a comparison between the tectonic stress measured in situ and stress parameters from induced seismicity at monticello reservoir south carolina during may and early june 1979 five three component digital seismographs were deployed near the monticello reservoir south carolina to determine the stress drops of reservoir induced earthquakes and compare them with earlier hydrofracture stress measurements of zoback and hickman this issue records for 327 events were obtained 10 of these events each recorded on four or more stations were analyzed to determine stress drops depths for the 10 events ranged from 0 5 to 1 4 km fault plane orientations were calculated from an inversion of the body wave displacements individual radiation pattern corrections were applied in calculating the moments at each station final estimates of seismic moment were obtained by averaging logarithmically the estimates from each component for each event an arithmetic moment was obtained from the individual estimates of the source radius and stress drop was then calculated once from the final estimates of seismic moment and source radius for each event moments of the 10 digitally recorded earthquakes ranged from 2 5 1017 to 2 7 1018 dyne cm for the p wave data and from 4 6 1017 to 4 6 1018 dyne cm for the s wave data the stress drops s wave data only generally ranged from about 0 2 to 4 bars four earthquakes were recorded by a strong motion instrument at the dam site magnitudes m for these events ranged from 2 8 to 3 0 moments taken as averages of the values from each component ranged from 1 7 to 3 4 1020 dyne cm and the stress drops from 13 to 92 bars large differences between the corner frequencies of the two components factors of 2 5 and 4 for two of the events correspond to a large relative uncertainty for these stress drop values nevertheless tens of bars of stress are apparently released for the largest events in the monticello sequence but only a few bars are released for the smaller magnitude events in comparison the in situ stress data measured in two holes give an estimate of shear stress of about 45 bars at 0 2 km depth and 30 to 70 bars at 1 km depth in the northern hole and from 15 20 bars near the surface to almost 70 bars at depth in the southern hole the variation in shear stress inferred from in situ measurements at the deeper levels indicates an inconsistency between the thrust faulting mechanisms of the earthquakes and the state of stress which is more consistent with thrust faulting at 0 2 km depth and strike slip or normal faulting below thus the estimates of shear stress from in situ measurements are of the same order as the stress drops of the m 2 8 3 0 events but about 1 order of magnitude larger than the stress drops obtained for the smaller events

global change in earth history a personal point of view the global changes of the past took place during the progress of geological cycles and marked a drastic passage from an ancient pangaean regime of continental emergence to a new tethyan regime of submergence they occurred with a certain violence and rapidity and represented critical phases in the destabilization and subsequent reorganization of the geosphere and biosphere this process resulted in the destruction of certain assemblages e g biotic mass extinctions and the rise of new ones e g the emergence of new taxa these major phases of evolution and growth were probably connected to the upwelling of hot mantle material from great depths and a subsequent process of lateral spreading and outward migration of the mantle melt the ensuing marked increase in mantle activity degassing and explosive volcanicity produced catastrophic environmental perturbations with turning points in tectonics global climate sea level ocean and atmospheric chemistry palaeocirculation and palaeogeography

propagating rifts and continental breakup a simple quantitative model is proposed whereby continental breakup starts with a phase of continental rifting and continues with the propagation of rifts toward locked zones these zones are deformed in the rifting process while oceanic crust is generated in the wake of the rift tip the deformed zones will cause overlaps when a continental reassembly is attempted the model accounts for the shape and distribution of magnetic quiet zones at ocean continent boundaries and for the detailed geometry of some v shaped zones of oceanic magnetic anomalies the former provide an estimate of the scale at which the hypothesis of rigid plates fails and the latter are used to measure the velocity of rift propagation illustrations are provided for present rifting in the red sea and gulf of aden and for early rifting of the south atlantic and breakup of pangea

modern estuarine siliceous spiculites tasmania australia a non polar link to phanerozoic spiculitic cherts biosiliceous sedimentary rocks are well known from the geologic record and many are correctly interpreted to have formed in deep water or cold water environments shallow non polar spiculites are also known from the rock record yet no modern analog has been documented for such environments bathurst harbour an estuarine system in southwest tasmania provides this much needed modern analog in this system a sharp halocline separates tannin rich low salinity surface waters from clear marine bottom waters tannins supply few nutrients and substantially reduce light penetration to bottom environments resulting in a thinned photic zone and the mixing of deeper water sub photic biotas of soft corals bryozoans and sponges with other organisms more typical of this temperate shallow water environment the well defined halocline allows a typically marine biota including echinoderms to live in bottom waters of this estuarine setting the bioclastic factory producing both carbonate and siliceous particles exists in marine subphotic bottom waters of incised channel and shallow rocky environments along the shoreline extensive organic rich soft sediments in protected embayments generate few bioclasts but contain allochthonous sponge spicules transported from the adjacent bioclastic factory trapping of organic material within the estuarine system lowers sediment ph and promotes dissolution of carbonate biofragments resulting in preferential preservation of siliceous sponge spicules this situation implies that many biosiliceous neritic deposits in the rock record may be the result of similar preferential preservation

african rift tectonics and sedimentation an introduction rifts are one of the most spectacular features of global morphology within oceans they separate plates as new oceanic crust is created within continents they may form deep valleys such as the rhine graben within which runs one of the world s busiest waterways they are often floored by deep lakes such as lake baikal the deepest lake in the world today whose floor lies 1700 m below the surface of the lake ancient rifts are the sites of petroleum accumulations beneath the margins of the atlantic in the north sea and in china of coals and oil shales and of minerals including phosphates barite cu pb zn sulphides and uranium robbins 1983 of all the world s rifts none can match in scale and diversity the great rift system which runs for over 7000 km and includes the east african rift system and its extension through the red sea into the dead sea to form a unique feature of global geology its study is important not only for what it can tell about the nature and origin of present day rifts the thermal magmatic and tectonic processes which gave rise to them climatic changes and sedimentary particularly lacustrine and volcaniclastic processes it is also essential for the understanding of the processes which formed passive continental margins all of which are underlain by rifted sedimentary basins and failed rifts whether they formed within continents or at the junction of continents and oceans early workers on rifts were impressed by the wide valleys 40 50 km across filled by young alluvial and lacustrine sediments and bordered by steep escarpments rising in some cases a few hundred metres in others up to 3 4000 m above the valley floor many rifts are the sites of volcanic activity sometimes of rather unusual composition these unusual volcanic source rocks may in turn be the cause of peculiar lake water chemistries many rift lakes containing unique suites of evaporitic minerals although at one time some people considered rifts to have been formed by compression rampvalley hypothesis discussion today revolves principally around the extent to which rift valleys are extensional features or are the result of oblique slip movements between two laterally moving blocks there is no doubt now that some rift valleys are the result of strike slip movement the dead sea gulf of elat rift lies along a lineament that separates two lithospheric plates and as arabia moves northwards relative to the palestinian mediterranean block and faults curve or sidestep each other extensional pull apart basins are formed such as the dead sea whose surface lies further below sea level than any other place in the world a feature of these strike slip rift valleys is that the extensional valleys pass along the rift into mountainous zones of compression and uplift rapid erosion from these mountains leads to substantial sediment supply for the basins from within the fault system itself ancient strike slip rift basins are therefore characterized by very thick rapidly accumulated basin fills with areas of contemporaneous compressional tectonics and unconformities not far away rift valley basins that are extensional features on a regional scale tend to sink rather more slowly have less sediment entering them and show no evidence of synchronous compressional tectonics in their neighbourhood cross sections through them show normal faulting probably listric in form the main controversy with regard to extensional rift valleys is whether magmatic activity in rifts reflects an underlying heat source such as a convection plume in the mantle or hot spot the rifting then being the consequence of expansion and uplift brought about by thermal activity or whether the magmatic activity is merely the result of regional or local extensional stresses which have passively allowed magma to come to the surface some rifts that penetrate continents are clearly failed rifts or aulacogens that began as one arm of a triple junction as ocean floor spreading developed along two arms one arm was left as a failed rift in the sense that new oceanic crust was not created perhaps the best known is the benuc trough within which the niger delta developed however the northern viking graben of the north sea has been claimed to be one whiteman et al 1975 and so has that part of the east african rift known as the afar triangle where thc red sea and the gulf of aden rifts successfully drifted whilst the afar triangle failed molnar tapponnier 1975 have argued that other rifts are the result of continental collision in particular that the impact of india with asia caused not only major lateral displacement along

simulations of permian climate and comparisons with climate sensitive sediments abstract we use a climate model to simulate two intervals of permian climate the sakmarian ca 280 ma at the end of the major permo carboniferous glaciation and the wordian ca 265 ma we explore the climate sensitivity to various levels of atmospheric co2 concentration and to changes in geography and topography between the two periods the model simulates large seasonality and high aridity in the continental interiors of both hemispheres for both periods the northern summer monsoon weakens and the southern monsoon strengthens between the sakmarian and the wordian owing to changes in geography and topography the northern middle and high latitudes cool in winter between the sakmarian and wordian associated with northward shift of the continents this high latitude cooling strengthens the winter westerlies and shifts the maximum storm track precipitation south in the southern hemisphere the winter westerlies weaken from the sakmarian to the wordian starting the simulations with no permanent i

