anthropogenic influence on sedimentation and intertidal mudflat change in san pablo bay california 1856 1983 analysis of a series of historical bathymetric surveys has revealed large changes in morphology and sedimentation from 1856 to 1983 in san pablo bay california in 1856 the morphology of the bay was complex with a broad main channel a major side channel connecting to the petaluma river and an ebb tidal delta crossing shallow parts of the bay in 1983 its morphology was simpler because all channels except the main channel had filled with sediment and erosion had planed the shallows creating a uniform gently sloping surface the timing and patterns of geomorphic change and deposition and erosion of sediment were influenced by human activities that altered sediment delivery from rivers from 1856 to 1887 high sediment delivery 14 1 10 6 m 3 yr to san francisco bay during the hydraulic gold mining period in the sierra nevada resulted in net deposition of 259 14 10 6 m 3 in san pablo bay this rapid deposition filled channels and increased intertidal mudflat area by 60 37 4 3 4 to 60 6 6 2 km 2 from 1951 to 1983 23 3 10 6 m 3 of sediment was eroded from san pablo bay as sediment delivery from the sacramento and san joaquin rivers decreased to 2 8 10 6 m 3 yr because of damming of rivers riverbank protection and altered land use intertidal mudflat area in 1983 was 31 8 3 9 km 2 similar to that in 1856 intertidal mudflat distribution in 1983 however was fairly uniform whereas most of the intertidal mudflats were in the western part of san pablo bay in 1856 sediment delivery through its affect on shallow parts of the bay was determined to be a primary control on intertidal mudflat area san pablo bay has been greatly affected by human activities and will likely continue to erode in the near term in response to a diminished sediment delivery from rivers 2007 elsevier ltd all rights reserved

first archaeomagnetic secular variation curve for the iberian peninsula comparison with other data from western europe and with global geomagnetic field models 1 a first secular variation sv curve for the iberian peninsula was computed by hierarchical bayesian method using a total of 134 archaeomagnetic directions with ages ranging from 775 to 1959 a d a general agreement is observed between the iberian curve and the french and german sv curves although some interesting differences were found such as the occurrence of lower inclinations between the 11th and 14th centuries in the iberian curve the analysis of these three reference curves indicates that sv in western europe is characterized by three major directional changes at 125 200 and 1350 a d it is suggested that these cusps are regional features of the geomagnetic field the iberian curve has been compared with the predictions of the jackson calsk7k 2 and hongre global models despite large differences recognized between these models even for the dipolar terms they predict reasonably well the iberian archaeomagnetic sv

archaeomagnetism of burnt cherts and hearths from middle palaeolithic amud cave israel tools for reconstructing site formation processes and occupation history abstract apart from magnetostratigraphy archaeomagnetism is rarely used in middle and late pleistocene sites here we present detailed palaeomagnetic analyses of cemented hearths and burnt chert items from amud cave israel 68 55 ka two types of materials common in levantine middle palaeolithic cave sites both materials are shown to be recorders of the geomagnetic field and were used to reconstruct either the ancient field direction for cemented hearths or intensity palaeointensity for chert at the time of the last burning or shortly after we test the utility of palaeomagnetic data to further our understanding of temporal aspects of occupations in the cave by comparing the dispersion of the palaeomagnetic data to the known characteristics of geomagnetic secular variation in the holocene we show that divergent palaeointensities can help identify diachronic burning events suggesting different activity patterns in two areas of the cave additionally we used palaeomagnetic directional vectors to distinguish between a well preserved hearth and one that had been mixed prior to cementation using rock magnetic investigations we demonstrate that magnetic methods can be used as a relatively fast and inexpensive method to identify burning of cherts in antiquity above 500 c the palaeomagnetic results are in agreement with results of previous studies at amud cave obtained by other independent methods this study shows that palaeomagnetic methods can serve as a powerful tool in the study of palaeolithic sites

sediment export and impacts associated with river delta channelization compound estuary vulnerability to sea level rise skagit river delta washington usa abstract improved understanding of the budget and retention of sediment in river deltas is becoming increasingly important to mitigate and plan for impacts expected with sea level rise in this study analyses of historical bathymetric change sediment core stratigraphy and modeling are used to evaluate the sediment budget and environmental response of the largest river delta in the u s pacific northwest to western land use change beginning in 1850 an estimated 142 28 m m3 of sediment accumulated offshore of the emergent skagit river delta in washington state between 1890 and 2014 and 68 of which was found in sand deposits the fraction of sediment retained in sand reservoirs represents 83 of the expected fluvial sand delivery over this time suggesting their potential utility to evaluate the relative contribution of different land uses to sediment runoff through time a significantly higher ratio of sand retention to delivery during the period 1890 1939 coincided with extensive watershed denudation clear cut logging and channel dredging relative to the period 1940 2014 which was characterized by improved forest practices and sediment management to protect endangered species but also more extensive river channelization retention in the delta foreset of 78 of the sand delivered by the river between 1890 and 1939 was associated with extensive sediment bypassing and delta progradation that is shown to be 5 10x higher than rates over the holocene comparable offshore sand retention over time and higher nearshore retention subsequent to 1940 after normalizing for the assumed reduction in sediment runoff with improved forest practices suggests that channelization has continued to influence sediment export at a magnitude equivalent to the effects of early logging adverse impacts of the bypassing sediment regime to natural hazards risk and ecosystem management concerns are discussed including the role of the lost sediment as a resource to mitigate subsiding coastal lands vulnerable to flood impacts the sediment budget and coastal change analyses provide a framework for evaluating opportunities to achieve greater resilience across several sectors of coastal land use important in low lying deltas worldwide

secular variation of the earth s magnetic field in the balkan region during the last eight millennia based on archaeomagnetic data summary the first archaeomagnetic secular variation sv curves for the whole southern balkan peninsula are presented these are based on all data within a 700 km circle centred at thessaloniki 40 60on 23 00oe this data set consists of 325 directional and 625 intensity data mainly from greece bulgaria serbia and southern hungary some data from southern italy are also included the sliding moving window technique was used to calculate a continuous sv curve for intensity while the directional sv curves were calculated using the bivariate extension of the fisher statistics these curves are well constrained and clearly show the main features of the geomagnetic field variation in this region during the last eight millennia comparisons with the predictions of the scha dif 3k and scha dif 8k regional and the cals7k 2 and arch3k 1 global geomagnetic field models show a good agreement for the last 3000 years but differences for older times the balkan sv curves identify several rapid changes of the geomagnetic field in eastern europe and can be used as reference curves for archaeomagnetic dating in the balkan peninsula

human influence and the changing geomorphology of mediterranean deltas and coasts over the last 6000 years from progradation to destruction phase the present geomorphology of the mediterranean s coasts is largely a product of an intricate long term relationship between nature and human societies a cradle of ancient civilisations the mediterranean has seen its shores occupied by humans since prehistory and is therefore a particularly pertinent unit of analysis the morphotectonic context and other forcing agents e g climate shaped out a highly diversified coastal morphology and generated a sediment supply regime potentially favourable to the formation of numerous open coast deltas and bay head deltas in infilled rias as sea level stabilised during the mid holocene this supply of riverine sediment has also been the key agent in mediating human occupation of the mediterranean s clastic coasts expressions of this relationship have been extensively archived in clastic coastal deposits including base level deltaic and estuarine sedimentary sinks which comprise records to explore the interactions between geosystems and the human environment the stratigraphic sequences in these coastal sedimentary archives comprise in many places a clearly identified anthropogenic signature notably in ancient harbours some of which underwent extremely rapid silting up due to massive sediment sourcing generated by new agricultural practices from the neolithic onwards increasing human influence especially over the last 3000 years has been in turn an important driver of changes in sediment supply strongly modulating deltaic development pulses of sediment supply from catchments rendered vulnerable by human perturbations during the roman period resulted in a new cycle of inception of many other deltas and in rapid delta growth e g the ebro the po the arno and the ombrone another progradation dynamic during the little ice age at a time of strong rural population growth river discharge increases technological developments and urbanisation further consolidated delta growth understanding the life cycle of these deltas since their initial formation is in turn key to unravelling the relative role of natural and anthropogenic forcing agents rapid climate changes are deemed to have contributed through both the stripping of landscapes rendered fragile by human activities and active fluvial sediment transport to the coast but disentangling climate change effects from human impacts in the mediterranean remains a challenge the patterns of subsequent deltaic growth and delta morphodynamics reflect adaptations to pulsed sediment supply river discharge variations the microtidal fetch limited context of the mediterranean and direct engineering interventions the progradation dynamic of the roman period and little ice age contrasts markedly with the situation of common coastal destabilisation over the last two centuries particularly well documented for the last 50 years this period has been characterised by reduced sediment flux to base level geosystems due to catchment reforestation retenion within reservoirs fluvial regulation and dredging resulting in the erosion of deltas and barrier lagoon and beach dune systems large stretches of shoreline and narrow coastal plains have been massively engineered for coastal defence and protection against erosion but also for the construction of marinas leisure harbours and artificial beaches resulting in the emergence of veritable artificial seafronts these interventions have collectively and progressively raised societies to a pervasive and overarching position in the geomorphic stability instability of the mediterranean s coasts a situation that will be exacerbated by pressures from sea level rise paving the way for rampant coastal erosion and delta destruction

archaeomagnetic secular variation in the uk during the past 4000 years and its application to archaeomagnetic dating this paper examines the limitations and deficiencies of the current british archaeomagnetic calibration curve and applies several mathematical approaches in an attempt to produce an improved secular variation curve for the uk for use in archaeomagnetic dating the dataset compiled is the most complete available in the uk incorporating published results phd theses and unpublished laboratory reports it comprises 620 archaeomagnetic directional data and 238 direct observations of the geomagnetic field and includes all relevant information available about the site the archaeomagnetic direction and the archaeological age a thorough examination of the data was performed to assess their quality and reliability various techniques were employed in order to use the data to construct a secular variation sv record moving window with averaging and median as well as bayesian statistical modelling the sv reference curve obtained for the past 4000 years is very similar to that from france most differences occurring during the early medieval period or dark ages two examples of dating of archaeological structures medieval and pre roman are presented based on the new sv curve for the uk and the implications for archaeomagnetic dating are discussed

different mechanisms of magnetisation recorded in experimental fires archaeomagnetic implications abstract we present here the archaeomagnetic and rock magnetic results obtained from the experimental recreation of prehistoric fires on a clayish soil substratum by using a system of thermocouples that allows the control of temperatures and heat penetration with depth the magneto mineralogical transformations as well as the ability to acquire magnetic remanences are studied a detailed set of rock magnetic analyses carried out both on surface and depth with a millimetre scale resolution shows the creation of post burn magnetite over the entire surface of the hearth thus promoting a distinguishable magnetic enhancement on the basis of a detailed control of temperatures interesting differences between areas centre vs periphery were observed and two different mechanisms of magnetisation have been recorded the central area which exceeded 600 c acquired a thermal remanent magnetisation trm and the periphery which was heated up to 300 c recorded a thermo chemical tcrm remanent magnetisation the most noticeable mineralogical changes are focused to the first centimetre of the central area where single domain magnetite has been created the implications of these results for archaeomagnetic and palaeointensity studies as well as their utility for the detection of fire in archaeological sites are discussed

combustion structures of archaeological level o and mousterian activity areas with use of fire at the abric romani rockshelter ne iberian peninsula abstract the human use of fire generates a cultural sedimentary record that can be used to characterize prehistoric activity areas the aim of this paper is to develop a field guide for recognizing and describing combustion structures the use of fire as suggested by the results of ethnoarchaeological and prehistoric archaeological studies has served as the foundation for the analytical design of the field observations of the combustion structures at the abric romani rockshelter flat and concave combustion structure types have been uncovered in archaeological level o the systematic recording of the sedimentary and dimensional attributes of the combustion structures can be used as empirical evidence with which to characterize the use of fire differences in the use of fire represent a significant finding in the cultural repertoires of neanderthals recognizing and recording the specific organizational patterns of these activity areas such as fire use in sleeping and resting activity areas indicate the definitive emergence of home bases in the spatial record of the living floors of the archaic human groups

is it possible to identify temporal differences among combustion features in middle palaeolithic palimpsests the archaeomagnetic evidence a case study from level o at the abric romani rock shelter capellades spain abstract archaeomagnetic dating is probably one of the most known applications of magnetic methods to archaeology but there are others still underutilized and of particular interest to palaeolithic archaeology here we report a novel application of archaeomagnetism as a technique to determine temporal diachronies among combustion features from the same surface within palaeolithic palimpsests the approach is based on the subtle directional changes of the earth s magnetic field through time secular variation sv and on the ability of burned materials to record such variations under certain conditions three middle palaeolithic hearths from level o ca 55 ka bp at the abric romani rock shelter ne spain were archaeomagnetically investigated the studied surface black homogeneous carbonaceous facies recorded the magnetic enhancement produced by fire with a tenfold increase in concentration dependent magnetic parameters in the uppermost centimetre with respect to its unburned or deeper counterparts pseudo single domain psd ti low titanomagnetite was identified as the main remanence carrier the irreversibility of thermomagnetic curves suggests that these samples did not undergo enough high temperatures as to record a full thermoremanence trm additionally the occasional occurrence of maghaemitized magnetite is interpreted as an indication of a thermochemical remanent magnetization tcrm making these samples unsuitable for absolute palaeointensity determinations two well defined 95

rock magnetic analyses as a tool to investigate archaeological fired sediments a case study of mirador cave sierra de atapuerca spain summary here we report a detailed mineral magnetic study of neolithic burnt levels in the mirador cave sierra de atapuerca burgos spain to reconstruct the burning history and to investigate their suitability for archaeomagnetic purposes as a consequence of the ancient burning a characteristic facies sequence was developed along the holocene stratigraphy from top to bottom it includes i 2 10 cm ash layers ii 2 cm underlying rubefied layers and iii clay mainly unburnt and of variable thickness in some cases a thermally altered facies 2 6 cm with a heterogeneous texture was identified facies tf usually between rubefactions and the unburnt levels 126 oriented samples from 4 units mir12 15 18 and 21 and a 2 m section all comprised between units mir21 6380 40 14c bp and mir9 5090 40 14c bp were analysed with rock magnetic methods in addition bulk sediment from each facies that comprise the neolithic sequence was investigated measurements included stepwise alternating field and thermal demagnetization of natural remanent magnetization nrm viscosity experiments determination of the anisotropy of the magnetic susceptibility ams the susceptibility frequency dependence at room temperature and determination of the temperature dependence of the susceptibility additional experiments consisted in the determination of the behaviour of anhysteretic and isothermal irm remanences magnetic hysteresis loops first order reversal curve diagrams and thermal demagnetization of three axial irm it appeared that the facies all show a fairly similar magnetic mineralogy and grain size dominated by low titanium magnetite that is often partially maghaemitized main differences constitute the amount of superparamagnetic particles that is higher in unburnt strata concurring with a less well defined nrm behaviour the magnetic mineral concentration is notably higher in ashes this homogeneity strongly suggests that similar sources and burial conditions prevailed during neolithic times agreeing with archaeological observations and favoured by rapid burial conditions very limited alterations have been deduced ams data revealed the absence of fluid flow in the ash lenses sampled demagnetization revealed a stable single nrm component in ashes a single or two component nrm in rubefactions and less stable multicomponent behaviour in clays in ashes magnetic minerals are likely secondary in origin formed by low temperature oxidization soon after burning although this thermochemical nature of the nrm invalidates the use of these sediments for palaeointensity studies archaeomagnetic directional data can be successfully obtained because the burning and oxidation are closely confined in time

the palimpsest problem hearth pattern analysis and middle paleolithic site structure abstract a principal behavioral issue in paleoanthropology centers on the degree to which the behaviors of neanderthals and modern humans may have differed efforts to address this problem have employed the analysis of living floors and site structure in which researchers have traditionally emphasized a dichotomy between the site structures thought to distinguish modern human and neanderthal occupations this thinking links complex site structures characterized by several discrete activity areas to modern humans in contrast to the simple structure of neanderthals as seen in single hearths associated with overlapping generalized activities correlations between prehistoric behaviors and site structures however may be masked distorted and even destroyed by a variety of natural and cultural agencies natural post depositional processes may be associated with bioturbation cryo turbation and the degradation of sediments through wind and water erosion both post and synch deposition disturbance of artifact distributions and features by human activities may involve cleaning scuffage and other site alterations perhaps the most vexing of problems associated with post depositional distortion is from subsequent overlapping occupations in which a smearing or blurring of artifact distributions occurs i e the palimpsest problem using the results of a multi year research program of stratified living floors at the late levantine mousterian rockshelter site of tor faraj southern jordan an introduction to a partial solution of addressing the palimpsest problem through hearth pattern and ring and sector analyses is described here

manganese micronodules a possible indicator of sedimentary environments abstract manganese micronodule distribution size internal features and chemical composition as well as the composition of associated sediments have been determined in eight sediment cores taken from the siliceous ooze area of the central indian basin cib micronodule abundance expressed as the number of micronodules per gram of dried sediment 0 375 n g and size 75 1000 m show considerable variation with core depth and are directly related to each other the morphology surface texture and internal features of the micronodules are similar to those of surface macronodules from the same basin micronodules have high contents of mn 35 02 cu 1 6 ni 1 4 and zn 0 37 high mn fe ratios 5 101 and very low fe 1 8 al 2 o 3 1 3 tio 2 0 30 sio 2 2 7 and rare earth element 522 ppm contents compared to surface and buried macronodules micronodule abundance size and composition depend on the redox characteristics of the sedimentary environment and can therefore be used as indicators of the sedimentary environment

are burnt sediments reliable recorders of geomagnetic field strength abstract this study tests if burnt soils and sediments can provide reliable records of geomagnetic field strength at the time of burning by carrying out an experiment to reproduce the prehistoric use of fire on a clayish soil substratum rock magnetic experiments showed that in the upper 0 1 cm of the central part of the burnt surface remanence is a thermoremanent magnetization carried by single domain magnetite and that samples are thermally stable fourteen specimens from that area were subjected to paleointensity experiments with the coe method 1967 an intensity of 42 9 5 7 t was estimated below 440 c whereas at higher temperatures magneto mineralogical alterations were observed corresponding successful microwave intensity determinations from two specimens gave a mean value of 47 6 t both results are in reasonable agreement with the expected field value of 45 2 t burnt soils of archeological fires thus have the potential to record accurately the paleofield strength and may be useful targets for archeointensity investigations coincident results obtained from two different paleointensity determination methods support this conclusion

growth of a manganese nodule from peru basin a radiochemical anatomy abstract attempts have been made to study the entire growth history of a manganese nodule from the northern part of peru basin in the pacific using radiochemical profiles of 230 th 232 th 227 th 230 th and 10 be 9 be combined with the observations on fe mn contents and textural variation the radiochemical data indicate that the nodule grew more or less concentrically throughout most of its existence since it formed 1 5 my ago receiving mn from both bottom water and pore water this condition appeared to have changed about 180 ky ago when the growth became asymmetric in that the top and bottom sides became fixed in their relative positions on the sea floor since then the bottom side accreted with a fast rate of close to 200 mm my apparently fueled by the supply of diagenetically remobilized mn in pore water from the sediment substrate in the meantime the top side accumulated at about 6 mm my a value which is in the normal range for deep sea nodules having their mn supplied from the hydrogenous source

geochemical and sedimentological studies of a box core from the western sector of the peru basin abstract the distribution of sediments micronodules and manganese nodules which has been studied in a number of cores from the peru basin is clearly related to the proximity of the basin to the c c d and to the equatorial high productivity zone one core from the peru basin has been looked at in considerable detail in this core an extensively bioturbated calcareous siliceous rich upper sedimentary unit is underlain by an overconsolidated dark brown clay characteristic differences in mineralogy and chemistry are observed in the composition of these sediment types with the dark brown clays having higher contents of mn fe co ni cu zn and p than the sediments of the upper horizon in addition these dark brown clays contain montmorillonite as the principal clay mineral whereas the sediments of the upper sediment horizon consist of montmorillonite kaolinite and illite micronodules are much more abundant in the coarse fraction 40 m of the dark brown clay horizon than in the upper sedimentary unit and are characterized by higher mn fe ratios and higher ni and cu contents than those from the upper sediment horizon this reflects the fact that these overconsolidated sediments are well oxidized and that element remobilization from the micronodules has not taken place within this sediment type in the upper sedimentary unit there is a sharp drop in the mn fe ratio and ni and cu contents of the micronodules immediately beneath the sediment surface reflecting the selective migration of mn and other transition elements such as ni and cu from the micronodules buried managanese nodules are found at two horizons within the sediment column these nodules show characteristic differences in their surface texture compared to surface nodules but no marked difference in composition the buried nodules are not associated with any well defined feature such as a sedimentary hiatus it is suggested that nodules are maintained at the sediment surface by bioturbation buried nodules are simply those nodules that have failed to be maintained at the sediment water interface

archaeomagnetic research in the andean highlands abstract eleven archaeomagnetic samples were collected from several sites near porco bolivia as part of the proyecto arqueologico porco potosi these samples were collected in order to 1 explore the availability of appropriate sample materials in the bolivian andes and 2 assess the feasibility of pursuing reference curve research for this region in addition this research explored the archaeomagnetic dating application of reference curves constructed from the global geomagnetic field model gufm1 jackson et al 2000 which covers the period from ad 1590 1990 this model is particularly applicable to our project since many of the project sites are late prehispanic pre ad 1532 and early historic ca ad 1532 1825 in age of the 11 samples three appeared to contain an insufficient amount of ferromagnetic minerals to provide reliable results while eight samples produced acceptable to good results the data from the eight good samples were compared to a reference curve for the period of ad 1600 2000 that was calculated for this project from the global field model gufm1 the archaeomagnetic dates obtained for two of the samples agreed with archaeological expectations while those for four other samples marginally or greatly postdated the archaeological age expectations two additional samples produced significantly different directions and could not be dated against the reference curve it is likely that the age discrepancies for four of the samples stem from inaccuracies in the archaeomagnetic data the archaeological age expectations the calculated reference curve or some combination of these factors

diagenetic mobilization of manganese in peru basin sediments abstract the mn contents and sedimentation rates of two cores from different areas of the peru basin have been determined the southern core is associated with mn nodules of conventional slow accretion rates mm 106 yr while the northern one accompanies nodules with very high growth rates 102 mm 106 yr the depletion of mn observed within the top 40 cm of the cores is interpreted as resulting from a diagenetic remobilization of mn 2 due to the oxidative characteristics of the sedimentary column in both cores the calculated flux of mn provided by the sediment is higher than the total mn recovered in the overlying nodules this indicates that the mn content of the peru basin nodules can be supplied by diagenetic processes from the sediment not only for the slowly growing nodules but also for the extremely fast growing concretions found in the north of the basin

the black layer of middle palaeolithic combustion structures interpretation and archaeostratigraphic implications certain aspects of the formation processes of simple flat archaeological combustion structures such as those present in the middle palaeolithic record remain unexplained such kind of combustion structures are commonly affected by postdepositional agents and often their only distinct well preserved component is a thin black lens on the ground hence understanding the nature of this black lens is essential towards archaeological interpretation from an interdisciplinary microstratigraphic approach we present a case study in which for an entire experimental series of flat combustion structures the black layer represents the fire altered topsoil on which the fire was made parallel analysis of archaeological middle palaeolithic combustion structures from the site of el salt alicante spain reveal similar patterns leading to significant implications for archaeological interpretation in the light of these results special attention must be paid to the formation processes of flat middle palaeolithic combustion features as black layers and the material contained in them are not necessarily linked with combustion but with preceding activities or events in such cases black layers represent intact remnants of occupation surfaces concealing significant behavioural and palaeoenvironmental information relevant to the reconstruction of middle palaeolithic societies

archaeomagnetic secular variation in germany during the past 2500 years summary the german archaeomagnetic data set was supplemented with 35 new directions from ger man sites mainly dating from the past 3000 yr together with archaeomagnetic data from the neighbouring countries of germany a database of 166 reliable archaeomagnetic directions has been compiled for the reference area which is defined by a 500 km radius circle around gottingen the retrieved directions come from well dated archaeological structures and about 40 per cent of the dating relay on natural science methods such as radiocarbon thermolumines cence dendrochronology dating or historical documents from this data set a secular variation sv reference curve has been calculated using a bivariate algorithm which fits a natural cubic spline based on roughness penalty to declination inclination and time simultaneously the error tube surrounding this curve was obtained from bayesian modelling of the experimental errors which can also take stratigraphic information into account the obtained sv reference curve for the past 2500 yr is similar to that from france but also significant differences are seen comparison of the curves does not show a simple westward drift of the sv pattern the german reference curve allows archaeomagnetic dating in the reference area and extends this dating technique to sites situated in middle europe

geoarchaeological investigations at diepkloof rock shelter western cape south africa abstract the sedimentary sequence at diepkloof rock shelter formed through a complex interaction of depositional and post depositional processes and was variously influenced by biogenic geogenic and anthropogenic agents here we present the results of a micromorphological study of the sediments at diepkloof focusing in particular on the numerous anthropogenic inputs and modifications recorded within the sequence by applying the microfacies concept we were able to identify hearth burning and maintenance bedding construction and burning and surface modification by trampling as major processes that contributed to the formation of the site the human activities recorded within the sediments show a marked change throughout the sequence implying a shift in the use of the site over time the present study also provides a context for evaluating other classes of artifacts and data collected from the site

growth history of manganese nodules and crusts of the peru basin abstract in the nodule field of the peru basin situated south of the zone of high bioproductivity a relatively high flux of biogenic matter explains a distinct redox boundary at about 10 cm depth separating very soft oxic surface sediments from stiffer suboxic sediments maximum abundance 50 kg m 2 of diagenetic nodules is found near the calcite compensation depth ccd currently at 4250 m there the accretion rate of nodules is much higher 100 mm ma 1 than on ridges 5 mm ma 1 highest accretion rates are found at the bottom of large nodules that repeatedly sink to a level immediately above the redox boundary there distinct diagenetic growth conditions prevail and layers of dense laminated mn oxide of very pure todorokite are formed the layering of nodules is mainly the result of organisms moving nodules within the oxic surface sediment from diagenetic to hydrogenetic environments the frequency of such movements is much higher than that of climatic changes two types of nodule burial occur in the peru basin large nodules are less easily moved by organisms and become buried consequently buried nodules generally are larger than surface nodules this type of burial predominates in basins at ridges where smaller nodules prevail burial is mainly controlled by statistical selection where some nodules are not moved up by organisms

archeomagnetic dating in western north america an updated reference curve based on paleomagnetic and archeomagnetic data sets 1 a robust database of paleomagnetic pm and archeomagnetic am data for western north america covering the past 4 millennia is assembled from three data sets 1 published pm data for dated lava flows 2 recently published am data generated by r l dubois and 3 published am data generated by j l eighmy chronologic information for the am data sets has been reassessed and the data points have been assigned to age ranges depending on their archeological contexts we have selected the computer program archeocourbe available from m le goff http www ipgp fr legoff or the auxiliary material see also http earthref org to construct am reference curves and to quantitatively estimate am dates for archeological and geological samples the updated curve provides a more detailed record of prehistoric secular variation for western north america than was previously available and shows a short interval of rapid secular variation sv in the 10th or 11th centuries at near excursional rates similar and coeval features in the hawaiian and to a lesser extent arkansan sv data sets possibly indicate a rapid amplitudinal shift in the regional nondipole field at that time

extended and revised archaeomagnetic database and secular variation curves from bulgaria for the last eight millennia the efforts of geophysicists to describe geomagnetic field behaviour in the past lead to creation of different geomagnetic field models on the other hand the established regional palaeosecular variations of geomagnetic elements are increasingly used for dating purposes in archaeology both of these goals can be achieved if sufficient amounts of long archaeomagnetic data sets exist for different geographical regions the accumulation of archaeomagnetic determinations began at the middle of the last century parallel with the progressive development of experimental methodology and acceptance criteria the presence of great number of old determinations requires their critical assessment the important question about the reliability of the associated dating intervals should be also re assessed all this requires the continuous refinement and extension of the accumulated databases this paper presents the last synthesis of bulgarian archaeomagnetic database and the local palaeosecular variation curves obtained using a statistical treatment based on bayesian approach rencurve software the rock magnetic characteristics of the newly included non published results are summarized

do manganese nodules grow or dissolve after burial results from the central indian ocean basin abstract fifty buried manganese nodules at different depth intervals were recovered in 12 sediment cores from the central indian ocean basin ciob a maximum of 15 buried nodules were encountered in one sediment core aas 22 gc 07 and the deepest nodule was recovered at 5 50 m below seafloor in core aas 04 gc 5a approximately 80 of the buried nodules are small in size 2 cm diameter in contrast to the atlantic ocean and peru basin pacific ocean where the majority of the buried nodules are large 8 cm and 6 cm respectively buried nodule size decreases with core depth and this distribution appears to be similar to the phenomenon of brazil nut effect buried nodules exhibit both smooth and rough surface textures and are ellipsoidal elongated rounded sub rounded irregular and polynucleated buried nodules from siliceous ooze are enriched in mn cu ni zn mo ga v and rb whereas those from red clay are enriched in fe co ti u th y cr nb and rare earth elements ree buried nodules from siliceous ooze suggest their formation under hydrogenetic early digenetic and diagenetic processes whereas those from red clay are of hydrogenetic origin ree are enriched more than 1 5 times in buried nodules from red clay compared to siliceous ooze however the mode of incorporation of ree into buried nodules from both sedimentary environments is by a single authigenic phase consisting of fe ti p shale normalized ree patterns and ce anomalies suggest that nodules from siliceous ooze formed under more oxidizing conditions than those from red clay nodules buried at depths between 1 5 and 2 5 m are diagenetic mn fe ratio 10 15 formed in highly oxic environments large positive ce anomalies and record aeolian dust high eu anomalies chemical composition surface texture and morphology of buried nodules are similar to those of surface nodules from the same basin furthermore buried nodule compositions do not exhibit any distinct patterns within the core depth suggesting that buried nodules neither grow nor dissolve after their burial in the sediment column

glaciofluvial infilling and scour of the puget lowland washington during ice sheet glaciation the puget lobe the southwesternmost extension of the cordilleran ice sheet last advanced into the puget lowland of western washington at about 15 ka the advancing ice sheet deposited voluminous sediment on a prograding proglacial outwash plain that extended from the olympic mountains to the cascade range herein recognized as the great lowland fill subsequent overrunning by the ice sheet excavated deep linear troughs now occupied by the large lakes and marine waters of puget sound excavation of these troughs and valleys of the puget lowland required the net transport of about 1000 km3 of sediment almost entirely during ice occupation and primarily by subglacial water these landforms of glaciofluvial deposition and erosion define the modern landscape here emphasizing the importance of these processes in the region s geomorphology

carbon isotopic variations on glacial to interglacial time scales in the ocean modeling and implications downcore variations in the deep sea 13c signal as recorded in benthic foraminifera are a function of past changes in global organic carbon inventory and ocean circulation thus the carbon isotopic composition of fossil benthic foraminifera constitutes a valuable geochemical proxy for reconstructing paleooceanographic conditions this study examines the mean ocean 13c 12c variations due to the climatically induced changes in the size of the two organic carbon pools terrestrial biomass forest soil and continental shelf sediment through modeling the paired foraminiferal 13c 18o data in the literature it is estimated that during the past several hundred thousand years in late quaternary transfer of organic carbon between these two pools and the ocean in response to glacial interglacial climate and sea level changes has resulted in global oceanic 13c fluctuations with a mean amplitude of about 0 32 the transfer has accounted for about two thirds of the observed carbon isotopic shift in the deep eastern pacific ocean circulation accounting for the remaining one third of 13c amplitude variations in the deep north atlantic ocean it has accounted for about one third of the shift of the two organic carbon reservoirs forest soil is roughly 2 5 times more responsible than shelf sediment in altering the mean carbon isotopic composition of the quaternary oceans destruction of organic matter from the shelf sediment reservoir is responsible for raising the oceanic nutrient inventory during glacial times by about 4 relative to the present interglacial level a level which is difficult to be assessed by the cadmium proxy marine deposition of organic carbon in glacial oceans increased by 3 10 in spite of a reduction in terrestrial biomass during ice ages isolating out the global climatic signals in 13c records shows that since about 300 kyr ago there has been a trend of increasing organic carbon accumulation toward the present at least in the equatorial e pacific it also shows that the contrast between the 13c values hence nutrient content of deep water in the atlantic and pacific observed in today s ocean was smaller during glacial periods in the northwestern indian ocean the global climate corrected 13c results reveal interglacial intensification of the monsoon driven upwelling and productivity back to at least oxygen isotopic stage 11 circa 400 kyr b p

phytolith evidence for hearths and beds in the late mousterian occupations of esquilleu cave cantabria spain esquilleu cave site has provided a moderately well preserved archaeological cave deposit from the late pleistocene in the cantabrian area phytolith quantification identification and determination of the refractive index have been carried out together with ftir analyses from sediment samples collected in the profile the comparison of the data obtained with the previous micromorphological results allows us to make inferences about the site formation processes and the neanderthals use of the cave phytolith results show the presence of grass leaves nearby the hearth suggesting the repetitive existence of a bedding zone on the same area neanderthal behavioral patterns should be revised on the light of high resolution analyses since diagenetic processes can obscure the existence of differentiated activity areas in the site

first directional european palaeosecular variation curve for the neolithic based on archaeomagnetic data neolithic cha1colithic and bronze age anthropogenic cave sediments from three caves from northern spain have been palaeomagnetically investigated 662 oriented specimens corresponding to 39 burning events ash carbonaceous couplets from the three sites with an average of 16 samples per fire were collected 26 new archaeomagnetic directions have been obtained for the time period ranging from 5500 to 2000 yr ca bc these results represent the oldest archaeomagnetic directions obtained from burnt archaeological materials throughout all western europe magnetisation is carried by pseudo singie domain low coercivity ferromagnetic minerals magnetite magnetite with no significant isomorphous substitution and or maghaemite rock magnetic experiments indicate a thermoremanent origin of the magnetisation although a thermochemical magnetisation cannot be excluded combination of the new data presented here and the recent updated bulgarian database allows us to propose the first european palaeosecular variation psv curve for the neolithic a bootstrap method was applied for the curve construction using penalised cubic b splines in time the new palaeosecular variation curve is well constrained from 6000 bc to 3700 bc the period with the highest density of data showing a declination maximum around 4700 bc and a minimum in inclination at 4300 bc which are not recorded by the recent global calslok 1 b and regional scha dif 8k models due to the use of lake sediment data dating resolution by using the proposed psv curve oscillates from approximately 30 yr to 200 yr for the period 6000 to 1000 yr bc reaching similar resolution as radiocarbon dating considering the good preservation age control and widespread occurrence of burnt archaeological materials across southern europe they represent a new source of data for geomagnetic field modelling as well as for archaeomagnetic dating

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

three millennia of directional variation of the earth s magnetic field in western europe as revealed by archeological artefacts directional secular variation of the geomagnetic field over the last 2000 years has been defined in western europe from numerous archeomagnetic studies however the number of archeomagnetic results for older periods is much more limited for this reason we present new data obtained from fired archeological structures found in two french sites loupiac and aspiran dated within the first millennium b c latest bronze earliest iron age transition 850 700 b c and iron age 525 475 b c respectively from a compilation of archeomagnetic results from western europe great britain italy and france and northern africa tunisia we propose a directional secular variation curve for western europe that covers the entire first millennium b c this curve exhibits a large clockwise motion with rapid changes during the first half of the millennium while the last four centuries b c are characterized by weak variations

carbonate preservation history in the peru basin paleoceanographic implications we studied preservation dissolution cycles and paleoproductivity in eight sediment cores from the peru basin south of the highly productive surface waters of the eastern equatorial pacific stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy sediment cores which span the last 8 m y were retrieved during cruise 79 with rv sonne close to the carbonate compensation depth ccd in general sediments show pacific type carbonate cycles we interpret a pronounced carbonate peak between 6 and 7 ma as the result of a western and northern extension of the highly productive peru current decreased carbonate contents from the late miocene to the late pliocene might be associated with a slow contraction of the latitudinal extent of the high productivity belt north of the study areas during the pliocene carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets which should have been associated with pulsations of the antarctic ice cap an abrupt collapse of the carbonate system occurred at 2 4 ma higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation during the quaternary carbonate fluxes are high during glacials and low during interglacials large amplitude variations with long broad minima and maxima associated with small migrations of the lysocline and the ccd 200 m are indicative of the preservation dissolution history in the peru basin during the early pleistocene climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record during the last 800 kyr variability in the carbonate record was dominated by the 100 kyr eccentricity cycle fluxes of biogenic material calcium carbonate organic carbon opal and barium were greatest during glacials which imply higher productivity and export production of the peru current during cold climatic periods dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate after the mid brunhes event 400 ka we observe a plateaulike shift to enhanced dissolution and to intensified productivity

evolution of a holocene delta driven by episodic sediment delivery and coseismic deformation puget sound washington usa episodic large volume pulses of volcaniclastic sediment and coseismic subsidence of the coast have influenced the development of a late holocene delta at southern puget sound multibeam bathymetry ground penetrating radar gpr and vibracores were used to investigate the morphologic and stratigraphic evolution of the nisqually river delta two fluvial deltaic facies are recognized on the basis of gpr data and sedimentary characteristics in cores which suggest partial emplacement from sediment rich floods that originated on mount rainier facies s consists of stacked sheet like deposits of andesitic sand up to 4 m thick that are continuous across the entire width of the delta flat lying highly reflective surfaces separate the sand sheets and comprise important facies boundaries beds of massive pumice and charcoalrich sand overlie one of the buried surfaces organic rich material from that surface beneath the massive sand yielded a radiocarbon age that is timecorrelative with a series of known eruptive events that generated lahars in the upper nisqually river valley facies cf consists of linear sandbodies or palaeochannels incised into facies s on the lower delta plain radiocarbon ages of wood fragments in the sandy channel fill deposits also correlate in time to lahar deposits in upstream areas intrusive sand filled dikes and sills indicate liquefaction caused by post depositional ground shaking related to earthquakes continued progradation of the delta into puget sound is currently balanced by tidal current reworking which redistributes sediment into large fields of ebb and flood oriented bedforms

sediments and micronodules in the northern and central peru basin the mineralogy and composition of sediments and manganese micronodules from the northern and central sectors of the peru basin are discussed because of the proximity of the basin to the carbonate compensation depth c c d surface sediments vary between calcareous oozes and siliceous muds besides biogenic components clay minerals are important by far the most abundant clay mineral is smectite which is thought to be of diagenetic origin on a carbonate free basis the surface sediments are rather uniform in composition throughout the basin and are similar in composition to those of the equatorial pacific sedimentation rates for the uppermost core sections are in the range of 3 to 5 mm 1000 yr

assessing post depositional processes in archaeological cave fires through the analysis of archaeomagnetic vectors abstract this paper presents a methodological application of archaeomagnetism and rock magnetism as a tool to evaluate post depositional mechanical alterations in archaeological cave fires most taphonomic and post depositional studies on anthropogenic sediments have mainly focused on the diagenetic alterations that these contexts undergo from a geochemical point of view however physical alterations are still largely assessed from mere macroscopic observations of the burnt facies comprising these fires this paper compares the archaeomagnetic directions recorded in the ashes of two holocene fires from the mirador cave sierra de atapuerca burgos spain one apparently well preserved and the other clearly bioturbated vector analyses of archaeomagnetic directions together with the study of magnetic properties combined with field macroscopic observations can provide a powerful tool to assess when a fire is actually in situ the anisotropy of magnetic susceptibility ams in both fires exhibits a dominant sedimentary fabric produced by compaction and also exhibits differences between the areas mechanically disturbed within these fires from those which are not the following set of magnetic features was identified when an archaeological fire preserves its primary position i univectoral and high intensity nrm orthogonal demagnetisation diagrams in ashes ii koenigsberger q n ratio values higher than unity indicative of an undisturbed thermo remanence trm or a partial thermoremanence p trm and iii a good clustering of characteristic directions defining an statistically representative mean archaeomagnetic direction the concurrence of these observations can be used as criterion to determine when an archaeological cave fire is physically in situ thus allowing a correct interpretation of the archaeological record

linking site formation processes to magnetic properties rock and archeomagnetic analysis of the combustion levels at riparo gaban italy this study focuses on archeomagnetic directional data that are obtained from combustion levels in the riparo gaban rock shelter northern italy in order to assess the degree of disturbance in the sediments and to provide new information to evaluate evolution of the geomagnetic field in the mid holocene combustion levels consist of ash rubefied levels or partially burned material and mixtures of these or polygenic material rock magnetic investigations show that superparamagnetic to single domain magnetite is the main carrier of the remanent magnetization but small amounts of hematite and maghemite may also be present in the different materials rock magnetic parameters e g the koenigsberger ratio q or the reversibility of thermomagnetic can be related to the degree of burning and the dispersion parameter k to the degree of preservation the grouping of archeomagnetic directions of a specific level is strongly dependent on the degree of physical disturbances directional means from thirteen levels can be compared with reference curves for paleosecular variation based on geomagnetic field models and other archeomagnetic data the data from this study are in agreement with other archeomagnetic data from the balkans in the time period 4900 bc to 4600 bc

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales