a high resolution pollen and geochemical analysis of late holocene human impact and vegetation history in southern cumbria england the historic era which in cumbria begins with the roman invasion of ad 71 is a frequently neglected period in palaeoecological research but its study can bring benefits in improving knowledge of landscape history and in understanding the significance and limitations of palaeoecological records pollen and geochemical data are presented for late holocene records from deer dyke and hulleter mosses in southern cumbria the records show initially low levels of anthropogenic impact followed by a phase of forest clearance and mixed agriculture from the 7th to 11th centuries ad the timing of these clearances suggests that they were initially anglo saxon in origin rather than norse further clearances in the 16th century ad are interpreted as a response to monastic dissolution and late tudor population pressures the landscapes reached their contemporary form following extensive clearances in the 17th century ad silicon and titanium concentrations at deer dyke moss were used to reconstruct past levels of atmospheric dust loading which is broadly related to soil erosion geochemical influx was found to peak during periods of landscape transition rather than from established land use this relationship with pollen data is thought to reflect the predominantly low levels of anthropogenic impact in the region which changes as substantial woodland clearances during the 16th century ad and continuous land use pressure since then have greatly increased the supply of airborne dust

stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

uplift and erosional history of the deccan traps india evidence from laterites and drainage patterns of the western ghats and konkan coast abstract the western ghats escarpment in the western coastal region of peninsular india is locally capped by plateau remnants on which a regional high level laterite carapace is preserved geochemical fingerprinting studies show that the laterite has been developed from a protolith of panhala formation basalts the youngest known formation of the deccan sequence the high level laterite is in detail structurally concordant with its underlying basalts and hence it is concluded that it represents the original top of the lava pile a younger low level laterite carapace is developed on the konkan plain below the escarpment where it lies discordantly on basalts of the ambenali and poladpur formations from which it developed in situ the low level laterite rises topographically northwards in response to differential uplift probably at a maximum in the nasik region the main structures of the ghats region excluding the coastal monocline are the nasik dome and the mahabaleshwar anticline these have no effect on regional drainage patterns and it is argued that they are largely secondary features developing in response to post volcanic uplift

elemental and nd sr pb isotope geochemistry of flows and dikes from the tapi rift deccan flood basalt province india abstract the deccan traps are a large rift associated continental flood basalt province in india parts of which have been studied extensively in terms of geochemistry palaeomagnetism and stratigraphy however the basalts of the tapi rift in the central part of the province have been little studied thus far two ene wsw trending tectonic inliers of the deccan basalts in this region forming ridges rising from younger alluvium are made up of basalt flows profusely intruded by basaltic dikes both of these ridges lie along a single lineament although they are not physically continuous the flows are aphyric plagioclase phyric and giant plagioclase basalts and the dikes are aphyric or plagioclase phyric we consider the two inliers to have been originally continuous from the presence of bouldery remnants of a major dioritic gabbro dike along both samples of this dike from both ridges have previously yielded typical deccan ages of 65 6 0 5 ma and 65 6 0 6 ma by the 40 ar 39 ar incremental heating technique initial 87 sr 86 sr ratios and end t values and present day pb isotopic ratios of most dikes indicate that they are isotopically similar to lavas of the mahabaleshwar and panhala formations of the western ghats about 450 km to the south their mantle normalized trace element patterns have small pb and ba peaks one dike has a strong bushe formation affinity and a nd sr isotopic composition more extreme than that of any other deccan rock yet sampled with end t 20 2 and 87 sr 86 sr t 0 72315 its mantle normalized element pattern shows large pb th and u peaks and large nb ta troughs its elemental and isotopic chemistry reflects substantial continental contamination the flows cut by the mahabaleshwar type dikes are isotopically similar to the poladpur formation lavas of the western ghats their mantle normalized element patterns show modest peaks at rb ba and pb and rather low nb and ta relative to la indicating that they have been contaminated to intermediate degrees the mantle normalized element patterns of all the flows and dikes show enrichment in the light rare earth elements with small or no eu anomalies the entire flow dike sequence is similar to the wai subgroup of the western ghats in terms of its elemental and isotopic chemistry and stratigraphic relationships wai subgroup like lavas i e some of the younger magma types originally identified from the southern part of the western ghats are previously known from the central northern and northeastern deccan and many have been thought to be far travelled flows erupted in the southwestern deccan although at least the dikes and probably the giant plagioclase basalt flows of our study area are locally generated and emplaced our new data extend the known outcrop area of these widespread magma types substantially and these magma types indeed appear to have a nearly province wide distribution

a ā lava flows in the deccan volcanic province india and their significance for the nature of continental flood basalt eruptions newly identified a lava flows outcrop intermittently over an area of 110 km2 in the western deccan volcanic province dvp india they occur in the upper thakurvadi formation in the region south of sangamner the flows one of which is compound are 15 25 m thick and exhibit well developed basal and flow top breccias the lavas have microcrystalline groundmasses and are porphyritic or glomerocrystic and contain phenocrysts of olivine clinopyroxene or plagioclase feldspar they are chemically similar to compound p hoehoe flows at a similar stratigraphic horizon along the western ghats petrographic and geochemical differences between a flows at widely spaced outcrops at the same stratigraphic horizon suggest that they are the product of several eruptions potentially from different sources their presence in the dvp could suggest relative proximity to vents this discovery is significant because a lavas are generally scarce in large continental flood basalt provinces which typically consist of numerous inflated compound p hoehoe lobes and sheet lobes their scarcity is intriguing and may relate to either their occurrence only in poorly preserved or exposed proximal areas or to the flat plateau like topography of flood basalt provinces that may inhibit channelization and a formation or both in this context the a flow fields described here are inferred to be the products of eruptions that produced unusually high effusion rate lavas compared to typical flood basalt eruptions whether these phases were transitional to lower intensity sustained eruptions that fed extensive low effusion rate p hoehoe flow fields remains unclear

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

geochemistry of the palitana flood basalt sequence and the eastern saurashtra dykes deccan traps clues to petrogenesis dyke flow relationships and regional lava stratigraphy recent studies of large mafic dyke swarms in the deccan traps flood basalt province india indicate that some of the correlative lava flows reached several hundred kilometers in length here we present field petrographic mineral chemical and whole rock geochemical including sr nd isotopic data on the palitana lava sequence and nearby dykes in the saurashtra region of the northwestern deccan traps these rocks are moderately evolved many with low ti nb characteristics we infer that most dykes are notably and systematically less contaminated by ancient continental crust than the palitana flows but four dykes are equally or significantly more contaminated with some of the most extreme sr nd isotopic compositions seen in the entire deccan traps initial end is as low as 18 0 a bhimashankar type and a poladpur type dyke are present several hundred kilometers from the type section of these magma types in the western ghats escarpment we find no geochemical correlations between the palitana sequence and three subsurface sequences in ne saurashtra containing abundant picritic rocks surface lavas previously studied from saurashtra or the western ghats sequence intriguingly the eastern saurashtra dykes cannot have been feeders to any of these lava sequences feeder dykes of these sequences may be located in southwestern or central saurashtra or in the dhule nandurbar dediapada areas across the gulf of cambay 200 300 km east of palitana our results indicate polycentric flood basalt eruptions not only on the scale of the deccan traps province but also within the saurashtra region itself

sr and nd isotopes in river sediments from the ganga basin sediment provenance and spatial variability in physical erosion 1 sr and nd concentrations and isotope compositions in sediment of the ganga river from gangotri to rajmahal and its tributaries have been measured to determine provenance and the spatial variability in physical erosion among the ganga subbasins sr and nd in silicates range from 37 to 138 and from 10 to 36 g g with 87sr 86sr and nd of 0 7474 0 8428 and 25 5 to 15 5 respectively the results suggest that 65 of ganga mainstream sediments are derived from the higher himalayan crystallines highlighting intense physical erosion in this region the 87sr 86sr values of sediments in the gangetic plain show nearly identical trends during two seasons with a sharp and significant decrease at barauni downstream of gandak confluence this brings out the major impact of the sediment contribution from the gandak to the ganga mainstream model calculation suggests that about half of the ganga sediment at rajmahal is sourced from the gandak the erosion rates in the himalayan subbasins of the ganga range between 0 5 and 6 mm a where a is years with the gandak having the highest erosion rate high relief and intense precipitation over the headwater basins of the gandak appear to drive the rapid and focused erosion of this basin the results of this study and those in literature suggest that the eastern syntaxis brahmaputra the western syntaxis indus and the gandak have much higher physical erosion rates than the other himalayan basins focused erosion in the hot spots of these river basins contributes significantly to the global riverine sediment budget and influence regional tectonics

stratigraphy structure and volcanology of the se deccan continental flood basalt province implications for eruptive extent and volumes the deccan volcanic province is one of the world9s largest continental flood basalt provinces and derives additional importance because its eruptions 64 67 ma straddle the cretaceous tertiary boundary to better assess the environmental impact of deccan volcanism and its possible effect upon cretaceous tertiary boundary biota it is necessary to document the stratigraphy chronology and volume of the eruptions new chemostratigraphical data permit mapping of the se deccan these data strengthen the likelihood that the rajahmundry traps of eastern india were originally fed by long distance flows and are an extension of the main deccan volcanic province an east west cross section reveals a depression or moat around the se periphery of the deccan volcanic province this provided a site in which shallow lakes initially formed and along which later lava eruptions became channelled and confined published palaeomagnetic data indicate that the lavas of the se deccan were erupted during chron 29r coeval with the cretaceous tertiary boundary and the chemostratigraphic data place the associated lake sediments i e lameta group beneath and within lavas of the wai subgroup finally these new map data are combined with previous work to provide a quantitative estimate for the original deccan volcanic province eruptive volume of c 1 3 10 6 km 3

grain sizes of susceptibility and anhysteretic remanent magnetization carriers in chinese loess paleosol sequences detailed rock magnetic studies show that susceptibility mass specific and anhysteretic remanent magnetization arm of the chinese loess paleosol sequences are carried by almost identical magnetic carriers therefore the ratio arm or equivalently arm where is defined as 0 and 0 is the intercept susceptibility of the plot of versus arm and arm is field normalized arm can be used to quantify the grain size of and arm carriers by determining this ratio for three chinese loess paleosol profiles jiuzhoutai yuanbao and yichuan characterized by different degrees of environmentally controlled pedogenesis and sedimentation rates we show that the lower grain size limit of aeolian magnetic particles in the less pedogenically altered loess units is about 100 300 nm in the finer grained pseudosingle domain psd grain size range in contrast the grain sizes of pedogenically produced magnetic particles for mature paleosols dominantly cover both the superparamagnetic sp and single domain sd ranges on the basis of plots of arm against samples can be divided into four regions i ii iii and iv region i corresponds to the least pedogenically altered primary loess samples with arm of 0 165 0 24 samples in region ii a transition zone between the least altered loess and the onset of development of paleosols have values identical to those in region i but have lower arm of 0 09 0 165 with increasing susceptibility in zone iii arm is positively correlated with indicating the gradually increasing influence of sp particles finally in zone iv with higher than 6 5 10 7 m3 kg 1 arm is independent of the variations in suggesting that arm is totally controlled by the pedogenic finest grained particles and the size distribution of these particles remains almost constant the development of soils in the chinese loess revealed by these three profiles from three sites can be clearly explained by a continuous process of pedogenesis increasing from zone i to zone iv the definition of the pedogenic zones can help to improve our understanding of the underlying mechanisms and variability of pedogenesis and thus could enable more successful and accurate separation of the authentic pedogenic signals from the background signal of the aeolian inputs at different loess sites worldwide

origin of the deccan trap flows at mahabaleshwar inferred from nd and sr isotopic and chemical evidence abstract the deccan flows at mahabaleshwar are divisible into a lower and an upper group based on nd and sr isotopic ratios which define two correlated trends this distinction is supported by incompatible element ratios and bulk compositions the data reflect contamination in a dynamic system of magmas from an lil depleted e juv 8 mantle by two different negative e juv endmembers one undoubtedly continental crust the other either continental crust or enriched mantle the depleted mantle source anomalously high in 87 sr 86 sr may have been in the subcontinental lithosphere or a region of rising indian ocean morb mantle

the possible role of magnetic measurements in the discrimination of sahara sahel dust sources the mineral magnetic properties of deposited dusts collected along a broadly north to south transect across niger have been investigated on both a bulk and particle size specific basis dusts display a general north to south gradient in fine grained ferrimagnetic mineral magnetite maghemite concentrations with samples south of the sahara sahel transition south of 15 5o n generally containing greater concentrations than dusts from further north where the climate is much drier this distinction is seen especially clearly in the clay 2 m fraction which harbours the products of weathering and pedogenesis this gradient in ferrimagnetic mineral concentrations broadly parallels that previously reported for surface soils sands across a similar latitudinal range we suggest that the regional distinction in both dust and surface soil sand magnetic properties can be related to differences in weathering regime between the arid saharan parts of the transect and the sahel sites where higher rainfall has permitted stronger weathering and pedogenesis given that the weathering related magnetic signatures in the clays dominate the magnetic properties of the 16 m fractions in these samples and that this particle size component is most likely to be involved in long range transport magnetic measurements hold out the potential of discriminating sahara and sahel dusts deposited in remote areas copyright 2011 john wiley sons ltd

tectonomagmatic setting of lava packages in the mandla lobe of the eastern deccan volcanic province india palaeomagnetism and magnetostratigraphic evidence

application of a textural geospeedometer to the late stage magmatic history of mil 03346 dynamic crystallization experiments performed on fe rich al poor basalt are employed as a textural calibration set to quantify the late stage igneous history of nakhlite miller range mil 03346 the ratio of crystal melt surface area to volume typifying morphologically distinct populations of ca pyroxene has been shown to vary as a strong function of cooling rate hammer 2006 furthermore a texture of phenocrysts surrounded by finer grained groundmass crystals arises by sequential nucleation events during constant rate cooling but multiple populations nucleate only if the cooling rate is 72 c h 1 textural analysis of meteorite mil 03346 reveals at least two distinct populations the ca pyroxene phenocryst and microphenocryst three dimensional 3d aspect ratios are 112 8 3 and 1530 160 mm 1 respectively by comparison with the calibration set the range of cooling rates consistent with 3d aspect ratios of both populations in mil 03346 is 20 c h 1 an additional experiment was performed approximating a conductive heat transfer profile in order to interpret and apply results of constant rate cooling experiments to the natural cooling of magma results suggest that the textures of constant rate experiments parallel the initial period of rapid cooling in natural magma initial cooling rates of 20 c h 1 in the lava hosting mil 03346 occur in conductively solidifying lava at depths of 0 4 m constraining the minimum total thickness to 0 8 m crystal accumulation beginning in a subsurface reservoir and continuing after lava emplacement as an inflated pahoehoe sheet satisfies all textural constraints on the late stage igneous history of mil 03346

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

dating of post glacial landforms in the central howgills little is known of holocene landform development in upland britain this paper describes a site at middle langdale in the howgill fells of cumbria where large but now stabilized and inactive gullies cut through periglacial material at the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor on these sediments and buried by the debris cones is a well developed organic soil from which two 14c dates have been obtained in an attempt to estimate the age range of the soil these dates range from 2580 55 years bp for the fine particulate fraction from the base of the organic horizon to 940 95 years bp for fossil rootlets from the uppermost organic layer immediately below the overlying debris cones the pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a juncus marsh with birch alder and hazel nearby the pollen from the surrounding upland area suggests woodland on the valley sides dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present the magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil the evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period the evidence then points to major geomorphological changes a wave of soil erosion gully development and debris cone deposition perhaps following the scandinavian introduction of sheep farming in the tenth century a d

robust chronologies for landform development obtaining chronological control for geomorphological sequences can be problematic due to the fragmentary and non sequential nature of sediment and landform archives the robust analysis of 14c ages is often critical for the interpretation of these complicated sequences this paper demonstrates a robust methodology for the 14c dating of geomorphological sequences using a case study from the lower ribble valley northwest england the approach adopted incorporates using greater numbers of ages targeting plant macrofossils obtaining replicate measurements from single horizons to assess the extent of reworking and the use of bayesian approaches to test models of the relative order of events the extent of reworking of organic materials and space time dynamics of fluvial change means that it is critical that chronological control is sufficiently resourced with 14c measurements as a result bayesian approaches are increasingly important for the evaluation of large data sets assessing the conformability of relative order models informed by interpretation of the geomorphology can identify contexts or materials that are out of sequence and focuses attention on problem materials reworking and errors in interpretation outlier ages these relative order models provide a framework for the interrogation of sequences and a means for securing probability based age estimates for events that occur between dated contexts this approach has potential value in constraining the sequence of geomorphological development at scales that vary from individual sites to a catchment or region furthering understanding of forcing and change in geomorphological systems copyright 2008 john wiley sons ltd

the mineral magnetic properties of an annually laminated holocene lake sediment sequence in northern sweden detailed mineral magnetic measurements were conducted on a 9000 year varved lake sediment sequence in northern sweden lake sarsjon the results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments which is controlled to a large extent by the intensity of the spring snow melt in contrast the concentration of ferrimagnetic magnetite reflected by initial magnetic susceptibility and magnetic hysteresis parameters is positively correlated to the concentration of organic carbon which is most likely of an autochthonous origin this magnetite has magnetic properties that are characteristic of stable single domain magnetite grains produced by magnetotactic bacteria the paramagnetic susceptibility record clearly points to a climatic excursion in the early holocene between 6100 174 bc and 5700 167 bc which can be correlated to an d18o excursion a cold event in the greenland ice cores and lake sediments in southern germany an

application of dynamic programming to the correlation of paleoclimate records 1 signal matching is a powerful tool frequently used in paleoclimate research but it is enormously time consuming when performed by hand previously proposed automatic correlation techniques require very good initial fits to find the correct alignment of two records a new technique presented in this paper utilizes dynamic programming to find the globally optimal alignment of two records geological realism is instilled in the solution through the definition of penalty functions for undesirable behavior such as unlikely changes in accumulation rate examples with synthetic and real data demonstrate that the dynamic programming technique produces accurate high resolution results with much less effort than hand tuning or preexisting automated correlation techniques

magnetostratigraphy and 40ar 39ar geochronology of the malwa plateau region northern deccan traps central western india significance and correlation with the main deccan large igneous province sequences abstract basaltic lava flows of malwa plateau together with the mandla area and the toranmal section constitute the northern deccan province in central western india with the present outcrop area of 80 000 km2 the malwa flows form an extensive but relatively thin sequence we sampled deccan basalts along two 100 km each n s and e w transects along the western and southern rims of the malwa plateau the 67 12 0 44 ma 40ar 39ar age obtained in the present study clearly shows that the eruption of the malwa flows started during the magnetochron c30n by mapping the magnetic c30n c29r transition on the western and southern edge of the plateau the total volume and eruption rate can be calculated 42 000 km3 0 03 km3 a furthermore the results point towards the narmada tapi rift zone as the possible source area for the malwa lava flows the malwa sequence is older and partly synchronous with the thick sequences of the western ghats since their eruption centers are spatially independent they should not be correlated with younger although geochemically similar formations of the western ghats other northern deccan flows show clear similarities with the malwa flows and can be magnetostratigraphically and geochemically correlated we therefore suggest a new subgroup for the northern deccan province the narmada subgroup defined on the geochemical and magnetic characteristics of the malwa mandla and toranmal flows the introduction of this new subgroup clarifies the position of the northern deccan province in the deccan stratigraphy and is a step towards a better understanding of the deccan eruption history

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

magnetic susceptibility of loess in china abstract the low field susceptibility of the loess deposits in the chinese loess plateau is due to both paramagnetic and ferromagnetic minerals paramagnetism can be seen in the less to unweathered loess horizons where superparamagnetic contributions which arise from ultrafine magnetite particles are not as strongly developed as in the heavily weathered palaeosols frequency dependent susceptibility and minimum unblocking temperatures of low temperature thermoremanent magnetization generally indicate finer grain sizes in the palaeosols as compared to the loess beds this grain size difference and the fact that susceptibilities of the same stratigraphic palaeosol layer vary by an order of magnitude between the western and central regions of the plateau are considered as strong evidence that the ultrafine magnetite is not of detrital aeolian origin but was formedin situ the pedogenetic processes are clearly related to palaeoclimatic changes therefore the various susceptibility properties may serve for a detailed reconstruction of the continental palaeoclimatic conditions for the last 2 5 ma since the palaeomagnetically dated beginning of loess sedimentation in china

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

holocene alluvial fan and terrace formation in the bowland fells northwest england in the bowland fells lancashire northwest england in the headwater valleys of the hodder river system is a suite of holocene fluvial landforms debris cones and alluvial fans at tributary junctions and river terraces along the main valleys post date late pleistocene forms and pre date the modern valley floor alluvial forms eight 14c dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of holocene erosion to be identified with debris cone fan deposition taking place after c 5400 bp but before c 1900 bp and again at c 900 bp some of the fans and cones are complex with deposits attributable to both phases others are simple and attributable only to the later phase in the headwaters an upper terrace at c 5400 bp pre dates the cones and a lower terrace is contemporaneous with the first debris cone phase lower downvalley the youngest of three terraces date from c 5000 bp or earlier indicating that the sequence is less complex downstream

temporal variations in 87sr 86sr and ɛnd in sediments of the southeastern arabian sea impact of monsoon and surface water circulation sr and nd isotopic composition of silicate fractions of sediments have been measured in two well dated gravity cores from the eastern arabian sea archiving a depositional history of 29 and 40 ka the 87 sr 86 sr and e nd in the northern core ss 3104g 12 8 n 71 7 e ranges from 0 71416 to 0 71840 and 8 8 to 12 8 these variations are limited compared to those in the southeastern core ss 3101g 6 0 n 74 0 e in which they vary from 0 71412 to 0 72069 and 9 0 to 15 2 respectively this suggests that the variation in the relative proportions of sediments supplied from different sources to the core ss 3104g are limited compared to core ss 3101g the 87 sr 86 sr and e nd profiles of ss 3101g exhibit two major excursions ca 9 ka and 20 ka coinciding with periods of holocene intensified monsoon phase imp and the last glacial maximum lgm respectively with more radiogenic 87 sr 86 sr and lower e nd during these periods these excursions have been explained in terms of changes in the erosion patterns in the source regions and surface circulation of the northern indian ocean resulting from monsoon intensity variations the intensification of north east ne monsoon and associated strengthening of the east indian coastal current in southwest direction during lgm transported sediments with higher 87 sr 86 sr and lower e nd from the western bay of bengal to the arabian sea in contrast enhanced south west sw monsoon at 9 ka facilitated the transport of sediments from the northern arabian sea particularly indus derived to the southeastern arabian sea this study thus highlights the impact of monsoon variability on erosion patterns and ocean surface currents on the dispersal of sediments in determining the sr and nd isotopic composition of sediments deposited in the eastern arabian sea during the last 40 ka

the timing of crustal extension and the eruption of continental flood basalts the association between mantle plumes continental flood basalt eruption and the extension and rifting of the crust is well recognized1 3 but there has always been controversy as to whether the plume or the rifting was the initiating factor4 5 was rifting triggered by doming above the thermal plume2 3 6 or was rifting the driving force preceding the associated volcanicity7 8 here i show that recent flow by flow mapping of two continental flood basalt provinces the columbia river basalt group and the deccan basalt group allows one to infer the relative timing of volcanicity and crustal extension in both provinces eruption of the main tholeiitic phase preceded significant extension and crustal thinning this suggests that the primary event in the formation of these provinces was the upwelling of a mantle plume and that the subsequent crustal extension rifting and decompression was in part a consequence of the initiation of that plume

intracanyon flows in the deccan province india case history of the rajahmundry traps the rajahmundry traps form small exposures of basaltic flows on either side of the godavari river near the east coast of india and they are thought to be late cretaceous early paleocene in age because they lie 400 km from the nearest surface exposures of the deccan traps their mode of formation remains unknown furthermore the rajahmundry traps show normal magnetic polarity indicating that they cannot be exact time equivalents of the large volumes of the deccan traps which show reversed magnetic polarity geochemical analyses reveal that the rajahmundry traps are of very uniform composition geochronological studies suggest an age of 64 ma marginally younger than the main sections western ghats of the deccan traps the only section of the main deccan province that may be stratigraphically equivalent on the basis of age geochemical signatures and magnetic polarity is the kolhapur formation at the southern end of the deccan province near the west coast 800 km from the rajahmundry traps we suggest that the rajahmundry traps and other basaltic material found near the mouth of the godavari river represent remnants of intracanyon flows that flowed eastward down the ancestral river systems of peninsular india away from the domed structure caused by the plume that led to the formation of the deccan traps similar intracanyon flows that have traveled 600 km from their source to the pacific coastline are well documented in association with the columbia river basalt province united states in the case of the rajahmundry traps the distance traveled would appear to be 1000 km

quantifying grain size distribution of pedogenic magnetic particles in chinese loess and its significance for pedogenesis quaternary glacial interglacial cycles have been imprinted on the chinese loess paleosol sequences through pedogenesis in order to accurately decode the paleoclimatic signals carried by these pedogenic particles it is essential to quantify the pedogenically produced magnetic particles in terms of mineralogy as well as grain size distribution gsd to date the gsd has not been accurately determined because of the dearth of available means for analyzing extremely fine grained nanometer scale pedogenic magnetic particles using low temperature techniques we systematically investigated the temperature dependency of fd defined as 1hz 10hz where 1hz and 10hz are ac magnetic susceptibility measured at 1 and 10 hz respectively from two characteristic loess profiles one located at the western chinese loess plateau and the other in the central plateau on the basis of neel theory for a shape anisotropy dominant grain and experimental analysis at low temperatures a quantitative gsd for pedogenic particles in chinese loess paleosols was constructed we found that the dominant magnetic grain size lies just above the superparamagnetic single domain threshold 20 25 nm and that the gsd is almost independent of the degree of pedogenesis this observation agrees well with other constraints from previous studies this new gsd model improves our understanding of the pedogenic processes in chinese loess enabling further explicit linkage of environmental magnetism to paleoclimate changes

investigations of the spatial and temporal variations of sr and nd isotopes in sediments from two indian rivers implications to source identification radiogenic isotopes of sr and nd provide crucial information on chemical and physical erosion processes therefore used as tracers for fingerprinting the sources of fluvial sediments moreover elemental geochemistry 87sr 86sr and 143nd 144nd signatures in silicate fractions of sediments primarily reflect intricate controls of characteristics and provenance of sediment a suite of sediment samples collected from two rivers of india narmada large and netravati small were analyzed for elemental concentrations 87sr 86sr and 143nd 144nd in silicate as well as acid leachable fractions 87sr 86sr in acid leachable sediment fractions from both the rivers 0 7094 0 0002 for narmada and 0 7158 0 003 for netravati showed more radiogenic 87sr 86sr in netravati compared to narmada indicating influence of source rocks in their watersheds weak correlation of sedimentary 87sr 86sr and 143nd 144nd with al and chemical index of alteration cia in silicate fraction indicate that isotopic compositions are primarily controlled by their sources and not by chemical weathering in both the rivers provenance of sediments in narmada is dominated by their supply from deccan deposits with secondary supply from mid late proterozoic vindhyan along with mesoproterozoic to mesoarchean tdmnd ages sediments from netravati reflected signatures of peninsular gneisses dominant with gneisses schists and granodiorite along with paleoarchean tdmnd ages based on variability of 87sr 86sr and 143nd 144nd present study highlight that sediment supplies from tributaries to the mainstream in narmada is inadequate as compared to that in netravati 87sr 86sr and 143nd 144nd signatures in narmada and netravati are comparable with global rivers this article is protected by copyright all rights reserved

volcanogenic upwelling of anoxic nutrient rich water a possible factor in carbonate bank reef demise and benthic faunal extinctions the middle cretaceous oceans were characterized by widespread anoxia high sea levels reef carbonate bank extinctions and at least in the pacific by intense widespread mid plate volcanism the demise of reefs on numerous pacific atolls has left a large number of guyots this synthesis explores the possibility that the middle cretaceous demise of mid pacific and other carbonate bank communities and related extinctions elsewhere reflects sporadic possibly volcanogenic upwelling of anoxic water the upwelling would have had to be rapid enough to overwhelm surface reoxygenation and frequent widespread enough to suppress recolonization according to the hallock schlager hypothesis upwelling of nutrient rich waters destroyed the carbonate bank communities nutrient excess and anoxia may well have worked together the globally widespread presence of at least mid depth anoxia h 2 s is reasonably well established the cenomanian turonian oceanic anoxic event perhaps was an extreme example as is the mortality of modern benthic invertebrates at o 2 levels below about 0 15 ml l recolonization times for modern reef corals imply that upwelling catastrophes if localized need have recurred on approximately decade time scales previously postulated cretaceous sea level fluctuations raising sea level at rates on the order of 5 10 m in 10 4 10 5 yr would then have sufficed to carry the intermittently stressed reef surfaces below the 5 to 10 m deep high carbonate production zone below which reef recovery chances diminish thus the episode of frequent localized but widespread upwelling events need have lasted only about 10 4 10 5 yr although intermittent deep water ventilation is known to have occurred on milankovitch time scales during the cretaceous thereby bringing anoxic and or nutrient rich waters to the surface geologic and ocean modeling evidence is necessary to establish whether a significant amount of rapid upwelling did or could occur because mid plate submarine volcanism was widespread and intense in the middle cretaceous pacific volcanogenic hydrothermal heating and entrainment of nutrient rich anoxic waters is one possible mechanism for catastrophic buoyant upwelling rudistid bank extinction and guyot formation the efficacy of this process depends principally on the buoyancy that is heat energy flux and the buoyancy brunt vaisala frequency typical hydrothermal plumes along the mid oceanic ridge axis rise only to 150 to 400 m heights above the sea floor but megaplumes rising 1 000 m are known simple plume models imply that only basalt eruptions comparable to the largest historically known would be sufficiently energetic 10 12 10 14 j s to bring bottom water to the ocean surface from normal mid oceanic ridge axial depths 3 km over much of the present ocean however these models are conservative through neglect of momentum overshoot and gas exsolution to the extent that higher eruption rates and lower brunt vaisala frequencies due to lower vertical temperature gradients prevailed in the middle cretaceous pacific anoxic deep waters would more readily have reached the ocean surface most cretaceous guyots are now in the north pacific but were carried across the equator by pacific plate motion normal tendencies to upwelling and oxygen deficiency along the equator would have made the carbonate banks most vulnerable during their equatorial transit

age limit and age underestimation using different osl signals from lacustrine quartz and polymineral fine grains as part of a systematic palaeohydrological reconstruction of lake level fluctuations during the last glacial maximum a transect of cores from ancient lake xinias in centra greece has already been studied with respect to pollen sediment and mineral magnetic analyses the chronology was based on c 14 ams dating of terrestrial plant macrofossil remains from peat and clayey peat palaeogeog palaeoclimatol palaeoecol 158 2000 65 this site thus provides an opportunity for the comparison of fine grain optically stimulated luminescence osl ages of water lain sediments with an independent chronology we present here infrared ir post ir blue and blue osl characteristics of the fine grain sediments from lake xinias and a preliminary comparison with independent ages the equivalent doses based on the ir results are about 40 of those based on post ir blue stimulation which in turn are 10 15 below those based on quartz osl we discuss the ages derived from the 3 signals in terms of the independent chronology and draw conclusions about initial bleaching of the quartz and feldspar components and the reliability of the post ir blue signal as a chronometer c 2003 elsevier science ltd all rights reserved less

holocene environmental reconstruction of sediment source linkages at crummock water english lake district based on magnetic measurements to reconstruct lateglacial and holocene environmental changes in the british uplands two c 5 8 m long sediment cores from crummock water nw england together with several hundred soil samples from the crummock water catchment were studied using magnetic techniques optically stimulated luminescence osl dating using fine silt quartz and 14c dating of terrestrial plant macrofossils were used to establish a chronology for the lake sediments a good agreement between optical and 14c ages indicates first that the osl dating method can be used to date lake sediments in the british isles second that macrofossil based 14c dating can be used to avoid the problem of old carbon error associated with bulk sample 14c dating of lake sediments and third that the established chronology is robust the lake sediment magnetic properties indicate a series of changes in sediment composition during the holocene which correlate well with sediment lithology water content and weight loss on ignition the first change corresponds to the lateglacial postglacial climatic shift at around 11400 years ago the subsequent suite of changes corresponds to a probable regional onset of human activity at 2000 bc and particularly to the intensification of human activity at around ad 900 a comparison of the lake sediment magnetic properties and those of the catchment soils shows a clear linkage for the lateglacial period and for the period after ad 900 in contrast detailed magnetic measurements of the early through mid holocene sediments suggest that their magnetic properties are dominated by bacterial magnetosomes

bacterial magnetite and the magnetic properties of sediments in a swedish lake a comparison of the magnetic properties of lake sediments and catchment materials from pajep njakajaure north sweden demonstrates that high concentrations of single domain sd magnetite in the upper 70 cm of gyttja in the deepest part of the basin are not of detrital origin tem and light microscope examination revealed the existence of bacterial cells and magnetosomes in the upper sediments which are responsible for the presence of the sd magnetite most of the fossil magnetosomes appear to have been dissolved through reductive processes at lower depths although some are preserved in the lower sediments and carry a post depositional remanent magnetization pdrm the results highlight the complex effects of post depositional processes on mineral magnetic assemblages and natural remanent magnetization aquisition and demonstrate how mineral magnetic measurements may be used to identify magnetic grain size changes brought about by sediment diagenesis

the deccan tholeiite lavas and dykes of ghatkopar powai area mumbai panvel flexure zone geochemistry stratigraphic status and tectonic significance abstract mumbai city situated on the western indian coast is well known for exposures of late stage deccan pillow basalts and spilites pyroclastic rocks rhyolite lavas and trachyte intrusions these rock units and a little studied sequence of tholeiitic flows and dykes in the eastern part of mumbai city constitute the west dipping limb of a regional tectonic structure called the panvel flexure here we present field petrographic major and trace element and sr nd isotopic data on these tholeiitic flows and dykes best exposed in the ghatkopar powai area the flows closely resemble the mahabaleshwar formation of the thick western ghats sequence to the east in sr nd isotopic ratios and multielement patterns but have other geochemical characteristics e g incompatible trace element ratios unlike the mahabaleshwar or any other formation the flows may have originated from a nearby eruptive center possibly offshore of mumbai two dykes resemble the ambenali formation of the western ghats in all geochemical characteristics though they may not represent feeders of the ambenali formation lavas most dykes are distinct from any of the western ghats stratigraphic units some show partial e g sr nd isotopic similarities to the mahabaleshwar formation and these include several dykes with unusual concave downward ree patterns suggesting residual amphibole and thus a lithospheric source the flows and dykes are inferred to have undergone little or no contamination by lower continental crust most dykes are almost vertical suggesting emplacement after the formation of the panvel flexure and indicate considerable east west lithospheric extension during this late but magmatically vigorous stage of deccan volcanism

infra red stimulated luminescence dating of holocene reworked silty sediments abstract infra red stimulated luminescence irsl ages are reported for holocene colluvial lacustrine and alluvial sediments and late glacial loess for colluvial sediments irsl ages concur with independent ages age overestimation occur in the case of very poorly bleached sediments such as young less than 2000 years floodloams for which a high suspended sediment load was deduced from sedimentation rates and actually observed floods age underestimates are observed for late glacial loess probably due to inadequate preheat procedures

bacterial magnetite in swedish varved lake sediments a potential bio marker of environmental change abstract detailed mineral magnetic measurements were carried out on three varved lake sediment sequences in sweden which extend to ca 7000 bc the comparison of the magnetic properties of the organic rich varved lake sediments with their respective catchment materials indicates that the magnetic properties of the sediments are dominated by relatively high concentrations of single domain magnetite magnetosomes produced by magnetotactic bacteria the dimictic nature of the lakes which help form and preserve the varves due to the weakly oxic or suboxic environment also appear to be suitable for a high degree of magnetosome preservation the concentration of the magnetosomes in two of the sequences as determined by mass specific magnetic measurements exhibits a positive linear relationship with the total organic carbon content and suggests that magnetic remanence measurements reflect lake productivity via processes of organic matter accumulation and decomposition further research should focus on the potential to use the fossil magnetosomes as proxy climate environmental change indicators and as recorders of geomagnetic field variations and behaviour

catchment hydro geomorphological responses to environmental change in the southern uplands of scotland lake sediment and geomorphic evidence from the loch of the lowes st mary s loch basin in the central southern uplands of scotland provide a multiproxy reconstruction of changing sediment availability and transmission through the catchment interrogation of magnetic geochemical and grain size parameters for lake and catchment materials suggests it is possible to identify independent proxies that reflect both supply availability and discharge capacity controls on the sediment signal chronological control for the lake sediment record is proposed by linking a 210pb 137cs chronology for the last c 120 yr to an age depth profile based on proposed temporal correlations between cyclic hirm lf variability and the north atlantic oscillation geochronological studies on debris cones and alluvial fans yield evidence for episodic hillslope gullying 2000 0 bc with more extensive region wide slope instability ad 700 900 1100 1300 and after ad 1450 1550 and gully stabilization over the last 150 years the latter two episodes coincide with the lake sediment evidence for increased sediment supply from ad 1600 declining after ad 1870 the capacity related lake proxies appear to identify phases of increased flooding ad 1625 1650 1680 1700 1730 1760 1800 1815 1850 1880 1910 1930 1960 1970 and possibly the 1990s close correspondence between the sediment flood archive and historical records of flooding in scotland suggests that lake catchment systems of this type have the potential to yield valuable information on past hydrological response

testing a cellular modelling approach to simulating late holocene sediment and water transfer from catchment to lake in the french alps since 1826 this paper describes the application of a hydrogeomorphological numerical model caesar to simulate at hourly time steps changes in the hydrological and sediment regime of the petit lac d annecy catch ment the outputs of the model were validated in three ways in the short term 5 years water discharge out puts were compared against observed instrumental data over the longer term modelled sediment discharge ad 1825 2005 was compared with proxies for detrital sediment influx environmental magnetism and accumu lation rates discerned from a 210 pb chronology for the lake sediments finally spatial validation of the modelled erosion and deposition of sediment was undertaken by comparison with a field and remotely sensed survey of catchment geomorphology the results suggest that while minor perturbations in forest cover during the last 180 years have partially conditioned the response of the sediment system the bulk of modelled sediment discharge and particularly the peaks in sediment discharge were controlled by flood duration and magnitude which in turn is driven by precipitation storms floods and snowmelt basin geometry and geomorphology of each sub catchment ire and tamie were also important in producing differences in the modelled sediment discharge in essence these differences were a function of sediment accommodation space and the ability of each system to store and release sediments modelled sediment discharge and para lake sediments display similar histories and thus are both interpreted as reflecting variations in detrital sediment supply intriguingly the style of mod elled sediment discharge from the ire a confined mountain torrent displays a greater similarity to and perhaps dominates the lake sediment record these results provide partial validation of the caesar model and indi cate that perhaps in the future it may be used as an exploratory and predictive tool in determining the impact of changes in climate meteorology and land use on lake catchment systems

constraints on the mantle sources of the deccan traps from the petrology and geochemistry of the basalts of gujarat state western india the late cretaceous early tertiary flood basalts in the gujarat area of the northwestern deccan traps kathiawar peninsula pavagadh hills and rajpipla exhibit a wide range of compositions from picrite basalts to rhyolites moreover the basaltic rocks have clearly distinct tio2 contents at any given degree of differentiation and strongly resemble the low titanium and hightitanium basalts found in most of the gondwana continental flood basalt cfb suites four magma groups are petrologically and geochemically distinguished 1 a low ti group characterized by rocks with varying sio2 saturation and with tio2 1 8 wt in picrites nb 19 p p m zr av 6 5 and tt v av 47 3 an intermediate ti group with tio2 contents slightly lower than the high ti rocks at the same degree of evolution and with correspondingly lower incompatible trace element contents and ratios in particular k2o nb ba and zr y av 5 2 4 a potassium rich group kt broadly similar in geochemical character to the high ti group but showing more extreme k rb and ba enrichment av k20 na20 l ba y 20 the most primitive low ti and high ti picrites when corrected for low pressure olivine fractionation show distinct major and trace element geochemistry in particular for cao ai2o3 cao tio2 and al2o3 tio2 and moderate but significant variations in their sio2 and fe2ost contents these characteristics strongly suggest the involvement of different mantle sources more depleted for the low ti picrites and richer in cpxfor the high ti picrites but with broadly the same pressures of equilibration 27 14 kbar this in turn suggests a strong lateral heterogeneity in the gujarat trap mantle low ti picrites and related differentiates in kathiawar are reported systematically for the first time here and suggest the existence of hfse depleted mantle in the northwestern deccan traps with extension at least to the seychelles islands and to the area of the bushe formation near bombay in the pre drift position before the development of the carlsberg ridge the absence of correlations between lile hfse ratios and sio2 argues against crustal contamination processes acting on the low ti picrites possibly owing to their probably rapid uprise to the surface consequently the mantle region of this rock group was probably re enriched by small amounts of ule rich materials the substantially higher trace element enrichment of the least differentiated high ti picrites relative to the basalts of the ambe noli and mahableshwar formations of the western ghats testifies also to the presence of more incompatible element rich oib4ike mantle sources in northern and northwestern gujarat these sources were geochemicaily similar to the present day reunion mantle sources

the detection of bacterial magnetite in recent sediments of lake chiemsee southern germany the sediments of lake chiemsee located in the alpine foreland in southern germany host a variety of magnetotactic bacteria mtb which contain intracellular crystals of magnetite arranged in linear chains to detect bacterial magnetite in the carbonate dominated surface sediments and further quantify its contribution to the magnetic signal of the sediments we conducted detailed rock magnetic measurements as well as complimentary non magnetic analyses electron microscopy powder x ray diffraction and sediment pore water analysis our results demonstrate that biogenic single domain magnetite characterized by bullet and truncated hexagonal prismatic shapes is the dominant ferrimagnetic component in the topmost few centimetres of the sediment the changes of magnetic properties with depth are due to the occurrence of live mtb and the downward increasing dissolution of biogenic magnetite moreover the ratios of remanence loss on warming through the verwey transition after field cooling and zero field cooling of saturation isothermal remanence dfc dzfc were determined as 1 47 and 1 25 for freeze dried and air dried sediment samples containing mtb respectively these low ratios suggest that the bacterial magnetite chains were disrupted to a large extent and or that the bacterial magnetosomes might have undergone partial

lake sediments erosion and landscape change during the holocene in britain and ireland abstract lakes are excellent repositories of air borne and especially stream borne materials it has long been recognised that lake sediments contain a strong record of catchment soils via the inputs of minerogenic and chemical erosional products to these may be added a variety of palaeoecological indicators including pollen fungi sphagnum leaves and faunal remains pollen analysis in particular enables land use change to be assessed over many millennia and demonstrates the landscape impacts of woodland clearance grazing and crop cultivation radiocarbon dating provides a chronology for environmental and agricultural change and acts as an indicator of erosion in its own right the use of such indicators to reconstruct past instances and patterns of erosion is demonstrated with reference mainly to 50 british and irish lake sites and especially those which have produced signals of erosion in the form of accelerated sediment accumulation and inversed or reversed sequences of radiocarbon dates during the mid and late holocene sites displaying even or decreased sedimentation through time are concentrated in northern and northwestern scotland and have either no clear signs of human impact or only so towards the latter part of the holocene this pattern probably reflects a combination of factors including low population densities thin soils and the sealing effect of blanket peat in contrast all sites with accelerated erosion have indications of anthropogenic impact this is often prior to levels of increased sedimentation showing a delay in system response while the spread of dates for the start of the rise in sediment accumulation spans 6200 940 bp three clusters are evident at 5295 4970 4530 4235 and 2980 2810 bp radiocarbon inversions mostly reversals are evident for 18 sites no obvious causal patterning is indicated and they probably demonstrate no more than the fact that catchment soils including peats around a particular site were pushed beyond an erosional threshold sufficient to age the sediments deposited within the lakes it is hoped that improvements in data quality will allow the refinement of such exercises in the future and that lakes will be valued as repositories of long term landscape sensitivity

geochemistry of flood basalts of the toranmal section northern deccan traps india implications for regional deccan stratigraphy unpublished data 1998 andthe southeastern deccan particularly the poladpur andambenali formations mitchell widdowson 1991 bilgrami 1999 for as much as 350 km from their south western type sections in addition lavas isotopically andchemicallyequivalenttothoseoftheambenaliformation fm arepresentinthenortheastern sectoroftheprovinceas far as 900 km from their southwesternmost counter parts mahoney 1988 deshmukh

flood stratigraphies in lake sediments a review abstract records of the frequency and magnitude of floods are needed on centennial or millennial timescales to place increases in their occurrence and intensity into a longer term context than is available from gauged river flow and historical records recent research has highlighted the potential for lake sediment sequences to act as a relatively untapped archive of high magnitude floods over these longer timescales abyssal lake sediments can record past floods in the form of coarser grained laminations that reflect the capacity for river flows with greater hydrodynamic energy to transport larger particles into the lake this paper presents a framework for investigating flood stratigraphies in lakes by reviewing the conditioning mechanisms in the lake and catchment outlining the key analytical techniques used to recover flood records and highlighting the importance of appropriate field site and methodology selection the processes of sediment movement from watershed to lake bed are complex meaning relationships between measureable sedimentary characteristics and associated river discharge are not always clear stratigraphical palaeoflood records are all affected to some degree by catchment conditioning fluvial connectivity sequencing of high flows delta dynamics as well as within lake processes including river plume dispersal sediment focussing re suspension and trapping efficiency with regard to analytical techniques the potential for direct e g laser granulometry and indirect e g geochemical elemental ratios measurements of particle size to reflect variations in river discharge is confirmed we recommend care when interpreting fine resolution geochemical data acquired via micro scale x ray fluorescence xrf core scanning due to variable down core water and organic matter content altering x ray attenuation we also recommend accounting for changes in sediment supply through time as new or differing sources of sediment release may affect the hydrodynamic relationship between particle size and or geochemistry with stream power where these processes are considered and suitable dating control is obtained discrete historical floods can be identified and characterised using palaeolimnological evidence we outline a protocol for selecting suitable lakes and coring sites that integrates environmental setting sediment transfer processes and depositional mechanisms to act as a rapid reference for future research into lacustrine palaeoflood records we also present an interpretational protocol illustrating the analytical techniques available to palaeoflood researchers to demonstrate their utility we review five case studies of palaeoflood reconstructions from lakes in geographically varied regions these show how lakes of different sizes and geomorphological contexts can produce comprehensive palaeoflood records these were achieved by consistently applying site validated direct and proxy grain size measurements well established chronologies validation of the proxy process interpretation and calibration of the palaeoflood record against instrumental or historical records

the superparamagnetism of yucca mountain tuff yucca mountain tuff contains small titanomagnetite grains with narrow size distributions in the superparamagnetic range schlinger et al 1988 magnetic measurements on three samples comprising hysteresis loops at low and ambient temperatures acquisition and demagnetization of isothermal remanent magnetization thermal demagnetization of the saturation remanence and of a low temperature thermoremanence and frequency and temperature dependent susceptibilities allow evaluation of the magnetic properties in terms of neel s 1949 single domain theory precise grain volume distributions have been obtained by applying the blocking volume concept to thermal demagnetization results in contrast an attempt to derive mean particle volumes by fitting a langevin curve to the room temperature magnetization curves fails probably because the precondition for the langevin function kv kt 1 is not met it is only for the sample with the smallest grains and in weak fields 20 mt that a langevin fit provides a reasonable volume estimate there is good agreement between the experimental results and the calculated frequency and temperature dependence of susceptibility thus verifying that neel s theory is sufficient for the magnetic description of single domain assemblages spanning the superparamagnetic stable single domain boundary however some deviations between modeled and measured susceptibilities exist and the physical causes may include size dependent anisotropy nonuniform magnetizations and also an uncertain preexponential time constant 0 while 0 10 11 s gives the best fit for the sample with the largest grains 0 10 9 s is more reasonable for the others thus 0 may indeed be size and temperature dependent as predicted by brown 1959 the commonly cited parameter fd frequency dependence of susceptibility reaches 30 at room temperature rt for one sample with a blocking temperatures just below rt while fd 0 at rt for a superparamagnetic sample with smaller grains these results thus exemplify that fd is not limited to 15 as a number of studies suggest and that fd 0 must not be taken to imply the absence of superparamagnetic grains

high resolution seismic imaging of a younger dryas and holocene mass movement complex in glacial lake windermere uk the stratigraphy and sedimentological processes operating over the last 15 000 years within glacial lake windermere uk at the mouth of cunsey beck were imaged by a decimetre resolution seismic reflection survey a complex of fifteen mass movement deposits was identified as contemporaneous with the younger dryas and two within the overlying holocene drape the high vertical resolution and dense grid of profiles allowed pseudo three dimensional mapping of individual events along with the determination of their relative temporal relationships the size of the mass wasting deposits has been estimated to range between 2100 and 100 000 m3 the geometry structure and relationship to the existing stratigraphy suggest a rapid emplacement of the younger dryas mass movement deposits facilitated by climatic changes making subaqueous slopes unstable with possible triggering by seismic activity morphometric parameters such as volume and planar surface area indicate a greater mobility of the younger dryas mass movement deposits compared to the holocene events the sediments of all imaged mass movement deposits are believed to originate from the slope deposits of the lake the age of two holocene mass movement deposits triggered by flooding or terrestrial debris flows is estimated to be 2400 and 4400 years bp

all age depth models are wrong but how badly the uncertainty and error associated with fitted age depth models were investigated by fitting a range of models to sets of simulated radiocarbon dates based on varved sediments and comparing the modelled relationship with the varve timescale with large numbers of dates cubic smooth splines out perform other models with few dates no model reliably provides a good fit to reality and calculated confidence intervals are over optimistic c 2003 elsevier ltd all rights reserved

source and differentiation of deccan trap lavas implications of geochemical and mineral chemical variations the basalt stratigraphy of the deccan trap between mahabaleshwar ghat and belgaum over steps the basement from north to south sr isotope and zr nb ratios and sr rb and ba concentrations correlate portions of the post poladpur stratigraphy over 250 km along the western ghats thereby confirming a southerly component of dip of 0 06 at the southwestern margin the stratigraphy extends upwards from the compositionally uniform ambenali formation cox hawkesworth 1984 into a sequence of grossly heterogeneous flow units which have been allocated to the mahabaleshwar and panhala formations lightfoot hawkesworth 1988 the mahabaleshwar formation is represented only by a sequence of highly fractionated flows termed the kolhapur unit with similar 87sr 86sr0 to the mahabaleshwar 0 7045 but with sr 2 25 succeeding the kolhapur unit are a series of flows with high 87sr 86sr0 0 7045 0 705 zr nb 13 and low sr 230 but trace element concentrations similar to the mahabaleshwar formation these have been allocated to the desur unit of the panhala geochemical variations in flows overlying the ambenali define two distinct trends one is attributed to gabbro fractionation and the other to variations in the compositions of the parental magmas and arguably their source regions there is little evidence for significant crustal contamination in these flows and the degree of fractionation and the composition of the phase extract are shown to vary along strike within the mahabaleshwar formation the high tio2 content of kolhapur unit flows is shown to be the result of shallow level gabbro fractionation rather than the presence of a primitive high ti magma mahabaleshwar formation basalts exhibit a broad negative correlation between the degree of fractionation and sr isotopic composition the endmember with lower 87sr 86sr0 has different zr y from the ambenali basalts and would appear to have been generated by lower degrees of melting of a similar source the other endmember has more radiogenic sr lower zr nb similar zr y but higher mg number the simplest interpretation is that these magmas were more primitive and hence hotter and more able to interact with the lithosphere en route to the surface and that they then mixed to produce the mahabaleshwar array the panhala formation basalts plot on the sr nd array defined by the mahabaleshwar formation and the desur unit basalts plot on an extension of this array this suggests that the source characteristics are also lithospheric the absolute elemental abundances may then be a function of melting and fractionation we are impressed by the apparent switch from crustal lithospheric contributions to mantle lithospheric contributions through the stratigraphy and suggest that this together with the more protracted fractionation of the magma reflects a change in the availability of the lithospheric components accompanying the southerly migration of the volcanic edifice

k t transition in deccan traps of central india marks major marine seaway across india deccan intertrappean sediments in central india are generally considered as terrestrial deposits of maastrichtian age but the cretaceous tertiary k t position is still unknown here we report the discovery of the k t transition a marine incursion and environmental changes preserved within the intertrappean sediments at jhilmili chhindwara district madhya pradesh integrative biostratigraphic sedimentologic mineralogic and chemostratigraphic analyses reveal the basal danian in the intertrappean sediments between lower and upper trap basalts that regionally correspond to c29r and the c29r c29n transition respectively intertrappean deposition occurred in predominantly terrestrial semi humid to arid environments but a short aquatic interval of fresh water ponds and lakes followed by shallow coastal marine conditions with brackish marine ostracods and early danian zone p1a planktic foraminifera mark this interval very close to the k t boundary this marine incursion marks the existence of a nearby seaway probably extending inland from the west through the narmada and tapti rift valleys the jhilmili results thus identify the k t boundary near the end of the main phase of deccan eruptions and indicate that a major seaway extended at least 800 km across india

hillslope gullying in the solway firth morecambe bay region great britain responses to human impact and or climatic deterioration abstract in the solway firth morecambe bay region of great britain there is evidence for heightened hillslope instability during the late holocene after 3000 cal bp little or no hillslope geomorphic activity has been identified occurring during the early holocene but there is abundant evidence for late holocene hillslope erosion gullying and associated alluvial fan and valley floor deposition interpretation of the regional radiocarbon chronology available from organic matter buried beneath alluvial fan units suggests much of this geomorphic activity can be attributed to four phases of more extensive gullying identified after 2500 2200 1300 1000 1000 800 and 500 cal bp both climate and human impact models can be evoked to explain the crossing of geomorphic thresholds and palaeoecological data on climatic change bog surface wetness and human impact pollen together with archaeological and documentary evidence of landscape history provide a context for addressing the causes of late holocene geomorphic instability high magnitude storm events are the primary agent responsible for gully incision but neither such events nor cooler wetter climatic episodes appear to have produced gully systems in the region before 3000 cal bp increased gullying after 2500 2200 cal bp coincides with population expansion during iron age and romano british times the widespread and extensive gullying after 1300 1000 cal bp and after 1000 800 cal bp coincides with periods of population expansion and a growing rural economy identified during norse times 9 10th centuries ad and during the medieval period 12 13th centuries ad these periods were separated by a downturn associated with the harrying of the north ad 1069 to 1070 the gullying episode after 500 cal bp also coincides with increased anthropogenic pressure on the uplands with population growth and agricultural expansion after ad 1500 following 150 years of malaise caused by livestock and human the black death plagues poor harvests and conflicts on the scottish english border the increased susceptibility to erosion of gullies is a response to increased anthropogenic pressure on upland hillslopes during the late holocene and the role of this pressure appears crucial in priming hillslopes before subsequent major storm events in particular the cycles of expansion and contraction in both population and agriculture appear to have affected the susceptibility of the upland landscape to erosion and the hillslope gullying record in the region therefore contributes to understanding of the timing and spatial pattern of human exploitation of the upland landscape

tholeiitic dykes in the seychelles and the original spatial extent of the deccan we report geochemical data from c deccan age tholeiitic dykes from praslin island in the seychelles a continental fragment which lay adjacent to the coast of india before sea floor spreading started in the arabian sea at 64 ma the dykes have compositions very similar to the distinctive bushe magma type from the deccan and hence constitute the first traces of deccan activity recognized on the seychelles fitting the seychelles and india back together to reconstruct the original extent of the deccan we find that the present estimate of 1 million km 2 needs to be revised upwards by c 25 to account for the deccan magmatism in the seychelles if dipping reflectors found on seismic lines to the northwest of the seychelles are also deccan age flows this would increase still further the area and volume estimates

paleomagnetic constraints on the structure of the deccan traps abstract new paleomagnetic results from two widely separated areas of the deccan traps allow one to test the simple normal reversed normal nrn magnetostratigraphic model previously proposed the new data from the mandla region to the northeast of the main outcrop of the deccan traps together with earlier apparently conflicting results are all compatible with the nrn stratigraphy provided the flows are not strictly horizontal but have a synform antiform structure with 500 m amplitude and 150 km wavelength the structure parallels the paleozoic narmada son rift system with slopes never exceeding 0 5 sampling in rajahmundry a remote southeastern outlier of the deccan with well constrained age allowed identification of the rn boundary in an area where only normal polarities had been reported it has also been possible to correlate the detailed geochemical stratigraphy in the western ghats with the nrn magnetic stratigraphy a compilation of 35 magnetic studies together with the above findings confirms the general applicability of the nrn model and reveals the large scale topography of the rn boundary which is an isochron over most of the deccan the rn isochron surface displays a boomerang shape with topography ranging from sea level to above 1600 m this observed topography is consistent with a simple model in which doming and renewed rifting and dyke intrusion resulted from impingement 70 65 ma ago of the reunion plume under the indian lithosphere the narmada son rift was rejuvenated and a continental rift system with minor extension with a triple junction in the cambay graben resulted and was subsequently covered by the deccan flows although in places tectonic faulting and volcanism continued to interfere the rajahmundry outcrops constrain the original extent and southeastward dip away from the triple junction of much of the traps a significant part of which has now been removed by erosion and rifting away of the seychelles

evidence for changes in holocene sediment flux in semer water and raydale north yorkshire uk article i nfo we present preliminary results from studies carried out in the lake and extensively gullied drainage basin of semer water in north yorkshire england the results obtained so far are limited by physical problems encountered during coring at the present day lake the complex nature of the sedimentary infill upstream in raydale and difficulties experienced in establishing a continuous holocene chronology for the site both magnetic measurements and organic geochemical analyses show that the bulk of the sediment sampled in semer water and in the alluvial area of raydale just upstream is derived from the catchment although in some cases the allochthonous magnetic signature is overprinted by contributions from bacterial magnetosomes growing in the lake or surface sediments significant traces of polyaromatic hydrocarbons pahs in sediments contemporary with the mesolithic occupation of the pennines reinforce evidence from elsewhere for the use of fire at this time several lines of evidence identify a mid holocene period of reduced allochthonous input rapid sediment accumulation during the period between 4200 and 3500 cal bp points to the likelihood of increased erosion during the bronze age geomorphological studies point to periods of alternating dissection and aggradation in the catchment during the last 2000 years the record presented gives some indication of the potential for uniting geomorphological palaeolimnological and organic geochemical research in an effort to trace the holocene evolution of a complex highly eroded system 2008 elsevier b v all rights reserved

sr nd and pb isotopic and chemical compositions of central deccan traps lavas and relation to southwestern deccan stratigraphy abstract sr nd and pb isotopic compositions and major and trace element abundances of lavas in five central deccan traps sections are generally very similar to those of lavas in the southwestern deccan western ghats escarpment the combination of strong isotopic and chemical similarities between lavas of the two regions indicates that they shared a closely similar petrogenesis our results indicate that unlike many lavas in the northeastern deccan most of the lavas studied in the central deccan sections can be grouped into different stratigraphic members and chemical types cts belonging to four formations thakurvadi bhimashankar khandala and poladpur present in the type sections of the western ghats bhimashankar and thakurvadi type lavas are found in a section near outram whereas only khandala type lavas make up the mhaishmal ellora and ajanta sections to the east and only poladpur type lavas are present in the easternmost section at lonar this west east sequence is the same as that seen going upward in the western ghats stratigraphy except that bushe type lavas which are located stratigraphically between the khandala and poladpur formations in the western ghats have not been found in this study overall our results indicate that the khandala and poladpur formations extend over west east distances of more than 300 km and some individual members e g the dhak dongar may extend over as much as 500 km the regional dip from igatpuri in the southwest to lonar in the east central deccan is less than 0 5 to the east which is similar to the southward regional dip in the southwestern deccan near horizontal flows in the central and southwestern deccan areas suggest that post deccan tectonic activity has had limited effects on the studied area large volumes of basaltic lavas derived from eruptive centers in the western deccan may have covered both the central and southwestern deccan areas

the mount pavagadh volcanic suite deccan traps geochemical stratigraphy and magmatic evolution abstract the patterns of eruption and dispersal of flood basalt lavas on the surface or as magmas in dykes and sills within the crust determine the volcanological and stratigraphic development of flood basalt provinces this is a geochemical and sr isotopic study of lavas of varied compositions that outcrop around mount pavagadh 829 m deccan traps an important outlier north of the main basalt outcrop most of the 550 m thick exposed section at pavagadh is made up of subalkalic basalts rich in the incompatible elements particularly nb ba and sr picrite and rhyolite dacite flows also occur the latter capping the sequence the relatively high initial 87sr 86sr ratios up to 0 7083 and chemical characteristics of the rhyolitic rocks of pavagadh are consistent with a small but significant involvement of the granitic basement crust in their genesis an assimilation fractional crystallization afc model involving the picrite lava and either a southern indian or a western indian granite as the contaminant explains the geochemical and sr isotopic variation in the basalts and the rhyolites quite well a systematic comparison of the basaltic lavas with binary plots normalized multielement patterns and discriminant function analysis to the well established lava stratigraphy of the western ghats 400 500 km to the south precludes any chemical genetic relationships between the two basalts exposed in sections closer to pavagadh 150 200 km in the toranmal navagam and barwani mhow areas have several flows with some similar chemical characteristics however the pavagadh sequence is significantly different from all of these sequences geochemically petrogenetically and in magnetic polarity to be considered independently built this result is significant in terms of eruptive models for the deccan traps as it is increasingly apparent that there were separate but possibly coeval eruptive centers with their own distinctive chemistries developed in various areas of this vast province

a geological map of the southern deccan traps india and its structural implications a geological map of an area of over 125 000 km 2 within the southern deccan traps india is presented which is based upon variations in the basalt geochemistry it represents a synthesis of new data and earlier work the use of large data sets has allowed stratigraphic boundaries to be established with greater accuracy over a much larger area than before the geochemical sections demonstrate that the southward overstepping stratigraphic style encountered along the ghats ridge has an essentially north to south polarity and that there appears to be detectable overstep in an east to west sense however the stratigraphy defines a pronounced coastward dipping monoclinal flexure across the western ghats ridge between 16 n and 18 n the data are consistent with two models of eruption the first considers the deccan eruptive focus to have been fixed throughout the volcanic episode producing an essentially annular flow pattern the second considers the flow pattern to have been generated from a southerly migrating eruptive centre resulting from the northerly drift of india over a fixed hotspot both hypotheses are consistent with recent quantitative models which suggest that rapid and voluminous flood basalt eruptions are the result of continental rifting events associated with plume generated thermal 9highs9 until a causal link between established plume hotspot trails and impact sites can be satisfactorily demonstrated we find it unnecessary to invoke a cataclysmic impact event as an explanation for the deccan eruptions

the geomorphological impact of loch lomond younger dryas stadial plateau icefields in the central lake district northwest england detailed geomorphological mapping has revealed evidence for the development of plateau icefields in the central fells of the english lake district during the loch lomond younger dryas stadial ca 12 9 11 5 ka the largest plateau icefield system which covered an area of approximately 55 km2 including outlet glaciers was centred on high raise to the west smaller plateau icefields developed on grey knotts brandreth and dale head covering areas of 7 km2 and 3 km2 respectively the geomorphological impact of these plateau icefields appears to have been minimal on the summits where the survival of blockfields and other frost weathered debris mostly peat covered implies the existence of at least patches of protective cold based ice ice moulded bedrock at some plateau edges however documents a transition to wet based erosive conditions prominent moraine systems were produced by outlet glaciers which descended into the surrounding valleys where their margins became sediment traps for supraglacial debris and inwash in some valleys ice marginal moraines record successive positions of outlet glaciers which actively back wasted towards their plateau source this interpretation differs from that of previous workers who assumed an alpine style of glaciation with reconstructed glaciers emanating from corries and valley heads it is likely that plateau icefields were more common at this time in upland britain than hitherto has been appreciated

chemical discrimination of columbia river basalt flows 1 the homogeneity and distinctive chemical composition of individual columbia river basalt flows are illustrated in a series of chemical plots and the procedure for flow identification is outlined the unique characterization of many individual eruptions permits units to be mapped from feeder dike to flow margins across the columbia plateau for hundreds of kilometers and so provides critical constraints on the physical and chemical evolution of this continental flood basalt province

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

optical dating of annually laminated lake sediments a test case from holzmaar germany abstract we present results of an optical dating feasibility study for annually laminated varved lake sediments the fine silt sized clastic fraction of the sediments was extracted stimulated with infrared and the 410 nm emission was detected a multiple aliquot additive dose protocol in combination with a subtraction technique was used for the equivalent dose determinations results are promising only for sediments with high amounts of clastic components for sediments with a high organic component results are inaccurate perhaps due to problems in dose rate calculation we speculate that besides the low concentrations of radio nuclides and disequilibria in the u series dose rate determination procedures are inaccurate for sediments with high contents of biogenic silica sediment compaction seems to account for minor effects only

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

origin of deccan trap lavas evidence from combined trace element and sr nd and pb isotope studies abstract geochemical and isotope results are presented from a new study of the most southern basalts in the deccan trap india three chemical formations are recognised two of which can be correlated with the established stratigraphy in mahabaleshwar and imply a regional southerly dip of 0 06 over a distance of 250 km in detail sr isotope variations within the ambenali and mahabaleshwar formations can be shown to reflect three distinct end members which provide new constraints for petrogenetic models pb isotope data for selected basalts exhibit a wide range with 206 pb 204 pb 16 87 22 45 and a linear correlation on a pb pb diagram the least contaminated ambenali basalts plot within the pb array and interaction with mantle lithosphere involves a shift to less radiogenic pb whereas contamination with crust is characterised by more radiogenic pb unlike the karoo and parana continental flood basalt provinces only four flow units within the southern deccan appear to contain a significant contribution from mantle lithosphere the mahabaleshwar and ambenali formation basalts exhibit a striking negative pb sr isotope trend which is presently regarded as one of the features of interaction with shallow level lithospheric mantle it further suggests that basalts from the walvis ridge kerguelen and ninetyeast ridge all remobilised such shallow level material and that the deccan basalts which were not affected by crustal contamination reflect interaction between asthenospheric material similar to t type morb but related to the reunion hotspot and continental mantle lithosphere of the indian plate

a post k t boundary early palaeocene age for deccan type feeder dykes goa india basaltic dykes exposed along the coast of goa represent the youngest phase of a number of different mafic suites intruding the complex precambrian terrain that forms the pre deccan basement of peninsular india these dykes crop out 50 80 km beyond the southern limits of the deccan continental flood basalt cfb province four of seven sampled dykes were dated using the whole rock 40ar 39ar step heating technique three 40ar 39ar determinations yield palaeocene plateau and isochron ages that clearly indicate an early post cretaceous i e danian age and as a weighted mean average of all four samples yields an age of 62 8 0 2 ma these intrusions are clearly significantly younger than the current estimates for the age range of deccan traps volcanism 65 69 ma the trace element signatures rare earth element patterns and 87sr 86sr ratios of these dykes are consistent with those of the nearby deccan basalts more specifically their geochemical signatures are similar to those of the basalt flows composing the volumetrically important ambenali mahabaleshwar formations which form the uppermost succession wai subgroup of the sw deccan these geochemical and age data demonstrate that deccan type magmatism continued to affect western india for at least 1 2 my after the k t boundary 65 0 0 1 ma and therefore their emplacement places important constraints upon the timing duration and evolution of this much debated cfb province the importance of these dykes is examined within the context of the deccan eruptions and the associated rifting of the western indian margin

basalts of the northeastern deccan traps india isotopic and elemental geochemistry and relation to southwestern deccan stratigraphy the northeastern deccan traps include flows with strong isotopic and elemental affinities to lavas in the southwest as far as 900 km away however many of the northeastern flows show a negative correlation of 206pb 204pb with end t and positive correlation of 206pb 204pb with 87sr 86sr t distinct from any of the isotopic fields for the southwestern formations this array from end t 5 87sr 86sr t 0 7041 206pb 204pb 17 9 to end t 0 87sr 86sr 0 7068 206pb 204pb 20 5 overlaps the ambenali formation fm field and runs toward that of the common signature peng et al 1994 that appears to have been an important magma type in several of the lower formations of the southwest this array appears to represent mixing between an ambenali type and 1 a common signature end member or 2 an end member with even higher 206pb 204pb and 87sr 86sr and lower end than the common signature such mixing has been postulated but not documented previously for the deccan lavas isotopically and chemically indistinguishable from the ambenali fm form the tops of sections near jabalpur and chikaldara beneath them are flows that chemically resemble the poladpur fm which sits immediately below the ambenali in the southwest and several lavas similar to the khandala fm beneath the poladpur and intervening bushe fm in the southwest given the general stratigraphic correspondence with the southwestern sequence many of these northeastern flows may be petrogenetically related to the respective southwestern formations lavas with broadly poladpurand khandala like elemental compositions are also abundant in a thick section south of mhow several other mhow area flows resemble the distinctive bushe fm however nearly all of the poladpur and khandala like northeastern deccan lavas analyzed have higher 206pb 204pb man any southwestern poladpur or khandala fm basalts if they indeed are related petrogenetically to these formations many of the northeastern magmas interacted less with low 206pb 204pb continental material and thus must have erupted from different feeder systems

late holocene environmental change in the howgill fells northwest england abstract new data from chapel beck in the southwest howgill fells combined with existing data support the identification of three phases of extensive hillslope gullying after 2200 between 1250 700 and after 500 cal bp examination of cumulative probability density function cpdf plots of the distribution of calibrated radiocarbon dates confirms the identification of these phases there are differences in the spatial distribution of geomorphic activity between these phases with the c 2200 1800 cal bp episode limited to the western howgill fells in comparison the 1250 700 and post 500 cal bp episodes are more widespread cross region phenomena and affected the more remote central fells pollen and geochemical data reveal several phases of increased human activity in these uplands with small scale temporary clearances during the late bronze age early iron age and more substantial clearances during the late iron age and romano british times 2300 1500 cal bp and these were followed by woodland expansion and decline in human activity during both the mid to late iron age and the period after the roman withdrawal from britain after 1500 cal bp the final substantial woodland clearances occurred from c 1100 900 cal bp after which there has been little woodland recovery a range of pollen sites across the howgill fells indicate that there is spatial variability in the level of human activity and impact iron age romano british woodland clearances appear to have affected the west of the region more than the remote central valleys whereas the later 1100 900 cal bp woodland reduction affected the entire region this pattern is similar to that identified from the geomorphology and demonstrates the importance of pollen sites that record local palaeo vegetation information and the significance of using a series of sites to explore intra regional variability in the vegetation history we suggest that human activity is a critical factor in mediating the late holocene geomorphic record but climate and particularly individual storms are the trigger mechanism responsible for erosion and incision on hillslopes and within the wider fluvial system palaeoclimate data humification and plant macrofossil from peat deposits at archer moss identify shifts to wetter conditions c 3100 2700 2400 1700 1300 1100 and after 650 cal bp and probably reflect increases in summer wetness of these the 2400 1700 1300 1100 and post 650 cal bp wetter phases coincide with increased geomorphic activity and perhaps encouraged incision on hillslopes rendered more susceptible to erosion by the activities of people

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research