origin of maghaemite in chinese loess deposits aeolian or pedogenic maghaemite and magnetite common ferrimagnetic minerals in surficial soils have physical properties which are similar except for the thermal instability of the former utilising this exception a study of thermomagnetic properties has been made to systematically separate these two magnetic components in loess and palaeosol samples from the upper parts of the luochuan section of the central chinese loess plateau this investigation has shown that although maghaemite thermally unstable component occurs in greater amounts in palaeosols ms 0 0187 am2 kg 1 1 1 than in loess units ms 0 0156 am2 kg 1 1 1 in relative terms its contribution to the ferrimagnetic component of magnetisation is higher in the loess units ms 32 2 2 0 than the soils ms 23 5 3 7 such an observation suggests that much of the maghaemite component originates in the aeolian source area with some addition of pedogenic maghaemite occurring in the palaeosols

the preparatory phase of the mw 6 1 2009 l aquila italy normal faulting earthquake traced by foreshock time lapse tomography

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

spatial variations of magnetic susceptibility of chinese loess for the last 600 kyr implications for monsoon evolution 1 we examine spatial variations in magnetic susceptibility ms over the loess plateau in china based on 50 sections in order to identify spatial changes in monsoon climate at key glacial interglacial and interstadial intervals for the last 600 kyr the results indicate strong coherence between ms variations during the interglacial periods and present day precipitation and temperature patterns this suggests that the strength of the summer monsoon had a dominant influence on the ms signals in soils through modulating pedogenic intensity the distribution of ms during glacial periods is characterized by weak s n gradients and rough w e zonal patterns indicating a negligible effect of the summer monsoon interstadial patterns are intermediate between the glacial and interglacial ones interglacial patterns for the last 600 kyr are essentially similar suggesting that the climate regime during these periods has not undergone significant changes and that the east asian summer monsoon has remained the main moisture carrier our estimates of the relative amplitudes of climate oscillations during these time slices are consistent with earlier paleoclimate studies these data associated with the available susceptibility based climofunctions may be used to estimate spatial changes of paleorainfall and paleotemperature for these key periods and hence to test climate models

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

climatic interpretation of a 1 9 ma environmental magnetic record of loess deposition and soil formation in the central eastern pampas of buenos aires argentina abstract much of what we know about quaternary climate has been learned from sedimentary records from the world s oceans with the exception of the extensive studies of the chinese loess paleosol sequence and more recent studies of long lake records there are few long terrestrial climate records particularly from the southern hemisphere the loess record of argentina provides an important opportunity to further our understanding of climate change from a terrestrial environment but its complexity and discontinuity have led to difficulty in formulating a climatological model of depositional and pedogenic processes in this study we present one of the longest and most continuous loess loessoid records from the central eastern pampas of argentina our age model is based on optically stimulated luminescent dates and a paleomagnetic reversal stratigraphy and indicates a basal age around 1 9 ma within the age model uncertainties we characterize the environmental magnetic properties associated with loess deposition and soil formation with respect to wind patterns moisture availability and temperature major changes in magnetic grain size are linked to a differential northward shift of the subtropical high pressure cell during glacial periods we suggest that coarser finer magnetic grains correspond to weaker stronger glacial periods when the high pressure cell is located in a more southerly northerly position and the source region is more proximal distal to our study area an abrupt increase in the ultrafine grained magnetic material around 0 9 ma is related to an increase in moisture transport from the south atlantic driven by an increase in summer sea surface temperatures at the mid pleistocene transition 1 ma in addition to these grain size variations there is a relative decrease in the amount of goethite compared to hematite beginning around 0 5 ma which has been related to the temperature increase observed after the mid brunhes event 450 ka in the epica ice core temperature record a more detailed comparison to insolation indicates that for portions of the record ferrimagnetic minerals are depleted during periods of low insolation this result suggests that argentine loess deposition and soil formation follows a model more similar to the alaskan loess sequences than the chinese loess sequences although further work is needed to validate the models and mechanisms proposed in this study our record indicates that the mineral magnetic properties of the loess and paleosol deposits record major changes in deposition and soil formation and provide insight into possible mechanisms relating to global and or hemispheric climate change

influence of orbital parameters on pleistocene loess deposition in central alaska few long proxy climatic records are available from terrestrial locations the isotope records of pleistocene climate change found in marine cores reflect worldwide ice volume and temperature changes forced by variations in the earth s orbital geometry comparable terrestrial records are rare loess wind deposited silt is perhaps the closest terrestrial analogue to marine sediments in that both result from more or less continuous deposition of fine grained sediment here we examine the hypothesis that mag netic susceptibility variations through loess sections reflect climate forcing we statistically tested cross correlations between high precision orbitally tuned marine oxygen isotope curves recording the past 250 000 yr bp and magnetic susceptibility profiles through a thick loess section in central alaska highly significant p 0 0001 correlations indicate strong thick palaeosols formed in arctic loess during early parts of interglacial periods correspond ing to isotope stages 7 and 5 thinner soils formed during interstadial events corresponding to early stage 7 and stage 3 autocorrelation and time series analysis of the loess data show spectral peaks at 125 000 41 000 and 23 000 yr bp showing for the first time that terrestrial orbital periodicities influenced and are recorded in proxy climatic data from terrestrial aeolian deposits at high latitudes

magnetic indicator of global paleoclimate cycles in siberian loess paleosol sequences abstract the loess paleosol sequences of china siberia alaska and many other regions along with lake sediments and glaciers provide the only accurate paleoclimatic terrestrial records for intervals of thousands to hundreds of thousand years the frequency dependence fd of magnetic susceptibility ms in such sequences has become the leading parameter for analyzing climatic change and milankovitch astronomical periodicity in siberian sequences it is always higher in soil horizons than in loess the enhanced fd parameter in soils is associated with ferromagnetic minerals mostly magnetite produced during pedogenesis the ms and fd parameters of 670 samples from five sections in siberia are reported here inter section correlation is used to produce a combined fd time series for the studied sections chronological control is established by absolute dating and stratigraphic correlation spectral analysis of the fd time series reveals the presence of milankovitch signals at 100 kyr eccentricity 40 kyr obliquity and 23 kyr precession and demonstrates that siberian loess paleosol sequences are excellent continental recorders of long term paleoclimatic changes this suggests that the fd parameter can potentially be used more widely for evaluation of climate periodicity in loess paleosol sequences in other parts of the world

characteristics and genesis of maghemite in chinese loess and paleosols mechanism for magnetic susceptibility enhancement in paleosols abstract morphological characteristics and microstructures of magnetic minerals extracted from chinese loess and paleosols were investigated using powder x ray diffraction xrd and high resolution transmission electron microscopy hrtem our results indicate that maghemite in loess paleosol sequences was transformed from magnetite through oxidation of magnetite maghemite transformed from eolian magnetite during chemical weathering has low angle grain boundaries among maghemite nano crystals some nano crystalline maghemites with nanoporous texture resulted from microbe induced precipitation of magnetite or transformation of poorly crystalline ferric fe oxy hydroxides in presence of fe reducing bacteria aggregates of euhedral maghemite nano crystals were transformed from magnetite magnetosomes both microbe induced nanoporous magnetite and microbe produced magnetite magnetosomes are directly related to microbial activities and pedogenesis of the paleosols it is proposed that the formation of nano crystalline maghemite with superparamagnetic property in paleosol results in the enhancement of magnetic susceptibility although the total amount weight percent of magnetic minerals in both paleosol and loess units is similar our results also show that nano crystalline and nanoporous magnetite grains prefer to transform into maghemite in semi arid soil environments instead of hematite although hematite is a thermodynamically stable phase this result also indicates that a decrease in crystal size will increase stability of maghemite it is also inferred that surface energy of maghemite is lower than that of hematite

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

magnetite dissolution in siliceous sediments 1 magnetite dissolution and consequent loss of magnetization is widely observed in reducing sedimentary environments where the decrease in eh ph values with depth is driven by bacterially mediated degradation of organic carbon we have observed low magnetizations in sediments with elevated pore water silica concentrations that arise from diagenesis of biogenic silica and or silicic volcanic ash these depletions in magnetization are greater than can be accounted for by dilution with magnetite poor sediments and suggest that postdepositional destruction of magnetite has occurred biosiliceous sediments usually also contain elevated concentrations of organic carbon which makes it difficult to separate organic carbon related magnetite dissolution from other possible mechanisms for magnetite dissolution however the extent of magnetite dissolution in the sedimentary sequences that we have studied is not obviously related to the redox state of the environment this suggests that other mechanisms might have given rise to magnetite dissolution in these siliceous sediments thermodynamic calculations indicate that magnetite is unstable under conditions of elevated dissolved silica concentrations and appropriate eh ph conditions and predict that magnetite will break down to produce iron bearing smectite a survey of magnetic susceptibility and pore water geochemical data from widely distributed ocean drilling program sites supports this observed link between high dissolved silica concentrations and low magnetic susceptibilities this observed link also holds for environments with low biogenic silica productivity and low organic carbon content but with high interstitial silica concentrations due to dissolution of silicic volcanic ashes dissolution of magnetite is therefore predicted to be a common feature of siliceous sedimentary environments

magnetic properties of loess deposits in australia and their environmental significance abstract there are vast dry areas in australia but few loess sections have been reported mackenzie s waterholes creek mwc profile in new south wales was the deepest and first dated loess profile in this paper various measurements of magnetic parameters from mwc were carried out and comparison was made with those of luochuan profile which lies in the central chinese loess plateau clp the types of magnetic minerals are similar to the clp magnetite maghemite limonite and hematite however the magnetic properties of the australian aeolian sediment are quite different frequency dependent magnetic susceptibility fd is rather high while values of magnetic susceptibility are low the relative content of hard paramagnetic magnetic components is much higher than clp whereas the content of maghemite and hematite is much less furthermore hard magnetic minerals increase with depth while soft maghemite decrease with depth maghemite is more sensitive than magnetite under pedogenic condition of waterlogged environments it increases along with enhancement of magnetic susceptibility in luochuan section however decreases in mwc profile this very likely indicates that the pedogenesic processes in mwc took place under an environment in which maghemite magnetite were unstable the modern annual precipitation in the mwc area is 924 mm which is about 300 mm higher than that in luochuan that extra moisture may lead mwc to exceed the stable range for maghemite magnetite those minerals therefore were gradually converted to more stable goethite causing magnetic susceptibility to decrease fe and mn nodules are abundant in the lower part of section implying mildly reducing conditions that allowed fe and mn to be mobilised and enriched in near the oxidation front indicating that under waterlogged and reducing conditions wind blown maghemite magnetite were transformed to iron hydroxides such as goethite limonite or other paramagnetic minerals resulting in reduced magnetic susceptibility the susceptibility from most of the section shows a generally positive relationship to the loess particle size and seems to fit the alaskan wind vigor model however fe chemical weathering and movement in mwc suggests that the precondition for the wind vigor model cannot be satisfied and that the susceptibility variation can only be explained by pedogenesis

the regional and temporal significance of primary aeolian magnetic fabrics preserved in alaskan loess abstract the anisotropy of magnetic susceptibility ams data presented herein underscore the resolving power magnetic anisotropy has in non lithified poorly consolidated sediments we turn our attention to primary aeolian sedimentary magnetic fabrics preserved along two coeval loess profiles in central alaska at the halfway house hh3 and gold hill steps ghs2 sites we first demonstrate that published preliminary results along hh1 and hh2 are reproducible moreover the new sample suite the first ever at ghs collected at a higher temporal resolution and statistical confidence permits a better evaluation of the significance of the inferred paleowind directions and their temporal variability the data demonstrate that the resolvability of the magnetic lineation is independent of both the eccentricity of the ams ellipsoid and the strength of the magnetic foliation furthermore the orientations and temporal variability of the most significant magnetic lineations are not artifacts of the data filtering process developed to isolate them we conclude that the temporal variations of inferred paleowind directions along hh3 track paleoclimatic glacial interglacial cycles as well as provide additional constraints to the geochronology of the loess deposit along ghs2 the limited coeval primary magnetic fabrics suggest an influence from a local microclimate not present at the hh site complicating the interpretation of small scale variability in paleowind directions however the overall average paleowind directions are similar to those inferred along hh3 confirming a regional spatial consistency of past surface air circulation

paleomagnetic evidence of a low temperature origin of carbonate in the martian meteorite alh84001 indirect evidence for life on mars has been reported from the study of meteorite alh84001 the formation temperature of the carbonates is controversial some estimates suggest 20 to 80 c whereas others exceed 650 c paleomagnetism can be used to distinguish between these possibilities because heating can remagnetize ferrimagnetic minerals study of two adjacent pyroxene grains from the crushed zone of alh84001 shows that each possesses a stable natural remanent magnetization nrm implying that mars had a substantial magnetic field when the grains cooled however nrm directions from these particles differ implying that the meteorite has not been heated significantly since the formation of the internal crushed zone about 4 billion years ago the carbonate globules postdate this brecciation and thus formed at low temperatures

rock magnetic record of the last glacial interglacial cycle from the kurtak loess section southern siberia summary detailed rock magnetic investigations grain size determination and x ray diffraction were carried out on loess and buried soils of the last glacial interglacial cycle from kurtak southern siberia the susceptibility and the sand fraction of 63 m fluctuate in parallel suggesting that the higher susceptibility values in the loess horizons are mainly associated with the coarse size fraction the frequency dependence of the magnetic susceptibility of the loess and buried soils is very low and uniform indicating the absence of superparamagnetic grains and negligible pedogenically induced enhancement of magnetic susceptibility the magnetic assemblage is dominated by multidomain like magnetite grains maghemite and haematite are also present in the buried soils and loess horizons goethite may have been formed from gleying or waterlogging processes under a cooler and more humid climate the coarse magnetite grains which contribute significantly to magnetic susceptibility are probably carried by valley winds and derived from local sources thus the coarser magnetite grains with higher susceptibility values in the loess horizons could mainly reflect stronger wind intensity during cold and semi arid conditions and the consequent ease with which dense magnetite particles can be transported the lower susceptibility values in the buried soil horizons are mainly caused by weaker wind intensity during interglacial and interstadial periods although post depositional processes associated with gleying modifications are also partially responsible for the observations

multiple origins and interpretations of the magnetic susceptibility signal in chinese wind blown sediments abstract in most chinese loess paleosol sequences high magnetic susceptibility values are found in the soil horizons with low values in the loess layers the susceptibility signal has been widely used as a proxy climatic indicator however both the causes and mechanisms which control susceptibility still remain controversial our recent studies challenge some earlier interpretations of the magnetic susceptibility signal in chinese wind blown sediments first the prevailing hypothesis of pedogenic origin cannot totally account for the susceptibility variations in many sections second in some cases the principal carrier of the magnetization seems not to be the ultrafine pedogenic minerals rather coarse lithogenic magnetic minerals derived from local sources can also contribute significantly to the susceptibility signal finally not all the chinese soils have higher susceptibility values than that of loess or sand layers opposite relationships do exist it is concluded that the source and causes of susceptibility may be different from site to site or even at different times at a given site any single hypothesis cannot completely account for the susceptibility variations in the chinese loess plateau and its surrounding regions besides the previous explanations of carbonate leaching pedogenic processes and organic decomposition the contribution of source materials to magnetic susceptibility must also be taken into account

a revised age for the kawakawa oruanui tephra a key marker for the last glacial maximum in new zealand abstract the kawakawa oruanui tephra kot is a key chronostratigraphic marker in terrestrial and marine deposits of the new zealand nz sector of the southwest pacific erupted early during the last glacial maximum lgm the wide distribution of the kot enables inter regional alignment of proxy records and facilitates comparison between nz climatic variations and those from well dated records elsewhere we present 22 new radiocarbon ages for the kot from sites and materials considered optimal for dating and apply bayesian statistical methods via oxcal4 1 7 that incorporate stratigraphic information to develop a new age probability model for kot the revised calibrated age 2 standard deviations for the eruption of the kot is 25 360 160 cal yr bp the age revision provides a basis for refining marine reservoir ages for the lgm in the southwest pacific

mineral magnetic variation of the jiaodao chinese loess paleosol sequence and its bearing on long term climatic variability 1 to retrieve reliable long term paleoclimatic signals from the chinese loess paleosol sequences deposited over the past 2 6 myr multiparameter mineral magnetic investigations have been conducted on the jiaodao section on the chinese central loess plateau first the lithogenic magnetic components and the pedogenic overprinting were chemically separated by the citrate bicarbonate dithionite cbd method the magnetic properties of the least pedogenically altered loess units and post cbd loess paleosols are dominated by coarse grained lithogenic magnetite increasing degree of pedogenesis increases both the concentration and grain size of pedogenic magnetite maghemite long term changes of the pre cbd magnetic properties suggest a long term decrease in summer monsoon intensity and a long term increase in winter monsoon intensity from the late pliocene to the late pleistocene long term variations of the post cbd magnetic properties suggest an increase in both concentration and grain size of coarse grained lithogenic psd md magnetite grains and hence indicate a long term increase in winter monsoon intensity over that period the coercivity decrease of the lithogenic component for the loess unit l15 may be related to the accelerated uplift of the tibetan plateau and its adjacent regions during the period of l15 deposition from paleosol s5 to loess l1 higher values of coercivity of the lithogenic component occur in typical loess and paleosols and lower values are found at the loess paleosol transition these coercivity variations are thought to be related to significant changes in the source region as well as dust deposition in the loess plateau caused by changes in ice snow or vegetational cover these new results lead to a better understanding of the relationships between the effects of tectonic paleoclimatic and paleoenvironmental processes in northwestern china

magnetostratigraphy and magnetic parameters of a sedimentary sequence in punta san andres buenos aires argentina abstract this contribution focuses on polarity changes and magnetic parameters obtained in late cenozoic sediments exposed on the cliffs in san andres chapadmalal buenos aires province the sedimentary section studied comprises the vorohue san andres miramar and arroyo seco formations the upper layers of vorohue and the base of san andres showed records of normal polarity and were attributed to the gauss normal polarity chron 2 6 ma the main portion of san andres formation appears to have been deposited during lower and middle matuyama polarity chron including the normal polarity subchron olduvai 1 78 2 02 ma miramar formation contains polarity changes that should be assigned to middle matuyama jaramillo 1 05 ma and to jaramillo upper matuyama 0 99 ma the upper portion of the miramar formation and the lower one of the arroyo seco formation show reverse polarity levels and were assigned to the upper matuyama 0 78 ma finally the upper part of arroyo seco formation seems to have been deposited during the brunhes polarity chron

500 000 year paleomagnetic record from new zealand loess abstract a paleomagnetic record of secular variation has been obtained from a 17 4 m long core drilled from loess in north island new zealand three dated rhyolitic tephra occur in the loess core at depths of 1 5 3 4 and 13 0 m with ages of 22 500 42 000 and 370 000 years respectively the base of the core is estimated to be 500 000 years old which makes this the longest continuous loess sequence yet described from the southern hemisphere two periods of anomalously low inclination in the core are correlated with the mungo event ca 35 000 years ago and the emperor event ca 490 000 years ago the blake event ca 115 000 years ago is not recorded