comparison of magnetic hysteresis parameters of unremagnetized and remagnetized limestones for white magnetite bearing mesozoic pelagic limestones from italy which carry a primary magnetization the values of mrs ms and hcr hc generally lie in the pseudo single domain psd field of the day et al 1977 plot the logarithmic plot of mrs ms against hcr hc gives a straight line r 0 814 with slope and intercept close to the empirical mixing line of parry 1982 for single domain sd and multidomain md magnetite for one of the white pelagic limestone formations maiolica formation samples with hysteresis ratios closer to the md field display increased paramagnetic susceptibility and are from the upper part of the formation characterized by increased detrital clay we therefore associate the increased md magnetite with increased detrital influx for pinkish and reddish varieties of the italian pelagic limestones the presence of hematite is manifest by high saturation fields a wide range of hcr hc and wasp waisted hysteresis loops attributed to the mixing of magnetite and high coercivity authigenic hematite the hysteresis ratios for a collection of paleozoic and mesozoic remagnetized magnetite bearing limestones from britain nevada alaska and the appalachians lie mainly outside the psd field and appear to follow a power law trend following jackson et al 1993 the high values of hcr hc and the characteristically wasp waisted hysteresis loops can be interpreted in terms of a fine grained subspherical high coercivity sd magnetite mixed with a high proportion of superparamagnetic magnetite the slope and intercept of the power law relationship for mrs ms and hcr hc in the remagnetized limestones are distinct from those observed for the italian limestones and may provide a means of fingerprinting magnetite of primary as opposed to diagenetic origin

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

calcrete profile development in quaternary alluvial sequences southeast spain implications for using calcretes as a basis for landform chronologies a detailed study of the morphology and micro morphology of quaternary alluvial calcrete profiles from the sorbas basin shows that calcretes may be morphologically simple or complex the simple profiles reflect pedogenesis occurring after alluvial terrace formation and consist of a single pedogenic horizon near the land surface the complex profiles reflect the occurrence of multiple calcrete events during terrace sediment aggradation and further periods of pedogenesis after terrace formation these complex calcrete profiles are consequently described as composite profiles the exact morphology of the composite profiles depends upon 1 the number of calcrete forming events occurring during terrace sediment aggradation 2 the amount of sediment accretion that occurs between each period of calcrete formation and 3 the degree of pedogenesis after terrace formation simple calcrete profiles are most useful in establishing landform chronologies because they represent a single phase of pedogenesis after terrace formation composite profiles are more problematic pedogenic calcretes that form within them may inherit carbonate from calcrete horizons occurring lower down in the terrace sediments in addition erosion may lead to the exhumation of older calcretes within the terrace sediment calcrete inheritance may make pedogenic horizons appear more mature than they actually are and produce horizons containing carbonate embracing a range of ages calcrete exhumation exposes calcrete horizons whose morphology and radiometric ages are wholly unrelated to terrace surface age composite profiles are therefore only suitable for chronological studies if the pedogenic horizon capping the terrace sequence can be clearly distinguished from earlier calcrete forming events thus a detailed morphological micro morphological study is required before any chronological study is undertaken this is the only way to establish whether particular calcrete profiles are suitable for dating purposes copyright 2003 john wiley sons ltd

paleomagnetic evidence for the miocene counter clockwise rotation of northeast japan rifting process of the japan arc paleomagnetic results have been obtained from more than 700 oriented samples in igneous rocks of cretaceous to miocene age from northeast japan the remanent magnetizations of welded tuffs with age between 32 ma and 21 ma old from 17 widely distributed sampling sites in northeast japan are fairly well grouped with a mean ofd 41 2 i 56 5 95 7 2 the remanent magnetization of welded tuffs of 14 ma and 11 ma from 4 sites shows a northerly direction d 11 7 i 60 5 95 15 3 these data imply that northeast japan was apparently subjected to a counter clockwise rotation through 47 14 about a vertical axis on the representative point of northeast japan 141 e 39 n during the past 21 ma comparing with the period of the clockwise rotation of southwest japan the differential rotation between northeast japan and southwest japan is concluded to have occurred concurrently during the period between 21 ma and 12 ma a rifting model of the japan arc is proposed northeast japan rotated counter clockwise through 50 about a northern pivot at 146 e 44 n while southwest japan rotated clockwise through 54 about a southern pivot at 129 e 34 n the differential rotation about different rotation pivots gives rise to the opening of a diamond shaped back arc basin the japan sea

paleomagnetism of tertiary rocks from the oga peninsula and the rotation of northeast japan we have made a paleomagnetic study of tertiary rocks from the oga peninsula northern honshu island volcanic and sedimentary rocks were sampled from 26 sites in the peninsula the ages of the rocks range from 62 ma to the present the results indicate a counterclockwise rotation of northeast japan with respect to eastern asia around a pole at 58 n 149 e between about 22 ma and 15 ma the amount of the rotation is about 20 before the rotation northeast japan was situated along the east coast of the asian continent

new insight into pedogenic processes in extremely arid environments and their paleoclimatic implications the negev desert israel abstract stratigraphic studies conducted on the alluvial fill of several ephemeral stream channels in the southern arava valley dead sea rift indicate the existence of a calcic soil developed 50 100 cm beneath the channel surfaces this anomalous calcic soil does not fall within the categories of any standard soil or paleosol definition and thus has been termed fluvial pedogenic unit fpu the fpu occurs at the lower limit of the contemporary scour and fill processes in the aerated zone and it defines the maximum scour and fill during floods the fpu is also found in late pleistocene and holocene terraces termed paleo fpu indicating that the hydrological regime of past floods was similar to the present one the formation of a calcic fpu in this unique environmental setting is associated with the cumulative influence of persistent differences in water availability to various parts of the channel before and during flood events the carbonate accumulation results from low recurrence of flood events relatively limited moisture amounts and almost no involvement of vegetation in its formation the isotopic analyses of calcic crusts in the fpu and in the paleo fpu indicate that arid climatic conditions prevailed during their formation this indicates that the flood regime under arid climatic conditions characterized most of the negev desert during the late pleistocene and the holocene however a clear difference in the 18 o and the 13 c values was detected between the active channels and the terraces this difference suggests a change in the rainwater composition rather than changes of temperature or amounts of rainfall

long term stability of flow path structure in crystalline rocks distributed in an orogenic belt japan most evaluations of the contaminant retardation processes likely to be important in geological disposal e g for high level radioactive waste hlw consider only the present characteristics of fractures and associated mineral infills relatively little attention has been given to possible long term changes in these features and their influence on groundwater flow the work reported here seeks to provide analogous evidence that such changes are not likely to be important and hence to improve confidence in the presently adopted evaluation methodology and its long term applicability in the orogenic belt that is formed by the japanese islands there are wide areas of crystalline rock the rocks in each area have a distinctive age sequence which is partly reflected in the characteristics of the fracture systems and associated mineral fillings that occur these characteristics generally imply that groundwater and solutes can be conducted through fracture networks except in the cases of fault zones or crushed zones the structural and mineralogical features of these networks readily illustrate how certain contaminants might react and be retarded by the fracture fillings and open pore geometry due to chemical sorption and or physical retardation here we describe the fracture systems developed in crystalline rocks with different ages that are intruded into the japanese orogenic belt the aim is to build a model for the long term fracturing process and hence to evaluate fracture dstabilityt i n particular the comparisons are made between the fracture geometries and the frequencies observed in the 1 9 0 8 ma takidani granodiorite the youngest exposed pluton in the world the ca 67 ma toki granite and the ca 117 ma kurihashi granodiorite located in central to northwest japan the observations show that all these crystalline rocks have similar fracture frequencies with 1 to 2 fractures per meter in the massive part of rock bodies mineralogical studies and dating analyses of fracture fillings also suggest that fractures are relatively physically stable major new fractures tend not to be created in the massive part of rock bodies even when a pluton has been subjected to the regional stresses of plate movements with a duration of about 100 ma the results show the unique characteristics of the fracture forming process and the relatively stable geometries of fracture network systems in crystalline rocks distributed within the orogenic belt this analogue also enables us to provide a model to build confidence in a technical approach applicable for modeling of hydrogeology and geology over long time scales under the

rapid rotation of southwest japan palaeomagnetism and k ar ages of miocene volcanic rocks of southwest japan summary miocene volcanic rocks have been sampled from the san in district in the central part of southwest japan reliable palaeomagnetic direction and k ar dating data have been obtained from 28 localities a clockwise deflection in declination d 38 5 is observed in the kawai formation having an age of 16 1 1 4 ma whereas a northerly declination is observed in formations younger than 14 2 0 6 ma these data indicate that southwest japan had ceased rotational motion by about 14 ma when compared with the amount of rotation estimated from cretaceous palaeomagnetic data it is apparent that more than 80 per cent of the overall clockwise rotation occurred between about 16 and 14 ma we conclude that the angular velocity of southwest japan about a rotation pole at 129 e 34 n reached 20 myr 1 at about 15 ma the corresponding rate of linear motion of the eastern part of southwest japan was 21 cm yr 1

sequence stratigraphy in lacustrine basins a model for part of the green river formation eocene southwest uinta basin utah u s a abstract in the middle green river formation of central nine mile canyon uinta basin utah several lacustrine dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences these lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences two types of sequence boundary are identified type a sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or rarely parallel unconformity and they typically juxtapose amalgamated braided fluvial channel sandstone late lowstand systems tract onto the profundal oil shale they also bound depositional sequences that show a distinct asymmetry being dominated by transgressive systems tracts 5 80 m thick highstand systems tracts are less than 4 m thick and may be removed completely by erosion on overlying sequence boundaries other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type b sequence boundaries type a sequence boundaries mark pronounced base level falls following times when the uinta lake had merged with a lake in an adjacent basin to form a much deeper lake such merging permitted the establishment of a new threshold at higher elevation following lake level balancing type b sequence boundaries are interpreted as marking base level falls from a barely merged lake or a lake that had an outflow over a 200 m stratigraphic thickness type a sequence boundaries are more common upsection indicating that with time a pluvial climate became more pronounced or that the adjacent lake was more easily filled type a sequence boundaries also become angular rather than parallel unconformities upsection suggesting increased tilting of the basin margin over time

large scale architecture in non marine basins the response to the interplay between accommodation space and sediment supply sedimentary successions of non marine basins can be considered in terms of accommodation space and sedimentary supply changes changes in accommodation space controlling the large scale architecture of non marine basins are different in areas with high and low sedimentary supplies uplift of intrabasinal monoclines and anticlines reduced the available accommodation space resulting in changes in both the geometry of the depositional sequences and the large scale architecture of fluvial mudflat and shallow carbonate lacustrine deposits main drainage fluvial systems record areas with a high sedimentary supply while mudflats and shallow fluctuating lakes represent areas that received less sediment two end members in the large scale architecture of main drainage fluvial system in the almazan basin spain are i ribbon shaped channel fills with low interconnectivity which pass laterally into mudflats dominated by mudstones and evaporites and into palustrine and shallow carbonate lacustrine deposits mainly in the a2 depositional sequence and ii sheet like channel fills with high interconnectivity laterally correlated with stacked calcretes in the marginal mudflats in the upper part of a3 ribbon shaped channel fills formed in areas of high accommodation space and sheet like channel fills formed in areas of reduced accommodation space

magnetism in rocks rock magnetism is the study of induced and remanent magnetization of ferrimagnetic mineral grains in rocks sediments soils and organisms its applications include environmental magnetism magnetic anisotropy sources of continental and oceanic magnetic anomalies records of geomagnetic field variations and polarity reversals and the paleomagnetic record of plate motions and the wilson cycle this paper reviews the beginnings of rock magnetism and then traces the development of six particularly interesting areas pseudo single domain behavior magnetic domains and micromagnetic structures diagnostic tests of the type and stability of remanent magnetization magnetic microanalysis thermoviscous remagnetization and chemical remanent magnetization other areas including sediment and soil magnetism are covered in a companion paper by verosub and roberts on environmental magnetism

belowground rhizomes in paleosols the hidden half of an early devonian vascular plant abstract the colonization of terrestrial environments by rooted vascular plants had far reaching impacts on the earth system however the belowground structures of early vascular plants are rarely documented and thus the plant soil interactions in early terrestrial ecosystems are poorly understood here we report the earliest rooted paleosols fossil soils in asia from early devonian deposits of yunnan china plant traces are extensive within the soil and occur as complex network like structures which are interpreted as representing long lived belowground rhizomes of the basal lycopsid drepanophycus the rhizomes produced large clones and helped the plant survive frequent sediment burial in well drained soils within a seasonal wet dry climate zone rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants predating the appearance of trees with deep roots in the middle devonian plant rhizomes have long functioned in the belowground soil ecosystem this study presents strong direct evidence for plant soil interactions at an early stage of vascular plant radiation soil stabilization by complex rhizome systems was apparently widespread and contributed to landscape modification at an earlier time than had been appreciated

an ocean bottom gravity study of the southern juan de fuca ridge we use seafloor and sea surface gravity data to model density structure along the southern juan de fuca ridge we determine the average density of the shallow oceanic crust at the ridge using seafloor gravity measurements and then use these data in conjunction with sea surface gravity observations to construct density structure models of 63 seafloor gravity measurements obtained 42 observations were distributed over the 3 km left lateral overlapping rift zone orz located at latitude 45 03 n and separating the juan de fuca ridge into the cleft and vance segments a 21 measurement seafloor gravity transect was made perpendicular to the ridge strike at latitude 44 52 n a region of linear ridge geometry on the cleft segment these seafloor gravity measurements which are sensitive to shallow crustal density variations were augmented by roughly 800 km of sea surface gravity measurements using a bathymetry bouguer anomaly analysis of the seafloor gravity data we determined the average density of the shallow roughly upper 2 km oceanic crust at these two locations to be 2630 kg m 3 50 kg m 3 within the uncertainties of the density determinations there is no difference between the average shallow oceanic crustal density at the linear cleft segment and at the cleft vance orz using the seafloor measurements we modeled the study area s underlying density to provide constraints on its fine scale structure localized porosity of up to 17 within the upper 500 m of oceanic crust layer 2a provide a possible explanation for the observed gravity anomalies at the cleft segment two dimensional density models of the crust underlying the linear cleft segment 44 52 n show that no deep source is required to explain the topographical asymmetry observed between the east and west sides of the ridge axis for the cleft vance orz three dimensional modeling suggests low density material between the rifts in agreement with thickened layer 2a from seismic observations in contrast layer 2a variations do not explain the low density inferred at the northern end of the cleft segment since seismic observations suggest a thin layer 2a the magmatic activity recently observed in this region may have a distinct deeper source

taphonomic and paleoecologic investigations of the late cretaceous santonian iharkut vertebrate assemblage bakony mts northwestern hungary abstract the iharkut vertebrate locality an open pit mine in the bakony mountains western hungary has provided a rich and diverse assemblage of late cretaceous santonian continental vertebrates the isolated and associated remains represent 31 different taxa including fish amphibians turtles lizards pterosaurs crocodilians non avian dinosaurs and birds sedimentologic investigations suggest that the iharkut depositional environment was represented by the floodplain of a very low gradient river the 10 50 cm thick bonebed of site sz 6 is the most important fossiliferous layer in the open pit mine and analysis of this site indicates alternating energy conditions during the bone accumulation which resulted in fossils of different states of preservation being deposited together the vertebrate assemblage of site sz 6 includes three main different subsets with widely different taphonomic history the characteristics and the preservation mode high rate of abrasion and the spherical shape of the bone pebbles suggest that this type of the isolated bones was more exposed to abrasion and probably the remains were transported from farther away than the other isolated bones the second group includes 88 of the iharkut collection containing most of the identified isolated bones and teeth and represents polytypic attritional remains transported and deposited by high density flow during ephemeral flood events meanwhile the monospecific ankylosaur skeletal material from iharkut site sz 6 may represent a mass death assemblage because seven skeletons of hungarosaurus were discovered from an area of approximately 400 m 2 and in many cases close to each other in the same layer the iharkut vertebrate assemblage is dominated by bones of aquatic semi aquatic animals while the number of terrestrial animal remains is subordinate the taphonomic analysis of the ankylosaur material from iharkut locality further strengthens the previously suggested hypothesis that some of the ankylosaurs preferred wetland habitats e g areas along fluvial systems while the other two herbivorous dinosaur groups from iharkut ornithopods and ceratopsians were probably living in distal habitats

forced regression across the marine to continental transition in jammu sub basin implication to the oligo miocene unconformity in the himalayan foreland abstract similar to the other sub basins marine to continental transition in jammu foreland also shows the presence of a characteristic greenish gray quartz arenite unit locally termed as white sandstone unit process based sedimentological and sequence stratigraphic work carried out across this white sandstone unit suggest that this unit was deposited in a shoreface settings during a forced regression the sharp base of the white sandstone unit represents a surf diastem a kind of regressive surface of marine erosion and does not signify a 10 myr unconformity the gradational top of the unit showing various degree of exposure and soil development has been interpreted as type 1 sequence boundary the white sandstone unit present along the entire stretch of the western sub himalaya also shows forced regressive nature in the subathu sub basin situated 350 km se of jammu so the forced regression across the marine to continental transition in the entire western himalayan foreland is a regional phenomena and not a local one contrary to the earlier works which proposed the presence of an unconformity spanning 10 myr encompassing the oligo miocene period the present study showed that the unconformity if present is of small duration possibly spanning

carbon isotopic evidence for organic matter oxidation in soils of the old red sandstone silurian to devonian south wales uk petrographic and calcrete carbon isotope data from seasonally waterlogged upper silurian p idoli to lower devonian pragian palaeo vertisols of the old red sandstone south wales uk are presented the 13 c values mostly range from 9 to 12 vpdb suggesting that the soils were inhabited by abundant vegetation that when oxidized perhaps with microbial assistance resulted in co 2 rich soils such soils would favour calcrete precipitation through equilibration of soil zone co 2 with the relatively lower atmospheric p co 2 however reliably estimating palaeoatmospheric p co 2 using these carbon isotope data is a challenge supplementary material detailed information on stable isotope measurement methods descriptions of the samples and carbon and oxygen isotope data are available at www geolsoc org uk sup18754

counterclockwise rotation of northeast japan paleomagnetic evidence for regional extent and timing of rotation early to late miocene welded tuffs have been sampled from northeast honshu island and the oshima peninsula of hokkaido island japan for paleomagnetic study characteristic directions with a high unblocking temperature component above 560 c are isolated from 24 sites westerly declinations d 1 91 are identified in welded tuffs older than 17 ma from these areas when combined with previous paleomagnetic data from welded tuffs the early miocene paleomagnetic poles derived from northeast honshu island and the oshima peninsula are statistically identical and indicate that northeast honshu island and the oshima peninsula were subjected to counterclockwise rotation as a single tectonic block these results establish that the rotating block of northeast japan extends north to the oshima peninsula to the latitude 43 n the dimension of this rotating block is of the order of 500 km the paleomagnetic data provide a best curve for the rotation process with the counterclockwise rotation reaching a climax at 15 0 ma and a net amount of rotation of 46 4 the 500 km long northeast japan block was rotated counterclockwise through more than 45 and accompanied a clockwise rotation of the 600 km long southwest japan block at about 15 ma

hydroacoustic detection of volcanic activity on the gorda ridge february march 1996 abstract beginning at 0700 gmt on 28 february 1996 intense seismicity was detected in the northeast pacific ocean using the t phase monitoring system developed by noaa pmel to access the u s navy s sound surveillance system sosus in the north pacific the event was preliminarily located on the northernmost segment of the gorda ridge near 42 67 n and 126 8 w in the vicinity of the ridge segment high narrowgate the nature of the seismicity was similar to that observed in june 1993 at the coaxial segment of the juan de fuca ridge which was later documented to be a lateral magma injection with subsequent eruption due to several gaps in the data the detection information was not as comprehensive as during the coaxial event but an initial migration of epicenters from the narrowgate area down rift is inferred based on arrival bearings from a single array there is evidence for an additional diking event on the second and third day of activity there is also indication of a concentration of epicenters located near 42 6 n as occurred during the coaxial episode at what was later determined to be an eruption site examination of t wave rise times generally supports this interpretation based on the nature and duration of the activity a response effort was initiated which later confirmed hot water plumes and fresh lava flows at the site based on both hydroacoustic information and field observations it is proposed that the episode began with a lateral dike injection possibly with eruptive activity in the summit region followed by multiple magma pulses and eventual focusing of the seismic activity and extrusion near 42 6 n

large scale facies sequences in alluvial overbank environments abstract gradational coarsening upwards or fining upwards sequences order of meters thick in overbank environments can be produced by progressive crevasse splay levee progradation or abandonment while the channel belt remains unchanged in position in contrast meter scale facies sequences related to periodic channel bell avulsion may show relatively abrupt changes in facies and paleocurrent direction simulation models suggest that the number of such avulsion related facies changes in any overbank sequence bounded above and below by channel belt deposits is on the order of 1 to 10 this is confirmed using an ancient example in this example the average thickness of each avulsion bounded overbank facies sequence was 3 m assuming an average recurrence interval for avulsions of about 1 000 ye rs the mean overbank deposition rate was about 3 mm per year

diagenetic sources of stable remanence in remagnetized paleozoic cratonic carbonates a rock magnetic study hysteresis measurements lowrie fuller tests cisowski tests and low temperature demagnetization experiments on samples of the knox dolomite trenton limestone and onondaga limestone indicate that the remanence in these remagnetized carbonate units resides principally in single domain magnetite in contrast to previous interpretations volumetrically however a significant fraction of the magnetite is coarser grained as previous scanning electron microscopic work on magnetic extracts has shown these conclusions are based mainly on the characteristic wasp waisted shape of the hysteresis loops and on the anomalously high ratios of remanent coercivity to bulk coercivity both of which clearly indicate a bimodal distribution of coercivities grain sizes the magnetization is controlled mainly by cubic magnetocrystalline anisotropy consistent with the spheroidal particles commonly observed in extracts hysteresis trends show that especially the finest particles lack shape anisotropy in view of these conclusions the two components of natural remanence in these rocks are interpreted as 1 a late paleozoic kiaman chemical remanence carried by single domain diagenetic magnetite and 2 a cenozoic thermoviscous overprint residing principally in coarser pseudosingle domain and multidomain magnetite also of late paleozoic diagenetic origin

a quantitative approach to soil occurrence in alluvial deposits and its application to the old red sandstone of britain palaeosols fossil soils are a major component of alluvial deposits in the geological record not only do these typically show considerable variations in their degrees of development within single formations but they also exhibit highly complex stratigraphic relationships with one another a simple quantitative approach to these variations is presented which provides a graphical means of assessing differences in soil palaeosol development within a sequence with calcic or petrocalcic horizons to illustrate the approach a range of palaeosols from the siluro devonian old red sandstone of britain are characterized in terms of the likely frequency and magnitude of depositional events which occurred during their formation in particular two alluvial suites from the manorbier area of south wales are analysed using this approach the technique should be widely applicable to other alluvial successions and provides a means of graphicallv presenting relationships between multiple palaeosols although the wide range of rates of formation of calcic and petrocalcic horizons precludes their use to provide narrow estimates of deposition rates