rare earth elements in the permian phosphoria formation paleo proxies of ocean geochemistry abstract the geochemistry of deposition of the meade peak member of the phosphoria formation mpm in southeast idaho usa a world class sedimentary phosphate deposit of permian age that extends over 300 000 km2 is ascertained from its rare earth element ree composition ratios of ree al2o3 suggest two sources seawater and terrigenous debris the seawater derived marine fraction identifies bottom water in the phosphoria sea as o2 depleted denitrifying suboxic most of the time and seldom sulfate reducing anoxic this interpretation is supported by earlier research that showed progressively greater ratios in the marine sediment fraction of cr ni v ni mo ni relative to their ratios in seawater for which marine cr v and mo can have a dominantly o2 depleted bottom water source and ni a photic zone largely algal source the water chemistry was maintained by a balance between bacterial oxidation of organic matter settling through the water column determined largely by primary productivity in the photic zone and the flux of oxidants into the bottom water via advection of seawater from the open ocean samples strongly enriched in carbonate fluorapatite the dominant ree host mineral have variable er sm tm sm and yb sm ratios their distribution may represent greater advection of seawater between the phosphoria sea and open ocean during deposition of two ore zones than a center waste and greater upwelling of nutrient enriched water into the photic zone however the mean rate of deposition of marine ni a trace nutrient of algae and po43 a limiting nutrient indicate that primary productivity was probably high throughout the depositional history an alternative interpretation of the variable enrichments of er tm and yb relative to sm is that they may reflect temporally variable carbonate alkalinity of open ocean seawater in permian time a more strongly negative ce anomaly for all phosphatic units than the ce anomaly of modern pelletal phosphate is further indicative of an elevated o2 concentration in the permo carboniferous open ocean as proposed by others in contrast to the depletion of o2 in the bottom water of the phosphoria sea itself the oceanographic conditions under which the deposit accumulated were likely similar to conditions under which many sedimentary phosphate deposits have accumulated and to conditions under which many black shales that are commonly phosphate poor have accumulated a shortcoming of several earlier studies of these deposits has resulted from a failure to examine the marine fraction of elements separate from the terrigenous fraction

frasnian famennian biotic crisis undervalued tectonic control the prime cause of the late devonian kellwasser crisis culminating in a mass extinction event near the frasnian famennian f f boundary remains conjectural nevertheless rapid sea level fluctuations of uncertain origin during tectono eustatic highstand paired with repeated oceanic anoxia and climatic changes are usually thought at present to be one of the main immediate triggers the cathles hallam model of stress induced changes in plate density accompanying rapid rift formation furnishes an alternative for understanding the enigmatic sudden eustatic variations in the non glacial time late devonian tectonic extension causing rifting and volcanicity appears to be strongly marked in several regions of eurasia particularly in kazakhstan and eastern laurussia all larger devonian continents were more or less tectonically affected a subtle record of this tectonic rearrangement is implied even for distant and apparently quiet carbonate platforms in local extensional block faulting and tilting hydrothermal mineralisation geochemical anomalies and localized blooms of siliceous biota interpreting the late frasnian regressive transgressive pattern in terms of the cathles hallam tectono eustatic model two major rifting events are hypothesized one at about the beginning of the rhenana zone and a second principal pulse in the late linguiformis zone that encompassed the f f transition developing the veimarn milanovsky scenario of the global extensional pulse it is assumed that the key endogenous factors were related to episodic super plume activity the tectonically triggered changes climaxed in thermal and nutrient pulses and induced the stepdown ecosystem destabilization observed in the f f bio crisis minor cometary strike s might have eventually participated in this prolonged multicausal environmental stress mainly due to additional thermal shocks but perhaps effective on a regional scale only

the carbonates of the post variscan basins of sardinia the evolution from carboniferous permian humid persistent to permian arid ephemeral lakes in a morphotectonic frameworkcarbonates of the post variscan basins of sardinialg costamagna late to post variscan sedimentary basins of sardinia were influenced during pennsylvanian to permian times by two main tectono sedimentary cycles a pennsylvanian to cisuralian cycle represented mainly by dark limnic deposits overlain by a guadalupian to a possibly lopingian cycle mostly characterized by red bed deposits lacustrine waterbodies developed in some sedimentary basins that were filled with siliciclastic to frequently early silicified carbonate deposits depending on the climate and environmental conditions landscape morphology and tectonic regime the limnic successions of the lower tectono sedimentary cycle were deposited in permanent tens of metres deep lakes in deep narrow tectonic strike slip basins under a temperate to warm humid climate they started as lakes with terrigenous sedimentary input and developed minor carbonate deposits mainly at the end of their story conversely the red bed successions of the upper cycle were deposited in ephemeral shallow playa lakes related to wider basins in an extensive alluvial plain under a hot and arid climate here the siliciclastic sediments are intercalated with thin carbonate beds that are typical of a high evaporation rate the evolution of the lake type could be related not only to a major climatic shift but also to the changing morphotectonic conditions of the variscan chain influencing the local microclimate comparisons with coeval successions in the provence basin the massif central aumance basin france and the saar nahe basin germany show both similarities and differences between the basins

coated phosphate grains proxy for physical chemical and ecological changes in seawater irrespective of geologic age phanerozoic coated phosphate grains deposited beneath productive surface waters in organic rich paleoenvironments are of only two types unconformity bounded grains contain internal discordances and erosional surfaces attributable to multiple episodes of phosphogenesis and sedimentary reworking during periods of stratigraphic condensation redox aggraded grains consist of concordant concentric phosphate laminae that are intimately interlayered with circumgranular layers containing pyrite chamosite or barite recording in situ diagenetic mineralization driven by changes in pore water redox potential such changes can be attributed to variations in biological oxygen demand within suboxic pore water environments resulting from fluctuations in sedimentation rate of organic carbon redox aggraded grains are thus sensitive indicators of variations in organic carbon export and record changes in primary productivity and or ecological dynamics of the surface ocean this concept of coated grain formation necessitates a long residence time just below the sediment water interface if sedimentation rate is too high grains are rapidly buried and so removed from the zone of active phosphate precipitation coated phosphate grains can therefore be considered the granular equivalents of condensed beds these concepts are equally applicable to the interpretation of other types of coated grains and concretions that contain eh sensitive minerals such as iron bearing ooids and polymineralic concretions

chemostratigraphy indicates a relatively complete late permian to early triassic sequence in the western united states although the latest permian mass extinction and associated 13 c excursion are well documented from the tethys ocean carbonate rocks preserving these events in the eastern panthalassic ocean western pangea are unknown we present 13 c carb from the gerster and thaynes permian and triassic formations in the western united states and document a negative excursion with no evidence for major breaks in continuity to further constrain the age of the 13 c carb excursion in the absence of index fossils we analyzed the same samples for 87 sr 86 sr when examining our new carbon and sr data in the context of biostratigraphy and sequence stratigraphy we conclude that parts of the western united states may preserve carbonate successions that span the latest permian extinction

seismic evidence for magma in the vicinity of mt katmai alaska p wave traveltime delays of as much as 0 9 sec are consistently observed at one seismic station from local and regional earthquakes 70 to 150 km deep this station is on the southwest flank of mt trident the most recently active volcano within katmai national park alaska delays from local shallow earthquakes are typically less than 0 3 sec suggesting that most of the major delay results from anomalous material at depths of more than a few kilometers this station is located near the center of a bowlshaped low in the bouguer gravity field that is approximately 15 km in diameter and more than 25 mgals deep these anomalies suggest but do not prove the presence of considerable amounts of magma in the shallow part of the crust that could have been the source for all magma erupted in the vicinity of mt katmai and mt trident this century

faunal turnover and changing oceanography late palaeozoic warm to cool water carbonates sverdrup basin canadian arctic archipelago abstract carbonate sedimentary rocks in the fosheim hamilton sub basin at the eastern end of the sverdrup basin contain a particularly sensitive record of changing palaeoceanography and faunal turnover during the northward movement of pangaea through the late palaeozoic carboniferous and earliest permian inner ramp carbonates are a photozoan association of colonial corals fusulinids algae and ooids with sparse heterozoan elements crinoids brachiopods and bryozoans based on modern analogues these biotic components reflect warm water oligotrophic marine environments contemporaneous mid ramp and basin biotas are dominated by a heterozoan fauna solitary corals crinoids bryozoans and brachiopods that grew in cooler deeper waters that may have been beneath a thermocline initial cooling began in the latest sakmarian with an influx of cool deep water and climatic deterioration allowing cool and warm waters to mix disrupting the thermocline and producing a sub tropical marine biota whose remains were reworked by storms and re deposited as tempestites faunas are heterozoan crinoids bryozoans brachiopods and sponges with photozoan elements colonial corals and symbiont bearing fusulinids prominent only in inner ramp facies by late artinskian these photozoan components are only present in shallowest basin margin environments artinskian subtropical waters contained somewhat elevated trophic resources that together with mixing of photozoan and heterozoan elements in the subtropical inner ramp produced the greatest faunal diversity seen in the sverdrup basin the biota was completely boreal in nature and warm shallow waters with a warm refuge biota were now supplemented by cool waters derived from the panthalassa ocean profound change took place in the kungurian coincident with localised uplift during the melville disturbance and increased siliciclastic input neritic storm dominated sediments are wholly heterozoan brachiopods bryozoans crinoids and sponges with no remaining photozoan elements nutrient levels are elevated but not eutrophic as indicated by phosphate and glauconite extensive bioerosion numerous infaunal foraminifers and an impressive and diverse shelly biota that during times of high siliciclastic input was replaced by a profuse zoophycos infauna brachiopod and bryozoan faunas are distinctly boreal continued cooling relatively high nutrients as indicated by abundant glauconite and phosphate and decreased siliciclastic input eventually resulted in an abundant heterozoan biota brachiopods bryozoans crinoids and sponges with local gigantism but reduced brachiopod and bryozoan diversity these middle permian rocks may be the coolest water deposits in the sverdrup basin the faunas are still part of a boreal arctic province with strong ties to cool water faunas of uralian basin the succession ends with late permian biosiliceous spiculitic cherts containing accessory heterozoan components brachiopods bryozoans and few crinoids these sediments in part coeval with evaporites and terrestrial red beds on the eastern european platform are interpreted to reflect a combination of cool waters elevated nutrients and mid latitude storminess

replacement of evaporites within the permian park city formation bighorn basin wyoming usa the permian park city formation consists of cyclically bedded subtidal to supratidal carbonates cherts and siltstones early diagenesis of park city formation carbonates occurred under the influence of waters ranging from evaporative brines to dilute meteoric solutions and resulted in evaporite emplacement syndepositional nodules and cements as well as dolomitization silicification and leaching of carbonate grains major differences are seen however in the diagenetic patterns of subsurface and surface sections of park city formation rocks subsurface samples are characterized by extensively preserved evaporite crystals and nodules and preserve evidence of significant silicification chert chalcedony and megaquartz and minor calcitization of evaporites in outcrop sections the evaporites are more poorly preserved and have been replaced by silica and calcite and also leached the resultant mouldic porosity is filled with widespread very coarse blocky calcite spar these replacements appear to be multistage phenomena field and petrographic evidence indicates that silicification involved direct replacement of evaporites and occurred during the early stages of burial prior to hydrocarbon migration siliceous sponge spicules provided a major source of silica and the fluids involved in replacement were probably a mixture of marine and meteoric waters a second period of replacement and minor calcitization is inferred to have occurred during deep burial under the influence of thermochemical sulphate reduction although the presence of hydrocarbons probably retarded most other diagenetic reactions during this time interval the major period of evaporite diagenesis however occurred during late stage uplift the late stage replacement and pore filling calcites have 13c values ranging from 0 5 to 25 3 and 18o values of 16 1 to 24 30 pdb reflecting extensive modification by meteoric water vigorous groundwater flow associated with mid tertiary block faulting led to migration of meteoric fluids through the porous carbonates to depths of several kilometres these waters reacted with the in situ hydrocarbon rich pore fluids and evaporite minerals and precipitated calcite cements the tosi chert appears to have been an even more open system to fluid migration during its burial and has undergone a much more complex diagenetic history as evidenced by multiple episodes of silicification calcitization ferroan and non ferroan and hydrocarbon emplacement the multistage replacement processes described here do not appear to be restricted to the permian of wyoming similarly complex patterns of alteration have been noted in the permian of west texas new mexico greenland and other areas as well as in strata of other ages thus multistage evaporite dissolution and replacement may well be the norm rather than the exception in the geological record

neoproterozoic peritidal phosphorite from the sete lagoas formation brazil and the precambrian phosphorus cycle the neoproterozoic sete lagoas formation ca 610 ma of the sao francisco basin brazil is a succession of siltstone limestone and phosphorite phosphorite forms part of a previously unrecognized 150 to 200 m thick unconformity bounded depositional sequence lithofacies stacking patterns indicate that deposition was punctuated by higher order fluctuations in base level that produced aggradational parasequences these shallowing upward cycles record the progradation of phosphate rich intertidal flats over shallow subtidal deposits as accommodation filled the presence of mudcracks authigenic chert nodules lack of coarse terrigenous clastics and the abundance of silt with fine abraded quartz grains suggests accumulation along an arid coastline with significant aeolian input delivery of phosphorus adsorbed on aeolian fe oxyhydr oxide and clay is interpreted as having stimulated phosphogenesis in peritidal environments lithofacies associations indicate that windblown phosphorus promoted the establishment of cyanobacterial communities along the coast which produced photosynthetic oxygen and the suboxic conditions necessary for the precipitation of authigenic carbonate fluorapatite as in other precambrian phosphatic systems nearshore oxygen oases were a prerequisite for phosphorite accumulation because redox sensitive phosphogenic processes were pushed into the sediment to concentrate phosphorus in more distal anoxic environments phosphorite could not form because these biotic and abiotic processes were suspended in the water column which cycled phosphorus in sea water rather than at the sediment water interface such shallow water phosphorite is unlike larger younger neoproterozoic phanerozoic phosphatic deposits inferred to have formed in deeper upwelling related environments the increasing size of phosphatic deposits through the latest precambrian is interpreted as reflecting the progressive ventilation of the oceans during the neoproterozoic oxygenation event and resultant expansion of phosphogenic environments into distal settings the widespread cycling of bioavailable phosphorus at the sea floor not only produced the first true phosphorite giants but may have also been an important precondition for the evolution of multicellular animals

the case for a shallow crustal anomalous zone magma body near the south end of hilton creek fault california including new evidence from an interpretation of pre s arrivals abstract seven independent lines of evidence can be cited for the existence of a shallow crustal anomalous zone at a site near the south end of hilton creek fault near mammoth lakes california they are 1 the presence of a persistent seismic gap since detailed observations began in 1979 2 s wave shadowing for travel paths crossing the site 3 a low velocity anomaly associated with the south end of hilton creek fault discovered by seismic tomography 4 the observation of two non double couple mechanisms for large earthquakes a few km east and west of the site 5 a concentration of pre s arrivals indicative of a possible reflection in the vicinity of this site 6 a geometric symmetry of source receiver paths showing pre s arrivals about this site and 7 new evidence presented herein travel time fits of strong pre s arrivals recorded at epicenter of the 1978 wheeler crest event m l 5 7

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

phosphorites glass ramps and carbonate factories the evolution of an epicontinental sea and a late palaeozoic upwelling system phosphoria rock complex this is the peer reviewed version of the following article matheson e j and frank t d 2020 phosphorites glass ramps and carbonate factories the evolution of an epicontinental sea and a late palaeozoic upwelling system phosphoria rock complex sedimentology doi 10 1111 sed 12731 which has been published in final form at https doi org 10 1111 sed 12731 this article may be used for non commercial purposes in accordance with wiley terms and conditions for use of self archived versions

permian deposits of the southern alps as product of initial alpidic taphrogenesis sedimentological and morphotectonic investigations of permian deposits between the val camonica and the karawanken mountains indicate the development of a complex rift system which initiated the alpidic sedimentation phase

controls on permo carboniferous precipitation over tropical pangaea a gcm sensitivity study abstract a series of late paleozoic climate model simulations was developed using the genesis atmospheric general circulation model to investigate the independent roles of gondwanan deglaciation atmospheric co 2 rise and regional tectonism on the long term 10 6 yr evolution of continental precipitation over tropical pangaea the model results indicate that either deglaciation or a co 2 increase from 1 to 8 present atmospheric levels could have caused substantial drying and warming at low latitudes a result that is consistent with late paleozoic proxy records yet the atmospheric processes that led to drying differ between these cases the deglaciation of gondwana reduces low latitude temperature gradients in the southern hemisphere decreasing by as much as 60 the meridional overturning in the southern hemisphere winter cell of the hadley circulation the decline in overturning reduces convective precipitation over equatorial pangaea in contrast high levels of co 2 have little effect on the large scale meridional overturning circulation but increase continental temperatures leading to high evaporation rates and reduced available soil moisture the source of convective precipitation on land in comparison to deglaciation and p co 2 regional uplift erosion of the central pangaean mountains cpms has a secondary effect on tropical precipitation in genesis and cannot explain the long term aridification and warming of western pangaea we suggest that the deglaciation of gondwana and a concomitant rise in atmospheric p co 2 could explain much of the late paleozoic climate change over low latitude pangaea

petrology and major element geochemistry of peru margin phosphorites and associated diagenetic minerals authigenesis in modern organic rich sediments abstract new petrographic and major element geochemical data from modern peru margin upper slope outer shelf phosphorites are presented which provide insight into their origin and paragenetic relationship with other authigenic minerals glauconite pyrite and dolomite occurring in organic rich sediments glauconites are precipitated relatively early following the partial reduction of ferric iron and following this process phosphate pyrite and then dolomite precipitation take place at progressively deeper levels in the sediment in association with microbial reduction of sulfate as in many ancient economic phosphorite deposits the phosphatic facies here consist of nodules crusts coatings and strata composed of phosphatic pelletal grains ooids structureless grains intraclasts clumps and biogenic grains in association with organic rich biosiliceous sediments all are considered to have formed within a few centimeters or within a few tens of centimeters below the sediment water interface important factors that influence which morphology will tend to develop include the amount of available pore space the presence of suitable nucleation sites the amount and size of siliciclastic detritus incorporated as inclusions and the relative solution chemistries of the precipitating solutions bacterial mediation may play an important but as yet unspecified role in the precipitation process textural data and factor analysis of chemical data suggest that structureless pellets are relatively inclusion free na f mg co3 substituted pore water precipitates whereas ooids are inclusion rich pore water precipitates poor in lattice substituted components variations in nodular cement birefringence and crystallinity are suggested to have been produced by similar lattice substitutions that directly reflect pore water carbonate ion concentrations and thus relative degrees of organic matter degradation phosphate and dolomite are intimately mixed yet mineralogically distinct phases in phosphatized dolomicrites depth stratified threshold carbonate ion concentrations may control the lower limit at which phosphatic minerals may precipitate below depths of a few centimeters excessive carbonate ion concentrations and diminished reactive iron and sulfate concentrations favor the development of dolomite while precluding further development of phosphatic minerals and pyrite periodic sediment reorganization bioturbation current winnowing and erosion mass wasting etc plays an important role in both concentrating pelletal grains and maintaining nodules and crusts at critical depth levels in the sediment as well as mixing ordered mineral parageneses into complicated sequences

importance of hercynian tectonics within the framework of the southern alps abstract the hercynian remnants present within the alpidic structural zones of the southern alps are reviewed the pattern of hercynian metamorphism is zonal from granulites in the western area to anchimetamorphic facies in the eastern one in the folded zone at the eastern margin a severe hercynian folding phase took place during the westphalian thrust sheets comprising sequences of different facies ranging in age from caradocian to early westphalian are sutured by late westphalian molasse deposits the assumption that the southern alps and the external dinarides remained outside the hercynian folding front is contradicted by field evidence

strike slip orogens an explanation for the hercynides the nature of oblique plate interactions is not yet well understood the oblique interaction of pacific and n american plates has resulted in large scale migration rotation and accretion of microplates intervening basins are ephemeral individually filled and deformed oblique motion results in zones of both compression and extension the latter may be sufficient to generate new oceanic crust and the former to obduct it both subduction and collision are restricted in time and space the resulting orogen is extraordinarily complex in detail the far more complicated hercynides are the result of dextral interaction between continental plates europe and africa the lateral variability of the orogen the major and long lived strike slip faults the bimodal volcanism and related ore deposits of the european trough the lizard ophiolite and its melanges the nw spanish ophiolites and the iberian pyrite belt are all explained using an oblique collision model in particular the generation deformation and obduction of ophiolites in oblique slip mobile zones is discussed

development of the palaeogeography of pangaea from late carboniferous to early permian abstract old and new well and poorly known lithofacies data of moscovian and artinskian age in the area limited by the arctic sea and central africa the atlantic ocean and the ural mountains have been plotted on present day maps the facies mapped and related environments allow the recognition of a series of different palaeogeographic palaeotectonic units including the late carboniferous to early permian deep sea to palaeo tethyan ocean west siberia kazakhstan continent and uralian kazakhstan tienshan arc uralian foredeep up to the closing arms of the uralian ocean precaspian basin russian platform donets rift basin caucasian moesian dobrogean polish oslo basinal belt syn tectonic hercynian foreland basin intramontane post hercynian basins iran anatolian hellenic dinaric carnic basin branching into the hungarian seaway apennine basin branching into the cantabrian and south portuguese basins oman iraq levantine sicily deep basin and inferred oceanic sea way south peri tethyan platform basins east arabian cratonic basin and north african intracratonic basins the subsidence sedimentation trends of these units were correlated and compared through lithostratigraphic logs bathymetric curves and uncorrected cumulative stratigraphic curves the sets of original and processed data were used to test two different palaeodynamic models a pangaea a model static from late carboniferous to triassic and a mobile pangaea b model with different dextral displacements between laurussia and gondwanaland in the same time interval the best fit for our data requires a strike slip offset of about 800 km from moscovian to artinskian time this model implies a first quasi pangaea or pangaea b assembly at the carboniferous permian transition an ephemeral pangaea b break up driven by an early permian oblique rift across the mediterranean to caribbean areas and a final pangaea a assembly in the mid to late permian the two palinspastic maps describing the model have been cross checked by comparison with an independent set of biogeographic features of late carboniferous and early permian overall floral reptile and marine benthic organism distribution is consistent with the early permian trans pangaea seaway inferred from facies and palaeodynamic analyses

where has all the aragonite gone mineralogy of holocene neritic cool water carbonates southern australia abstract surficial carbonate sediments on the southern continental shelf of australia are cool water in aspect and composed of biogenic particles produced largely during the late quaternary current understanding is that such sediments are calcite dominated as were their older cenozoic counterparts the holocene fraction of these sediments in modern open shelf neritic environments between 30 and 350 meters water depth is however 50 to 80 aragonite scant evidence of significant former aragonite in many cool water carbonate sedimentary rocks implies that most aragonite is lost before such sediments exit the marine diagenetic environment although marine dissolution must be taking place in such settings the conundrum is exacerbated because seawater over the shelf in southern australia is saturated with respect to aragonite it is proposed that the aragonite from skeletons of gastropods infaunal bivalves and certain bryozoans is dissolved in the shallow subsurface probably as the byproduct of bacterial degradation of sedimentary organic matter as a consequence the geological and paleontological record of many cool water carbonates is strongly biased and the inferred original calcitic composition of such sediments is the product of early diagenetic taphonomic loss not selective biogenic productivity the net result is not only dissolution of aragonite but also neomorphism of mg calcite to calcite with a marine geochemical signature synsedimentary aragonite loss by removing caco3 that is usually available for calcite cementation during meteoric diagenesis leads to retarded lithification of these cool water carbonates until deeply buried such removal of a significant carbonate fraction during deposition likely contributes to the low rates of cool water sediment accumulation

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

time specific aspects of facies state of the art examples and possible causes abstract the term time specific facies tsf was introduced to the scientific community by the late otto h walliser to refer to unique facies typical of particular narrow intervals some of which were related to bioevents in some senses however the concept was recognized much earlier and is even engrained in the very names of some geologic periods the concept of time specific facies is expanded slightly herein to include distinctive or unique regional to global characteristics of the sedimentary record that characterize particular intervals of geologic time the recognition of time specific and widespread processes in the sedimentary record is a critical step in unraveling the interplay between processes of differing scale these range from very short term but widespread facies that overlap with event deposits to general facies types that may persist for intervals up to 10s of millions of years in duration this paper briefly summarizes the history of development of the tsf concept provides examples to illustrate a few of the key aspects of time specific facies and offers a few tentative explanations for this phenomenon among the factors that control tsfs abrupt changes in redox conditions and early diagenetic mineralization sedimentary condensation often associated with abrupt sea level change altered climate and paleoceanography and biotic evolution and extinction seem to be most critical and permit a preliminary genetic classification of tsfs inevitably however many tsfs reflect multiple effects and some remain largely unexplained

sponge meadows and glass ramps state shifts and regime change abstract glass ramps are coastal marine sedimentation regimes of siliceous biomineralization and present alternatives to carbonate or siliciclastic deposition prominent chert deposits around the world record glass ramps from the eocene jurassic permian and mississippian these events ranged from regional to continental scale and lasted from a couple million years to over ten million years this review compares established cases of glass ramp deposition to clarify the bio depositional features that distinguish glass ramps from other bedded or mounded biosiliceous deposits and from carbonate ramp regimes it also compares environmental contexts of glass ramp initiation and persistence the primary sediment on these glass ramps is disaggregated spicules of siliceous sponges the sponges formed meadows on level bottom inner and mid ramp settings and loose spicules were redistributed along the shelf carbonate bioclasts were generally present but diluted by the great abundance of spicules carbonate factories were either limited to small dense patches moved offshore or re established at a later time glass ramps initiated in a wide variety of climates and oceanographic settings but appeared to initially require partial protection from storm energy the importance of marine silicic acid for such widespread biosiliceous factories is also estimated showing that glass ramps required long term adjustments in silica supply glass ramps lack modern analogues but their ecology can be interpreted in light of stable state dynamics in other modern invertebrate communities it is suggested that siliceous sponge meadows were an alternate stable state locally on carbonate ramps occurring with greater frequency and carrying greater ecological significance than have been previously expected this model warrants additional scrutiny on sponge meadows possible stabilizing feedbacks and on the thresholds of state switching

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

palaeozoic strike slip rift pulses and palaeogeography in the circum mediterranean tethyan realm abstract five main rifting cycles supported by different types of field evidence including magmatism sedimentation and tectonics have been recognized in the circum mediterranean area western tethys realm before the opening of the jurassic tethys proper they occurred roughly in the late cambrian early ordovician early silurian late devonian dinantian early mid permian and mid triassic times each of these rifting cycles began with intracontinental mainly shallow marine conditions evolving usually to basinal environments of quite different bathymetry the palaeozoic ccd has been proved to be much less deep than the post liassic one minor suboceanic seaways cut across and fragmented the gondwana south european plate following the early palaeozoic rifting cycles the long mid palaeozoic devono dinantian rifting cycle migh possibly have resulted in a wider system of suboceanic sea ways connecting a palaeo tethys ocean to the east of gondwana with the rheic ocean to the west of it the birth of palaeo tethys or of its westward extension would have been directly linked with the gradual death of the devono mississippian rheic ocean a complex large scale dextral transform system is inferred to have connected the two respectively expanding and contracting oceans fragmentation and mutual displacement of microblocks in the connection area the circum mediterranea area and southern europe resulted from strike slip oblique rift pulses with coeval local contractional and extensional processes a major change of the gondwana rotational vector is believed to have produced the mid late carboniferous transpressional strike slip hercynian orogen this is a good explanation of the peculiar thermal regime of the hercynian diastrophism all over europe there is no support for the hypothesis of a very wide more than 3000 km palaeozoic ocean separating northern europe from southern europe or gondwanaland this idea was mainly based on poor palaeomagnetic data and is heavily contradicted by palaeobiogeographical and geological data furthermore it ignores the dramatic shortening of the hercynian orogen all over europe the early palaeozoic to early mesozoic history of the circum mediterranean area involves the cyclic recurrence of oblique rifts culminating in the early jurassic strike slip rift and subsequent limited opening of the tethys proper to avoid confusion in terminology one should use prefixes referring to age bathymetry physiography and geotectonic setting to qualifying the general term tethys e g shallow cretaceous tethys basinal intracontinental devonian tethys oceanic jurassic tethys etc

a paleozoic pangaea paleozoic paleogeographies should be consistent with all available reliable data however comparison of three different devonian paleogeographies that are based largely or wholly on the data of remanent magnetism show them to be inconsistent in many regards when these three paleogeographies are provided with possible ocean surface current circulation patterns and have added to them lithofacies and biogeographic data they also are shown to be inconsistent with such data a pangaeic reconstruction positioned in the southern hemisphere permits the lithofacies and biogeographical data to be reconciled in a plausible manner

eolian derived siltstone in the upper permian phosphoria formation implications for marine upwelling previously described organic rich shale facies of the meade peak member of the phosphoria formation at soda springs idaho consist of well sorted laminated siltstone containing little or no clay the planar parallel fabric preserved in many of the siltstone beds suggests suspension settling onto the outer shelf or upper slope most likely under low oxygen conditions evidence for transport of silt to the depositional site by sediment gravity flows is absent as are sandstone beds we propose that meade peak siltstone facies record subaqueous deposition of windborne silt that was transported southward from central montana as such they provide the first direct geologic evidence of a wind regime favorable for marine upwelling the process commonly postulated to have localized the deposition of permian phosphatic sediments they may also provide indirect evidence of upwind eolian sand transport at that time

lithospheric strength variations as a control on new plate boundaries examples from the northern red sea region abstract the complex plate boundary between arabia and africa at the northern end of the red sea includes the gulf of suez rift and the gulf of aqaba dead sea transform geologic evidence indicates that during the earliest phase of rifting the red sea propagated nnw towards the mediterranean sea creating the gulf of suez subsequently the majority of the relative movement between the plates shifted eastward to the dead sea transform we propose that an increase in the strength of the lithosphere across the mediterranean continental margin acted as a barrier to the propagation of the rift a new plate boundary the dead sea transform formed along a zone of minimum strength we present an analysis of lithospheric strength variations across the mediterranean continental margin the main factors controlling these variations are the geotherm crustal thickness and composition and sediment thickness the analysis predicts a characteristic strength profile at continental margins which consists of a marked increase in strength seaward of the hinge zone and a strength minimum landward of the hinge zone this strength profile also favors the creation of thin continental slivers such as the levant west of the dead sea transform and the continental promontory containing socotra island at the mouth of the gulf of aden calculations of strength variations based on changes of crustal thickness geotherm and sediment thickness can be extended to other geologic settings as well they can explain the location of rerifting events at intracratonic basins of backarc basins and of major continental strike slip zones

iron and macronutrients in california coastal upwelling regimes implications for diatom blooms the supply of iron relative to that of the macronutrients nitrate phosphate and silicic acid plays a critical role in allowing extensive diatom blooms to develop in coastal upwelling regimes the presence or absence of a broad continental shelf influences the supply of iron the iron input to central california upwelling waters varies spatially and can be characterized by two end member regimes one end member which includes monterey bay and extending north to pt reyes is an iron replete regime where upwelling occurs over a relatively broad continental shelf that results in waters with high concentrations of dissolved and particulate iron 10 nm entrained together with high concentrations of nitrate and silicic acid in these iron replete regions extensive blooms of large diatoms deplete macronutrient concentrations which results in correspondingly high chlorophyll a concentrations the other end member located to the south of monterey bay off the big sur coast is an iron deplete regime where upwelling is focused offshore of a narrow continental shelf upwelled waters in the big sur region are characterized by low dissolved and particulate iron concentrations 1 nm together with high concentrations of nitrate and silicic acid extremely low iron concentrations unused nitrate and silicic acid and a low abundance of large diatoms characterize surface waters in these iron deplete regions and thus represent coastal upwelling high nutrient low chlorophyll systems limited by the micronutrient iron

extremely high temperatures and paleoclimate trends recorded in permian ephemeral lake halite although the late paleozoic deglaciation is arguably one of the best deep time analogs for current and predicted climate change quantitative paleotemperature data from this interval are generally lacking we reconstruct extreme paleoweather conditions and paleoclimate changes from permian nippewalla group probably uppermost leonardian kungurian north america ephemeral lake halite by using fluid inclusion homogenization temperatures to directly measure the water temperature when the halite precipitated in these depositional settings this is an excellent air temperature proxy extremely high temperatures to 73 c and large diurnal temperature ranges are evidenced in the lower nippewalla group suggesting conditions more extreme than anywhere on earth today in contrast the upper nippewalla group was cooler maximum temperature was 43 c and diurnal temperature ranges were smaller though even these conditions are similar to modern extremely hot environments comparison to prior studies suggests that these results may be indicative of regional patterns this study represents the first pre quaternary high resolution quantitative data set of extreme paleoweather and possible paleoclimate trends from fluid inclusions in halite and provides new insight into climate change during the late paleozoic deglaciation

salinity stratification in the permian phosphoria sea a proposed paleoceanographic model the late permian phosphoria formation of the western united states contains 1 7 10 12 t of phosphate and locally as much as 32 9 total organic carbon the mineral wealth of the phosphoria formation is generally attributed to late permian upwelling along the western margin of the continent unlike in most modern environments upwelling in the late permian occurred proximal to a broad shallow evaporative sea rather than an abrupt continental margin evaporite deposits that are contemporaneous with the organic and phosphate rich strata are present within the phosphoria and adjacent basins elevated concentrations of the biomarker gammacerane are ubiquitous in the organic rich facies of the phosphoria formation which suggests that the basin was salinity stratified depositional environments incorporating both upwelling and salinity stratification are unusual and poorly documented in modern settings we infer the presence of salinity stratification in the phosphoria basin and propose a paleoceanographic model of the phosphoria sea during the deposition of organic and phosphate rich sediment from the western margin of the continent upwelling water flowed into the evaporative phosphoria sea replacing and overriding hypersaline bottom water that drained westward this paleoceanographic model of the phosphoria sea may help to explain the distribution and preservation of organic and phosphate rich strata in the phosphoria formation

a mid permian chert event widespread deposition of biogenic siliceous sediments in coastal island arc and oceanic basins abstract radiolarian and conodont of permian siliceous rocks from twenty three areas in teh the circum pacific and mediterranean regions reveal a widespread permian chert event during the middle leonardian to wordian radiolarian and or sponge spicule rich siliceous sediments accumulated beneath high productivity zones in coastal island arc and oceanic basins most of these deposits now crop out in fault bounded accreted terranes biogenic siliceous sediments did not accumulate in terranes lying beneath infertile waters including the marine sequences in terranes of northern and central alaska the permian chert event is coeval with major phosphorite deposition along the western margin of pangea phosphoria formation and related deposits a well known analogue for this event is middle miocene deposition of biogenic siliceous sediments beneath high productivity zones in many parts of the pacific and concurrent deposition of phosphatic as well as siliceous sediments in basins along the coast of california interrelated factors associated with both the miocene and permian depositional events include plate reorientations small sea level rises and cool polar waters

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

new u pb constraints identify the end guadalupian and possibly end lopingian extinction events conceivably preserved in the passive margin of north america implication for regional tectonics the discovery and dating of a volcanic ash bed within the upper phosphoria formation in se idaho usa is reported the ash occurs 11 m below the top of the phosphatic meade peak member and yielded a 206 pb 238 u date of 260 57 0 07 0 14 0 31 ma i e latest capitanian guadalupian the stratigraphic position of this ash near the top of the meade peak phosphatic member of phosphoria formation indicates plausible completeness of the sedimentation within the guadalupian lopingian and probably at the permo triassic p t transitions the new radiometric age reveals that the regional biostratigraphy and palaeontology of phosphoria and park city formations requires serious reconsideration particularly in cool water conodonts bryozoans and brachiopods the new age proposes that the guadalupian lopingian boundary glb coincides with the meade peak rex contact and consequently with the end guadalupian extinction event the lack of a major unconformity at the p t transition suggests that the effects of the sonoma orogeny were not as extensive as has been assumed

a nomenclature system for granular phosphate rocks according to depositional texture abstract because of their striking textural similarities to carbonates a nomenclatural scheme for the classification and interpretation of phosphate sediments is proposed based on the dunham embry and klovan classification for carbonate rocks allochemical phosphate rocks and phosphorites comprise orthochems and allochems matrix cement ooids bioclasts intraclasts and lithoclasts to distinguish such components and their resulting rocks as being phosphatic a phos prefix is proposed i e phosclast mudstone phosclast wackestone phosclast packstone etc this classification nomenclature emphasizes fabrics as well as palaeoenvironmental criteria

paleozoic evolution of the armorica plate on the basis of paleomagnetic data new paleomagnetic data support the contention that armorica and gondwana formed a coherent block until ordovician time however by early devonian time armorica collided with the north american northern european assembly to form the old red continent and the collision itself was responsible for the acadian orogeny not for the earlier taconic orogeny as postulated previously the carboniferous collision of gondwana with the old red continent subsequently formed pangaea and produced the appalachian hercynian orogeny

periodicity in the early palaeozoic marine realm evidence from the british isles suggests that during 3 intervals in the early palaeozoic conditions approximating to those of a non uniformitarian greenhouse g state earth were realized middle early upper cambrian st davids merioneth ages 30 ma mid ordovician llandeilo caradoc ages 32 ma and early silurian llandovery early wenlock ages 12 ma during these times sea levels were high and ocean waters below the zone of surface overturning poorly aerated and at times euxinic pelagic biotas graptoloids were diverse and in aerated portions of the highly productive shelf seas benthic biotas brachiopods flourished opposing conditions marking a well oxygenated o state earth occurred to varying degrees in the intervening intervals early cambrian comley age 20 ma late cambrian mid ordovician tremadoc late llandeilo ages 46 ma late ordovician ashgill age 4 ma and mid to late silurian post early wenlock age 15 ma within the constraints of the present data perturbations in the early palaeozoic marine realm do not appear to follow the same regular periodicity as in the mesozoic and caenozoic among a number of likely causes for this the greater tendency for the early palaeozoic seas to become anoxic seems the most important

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

the 1998 earthquake sequence south of long valley caldera california hints of magmatic involvement a significant episode of seismic and geodetic unrest took place at long valley caldera california beginning in the summer of 1997 activity through late may of 1998 was concentrated in and around the south moat and the south margin of the resurgent dome the sierran nevada block snb region to the south southeast remained relatively quiet until a m 5 1 event occurred there on 9 june 1998 ut a second m 5 1 event followed on 15 july ut both events were followed by appreciable aftershock sequences an additional distinct burst of activity began on 1 august 1998 the number of events in the august sequence over the first week or two was similar to the aftershock sequence of the 15 july 1998 m 5 1 event but the later sequence was not associated with any events larger than m 4 3 all of the summer 1998 snb activity was considered tectonic rather than magmatic in general the snb is considered an unlikely location for future eruptions however the august sequence an aftershock sequence without a mainshock is suggestive of a strain event larger than the cumulative seismotectonic strain release moreover a careful examination of waveforms from the august sequence reveals a small handful of events whose spectral signature is strikingly harmonic we investigate the waveforms of these events using spectral autocorrelation and empirical green s function techniques and conclude that they were most likely associated with a fluid controlled source our observations suggest that there may have been some degree of magma or magma derived fluid involvement in the 1998 snb sequence

coupling between sulfur recycling and syndepositional carbonate dissolution evidence from oxygen and sulfur isotope composition of pore water sulfate south florida platform u s a sulfur cycling in fe poor organic rich shelf carbonates known to have rapid rates of so4 2 reduction remains poorly studied despite the volumetric significance of shelf deposits in modern and ancient carbon budgets we investigated sulfur cycling in modern carbonates of the florida platform from end member depositional environments muddy sands from the atlantic reef tract and finer grained mudbank and island flank deposits from florida bay relations between pore water chemistry so4 2 co2 ca 2 cl and oxygen and sulfur stable isotope compositions of so4 2 require direct coupling between sulfur redox cycling and syndepositional carbonate dissolution oxygen isotope compositions of pore water sulfate were remarkably shifted away from the established value for marine so4 2 9 5 despite near normal so4 2 cl ratios chemical evolution was least in reef tract pore waters and greatest in florida bay relative to overlying seawater mudbank sediments exhibited sulfate depletion with 18oso4 and 34sso4 values both increasing by about 7 more bioturbated island flank sediments colonized by thalassia grass had a 5 increase in 18oso4 variable 34sso4 values 17 7 to 23 3 and exceptionally high ca 2 cl ratios the large excess of ca 2 up to 1 7 mm requires a much larger acid source than the amounts derived from utilization of dissolved o2 0 3 mm and small degrees of net so4 2 reduction 0 5 mm reduced a conceptual model was constructed using chemical and isotopic data on natural pore waters and on sulfate isotope fractionation factors obtained from sediment incubation experiments the model outputs show that pore water compositions can be explained by a redox cycle where microbial so4 2 reduction is followed by very efficient h2s oxidation thus maintaining virtually invariant so4 2 cl ratios the enhanced o2 transport may be driven by associated marine grass rhizome systems and microbial communities established in bioturbated sediments the net result of the cycle is that the rate of sulfide oxidation which is largely balanced by the rate of microbial sulfate reduction is stoichiometrically related to the rate of carbonate dissolution this is consistent with previously reported rates of carbonate dissolution 400 mol cm2 yr and average rates of sulfate reduction 200 mol cm2 yr from the florida platform and a 2 1 stoichiometry

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

sedimentary phosphate formation in warm shallow waters new insights into the palaeoceanography of the permian phosphoria sea from analysis of phosphate oxygen isotopes abstract oxygen isotopic analyses of the structural phosphate 18 o p in sedimentary phosphorites of the upper permian phosphoria formation reveal that phosphogenesis occurred across a broad range of palaeoenvironments the 18 o p values from well preserved hand picked phosphate grain separates range from 20 2 to 13 7 0 5 smow with the lowest values in the most landward shallow water deposits and the highest values in the most basinward deeper water deposits the relationship between the maximum burial depth and 18 o p is opposite to that predicted if burial diagenesis was responsible for the isotopic signature of these phosphate grains this suggests that the regional trend in oxygen isotopic data is not due to burial diagenesis the range in oxygen isotopic values does correspond to the potential range of palaeotemperatures in the shallow and broad epicontinental phosphoria sea the range is 14 42 c 3 5 c assuming a seawater 18 o of 2 5 smow palaeotemperatures along an offshore to onshore transect indicate that upwelling involved temperate 14 26 c mean of 21 c but not cold waters and that warming across the palaeoshelf resulted in mean shallow water temperatures of 34 37 c the latter values approximate those predicted by climate and ocean circulation models these warm palaeotemperatures provide further evidence that phosphogenesis in the epicontinental phosphoria sea occurred under palaeoceanographic conditions that were different from modern phosphorite depositional systems this suggests that a purely actualistic approach to the interpretation of the phosphoria phosphorites is not valid

outline of upper precambrian and lower paleozoic evolution of the iberian peninsula according to u pb dating of zircons in the northwestern part of the iberian peninsula recent geological studies have defined the following stratigraphic sequence from bottom to top basal orthogneiss of miranda do douro is overlain by a complex of schist and greywacke which have been assigned to the cambrian or late precambrian these are followed by the ollo de sapo gneisses of volcanic sedimentary origin which in turn are overlain by the fossiliferous layers of the lower ordovician the schist and greywacke complex and the lower part of the ollo de sapo formation are transected by granitic dikes viana del bollo orthogneiss all these rocks were folded faulted metamorphosed and intruded by granite plutons during variscan times the emplacement of the miranda do douro and viana del bollo orthogneisses have been respectively dated at 618 9 ma and 465 10 ma by the u pb method on zircons these data yield lower and upper limits for the deposition of the ollo de sapo formation and demonstrate the occurrence of a precambrian basement pan african or cadomian orogeny in the variscan belt in the northwestern part of the iberian peninsula the emplacement of viana del bollo orthogneiss could be genetically related to the main phase of crustal thinning 470 520 ma characteristic of the prevariscan evolution of western europe typology and u pb data of the ollo de sapo zircons indicate the occurrence of inherited old precambrian zircons and yield an age of 325 3 ma for the variscan main thermal event in the area considered four possible evolutionary models for the u pb system of the ollo de sapo zircons are discussed

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

pre mesozoic paleomagnetism and plate tectonics although the arguments perhaps did not convince everyone at the time the paleomagnetic polar wander paths for europe and north america plotted by runcom 1956 certainly convinced me as a young graduate student that continental drift as we called it in those pre plate tectonic days deserved serious attention then throughout the 1960s the geoscience world seemed busy documenting and refining the models of seafloor spreading and plate tectonics that governed the opening of today s oceans as the number of publications espousing plate tectonics seemed to grow exponentially an often tacit assumption was that the continental breakup was a unique event and that pangea was a quasi primordial continental configuration ahead of his time however j tuzo wilson 1966 queried in a now classical paper did the atlantic close and then re open the 1973 penrose conference in vail colorado on pre mesozoic plate tectonics dewey spall 1975 showed that by then many earth scientists were preoccupied with proving that the tacit assumption was wrong and that wilson was right but compared to mesozoic and later plate tectonics the task of quantifying pre mesozoic continental movements is much more difficult since there are no seafloor magnetic anomalies to work with and much of the potential evidence e g ophiolites diagnostic supracrustal sequences high pressure low temperature metamorphic rocks has been destroyed by that ultimate plate tectonic process the continent continent collision and by sub sequent uplift and erosion nevertheless a multitude of observations facts interpretations reinterpretations proposals and hypotheses can now be found in the literature for virtually any pre mesozoic period and any geographic

coupled carbon isotopic and sedimentological records from the permian system of eastern australia reveal the response of atmospheric carbon dioxide to glacial growth and decay during the late palaeozoic ice age abstract proxy geochemical records from high latitude ice proximal deposits have the potential to provide key insights into past icehouse climates but such records are rare the permian system of eastern australia contains a rich record of environmental and climatic changes that occurred in areas proximal to glaciation during the acme and waning stages of the late palaeozoic ice age within this succession a wealth of fine grained organic matter rich facies provides an opportunity to construct a bulk 13corg record that records changes in atmospheric co2 through the permian fluctuations in 13corg track changes in climate determined independently on the basis of sedimentological criteria in the same strata these patterns are also broadly consistent with multiple proxy records derived from palaeoequatorial sites the results of this geochemical investigation 1 support recent studies using the high latitude ice proximal sedimentologic and stratigraphic record and palaeoequatorial geochemical proxies that document highly variable climatic conditions within the overall permian icehouse to greenhouse transition and 2 confirms that the sedimentary record of glaciation from eastern australia reflects global changes in atmospheric co2 on several m y order timescales

the mesozoic continental rifting in the mediterranean area insights from the verrucano tectofacies of southern tuscany northern apennines italy in the alpine mediterranean region the continental redbeds and shallow marine siliciclastics related to the early depositional phases of the late permian mesozoic continental rifting are referred to as the most common representative of the verrucano tectofacies the verrucano type successions exposed in southern tuscany are diachronous spanning from triassic to earliest jurassic in age and accumulated within the tuscan domain a paleogeographic region of continental crust that due to the opening of the piedmont ligurian ocean formed part of the adria passive margin they belong to the metamorphic verrucano group and the non metamorphic pseudoverrucano fm viewed overall these verrucano type successions appear to manifest five episodes or pulses of an ongoing continental rifting with the exception of the first episode that developed entirely within a terrestrial setting each one is represented by basal verrucano type continental siliciclastics overlain by compositionally mixed marine deposits which resulted from four diachronous post middle triassic transgressions this suite of tectonic pulses produced the progressive westward widening backstepping of the tuscan domain in the rifting south tuscany area

paleopositions of the western europe hercynides during the late carboniferous deduced from paleomagnetic data consequences for stable europe abstract paleomagnetic investigations have been carried out in different areas of the variscan belt armorican massif central massif ardenne vosges and the black forest in order to unravel the paleogeographic evolution of the hercynides during the carboniferous subsequent to important southerly or northerly drifts the central massif and vosges underwent a large rotation of a still undetermined direction in latest visean namurian times during the namurian westphalian the whole belt was oriented n s all investigated areas yield wsw ene directions for that period these directions question the validity of carboniferous mean poles available for stable europe a european plate rotated counterclockwise by about 40 relative to its permian position would be more consistent with these results during the latest westphalian stephanian period i e within the 310 290 ma timespan the western europe hercynides rotated clockwise by 40 50 perhaps together with the whole of europe late variscan strike slip faulting and overthrusting probably result from that rotation

nearshore along strike variability is the concept of the systems tract unhinged sequence stratigraphic models assume that nearshore strata have relatively consistent and laterally persistent stacking at the systems tract scale and therefore may not fully describe the three dimensional stratigraphic architecture in areas displaying marked nearshore along strike variability a stratigraphic model of nearshore deposits is presented that corrects for this assumption by explaining variations in along strike stratal geometries in terms of a systematic change in the orientation of a shoreline trend or clinoform rollover a scenario comparable to deflection around a hinge the model defines hinge zones that are both fixed and moving with respect to time and was created from outcrop well log and seismic reflection data model end members predict contemporaneous progradational aggradational and retrogradational stacking bounded by surfaces displaying significant along strike changes in architecture implying that sequence stratigraphic surfaces can be diachronous we advocate examining the impact of stratigraphic variations parallel to depositional strike by testing for the presence of uniform versus differential progradation phenomena responsible for creating unhinged and hinged nearshore depositional systems respectively understanding these differences will improve subsurface predictions and provide a more complete understanding of the stratigraphic evolution of sedimentary basins

the late palaeozoic early mesozoic from the catalan pyrenees spain 60 myr of environmental evolution in the frame of the western peri tethyan palaeogeography the eastern catalan pyrenees form the southernmost segment of the pyrenean axial zone they experienced complex multistage process as the result of both the variscan and the pyrenean orogenic cycles after the late palaeozoic several small extensional sub basins were filled by continental successions as a response to the changing tectonic setting within the frame of the southwestern europe this stratigraphic record perfectly exposed in the studied eastern pyrenean areas preserves the signatures of the late palaeozoic pangea break up during the progressive dismantling of the variscan chain up to the triassic diffused extension despite structural network being severely affected by cenozoic reworking the stratigraphic framework can be unravelled by the detailed sedimentological and stratigraphical analysis of the well exposed sequences in short this paper addresses facies patterns and architectural elements of late carboniferous permian triassic continental sections studied in the catalan pyrenees and aims to use these signatures for correlation not only at a regional scale but also within the broader picture of the southwestern europe our stratigraphical reconstruction clearly demonstrates that the thick studied succession consists of fluvial lacustrine basal units affected by intense volcanic activity and overlaying predominantly fluvial fining upwards units for each unit several lithofacies architectural elements and bounding surfaces of different order have been identified and their lateral and vertical staking characterized deposition and erosion processes are controlled by alternating periods of tectonic activity producing different stages of high and low subsidence the uplift of the sub basin margins and subsequent extended erosive events marked by angular unconformities on the strength of the major rank bounding surfaces analysis the studied sedimentary packages have been grouped into different tectono stratigraphic units and then correlated they have been contextualized within the latest palaeogeographic reconstructions of the studied sector contributing to detail the role of the study area within the frame of the s european palaeogeography

cephalopod limestone deposition on a shallow pelagic ridge the tafilalt platform upper devonian eastern anti atlas morocco as a result of early variscan tectonic movements and of differential subsidence a platform and basin topography was created along the northern margin of the sahara craton during the late devonian in the moroccan anti atlas mountains the tafilalt platform is an approximately n s running ridge which developed since the late middle devonian it separated a slowly subsiding shallow basin in the east tafilalt basin from a rapidly subsiding furrow in the west mader basin platform deposits are characterized by highly reduced thicknesses shallow subtidal to supratidal deposits in the late frasnian and by unconformities at the lower upper frasnian and the frasnian famennian boundaries after a local transgression over emergent areas in the north water depth probably never reached more than several tens to about 100 m in the lower famennian cephalopod limestones of this age deposited on the platform represent a very diverse facies pattern comprising quartz rich brachiopod coquinas crinoidal limestones thick bedded cephalopod limestones and nodular limestones sedimentation rates ranged from 1 to 5 mm 1000 yr in the late famennian more uniform marl and nodular limestone facies suggest slightly deeper environments platform margins are characterized by higher rates of subsidence debris flow deposits and slump structures in the relatively shallow tafilalt basin marls with intercalated nodular limestones were deposited in the mader basin sandy and calcareous turbidites suggest deeper water conditions in the late devonian during the strunian tournaisian the whole area was overwhelmed by a thick deltaic sequence the general facies distribution is in agreement with depositional models of other upper devonian and lower carboniferous cephalopod limestones in the european variscan orogenic belts in all these cases condensed cephalopod limestones occupy a distinct palaeogeographic position in predictable facies sequences that reflect pre orogenic phases in the variscan geodynamic cycle moreover close parallels exist with condensed sequences in the triassic and jurassic that occur in a very similar position within the alpine orogenic cycle

relationship of biomarker distribution to depositional environment phosphoria formation montana u s a from biomarker distributions it is possible to distinguish extracts from four different members facies meade peak rex retort and tosi of the permian phosphoria formation at little sheep creek montana these distributions relfect changes in floral and faunal distribution in response to a changing depositional environment and suggest that the retort and tosi members the second cycle of deposition were deposited under more anoxic conditions and at higher salinity than meade peak and rex members the first cycle correlations between biomarker indicators of anoxia and salinity suggest that anoxia was in part the result of a chemocline separating normal marine waters above from more saline bottom waters anoxia and salinity in the bottom waters increased with time making conditions in the basin progressively more hostile to benthic organisms development of extreme environmental conditions in continental shelf habitats such as those suggested by biomarker parameters at little sheep creek may have compounded spatial problems created by continental suturing suggested to be a cause of permian extinctions factor analysis indicates that four factors for 75 3 of the variance in biomarker ratios these factors are suggested to be source organisms types of eukaryotic plankton salinity eh and mineralogy the grandeur member of the phosphoria which is a typical reservoir rock for phosphoria derived oils yields an extract containing a novel c30 nitrogen containing steroid this unique steroid is not abundant in any other known extracts or oils which along with the extremely low porphyrin maturity parameter of all the extracts pmp 0 01 confirms the absence of migrated oils in the phosphoria at little sheep creek the biomarker ratios c29 ga a steranes ts ts tm triaromatic triaromatic monoaromatic steroids short long short chain monoaromatic steroids and short long short chain triaromatic steroids are commonly used to determine the thermal maturity of oils and source rock extracts however these ratios show considerable variation in core extracts of the same thermal maturity from different facies in contrast the thermal maturity parameters c29 20s 20s 20r steranes and porphyrin maturity parameter pmp show little variation indicating that these parameters are less affected by changes in depositional environment and may be most useful for thermal maturation determinations of phosphoria related oils and source rocks this study supports previous work suggesting environmental effects must be considered if correct determination of thermal maturity of an oil or extract is to be made this is especially true of oils and extracts from source rocks with high sulfur concentrations and or those deposited at elevated salinities

sedimentology of ancient saline pans an example from the permian opeche shale williston basin north dakota u s a abstract the mid permian opeche shale of north dakota consists of bedded evaporites and red bed siliciclastics detailed core and petrographic study has documented sedimentary and early diagenetic features in order to develop a depositional model and to refine paleoclimatic data and paleogeographic setting for the late paleozoic of the u s midcontinent lithologies and sedimentary features indicate lacustrine distal alluvial and minor eolian deposition subaerial exposure and soil formation bedded halites consisting of chevron and cumulate crystals dissolution surfaces and pipes and mudcracked microcrystalline salt crusts were deposited in a saline pan dominated by flooding evaporative concentration and desiccation bedded halites containing chevron and cumulate crystals but lacking any dissolution or desiccation features formed in perennial saline lakes chaotic halite composed of red mudstone and siltstone with displacive halite crystals represents saline mudflat deposits red mudstone and siltstone with little or no displacive halite but with abundant cracks and root features suggest deposition in a dry mudflat red bed sandstones and conglomerates composed of poorly sorted subrounded quartz grains cemented with halite indicate distal alluvial deposition with possible transport by ephemeral streams sheet floods and debris flows most deposition took place in halite dominated shallow perennial and ephemeral saline lakes surrounded by saline and dry mudflats evaporation desiccation flooding and wind played significant roles in this environment therefore the opeche evaporites and red beds are representative of an ancient saline pan system an inland playa setting is favored as a depositional model for the opeche shale the abundance of soil features and halite dominance as well as lack of nearshore carbonates and lack of restricted marine fossils suggest a closed basin nonmarine setting for the mid permian of the u s midcontinent

radioisotopic calibration of the guadalupian middle permian series review and updates abstract four high precision u pb ca idtims dates for the roadian lower guadalupian of 274 0 0 12 and 273 1 0 1 ma and for the wuchiapingian lower lopingian of 260 16 0 39 and 258 14 0 20 ma were obtained from permian tuff beds in the periphery of the okhotsk massif n e russia the beds are well constrained within the local lithostratigraphic and regional biostratigraphic framework besides regional bivalves and brachiopod faunas the ammonoid sverdrupites harkeri occurs close to the recovered roadian tuffs this ammonoid provides direct correlation of the tuffs with the kazanian stage on the russian platform and the roadian stage in the canadian arctic where the conodont index species of the roadian stage jinogondolella nankingensis gracilis and sverdrupites harkeri and other roadian ammonoids are documented from the assistant formation our review of the kungurian roadian wordian successions in the main well studied regions suggests that the base of the roadian stage should be extended down to approximately 277 ma and the roadian wordian boundary should be placed at approximately 271 ma the new calibration of the roadian stage reduces the duration of the enormously long kungurian stage from about 10 myr approximately to 6 0 6 5 myr if the proposed calibration is correct the duration of guadalupian series would be almost twice as great as in the previous estimates our results also suggest a possible correlation of the p3 alpine glacial event in the eastern australia with the wordian and possible uppermost roadian stages this p3 event corresponds with the disappearance of ammonoids and conodonts in the upper roadian and wordian in high latitudes regions i e n e russia russian and canadian arctic and australia perhaps due to extreme cooling of these areas the new radioisotopic ages in the okhotsk massif and surrounding regions improve the numerical calibration of the palynological zonation in the eastern australia and provide a direct correlation of the regional biostratigraphic brachiopod and bivalve zonation of n e russia with the international geologic time scale this zonation becomes a solid and reliable regional correlation tool within the vast territory from taymyr and east siberia to entire n e russia and transbaikalia

sedimentary evidence of a cambro ordovician orogenic event in the northwestern himalaya abstract the late proterozoic early paleozoic sequence of the tethys himalaya provides evidence of an orogenic episode close to the cambrian ordovician boundary late pan african event pre middle cambrian sediments were deposited on a terrigenous tidal flat gradually passing upward to a peritidal carbonate platform the succession shows an overall transgressive trend which is reproduced at smaller scale by second and third order coarsening upward cycles terminated by the landward shift of carbonate facies during highstands of sea level sandstone petrography suggests a passive continental margin setting for this part of the sequence in middle cambrian times the carbonate platform underwent gradual drowning and outer shelf slope shales with intercalated tuffaceous material erupted from a nearby immature volcanic arc were deposited the shales are overlain by basinal turbidites attesting to the growth of a sandstone lobe enclosed in lobe fringe siltstones in the middle ordovician unconformable alluvial fan conglomerates and braid plain sandstones derived from uplifted sedimentary sequences indicate erosion of a newly formed orogenic belt comparison with early paleozoic and recent counterparts allows to interpret the cambro ordovician sedimentary evolution in terms of foreland basin development the thermal subsidence of a passive margin temporarily reduced by the passage of a peripheral bulge was enhanced strongly by flexural downwarping towards a subduction zone collision of a buoyant continental margin at the trench hampered subduction rapid uplift ensued with formation of a foreland fold thrust belt shedding sedimentary detritus into the adjacent molasse basins

upper cretaceous campanian phosphorites in jordan implications for the formation of a south tethyan phosphorite giant a record of sedimentary authigenic and biological processes are preserved within the upper cretaceous campanian alhisa phosphorite formation ap in central and northern jordan the ap formed near the eastern extremity of the south tethyan phosphorite province stpp a carbonate dominated upper cretaceous to eocene phosphorite giant that extends from colombia north africa to the middle east multidisciplinary research of the ap and associated cherts chalks and oyster buildups indicate that phosphatic strata formed on a highly productive storm dominated east west trending epeiric platform along the south tethyan margin the onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the ajlun group pristine phosphates are associated with well developed micrite concretionary horizons and contain abundant non keeled spiral planktic foraminifera and a low diversity benthic assemblage of buliminacean foraminifera suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter the bulk sediment composition and absence of fe bearing authigenic phases such as glauconite pyrite including pyrite molds siderite and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that iron pumping played a minimal role in phosphogenesis authigenic precipitation of phosphate occurred in a broad array of sedimentary environments herein termed a phosphorite nursery that spanned the entire platform this is a non uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings wherever the conditions were suitable for phosphogenesis sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing and storm generated shelf parallel geostrophic currents economic phosphorites formed through the amalgamation of storm induced event beds stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite syndepositional phosphogenesis reworking and amalgamation to form phosphorites contrasts sharply with the principles of baturin cycling a transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis storm reworking of pristine

thermal history of the carnic alps southern alps austria and its palaeogeographic implications abstract the thermal history of the carnic alps southern alps austria has been investigated by means of organic petrology clay mineralogy and microthermometry in the tectonic framework of the carnic alps the metamorphic overprint from the lower anchizone up to the epizone is exposed in a continuous n s trending metamorphic section the metamorphic zonation is disturbed by shear zones related to the strike slip movement of the periadriatic lineament all obtained data a methodical correlation and a numeric 1d simulation of the burial history result in the model of a multistage thermal history 1 a variscan tectonothermal event caused a syntectonic anchi to epizonal metamorphism with the development of local overpressured zones characterized by convective heat transfer 2 major strike slip faults operating during the sedimentation of the late carboniferous molasse are related to enhance the heat flow 3 the alpine metamorphic overprint shows the same intensity as the variscan event 4 high temperature fluid inclusion phases are related to oligocene plutonic activity along the periadriatic lineament these data from the carnic alps are discussed in a general framework of the non to low grade metamorphic units of the internal alps and carpathians in the uppermost tectonic units of the eastern and southern alps a spatial and temporal shift of the alpine very low grade metamorphic overprint from north to south is observed this zonation indicates the pannonian transdanubian range which suffered no alpine metamorphism as an exotic block inside an alpine heated domain the gailtal line as a segment of the periadriatic lineament separates two terrains with the same alpine overprint

the chemistry of eolian quartz dust and the origin of chert abstract among the numerous models that have been suggested for the primary and predominant source of silica for chert we suggest that eolian dust is worthy of further considerations such considerations are supported by the common association of phanerozoic chert with evaporites limestones dolomites or other strata that were deposited within or near arid paleoclimates this association suggests a direct or indirect causal link between aridity and chert formation in addition eolian processes export large quantities of quartz rich dust from arid climate ergs or loess lands the chemistry of abraded quartz particles derived therefrom is consistent with chert formation abrasion of quartz particles produces an amorphous surface layer and underlying lattice disorder an inverse relation between particle size distribution 64 m and the enthalpy of solution of abraded quartz is indicative of the degree of lattice disorder as particle size decreases the enthalpy of solution increases the amorphous surface layer and underlying lattice disorder enhance both the rate and amount of dissolution of quartz dust particles the solubilized silica can then be reprecipitated and diagenetically altered to the various silica polymorphs that occur in chert an eolian supply and the chemistry of eolian abraded quartz particles may account for chert formation in disparate depositional environments that encompass deep sea chert chert in epicontinental seas including shallow shelves and chert that formed in continental eolinites lakes and soils arid climate silcretes

location and configuration of magma bodies beneath long valley california determined from anomalous earthquake signals recordings of 281 small earthquakes which occurred recently near the southern edge of long valley caldera at depths from 1 to 15 km are used to map the subsurface geometry of shear wave attenuating bodies in the caldera signatures of these events recorded northwest north northeast and east of long valley with ray paths through the caldera are often anomalous in that s wave arrivals have very low amplitudes and high frequency p and s wave energy is missing for the same station event combinations the volcanic and geothermal history of the region suggests that ray paths for these anomalous signals have passed through magma which absorbed much of the s wave energy and also attenuated the higher frequencies with over 1200 normal and anomalous ray paths through the caldera we have located two apparently massive magma bodies in the central and northwest caldera as well as two more dispersed magma areas in the southern caldera and beneath crowley lake the central magma body extends from 4 5 to at least 13 km beneath the surface and the northwest body is as shallow as 5 5 km these two magma bodies are probably connected below about 8 km secondary arrivals seen on select seismograms are tentatively interpreted as reverberations inside the central magma chamber and are consistent with the interpreted lateral extent of the magma the northwest and central magma bodies lie beneath the northwest and southeast corners of the caldera s resurgent dome and probably connect beneath the dome s center also the shallower parts of these magma bodies and the southern anomalous area lie beneath the surface expression of the medial graben faults suggesting that structural features seen at the surface of the valley may be related to magma location at depth

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

an upwelling model for the phosphoria sea a permian ocean margin sea in the northwest united states the permian phosphoria formation a petroleum source rock and world class phosphate deposit was deposited in an epicratonic successor basin on the western margin of north america we calculate the seawater circulation in the basin during deposition of the lower ore zone in the meade peak member from the accumulation rates of carbonate fluorapatite and trace elements the model gives the exchange rate of water between the phosphoria sea and the open ocean to the west in terms of an upwelling rate 84 m yr 1 and residence time 4 2 yr of seawater in the basin these hydrographic properties supported a mean rate of primary productivity of 0 87 g m 2 d 1 of carbon in the uppermost few tens of meters of the water column the photic zone and denitrifying redox conditions in the bottom water below approximately 150 m depth high rain rates onto the sea floor of the organic matter that hosted the phosphate and several trace elements contributed to the accumulation of phosphorite chert and black shales and mudstones evaporation in the goose egg basin to the east of the phosphoria basin ensured the import of surface seawater from the phosphoria sea budgets of water salt phosphate and oxygen plus the minor accumulation of the biomarker gammacerane show that exchange of water between the two basins was limited possibly by the shallow carbonate platform that separated the two basins

early diagenesis of organic matter in peru continental margin sediments phosphorite precipitation abstract pore water chemistry total dissolved co 2 nh 4 no 3 no 2 po 4 si oh 4 ca mg fe mn so 4 h 2 s and f and titration alkalinity solid phase chemistry c org p org c tot n tot f si opal and s ii and sediment characteristics porosity dry bulk density and formation factors were determined on a centimeter scale spacing in the upper 20 40 cm of sediments under intense upwelling areas on the peru continental shelf these data demonstrate that carbonate fluorapatite cfa is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content up to 20 c org very high porosity 0 96 ml cm 3 and very low dry bulk density 3 dissolved phosphate concentrations at the sediment water interface range from 20 to 100 m orders of magnitude higher than bottom water concentrations and much higher than predicted from regeneration of organic matter the mechanism of this interfacial phosphate release is unclear but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments fluoride is incorporated into cfa by diffusion from the overlying seawater and carbonate ions are provided from pore water alkalinity magnesium concentrations in this reaction zone are not significantly different from those of seawater suggesting that magnesium depletion is not a necessary prerequisite for cfa precipitation the environment of precipitation is interface linked rather than driven by organic diagenesis of phosphorus deeper in the sediment most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region but almost all show the precipitation signature near the interface this interface linked early diagenetic porewater environment for the precipitation of cfa explains many of the geochemical characteristics of phosphorites and provides a testable model to compare the modern phosphogenic analog with ancient phosphorite deposits two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites