of the jurassic syenite also were indistinguishable from its zircon u pb age the kinnekulle a 1 bentonite gives a minimum age of 446 3 ma for the early caradocian diplograptus molestus zone the cerberean cauldron volcanics give a minimum age of 367 2 ma for the early frasnian these data are consistent with a small upwards revision of the ages in gale et al 9s 1979 time scale as proposed by gale et al 1980

stratigraphic and interregional changes in pennsylvanian coal swamp vegetation environmental inferences abstract quantitative analysis of pennsylvanian coal swamp vegetation provides a means of inferring organization and structure of communities distribution of these communities further provides inferences about environmental factors including paleoclimate our observations are based on in situ structurally preserved peat deposits in coal ball concretions from 32 coal seams in the eastern one half of the united states and from several seams in western europe and on spore assemblages from more than 150 seams there were three times of particularly significant and nearly synchronous vegetational changes in the midcontinent and appalachian coal regions during the pennsylvanian period each was different in kind and magnitude the first marked changes occurred during the early part of the middle pennsylvanian with the fluctuating decline in the high level of lycopod dominance the abundance of cordaites increased there was a rise in the occurrences of the lycopod herbs to form intercalated marshlands and an overall increase in floral diversity changes ensuing from this time also include shifts in dominant species of lycopod trees and a sustained rise in abundance and diversity of tree fern spores the next significant time of change was during the middle part of the middle pennsylvanian representing both a culmination of earlier trends and expansions of cordaites in the midcontinent where there was a maximum change in species without net loss of diversity tree ferns and medullosan pteridosperms attained subdominant levels of abundance and diverse lycopod species dominated except in the atokan desmoinesian transition of the midcontinent the third and sharpest break occurred near the middle late pennsylvanian boundary when extinctionsof the dominant coal swamp lycopods allowed development of tree fern dominance the late pennsylvanian coal swamps apparently were colonized or recolonized mainly by species from outside coal swamps rather than by the survivor populations of the middle pennsylvanian swamps paralleling the changes in floras through the pennsylvanian are changes in preservational aspects of the peat these include a decline in shoot root ratios from approximately 1 to

stable sulfur and oxygen isotope ratios of the świetokrzyski national park spring waters generated by natural and anthropogenic factors south central poland abstract this paper presents the results of an isotopic study of spring waters in wietokrzyski holy cross mountain national park np south central poland the 34 s v cdt and 18 o v smow of soluble sulfates n 40 varied from 0 5 to 18 1 and from 3 5 to 12 2 respectively the average 34 s values are closely similar to those of rainwater soils and rocks comprising scattered pyrite this suggests that soluble sulfates in the springs originated from mixing of recent and historic deposition sulfates derived from pyrite oxidation and cs mineralization in soils and debris an additional anthropogenic sulfur input inorganic fertilizer occurs in the water of spring s 61 located in the wietokrzyski national park buffer zone the 18 o v smow of spring waters n 4 were in the range of 10 6 to 10 2 indicating that they are derived from vadose groundwater in np this was the first isotope study of spring waters in the national parks of poland it enabled the determination of sulfur pathways and discrimination between natural and anthropogenic sources of this element in a relatively pristine area

new constraints on the evolution of the inner northern apennines by k ar dating of late miocene early pliocene compression on the island of elba italy

distribution paleoenvironmental implications and stratigraphic architecture of paleosols in lower permian continental deposits of western kansas u s a abstract cumulic paleosols in core from the lower permian asselian sakmarian council grove group of western kansas contain a diverse suite of pedogenic features including carbonate nodules gleying fossil burrows rhizoliths peds and cutans abundant gleying burrowing by organisms with a high soil moisture requirement and extensive plant growth are evidence of at least intermittently high soil moisture during this time paleosol character was strongly influenced by regional topography and paleogeographic position as well as the climate changes accompanying hierarchical glacioeustatic cycles the distribution of pedogenic features across formations also indicates a shift toward more humid conditions during a larger 3rd order regression climatic variability during the interval of soil formation resulted in overprinting and close stratigraphic juxtaposition of both humid and arid climate indicators variability is likely the result of exposure to multiple 5th order eustatic and climatic cycles during the lowstands of 4th order cycles fifth order cycles are expressed as lithologic changes in stratigraphically equivalent outcrops across the state but lack of accommodation space prevented cycles from being expressed as differing lithologies in the study area biologic activity assisted in consolidation and stabilization of eolian and alluvially deposited sediments this study emphasizes that detailed quantitative study of pedogenic features can reveal important paleoclimatic and paleoenvironmental information in otherwise lithologically similar paleosols close juxtaposition of opposing climatic indicators over intervals of known sea level change adds evidence to the hypothesis of a link between sea level change and climate change in the early permian pedogenic features thus support a semiarid or wetter climate for the midcontinent during the early permian

extensive microbial modification of formation water geochemistry case study from a midcontinent sedimentary basin united states the upper devonian antrim shale in the michigan basin is an economically significant source of microbially produced methane along the basin margins where meteoric recharge has been focused oxygen and hydrogen stable isotope compositions of antrim formation waters show that fresh waters recharged from pleistocene glaciation and modern precipitation suppressed basinal brine salinity to great depths and enhanced methanogenesis this paper presents results of integrated elemental and isotope analyses of antrim shale formation waters from the margins and center of the michigan basin focusing on solute sources and geochemical modifications associated with regionally extensive microbial methanogenesis cl br na systematics reveal that salinity is controlled not only by mixing between variable amounts of basinal brine and meteoric water but also by halite dissolution where fluids recharged through underlying devonian carbonate aquifers with localized evaporite deposits divalent cations carbonate system parameters and carbon isotope compositions of dissolved inorganic carbon have been systematically and profoundly altered by microbial methanogenesis large decreases in formation water ca mg and ca sr ratios accompany increasing carbonate alkalinity values in areas with high rates of microbial gas production thermodynamic and reaction path modeling show that these changes are consistent with calcite precipitation during progressive microbial methanogenesis similar variations in fluid chemistry are evident in databases from other sedimentary basins containing black shales and coal beds associated with microbial gas microbial methanogenesis may play an important role in the geochemical evolution of divalent cation relationships in crustal fluids and should be considered in models of formation water origin and evolution

cyclicity in the middle eocene yamak turbidite complex of the haymana basin central anatolia turkey the haymana basin in central anatolia turkey formed on a late cretaceous to middle eocene fore arc accretionary wedge a sequential model is proposed for the 1 km thick lutetian yamak turbidite complex ytc which is the youngest paleotectonic unit of the basin the ytc represents a prograding submarine fan subdivided into three depositional sequences ds each several hundred meters thick each depositional sequence consists of a turbidite system ts with sandstone and conglomeratic sandstone beds alternating with mudstones overlain by basin plain mudstones in each turbidite system the sandstone and mudstone sequential organization allows the distinction of smaller subdivisions namely basic sequences bs and basic units bu with each basic sequence being composed of several basic units this subdivision associated with a two dimensional geometric reconstruction of the ytc leads to a better understanding of the evolution in time and space of the submarine fan system lower to middle fan depositional lobes and upper fan and slope channels are represented as a whole the ytc progressed from a sand poor to a sand rich system depositional sequences ds of the ytc may correspond to third order sea level cycles of tectonic origin accordingly fourth and fifth order cycles might be proposed for the bs and bu respectively however partly because of the limited extent of exposures the allocyclic origin of these finer subdivisions remains problematic

fcs ek a new sampling of the fish canyon tuff 40ar 39ar neutron flux monitor sanidine from the fish canyon tuff is regularly used as a neutron flux monitor by 40 ar 39 ar geochronologists a new sampling of the fish canyon tuff denoted fcs ek has yielded sanidine that relative to fc 2 is confirmed here to have an r value of 0 9997 0 0100 which is indistinguishable from 1 the new sample will allow for continuity as many 40 ar 39 ar laboratories have exhausted their supplies of fc 2 fcs ek is now available in significant quantities from the scottish universities environmental research centre

episodic accumulation and the origin of formation boundaries in the helderberg group of new york state at any single locality in the helderberg group of new york state most formation and member boundaries coincide with boundaries of punctuated aggradational cycles in each case of coincidence the boundary is a discontinuity that was produced by a rapid rise of relative base level rather than a facies contact representing gradual migration of contiguous paleoenvironments apparently diachronous formation boundaries in the sequence are not single continuous surfaces instead each diachronous boundary is actually a stratigraphic series of isochronous surfaces that are separate punctuated aggradational cycles pac boundaries produced by distinct geologically instantaneous base level rises these conclusions about the origin of formation boundaries suggest that the concept of the formation as a fundamental unit of stratigraphic description and interpretation may need revision if the stratigraphic record accumulated episodically on a small scale

astronomical calibration of 40ar 39ar reference minerals using high precision multi collector argusvi mass spectrometry the new generation of multi collector mass spectrometers e g argusvi permit ultra high precision 1 in 40k decay constants and the ages of natural reference minerals that form the basis of the technique for example reported ages for widely used 40ar 39ar reference materials such as the ca 28 ma fish canyon tuff sanidine fcts and the ca 1 2 ma alder creek rhyolite sanidine acrs vary by 1 recent attempts to independently calibrate these reference minerals have focused on k ar analyses of the same minerals and inter comparisons with astronomically tuned tephras in sedimentary sequences and u pb zircon ages from volcanic rocks most of these studies used older generation effectively single collector mass spectrometers that employed peak jumping analytical methods to acquire 40ar 39ar data in this study we reassess the inter calibration and ages of commonly used 40ar 39ar reference minerals fish canyon tuff sanidine fcts alder creek rhyolite sanidine acrs and mount dromedary biotite md2b equivalent to ga 1550 biotite relative to the astronomically tuned age of a1 tephra sanidine a1ts faneromeni section crete rivera et al 2011 using a multi collector argusvi mass spectrometer these analyses confirm the exceptional precision capability 0 1 in the 40ar 39ar ages of reference minerals without consideration of recoil artefacts thus limiting the benefits of high precision multi collector analyses significant improvement to the accuracy of the 40ar 39ar method 0 1 will require further inter laboratory 40ar 39ar studies utilizing multi collector mass spectrometry additional constraints on recoil 39ark loss from reference minerals further resolution of discrepancies between astronomically tuned sedimentary successions and refinement of the 238u 206pb zircon age cross calibration approach

punctuated aggradational cycles a general hypothesis of episodic stratigraphic accumulation according to the hypothesis of punctuated aggradational cycles presented here the stratigraphic record consists of small scale 1 5 m thick shallowing upward cycles pacs separated by surfaces marked by abrupt change to deeper facies this motif pervasive in time and environment is produced by relatively long periods tens of thousands of years of base level stability punctuated by geologically instantaneous relative base level rises of at least basin wide extent as basin wide lithologic time stratigraphic units pacs are fundamental to all aspects of stratigraphic analysis including correlation paleoenvironmental interpretation and paleogeographic reconstruction of several possible allogenic mechanisms for a pervasively cyclic stratigraphic record glacial eustasy driven by orbital perturbations is preferred the pac hypothesis is presented as a comprehensive model to be tested and modified by examination of the stratigraphic record from an episodic perspective

barium and radium discharged from coal mines in the upper silesia poland waters discharged from coal mines in the upper silesia in poland cause contamination of rivers and their sediments saline waters discharged from coal mines of the southern region contain elevated barium and radium the discharge of these elements can be reduced by treating these waters with sulphates in mine workings sources of sulphate used in treatments include gypsum anhydrite and industrial wastes such as fly ash slags and flotation tailings gypsum and anhydrite are used in the coal mine workings as components of the fire protection walls industrial wastes from power plants are stored in the mine workings as fire and methane protection agents sulphates precipitate barium and radium from saline waters inflowing into the mine workings the waters can be treated by flowing them through old mine workings in this case the source of sulphates is the natural oxidation of pyrite mining activities and the natural process of desulphurisation of the carboniferous rocks reduce the amount of barium and radium that is discharged in the southern region of upper silesia the processes for reducing the environmental impact of toxic discharges from the mines should be monitored

a new method for u pb geochronology of cassiterite by id tims applied to the mole granite polymetallic system eastern australia abstract we present a new method for precisely determining the u pb isotopic composition of cassiterite by isotope dilution thermal ionisation mass spectrometry id tims complete sample dissolution and spike sample equilibration is accomplished in a pressure vessel with hbr isolation of small quantities of u and pb from the tin rich matrix is based on a novel tru spec column separation with total procedural blanks of yuan et al 2011

sequences cycles and basin dynamics in the silurian of the appalachian foreland basin abstract field stratigraphic analysis of the early and medial silurian strata of ontario new york and pennsylvania permits recognition of six major sequences reflecting 3rd order cycles in the niagaran llandoverian ludlovian of new york and adjacent regions these sequences correspond approximately to the medina lower clinton middle clinton upper clinton two sequences and lockport groups each is bounded by widespread unconformities produced by the interplay of eustatic sea level drop and local tectonic uplift in general erosional sequence boundaries and transgressive surfaces are merged with no record of the lowstand wedge each sequence is subdivisible into two to five sub sequences that are marked by sharp though generally non erosional basal discontinuities investigation of the clinton and lockport groups corroborates earlier suggestions that carbonate and siliciclassic tongues extended basinward from opposite margins synchronously in response to sea level drops analysis of the thickness and basinward extent of the progradational tongues reveals the existence of multi scale sedimentary cycles sequences and component sub sequences are correlative basinwide and are synchronous within the resolution of bio and event stratigraphy major drops in relative sea level are represented by the sequence bounding discontinutiies these surfaces are overlain by siliciclastic wedges near terrigenous source areas or winnowed carbonate pack and grainstones on the tectonically passive margin overlying highstand deposits typically shales calcareous mudstones and limestones are separated from lowstand or transgressive deposits by thin condensed intervals commonly marked by phosphatic or glauconitic material and or surfaces of maximum sediment starvation the relative highstand deposits of sequences and sub sequences are developed in relatively deep water facies and are at most slightly progradational hence most sequences and sub sequences are sharply bounded roughly upward deepening to slightly shallowing successions of strata in turn sub sequences are further divisible into widespread minor parasequences and parasequence sets probably corresponding to 6th and 5th order cycles respectively the smaller scale units 0 2 5 mthick commonly display an upward shallowing motif the nested relationship of these cycles supports the hierarchical model of transgressive regressive allocycles proposed by busch and rollins 1984 niagaran cycles discussed herein are equivalent to third fourth and fifth order cycles and are traceable circumbasinally depocenters of successive sequences and sub sequences display a pattern of eastward westward eastward basin axis migration through the silurian during early llandoverian the taconic queenston deltaic complex began to subside and the basin axis depocenter and eastern shoreline shifted eastward approximately 200 km over a 6 million year period as the basin axis migrated eastward the western basin ramp forebulge was repeatedly upwarded and eroded resulting in the generation of regionally angular unconformities at the bases of sequences ii iv and vi the pattern of unconformity greatest to the west suggests rise of the algonquin arch concomitant with eastward basin axis migration during the late llandoverian to early wenlockian the algonquin arch subsided slightly concurrently with a reversal in direction of basin axis migration during deposition of upper clinton and lockport vernon strata sequences v vi the basin axis shifted approximately 300 km back to the west eastward migration of the basin axis corresponds with a time of tectonic quiescence and probable thrust load relaxation the abrupt reversal of migration in the late llandoverian may be a signal of renewed thrusting in the hinterland at the onset of the salinic disturbance

perspectives on 40ar 39ar dating isotopic dating of geological samples using the k ar method and its variant the ar ar dating technique provides ages that in favourable circumstances are precise and accurate to within 1 limiting factors include the accuracy of the decay constants for k and the age of neutron fluence monitor minerals for rapidly cooled igneous rocks a k ar or ar ar age normally will give a good estimate of the age of eruption but for slowly cooled igneous rocks or metamorphic rocks an age measured on a sample is likely to be a cooling age as ar ar ratios can now be determined often to better than 0 1 the main limitation on accuracy relates to how well the k decay constants are known better determination of the and decays of k the basis for the decay constants is suggested at the present time rather than adoption of new decay constants linked to another decay scheme until improved independently measured decay constants for k become available there may be some circumstances where the newly proposed decay constants need to be used especially when comparing ages on volcanic igneous rocks with those measured in another system

thrust ridge paleodepositional model for the upper freeport coal bed and associated clastic facies upper potomac coal field appalachian basin u s a abstract a blind thrust ridge model is proposed to explain the lack of coarse clastic material in the vast minable upper freeport coal bed uf this coal bed contains only fine elastic partings and is overlain by regionally extensive closely spaced channel belt deposits in the upper potomac coal field of the appalachian basin a blind thrust ridge may have formed a sediment trap and prevented c coarse fluvial sediments from entering the swamp during a period westphalian d when the thick upper freeport peat accumulated anticlinal thrust ridges and associated depressions may have existed uninterrupted for about 40 km parallel to the appalachian orogen sediment shed from the breached anticlinal ridges accumulated in the sediment trap and was carried out of the ends of the trap by streams that occupied the shear zone at the ends of the blind thrust ridge the extent parallel to the orogen of thick areally extensive uf is related to the length of the blind thrust ridge that in turn controlled the spacing of the river derived coarse clastic sediments that entered the main basin from the east the thrust plane eventually emerged to the surface of the blind thrust ridge and peat accumulation was terminated when the ridge became eroded and the sediment trapped behind it was released the peat was buried by abundant coarse clastic sediment which formed closely spaced channel belts and intervening flood basins this model has implications for widespread peat deposits now coal that developed in tropical regions a few hundred kilometers from the sea in a tectonically active foreland basin

la icp ms apatite fission track dating a practical zeta based approach abstract the la icp ms method is becoming increasingly popular for uranium determinations in fission track dating of apatite zircon or titanite this is because the approach has several advantages over the classical external detector method edm including faster sample throughput simultaneous acquisition of additional data such as u pb age information and trace element abundances while removing the need for neutron irradiation two different approaches are used to determine u contents in la icp ms fission track dating an absolute dating approach or a zeta based determination analogous to the classical edm absolute age dating by la icp ms potentially suffers from small but systematic deviations in apatite u contents which in turn propagate through to minor systematic deviations in the accuracy of absolute fission track age determinations a zeta based approach typically requires time consuming counting of large numbers of zeta standard grains usually durango apatite so as to yield a precise zeta factor for every la icp ms session containing unknowns the modification of the zeta based approach proposed here has two major advantages firstly it employs just one large primary la icp ms session to determine a precise primary zeta factor on a large number of counted durango primary zeta grains during subsequent secondary la icp ms sessions with unknowns no further fission track counting of the primary zeta standard is required this is because we reanalyse a subset of the primary zeta grains to calculate a session specific zeta fractionation factor which is related to variations in the instrumental operating conditions primarily plasma tuning between primary and secondary la icp ms sessions this enables us to reuse the primary zeta factor and thus avail of its precision derived from the large spontaneous track count the second advantage is that reusing the primary zeta grains by applying a session specific zeta fractionation factor allows us to verify that background and drift corrections applied during the secondary la icp ms session were fully appropriate this method has been successfully tested by dating samples of known apatite fission track age by comparing edm and la icp ms data from the same sample and by participating in a round robin test between international fission track laboratories where blind fission track dating of two unknown samples was undertaken our la icp ms apatite fission track dating approach is also easily modifiable for fission track dating of zircon or titanite if suitable age standards are employed

hawaiian hotspot volcanism mainly during geomagnetic normal intervals according to their airborne detected magnetic anomalies volcanoes forming the islands banks and seamounts along the hawaiian emperor seamount chain erupted predominantly during intervals of normal polarity of earth9s magnetic field for the past 10 m y of hotspot activity when the field was 50 normal and 50 reversed 19 of 23 volcanic edifices from hawaii to necker island were dominantly normal one probably was normal and three were dominantly reversed statistical probabilities consideration of induction in the present normal field and possibilities of field reversals during rapid edifice building nevertheless show that eruptions were not random with respect to the magnetic field similar conclusions where data are fewer are good for the older hawaiian ridge 29 of 36 normal and are fair for the emperor seamounts 3 of 3 known normal the correspondence suggests that hotspot plumes are generated near the core mantle boundary spreading center and magmatic arc volcanism on the other hand are mainly upper mantle processes the jurassic and cretaceous long normal invervals however were times of such high heat flux that sea floor spreading as well as hotspot activity increased larger hotspots under continental lithosphere during those normal intervals may have initiated continental rifting