morphology and distribution of fossil soils in the permo pennsylvanian wichita and bowie groups north central texas usa implications for western equatorial pangean palaeoclimate during icehouse greenhouse transition analysis of stacked permo pennsylvanian palaeosols from north central texas documents the influence of palaeolandscape position on pedogenesis in aggradational depositional settings palaeosols of the eastern shelf of the midland basin exhibit stratigraphic trends in the distribution of soil horizons structure rooting density clay mineralogy and colour that record long term changes in soil forming conditions driven by both local processes and regional climate palaeosols similar to modern histosols ultisols vertisols inceptisols and entisols all bearing morphological mineralogical and chemical characteristics consistent with a tropical humid climate represent the late pennsylvanian suite of palaeosol orders palaeosols similar to modern alfisols vertisols inceptisols aridisols and entisols preserve characteristics indicative of a drier and seasonal tropical climate throughout the lower permian strata the changes in palaeosol morphology are interpreted as being a result of an overall climatic trend from relatively humid and tropical moist conditions characterized by high rainfall in the late pennsylvanian to progressively drier semi arid to arid tropical climate characterized by seasonal rainfall in early permian time based on known late palaeozoic palaeogeography and current hypotheses for atmospheric circulation over western equatorial pangea the pennsylvanian palaeosols in this study may be recording a climate that is the result of an orographic control over regionalscale atmospheric circulation the trend towards a drier climate interpreted from the permian palaeosols may be recording the breakdown of this preexisting orographic effect and the onset of a monsoonal atmospheric circulation system over this region

occurrences and genesis of calcrete and dolocrete in the mio pleistocene fluviatile sequence in kuwait northeast arabian peninsula abstract sedimentologic and petrographic investigation of the subsurface mio pleistocene clastic sequence of the kuwait group in umm ghudair water field southwest of kuwait revealed the occurrence of successive cycles of calcrete profiles the calcrete host sediment kuwait group is mainly represented by a sequence of muddy sands interbedded with mud and sand layers with occasional lenses of gravels individual calcrete profile has vertical gradational maturity pattern which is manifested by the occurrence of well differentiated horizons arranged from bottom to top as follows non calcretized host sediment incipient calcrete nodular calcrete concretionary calcrete massive laminar calcrete abundance of organosedimentary structure mainly plant roots and diversity of calcite crystal fabrics suggest that the studied calcrete profiles were developed within two stages of calcretization a pedogenic stage followed by a phreatic stage the variation in the mineralogical composition between umm ghudair calcrete profiles and the dolocrete profiles that occur within the same clastic host sediment but at distal location within the kuwait group flood plain about 80 km to the northeast is mainly attributed to differences in the chemical composition of the groundwater and its flow pattern it is suggested that the hydrogeological and hydrogeochemical settings may play a significant role in the development of cyclic pedogenic phreatic and polygenetic calcretes and dolocretes within the same sedimentary basin alternation of tectonically stable and unstable periods may be responsible for the cyclicity of calcretization dolocretization

sediment recycling on siluro devonian floodplains some of the red mudstones in the red mark old red sandstone of llansteffan dyfed are interpreted as originating as sand sized mud aggregates pellets produced in soils and deposited from bed load in small sinuous channels by analogy with the channel country of australia such channels may represent periods of low discharge and reduced hydraulic efficiency when the floodplains were locally reworked in contrast larger channel fills with extraneous sediments may represent pluvial periods with increased discharge

lithofacies associations and stable isotopes of palustrine and calcrete carbonates examples from an indian maastrichtian regolith detailed information on semi arid palustrine carbonate calcrete lithofacies associations in a sheetwash dominated regolith setting is sparse this is addressed by studying the lower limestone of the lameta beds a well exposed maastrichtian regolith in central india the general vertical lithofacies assemblage for this unit comprises a basal calcareous siltstones and marls with charophytes ostracods and gastropods b buff micritic limestones associated in their upper parts with calcretized fissure fill sandstones c sheetwash as fissure fill diamictites and thin pebbly sheets locally developed over a few metres and d sandy nodular brecciated and pisolitic calcretes at the top the sequence is regressive with upsection filling of topographic lows by increased sheetwash lateral lithofacies change is marked but there are no permanent open water lake deposits in topographic lows close to the water table marshy palustrine or groundwater calcretes formed whereas on better drained highs brecciation and calcretization occurred prolonged exposure is implied suggesting that shrinkage was the main cause of brecciation evidence for rhizobrecciation and other biological calcrete fabrics is sparse contrasting with the emphasis on root related brecciation in many studies of palustrine lithofacies stable isotope d18o and d13c values are consistent with the palustrine limestones being fed from meteoric derived groundwater with a strong input of soil zone carbon there is overlap of both d18o and d13c values from the various palustrine and calcrete fabrics co occurring at outcrop this suggests that in groundwater supported wetlands conversion from palustrine carbonate to calcrete need not show isotopic expression as the groundwater source and input of soil zone carbon are essentially unchanged cretaceous tertiary d18o and d13c values from palustrine lithofacies and associated calcretes appear to be strongly influenced by the inherited values from lakes and wetlands hydrologically closed lakes and marine influenced water bodies tend to result in low negative palustrine d18o and d13c values during brecciation and calcretization the degree of isotopic inheritance depends on whether or not alteration occurs in waters that are different from those of the original water body or wetland marked biological activity e g rhizobrecciation or root mat development during calcretization may lower d13c values where c3 plants are abundant but in shrinkage dominated systems d13c values will be largely inherited from the palustrine limestones

morphology and stable and radiogenic isotope composition of pedogenic carbonates in late quaternary relict soils new mexico u s a an integrated record of pedogenic overprinting abstract this petrographic and stable 13c and 18o and radiogenic 14c isotope study of pedogenic carbonates from late quaternary soils in the rio grande rift region of new mexico documents that carbonate formation in semiarid to arid soils aridisols occurs principally by overprinting and can result in a complex petrographic and isotopic record with increasing duration of exposure 7 to 900 ky of the four studied profiles pedogenic carbonates exhibit 1 an increase in the degree of intraprofile 13c and 18o heterogeneity 2 increased development of down profile 13c and 18o trends 3 an increase in the degree of intermorphologic and intramorphologic stable isotope variation commonly in samples distributed laterally within narrow depth intervals and 4 development of covariation between 13c and 18o values radiocarbon ages of the carbonates permit assessment of the degree of isotope heterogeneity in contemporaneous carbonates and recognition of temporal isotopic trends the range of exposure times recorded by the studied soils are analogous to those associated with the formation of fossil soils this makes the studied soils ideal for evaluating the origin of stable isotope heterogeneity in paleosol carbonates and the implications of those heterogeneities for the use of stable isotopes as paleoenvironmental proxies specific implications of this study include the following 1 pedogenic carbonates that form by overprinting are a cumulative record of the soil conditions present during their accumulation thus isotope analysis of overprinted carbonates can result in time averaging of changing climatic paleoenvironmental and paleoecologic conditions 2 carbonates may record only a fraction of the duration of development of their host profile 3 there is a high level of uncertainty associated with using the sequence of morphologic development of carbonate as a function of time or maturity in paleosols 4 an exponential decrease in carbonate 13c values with depth in a paleosol does not imply that the carbonates are contemporaneous or accumulated under invariant soil conditions 5 shifts in soil and paleoclimatic conditions may be recorded by the 13c and 18o values of carbonates distributed within narrow depth intervals of a given soil in addition to those distributed down profile or even from within individual carbonate samples

quantifying time scales of pedogenic calcrete formation using u series disequilibria abstract time scales of pedogenic calcrete development are quantified by subsampling carbonate from within a mature stage v pedogenic calcrete profile from southeast spain and dating the material by u series disequilibria the location of the earliest and latest cements can be estimated by comparing previous studies of calcrete morphological development with micromorphological analysis of the study profile carbonate was sampled and dated from three locations within the profile 1 below the lower surface of clasts within the hardpan representing the earliest cement present 207 11 ka 2 from the centre of cement filled pores within the hardpan reflecting the final plugging of the calcrete hardpan 155 9 ka and 3 from the laminar calcrete overlying the hardpan representing the latest cement 112 15 ka these results show that the hardpan took between 73 and 31 ka to form whilst the mature stage v profile took between 121 and 69 ka to form this is the first time that rates of mature calcrete development have been established by direct radiometric dating of the authigenic carbonate the technique is appropriate for dating mature calcretes in dryland regions worldwide and offers the opportunity of increasing our understanding of the spatial and temporal variability in rates of pedogenic calcrete development

sea level changes across the paleocene eocene interval in the spanish pyrenees and their possible relationship with north atlantic magmatism the issue of whether major and rapid global sea level changes existed on a preglacial earth can be resolved by the detailed study of the paleocene eocene p e interval where a large and rapid carbon isotope excursion linked to an important global warming event the paleocene eocene thermal maximum allows for high resolution correlation between terrestrial coastal and marine settings based primarily on outcrop and borehole information from the tremp graus basin in the southern spanish pyrenees it is shown that a sea level fall of at least 20 m occurred less than 75 kyr prior to the petm this forced a seaward displacement of the shoreline of ca 20 km a widespread incision of valleys in the alluvial plains and the subaerial exposure and excavation of the adjacent marine carbonate platform the subsequent sea level rise caused the infilling of the incised valleys a process completed before the onset of the petm and continued rising during and after the event leading to the aggradation of the alluvial plain and eventually to the transgression of the whole tremp graus basin however the sea level did not regain its pre fall position until near the end of the petm therefore although rising the sea level was comparatively low in the southern pyrenean area during most of the petm the pre petm sea level fall has been reported in other basins of the southern pyrenees in the north sea area the austrian alps and in egypt and the subsequent sea level rise has been documented in widely separated sites around the earth an evidence of their global eustatic scope the causal mechanism s of the pre petm sea level fall is are unresolved although glacioeustasy may have played a role the subsequent sea level rise was most likely caused by tectonomagmatic activity in the north atlantic c 2013 elsevier b v all rights reserved less

double saloon door tectonics in the japan sea fossa magna and the japanese island arc abstract a number of criteria considered diagnostic of double saloon door rifting and seafloor spreading are matched by data from the japanese arc these include i a pair of terranes sw and ne honshu which rotated in opposite directions from 22 21 ma to 14 11 ma ii rotated terranes which comprise a retro arc fold thrust belt attached to an accretionary wedge intruded by a magmatic arc iii contemporaneous backarc extension from 24 to 21 ma which is brought to a halt by progressive collision of the izu bonin and japan arcs from 15 to 5 ma iv isolation of blocks of thicker continental crust by areas of thin continental or oceanic crust during backarc rifting v such isolation may be due to simultaneous rifting or to progressively seaward rifts associated with ridge jumps towards the subduction zone vi opposite rotations are accommodated by subduction rollback demonstrated by seaward migration of the volcanic front from 30 26 ma to 16 15 ma vii concurrent development of a major arc orthogonal rift the fossa magna from 23 18 ma to 14 ma which was thereafter inverted from 15 ma to the recent viii a northeast propagating rift in the northern japan basin demonstrated by the relationship of linear magnetic anomalies to the mapped continent ocean boundary driving mechanisms for double saloon door tectonics are discussed in relation to various reconstructions of the northwest pacific opposite rotational torques leading to opposite terrane rotations may be caused by rollback of a curved trench hingeline or by the divergent slab sinking forces of the pacific and philippine sea plates

magnetic susceptibility of loess in china abstract the low field susceptibility of the loess deposits in the chinese loess plateau is due to both paramagnetic and ferromagnetic minerals paramagnetism can be seen in the less to unweathered loess horizons where superparamagnetic contributions which arise from ultrafine magnetite particles are not as strongly developed as in the heavily weathered palaeosols frequency dependent susceptibility and minimum unblocking temperatures of low temperature thermoremanent magnetization generally indicate finer grain sizes in the palaeosols as compared to the loess beds this grain size difference and the fact that susceptibilities of the same stratigraphic palaeosol layer vary by an order of magnitude between the western and central regions of the plateau are considered as strong evidence that the ultrafine magnetite is not of detrital aeolian origin but was formedin situ the pedogenetic processes are clearly related to palaeoclimatic changes therefore the various susceptibility properties may serve for a detailed reconstruction of the continental palaeoclimatic conditions for the last 2 5 ma since the palaeomagnetically dated beginning of loess sedimentation in china

