reconstructing recent environmental changes from proglacial lake sediments in the western alps lake blanc huez 2543 m a s l grandes rousses massif france abstract the evolution of high altitude glaciers and human activities in the grandes rousses massif is documented by high resolution seismic reflection profiling and multiproxy analysis of short sediment cores in proglacial lake blanc huez these lacustrine data are compared with historical chronicles geomorphological features and glaciological studies in this region of the western alps and they allow the documentation of recent environmental changes the specific geometry of high amplitude reflections in the uppermost seismic unit the lithology of short cores and the available limnological data in the lake suggest that clastic particles eroded by the glaciers and transported in suspension by glacial melt waters in early summer essentially develop homopycnal flood events in the lake a conceptual model linking fluctuations of glacier equilibrium line altitudes in the catchment area with sedimentary facies retrieved in the lake basin is proposed this approach allows reconstructing continuous glacier fluctuations since ad1820 1850 and suggests several phases of glacier fluctuations during the little ice age lia these reconstructions are based on changes in lacustrine sediment laminations density magnetic susceptibility reflectance spectra organic matter and arsenic content the age depth model of short sediment cores is provided by 210 pb 137 cs and 241 am radionuclide dating this chronology is further supported by identifying in lacustrine sediments the impact of i the nearby m 5 3 correncon earthquake in ad 1962 ii the development of the ski resort at high altitude close to the lake and iii the last advance of glaciers during the lia in ad1820 1850 and the following phase of glacier retreat observed in the alpine region at the end of the lia in ad 1880 frequent sandy layers enriched in organic matter and associated with fluctuations in the arsenic concentrations may result from hydraulic remobilisation of middle age mine tailings at the lake shore by snow melt or heavy rain fall events during the lia

10be inventories in alpine soils and their potential for dating land surfaces abstract to exploit natural sedimentary archives and geomorphic landforms it is necessary to date them first landscape evolution of alpine areas is often strongly related to the activities of glaciers in the pleistocene and holocene at sites where no organic matter for radiocarbon dating exists and where suitable boulders for surface exposure dating using in situ produced cosmogenic nuclides are absent dating of soils could give information about the timing of landscape evolution this paper explores the applicability of soil dating using the inventory of meteoric 10be in alpine soils for this purpose a set of 6 soil profiles in the swiss and italian alps was investigated the surface at these sites had already been dated using the radiocarbon technique or the surface exposure determination using in situ produced 10be consequently a direct comparison of the ages of the soils using meteoric 10be and other dating techniques was made possible the estimation of 10be deposition rates is subject to severe limitations and strongly influences the obtained results we tested three scenarios using a the meteoric 10be deposition rates as a function of the annual precipitation rate b a constant 10be input for the central alps and c as b but assuming a pre exposure of the parent material the obtained ages that are based on the 10be inventory in soils and on scenario a for the 10be input agreed reasonably well with the age using surface exposure or radiocarbon dating the ages obtained from soils using scenario b produced ages that were mostly too old whereas the approach using scenario c seemed to yield better results than scenario b erosion calculations can in theory be performed using the 10be inventory and 10be deposition rates an erosion estimation was possible using scenario a and c but not using b the calculated erosion rates using these scenarios seemed to be plausible with values in the range of 0 57 mm ky the dating of soils using 10be has several potential error sources analytical errors as well as errors from other parameters such as bulk soil density and soil skeleton content have to be taken into account the error range was from 8 up to 21 furthermore uncertainties in estimating 10be deposition rates substantially influence the calculated ages relative age estimates and under optimal conditions absolute dating can be carried out age determination of alpine soils using 10be gives another possibility to date surfaces when other methods fail or are not possible at all it is however not straightforward quite laborious and may consequently have some distinct limitations

palaeomagnetic and rock magnetic reliability criteria in ophiolitic rocks a case study from the palaeozoic ballantrae ophiolite scotland abstract palaeomagnetic studies of the ballantrae ophiolite southwest scotland are assessed in the light of palaeomagnetic and rock magnetic reliability criteria the remanence directions are palaeomagnetically reliable but have only limited significance for apparent polar wander path construction rock magnetic reliability criteria are found to be ambiguous when treated in isolation original grain size effects are detected in magnetic properties across three sections through pillow lavas we propose that a systematic study of spatial magnetic property variations within pillow lavas can provide an additional field test in the assessment of reliability thermomagnetic analyses and microscopic observations suggest three remanence carrying magnetic phases exist within the extrusive layer of the ophiolite these are almost pure magnetite hematite and titanomaghemite palaeomagnetic rock magnetic and geological observations are best satisfied by a pre obduction magnetisation age this study links the remagnetisation of an ultra oceanic conglomerate to local hydrothermal circulation rather than to a pervasive remagnetisation event as previously suggested

assessment of the potential occurrence of acid rock drainage through a geochemical stream sediment survey during large constructions of roads or structures unexpected acid rock drainage ard can be caused by local mineralization containing sulfides in the geology the potential of ard occurrence of a certain area sometimes must be assessed before initiation of any engineering earth works however it is difficult to assess the entire area through collecting rock samples and predicting the potential by laboratory tests such as the acid base accounting method in this study a new prediction protocol using a geochemical exploration survey technique of stream sediment is proposed sediment samples were collected at the case study area where a large development is expected in the future and the contents of some major and heavy metal elements were compared according to the major geologies of the sampling points the modified geoaccumulation indices i geo of fe pb and as could indicate a possible zone of pyrophyllite mineralization which may cause the occurrence of ard at the study area using the enrichment index of the three elements relative to the median values of the area a high potential zone of ard could be designated which was in agreement with the laboratory ard prediction tests of the rock samples in the other areas with different mineralization processes other metallic elements can be selected as indicators of the ard potential likewise the potential of the occurrence of ard at an area can be assessed by evaluating the geochemical distributions and drawing the indicator elements for ard through a stream sediment survey

landscape evolution in val mulix eastern swiss alps soil chemical and mineralogical analyses as age proxies towards the end of the last glacial cycle repeated re advances of valley glaciers in the european alps combined with periglacial processes led to the formation of a variety of climate related landforms independent age measurements of moraines and rock glacier lobes using both in situ produced and meteoric 10be allows for the use of soil formation as an age proxy in this complementary study we present chemical and mineralogical data from five podzols from val mulix in eastern switzerland two of them developed on granitic lateglacial moraines 14 9 ka and 10 7 ka respectively and three were sampled on lobes of a morphostratigraphically connected relict rock glacier covering an age range of approx 10 7 ka to 8 6 ka besides the evaluation of the suitability of selected pedosignatures for a relative age separation we hypothesised that these pedosignatures should give further information about the evolution of the specific sites although the soils had a high skeleton content and the oldest soil started its development in a slightly colder climatic phase typical weathering trends could still be detected whereas weathering indices such as the k ca ti ratio or the b index reflect time trends reasonably well the mineralogical composition of the fine earth and clay fraction yielded a slightly more inconsistent picture to a lesser extent some inconsistencies were also exhibited when using the weathering mass balance approach this is especially true for the relict rock glacier and it supports the suggested complex development history of these soils as well as the presence of pre weathered material techniques that include several surface soil horizons and the soil skeleton such as the k ca ti ratio the b index and the mass balance approach gave more robust results in terms of the expected chronology than the ones that only referred to single horizons clay mineralogy errors or variations due to potential reallocation processes within the soil horizons but without a prominent change of the overall soil characteristics are minimised using such an approach weathering indexes and the clay mineral assemblage provided a differentiation of soils even within a relatively narrow time range and gave insight into processes that have occurred at the specific sites the combined relative numerical dating approach used here not only enables an extended interpretation and mutual control but ultimately leads to a better understanding of landscape reconstruction and evolution

palaeomagnetism and rb sr ages of the ratagan and comrie intrusions the newer igneous rocks in the scottish highland region which post date the main grampian metamorphism and tectonism range in composition from basic to granitic two members of this suite were chosen for palaeomagnetic study in an attempt to refine the apparent polar wander path for scotland in the palaeozoic this paper describes the results of the detailed palaeomagnetic analysis which has been carried out thermal and alternating field af demagnetization was supplemented by rock magnetic experiments on a limited selection of specimens from each sampling site to help characterize the remanence carriers these consisted of thin section observations and the measurement of thermomagnetic and hysteresis properties each complex provides an example of the widespread variability in remanence behaviour which may be encountered in a single intrusion for an accurate interpretation of palaeomagnetic data from any formation an estimate of the age of the rock is required brown miller grasty 1968 give a poorly defined k ar now at bp research centre str epd chertsey road sunbury on thames middlesex tw16 7ln

palaeomagnetism of nw scotland syenites in relation to local and regional tectonics summary a detailed thermal demagnetization study has been carried out on a number of syenitic intrusions from north of the great glen fault in scotland multicomponent remanences of normal and reversed polarity have been recognized these define a series of palaeomagnetic poles from which an ordovician to silurian apparent polar wander path for northern scotland is deduced comparison of this apparent polar wander path with the established path for britain throws new light on the sequence of thrusting and magmatic activity in the nw highlands and precludes large scale 1500 km movement along the great glen fault later than the ordovician the data emphasize previously published discrepancies between the apparent polar wander paths of britain baltica and laurentia and are consistent with the suggestion that britain was among a set of intracratonic microplates which underwent complicated distinct movements throughout the caledonian orogeny

implications for caledonian plate tectonic models of chemical data from volcanic rocks of the british old red sandstone volcanic rocks associated with the continental sediments known as the old red sandstone outcrop widely in northern britain and form a dominantly calc alkaline suite comparable to those developed on modern continental margins rocks rich in ni and cr are unusually abundant and are thought to have incompatible element concentrations little different from those of primary magmas such rocks show pronounced spatial chemical variation with concentrations of sr ba k light rare earth elements and p 2 o 5 and the ratio la y showing up to a six fold increase in a northwestward traverse across scotland in more evolved rocks a similar increase is shown by sr ba and la y but regional comparisons are made difficult by the varying effects of fractional crystallization the chemistry of all old red sandstone volcanic rocks n of the southern uplands fault is consistent with the former existence of a subduction zone that changed in strike from ene in ireland and southern scotland to n in the north sea this orientation in conjunction with almost e w plate motion may explain the great contrast in end silurian deformation styles between britain and scandinavia old red sandstone volcanic and plutonic rocks s of the southern uplands fault are thought to be younger and are perhaps unrelated to subduction activity

late pleistocene holocene surface processes and landscape evolution in the central swiss alps abstract the european alps are a geomorphologically active region and experience a number of gravity driven hillslope processes soil and landscape formation in the alps has consequently undergone several minor and major traceable changes of developmental trajectories during the holocene soil development is hypothesised to be often non linear with time and characterised by stages of progressive and regressive evolution caused by upbuilding formation profile deepening and erosion profile shallowing several cold and warm climate phases are identified during the holocene but it is largely unknown which effects these might have had on slope processes by using datable moraines 10 be and mires 14 c we have constructed a temporal framework for these processes using the geochemical imprint of mires in the alpine setting of the goschener valley of the central swiss alps we reconstructed general mostly erosional landscape processes for the last ca 10 ka as this is the type locality for the goschener cold phase we assumed that this phase goschener cold phase i and ii 1 5 and 2 5 ka bp should have left easily recognizable traits after deglaciation 11 12 ka bp soil evolution was progressive beginning around 8 ka bp we detect a distinct increase in erosion here together with a vegetation change towards tundra vegetation and the highest measured rates of carbon sequestration other phases of high geomorphic activity were recognised ca 5 6 ka bp 4 ka bp and to a lesser extent 1 3 ka ago the cold phase at 5 6 ka bp corresponds to a less distinct change in vegetation and lessened erosion human impact is increasingly obvious since about 2 4 ka bp which overlaps with the goschener cold phase nonetheless erosion processes were not extraordinarily high during this period and a climate effect cannot be distinguished we detect evidence of increasing human disturbance regressive soil evolution for about the last 1 ka we also detect an increase in dust flux during the last ca 4 5 ka presumably due to the landscape change s in the sahara during this time

