biological remains geochemistry and stable isotopes for the reconstruction of environmental and hydrological changes in the holocene lakes from north sahara abstract a detailed reconstruction of the holocene palaeoenvironments and palaeohydrology is presented for wwamp and lacustrine calcareous sediments which lie in closed depressions along the northern margin of the great western erg algeria it is based on a multidisciplinary approach using numerous techniques the chronological framework is established on the basis of 23 14 c dates on inorganic calcite and mollusc shells ranging from ca 9300 to 3000 yr b p and on an isolated 14 c age of ca 10 900 yr b p the significance of various environmental markers is discussed biological remains are abundant and diversified about 150 taxa including diatoms chrysophytes charophytes ostracods molluscs and foraminifera they provide information on the water chemistry total salinity ionic ratio ph and partial pressure of carbon dioxide and on the habitats water depth development of aquatic plants ephemerality etc emphasis is given to the total salinity individual organisms and palaeobiological assemblages are ordered as a function of their salt requirements and tolerances calibration based on modern diatom samples allows a tentative estimate of the palaeosalinities which range from fresh to marine like and even hypersaline waters attention is drawn to the possible colonization of marine organisms in continental basins without any connection with the sea stable isotope analyses have been carried out on both inorganic and biogenic mollusc and ostracod shells charophyte gyronites carbonates the 18 o contents demonstrate wide changes in the hydrological balance fluctuations in 13 c contents inform on water mixing residence time and on the importance of biological effects on total dissolved inorganic carbon geochemical analyses were performed on inorganic calcite and on ostracod shells high contents in fe and mn indicate reducing environments during stages of high salinity sr ca and mg ca are used as salinity indicators zn mg ratios suggest that the major water supply was the aquifer of the great western erg today down to about 50 m rather than surface waters from the atlas mountains salinities resulted from the balance between inputs from the water table evaporation rate leaching of pre existing salt crusts and seepage through the lake bottom a reconstruction of the evolution of the palaeosystems through time and space has been attempted with special attention to the instability of the water and ionic balances for different time scales short term fluctuations occurring during a single hydrological cycle annual or seasonal are deduced from the apparent discrepancies between the various indicators found in a given sample long term 10 2 10 3 years changes confirm the existence of a climatic phase being wetter than today from at least ca 9300 and may be from ca 10 900 yr b p to 3000 yr b p for the first time the salinity deduced from diatoms and the 18 o content of the water deduced from that of the carbonate at 25 c are used simultaneously to model the hydrological history of the basins and to estimate the relative humidity of the atmosphere during the holocene major environmental trends recorded from ca 9300 to 3000 yr b p do not show a clear synchronims between the different profiles studied therefore they cannot be interpreted in terms of palaeoclimate but instead demonstrate the importance of local hydrology in the evolution of closed basins associated with groundwater a common situation in arid and semi arid zones

palaeoenvironmental reconstruction of a middle miocene alluvial fan to cyclic shallow lacustrine depositional system in the calatayud basin ne spain the middle miocene sedimentary fill of the calatayud basin in north eastern spain consists of proximal to distal alluvial fan floodplain and shallow lacustrine deposits four main facies groups characteristic of differentsedimentary environments are recognized 1 proximal and medial alluvial fan facies that comprise clast supported gravel and subordinate sandstone and mudstone the latter exhibiting incipient pedogenic features 2 distal alluvial fan facies formed mainly of massive mudstone carbonate rich palaeosols and local carbonate pond deposits 3 lake margin facies which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system i e front lithofacies a comprising massive siliciclastic mudstone and tabular carbonates or lateral lithofacies b showing laminated and or massive siliciclastic mudstone alternating with tabular and or laminated carbonate beds and 4 mudflat shallow lake facies showing a remarkable cyclical alternation of green grey and or red siliciclastic mudstone units and white dolomitic carbonate beds the cyclic mudflat shallow lake succession as exposed in the orera composite section ocs is dominantly composed of small scale mudstone carbonate dolomite cycles the mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods the deposits evolving either under subaerial exposure or water saturated conditions depending on their location on the lacustrine mudflat and on climate the dolomite intervals accumulated during lake level highstands with mg rich waters becoming increasingly concentrated lowstand to highstand lake level changes indicated by the mudstone dolomite units of the small scale cycles reflect a climate control from dry to wet conditions on the sedimentation in the area the spatial distribution of the different lithofacies implies that deposition of the small scale cycles took place in a low gradient shallow lake basin located in an interfan zone the development of the basin was constrained by gradual alluvial fan aggradation additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of 1 8 o and 1 3 c values varying from 7 9 to 3 0 pdb and from 9 2 to 1 7 pdb respectively more negative 1 8 d and 1 3 c values are from carbonate rich palaeosols and lake margin carbonates which extended in front of the alluvial fan systems whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment the results show a clear trend of 1 8 o enrichment in the carbonates from lake margin to the centre of the shallow lake basin thereby also demonstrating that the lake evolved under hydrologically closed conditions

nd sr isotopic geochemical and petrographic stratigraphy and paleotectonic analysis mesozoic great valley forearc sedimentary rocks of california measurements of nd sr isotopes major and trace elements and model mineralogy were made on upper jurassic and cretaceous great valley forearc sedimentary rocks to test models for the temporal and spatial evolution of sierra nevada arc sources isotopes and major and trace elements are sensitive provenance indicators because of the large west east isotopic geochemical and age gradients in the plutonic rocks of the sierra nevada batholith and because petrographic models indicate that source areas moved east during the cretaceous isotopic and chemical variations are correlated in the forearc sandstone as nd decreases th u la nb zr hf pb rb sio2 and k2o concentrations increase and feo mgo tio2 ni and cr concentrations decrease this relation is the same as that observed in the plutonic rocks and indicates that the arc was the primary source of sediment and that the sandstone chemistry was not disturbed by sedimentary processes the nd sr relation of san joaquin valley sandstone is the same as the plutonic rocks but sacramento valley sandstone is elevated in sr because of seawater exchange weathering and diagenesis whole rock sandstone decreases in nd from 7 to 5 and increases in 87sr 86sr from 0 7045 to 0 7073 with decreasing stratigraphic age the nd sr isotopic composition is correlative with the plagioclase to feldspar ratio and indicates that source areas moved inland during the cretaceous upper cretaceous san joaquin valley shale is similar in nd to the sandstone indicating that sandstone and shale were derived from the same source and that the nd isotopic composition is independent of grain size the shale is higher in 87sr 86sr than the sandstone possibly due to concentration of biotite in the fine fraction during transport and subsequent rb loss during diagenesis nd sr isotopes were used to construct models to locate source areas parameters include lithology drainage basin geometry and erosion rate the age and isotopic compositions of the calculated igneous component of the sandstone correspond to the age and isotopic compositions of the plutonic rocks of the batholith this correspondence indicates that 1 the isotopic composition of the plutonic rocks and the coeval volcanic cover were similar 2 the volcanic front was denuded within a few million years and 3 the sediment was derived from the head of the drainage basin located at the migrating volcanic front

pattern of sedimentary infilling of fossil mammal traps formed in pseudokarst at cerro de los batallones madrid basin central spain fossil mammal sites of late miocene age ca 9 ma occur in hourglass shaped non interconnected cavities up to 15 m deep hosted in mudstone mostly sepiolite chert and carbonate bedrock in cerro de los batallones this paper provides a model for the sedimentary infilling of the cavities which functioned as traps for vertebrate faunas and contain one of the richest and best preserved neogene mammal assemblages of the iberian peninsula generation of the mammal bearing cavities started with the solution of underlying evaporites which resulted in fissures that were subsequently enlarged by subsurface piping a process rarely preserved in the ancient sedimentary record the system of subterranean cavities evolved into a pseudokarst landscape resulting in doline like shafts reaching the ancient land surface the sedimentary infilling of the cavities comprises both clastic and carbonate lithofacies that were investigated by outcrop observation standard and scanning electron microscope petrography mineralogical analysis and stable isotope geochemistry gravel and breccia talus deposits clast and mud supported gravel pebbly sandstone and mudstone are common detrital infill deposits mostly derived by overflow erosion of bedrock the deposits containing the mammal bones are marls and occur both in subsurface cavities and doline like depressions in the underground cavities marlstone was mainly of clastic origin and accumulated in ponds scattered over the floor of the cavity in contrast marlstone deposits in the surface dolines formed mostly as a result of biochemical carbonate deposition in small shallow lakes subjected to fluctuation of the water level the 18o and 13c carbonate values indicate different origins for the two kinds of marls during the final phases of pipe infill the doline marlstone sealed the mammal sites usually off lapping the adjacent bedrock

response of the indian ocean to the tibetan plateau thermal forcing in late spring abstractthe thermal effect of the tibetan plateau tp is known to exert substantial impacts on the atmospheric general circulation suggesting that it may also influence the wind driven circulatio

spring related carbonate rocks mg clays and associated minerals in pliocene deposits of the amargosa desert nevada and california the amargosa desert of nevada california is a spring fed structural basin containing large amounts of pliocene carbonate rocks and mg clays deposited in playas marshland ponds and flood plains pliocene basin fill deposits dated at 2 4 to 3 2 ma are subdivided into three lithofacies designated tpa tld and tpl tpa is chiefly limestone and was deposited in marshland and ponds tld consists chiefly of limestone and montmorillonite claystone that were deposited in varied environments including ponds and flood plains tpl is almost entirely mg clays limestone and dolomite which were deposited in playas and associated marshland the largest area of playa sediments termed east playa is in the east central part of the basin limestone and dolomite seepage mounds and caliche breccia musses were formed along zones of ground water leakage within east playa chemically precipitated mg smectite and sepiolite form large deposits in tpl sepiolite was formed in water of low salinity whereas mg smectite was formed in water of higher salinity authigenic celadonitic illite and k feldspar are commonly associated with mg smectite and are very likely reaction products of montmorillonite in saline alkaline water silicic vitric ash layers were locally altered to phillipsite and k feldspar in saline alkaline water and to montmorillonite as a result of leaching by water of low salinity carbonate rocks are locally silicified along seepage zones carbonate minerals of the pliocene deposits have stable isotopic compositions that vary with their lithofacies tpa limestones deposited in or near areas of spring discharge have low 18o values averaging 16 6 tld limestones recrystallized in the vadose zone have higher 18o values averaging 18 1 carbonate minerals of tpl are the most 18o rich with calcite averaging 20 3 and dolomite 24 3 reflecting evaporative concentration in playas much of the dolomite is of replacement origin yet is in approximate isotopic equilibrium with the calcite it replaces relatively pure sepiolite has lower 18o values than do mg smectite clays which fits with the lower salinity inferred for sepiolite precipitation sepiolite and mg smectite disseminated in limestone fall outside the oxygen isotopic limits of the relatively pure clays possibly because of diagenetic recrystallization the pliocene climate was wetter than that of the present and springs were more widespread in the amargosa basin this dolomite may have formed in water isotopically and chemically about the same as that of the calcite and dolomitization may have been chiefly a result of the differing crystallization kinetics of calcite and dolomite and of fluctuating water chemistry in a playa environment the saline alkaline water of east playa resulted from evaporation of a mixture of alkali bicarbonate runoff from the volcanic terrane to the north with ca mg bicarbonate water discharged in springs from the ash meadows ground water system whose recharge area is principally in paleozoic carbonate rocks to the east and northeast seepage along fault zones in east playa was initially of ash meadows type low in silica and changed to siliceous water derived from volcanic rocks resulting in silicification of carbonate deposits caliche breccias along the western margin of the basin record a similar change in the composition of ground water seepage which may be attributed to a period of decreased precipitation about 2 5 ma which reduced recharge from nearby carbonate rocks relative to that from more distant volcanic rocks to the north and northwest

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

paleoenvironmental and paleohydrochemical conditions of dolomite formation within a saline wetland in arid northwest australia abstract groundwater dolocrete occurring within the fortescue marsh a large inland wetland in the pilbara region of northwest australia has been investigated to provide paleoenvironmental and paleohydrological records and further the understanding of low temperature dolomite formation in terrestrial settings over the quaternary period two major phases of groundwater dolocrete formation are apparent from the presence of two distinct units of dolocrete based on differences in depth 18o values and mineral composition group 1 g1 occurs at depth 20 65 m b g l below ground level and contains stoichiometric dolomite with 18o values of 4 02 0 71 group 2 g2 is shallower 0 23 m b g l occurring close to the current groundwater level and contains ca rich dolomite secondary calcite with a comparatively lower range of 18o values 7 74 and 6 03 modelled 18o values of paleogroundwater from which older g1 dolomite precipitated indicated highly saline source water which had similar stable oxygen isotope compositions to relatively old brine groundwater within the marsh developed under a different hydroclimatic regime the higher 18o values suggest highly evaporitic conditions occurred at the marsh which may have been a playa lake to saline mud flat environment in contrast g2 dolomite precipitated from comparatively fresher water and modelled 18o values suggested formation from mixing between inflowing fresher groundwater with saline brine groundwater within the marsh the 18o values of the calcite indicates formation from brackish to saline groundwater which suggests this process may be associated with coeval gypsum dissolution in contrast to the modern hydrology of the marsh which is surface water dependent and driven by a flood and drought regime past conditions conducive to dolomite precipitation suggest a groundwater dependent system where shallow groundwaters were influenced by intensive evaporation

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

abiotically formed primary dolomite in the mid eocene lacustrine succession at gebel el goza el hamra ne egypt an approach to the role of smectitic clays abstract this study discusses the role of smectitic clays in the formation of an abiotic physio chemical primary dolomite within an evaporative alkaline saline marginal lake system in the absence of carbonate precursor and microbes the present work has been achieved in terms of textural mineralogical and geochemical characteristics of dolostones in the mid eocene bartonian lacustrine succession cropping out at gebel el goza el hamra shabrawet area ne egypt this lacustrine succession is 15 16 m thick and made up of alternating horizontal beds of dolostone marlstone and mudrock that show some pedogenic and subaerial exposure features the dolostones are composed mainly of dolomite 60 90 smectite 20 30 and quartz grains 5 10 the dolomite comprises fine crystalline rhombs to micro spherical crystals with no obvious relics of microbial activity and or carbonate precursor it is ordered nearly stoichiometric with 46 50 mole of mgco 3 and has 18 o and 13 c values ranging from 0 44 to 2 96 vpdb and 0 93 to 8 95 vpdb respectively the smectite occurs as thin mats that are commonly intergrown and associated with dolomite mineralogical textural and stable isotopic results of the dolomite indicated that the dolomite was formed as an abiotic primary precipitate in alkaline saline lacustrine systems in this respect the gel like highly viscous smectitic medium plus progressive co 2 degassing elevated evaporation low sedimentation rate low sulphates level and alkaline soil solution lowered the kinetic barriers of dolomite precipitation from solution and promoted the incorporation of mg 2 in the structure of dolomite consequently the presence of smectitic clays in evaporative saline lakes is significant for dolomite formation because they can generate a gel like highly viscous medium and provide mg 2 that can facilitate the physcio chemical precipitation of primary dolomite from solution at ambient temperatures however more work is needed to better characterize the role of clays during dolomite formation in alkaline lacustrine environments at ambient temperatures

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

zeolitic diagenesis of late quaternary fluviolacustrine sediments and associated calcrete formation in the lake bogoria basin kenya rift valley late quaternary fluviolacustrine siltstones mudstones and claystones loboi silts on the northern margins of the saline alkaline lake bogoria in the kenya rift valley contain up to c 40 authigenic analcime and minor natrolite the zeolitic sediments are reddish brown and up to 1 m thick the amount of analcime increases upward in the profile but decreases with distance from the lake the altered sediments show many pedogenic features including zeolitic root mats rootmarks concretions and carbonate rhizoliths residual patches of calcrete locally cap the zeolitic rocks the profile is interpreted as an exhumed palaeosol and land surface on the former margins of the lake the analcime occurs as submicroscopic 0 5 2 5 m subhedral and euhedral crystals which have an average si a 1 ratio of 2 33 as determined by x ray microanalysis or 2 18 d value of 639 analcime peak the analcime formed in lake marginal sediments soils by reaction of silicate detritus with na2co3 rich pore waters concentrated close to the land surface by evaporative pumping and evapotranspiration poorly ordered clay minerals were probably the main reactants authigenic illite may have been a by product of the reactions chemical analyses suggest that pore waters supplied some of na and possibly k and sio2 the associated calcrete and rhizoliths were formed during or shortly after the main period of zeolitic alteration the ca2 may have originated from infiltrating dilute runoff and groundwater authigenic smectite was precipitated in open porosity following analcime formation the zeolitic alteration at lake bogoria provides a relatively recent analogue for lake marginal zeolites found in many ancient saline alkaline lake sediments

far field effects of alpine plate tectonism in the iberian microplate recorded by fault related denudation in the spanish central system abstract apatite fission track analysis was performed on 56 samples from central spain to unravel the far field effects of the alpine plate tectonic history of iberia the modelled thermal histories reveal complex cooling in the cenozoic indicative of intermittent denudation accelerated cooling events occurred across the spanish central system scs from the middle eocene to recent these accelerated cooling events resulted in up to 2 8 0 9 km of denudation in the western sierra de gredos and 3 6 1 0 km in the central and eastern gredos assuming a paleogeothermal gradient of 28 5 c and a surface temperature of 10 c the greatest amount of denudation 5 0 1 6 km occurred in the sierra de guadarrama accompanying rock uplift was 4 7 1 0 and 5 9 1 6 km in the eastern gredos and guadarrama respectively most denudation in the gredos occurred from the middle eocene to the early miocene and can be related to the n s stress field induced by the pyrenean compression in the guadarrama the greatest denudation was pliocene to recent of age and seems related to the ongoing nw se betic compression the fact that the formation of the e w trending gredos coincides with the n s pyrenean compression and the creation of the present day morphology of the ne sw trending guadarrama with the younger nw se betic compression indicates that they record the far field effects of alpine plate tectonics on iberia the trend of pre existing lineaments was of major importance in influencing the style and magnitude of these of far field effects

mid neoproterozoic 830 750 ma isotope stratigraphy of australia and global correlation abstract carbon and strontium isotope studies of numerous drillcore and outcrop sections within individual australian neoproterozoic basins in a tectonic and sedimentologic framework have allowed the construction of isotopic records for the interval 830 750 ma this combined with the discovery of a restricted stratigraphic range for the acritarch cerebrosphaera buickii in mid neoproterozoic strata of australia makes possible correlation with successions in canada namibia and spitsbergen that part of the mid neoproterozoic succession in spitsbergen which contains c buickii was previously considered younger than the sturtian glacial epoch but this study has indicated that the akademikerbreen group is older than that a correlation scheme is proposed along five tie lines and is based on a correlation between australia and canada at 830 ma and australia spitsbergen and namibia at 760 ma the lowest ever recorded seawater 87 sr 86 sr ratios in the upper shaler supergroup of canada 0 70561 0 70670 compare with ratios in evaporites of the 830 ma bitter springs formation amadeus basin australia 0 70568 0 70720 comparable 13 c carb records support a correlation at about 760 ma a correlation is made between the heaviest mid neoproterozoic 13 c carb values of 7 2 upper burra group adelaide rift complex and 8 1 kanpa formation western officer basin in australia 8 5 in spitsbergen backlundtoppen formation akademikerbreen group and 8 5 in namibia ombombo subgroup congo craton the stratigraphic range of c buickii in australia and spitsbergen supports this correlation a compilation of 13 c carb and 87 sr 86 sr records between about 830 and 750 ma from australia canada namibia and spitsbergen reveals numerous negative excursions which are not associated with preserved glacial deposits it is necessary therefore to consider additional models to the snowball earth to explain the large and rapid carbon isotopic excursions

mineralogical petrographic and geochemical study to identify the provenance of limestone from two archaeological sites in the sulmona area l aquila italy abstract mineralogical petrographic paleontological and geochemical studies were carried out in order to identify the limestone used to build the ercole curino sanctuary iv iii centuries b c and the foundation walls of a roman domus i century b c ii century a d which was brought to light during restoration works in 1991 in the s s annunziata complex xiv xv centuries a d at sulmona l aquila italy results identified the lithofacies of the stone used for these monuments most of the ercole curino sanctuary samples are calcareous dolomitic lithotypes from the dolomie di castelmanfrino formation lias dogger samples from the artistically more remarkable stone show features similar to those of the limestone of the calcari cristallini formation upper cretaceous paleocene samples from the s s annunziata complex show petrographic characteristics and fossil contents similar to those of the limestone of the terratta formation dogger lower cretaceous the provenance of the monuments stone from a quite small area is supported by the homogeneity of trace element contents being substantially close to those of samples collected from outcrops near the monument for the ercole curino sanctuary and at cave di introdacqua located at about 3 km sw sulmona for the s s annunziata complex carbon and oxygen isotopic compositions supply further support to the identity of provenance of the stone of the sanctuary on the contrary isotopic data of samples from the domus at the s s annunziata complex do not reveal any consistent or clear correspondence with the sampled geological formations the stone used in the artistically more valuable features of the sanctuary shows chemical characteristics similar to those of samples collected at the colle mitra outcrop about 5 km from the archaeological site