cenozoic calcretes from the teruel graben spain microstructure stable isotope geochemistry and environmental significance in the teruel graben northeast spain laminar and nodular calcretes formed in a variety of cenozoic deposits ranging in age from palaeogene to pleistocene these calcretes developed in a relatively small area under the influence of the same highlands consequently differences in their microstructure and isotopic composition c and o must be related to differences in host rock climate vegetation and duration of development nine profiles developed in different sedimentary settings from proximal areas to lacustrine environments were studied to determine whether the microstructure and stable isotope composition changed during the cenozoic these characteristics might be used as indicators of the prevailing climate and vegetation and reveal any changes that occurred during this time most of the laminar calcretes studied are compound profiles that formed on hard substrates e g jurassic limestones or coarse detrital deposits e g palaeogene pliocene and plio pleistocene sandstones and conglomerates these profiles formed in proximal areas of the basin and also in fluvial terraces microstructures include biogenic features such as alveolar septal structures root tubes calcified root cells and calcified organic filaments underside coatings of micrite and fibrous vadose cements are common around gravel clasts on the other side spherulites are only preserved at the very top of the youngest calcretes nodular calcretes developed on fine detrital substrates e g on palaeogene miocene and pliocene red mudstones and sandy mudstones of distal alluvial and floodplain environments and in some places grade vertically into palustrine limestones the nodules consist of micrite and were elongated vertically show desiccation cracks and mottling micritic coatings some alveolar septal structures and root traces microcodium of type 1 occurs in both laminar and nodular calcretes but only in those of palaeogene age while calcified root cells microcodium of type 3 are seen in the pliocene calcretes the stable isotope composition covers a wide range 8 23 18o 4 29 pdb and 7 29 13c 3 42 pdb nodular laminar and palustrine facies occupy overlapped isotopic fields displaying an overall negative covariant trend location within the basin prevailing climate and density of vegetation are responsible for differences in isotope values the palaeogene samples show a wide range of values and are difficult to separate from the others however there is as significant change to lighter carbon values from the miocene to the pliocene profiles this change may be related to the cooler climatic conditions that prevailed during the pliocene and is reverse to the expected shift to heavier 13c values which is related to the increase of c4 vegetation that occurred in many areas of the world during the miocene or to the transit to the pliocene the formation of these calcretes seems to have occurred in semi arid conditions with prevailing c3 vegetation

late silurian and early devonian terrestrialisation ichnological insights from the lower old red sandstone of the anglo welsh basin u k abstract late silurian to early devonian deposits from the lower old red sandstone anglo welsh basin preserve a diverse assemblage of trace fossils that collectively comprise an important record of early terrestrialisation five main palaeoenvironmental categories are represented 1 perennial rivers 2 ephemeral rivers 3 floodplain lakes 4 alluvial fan and 5 marginal marine ichnocoenoses mainly reflect the activity of aquatic and or semi aquatic animals fluvial deposits preserve evidence for colonisation by eurypterids fish and myriapods ephemeral river channel margins splays preserve the most diverse ichnofauna composed of deposit feeders burrows and trackways produced by arthropods feeding and foraging in channel margin soft grounds that were colonised after fluvial flood events high densities of deposit feeding structures may indicate of explosive population growth in response to periodic acyclical replenishment of nutrients in these aquatic settings ichnotaxa common to both perennial and ephemeral fluvial environments suggest that there might have been only one aquatic ecosystem the degree to which the channel margin ichnofaunas record a truly subaerial terrestrial arthropod signature is difficult to ascertain and most trace makers were probably semi aquatic some terrestrial animals invaded channel margin areas to feed and were also capable of inhabiting high energy alluvial fan environments however the fans contain low diversity ichnological assemblages and were likely to have been inhabited by an opportunistic fauna possibly the only truly subaerial terrestrial ichnocoenosis is that of pedogenically modified mudrock with scoyenia which represents an early soil ichnofauna the majority of ichnocoenoses described from continental palaeoenvironments could be classified under the scoyenia ichnofacies marginal marine deposits contain an impoverished skolithos cruziana ichnofacies typical of silurian devonian brackish water assemblages

overview of the stability and barrier functions of the granitic geosphere at the kamaishi mine relevance to radioactive waste disposal in japan abstract the kamaishi in situ studies were carried out in order to provide a technical basis for the studies of the geological disposal of high level radioactive waste hlw in japan the studies were conducted in drifts located at ca 300 m and ca 700 m below the surface in the former kamaishi iron ore mine situated in the kurihashi granodiorite an early cretaceous granitic rock 110 120 ma in the kitakami area iwate prefecture northeastern japan the fractures identified in the kurihashi granodiorite were mainly formed during the early stages of the cooling process the mineralogical and dating data suggest that almost no new fractures have been generated since 70 60 ma ago the fractures have high porosity fracture fillings with relatively high sorption values that imply the fractured granitic rock could have a significant retardation capability for contaminant transport through the granite monitoring of hydrological and geochemical conditions of groundwater for 10 years showed that even fractured granitic rock close to the drift is not thoroughly oxidized and there are only negligible changes of hydrological conditions and groundwater geochemistry due to earthquakes this information is of considerable importance for the practical design of a hlw repository and to assess any impact of the pre closure conditions on the post closure performance of the geological repository finally the results of the study methodology and tools developed help increase confidence in the technical feasibility of geological disposal of hlw in japan

buried vertisols in lacustrine facies of the pliocene fort hancock formation hueco bolson west texas and chihuahua mexico buried vertisols which are commonly preserved in smectite rich clay and sandy clay facies of the upper tertiary fort hancock formation are products of the late tertiary depositional and paleoclimatic environment in the hueco bolson west texas united states and chihuahua mexico fort hancock clayey facies are in part laminated and contain abundant desiccation cracks and locally gypsum beds suggesting deposition in an ephemeral or playa lake buried vertisols apparently resulted from repeated shrink swell cycles due to drying and wetting of expansive clays in the ephemeral lake basin lacustrine facies are interbedded with gravel sand and sandy mud facies that were likely deposited as alluvial fans and fan deltas at the lake margin calcic soil horizons which form mostly in arid to subhumid modern climates and consist of caco 3 nodules and filaments are present in most buried vertisols of the fort hancock formation collectively buried vertisols with calcic soil horizons and ephemeral lake and alluvial fan deposits suggest that the fort hancock formation accumulated in an arid to semiarid climate

braided river deposits in a muddy depositional setting the molina member of the wasatch formation paleogene west central colorado u s a the molina member is a paleogene sand rich interval up to 125 meters thick found within the otherwise mud dominated nonmarine wasatch formation of west central colorado sandstone beds of the molina member form sheet like units interbedded with subordinate volumes of mudstone the sandstones contain a low diversity assemblage of sedimentary structures that is commonly dominated by horizontal planar laminae and bedding is locally contorted by large scale soft sediment deformation a braided fluvial model best explains the characteristics of these strata yet the existing braided river models do not fully account for the assemblage of sedimentary structures or the relatively high volumes up to half of the section of interbedded mudstones two modern braided rivers medano creek colorado and the prairie dog town fork of the red river texas have rapid shallow flows that form horizontal planar bedding in both systems the presence of large volumes of easily mobilized sandy sediment a flashy discharge regime and a lack of reworking between flood stages lead to the development of high energy shallow water bedforms and the preservation of the resulting high energy sedimentary structures similar conditions and processes are suggested to have controlled deposition of the sand dominated molina member which is a depositional anomaly within the otherwise muddy wasatch formation short term availability of readily eroded second cycle sandstones from a newly elevated source area to the southeast is the most likely reason for the abrupt change from a mud dominated fluvial system to the sandy molina system

development of microcracks in granites during cooling and uplift examples from the variscan basement in ne bavaria germany abstract microcracks in two late variscan granites in ne bavaria provide information about regional paleostress directions and p t conditions during cooling and uplift in both granites three prominent generations of healed microcracks called ci cii ciii constitute an orthorhombic fabric the orientation of which is closely related to the mesoscopic joint pattern we present a model relating this orthorhombic crack fabric not only to external deviatoric stresses but also to internal stresses on the grain scale resulting from the strong thermal contraction of quartz relative to the feldspar framework at the deepest level 1 subvertical steep ci cracks developed normal to 3 and selectively in the quartz their formation caused a stress uncoupling of quartz aggregates from the external 3 direction so that further contraction of quartz produced steep cii cracks normal to 2 forming bridges between ci cracks at higher levels 2 subvertical the same process reactivated the ci cracks and now formed horizontal crack bridges ciii p t estimates based on fluid inclusion data and inferred geothermal gradients are 250 400 c at 1 5 3 kbar for ci cii cracks and 150 200 c at 1 2 kbar for ciii cracks the orientation of the younger open cracks which formed at higher crustal levels partly corresponds to the present regional stress field

preservation of titanosaur egg clutches in upper cretaceous cumulative palaeosols los llanos formation la rioja argentina abstract studies of the palaeobiology of titanosaur eggs are significantly more common than studies of titanosaur egg bearing strata nevertheless the latter provide significant insight into palaeoenvironmental conditions associated with the egg laying behaviour this study examines titanosaur egg bearing strata of the upper cretaceous los llanos formation la rioja argentina and relates them to the laying and preservation of titanosaur egg clutches los llanos formation is a predominantly sandstone succession throughout represented by palaeosol profiles five titanosaur egg clutches were recovered from the bw horizon of an inceptisol profile this palaeosol type named tama pedotype constitutes 69 of the entire succession by thickness rare planar and undulating lamination and cross stratification quartz grain surface microtextures and ventifacts are indicative of the interaction of fluvial aeolian processes of sedimentation during accumulation of the parent material on the distal part of a coalescent alluvial fan system bajada highly abundant root traces reddish colour clay coatings and calcium carbonate nodules testify that the tama pedotype had abundant vegetation cover and was developed in well drained conditions under the influence of a semiarid climate regime palaeosol horizons with exaggerated thickness and diffuse boundaries indicate a cumulative pedotype whereby the soil developed in response to continuous accretion via on going sedimentary processes morphological features of eggshells suggest that titanosaurs dug holes in the topographic surface to lay eggs thus palaeosols seem to have been putative areas for the laying of titanosaur eggs actually it is uncommon for palaeosols to constitute sites for the preservation of eggs since soils typically develop in response to long episodes of weathering however cumulative palaeosols can provide ideal conditions for egg burial and preservation in cumulative soils the residence time of an object within the weatherable thickness of a soil is reduced to 3 years thereby significantly increasing the long term preservation potential of eggs

towards zircon fission track thermochronology reference framework for confined track length measurements abstract horizontal confined track hct lengths and angles to the crystallographic c axis were measured for both unannealed spontaneous and induced fission tracks ft in zircons to establish a reference framework of hct length measurement induced track lengths were analysed on eleven zircon separates from various rock types including four age standards and spontaneous lengths on three zircon standards were analysed in general the observed hct lengths in each sample are slightly anisotropic with shorter tracks having greater angles to the c axis in addition all samples show large anisotropy in the number of observed hct s particularly for induced tracks as an observed mean hct length is controlled by the combined influence of these two anisotropies selective measurement of tracks that have specified azimuth angles to the c axis e g 60 90 is recommended in annealing studies or thermochronological applications mean spontaneous and induced hct lengths of 60 90 are approximately concordant for individual age standards although slightly controlled by the difference in overetching effects due to the different etching criteria adopted this indicates that natural track annealing at an ambient surface temperature at geological timescales is negligible in zircon in contrast to the case in apatite mean lengths of induced hct s do not differ significantly between the zircons analysed therefore the overall mean and standard deviation values of hct lengths for 60 90 azimuth angles i e 10 50 0 04 1 standard error m and 0 76 0 03 m for spontaneous tracks and 10 73 0 04 and 0 63 0 03 m for induced tracks respectively offer reliable references for hct length measurement in zircon ft thermochronology

shrinkage and sediment supply control on multiple calcrete profile development a case study from the maastrichtian of central india multiple calcrete profiles of the mottled nodular beds form part of an extensive dinosaur bearing infratrappean regolith in central india the profiles have clear variations in the distribution of carbonate morphologies powdery nodular and sheet platy calcretes sheet calcrete is however distinctive and resembles to some extent a k horizon these calcretes are interpreted as having formed in the soil vadose zone profile development was governed mainly by the pattern and depth of shrinkage it is possible that the mature stage 3 to incipient stage 4 calcrete sheets of these shrinkage related profiles formed quite rapidly and certainly in no more than about 400 000 years prominent shrinkage cracking appears to have favoured quite rapid calcrete formation and associated rhizocretion formation was also likely to have been rapid a combination of climatic conditions carbonate availability and volcanism induced sediment starved conditions resulted in the development of a stack of fourteen calcrete profiles sediment starvation allowed most of the stratigraphic interval to be affected to some degree by calcareous pedogenesis this contrasts with other phanerozoic calcrete stacks where nodular carbonate typically occurs in discrete horizons caused by relatively higher sediment supply

alluvial response to the paleocene eocene thermal maximum climatic event polecat bench wyoming u s a abstract the stratigraphic interval spanning the paleocene eocene thermal maximum in the northern bighorn basin wyoming shows changes in the alluvial record that can be tied to a high resolution climate record the complexity and stratigraphic spacing of paleosols change through the study section comparison to the climate record reconstructed from paleosols indicates the changes correspond to paleocene eocene thermal maximum climatic fluctuations in particular the middle of the section contains thick welded paleosols and thin avulsion deposits that link to times of well drained floodplains and lower mean annual precipitation stratigraphic intervals below and above the main part of the paleocene eocene thermal maximum interval correspond to times of less well drained floodplains and higher mean annual precipitation these strata contain thinner paleosols and thick avulsion deposits differences in paleosol complexity and spacing suggest that sediment flux to the depositional site varied in response to precipitation fluctuations associated with the paleocene eocene thermal maximum welded paleosols and thin avulsion deposits indicate reduced floodplain accretion during deposition of the middle of the paleocene eocene thermal maximum intervals with widely spaced paleosols indicate more rapid accretion we hypothesize that drier episodes associated with warming caused reduced vegetation in source areas and promoted erosion and increased sediment yield because precipitation was reduced much of that sediment was stored in upstream reaches of the fluvial system rather than moving to the depositional basin welded paleosols formed because of diminished sediment supply to the basin with a return to wetter conditions during the recovery phase of the paleocene eocene thermal maximum upstream water flux increased stored sediment moved to the basin and vertically spaced thinner paleosols developed the results demonstrate how vertical sections of alluvial paleosols can provide information on how climate fluctuated through time and how the fluvial system responded to climate change

age dependent porosity of young upper oceanic crust insights from seafloor gravity studies of recent volcanic eruptions 1 an october 1997 alvin program collected a series of seafloor gravity stations over the february 1996 volcanic eruption site on the northern gorda ridge 46 41 n 126 47 w these measurements yielded estimates of the density and porosity of mid ocean ridge crust in the first few decades following formation the estimated crustal density for this pillow eruption of 2270 260 kg m3 is very low but in good agreement with the estimated densities of other recent seafloor volcanic flows rock matrix densities measured from hand samples retrieved from the study area give a bulk porosity for this flow of 34 16 this data when included with similar estimates of upper crustal porosity argue for a rapid evolution of upper crustal porosities from very high values 30 for recent eruptions to much lower values 10 15 where the seafloor is older than 0 5 million years these variations of density and porosity are of a magnitude consistent with previously observed changes in seismic compressional wave velocity and permeability of ocean crust

natural long term annealing of the zircon fission track system around a granitic pluton we measured 24 ages and 14 length distributions of fission tracks in zircons separated from basement sandstones around a granitic pluton to investigate natural long term annealing behaviors of the zircon fission track zft system samples were collected from three cretaceous coherent units of the shimanto accretionary complex shikoku japan along an eastward traverse at distances of between 1 6 and 10 6 km from the intrusion contact of 15 ma takatsukiyama granite exposing about 5 km in diameter sampling was carried out around the expected position of the transition zone of track retention i e the fossil partial annealing zone fpaz based on previous regional zft age distributions approaching the contact original zft ages of 100 ma show a continuous reduction to 15 ma at 3 km distance their single grain age distributions accordingly change from widespread multimodal patterns reflecting provenance ages to unimodal ones characterizing the secondary heating by the granite intrusion mean and distributions of zft lengths also show notable variations within the fpaz as a result of mixing both preexistent tracks that were shortened by the miocene heating and unannealed ones having original long lengths that have been formed and accumulated after the cooling of the pluton these facts along with observed track segmentation and annealing anisotropy suggest that the shortening patterns of tracks in nature a heating duration of 105 106 years estimated from thermal modeling are indistinguishable from those previously demonstrated at laboratory timescales this basically validates the conventional approach of extrapolating laboratory based kinetic parameters to geologic timescales the observed fpaz and thermal modeling results in conjunction with laboratory heating data previously reported and recent constraints from an ultradeep borehole favor a relatively narrow temperature range for the partial annealing zone i e 230 to 330 c for a heating duration of 106 years

paleomagnetism rock magnetism and fission track dating of the kurihashi granodiorite in northeast japan evidence for a cretaceous hydrothermal event and differential rotation along the eastern eurasian margin samples from the late cretaceous kurihashi granodiorite on the pacific coast of northeast japan are divided into two groups based on paleomagnetic data one group a preserves stable single thermoremanent magnetizations trm with large westerly deflected declinations the other group b has two or three distinct components of natural remanent magnetization nrm components with high middle and low unblocking temperatures show westerly declinations nearly identical with the stable trm directions of group a as well as northerly and easterly declinations rock magnetic experiments indicate that the dominant magnetic mineral of both groups is ti poor titanomagnetite group a samples contain superparamagnetic sp titanomagnetite because they show a frequency dependence with the initial susceptibility measurements hysteresis parameters of group b samples are consistent with a mixture of single domain sd and multidomain md grains electron microscopy confirms the presence of md size magnetite in the group b samples fission track thermochronology indicates that the kurihashi granodiorite underwent a post cooling hydrothermal event during the late cretaceous thus the northerly and easterly nrm components seem to have a thermoviscous origin many samples have anomalously high unblocking temperatures up to 560 c compared to predictions of sd theory and probably result from long thermal demagnetization tails of thermoviscous remanent magnetizations tvrm carried by md magnetite a strong tvrm was acquired during the hydrothermal event and is correlated with the long normal polarity superchron of the geomagnetic field because highly oblique left lateral subduction was active along the eastern eurasian margin during the same period the primary trm and tvrm components record counterclockwise rotation 120 of the kurihashi granodiorite and remarkable wrench deformation along the continental margin

palaeosols as indicators of geomorphic stability in two old red sandstone alluvial suites south wales palaeosols fossil soils are abundant in the alluvial late silurian early devonian moor cliffs formation and rat island mudstone freshwater west formation of south dyfed south wales the palaeosols occur in thick mudstones deposited on floodplains under a seasonal semi arid climate and represent vertisol type soils simple single profiles are rare and most of the mudstone intervals exhibit complex overprinted profiles however a major difference exists between the palaeo vertisols in each of the two units studied the moor cliffs formation contains thick floodplain intervals with evidence of frequent erosion and reactivation of earlier soil horizons the associated coarser channel deposits mainly represent ephemeral streams the alluvial system was unstable flashy and prone to extensive stripping of stored floodplain sediment arroyos unstable ephemeral stream channels probably developed during this interval evidence for any marine influence on soil development is missing and previous speculations that the formation may represent deposition in an upper intertidal or supratidal system are not supported the rat island mudstone represents a complete contrast in that there was little or no stripping of floodplain sediments the channel deposits are typically of the fining upwards type representing more stable low sinuosity channels and with ephemeral stream floods by integrating the palaeosols a more detailed picture of the geomorphic history of these units can be formulated comparison with contemporary drainage basins indicates that a change in climate was a possible cause for the differences between the two units less frequent and more severe storms occurring during the deposition of the rat island mudstone

calcrete and palustrine assemblages on a distal alluvial floodplain a response to local subsidence miocene of the duero basin spain abstract in the upper miocene of the eastern duero basin two carbonate units cu 1 and cu 2 display a lateral transition from distal alluvial floodplain red mudstones to calcrete and an upwards transition from calcrete to palustrine facies the carbonate content in the calcrete increases upwards as shown in sequences from red or reddish brown mudstones with diffuse calcification to nodular calcrete facies to massive calcretes the palustrine facies display a broad range of textures related to the degree of exposure peloidal intraclast textures formed during the most prolonged phases of exposure and are those most commonly seen in the palustrine facies the transition from calcrete to palustrine facies occurs in two ways 1 as an indurated limestone level with mixed features of calcrete and palustrine facies and 2 a well delimited boundary between the two facies which show very similar characteristics in the vicinity of this boundary the 13cpdb and 18opdb values of the calcretes are similar to those of the palustrine facies this is because their genesis was related to groundwaters which inherited the isotopic signature of meteoric waters good covariance between 13c and 18o palustrine values r 0 78 is typical of lakes in semi arid regions with long water residence times in closed basins the calcrete palustrine association records a progressive decrease in the terrigenous supply and a continuous elevation of the groundwater table until it intersected with the surface to create a pond the rise in the groundwater table resulted from local subsidence that was not compensated by terrigenous supply leading to a lowering of the floodplain changes in the thickness of palustrine facies from central to marginal pond areas with ubiquitous exposure features suggest that the pond was progressively filled up by bio chemical carbonate precipitation balancing the available space created by subsidence this maintained the shallow character of the pond deposits

morphology and significance of super mature calcretes from the upper old red sandstone of scotland thick calcrete profiles occur in the late devonian early carboniferous kinnesswood formation of the midland valley of scotland these profiles consist of highly brecciated peloidal and coated grain fabrics with laminar calcrete horizons and linings to fractures the profiles resemble supermature calcretes associated with late cenozoic surfaces in the southwestern united states and reflect pedogenesis over periods of several hundred thousand years or more the possible origins of the highly complex fabrics seen are reviewed and the polygenetic nature of such profiles is stressed it is suggested that brecciation takes place co incident with subaerial exposure of the calcrete mature profiles may be predisposed to brecciation and surficial weathering because of their susceptibility to soil erosion as a result of changes in vegetation cover the calcretes underwent phreatic cementation burial dolomitization and silicification

estimating rates of calcrete formation and sediment accretion in ancient alluvial deposits the use of calcrete horizons as a means of assessing rates of sediment accretion in ancient alluvial sequences is reviewed any attempt to use such horizons in quantifying ancient alluvial deposition must appreciate that accurate data on rates of formation of quaternary calcretes are limited such data show considerable variations in the rates and no reliable data exist at all for some calcrete types the abundance of calcretes in the geological record warrants a new initiative to improve our understanding oftheir origins and rates of formation

jurassic and cretaceous apparent polar wander relative to south america some tectonic implications late mesozoic apparent polar wander apw with respect to stable south america has been difficult to define it appears that this observation has a simple explanation very little apw occurred and none at all during a 50 m y period 165 to 115 ma it is possible to compute a stillstand pole for this interval 88 8 s 72 4 e k 244 7 a95 4 9 from five reliable studies comprising a total of 523 sites a second stillstand of much shorter duration 70 80 ma is defined by four poles 52 sites this is located at 80 8 s 346 7 e k 457 7 a95 4 3 apw of 9 2 occurred during the interval 115 80 ma a comparable stillstand is found in the north american record e g van fossen and kent 1992 this has a similar degree of scatter k 421 and spans at least 36 m y 124 to 88 ma thus north america and south america both were rotating due westward during a large part of the cretaceous this has some important implications for global tectonics

rock magnetism of remagnetized paleozoic carbonates low temperature behavior and susceptibility characteristics we have conducted a new set of rock magnetic experiments on samples of remagnetized paleozoic carbonates of eastern north america these experiments were designed to investigate the origin of the unusual hysteresis behavior of these rocks by evaluating 1 the importance of ferrimagnetic pyrrhotite as a remanence carrier and 2 the sources of low field susceptibility low temperature measurements of saturation isothermal remanent magnetization sirm indicate that the pyrrhotite magnetic transition at 32 k is absent in the trenton and onondaga limestones of new york this transition is observed but poorly expressed in the knox group of east tennessee room temperature sirms cooled to 10 k in zero field lose a small fraction of their intensity between 30 and 35 k samples from all three formations show a broad peak in irm intensity at about 200 k which is typical of pyrrhotite in the trenton and onondaga samples the ferrimagnetic component of low field susceptibility is significantly larger than the ratio mrs hcr and is thus probably due dominantly to magnetite in some of the knox samples the reverse is true suggesting an important pyrrhotite contribution for all of the samples the ferrimagnetic susceptibility normalized by the saturation magnetization is anomalously high about a factor of 5 or 10 higher than the typical value for magnetite we believe that this indicates a very substantial contribution from superparamagnetic particles strong frequency dependence of susceptibility and very high ratios of anhysteretic to saturation remanence confirm the importance of ultrafine particles spanning the superparamagnetic single domain boundary all three of these chemically remagnetized carbonates units exhibit the following properties which have not previously been found together for any rock or synthetic analog and which therefore appear to constitute a diagnostic set of rockmagnetic criteria for recognizing chemically remagnetized rocks mrs ms 0 89 hcr hc 0 6 k ms 50 m a arm sirm 20 ka mrs hcr 50

carbonate deposition in an ephemeral siliciclastic alluvial system jurassic shuttle meadow formation newark supergroup hartford basin usa abstract nonmarine carbonate accumulation from a sedimentologic perspective has multiple possible origins clastic load springs groundwater discharge soil development biochemical seasonal changes cave speleothems and eolian influx many of these carbonates contain diagnostic textures from which origin is easy to ascertain however differentiating between clastic and spring groundwater carbonates especially in depositional systems dominated by siliciclastics is not always simple here criteria for recognition are developed subsurface hydrology and tectonic origin of the depositional basin source rocks surrounding the basin sedimentologic packaging and extent of the carbonates in question as well as their sedimentary structures and fossil content and stable isotopic analyses of the carbonates can all aid in determining carbonate origin and correctly assessing sedimentary and basin evolution the present study focuses on a nonmarine carbonate deposit found within the jurassic shuttle meadow formation of the hartford basin one of many rift basins which formed as a result of the opening of the north atlantic ocean during the late triassic to early jurassic the upper 50 m of the formation at plainville connecticut is interpreted as continental in origin and is composed of five facies red ripple cross laminated muddy siltstones to sandstones fr sr massive red siliciclastic mudstones fm buff fine to medium grained horizontally laminated sandstones sh red to white disrupted calcareous shales fl3 and rare micritic carbonates pm facies fr sr sh and fm are interpreted as an alluvial plain system in an ephemeral setting with bedload sheetflooding as the dominant depositional mechanism similar to the channel country drainage system of central australia in addition preservation of lateral accretion sandstone sheets accretionary benches indicate that the shuttle meadow alluvial system was rapidly accreting the anomalous existence of carbonate beds in facies fl3 and pm in the smf bedload dominated siliciclastic sequence is attributed mainly to the unique nature of the clastic sediment load in the basin no direct evidence for a spring groundwater input is apparent the shallow carbonate lake margin or a pond with vegetation and periodic exposure is envisioned as the depositional environment the intraclastic texture of the micrites with rare primary relict lamination indicates early diagenetic alteration from root penetration desiccation cracks and burrowing

age variation in the physical properties of oceanic basalts implications for crustal formation and evolution the time dependent variability of the physical properties of upper oceanic crustal rocks have been characterized by compiling acoustic velocity density porosity iron oxidation state and h2o data from the upper 50 m of all deep sea drilling project and ocean drilling program drill holes which recovered basalt samples from normal oceanic basement this data compilation is interpreted in terms of the geological processes responsible for these changes as the seafloor ages drill site averages of both acoustic velocity and bulk density show a decrease with increasing age for crustal ages less than 100 ma similarly chemical data from the same drill cores indicate the presence of two distinct alteration processes oxidation of ferrous to ferric ions within the rock forming minerals proceeds rapidly within the first 5 ma after formation slows in the subsequent 5 to 20 m y period and then appears to stop hydration of the silicate minerals also appears to generally increase with age over the full 150 m y age range of the samples although at a slower rate than oxidation the observed distribution of the physical properties of the upper crustal rocks for the first 100 ma can be explained by three processes 1 a large initial variability of vp and density caused by the range of original porosity of the rocks 2 an age progressive alteration associated with oxidation that systematically reduces both vp and density with increasing age for the first 5 m y and 3 an additional nonoxidative alteration that increases the hydration of the silicate minerals with a resulting major impact on the physical properties still unexplained however is the lack of an expected trend of decreasing porosity with increasing age and alteration and the large nonsystematic scatter in the physical property data for samples older than 100 ma

record of the carnian wet episode in strata of the chinle group western usa the late triassic carnian wet episode was an interval of humid climate evident in the lowermost strata of the upper triassic chinle group in the western usa chinle deposition began with the development of major river systems of the shinarump formation and equivalents laterally equivalent to and or overlain by floodplain deposits containing kaolinitic gleyed to spodic palaeosols and local coal beds the chinle strata immediately above these wet episode strata are deposits of smaller rivers that lack coal or carbonaceous strata and contain non kaolinitic palaeosols that are locally calcareous and vertic indicative of drier but strongly seasonal climates the lowermost chinle strata contain fossil tetrapods palynomorphs and conchostracans that are consistent with other data that indicate that the basal chinle strata are of julian age and immediately overlying lower chinle strata are early tuvalian so these strata are the age of the carnian wet episode identification of a long norian stage places the norian base in the chinle group near the top of the strata of the wet episode which means that norian strata sit directly on early carnian strata but there is no unconformity at this level to support recognition of such a long norian in the chinle section

a logical system of paleopedological terms abstract standardization of paleopedological nomenclature should rely on pedogenetic characteristics logical definitions of neo paleo recent relict fossil and buried soils and horizons are presented with criteria for their differentiation disharmonic intertype soils horizons is suggested as a collective term for soils and horizons showing characteristics of both neo and paleo formations the so called genetic soil types the last known pedogenetically effective change of climate should be fixed as a time demarcation between paleosols paleohorizons and neo formations in central europe this corresponds with the end of the atlantic period

an unrecognized major collision of the okhotomorsk block with east asia during the late cretaceous constraints on the plate reorganization of the northwest pacific abstract interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions however the traditional tectonic model for the east asian margin during the mesozoic invoking successive episodes of paleo pacific oceanic subduction does not provide an adequate context for important late cretaceous dynamics across east asia including continental scale orogenic processes significant sinistral strike slip faulting and several others the integration of numerous documented field relations requires a new tectonic model as proposed here the okhotomorsk continental block currently residing below the okhotsk sea in northeast asia was located in the interior of the izanagi plate before the late cretaceous it moved northwestward with the izanagi plate and collided with the south china block at about 100 ma the indentation of the okhotomorsk block within east asia resulted in the formation of a sinistral strike slip fault system in south china formation of a dextral strike slip fault system in north china and regional northwest southeast shortening and orogenic uplift in east asia northeast striking mountain belts over 500 km wide extended from southeast china to southwest japan and south korea the peak metamorphism at about 89 ma of the sanbagawa high pressure metamorphic belt in southwest japan was probably related to the continental subduction of the okhotomorsk block beneath the east asian margin subsequently the north northwestward change of motion direction of the izanagi plate led to the northward movement of the okhotomorsk block along the east asian margin forming a significant sinistral continental transform boundary similar to the san andreas fault system in california sanbagawa metamorphic rocks in southwest japan were rapidly exhumed through the several kilometer wide ductile shear zone at the lower crust and upper mantle level accretionary complexes successively accumulated along the east asian margin during the jurassic early cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike slip fault system the departure of the okhotomorsk block from the northeast striking asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin in the campanian the block collided with the siberian margin in northeast asia at about 77 ma a new oceanic subduction occurred to the south of the okhotomorsk block ending its long distance northward motion based on the new tectonic model the abundant late archean to early proterozoic detrital zircons in the cretaceous sandstones in kamchatka southwest japan and taiwan are interpreted to have been sourced from the okhotomorsk block basement which possibly formed during the late archean and early proterozoic the new model suggests a rapidly northward moving okhotomorsk block at an average speed of 22 5 cm yr during 89 77 ma it is hypothesized that the okhotomorsk east asia collision during 100 89 ma slowed down the northwestward motion of the izanagi plate while slab pull forces produced from the subducting izanagi plate beneath the siberian margin redirected the plate from northwestward to north northwestward motion at about 90 89 ma

progressive segmentation and systematic block rotation within a plutonic body palaeomagnetism of the cretaceous kurihashi granodiorite in northeast japan summary intensive palaeomagnetic and rock magnetic studies clarify the history of multiple block rotational events within an active plate margin the cretaceous kurihashi granodiorite in northeast japan preserves multi component remanent magnetization high unblocking temperature tub thermoremanent magnetization trm acquired during the initial cooling of the granodiorite and middle low tub thermoviscous remanent magnetization tvrm acquired during succeeding hydrothermal activities the observed directional difference between the three magnetic components requires the first counter clockwise rotation event within a part 1 km of northeast japan as a result of left lateral plate motion in the late cretaceous later clockwise rotation probably related with right lateral faulting during the course of the miocene backarc spreading of the japan sea is indicated by significant easterly deflections in the low tub component on the other hand scatter in the high tub trm declinations implies that the second deformation phase was achieved as non rigid rotation of fault bounded blocks as wide as 100 m the latest and most confined rotation events are confirmed by complicated deflections of the trm and tvrm in a fault zone a shear zone as wide as 30 m with dense fractures near the main fault is sharply divided into three compartments which have been rotated around three orthogonal poles systematic block rotations may accommodate differential slips on fault planes within a plutonic body genetically containing orthogonal fractures as reactivated intrinsic cooling joints we interpret our results to show that the kurihashi granodiorite has been progressively segmented since the cretaceous under varied stresses

geomagnetic and gravity modeling of the fore arc shelf of north east japan abstract northeast japan is one of the continental slivers of the eurasian continent rifted by the miocene fan shaped genesis of the japan sea a pair of longitudinal geomagnetic anomalies are traced along the pacific coast of northeast japan basement core samples obtained from miti kesennuma oki well drilled on the southernmost part of anomaly belt are examined the basement which is identified as biotite granite and characterized by sheared fabric shows early cretaceous radiometric ages through rock magnetic experiments it was confirmed that the granitic basement holds thermoremanent magnetization trm strong enough to cause the observed anomaly with a minor contribution from induced magnetization the carrier of trm is multi domain titanomagnetite on the basis of experimental results two dimensional geomagnetic and gravity modeling for semi infinite magnetized polygons have been constructed along two e w seismic lines on the fore arc shelf of northeast japan vector components of magnetization are tuned through fitting anomaly peaks caused by basement topography delineated by seismic survey as for the northern part of study area the inclination of westerly deflected magnetization vector should be 30 or smaller the amount required to restore the cretaceous northeast japan to the south of southwest japan the gravity model for the same lines as the geomagnetic modeling suggests that fore arc basement off the northern kitakami terrane consists of granitic rocks except for a conspicuous basalt whereas the non magnetic basement off the southern abukuma terrane consists of a variety of blocks of different density the anomalous direction of remanent magnetization and variety in gravity data are linked to nnw sse sinistral transcurrent faults activated throughout the paleogene

unravelling calcrete environmental controls in volcanic islands gran canaria island spain abstract volcanic islands are unique contexts to analyze the controls on calcrete development in settings with varied relief climate and vegetation and lacking carbonate host rocks this paper discusses the formation of quaternary calcrete profiles in gran canaria volcanic island under direct influence of the sal saharian air layer calcrete profiles are multi storey and composed of prismatic massive laminar pisolithic ooid bearing sandy mudstones with rhizoliths and brecciated horizons host rocks include basalts siliceous mudstones volcanic sands and gravels and bioclastic rich sands carbonate is mostly calcite but some dolomite occurs in massive horizons the main microfabrics include laminated micrite fine crystalline dolomite desiccated micrite micrite clay groundmass oriented mg rich clays peloids spherulites and coated grains 13c varies from 3 26 to 9 18 vpdb and 18o from 0 86 to 3 24 vpdb the 87sr 86sr ratios are between 0 707504 and 0 708860 indicating that calcium was mostly supplied from the caco3 rich aeolian dust coming from the sahara desert calcrete profiles are mostly pedogenic with roots and microorganisms enabling carbonate precipitation within the soils the correlation trend of 13c and 18o points to a climate control on precipitation with the heavier isotope values in the horizons containing dolomite sedimentation rates interplayed with calcrete formation processes and erosion to outline the profiles horizons amalgamated laminar horizons formed when the rate of calcrete formation was higher than sedimentation and erosion whereas areas or periods with relatively higher sedimentation allowed the separation of calcrete horizons the direction of the winds supplying aeolian dust and the varied relief vegetation and climate favored better development of calcretes in the relatively arid and lowland areas of the eastern side of the island our study shows that calcretes contain the record of the paleoenvironmental controls that operated in volcanic islands with no previous carbonate substrates

taphonomical and palaeoecological investigation of the late cretaceous maastrichtian tustea vertebrate assemblage romania haţeg basin insights into a unique dinosaur nesting locality abstract the tustea vertebrate locality at oltoane hill northwestern part of the ha eg basin romania has provided a rich and diverse assemblage of late cretaceous maastrichtian continental vertebrates more than 800 vertebrate fossils were recovered from this locality the isolated and associated remains represent 21 different taxa including amphibians turtles lizards snakes crocodyliforms pterosaurs dinosaurs and mammals the local assemblage is overwhelmingly dominated by dinosaurs with the rhabdodontid zalmoxes as the most abundant taxon the bonebeds that yielded this fossil material occur in a stacked series of mudstone calcrete units belonging to the middle member of the densus ciula formation the taphonomical investigations suggest that the tustea assemblage is made up of attritionally accumulated politaxic remains and that it is a parautochthonous assemblage with no evidence for significant bone transport or reworking according to the synthesis of all available field data two outstanding fossiliferous levels can be identified within the tustea locality where megaloolithus eggs and hadrosauroid hatchling material are preserved together recognized here as two superposed nesting grounds such co occurrence was considered controversial since there is a long standing and quasi general consensus that eggs of the megaloolithus oogenus were laid by titanosaurian sauropods we present several alternative scenarios to account for the co occurrence of telmatosaurus hatchling remains and megaloolithid eggs in the nesting horizons and explore these alternative hypotheses by weighing the arguments supporting or contradicting them the burden of evidence derived from our sedimentological taphonomical and palaeoecological investigations at tustea is still in favour of the autochthony of the hatchlings preserved within their own nesting grounds whereas there is no such support for a titanosaurian origin of the tu tea megaloolithid eggs

geology mineralogy and geochemistry of late miocene paleosol and calcrete in the western part of the central anatolian volcanic province cavp turkey abstract the late miocene was characterized by high global temperatures and partly to nearly complete desiccation of the mediterranean sea throughout the latter part of the messinian age the messinian salinity crisis the non marine paleoenvironmental and paleoclimatic records from the mediterranean area are highly limited in their spatial range late miocene river flood plain sediments in the central anatolian volcanic province cavp of central turkey consist of siliciclastic and pyroclastic sediments with paleosols and calcrete five lithofacies were identified as a massive conglomerate b trough cross bedded sandstone c massive mudstone d disrupted mud e and disrupted matrix supported conglomerate the paleosols were composed predominantly of smectite and illite with smaller amounts of feldspar quartz opal a pyroxene and amphibole and the calcretes were composed mainly of calcite with smaller amounts of feldspar quartz and opal a and minor amounts of smectite chlorite and illite authigenic clay minerals and micritic calcite coating on the detrital grains and soil peds and pendant cement in the calcrete and paleosol horizons were evidence of a vadose zone in contrast the large equant spar drusy mosaics were formed in phreatic environments the weathering of ignimbrite and marble led to the depletion of sio2 cao al2o3 fe2o3 tio2 and k2o through the precipitation of smectite and illite in the paleosols and cao in the form of micrite and calcite in the calcrete horizons field observations mineralogy geochemistry and the results of 18o and 13c isotopic analysis reveal that alternating wet and dry periods resulted in an upward increase in precipitation of authigenic smectite and illite within the late miocene sections under the influence of geochemical and ph fluctuations in phreatic or vadose water within the river flood plain paleoenvironment

biologically mediated weathering in modern cryptogamic ground covers and the early paleozoic fossil record specific micro weathering features and biochemically derived residues formed by living organisms can be used as biomarkers to infer the presence of biological communities within sedimentary units of ancient ecosystems we examined basaltic soil minerals from modern cryptogamic ground covers cgcs in iceland and compared these with two early paleozoic fossil systems nine biologically mediated weathering features bwfs were identified in modern soils including micron scale surface trenching and penetrative tunnels which are attributed to the actions of bacteria fungi and exudates specific bwfs are associated with fe residues and with fe rich bio precipitated nodules further putative comparable features and fe enrichment are identified in palaeosols from the late silurian llansteffan south wales and the early devonian rhynie chert scotland although we are cautious about attributing biological affinity to individual isolated features our results demonstrate the potential of using multiple bwf types as a collective together with their chemical signatures as new proxies to understand community structure and interactions in early terrestrial ecosystems this new information is the first evidence of interactions between ancient cgc like organisms and substrate or soil inorganic components in the fossil record and demonstrates the ability of cgc like biospheres to contribute to mineral weathering soil development and biogeochemical cycling during the early paleozoic supplementary material fieldwork geomorphological information and triplot sem eds data are available at https doi org 10 6084 m9 figshare c 4373717

tectonic systems tract and depositional architecture of the western border of the triassic iberian trough central spain abstract during the permian and triassic a sedimentary wedge developed overlying a listric normal fault on the western border of the iberian trough central spain an area was selected for study that provides optimal conditions for a detailed analysis to be made of relationships between geometric strata arrangements tectonic control and sedimentary responses the excellent quality of the outcrops allows the observed patterns of strata to be related to fault growth and developmental of the basin the recognition and mapping of local discontinuities throughout the study area were possible packages of similar strata with different angularity can be discerned between the two main discontinuities geometrical relationships can be established for depositional unit boundaries the architectural style and sediment dispersal patterns interpreted as the results of interactions between sedimentation and tectonics are integrated into a three dimensional tectono sedimentary facies model to explain the basin s infilling is interpreted to be tectonic the rift related three dimensionally linked depositional systems recognized might be defined as tectonic systems tract prosser s 1993 rift related linked depositional systems and their seismic expression in williams g d dobb a eds tectonics and seismic sequence stratigraphy geol soc london spec publ 71 35 66 five such tracts are recognized and related to specific phases of tectonic development

seafloor gravity evidence for hydrothermal alteration of the sediments in middle valley juan de fuca ridge abstract gravity data collected at two different levels sea surface and seafloor are compared and interpreted to characterize the effect of hydrothermal circulation on the sediment density in middle valley a deeply sedimented spreading center on the juan de fuca ridge the sea surface gravity data constrain density variations at depth beneath the seafloor whereas sea bottom measurements are more sensitive to shallow sources at least two different types of hydrothermal signatures in the sediments can be distinguished from the gravity data short wavelength anomalies associated with sulfide deposits and broader anomalies associated with areas of lithified sediments in middle valley three distinct gravity anomalies were identified a an anomaly over a sulfide mound south of bent hill shows that the sulfide body extends to depths of 120 to 180 m and has been fed by several near surface conduits b an anomaly at the base of the fault bordering the valley to the east is interpreted as a regional anomaly combined with the local effect of lithified sediments and possibly sulfide deposits c an anomaly paralleling an intra valley fault that limits the deepest part of the graben is interpreted as indicating lithification of the upper sediment layer a high heat flow anomaly is located 1 to 2 km east of this fault suggesting that sediment lithification occurred in a wide band above the fault and eastward to the current high heat flow area due to the progressive migration of the hot fluid circulation

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

a model of late cenozoic transcurrent motion and deformation in the fore arc of northeast japan constraints from geophysical studies abstract we use recently acquired seismic reflection data and reprocessed sections to interpret the structure of the northern part of the ne japan forearc we identify a nnw sse trending deformation zone bounded by large transcurrent faults trends t1 t4 from west to east on the upper continental slope the lower slope is characterized by a frontal prism and reverse faults bathymetric data reveal several en echelon topographic bulges with nw se elongation aligned parallel to the fault trends the bulges are interpreted as a dextral wrench zone that has developed since the neogene based on structural contours of two late cenozoic seismic horizons clockwise rotation associated the wrenching is indicated by the paleomagnetism of paleogene marine sediments obtained from a drill hole within the faulted zone close to trend t1 a previous seismic refraction study shows remarkable contrast in p wave velocity across trend t2 indicating a considerable rearrangement of crust associated with transcurrent motion along this fault we propose a paleogeographic reconstruction assuming 200 km southward trenchward lateral transportation along trend t2 and its northern extension in our model subduction erosion at the northern japan trench was enhanced by trenchward migration of the fore arc sliver but steadied following rearrangement of the sliver along the transect the calculated variation in subduction erosion is consistent with subduction histories based on existing well data

development and lithogenesis of the palustrine and calcrete deposits of the dibdibba alluvial fan kuwait abstract a model is proposed for the development of the quaternary palustrine carbonate calcrete association which occurs as hard crust capping low hills at a distal flood plain of al dibdibba alluvial fan located at southwestern kuwait field occurrence detailed petrographic investigation and geochemical analysis revealed that a single cycle of groundwater calcrete with vertical gradational maturity pattern was developed this represents a continuous sedimentological cycle during which flood sheet conditions prevailed with intermittent periods of humid and arid conditions subsequently calcitic micrite was continuously precipitated from small shallow local isolated and short lived ponds fringed by freshwater marshes with abundant charophyte meadows the latter were developed as a result of flooding scattered depressions by groundwater supersaturated with respect to calcite due to rise of groundwater table the deposition of two facies of carbonate muds namely biomicrite and pelintraclasts skeletal micrites was followed by a drought phase which witnessed desiccation of the fresh water ponds and significant drop in groundwater level a sequence of pedogenic and diagenetic processes acted on the deposited carbonate muds are manifested by a desiccation cracks b micrite neomorphism c infilling of root burrows and some cracks by aeolian siliciclastics d karstification e marmorization f calcretization of root burrow infill and development of pseudo rhizocrete g calcite cementation and mineral authigenesis and h silcretization these processes are responsible for the development of hard palustrine carbonate crust at the advent of aridity the whole system of al dibdibba alluvial fan was subjected to deflation this resulted in reversing the paleotopography of the hard crusted palustrine depressions into carbonate capped domal hills

near surface shrinkage and carbonate replacement processes arran cornstone formation scotland a 47 m thick succession of conglomerates sandstones and mudstones of late devonian or early carboniferous age outcrops at fallen rocks in northeast arran western scotland it is defined here as the type section of the arran cornstone formation at numerous levels in the succession varieties of fissures and carbonate concretions formed during the accumulation of the formation the fissures opened as a result of drying shrinkage and were closed again either by filling with different sediment or by wetting and expansion of the fissure wall sediment carbonate concretions form complete beds discontinuous bedding concordant sheets or bedding discordant nodules or rods the rod cornstones these concretions formed close enough to the surface to be incorporated after erosion and redeposition as clasts into overlying beds the concretions were formed by growth of micrite mainly by replacement but shrinkage displacement played an important role in subsequently fracturing and reworking the micrite the micrite was also locally replaced by microspar and spar and this involved dissolution and precipitation no independent evidence of biological influence in any of these processes has been found

paleothermometry of the sydney basin evidence from overprinting of magnetizations of late permian and mesozoic rocks and from the rank of permian coals and mesozoic phytoclasts coal particles suggests that surface rocks in the sydney basin eastern australia have been raised to temperatures of the order of 200 sup 0 c or higher as vitrinite reflectance an index of coal rank or coalification is postulated to vary predictably with temperature and time estimates of the paleotemperatures in the sydney basin based on observed vitrinite reflectance measurements can be made in conjunction with reasonable assumptions about the tectonic and thermal histories of the basin these estimates give maximum paleotemperatures of present day surface rocks in the range 60 249 sup 0 c depending on factors such as location in the basin the thickness of the sediment eroded and the maximum paleogeothermal gradient higher coal rank and consequently larger eroded thicknesses and paleogeothermal gradients occur along the eastern edge of the basin and may be related to seafloor spreading in the tasman sea on the basin s eastern margin a theory of thermal activation of magnetization entailing the dependence of magnetic viscosity on the size distribution of the magnetic grains is used to obtain an independent estimate of the maximum paleotemperaturesmore in the sydney basin this estimate places the maximum paleotemperature in the range 250 300 sup 0 c along the coastal region both coalification and thermal activation of magnetization models provide strong evidence of elevated paleotemperatures which in places exceed 200 sup 0 c and the loss of sediment thicknesses in excess of 1 km due to erosion less

depositional setting of the lower old red sandstone at pantymaes quarry central south wales new perspectives on the significance and occurrence of senni beds facies

possible climate variability in the lower old red sandstone conigar pit sandstone member early devonian south wales uk abstract the early devonian conigar pit sandstone member cpsm of the freshwater west formation lower old red sandstone lochkovian age at freshwater west in south wales comprises a heterolithic predominantly alluvial suite mudstones fine to coarse grained sandstones conglomerates with varying depositional architecture a number of discrete facies associations are observed the fine grained inclined and non inclined heterolithic association is dominant within the cpsm it represents dryland sinuous channelized flow ihs bedsets and unconfined flow non inclined bedsets at terminal and intermediate floodouts deposited under semi arid conditions mudstones were deposited in two distinct environments associated with this semi arid river system laminated and burrowed reddish brown mudstones were deposited in shallow semi permanent lakes or pools on the floodplain massive mudstones were deposited as within channel muddy braid bars with sedimentary structures being lost during subsequent compaction the mudstones exhibit vertisol pedogenesis reflecting the seasonal wetting and drying associated with the semi arid climate periods of intense desiccation are indicated by deep desiccation cracks and associated rubbly surfaces possible though unproven tidal conditions influenced a small percentage of the heterolithic channels at freshwater west the extent of these channels is uncertain the coarser grained multi storey sandstone association was deposited by low sinuosity rivers with a fluctuating but perennial discharge associated with these laterally extensive sandbodies was a high water table with surface ponding wetlands that enabled the preservation of plant detritus during high discharge events flow expanded over the contemporaneous floodplain depositing the sheet sandstone association within splay complexes the interpretation that perennial discharge may have been triggered by basin wide climate change challenges the long held view that the lower ors climate was continuously semi arid in nature the spatial temporal extent of this climate change is uncertain as it is possible that the multi storey sandbodies were deposited by allogenic rivers draining a distant possibly uplifted source area a decrease in the observed frequency and maturity of vertisol profiles and a corresponding increase in multi storey sandbodies upward through the succession may reflect a long term episodic pattern of climate change

cenozoic northward translation of the kitakami massif in northeast japan paleomagnetic evidence abstract paleogene and early cretaceous welded tuffs have been sampled from eleven sites at the omoe peninsula 39 6 n 142 0 e in the kitakami massif of northeast japan for paleomagnetic study characteristic paleomagnetic directions with a high unblocking temperature component above 560 c are isolated westerly declinations with shallow inclination are identified after tilt correction in the 62 71 ma heizaki volcanics d 283 5 i 9 4 95 8 0 and in the 114 119 ma harachiyama formation d 274 2 i 20 4 the shallow inclination which was previously reported from early cretaceous plutonic rocks without tilt correction in the kitakami massif has been discovered in the tilt corrected paleomagnetic directions the presence of both normal and reversed polarities suggests reliability of this shallow and westerly paleomagnetic direction the shallow inclination indicates that the kitakami massif was located at low latitude 5 4 n at 71 62 ma taking into account a reference paleomagnetic pole of the paleocene expected from sikhote alin the kitakami massif was translated northward over 25 in latitude since 65 ma the kitakami massif can be subjected to latitudinal northward motion more than 24 during the last 70 ma when it was transported by push of the moving pacific plate and reached the asian continental margin near sikhote alin later than 30 ma we conclude that the kitakami massif was incorporated into northeast japan at some time between 30 and 22 ma after the cenozoic northward translation

pedogenic carbonate crusts calcretes in karstic landscapes as archives for paleoenvironmental reconstructions a case study from yucatan peninsula mexico abstract in the northeastern margin of the yucatan peninsula which is located in southeastern mexico three levels of compact carbonate crusts calcretes interlayered with indurated coastal calcareous sediments calcarenites are discernible since both the calcretes and calcarenites form a continuous carbonate sequence a combined methodology macro and micromorphology geochemistry and mineralogy is used to differentiate them additionally the calcrete layers are dated using the uranium thorium method in order to establish a chronological framework the carbonate differentiation and chronology are then used to establish the paleoenvironmental conditions that prevailed during calcrete formation as well as to reconstruct the coastal landscape evolution and its relation to pleistocene sea level changes during marine isotope stages mis 6 and 5 samples of calcrete layers and calcarenites were taken from two sections in the cancun tulum corridor the lowest level of calcrete underlies a sequence of calcarenites and the two younger levels cap the sequence in calcretes the micromorphology provides evidence of the presence of a relict soil with subangular blocky microstructure root traces and needle fiber calcite associated with soil fungi interactions in contrast the micromorphology of the calcarenites shows ooids and bioclasts typical of a coastal environment geochemically calcretes are depleted in 13c compared to calcarenite with values ranging between 2 and 10 and they have a lower proportion of rare earth elements calcrete mineralogy consists mainly of calcite over aragonite with a low proportion of mg calcite u th dating indicates that the oldest calcrete was formed during the penultimate glacial maximum pgm in mis 6 and the two younger calcretes correspond to the last interglacial period in mis 5c the calcarenite formation occurred earlier also during mis 5 soil formation strong karstification and soil erosion have occurred on younger calcretes this study suggests that these processes developed between mis 4 to mis 1

fore arc transcurrent faults in northeast japan hybrid geophysical models of an island arc upper crust origin of a conspicuous longitudinal geomagnetic anomaly on the fore arc of northeast japan kitakami magnetic belt kmb is investigated on the basis of fission track dating rock magnetic experiments reflection seismic interpretation and potential field modeling radiometric ages suggest that the basement core samples obtained from the numanohata sk 2d southern hokkaido and ministry of international trade and industry kesennuma oki offshore honshu boreholes are part of the voluminous cretaceous plutons in northeast japan two dimensional gravity models on fore arc seismic profiles show that acoustic basement with geomagnetic anomaly has densities comparable with those of cored granites magnetic carrier of the granite is identified as multi domain sized titanomagnetite strong thermoremanent magnetization trm and high qn ratios of the samples indicate significant contribution of trm of the granitic basement as a source of observed anomaly conspicuous paired anomaly is caused by consistent normal remanence of the granitic basement acquired during the cretaceous long normal chron c34n as a result of geomagnetic modeling optimized direction of the remanence is characterized by westerly deflection and abnormally shallow inclination 30 which requires to restore the kitakami massif northern part of northeast japan to the south of southwest japan significant northward translation since the cretaceous may have been compensated by left lateral motions on transcurrent faults along the eurasian margin such as the offshore trend a identified in this study gravity modeling indicates that the basement off the abukuma massif southern part of northeast japan which does not show geomagnetic anomaly consists of varied density blocks that are bounded by transcurrent faults

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

tectonic stress state in ne japan as part of the okhotsk plate abstract an existing geodetic flow velocity model obtained by using an internal free network adjustment technique is used to derive estimates for various strain rates parameters in ne japan the greatest shortening rates of the principal strains trending e w are located in regions where much steady internal frame invariant plastic flow deformation is observed to be taking place the internal geodetic adjustment technique yielded the internal deformation in the tohoku arc most of the intraplate deformations including the much folding deformations observed in the inner zone are produced from within an interseismic transient elastic loading at a strongly coupled locked japan trench would not be needed the observed ongoing extensive ductile folding deformation in the inner zone of tohoku may mean that the geodetic strain rates causing shortening at 2 3 cm yr probably reflect the more correct level of the deformation which is steady permanent in ne japan as compared with seismic faulting data which indicate 0 5 cm yr shortening the calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework the tectonic stress state in ne japan as part of the okhotsk plate could mostly be influenced by the okhotsk plate which is extruding southward to lessen the significant accumulated contractional deformation in ne asia in the verkhoyansk cherskii mountains the principal strain rates are n s extensional essentially everywhere in ne japan as a result of the southerly extrusion except in its southernmost leading edge in the uetsu fossa magna province where the japan alps rampart rises in front of the extrusion here an e w compressional stress state prevails a second e w contractional zone is found in north central tohoku extending from the sanriku province in the outer zone to the inner zone in the japan sea side being more prevalent in the latter zone the calculated rotation rates from the geodetic flow model are clockwise cw in both of the e w contractional regions ne japan extruding southward faces buttresses in 1 the oga ojika line ool and or a crustal weakness zone between the northern and the southern halves of tohoku approx at 38 5 n latitude and especially 2 the japanese alps rampart these obstacles cause the northern and southernmost tohoku to veer to its right and rotate cw thereby setting up the e w trending compressional deformation in their respective inner zones between the ool or the 38 5 n boundary and the kanto tectonic line ktl the sense of the differential rotations is counterclockwise ccw towards the ocean to the se the northern tohoku north of the ool and the southernmost tohoku south of the ktl cannot rotate ccw towards the ocean because of the izu block s collision in the south and the relatively strong coupling along the subduction interface beneath the japan trench in the north off sanriku the relatively stronger long term coupling between the northern tohoku and the pacific plate at the sanriku coast with respect to that in off fukushima is due to a flatter subduction of the pacific slab there increasing the plates interface contact area the flattening of the subduction dip angle was caused by ccw rotation and shifting of the northern tohoku along the dextral honjo matsushima line roughly corresponding to the ool towards the pacific and overriding of the subduction zone during the formation of the japan sea

fossil soils as grounds for interpreting long term controls on ancient rivers abstract the main factors controlling fluvial systems are time initial topographic relief geology climate vegetation base level upland runoff upland drainage network hillslope morphology downstream deliveries channel behavior and pattern of deposition similar factors control soil formation in drainage basins climate organisms topographic relief parent material and time effects of these factors may be preserved as well or better in fossil soils of alluvial sequences as in sedimentary structures facies and mineralogy of paleochannels for example former rainfall may be interpreted from depth to the top of the calcic horizon from percent clay from percent of different kinds of clay minerals from quartz feldspar ratio from hue and from identification of fossil soils interpretation of the role of these factors in producing a particular stratigraphic section should take into account its resolution the proportion of geological time represented temporal completeness of original sediment preserved lithological completeness and of original fossils preserved paleontological completeness temporal and lithological completeness can be estimated by comparison with the most likely rates of sediment accumulation and most likely thicknesses respectively for pertinent sedimentary environments and time scales paleontological completeness can be estimated by comparing the preserved fossils with expectations based on former ecosystems indicated by fossil soils likely controls and resolution of a sequence of eocene and oligocene fossil soils from badlands national park south dakota were studied as a guide to the periodicity and causes of episodic sedimentation there short term episodicity and filtering of sedimentation events of particular magnitude were apparent from superposition of paleosols but resolution of the sequence was not sufficient to permit a detailed analysis of their individual causes long term paleoenvironmental changes and four episodes of erosional downcutting could be recognized all four occasions of landscape instability and erosion were times of drier climate and sparser vegetation than usual local uplift and supply of volcanic ash were contributing factors in some episodes of erosion when allowances are made for time scales and completeness of sequences of fossil soils they can be useful indicators of changes in former environment biota and fluvial regimen