filling the bushveld complex magma chamber lateral expansion roof and floor interaction magmatic unconformities and the formation of giant chromitite pge and ti v magnetitite deposits his mind was like a soup dish wide and shallow irving stone on william jennings bryan a compilation of the sr isotopic stratigraphy of the bushveld complex shows that the evolution of the magma chamber occurred in two major stages during the lower open system integration stage lower critical and lower main zone there were numerous influxes of magma of contrasting isotopic composition with concomitant mixing crystallisation and deposition of cumulates larger influxes correspond to the boundaries of the zones and sub zones and are marked by sustained isotopic shifts major changes in mineral assemblages and development of unconformities during the upper closed system differentiation stage upper main zone and upper zone there were no major magma additions other than that which initiated the upper zone and the thick magma layers evolved by fractional crystallisation the lower and lower critical zones are restricted to a belt that runs from steelpoort and burgersfort in the northeast to rustenburg and northam in the west and an outlier of the lower and lower critical zone up to the lg4 chromitite layer in the far western extension north of zeerust it is only in these areas that thick harzburgite and pyroxenite layers are developed and where chromitites of the lower critical zone occur these chromitites include the economically important c 1 m thick lg6 and mg1 layers exposed around both the eastern and western lobes of the bushveld complex the upper critical zone has a greater lateral extent than the lower critical zone and overlies but also onlaps the floor rocks to the south of the steelpoort area the source of the magmas also appears to have been towards the south as the mg chromitite layers degrade and thin northward whereas the lg layers are very well represented in the north and degrade southward sr and os isotope data indicate that the major chromitite layers including the lg6 mg1 and ug2 originated in a similar way extremely abrupt and stratigraphically restricted increases in the sr isotope ratio imply that there was massive contamination of intruding melt which hit the roof of the chamber and incorporated floating granophyric liquid which forced the precipitation of chromite kruger 1999 kinnaird et al 2002 therefore each chromitite layer represents the point at which the magma chamber expanded and eroded and deformed its floor nevertheless this was achieved by in situ contamination by roof rock melt of the intruding critical zone liquids that had an orthopyroxenitic to noritic lineage the main zone is present in the eastern and western lobes of the bushveld complex where it overlies the critical zone and onlaps the floor rocks to the south and the north where it is also the basal zone in the northern lobe the new magma first intruded the northern lobe north of the thabazimbi murchison lineament interacted with the floor rocks incorporated sulphur and precipitated the platreef along the floor rock contact before flowing south into the main chamber this exceptionally large influx of new magma then eroded an unconformity on the critical zone cumulate pile and initiated the main zone in the main chamber by precipitating the merensky reef on the unconformity the upper zone magma flowed into the chamber from the southern bethal lobe as well as the tml this gigantic influx eroded the main zone rocks and caused very large scale unconformable relationships clearly evident as the gap areas in the western bushveld complex the base of this influx which is also coincident with the pyroxenite marker and a troctolitic layer in the northern lobe is the petrological and stratigraphic base of the upper zone sr isotope data show that all the pge rich ores including chromitites are related to influxes of magma and are thus related to the expansion and filling of the magma chamber dominantly by lateral expansion with associated transgressive disconformities onto the floor rocks coincident with major zone changes these positions in the stratigraphy are marked by abrupt changes in lithology and erosional features over which succeeding lithologies are draped the outcrop patterns and the concordance of geochemical isotopic and mineralogical stratigraphy indicate that during crystallisation the bushveld complex was a wide and shallow lobate sill like sheet and the rock strata and mineral deposits are quasi continuous over the whole intrusion

paleomagnetism of rocks from burin peninsula newfoundland hypothesis of late paleozoic displacement of acadia criticized the posttectonic st lawrence granite 360 5 ma and associated subvertical dikes have two magnetizations n and h n points north with an intermediate upward inclination declination 005 inclination 50 alpha 95 10 paleopole 12 n 120 e we consider n to have been acquired close to the time of initial cooling the h magnetization points south with low inclination h is also the dominant magnetization in the nearby permo carboniferous spanish room formation h is considered to be an overprint acquired chemically during the kiaman reversed superchron late carboniferous and permian the n magnetization corresponds to a paleolatitude of 31 7 s very different from the near equatorial values expected from the commonly accepted late devonian and earliest carboniferous tournaisian reference paleofields for cratonic north america this is generally consistent with the hypothesis of a southerly displaced acadia proposed by kent and opdyke although the displacement is much greater 30 rather than 15 however we show that all inclinations observed from middle to upper devonian and tournaisian rocks from the craton are not significantly different either from the kiaman paleofield or from the h overprints observed from newfoundland some of these cratonic studies are not very detailed but it is noteworthy that the declination observed in the most comprehensive of them catskill red beds also agrees with the kiaman paleofield and with the h overprints from newfoundland declinations in some other cratonic studies show small departures of only a few degrees with one exception based on limited sampling and two from the colorado plateau which may have been rotated which could be caused by experimental inaccuracies moreover the directions obtained from cratonic studies are 97 reversed as they are in rocks with kiaman magnetizations we suggest therefore that the commonly accepted late devonian to earliest carboniferous reference paleofield for north america is either entirely kiaman in age or has been seriously affected by kiaman overprinting consequently the 30 of southerly displacement which the n magnetization of the st lawrence granite apears to indicate and the 15 invoked by kent and opdyke we consider to be illusory three late precambrian rock units 623 to 606 ma have scattered declinations but similar inclinations yielding paleolatitudes of about 35 the scattered declinations presumable were caused by local pre carboniferous relative rotations there is little or no evidence of kiaman overprinting in precambrian rocks indicating that overprinting is comparatively superficial and is probably related to late paleozoic groundwater circulation

synfolding and prefolding magnetizations in the upper devonian catskill formation of eastern pennsylvania implications for the tectonic history of acadia the upper devonian catskill formation was sampled for paleomagnetic study in east central pennsylvania 41on 76ow in one area the dominant component of magnetization se is revealed over a broad spectrum of demagnetization temperatures ranging to at least 660oc a conventional fold test is positive at the 99 confidence level however statistical analysis of dispersion with incremental bedding tilt correction shows a significant peak in the precision parameter after about 3 4 unfolding the magnetization is therefore secondary with a mean direction of d 166 6 o i 1 8 o the

multicomponent magnetization in the helmsdale granite north scotland geotectonic implication abstract a palaeomagnetic study of the helmsdale granite u pb 420 m y k ar 400 m y northeast scotland has revealed a multicomponent remanence dominated by two characteristic axes of magnetization the suggested oldest of these magnetizations the direction of which is nearly horizontal and directed n s is thought to have been acquired in upper silurian lower devonian times the existence of this shallow direction of magnetization discounts a recent hypothesis of a ca 2000 km sinistral offset along the great glen fault the second component of magnetization appears to be partly carried by haematite that apparently formed through disintegration of biotite and or plagioclase this secondary magnetization has a direction that can be associated with a permian early mesozoic age similar overprinted magnetizations are characteristic features also in the devonian sedimentary sequences north of helmsdale

an evaluation of geochemical weathering indices in loess paleosol studies abstract applying geochemical proxies as measure for the weathering intensity of paleosols and sediments such as loess the quaternary scientist is confronted with various element ratios that have been proposed in literature this paper gives an overview on the principle of geochemical weathering indices different types of indices are evaluated with respect to the suitability for loess paleosol sequences regarding the special characteristics of this type of sediments and paleosols case examples in this study are key sections in southeastern and eastern europe the loess paleosol sequences batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine which represent archives of the late and mid pleistocene climate change of the region considering element behavior during weathering or diagenesis the chemical proxy of alteration cpa i e the molar ratio al2o3 al2o3 na2o 100 is proposed as the most appropriate index for silicate weathering the cpa was evaluated against commonly used weathering indices including the chemical index of alteration cia the chemical index of weathering ciw the plagioclase index of alteration pia the index b of kronberg and nesbitt and the ba sr and rb sr ratio depth profiles of sr type indices e g ba sr rb sr are likely to be influenced by the dynamics of secondary carbonate on the other hand common na type indices e g cia pia ciw may suffer from uncertainties in separating carbonate ca from silicate ca or from biases due to k fixation illitization the cpa is insensitive against such effects additionally using the cpa as with other na type indices provides the possibility to evaluate the homogeneity of the parent material regarding the relevant host minerals via the a cn k diagram

palaeozoic palaeomagnetic results from scotland and their bearing on the british apparent polar wander path abstract palaeomagnetic studies of the lower and upper old red sandstone ors western midland valley indicate the presence of two principal remanence components ib and hb both components can be demonstrated to be of secondary post upper ors origin component ib compares with palaeomagnetic results from upper carboniferous permian dykes and sills in the midland valley whereas hb conforms to palaeomagnetic results from the overlying lower carboniferous lavas a combination of hb components from the lower upper ors and lower carboniferous lavas western midland valley yields a relative pole position near s14 and e322 which compares well with lower carboniferous data from the kinghorn and burntisland lavas eastern midland valley s14 and e332 from kinghorn the palaeomagnetic data can be demonstrated to be of primary lower carboniferous origin seen in conjunction with the british polar wander path the lower carboniferous poles reported here seemingly dissociate middle upper devonian and upper silurian lower devonian poles owing to the lack of magnetic age control in the middle upper devonian data base it is argued that the majority of middle upper devonian data from the british isles should be reconsidered as carboniferous magnetic overprints this carries the implication that any tectonic models based on middle upper devonian palaeomagnetic results should be considered highly suspicious

paleomagnetic study of devonian rocks from ste cecile st sebastien region quebec appalachians three devonian rock units were collected for paleomagnetic study from the ste cecile st sebastien region located in the gaspe connecticut valley synclinorium of quebec appalachians 15 sites 48 samples from the metasediments subgreenschist facies siltstones sandstones of the compton formation early middle to late early devonian age based on fossil plants which were tightly folded during middle devonian acadian orogeny 14 sites 61 samples from the ste cecile st sebastien granitic body 362 m y k ar age which intruded the metasediments 14 sites 62 samples from the hornfels created subsequent to the emplacement of the intrusive detailed thermal cleaning of the metasediments yielded a mean remanence direction characterized by linear vector trajectories after tilt correction at d 209 i 20 k 30 95 7 2 with unblocking temperature spectrum 300 550 c carried probably by magnetite the predeformational origin of this remanence is tested at 99 confidence level as well as antipodal normal and reverse polarity directions the corresponding paleomagnetic pole ms falls at 28 n 77 e dp dm 6 11 in agreement with the recently reported poles which are mostly early devonian in age and derived from the southeastern margin of the presumed proto atlantic ocean af demagnetization of granites resulted in a univectorial mean remanence at 1 d 332 i 39 k 31 for n 5 sites in fine grained granite fg unit 2 d 313 i 25 k 19 for n 9 sites in medium grained granite mg unit and 3 d 319 i 30 k 17 for all the total n 14 granite g sites af demagnetization of hornfels revealed a post intrusive mean remanence direction hf at d 346 i 22 k 8 for n 14 sites the individual site mean remanence directions with coercivity spectra 10 60 mt from both granites and hornfels suffer from a large declination spread of about 60 but the confidence ovals for the fg and hf remanences overlap this indicates that the fg and hf remanences are indistinguishable from each other and therefore are proximal in time and probably originated during middle to late devonian period interpretation of this kind is speculative in the absence of a convincing evidence for a two fg younger than mg or three phase intrusive history of the pluton since the pole positions of g 18 n 150 e mg 18 n 158 e fg 18 n 137 e and hf 32 n 125 e spread over 40 in longitude these data cannot confirm or negate the possibility of a mid paleozoic transcurrent motion proposed for northern appalachians we regard only the pole ms with probable late early or early middle devonian age as reliable for the apparent polar path construction

geochemical signature of provenance tectonics and chemical weathering in the quaternary flood plain sediments of the hindon river gangetic plain india abstract the ganga basin in the himalayan foreland is a part of the world s largest area of modern alluvial sedimentation flood plain sediments of the hindon river of the gangetic plain have been analyzed for sediment texture major and trace elements including rare earth elements rees the results have been used to characterize the source rock composition and to understand the intensity of chemical weathering tectonics and their interplay in the hindon flood plain the sediments of the hindon flood plain dominantly consist of sand sized particles with little silt and clay the geochemistry of the hindon sediments has been compared to the siwalik mudstone of the siwalik group siwaliks the siwalik sedimentary rocks like sandstones mudstones and conglomerates are the known source rocks for the hindon flood plain sediments mudstone geochemistry has been considered best to represent the source rock characteristics the ucc upper continental crust normalized major and trace elements of the hindon flood plain sediments are very similar to the siwalik mudstone except for th and cr furthermore the average chondrite normalized ree pattern of the hindon flood plain sediments is similar to the siwalik mudstone textural immaturity k rb ratios and the average cia chemical index of alteration and pia plagioclase index of alteration values of the hindon flood plain sediments indicate that the sediments have not been affected by chemical weathering our study suggests that the active tectonics of the himalayas and monsoon climate enhances only physical erosion of the source rocks siwaliks rather than the chemical alteration these factors help the hindon sediments to retain their parental and tectonic signature even after recycling

assessing parent material uniformity of a red and black soil complex in the landscapes abstract the distribution of red and black soil xeralfs xerolls associations in the monarto area south australia is complex and their genesis either being derived from a uniform parent material or a lithologic discontinuity is not known the objectives of this study were i to assess zr and ti bearing grains as minerals resistant to chemical weathering prior to employing zr and ti in determining parent material uniformity and ii to confirm whether pedological processes or a lithologic discontinuity may be responsible for the textural contrast within the red and black soil profiles scanning electron microscopy sem and energy dispersive x ray analysis edax were used to study chemical weathering and elemental composition of surfaces of zr and ti bearing grains x ray fluorescence xrf analysis was used to determine elemental concentrations in various soil fractions results showed that zr bearing grains consisted of only zircon having smooth clean surfaces which are characteristic of a mineral resistant to chemical weathering edax spectra confirmed that zr was a specific element to represent zircon suggesting its reliability to be used in assessing parent material uniformity on the other hand ti derived not only from minerals rutile anatase resistant but also from minerals ilmenite pseudorutile biotite susceptible to chemical weathering this limited the usefulness of ti as an index mineral for soil development studies except for zr ti ratio all other indicators of parent material uniformity i e depth distribution curves of zr and y in various fractions and y zr ratio showed no considerable inflection and variation with depth in a xeralf red soil this indicated the xeralf derived from a uniform parent material mica schists thereby texture contrast within a profile is due to pedological processes on the other hand depth distribution curves showed clear inflection and variation in xerolls black soils indicating soils developed from lithologic discontinuities so different trends in particle size fractions between 0 48 cm for ma5 and 0 59 cm for ma3 profiles compared to the underlying layers are due to parent material differences and not pedogenesis the presence of complex red and black soil association in the landscape is attributed to the difference in parent materials where the red soil developed from mica schist and the black soils from calcareous deposits

the petrogenesis of platinum group element reefs in the upper main zone of the northern lobe of the bushveld complex on the farm moorddrift south africa boreholes have intersected the interval hosting the pyroxenite marker at the base of the upper main zone on the farm moorddrift in the northern bushveld complex the concentrations of the major and compatible trace elements in the rocks are in the range of other pyroxenite marker intervals elsewhere in the bushveld complex mgo up to 22 wt cr up to 300 ppm over a stratigraphic height of some 300 m the interval is characterized by a broad but irregular reversal in mg number and cr v analogous to stratigraphically equivalent horizons elsewhere in the bushveld complex the rocks have distinctly higher concentrations in incompatible trace elements particularly large ion lithophile elements lile and light rare earth elements lree than other main zone rocks and thus appear to contain an elevated crustal component the interval hosts several thick meters to 10s of meters but mostly relatively low grade and laterally discontinuous pge reefs that have been delineated over a strike length of ca 1 km pge contents locally reach approximately 16 ppm pt pd au in rocks containing up to approximately 4 to 5 percent sulfides the pge tenors of most sulfides are 100 ppm pt pd ratios are above unity and pd ir is 200 based on well defined positive correlations between pt and pd with ir we interpret the mineralization as being largely of primary magmatic origin most previous models interpreted the pyroxenite marker to have formed from a major replenishment to the bushveld magma chamber with relatively primitive magma the new magma would have been emplaced on top of an approximately 4 km thick cumulate package consisting of the ultramafic mafic lower and critical zones and the lower to central portions of the gabronoritic main zone here we propose that the upper main zone including the pyroxenite marker did not result from a magma replenishment instead it crystallized from the s saturated residual magma of the upper critical zone cumulates and originally directly overlaid the latter the approximately 1 to 2 km thick lower central main zone package formed from a crystal charged magma emplaced at a relatively late stage in the solidification history of the bushveld chamber between the largely consolidated upper critical and upper main zones we envisage that the emplacement of this large magma batch resulted in subsidence of the center of the layered suite perhaps in response to the evacuation of a putative lower staging chamber from which the bushveld complex was fed semiconsolidated portions of the cumulate package sagged and slumped toward the center of the complex and the flowing crystal mushes underwent mechanical unmixing of light relatively buoyant plagioclase from denser pyroxenes oxides and sulfides this resulted in the formation of an interlayered sequence of relatively melanocratic sulfide enriched with relatively leucocratic sulfide poor layers reef formation is thus partly the result of cumulate reorganization in response to the emplacement of the main zone magma

multiphase magnetic overprints in the moine thrust zone palaeomagnetic studies from the southern part of the moine thrust zone mtz indicate a complex pattern of four major secondary remanence components a d their relative ages appear to vary from mid ordovician to recent tertiary the oldest remanence a is tentatively interpreted as associated with the formation of the lochalsh syncline dl and or d2 however the consistency between component a and the regional southeast plunging lineation makes it uncertain to what extent component a reflects the structural grain rather than a true palaeofield record component b appears to be associated with early devonian uplift along the mtz relating to localized shearing high level brittle thrusting and is almost synchronous with the emplacement of lamprophyre and felsic dykes in the inverted limb of the lochalsh syncline and beneath the balmacara thrust possible permian component c and recent tertiary magnetic overprints are recognized component c is partly of high magnetic stability and may indicate localized shears in the inverted limb usually considered as caledonian shearing it is uncertain to what extent the youngest component d essentially recorded in rocks close to the balmacara thrust in mylonites and fault breccias reflects important tectonic reactivation and magnetic resetting this component is governed by low stability magnetic phases with blocking temperatures below 200 c

mobility of rare earth elements during weathering of till in northern sweden abstract continuous volume controlled sampling from the surface down to a depth of 130 cm was conducted at two stations on weathered till typic haplocryods all the samples were analysed for major and trace elements including the rare earth elements ree eight thousand seven hundred years of weathering since the glacial ice left the area has resulted in a strong depletion of ree in the e horizon this loss decreases as atomic number increases so that 80 85 of the la and 54 60 of the yb have been lost europium has been lost to a greater degree than have the neighbouring elements possible explanations for the release of ree are weathering of common silicates such as hornblende and epidote and plagioclase in the case of eu weathering of apatite weathering of rare but ree rich minerals such as allanite and monazite and release of ree adsorbed on clay minerals further studies on various size fractions and minerals are needed to quantify the importance of the various possible mechanisms of ree release the release of ree continues within and below the bs1 horizon but the results from one station show that light ree can be enriched in the bs1 horizon this secondary enrichment could be caused by adsorption on secondary oxy hydroxides on clay minerals or on organic material however the net result of the weathering is that all ree have been released to the groundwater

non reversible geosystem destabilisation at 4200 cal bp sedimentological geochemical and botanical markers of soil erosion recorded in a mediterranean alpine lake a 144 cm long core was obtained in lake petit 2200 m a s l mediterranean french alps in order to reconstruct past interactions between humans the environment and the climate over the last five millennia using a multidisciplinary approach involving sedimentological geochemical and botanical analyses we show a complex pattern of environmental transformation from 4800 to 4200 cal bp podzol type soils progressively developed under forest cover this stable situation was interrupted by a major detrital pulse at 4200 cal bp that we consider as a tipping point in the environmental history at this point pedogenetic processes drastically regressed leading to the development of moderately weathered soils more frequent detrital inputs are recorded since 3000 cal bp ad 1050 as the human impact significantly increased in the catchment area we conclude that destabilisation of the environment was triggered by climate and exacerbated by human activities to a stage beyond resilience

soil landscape relationship in a chronosequence of the middle madeira river in southwestern amazon brazil abstract high temperatures and rainfall prevail in the brazilian amazon but some areas have soils with high clay mineral contents of 2 1 and there is limited information concerning their properties therefore it is important to study the soil formation and understand the environmental conditions in which they were formed this study aimed to investigate the physical chemical and mineralogical properties of the soil in relation to the environmental factors acting on a chronosequence in the late pleistocene sediments of the middle madeira river soil profiles were selected on three alluvial terraces morphological physical chemical mineralogical x ray fluorescence tem and sem characterizations were performed the soils that exhibited a clayey texture acidic reaction low values of exchangeable bases and high values of aluminum had profiles containing a considerable presence of 2 1 clay minerals especially illite vermiculite mica vermiculite hydroxyl interlayered vermiculite and pyrophyllite soil mineralogy indicated that these soils were recently weathered where the low values of sum of bases correspond to the low presence of these cations in the parent material meanwhile high values of exchangeable aluminum were derived from the pyrophyllite alteration different parent material and 2 1 clay minerals recent alteration therefore the parent material presence of amorphous silica different climate conditions in the past and current drainage restriction contribute to the slow alteration rate of 2 1 clay minerals of the soils of the humid tropical amazon environment

reappraisal of scottish ordovician palaeomagnetism summary critical re evaluation of scottish ordovician palaeomagnetism comprising data from the nw scotland syenites the aberdeenshire gabbros and the pre tectonic i e pre late ordovician silurian magnetic overprinting of dalradian tillites appears to provide a refined mid ordovician to silurian apparent polar wander path post closure magnetizations silurian across the great glen fault agree extremely well after correction for a 20d net clockwise rotation of the northern highlands the data emphasize a previous assumption that some of the existing discrepancies in british ordovician palaeomagnetism may disappear when the prevalence of multicomponent magnetizations is adequately considered the data also support the conclusion from an earlier analysis requiring an anticlockwise rotation of the british isles relative to the geomagnetic field during the ordovician however a recent suggestion that the aberdeenshire gabbros record the slow post orogenic cooling of the ne highlands is shown to rest on an inadequate palaeomagnetic basis

a review of paleomagnetic results from the carboniferous of north america the concept of carboniferous geomagnetic field horizon markers results from the east coast carboniferous basin contain an important time stratigraphic horizon of possible global significance late carboniferous units are found to have mostly reversed magnetizations while older carboniferous units may have normal reverse or most frequently dual polarity magnetizations this feature records the change in geomagnetic field from a period of common polarity changes to a period of mainly reversed polarity the kiaman magnetic interval recognition of the stratigraphic position of this polarity feature provides a time line for correlation of units within and among carboniferous basins in the east coast carboniferous basin of atlantic canada this horizon has now been located at the riversdale group level early pennsylvanian namurian westphalian boundary since remanence acquisition of red sediments is often a lengthy process possibly spanning field reversal time scales red bed units pre dating and post dating this time line can in most instances be readily distinguished the former generally recording both polarities and the latter just one reverse polarity a polar displacement of at least 16 is recorded in the results from the east coast carboniferous basin paleolatitude maps show that the area was located near the equator and was displaced northwards by about 8 during the pennsylvanian it cannot be ascertained if those observations are representative of the whole of north america or merely the atlantic seaboard poles derived from other areas of north america do not all fit the regular pattern observed on the atlantic coast using the horizon marker as a tool it is suggested that those poles are post time line in age so that none of them is representative of the position of north america prior to the time line

temporal variations in the fractionation of the rare earth elements in a boreal river the role of colloidal particles rare earth element ree data from weekly sampling of the filtered 0 45 m and suspended particulate phase during 18 months in the kalix river northern sweden are presented together with data on colloidal particles and the solution fraction 3 kda the filtered ree concentration show large seasonal and temporal variations in the river lanthanum varied between approximately 300 and 2100 pm high ree concentration in the filter passing fraction is related to increased water discharge and there is a strong correlation between the ree concentration organic carbon al and fe physical erosion of detrital particles plays a minor role for the yearly transport of particulate ree in this boreal river system the suspended particulate fraction which is dominated by non detrital fractions accounted for only 35 of the yearly total transport of la in the river approximately 10 of the ree were transported in detrital particles during winter at spring flood in may about 30 of the lree and up to 60 of the hree where hosted in detrital particles ultrafiltration of river water during spring flood shows that colloidal particles dominate the transport of filter passing ree less than 5 of the filtered ree are found in the fraction smaller than 3 kda the colloidal fraction shows a flat to slightly lree enriched pattern whereas the solution fraction 3 kda show an hree enriched pattern compared with till in the catchment suspended particles show a lree enriched pattern data indicate that the ree are associated with two phases in the colloidal and particulate fraction an organic rich phase with associated al fe and an fe rich fe oxyhydroxide inorganic phase the ce anomaly in the suspended particulate fraction in the river shows systematic variations and can be used to interpret fractionation processes of the ree during weathering and transport there was no anomaly at maximum spring flood but during the ice covered period the anomaly became more and more negative the temporal and seasonal variations of the ce anomaly in the suspended particulate phase reflect transport of ree c al fe enriched colloids from the upper section of the till and or from mires to the river at storm events

a shallow detachment beneath the north greenland fold belt implications for sedimentation and tectonics in northern greenland in early palaeozoic time a turbidite trough the eastward extension of the hazen trough of arctic canada was flanked to the south by a carbonate platform the trough was deformed during the mid palaeozoic ellesmerian orogeny to form the e w trending north greenland fold belt this fold belt was deformed further by eurekan tertiary structures important among which is a major fault complex the harder fjord fault zone hffz the suggestion has been made that this fault zone controlled early cambrian sedimentation even though the fault trace does not coincide with the trough platform facies transition in sediments of that age this has led to some controversy we report new information from a mapping programme by the geological survey of greenland which has established the thin skinned nature of ellesmerian deformation at the trough platform transition and implies that much of the fold belt is underlain by a shallow detachment this in turn implies that the hffz exists in the hanging wall of the detachment while the early cambrian trough platform transition is located autochthonously in the foot wall we adduce evidence to show that the latter was probably controlled by syndepositional faulting with actively eroding fault scarps and suggest that these basement structures were reactivated in a dextral strike slip mode in early tertiary time to form the hffz as now observed

was the climate of the eemian stable a quantitative climate reconstruction from seven european pollen records the aim of the present study is to estimate the range of the climatic variability during the eemian interglacial which lasted about 10 000 years marine isotopic stage 5e the modem pollen analogue technique is applied to seven high resolution pollen records from france and poland to infer the annual precipitation and the mean temperature of the coldest month the succession of pollen taxa and the reconstructed climate can be interpreted coherently the warmest winter temperatures are centred in the first three millennia of the eemian interglacial during the mixed oak forest phase with quercus and corylus as dominant trees a rapid shift to cooler winter temperatures of about 6 degrees to 10 degrees c occurred between 4000 and 5000 years after the beginning of the eemian related to the spread of the carpinus forest this shift is more obvious for the reconstructed temperatures than for precipitation and is unique and irreversible for the whole eemian period following this climatic shift of the eemian variations of temperature and precipitation during the fast 5000 years were only slight with an amplitude of about 2 degrees to 4 degrees c and 200 to 400 mm yr the estimated temperature changes were certainly not as strong as those reconstructed for the stage 6 5e termination or the transition 5e 5d this is consistent with the constantly high ratio of tree pollen throughout the eemian indicative of a succession of temperate forest types this gradual transition between different forest landscapes can be related to intrinsic competition between the species rather than to a drastic climatic change c 1998 elsevier science b v all rights reserved

human induced development of mollic and umbric horizons in drained and farmed swampy alluvial soils abstract river regulation since the 17th century large scale drainage and intensive farming have seriously transformed soils in the river valleys of poland flood suppression and groundwater lowering have created oxidizing conditions in topsoil and allowed biological activity and plant rooting which has retarded original stratification of the alluvial substratum however ploughing has led to the development of thick humus horizons in particular soils with organic topsoil horizons have been changed i e they have lost their initial swampy nature and have undergone an anthropogenic transformation to mineral soils despite the long term agricultural land use it is still possible to recognize the peaty character of organic matter in some soils and this allows reconstruction of their origin this study investigated a sequence of soils in the valley of the river barycz i occasionally flooded very moist fluvic histic gleysols with a murshic organic layer ii weakly drained soils with a high groundwater table deeply ploughed where the sandy plough layer contains easily recognizable peat derived organic material weakly bound to the mineral fraction fluvic anthromollic gleysols and iii deeply drained soils deeply ploughed where organic carbon content in the plough layer is below 10 but peat derived particles of organic matter are still recognizable and are weakly bound to the mineral fractions endogleyic phaeozems anthric or endogleyic umbrisols anthric none of the thick plough layers although intentionally created by humans by mixing the organic layer with underlying sandy material fulfill the requirements of the anthropogenic diagnostic horizons therefore two new qualifiers are proposed to the wrb classification in relation to the recent addition of the murshic qualifier namely anmooric and atric to allow accurately naming the postswampy soils at subsequent stages of their transformation

a paleomagnetic reinvestigation of the upper devonian perry formation evidence for late paleozoic remagnetization america we undertook a reinvestigation of the upper devonian perry formation of coastal maine and adjacent new brunswick thermal demagnetization of samples from the redbeds yielded a characteristic direction d 166 l 4 that fails a fold test comparison of the corresponding paleopole 312 e 41 s with previously published paleozoic poles for north america suggests that the sediments were remagnetized in the late carboniferous after the removal of a steep northerly component the volcanics also reveal a shallow and southerly direction d 171 1 25 without tilt correction no stability test is available to date the magnetization of the volcanics however similarity of several of the directions to those seen in the sediments raises the suspicion that the volcanics are also remagnetized although the paleopole without tilt correction 303 e 32 s could be taken to indicate an early carboniferous age for the remagnetization scatter in the data suggests that the directions are contaminated by the incomplete removal of a steeper component due to present day field thus it is more likely that the volcanics were remagnetized at the same time as the sediments isothermal remanent magnetization irm acquisition curves blocking temperatures coercivities and reflected light microscopy indicate that the magnetization is carried by hematite in the sediments and by both magnetite and hematite in the volcanics it is therefore likely that the remagnetization of the perry formation involved both thermal and chemical processes related to the variscan alleghe nian orogeny our results indicate that previously published directions for the perry formation were based on the incomplete resolution of two magnetic components these earlier results can no longer be considered as representative of the devonian geomagnetic field

palaeomagnetism of caledonian intrusive suites in the northern highlands of scotland constraints to tectonic movements within the caledonian orogenic belt abstract to evaluate the scale of tectonic movements within the northern sector of the 500 400 ma caledonian orogenic belt and its precambrian foreland zone between the great glen fault ggf zone to the southeast and the laurentian block to the northwest we have studied the palaeomagnetism of minor intrusive rocks within the northern highlands terrain these rocks include 1 1 amphibolites and other metamorphic rocks predating deformation 2 2 microdiorities dolentes and related suites emplaced and probably magnetised between 450 and 420 ma and 3 3 lower middle devonian lamprophyres a range of predominantly nne negative and ssw positive components are resolved by cleaning treatment with a dispersion of declinations towards a minority wnw ese axis isolated southerly negative directed hematite held components suggests limited but no widespread remagnetisation in devonian carboniferous times comparison is made with data from other tectonic divisions in the caledonian orogenic belt and the bordering forelands palaeopoles from the northern highlands closely conform in part with north american ordovician poles and in part with the post ordovician palaeopoles from britain south of the ggf the definitive motions of the british caledonides to emerge from the palaeomagnetic analysis are an anticlockwise rotation of the caledonian terrain in early ordovician times small relative motions during the remainder of ordovician times followed by large clockwise and then anticlockwise rotations during late ordovician to early silurian times contemporary with the last major movements on the moine thrust ca 430 ma late silurian devonian movements along the ggf were probably below the limits of palaeomagnetic detectability the collective data require that apparent polar wander movements and concomitant continental movements have currently been incompletely recovered by north american studies and the path for lower palaeozoic times is more complex than recognised hitherto

palaeomagnetism of the loch doon granite complex southern uplands of scotland the late caledonian palaeomagnetic record and an early devonian episode of true polar wander abstract the southern uplands terrane is an ordovician silurian back arc foreland basin emplaced at the northern margin of the iapetus ocean and intruded by granite complexes including loch doon 408 3 1 5 ma during early devonian times protracted cooling of this 130 km 3 intrusion recorded magnetic remanence comprising a predominant a magnetisation linked to initial cooling with dual polarity and mean direction d i 237 64 95 4 palaeopole at 316 e 21 n subsidiary magnetisations include mesozoic remanence correlating with extensional tectonism in the adjoining irish sea basin b d i 234 59 and minority populations c d i 106 2 and d d i 199 1 recording emplacement of younger 395 ma granites in adjoining terranes and the variscan orogenic event the a directions have an arcuate distribution identifying anticlockwise rotation during cooling a comparable rotation is identified in the orthotectonic caledonides to the north and the paratectonic caledonides to the south following closure of iapetus continental motion from midsoutherly latitudes 40 s at 408 ma to equatorial palaeolatitudes by 395 ma is identified and implies minimum rates of continental movement between 430 and 390 ma of 30 70 cm year more than double maximum rates induced by plate forces and interpreted as a signature of true polar wander silurian devonian palaeomagnetic data from the british scandinavian caledonides define a 430 385 ma closed loop comparable to the distributed contemporaneous palaeomagnetic poles from gondwana they reconcile pre 430 ma and post 380 ma apw from this supercontinent and show that laurentia baltica avalonia lay to the west of south america with a relict rheic ocean opening to the north which closed to produce variscan orogeny by a combination of pivotal closure and right lateral transpression

experimental crm production in a basaltic rock evidence for stable intermediate palaeomagnetic directions summary remagnetization experiments involving secondary thermoremanent and chemical remanent magnetization trm crm have been carried out on samples from a basaltic lava flow the rock carries a stable nrm residing in deuterically oxidized class 11 111 titanomagnetite grains and some haematite formed by lowtemperature oxidation heating to 525 c in a controlled field of 52pt for periods ranging from 1 to 400 hr resulted in oxidation to haematite of a parent phase close to magnetite in composition the direction of the resulting crm is controlled both by the remagnetizing field and the primary remanence nrm giving rise to stable high blocking remanence components with intermediate directions and precluding identification of the primary nrm component control experiments carried out on chemically stable specimens gave a partial trm ptrm parallel to the remagnetizing field with blocking temperatures in agreement with single domain theory after removal of this secondary ptrm the primary direction in these specimens was regained the results imply that caution is advisable in analysing the palaeomagnetic directions of any rock which has undergone a thermochemical event

soil formation on calcium carbonate rich parent material in the outer carpathian mountains a case study abstract in this study ten stratified calcium carbonate rich soil profiles from the polish outer carpathians were investigated in order to identity the influence of parent material variability and slope processes on soil diversity and their evolution moreover we evaluated the morphological and physico chemical soil properties to recognize the diagnostic horizons and classification of such soils while it is usually thought that carbonate rich soils are considered as formed in situ these study soils clearly presented layering and contribution of materials as they were developed from mixed substrates of different origin e g as the result of mass movements and possible aeolian silt contribution irrespective of the type of parent material every investigated soil showed traces of slope processes resulting in heterogeneous soil profiles further a few different patterns of primary calcium carbonate arrangement were found in general the studied soils were characterized by enrichment with calcium carbonate not only due to inheritance from calcium carbonate rich parent material but also translocation of calcium carbonate within soil profiles the latter depending on soil stratification based on the obtained results four pathways of soil evolution were formulated leptosols which represent initial calcium carbonate rich soils may evolve in different directions first formation of the thick layer suitable for cambic horizon development under deciduous forests which enables the classification of such soils as cambisols depends on slope processes and allochthonous material deposition in turn the decrease of mineralization rates for organic matter delivery of soil material from the upper parts of the slope as well as mixing of organic matter by mesofauna result in the formation of mollic horizons and transformation of leptosols into phaeozems further erosion and redeposition of fine soil material provide two types of slope sediments i those with silt loam texture dominance and ii clay loams interstratified with silty substrates the first type of sediments are more suitable for water percolation and after carbonate leaching clay dispersion and translocation occur in such materials luvisols may develop sediments with a prevalence of clay loam aided stagnosol formation in which pools of carbonates were stabilized due to the reduction of water percolation leading to stagnation

palaeomagnetism of the foyers and strontian granites scotland abstract palaeomagnetic data from the newer granites of foyers and strontian show similar directions of magnetization with southerly declinations and horizontal to intermediate mostly downward dipping inclinations these palaeomagnetic directions which accord with previous data from the helmsdale granite are thought to be of siluro devonian age the present results are not sufficiently precise to justify discussion of possible lateral displacements along the great glen fault of the order of a few hundred kilometres but it is clear that the recent idea of a c 15 20 latitudinal offset along the fault in the carboniferous has to be disregarded

geochemical exploration for platinum group elements in the bushveld complex south africa analyses of stream sediment and soil samples from the bushveld complex south africa have revealed enhanced precious metal concentrations which can be related both to mining activities and the presence of hidden concentrations of platinum group elements pges and gold the economically important pge deposits hosted by the upper critical zone of the rustenburg layered suite are revealed by a high pge and au content in the overlying soils a second zone of elevated precious metal concentrations straddles the boundary between the main and upper zones and has to date been traced for more than 100 km this zone follows the igneous layering of the rustenburg layered suite and is offset by the brits graben it is therefore thought to be the reflection of a magmatic pge au mineralisation

holocene vegetation history and soil development reflected in the lake sediments of the karkonosze mountains poland a 11 m long lake sediment core of a mountain lake situated at 1225 m a s l in the karkonosze mountains poland provided a unique multi proxy archive to reconstruct natural and human induced environmental changes over the entire holocene period pollen analyses allowed for the local and regional reconstruction of vegetation history the chemical composition of the core and the determination of amorphous fe and al phases enabled to trace back soil formation in the surrounding catchment about 11 ka ago birch pine and pine birch communities started to develop in the preboreal chronozone subsequently the vegetation cover changed to corylus picea abies fagus in the higher and middle mountain zones and to ulmus quercus carpinus in the mountain foreland and footslopes the decline of forests that started in the 11th century because of clearing was accompanied by the expansion of grasses both as pastures in the mountains and cereal crops in the foreland at the same time the mining and smelting gave ri

was the devonian geomagnetic field dipolar or multipolar palaeointensity studies of devonian igneous rocks from the minusa basin siberia and the kola peninsula dykes russia

paleomagnetism of the upper devonian catskill formation from the southern limb of the pennsylvania salient possible evidence of oroclinal rotation multiple components of magnetization were isolated in the natural remanent magnetiza tion of samples of the upper devonian catskill formation red beds taken from the southern limb of the pennsylvania salient the dominant ther mally distributed component sf previously thought to predate folding is demonstrably syn folding in origins the mean direction for sf based on data from the current study and a pre vious study is declination inclination 161 6o 7 9 o a95 3 9 o pole position 127 3oe 43 1on a95 3 1 o n 14 sites although the remagnetization is clearly synfolding in most areas the relative ages of folding and remagne tization vary locally a subordinate high unblocking temperature component ht has a mean tilt corrected direction of 160o 36 o a95 16 o pole position 123 5oe 26 ion a95 15 4 o s n m 7 samples comparison of ht with the prefolding magnetization isolated in the northern limb of the salient suggests that the paleolatitude of this part of north america was about 16os and that part of the curvature of the salient was acquired during orogenesis

a fluid inclusion and stable isotope study of 200 ma of fluid evolution in the galway granite connemara ireland fluid inclusions in granite quartz and three generations of veins indicate that three fluids have affected the caledonian galway granite these fluids were examined by petrography microthermometry chlorite thermometry fluid chemistry and stable isotope studies the earliest fluid was a h2o co2 nacl fluid of moderate salinity 4 10 wt nacl eq that deposited late magmatic molybdenite mineralised quartz veins v1 and formed the earliest secondary inclusions in granite quartz this fluid is more abundant in the west of the batholith corresponding to a decrease in emplacement depth within veins and to the east this fluid was trapped homogeneously but in granite quartz in the west it unmixed at 305 390 c and 0 7 1 8 kbar homogeneous quartz 18o across the batholith 9 5 0 4 n 12 suggests v1 precipitation at high temperatures perhaps 600 c and pressures 1 3 kbar from magmatic fluids microthermometric data for v1 indicate lower temperatures suggesting inclusion volumes re equilibrated during cooling the second fluid was a h2o nacl kcl low moderate salinity 0 10 wt nacl eq moderate temperature 270 340 c high d 18 2 low 18o 0 5 2 0 fluid of meteoric origin this fluid penetrated the batholith via quartz veins v2 which infill faults active during post consolidation uplift of the batholith it forms the most common inclusion type in granite quartz throughout the batholith and is responsible for widespread retrograde alteration involving chloritization of biotite and hornblende sericitization and saussuritization of plagioclase and reddening of k feldspar the salinity was generated by fluid rock interactions within the granite within granite quartz this fluid was trapped at 0 5 2 3 kbar having become overpressured this fluid probably infiltrated the granite in a meteoric convection system during cooling after intrusion but a later age cannot be ruled out the final fluid to enter the granite and its host rocks was a h2o nacl cacl2 kcl fluid with variable salinity 8 28 wt nacl eq temperature 125 205 c d 17 to 45 18o 3 to 1 2 13cco2 19 to 0 and 34ssulphate 13 23 that deposited veins containing quartz fluorite calcite barite galena chalcopyrite sphalerite and pyrite v3 correlations of salinity temperature d and 18o are interpreted as the result of mixing of two fluid end members one a high d 17 to 8 moderate 18o 1 2 2 5 high 13cco2 4 low 34ssulphate 13 high temperature 205 230 c moderate salinity 8 12 wt nacl eq fluid the other a low d 61 to 45 low 18o 5 4 to 3 low 13c 10 high 34ssulphate 20 23 low temperature 80 125 c high salinity 21 28 wt nacl eq fluid geochronological evidence suggests v3 veins are late triassic the high d end member is interpreted as a contemporaneous surface fluid probably mixed meteoric water and evaporated seawater and or dissolved evaporites whereas the low d end member is interpreted as a basinal brine derived from the adjacent carboniferous sequence this study demonstrates that the galway granite was a locus for repeated fluid events for a variety of reasons from expulsion of magmatic fluids during the final stages of crystallisation through a meteoric convection system probably driven by waning magmatic heat to much later mineralisation concentrated in its vicinity due to thermal tectonic and compositional properties of granite batholiths which encourage mineralisation long after magmatic heat has abated

palaeomagnetism of the middle upper devonian esha ness ignimbrite w shetland abstract the ignimbrite division of the esha ness volcanics of w shetland has been studied palaeomagnetically the major blocking temperature spectrum ranges between 650 and 680 c implying that haematite is the principal remanence carrier the magnetization build up is simple a minor low stability magnetization aligned along the direction of the present earth s field is superimposed on a well defined and highly stable palaeomagnetic component with dec 220 and inc 3 the esha ness volcanic sequence is folded into a gentle syncline trending nne the rock collection concerned covers 8 sites 7 from the western flank and 1 from the eastern flank of the syncline the 7 sites on the west flank are consistently reversely magnetized while the site on the east flank has a normally directed magnetization after structural unfolding the normal and reverse directions are almost perfectly antiparallel i e the stable magnetization most likely predates the tilting which is probably of devonian age esha ness is located some 12 km to the west of the walls boundary fault wbf which is considered as the northward continuation of the great glen fault ggf the shallow palaeomagnetic inclination found in old red sandstone rocks to the west of ggf wbf corresponds to that encountered in most other european old red formations discounting therefore megascale 1000 km late post devonian movements along this dislocation

implications of early devonian poles from the canadian arctic archipelago for the north american apparent polar wander path lower devonian red beds from the upper member of the peel sound formation at prince of wales island canadian arctic yield two different paleopoles at 25n 099e and at 01n 091e the first one being

early proterozoic oceanic crust and the evolution of subcontinental mantle eclogites and related rocks from southern africa seven eclogitic nodules from kimberlites in southern africa have been studied in detail for whole rock major and trace element geochemistry petrography and mineral chemistry by electron microprobe high purity mineral separates from six of these samples have been analyzed for trace elements and for the isotopic composition of sr nd and oxygen three eclogite groups are recognized group a eclogites have very high mg fe low na in pyroxene moderate 18o 4 7 to 5 3 and low 87sr 86sr and 143 144nd olivine and enstatite may also be present as accessory phases in this group group b eclogites have moderate to high mg fe ratios high na in pyroxene low 18o 3 0 to 3 4 high 87sr 86sr and 143nd 144nd ratios and extremely lree depleted hree enriched garnets with no eu anomalies group c eclogites have low mg fe ratios high na in pyroxene and variable sr nd and o isotope compositions accessory feldspar is present in one sample that may be of crustal origin mineral separates of garnet and pyroxene have positive eu anomalies the group a eclogites are too refractory to represent magma compositions and must have formed as cumulate dike rocks in the upper mantle that contain a minor trapped liquid component this is supported by the presence of accessory olivine and enstatite and by their ksm and knd which are similar to empirical pyroxene garnet partition coefficients the group b eclogites are extremely depleted in incompatible elements and have ndvalues 10x to 20x morb the high 87sr 86sr of these eclogites is not consistent with their strongly depleted lree and high nd and cannot be primary it must have been imposed on the protolith the low 18o of these eclogites cannot form by mantle fractionation processes and must also be inherited from the protolith both the sr and oxygen isotope data are consistent with high temperature hydrothermal alteration of a basaltic protolith followed by partial melting to form the refractory compositions observed now the hydrothermal fluid may have been sea water but secondary enrichment of the protolith in rb is required to generate the observed high sr ratios the high na content of the pyroxenes supports a spilitic alteration event the major and trace element characteristics of the group c eclogites are consistent with recrystallization of a cumulate gabbro protolith one group c rock is probably a garnet granulite derived from the lower crust the other may represent the plutonic portion of oceanic crust a reconstructed whole rock isochron for the three bellsbank eclogites yields an age of 2 1 0 1 b y this implies that plate tectonic processes involving the generation and subduction of oceanic crust have been active since the early proterozoic the early proterozoic ocean crust consisted of two components a plutonic section of gabbro cumulates group c eclogites and a volcanic section of basalt group b eclogites the volcanic component has undergone substantial hydro thermal alteration and subsequent partial melting to form a refractory residue the plutonic component is less modified

layering and precious metals mineralization in the rincon del tigre complex eastern bolivia geologic investigations supporting recent technically successful platinum exploration of the rincon del tigre complex a ca 4 6 km thick layered sill have provided significant new understandings of the layering development and precious metals mineralization of one of south america s largest mafic ultramafic intrusions three macrocyclic units are recognized from the base up basal unit unit 1 and unit 2 each most likely the product of a major replenishment with mafic magma of one compositional type the ultramafic rocks of all three macrocyclic units largely comprise repeated minor cyclic units of poikilitic harzburgite granular harzburgite olivine bronzitite each a few meters thick with occasional development of bronzitite at the top mafic rocks absent from unit 1 and present only locally in the basal unit form a well developed norite gabbro magnetite gabbro sequence in the upper half of unit 2 associated with the base of the magnetite gabbro is the precious metals zone a persistent zone of low grade subeconomic sulfide and precious metals mineralization 80 to 185 m thick the precious metals zone comprises an upper cu sulfide rich portion its base the sulfide phase boundary about 23 to 70 m above the magnetite phase boundary and a lower precious metals rich portion the lower part straddling the magnetite phase boundary the individual precious metals are concentrated in separate sulfide poor subzones each up to many tens of meters thick in the stratigraphic order rh pt pd au with peak offsets at the same scale modal layering of silicates and magnetite is well developed in the mafic rocks as is modal and cryptic precious metals layering of the sulfides in the precious metals zone all at three different superimposed scales from about 3 m to several tens of meters a possible interpretive framework for the cryptic layering and perhaps for much of the other layering including the meter scale layering of the ultramafic rocks is provided by the likely compositional stratification of the resident magma initiated by the fluid dynamics of the replenishment and mixing processes and in the magnetite gabbro by repeated convective overturns caused by the onset of magnetite precipitation the characteristics of the precious metals zone fit an orthomagmatic model the composition stratigraphic relations and modal correlation with magnetite of the sulfides all imply that s saturation was induced by loss of feo to magnetite precipitation this took place after prolonged closed system fractionation following the last major magma injection at the base of unit 2 during which crystallization of olivine pyroxene plagioclase and finally magnetite precipitation led to overall s cu and precious metals enrichment and ni and finally fe depletion of the magma the development of the mineralization and its complex layering was controlled by sulfide segregation rayleigh fractionation the different but generally very high partition coefficients dsilicate sulfide for each precious metal and repeated convective overturns at three different superimposed scales the decoupled metals distribution is analogous and similar in origin to that of the main sulfide zone of the great dyke zimbabwe and of the main sulfide layer offset portion of the munni munni complex western australia but the stratigraphic order of metal enrichment peaks is different pt pd au vs pd pt au this suggests a reversal in the relative magnitudes of the partition coefficients dpt and dpd that was possibly brought about by changes in the temperature and o s and fe activities of the magmas between the middle and late stages of crystallization constancy of d values during fractionation of mafic magma should not be assumed the precious metals zone is one of several skaergaard type strata bound precious metals zones associated with magnetite gabbros in the upper levels of many layered intrusions and the origin of the skaergaard mineralized zone itself including the potentially economic platinova reefs can be explained in terms of the precious metals zone model presented here the very low grade great thickness and wide separation of individual metal subzones in the precious metals zone are similar to those of the subeconomic axial facies of the main sulfide zone in the wider parts of the great dyke cf the economic more compact marginal facies on the basis of the lateral and vertical thermal model of the great dyke magma chamber the subeconomic status of the precious metals zone may be in large part a function of the specific fluid dynamics of the rincon del tigre magma chamber

british paleomagnetism iapetus ocean and the great glen fault new paleomagnetic data for britain establish the width of the iapetus ocean as 1000 km in mid ordovician time but do not yet allow precise estimates of the rate of its subsequent closure the new lower paleozoic data from northern scotland are similar to data from the rest of britain but are not compatible with north america data on the bullard et al reassembly if this discrepancy is correct lines of major transcurrent dislocation have yet to be identified either in the north atlantic continental shelves and margins or in eastern north america and the great glen fault was not the main locus of offset between britain and north america the tectonic complexities associated with this configuration require further evaluation

pre alpine mire sediments as a mirror of erosion soil formation and landscape evolution during the last 45 ka peat and lake sediments as well as a nearby soil catena were sampled to reconstruct the environmental history of a small infilled lake basin mire in the central alpine foreland of switzerland soil evolution is best regarded as discontinuous over time and conceptualised by progressive or regressive process phases we analysed the surrounding soils and used corresponding pedosignatures in the mire sediments to characterise notable phases of erosion and deposition we assumed that the mire sediments would reflect these phases that elemental composition major and minor compounds and rare earth elements rees would allow us to differentiate past processes and that progressive and regressive phases of soil development can be discerned although radiocarbon ages are equivocal it appears from pollen analyses that a lake was present here by c 45 ka bp after the retreat of the glacier from this area following the lgm continuous sedimentation occurred until a mire developed during pleistocene holocene transition this transition period was accompanied by more intense erosion as characterised by chemical signatures a stable phase developed between c 10 5 ka bp giving rise to progressive soil evolution between 5 and 4 ka bp evidence appears for several erosional phases predominantly detectable at the margin of the mire these erosion phases coupled with accumulation in the mire are even more evident after 4 ka bp and especially after 2 1 ka bp based on soil investigations elemental fluxes are detected along the slopes with distinct accumulations at the footslope evidence for anthropogenic influences and subsequent regressive soil formation phases appear in this pre alpine landscape about 5 ka bp neolithic early bronze age which appears to intensify after 2 1 ka bp roman period to present multi elemental signatures enabled us to identify the important geochemical processes that have occurred here together with radiocarbon and pollen analyses we placed these processes in a logical temporal context the use of lacustrine lake or mire sediments has great potential to decipher and detail the surrounding landscape history and soil evolution of this region of switzerland

magnetostratigraphy of the plio pleistocene kap kobenhavn formation eastern north greenland abstract the newly discovered late cenozoic kap kobenhavn formation in peary land eastern north greenland 82 30 n 21 w which consists of at least 100 m unconsolidated sands silts and clays deposited in marine shallow waters covers an area of some 500 km2 the time of deposition spanned by the sequence is estimated by comparisons with typical rates of isostatic rebound in greenland to be roughly of the order of 3 104 years abundant content of organic remains indicates a warmer climate than at present a number of 185 oriented palaeomagnetic specimens from two parallel composite profiles indicate after af cleaning that the sampled part of the formation was deposited during a period of reversed geomagnetic polarity combining the polarity information with information from biostratigraphy and amino acid ratios the most likely age of the kap kobenhavn formation is estimated to be constrained to the older part of the matuyama reversed polarity chron i e with an age of between 1 87 ma pre olduvai and 2 48 ma post gauss the most reliable least scattered parts of the magnetic record give cleaned mean inclinations of 77 and 59 respectively indicating a systematic departure from the axial dipole in the near sided sense in contrast to most other late tertiary palaeomagnetic results

short paper palaeomagnetic constraints on the geological terrane models of the scottish caledonides a compilation of new and published palaeomagnetic data from the scottish caledonides allows construction of apparent polar wander paths apwps for the grampian highlands midland valley and southern uplands terranes geological incompatibilities between terranes are the result of predominantly palaeolongitudinal movements prior to late silurian times a common late silurian early devonian corner in each apwp suggests the terranes to have docked to within the errors of the individual determinations by this time

palaeomagnetic re examination of the basal caithness old red sandstone aspects of local and regional tectonics abstract a palaeomagnetic re examination of the basal strata of the caithness old red sandstone has given results that are fully compatible with previous palaeomagnetic findings in this region after structural correction the dominant remanence component has d 205 i 3 95 6 4 n 27 the existence of this shallow inclined magnetization in the middle devonian strata of caithness invalidates the model proposed by van der voo and scotese 1981 involving a ca 2000 km sinistral offset along the great glen fault in the carboniferous however the available data are in favour of a few hundred kilometres sinistral movement along this fracture zone however the possibility of there having been a much larger transcurrent shift between europe and north america in late post devonian times accumulated along various fracture zones within the caledonian fold belt is discussed on the basis of an inferred overprinted magnetization it is tentatively concluded that the tectonic deformation of the old red sandstone of caithness has a mid jurassic or younger age

weathering mineralogical evolution and soil organic matter along a holocene soil toposequence developed on carbonate rich materials a toposequence of holocene soils located between 1100 2400 m asl in the italian alps served as the basis for the following analyses the weathering of limestone and dolomite the calculation of mass balances understanding the formation of pedogenic fe and al the determination of soil mineral and clay mineral reactions and transformation and the measurement of accumulation and stabilisation mechanisms of soil organic matter leaching of carbonates is most intense at the lower elevations although calcite and dolomite have a higher solubility at low temperatures the pco2 in the soil is higher at lower elevations and weathering is driven mainly by carbonic acids at higher elevations organic acids appear to determine the mineral transformations and weathering reactions to a greater extent this suggests that two very different weathering regimes carbonic and organic acid weathering exist along the toposequence the transformation of mica into vermiculite is the main process in both the clay and fine earth fraction weathering of silicate minerals started even before the carbonates had been completely removed from the soils the transformation mechanisms of silicate minerals in the a and o horizon at higher elevations was at least as intensive as that at the climatically warmer sites the neoformation of pedogenetic clays at climatically cooler sites was slightly greater than that at the warmer sites however the formation rate of secondary fe and al phases was more pronounced at lower elevation which means that this process seemed to be driven dominantly by carbonic acid weathering of primary minerals soil organic matter som abundance in the mineral soil is nearly 15 kg m2 at all sites and surprisingly no climate driven effect could be detected in general the preservation and stabilisation of som was due to poorly crystalline al and fe phases and vermiculite regardless of some variations in the composition of the parent material varying calcite dolomite ratio

palaeomagnetic study of the cairnsmoor of fleet granite and criffel dalbeattie granodiorite contact aureoles caledonian tectonics of the southern uplands of scotland and devonian palaeogeography the plutons of cairnsmoor of fleet 392 2 ma and criffel dalbeattie 397 2 ma both mineral isochron ages comprise two of four major post tectonic granitic complexes emplaced into the southern uplands an ordovician silurian back arc and foreland basin complex formed at the northern margin of the iapetus suture to expand the palaeomagnetic record of the southern uplands we have studied palaeomagnetism and magnetic fabrics in traverses spanning contacts of these intrusions with host mudrocks a uniform anisotropy of magnetic susceptibility ams fabric across the cairnsmoor of fleet contact has been enhanced by recrystallization into hornfels near the contact and records a late acadian regional stress operative during or soon after emplacement of the pluton in middle devonian times magnetization during slow cooling recorded a dual polarity a remanence in granite and hornfels with mean direction d i 92 2 95 6 5 yielding a palaeopole q 6 at 2 n 265 e linked to cooling at c 392 ma subsidiary magnetizations are overprints imparted during variscan tectonism b d i 194 6 and jurassic rifting within the adjoining irish sea basin c c 160 140 ma d i 172 52 the criffel dalbeattie pluton has more complex ams fabrics recording both deformation and emplacement effects hematite of secondary hydrothermal origin is a significant feature of the rock magnetic record in the aureole which is otherwise dominated by paramagnetism the granodiorite is more strongly magnetized than the country rocks accounting for a positive aeromagnetic anomaly a fairly dispersed dual polarity remanence mean d i 115 55 95 18 in granodiorite and late tectonic porphyrite dykes is probably the oldest magnetization preserved in this pluton because it correlates with an excursion of britain into southerly palaeolatitudes at c 410 ma and indicates an early devonian emplacement age the palaeofield at c 397 ma the currently accepted isotopic age is recorded by a minority overprinted remanence mean d i 272 2 95 12 similar to the record in the cairnsmoor of fleet pluton and granites from the adjoining lake district terrane granite complexes of the southern uplands block collectively record regional rotation and excursion of britain into southerly latitudes between c 410 and 390 ma comparable silurian devonian palaeomagnetic poles identify common apparent polar wander apw in paratectonic and orthotectonic terranes from the variscan front in the south to the laurentian foreland in the north following climactic acadian deformation apw between 430 and 390 ma embracing the post closure history of the caledonian orogen is a loop executed at rates much higher than typical rates of plate motion and appears to record a component of true polar wander the 110 arc length is identical to polar shift identified between mid silurian and lower middle devonian poles from gondwana the two paths superimpose to show that the western margin of gondwana was in proximity to the se margin of laurentia during acadian deformation in early middle devonian times and remote from the caledonides the residual rheic ocean subsequently closed by a combination of pivotal and left lateral strike slip motions

evaluating the use of weathering indices for determining mean annual precipitation in the ancient stratigraphic record abstract different quantitative methods have been developed to determine paleo rainfall using paleosols of particular interest are methods that use bulk geochemistry to calculate a weathering index and from that mean annual precipitation twenty three paleosols that formed during a time of significant climate change the paleocene eocene thermal maximum petm were analyzed to evaluate the relative merits of two geochemical proxies that have been developed for estimating paleoprecipitation one depends on the chemical index of alteration without potash cia k and the other uses the calmag weathering index which depends on cao and mgo the paleosols are located in the paleogene fort union and willwood formations in the bighorn basin wy morphologic differences among the paleosols indicate that they formed under varied soil moisture conditions a morphology index was developed from pedogenic features that are sensitive to soil drainage and thus to rainfall to assess that variability quantitative mean annual precipitation map values were calculated for each paleosol using the cia k index and the calmag index which was developed specifically for vertisols those results were compared to the morphology index for 23 paleosols the results indicate that increases and decreases in map calculated from both methods correlate relatively well to changes in the soil morphology index however the results from the calmag weathering index show a stronger correlation the results suggest that the calmag proxy provides a more robust map estimate for vertisols in addition to comparing map estimates to the soil morphology index we compared the map values to paleorainfall estimates determined from paleofloras at the same stratigraphic levels as three of the paleosols that comparison confirms that the calmag method is reliable for reconstructing map from ancient vertisols the results also show that in the bighorn basin vertisols with a b horizon

environmental changes of a shallow kettle lake catchment in a young glacial landscape sumowskie lake catchment north central poland abstract on the basis of detailed analysis sedimentological palynological macroremains geochemical and gis analysis the development of the sumowskie paleolake was reconstructed obtained results led to distinguish three main stages of the evolution of the basin and its catchment during the late glacial and the holocene the lacustrine stage the lake overgrowth stage and the post lacustrine stage study site is located in the western part of the brodnica lakeland north eastern poland within the former sumowskie lake bottom multidisciplinary research was conducted for two cores sedimentological palynological plant macroremains sum a 149 cm and sum c 51 cm and the soil profile sum 3 sedimentological geochemical gis analyses land cover and water level changes were carried out for the nowadays sumowskie lakes catchment it was confirmed that climate was the most important factor influencing the evolution of the lake and its surrounding although the role of this factor decreased in the neo holocene period in favor of rapidly growing human impact changes of the water level were much more abrupt and lasted longer e g 9500 5000 bp hiatus caused by the water level decrease than in other described basins of the region due to the specific geomorphologic situation shallow kettle basins could alternately act as lakes and wetlands as they are well spread in the young glacial area the strong influence of this abrupt and long term events should be reconsidered

paleomagnetism of the lower devonian traveler felsite and the acadian orogeny in the new england appalachians a suite of felsic extrusive rocks from the lower devonian traveler felsite north central maine 46 1 n lat 68 9 w long was collected for paleomagnetic study 28 samples from 5 sites in the lower pogy member 56 samples from 10 sites in the upper black cat member and 13 samples from 10 cobbles in the basal conglomerate of the overlying trout valley formation characteristic magnetizations based on af demagnetization analyses and supported by thermal studies give a formation mean direction after simple correction for bedding tilt of d 25 2 i 20 2 95 10 6 for 13 sites in the traveler felsite the occurrence of normal and reversed magnetozones under stratigraphic control and the antiparallel directions of the polarity units following the tilt correction indicate an acquisition of remanence near the time of formation of the rock units the mean direction corresponds to a south paleopole position of 29 s lat 262 e long p m 6 11 for the traveler felsite this pole position is in close agreement with poles from two other rock units of similar age from the same lithostratigraphic belt in the northern appalachians the mean of these three poles is distinct from late silurian and middle devonian poles from cratonic north america laurentia and from early devonian results from the acadia displaced terrane suggesting that this area constituted a separate tectonic unit during the early devonian we propose a tectonic model in which a traveler terrane is rotated 20 to 30 while converging with laurentia and undergoing deformation during the early to middle devonian acadian orogeny

evidence against large scale carboniferous strike slip faulting in the appalachian caledonian orogen kent and opdyke1 have argued that during the late devonian and early carboniferous the eastern part of the northern appalachians acadia was situated 1 500 km further south relative to cratonic north america than it is at present and that it moved to its present position sometime later in the carboniferous fig 1 van der voo and scotese2 proposed an even greater displacement of 2 000 km which they attribute to motion between cratonic north america and europe acadia being attached to europe fig 1 the argument is that palaeolatitudes p derived palaeomagnetically from upper devonian and lower carboniferous rocks of cratonic north america are 15 20 more northerly than those of acadia and europe the proposed shear zone passes through central newfoundland using palaeomagnetic results from eastern and western newfoundland we show here that no such motion occurred we also show that kiaman late carboniferous and permian overprinting is widespread in newfoundland and that these secondary magnetizations agree with two exceptions attributed to dextral rotation of the colorado pleateau with observations from late devonian and early carboniferous rocks of the north american craton confirming the proposal3 that magnetizations of the cratonic early carboniferous rocks are kiaman not early carboniferous in age our results also enable us to extend this proposal3 to late devonian rocks of the craton hence the palaeolatitudinal offset of fig 1 is almost certainly not tectonic but is an artefact of the wrong assumption of the equivalence of rock and magnetization ages

distinguishing subalpine soil types using extractible al and fe fractions and ree geochemistry article i nfo only a few paleoecological studies have attempted to use the geochemistry of lacustrine sediments to reconstruct the history of soil genesis the geochemical signatures of modern soils must firstly be determined before using them to investigate lake sediments our study explores the geochemical variability between eight subalpine soil profiles from the internal zone of the alps to find relevant sediment tracers for present day soils based on the concentrations of secondary al and fe bearing phases as well as major element and rare earth element ree geochemistry different subalpine soil types can be clearly differentiated in the study area although formed in similar geomorphological settings the soil typologies are diverse podzol group soils are developed under old growing coniferous forest whereas cambisols occur under present day old meadows by applying pca including pedological and geochemical parameters we can clearly discriminate between podzol and cambisol samples revealing differences that reflect the intensity of chemical weathering in contrast deep and surface samples can be distinguished using the degree of physical weathering the proportions of organic bound al and fe are significantly higher in podzols thus providing a sediment tracer to reconstruct the intensity and degree of podzolisation the increase of light ree fractionation from the c horizons to the topsoil horizons is explained in terms of soil processes the high field strength element nb is used to estimate enrichment or depletion relative to the unweathered parent material the resulting normalized ree patterns indicate that podzol profiles are more depleted than cambisols moreover normalized ree patterns of a and bw horizons are similar in the cambisol profiles whereas the e and bs horizons of podzols exhibit large variations normalized ree patterns may thus provide a precise tracer of the degree of weathering of materials hence we suggest that ree behaviour and soil weathering are clearly related this study also highlights the effects of millennial scale agricultural practices on soils e g the eventual depodzolization related to deforestation

modelling soil landscape genesis a time split approach for hummocky agricultural landscapes abstract here we present a scheme for modelling soil landscape development in hummocky agricultural landscapes of formerly glaciated terrains soil landscape development is regarded as discontinuous over time long term progressive soil development during the holocene was replaced abruptly by an intense period of regressive pedogenesis during the last 50 years which is deduced from published 137 cs data and catchment scale mass balances consequently our primary working hypothesis is that the recent soil pattern is mainly a result of human influence during the last 50 years the paradigm behind our approach is that we have to couple geological historical information with recent dynamics of relevant processes to understand soil landscape development spatially distributed erosion and sedimentation are the most important processes during that period the intensity and extent of these processes is however also a function of the spatial pattern of soils erodibility which evolved in the progressive period therefore we developed a time split modelling approach for the progressive period relevant pedogenic processes de carbonatization silicate weathering clay translocation have to be quantified by a spatially distributed coupled water flow and solute transport model based on reconstructed initial and upper boundary conditions geomorphic units climate history relevant outputs e g topsoil textural properties are used as a spatially distributed input for the model of the regressive period for the latter we use a modified version of the dynamic physically based erosion 3d model schmidt j von werner m michael a 1996 erosion 2d 3d a computer model to simulate water erosion in german sachsische landesanstalt fur landwirtschaft dresden which allows spatially distributed modelling of water related soil erosion and deposition relevant topsoil properties are iteratively adapted to the rates of spatially distributed erosion and deposition preliminary results suggest that a coupling with tillage erosion plays an important role in our landscapes explicit analyses of the soil pattern using digital soil mapping techniques will be applied for model validation

the timing of glacier advances in the northern european alps based on surface exposure dating with cosmogenic 10be 26al 36cl and 21ne

mass fluxes and clay mineral formation in soils developed on slope deposits of the kowarski grzbiet karkonosze mountains czech republic poland abstract weathering mineral formation and transformation processes along slopes are complex in cool mountainous regions undisturbed soil development with a strong vertical leaching element may abruptly change as a result of erosion accumulation lateral water fluxes and aeolian input we investigated soils in the eastern karkonosze mountains that have developed on silicatic slope deposits to date illite vermiculite and chlorite are the minerals that have been detected in the clay fraction although the climate and parent material should be favourable for the formation of smectites expandable phases were not verified so far we investigated if expandable phases could be detected and how they related to elemental fluxes along a short slope sequence 1142 1268 m a s l on the border between the czech republic and poland mass balance calculations indicated intensive mineral weathering together with a significant leaching of mg al ca and mn on the shoulder and foot slope positions in the middle zone which has a concave or undulating surface shape however the mass balances of several elements na k al p revealed a less pronounced leaching corresponding to a lower degree of podsolization and in some cases even accumulation at all sites mass balance calculations and detected soil minerals e g the increase in illite towards the surface together with an increase in al and k indicate some aeolian input kaolinite was detected in all soil horizons its concentration slightly increased towards the soil surface together with the pronounced leaching of ca part of kaolinite originates from plagioclase weathering besides being a weathering product of primary minerals part of the kaolinite is inherited from the parent material and probably is also due to aeolian input in all soils illite was being transformed into vermiculite and smectites through regularly interstratified illite smectite phases in addition the content of chloritic components which increases with depth indicated their concurrent weathering and transformation into smectites amphibole also may have acted as a source of smectites not all smectite is being actively formed in the soil most likely due to slope processes cover beds that affected even the subsoil some smectite has been transferred along the slope part of the smectite also seems to derive from the parent material active formation of expandable clay minerals is related to convex and planar landscape forms this relationship suggests intense element leaching inheritance from the parent material and cover bed mixing processes have contributed to the presence of smectite along the slope zones with predominant vertical transport shoulder foot slopes may repeatedly be interchanged with zones dominated by lateral transport undulating slope concave forms

palaeomagnetism of silurian sediments in w ireland evidence for block rotation in the caledonides summary a palaeomagnetic study of mid silurian wenlock sediments of the salrock formation in nw galway yields a reliable silurian palaeomagnetic pole position for w ireland at latitude 1 6 s longitude 287 7 e dp 2 5 dm 4 6 n 27 sites a further 12 sampling sites were located in silurian redbeds on clare island s mayo where a palaeomagnetic remanence of silurian age was also identified both remanences pre date local late caledonian folding however the clare island result has an anomalous azimuth when compared with the salrock result and with published silurian results for britain the two irish results can be reconciled by anticlockwise block rotation of the clare island region through 40 50 the rotation brings both palaeomagnetic and structural trends within the two sampling regions into alignment strike slip displacement across the clew bay fault zone producing a sinistral shear couple might have enabled such a rotation the timing and geographic extent of the proposed block rotation is as yet poorly defined however a younger age limit for rotation is provided by a late devonian or carboniferous partial magnetic overprint observed throughout both study areas and from geological evidence it seems likely that rotation is confined to the clew bay fault zone the dalradian rocks of the connemara massif located to the south of the salrock district have an e w structural grain some workers have proposed clockwise rotation of the connemara massif of ca 30 at between 500 and 390 ma which would bring the structural trends in w ireland into parallelism with caledonian trends in scotland because the silurian salrock succession which rests unconformably on the dalradian basement of connemara shows no such anomaly it provides a younger age limit for the possible rotation of connemara

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

progressive and regressive soil evolution phases in the anthropocene soils have a substantial role in the environment because they provide several ecosystem services such as food supply or carbon storage agricultural practices can modify soil properties and soil evolution processes hence threatening these services these modifications are poorly studied and the resilience adaptation times of soils to disruptions are unknown here we study the evolution of pedogenetic processes and soil evolution phases progressive or regressive in response to human induced erosion from a 4000 year lake sediment sequence lake la thuile french alps erosion in this small lake catchment in the montane area is quantified from the terrigenous sediments that were trapped in the lake and compared to the soil formation rate to access this quantification soil processes evolution are deciphered from soil and sediment geochemistry comparison over the last 4000 years first impacts on soils are recorded at approximately 1600 yr cal bp with the erosion of surface horizons exceeding 10 t km 2 yr 1 increasingly deep horizons were eroded with erosion accentuation during the higher middle ages 1400 850 yr cal bp reaching 1000 t km 2 yr 1 and leading to the remobilization of carbonated and poorly weathered material hence rejuvenating soil development erosion exceeded the soil formation rate and constituted a regression in the development of soils the tolerable erosion limit is thus defined for erosion from 25 to 30 t km 2 yr 1 beyond this limit the sustainability of the agroecosystem is limited and ecosystem services decrease afterwards pedogenesis evolved again from progressive 700 300 yr cal bp to regressive 300 yr cal bp today phases erosion was less important during the last 700 years than during the middle ages but with the same weathering stages indicating that soils were deeply affected during the middle age and have yet not recovered our results highlight the importance of the human factor in the pedogenesis over last millennia and suggest that the studied agro ecosystem entered the anthropocene 1400 years ago

palaeomagnetic signature of slow post orogenic cooling of the north east highlands of scotland recorded in the newer gabbros of aberdeenshire summary consideration of previous work and new data show a systematic distribution of the directions of high coercivity and high blocking temperature magnetization in the newer gabbros of aberdeenshire the site mean directions show a non fisherian distribution with the corresponding pole positions distributed along a published early palaeozoic apparent polar wander path for great britain the mean of the distribution closely agrees with the mean direction previously reported and widely quoted there is a close correlation of the site mean directions with the position of the sampling sites with respect to the contours chrontours of the k ar coolingage sites where stable nrm has se declinations and shallow 20 inclinations have the oldest chrontour ages 468 myr the mean palaeomagnetic direction progressively shifts and the sites with the youngest chrontour ages 428 myr have sw declinations with moderately steeper 45 inclination the relative age of magnetization determined from the position of the corresponding pole on the apparent polar wander path is consistent with the relative chrontour age the gabbros have therefore recorded the shift of the north east highlands with respect to the palaeomagnetic pole during the slow cooling of the terrain the slow cooling is presumably related to uplift and erosion and the resulting downward migration of isothermal surfaces a previously published suggestion that all magnetizations with southerly declinations and moderately downward inclination are the resultant of normal and reversed magnetizations with shallow inclination is shown to be incorrect

magnetism of igneous rocks from the tourmakeady and glensaul inliers w ireland mode of emplacement and aspects of the ordovician field pattern summary results of palaeomagnetic and rock magnetic studies are reported mainly for quartz porphyry collected at 18 sites from an ordovician igneous sedimentary succession at tourmakeady and glensaul in co mayo eire both magnetite and haematite are shown to be prominent magnetic constituents the magnetite is usually in the form of large multidomain grains these are held responsible for a soft remanence component called the b magnetization with d i 000 75 95 3 7 i e practically identical to the direction of the present axial geocentric dipole field in the area hence it is inferred that the b magnetization which is dominant at most sites is of recent origin haematite which has a more patchy occurrence apparently formed through high temperature oxidation of magnetite haematite is the main carrier of the palaeomagnetically significant component the a magnetization which gave well grouped in situ directions 29 samples from 10 sites with a mean value of d i 182 6 corresponding to a north pole at 31 n 169 e dp dm 2 1 4 2 correction for folding along the glensaul tourmakeady are shows that the a magnetization is of post folding age an earlier suggestion that the rocks represent a lower ordovician extrusive suite is discussed and discounted it is inferred that the quartz porphyries constitute syntectonic intrusions having formed during the taconic orogeny these rocks as well as their characteristic magnetization are therefore regarded as late ordovician in age it is concluded that a c 50 relative clockwise shift between the mid ordovician and late ordovician silurian geomagnetic field axes previously demonstrated for scotland has now been recognized also in ireland

structure of remanent magnetization and magnetic mineralogy of the cheviot lavas lower devonian northeast england abstract demagnetization data and magnetomineralogical results from the lower devonian cheviot lavas have revealed a complex remanence structure associated with extensive low temperature alteration of the primary magnetic oxides the original cooling magnetization has apparently been replaced by chemical remanences acquired in one or more dual polarity fields superposition of normal and reverse field components appears to have created fairly stable but what may be palaeomagnetically irrelevant directions which if not recognized or experimentally resolved may easily lead to incorrect conclusions evaluation of the total data base suggests that the characteristic palaeomagnetic axis is sub horizontal with an approximately n s declination the age range of this magnetization may vary from lower devonian to lower carboniferous the new experimental results throw into question some previous palaeomagnetic conclusions regarding the british lower old red sandstone lavas further critical study of the fossil magnetization of lower devonian rocks from britain should be on intrusive masses as such rocks are likely to have escaped at least the extensive surface oxidation and associated remagnetization complexities that have apparently developed in the extrusive suites

paleomagnetism of the silurian devonian andreas redbeds evidence for an early devonian supercontinent two components of magnetization were isolated in the silurian devonian andreas redbeds of the central appalachians of pennsylvania lat 40 75 n long 75 78 w a thermally distributed synfolding b component and a thermally discrete pre alleghenian age folding c component the c component mean direction and associated pole position correspond to a silurian devonian paleolatitude for the andreas location of about 35 s which in conjunction with early devonian results from gondwana is consistent with an early devonian supercontinent configuration

palaeomagnetic studies within the ballantrae ophiolite southwest scotland magnetotectonic and regional tectonic implications abstract the early arenig slockenray formation within the ballantrae ophiolite southwest scotland displays a multivectorial magnetisation structure two components s and m are identified delineated by differing blocking temperature coercivity spectra component s is removed around 200 c 10 mt and is regarded to be of recent viscous origin component m forms the characteristic formation magnetisation and resides in both magnetite and haematite extensive sampling of all exposed lithologies reveals an in situ non fisherian distribution of the characteristic magnetisation defining an envelope from se moderate positive to sw shallow negative directions a negative infra formation conglomerate test identifies this component as a pervasive overprint a second conglomerate test performed in the overlying benan conglomerate of llandeilo age reveals dispersely directed magnetisation with a stability range equivalent to that of component m this field test therefore defines a maximum remagnetisation window of 30 million years for the characteristic remanence hard viscous magnetisations are identified both in the benan conglomerate and at some sites within the slockenray formation structurally corrected site mean results from the slockenray formation define a non fisherian distribution and form a small circle partial arc centred on a vertical axis nw moderate positive to sw moderate positive directions a combined palaeomagnetic fold and fault test suggests that acquisition of component m pre dates both folding and faulting the resulting palaeolatitude of remanence acquisition 28 8 s implies a tectonic position close to the southern laurentian margin for the ballantrae ophiolite in arenig times

a multicomponent dual polarity palaeomagnetic regional overprint from the moine of northwest scotland abstract palaeomagnetic remanence may be reset by orogeny in a manner analogous to isotopic systems the heavy mineral seams and associated psammite in the deformed and metamorphosed lower morar division of the moine assemblage of northwest scotland have a palaeomagnetic signature that is characteristic over a wide area the various components of the magnetization are resolved by detailed thermal demagnetization these components are post tectonic as they are not affected by any structural fabric they may be classified according to blocking temperature and when statistically distinguishable show a systematic change of direction from high to lower temperature possibly associated with apparent polar wander comparison to the european palaeomagnetic record suggests a late silurian to early devonian age of magnetization for the localities south of the strath conon fault the distribution of remanance directions and blocking temperatures is not consistent with the pattern of potassium argon ages in this part of the british caledonides if the magnetization is purely of thermal origin the palaeomagnetic record indicates higher temperatures at later time than does the potassium argon record this remagnetization event is related to the closing stages of the caledonian orogeny

palaeomagnetism of middle proterozoic c 1 25 ga dykes from central north greenland summary from a nunatak in central north greenland 81 son 44 7 w nine sites of middle proterozoic basic dykes cutting archaean basement were palaeomagnetically investigated after af and thermal cleaning the nine dyke sites and three adjacently baked gneiss sites give a stable characteristic remanent mean direction of d 2654 i 21 5 n 12 ags 5 6 the direction being confirmed by a detaded and positive baked contact test the polarity of the dykes in the nunatak area is opposite to that of the zig zag dal basalts and the midsommers dolerites in eastern north greenland some 200 300 km away the volcanics of which are assumed to be of similar age about 1 25 ga the remanent directions of the two sets of data are antiparallel within the 95 per cent significance level of confidence when rotating greenland 18 clockwise back to north america by the bullard fit the pole of the central north greenland dolerites ndl falls at 14 3 n 144 3 w the reversed pole 14 3 s 35 7 e fits well on to the loop between 1 2 and 1 4 ma on the apparent polar wander swath of berger york for cratonic north america the palaeomagnetic results from the middle proterozoic basic dykes from central north greenland thus strengthen previous palaeomagnetic results from the midsommersa dolerites and zig zag dal basalts from the peary land region in eastern north greenland suggesting that greenland was part of the north american craton at least for the period between c 1 3 and 1 ma and probably up to the end of cretaceous time the major geographical meridian of greenland was orientated approximately e w and the palaeolatitude of greenland was about 10 150

a new siluro devonian paleopole from early paleozoic rocks of the franklinian basin north greenland fold belt demagnetization of dolomitic shales dolomites and carbonate breccias of the cambro ordovician kap stanton formation within the franklinian basin sequence of the north greenland fold belt yields a characteristic direction declination inclination is 16 16 tilt corrected from 14 of the 28 sites a negative breccia test and positive local and regional fold tests bracket the age of the magnetization as postdepositional but pre ellesmerian pre carboniferous after rotating the corresponding paleopole 1 n 302 e to account for the cretaceous tertiary opening of the labrador sea the greenland pole remains removed by approximately 20 from the existing north american apparent polar wander path apwp however the rotated paleopole 2 s 284 e in north american coordinates is similar to british silurian and devonian paleopoles in a bullard et al 1965 reconstruction pole is 2 s 322 e in british coordinates we interpret our new paleopole as late silurian to early devonian in age requiring a modification of previously published apwps for laurentia if the age assignment is correct the new paleopath for north america greenland and that for great britain can be brought into good agreement by closing the atlantic ocean thus indicating that north america greenland and great britain were assembled in a supercontinent in late silurian to early devonian time

paleomagnetic results from the peterhead granite scotland implication for regional late caledonian magnetic overprinting abstract palaeomagnetic results from the peterhead granite silurian ne grampian highlands define a characteristic magnetization with overall parameters of dec 180 4 inc 22 3 and a 95 5 2 these results agree with other newer granite data from north scotland an east west trending dyke cutting the peterhead granite shows an extremely well defined paleomagnetic direction with dec 192 5 inc 19 1 and a 95 1 3 suggesting a permo carboniferous age the peterhead granite results are seen in conjunction with other palaeozoic palaeomagnetic data from scotland it is concluded that the observed directional spread of characteristic remanence directions previously reported from the aberdeenshire gabbros are not related to slow post orogenic cooling watts and briden but is rather seen as the result of late caledonian magnetic overprinting

lateral podzolization in a sandstone catchment a sandstone catchment of the cool perhumid black forest germany was studied with respect to podzolization processes on a landscape scale soil mapping along a steep slope 25 revealed spodosols with thick e horizons combined with thin spodic horizons in the upper catchment area lowermost parts of the landscape showed thinnest e and thickest bhs horizons this catenary trend was quantified by a non linear increase of the illuviation eluviation ratio of podzolization ierpodzol soil texture pedogenic oxides feo fed alo mnd ph cacl2 corg and mineralogical composition of the clay and medium sand fraction were determined in six representative pedons chemical analysis matched morphology in that very low contents and mass densities of feo fed alo and mnd were found in upslope soils the distal pedons were 2 5 fold higher in these elements the catenary trends corresponded to a downslope increase in ph as well as organic carbon in mineral soils mineralogical analysis showed a decrease in feldspar weathering and an increase in hydroxy interlayered vermiculites towards the downslope soils the morphological chemical and mineralogical results led to the conclusion of a process sequence of i an upslope mobilization and depletion of iron manganese and aluminum e spodosols ii a lateral translocation 30 of catchment discharge occurred as interflow and iii a downslope immobilization resulting in a relative or absolute accumulation of the translocated soil compounds bs spodosols the immobilization probably was controlled by an admixture of fe and base richer rocks into the parent material downslope the concept of lateral podzolization developed in a granite landscape was confirmed in the sandstone area studied

palaeomagnetic resetting in the barrovian zones of scotland and its relationship to the late structural history the haematite schists in the lowest kyanite and the staurolite barrovian zones exposed in glen lethnot and glen esk angus scotland have a characteristic magnetization with blocking temperatures generally greater than 600 c and less than 695 c and coercivity greater than 200 mt the mean palaeomagnetic direction derived from 54 samples collected from n 10 sites isd 159 i 45 k 47 95 7 1 with the associated south pole position oflat 3 long 22 e dp 5 7 anddm 9 0 this magnetization is younger than folds of d3 generation and older than folds of d4 generation the pole position falls on the aberdeenshire polar wander track in a place consistent with an average kar biotite chrontour age of 455 m y a comparison of the blocking temperatures of magnetization to the estimated peak temperature of metamorphism suggest the magnetization is a chemical remanent magnetization crm possibly acquired during the metamorphic chemical reactions

evolution of the early paleozoic deep water basin of north greenland aulacogen or narrow ocean a major lower paleozoic deep water sequence is exposed for more than 800 km along the coast of north greenland the maximum preserved width of the basin is about 200 km and the thickness of the sedimentary sequence may reach 8 km nine evolutionary stages in basin evolution are recognized each characterized by distinct sedimentary facies and structural style of the shelf basin boundary 1 the oldest sequence of unknown age is so deformed that inferences about the depositional environment are precluded 2 late precambrian early cambrian incipient basin 3 early cambrian narrow turbidite basin 4 middle cambrian ordovician basin expansion and initial starvation 5 latest ordovician early silurian longitudinally filled turbidite basin 6 middle silurian basin expansion and starvation 7 middle late silurian wide turbidite basin 8 middle late silurian caledonian thrusting and conglomerate deposition and 9 probably latest silurian megasliding and advance of the caledonian front the basin evolution that came to an end during the mid paleozoic ellesmerian orogeny was punctuated by events related to the closure of the iapetus ocean and formation of the caledonian mountain belt to the east the basin may have been fully ensialic and formed during the early rifting stages preceding back arc spreading or it may have reached a narrow ocean stage at present however we are inclined to favor an interpretation of the basin as being an aulacogen extending deeply into an old continent at a right angle to the caledonian orogenic front to the east

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

magnetic properties of the lower old red sandstone lavas in the midland valley scotland palaeomagnetic and tectonic considerations abstract thermal demagnetization studies of lavas in the strathmore area of the midland valley scotland support overall palaeomagnetic data found in previous studies of these rocks reduced directional scatter as compared to some earlier studies is attributed to more effective demagnetization resolving some of the directional complexity of previous studies combined magnetic fabric and directional analysis suggest that at least some deviating directions may be explained by local tectonism the existence of almost antiparallel directional groups and field tests give supporting evidence for a primary deuteric origin of the main magnetization of these rocks additionally a second remanence component having shallow reverse directions of magnetization is attributed to later remagnetization in old red sandstone time the midland valley results are seen in conjunction with other palaeozoic palaeomagnetic results and possible geodynamic implications are discussed