miocene pliocene boundary magnetostratigraphy at capo sopartivento calabria itlay a magnetostratigraphic study at capo spartivento calabria southern italy indicates that the miocene pliocene boundary lies in the lowest reversed interval chron 3r of the gilbert chron the magnetostratigraphic time frame gives an estimate close to 19 ka for the duration of individual limestone marl couplets that characterize the lithology the eight couplets within chron 3r indicate that the age of the miocene pliocene boundary is about 154 ka older than the age of the reversal at the top of chron 3r 4 78 ma we therefore estimate the age of this boundary as 4 93 ma which is 420 ka younger than that given by berggren et al and 100 ka older than that given by zijderveld et al the first appearance datums of globorotalia margaritae and globorotalia puncticulata are similarly estimated to have ages of 4 66 and 4 15 ma respectively the former being considerably younger than its first appearance in the open ocean

tectonics and sequence stratigraphy in messinian basins sicily constraints on the initiation and termination of the mediterranean salinity crisis deposits within the caltanissetta basin of central sicily have been important for developing the desiccating deep basin model for the messinian salinity crisis in the mediterranean linked structural and stratigraphic studies show that the sicilian depocenters are synclines related to underlying thrust structures of the frontal part of the maghrebian chain prior to the salinity crisis these basins were hydrodynamically linked through the foredeep to the mediterranean the precursor sediments terravecchia formation formed a delta sourced from the north early messinian regression acted on a range of paleobathymetries shallow in the north and progressively deeper in the south locally complicated by active thrust structures initial draw down of mediterranean base level is marked across the thrust belt by first cycle carbonates and evaporites on the structural highs and lows respectively vast accumulations of halite and potassium salts up to 1200 m are restricted to growing thrust synclines the different evaporite signatures may be related to different water conditions reflecting various meteoric and marine circulations across various subbasins with cyclicity reflecting high frequency variations in sea level a sequence stratigraphic model is developed to explain fractionation of evaporite facies between different paleobathymetric settings and to predict the temporal evolution of the successions in different subbasins thrusting provides accommodation space for evaporites and also controls the water pathways into the desiccating basins the intra messinian unconformity separating first and second cycle evaporites is a type 1 sequence boundary related to the forced regression associated with the acme of mediterranean desiccation an interpretation supported by local ravinement and incised valley fills the overlying second cycle evaporites are a combination of detrital reworked first cycle material and primary gypsum formed under brackish water regional onlap relationships and bed continuity suggest that this water body was of regional extent with a systematically rising base level these interpretations have several implications for messinian correlations in the mediterranean the deep basin evaporites correlate with an intra messinian unconformity that separates the two cycles on sicily and postdate the first cycle deposits regional base level was largely restored before the end of the salinity crisis

models of rock varnish formation constrained by high resolution transmission electron microscopy nanometre scale transmission electron microscope imagery of manganiferous rock varnishes from death valley california peru antarctica and hawaii confirms prior infrared mineralogy studies the building blocks of rock varnish are clay minerals that are cemented to the rock by oxyhydroxides of manganese and iron rock varnish is layered on the scale of nanometres with the basic structure defined by the subparallel alignment of detrital clay minerals although only a few examples of bacteria were found possible cell wall encrustations are ubiquitous and aligned with the clay minerals mn fe oxides appear to be mobilized from bacterial casts and then reprecipitate on clay minerals that weather into monolayers these observations have implications for varnish dating and palaeoenvironmental techniques k ar and uranium series dating of rock varnish oxides can only yield minimum ages however this small spatial scale of mobilization would not alter the signal from micron scale microchemical laminations

trace element evidence for the origin of desert varnish by direct aqueous atmospheric deposition abstract smooth rock surfaces in arid environments are often covered with a thin coating of fe mn oxyhydroxides known as desert varnish it is debated whether such varnish is formed a by slow diagenesis of dust particles deposited on rock surfaces b by leaching from the underlying rock substrate or c by direct deposition of dissolved constituents in the atmosphere varnishes collected from smooth rock surfaces in the mojave desert and death valley california are shown here to have highly enriched and fractionated trace element abundances relative to upper continental crust ucc they are highly enriched in co ni pb and the rare earth elements rees in particular they have anomalously high ce la and low y ho ratios these features can only be explained by preferential scavenging of co ni pb and the rees by fe mn oxyhydroxides in an aqueous environment high field strength elements hfses zr hf ta nb th however show only small enrichments despite the fact that these elements should also be strongly scavenged by fe mn oxyhydroxides this suggests that their lack of enrichment is a feature inherited from a solution initially poor in hfses the first two scenarios for varnish formation can be ruled out as follows the high enrichment factors of fe mn and many trace elements cannot be generated by mass loss associated with post depositional diagenesis of dust particles because such a process predicts only a small increase in concentration in addition the highly fractionated abundance patterns of particle reactive element pairs e g ce la and y ho rules out leaching of the rock substrate this is because if leaching were to occur varnishes would grow from the inside to the outside and thus any particle reactive trace element leached from the substrate would be quantitatively sequestered in the fe mn oxyhydroxide layers prohibiting any significant elemental fractionations one remaining possibility is that the fe mn and trace metals in varnish are derived from leaching of dust particles entrained in rain or fog droplets either in the atmosphere or during wet atmospheric deposition the high trace metal enrichment factors require that most of the dust was physically removed before or during varnish formation the remaining aqueous counterpart would be depleted in hfses and th relative to the rees co ni and pb because the former are more insoluble and hence largely retained in the removed dust fraction the high ce la ratios suggest that precipitation of trace metals may have been governed by equilibrium partitioning in an excess of wet atmospheric deposition if varnishes are indeed derived from wet atmospheric deposition they may provide a record of the aqueous component of atmospheric dust inputs to various environments

strontium isotopes as tracers of ecosystem processes theory and methods abstract the strontium sr isotope method can be a powerful tool in studies of chemical weathering and soil genesis cation provenance and mobility and the chronostratigraphic correlation of marine sediments it is a sensitive geochemical tracer applicable to large scale ecosystem studies as well as to centimeter scaled examination of cation mobility within a soil profile the 87sr 86sr ratios of natural materials reflect the sources of strontium available during their formation isotopically distinct inputs from precipitation dryfall soil parent material and surface or groundwater allow determination of the relative proportions of those materials entering or leaving an ecosystem the isotopic compositions of labile soil exchange complex and soil solution strontium and sr in vegetation reflect the sources of cations available to plants strontium isotopes can be used to track the biogeochemical cycling of nutrient cations such as calcium the extent of cation contributions from in situ weathering and external additions to soil from dust and rain can also be resolved with this method in this paper we review the geochemistry and isotopic systematics of strontium and discuss the use of this method as a tracer of earth surface processes

how fast does rock varnish grow rates of rock varnish accumulation have never been systematically documented owing to the difficulty in accurately determining both varnish thickness and age in this study we quantitatively assess varnish accumulation rates through thin sectioning and microscopic examination of rock varnish from radiometrically dated geomorphic features of late quaternary age in the western united states drylands our data indicate that rock varnish grows at rates ranging from 1 to 40 m k y on subaerially exposed rock surfaces and rarely reaches a thickness exceeding 200 m regardless of age our data also indicate that varnish accumulation rates vary greatly from sample to sample at a given site suggesting that varnish thickness does not correlate with the age of the associated geomorphic feature invalidating the potential use of varnish thickness as a relative age indicator in geomorphology and archaeology nevertheless being the slowest known accumulating terrestrial sedimentary deposit rock varnish constitutes a unique long term microscale sedimentary archive of past environmental changes in deserts

decoding the mediterranean salinity crisis this historical narrative traces the steps to unravel over a span of 40 years an extraordinary event in which 5 of the dissolved salt of the oceans of the world was extracted in a fraction of a million years to form a deposit more than 1 million km 3 in volume a buried abyssal salt layer was identified with reflection profiling and sampled during the deep sea drilling project leg 13 the dolomite gypsum anhydrite and halite in the drill cores paint a surprising picture of a mediterranean desert lying more than 3 km below the atlantic ocean with brine pools that shrank and expanded by the evaporative power of the sun the desert drowned suddenly when the gibraltar barrier gave way the explanation of deep basin shallow water desiccation and the notion of a catastrophic zanclean flood had a mixed reception however the hypothesis became broadly accepted following subsequent drilling expeditions nevertheless as experts examined the evaporate facies and sequences of equivalent age in the terrestrial outcrops weaknesses appeared in the concept of repeated flooding and drying to account for the magnitude of the deposits the rosetta stone used to decipher conflicting interpretations turns out not to be the deposits but the erosion surfaces that enclose them these surfaces and their detritus formed in response to the drop in base level during evaporative drawdown extend to the basin floor evaporative drawdown began halfway through the salinity crisis when influx from the atlantic no longer kept up with evaporation prior to that time a million years passed as a sea of brine concentrated towards halite precipitation during the later part of this interval more than 14 cyclic beds of gypsum accumulated along shallow margins modulated by orbital forcing the thick salt on the deep seabed precipitated in just the next few cycles when drawdown commenced and the brine volume shrank upon closure of the atlantic spillway the remnants of the briny sea transformed into salt pans and endorheic lakes fed from watersheds of eurasia and africa the revised model of evaporative concentration now has shallow margin shallow water and deep basin deep water precursors to desiccation

application of strontium isotopes to late miocene early pliocene stratigraphy measurements of sup 87 sr sup 86 sr ratios of planktonic foraminifers from paleomagnetically dated deep sea drilling project dsdp cores indicate that the sup 87 sr sup 86 sr ratio of seawater increased linearly between 6 and 4 ma with a slope of 87 times 10 sup minus 6 m y this suggets that sup 87 sr sup 86 sr variation in this time interval are useful for estimating ages in marine sequences the theoretical stratigraphic resolution of the technique is 0 23 m y but the practical resolution is estimated to be 0 3 0 5 m y strontium isotope ratios of five samples at the base of the miocene pliocene m p boundary stratotype at capo rossello sicily have a mean sup 87 sr sup 86 sr value of 0 708995 plus minus 0 00002 applying the regression equation derived from our sup 87 sr sup 86 sr vs age data set for deep sea sequences yields an age of 4 94 plus minus 0 50 ma 95 confidence interval for the m p boundary stratotype similar to ages estimated by biostratigraphic and magnetostratigraphic methods correlation of this mean sup 87 sr sup 86 sr ratio to the section at dsdp site 519 suggests that the boundary is coincident with the onset of a major early pliocene transgression as recorded by a decrease in oxygen isotope values for benthic foraminifers this studymore demonstrates the potential application of strontium isotope stratigraphy for correlating and dating problematic sequences such as those deposited in restricted shallow water or high latitude environments less

anthropogenic lead as a tracer of rock varnish growth implications for rates of formation rock varnish is a thin dark coating best known from deserts and is believed to grow extremely slowly varnish samples from near socorro new mexico united states contain as much as 3 7 pbo derived from nearby smelters operating from a d 1870 to 1931 additional varnish measuring as much as 4 m beyond the pb rich layer indicates continued growth from 1931 to 2003 comparison with other varnish confirms that the pb is not an artifact based on pb layer thickness and the period of smelter operation these very young rock varnishes yield growth rates of 28 639 m k y substantially higher than previously documented fastest rates of 40 m k y these rates imply that the average 1 2 m k y rate for older varnish is not the active growth rate rather it is a long term value including periods of nondeposition erosion and active growth therefore models of rock varnish formation should be reevaluated with consideration of much faster maximum growth rates

competing deformation mechanisms and slaty cleavage in deformed quartzose meta sediments abstract summary quartzose sediments from the lower palaeozoic orogen of svalbard have suffered metamorphism to low grade 6 kb and a maximum of 500 c studies of the deformed micro structures of these rocks reveal that pressure solution and intracrystalline deformation mechanisms are the major processes by which deformation occurs the dominant mechanism for any given lithology at approximately the above conditions of pressure and temperature appears to depend on the rock composition quartzose rocks containing micaceous and other impurities tend to deform by pressure solution those containing little or no other material apart from quartz tend to deform by intracrystalline deformation mechanisms

origin and age of the mediterranean messinian evaporites implications from sr isotopes strontium isotope ratios from the messinian late miocene 6 4 to 4 85 ma evaporites of the mediterranean basin 1 2 support a subdivision into stratigraphically lower predominantly marine deposits lower evaporites lev lower gypsum and main salt characterized by sr isotopic ratios generally equivalent to those of messinian seawater and stratigraphically higher deposits upper evaporites uev with 87sr 86sr ratios lower than messinian seawater the range of 87sr 86sr ratios of the lev unit from the eastern mediterranean overlap with values obtained from essentially coeval red sea evaporites 3 strontium isotopic ratios measured from the upper evaporites however are lower and a high proportion of this sr was probably derived from low 87sr 86sr continental runoff that characterizes much of this basin 4 these results therefore strongly support depositional models utilizing a deep desiccated basin 1 with a constant marine inflow during the early stages including salt formation followed by a series of long lasting and sometimes isolated desiccation events that produced a strong but variable continental influence on the sr isotopic compositions of the uev strontium isotopic measurements can also be used to asses the actual timing of the deposition of the lev ratios obtained from oyster fragments and foraminifers from pre evaporitic units at odp site 654 tyrrhenian sea suggest that the major rifting phase in this region occurred between 8 and 6 5 ma ratios obtained from the early lev from the mediterranean sea suggest that initiation of evaporite deposition began about 5 65 ma ago results from units immediately overlying the uev in sicily suggest termination of evaporite deposition about 4 9 ma ago errors associated with these age estimates are about 0 5 ma 2

pyrite deformation in stratiform lead zinc deposits of the canadian cordillera pyrite textures in five stratiform lead zinc deposits from lower to upper greenschist facies environment of the canadian cordillera are described and discussed in terms of deposition early diagenesis deformation metamorphism and hydrothermal alteration processes overgrowth is an important process during both diagenesis and deformation diagenetic and deformational overgrowths can be distinguished diffusive mass transfer involving pressure solution and oriented overgrowth of pyrite is the main deformation mechanism in pyrite deposits at low metamorphic grades although diffusive mass transfer favours fine grained mineral aggregates its effect on coarse pyrite grains has also been identified ore minerals dissolved by pressure solution may be transported with the assistance of pore fluids within fractures and grain boundaries over distances significantly greater than the scale of individual grains to give a range of pressure solution overgrowth textures the textural modification of pyritic ores from the early stages of diagnesis through metamorphism and deformation to post deformation thermal annealing has important implications for the distribution of trace elements and isotopic compositions in pyritic ores

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

a note on the characteristics and possible origins of desert varnishes from southeast morocco two substrate controlled varnish types were identified from arid southeast morocco 1 patchy varnish interspersed with silica glaze on silicified limestone and 2 a complete varnish cover on partially silicified limestone electron probe microanalysis was used in conjunction with scanning electron microscopy to investigate their chemical composition in both instances varnishes are predominantly silica and iron rich with localized concentrations of manganese inorganic fixation of iron and manganese is the preferred explanation with manganese and iron derived predominantly from external sources possibly wind blown dust some iron and silica may also be derived by outward migration from within the substrate particularly on partially silicified limestone

magnetobiostratigraphy of a late miocene section from the moroccan atlantic margin abstract paleomagnetic study of a late miocene section from atlantic morocco correlated with detailed biostratigraphic data suggests an assignment of the observed polarity sequence to the uppermost part of chron 7 to entire chron 6 and to the beginning of chron 5 comparison with time equivalent sections in the southern hemisphere does not suggest noticeable delay in long faunal migration between the northern and southern hemisphere during the late miocene thus the postulation of a delay in arrival of species in the eastern mediterranean at the base of the messinnian has to be explained by the presence of selective barriers which could have been located either between the mediterranean and atlantic or between the western and eastern mediterranean in the basins delineated during the final evolution of the tethys this study also indicates a possible application of biomagnetostratigraphy to the reconstruction of basin interconnections

sea level events in the south pacific linked with the messinian salinity crisis cores drilled through the carbonate cap of niue a mid oceanic carbonate platform in the south pacific contain an unusually well resolved stratigraphic section of the latest miocene at 35 to 140 m depth below sea level intensely leached and chalky intervals associated with pronounced 18 o and 13 c depletions mark the position of dissolution unconformities representing eight episodes of eustatic falls that outstripped the local rate of subsidence we demonstrate on the basis of sr isotope chronostratigraphy that these eustatic changes are correlative with the messinian salinity crisis events in the mediterranean sea level changes of about 10 m amplitude commenced at 6 14 ma and culminated in a large sea level fall that reached at least 30 m at 5 26 ma corresponding to the miocene pliocene boundary evaluation of the sea level history reported here and the contemporaneous mediterranean events supports the model of coupling between tectonic and eustatic factors that caused the onset and demise of the salinity crisis the available evidence suggests that during messinian time glacio eustatic falls and rises are likely to have modulated the connection between the atlantic and the mediterranean and influenced the evaporite deposition and may have contributed significantly to the final phase of isolation and desiccation of the mediterranean and its subsequent refilling during the zan clean deluge

miocene unconformities in the central apennines geodynamic significance and sedimentary basin evolution abstract this paper shows the results obtained from an integrated study geology biostratigraphy and geochemistry carried out on the miocene edimentary deposits in central italy in order to define the timing of the sedimentary basin evolution this paper deals also with the causes of the unconformities recorded in these basins in the miocene deposits of the latina valley and the ernici simbruini mts several unconformities which distinguish different stratigraphic sequences have been recognized d 0 d 1 d 2 d 3 and d 4 for each unconformity a general description together with a geodynamical significance is provided in particular d 0 unconformity appears to be related to a regional tectonic event adria europe collision as a consequence the adria lithosphere folded and the area underwent a regional erosive event d 1 d 2 and d 3 unconformities have had a more local tectonic control since they represent the stratigraphic record of the migration of the apennines thrust belt foredeep system d 1 and d 2 unconformities are related to the late tortonian foredeep stage whereas d 3 is linked to the early messinian piggy back stage moreover the d 4 unconformity which took place during the messinian piggy back stage is strictly linked to the sea level drop of the messinian salinity crisis in this paper the genesis and evolution of a late tortonian foreland basin is also stressed latina valley foredeep basin finally taking into account sequence boundaries nannofossil biostratigraphy and geochemistry isotopic data a comparison with the curve of the 3rd order of the relative coastal onlap haq et al 1988 has been attempted in order to distinguish the unconformities controlled either by tectonic or eustatic processes

characteristics of desert varnish from nanometer to micrometer scale a photo oxidation model on its formation abstract rock varnish is a widespread mn rich rock coating commonly developed in arid environments but the mechanism for its formation is still under debate in this study rock varnish and adjacent soil dust collected from gobi desert were analyzed for exploring the possible abiotic oxidation mechanism of mn oxides the occurrence of rock varnish shows a direct and close relationship with strong irradiation of sunlight giving the first evidence of photochemical genesis abundant caves and tunnels with average diameter of 1 5 m are observed on varnish surface regions which facilitate the penetration of sunlight and water metal oxyhydr oxides including birnessite hematite goethite rutile and anatase account for the major components of rock varnish which are all solar light responsive semiconducting minerals the trace elements enrichment patterns revealed by la icp ms provide the indication of an aqueous origin the positive ce anomalies in varnish in contrast to the rock substrate as well as the positive correlation between ce and mn suggest a strong oxidizing environment in the genesis of rock varnish therefore the photo generated holes and reactive oxygen species ross on metal oxides in varnish can promote mn ii oxidation which are further demonstrated from thermodynamic and kinetic considerations ross including 1o2 and oh with strong oxidizing capability are detected by epr in varnish suspension providing the direct evidence for mn ii oxidation laboratory experimental simulations show the photocatalysis of metal oxides in rock varnish greatly promote mn ii oxidation by 2 10 7 97 times in comparison with homogenous solution oxidation all these lines of evidence suggest that light induced abiotic process may play important roles in the formation of rock varnish together with other abiotic and biotic pathways which can even provide implications for the evolution of mn oxides on surface of terrestrial planets

deformation history of the puna plateau central andes of northwestern argentina abstract two tectonic shortening events created the first order structural characteristics of the puna plateau one in the paleozoic and a second during the andean orogeny in the cenozoic to constrain the structural characteristics and timing of andean deformation in the puna plateau we focus on differentiating these two shortening events and provide cooling ages apatite fission track and apatite u th he to determine the amount of andean exhumation on the hanging wall of major cenozoic faults two contrasting expressions of shortening are documented in ordovician strata strain requires four stages folding flattening through cleavage formation low angle faulting and local distributed shear in the mesozoic and cenozoic strata shortening is expressed as reverse faults fault propagation folds and dipping panels dissimilarities reflect different p t conditions and amount of strain as structures in the ordovician rocks require higher temperatures and strain than andean structures in the mesozoic and cenozoic strata furthermore local cretaceous aft cooling ages in pervasively cleaved ordovician rocks reveal these rocks did not reach temperatures compatible with cleavage formation during the andean event lastly our data show a middle eocene to oligocene exhumation history that supports an overall continuous development of the andean thrust belt in the puna plateau since the early cenozoic

late miocene magnetobiostratigraphy of crete six upper miocene marine clay sections on crete greece have been subjected to a detailed magnetobiostratigraphic analysis six correlatable polarity zones are recognized and these demonstrate the regional synchrony of planktonic foraminiferal biohorizons by way of correlation to the magnetic polarity time scale of lowrie and alvarez 1981 the cretan sequence is assigned to polarity chronozones 5 anomaly 3a and 6 the new chronology provides an age of 5 6 ma for the first occurrence datum fod of thegloborotalia conomiozea group in the mediterranean an age of 6 0 ma for the fod ofg menardii form 5 and an age of 6 6 ma for the last occurrence datum lod ofg menardii form 4 correlating the polarity record of the new zealand blind river section kennett and watkins 1974 with the magnetic polarity time scale provides an age of 6 0 ma for the evolutionary appearance ofgloborotalia conomiozea which is in complete agreement with the age of 6 1 0 1ma given by loutit and kennett 1979 the demonstrated diachrony of 0 4 ma between the new zealand fod ofg conomiozea and its mediterranean counterpart is explicable in view of the different nature of the two events the one in new zealand being evolutionary and the one in the mediterranean migrational the fod of theg conomiozea group in the tortonian messinian boundary stratotype section coincides with the level proposed by colalongo et al 1979 to mark the base of the messinian since the fod of theg conomiozea group in crete and in sicily are most probably time equivalent the age of the tortonian messinian boundary is fixed at 5 6 ma the youngest sediments incorporated in this study extend into the gilbert chronozone and antedate the main evaporitic phase consequently the messinian evaporitic body is younger than the base of the gilbert chronozone the age of which is fixed at 5 3 ma adopting an age of 5 0 ma for the miocene pliocene boundary would imply that evaporites and post evaporitic lago mare sediments were deposited in some 300 000 years and suggests that in the central parts of the mediterranean basins evaporites must have accumulated at rates of some 3 m per 1000 years

nanometer scale complexity growth and diagenesis in desert varnish nanometer scale element mapping and spectroscopy of desert varnish from the northern sonoran desert in southwestern arizona reveal a dynamic disequilibrium system characterized by postdepositional mineralogical chemical and structural changes activated by liquid water lack of equilibrium is suggested by the large variety of coexisting mn phases sparse secondary ba and sr sulfates also occur as do carbonaceous particles individual mn oxide particles contain variable concentrations of ba and ce reflecting their role as repositories of trace elements presumably derived from atmospheric aerosols desert varnish is analogous to more familiar sediments in displaying authigenic and diagenetic structures but with total sediment thicknesses 1 mm and structures at the nanometer scale as such it is neither a weathering rind nor patina but a unique subaerial sediment that is in dynamic disequilibrium our results suggest continuing adjustment of varnish to changing environmental conditions

an important current reversal influx in the rifian corridor morocco at the tortonian messinian boundary the end of tethys ocean atlantic psychrospheric and temperate mesopelagic faunas found in the lower messinian marls in morocco indicate that a strong eastward flowing bottom current was present in the rifian corridor before the salinity crisis this influx began just before diatomite deposition in the paleo mediterranean continued during a decrease in species diversity in coral reef formation and diminished with the initial stages of brine concentration in the deep water phase of the crisis the influx is most readily studied in a condensed section of marl in the bou regreg valley near rabat the beginning of this siphon event coincides with the tortonian messinian boundary 6 4 ma subchron 6n1 it is identified by 1 a change in the planktonic foraminifera from dominance of warm tropical epipelagic globorotalia menardii with globigerinoides to the temperate mesopelagic gl miotumida plexus with conomiozea 2 the sudden appearance of an upper psychrospheric ostracode fauna with agrenocythere pliocenica and oblitacythereis ruggierii 3 a change in nannoflora and 4 beginning of the 6 3 ma global carbon shift the initial strong influx stage of the siphon lasted at least 0 7 m y decreasing after the middle of chron 5 ca 5 7 to be lost ca 5 3 ma conditions for the siphon formed when the continental climate created a deficit in the water budget of the paleo mediterranean sea the reversal took place when tectonic movement in the foredeeps of the betic rif orogene changed the thresholds of the twin straits the rifian corridor and the iberian portal inflow increased rapidly in the southern corridor to draw in waters from beneath the rising atlantic pycnocline while paleo mediterranean overflow water pmow continued out of the northern iberian portal the invasion of nappes or olistoliths first into the portal and then into the corridor led to the end of the outflow of the pmow terminating the need for the siphon and then to the isolation of the paleo mediterranean

the abad composite se spain a messinian reference section for the mediterranean and the apts a high resolution integrated stratigraphy is presented for the abad marls of the sorbas and nijar basins in se spain preevaporitic messinian of the western mediterranean detailed cyclostratigraphic and biostratigraphic analyses of partially overlapping subsections were needed to overcome stratigraphic problems in particular encountered at the complex transition from the lower to the upper abad the resulting abad composite section contains a continuous stratigraphic record from the tortonian messinian boundary up to the transition to the messinian evaporites of the yesares member all together 18 calcareous plankton events were recognized which were shown to be synchronous throughout the mediterranean by means of detailed bed to bed cyclostratigraphic correlations the magnetostratigraphy allowed the identification of the four magnetic reversals of chron c3an in the upper abad details in the sedimentary cycle patterns allowed the abad composite to be astronomically calibrated this calibration to the 658n summer insolation curve of solution la90 1 1 yielded astronomical ages for all sedimentary cycles calcareous plankton bioevents ash layers and paleomagnetic reversals up to now the abad composite is the only astronomically well calibrated section that provided a reliable cyclostratigraphy magnetostratigraphy and calcareous plankton biostratigraphy as such it will serve as a reference section both for the pre evaporite messinian in the mediterranean as well as for the messinian interval in the astronomical polarity time scale q 2001 elsevier science b v all rights reserved

revisiting alexander von humboldt s initiation of rock coating research abstractsecondary backscattered high resolution transmission and energy dispersive spectroscopy tools of electron microscopy reexamined alexander von humboldt s field site of brownish black crust s covering rocks along cataracts of the orinoco river modern tools confirm eighteenth century analysis that the basic composition includes an abundance of manganese iron and carbon additional major constituents include clay minerals calcium and sometimes barium and cobalt backscattered and secondary electron imaging confirms the 2 century old hypothesis of an accretionary nature of the orinoco coating the remarkable orinoco sheen is produced by a smooth lamellate micromorphology and high concentrations of manganese the same conditions required to produce lustrous varnishes formed in warm deserts although von humboldt deduced and we agree that coating constituents must derive from the orinoco electron microscope observations of mn enriched diatom fragments mn enriched cocci bacterial forms and

magnetostratigraphic biostratigraphic and stable isotope stratigraphy of an upper miocene drill core from the sale briqueterie northwestern morocco a high resolution chronology for the messinian stage we report a high resolution stable isotope carbonate magnetostratigraphic and biostratigraphic record from a 175 m drill core from the sale briqueterie which is part of the bou regreg section in northwestern morocco the sale drill core spans the interval from paleomagnetic chron c4n partim to c3r earliest gilbert which represents the time leading up to and including the isolation and desiccation of the mediterranean i e the messinian salinity crisis during chrons c3an and c3ar 6 935 to 5 894 ma the isotope and carbonate signals display quasi periodic variations with estimated periods of 40 and 100 kyr respectively we interpret the 40 kyr 18o variations as reflecting changes in global ice volume caused by obliquity induced changes 41 kyr in solar insolation in polar regions the 100 kyr carbonate variations probably represent long term modulation of the amplitude of the precessional cycle 21 kyr which is not resolved by our sampling frequency the cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of shackleton et al 1994a from stage tg24 in chron c3r earliest gilbert to stage c3ar 18o 18 at the base of chron c3ar 6 935 ma a major change in paleoceanographic conditions is recorded across the tortonian messinian boundary which we correlate to chron c3bn at 7 04 ma benthic foraminiferal 18o values increased by an average of 0 4 in two steps at 7 17 ma and 6 8 ma and 13c values decreased by 0 7 0 8 between 7 1 and 6 8 ma representing the late miocene carbon shift the first step in 18o values coincides with an inferred reversal in deep water circulation through the rifian corridor and the second correlates with the base of the tripoli formation and onset of crisis conditions in the mediterranean we suggest that the increase in 18o values represents at least in part an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the mediterranean average 18o values remained high throughout most of chrons c3ar and c3an reaching maximum 18o values during isotope stages tg20 and 22 in chron c3r earliest gilbert the glacio eustatic falls associated with these events may have resulted in the complete isolation of the mediterranean from the world ocean shackleton et al 1994a following stage tg12 in the sale record there exists a trend toward progressively lower 18o values that may represent a series of marine transgressions that eventually reflooded the mediterranean and ended the salinity crisis

toward a high resolution chronology for latest miocene paleoceanographic events it is now widely accepted that expansion of continental glaciers is one manifestation of profound paleoenvironmental change in latest miocene time the oxygen isotopic record in deep sea cores is inferred to document brief pulses in glaciation based on covariance of 18o in benthic and planktonic foraminifera which probably lowered latest miocene sea level by a minimum of 60 m additional evidence of glacial activity in the oxygen isotope record is obscured by the small signal amplitude before further details of paleoenvironmental change can be investigated it is essential to have a high resolution stratigraphy and chronology this has not been achieved previously because most studies of the latest miocene have had a sampling interval greater than the duration of events they seek to resolve a high resolution stable isotope record from the north atlantic deep sea drilling project dsdp 552 is correlated with a second record from the southwest pacific dsdp 588 each core has magnetostratigraphy but there are two possible interpretations of magnetic results in the atlantic core by assuming that brief events of 18o enrichment and 13c depletion in each core are synchronous it is possible to assign the most likely age model to the atlantic core results of this exercise indicate that two 18o maxima occurred at 4 8 and 5 2 ma if these events reflect continental glaciation and if sea level was lowered enough to contribute to isolation and desiccation of the mediterranean then the miocene pliocene boundary must be close to 4 8 ma in age because messinian deposits are latest miocene in age this interpretation is consistent with biostratigraphy at dsdp 552 magnetostratigraphy biostratigraphy and isotope stratigraphy at a site commonly referred to because of its proximity to the mediterranean dsdp 397 northwest african continental margin and recent work on land in the mediterranean region

controls on faunal and sediment cyclicity within the tripoli and calcare di base basins late miocene of central sicily abstract cyclicity within the late miocene tripoli and calcare di base formations of sicily was controlled by two processes a partial evaporation of palaeomediterranean waters but with periodic replenishment by atlantic derived inflow on several occasions during the late tortonian and messinian stages b deformation of a regional foreland basin and associated satellite basins perched above south verging sedimentary thrust sheets these were intermittently set in motion by active plate collision onto the passive african plate margin although it is not possible to discriminate fully the world eustatic signal under such a scenario nevertheless sufficient recolonization by marine faunas in these sicilian basins occurred to permit modelling of onlap offlap events for the late miocene intervals basin wide correlation of these variably fossiliferous formations hangs on the recognition of a late tortonian early messinian onlap event marked by coral reef development at the top of the terravecchia formation around the northern margins of the region a further carbonate episode calcare di base formation lies above a transgressive surface and directly overlies fluvial conglomerates at the top of the terravecchia formation around the northern margins of the basin the calcare di base is partly diachronous with the top of the tripoli formation in the foreland basin but further north it oversteps the coral reefs on the southern margins of the madonie mountains a variable number of internal tripoli formation cycles confirmed on both faunal and sedimentological grounds and calcare di base cycles demonstrated only by sedimentation patterns have been recognized this minor cyclicity is considered to have resulted from periodic tectonic uplift and isolation of foreland basin and associated perched basins this isolation controlled both influx of siliciclastic sediment and access by marine biota prolonged basin isolation during the deposition of the tripoli formation lead to rapidly declining diversity patterns in both benthonic and planktonic communities benthonic foraminifera disappeared early in many cycles with oligotypic planktonic foraminifera and radiolaria remaining longest under increasingly hostile conditions only diatoms remained each new cycle is marked at its base by a return to near normal conditions and a relatively diverse biota although faunas were stressed during the isolation events no clear evidence of salinity increase is seen rather we consider that a combination of oxygen depletion especially on basin floors receiving prolific algal bioproduction and toxin build up generally as the by product of algal metabolic processes was the cause the calcare di base cycles are more difficult to interpret on account of the virtual absence of biota here the cycles are clearly related to desiccation and salinity increase during times of restriction the base of each cycle is marked by brine dilution and basin flooding with some evidence of low diversity microfauna input in the early cycles we envisage a late miocene palaeogeography with thrust fold belts well established to the north of sicily and a ne sw oriented seaway developed ahead of them to the south of this seaway lay an en echelon belt of ne sw oriented submarine ridges and localised basins which effected a sill or at times a barrier between the seaway and the tripoli basins a broad diatom dominated perched basin complex extended along the southern margin of the thrust related ridges and was intimately linked to a broad foreland basin also diatomitic lying immediately to the south the foreland basin was separated from a further open sea area in southern sicily by a second ne sw oriented sill now hidden by later overthrusting it is suggested that similar tectonic scenarios were responsible for isolating diatomaceous basin elsewhere in the mediterranean during late miocene times

latest miocene benthic δ 18 o changes global ice volume sea level and the messinian salinity crisis oxygen isotope evidence indicates high but variable 18o values in benthic foraminiferal calcite during the latest miocene and earliest pliocene these high values may represent increases in global ice volume and associated sea level fall the 18o record resembles glacial interglacial cycles but with only one third the amplitude of the late pleistocene signal this variability may reflect instability in the antarctic ice sheet and palaeomagnetic correlation points to an isotopic event coinciding with the isolation and desiccation of the mediterranean basin during the latest messinian

did glacio eustatic sea level drop trigger the messinian salinity crisis new evidence from ocean drilling program site 654 in the tyrrhenian sea it has long been speculated that glacio eustatic sea level drop may have caused or contributed to the isolation and consequent desiccation of the mediterranean in the late miocene the messinian salinity crisis ocean drilling program site 654 on the sardinia margin of the tyrrhenian sea is the first deep sea drill site to penetrate through upper messinian evaporites into lower messinian upper tortonian open marine sediments and thus offers a unique opportunity to date the onset of the salinity crisis a reexamination of the magnetostratigraphic biostratigraphic and stable isotope stratigraphic constraints on the preevaporite sediments of site 654 has yielded two possible ages for the contact between salinity crisis sediments and the underlying normal marine sediments one magnetostratigraphic interpretation plus the biostratigraphically determined position of the tortonian messinian boundary imply a date of about 6 2 ma for the youngest presalinity crisis sediments an alternative magnetostratigraphic interpretation plus the carbon isotope stratigraphy imply a date of about 5 2 ma the younger of these dates coincides with a 18o spike in open ocean sediments keigwin 1987 which is attributed to increased ice volume

the composition and origin of brines during the messinian desiccation event in the meditterranean basin as deduced from concentrations of ions coprecipitated with gypsum and anhydrite abstract gypsum and anhydrite from the upper miocene messinian evaporites of the mediterranean basin were analysed for their coprecipitated ion compositions the concentrations of mg na k sr and cl in gypsum and anhydrite samples from dsdp leg 42a sites 372 374 and 376 and from boreholes yafo 1 ashdod 2 talme yafe 3 and afiq 1 from the coastal plain of israel were used to calculate the composition of the brines from which these calcium sulfate minerals were deposited or in which they have undergone recrystallization or phase transformation results reveal basic differences between the eastern central and western mediterranean basins during the last stage of the messinian salinity event the western mediterranean and the ionian basin were characterized by marine brines during most of the second stage of the salinity event upper evaporite member during this period the eastern mediterranean basins were fed with brines of continental origin these brines are characterized by high ca concentrations relative to seawater brines one core from the eastern mediterranean yafo 1 indicated that anhydrite was deposited along the continental margin of the eastern mediterranean from brines of marine composition which evolved into carich continental brines following a marine regression

the age of the miocene pliocene boundary in the capo rossello area sicily detailed correlations of magnetostratigraphy biostratigraphy and lithostratigraphy reveal that the basal pliocene is equally complete in the eraclea minoa and capo rossello sections sicily and the singa section calabria and that in accordance with the model of the pliocene flooding event in the mediterranean the deposition of the pelagic marls of the trubi formation started synchronously on sicily and in adjacent calabria in addition the data obtained from the trubi in the eraclea minoa section allows the age of the miocene pliocene boundary to be adjusted slightly from 4 83 4 84 1 to 4 86 ma because downward extrapolation of both sedimentation rate and average duration of small scale sedimentary cycles in the trubi yields this age for the boundary in this section linearly interpolated ages for the top of the sphaeroidinellopsis acme and the first substantial increase in globorotalia margaritae the fod of this species is non existent in the mediterranean pliocene at eraclea minoa arrive at 4 74 and 4 63 ma respectively because of the detailed magnetostratigraphy and the very accurate dating of the miocene pliocene boundary it is preferable to select the eraclea minoa section as the boundary stratotype rather than the capo rossello section finally this age of 4 86 ma for the miocene pliocene boundary suggests that the beginning of the pliocene is connected with the termination of a series of latest miocene glaciations and that the re establishment of open marine conditions in the mediterranean might be of glacio eustatic origin

post messinian evolution of the southeastern levant basin based on two dimensional stratigraphic simulation abstract the evolution of the southeastern levant basin following the messinian salinity crisis was interpreted using observations derived from seismic sections and well data and from output of a two dimensional forward stratigraphic simulation program sedpak the working assumption was that the thick evaporitic messinian sequence was generated in a shallow water albeit a topographically deep basin the sea level dropped at least 800 m below its present level and may have been as low as 1300 m the latter value representing the reconstructed depth of the top messinian in the deep part of the basin the top of the evaporitic sequence in that part of the basin was virtually horizontal at the end of the messinian crisis and thus may be used as a regional datum subsidence rates measured for the shelf and coastal plain of israel indicate a reduction of these rates for the pleistocene when compared to the pliocene during the pleistocene subsidence rates for the base slope increased and dictated the modern physiography of the margin earlier in the middle to late pliocene small scale salt movements occurred in the deep basin producing the fragmented and irregular shape of the m horizon the seismic event marking the top of the evaporitic sequence and deforming the overlying pliocene section the simulated rate of sediment supply indicates a constant increase over time for the pliocene and the pleistocene probably in response to an increased influx of nile derived along shelf sediment transport

reactive oxygen species at the oxide water interface formation mechanisms and implications for prebiotic chemistry and the origin of life the goal of our study is to identify free radical formation pathways on mineral surfaces organic molecules on early earth might have been modified or decomposed by such pathways thus affecting the total organic inventory for prebiotic synthesis reactions specifically we evaluated several common oxide minerals under a range of environmental conditions and combinations of conditions ph o2 level uv wavelength and particle loading for formation of highly reactive oxygen species ros at the oxide surfaces by quantifying the generated oh and h2o2 we identified anatase rutile tio2 tio2 and hematite fe2o3 as active in ros production and importantly found different dominant pathways for ros formation on anatase rutile versus hematite hydroxyl radicals oh in anatase and rutile suspensions were generated mainly through the oxidation of oh by photo generated holes and h2o2 was generated through the combination of an oh radical with an oh and a hole this pathway for the tio2 phases did not require the presence of o2 and was not shut down under anaerobic conditions in contrast formation of h2o2 and oh in hematite suspensions involved reduction of o2 by electrons which was inhibited under anaerobic conditions the surface ros as well as free radicals formed by reactions with other gases on early earth atmosphere were capable of destroying molecules such as lipids and pre rna or rna essential to assembly of protocells and survival of the earliest cells at the same time surface associated ros and other free radicals may also have promoted aminoamide formation thus the surface ros would have affected prebiotic organic compound inventory and protocell early life evolution

characterization and differentiation of rock varnish types from different environments by microanalytical techniques abstract we investigated rock varnishes collected from several locations and environments worldwide by a broad range of microanalytical techniques these techniques were selected to address the challenges posed by the chemical and structural complexity within the micrometer to nanometer sized structures in these geological materials femtosecond laser ablation inductively coupled plasma mass spectrometry fs la icp ms scanning transmission x ray microscopy near edge x ray adsorption fine structure spectroscopy stxm nexafs in combination with scanning electron microscopy sem of focused ion beam fib ultra thin 100 200 nm sections conventional and polarization microscopy as well as electron paramagnetic resonance epr measurements were used to obtain information about these rock varnishes rock varnishes from different environments which cannot readily be distinguished based on their macroscopic appearance differ significantly in their constituent elemental mass fractions e g of mn fe ni co ba and pb and their rare earth element ree patterns structural characteristics such as the particle sizes of embedded dust grains internal structures such as layers of mn fe and ca rich material and structures such as cavities varied between varnishes from different environments and regions in the world the epr spectra were consistent with aged biogenic mn oxides in all samples but showed subtle differences between samples of different origin our observations allow us to separate rock varnishes into different types with differences that might be indicators of distinct geneses five different types of rock varnish could be distinguished type i v of which only type i might be used as potential paleoclimate archive each varnish type has specific characteristics in terms of their elemental composition element distribution and structures the combination of element ratios mn ba al ni mn rey mn ce mn pb lan ybn and ce ce total ree contents and structures can be used to separate the different types of rock varnish from each other

oxidation of manganese in an ancient aquifer kimberley formation gale crater mars the curiosity rover observed high mn abundances 25 wt mno in fracture filling materials that crosscut sandstones in the kimberley region of gale crater mars the correlation between mn and trace metal abundances plus the lack of correlation between mn and elements such as s cl and c reveals that these deposits are mn oxides rather than evaporites or other salts on earth environments that concentrate mn and deposit mn minerals require water and highly oxidizing conditions hence these findings suggest that similar processes occurred on mars based on the strong association between mn oxide deposition and evolving atmospheric dioxygen levels on earth the presence of these mn phases on mars suggests that there was more abundant molecular oxygen within the atmosphere and some groundwaters of ancient mars than in the present day

variations in the strontium isotopic composition of seawater during the neogene the authors report 261 strontium isotopic analyses of well preserved planktonic foraminifers from three deep sea drilling project sites 519 588 and 607 these samples cover the period from 24 ma to present with an average of approximately one sample per 100 ka the combination of high sample density and uniformity of analytical procedures has produced a well defined record of changes in the sup 87 sr sup 86 sr of seawater during the neogene the record can be viewed as a series of essentially linear segments with slopes ranging from as high as 6 times 10 sup minus 5 m y to as low as 0 m y the times associated with major inflections in the curve do not appear to correspond to simple geologic phenomena such as eustatic cycles but are probably controlled by a combination of tectonic and climatic factors that influenced the abundance and isotopic composition of terrestrial strontium input to the oceans the strontium isotopic data are consistent with a progressive increase in the chemical weathering rates of the continents during the neogene probably related to repeated glaciations increased exposure of continents by lowered sea level and increased continental relief resulting from high rates of tectonic uplift

estuarine lago mare fauna from the tertiary piedmont basin indicates episodic atlantic mediterranean exchange during the final stage of the mediterranean salinity crisis abstract the geochemical signature of fossils from lago mare deposits at moncucco torinese nw italy indicates a temporary marine ingression into the tertiary piedmont basin just before the miocene pliocene boundary isotope 18o 13c 87sr 86sr and trace element sr ca ba ca data from mollusk shells of multiple species and croaker otoliths indicate an upper estuarine environment with considerable seasonal variability in evaporation and freshwater input reconstructed salinities the presence of a paralic paleobiotope with thalassogenic water in the tertiary piedmont basin contradicts ideas of the mediterranean as a brackish lake fed by the paratethys during the latest stage of the mediterranean salinity crisis instead our data support previous notions of temporary atlantic mediterranean exchange during sea level highstands preceding the permanent re connection at the miocene pliocene transition the establishment of short lived and disjunct estuarine and lagoonal environments such as in the tertiary piedmont basin during marine ingressions also puts highly variable 87sr 86sr values and occurrences of shallow water benthic foraminifera in lago mare deposits of other mediterranean basins into a new perspective

messinian deep water turbidites and glacioeustatic sea level changes in the north atlantic linkage to the mediterranean salinity crisis our benthic foraminiferal data clearly indicate eight layers of deep water turbidites during the messinian mtl 1 8 and one in the early pliocene ptl 1 in ocean drilling program leg 105 site 646b these deep water tuibidite deposits are characterized by highly concentrated agglutinated marsh benthic foraminifera e g trochammina cf squamata ammotium sp a miliammina fusca rounded quartz polished thick walled benthic foraminifera wood fragments plant seeds plant fruit and highly concentrated mica and are interbedded with sediments containing deep water benthic faunas we suggest these turbidites deposited during sea level low stands 80 100 m below sea level and their ages are tentatively correlated to 6 59 6 22 6 01 5 89 5 75 5 7 5 65 5 60 and 5 55 ma respectively based on the messinian oxygen isotope enrichments at site 552a of deep sea drilling project leg 81 the turbidites layers during the late messinian coeval with frequent climate changes suggested by six oxygen enrichment excursions of site 552a may have been in part linked to the late messinian evaporite deposits in the mediterranean basin the most profound climate changes at 5 75 and 5 55 ma may have been related to the lower and upper evaporites in the mediterranean basin an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd apend typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 96pa00572 messinian deep water turbidites and glacioeustatic sea level changes inthe north atlantic linkage to the mediterranean salinity crisis jijunzhang and david b scott diskette may be ordered from americangeophysical union 2000 florida avenue n w washington d c 20009 15 00 payment must accompany order

deep water clastic evaporites deposition in the messinian adriatic foredeep northern apennines italy did the mediterranean ever dry out a new genetic facies model for deep water clastic evaporites is presented based on work carried out on the messinian gessoso solfifera formation of the northern apennines during the last 15 years this model is derived from the most recent siliciclastic turbidite models and describes the downcurrent transformations of a parent flow mainly composed of gypsum clasts the model allows clearer comprehension of processes controlling the production and deposition of clastic evaporites representing the most common evaporite facies of the northern apennines and the definition of the genetic and stratigraphic relationship with primary shallow water evaporites formed and preserved in marginal settings due to the severe recrystallization processes usually affecting these deposits petrographic and geochemical analyses are needed for a more accurate interpretation of the large spectrum of recognized gravity driven deposits ranging from debrisflow to low density turbidites almost all the laminar balatino gypsum previously considered a deep water primary deposit is here reinterpreted as the fine grained product of high to low density gravity flows facies associations permit the framing of the distribution of clastic evaporites into the complex tectonically controlled depositional settings of the apennine foredeep basin the messinian salinity crisis occurred during an intense phase of geodynamic reorganization of the mediterranean area that also produced the fragmentation of the former miocene apennine foredeep basin in this area primary shallow water evaporites equivalent to the mediterranean lower evaporites apparently only formed in semi closed thrust top basins like the vena del gesso basin the subsequent uplift and subaerial exposure of such basins ended the evaporite precipitation and promoted a widespread phase of collapse leading to the resedimentation of the evaporites into deeper basins vertical facies sequences of clastic evaporites can be interpreted in terms of the complex interplay between the messinian tectonic evolution of the apennine thrust belt and related exhumation erosional processes the facies model here proposed could be helpful also for better comprehension of other different depositional and geodynamic contexts the importance of clastic evaporites deposits has been overlooked in the study of other mediterranean areas based on the apennine basins experience it is suggested here that evaporites diffused into the deeper portions of the mediterranean basin may consist mainly of deep water resedimented deposits rather than shallow water to supratidal primary evaporites indicative of a complete basin desiccation

sr isotope constraints on the mediterranean environment at the end of the messinian salinity crisis probably the most profound event that has affected the mediter ranean is the desiccation which occurred at the end of the miocene1 8 during this period there was a very rapid change from deep open marine conditions to environments of shallow water carbonate and massive evaporite deposition1 10 here we show that ostracod valves found in messinian lago mare lake sea sediments have a uniform but generally lower sr isotopic composition than contemporary sea water thus providing evidence that some of the major mediterranean basins for example balearic and levantine basins formed large lacustrine systems that were probably interconnected towards the end of the messinian salinity crisis1 3 after the major evaporites were deposited the most likely source of fresh water is from continental rivers flowing from the eastern european inland paratethys sea or perhaps the nile river in the lower part of the lago mare some ostracods have sr isotopic compositions identical to contemporary sea water indicating a transient influence of marine derived water sr compo sitions greater than that in contemporary sea water are only found in ostracods from onshore sediments in the sorbas basin4 5 of southeastern spain suggesting that this small basin adjacent to the straits of gibraltar became isolated after the deposition of the major evaporite sequences

an overview of neogene brackish leptocytherids from italy and spain biochronological and palaeogeographical implications abstract an overview of the neogene euryhaline leptocytherids from italian and spanish basins is reported together with their chronological and geographical distributions eight genera or subgenera have been considered mediocytherideis s s m sylvestra chartocythere leptocythere tavanicythere amnicythere euxinocythere s s and e maeotocythere the study has shown that these leptocytherids could be a valuable biochronological tool in both marginal marine and the athalassic saline environments since even at generic level they show separate temporal distributions for example the presence of chartocythere and euxinocythere s s in the mediterranean seems to be limited to the late serravallian tavanicythere seems to have been exclusively distributed during the late miocene with different species spanning the late tortonian and early messinian m sylvestra seems to attain its maximum diversity in the same time interval the widespreading of amnicythere and e maeotocythere in the mediterranean marks the latest messinian lago mare event about 5 5 5 3 ma the important radiation of leptocythere characterises the pliocene moreover a comparative analysis between neogene mediterranean and paratethyan leptocytherids has shown that the geographical and stratigraphical distribution of the eight genera analysed matches the palaeogeographic events that affected the peri tethyan realm during neogene

paratethyan mediterranean connectivity in the sea of marmara region nw turkey during the messinian the sea of marmara region is thought to have been a gateway between paratethys and the mediterranean since the middle miocene and is therefore an important control on water mass exchange between the two realms the miocene successions in the northeastern aegean and northwestern marmara regions indicate that the first mediterranean marine transgression to affect these areas occurred during the late serravallian in the northeastern aegean region frequent marine incursions occurred during the tortonian and messinian stages the messinian stage in this area is represented by a package of brackish to fresh water carbonates with some marine sandstone siltstone interbeds alcitepe formation which conformably overlies the tortonian kirazli formation the messinian sequence is overlain with an erosional contact by a shallow marine siliciclastic sequence goztepe formation of zanclean age with its brackish to fresh water carbonates and broadly constrained age the messinian sequence is interpreted as being coeval with the upper evaporite lago mare sequence observed in western mediterranean basins in the western marmara region the pontian messinian alcitepe formation consists of bioclastic and oolitic limestones with basal clastic rocks it conformably overlies the fluvio lacustrine siliciclastic sediments of the middle to upper miocene kirazli formation and is overlain by fluvio lacustrine sediments of the kimmerian 5 5 3 2 ma truva and tevfikiye formations with an erosional contact the bioclastic limestones of the alcitepe formation in the western marmara region contain a molluscan and ostracod fauna that are endemic to paratethys these fauna indicate deposition in a shallow brackish to fresh water environment faunal and paleomagnetic analyses of a section of the alcitepe formation at yenimahalle canakkale confirm that the formation is of pontian age and represents chron c3r 6 04 5 24 ma the ostracod analysis indicates that during deposition of the alcitepe formation salinity increased from brackish in the lower part to more saline conditions in the upper part ostracod valves have low 87sr 86sr values relative to coeval late miocene ocean water this indicates that exchange between the sea of marmara region and the global ocean was restricted throughout this period fossil and sr isotope evidence suggests however that there was a paratethyan marmara connection during the deposition of the lower part of the alcitepe formation with paratethyan influence reaching the north aegean connection via marmara between paratethys and the mediterranean was not re established until the late aktchagylian late pliocene the re connection was caused by both increased activity on the north anatolian fault and global sea level rise

sr ca mg ca ratios and sr and stable isotopes of biogenic carbonates from the late miocene velona basin central apennines italy provide evidence of unusual non marine messinian conditions abstract the sr ca and mg ca ratios of fossil ostracod and mollusc shells from a late miocene early messinian lacustrine sequence in the velona basin central apennines italy were used to calculate the sr ca and mg ca of waters in which these taxa lived sr ca of these waters were always higher than the sr ca calculated for the messinian seawater despite the broad salinity ranges fresh water oligo mesohaline inferred from the paleontological analyses the estimated mg ca water from the velona samples are below the mg ca value for coeval seawater even though they represent relatively high values when compared with many non marine waters the salinity variations of the velona lacustrine system recorded by changes in faunal assemblages are linked to variable inputs of na cl from deep groundwaters and are not reflected in significant changes in sr ca and mg ca of the waters calculated from shell chemistry the combination of 18 o signatures and sr isotopic ratios from molluscs from the velona basin suggests a non marine environment during some episodes of the lake history given the saline inputs the waters in the lake would attain a large solute concentration oligo to mesohaline although they retained the meteoric 18 o signature we compare the paleohydrochemical inferences from the studied sequence with other messinian records and we show the importance of combining paleoecological and geochemical proxies to obtain consistent paleoenvironmental reconstructions

the messinian calcare di base sicily italy revisited three different types of carbonate deposits are included within the calcare di base commonly envisaged to record the messinian salinity crisis onset type 1 consists of sulfur bearing limestones representing the biogenic product of bacterial sulfate reduction after original gypsum type 2 comprises dm thick laminated dolomitic limestones interbedded with diatomites sapropels and marls found at the top the tripoli formation type 3 the most common variety consists of m thick brecciated limestones interbedded with shales and clastic gypsum type 3 shows sedimentary features suggesting a clastic origin and deposition from high to low density gravity flows thus these deposits can be regarded as an end member of a large variety of evaporite bearing gravity flow deposits with a dominant carbonate component the genetic and stratigraphic characterization of these carbonates has strong implications for a better comprehension of messinian events the three types of calcare di base seem to have formed during different stages of the messinian salinity crisis msc type 2 formed in the first stage 5 96 5 60 ma and is the only type that can be regarded as the lower gypsum time equivalent type 3 was deposited in the second stage 5 60 5 55 ma and its base is associated with a regional scale hiatus and erosion messinian erosional surface type 1 formed even later likely in post messinian time through diagenetic processes affecting resedimented gypsum deposited during the second stage of the msc it follows that not all the calcare di base deposits record the onset of the messinian salinity crisis as commonly thought thus a detailed facies characterization of these carbonate deposits is fundamental for both stratigraphic reconstructions and a better comprehension of messinian events

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

palaeomagnetic chronology of the evaporitic sedimentation in the neogene fortuna basin se spain early restriction preceding the messinian salinity crisis abstract the magnetostratigraphic study of the evaporitic rio chicamo section 240 m in the neogene fortuna basin murcia southeast spain has identified the record of five magnetozones the most probable correlations with the standard geomagnetic polarity time scale gpts imply that the marine evaporitic sedimentation of this basin was not coeval with the messinian evaporites of the sorbas basin almeria southeast spain and the caltanissetta basin central sicily assigned to the reverse chron c3r late messinian by gautier et al 1994 the marine evaporites and diatomites from the fortuna basin are older late tortonian to early messinian than the evaporites of those basins the chronological framework for the sedimentation in the fortuna basin together with the isotopic data from the sulphates in these evaporitic units indicate the following 1 restriction and confinement in the basin initiated as early as uppermost tortonian leading to deposition of evaporites under mixed marine continental conditions 2 the subsequent sedimentation of marine evaporites and diatomites in this basin occurred in a period between the tortonian and messinian transition and the early messinian the onset of this sedimentation pre dates similar sediments of restricted marine environments in the eastern betics basins and possibly of the western mediterranean region also 3 episodes of restriction and reflooding in the basin would have occurred in response to periodic fluctuations of the oceanic level under local tectonic controls in the fortuna basin the global base level drop associated with the late messinian salinity crisis was recorded by the progradation of alluvial fans leading to thick clastic deposits overlying the youngest evaporites these observations hint to a the peculiar characteristics and sensitiveness of some of the marginal intramontane basins in the eastern betics to reflect structural controls framed in the late neogene global climatic changes and b the diachronism of the beginning of the marine evaporitic deposition in the mediterranean region linked to the salinity crisis during the messinian

diversity of rock varnish bacterial communities from black canyon new mexico 1 scientists vigorously debate the degree to which rock varnish is formed through the actions of microorganisms to investigate this enigma we utilized a three pronged approach that combined 1 culture independent molecular methods to characterize bacterial communities associated with varnish that coats the rhyolitic volcanic rocks of black canyon new mexico and rocks with no visible varnish 2 culturing of varnish in media supplemented with reduced forms of manganese and or iron and no or low amounts of carbon to isolate bacteria capable of precipitating iron and or manganese oxides and 3 scanning electron microscopy sem of varnish and nearby rock that lacks macroscopically visible varnish our culture independent studies revealed significant differences between varnish and nonvarnish communities chloroflexi and ktedobacteria dominated one varnish site while the other varnish site was dominated by cyanobacteria the nonvarnish sites were dominated by actinobacteria and to a lesser extent cyanobacteria and were the only samples to contain deinococcus thermus sequences approximately 65 of varnish cultures produced visible manganese precipitates most culture isolates were not closely related to known manganese oxidizers with the exception of bacillus spp sem revealed microbial morphologies and two types of varnish morphologies 1 relatively smooth layers and 2 patches of botryoidal pinnacles which were often associated with increased manganese concentrations bare rock showed evidence of incipient varnish these results have important implications for the detection of life on extraterrestrial planets such as mars where putative varnish coatings have been observed and represent some of the first culture independent characterizations of varnish communities

alpine deformation and 40ar 39ar geochronology of synkinematic white mica in the siviez mischabel nappe western pennine alps switzerland we explore the timing of deformation and exhumation of the siviez mischabel nappe western swiss alps which has been considered a classic example of a midcrustal crystalline nappe since the studies of argand 1916 this study presents 40ar 39ar ages obtained on both synkinematic white mica from permo triassic cover sediments and more complex white mica populations from basement gneisses of the siviez mischabel and middle pennine nappes primary foliation developed in cover units by nucleation growth and rigid rotation of mica grains during noncoaxial alpine deformation although some samples show a crenulation of this primary foliation mica growth appears to have occurred only during the development of primary foliation the main phase of greenschist facies deformation related to imbrication of the siviez mischabel nappe and other middle pennine nappes good agreement exists between independent estimates of the timing of deformation and reported 40ar 39ar white mica ages from cover units of the central and southern siviez mischabel nappe in cover units from the central and southern siviez mischabel regions of the study area 40ar 39ar ages appear to date synkinematic white mica growth results suggest that the siviez mischabel nappe was emplaced and developed foliation during a 5 m y period from 41 to 36 ma in cover units from the eastern siviez mischabel however 40ar 39ar white mica ages appear to date postkinematic thermal events these thermal events may be related to oligocene magmatic activity in the lower pennine nappes or to miocene development of the simplon fault zone variations in the relation between alpine age and grain size for cover samples from the central eastern and southern siviez mischabel correlate well with the regional variations in temperature inferred from quartz microfabrics and the pattern of regional metamorphism when considered in concert with other recent isotopic studies on the timing of major tectonic and thermal events in the western swiss alps these data support arguments that the relative timing of events such as thrusting and back thrusting of crystalline nappes in hinterland units and exhumation of high pressure units in the suture zone of the western alps are intimately related and synchronous on the scale of a few million years

stable carbon isotope ratios of rock varnish organic matter a new paleoenvironmental indicator stable carbon isotope ratios of organic matter in rock varnishes of holocene age from western north america and the middle east show a strong association with the environment this isotopic variability reflects the abundance of plants with different photosynthetic pathways in adjacent vegetation analyses of different layers of varnish on late pleistocene desert landforms indicate that the carbon isotopic composition of varnish organic matter is a paleoenvironmental indicator

the rossello composite a mediterranean and global reference section for the early to early late pliocene a high resolution magnetostratigraphy planktonic foraminiferal biostratigraphy and cyclostratigraphy is presented for the pliocene trubi marls in the punta di maiata section on sicily the integrated stratigraphy of the rossello composite section of hilgen 1 newslett stratigr 17 1987 is thereby completed this composite section provides an unprecedented high quality reference section for the early to early late pliocene containing a continuous sequence ranging from below the thvera subchron into the matuyama chron 4 86 2 45 ma the punta di maiata section extends from the sidufjall subchron of the gilbert into the gauss chron 4 50 3 30 ma linear interpolation between paleomagnetic datum planes in this section yields first order age estimates of 3 72 0 01 and 3 59 0 01 ma for the last common occurrence lco and the actual last occurrence lo of globorotalia margaritae in addition this age of 3 59 ma provides an accurate age for the zanclean piacenzian z p boundary provided the lo of g margaritae is maintained as a criterion to define this boundary in the mediterranean irrespective however of the criterion used the punta di maiata and punta piccola subsections of the rossello composite are at present the most suitable sections to be designated as stratotypes for the z p boundary the global significance of the rossello composite is further strongly enhanced by the establishment of an astronomically calibrated geomagnetic polarity time scale based on the correlation of the trubi sedimentary cycles with the astronomical record

the sedimentology and development of terravecchia formation carbonates upper miocene of north central sicily possible eustatic influence on facies development abstract on at least two occasions during the late tortonian siliciclastic deposition ceased and carbonates accumulated at the northern margin of the caltanissetta basin in north central sicily bioclastics dominated in the shallower proximal areas while coral reef facies developed where shallow water sand and cobble substrates existed or where sea floor highs has created local shallows the genetic model proposed is that siliciclastic deposition was repeatedly terminated during the late tortonian by rises in sea level which transgressed fluviatile and deltaic environments carbonate deposition was widespread but later erosion and reworking removed much of the sediments except within abandoned delta distributary channels and minor sea floor depressions reef developments associated with channel mouths and the shelf slope break have been preserved in situ whereas channels in more proximal locations are filled with siliciclastic bioclastic and intraclastic rubble from elsewhere on the delta top the wide lateral extent of the truncated tops of the carbonate beds argues for eustatic rather than tectonic controls of erosion and subsequent reworking these events may be closely related in time to other recorded late tortonian eustatic events in the foreland zones such as the hyblean plateau and the maltese islands further south collectively they give some support to a model involving multiple eustatic fluctuations associated with the onset of the messinian desiccation of the mediterranean

cerium a chemical tracer for paleo oceanic redox conditions abstract the ce anomalies found in marine carbonates provide a sensitive indicator for the study of paleo oceanic redox conditions the dependency of cce the observed ce concentration and cepo04 the activity of the cepo4 complex to the po2 ph and pco2 of seawater can be used for deciphering some aspects of the paleo ocean chemistry and is log c ce log cepo 0 4 13 2 0 25 log p o 2 3 0 ph 1 95 0 25 log p o 2 1 50 log p co 2 1 50 log ca the ph which is related to pco2 and po2 are major factors for controlling the ce concentration in seawater therefore ce anomalies ceas ce observed ce interpolated between la and pr or nd serve as indicators for ph or pco2 or po2 changes nearly uniform ce abundances found in pacific 5000 m water columns piepgras and jacobsen 1988 and the ceas in ichthyoliths can be explained using this model a general cea shift in sediments from d s d p holes 525a 530a b 516 516f suggest that the entire south atlantic water redox condition changed from reducing to oxidizing at 56 my in the north atlantic the galicia margin samples show a redox change between 132 148 my indicating active surface currents between the atlantic ocean and the shallow sea off the iberian peninsula the carbonate samples from d s d p hole 316 in the central pacific yielded an average cea of 0 15 0 01 which is 2 3 the ceas observed in deep pacific seawater by piepgras and jacobsen 1988 the relative enrichment of ce in these samples is ascribed to coprecipitation of ce oh 4 onto fe mn o coatings the striking similarities in the trace element profiles of ree sc hf th and ceas and the low u abundances 0 08 ppm in many marine carbonates indicate insignificant ce redox and trace elemental concentration changes for the pacific ocean over the past 95 my no significant ce redox change occurred in the pacific ocean within k t boundary one 240 my china limestone deposited under oxic sedimentary conditions yielded a cea of 0 53 calculations indicate a pco2 of 1 9 present value prevailed over the 240 my tethyan ocean u th ratios and low u concentrations are diagnostic indicators for obtaining reliable ceas in marine carbonates and perhaps for biogenic apatites and conodonts as well

rock varnish in new york an accelerated snapshot of accretionary processes abstract samples of manganiferous rock varnish collected from fluvial bedrock outcrop and erie barge canal settings in new york state host a variety of diatom fungal and bacterial microbial forms that are enhanced in manganese and iron use of a dual beam focused ion beam scanning electron microscope to manipulate the varnish in situ reveals microbial forms that would not have otherwise been identified the relative abundance of mn fe enriched biotic forms in new york samples is far greater than varnishes collected from warm deserts moisture availability has long been noted as a possible control on varnish growth rates a hypothesis consistent with the greater abundance of mn enhancing bioforms sub micron images of incipient varnish formation reveal that varnishing in new york probably starts with the mortality of microorganisms that enhanced mn on bare mineral surfaces microbial death results in the adsorption of the mn rich sheath onto the rock in the form of filamentous networks clay minerals are then cemented by remobilization of the mn rich material thus the previously unanswered question of what comes first clay mineral deposition or enhancement of mn can be answered in new york because of the faster rate of varnish growth in contrast very slow rates of varnishing seen in warm deserts of microns per thousand years make it less likely that collected samples will reveal varnish accretionary processes than samples collected from fast accreting moist settings

odp leg 107 in the tyrrhenian sea insights into passive margin and back arc basin evolution leg 107 of the ocean drilling program drilled a west northwest east southeast transect of seven sites across the tyrrhenian sea the youngest of the sub basins of the mediterranean sea sites 654 653 652 and 656 document the rifting and subsidence of the sardinia passive continental margin on the upper margin site 654 we cored a classic transgressive sequence subaerial conglomerates overlain by oyster bearing sands overlain by marine marl comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are tortonian late miocene to messinian latest miocene in age whereas synrift sediments on the lower margin are messinian to pliocene in age during the messinian desiccation of the mediterranean sites 654 and 653 now on the upper sardinian margin apparently occupied a basinal setting where they received nannoplankton bearing clays interbedded with laminated gypsum sites 656 and 652 now on the lower sardinia margin were apparently higher standing during the desiccation event their messinian facies are subaerial and lacustrine respectively we infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a rolling back subduction zone or in terms of extension of continental crust by shear along a deep detachment fault sites 655 651 and 650 were drilled into two small basalt floored basins of the central and eastern tyrrhenian emplacement of basaltic crust in the central tyrrhenian vavilov basin apparently began more than a million years before emplacement of basaltic crust in the eastern tyrrhenian marsili basin this observation is compatible with previous suggestions that the tyrrhenian has grown southeastward in response to rollback of the down going slab that currently dips northwestward under the toe of italy at the easternmost site high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2 500 m it has apparently subsequently subsided to its present depth of 4 100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid ocean ridge

sedimentology and paleoenvironmental evolution of messinian evaporites in the iskenderun hatay basin complex southern turkey abstract messinian evaporites which resulted from the salinity crisis during the final closure of the mediterranean sea are exposed in se turkey these evaporites formed in two isolated sub basins iskenderun arsuz ia and hatay samandag hs which belong to different depositional configurations and tectonic structures the neogene fill of these sub basins consists of a thick sedimentary succession that started with early miocene terrestrial clastics followed by reefs middle miocene and shallow water siliciclastics tortonian early to late miocene and finally messinian evaporates these sub basins accumulated in a diverse range of depositional environments from very shallow to deeper water evaporite facies in the ia sub basin consist of sabkhas saline lagoons and ponds they are mainly represented by chemical deposits such as scattered gypsum nodules and balls nodular bedded gypsum laminated gypsum type a and selenites type s1 evaporites in the hs sub basin mainly consist of detrital gypsum composed of gypsum laminae type b c gypsum arenite rudites and deeper water selenites 20 m and resedimented selenites type s2 which were deposited on a sulfate platform with a slope basin transitional zone secondary gypsum with alabastrine and porphyroblastic textures as well as satin spar veins is commonly associated with the sabkha type evaporites of the ia sub basin deeper water clastic evaporites of the hs sub basin have generally remained as primary gypsum or have only been slightly affected by diagenetic alterations the isotope values 87 86 sr 18 o smow and 34 s cdt from the different kinds of gypsum lithofacies of the sub basin are similar to those of the messinian evaporites in other peri mediterranean basins indicating an origin from marine water without external or basinal contributions the messinian evaporites examined in this paper are overlain by early pliocene zanclean deposits composed of shallow and deep water siliciclastics and carbonates with local intercalations of lago mare type strata throughout the messinian evaporitic stage the ia sub basin was mainly comprised of shallow water evaporites while the hs sub basin underwent deepening related to regional tectonics induced by the dead sea fault during the construction of the hatay graben

blind testing of rock varnish microstratigraphy as a chronometric indicator results on late quaternary lava flows in the mojave desert california rock varnish is a manganiferous dark coating ubiquitous in desert landscapes to test the validity of varnish microstratigraphy as a chronometric indicator varnish samples were collected from radiometrically dated and undated late quaternary lava flows in amboy cima and pisgah volcanic fields avf cvf pvf in the mojave desert of california western united states varnish microstratigraphies show a replicable layering sequence that appears to record regional climate changes that likely correspond in time to the younger dryas and heinrich events in the north atlantic region microstratigraphic patterns on these volcanic fields match patterns found in varnishes from other western us sites with available radiometric age constraints based on this regional chronology varnishes from the a flow h flow and a stone pavement surface in the cima volcanic field were estimated to be 16 5 24 74 85 and 74 85 ka respectively these ages are consistent with previously published cosmogenic 3 he ages of 18 20 72 74 and 80 85 ka for these geomorphic surfaces varnishes from the i flow at cima yielded a puzzling age estimate of 39 ka which is consistent with an older 3 he age of 37f6 ka reported for the i flow but inconsistent with a younger 3 he age of 31f7 ka and a cosmogenic 36 cl age of 27f1 3 ka for the same flow reinterpretation of the original varnish age data with knowledge of then available field mapping results of the i flow suggests that the i cone is polycyclic and different flow units were probably unintentionally sampled in the field the revised varnish ages of 30 and 39 ka for the i flow thus may be in good agreement with their corresponding 3 he and 36 cl ages in a blind test of the method varnishes from the phase 1 flow at pisgah an unnamed flow called here the ivflow at cima and the amboy flow were estimated to be 24 30 46 60 and 74 85 ka respectively these ages agree well with 36 cl ages of 22 5f1 3 46f2 and 79f5 ka reported for the same flows by phillips geomorphology 2002 these test results provide convincing evidence that varnish microstratigraphy once radiometrically calibrated can be used as a valid dating tool to estimate surface exposure ages of desert landforms in the western us drylands d 2002 elsevier science b v all rights reserved

mn fe enhancing budding bacteria in century old rock varnish erie barge canal new york abstractfossil remnants of bacteria involved in the enhancement of manganese and iron rarely occur within the microstratigraphy of rock varnishes collected from warm desert environments because varnish formation processes ultimately destroy these microfossils through remobilization of mn fe and reprecipitation in a clay mineral matrix in contrast mn fe encrustations on budding bacteria commonly occur within varnishes that formed within just a century along the erie barge canal new york nanoscale imagery and elemental analyses reveal that these budding bacterial forms greatly enhance mn fe or both in encrustations surrounding hyphae and cells the mn and fe precipitates have a granular texture on the scale of 1 nm to 10 nm the precipitates also have a stringy texture where strings are typically only a few nanometers wide these in situ observations are consistent with expectations from studies of budding bacteria cultures and with the polygenetic model of varnish formation given that the erie c

from dust to varnish geochemical constraints on rock varnish formation in the negev desert israel abstract chemical compositions of rock varnish from the negev desert of israel and local settled dust were used to constrain the mechanisms of varnish formation and patterns of mn enrichment and accumulation in the varnish rock varnish was sampled from coeval undisturbed prehistoric flint artifacts along a south north climatic transect 30 120 mm yr of rain our analyses indicate that mn ba and pb in the varnish are significantly enriched 100 in respect to the local settling dust and that mn content systematically fluctuates with depth in the varnish the varnish and settled dust data combined with basic thermodynamic and kinetic reasoning are used to constrain the following geochemical model of rock varnish formation dust accumulates in micro basins on exposed rock surfaces under ph 8 common negev value and during wetting by dew and rain mn in the dust is mobilized and leached to a depth of 5 m under the varnish surface where hollandite mn oxides precipitate and are adsorbed onto and between the porous clay minerals that comprise most of the varnish during its mobile phase mn oxide is negatively charged and adsorbs rare earth elements once the solution dries abrasion removes the upper weakly cemented dust sediment which contains mainly si al and fe which are not mobile at ph 8 ca is also removed in large quantities mn ba pb and the ree are deposited at a depth and thus protected from erosion reoccurrences of these processes result in a noticeable accumulation of these elements but not of si al or fe the alternating mn rich and mn poor laminas form as a result of a competition between the leaching rate of mn and the adhesion rate of the clay minerals when moisture is high low lamina with high low mn clay mineral ratio forms

high concentrations of manganese and sulfur in deposits on murray ridge endeavour crater mars mars reconnaissance orbiter hirise images and opportunity rover observations of the 22 km wide noachian age endeavour crater on mars show that the rim and surrounding terrains were densely fractured during the impact crater forming event fractures have also propagated upward into the overlying burns formation sandstones opportunity s observations show that the western crater rim segment called murray ridge is composed of impact breccias with basaltic compositions as well as occasional fracture filling calcium sulfate veins cook haven a gentle depression on murray ridge and the site where opportunity spent its sixth winter exposes highly fractured recessive outcrops that have relatively high concentrations of s and cl consistent with modest aqueous alteration opportunity s rover wheels serendipitously excavated and overturned several small rocks from a cook haven fracture zone extensive measurement campaigns were conducted on two of them pinnacle island and stuart island these rocks have the highest concentrations of mn and s measured to date by opportunity and occur as a relatively bright sulfate rich coating on basaltic rock capped by a thin deposit of one or more dark mn oxide phases intermixed with sulfate minerals we infer from these unique pinnacle island and stuart island rock measurements that subsurface precipitation of sulfate dominated coatings was followed by an interval of partial dissolution and reaction with one or more strong oxidants e g o 2 to produce the mn oxide mineral s intermixed with sulfate rich salt coatings in contrast to arid regions on earth where mn oxides are widely incorporated into coatings on surface rocks our results demonstrate that on mars the most likely place to deposit and preserve mn oxides was in fracture zones where migrating fluids intersected surface oxidants forming precipitates shielded from subsequent physical erosion

the age of the tortonian messinian boundary the tortonian messinian boundary is marked by the first occurrence datum fod of globorotalia conomiozea which is found all over crete in open marine marls with good palaeomagnetic properties within the framework of the miomar project the previously studied sections of langereis et al 1 have been extended and partly resampled here we present new magnetostratigraphic and biostratigraphic results from sections on eastern crete faneromeni central crete kastelli and western crete potamida and skouloudhiana supplemented by cyclostratigraphic data the recently developed geomagnetic polarity time scale ck92 of cande and kent 2 allows an unambiguous correlation of the polarity sequences on crete the fod of g conomiozea occurs in the reversed interval of anomaly c3bn lr this leads to a new age determination of 6 92 ma for the tortonian messinian boundary and a duration of 1 76 myr for the messinian a slightly modified version of ck92 if we use more recent age estimates provides an age of 7 10 ma and a duration of 1 78 myr respectively bipartite sedimentary cycles are distinctly present in the cretan sections studied assuming that these cycles are precession induced and using an average periodicity of 21 7 kyr enables us to independently estimate the duration of the successive individual polarity zones the astronomically derived durations of the cretan polarity zones are in good agreement with ck92 but are approximately 10 shorter

manganese rich rock varnish does occur in antarctica abstract despite accounts to the contrary we have found that mn rich rock varnish is present in antarctica as others have before it is chemically and texturally similar to many varnishes found in lower latitudes antarctic varnishes show considerable potential as a dating and paleoenvironmental research tool

stable isotope stratigraphy of latest miocene sequences in northwest morocco the bou regreg section oxygen and carbon isotopic ratios of foraminifers were measured from outcrop and drill core sequences from the bou regreg section northwest morocco this composite section was located at the western end of the rifian corridor during the late miocene and thus potentially contains a record of water exchange between the atlantic and mediterranean during the late tortonian and messinian stages here we correlate isotopic and sedimentologic events in the bou regreg section with mediterranean and deep sea sequences during the time leading up to and including the deposition of the messinian evaporites the late miocene chron 6 carbon shift was identified in two moroccan sequences providing a valuable 6 3 ma datum level in both sections the carbon shift coincides with the first occurrence of globorotalia conomiozea and the tortonian messinian boundary near this boundary a major faunal turnover occurred in ostracod planktonic foraminiferal and nannofossil assemblages that indicates a cooling of surface and deep water in the rifian corridor at 6 1 ma just above the tortonian messinian boundary mean 18o values of benthic foraminifers increased by 0 4 0 5 suggesting decreased temperature and or increased continental ice volume the faunal and isotopic changes are interpreted as reflecting a reversal in the direction of deep water flow through the rifian corridor that occurred between 6 3 and 6 1 ma at this time cold nutrient rich waters filled the mediterranean basins from intermediate depths of the atlantic and the production of mediterranean outflow water ceased the upwelling of nutrient rich atlantic intermediate water stimulated productivity in the mediterranean which led to the deposition of organic rich strata such as those found in the tripoli formation at 5 5 ma coincident with a coiling shift in neogloboquadrina acostaensis the variability of the benthic 18o signal increased markedly and strong color variations appeared in the sediments alternating between red and blue marls these isotopic and sedimentologic changes at bou regreg represented markedly fluctuating oceanographic conditions in the rifian corridor between 5 5 and 4 8 ma we speculate that these cycles were related to sea level variations that controlled the periodic influx of marine water into the mediterranean during the time of evaporite deposition the onset of these cycles occurred at 5 5 ma and is correlated to a eustatic fall in sea level at the base of the caliza tosca formation in carmona spain and to the base of the lowermost evaporite unit in the mediterranean e g calcare di base in sicily in this proposed scenario the duration of the messinian salinity crisis was 700 000 years and lasted between 5 5 and 4 8 ma

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

geochemical insights into the relationship of rock varnish and adjacent mineral dust fractions abstract rock varnishes are m thin dark manganese mn rich crusts that accrete in the order of few m ka on weathering resistant lithologies although these crusts can form in all climates they are best known in arid to semi arid settings aeolian dust is understood as a major contributor to the distinct trace metal and ree enrichments in rock varnish however the exact proportions of abiotic and biotic formation mechanisms that may explain the oxidation reactions of mn2 to mn4 present as mn oxyhydroxides in the varnish are still a matter of ongoing debate we present here the first systematic study of trace element enrichment processes between the uppermost layer of the varnish sequence and their adjacent 50 m dust fractions across a selection of 41 major and trace elements this approach is used to investigate samples from three fully arid deserts the an nafud in saudi arabia the negev in israel and the mojave in the usa which are compared to the significantly different environment of the semi arid knersvlakte in south africa a new in situ trace element analysis protocol was developed to perform femto and nanosecond sector field la icp ms microanalyses at high spatial resolution which allows us to measure the most recent varnish layers for their comparison with recent dust in agreement with previous studies all varnishes are enriched in mn pb ce co ba zn ni and the rare earth elements ree here we demonstrate that fine 50 m has low trace element mass fractions and enrichment patterns plotting distinctly away from varnish and fine dust based on these geochemical patterns our results indicate a general enrichment mechanism from fine dust to varnish previous studies suggested dust to play an integral role in providing the trace elements that are incorporated into the varnish by ph eh fluctuations in short term rain and fog events we amalgamate and refine previous growth models by providing direct evidence that leaching of about 10 of the mn and other trace elements from clay minerals in rain or fog droplets at ph 5 and subsequent scavenging on varnish surfaces at ph 8 leads integrated over time to the distinct enrichment patterns of the varnish while initial mn oxyhydroxide formation is suggested to follow pathways of metal oxide mediated photo catalysis for the semi arid occurrence in the knersvlakte we present a distinct growth model as both environment varnish and dust composition differ significantly from the arid settings here thick metallic looking varnish occurs mainly on the rim of quartz pebbles lacks microlamination and likely has upscaled growth processes among other aspects we suggest a more complex interplay between photo catalysis nocturnal condensation events on quartz pebbles with subsequent water trapping at the rock soil atmosphere interface due to a salic top soil layer to mainly account for these differences

high manganese concentrations in rocks at gale crater mars the surface of mars has long been considered a relatively oxidizing environment an idea supported by the abundance of ferric iron phases observed there however compared to iron manganese is sensitive only to high redox potential oxidants and when concentrated in rocks it provides a more specific redox indicator of aqueous environments observations from the chemcam instrument on the curiosity rover indicate abundances of manganese in and on some rock targets that are 1 2 orders of magnitude higher than previously observed on mars suggesting the presence of an as yet unidentified manganese rich phase these results show that the martian surface has at some point in time hosted much more highly oxidizing conditions than has previously been recognized

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

spatial temporal and geographic considerations of the problem of rock varnish diagenesis article i nfo the rock varnish literature hosts an abundance of prima facie contradictory empirical data past and perhaps future empirical contradictions however can be resolved by theoretical considerations of different spatial and temporal scales of varnish diagenesis as well as the geomorphic position of different types of varnishes for example twentieth century contamination by lead and other heavy metals has led to claims of accumulation rates in the last century far more rapid than prior published empirical studies a consideration of spatial scales resolves this contradiction nanoscale processes allow migration of lead into varnish deposited well before the twentieth century time of heavy metal pollution evidence of nanometer scale disequilibrium in three samples led to claims that varnish cannot be used in paleoclimatic research these data rest in contrast to replicable patterns in varnish deposition observed by dr tanzhuo liu and others in over ten thousand micro sedimentary basins this contraction can be resolved by understanding that the types of varnishes studied differ and that processes differ substantially between the nanoscale and the micron scale a lack of evidence of mn oxidizers in genetic analyses contrasts with culturing studies and in situ evidence of mn enhancement by bacteria this contradiction has a likely resolution in vastly different temporal scales dna material analyzed may be no older than 200 years but in situ fossilized remains of bacteria may be preserved for thousands of years recording palaeoecological conditions favoring growth of mn enhancing bacteria

hypersaline conditions during deposition of the calcare di base revealed from archaeal di and tetraether inventories abstract the calcare di base is a widespread messinian carbonate formation in the mediterranean especially in sicily and calabria italy the environmental conditions under which these limestones were deposited their formation mechanism and the timing of deposition are a matter of debate in order to shed new light on their formation the lipid biomarker inventories of calcare di base from four locations in sicily and calabria were studied following petrographical and mineralogical characterization of the limestone samples the mineralogy is chiefly calcite the microfabric is mostly peloidal and partly laminated or brecciated deposition took place at high salinity as confirmed by numerous pseudomorphs after halite long chain n fatty acids were the most abundant lipid biomarkers in samples from all sites but isoprenoid alcohols were also abundant the most prominent archaeal compounds were diphytanyl glycerol diethers dgds and glycerol dibiphytanyl glycerol tetraethers gdgts among these archaeol and gdgt 0 caldarchaeol predominated respectively other gdgts were virtually absent minor amounts of c 20 25 dgd extended archaeol a biomarker for halophilic archaea were detected in all samples the 13 c values of caldarchaeol avg 20 and archaeol avg 11 varied widely indicating that these compounds derived from distinct archaeal precursor lipids based on lipid biomarker patterns the calcare di base had been previously considered to represent a normal marine deposit in contrast to the evaporitic gypsum and halite deposits in messinian successions the archaeal biomarker inventories from the calcare di base samples reported here in conjunction with the occurrence of pseudomorphs after halite reveal that deposition took place in a hypersaline environment

how dry was the mediterranean during the messinian salinity crisis the messinian salinity crisis msc 5 97 5 33 ma is an enigmatic episode of paleoceanographic change when kilometers thick evaporite units were deposited in the mediterranean basin it is generally accepted that during the msc interval there was a dry climate in the mediterranean region it is difficult to assess how dry the climate was during the msc because a modern analogue in size and duration is absent here we reconstruct hydrological changes in the mediterranean basin during the three main msc stages using excellently preserved biomarkers we used the hydrogen isotopic composition of the long chain n alkanes dn alkanes to reconstruct the hydrological changes on the land adjacent to the mediterranean sea additionally the d of long chain alkenones dalkenones is used to observe changes in the mediterranean sea water source the dn alkanes recorded during the deposition of primary lower gypsum stage 1 in monte tondo indicate a d of the precipitation comparable to the present day mediterranean implying a similar hydrologic regime indicated by experiments modelling the miocene pliocene transition elevated dalkenones values from halite unit stage 2 of the realmonte mine are associated with kainite and giant polygons consistent with presumably high evaporative conditions during halite deposition the dn alkanes recorded during the deposition of upper gypsum stage 3 in eraclea minoa indicate a dprecipitation typical for much drier settings similar to the red sea region the relative contribution of the different alkenones from eraclea minoa is similar to the one observed in present day marine settings suggesting that during stage 3 connections to the open ocean were likely maintained however the dalkenones records during deposition of the evaporites in eraclea minoa are similar to those synchronously registered in the black sea implying that a similar hydrologic regime characterized by extended drought covered large areas of southeastern europe based on the dalkenones similarity and the paratethys type of lago mare fauna in the mediterranean we speculate that the surface water during stage 3 was at times derived from the black sea

transition from marine to hypersaline conditions in the messinian tripoli formation from the marginal areas of the central sicilian basin abstract three sections of the early messinian tripoli formation from the northern and southern margins of the central sicilian basin serra pirciata torrente vaccarizzo and marianopoli have been studied with the aim to reconstruct the sedimentary and environmental changes which occurred during the transition between marine conditions and the evaporitic events of the salinity crisis recorded in the overlying calcare di base formation a detailed biostratigraphic and cyclostratigraphic study provided the opportunity of cycle by cycle correlations between the marginal sections and the reference section of falconara the main paleoenvironmental changes are recorded by 1 the evolution of calcareous microfossils towards low diversity and their complete disappearance 2 the composition of the carbonate fraction which commonly changes from calcite mostly related to calcareous microfossils to authigenic carbonate phases consisting of either calcite dolomite and or aragonite 3 the appearance of shallow water deposits and evaporite pseudomorphs 4 the variation of the stable isotope composition of the carbonate fraction indicative of large fluctuations of the freshwater dilution evaporation balance with a general trend towards hypersaline conditions both mineralogical and isotope data indicate that the dolomite precipitated generally from concentrated pore waters while other carbonates formed in the water column submitted to large fluctuations of salinity except locally the increase in salinity did not reach concentrations high enough to precipitate significant volumes of evaporites as during the deposition of the overlying calcare di base the transition from normal marine to hypersaline conditions is recorded diachroneously in the three sections respectively in cycle 34 6 32 ma at serra pirciata cycle 42 6 15 ma at torrente vaccarrizzo and cycle 44 6 12 ma at marianopoli these changes represent the hydrological and sedimentary response to the fragmentation of a large marine basin into different subbasins which ended in the more or less complete closure recorded by the deposition of the overlying evaporite rich calcare di base fm true onset of the evaporitic event two hypotheses not exclusive may explain this change either the regional consequence of the compressive tectonics or the incipient drop of the global sea level which led to the salinity crisis our results confirm that the salinity crisis was preceded by evaporative episodes in the evolution towards hypersaline conditions which occurred diachroneously as a response to the diversity of paleogeographical settings even if the paroxysmal phase seems to have affected the basin at the same time

evidence for slowly changing 87sr86sr in runoff from freshwater limestones of southern france abstract 87 sr 86 sr ratios have been determined in modern rivers and freshwater limestones dating from 65 ma to the present over an area extending from the pyrenees to the massif central southern france about 40 ma ago the alpine mountain range of the pyrenees was strongly uplifted by the alpine orogenic activity and its pre hercynian basement dominated by schists gneisses and granites was rapidly exposed from beneath its blanket of mesozoic marine limestones meanwhile the 87 sr 86 sr ratio of the rivers has remained remarkably constant in both space with the exception of the very few northernmost samples and time in this area extreme variations through the orogenic period are small with 87 sr 86 sr lying between 0 7073 and 0 7084 at 55 65 ma and 0 7077 0 7096 for the last 30 ma river sr is controlled by a nearly binary mixing of silicate 3 4 and 1 4 end members with negligible influence of evaporites it is inferred that the silicate sediment contribution ratio of the world average rivers to seawater sr changes at a very slow rate even taking major basaltic events into account does not alter this conclusion as their contribution to the river sr is very subordinated to other components it is inferred that the seawater 87 sr 86 sr secular main trend over the phanerozoic is controlled by hydrothermal alteration of oceanic basalts and slow variation of the limestone silicate contribution ratio to the riverine sr oceanic events changes in organic productivity and carbonate compensation depth ccd may produce intense short term variations but recovery of steady state seawater 87 sr 86 sr is delayed by 40 80 ma through diagenetic sr remobilization in carbonate sediments

nanometer scale layering in rock varnish implications for genesis and paleoenvironmental interpretation manganiferous rock varnish collected from death valley and antarctica contains the smallest known terrestrial sedimentary deposits with some layers only a few nanometers thick irregularities in these nanometer scale layers are consistent with shrinking cracking and weathering of clay minerals in the death valley rock varnish very different high resolution transmission electron microscope hrtem textures coexist that may be related to climatic change hrtem observations contradict previous microbial models of mn fe enhancement requiring a new three step model of biomineralization and diagenesis for varnish formation

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

manganese rich rock coatings from iceland manganese rich rock coatings are widespread in iceland especially in fractures in basalt lavas three common types of coating are described a thick subsurface coating is found on whaleback forms on high plateaux the most common type is thinner and occurs in hydrothermal clay filled fracture systems which are especially well developed in tholeiite lavas a third type occurs in younger rocks and is associated with tephra rich loessic sediment which fills open fractures and vesicles there are differences in the chemistry morphology and mineralogy of these coatings which are interpreted as being due to the different microenvironments in which they form the fracture microenvironment is regarded as being of much more importance to coating thickness and chemistry than simple age and in this respect the hydrothermal clays seem to favour rapid manganese concentration on the other hand there are variations in coating type both laterally and vertically through the lava succession which are related to regional distribution of hydrothermal alteration and rock type the regional patterns are the result of iceland s lateral drift and as a result there is an incidental connection between coating type and rock age there is some evidence to suggest that the manganese coatings may be both forming and being degraded rapidly in the present environment

holocene rock varnish microstratigraphy and its chronometric application in the drylands of western usa abstract analyses of hundreds of rock varnish samples from latest pleistocene and holocene geomorphic features in the drylands of western usa reveal a regionally replicable holocene microlamination sequence this sequence consists of 12 approximately evenly spaced weak dark layers intercalated with 13 orange yellow layers preliminary radiometric age calibration indicates that six dark layers in the upper portion of the sequence were deposited during the last 6000 yr diagnostic of the little ice age and late holocene wet events five dark layers in the lower portion of the sequence were deposited after the termination of the pleistocene but slightly before 7000 ybp indicative of the early holocene wet events and one dark layer in the middle portion of the sequence was deposited around 6500 ybp suggestive of the middle holocene wet phase our age calibration further indicates that the holocene wet events represented by the dark layers largely correlate in time with the millennial scale holocene cooling events in the north atlantic region this radiometrically calibrated and climatically correlated holocene microlamination sequence was then used as a unique correlative dating tool to determine surface exposure ages of geomorphic and geoarchaeological features in western usa deserts the varnish microlamination vml dating of debris flow fan deposits in death valley california yields minimum ages of 12 500 12 500 11 100 11 100 10 300 9400 and 2800 ybp for six debris flow fan building events suggesting that such events were more likely to have occurred during relatively wet periods of the holocene the vml dating of a prehistoric grinding stone from chili of northern new mexico yields a minimum age of 900 1100 ybp for the abandonment of this occupation site by the anasazi indians the vml dating of a prehistoric flaked stone a primary core from ocotillo southern california yields a minimum age of 12 500 ybp for the flaking of this stone artifact suggesting at least a paleo indian human occupation at ocotillo during the terminal pleistocene these results indicate that when properly applied the vml dating technique has the great potential to yield numerical age assignments for surface stone tools petroglyphs and geoglyphs of prehistoric age in the drylands of western usa

pressure solution and coble creep in rocks on 5 november 1976 the tectonic studies group of the geological society held a lively discussion meeting at imperial college on the subject of pressure solution and coble creep deformation mechanisms may be divided into three broad categories 1 cataclastic processes 2 intracrystalline processes involving dislocations 3 diffusive mass transfer processes we are concerned here with group 3 processes flow by diffusive mass transfer of matter from grain boundaries which are subjected to high normal stress to less highly stressed grain boundaries if the diffusion is predominantly through the grain the process is termed nabarro herring creep whereas if it is predominantly around grain boundaries the flow is termed coble creep in general grain boundary sliding must occur to accommodate the grain shape changes due to diffusion for these processes to proceed at rates which are detectable the temperature must be at a large fraction of the absolute melting temperature of the material geologists have long recognized in low grade metamorphic rocks textures in dicative of deformation by diffusive mass transfer even over the relatively long time available for geological deformations at the low temperatures concerned solid state diffusivities would be too slow to account for the observed strains it is therefore inferred that the rate of diffusive mass transfer is enhanced by the presence of an intergranular fluid film hence the use of the term pressure solution to describe the process thus coble creep and pressure solution are similar in that they both involve intergranular diffusion the meeting was intended to