the permian triassic transition and the onset of mesozoic sedimentation at the northwestern peri tethyan domain scale palaeogeographic maps and geodynamic implications the main aim of this paper is to review middle permian through middle triassic continental successions in european secondly areas of middle late permian sedimentation the permian triassic boundary ptb and the onset of triassic sedimentation at the scale of the westernmost peri tethyan domain are defined in order to construct palaeogeographic maps of the area and to discuss the impact of tectonics climate and sediment supply on the preservation of continental sediment at the scale of the western european peri tethyan basins the upper permian is characterised by a general progradational pattern from playa lake or floodplain to fluvial environments in the northern variscan belt domain areas of sedimentation were either isolated or connected to the large basin which was occupied by the zechstein sea in the southern variscan belt during the late permian either isolated endoreic basins occurred with palaeocurrent directions indicating local sources or basins underwent erosion and or there was no deposition these basins were not connected with the tethys ocean which could be explained by a high border formed by corsica sardinia palaeorelief and even parts of the kabilia microplate the palaeoflora and sedimentary environments suggest warm and semi arid climatic conditions at the scale of the whole study area an unconformity more or less angular is observed almost everywhere between deposits of the upper permian and triassic except in the central part of the germanic basin the sedimentation gap is more developed in the southern area where in some basins upper permian sediment does not occur the large sedimentary supply erosion and or lack of deposition during the late permian as well as the variable palaeocurrent direction pattern between themiddle late permian and the early triassic indicate a period of relief rejuvenation during the late permian during the induan all the intra belt basins were under erosion and sediment was only preserved in the extra belt domains the northern and extreme southern domains in the northern domain the central part of the germanic basin sediment was preserved under the same climatic conditions as during the latest permian whereas in the extreme southern domain it was probably preserved in the tethys ocean implying a large amount of detrital components entering themarinewaters mesozoic sedimentation began in the early olenekian the ephemeral fluvial systems indicate arid climatic conditions during this period three distinct areas of sedimentation occur a northern and southern domain separated by an intra belt domain the latter accumulated sediments during the early middle permian and experienced erosion and or no deposition conditions between the middle late permian and the beginning of mesozoic sedimentation dated as anisian to hettangian at the top of the lower triassic another tectonically induced more or less angular unconformity is observed the hardegsen unconformity which is dated as intra spathian and is especially found in the north european basins this tectonic activity created new source areas and a new fluvial style with marine influences at the distal part of the systems during the anisian and ladinian continental sedimentation was characterised by a retrogradational trend in other words the fluvial system evolved into fluvio marine environments attesting to a direct influence of the tethys ocean in the southern and northern domains both at the end of the olenekian spathian and during the anisian the presence of palaeosols micro andmacrofloras indicate less arid conditions throughout this domain

bedload transported pedogenic mud aggregates in the lower old red sandstone in southwest wales siltstones which exhibit large scale cross stratification and three dimensional bedforms in the ridgeway conglomerate formation are interpreted as partly representing bedload transported pedogenic mud aggregates the siltstones contain mixed layer swelling clays abundant desiccation cracks calcrete nodules and pseudoanticlinal slip planes which suggest the presence of vertic palaeosols and a hot seasonal climate compaction obliterated much of the original mud aggregate texture which is retained only where quartz grains surround individual aggregates

ice cores record significant 1940s antarctic warmth related to tropical climate variability although the 20th century warming of global climate is well known climate change in the high latitude southern hemisphere sh especially in the first half of the century remains poorly documented we present a composite of water stable isotope data from high resolution ice cores from the west antarctic ice sheet this record representative of west antarctic surface temperature shows extreme positive anomalies in the 1936 45 decade that are significant in the context of the background 20th century warming trend we interpret these anomalies previously undocumented in the high latitude sh as indicative of strong teleconnections in part driven by the major 1939 42 el nino these anomalies are coherent with tropical sea surface temperature mean sh air temperature and north pacific sea level pressure underscoring the sensitivity of west antarctica s climate and potentially its ice sheet to large scale changes in the global climate

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

freshwater carbonates within a late triassic siliciclastic fluvial system in a gondwana rift basin the maleri formation india abstract spring related carbonates are valuable repositories for information on physical and biotic environments of the past however for mesozoic and earlier records their use is limited due to their low preservation potential and difficulties in accurate identification of the carbonate type this study aims to characterise the source of carbonate clasts preserved as thin beds of cross bedded grainstones in late triassic siliciclastic fluvial deposits the maleri formation pranhita godavari rift basin india the microfabric and stable isotopic compositions of the grainstones and thin and discontinuous beds of impure limestones of this formation are presented here these features help in identifying the freshwater carbonate precipitating environments that existed in an ancient continental rift basin though such deposits are not primarily preserved in this case the microfabric of the carbonate grains provides evidence for carbonate precipitation in aquatic environment related to karstic springs taking together the microfabric stable isotopic compositions as well as the associated geological and palaeontological information it could be shown that the calcium carbonate precipitation took place in palustrine pools related to tufa like spring systems and in alluvial swamps under a pluvial climatic setting this research thus demonstrates that carbonate grains derived from spring related carbonate deposits formed mainly near the margins of rift basins can be incorporated into nearby siliciclastics if interpreted correctly they can be used in reconstructing ancient karstic carbonate environments even when in situ primary record is not preserved therefore making it possible to access the information stored in freshwater carbonates

mudflat distal fan and shallow lake sedimentation upper vallesian turolian in the tianshui basin central china evidence against the late miocene eolian loess the tianshui basin in central china contains a thick sedimentary sequence 1400 m of continental deposits aragonian to villafranchian miocene pliocene in age intense himalayan movements around the paleogene miocene boundary triggered the uplift of mountain ranges around the tianshui basin providing the deposition site for continental sediments the sedimentary infill of the basin consists of four stratigraphic units i to iv this paper focuses on unit ii most of the accommodation space was occupied by unit i so during the sedimentation of unit ii the morphology of the basin was relatively flat promoting the development of wide distal fan mudflat areas and wide shallow lakes deposits include red mudstones pedogenic and groundwater calcretes reworked calcrete deposits sheet floods fluvial channels rippled sandstones siltstones ooidal peloidal packstones palustrine limestones bioturbated marls and intraclastic limestones marls the characteristics and organization of the deposits indicate the gradual transition from alluvial to lake environments within the distal fan mudflat the deposition of reworked calcrete clasts as one of the most striking facies of the basin may be attributed to substantial recycling of calcrete levels and red clays at the lake margins the presence of ooids and palustrine limestones suggests the possibility of ramplike margins within different energy settings the origin of some of the deposits of the basin s qa i section is under discussion and their consideration as eolian has been recently proposed however we believe this possibility is precluded by the characteristics of the deposits our proposal has important implications for revising the interpretation of miocene paleoclimatic conditions in central asia

comparison of lacustrine successions and their palaeohydrological implications in two sub basins of the triassic cuyana rift argentina fil benavente cecilia andrea consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet mendoza instituto argentino de nivologia glaciologia y ciencias ambientales provincia de mendoza instituto argentino de nivologia glaciologia y ciencias ambientales universidad nacional de cuyo instituto argentino de nivologia glaciologia y ciencias ambientales argentina

could acidity be the reason behind the early triassic biotic crisis on land abstract in recent years there is growing evidence of the importance of the smithian spathian early triassic ecological crisis to explain the delayed recovery of life after the permian triassic boundary mass extinction this study focuses on sedimentary continental rocks of middle permian to middle triassic age from four different peritethys basins in subequatorial latitudes similar distribution patterns of aluminum phosphate sulfate aps minerals contents in these rocks in the four studied basins provide evidence of increased acidity during the smithian spathian transition coinciding with a lack of indicators of organic activity in the same interval thus this period of high acidity on land may have been one of the causes of this biological crisis based on the quantification of aps minerals in the studied sedimentary sequences we propose that it was not until acidity in the environment diminished that biotic recovery was possible aps data may also be useful to interpret other past biotic crises

stratigraphical and palaeogeographical significance of the continental sedimentary transition across the permian triassic boundary in spain abstract the permian triassic transition a time of phenomenal palaeoenvironmental and palaeogeographical change represents the largest episode of mass extinctions known to palaeontologists this episode is however very poorly understood and a lack of sediments and palaeontological data particularly in the continental record is a feature common to every basin despite compelling information on the continental permian triassic boundary ptb emerging from recent efforts evaluating vertebrate evolution fungal events and isotope curves results are still insufficient to make any valuable correlations among continental basins and are even less appropriate for relating sediments of continental to those of marine origin the present report discusses and attempts to locate the ptb in the basins of iberia and balearic islands through an analysis of the palaeontological and sedimentary record across the permian triassic transition the aim of the paper is to contribute to our present knowledge of the palaeogeographical and stratigraphical significance of the permian and triassic continental units of western europe the present day iberian ranges catalonian ranges and balearic islands hold the most complete late permian early triassic sedimentary record in iberia this record consists of alluvial sediments mainly of braided fluvial systems corresponding to the saxonian and buntsandstein facies all the units examined so far have been dated through palynological associations the two saxonian facies formations are of thuringian age although the lower one shows some palynological elements of autunian affinities the buntsandstein units range from thuringian to anisian in age there being no evidence up to now of the scythian in iberia the exact position of the ptb in iberia is up to now impossible to pinpoint with the precision of the marine series sedimentary characteristics and palynological data in the iberian ranges point that it lies at the sedimentary interval 10 to 30 m thick formed by the upper member of the la hoz del gallo formation and the lowermost beds of the canizar formation or its time equivalent the prades and eramprunya units in the catalonian ranges and the asa and b 1 in the balearic islands we compare a normalized standard late permian middle triassic column of the iberian ranges with standards from western and central europe and the southern urals using recent permian time scales a palaeogeographic essay map of the permian triassic transition is provided for the iberian plate the plate was located in a northern subtropical position 200 400 km from the westernmost tethys coast as part of the central pangean mountain range comprised of the appalachian mauretanide variscan orogenic belts of estimated altitudes 2000 4000 m based on this palaeogeographic location sedimentary characteristics and the main wind flows established for the tethys we can infer conditions of high precipitation dominated by monsoon and seasonal regimes with isolated semiarid areas for the iberian plate during the transition

stable isotope air temperature relationships in ice cores from dolleman island and the palmer land plateau antarctic peninsula whilst stable isotope analysis of ice cores yields the best quantitative evidence for past climate there remains considerable uncertainty about the detailed relationship between the isotopic composition and air temperature analysis of two ice cores from the antarctic peninsula a 47 2 m core from the palmer land plateau 74 oi s 70 38 w and a 32 m core from dolleman island 70035 2 s 60055 5 w has shown that an oxygen isotope temperature relationship exists at a resolution of inter annual variations during the period 1938 86 all the major regional temperature anomalies known from climatic records at several stations are visible in the isotope profiles including the overall temperature increase between 1960 and 1980 an isotope temperature gradient of 0 5 o 6 c is indicated for the climatic interpretation of isotopic fluctu

soil landscape and climatic relationships in the middle miocene of the madrid basin the miocene alluvial lacustrine sequences of the madrid basin spain formed in highly varied landscapes the presence of various types of palaeosols allows assessment of the effects of local and external factors on sedimentation pedogenesis and geomorphological development in the northern more arid tectonically active area soils were weakly developed in aggrading alluvial fans dominated by mass flows reflecting high sedimentation rates in more distal parts of the fans and in playa lakes calcretes and dolocretes developed the former were associated with mg poor fan sediments while the latter formed on mg rich lake clays exposed during minor lake lowstands the north east part of the basin had a less arid climate alluvial fans in this area were dominated by stream flood deposits sourced by carbonate terrains floodplain and freshwater lake deposits formed in distal areas the high local supply of calcium carbonate may have contributed to the preferential development of calcretes on the fans both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources palaeosols also developed on pond and lake margin carbonates and led to the formation of palustrine limestones the spatial distributions and stratigraphies of palaeosols in the madrid basin alluvial fans suggest that soil formation was controlled by local factors these palaeosols differ from those seen in quaternary fans which are characterized by climatically induced periods of stability and instability

antarctic temperatures over the past two centuries from ice cores 1 we present a reconstruction of antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high resolution precisely dated ice cores both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability with the dominant pattern being anti phase anomalies between the main antarctic continent and the antarctic peninsula region comparative analysis of the instrumental southern hemisphere sh mean temperature record and the reconstruction suggests that at longer timescales temperatures over the antarctic continent vary in phase with the sh mean our reconstruction suggests that antarctic temperatures have increased by about 0 2 c since the late nineteenth century the variability and the long term trends are strongly modulated by the sh annular mode in the atmospheric circulation

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

sequence stratigraphic analysis and paleogeographic interpretation of the buntsandstein and muschelkalk facies permo triassic in the se iberian range e spain abstract the iberian ranges is an alpine structure trending nw se in central spain they first appeared as small intracratonic basins in the early permian and experienced different periods of extensional tectonics during the mesozoic and cenozoic controlled by ancient hercynian or older fracture systems and at least two periods of compressive inversion tectonics the permian and triassic of the se iberian ranges are of germanic type within the prevailing buntsandstein and muschelkalk facies eight formations are recognized pollen and spore assemblages and some ammonoid horizons allow for age assessments ranging from thuringian late permian to carnian late triassic two phases of sedimentation can be distinguished during the early extensional period the first phase rift phase led to the development of the lower buntsandstein facies bounded by two angular unconformities and subdivided into two depositional sequences ds 1 and ds 2 the lower one is dominated by alluvial fans deposited in half grabens and the upper one by sandy braided rivers in more symmetrical grabens the second phase thermal or flexural subsidence phase led to the deposition of the uppermost buntsanstein rot and muschelkalk facies mostly shallow marine carbonates subdivided into two depositional sequences ds 3 and ds 4 with well developed lowstand transgressive and highstand systems tracts lst tst and hst intervals the criteria for separating systems tracts and the interplay of tectonics eustatism and rate of sedimentation are discussed ds 3 and ds 4 broadly correspond to 2 1 and 2 2 third order cycles but their limits are about 3 4 m y younger this may be explained by local tectonic factors

spatial and temporal evolution of a terminal fluvial fan system the permian organ rock formation south east utah usa the recognition of terminal fluvial systems otherwise termed terminal fans or distributary fluvial fan systems preserved in the ancient rock record is based primarily on the recognition of facies characteristics indicative of a progressive downstream decrease in i fluvial discharge ii channel depth and width iii lateral and vertical connectivity of channel fill elements and iv evidence for channellized flow and a systematic increase in i evidence for sheetflood deposition ii aeolian and or playa deposits and iii channel bifurcation however despite these criteria having been applied previously to a variety of outcrop successions there is still no unifying facies model that adequately accounts for the complex stratigraphic architectural relationships expected for such systems based on the varied styles of fluvial activity and system interaction known from modern examples moreover few previous studies have given significant consideration to the long term temporal evolution of terminal fluvial fans these issues are addressed by this study of the permian leonardian artinskian organ rock formation of the paradox basin south east utah a detailed stratigraphic framework based on 84 sedimentary logs demonstrates proximal to distal variations in sedimentary style integration of these data with high resolution architectural panels depicting the geometry and facies characteristics of individual fluvial elements has enabled the development of a series of depositional models that account for both the spatial and temporal evolution of the system and which are representative of i initial progradation of the fluvial system into the paradox foreland basin ii retreat of the fluvial system and expansion of a distal aeolian dune system iii the final phase of fluvial progradation following aeolian dune deflation and iv the final retrogradation of the fluvial system back towards the hinterland

nonmarine sequence stratigraphy updip expression of sequence boundaries and systems tracts in a high resolution framework cenomanian dunvegan formation alberta foreland basin canada ten allomembers labeled j a have been mapped in the deltaic dunvegan formation using 2340 wells and 63 outcrop sections each allomember spans about 200 k y is bounded by regional transgressive surfaces and consists of 3 10 component shingles apparently of autogenic origin allomembers h e are discussed in this article their internal stacking patterns and bounding surfaces permit interpretation as depositional sequences sequences h f have a sigmoidal prismatic geometry downlap to the southeast and thin northwest onto the coastal plain no differential thickening exists toward the orogen in the southwest in contrast sequence e thickens markedly toward the northwest the tabular geometry of sequences h f suggests accommodation was controlled by sea level change whereas the wedge geometry of sequence e suggests significant tectonic tilting subaerial unconformities that bound valleys and extend onto adjacent interfluve paleosols can be traced 120 330 km updip into outcrop the base of each sequence is characterized by shoreline backstep of 80 150 km transgressive and highstand shingles in each sequence comprise marine deltaic deposits that pass landward into coastal plain strata falling stage shingles offlap seaward with little or no nonmarine equivalents updip whereas lowstand shingles show renewed coastal onlap in outcrop three nonmarine systems tracts are recognized 1 a channel dominated low accommodation systems tract fills valleys up to 35 m deep and is equivalent to the early transgressive systems tract begin page 1968 2 a lacustrine dominated high accommodation systems tract comprises mudstone enclosing ribbon channel sandstones blankets interfluves and forms the bulk of each sequence it is equivalent to late transgressive and early highstand systems tracts 3 a paleosol dominated low accommodation systems tract occupies the upper part of each sequence and is capped by the sequence boundary it is equivalent to the late highstand systems tract sequence bounding interfluve paleosols represent tens of thousands of years of pedogenesis related to slow aggradation followed by fluvial entrenchment and clastic bypass and represent the late highstand falling stage lowstand and early transgressive systems tracts coastal plain deposits record only part perhaps

ice core evidence for significant 100 year regional warming on the antarctic peninsula we present a new 150 year high resolution stable isotope record delta o 18 from the gomez ice core drilled on the data sparse south western antarctic peninsula revealing a similar to 2 7 degrees c rise in surface temperatures since the 1950s the record is highly correlated with satellite derived temperature reconstructions and instrumental records from faraday station on the north west coast thus making it a robust proxy for local and regional temperatures since the 1850s we conclude that the exceptional 50 year warming previously only observed in the northern peninsula is not just a local phenomena but part of a statistically significant 100 year regional warming trend that began around 1900 a suite of coupled climate models are employed to demonstrate that the 50 and 100 year temperature trends are outside of the expected range of variability from pre industrial control runs indicating that the warming is likely the result of external climate forcing citation thomas e r p f dennis t j bracegirdle and c franzke 2009 ice core evidence for significant 100 year regional warming on the antarctic peninsula geophys res lett 36 l20704 doi 10 1029 2009gl040104

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

landscape and depositional controls on palaeosols of a distributive fluvial system upper cretaceous brazil abstract the stratigraphic record of distributive fluvial systems is commonly characterised by frequent and complex interstratification of palaeosols among channel and overbank deposits however current models focus primarily on sedimentation and pay only limited attention to palaeopedogenesis thereby failing to incorporate important palaeoenvironmental and stratigraphic information this study proposes a pedosedimentary model for distributive fluvial systems that depicts and accounts for two palaeopedogenetic trends one downdip in relation to distality from the fan apex and one along strike in relation to distance from active channel belts palaeosols are reported in detail from an upper cretaceous succession of the bauru basin southeastern brazil through the application of macro micromorphological and geochemical studies combined with facies and architectural element analyses of sediments in the downdip palaeopedogenetic trend the proximal zone of the depositional system is characterised by a dominance of well drained inceptisols that develop on amalgamated channel fills in the medial zone inceptisols occur interlayered with overbank deposits containing entisols and poorly drained vertisols the distal zone preserves more mature and poorly drained inceptisols developed on deposits of overbank and sporadic distal channel fills these pedotypes show an increase in maturity and hydromorphism moving away from the apex to the fan toe this is likely linked to i the progressive approach of the topographic surface to the water table and ii the average increase in distance to an active channel belt in distal locations the along strike palaeopedogenetic trend culminates in poorly developed palaeosols in floodplain regions that correspond to topographic depressions located between channel belts and which were subject to recurrent floods because palaeopedogenesis in the floodplain region is penecontemporaneous to sedimentation pedotypes show an increase in maturity bioinduced calcification and hydromorphism with distance from the active channels they pass laterally from entisols and inceptisols near active channels to vertisols away from active channels conversely following avulsion abandoned channel belts remain as topographically elevated alluvial ridges located at some distance from the newly active channels and positioned above the water table and this leads to the development of better drained and better developed inceptisols relative to pedotypes of the floodplain region overall both palaeopedogenetic trends demonstrate the overriding controls of topography sedimentation rate and parent material on pedogenesis with only minor climatic influence this work offers a novel pedosedimentary model for distributive fluvial systems and highlights the palaeoenvironmental significance of palaeosol trends providing new constraints for the recognition of distributive fluvial systems in the rock record

petrology of caliche derived peloidal calcirudite calcarenite in the late triassic maleri formation of the pranhita godavari valley south india abstract the maleri formation late triassic of the pranhita godavari valley south india is a continental red bed sequence represented mainly by red clays with a few sheet like bodies of channel fill sandstone crudely bedded and cross bedded peloidal calcirudite calcarenite occurs at the base of fining upward sequences in multistorey sand bodies and also as discrete solitary lenses within red clay the calcirudite calcarenite consists mainly of calcite cemented spherical peloids which are made up of micrite and microspary calcite with microfabrics characteristic of caliche pure calcitic peloids are often reddened and those having a quartzose component are generally not red the paucity of broken and abraded peloids close association with intraformational materials and other evidence indicate a local source of the peloids the microfabric of the peloids suggest their derivation from caliches available evidence favours a pedogenic origin for the peloids which mostly developed by displacive precipitation in a set up of alternate wetting and drying the lack of in situ caliche profiles in the maleri sequence and the rarity of compound grains imply that the peloids were derived from incipient caliche profiles which were localized at or near the surface and were completely stripped off by subsequent erosion the ghost caliche profiles suggest the presence of periodically stable levels in the maleri alluvial plain and low to moderate rates of alluviation the residence intervals of channels were long enough to allow incipient pedogenesis in the temporarily stable inactive areas in the present context the predominance of smectite in fines the poor floral content the maleri faunal assemblage and the paucity of evaporites point to a low seasonal rainfall in a semi arid climatic environment

identification of an anastomosing river system in the early cretaceous khorat basin northeastern thailand using stratigraphy and paleosols abstract the phu kradung and phra wihan formations of the early cretaceous khorat group were investigated to characterize the depositional system and paleoclimate based on stratigraphy paleosol features paleosol profiles and reworked deposits the sediments of both formations are classified into 12 facies on the basis of their primary depositional attributes such as bedding grain size texture and sedimentary structures furthermore these facies are grouped into eight architectural elements based on stratigraphic relationships and outcrop scale macroforms the proportions of each architectural element indicate that the depositional system was that of an anastomosing river the anastomosing river system in the studied section is characterized by a high rate of vertical floodplain aggradation and the development of a relatively stable crevasse channel paleosols are developed mainly in floodplain deposits and are characterized by the development of calcretes a semi arid to sub humid paleoclimate is deduced from the occurrence of the calcretes in addition their microstructures suggest that these calcretes were formed under several different conditions with micritic carbonate precipitating under relatively arid climates and alveolar septal structures under semi arid to sub humid conditions using the thicknesses of the calcrete horizons we conclude that the difference in the amount of precipitation between the wet and dry periods was highly variable without any order during deposition of the studied section the thicknesses of intervals between successive calcrete horizons indicate that the inflow of fine materials occurred randomly across the floodplain partly superimposed multiple calcrete horizons were developed during periods of low sediment supply a random deposition of floodplain sediments appears to characterize the anastomosing river system of the khorat basin

climatic versus halokinetic control on sedimentation in a dryland fluvial succession fluvial systems and their preserved stratigraphic expression as the fill of evolving basins are controlled by multiple factors which can vary both spatially and temporally including prevailing climate sediment provenance localized changes in the rates of creation and infill of accommodation in response to subsidence and diversion by surface topographic features in basins that develop in response to halokinesis mobilized salt tends to be displaced by sediment loading to create a series of rapidly subsiding mini basins each separated by growing salt walls the style and pattern of fluvial sedimentation governs the rate at which accommodation becomes filled whereas the rate of growth of basin bounding salt walls governs whether an emergent surface topography will develop that has the potential to divert and modify fluvial drainage pathways and thereby dictate the resultant fluvial stratigraphic architecture discerning the relative roles played by halokinesis and other factors such as climate driven variations in the rate and style of sediment supply is far from straightforward diverse stratigraphic architectures present in temporally equivalent neighbouring salt walled mini basins demonstrate the effectiveness of topographically elevated salt walls as agents that partition and guide fluvial pathways and thereby control the loci of accumulation of fluvial successions in evolving mini basins drainage pathways can be focused into a single mini basin to preserve a sand prone fill style whilst leaving adjoining basins relatively sand starved by contrast over the evolutionary history of a suite of salt walled mini basins region wide changes in fluvial style can be shown to have been driven by changes in palaeoclimate and sediment delivery style the triassic moenkopi formation of the south western usa represents the preserved expression of a dryland fluvial system that accumulated across a broad low relief alluvial plain in a regressive continental to paralic setting within south eastern utah the moenkopi formation accumulated in a series of actively subsiding salt walled mini basins ongoing evolution of which exerted a significant control on the style of drainage and resultant pattern of stratigraphic accumulation drainage pathways developed axial parallel to salt walls resulting in compartmentalized accumulation of strata whereby neighbouring mini basins record significant variations in sedimentary style at the same stratigraphic level despite the complexities created by halokinetic controls the signature of climate driven sediment delivery can be deciphered from the preserved succession by comparison with the stratigraphic expression of part of the system that accumulated beyond the influence of halokinesis and this approach can be used to demonstrate regional variations in climate controlled styles of sediment delivery

climate since ad 1510 on dyer plateau antarctic peninsula evidence for recent climate change a 480 year record of the oxygen isotope ratios dust content chemical species and net accumulation from ice cores drilled in 1989 90 on dyer plateau in the antarctic peninsula is presented the continuous analyses of small sub annual samples reveal well preserved annual variations in both sulfate content and 18o thus allowing an excellent time scale to be established this history reveals a recent pronounced warming in which the last two decades have been among the warmest in the last five centuries furthermore unlike in east antarctica on dyer plateau conditions appear to have been fairly normal from ad 1500 to 1850 with cooler conditions from 1850 to 1930 and a warming trend dominating since 1930 reconstructed annual layer thicknesses suggest an increase in net accumulation beginning early in the 19th century and continuing to the present this intuitive conflict between increasing net accumulation and depleted 18o cooler climate in the 19th century appears widespread in the peninsula region and challenges our understanding of the physical relationships among moisture sources air temperatures and snow accumulation the complex meteorological regime in the antarctic peninsula region complicates meaningful interpretation of proxy indicators and results in a strong imprint of local high frequency processes upon the larger scale climate picture

glacier acceleration and thinning after ice shelf collapse in the larsen b embayment antarctica 1 ice velocities derived from five landsat 7 images acquired between january 2000 and february 2003 show a two to six fold increase in centerline speed of four glaciers flowing into the now collapsed section of the larsen b ice shelf satellite laser altimetry from icesat indicates the surface of hektoria glacier lowered by up to 38 6 m in a six month period beginning one year after the break up in march 2002 smaller elevation losses are observed for crane and jorum glaciers over a later 5 month period two glaciers south of the collapse area flask and leppard show little change in speed or elevation seasonal variations in speed preceding the large post collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics

shallow burial dolomitisation of middle upper permian paleosols in an extensional tectonic context se iberian basin spain controls on temperature of precipitation and source of fluids this work is focused on carbonate paleosols developed in three stratigraphic sections landete talayuelas and henarejos of themiddle late permian alcotas formation in the se iberian basin the alcotas formation of alluvial origin was deposited in semi connected half grabens developed during the early stages of the permian triassic rifting stage that affected the iberian basin the studied sections were located in two of these half grabens the henarejos section being much closer to the basin boundary fault than the other two sections the mineralogy and texture of the carbonate precursor of paleosols in the three studied sections are not preserved because original carbonate is replaced by coarse crystals of dolomite and or magnesite dolomite crystals are typically euhedral displaying rhombohedral shapes and reddish luminescence although in the henarejos section dolomite displays non planar boundaries and frequently saddle habit micas are deformed and adapted to dolomite crystals which in turn are affected by stylolites suggesting that dolomite precipitated before mechanical and chemical compaction carbon and oxygen isotopic compositions of dolomite fromthe three sections showdifferent values 13cvpdb mean values 6 7 5 5 and 7 5 18ovpdb mean values 4 0 5 6 and 8 2 at landete talayuelas and henarejos sections respectively the 87sr 86sr ratios are similar in the three sections yielding values between 0 71391 and 0 72213 the petrographic and geochemical features of dolomite in the three studied sections suggest precipitation fromsimilar fluids and during shallow burial diagenesis assuming that theminimum temperature for dolomite precipitation in the henarejos sectionwas 60 c as suggested by the presence of non planar saddle habit and that the dolomitizing fluid had similar 18o values at the three localities then dolomite in the talayuelas and landete sections precipitated at temperatures around 16 and 25 c cooler respectively in addition the 18ovsmow values of the water from which dolomite precipitated would have ranged between 0 3 and 2 9 dolomite is partially or totally replaced by non to dark dull luminescent magnesite in the landete and talayuelas sections magnesite crystals are affected by stylolites indicating that it precipitated before chemical compaction the 13c mean values are 6 5 and 6 0 and the 18ovpdb mean values are 6 7 and 7 8 in the landete and talayuelas sections respectively the 87sr 86sr ratios of magnesite are similar in both sections yielding values between 0 71258 and 0 72508 this suggests that they probably precipitated from similar fluids during progressive burial and at higher temperatures than dolomites at the same sections assuming thatmagnesite precipitated froma fluid with similar 18o values in both sections then it had to precipitate at a temperature around 8 c higher in talayuelas than in the landete section dolomitisation and magnesite precipitation probably occurred via reflux of saline to hypersaline brines from the overlying mid late triassic muschelkalk and or keuper facies the temperatures inferred for dolomite precipitation however are too high for shallow burial if a normal geothermal gradient is applied thus it can be inferred that salinefluidswere heated as theyflowed through the syn sedimentary extensional faults that controlledmiddle permian to middle triassic sedimentation consequently fluidswould have been at higher temperatures near the henarejos area which was closer to the basin boundary fault than at the talayuelas and landete areas whichwere situated further away this contention is in agreement with recent studies which demonstrate that an important thermal event took place during late triassic early jurassic times in the iberian peninsula

changes in antarctic temperature wind and precipitation in response to the antarctic oscillation output of a 14 year integration with a high resolution 55 km 55 km regional atmospheric climate model is used to study the response of antarctic near surface climate to the antarctic oscillation aao the periodical strengthening and weakening of the circumpolar vortex in the southern hemisphere in spite of the relatively short record wind temperature and precipitation show widespread and significant aao related signals when the vortex is strong high aao index northwesterly flow anomalies cause warming over the antarctic peninsula ap and adjacent regions in west antarctica and the weddell sea in contrast cooling occurs in east antarctica the eastern ross ice shelf and parts of marie byrd land most of the annual temperature signal stems from the months march august the spatial distribution of the precipitation response to changes in the aao does not mirror temperature changes but is in first order determined by the direction of flow anomalies with respect to the antarctic topography when the vortex is strong high aao index the western ap becomes wetter while the ross ice shelf parts of west antarctica and the lambert glacier basin east antarctica become drier

use of micromorphology for palaeoenvironmental interpretation of complex alluvial palaeosols an example from the mill creek formation albian southwestern alberta canada abstract field observations are often not sufficient for process based interpretations of palaeosols particularly where they form parts of thick aggradational pedocomplexes within alluvial successions under such conditions micromorphology provides genetic temporal and spatial information on soil forming processes that is critical to an understanding of past environmental conditions thick alluvial successions of the albian mill creek formation contain abundant evidence of pedogenesis but few well developed palaeosol profiles and therefore provide an ideal case study in which to demonstrate the usefulness of micromorphological data for palaeoenvironmental interpretation the micromorphological features of greatest interpretive value are types of clay coatings and ferruginous segregations structure and fabric papules evidence of bioactivity and ferruginous concretions provide information on geomorphic surface stability and assist in reconstructing temporal changes in drainage conditions while individual features can provide some palaeoenvironmental information the relationships of features to one another and assemblages of features provides additional information when analysed hierarchically to establish a sequence of sedimentologic and pedogenic events a common recurring sequence of palaeoenvironmental events subject to local variations can be recognized throughout the mill creek formation the presence of illuvial clay requires that water percolated through the soil and that the soil periodically dried out so that the translocated clay was retained dark reddish clay coatings indicate clay illuviation under freely drained conditions while pale yellow and silty clay coatings suggest that phases of free drainage alternated with phases of poorly drained or saturated soil conditions the presence of iron depletion coatings iron nodules and quasiferrans indicates that these units were at least periodically saturated and the occurrence of multiple overlapping phases within single thin sections demonstrates that redox conditions fluctuated strongly suggesting development in the vadose zone recent soils containing similar assemblages of features develop under warm temperate seasonal climates alternating phases of well drained and saturated conditions on the mill creek floodplains are attributed to changing sediment supply and local palaeogeomorphology rather than to any major regional climate change this type of process based micromorphological analysis should have broad application in other complex pedogenically modified alluvial successions and similar studies would lead to a more detailed understanding of ancient palaeoenvironments

the distribution and discrimination of shallow authigenic carbonate in the pliocene pleistocene palomas basin southern rio grande rift nine types of authigenic carbonate are present in the pliocene pleistocene alluvial fan and axial fluvial sediment of the palomas half graben in the southern rio grande rift pedogenic and other vadose carbonate includes 1 pedogenic carbonate of stage ii and stage iii morphology underlying bw and bt horizons 2 mudstones in which the carbonate nodules may be pedogenic or the result of shallow groundwater invasion of the vadose zone 3 pedogenic calcic nodules and tubules in eolian sand and 4 gully bed cement of proximal fan conglomerates formed by infiltration and evaporation of surface runoff shallow groundwater carbonate exists as 5 thin 30 50 cm massive beds with an upper fringe of nodules and tubules precipitated at the water table and in the capillary fringe 6 thick 1 5 3 m massive beds deposited by lateral flow of groundwater or at springs and 7 thin 30 cm calcified root mats associated with near surface water saturated sediment or springs phreatic spar cements 8 occupy the interstices of conglomerates and sandstones and locally exist as 9 oriented concretions groundwater carbonates are best developed near the toes of the large hanging wall derived alluvial fans whereas phreatic cement preferentially exists in footwall derived alluvial fan conglomerates pedogenic carbonate is distinguished from groundwater carbonate by the association with other diagnostic paleosol horizons a predominantly vertical arrangement of root traces peds desiccation cracks and calcic tubules and by gradational contacts the 13 c and 18 o values are similar among pedogenic and shallow groundwater carbonate although locally nodules in eolian sand and gully bed cement have higher 18 o values perhaps due to the effects of evaporation some phreatic cements may be distinguished from pedogenic and shallow groundwater carbonate by lower values of 13 c and 18 o authigenic carbonate in footwall derived alluvial fan sediment has consistently higher values of 13 c than that in hanging wall derived sediment which may reflect differences in vegetative type and or density on either side of the basin

evolution of an ancient coastal plain palaeosols interfluves and alluvial architecture in a sequence stratigraphic framework cenomanian dunvegan formation ne british columbia canada to date discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on floodplains has primarily been from a conceptual standpoint few case studies are available against which to test ideas one hundred and thirty metres of non marine strata of the dunvegan formation were examined in 14 closely spaced sections in the canyon of the kiskatinaw river ne british columbia canada this site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments fluvial channels in the kiskatinaw river section are of two types small single storey very fine to fine grained sandstone ribbons with w t ratios 30 are interpreted as the deposits of meandering rivers filling incised valleys interchannel facies include the deposits of crevasse channels and splays lakes floodplains and palaeosols floodplain palaeosols consist of laterally heterogeneous simple palaeosol profiles and pedocomplexes similar to modern entisols inceptisols and hydromorphic soils interfluve sequence bounding palaeosols adjacent to incised valleys are laterally continuous up to 3 m thick and can be reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure colour degree of rooting and 3 micromorphological features such as evidence of bioturbation clay coatings ferruginous features and sphaerosiderite interfluve palaeosols are similar to modern alfisols and ultisols correlation of the local stratigraphic succession with the regional sequence stratigraphic framework based on 2340 well logs and 60 outcrop sections shows that the vertical changes in coastal plain character more coals and lakes vs more pedogenesis can be related to relatively high frequency base level cycles eustatic that are expressed as transgressive regressive marine cycles in downdip areas regional isopach maps show that these cycles were progressively overprinted and modified by an increasing rate of tectonic subsidence in the north and west the character of palaeosols developed on aggrading floodplains primarily reflects local sediment supply and drainage in contrast well developed interfluve palaeosols record pedogenesis during periods of reduced or negative accommodation base level fall vertical changes in floodplain palaeoenvironments and palaeosol types reflect changes in accommodation rate the detailed micromorphological analysis of interfluve palaeosols represents a powerful application of an under used technique for the recognition of key surfaces in the geological record this has broad implications for non marine sequence stratigraphy

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

calcretes in semi arid alluvial systems formative pathways and sinks late quaternary deposits in gujarat western india show an abundant development of calcretes three major sinks of carbonate in the alluvial deposits are recognized 1 groundwater calcretes 2 pedogenic calcretes and 3 calcrete conglomerates groundwater calcretes originate from carbonate saturated waters travelling preferentially along stratification planes pedogenic calcretes form through soil forming processes typically in extra channel areas calcrete conglomerates occur as ribbons sheets and lenses due to the reworking of both pedogenic as well as groundwater calcretes as a result a pathway of calcretization develops that has the route groundwater calcrete to pedogenic calcrete to calcrete conglomerate the formation of pedogenic calcretes over sediments containing groundwater calcretes demonstrates that 1 apart from aeolian dust river waters are also a major source of carbonate and 2 pedogenic carbonates may attain large sizes at accelerated rates due to the presence of pre existing groundwater calcretes consequently the maturity of a soil may be overestimated if determined by following established morphogenetic sequences

tectonically induced climate and its control on the distribution of depositional systems in a continental foreland basin cloverly and lakota formations lower cretaceous of wyoming u s a abstract continental sediments of the cloverly and lakota formations lower cretaceous in wyoming are subdivided into three depositional systems perennial to intermittent alluvial intermittent to ephemeral alluvial and playa chert bearing sandstones conglomerates carbonaceous mudrocks blocky mudrocks and skeletal limestones were deposited by perennial to intermittent alluvial systems carbonaceous mudrocks contain abundant wood fragments cuticle and cortical debris and other vascular plant remains representing deposition in oxbow lakes abandoned channels and on floodplains under humid to seasonal conditions intraformational conglomerates sandstones bioturbated and blocky mudrocks with caliche nodules and bioturbated limestones characterize deposition in intermittent to ephemeral alluvial systems bioturbated limestones are encased in bioturbated mudrocks with abundant pseudo slickensides the presence of caliche nodules in some of the blocky to bioturbated mudrocks is consistent with supersaturation and precipitation of calcium carbonate from groundwater under semi arid conditions caliche nodules pseudo slickensides and carbonate rich floodplain sediments are interpreted to have been deposited by intermittent to ephemeral alluvial systems under seasonal to semi arid climatic conditions laminated mudrocks siltstones vuggy carbonates bedded to nodular evaporites pebbly mudrocks and diamictites were deposited in evaporative alkaline lakes or playas pebbly mudrocks and diamictites are interpreted to represent deposition from channelized and unchannelized hyperconcentrated flows on a playa resulting from intense rain events within the basin the areal abundance and distribution of these depositional systems change systematically across the overfilled portion of the early cretaceous cordilleran foreland basin in wyoming the lower part a interval of the cloverly and lakota formations is characterized by deposits of perennial to intermittent rivers that existed 300 to 1000 km east of the sevier fold and thrust belt proximal to the sevier fold and thrust belt the a interval of the cloverly formation and upper ephraim formation of the gannett group are typified by deposits of intermittent to ephemeral rivers and their associated floodplains in the middle part b interval of the cloverly formation intermittent to ephemeral alluvial systems expand to 600 km into the basin the upper part c interval of the cloverly formation is characterized by playa deposits in the bighorn and wind river basins and intermittent to ephemeral alluvial deposits along the front of the ancestral sevier mountains deposits of perennial to intermittent alluvial systems in the c interval of the cloverly and lakota formations are restricted to the black hills region almost 900 km to the east of the sevier mountains the change in the areal distribution of depositional systems through time within this continental foreland basin may be attributed to the development of a rain shadow associated with the uplift of the sevier mountains in the early cretaceous

extending the antarctic meteorological record using ice sheet temperature profiles abstract two vertical ice temperature profiles from locations in the antarctic peninsula unaffected by meltwater are presented a simple time dependent heat diffusion advection model is used to infer broad surface temperature variations in the antarctic peninsula over the century prior to the start of local meteorological records air temperature records from two representative meteorological stations faraday and halley are used to determine the ice surface boundary conditions in the later stages of the model runs earlier temperature histories are then devised to provide best fits between the modeled and observed ice temperature profiles results of the modeling suggest that the surface temperature in the antarctic peninsula dropped by 1 6 0 2 c between the beginning of the nineteenth century and the start of the faraday record in 1944 on time scales of several decades the faraday air temperature record began during a period colder than the average and temperatures in the early 1800s were probably

esr dating of fossil shells in the middle to upper pleistocene strata in japan abstract the accuracy of the esr ages of fossil shells from the boso peninsula ooiso hills and the miyazaki plain in japan in the middle to upper pleistocene were examined the measurement test with a thermoluminescent dosimeter at the sampling point suggests that the dose rate of cosmic rays must be added to the calculated dose rate from chemical analysis the results show that the esr ages are in good agreement with the stratigraphically estimated ages however according to the chemical analysis of the mollusc shell itself several shells give an abnormally high concentration of uranium this may indicate that the shell has absorbed uranium from outside especially in sandy sediments

palaeoenvironmental significance of late permian palaeosols in the south eastern iberian ranges spain the late permian wuchiapingian alcotas formation in the se iberian ranges consists of one red alluvial succession where abundant soil profiles developed detailed petrographical and sedimentological studies in seven sections of the alcotas formation allow six different types of palaeosols with distinctive characteristics and different palaeogeographical distribution to be distinguished throughout the south eastern iberian basin these characteristics are in turn related to topographic climatic and tectonic controls the vertical distribution of the palaeosols is used to differentiate the formation in three parts from bottom to top showing both drastic and gradual vertical upwards palaeoenvironmental changes in the sections reconstruction of palaeoenvironmental conditions based on palaeosols provides evidence for understanding the events that occurred during the late permian some few millions of years before the well known permian triassic global crisis

the impact of a changing southern hemisphere annular mode on antarctic peninsula summer temperatures since the mid 1960s rapid regional summer warming has occurred on the east coast of the northern antarctic peninsula with near surface temperatures increasing by more than 2 degrees c this warming has contributed significantly to the collapse of the northern sections of the larsen ice shelf coincident with this warming the summer southern hemisphere annular mode sam has exhibited a marked trend suggested by modeling studies to be predominantly a response to anthropogenic forcing resulting in increased westerlies across the northern peninsula observations and reanalysis data are utilized to demonstrate that the changing sam has played a key role in driving this local summer warming it is proposed that the stronger summer westerly winds reduce the blocking effect of the antarctic peninsula and lead to a higher frequency of air masses being advected eastward over the orographic barrier of the northern antarctic peninsula when this occurs a combination of a climatological temperature gradient across the barrier and the formation of a fohn wind on the lee side typically results in a summer near surface temperature sensitivity to the sam that is 3 times greater on the eastern side of the peninsula than on the west sam variability is also shown to play a less important role in determining summer temperatures at stations west of the barrier in the northern peninsula similar to 62 degrees s both at the surface and throughout the troposphere this is in contrast to a station farther south similar to 65 degrees s where the sam exerts little influence

recognition of interfluve sequence boundaries integrating paleopedology and sequence stratigraphy in shallow marine and coastal plain strata sequence boundaries are easily recognized at the base of incised valley fills between valleys however it is more difficult to recognize sequence boundaries where they are expressed as interfluve paleosols we suggest that interfluve paleosols can be most reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure color and degree of rooting and 3 micromorphological features such as bioturbation fabric clay coatings ferruginous features and siderite and barite only micromorphology permits recognition of temporal changes in drainage surface stability and protracted pauses in sedimentation that typify these surfaces this three part approach has been successfully employed to identify interfluve sequence bounding paleosols in the cenomanian dunvegan formation in alberta and british columbia canada

distinguishing faults from flooding surfaces on spectral gamma ray logs elevated gamma ray emission from discrete beds in sedimentary deposits may conventionally be interpreted as representing flooding surfaces or transgressive beds potassium k uranium u or less commonly thorium th concentrations in outcrop or borehole successions cause such elevated gamma ray emission and may be linked to the presence of specific mineral hosts furthermore specific th k and th u ratios occur at correlated stratigraphic surfaces and form part of a pattern that reflects a sequence stratigraphic hierarchy spectral gamma ray logs from uncored boreholes or weathered cliffsides and acquired without full petrographic descriptions can intersect low angle faults such as thrusts our study demonstrates that bedding parallel faults can be mistaken for flooding surfaces we document the spectral gamma ray response through a range of visually obvious and cryptic faults that may serve as proxy examples for other areas finally we derive a preliminary generic model for the origin of spectral gamma ray variations in faulted sandstones limestones and metamorphic successions this shows why fluid rock interactions along bedding parallel zones of deformation generate elevated k and u and depressed th k and th u our observations may aid subsurface studies of the complex stratigraphy below thrusts

multi storey calcrete profiles developed during the initial stages of the configuration of the ebro basin s exorrheic fluvial network abstract multi storey calcrete profiles developed in the quaternary on strath terraces of the cinca and alcanadre rivers tributaries of the ebro river in ne spain two calcrete profiles tor 1 and tor 2 near the village of el tormillo show horizons with an arrangement that differs from that of commonly described calcrete profiles significant lateral changes occur in these profiles within a distance of less than 200 m reflecting their pedofacies relationship the tor 1 profile on terrace qt1 the highest and oldest consists of six horizons from bottom to top 1 coarse fluvial gravels 2 mudstones with carbonate nodules 3 a chalky horizon 4 laminar horizons including one peloidal horizon 5 a multi storey horizon formed of at least six minor sequences each of which includes a lower detrital layer a pisolithic horizon and a thin discontinuous laminar horizon these sequences indicate several cycles of brecciation and or reworking and 6 a topmost laminar and brecciated horizon also including reworked pisoliths some 200 m to the north of tor 1 horizon 5 undergoes a lateral change to channel fill deposits the infill of the channels shows a fining upwards sequence ranging from clasts of about 10 cm in diameter to red silts with sparse pebbles all the clasts come from the underlying calcrete horizons laminar horizons are interbedded with the clastic channel deposits the youngest calcrete profiles developed on terrace qt3 of the cinca river and on the qp4 and qp6 mantled pediment levels all show relatively simple profiles composed mostly of lower horizons of coated gravels with thin laminar horizons at the top most of the horizons especially the laminar ones show biogenic features such as alveolar septal structures calcified filaments biofilms spherulites micropores and needle like calcite crystals these features indicate the important role of vegetation in the formation of all the above profiles the interbedding of clastic sediments and pisolithic horizons within the tor 2 profile indicates several stages of stabilisation during profile formation these sequences are an indication of the sedimentation soil formation and reworking processes operating on the soil surface the alternation of these processes is interpreted as the result of climate vegetation changes the channel fills of tor 2 indicate erosion and reworking of the hard laminar calcrete horizon both tor 1 and tor 2 are multi storey profiles reflecting the complex sedimentation erosion pedogenesis relationships at the final stages of the development of its corresponding fluvial terrace the study of these calcretes shows that these supposedly abandoned terraces continue to be active even though the fluvial network is entrenched both the pedofacies relationships and the complexity shown by tor 1 and tor 2 reflect the complex and unstable geomorphic setting in which these profiles developed after the establishment of the exorrheic network less complex calcrete profiles were produced in the lower terraces

calcified root cells in miocene pedogenic carbonates of the madrid basin evidence for the origin of microcodium b abstract calcified root cells forming microspar and pseudospar mosaics of calcite and or dolomite crystals constitute a major component of calcretes and dolocretes from the miocene of the madrid basin the calcified cells occur in massive nodules or fill root tubes in the calcrete dolocrete profiles the arrangement of the cells within the mosaics and their internal features together with the isotopic data clearly indicate that the crystals formed through the calcification of root cells and not through recrystallization or dolomitization calcified root cells formed in a favourable microenvironment caused by biochemical phenomena associated with plant growth in these examples the calcification is incomplete as only in the innermost part of the root the cells were totally calcified whereas in the root cortex only the cell walls were calcified the distribution of the calcified cells within the roots was controlled by the different ionic environments which prevail within an active root system in the inner part the ionic conditions were mostly controlled by the cellular activity of the root creating a suitable microenvironment for the biomineralization of the cells this differs notably from most published examples of calcified root cells in which it is usual for the cortical cells of roots to be completely calcified the calcified root cells of the madrid basin resemble unequivocally the problematic microcodium b which suggests that this type of microcodium formed through calcification of root cells

palaeoenvironment of a late quaternary lacustrine palustrine carbonate complex zarand basin saveh central iran abstract the continental carbonate deposits of the zarand basin were deposited within an intra continental strike slip basin situated in the northwestern corner of central iran they consist of distal alluvial mudstones to marlstones carbonate pond deposits carbonate and siliciclastic infilled channels and lacustrine carbonates deposited within a distal alluvial lacustrine palustrine complex both sedimentological and palaeontological evidence suggest that these sediments mostly formed within an open hydrological system the common presence of root traces greyish green mudstones calcareous nodulisation mottling and desiccation breccias indicate a palustrine setting the carbonate deposits of the zarand basin were formed under an overall semi arid climate but periods of more aridity characterised by extensive calcretization can be distinguished in the stratigraphical sections both tectonics and climate have contributed in controlling the sedimentation of the zarand basin archaeological and geomorphological evidence provides a unique sub recent analogue for ancient palustrine limestones developed within an intra continental basin under a semi arid climatic regime the combination of geological and archaeological data and their comparison with historical documents show that the so called historical lake of saveh was the remnant of the more ancient wetland system which dominated the zarand region during the late quaternary

the atlas east variscan elbe shear system and its role in the formation of the pull apart late palaeozoic basins the variscan orogeny occurred as a result of the late devonian to late carboniferous collision and accretion of gondwana derived microcontinents and continental masses with those of laurussia the irregular boundaries of the colliding continents caused isochronous transpressional and transtensional tectonics accompanied by a complex pattern of intracontinental shear zones at the scale of the southern european variscides these shear zones and their configuration controlled the subsequent evolution of permian to middle triassic paleogeography the geographic distribution from morocco to the eastern alps of the late carboniferous permian up to triassic basins most of which are considered as pull apart basins was related with the development of the late palaeozoic intracontinental shear network our analysis of the stratigraphic tectonic and volcanic features of the late carboniferous permian continental basins across the laurussia gondwana boundary reveals the role of the east variscan shear zone during this time as a precursory lineament for the development of the permian to triassic rifting of pangaea and the following opening of oceanic basins e g the neothetyan ocean

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

initial stages of laminar calcrete formation by roots examples from the neogene of central spain thin carbonate laminae formed by root activity are common within miocene detrital deposits of the duero and madrid basins the laminae are about 3 cm thick extending several metres laterally and displace the original detrital sediment which ranges in grain size from fine gravel to sandy clay the thickness morphology microstructure and stable isotope compositions of the laminae indicate that they formed by the activities of roots and associated microorganisms within the soil the laminae are similar to those commonly recognised in thick laminar calcrete profiles three types of laminae are recognised differences in the micromorphology of the laminae are explained as reflecting the different organisms involved and whether calcification occurred when the root was alive or decaying the first type occurs in a profile at paracuellos the jarama where the laminae consist of a mosaic of 20 mm calcite crystals whose arrangement indicates that calcification took place in the medulla of the root and probably occurred while the plant was alive in a second type in the villacadima profile laminae comprise calcified root mats whose formation indicates the interplay of roots and fungi calcification of the cell walls and intracellular spaces took place in the cortices of the roots and not in the medullas as revealed by the presence of central pores in every calcified root a third type of lamina is recognised in profiles at vin egra de moran a and consists of mucilaginous sheets coated by needle fibre calcite crystals the occurrence of associated small root casts indicates that formation of the laminae occurred while the root was decaying and was also influenced by fungal activity these laminae occur within poorly developed soils and their formation was controlled by the relationship between sedimentation erosion and soil formation processes thus the occurrence of these laminae interbedded with detrital sediments reflects environments where sedimentation was relatively low and episodic so after the detrital sediment input surfaces were stable and root mats were able to develop renewed sedimentation accounted for the death of the root mats and the development of new ones on the new surfaces where the sedimentation rate is lower the laminae tend to amalgamate and thicker laminar calcrete profiles form with little or no interbedded detrital sediment

calcrete as a source of heterogeneity in triassic fluvial sandstone aquifers otter sandstone formation sw england carbonate is not generally considered as a potential source of large scale heterogeneity in permo triassic sandstone aquifers this study shows that carbonate in the form of early diagenetic calcrete forms an abundant component of the triassic otter sandstone formation in south devon three types of calcrete are described from the outcrop of this fluvial sandstone dominated aquifer rhizocretions calcrete sheets and calcrete conglomerates data obtained from core plugs show that calcrete reduces sandstone permeability to less than 10 15 m2 and porosity to less than 12 calcrete can be sufficiently abundant to produce a significant up to 30 reduction in the total effective porosity of the aquifer moreover calcrete conglomerates can form laterally extensive up to 1 km low permeability sheets that will represent major baffles to vertical flow

late permian to middle triassic correlations and palaeogeographical reconstructions in south western european basins new sedimentological data from minorca balearic islands spain description of sedimentary sections and interpretations of sequence stratigraphic evolution of permian triassic red beds of minorca allow a new proposal of palaeoenvironment reconstructions the permian sediments mainly correspond to floodplain and pond deposits with sheetflood sand bed rivers environment de 1 within a warm and semi arid climate and the preserved succession forms one complete stratigraphic cycle the retrogradational phase of this cycle is represented by alluvial colluvial deposits grading upwards to environment de 1 and to extensive floodplain and pond deposits the progradational phase is characterized by increasing fluvial influence with palaeocurrent mainly oriented to the sw palaeosol horizons and preservation of a late permian palynoflora the uppermost part of this succession is truncated by a major erosional surface the sediments above this unconformity are characterized by braided river deposits environment de 2 with palaeocurrent oriented to the ssw within the more basal conglomeratic facies and to the wnw in overlying units the absence of extensive floodplain deposits a paucity of evidence for biogenic activity and palaeosols together with the presence of ventifacts indicate an arid climatic setting for the succession this environment evolved from braided rivers palaeocurrents mainly oriented to the se environment de 3 with in situ palaeosols and reworked breccias to fluvial coastal and shallow marine deposits environment de 4 dated as upper anisian to ladinian this succession characterizes a retrogradational trend although the transition between de 2 and de 3 was not observed a switch in palaeocurrent directions may indicate a change in source area a comparison at a regional scale with other peri tethyan basins allows the succession to be placed within a broader palaeoenvironmental and stratigraphic context during late permian to middle triassic during the late permian sedimentation occurred in alluvial playa lake or ponded environments where fluvial systems generally flowed southward except in south eastern france oriented to the ne within these sw european basins such as minorca the late permian succession shows a major retrogradational evolution from fluvial or alluvial fan deposits to extensive lake playa or floodplain deposits and a progradational trend fluvial or alluvial fan deposits the permian triassic transition corresponds to an unconformity overlain by braided river deposits with arid climate indicators aeolian deposits ventifacts and aeolian dune sedimentation at the scale of western europe this arid episode is dated as smithian and the induan age sedimentation deposits seem to be preserved only in the central part of the germanic basin as with all other peri tethyan basins environment de 2 of minorca above the major erosional surface is attributed to the smithian in the upper part of the studied succession braided river deposits indicative of less arid climatic conditions are preserved this succession contains the earliest mesozoic palaeosols dated as anisian by palynomorphs and expresses a vertical evolution from fluvial to open marine depositional environments attributed to the muschelkalk transgression

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

biogenic laminar calcretes evidence of calcified root mat horizons in paleosols laminar calcretes are described from the lower carboniferous of south wales the upper jurassic of southern england and the upper jurassic lower cretaceous of northern spain they are interpreted as calcified root mats horizontal root systems and are compared with other examples in the geological record and with possible modern analogues all three occurrences consist of virtually identical centimetre to decimetre thick locally organic carbon rich laminar micrites containing up to 50 by volume of millimetre sized typically calcite filled tubular fenestrae set in an irregular but very finely laminated matrix it is suggested that root mat calcretes are probably very common in the geological record in peritidal lacustrine margin and floodplain deposits but owing to their crudely biogenic microstructure they more closely resemble cryptalgal laminites than do other laminar calcretes the recognition of such root mat calcretes in sedimentary sequences not only provides evidence of subaerial exposure and vegetation cover but can also indicate positions of palaeo water tables in certain circumstances

reworked calcretes their significance in the reconstruction of alluvial sequences permian and triassic minorca balearic islands spain the permian and triassic of minorca balearic islands consists of a 670 m thick red alluvial succession that includes in situ calcrete profiles and reworked calcrete material in the permian succession the calcretes vary from laminar forms developed on the carboniferous basement to weakly developed nodular calcretes in fluvial sediments the palaeosols in the triassic are mostly dolomitic and the profiles reach up to stage iii of soil development spec pap geol surv am 203 1995 1 the clasts formed through reworking of the palaeosol profiles are about 0 5 10 cm across and include mosaics of calcite dolomite crystals brecciated clasts rhizolith fragments and aggregates of clay and or silt these clasts appear in three different types of deposits type 1 corresponds to lenticular bodies that fill small scour surfaces and consists only of intraformational conglomerates these deposits are interpreted as ephemeral channels and sheet floods that represent the interfluvial drainage systems that captured only the precipitation falling on the alluvial plain type 2 includes sand dune 3 d bodies with flat bottoms and convex tops these bodies are about 20 cm high and 2 m wide and were formed by floodwaters that flowed down the levees of the major streams type 3 channel deposits contain reworked calcretes and extrabasinal clasts which overlie erosive surfaces and are found in layers within cross bedded sandstones and conglomerates these are interpreted as channel floor lag deposits of major channels that entered from distant uplands and drained the alluvial plain variations in the aggradation rates of the floodplain resulted in five different infill stages in the lowstand to early transgressive interval as in stages i p1 and iv b1 the fluvial deposits filled palaeovalleys calcretes and reworked calcrete deposits were of difficult formation apart from terraces and preservation accommodation space was at its greatest in the transgressive stages ii p2 and v b2 this caused the greatest aggradation of the floodplains which are formed of thick sequences of fine grained sediments isolated meandering channels weakly developed calcretes compound and reworked calcrete deposits mostly of types 1 and 2 the density of channels notably increased in stage iii p3 highstand interval because of the reduction of accommodation space this could favour the formation of composite or even cumulative palaeosols but of difficult preservation reworked calcrete deposits are mostly of type 3 but types 1 and 2 are also recognised the reworked calcrete deposits are an important part of the permian and triassic fluvial sediments and their occurrence and characteristics are important in order to interpret the infill of terrestrial basins and the construction of floodplains

discriminating between tectonism and climate signatures in palustrine deposits lessons from the miocene of the teruel graben ne spain the upper miocene vallesian turolian unit ii of the teruel graben comprises at its top a 25 m thick sequence of palustrine deposits deposition of the entire unit commenced some 9 to 7 ma ago in a halfgraben basin here via a recent quarry we examine in detail the lateral and vertical distribution of unit ii s palustrine facies and their features to determine the palaeogeography and main controls on deposit formation our findings suggest the deposits formed at a low gradient lake margin with different energy levels these energy levels controlled the type of primary deposit within the lake wackestone to packstone sediments formed in low energy conditions whereas cross bedded rudstones to floatstones formed under higher energy conditions by erosion and redeposition of prior lacustrine deposits pedogenic and diagenetic modifications of the primary sediments took place during sedimentary discontinuities sd when the lacustrine sediments were subaerially exposed these processes serve to explain the formation of eight different palustrine limestones limestones with root traces mottled limestones brecciated limestones flat pebble breccias granular limestones micro karstified limestones with laminar calcretes carbonate mounds and clayey limestones with laminar calcretes based on the features and thicknesses of the modified sediments five different morphological stages i to v of palustrine carbonates are defined stage i is characterized by incipient mottling and brecciation stage ii shows mottling and strong brecciation that lead to the formation of intraclast breccias in which the fragments are mostly in situ in stage iii the primary fabric is totally changed intraclasts have moved and may have lost their initial morphology this stage iii may also be characterized by the formation of micro karst stage iv is typified by the presence of coated grains and thin root mats the chronological data available suggest that the formation of stage iii lacustrine deposition palustrine modification would require about 40 000 yr facies and the sd record changes across short horizontal distances and thus reflect the topography of prior sedimentation modification events small 50 cm highs with micro karst have their sd counterparts in lower areas of the lake in which the sd is indicated by desiccation and mottling the topographic differences of the micro karst were filled by intraclastic rudstones sourced by the adjacent carbonate flats the example examined not only clearly sketches the morphology of ancient palustrine systems or wetlands it also provides evidence that recycling of previous carbonate deposits played an important role as a sediment source apart from biogenic or physical chemical production processes our geochemical data indicate lmc low magnesian calcite as the main component and fe contents lower than 1 except for the mottled areas that are richer in feo stable isotope compositions provide 18o values close to 6 5 vpdb and more varied 13c 3 39 to 6 97 pdb oxygen and carbon values reveal no covariation and clear trends are lacking the homogeneity of 18o values reflects the intense effects of meteoric waters the deposition of these palustrine limestones took place under suitable semi arid to sub humid climates climate could also have a role in determining subaerial exposure periods however its imprint is not easy to detect neither in the geochemical signals nor in the vertical arrangement of the facies this could be attributed to climate changes probably occurring over shorter periods than those that can be recorded in this type of sediment such as the astronomical precession cycles and suggests the unsuitability of palustrine carbonates for detailed palaeoclimate analyses tectonism controlled the location of the main lacustrine depocentre close to the basin s main fault the activity of this normal fault during the sedimentation of unit ii determined long and short term sedimentary sequences such sequences are the response to small scale subsidence pulses followed by the infill of the created accommodation space by shallow lacustrine deposits which underwent early pedogenic and diagenetic processes after subaerial exposure

climatic and diagenetic signals in the stable isotope geochemistry of dolomitic paleosols spanning the paleocene eocene boundary abstract the precipitation of primary dolomite in soil is rare and controversial and its occurrence indicates highly unusual geochemical and climatic conditions we utilize isotopic and petrographic techniques including clumped isotope thermometry to evaluate diagenetic alteration and preservation of primary climatic signal in dolomitic paleosol nodules from a section spanning the paleocene eocene boundary in central utah isotopic measurements differentiate samples into groups that may be interpreted in terms of alteration however moderate burial depths and extreme warmth during the interval of soil formation make it difficult to reach definitive conclusions from isotope values alone with the addition of petrographic analysis including cathodoluminescence and scanning electron microscopy we are able to identify textural differences between samples suggesting differing amounts of recrystallization we conclude that while some nodules have experienced significant diagenetic alteration the original nodule mineralogy is dolomite and the majority of sampled nodules retain a primary paleoclimate signal early paleogene temperatures recorded at this site are considerably warmer than those suggested for the continental interior from alternate proxies a result that may be partially the result of the clumped isotope temperatures recording warm season soil temperatures rather than mean annual air temperature soil water isotopic composition is suggestive of heightened aridity particularly through the paleocene eocene thermal maximum petm

rapid recent warming on rutford ice stream west antarctica from borehole thermometry 1 the antarctic peninsula has warmed faster than the global average rate of warming during the last century due to limited availability of long term meteorological records the geographical extent of this rapid warming is poorly defined we collected borehole temperature measurements in the upper 300 m of rutford ice stream west antarctica and employed an inverse modeling scheme with a heat diffusion advection equation to determine the recent surface temperature history of the borehole position our results reveal recent warming of 0 17 0 07 c decade 1 since 1930 this result suggests that at least in an attenuated form the rapid warming observed over the antarctic peninsula extends as far south as rutford ice stream this result agrees with other recent results that show a warming trend across much of the west antarctic ice sheet

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

morphology and origin of dolomite in paleosols and lacustrine sequences examples from the miocene of the madrid basin the northern madrid basin contains paleosols and lacustrine sequences composed of ordered dolomite smectite rich mudstones with analcime deposited in distal alluvial fans affected by pedogenic processes mudstones contain dolomite and silica laminae interpreted as mineralized root mats dolostones with prismatic structure constitute stage iii dolocretes homogeneous lacustrine dolomudstones show some features indicative of subaerial exposure dolomite textures include microcrystalline dolomite coarse crystalline mosaics located in root cavities dolomite dumbbells and dolomite spheroids replacing clays dolomudstones or opal mol values of mgco3 of dolomites vary between 47 67 and 53 34 mol 18o values range between 3 65 and 5 51 vpdb 13c values range between 7 19 and 8 38 vpdb dolomicrite formed in alkaline lakes by direct precipitation and replacement of clays in soils the rhizosphere was favorable for dolomite mosaic and dumbbells formation spheroidal dolomite replaced clays and opal under early phreatic diagenesis trioctahedral smectites silica and analcime indicate that these pedogenic and lacustrine environments were alkaline smectites and or carboxyl groups acted as a catalyst favoring the incorporation of mg into dolomite in these non saline settings the kinetic barriers for dolomite precipitation lowered by high ph and mg enrichment ordered dolomite formation occurred under biogenic and abiogenic conditions during sedimentation pedogenesis and early diagenesis

the origin and significance of pedogenic dolomite from the upper permian of the south urals of russia pedogenic carbonate nodules from six sections spanning the continental permian triassic boundary in the south urals russia were analysed morphological petrographic sem and xrd analyses have demonstrated that many of the latest permian palaeosols are dolomitic this dolomite forms the microcrystalline 5 16 m groundmass of the nodules later diagenetic phases represented by coarser crystalline textures were identified as calcite isotopic analysis of the microcrystalline dolomite has revealed it to be similar in isotopic composition to authigenic dolomite forming today in saline soils in alberta canada these data indicate that the dolomite found in these nodules is pedogenic and formed in equilibrium with the atmosphere upper permian pedogenic dolocretes in the studied sections are most frequent in a palaeosols that formed on palaeo highs and b in the latest permian period changhsingian which may indicate that there was an increase in seasonality and evaporation in the south urals region at this time the presence of only calcitic palaeosols in the earliest triassic may reflect a subsequent dramatic change in the basin conditions possibly relating to the permian triassic mass extinction which stopped the conditions that are necessary for dolomite formation

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis