the twin rivers kopje zambia stratigraphy fauna and artefact assemblages from the 1954 and 1956 excavations abstract earlier lupemban assemblages from brecciated fissure sediments on twin rivers kopje are of great interest in view of the appreciably greater antiquity recently suggested for the earlier middle stone age the twin rivers assemblages are compared with those from kalambo falls the congo basin and zimbabwe the assemblages combine components from both the forested grasslands of equatoria and the savanna woodlands of east and south central africa faunal remains suggest that the early middle stone age sequence reflects several episodes of climatic change between 130 000 years bp and bp

hydrothermal source of radiogenic sr to himalayan rivers 1 k 1 and cl 2 all of which are high in the hydrothermal waters cation concentrations decrease along the lesser himalayan reach of the river hot spring dissolved co2 has a d 13 c value to 15 9 indicating that metamorphic decarbonation reactions contribute co2 to the fluids hydrothermal co2 is partially neutralized in high temperature weathering reactions which generate alkalinity and yield abundant radiogenic sr radiogenic hydrothermal carbonate can form from these solutions and later weather releasing silicate sr but imparting carbonate characteristics to the overall water chemistry

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

climatic significance of holocene beachrock sites along shorelines of the red sea mozley and burns 2006 discussion reminds me of current discussions on paleotemperature elsewhere in the july 29 2005 issue of science the following statements are presented two teams of researchers studying the same evidence with the same techniques have painted diametrically opposite pictures of a key period in the history of earth s climate which climatologists are probing it s a tough issue to sort out what s at stake is the regional distribution of climate both past and future kerr 2005 p 687 we have to wait for more data this is difficult work and it is easy to be misled before answering specific criticism please note that my study was a geologic note and not a full article my detailed article friedman 2004 was published as part of a special publication series requested by the geochemical society as part of its tribute to isaac r kaplan i refer mozley and burns 2006 to the details of my article i shall answer their criticism the studied beachrock is composed of 1 terrigenous debris derived from nearby bedrock 2 carbonate particles of local origin and 3 carbonate cement friedman 1988 table 1 view this table table 1 x ray diffraction mineralogical analysis the most common beachrock lithology is terrigenous calcipebblestone figure 1 and calcisandstone in which skeletal debris is minor or absent terrigenous rock fragments are dominant and carbonate cement is abundant terrigenous debris does not affect radiocarbon dating nor carbon or strontium isotopic measurements because in most of the samples the debris does not generally contain carbonates the samples selected for the study contain fossils only sporadically or at best fossils are entirely absent figure 1 beachrock with abundant included terrigenous pebbles paving intertidal zone and extending into supratidal zone on the west side of the gulf of aqaba terrigenous particles in the studied beachrocks consist of igneous and

renewed investigations into the middle stone age of northern malawi j desmond clark and his colleagues were first to investigate the rich middle stone age msa from ca 285 to 30 000 years ago deposits in the karonga district of northern malawi in the 1960s this work demonstrated the enormous potential of the area to inform about middle to late pleistocene hominin lifeways but further studies were hindered by difficulties in dating the sites and understanding their fine scale depositional and paleoenvironmental contexts with the advances that have been made in the fields of geoarchaeology lithic analysis palaeoenvironments and geochronology over the last fifty years the time is ideal to renew these investigations recent survey and excavation in karonga malawi show that msa lithic artifacts are preserved in a variety of stratified sedimentary contexts and that they exhibit limited weathering or other indications of post depositional transport these deposits are in close proximity to the high resolution paleoenvironmental records derived from sediments at the bottom of nearby lake malawi which provide context for the human behavior recorded by the artifacts results of excavations at one of these stratified sites the airport site are detailed here this provides a renewed example of the site formation and behavioral data available in the region

long term fluvial incision rates and postglacial river relaxation time in the french western alps from 10be dating of alluvial terraces with assessment of inheritance soil development and wind ablation effects studying river long profile development as a response to tectonic and climatic controls requires reliable age dating of paleo profile remnants preserved as river terraces cosmic ray exposure cre dating often represents the only method available to date river terraces but the interpretation of cosmogenic nuclide concentrations is complicated by pre depositional inheritance and post depositional disturbance of the terrace deposits through pedogenesis and surface inflation or deflation here we use cosmogenic 10be measurements to date alluvial terraces in the french western alps in order to estimate river incision rates and to infer river response to climatic fluctuations and tectonic forcing we assess inheritance by constructing 10be concentration vs pebble depth profiles and use a monte carlo technique to estimate terrace ages we find that inheritance is negligible on all terraces enabling us to date terraces as young as 5 ky terraces that predate the last glaciation experienced intense pedogenesis and wind ablation which led to significant scatter in the 10be concentrations of surface samples we assess these effects using a model of 10be ingrowth and show that the oldest cre ages of surface clasts are close to the probable terrace age we study two catchments which have undergone varying degrees of glacial disruption the buech river experienced variations in runoff and sediment flux during the last glaciation as well as occasional ice dammings of its outlet its upper terraces record incision rates averaged over 190 ky of 0 8 mm yr consistent with denudation rates estimated in the surrounding areas and suggesting long term stability of river incision rates climatic forcing is well documented for the drac river which was repeatedly dammed by glaciers during cold periods its postglacial incision history was triggered by an 800 m drop in base level following ice dam disappearance long profile development by knickpoint propagation explains the time lag of 2 5 ky between this base level drop and terrace abandonment upstream as well as subsequent peak incision rates of 6 cm yr followed by a gradual decrease in incision rates the present knickpoint location 55 km upstream from the glacial damming site enables us to calculate a fluvial response time of 15 20 ky controlled by knickpoint propagation rates of several meters per year within the drac river

a geologically constrained monte carlo approach to modeling exposure ages from profiles of cosmogenic nuclides an example from lees ferry arizona we present a user friendly and versatile monte carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides tcns our program available online at http geochronology earthsciences dal ca downloads models html permits the incorporation of site specific geologic knowledge to calculate most probable values for exposure age erosion rate and inherited nuclide concentration while providing a rigorous treatment of their uncertainties the simulator is demonstrated with 10be data from a fluvial terrace at lees ferry arizona interpreted constraints on erosion based on local soil properties and terrace morphology yield a most probable exposure age and inheritance of 83 9 14 1 19 1 ka and 9 49 2 52 1 21 104 atoms g 1 respectively 2 without the ability to apply some constraint to either erosion rate or age shallow depth profiles of any cosmogenic nuclide except for nuclides produced via thermal and epithermal neutron capture e g 36cl cannot be optimized to resolve either parameter contrasting simulations of 10be data from both sand and pebble sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with tcn depth profiles and when possible sand not pebbles should be used for depth profile exposure dating

reply to comment by p rydelek et al on earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records 1 based on the analysis of mediterranean near source strong motion records zollo et al 2006 hereinafter referred to as zln showed that peak displacement amplitudes of initial pand s wave seismic signals scales with the earthquake size in the moment magnitude range 4 6 1 9 in figure 1 we report data distribution vs magnitude and hypocentral distance note that the distance distribution of analyzed events for japan figure 1 is clearly different from that for the mediterranean med earthquakes given by zln whereas most of med records occur at an hd 40 km 10 at odds with rwh we did not apply any cut off at m 5 5 on hypocentral distance for small and moderate events indeed this may introduce a bias on the estimation of attenuation law parameters retrieved from both small and large earthquakes records we follow the zln procedure involving among others sensitivity correction p and s phase identification double integration filtering in a frequency band 0 075 3 hz peaks are read on the modulus of displacement expressed in meters starting from the pwave and s wave picked arrivals we measure peaks within a 2 second window for the p arrival we also test the method with 4 second windows 11 the distance attenuation effect is corrected for by assuming a simple log linear model wu and zhao 2006 zln the amplitudes are normalized to a reference distance of 10 km i e the same as for zln in the mediterranean study to facilitate comparison though rwh show data normalized at a distance of 20 km zln figures 2a and 2b the use of a different normalization distance does not change the slope of the log peak vs magnitude relationships and thus does not alter the graphical interpretation 12 in figure 2 we show the relation between the logarithm of distance normalized peak displacement for p and s waves in different time windows vs final magnitude of the events following zln statistical significance was geophysical research letters vol 34 l20303 doi 10 1029 2007gl030560 2007 click here for full article

new chronology for the southern kalahari group sediments with implications for sediment cycle dynamics and early hominin occupation abstract kalahari group sediments accumulated in the kalahari basin which started forming during the breakup of gondwana in the early cretaceous these sediments cover an extensive part of southern africa and form a low relief landscape current models assume that the kalahari group accumulated throughout the entire cenozoic however chronology has been restricted to early middle cenozoic biostratigraphic correlations and to osl dating of only the past 300 ka we present a new chronological framework that reveals a dynamic nature of sedimentation in the southern kalahari cosmogenic burial ages obtained from a 55 m section of kalahari group sediments from the mamatwan mine southern kalahari indicate that the majority of deposition at this location occurred rapidly at 1 1 2 ma this pleistocene sequence overlies the archaean basement forming a significant hiatus that permits the possibility of many phanerozoic cycles of deposition and erosion no longer preserved in the sedimentary record our data also establish the existence of a shallow early middle pleistocene water body that persisted for 450 ka prior to this rapid period of deposition evidence from neighboring archeological excavations in southern africa suggests an association of high density hominin occupation with this water body

age and evolution of the grand canyon revealed by u pb dating of water table type speleothems the age and evolution of the grand canyon have been subjects of great interest and debate since its discovery we found that cave mammillaries water table indicator speleothems from nine sites in the grand canyon showed uranium lead dating evidence for an old western grand canyon on the assumption that groundwater table decline rates are equivalent to incision rates samples in the western grand canyon yielded apparent water table decline rates of 55 to 123 meters per million years over the past 17 million years in contrast to eastern grand canyon samples that yielded much faster rates 166 to 411 meters per million years chronology and inferred incision data indicate that the grand canyon evolved via headward erosion from west to east together with late stage 3 7 million years ago accelerated incision in the eastern block

the malawi rift geology tectonics and seismicity the malawi nyasa rift is a southern extension of the western branch of the cenozoic east african rift system it extends for socl km from the rungwe volcanics in southern tanzania to the middle shire river the rift structures extend for a further 600 km to the south by the urema graben and dombe trough in mozambique fig 1 crow and crossley 1980 the malawi rift which is largely occupied by lake malawi consists of a series of half grabens the geology of the lake bed has been revealed by seismic reflection data obtained under project cegal cenozoic environments and geodynamits of african lakes in 1981 rosendahl and livingstone 1983 ebinger et al 1984 and project probe 1985 87 scholz et al 1989 the seismic reflection data has shown that the lake consists of several asymmetric basins with complex fault geometries infilled with thick sedimentary sequences with dyke like bodies scholz et al 1989 the rift is seismically active with most of the activity being associated with the rift faults the major part of the malawi rift is underlain by precambrian gneisses and granulites of sedimentary or igneous origin karroo sequences of conglomerates sandstones and coal measures are found onshore in livingstone province bandawe metangula nkhotakota province and chikwawa nsanje in the shire province in the

linking morphology across the glaciofluvial interface a 10be supported chronology of glacier advances and terrace formation in the garonne river northern pyrenees france abstract the garonne river drains an important part of the northern pyrenees and its northern foreland we investigated the middle reaches of the garonne river establishing a detailed morphogenetic profile of its foreland terrace staircase and the preserved palaeoglacier margins we particularly focussed on the glaciofluvial interface linking also genetically the fluvial sediment archives in the foreland with the terminal glacial basin upstream of the pyrenees mountain front using cosmogenic nuclide 10be analyses two terrace exposures have been dated including a prominent fluvioglacial outwash fan at the foreland transition we identified three terminal margins of late pleistocene glacier advances the prominent garonne staircase consists of three major terrace complexes comprising eight individual terrace levels results indicate a young age of the lower terrace complex of the garonne staircase mis 4 2 the morphogenetic relationships and the new 10be exposure age constraints suggest that during the last glaciation wurmian the garonne glacier reached its maximum extent at the north pyrenean mountain front apparently already during mis 4 two different ice margins were associated with mis 2 indicating close to maximum ice extent during early mis 2 lgm and relatively stationary ice recession in the late mis 2 the extensive garonne terrace complexes formed under cold climate conditions and were abandoned by incision during major glacial interglacial transitions during warm cold climate transitions lateral erosion caused the reworking of previously abandoned palaeofloodplains the long term quaternary incision of the garonne and other north pyrenean rivers indicates that the proximal aquitaine foreland basin experienced uplift however non uniform lateral course migrations and valley asymmetries of the north pyrenean piedmont rivers indicate that uplift magnitude is variable with maximum amounts in the centre of the molasse fan of lannemezan rivers on the western part of the fan were tilted toward the west whereas rivers in the eastern part like the garonne were tilted to the east

sequential evolution and diagenesis of pleistocene coral reefs south sinai egypt abstract the uplifted pleistocene coral reefs in south sinai represent two major depositional sequences they generally form two morphological terraces which locally are tilted and offset by still active faulting the major reef sequences are composed of several small scale sequences corals grew rapidly when accommodation space was created by eustatic sea level rise or fault block subsidence as the accommodation decreased coral rubble and siliciclastic sands prograded over reefal and lagoonal sediments thus creating a shallowing upward sequence terrigenous input was further stimulated by a more humid climate during interglacial times 230 th 234 u dating places the older reef cycle between 350 000 and 270 000 years b p which corresponds to the interglacial period of isotope stage 9 the younger reef cycle has been dated between 140 000 and 60 000 years b p isotope stage 5 an intermediate relic sequence found in only one outcrop can be attributed to isotope stage 7 correlation of the small scale sequences is difficult age dating is not precise enough and local tectonic activity in many cases overruled the smaller eustatic fluctuations the younger reef sequence commonly exhibits marine cements whereas the older sequence was exposed to freshwater dissolution and cementation an important feature is the locally pervasive dolomitization especially of the older reef oxygen and carbon isotope values suggest that the dolomite formed in a seawater dominated mixing zone multiple phases of dissolution cementation and dolomitization point to a very complex diagenetic history

earthquake frequency distribution and the mechanics of faulting the level of intraplate seismicity in japan generally shows a positive correlation with the density of quaternary faulting in southwest japan where intraplate seismicity is concentrated on land rates of seismic moment release m 0 are similar when calculated from either the 400 year historical record of seismicity or geologically determined slip rates of quaternary faults a data set of 18 earthquakes with seismic moments m0 ranging from 0 01 to 3 1027 dyn cm shows a relationship between rupture lengthl and m0 log m0 23 5 1 94 log l when seismic moment on each quaternary fault is assumed to occur in discrete events every t m0 m 0g years where m0 is estimated for a rupture extended over the entire fault length and m 0g is proportional to the slip rate of each quaternary fault the moment frequency distribution of earthquakes log n a b log m0 predicted from the geologic record is virtually identical to that seen with the 400 year record of seismicity in contrast if it is assumed that earthquakes on each fault occur according to the gutenberg richter relation we obtain poor agreement with the observed seismicity thus while regional seismicity satisfies the relation log n a b log m0 or equivalently log n a b log m where m is magnitude it appears that seismicity on individual faults does not this further implies that the primary factor that leads to the magnitude frequency distribution in regional seismicity studies is the relative distribution of the slip rates and lengths of preexisting faults

a cosmic trip 25 years of cosmogenic nuclides in geology terrestrial cosmogenic nuclides produced by secondary cosmic ray interactions in the atmosphere and in situ within minerals in the shallow lithosphere are widely used to date surface exposure of rocks and sediments to estimate erosion and weathering rates and to date sediment deposition or burial their use has transformed geomorphology and quaternary geology for the first time allowing landforms to be dated and denudation rates to be measured over soil forming time scales the application of cosmogenic nuclides to geology began soon after the invention of accelerator mass spectrometry ams in 1977 and increased dramatically with the measurement of in situ produced nuclides in mineral grains near earth s surface in the 1980s the past 25 yr have witnessed the development of cosmogenic nuclides from their initial detection to their prevalence today as a standard geochronological and geochemical tool this review covers the major developments of the past 25 yr by comparing the state of the field in 1988 with that of today and by identifying key advances in that period that moved the field forward we emphasize the most commonly used in situ produced nuclides measured by ams for geological applications but we also discuss other nuclides where their applications overlap our review covers ams instrumentation cosmogenic nuclide production rates the methods of surface exposure dating measurement of erosion and weathering and burial dating and meteoric 10 be in memoriam devendra lal 1929 2012 whose vision inspired the field

beachrock cementation in alexandria egypt beachrock is found in the intertidal and sublittoral zones along the mediterranean coast of alexandria egypt it occurs as beds or patches and shows several stages of cementation and hardness the seaward dip of the beachrock is similar to that of the slope of the foreshore the fabric shows micrite and fringe cement types aragonite was not identified in the beachrock at alexandria the average concentrations of ca mg sr fe and mn in the beachrock are similar to those of the beach deposits the process of beachrock cementation in alexandria is rather recent and typically marine

an automatic processing system for broadcasting earthquake alarms in japan most of the damage caused by large earthquakes is concentrated within areas less than about 100 km from the focal regions we have developed an earthquake alarm system that determines earthquake parameters within a few seconds of the p wave s arrival at the closest station and then transmits the earthquake information before the s wave arrival in areas of possible serious earthquake damage since an earthquake alarm system requires the determination of reliable earthquake parameters as quickly as possible it is unreasonable to wait until waveform data from numerous stations have been collected for analysis for this reason we have developed a novel method of determining the hypocentral location by using the arrival times for only a few stations as well as the lack of p wave arrivals at other stations at a given time the use of not yet arrived data makes it possible not only to determine reliable hypocenter parameters within a few seconds but also to detect erroneous arrival time readings and remove them automatically since the available waveform data increases with time the system was designed to redetermine earthquake parameters every second our method was deployed in a real time system starting in july 2002 the real time system locates 10 20 events per day which includes a few felt earthquakes occurring in and around japan it was shown from the waveform data for about 100 felt earthquakes that almost all the events except those far from the network could be located within a few seconds when most of seismic energy has not even arrived at some stations close by we recently started widespread broadcasting of earthquake information in real time by using a satellite transmission system

beach cement incipient caco 3 cemented beachrock development in the upper intertidal zone north uist scotland abstract beachrock has only rarely been observed previously along high latitude coasts on several beaches on north uist nw scotland at over 57 n there is evidence of small scale beach cementation an area of beach cement at the back of traigh ear as well as unconsolidated sands from the beach and the adjacent traigh hornais have been studied using sem xrd and petrographical thin sections to throw light on the nature and causes of cementation unconsolidated sands from both beaches are similar in grain sizes shape and mineralogy but traigh ear grains commonly possess abundant cover of high mg calcite the beach cement on traigh ear exhibits low porosity with abundant micritic and aragonitic cements showing no evidence of vadose cementation along with traces of microorganisms these findings contrast with the vadose low mg calcite cements commonly reported from temperate zone beachrocks

26al 10be dating of an aeolian dust mantle soil in western new south wales australia abstract aeolian dust mantle soils are an important element of many landscapes in south eastern australia though the age of these aeolian deposits has not been radiometrically determined at fowlers gap in western new south wales surface cobbles of silcrete and quartz overlie a stone free aeolian dust mantle soil which has a thickness of about 1 6 m the clay rich aeolian dust deposit in turn lies upon a buried silcrete and quartz stone layer modelling in situ cosmogenic 26 al and 10 be concentrations measured in both the surface quartz stones and in the buried quartz layer of rocks reveals that each has experienced a complex exposure burial history due to the absence of quartz stones or sand at intermediate depths our cosmogenic 26 al and 10 be modelling was not able to determine a definitive mechanism of stone pavement formation and stone burial various scenarios of stone formation transport burial and exhumation were tested that constrain the age of the deposit to range from 0 9 0 2 ma to 1 8 0 2 ma based largely on different assumptions taken for the time dependency of the net sedimentation rate this corresponds with the initiation of the simpson desert dune fields and the deflation of lakes in central australia which probably responded to the shift to longer wavelength larger amplitude quaternary glacial cycles at around 1 ma sensitivity analyses were carried out to identify those parameters which better constrained model outputs within model errors which largely are the result of analytical errors in measured 26 al and 10 be concentrations all three competing theories of colluvial wash upward displacement of stones and cumulic pedogenesis are possible mechanisms for the formation of the surface stone pavement

cosmogenic nuclide age constraints on middle stone age lithics from niassa mozambique abstract the late phases of the middle stone age msa in the east african rift system ears are known for their evolutionary shifts and association with bottlenecks transcontinental expansion and climatic fluctuations the chronology of msa sites contemporaneous with these eco demographic upheavals is uncertain because of the scarcity of datable sites and the poor understanding of their depositional and erosional histories we apply terrestrial cosmogenic nuclide dating in a stratigraphic section with a complex exposure history to the study of the luchamange beds a widespread sedimentological unit underlying msa sites from the shores of lake niassa mozambican ears we use an innovative approach which may be applicable elsewhere to calculate their age using a monte carlo based bayesian model that links depth profiles of 26al and 10be and uses other geomorphic and cosmogenic nuclide age constraints on episodic erosion and burial the age of the basal luchamange beds is 42 77 15 ka and the msa occupation on top is 29 3 11 ka these dates suggest temporal overlap between msa and the earliest later stone age and diversity in cultural manifestations at the end of the msa

climate change conflict of observational science theory and politics debate over whether human activity causes earth climate change obscures the immensity of the dynamic systems that create and maintain climate on the planet anthropocentric debate leads people to believe that they can alter these planetary dynamic systems to prevent what they perceive as negative climate impacts on human civilization although politicians offer simplistic remedies such as the kyoto protocol global climate continues to change naturally better planning for the inevitable dislocations that have followed natural global climate changes throughout human history requires us to accept the fact that climate will change and that human society must adapt to the changes over the last decade the scientific literature reported a shift in emphasis from attempting to build theoretical models of putative human impacts on climate to understanding the planetwide dynamic processes that are the natural climate drivers the current scientific literature is beginning to report the history of past climate change the extent of natural climate variability natural system drivers and the episodicity of many climate changes the scientific arguments have broadened from focus upon human effects on climate to include the array of natural phenomena that have driven global climate change for eons however significant political issues with long term social consequences continue their advance this paper summarizes recent scientific progress in climate science and arguments about human influence on climate

single crystal 40ar 39ar dating of pyrite no fool s clock single crystals of dispersed trace pyrite from two igneous rocks were dated by using the 40 ar 39 ar laser probe method and the resulting ages were compared to step heating ages of associated amphibole and phlogopite the isochron ages for 0 1 0 3 mm cubes of pyrite agree well with the respective amphibole ages of these igneous samples preliminary step heating analyses of single pyrite crystals yield internal isochrons with indistinguishable although less precise ages both pyrite and amphibole are significantly older than associated phlogopite in one sample which has undergone postcrystallization alteration these results suggest that pyrite can give reliable and precise 40 ar 39 ar ages even in the presence of subsequent alteration given the ubiquity of pyrite in many geologic environments this technique has great promise for application to the dating of ores sediments and hydrocarbon migration all of which have been very difficult to date directly

cosmogenic dating of rock avalanches constraining quaternary stratigraphy and regional neotectonics in the argentine central andes 32 s abstract this paper provides a comprehensive review of the chronostratigraphy of six rock avalanches clustered in the northern extreme of the cordon del plata range these rock avalanches are stratigraphically related to pleistocene glacial drifts and valley fill deposits documenting the regional neotectonic activity we used cosmogenic dating tcn to directly date block surfaces of rock avalanche deposits as well as optically stimulated luminescence dating osl of paleo lakes dammed by these rock avalanches our new direct dates 17 tcn and 4 osl determine the middle to late pleistocene age of these collapses these are in contrast to the previously established chronostratigraphy based on relative dating techniques paleontological context and tephrochronology these new data help to redefine the geomorphological evolution of the mendoza river valley especially the new data indicate that the glacial stratigraphy earlier proposed must be reconsidered we redefine this stratigraphy as far as possible with our data and discuss the data in relation with other recently published results however it becomes clear that the glacial history of the mendoza valley has to be studied anew by using modern dating techniques in addition our data suggest that the carrera fault system bounding the valleys of the cordillera del plata has been active more recently than proposed earlier

carbonate cements in holocene beachrock example from bahiret et biban southeastern tunisia abstract holocene beachrock has been studied on the northern and western shores of bahiret el biban a shallow restricted lagoon in southeastern tunisia the beachrock consists of horizontal cemented layers which are 2 15 cm thick early cementation took place at the water table below beach ridges where geochemical hydrodynamic and possibly also microbiological conditions favored rapid precipitation of aragonite and or high mg calcite locally superimposed low mg calcite cements point to subsequent freshwater influence at one site six vertically stacked beachrock beds are found total rock 14c dating shows that the highest beachrock bed is older than the one of the same petrographic composition situated at the present groundwater level this implies a downward progression of cementation which probably monitored the sea level fall following a local highstand about 3000 years ago

probabilistic estimation of earthquake growth to a catastrophic one 1 we propose a method to estimate the probability of earthquake growth to a catastrophic one immediately after observing its initiation for practical usage in an earthquake early warning system this method is essentially an application of the conditional probability theory where the magnitude frequency relation plays a crucial role we apply it to the nankai trough region japan where a catastrophic earthquake is expected in the near future based on the historical catalogue we estimate the probability density of magnitude using a bayesian approach we then estimate the probability of earthquake growth to a catastrophic one if the observed earthquake magnitude reaches 6 5 the estimated probability that the final magnitude exceeds 7 5 is 25 41 according to previous studies the time taken for the magnitude to increase from 6 5 to 7 5 is approximately 10 15 seconds our method is highly beneficial in that it enables an earlier alarm to be issued

climatic significance of holocene beachrock sites along shorelines of the red sea discussion the geologic record of climate change is currently a very active area of research the results of such studies have the potential to greatly improve our understanding of the different factors that influence climate and consequently may help to guide policy initiatives regarding global warming given the importance of such studies it is imperative that they be scientifically rigorous and thorough friedman 2005 falls short on both counts in this article friedman attempted to use the oxygen isotopic composition of a series of 14c dated beachrock samples to infer past changes in temperature on the basis of increasing 18o values for beachrock with decreasing age he concluded that global temperature has decreased dramatically during much of the holocene the conclusions of the study regarding changing temperature are not supported by the data presented alternative hypotheses not considered in the study are far more likely explanations for the observed isotopic trend than decreasing temperature the principal problems with the article are that 1 critical assumptions are unsupported and there is no discussion of alternative hypotheses 2 there is no description of the petrographic characteristics of the samples 3 no information on methodology is included 4 the existing literature on beachrock much directly relevant to the study is completely ignored and 5 the conclusions are contradicted by a large number of paleoclimate studies for the same period these problems are discussed in detail below friedman makes several important assumptions without adequately justifying them the first assumption is that cements in the beachrock precipitated from unaltered seawater he acknowledges that ground water discharge mixing with river water and evaporation effects particularly significant in the gulf of aqaba friedman 1968 can alter the isotopic composition of local seawater but proceeds to assume for the purpose of the subsequent

quaternary soils and dust deposition in southern nevada and california eoliandustconstitutesmuchofthepedogenic material in late pleistocene and holocene soils of many arid regions of the world comparisonofthecompositionsand influx rates of modern dust with the eolian component of dated soils at 24 sites in southern nevada and california yields informationon 1 thecompositionandinflux rate of dust in late pleistocene and holocene soils 2 paleoclimate and its effects on the genesis of aridic soils especially with regard to dustfall events 3 the timing and relative contribution of dust from playa sources versus alluvial sources and 4 the effects of accumulation of dust in soil horizons the 2mmfractionsofaandbhorizons of soils formed on gravelly alluvial fan deposits in the study area are similar to moderndustingrainsize contentofcaco3and salt majoroxides andclaymineralogy thus they are interpreted to consist largely of dust the major oxide compositions of the shallow soil horizons are nearly identical to that of the modern dust but the compositions of progressively deeper horizons approachthatoftheparentmaterial theclay mineralogyofmoderndustatagivensiteis similar to that of the av horizons of nearby holocene soils but is commonly different from the mineralogies of deeper soil horizonsandoftheavhorizonsofnearbypleistocenesoils theseresultsareinterpretedto indicate that dust both accumulates and is transformed in av horizons with time changes in soil accumulation rates provide insights into the interplay of paleoclimate dustsupply andsoil formingprocesses modern dust deposition rates are more than large enough to account for middle and late holocene soil accumulation rates at nearly all sites however the early holocene soil accumulation rates in areas near late pleistocene pluvial lakes are much higher than modern rates and clearly indicate a dust deflation and deposition event that caused rapid formation offine grained shallow soil horizons on uppermost pleistocene and lower holocene deposits we interpret late pleistocene soil accumulation rates to indicate that dust deposition rates were low during this period but that increased effective moisture during the late wisconsinan favored translocation of clay andcaco3fromnearthesurfacetodeeper inthesoilprofile pre latepleistocenerates are very low in most areas mainly due to a pedogenic threshold that was crossed when accumulations of silt clay and caco3 began to inhibit the downward transport of eolian material but in part due to erosion

stable isotopic composition of carbonate cemented recent beachrock along the mediterranean and the red sea coasts of egypt abstract recent beachrocks on the mediterranean and the red sea coasts of egypt have been studies in the mediterranean beachrock skeletal particles mainly molluscan fragments are the most abundant grain type comprising approximately 60 of the framework grains intraclasts make up the remaining 40 in contrast the red sea beachrocks are dominantly composed of igneous and metamorphic crystalline basement rock fragments that range in dimension from large boulders in proximal parts of the fan to gravels sands and silts in the distal parts high energy conditions as well as the presence of relatively coarse high porous and permeable sediments ensure that adequate volumes of supersaturated water are able to move through the pore system to accomplish the cementation process textural study light and sem microscope on samples from both localities reveals that high mg calcite cements occur as thick to thin bladed isopachous crusts which sometimes occlude all pore spaces aragonite cements are also present as thin circumgranular acicular crusts however some samples along the red sea coast contain high mg calcite displaying scalenohedral crystal forms the isotopic composition of these beachrock cements generally show high values of 18 o and 13 c in the mediterranean beachrock cements the 18 o and 13 c values range from 0 4 to 1 2 and from 1 0 to 2 1 pdb respectively whereas the 18 o and 13 c values of red sea beachrock cements range from 0 1 to 1 2 and from 2 1 to 4 5 pdb respectively the oxygen and carbon isotopes together with the texture and mineralogical composition of these cements are good indicators of the conditions of primary cementation and reflect the gross of stable isotopic and chemical composition of marine water

glacial interglacial variation in denudation rates from interior texas usa established with cosmogenic nuclides abstract the brazos colorado and trinity rivers of texas drain a tectonically quiescent non glaciated and low relief landscape inland from the gulf of mexico where long term 10 3 10 5 a changes in denudation rates are probably driven largely by climate change here we use cosmogenic 10be to obtain spatially averaged denudation rates for these river catchments primarily from terrace deposits associated with glacial or interglacial intervals over the past half million years the denudation rates are 30 35 higher during interglacial periods than during glacial periods and correlate broadly with temperature the results are consistent with predictions from the bqart sediment flux model and support the hypothesis that increased weathering rates associated with warmer climates will accelerate landscape erosion furthermore by analyzing 26al 10be in these deposits we can estimate the bed load sourced from up catchment surfaces the stored coastal plain fraction varies from 10 to 30 and is greater during times of relatively lower sea level the results indicate that although sediment flux is moderated by coastal plain storage increased up catchment flux during warmer interglacial periods outpaces evacuation of stored sediment during glacial periods resulting in a net increase in sediment flux to the ocean during warm intervals if this temperature sediment flux relationship is valid beyond the plio pleistocene transition then global sediment flux to the ocean from passive non glaciated and low relief landscapes would have been greater during the pliocene than in the cooler quaternary

paleo erosion rates in central asia since 9 ma a transient increase at the onset of quaternary glaciations erosion is a fundamental player of the interactions existing between internal geodynamics and climate in particular through its influence on the carbon dioxide budget however long term 1 ma erosion rates estimated indirectly from sediment budget remain poorly constrained while some studies suggest that worldwide erosion rates increased at the plio pleistocene climatic transition 4 2 ma the validity of this observation and its significance is a matter of debate due to potential biases of the sedimentary record and to the influence of sea level fall on the global sedimentary flux to marginal basins in the present study we estimate erosion rates over the last 9 ma using in situ produced cosmogenic 10be concentrations measured in magnetostratigraphically dated continental sediments we focus on an intracontinental endorheic watershed draining the northern tianshan in central asia a key region regarding the ongoing debate while erosion rates between 0 1 and 1 mm yr 1 are derived from most of our record they reach values as high as 2 5 mm yr 1 from 2 5 to 1 7 ma then after 1 7 ma recent and modern erosion rates fell below 1 mm yr 1 this temporary increase is correlated with the onset of quaternary ice ages and suggests that global climate had a significant and transient impact on erosion

improved chronostratigraphic reference curve of late neogene seawater 87sr 86sr we present a reference curve of seawater 87 sr 86 sr variation through the past 7 m y based on 455 samples of planktonic foraminifera from ocean drilling program odp site 758 in the indian ocean this single site curve is superior to extant curves because of several features 1 a continuous sedimentary section free of disturbances 2 a well determined and precise chronostratigraphy that is calibrated to numeric age on the basis of continuous magnetostratigraphy and a refined astronomical time scale 3 a high temporal resolution sample interval averages 15 ka 4 an improved analytical reproducibility and 5 a uniformly high sample quality the gross structure of the site 758 curve is generally similar to that observed in previous work but the increased temporal resolution and decreased analytical scatter of the curve provide improved chronostratigraphic resolution at the 95 confidence level uncertainties on age estimates range from 0 60 m y in the lower pleistocene and upper miocene to 2 03 m y in the middle pliocene moreover this detailed record identifies two periods of steplike increases in seawater 87 sr 86 sr 6 10 to 5 80 ma and 1 46 to 1 13 ma that are characterized by rates of change of 150 10 6 m y these features if verified at other sites indicate abrupt changes in the sr mass balance of the ocean and may be used as precise event markers in late neogene marine sections

cryptic intertidal microbialites in beachrock heron island great barrier reef implications for the origin of microcrystalline beachrock cement microbialites with microcolumnar growth morphology occur on the surfaces of solution enlarged crypts in modern beachrock an heron island great barrier reef australia the microbialites consist predominantly of felted aragonite but blocky mg calcite and fringes of acicular aragonite also occur a variety of microbial bodies and filaments occur within and on the surface of the microbialites although most heron beachrock is cemented by isopachous fringes of acicular aragonite irregular micritic cement is common adjacent to the microbialites the micritic cement consists predominantly of felted aragonite and contains microbial filaments and organic matter similar to those in the microbialites both the microbialite and the micritic cement are interpreted to be biologically induced although physico chemical models including co2 degassing and evaporation are commonly held to be sufficient to promote the formation of beachrock the similarity of heron cryptic beachrock microbialite with micritic beachrock cements supports the contention that some beachrock cements are biologically induced additionally the primary difference between fringes of acicular aragonite and the felts of aragonite in microbialites appears to be that the former nucleated on a well defined surface of organic matter whereas the latter nucleated within a framework of organic matter that contained irregularly disposed nucleation sites hence aragonite fringe cements may also be localized and or induced by films of organic matter c 1999 elsevier science b v all rights reserved

use of a new 10be and 26al inventory method to date marine terraces santa cruz california usa marine terraces along active continental margins reflect the interplay between sea level oscillations and rock uplift well dated marine terraces record the timing of sea level highstands and delimit both uplift and geomorphic rates cosmogenic radionuclides provide a new tool for dating previously undatable terraces because the five marine terraces north of santa cruz california are capped by well developed soils formed in regressive marine sands both predepositional cosmogenic radionuclide inheritance and bioturbation of the profile must be accounted for we present a new cosmogenic radionuclide inventory method that uses the depth integrated cosmogenic radionuclide concentration to determine the terrace age this method yields terrace ages that correlate well with sea level highstands of marine oxygen isotope stages 3 5a 5c 5e and 7 the implied uplift rate is steady at 1 1 mm yr and is two to three times higher than rates suggested by earlier studies

marine vadose beachrock cementation by cryptocrystalline magnesian calcite maui hawaii abstract active precipitation of high magnesian cryptocrystalline calcite cement 15 5 mole mgco3 in the intertidal zone on the north shore of maui hawaii results in formation of an extensive beachrock exposure at hookipa park framework grains in the beachrock are coarse algal molluscan and intraclast bearing sands meniscus fabric is dominant in the cement indicating that most lithification occurs in the vadose zone the cryptocrystalline cement is generally brownish gold in color but very thin clear isopachous fringes of microcrystalline calcite surround darker cryptocrystalline cement especially in upper horizons of the beachrock peloidal texture is scarce in the cement but is present in a few samples silt and fine sand sized skeletal fragments have been trapped in he evolving cement resulting in cement supported fabric hollow rims of microcrystalline calcite occupy some pore spaces these hollow rims may have precipitated at the air water interface of bubbles that formed in pores and they may therefore be additional evidence of cementation in the vadose zone interstitial water samples from wells that penetrate portions of the beachrock and unconsolidated beach sands reveal temporal chemical variations that suggest the importance of co2 degassing in the formation of beachrock cement when chemical and tidal cycles fluctuate with the same period pco2 values in pore water of the intertidal zone generally bear a direct relationship to tidal stand increasing values of pco2 most often occur during semi daily rising tides and decreasing values of pco2 occur during falling tides saturation ratios with respect to calcite vary in direct proportion to pco2 saturation levels generally increase during rising tides and decrease during falling tides t ese data suggest that co2 degassing during falling tides results in precipitation of calcite cement from pore water of the beach

dating soils and alluvium with cosmogenic 21ne depth profiles case studies from the pajarito plateau new mexico usa abstract 21 ne depth profiles measured from amalgamated samples of sand sized quartz from the quaternary bandelier tuff were used to estimate inheritance corrected exposure ages in stream terraces and an alluvial fan on the pajarito plateau stable alluvium and associated soils display a downward decreasing type i nuclide profile pattern bioturbated colluvium with uniform type iii nuclide concentrations has buried these alluvial surfaces another possible profile type with downward increasing nuclide concentrations type ii is described but was not found on the pajarito plateau we present mathematical models for each of the profile patterns relating nuclide concentration to inheritance time averaged bulk density and either exposure time or burial rate curve fits of type i profiles are used to estimate the age of alluvial landforms a burial correction technique for deposits buried by younger colluvium is also presented inheritance and burial corrected 21 ne surface exposure ages of 144 17 ka and 63 8 ka for two pajarito plateau stream terraces agree within error with independent soil profile development index dates of 160 ka and 68 78 ka a soil overlying the 50 60 ka el cajete pumice yields an inheritance corrected 21 ne exposure age of 44 11 ka that also agrees closely with a 14 c age on soil charcoal of 41 ka these results demonstrate that reliable cosmogenic 21 ne exposure ages can be obtained for fine grained alluvial surfaces with the depth profile technique

probabilistic prediction of rupture length slip and seismic ground motions for an ongoing rupture implications for early warning for large earthquakes earthquake earlywarning eew predicts future ground shaking based on presently available data long ruptures present the best opportunities for eew since many heavily shaken areas are distant from the earthquake epicentre and may receive long warning times predicting the shaking from large earthquakes however requires some estimate of the likelihood of the future evolution of an ongoing rupture an eew system that anticipates future rupture using the present magnitude or rupture length together with the gutenberg richter frequencysize statistics will likely never predict a large earthquake because of the rare occurrence of extreme events however it seems reasonable to assume that large slip amplitudes increase the probability for evolving into a large earthquake to investigate the relationship between the slip and the eventual size of an ongoing rupture we simulate suites of 1 d rupture series from stochastic models of spatially heterogeneous slip we find that while large slip amplitudes increase the probability for the continuation of a rupture and the possible evolution into a big one the recognition that rupture is occurring on a spatially smooth fault has an even stronger effect we conclude that aneewsystem for large earthquakes needs some mechanism for the rapid recognition of the causative fault e g from real time gps measurements and consideration of its smoothness an eew system for large earthquakes on smooth faults such as the san andreas fault could be implemented in two ways the system could issue a warning whenever slip on the fault exceeds a few metres because the probability for a large earthquake is high and strong shaking is expected to occur in large areas around the fault a more sophisticated eew system could use the present slip on the fault to estimate the future slip evolution and final rupture dimensions and using this information could provide probabilistic predictions of seismic ground motions along the evolving rupture the decision on whether an eew system should be realized in the first or in the second way or in a combination of both is user specific

development of the mozambique and ruvuma sedimentary basins offshore mozambique two major sedimentary basins have been identified on the continental margin of mozambique mozambique basin and ruvuma basin the formation of the basins is related to the break up of gondwana and opening of the western part of the indian ocean the basins are relatively young having developed discordantly to the structural plan of gondwana sedimentary basins the history of the formation of the east african continental margin sedimentary basins within mozambique has been studied on the basis of the present day concept of gondwana break up and madagascar s drift with respect to africa two stages in the history of the east african basins can be recognized late gondwana and post gondwana the late gondwana stage 303 157 ma is typified by sedimentary and volcanogenic rocks of the karoo group the post gondwana stage 157 0 ma corresponds to the period of active gondwana break up and the formation of indian ocean marginal basins the mozambique basin occupies both central and southern parts of the coastal plain of mozambique extending onto the continental shelf and slope the sedimentary fill is composed of upper jurassic cretaceous and cenozoic rocks which discordantly overly the karoo basalts the upper jurassic occurs as continental red beds mostly distributed within buried grabens cretaceous rocks occur as terrigenous sediments of continental and marine genesis cenozoic deposits are of predominantly marine and deltaic origin the ruvuma basin situated in the north of mozambique is part of an extended east african marginal basin which includes parts of the coastal plains and continental margins of tanzania and kenya the basement of the basin is composed of crystalline and metamorphic rocks of pre cambrian age the sedimentary fill is represented by continental terrigenous karoo sediments marine and lagoonal jurassic deposits and marine and deltaic rocks of cretaceous and cenozoic age the main difference between the sedimentary fill of the mozambique and ruvuma basins is related to the changing sedimentary environment in the period of gondwana break up jurassic and early cretaceous when the drift of madagascar and sea floor spreading took place and the marine basin gradually extended southwards between the east african margin and madagascar from the late cretaceous on the sedimentary environment within both basins was similar the mozambique and ruvuma basins forming a single system on the east african continental margin the main stages of the basins development are illustrated by a series of palaeogeographic reconstruction maps

rapidity of freshwater calcite cementation implications for carbonate diagenesis and sequence stratigraphy abstract in less than 10 years subaerially exposed holocene oolitic sand on eleuthera island bahamas was completely case hardened by freshwater vadose calcite cementation this phenomenon demonstrates the rapidity of freshwater carbonate diagenesis and explains in part why carbonate platforms preferentially shed unconsolidated sediment during highstands and not during lowstands when they are subaerially exposed it further proves contrary to what the exxon conceptual sequence stratigraphic models imply that carbonate deposits do in fact respond differently to subaerial exposure than siliciclastic deposits case hardening of unconsolidated carbonate sediment in response to subaerial exposure and early near surface freshwater diagenesis helps explain why shallow water platform sediments are preferentially shed into adjacent basins during highstands of sea level and not during lowstands during lowstands rapid subaerial lithification of carbonate sediments retards their reworking by wind or water once lithified these deposits are further stabilized by vegetation and karstification inhibiting their transport as unconsolidated sediment into adjacent deeper water basins observations from eleuthera island also document the reciprocal processes associated with freshwater carbonate diagenesis calcium carbonate released by partial dissolution of aragonitic ooids was locally reprecipitated as pore filling low magnesian calcite cement this reciprocity is confirmed by the confinement of freshwater dissolution and cementation to the upper 10 20 cm of the subaerially exposed body of oolitic sand below this case hardened surface oolitic sands remained unconsolidated only very minor amounts of calcite cement were required for effective casae hardening

paleoenvironmental events during the last 13 000 years in the central red sea as recorded by pteropoda a high resolution record was obtained by investigating a sedimentary sequence from two cores taken in the central red sea r v meteor cruise 5 leg 2 the numerical variations between nonmigratory and migratory pteropods and their stable isotopic record were studied together with variations in the carbonate and total organic carbon content in order to estimate changes in the structure of the water column during the last 13 kyr the results indicate the existence of a highly stratified water column during deglaciation and early holocene 13 8 5 ka during this period the depth of the mixed layer varied between less than 50 100 m at most and productivity was markedly reduced in comparison to the recent situation the intermediate and deep water were constantly highly depleted in oxygen a pronounced younger dryas event was recognized at 10 4 ka which coincides with an arid phase on the border land the oxygenation of the intermediate water improved remarkably after 7 5 ka and peaked during the period between 4 6 and 2 0 ka during this period the mixed layer reached its present depth and the productivity which was maximal during middle holocene attained present level during the last 4 6 kyr

cosmogenic 10be as a tracer for hillslope and channel sediment dynamics in the clearwater river western washington state we use the 10be concentration in alluvial sand and gravel to document hillslope exposure history and trace the reduction in grain size of river alluvium in the clearwater river basin western washington state clearwater tributary basins wilson creek wc 6 km2 and east fork miller creek efmc 12 km2 were each sampled in headwater and downstream sites for 10be in alluvial sand 0 25 0 50 mm and gravel 22 6 90 mm grain size distributions were determined at each sampling site as well as at several locations along the main stem of the clearwater river channel and watershed geomorphology were quantified using long profile modeling and related morphometric analyses we found that the 10be concentrations differ significantly between the two grain size fractions at all four sampling locations at both headwater sites the gravel exhibits 25 lower 10be concentrations compared to the sand similarly the downstream site of lower wc exhibits 55 lower 10be concentration in the gravel compared to the sand in contrast the gravel from the downstream site on lower efmc exhibited 22 higher 10be concentration in the gravel compared to the sand the disparity in 10be concentration at the wc sites is best explained by shielding of the coarser grain size fraction and its delivery to the channel by deep seated landslide processes more intense landsliding in the downstream wc site is consistent with the increased disparity of 10be between the sand and gravel fractions at that site the inverse relationship between the sand and gravel 10be concentrations at the headwater efmc site is best explained by a sediment provenance mechanism where the hillslope weathering rate exceeds the down slope transport rate for this particular basin the inverse grain size dependency gravel sand observed in the downstream efmc site requires a more complex interplay between hillslope and channel processes including cobble weathering and grain size reduction during fluvial transport resulting in a dilution of the 10be signal in the sand fraction downstream these results underscore the importance of geomorphic consideration and the grain size sampled in the correct interpretation of basin average erosion rates

age erosion constraints on an early pleistocene paleosol in yukon canada with profiles of 10be and 26al evidence for a significant loess cover effect on cosmogenic nuclide production rates abstract wounded moose type paleosols developed on remnant deposits of late pliocene to early pleistocene pre reid cordilleran ice sheet cis glaciations in central yukon canada it is an important regional soil geomorphic marker at the boundary between early cis advances and the non glaciated regions of yukon and alaska yet at present its age is poorly constrained between the reid 0 2 ma and earliest 2 84 ma cis advances here we apply depth profiles of in situ produced cosmogenic 26al and 10be to obtain both a minimum exposure age 1 12 0 44 0 36 ma 2 and maximum erosion rate 1 1 0 9 0 5 m myr 1 for the wounded moose paleosol our results show that this soil formed under exceptionally stable conditions max erosion rate similar to polar bedrock erosion rates and that it pre dates the emergence of the 100 ka eccentricity climate cycle contrasting our results from single and joint nuclide depth profile models reveals a significant discrepancy between calculated and effective 10be and 26al production rates 40 65 of expected values we interpret this discrepancy as the result of intermittent loess cover with a time averaged depth between 60 and 110 cm which significantly reduced apparent exposure ages obtained from the single nuclide model the observation of such a significant loess cover effect on cosmogenic nuclide production has implications for exposure dating in glacial and periglacial environments a multi nuclide sampling strategy is required to quantify this effect

earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records 1 we show that the low pass filtered peak amplitudes of initial p and s wave seismic signals recorded in the vicinity of an occurring earthquake source correlates with the earthquake magnitude and may be used for real time estimation of the event size in seismic early warning applications the earthquake size can be therefore estimated using only a couple of seconds of signal from the p or s wave onsets i e while the rupture itself is still propagating and rupture dimension is far from complete we argue that dynamic stress release and or slip duration on the fault in the very early stage of seismic fracture scales both with the observed peak amplitude and with the elastic energy available for fracture propagation the probability that a fracture grows to a larger size should scale with the energy initially available citation zollo a m lancieri and s nielsen 2006 earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records geophys res lett 33 l23312 doi 10 1029 2006gl027795

quaternary calcareous hard rocks and the associated sediments in the intertidal and offshore zones of kuwait abstract the geomorphological and petrographical characteristics of the quaternary calcareous hard rocks in the offshore and intertidal zone of kuwait northern arabian gulf were investigated these rocks can be divided into three types 1 submerged calcareous hard layers 2 beachrocks and 3 lithified intertidal terraces submerged calcareous hard layers usually cover a submarine terrace about 15 m below present sea level this hard rock is generally underlain by an uncemented oolitic sand and overlain by holocene mud which reaches up to 13 m in thickness submerged calcareous hard layers are generally lithified allochemical limestone four types were recognized biosparite biomicrite oosparite and oomicrite beachrocks outcrop over distances of several hundred metres along the coast of kuwait they are partially eroded by mechanical and biological processes the field occurrences and petrography of the beachrocks vary from place to place however two main types were recognized quartzitic and calcarenitic the occurrence of each type is related to the nature of the coastal bedrock from which the framework grains of the beachrocks were derived lithified intertidal terraces are almost flat benches of hard calcareous layers which are petrographically similar to beachrock but genetically different they are developed as a result of intertidal lithification of the surficial part of the quaternary semiconsolidated coastal terraced deposits textural and mineralogical investigations of the intertidal sands indicate that these sands are derived from the coastal deposits high energy waves are responsible for the good sorting of these sands along the southern coast

middle stone age starch acquisition in the niassa rift mozambique the quest for direct lines of evidence for paleolithic plant consumption during the african middle stone age has led scientists to study residues and use wear on flaked stone tools past work has established lithic function through multiple lines of evidence and the spatial breakdown of use wear and microscopic traces on tool surfaces this paper focuses on the quantitative analysis of starch assemblages and the botanical identification of grains from flake and core tools to learn about human ecology of carbohydrate use around the niassa woodlands in the mozambican rift the processing of starchy plant parts is deduced from the occurrence of starch assemblages that presumably got attached to stone tool surfaces by actions associated with extractive or culinary activities specifically we investigate starch grains from stone tools recently excavated in northern mozambique at the site of mikuyu which presumably spans the middle to late pleistocene and represents similar sites found along the malawi niassa corridor that links east southern and central africa starch was extracted and processed with a diverse tool kit consisting of scrapers cores points flakes and other kinds of tools the microbotanical data suggests consumption of seeds legumes caryopses piths underground storage organs nuts and mesocarps from more than a dozen families our data suggest a great antiquity for starch use in africa as well as an expanded diet and intensification

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

shell beaches to beachrock diagenetic stable isotopic trends abstract modern shell accumulations on padre island texas gulf coast are composed of pristine aragonite whereas laterally adjacent pleistocene beachrock on the mainland shores of laguna madre are made up of the same taxa but display a range of mixtures of aragonite and diagenetic low mg calcite cements and pedogenic crusts associated with the beachrock are 100 low mg calcite stable isotopic values for shells composed of 0 15 20 45 75 and 90 calcite display high correlations between the 18o values and mineralogy r2 0 95 and 13c values and mineralogy r2 0 87 the highly correlated changes in the stable isotopic compositions and mineralogy of the skeletal material are also evident in the data from the analyses of the pure calcite cements and pedogenic crusts changes in stable isotopic composition of the shells are the result of the early diagenetic alteration of the original aragonitic composition to low mg calcite

sediment and pollen evidence for an early to mid holocene humid period in the eastern sahara a major problem in the study of holocene palaeoenvironments of the arid and wind deflated sahara is the low preservation potential of sediments from which a record of past climatic change can be established several indirect and imprecisely dated pieces of evidence have suggested humid episodes in the holocene that may have supported more productive ecosystems and denser human populations than today searches for reliable proxy data on past climates however have failed to yield satisfactory results we report here the discovery of buried lake muds in north west sudan in the hyperarid core of the eastern sahara which yield sedimentological and palynological data clearly interpretable as recording an early to mid holocene humid episode that supported a relatively deep stratified lake surrounded by tropical savanna woodland vegetation

first record of beachrock on black sea coast of turkey implications for late holocene sea level fluctuations abstract we present new data on the diagenetic characteristics subsurface nature and radiocarbon ages of beachrock from the thracian black sea coast of turkey indicative of sea level changes and climatic conditions favoring lithification of beach sands between 5 4 ka and 3 5 ka cal bp micrite coatings and succeeding meniscus cements typify diagenetic history and suggest a two stage cementation over this timeframe the early cements are typical of upper intertidal zone when the sea level was likely similar to that of today the ensuing intergranular bridges refer to an approximate 2 m decline in sea level favoring downward percolation of meteoric waters related to subaerial exposure marked by a reduction in mg concentration and dissolution pits on early cement coatings formation of beachrock during this bimillennial period could be associated with relatively drier conditions promoting the precipitation of connective cements

atmospheric scaling of cosmogenic nuclide production climate effect 1 absorption of cosmic rays by atmospheric mass varies temporally due to a redistribution of atmospheric pressure by ice sheets during glaciations the compression and expansion of the atmosphere due to cooling and warming and changes in katabatic winds near large ice masses these atmospheric processes can result in changes in production rates of cosmogenic nuclides which when integrated over long exposure durations may result in 0 to 5 adjustments in site production rates depending on location combining a ccm3 model with imbedded ice sheets for 20 ka we show that production rates changes relative to today are greatest at high elevations 6 7 at 5 km altitude due to atmospheric compression from decreased temperature production rates at specific times for sites near ice sheet margins can be reduced more than 10 due to a combination of katabatic winds draining off the ice sheet margins and atmospheric cooling nunatak settings may be significantly affected by the climate effect due to persistent glacial atmospheric conditions atmospheric variability may explain some of the disparities among cosmogenic nuclide production rate calibrations

early diagenesis in pleistocene coral reefs southern sinai egypt response to tectonics sea level and climate the uplifted pleistocene terraces along the coast of southern sinai exhibit a well developed reef system formed during isotope stage 9 and a younger one formed during isotope stage 5 an intermediate reef corresponding to isotope stage 7 occurs only as an erosional relic in the study area the sediments comprise reefal framestones peri reefal facies coral rubble and siliciclastic dominated beach and aeolian facies the compositional and textural complexity of the sediments leads to a highly variable spatial distribution of diagenetic features however the geometric relationships and elemental analyses allow a reconstruction of the general diagenetic evolution during the major eustatic sea level highstand of isotope stage 9 the older reef was constructed and cemented with aragonite and high mg calcite climate was probably semiarid with some rainy periods which permitted the installation of ephemeral freshwater lenses especially during the minor sea level lowstand within isotope stage 9 in these lenses and during the subsequent major sea level lowstand some freshwater dissolution occurred the highstand during isotope stage 7 led to the construction of the intermediate reef in the older reef some high mg calcite precipitated at that time dolomite cement formed either in marine interstitial waters modified by some freshwater input or in a hypersaline context phreatic meteoric low mg calcite cement covers and partly replaces previous marine cements and dolomite but is still attributed to the major highstand of isotope stage 7 when freshwater lenses could develop during minor sea level lowstands the subsequent major sea level lowstand was dominated by an arid climate and only a little freshwater corrosion occurred the younger reef formed during the major highstand of isotope stage 5 aragonite and high mg calcite cements as well as some dolomite are common within the reef whereas freshwater cements are limited to beach and aeolian facies due to tectonic uplift only the lower part of the older reef was reflooded during isotope stage 5 and only some aragonite crystals precipitated on top of dolomite or low mg calcite the interrelationships between tectonics sea level variations of different orders and climatic changes thus had a profound impact on the diagenetic history of these reef systems

holocene cemented beach deposits in belize abstract two types of cemented beach deposits occur on reef islands off the coast of belize these are 1 intertidal beachrock that is dominantly cemented by marine aragonite and high magnesium calcite cements and 2 supratidal cayrock that is cemented mainly by vadose low magnesium calcite cements besides differences in position relative to present sea level and resulting early diagenesic features beachrock and cayrock can be distinguished on the basis of differences in composition texture geographical position and age whereas the composition of beachrock is similar to that of the adjacent marginal reef sediments cayrock is enriched in benthic foraminifera intertidal beachrock is moderately to well sorted and well cemented while supratidal cayrock is very well sorted poorly cemented and friable beachrock occurs preferentially on windward beaches of sand shingle gays on the middle and southern barrier reefs and on the isolated platforms glovers and lighthouse reefs cayrock only occurs on larger mangrove sand gays of the isolated platforms turneffe islands lighthouse reef and the northern barrier reef 14c dating of ten whole rock and mollusk shell samples produced calibrated dates between ad 345 and ad 1435 for beachrock and between bc 1085 and ad 1190 for cayrock the large scale distribution of beachrock in belize supports the contention that physical processes such as water agitation rather than biological processes control beachrock formation and distribution only on windward sides of cays that are close to the reef crest where large amounts of seawater flush the beaches considerable amounts of cements can be precipitated to produce beachrock cayrock forms due to cementation in the vadose zone and is only preserved on larger stable mangrove sand cays

sr isotopic variation in shallow water carbonate sequences stratigraphic chronostratigraphic and eustatic implications of the record at enewetak atoll sr isotope data from two boreholes within the lagoon at enewetak atoll have been used to evaluate the use of such data to correlate date and monitor sea level change in shallow water carbonate sequences correlative stratigraphic intervals of relatively invariant 87sr separated by abrupt transitions to lower 87sr with increasing depth are recognized in both boreholes conversion of 87sr values to age via calibration with the seawater 87sr trend with age indicates that correlative and synchronous deposition of atoll sediments occurred at 0 4 1 2 and 2 1 ma in contrast a 5 m y hiatus is recognized in one borehole but not the other sr isotope stratigraphy sis is a powerful stratigraphic and chronostratigraphic tool in shallow water carbonate sequences only when significant secular variation of 87sr occurs and retention of depositional 87sr values is demonstrated the latter is best demonstrated when 87sr data are integrated with 18o 13c sr content data and petrographic observations several diagenetically altered intervals have greater 87sr values low 13c values and low sr ca ratios relative to adjacent intervals a combination that is consistent with open system meteoric diagenesis calcite cements from these intervals have early pleistocene 1 2 ma 87sr values despite their occurrence well within the late pliocene 2 1 ma sequence thus local sedimentological and diagenetic processes have produced intralagoon variability in the sis of the two boreholes complicating subsurface stratigraphic correlations the occurrence of anomalously young calcite cement relative to adjacent limestone is a direct response of the interaction of sea level change and meteoric phreatic diagenesis whereby overlying metastable carbonates with greater 87sr values are dissolved during periods of atoll emergence and sea level lowstand liberating sr and soil gas co2 to the pore fluid which is then incorporated into downflow meteoric phreatic diagenetic calcite the stratigraphic relation between the sites of carbonate dissolution and diagenetic calcite precipitation suggest an early pleistocene 1 2 ma sea level fall of between 34 and 64 m moreover the stratigraphic position and inferred age of paleophreatic lens calcite when backtracked for subsidence suggest that early pleistocene 1 2 ma sea level was 72 81 m range of 60 100 m below present sea level the enewetak record of early pleistocene sea level lowstand elevation agrees reasonably well with proxy sea level records inferred from sequence stratigraphy and deep sea foraminiferal 18o data however the enewetak record of the amplitude of early pleistocene sea level change is more consistent with the deep sea foraminiferal 18o proxy than the sequence stratigraphy proxy

mid holocene stable isotope record of corals from the northern red sea we present a study based on x ray chronologies and the stable isotopic composition of fossil porites spp corals from the northern gulf of aqaba red sea covering the mid holocene period from 5750 to 4450 14c years bp before present the stable oxygen and carbon isotopic compositions of five specimens reveal regular annual periodicities compared with modern porites spp from the same environment the average seasonal 18o amplitude of the fossil corals is higher by ca 0 35 0 60 whereas annual growth rates are lower by ca 3 5 to 2 mm year this suggests stronger seasonality of sea surface temperatures and increased variability of the oxygen isotopic composition of the sea water due to changes in the precipitation and evaporation regime during the mid holocene most likely summer monsoon rains reached the northern end of the red sea at that time average annual coral growth rates are diminished probably due to an increased input and resuspension of terrestrial debris to the shallow marine environment during more humid conditions our results corroborate published reports of paleodata and model simulations suggesting a northward migration of the african monsoon giving rise to increased seasonalities during the mid holocene over northeastern africa and arabia

the boon and bane of radiocarbon dating radiocarbon is widely used to determine the age of samples that are less than 50000 years old but the conversion of radiocarbon ages to calendar ages is not always straightforward in their perspective guilderson et al 1 analyze the calibrated age ranges that can be obtained from the current calibration standard the intcall98 curve they take into account not only the inherent limitations of the radiocarbon calendar calibration curve but also analytical uncertainties the results bear directly on our ability to understand the dynamic climate system and the relations between climate and past societies 1 http www sciencemag org cgi content full 307 5708 362

longevity and progressive abandonment of the rocky flats surface front range colorado abstract the post orogenic evolution of the laramide landscape of the western u s has been characterized by late cenozoic channel incision of basins and their adjacent ranges one means of constraining the incision history of basins is dating the remnants of gravel capped surfaces above modern streams here we focus on an extensive remnant of the rocky flats surface between golden and boulder colorado and use in situ produced 10be and 26al concentrations in terrace alluvium to constrain the quaternary history of this surface coal and ralston creeks both tributaries of the south platte river abandoned the rocky flats surface and formed the verdos and slocum pediments which are cut into cretaceous bedrock between rocky flats and the modern stream elevations rocky flats alluvium ranges widely in age from 2 ma to 400 ka with oldest ages to the east and younger ages closer to the mountain front numerical modeling of isotope concentration depth profiles suggests that individual sites have experienced multiple resurfacing events preliminary results indicate that verdos and slocum alluvium along ralston creek which is slightly larger than coal creek is several hundred thousand years old fluvial incision into these surfaces appears therefore to progress headward in response to downcutting of the south platte river the complex ages of these surfaces call into question any correlation of such surfaces based solely on their elevation above the modern channel

experimental modelling of beachrock cementation under microbial influence a laboratory model has been developed which reproduces natural conditions of beachrock formation these conditions include the porosity of beach sand tidal movements alternation of phreatic and vadose conditions temperature evaporation illumination and water composition seawater with a control of the following parameters salinity ca mg co2 ph caco3 saturation the conditions of two beachrocks from the red sea egypt and shark bay australia have been simulated and the influence of the micro organism population undetermined sampled in these beachrocks was observed for 3 4 months in the experiments inoculated with micro organisms biomineralization produced characteristic crystals of various forms from 1 to 20 m in size the precipitates resemble the micritic cements of natural beachrocks on the contrary precipitation was much less developed in the control experiments under nearly sterile conditions these results confirm the importance of microbial activity during beachrock formation the first micritic cement which seems to control cementation and produce the initial consolidation is formed under a strong microbial influence in or near a biofilm covering the grain surface the presence of this micritic cement is necessary for the development of the subsequent prismatic cement which probably results from an abiotic precipitation during higher fluid circulation

rapidity of marine carbonate cementation implications for carbonate diagenesis and sequence stratigraphy perspective abstract lithification is a rapid process but how rapid is rapid a year after one of my visits to joulter s cay bahamas i found a sardine can from my previous visit the cementation of carbonate particles in and around the can was surprising 382 g of ooids and skeletal material had filled the can and lithified therein or had become cemented to the outside of the can the rapidity of marine carbonate cementation implies that during highstand of sea level shallow water platform carbonate sediments are subject to marine lithification which retards erosion this conclusion is at variance with that of other workers who rely on freshwater cementation during lowstands to generate cement which retards reworking clearly the historical debate over highstand versus lowstand of shallow water marine carbonates is not yet over

on global forces of nature driving the earth s climate are humans involved the authors identify and describe the following global forces of nature driving the earth s climate 1 solar radiation as a dominant external energy supplier to the earth 2 outgassing as a major supplier of gases to the world ocean and the atmosphere and possibly 3 microbial activities generating and consuming atmospheric gases at the interface of lithosphere and atmosphere the writers provide quantitative estimates of the scope and extent of their corresponding effects on the earth s climate quantitative comparison of the scope and extent of the forces of nature and anthropogenic influences on the earth s climate is especially important at the time of broad scale public debates on current global warming the writers show that the human induced climatic changes are negligible

middle stone age archaeology at olduvai gorge tanzania abstract this paper describes the motivation procedures and results of archaeological and geological field survey of the ndutu unit olduvai gorge conducted in june and july of 2013 survey focused upon the area of olduvai gorge between the second fault and the obalbal depression although selective survey occurred in other areas in and around the gorge over 72 archaeological find spots were recorded and hundreds of middle stone age msa artifacts were recovered as was a small sample of fauna geological observations provisionally suggest that the ndutu was formed in part from a series of pyroclastic density flow and ash fallout events from neighbouring volcanoes this contrasts slightly with previous interpretations of the deposits in that at least some of the beds are thought to be in primary stratigraphic context our initial field findings are conducive to discussions of a number of issues directly relevant to the msa in east africa and overall we conclude that there is strong potential for olduvai s ndutu unit to shed light on the behavior adaptations and evolution of homo sapiens prior to during and just after its physical emergence