hf isotopic composition and age constraints on the evolution of the archean central uchi subprovince ontario canada the archean uchi subprovince located in the northwestern superior province comprises greenstone belts and granitoid complexes that formed in the course of a multistage history between about 3000 and 2690 ma the earliest volcanic plutonic complexes were assembled into a microcontinent which then progressively grew by the addition of magmatic arcs and tectonic slivers a major compressional orogeny concluded this evolution at around 2700 ma lu hf isotopic compositions for well dated zircon populations from volcanic and plutonic rocks of the central part of the subprovince have hf values that range from 6 1 to 1 4 these results show that the bulk of the province was derived predominantly from depleted mantle sources but there is a superimposed trend showing involvement of the oldest greenstone and crustal sequences in the generation of the youngest magmatic complexes the temporal and isotopic relationships of the uchi subprovince contrast with the situation observed in the southern abitibi greenstone belt which developed within a time span of less than 80 m y in an intraoceanic setting and exhibits quite uniform depleted mantle like isotopic values revealing only very subordinate degrees of recycling of older crust

comparisons between tethyan anorthosite bearing ophiolites and archean anorthosite bearing layered intrusions implications for archean geodynamic processes

early human occupation of iberia the chronological and palaeoclimatic inferences from vallparadis barcelona spain abstract vallparadis is one of the best calibrated and most accurately dated archaeological sites from the european early pleistocene chronological analyses combined with palaeomagnetism esr u series and osl and the biochronology of macro and micromammals are fully consistent and situate the site just above the upper limit of the jaramillo subchron in this article we compare the mandibular first molar m1 of individual adult specimens of mimomys savini recovered from level 10 evt7 at vallparadis with specimens from the stratigraphic sequence at gran dolina atapuerca fuente nueva 3 and barranco leon d orce this comparison allows us to chronostratigraphically relate level 10 at vallparadis with level td5 at gran dolina and to fix the former s chronology to around 0 98 0 95 ma mis 27 and therefore prior to level td6 in which fossil remains of homo antecessor were recovered the chronology of vallparadis and the set of contemporary palaeoclimatic proxies regarding the iberian peninsula strengthen the hypothesis that hominins continuously populated europe at least in iberia throughout the late early pleistocene between the jaramillo subchron and the matuyama brunhes boundary by overcoming the climatic fluctuations and changes to the landscape that occurred during this period

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

geology genesis and metamorphic history of the namew lake ni cu deposit manitoba the namew lake fe ni cu sulfide deposit 60 km south of flin flon manitoba is hosted by an undifferentiated metapyroxenite sill enclosed within early proterozoic orthogneisses and covered by paleozoic sedimentary rocks the namew lake pyroxenite contains a relict igneous mineral assemblage of olivine orthopyroxene clinopyroxene or spinel or sulfides suggesting derivation from a low mg komatiitic or high mg basaltic magma sulfide ore in the namew lake pyroxenite occurs as 3 to 10 mm blebs of disseminated fe ni cu sulfides that accumulated during crystallization of olivine and pyroxene a 0 5 to 5 m thick layer of massive sulfide at the hanging wall contact may represent a gravitationally segregated basal layer of a sill and suggests that the mine stratigraphy is inverted although the massive sulfides were compositionally modified during metamorphism and supergene alteration the disseminated sulfides exhibit coherent geochemical trends and may preserve the average composition of the sulfide melt recalculated to 100 sulfide ca 36 s 42 fe 16 ni 6 1 cu 0 23 zn 148 ppm pb 5 300 ppb pd and 88 ppb ir assuming a silicate sulfide mass ratio of ca 560 calculated from the platinum group element pge contents the ni content of a parental magma that would be in equilibrium with sulfides of that composition is similar to that of typical komatiites but the cu zn and pb concentrations are much higher thus a komatiitic magma with ordinary ni and pge contents may have partially assimilated volcanogenic cu zn pb sulfides resulting in a high mg basaltic magma from which the silicates and sulfides subsequently crystallized and equilibrated the namew lake pyroxenite and associated sulfides were affected by five phases of deformation and three phases of metamorphism the first deformational event in the area d 1 involved migmatization and isoclinal folding at upper amphibolite facies conditions in addition sheeted tonalites and diorites intruded prior to or during d 1 d 2 folded the gneisses into domes synforms and antiforms d 3 involved minor boudinage of the pyroxenite intrusion of dikes and displacement of the sulfides updip d 4 shearing locally increased the thickness of the pyroxenite d 5 and subsequent deformations produced brittle faulting with minor displacement open folds of the ore horizon and large scale domain bounding faults the namew lake pyroxenite was metamorphosed at upper amphibolite facies m 1 at lower amphibolite facies m 3 and at greenschist facies m 5 m 1 metamorphism of the pyroxenite produced partial replacement of the host pyroxenite by pargasitic amphibole m 3 produced successive partial replacement by talc dolomite tremolite and biotite with greatest alteration at the edges of the pyroxenite and near crosscutting dikes m 5 produced minor serpentine and cummingtonite most or all elements including rare earth elements ree were mobile to varying degrees during m 1 m 3 and m 5 resulting in the observed compositional variability of the namew lake pyroxenite

the effect of mining and related activities on the sediment trace element geochemistry of lake coeur d alene idaho usa part iii downstream effects the spokane river basin during 1998 1999 surface and subsurface sediment samples were collected along the entire length of the spokane river from its outlet at the northern end of lake coeur d alene cda idaho to lake roosevelt on the columbia river washington the study was conducted to determine if the trace element enrichments observed in lake cda and on the floodplain and in the cda river extend through the spokane river basin srb as in lake cda surface sediments in the srb are enriched in pb zn as cd sb and hg relative to local background levels pb cd and zn are the most elevated with maximum enrichment occurring in the upper spokane river in close proximity to lake cda on average enrichment decreases downstream apparently reflecting both increased distance from the inferred source the cda river basin as well as increased dilution by locally derived but unenriched materials only cd and zn display marked enrichment throughout the srb pb zn and cd seem to be associated mainly with an operationally defined iron oxide phase whereas the majority of the as and sb seem to be matrix held subsurface sediments also are enriched in pb zn as cd sb and hg relative to background levels based on 137cs and excess 210pb dating trace element enrichment began in the middle part of the srb long lake between 1900 and 1920 this is contemporaneous with similar enrichments observed in lake cda as well as the completion of long lake dam 1913 in the most downstream part of the basin spokane river arm of lake roosevelt enrichment began substantially later between 1930 and 1940 the temporal difference in enrichment between long lake and the river arm may reflect the latter s greater distance from the presumed source of the enrichment the cda river basin however the difference is more likely the result of the completion of grand coulee dam 1934 1941 which formed lake roosevelt backed up the spokane river and increased water levels in the river arm by about 30 m

in situ u pb granulite hosted zircon dates kapuskasing structural zone ontario a late archean large igneous province lip as a substrate for juvenile crust abstract a geochronological study of the kapuskasing structural zone ksz a section of late archean lower crust within the southern superior province canadian shield was undertaken to test a plate tectonic model for the late archean abitibi opatica terrane as a modified large igneous province lip new geochronological data allow us to interpret 1 construction of the lip in an environment where inherited zircons were derived from an older sialic crust and preserved in the granulite grade lower crust and 2 high grade metamorphism in the lower crust related to crustal refinement of the lip u pb and pb pb dates were obtained by la icp ms with beams of 8 30 m the study yielded 21 interpretable zircon dates spanning 500 m yr from one mafic granulite and two garnetiferous metatonalites nine of the dates are significantly older than the oldest known magmatic event recorded in the upper crust of the abitibi opatica terrane and indicate 2760 ma proto crustal material in the ksz lower crust the rema

biochronology of spanish quaternary small vertebrate faunas abstract thousands of fossils of small vertebrates are recorded in one of the most complete stratigraphic sequences of the continental european pleistocene in the sierra de atapuerca this sequence with a few interruptions spans the last 1 5 million years the stratigraphic series is recorded in six karstic cavities in the sierra de atapuerca from the oldest record to the most modern one these are the sima del elefante gran dolina galeria zarpazos sima de los huesos el portalon and el mirador the faunal successions of continental microvertebrates have made it possible to divide the atapuerca sequence into 7 faunal units atapuerca faunal units ata fus which are based on the first and last local appearances of taxa lo ho the spanish quaternary small vertebrate faunas are grouped into 5 distinct biozones from the oldest to the most recent allophaiomys pliocaenicus allophaiomys lavocati allophaiomys chalinei iberomys brecciensis and iberomys cabrerae these are calibrated with radiometric and palaeomagnetic dating allowing the proposal of a continental biochronological scale for the pleistocene of the iberian peninsula

chemical composition of bottom sediments within black hills region reservoirs of south dakota and wyoming the objectives of this study were to determine the effect of heavy metals transported from mining areas due to historical mining activities within the black hills region of south dakota and wyoming us and to evaluate the presence of major and trace elements resulting from influence of provenance weathering erosion and sediment sorting within reservoir sediments soil core samples were collected from both inflow and outflow of the reservoirs x ray florescence analyses were performed to determine the presence of major and the trace elements concentration pactola and sheridan lakes had the highest concentration of as fe mn and rb sr ratios while the belle fourche reservoir had the highest u concentration spatial and temporal patterns of rb sr ratio of the reservoir sediments were used to determine the weathering intensity of the catchment areas with the exception of angostura and lak reservoirs all black hills reservoirs were dominated by physical weathering processes within their respected watersheds immobile high field strength elements from within the reservoir sediments were higher compared to upper continental crust ucc concentrations and further suggest the dominance of physical weathering processes for all reservoirs except lak spider diagrams normalized to ucc concentrations indicate that black hills regional reservoirs were elevated in zr hf and u further supporting the dominance of physical or mechanical weathering influences from their watersheds watersheds dominated by physical weathering processes are commonly subjected to high erosion anthropogenic activities and or high precipitation processes

the effect of mining on the sediment trace element geochemistry of cores from the cheyenne river arm of lake oahe south dakota u s a abstract six cores ranging in length from 1 to 2 m were collected in the cheyenne river arm of lake oahe south dakota to investigate potential impacts from gold mining operations around lead south dakota sedimentation rates in the river arm appear to be event dominated and rapid on the order of 6 7 cm yr 1 all the chemical concentrations in the core samples fall within the wide ranges previously reported for the pierre shale of cretaceous age and with the exception of as generally are similar to bed sediment levels in the cheyenne river lake oahe and foster bay based on the downcore distribution of mn it appears that reducing conditions exist in the sediment column of the river arm below 2 3 cm the reducing conditions do not appear to be severe enough to produce differentiation of fe and mn throughout the sediment column in the river arm cross correlations for high level metal bearing strata within the sediment column can be made for several strata and for several cores however cross correlations for all the high level metal bearing strata are not feasible as is the only element which appears enriched in the core samples compared to surface sediment levels well crystallized arsenopyrite was found in high as bearing strata from two cores and probably was transported in that form from reducing sediment storage sites in the banks or floodplains of whitewood creek and the belle fourche river it has not oxidized due to the reducing conditions in the sediment column of the cheyenne river arm some as may also be transported in association with fe and mn oxides and hydroxides remobilized under the reducing conditions in the river arm and then reprecipitated in authigenic sulfide phases in either case the as appears to be relatively immobile in the sediment column

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

natural enrichment of arsenic in loch lomond sediments abstract concentrations of arsenic in surface or near surface sediment in 12 of 13 cores from the three major basins of loch lomond are substantially enhanced up to 675 mg kg compared with background values of 15 50 mg kg sedimentary as profiles are attributed to post depositional enrichment processes since there are no recent significant sources of environmental as contamination anthropogenic or natural in the loch lomond area the enrichments can be interpreted in terms of post depositional diagenetic remobilization processes in sediment reducing zones followed by upward migration of as through interstitial waters and oxidation adsorption precipitation reactions in near surface oxidizing layers confirmation of the diagenetic adsorption hypothesis is provided directly by the analysis of as species 1 5 81 g l in pore water and indirectly via comparison with sedimentary phosphorus

geochronological constraints on the timing of magmatism deformation and gold mineralization in the red lake greenstone belt northwestern ontario the paper presents u pb ages on zircon baddeleyite titanite rutile and monazite from volcanic and plutonic rocks of the red lake greenstone belt in the northern superior province the purpose of the study was to refine a previously outlined time frame for the volcanic evolution of the belt define the time of major plutonism and deformation and constrain the age of formation of gold deposits volcanism spanned at least 270 ma between 3000 and 2730 ma new ages of 2989 3 and 2894 2 ma for units of a lower volcanic sequence and and 2744 1 ma for units of an upper volcanic sequence corroborate and refine the previously established relationships local gabbroic and felsic intrusions cutting through the lower sequence yield ages of 2870 15 and respectively volcanism was succeeded by major plutonism deformation alteration and metamorphism between about 2730 and 2700 ma these processes were interrelated and progressed as a relatively continuous sequence of events accentuated by major activity d

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

effect of mining and related activities on the sediment trace element geochemistry of lake coeur d alene idaho usa part i surface sediments during the summer of 1990 12 gravity cores were collected in lake coeur d alene idaho at various depths and in a variety of depositional environments all core subsamples were analysed to determine the bulk sediment chemistry selected subsamples were analysed for trace element partitioning and 137cs activity the purpose of these analyses was to determine the trace element concentrations and distributions in the sediment column and to try to establish a trace element geochemical history of the lake in relation to mining and mining related discharge operations in the area substantial portions of the near surface sediments in lake coeur d alene are markedly enriched in ag as cd hg pb sb and zn and slightly enriched in cu fe and mn variations in the thickness of the trace element rich sediments which range from more than 119 cm to as little as 17 cm indicate that the source of much of this material is the coeur d alene river an estimated 75 million tonnes of trace element rich sediments have been deposited on or in the lake bed estimated trace element masses in excess of those considered representative of background conditions range from a high of 468 000 tonnes of pb to a low of 260 tonnes of hg the similarity between the trace element rich surface and subsurface sediments with respect to their location their bulk chemistry their interelement relations and their trace element partitioning indicate that the sources and or concentrating mechanisms causing the trace element enrichment in the lake sediments have probably been the same through out their depositional history based on a mt st helens ash layer from the 1980 eruption ages estimated from 137cs activity and the presence of 80 discernible and presumably annual layers in a core collected near the coeur d alene river delta indicate that deposition rates for the trace element rich sediments have ranges from 2 1 to 1 3 cm year these data also indicate that the deposition of trace element rich sediments began at least in the coeur d alene river delta some time between 1895 and 1910 dates consistent with the onset of mining and ore processing activities that began in the area in the 1880s

late quaternary stream piracy and strath terrace formation along the belle fourche and lower cheyenne rivers south dakota and wyoming abstract stream piracy substantially affected the geomorphic evolution of the missouri river watershed and drainages within including the little missouri cheyenne belle fourche bad and white rivers the ancestral cheyenne river eroded headward in an annular pattern around the eastern and southern black hills and pirated the headwaters of the ancestral bad and white rivers after 660 ka the headwaters of the ancestral little missouri river were pirated by the ancestral belle fourche river a tributary to the cheyenne river that currently drains much of the northern black hills optically stimulated luminescence osl dating techniques were used to estimate the timing of this piracy event at 22 21 ka the geomorphic evolution of the cheyenne and belle fourche rivers is also expressed by regionally recognized strath terraces that include from oldest to youngest the sturgis bear butte and farmingdale terraces radiocarbon and osl dates from fluvial deposits on these terraces indicate incision to the level of the bear butte terrace by 63 ka incision to the level of the farmingdale terrace at 40 ka and incision to the level of the modern channel after 12 9 ka similar dates of terrace incision have been reported for the laramie and wind river ranges hypothesized causes of incision are the onset of colder climate during the middle wisconsinan and the transition to the full glacial climate of the late wisconsinan pinedale glaciation incision during the holocene of the lower cheyenne river is as much as 80 m and is 3 to 4 times the magnitude of incision at 63 ka and 40 ka the magnitude of incision during the holocene might be due to a combined effect of three geomorphic processes acting in concert glacial isostatic rebound in lower reaches 40 m a change from glacial to interglacial climate and adjustments to increased watershed area resulting from piracy of the ancestral headwaters of the little missouri river

physical and chemical characteristics of a metal contaminated overbank deposit west central south dakota u s a a metal contaminated overbank deposit in west central south dakota resulted from the discharge of a large volume of mine tailings into a river system between the late 1800s and 1977 the deposit along the belle fourche river is typically up to 2 m thick and extends about 90 m away from the channel along the insides of meander bends the sediments contain above background levels of copper iron manganese zinc and particularly arsenic which is commonly two orders of magnitude above background level in the contaminated sediments carbonate minerals in the deposit limit the desorption of arsenic by preventing acid formation arsenic concentrations provide a measure of the dilution of mine tailings by uncontaminated sediment the arsenic appears to have been transported and deposited as arsenopyrite but is now at least partially associated with iron oxides and hydroxides within individual samples arsenic concentration has an inverse relation with grain size that results from the more efficient accumulation of arsenic on the greater surface area of the smaller particles arsenic concentration is inversely related to the sample weight percent finer than 16 m however as a consequence of the dilution of the contaminated sediments by uncontaminated sediment with a finer grain size distribution dilution by uncontaminated sediment from tributaries cause arsenic concentrations to decrease by a factor of 3 along 100 km of floodplain an influx at high streamflow of uncontaminated sediment from terraces and the premining floodplain as well as from tributaries causes arsenic concentrations in parts of the contaminated deposit that are farthest away from the channel to be two to three times less than arsenic concentrations in overbank sediment that is immediately adjacent to the channel

u pb zircon ages for magmatism in the red lake greenstone belt northwestern ontario u pb dating was carried out on nine volcanic rocks and two felsic intrusions from the red lake greenstone belt in order to establish an absolute time framework for the magmatic evolution of the area and yield first indications on the time of deformation and gold mineralization the data indicate a protracted period of igneous activity spanning at least 270 ma felsic volcanic rocks near the top of the tholeiitic to komatiitic sequence in the eastern part of the belt yield ages of and a third unit dated at contains inherited zircons older than 2982 ma which casts some uncertainty on the validity of the inferred intercept age rocks in the western part of the belt previously believed to form a relatively young calc alkalic sequence but now known to be dominantly tholeiitic are shown to be relatively old with ages of and these two dates also bracket the age of stromatolites occurring in chemical sediments that are under and overlain by the dated units another volcanic horizon in the centre of the b

transport and accumulation of radionuclides and stable elements in a missouri river reservoir several long sediment cores from the cheyenne river embayment of lake oahe a 250 km long missouri river reservoir in south dakota have been analyzed for radionuclides and stable elements the combination of fine scale sampling and rapid sedimentation produces radionuclide distributions that can be used to estimate the detailed chronology of particle transport processes in the oahe reservoir system a self consistent and quantitative treatment of the 137cs data suggests processes to which characteristic times may be associated times that characterize system wide processes include 1 an integration time of several years reflecting retention of the sediment bound tracer in regions within or external to the reservoir 2 a relaxation time of approximately 15 years reflecting a decreasing rate of sediment accumulation ascribed to shoreline stabilization 3 a time of a few months characterizing the breadth of riverine signatures in cores due to integration effects in the cheyenne river system and deltaic deposits and 4 times of a few years associated with propagation of riverine load signatures along the embayment the distribution of total sedimentary arsenic confirms the validity of the variable sedimentation model in 1977 a tailings retention facility was built at the homestake mine site and the unrestricted input of as ceased as a result of this remedial action the concentration of sedimentary as decreased dramatically in the upper section of the core above the depth represented by the year 1976 the concentration of as decreases tenfold in this same core the distribution of lithologically discriminating chemical elements calcium and vanadium relate to major flow events in the cheyenne river basin because there is minimal diagenesis of chemical constituents in these rapidly accumulating sediments stable element signatures in addition to radiotracers may be used to reconstruct hydrologic events in drainage basins that contribute sediment to lakes and reservoirs

u pb geochronology of the central uchi subprovince superior province u pb zircon and titanite ages for rocks of the central uchi subprovince in northwestern ontario indicate a late archean magmatic and tectonic development spanning over 200 ma an early period at 2900 2800 ma formed volcano plutonic complexes presumably linked to 3 1 2 8 ga terrains of the northwestern superior province a later period of southward growth by magmatic and tectonic accretion occurred at 2750 2710 ma and was concluded by large scale compression and plutonism at 2700 ma the oldest 2890 2860 and 2840 2820 ma components occur in the pickle lake and meen dempster greenstone belts and as gneisses in the seach achapi and the lake st joseph batholiths in northern and central sectors of the region together with distinct 2750 2740 ma volcano plutonic complexes they form a collage assembled by multiple episodes of tectonic juxtaposition and magmatic accretion plutons of 2730 2710 ma age are intrusive into these older northern domains whereas their volcanic counterparts compose the lake st joseph and miminiska fort hope greenstone belts to the south late tectonic to posttectonic granitoid rocks intruded a region extending from the northern berens river subprovince to the southern english river subprovince at 2700 ma these plutons were cut by regional scale faults formed by residual north northwest directed shortening the timing of this movement seems to be recorded by titanite ages of 2690 2670 ma reactivation of the same faults may account for proterozoic pb loss observed in some of the zircon populations the age patterns are consistent with crustal growth along a continental margin in a north dipping subduction environment

micromammals from the 1995 mammoth excavation at west runton norfolk uk morphometric data biostratigraphy and taxonomic reappraisal abstract in this paper the small mammals recovered from sediments associated with the west runton elephant have been analysed and compared with sites in other parts of europe major taxonomical problems are indicated and we suggest ways of utilising such morphological complexity to refine biostratigraphical and chronostratigraphic attributions the micromammal assemblage from the west runton elephant site so far totals 16 species from the west runton freshwater bed wrfb there are strong similarities with the arvicolid spectrum of basal layer h8 in the kon prusy c 718 profile czech republic which accumulated under cooler conditions preceding the thermal maximum of an early middle pleistocene interglacial rare steppic indicators e g cricetus at west runton also imply a somewhat cooler and more continental climate than the present day but overall the fauna is fully temperate in character west runton shares several stratigraphically significant small mammal taxa with voigtstedt central germany and morphometric comparisons suggest that voigtstedt may be slightly younger than west runton the presence of mimomys savini with a latest occurrence in the early part of marine isotope stage mis 15 together with the palaeomagnetic evidence suggests the wrfb may have been emplaced during the early part of mis 17 however given the complexity of the marine isotope curve during the early part of the brunhes chron and differences between global and regional climatic evolution it is difficult to assign the normally magnetised wrfb to a particular marine isotope stage mis

data review on the small mammals from the late early pleistocene of vallparadis estacio layer evt7 valles penedes basin ne iberian peninsula biochronological and palaeoenvironmental implications abstract the chronology of layer evt7 of the vallparadis estacio section has been a hotly debated topic during recent years with some authors supporting an age close to the early middle pleistocene boundary 0 83 ma others favouring an age older than the jaramillo magnetostratigraphic subchron ca 1 2 ma and others proposing a chronology between 0 98 and 0 95 ma for layer evt7 here we review the biochronological data from evt7 and review the biochronology based on the study of mimomys savini using all the available remains of this species which is the most abundant rodent species from this layer based on the morphologic and biometric comparison with remains of the same species from other similarly aged iberian localities gran dolina td4 6 from atapuerca and barranco leon d and fuente nueva 3 from the guadix baza basin we propose an estimated age for evt7 in the chronologic range from 0 99 to 0 94 ma we further perform a paleoenvironmental study based on the whole small mammal assemblage from evt7 which allows us to infer an open and humid environment in the vicinity of a lacustrine area or fluvial course recently published work also studied the rodent assemblage from evt7 however in this study only a part of the small mammals recovered from evt7 was studied and therefore its results can be partially biased