history and controls of subsidence in the late cretaceous tertiary great valley forearc basin california abstract analysis of the upper cretaceous tertiary fill of the great valley forearc basin of california reveals a complicated history of subsidence partitioned in time and space western oceanward parts of the basin record subsidence then uplift in apparent response to the angle and rate of descent of the underlying subducting plate specifically uplift in the forearc basin corresponds to the onset of the laramide orogeny and inferred low angles of subduction in contrast eastern arcward parts of the basin display subsidence histories suggestive of thermal contraction and compatible with continentward migration of sierran arc magmatism in the late cretaceous these results imply that subsidence histories of forearc basins are likely to be much more complicated and less predictable than those of rifted continental margins and foreland basins where single subsidence mechanisms predominate and time varying subduction is not an underlying controlling factor

a middle late pleistocene palustrine lacustrine travertine system borj edouane unit nw tunisia sedimentology stable isotopes and palaeohydrological implications the carbonate borj edouane unit represents the northernmost documented middle late pleistocene continental carbonate deposits in tunisia the unit consists of two main facies associations asymmetrically distributed 1 calcrete palustrine laminar crust 2 microbialites the first accumulated carbonate formed in the distal zone of alluvial fans calcretes and in shallow lakes subjected to periodic exposure palustrine facies that occupied the westernmost strip of the basin the second association formed in permanent lakes stromatolites oncoids and planar stromatolites located in the central areas of the basin fed by springs associated with a concentration of vertical faults in the eastern area of the basin travertine facies at time of deposition these facies communicated with the lake via a transitional lacustrine travertine environment transitional travertine stromatolite facies all facies show a restricted range of 18o values around 5 8 0 5 suggesting formation from paleoprecipitation largely of atlantic derivation brought about by westerly winds as for the 13c values these show a wide range 6 4 to 11 7 overall relatively high values for all facies with the lower values corresponding to the calcrete palustrine association and the higher ones linked to the microbialite facies the trend in travertines probably mimics an increasing influence of carbon derived from dissolution of carbonate bedrock of the cretaceous substrate while that of palustrine samples records increasing respired c contribution the sedimentological and isotopic characteristics of the borj edouane unit reflect wetter conditions at the time of deposition and point to a humid period at the middle late pleistocene transition

thermal consequences of thrust faulting simultaneous versus successive fault activation and exhumation abstract when converting temperature time curves obtained from geochronology into the denudation history of an area variations in the isotherm geometry should not be neglected the geothermal gradient changes with depth due to heat production and evolves with time due to heat advection if the deformation rate is high furthermore lateral variations arise due to topographic effects ignoring these aspects can result in significant errors when estimating denudation rates we present a numerical model for the thermal response to thrust faulting which takes these features into account this kinematic two dimensional model is fully time dependent and includes the effects of alternating fault activation in the upper crust furthermore any denudation history can be imposed implying that erosion and rock uplift can be studied independently to each other the model is used to investigate the difference in thermal response between scenarios with simultaneous compressional faulting and erosion and scenarios with a time lag between rock uplift and denudation hereby we aim to contribute to the analysis of the mutual interaction between mountain growth and surface processes we show that rock uplift occurring before the onset of erosion might cause 10 to more than 50 of the total amount of cooling we applied the model to study the cenozoic development of the sierra de guadarrama in the spanish central system aiming to find the source of a cooling event in the pliocene in this region as shown by our modeling this temperature drop cannot be caused by erosion of a previously uplifted mountain chain the only scenarios giving results compatible with the observations are those incorporating active compressional deformation during the pliocene which is consistent with the ongoing nw se oriented convergence between africa and iberia

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

petrofacies and provenance of late mesozoic forearc basin northern and central california data from the great valley group sequence represent the most complete information regarding sandstone petrology of sediment derived from a magmatic arc this information is useful in documenting tectonic and magmatic events within the arc and related terranes and forms the basis for the establishment of petrostratigraphic units for mapping and correlation sandstone and conglomerate compositions are controlled by changes in provenance many of which were basinwide and synchronous clay mineral composition is controlled primarily by burial metamorphism careful attention to sample collection sample preparation and petrographic techniques is essential for uniform results seven petrographic parameters p f lv l m qp q q f and l listed in decreasing importance to petrofacies discrimination define eight petrofacies stony creek platina lodoga grabast boxer cortina los gatos and rumsey listed in approximate order of decreasing age the upper jurassic lower cretaceous petrofacies stony creek platina and lodoga contain higher lithic contents supracrustal sources whereas the upper cretaceous petrofacies especially the rumsey contain higher proportions of plutoniclastic components quartz feldspar and micas the proportion of potassium feldspar increases from near zero in the upper jurassic to nearly 50 of all feldspars in the uppermost cretaceous the lower part of the great valley group upper jurassic and lower cretaceous contains significant quantities of sedimentaclastic and metamorphiclastic material eroded from accreted and deformed terranes tectonic highlands formed by the arc arc collision nevadan orogeny that occurred prior to initiation of the franciscan great valley sierra nevada arc trench system the klamath mountains area provided a major proportion of this detritus ophiolite and serpentinite detritus was deposited locally near the base of the great valley group as a result of deformation along the east side of the growing franciscan subduction complex volcaniclastic detritus was fed into the entire forearc basin as magmatism increased in the sierra nevada area during the cretaceous as the volcanic cover was stripped off plutoniclastic and metamorphiclastic detritus from the underlying batholithic terranes was provided in abundance to the forearc basin crustal components were more continental in the southern sierra nevada and more oceanic in the northern sierra nevada as demonstrated by the higher proportions of metamorphiclastic detritus and by the more felsic nature of volcaniclastic detritus to the south by the middle of the late cretaceous extensive batholithic terranes provided potassium feldspar rich arkosic detritus to the entire forearc basin by the paleogene arc magmatism had migrated eastward sufficiently that deeper levels of the california part of the arc were exposed by erosion tectonic activity decreased in the forearc basin and the basin was filled to sea leve in most parts

paleoenvironmental clues archived in non marine pennsylvanian lower permian limestones of the central appalachian basin usa abstract nonmarine limestones are a key component of the upper middle pennsylvanian through lower permian succession in the appalachian basin previous interpretations of their environments of deposition range from brackish coastal mudflats to hydrologically open freshwater lake complexes with peat forming vegetated marshes to semi closed or closed possibly saline shallow lakes developed on a distal alluvial plain ostracode wackestones packstones some exhibiting laminations and with fish debris articulated ostracode shells and phosphatic clasts define the lower portions of limestone beds or benches passing upward into ostracode peloidal wackestones packstones and intraclastic skeletal peloidal packstones grainstones desiccation features and rooting structures which are developed in the upper portions of the limestones record subaerial exposure pedogenic alteration and desiccation pseudomicrokarst and caliche like vadose and early diagenetic phreatic cements suggest a seasonally dry subhumid to semi arid regional climate many of the sedimentologic and diagenetic features of the limestones are characteristic of palustrine carbonates which coupled with their stratigraphic relation to paleo vertisols siliciclastics and coals indicate that they formed in broad seasonal wetland pond complexes that developed on distal regions of a low gradient distal alluvial plain under seasonally dry subhumid to semi arid climates integration of sr isotopic compositions of shark teeth with previously published stable isotope compositions of the limestones suggests that these purely continental environments were hydrologically semi closed to closed systems repeated stacking of these features at the bed to limestone bench scale defines repeated shallowing upward drying cycles at the 103 to 104 yr scale which were likely climate driven

the role of biomineralization in the origin of sepiolite and dolomite sepiolite is an important industrial mineral whose mechanism of formation and detailed origin are still not clear sepiolite is frequently found with dolomite mg smectites or palygorskite in the intermediate unit of miocene sediments of the madrid basin herein we describe mineralogy texture and mineral chemistry of sepiolite rich layers up to 90 concentration in marl clay sediments either with gypsum chert micro crystalline quartz or dolomite that are up to 2 to 3 m thick the materials studied were formed in shallow lake environments or mudflats these sediments contain dolomite aggregates resembling mineralized microorganisms biomorphs with ovoid morphologies and spherical to tubular internal voids the regular size and relatively uniform shape of the aggregates are likely controlled by the shape and size of the microorganisms the paper describes the presence of organic debris silicification processes and potassium silicate depletion related to the basal sediments that preceded sepiolite rich layers potassium depletion as a nutrient in detrital components and the occurrence of organic and reduced sediment u and sulfide concentration at the interface with sepiolite also can be linked to biosignatures related to the origin of sepiolite in addition the occurrence of dolomite with carbon that has 13c pdb values of

pseudospherulitic fibrous calcite in paleo groundwater unconformity related diagenetic carbonates paleocene of the ager basin and miocene of the madrid basin spain abstract massive decimeter thick intervals formed by mosaics of subspherical calcite crystals displaying an intracrystalline fibrous microfabric have been found in paleocene and miocene strata in spain the fibrous microfabric is marked by inclusion defined fibers that radiate from the central parts of the crystals which can be termed pseudospherulites and not spherulites because they are single crystals and not polycrystalline aggregates the horizons of pseudospherulitic calcite appear in meter scale laterally persistent levels of crystalline limestones that exhibit complex pseudospar fabrics they are interbedded with peritidal and or lacustrine deposits they grade downward into bedded dolomicrites and they can be linked to unconformities several meters higher in the section above intervening unaltered limestones the pseudospar zones are interpreted as early diagenetic paleo groundwater alteration products after dolomicrites the pseudospherulites are composed of low mg calcite with low contents of fe and mn and they have a stable isotope composition indicative of precipitation from meteoric water they form xenotopic mosaics in which goethite palygorskite and sepiolite may be present as inclusions and in the intercrystalline matrix cathodoluminescence microscopy reveals peripheral growth of the pseudospherulites which results from several phases of precipitation and even of dissolution the first phase of crystal growth may show rhombic habits and may contain corroded dolomite inclusions interpreted as an indication of growth at the expense of dolomicrite by a dissolution precipitation process the second phase of crystal growth is fibrous sensu stricto exhibits lobate growth laminae and shows indications of displacive growth the pseudospherulitic fabric is not relict and the pseudospherulites do not represent speleothems recrystallized microcodium or neomorphosed spherulitic carbonate instead they are interpreted as split crystals that grew within dolomicritic host sediments in part by dissolution precipitation and in part by displacement the hypothesis of a dolomicritic host is supported by the geological and diagenetic setting by the presence of corroded dolomite inclusions within the pseudospherulites and by the relationship between their growth and the authigenesis of sepiolite palygorskite and goethite the pseudospherulites grew in the shallow subsurface at or near the water table from predominantly oxidizing meteoric water and under periodically fluctuating geochemical conditions saturation redox caused by fluctuations of the water table during periods of subaerial exposure the presence of fossil bacteria within the pseudospherulites the anastomosing pattern of the inclusion defined fibers and the lobate growth forms of the fibrous calcite suggest some bacterial influence in the genesis of the pseudospherulitic fabric

pedogenic and early diagenetic processes in palaeogene alluvial fan and lacustrine deposits from the sado basin s portugal abstract the palaeogene deposits of the sado basin were deposited in a continental basin that shows a typical pattern with alluvial fans system in the margins of the basin passing towards distal areas of mudflat facies where in some areas the installation of shallow water bodies favoured the development of palustrine conditions the deposits of this basin vary form coarse conglomerates and sandstones to palustrine carbonates these sediments were affected by pedogenesis and early diagenetic processes that promoted important modifications on their primary features these modifications have been studied by the analyses of four profiles developed on proximal middle and distal fan deposits and the fourth one on lacustrine deposits the overall analyses of the sedimentological pedogenic diagenetic features and their relationships indicate that three main processes took place throughout the basin soil formation palygorskite neoformation and dolomitization soil formation processes led to illuviation of clays and carbonate precipitation mostly around roots pedogenic carbonates increase towards distal areas whereas hydromorphic features are present throughout the basin palygorskite neoformation was partially diagenetic being maximum in proximal areas and palustrine deposits this neoformation is attributed to the percolation of alkaline mg rich soil and groundwaters through smectitic rich sediments promoting important clay transformation dolomitization was an early diagenetic process that occurred mainly in carbonate rich deposits of distal and lacustrine environments as a result of the increasing mg ca ratio of the percolating groundwaters in all these processes there has been a close spatial and temporal interplay between pedogenesis and diagenesis driven by the chemistry of soil particles and groundwaters

overlapping of pedogenesis and meteoric diagenesis in distal alluvial and shallow lacustrine deposits in the madrid miocene basin spain the miocene distal alluvial fan and palustrine deposits of the madrid basin paracuellos de jarama area were examined to establish the sequence of its pedogenic diagenetic processes and the main factors controlling them in this area the diagenetic processes operated not only on carbonates as commonly studied but also in high magnesium clays and opaline cherts this paper provides a dynamic model for saline alkaline lake margins that complements the existing freshwater palustrine model three sections ber pel and upc containing limestones sepiolite dolostones and opaline cherts were examined these represent the entire transition from alluvial fan deposit to lake environment the alluvial fan deposits pel section show the most complex sequence of processes after a weak edaphic imprint the primary mudstone and siltstones are affected by silicification opaline levels formed mainly by selective replacement of sepiolites and later dolomitization several types of dolomite are present rounded crystals spherules and globular bodies being the most characteristic in the ponds situated at the foot of the alluvial fans or in interfan areas sepiolite precipitated within free water bodies ber section and an intense pedogenesis led to the formation of palustrine sepiolite deposits later the intense silicification of the sepiolite produced lenticular opaline levels that were locally transformed to quartz by aging in the shallow lakes upc section palustrine limestones and sepiolite were deposited the carbonates are partially affected by silicification the sepiolite becoming completely silicified the opaline levels clearly preserve the structure of the limestones and sepiolite host rocks all the opaline levels show local aging processes the silicification processes were different in the three settings due to the interplay of groundwater with sedimentary environments and facies in the distal alluvial fan sediments of the pel section the initial host rock affected by silicification is not preserved due to the later dolomitization that erased both it and its textures the silicification environment was therefore not easy to determine in the ber and upc section the main silicification took place in groundwater influenced environments but evidence was seen of cements and silicifications in vadose environments in all study settings the overlapping of pedogenic vadose and groundwater processes was controlled by changes in the position of the water table four stages were concluded to explain the transformation from the primary deposits to the later dolomitization process and the formation of vadose cements the majority of the silicifications seen occurred as responses to changes in the water table position linked to the aggradation of this closed basin in all the studied environments the sepiolite deposits were preferentially silicified their fibrous structure and high absorption capacity helping to retain interstitial fluids moreover sepiolite and opal are stable under relatively similar geochemical conditions in arid environments the dissolution of the sepiolite caused an increase in silica in the interstitial fluids favouring silicification and ruling out the need of a biogenic source the replacement of limestones by silica is usually driven by variations in ph and salinity which are very common in surface environments such as shallow lakes and soils

provenance and thermal history of the franciscan accretionary complex constraints from zircon fission track thermochronology the franciscan accretionary complex of california contains large belts of sediments that were subducted to depths of 10 to 30 km metamorphosed under high pressure and low temperature conditions and later returned to the surface reconnaissance zircon fission track ft data 21 samples place constraints on the sedimentary provenance thermal history and or exhumation history of various franciscan units in a transect across the northern coast ranges through mendocino pass metagraywacke samples from the valantine springs formation of the franciscan eastern belt experienced maximum temperatures tmax ranging from 250 to 310 c zircon ft and previously reported apatite ft data indicate that parts of the western eastern and eastern central belts cooled at about 100 70 ma from 300 c to 100 c considering the low paleogeothermal gradient of roughly 9 c km during franciscan subduction these rocks were apparently uplifted and exhumed from 30 to 10 km depth at this time one sample from the eyler mountain sequence in the northwestern diablo range similarly shows tmax 310 c and major cooling at 100 70 ma this uplift and exhumation may have reflected accelerated accretion at the base as well as the front of the franciscan wedge accompanied by extensional thinning at shallower levels as a result of massive sediment influx into the franciscan trench from the sierra nevada magmatic arc in the northern coast ranges the western part of the central belt and the coastal belt experienced lower tmax probably 200 c and retain source area detrital zircon ft ages burnt hills terrane samples in the diablo range also experienced tmax 230 c and retain detrital ages the detrital single grain age patterns from these areas are compatible with those expected from the sierra nevada magmatic arc and its country rocks this is consistent with derivation of franciscan sediments from arc terranes in california and provides no particular suggestion that these parts of the franciscan are highly allochthonous paleogene coastal belt sandstones also yield detrital ages compatible with derivation from the sierra nevada but also include early tertiary zircon populations compatible with reconstructions suggesting these sandstones were sourced partly from the idaho batholith

impact of mongolian plateau versus tibetan plateau on the westerly jet over north pacific ocean mountains have long been considered to play an important role in the formation of modern climate particularly in the asia pacific sector the existence of tibetan plateau tp is believed to maintain the stationary planetary wave patterns and to intensify the westerly jet over north pacific however the potential role of mongolian plateau mp has often been neglected in these studies with an atmospheric general circulation model we show that the mp despite its smaller size exerts a great influence on the planetary scale circulation and the subtropical westerly jet the mp amplifies the meridional thermal gradient at the mid upper troposphere and thus strengthens the jet which is primarily facilitated by its high latitude location by blocking westerly winds the mp forces their northern branch further northward which allows the southward penetration of cold air at the lee side and intensifies the east asian trough in contrast the impact of the tp itself is not as large as expected hence one should not simply ascribe all the mountain induced climate change to the tp uplift because other smaller topography might be also very important

mineralogy and pressure temperature time path of cretaceous granulite gneisses south eastern san gabriel mountains southern california mid cretaceous granulite gneisses crop out in a narrow belt in the cucamonga region of the south eastern foothills of the san gabriel mountains southern california interlayered mafic granulites and pelitic carbonate calc silicate and quartzofeldspathic metasediments record hornblende granulite subfacies metamorphism at approximately 8 kbar and 700 800 c regional deformation and formation of banded gneisses ceased by c 108 ma although mafic intermediate magmatism and high grade metamorphism continued locally as late as c 88 ma garnet zoning in metapelitic gneisses suggests that peak metamorphism was followed locally by a period of near isobaric cooling but this interpretation requires diachronous cooling of the granulite belt which cannot be demonstrated without detailed thermo chronological data it is more likely that the entire terrane remained at granulite facies p t conditions until 88 ma followed by rapid uplift associated with juxtaposition against adjacent middle and upper crustal arc terranes uplift occurred between c 88 and 78 ma at rates of approximately 1 2 km ma 1 the geotectonic evolution of the cucamonga granulites is similar to mid cretaceous high p granulites in the sierra nevada and salinian block of central california late cretaceous uplift common to these granulites may provide an important tectonic link between dismembered mesozoic batholithic terranes in the california cordillera

developments in the understanding and application of lithium isotopes in the earth and planetary sciences the significant relative mass difference c 16 between the two stable isotopes of li approximately 6li 7 5 7li 92 5 coupled with broad elemental dispersion in earth and planetary materials makes this a system of considerable interest in fingerprinting geochemical processes determining mass balances and in thermometry natural mass fractionation in this system is responsible for c 6 variation among materials examined to date fig 1 although the modern era of li isotope quantification has begun there are still many questions about the li isotopic compositions of fundamental materials and the nature of fractionation by important mechanisms that are unanswered e g hoefs 1997 figure 1 summary of lithium isotopic compositions of earth and planetary materials filled bars are solid samples open bars are liquids see text for references and details the purpose of this chapter is to summarize the current understanding of li isotopes in geo and cosmochemical systems and to indicate 1 where li isotopes have a high probability of adding new understanding of these systems 2 where some of the more significant deficits in knowledge exist the small but burgeoning li isotope community has not yet compiled the volume of peer reviewed literature needed to adequately assess even that which has been studied to date as a result significant portions of this chapter are based on data reported in abstracts and as such are more than normally subject to revisions over time this chapter is anticipated to serve as a starting point for those interested in research incorporating li isotope geochemistry or in understanding the state of extant research experiments in li isotope fractionation knowledge of significant li isotopic fractionation during basic chemical processes is long standing the early experiments by taylor and urey 1938 in which li isotopes were fractionated by incomplete extraction of an aqueous solution from a zeolite exchange

dedolomitization and other early diagenetic processes in miocene lacustrine deposits ebro basin spain abstract a variety of meteoric diagenetic features reveal the development of a syngenetic karst on lacustrine deposits of the ebro basin diagenetic processes that operated on lacustrine laminated and stromatolitic carbonates include the following 1 a first syndepositional stage with processes such as dolomitization desiccation and related breccia formation and sulphate precipitation either as lenticular gypsum crystals or nodules this stage took place under progressive evaporation due to lake level fall when the previous carbonate deposits became exposed as a supra littoral fringe surrounding saline mud flats of adjacent sulphate depositional environments 2 a second early diagenetic stage in which processes such as sulphate dissolution and collapse brecciation dedolomitization calcite spar cementation and silicification occurred as a result of meteoric water input that caused a progressive rise in lake level light isotopic compositions 13 c and 18 o of diagenetic calcites versus heavier compositions in primary laminated and stromatolitic limestones confirm a meteoric influence the syngenetic karst is best developed at the boundary between two allostratigraphic units and coincided with one of the extensive stages of sulphate deposition at the end of the early miocene the karst facies occurred in an area that was a low relief barrier that separated two sites of sulphate deposition during low lake levels this indicates that the karst development was controlled by topographic changes within the basin and record a shift from arid to wetter climatic conditions as suggested by the overlying freshwater carbonate deposits the presence of diagenetic features such as those described in the central ebro basin affecting saline lacustrine carbonates is relevant because they can be used as indicators of subaerial exposure periods in terrestrial environments and they also reveal important palaeogeographic and palaeoclimatic events of basinal extent

palaeogroundwater evolution in playa lake environments sedimentary facies and stable isotope record palaeogene almazan basin spain the palaeogene history of the almazan basin is that of a non marine basin sediments derived from fluvial distributary systems and lateral playa lakes the coeval uplifting of the cameros massif and the aragonian branch of the iberian chain during alpine compression exposed triassic evaporites which became the main source of sulphates to the playa lake system as recorded by the bordalba formation this unit exhibits the classical facies distribution of gypsum precipitating playa lakes which can be grouped into two main settings 1 distal alluvial mud flat and 2 saline mud flat ephemeral lake the stable isotope data for gypsum from the distal alluvial mud flat areas 12 2 18osmow 16 5 10 8 34scdt 13 0 lie within the range of values of neighbouring triassic gypsum or are slightly lower for 34scdt this agrees with palaeogeographical interpretations suggesting that the triassic evaporites were the source of gypsum for the almazan basin the slightly lower values could be explained in terms of a minor contribution through the oxidation and dissolution of palaeozoic derived sulphides the isotopic values for gypsum of the saline mud flat ephemeral lake environments 19 8 18osmow 23 82 15 6 34scdt 19 9 are higher than those of the distal alluvial mud flat the higher 18osmow in the saline mud flat ephemeral lake environments is interpreted as being a consequence of the progressive evaporation of shallow groundwaters from proximal to distal areas the heavier values for the 34scdt in the saline mud flat ephemeral lake environments are interpreted as reflecting the activity of sulphate reducing bacteria which is evidenced by spheroidal dolomite aggregates on gypsum crystals and by the grey colours of the gypsum facies

role of the tibetan plateau thermal forcing in the summer climate patterns over subtropical asia the mechanism of the tibetan plateau tp thermal forcing in influencing the summer climate patterns over subtropical asia is investigated by means of ncep ncar reanalysis diagnosis results show that since the tp is a huge elevated heating source with the strongest heating in the surface layers in summer the thermal adaptation results in a shallow cyclonic circulation near the surface and a deep anticyclonic circulation above it according to the steady barotropic vorticity equation for large scales airflow must converge in the lower layers and diverge in the higher layers over the eastern side of the tp however the western side of the tp is characterized by a reversed structure i e divergence in lower layers but convergence in higher layers hence pumping and sucking processes bring in upward and downward movement over the east and west sides of the tp respectively such a circulation is embedded in the large scale circulation that is forced by the eurasian continental heating because the tp together with iran plateau are located at the central and eastern parts of the continent and because the orography induced circulation is in phase with the continental scale circulation the role of the tp thermal forcing is to intensify the east asian monsoon to its east and the dry and hot desert climate in mid asia to its west the summertime thermal forcing of the rockies and andes can generate similar circulations along the two subtopics as the tp does since they are located near the western coasts but the lower troposphere poleward flow that is induced by orographic thermal forcing does not coincide with the poleward flows over the eastern coastal region that is induced by continental heating and the monsoon rainfall in north and south america is not as strong as in east asia however the equatorward flow and the associated subsidence induced by the two mountain ranges along the western coasts of both north and south america are in phase with those induced by continental heating these contribute to the formation of the stable low stratus clouds and strong long wave radiative cooling over the eastern subtropical pacific regions just off the western coast of the continent

cyclical processes in the north american cordilleran orogenic system to understand linkages among processes that combined to build the north american cordillera we synthesize its tectono magmatic history from the california accretionary wedge to the retroarc foreland of wyoming at this latitude the cordilleran magmatic arc experienced high flux events hfes at ca 160 150 ma and ca 105 90 ma retroarc shortening provided the main source of hfe magmas which in turn created eclogitic arc roots that later foundered into the mantle and cleared the sub arc region of excess mass and provided space to accommodate renewed retroarc shortening the forearc arc and retroarc regions all responded variably to this cycle of tectono magmatic processes and laramide flat slab subduction may have both disrupted and been enhanced by events within this cycle

the link between tibetan plateau monsoon and indian summer precipitation a linear diagnostic perspective the thermal forcing of the tibetan plateau tp is analyzed to investigate the formation and variability of tibetan plateau summer monsoon tpsm which affects the climates of the surrounding regions in particular the indian summer monsoon precipitation dynamic composites and statistical analyses indicate that the indian summer monsoon precipitation is less greater than normal during the strong weak tpsm strong weak tpsm is associated with an anomalous near surface cyclone anticyclone over the western part of the tibetan plateau enhancing reducing the westerly flow along its southern flank suppressing favoring the meridional flow of warm and moist air from the indian ocean and thus cutting providing moisture supply for the northern part of india and its monsoonal rainfall these results are complemented by a dynamic and thermodynamic analysis i a linear thermal vorticity forcing primarily describes the influence of the asymmetric heating of tp generating an anomalous stationary wave flux composite analysis of anomalous stationary wave flux activity after plumb in j atmos sci 42 217 229 1985 strongly indicate that non orographic effects diabatic heating and or interaction with transient eddies of the tibetan plateau contribute to the generation of an anomalous cyclone anti cyclone over the western tp ii anomalous tpsm generation shows that strong tpsm years are related to the positive surface sensible heating anomalies over the eastern tp favoring the strong diabatic heating in summer while negative tpsm years are associated with the atmospheric circulation anomalies during the preceding spring enhancing northerly dry cold air intrusions into tp which may weaken the condensational heat release in the middle and upper troposphere leading to a weaker than normal summer monsoon over the tp in summer

the lithium isotopic composition of waters of the mono basin california mono lake a major closed basin alkaline salt lake in eastern california derives its water from a mixture of creeks and springs with the former providing in excess of 75 of the total the li isotopic composition of lake water has not varied significantly over a 4 year meromictic period 7li 19 5 springs are isotopically distinct groundwater springs and seeps carry water enriched in isotopically heavy li whereas thermal springs supply isotopically light 7li 50 of the li to the lake 2 the li budget is sensitively balanced on small thermal spring contributions 3 of the total spring inflow and 3 the residence time of li in the lake is 28 ka other great basin closed lakes have variable li isotopic compositions 7li from 16 7 to 23 7 all of which differ significantly from those of several major lakes and seawater homogeneously 32

an isotopic study of paleosol carbonates from olduvai gorge the isotopic composition of paleosol carbonates from olduvai gorge can be used to give estimates of the paleoclimatic history of east africa during the plio pleistocene oxygen isotopes are indicative of major changes in the isotopic composition of meteoric water while carbon isotopes are indicative of major changes in the fraction of biomass using the hatch slack c4 photosynthetic pathway three major periods of climatic change in this terrestrial setting occurred at about 1 67 1 3 and 0 6 myr these involved major changes in flora as well as major changes in the isotopic composition of meteoric water overall the climate has become warmer and more arid over the past 2 2 myr

carbonates associated with alluvial fans an example from the messinian colombacci formation of the pietrarubbia basin northern marche italy abstract the carbonates known as colombacci of a terrestrial series deposited within an upper messinian basin in marche italy have been examined by means of stable isotope analyses aas analyses study of thin sections and sem observations the results of the analyses attest to the in situ production of the carbonates in shallow ponds induced by biological activity as well as to the considerable influence of meteoric waters on late messinian sedimentation the carbonates were compared to coeval limestones from neighbouring basins the composition of the latter is indicative of precipitation out of meteoric water as well minor differences reflect the distinct settings of the separate marginal basins of the messinian mediterranean

rapid late miocene rise of the bolivian altiplano evidence for removal of mantle lithosphere abstract the oxygen isotopic compositions of carbonates deposited in the northern altiplano demonstrate a rapid change in late miocene time which we attribute to an increase in elevation rainfall samples over an elevation transect adjacent to the altiplano of northern bolivia display a systematic decrease in mean annual 18 o values and define a local 18 o vs altitude gradient r gonfiantini m a roche j c olivry j c fontes g m zuppi the altitude effect on the isotopic composition of tropical rains chem geol 181 2001 147 167 which we apply to paleo meteoric water values determined from carbonates age constraints from magnetostragraphy and paleoelevation estimates suggest surface uplift of 2 5 to 3 5 km occurred between 10 3 ma and 6 8 0 4 ma when the altiplano rose to its current elevation only the removal of dense eclogitic lower crust and mantle lithosphere can generate a change of this magnitude and rapidity this change coincides with an 30 decrease in the rate of convergence between the south america and nazca plates and the propagation of deformation into the eastern subandean zone which we infer to have resulted from the increase in the force per unit length applied by the elevated andean plateau to the surrounding lowlands

fresh water carbonates from the lower freshwater molasse oligocene western switzerland sedimentology and stable isotopes abstract the lower freshwater molasse of western switzerland comprises a thick series of continental deposits of late oligocene early miocene age fresh water carbonates occur at two main horizons within this succession lower chattian palustrine carbonates calcaires inferieurs show a shallow fresh water fauna flora of ostracods and charophytes but display clear evidence of subaerial exposure in the form of glaebule pisoid formation circumgranular cracking rhizoliths and microkarstic cavities repeated desiccation led to locally intense modification by pedogenesis these horizons record the development of shallow ephemeral lakes at the northern margin of the swiss molasse basin stable isotope analyses were carried out on 46 calcite samples data from matrix and intraclasts reveal typical fresh water compositions 13c 5 to 7 5 18o 5 5 to 9 a weak co variant trend suggests deposition in hydrologically closed lakes although the range of 13c values recorded is also consistent with pedogenetic overprinting associated with subaerial exposure spar cements and vadose crystal silts display 13c compositions from 6 to 7 but show light 18o values from 10 to 11 recording formation from meteoric waters upper chattian carbonates calcaires d eau douce et dolomie include algal ostracodal laminites interpreted as profundal lake deposits as well as bioturbated shallow lake charophyte ostracod mudstones and wackestones sandy wackestones and white dolomite stable isotope analyses 20 calcites 2 dolomites show 13c values from 2 to 6 and 18o from 6 to 11 data for laminites and biomicrites plot in different fields variations in carbon isotopic composition may be attributable to higher organic productivity during high lake stands the laminites show heavier 13c values or to areal differences in the proportions of biogenic authigenic and detrital carbonate 13c values are generally higher in areas of greater detrital carbonate supply the heavier 18o values shown by the dolomites 13 c 3 18 o 0 to 1 suggest formation from evolved evaporitic lake waters these carbonates record deposition in an extensive possibly deeper lake complex subject to clastic input from the alps in the south

sedimentology and geochemistry of carbonates from lacustrine sequences in the madrid basin central spain abstract lacustrine and alluvial carbonate facies have been investigated in middle miocene successions of the western side of the madrid basin in order to evaluate paleoenvironments in which carbonates formed carbonate facies are varied and include 1 calcrete and dolocrete 2 pond deposits 3 lake margin dolostone 4 mudflat carbonate and 5 open lake carbonate facies the dominant mineralogy of these is dolomite and or low mg calcite no high mg calcite or aragonite have been detected in any sample 18 o and 13 c values range from 8 20 to 1 80 pdb and 10 25 to 0 70 pbd respectively more negative 18 o and 13 c values correspond to predominantly calcite calcretes and to carbonate deposited in ponds at the foot of arkosic alluvium higher 18 o values are from both lacustrine carbonate and dolocrete this latter lithofacies has strong geochemical similarities to dolostones deposited in a lake margin environment mudflat carbonate deposited on shallow platforms subject to lake water oscillation shows great heterogeneity in both stable isotope value and trace element content the mineralogy of these carbonates is dominated by calcite and the limestones contain molds of gypsum occurrence of calcitized dolomite textures in these facies suggests the influence of fresher water during expanding lacustrine cycles or further interaction with less saline groundwater trace element contents are considered to be potential indicators of the different carbonate facies types thus aiding the paleoenvironmental interpretation however discrimination among carbonate facies on the basis of trace element contents appears to be dependent on the statistical method utilized for treatment of data more information is needed to ascertain their use as paleoenvironmental indicators

implications of franciscan complex graywacke geochemistry for sediment transport provenance determination burial exposure duration and fluid exchange with cosubducted metabasites 1 interpretation of graywacke provenance has long been used to evaluate the record of tectonic process in orogenic belts our geochemical data from graywackes of the franciscan subduction complex california show that the connection between sedimentary record and geologic processes may be more complex than previously believed trace elements and nd sr pb isotopes of franciscan graywackes indicate two sources types one group lacking negative eu anomaly eu eu 0 9 shows slightly concave up heavy rare earth elements arc like trace element patterns and western pacific island arc like pb isotopes reflecting derivation from older accreted oceanic arc terranes in the sierra nevada klamath mountains the other group displays small negative eu anomalies with trace element patterns resembling post archean australian shale and pb isotopes similar to jurassic cretaceous sierran batholith there is no systematic separation of these two groups by depositional ages thus geochemistry of the graywackes may partly reflect variation in location of sediment delivery systems rather than solely reflecting evolution of the neighboring arc variation of nd sr isotopes with stratigraphic age for the graywackes mimics the trends of the coeval great valley group clastic rocks suggesting that 1 they share the same sediment sources 2 there are no exotic sediment sources that fed the franciscan trench and 3 burial exposure cycles for franciscan clastic rocks were comparatively brief comparison of franciscan graywacke and metabasite geochemistry corroborates earlier conclusions that metabasites had little or no chemical exchange with fluids from cosubducted graywacke detrital zircon age populations major element chemistry and detrital framework modes when compared to our data suggest that the former three parameters underrepresent the mafic component of clastic sediment provenance

carbonate production within the orcadian basin northern scotland a petrographic and geochemical study a number of primary phases and textures are described for the debonian lacustrine carbonates of the orcadian basin textural and mineralogical variations record changes in the original lake water chemistry stable isotopic and trace element studies of the primary carbonate phases support the conclusion that the orcadian basin was the site of a lacustrine system that fluctuated between two end member conditions 1 one or a number of shallow evaporative playa lacustrine systems and 2 a deep probably stratified freshwater lake or lakes the basin was receiving 18o depleted meteoric groundwaters derived from the adjacent caledonian mountains from relatively fresh waters with a 18o composition of 7 or less primary precipitates of low mg calcite or pure calcite are preserved as calcite at times of low lake stand with a water composition of 3 or greater high mg calcite aragonite or protodolomite was precipitated and dolomitized sodium contents of the carbonates generally increase with dolomite content and the grain size of primary calcite precipitates was greater at higher lake levels

sensitivity of east asian monsoon climate to the uplift of the tibetan plateau abstract using the cola center for ocean land atmosphere studies general circulation model a series of numerical experiments were conducted to examine the impact of uplift of the tibetan plateau on the evolution of the monsoon climate in east asia an attempt was made to isolate the effect of the plateau uplift from the changes in other forcing mechanisms we examined the spatial and temporal variation patterns of a variety of climatic variables and indices including monsoon intensity sea level pressure surface and upper air winds temperature at different levels precipitation air humidity and soil moisture our results suggest that the evolution of the east asia monsoon may be more sensitive to the uplift of the tibetan plateau than that of the south asia monsoon moreover the effect of the plateau uplift on the east asia winter monsoon is more significant than that on the summer monsoon in the northern part of east asia north china the formation of the monsoon climate is marked mainly by the establishment of the northerly winds in winter or the winter monsoon system corresponding to the uplift of the plateau when the height reaches approximately 50 of its current elevation on the other hand the establishment of the monsoon climate in the southern part of east asia the yangtze river valley and the area south of it may be much earlier than that in the northern part

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

a numerical model study on the behaviour of asian summer monsoon and amoc due to orographic forcing of tibetan plateau simulations using the echam5 mpi om coupled atmosphere ocean model both with and without the tibetan plateau are performed in order to study the large scale effects of orographic forcing on the behaviour of the asian summer monsoon system our analysis emphasises the significant impact of plateau forcing on the atmosphere ocean interactions it is argued that in addition to the orographic forcing of the tibetan plateau on the climate of asia such as sensible heat pumping and thermal insulation other significant direct processes exist which link the asian summer monsoon to the sea surface temperatures in the north atlantic ocean the removal of the tibetan plateau modifies the wind driven ocean circulations over the north atlantic which leads to a decrease in the surface heat advection over the north atlantic ocean and a decrease in the atlantic meridional overturning circulation this in turn affects via teleconnections both the monsoon rainfall and the position of the intertropical convergence zone

modern non marine dolomite in evaporitic playas of western victoria australia abstract although considerable effort has been made during the past 30 years to understand the occurrence of recent dolomite there are surprisingly few well documented examples of dolomite precipitation in modern continental lacustrine environments fine grained poorly ordered non stoichiometric dolomite occurs in association with magnesite and clay minerals in the modern and holocene sediment of numerous evaporitic lacustrine settings in western victoria we conclude that this dolomite is primary i e nucleated from solution and accumulated as a primary sediment rather than secondary replacement of a precursor carbonate cores from selected basins show that this dolomite micrite has been accumulating for over 10 000 years

comparative study of major element geochemistry of gypsum ghost limestones and selenite lithofacies from the miocene of northern carpathian foredeep implication to the model of massive replacement of solid sulphates by calcium carbonates abstract gypsum ghost limestones and selenite gypsum facies commonly believed to be as lithological equivalents caused by massive replacement of selenites by limestones occur in the same miocene evaporitic series of the northern carpathian foredeep southern poland and differ considerably with regard to their sedimentological features and major element compositions the differences dealing with variation of contents ranges means patterns of distribution correlations and interelement ratios of the major elements clearly do not indicate any geochemical similarities between the gypsum ghost limestones and the selenite gypsum lithofacies mass balance chemistry shows a deficit of calcium and sulphur contents in the limestones compared to the composition of the selenitic gypsum and implies that the gypsum ghost limestones system was open to mass transfer and cannot be related to simple and regionally extended replacement of solid sulphate rocks by limestones plus native sulphur the major element geochemistry of the gypsum ghost limestones and the selenites represent their original compositions which in turn reflect original depositional settings rather than pore water chemistry during replacive diagenesis both the lithological units developed in co eval depositional domains carbonate and sulphate constituting an evaporitic system but corresponding to different sedimentary settings of the system the gypsum ghost limestones reflect the unique situation of simultaneous formation of carbonate and selenites in a sedimentary transitional milieu between the carbonate and gypsum domains where bottom calcium carbonate deposition was alternating with the growth of selenite crystals the results are clearly inconsistent with the epigenetic model of formation of the polish sulphur deposits which assumes massive and regionally extended replacement of sulphate deposits by carbonates

impacts of extremely asymmetrical polar ice sheets on the east asian summer monsoon during the mis 13 interglacial abstract marine isotope stage mis 13 500 ka ago was a relatively weak interglacial according to the benthic 18o and antarctic ice core records however proxy records from the northern hemisphere indicate that mis 13 was at least as warm as or even warmer than more recent interglacials with an extremely strong summer monsoon and possible melting of the greenland ice sheet in this study assuming an asymmetric hemispheric climate we investigate the response of the east asian summer monsoon to various greenland and antarctic ice sheet sizes using a set of sensitivity experiments with the hadcm3 model through factor separation analysis results show that with no greenland ice sheet and a large antarctic ice sheet there is an enhancement of summer monsoon precipitation in the east asian monsoon region of up to 7 in agreement with the direction of change from proxy reconstructions for china this enhancement is associated with a stronger land sea thermal contrast more water vapor transport to east asia and a northward shift of the intertropical convergence zone the response to the greenland ice sheet removal is related to thermodynamic and topographical effects that influence the east asian monsoon through an orographically induced wave train the response to the larger antarctic ice sheet involves stronger upwelling of circumpolar deep water in the southern ocean melts the sea ice leading to a warmer sst this warming propagates to the north affecting the east asian summer monsoon

a model for the distribution of trace elements between calcite and dolomite abstract a crystal growth model is proposed which allows ions of a trace element to enter the ca and mg sites of dolomite in proportion to the size of the ions relative to that of ca and mg ions and which assigns equal portions of the trace element to the ca site of dolomite and the ca site of associated calcite the model produces calcite dolomite distribution coefficients of 0 79 for mn and 0 43 for fe which may be compared with 0 85 and 0 28 as observed in marble and a distribution coefficient of 2 0 for sr and ba which may be compared with observed values of 2 3 for sr and 1 8 for ba

models of miocene marginal lacustrine sedimentation in response to varied depositional regimes and source areas in the madrid basin central spain abstract a succession of lake complexes formed through miocene times in the madrid basin central spain the complex formed during the aragonian stage provides an outstanding opportunity to evaluate the role of source areas and depositional regimes in the construction of coeval marginal lacustrine deposits sedimentary facies of the aragonian lake indicate a shallow lake that was fringed to the nw and s by arkosic alluvium to the n by litharenitic alluvial fans and to the ne and e by alluvial fans distally dominated by large floodplains marginal lacustrine deposits in the arkosic realm mostly consist of mg smectites and dolomite sequences that laterally interfinger with sepiolite beds which were deposited in small discontinuous ponds in the distal alluvial fan areas occasionally micaceous rich sandy streams entered the lake forming sheets at their entry points in contrast the northern margin of the lake was formed by muddy flats which were influenced by fluctuation in the water table in this setting illitic mudstones are commonly interbedded with biotite rich flood sands showing a sheet like geometry meandering channels occasionally cut into the mud flats facies assemblages on this side of the lake were mainly derived from low grade metamorphic areas to the northeast the marginal lacustrine facies consist of silty clays carbonate paleosols and paludal to lacustrine limestones these facies reflect an interfingering between the lake and a wide stream floodplain system derived from a carbonate source area the mosaic of marginal lacustrine facies in the madrid basin during the aragonian is discussed in the light of lithological and geochemical factors related to variations in source areas

high elevation of the nevadaplano during the late cretaceous during the late cretaceous central nevada may have been a high elevation plateau the nevadaplano some geodynamic models of the western us require thickened crust and high elevations during the mesozoic to drive the subsequent tectonic events of the cenozoic while other models do not to test the hypothesis of high elevations during the late mesozoic we used carbonate clumped isotope thermometry to determine the temperature contrast between late cretaceous to paleocene carbonates atop the putative plateau in nevada versus carbonates from relatively low paleoelevation central utah site lacustrine carbonates from the nevada site preserve summer temperatures 13 c cooler than summer temperatures from paleosol carbonates from the utah site after correcting for 1 2 c of secular climatic cooling between the times of carbonate deposition at the two sites this 13 c temperature difference implies an elevation difference between the two sites of 2 2 3 1 km including uncertainties from age estimation and climate change broadens this estimate to 2 km our findings support crustal thickness estimates and cenozoic tectonic models that imply thickened crust and high elevation in nevada during the mesozoic

what do we really know about early diagenesis of non marine carbonates abstract non marine carbonate rocks including cave spring stream calcrete and lacustrine palustrine sediments are susceptible to early diagenetic processes these can profoundly alter the carbonate fabric and affect paleoclimatic proxies this review integrates recent insights into diagenesis of non marine carbonates and in particular the variety of early diagenetic processes and presents a conceptual framework to address them with ability to study at smaller and smaller scales down to nanometers one can now observe diagenesis taking place the moment initial precipitates have formed and continuing thereafter diagenesis may affect whole rocks but it typically starts in nano and micro environments the potential for diagenetic alteration depends on the reactivity of the initial precipitate commonly being metastable phases like vaterite ca oxalates hydrous mg carbonates and aragonite with regard to the ambient fluid furthermore organic compounds commonly play a crucial role in hosting these early transformations processes like neomorphism inversion and recrystallization cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex primary microtextures if early diagenetic modifications are completed in a short time span compared to the annual to millennial time scale of interest then recorded paleoenvironmental signals and trends could still acceptably reflect original depositional conditions however even compact non marine carbonate deposits may behave locally and temporarily as open systems to crystal fluid exchange and overprinting of one or more geochemical proxies is not unexpected looking to the future relatively few studies have examined the behaviour of promising geochemical records such as clumped isotope thermometry and non conventional stable isotopes in well constrained diagenetic settings ongoing and future in vitro and in situ experimental approaches will help to investigate and detangle sequences of intermediate diagenetic products processes and controls and to quantify rates of early diagenesis bridging a gap between nanoscale molecular lab studies and the fossil field rock record of non marine carbonates

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

dolomitization gypsum calcitization and silicification in carbonate evaporite shallow lacustrine deposits this paper describes and interprets the mineral and facies assemblages that occur in carbonate evaporite shallow lacustrine deposits considering the importance of the processes pathway i e dolomitizacion gypsum calcitization and silicification the palaeogene deposits of the deza formation almazan basin central northern spain are selected as a case study to determine the variety of physico chemical processes taking place in carbonate evaporite shallow lakes and their resulting diagenetic features dolostones are the predominant lithology and are composed mainly of dolomite with variable amounts of secondary calcite 5 to 50 which mainly mimic lenticular gypsum pseudomorphs five morphological types of dolomite crystal were identified dolomite tubes dolomite cylinders rhombohedral dolomite spheroidal and quasi rhombohedral dolomite and cocoon shaped dolomite the dolomite cylinders and tubes are interpreted as the dolomitized cells of a widespread microbial community the sequence of diagenetic processes started with growth of microlenticular interstitial gypsum in a calcareous mud deposited on the playa margin mudflats and that sometimes included microbial sediments immediately following growth of gypsum dolomite replaced the original calcite aragonite muds the microbial community and the gypsum partial or total replacement of gypsum by dolomite was related mainly to the biomineralization of endolithic microbial communities on gypsum crystals later calcitization took place under vadose subaerial exposure conditions the development of calcrete in distal alluvial settings favoured the release of silica and subsequent silicification on the playa margin mudflats stable isotope compositions of calcite range range from 9 02 to 5 83 13cpdb and 7 10 to 1 22 18opdb for the dolomite these values vary from 8 93 to 3 96 13cpdb and 5 53 to 2 4 18opdb quartz from the cherts has 18osmow values ranging from 27 1 to 31 1 wide variation and relatively high 18osmow values for dolomite indicate evaporitic and closed hydrological conditions increased influx of meteoric waters reigned during the formation of secondary calcite spar this article is protected by copyright all rights reserved

the relationship between carbonate facies volcanic rocks and plant remains in a late palaeozoic lacustrine system san ignacio fm frontal cordillera san juan province argentina the san ignacio fm a late palaeozoic foreland basin succession that crops out in the frontal cordillera argentinean andes contains lacustrine microbial carbonates and volcanic rocks modification by extensive pedogenic processes contributed to the massive aspect of the calcareous beds most of the volcanic deposits in the san ignacio fm consist of pyroclastic rocks and resedimented volcaniclastic deposits less frequent lava flows produced during effusive eruptions led to the generation of tabular layers of fine grained greenish or grey andesites trachytes and dacites pyroclastic flow deposits correspond mainly to welded ignimbrites made up of former glassy pyroclasts devitrified to microcrystalline groundmass scarce crystals of euhedral plagioclase quartz and k feldspar opaque minerals aggregates of fine grained phyllosilicates and fiammes defining a bedding parallel foliation generated by welding or diagenetic compaction widespread silicified and silica permineralized plant remains and carbonate mud clasts are found usually embedded within the ignimbrites the carbonate sequences are underlain and overlain by volcanic rocks the carbonate sequence bottoms are mostly gradational while their tops are usually sharp the lower part of the carbonate sequences is made up of mud which appear progressively filling interstices in the top of the underlying volcanic rocks they gradually become more abundant until they form the whole of the rock fabric carbonate on volcanic sandstones and pyroclastic deposits occur with the nucleation of micritic carbonate and associated production of pyrite cyanobacteria which formed the locus of mineral precipitation were related with this nucleation the growth of some of the algal mounds was halted by the progressive accumulation of volcanic ash particles but in most cases the upper boundary is sharp and suddenly truncated by pyroclastic flows or volcanic avalanches these pyroclastic flows partially destroyed the carbonate beds and palaeosols microbial carbonate clasts silicified and silica permineralized tree trunks log stumps and other plant remains such as small branches and small roots inside pieces of wood interpreted as fragments of nurse logs are commonly found embedded within the ignimbrites the study of the carbonate and volcanic rocks of the san ignacio fm allows the authors to propose a facies model that increases our understanding of lacustrine environments that developed in volcanic settings

rapid northward shift of the indian monsoon on the tibetan plateau at the end of the little ice age variations in the indian monsoon im and westerlies ws significantly affect the climate on the tibetan plateau tp and have widespread ecological and socioeconomic impacts on the whole of asian society so far however the rate and magnitude of changes in the im have still remained unclear here we report for the first time that the im rapidly shifted northward at the end of the little ice age lia we used sediment proxies for humidity and moisture sources from the taro co lake which is located in the transition zone between the ws and im our comprehensive survey of climate records for the tp and its peripheral mountain ranges revealed that the northern boundary of the im i e the southern boundary of the ws lay along the southern slope of the gandise range 29 5 n in the late lia in contrast it passed quickly over the gandise range by at least 1 5 in latitude at the end of the lia our results suggest that this rapid climatic shift was potentially triggered by the counteracting effects of blocking by the tp and its marginal orography which hindered the northward movement of the im and the pulling thermal gradient of the tp

early cretaceous transition from nonaccretionary behavior to strongly accretionary behavior within the franciscan subduction complex 1 during subduction at the franciscan trench beginning at 170 160 ma and continuing to the present marine sedimentary and lesser volcanic rocks have been underthrust accreted and metamorphosed to form the franciscan accretionary wedge the south fork mountain schist sfms forms the eastern margin and structural top of the wedge and so was apparently the first unit of substantial size to accrete into the franciscan new u pb ages of detrital zircons and 40ar 39ar ages of metamorphic white micas indicate that the sfms accreted surprisingly late in the time span of franciscan subduction probably at ca 123 ma at least parts of the valentine spring formation and yolla bolly terrane accreted soon thereafter therefore accretion of the sfms apparently marks a fundamental transition from virtually nonaccretionary behavior to strongly accretionary behavior in the franciscan forearc about 75 of modern forearcs are nonaccretionary so recognition of an early nonaccretionary period is consistent with modern examples the franciscan mafic high grade exotic blocks and related very small slabs which yield ca 132 to 169 ma metamorphic ages are the only well documented rock record of the early 40 m y long nonaccretionary period and represent very sparse accretion during that interval the transition into an accretionary regime at ca 123 ma was essentially synchronous with the end of the late jurassic early cretaceous magmatic lull in the sierra nevada magmatic arc with the waning of early cretaceous faulting and warping within the great valley forearc basin and possibly with changes in motion vectors of the pacific and farallon plates

does burial diagenesis reset pristine isotopic compositions in paleosol carbonates abstract sedimentological study of early oligocene continental carbonates from the fluvial dagshai formation of the himalayan foreland basin india resulted in the recognition of four different types namely soil palustrine pedogenically modified palustrine and groundwater carbonates stable oxygen and carbon isotopic 18 o and 13 c analyses of fabric selective carbonate microsamples show that although the pristine isotopic compositions are largely altered during deep burial diagenesis complete isotopic homogenization does not occur 18 o and 13 c analyses of 200 calcrete and palustrine carbonates from different stratigraphic horizons and comparison with 18 o of more robust bioapatite fossil vertebrate tooth phase show that dense micrites 70 carbonate invariably preserve the pristine 18 o value mean of 9 8 while altered carbonates show much lower 18 o value 13 8 such inhomogeneity causes large intra sample and intra soil profile variability as high as 5 suggesting that soils behave like a closed system where diagenetic overprinting occurs in local domains a simple fluid rock interaction model suggests active participation of clay minerals to enhance the effect of fluid rock ratio in local domains during diagenesis this places an upper limit of 70 micrite concentration above which the effect of diagenetic alteration is minimal careful sampling of dense micritic part of the soil carbonate nodules therefore does provide pristine isotopic composition and it is inappropriate as proposed recently to reject the paleoclimatic potential of all paleosol carbonates affected by burial diagenesis based on pristine 13 c value of 8 8 0 2 in soil carbonates an atmospheric co 2 concentration between 764 and 306 ppmv is estimated for the early oligocene 31 ma dagshai time these data show excellent agreement between two independent proxy records viz soil carbonate and marine alkenone and support early oligocene survival of the antarctic ice sheet

continental brackish and marine carbonates from the lower cretaceous of kolone barbariga istria croatia stratigraphy sedimentology and geochemistry abstract during the early cretaceous wide areas of the dinaric adriatic carbonate platform emerged for long periods the hauterivian barremian carbonates from kolone barbariga show a few typical examples of lacustrine facies with dinosaur bones and brackish palustrine facies the sequence of the platform is made for the most part by subtidal and intertidal limestones the bone levels are located in a large depression few meters deep in the uppermost hauterivian marine limestones the filling facies of this depression are made by oncolitic rudstones and algal boundstones which represent marginal lacustrine facies and by laminated limestones thin stromatolitic levels and distal fringes of rudstones which represent relatively open lacustrine facies the fossil content is characterized by rare charophyte stems ostracods gastropods and plant remains while typical marine fauna is absent at the hauterivian barremian boundary a major emersion event has been observed then a slow transgressive phase occurred the transgressive facies are primarily made by mudstones with ostracods charophytes and spirillina brackish and probably freshwater facies wackestones with ophtalmidiidae and rare dasyclad algae storm layers with gastropods and miliolids and breccia like dinoturbated beds wackstones packstones and very rich in dasyclad grainstones outcrop at the top of the section representing the maximum of the transgression trace elements content carbon and oxygen stable isotope analyses have been performed to aid the palaeoenvironmental interpretation in this geological setting barium seems to discriminate between brackish and freshwater facies the isotopic values of the marine carbonates appear to depend on early diagenetic processes meanwhile lacustrine facies seem to show a weak signal of the depositional environment

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

dolomite silica stromatolites in miocene lacustrine deposits from the duero basin spain the role of organotemplates in the precipitation of dolomite this research provides an ancient analogue for biologically mediated dolomite precipitation in microbial mats and biofilms and describes the involvement of highly structured extracellular polymeric secretion eps templates in dolomite nucleation the structure of eps is shown to match the hexagonal trigonal lattice geometry of dolomite which favoured the epitaxial crystallization of dolomite on the organic substrate this structure of eps also matches the arrangement of silica nanospheres in opal which further accounts for the organically templated formation of opal enabling the non replacive co existence of dolomite and silica the study is focused on a 50 m thick dolomite succession that is exposed in central areas of the tertiary duero basin and was deposited in a mudflat saline lake sedimentary complex during the middle to late miocene 9 to 15 ma in the intermediate intervals of the succession poorly indurated dolomite beds pass gradually into silica beds on the basis of sedimentological compositional geochemical and petrographic data silica and dolomite beds have been interpreted as mineralized microbial mats the silica beds formed in marginal areas of the lake in response to intense evaporative concentrations this resulted in the rapid and early precipitation of opal silicification accounted for the exceptional preservation of the microbial mat structure including biofilms filamentous and coccoid microbes and eps extracellular polymeric secretions have a layered structure each layer being composed of fibres which are arranged in accordance with a reticular pattern with frequent intersection angles at 120 and 60 therefore the structure of eps matches the lattice geometry of dolomite and the arrangement of silica nanospheres in opal additionally eps binds different elements with preference to si and mg the concurrence of suitable composition and surface lattice morphologies in the eps favoured the crystallization of dolomite on the substrate in some cases dolomite nucleation took place epicellularly on coccoid micro organisms which gave way to spheroid crystals organic surfaces enable the inorganic mineral precipitation by lowering the free energy barrier to nucleation most of the microbial mats probably developed on the lake floor under sub aqueous conditions where the decomposition of organic matter took place the subsequent formation of openly packed dolomite crystals with inter related si enriched fibrils throughout is evidence for the pre existence of fibrillar structures in the mats miocene dolomite crystals are poorly ordered and non stoichiometric with a slight ca excess up to 5 which is indicative of the low diagenetic potential the microbial dolomite has towards a more ordered and stoichiometric structure this confirms that microbial imprints can be preserved in the geological record and validates their use as biosignatures

lacustrine microbialite pinnacles in the palaeogene of patagonia argentina facies and controls abstract large carbonate microbialite build ups are relatively uncommon in ancient fresh water lacustrine basins as compared with those marine and saline environments this paper discusses the formation of a large continental lacustrine deposit the oligocene miocene carinao formation in argentina which contains large bioherms the lacustrine formation occurs in n s corridor and is mostly composed by meter scale pinnacles and sheet like carbonate beds that grade to detrital deposits towards the more subsident southern areas the main facies are autochthonous and allochthonous limestones and detrital deposits the autochthonous limestones include the carbonate pinnacles which are about 4 m high and 0 5 m in diameter and coalesce laterally to form very continuous beds several kms the pinnacles are formed by plate like dome vertically elongated and irregular horizontal bioherms most of them with radial structure the bioherms are boundstones of fibrous fans and spherulites and feather calcite crystals micrite and inequigranular calcite mosaics both biogenic and abiogenic processes interfered in carbonate precipitation allochthonous limestones include peloidal ostracod and intraclastic limestones some containing coated grains polymictic conglomerates and cross bedded hybrid arenites deposited in a fluvial deltaic system located at the southwest of the basin 13c values vary between 0 4 and 3 2 vpdb and 18o are comprised between 5 7 and 8 6 vpdb the 87sr 86sr ratios range between 0 7061 and 0 7056 the carinao formation deposited in a fresh water lake sourced by meteoric and deep groundwater tectonics was a main control determining the configuration of the lake system the water supply and the alignment of some bioherms the vertical succession or the different bioherms morphologies reflects well the lake level changes controlled by both tectonic and climate

groundwater dolocretes from the upper triassic of the paris basin france a case study of an arid continental diagenetic facies thick dolomite cemented horizons dolocretes occur within a fluvial sandstone mudstone sequence of late triassic age in the western part of the paris basin france two types of dolomites can be distinguished a nodular dolomitic beds less than a few metres thick which formed within mottled overbank siltstones and mudstones and b massive dolomite up to 16 m thick which occurs in coarse grained channel sandstones and conglomerates the majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and less commonly dolomicrite glaebules irregular spar filled cracks spheroidal dolomite silicification and vuggy porosity are locally abundant in the massive dolomite in contrast biologically induced micromorphological features such as rhizocretions and alveolar septal fabrics were observed in the thin nodular dolomite beds the dolomite is near stoichiometric well ordered and non ferroan 18o values range from 7 7 to 0 4 o pdb and 18o values range from 5 1 to 1 8 0 pdb and no obvious difference in the stable isotopic composition between both types of dolomites was observed sr isotope ratios range from 0 7101 to 0 7126 and are invariably higher than the contemporary triassic sea water a vadose pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures several features however argue against a pedogenic origin for the massive carbonates most notably the absence of biologically induced structures the occurrence in coarse grained channel and not overbank deposits and the great thickness these units are thus interpreted as groundwater in origin phreatic calcretes of quaternary age widespread in inland australia are regarded as a modern analogue for the triassic paris basin dolocretes petrographic observations argue in favour of primary proto dolomite precipitation although early diagenetic replacement of calcite by proto dolomite cannot be ruled out strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non marine continental origin for the groundwaters the poorly ordered and non stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near stoichiometric well ordered dolomite that clearly lacks evidence for pervasive recrystallization

the nonlinear response of the atmosphere to large scale mechanical and thermal forcing abstract the subject of large scale mountain waves is reviewed briefly existing mountain wave theory based on a linear system is shown to give an inadequate description of the balance of angular momentum the response of the atmosphere to mechanical forcing in a nonlinear framework is then discussed using a two level quasi geostrophic long wave spectral model based on spherical coordinates including diabatic heating surface friction and mountains the nonlinear theory shows that there exists a critical mountain height hc which is a function of the frictional coefficient as well as the phase difference between the mountain and the surface pressure field if and only if the mountain height is less than this critical value can the deflection effect of the mountain be neglected and the response regarded as approximately linear this critical mountain height is only about 1 km thus most of the atmospheric response to large scale mountains must be nonlinear in the nonlinear case as the mountain heigh

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

recognition of lake level changes in miocene lacustrine units madrid basin spain evidence from facies analysis isotope geochemistry and clay mineralogy abstract the miocene lacustrine sequence exposed near esquivias in the central area of the continental tertiary madrid basin is formed of two main lithostratigraphic units that represent two different stages of a palaeolake system unit i consists of five lithofacies a nodular carbonates and marls b massive dolostones c bioclastic limestones d mudstones and e chert which are characteristic of sedimentation and early diagenesis in a shallow lacustrine environment two main stages of the same general lowstand situation are reflected in mineralogy and isotope geochemistry results an initial stage is suggested by the presence of non stoichiometric dolomite and trioctahedral smectites high 18o and 13c values of the dolomites 5 5 and 2 9 respectively indicate strongly evaporative conditions a second stage is characterized by the presence of calcite fibrous clay minerals and by generally lower 18o from 1 5 to 6 5 and 13c from 1 to 9 8 values for carbonates which suggest more diluted waters during this lowstand phase of the lake unit ii comprises seven lithofacies a conglomerates b intraclastic mudstones c laminated marls d massive mudstones e diatomaceous marls f laminated bioclastic limestones and g root bioturbated limestones both conglomerates and intraclast mudstones fill sharply eroded contacts in the underlying deposits of unit i we demonstrate how the arrangement of facies supported by isotopic results from the carbonates 18o from 0 7 to 7 2 13c from 4 2 to 8 6 is clearly indicative of deeper lake conditions the basal reworked facies mark the initial phase of a lake transgression in contrast with unit i the clay mineral assemblage from unit ii is mainly detrital clay minerals thus also support the interpretation of a dilute water body consistent with a highstand of the palaeolake